How to purify glycerine

Written by jaimer
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How to purify glycerine
Although food-grade glycerine is an ingredient in soap, glycerine purified from biodiesel at home is not pure enough to make into facial soap. (natural soaps 3 image by samantha grandy from

When biodiesel is made, glycerine is created as a byproduct. Many people who make biodiesel wish to purify the leftover glycerine so it can be used or composted. The glycerine 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 glycerine 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 glycerine found in cosmetics.

Skill level:

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Things you need

  • Crude Glycerin
  • Phosphoric Acid
  • Heat Condenser
  • Goggles
  • Heat Resistant Gloves

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  1. 1

    Find a well ventilated area to work in. The glycerine 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 glycerine left over from making biodiesel.

  2. 2

    Mix phosphoric acid into the unfiltered glycerine 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 millilitres of phosphoric acid, in an 85 per cent solution.

  3. 3

    Observe as the acid causes the glycerine 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.

  4. 4

    Heat the glycerine to above 65.6 degrees Celsius in the pressure cooker. This will cause the methanol to separate out from the glycerine.

  5. 5

    Allow the glycerine to boil for at least an hour. The methanol will boil out. Alternately, leave the glycerine to sit in a well ventilated area for three weeks, and the methanol will evaporate.

  6. 6

    Pour the glycerine into your desired storage container. Once cooled, the liquid glycerine will harden into a brown, waxlike object.

Tips and warnings

  • Purified glycerine can be ecologically disposed of by composting it.
  • Be careful when working with the phosphoric acid.
  • Burns may result from mishandling the heated glycerine.
  • Only heat the crude glycerine in a well ventilated area to avoid breathing the methanol fumes.

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