| Molecular sieving carbon membranes (MSCMs), a new type of membrane materials featuring with molecular sieving property, are mainly prepared by pyrolysis of polymers as precursors. Compared with polymeric membranes, MSCMs possess numerous advantages, such as high gas seperation factor, good thermal resistance and chemical inertness, etc. MSCMs can be used in various fields for gas separation, including oxgen enrichment, nitrogen enrichment, hydrogen recovery, acid gas removal from natural gas and vapor removal from air. However, MSCMs are still commercially unavailable because of their high-cost, low production and poor reproducibility. Therefore, it is necessary to find or design precursors with best perpfrmance vs price compromise, together with intensive investigations of the pyrolytic mechanisms of precursors and the microstructure (carbon structure and pore structure) formation of MSCMs to ascertain the relationship between the microsctructure and gas separation performance. Based on those sysmatical works, it would be helpful to guide the preparation of MSCMs in principle and to resolve the aforementioned problems (i.e., poor reproducibility and low permeability) of MSCMs. Moreover, it would promote the industrialized and commercialized progresses for MSCMs.In the viewpoint of property and structure of polymers, two novel precursors as poly(phthalazinone ether sulfone ketone) (PPESK) and HQDPA-ODA type polyimide (PI) were adopted to prepare MSCMs for gas separation. The molecular structure (i.e., molecular rigidity, fractional free volume, thermal stability and char yield) and the chemical structure changes of precursors during pre- heattreatment and pyrolysis were monitored and analyzed by thermogravimmetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy (FT-IR), X photoelectron spectroscopy (XPS). The microstructure formation and evolution of MSCMs during pyrolysis were measured in order to find the relationship between microstructure and gas separation performance by scanning electron microscopy (SEM), transmission electron microscopy (TEM), XRD, Raman spectroscopy (Raman) and N2 adsorption. The effects of chemical structure in precursor as sulfone/ketone, pre- heattreatment temperature, pyrolytic temperature, atmosphere, and permeating temperature on the gas permeation of MSCMs were mainly investigated by gas permeation technique. Additionally, two methods as charging additives (i.e. polyvinyl pyrrolidone (PVP) and zeolite (ZSM-5)) and introducing sulfonated acid functional groups into precursor membranes were used to improve the permeability of MSCMs.The results have shown that: (1) PPESK and HQDPA-ODA type PI with high molecular rigidity and FFV, high thermal stability and char yield, were two satisfactory precursors to prepare MSCMs. During pyrolysis, hetero- atom as oxgen, nitrogen and sulfone would peel off from the matrix of PPESK in the form of small gases, remaining large area graphite-like microproe structure as the result of coalescent and rearrangement of residual structure. (2) The pre- heattreatment is an important step. In this step, stable ester and anhydride cross-linking structure would be formed. Pre- heattreatment can inhibit the growth of microcrystal of carbon and retard the graphitization process during pyrolysis. It is helpful to increase the microporous volume and to decrease the pore width. The graphitization degree is gradually increased together with the formation of large amount of microporous structure with increasing pyrolytic temperature. (3) The micropore structure of MSCMs was constitued by supermicropore and ultramicropore, which were formed by the stacking of microcrystal and carbon layers in MSCMs, respectively. The supermicropore contributes MSCMs with high permeability while ultramicropore with high selectivity. (4) When PPESK based MSCMs were prepared by pre- heattreatment at 460℃and pyrolysis at 800℃, the gas permeabilities and selectivities for H2, CO2, O2, N2 and H2/N2, CO2/N2 and O2/N2 were 47.90 Barrer (1Barrer=1×10-10 cm3 (STP) cm/cm2 s cmHg=7.5×10-5 cm3 (STP) cm/cm2 s kPa), 30.90 Barrer, 4.43 Barrer, 0.18 Barrer, 266.1, 171.7 and 24.6, respectively. When HQDPA-ODA type PI based MSCMs were prepared by pre- heattreatment at 460℃and pyrolysis at 700℃, the gas permeabilities and selectivities for H2, CO2, O2, N2 and H2/N2, CO2/N2 and O2/N2 were1077.23 Barrer, 741.53 Barrer, 108.92 Barrer, 7.66 Barrer, 140.9, 96.9 and 14.2, respectively. (5) With increasing the sulfonation degree in precursor from 59％to 75％, the O2 permeability of MSCMs prepared at 650℃was improved from 29.81 Barrer to 52.07 Barrer, together with the O2/N2 was reduced from 11.9 to 7.5. With introducing of zeolite (ZSM-5) and polyvinylpyrrolidone (PVP), the O2 permeability of their derived MSCMs were increased from 10.80 to 199.70 Barrer and 124.89 Barrer, respectively; together with the O2/N2 were decreased from 15.9 to 10.3 and 4.2, respectively.
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