Preparation Of Organic-inorganic Heteropolyacid Salt And Its Catalytic Properties For Ammoximation Of Cyclohexanone

Cyclohexanone oxime is an important intermediate of caprolactam production. cyclohexanone -hydroxylamine process and cyclohexanone ammoximation process are the main industrial technology. Currently, using Titanium Silicate-1 as catalyst, cyclohexanone, ammonia and hydrogen peroxide are used for preparing cyclohexanone oxime in ammoximation process, which has mild reaction condition, high selectivity and less byproducts. However, TS-1 is very expensive, and it's small particle size causes difficulties in separation and recycle. Therefore, researching an efficient and recyclable catalyst to replace TS-1 is a viable solution.Several patents are reported to use heteropoly acid as catalyst for ammoximation of cyclohexanone, in which the conversion of cyclohexanone and the selectivity of cyclohexanone oxime can reach 93% and 93% respectively. But the difficulty of recycling constraints its development. In recent years, many studies focus on heteropoly acid (salt) immobilized on the porous supports, but the leaching of active components makes the recyclability of the catalyst unsatisfactorily. Then some studies about a kind of recyclable quaternary ammonium phosphotungstate salt are reported, such as, cetylpyridinium peroxide phosphotungstic acid quaternary ammonium salt for the catalysis of epoxidation of propylene, 1-butyl-3-methylimidazolium phosphotungstate for the catalysis of esterification. The heteropoly acid quaternary ammonium salt can be recycled and reused in the reaction system mentioned above . But in the ammoximation system with strong polar such as ammonia and hydrogen peroxide, the application of these catalysts has not been reported.This thesis mainly aims to the synthesis of a new multifunctional compound by leading organic groups into the secondary structure of heteropoly, which has the structure of amphipathicity and shuttle between oil and water. So the new multifunctional heteropoly compound has phase transfer function as well as strong acidic and redox,and the conversion of cyclohexanone and cyclohexanone oxime selectivity may be improved. Firstly,different carbon chain length of pyridine, imidazole and quaternary ammonium cations and phosphorus acid anion are designed to prepare a series of organic-inorganic heteropolyacid salt. The catalysts are charecterized by means of Fourier infrared spectroscopy, TGA/DSC simultaneous thermal analysis, elemental analysis and XRD. The results show that three catalysts all preserve the primary keggin structure, and has a structure as A3B. With the growth of carbon chain,the thermal stability of organic-inorganic composite heteropoly acid salt are worse, and it's carbon chain lean to break more easily.The catalytic properties of the organic-inorganic heteropolyacid salt are estimated by the liquid-solid ammoximation The optimal evaluation conditions are: temperature 20℃, molar ratio of hydrogen peroxide/cyclohexanone 1.6/1, hydrogen peroxide drops for 4h, and then reacts for 1h, molar ratio of ammonia/cyclohexanone 3.0/1, ammonia is once joined, the amount of catalyst is added by n (cyclohexanone): n (catalyst) = 1:0.0078. the conversion of cyclohexanone and the selectivity of cyclohexanone oxime can reach 90% and 80% respectively. The organic-inorganic heteropolyacid salts exhibite high catalytic activity. Reusing and recycling the catalysts, it is proved that the pyridine phosphotungstate shows good reusability and the catalytic selectivity increase.The influence of different anions of pyridine heteropoly acid on ammoximation of cyclohexanone is also studied in this thesis. The results show that different anions pyridine heteropoly acid catalytic ammoximation has different catalytic properties and the phosphotungstic anion has the highest activity. Solubility of pyridine phosphotungstate catalyst in three different polarity solvents, such as water, tert-butanol and cyclohexane, are mensurated. Also the activity and recyclability of pyridine phosphotungstate in the cyclohexanone ammoximation reaction with three different polarity solvents are investigated. The results show that the higher polarity, the greater solubility of pyridine phosphotungstate , and with the growth of pyridine cation carbon chain, the solubility decreased. The recycled catalysts are charecterized by Fourier infrared spectroscopy, TGA/DSC simultaneous thermal analysis to study the changes of structure and composition. Moreover, the effect of pretreatment of fresh catalyst on its catalytic properties is studied. The results show that the recovered catalyst keeps keggin similar structure, but the breaking of carbon chain changes it's composition. The similar results are obtained when the catalyst pretreated with hydrogen peroxide and ammonia. So it is proved that pretreatment of fresh catalyst can not get the anticipative high selectivity and recyclability.