RECUPERATIVE PARAMETRIC PUMPING IN ADSORPTIVE MEMBRANES

Recuperative parametric pumping in adsorptive membranes, a cyclical ad sorptive separation process, can lead to two distinct mechanisms of se paration: rejection and preferential transport. During rejection, the adsorptive membrane rejects an adsorbing solute while permitting the t ransport of nonadsorbing solutes. During preferential transport the re verse occurs; the adsorptive membrane selectively transports an adsorb ing solute while preventing the transport of nonadsorbing solutes. Swi tching fr om rejection to preferential transport can be accomplished b y merely decreasing the ratio of the stroke volume (cyclical volume of solution pumped into and out of the membrane) to the membrane void vo lume. Preferential transport, earlier called an ''inverse separation, ''results from the adsorbing solute crossing over from an adsorbing to a desorbing region in the interior of the membrane and is governed by the shape of the equilibrium isotherms and by process variables In ex periments with lysozyme and a membrane chromatography cartridge, selec tivities obtained by preferential transport were on the order of 5 and agreed With theoretical predictions. Theoretical predictions suggest that to further improve separation by preferential transport, experime nts need to be conducted on low dispersion membranes (Pe > 10(4)) and that both rejection and preferential transport can lead to continuous concentrated streams of the adsorbing solutes.