Zeolite RHO, a microporous zeolite, has the great possibility for N 2 /CH 4 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 N 2 /CH 4 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 N 2 and CH 4 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 N 2 /CH 4 , which are used to comprehensively evaluate the selectivity of N 2 /CH 4 . 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 N 2 /CH 4 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 N 2 working capacity of ETS-4 in industrial application.
Dan Liang,Yunfeng Hu,Qiang Bao,Jian Zhang,Jiawei Feng,Penglai Sun,Yutong Ma,Hongsheng Zhang
Rho zeolite was successfully synthesized by hydrothermal synthesis adopting 18-crown-6 as template, and the cations (H + , Na + , K + , Cs + , Cd 2+ and Pb 2+ ) of different radii were introduced into the framework of Rho by ion exchange. The samples were characterized by XRD, SEM-EDX, ICP and N 2 -BET. The adsorption behavior of CO 2 and CH 4 on cation-exchanged Rho was measured, and the adsorption isotherm was fitted by Langmuir equation to study the adsorption performance of these zeolites. The adsorption results show that the pore size of Rho is not solely dependent on the cation radius, the different positions of the cations are also more crucial in pore size adjustment. In all researched Rho, the introduction of Cd 2+ and Pb 2+ can more significantly reduce the pore size, and completely restrict the entry of CH 4 , thereby further improving the CO 2 /CH 4 selectivity. Therein, Cd-Rho has the best adsorption performance, with considerable CO 2 adsorption capacity, and extremely high CO 2 /CH 4 selectivity and CO 2 working capacity, which provides a new clue for the development of adsorbents for CO 2 and CH 4 separation in PSA process.
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