Study On The Effect Of ZSM-5 Molecular Sieve Acidity Regulation On The Coupled Preparation Of Light Aromatic Hydrocarbons From Methanol/Huaning Lignite Pyrolysis Volatiles

China is a major energy country dominated by coal.The dominant position of coal in China’s energy composition cannot be shaken.During coal pyrolysis,some compounds with high added value can be generated,among which aromatic hydrocarbons are important basic raw materials for organic chemical engineering,especially light aromatic hydrocarbons.Selecting HZSM-5 molecular sieve for catalytic upgrading of coal pyrolysis components can achieve targeted conversion of products and increase the yield of light aromatic hydrocarbons.By adjusting the acidity and pore structure of ZSM-5 molecular sieve through metal modification and acid treatment,the catalytic hydrogenation deoxygenation of the main components of tar is promoted.Combined with DFT theory,the reaction process of pyrolysis component model compounds is simulated,and the activation energy of each step and the rate control steps of the entire process are obtained.The specific research content is as follows:Using Yunnan Huaning lignite as raw material,the effect of composite acid treatment on the coupling of low rank coal pyrolysis components and methanol to prepare light aromatic hydrocarbons was first investigated.Acid etching can cause a small amount of mesoporous formation,with an increase in micropore volume and specific surface area.Compared to single strong acid treatment,the addition of citric acid can alleviate the degree of acid etching,utilize its large steric hindrance,and reduce the damage of nitric acid to the molecular sieve skeleton structure.The catalytic performance of HZSM-5 treated with composite acid has been improved,and the yield of BTEXN has significantly increased compared to the parent HZSM-5 and HZSM-5treated with a single acid.Secondly,the effect of Al modification on the acid properties of molecular sieve Lewis was investigated,and different amounts of Al were loaded onto HZSM-5molecular sieve through equal volume impregnation method.The yield of BTEXN in tar improved with 2%and 5%aluminum loading,while decreased with 8%aluminum loading.This indicates that the appropriate introduction of Al can increase the content of L-acid in ZSM-5,facilitate the occurrence of hydrogen transfer reactions,and improve catalytic cracking performance.Introducing excessive Al can actually cause the acidic sites of the molecular sieve to be covered,leading to a decrease in catalytic activity.At the same time,it can also cause pore blockage,increase carbon deposition,and reduce catalyst stability.At the same time,this paper also studied the effect of acid regulation on the reaction performance through density functional theory calculation.On the one hand,under the premise of ensuring the same Br?nsted acid center,a HZSM-5 molecular sieve cluster model with different Al distributions and different proton H sites was constructed,and o-cresol was selected as the model compound to simulate its reaction with methanol on the molecular sieve.The acid strength of the HZSM-5 cluster model is closely related to the fall of proton H.The closer the fall of proton H,the closer it is to the Br?nsted acid active center,and the stronger the acid strength.The different reaction activities of the HZSM-5 molecular sieve fully depend on the chemical environment near the active site.At the same time,the transition state energy barrier of the whole reaction rate control step is related to the strength change of zeolite Br?nsted acid.The greater the strength of Br?nsted acid,the easier the reaction will occur.On the other hand,constructing HZSM-5 molecular sieves containing different non skeletal Al species results in different Br?nsted acid strengths.The order of their enhancement ability is Al（OH）²⁺>Al（OH）₃>Al O⁺>Al³⁺.Similarly,the higher the Br?nsted acid strength,the more favorable the reaction is.In each step of the reaction,the hydrogen transfer rate constant is the smallest,which is the rate control step of the entire reaction.