Dimethyl Carbonate Production from Methanol

The process under analysis comprises three major sections: (1) Reactors Train; (2) Off-gases Treatment; and (3) Purification.

Reactors Train. This section of the plant is composed of two reactors in series, a partial condenser and a knock out drum. CO, O2 and methanol react, in the presence of copper chloride (CuCI) as the catalyst, to form Dimethyl Carbonate (DMC). Each reactor is comprised of two tall vertical cylindrical tubes connected to each other at the top and bottom. Compressed CO and O2 are fed at the bottom of one vessel so the more dense gas-poor liquid phase circulates from the second tube to the first one. The circulation also provides the required agitation for mixing the liquids, enabling the reaction to occur. The gas-phase is withdrawn from the top of the first reactor and fed to the bottom of the first tube of the second reactor, which is also fed with fresh and recycled liquid methanol.

Off-gases Treatment. The off-gases generated along the process are treated to remove organic compounds such as chloroformates, DMC and methanol, which sent back to solid-liquid separation. The gaseous mixture of carbon oxides is washed with an aqueous piperazine activated MDEA solution for the removal of CO2. The CO2 removed is routed to an integrated unit that converts CO2 to CO. Carbon monoxide is compressed and recycled to the reactors.

Purification. The reaction product is withdrawn from the second reactor as a gaseous stream through a cyclone. This stream is then led to a partial condenser that generates a DMC-rich liquid stream and a gaseous stream containing mostly CO and CO2. The liquid portion of the reaction product is fed to a flash drum, which reduces the pressure at nearly atmosphere. A gaseous stream comprising any residual gases and volatile organics is generated. The liquid phase is treated for recovery of residual catalyst and acid compounds, and then subjected to distillation operations that first recover unreacted methanol as a methanol/DMC azeotrope - that is recycled to reaction - and then separate a DMC/water azeotropic mixture into a wastewater stream and purified DMC product with purity higher than 99.8 wt%.