Continuous CO2 esterification to diethyl carbonate (DEC) at atmospheric pressure: application of porous membranes for in situ H2O removal

The direct synthesis of diethyl carbonate (DEC) from ethanol and carbon dioxide over Ce0.8Zr0.2O2 catalysts was investigated in continuous mode at atmospheric pressure. Three main parameters, namely molar ratio of ethanol/CO2, flux and temperature, have significant influence on the formed DEC amount and were studied systematically. With 32 mmolDEC L−1cat h−1 achieved at ambient pressure, an ethanol/CO2 molar ratio of 3 and a temperature of 100 °C the continuous approach offers a higher productivity compared to batch reactions, normally performed in autoclaves under much higher pressure. Moreover, in order to shift the equilibrium to promote the formation of DEC, four inorganic porous membranes, (i) MFI zeolite, Si/Al ratio ∼57; (ii) MFI zeolite, Si/Al ratio ∼270; (iii) LTA (NaA) zeolite; and (iv) a microporous carbon membrane, have been applied for product removal in a catalytic membrane reactor. A relationship between the amount of removed water achieved by the membranes and the enhancement of formed DEC amount was found. The productivity can be increased to 47 mmolDEC L−1cat h−1 using an MFI-57 membrane.