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Preparation Of Tungsten Catalysts And Its Applications In The Green Synthesis Of Adipic Acid, Etc.

Posted on:2008-12-12Degree:MasterType:Thesis
Country:ChinaCandidate:X H CaoFull Text:PDF
GTID:2121360215487926Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Adipic acid is necessary for the manufacture of fibres, and the industrialprocesses of its production can generate inevitable pollution of the environment.Therefore, many efforts have been done on the cleaner synthesis of adipic acid. Inthis work, tungsten resource with ample supply in China especially in Jiangxiprovince was used as catalysts in the green synthesis of adipic acid, cyclohexene.And we mainly carried out the following aspects of research works:1. A dawson structure heteropoly acid H6P2W18O62·32H2O and the solidsuperacid SO42-/TiO2-WO3 were prepared through hydrothermal method andhydrothermal modification respectively. Then they were characterized by IR, XRDand their catalytic activity were studied.2. Adipic acid was synthesized by four kinds of different tungsten catalystscatalyzed oxidation cyclohexanone with 30 percent hydrogen peroxide in watersolution in the absence of organic solvent and phase-transfer respectively. The efectsof reaction condion (the amount of catalyst, ratio of H2O2/cyclohexanone, reactiontemperature, reaction time, et al.) on the green process of cyclohexene oxidationwere studied. Then the possible active species and reaction mechanism were alsodiscussed. The results show that under the optimal condition, i.e.(1) the mole ratio of cyclohexanone:H2O2:H2WO4:H3PO4=100:500:2.5:2.5, thereaction temperature is 90℃and the reaction time is 5h, the isolated yield of adipicacid can reach 86.7%. If the tungstic acid alone was used as catalyst, the isolatedyield of adipic acid was only 69.4%. The active structure of catalyst may beH2[W2O3(O2)4(H2O)2], {PO4[WO(O)2]4}3-.(2) the mole ratio of cyclohexanone:H2O2:WO3 was 100:500:2, and thereaction temperature was 120℃, the reaction time was 6h, the isolated yield ofadipic acid could reach 80.3% and its purity was 99.8%. The catalyst could be reusedfor 5 times and the isolated yield of adipic acid was still above 70.2%. The peroxo-polytungstic acid {H2[W2O3(O2)4(H2O)2]} which was synthesized by the reaction ofhydrogen peroxide and tungsten trioxide is the probable active substance of the catalyst.(3) the reactant molar ratio of H3PW6Mo6O40·6~7H2O:H2O2:cyclohexanone=0.15:400:100, the reaction temperature of 90℃and time of 5h, the isolated yield ofadipic acid can reach 75.8%. The active structure of catalyst is presumed to be{PO4[WO(O2)2]4}3-, {PO4[MoO(O2)2]4}3-, {PO4[Mo4-XWXO20]4}3-.(4) n(cyclohexone):n(H2O2):n(H2C2O4):n(H6P2W18O62·32H2O)=100:450:1.0:0.125, reaction temperature was 100℃and reaction time was 5h, the isolated yieldof adipic acid could reach 74.5%.According to the literatures and the phenomenon appearing in our experiments,the possible mechanism of tungsten catalysts catalyzed oxidation cyclohexanone with30 percent hydrogen peroxide in water solution is suggested as follows:3. Two new "green" routes to the synthesis of cyclohexene were studied in thispaper. The results showed :(1) when the mass of the catalyst(H6P2W18O62·32H2O) used to the reactantswas 4.2% of the quantity of cyclohexanol, the reaction temperature was about170~180℃, the reaction time was 35 min. The yield of cyclohexene could reachmore than 93.0%. The catalyst could be reused for 5 times and the yield was stillabove 75.0%.(2) On the optimum experiment conditions, i.e., w(SO42-/TiO2-WO3)=5.3%, thereaction temperature was in the range of 170~180℃, the reaction time was 45 min,the yield of cyclohexene could reach 95.6%. The catalyst could be reused for 5 timesand the yield was still above 88.9%. If the catalyst which had been reused for five times was regenerated, then its activities could be enhanced as high as the fresh one.Catalyst prepared by this method has a 5.65% higher yield than the catalyst preparedby the ordinary method.
Keywords/Search Tags:tungsten catalysts, adipic acid, hydrogen peroxide, cyclohexanone, cyclohexene, green synthesis
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