Simulated moving-bed adsorber

Hashimoto K, Adachi S, Shirai Y, Mortshita M (1992) Operation and Design of Simulated Moving Bed Adsorbers. In Ganetsos G, Barker PE (eds) Preparative and Production Scale Chromatography, Marcel Dekker, New York... 

Hashimoto K., Adachi S. and Shirai Y., Continuous Desalting of Proteins with a Simulated Moving-bed Adsorber, Agric. Biol. Chem. 52 (1988) pp. 2161. 

Hashimoto K., Adachi S., Noujima H. and Maruyama A., Models for separation of glucose-fructose mixture using a simulated moving bed adsorber, J. Chem. Engng. Japan. 16 (1983) pp. 400-406. 

Hashimoto, K., Adachi, S., Shirai, Y. Operation and design of simulated moving-bed adsorbers in Preparative and Production Scale Chromatography, Ganetsos, G., Barker, P. E. (Eds.), Marcel Dekker Inc., New York, 1993a. 

Saska, M., Clarke, S. J., Iqbal K. Continuous Separation of Sugarcane Molasses with a Simulated-Moving-Bed Adsorber Absorption Equilibria, Kinetics and Applications, Sep. Sci. Tech., 1992, 27, 1711-1732. 

Maki H., Fukuda H. and Morikawa H. 1987. The separation of glutathione and glutamic acid using a simulated moving bed adsorber system. J. Ferment. TechnoL, 65, 61. 

Fig. 8. UOP Parex simulated moving bed for adsorptive separation. AC = adsorbent chamber RV = rotary valve EC = extract column ...

Since the 1960s the commercial development of continuous countercurrent processes has been almost entirely accompHshed by using a flow scheme that simulates the continuous countercurrent flow of adsorbent and process Hquid without the actual movement of the adsorbent. The idea of a simulated moving bed (SMB) can be traced back to the Shanks system for leaching soda ash (58). 

Aromatic and Nonaromatic Hydrocarbon Separation. Aromatics are partially removed from kerosines and jet fuels to improve smoke point and burning characteristics. This removal is commonly accompHshed by hydroprocessing, but can also be achieved by Hquid-Hquid extraction with solvents, such as furfural, or by adsorptive separation. Table 7 shows the results of a simulated moving-bed pilot-plant test using siHca gel adsorbent and feedstock components mainly in the C q—range. The extent of extraction does not vary gready for each of the various species of aromatics present. SiHca gel tends to extract all aromatics from nonaromatics (89). 

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

Njlene Separation. -Xylene is separated from mixed xylenes and ethylbenzene by means of the Parex process (Universal Oil Products Company). A proprietary adsorbent and process cycle are employed in a simulated moving-bed system. High purity -xylene is produced. 

The UOP Ebex process has been available for license since the 1970s. This process is a rejective simulated moving bed process where the ethylbenzene is the least adsorbed member of the mixed xylenes and is recovered in high purity in the raffinate stream [47]. Other liquid phase simulated moving bed concepts selective for ethylbenzene have been considered. These would ostensibly require less adsorbent circulation per unit feed because ethylbenzene is typically at <20% concentrahon in mixed xylenes [48, 49]. A process is disclosed by Broughton [50] that produces a pure m-xylene stream along with a pure ethylbenzene stream. 

A simulated moving bed system has been proposed for the production of p-cresol from mixtures of cresol isomers even derived from coal tar [52]. Neuzil et al. give details of the development of the adsorbent and desorbent system reviewing balancing mass transfer issues with selechvity [53]. The desorbent for the cresol system is 1-pentanol. For these Hquid adsorptive systems where highly polar molecules are adsorbed and desorbed with polar desorbents, the tolerance of the system for trace polar contaminants is higher because the feed and desorbent can more easily exchange with them on the surface of the zeolites. 

The Molex process developed by U.O.P. is unique not only in its liquid-phase operation but also in its adsorption system (1-8). Its adsorption system consists of a single adsorption tower with multiple inlet-outlet points and a special rotary valve. The adsorption tower has many smaller adsorption chambers interconnected in series, and it operates under the so-called simulated moving bed operation. Instead of moving the adsorbent bed, the simulated moving bed operates by simultaneously advancing inlet-outlet points periodically. At any time, the adsorber has four zones—viz., adsorption, primary rectification, desorption, and secondary rectification zones, and these zones advance simultaneously as the rotary valve turns periodically. Desorption of n-paraffins is achieved by displacement. 

Olefin Separation. U.O.P. s Olex Process. U.O.P. s other hydrocarbon separation process developed recently—i.e., the Olex process—is used to separate olefins from a feedstock containing olefins and paraffins. The zeolite adsorbent used, according to patent literature 29, 30), is a synthetic faujasite with 1-40 wt % of at least one cation selected from groups I A, IIA, IB, and IIB. The Olex process is also believed to use the same simulated moving-bed operation in liquid phase as U.O.P. s other hydrocarbon separation processes—i.e., the Molex and Parex processes. 

DEVELOPMENT OF SIMULATED MOVING BED REACTOR USING A CATION EXCHANGE RESIN AS A CATALYST AND ADSORBENT FOR THE SYNTHESIS OF ACETALS... 

The countercurrent movement of a stationary phase is cumbersome in practice but it can be circumvented by an array of short columns connected by multi-position valves connected with eluent, feed, extract and raffinate, a method referred to as simulated moving bed chromatography (SMB) (Schulte and Strube, 2001). In SMB chromatography, the continuous countercurrent flow of the fluid and of the solid adsorbent is simulated by periodically switching the different inlets and outlets in the multi-column unit. Enantioselective SMB-LC has first been demonstrated for racemic 1-phenylethanol resolved on the polysaccharide CSP Chiralcel OD. In this pioneering work the principle of the method and the set-up has been depicted in a lucid educational fashion (cf. Figures 22 23) (Negawa and Shoji, 1992). 

Today the melt crystallization can be advantageously replaced by a more challenging separation method known as simulated moving bed (SMB) technology. The method exploits the differences in affinity of zeolitic adsorbents for p-xylene with respect to other A8 components. Despite the name, the adsorbent phase is stationary and only fluid phase is distributed in a cyclic manner by a multivalve system. Operation parameters are temperatures of 125 to 200 °C and pressures up to 15 bar. Lighter (toluene) or heavier solvents (p-diethylbenzene) may be used as a desorbent. The Parex process working on this principle today has many applications. 

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