Studies On The Performance Of Ni-W/γ-Al₂O₃ Catalyst In The HDS And HDN Of Coal Tar

Coal tar hydrogenation aims at obtaining distillate fuels such as gasoline,diesel, kerosene under high temperature and pressure under action of catalyst.Preparation of fuel oil from coal tar is not only effective use of the by-products from coal chemical industry, but also can act as an effective oil substitutes to ease the supply of crude oil. The low-middle temperature coal tar generally consists of carbon, hydrogen, sulfur, nitrogen, oxygen and a few metal elements,in which the nitrogen content（0.45% 1.30%） and sulfur content（0.29% ⁰.40%） are higher. If the coal tar were used as crude fuel, it will generate a mass of SOx and NOx in the flue gas that does not conform to emission standards.This makes hydrodenitrogenation（HDN） and hydrodesulfurization（HDS）become one of the most important problems to be solved during the coal tar hydrogenated process.In this paper, Ni-W catalysts with different metal contents, in whichγ-Al₂O₃ was used as support, were prepared. The physical properties of the catalysts were characterized by the X-ray diffractogram（XRD）, X-rayphotoelectron spectroscopy（XPS）, temperature programmed desorption of NH3（NH3-TPD）, N2 adsorption and high resolution transmission electron microscopy（HRTEM）. The HDN and HDS performance of the catalysts was evaluated by using the low and middle temperature coal tar. The results showed that the amount of total acid decreased and focused intermediate, strong acid after the metal was loaded. the sulfidation degree of the catalysts increased with increasing metal content within a certain experimental range. The HDN activity of the catalysts increased first and then decreased. The HDN activity of the catalyst with a loading of 24 wt.-% WO3 was the best. The HDS activity increased gradually with increasing metal content.Fluoridation can improve the activity of the NiW/γ-Al₂O₃ catalyst. So a series of NiWF/γ-Al₂O₃ with different fluoride content were prepared,characterized by a variety of method and evaluated the activity. The results showed that the NiW metal could disperse uniformly with low fluoride content,while W19O55 particles were detected with high fluoride content of（ NiWF（x）（x=0.75, 1.00））; the amount of acid on the surface of the catalysts increased first and then decreased with the increase of fluoride content, which was consistent with the variation trend of HDN and HDS. The sulfidation degree of Ni and W species improved slightly with increase the fluoride content because that the dispersion of the metal decreased after the fluoridation of the catalysts.The HDN activity of the catalysts with the fluoride loading increased initially and reached an optimum at the concentration of 0.50 mol?L-1of NH4 F solution,and then decreased, while the HDS activity increased slightly which demonstrated that different reaction taked place on distinct active sites and the numbers of active sites for HDN were much more than for HDS.