Preparation And Structural Characteristic Of Polyacrylonitrile-based Carbon-carbon Composite Membrane

The latest development of membrane separation, especially carbon membranes on the category, preparation, separation mechanism, application and future direction are presented in the thesis. A carbon-carbon composite membrane is prepared by pyrolysing polyacrylonitrile membrane using dip-coating method on tublar carbon support derived from coal. The experiments are carried out to investigate the effects of membrane formation conditions such as concentration of PAN solution, dip-coating parameters, drying parameters and coating numbers, preoxidation conditions, carbonization conditions and additives on the properties of PAN-based carbon membranes. The pyrolysis mechanism, the reaction kinetics, the formation of carbon and pore structure of PAN-based carbon-carbon composite membrane formed in Ar and vacuum are studied by SEM, TG, FTIR , XRD and Raman analysis and their differences are compared.The results indicate that a thin, crack-free PAN-based composite carbon membrane can be prepared by optimizing the experimental parameters. There are three stages during pyrolysis of PAN membrane. In the early stage, dehydration and solvent volatilization of PAN membrane are obvious. Three kinds of reactions such as cyclization, crosslinkling and cleavage of liner PAN chain occur in second stage. In the final stage, the cross-link degree of molecular chain increases and transforms into ladder-shaped reticular structure. The three reactions occurred in the second stage all follow the first order reaction and the corresponding parameters such as activation energy and pre-exponertial factor are different. With the increase of pyrolysis temperature, the graphitic layer planes gradually grow along a axis direction and the doo2 values increase. It indicates that PAN transits from the linear molecular structure to the turbostratic graphitic structure. By comparing the pyrolysis process of PAN in Ar with that in vacuum, it is found that the thermal activation energy in vacuum is lower than that in Ar, which indicates that the vacuum atmosphere favors the degradation reaction. Furthermore, the carbon membrane prepared in vacuum has higher order degree, lower structure defect and smaller pore than that prepared in vacuum. According to pore model, the theoretical pore sizes formed in vacuum and Ar are approximately 0.71×1.23×1.28 nm and 0.72×1.48×1.56nm, respectively.