Chloroperoxidase-mediated modifications of petroporphyrins and asphaltenes

Abstract

Octaethylporphine, nickel octaethylporphine, vanadyl octaethylporphine, and a petroporphyrin-rich, low-molecular-weight fraction of asphaltenes from Cold Lake heavy oil were treated with chloroperoxidase from Caldariomyces fumago. Reactions in aqueous phosphate buffer (pH 3.0) or in a ternary solvent system of toluene, isopropanol, and water (3 m m phosphate buffer, pH 3.0) were absolutely dependent on the presence of hydrogen peroxide and chloride. Enzyme treatment resulted in reduction of the absorption of the Soret peak. The porphyrins and asphaltenes were insoluble in the aqueous buffer system; thus, mass transfer limited the reactions. These substrates were more soluble in the ternary system and the reactions were more complete, yielding decreases in metal recovery associated with the methylene chloride-soluble porphyrin-containing material. These decreases were: 93% of the Ni from nickel octaethylporphine, 53% of the V from vanadyl octaethylporphine, and 20% of the total Ni and V from the asphaltene fraction. This work clearly demonstrated that an extracellular enzyme, chloroperoxidase, can alter components in the asphaltene fraction of petroleum. Because of the requirement for chloride, the enzyme-mediated reactions likely yield chlorinated products which would be undesirable in a refinery feedstock if this enzymatic process was used for the demetallation of petroleum.