Improvement of CO2/N2 separation characteristics of polyvinylamine by modifying with ethylenediamine

In this work, the idea of modifying the fixed carrier membrane for CO2 separation by a cross-linking agent containing carriers to simultaneously improve the CO2-induced plasticization resistance, the CO2 permeance and the CO2/N-2 selectivity of the membrane was suggested and confirmed. Polyvinylamine (PVAm), a polymer to prepare fixed carrier membrane for CO2 separation, was synthesized by partial acidic hydrolysis of poly(N-vinylformamide) and further modified by using ethylenediamine (EDA). Elemental analysis, ATR-FTIR, XPS and XRD were employed to characterize the EDA modified PVAm. The result of ATR-FTIR and XPS showed that the EDA can effectively cross-link PVAm by the hydrogen bonds formed between amine groups of EDA and either amine or amide groups in PVAm. The composite membranes were developed by coating the PVAm-EDA mixed solutions with different mass ratio of EDA/PVAm (m(EDA)/m(PVAm)) on polysulfone (PS) ultrafiltration membrane. The effects of m(EDA)/m(PVAm) in coating solution and wet coating thickness on the gas performance of the PVAm-EDA/PS composite membranes were investigated. The PVAm-EDA/PS membrane prepared by using coating solution with proper m(EDA)/m(PVAm) (from 1 to 3) showed higher CO2 permeance and much higher CO2/N-2 selectivity as well as better CO2-induced plasticization resistance than that of the PVAm/PS membrane. It is attributed to two factors: (1) the densification of polymer matrix by moderate hydrogen bond cross-linking; and (2) the increase of total carrier content in membrane. As CO2-induced plasticization resistance improves, the selective layer thickness of the PVAm-EDA/PS membrane can be further reduced to obtain a higher CO2 permeance and a proper CO2/N2 selectivity simultaneously. For CO2/N2 gas mixture (20/80 by volume), the PVAm-EDA/PS membrane prepared by using coating solution with m(EDA)/m(PVAm) of 3 and 50 mu m wet coating thickness displayed a CO2 permeance of 607 CPU and CO2/N2 selectivity of 106 at CO2 partial pressure of 0.02 MPa. The separation performance stability of the PVAm-EDA/PS membranes was investigated for 300 h and no deterioration in membrane permselectivity was observed. Moreover, the PVAm-EDA/PS membrane had no obvious degradation after exposure to H2O-saturated SO2 of 300,000 ppm h. (C) 2011 Elsevier B.V. All rights reserved.