Study On The Synergistic Effect Of Naphthenic Aromatics Catalytic Cracking On Different Zeolites

In recent years,my country’s fuel oil consumption structure has undergone fundamental changes,and the consumption ratio of diesel and gasoline has decreased.At the same time,the growth rate of demand for chemical raw materials far exceeds the growth rate of demand for fuel oil.There is a surplus of diesel products,and it is difficult to find a way out for low-quality catalytically cracked diesel(LCO).The combined hydrogenation-catalytic cracking process can partially saturate the polycyclic aromatic hydrocarbons in the LCO into cycloalkane aromatics,and then undergo selective ring-opening cracking reactions to generate high-value light aromatics and low-carbon olefins.Therefore,this process is one of the ideal ways for the high-value utilization of LCO.This article explores the catalytic cracking reaction performance of tetralin and methylindan,and investigates the synergistic effect of different types of zeolites on the catalytic cracking reaction of tetralin.The synergistic effect of Y and ZSM-5 zeolite catalysts on the catalytic cracking reaction of hydrogenated LCO was verified on the riser catalytic cracking pilot plant.Firstly,the catalytic cracking reaction performance of tetrahydronaphthalene and methylindan on different zeolites was investigated on a fixed-bed microreactor experimental device.Compared with tetrahydronaphthalene,the five-membered ring tension of methylindan is larger,the ring-opening cracking reaction is easy to occur,and the dehydrogenation reaction is difficult to occur.Therefore,the ring-opening cracking selection of methylindan is high,and the dehydrogenation selectivity is low.Methylindan has better cracking performance on USY zeolite,and its conversion is up to 91.94 wt.%,which is 1.38 wt.% higher than tetralin.The ring-opening cracking selectivity of methylindan is 68.22%,and the hydrogen transfer selectivity is 29.41%,while the ring-opening cracking selectivity and hydrogen transfer selectivity of tetralin are respectively 47.39% and 49.39%.Beta zeolite has strong isomerization ability,tetralin is firstly isomerized to form methylindan and then catalytic cracking reaction occurs,the cracking performance of the two is similar;On the ZSM-5 zeolite,methylindan has steric hindrance,its conversion rate is 2.08 wt.% lower than tetralin,and the ring-opening cracking selectivity is 26% lower than tetralin.Tetralin has better cracking performance on ZSM-5 zeolite.Secondly,the synergistic effect of USY zeolite and Beta zeolite in the catalytic cracking of tetralin was investigated.Through layered packing and mechanical mixing,it is clear that USY and Beta zeolites have a synergistic effect on the catalytic conversion of tetralin.Beta zeolite mainly plays the role of isomerization,and tetralin is firstly formed into methylindane on it;USY zeolite is mainly responsible for cracking,and its large pores and high acid density facilitate the catalytic cracking of methyl indane into light aromatics and Low-carbon olefins.The first isomerization of tetralin to methylindan and then cracking is the best reaction path for the conversion of naphthenic aromatics.In addition,under the same mixing ratio,the conversion and ring-opening cracking selectivity of tetralin are as follows: Beta is in the upper layer>Mechanical mixing>USY is in the upper layer,indicating that reducing the spacing of different zeolites helps to enhance the synergy.Under the condition of USY: Beta =6:4(mass ratio),when Beta is in the upper layer,the conversion of tetralin is 96.54 wt.%,and the ring-opening cracking selectivity is 65.02%;When USY is in the upper layer,the conversion rate and ring-opening cracking selectivity of tetralin are 93.15 wt.% and 54.12%,respectively;When mechanically mixed,the conversion rate of tetralin was 96.37 wt.%,and the ring-opening cracking selectivity was 56.87%..Finally,on the riser pilot test device,the synergistic effect of Y-type and ZSM-5 zeolite catalysts on the catalytic cracking of hydrogenated LCO was verified.The results show that the cracking performance of LCO after hydrogenation is improved,and the raw material conversion and product distribution are improved.Compared with LTB-2 catalyst(active component is ZSM-5 zeolite),MMC-2 catalyst(containing both Y-type and ZSM-5 molecular sieve)has better cracking performance under milder reaction conditions,and the LCO conversion and light oil yield are similar to the former.The synergistic effect of Y zeolite and ZSM-5 zeolite improves the selectivity of the ring-opening cracking of naphthenic aromatics.The obtained gasoline and other products have higher monocyclic aromatics content and better economic benefits.This shows that the multi-active component catalyst has important application value in industrial applications.