Study On The Vapor-phase Nitration From Cyclohexane To Nitro-cyclohexane

The nitration of aromatic hydrocarbon has been widely used in present industrial production, while the nitration of aliphatic hydrocarbons and low carbon cycloalkane (C≤8) were rarely studied, especially the vapor-phase nitration of low carbon alkanes. Recently, the mixed acid of nitric acid and sulphuric acid was usually used in liquid phase nitration process of aliphatic hydrocarbons. This traditional liquid phase nitration process has many defects, such as strong corrosiveness to equipment, non-economic utilization of atoms, serious environmental pollution, and complicated technological process and so on. Therefore, exploring green nitration process of low-carbon hydrocarbons will be a significant research field for the organic nitration in future.Cyclohexane has wide applications in the chemical industry and it is used to produce fine chemicals, such as cyclohexanone, cyclohexanol, adipic acid, nitro-cyclohexane and caprolactam et al. Among these chemicals, nitro-cyclohexane could be converted to cyclohexanone oxime by partial hydrogenation reduction. It is a new important approach to prepare caprolactam from cyclohexanone oxime Beckmann rearrangement.Firstly, this paper focused on vapor-phase nitration of cyclohexane to nitrocyclohexane, and established a quantitative analysis method for the nitration product of cyclohexane by chlorinated benzene was used as internal standard sample, and the accuracy of the internal standard method was tested. The results showed that the method was fast, convenient and high accuracy.Secondly, the vapor-phase non-catalytic nitrification of cyclohexane to nitro-cyclohexane at atmospheric condition was mainly studied in this work. The effects of reaction temperature, residence time and malor ratio of materials on cyclohexane conversion and nitro-cyclohexane selectivity were investigated respectively, and the optimal reaction conditions were obtained. The results showed that the conversion of cyclohexane was 12.91% with 94.50% of the selectivity to nitro-cyclohexane under the reaction conditions that the temperature was about 250℃, the molar ratio of cyclohexane to NO₂ was 1.5:1 and the residence time was 71.12 s. This nitration method provided a novel clue and lays for preparing nitro-alkanes from aliphatic hydrocarbons by gas phase nitration, especially from low-carbon hydrocarbon, and established a good experimental basis for industrial applications in the future.In addition, the vapor phase catalytic nitration process of cyclohexane was examined in this work. A series of molecular sieves, transition metal complex, N-hydroxy phthalimide (NHPI), NHPI with 9, 10-anthraquinone (9, 10-AQ) and other catalysts were used as catalysts in vapor-phase nitration of cyclohexane. The effects of reaction temperature, residence time and malor ratio on the gas phase catalytic nitrations of cyclohexane were mainly examined. The results showed that the conversion of cyclohexane was evidently improved Especially, the cyclohexane conversion can reached 16.56% with 76.83% of the selectivity to nitro-cyclohexane under the conditions that the reaction temperature was 250℃, the molar ratio of cyclohexane to NO₂ was 1.5:1 and the residence time was 71.12 s when NHPI and 9, 10-AQ was used as a composite catalyst.Finally, on the base of previous studies, the possible reaction mechanism of vapor-phase catalytic nitration of cyclohexane was proposed in this work.