Periodic state heat effects in pressure swing adsorption solvent vapor recovery

Heat effects in the pressure swing adsorption (PSA)-n-butane vapor recovery process were investigated at the periodic state by computer simulation. The PSA, process utilized a two-bed, four-step, vacuum swing cycle and BAX activated carbon as the adsorbent. The heat effects were manifested by varying the heat transfer coefficient (h) from isothermal to adiabatic, while simultaneously varying the adsorbed phase heat capacity (Cp-a) from zero to that of the saturated liquid. In terms of the bed capacity factor (BCF), isothermal operation always resulted in the best performance, whereas adiabatic operation was not the worst; independent of Cp-a, the worst performance occurred at an intermediate h. Cp-a also had a significant effect on the BCF, where a larger Cp-a (i.e., a larger heat sink) always decreased the BCF and thus improved the process performance. A factorial analysis showed that the effect of Cp-a on the BCF became even more pronounced as the cycle time increased. It and Cp-a had essentially no effect on the solvent vapor enrichment under the conditions investigated. Overall, this study demonstrated that the effects of h and Cp-a are uniquely coupled; thus knowing their magnitudes is paramount to obtaining accurate predictions from a PSA-solvent vapor recovery model.