For fuel ethanol, build a packed reflux column if you can: a pot still gives about 40-60% in one pass and about 70-80% after a second run, with a ceiling near 85%, while a column on the same pot reaches 92-95% in one pass. A pot still is simpler to build and run, and is enough for lamp or stove fuel, but engines want the stronger product.
Part of Ethanol Fuel Production
A pot still boils a batch and condenses the vapour once; a column still returns condensed vapour down a packed tube so the ethanol is concentrated in stages.
One Boil Versus Many Stages In One Tube
A pot still is a closed kettle with a pipe to a condenser. All the enrichment happens in a single boil. The parent’s figures: 40-60% ethanol in one pass (“low wines”), 70-80% on a second pass, and about 85% as the practical maximum without a column.
A column still adds a vertical tube above the pot, packed with copper mesh, glass marbles, stainless scouring pads or ceramic pieces. Rising vapour condenses on the packing and drips back, meeting fresh vapour on the way up; each contact enriches the ethanol. The parent’s column is 60-120 cm tall and 5-10 cm across and reaches 92-95% in one pass (Reflux Column Design).
| Pot still | Reflux column | |
|---|---|---|
| Strength in one pass | 40-60% | 92-95% |
| Runs needed for engine fuel | two or more, and then it may still fall short | one, then dehydrate if needed |
| Build | kettle, tube, condenser | the same plus a packed tube |
| Control | forgiving | needs steady heat and a thermometer |
| Throughput | highest | lower, set by what the column can pass |
The Heat Bill Is Not The Reason To Choose
A rough comparison for 1 litre of ethanol from a 10% wash (inputs in Yield per Hectare Comparison):
- Pot, two runs. Run 1 heats 9.9 kg of wash by 67 K (2.7 MJ) and boils 1 L of ethanol plus about 1 kg of water over (0.789 × 846 + 1.0 × 2,257 = 2.9 MJ): 5.6 MJ. Run 2 heats about 1.9 kg of low wines by 58 K (0.4 MJ) and boils 1 L of ethanol with about 0.36 kg of water (0.789 × 846 + 0.36 × 2,257 = 1.5 MJ): 1.9 MJ. Total about 7.5 MJ for a 70-80% product.
- Column, one run. 5.1-6.7 MJ for a 92-95% product, depending on the reflux ratio (2 to 4).
So the column is not the more fuel-hungry choice; it simply needs more care. These are estimates from standard constants, not measurements.
What You Need
Pot: kettle or drum, tube, condenser (Condenser Coil), sealed joints (Sealing Joints). Column: the above plus a food-safe or fuel-safe tube and packing, and a thermometer at the top.
Common Mistakes
- Packing the column with a reactive metal. Choose copper, stainless steel, glass or ceramic, as the parent lists, not zinc or galvanised pieces.
- Running a pot still hot and fast to get volume; the strength falls through the run, and the average product can be far weaker than the first drops.
- Choosing by looks. An engine needs the stronger spirit; a lamp does not.
The vapour is flammable at every stage
Both stills pass hot ethanol vapour, 1.59 times as heavy as air, through pipes. A loose joint spills it at floor level. Heat without open flame, seal every joint, and never leave the apparatus unattended (Distillation).
What’s Next
- Learn next: Reflux Column Design, if you are building the column
- Combine with: Pot Design, for sizing and filling the pot