Electrostatic Potential Gradient Modulation by Organic Cations in Zeolite for Efficient C <sub>2</sub> H <sub>2</sub> /CO <sub>2</sub> Separation
Renhao Li, Chenxu Liu, Ziyi Zhao, Zhiqiang Liang, Donghai Mei, Xiaowei Song, Jihong Yu
Abstract
The separation of acetylene (C 2 H 2 ) and carbon dioxide (CO 2 ) presents significant challenges due to the similar kinetic diameters and polarities. Traditional strategies to enhance C 2 H 2 binding in zeolites via weak chemisorption are hindered by limitations such as low selectivity, high-temperature desorption, and inadequate stability. Herein, by leveraging the different priority affinity for complementary electrostatic environments (C 2 H 2, negative potentials; CO 2, positive potentials), we propose an innovative strategy for modulating the electrostatic potential gradient through introduction of low-charge density tetramethylammonium (TMeA + ) cations within Y zeolite, systematically attenuating the positive electrostatic environment within the channel. This approach successfully achieves highly efficient C 2 H 2 /CO 2 separation in TMeA-Y-5.8 (TMeA + exchanged Y zeolite with a Si/Al ratio of 5.8) while circumventing the weak chemisorption, delivering an ideal adsorbed solution theory (IAST) selectivity of 16.1 for C 2 H 2 /CO 2 (50/50, v/v) and a C 2 H 2 adsorption capacity of 34.6 cm 3 /g at 10 kPa and 298 K. The dynamic C 2 H 2 /CO 2 separation factor of TMeA-Y-5.8 (13.1) significantly outperforms that of NaY-5.8 (3.27) and NH 4 Y-5.8 (4.45) while maintaining a comparable C 2 H 2 breakthrough time (C 2 H 2 /CO 2 /Ar = 10/5/85, v/v/v, 8 mL/min, 298 K). Periodic density functional theory (DFT) calculations and differential charge density conclusively revealed a selective and significant attenuation of the interactions between CO 2 and TMeA-Y-5.8, coinciding with a diminished positive electrostatic potential within zeolite channels. Additionally, TMeA-Y-5.8 could achieve one-step purification of C 2 H 2 from a ternary mixture of C 2 H 2 /C 2 H 4 /CO 2 . The exceptional regeneration capability (333 K), outstanding moisture resistance, and stable recyclability of TMeA-Y-5.8 collectively demonstrate the effectiveness and practical applicability of this electrostatic potential gradient modulation strategy.