Experimental Study On Catalytic Cracking Of Naphthalene In Biomass Tar With Composite Bentonite-Based Foam Ceramics

Efficient degradation of biomass tar is an urgent problem to be solved in biomass gasification.Catalytic cracking technology can effectively improve the degradation efficiency of biomass tar,which has attracted extensive attention from scholars at home and abroad.Polycyclic aromatic hydrocarbon compounds are the leading organic components that are difficult to remove in biomass tar.Because of the degradation of these compounds,naphthalene was selected as the model compound of polycyclic aromatic hydrocarbons in biomass tar in this experiment.Considering the strong adsorption properties and high specific surface area of bentonite,the physicochemical properties of bentonite-based foam ceramics loaded with different metal oxides（NiO,Fe₂O₃,Fe₃O₄）were investigated using bentonite as the ceramic substrate.The catalytic degradation law and product characteristics of biomass tar by foam ceramics and the evolution law of metal oxides in the catalytic process were deeply analyzed.The specific contents of this thesis are as follows:（1）The catalytic degradation performance of bentonite-based foam ceramics was investigated using a two-stage pyrolysis reactor.The gas-phase product yield was significantly improved under the catalysis of bentonite-based foam ceramics.At 850°C,the gas-phase product yield increased from 13.07%without catalysis to 48.09%,an increase of 35.02%.By GC-MS detection,it was found that the main components of the degradation products were light aromatic hydrocarbon compounds and light polycyclic aromatic hydrocarbon compounds,of which the naphthalene cracking rate reached 24.45%.（2）The composite foam ceramics were prepared by loading NiO,Fe₂O₃,Fe₃O₄,and the catalytic performance of bentonite-based composite foam ceramics was explored.Among them,loading NiO is the best,and the gas-phase product yield can be increased by 45.89%at 850°C,while the loading of Fe₂O₃and Fe₃O₄can increase by 25.80%and 21.33%,respectively.It using GC-MS detection,it was found that under the catalysis of NiO,Fe₂O₃,and Fe₃O₄composite foam ceramics,the naphthalene cracking rates reached 88.35%,41.93%,and 71.29%,respectively.However,in the repeated use test at 850°C,the gas-phase product yield of NiO syntactic foam ceramics decreased from 93.63%for the first time to 50.12%for the fourth time,a decrease of 43.51%.（3）Through repeated use experiments,EDS analysis,and SEM characterization,it was found that the carbon deposition and sintering resistance of NiO syntactic foam ceramics were effectively improved after the introduction of iron oxides as metal additives.After four repeated use at 850℃,the gas-phase product yield of Ni-Fe₂O₃composite foam ceramics decreased by20.29%,while Ni-Fe₃O₄composite foam ceramics decreased by 17.98%.The GC-MS test found that under the catalysis of Ni-Fe₂O₃composite foam ceramics and Ni-Fe₃O₄composite foam ceramics,the cracking rate of naphthalene reached 100%.This paper used bentonite-based foam ceramics as catalyst negative carriers loaded with monometallic and bimetallic oxides.The catalytic effects of different catalysts on biomass tar model compounds were obtained.It provides some theoretical support for the catalytic cracking of biomass tar and has some guidance for preparing and selecting catalysts in the actual production process.