Design of simulated moving bed and Varicol processes for preparative separations with a low number of columns

Simulated moving bed (SMB) chromatography has received significant attention in the last decade, particularly as regards the production of very valuable products, such as enantiomerically pure pharmaceutical compounds. Recent applications in the pharmaceutical industry use SMB systems containing a low total number chromatographic columns, usually four to eight. This paper deals with the modeling and simulation of SMB systems with only four, five and six columns. In particular, two modeling strategies, the equivalent true moving bed and the real SMB models, are compared for these units in terms of separation regions and system productivity. Also, the recently proposed Varicol process is analyzed and compared with the classical SMB operation, and the advantages of this new operation mode are shown for systems using a low number of columns.     

Simulated moving bed chromatography for the separation of enantiomers

Simulated moving bed (SMB) chromatography, a continuous multi-column chromatographic process, has become one of the preferred techniques for the separation of the enantiomers of a chiral compound. Several active pharmaceutical ingredients, including blockbuster drugs, are manufactured using the SMB technology. Compared to single column preparative chromatography, SMB separations achieve higher productivity and purity, while reducing the solvent consumption. The SMB technology has found applications both at small and large scales. Design methods have been developed for robust operation and scale-up, using data obtained from analytical experiments. In the last few years, rapid developments have been made in the areas of design, improved process schemes, optimization and robust control. This review addresses these developments, as well as both the fundamentals of the SMB science and technology and some practical issues concerning the operation of SMB units. Particular emphasis is placed on the consolidation of the “triangle theory”, a design tool that is used both in the academia and industry for the design of SMB processes.     

Simulated moving bed technology with a simplified approach for protein purification. Separation of lactoperoxidase and lactoferrin from whey protein concentrate

Simulated moving bed (SMB) technology is a continuous chromatographic technique proven to have many advantages compared to conventional batch chromatography, such as: raised productivity and product concentration, reduced buffer consumption as well as more efficient use of raw material. In this study a 20 column SMB process for the separation of lactoperoxidase and lactoferrin from whey protein concentrate (WPC) was developed. A simplified approach with data from a single column experiment was used when designing the process. The SMB process data were compared to a theoretical scale-up of the breakthrough experiment reflecting the same 20 column set-up run in non-moving bed mode. The outcome of the comparison is a 48% raise in productivity, a 4.3 times decrease in buffer consumption, 6.5 times raise in target protein concentration with a raw material utilization which is slightly better for the SMB process.     

模拟移动床色谱法拆分甲霜灵对映体

模拟移动床(SMB)色谱作为一种精确、高效的制备色谱技术引起研究者的极大关注。本文以EnantioPak OD填料为手性固定相,正己烷-乙醇(70 : 30, v/v)为流动相,在四区模拟移动床上手性拆分甲霜灵外消旋体。采用旋光检测器研究甲霜灵异构体在手性柱上的洗脱顺序;探讨进样浓度、进样流速、各区流速和切换时间等条件对手性分离甲霜灵外消旋体的影响,并与制备色谱进行比较。结果表明:S-(+)-甲霜灵先于R-(-)-甲霜灵被流动相洗脱,R-(-)-甲霜灵在色谱柱上的保留强于S-(+)-甲霜灵;在线性和非线性条件下,模拟移动床都能很好地拆分甲霜灵外消旋体,在优化SMB工艺条件下,S-(+)-甲霜灵和R-(-)-甲霜灵的光学纯度都大于99%;在样品质量浓度为15 mg/mL的条件下,模拟移动床色谱分离的样品量显著高于制备色谱,而流动相消耗仅为后者的1/9。这对于发展大规模色谱拆分甲霜灵工艺具有良好的指导意义。     

Enantioseparation of a chiral epoxide by simulated moving bed chromatography using Chiralcel-OD

Summary The feasibility of using simulated moving bed (SMB) chromatography for the chiral separation of a racemic epoxide with Chiralcel-OD as the stationary phase is demonstrated on a semi-preparative scale. Operating conditions for the separation are chosen with the help of a simple chart that depicts visually the interrelationships between the system flow rates and the SMB design criteria. The 12 column (each 100 mm×16 mm ID) SMB system continuously resolved the racemic mixture at a rate of 11.5 g/24 hr into streams with 95% and 94.4% e.e. (enantiomeric excess). A comparison of the SMB process with an optimized multiple-injection conventional chromatographic separation showed similar specific production rates for both methods, but a seven-fold lower solvent consumption for the SMB.     

Continuous voltage gradients and their application to true moving bed electrophoresis

Gradient elution has been practiced in chromatographic separations for many years. The application of discontinuous "step" gradients in simulated moving bed (SMB) chromatography has been very successful in increasing both processing rates and column productivity, resulting in a reduction in the number of SMB columns required. With the advent of the field gradient focusing techniques, electrophoresis has gained the ability to apply a continuous electric field gradient to a true moving bed (TMB) electrophoretic separation. Application of a spatial gradient allows a large degree of control of the product concentrations inside the separation unit as well as a large increase in product throughput. A model of moving bed electrophoretic separations has been developed that demonstrates the potential advantages of applying a continuous gradient to the moving bed process. These advantages include the reduction of detrimental peak tailing and the ability to decrease the concentrations of the compounds being separated in comparison with commonly used step gradient elution.     

Optimization of a hybrid chromatography-crystallization process for the separation of Tröger's base enantiomers

This paper presents an analysis of a hybrid process consisting of simulated moving bed (SMB) chromatography and crystallization and studies its performance for the separation of the Tr?ger's base enantiomers. The SMB is simulated using a detailed model including column efficiency, thus, implying a proper evaluation of the effect of column size on column efficiency and separation performance. The crystallization operations are accounted for through material balances, assuming equilibrium between enantiopure crystals and mother liquor. A genetic algorithm is used to optimize the combined process, using proper definitions of objective functions. Multi-objective optimization of this hybrid process for productivity and evaporation cost in terms of operating parameters, column length, and SMB feed concentration shows an optimum SMB purity value as a trade off between increased SMB performance and recycle of the mother liquor.     

Optimal operation of simulated moving bed chromatographic processes by means of simple feedback control

In this contribution, simple methods are presented for controlling a simulated moving bed (SMB) chromatographic process with standard PI (proportional integral) controllers. The first method represents a simple and model-free inferential control scheme which was motivated from common distillation column control. The SMB unit is equipped with UV detectors. The UV signals in the four separation zones of the unit are fixed by four corresponding PI controllers calculating the ratio of liquid and solid flow in the respective separation zone. In order to be able to adjust the product purity a second, model-based control scheme is proposed. It makes use of the nonlinear wave propagation phenomena in the apparatus. The controlled chromatographic unit is automatically working with minimum solvent consumption and maximum feed throughput--without any numerical optimization calculations. This control algorithm can therefore also be applied for fast optimization of SMB processes.     

Regeneration of tetrabutylammonium ion-pairing reagent distribution in a gradient elution of reversed phase ion-pair chromatography

The regeneration of ion-pairing reagent distribution on liquid chromatography columns after gradient elution has been well recognized as the cause for long column equilibration time, a major drawback associated with gradient elution reverse phase ion-pair chromatography. To date, the majority of studies have focused on optimizing the separation conditions to shorten the equilibration time. There is limited understanding of the ion-pairing reagent distribution process between the mobile phase and stationary phase in the course of gradient elution, and subsequent column re-equilibration. The focus of this work is to gain a better understanding of this process. An ion-pair chromatographic system, equipped with a YMC ODS C(18) column and a mobile phase containing tetrabutylammonium (TBA) hydroxide as the ion-pairing reagent, was used in the study. The TBA distribution profile was established by measuring its concentration in the eluent fractions collected during the gradient cycle using different column equilibration times with an ion chromatographic method. Furthermore, the analyte retention time was evaluated as the function of the column equilibration time and TBA concentration in the mobile phase. The column equilibration and its impact on the method robustness will also be discussed.     

Model-based design of a pilot-scale simulated moving bed for purification of citric acid from fermentation broth

One of the conventional processes used for the recovery of citric acid from its fermentation broth is environmentally harmful and cost intensive. In this work an innovative benign process, which comprises simulated moving bed (SMB) technology and use of a tailor-made tertiary poly(4-vinylpyridine) (PVP) resin as a stationary phase is proposed. This paper focuses on a model-based design of the operation conditions for an existing pilot-scale SMB plant. The SMB unit is modeled on the basis of experimentally determined hydrodynamics, thermodynamics and mass transfer characteristics in a single chromatographic column. Three mathematical models are applied and validated for the prediction of the experimentally attained breakthrough and elution profiles of citric acid and the main impurity component (glucose). The transport dispersive model was selected for the SMB simulation and design studies, since it gives a satisfactory prediction of the elution profiles within acceptable computational time. The equivalent true moving bed (TMB) and SMB models give a good prediction of the experimentally attained SMB separation performances, obtained with a real clarified and concentrated fermentation broth as a feed mixture. The SMB separation requirements are set to at least 99.8% citric acid purity and 90% citric acid recovery in the extract stream. The complete regeneration in sections 1 and 4 is unnecessary. Therefore the net flow rates in all four SMB sections have been considered in the unit design. The influences of the operating conditions (the flow rate in each section, switching time and unit configuration) on the SMB performances were investigated systematically. The resulting SMB design provides 99.8% citric acid purity and 97.2% citric acid recovery in the extract. In addition the citric acid concentration in the extract is a half of its concentration in the pretreated fermentation broth (feed).     

双柱交替循环色谱分离甘露醇山梨醇过程

本文在非线性非平衡双柱循环色谱分离过程数学模型的基础上,进行了双柱交替循环色谱分离甘露醇山梨醇的实验,对模型进行了实验验证。结果表明：采用非线性非平衡双柱循环色谱模型计算的流出曲线与实验结果相吻合。计算机模拟的结果从理论上证明了对本实验体系采用双柱交替循环色谱分离模式比采用传统的色谱分离模式能获得更高的分离产率,产率随循环次数的增加而增加,使用双柱交替循环色谱分离操作模式获得的分离效率超过使用传统长色谱柱操作模式获得的分离效率。当轴向扩散比较严重、液固两相间的传质阻力较大,或者吸附的表观选择性系数较小时,采用双柱循环色谱模式比使用传统单柱色谱模式能获得更高的产率。     

Optimal design of batch and simulated moving bed chromatographic separation processes

Preparative chromatography, especially simulated moving bed (SMB) chromatography, is a key technology for the separation of fine chemicals on a production scale. Most of the design methods for batch and SMB processes proposed in the open literature deal with the optimisation of the operating conditions for a given chromatographic unit only. Therefore, a comparison of the process economy may lead to incorrect results. In this contribution, an effective strategy for the optimal choice of all process parameters (operation and design parameters) is proposed. The main idea of this strategy is to apply a detailed and experimentally validated process model and to reduce the number of influencing parameters by introducing and optimising dimensionless process parameters. It is shown that there is an infinite choice of design and operating parameters to achieve maximum productivity or minimum separation costs and not at the maximum pressure drop only. The detailed design of the chromatographic unit and the selection of the operating conditions can be adjusted by considering the availability of columns and packing materials. As the model system, the separation of a racemic mixture (EMD53986) on Chiralpak AD was investigated. After complete optimisation of a batch and a SMB unit, a real comparison of the process economy can be achieved. Finally, the influences of two different objective functions, productivity and specific separation cost, are analysed.     

On-line high-performance liquid chromatographic diode array spectrophotometric analysis of steroidal hormones in illegal preparations

An on-line high-performance liquid chromatographic diode array spectroscopic analytical method for the identification of more than 60 different steroidal compounds is described. For the chromatographic separation, a gradient elution that could distinguish the esterified and non-esterified steroids in the same run on a reversed-phase C18 column, using methanol as modifier, was developed. For both types of compound an internal standard was chosen to establish reproducible relative retention times that could be used as one element of the identification; the second element is the UV spectrum, which is recorded on-line during the separation. The combination of chromatographic and UV spectroscopic recordings selects only a few probable steroids, which could be the unknown. This approach has been applied to forensic analysis of illicit preparations used in cattle-breeding, some examples of which are shown. For those steroids that are very difficult to distinguish using this procedure, because of their chromatographic and spectroscopic similarity on this system, other solvent mixtures are used in place of methanol as modifier, namely acetonitrile or tetrahydrofuran, or both, with the same solvent strength, as proposed by Snyder. In this way totally different elution patterns and separations are obtained, providing complementary information for identification, as shown by the systematic analysis on two other isoeluotropic solvent systems.     

Liquid chromatography techniques for characterizing poly(Vinyl Alcohol)

Poly(vinyl alcohol) (PVOH) samples may contain several heterogeneities requiring the development of chromatographic techniques for characterization. Size exclusion separations have been carried out using a number of aqueous eluents, incorporating electrolyte, or electrolyte/organic modifier, or surfactant. The most favourable molecular size separation was obtained using 0.25% w/v sodium lauryl sulfate as eluent. Reasonable values for molecular weights of PVOH samples have been determined. Compositional distributions in copolymer systems can be assessed using high-performance liquid chromatography employing a reversed-phase separation mechanism. For poly(vinyl alcohol), gradient elution with water/tetrahydrofuran (THF) with a wide pore polystyrene-based packing produced separations dependent on degree of hydrolysis and sequence length distribution. The elution results were verified with a column packed with non-porous beads. Partially hydrolysed PVOH samples appeared to have a broad distribution of composition.     

Intermittent simulated moving bed chromatography: 1. Design criteria and cyclic steady-state

The intermittent SMB (I-SMB) process is a multi-column chromatographic process, which is a modification of the conventional SMB process, has been applied so far only in the sugar industry and is claimed to achieve higher productivity. In the I-SMB process the time interval between two port switches is divided in two sub-intervals, and only during the first the product streams are collected. The potential of the I-SMB technology is demonstrated in the case of the separation of a binary mixture subject to the linear isotherm by using both the equilibrium theory of chromatography and detailed simulations. It is shown that a I-SMB with only four columns can achieve much higher separation performance than a SMB unit with four columns.     

Active flow management in preparative chromatographic separations: a preliminary investigation into enhanced separation using a curtain flow inlet fitting and segmented flow outlet fitting

Active flow management in the form of curtain flow sample introduction and segmented outlet flow control has been shown to enable sample to elute through a chromatography column under the principles of the "infinite diameter column". Such an elution process avoids the detrimental effects of the heterogeneity of particle-packed chromatographic columns by injecting the sample directly into the radial core region of the column, thus avoiding wall effects. The process described herein illustrates how the principles of the infinite diameter column can be applied using conventional injection devices suitable for long-term analysis that requires robust protocols. Using this approach, sensitivity in separation was 2.5 times greater than conventional chromatography, yielding a product at twice the concentration. Benefits of curtain flow injection are thus relevant to both preparative-scale and analytical-scale separations.     

Construction and development of a new single-column simulated moving bed system on the laboratory scale

Simulated moving bed (SMB) chromatography combines high productivity and high purities with reduced buffer consumption. We have developed a laboratory scale single column SMB (SC-SMB) unit with all four separation zones in one column. Distributors embedded within the chromatographic medium allow introduction and withdrawal of liquid between the zones. This single column unit exhibits homogenous packing in all zones, reduced headspace, less complex tubing, fewer valves, and almost undisturbed plug flow between the separation zones. The separation performance of the column was investigated with two different binary model mixtures. Furthermore, the SC-SMB unit is operated with a modified AKTA Explorer workstation, which has been specifically developed for the handling of biological fluids.     

Application of Thin-Layer Chromatography to High-Performance Liquid Chromatographic Separation of Steroidal Hormones and Cephalosporin Antibiotics

Abstract

High-performance liquid chromatographic (HPLC) separation of steroidal hormones and cephalosporin antibiotics was investigated by adsorption chromatography and reversed-phase chromatography, respectively.

Prior to the HPLC separation of these pharmaceuticals, silica gel thin-layer adsorption chromatography of steroidal hormones and reversed-phase thin-layer partition chromatography of cephalosporin antibiotics with chemically bonded dimethylsilyl silica gel were performed in order to obtain suitable HPLC separation systems.

In the separation of steroidal hormones, the same binary mobile phase ratios of TLC did not give satisfactory results in HPLC. For the sharp separation in HPLC, solvent strength in the binary solvent mixture used for TLC had to be decreased.

The difference in solvent strength for efficient separation between TLC and HPLC might be attributed to the fact that in HPLC the solvent elution power acts in an isocratic manner while in TLC it acts in a gradient manner.

On the other hand, a correlation of mobility between TLC and HPLC separation for cephalosporin antibiotics was obtained, and the possibility of direct transfer of chromatographic systems from TLC to HPLC for separation of these antibiotics was confirmed.     

Calcium-modulated conformational affinity chromatography. Application to the purification of calmodulin and S100 proteins.

The purification of proteins by affinity chromatography is based on their highly specific interaction with an immobilized ligand followed by elution under conditions where their affinity towards the ligand is markedly reduced. Thus, a high-degree purification by a single chromatographic step is achieved. However, when several proteins in the crude mixture share affinity to a common immobilized ligand, they may not be resolved by affinity chromatography and subsequent "real" chromatographic purification steps may be required. It is shown that by using properly selected gradient elution conditions, the affinities of the various proteins towards the immobilized ligand may be gradually modulated and their separation may be achieved. This is exemplified by the isolation and separation of a group of Ca(2+)-activated proteins, Calmodulin, S100a and S100b, from bovine brain extract, using a melittin-Eupergit C affinity column which is developed with Ca(2+)-chelator gradients. As expected, separation of the three proteins into individual peaks, eluted in order of increasing affinity to the matrix, was obtained. Sigmoid selectivity curves calculated from the elution volumes under different elution conditions for each of the proteins were obtained, illustrating the chromatographic behaviour of the gradient affinity separation system.     

Chromatographic resolution of the enantiomers of a pharmaceutical intermediate from the milligram to the kilogram scale.

The preparative chromatographic resolution of racemic mixtures is rapidly becoming a standard approach for the generation of enantiomers in pharmaceutical R&D. This paper will discuss the optical resolution of a pharmaceutical intermediate as the separation is scaled up from the milligram to the kilogram scale. Difficulties encountered and their solutions at each scale will be discussed. In addition, the exploration of Simulated Moving Bed (SMB) for the separation will also be discussed. Finally, a comparison of the productivities and solvent consumption for each method and scale will be presented.