(444d) Modelling and Design Strategies for Lab-Scale SMB Units Accounting for Dead Volumes and Tubing Connections – the Flexsmb-Lsre Unit

The practical application of the so-called "non conventional modes of operation" in Simulated Moving Bed (SMB) units is per itself a challenge. Generally an SMB unit, industrial, pilot of laboratory-scale, is limited to one or two modes of operation and to implement a new operating mode is necessary to contact the supplier, do adjustments, even to reformulate the entire unit if not to acquire a new one. Therefore, flexibility (at least at laboratory-scale) is seen as one of the more relevant qualities for this kind of equipment. This aspect was the main reason that led to the design and construction of a 6 columns unit at LSRE, the FlexSMB-LSRE, hereby presented.

Generally, modelling and simulation methodologies for simulated moving bed (SMB) units do not account for pipe transfer lines as the surrounding equipment (valves, degassers, pumps). In the industrial-scale SMB units the relative volume of the connection lines is not so significant as for pilot or lab-scale units, nevertheless, is has been studied in detail and different techniques are applied to overcome the associated negative impacts. For instance, 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) [1], previously analyzed by Minceva and Rodrigues [2]. In pilot or lab-scale SMB units, the relative volume associated with equipment and transfer lines is indeed an issue and usually these type of units are designed to account for it in its own operation mode. Nevertheless, is still a proxy to the use of more detailed models and some differences are noted [3,4,5]. In this work, a detailed model accounting for dead volumes and tubing connections, as well some compensating strategies and optimization procedures, are presented for pilot (Licosep) and lab-scale (FlexSMB-LSRE) units.

References:

[1] - Stine, L.O., Springs, W., Broughton, D.B., Continuous separation process with emphasis of product purity. US Patent 3,201,491, August 17, 1965.

[2] - Minceva, M., Rodrigues, A.E., Influence of the Transfer Line Dead Volume on the Performance of an Industrial Scale Simulated Moving Bed for p-Xylene Separation, Separation Science and Technology Vol. 38, No. 7, pp. 1463, 2003

[3] - Azevedo, D.C.S., Neves, S.B., Ravagnani, S.P., Cavalcante, C.V., Jr., Rodrigues, A.E. The influence of dead zones of simulated moving bed units. Fundamentals of Adsorption 6; Elsevier: Amsterdam, 1998; 521.

[3] - Migliorini, C., Mazzotti, M., Morbidelli, M., Simulated Moving-Bed Units with Extra-Column Dead Volume, AIChE Journal Vol. 45, No. 7, pp. 1411, 1999.

[4] - Zabka, M, Sa Gomes, P., Minceva, M. and Rodrigues, A.E. Chiral Separation of R,S-a-Tetralol by Simulated Moving Bed, accepted on Separation Science and Technology, 2007.