A 20-litre biodiesel batch uses 4 litres of methanol, 70 g of NaOH for clean oil plus 1 g for every millilitre of titration, and runs as six stages: prepare and titrate the oil, make the methoxide, react at 55-60°C for an hour, settle 8-24 hours, wash gently 3-4 times and dry at 100°C. It takes about two days, and every stage that touches methanol or lye needs eye protection, gloves, ventilation and no flame.
Part of Biodiesel Production
The biodiesel production process is the sequence from raw oil to finished fuel: preparation, reaction, separation, washing and testing.
Quantities For One Batch
From the parent’s per-litre rules (200 ml of methanol, 3.5 g of NaOH per litre of clean oil):
| For | 20 litres of oil |
|---|---|
| Methanol | 20 × 0.2 = 4.0 litres |
| NaOH (clean oil) | 20 × 3.5 = 70 g |
| NaOH extra for titration | 20 g per mL of titre; a titre of 2 mL adds 40 g, total 110 g (5.5 g per litre) |
| KOH instead | 1.4 times the NaOH mass: 98 g for clean oil (Lye Catalyst) |
| Wash water | 1/3 of the biodiesel volume per wash |
The parent’s equipment list covers 20-50 litres per batch; five litres of methanol per 25 litres of oil is the same ratio.
The Stages
- Prepare the oil: filter, settle, dry, titrate (Oil Preparation & Titration, Waste Cooking Oil).
- Make the methoxide and react at 55-60°C for an hour (Mixing & Reaction).
- Settle 8-24 hours and drain the glycerin (Settling & Separation).
- Wash and dry at 100°C (Washing & Drying).
- Test (Quality & Testing).
Timeline for 20 litres: a few hours of preparation, 1 hour of reaction, a night of settling, then three or four washes of 2-4 hours each, about two days overall.
Setting Up Safely
- Site: outdoors, in the open air, or under a roof open on all sides, never in a closed room or cellar. Methanol vapour is flammable (about 6-36% in air, a recalled figure) and its vapour is slightly heavier than air (32 ÷ 29 = 1.1).
- Fire: nothing hot or sparking in the area: no flame, no stove, no switch. Heat the oil in a water bath rather than over a flame.
- People: one person measures the methanol, another keeps clear; children and animals kept away; a water supply for flushing skin and eyes.
- Protective gear: goggles, gloves, apron and boots every time (Protective Gear).
- Measuring methanol: pour from the original container through a funnel into a closed, marked container, with a lid back on after each step. Never measure by hand-holding an open vessel close to the face and never with bare hands.
- Labelling: every container named and marked poison, and no food containers.
Common Mistakes
- Rushing the settle, then draining a soapy emulsion.
- Skipping titration on used oil.
- Mixing in a closed shed. Fumes reach a dangerous level and a spark finds them.
Methanol, lye and heat in one place
Methanol is toxic through skin, vapour and mouth and causes permanent blindness; lye burns; methoxide is both, and flammable. Without eye protection, gloves and ventilation, do not start. See Methanol Hazards and Spill Response. The wash water and the glycerin layer remain hazardous too.
What’s Next
- Learn next: Oil Preparation & Titration, the first step
- Combine with: Chemistry of Transesterification, for why the steps are as they are