Manipulation of the pore size of clinoptilolite for separation of ethane from ethylene

• Clinoptilolite was used and modified for ethane/ethylene separation.
• Separation performance was evaluated after ammonium exchange.
• Effect of different steaming temperatures on de-alumination and separation was studied.
• Adsorption characteristics of modified zeolite were examined.

Naturally occurring zeolites are uniquely useful for small molecule separations due to the effective size of their pores. While the crystal structure of clinoptilolite has large 12-ring pores, the effective pore size of the zeolite excludes molecules larger than ~0.4 nm. In this work, the structure of a naturally occurring clinoptilolite was modified through ammonium exchange, calcination, and post-calcination steam treatment. The ammonium exchange removed some fraction of the structural cations, which caused the framework to expand, while steam treatment at 600 °C causes a contraction in the structure. The effective pore size of the modified clinoptilolite allowed it to adsorb ethylene and exclude ethane in a dynamic adsorption experiment. By incrementally changing the pore size of clinoptilolite, a new rate-based adsorbent for the adsorptive separation of ethylene from ethane was created.

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