Alcohol distillation’s environmental impacts may not be as well known as those associated with gasoline production, yet both share many of the same environmental concerns, including flammability, biodegradation and the production of hazardous substances.
At an alcohol plant, the first distillation column works to extract alcohol from water by boiling. The amount of alcohol vapor condensed depends on its reflux ratio – as more is produced, but also energy costs increase due to more space being taken up by ethanol vapor than water vapor.
The second column recombines alcohol and water vapors into an approximately 90 to 95% pure alcohol mixture called heads or tails, which also contains small quantities of methanol which has an extremely lower boiling point than ethanol, yet its molecules cling together tightly within the still and are difficult to separate – Methanol is highly toxic to humans, and must be separated and discarded as soon as possible since prolonged exposure could result in blindness.
Bottoms is a liquid product resulting from distilling of the rest of the methanol-water vapor, collected in the third distillation column and condensed as bottoms. This material may then be burned to generate electricity or mixed with gasoline to make ethanol fuel, although for this latter option an extra energy-consuming blending tank must be installed as this adds further costs associated with distillation system operation.