Sustainable synthesis of diethyl carbonate from carbon dioxide and ethanol featuring acetals as regenerable dehydrating agents

Abstract

CO₂ valorization, which helps to offset the negative environmental impact of anthropogenic CO₂ emission, is a key aspect of the circular economy and a promising carbon capture and utilization strategy. Among the products of this valorization, dialkyl carbonates such as diethyl carbonate (DEC) draw much attention because of their low toxicity, high polarity, and broad application scope, and the related cost-effective and scalable synthesis methods are therefore highly sought after. Herein, DEC was sustainably synthesized from CO₂ and ethanol in the presence of acetals as regenerable organic dehydrating agents and dibutyltin(IV) oxide as a catalyst under optimized conditions (ethanol/acetal ratio, temperature, reaction time, presence or absence of Lewis-acidic additive). DEC yield, which was positively correlated with acetal hydrolyzability and negatively correlated with acetal regeneration efficiency (regenerability), increased in the presence of the Lewis-acidic acetal hydrolysis promoter (scandium(III) triflate). Acetal regenerability was strongly impacted by the ethanol/acetone ratio, molecular sieve amount, and the type of acetal regeneration catalyst, e.g., an acidic ion exchange catalyst (Amberlyst) showed high activity and stability for the regeneration of various acetals. The obtained findings pave the way for the use of acetals as sustainable dehydrating agents for direct closed-loop DEC synthesis and thus contribute to the establishment of a greener society.