(115b) Multi-Objective Optimization Method to Design the Pseudo-SMB Process for the Separation of Ternary Mixtures

Pseudo-SMB called "J-O system" is a hybrid batch chromatography-SMB system which is operated with the two steps shown in the Figure to separate ternary mixtures. While feed solution is fed into zone 3 (feed port), zones 2 and 3 are disconnected and the intermediate retained component is collected at the end of zone 2 (intermediate port) by the desorbent fed at desorbent port (between zones 1 and 2). In this chromatographic step, there is no collection of the most and least retained component at raffinate (between zones 3 and 4) and extract (between zones 1 and 2) ports, respectively. After feeding, feed and intermediate ports are closed and zones 2 and 3 are reconnected while the least and most retained components are collected at raffinate and extract ports, respectively. This operation can be thought of as SMB operation with no feed or as equivalent to moving port operation of closed inline recycle chromatography. Previous researchers analyzed the solute behaviors in the column with the migration velocity of batch chromatography and TMB separately. However, explanation of the migration behavior of solute for the pseudo-SMB system is complicated and only one operating procedure was studied. We used the zone flow-rate ratio (ratio of liquid phase velocity to the solid phase velocity simulated by port switching) of the Triangle theory to explain the migration behaviors of solutes during the SMB operation (m_j^SMB) and the mean flow-rate ratio in one cycle (m_j^Cycle). This allows one to study multiple cycles of SMB operation and thus to optimize the feeding interval. There are five design parameters (m₁^Cycle, m₂^Cycle, m₃^Cycle, m₄^Cycle, and m₃^SMB) when feed stream and liquid phase flow rate in zone 3 are fixed. To optimize these five design parameters, a multi-objective optimization method was used with four linearized objective functions. Each objective function was used to optimize the corresponding zone flow-rate ratio at a fixed value of (m₃^Cycle – m₃^SMB), which decides the loading volume of feed solution. The optimizations were performed to achieve high purity and productivity of the intermediate retained component. For the simulation work, three nadolol isomers which follow linear or competitive Langmuir isotherms depending on the feed concentration were used as a solute system and Aspen Chromatography¢ç (Ver. 2006, Aspen Tech Inc., USA) simulator was used for detailed simulations. For this particular system in the linear range the optimum operation of the pseudo-SMB used two and half complete cycles of the SMB part of the operation, which is different than results reported previously.

Figure 1. Schematic illustration of pseudo-SMB process.