Molecular sieving mixed matrix membranes embodying nano-fillers with extremely narrow pore-openings

Abstract

Polysulfone-based mixed matrix membranes (MMMs) embodying metal-organic framework ZIF-11 with extremely narrow pore-openings (~3.0 Å of aperture windows) as the nano-fillers were fabricated and applied in CO2/CH4 separation for natural gas upgrading. The proper dispersion of ZIF-11 nano-fillers, below a threshold loading, led to defect-free free-standing membranes. The CO2/CH4 separation factor and CO2 permeability of MMMs with filler loading of 24 wt% showed a 43.5% and 99.5% of increment compared with the pure polysulfone (PSF) membrane, respectively. Adsorption/diffusion coefficients and the corresponding selectivities of gases for ZIF-11/PSF MMMs were quantitatively determined. Importantly, the diffusion coefficient of CO2 of MMMs with 24 wt% of ZIF-11 nanoparticles increased by 48.8% compared with that of the pure polymer membrane, but the diffusion coefficient of CH4 decreased by 42.7%. Accordingly, the CO2/CH4 diffusion selectivity increased by 160%, indicating that the restricted aperture windows of ZIF-11 permit CO2 to pass through but imped CH4. A clear molecular sieving process was realized in MMMs with ZIF-11 nano-fillers.