Research On Molding Process Conditions Of Hierarchically Porous Zeolite

Hierarchically porous zeolite is a kind of new catalytic material developed in recent ten years.It not only inherits acidic properties,good thermal stability and ion exchange properties of microporous zeolite,but also improves the adsorption and diffusion properties of bulky molecules because of the introduction of mesopores,and thus greatly enriches the scope of applications of zeolite.As the researches of hierarchical zeolite advance,its synthesis methods have been basically mature.However,little attention has been paid to its molding process.Therefore,in this paper,the extrusion of hierarchical zeolite and its mechanism were investigated firstly.Then the process factors,i.e.,binder kind,pseudo-boehmite content,nitric acid content and extrusion speed were examined.Specific work is as follows.The extrusion of hierarchical zeolite and its mechanism have been investigated.The results show as well as microporous zeolite,that extudates of hierarchical zeolite are typical material and their strength failure is due to brittle fracture.The strength data distribute discretely and they are well investigated by Weibull statistics.After extrusion,micropores in hierarchical zeolite are influenced by extrusion process,while mesopores are more related to the new mesopores generated by the interaction between the zeolite grains.Wherein the micrcopores in the extrudates are mainly derived from its zeolite crystal,and the mesopores are mainly from the interior of zeolite crystal and generated by the accumulation of grains.In addition,when hierarchical zeolite is extruded,it is entirely possible to improve the mechanical strength and stability under all textural properties is constant by optimizing the extrusion process conditions.The effects of binder type on extrusion of hierarchical ZSM-5 zeolite have been studied.Results show that the extrudates with pseudo boehmite and AIPO4 binder have the highest and most reliable mechanical strength,while extrudates with pseudo boehmite and ?-Al2O3 have more excellent pore structure.Except AIPO4 binder,mesopores increase a lot because of many new mesopores generated by accumulation between zeolite grains and when ZSM-5 is extrude with other binders.In addition,it is concluded that pseudo boehmite is chosen as a best binder in ZSM-5 extrusion process,which not only retains an excellent pore structure,but also obtains sufficient reliable mechanical strength.The process factors of extrusion of hierarchical ZSM-5 zeolite have been investigated.Results show that as pseudo boehmite content,nitric acid content and extrusion speed increase,the corresponding extrudates increase gradually.However,pore structure of the extrudates is mainly determined by pseudo boehmite content and nitric acid content.Linking with extrusion process conditions,it is found that the extrudates of hierarchical ZSM-5 will have high mechanical strength,high mechanical reliability and excellent pore structure when pseudo boehmite content,nitric content and extrusion speed are 33 wt%,13 wt%and 50 r/min,respectively.