Uncommon Adsorption Isotherm of Methanol on a Hydrophobic Y-zeolite

Abstract

The physisorption of methanol vapor on a dealuminated, commercial Y type zeolite (CBV-901) at temperatures from 0 to 80 °C, produces a rare Type V adsorption isotherm. In contrast to some microporous carbons and AlPO4-5 derivatives that give Type V isotherms only with water, CBV-901 barely adsorbs water at p/po < 0.7 relative pressures. Micropore filling with methanol takes place near p/po ≈ 0.2, which is unusually low for Type V isotherms. To our knowledge, such isotherms have not been reported over zeolites before. Pore size measurements and grand canonical Monte Carlo molecular simulation experiments indicate that the selective micropore condensation of methanol is intimately associated with the micropore structure and the force field of the dealuminated Y-zeolite. Mesopores or lattice defects including silanol groups and detached crystal fragments play a secondary role in shaping the methanol isotherms. The unique combination of high adsorption capacity and low relative pressures both for adsorption and regeneration is desirable for various applications including pressure swing separations, air pollution abatement, and adsorptive heat pumps.