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

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 S 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.