PEP Review 92-1-1
Coproduction of Dimethyl Carbonate and Ethylene Glycol by Transesterification
Published: May 1993
Texaco has developed a process for the coproduction of dimethyl carbonate (DMC) and ethylene glycol (EG) from ethylene carbonate (EC) and methanol by transesterification. Several classes of catalysts can be used. The most effective one, though with low thermal stability, is a weakly basic gel-type anion exchange resin having tertiary amine functionality. In this process, EC reacts with an excess of methanol at 1005C (2125F) and 115 psia to form DMC and EG in a fixed-bed reactor packed with an anion exchange resin catalyst, preferably Amberlite IRA-68. The reactor effluent is then separated to recover DMC via the DMC/methanol azeotrope. Unreacted methanol and EC are recycled. Trace amounts of EC in EG are hydrated in the presence of the same resin used for transesterification. EG is recovered after water removal.
In this review, we evaluate the Texaco process and compare the economics to those of DMC and EG coproduction using thallium catalyst and of DMC production by oxidative carbonylation. Because DMC has potential uses ranging from specialty chemicals to gasoline octane improver, we evaluate DMC capacities ranging from 19.4 million to 560 million lb/yr (8,800 to 254,000 t/yr). We also compare the economics of oxygenated gasoline blending using DMC versus methyl t-butyl ether (MTBE).