Performance Of Simulated Moving Bed Research Articles

Shortcut design method for multicomponent gradient simulated moving beds

AbstractThis work describes a method for design (and verification) of isocratic and gradient simulated moving bed (SMB) chromatography, based on the triangle theory. The method is tested using both constant selectivity and nonconstant selectivity isotherms as well as implicit and explicit isotherms through the Linear, Langmuir, and SMA isotherms. The results show that the method is applicable to a wide range of isotherms and to multicomponent systems. The study also investigates the influence of modifier concentrations on gradient SMB performance, by determining the optimal flow rate ratios for calculating volume‐specific productivity and eluent consumption. These findings demonstrate the potential of the method to improve the performance of a gradient SMB and serve as a useful initial step in the design and optimization of operational flow rates and modifier concentrations.

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.

Experiment and modeling for the separation of guaifenesin enantiomers using simulated moving bed and Varicol units

The separation of guaifenesin enantiomers by both simulated moving bed (SMB) process and Varicol process was investigated experimentally and theoretically, where the columns were packed with cellulose tris 3,5-dimethylphenylcarbamate (Chiralcel OD) stationary phase and a mixture of n-hexane and ethanol was used as mobile phase. The operation conditions were designed based on the separation region with the consideration of mass transfer resistance and axial dispersion, and the experiments to separate guaifenesin enantiomers were carried out on VARICOL-Micro unit using SMB process with the column configuration of 1/2/2/1 and Varicol process with the column configuration of 1/1.5/1.5/1, respectively. Single enantiomer with more than 99.0% purity was obtained in both processes with the productivity of 0.42genantiomer/dcm3 CSP for SMB process and 054genantiomer/dcm3 CSP for Varicol process. These experimental results obtained from SMB and Varicol processes were compared with those reported from literatures. In addition, according to the numerical simulation, the effects of solid-film mass transfer resistance and axial dispersion on the internal profiles were discussed, and the effect of column configuration on the separation performance of SMB and Varicol processes was analyzed for a few columns system. The feasibility and efficiency for the separation of guaifenesin enantiomers by SMB and Varicol processes were evaluated.

Enhanced performance of a three-zone simulated moving bed chromatography for separation of succinic acid and lactic acid by simultaneous use of port-location rearrangement and partial-feeding

The performance of a three-zone simulated moving bed (SMB) chromatographic process for separation of succinic acid and lactic acid has been improved to a certain extent in previous researches by applying either a partial-feeding (PF) or a port-location rearrangement (PR) to its operation. To make a further improvement, the strategy of applying both PF and PR simultaneously to the three-zone SMB operation was proposed in this study. The results from both equilibrium-theory analysis and detailed simulation proved that the proposed strategy, which was called PF–PR in this article, had the benefit of a synergy between the individual merits of PF and PR in the three-zone SMB performance. As a consequence, the PF–PR mode could surpass the PF and the PR modes by a wide margin and the classical mode by a dramatic margin in the aspects of separation performance and throughput.

Model-based identification of optimal operating conditions for amino acid simulated moving bed enantioseparation using a macrocyclic glycopeptide stationary phase

Teicoplanin aglycone columns allow efficient separation of amino acid enantiomers in aqueous mobile phases and enable robust and predictable simulated moving bed (SMB) separation of racemic methionine despite a dependency of the adsorption behavior on the column history (memory effect). In this work we systematically investigated the influence of the mobile phase (methanol content) and temperature on SMB performance using a model-based optimization approach that accounts for methionine solubility, adsorption behavior and back pressure. Adsorption isotherms became more favorable with increasing methanol content but methionine solubility was decreased and back pressure increased. Numerical optimization suggested a moderate methanol content (25–35%) for most efficient operation. Higher temperature had a positive effect on specific productivity and desorbent requirement due to higher methionine solubility, lower back pressure and virtually invariant selectivity at high loadings of racemic methionine. However, process robustness (defined as a difference in flow rate ratios) decreased strongly with increasing temperature to the extent that any significant increase in temperature over 32°C will likely result in operating points that cannot be realized technically even with the lab-scale piston pump SMB system employed in this study.

Backfill-simulated moving bed operation for improving the separation performance of simulated moving bed chromatography

The Backfill-SMB (BF-SMB) strategy was designed to improve the separation performance of simulated moving bed (SMB) chromatography. In the BF-SMB operation, a limited amount of products from raffinate and/or extract was re-fed to the SMB circuit as a backfill-feed. Two additional operating variables, backfill ratio (BR) and backfill length (BL), were suggested to determine the amount and injection length of backfill-feed. This strategy was applied to a four-zone SMB with one column (1-1-1-1) and two columns (2-2-2-2) per zone using a binary mixture with a nonlinear isotherm. Various BF-SMB operational methods were designed to supply backfill-feed to the feed node and/or intermediate node. The separation performances of conventional SMB and BF-SMB were compared in terms of purity, recovery, and eluent consumption. The BF-SMB successfully improved the separation performance of the conventional SMB because backfill-feed led to the rich condition of the main component at each product withdrawal node. Due to the ‘TMB effect’ caused by backfill-feed, the BF-SMB operation was more efficient in the 1-1-1-1 configuration than in the 2-2-2-2 configuration, showing maximum improvement of 5–7% purity and recovery from the performance of conventional SMB. In addition, partial recycling of eluent by backfill-feed resulted in a decrease in eluent consumption up to 10% even with improved purity and recovery in BF-SMB.

A three-zone simulated moving-bed for separation of immunoglobulin Y

Separation of immunoglobulin Y (IgY) from hen eggs is an interesting topic for investigating antibody purification. Understanding of IgY separation by chromatography is necessary to prepare antibody. IgY preparation in SMB was simulated by Aspen chromatography and was experimented by assembling a 3-zone simulated moving bed (SMB). With change of stream flow rates, the SMB performance was studied. Simulation of IgY batch HPLC chromatography was also done and confirmed by HPLC experiments. Based on these, good operating conditions of SMB chromatography were determined. Three-zone SMB equipment was set up by connecting three C18-HPLC columns, four HPLC pumps, and six multiposition valves. Batch chromatography of IgY was conducted to determine the isotherms of IgY and contaminating impurity. The outlet streams of SMB, raffinate and extract were sampled and analyzed by analytical HPLC system. The adsorption isotherms of IgY and impurity were determined as HIgY=0.1 and Himpure=1.1. The highest experimental purity of IgY from SMB was obtained as 98% for the operating parameters of Qfeed=0.2mL/min, Qdesorbent=0.31 mL/min, Qextract=0.2 mL/min, Qraffinate=0.3 mL/min, and switching time=8.47 min.

Improving performance of a five-zone simulated moving bed chromatography for ternary separation by simultaneous use of partial-feeding and partial-closing of the product port in charge of collecting the intermediate-affinity solute molecules

The performance of a five-zone simulated moving bed (SMB) chromatographic process for ternary separation has been improved to a certain extent in previous researches by applying either a partial-feeding (PF) or a partial-closing of the extract-2 port (PCE 2) to its operation. To make a further improvement, the strategy of applying both PF and PCE 2 simultaneously to the five-zone SMB operation was proposed in this study. The results from both equilibrium-theory analysis and detailed simulation proved that the proposed strategy, which was called PF-PCE 2 in this article, had the benefit of a synergy between the individual merits of PF and PCE 2 in the five-zone SMB performance. As a consequence, the PF-PCE 2 mode could surpass the PF and the PCE 2 modes by a wide margin and the standard mode by a much wider margin in the aspects of ternary-separation performance and throughput. For the separation system considered, the PF-PCE 2 mode was found to achieve more than 100% improvement, compared to the standard mode. Furthermore, such advantage of the PF-PCE 2 over all the other modes was greater as the selectivity between the intermediate-affinity and the highest-affinity components was reduced.

Partial port-closing strategy for obtaining high throughput or high purities in a four-zone simulated moving bed chromatography for binary separation

The “partial port-closing” operation strategy for a four-zone simulated moving bed (SMB) chromatographic process for binary separation was developed to improve the SMB performance. This strategy included the partial extract-closing (PEC) and the partial raffinate-closing (PRC) operations. In case of the PEC operation, the extract port is made to be closed during the first-half stage of a switching period. During the latter-half stage, the extract port is made to be open. In case of the PRC operation, the raffinate port is made to be open during the first-half stage of a switching period. During the latter-half stage, the raffinate port is made to be closed. If the operating conditions are chosen properly in each operation using a highly efficient optimization tool, the product stream can be collected during only the period that the product is almost separated from impurity. During the other period that the product is contaminated with impurity, the collection of the product stream can be stopped by closing the product port. The uncollected product stream is then allowed to keep migrating through the adjacent zone within the SMB process. Such a partial port-closing operation including PEC and PRC was found to surpass a conventional SMB operation remarkably in throughput and product purity.

Enhanced Separation Performance of a Five-Zone Simulated Moving Bed Process by Using Partial Collection Strategy Based on Alternate Opening and Closing of a Product Port

A five-zone simulated moving bed (SMB) process for ternary separation has been developed previously and applied to the purification of biochemicals in the literature. Although this process was effective to some degree in many of previous research studies, its separation performance was always limited by the presence of overlap between the highest-affinity and the intermediate-affinity solutes. Since a proper control of the overlap was almost impossible under the current configuration and operation method, the application scope of a conventional five-zone SMB was restricted within the separation tasks that permitted either relatively medium purities or low throughput. To overcome such a limitation, an efficient operation strategy for improving the five-zone SMB performance was proposed in this study. The core of the proposed strategy is to partially collect the product stream by alternate opening and closing of the extract-2 port, which is in charge of recovering the intermediate-affinity solute molecules. Simultaneously, the zone II flow rate during the port-opening state is adjusted properly for complete desorption of the intermediate-affinity solute in zone II. The application of such a strategy was found to improve the five-zone SMB performance dramatically. One of the noteworthy improvements was that all three products could be recovered with extremely high purities at the same time. Furthermore, a marked increase in the throughput could also be obtained under the given purity requirements. Therefore, the strategy proposed in this study is expected to substantially upgrade the five-zone SMB performance, allowing its application to the separation tasks that demand either high purities or high throughput.

Simulated moving bed separation of tocopherol homologues: simulation and experiments

Chromatograms of tocopherol homologues were obtained by a column of analytical size (inner diameter (ID) 0.46 cm cm×10 cm) packed with silica gel. Adsorption isotherms and film mass-transfer coefficient were estimated from the chromatograms by using a general rate model, which considers axial dispersion, external mass-transfer and intraparticle diffusion. Based on the obtained isotherms and mass-transfer coefficient, the separation process of tocopherol homologues on simulated moving bed (SMB) was simulated using the same model. According to the simulated results, a mixture of α-, γ-, δ-tocopherols and other impurities was separated on an SMB equipment. The SMB equipment was composed of 8 columns of ID 2 cm×10 cm, with 2 columns in each section. The solid phase was silica gel, and the mobile phase was n-hexane/2-propanol (99/1 by volume). γ- and δ-tocopherols of purity greater than 98% were obtained with recovery greater than 98%. The effects of operating conditions (flow rates and switching time) on the performance of SMB were studied by both simulation and experiments. It was found that all the simulation results were quite close to the experimental results. We conclude that process development and optimization of operating conditions of SMB by simulation are feasible.

Effect of Subdividing the Adsorbent Bed in a Five‐Zone Simulated Moving Bed Chromatography for Ternary Separation

A five‐zone simulated moving bed (SMB) chromatography, which has been successful in achieving a ternary separation so far, was optimized in this study to separate three nucleoside components (2′‐deoxycytidine, 2′‐deoxyguanosine, and 2′‐deoxyadenosine) with high purity. For such an optimized process, we investigated how the subdivision of its chromatographic bed affects the wave dynamics and separation performance, which has been one of the important issues in the area of a continuous chromatographic separation process design. It was found that the migration or propagation behavior of the highest affinity component (2′‐deoxyadenosine) virtually controlled the wave dynamics and separation performance of the five‐zone SMB chromatography. Unlike the lowest affinity and the intermediate affinity components (2′‐deoxycytidine and 2′‐deoxyguanosine), the highest affinity component generated more than two solute bands, which were scattered in several zones. As the degree of bed subdivision became higher, the scattered solute bands of the highest affinity component were gradually merged, leading to a seemingly single solute band with a wavy plateau. Eventually, the wavy plateau became flat. Such behavior of the highest affinity component brought about a visible change in its average concentrations at the two product ports, and a significant reduction in the purity of the intermediate affinity component. The results of this study can serve as a useful summary of five‐zone SMB behaviors, and as the first step for the development of new strategies on five‐zone SMB performance.

Operation Strategies for Simulated Moving Bed in the Presence of Adsorbent Ageing

The effect of adsorbent ageing on the operation of Simulated Moving Bed (SMB) units is addressed, for two different systems (linear and non‐linear isotherms). Two different consequences of adsorbent deactivation are considered, one involving the loss of adsorption equilibrium capacity and the other related to the increase of mass transfer resistance. For each of these cases one direct and straightforward compensation measure is presented: the increase of the solid velocity (decrease of switching time) to compensate the adsorbent capacity decline and the decrease of solid and internal flow rates to compensate the mass transfer resistances increase. It is possible to compensate the adsorbent capacity decline, maintaining all SMB performance parameters, limited to the reduced contact time when high solid velocities are used. In the second case, when mass transfer resistance increases, it has been shown that the direct compensation strategy would lead to a decrease of productivity, to keep the same purity and recovery as with fresh adsorbent. Another possible corrective method to the ageing problem is the use of variable switching times in the non‐conventional “modus operandi”‐Varicol, a sort of re‐arrangement of the SMB columns distribution by sections, here tested for the case of adsorbent capacity decline case as a consequence of adsorbent ageing mechanisms.

Large scale nonlinear optimization for asymmetric operation and design of Simulated Moving Beds

Simulated Moving Bed (SMB) was developed as a realization of continuous countercurrent operation of chromatographic separation. An SMB unit consists of several columns of the same length connected in series, where feed and desorbent are supplied and extract and raffinate are withdrawn continuously. This operation is repeated by shifting the supply/withdrawal points at a regular interval, making the operation symmetric. In this study, we explore asymmetric operation and design through a full-cycle optimization model, where the operation of the entire cycle is described within a nonlinear programming (NLP) problem and the Partial Differential Algebraic Equations (PDAEs) are fully discretized both in temporal and spatial domains. The NLP problem is implemented within the AMPL modeling environment and is solved using IPOPT, an interior-point NLP solver. We found that this problem is solved efficiently, and introducing a full-cycle formulation has the potential to improve the performance of SMB, as shown through single and multi-objective optimization studies.

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 Tröger'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.

Novel Analytical Solution for a Simulated Moving Bed in the Presence of Mass-Transfer Resistance

A novel analytical solution for a simulated moving bed (SMB) with a linear adsorption equilibrium isotherm in the presence of mass transfer was derived. The proposed solution is based on the equivalent steady-state true moving bed (TMB) analogy. This analytical solution allows for the calculation of the liquid and solid concentration profiles in all sections of the SMB. The analytical solution was used in the prediction of the “separation volume” for glucose/fructose separation. Emphasis was placed on the effects of the liquid/solid velocity ratios in sections I and IV (γI and γIV, respectively) on the performance of the SMB. The value of γI more significantly affects the SMB performance than the value of γIV and should be tuned carefully in a narrow zone of values. The main advantage of the presented solution is the rapid determination of the separation volume in the presence of mass-transfer limitations, according to the required purity of the extract and raffinate.

Continuous Separation of Enantiomers by Simulated Moving Bed Chromatography: Effect of Operating Parameters on the System Performance

The separation of 1,1’-bi-2-naphthol racemic mixtures by the simulated moving bed (SMB) method with chiral columns of Pirkle D-Phenylglycine was investigated in this study. First, a steady-state true moving bed (TMB) model, considering non-linear equilibrium, lumped kinetic and axial dispersion effects, was developed for predicting the cyclic steady-state behavior of the SMB system. The “triangle theory” was used to provide guidelines for the selection of feasible operating parameters of the SMB system, including liquid flow rates, switch time, feed concentration and zone length. Then, the effect of various operating parameters on the SMB performance, characterized by product purity, recovery, solvent consumption, and productivity, and the exact good separation region were studied through simulation of the TMB model. The package is an important tool to select the optimal operating conditions for the SMB operation.

Influence of the Transfer Line Dead Volume on the Performance of an Industrial Scale Simulated Moving Bed for p-Xylene Separation

The modeling and simulation of simulated moving bed (SMB) unit is needed for the choice of its operating conditions; however, it usually does not consider the surrounding equipment (pipe transfer lines, valves, and pumps). The effect of the dead volume on SMB performance is normally associated with laboratory scale units, where the volume of the surrounding equipment could represent significant part of SMB unit volume. The presence of the dead volume is also significant in the industrial-scale SMB units applied for production of high purity component; for example, p-xylene. Different techniques are applied in industry to overcome the negative impact of the dead volume on the SMB performance. In this work, the UOP technique for flushing of the transfer lines before withdrawing the extract, applied in Parex process/(industrial scale SMB unit for p-xylene separation) was analyzed. First, the need of the flushing lines was assessed by simulation of SMB unit in presence of the transfer lines’ dead volume. The simulated moving bed strategy of modeling was used; the transfer lines’ dead volume was introduced into the model through the node mass balances and was assumed as plug flow and continuous stirred tank in different stages of the transfer line use. The transfer lines’ dead volume has negative effect on the extract purity. The extract purity falls to 85.54% and 75.22% when the total transfer line dead volume is 0.6% and 1% of the total SMB unit volume, respectively. The advantage of the flushing lines in presence of transfer line dead volume was demonstrated by simulation of Parex unit allowing extract purity above 99.9% and recovery above 98.5%.

Modeling and Simulation of a Simulated Moving Bed for the Separation of p-Xylene

The industrial-scale adsorptive separation of p-xylene from a mixture of C8 aromatics in a four-section simulated moving bed (SMB) unit is analyzed through simulation. In the order to describe the behavior of the SMB unit by means of a mathematical model, two approaches were used: the true moving bed (TMB) approach and the SMB approach. Both approaches assume a constant selectivity nonstoichiometric Langmuir isotherm, an axial dispersion for the fluid flow, and a linear driving force for the intraparticle mass transfer. The TMB and SMB model predictions of steady-state performance of the SMB unit are very close. Therefore, the TMB model was selected to study the effect of the switching time period, adsorbent deactivation, and mass-transfer resistances on the process performance. The adsorbent deactivation which occurs during its lifetime will influence the SMB performance; to keep the p-xylene purity and acceptable recovery, the switching time should be decreased. The TMB package is a useful tool for fast visualization of the SMB process behavior under particular operating conditions. The novel “separation volume” methodology is used to find the operating conditions of the SMB unit in the presence of mass-transfer resistances.

The use of simulated moving bed in chromatographic separation: study of the SMB configuration

The simulated moving bed (SMB) unit in a chromatographic separation of enantiomers has been modeled and simulated by a computational program. The mathematical model of the unit considers the plug flow model with axial dispersion for the fluid phase and the linear driving force approximation for the intraparticle mass transfer rate. The model assumes the switching of the inlet and outlet streams of the unit for each time interval, and then, allows accompanying the evolution of the internal profiles of enantiomer concentration for the transient operation of the SMB. The mathematical equations with the respective boundary and initial conditions are numerically solved by finite volume method. The influence of bed configuration on the SMB performance has been studied using a computational program. However the purity and recovery of some species are slightly affected by configuration.