Membrane separation of light olefins has been drawn attention as a novel energy-saving process. We have recently reported that Ag+-exchanged X-type zeolite membrane shows superior propylene/propane separation properties. In this report, we will discuss the mechanism for the appearance of high propylene selectivity through Ag-X membrane. Na-X type zeolite membrane was synthesized by a secondary growth method on porous α-alumina tubular support. Ag-X membranes were obtained by an ion exchange method for obtained Na-X membranes. Adsorption measurement for Ag-X membrane was arried out by a volumetric method with a special sample holder that we developed. The membrane sample was outgassed at 373 K for 36 h under vacuum prior to the adsorption test. Adsorption measurements were carried out at 313 K. Fig. 1 gives the adsorption isotherms of propylene and propane on Na- and Ag-X zeolite membranes in unary systems. On both membranes, propylene isotherm showed steep increase in a low pressure region. This trend is much remarkable with Ag-X membrane and the adsorption of propylene almost saturated at 1 kPa, suggesting that propylene very strongly interacted with Ag-X membrane. We evaluated the relationship between propylene molar fractions adsorbed and gas phases for propylene/propane binary mixtures. The propylene molar fractions in the adsorbed phase on Ag-X membrane were substantially larger even at low propylene concentration in gas phase. As a result, we consider that high permselectivities for propylene appeared by strong interaction between Ag+ in zeolite and olefin.

Propane/propylene separation mechanism through Ag-X type zeolite membrane

2019 Fall National Meeting

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