Synthesis Of Floral Hierarchical Zsm-5Zeolite By Single Template

Zeolites are aluminosilicate crystal having a regular uniform skeletal structure,due to its high specific surface area,uniform pore,good hydrothermal and thermal stability and strong acidity and so on,which is widely used in adsorption separation,ion exchange,catalysis,petrochemical and other fields.ZSM-5 zeolite,is synthesized in the 1970s by American Mobile company,has a 10-dimensional pore structure,hasn't cage-like cavity and aren't easy to deposit carbon.ZSM-5 zeolite has a medium pore size;it has a good shape-selective property and catalytic property.However,ZSM-5 zeolite's pore size is only 0.5-0.6nm,smaller than many organic molecules'kinetic diameter,the effective utilization of zeolite active sites is not high and organic guest molecules in zeolite pore have diffusion limitations.How to solve this problem,and now there are more popular two solutions,one for the synthesis of nanoparticle ZSM-5 zeolite;two for synthesis of hierarchical ZSM-5 zeolite.Hierarchical ZSM-5 zeolite is introduced mesoporous based on microporous and crystalline framework structure retained in the zeolite,it retain good thermal stability and strong acidity of the microporous ZSM-5 zeolite,and it also change the diffusion path of the guest molecules and improve the utilization of zeolite active sites.Present method of synthesizing ZSM-5 zeolite mainly are post-treatment method and template method,but there are a variety of problems,post-treatment need the premade ZSM-5 zeolite and need to use the template.post-treatment is easy to handle destruction of ZSM-5 zeolite crystal framework structure,crystallinity decreased;Template method requires to use multiple template and process is complex and cost is high.Although the single template is simple but the structure is complex and the cost is so high.These factors limit its industrial application.The issue succeed to use the ordinary surfactants MWS to synthesis the hierarchical ZSM-5 zeolite,not only simplify the synthesis process and reduce the cost of hierarchical ZSM-5 zeolite.The experimental results show the possibility of industrial production.The study includes:1.The issue synthesis the hierarchical ZSM-5 zeolite in pre-crystallization method.Firstly,the issue examine the different MWS amount to synthesis ZSM-5zeolite,synthetic ZSM-5 zeolite have a higher degree of crystallinity in the MWS ratio of 4.5 to 11.2;then the issue select MWS 4.5 and 6.7 to synthesis ZSM-5zeolite seed and select the appropriate pre-crystallization time to synthesis hierarchical ZSM-5 zeolite.By comparing different pre-crystallization time the issue select 30h successfully synthesis hierarchical ZSM-5 zeolite.The outer specific surface reaches 210m~2/g and mesopore volume reaches 0.418cm~3/g significantly improved than conventional ZSM-5 zeolite.After hydrothermal treatment the outer surface area reaches 208m~2/g and mesopore volume reaches0.384cm~3/g,synthesized hierarchical ZSM-5 zeolite have high hydrothermal stability.2.The issue synthesis directly hierarchical ZSM-5 zeolite.Try to directly synthesis the hierarchical ZSM-5 zeolite,succeed to synthesis directly the hierarchical ZSM-5 zeolite.Synthesized hierarchical ZSM-5 zeolite have floral particle,have a particle size in the 4-6?m,have excellent hydrothermal stability.Each petal thickness is less than 50 nm.Its the outer specific surface reaches 291m~2/g,the mesopore volume reaches 0.315 cm~3/g than conventional ZSM-5 zeolite significantly.At the same time in a pilot scale,using 200mL?500mL?5L autoclave were successfully synthesized hierarchical ZSM-5 zeolite.It proved that the method is suitable for industrial scale production.And by studying Si/Al,alkalinity,alcohol ratio,MWS and other factors on synthesis results of hierarchical ZSM-5 zeolite.When the Si/Al is greater than 50 and Na/Si is between 0.29 to 0.35 and alcohol-water ratio from 0.038 to 0.064 and MWS/Si is 112,hierarchical ZSM-5 zeolite can be successfully synthesized.3.Inquiry the synthesis mechanism of hierarchical ZSM-5 zeolite,the issue examine the different crystallization time of the hierarchical ZSM-5 zeolite and identify long induction period in synthesis process.Five-membered ring stretching vibration characteristics of the ZSM-5 zeolite can be watched through infrared spectroscopy when crystallization time is 3 d,ZSM-5 zeolite characteristic diffraction peak can be seen from X-ray diffraction spectrum when the crystallization time is 5 d.When crystallization time is from 5 d to 8 d,X-ray diffraction peak intensity does not substantially change.When crystallization time is from 8 d to 10 d,zeolite synthesis rate speed.When crystallization time is 10 d,hierarchical ZSM-5 zeolite grows completely.Small angle X-ray diffraction peaks can be seen and small angle diffraction peak intensity gradually weaken.In synthesis process mesoporous formed by zeolite crystals is changed from ordered mesoporous formed by amorphous aluminosilicate.When crystallization time is 9 d to 10 d,there is the critical point ordered that mesoporous formed by amorphous aluminosilicate is completely converted into mesoporous formed by zeolite crystals.