A suitable zeolite Rho for separating CO2/CH4 in pressure swing adsorption (PSA) process

Rho zeolite was successfully synthesized by hydrothermal synthesis adopting 18-crown-6 as template, and the cations (H+, Na+, K+, Cs+, Cd2+ and Pb2+) of different radii were introduced into the framework of Rho by ion exchange. The samples were characterized by XRD, SEM-EDX, ICP and N2-BET. The adsorption behavior of CO2 and CH4 on cation-exchanged Rho was measured, and the adsorption isotherm was fitted by Langmuir equation to study the adsorption performance of these zeolites. The adsorption results show that the pore size of Rho is not solely dependent on the cation radius, the different positions of the cations are also more crucial in pore size adjustment. In all researched Rho, the introduction of Cd2+ and Pb2+ can more significantly reduce the pore size, and completely restrict the entry of CH4, thereby further improving the CO2/CH4 selectivity. Therein, Cd-Rho has the best adsorption performance, with considerable CO2 adsorption capacity, and extremely high CO2/CH4 selectivity and CO2 working capacity, which provides a new clue for the development of adsorbents for CO2 and CH4 separation in PSA process.