When biodiesel is made, glycerin is created as a byproduct. Many people who make biodiesel wish to purify the leftover glycerin so it can be used or composted. The glycerin can be purified using chemicals and heat, which will remove the majority of the methanol and soap remaining from the biodiesel making process. In this process the glycerin will reach a relatively pure state, and could be used in industrial applications or as a crude household soap. However, it will not reach the same level of purity as the food-grade glycerin found in cosmetics.
Find a well ventilated area to work in. The glycerin will release methanol fumes during the purification process, which can be hazardous. Take safety precautions by wearing goggles, protective clothing, and heat resistant gloves. You will begin with the byproduct glycerin left over from making biodiesel.
Mix phosphoric acid into the unfiltered glycerin to remove the soap. To determine the amount of acid you should use, you will need to refer back to how much sodium lye you used when making the biodiesel. According to the Journey to Forever website, for each gram of sodium lye used, you should use 1.5 to 1.7 milliliters of phosphoric acid, in an 85 percent solution.
Observe as the acid causes the glycerin to separate. The soap will break down and float to the top, where it can be removed by skimming it from the surface. Be careful when working with the acid.
Heat the glycerin to above 150 degrees Fahrenheit in the pressure cooker. This will cause the methanol to separate out from the glycerin.
Allow the glycerin to boil for at least an hour. The methanol will boil out. Alternately, leave the glycerin to sit in a well ventilated area for three weeks, and the methanol will evaporate.
Pour the glycerin into your desired storage container. Once cooled, the liquid glycerin will harden into a brown, wax-like object.
