Transport of butane in a porous Vycor glass membrane in the region of condensation pressure

Abstract

The transport and the separation efficiency in porous membranes can be strongly influenced by the condensation of permeating gases. An accurate experimental monitoring of permeating vapors and condensates in small pores of membranes is very desirable. The dynamic permeation method is one of the methods which can be used to perform a corresponding study. The following experimental arrangement was applied: a constant higher pressure P 1 was set on an open side of the membrane; on the opposite closed side the change of a lower pressure P 2 was measured. The dynamic permeation set-up was used at first in transport measurements of a noncondensable gas through a Vycor glass membrane (mean pore radius around 2 nm). The obtained data were compared with the results of alternatively performed steady state permeation measurements. Subsequently, the permeability was studied for the condensable gas butane through the Vycor glass membrane, particularly for elevator pressure conditions near the saturated vapor pressure. Also for this purpose the dynamic permeation experiment was found to be very convenient. It enables to measure the mass transport for very small pressure gradients across the membrane. The permeation results obtained correspond well with the liquid butane permeability of Vycor membrane quantified previously in independent pervaporation experiments. This agreement confirms the presence of liquid butane in small pores of Vycor glass during the transient gas transport at relatively high pressures.