Beyond running a diesel engine, a biodiesel batch has three further outputs worth using: the excess methanol (about 74 mL per litre of oil beyond what the reaction needs), which can be recovered and reused; the glycerin, which goes into soap once the methanol is out; and the washed, dried, tested fuel itself, which burns in a wick lamp or an oil burner. Each use needs the methanol and lye dealt with first.
Part of Biodiesel Production
Other uses of biodiesel production are the byproducts and secondary uses of the fuel beyond its main job in a diesel engine.
Recover The Methanol: It Is A Finite Stock
The parent’s batch uses 200 mL of methanol per litre of oil against 126 mL actually needed (Triglyceride + Methanol → FAME + Glycerin), so up to 74 mL per litre of oil is excess: 200 − 126 = 74. For a 20-litre batch that is up to 20 × 74 = 1,480 mL, nearly 1.5 litres in the glycerin layer and the first wash. The parent sources methanol from salvaged fuel and solvent stores, which run out. Recovering excess methanol by distilling it off (boiling point 64.7°C), with a condenser and a closed, sealed set-up, lets a community stretch its stock. The risk is that of a still: flammable vapour and a poison in the receiver (Distillation for the apparatus principles, Methanol Hazards). The corpus has no sourced recovery procedure, and the figure above is an upper bound, not a yield.
Glycerin Into Soap
Once the methanol is removed, the glycerin can go into soap as a small share of the recipe (Soap Making from Glycerin). The parent’s other suggestions, composting it or using it as fire starter, are not safe for the crude layer (Glycerin Byproduct).
The Fuel Beyond Engines
- Lamps and burners. The corpus’s lamp guide names rendered fat and vegetable oil as safe lamp fuels and bars solvents and alcohol because they give off ignitable vapour at room temperature (Fuel Sources). Washed, dried and tested biodiesel is an oil-like fuel and the parent’s quality check burns it in a lamp (Oil Lamp Construction), but an unwashed batch still holds methanol and must never go in a lamp.
- Heating. A wick or drip burner designed for oil can use it; engines and burners sold for petroleum diesel may need new seals (Diesel & Heating Oil).
- Cleaning grease. Biodiesel is a solvent for grease and tar (a recalled property, not from the corpus) and can soften paint and rubber; test on a scrap first.
What You Need
- A decision about each stream before the batch: where the glycerin, wash water and recovered methanol will go
- Labelled, closed containers for each
Method: Plan The Byproducts
Step 1: Before each batch, label three containers: glycerin, methanol recovered, wash water.
Step 2: After settling, put the glycerin layer in its container and hold it.
Step 3: Decide which use you can do safely this week. If none, store sealed.
Common Mistakes
- Using unwashed fuel as lamp or stove fuel.
- Using the byproducts in the garden.
- Reusing methanol without testing for water. Wet methanol makes soap.
Methanol vapour and caustic liquids
Recovered methanol is as poisonous as the new; the glycerin and early wash water are caustic. Keep every stream labelled and sealed and never use them near food, drink or growing crops.
What’s Next
- Learn next: Soap Making from Glycerin
- Combine with: Feedstock Sources, for the full material flow