Simulated Moving Bed SMB Processes

The productivity of the plant was assessed to amount to about 5 kg DNB-D-Leu and DNB-L-Leu per mol of carrier with a purity of 99% (i.e., 98% ee). If a similar amount of selector is immobilized on silica gel and the CSP operated in a simulated moving bed (SMB) process, it was assumed to achieve roughly productivities between 1 and 7 kg pure enantiomer per day. Hence, it was concluded that a SLM process could be quite competitive to a SMB process in the production of pure enantiomers. 

Continuous processes are more efficient than batch processes, as the use of stationary phase is optimized and the amount of eluent needed for the purification is significantly reduced. The concentration of feed mixture inside the column can be much higher than it is in the case of a batch process. As a consequence, productivity is multiplied by a factor of two to five, less manpower is required, usage of stationary phase is optimized, and the amount of solvent used is reduced by a factor of two to ten. Two multicolumn continuous chromatography processes have been commercially implemented at commercial scale for pharmaceutical chiral separahons, these being the simulated moving bed (SMB) process and the Varicol process [15-17]. 

Preparative chromatography is a proven technology for the separation of specialty chemicals mainly in food and pharmaceutical industries, particularly the enantioseparation of chiral compounds on chiral stationary phases. The potential of preparative chromatographic systems were further increased by the development of continuous chromatographic processes like the simulated moving bed (SMB) process. Compared to the batch column chromatography, the SMB process offers better performance in terms of productivity and solvent consumption [2]. 

In the chemical industry, chromatographic separation process is an emerging technology for the separation of pharmaceutical products, food and fine chemicals. To improve the economic viability, a continuous countercurrent operation is often desirable but the actual movement of the solid leads to a serious operating problem. Therefore, the simulated moving bed (SMB) process is an interesting alternative option. 

Due to the similarity between true moving (TMB) and simulated moving bed (SMB) processes (Chapter 6.7) the TMB approach is quite often used to estimate the operating parameters of SMB units. Operating parameters for TMB processes are the liquid flow rates in the four sections, V tmb, and the volumetric flow rate of the adsorbent, Vads. These TMB parameters can be transferred into SMB operating parameters (Vj smb and tshift) following the relationships listed below. 

The simulated moving bed reactor (SMBR) based on the simulated moving bed (SMB) process is a practical alternative for implementing counter-current continuous reactors. Counter-current movement of the phases is simulated by sequentially switching the inlet and outlet ports located between the columns in direction of the liquid flow (Fig. 8.4). As with the SMB process, two different concepts are known to realize the counter-current flow. One is based on switching the ports and the other on the movement of columns. However, both require elaborate process control concepts to realize the movement. Owing to the periodical changes of the set-up the pro-... 

Simulated moving bed (SMB) processes are related to the separation of chemical products. Efficient purification techniques are crucial in chemical process industries. Liquid chromatographic separation has been widely used for products with an extremely high boiling point, or thermally unstable products such as proteins. In liquid chromatographic processes, a small amount of feed mixture is supplied to an end of a column which is packed with adsorbent particles, and then pushed to the other end with desorbent (water, organic solvent, or mixture of these). 

Concerning its performance, steady-state recycling chromatography can be seen as an intermediate between simple batchwise or CLRC operation and continuous simulated moving bed (SMB) processes (Section 5.2). It combines lower complexity and equipment requirements than an SMB system with higher productivities and lower eluent consumption than obtained in batch chromatography. 

Simulated moving-bed (SMB) processes have been widely nsed for difficult, liquid-phase separations (Ruthven, 1984 Humphrey and Keller, 1997 Juza et al 2000). Sorbex is the generic name used by UOP for these processes. The most important application is the separation of the xylene isomers, named the Parex process. Other commercialized SMB separations include n-paraffins/isoparaffins (Molex), olefins/paraffins (Olex), fructose/glucose (Sarex), and chiral SMB separations (Juza et al., 2000). A host of other separations have been demonstrated (Humphrey and Keller, 1997), although the commercial status of these applications is unknown. These demonsffated separations include separation of hydroxyparaf-finic dicarboxylic acids from olefinic dicarboxylic acids removal of thiophene, pyridine, and phenol from naphtha separation of unsaturated fatty acid methyl esters from saturated fatty acid methyl esters and separation of saturated fatty acids from unsaturated fatty acid (Humphrey and Keller, 1997). 

---