Research On The Catalytic Oxidative Desulphurization Of Vacuum Gas Oil From Saudi High-Sulfur Crude Oil

Vacuum gas oil?VGO?is the major feed to produce gasoline and diesel by FCC.There are so many sulfides in the most VGO feed that desulfurization process of VGO is quite important to produce low-sulfur or ultra-low-sulfur fuel oil.The sulfides in VGO exist in form of benzothiophene,4,6-dimethyldibenzothiophene and their derivatives,which increase the difficulties to HDS,such as high temperature,high hydrogen pressure and high activity catalysts.As a result,non-hydrogenation desulfurization processes?NHDS?are taken seriously by a large number of researchers.And among those NHDS,oxidative desulfurization process?ODS?is chosen to research because it has many advantages such as mild reaction conditions,high desulfurization efficiency and low operating cost.In this paper,SiO₂ was synthesized by sol-gel method and Al₂O₃ was synthesized by cation-anion double hydrolysis method.The supported catalysts MoO₃/SiO₂ and MoO₃/Al₂O₃ were prepared by incipient impregnation method with the SiO₂ and Al₂O₃ as support respectively.The effect of different synthesis conditions of SiO₂ and Al₂O₃ on the pore structure and oxidative desulfurization have been investigated respectively.The results indicate that the optimum synthesis conditions of SiO₂ are concentration of silica source of0.68 mol/L,CTAB/TEOS mole ratio of 11:50 and aging time of 2 h;the optimum synthesis conditions of Al₂O₃ are P123/H₂O mass ratio of 1:21.5,pH of 8 and crystallization temperature of 120^oC.Then MoO₃/SiO₂ was modified by the introduced citric acid?CA?,Ce?NO₃?₃·6H₂O,Fe?NO₃?₃·9H₂O and La?NO₃?₃·6H₂O.The order of their desulfurization performance is Ce-Mo O₃/SiO₂>Fe-MoO₃/SiO₂>CA-MoO₃/SiO₂>La-MoO₃/SiO₂.And MoO₃/Al₂O₃ was also modified by the introduced citric acid?CA?,Ce?NO₃?₃·6H₂O and K₂CO₃;what's more the Al₂O₃ support was pretreated by NH₄Cl solution.The order of their desulfurization performance is MoO₃/Al₂O₃-IX?Ion Exchange?>Ce-MoO₃/Al₂O₃>K-MoO₃/Al₂O₃>CA-MoO₃/Al₂O₃.The researches indicate that both tetra-coordinated[MoO₄]^2-and hexa-coordinate[MoO₆]^6-are the active sites of oxidative desulfurization reaction,whereas the activity of hexa-coordinate[MoO₆]^6-is superior to tetra-coordinated[MoO₄]^2-.The conditions of catalytic oxidative desulphurization reactions were optimized with Ce-MoO₃/SiO₂ as catalyst and H₂O₂ as oxidant.And the best conditions of oxidation process are reaction temperature of 70^oC,n?O/S?of 8,reaction time of 2 h and dosage of catalyst of 15wt%;The best conditions of extraction process are DMF as extractant,extraction time of 45min and extraction temperature of 30^oC.The desulphurization rate under the optimal condition was as high as 68.5%.Different cationic modified adsorbents named as Ce-Al₂O₃,La-Al₂O₃,Cu-Al₂O₃,Fe-Al₂O₃ were obtained by liquid-phase ion exchange between 0.1 mol/L Ce?NO₃?₃,La?NO₃?₃,Cu?NO₃?₂,Fe?NO₃?₃ solution and Al₂O₃,respectively.The results indicated the order of their static adsorptive desulfurization performance was Cu-Al₂O₃>Fe-Al₂O₃>La-Al₂O₃>Ce-Al₂O₃.Then the conditions of adsorptive desulfurization were researched with Cu-Al₂O₃ as adsorbent.And the optimal conditions are adsorbent/oil ratio of 10:1,reaction temperature of 50^oC and reaction time of 3 h,under which conditions the desulfurization rate was 40.5%.