Potentials for CO₂ Utilization: Diethyl Carbonate Synthesis from Propylene Oxide

Production of dimethyl carbonate (DMC) has received much attention in CO₂ utilization recently. The conventional route of DMC synthesis from CO₂ is converting CO₂ with ethylene oxide into ethylene carbonate and followed by transesterification with methanol. However, the azeotrope of methanol-DMC mixture makes separation system energy intensive. In this paper, CO₂ utilization to instead produce diethyl carbonate (DEC) is investigated. Fortunately, because ethanol-DEC mixture would not generate azeotrope, the energy consumptions of this CO₂ utilization route to produce DEC is much less than the DMC route. Three alternative processes to produce DEC are rigorously designed in this paper. The first one is the conventional two-step process to produce DMC and then followed by transesterification of DMC with ethanol to produce DEC. Two other alternative DEC synthesis routes are proposed: (1) converting CO₂ with propylene oxide into propylene carbonate and then transesterification of propylene carbonate with ethanol, (2) one-pot synthesis of converting CO₂, propylene oxide and ethanol into DEC. These two routes would not involve DMC, therefore, separation is easier. For these two alternative routes, propylene glycol is the by-product instead of ethylene glycol in the conventional process. Rigorous simulation of three routes and CO₂ emission calculation are performed in Aspen Plus V8.8. Due to lack of reaction kinetics of one-pot reaction, hypothetical simulation and discussion are made based on the experimental data from a recent paper. Result shows that the first alternative route avoids 46.0 % of CO₂ emission per unit weight of DEC produced as compared with the conventional process. In addition, it saves 24.0 % for capital cost and 35.3 % for utility cost. The one-pot synthesis route also has potential to reduce CO₂ emission of 17.7 %.