The Regulation Of HZSM-5 Al Distribution With Straight-chain Alcohols For Catalytic Cracking Of N-butane

Light olefins（ethylene,propylene and butene）are very important chemical materials.At present,the main process to producing ethylene in refinery is steam cracking.However,this process has some disadvantages such as high energy consumption and low yield in target products.Moreover,A large amount of n-butane produced as by-product of petroleum refining and petrochemical industry has not been used effectively,most of which are just simply burned as fuel.Therefore,using this n-butane as feedstock in catalytic cracking to produce high value-added light olefins has great economic potential and application prospect.And in the catalytic cracking process,one of the most important parts is to choose efficient cracking catalyst.ZSM-5 zeolite has attracted extensive attention benefiting from its suitable acid properties,unique pore structure and well stability.This thesis use different straight-chain alcohols as organic template to prepare ZSM-5 samples which have different content of Single Al and Close Al,which could achieve the regulation of n-butane cracking reaction pathway at the molecular level.On this basis,introducing Co component to design dehydrogenation-cracking bifunctional catalyst could improve the catalytic performance further.In the first part,a series of straight-chain alcohols are used as pore filling agents to prepare ZSM-5 by crystal seed method.Specifically in the synthesis process,the straight-chain alcohols are placed in the pore of the molecular sieve,due to the presence of alkaline template,and the electronegativity of the alcohol hydroxy group is enhanced,which could change the Al atom position in the pore of the molecular sieve by competition with Al O₂^-.With NH₃-TPD to characterize macroscopic acid property of catalyst sample,it could be found that comparing with the sample without alcohol,the macroscopic acid property of the samples synthesized with straight-chain alcohols are not changed significantly.Characterization of microscopic acid property with ICP-OES,it illustrates that the content of Single Al in the ZSM-5 synthesized with straight-chain alcohols are significantly improved,which could be varied form 48.3%to 60.9%.Introducing the samples into n-butane catalytic cracking,Al distribution in the samples can significantly change the product distribution.At 600℃,the HZ5-EG synthesized with glycol has the highest yield of ethylene and propylene of 44.2%.Based on HZ5-EG with the high Single Al content,Co with dehydrogenation activity was introduced by ion exchange method to synthesize the metal-zeolite bifunctional catalyst,aiming to investigate the effect of interaction between the cracking function of zeolite and the dehydrogenation function of Co in catalytic cracking of n-butane.NH₃-TPD profiles show that after Co²⁺ion exchange,the acidity of the bifunctional catalyst,especially the strong acid,decreased significantly.It suggested that Co²⁺replace H⁺of Close Al site.The introduction of Co²⁺can further improve the activity of the catalyst,maintained the highest conversion of n-butane in the process.At 625℃,yield of ethylene propylene over bifunctional catalyst can reach to the maximum of 45.6%.