High pressure N2/CH4 adsorption measurements in clinoptilolites

The ability of clinoptilolite, a naturally occurring zeolite, to separate a nitrogen/methane gas mixture was studied experimentally. High-pressure nitrogen and methane adsorption isotherms at 273 and 298 K were measured for the raw material as well as for monovalent (Li+ and Na+) cation exchanged derivatives. The raw material showed promising results as a potential sorbent for kinetic pressure swing adsorption (PSA) processes. The type and population distribution of the charge-balancing cations affect significantly the adsorption and kinetic characteristic of the clinoptilolite samples. Both N2 and CH4 diffusion is activated, and thus sorption kinetics are a strong function of temperature. Based on our experimental data CH4 is more hindered and its mobility is significantly decreased at low temperatures. In this respect a kinetic PSA with fast cycles at low temperatures seems favourable.