Preparation Of Carbon-based Material Gas Catalytic Pyrolysis Of Biomass

In nowadays, the raw materials of carbon fiber and carbon nanotubes are mostly from methane gas, natural gas and liquefied petroleum gas (LPG), and the hydrogen is generally produced by water electrolysis or gasification of fossil fuel conversion system. If the carbon and hydrogen can derive from biomass biogas or biomass cracking hydrocarbons, the carbon fixation and the formation of carbonaceous materials can result in zero emissions of carbon dioxide, and large amounts of hydrogen can be produced. Before consuming, fixing carbon and then converting to carbon materials from the source by means of catalytic decomposition of biomass and production of pure hydrogen as the fuel cell power generation fuel are of great significant.In this thesis, the carbon nanotubes were prepared by the Chemical Vapor Deposition (CVD). The methane gas and analog biogas as raw material were catalytic decomposed with the homemade nickel catalyst. The performance of the catalyst and the hydrocarbon cracking characteristics were discussed. The influence factors of CO2, ammonia and other impurities on the lifetime of the catalyst and the carbon deposition rate were investigated.First the optimum reaction temperature and the carbon deposit rate of methane catalytic decomposition were researched for determined the optimal performance of catalyst under several kinds of commonly used metal catalyst, activated carbon and homemade nickel-based catalyst in the thermo gravimetric analyzer. Then the influences of catalytic reaction temperature, concentration of N2(CH4/N2system), concentration of CO2(CH4/CO2system) and NH3concentration (CH4/NH3system) on methane catalytic decomposition process were investigated in tube furnace reactor, and the purity of carbon material in the system of CH4/N2and CH4/CO2system were investigated through thermo gravimetric analysis. Finally the analysis methods such as XRD, SEM and TEM were applied to characterize the surface morphology of carbon deposited on the catalyst.The research results show that the activation energy of the homemade nickel-based catalyst (96%Ni), which has much higher catalytic performance than Ni, Fe, Cu and activated carbon (AC) catalyst is94.61kJ/mol during492℃to625℃, and the service lifetime of the catalyst is improved. At539℃the carbon deposition rate which is242.5%reaches maximizing. The carbon deposit rates of methane catalytic decomposition was approximately linear with the methane concentration approximation. The analysis results of SEM and TEM confirmed that the precipitation of carbon in catalyst surface material is belong to carbon nanotubes. Under the condition of CH4concentration of60%, carbon deposit rate of CH4/CO2catalytic decomposition is obviously lower than that of CH4/N2when the reaction temperature is between500℃to680℃. The influence of CO2and N2is essentially the same during680℃to900℃. The morphology of carbon nanotubes prepared by CH4/N2system and CH4/CO2system have the similar characteristics, but the former has a higher purity of carbon nanotubes. With the increase of CO2concentration, carbon deposit rate gradually decreases. The best catalytic decomposition temperature of the simulation of methane (60%CH4and40%CO2) is at650℃, and carbon deposit rate reaches215.2%. The methane catalytic decomposition process is restrained from NH3. When NH3concentration reaches a certain amount (30%), methane catalytic decomposition has not happen again.