The Research On The Rtructure-activity Relationship Of Catalyst For High Efficiency Alkylation Of Benzene With Methanol

The synthesis of toluene,paraxylene or other aromatic hydrocarbons is exemplary project in the chemical field.Benzene and methanol is great importance product in petrochemical industry and coal chemical industry,respectively,and relative overproduction.According to the resources allocation?Oil-shortage,Gas-less,Coal-rich?of our country,where toluene and p-xylene of the high added value will be preparated by alkylation of benzene with methanol.This synthesis method will give the stronger competition ability,which can make the future coupling development of petrochemical industry and coal chemical industry enter a new situation.However,the key difficulties in the alkylation of benzene with methanol were that the reaction conditions were harsh,the utilization rate of methanol was low,by-products were more and the catalyst was easy to deactivate,etc.These weaknesses would greatly hinder the alkylation reaction for being put into industrial production.Therefore,the purpose of overcoming the difficulties was to develop highly efficient and stable catalysts.The specific research contents were as follows:?1?ZSM-5,Beta and Y zeolites were prepared by hydrothermal synthesis,which were modified by several times of ion exchange and recorded as HZSM-5,H-beta and M-Y.The physical and chemical properties of the catalysts were characterized by XRD,N₂sorption/desorption,FT-IR and Py-IR.The catalytic properties of three catalysts were investigated for the alkylation of benzene and methanol.Under the optimal reaction conditions,the results showed that if toluene as the target product,M-Y catalyst was the best choice.HZSM-5 catalyst was the best choice when paraxylene was the main product.?2?For the target product-toluene:the precise regulation of acidity for Y zeolite catalyst by different modifiers was studied and characterized by XRD,BET,SEM,FT-IR and Py-IR.The performance of catalyst in alkylation of benzene and methanol was evaluated.The results showed that the conversion rate of benzene was 43.9%,and the selectivity of toluene was 87.7%under the following conditions^catalytic 0.5 g,WHSV=2.5 h^-1,temperature 400 ^oC,reaction time 3 h,benzene/methanol 1:1,normal pressure.However,M-Y catalyst had a fatal disadvantage that was easy to carbon deposition.Therefore,the catalyst was modified with Cs₂O,the results showed that the method could effectively inhibit coke and extend the service life of the catalyst.Based on the potential of M-Y catalyst for preparing toluene,the theoretical calculation of the catalytic effect of M-Y catalyst in the alkylation of benzene and methanol to prepare toluene was studied.According to the determination of Na⁺content by ICP,the value measured in this experiment was basically equal to the theoretical value that was not easily exchanged in the molecular sieve.Therefore,the geometric model of density functional calculation was established.The transition states and corresponding energy barrier of the toluene reaction by alkylation of benzene with methanol over M-Y catalyst were calculated by density functional theory.The results showed that,compared with HZSM-5?149 kJ/mol?,M-Y catalyst had the lowest energy barrier for benzene alkylation?141 kJ/mol?.The reason why M-Y catalyst was the best catalyst for preparing toluene was explained.At the same time,it was found that the C-C bond between benzene ring and methyl group might be break,in which alkylation by-product?methane?and C₆H₅⁺carbocation would be produced.Therefore,precise regulation of acidity and theoretical calculation can provide new ideas and methods for obtaining more active catalysts for preparing toluene by alkylation.?3?Paraxylene as the research target:HZSM-5 was used for alkylation of benzene and methanol to produce paraxylene,which had problems such as low utilization rate of methanol and easy carbon deposition.Therefore,silanization etching technology was used to modify HZSM-5for preparing the catalyst of alkylation.To solve these problems,HZSM-5 was etched by3-aminopropyltriethoxysilane as silanization reagent and a series of catalysts were obtained.The structure and properties of the catalyst were characterized by XRD,SEM,NH₃-TPD,EDS,Zeta potential and Contact Angle Measurement.The catalytic properties of HZSM-5 catalyst before and after modification in the alkylation of benzene/methanol were studied.The results showed that DMCS²⁰-HZSM-5 catalyst had the best catalytic activity,could enhance the utilization rate of methanol and suppress by-products,especially carbon deposition.Although silanization technology could enhance the utilization of methanol and reduce the amount of by-products and carbon deposition,the MTO side reaction was not fundamentally eliminated,so carbon deposition was still easy generated in the long-term reaction.Therefore,Ru/HZSM-5 catalyst was prepared by impregnation-precipitation method and was characterized.Meanwhile,the MTO side reaction eliminated strategy in the alkylation process of benzene and methanol was studied.The performance evaluation showed that the catalyst could completely annihilate the MTO side reaction,thereby annihilated the by-product ethylbenzene,reduced carbon deposition and prolonged greatly the life of the catalyst.Ru based&acid bifunctional catalyst was prepared by one-step method,which pioneered new ways to eliminate the MTO response for alkylation of benzene with methanol.?4?By thermodynamic calculation of alkylation of benzene with methanol for preparing toluene and xylene,combining with the experimental data of the catalyst performance evaluation and density functional theory calculations,the catalytic reaction mechanism of benzene alkylation with methanol was comprehensive concluded.For the process conditions optimization of benzene alkylation with methanol and mechanism research has a guiding significance.