| Carbon membranes have shown extremely attractive prospect in many separation fields, such as air separation, natural gas purification, desulfurization, dehumidification, organic mixtures separation, hydrogen absorption, carbon dioxide capture, waste water treatment, drinking water purification and and so on, due to their feature of good chemical stability, excellent separation property, high thermal stability. The study of carbon membranes is one of the most hot topics for membrane science and technology. However, the disadvantages of expensive cost, poor mechanical performance limit its large-scale development and industrial application. Therefore, it is the key to exploit cheap precursor with high performance and optimum fabrication process, to obtain high separation performance carbon membrane so as to improve its performance-price ratio and utilization value. For that reason, on the basis of our early work, supported composite carbon membranes were prepared through chemical crosslinking technology and optimizing processing method by choosing cheap 3, 3’, 4, 4’-oxydiphthalic dianhydride-4, 4’-oxydianiline(ODPA–ODA) type polyetherimide(PEI) as precursor. This work is regarded to enrich membrane material preparative technique and promote application and development of carbon membrane for building a good foundation.First, choosing ethylene glycol was adopted as chemical crosslinking agent for pretreatment of precursor membrane, of which the process was analyzed in assosiation with the cross-linking mechanism. Furthermore, supported carbon membranes with high separation and good mechanical properties were prepared. The as-abtained polymeric and carbon membranes were investigated by using thermal gravimetric analysis, infrared spectroscopy, x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy analysis, pore size distribution, porosity and gas permeation technology. The effecs of chemical crosslinking condition and preparation condition on the membrane forming, microstructure and gas separation performance were investigated. The factors include pre-oxidation heating rate, pre-oxidation final temperature, ethylene glycol content, ACF content, permeation temperature, permeation pressure, carbonization temperature, etc.Results showed that:(1) The adopted chemical crosslinker ethylene glycol can react with the present precursor by forming crosslinking structure, so as to faciliate the formation of gas separation carbon membranes with integrated membrane surface. Compared with pre-oxidation method, chemical cross-linking method is more favorable for the preparation of unsupported carbon membranes with higher permeability. When the amount of crosslinker is 10%, the gas permeabilities can reach to 8219Barrer(H2), 462Barrer(CO2), 1300Barrer(O2), together with the selectivities of 7.77(H2/N2), 1.47(O2/N2), 17.77(H2/CO2). When the precursor is further incorporated with 0.5% ACF, the gas permeabilities of obtained carbon membranes can reach 12351 Barrer for H2.(2) When supported carbon membranes were prepared at the ethylene glycol amount of 10%, spin-coating was better than dropping-coating in aspect of membrane forming conditon and gas separation performance. At the permeation condition of T=30℃, P=0.1MPa, the gas permeabilities for the former are H2=221Barrer, CO2=46Barrer, O2=65Barrer, N2=61Barrer, and the selectivities are O2/N2=3.63, H2/CO2=1.07, H2/N2=4.82. When the precursor is doped with ACF, the final permeability and selectivity would further dropped.(3) If the support body was underwent a pre-carbonization at 280 ℃before spin-coating a separation layer, it was more beneficail to enhance the mechanical properties of the support body. When the carbon membranes were prepared by using a support with pre-oxidation procedure at a heating rate of 0.25℃/min from room temperature up to 380℃ After carbonization, their permeabilities can reach to 10384.8Barrer(H2), 1405.2Barrer(CO2) and 3217.9Barrer(O2). |
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