Preparation Of Azelaic Acid With Oxidative Cracking Of Oleic Acid In Hydrogen Peroxide

Using renewable resources to replace petrochemical resources,preparing fine chemicals under green and mild conditions,and reducing carbon dioxide emissions at source are effective means to achieve green and sustainable production.Bio-based dibasic acids such as azelaic acid are important fine chemicals for the preparation of nylon,lubricants,etc.At present,ozone oxidation method has adopted to crack natural unsaturated fatty acids to prepare dibasic acid,which has the disadvantages of high energy consumption,poor selectivity,and low safety.The difficulty of production is the main reason why the supply of azelaic acid and other dibasic acids has long exceeded the demand.Therefore,the development of a new method for oxidative cracking of natural unsaturated fatty acids under mild conditions will greatly reduce the cost,reduce the emission of three wastes,and meet the needs of green and sustainable production.Hydrogen peroxide is a powerful and environmentally friendly oxidation method,which has attracted much attention in recent years for the oxidative cracking of unsaturated fatty acids.In this paper,we use a microchannel reactor to solve the current problems of long reaction time and harsh reaction conditions for oxidative cracking of oleic acid;meanwhile,we develop a twin-type phosphotungstic acid quaternary ammonium salt catalyst to achieve efficient recovery of phosphotungstic acid catalyst in a kettle reactor;in addition,we develop a tandem process of double hydroxylation/oxidative cracking of oleic acid to improve the selectivity of azelaic acid while reducing the amount of hydrogen peroxide used.The dissertation research is as follows:（1）Using phosphotungstic acid as a catalyst,azelaic acid is prepared by oxidatively cracking oleic acid in a microchannel reactor,and the optimal reaction conditions are obtained through single-factor optimization:reaction time of 314 s,reaction temperature of 80℃,phosphotungstic acid dosage of 8 wt%,hydrogen peroxide to oleic acid mass ratio of 3:1,and tube diameter of 1 mm.The conversion of oleic acid was 95.8%and the gas-phase yield of azelaic acid was 81.2%under the conditions of tert-butanol to oleic acid mass ratio of 2:1 and tube diameter of 1 mm.Compared with the intermittent kettle reactor,the reaction time was greatly reduced and the reaction temperature was significantly lowered,which greatly improved the reaction efficiency and operational safety.（2）The baryonic cationic surfactants were synthesized by brominated alkanes and tetramethylethylenediamine,and the baryonic phosphotungstic acid quaternary ammonium salts were synthesized by co-precipitation,the physicochemical properties of the catalysts were investigated by nuclear magnetic resonance,Fourier infrared spectroscopy,X-ray diffraction,scanning electron microscopy,X-ray energy spectroscopy,and thermogravimetric analysis.The catalytic activity and cyclic stability of the baryonic phosphotungstic acid quaternary ammonium salt in the oxidative cracking reaction of oleic acid were examined,and[C₄₂H₉₀N₂]HPW₁₂O₄₀ was screened as the optimal catalyst.The reaction conditions were optimized by the single-factor optimization method,and response surface analysis was performed to investigate the optimal reaction conditions for the oxidative cracking of oleic acid:the reaction temperature was 100℃,the reaction time was 4.3 h,the amount of[C₄₂H₉₀N₂]HPW₁₂O₄₀ was 8.7 wt%,the mass ratio of hydrogen peroxide to oleic acid was 3.4:1,and the amount of sodium stannate was 0.5 wt%.The optimum gas-phase yield of azelaic acid was 85.8%at this time.Under the optimal conditions,the catalyst can be recycled four times and the gas-phase yield of azelaic acid is still above 82%.（3）The tandem oxidation method was used to prepare 9,10-dihydroxystearic acid by catalyzing the dihydroxylation of oleic acid at a lower temperature and hydrogen peroxide dosage,after which the target product was obtained by cleavage of 9,10-dihydroxystearic acid without separating the intermediate and directly adding hydrogen peroxide and increasing the reaction temperature.The optimal reaction conditions were obtained by single factor optimization:the dosage of[C₄₂H₉₀N₂]HPW₁₂O₄₀ was 8.7wt%,the dosage of sodium stannate was 0.5wt%,the first step reaction temperature was 45℃,the time was 60 min,the mass ratio of hydrogen peroxide to oleic acid was 1:1,the second step reaction temperature was 100℃,the time was 3 h,the mass ratio of hydrogen peroxide to oleic acid was 2:1.Under the optimal conditions,the gas phase yield of azelaic acid was 89.8%,the amount of hydrogen peroxide was reduced by 11.8%and the gas phase yield of azelaic acid was increased by 4.7%compared with that of oleic acid by one-step oxidation cracking.