Ethylene glycols technology

Ethylene glycol (EG) or monoethylene glycol (MEG), the adduct of ethylene oxide (EO) and water, is the simplest glycol. It is the first of a homologous series of three dihydroxy alcohols discussed in this article. Diethylene and triethylene glycols (DEG, TEG) are the other two. These glycols are composed solely of carbon, hydrogen and oxygen. Although they have similar chemical properties, their applications vary mainly with physical properties such as viscosity, hygroscopicity and boiling point. The commercial route to ethylene glycols in use today involves the noncatalyzed thermal hydrolysis of ethylene oxide in water. This process produces chiefly mono-, di- and triethylene glycols and a small amount of tetraethylene and heavier glycols. The yield of monoethylene glycol via hydrolysis is controlled by the water-to-ethylene oxide ratio in the feed to the reactor system. Removal of excess water following the glycols-forming hydrolysis is energy intensive and requires capital investment in evaporators. Such costs limit the amount of excess water which is used. In practice, reactor feed water content is such that the selectivity to monoethylene glycol achieved ranges from 89-91%. The equipment elements in a simplified process flow diagram are discussed along with recommended materials of construction. Among other items discussed are a) a brief review of economic factors; b) health, safety and environmental issues; and c) commercial applications of the three glycols, MEG, DEG and TEG. Finally, recommendations for shipping, handling and storage are discussed.