Bed Chromatographic Separation Research Articles

Modelling binary non-linear chromatography using discrete equilibrium data

The determination and description of adsorption equilibria is critical for the design of several separation processes. In some instances, the dependence of the solid phase loading on the fluid phase concentration is complex and it is difficult to find a suitable functional form to represent the adsorption equilibria. This difficulty can be overcome by the use of discrete equilibrium data, i.e., using the experimental data of solid phase loadings and the corresponding fluid phase concentrations in its discrete form, without the use of a functional form to describe the adsorption isotherms. In this work we demonstrate how discrete equilibrium data can be used to predict binary competitive equilibria using the ideal adsorbed solution theory. Two approximations to generate data outside the range of measured values are proposed. The effectiveness of these methods in predicting competitive equilibria and elution profile of binary injections is demonstrated using numerical simulations. The application of this framework to estimate the regions of achievable separation for a multi-column simulated moving bed chromatographic separation is also discussed.

An optimal three fractions yielding simulated moving bed chromatographic separation: Triple switch SMBC

Among the various degrees of freedom Simulated moving bed chromatography possesses, the current work deals with manipulation of operating conditions comprising internal flow rates and switching period. The conventional mode of operation yields a single fraction of the extract and raffinate with a single set of operating conditions whereas the current work proposes a novel triple switch mode of operation which is characterised by three sets of internal flow rates and switching period and yields three fractions. Under optimal conditions, the higher degrees of freedom have the potential of yielding higher extract purities than conventional as well as dual switch modes of operation with two sets of operating conditions. A multi-objective optimisation problem has been solved which maximizes the purity of one of the three extract fractions, for a certain minimum extract recovery and minimum feed flow rate. It is through a lower purity in two of the three fractions that a superior extract purity is achieved. This finding has been corroborated by a modeling based study on the linear adsorption isotherm based separation of fructose-glucose in deionised water on a cation exchange resin.

Model Predictive Control Method of Simulated Moving Bed Chromatographic Separation Process Based on Subspace System Identification

Simulated moving bed (SMB) chromatographic separation is a new type of separation technology based on traditional fixed bed adsorption operation and true moving bed (TMB) chromatographic separation technology, which includes inlet‐outlet liquid, liquid circulation, and feed liquid separation. The input‐output data matrices were constructed based on SMB chromatographic separation process data. The SMB chromatographic separation process was modeled by utilizing two subspace system identification algorithms: multivariable output‐error state‐space (MOESP) identification algorithm and numerical algorithms for subspace state‐space system identification (N4SID), so as to obtain the 3rd‐order and 4th‐order state‐space yield models of the SMB chromatographic separation process, respectively. The model predictive control method based on the established state‐space models is used in the SMB chromatographic separation process. The influence of different control indicators on the predictive control system response performance is discussed. The output response curves of the yield models were obtained by changing the related parameters so that the yield model parameters are optimized set meanwhile. Finally, the simulation results showed that the yield models are successfully controlled based on the each control period and given yield range.

Dowex 1X4 and Dowex 1X8 as substitute of Diaion MA03SS in simulated moving bed chromatographic separation of sulfuric acid and sugars in concentrated sulfuric acid hydrolysates of bamboo

Abstract To find commercially available ion exchange resins comparable to a strong-base anion exchange resin Diaion MA03SS, which is specialized for the separation of sulfuric acid and sugars in concentrated sulfuric acid hydrolysates of non-food biomass by means of a simulated moving bed (SMB) chromatography, the screening test of 6 kinds of commercially available resins containing quaternary ammonium groups was carried out by a batch column-mode chromatographic separation of glucose and sulfuric acid at 50 °C. Based on results of the screening test, Dowex 1X4 and Dowex 1X8 were selected as replacements of Diaion MA03SS. The following SMB study using Diaion MA03SS, Dowex 1X4 and Dowex 1X8 at 50 °C clarified that Dowex 1X8 showed performances almost the same as those of Diaion MA03SS in the separations of sulfuric acid and sugars (mainly glucose and xylose) in hydrolysates of bamboo with 27 wt% sulfuric acid under the averaged flow rate of feed loading from 0.136 to 0.273 L/(h L-resin). For Dowex 1X8, recoveries of sulfuric acid were 90.5–93.4% and recoveries of glucose and xylose were 94.9–99.7% and 82.8–88.3%, respectively. Dowex 1X4 showed slightly higher recoveries for three solutes; namely sulfuric acid recoveries were 95.0–95.5% and glucose and xylose recoveries were 100–101% and 86.1–91.7%, respectively. However, the highest averaged flow rate of feed loading for Dowex 1X4 was 0.205 L/(h L-resin) because of the higher column pressure loss owing to its high shrinking in 30 wt% sulfuric acid. Thus, it became clear that Dowex 1X8 exhibit excellent performances comparable to or higher than those of Diaion MA03SS in the SMB chromatographic separation of sulfuric acid and sugars in concentrated sulfuric acid hydrolysate of bamboo.

An optimization-driven novel operation of simulated moving bed chromatographic separation

Improvements of conventional SMB operation, such as in Varicol, Modicon, and Powerfeed, have enhanced SMB performance in the past decade. In this work, we propose a novel strategy that incorporates changing internal flow rates and switching periods periodically to enhance flexibility of operation and simultaneously enhance the purity of key product. This mode of operation, called as a dual switching strategy, has been investigated from a modelling perspective with simulation studies to validate the findings. The study incorporates detailed multiobjective optimization problem formulation focusing on performance metrics such as extract purity, recovery and throughput. Unlike the classical SMB processes, dual switching offers a wider scope with its larger degrees of freedom to mutually enhance purity and concentration of key product without the need for SMB configuration modifications. The results reveal a possible fractionating effect on the product side leading to two different purity fractions. Superior performance over the conventional operation has been validated by comparison with classical operation on an SMBC process for separation of glucose and fructose using Ca++ exchange resin.

Cycle to cycle adaptive control of simulated moving bed chromatographic separation processes

The simulated moving bed (SMB) technology is increasingly applied in various fields, ranging from the food to the pharmaceutical sectors, for the chromatographic separation of fine (bio)chemicals. In this study, an adaptive controller acting on the fluid flow rates and commutation period is used to regulate the spatial location of the adsorption and desorption waves, and in turn the purity and productivity of the raffinate and extract effluents. This controller is based on a simple discrete-time model of the concentration fronts movement, derived from wave theory. A simple parameter adaptation scheme makes this controller robust to parameter uncertainties and drifts, and allows process start-up with minimum a priori knowledge of the separation parameters. In this study, the performance of the controller is demonstrated for two different applications: the separation of fructo-oligosaccharides (linear isotherms) and cyclopentanone–cycloheptanone (competitive Langmuir isotherms). Different plant/sensor configurations are also examined, indicating the potential of the control strategy even with reduced measurement information.

A simple robust control for simulated moving bed chromatographic separation

Simulated moving bed (SMB) is a continuous chromatographic process used for the separation of chemical mixtures. This paper presents an almost plug-and-play control strategy, which requires little prior knowledge about the adsorption properties. A discrete-time nonlinear model derived from the wave theory is the basis to control the position of the adsorption and desorption fronts. The front velocities are estimated on-line enabling the compensation of initial parameter discrepancies, and drift due to adsorbent aging or temperature fluctuation. The overall performance of the control strategy is evaluated using numerical simulation for two case studies relative to the separation of fructo-oligosaccharides and cyclopentanone – cycloheptanone, respectively.

Simulated Moving Bed Chromatographic Separation of a Two-Component Steroid Mixture

A method, combining laboratory scale equilibrium and elution experiments, simplified model based and heuristic rules, as well as sophisticated dynamic simulation was applied to design the separation of a two-component steroid crude mixture in a given laboratory-scale Simulated Moving Bed unit. The adsorption equilibrium isotherms of the pure components were determined by Frontal Analysis method. Langmuir isotherm model was fitted to the measured isotherm data. With the knowledge of these a priori data, elution chromatograms of the pure components were measured for the identification of the hydrodynamic and kinetic parameters in the SMB columns. The process simulation was made by the new method, based on the Direct Computer Mapping of the Generic, Bi-layered Net model. The first estimations of the SMB parameters were derived by means of the Morbidelli’s triangle theory. Starting from a feasible solution, stepwise improvement of the SMB process was carried out by the detailed dynamic simulation, according to a strategy, based on the role of the design parameters. Simultaneously, some laboratory-scale SMB experiments were carried out. Good agreement of the measured and calculated data was found. Recently, the dynamic simulation has been applied for the increase of the production rate of the SMB separation.

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.

Modellierung und effektive numerische Simulation von chromatographischen Trennprozessen im SMB‐Betrieb

AbstractModeling and Efficient Computational Simulation of Simulated Moving Bed Chromatographic Separation Processes.Chromatographic separation processes provide a powerful tool for the separation of mixtures in which the components have different adsorption affinities, especially when high purities are required. In this area, simulated moving bed (SMB) technology is becoming an important technique for large‐scale continuous chromatographic separation processes since it provides the advantages of a continuous countercurrent operation while avoiding the technical problem of a true moving bed. Because of the complex dynamics of the process, the choice of the optimal operation parameters and the control of the process in order to keep the product specifications at any time is not straightforward. For this challenging task, a reliable dynamic model of the process is necessary which is accurate enough as well as efficient enough in order to permit its online use for model based control. The purpose of this contribution is to review the state of the art in dynamic modeling of SMB chromatographic separation processes, highlighting new trends and results in the design of computationally effective simulation models suitable for online applications.

A MILP-method for optimizing a preparative simulated moving bed chromatographic separation process

In the present paper a mixed integer linear programming (MILP) formulation for a chromatographic separation process is described. What in this case makes the paper especially interesting, is the fact that hardly any mathematical programming method has been described for this kind of separation system, although many formulations have been described for other kinds of separation systems, e.g. distillation. The objective is to formulate the process in a linear form and to optimize the production.