Oxidation of sulfur components in diesel fuel using Fe-TAML® catalysts and hydrogen peroxide

Dibenzothiophene-derivatives are catalytically oxidized to their corresponding sulfone product in homogeneous and two-liquid phase systems by H2O2 with an iron containing tetraamidomacrocyclic ligand (TAML) catalyst, Fe-TAML®. The reaction medium is slightly caustic, pH 8, and uses t-BuOH as a co-solvent for solubilizing the dibenzothiophene starting compounds and their oxidation products. Fe-TAML® catalyst concentrations are in the low micromolar range. H2O2 consumption is nearly stoichiometric (two-equivalents) in homogeneous conditions and only slightly less efficient under two-liquid phase conditions. The catalytic process when applied to a sample of commercial diesel fuel occurs under mild conditions with respect to temperature (50 °C), pressure (1 atm), and time (3 h), to remove greater than 75% of the total sulfur content of the fuel after secondary treatment with silica. Both alkyl-benzothiophenes and alkyl-dibenzothiophenes compounds in the diesel fuel were oxidized by the Fe-TAML®/H2O2 system which facilitated their adsorption onto the silica. The mild reaction conditions result in no detectable over-oxidation of alkyl-dibenzothiophenes.