Study On The New Method Of Synthesizing The Layered SAPO-34 Molecular Sieve And The MTO Catalyst Performance

Under the pressures of a shortage of oil resources and environmental protection,methanol,as an alternative energy sources,attracted much attention,because of its intensive sources that can be produced from coal,natural gas and biomass.And as people's living standard continuously improved,the demands of ethylene and propylene that is the most basic chemical raw materials also increase constantly.However,ethylene and propylene production is mainly obtained from oil cracking at present.As a result,methanol to olefins?MTO?technology development is particularly important for China.Because it can turn low value-added methanol into high value-added hydrocarbon products,not only solves the shortage of ethylene and propylene,but also conforms to our country's condition of�rich coal less oil�.In nearly a decade,methanol to olefins technology has been a hot research topic in the field of coal chemical industry research,and the core technology of MTO is mainly the research and development of catalyst used.SAPO-34 molecular sieve is the best catalyst of the methanol to olefins reaction,because it has a unique pore structure,appropriate acidity and good thermal stability.It showed great low carbon olefins selectivity,and total selectivity of ethylene and propylene can reach more than 85%in the MTO catalytic reaction.However,it's easy to produce carbon deposition in the reaction process,leading to short life of catalyst.So far,there are two main ways to prolong catalyst life.1.Synthesized hierarchical SAPO-34 zeolite.2.Synthesis of nano-sized SAPO-34 molecular sieve.But both of two are difficult to realize in present industrial technology level.It has reported that layered SAPO-34 has a shorter diffusion path,good thermal stability and a longer lifetime in MTO reaction.Thus it has investigated some factors that influence crystal size and morphology,including template agent,aluminum source and crystal seed.We also created a new method to prepare the layered SAPO-34 successfully by adding a certain amount of hydroxide hexamethonium in the initial gel.Finally,with different morphology of SAPO-34 molecular sieve powder as active ingredients,the industrial catalysts have been prepared and evaluated to acquire better performance in MTO reaction.The paper mainly has done the following work.Crystal size and morphology of synthesized SAPO-34 zeolite were studied,using triethylamine,tetraethyl-ammonium hydroxide and their mixture as template agent.And the samples that were prepared with different aluminum source were characterized by XRD,SEM,BET,XRF,NH₃-TPD and the catalytic performances of MTO reaction.Also we investigated the influences of crystal seed and seed solution on particle size and morphology of SAPO-34 zeolite.We found that they all have influence on the size and morphology of production.Secondly,layered SAPO-34 zeolite was successfully synthesized by adding different amount of hydroxide hexamethonium in the initial gel.The samples were studied and analyzed by XRD,SEM,BET,XRF,NH₃-TPD and catalytic performances of MTO reaction,and hydrothermal stability of the layered SAPO-34 molecular sieve was investigated too.The results showed that layered SAPO-34 molecular sieve have longer lifetime,higher low carbon olefin selectivity and good hydrothermal stability in MTO catalytic reation.At last,the industrial catalysts were prepared by spray forming method,according to certain proportion to different morphology?cube,layer?of SAPO-34 molecular sieve powder mixed with binder,carrier.The physicochemical properties of catalysts,such as specific surface area,pore structure,abrasion resistance,particle size distribution and bulk density and so on,were measured accurately.And at different catalytic reaction temperature?450?,480?and520??,adopted fixed-fluidized bed reaction device,catalytic performances of different samples were obtained respectively.Moreover,carbon deposition on the deactivation catalysts was analyzed.As MTO reation temperature increasing,ethylene selectivity was improved and propylene selectivity was decreased.In same MTO catalyst reaction conditions,the catalyst that was synthesized with layered SAPO-34 molecular sieve had smaller carbon deposition rate,longer lifetime and higher low carbon olefin selectivity.