Green Synthesis of Highly CO<sub>2</sub>-Selective CHA Zeolite Membranes in All-Silica and Fluoride-Free Solution for CO<sub>2</sub>/CH<sub>4</sub> Separations
Junjing Zhou, Feng Gao, Kuo Sun, Xiaoyu Jin, Yue Zhang, Bo Liu, Rongfei Zhou
Abstract
Zeolite membranes with higher Si contents displayed higher resistances to water vapor in gas mixtures. CHA zeolite membranes from an all-silica gel/solution (namely, Si-CHA herein) were always prepared by the fluoride route. High-quality Si-CHA zeolite membranes were prepared using a green and fluorite-free synthesis route in a diluted all-silica solution via a single hydrothermal synthesis step in this study. The as-synthesized membranes had a compact CHA zeolite layer with a Si/Al ratio in the framework of ∼75 and a thickness of 2.5 μm. A trace of aluminum in the membrane came from the alumina support. Separation performances through Si-CHA zeolite membranes as functions of pressure drop and temperature were measured. The best membrane displayed a CO2 permeance of 1.2 × 10–6 mol (m2 s Pa)−1 and CO2/CH4 selectivity as high as 480 for an equimolar CO2/CH4 gas mixture at 298 K and 0.2 MPa pressure drop. Si-CHA zeolite membranes displayed good and stable separation performance in a wet mixture.