Improvement of CO 2/N 2 separation characteristics of polyvinylamine by modifying with ethylenediamine

Abstract

In this work, the idea of modifying the fixed carrier membrane for CO 2 separation by a cross-linking agent containing carriers to simultaneously improve the CO 2-induced plasticization resistance, the CO 2 permeance and the CO 2/N 2 selectivity of the membrane was suggested and confirmed. Polyvinylamine (PVAm), a polymer to prepare fixed carrier membrane for CO 2 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 CO 2 permeance and much higher CO 2/N 2 selectivity as well as better CO 2-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 CO 2-induced plasticization resistance improves, the selective layer thickness of the PVAm–EDA/PS membrane can be further reduced to obtain a higher CO 2 permeance and a proper CO 2/N 2 selectivity simultaneously. For CO 2/N 2 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 μm wet coating thickness displayed a CO 2 permeance of 607 GPU and CO 2/N 2 selectivity of 106 at CO 2 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 H 2O-saturated SO 2 of 300,000 ppm h.