455982 Enrichment of CH4 from CO2-CH4 Mixtures By Selective CO2 Separation with Ion-Exchanged Zeolite Membrane
A high silica Na-type chabazite (CHA) zeolite membrane was hydrothermally synthesized on the outer surface of a porous a-alumina tube. The synthesized membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Energy-dispersive X-ray spectroscopy (EDX). The results of this study show that it is useful for CO2/CH4 separation. Single-gas permeation for CO2 and CH4 was tested over the temperature range of 313~373 K. Then the Na-CHA zeolite membrane was ion-exchanged with K or Cs, or both cations. The cation composition was determined with the EDX measurement. K-, Cs-, and KCs-type CHA membranes showed higher CO2 permselectivity compared with the Na-type CHA membrane before ion-exchange. This was because with increasing cation diameter in the order Na, K and Cs the effective zeolite pore size became small, whereby decreasing the CH4 permeance. Especially, KCs-CHA zeolite membrane had the highest CO2 permeance and selectivity, which were corresponded to the world highest level.