The Synthesis And Hydrogenation Performance Of The Unsupported Ni-Mo-W Catalyst

In order to satisfy the increasingly stringent regulations on sulfur content of diesel oil, deep desulfurization of the diesel oil becomes more and more important. Ultra low sulfur diesel having lower sulfur content than 10μg·g^-1 can be produced under routine conditions using unsupported hydrogenation catalyst. So the preparation of this type of catalyst has garnered particular attention. In this paper, a series of unsupported catalysts were synthesized with the porous polymetallic mixed oxides as the precursors, and the influence of different synthesis conditions on the characters and activities of the catalysts was discussed. The main contents are as follows.A series of Ni-Mo-W, Ni-Mo and Ni-W mixed oxides were synthesized by hydro-thermal synthesis method, and characterized by XRD and BET. The influence of synthesizing process on the crystalline phase, specific surface and structure of Ni-Mo-W mixed oxides was also investigated. By optimizing the conditions, we found that under a synthesis condition when Ni:Mo:W is 2:1:1, temperature is 150℃,time is 5h,the Ni-Mo-W mixed oxide has a larger specific surface and contains(NH₄) HNi₂(OH)₂(MoO₄)₂ crystalline phase as well.The activities of the unsupported catalysts which had been prepared under different synthesis conditions were evaluated in a high pressure micro-reactor, using 5wt% naphthalene +1.5wt% DBT +2wt% quinoline - petroleum ether solution as a model compound. The results show that HDS activities of the catalysts are: NiMo>Ni₂MoW>NiW; HDN and HDAr activities are: NiW >NiMo>Ni₂MoW.Aiming at the effluent, a new process for cyclic utilization is developed. The experimental results demonstrate that metal recovery rate is greatly improved, effluent is relevant reduced, and some material can be used to optimize the structure of the mixed oxides, and catalyst prepared by this kind of mixed oxides have a higher activities, which have been evaluated.The influence of presulfidation temperature and presulfiation time on the structure and activity of the unsupported catalysts has been investigated using 3wt%CS₂-cyclohexane solution as presulfidation agent. The sulfided catalysts were characterized by X-ray Diffraction, high resolution transmission electron microscopy analysis and X-ray fluorescence. And the results show that the sulfided unsupported Ni-Mo-W catalysts mainly present Ni₃S₂,MoS₂ and WS₂ diffraction peak, and within the process of presulfidation, the diffraction peak strength increased. Activity comparation between catalysts under different presulfidation conditions shows that catalysts presulfided at 320℃for 10 hours perform higher activity. The MoS₂/WS₂ average lamellar length of sulfided catalyst at this time is 7.2nm,and the average packing layer number is 4.5.A suitable process conditions for naphthalene hydrogenation to form decalin was optimized by the study of various factors using unsupported catalysts in hydrogenation process. The results show that when the temperature is 240℃, the pressure is 6-7.5MPa, space velocity is 1h^-1, the conversion rate of naphthalene could reach to 99% or above and the concentration of decalin could reach to 98% or above.The activities of the unsupported catalysts were evaluated utilizing diesel oil as the material in a 100mL diesel hydrogenation unit, and the synthesize conditions of unsupported Ni-Mo-W catalysts were studied comprehensively. The results indicated that the unsupported Ni-Mo-W catalyst obtained under the optimal conditions performs higher activity. The ratio of HDS and HDN could reach 99.8%, and the enhancement of the cetane number was about 14.8 units when the reaction tempereture was 360℃. Comparing the hydrotreating activity of unsupported catalysts of Ni-Mo, Ni-W, Ni-Mo-W, and industrial supported catalyst FH-UDS, it was shown that the hydrotreating activity of unsupported catalyst is obviously higher than that of supported catalysts. At a lower temperature(340℃), the order of the activity was Ni-W>Ni-Mo-W>Ni-Mo>FH-UDS; while at a higher temperature(360℃) , the unsupported Ni-Mo-W catalyst performs higher activity of HDS and HDN. At this point the sulfur content of diesel fuel can be removed from 10316μg·g^-1 to 18μg·g^-1, which can meet the more and more stringent regulations.