Preparation,Scale Up And Catalytic Applications Of Hierarchical ZSM-5 Zeolite

With the rapid development of human society,the gap between supply and demand of propylene and other light olefins is greatly increasing.Fluid catalytic cracking(FCC)is regard as the most effective way to increase propylene.ZSM-5 zeolites commonly utilized in catalytic cracking owing to its superior physico-chemical properties such as adjustableacidity,excellent hydrothermal stability and shape-selectivity features.However,with the increased output of heavy oil throughout the world,poor intracrystalline diffusion of large molecules limits its practical application in the traditional ZSM-5 micropores.In this study,the commercial ZSM-5 zeolite was used as the raw material and sequential desilication-dealumination was introduced to get hierarchical ZSM-5 zeolite to reduce the diffusion resistance.We systematically investigated and optimized the synthesis parameters including concentration,temperature,dissolution time and liquid-solid ratio using NaOH and HCl as desilication and dealumination reagent,respectively.Besides,the preparation was scaled up from laboratory to pilot scale(50 L)at the liquid-solid ratios are 30 mL/g,10 mL/g and 5 mL/g.We studied the influence of amplification experimentsof hierarchical ZSM-5 on relative crystallinity,structure of pores and acidity.The results manifest that:(1)sequential desilication-dealumination can effectively intracrystalline mesoporosity with high diffusivity,improve the acid site accessibility in zeolites through desilication in alkaline medium and remove the non-framework aluminum in dilute acid medium;(2)compared with alkali treatment,hierarchical ZSM-5 through concomitant dealumination as FCC additives,can improve the Indexed Hierarchy Factor(IHF)and Accessibility Index(ACI)obviously.In addition,it can also promote the heavy oil conversion rate and the yield of propylene;(3)this experiment has good prospect of industrialization owing to the simple operation and repeatability.