Fabrication of polyimide-derived carbon molecular sieve membranes via hydrocarbon vapors-assisted carbonization for enhanced gas separation

Carbon molecular sieve (CMS) membranes exhibit good separation performance for gas pairs with similar kinetic diameters and superior environmental resistance. Chemical vapor deposition (CVD) modification is one of the most effective techniques for enhancing the selectivity of CMS membranes. Compared with gaseous CVD reagents, liquid reagents have lower transportation costs and are easier to trap outside the apparatus. We have previously reported that the addition of toluene vapor markedly enhances selectivity of H 2 , and have investigated the effect of carbonization temperatures and duration of toluene vapor on separation performance. Here, xylene isomers of vapors are also used to prepare CMS membranes at 675 °C for the addition of 30 min. The effect of the heating dwell time and volume concentration on separation performance of CMS membranes with the addition of p -xylene vapor is also investigated. The results show that the addition of p -xylene vapor had a stronger effect on permeation performance than varying the heating dwell time. Furthermore, addition of hydrocarbon vapors significantly improves the selectivity between small and large molecules, as exemplified by the He/CH 4 and H 2 /CH 4 separations. CMS membranes with p- xylene vapor obtain the highest He/CH 4 and H 2 /CH 4 selectivity, 15,073 and 12,968, respectively, when the concentration is 0.8 vol%. This work provides a strategy for the separation of small and large molecules.