Biodiesel is made from treating cooking oil with methanol and potassium hydroxide. The resulting glycerine is then separated from the biodiesel and becomes a byproduct that needs to be disposed of. There is a market for pure glycerine, but the byproduct is toxic and must have the methanol removed before it can be handled. Methanol is a clear liquid that is toxic if inhaled, ingested or if it comes in contact with the skin. The glycerine cannot be used in any form until it has been removed.
- Skill level:
- Moderately Challenging
Things you need
- Safety equipment, including goggles, gloves and mask
- Portable burner
- Pot large enough to contain the glycerine
- Large, hot, aerobic compost heap with dry vegetation
Pour the glycerine into a pot. This pot should be used only once for the glycerine. Wear safety gear while you do this and stay in a well-ventilated area, preferably outside.
Bring the glycerine to a boil on a portable burner. The boiling point of glycerine is 66.1 degrees Celsius, so you must have a strong heat source. Let the glycerine boil for several hours until the methanol has boiled off. Once the methanol is gone, the glycerine is safer.
Compost the glycerine in a large compost pit. Stir the compost into dry vegetation and mix thoroughly. To decompose, air and bacteria must reach the glycerine. In a well-maintained compost pile, glycerine will decompose quickly. It will even add to the compost by acting as a compost activator, adding heat to the pile.
Place the glycerine in the pot and leave without a lid in a well-ventilated area. The glycerine should be in a location where children and pets won't be able to reach it.
Stir the glycerine occasionally over the next three or four weeks. The methanol will slowly evaporate from the glycerine. Once the methanol is gone you will be able to work with the glycerine.
Compost the glycerine as in the first section. Use a large compost pit and mix is thoroughly with dry vegetation.
Tips and warnings
- Once the methanol is removed, glycerine can be disposed of in many ways. Composting is the most common method, but it can be made into soap, mixed with kerosene for use as an engine cleaner or neutralised with an acid and poured down the drain.
- Wood shavings can be poured into a cardboard milk container and glycerine poured over. Once the glycerine solidifies, the end product can be used as a fire log.
- Commercial biodiesel producers may be able to dispose of the glycerine for you.
- Check if your city has a toxic waste dump to dispose of untreated glycerine or an anaerobic digester, which will turn it into methane.
- Always wear safety gear. Glycerine from biodiesel is not pure and contains toxins including methanol, which is hard on the lungs.
- Methanol can only be removed from glycerine if the biodiesel was made using potassium hydroxide or another potassium compound instead of sodium hydroxide.
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