Process and Procedure - Class Lab
Note: The following procedure is for synthesizing a biodiesel mini-batch from 100% pure unused vegetable oil. This method can easily be modified for other oils such as canola, olive, soybean peanut etc. You may bring an oil of your choice from home.
1. Warm up 10 mL of 100% pure vegetable oil to about 60°C in a 100 mL beaker. Warming the oil up is not necessary, but increases the reaction rate.
2. Transfer 2ml of Sodium methoxide solution (be sure the solution is well mixed – should appear cloudy) to a 50ml beaker with a magnetic stirrer. Stirring gently, add 10ml of warm oil. Cover with watch glass and turn up stirrer to position 7 or 8. Stir for about 30 minutes.
3. While you are waiting for the reaction to finish, form a group of 4-6 people and begin to build the reactants and products for this reaction with the large molecular model sets. Once you have the molecules built, use the models to demonstrate to each other how the reaction works. Finally, draw a picture of the reaction (including lewis structures of all molecules) on a large piece of paper and identify the bond angles around each central atom.
4. Transfer the contents of the beaker into a 15 mL plastic centrifuge tube and spin for 5 minutes (don’t forget to counterbalance the centrifuge). The mixture will separate into two different layers. The glycerol and methanol layer will fall to the bottom, and the methyl ester (biodiesel) will float to the top. Draw off the top layer (biodiesel) Make sure not to get glycerol (bottom darker layer) in the biodiesel. Add 5 drops of water and stir for a minute, place the mixture in a centrifuge tube and spin for another 5 minutes. If the layers have not separated continue to centrifuge for another 5 minutes.
5. Using a transfer pipet, carefully draw off the top layer of biodiesel.
6. Measure the volume of the 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% and propose reasons for any major deviations.