Advanced Operating Strategies to Extend the Applications of Simulated Moving Bed Chromatography

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.

Advances and applications of chiral resolution in pharmaceutical field

The attention to chiral drugs has been raised to an unprecedented level as drug discovery and development strategies grow rapidly. However, separation of enantiomers is still a huge task, which leads to an increasing significance to equip a wider range of expertise in chiral separation science to meet the current and future challenges. In the last few decades, remarkable progress of chiral resolution has been achieved. This review summarizes and classifies chiral resolution methods in analytical scale and preparative scale systematically and comprehensively, including crystallization-based method, inclusion complexation, chromatographic separation, capillary electrophoresis, kinetic resolution, liquid-liquid extraction, membrane-based separation, and especially one bold new progress based on chiral-induced spin selectivity theory. The advances and recent applications will be presented in detail, in which the contents may bring more thinking to wide-ranging readers in various professional fields, from analytical chemistry, pharmaceutical chemistry, natural medicinal chemistry, to manufacturing of drug production.

Effect of radial distribution of injected flow on simulated moving bed performance

In the modeling of a simulated moving bed, several assumptions are considered, the key assumption is there are no radial concentration gradients based on perfect mixing. However, it is difficult to achieve perfect mixing because the injected flowrate of the bed is periodically changed in the process. In this study, the performance of the simulated moving bed process was analyzed when the injected flow such as the feed or desorbent stream was unevenly distributed. To this end, the distribution function of the injected flow was calculated and applied to the model. Two types of distribution functions were obtained using the experimental results of a previous study, and the simulation results were compared with classical modeling assuming perfect mixing. In the base case simulation, the purity was similar in all cases, the productivity was higher more than 5% in the even distribution case compared to the most uneven distribution case. The effect of distribution was analyzed through sensitivity analysis by changing the overall flow rate, switching time, bed length, and flow rate of sections 2 and 3. As a result, regardless of the distribution applied, the trends of the performance parameters were the same. However, the more uneven the distribution, the greater the difference in productivity, recovery, and desorbent consumption compared to the even distribution case. It was confirmed that the design that distributes the injected flow more evenly has a better performance.

Optimal performance comparison of the simulated moving bed process variants based on the modulation of the length of zones and the feed concentration

The VariCol and ModiCon processes are two variants of the simulated moving bed (SMB) process, characterized by the modulation of the length of zones of the chromatographic column train and the feed concentration. These features give more flexibility than the conventional operation, leading to essential improvements in the separation and purification of mixtures. The optimal performance comparison of these two variants, the hybrid formed by their combination, and the conventional SMB process are scarce in the literature. This comparison helps discover new characteristics of each single and combined operation mode and creates guidelines to select the appropriate operation mode for possible real applications. In this work, the performance comparison of the ModiCon, VariCol, ModiCon+VariCol, and SMB processes is carried out in terms of maximal throughput for specific product purity values. Particular emphasis is placed on both the ModiCon and the hybrid ModiCon+VariCol processes characteristics. A strategy for combining and optimizing the ModiCon and the VariCol processes was determined. As a case study, the enantioseparation of guaifenesin was considered. In the ModiCon process, more than two modulation subintervals did not improve the performance in the separation. The optimal pattern, based on two subintervals, has zero feed concentration in the first subinterval and the maximal concentration in the second one. The best result for the hybrid operation (ModiCon+VariCol) was reached when the feed port moves simultaneously as the SMB process switching period. The optimal throughput of the ModiCon and the ModiCon+VariCol processes was almost doubled than that of the SMB process. These performances were based on larger zones I and II and not in zones II and III as occur with the SMB and VariCol process. The throughput in the hybrid operation increases more significantly than the ModiCon process when 5 columns were considered instead of 6. The hybrid operation could be more attractive for a system with a few numbers of columns.

Separation Processes to Provide Pure Enantiomers and Plant Ingredients

Enantiomer separation and the isolation of natural products from plants pose challenging separation problems resulting from the similarity of molecules and the number of compounds present in synthesis or extract mixtures. Furthermore, limited theory is available to predict productivities for possible alternative separation techniques. The application and performance of chromatography- and crystallization-based processes are demonstrated for various case studies devoted to isolating valuable target compounds from complex initial mixtures. In all cases, the first emphasis is set to determine the process-specific phase equilibria to identify feasible process options. For all examples considered, yields and productivities are evaluated and compared for different scenarios. Guidelines to approach and solve similar separation tasks are given.

Chiral Separations in Preparative Scale: A Medicinal Chemistry Point of View

Enantiomeric separation is a key step in the development of a new chiral drug. Preparative liquid chromatography (LC) continues to be the technique of choice either during the drug discovery process, to achieve a few milligrams, or to a scale-up during the clinical trial, needing kilograms of material. However, in the last few years, instrumental and technical developments allowed an exponential increase of preparative enantioseparation using other techniques. Besides LC, supercritical fluid chromatography (SFC) and counter-current chromatography (CCC) have aroused interest for preparative chiral separation. This overview will highlight the importance to scale-up chiral separations in Medicinal Chemistry, especially in the early stages of the pipeline of drugs discovery and development. Few examples within different methodologies will be selected, emphasizing the trends in chiral preparative separation. The advantages and drawbacks will be critically discussed.

Innovation of Expanded-Bed Adsorption by Integrating Simulated Moving-Bed Technology

Bio‐based industries need efficient downstream solutions to process complex streams. This was addressed through a technology integration approach, where expanded‐bed adsorption (EBA) is integrated with simulated moving‐bed (SMB) technology. Current work involved adaptation of an SMB apparatus and control principle to implement expanded‐bed level control. As an outcome, EBA‐SMB technology was successfully applied for purification of γ‐aminobutyric acid (GABA). This resulted in two‐fold increase in productivity and a GABA purity ≥ 92 % in one step from unclarified fermentation broth, compared to ≥ 93 % purity in case of clarified broth and packed‐bed SMB. These results proved that EBA‐SMB technology is able to enhance process efficiency and economics of bioprocesses.

Model-based design of an intermittent simulated moving bed process for recovering lactic acid from ternary mixture

An intermittent simulated moving bed (3F-ISMB) operation scheme, the extension of the 3W-ISMB to the non-linear adsorption region, has been introduced for separation of glucose, lactic acid and acetic acid ternary-mixture. This work focuses on exploring the feasibility of the proposed process theoretically and experimentally. Firstly, the real 3F-ISMB model coupled with the transport dispersive model (TDM) and the Modified-Langmuir isotherm was established to build up the separation parameter plane. Subsequently, three operating conditions were selected from the plane to run the 3F-ISMB unit. The experimental results were used to verify the model. Afterwards, the influences of the various flow rates on the separation performances were investigated systematically by means of the validated 3F-ISMB model. The intermittent-retained component lactic acid was finally obtained with the purity of 98.5%, recovery of 95.5% and the average concentration of 38 g/L. The proposed 3F-ISMB process can efficiently separate the mixture with low selectivity into three fractions.