(341d) Effects of Operating Parameters, Equipment Parameters, and Material Properties in Ternary Separations in SMB

Simulated moving bed (SMB) systems have been used in a variety of separation applications. Compared to batch systems, SMB systems require less solvent and are more productive per unit sorbent. While there are many advantages to SMB systems, there are several key barriers still in place that prevent their use in many industrial applications. One of the key barriers is the large number of design parameters for SMB processes. A four-zone, ternary, linear SMB has 27 design parameters for operation. Additionally, it is unclear how the design parameters, which include operating parameters, equipment parameters, and material properties, are related to solvent consumption and sorbent productivity in ternary systems.

The Standing Wave Design equations for ternary linear systems are solved in terms of dimensionless groups to obtain analytical expressions for solvent consumption and sorbent productivity. The Speedy Standing Wave Design (SSWD) equations that result provide a framework for exploring the relationships between the design parameters and the resulting separations.

This study utilizes the SSWD equations and rate-model simulations to elucidate the relationship between operating parameters such as cycle time and zone velocities to productivity and solvent efficiency. Longer cycle times result in lower productivities, but higher solvent efficiencies. By quantifying these effects on unit sorbent cost, solvent cost, and equipment cost, an optimal overall separation cost can be achieved. Because the equations are dimensionless, the resulting design principles are easily scalable. The equations for the column configuration that gives the maximum productivity in four zone SMB systems are derived. The lengths of zones I and IV have no effect on the productivity of the SMB and thus by minimizing these zone lengths, higher productivities are achieved. The optimal lengths of zones II and III can be determined based on material properties. It is also shown that changing the column configuration to maximize productivity has very little effect on the solvent efficiency of the system.

The effects of material properties on productivity and solvent efficiency are revealed through the SSWD equations. Larger differences in heavy key and light key retention factors are shown to increase both productivity and yield. However, for a set difference in heavy key and light key retention factors, minimizing the overall range of retention factors can significantly improve the solvent efficiency of a separation without sacrificing productivity. Larger diffusivities in all the components of the separation lead to higher productivity and higher solvent efficiency by minimizing mass transfer effects. These general design rules can be applied when selecting a solvent-sorbent system or when determining splitting strategies in ternary systems.