Study On The Synthesis Of2,6-dimethylaniline By Hydrocatalytic Amination

2,6-dimethylaniline is an important intermediates for the fine chemical andpharmaceutical industries. Catalytic amination of2,6-dimethylphenol is one of themost applied value methods for the manufacture of2,6-dimethylaniline. The catalyticamination of2,6-dimethylphenol to2,6-dimethylaniline is investigated systematicallyin this paper.1. A series of catalysts were prepared and examined. The Pd1/γ-Al₂O₃-MgOcatalyst was selected because of the high activity. The effect of reaction conditionswas discussed over the optimum catalyst. The optimum reaction conditions are asfollows：reaction temperature is210℃, the flow rates of hydrogen and ammonia are160mL/min and80mL/min respectively, the flow of2,6-dimethylphenol is0.3mL/min （10wt%,1,4-dioxane）. Over the optimum reaction cinditions, the conversionof2,6-dimethylphenol is93.25%, the selectivity and yield of2,6-dimethylaniline are86.93%and80.56%, respectively.2. The stability of the catalyst was investigated. And it was found that thecatalyst deactivated. BET, XPS, IR, TEM, TG-DTG and atomic absorptionspectrometry were employed for analyzing reasons of the behavior of the fresh andthe deactivated catalysts. The results showed that the coke was formed and so coveredthe activity centers, which was the main reason for the catalyst deactivation. To solvethe problem of the catalyst deactivation we added a series of alkaline metal oxide intoPd1/γ-Al₂O₃for modification. Pd1/γ-Al₂O₃-BaO exhibited the best catalyticperformance and stability of the modified catalysts. In320hours, the conversion of2,6-dimethylphenol is keeping above99.2%, and both the selectivity and the yield of2,6-methylaniline are stable at85%⁸8%over Pd1/γ-Al₂O₃-BaO. The effects of BaOinto catalyst were investigated by XRD, NH₃-TPD, TEM, H₂-TPR and XPS. Theobtained results indicated that a spinel structure was formed effectively after theaddition of BaO into Pd1/γ-Al₂O₃catalyst and therefore decreased the number ofstrong acid sites of Pd1/γ-Al₂O₃, which led to a positive impact on the desorption ofamino-compounds （2,6-dimethylaniline and2,6-dimethylcyclohexanamine） that wereproduced in the process of the reaction. Furthermore, it also promoted the reducibilityof PdO and improved the dispersion of Pd. So the rection activity and selectivity increased.3. Because the Pd-based catalyst price is expensive, so the Ni-based catalystmodified by Cu and Cr for catalytic amination of2,6-dimethylphenol. And foundNi20Cu10Cr10/γ-Al₂O₃exhibited the best activity and selectivity. XRD, XPS, H₂-TPRand NH₃-TPD were employed for invested the catalyst. It was found that Cu and Crelement are exist in the form of Cu0and Cr3+respectively and the addition of Cu andCr improved the dispersion of the active component Ni and the reducibility of NiO.