Creative Inquiry in Green
Energy and Biofuels
Research – Spring, 2011
Faculty Mentors: Biological Systems Engineering Professor Terry Walker, Research Associate David Thornton.
Participating Students Shwetha Sivakaminathan, Karris Roland, Kaitlyn Murray, Jovan Popovic, Lindsay Burton,
Allison Rue, Dexter Pearson, Cynthia Westmoreland, Kirby Tate, Kiah Baker, Holly Garrett.
Clemson Sustainable Biofuels Initiative
What We Do
The Clemson Biofuels Creative Inquiry is an on- Clemson House, Harcombe and Schilletter
campus graduate and undergraduate student
Dining Halls and produce biodiesel on the C.U.
assisted biodiesel production project that
Mobile Sustainable Biofuels Pilot Plant. Current
converts campus waste vegetable oil (and other focus is on bioprocessing and quality control
oil sources) into biodiesel fuel for the University analytics. Future endeavors include engineering
fleet. Biological Systems Engineering Professor for optimization of methanol recovery,
Dr. Terry Walker and Research Associate David optimization of energy balance, sequestration of
Thornton lead a Creative Inquiry group
CO2 emissions and extraction of value added coeach week to maintain and run the pilot plant in products.
McAdams Hall. Additional support also comes
from Director of Utilities, Tony Putnam and
Robert Clark of Environmental Health and Safety.
Each year, Clemson University's campus
produces 5,000 gallons of waste vegetable oil.
The conversion ratio is roughly one to one,
meaning that one gallon of waste oil will convert
into one gallon of biodiesel. Using our onecylinder diesel truck, “the Grease Goblin”, we
collect used vegetable oil from Fernow Street
Cafe, Madren Center, Hendrix Student Center,
Our Process
of methyl ester to one mole of triglyceride reacted.
Transesterification
A transesterification reaction is when one ester is
Crude Biodiesel Glycerin (CBG) is about 75% pure.
converted to another ester. Fats and oils are
Refining CBG involves removing residual organic
composed of triglycerides, a type of ester. A
triglyceride is a glycerin molecule bonded to three fatty nonglycerin matter, water, salt and odors. If CBG is
refined, the glycerol may then be used for a variety of
acids composed of long hydrocarbon chains.
uses, including products such as soap (a powerful
degreaser), cosmetics, pharmaceuticals, solvents,
The chemistry of transesterification for biodiesel
production is, for the most part, simple. It breaks down adhesives, and bioplastics.
the triglycerides found in vegetable oils and animal fats
and forms new esters with similar characteristics to
conventional diesel fuel.
A transesterification reaction begins with the
protonation of the carbonyl oxygen. The protonated
carbonyl group reacts better than a nonprotonated
carbonyl group in nucleophilic substitution reactions.
The alcohol then adds to the carbonyl carbon which
forms a tetrahedral intermediate. Next the oxygen
attached to the rest of the triglyceride molecule is
protonated and another tetrahedral intermediate is
formed. Finally, each of the tetrahedral intermediates
collapses, one of which forms the methyl ester and
another forms diglyceride. This reaction mechanism
repeats for each of the glycerides on the triglyceride
until the final products are formed: glycerol and methyl
ester. Since there are three glycerides in a triglyceride
molecule this reaction produces a yield of three moles
First, the collected oil is tested to determine the percentage of free fatty acids (FFA's) in
the oil. The older and more heavily used the oil, the more FFA's which need to be
neutralized. A titration is performed by determining how much base it takes to neutralize
the FFA's in the oil. We also test the moisture content of the oil, since any water in the
reaction will turn to soap.
After we have performed the initial tests, we use an Excel spreadsheet to calculate how
much catalyst (potassium hydroxide) and methanol we will add to have the reaction go to
completion. The oil is loaded into the reactor vessel and the potassium hydroxide and
methanol are added into the methoxide mixing tank and mixed until dissolved. The oil is
heated up to 130 degrees F, and the catalyst is introduced slowly into the oil (also using
cavitation to aid in mixing and reaction) and mixed for 2 hours. The final product is two
distinct layers, which are biodiesel (on top) and glycerol (on bottom).
Once the oil is converted to biodiesel, we take a small sample and check for
conversion. By using a simple solubility test, we determine if the reaction went to
completion. We also determine the soap number by using another titration as well as the
moisture content. From here, the glycerol is decanted and the remaining fuel is
processed further.
We recover residual methanol from the reaction by passing the biodiesel and glycerin
phases separately through a heat exchanger and condensing the hot methanol
vapor. This also helps to remove any soap or excess water. The next "wash" step
involves spraying a fine mist of the fuel while sparging the fuel, two mechanical methods
to help evaporate any residual methanol or water. Before passing the fuel through our
final step, the ion exchange column, we check it one more time for soap number and
moisture content to make sure they are not too high, which would harm the ion exchange
resins or fowl the fuel.
The final fuel is collected in a 55 gallon drum and transported to a larger storage tank on
campus maintained by Tony Putnam's crew of Facilities and Maintenance. This fuel is then
blended to B20 (20% biodiesel, 80% petroleum) and used in all campus diesel vehicles
including trucks, tractors, back-hoes, garbage trucks...and maybe someday buses!
A generator running on 100% biodiesel
supplies the electrical needs of our pilot
plant. Our design also takes advantage of
co-generation utilizing the heat which
typically leaves the generator via the
coolant or exhaust to heat and maintain the
process temperatures. We have also
connected our lab equipment inside the
building to solar panels on the roof, so our
electrical needs inside are approaching
carbon neutral and helping us on our goal of
being carbon neutral and energy
independent.
Quality Control Analytics
Analytical procedures are carried out to monitor the presence of partially reacted or unreacted starting materials (mono, di or tri-glycerides,
methanol and catalyst-KOH), as well as the glycerol and fatty acid alcohol esters that are formed during the reaction. At our pilot plant at
Clemson University, we do five important tests to verify the quality of our biodiesel. These include tests for acid number, soap number, moisture
content, glycerol content and flash point.
free –OH groups, they are not affected. Only the mono, di and
triglycerides and FFA’s are silylated. This aids GC analysis in adequate
separation and quantification of the compounds. ASTM d6751 only
permits .24% wt % total glycerides, of which at most .02% may be free
glycerin.
Acid Number
The acid number titration determines the percentage of FFA in the oil
feedstock and to ensure the quality of the finished product. The acid
number is estimated by titrating a known amount of the sample with
0.1N KOH and phenolphthalein indicator. By observing the volume of
KOH required to reach the end point, we can establish the FFA% in the Flash Point Test
sample of biodiesel and create our recipe for our batch. After the
The flash point of a volatile liquid is the lowest temperature at which it
reaction, per ASTM d6751 standards, finished fuel must be below 0.5 can vaporize to form an ignitable mixture in air. For this test a closed
mg KOH/ g biodiesel.
cup flash point device is used. The biodiesel sample is loaded into the
oil cup which is heated by a water bath. The cups are sealed with a lid
Soap Number
through which the ignition source can be introduced. The flash point for
The soap number titration determines the amount of sodium or
B-100 biodiesel as per ASTM standards must be above 93oC. This
potassium salts of fatty acids in the sample. By titrating a known
indicates complete removal of residual methanol.
amount of sample with 0.01N HCl and bromophenol blue as indicator,
we arrive at the endpoint. This gives us an estimate of the amount of
soap in the biodiesel. Soap number is not directly tested per ASTM
d6751, but soap concentrations will impact tests for potassium and
sodium metals, therefore soaps in finished fuel should not exceed 50
ppm.
Moisture Content
The Sandy Brae Water Testing Kit is our standard protocol to test the
moisture content in oil, biodiesel, methanol or glycerol samples. The
equipment has two chambers inside and a pressure gauge on top.
One chamber contains the oil and the reagent while the other holds
calcium hydride. Upon shaking, CaH2 reacts vigorously with water
liberating hydrogen gas, thereby increasing the pressure, indicated by
the gauge. The pressure (psi) is correlated to the amount of moisture
in the biodiesel. According to ASTM, finished fuel must stay below a
moisture content of 500 ppm.
GC Analysis
Analysis for FAME (fatty acid methyl esters) and FFA’s utilize gas
chromatography. For compounds of high molecular weight or low
volatility such as bonded glycerol components, GC analysis can be
used by performing silylation. This reaction adds a trimethylsilyl group
to all the –OH groups present in the fuel sample which increases the
volatility of those compounds. Since FAME and triglycerides contain no