Synthesis, Characterization And Catalytic Activity Of Heteropoly Acids(Salts) For Ammoximation Of Cyclohexanone

Cyclohexanone oxime is one of the most important intermediate in the industrial caprolactam technology in which benzene is used to be raw material. Conventionally it is synthesized in the cyclohexanone-hydroxylamine process. Using Titanium Silicate-1(TS-1) as catalyst, cyclohexanone oxime can be prepared from cyclohexanone, ammonia and hydrogen peroxide, which is called liquid phase ammoximation process. It can not only proceed in mild reaction condition, reach high selectivity, but also can avoid byproducts, finally realize"Zero Emission". In 1990, Enichem of Italy developed and built an industrial equipment of liquid phase ammoximation catalyzed by titanium silicate-1, which opened a new period of cyclohexanone oxime industrial producing. However, TS-1 is very expensive and with small-granularited catalyst, which causes difficulties in industrial production, for example separation and recycle. So, how to separate and reclaim the titanium silicate-1 zeolite is becoming the most urgent problem to be resolved in the research and development of ammoximation of cyclohexanone.In this thesis, environment-friendly heteropoly acid(salts) catalyst are used in the ammoximation reaction of cyclohexanone. In the first part, a series of heteropoly acid(salts) are successfully synthesised, in which P is acted as the central atom and W,Mo,V are acted as coordinating group. They are characterized by FTIR, XRD, ICP and the results reveal that heteropoly acids get the Keggin-type structure. Then, the main factors which affect the yield of heteropoly acids are studied, such as reaction temperature, material ratio, pH value and quantity of solvent. The experiment results show that under condition of boiled and pH 1.6~1.8, the yield of heteropoly acids can reach up to 82.51%.In chapter two, the synthesised heteropoly acids(salts) are estimated by ammoximation of cyclohexanone system. Results show that the heteropoly acids with Keggin structure have the advantages of high catalyse ability, excellent selectivity and stability, mild reaction condition and free of pollution. Using heteropoly acids as catalyst, the ammoximation reaction process are optimized and effects of the dosage of catalyst, reaction temperature, reaction time, the dosage of H2O2 and solvent on reaction are inverstigated. The results indicate that using water as solvent, at 20℃for 5.0h, with H3PW12O40 19.6g/1mol cyclohexanone and ratio of hydroperoxide/acetone 1.6/1, the conversion of cyclohexanone and the selectivity of cyclohexanone oxime can reach 89.41% and 98.38% respectively.On the base of plenty preliminary experiments, the reaction mechanism of ammoximation catalyzed by heteropoly acids(salts) is studied. In the proposed mechanism, the Keggin-type heteropoly negative ion is bonded with H2O2 in aqueous phase, forms the active peroxidized heteropoly compounds and transfers most of the peroxidized polyacid into the organic phase, then oxygen is transfered from peroxidized polyacid to the substrate, which catalyzes the ammoximation. Moreover, the electrophilicity of the carbonyl group can increase the acidity of heteropoly compound. This not only creats a suitable condition for the attack of nucleophilic reagent, but also make the hydroxyl group in alcohols and amine protonation, which benefit the formation of cycohexanoxime. Meanwhile, results indicated that high concentration of hydroperoxide has no significant influence on the selectivity of oxime, which supposes that the mechanism of ammoximation is hydroxylamine approach.At the last part of this thesis, on the basis of systemic research experiments, the immobilized catalysts, which supported on silicon dioxide, active carbon and active alumina, are prepared and characterized by BET, FTIR, XRD. Results proved that the active ingredient is combined with carrier and the characteristic structure is unchanged. The result of ammoximation catalyzed by immobilized heteropoly acids(salts) for the first time shows that the Al2O3-based catalyst exhibits the highest activity with a yield of 90.23% and a selectivity of 99.78%, even better than homogeneous catalyst. Though the immobilized catalyst is easily separated, but active ingredient is also easy off-bonded and the reuse of catalyst can not achieve the prospective results.