Preparation Of Dissel Hydrotreating Catalyst With High Direct Desulfurization Selectivity

With the increasingly strict environmental protection regulations,the quality of diesel needs to be further improved.China began to implement national V vehicle diesel standard with a sulfur content less than 10?g/g from 2018,which puts new demands on the depth of diesel hydrodesulfurization.The most difficult compound to remove in the diesel hydrodesulfurization process is 4,6-dimethyldibenzothiophene?4,6-DMDBT?.The main factor limiting the depth of hydrodesulfurization is desulfurization route,and difference of desulfurization route mainly depends on adsorption method.Under the current industrial catalyst conditions,4,6-DMDBT is mainly lying adsorption on the catalyst and then react in hydrodesulfurization?HYD?route.Compared with the HYD route,direct desulfurization?DDS?route react by endpoint adsorption,which has the advantages of low hydrogen consumption and low reaction severity.If the DDS route selectivity in diesel desulfurization process can be increased,sulfur content of diesel will be further reduced,hydrogen and energy will be saved.It is necessary to change the adsorption state for improving the DDS selectivity of4,6-DMDBT.The state of adsorption depends on the structure of active phase,and structure of active phase depends on the element's electronic structure.If a metal element with suitable electronic structure can be added in Ni Mo-Al₂O₃,it will affect the Ni-Mo-S active phase,which may be beneficial to the endpoint adsorption of 4,6-DMDBT,the X-Ni-Mo-S active phase could increase the proportion of DDS route in the 4,6-DMDBT hydrodesulfurization process.Niobium/Gallium/Rhenium was step impregnated in prepared Ni Mo-Al₂O₃with extrusion method,and physicochemical properties of the catalyst were characterized by multiple methods.4,6-DMDBT is used as a model sulfide to investigate the influence of a series of factors,including of element type,heteroatom contents,reaction temperature and reaction pressure on the 4,6-DMDBT conversion rate and DDS route selectivity.Because of the high 4,6-DMDBT conversion rate and high DDS route selectivity of step impregnated Re-Ni Mo-Al₂O₃,co-impregnated Re-Ni Mo-Al₂O₃ were further prepared for comparison of different impregnation methods.The experimental results show that step impregnated niobium has most obvious effect on the DDS route selectivity of 4,6-DMDBT.Step impregnated gallium has the best effect on the conversion of 4,6-DMDBT,Rhenium improve both DDS route selectivity and conversion rate of 4,6-DMDBT well.Step impregnated Re-Ni Mo-Al₂O₃is superior than the co-impregnated Re-Ni Mo-Al₂O₃ in DDS route selectivity,but Co-impregnated Re-Ni Mo-Al₂O₃ is superior than step impregnated Re-Ni Mo-Al₂O₃ in 4,6-DMDBT conversion rate.In addition,the step impregnated Re-Ni Mo-Al₂O₃ also showed selectivity for the CHB chair conformation of the 4,6-DMDBT intermediate.