Structural characterization of polyetherimide-based carbon molecular sievemembranes

Supported carbon molecular sieve membranes (CMSMs) were prepared by the pyr olysis of a polyetherimide (PEI) polymeric precursor The membranes were cha racterized by scanning electron microscopy, energy dispersive spectroscopy, and micropore analysis, using gas adsorption techniques to relate their mi crostructure characteristics to their transport and separation characterist ics. The analysis shows that preparation conditions determine whether the c arbon molecular sieve layer forms within or outside the gamma -alumina laye r of the substrate. Micropore CO2 and N-2 adsorption analysis of both suppo rted and unsupported CMSMS showed a sharp peak at about (3.6-3.8) x 10(-10) m using the Horvath-Kawazoe method For the supported CMSMs it was observed that consecutive coating/carbonization steps reduced the pore volume in th e micro- and mesoporous regions, without greatly affecting the volume of po res in the range of (3.5-6) x 10(-10) m. The reduction of the pore volume i n the micro- and mesoporous regions is accompanied by an increase in the se paration factor and a decrease in the permeance after each coating/carboniz ation cycle. Micropore analysis of a membrane, whose performance had degrad ed, indicated that its volume of pores between (3.6-6) x 10(-10) m had dras tically decreased from the corresponding value of the as-prepared membranes .