Effects of Diatomaceous Earth Addition on the Microstructure and Gas Permeation of Carbon Molecular Sieving Membranes

Abstract Carbon molecular sieving (CMS) membranes were successfully prepared using polyimide as precursor and diatomaceous earth (DE) as dopants through the processes of membrane formation and pyrolysis. The thermal stability, surface functional groups, microstructure and morphology of membrane samples were characterized by the thermogravimetric analysis, X‐ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscope, respectively. The effects of DE dosage, support and permeation temperature on gas permeation of the CMS membranes were investigated. The results show that the addition of DE improves the thermal stability of precursor and the graphitization degree of derived CMS membranes. The incorporation of DE increases the gas permeability and microporous structure of CMS membranes at a loss of selectivity. The permeability of CMS membranes increases with elevating the permeation temperature. When DE composite CMS membranes are prepared by adding 0.4% DE in starting materials on plate supports, the optimum gas permeability reaches to 998.7 Barrer for H 2 , 262.3 Barrer for CO 2 , 231.6 Barrer for O 2 , along with the selectivity of 20.7 for H 2 /N 2 , 5.4 for CO 2 /N 2 and 4.8 for O 2 /N 2 .