Adsorption of carbon dioxide and nitrogen on zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether

Zeolite rho was prepared by hydrothermal synthesis using an 18-crown-6 ether (18C6) as a structure-directing agent, and the effects of the calcination temperature for removal of 18C6 on the physicochemical properties and CO(2)-adsorption properties were investigated. CO(2) adsorption on zeolite rho calcined at 150°C was lower than that on samples calcined at temperatures above 300°C. For samples calcined above 300°C, CO(2) adsorption increased with increasing calcination temperature up to 400°C. It is thought that the pore volume for adsorption of CO(2) increased as a result of 18C6 removal, resulting in increasing CO(2) adsorption. A decrease in CO(2) adsorption for calcination from 400°C to 500°C was observed. The particle size of zeolite rho increased with increasing 18C6 molar ratio. Particle sizes of 1.0-2.1 μm and 1.4-2.6 μm were found by field-emission scanning electron microscopy and dynamic light-scattering, respectively. The particle size is controlled in these regions by adjusting the 18C6 molar ratio. XRD showed that zeolite rho samples with 18C6 molar ratios of 0.25-1.5 had high crystallinity. The adsorbed amount of CO(2) is almost constant, at 3.4 mmol-CO(2)g(-1), regardless of the 18C6 molar ratio. However, CO(2) selectivity, which is the CO(2)/N(2) adsorption ratio, decreased. The amount of CO(2) adsorbed on zeolite rho is lower than that on zeolite NaX, but higher than that on SAPO-34. The CO(2)/N(2) adsorption ratio for zeolite rho was higher than those for SAPO-34 and zeolite NaX.