Preparation Of Ni Modified Y Zeolite And Its Application In Hydrodesulfurization Of Inferior Diesel Oil

Due to the increasingly stringent environmental regulations,the sulfur content in automotive diesel needs to be further reduced.Hydrodesulfurization（HDS）is the main way for the production of clean diesel in industry scale.Catalysts are the core of the hydrogenation process.However,traditional alumina-supported hydrodesulfurization catalysts can not meet the requirement of deep desulfurization(10μg·g^-1)which was proposed by many countries including EU,USA and our country.Dibenzothiophene sulfides with sterically hindered methyl groups are the least active sulfur compounds.There is an urgent need to develop high performance catalysts that can produce clean diesel fuel under less severe conditions.To study the properties of supports for the removal,adsorption and hydrodesulfurization of complex sulfides is of great importance.Y zeolite has widely been used in the petrochemical industry because of its pore properties and tunable acidity.Generally,the strong acidity of Y zeolite can easily cause carbon deposition or cracking of the recant molecules,which may cause catalyst deactivation or reduce the recovery of diesel products.Therefore,it’s necessary to modify Y zeolite before it’s used.HY zeolite was prepared by a two-step hydrothermal method.Different kinds of Ni-modified Y zeolites were prepared separately by post-impregnation,ion-exchange and in-situ modification method.The Ni content（denoted by NiO content）in Y zeolite was changed from 2wt.%to 5wt.%.The effect of Ni modification method and the effect of Ni content on the physical and acidic properties were investigated.The modified zeolite was used as matrix material for HDS catalysts.NiMo model catalysts were prepared by using pure zeolite as support material.NiMo catalysts for inferior diesel hydrodesulfurization were prepared by using zeolite and pseudo-boehmite as co-support.All these NiMo catalysts were prepared by incipient wetness coimpregnation method.4,6-dimethyldibenzothiophene（4,6-DMDBT）was used to evaluate the effect on desulfurization activity and selectivity caused by Ni modification method.The HDS performance for inferior diesel was also investigated.The experiment results show that Y zeolite could maintain good texture properties when Ni content is within 3 wt.%.With an increase of Ni content,the amounts of weak acid in Y zeolite increase and the B/L acid proportion decreases.All the adsorption capacities of Ni modified Y zeolites are improved compared with that of HY zeolite and the in-situ modified NiY has the best adsorption ability.The impregnation method was found to promote the dispersion of active metals most strongly,and the ion-exchange method was found to enhance the sulfidation degrees of NiMo the most strongly.All these modification methods promote the conversion of 4,6-DMDBT and the in-situ modification method has the best HDS performance.In-situ Ni modification reduces the metal-support interaction.The MoS₂ stacking layers concentrate at 2⁴ layers and the proportion of less active monolayer decreases.The layer length concentrates at 2⁴ nm.Catalyst NiMo/USNiY has the highest active phase ratio,reaching 48%.And this catalyst has the highest conversion of 4,6-DMDBT,due to an increase of HYD route selectivity.NiMo/A3NiY catalyst which was in-situ modified by 3wt.%Ni had the highest desulfurization rate for inferior diesel,and the sulfur content was reduced from4842μg·g^-1 to 23μg·g^-1.When the reaction condition was fixed at 360℃,6 MPa and 2h^-1,the sulfur content in diesel product treated with NiMo/ANiY catalyst was reduced by 35%compared with that of unmodified NiMo/AHY catalyst and the recovery of liquid product increased from 93.1%to over 98%.