Optimization of a simulated-moving-bed process for continuous separation of racemic and meso-2,3-butanediol using an efficient optimization tool based on nonlinear standing-wave-design method

The feasibility of using a simulated-moving-bed (SMB) process for continuous-mode separation of biotechnologically produced 2,3-butanediol (BD) into racemic-BD and meso-BD has been verified recently. One of the important tasks for facilitating the industrial application of such a BD-isomer separation SMB is to make a substantial improvement in its production rate and/or productivity while meeting the requirements on BD-isomer purities and pressure drop. To address this issue, the comprehensive optimization for a BD-isomer separation SMB was attempted in this study. First, an efficient SMB optimization tool based on a Langmuir isotherm standing-wave-design method was prepared and then applied to comprehensively optimizing the operation and system parameters of the considered SMB. The results revealed that the production rate (Prate), under a given column length, could reach its maximum when feed concentration (C_feed,BD) was selected at the one where the negative effect of nonlinearity increase on Prate could be balanced with the positive effect of C_feed,BD increase on Prate. The Prate could be improved further by modulating column length (L_c) to be a little lager than the L_c leading to a maximum in feed flow rate (Q_feed), which was effective in increasing C_feed,BD high enough to outweigh the resultant decrease of Q_feed. It was also found that the productivity (Prod) could be enhanced by adopting the L_c smaller than that for a maximum in Q_feed, which could allow a sufficiently large savings of adsorbent to outweigh the resultant decrease of Q_feed and C_feed,BD. Finally, it was confirmed that the comprehensively optimized SMB in this study could lead to more than 17 times the Prate and Prod, compared to the previously reported BD-isomer separation SMB.