Effect of polymer precursors on carbon molecular sieve structure and separation performance properties

Polymer precursor and processing method have a significant effect on the separation performance of carbon molecular sieve (CMS) membranes. The authors previously developed a polymer processing method involving oxygen exposure during pyrolysis using synthesized polyimide, 6FDA/BPDA-DAM. The objectives of this work were (i) to demonstrate the generality of the oxygen doping method with a commercially available polymer Matrimid®, (ii) to investigate resultant CMS membrane structures, and (iii) to engineer the CMS performance observed with Matrimid® precursor by tuning the pyrolysis temperature. The investigation of the pore structures is challenging due to their amorphous structures. Various researchers investigated using traditional characterization methods, such as XRD and adsorption, yet molecular sieving structure in ultramicropore region is still not known. Here, the authors investigated using gas molecules as a probe. By interpolating the characterization results, hypothetical ultramicropore size distributions for each CMS membranes are suggested. The results are used to explain dramatically different separation performance trends observed between 6FDA/BPDA-DAM and Matrimid® CMS membranes and to adapt the doping method on Matrimid® CMS membrane for better performance.

Figure optionsDownload as PowerPoint slideResearch highlights
► O2 doping controls permselectivity, α  , & permeability, PCO2PCO2.
► “Molecular rulers” probe number of pores (#) and size (d).
► O2 doped CMS separation performance is predictable.