Biodiesel Lab
Introduction
The production of biodiesel fuel from used vegetable oil has received a lot of attention in the last few years and
“biodiesel” has even been used in recent presidential speeches relating to Department of Agriculture appointees.
Joshua Tickell helped initiate the excitement in 1996 by driving across the nation in his veggie van and making
his biodiesel from used cooking oil found at fast-food restaurants along the way [1]. This is a laboratory that we
use to conclude the first semester of general chemistry after covering organic structures and intermolecular
forces. It reinforces concepts, helps students with nomenclature, and it excites the students to study their
chemistry more, even organic chemistry! They leave the course feeling like they have learned something very
practical, and they can visualize the central role that chemistry will play in the near future as the world
undergoes a paradigm shift to renewable energy sources.
Background
The diesel engine was first developed by Rudolf Diesel in 1895 as an efficient and strong engine that can
operate using fuels comprised of 12-to-18-carbon hydrocarbon chains that ignite upon compression (no spark
needed). The original vision of Rudolf Diesel was that the diesel engine would offer an alternative to gasoline
engines that require refined gasoline comprised of 7-to-11-carbon hydrocarbon chains and need a spark for
ignition. The first diesel engines were designed to run on vegetable oil [2]; however, the high viscosity of
vegetable oil and the cheap production of petroleum diesel as a byproduct of gasoline refining resulted in diesel
engines that were modified to run on petroleum diesel fuel [2]. Perhaps the time has come to revisit Rudolf
Diesel’s dream!
The use of petroleum diesel fuel is known to contribute to air pollution, especially from particulates and
carcinogenic polyaromatic hydrocarbon (PAH) compounds [3–5]. It is also a product that is obtained by the
fractional distillation of petroleum, which is a nonrenewable fossil-fuel resource and the subsequent combustion
of petroleum diesel contributes to a net increase in carbon dioxide in the atmosphere. A viable substitute for at
least some of the demand for diesel fuel is biodiesel. Biodiesel is the methyl (or ethyl) ester of the fatty acids
found in vegetable oils and animal fats. A first step in replacing petroleum diesel with biodiesel is to use
discarded, waste vegetable oil from restaurants as starting material for biodiesel. It is difficult to estimate how
much used cooking oil is available in the United States, but estimates are in the range of one-to-three billion
gallons annually [6]; however, most biodiesel production plants are small-scale and serve personal vehicles or a
small fleet of company diesel vehicles due to collection difficulties from decentralized sources of used cooking
oil [7–9]. Many colleges have developed small-scale biodiesel facilities and students have been leading the
movement to collect and convert the used cooking oil from campus cafeterias [10]. For example, at The
Colorado College our student cafeteria discards about thirty gallons of used vegetable oil each week from deepfat-fryer operations. In this laboratory, however, we will synthesize biodiesel from virgin vegetable oil to
illustrate the chemical process and laboratory techniques involved while avoiding the complications associated
with used cooking oil. The additional considerations required for a laboratory that starts with used cooking oil
are addressed in the summary of this manuscript. There are many available references that provide detail about
going from small-scale production utilizing virgin vegetable oil to large-scale production using waste cooking
oil [11, 12].
There are four important considerations that warrant attention when discussing biodiesel. First, using waste
cooking oil as stock material converts an industrial waste into a usable commodity and avoids the criticism that
biodiesel production will deplete valuable food stocks to produce transportation fuel. Second, the energy output
of biodiesel combustion is less than petroleum diesel output because of oxygenation and unsaturation present in
the fatty acid esters of biodiesel [13]. Third, biodiesel combustion does not contribute to a net increase in
atmospheric carbon dioxide, a greenhouse gas, because we are operating within the present-time carbon cycle.
Fourth, the combustion of biodiesel in diesel engines generally results in a tradeoff between higher NO x
emissions on the negative side and lower carcinogenic particulate (PAH) emissions on the positive side when
compared to petroleum diesel [14]. Nevertheless, when all factors are considered, biodiesel is agreat option for
at least some of our diesel fuel needs, and knowledge pertaining to the production process is very valuable and
empowering.
Experimental
Supplies. The following equipment, supplies, and reagents are needed: hot/stir plate, stir bars, 25-mL graduated
cylinder, 100-mL graduated cylinder, 100-mL Erlenmeyer flask, 125-mL separatory funnel, Buchner funnel,
filter flask (side-arm Erlenmeyer flask), qualitative filter paper, methanol (reagent grade), sodium hydroxide,
and vegetable oil.
Hazards. Students should be directed to the material safety data sheets (MSDS) for methanol and sodium
hydroxide. It is necessary to have enough hood space for the students to carry out the reaction and to drive off
the excess methanol from the glycerol. For best results the methanol and vegetable oil should be as free from
water contamination as possible, and all glassware should be dry before used in the experiment.
Procedure.
Step A. Measure 14.0 mL of methanol (CH3OH) into a 100-mL Erlenmeyer flask (before handling methanol
read the material safety data sheet (MSDS).
Step B. Weigh out 0.50 g of sodium hydroxide (NaOH, before handling NaOH read the material safety data
sheet, MSDS). Crush the NaOH pellets into a powder using a mortar and pestle and then transfer this powder
into the Erlenmeyer flask containing the methanol. The NaOH can be dissolved with continuous stirring on a
magnetic stir plate for about 5 to 10 min. At this point you have added the strong-base catalyst (NaOH) to the
methanol (CH3OH) to initiate the formation of sodium methoxide according to the following reaction:
NaOH + 3CH3OH → NaOCH3 + H2O
(Good results can be achieved using sodium methoxide in place of sodium hydroxide, but sodium methoxide is
more expensive and rarely used in actual biodiesel production.)
Step C. Use a graduated cylinder to measure 60.0 mL of vegetable oil and add this to the methanol solution in
the Erlenmeyer flask. Using a hot plate, gently heat the solution to a temperature between 35 °C and 50 °C for
20 to 30 min with continuous stirring so that the mixture does not separate into two layers. At this point you
have initiated the transesterification reaction where the methoxide generated in step B attacks the triglyceride
(oil) and cleaves off a fatty acid chain. The reactants for this step are
This process is repeated three times for every triglyceride because a triglyceride has three fatty acid chains per
molecule. This is a generalized triglyceride structure where there are three fatty acids bonded to a glycerol
structure. The actual fatty acid entities are dependent upon the source of the triglyceride (oil) and do not have to
be the same within a given molecule. For instance, the four primary fatty acid constituents of olive oil are oleic
acid (80%), linoleic acid (7%), stearic acid (5%) and palmitic acid (5%).
Step D. Pour the warm reaction mixture into a 125-mL separatory funnel and allow the solution to cool and
partition into two product layers. The products from the completed reaction are
Step E. Draw off the bottom layer, which contains glycerol, residual methanol, trace water, and salts, into a
small, weighed (tared) beaker. (If the reaction was heated above 50 °C and the separation step is allowed to sit
for a long period of time, the bottom layer may become a solid plug.) Heat this glycerol mixture to 70 °C on a
hot plate in the fume hood to remove the residual methanol. After 10 min at 70 °C, remove the beaker and cool
the glycerol to room temperature. Note the viscosity of this product and compare your collected glycerol with a
sample of pure glycerol. Suggest a reason for any observed differences. Reweigh the beaker with the glycerol
–1
and calculate the volume of glycerol collected given that the density of glycerol is 1.26 g mL . In any biodiesel
production process there is always the possibility that this glycerol side product can be used in cosmetics where
it serves as a moisturizer and a facial soap. Production processes can also capture the residual methanol that was
removed in this step and reuse it in future reactions.
Step F: The top layer in the separation funnel is the biodiesel product. Vacuum filter this biodiesel layer into a
clean, dry side-arm Erlenmeyer flask using a Büchner funnel and qualitative filter paper (Whatman #1 or
equivalent). Gravity filtration can be used but will take more time because of the high viscosity of the product.
Note and compare the product viscosity with that of the starting oil and glycerol. Measure the volume of
biodiesel collected and calculate the percent (by volume) of biodiesel conversion based on the starting volume
of oil and the volume of biodiesel obtained. Compare your calculated percent biodiesel conversion to the
generally expected conversion of 70% (by volume) and propose reasons for any major deviations.
Step G. Pour the glycerol and biodiesel into the proper collection bottles.
Step H. The glassware used in this laboratory is best cleaned using a concentrated, warm solution of water and
Alconox cleaning detergent (available from Alconox, Inc.).