Equilibrium theory for solvent vapor recovery by pressure swing adsorption: analytical solution for process performance

Abstract A simple, analytic, equilibrium theory model based on wave interactions that occur in adsorption columns, has been formulated to predict directly the periodic state and to analyze the application of pressure swing adsorption (PSA) for solvent vapor recovery (SVR). The analysis of this cyclic process has been carried out using a fully convex, Langmuirian isotherm, with and without breakthrough of the solvent vapor into the light (inert) product. The analytic structure of this model shows the infeasibility of a periodic state with complete containment of solvent vapor, when the purge-to-feed ratio is less than unity. Analytic expressions have also been derived in terms of the key process performance indices: heavy component enrichment and recovery, and light product impurity. Results obtained from these expressions, when studying the effects of the purge-to-feed ratio, pressure level, pressure ratio, feed flow rate, feed mole fraction, cycle time, and bed length-to-diameter ratio, compare qualitatively with results obtained from a more rigorous numerical model. The comparison with a more rigorous model also exposes subtleties about the effect of model approximations on the predicted process performance, in that the cancellation of the effects of certain simplifying assumptions results in near quantitative agreement with the more rigorous model, in some cases.