Synthesis of Biodiesel Fuel
Synthesis of Biodiesel Fuel
from Vegetable Oil
References:

Pavia - p. 207 – 216
- p. 194 – 202 (Essay – Petroleum and
Fossil Fuels

Schornick
http://classweb.gmu.edu/jschorni/chem318
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Synthesis of Biodiesel Fuel

Background

Fossil fuels

Slow decay of marine animal and plant organisms
over periods of millions of years

Significant source of pollution

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Significant contributor to green house gases,
principally CO2

High potential for environmental disasters such as
oil spills, drilling rig failures, chemical plant
explosions & fire, etc.

Finite – We are depleting this non recoverable
supply
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Synthesis of Biodiesel Fuel

Background
 Biofuels: Fuels produced from biological materials
 Ethanol (Gasohol)
 Starch (polymer of Glucose)
 Corn (Enzymes catalyze corn starch into glucose
 Expensive to produce
 Energy inefficient
 Produces more green house gases
 Sucrose (Fermentation of Sugar Cane & Beets)
 Cellulose
 Switchgrass
 Agricultural waste, including corn stalks
 Waste wood from milling
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Synthesis of Biodiesel Fuel

Background

Biofuels

Ethanol

Syngas (CO & Hydrogen converted to Alcohol)

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Utilizes wide array of Carbon-containing matter

Municipal Waste

Old Tires

Agricultural Waste

More Energy Efficient Than Ethanol

Produces less greenhouse gases
4
Synthesis of Biodiesel Fuel

Background
 Biofuels
 Biodiesel (from fats & oils, including vegetable oil)
 Farm products
 Large investment in farmland not dedicated to
food production
 Net energy produced is greater than from
Ethanol but less than for cellulose
 Produces more greenhouse gases than fossil
fuels
 Destruction of forested areas to establish
farmland (loss of forest’s capacity to absorb
CO2)
 New higher efficiency method emerging utilizing
a Sulfated Zirconia catalyst
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Synthesis of Biodiesel Fuel

Background

Biofuels

Biodiesel (from fats & oils, including vegetable oil)

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Algae

Can produce oils for making biodiesel

Grown in ponds or sewage waste water

Several approaches, catalysts, self-contained
manufacturing facilities, etc. are being
investigated in search of economically viable
processes
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Synthesis of Biodiesel Fuel

The Experiment

In the Banana Oil experiment, an organic acid is
combined with an alcohol in a catalyzed Fischer
Esterification (condensation) reaction to produce a mono
ester

In this experiment the reverse of the process (hydrolysis
by H2O, Acid or OH- to the alcohol and acid) is modified
in a transesterification reaction, in which an original
trimester is converted to three (3) mono esters by
reaction with an alkoxide base
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Synthesis of Biodiesel Fuel

Analysis of Biodiesel product

The trimester is cleaved sequentially by the alkoxide
base (a mixture of Potassium Hydroxide and Methyl
Alcohol), liberating the mono-esters and glycerol

The Mono esters are produced sequentially because
the Alcohol/Alkoxide base has only one Hydroxyl
group

The mono esters are Fatty Acid Methyl Esters (FAME)

The Vegetable oil and biodiesel product molecules
have variable composition

Three Methyl esters of fatty acids are formed each
with a different “R” group consisting of 12-18 carbons
arranged in straight chains
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Synthesis of Biodiesel Fuel

Analysis of Biodiesel product

Thus, the computation of moles directly from the
peanut oil mass is not practical

Show the stoichiometric and mechanism reactions

The Methyl Alcohol is in excess, but the theoretical
yield cannot be determined; omit summary table

Calculate a “percent yield” from the initial mass of the
Vegetable oil and the mass of the diesel fuel product

Compare the original IR of the vegetable oil (see
p. 102 in Slayden Manual) to the biodiesel IR
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Synthesis of Biodiesel Fuel

Reaction
Alkoxide
Fatty Acid Methyl Esters (FAME)
An Alkoxide is the Conjugate Base of an Alcohol
It consists of an organic group bonded to a negatively
charged Oxygen atom
Alkoxides are strong Bases and, when R is not bulky,
good nucleophiles and good ligands
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Synthesis of Biodiesel Fuel

Reaction – Mechanism
Trimester of Glycerol (1,2,3-propanetriol)
and a long chain fatty acid
The negative charge of the Alkoxide (Methoxide)
ion attacks the positive charge of the carbonyl
carbon atom (from the resonance dipole form of
the carbonyl group)
Alkoxide ion
Fatty Acid Methyl Ester (FAME)
Tetrahedral (sp3)
Intermediate
1st Stage
Repeat for stages 2 & 3
The same mechanism is repeated two more times on the 2
other ester groups of the trimester until the final product is
3 Fatty Acid Methyl esters (FAME) and one glycerol.
The three reactions occur sequentially.
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Synthesis of Biodiesel Fuel

Procedure

Reagents

10 mL Vegetable Oil (Crisco) – A Trimester

2.0 mL Potassium Hydroxide/Methyl Alcohol solution
(forms Methoxide ion, an Alkoxide ion)

Prepare a water bath in a 150 mL beaker on a hot plate

Heat the water bath to a temperature of 55oC

Tare weight an empty 100 mL beaker or small cork ring
sitting on the balance to the nearest 0.001 g

Place an empty 25 mL round-bottom flask onto the
beaker top or on the cork ring

Determine the mass of the empty flask by difference
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Synthesis of Biodiesel Fuel

Procedure (con’t)
 Place 10 mL of vegetable oil into the pre-weighed
distillation flask
 Determine the mass of the flask and vegetable oil
 Determine the mass of the vegetable oil by difference
 Add ~2.0 mL of the fresh KOH/CH3OH solution to the
distillation flask
 Swirl the mixture to ensure a uniform solution
 Insert a small magnetic stir bar into the flask
 Attach and secure (with a blue plastic clamp) the flask
to a water-jacket condenser clamped vertically to a
ring stand
Note: No need to run water through the condenser
 Lower the distillation flask into the water bath
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Synthesis of Biodiesel Fuel
Condenser
No Water Flow
Blue Plastic
Clamp
Mixture of vegetable oil,
Methyl Alcohol, and
Potassium Hydroxide
Water Bath
55oC
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Synthesis of Biodiesel Fuel

Procedure (con’t)
 Turn on the magnetic stirrer (Left knob on hot plate)
to the highest level possible that allows the bar to
spin smoothly
 Stir for 30 minutes
 Transfer all of the liquid in the flask to a 15-mL
centrifuge tube with a cap
 Let the mixture sit for about 20 minutes
 Two layers should form
 The top layer is the biodiesel product
 The lower layer is mainly glycerol
 Using a plastic pipet, carefully remove the top layer
and transfer product to a pre-weighed 50-mL beaker
(leave a little product behind with the bottom layer to
avoid contamination)
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Synthesis of Biodiesel Fuel

Procedure (con’t)


Place the beaker on the hot plate and insert a
thermometer into the biodiesel, holding the
thermometer in place with a clamp
Heat the biodiesel to about 70oC for 15-20 minutes to
remove all the Methyl Alcohol

Remove the beaker from the hot plate and allow it to
cool to room temperature

Weigh the beaker and obtain the mass of biodiesel
produced

Record the appearance of the biodiesel

Obtain an IR spectrum

CAS No. for diesel fuel – 68476-34-6
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