Study On The Structure-activity Relationship Of Catalysts In Propane-methanol Co-aromatization System

Aromatics are important bulk chemicals,which are mainly derived from crude oil cracking in the world.However,due to the resource endowment of "rich in coal,poor in oil and little in gas",the domestic production of petroleum-based aromatics is affected by the international oil price,and the economic fluctuations of the process are significant.Aromatics synthesis with carbon-based materials such as coal is suitable for Chinese situation,and it is very potential to obtain aromatics products efficiently through rational reaction process design.As an important platform compound in coal chemical process,methanol has mature synthesis technology,sufficient production capacity and friendly price.As a byproduct of many chemical processes,propane has a wide range of sources and mild activation conditions.Coupling the aromatization process of propane and methanol can not only effectively utilize cheap raw materials and improve the economy of the process,but also coupling the strongly exothermic methanol aromatization process and endothermic propane aromatization process from the perspective of thermodynamics,realizing the energy coupling at the molecular level.It can not only inhibit the mild carbon deposition of catalyst bed during the methanol aromatization process,but also promote the dehydrogenation activation of propane by generating common aromatization intermediates,which provides a new reaction path and research idea for the utilization of propane and methanol conversion.Based on the above background,this study took propane methanol coupling aromatization as the model system,took metal modified molecular sieve aromatization catalyst as the research object,investigated the synthesis and modification of metal modified HZSM-5 catalyst,physical and chemical properties and microstructure,and catalytic performance of propane methanol coupling aromatization reaction.The structure-activity relationship of catalyst in propane-methanol coupling aromatization was analyzed and explored.The specific contents of this study are as follows:1.The effect of modified metal types on the structure-activity relationship of catalysts.Zn,Ga,La,Ce and Fe metal-modified catalysts with 2% metal content were prepared.It can be seen from the characterization that the acid site and acid content of the catalyst were modified by metal modification,and the B-acid decreased while the L-acid increased,which promoted the dehydrogenation of propane,inhibited the cracking and hydrogen transfer reactions,promoted the aromatics conversion and improved the aromatics selectivity.The propane conversion and BTX selectivity of 2%Zn/HZSM-5 catalyst for 16 h were 95.95% and 49.17%respectively.Different kinds of modified metals have different effects on the distribution of aromatic products.The content of p-xylene in the catalytic products of 2%Zn/HZSM-5 catalyst is the highest,reaching 26.19%,and the catalytic effect is relatively good.2.The effect of modified metal content on the structure-activity relationship of catalyst.The coupling aromatization of propane and methanol was catalyzed by HZSM-5 zeolite modified with different contents of Zn.Correlation analysis was conducted on the characterization results of catalysts and the evaluation data of catalytic performance.The correlation analysis between the characterization results and the evaluation data of catalytic performance showed that the catalytic performance of the catalysts modified with metal Zn was improved,and the effects of different content of metal Zn on the catalyst acidity were different.The B/L value of2%Zn/HZSM-5 catalyst was the lowest,and the L acid was the most in the catalyst,which promoted the dehydrogenation reaction.The BTX selectivity in the product is higher.The amount of acid of weak acid and strong acid decreased,and the amount of acid of medium strong acid increased,which was conducive to the conversion of propane.Therefore,when the content of Zn is 2%,the catalytic performance of Zn modified catalyst is the best.3.Influence of the evaluation conditions of propane-coupled methanol aromatization reaction on catalyst performance.The process conditions of propane methanol coupling aromatization reaction were investigated,and the optimal process conditions were selected by comparing the propane conversion and BTX selectivity of propane methanol coupling aromatization reaction at different space velocity,temperature and feed ratio.Under the process conditions of space velocity 1h-1,temperature 480℃ and propane methanol feed molar ratio of 1:3,The catalytic performance of propane methanol coupling aromatization is better.