Oxidation Of Cyclohexane/O₂ To KA Oil Under Mild Conditions Basing On Heterogeneous Catalysts

The catalytic oxidation of cyclohexane to KA oil (cyclohexanone + cyclohexanol), being an important representative of the oxidation of alkanes, has been being paid much attentions from both scientific and industrial domains. The current arts for the industrial production of KA oil are basing on either non-catalytic or homogenous catalytic oxidation of cyclohexane. However, neither of the above processes is environmental-friendly, since they are associated with a few of issues, such as, the low conversion and selectivity, the rigorous reaction conditions, the hard separation of reaction mixtures, the lack of safty in operation. The exploration of environmental-friendly process of the oxidation of cyclohexane over heterogeneous catalysts is therefore of both significant academic and realistic interests.This paper presents two green arts for the oxidation of cyclohexane basing respectively on photo- and heterogeneous catalysts under mild conditions and the main points are described as follows.For the photocatalytic oxidation of cyclohexane, a series of metal-doped TiO2 catalysts with mesostructures had been synthesized using glycerol and triethanol amine as organic additives and characterized by means of XRD, DRS UV-Vis, TEM and N2-physipotion. It was revealed that the mesostructures was a result of the supramolecular assembly of a polyglycerol template, of which the degree of polymerization and crosslinking was affected obviously by the content of metal ions.The photocatalytic performance of the oxidation of cyclohexane using O2 as oxidant and over the metal-doped TiO2 was evaluated in a self-designed photocatalytic reactor, which was equipped with a 125 W high pressure mercury lamp. It was found that the catalytic performance of the Zn-doped TiO2 catalyst was higher than those for other metal-doped TiO2 ones, and over a Zn-TiO2 with a molar ratio of Zn/Ti = 0.05 presented an as high as 2.34% conversion of cyclohexane at a 100 % selectivity to KA (cyclohexanone 68% and cyclohexanol 32%).For oxidation of cyclohexane under mild conditions, a series of Co- and/or Mn-modified APO catalysts were hydrothermally synthesized. The catalysts were characterized by means of XRD, FT-IR, DRS UV-Vis and AAS and the results showed that the catalysts possessed a Berlinite structure, in which Co and/or Mn was incorporated. The oxidation of cyclohexane was performed under the atmospheric pressure and at a temperature below the boiling point of cyclohexane. Influencing factors, such as, the loading of Co and/or Mn, the reaction time, the reaction temperature and the flowrate of O2, was systematically investigated. It was shown that, under the optimal conditions, i.e., reaction temperature = 348 K, reaction time = 8 h, amount of catalyst = 0.4 g, cyclohexane to acetic acid = 1:1 (g/g), molar initiator (cyclohexanone) : cyclohexane = 0.05 : 1 (g/g) and flowrate of O2 = 8.7 ml/min, aa as high as 3.1 % conversion of cyclohexane at a 95 % selectivity to cyclohexanol could be achieved over a CoMnAPO with a 0.2 mol % total content of Co and Mn and a molar ratio of Co/Mn = 1:1.The above reaction processes are characteristic of the involved heterogeneous catalysts and mild conditions, being operated under the atmospheric pressure and at the temperatures below the boiling point of cyclohexane. The conversion of cyclohexane and selectivity to KA oil under the optimal conditions reported in this paper has been much higher than those derived from the current industrial process for the oxidation of cyclohexane. This enables a promising foreground for a practical application of the reaction processes developed here in this work.