Preparation and Gas Permeation Properties of Composite Carbon Molecular Sieve Membranes Derived from Polyimides with Thermally Decomposable Sulfonic Acid Salt and/or Hexafluoroisopropylidene Group

Abstract

Carbon molecular sieve (CMS) membranes were prepared from polyimides with sulfonic acid triethylammonium salt (SO 3 NH(C 2 H 5 ) 3 ) and/or hexafluoroisopropylidene (-C(CF 3 ) 2 -) groups by pyrolyzing precursor composite membranes at the temperatures ranging from 773 to 973 K in an N 2 flow for 1 h. The precursor membranes were prepared by coating the polyimides on ceramic porous support tubes. The sulfonic acid salt and the -C(CF 3 ) 2 -group decomposed in the ranges of 573 to 673 K and 723 to 973 K, respectively. The composite CMS membranes prepared here had a defect-free top layer of 1.5 to 5 µ µ µ µ µm thick. The CMS membrane derived from the polyimide with both the thermally decomposable groups displayed the highest gas permeances. The decomposition of sulfonic acid groups followed by the decomposition of the -C(CF 3 ) 2 -group just before the substantial decomposition of the polyimide backbone seemed to significantly enhance the micropore structure of the resultant pyrolytic layer. Compared to the CMS composite or hollow-fiber membranes reported in the literature, the membranes prepared in this study displayed higher O 2 and CO 2 gas permeances with reasonably high ideal separation factors for O 2 /N 2 and CO 2 /N 2 separations.

Gas separation using Knudsen and surface diffusion II: Effects of surface modification of epoxy/porous SiO2 composite

“…Gas separation using porous materials has lately attracted attention from the perspective of low running costs. Therefore, zeolite [1][2][3][4][5][6][7], carbon [8][9][10][11][12][13][14], and silica membranes [15][16][17][18][19] have been actively investigated. Mesoporous silica membranes are now being examined with interest because the pore wall surface is easily modified by silane coupling agents [17][18][19].…”

Preparation and gas permeability of the surface-modified porous Al2O3 ceramic filter for CO2 gas separation

“…For instance, Abidi et al [9] modified titania with fluorinated organosilane to produce separation membrane of a CO 2 /N 2 selectivity of 12. The carbon membrane is prepared by carbonizing polymers [13][14][15], in which the membrane preparation condition affects the performance significantly. Islam and Tanaka [14] reported a CO 2 /N 2 selectivity of 20-30 of separation membrane produced from polyimide.…”

“…The carbon membrane is prepared by carbonizing polymers [13][14][15], in which the membrane preparation condition affects the performance significantly. Islam and Tanaka [14] reported a CO 2 /N 2 selectivity of 20-30 of separation membrane produced from polyimide. Because these filters have poor gas permeability in spite of excellent gas selectivity and gas separation ability, thinning of various separation membranes is studied for the improvement of permeability.…”