Oxidative desulfurization of fuel catalyzed by metal-based surfactant-type ionic liquids

Metal-based surfactant-type ionic liquids (MSILs) methyltri-n-octylammonium peroxomolybdate [(CH3)N(n-C8H17)3]2Mo2O11 and peroxotungstate [(CH3)N(n-C8H17)3]2W2O11 were synthesized and characterized, which have been extended to new families and generations of functionalized ILs. Here the MSILs were applied in removal of sulfur-containing compounds with H2O2 and possessed of the character of reaction-induced self-separation catalysis. The effects of H2O2/DBT (molar ratio), oil/MSIL (mass ratio) and the agitation rate were studied to estimate the optimal conditions for the desulfurization system catalyzed by [(CH3)N(n-C8H17)3]2Mo2O11. The quaternary ammonium cation could transfer the catalytic active species to the aromatic sulfur compounds under the reaction conditions and higher oxidative reaction rate was achieved. Kinetic experiments revealed that the oxidative desulfurization reaction was in accordance with pseudo-first-order kinetics and the reaction rate constant and half-life were calculated. Furthermore, the oxidation reactivity of different substrates was in the following order: DBT > 4,6-DMDBT > BT. The MSIL [(CH3)N(n-C8H17)3]2Mo2O11 could be recycled for 10-times with a slight decrease in activity. [(CH3)N(n-C8H17)3]2Mo2O11 was also an efficient catalyst to remove the sulfur-containing compound in different solvents. Multiple reactions of oxidation desulfurization process were feasible and effective for prehydrotreated gasoline.

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► MSILs were designed by pairing quaternary ammonium cation with polyoxometalate anions.
► [(CH3)N(n-C8H17)3]2Mo2O11 can be self-separated at the end of the reaction.
► For self-separation, [(CH3)N(n-C8H17)3]2Mo2O11 is convenient for recycle.
► MSILs can deeply remove refractory organosulfur in both model oil and prehydrotreated gasoline.