A Study On The Pyrolysis Mechanism Of Lignocellulosic Biomass

Biomass energy is currently the only renewable energy source that can be directly converted into a carbon-containing liquid fuel.China has huge biomass energy reserves and huge development potential,but the current utilization rate is still very low.Therefore,it is of great significance to realize the thermochemical conversion of biomass into high-grade liquid fuel and partially replace traditional fossil fuels.How to realize this process is the core of current research.Clarifying the entire biomass thermochemical conversion process from the mechanism has an important and positive effect on solving the scientific problem of"high-grade conversion".This article analyzes this basic problem and starts research from basic research.First of all,a new detection technology,electron paramagnetic resonance technology?EPR?,combined with other existing detection methods,was used to study the pyrolysis mechanism of lignin,one of the three major components of lignocellulose biomass.The in-situ detection technology and the cold trap-capture technology were used to detect and capture the intermediate products of the pyrolysis reaction of the model compounds of lignin.And free radicals were finally detected which plays a huge role in the pyrolysis process.Then,using experimental results combined with density functional theory,the reaction mechanism of G-type lignin monomers in lignin during pyrolysis was clarified,and several reaction paths were determined.Later,using this theoretical guidance,the catalytic pyrolysis of basic lignin,a lignin model compound,was studied,and the specific reaction law was also determined,and targeted control was achieved through theoretical support.Finally,the catalytic pyrolysis of hemicellulose model compounds,which are also one of the three major components of biomass,was studied.The effects of different reaction conditions on catalytic pyrolysis and product selection were clarified.For the mechanism of lignin model compounds,guaiacol and vanillin were selected as the model compounds of lignin respectively,and some free radicals generated during the reaction were detected.Electron paramagnetic resonance?EPR?technology was used to directly detect and capture some free radicals during in situ pyrolysis and cold trap-capture processes,respectively.Analytical methods combined with existing testing techniques were used to analyze in situ for guaiacol,the precursor free radicals of the reaction coking intermediate o-methylenequinone and partially stable coke free radicals,cold trap-The main methyl radicals were captured,and it was determined that?C₆H₄?OH?O*?radicals were also present during the pyrolysis of guaiacol;for vanillin,the same was detected in situ with methylene The precursor of quinone and a large part of stable carbon free radicals,while the cold trap-captured free radicals are mainly benzoyl radical,methyl radical,OH radical and H radical.It is proved that the pyrolysis reaction of guaiacol and vanillin is indeed a free radical reaction,which provides basic support for subsequent research work.Based on the detection of free radicals,through the analysis of intermediate products and existing GC/MS analysis techniques,combined with density functional theory simulation calculations,the reaction paths and mechanisms of guaiacol and vanillin pyrolysis reactions were sorted out.The laws of energy input to product distribution and path trend under different temperature conditions are analyzed.HZSM-5 molecular sieve catalyst was selected for catalytic pyrolysis of basic lignin,and the ratios of different catalysts to reactants,the effects of different reaction temperatures on the product structure,and the HZSM-5 catalysts with different silicon-aluminum ratios?compared catalysts?were compared.Acidity),combined with the pyrolysis mechanism of the G-type lignin model compounds involved in the previous article,summarized the basic pyrolysis mechanism and reaction path of basic lignin,and determined the regulation effect of reaction conditions on product results.It is proposed that 650?,5:1 catalyst ratio and the most acidic HZSM-5?23?catalyst be used to achieve the targeted control of aromatic hydrocarbon products.Using xylan as a model compound of hemicellulose,different catalysts and reactions were selected to study the pyrolysis reaction and catalytic pyrolysis reaction of hemicellulose alone under the high temperature conditions of subsequent pyrolysis with lignin.The effects of different reaction ratios on the structure of the product,and the HZSM-5 catalyst with different silicon-alumina ratios were investigated.The catalytic pyrolysis of xylan was pointed out,and its target products were mainly polycyclic aromatic hydrocarbons.In consideration of economy and product yield,HZSM-5?50?catalyst was used to achieve polycyclics at a dose of 5:1.The maximum production of aromatic hydrocarbons and the minimum waste of catalysts are achieved by using a pyrolysis temperature of 650?.