Preparation and characterization of carbon molecular sieve membranes for gas separation the effect of incorporated multi-wall carbon nanotubes

A new class of multi-wall carbon nanotubes (MWCNTs)/carbon nanocomposite thin films was successfully prepared by incorporating (MWCNTs) into polyimide (PI) precursor solution. The carbon films were obtained in only one coating step by spin-coating technique on a macroporous alumina substrate and were pyrolyzed at 773 K. The structure and single gas permeation properties of PI-based carbon membranes incorporated with or without MWCNTs were investigated. From the FE-SEM images, the pure carbon membranes have a thin dense permselective layer with few closed pores while the permselective layer of the MWCNTs/carbon nanocomposite thin films are porous due to the structure of nanotubes. The MWCNTs/carbon nanocomposite thin films exhibited that the ideal carbon dioxide flux was 866.6 Barrer (1 Barrer = 1 )/10(10 cm3 (STP) cm cm(2 s(1 cm Hg(1) and the separation factor of CO2/N2 was 4.1 at room temperature and 1 atm, which was 2 Á 4 times of magnitude higher than that of pure carbon membrane prepared by the same procedures and conditions.

In this study, MWCNTs/carbon nanocomposite membranes with excellent gas separation performance are successively prepared by one time coating MWCNTs-incorporated PI suspension. FE-SEM images of the synthesized membranes suggested that many pores formed on the permselective layer to pass the different gas molecules. Therefore, the nanotubes offered a favorable effect in increasing gas permeability by decreasing the gas diffusion resistance. Furthermore, MWCNTs accelerate the transport of easily condensable gases like CO2 and O2. This may be exploited to improve biogas separation and air separation.