Making Soap & Biodiesel - A Guide for Making your own Soap www.scribd.com/doc/239851214

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Experiment 11: Saponification and
Transesterification: Making Soap and Biodiesel
Animal and vegetable fats are composed of triglycerides, esters of glycerol (1,2,3
trihydroxypropane) and “fatty acids” carboxylic acids with long, hydrophobic alkyl chains. In
this experiment we will be reacting fatty acids in two ways. The first, called “saponification” is
hydrolysis of the esters with hydroxide to form salts of the fatty acids or “soaps”. The second is
a transesterification reaction, conversion from the glycerol ester to another ester, in this case
you’ll be making the methyl ester. Esters of fatty acids are used as “biodiesel” an alternative
fuel.
O
O
O
O
O
O
n
n
n
NaOR
R=H or CH3
OH
OH
OH
RO
O
n
Note, when R = H there is
a deprotonation step that results
in the sodium salt of the fatty acid.
Background: Soap
Soap works by helping greasy dirt particles
dissolve in water. The soap molecules have a hydro-
philic “head group” the carboxylate anion, which
interacts well with water and a long, greasy hydropho-
bic “tail” which interacts well with non-polar grease.
When soap molecules are dissolved in water they
organize themselves into clusteres called micelles with
all of the hydrophobic tails pointed inward and the
hydrophillic head groups pointed out into the sur-
rounding water.
When soap molecules help dissolve grease, the
hydrophobic tails become associated with the grease
and the soap molecules surrround it, forming a micelle
around the grease and bringing it into the water.

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“Soap scum” forms when soap becomes less soluble in water. This happens when divalent
counterions like Ca2+
and Mg2+
from the water become associated with two soap molecules.
The soap loses its ability to form micelles because the polar head group is now at the center of a
molecule with two hydrophobic tails. This pair of soap molecules is “greasy” by itself and
coats the tile in your tub (and you!) instead of washing away. “Soft” water has relatively low
concentrations of these divalent cations. Water softeners work by exchanging sodium cations
for calcium and magnesium ions.
Soap Scum

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Phase Transfer Catalysis
Since the fat or oil starting materials are not soluble in water, the saponification reaction
proceeds very slowly unless some pathway exists to bring the fatty ester and base into the
same phase. One method is to use alcohol as a solvent to solubilize the fat and base together
and then the alcohol is removed at the end to isolate the soap, but, as you can see from the
biodiesel experiment, this often results in ester products, rather than carboxylic acids. Another
approach is to use a tetraalkylammonium salt as a phase transfer catalyst to bring the base into
the oil phase thereby speeding up the hydrolysis.
In this experiment, partially hydrogenated vegetable shortening will be saponified using
aqueous sodium hydroxide with tetrabutylammonium bromide as a phase transfer catalyst.
Background: Biodiesel
Biodiesel is an alternative fuel produced from the transesterification (conversion from
one ester to another) of triglycerides such as vegetable oils and animal fats. Used cooking oils
may be easily recycled and used to make biodiesel. Since regular diesel engines like those in
tractor trailer trucks and heavy construction equipment can use biodiesel in their existing
engines, it is one of the simplest alternative fuels to use. The most commonly used fuel that
contains biodiesel is a mixture of 20% biodiesel and 80% regular petroleum diesel called B20.
Fuel that is 100% biodiesel is called B100. The US Navy is currently the world’s largest
consumer of biodiesel, using B20 for all non-tactical vehicles. Many other government
organizations are converting their vehicles to either biodiesel or ethanol based fuels.
Carbon dioxide (CO2
) is a major greenhouse gas produced by combustion. Because
biodiesel is made from plants the amount of CO2
given off when it is burned is the same as the
amount that the plant took in to make it. As you can see from the table below, many other
hazardous byproducts of the combustion of diesel fuel are reduced.
Average Biodiesel Emissions Compared to
Conventional Diesel according to EPA
Emission Type B100 B20
Total Unburned Hydrocarbons -67% -20%
Carbon Monoxide -48% -12%
Particulate Matter -47% -12%
NOX
+10% +2% - -2%
Sulfates -100% -20% (estimated from B100)
The increased oxygen content of biodiesel (the presence of the esters) helps it to burn
more completely, reducing both unburned hydrocarbons and carbon monoxide emissions.
Sulfates aremajor components of acid rain and are nearly entirely reduced by using biodiesel.
One disadvantage to using biodiesel is the slight increase in emissions of nitrogen
oxides (NOX
). Nitrogen oxides are a major component of smog and contribute to the
formation of ground-level ozone and acid rain. Another disadvantage to biodiesel is that it
increases in viscosity when it gets cold, making it unsuitable for use in cold weather.

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While biodiesel can be made from any triglyceride, even used cooking oils, the major
source of oil will be soybean oil. Soy beans are approximately 18% oil and their production is
currently in surplus. The Department of Energy estimates that by combining these sources
there is enough oil to produce 1.9 billion gallons of biodiesel, enough to replace 5% of the on-
road diesel used in the United States. According to the National Biodiesel Board, biodiesel
production has a positive energy balance, you get 3.24 times as much energy out of the
biodiesel produced as it takes to manufacture it. You will be asked to calculate whether it is
possible for the United States to produce enough soybeans to replace petroleum diesel with
biodiesel as part of your lab report.
Sources: TheNational Biodiesel Board www.biodiesel.org
The Department of Energy’s Alternative Fuels Data Center www.eere.energy.gov/afdc/
Soap Procedure:
Partially hydrogenated vegetable shortening (2.0 g) is placed in a 50 mL beaker along
with 2 mL of 25% aqueous sodium hydroxide and 0.020 g of tetrabutyammonium bromide. The
mixture is heated on steam bath with occasional stirring with a glass rod for 20 minutes, or
until the oil phase has disappeared and only soap solids and a clear aqueous phase remain. The
mixture is allowed to cool to room temperature then cooled in an ice bath while 5 mL of ice
cold water is slowly added. The suspension of soap solids is stirred while keeping it in the ice
bath, then suction filtered using a Buchner funnel. The soap solids are rinsed with a few mL of
ice cold water and air dried in the Buchner funnel.
Testing the Solubility and Foaming Properties of Soap in Soft and Hard Water.
A small amount of the soap is dispersed in about 20 mL of distilled water in a clean 50
mL beaker. The soap dispersion is transferred to a 60 mL separatory funnel and shaken
vigorously. The solubility and foaming properties of the resulting solution are observed and
recorded. The procedure is repeated using 20 mL of regular tap water. How do the solubility
and foaming properties of the soap in the hard water compare to the distilled water?
Biodiesel Procedure:
Dissolve 0.2g (two pellets) of NaOH in 10 mL of methanol in a beaker. Ensure the
NaOH is completely dissolved.
While the NaOH dissolves, begin slowly heating 50 mL of vegetable oil in a 125 mL
erlenmeyer. Place a thermometer in the oil and monitor its temperature. Transfer the stir bar
from the beaker of NaOCH3
to the flask containing the oil with a stir bar retriever. With the oil
stirring quickly, slowly add the entire sodium methoxide solution to the oil. Place a
thermometer in the flask and gently heat the mixture to 45-50°C for 20 minutes. Do not let the
temperature go above 60°C. Transfer the reaction mixture to a 125 ml separatory funnel.
After about 15 minutes, separation can be observed.
Wait until there is good separation between the two products. Carefully drain off the
viscous bottom glycerol layer. Drain off the top biodiesel layer into a small erlenmeyer and
dry it with magnesium sulfate. Reheat the biodiesel to 60-70°C to decrease its viscosity and
suction filter it to remove the magnesium sulfate. Take a sample of the biodiesel (top layer)

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and record its pH range (alkaline, neutral or acidic) in your lab notebook. Obtain the mass and
volume of your dried biodiesel product, and compare it to the volume of vegetable oil you
started with. Also record the characteristics of your biodiesel (color, viscosity, odor) and
compare them to those of the original oil.
In your lab report:
Write a general mechanism for saponification and transesterification reactions
Discuss how soap works.
Discuss the results of the solubility and foaming experiment.
Explain the role of the phase transfer catalyst in the saponification experiment.
Is biodiesel really geen? Explain at least one argument in support of the idea that biodiesel is a
“greener” fuel. Also present one argument that biodiesel is not a greener fuel.
Using the data below, could the United states expect to grow enough soybeans to replace
petroleum diesel with biodiesel? Show your calculations.
Quantities in the United States
41 pounds of soy beans are needed to make 1 gallon of soydiesel
1 ton of soybeans makes 47.33 gallons of oil
1 bushel of soybeans is 60 pounds
By weight, soy beans are about 20% oil
60 pounds of soybeans yield 1.42 gallons of oil
38.1 average bushels of soybeans are produced per acre (year 2000)
54.4 gallons of soy bean oil are produced per acre
Agriculture in the United States
2.2 million farms and nearly 990 million acres (47.3% crops, 52.6% livestock/other)
74 million acres are in surplus
Energy in the United States
Soy diesel yield 117,093 BTUs per gallon; Gasoline yields 114,264 BTU per gallon
Soydiesel requires 23,620 BTUs per gallon to make
Gasoline requres about an equal amount of energy (BTUs) to make
Volume used in the United States:
30 billion gallons of diesel used per year
18 million barrels of petroleum used per day (about 6.6 billion barrels per year)
42 gallos of petroleum per barrel
277 billion gallons of petroleum per year