Forming And Modification Of ZSM-35 Catalysts For Skeletal Isomerization Of N-butene

As a basic chemical raw material,isobutene has an extremely wide range of applications in industrial production.In recent years,n-butene is produced in excess and isobutene production is insufficient.Therefore,it is of practical significance to make isobutene from n-butene skeletal isomerization.Due to its unique pore structure,good hydrothermal stability and high selectivity of isobulene,ZSM-3 5 molecular sieve has become the most useful catalyst for butene skeletal isomerization in the industry.In this thesis,strength characterization,XRD,NH3-TPD,other characterization methods and n-butene skeletal isomerization reaction device were used to examine the effect of forming aid,reaction process and different modification methods on the structure and catalytic performance of HZSM-35 molecular sieve.Thus,better molding process conditions and modification methods were determined,which provided a scientific basis for the further improvement of the macroscopic properties of the molecular sieve.In this paper,the extrusion molding method was first used to explore the effects of binder type,binder amount,pore-enlarging agent type and quantity on catalyst strength,crystal structure,acidity,catalytic activity,selectivity and stability.The results showed that:SB powder should be selected as the binding agent,and the addition amount is 25wt%.The obtained catalyst has high mechanical strength and good catalytic performance.The addition of pore-enlarging agent will reduce the strength of the shaped catalyst,but the yield of isobutene is high and the stability is good.The suitable pore-enlarging agent is polyethylene glycol 6000 and the amount added is 5wt%.The process conditions for the n-butene isomerization were optimized.The reaction temperature was 420 ?,and the space velocity of n-butene was 20 h-1.Different methods were used to modify the self-made HZSM-35 molecular sieve.The results showed that:(1)The modification of HZSM-35 molecular sieve by phosphoric acid and boric acid can effectively eliminate the strong acid sites,which caused side reactions decrease and the selectivity of isobutene increase.The catalytic performence was the best when the B loading was 0.5wt%and the P loading was 1.5wt%.(2)W has a synergistic effect on the formation of isobutene,which made the yield of isobutylene more stable.And the loading of Pd makes conversion decrease,which leads to a decrease in yield.(3)Alkali treatment and recrystallization as a modification method have positive significance for the improvement of catalytic performance.The catalyst which was treated with 1 mol/L NaOH and recrystallized had the best catalytic effect.(4)When using the hydrothermal synthesis method,different rotation speeds will affect the crystallite size and crystallinity of the zeolite.When the rotation speed was 60r/min,the HZSM-35 catalyst had the best catalytic performence on the butene skeletal isomerization.