SPIR4120 - Technical guidance: Can you explain how industrial ethanol is produced?

In the UK, industrial ethanol is normally produced by the hydration of ethylene gas. Tobe commercially viable, the 'distiller' needs uninterrupted access to huge supplies of ethylene gas. A typical industrial ethanol 'distiller' produces around 16,000,000 litres of alcohol per month.

The process

Ethylene gas and water are piped into a furnace where they are heated to 300 degreesCelsius. The heated mixture then passes to the reaction chamber, where a catalyst is used to speed up the reaction. Here, under pressure, some of the ethylene gas and water combines to form ethanol vapour which is condensed into a weak solution of ethanol and water. This solution is fed into the purification system. Around 95% of the original ethylene gas remains unreacted and is returned to the start of the process and used again. The basic chemical reaction is:

ethylene + water ð ethanol

CH2=CH2 + water ð CH3-CH2-OH

The purification system consists of a number of distillation columns. The weak ethanol solution is fed into the middle of the distillation column where the ethanol vapourises and rises up the column leaving the water to fall to the bottom. The ethanol vapours then pass to a second column and so on until the strongest possible solution is achieved, i.e. 96% ethanol, 4% water. This is industrial grade ethanol.

To produce the premium industrial grade known as 'dry' ethanol, the ethanol is mixed with a water removing hydrocarbon, e.g. cyclohexane. When this mixture is distilled ethanol of almost 100% purity is produced.

The finished industrial ethanol and dry ethanol are piped to 'day-tanks' for intermediate storage then onto the spirit receivers where account is taken.