One-step Preparation Of Adipic Acid And Glutaric Acid From Oxidation Of Cyclohexane With Molecular Oxygen

Adipic acid and glutaric acid are important organic chemical raw materials,mainly used to produce nylon-66 fiber,resin,polyurethane foam and other polymer materials.The synthesis of adipic acid and glutaric acid in the traditional industry mainly use cyclohexane as a raw material,and then prepared by oxidizing alcohol and ketone intermediates with nitric acid.According to the requirements of green,low-carbon and environmentally friendly chemical process,the large amount of nitrogen oxides produced in this process has been plagued by the development of adipic acid industry chain.Therefore,through scientific and technological innovations with catalysis as the core,the preparation of catalysts controlled from the perspective of molecular engineering is expected to develop a new method for one-step oxidation of cyclohexane to adipic acid and glutaric acid.In this paper,different metal-modified hollow titanium silicalite molecular sieves were explored to activate molecular oxygen and adjust the structure-activity relationship between the structure of catalysts and the catalytic reaction performance,which provided a new idea for the one-step oxidation of cyclohexane to adipic acid and glutaric acid.（1）Titanium silicalite molecular sieve（TS-1）prepared by recrystallization method was expanded and modified to synthesize HTS,and the surface structure of HTS was modified with different transition metal salts.The results showed that Ni-modified HTS was the best catalyst for cyclohexane oxidation reaction.Under the reaction conditions of 1.2MPa and 140℃,the cyclohexane conversion was 24.6%and the total selectivity of adipic acid and glutaric acid reached 74.2%with acetonitrile and 1%Ni/HTS as the solvent and catalyst respectively.Cycling experiments showed that the activity of catalyst remained basically unchanged after reusing seven times.The structure of catalysts was characterized by FT-IR,UV-Vis,N₂ adsorption-desorption isotherm,XRD,Raman,TEM and XPS.The results confirmed that the prepared Ni species were highly dispersed on the surface of HTS.Based on the experimental results and characterization analysis,it was shown that the dispersed Ni species and tetrahedral Ti species in the HTS structure were the key catalytic active sites for cyclohexane oxidation,which synergistically promoted the reaction of cyclohexane to adipic acid and glutaric acid.At the same time,the catalytic performance and structure difference between fresh and used HTS were explored.The 7%Ni/used HTS catalyst showed the best catalytic activity,which could achieve 28.4%cyclohexane conversion with 74.0%total selectivity of adipic acid and glutaric acid.Combined with the characterization,it was found that the used HTS framework structure was not damaged,but the skeleton Ti was partially lost.（2）Different ketones were explored as the reaction medium for cyclohexane oxidation.It was found that 3-pentanone was the most effective medium for this oxidation process.Under the conditions of 1.4MPa and 130℃,the cyclohexane conversion was as high as 33.6%with74.9%carboxylic acid selectivity,of which the adipic acid selectivity reached 65.7%.Based on the above experimental data and conclusions,the active species produced during the reaction process were initially explored.GC-MS and UV-Vis spectra showed that the acetic acid,propionic acid and peroxide produced by co-oxidation of 3-pentanone and cyclohexane were the key active species for C-H bond activation of cyclohexane.Combined with the experimental results and characterization analysis,it further showed that the reaction was a free radical reaction process.