ENERGY ISSUES IN THE UTILIZATION OF CO2 IN THE SYNTHESIS OF CHEMICALS: THE CASE OF THE DIRECT CARBOXYLATION OF ALCOHOLS TO DIALKYL-CARBONATES

摘要

This paper aims at highlighting the hurdles and traps on the way back from CO2 to chemicals (or even fuels). The case of the synthesis of dialkylcarbonates is discussed, considering several synthetic conditions and comparing the energy necessary for product separation. The calculations show that the post-reaction separation process may share an important part of the energy consumption in the whole synthetic procedure and make, in some conditions, the reaction a strong CO2 emitter more than a CO2 consumer. In this paper we shall compare the energetics of: i. Direct carboxylation of methanol (or ethanol) and product separation by distillation; ii. Use of a pervaporation membrane for water separation and enrichment of the mixture in the carbonate, followed by distillation, iii. Use of CH3CN (at two different concentrations) as organic water trap and product separation by distillation iv. Conversion in a supercritical system with water separation by formation of a liquid phase.