•High performance carbon molecular sieve membrane for gas separation is prepared.•Ultra-micropore structure is tailored by intrinsic viscosity of precursor.•Precursor with low intrinsic viscosity leads to high selective CMS membranes.Here we report the permeability and separation performance of self-standing carbon molecular sieve (CMS) membranes formed by pyrolysis of polyimide (PI) precursors derived from poly(amic acid) (PAA) with varying intrinsic viscosity. CMS resulted in ultra-microporous membranes showing a classical molecular sieving structure as gas permeation was high for smaller molecular gas (H2), which then decreased sequentially as the molecular sizes increased in the order of CO2, O2 and N2. An important relationship was found when the intrinsic viscosity of the PAA precursor decreased from 1.66 to 0.65 dl g−1, the ideal gas selectivity jumped to higher values such as from 101.8 to 163.1 for H2/N2, from 21.5 to 34.6 for CO2/N2 and from 6.7 to 10.7 for O2/N2 while the permeability decreased such as from 1816 to 1487 Barrer for H2, from 383.4 to 314.8 Barrer for CO2, from 119.0 to 97.7 Barrer for O2, from 17.8 to 9.1 Barrer for N2. The low intrinsic viscosity conferred a superior pore size control of the CMS structure, with an average ultramicropore size around 3 Å. The O2/N2 and H2/N2 ideal selectivity versus permeability results were all above the Robeson’s upper bound line, thus demonstrating the effect of low intrinsic viscosity precursors in the synthesis of high performance CMS membranes.Download high-res image (156KB)Download full-size image

Mesoporous polyacrylonitrile and carbon fibers have been prepared by electrospinning and subsequent supercritical drying and carbonization. Polyvinylpyrrolidone was used as a template. Ambient drying, oxidation, and supercritical drying were conducted to investigate the effects of treatment methods on the structure of the fibers. Interesting surface morphologies of the fibers, including nanoconvexities and nanorods, were found when the different drying methods were used. The surface area of the mesoporous carbon fibers was estimated as 602.0 m2 g−1, with an average pore size of 3.6 nm.

Methylene diphenyl dicarbamate (MDC) was synthesized from methyl phenyl carbamate (MPC) and trioxane using sulfuric acid (H2SO4) as catalyst. The effects of reaction temperature, reaction time, molar ratio of reactants and the content of catalyst have been studied in details. The results showed that H2SO4 exhibited high catalytic activity with the merits of moderate reaction velocity. Under the conditions of n(MPC)/n(trioxane) = 3:1, reaction temperature of 95°C, reaction time of 3.5 h and 30% H2SO4, the conversion of MPC reached 99.0% with the selectivity of MDC 81.6%. Moreover, the H2SO4 catalyst was reused five times without obviously activity decrease. Based on the identification of byproducts, a possible reaction mechanism was proposed.