Variable desorbent strength: influence on SMB operating conditions and performance
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Variable desorbent strength: influence on SMB operating conditions and performance Catherine Laroche · Damien Leinekugel-le-Cocq · Philibert Leflaive
Received: 12 May 2010 / Accepted: 18 October 2010 / Published online: 4 November 2010 © Springer Science+Business Media, LLC 2010
Abstract The aim of this work was to evaluate the role of desorbent selectivity variation on the tuning and the performance of a SMB process. For this purpose a separation regions study in the case of a four-zones non-linear transfer limited SMB was carried out. The SMB unit was modelled considering the equivalent True Moving Bed (TMB). A set of 11 desorbents with different strength was considered: 3 desorbents with constant strength and 8 desorbents with variable strength. For each system, the optimal operating conditions are determined using the separation regions approach, with plots in both (Q2 , QF ) and (Q4 , QD ) planes. Depending on the separation considered, a variable selectivity desorbent can lead to an improvement or can be detrimental to process performances. A careful choice of desorbent selectivity (either constant or variable) is then crucial to achieve maximal process performance. Keywords Simulated Moving Bed (SMB) · Desorbent strength · Robust operating conditions · Separation regions study
1 Introduction Simulated Moving Bed technology is commonly used in the petrochemical industry for xylene isomers or linear paraffins separations. Those applications need very large scale industrial units to produce low value products. One of the major operating costs in such a process is due to downstream separations. Minimizing desorbent consumption is then a major C. Laroche · D. Leinekugel-le-Cocq · P. Leflaive () IFP Energies Nouvelles, Rond-Point de L’échangeur de Solaize, BP 3, 69360 Solaize, France e-mail: [email protected]
requirement to minimize downstream distillation cost. For petrochemical applications, desorbent consumption is therefore a key performance criterion as important as purity, recovery or productivity. In this paper, we will focus on the impact of desorbent strength on SMB operating conditions and performance, particularly in terms of productivity, desorbent consumption for a given purity and recovery. The robustness of the operation is also addressed (which is also a major issue in industrial operation). Several constant desorbent strengths are considered, as well as several variable desorbent strengths.
2 SMB principle and role of the desorbent Simulated moving bed (SMB) is a continuous multi-column adsorption process which derives from the true moving bed (TMB), an adsorption-based separation process implying a fluid-solid counter-current. For TMB, the solid phase flows down counter-currently to the mobile phase stream. The feed mixture is introduced in the column and the most adsorbed component is carried by the solid to the bottom of the column (where it will be collected in the extract) whereas the less retained component is carried upward with the mobile phase and collected in
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