Study on a pseudo-simulated moving bed with solvent gradient for ternary separations.

There is a trapping effect on the solute in the simulated moving bed (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 the medium retained solute from a ternary mixture by selectively trapping the medium retained solute. Once the columns in zones II and III are saturated with the target solute, the solvent dissolving the feed is introduced at the feed-port to remove the least retained solute from the raffinate-port and the most retained solute from the extract-port. Finally, the target solute is recovered. A model simulation was used to investigate the behavior and performance of a system operating with this technology. The results showed that increasing the columns in zone III could trap more target solutes since the eluotropic strength decreased from zone II to zone III. Partial recovery in combination with incomplete purification could improve the separation performance in terms of the productivity and solvent consumption without losing purity.