Study On A Simulated Moving Bed With Solvent Gradient For Ternary Separations

A simulated moving bed based on the solute trapping effect was suggested to separate a ternary mixture:a open-loop SMB with three zones was used, and a solvent gradient was created to make the solvent strength decreasing from zone Ⅱ to zone Ⅲ. Under suitable conditions, the target medium retained solute moves quicker in zone Ⅱ than that in zone Ⅲ during each switch interval. As a result, the solute moved forward in zone Ⅱ but backward in zone Ⅲ due to the column switching, which made it selectively trapped in the two zones and separated from other solutes.The scheme was validated through the successful separation of dihydrocapsaicin from capsaicinoids. The separation process consisted of three steps:feeding, purification and recovery. In the feeding step, the solvent strength of the eluent was higher than that of the solvent for dissolving solutes, so that the medium retained solute B was trapped in zones Ⅱ and Ⅲ, whereas the less retained solute A was removed from the raffinate-port and the more retained solute C from the extract-port, respectively. In the purification step, the feed was replaced by the solvent for dissolving solutes without changing the other operating conditions. The most and least retained solutes remaining in zones Ⅱ and Ⅲ were removed to purify solute B trapped in zones Ⅱ and Ⅲ. In the recovery step, solute B was recovered from the extract port by stopping the liquid flow in zone Ⅱ and Ⅲ. The result showed that the medium retained solute could be separated from a ternary system by this method.Effects of the switch interval, column distribution and purification method on the separation were studied. The results showed that reducing the switch interval was beneficial for trapping the target solute, increasing the columns in zone Ⅱ and zone Ⅲ could improve separation performance, and incomplete purification in combination with fractional collection reduced the solvent consumption. The suitable operation conditions:ODS silica gel as the stationary phase; methanol/water(80/20, v/v) as the eluent. methanol/water(60/40, v/v) as the solvent for dissolving solutes, switch interval5.5min,1-1-6configuration and incomplete purification was used. Under above conditions, dihydrocapsaicin was separated successfully with a purity of100%, and the recovery, productivity and mobile phase consumption were 77.3%,7.87g/L/h and0.862L/g, respectively. Compared to the results by the preparation chromatography, this new SMB was distinctly superior:the solvent consumption was reduced by45.4%, while the productivity was increased by225%. Besides, the concentration of the product was far greater than that of the raw material(increased by436%).Finally, capsaicinoids and paclitaxel were successfully purified from the chilli extraction and the taxus extract with this method, respectively, which extended it to the separation of a group of solutes eluted successively and microcomponents.