To make ethanol of 90% or better, run a packed reflux column at steady heat, collect the output in small numbered jars, measure each with a hydrometer or alcoholmeter at a stated temperature, pool only the jars above your target and put the weaker ones back through the next run. The practical ceiling is the azeotrope at 95.6% by mass, roughly 96-97% by volume, because ethanol and water then boil together and no further boiling will separate them.
Part of Ethanol Fuel Production
Reaching 90% or better ethanol is a matter of column control and measurement; the limit is a physical constant, not workmanship.
95.6% Is A Wall, Not A Target To Beat
A boiling ethanol-water mixture of 95.6% ethanol by mass (roughly 96-97% by volume) gives a vapour of the same composition, so a column that reaches it can enrich no further. The parent’s column is credited with 92-95%; if those figures are by volume they sit just under the wall, and if by mass they are lower than the limit. State which you mean and measure it the same way every time. Strengths in this corpus are written as % ABV, alcohol by volume; US proof is twice the ABV, so 85% is 170 proof and 95% is 190 (Fuel Applications sets engine fuel at a minimum of 170 proof, optimum 190+).
What You Need
- Reflux column (Reflux Column Design)
- An alcoholmeter or hydrometer reading ethanol-water mixtures, and a thermometer for the sample. A scale reading is only valid at the temperature the instrument is marked for, usually 20°C; correct or cool the sample first
- Several clean jars with lids, numbered, 200-500 ml each
- A log
Method
Step 1: Start a steady run. Heat gently, reach total reflux and steady head temperature at 78-80°C, then open the take-off slowly.
Step 2: Collect in jars. Fill and number jars in order. Stop at the first sign of weakness: the parent says stop collecting above 85°C at the head.
Step 3: Measure each jar at the calibration temperature. Record strength.
Step 4: Pool. Combine only jars at or above your target (for example 90%). Strength after mixing is closer to the volume-weighted average, but mixing alcohol and water shrinks the total by a few per cent, so remeasure the pool.
Step 5: Recycle the weak jars. Add them to the next batch of wash, or re-run them alone through the column; that second pass is what lifts 70-80% runnings toward the top of the range.
Step 6: Seal and label. Strong ethanol takes water from damp air; keep jars tight (storage notes in the parent).
Measure, Do Not Burn-Test
A burn test shows only that a spirit is strong enough to burn, not whether it is 70% or 95%. It also lights a sample beside a vessel of flammable vapour. Measure with an instrument; if you must improvise a hydrometer, calibrate it against mixtures you make by weight and keep the calibration temperature in mind.
Worked Example: How Much Water Is Left?
At 90% by volume, a litre of spirit holds about 100 mL of water. Reaching the 95% end of the range leaves about 50 mL. Neat-ethanol engines tolerate some water and blending with gasoline does not: that is the job of the next page, Dehydration to Fuel Grade. From the wall: 4.4% water by mass in a litre of azeotrope (about 804 g) is 4.4% × 804 = 35 g of water.
Common Mistakes
- Mixing volume and mass percentages. 95.6% by mass is not 95.6% by volume.
- Reading a hot sample. The scale reads wrong at temperatures other than its marking.
- Pooling everything. One weak jar drags the strength of the pool down.
- Heating hard for speed. More vapour means flooding and weaker product (Reflux Column Design).
Samples are fuel
Keep sample jars away from the still and any flame, do not smell-test vapour from a strong sample directly (ethanol vapour irritates and ignites at 3.3-19% in air), and label every jar as fuel and not for drinking. See Fire Safety and Methanol Hazards.
What’s Next
- Learn next: Dehydration to Fuel Grade, to go beyond the azeotrope
- Combine with: Ethanol in Gasoline Engines, to see what strength each use needs