| + | Tuesday, 15 October 2013 |
Making Biodiesel from Vegetable Oil and Fuel Efficiency
Today we made biodiesel from vegetable oil. Our group decided to use corn oil.Basically, vegetable oil undergoes a process called transesterification to become biodiesel. In transesterification, one ester is transformed into another ester in the presence of a catalyst such as concentrated sulfuric acid or sodium hydroxide.
Fig 1. R' group and R'' group are exchanged with each other. R' and R'' denote an alkyl or aryl group.
We first found out the vegetable oil, although it is an oil, could not be used as fuel for a car as the molecules are too large and hence it is not efficient. (Vegetable oil molecules are 3 times as large as biodiesel molecules!) The vegetable oil molecule is a triglyceride, meaning there is a glycerol with 3 fatty acids.
Fig 2. A vegetable oil molecule is a triglyceride, made up of one glycerol and three fatty acids.
A biodiesel molecule, however, is smaller and hence much more efficient and can be used as fuel. The product, in this case, is methyl pentadecane.
Fig 3. A biodiesel molecule is smaller than a vegetable oil molecule.
Armed with information on the chemistry of the reactions, we embarked on our journey in making biodiesel!
We measured, weighed and heated corn oil in a conical flask on a hot plate, adding methanol and 0.1M sodium hydroxide in 8 intervals of 5 minutes each. We had to make sure that the temperature of the oil did not go above 70-80 degrees Celsius as it would boil over.
Fig 4. Making biodiesel: heating the oil on a hot plate and measuring temperature with a thermometer.
Next, we added acetic acid to the mixture to help separate the glycerol (which we do not want) from the biodiesel (which we want). We then transferred this to a separating funnel and discarded the lower layer, which is that of the denser glycerol, and poured the layer of biodiesel into a conical flask, measuring our yield.
Table 1. Table showing initial mass of corn oil and final mass of biodiesel.
We tested the effectiveness of different fuels - methanol, cyclohexane and our biodiesel.
To test the effectiveness, a small wad of cotton wool is placed in a crucible. 10ml of methanol is measured using a measuring cylinder and poured onto the cotton wool in the crucible. Measure 100ml of water into a beaker and record initial temperature. Place the beaker on a retort stand. Using the flame from a bunsen burner, we lit up a wooden splint and used it to set fire to the fuel. We then shifted the beaker of water above the flame and heated it up for 3 minutes. The final temperature of the water was recorded. Repeat the entire procedure with cyclohexane and biodiesel.
Whilst the experiment yielded results when using methanol and cyclohexane, our biodiesel did not manage to work. We suspect it is due to too much water inside the biodiesel. However, the flame did not extinguish immediately, meaning that there is still some biodiesel inside, but the purity is not high enough (i.e. there is too much water) so the a fire cannot be sustained. Hence, there are no results for biodiesel.
Table 2. Table showing final and initial temperature of water when heated using 10ml of cyclohexane and 10ml of methanol.
To determine the efficiency of cyclohexane and methanol, we did the following:
First, we found out the mass of fuel used by multiplying density x volume. Then we found the heat supplied to the water, Q, by using the equation Q=m x c x change in temperature. Efficiency was calculated using the equation heat supplied / moles of substance.
Mass of methanol = 791.30 x 0.01 = 7.913
Qwater = 0.01 x 4.181 x (100.0-31.0) = 2.8849
Efficiency of methanol = 2.8849 / (7913/32) = 11.7 kJ/mol
Mass of cyclohexane = 779.0 x 0.01 = 7.79
Qwater = 0.01 x 4.181 x (75.0-31.0) = 1.8396
Efficiency of cyclohexane = 1.8396 / (7.79/86) = 20.3 kJ/mol (3 sf)
Hence, the conclusion is that cyclohexane is more efficient than methanol as a fuel.