Design of pseudo-simulated moving bed process with multi-objective optimization for the separation of a ternary mixture: linear isotherms.

Pseudo-SMB, often called "J-O process", is a modified SMB process to completely separate a ternary mixture with two discrete steps per one cycle. For improved separation, two new design parameters, the position of step 1 (chi(S1)) and the number of port switches during step 2 (n(SMB)), were introduced. A multi-objective optimization method was used to optimize the operating conditions of the pseudo-SMB process with four average zone flow-rate ratios for one cycle. Nadolol isomers were selected for the model solutes and the global objective for the design of the pseudo-SMB was to collect 99% of the intermediate retained solute. The separation was optimized for 8-column pseudo-SMB system with three column lengths (2.5, 5.0, and 10 cm) and three feed composition ratios (1/1/1, 1/2/1, and 2/1/2). The simulation results showed that productivity was increased 4.3 times (n(SMB)=20, chi(S1)=0.5, 1/1/1) and desorbent to feed ratio D/F was decreased 45% (n(SMB)=16, chi(S1)=0.5, 1/1/1) compared to normal operation (n(SMB)=8, chi(S1)=0.5, 1/1/1). Productivity and D/F were significantly improved when short columns were used in the pseudo-SMB process. The pseudo-SMB was compared with recycle chromatography and SMB cascades for the same total amount of adsorbent. Recycle chromatography and 8-column SMB cascades using 20 cm and 40 cm of total column lengths were not able to separate the intermediate component with the target purity and the same feed rate of the pseudo-SMB process.