Transport and Morphological Characteristics of Polyetherimide-Based Carbon Molecular Sieve Membranes

Abstract

A new class of carbon molecular sieve membranes (CMSMs) has been prepared by carbonization of polyetherimide-coated mesoporous tubular supports. The membranes show higher permeance and better separation factors than other supported CMSMs reported in the literature for the CO2/CH4 and H2/CH4 binary mixtures as well as for the CO2/H2/CH4 ternary mixture. CO2/CH4 separation factors as high as 145 for the equimolar binary and 155 for the ternary mixture were obtained with a CO2 permeance about 0.15 (cm3/cm2·psi·min). The corresponding H2/CH4 separation factors for the equimolar binary and ternary mixtures were 68 and 50, respectively, with a H2 permeance of 0.13 (cm3/cm2·psi·min). The membrane also shows good stability when tested with CO2 and Ar single gases, as well as with an equimolar mixture of CO2/CH4. To study the mechanism of permeation and separation in CMSMs, tests with single gases as well as with binary and ternary mixtures were performed at different temperatures, transmembrane pressure differences, and feed compositions. Elemental analysis, scanning electron microscopy, and gas adsorption were also employed to study the morphology of the resulting membranes. Elemental analysis shows that although the structure consists mostly of carbon, it also still contains oxygen, nitrogen and hydrogen. Scanning electron microscopy of the cross section of the carbonized membrane shows that the carbonized layer lies essentially within the mesoporous γ-alumina layer, a result also verified by N2 adsorption analysis at 77 K. The experimental data were compared with simulation results with the same mixtures using a nonequilibrium molecular dynamics method.

Novel approaches to fabricate carbon molecular sieve membranes based on chemical modified and solvent treated polyimides

“…Polymers with thermosetting properties, which do not melt and retain its structure during carbonization, are key criteria for carbon membrane materials [9]. In view of this, aromatic polyimides appear as a popular material for the carbonization of carbon membranes due to their superior separation performance and high thermal resistance [6,27,28]. A commercially available polyimide was used as the precursor in this study, which was Matrimid â 5218 (BTDA-DAPI, 3,3 0 4,4 0 -benzophenone tetracarboxylic dianhydride and 5(6)-amino-1-(4 0 -aminophenyl-1,3-trimethylindane).…”

“…CMSMs compare favorably with their polymer precursors by exhibiting intensive gas transport properties. It can achieve higher selectivity without loosing the productivity [2][3][4][5][6][7][8][9] and thus surpass the upper bound limit of polymeric membranes. CMSMs have also been recognized with advantages of higher thermal and chemical stability [2,[9][10][11][12][13].…”

“…Many studies have reported that a CMSM with tailored microstructure (pore size, pore volume, etc.) could be obtained by controlling the pyrolysis conditions [2,6,9,13,15,[17][18][19] and post-/pre-treatment conditions [7,10,[20][21][22][23][24]. On the other hand, CMSMs can be modified to improve their permeation properties or to solve several problems inherent to their structures.…”

Gas Separations using Ceramic Membranes

“…In this project, we developed a membrane-based sour gas removal process using a new class of membrane material, a carbon molecular sieve (CMS) composite membrane, i.e., CMS membranes supported on commercial porous inorganic membranes as substrates. CMS membranes have been demonstrated in a variety of laboratory studies to be superior to polymeric membranes in terms of permeability, selectivity, and robustness [2][3][4][5][6][7][8][9][10][11][12][13][14][15][20][21][22][23][24]. In comparison to competing membrane technologies for natural gas upgrading, the CMS composite membranes have the potential to reduce both capital and operating costs.…”

Carbon molecular sieve membranes for desalination

“…This prevents the formation of large graphite-like crystals during carbonisation which may adversely affect separation performance. The carbonisation process removes most of the heteroatoms originally presented in the polymeric macromolecules, while leaving a cross-linked and stiff carbon matrix behind (Sedigh, Xu et al 1999). Finally the resultant amorphous carbon material should exhibit a distribution of micropore dimensions (d p < 2 nm) with only short-range order of specific pore sizes, although as with all amorphous materials, pores larger than the ultramicropores may also be formed.…”