Significant improvement in CH4/N2 selectivity achieved through ammonium exchange in mordenite

Abstract

Adsorption-based CH4/N2 separation processes are promising and attractive, but remain a challenging task due to the lack of effective adsorbents. In this study, we present a strategy for the straightforward ammonium exchange of low-cost non-polluting sodium-type mordenite (MOR), obtaining MOR with varying ammonium contents (NH4-MOR) and exploring their effects on the CH4/N2 separation performance. The results showed that the CH4/N2 selectivity significant increase on NH4-MOR as the ammonium exchange degree increases. In particular, NH4-MOR-95 % exhibits a selectivity of CH4/N2 up to 4.6, far exceeding that of the pristine Na-MOR (1.9), while also maintaining a high level of CH4 adsorption (16.8 cm3/g) at 25 °C and 1 bar. The simulation results demonstrate that the introduction of ammonium ion significantly enhances the disparity in CH4 and N2 affinity on NH4-MOR. The breakthrough experiments confirmed that NH4-MOR has outstanding CH4/N2 separation ability. Furthermore, it was demonstrated that this exceptional separation properties of NH4-MOR are maintained at a high level even with an increased activation temperature. This fully validates the effectiveness of the ion exchange strategy and the potential applications of mordenite in the efficient CH4/N2 separation in the industry, where it was previously underutilized.