Synthesis Of ZSM-5 Molecular Sieve By Dry Gel Conversion And Its Application

ZSM-5 molecular sieve possesses a unique two-dimensional channel system defined by 10-ring and shows a favorable thermal stability,acidity and shape-selectivity.Therefore,it has been widely used in catalysis,sorption-sepatation and ion-exchange applications.Its extensive potential greatly promotes its study on production in a commercial scale.ZSM-5 molecular sieve was commonly prepared by hydrothermal method in a commercial scale,the hydrothermal method system simulate the natural environment of high temperatures,high pressure and alkali environment to prepare ZSM-5 molecular sieve.In hydrothermal system,a large amount of liquid is required,thereby which results in low yield and large amount of waste liquid.This paper is committed to adopt a method with characteristics of clean production to prepare ZSM-5 zeolite.The concept of cleaner production is the prevention of the whole environment strategy for application in the production process,product and service,thus increase ecological efficiency and reduce the risk of humans and the environment.Clean production requires fewer materials,energy consumption,low toxicity and less quantity in the produce process.Preparing zeolite by dry-gel conversion method could meet the requirements of the clean production.Higher yield,less energy consumption and emission waste could be gained by dry-gel conversion method.This article adopt a dry-gel conversion system to prepare different morphologies of ZSM-5 zeolite and binder-free ZSM-5 zeolite catalysts/adsorbent.The application of materials was also studied in the article.In the article,the effects of different dry-gel composition and dry-gel preparation condition to the dry-gel conversion process were studied.Ludox,silicic acid and silica gel were selected as the silica source to prepare the dry-gels;the as-prepared dry-gels were converted under the same condition.The products converted from different dry-gel were characterized,results shows different morphologiesh of the products from differents dry-gels.Products from dry-gels by different aluminum source also show different properties.In the systhesis system,the dry-gel from sodium aluminate can converted into ZSM-5 zeolite with high relative crystallinity,but the dry-gel from aluminum sulfate can not.The effects of inherent moisture of the dry-gel and the time of material pretreatment to the conversion procee were studied in the paper.The inherent moisture was controlled by the drying container,the products from dry-gels with different inherent moisture show different morphologies.The dry-gel conversion process could also influenced by the material pretreatment and the added amout of alkali.The effects of crystallization conditions to the dry-gel conversion were studied in the paper.The amount of added water,crystallization temperature and crystallization time were selected as the investigate factors.Results show that ZSM-5 zeolite could be obtained under 150 ? after 48 h when the mass ratio of the dry-gel to the water is above 12.5,the morphologies could be affected by the amount of added water.The dry-gel can be converted to ZSM-5 zeolite under the temperature between 150 ? and 180 ?.The particle size of the crystal increased with the raising of the crystallization temperature.The dry-gel can be converted to ZSM-5 zeolite after 18 h to 72 h,the conversion procee was conjectured by the change of the morphologies of products under different crystallization time.The catalysis performance of the productions by dry-gel conversion on the MTP reaction was studied in the pater.The small crystal ZSM-5 zeolite and the hierarchical ZSM-5 show good catalysis performance on MTP reaction.The small crystal ZSM-5 was bodied with the binder,and the as-prepared dry-gel was converted into binder-free ZSM-5 catalyst with self sustained structure.The binder-free ZSM-5 catalyst shows greater catalysis performance than the ones with binder.Zeolite powder can not be used directly,but zeolite bodied with binder would get the pore blocked and surface reduced because of binder.Finally,the zeolite bodied with binder would be less efficient than zeolite powder.Binder-free bodied ZSM-5 zeolite adsorbent was prepared by dry-gel conversion method in this paper.The adsorption and desorption performance of as-sythesized was studied.ZSM-5 zeoite possesses a unique channel and shows a favorable thermal stability;thereby it was widely used in many areas.There would be quite a long time since one zeolite was explored on experiment scale to produce on industry scale,and the block between them is the scale-up effect.The scale-up sythesis of small crystal ZSM-5 zeolite in quasi-like system was studied in the paper.The scale-up sythesis of zeolite was studied by the flow field information for the first time.The flow field in the reactor was optimized by changing the stirrer condition,and finally the condition of the scale-up sythesis was improved.The morphology of the ZSM-5 zeolite was controlled by turning the stir speed.A sythesis reactor with template reclaimed system for the dry-gel conversion was designed in this paper.The scale-up effect of the sythesis of ZSM-5 zeolite by dry-gel conversion on the scale of 5 L was crippled through changing the added water.Finally,binder-free bodied ZSM-5 zeolite with good mechanical strength and high relative crystallinity was gained in 5 L scale sythesis.