Transport and morphological characteristics of polyetherimide-based carbonmolecular sieve membranes

A new class of carbon molecular sieve membranes (CMSMs) has been prepared b y carbonization of polyetherimide-coated mesoporous tubular supports. The m embranes show higher permeance and better separation factors than other sup ported CMSMs reported in the literature for the CO2/CH4 and H-2/CH4 binary mixtures as well as for the CO2/H-2/CH4 ternary mixture. CO2/CH4 separation factors as high as 145 for the equimolar binary and 155 for the ternary mi xture were obtained with a CO2 permeance about 0.15 (cm(3)/cm(2).psi.min). The corresponding H-2/CH4 separation factors for the equimolar binary and t ernary mixtures were 68 and 50, respectively, with a H-2 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. T o study the mechanism of permeation and separation in CMSMs, tests with sin gle gases as well as with binary and ternary mixtures were performed at dif ferent temperatures, transmembrane pressure differences, and feed compositi ons. Elemental analysis, scanning electron microscopy, and gas adsorption w ere also employed to study the morphology of the resulting membranes. Eleme ntal analysis shows that although the structure consists mostly of carbon, it also still contains oxygen, nitrogen and hydrogen. Scanning electron mic roscopy of the cross section of the carbonized membrane shows that the carb onized layer lies essentially within the mesoporous gamma-alumina layer, a result also verified by N-2 adsorption analysis at 77 K. The experimental d ata were compared with simulation results with the same mixtures using a no nequilibrium molecular dynamics method.