Tailored Clinoptilolites for Nitrogen/Methane Separation

Clinoptilolites were tailored through controlled ion exchange with both indigenous cations, such as Na+ and Mg+, and other cations, such as Li+, Sr2+, and Ce3+. These partially exchanged clinoptilolites are characterized through neutron activation analysis, and the adsorption isotherms and diffusion rates of nitrogen and methane were measured. Partially exchanged Ce clinoptilolite showed reversal of equilibrium selectivity from nitrogen to methane as the extent of Ce3+ exchange increased, while mixed Na/Li (also referred to as partially exchanged Li+) clinoptilolites showed reversal of equilibrium selectivity as the extent of Li+ exchange decreased. High-pressure isotherms on mixed Mg/Na clinoptilolites and partially exchanged Ce clinoptilolites were measured through the differential adsorption bed technique. Pressure swing adsorption (PSA) simulations were performed on a two-stage PSA process operating on a five-step PSA cycle for the tailored clinoptilolite sorbents. The simulation results of tailored clinoptilolites were compared against those of the commercial sorbent ETS-4 and the purified clinoptilolite. The tailored clinoptilolites gave slightly less recovery than purified clinoptilolite and ETS-4 but showed 50% improvement in product throughput, making tailored clinoptilolites suitable for use in a PSA process for nitrogen/methane separation.