(444c) Comparisons of Recycle Chromatography and Simulated Moving Bed for Pseudo-Binary Separations

The simulated moving bed (SMB) process, which is basically designed for binary separations, has been applied to many industrial separations and has been modified to separate multi-component mixtures, particularly pseudo-binary mixtures. In pseudo-binary mixtures because only one of the components is desired the other components do not have to be separated. The UOP Parex process for p-xylene purification is an example. When non-target components have similar adsorption behaviors and the target component is the most or least retained in the adsorption bed, the SMB has higher productivity and requires less desorbent compared to batch chromatography. However, these advantages are dependent on the difference of adsorption behaviors of the non-target components. When the most retained component is the target, productivity and desorbent consumption is related to the retention behaviors of the most and least retained non-target components, respectively.

In this research, the performance of batch chromatography with a single recycle stream is compared to a SMB process for pseudo-binary separations with competitive Langmuir isotherms. A ternary nucleoside separation was used as a model system for the simulation of batch and SMB processes. The selectivities of intermediate/least retained solutes and the most retained/intermediate solutes are 3.05 and 2.89, respectively. To determine the optimized operating condition of the SMB process, a multi-component hodograph transformation was numerically calculated to obtain the separation region in the m2-m3 plane and the regeneration region in the m1-m4 plane. The differences between m2 and m3 in the SMB process and the threshold values for the elution band in recycle batch chromatography were changed to obtain different purities and product yields in the detailed Aspen Chromatography simulations. When the most retained component is the target, desorbent consumption of recycle batch chromatography was much lower than desorbent consumption for the SMB process. At relatively low purities the SMB productivity was much higher than recycle batch chromatography productivity. However, recycle batch chromatography is a simpler system and the difference in productivities became smaller when higher purity product was required.