Extrusion Of Hierarchically Porous ZSM-5 Zeolite And Mechanical Properties Of Extrudates

Hierarchically porous ZSM-5 zeolite not only inherits the advantages of traditional zeolite,but also overcomes its limitations in macromolecule diffusion.For powdered catalysts,shaping is one of the most essential steps in industrial applications,and the mechanical properties of the shaped catalysts are key parameters for ensuring reliable operation of reaction system.Therefore,in this paper the extrusion of hierarchically porous ZSM-5 zeolite was conducted,and the effects of drying and calcination processes on the mechanical properties of the extrudates were systematically studied.The main work and results are as follows:First,the effects of drying and calcination processes on the properties of ZSM-5 extrudates were preliminarily investigated by a single-factor method.The experimental results show that both drying and calcination significantly affect the mechanical strength and reliability of ZSM-5 extrudates.Therefore,the ranges of factors which have remarkable effects on the mechanical properties of ZSM-5 extrudates were determined through this experiment.Then,the effects of drying temperature,drying time,and moisture content on the mechanical properties of ZSM-5 extrudates were studied by a central composite orthogonal design.The mathematical models for mechanical strength and Weibull modulus of ZSM-5 extrudates were established by means of response surface methodology.The experimental results show that both mechanical strength and Weibull modulus of ZSM-5 extrudates decrease with the increase of drying temperature;the mechanical strength decreases with increasing drying time,whereas the effect of drying time on the Weibull modulus is statistically less significant;the middle level of moisture content results in higher mechanical strength and Weibull modulus within the experimental domain.The characterization results show that the pore structure of ZSM-5 extrudates is greatly affected by kneading and extrusion processes,while the drying process significantly affects the internal crack size of the particles.In summary,it was pointed out that the mechanical properties of the extrudates are improved mainly due to the reduction of crack size of ZSM-5 extrudates.Finally,the effects of calcination temperature,calcination time,and heating rate on the mechanical properties of ZSM-5 extrudates were studied by a central composite rotatable design.The experimental results show that calcination process is always beneficial to improvement of the mechanical properties of ZSM-5 extrudates.The mechanical strength of the extrudates increases steadily with increasing calcination temperature and calcination time,the mechanical strength decreases first,reaches a minimum at 10 ?/min,and then increases with increasing heating rate;the Weibull modulus of the extrudates increases first,reaches a peak at 600 ?,and then decreases as calcination temperature increases;and the middle levels of calcination time and heating rate result in a higher Weibull modulus.The optimum condition was derived by parameter optimization: calcination temperature of 673.5 ?,calcination time of 5.77 h,heating rate of 12.62 ?/min,and the corresponding mechanical strength of 90.7 N,Weibull modulus of 6.412.Under this condition,the extrudates would possess both higher mechanical strength and Weibull modulus,resulting in higher fracture loads with low probabilities of failure.According to the theory of mechanical strength and reliability,the extrudates exhibit the best mechanical properties.