Final Senior Design Report
Team 14: GRE-cycle
Hannah Albers, Ben Guilfoyle, Melanie Thelen, and Cole Walker
ENGR 340--Senior Design Project
May 13, 2015
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Abstract
Waste cooking oils (WCOs) contain high levels of triglycerides, which store large amounts of energy.
The team designed a biodiesel production plant that uses WCO from restaurants and other businesses as
its primary feed source. The plant will be located in Miami, FL as the size of the Miami area will allow
significant grease collection for the production of a substantial amount of biodiesel. Based on the number
of restaurants in the area and the understanding that grease will not be obtained from every one of these
sources, the plant is designed to produce 9.5 million gallons of biodiesel per year. The team assessed the
possibility of blending the produced biodiesel at the plant, however it was determined that this was
outside the scope of the project. The plant will be used exclusively to produce the biodiesel that will be
blended elsewhere.
The plant was designed to produce biodiesel through pretreatment, conversion, and product
purification steps. The pretreatment reactor was modeled as a plug-flow reactor in UNISIM as this reactor
type was sufficient to decrease feed FFA content to the desired range. The transesterification reactor was
simulated as a batch and plug-flow reactor, and a plug-flow reactor was selected as optimal. Additional
reactor types were considered and eliminated due to higher operating expenses and higher risk of failure.
The primary method of product purification is membrane separation and the primary method of methanol
recovery is distillation. The biodiesel production process was simulated in UniSim, but has supplemental
design calculations for further accuracy. The plant will require methanol, sulfuric acid, and sodium
hydroxide to react to process WCO. The methanol used for plant operations will be biomethanol, which
is produced by a less energy-intensive process than standard methanol.
Upon estimating capital, raw material, and operating costs, if biodiesel is sold for $3.50/gal, which is
approximately $0.50/gal lower than the average biodiesel price, the plant receive a 20% rate of return
over the 20 year lifespan. With this conservative selling price, our plant will be profitable despite mild
market fluctuations. It is important to note that $1.00 per gallon comes from a government subsidy.
Without this added dollar, the plant would not be profitable. This indicates that this fuel requires further
development to be a profitable enterprise.
The plant will profit 4.2 million dollars a year, with 16.5 million dollars in capital costs.
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Table of Contents
Abstract ......................................................................................................................................................... 2
Table of Contents .......................................................................................................................................... 3
Table of Figures ............................................................................................................................................ 6
Table of Tables ............................................................................................................................................. 7
1. Introduction ............................................................................................................................................... 8
1.1 Background Information ..................................................................................................................... 8
1.2 Objective ............................................................................................................................................. 9
1.3 Scope ................................................................................................................................................... 9
1.4 Past Project Teams ............................................................................................................................ 10
1.5 Feasibility.......................................................................................................................................... 10
1.6 Comparing Biodiesel and Petroleum Diesel ..................................................................................... 11
1.6.1 Differences in Chemistry ........................................................................................................... 11
1.6.2 Engine Modification .................................................................................................................. 12
1.6.1 Engine Performance ................................................................................................................... 12
2. Design Norms ......................................................................................................................................... 13
2.1 Stewardship ....................................................................................................................................... 14
2.2 Caring................................................................................................................................................ 14
2.3 Transparency ..................................................................................................................................... 14
3. Project Management ............................................................................................................................... 15
Team Responsibilities ......................................................................................................................... 16
Hannah Albers .................................................................................................................................... 16
Ben Guilfoyle ...................................................................................................................................... 16
Melanie Thelen ................................................................................................................................... 16
Cole Walker ........................................................................................................................................ 16
4. Process Overview.................................................................................................................................... 17
4.1 Process Research ............................................................................................................................... 17
4.1.1 Block Flow Diagram .................................................................................................................. 17
4.1.2 Reaction Chemistry .................................................................................................................... 17
4.1.3 Key Variables............................................................................................................................. 19
4.1.4 Design Alternatives .................................................................................................................... 21
4.2 Material Research ............................................................................................................................. 22
4.2.1 Feed Sources .............................................................................................................................. 22
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4.2.2 Feed Composition Research....................................................................................................... 22
4.2.3 Feed Composition Model ........................................................................................................... 25
4.2.3 Alcohol....................................................................................................................................... 26
4.2.4 Product ....................................................................................................................................... 27
5. Design ..................................................................................................................................................... 28
5.1 Pre-Treatment Section ...................................................................................................................... 28
5.1.1 Water Removal .......................................................................................................................... 28
5.1.2 Filter ........................................................................................................................................... 29
5.1.3 Acid Treatment .......................................................................................................................... 31
5.1.4 Waste Separation........................................................................................................................ 35
5.2 Transesterification Reactor ............................................................................................................... 40
5.2.1 Mass Transfer Limitations ......................................................................................................... 41
5.2.2 Design Alternatives .................................................................................................................... 42
5.2.3 Polymath Kinetic Modeling ....................................................................................................... 45
5.2.4 Design Decision ......................................................................................................................... 46
5.2.5 Catalyst ...................................................................................................................................... 47
5.3 Post-Treatment Section ..................................................................................................................... 48
5.3.1 Glycerin Separation.................................................................................................................... 48
5.3.3 Waste Water Treatment ............................................................................................................. 51
6. Equipment ............................................................................................................................................... 52
6.1 Equipment Listing............................................................................................................................. 52
7. Safety Considerations ............................................................................................................................. 56
7.1 Chemicals.......................................................................................................................................... 56
7.2 Operating........................................................................................................................................... 56
8. Quality Control ....................................................................................................................................... 58
9. Business Plan .......................................................................................................................................... 60
9.1 Market Study..................................................................................................................................... 60
9.1.1 Customer .................................................................................................................................... 61
9.1.2 Competition................................................................................................................................ 61
9.2 Tax Information ................................................................................................................................ 63
9.3 Costs.................................................................................................................................................. 64
9.3.1 Capital Costs .............................................................................................................................. 64
9.3.2 Operating Costs .......................................................................................................................... 66
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9.4 Profitability ....................................................................................................................................... 67
10. Conclusion ............................................................................................................................................ 70
References ................................................................................................................................................... 71
Appendices Table of Contents .................................................................................................................... 75
Appendix 1. Overall Process Mass Balance and UniSim design ............................................................ 76
Appendix 2. Component Stream Table ................................................................................................... 78
Appendix 3: Settling Tank Calculations ................................................................................................. 79
Appendix 4. Particulate Removal Calculations ...................................................................................... 80
Appendix 5. Competing Biodiesel Plants in Florida............................................................................... 81
Appendix 6. Transesterification Kinetics Calculations ........................................................................... 82
Appendix 7. Membrane Filter Calculations ............................................................................................ 84
Appendix 8. Vessel Cost Details............................................................................................................. 86
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Table of Figures
Figure 1: Biodiesel molecule ...................................................................................................................... 11
Figure 2: Petroleum Diesel Molecule ......................................................................................................... 11
Figure 3: Work Breakdown Schedule Organized as Critically Linked Tasks ............................................ 15
Figure 4: Process Overview (above) and Block Flow Diagram (below) .................................................... 17
Figure 5: Triglyceride Molecule ................................................................................................................. 18
Figure 6: Overall Biodiesel Reaction .......................................................................................................... 18
Figure 7: Saponification of Free Fatty Acids to form soap ......................................................................... 20
Figure 8: Water formation in an acid catalyst reaction to convert Fatty acids to biodiesel ........................ 20
Figure 9: Standard Curve of Linoleic Acid ................................................................................................. 24
Figure 10: TLC Plate of Butter, Linoleic Acid and Grease Extract ............................................................ 24
Figure 11. Kinetic comparison of oils with different feed compositions. ................................................... 26
Figure 12:Pre-Treatment Block Flow Diagram .......................................................................................... 28
Figure 13: Maximum Water Content vs Maximum FFA Content .............................................................. 29
Figure 14:Levenspiel Plot of the Pre-Treatment Reaction .......................................................................... 33
Figure 15: Effect of Pre-Treatment Reactor Volume on FFA Composition ............................................... 34
Figure 16: Effect of Trays on Distillation Cost........................................................................................... 38
Figure 17: Overall Cost of the Distillation Column .................................................................................... 38
Figure 18: Methanol Feed Required at Different Reflux Ratios ................................................................. 39
Figure 19: Transesterification of triglycerides to form biodiesel (methyl esters) ....................................... 41
Figure 20: PFR and batch reactor comparison with Polymath with methanol:oil ratio and entering flow
rates held constant ....................................................................................................................................... 46
Figure 21: Post-Treatment Block Flow Diagram ........................................................................................ 48
Figure 22: Materials of Construction for Handling Caustic Solution ......................................................... 53
Figure 23: Plant Piping and Instrumentation Diagram ............................................................................... 59
Figure 24: Million barrels of biodiesel produced in the United States per year ....................................... 600
Figure 25: Cash flow diagram of Plant Construction and Operation .......................................................... 69
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Table of Tables
Table 1. Fatty acid composition of WCO and various oils., ....................................................................... 25
Table 2: EPA Biodiesel Specifications ....................................................................................................... 27
Table 3. EPA biodiesel specifications met by final design. ....................................................................... 27
Table 4. Pretreatment PFR operating parameters. ...................................................................................... 35
Table 5: Membrane Filter Specifications .................................................................................................... 37
Table 6: Distillation Column Specifications ............................................................................................... 40
Table 7. Transesterification reactor alternatives ........................................................................................ 43
Table 8. Transesterification PFR operating parameters. ............................................................................ 47
Table 9: Relative densities of effluent stream components ........................................................................ 49
Table 10: Equipment and Materials of Construction .................................................................................. 54
Table 11: Vessel Volumes based on Storage Density Contents. An asterisk denotes vessels that are
incorporated into the process but are not represented in the process flow diagram .................................... 55
Table 12: Vessel Capital Costs as Calculated by Guthrie Cost Estimation Tool ........................................ 64
Table 13: Plant Development Capital Costs ............................................................................................... 65
Table 14: Hourly Costs of Raw Materials .................................................................................................. 66
Table 15: Hourly Operating Costs .............................................................................................................. 67
Table 16: Income from Products................................................................................................................. 68
Table 17. Rate constants and activation energies for biodiesel production with soybean oil and NaOH
catalysis. ...................................................................................................................................................... 82
Table 18. Thermodynamic properties of reactants and products. .............................................................. 83
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1. Introduction
1.1 Background Information
Fossil fuels account for approximately 82% of the United States’ energy supply. Though
geologists estimate that less than half the total volume of crude in below-ground reserves will be depleted
by 20301, it remains a fact that the supply of crude oil continues to decrease as the energy demand
necessary to support the rapidly advancing lifestyles around the world increase. Oil has done well to
advance human technology to the point where it is today, but the drawbacks of crude oil cannot be
ignored. The demand for crude oil has caused wars, damaged the atmosphere, and eventually must be
replaced by more sustainable energy sources.
Used restaurant grease contains high levels of triglycerides, which store large amounts of energy.
According to USA Today2, approximately 3 billion pounds of grease are produced in the United States
each year. The average fast food restaurant produces about 150 - 250 pounds of grease every week, says
the New York Times3. The disposal of waste grease has been a large burden on restaurants, since grease
cannot be processed in a wastewater treatment plant. It must be collected in a grease trap and disposed of
in alternative ways. Restaurants recently have been selling their used grease to recycling companies that
convert the used grease into fresh cooking oil. Rather than recycling the grease for consumption, the
burden of grease waste disposal can be alleviated by instead converting the grease into fuel.
Also, in contrast to fossil fuels, biofuels are produced from renewable plant and animal materials
such as vegetable oils, grease, or animal fats. Over the past decade, interest in producing biodiesel from
oils and grease has grown into a marginally successful industry as the future availability of fossil fuels
became uncertain. Additionally, burning biodiesel produces 56-87% less greenhouse gas emissions than
conventional diesel4, which makes it a viable and promising option as an alternative to crude oil.
1
Institute for Energy Research, 2014
Ron, Barnett. "Restaurants' Grease a Hot Item for Thieves." USA Today
3 Saulny, Susan. "As Oil Prices Soar, Restaurant Grease Theft Rises." The New York Times
2
4
Beer, T, T Grant, and PK Campbell. "Biodiesel could reduce greenhouse gas emissions." CSIRO. CSIRO, 27 Nov. 2007.
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1.2 Objective
The main objective of this project is to design a biodiesel production plant that will provide a
clean alternative to diesel. Petroleum production is unsustainable whereas the supply of restaurant grease
is readily available. Obtaining feedstock for the plant will require the participation of restaurants, which
currently sell the grease to an outside source in order to dispose of the grease they generate on a daily
basis. By establishing the plant in a populous area with a lot of restaurants, a significant amount of
biodiesel feedstock will be available.
Secondly, the team purposes to make the plant profitable. Biodiesel production will not increase
unless there is money to be made in the industry. Despite its environmental implications, production will
be limited if it continues to be more economical to use fossil fuels to run our vehicles. By designing a
profitable biodiesel plant, the team hopes to prove that biodiesel production is part of the answer for a
more sustainable future.
1.3 Scope
The team plans to design a production plant in the Miami area that will buy used grease from
surrounding restaurants and convert it into pure biodiesel. The size of the Miami area will allow
significant grease collection for the production of a substantial amount of biodiesel. Based on the number
of restaurants in the area and the fact that grease will not be obtained from every one of these sources, the
production of biodiesel is anticipated to be in the hundreds of barrels per day range. This comes from the
estimation of available feed at 130,000 kg/day. This calculation can be found in section 4.2.1.
Biodiesel is commonly blended with conventional diesel in 50:1, 20:1, or 5:1 diesel to biodiesel
ratios. The team assessed the possibility of blending the produced biodiesel at the plant but determined
that this was outside the scope of the project. The plant will be used exclusively to produce purified
biodiesel that can be blended by an outside source.
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1.4 Past Project Teams
Several senior design teams have completed projects pertaining to biodiesel production. In 2001,
Team FAME designed a plant that produced biodiesel in a continuous process for missionary
transportation services in third world countries. In 2008, Team Rinnova designed a small scale biodiesel
batch reactor for home users using feedstock from Calvin College Dining Services. Rinnova met their
project goals but included recommendations for a second prototype. Suggested changes included adding
a completely electronic control system, using better materials for piping, and installing a coarser filter.
The Diesel Crew took these recommendations in 2013-2014 and designed a second prototype for home
users. Their design utilized a microwave reactor, unlike the batch reactor designed by Rinnova, as the
Diesel Crew was interested in designing a continuous system.
Though the scope of this report includes a full-scale plant design, references to these project
groups are found scattered throughout this report, particularly in the design alternatives for each plant
section. The team will not be directly using other team projects by scaling up the past designs, but will
instead take into consideration their design decisions while evaluating alternatives.
1.5 Feasibility
The use of biodiesel compared to currently available diesel has both advantages and
disadvantages. For one, restaurant grease can be obtained inexpensively, which makes the plant more
economically feasible by lowering operating costs. Additionally, biodiesel has positive environmental
implications as it produces less hydrocarbons and carbon monoxide than regular diesel when burned5. The
proposed process is more sustainable by helping the environment and eliminating waste. The traditional
diesel process requires a depletion of Earth’s natural resources to produce the fuel, while biodiesel uses
otherwise useless waste as its feedstock.
5
"How Much Does Biodiesel Reduce Air Pollutants?" AllegroBiodiesel.
10
Despite these advantages, the use of biodiesel instead of traditional diesel does pose some
challenges, most notably gelling. In colder weather, some biodiesels solidify into a gel that renders them
unusable. This is one reason the plant will be placed in Florida. Considering the warm climate in the state,
gelling should not be a concern. Though biodiesel significantly decreases carbon emissions, it is less
efficient than normal diesel. It has been found that fuel efficiency is reduced by 10% compared to regular
diesel6. Despite these drawbacks, the team feels that the economic and environmental considerations
make the proposed process a valuable and feasible project to pursue.
1.6 Comparing Biodiesel and Petroleum Diesel
1.6.1 Differences in Chemistry
Figure 1 depicts a typical biodiesel molecule. It is composed of a long carbon atom chain
(average of 16-20 carbons) with an ester functional group, shown in blue, on one end.
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Figure 1: Biodiesel molecule
A typical petroleum diesel molecule looks very similar, except it does not have the same ester
functional group attached to one end.
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Figure 2: Petroleum Diesel Molecule
The ester group on the biodiesel molecule makes the fuel much less toxic and more biodegradable
than petroleum diesel. Enzymes such as esterase recognize the ester group on the biodiesel and begin fatty
6
"Biodiesel." fueleconomy.gov. US Department of Energy
”The Chemistry of Biodiesel”. Goshen College
8
”The Chemistry of Biodiesel”. Goshen College
7
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acid degradation9. This process breaks the molecule down to generate acetyl-CoA, which can be
metabolized and thus is biodegradable and non-toxic. Biodiesel is safer for both the environment and
human contact due to these characteristics. A biodiesel spill would be much less concerning than a
petroleum diesel spill and since biodiesel can be metabolized, it is not as toxic to humans.
1.6.2 Engine Modification
Due to the similarity in chemical structure, a diesel engine can run on biodiesel fuel with minor
modification. Diesel engines manufactured pre-1993 may contain rubber tubing that may soften with
biodiesel fuel and should be replaced with biodiesel-rated components. These are typically made of
fluoroelastomers like Teflon and will not degrade with biodiesel10. If the biodiesel fuel is a blend with less
than 20% pure biodiesel, there is no need to replace the rubber tubing. There is most likely no need to
replace the tubing on a car manufactured post-1993 either, but a mechanic should examine the engine
before switching to biodiesel.
Also, biodiesel is more viscous than petroleum diesel so it may gel, causing engine issues while
trying to start the car11. In cool climates, engines may have to be modified by adding a fuel heating system
or using a fuel additive that will lower the viscosity. Viscosity lowering fuel additives are available
commercially, such as Wintron®, a Biodiesel Cold Flow Additive12.
1.6.1 Engine Performance
Overall the engine performance using biodiesel is comparable to using petroleum diesel;
however, some discrepancies occur in fuel efficiency and engine power. The energy content of biodiesel
is slightly less than petroleum diesel, so the overall fuel efficiency is approximately 10% less. Also,
McKay, DB, “Degradation of triglycerides by a pseudomonad isolated from milk”
“Using Biodiesel Fuel in Your Engine” Penn State Extension.
11
“Engine Modification,” University of Strathclyde Engineering
12
”Biodiesel Cold Fuel Additives,” Biofuel Systems Group LTD
9
10
12
engine power is reduced by 3 to 5% while using biodiesel since it has less energy per unit volume than
petroleum diesel.13
Engine clogging can occur if low-quality biodiesel is used since it will contain more deposits and
viscous materials. However, this should not be an engine performance concern if high quality biodiesel is
used. Also, care should be taken that the biodiesel does not oxidize and thus polymerize before it is
burned, since this may clog a standard diesel engine. As long as the biodiesel is stored properly before
being distributed, this should not be a major concern. Proper storage includes storing at moderate
temperatures and not allowing the biodiesel to sit for extensive amounts of time before use.14
As mentioned in the introduction, engine emissions are also significantly reduced using biodiesel.
Sulfur emissions are in effect non-existent and hydrocarbon emissions are reduced by an average of
50%15. The only trade-off is a slight increase in nitrogen oxide emissions. Nitrogen oxide (NOx) is a
greenhouse gas and can cause smog and acid rain16. However, the reduction in the carbon emissions is so
beneficial that the slight increase in NOx is negligible.
2. Design Norms
Crucial to the sustainability of the proposed plant from both business and ethical standpoints is
the promotion and prioritization of certain design norms, three of which are detailed in this report. These
norms should be integrated into early planning stages of the plant and throughout the detailed design
work, construction, and daily operation to ensure the health, well-being, and integrity of employees and
customers alike.
“Using Biodiesel Fuel in Your Engine” Penn State Extension.
“Using Biodiesel Fuel in Your Engine” Penn State Extension.
15
“Biodiesel Emissions,” Biodiesel: America’s Advanced Biofuel.
16
”Nitrogen Oxide,” U.S. National Library of Medicine.
13
14
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2.1 Stewardship
From its conception, the biodiesel plant proposal is centered on the importance of environmental
stewardship. The proposed biodiesel plant would lower total emissions, generate less hazardous waste,
and draw from a readily available and constant feed source of grease and turn something originally
considered waste into a desirable product. Furthermore, it becomes increasingly vital in a world of
unlimited demand and limited resources to think forward to a time when the nonrenewable resources
currently used for energy generation are no longer a feasible option. Additionally, exercising stewardship
requires examining the consequences of energy consumption and making every effort to mitigate the
problems (greenhouse gas emissions or high volumes of dangerous waste material) faced by the energy
industry.
2.2 Caring
Once built, the proposed plant would require employees to operate the plant equipment. Caring,
one of the design norms, becomes an important attribute of the design engineers for the safety of all
employees. From the reactor catalyst selection to the layout of the plant units, care must be exercised to
ensure employees aren’t required to put themselves in harm’s way as part of their job description and to
ensure safety procedures are established for routine and non-routine tasks. This design norm will be
practiced when designing the controls used in the plant and by not introducing dangerous chemicals into
the design without taking proper safety measures.
2.3 Transparency
The potential for dangerous situations extending beyond the plant property are necessary to
internally evaluate and communicate to local government and local citizens who could be negatively
affected by the plant. Transparent business practices require full disclosure to employees and citizens of
potential hazards, Furthermore, since the final product must meet certain governmental standards to be
used in diesel engines, it is important to the team to ensure that the plant meet or even go beyond these
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standards. No shortcuts or half-measures will be taken in the design process in an attempt to promote the
profitability of the design over the quality.
3. Project Management
Task deadlines were assigned based on both class and team-specific deadlines. Professor Jeremy
VanAntwerp was assigned to the team as a project advisor, and he met with the team every other week to
discuss progress and design challenges. Professor VanAntwerp connected the team with Randy and Doug
Elenbaas, who served as an industrial consultant. Randy Elenbaas is a chemical engineer employed at
Vertellus Specialties, Inc. in Zeeland, Michigan with valuable knowledge of process design and project
management. Doug Elenbaas is a professional engineer at El Energy Consulting LLC, with over 30 years
of engineering experience.
As seen in Figure 3, the project could be divided into three sections with research integrated
throughout the process: the main reaction with pretreatment, the main reaction without pretreatment, and
post-treatment. This schedule illustrates the team’s method of approach for choosing the most profitable
design.
Post-treatment
Tranesterification Reaction
Need for
Pretreatment
Research
Design Criteria
Research
Design Criteria
Design Criteria
Design Decision
Design Decision
Design Decision
Economic Optimization
Figure 3: Work Breakdown Schedule Organized as Critically Linked Tasks
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Team Responsibilities
Hannah Albers
Hannah was tasked with the transesterification reactor design including catalyst selection, kinetic
modeling, reactor type, and reactor sizing. She was also responsible for feed selection and
characterization, and recording the team’s weekly progress to be reported to Professor VanAntwerp
during regular meetings.
Ben Guilfoyle
Ben was tasked with pretreatment design including esterification reaction kinetics, sizing, and
design alternatives, and he was also responsible for feedstock research in the Miami area. Ben was also
responsible for product purification simulations and worked on economic analysis to prove the plant’s
profitability. He is the team’s webmaster and kept the team’s website up to date throughout the year.
Melanie Thelen
Melanie was responsible for economic analysis for the optimized plant and UniSim design work.
She headed research pertaining to governmental biodiesel standards and regulations and safety, and she
kept the team organized by ensuring all class deadlines were met and deliverables were submitted on
time.
Cole Walker
Cole was tasked with the preliminary pretreatment design including filter selection, membrane
design, and batch reactor simulations in SuperPro designer. He was also responsible for financial
research pertaining to market trends and plant profitability. Melanie and Cole completed laboratory work
with grease samples to help the team better quantify % FFA of restaurant grease for the design.
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4. Process Overview
4.1 Process Research
4.1.1 Block Flow Diagram
Acid Catalyst
WCO
Methanol
Methanol
Basic Catalyst
Pretreatment
Main Chemistry
Purification
Lower free fatty acid
content
Methanol recovery
Transesterification
WCO conversion to
biodiesel
Methanol recovery
Glycerin separation
Biodiesel
Glycerin
Waste Water
Figure 4: Process Overview (above) and Block Flow Diagram (below)
4.1.2 Reaction Chemistry
The precursor to biodiesel molecules is a triglyceride. A triglyceride is an ester composed of
three fatty acids connected with a glycerin backbone (see Figure 5. The fatty acids in waste grease can
either be saturated (animal fat derivative) or unsaturated (vegetable oil derivative). A glycerin molecule
17
consists of three hydroxyl (HO-) groups, which form ester bonds with the carboxyl (-COOH) groups in
the fatty acids. Triglycerides can be burned on their own in diesel engines but the three “tails” can
become tangled, increasing the viscosity. A highly viscous fuel could congest fuel injectors and other
engine internals. Instead, transforming triglycerides into biodiesel molecules will lower the viscosity.
Figure 5: Triglyceride Molecule17
The main reaction that converts a triglyceride to biodiesel is called transesterification. In this
process, triglycerides are contacted with methanol, which causes the single carbon-oxygen bonds to
break. The methanol then reacts with the free end of the fatty acid to form a methoxy group, creating a
biodiesel molecule. Since one triglyceride molecule “frees” 3 fatty acids, 3 molecules of biodiesel are
produced for every one triglyceride. As shown in Figure 6, the final biodiesel molecule will have a long
carbon chain with an ester group, formed by the addition of the methoxy group. The overall reaction is
shown in Figure 6.
Figure 6: Overall Biodiesel Reaction18
17
”The Chemistry of Biodiesel”. Goshen College
18
Lasry, Sophie, “Renewable Energy”
18
where R1, R2, R3 are alkyl groups that can be the same or different. When methanol breaks the carbonoxygen bonds in the triglyceride, the entire backbone molecule remains intact and becomes glycerol—or
soap. As seen in the chemical mechanism, a base catalyst is used this reaction and will be discussed in
depth in section 5.2.5 Catalyst.
4.1.3 Key Variables
The feedstock to be used in the process will be trap grease—that is food waste grease that is
unable to be processed as wastewater. The oil portion of the grease may or may not be solid at room
temperature but it will contain solid food particles that need to be filtered out. Within trap grease, there
are two main types of grease: brown grease and yellow grease. Brown grease is essentially rotten food oil
while yellow grease is rendered animal fat and used vegetable frying oil. The most significant difference
in regard to biodiesel production is the free fatty acid (FFA) content of the grease. Brown grease contains
more than 15% FFA while yellow grease has less than 15%. An increased amount of FFA is undesirable
since it decreases the amount of triglycerides that can be turned into biodiesel. However, there are
methods of turning FFAs into esters, which will be discussed later. Yellow and brown grease can either
be processed simultaneously or separated beforehand. The rest of the grease is composed of triglycerides,
which can be directly converted to biodiesel, as seen in Figure 6.
The majority of processes involve a pre-treatment of high FFA feedstock with an acid catalyst.
An acid catalyst, like sulfuric acid, will convert the FFAs to esters, increasing the overall conversion and
product quality. It has been found that feed stocks need to have approximately 1% FFAs or less to provide
acceptable product quality19. One problem with pre-treatment is the formation of water as a byproduct of
the FFA to ester reaction. This water needs to be removed since it would otherwise contaminate the final
product. Another issue with the acid pre-treatment is potential damage to vessels, so an appropriate
material of construction needs to be selected for the vessels. This acid pretreatment can be repeated to
19
Encinar, “Study of biodiesel production from animal fats with high free fatty acid content”
19
lower the FFA level to less than 1% since a lower FFA content indicates a higher overall process
conversion to biodiesel.
Additionally, FFAs can cause undesirable side reactions in the reactor, such as saponification.
Saponification is a soap formation process, as seen in Figure 7.
Figure 7: Saponification of Free Fatty Acids to form soap20
The FFA needs to be removed or converted before contacting with NaOH base in the main
reactor to prevent the soap formation. The saponification reaction occurs in the presence of water, so the
water formed in the acid catalyst reaction, seen in Figure 8, needs to be removed.
Figure 8: Water formation in an acid catalyst reaction to convert Fatty acids to biodiesel 21
Despite pretreatment, some soap (glycerin, in this case) will inevitably form and pass through to
the main reactor. Glycerin separation techniques will be discussed later in this report.
Upon completing the pretreatment, the feed is transferred to the main reactor where it is heated to
between 50°C and 60°C. The temperature must remain below the boiling point of the chosen alcohol so it
remains in the liquid phase without pressurizing the reactor. A solution of alcohol and alkaline catalyst is
prepared separately and added to the reactor. The alkaline catalyst is present to speed the reaction of
20
21
”Biotechnology Trends,” Best Biotech
”Water Formation in Biodiesel Production,” Intech Journals
20
triglycerides to methyl esters and convert any remaining FFA to soap. An agitator is used for up to one
hour to ensure proper mixing, and the new solution settles. After proper separation, there will be a layer
of biodiesel at the top of the reactor, and any soap formed will settle at the bottom. Once these layers are
separated, biodiesel is ready for use. The variables to be manipulated in this process are:
·
·
·
·
·
·
·
·
·
Number of pre-treatment cycles (0, 1, or 2)
Acid catalyst used in pre-treatment (sulfuric , hydrochloric , or other)
Alcohol used in pre-treatment (methanol or ethanol)
Ratio of acid catalyst to alcohol
Temperature
Alkaline catalyst (NaOH, KOH, NaOCH3, metallic Na, or other)
Ratio of alkaline catalyst to alcohol
Agitator time
Settling Time
It is important to note that this process assumes a given feedstock where the initial composition
cannot be predicted or manipulated with accuracy.
4.1.4 Design Alternatives
In addition to the process described above, there are many alternative processes to convert used
grease to biodiesel under development. One option is using a supercritical reactor for processing grease
with high FFA compositions. This process operates at high temperature (275°C to 325°C), high pressure,
and therefore must take place in pressure-rated reaction vessels. This reactor does not require a catalyst
because of the high temperature and pressure, so some separation steps are no longer necessary to purify
the downstream product. Furthermore, side-reactions are less of a concern with no catalyst present. Initial
FFA content, water formation and subsequent glycerol formation due to the high operating conditions
affect the process less. However, the capital and operating costs are very high. This is not a feasible
option for a start-up plant of this scope. It would be better implemented as part of a revamp for a current
facility since capital costs associated with pressure-rated vessels are higher.
Another process is glycerinysis, a process that can handle feed stocks with greater than 10% FFA.
Glycerin is heated to 400F and reacted with the FFAs in the feed to form monoglycerides. These
monoglycerides can be processed as normal with the triglycerides by using an alkaline catalyst to form
21
biodiesel. Problems with this process include high operating costs due to the high heat, a high-pressure
boiler to keep the process in liquid phase, and a vacuum to remove any formed water. Glycerinysis is
similar to the process mentioned earlier because the glycerin must be separated at the end, but there is
much more glycerin produced in glycerinysis.
Finally, the use of solid acid catalyst is an emerging option for processing grease. The mixture of
grease and alcohol flows through the solid acid catalyst packed bed reactor. Water is still formed during
the reaction though, so the alcohol/water solution separated the end must be distilled to recycle the
alcohol. Also, contaminants in the oil like phosphorus and water can foul the catalyst.
4.2 Material Research
4.2.1 Feed Sources
The feed grease will be collected from restaurants in the Miami area. In the greater-Miami area
there are approximately 10,750 restaurants22. It was also found that an average restaurant produces about
35 lbs of grease per day23. This means that about 375,000 lbs of waste restaurant grease is produced per
day in the Miami area. The greater Miami area is 6,137 square miles, which is well within reason to
expect the plant’s trucks to be able to collect from the entire area. At the same time, it is not feasible to
expect every restaurant to contribute to the plant’s feed stock, so it was estimated that the plant could
collect approximately 75% of this waste grease. This leads to the estimation the plant will operate with a
feed of 130,000 kg of waste restaurant grease per day.
4.2.2 Feed Composition Research
In conjunction with BIOL383L, research was done to analyze the average composition of a
sample of restaurant waste grease. The grease was obtained from Johnny's Café where they make both
vegetable and animal products in the fryer.
22
23
Knight, Lauren. "How Many Restaurants and Bars are there in Miami?"
Rosinski, Alan. "How Much Grease Fast Food Places Put Out." greener ideal
22
4.2.2.1 Methods
First, the waste grease was heated until homogenous and filtered through a cheesecloth to remove
any suspended particles. Then, the grease was washed to reveal a lipid extract phase. A separatory funnel
was used along with a chloroform-methanol solution to separate the lipid phase.
Thin layer chromatography (TLC) was used to analyze the lipid phase. This method uses a highpolarity silica coated plate and a low-polarity solvent that travels up the plate. A dot of the sample to be
analyzed is placed at the bottom of the plate, and the plate is placed in a beaker with a small amount of
solvent on the bottom. As the solvent travels up the plate, the movement of the sample depends on its
polarity.
Standards were created to compare the lipid sample movement to known compounds. Butter was
used to simulate triglycerides and linoleic acid was used to simulate free fatty acids. Known
concentrations of each of the standards and the lipid extract were run on a TLC column. Then the plates
were stained with iodine chips to reveal the spots of sample. The area of the sample spot directly
correlates to the concentration of the sample.
4.2.2.2 Results
The area of the samples were calculated using a program called ImageJ, which counts the number
of pixels in a traced area. Standard curves were generated which compared the known concentration to
the number of pixels in the spot.
23
Figure 9: Standard Curve of Linoleic Acid
Then the extract was run and the area of the triglyceride spot and FFA spot were compared to the
standard curves.
Figure 10: TLC Plate of Butter, Linoleic Acid and Grease Extract
It was determined that this grease contains 29% FFAs. This agrees with literature values, which say that
yellow grease contains 4-15% FFAs and brown grease contains 50-100% FFAs24. Yellow grease comes
from vegetable oil and brown grease comes from animal fat. Since the sample contains both, 29% is a
reasonable result and representative of waste grease from many restaurants that serve both animal and
24
”Brown Grease Feedstock for Biodiesel.” National Renewable Energy Laboratory
24
vegetable fried products. This value will be used to determine the amount of pre-treatment needed to
reduce the FFA content to less than 1% (the standard for adequate conversion).
4.2.3 Feed Composition Model
The variable nature of waste cooking oil (WCO) presents a challenge when modeling feedstock
characteristics. Table 1 displays average fatty acid composition of WCO compared to several pure oils
with known chemical properties necessary for creating a kinetic model, and all candidates listed in Table
1 have been used by the scientific community as models for WCO. WCO composition best fits within the
soybean oil fatty acid percentages. The kinetics of different oils were simulated to quantify the effect of
feed composition variations on biodiesel conversion, and these differences were determined to be very
significant. Figure 11 compares the conversion of jatrophas oil25 and soybean oil26, which differ by
approximately 50% triglyceride overall conversion, all other reaction conditions being the same. This
comparison emphasized the sensitivity of feed composition on product yields.
Table 1. Fatty acid composition of WCO and various oils.27,28
Fatty Acids
WCO
Soybean Oil
Sunflower Oil
Jatrophas Oil
Linseed Oil
Linoleic Acid
44%
43-56%
44-75%
19-41%
17-24%
Linolenic Acid
5%
5-11%
--
--
35-60%
Oleic Acid
34%
22-34%
14-35%
37-63%
12-34%
Palmitic Acid
14%
7-11%
3-6%
12-17%
4-7%
Stearic Acid
4%
2-6%
1-3%
5-9.5%
2-5%
Given these results, the decision was made to model WCO as soybean oil for the most accurate
process model. The free fatty acids also present in the feed were modeled as a combination of the fatty
25
Aransiola, 2013
Noureddini, 1997
27
Abidin, 2013
28
Chempro, Fatty Acids Composition
26
25
acid chains that would convert to the methyl ester form when pretreated with methanol and sulfuric acid
(e.g. oleic acid converting to methyl oleate).
1
Triglyceride Conversion
0.9
0.8
Jatrophas
0.7
Soybean
0.6
0.5
0.4
0.3
0.2
0.1
0
0
200
400
600
800
1000
1200
1400
1600
1800
2000
PFR Transesterification Reactor Volume (L)
Figure 11. Kinetic comparison of oils with different feed compositions.
4.2.3 Alcohol
There are two alcohols that would be suitable for this process: methanol and ethanol. The purpose
for the alcohol will be discussed in the pre-treatment and transesterification reactor sections. Methanol
was chosen over ethanol as the pretreatment alcohol because it is more commonly used and is
significantly cheaper than ethanol29. However, methanol is typically produced from natural gas in a
petroleum refinery. Not only is this source non-renewable, it is also requires high amounts of energy to
produce. This counteracts the purpose of creating a biofuel if a petroleum-based product was used in the
process.
Therefore, it was determined that a bio-based methanol should be used. Bio methanol is most
typically produced by gasifying a variety of organic materials such as wood waste, algae and glycerin—a
by product of the biodiesel production process30.
29
30
"Ethanol and Unleaded Gasoline Average Rack Prices." State of Nebraska. 2014.
http://www.chemicals-technology.com/features/feature77667/
26
4.2.4 Product
Table 2 features the federal EPA specifications for 100% biodiesel stock fuel, but a majority of
the EPA specifications pertain to compounds that were outside the scope of the feed composition model.
Table 3 presents the specifications met by the final process.
Table 2: EPA Biodiesel Specifications
Table 3. EPA biodiesel specifications met by final design.
Property
Water and sediment
Total glycerin
Methanol content
Limits
0.050 max
0.24 max
0.2 max
27
Simulation Result
0.008
0.22
0.198
Units
vol%
wt%
vol%
5. Design
5.1 Pre-Treatment Section
Figure 12:Pre-Treatment Block Flow Diagram
5.1.1 Water Removal
Before the feed can enter the pre-treatment section, the water content needs to be reduced to less
than 0.2 wt%31. The most common problem that biodiesel producers face is excessive water in the feed.
This will compromise the product quality by limiting reactions and creating unwanted glycerin instead of
biodiesel. First, free water will be removed by gravity separation. The feed will sit in a heated storage
tank for 24 hours, during which the oil and water will separate and the water (which is heavier than oil)
will settle to the bottom. The tank is heated in order to make the oil phase thinner, thus speeding up the
separation process. Now, the water content is approximately 0.4 wt%, still double the allotted amount.
After the free water has been removed by gravity separation, the oil phase will be moved to an
evaporator to remove any entrained water. The evaporator will be heated and agitated for 8 hours. During
this time, additional water will be evaporated, lowing the total water content to <0.2 wt%. The following
31
Springboard Biodiesel. "How to Prepare Your Feedstock." N.p., 2014. Web.
28
chart shows the maximum water and FFA content in order to have acceptable conversion. Feed stocks in
Region A are completely unusable for processing; Region B will create some problems but some
conversion will occur. Region C is the feedstock target area.
Figure 13: Maximum Water Content vs Maximum FFA Content32
Lowering the water content results in the process being able to handle a higher FFA content.
Although the target is 1% FFA, the process will be able to handle deviations in that specification if the
water content is low enough. FFA content control will be discussed further in the Acid Treatment Section.
There will be two storage tanks and two evaporators, so there is enough feed to run a continuous
process.
5.1.2 Filter
The feedstock contains food debris and particulates that must be removed to prevent waste build
up in the pumps and pipes and to control the quality of the feed entering the acid treatment. The pretreatment filter must be able to remove the roughly 3% solids from the feed.
32
Springboard Biodiesel. "How to Prepare Your Feedstock." N.p., 2014. Web.
29
5.1.2.1 Leaf Filter:
Vertical pressure leaf filters are used for liquids with low solid content (roughly 1% to 7%). The
vessel of the leaf filter can be suited with a steam jacket to control the temperature in the filter for liquids
that require higher operating temperatures. Vertical pressure leaf filters can be used, rather than horizontal
filters, in cases where light/fine particles are removed to minimize floor space. Vertical pressure leaf
filters have applications in the fuel and biofuel industry to filter crude oil and fatty acids. The fact that
these filters have been used in the industry previously ensures they would be a good choice for the plant.
Also, the maximum filter area in a vertical leaf filter is approximately 100 m2. This should be noted, as
multiple vertical leaf filters would be needed in this process to achieve the necessary filtration. The steam
jacket capability of the vertical pressure leaf filter is essential to maintain a low viscosity of grease,
meaning if this filter is chosen the steam jacket will most likely be necessary.
5.1.2.2 Centrifuge:
Centrifuges are commonly used to separate solids from liquids. It uses centripetal acceleration to
separate a mixture based on density; the denser substance will move farther from the axis of rotation,
while the lesser dense substance will be pushed toward the axis. Large industrial centrifuges are used to
separate waste grease into white, yellow, and brown grease based on fatty acid concentration. It is also
used in the biofuel industry for fuel purification.
Using a centrifuge for the pretreatment would not only separate the solids from the grease, but
also separate the grease into a heterogeneous mixture; yellow and brown grease. The centrifuge would
most likely result in four separate phases: solids, brown grease, yellow grease, and water. The separation
of the liquid phase would complicate the system. The different phases would have to be treated separately
and the system would have to include two processes; a process to treat the yellow grease and a separate
process to treat the brown grease. This would involve multiple pretreatments stages and reactors.
30
To simplify the system and reduce capital costs, a single homogeneous liquid phase for the grease
feed is desired. Therefore, the centrifuge would not be a desirable filtering method for the system.
5.1.2.3 Design Decision
Vertical leaf filters were selected to separate out the solids from the waste grease feed. This
selection was made because the equipment’s capabilities are best applicable for the filtration of grease for
this process. The leaf filters are able to handle the expected solid content of the feed (3 wt %) and are
widely used to filter fatty acid mixtures. The vertical leaf filter can also be fitted with a steam jacket,
which is necessary to maintain high temperature in the filter vessel and minimize grease viscosity. In
order to size the filters needed the following equation was employed.
LA(1-ε)ρp = cs(V+εLA)
In the above equation, L is the cake thickness, ε is the porosity of the cake, ρp is the density of the
solid particles in the cake, cs is the weight of solids per volume of filtrate, and V is the volume of filtrate.
These are used to solve for A, or the filter area needed in the process. A complete calculation and the
values used for the above properties can be found in Appendix 4. From this, it was determined that 225
m2 of filter area would be needed for the process. As the maximum filter area of a vertical leaf filter is
100 m2, it was decided that three 75 m2 vertical leaf filters will be used in parallel for the process.
5.1.3 Acid Treatment
An acid pretreatment is needed prior to the transesterification reaction to lower the FFA content
in the feed to less than 1%. This prevents unwanted soap formation during the main reaction. In the pretreatment reactor, sulfuric acid will be used as an acid catalyst. Methanol, in the presence of this acid,
esterifies the FFAs. This not only increases the overall conversion in the main reactor, but also improves
the quality of the biodiesel product by removing impurities. If the FFA content is above the 1%
specification mentioned previously, the quality of the product will not be sufficient to meet regulations.
31
It was determined that this acid treatment will take place in a PFR. This was selected by
analyzing results from an experiment found in the Iraqi Journal of Chemical Engineering33. The PFR
provides higher ester formation than a CSTR of the same volume. An isothermal batch system could
provide the needed conversion will similar efficiency, however the drawbacks of a long set up and
cleaning time leads to the selection of the PFR.
Knowing the intended flow rates of each component in the plant through the process flow
diagram, a preliminary volume of the pretreatment reactor was determined based on a simplified rate law.
For the preliminary design, it was assumed that the reaction follows an elementary rate law. This was
modeled as follows;
-rFFA = kCFFACMeOH.
Further modifications were made to this rate law in order to express it in terms of conversion. The
derivation led to the rate law being expressed as,
-rFFA = kC2FFA,0(1-X)(θ-X).
Here, θ refers to the ratio of methanol concentration to free fatty acid concentration entering the
reactor. These initial concentrations were found by using molar masses and densities with initial molar
flow rates. From this, it was found that the initial concentration of FFAs is 1.046 mol/L and the initial
concentration of methanol is 24.71 mol/L. Through research it was found that typical k values in these
types of reactions average 0.0833 L/mol hr34.
33
34
Abbas, Ammar S., and Sura M. Abbas. "Kinetic Study and Simulation of Oleic Acid Esterification in Different Type of Reactors." IASJ.
Barrios, M, J Siles, and A Martin. "A kinetic study of the esterification of free fatty acids (FFA) in sunflower oil."
32
Using the values and equations outlined above, a Levenspiel plot was made which plotted
conversion on the x-axis and the value of FFA molar flow rate divided by the reaction rate on the y-axis.
Figure 14:Levenspiel Plot of the Pre-Treatment Reaction
Using the process flow diagram it was determined that a conversion of 97% in the pre-treatment
is needed to keep the FFA content entering the main reactor under 1%. The volume of the PFR needed is
then equal to the area under the curve in Error! Reference source not found. from a conversion of 0 to
0.97. This area was calculated by first fitting a polynomial equation to the Levenspiel plot. This
polynomial was then integrated and solved using the above limits to find the necessary volume of 460 L.
The preliminary recommendation was then to use a 460 liter PFR to produce the needed FFA
concentration entering the main reactor.
5.1.3.1 Pre-Treatment Reactor Optimization
It was discovered after simulation that the preliminary estimated volume of the pre-treatment
reactor of 460 liters is not sufficient to reduce the FFA content under the needed 1%. This is because of
the rate law involved with the reaction is more complex than originally thought. The FFA esterification
does not follow the elementary rate law as assumed previously but rather one in the form,
-rFFA = k1CFFA-k2CMECH20.
33
The reverse reaction is driven by the methyl esters and water formed during the course of the
reaction. This makes reaching the needed conversion more difficult and in turn leads to the need for a
larger reactor.
To optimize the size of the pre-treatment reactor the UniSim simulation was used. The above
kinetic model is entered into UniSim, which allows it to calculate the output from the reactor. Reactor
volume is able to be directly changed in the program, and the resulting FFA concentration exiting the
reactor is tracked. By varying this reactor volume, the following plot was created.
Figure 15: Effect of Pre-Treatment Reactor Volume on FFA Composition
Using Figure 15, it was determined that a reactor volume of 3 m3 is needed to ensure a feed with
less than 1 wt % FFA enters the main reactor. This is approximately six times as big as the size estimated
prior to simulation. Again, this is due to the more sophisticated kinetics used and shows the need for good
simulation software in the design process. Including kinetics which model the reverse reaction greatly
impacts the volume needed to achieve high conversion. The final recommendation for the pre-treatment
reactor is then to use a 3.5 m3 PFR, and further reaction specifications are listed in Table 4. While a 3 m3
reactor is sufficient, a slightly larger one is recommended to deal with fluctuations in the feed
34
composition. If the feed has a greater FFA content, the minimum reactor volume would no longer be
sufficient for the task.
Table 4. Pretreatment PFR operating parameters.
Parameter
Inlet Temperature
Inlet Pressure
Outlet Temperature
Reactor Volume
Length
Diameter
Pressure Drop
Heat Transfer
Error! Reference source not found.
Value
25
101.3
17
3.5
7
0.8
0
Unit
C
kPa
C
m3
m
m
kPa
Adiabatic
-
5.1.4 Waste Separation
The stream leaving the pretreatment reactor is comprised of waste water, methanol, biodiesel,
triglycerides, and trace amounts of unreacted FFAs. Water, created in the pretreatment reaction, must be
removed from the stream before it enters the transesterification reactor. Otherwise, the water and FFAs
will react to form undesired soap products and lower biodiesel selectivity. In order to separate the waste
water and recycle the methanol back into the pretreatment section, membrane filtration will be used. This
method of separation will take advantage of the small compound size of both the water and methanol
relative to the large compound size of the biodiesel, triglycerides, and unreacted FFAs. After permeating
through the membrane filter, the water and methanol will enter a distillation column where the waste
water and methanol will be separated. The wastewater will be sent to an off-site waste water treatment
facility.
5.3.4.1 Membrane Separation
Membrane separation will be implemented at two sections in the production process; after the
pretreatment reactor to remove waste water and recycle methanol back into the pretreatment reactor, and
another after the main reactor to recycle methanol for the main reactor. This separation method will take
35
advantage of the small compound sizes of the water and methanol relative to the biodiesel, triglycerides,
and FFAs. Data from the Deacidification of Soybean Oil by Membrane Technology35 was utilized in the
selection and sizing of the membrane filters. Desal-5 membranes were selected for the process because it
contained both high methanol and water permeability.
The sizing of the Desal-5 membranes were calculated using the following equation:
𝐽 ∗ (𝑟𝑒𝑗𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛) =
𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒
𝑚𝑒𝑚𝑏𝑟𝑎𝑛𝑒 𝑎𝑟𝑒𝑎
Where J refers to the flux in liters of permeate per meter cubed of membrane per hour (Lm-2h-1)
and rejection fraction is the fraction of FFA that permeates through the membrane.
The flux is linearly dependent on the FFA concentration entering the filter as well as the pressure.
From the data flux equations were determined for various feed concentrations as a function of pressure, as
shown below.
@ 𝐹𝐹𝐴 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛(𝑀):
𝐽 = 𝑠𝑙𝑜𝑝𝑒 ∗ 𝑥 + 𝑏
Where x is pressure in MPa. A flux equation as a function of pressure is created for each membrane filter
by interpolating the functions from the data to fit the specific concentration entering each filter. Using
FFA concentration and permeate flowrates from the UniSim model along with the above equations, a
membrane area was calculated for each filter. Equipment suitable for the modeled operation conditions
and minimum membrane area were selected. The membrane area required for the main filter is too large
for a single filter; therefor 2 membrane filters will be used in parallel to separate the products exiting the
main reactor. The results are shown in the table below.
35
Raman, L. P., M. Cheryan, and N. Rajagopalan. "Deacidification of Soybean Oil by Membrane Technology." Journal of the American Oil
Chemists’ Society 73.2 (1996): 219-24. Web
36
Table 5: Membrane Filter Specifications
Pretreatment Membrane Filter
Main Membrane Filter
Calculated membrane area
7.92 m2
65.7 m2
Equipment
1; Lenntech GM4040F1020, Stinger
2; Lenntech GM8040F1001
Equipment membrane area
8.5 m2
2; 34.4 m2
Each of the filters are capable of operating in the desired flux, operating pressure, and permeate
flow. The calculations can be found in Appendix 7 along with filter equipment information.
5.1.4.2 Methanol Recovery
The methanol and water mixture leaving the filter is separated to recycle pure methanol back to
the pre-treatment reactor. After considering various separation methods such as pervaporation and
extraction, it was quickly determined that this separation would be best accomplished with distillation
column. Methanol and water have very different boiling points, which is the trait distillation columns
exploit. Methanol boils at approximately 65 C, allowing it to be easily separated from water and collected
from the top of the column.
The optimization of the distillation column was performed using the UniSim simulation in
conjunction with given Guthrie economic spreadsheets. The Guthrie spreadsheets were used to estimate
the upfront capital costs to purchase the tower. As more trays are added to the column the purchasing cost
increases proportionally. The number of trays in the column modeled in UniSim were then varied. As the
number of trays increases, the purity of the recycle stream also increases, however, it does so at a
decreasing rate. This recycle purity is directly linked to the amount of methanol feed that must be
purchased and introduced into the pre-treatment reactor. A less pure recycle leads to more feed methanol
required for the process. This feed cost was then calculated on an hourly basis and plotted in addition to
the tower capital cost, as shown in Figure 16: Effect of Trays on Distillation Cost.
37
Figure 16: Effect of Trays on Distillation Cost
As shown in Figure 16, increasing the number of trays increases the capital cost of the tower, but
decreases the hourly material cost for the plant. These competing factors indicate an optimal number of
trays exists that minimize total cost. To find this optimal value, the methanol feed costs over the entire
lifespan of the plant were calculated and added to the capital costs in order to model the overall costs
associated with the distillation column. The results of this analysis are detailed in Figure 17.
Figure 17: Overall Cost of the Distillation Column
38
Figure 17 reveals a minimum cost over the lifespan of the plant obtained when the tower has nine
trays. Additional trays do not save money because the recycle purity remains nearly constant at these
levels. This means that the material costs remain constant at any number of trays over 9, but the capital
costs continue to increase, resulting in a minimum seen in the figure.
Another key specification considered for in the distillation tower was reflux ratio, or the ratio of
the amount of distillate sent as product to the amount sent back into the column. As more liquid is sent
back to the column, the purity of the distillate increases, however a larger diameter column is needed to
hold the extra liquid. Similar to the distillation column tray optimization case, this leads to a tradeoff
between capital and operating costs. With a larger reflux ratio, less methanol feed is needed entering the
pretreatment reactor, decreasing operating costs. However, building a larger column increases capital
costs. Figure 18: Methanol Feed Required at Different Reflux Ratios below explores the effect of reflux
ratio on methanol feed needed.
Figure 18: Methanol Feed Required at Different Reflux Ratios
As expected, Figure 18 reveals that the methanol feed required for the pretreatment reactor
decreases as the reflux ratio increases. Again, this is because greater reflux ratio increases the purity of
39
the methanol recycle stream. From the above graph, a reflux ratio of 1.5 was chosen as the column
specification. This ratio was chosen based on the diminishing returns indicated by the figure. Larger
reflux ratios do not substantially decrease the operating costs, however it would significantly increase the
size and capital cost of the tower.
In addition to the number of trays needed and reflux ratio, other specs for the distillation column
were determined. For one, the height of the column was calculated as the number of trays needed
multiplied by a nominal tray spacing of 24 inches. This spacing was chosen as it is a typical value used in
distillation. This tray spacing requires a total tower height of 18 feet. Finally, the material of construction
for the tower was selected to be stainless steel 316. Stainless steel was chosen over standard carbon steel
to handle the amounts of sulfuric acid that will be present in the tower in addition to the methanol and
water. Table 6 details the specifications of the distillation column. Reboiler and condenser duties and
temperatures were gathered from the UniSim simulation.
Table 6: Distillation Column Specifications
Distillation Column Specs
Number of Trays
9
Tray Spacing
24 in
Tower Height
18 ft
Tower Diameter
6 ft
Reflux Ratio
1.5
Material of Construction SS 316
Reboiler Duty
114 kW
Condenser Duty
113 kW
Reboiler Temperature
64.5 C
Condenser Temperature 99.0 C
Operating Pressure
1 atm
5.2 Transesterification Reactor
Upon pretreatment, WCO is reacted with methanol to form biodiesel methyl esters according to
the reaction presented in Figure 19. As shown in by the stoichiometric coefficients, three methyl ester, or
biodiesel, molecules are formed for every one triglyceride.
40
Figure 19: Transesterification of triglycerides to form biodiesel (methyl esters)
This overall reaction does not do justice to the chemistry taking place during transesterification.
In reality, the reaction proceeds as three total moles of methanol subsequently remove each fatty acid
chain from the glycerin backbone, which results in three transesterified methyl esters and the remaining
glycerin.
5.2.1 Mass Transfer Limitations
Mass transfer primarily limits the yield and purity of the biodiesel product. Triglycerides and
methanol form two immiscible phases when combined, and the rate of reaction is directly influenced by
the degree of mass transfer between phases. According to the Wilke-Change empirical model for
diffusivity, the diffusivity coefficient between two liquid phases decreases with increasing viscosities, and
highly viscous triglycerides impede diffusion into methanol.
Increasing the interfacial area between phases enhances mass transfer. Most non-continuous
reactors have some form of agitation such as impellers or baffles that use shear forces to decrease the
droplet size of methanol and triglycerides, increasing the interfacial area of both phases. Higher mass
transfer occurs in turbulent flow, which is simulated by high agitation speeds or smaller pipe diameters in
the case of some continuous reactors. Other methods to increase interfacial area between phases include
acoustic cavitation, or the rapid growth and collapse of cavities in the reactor. When the cavities collapse,
the liquid rushing into the preoccupied space creates shear forces that are capable of breaking chemical
bonds of the triglyceride molecules and thus reducing droplet size. Alternatively, running the reaction
above the supercritical temperature of methanol forces it to form a homogeneous phase with the
41
triglycerides, but high energy costs to heat the reactor feed accompany this scenario. The use of multiple
micro-reactors also promotes mass transfer. Interfacial area in micro-channels increases with decreasing
micro-channel reactors, which promotes high conversion.
All biodiesel reactor types either contain or can be modified to contain mass transfer promoting
elements, but these characteristics also contribute to more difficult post-treatment, as smaller droplets are
more stable when dispersed than larger droplets. Both mass transfer and subsequent separation must be
considered in selecting a reactor.
5.2.2 Design Alternatives
Selecting a reactor for optimal biodiesel production required quantifying the tradeoffs between
high capital costs, reaction times, energy requirements, and conversion. Table 7 details the reactor
alternatives that were considered along with advantages and disadvantages of each type. A wide variety
of reactors are used in biodiesel production because many reactor types are designed to overcome mass
transfer limitations in different ways. Batch, semi continuous, and continuous reactors were considered in
the design, but more complex reactors with more moving parts, higher energy costs, and higher
maintenance risks were eliminated in favor of reactors that would perform consistently. With this
preliminary, qualitative criteria, batch and plug-flow (PFR) reactors were selected as optimal choices. A
more quantitative analysis of the benefits and shortcomings of each reactor type was necessary to select a
reactor, so both were simulated and optimized to determine which would be the best addition to the
process. Designing a more complex, less reliable reactor would be necessary if both simulated reactors
were unable to achieve the desired conversion.
42
Table 7. Transesterification reactor alternatives
Type
Description
Batch
tank with agitation
Plug-Flow (PFR)
tubular reactor with no
radial dispersion
Packed Bed (PBR)
tubular reactor with solid
catalyst
Continuous stirred
tank (CSTR)
vessel with agitation;
continuous
Membrane
membrane selectively
permeable to methanol
and biodiesel product
Micro-reactor
PFR with smaller
channels
Microwave
batch process that heats
reactants through
microwave radiation
Advantages
handles variable feed compositions
increased conversion with agitation
low capital costs
Simple
high conversion
compatible with liquid catalysts
less complex control system
Simple
compatible with CaO, heterogeneous catalysts
Simple
Disadvantages
long total reaction time
complex control system
higher volume reactor is necessary
not compatible with liquid catalyst
long tube lengths
long residence time required
requires catalyst regeneration
simple
several reactors in series needed for high
conversion
eases downstream separations
membrane must be occasionally replaced
variable materials of construction
low operating costs
handles variable FFA content
made from plastic resins to mitigate corrosion
high conversion with shorter reaction times
long reaction time
high conversion with shorter reaction times
difficult to scale up to industrial size
lower FFA content required
difficult kinetic modeling
43
Type
Description
Cavitational
continuous reactors that
generate cavities that
grow and collapse to
create emulsions
Oscillatory
Baffled (OBR)
Reactive
Distillation
PFRs with evenly spaced
baffles and oscillating
flow throughput
reaction and methanol
separation take place in
distillation column
Advantages
lower methanol:oil ratio; easier downstream
separation
increased mass transfer; high conversion
Disadvantages
difficult to scale up to industrial size
higher energy requirement
higher operating cost
compatible with homogeneous and
heterogeneous catalysts
higher energy requirement
increased mass transfer; high conversion
higher operating/maintenance costs
some have built-in methanol recovery system
Eases downstream separations
average conversion
44
complex control system
high operating/maintenance costs
high energy requirements
incompatible with feedstock
5.2.3 Polymath Kinetic Modeling
While Figure 11 shows the net biodiesel reaction, a more specific reaction pathway is required for
simulation. In this more accurate model, triglycerides are converted to biodiesel through a three-step
reaction process involving the subsequent breakdown of tri-, di-, and monoglycerides. The net reaction
was simulated in UniSim, but UniSim was unable to model the di- and monoglyceride intermediates. For
this reason, a conversion reactor was used in place of a PFR with the net reaction modeling the reactor
chemistry. The product yield achieved by the conversion reactor was selected according to a more
detailed kinetic analysis in Polymath ODE solver. This analysis relied on flow rates and temperatures in
UniSim upstream of the main reactor to characterize the incoming feed. Soybean oil was modeled as
triglycerides with rate constants and activation energies from the literature,36 which was considered to be
accurate for the purposes of the project. The details of the kinetic analysis for both batch and PFR
reactors can be found in Appendix 6. This analysis compared using a single batch reactor and single PFR
instead of a series of reactors. In reality, two batch reactors would be required in order for a transient unit
to fit well within a continuous process.
Figure 20 displays the results of Polymath optimization of both reactors. Holding methanol:oil
ratio and entering flow rates constant, the residence (or reaction) time, temperature, and volumes of each
reactor were optimized to achieve approximately 95% triglyceride conversion, which translates to a yield
that, upon purification, meets the projected plant’s capacity and product specifications. It is notable that
though the reaction time for the batch reactor was optimized at 25 minutes, this time does not include
reactant loading, cleaning, preparation, and unloading the reactor effluent stream. In reality, the batch
operation would take closer to one hour if 30 minutes were allotted for these extra steps.
36
Nourredini, 1997
45
0
200
400
PFR Reactor Volume (L)
600
800
1000
1200
1400
Conversion
1
0.9
4000 L Batch, 25 min
0.8
1500 L PFR, 13 min
0.7
0
5
10
15
20
25
Batch Reaction Time (min)
Figure 20: PFR and batch reactor comparison with Polymath with methanol:oil ratio and entering flow rates held constant
5.2.4 Design Decision
From the Polymath analysis, it was determined that a PFR would be best because 95.8%
triglyceride conversion was achieved with a lesser volume and residence time. Additionally, the down
time required for the batch system to be cleaned, loaded, unloaded, and prepared for the next reaction
involves a more complex and expensive control system as well as manpower to accomplish. If employees
are required to assist with cleaning and loading the reactor, an additional safety risk and source of
operating error is imposed on the overall system. Batch processes are preferred over continuous
processes when a larger degree of control over the system is required, but biodiesel production does not
require this.
The operating conditions of the PFR are shown in Table 8. Two reactor specifications are
notable. First, the transesterification reaction is only slightly endothermic such that the Polymath analysis
predicted that there would be no temperature drop across the reactor. This reality does not directly
46
transfer to the UniSim model due to the limitations of the conversion reactor. In UniSim, a temperature
drop of approximately 10 C is observed. This effect is offset by a heater directly downstream of the
reactor that heats the effluent stream to 50 C such that the membrane and settling tank are not affected.
Secondly, the desired conversion can be achieved at an operating temperature of 58 C. Higher
conversions can be achieved with a higher entering temperature, which can be implemented if, during the
course of plant operation, the final product is off specifications or a greater conversion is needed. Since
95.8% conversion is adequate to meet EPA specifications, additional heating costs are avoided.
Table 8. Transesterification PFR operating parameters.
Parameter
Inlet Temperature
Inlet Pressure
Conversion
Reactor Volume
Pressure Drop
Heat Transfer
Value
58
101.3
95.8
1.5
0
Unit
C
kPa
%
m3
kPa
Adiabatic
-
5.2.5 Catalyst
The catalyst selected for biodiesel transesterification was required to meet certain criteria, and
one of the most important considerations is cost. The catalyst should minimize undesirable side reactions,
and a significant portion must be recycled in an energy efficient manner to further cut costs.
Common biodiesel catalysts are either homogeneous or heterogeneous. Homogeneous bases such
as NaOH, KOH, and methoxides (reacting alkali bases with an alcohol such as methanol) are commonly
used because they are inexpensive, promote high reaction rates, and are not accompanied by high energy
requirements. Alkali catalysts are disadvantageous in that they react with FFAs to produce soaps, which
decreases overall methyl ester yields and create emulsions that make product purification difficult.
Though heterogeneous catalysts tend to facilitate downstream product separation, homogeneous catalysts
tend to be less expensive than heterogeneous catalysts that must be regenerated often.
47
Both KOH and NaOH were considered for the transesterification because both alkali catalysts are
inexpensive. The cost difference between KOH and NaOH is marginal since the catalyst is already one of
the least costly aspects of the design. KOH is preferred over NaOH in some scenarios because it
dissolves more readily in methanol37. Ultimately, the team chose NaOH over KOH due to the availability
of kinetic data for NaOH-catalyzed biodiesel reaction. The accuracy of the kinetic model was considered
more vital to the process than the marginal benefits of one catalyst over the other.
5.3 Post-Treatment Section
Figure 21: Post-Treatment Block Flow Diagram
The products leaving the main reactor are primarily methyl esters, excess methanol, and glycerin.
The objective of the post-treatment section is two-fold: the methyl esters must be purified to meet
government specifications, and the excess methanol must be recovered and fed back to the main reactors.
5.3.1 Glycerin Separation
The EPA specifies that up to 0.24 wt% glycerin can be present in biodiesel product. Even with a
rigorous pretreatment process to mitigate soap generation, glycerin in the reactor effluent must be
37
Rinnova, 2008
48
separated from the biodiesel, and one way to accomplish this is adding a large settling tank downstream
of the reactor. The glycerin will enter the tank with the liquid products and settle to the bottom. A
settling tank would be simple and effective because other components in the effluent stream are much less
dense, as shown in Table 9, and the product flowing out of the tank would have only trace amounts of
glycerin.
Table 9: Relative densities of effluent stream components
Effluent Stream
Density (g/L)
Glycerin
1.26
Methanol
0.792
Methyl Esters
<1
Triglycerides (unreacted)
<1
The team was advised to avoid a solid-liquid separation. Solids are usually avoided in industry as
they are harder to work with than liquids. The glycerin is a liquid when leaving the reactors, but has a
melting point near room temperature (64 F). As this is still a lower temperature, the team found it wise to
add some form of heat exchange to ensure glycerin remains a liquid. The most obvious alternative is to
heat the stream entering the settling tank, and a heater was chosen as the best alternative.
A sizing analysis of this settling tank was conducted to determine key specifications. For these
calculations, methanol was neglected because it has the lowest density and therefore is not expected to
interfere with the separation between the methyl esters and glycerin.
The first step in sizing the tank is to determine the dispersed phase. To do this, the equation
49
is employed. Here, Q refers to volumetric flow rates, which are gathered from the process flow diagram, ρ
refers to fluid densities and µ refers to fluid viscosities. The subscript l is a reference to the light phase
and h is to the heavy phase. As indicated previously, in this case the biodiesel is the light phase and
glycerin is the heavy phase. This equation produces a θ of 7.83, which means the heavy phase, or
glycerin, is dispersed38. Precise values for these variables can be found in Appendix 3, along with a full
calculation of the settling tank sizing. Viscosities were taken at 25 C as this slightly raised temperature
ensures liquid phase is maintained.
After determining the dispersed phase, it is necessary to decide which settling law applies. The
following equation was used to do this.
Above, subscript f refers to the biodiesel and subscript p refers to the glycerin. The variable dp is
the average droplet size of the dispersed phase, glycerin, which forms as it falls out of mixture. This
diameter is best approximated as 70 µm39. When this value is used in the above equation, Kc is found to
be equal to 0.38. For Kc values less than 3.3 and droplet sizes between 3-100 µm, Stoke’s Law is used to
find the settling velocity40. It is also important to note that flow into the settler must be laminar to utilize
Stoke’s Law, a condition that will be maintained with the implemented piping.
As mentioned above, Stoke’s Law allows for the calculation of the settling velocity of the
mixture. This can then be used to size the tank. Stoke’s Law expresses
38
Seader, Henley, and Roper. Separation Process Principles. 3rd ed. 795.
Abeynaike, A, AJ Sederman, Y Khan, ML Johns, and JF Davidson. "The experimental measurement and modelling of sedimentation and
creaming for glycerin/biodiesel droplet dispersions." Malcolm Mackley. Chemical Engineering Science
40
Seader, Henley, and Roper. Separation Process Principles. 3rd ed. 793.
39
50
From this equation, the settling velocity, ut was calculated to 4.19 x 10-4 m/s. This value must be
equal to or larger than the quotient of biodiesel volumetric flow and interface area. The interface area is
estimated as the diameter of the tank times its length. A ratio for length to diameter of 5 is used, which is
taken as a guideline from references41. This leads to the derivation of the equation
The minimum diameter is then calculated to 0.77 m. A safety factor is added, resulting in the
preliminary design of a 1 m tank diameter. Using the length to diameter ratio, the final dimensions of the
settling tank are 5 meter long by 1 meter in diameter.
5.3.3 Waste Water Treatment
Despite the use of separation units and recycling methods, the facility will still produce waste.
The waste produced by the plant is 97mol% water containing trace amounts of sulfuric acid, methanol
and other contaminants. According to the Vanderbilt Environmental Health and Safety Guide to Sewer
Disposal of Wastes42, methanol is forbidden from sewer disposal in any concentration and cannot be
treated using conventional wastewater treatment methods. Therefore the waste water produced by the
facility will be labeled as hazardous waste and will be sent off-site to be treated by a separate company.
The plant will produce roughly 3400 gallons of the hazardous waste every week. The waste will be stored
in a storage tank and will be emptied biweekly and transported to a nearby Hazardous Waste Experts
treatment facility, located in Miami.43 As this volume of waste is relatively small, it was determined that
off-site treatment would be more cost effective than adding a water treatment facility to the plant.
41
Seader, Henley, and Roper. Separation Process Principles. 3rd ed. 794.
"Guide to Laboratory Sink/Sewer Disposal of Wastes." Vanderbilt University Environmental Health and Safety. N.p., n.d. Web. 26 Apr. 2015.
<http://www.safety.vanderbilt.edu/waste/chemical-waste-sewer-disposal.php#summary_forbidden>
43
"Hazardous Waste Disposal in Miami Florida." Hazardous Waste Experts Hazardous Waste Disposal RSS. N.p., n.d. Web. 26 Apr. 2015.
<http://www.hazardouswasteexperts.com/hazardous-waste-disposal-miami-florida/>
42
51
6. Equipment
6.1 Equipment Listing
Table 10 describes the equipment and materials of construction necessary for the process.
Carbon steel is a standard material of construction because of its affordability and commonality in the
chemical industry. In units where corrosion is a concern due to acids or bases, such as the sulfuric acid
and sodium hydroxide in this process, more corrosive resistant materials must be considered. The
esterification plug flow reactor and pretreatment distillation column will contain significant amounts of
sulfuric acid. For these vessels, carbon steel coated with stainless steel inner coating was selected as the
best material. Additionally, the mixer and transesterification reactor come into contact with small
amounts of sodium hydroxide. Figure 22 was used to determine the materials of construction for the
mixer and transesterification reactor. No more than 4% sodium hydroxide is expected to exist within the
vessels at any point of the process and the temperature of the solution will be about 60°C. Under these
conditions, the solution is located in Area A of Figure 22, indicating that carbon steel is a suitable
material for the mixer and transesterification reactor.
Table 10 was generated in conjunction with Figure 22 and material research, showing the
appropriate material of construction for each of the process vessels.
52
Figure 22: Materials of Construction for Handling Caustic Solution44
44
"Caustic Soda Solution Storage Tank Lining." Dow Answer Center. The Dow Chemical Company, 6 Nov. 2014. Web. 07 Dec. 2014.
53
Table 10: Equipment and Materials of Construction
Vessel
MOC
Feed Storage Tank
Methanol 1 Storage Tank
Sulfuric Acid Storage Tank
NaOH Storage Tank
Methanol 2 Storage Tank
Biodiesel Storage Tank
Glycerin Storage Tank
Mixer-100
Carbon Steel
Carbon Steel
Stainless Steel 316
Rubber lined Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
Stainless Steel Lined
Carbon Steel
Carbon Steel
Carbon Steel
Stainless Steel 316
Stainless Steel Lined
Carbon Steel
Carbon Steel
Carbon Steel
Stainless Steel Lined
Carbon Steel
Carbon Steel
Mixer-101
Mixer-102
Mixer-103
Distillation Column
Membrane 1
Membrane 2
3-Phase Separator
Pre-Treatment Reactor
Transesterification Reactor
Further equipment will be necessary to ensure necessary energy is supplied and removed from the
system to achieve the desired volume of product. This equipment will include, but is not limited to, heat
exchangers, pumps, valves, and vessels. The number of vessels and respective volumes are shown in
Table 11. The appropriate quantity and energy requirements of other necessary equipment will
be determined once additional design decisions are made, the most important of which is the main reactor.
54
Table 11: Vessel Volumes based on Storage Density Contents. An asterisk denotes vessels that are incorporated into the process
but are not represented in the process flow diagram
Vessel
Volume (m3)
Feed Storage Tank*
Methanol 2 Storage Tank*
Biodiesel Storage Tank*
Glycerin Storage Tank*
Methanol 1 Storage Tank*
Sulfuric Acid Storage
Tank*
NaOH Storage Tank*
3-phase Separator
Mixer-100
Mixer-101
Mixer-102
Mixer-103
Distillation Column
Membrane 1
Membrane 2
Pre-Treatment Reactor
Transesterification Reactor
500
500
500
500
100
55
10
10
15
10
10
10
10
10
5
5
1
1
7. Safety Considerations
7.1 Chemicals
The main chemicals used in this process that present safety concerns are the acid catalyst, the
base catalyst and the alcohol, which are sulfuric acid, sodium hydroxide and methanol, respectively.
Sulfuric acid is a colorless, odorless, and highly-corrosive material. The main acute exposure
hazard is severe burns to skin and eyes. It is more harmful than other strong acids due to the dehydrating
nature of the chemical, which releases extra heat, causing secondary burns. It will cause temporary or
permanent blindness if contacted with eyes in either liquid or vapor form. Long term exposure also causes
lung damage, vitamin deficiency and potentially cancer.
Sodium hydroxide is a caustic base and white solid that is typically available in flakes or pellets.
It is a highly corrosive alkali that will decompose living tissue on contact. It also causes secondary burns,
as the decomposition reaction is highly exothermic. Aqueous sodium hydroxide is more dangerous than
solid, although solid NaOH will also exhibit some corrosive behavior if there is any water present
(including sweat or humid air). There are no known long-term exposure effects of NaOH; all of the health
effects are acute effects due to corrosivity.
Methanol is a colorless, flammable liquid with a distinct odor. If ingested, methanol will be
metabolized to formic acid, which damages the central nervous system and causes blindness, coma or
death. The adverse health effects associated with methanol all occur internally. While contact with skin
will not cause external damage, it may provide a route for the chemical to enter one’s central nervous
system. Methanol is highly flammable and easily ignites.
7.2 Operating
Sulfuric acid must be stored in a vessel made of a non-reactive reactive material, such as glass.
Great care should be taken that the acid does not contact the operator’s skin. Proper personal protective
56
equipment (PPE) for handling sulfuric acid includes: safety goggles, face shield, boots, gloves and aprons
made from a suitable material (see material safety data sheets for more information). Sulfuric acid will be
pumped directly from the storage vessel to the pre-treatment vessel, limiting the amount of operator
contact needed. If sulfuric acid does contact the skin, any contaminated clothing must be removed and the
affected person must wash the acid off under a safety shower for at least 15 minutes. Medical attention
must be sought immediately. When diluting the sulfuric acid the acid must be added to the water instead
of water added to the acid. This way, the high heat capacity of water will absorb the heat released as the
chemicals mix.
Sodium hydroxide must also be stored in a non-reactive vessel, preferably the container in which
it was delivered. Keep sealed tightly in a cool, dry, well-ventilated area. When handling sodium
hydroxide, the same PPE should be worn as for sulfuric acid. If an operator needs to create the sodium
hydroxide solution, a respirator should also be worn. The same procedure as for the sulfuric acid should
also be followed if sodium hydroxide contacts skin.
Methanol must be stored in a cool, dry, well-ventilated area away from any potential sparks. If
the methanol does ignite, water will not extinguish the fire. A fire extinguisher will be necessary.
Methanol will be pumped directly from a storage container to the various vessels, so operator contact with
methanol is limited. If an operator must come into contact with the methanol, the same PPE as for sulfuric
acid must be worn. If the area is not well ventilated, a respirator must also be worn. If methanol is
ingested, the exposed person must drink two glasses of water and seek medical attention immediately. If
methanol contacts any part of the body, the same procedure used for sulfuric acid must be followed.
All three chemicals are considered hazardous waste and need to be properly disposed of
according to OSHA standards. See Waste Water Treatment (Section 5.3.3) for more information.
57
8. Quality Control
Process control is necessary to ensure that the final product is up to EPA standards. The piping
and instrumentation diagram for the plant is shown in Figure 23. Temperature, pressure, and composition
measurements are the primary method by which product quality will be ensured.
As shown in the diagram, every stream has temperature and pressure gauges. Composition
measurements are particularly important before and after the reactors and the distillation column.
Conditions of the pretreatment reactor must be adjusted based on the FFA content of the entering WCO.
More methanol must be fed to the pretreatment reactor for higher percentages of FFA. In reference to the
main reactor, the reaction temperature or the methanol flow rate must be adjusted if WCO conversion is
low or if the final biodiesel product is off specification. Finally, the purity of the methanol leaving the
distillation column must be high in order for downstream processes to be unaffected; this also requires a
concentration measurement.
The distillation column will require master-slave controllers to achieve the desired component purity.
The cascade controllers will use temperature and reflux ratio measurement to control the system. Since
both temperature and methanol flow rates can be manipulated to achieve a meet the soybean oil
conversion setpoint, the transesterification reactor will require a multiple input, multiple output controller.
Since the pretreatment reactor proceeds at ambient conditions, the primary control method for ensuring
low FFA content will be a composition measurement. If the FFA content leaving the pretreatment reactor
is higher than the desired output, a feed forward temperature controller will increase the stream
temperature entering the transesterification reactor such that the final product will be up to standards.
Composition measurements will be taken offline since automated control would be more expensive.
Several times a shift, an operator will take a sample from each stream of interest and run analyses to
determine composition. Thin layer chromatography or pH measurement are potential methods that could
be performed.
58
Figure 23. Plant Piping and Instrumentation Diagram.
59
9. Business Plan
9.1 Market Study
Despite being a relatively new energy source with oldest plants dating back to the mid-2000s,
biodiesel is a growing market in the United States. According to the US Energy Information
Administration, approximately 100 million gallons of biodiesel per month are produced in 96 US plants
that have a combined capacity of 2 billion barrels every year. Biofuels provide nearly 6% of the energy
supplied annually, and as of 2009 the United States produces the second largest volume of biofuels.
Figure 24 Error! Reference source not found.depicts the amount of biofuel produced yearly in the US.
It can be see that the volume steadily increases overall as more biodiesel plants are built every year.
Figure 24: Million barrels of biodiesel produced in the United States per year
Producing biodiesel is profitable due to a $1 per barrel tax credit for blenders. Without this
incentive, expensive feed and raw materials prevent biodiesel from competing with conventional diesel
60
prices. Some states provide further benefits to biodiesel producers, as detailed in a following report
section.
9.1.1 Customer
The final product will be marketed and sold to blenders who have the capacity to blend large
volumes of purified product and who will ultimately supply the blended fuel to consumers with diesel
engines. These customers would potentially be community leaders or retail gas station owners who value
sustainability and desire to promote alternative energy sources. In keeping with the project objective of
introducing a competitive product into the market, the target customer is one who would benefit from
cheaper diesel.
The customer can further be expanded to include any industry using equipment powered by
diesel that desires to use a greener energy source for their operations. Several such industries are
power companies that use diesel for electricity generation, the sugar industry that uses diesel to fuel
sugar boiler vessels, paint companies for wood preservatives, and the agricultural industry for aerial
spraying. Ultimately, any company interested in biodiesel would be interested from an
environmental standpoint or out of a desire to promote themselves as an energy-conscious company.
The plant will be designed to operate for 20 years. At the end of the period the team will decide,
depending on the market, to either sell the plant or specific pieces of equipment at salvage value for
further profits or refurbish the equipment to continue biodiesel production for an extended period. In the
scenario of retiring the plant, future customers would include those who have interest in producing
biodiesel themselves or interest in a similar process.
9.1.2 Competition
The competition in the biodiesel market comes from inside the biodiesel industry and the
alternate fuel industries.
61
The competition from the biodiesel industry comes from similar biodiesel production plants in the
area. For the team, this competition pertains to the biodiesel production plants in Florida, who will
compete for the business of the diesel blenders. According to the plants listing section of biodiesel.org,
there are currently five companies in Florida that produce biodiesel (see Appendix 4). These business will
need to sell their product to blenders who will then blend the biodiesel with diesel made from crude oil.
The blended product is what will be sold to the public as biodiesel at the pump.
There is also competition from the industries creating fuel other than biodiesel. The most
comparative competition comes from the diesel industry because biodiesel is compatible with diesel
engines. If there is a large discrepancy between the price of biodiesel and diesel, the environmental
benefits of biodiesel will not be enough to overcome the financial burden. This would result in the public
being unwilling to buy biodiesel versus regular diesel at the pump and consequently blenders will lose
interest in purchasing biodiesel from the production businesses. This is unlikely because crude oil is a
limited resource and trends show the price of diesel only increasing in the future. Therefore, the cost
difference of biodiesel and diesel will continue to decrease until biodiesel becomes more cost effective
than diesel.
A more likely source of competition comes from the alternative fuel industry. There is a large
effort to find alternative fuels such as electricity, wind, water, etc. Today vehicles either run on
combustion engines, electric engines, or a combination of both. The biodiesel industry depends on the
continual use of combustion engines. However, as electric motors become more efficient, combustion
engines might eventually become obsolete. With so much research invested into alternative fuels, it is
difficult to tell how the market will change in the future which is a main reason why the expected plant
life is only 20 years.
62
9.2 Tax Information
Under federal law, a $1 per-gallon tax credit will be applied for the production of biodiesel that
complies with fuel standards and Clean Air Act requirements. This credit will be increased to $1.10 for
the first 15 million gallons produced (approximately 1.5 years of production)45. It is estimated that the
production facility will receive tax credit for 100% of taxes with the 75% state rebate and $1.10/gallon
rebate from the federal government. This credit is valid through 2017 and is expected to be renewed
further.
A major factor in determining the location of the plant was the tax credits available in certain
states beyond the standard $1-per-barrel credit. Overall, Florida is the most helpful for renewable fuel
plant start-ups and provides the proposed plant with the greatest chance of being competitive with diesel
providers.
According to the U.S. Department of Energy, in Florida: “An income tax credit is available for
75% of all capital, operation, maintenance, and research and development costs incurred in connection
with an investment in the production, storage, and distribution of biodiesel (B10-B100), ethanol (E10E100), or other renewable fuel in the state, up to $1 million annually per taxpayer and $10 million
annually for all taxpayers combined.”46
This tax credit makes biodiesel production possible, since the process is not efficient enough to
make a profit on its own. This credit is good through December 31, 2018. The credit may only be applied
toward taxes; no rebates will be issued. Due to the size and capacity of our plant, government tax
subsidies will completely cover all tax costs.
45
46
"Senate Biodiesel Tax Credit Could Dramatically Change Outlook For The Industry."
"Biofuels Investment Tax Credit." Alternative Fuels Data Center
63
9.3 Costs
9.3.1 Capital Costs
An efficient way to estimate the capital cost of the plant is to use the Guthrie Cost Estimating
Tool. This tool contains modules for each different type of equipment where specifications are entered
and subsequent costs are calculated. This tool calculates the price of the equipment in 1970 and then uses
the current Chemical Engineering Plant Cost Index (CEPCI) to scale up the costs to present values. The
most recent index found was 580, from the Fall of 201447. The following tables show the capital costs for
vessels and plant development costs.
Table 12: Vessel Capital Costs as Calculated by Guthrie Cost Estimation Tool
Vessel
Cost
Distillation Column
Sulfuric Acid Storage Tank
De-watering Vessel
NaOH Storage Tank
Transesterification Reactor
Mixer-101
Feed Storage Tank
Methanol 2 Storage Tank
Biodiesel Storage Tank
Glycerin Storage Tank
Filter Vessel
Pre-Treatment Reactor
Membrane 1
Membrane 2
Mixer-100
Mixer-102
Mixer-103
Fired Heater 1
Fired Heater 2
Methanol 1 Storage Tank
3-Phase Settler
47
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
668,472
495,940
374,532
231,945
221,168
199,069
125,897
125,897
125,897
125,897
123,364
112,400
100,000
100,000
99,534
99,534
99,534
92,326
83,903
47,070
32,455
"Chemical Engineering Plant Cost Index (Cepci) - Student." Cheresources.com Community
64
Table 13: Plant Development Capital Costs
Capital
Cost
Piping, valves and fittings
$ 2,200,000.00
Safety Protection System
$ 1,809,520.10
Contingency Fee
$ 1,490,000.00
Transportation Trucks
$ 1,467,076.00
Installation
$ 1,436,501.00
Site Development
$ 1,364,840.47
Land Plot
$ 1,200,000.00
Building Cost
$ 1,050,399.05
Instruments and Controls
$
770,000.00
Installation was estimated as 15% of the total capital costs. Transportation trucks are necessary to
transport restaurant waste grease to the plant, and then the biodiesel to blending facility. The land plot
was found in the Miami area using a relator search tool. Building Cost and Site Development were both
calculated using the Guthrie Cost Estimating Tool. Using this, the total capital cost for this plant is
estimated at $16.5 million. The cost for the membrane separators are estimates based on market values, as
there is not a membrane module in the Guthrie Cost Estimating Tool.
Capital costs were also estimated using the Lang Factor method. In this method, the total vessel
costs are multiplied by a specific factor, based on the type of chemical plant, to estimate the capital costs.
The Lang Factor for a liquid chemical processing plant is 4.7448, making the total capital costs $17.3
million. The Guthrie method is validated, since the Lang Factor method is within 5% of the original
capital cost estimation.
48
Turton, Richard. Analysis, Synthesis, and Design of Chemical Processes. 3rd ed.
65
9.3.2 Operating Costs
The operating costs were estimated on an hourly basis. Using the yearly production of 9.5 gallons
per year, the following table shows the hourly costs necessary for the production of biodiesel.
Biomethanol costs significantly more than methanol from natural gas—anywhere from 1.5 to 4 times
more. The following table of operating costs uses a cost estimate for bio methanol of 4 times the cost of
natural gas methanol, to ensure the process is still profitable using bio methanol.
Table 14: Hourly Costs of Raw Materials
Raw Materials
Feed
Methanol
Sulfuric Acid
Methanol 2
NaOH
Flow rate
Units
4.367 M3/h
3
0.1665 m /h
0.01621 m3/h
1.186 m3/h
0.02244 m3/h
Cost per unit
Total Cost/hr
$
105.67
$
461.45
$ 1,526.06
$
254.09
$
724.89
$
11.75
$ 1,526.06
$
$
$
774.81
1,809.91
17.39
Then, operating costs associated with general utilities were calculated, and shown in the table
below. Again, all operating costs were distributed on an hourly basis.
66
Table 15: Hourly Operating Costs
Duties
CndsDuty
Rb Duty
Heat1
Heat2
Electricity
kJ/hr
kWh /hr
$/kWh
Total Cost/hr
4.08E+05
$113.25
$0.08
$8.99
4.11E+05
$114.11
$0.08
$9.06
3.82E+05
$105.97
$0.08
$8.41
2.82E+05
$78.33
$0.08
$6.22
7.52E+06
$2,088.89
$0.08
$165.86
$232,959.00
$29.12
Salary
Hourly Rate
$75,000.00
$36.06
$32,000.00
$15.38
$45,000.00
$21.63
$50,000.00
$24.04
$140.63
$160.00
$84.38
$437.50
$/year
Process Water
Labor
Engineers
Operators
Office
Truck Drivers
--
--
# of staff
3
8
3
14
Yearly Maintenance Fee
Maintenance
$250,000.00
Transportation # of trucks gallons/hr $/gallon
15
3.5
$31.25
3
$157.50
Total Utilities Costs/hr
$1,238.91
9.4 Profitability
In order to determine the profitability of the proposed plant, a rate of return on investment over
the lifespan of the plant was calculated. It was determined that a return rate of at least 10% was needed to
label the project as economically feasible.
The first step in doing this was to calculate the costs of the needed chemical inputs. The costs for
each of the process materials used can be found in the Operating Costs section. The totals cost per year
from operating costs calculated previously, is $31.8 million. Yearly costs assume 8000 operating hours
per year, allowing for shut down time. The total revenue of the plant comes from the sale of biodiesel and
the side product glycerin. The following table shows the income gained from selling the two products.
67
Table 16: Income from Products
Product
Flow Rate (m3/hr)
Flow rate (gal/hr)
Biodiesel
4.632
1224
$3.50
$4,282.76
Flow Rate (kg/hr)
Flow Rate (lb/hr)
$/lb
Total Income/hr
942.9
2079
$0.10
$207.87
Bi Product
Glycerin
$/gallon
Total Income/hr
The cash flow diagram was created assuming a construction time of one year. For this reason the
entire capital cost was placed in year -1 of the diagram. As stated above a 20 year life span was assumed
as this is a typical plant life. So, the salvage price of the plant, 10% of the capital costs, and the working
capital was added to year 20 of the cash flow diagram. Using this knowledge equations were used to bring
all costs back to present value. Moving the plant construction cost from year -1 to year 0 was done with
the equation,
$16.5E(1+i)1.
Similarly the salvage and working capital were brought to present value with the equation,
$3.3E6(1+i)-20.
The return on investment (i) can then be solved for using the yearly profit of the plant with the
following equation and Microsoft Excel Solver,
($4.2 E6)((1+i)20-1)/(i(1+i)20) = $2.8E6(1+i)-20 - $14.8E6(1+i)1.
From this, it was found that the plant produces a 20% return on investment with $4.2 million in
yearly profit. As this is above the minimum acceptable return of 10%, it is concluded that the process is
economically feasible. This calculation was done using a biodiesel selling price of $3.50 per gallon. $1 of
that price would come from the government tax credit described in the Tax Information Section (Section
8.2). With this, the biodiesel blender would pay the production facility $2.50 per gallon. According to
research, this falls well within the reasonable selling price for biodiesel plants, meaning that the process
68
will be profitable. The average selling price of biodiesel B100 is $4.0249. By undercutting the average
price, the assumption of infinite demand is more valid. The complete cash flow diagram that had been
described previously can be seen in Figure 25 below.
Cash Flow Diagram of the Plant Lifetime
$7,500,000.00
$5,000,000.00
$2,500,000.00
$$(2,500,000.00)
-1
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Year
$(5,000,000.00)
$(7,500,000.00)
$(10,000,000.00)
$(12,500,000.00)
$(15,000,000.00)
$(17,500,000.00)
Figure 25: Cash flow diagram of Plant Construction and Operation
However, the government tax credit that gives the production plant $1 per gallon of biodiesel may
not last the 20 year lifespan of the plant. The tax credit expires in 2018, and if it is not renewed, the plant
would only receive $2.50 per gallon of biodiesel. With this reduced profit, the plant would be losing $5.6
million per year. If the tax credit expires after the plant has been in production, switching from bio
methanol to natural gas methanol will still allow the plant to be profitable. Although the biodiesel would
not truly be “green” with the use of natural gas-based methanol, the plant would not have to be shut down
early due to profit loss. This shows that the biodiesel industry is heavily dependent on government
assistance. Significant technology improvement, in conjunction with the inevitable price increase of fossil
fuel based products, needs to occur in order for this industry to be profitable on its own.
49
"Fuel Prices." Alternative Fuels Data Center l
69
10. Conclusion
In conclusion, opening a 9.5 million gallon per year biodiesel production plant will generate a
$4.2 million profit per year. The final design was economically optimized within the limitations of the
equipment used and is presented above as the best case scenario. While this plant alone will not solve the
energy crisis, it can be used to demonstrate profitability for others looking to open biodiesel production
plants. With a selling price of $3.50 per gallon, the plant will produce a 20% rate of return over a 20 year
lifespan. However, if the $1 per gallon tax credit expires, the plant will no longer be profitable with the
current design. The methanol source would have to be changed, compromising the idea of a renewable
fuel. This demonstrates the need for improvement in the biodiesel production industry. Further work
could be done to explore the possibility of converting the glycerin byproduct to bio methanol. Glycerin
can be gasified to produce syngas, a precursor to methanol. If this plant had that capability, the plant
would be profitable and generate a fully renewable fuel source, even if the $1 per gallon tax credit
expires. For now, this design work proves that a biodiesel production plant can be profitable in the United
States with government tax credit assistance.
70
References
Abbas, Ammar S., and Sura M. Abbas. "Kinetic Study and Simulation of Oleic Acid Esterification in
Different Type of Reactors." IASJ. Iraqi Journal of Chemical and Petroleum Engineering, June
2013. Web. 15 Oct. 2014. <http://www.iasj.net/iasj?func=fulltext&aId=75022>.
Abeynaike, A, AJ Sederman, Y Khan, ML Johns, and JF Davidson. "The experimental measurement and
modeling of sedimentation and creaming for glycerin/biodiesel droplet dispersions." Malcolm
Mackley. Chemical Engineering Science, n.d. Web. 5 Dec. 2014.
Abidin, Sumaiya Z., Dipesh Patel, and Basudeb Saha. "Quantitative Analysis of Fatty Acids Composition
in the Used Cooking Oil (UCO) by Gas Chromatography-Mass Spectrometry (GC-MS)." The
Canadian Journal of Chemical Engineering91.12 (2013): 1896-903. Wiley Online Library. Web.
20 Apr. 2015. <http://onlinelibrary.wiley.com/doi/10.1002/cjce.21848/full#cjce21848-note0001>.
Ahmad, S, D Papadias, and Rick Farmer. "Hydrogen From Glycerin: A Feasibility Study." Hydrogen
Energy. N.p., 2010. Web. 2 Nov. 2014.
<http://www.hydrogen.energy.gov/pdfs/progress10/ii_a_3_ahmed.pdf>.
Alexander, Adam, Michael Lubben, Angus Richeson, and Thomas Voss. "Senior Design Final Report."
Team 1: The Diesel Crew. Ed. Adam Alexander. Calvin College, 15 May 2014. Web. 1 Oct.
2014. <http://www.calvin.edu/academic/engineering/2013-14team1/Documents/Senior%20Design%20Final%20Report4.pdf>.
Aransiola, Elizabeth F., Michael O. Daramola, Tunde V. Ojumu, Bamidele O. Solomon, and Stephen K.
Layokun. "Homogeneously Catalyzed Transesterification of Nigerian Jatropha curcas Oil into
Biodiesel: a Kinetic Study." Scientific Research 2 (2013): 83-89. Web. 26 Apr. 2015.
Barrios, M, J Siles, and A Martin. "A kinetic study of the esterification of free fatty acids (FFA) in
sunflower oil." FUEL(2006): 2383-88. Web. 7 Nov. 2014.
Barnett, Ron. "Restaurants' Grease a Hot Item for Thieves." USA Today. USA Today, n.d. Web. 4 Oct.
2014. <http://usatoday30.usatoday.com/news/nation/2010-09-29-restaurant-greasethieves_N.htm>.
Beer, T, T Grant, and PK Campbell. "Biodiesel could reduce greenhouse gas emissions." CSIRO. CSIRO,
27 Nov. 2007. Web. 6 Dec. 2014. <http://www.csiro.au/OrganisationStructure/Divisions/Energy-Technology/BiodieselBlends.aspx>.
"Biodiesel." fueleconomy.gov. US Department of Energy, n.d. Web. 16 Oct. 2014.
<http://www.fueleconomy.gov/feg/biodiesel.shtml>.bl
"Biofuels Investment Tax Credit." Alternative Fuels Data Center. N.p., n.d. Web. 12 Oct. 2014.
Buasri, Achanai, et al. "Transesterification of waste frying oil for synthesizing biodiesel by KOH
supported on coconut shell activated carbon in packed bed reactor."ScienceAsia 38 (2012): 28388. Engineering Research Database. Web. 13 Oct. 2014.
Buasri, Achanai, Bussarin Ksapabutr, Manop Panapoy, and Nattawut Chaiyut. "Biodiesel production
from waste cooking palm oil using calcium oxide supported on activated carbon as catalyst in a
fixed bed reactor." Korean Journal of Chemical Engineering 29.12 (2012): 1708-12. SciFinder
Scholar. Web. 13 Oct. 2014.
71
Buasri, Achanai, Nattawut Chaiyut, Vorrada Loryuenyong, Chao Rodklum, Thechit Chaikwan, and
Nanthakrit Kumphan. "Continuous Process for Biodiesel Production in Packed Bed Reactor from
Waste Frying Oil Using Potassium Hydroxide Supported on Jatropha curcas Fruit Shell as Solid
Catalyst." Applied Sciences 2.3 (2012): 641-53. SciFinder Scholar. Web. 29 Oct. 2014.
Canter, Neil. "Making Biodiesel in a Microreactor." Tribology & Lubrication Technology 62.8 (2006):
15-7. ProQuest. Web. 29 Oct. 2014.
"Caustic Potash." ICIS. ICIS Chemical Business, 3 June 2006. Web. 4 Nov. 2014.
<http://www.icis.com/resources/news/2006/06/03/2014563/caustic-potash/>.
"Chemical Engineering Plant Cost Index (Cepci) - Student." Cheresources.com Community. N.p., n.d.
Web. 15 Mar. 2015.
Chen, Ching-Lung, et al. "Biodiesel Synthesis Via Heterogeneous Catalysis using Modified Strontium
Oxides as the Catalysts." Bioresource technology 113 (2012): 8-13. ProQuest. Web. 4 Nov. 2014.
Chilakpu, K. O., et al. "Modification of Biodiesel Batch Reactor." Journal of Emerging Trends in
Engineering and Applied Sciences 5.4 (2014): 262-4. ProQuest. Web. 29 Oct. 2014.
Encinar, J. M. "Study of Biodiesel Production from Animal Fats with High Free Fatty Acid
Content." Study of Biodiesel Production from Animal Fats with High Free Fatty Acid Content.
Elsevier, 25 July 2011. Web.
"Ethanol and Unleaded Gasoline Average Rack Prices." State of Nebraska. Official Nebraska
Government Website, 1 Dec. 2014. Web. 6 Dec. 2014.
<http://www.neo.ne.gov/statshtml/66.html>.
"Fossil Fuels." Institute for Energy Research. IER, 2014. Web. 4 Nov. 2014.
<http://instituteforenergyresearch.org/topics/encyclopedia/fossil-fuels/>.
"Fuel Prices." Alternative Fuels Data Center:. N.p., n.d. Web. 21 Nov. 2015.
"Guide to Laboratory Sink/Sewer Disposal of Wastes." Vanderbilt University Environmental Health and
Safety. N.p., n.d. Web. 26 Apr. 2015. http://www.safety.vanderbilt.edu/waste/chemical-wastesewer-disposal.php#summary_forbidden
Harbert, Joshua, Christian Ocier, Mitch Kenyon, Fred Thielke, and Adebo Alao. "Final Report-Senior
Design Project." Rinnova Renewable Energy. Ed. Joshua Harbert. Calvin College, 7 May 2008.
Web. 31 Oct. 2014. <http://www.calvin.edu/academic/engineering/seniordesign/SeniorDesign07-08/Team11/downloads/Final_Report.pdf>.
"Hazardous Waste Disposal in Miami Florida." Hazardous Waste Experts Hazardous Waste Disposal
RSS. N.p., n.d. Web. 26 Apr. 2015. <http://www.hazardouswasteexperts.com/hazardous-wastedisposal-miami-florida/>
Hofstrand, Don. "Tracking Biodiesel Profitability." Iowa State University. ISU, n.d. Web. 6 Nov. 2014.
<http://www.extension.iastate.edu/agdm/energy/html/d1-15.html>.
Hosseini, Mehdi, Ali Mohammad Nikbakht, and Meisam Tabatabaei. "Biodiesel Production in Batch
Tank Reactor Equipped to Helical Ribbon-like Agitator." Modern Applied Science 6.3 (2012):
40-45. ProQuest. Web. 29 Oct. 2014.
"How Much Does Biodiesel Reduce Air Pollutants?" AllegroBiodiesel. N.p., 2007. Web. 6 Oct. 2014.
<http://www.allegrobiodiesel.com/howmuchdoesbiodieselreduceairpollutants.html>.
72
Irwin, Scott. "Pricing of 2014 Biodiesel RINs under Alternative Policy Scenarios." Farmdoc Daily.
Department of Agriculture and Consumer Economics, University of Illinois Urbana, 15 Oct.
2014. Web. 9 Nov. 2014. <http://farmdocdaily.illinois.edu/2014/10/pricing-of-2014-biodieselrins.html>.
Ito, Takuya, Yusuke Kakuta, Katsumi Hirano, and Toshinori Kojima. "Study on Continuous Production
of Biodiesel Using Fixed Bed Reactors Filled With Anion-Exchange Resins." Energy and
Environmental Research 4.2 (2014): 47-54.Engineering Research Database. Web. 1 Nov. 2014.
Knight, Lauren. "How Many Restaurants and Bars are there in Miami? ." shiftgig. N.p., Dec. 2012. Web.
15 Sept. 2014. <http://www.shiftgig.com/articles/how-many-restaurants-and-bars-are-theremiami>.
Kyte Centrifuge. N.p., n.d. Web. 9 Nov. 2014. <http://www.kytecentrifuge.com/applications/biodiesel>.
Martin, Norbert. "Removal of Methanol by Pervaporation." Sulzer Technical Review. Sulzer Chemtech,
2003. Web. 8 Nov. 2014. <http://www.sulzer.com/ms//media/Documents/Cross_Division/STR/2003/2003_01_19_martin_e.pdf>.
Mazubert, Alex, Martine Poux and Joelle Aubin. Intensified processes for FAME production from waste
cooking oil: A technological review. 26 July 2013. PDF.
"Member Plants Listing - Biodiesel.org." Member Plants Listing - Biodiesel.org. N.p., n.d. Web. 09 Nov.
2014. <http://www.biodiesel.org/production/plants/plants-listing>.
"Miami Metropolitan Area." Wikipedia. Wikipedia, n.d. Web. 9 Oct. 2014.
<http://en.wikipedia.org/wiki/Miami_metropolitan_area>.
Neji, Soumaya Bouguerra, Mahmoud Trabelsi, and Mohamed H. Frikha. "Esterification of Fatty Acids
with Short-Chain Alcohols Over Commercial Acid Clays in a Semi-Continuous Reactor."
Energies 2.4 (2009): 1107-17. ProQuest. Web. 29 Oct. 2014.
Noureddini, H, and D Zhu. "Kinetics of Tranesterification of Soybean Oil." Journal of the American Oil
Chemists' Society 74.11 (1997): 1457-63. Web. 26 Apr. 2015.
Raman, L. P., M. Cheryan, and N. Rajagopalan. "Deacidification of Soybean Oil by Membrane
Technology." Journal of the American Oil Chemists’ Society 73.2 (1996): 219-24. Web
"Renewable Energy." Institute for Energy Research. IER, 2014. Web. 4 Nov. 2014.
<http://instituteforenergyresearch.org/topics/encyclopedia/fossil-fuels/>.
Rosinski, Alan. "How Much Grease Fast Food Places Put Out." greener ideal. N.p., 25 June 2013. Web.
30 Sept. 2014. <http://www.greenerideal.com/business/0624-restaurant-grease-being-tolen/>.
Saqib, Muhammad, Muhammad Waseem Mumtaz, Asif Mahmood, and Muhammad Imran Abdullah.
"Optimized Biodiesel Production and Environmental Assessment of Produced Biodiesel."
Biotechnology and Bioprocess Engineering 17 (2012): 617-23. Engineering Research Database.
Web. 6 Nov. 2014.
Saulny, Susan. "As Oil Prices Soar, Restaurant Grease Theft Rises." The New York Times. The New York
Times, n.d. Web
Seader, , Henley, and Roper. Separation Process Principles. 3rd ed. N.p.: John Wiley & Sons Inc., 2011.
792-95. Print.
73
"Senate Biodiesel Tax Credit Could Dramatically Change Outlook For The Industry." Senate Biodiesel
Tax Credit Could Dramatically Change Outlook For The Industry. N.p., n.d. Web. 21 Apr. 2015.
Springboard Biodiesel. "How to Prepare Your Feedstock." N.p., 2014. Web.
"Top-Notch Technology in Production of Oils and Fats." ChemPro. ChemPro Technovation Pvt. Ltd.,
n.d. Web. 1 Apr. 2015. <http://www.chempro.in/fattyacid.htm>.
Turton, Richard. Analysis, Synthesis, and Design of Chemical Processes. 3rd ed. Upper Saddle River, NJ:
Prentice Hall, 2009. Print.
"USDA Livestock, Poultry & Grain Market News." USDA Agricultural Marketing Service. USDA, 7
Nov. 2014. Web. 7 Nov. 2014. <http://www.ams.usda.gov/mnreports/lswagenergy.pdf>.
"Vertical Leaf Filter." Vertical Leaf Filter. N.p., n.d. Web. 09 Nov. 2014. <http://www.solidliquidseparation.com/pressurefilters/verticalleaf/verticalleaf.htm>.
"Vertical Pressure Leaf Filter." , Vertical Leaf Filter, Pressure Leaf Filter, Leaf Filters Manufacturer &
Supplier in Navi Mumbai, Used for Filtration of Crude Oil. N.p., n.d. Web. 09 Nov. 2014.
<http://www.sharplex.com/vertical-pressure-leaf-filter.htm>.
Vicente, Gemma, Mercedes Martinez, and Jose Aracil. "Integrated biodiesel production: a comparison of
different homogeneous catalysts systems." Bioresource Technology 92 (2003): 297-305. Elsevier.
Web. 9 Nov. 2014.
74
Appendices Table of Contents
Appendix 1: Overall Process Mass Balance and UniSim Design
Appendix 2: Component Stream Table
Appendix 3: Settling Tank Calculations
Appendix 4: Grease Particulate Removal Calculations
Appendix 5: Competing Biodiesel Plants in Florida
Appendix 6: Transesterification Kinetics Calculations
Appendix 7: Membrane Filter Calculations
Appendix 8: Vessel Cost Details
75
Appendix 1. Overall Process Mass Balance and UniSim design
76
77
Appendix 2. Component Stream Table
78
Appendix 3: Settling Tank Calculations
First, determine the dispersed phase using:
𝑄𝑙 𝜌 𝜇
𝜃 = ( ) [ 𝑙 ℎ⁄𝜌ℎ 𝜇𝑙 ]0.3
𝑄ℎ
Ql – Biodiesel Volumetric Flow Rate – 1.255x10-3 m3/s from PFD
Qh – Glycerin Volumetric Flow Rate – 9.144x10-5 m3/s from PFD
𝜌𝑙 – Biodiesel Density - 875 kg/m3
𝜌ℎ – Glycerin Density - 1260 kg/m3
𝜇𝑙 – Biodiesel Viscosity – 4.5x10-3 Pa.s
𝜇ℎ – Glycerin Viscosity – 1.0x10-3 Pa.s
It was determined from this that θ = 7.83, meaning glycerin is dispersed. Next the settling law to be used
was determined with:
(𝜌𝑓 )(𝜌𝑝 − 𝜌𝑓 ) (1)
𝐾𝑐 = 34.81𝑑𝑝 [
]3
𝜇𝑓2
dp – glycerin droplet size falling from mixture – 70 µm from Literature
(Densities and viscosities are same as above with subscript f referring to biodiesel and p to glycerin.)
These values were converted to American Engineering Units, which are needed for the equation, resulting
in a Kc value of 0.385. This means the Stoke’s Equation is applicable. The Stoke’s equation is,
𝑢𝑡 =
𝑔𝑑𝑝2 (𝜌𝑝 − 𝜌𝑓 )
18𝜇𝑓
All values are the same as ones used above. These are used to solve for ut, or settling velocity.
𝑢𝑡 = 4.19𝑥10−4 𝑚/𝑠
Setting a constraint of L/D=5, and knowing interface area (A) = DL, the following equation was derived,
𝑄𝑏𝑖𝑜𝑑𝑖𝑒𝑠𝑒𝑙
≥ 𝑢𝑡
5𝐷 2
Minimum D is found to be 0.77 m.
Design suggested: D = 1m & L = 5m
79
Appendix 4. Particulate Removal Calculations
LA(1 - ε)ρp = cs (V + εLA)
Cake thickness (L): estimated to 1cm
Porosity (ε): estimated at 0.5
Volume of filtrate (V): used PFD and molar flows/density to find a volumetric flow of 145 m^3/day
Weight of solids per volume of filtrate (cs): weight of solids = (3 wt %)(130,000 kg/day)
cs=26.85 kg/m^3
Density of Solid Particles in Cake: used an average cake density of 3500 kg/m^3
Used in above equation to find Area of Filtration Needed per Day: 225 m^2
80
Appendix 5. Competing Biodiesel Plants in Florida
81
Appendix 6. Transesterification Kinetics Calculations
Biodiesel transesterification proceeds according to the three-step reaction shown below. The
ideal PFR and batch design equations were used to determine reactor specifications and resulting
conversion according to the rate laws, constants, and activation energies specific to soybean oil and the
design method detailed in Fogler’s Elements of Chemical Reactions Engineering.
𝑇𝐺 + 𝐶𝐻3 𝑂𝐻 ↔ 𝐷𝐺 + 𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3
𝐷𝐺 + 𝐶𝐻3 𝑂𝐻 ↔ 𝑀𝐺 + 𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3
𝑀𝐺 + 𝐶𝐻3 𝑂𝐻 ↔ 𝐶3 𝐻8 𝑂3 + 𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3
These translate into the following rate laws with given rate constants and activation energies:
𝑑[𝑇𝐺]
= −𝑘1 [𝑇𝐺][𝑀𝑒𝑂𝐻] + 𝑘11 [𝐷𝐺][𝑀𝑒𝑂𝐻]
𝑑𝑡
𝑑[𝐷𝐺]
= 𝑘1 [𝑇𝐺][𝑀𝑒𝑂𝐻] − 𝑘11 [𝐷𝐺][𝑀𝑒𝑂𝐻] − 𝑘2 [𝐷𝐺][𝑀𝑒𝑂𝐻] + 𝑘22 [𝑀𝐺][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
𝑑𝑡
𝑑[𝑀𝐺]
= 𝑘2 [𝐷𝐺][𝑀𝑒𝑂𝐻] + 𝑘22 [𝑀𝐺][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ] − 𝑘3 [𝑀𝐺][𝑀𝑒𝑂𝐻] + 𝑘33 [𝐶3 𝐻8 𝑂3 ][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
𝑑𝑡
𝑑[𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
𝑑[𝑀𝑒𝑂𝐻]
=−
𝑑𝑡
𝑑𝑡
= 𝑘1 [𝑇𝐺][𝑀𝑒𝑂𝐻] − 𝑘11 [𝐷𝐺][𝑀𝑒𝑂𝐻] + 𝑘2 [𝐷𝐺][𝑀𝑒𝑂𝐻] − 𝑘22 [𝑀𝐺][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
+ 𝑘3 [𝑀𝐺][𝑀𝑒𝑂𝐻] − 𝑘33 [𝐶3 𝐻8 𝑂3 ][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
𝑑[𝐶3 𝐻8 𝑂3 ]
= 𝑘3 [𝑀𝐺][𝑀𝑒𝑂𝐻] − 𝑘33 [𝐶3 𝐻8 𝑂3 ][𝐶𝐻3 𝐶𝑂𝑂𝐶𝐻3 ]
𝑑𝑡
Table 17. Rate constants and activation energies for biodiesel production with soybean oil and NaOH catalysis.
Reaction
TG DG (1)
DG TG (11)
DG MG (2)
MG DG (22)
MG GL (3)
GL MG (33)
Rate Constant (L/mol*s)
0.05
0.11
0.215
1.228
0.242
0.007
82
Activation Energy (cal/mol)
13145
9932
19860
14639
6421
9588
Table 18. Thermodynamic properties of reactants and products.
Component
TG
DG
MG
MeOH
Biodiesel
GL
Specific Heat (J/molK)
1561.56
1163.96
766.36
115.5
492.4
236.2
Heat of Formation (kJ/mol)
-783
-238.4
-670
-1268.47
-1849.72
-2430.96
Heat of Reaction (kJ/mol)
--36.64
36.66
--53.87
---
Kinetic modeling was completed with Polymath ODE solver. The above equations were used to
determining flow rate profiles as a function of batch reaction time or as a function of PFR volume.
Polymath code used to determine reactor conversions are located in the team’s folder in the S: drive.
S:\Engineering\Scratch\SD Team 14\Research\Kinetics Main Reactor
83
Appendix 7. Membrane Filter Calculations
Desal-5 Data Equations
@0 (g/L) FFA concentration: J=27.6*p
@32.5 (g/L) FFA concentration: J=25.45*p – 9.54
Membrane Area Equation
J*(rejection fraction)=(permeate flowrate)/(membrane area)
where FFA concentration is entering feed concentration and is measured as grams of FFA per liter of
feed (g/L), J is flux and is measure as liters of permeate per square meter of membrane per hour
(Lm-2h-1), and pressure is in megapascels (MPa). The membrane has a rejection fraction of .975 +/- .01.
i.
ii.
Pretreatment Membrane Filter
The feed entering the filter has a concentration of 15.15 g/L by interpolating the data
above the flux as a function of pressure becomes
J=26.6*p-4.45
Using a pressure of 1.3 MPa
J=26.6*(1.3) -4.45
J=30.13 Lm-2h-1
The permeate flowrate is 232.7 Lh-1
(30.13 Lm-2h-1)*(.975) = (232.7 Lh-1)/(x )
x= 7.92 m2 pretreatment membrane area
Main Membrane Filter
The feed entering the filter has a concentration of 3.05 g/L by interpolating the data
above the flux as a function of pressure becomes
J=27.4*p - 0.896
Using a pressure of 1.3 MPa
J=27.4*(1.3) – 0.896
J=34.72 Lm-2h-1
The permeate flowrate is 2224 Lh-1
(34.72 Lm-2h-1)*(.975) = (2224 Lh-1)/(x )
x= 65.7 m2 main membrane area
84
Membrane Filter Equipment
85
Appendix 8. Vessel Cost Details
Vessel
Distillation Column
Sulfuric Acid Storage
Tank
De-watering Vessel
NaOH Storage Tank
Transesterification Reactor
Mixer-101
Feed Storage Tank
Methanol 2 Storage Tank
Biodiesel Storage Tank
Glycerin Storage Tank
Filter Vessel
flowrate
(m^3/hr)
2 week
supply
Volume
(m^3)
Volume
(gallons)
0.01621
horizontal tube
evaporator
0.02244
5.44656
10
41649.91
5.873
2.098
6.358
1.241
pressure leaf
wet filter
MOC
Stainless Steel 316
Cost in 1970
$145,124.23
Cost Today
$ 668,472.00
2641.72
Stainless Steel
$107,668.00
$ 495,940.91
7.53984
5
10
1
1320.86
2641.72
264.172
$ 81,310.44
$ 50,355.00
$ 48,015.23
$ 374,532.55
$ 231,945.47
$ 221,168.00
1,567.80
1973.328
704.928
2136.288
416.976
10
500
500
500
500
2641.72
132086
132086
132086
132086
Carbon Steel
Rubber lined C Steel
stainless steel 316
carbon steel coated
with stainless steel
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
$ 43,217.70
$ 27,332.00
$ 27,332.00
$ 27,332.00
$ 27,332.00
$ 199,069.62
$ 125,896.80
$ 125,896.80
$ 125,896.80
$ 125,896.80
$ 26,782.22
$ 123,364.42
$ 24,401.87
$ 112,400.00
estimated
estimated
$ 21,608.85
$ 21,608.85
$ 21,608.85
$ 20,043.83
$ 18,215.21
$ 10,219.00
$ 7,045.93
$ 100,000.00
$ 100,000.00
$ 99,534.81
$ 99,534.81
$ 99,534.81
$ 92,326.00
$ 83,903.00
$ 47,070.81
$ 32,455.00
Pre-Treatment Reactor
1
264.172
Membrane 1
Membrane 2
Mixer-100
Mixer-102
Mixer-103
Fired Heater 1
Fired Heater 2
Methanol 1 Storage Tank
3-Phase Settler
5
5
10
10
10
1320.86
1320.86
2641.72
2641.72
2641.72
Carbon Steel
carbon steel coated
with stainless steel
carbon steel coated
with stainless steel
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
100
15
26417.2
3962.58
Carbon Steel
Carbon Steel
20824.95
20824.95
20824.95
783.90
783.90
783.90
0.0565
18.984
86
© 2015, Calvin College and Hannah Albers, Ben Guilfoyle, Melanie Thelen, and Colton Walker
87