Distillation raises a fermented wash of about 10% alcohol to the 85-95% an engine needs by heating it so the ethanol, which boils at 78.4°C against water’s 100°C, leaves as vapour first and is condensed back to liquid. A simple pot still reaches roughly 40-60% in one pass, a reflux column 92-95%, and no distillation can pass 95.6% by mass because ethanol and water then boil together.
Part of Ethanol Fuel Production
Distillation separates ethanol from water by boiling the wash and condensing the vapour, concentrating the alcohol for fuel.
Heat The Wash, Catch The Vapour, Cool It To Liquid
Ethanol boils at 78.4°C and water at 100°C. A boiling wash gives off a vapour richer in ethanol than the liquid it came from. Run that vapour through a cooled tube and it condenses into a stronger liquid. Repeat the boil-and-condense several times, which is what a reflux column does inside one still, and the strength climbs towards the limit.
The limit is the azeotrope, a mixture of 95.6% ethanol by mass (roughly 96-97% by volume) that boils at one temperature and so cannot be separated further by boiling. Reaching engine-ready dryness beyond that takes a chemical or sieve step (Dehydration to Fuel Grade).
The parent’s figures: a pot still gives 40-60% in one pass and about 85% at best without a column; a reflux column gives 92-95%. Engine fuel wants at least 85% and is better at 95%.
The Stages In This Guide
- Which still: Column Still vs Pot Still
- How a column works: Reflux Column Design
- How to reach the top of the range and read it: Achieving 90%+ Purity
- Beyond the azeotrope: Dehydration to Fuel Grade
The corpus also has a general guide to building one (Still Construction), pot proportions (Pot Design) and condensers (Condenser Coil). Those are written for alcohol production in general.
The Cost Is Heat, And The Heat Is Fuel
Distilling a 10% wash to near-azeotrope takes about 5-7 MJ of heat per litre of ethanol at the liquid, before the fire’s losses, against the 21.1 MJ the litre holds; the working is on Yield per Hectare Comparison. A community should expect the still to consume a large share of what it makes unless it recovers heat or burns waste fuel.
What This Guide Does Not Cover
This is fuel distillation. It says nothing that makes a distillate safe to drink. Methanol is spread through almost every fraction of a run, not only the first, and no home cut rule is a safe margin for something a person might swallow; see Methanol Hazards. Fuel alcohol should be treated as poison and labelled so.
A still is a fire waiting for a leak
Ethanol vapour is 46 ÷ 29 = 1.59 times as heavy as air, colourless and flammable at 3.3-19% in air. It runs along the ground to a flame or spark metres away. Never run a still near an open flame (heat it electrically or with steam, or put the firebox where no vapour can reach it), never leave it unattended, keep every joint sealed (Sealing Joints), work in ventilation, and keep sand and a bucket of water within reach. The petroleum-vapour rules in Fire Prevention (petroleum vapour) apply to the vapour, but note that water is an acceptable extinguisher for a small ethanol fire where it is not for petroleum (Fire Safety).
What’s Next
- Learn next: Column Still vs Pot Still, to choose the apparatus
- Combine with: Fermentation, which makes the wash