Separation of F-gases (HFC-134a and SF6) from gaseous mixtures with nitrogen by surface diffusion through a porous Vycor glass membrane

Separation of condensable greenhouse gases containing fluorine (F-gases), i.e., SF6 and HFCs-134a, from mixtures containing nitrogen was experimentally studied by using a porous Vycor membrane with a mean pore diameter of 4 nm. The separation principle was based on the difference in surface diffusion between the F-gases and nitrogen. The experimental results demonstrated that both the F-gases, SF6 and HFC-134a, could be enriched by the porous Vycor glass membrane. A higher selectivity was observed under conditions of lower temperature (275 K) and higher partial pressure of the F-gas component on the feed side. The results can be explained by the enhancement of the permeation flux of the F-gases due to a surface diffusion mechanism, and the pore blocking effect of the adsorbed phase of the F-gas molecules, and capillary condensate at higher pressure conditions, on the gaseous diffusion of nitrogen.