K-RHO zeolite with high nitrogen selectivity for N2/CH4 separation by PSA process

Zeolite RHO, a microporous zeolite, has the great possibility for N2/CH4 separation by regulating the size of the eight-membered ring window on the RHO framework. In this work, the ability of ion-exchanged RHO zeolites for N2/CH4 separation is investigated, and a highly nitrogen selectivity adsorbents are developed. RHO samples were prepared by hydrothermal synthesis. Alkali metal cations (Na+, K+, Cs+) was used for ion exchange. Adsorption equilibrium isotherms of N2 and CH4 were measured at normal temperature and fitted by the Langmuir equation. The adsorbent selection parameters (S parameters) were calculated based on the working capacity and equilibrium selectivity of N2/CH4, which are used to comprehensively evaluate the selectivity of N2/CH4. The results indicate that the cations have effects on the regulation of the eight-membered ring window. In particularly, K-RHO no.2 sample which is obtained by ion exchange of K+ cations exhibit the best N2/CH4 separation performance, which is a potential nitrogen selective adsorbent. In addition, the product throughputs of RHO and the commercial adsorbent ETS-4 were compared by common PSA simulation process with essentially the same product purity and recovery. The results show that K-RHO no.2 has 36 % higher product throughput than ETS-4, which can compensate for the problem of low N2 working capacity of ETS-4 in industrial application.