| Chromatographic reactors where conversion and separation occur simultaneously are attractive for different applications such as equilibrium limited reactions and cases where accumulation of products causes deactivation of the catalyst. Enzymatic esterifications are often equilibrium limited and have shown drastic catalyst deactivation as the water produced in the reaction accumulates on the biocatalyst. Thus, these reactions are good candidates for implementation in adsorptive reactors using a water-selective adsorbent medium. The equilibrium limited esterification of propionic acid and 2-ethyl-1,3-hexanediol with a Mucor miehei lipase immobilized on a macroporous anion exchange resin as the biocatalyst is considered in this work. This reaction shows high selectivity for the primary monoester; however, the catalytic activity declines as water is adsorbed on the biocatalyst. To overcome these limitations, the esterification is carried out in hexane using catalytically inert ion exchange resins in sodium form as selective water adsorbents. Both batch and fixed bed adsorptive reactors are considered. While these adsorptive reactors offered performance improvements over conventional reactors, their operation is discontinuous. Thus, a simulated moving bed reactor (SMBR) system was developed for continuous operation integrating reaction, adsorption, and regeneration. The SMBR system comprises a number of fixed beds arranged in three zones. The beds are periodically advanced in a “merry-go-round” fashion to simulate counter-current flow. The SMBR allows continuous operation while reducing desorbent consumption and improving conversion relative to a conventional fixed-bed reactor. A model was developed based on independently determined reaction kinetics, adsorption equilibria, and adsorption rates. Predictions based on this model were found to be in good agreement with the experimental process behavior, thus, providing a powerful tool for optimization and scale-up. |
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