Microwave synthesis of high-flux NaY zeolite membranes in fluoride media

Abstract

High-flux NaY zeolite membranes were synthesized using low-cost mullite supports by microwave heating in fluoride media. Pervaporation and vapor permeation performances of these membranes were evaluated at temperature range of 303–383 K. The thickness of NaY zeolite membrane prepared by microwave heating was thinner than that prepared by conventional heating. Six membranes synthesized by microwave heating displayed fluxes of 3.43 ± 0.13 kg (m² h)⁻¹ and separation factors 1300 ± 390 for a 95 wt% n-butanol aqueous solution at 348 K. The water fluxes of these membranes were 60–80% higher than those of NaY membranes prepared by conventional heating. Water fluxes and water/alcohol separation factors of these membranes increased with the increasing kinetic diameter of alcohols for the water/methanol, water/ethanol, water/i-propanol and water/n-butanol binary mixtures. The separations of water/alcohol mixtures through these high-flux membranes were affected by concentration polarization. Increasing flow rates from 9.5 L h⁻¹ (Reynolds number = 1300, laminar flow state) to 37.8 L h⁻¹ (Reynolds number = 5200, turbulent flow state) at 363 K decreased the polarization boundary layer, and thus increased membrane flux and membrane selectivity by 26% and 23%, respectively.