Preparation Of Ni/γ-Al₂O₃ Catalyst With High Hydrothermal Stability And Study On Its Perpormance For Hydrogenation Of Butynediol

1,4-Butanediol(BDO) is a basic organic chemical raw with high additional value material and useful intermediate in the manufacture of fine chemicals.Many processes are used to manufacture BDO at present. The most prevalent method is Reppe method, which of hydrogenation route is divided into two stage:The first was the hydrogenation of 1,4-butynediol carried out in slurry bed.The second stage was the hydrogenation of the crude 1,4-butanediol aqueous solution which contains about 65% H2O,30% 1,4-butanediol,and a small amount of unsaturated carbonyl compounds. From the above mentioned, the second stage of the Reppe method is a typical process under hydrothermal conditions.Commonly, supported nickel catalyst is used in industry in the second stage, and the carrier is alumina mainly.Ni-based catalysts supported on theγ-Al2O3 with high catalytic performance have been developed in our study team, which have been employed in industry triumphantly. In the previous work, we found that, as the runtime of the catalyst extend, the catalytic activity of Ni/γ-Al2O3 catalyst declined under hydrothermal treatment because of the aggregation of Ni crystallite.In this paper, aiming at such a question, Ni/γ-Al2O3 catalyst with 17% nickel loading was prepared by impregnation method. Firstly, an accelerated decay procedure under hydrothermal condition was designed simulating the conditions of the liquid phase hydrogenation of the crude BDO aqueous solution.Ni/γ-Al2O3 catalyst was treated under hydrothermal condition for different time and different temperature under 4 MPa H2 pressure.The effect of hydrothermal treatment on the structure and the performance of Ni/γ-Al2O3 catalyst in the hydrogenation of 1,4-butynediol was investigated. Based on the preliminary study, the effect of the addition of promoters (SiO2, TiO2, ZnO, MgO, CeO2, etc.)with impregnation on the catalytic performance and hydrothermal stability of the Ni/γ-Al2O3 catalyst was investgated, aiming at choosing the optimal promoter which can improve the hydrothermal stability of Ni/γ-Al2O3 catalyst in the premise of maintaining high catalytic activity. In addition, the content of the best promoter SiO2 was investgated.The possible reasons for improve of the catalytic activity and hydrothermal stability of the Ni/γ-Al2O3 catalyst after addition of the promoter were given through a variety of characterization methods.The main results are as follows:1.By simulating the conditions of 1,4-butynediol hydrogenation reaction, the Ni/γ-Al2O3 catalysts were treated under hydrothermal condition.It is found that the hydrothermal treatment under H2 atmosphere resulted in the rehydration of supportγ-Al2O3 to boehmite.The rehydration was affected by the hydrothermal treatment time and temperature.The crystallinity of the boehmite increased with the extension of the hydrothermal treatment time and the improvement of the hydrothermal treatment temperature.Moreover, the hydration of supportγ-Al2O3 caused the obvious aggregation of Ni crystallite, and the decrease of both specific surface area and pore volume, which led to the decay of the catalytic activity.2.The effects of addition of promoters on the activity and hydrothermal stability of Ni/γ-Al2O3 catalyst were investgated combined with a series of characterizations.The results show that SiO2 is the best one in the range of promoters investgated, which can improve the hydrothermal stability of Ni/γ-Al2O3 catalyst in the premise of maintaining high catalytic activity.3.From the investigation of the effect of the SiO2 content on the hydrothermal stability of Ni-SiO2/γ-Al2O3 catalyst, it is found that the extent of rehydration of supportγ-Al2O3 to boehmite increases with the increasing of SiO2 content. Combined with a series of characterizations, it is found that the best content of SiO2 is 3wt%.At the same time, the catalytic stability of Ni/γ-Al2O3 and Ni-SiO2/γ-Al2O3 (3wt% SiO2) in the hydrogenation of the crude 1,4-butanediol aqueous solution are investgated in the fixed bed flow stainless steel reactor, and the results further prove that SiO2 can improve the hydrothermal stability of Ni/γ-Al2O3 catalyst. The characterization of FT-IR indicates that SiO2 introduced with impregnation method in our study not cover on the surface ofγ-Al2O3,but grafts to the surface ofγ-Al2O3 by the formation of Si-O-Al bridge, which covers the Al3+ exposing on the surface ofγ-Al2O3 (that is anionic vacancies) for the adsorption of water and lead to that the reactions between water andγ-Al2O3 are difficult to take place.This explains why the addition of SiO2 can inhabit the hydration of supportγ-Al2O3 to boehmite under hydrothermal condition and futher improve the hydrothermal stability of Ni/γ-Al2O3 catalyst.