Study On The Preparation Of Isopropyl Alcohol By The Hydrogenation Of Acetone Over Ni Based Catalysts

Isopropyl alcohol is a chemical product which has significant value of industrial application. It can be used in printing ink, painting, medicine, electronic industry and many other fields. The preparation method of isopropyl alcohol by hydrogenation of acetone has many advantages such as low energy consumption, simple process and light equipment corrosion. The core technology of this method is to develop a good catalyst with excellent catalytic performance, good efficiency and simple method of preparation. In this paper, nickel that has good hydrogenation activity and relatively cheap price and ZSM-5 carrier were used to prapare the Ni/ZSM-5 catalyst by the isometric impregnation method. Cu, Zn, Fe, Co, Mg, Mn, Ca, K were added as active agents. The effects of different preparation conditions and different reaction conditions in preparation of isopropyl alcohol by hydrogenation of acetone over Ni based catalysts were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), N2 adsorption/ desorption and temperature-programmed desorption of NH3 (NH3-TPD) were used to characterize the catalysts. The structure, acidity, states of elements and pore architecture of the catalysts were researched.Firstly, a series of Ni/ZSM-5 catalysts were synthesized with isometric impregnation method and used for catalytic hydrogenation of acetone in this study, influence of the different impregnation conditions and reaction conditions on the catalyst performance were evaluated. The results show that catalysts with optimal performance is prepared by conditions of dipping at 40℃ for 3 hours with optimal Ni content of 12 wt.%. And the appropriate reaction process conditions are as follows:the temperature and time at hydrogen reduction treatment of catalysts is 450℃ for 4 hours, the reaction temperature and pressure are 130℃ and 3.5 MPa, respectively, the feeding mole ratio of hydrogen and acetone are kept as 5:1. The activity tests also reveal that catalysts possess good stability.Secondly, a series of Ni-M/ZSM-5 (M= Zn, Fe, Cu, Mg, Co, Mn, Ca, K) catalysts with different auxiliary agents were prepared by isometric impregnation method and their activities on hydrogenation of acetone were researched. The results show that the best auxiliary agent is Ca and the best content of Ca is 9 wt.%. XRD results reveal that the Ca can optimize the dispersion of Ni on the surface of ZSM-5 carrier and greatly reduce the size of Ni particles; XPS results indicate that the existence modes of Ni and Ca are NiO and CaO respectively, the electron cloud density of nickel catalysts is increased by Ca agent, the interaction between nickel and hydrogen atom reduces and the desorption of hydrogen on the catalysts become easily, so it is advantageous to the hydrogenation reaction. The presence of CaO inhibits the interaction between Ni and carrier, prevents the generation of NiAl2O4 species and promotes the reduction of Ni2+. N2 adsorption/desorption results comfirm that aperture of catalysts is reduced after the introducing of Ca auxiliary facilitating the main reaction. The results of NH3-TPD show that the Ca can reduce the amount of acid sites especially strong acid sites in the catalysts, thus modifies channel structure of ZSM-5 carrier and optimizes the dispersion of active components on the carrier. It also adjusts the chemical environment of Ni/ZSM-5 catalyst and enhances the reducibility and hydrogenation activity of the catalyst.Finally, a series of Ni-Ca/ZSM-5 catalysts were prepared by isometric impregnation method under different calcination temperatures. The impacts of different calcination temperatures on hydrogenation performance, morphology, dispersion and pore structure of Ni-Ca/ZSM-5 catalysts were researched. The results show that Ni-Ca/ZSM-5 catalyst calcinated at 450℃ achieves optimal performance. It can be found from SEM micrographs that Ni-Ca/ZSM-5 catalysts calcinated at 450℃ possess relatively rough surface and distributed active components; otherwise, the Ni-Ca/ZSM-5 catalysts calcinated at 700℃ with smooth surface and neat architecture exhibit relatively concentrated particle distribution, that may inhibit dispersibility of activie components. N2 adsorption/desorption curves show that the specific surface area of Ni-Ca/ZSM-5 catalyst calcinated at 450℃ is higher than that of pristine ZSM-5 carrier; the improved calcination temperature may lead to the collapse of pore structure, thus enlarge average pore diameter and reduce total surface area of catalyst. The XRD patterns show that the NiO grain structures of catalyst calcinated under 700℃ become more uniform and higher crystallization extent, which reduce catalytic performance of Ni-Ca/ZSM-5.