ETHANOLAMINES

The ethanolamines monoethanolamine (MEA, HOCH ₂CH ₂NH ₂, melting point: 10.5 C, boiling point: 171 C, density: 1.018), diethanolamine [DEA, (HOCH ₂CH ₂) ₂NH, melting point: 28.0 C, boiling point: 270 C, density: 1.019], and triethanolamine [TEA, (HOCH ₂CH ₂) ₃N, melting point: 21.2 C, boiling point: 360 C, density: 1.126] are manufactured by reacting ethylene oxide and excess ammonia, followed by separation of unreacted ammonia and the three ethanolamines. The proportion of the three products depends on reaction conditions.

Mono- and triethanolamine are miscible with water or alcohol in all proportions and is only slightly soluble in ether. Diethanolamine will dissolve in water, is very soluble in alcohol, and is only slightly soluble in ether. All of the compounds are clear, viscous liquids at standard conditions and white crystalline solids when frozen. They have a relatively low toxicity. In early processes, the ethanolamines were manufactured by reacting ethylene chlorohydrin (ClCH ₂CH ₂OH) with ammonia (NH ₃). Current processes react ethylene oxide with ammonia usually in aqueous solution. The ratio of mono-, di-, and triethanolamines varies in accordance with the amount of ammonia present. This is controlled by the quantities of monoethanolamine and diethanolamine recycled.

Higher ammonia-ethylene oxide ratios favor high yields of diethanolamine and triethanolamine, whereas lower ratios are used where maximum production of monoethanolamine is desired. The reaction is noncatalytic. The pressure is moderate, just sufficient to prevent vaporization of components in the reactor. The bulk of the water...