Regulating the Si/Al ratio of GIS zeolite with bulky primary particles for selective CO2 capture from hydrocarbons

Abstract

Carbon dioxide (CO2) capture from hydrocarbons using low-energy adsorption separation techniques is a promising alternative to conventional low-temperature distillation, but limited by the shortness of low-cost and efficient physical adsorbent, especially for the direct acetylene (C2H2) purification because of their very similar size and physiochemical properties. In this work, GIS zeolites with tunable Si/Al ratio were synthesized in an unusual acid co-hydrolysis route to enable the formation of large-sized primary particles, which greatly reduce the outside surface adsorption to enhance the sieving effect of 8-membered ring microchannels. The obtained GIS zeolites afforded high CO2 uptake (3.5 mmol g-1 and 128 cm3 cm-3) while negligible adsorption towards other gases including C2H2, N2, CH4, C2H4, and C2H6, showing the remarkable selective CO2 adsorption from a CO2-C2H2(N2 or CH4) mixture with the CO2/C2H2 (50/50 v/v) selectivity up to 8.5 × 1010. Breakthrough experiments revealed the favorable dynamic separation behavior with better performance on the sample with the comparatively high Si/Al ratio of 3.1. The CO2 adsorption at 195 K and structural refinement results demonstrated that the excellent separation performance was attributed to the less Na+ ions inside the microchannels providing more inner space for the accommodation of guest molecules.