On the Subject of Biodiesel as a Practical Energy Resource
Anna Greve, Civil Engineering, University of Cincinnati
Kathe Pocker, Biomedical Engineering, University of Cincinnati
Abstract
Currently, there is a high demand for energy in the world. Unfortunately, many of the energy
sources that are presently relied upon, such as petroleum diesel, come from nonrenewable resources. In
addition, many of these nonrenewable resources are also harmful to the Earth’s environment due to
emission of air pollutants, greenhouse gases, and production of solid waste. The purpose of this project
was to examine various ways of producing biodiesel. Biodiesel fuel is made from vegetable oil, recycled
restaurant greases, or animal fats, and it solves several of the problems stated above. Biodiesel is a
renewable resource, it releases fewer air pollutants, it releases fewer greenhouse gases, and it can be
used in most diesel engines. Some barriers to biodiesel production include the cost associated with raw
materials and making use of glycerol, a major byproduct of the reaction. This project utilized two main
methods for biodiesel production: extraction of biodiesel from waste cooking oil (WCO) and extraction of
biodiesel from waste coffee grounds (WCG). Data collected indicates that longer reaction times during
WCO extractions results in a higher percentage of biodiesel produced, as well as shorter times required
for biodiesel and glycerol separation. Waste coffee ground extractions were performed for WCG mixtures
containing 5% NaOH, 5% KOH, and 10% KOH. In the future, more time trials should be completed for
WCO extractions and purity should be assessed for both WCO and WCG extractions. Determining
whether reaction time can be reduced could result in shorter extraction times, which could in turn reduce
production costs. Biodiesel is a promising energy resource, and its potential should continue to be
explored.
Introduction
As petroleum diesel becomes more expensive, more difficult to produce, and continues to harm
the environment, interest in alternative energy sources is increasing. Biodiesel in particular has gained
attention over the years. Biodiesel is an alternative diesel fuel that can be produced from vegetable oils,
recycled restaurant greases, or animal fats by reacting with alcohol and in some circumstances a
catalyst. Transesterification is the most common method used to produce biodiesel from vegetable oils.
The triglycerides from the vegetable oils and alcohol, often times methanol, are converted into esters (the
biodiesel) and glycerol, and a catalyst (commonly sodium or potassium hydroxide) is often used to speed
up the reaction.6 The chemical reaction for the production of biodiesel by transesterification is as follows:
Figure 1: General transesterification equation9
Petroleum diesel has been a reliable source of energy over the years, but many problems with its
use have arose. These problems include the fact that these sources are not sustainable, dependency on
foreign countries for oil, high costs, and the inevitable negative environmental impact. In contrast,
biodiesel serves as a renewable resource with a very low environmental impact. 7 The physical properties
of biodiesel are similar to those of petroleum diesel, but biodiesel is a cleaner-burning alternative and
significantly reduces emissions of toxic air pollutants and greenhouse gases. While biodiesel can be used
in its pure form (B100, meaning 100% biodiesel), it is commonly blended with petroleum diesel. One of
the current disadvantages is that use of blends higher than B5 (5% biodiesel, 95% petroleum diesel) is
not currently approved by most automakers. There are also concerns circulating that B100 may be
harmful to car engines, especially at lower temperatures.3 Another issue with current biodiesel production
is the cost of the raw materials, as anywhere from 70-95% of total biodiesel production costs come from
raw material expenses.2
The goal of this project is to examine biodiesel as a practical energy resource, as well as to work
on refining the process of biodiesel production from waste feedstock in order to reduce cost and time and
make biodiesel a more practical energy source. Being able to diminish biodiesel production costs and the
time associated with biodiesel production would help to further reduce dependency on fossil fuels and
make biodiesel a more viable alternative to petroleum diesel. More specifically, this project has two main
objectives: to determine how variation in reaction times affects the biodiesel yield, and to further examine
the effects of using various waste coffee ground mixtures (5% NaOH, 5% KOH, and 10% KOH) to
produce biodiesel.
Materials and Methods
During this project, biodiesel was produced from waste cooking oil (WCO) and waste coffee
grounds (WCG). Both extractions required different techniques, and aspects of each extraction were
varied as part of this research project.
The WCO utilized in this project was obtained from the Cincinnati Zoo and Botanical Gardens
and from the dining hall facilities located on the University of Cincinnati campus.To extract biodiesel using
WCO, the first step was to perform a small titration using 1 mL WCO, 10 mL ethanol, and 2 drops of an
indicator. 0.01% NaOH solution was added in 0.5 mL or 1.0 mL increments until the solution turned pink.
At that point, the amount of NaOH that was needed to be added to a larger amount of WCO in order to
neutralize all the acid could be calculated. After this calculation was done, the correct amount of NaOH
could be obtained (0.35 g catalyst plus the amount needed to neutralize the acid) and was dissolved in 20
mL of methanol. This solution was then set on a heat/stir plate to dissolve. Once all of the NaOH was
dissolved, the solution was added to 50 or 100 mL of WCO. After adding a stir bar and covering the
beaker with parafilm, the solution was set on a heat/stir plate at 60 o C - 65o C to heat and neutralize for a
period of time ranging from twenty minutes to one hour. Once the solution was heated, it was poured into
a container and allowed to separate. The biodiesel is a light gold color that settles on the top, while the
glycerol is a dark brown color that settles on the bottom (see Figure 2). When a clear distinction between
the two layers was visible, the glycerol was removed and the biodiesel was washed with water
approximately three times. Washing was done to ensure that any leftover NaOH or other chemicals were
removed, and water was poured slowly to ensure no emulsion was formed. The biodiesel was removed
from the opposite end of the container than the water and glycerin were. This was done to ensure that
any remaining water does not contaminate the biodiesel. The biodiesel was then weighed so that a
percent recovery could be obtained.
Figure 2: Biodiesel and glycerol before separation (left) and after separation (right)
The WCG used in this project were obtained from the Starbucks facilities on the University of
Cincinnati campus. Conversion of biodiesel from WCG first required 5 g of the WCG to be weighed out.
Various types of pre-prepared WCG were used (samples contained either 5% KOH,10% KOH, or 5%
NaOH). Next, 200 mL of methanol was added, a stir bar was put in the beaker, the beaker was covered
with parafilm, and the mixture was stirred and heated at 60o C - 65o C. The reaction was allowed to occur
for two and a half hours, with 1.5 mL samples being taken every half an hour so that the yield of the
biodiesel extracted at each time could be determined through later analysis. After two and a half hours,
the solution was taken off of the heat source and left in the refrigerator to cool, and the next day the
methanol was removed via evaporation in a rotary evaporator (see Figure 3). This device heats the
methanol/biodiesel solution, and allows the methanol to be evaporated and used again during future
experiments. The biodiesel remained behind in the flask, which was then rinsed with a small amount of
methanol to remove any biodiesel that adhered to the wall of the flask. This solution was poured into a
graduated cylinder, and any remaining methanol was evaporated either by heat, by airstream, or by a
combination of both.
Figure 3: Rotary evaporator for biodiesel produced from WCG
Results and Discussion
The percent yields of the biodiesel production from the WCO are shown in Figure 4. To determine
these yields, the amount of biodiesel produced was divided by the starting amount of WCO for each
variation of reaction time. Each reaction time was tested with two separate samples, and Figure 4
displays the average percent recoveries for each reaction time. The average percentage of biodiesel
produced was 88.47%. The results are as follows:
Figure 4: Reaction Time vs. Percent Recovery Biodiesel
The results of this experiment indicate that variation in reaction times can alter the amount and
purity of biodiesel produced. Although the data shows that a very short reaction time (twenty minutes)
appears to have the highest extraction rate, the biodiesel produced from this reaction time was likely
much less pure than the others. This is due to the fact that there was likely unreacted WCO remaining in
the biodiesel because of the short reaction time allocated. Unfortunately, the purity of each time sample
was unable to be tested in the course of this project. Looking at the overall trend, though, this data
indicates that the longer the reaction time, the greater the yield of biodiesel produced from the WCO.
After the methanol, NaOH, and WCO had been combined, it was necessary to let the solution sit
until the glycerol had settled to the bottom. The settling time varied based on how long the reaction was
allowed to proceed, and these results are seen in Figure 5 below.
Figure 5: Reaction Time vs. Time Required to Settle
This data indicates a downward trend, meaning that the longer the reaction is allowed to proceed,
the less time is necessary to let the glycerol settle to the bottom of the container. This information does
not affect the purity or amount of the biodiesel produced, but it does impact the overall amount of time
required for biodiesel production. It also shows that even though the shorter reaction times may obviously
be less time consuming, it takes longer for those samples to settle and in the end the amount of time
required for each sample is relatively similar.
One of the benefits of extracting biodiesel (not only from waste cooking oil but from all biodiesel
production processes) is that the main byproduct, glycerol (also known as biodiesel glycerin or glycerine),
can be removed and utilized. Glycerol is a thick, colorless, and odorless liquid that can be used for
medical, weapon, and cosmetic industrial productions. Before it can be used, though, glycerol must be
filtered and transformed into 100% pure glycerin. This process safely purifies the crude biodiesel glycerol
and turns the otherwise hazardous waste into an environmental-friendly alternative. The glycerol is
filtered by fractional vacuum distillation or chemical reactions, depending on what degree of purity is
desired.
The percentage of glycerol produced during these experiments stayed more consistent than the
percentage of biodiesel produced, as can be seen by comparing the two graphs. The average amount of
glycerol recovered was 17.01%.The following graph (Figure 6) shows the percent recovery of glycerol
from these experiments:
Figure 6: Reaction Time vs. Glycerol Yield
While better purification processes are needed for glycerol to be fully utilized, it has great
potential and is a useful byproduct to biodiesel production. Glycerin can then be used in drug fabrication,
as a moisturizing agent in soaps and other body products, in food processing, as a fertilizing agent, and in
weapon production.5 A number of companies including Cargill, Dow Chemical, Solvay, and Archer
Daniels Midland have also announced planned construction of new chemical facilities using glycerin as
feedstock.4 Being able to sell a byproduct makes the biodiesel production process more economically
viable. The price of glycerin has varied over the years. The variation can be seen in the following table:
Figure 7: Refined Glycerol (USP) Prices (1980-2007), Source: www.purchasing.com
The current market price for methanol is $0.30 per liter. The price for sodium hydroxide can range
anywhere from approximately $0.20 - 0.55 per kilogram. As shown above, the price that glycerin can be
sold for varies, but it can range anywhere from approximately $0.30 to $1.10 per pound. Knowing these
prices is crucial for the economic analysis of the viability of biodiesel as an energy resource. As an
example, in order to produce biodiesel from 100 mL of WCO, approximately the following would be
required:
●
20 mL methanol
●
0.50 g NaOH
This would produce approximately:
●
20 mL of glycerin
●
80 mL biodiesel
With the following prices:
●
$4.327/gal methanol
●
$0.008234/g NaOH
●
$0.30 per pound glycerol
●
$0.0013 per mL oil
The raw material cost would be $0.022860 (methanol) and $0.004117 (NaOH) for a total cost of
$0.026977. The glycerol (with the price assumed) would sell for $0.0166647. This leaves a deficit of
$0.0103123. Thus, just to break even regarding the cost of raw materials, the biodiesel would have to sell
for $0.000129 per mL, or $0.488 per gallon. However, this cost does not include the cost of labor,
facilities, storage, water washing, etc. In 2008, biodiesel was selling for well over $4 a gallon, while
petroleum diesel only cost $3.30 per gallon.8 It is evident that cost of biodiesel production, whether in raw
material prices or production costs, needs to decrease before biodiesel can become a commonly used
resource.
Conclusion
Currently, the world relies on a few major sources, mostly fossil fuels, for energy. These sources
are running out, though, and they are becoming more expensive and harmful to the environment.
Biodiesel is similar in terms of physical properties to petroleum diesel, but it is a much cleaner-burning
alternative, it is a sustainable resource, it allows independence from foreign countries to produce fuel, and
it makes good use of waste products such as restaurant greases that can be difficult to dispose of
properly. The research presented here validates successful production of biodiesel from waste cooking oil
and waste coffee grounds. Increasing reaction time during WCO extraction overall appeared to result in a
higher percentage of biodiesel yield, along with shorter separation times. The amount of glycerol
produced remained fairly constant across reaction times. Waste coffee ground extractions were also
performed successfully, and in the future, purity of these samples will be assessed. One of the current
obstacles to biodiesel production is the cost, particularly that associated with the raw materials. In order
for biodiesel use to become widespread, production and material costs must decrease. These results
need to be explored further to see if reaction time can in fact be reduced with WCO extraction so that
production costs could decrease on a large scale. Biodiesel should continue to be researched and used
as an alternative energy source.
Acknowledgments
The authors would like to thank the following people for their invaluable support in this project:
●
Dr. Mingming Lu, faculty advisor.
●
Yang Liu, graduate assistant.
●
Qingshi Tu, graduate assistant.
Funding for this research was provided by the NSF CEAS AY REU Program, Part of NSF Type 1
STEP Grant, Grant ID No.: DUE-0756921. The support of this grant is gratefully acknowledged.
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