Diethyl carbonate synthesis from ethanol and liquid carbon dioxide in supercritical condition over CeO₂-ZrO₂ catalysts

Abstract

The synthesis of diethyl carbonate (DEC) from ethanol (EtOH) and liquid carbon dioxide (CO₂) in supercritical condition over ceria-zirconia mixed oxides (CeO₂-ZrO₂) catalysts using a high-pressure batch reactor system was studied by varying reaction temperatures from 110 to 170°C, reaction time from 0 to 8 h, and CO₂/EtOH feed molar ratios at 1:1, 2:1, and 4:1. The catalysts were prepared by co-precipitation method followed by calcination at 500 or 700°C, with percentages by mole of Ce in the mixed oxides at 0, 7, 20, and 40. The catalysts were characterized by TG-DTA, XRD, BET, and TPD. The results revealed that the Ce₀.₀₇Zr₀.₉₃O₂ calcined at a temperature of 700°C operated at a feed molar ratio of 1:1, a reaction temperature at 140°C, and a reaction time of 8 h, gave the highest catalytic activity resulting in DEC selectivity of 97.5%. The presume of tetragonal phase and weak acid-base properties of the Ce₀.₀₇Zr₀.₉₃O₂ were essential for the synthesis of DEC. By comparison between supercritical and gas phase conditions used for the synthesis, it was found that the amount of DEC produced could be enhanced when operated in supercritical condition.