Decomposition Of Toluene With Charcoal As Catalyst Under Microwave Irradiation

With syngas as the target product of the biomass gasification process, there inevitablely exists some aromatic hydrocarbons such as benzene, toluene, xylene and naphthalene in the product of gas phase. The presence of these substances will influence the quality of gas product, what is more, they will be condensed into tar in the downstream stage of the gasification process, that would affect the normal work of the device. So removing this tar is an important problem that must be solved in the process of biomass gasification. Nowadays, catalytic pyrolysis is the most effective solution to remove the tar.In microwave field, the catalytic reaction has some advantages like lower reaction temperature, higher conversion, higher target product yield and etc. However, the premise of a catalytic reaction that can be placed in the microwave field is that there exists absorbing agent to absorb the microwave energy and to covert the absorded energy into heat. Charcoal can not only act as catalyst for biomass tar, but also as the absorbing agent in microwave field. Thus, in this thesis, charcoal was chosen as absorbing agent and catalyst, toluene was chosen as the model compound of biomass tar. The decomposition characteristic of toluene was evaluated over charcoal packed fixed-bed reactor in microwave field.The ability of absorbing microwave of charcoal, active carbon, and silicon carbide was firstly investigated under microwave irradiation. Then, the decomposition of toluene over charcoal packed bed was studied with microwave heating. Considering the strong adsorption ability of active carbon and the weak adsorption ability of silicon carbide, active carbon and silicon carbide were chosen as contrast absorbing agent of charcoal. The decomposition behaviors of toluene over these three absorbing agents were investigated and compared with each other. The practicality and advantage of charcoal as the biomass tar catalyst in microwave field were presentedThe experimental indicate that the absorbing ability of these three absorbing agents is different when they are under the same irradiation power of microwave. But they all show similar behavior of absorbing microwave, for example, the ability of absorbing microwave irradiation is increased with increasing input power, decreased with the increase of the sample loading and carrier gas velocity. The experimental results of toluene’s decomposition over charcoal fixed bed has showed that a short residence time(1.0-1.2s) makes for a higher toluene cracking; A certain amount of water vapor in the system makes for a higher conversion of toluene and a higher yield of syngas product. When the water carbon ratio (S/C) is2.5with charcoal bed temperature of800℃, the toluene has its highest cracking rate of81.6%, and the total content of H2and CO in gas production is above81%; Along with the increase of charcoal bed temperature, the cracking rate of toluene is increased, and when the charcoal bed temperature get850℃, the toluene cracking rate get98.1%. XRD analyses of the charcoal before and after reaction show that the hot spots effect under microwave heating is one of the important reasons for the enhanced toluene conversion. Through the contrastive investigation of toluene cracking over charcoal, activated carbon and silicon carbide bed with microwave irradiation, is found that activated carbon has the highest ability of cracking toluene, and then is the charcoal, silicon carbide has the lowest ability of cracking toluene. Compared the source, price, applicable scope of activated carbon, silicon carbide, and charcoal, it is revealed that charcoal is the most cost-effective for biomass tar cracking in microwave field.