Study on CO₂ facilitated separation of mixed matrix membranes containing surface modified MWCNTs

Mixed matrix membranes (MMMs) for CO₂-facilitated separation were prepared by incorporating different surface-modified multiwalled carbon nanotubes (MWCNTs) in a fixed carrier membrane material. Polymer containing amino groups, poly(vinylalcohol-co-vinylamine) (VA-co-VAm) was synthesized as polymeric matrix. MWCNTs as well as MWCNTs surface-modified with OH and NH₂ were applied as nanofillers. The physical property, chemical structure, and membrane morphology were characterized by FT-IR, TG, XRD, DSC, CA, XPS, and SEM. The effects of content, functional group, temperature, and pressure on gas permselectivity were studied. Results show that the incorporation of nanofillers can effectively restrict the polymer chain packing and lead to low crystallinity. The MMMs exhibited higher CO₂ permselectivity than the pure polymeric membrane. For all the MMMs, the CO₂ permeance and selectivity increased with MWCNTs contents to a maximum and then decreased. MWCNT-NH₂ can be regarded as the most effective nanofiller. MMMs with 2.0 wt % MWCNT-NH₂ displayed the highest CO₂ permeance of 132 GPU and CO₂/N₂ selectivity of 74. Both CO₂ permeance and selectivity were decreased with feed gas pressure and temperature. The membrane exhibited good stability in the testing with the binary gas mixtures of CO₂/N₂ for 110 h under 0.54 MPa.