Abstract
Carbon molecular sieve (CMS) membranes were prepared by pyrolysis of polyimides containing carboxylic acid groups, in order to investigate their permeation properties for He, CO 2, O 2 and N 2. The polyimides were synthesized with a varying number of carboxylic acid groups in the diamine. Wide-angle X-ray diffraction and nitrogen gas sorption isotherms were employed to characterize the carbon structures. From pure gas permeation experiments, it was found that the removal of carboxylic acid pendent side groups during the pyrolysis resulted in a large pore volume in the carbon matrix, which significantly affected the gas separation performance of the final CMS membranes. The gas permeabilities of the CMS membranes pyrolyzed at 700 °C improved with increasing carboxylic acid group content. The CMS membranes derived from polyimide containing 50 mol% diamines showed maximum gas permeability for O 2 of 707 Barrers (1×10 −10 cm 3 (STP) cm/cm 2 s cmHg) and an O 2/N 2 selectivity of 9 at 25 °C.
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