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Zeolite -based bifunctional catalysts and their catalytic isomerization Performance

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Tutor: WuWei
School: Heilongjiang University
Course: Chemical processes
Keywords: ZSM-22 zeolite,isomorphous substitution,dealumination,bifunctional catalyst,hydr
CLC: O643.36
Type: Master's thesis
Year:  2011
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Abstract:
In this paper, ZSM-22 zeolite synthesized by hydrothermal method were investigated the effects of the composition of initial gel, the dosage of template, water, alkali and crystallization time on the structure and optimize the best synthesis conditions,the molecular chemical composition of the synthesis gel was: OH-/SiO2=0.2,DAH/SiO2=0.3,H2O/SiO2=35,SiO2/Al2O3¡Ý70, crystallization at 160¡æfor 34 h. The ZSM-22 zeolite with diffrente SiO2/Al2O3 were characterized by XRD, N2 absorption-desorption, SEM, NH3-TPD,FT-IR, et al. The roating and static hydrothermal with DAH as a template were compared , the results showed that the static hydrothermal synthesis of ZSM-22 zeolite had fewer acid sites and larger mesoporous pore volume. At the same time,the effect of template for the morphology and acidity of ZSM-22 zeolite was studied, the results showed that ZSM-22 zeolite synthesized with EtPBr had more acid sites and larger microporous pore volume and microporous surface area, and ZSM-22 synthesized with DAH owned smaller crystal size and larger mesoporous pore volume.The influence of reaction temperature, reaction pressure, hydrogen flow rate and space velocity on n-decane hydroisomerization reaction were investigated to optimize the best reaction conditions. Under the optimized reaction conditions , the catalytic properties of ZSM-22 zeolite with different molar ratio of SiO2/Al2O3 showed that the high selectivity of Z-22£¨90RD£© zeolite due to the smaller crystal size to shorten the process from the proliferation of products. The zeolite synthesis in static methods had higher acid strength lead to high hydrocracking selectivity . The zeolite Z-22£¨110RE£© synthesized with EtPBr as template had weaker acid strength lead to high selectivity on n-decane hydroisomerization reaction.The ZSM-22 zeolite isomorphous replacement with different density £¨NH4£©2SiF6, Although the acid strength and acid amount decreased with the modification of ZSM-22, the diffusion of product was improved by the increament of secondary mesoporous structure. The conversion of n-decane and the isomerization selectivity were 77 % and 80 % on bifunctional catalysts Pd /ZSM-22 which modified by the 0.3 M £¨NH4£©2SiF6. The ZSM-22 zeolite was dealuminated with citric acid and hydrochloric acid, The strength acid sites provided by zeolite framework aluminum selective removal by chelation with low concentration citric acid . Due to the interaction of realumination and dealumination ,the acid site reduced slightly with higher concentration citric acid£¨1 M£©. The ZSM-22 dealuminated with different concentration citric acid had larger mesoporous pore volume was caused by secondary mesoporous structure. With the increased concentration of hydrochloric acid, the relative crystallinity and acid sites were reduced , the diffusion of product was improved due to mesoporous pore volume and microporous surface area increased with dealumination, The conversion of n-decane are 85.21 % and 80.34 % ,and the isomerization selectivity are 65.70 % and 70.06 % on bifunctional catalysts Pd /ZSM-22 modified by the 0.2 M citric acid and 8M hydrochloric acid.
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