Catalytic Pyrolysis Mechanism Of Biomass Model Compounds Based On Online Mass Spectrometry

In recent years,high value utilization of biomass has become a global focus.Among many biomass high-value utilization technologies,upgrading quality of its economic feasibility is still facing the target product,such as low yield and poor quality problems,one of the important reasons for catalyst deactivation rate is too fast,stability,catalytic efficiency and a high value for biomass utilization has brought serious challenges.The key to solve the above problems is to deeply understand the reaction path and mechanism of biomass catalytic pyrolysis.In this paper,the catalytic pyrolysis reaction mechanism of biomass at the molecular level will be understood through the catalytic pyrolysis reaction pathway of graduate material model compounds and its influence on catalyst deactivation.In this experiment,a two-stage micro-fixed bed catalytic pyrolysis reaction device was connected with an online photoionization time-of-flight mass spectrometry analysis instrument as the main experimental means.At the same time,GC-MS,thermogravimetric analyzer and BET tester were used for auxiliary analysis of the catalytic products or catalysts.The commonly used HZSM-5 solid acid catalyst was selected,and 17 typical model compounds were selected as experimental samples.According to their source,they can be divided into three categories: carbohydrate compounds,phenolic compounds and intermediate compounds.On-line photoionization mass spectrometry(SPI-MS)can be used to monitor the chemical composition of gaseous products during catalytic pyrolysis and their dynamic changes with the catalyst deactivation process.By comparing the distribution and variation rules of pyrolysis products and catalytic pyrolysis products of different model compounds,the generation path of typical products and the main factors causing catalyst deactivation were analyzed,which provided theoretical guidance for analyzing the reaction mechanism of biomass catalytic pyrolysis and catalyst deactivation mechanism.The relevant research results in this paper include :(1)The transformation of aromatic hydrocarbons by cellulose model compounds under the action of HZSM-5catalyst mainly includes ring-opening reaction and Diels-Alder reaction.(2)Decarboxylation,side chain breaking,cyclization and methyl rearrangement are the main pathways of lignin model compounds to aromatic hydrocarbons.(3)Lignin has a more complex structure than cellulose,and oxygen-containing phenolic compounds are easier to form coke than cellulose model compounds,which reduces the catalytic efficiency of biomass.(4)Compared with cellulose compounds,the benzene side chains of lignin compounds play an important role in the conversion process of biomass to aromatic hydrocarbons,including the alkane side chain to promote the generation of PAHs,and the presence of methoxy side chain will lead to the formation of more coke,which has a negative impact on catalytic pyrolysis.(5)The decarboxylation reaction of benzofuran under the action of HZSM-5 catalyst will produce a large amount of coke to block the pore of the catalyst,resulting in the deactivation of the catalyst.