Optimum Conditions for the Synthesis of CHA-Type Zeolite Membranes Applicable to the Purification of Natural Gas

Abstract

The synthesis and characterization of CHA-type zeolite membranes was carried out in this work. Chabazite seeds were synthesized by the hydrothermal treatment of zeolite Y. The obtained chabazite particles were evaluated in the adsorption of CO2 and CH4. CHA membranes were synthesized by a secondary growth method on α-alumina substrate. Four synthesis temperatures of 100, 120, 140, and 160 °C and a duration of 20 h were employed for the synthesis of membranes. The structures and morphologies of the synthesized CHA zeolite seeds and membranes were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Moreover, single-gas permeation analyses were performed to evaluate the potential of CHA membranes in capturing CO2 from CH4 as a model of natural gas. The results revealed that the gas permeation first decreased with increasing synthesis temperature from 100 to 140 °C and subsequently increased with further enhancement of synthesis temperature to 160 °C. Reverse trends were observed in the case of the CO2/CH4 ideal selectivity. Increasing the synthesis temperature caused the formation of an integrated zeolite layer at the surface of the substrate. The latter decreased the permeation through the membranes. The optimum conditions for the synthesis of CHA zeolite membranes were obtained as a synthesis temperature of 140 °C and a synthesis duration of 20 h. CHA-type zeolite membranes showed great capability for the removal of CO2 from CH4.