(115e) The Outlet Streams Swing Simulated Moving Bed Mode of Operation
It is known that industrial-scale continuous adsorption processes are preferable to batch ones. The use of continuous chromatographic counter current operation in particular (TMB, True Moving Bed), maximizes the mass transfer driving force, providing a better utilization of the adsorbent, which may have a rather low selectivity. In addition, with TMB it is possible to reduce the solvent consumption, increase of productivity and purity and therefore less diluted product streams. Contrary to the TMB units, where the solid phase moves counter currently to the fluid phase, in the SMB (Simulated Moving Bed) (Broughton and Gerhold, 1961) units the solid motion is simulated by a synchronous shift of all inlet and outlet ports, while the solid phase is held immobile.
This technology experienced an emergent interest in the last decade (Sá Gomes et al., 2006), mainly related with its successful application to drugs resolution in the pharmaceutical, biotechnological and other fine chemical separation industries. This late demand on the SMB technique, directly linked to a considerable research effort, led to the formulation of quite different operation modes since the original patent. From these so-called non conventional operating strategies one can just emphasize those based in the periodic modulation of inlet/outlet streams flow rates, such as:
* the Partial-Feed, (Zang and Wankat, 2002; Zang and Wankat, 2002), in the limit the PowerFeed, (Kloppenburg and Gilles, 1999; Zhang et al., 2003; Zhang et al., 2004; Kawajiri and Biegler, 2006), in which an inlet feed flow rate varies along the time compensated by the raffinate flow rate;
* the Partial-Discard (or partial Withdraw) (Zang and Wankat, 2002; Bae and Lee, 2006), preformed by a partial collection in the extract and/or raffinate streams; the fraction that has not been ?collected? can be the be recycled back to the feed after a possible concentration step (Kessler and Seidel-Morgenstern, 2008; Kessler and Seidel-Morgenstern, 2008; Seidel-Morgenstern et al., 2008);
* the ISMB (Improved SMB) mode of operating, commercialized by the Nippon Rensui Co. (Tokyo, Japan), (Tanimura et al., 1989), with two different nodes a first step the unit is operated as a conventional SMB but without any flow in section IV; in the second step the inlet and outlet ports are closed and the internal flow through the four sections allowing the concentration profiles to move to adjust their relative position with respect to the outlet ports (Rajendran et al., 2009).
Considerable performances improvements have been noted by the application of such techniques; however, any refers to the possibility of varying the eluent/desorbent flow rate. While the partial feed strategy has been considerably studied over the time, resulting in significant productivity improvements, the analysis of a similar of eluent/desorbent flow rate variation has not been so much addressed. Based in this statement and also on the partial discard as ISMB techniques a new operation technique was introduced the Outlet Streams Swing (OSS) (Sá Gomes and Rodrigues, 2007), hereby presented.
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