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Study on the New Synthesis and Immobilization Method of12-Tungstophosphoric Heteropoly Acid Catalyst

Author: LiDongWei
Tutor: LiJie
School: Central South University
Course: Physical Chemistry of Metallurgy
Keywords: 12-tungstophosphoric acid hydrothermal synthesis salting-out method SBA-15 active carbon supported catalysts
CLC: O643.36
Type: Master's thesis
Year: 2012
Downloads: 265
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Abstract


12-Tungstophosphoric acid (TPA) catalysts are widely used in petrochemical and other chemical industry due to its special structure and strong acidity. However, some problems hold back its utilization in the application. Such as ethyl extracting agent was used in TPA synthetic process which may lead to environmental pollution and safety hazards. Moreover, TPA was difficult to recycle. In this paper, a two-step synthesis method and a ultrasound assisted impregnation method were employed to solve the problems summarized above.(1)12-Tungstophosphoric acid was synthesized by a two-step method using sodium tungstate. In the process, TPA can be precipitated from the solution by adding inorganic salts. The chemical composition of the products was investigated by elemental analysis and turn out to be H3PW12O40. The results indicate that the acidification pH of sodium tungstate solution and the hydrothermal conditions were the key factors of TPA synthesis process. The yield of12-tungstophosphoric acid can reach95%under controlling the acidification pH of sodium tungstate solution at7.0, hydrothermal temperature at135℃, hydrothermal time at10h and H3PO4acidzing pH value at2.06.(2) Mesopore molecular sieve (SBA-15) and active carbon (C) carriers supported TPA catalysts (TPA/SBA-15and TPA/C) were prepared by ultrasound assisted impregnation method. Both samples are mesoporous materials, but their pore structure were different. The specific surface area of TPA/SBA-15and TPA/C are975.6m2·g-1and77m2·g-1, respectively. There are6strong acid sites in TPA/SBA-15, for TPA/C sample, there are5strong acid sites. Moreover, the acidity of acid sites in TPA/SBA-15is stronger than that of in TPA/C. The thermal decomposition temperature of TPA increased to650℃after being loaded with SBA-15. Water gradient elution treatments show that the remained amount of active component of TPA/SBA-15and TPA/C are22%and75%after solvent gradient elution, respectively. The anti-solvent elution ability of TPA/C is better than that of TPA/SBA-15. The catalytic preformnce of the catalysts was evaluated in the transesterification of acetic acid and ethanol. TPA/SBA-15showed100%selectivity, and the convertion of acetic acid reached92%when TPA/SBA-15was initial used. TPA/SBA-15still had activity and the yield of the the convertion of acetic acid remained above70%after being recycled11times. However, the catalytic activity of TPA/C reduced significantly after being recycled4times, and exhibited deactivated after being recycled8times. The catalytic performance and stability of TPA/SBA-15is superior to that of TPA/C.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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