Preparation Of Ni/?-Al₂O₃ And Its Catalytic Performance For Hydrogenation Of 2-Ethyl-2-hexenal To 2-Ethyl-Hexanol

2-Ethylhexanol is an important organic chemical raw material which is mainly used in the production of plasticizers.The hydrogenation of 2-ethyl-2-hexenal is one of the three steps for the industrial production of 2-ethylhexanol.The research on the catalyst used in this reaction process has important academic and application value.First of all,in order to illustrate the influence of acid-base properties of the reaction system on the hydrogenation of 2-ethyl-2-hexenal,?-Al₂O₃ with high specific surface area was prepared by three different methods and then Ni/?-Al₂O₃ catalyst was prepared.The activity evaluation result showed that?-Al₂O₃ was prepared by sucrose-assisted method possessed the best activity.With?-Al₂O₃ as a support,the metal active ingredients were screened and the result indicated that Ni/?-Al2O3 showed the best catalytic activity in the hydrogenation of 2-ethyl-2-hexenal;the conversion of 2-ethyl-2-hexenal was 100%and the yield of 2-ethylhexanol was 92.8%.Then the effect of acid-base properties of the reaction system on the hydrogenation of 2-ethyl-2-hexenal was investigated.The result showed that adding acid or alkali substance in the reaction system can not increase the yield and the selectivity of 2-ethylhexanol,but?-Al₂O₃ with both weak acid and weak base center can improve the hydrogenation of 2-ethyl-2-hexenal.Secondly,Ni/?-Al₂O₃ catalyst was prepared and the influence of reaction condition on the hydrogenation of 2-ethyl-2-hexenal was investigated.The suitable reaction conditions were obtained as follows:m?catalyst?:m?2-ethyl-2-hexenal?=0.15:1,reaction temperature of180?,reaction pressure of 2.0MPa,and reaction time of 80min.The yield of2-ethylhexanol was 94.2%under this condition.And then the reusability test results showed that Ni/?-Al₂O₃ could be reused five times without a significant loss in its catalytic performance.Then the suitable reduction conditions of Ni/?-Al₂O₃ were investigated by the orthogonal test.The optimal reduction conditions were obtained as follows:reduction time of 8h,the volume ratio of H₂/N₂ was 0.15,and the flow rate of the mixed gas was 150mL/min.The volume ratio of H2/N2 was the most significant determinant in the three factors.Finally,the reaction mechanism of hydrogenation of 2-ethyl-2-hexenal was studied via React-IR.The results showed that the reaction carried out by two steps.Firstly,2-ethylhexanal was synthesized by the hydrogenation of C=C bond and then the hydrogenation of C=O bond to 2-ethylhexanol began after the end of the hydrogenation of C=C bond.The reaction kinetics investigation result showed that the hydrogenation of2-ethyl-2-hexenal to 2-ethylhexanal and the hydrogenation of 2-ethylhexanal to2-ethylhexanol are both first-order reactions.Their activation energies are separately 19.88kJ·mol^-1and 68.95 kJ·mol^-11 and the pre-exponential factors are 6.726 L·?mol·min?^-1and62.117×10⁵ L·?mol·min?^-1,respectively.