Synthesis Of Biomimetic Material PVI-Zn And Its Composite Membrane Used For CO₂/N₂Separation

Carbonic anhydrase （CA）, a typical biological enzyme, can catalyze the reversiblehydration of carbon dioxide, and the maximal catalytic rate of CA is above10⁶s^-1. Ithas great potential in the field of CO₂absorption and separation. But, the deactivationof CA makes it difficult to be widely used in industrial scale. Here, a novalbiomimetic polymer material, poly（N-vinylimidazole）-zinc complex （PVI-Zn）, whichhas similar structure to active centre of CA, was successfully preapared and thecomposite membrane used for CO₂/N₂separation was fabricated with PVI-Zn. Theperformance of the composite membranes was also investigated.Poly（N-vinylimidazole）-zinc complex was prepared by complex betweent zincacetate and poly（N-vinylimidazole）, which was prepared through precipitationpolymerization of N-vinylimidazole. Ultraviolet spectrum, Fourier Transform InfraredSpectroscopy, Nuclear Magnetic Resonance, et al. were employed to characterize thepolymer. The results show that the specific coordination structure was formed betweenPVI and Zn²⁺.PVI-Zn/PS composite membrane was prepared by PVI-Zn as active layers and PSultra-filtration membrane as the support. The gas permselectivities of the membraneswere measured with CO₂/N₂mixed gas. The effects of PVI/Zn mole ratio, PVImolecular weight, active layer thickness, zinc salts, pH of coating solution onmembrane performance were investigated. The results show that the membrane has goodpermselectivities to CO₂. When PVI/Zn mole ration is10, the PVI-Zn/PS membraneshows the best performance and the optimum steric-complex is formed. The ultrathinmembrane prepared by using high molecular weight PVI-Zn displayed a CO₂permeanceof984GPU and CO₂/N₂selectivity of67under0.11MPa, a CO₂permeance of213GPU and CO₂/N₂selectivity of8under1.6MPa. By heat treatment at120oC for30min, CO₂-induced plasticization resistance and CO₂/N₂selectivity of membranewere both improved. The acidity of coating solution significantly affects the stabilityand stero-structure of the complexes, and the amount of complexes. The membraneprepared at pH5shows the best performance. The CO₂permeance and CO₂/N₂selectivity were as high as1147GPU and83under0.11MPa, respectively. Futhermore,the effects of operating temperature and humidity on the membrane performance were also discussed in detail. The results show that PVI-Zn/PS membrane has goodstability under high temperature and the permselectivities drop obviously withouthumidification.Other complexion materials were also prepared by Cu²⁺or Mg²⁺as metal ionsand PVI as ligand. PVI can coordinate with Cu²⁺or Mg²⁺effectively, but the CO₂separation ability of materials is different. The order of CO₂permeance isPVI-Cu/PS<PVI-Mg/PS<PVI-Zn/PS. Permselectivities of PVI-Mg/PS membrane isslight lower than that of PVI-Zn/PS membrane. PVI-Mg complex can be used for CO₂separation as another biomimetic polymer material.