Low-cost Synthesis Of Hierachical ZSM-5 Zeolite

Zeolite ZSM-5 was widely used in chemical process,due to its good shape selection,adjustable acidity and high hydrothermal stability.However,its single micropore channels still suffers from the diffusion limitation of great molecules and inactivation trend.Therefore,the development of hierarchical ZSM-5 with the introduction of mesoporous into presnet micropores,is highly desired.In order to obain hierarchical ZSM-5,various strategies were carried out in this paper,including double template agent method and kaolin crystalline method.More interestingly,adjusing of pH value of synthesis system is achieved by the employing of water glass and silicon powder.Consequently,the addition of sulfuric acid with corrosivity was replaced by this novel process:1.In this article,a hierarchical ZSM-5 zeolites was synthesized by using tetra-propylammonium bromide(TPABr)as a microprogen,and the bifunctional template(Mesotemp)as a mesoprogen.In the typical process,Mesotemp hydrolyzed to-Si(OH)3 by-Si(OCH3)3 in an alkaline environment.As a result of this,the yield of-Si-O-Si-and-Si-O-Al-will leads to the bond linkage of Mesotemp on the framework of zoelites.On the other hand,Mesotemp micelles obtained in the alkaline media would template the formation well-arranged mesopores.To study the feasibility of industrial production of hierarchical ZSM-5 molecular,this sample was obtained by employing a 1 m3 kettle for crystallization.From the results of BET and XRD studies,it can be seen that the hierarchical ZSM-5 obtained has a relative crystallinity 94%,total specific surface area 386.2 m2/g,and external specific surface area 179.4 m2/g.2.A hierarchical ZSM-5 zeolites was synthesized by using butylamine(BA)as a microprogen,and the bifunctional template(Mesotemp)as a mesoprogen.In this process,the effect of system alkalinity and template dosage on synthetic samples was investigated.In this strategy,a graded crystallization of 90℃ crystallization 6 h and 170℃ crystalline 6 h was carried out in this synthesis process.A pilot scale synthesis was carried out in a 10 L pilot autocalve.The sample was featured with characterization of a relative crystallinity 90%,the total surface area 407.7 m2/g,and external specific surface area 173.2 m2/g.3.A hierarchical nano-ZSM-5 zeolite by using tetra-propylammonium bromide(TPABr)as a microprogen,with high crystalline degree was prepared by combining the synthesis strategy of two-step crystallization and amino acid assistance.In this strategy,a successive crystallization of low-temperature and high-temperature was carried out in this synthesis process.As the direct consequence of graded crystallization,the samples obtained was characterized with reduced sized,high crystallization,and high surface area.From the results of BET and XRD studies,it can be seen that the hierarchical ZSM-5 obtained has a relative crystallinity 98%,total specific surface area 366.2 m2/g,external specific surface area 188.1 m2/g,and mesoporous volume 0.14 cm3/g.4.Kaolin/ZSM-5 composites were obtained by empoying metakaolin powder(calcination at 850℃ 4 h)as Al source and silica powder as Si source.In this process,pH value was achieved by the the additon of silicon powder,and micropores of ZSM-5 was inherited from tetra-propylammonium bromide(TPABr).From the results of BET and XRD studies,it can be seen that the hierarchical ZSM-5 obtained has a relative crystallinity 77%,total specific surface area 398.6 m2/g,and total pore volume 0.24 cm3/g.