Holy Spirit University of Kaslik (USEK)
Faculty of Engineering
Department of Chemical Engineering
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Waste cooking oil pretreatment for biodiesel production
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Guy El Fakhry
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This proposal is submitted in partial fulfillment of the requirements for the Bachelor of Engineering
degree in Chemical Engineering
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Examining Committee:
Committee Chair:
First Evaluator:
Second Evaluator:
FYP Supervisor: Dr Nancy Zgheib
Defense Date: 22/12/2016
DECLARATION
I hereby declare that this work has been done by myself and no portion of the work contained
in this report has been submitted in support of any application for any other degree or
qualification of this or any other university or institute of learning.
Signature:
Name: Guy El Fakhry
Student ID: 201103026
Date: 14/12/2016
1
ACKNOWLEDGEMENT
“If I am walking with two other men, each of them will serve as my teacher. I will pick out the
good points of the one and imitate them, and the bad points of the other and correct them in
myself.” ~ Confucius (551 BC - 479 BC)
“What the teacher is, is more important than what he teaches.” ~ Karl Menninger (1893 - 1990)
Since not everybody who went to university and obtained a degree in some field can be
considered a teacher and because I was lucky enough to find true teachers who helped me, I
would firstly like to thank dr. Nancy Zgheib who guided me all the way in addition to continuous
support and encouragement.
Dr. Hosni Takache and dr. Hamza Javar Magnier, for offering me advice and recommendations
in certain areas of my project.
Dr. Mira Makhoul who helped me understand and conduct the dry-freezing technique.
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ABSTRACT
Waste cooking oil consists of a mixture of triglyceride, impurities and free fatty acids (FFA). The
presence of water and FFA in the oil can lower the yield of the transesterification reaction
which transforms the oil into biodiesel and glycerol. The purpose of this research is to design a
feasible and economical system whose objective is to reduce the free fatty acids and water
content in the waste cooking oil to less than 2.0 wt% and 0.1 wt% respectively.
This is mainly accomplished via the esterification reaction carried out in a CSTR and the
optimum conditions for the reaction are: sulfuric acid usage of 10 wt% (relative to the weight of
the free fatty acids), methanol-to-FFA molar ratio of 40/1 and a temperature of 60 °C. An entire
system able to process approximately 125 L of oil per hour, reducing the free fatty acids from ≈
5 wt% to 0.74 wt% and the water content from 0.28 wt% to 0.07 wt% is designed. At the end of
the report an economic study is also performed.
Keywords: biodiesel, pretreatment, waste cooking oils, free fatty acids, design.
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Résumé
L'huile de cuisson usée se compose d'un mélange de triglycérides, impuretés et d'acides gras
libres (FFA). La présence d'eau et de ces acides dans l'huile peut abaisser le rendement de la
réaction de transestérification qui transforme l'huile en biodiesel et glycérol. Le but de cette
recherche est de concevoir un système réalisable et économique dont l'objectif est de réduire
les acides gras libres et la teneur en eau dans l'huile de cuisson usée à moins de 2,0% en poids
et 0,1% en poids, respectivement.
Ceci est principalement réalisé par la réaction d'estérification effectuée dans un réacteur à
réservoir agité continu (CSTR) et les conditions optimales pour la réaction sont: l'utilisation
d'acide sulfurique de 10% en poids (par rapport au poids des acides gras libres), un rapport
molaire méthanol-FFA de 40/1 à une température de 60 ° C. Un système entier capable de
traiter environ 125 L d'huile par heure, réduisant les acides gras libres de ≈ 5% en à 0,74% en
poids et la teneur en eau de 0,28% à 0,07% en poids est conçu. À la fin du rapport, une étude
économique est également réalisée.
Mots-clés: biodiesel, prétraitement, huiles de cuisson usées, acides gras libres, design.
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Table of contents
Table of figures : ........................................................................................................................................... 7
List of tables : ................................................................................................................................................ 8
List of acronyms: ........................................................................................................................................... 9
Introduction ................................................................................................................................................ 10
1- Biodiesel literature review ...................................................................................................................... 11
1.1- Why do we need it? ......................................................................................................................... 11
1.2- What is it? ........................................................................................................................................ 11
1.3- Benefits ........................................................................................................................................... 12
1.4 - Environmental impact..................................................................................................................... 13
1.5 - Economical impact .......................................................................................................................... 14
2- Problems encountered and possible solutions....................................................................................... 15
3- Pretreatment system .............................................................................................................................. 17
3.1- Is it crucial? ...................................................................................................................................... 17
a) Hydrolysis ...................................................................................................................................... 17
b) Saponification ................................................................................................................................. 18
3.2- Transesterification catalysts ............................................................................................................ 19
4- Concepts generation ............................................................................................................................... 20
4.1- Separation techniques ..................................................................................................................... 20
a) Solid particles removal .................................................................................................................... 20
b) Dewatering system ......................................................................................................................... 21
4.2- FFA removal ..................................................................................................................................... 21
a) Glycerolysis ..................................................................................................................................... 21
b) Enzymatic method .......................................................................................................................... 22
c) Acid catalysis followed by alkali catalysis method .......................................................................... 22
4.3- Decision variables ............................................................................................................................ 23
a) Alcohol type .................................................................................................................................... 23
b) Catalyst types .................................................................................................................................. 23
5- Process description ................................................................................................................................. 24
6- Experimental scale .................................................................................................................................. 25
5
7- Aspen simulation .................................................................................................................................... 28
8- Equipment design ................................................................................................................................... 29
8.1- CSTR ................................................................................................................................................. 29
a) Material balance ............................................................................................................................. 29
b) Sizing calculation............................................................................................................................. 31
8.2- Heat exchanger ................................................................................................................................ 33
8.3- Distillation column ........................................................................................................................... 41
a) Condenser calculations: .................................................................................................................. 49
b) Reboiler calculations: ...................................................................................................................... 51
8.4- Decanter .......................................................................................................................................... 53
8.5- Filter ................................................................................................................................................. 55
10- Cost analysis.......................................................................................................................................... 56
10.1- Equipments .................................................................................................................................... 56
10.2- Utilities & raw materials cost......................................................................................................... 57
11- HAZOP ................................................................................................................................................... 60
12- Conclusion and future recommendation.............................................................................................. 63
13- Appendix ............................................................................................................................................... 65
13.1- AOCS official method CD 3A-63 for acid value test ....................................................................... 65
13.2- Aspen complete stream table ........................................................................................................ 66
13.3- Aspen DSTWU column results ....................................................................................................... 67
13.4- Cost correlations used ................................................................................................................... 68
14- Bibliography .......................................................................................................................................... 70
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Table of figures :
Figure 1: Transesterification reaction ......................................................................................................... 12
Figure 2: Biodiesel fuel standards .............................................................................................................. 12
Figure 3: Environmental impact of the 2 processes ................................................................................... 14
Figure 4: Hydrolysis of triglyceride oils ....................................................................................................... 17
Figure 5: Effects of water on FAME yields .................................................................................................. 18
Figure 6: Saponification reaction ................................................................................................................ 18
Figure 7: Esterification reaction .................................................................................................................. 23
Figure 8: Process BFD for the pretreatment process .................................................................................. 25
Figure 9: WCO in the freeze-drying machine .............................................................................................. 26
Figure 10: WCO experimental apparatus.................................................................................................... 27
Figure 11: Aspen flowsheet of the entire process ...................................................................................... 28
Figure 12: Correction factor ....................................................................................................................... 40
Figure 13: Feed lines ................................................................................................................................... 43
Figure 14: K values for methanol/water mixture obtained from Aspen .................................................... 44
Figure 15: Antoine coefficients for methanol ............................................................................................. 44
Figure 16: Antoine coefficients for sunflower oil ....................................................................................... 46
Figure 17: Droplet diameter vs. emulsion types ......................................................................................... 54
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List of tables :
Table 1: Fuel properties of some vegetable oils, their methyl esters and #2 diesel fuels.......................... 13
Table 2: Economical impact of biodiesel production with & without FFA pre-treatment ......................... 15
Table 3: Different types of FFA's ................................................................................................................ 16
Table 4: Effect of palmitic acid on the ester conversion and specific gravity of the methyl ester (reaction
conditions: methanol/oil molar ratio: 6/1; Sulfuric acid amounts: 3% wt; reaction time: 96 hours;
reaction temperature: 60 ⁰C)...................................................................................................................... 19
Table 5: Effect of water on the ester conversion and specific gravity of the methyl ester ........................ 19
Table 6: Liquid-solid separators .................................................................................................................. 20
Table 7: Ethanol vs. Methanol ................................................................................................................... 23
Table 8: Catalyst types ................................................................................................................................ 24
Table 9: Acid value titrations ...................................................................................................................... 27
Table 10: Components used in Aspen simulation....................................................................................... 28
Table 11: Reactions in Aspen simulation .................................................................................................... 29
Table 12: Components molar mass............................................................................................................. 29
Table 13: Moles balance in CSTR ................................................................................................................ 31
Table 14: Reactants properties and moles number for 125 L of WCO ....................................................... 32
Table 15: Heat exchanger types .................................................................................................................. 33
Table 16: Components specific heat data ................................................................................................... 33
Table 17: Parameters for condenser design ............................................................................................... 51
Table 18: Parameters for reboiler design ................................................................................................... 53
Table 19: Equipments cost .......................................................................................................................... 56
Table 20: Hazards and 1st aid measures for chemicals used....................................................................... 61
Table 21: Equipments failure, causes and solutions ................................................................................... 61
Table 22: Problematic scenarios, causes and solutions .............................................................................. 63
Table 23: Stream table in Aspen simulation ............................................................................................... 67
Table 24: DSTWU results............................................................................................................................. 68
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List of acronyms:
Word
Definition
FAME
FFA
A.V.
USA
AKA
Wt
Vs.
H
L
μ
&
PEI
BFD
WAR
EPA
CSTR
PFR
PBR
£C
$C
Fatty Acid Methyl Ester
Free Fatty Acids
Acid Value
United States of America
Also Known As
Weight
Versus
Hours
Liters
Micro
And
Potential Environmental Impacts
Block Flow Diagram
Waste Reduction algorithm
US Environmental Protection Agency
Continuous Stirred Tank Reactor
Plug Flow Reactor
Packed Bed Reactor
Cost in pounds
Cost in dollars
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Introduction
It was first proposed to utilize vegetable oil fuels for motive power by the creator of the diesel
engine himself, Rudolf Diesel (and he succeeded in doing so in 1900 at the world exhibition in
Paris when he ran a combustion engine using only peanut oil for fuel). On 13 April 1912, Diesel
declared that, with vegetable oils “Motive power could still be made from the heat of the sun,
always existing, even when the usual liquid and solid fuels are totally worn out”. These
visionary words showed that Diesel was incredibly farseeing, cautiously taking into
consideration the instability of the fossil fuels well before the regular user was even imagining
that they were limited. Throughout time, the economy selected the use of petro diesel over the
more pricey virgin oils such as hemp and peanut. The diesel engine was then enhanced for
petro diesel use only and the dream of Rudolf Diesel to run his engine on clean, renewable
energy was ancient history.
It was not before 1973 (almost 60 years after Diesel’s death) that diesel’s idea of using
vegetable based fuels to run his engine was reawakened during the oil embargo. With the oil
embargo in full motion in the fall of 1973, oil products and provisions were extremely limited.
By 1974, the cost of the oil barrel inflated from 3$ to 12$. Clean, renewable fuel finally caught a
break and biodiesel was gaining more and more attention from the public [18].
Jumping to the present day, vegetable oil that were once the main feedstock for producing
biodiesel are experiencing a large inflation, which could translate into even more trouble for
the biodiesel industry who is already struggling to keep the production going in most countries.
A possible solution for this is to use cheap feedstocks which mean replacing the expensive oils
with inexpensive waste cooking oils. However, WCO have relatively large contents of free fatty
acids and water that extremely lower the overall yield and increase separation difficulties at the
end of the process.
This research aims to develop an efficient and economically feasible pretreatment process in
order to reduce the free fatty acids and the water present in the waste cooking oils to less than
2.0 wt% and 0.1 wt% respectively. We will start by studying several pretreatment methods from
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the literature, then we will choose the most suited one for our process. Once the design
decisions are taken we will start by simulating, designing and optimizing the process. At the end
of the report a cost estimation is performed.
1- Biodiesel literature review
1.1- Why do we need it?
With the exception of solar power and hydroelectricity, the main energy needs are provided
through petrochemical resources like natural gas, oil and coal. All of these resources are
limited, and at present consumption, it won’t be very long before they’re all depleted. The
exhaustion of world petroleum reserves as well as their augmented environmental impacts has
inspired current attraction towards alternative resources like biodiesel instead of petroleum
based fuels.
1.2- What is it?
Biodiesel is a mono-alkyl ester of long chain fatty acids possessing a chemical structure of fatty
acid alkyl esters (usually Fatty Acid Methyl Ester, FAME), made from sustainable feedstock
(such as vegetable oils, waste cooking oils, animal fats…) and is lately becoming a substitute for
diesel fuel.
In a simplified manner, vegetable oil approximated chemically as triacylglycerol (aka
triglyceride), reacts with an alkyl alcohol (usually methanol) in the existence of a catalyst (either
alkali or acid), to make glycerol and alkyl esters. This reaction is called transesterification, which
associate the conversion of the oil to FAME. Glycerol is also produced in this reaction as a
byproduct.
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Figure 1: Transesterification reaction
Below are the international biodiesel standards that manufacturers need to respect:
Figure 2: Biodiesel fuel standards [13]
1.3- Benefits
Biodiesel has countless benefits over conventional diesel which makes it a viable substitute:
o Non toxic and biodegradable since 99.6 % of it was biodegraded in just 21 days and
100% in less than 1 month (based on European tests done on rapeseed biodiesel).
o Emits far less air pollutants then petroleum products when burned, thus reducing many
pollution caused deceases (47% less carbon monoxide; 50% less volatile organic carbon;
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39% less particulate matter; 99% less sulfur compounds; 85% less aromatic polycyclic
hydrocarbons etc…) ~ based on rigid trucks measurements.
o It’s a domestic , renewable energy supply; given that it’s feedstock consist mainly on
animal fats or vegetable oils (used or new), it enables each country to meet its own fuel
demands, therefore relieving the reliance on foreign energy imports.
o Requires very few alterations when used in a conventional diesel motor.
o Better engine lubrication than conventional diesel (Krawczyk 1996, Wedel 1999).
o Bigger cetane number than diesel fuels which translates into better ignition quality
(smaller ignition delay, giving additional time for the fuel burning process to be
completed).
o Higher flash point than petroleum based diesel, making it much less volatile and safer
for transportation and handling.
The table 1 below lists the fuel properties of some vegetable oils and their methyl ester and
compares them to those of number 2 diesel fuels [18].
Table 1: Fuel properties of some vegetable oils, their methyl esters and #2 diesel fuels
1.4 - Environmental impact
According to a study done on Waste Reduction Algorithm (WAR) software
[14],
the potential
environmental impact of the process of biodiesel production from WCO without FFA
pretreatment is more environmentally friendly than the process with FFA pretreatment (figure
3).
The considered factors were:
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Human toxicity by dermal/inhalation way (HTTPi)
Human toxicity by ingestion way (HTTPe)
Terrestrial toxicity (TTP)
Aquatic toxicity (ATP)
Global warming (GWP)
Ozone depletion (ODP)
Photo-chemical oxidation (PCOP)
Acidification (AP)
WAR gave the following results:
Figure 3: Environmental impact of the 2 processes
This is to be expected as we are using more chemicals and energy in order to decrease the FFA
content. To reduce the energy consumed during the process an energy system integration is
highly recommended in the process design in order to render the process more eco-friendly.
1.5 - Economical impact
An economic study done by Mata et al.
[14]
was performed to determine which of the two
methods (with or without FFA pretreatment) is more profitable, since this was what mattered
most to industrialists.
The considered factors were:
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Total investments in Euros
Net present value in Euros (NPV)
Internal rate of return (IRR)
Payback period in years.
The results came as follows:
Table 2: Economical impact of biodiesel production with & without FFA pre-treatment
As we can see from the above table, in regards to the process with FFA pretreatment the initial
investment price is almost twice the investment price for the process without pretreatment.
However, if we were to take a closer look, we’ll find out that the FFA pretreatment process is
more advantageous economically since it has a superior IRR and NPV along with a smaller
payback period.
This is mainly due to the improved yield that the FFA pretreatment method induces compared
to the process without pretreatment.
2- Problems encountered and possible solutions
Edible and non-edible vegetable oils like jatropha, canola, soapnut, palm… have been used in
order to manufacture biodiesel and showed promising results, for example in France and Italy
they use mainly sunflower oil, in the USA soybean while in Canada canola is the most used.
However, a main problem in the wide commercialization of biodiesel made from vegetable oils
is its soaring production cost. Many investigations and studies have reported that 70 to 90% of
the biodiesel cost is due to the feedstock. For instance, if we’re producing biodiesel from beef
tallow, approximately 70% of the production cost will go for feedstock; whereas it would be
90% if we’re using soybean oil. The feedstock for biodiesel production varies from a place to
another and between countries. In Iran as an illustration, over 90% of edible oil is imported. [18]
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Furthermore, the cultivation of inedible plants has not been practiced so far, and with
vegetable oils prices increasing every year, a cheap feedstock alternative must be found.
Waste cooking oil was proposed as a promising, cheap (40-70% cheaper than edible oils) and
abundant (1 to 3 billion gallons of WCO are generated annually in the USA alone ~ Greer, 2010)
resource to help decrease biodiesel prices.
On the other hand, WCO have large contents of FFA, H2O and solid wastes which were proven
to have a negative impact on the biodiesel yield and purity especially when an alkali catalyst
was used.
As a consequence, a pretreatment process must be developed to purify the WCO with the
minimum operational cost.
WCO are classified into 2 groups according to the FFA content: brown grease (FFA content
>15%) and yellow grease (FFA content <15%). Because of the larger FFA concentrations in
brown grease, processing requires many stages as well as extra byproduct separation and
purification steps
[7].
Currently, conversion of very high FFA oils to biodiesel is pricey and
impractical causing the use of brown grease as the main feedstock for biodiesel production very
rare. [3] The table 1 below shows the different types of FFA’s in oils.
Fatty acid (trivial name
/rational name)
Structure
Common
acronym
Methyl ester (trivial name /
rational name)
Palmitic acid /
Hexadecanoic acid
Stearic acid / Octadecanoic
acid
Oleic acid / 9(Z)octadecenoic acid
Linoleic acid / 9(Z),12(Z)octadecadienoic acid
Linolenic acid /
9(Z),12(Z),15(Z)octadecatrienoic acid
R-(CH2)14-CH3
C16:0
R-(CH2)16-CH3
C18:0
R-(CH2)7-CH=CH(CH2)7- CH3
R-(CH2)7-CH=CH-CH2CH=CH- (CH2)4-CH3
R-(CH2)7-(CH=CHCH2)3-CH3
C18:1
Methyl palmitate /
Methyl hexadecanoate
Methyl stearate /
Methyl octadecanoate
Methyl oleate / Methyl
9(Z)-octadecenoate
Methyl linoleate / Methyl
9(Z),12(Z)- octadecadienoate
Methyl linolenate /
Methyl 9(Z),12(Z),15(Z)octadecadienoate
C18:2
C18:3
Table 3: Different types of FFA's [7]
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3- Pretreatment system
3.1- Is it crucial?
As stated earlier, water and FFA present in WCO lower yields and increase separation
difficulties; this is primarily due to 2 reactions:
a) Hydrolysis
Triglyceride oils, in the presence of water, will be hydrolyzed into long chain fatty acids and
glycerol. Hydrolysis is an endothermic reaction. The intensity of hydrolysis increases with
increasing temperature. Also, the miscibility of water in lipid increases at high temperatures
and pressures, thereby enhancing the rate of the hydrolysis reaction. At high temperatures,
these triglycerides and fatty acids derived from the reaction will undergo undesired thermal
decomposition causing deterioration in odor or color and a reduced yield of FAME [1].
Figure 4: Hydrolysis of triglyceride oils
Below are the results of an experiment that was conducted to see the effects of water wt % in
the oil on the ester conversion. As we can see from this study, the more water we have in the
oil, even with the optimum conditions, the lower the conversion will be (almost 16% at 12%
water).
[21]
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Figure 5: Effects of water on FAME yields
b) Saponification
In the presence of FFA and when the sodium hydroxide is used for the conversion of
triglycerides into FAME, salts and water are formed according to the reaction below:
Figure 6: Saponification reaction
This reaction is undesirable since soap lowers the biodiesel yield and prevents the separation of
esters from the glycerol. Additionally, soaps binds with the catalyst so that further catalyst will
be required and thus the process will be pricier. Besides, alkaline catalysts can’t convert FFA to
biodiesel; hence they should be removed as much as possible from WCO (at least <2 wt % of
the entire WCO) so that their effects will become negligible [1].
It should also be noted that FFA’s have another negative effect on biodiesel production, as their
concentration increases, so does the glycerin % (aka glycerol) and specific gravity of the final
product (FAME), as confirmed by the study of M. Canakci.
Additionally, the American Society for Testing and Materials (ASTM) will consider in the near
future that the % of glycerol in biodiesel should be inferior to 0.24% hence the removal of FFA
will become extremely important [4].
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3.2- Transesterification catalysts
Acid catalysts could be used for WCO transesterification and the reaction conversion is not
affected by feedstock purity, however the reaction is very slow and low yields are obtained
which make their industrial usage very limited compared to alkaline catalysts. As an illustration,
Freedman et al tried to transform soybean oil to biodiesel using 1 % wt (based on oil) sulfuric
acid catalyst, 30:1 methanol to oil molar ratio at 65 ⁰C. The reaction took a staggering 69 hours
to obtain over 90% conversion to methyl esters
[3].
Also, and contrary to popular believes,
recent researches have showed that not only base catalysts are affected by the presence of FFA
and water but also acid catalysts. These experiments were done by M. Canakci who observed
the effects of FFA’s and water content on the conversion % and specific gravity of the esters
while using sulfuric acid as catalyst. As we can see from the table below, the higher the FFA
(palmitic acid) content is the smaller the yield will be and the higher the value of specific
gravity.
Table 4: Effect of palmitic acid on the ester conversion and specific gravity of the methyl ester (reaction conditions:
methanol/oil molar ratio: 6/1; Sulfuric acid amounts: 3% wt; reaction time: 96 hours; reaction temperature: 60 ⁰C)
The influence of the water content on ester conversion and specific gravity of the ester were
also studied by the same author. The same procedure was followed, while keeping the same
testing conditions and the results are summarized in the table below:
Table 5: Effect of water on the ester conversion and specific gravity of the methyl ester
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From this experiment, we notice that the conversion is much more affected by water content
then by FFA levels. Additionally, when FFA and alcohol react together they produce methyl
ester and water, and with water staying in the mixture it will start quickly slowing the
transesterification reaction down until complete stoppage, generally well before reaching
completion. [4]
Another type of catalyst where also used for the transesterification of WCO like the enzymatic
catalyst, however when using these catalysts the reaction is very slow and until this date, all of
the trials were done on a laboratory scale.
Alkali catalysts (like sodium hydroxide), are used in the majority of biodiesel processes for the
transesterification reaction as they possess high activity, require moderate conditions and give
high yields. On the other hand, alkali catalysts are particularly sensitive to feedstock purity, so a
pretreatment system for the WCO is required.
4- Concepts generation
4.1- Separation techniques
Before removing the FFA’s from the WCO, small food particles and water also present in the oil
need to be taken out.
a) Solid particles removal
The process screening below shows many possible techniques used in order to remove the solid
portion of the oil.
Technique
Filtration
Thickeners Clarifiers
Centrifuges
Evaporation
Flocculation
Energy requirement
Time
Efficiency
Price of equipments
Score
0
0
0
0
0
+
-2
+
-2
+
+
-1
+
-2
Table 6: Liquid-solid separators
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Apparently, filtration is the best choice for removing small food particles from WCO. On an
industrial scale a 100 μm filter will be sufficient to eliminate particles from the majority of
feedstocks. [7] We will use this size in our design since smaller size filters will not allow the WCO
to flow unless under vacuum conditions, thus increasing cost and complexity of this simple
technique.
b) Dewatering system
On an industrial scale, a centrifuge might be used to separate water from oil; however this
process is costly and consumes a lot of energy. In our case we choose to heat the WCO in a
drum at ≈ 140 °C for 15 minutes with fast stirring in order to evaporate the water as quickly as
possible.
4.2- FFA removal
When the FFA content in WCO is less than 2 wt%, its presence could be neglected. If FFA
content is between 1 and 3 wt % adding excess alkali catalyst during the transesterification
process can be sufficient. In this case, a fraction of the catalyst will go for neutralizing the FFA
by forming soap, while still leaving sufficient quantities for the reaction. For feedstocks with
superior levels of FFA, addition of extra quantity of sodium hydroxide is not advised, since the
large amount of soap created will gel preventing the separation of the esters from glycerol.
Furthermore, this method will be converting FFA to a waste product instead of converting them
to FAME [7].
In the literature three methods where used for processing feedstock with high (>3%) FFA
content:
a) Glycerolysis
This technique implicates the addition of glycerol, with zinc chloride to the feedstock and
heating the mixture to an elevated temperature (200 ⁰C). Under these conditions the glycerol
will react with the FFA forming mono and diglycerides. This method reduces the FFA content to
less than 2 wt. % and the feed could then be transformed to biodiesel using conventional alkalicatalyzed techniques.
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The downsides of glycerolysis is that it is an energy intensive process, the reaction is very slow
(more than 5 hours) and the catalyst zinc chloride is expensive (5 g cost 86.2 €).
b) Enzymatic method
Because of the expensive price of the enzymes and very slow conversion rate, nobody is using
this method on an industrial scale.
c) Acid catalysis followed by alkali catalysis method
Given that acid catalysts are relatively fast for the conversion of FFA’s to FAME and slow with
the transesterification of triglycerides into FAME, they could be used for pretreatment of high
FFA content feedstocks. Subsequently, when the FFA content is lowered to less than 2 wt. %,
the alkali catalyst is added to convert the triglycerides to biodiesel. This process is the most
promising one since it converts FFA rapidly, effectively and inexpensively.
However, water formation will remain a problem in the pretreatment phase (because of
hydrolysis); to counter this, some solutions consists of:
1: Adding exceedingly large amounts of methanol (as much as 40/1 alcohol/FFA molar ratio) in
the pretreatment phase thereby, the water produced will be diluted and does not limit the
reaction. A large part of the methanol is retrieved later on in the process.
2: The acid-catalyzed esterification (conversion of FFA’s to methyl esters) proceeds as much as
it can go until it is blocked by water formation. Later, the mixture is boiled off to get rid of the
water and alcohol. If FFA level is still higher than 2%, then extra acid catalyst and methanol will
be added to keep the reaction going. This step can be repeated multiple times until the wanted
results are achieved.
3: Using fluids such as glycerol to wash off the water from the mixture at the end of the
esterification reaction.
4: Using a decanter at the end to remove the majority of water since it possesses the highest
density in the mixture.
→ Method 1 followed by method 4 will be chosen for optimum results.
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4.3- Decision variables
The process of FFA’s reacting with alcohol in the presence of an acid catalyst to yield alkyl
esters and water is called esterification.
Figure 7: Esterification reaction
This reaction is reversible; therefore an excess amount of alcohol must be used to push it
forward. This crucial transformation will be the only way for eliminating FFA’s from WCO.
a) Alcohol type
Ethanol and methanol are the two most promising candidates for this process, each having its
own pros and cons.
Alcohol
Ethanol
Methanol
Operating Temperature
Efficiency
Price
Separation difficulties
Toxicity
Environmental impact
Score
+
+
-2
+
+
+
+
2
Table 7: Ethanol vs. Methanol [4]
As we can observe from the table above, methanol is the clear winner here; nevertheless it is
more toxic to humans than ethanol, so special precautions (protective glasses, gloves, vapor
respirator…) will be taken while handling it.
b) Catalyst types
In order to choose the best catalyst suited for our reaction, we did a process screening below:
23
Catalyst
BIMHSO4
Sulfuric acid
Ferric sulphate
WOX/Al2O3 (WAL)
WOX/SIO2 (WS)
Optimum
temperature (⁰C)
Optimum catalyst
weight
Methanol/Oil
molar ratio
Time needed (h)
Reusability
Final A.V. reached
(mg KOH/g)
Price ($/ton)
Reference
160
65
95
110
110
5 wt % (relative
to WCO)
15/1
3.5 wt % (relative to
WCO)
10/1
1 wt % (relative to
WCO)
0.3/1 (weight ratio)
1 wt % (relative to
WCO)
0.3/1 (weight ratio)
1
No
0.41
10 wt % (relative
to FFA)
40/1
(relative to FFA)
2
No
<1
4
Yes
<1
2
Yes
4.7
2
Yes
5.6
NA
[19]
≈ 300
[10]
≈ 400
[15]
NA
[3]
NA
[3]
Table 8: Catalyst types
For being cheap, fast, efficient and able to work under mild conditions, sulfuric acid will be
chosen as catalyst in our process.
5- Process description
Our future work will follow the pretreatment production process shown in the block flow
diagram below:
24
Figure 8: Process BFD for the pretreatment process
In our design we are going to consider that we will receive approximately 500 L of WCO from
the university cafeteria Zouki plus a few neighboring restaurants, this volume will be divided
into 4 volumes of 125 L each to be processed in 1 session/week through our system, because
otherwise, our volumes would be too small and we would end up working in an experimental
scale instead of the pilot scale we’re aiming for.
After the filtration step is over, the WCO will be dewatered, tested for FFA then will pass
through a heat exchanger to raise its temperature as much as possible before it enters the
CSTR. An appropriate amount of methanol and sulfuric acid will be mixed with the WCO in the
CSTR maintained at 60 °C. Then the mixture is sent to a distillation column where 95% of the
excess methanol used will be recovered and recycled back to the CSTR. The methanol-free
liquid will then go to the last unit in our process, the decanter. In the decanter the water will be
separated from the FFA free WCO. Finally the treated WCO will be collected and stored in an air
proof tank (so it doesn’t collect moisture from the air) for further processing later on.
In the following sections we will focus on designing the main elements of our process which are
the reactor, the distillation column, the heat exchanger and the decanter along with an
estimation of their costs.
6- Experimental scale
Before any experiment could begin, the oil needed filtration then dewatering since even the
tiniest amount of water would lower the yield significantly.
For the filtration, we used a 100 micron filter which was sufficient enough to remove the food
particles floating in the oil.
In order to remove the water, the oil was heated at 140⁰C while stirring at high speed for no
less than 15 min. Then the quantity of water in the sample is measured before and after the
water removal step using the freeze-drying method. This technique shows that after heating
25
the oil, the quantity of water has decreased from 0.28 wt% to 0.07 wt% which is lower than the
permissible water content value (0.1 wt%).
Figure 9: WCO in the freeze-drying machine
Two titrations were performed on the WCO (using the AOCS OFFICIAL METHOD CD 3A-63)
received from the university cafeteria Zouki in order to determine the FFA content. Both of
them have shown an acid value of ≈ 9.95 mg KOH/g which correspond to 5 wt% of FFA (dividing
the acid value by 1.99).
After the titrations, we conducted the esterification reaction on a laboratory scale. The figure
13 below shows the experimental setup of the reaction.
26
Figure 10: WCO experimental apparatus
After removing the water, we added to the sample the required amounts of methanol and
sulfuric acid (based on 5 wt% FFA) and the esterification reaction was then performed at 60 ⁰C.
During the reaction many samples were withdrawn at different intervals of time (0, 5, 10, 20,
30, 60, 90 and 120 min) and cooled in an ice bath to stop the reaction. Then using a centrifuge
(5000 RPM for 5 min), we separated the methanol and sulfuric acid from the oil. The titration of
the oil was then performed the following day.
The following results were obtained:
Sample #
0
1
2
3
4
5
6
7
Time (min)
0
5
10
20
30
60
90
120
A.V.
10.03
7.18
4.74
3.51
2.65
1.47
1.12
0.63
FFA wt%
5.040
3.608
2.382
1.764
1.332
0.739
0.563
0.317
Conversion %
0
28.415
52.742
65.005
73.579
85.344
88.834
93.719
Table 9: Acid value titrations
27
These results show that 1h of reaction (85% conversion) is sufficient to reduce the FFA wt%
content to less than the permissible value (2 wt%).
7- Aspen simulation
Using the Aspen Plus software, we were able to completely model our pretreatment plant in an
accurate manner.
Figure 11: Aspen flowsheet of the entire process
The method used for this simulation was NRTL.
The components used are:
Component ID
Component name
Alias
METHANOL
WATER
METHY-01
OLEIC-01
SULFU-01
TRIOL-01
METHANOL
WATER
METHYL-OLEATE
OLEIC-ACID
SULFURIC-ACID
TRIOLEIN
CH4O
H2O
C19H36O2
C18H34O2
H2SO4
C57H104O6
Table 10: Components used in Aspen simulation
The simulation starts by warming up the cold WCO via a heat exchanger using the feed coming
out from the CSTR. Then the WCO is mixed with methanol and sulfuric acid and pumped into
the CSTR where the following reactions take place:
28
Reaction Reaction
No.
type
1
2
Kinetic
Kinetic
Stoichiometry
OLEIC-01(MIXED) + METHANOL(MIXED) --> METHY-01(MIXED) + WATER(MIXED)
METHY-01(MIXED) + WATER(MIXED) --> OLEIC-01(MIXED) + METHANOL(MIXED)
Table 11: Reactions in Aspen simulation
The feed coming out of the CSTR will have a significant reduction in FFA. The FFA free feed
enters the exchanger then a DSTWU column in order to recover 95% of the excess methanol.
The recycled methanol will be mixed with the initial methanol feed. Finally, the last step
consists of separating the water and traces of sulfuric acid from the WCO.
The complete stream table is presented in the appendix.
8- Equipment design
8.1- CSTR
a) Material balance
For an average flow of 125 L/h (114.875 kg/h; 131.14 mol/h) of sunflower oil (M=876 g/mol; d =
0.919 g/mL) with a 5% wt of FFA (5.74 kg/h) approximated by oleic acid (M=282.46 g/mol; d =
0.895 g/mL)
C18H34O2 + CH3OH →
C19H36O2
+ H2O
Oleic acid + methanol → Methyl oleate + Water
❖ Molar mass:
Component
Molar mass (g/mol)
Oleic acid
Triolein
Methanol
Methyl oleate
Water
Sulfuric acid
282.46
885.43
32.04
296.49
18.02
98.08
Table 12: Components molar mass
29
❖ Conversion:
≈ 85%
❖ Mass balance:
m
5740
•
noleic =
•
mcatalyst = 0.1 x mFFA = 0.574 kg/h = 5.85 mol/h
•
Knowing that we have introduced methanol in excess with regards to oleic acid (40 to 1
M
=
282.46
= 20.33 mol/h
molar ratio), the surplus needs to be recycled. However, considering that not all of it can
be recycled (assuming just 95% of it can be), the fresh methanol fed to the CSTR needs
need to cover not just the methanol consumed in the reaction, but also the 5% waste.
nmethanol = noleic x 40 = 813.2 mol/h
nmethanol consumed = noleic consumed = 17.28 mol/h
nmethanol recycled = (nmethanol - nmethanol consumed) x 0.95 = (813.2 -17.28) x 0.95 = 756.12 mol/h
nFresh methanol = nmethanol consumed + 0.05 x (nmethanol - nmethanol consumed) = 57.08 mol/h
•
The quantity of water remaining in the sample after heating the oil is equal to 0.07 wt%,
and this corresponds to ≈ 0.08 kg/hr or 4.46 mol/h.
So the water coming out from the reactor will include the already existing water + the
water generated from the reaction.
nH2O generated = nMethyl oleate = nmethanol consumed = 17.28 mol/h
nH2O total = nH2O generated + nH2O existing = 21.74 mol/h
•
For the Aspen simulation, the sunflower oil will be approximated by the compound
triolein:
ntriolein = ntotal – noleic acid – nwater = 131.14 – 20.33 – 4.46 = 106.34 mol/h
30
Moles number (mol/h)
Component
Triolein
Oleic acid
Sulfuric acid
Methanol
Methanol consumed
Methanol Recycled
Fresh methanol fed to CSTR
Methyl oleate
Water
Before
After
106.34
106.34
20.33
5.85
3.0495
5.85
813.2
795.9195
17.2805
756.1235
57.076475
0
17.2805
4.46
21.7405
Table 13: Moles balance in CSTR
b) Sizing calculation
In this section we will be calculating the volume of the CSTR needed.
Data given:
K = A. exp
−ΔE
R.T
For the forward reaction: [8]
A = 207.41 min-1
ΔE = 24440.67 J/mol
R = 8.314 J.K-1.mol-1
T = 333.15 K
➔ K = 0.031 min-1
The reverse reaction can be neglected as it is more than 200 X smaller than the forward
reaction [8].
31
With the university cafeteria Zouki providing 60 L/month of WCO and another 440 L/month
from neighboring restaurants, we can afford to run our reactor for only 1 h/week.
500 L (459.5 Kg) of WCO will contain 22.98 kg (81.34 mol) of oleic acid and will produce 20.5 kg
of methyl oleate (69.14 mol).
Since we will be running our pilot scale experiment 4 times/month, this means that each week
we will be processing 125 L of WCO, containing 20.34 mol of oleic acid, transforming into
17.285 mol of methyl oleate.
Component
# moles
Molar mass (g/mol)
Density (Kg/L)
Volume (L)
Oleic acid
Methanol
Sulfuric acid
Sunflower oil
20.34
813.6
5.86
131.14
282.46
32.04
98.08
876
0.895
0.792
1.84
0.919
6.42
32.91
0.31
125
Table 14: Reactants properties and moles number for 125 L of WCO
However oleic acid is in the sunflower oil, so its volume (6.42 L) shall be incorporated with the
125 L of the WCO.
Coleic =
𝑛
𝑉
=
20.34
125+32.91+0.31
= 0.129 mol/L
▪
-rA = k.CA0 = 4 x 10-3 mol/L.min (the esterification reaction is a 1st order reaction.)
▪
t = 1 hour for a proper esterification reaction.
▪
X will be approximated as 0.85 (as this conversion brought us to a very low acid value. in
just 1 hour.)
CSTR:
o FA0 = 20.34 mol/h = 0.339 mol/min
o FA = FA0 (1-X) = 17.285 mol/h = 0.288 mol/min
32
o -rA = 4 x 10-3 mol/L.min
➔ VCSTR = 12.75 L
8.2- Heat exchanger
As there are many heat exchangers configurations; a process screening is required in order to
choose the most suited one. The shell & tube exchanger will be our reference since it’s the
most known/used around the world.
Criteria/Type
Shell & Tube
Compact
Air Cooled
Versatility
Efficiency
Ruggedness
Fouling/plugging sensitivity
Cost
Maintenances
Final score
0
0
0
0
0
0
0
+
0
-3
0
0
+
-2
Table 15: Heat exchanger types
Based on the above scores, the shell & tube heat exchanger will be the one selected for our
operations.
The cold WCO will enter the shell while the hot mixture coming out from the CSTR will enter
the tubes, this is due to the corrosiveness of the sulfuric acid contained in the mixture and the
higher viscosity of the cold WCO. The fluids will enter in a countercurrent manner for a superior
efficiency.
Available specific heat data (at 45 °C):
Components
Cp (kJ/kg.°C)
Water
Sunflower oil
Oleic acid
Methanol
Methyl oleate
Sulfuric acid
4.179
2.257
2.046
2.669
2.091
1.465
Table 16: Components specific heat data
33
In order to determine the Cp of the WCO coming in at 20 °C and the mixture coming out from
the CSTR at 60 °C we need to multiply the weight fraction of the components by their
respective heat capacities Cp’s.
The cold WCO can be approximated by the sunflower oil containing 5wt. % oleic acid
and no water:
CpWCO = 0.95 x 2.257 + 0.05 x 2.046 = 2.246 kJ/kg.°C
The hot mixture can be represented by: 74.28 wt.% sunflower oil; 20.17% methanol;
4.1% methyl oleate; 0.45% sulfuric acid; 0.68% oleic acid and 0.32% water.
CpMixture = 0.7428x2.257 + 0.2017x2.669 + 0.041x2.091 + 0.0045x1.465 + 0.0068x2.046 +
0.0032x4.179 = 2.334 kJ/kg.°C
N.B: In order not to get a huge area for the heat exchanger, we won’t be using the maximum
possible heat transfer that could be achieved, instead, we will be setting the exit temperature of
the cold WCO to 45 °C, therefore:
Q = ṁ.Cp.ΔTwco = 0.032 x 2.246 x (45 – 20) = 1.8 kW
ΔTmix =
Q
ṁ.Cp
=
LMTD: ΔTm =
1.8
0.048 x 2.334
=16.07 °C → Tmix out = 43.93 °C
(Th1−Tc2) − (Th2−Tc1)
(Th1−Tc2)
ln (
)
Th2−Tc1
=
(60−45)− (43.93−20)
ln (
15
)
23.93
= 19.12 °C
As a design choice, the shell & tube exchanger will have 2 rows of tubes, 2 tubes per row.
The outer diameter of the tubes shall be 16 mm (with a wall thickness of 2 mm), although we
need a much smaller diameter than this, this is the minimal one that heat exchangers are
designed for.
The horizontal and vertical spacing between our in-line tubes will be selected as:
34
Sn = Sp = 2 x DOut = 32 mm
The properties of the WCO and mixture are evaluated at Tf = 40 °C
To calculate the maximum velocity we use the formula: Vmax = Vinf .
To calculate Vinf between the tubes we use the formula: Vinf =
Sn
Sn−D
ṁ
φ. A
Flow area = Baffles x Width
Baffles = 2/3 . Width
Width = Sp . (N + 2)
Starting with the width:
Width = 0.032 x (4 + 2) = 0.192 m
Baffles = 2/3 x 0.192 = 0.128 m
Area = 0.128 x 0.192 = 0.025 m2
Vinf =
ṁ
φ. A
=
0.032
919 x 0.025
→ Vmax = Vinf .
Sn
Sn−D
= 1.39 x 10-3 m/s
= 1.39 x 10-3 x
32
32−16
= 2.79 x 10-3 m/s
The kinematic viscosity of the mixture (approximated by sunflower oil and methanol only) can
be calculated using Gambill method: μmix1/3 = xwco. μwco1/3 + xmet. μmet1/3
μmix1/3 = 0.75 x (3.37 x 10-5)1/3 + 0.25 x (5.7 x 10-7)1/3
35
→ μmix = 1.82 x 10-5 m2/s
The density of the mixture (approximated by sunflower oil and methanol only) can be
calculated by: ρmix ≈ 0,75 . ρWCO + 0,25 . ρMet
→ ρmix ≈ 0.75 x 904 + 0.25 x 773 = 871.3 kg/m3
The Reynolds number can now be calculated:
Re =
V.D
μ
=
2.79 x 10−3 x 0.016
1.82 x 10−5
= 2.45
 1st we need to calculate the heat transfer coefficient across the tubes:
For the WCO flow across the pipes, the Nusselt number can then be determined by the
correlation of Knudsen and Katz:
Nu =
h .D
K
= C . Ren . Pr1/3
Where:
μ: kinematic viscosity in m2/s
μ’: absolute viscosity in kg/m.s
h: heat transfer coefficient (W/m2.K)
D: Outer diameter of tubes in the shell (m)
K: Thermal conductivity (W/m.K)
C, n: Constants determined from the value of the Reynold number ( C = 0.989 & n = 0.33)
36
Pr: Prandtl number calculated by: PrWCO =
Applying the above formula: Nu =
h .D
K
μ′ . Cp
K
=
0.03 x 2257
0.165
= 410.36
= C . Ren . Pr1/3
Nu = 0.989 x 2.450.33 x 410.361/3 = 9.88
h=
Nu .K
D
=
9.88 x 0.165
0.016
= 101.89 W/m2.K
This is the heat-transfer coefficient that would be obtained if there were 10 rows of tubes in
the direction of the flow. Because there are only 2 rows, this value must be multiplied by the
correction factor 0.8:
hout = h x 0.8 = 81.51 W/m2.K
 Now we need to calculate the heat transfer coefficient inside the tubes:
We will start by calculating the mean velocity inside each tube: Vm =
ṁ
φ .A. N
Where:
ṁ: mass flow rate of the mixture (kg/s)
φ: Density (kg/m3)
A: area of each tube: π. R2 = 3.14 x (7 x 10-3)2 = 2.01 x 10-4 m2
N: number of tubes: 2 x 2 = 4
Vm =
ṁ
φ .A. N
=
0.0485
871.3 x 2.01 x 10−4 x 4
= 0.07 m/s
37
Re (inside the tubes) =
V.Di
μ
=
0.07 x 0.014
1.82 x 10−5
= 53.85 < 2100: Laminar flow
KMix ≈ KWCO x 0.75 + KMethanol x 0.25 =0.165 x 0.75 + 0.2 x 0.25 = 0.174 W/m.K
D
L
0,0668 .( ).Re .Pr
Using Hausen correlation: Nu = 3,66 +
D
L
1+0,04 [( ) .Re .Pr]
PrMix =
μ′ . Cp
K
=
0.016 x 2334
0.174
2/3
= 214.62
As for L (length of the tubes), it will be approximated by 1 m (which is more than enough for
these volumetrics) so that:
D
L
0,0668 .( ).Re .Pr
Nu= 3,66 +
2/3
D
L
= 3.66 +
1+0,04 [( ) .Re .Pr]
hint =
Nu .K
D
=
8.6 x 0.174
0.014
0.014
) x 53.85 x 214.62
1
2/3
0.014
0.0668 x (
1+ 0.04 [(
1
= 8.6
) x 53.85 x 214.62 ]
= 106.89 W/m2.K
Bundle configurations:
Let’s start by getting the diameter of our circular bundle of pipes:
Apipe + spacing = π . R2 = 3.14 x (0.008 + 0.016)2 = 1.81 x 10-3 m2
Aall pipes = Apipe . Number pipes = 1.81 x 10-3 x 4 = 7.24 x 10-3 m2
A
Aall pipes = π . R2 → R = √ = 0.048 m → Dbundle = 2 . R = 0.096 m
π
38
With the inner and outer heat transfer coefficients calculated, and assuming that the tubing’s
walls are negligibly thin (so that Dout ≈ Din → Aout ≈ Ain ≈ A), we can calculate the overall heat
transfer coefficient U by:
1
U. A
1
U
=
=
1
+
ho . A
1
81.51
+
1
hi . A
1
106.89
Uclean = 46.25 W/m2.K
Taking the fouling factor Fo into consideration:
Fo = 1/Udirty – 1/Uclean
0.00053 = 1/Udirty – 1/46.25
Udirty = 45.14 W/m2.K
q = U.A.F.ΔTm
 For the correction factor F, it can be calculated but it needs 2 sets of data:
R=
P=
(Tc1−Tc2)
(Th2−Th1)
(Th2−Th1)
(Tc1−Th1)
=
=
20−45
43.93−60
43.93−60
20−60
= 1.56
= 0.4
→ F ≈ 0.785 (For an exchanger with one shell pass and two, four, or any multiple of tube
passes.)
39
Figure 12: Correction factor [22]
Finally, we can now determine our heat exchanger area with q = U.A.F.ΔTm
A=
𝐪
𝐔.𝐅.𝚫𝐓𝐦
=
𝟏𝟖𝟎𝟎
𝟒𝟓.𝟏𝟒 𝐱 𝟎.𝟕𝟖𝟓 𝐱 𝟏𝟗.𝟏𝟐
= 2.66 m2 [22]
With the area obtained, we can measure the tube-side pressure drop ΔPt.
But we need first the number of tube passes:
The total cross-sectional area Ac per pass:
Aci =
ṁ
φ.V
=
0.0485
871.3 x 0.07
= 7.95 x 10-4 m2
The number of tubes per pass Nt:
Nt =
Aci
π . R2
=
7.95 x 10−4
3.14 x (7 x 10−3 )2
= 5.16 ≈ 6 tube/pass
The heat transfer area At per tube:
40
At = π . Di . L = 3.14 x 14 x 10-3 x 1 = 0.044 m2/tube
The number of tube passes Np:
Np =
A
At . Nt
→ ΔPt =
=
2.66
0.044 x 6
≈ 10 passes
2 .(Np – 1). φ. V2
gc
=
2 x (10 – 1) x 871.3 x 0.072
1
= 76.85 Pa = 0.011 psi : Acceptable value
8.3- Distillation column
Let us begin by performing a very basic material balance on the distillation column so we may
be able to design it later on [25].
Feed = Distillate + Bottom
According to the CSTR mass balance, and since the methanol is the most volatile compound in
the mixture (boiling point: 64.7 °C) followed by water (boiling point: 100 °C); we want the
distillate to be composed of 95% of the unreacted methanol and just 1% of the formed water
(accounting for the separation not being perfect). The bottom will contain everything else.
The temperatures for the distillate and bottom feeds were obtained from Aspen.
➢ Distillate: (T = 64.5 °C)
nMethanol distillate = (nmethanol - nmethanol consumed) x 0.95 = 756.12 mol/h = 24.226 kg/h
nH2O distillate = nH2O total x 0.01 = 0.22 mol/h = 3.92 g/h
→ DTotal: 756.34 mol/h or 24.23 kg/h
➢ Bottom: (T = 104 °C)
nMethanol bottom = (nmethanol - nmethanol consumed) x 0.05 = 39.8 mol/h = 1.275 kg/h
nH2O bottom = nH2O total x 0.99 = 21.52 mol/h = 0.388 kg/h
41
nSulfuric acid = 5.85 mol/h = 0.574 kg/h
nTriolein = 106.34 mol/h = 94.16 kg/h
nOleic acid = 3.05 mol/h = 0.862 kg/h
nMethyl oleate = 17.28 mol/h = 5.12 kg/h
→ BTotal: 193.84 mol/h or 102.379 kg/h
Specifications of the distillation column:
Quality of the feed, q =
Ḹ−L
F
Ḹ: The liquid volume descending the striping section in the column
L: The liquid volume descending the rectifying section in the column
F: Our main feed entering the column
Approximating our feed as only being composed of a saturated liquid phase, than Ḹ = F and L =
0.
➔ Q=1
➔ The feed line will be perpendicular to the Y axis.
42
Figure 13: Feed lines
We also need z (the mole fraction of the most volatile compound in the feed, methanol).
Z = nmethanol/nTotal = 795.92 / (106.34 + 3.05 + 5.85 + 795.92 + 17.28 + 21.74) ≈ 0.838
As an approximation, we will consider only having 3 components in our distillation column:
Methanol (considered as the light key LK); water (considered as the heavy key HK) and triolein
(considered as the heavy non-key HNK)
First we need to calculate the relative volatility α between the light and heavy keys, both at the
top of the column and at its bottom in order to calculate the average volatility later.
αL-H Top =
K methanol
K water
1
= 0.4 = 2.5
43
Figure 14: K values for methanol/water mixture obtained from Aspen
For the bottom volatility we need to take a different approach, as it becomes more complex
than a system of binary components:
Pmet/Xmet
αL-H Bottom = Pwat/Xwat
❖ Pmethanol can be approximated by Raoult law:
Pmethanol = Xmethanol . P*methanol
Where P*methanol is the pressure of pure methanol at 104 °C
Figure 15: Antoine coefficients for methanol
P*methanol(using Antoine coefficients) = 103.47 = 2947.27 mm Hg
Xmethanol = 0.2053
→ Pmethanol = 605.07 mm Hg
44
❖ Pwater can be approximated by:
→ Pwater ≈ Xwater . P*water ≈ 0.111 x 873 = 96.9 mm Hg
So that:
Pmet/Xmet
αL-H Bottom = Pwat/Xwat =
605.07 /0.2053
96.9 /0.111
= 3.376
Now we can calculate αAverage:
αAverage = √( αL-H Top . αL-H Bottom) = 2.905
Using the average volatility that we just calculated, we can use Fenske’s equation to get the
minimum number of stages for the column:
Where:
XL,top
0.9997
XH,top 0.0003
XL,bot
0.205
XH,bot 0.111
➔ Nmin = 7.03 (Close to the result given by the aspen simulation of 7.95 stages)
Taverage =
T top +T bot
2
=
64.5+104
2
= 84.25 °C
For this temperature the volatilities (with methanol as our reference) will be:
Pwat/Xwat
9.775/0.023
✓ αWater-Methanol = Pmet/Xmet = 1319/0.838 = 0.27
45
Pmethanol = Xmethanol,feed . P*methanol = 0.838 x 103.197 = 1319 mm Hg
Pwater ≈ Xwater,feed . P*water = 0.023 x 425 = 9.775
Psun/Xsun
4.37 x 10^−13/0.115
✓ αsunflower-Methanol = Pmet/Xmet =
1319/0.838
= 2.41 x 10-15
Psunflower ≈ Xsunflower,feed . P*sunflower = 0.115 x 10-11.42 = 4.37 x 10-13
Figure 16: Antoine coefficients for sunflower oil
Since methanol is our reference we can write:
1-q=
0=
α water,methanol . X water
α water,methanol − φ
0.27 x 0.023
0.27 − φ
+
+
α sunflower,methanol . X sunflower
2.41 x 10^−15 x 0.115
2.41 x 10^−15 − φ
φ1 ≈ -9000
α sunflower,methanol − φ
+
+
α methanol,methanol . X methanol
α methanol,methanol − φ
1 x 0.838
1−φ
φ2 = 0.2754
φ1 will be ignored while φ2 will be taken.
Having obtained φ, we can now find the minimal reflux ratio: Rmin:
𝑛
From the Underwood equations: Rmin + 1 = ∑
𝑖
Rmin + 1 =
=
α i,ref . Xi,top
α i,ref − φ
α water,methanol . X water,top α methanol,methanol . X methanol,top
α water,methanol − φ
0.27 x 0.0003
0.27 − 0.2754
+
α methanol,methanol − φ
1 x 0.9997
+ 1 − 0.2754 = 1.37
Rmin = 1.37 – 1 ≈ 0.37
Choosing R as: R = 1.3 x Rmin = 0.48
46
Using Gilliland correlations fitted into equations by Liddle, let x = [L/D – (L/D)min]/(L/D + 1),
(finding x is essential for finding the plates number N):
x = 0.074 → we have to use the 2nd equation:
N−Nmin
N+1
N−7.03
N+1
= 0.545827 – 0.591422x +
0.002743
x
= 0.54 → N= 16.45 (Aspen gave 15.9, so the numbers are really close)
The optimum feed plate location Nf can also be estimated from Gilliland correlations:
And then, assuming that the relative feed location is constant as we change the reflux ratio
from total reflux to a finite value:
Nf,min
Nmin
=
Nf
N
0.9997
ln [ 0.0003
0.838 ]
NF,min =
0.023
ln 3.703
= 3.45
47
Nf,min
Nmin
=
Nf
N
→
3.45
7.03
=
Nf
16.45
→ Nf = 8.07
The overall efficiency of the column can be calculated by: ϵ = Nmin/N ≈ 7.03/16.45 = 0.43 = 43%
Plate spacing L will be selected as 25 cm as this spacing can be used for pilot scales. Taking this
value, the column height will be equal to: (2 + 17 + 3) x 0.25 ≈ 5.5 m
As a rule of thumb, the entire column height should be raised by an average of 2 plates above
the top plate (for reflux piping and distributor) and 3 plates beneath the bottom plate (to
supply a head for the reboiler feed) [26].
Let’s calculate now the maximum vapor velocity (m/s) in the column, it is recommended as a
rule of thumb, that the vapor velocity in the column should not exceed 80% of its maximum
value Umax, for that we will need the density of the liquid and vapor phase.
Umax = (– 0.171 L2 + 0.27 L – 0.047).√
ρl
ρv
With:
L = 0.25 m
ρl = 728.74 kg/m3 (from previous results)
ρv can be approximated by the density of methanol vapor alone, as water make a negligible
amount of the mixture (0.31 wt.%) and all the other components have extremely low volatility.
Using the ideal gas law: ρv =
P.M
R.T
=
1 x 32.04
0.0821 x 313.15
= 1.246 g/L = 1.246 kg/m3
→ Umax = 0.237 m/s → Uv = 0.8 x Umax = 0.19 m/s
48
To determine the volumetric flow of the vapor we need:
Qv =
Mass flow rate of the vapor
Vapor density
=
35.86 kg/h
1.246 kg/m3
= 28.78 m3/h = 8 x 10-3 m3/s
The mass flow rate of the vapor can be calculated now that we have the reflux ratio L 0/D:
V = L0 + D = D.L0/D + D = 24.23 x 0.48 + 24.23 = 35.86 kg/h
With the volumetric flow of the vapor we can get the cross sectional area Ac:
Ac =
volumetric flow
U
=
0.008
0.19
= 0.042 m2
With all this data, we can finally estimate the column diameter D c:
Dc = √
4 x Ac
π
= 0.232 m
a) Condenser calculations:
For the calculation of our total condenser area A cond we need several variables:
756.12 mol/h of methanol = 0.21 mol/sec
 D Total = 756.34 mol/h
0.22 mol/h of water
As an approximation, we will neglect the very small quantity of water present.
H condensation (64.5 °C) = 35210 J/mol
Q cond = nMet . Hcond = 0.21 x 35210 = 7394.1 W
We can use this number to determine the mass flow rate of the cooling sea-water needed:
Q = ṁ. Cp . ΔT
49
We chose to let the sea water get heated from its normal temperature of 20 °C to 50 °C max
(14.5 °C less than the temperature of the condensate.)
ṁwater =
Q
C . ΔT
=
7394.1
4.185 x (50−25)
= 70.67 g/sec = 254.412 kg/h
 For the methanol piping; assuming a turbulent flow and < 1 inch diameter: D i,opt = 4,7
(ṽ0.49).( ρ0.14)
Where:
ṽ = flow rate (ft3/s)
ρ = density (lb/ft3)
ṽDistillate = mass flow rate / density = 24.23 / 750 = 0.0323 m3/h = 3.17 x 10-4 ft3/sec
ρ = 750 kg/m3 = 46.82 lb/ft3
Di,opt = 0.155 in = 0.00394 m
Now we can calculate the velocity V inside our circular pipe:
V = 1.273 ṽ/Di2 =1.273 x 8.97 x 10-6 / (0.00394)2 = 0.736 m/s
The Reynolds number is: Re =
ρ.V.Di
μ
=
750 x 0.736 x 0.00394
0.00035
=6214 (our assumption was correct)
 For the cooling water piping; assuming a turbulent flow and < 1 inch diameter: Di,opt =
4,7 (ṽ0.49).( ρ0.14)
ṽDistillate = mass flow rate / density = 70.67 / 995 = 0.071 L/sec = 0.0025 ft3/sec
ρ = 995 kg/m3 = 62.12 lb/ft3
Di,opt = 0.445 in = 0.0113 m
Now we can calculate the velocity V inside our circular pipe:
V = 1.273 ṽ/Di2 =1.273 x 7.1 x 10-5 / (0.0113)2 = 0.708 m/s
The Reynolds number is: Re =
ρ.V.Di
μ
=
995 x 0.708 x 0.0113
0.000798
= 9975 (our assumption was correct)
50
Utilizing the parameters listed in the table below we have calculated the overall heat transfer
coefficient U.
Parameter
Hot
Cold
Material
Di,opt (m)
Flowrate (kg/h)
Inlet temperature (°C)
Outlet temperature (°C)
Fouling factor (m2.°C/W )
Density (kg/m3)
Viscosity (kg/m.s)
Specific heat (kJ/kg.°C)
Thermal conductivity (W/m.K)
Copper
0.00394
24.226
64.5
50
0.00009
750
0.00035
2.745
0.192
Copper
0.0113 + 0.00394 = 0.01524
254.412
25
50
0.00009
995
0.000798
4.1806
0.164
Table 17: Parameters for condenser design
U = 133.22 kcal/h.m2.°C = 154.93 W/m2.°C
And LMTD: ΔTm =
(Th1−Tc2) − (Th2−Tc1)
ln
(Th1−Tc2)
(
)
Th2−Tc1
=
(64.5−50)− (50−25)
14.5
)
25
ln (
= 19.28 °C
With the overall heat transfer coefficient and LMTD determined we can now calculate the area
of the condenser: Q cond = U cond . A cond . ΔTlm
A cond =
Q
=
U . ΔT
7394.1
154.93 x 19.28
≈ 2.48 m2
b) Reboiler calculations:
In order to determine the mass flow rate of the heating fuel oil, we took the value of heating
duty obtained from Aspen which is equal to 13411.7 W:
Q = ṁ. Cp. ΔT
We chose to let the fuel oil get heated to 200 °C max and be cooled to 120 °C (16 °C more than
the bottoms exiting temperature.)
ṁF.O. =
Q
C . ΔT
=
13411.7
1.842 x (200−120)
= 91.01 g/sec = 327.65 kg/h
51
 With the mixture exiting from the bottom distillation column, approximated as being
formed from sunflower oil alone along with assuming a laminar flow and < 1 inch
diameter, the optimal piping internal diameter will be: Di,opt = 3.6 (ṽ0.4).( μ0.2)
ṽMixture = mass flow rate / density = 102.379/919 = 0.1114 m3/h = 0.0011 ft3/s
μ = 0.02 kg/m.s = 0.0134 lb/ft.s
Di,opt = 0.1 in = 0.00254 m
Now we can calculate the velocity V inside our circular pipe:
V = 1.273 ṽ/Di2 =1.273 x 3.09 x 10-5/ (0.00254)2 = 6.1 m/s
The Reynolds number is: Re =
ρ.V.Di
μ
=
919 x 6.1 x 0.00254
0.02
=712 (our assumption was correct)
 For the heating oil piping; assuming a turbulent flow and < 1 inch diameter: D i,opt = 4,7
(ṽ0.49).( ρ0.14)
ṽMixture = mass flow rate / density = 327.65/790 = 0.415 m3/h = 0.0041 ft3/s
ρ = 790 kg/m3 = 49.32 lb/ft3
Di,opt = 0.549 in = 0.014 m
Now we can calculate the velocity V inside our circular pipe:
V = 1.273 ṽ/Di2 = 1.273 x 1.152 x 10-4/(0.014)2 = 0.75 m/s
The Reynolds number is: Re =
ρ.V.Di
μ
=
790 x 0.75 x 0.014
0.00144
= 5760.4 (our assumption was
correct)
Utilizing the parameters listed in the table below we have calculated the overall heat
transfer coefficient U.
Parameter
Cold
Hot
Material
Di,opt (m)
Flowrate (kg/h)
Inlet temperature (°C)
Outlet temperature (°C)
Stainless steel
0.00254
102.379
58
104
Stainless steel
0.014 + 0.00254 = 0.01654
327.65
200
120
52
Fouling factor (m2.°C/W )
Density (kg/m3)
Viscosity (kg/m.s)
Specific heat (kJ/kg.°C)
Thermal conductivity (W/m.K)
0.00053
919
0.01
2.257
0.164
0.00018
790
0.004
1.842
0.12
Table 18: Parameters for reboiler design
U = 27.91 kcal/h.m2.°C = 32.46 W/m2.°C
And LMTD: ΔTm =
(Th1−Tc2) − (Th2−Tc1)
ln
(Th1−Tc2)
(
)
Th2−Tc1
=
(200−104)− (120−58)
96
62
ln ( )
= 77.77 °C
With the overall heat transfer coefficient and LMTD determined we can now calculate the area
of the reboiler: Q reb = U reb . A reb . ΔTlm
A reb =
Q
U . ΔT
=
13411.7
32.46 x 77.77
≈ 5.31 m2
8.4- Decanter
The hot mixture coming out from the bottom of the distillation column must have the sulfuric
acid in it removed so it doesn’t interact negatively with the transesterification reaction later on
in the process, without forgetting the extra water generated from the esterification reaction in
the CSTR. However, if we wish to uniquely separate the sulfuric acid from the mixture, it will be
extremely difficult and pricey; so instead, we will be separating the water from the mixture by
decantation, and since sulfuric acid has great affinity for water, the majority of the acid will be
decanted with the water.
Methanol will not be removed from the mixture as later on, in the transesterification reaction,
it will be added in large quantities to form biodiesel.
Taking water as the dispersed phase and WCO as the continuous phase (all properties
determined at 104 °C):
53
Figure 17: Droplet diameter vs. emulsion types
Water average droplet diameter: 40 μm (assuming a loose emulsion)
Water flow rate: 0.388 kg/h
Density: 959 kg/m3
WCO flow rate: 100.142 kg/h
Density: 867 kg/m3 (at 104 °C)
Dynamic Viscosity: kinematic viscosity . density = 7.78 x 10-6 x 867 = 6.75 x 10-3 N.s/m2
Vd = Dd2 .
g.(φwat – φwco)
18 . μwco
= (40 x 10-6)2 x
9.81 x (959 – 867)
18 x 6.75 x 10−3
= 1.19 x 10-5 m/s (falling)
Since the flow rate is small, we’ll be using a vertical cylindrical vessel, calculating the
continuous phase volumetric flow rate Lc (in m3/s):
Lc =
ṁ wco
φ wco
x
1
3600
=
100.142
867
x
1
3600
= 3.21 x 10-5 m3/s
With Vd = Lc/Ai → Ai = Lc/ Vd
Ai = (3.21 x 10-5)/(1.19 x 10-5) = 2.7 m2
54
R=
√Ai
√π
=√
2.7
3.14
= 0.927 m
Diameter D = 2 . R = 1.853 m
A fair approximation for the height of the cylinder would be: H = 2 x Diameter = 3.71 m
[24]
➔ Final dimensions for our decanter will be: - D = 1.853 m
- H = 3.71 m
- Ai = 2.7 m2
- V = A . H = 10.02 m3
8.5- Filter
To find the area of the filter needed to remove the solid particles from the WCO we use the
following formula:
Cs . (ṽ + ε . L . A) = L . A . ρs . (1 - ε)
Where:
A: Area of filtration required per hour
L: Cake thickness ≈ 1 cm = 0.01 m
ε: Porosity ≈ 0.5
ṽ: Volumetric flow rate of WCO trough the filter = 125 L/h = 0.125 m3/h
ρs: Density of Solid Particles in Cake ≈ 3500 kg/m3
Cs: Solids concentration per volume of filtrate: solids weight ≈ (2 wt.%)x(115 kg/h) = 2.3 kg/h
Cs =
2.3
0.125
= 18.4 kg/m3
➔ A = 0.132 m2/h
55
10- Cost analysis
10.1- Equipments
Using cost correlations, we will estimate in this section the average price of the various
equipments used.
Equipments
Variables
Cost (in $)
Reactor
Heat exchanger
V = 12.75 x 10-3 m3
A = 2.66 m2
MF: 2.341
A = 2.48 m2
MF = 2.705
A = 5.31 m2
MF =3.477
D = 0.232 m
MF = 2.1
H = 5.5 m
D = 0.232 m
NTrays = 22
MF = 1.9
NF = 1.04
P = 3.14 x 10-3 kW
MF = 2.0
C = 2400
S = 10.02 m3
n = 0.6
C = 2400
S = 0.5 m3
n = 0.6
C = 1900
S = 0.25 kW
n = 0.5
7069
12703
Distillation column
Condenser
Distillation column
Reboiler
Distillation column
Column shell
Distillation column
Sieve trays
Peristaltic pump
Vertical tank (decanter) [24]
Vertical tank
(mixer/water removal tank) [24]
Agitator – propeller [24]
Total equipments cost
Piping, safety, construction…
New total equipments cost
+ 2.51%
14543
29072
12906
20752
933
9566
1584
950
110078
2763
112841
Table 19: Equipments cost
56
10.2- Utilities & raw materials cost
The following numbers were estimations for ≈ 1.5 operating hours/week or 78 hours/year [24].
Sulfuric acid:
Consumption: 573.77 g/h or 44.76 kg/year
Price: 300$/ton (98% purity)
$C = 13.43 $/year
Methanol:
Consumption: 1893.6 g/h or 147.7 kg/year (with recycling)
Price: 650$/ton (99% purity)
$C = 96 $/year
WCO:
Consumption ≈ 115 kg/h or 8970 kg/year
Price ≈ 500 L.L./Liter or 0.362 $/Kg
$C = 3250 $/year
Cooling water:
Consumption: 254.412 kg/h or 19844.14 kg/year
Price ≈ 5$/m3 or 5$/ton
$C = 99.3 $/year
57
Fuel oil #2:
Consumption: 327.65 kg/h or 327.65 kg/year (we’re not burning the fuel we’re recycling it)
Price ≈ 1.4$/gallon or 0.402 $/kg
$C = 131.72 $/year
100 microns filter:
Consumption: 0.132 m2/h or 10.3 m2/year
Price ≈ 20$/m2
$C = 206 $/year
Electricity:
Consumption: The biggest consumption will be for the dewatering step at the beginning since
we need to raise the temperature of our WCO from ≈20 °C to 140 °C in order to evaporate the
water in it.
•
W . t = Cp . m . ΔT
Where:
W: Wattage of the element (in kW)
t: Time (in sec)
Cp: Specific heat of the WCO (in kJ/kg.°C)
m: Mass of the WCO (in Kg)
58
ΔT: Change in temperature
W=
Cp . m . ΔT
t
=
2.257 x 115 x (140−20)
30 x 60
= 17.3 kW
There’s also the consumption of the CSTR:
•
QCSTR = ṁ . cp . ΔT
Where:
Q: heat transfer needed (in kW)
ṁ: the mass flow rate of the WCO entering the CSTR (in kg/sec)
ΔT: Change in temperature
Q = 0.035 x 2.334 x (60 – 45) = 1.232 kW
And the consumption of the reboiler:
QReboiler = 13411.7 W = 13.41 kW
Adding the consumption of the other equipments, the total consumption becomes:
→ W ≈ 32.2 kW/h or 2511.6 kW/year
Price: 140 L.L./kW or 0.093 $/kW
$C = 233.6 $/year
59
Total utilities & raw materials cost:
➔ Utilities: 670.7 $/year
➔ Raw materials: 3359.5 $/year
11- HAZOP
Below are the hazards and 1st aid measures of all the chemicals used in this study:
Molecule
Dangers
1st Aid Measures
Methanol
Inhalation of high airborne concentrations can irritate
mucous membranes. Methanol is moderately
irritating to the skin. Methanol is a mild to moderate
eye irritant. Swallowing even small amounts of
methanol could potentially cause blindness or death.
Corrosive, causes redness, pain, blisters and burns if it
touches the skin. If inhaled, causes burning sensation,
sore throat, cough and shortness of breath.
Swallowing may lead to abdominal pain, a burning
sensation or collapsing.
Slightly hazardous in case of skin contact (irritant), eye
contact (irritant), inhalation or ingestion.
In case of contact, immediately flush eyes with
lots of running water for at least 15 minutes.
Wash affected areas with soap and water for
at least 15 minutes. If inhaled, get some fresh
air, artificial respiration may be needed.
In case of contact, rinse contaminated area
with lots of running water, get some fresh air,
artificial respiration may be needed if inhaled.
If swallowed, rinse mouth but don’t induce
vomiting. In all cases consult a doctor.
In case of eye contact, immediately flush eyes
with plenty of water for at least 15 minutes.
Cover the irritated skin with an emollient. If
inhaled, get some fresh air.
In case of contact, rinse contaminated area
with lots of running water, get some fresh air,
artificial respiration may be needed if inhaled.
If swallowed, don’t induce vomiting, instead
call immediately for medical assistance.
Sulfuric acid
Oil (Triolein)
Benzene
Isopropyl
alcohol
Highly flammable. Irritating to eyes. Vapors may cause
drowsiness and dizziness, long-term exposure, even at
low concentrations, may result in various blood
disorders. Skin exposure causes irritation, redness,
and burning sensation. Vapors may form explosive
mixtures with air.
Flammable. Irritating to eyes and skin. Vapors may
cause drowsiness, dizziness and headaches.
In case of contact, wash contaminated area
with soap and water, get some fresh air,
artificial respiration may be needed if inhaled.
If swallowed, do not induce vomiting; instead
give plenty of water to drink and call for
medical assistance.
60
Potassium
hydroxide
Irritating to eyes and skin, can cause severe burns. If
inhaled causes cough and sneezing. If swallowed,
causes vomiting and diarrhea.
In case of contact, wash contaminated area
with soap and water. If inhaled get some fresh
air. If swallowed, do not induce vomiting;
instead give plenty of water to drink and call
for medical assistance.
Table 20: Hazards and 1st aid measures for chemicals used
Beneath, is a brief study of possible problems which could cause deviations on the operability
of the pilot plant and their possible solutions.
Component
Heat exchanger
Pump
Condenser
Temperature
control valve
Level control valve
Wall of any
containment unit
Failure causes
Tube failure
- Pump stop
- Power failure
- Cooling fluid pipe
rupture
- Power failure
- Electric device
failure
- Power failure
-Electric device
failure
- Power failure
Wall rupture
Consequences
- Elevated pressure that may cause the
rupture of the pipes
- No temperature difference between the
flows coming in and out of the exchanger
- No production
- Could cause damage to the pump
- No production
- No liquefaction of methanol
- Lower flow rate at the entrance
- High flow rate from the column’s bottom
- No production
Can cause temperature deviations that will
accelerate equipment failure and may
lower yields
Fluid will surpass the vessel’s level causing
it to rupture or overflow.
Leakage of fluids on the ground, causing
the production to stop for a long time and
a big safety hazard
Actions
Schedule inspection and
preventive maintenance
- Schedule inspection and
preventive maintenance
- Backup power generator
- Schedule inspection and
preventive maintenance
- Backup power generator
- Schedule inspection and
preventive maintenance
- Backup power generator
- Schedule inspection and
preventive maintenance
- Backup power generator
Schedule inspection and
preventive maintenance
Table 21: Equipments failure, causes and solutions
61
Guide
Word
No
Deviation
No flow
Possible causes
- Blockage in line
- No raw materials in
storage tanks
Consequences
- Reduction in production rate
until no production
Actions
- Cleaning of lines
- Level control system
- Preventive maintenance on pipes
- Rupture of feed pipe
- Automatic valves
- Rupture of supply pipe
- Automatic pumps
- Closed valve
- Closed pump
Less of
Less flow rate at
reactor entrance
- Valves are opened less
than required
- Low recovery of methanol
in distillation column
- WCO has high FFA levels
- Smaller product flow rate
- Automatic valves
- Bigger temperature in the
feed going to the reactor
- Increase pumping power
- Decrease in recycle stream
flow rate
- Increase methanol and sulfuric acid
flow
- Cavitations
More of
As well
as
More flow rate
at reactor
entrance
Impurities in
feed stream
- Valves are opened more
than required
- Inferior temperature in the
feed going to the reactor
- Low conversion in
previous pass
- Explosion risk
- WCO has low FFA levels
- Increase in recycle stream
flow rate
- Raw material problems
- Smaller conversion rates
- Pipes fouling
-Decrease in product quality
- Impurities will lower
equipments performance
Reverse
Reverse of flow
No probable cause
Reduction in production rate
until production stoppage
- Automatic valves
- Decrease pumping power
- Decrease methanol and sulfuric
acid flow
- Regular quality control checks on
product and raw materials
- Preventive maintenance/cleaning
on all equipments
Check interlock in feed stream
62
High
- Pressure
- Temperature
- Small flow rate of cooling
fluid
- Accumulation of
methanol vapor
- Relief valve malfunction
- Excess heating
- Weather conditions
Low
- Pressure
- Temperature
- Big flow rate of cooling
fluid
- Relief valve malfunction
- Lack of heating
- Weather conditions
- Explosion
- Chemical breakdown
- Boiling of methanol
- Accelerate equipment failure
- Variable yields
- Safety hazards
- Higher flow rate in recycle
stream
- Lower yields
- Cavitations
- Higher viscosities
- Accelerate equipment failure
- Lower flow rate in recycle
stream
- Increase flow rate of cooling fluid
- Decrease heating
- Keep monitoring pressure and
temperature sensors
- Automatic relief valves
-Decrease methanol flow rate
- Decrease flow rate of cooling fluid
- Increase heating
- Keep monitoring pressure and
temperature sensors
- Automatic relief valves
-Decrease raw material flow rate
Table 22: Problematic scenarios, causes and solutions
Safety systems that should be included in any factory:
 All kind of sensors attached to alarms (pressure, temperature, smoke, gas…)
 Regular preventive maintenance and cleaning for all equipments
 Emergency shutdown arrangements
 Fire fighting response
 Emergency training
 Regular safety tests
 TLVs (threshold limit value) of process materials and detection methods
 First aid/medical resources available at all times
 Disposal of vapor and effluent
 Safety equipment testing
Compliance with national and local regulations
12- Conclusion and future recommendation
63
In this project, we screened various pretreatment methods with many variables and chose an
efficient design to reduce FFA and water levels below the permissible amounts of 2 wt% and 0.1
wt% respectively. The optimal conditions were chosen to be: methanol to FFA molar ratio: 40-1;
sulfuric acid weight: 10 wt % (relative to FFA); temperature: 60 °C.
The WCO is first heated to 140 ⁰C for 15 minutes to reduce water content in it to 0.07 wt%, it is
heat exchanged to raise its temperature before being pumped into the CSTR where it will
undergo the esterification reaction for 1 hour, reducing its FFA levels to ≈ 0.74 wt%. 95% of the
excess methanol will be recovered in a distillation column while the water generated from the
reaction and the sulfuric acid will be separated in a decanter at the end of the process.
The pilot scale designed here should be able to process 125 L/hour in a reliable manner with
relatively cheap expenses.
For future recommendations, this project hasn’t gone extensively into design details, so this
work can be regarded as guidelines and very close estimations of the desired WCO treating
plant.
We recommend attaching the dewatering system to the entire process so there will be no
waste of energy in the system and no need for a heat exchanger, hence a significant reduction
in costs.
We recommend buying a Karl Fischer electronic titrator, which gives instantaneous numbers
regarding the water content in the oil, instead of waiting many hours for the freeze drying
method to be over.
Since the distillation column is the most expensive equipment in this process, we recommend
trying a flash drum in its place then comparing the results afterwards to see if it works.
Also, a solid catalyst such as iron (III) sulfate hydrate Fe2(SO4)3, which has showed lots of
potential on a laboratory scale, could be tried in the future. The results obtained could then be
compared with those resulting from the use of sulfuric acid.
64
13- Appendix
13.1- AOCS official method CD 3A-63 for acid value test
The acid value is the number of milligrams of potassium hydroxide (KOH) necessary to
neutralize the free acids in I gram of sample. This method is applicable to crude and refined
animal, vegetable, and marine fats and oils, and various products derived from them. The
necessary apparatus, reagents, test procedure and the calculations for the acid value test are
explained below.
Apparatus:
1. Erlenmeyer flasks, 250 ml.
2. Burette, 50 ml.
Reagents:
1. Potassium hydroxide (KOH), 0.1 N and 0.0I N in water.
2. Solvent mixture contains of equal parts by volume of isopropyl alcohol and toluene.
3. Phenolphthalein indicator solution, 1.0% in isopropyl alcohol.
Procedure:
1. Add 0.8 ml phenolphthalein indicator solution to 50 ml of solvent mixture (1:1 isopropyl
alcohol - toluene) and neutralize with alkali (0.0I N KOH) to a faint but permanent pink color.
The amount of alkali (0.0I N KOH) used to neutralize the solvent mixture is the blank (B).
2. Determine the sample size from the table below by comparing the expected acid value.
Higher acid value needs less amount of sample and lower acid value needs a large amount of
sample.
65
3. Weigh the specified amount of sample from Table 1 into an erlenmeyer flask.
4. Add 50 ml of solvent mixture (1:1 isopropyl alcohol - toluene). Be sure that the sample is
completely dissolved. Warming may be necessary in some cases.
5. Shake the sample vigorously while titrating with standard alkali (0.1 N or 0.0I N KOH
depending upon intensity of acid value in the sample) to the first permanent pink color of the
same intensity as that of the neutralized solvent. The color must persist for 30 seconds. The
amount of standard alkali used in this step is A, where A is defined below.
Calculation:
The acid value, mg KOH/g of sample = (A-B) * N * 56.1/W
Where; A= ml of standard alkali (0.1 N or 0.01 N KOH) used in the titration
B= ml of standard alkali (0.1N or 0.01N KOH) used in the titrating the blank
N= normality of the standard alkali (0.1 or 0.01 N KOH)
W= grams of sample
13.2- Aspen complete stream table
66
Temperature
K
Pressure
atm
Vapor Frac
Mole Flow
kmol/hr
Mass Flow
kg/hr
Volume Flow
l/min
Enthalpy
MMBtu/hr
Mole Flow
METHANOL
WATER
METHY-01
OLEIC-01
SULFU-01
TRIOL-01
ACID+MET
WCO
MI
PU
WARMWCO
FFAFREE
HOT
RECYCLE
OIL2
LIGHT
HEAVY
293.1
293.1
332.6
332.6
318.1
333.1
330.4
337.7
377.2
298
298
1
1
1
1
1
1
1
1
1
1
1
0
0.065
0
0.131
0
0.951
0
0.951
0
0.131
0
0.951
0
0.951
0
0.755
0
0.196
0
0.175
0
0.021
2.467
99.982 126.64 126.64
99.982
126.64
126.64
24.192
0.045
2.087
3.985
3.985
2.111
3.993
3.984
0.542
2.605
2.38
0.006
-0.018
-0.206
-0.391
-0.391
-0.206
-0.39
-0.39
-0.168
-0.221
-0.217
-0.006
0.814
0.005
trace
0.02
0.006
0.106
0.814
0.005
trace
0.02
0.006
0.106
0.795
0.024
0.019
0.001
0.006
0.106
0.795
0.024
0.019
0.001
0.006
0.106
0.755
< 0.001
0.04
0.024
0.019
0.001
0.006
0.106
0.04
0.002
0.019
0.001
0.006
0.106
0.059
0.004
0.02
0.006
0.106
0.004
0.02
0.106
102.448 102.063
Table 23: Stream table in Aspen simulation
13.3- Aspen DSTWU column results
Name
DSTWU
Property method
Henry's component list ID
Electrolyte chemistry ID
Use true species approach for electrolytes
Free-water phase properties method
Water solubility method
Number of stages
Reflux ratio
Light key component recovery
Heavy key component recovery
NRTL
YES
STEAM-TA
3
16
0.95
0.01
67
0.385
0.021
Distillate vapor fraction
Minimum reflux ratio
Actual reflux ratio
Minimum number of stages
Number of actual stage
Feed stage
Number of actual stage above feed
Distillate temperature [K]
Distillate to feed fraction [K]
Total feed stream CO2e flow [kg/hr]
Total product stream CO2e flow [kg/hr]
Net stream CO2e production [kg/hr]
0
0.542346
0.757423
7.95104
16
10.9894
9.98942
337.69
377.209
0
0
0
Table 24: DSTWU results
13.4- Cost correlations used
68
$C = C. Sn
69
14- Bibliography
[1] Akhtar, T. (2011). Synthesis of Biodiesel from Triglyceride oil. 1-18.
[2] Altic, L. E. (2010). Characterization of the Esterification Reaction in High Free Fatty Acid Oils. 1-48.
[3] Amin Talebian-Kiakalaieh, N. A. (2012). A review on novel processes of biodiesel production from
waste cooking.
[4] Canakci, M. (2001). Production of biodiesel from feedstocks with high free fatty acids and its effect
on diesel engine performance and emissions. 74-123.
[5] Carlos A. Guerrero F., A. G.-R. (2012). Biodiesel Production from Waste Cooking Oil. 1-11.
[6] Ibrahim, H. G. (2015). Recycling of Waste Cooking Oils (WCO) to Biodiesel Production.
[7] J. Van Gerpen, B. S. (2004). Biodiesel Production Technology. 43-55.
[8] M. Berrios, J. S. (2007). A kinetic study of the esterification of free fatty acids (FFA) in sunflower oil.
[9] Manop Charoenchaitrakool, J. T. (2010). Statistical optimization for biodiesel production from waste
frying oil through two-step catalyzed process.
[10] Ming Chai, Q. T. (2014). Esterification pretreatment of free fatty acid in biodiesel production.
[11] Nguyen, N. T. (2012). Optimization of Biodiesel Production Plants. 1-9.
[12] R., M. A. (2015). Biodiesel production from waste cooking oil.
[13] Sani, W. (2014). Multistage methanolysis of crude palm oil for biodiesel production in a pilot plant.
11-21.
[14] Sérgio Morais, S. C. (2010). Designing Eco-Efficient Biodiesel Production Processes from Waste
Vegetable Oils.
[15] Suyin Gan, H. K. (2010). Ferric sulphate catalysed esterification of free fatty acids in waste cooking
oil.
70
[16] W.N.N. Wan Omar, N. N. (2009). A two-step biodiesel production from waste cooking oil:
Optimization of pre-treatment step.
[17] Y. Zhang, M. D. (2003). Biodiesel Production from Waste Cooking Oil. 1: Process Design and
Technological Assessment.
[18] Yi, Z. (2002). Design and economic assessment of biodiesel production from waste cooking oil.
[19] Zahoor Ullah, M. A. (2015). Biodiesel production from waste cooking oil by acidic ionic liquid as a
catalyst.
[20] Zi-Zhe Cai, Y. Y.-L.-M.-W.-W.-P. (2015). A two-step biodiesel production process from waste cooking
oil via recycling crude glycerol esterification catalyzed by alkali catalyst.
[21] Raghunath D POKHARKAR, P. F. (2008). Synthesis and Characterization of Fatty Acid Methyl Ester
.
by In-Situ Transesterification in Capparis Deciduas Seed.
[22] Holman, J. (2010). Heat transfer.
[23] Maloney, J. O. (2008). Perry's handbook of chemical engineering .
[24] Richardson’s, C. &. (2005). Chemical Engineering Design.
[25] Wankat, P. C. (2011). Separation process engineering.
[26] Hall, S. (2012). Rules of Thumb for Chemical Engineers.
71