Clinoptilolites for nitrogen/methane separation

• Published in: Chemical engineering science 2004-06, Vol.59 (12), p.2407-2417
• Main Authors: Jayaraman, Ambalavanan, Hernandez-Maldonado, Arturo J., Yang, Ralph T., Chinn, Daniel, Munson, Curtis L., Mohr, Donald H.
• Format: Article
• Language: English
• Subjects: Adsorption; Applied sciences; Chemical engineering; Clinoptilolite; ETS-4; Exact sciences and technology; Ion exchange; Ion-exchanged clinoptilolite; Mixed ion exchange; Nitrogen/methane separation; PSA simulation; Purified clinoptilolite
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2003.10.030

Clinoptilolites, naturally occurring zeolites, currently used by nuclear industry for ion exchange and drying, were evaluated for the nitrogen/methane separation. Ion exchange of purified clinoptilolite was carried out individually with the cations Na +, Mg 2+, Ca 2+, K + and H +, and the adsorption isotherms and diffusion rates were measured. Purified and Mg-clinoptilolite show potential for nitrogen/methane separation and high-pressure adsorption isotherms were measured in a differential absorption bed. Pressure swing adsorption simulations were performed for purified clinoptilolite, Mg-clinoptilolite and the commercial sorbent ETS-4. Purified clinoptilolite shows slightly higher recovery and lower productivity than ETS-4 for similar product purity (∼95%). Mixed ion-exchanged clinoptilolites of Mg/Ca cations, K/Na cations and Mg/Na cations were also prepared and studied for the nitrogen/methane separation. Mg/Na (50/50) mixed ion-exchanged clinoptilolite exhibits very good equilibrium and kinetic selectivity in the low-pressure range, better than purified clinoptilolite. Mixed-exchange clinoptilolites were also found to show a wide range of adsorption characteristics with varying ratios of cation exchange, thereby making them suitable for further improvements in nitrogen/methane separation.