Synthesis of tungsten-doped MFI zeolite membranes with improved performance for CO2/N2 separation

The separation of CO 2 from N 2 using MFI-type zeolite membranes relies on a mechanism dominated by adsorption and diffusion processes. In this investigation, we employed a tungsten (W) doping approach to elevate the CO 2 separation selectivity of MFI zeolite membranes. Isothermal adsorption assessments demonstrated an elevated heat of adsorption (Q st ) for CO 2 and a reduced pore sizes after W doping, corroborating the enhanced CO 2 /N 2 separation efficiency observed. Specifically, the W-doped MFI membrane exhibited a selectivity of 38.8 under dry conditions, a substantial improvement over the 8.7 selectivity achieved by the undoped Si-MFI membrane, while the CO 2 permeance remained comparable (3.9 × 10 -7 vs 4.5 × 10 -7 mol·m -2 ·s -1 ·Pa -1 ). Furthermore, the incorporation of tungsten curtails the formation of silanol groups by stabilizing the zeolite framework via energetically favorable W-O-Si linkages. These linkages diminish silanol-related defects, typically prone to water adsorption, thereby enhancing the membrane’s hydrophobicity. Consequently, the W-doped MFI membrane maintains a CO 2 /N 2 selectivity of 29.5 and a CO 2 permeance of 1.8 × 10 -7 mol·m -2 ·s -1 ·Pa -1 in the humid environments, outperforming most reported zeolite membranes and showing potential ability for practical post-combustion carbon capture applications.