Abstract
A novel separation process of condensable gases from the gaseous mixture with non-condensable gases using surface flow and capillary condensation in porous inorganic membranes was proposed. The concept was applied to the enrichment of condensable greenhouse gases such as hydrofluorocarbons (HFCs) and sulfur hexafluoride (SF6) from mixtures with nitrogen. These gases are occasionally used as mixtures with non-condensable components such as nitrogen, and therefore, an enrichment process of these gases would be necessary for recycling or reuse. Because of their larger sizes and molecular weights, enrichment of these gases from nitrogen by molecular diffusion or molecular sieving mechanism would be difficult. Condensable properties of these gases could enhance the surface transport mechanism such as surface flow and the transport of capillary condensate phase, whereas the transport of the non-condensable component would be retarded due to the decrease in the effective pore size by the adsorbed molecules or capillary condensate. Thus, a significant improvement in the separation performance would be anticipated by using the surface transport mechanisms. Experimental studies were conducted using porous Vycor glass membrane (4 nm pore size) to investigate the separation performances under various conditions. The results indicate that HFC-134a was highly enriched, especially under high-pressure conditions close to the capillary condensation pressure. The proposed separation process was evaluated in terms of the energy consumption as well as the separation performance with the conventional processes such as liquefaction process.
