Effects of Casting Solvents and Non-Solvents on the Structure of 13X Zeolite and Its CO2/N2 Adsorption–Separation Performance

Abstract With escalating industrial CO2 emissions and the widespread application of gas separation membranes, 13X zeolite is extensively incorporated as a critical filler material into mixed matrix membranes (MMMs). As zeolite gas uptake is determined by both intrinsic characteristics and the surrounding environment, clarifying the influence of the membrane fabrication solvent and nonsolvent environment on filler properties is a necessary consideration. In this study, the effects of immersion and ultrasonic treatment in typical casting agents, including N,N-dimethylformamide (DMF), polyethylene glycol 400 (PEG400), deionized water, ethanol, and a mixed DMF/PEG400 agent (DP), on the crystal structure, pore characteristics, and CO2/N2 separation performance of 13X zeolite are systematically investigated. The results show that although treatments with casting solvents and nonsolvents do not destroy the macroscopic framework of the zeolite, strongly polar solvents (particularly DMF) cause the micropore walls to undergo localized perturbation and framework relaxation and generate secondary textural mesoporosity. This structural evolution simultaneously decreases the CO2 uptake. At 298 K and 1 bar, the CO2 adsorption capacity of 13X zeolite treated with DMF decreases by 21.5% compared with the untreated 13X zeolite. Notably, the ethanol exchange strategy effectively removes residual high-boiling-point agents from the pore channels, enabling the regenerated zeolite to achieve a recovery rate of 89.4%. At the same time, the dynamic separation factor of CO2/N2 for 13X zeolite after the final ethanol displacement at room temperature is 15.5, which is close to the 16.7 value for the original 13X zeolite. The membrane fabrication environment, including single and mixed agents, is systematically linked to the structural evolution and CO2/N2 separation performance of the zeolite filler in this study. The results reveal agent-induced filler deactivation and an ethanol-enabled regeneration route, providing insights into agent–filler interactions and a practical route for regenerating zeolite fillers after exposure to casting solvents and nonsolvents.