Reaction Kinetics Of N-butanal Aldol Condensation Over Ce-Al₂O₃ Catalyst And Its Catalytic Stability

n-Butyraldehyde aldol condensation to 2-ethyl-2-hexenenal（2E2H）is an important step for commercial production of 2-ethylhexanol（2EHO）.Research on this reaction process and its catalyst is of importance in academia and application.First of all,the intrinsic reaction kinetics of n-butyraldehyde self-condensation catalyzed by Ce-Al₂O₃ was studied in an autoclave.The result showed that both the forward and backward reactions are second order and the respective activation energy was 79.60 kJ/mol and 74.30 kJ/mol while the the pre-exponential factor was separately 5.745×10⁵ m³/（kmol.s）and 2.146×10⁴ m³/（kmol.s）.The pre-exponential factor of the reaction catalyzed by Ce-Al₂O₃ is much less than those catalyzed by the conventional inorganic acid and base catalysts but is equivalent to that catalyzed by sulfonic acid functionalized ionic liquid.The reason is possibly because the self-condensation of n-butyraldehyde catalyzed by Ce-Al₂O₃ is a liquid-solid heterogeneous catalytic reaction and the resistance of mass transfer is larger.Secondly,the results of XPS analysis of Ce3d and activity evaluation of Ce-Al₂O₃ catalyst demonstrated that Ce⁴⁺spices is the active site and the valence state of cerium affected the catalytic performance to some extent but not predominantly.Instead the acid-base property of Ce-Al₂O₃ played a dominant role in the catalytic performance.Thirdly,the catalytic performance and stability of Ce-Al₂O₃ was investigated in a fixed bed reactor.On the basis of elimination of effect of internal and external diffusion,the suitable reaction conditions was obtained as follows:reaction temperature of 180℃,reaction pressure of 1MPa,space-time of 0.4 g.min/ml,flow rate of N₂ of 8 ml/min,and pumping rate of liquid n-butyraldehyde of 0.027ml/min.The conversion of n-butyraldehyde and yield of 2E2H attained the highest,74.0%and 60.2%,respectively.The conversion of n-butyraldehyde in the outlet of the fixed bed reactor under the suitable reaction conditions was simulated by Aspen software using the reaction kinetic equation obtained previously and the result showed that the simulated conversion of n-butyraldehyde was slightly lower than the experimentally measured value.The experimental result of catalytic stability of Ce-Al₂O₃ indicated that the stability was good at the first of 12h and then the fixed bed was blocked little by little due to the hydration of the catalyst and carbon deposition.The study on the improvement of hydrothermal stability ofγ-Al₂O₃ was conducted and the result showed that MgAl₂O₄ could restrain the hydration.The catalytic activity of MgAl₂O₄kept unchanged after reused for two times and then it began to become deactivated gradually.A bifunctional Ni/MgAl₂O₄ catalyst was perpared by impregnation method and its catalytic performance for the integration of self-condensation of n-butyraldehyde and the hydrogenation of 2E2H was explored preliminarily.