Performance of catalytic cycloaddition of CO2 to styrene oxide in three-phase co-current (micro)fixed-bed and monolith reactors

Synthesis of cyclic carbonates via catalytic cycloaddition of CO2 to epoxides represents one of the most promising green routes for CO2 utilization. The present work investigates, from a multiphase reactor engineering perspective, the design of three-phase catalytic reactors for cycloaddition of CO2 to styrene oxide in the presence of non-deactivating silica-supported pyrrolidinopyridinium iodide catalyst via an exhaustive modeling framework containing a series of isothermal unsteady-state two-dimensional models. A comparative analysis is made for fixed-bed reactors/microreactors and three-phase monolith reactors. The results show a remarkable performance of fixed-bed microreactor which significantly outperforms both fixed-bed and monolith reactors and hold great promise for efficient implementation of CO2 cycloaddition process under relatively mild reaction conditions. At equal liquid space velocity, upflow monolithic reactor outperforms downflow/upflow fixed-bed reactors due to reduced resistance to external and internal diffusion in catalyst pore network, but it would require a higher reactor volume for the same amount of catalyst. A confinement-induced amplification of concentration of CO2 adsorbed on the surface of catalyst generates an enhanced performance of styrene carbonate synthesis process due to increased sorption of CO2. Fixed-bed microreactor generates the smallest confinement-induced performance improvement, possibly because catalytic process is controlled by the considerable improvement in mass transfer.