Practical Aspects of Integrated Operation of Biotransformation and SMB Separation for Fine Chemical Synthesis

Abstract

Integrated operation of biotransformation and simulated moving bed (SMB) separation is an attractive option for high-yield manufacturing of commercially relevant compounds such as rare sugars and sialic acids from equilibrium-limited isomerase- or aldolase-catalyzed reactions. Here, we present the first lab-scale implementation of such a process using the production of d-psicose, which is currently under consideration as low calorie sweetener, by d-tagatose epimerase-catalyzed epimerization from d-fructose as a model system. While a typical batchwise eprimerization of d-fructose would stop at 25%, a yield of 97% was obtained when operating the fully integrated process consisting of SMB, enzyme membrane reactor (EMR) and nanofiltration (NF) for a number of days with absolute product purities. Next to the proof of principle, important process characteristics such as startup time, stability and robustness were investigated. By pre-equilibrating the NF unit to the projected conditions, startup times could be reduced to the contributions from EMR and SMB (in this case below 5 h) which was perfectly in line with the projected range of operation time of a few days. Robustness was probed by introduction of a perturbation, specifically a 2-fold increase in process feed concentration, which did not compromise any of the set specifications. Next, long-term operation of the respective units indicated a potential process time of at least 5 days, which could be easily extended in the future by engineering a more stable enzyme variant and implementing a cleaning-in-place approach for SMB column regeneration. In summary, the principle feasibility of such process integration for fine chemical synthesis could be successfully demonstrated.