Alcohol

Alcohols are produced industrially from petroleum, coal, or other natural products. The "cracking" of crude petroleum yields many lower-molecule-weight chemical compounds, including some starting materials for alcohols such as ethylene and propylene. Ethylene reacts with hot steam over a catalyst to yield ethanol directly. A process known as hydration produces isopropyl alcohol when water is chemically added to propylene.

When "gasified," coal yields a mixture of hydrogen gas and carbon monoxide called synthesis gas, an important starting material for a variety of low- or high-molecular-weight alcohols. Methanol is now made almost entirely from synthesis gas. Before direct chemical synthesis was available, methanol was produced by the destructive distillation of wood (hence its older name, wood alcohol). Wood heated to a high temperature without air does not burn in the regular sense but decomposes into a very large number of different chemicals, of which methanol and some other alcohols are a small fraction.

Distilling the ethanol from fermentation products gives a mixture of 95% ethanol and 5% water, resulting in an azeotrope. This is when two chemicals distill together instead of separating at their different boiling temperatures. Most industrial ethanol is 95% alcohol unless there is specific need for very dry ethanol.