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/N2 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 (mEDA/mPVAm) on polysulfone (PS) ultrafiltration membrane. The effects of mEDA/mPVAm 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 mEDA/mPVAm (from 1 to 3) showed higher CO2 permeance and much higher CO2/N2 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 mEDA/mPVAm of 3 and 50 μm wet coating thickness displayed a CO2 permeance of 607 GPU 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.