Kinetics Of Styrene Oxidation For Benzaldehyde Over Bi₂SiO₅/SiO₂Catalyst

Benzaldehyde is the raw material and intermediate widely used in flavor、 food、pharmaceuticals and daily chemical series products. At present, most of the benzaldehyde inChina is produced through the by-product of the synthesize process of benzoic acid anddichlorotouene hydrolyzation process. However, there are many limiting factors, for example,the output of them are low, the chloride caused the corrosion of chemical engineeringequipments and more the chemical separation and purification is complicate. Concerning theincreasing seriously environmental problems, more and more countries have constituted somestrict controls for the pollution.therefore, It has now attracted more research groups in finding amore economical and efficient process to obtain benzaldehyde.In recent years, Styrene oxidation for benzaldehyde withH2O2as oxidant has been paidmore attention due to its mild reaction conditions and environmental protection.In our thesis,using the self-made Bi2SiO5/SiO2catalyst, benzaldehyde was prepared by oxidation of styrene,and the reaction conditions were studied. the major content of this paper is composed of threeparts:1、Study on the oxidation of styrene for benzaldehyde with self-made Bi2SiO5/SiO2catalyst.Benzaldehyde was prepared by oxidation of styrene using Bi2SiO5/SiO2as catalyst andhydrogen peroxide as oxidation. And the effect of temperature、the ratio of styrene andhydrogen peroxide、reaction time、 solvent and the weight of catalyst on reaction were studied.The results showed that the conversion of styrene was increased with an increase in temperatureandVH2O2/Vs tyrene; the yield of benzaldehyde can be improved with reaction time prolonging;when the reactants were excess, the catalytic activity was raised with the quality of the solvent,while taking an overdose of solvent, the catalytic activity was depressed; and the yield ofbenzaldehyde seemed independent of the weight of catalyst.2、Study on kinetics of hydrogen peroxide decompositionKinetics of hydrogen peroxide decomposition was studied without adding styrene and withadding styrene respectively. And the kinetic parameters were obtained. The equations are as follows:Without styrene, the value of activation energy of hydrogen peroxide decomposition is3.76×104, and the order of hydrogen peroxide is0.85, when the concentration ofH2O2is lessthan1.2mol/L and the range of temperature is between60℃and80℃。With styrene, the concentration of styrene is between0.30mol/L and0.62mol/L,CH2O2<1.2mol/L and the temperature is from70℃to85℃, the value of activation energy ofhydrogen peroxide decomposition is5.87×104, and the order of hydrogen peroxide and styreneis5.08and-0.35, respectively.3、Study on intrinsic kinetics of styrene oxidation to benzaldehydeBased on the Langmuir Hinshelwoodmechanism, a reaction mechanism of styreneoxidation for benzaldehyde is supposed to accord with the collaborative mechanism, styreneabsorbed is substantiated by regressing the data of kinetic reaction. The mechanism is obtained.The related equilibrium constants of intrinsic kinetics model were calculated by data-fitting.