Study On Carbon Membranes Derived From Polyvinyl Chloride

Recently,the research and development of carbon membrane have received much attention due to its many advantages,including high thermal stability,high organic solvents resistance and superior permeabilities-selectivity.Polyvinyl chloride?PVC?is a general-purpose resin and widely used in many fields with its large production capacity and low prices.The use of PVC as a precursor to prepare carbon membranes will benefit from cost saving.In this paper,PVC was used as the precursor to prepare carbon membran and the effect of pre-oxidation and carbonization conditions on structures and performances was explored;PVC/Zn O composite carbon membranes containing zinc oxide and PVC/lignin composite carbon membranes with loadings of lignin were prepared,respectively.The main research contents and results are as follows:1.Carbon membranes were fabricated through the pre-oxidation and pyrolysis of polyvinyl chloride?PVC?,which were prepared by dissolving and casting using N,N-dimethylformamide?DMF?as a solvent.Their chemical composition and structure morphology were characterized using FTIR,SEM and XRD;their CO₂ and N₂ adsorption isotherms were measured at 25°C.The experimental results showed that the heating rate and holding time have great influences on the pore structure during the pre-oxidation process as well as the carbonization process.The pore structure of the carbon membranes was also influenced by carbonization temperature.The carbon membrane obtained at 700°C had the largest CO₂ adsorption capacity of 1.45 mmol/g at 101 kPa.The carbon membrane prepared at heating rate of 3°C/min and holding time of 0.5 h at 800°C displayed an excellent adsorption selectivity of CO₂ over N₂evidenced by the fact that its CO₂ adsorption capacity could reach 1.1mmol/g and while it does not significantly adsorb N_2.2.The research on incorporation of inorganic particles into polymer films to improve properties and adjust the structure of the carbon membranes was carried out.ZnO was selected as a dopant and PVC films containing different amounts of ZnO particles were prepared.The effect of Zn O on the structure and properties of the composite films was investigated.The thermal performance results showed that the addition of ZnO accelerated the dehydrochlorination of PVC chains,and affected the volatilization amount of the evolved gas during thermal degradation,but composite films had more residual carbon than that of the pure PVC film.The composite carbon membranes appeared to have a more rich microporous structure due to the presence of ZnO,which promoted the specific surface area of the carbon membranes.When the zinc oxide content was 7.5 wt%,the specific surface area of the carbon membrane can reach 134.8 m²/g.Compared to that of pure PVC-based carbon membrane,PVC/ZnO composite carbon membranes had better gas adsorption performance.3.Lignin was selected as a common carbon source to prepare PVC/lignin composite films.The studies on effects of lignin addition on the residual carbon content of carbon membranes and the content of lignin on the structure and properties of carbon membranes were investigated.The results showed that the addition of lignin could inhibit the decomposition PVC films in the medium-term of decomposition,and could increase the residual carbon content of carbon membranes.When the content of lignin was 50 wt%,the residual carbon content of the composite film was 31.6%,which was 51.2%higher than that of pure PVC.The addition of lignin had a great influence on the structure and morphology of carbon membranes.The carbonization temperature played the greater influence on the pore structure of PVC/lignin carbon membrane with the content of lignin was 30 wt%.And the lignin could also improve the gas adsorption performance of the carbon membranes,but hinder the carbonization process of the composite film.