Oxidation Of Cyclohexane/O₂to KA Oil And Adipic Acid Basing On Heterogeneous Catalysts

The catalytic oxidation of cyclohexane to KA oil (cyclohexanone+cyclohexanol) and adipic acid, being an important representative of the oxidation of alkanes, has been being paid much attention 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 high expense for transportation and so on. They are therefore non-environmental friendly processes. In the present work, a series of novel heterogeneous catalysts were developed and utilized in the aerial oxidation of cyclohexane to KA oil or adipic acid. The results exhibit a promising industrialization foreground of cyclohexane aerial oxidation to KA oil or to adipic acid over heterogeneous catalysts. The main points are as follows:A series of Co-and/or Mn-modified APO catalysts were hydrothermally synthesized investgating the effects both on the variety of the molar ratio between metal ions and Aluminum Chlorohydrate and the crystallization temperature at a rigid molar ratio. The favourable molar ratio between metal ions and Aluminum Chlorohydrate and the crystallization temperature were optimized at respectively0.02:1as well as180℃by oxidation function method. Considering that the reaction kettle to synthesize would be transferred from experimental small pot to industrial reaction kettle, the factors of crystallization time and the stirring while crystallization were studied with the best result at48h and no stirring while crystallization. The optimized catalysts were characterized by means of XRD, FT-TR UV-Visual and SEM. The results showed that the catalysts possessed a Berlinite structure, in which Co and/or Mn was incorporated.The oxidation of cyclohexane was performed in normal reaction kettle of500ml with the optimal Co-and Mn-modified APO catalysts. Influencing factors, such as, the reaction pressure, the reaction time, the reaction temperature, the amount of catalyst and the flow rate of tail gas, were systematically investigated. It was shown that, under the optimal conditions, i.e., reaction temperature=100℃, reaction time=6h, amount of catalyst=6.0g, cyclohexane to acetic acid=1:1(g/g), molar initiator (cyclohexanone):cyclohexane=0.05:1(g/g) and flow rate of tail gas0.4L/min, yield as high as12.1%to adipic acid could be achieved over a CoMnAPO with a0.2mol%total content of Co and Mn and a molar ratio of Co/Mn=1:1with the crystallization temperature at180℃For the above results of a lot adipic acid and comparatively less cyclohexanone and cyclohexanol, an unprecedented gas-liquid-solid reaction kettle was invented with the purpose of more KA oil. From the reaction phenomenon and results, the selectivity of cyclohexanone and cyclohexanol was heightened with＞5%in the new reaction kettle while comparing with the normal one using the same catalyst and reaction conditions.The above reaction processes are characteristic of the involved heterogeneous catalysts and mild conditions, being operated under the conditions of100℃and1.OMPa. The conversion of cyclohexane and selectivity to adipic acid 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 an industrial application of the reaction process developed here in this work.