Most is manufactured from in one of two processes:
1. By indirect hydration by addition of H₂SO₄ and subsequent saponification of the sulfuric acid ester.
2. By direct catalytic hydration.

The indirect hydration has been used industrially since 1930. Ethylene-containing gases, in which the ethylene content may vary between 35 and 95%. are reacted with 94-98% H₂SO₄ in a system consisting of several absorption columns at 55-80°C and 10- 35 bar. Mono- and diethyl sulfate are formed exothermically in this step, which can be catalyzed by Ag₂SO₄:

After adjusting the H₂SO₄ concentration to 45-60 wt%, both sulfuric acid esters are hydrolyzed to ethanol in acid-resistant, lined columns at temperatures between 70 and 100°C. Diethyl ether is formed as a byproduct, particularly at higher temperatures:

The dilute H₂SO₄ is concentrated using submerged burners, which evaporate the water in the sulfuric acid with an open flame. Small amounts of SO₂ are also produced.

Ethanol selectivity is about 86% (based on C₂H₄).

In this process, the aqueous sulfuric acid is Concentrated in a forced circulation concentrator made of glass-lined steel in the last step. If necessary, organic contaminants are removed by addition of an oxidizing agent (generally 65% HNO₃) without the production of undesired waste gases.

There are many industrial applications of this technology.

The catalytic hydration of ethylene was first used commercially by Shell in 1947. Thc addition of water is carried out in the gas phase, generally over acidic catalysts:



H₃PO₄/SiO₂ catalysts have proven to be particularly useful in scvcral different processes. Typical reaction parameters are 300°C, 70 bar, and a short residence time to limit the formation of byproducts such as diethyl cthcr and ethylene oligomers. Under these conditions of temperature and pressure, only about 30% of the equilibrium ethanol concentration is obtained. The partial pressure of steam is limited, since it lowers catalyst activity and shortens catalyst lifctimc by loss of phosphoric acid. Thus, the mole ratio of water to ethylene is limited to 0.6. Ethylene conversion is only about 4%. Since the ethylene must be recycled many times to use it economically, either it must be very pure or a larger portion must be vented to avoid building up inert gases in the recycle gas. The gas flow from the reactor is cooled to separate the condensable products, and the ethylene (for recycling) is once again brought to reaction temperature. The aqueous crude alcohol is concentrated and purified by extractive distillation. The selectivity to ethanol is 97%. Well-known processes of this type have been developed by such companies as BP, Shell, UCC, USI, and Veba (now Hiils). Single units can have a production capacity as high as 380000 tonncs per year.

Basic disadvantages of this otherwise elegant catalytic process are the high ethylene purity necessary and the low conversion. These arc also the reasons why the older H₂SO₄ process can still be competitive today.