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

Abstract

The separation of CO₂ from N₂ 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 CO₂ separation selectivity of MFI zeolite membranes. Isothermal adsorption assessments demonstrated an elevated heat of adsorption (Q_st) for CO₂ and a reduced pore sizes after W doping, corroborating the enhanced CO₂/N₂ 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 CO₂ 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 CO₂/N₂ selectivity of 29.5 and a CO₂ 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.