Study On Clean Catalytic Oxidation Of Cyclohexene To Adipic Acid

In this paper,phosphotungstic acid which has good thermal stability is adhered at the surface of the SBA-15 mesoporous material to enhance and modify the acidity and catalytic activity of the catalysts which are used in the synthesis of adipic acid.And a new type of catalyst PW/SBA was prepared by post-synthesis method.The synthesis process of the catalyst is simple and non-polluting to the environment.As is known however,using the catalyst to synthesize of adipic acid have not been reported.In the present study,in accordance with the molecular structure characteristics of the cyclohexene,adipic acid is synthesized by means of a "one-pot" reactive mode with cyclohexene and hydrogen peroxide(w=30%) using modified catalysts.The process without organic solvents is used by direct oxidation of cyclohexene which is the scientific methods of clean synthesis.First of all,the base route of synthesizing adipic acid was determined by pre-experiment program.Then the orthogonal experiments method and the single factor test method was used to optimize the conditions of reaction process.Finally,the better process of synthetic routes and conditions was tested using the parallel experiment methods.The obtained conditions are reaction time 12h,temperature 80℃,the amount of catalyst 1.75g,n(H₂O₂): n(cyclohexene)=5.47:1,adding the amount of another 1/2H₂O₂ after reaction time is 3.5h.A method was developed for the quantitative analysis of adipic acid by GC.The sample is esterified with 10%H₂SO₄-CH₃OH,extracted by trichloromethane,dried the organic phase and determined the yield and purity quotient of adipic acid by GC. The adipic acid standard is used as the standard sample to verify the feasibility of the method.The esterifiable rate is nearly up to 100%.The self-made adipic acid's melting point was determined by the digital melting point instrument;and its IR spectrum was measured by FT-IR spectrometer;and compared to the adipic acid standard's spectrum.The results show that product of the synthesis process is indeed adipic acid. A series of properties of catalyst were characterized by thermal analysis techniques and multi-point BET adsorption-desorption principle.The results of the DSC and the DTG curves show that the catalyst has higher thermal stability.The nitrogen adsorption-desorption isotherm of the PW/SBA catalyst was mensurated. The surface area of catalyst is 367.1m²·g^-1,pore volume V is 0.2cm³·g^-1 and pore size R is 1.089nm.The standard combustion enthalpy of adipic acid was determined by XRY-1C calorimeter,which is -2801.0 kJ·mol^-1 at the standard condition.The reliability of instrument is tested by chemical agent naphthalene,the absolute error is 5.6 kJ·mol^-1 and the relative error is 0.109%for the comparison between the setimated value and literature value about the standard combustion enthalpy of naphthalene.According to the thermodynamic relationship,the standard formation enthalpy of adipic acid was calculated to be -989.32 kJ·mol^-1.The melting point and the melting enthalpy were determined by DTA-TGA for adipic acid,which are 152.5℃and -2520 J·g^-1, respectively.