Titrating Biodiesel Fuel - A Chemistry Experiment

Titrating Biodiesel Fuel - A Chemistry Experiment
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Biodiesel…Cheaper Fuel and Environmentally Friendly

Why is biodiesel getting so much press? Perhaps it’s because it is a relatively cheap way to get fuel for vehicles, or maybe because

the process uses vegetable oil that was once considered a nuisance to get rid of. Another reason it could be gaining in popularity is that its main raw ingredient, vegetable oil, is produced from renewable resources like soybeans and corn, unlike petroleum, which is a non-renewable resource.

Biodiesel is such a new term that it still makes my spell checker go crazy. The concept is this: Take vegetable oil, react it with a mixture of lye and methanol and let the fuel form.The fuel can be used in any diesel engine.The procedure does contain a few steps where the biodiesel is separated from unwanted components and washed, but it’s really a simple process.

While it is interesting to note that forming biodiesel from vegetable oil is really an organic transesterification reaction, the need for titration actually comes before the vegetable oil is reacted with the lye/methanol mixture.

Many biodiesel enthusiasts get used vegetable oil from restaurants. After filtering this well-used oil it is almost ready for production. First, however, the oil’s acidity must be checked because used vegetable oil tends to become more acidic than “clean” oil. Extra lye will be added to the oil once its acidity has been determined, to neutralize the extra acid. This is where the titration comes in. A known amount of oil will be reacted with a known amount of lye (base), which will reveal the acidity of the oil and let the fuel-make know how much extra base is needed for neutralization.

How to do a used-vegetable oil titration:

  1. Make a standard solution KOH by dissolving 1.0 gram of KOH in 1000 ml of distilled water to make a 17.8 millimolar solution.
  2. Add 10 ml of isopropyl alcohol and 3 drops of phenolphthalein to a 250 ml beaker.
  3. Add 1.0 ml of warm vegetable oil to the beaker and stir.
  4. Fill a buret with the standard solution. Add KOH drop-wise to the oil/alcohol mixture until a slight pink color forms (it should remain for at least 30 seconds).
  5. Note how many milliliters of standard solution were used.
  6. Repeat the process.
  7. Assuming that the acid in the vegetable oil is a strong acid, we can use the formula MV=MV to calculate the concentration of the acid, or M.This will indicate how much extra KOH needs to be added to the reaction for neutralization to occur.

Hopefully this demonstration will capture your students’ interests. Who knows, it may even inspire some to starting making and using their own biodiesel!