General Chemistry
Biodiesel Synthesis
Spring 2011
Adapted from Introduction to Green Chemistry, Mary Ann Ryan and Michael
Tinnesand, Editors. The American Chemical Society, 2002.
Background information
Diesel is a common fuel used to power many large trucks and heavy
equipment. Diesel fuel is made from crude oil that was formed over millions of years
by the decomposition of prehistoric plants and animals. Crude oil is pumped out of
the ground and transferred, often by large ocean tankers, to oil distillation units.
Crude oil contains a wide variety of organic chemicals that range in size from
small molecules with only 1 carbon atom (C1) to very large molecules with more
than 20 carbon atoms (>C20). Crude oil is separated into various fractions based on
the size of the molecule by using a distillation tower: smaller, more volatile
compounds have lower boiling points, while larger, less volatile compounds have
higher boiling points. A distillation tower works much like a distillation apparatus
you might use in a laboratory setting. Crude oil is heated as it enters the distillation
tower and then gradually cooled as it rises up the tower. Since less volatile
compounds condense at higher temperatures, they are separated early on their way
up the tower.
Chemists have created a substitute for diesel by chemically changing various
fats and oils. Fats and oils can be burned without any chemical alteration. Old
whaling ships used to burn the “blubber” or fat from whales in their oil lamps. By
using transesterification (shown below), chemists can turn oils from various crops
such as canola and soy oils into alkyl esters, a viable diesel substitute.
One of the major advantages of using biodiesel instead of diesel is that
it is derived from a renewable resource. As mentioned before, diesel comes from
crude oil, which takes millions of years to form. During the next few million years,
more underground pools of crude oil will be formed; however, it is consumed at a
rate that is drastically faster than that at which it is forming. Most experts believe
that at current production, crude oil will be economically exhausted in the next 40
years.
Conversely, biodiesel is made from renewable resources, namely, oils derived
from farm crops. One major focus of green chemistry is to develop new chemical
processes and products that eliminate the need for using nonrenewable starting
materials by replacing them with renewable starting materials. Biodiesel also
creates lower sulfur emissions when it is burned, which helps reduce acid rain. It
also breaks down more quickly in the environment, thus lessening the severity of an
accidental spill compared with crude oil.
Finally, unlike fossil fuels such as gasoline, biodiesel does not cause an
overall increase in the amount of CO2, a greenhouse gas, in the atmosphere when the
fuel is burned. Soybeans and other plants that produce oils for making biodiesel take
up CO2 from the atmosphere as they grow. When oil is extracted from the mature
plants and burned, and the remainder of the plant material decomposes, CO2 is
returned to the atmosphere. Thus there is a balance between the amount of CO2
removed from the atmosphere by growing plants and returned to the atmosphere
by the same plants: no excess CO2 is produced to contribute to global climate
change.
Biodiesel is a mixture of methyl esters of fatty acids. It can be made very
easily from vegetable cooking oil. Enough fuel can be produced from this lab to burn
in a later activity, although it is not pure enough to actually be used as fuel in a car
or truck. The synthesis is a simple chemical reaction that produces biodiesel and
glycerol. Cooking oil is mixed with methanol, while potassium hydroxide is added as
a catalyst. The products separate into two layers, with the biodiesel on the top. The
biodiesel is separated and washed and is then ready for further experimentation.
Part 1: Making biodiesel
Materials
 1 250-mL Erlenmeyer flask
 2 100-mL beakers
 1 25-mL graduated cylinder
 1 100-mL graduated cylinder
 transfer pipettes
 distilled water
 100 mL canola or other vegetable oil
 30 mL methanol
o Cautionary note: Flammable, dangerous fire risk, toxic by ingestion
 5 ml 9 M potassium hydroxide (KOH) solution
o Cautionary note: Skin contact causes severe blisters, strongly corrosive,
very harmful if swallowed, extremely dangerous to eyes, generates large
amounts of heat when solution is prepared. Consider immersing solution
container in ice bath when preparing.
Safety
 You must wear goggles and a lab coat.
 Methanol is flammable and poisonous.
 Potassium hydroxide is corrosive. Dispose of excess potassium hydroxide by
neutralizing with 3 M hydrochloric acid and flushing neutral solution down
the drain with lots of water.
Procedure
1. Measure 100 mL of vegetable oil
2. Carefully add 30 mL of methanol
3. Slowly add 2 mL of 9 M KOH
4. Stir or swirl the mixture for 20 min.
5. Allow the mixture to sit and separate for 20 min.
6. Carefully remove the top layer – your biodiesel - using a transfer pipette;
measure the volume of biodiesel
7. Mix the product and 20 mL of distilled water in a separation funnel
8. Allow the mixture to sit and separate
9. Carefully drain-off the bottom layer, and save the top layer – this is your
biodiesel!
10. Measure the volume of biodiesel you have collected and compare it to the
volume of vegetable oil you started with.
Questions
1. What changes did you see between the characteristics of the starting
materials (cooking oil, methanol, and potassium hydroxide solution) and the
final products (biodiesel and glycerol)?
2. What signs did you observe that a chemical reaction had taken place?
3. What is the purpose of the washing in step 7 above?
4. Using the equation for the reaction given above (is it balanced?), calculate the
limiting reactant and the theoretical yield of the biodiesel (the version of
alkyl esters you made here are methyl esters). Use 885.4 g/mol as the
approximate molar mass of the vegetable oil.
5. Using your actual yield, calculate the percent yield of your reaction.
6. In the commercial production of biodiesel, 1200 kg of vegetable oil produces
10920 kg of crude biodiesel. What is the yield of this reaction and how does
your yield compare?