Laboratory #1
Making biodiesel is a very simple process. If you are making it from yellow grease it's even easier. First go to a restaurant and ask them for some of their used oil. They usually have to pay people to take it away, so most places will give it to you for free. If you're making it from scratch it's a little bit more complicated. Here is a lab you could do with your kids, a step by step guide to how to make biodiesel. Depending on the class you're in you could focus your questions on the energy transfer, material transfer, or changing bonds.
The first step when making it from yellow grease is to strain it to get out any food particles that may have been in it. This is most easily done by running the oil through nylon stockings but other things can be used.
The next step is optional, sometimes people want to boil off water that is in the yellow grease. It is usually not necessary, but it can be done. To do this heat the oil to 100 ?C and stir until bubbling stops. If you do this, be careful to keep stirring because you do not want water that may be present to bubble up in large bubbles. After the bubbling is almost finished, raise the temperature to 130 ?C and stir for 10 minutes. The oil itself will not boil or catch fire at this temperature. After the ten minutes at 130 ?C let the oil cool.
The next step is by far the most sensitive. Take 10 mL's of isopropyl alcohol and add 1 mL of the oil. Add 2 drops of phenolphthalein solution to the mixture. Then add 1g of lye to 1L of deionized water. Very carefully add measured amounts of the lye solution to the oil solution. If you can get them, burettes measured to at least a 10th of a mL are best, but anything that measures to a 10th of a mL works. Slowly add drops of the lye solution (stirring between each drop) until the oil solution turns pink for a few seconds. This indicates a pH of around 8. You can expect to use about 1 to 4 mL's of lye depending on how the oil was previously used.
Next you take the number of grams of lye solution used and add the number 3.5. You then multiply the sum by the number of Liters of oil you plan on processing. The answer is the number of grams of lye you'll need.
Then you mix .2L (20% by mass is the exact amount needed, but using volume is good enough unless you're planning on doing this commercially) of methanol with the lye and stir. Be careful with this solution, it is very basic. If it touches your skin you will not feel the burn that is occurring, but continue to wash for at least 15 minutes. Wear gloves and other protective equipment. Also, do not use plastic containers. Real glass or stainless steel is recommended from here on out.
Next heat your oil to 50 ?C. Then use a stirrer (a piece of wood or a metal paint stirrer attached to a variable speed drill works well, but you can use whatever) and adjust the speed so that a vortex is just appearing on the top of the oil while keeping the oil heated. Once the stirrer is set add the lye/methanol solution (sodium methoxide) and keep the contraption going for about an hour (30 minutes is probably sufficient, but to be on the safe side…). Then let the liquids sit and cool for approximately 8 hours.
You now have approximately 70% biodiesel (which should be on the top and darker in color) and 30% glycerin (which should be on the bottom and lighter in color and may solidify). You can decant the biodiesel and if the glycerin has solidified heat it up to near 38 ?C to pour out. If you are doing this on a large scale you may want to put a pour spout on the bottom of you container.
Your biodiesel is ready to use. The glycerin can be distilled into pure glycerin, allowing you to reclaim most of the methanol and lye, but this procedure is a bit more complicated and beyond the scope of this unit. AP chemistry teachers may want to use this as an additional lab to find triple points and PVT curves and to learn distillation.
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