A pseudo three-zone simulated moving bed with solvent gradient for quaternary separations

Research Progress on the Typical Variants of Simulated Moving Bed: From the Established Processes to the Advanced Technologies

Simulated moving bed (SMB) chromatography is a highly efficient adsorption-based separation technology with various industrial applications. At present, its application has been successfully extended to the biochemical and pharmaceutical industrial sectors. SMB possesses the advantages of high product purity and yield, large feed treatment capacity, and simple process control due to the continuous operation mode and the efficient separation mechanism, particularly for difficult separation. Moreover, SMB performs well, particularly for multi-component separation or complicated systems’ purification processes in which each component exhibits similar properties and low resolution. With the development of the economy and technology, SMB technology needs to be improved and optimized to enhance its performance and deal with more complex separation tasks. This paper summarizes the typical variants or modifications of the SMB process through three aspects: zone variant, gradient variant, and feed or operation variant. The corresponding modification principles, operating modes, advantages, limitations, and practical application areas of each variant were comprehensively investigated. Finally, the application prospect and development direction were summarized, which could provide valuable recommendations and guidance for future research in the SMB area.

Fast and accurate separation of the paclitaxel from yew extracum by a pseudo simulated moving bed with solvent gradient

A pseudo simulated moving bed (SMB) with solvent gradient was used to trap and separate paclitaxel from yew extracum. This SMB process consisted of three steps: feeding, purification and recovery. In comparison with methanol/water as an eluent, acetonitrile/water could give a better separation but had a poor dissolubility of the yew extracum, and therefore methanol/water was used in the feeding followed by acetonitrile/water in the purification. In the first two steps, water was deliberately added into zone III to modulate the eluotropic strength of the liquid entering zone III, so as to make paclitaxel separation from impurities be more efficient. Once most of impurities discarded, the columns were in turn eluted to recover the trapped paclitaxel of 98% yield with a purity of 78% from the yew extracum containing 1.5% paclitaxel. Afterward, an additional operation of crystallization improved the purity further to 97.8% with the yield of 95%.

Analyses of simulated moving bed with internal temperature gradients for binary separation of ketoprofen enantiomers using multi-objective optimization: Linear equilibria

Gradient operation of a simulated moving bed (SMB) can improve the separation and purification performance by adjusting adsorption strength in each individual zone according to its functional role. The feasibility of an internal temperature gradient (ITG) established by a difference between feed and desorbent temperatures for binary separation of ketoprofen enantiomers was investigated based on simultaneous optimization of purity and productivity of S-ketoprofen, the preferentially adsorbed species and desired product. ITG operation with a temperature difference of 20K has a unit productivity higher than isothermal mode by about 20%. Due to the combined effects of temperature transition and downstream dilution, concentration profile may exhibit a remarkable peak and a pattern of two-step drop in the temperature descending and ascending areas, respectively. Both areas, if properly located under optimal conditions, are favorable for unit productivity, which cannot be predicted by the direct use of triangle theory and average Henry's constants. Modifications of the SMB operations to reduce solvent consumption were also discussed based on analyses of parametric sensitivity and internal concentration profiles.