Single-cascade simulated moving bed (SMB) systems with a side-stream withdrawal are developed for separating ternary systems. Several single-cascade SMB systems are studied for the separation of ternary mixtures within the linear range. Design parameters, operating conditions, minimum desorbent-to-feed ratios, and productivities are determined with the local equilibrium theory, and purities are determined through detailed Aspen Chromatography simulations. A series of initial feed compositions are simulated to determine the optimal regions. The single-cascade SMB is particularly applicable when there is little of the most strongly adsorbed component, a significant amount of the middle component, and the separation between these components is easy. A surprising finding is that the purity of the middle-component product is usually higher in an SMB than in a true moving bed. A few quaternary separations with a side-stream SMB followed by a binary SMB are also studied.

Scaling rules and intensification procedures de®eloped for single adsorption or chromatographic columns are extended for both linear and nonlinear isotherms to simulated ( ) mo®ing-bed SMB systems. The effects of particle diameter, column length, column diameter, switching time, flow rates, mass transfer, axial dispersion, and dead ®olume are studied in order to design a new SMB. Changes in the pressure drop, separation, and throughput can be changed as desired. Once an original design has been de®eloped, the scaling procedure requires only algebraic manipulation. Simulations done by Aspen Chromatography showed that the new designs were remarkably good at producing the same product purities and pressure drops as the original design. Intensification is predicted when particle diameter is decreased. The limitations of the technique are that the number of columns per zone cannot be changed, the relati®e ®elocities in each zone are fixed, and for nonlinear systems the results apply only for the same feed concentration.

separation tasks occurs frequently in bio-product purification processes. The use of one more SMB unit, however, results in much higher operation and maintenance costs, compared to the use of a single SMB unit. It is obvious that the application of a single SMB unit is more advantageous if it can meet the product specification such as product purities.Recently, there have been several studies on the use of a single SMB unit for ternary separation or centre-cut separation. Among them, major attention has been paid to a single SMB unit with five zones (hereafter "five-zone SMB") (Beste and Arlt, 2002;Kim et al., 2003;Wang and Ching, 2005) and a single SMB unit with two zones (hereafter "two-zone SMB") Wankat, 2005, 2006;. The structure of a five-zone SMB is briefly explained below while the details of a two-zone SMB A ternary separation usually requires the use of two simulated moving bed (SMB) units in series. Since an increase in the number of SMB units leads to a significant increase in capital and operational costs, the use of a single SMB unit is preferred if its structure can be modified to treat a ternary separation. Such a modified single SMB unit has been typified by a five-zone SMB or a two-zone SMB so far. The separation performances of a five-zone SMB and a two-zone SMB are compared in this paper by using the ternary amino acid mixture as a model system. A five-zone SMB is designed with the safety margin method while a two-zone SMB is optimized using genetic algorithm. A five-zone SMB based on the maximum allowable safety margin, although it may not guarantee the global optimum solution, results in much better separation performance than a two-zone SMB at its global optimum state.Une séparation ternaire fait habituellement appel à deux unités de lits mobiles simulés (SMB) en série. Étant donné qu'une augmentation du nombre d'unités SMB entraîne une hausse significative des coûts en capital et de fonctionnement, l'utilisation d'une seule unité SMB est préférable si sa structure peut être modifiée pour traiter une séparation ternaire. Ce type d'unité SMB unique modifiée prenait jusqu'ici la forme d'un SMB à cinq zones et d'un SMB à deux zones. Dans cet article, on compare les performances de séparation d'un SMB à cinq zones et d'un SMB à deux zones en utilisant un mélange ternaire d'acides aminés comme système modèle. Un SMB à cinq zones a été conçu à l'aide d'une méthode avec marges de sécurité tandis que le SMB à deux zones a été optimisé à l'aide d'un algorithme génétique. Le SMB à cinq zones basé sur une marge de sécurité possible maximale, bien qu'elle ne garantisse pas forcément la solution optimale globale, présente une performance de séparation nettement meilleure que le SMB à deux zones à son meilleur état optimal.

The principles of simulated moving bed (SMB) and thermal swing adsorption (TSA) are combined to develop a traveling wave mode, thermally assisted SMB. The four-zone, thermal SMB and the corresponding one-column, thermal Analog to the SMB are studied for separating binary systems with linear isotherms. Design parameters and operating conditions are determined using the local equilibrium theory and detailed simulations are done with the commercially available chromatography/SMB software package Aspen Chromatography v12.1. Simulations were performed for the separation of toluene/xylene with silica gel as the adsorbent and n-heptane as the desorbent. The SMB and Analog are operated with a heat exchanger heating or cooling the fluid before it enters each adiabatic column. The advantage of the traveling wave mode compared to the direct mode of heat transfer is since heat transfer rates are not limiting, the SMB and Analog systems can be scaled up easily.

The design and synthesis of distillation cascades using side-stream columns with less than N -1 columns (two or one) for separations of relatively ideal four-component mixtures are studied. Condenser and reboiler heat duties are used to compare operating costs of cascades with less than N -1 columns to base cases with three columns. A dimensionless volume index, ∑(V j N j / F T ), is used to compare capital costs. Quaternary feeds containing four of the five components n-butane, n-pentane, n-hexane, n-heptane, and n-octane were simulated using the commercially available software package Aspen Plus version 11.1. Columns were operated at L/D ) 1.15(L/ D) min and with optimum feed and product withdrawal locations. For systems with low concentrations of one component in the feed, side-stream cascades often show significantly lower operating and capital costs compared to the base cases. Low purity requirements (sloppy separations) also favor side-stream cascades. Tentative heuristics are developed to predict which cascade will have the lowest energy consumption and capital cost.