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 muM DBT with 1.5 mM ABTS required a molar ratio [O-2]/[ABTS] = 140 and 72 h at 40 degreesC in a water-acetonitrile reaction mixture, showing a rate constant of k(1) = -6.3 x 10(-4) min(-1). Whereas peroxide oxidation of 10 mM DBT with 39 muM phosphotungstic acid required only a molar ratio [H2O2]/[DBT] = 2, showing a rate constant of k(2) = -6.1 X 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 muM phosphotungstic acid dissolved in ethanol, in less than 3 h at 60 degreesC and atmospheric pressure. No sulfur could be detected in these samples after an additional extraction with an equal volume of ethanol. (C) 2004 Elsevier B.V. All rights reserved.