Separation of guaifenesin enantiomers by simulated moving bed process with four operation modes

It has been validated experimentally and theoretically that guaifenesin enantiomers could be separated effectively by six-column simulated moving bed (SMB) process with Chiralcel OD stationary phase and n-hexane/ethanol mobile phase in our previous work. Based on the existed experimental conditions, we make further investigation for the effect of operation modes on the separation performance of SMB unit, including the asynchronous shifting of inlet/outlet ports (VariCol mode), varying feed flow rate (PowerFeed mode), and varying feed concentration (ModiCon mode) within the switching interval. The mathematical models of multicolumn SMB process are established, and the separation performances of SMB unit with four operation modes are compared at similar operation conditions. It is found that the effect of operation mode on the separation performance is more significant for the SMB system with a small number of columns. Compared with the conventional six-column SMB process at the purity criterion of single enantiomer in products up to 99%, ModiCon 1 with feed concentration adjusting "First low last high" within the switching interval is the best one with the productivity increasing 27.5% and the solvent consumption decreasing 21.7%; PowerFeed mode also has some improvement with the productivity increasing 10.6% and solvent consumption decreasing 8.7%; five-column VariCol mode has the improvement on the productivity increasing 26% due to the benefit to save one packed column with the expensive chiral stationary phase.