Study On The Synthesis,characterization Analysis Of ZSM-5 Zeolite With Hierarchical Porosity And Their Catalytic Performances For The Cracking Of Hydrocarbons

Ethylene,propylene,as important organic chemical raw materials,plays an important role in the petrochemical industry.Hydrocarbon catalytic cracking technology is an important process route for the production of light olefins such as ethylene and propylene.The development of high efficiency catalysts is one of the key technologies.The catalytic performance of ZSM-5 zeolite stands out among many catalysts.However,the conventional ZSM-5 zeolite only has a single micropore,which has many disadvantages such as limited diffusion and mass transfer capacity,poor accessibility to acid sites,and easy carbon deposition and deactivation.In view of the above problems,from the perspective of practical application,this paper is devoted to the green and solvent-free synthesis of ZSM-5 zeolites with suitable acidity,adjustable hierarchical porosity structure and regular crystal morphology to improve its catalytic performance.This paper mainly carried out the following work:?1?A series of hierarchical nano-ZSM-5 zeolites were prepared by dry gel conversion method with tetrapropylammonium hydroxide?TPAOH?and tetrabutyl phosphorus hydroxide?TBPOH?as dual-template agents.The effects of the crystallization temperature,the amount of template agent,the amount of water,and the mole ratios of the dual-template agent on the physicochemical properties of the samples were investigated.The results show that the prepared ZSM-5-1/5 sample has higher external specific surface area,stronger acidity and special hierarchical porosity structure.When the reaction temperature is 410�C,the conversion of n-octane and the yield of ethene plus propene are 79.0%and 18.3%,respectively,which are 68.8 and15.6 percentage points higher than those of commercial zeolite under the same conditions.?2?ZSM-5 zeolite was synthesized by solvent free method.The morphology,physicochemical properties and catalytic properties of ZSM-5 zeolite were regulated by adding NaCl,Na₂CO₃ and KCl inorganic additives.It was found that the addition of NaCl and KCl additives was beneficial to reduce the crystal size of the zeolite,while the addition of Na₂CO₃ slowed down the agglomeration of zeolite,but the sample morphology was irregular.The results of catalytic cracking reaction evaluation showed that adding appropriate amount of additives is beneficial to improve catalytic activity and the yield of light olefins.?3?The effects of glucose,urea,cetyltrimethylammonium bromide?CTAB?and TBPOH organic additives on the physicochemical properties and catalytic performance of ZSM-5 zeolites by solvent free method were further investigated.The results showed that the additive could regulate the anisotropic growth rate of the zeolite,and the thickness of the crystal along the b-axis could be reduced by adding glucose and urea.The addition of TBPOH significantly affected the morphology of the zeolite.With the increase of the content of TBPOH,the morphology of the zeolite is in the order of hexagonal prism,truncated hexagonal prism and polyhedral ellipsoid.And the morphology of molecular sieve crystal was hexagonal prism,angular hexagonal prism and polyhedron ellipsoid in turn.In addition,the additives also changed the acid properties of the zeolite,resulting in different catalytic performance;The ZSM-5 zeolite catalyst synthesized by adding 0.50g of TBPOH has good catalytic activity.When the reaction temperature is 650�C,the yields of ethylene and propylene are 27.8%and 29.2%,respectively.