Bulk multicomponent gas separation and pressure transients in adsorption systems
Abstract
Three displacement chromatography/pressure swing adsorption processes for bulk multicomponent gas separation are outlined. Process A, classical displacement chromatography applied to gas systems, employs two mass separating agents: presaturant and displacer. Process B employs the lightest adsorbed feed component as presaturant. Process C uses the lightest feed component as presaturant and the heaviest feed component as displacer. Processes B and C are novel. Experiments showed that displacement development occurs with all three processes and results for Processes A and B are compared with predictions of a local equilibrium theory for binary PSA. During the feed step of the displacement chromatography/PSA processes large pressure and flow transients were observed. The results of a single stage model confirmed that they are caused by large differences in adsorptivities. Oscillations in pressure and flow, linked to shock wave propagation, were predicted to occur by a tanks-in-series model; they smooth out as the plug flow limit is approached. Experiments with columns in series exhibited oscillations in qualitative agreement with model predictions. Experimental results obtained using a fully automated data acquisition system constructed to study the transients compared well with predictions of a PDE model. It is shown that the lowering in column pressure results in loss of adsorption capacity. A criterion for an a priori determination of the magnitude of these transients is proposed. Oscillations occur when columns are connected in series. The extent of oscillations depends on the dead volume between columns. The PDE model was employed to study Processes A, B, and C. The role of pressure and flow transients in gas phase adsorptive reactors is studied using a staged model. The gas phase reaction, A + B $\rightleftharpoons$ C, is considered under three situations: (1) a non-reacting feed component, D, adsorbed, (2) both the reactants, A and B, adsorbed, and (3) the product, C, adsorbed. Each of these cases is studied using one, three, and twenty-five stages (plug flow approximation). The pressure and flow transients are shown to influence reaction rates and product concentrations. For oscillations to occur, the sink (adsorbent) should have a finite capacity for the component that is removed.
Degree
Ph.D.
Advisors
Wankat, Purdue University.
Subject Area
Chemical engineering
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