Study On La-P/HZSM-5 Catalyst Applied To The Preparation Of Light Olefins By Catalytic Cracking Of Light Naphtha

Triene(ethylene,propylene,butene)plays an indispensable cornerstone role in the petrochemical industry,and its demand has increased in recent years.Nearly half of olefin demand is still dependent on imports in China,and it is an urgent challenge to increase olefin production.At present,the steam cracking process with high temperature and high energy consumption is still the main method for producing olefins.The use of light naphtha or methanol coupled catalytic cracking to produce olefins has the advantages of low reaction temperature(500-700?),multiple raw material sources and adjustable olefin ratio.The HZSM-5 used in this article were all purchased from Nankai University Catalyst.The HZSM-5-50 catalyst was prepared by impregnation method with La content of 1wt.%and P content of 0.5wt.%.The effects of catalyst preparation methods and reaction conditions on the catalytic cracking of n-hexane to olefins were investigated,and the further optimization of the light naphtha catalytic process by the addition of methanol was explored.research shows:Firstly,the effects of different types of solid acids such as silicate,Y,SAPO34,and HZSM-5,the silica-to-aluminum ratio of molecular sieves,and the amount of pseudoboehmite on the acidity change and catalytic performance of the catalyst were compared.HZSM-5-50:Pseudoboehmite=7:3 is preferred as the best catalyst.Secondly,the performance of catalysts modified by different metals and acid oxides was compared,and the content of P2O5 and La2O3 was optimized.the catalytic effects of ammonium phosphate and boric acid modification were also compared with XRD,BET,NH3-TPD for characterization.Thirdly,the effects of high-temperature hydrothermal pretreatment,reaction temperature,liquid-time space velocity,and raw material composition on the catalytic performance and product distribution were compared.and the stability and regeneration performance of the catalyst were examined.The preferred reaction conditions are:when the liquid hourly space velocity of n-hexane is 0.5h-1 and the reaction temperature is 650?,the conversion of n-hexane is 98.2%,the maximum yield of ethylene is 27.9%,and the maximum yield of propylene is 23.5%.Finally,a coupling catalytic reaction system for the catalytic cracking of light naphtha and methanol to olefin was proposed.When the coupling reaction conditions are normal pressure,the reaction temperature is 600?,and the hydrocarbon alcohol feed ratio is 1,the methanol conversion rate is 100%,the n-hexane conversion rate is 98.6%,and the total triene yield reaches 55.4%.From the choice of catalyst carrier to the determination of the type and content of active components,to the optimization of reaction conditions and the establishment of a coupled reaction system,experimental ideas are progressive and interlocking.The optimized initial activity and total olefin yield of the 1La-0.5P/HZSM-5-50 catalyst have reached the level of industrialization,and a new idea for the development of new low-carbon olefin production technology with naphtha and methanol coupling reaction system is explored.