Aromatization Performance Over ZSM-5 With Different Morphology

Aromatic hydrocarbons was an important row material for organic synthesis,which was produced by petrochemical routes mostly.Coal-based routes using by-product to produce aromatic hydrocarbons was highlighted.On the one hand,by-product was transferred into high added value products;On the other hand,it can reduce the dependence of aromatics productions on petroleum resources.But the constitution of by-product was complicated,Aromatization reactions were complicated.The aromatization reactions of LPG and light naphtha have been studied and industrialized in part,As regards about understanding of the influence of catalyst morphology(pore structure)on activity and kinetics are still relatively few,In this paper,n-hexane with high content of by-product hydrocarbons from methanol was used as raw material to study the relationship between morphology and aromatization reaction activity and reaction kinetics,understanding the influence of morphology on the aromatization reactions.In addition,the catalytic performance of silicon surface modification on catalysts for aromatization of methanol to aromatics was also investigated.1.A nanosheet ZSM-5 molecular sieve with a thickness of only 30-40 nm was synthesized.The zeolites ZSM-5(NSZ5)and ZSM-5(BZ5)with different morphologies were hydrothermally synthesized by hydrothermal synthesis.The loading of Zn was modified and the crystal structure and crystal shape were investigated.Appearance,pore structure,acid properties,activity and product distribution.The loading of Zn had no obvious effect on the crystal structure and morphology,but significantly changed the acid distribution,increaseing the L acid on the surface of the molecular sieve and the L/B ratio,favors the aromatization reaction,and improves the selectivity and yield of aromatics.Especially when the impregnation amount was 3%wt,the aromatic selectivity of Zn/BZ5 and Zn/NSZ5 reached 70.6%and 18.0%respectively,far exceeding 5%of BZ5 or NSZ5,The aromatic selectivity of the nanosheet ZSM-5 zeolite was much lower than that of the large crystal ZSM-5.Except that the distribution ratio of B and L acids were not suitable,the lamellar structure makes the molecular diffusion significantly faster,which is not only unfavorable to the raw materials of n-hexane.The conversion,at the same time,greatly reduces the selectivity of the aromatic product that can be obtained after a series of reactions due to the short contact(diffusion)time,indicating that the pore structure(morphology)is crucial to the influence of the aromatization reaction.The coal-produced by-produced hydrocarbon mixture can also be experimentally shown to be similar to the model compound n-hexane on the 3%Zn/BZ5 molecular sieve to obtain the conversion rate and the initial aromatic selectivity.2.The lumped kinetics of two different molecular sieve catalysts were studied,kinetic equations were established,and kinetic parameters were obtained.The experimental results show that the chain extension reaction of propylene and ethylene were very easy to proceed on the two catalysts,followed by the cleavage reaction of n-hexane and xylene,and the reaction to generate aromatics(BTX)were the most difficult to proceed.The kinetic datas suggest that complex intermediate reactions and side reactions such as catalytic cracking,thermal cracking,etc.it not affect the selectivity of aromatics at all times.In order to increase the selectivity of aromatics,it may be advantageous to appropriately increase the diffusion limit.The experimental results of the reaction conditions show that increasing the temperature not only helped to increase the conversion rate but also favored the formation of aromatics;lowering the space velocity favored the conversion and the production of aromatics;lowering the dilution ratio also favored the conversion and aromatics production.3.Simultaneous silicon modification of the outer surface of the molecular sieve and its application in methanol aromatization(MTA)studies.The results showed that the external surface of the silicon modified to reduce the acid amount,but it significantly increased the ratio of pX in xylene,from about 1%to 35%,due to the coverage of the acid center on the outer surface The secondary reaction of pX was inhibited.