Preparation, Characterization And Catalytic Properties Of The Novel Catalysts For One-step Synthesis Of ε-caprolactam From Cyclohexane Nitrosation

ε-Caprolactam is a very important intermediate materials for nylon-6synthesis. All current commercial ε-caprolactam synthesis processes are based on phenol, benzene or toluene and the production methods include the reaction of cyclohexanone and hydroxylamine, the photonitrosation of cyclohexane and the nitrosation of cyclohexanecarboxylic acid, which is obtained from toluene as the raw material. Nowadays, most of the ε-caprolactam synthesis is still based on the classical technologies. The cyclohexanone reacts with hydroxylamine sulfate to form cyclohexanone oxime, which can be concverted to ε-caprolactam through Beckmann rearrangement in the presence of oleum. However, these methods of ε-caprolactam synthesis have several disadvantages such as complex routes, low atom efficiency, reactor corrosion, environmental pollution and large amounts of ammonium sulphate are formed as by-products. Therefore, to overcome the former mentioned disadvantages, it is very attractive to simplify the traditional ε-caprolactam synthesis processes and develop a green chemistry method for ε-caprolactam production. Based on the previous works of our research group, we prepared and characterized a series of catalysts and their catalytic properties in the one-step nitrosation of cyclohexane to ε-caprolactam were performed.Mesoporous crystalline SiO2-Al2O3and its supported catalysts were designed and prepared by hydrothermal synthesis and impregnation method and their catalytic properties in the one-step nitrosation of cyclohexane to ε-caprolactam were performed. The different resources of template, Si and Al and preparation conditions were discussed in detail. The optimum reaction conditions in the reaction medium of oleum were obtained under the catalysis of SiO2-Al2O3. It is revealed that the catalyst with middle Si/Al molar ratio, calcined at600℃for6h with resources of triethylamine, silicasol and pseudoboehmite exhibits larger surface areas and has more uniform meosoporous structure, shows better cyclohexane conversion and selectivity toε-caprolactam. It indicates that both Br(?)nsted and Lewis acid sites exist on the supported transition metal catalysts and Mn/SiO2-Al2O3with stronger acidity and relatively larger BET surface area gives the result of conversion of7.34%and ε-caprolactam selectivity of50.59%.Crystallization of AlPO-5and its metal substituted catalysts were prepared by hydrothermal method and characterized. Their catalytic properties were studied in cyclohexane nitrosation for the production of ε-caprolactam. The metal substituted catalysts show stronger Br(?)nsted acid sites when the Si or metals are introduced into the framework of AlPO-5and the number of Lewis acid sites increase simultaneously. The results show that the catalytic activity increases with the increment of the BET surface area and the Br(?)nsted acid sites are helpful to cyclohexane nitrosation to give better selectivity to the ε-caprolactam. Among these catalysts, the CrAPO-5with larger BET surface area, more Lewis acid sites and stronger Br(?)nsted acid sites gives better result of conversion of8.16%and ε-caprolactam selectivity of68.17%.A series of SO42-/ZrO2and its supported catalysts were prepared by precipitation and co-precipitation method and their catalytic properties were studied in cyclohexane nitrosation for the production of ε-caprolactam. The results indicate that there is no ε-caprolactam obtained in the absence of oleum under catalysis of SO42-/ZrO2. When the reaction was carried out in the presence of oleum under these catalysts, the selectivity to ε-caprolactam is less than30%.The HY and its supported catalysts were prepared by ion exchange method and impregnation method and and their catalytic properties were studied in cyclohexane nitrosation for the production of ε-caprolactam. The optimum reaction conditions in the reaction medium of concentrated sulfuric acid were obtained under the catalysis of HY. The results indicate that the stronger Br(?)nsted acid sites appear when the metals and phosphotungstic acid are introduced into the HY and the increment of the Br(?)nsted acid sites has positive effect on the cyclohexane nitrosation to ε-caprolactam. Among these catalysts, the PW/HY gives better result of cyclohexane conversion9.9%and selectivity to ε-caprolactam75.9%.The amorphous SiO2-Al2O3and its supported catalysts were prepared by sol-gel method and impregnation method, and the influences of the preparation conditions including the loading content of cobalt and the calcination temperature were studied in detail. The20%Co3O4/SiO2-Al2O3calcinated at500℃has the smallest particle size, highest content of cobalt and most Br(?)nsted acid sites and the20%CrO3/SiO2-Al2O3catalyst calcinated at400℃has the smallest particle size, largest surface area and most Br(?)nsted acid sites. The Cr2O3/SiO2-Al2O3gives the better result of conversion of10.8%and ε-caprolactam selectivity of79.9%and the Co3O4/SiO4-Al2O3gives the best result of conversion of11.2%and ε-caprolactam selectivity of83.3%. The catalytic performances as well as the physical properties of the catalysts suggest that the Br(?)nsted acid sites are supposed to be the selective sites for the cyclohexane nitrosation to ε-caprolactam.In addition, liquid chromatography, liquid chromatograph-mass spectrometer, gas chromatograph-mass spectrometer and fourier transform infrared were used for the quantitative and qualitative analysis of the products of cyclohexane nitrosation. Combined with the quantum mechanical methods, a possible mechanism for liquid phase nitrosation of cyclohexane in different reaction medium was proposed.In this work, we prepared and studied several new catalysts for one-step cyclohexane nitrosation to ε-caprolactam and the results have been improved greatly compared with the previous works.