| Carbon membranes (carbon molecular sieve membranes for full name) are usuallyfabricated by the pyrolysis of organic membranes, which can effectively separate gas mixturedepending on molecular sieving mechanism. Over the past30years, carbon membranes havegained much attention because of its advantages, such as high efficiency, energy saving,environmental protection, convenient operation, easy control, easy scaleup and easy operation.Carbon membranes show a good appilication prospect in gases or liquid separation, biomasspurification, membrane reactor, fuel cell and so on. However, the industrial development ofcarbon membranes is still limited by the vital restriction of high-cost and brittlement. To solvethese problems the following solutions were proposed in this thesis: first, carbon membraneswere preparaed by compositing a separation layer on the support to improve the mechanicalperformance. Second, the as-prepared carbon membranes were applied for the intensificationof chemical reaction process with high added value. It is believed that the present work isfavorable for resolving the issues confronted by carbon membranes and consequentlypromotes the commercial application by building the academic and practical foundation.First, the support was fabricated with inexpensive phenolic resin. The effect of mouldingpressure and the dosage of ZSM-5on the pore size distribution and porosity were investigated.Composite carbon membranes were prepared by adopting6FAPB-CBDA type polymide asprecursor material and ZSM-5as modifier by two membrane-forming methods of drop-coatingand spin-coating methord, respectively. Thermogravimetry, Fourier transformed infraredspectroscopy, scanning electron microscopy, transmission electron microscopy, x-raydiffraction, nitrogen adsorption and permeation, etc., were utilized to analysis the thermalstability of precursor, evolution of functional groups, morphology, pore structure, carbonstructure and gas separation performance of the samples. The influence factors, such asmembrane-forming method, the dosage of ZSM-5, permeating-temperature and pressure, andcarbonization temperature, on the separation performance of carbon membranes wereinvestigated. Finally, the carbon membranes with excellent separation performance werecouplied in the reactor and used to intensify the reaction of hydrogen product from methanolsteam reforming. The effect of reaction temperature, the carbonization temperature of carbonmembranes and the type of reactor on the methanol conversion and hydrogen yield wasstudied.Results have shown that:(1) The pore radius size of support carbonized at900°Cdecreases with the increase of moulding pressure. The optimum moulding pressure is2MPa, from which the pore radius size of as-sythesized support is mainly distributed in0.4-0.6μmalong with the porosity of53.25%. The modified support with ZSM-5is beneficial to theenhancement of mechanical strength. Nevertheless, it is not suitable for the usage of supportdue to the silmutanuous reduction of porosity.(2) For drop-coating, the optimum separationperformance is achived at the selectivities of132.52(H2/N2),18.47(CO2/N2),8.27(O2/N2)and5.3(compressed air) when the preparation condition is carbonization temperature at650°C and20droplets.(3) For spin–coating, the optimum separation performance is achived atthe selectivities of490.2(H2/N2),67.66(CO2/N2) and34.84(O2/N2) when the preparationcondition is coating-drying cycles6times and carbonization at650°C. In comparison, theincorporation of ZSM-5into membranes results into the reduction of permeability andselectivity of carbon membranes prepared by spin-coating and coating-drying of6cycles.(4)When the abovementioned optimum carbon membranes from spin-coating method wereapplied to intensify the reaction, the optimum results is reached to51.5%(hydrogen yield)and75%(conversion) at the conditions of reaction temperature of260°C. Those two valuesare correspondingly1.21time and1.24times in magnitude in contrast with traditional fixedbed reactor. |
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