A pseudo three-zone simulated moving bed with solvent gradient for quaternary separations

In a SMB with solvent gradient, as the eluotropic strength of the liquid in zone II (between the extract-port and feed-port) is higher than that in zone III (between the feed-port and the raffinate-port), the solute can move forward in zone II but backward in zone III to be trapped in the two zones consequently. On this basis, a pseudo-SMB was proposed to separate two medium retained solutes (B1 and B2) from a quaternary mixture by selectively trapping the two solutes. Once the columns in zones II and III are saturated with the target solutes, the solvent dissolving the feed is introduced at the feed-port to remove the least retained solute (A) from the raffinate-port and the most retained solute (C) from the extract-port. The two target components trapped in zones II and III are purified accordingly. At the same time, solute B1 would distribute in the columns of zone III whereas solute B2 spread in the columns of zone II if solute B2 had a stronger retention than solute B1. Thereby, the two medium retained solutes B1 and B2 could be recovered separately from the columns in zones II and III. This scheme was validated by the successful separation of capsaicin (B1) and dihydrocapsaicin (B2) from a crude capsaicinoids.