Study On Catalytic Cracking Of Biomass Tar Model Compound Toluene By Calcined Mussel Shell Supported Nickel Catalyst

Biomass gasification is one of the most promising biomass utilization technologies,but the formation of by-product tar in the gasification process has always restricted the wide application of this technology.Catalytic cracking is an ideal tar removal technology because of its effectiveness and advanced nature.Due to the complexity of tar composition in biomass gasification,toluene is often used as the model compound of biomass tar to study the catalytic reforming characteristics of catalysts.The catalytic properties of nickel-calcined mussel-based catalysts and catalysts modified by different promoters?Fe,Co,Cu and Ce?were evaluated in a fixed-bed reactor.Quantum chemical analysis of toluene cracking under the catalysis of Fe and Ni catalysts was carried out by using quantum chemical calculation software.This paper mainly includes the following three parts:Firstly,the calcined mussel shell supported NiO catalyst was prepared by impregnation method.The catalytic performance of NiO/CMS for steam reforming of toluene was evaluated in a fixed bed reactor.The physicochemical properties of the catalyst were analyzed by X-ray diffraction?XRD?,hydrogen temperature programmed reduction?H₂-TPR?,scanning electron microscope?SEM?and thermogravimetric analyzer?TG?.The effects of nickel loading?5-12wt.%?,reaction temperature?700-900??,S/C molar ratio?1.0-4.0?and space velocity(0.83-2.06h^-1)on the catalytic conversion of toluene were studied.The activity of CMS and its supported nickel catalyst was compared with that of calcium oxide and and its supported nickel catalyst.The results show that l0%wt.NiO/CMS catalyst has higher carbon conversion under reaction temperature of 850?,S/C molar ratio of 3.0 and reaction space velocity of 0.83h^-1,and the carbon conversion reaches 66.0%.The NiO/CMS catalyst have higher activity than CMS,CaO and NiO/CaO catalyst.The self-reduction of NiO/CMS catalyst depends on the reaction temperature.The catalyst can be reduced by syngas?such as H₂,CO?at above 800?.TG results show that the amount of carbon deposited on the catalyst decreases with the increase of reaction temperature and S/C molar ratio and the decrease of reaction space velocity.The amount of carbon deposited on 10%NiO/CMS is about17.1mg/100mg under the optimum reaction conditions.Than,NiO/CMS catalysts modified with different additives?Fe,Co,Cu and Ce?were prepared by co-impregnation.The catalysts were characterized by XRD,H₂-TPR,CO₂-TPD.The effects of reaction temperature,S/C ratio,space velocity and promoter loadings on toluene conversion were investigated in a fixed bed reactor.The results show that the optimum reaction temperature is 850?,S/C mole ratio is 3.0,the optimum space velocity is 0.83h^-1,which is similar to NiO/CMS.The toluene conversion and H₂yield of Ni/Fe bimetallic catalyst were higher,reaching 90.0%and 218.9g H₂/kg_Tolueneoluene under the optimum reaction conditions,respectively.The carbon conversion of the bimetallic catalyst increased first and then decreased with the increase of the ratio of promoter loadings.The optimum ratio of Fe/Ni,Ce/Ni,Cu/Ni and Co/Ni were 0.5,0.3,0.5 and 0.5 respectively.The activation energy of 10Ni5Fe/CMS bimetallic catalyst is66.91 KJ/mol according to Arenius equation.The carbon deposition of used catalyst was characterized by TG,and the kinetics of charring was analyzed.The results showed that the addition of promoter reduced the amount of carbon deposited,and the Fe oxide promoter is the best.The activation energy of carbon burning of 10Ni5Fe/CMS bimetallic catalyst was lower,which was 144.2KJ/mol.Finally,based on the density functional theory?DFT?,the decomposition of toluene catalyzed by Fe and Ni catalysts was studied by using the quantum chemical calculation software Gaussian 09.The reaction enthalpy analysis and the Mulliken bond population analysis were used to analyze the pyrolysis of toluene under the catalysis of Fe and Ni catalysts.The results show that after toluene radical is adsorbed on the surface of Fe and Ni,the Mulliken bond population of carbon bond in toluene decreases to some extent,and the stability of corresponding carbon bond decreases,that is,Fe and Ni have obvious catalytic effect on toluene cracking.When toluene is adsorbed on Ni,the Mulliken bond population of the corresponding carbon bond decreases more obviously,and the carbon bond breaks more easily,that is,the catalytic effect of Ni on the cracking of toluene is more obvious.