Industrial alcohol can be produced (1) synthetically from ethylene, (2) as a by­product of certain industrial operations, or (3) by the fermentation of sugars, starch, or cellulose. There are two principal processes for the synthesis of alcohol from ethylene. The original method (first carried out in the 1930s by Union Carbide) was the indirect hydration process, alternately referred to as the strong sulfuric acid-ethylene process, the ethyl sulfate process, the ester­ification hydrolysis process, or the sulfation hydrolysis process. The other synthetic process, designed to eliminate the use of sulfuric acid, is the direct hydration process, where ethanol is manufactured by directly reacting ethyl­ene with steam. The hydration reaction is exothermic and reversible; that is, the maximum conversion is limited by chemical equilibrium.

CH2 = CH2(g) + H2O(g} ^ CH3CH2OH(g) (-AH2098) = 45 kJ / mol

Only about 5% of the reactant ethylene is converted into ethanol per each pass through the reactor. By selectively removing the ethanol from the equilibrium product mixture and recycling the unreacted ethylene, it is possible to achieve an overall 95% conversion. Typical reaction conditions are: 300°C, 6-7 MPa, and employing phosphoric (V) acid catalyst adsorbed onto a porous support of silica gel or diatomaceous earth material. This catalytic process was first utilized on a large scale by Shell Oil Company in 1947.

In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have also been suggested [11-14]. However, none of these has been successfully implemented on a commercial scale.