Preparation Of Ni-Mo-S Catalyst And It’s HDS Performance For Coal Tar

The industry of modern coal chemical industry in China is in a highly development stage. Coal tar is an inevitable byproduct in coal conversion, the production of coal tar is a not-so-trivial, and output is increasing year by year. Therefore further processing of coal tar has a vast application prospect. Like crude oil, shale oil and other non-renewable energy resources, coal tar is the energy resource that to produce LPG, gasoline, diesel after hydrotreating, coal tar is the important supplement of transportation fuels. Supercritical fluids has quite unique properties, such as both gas and liquid characteristics, low viscosity, solubility and density can adjustable, high diffusion ability, good mass transfer abilities. It’s benefits to increase the rate of hydrogenation, furthermore the catalytic activity and life of catalyst can also improve in supercritical fluids. Thus the application of supercritical fluid technology to coal-tar processing is meet the requirements for development of green chemical and cleaner production.It is certain that high nitrogen content and low sulfur content for coal tar, but contains almost all sulfur-contain compounds. So it is advisable to design specialized hydrodesulfurization catalyst for coal tar. The supported Ni-Mo-S catalysts were prepared by two step method （Impregnation method or Precipitation method） in this paper. The problem of hard to convert oxide to sulfide completely in traditional hydrotreating catalysts is solved, meanwhile the loading of active component was increased and improved the utilization of sulfur atoms in ammonium tetrathiomolybdate by using this new process. The performance of the catalysts for hydrodesulfurization of model sulfur-contained compounds, dibenzothiophene a typical sulfur compounds in coal tar, was investigated in supercritical microreactor system, supercritical heptane as a solvent. The main research results have been obtained as follows:（1） Based on the results of XRD and XPS, in the process of catalytic activation, when reduced MoS₃ under hydrogen atmosphere, the H₂S generated from decomposing MoS₃ served as a sulfurizing agent that turned nickel oxide into nickel sulfide （NiSx or NiMoS species） to take full use of sulfur atom, at the same time,the inactivated MoS₃ also transform into active phase-MoS₂; This method provided a new way in the preparation of supported Ni-Mo-S catalysts, which is an innovation of this article.（2） Optimized for best support and the source of nickel:For preparing support Ni-Mo-S catalysts. γ-Al₂O₃ , NaY and MCM-41 as support, nickel hypophosphite and nickel nitrate as nickel resource, respectively. A significant difference catalytic activity was found, due to the thermal stability and the surface acidity of different carrier; then the nickel resource also has strong influence on catalytic activity, the results showed that the Ni-Mo-S/γ-AlO₃ catalysts exhibit better activity.（3） And studied the effect of introducing method of Ni on catalytic activity, four different method, namely the Precipitation （CO₂-3）-Precipitation（H⁺） method, the Impregnation-Precipitation （H⁺） method, the Precipitation （H⁺）-Precipitation (CO₃^2-) method, the Precipitation（H⁺）-Impregnation method, the results indicated that the catalyst prepared by Precipitation （CO₂- 3）-Precipitation （H⁺） method shows higher activity than other methods.（4） A series of Ni-Mo-S/γ-Al₂O₃ catalysts with various metal loadings were prepared by the Precipitation （CO32-）-Precipitation （H⁺） method, then characterized by N2-physisorption, XRD, XPS SEM and TEM-EDX. The results indicated that the mesoporous structure was maintained and the MoS2, NiMoS, NiSx phases were presented, morphology of these catalysts were strongly influenced by the contents including active component and promoter of loadings, For the Ni-Mo（15）-S/γ-Al₂O₃ catalyst,at the lower sulfur content,the DBT conversion were approximately equal, （DBT=0.5%wt.,x>99.5% and DBT=1.0%wt.,x>90.0%）, only the HYD/DDS ratios were different, however, once the DBT concentration higher than 2.0%wt, Ni（2.0）-Mo（15）-S/γ-Al₂O₃ catalyst exhibit superior activity than others, for example, when the DBT concentration is 3.0%wt.,the optimal result:x=76.62%, k=19.35×10-7 mol/（g.s） for Ni（2.0）Mo（15）S/γ-Al₂O₃ catalyst, was much higher than the others.Finally, the network of HDS of DBT under supercritical condition was proposed based on the different catalytic activity restluts.