Oxidation of dibenzothiophene by laccase or hydrogen peroxide and deep desulfurization of diesel fuel by the later

Enzymatic oxidation of dibenzothiophene (DBT) catalyzed by laccase in the presence of 2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was compared with the chemical oxidation with hydrogen peroxide catalyzed by phosphotungstic acid. Enzymatic oxidation with laccase (2.4 U/ml) of 25 μM DBT with 1.5 mM ABTS required a molar ratio [O2]/[ABTS]=140 and 72 h at 40 °C in a water–acetonitrile reaction mixture, showing a rate constant of k1=−6.3×10−4 min−1. Whereas peroxide oxidation of 10 mM DBT with 39 μM phosphotungstic acid required only a molar ratio [H2O2]/[DBT]=2, showing a rate constant of k2=−6.1×10−2 min−1 in a hexane–ethanol system. A sample of diesel fuel, containing 342 ppm of sulfur, was chemically oxidized by an excess of hydrogen peroxide and 119 μM phosphotungstic acid dissolved in ethanol, in less than 3 h at 60 °C and atmospheric pressure. No sulfur could be detected in these samples after an additional extraction with an equal volume of ethanol.