New insights into pervaporation mass transport under increasing downstreampressure conditions: Critical role of inert gas entrance

The influence of the total downstream pressure on the pervaporation flux of a pure compound through a dense polymer membrane has been the subject to c ontroversial debates recently. Experimental arguments in favor of either th e solution-diffusion model or the newly proposed pore-flow model are altern atively reported on different systems. To critically reexamine this debate, an experimental study under controlled downstream conditions has been perf ormed for pure methanol and pure 2-propanol pervaporation through a poly(di methylsiloxane) film, the latter having been previously reported to follow pore-flow model predictions. It is shown that a rational analysis of the ef fects of the downstream pressure on the results can be achieved according t o the classical solution-diffusion model, provided that the influence of ai r leaks in the installation is properly taken into account. Based on this o bservation, the implications of an inert gas contribution, generally speaki ng, on pervaporation operation are discussed.