CHLOROPEROXIDASE-MEDIATED MODIFICATIONS OF PETROPORPHYRINS AND ASPHALTENES

Octaethylporphine, nickel octaethylporphine, vanadyl octaethylporphine , and a petroporphyrin-rich, low-molecular-weight fraction of asphalte nes from Cold Lake heavy oil were treated with chloroperoxidase from C aldariomyces fumago. Reactions in aqueous phosphate buffer (pH 3.0) or in a ternary solvent system of toluene, isopropanol, and water (3 mm phosphate buffer, pH 3.0) were absolutely dependent on the presence of hydrogen peroxide and chloride. Enzyme treatment resulted in reductio n of the absorption of the Soret peak. The porphyrins and asphaltenes were insoluble in the aqueous buffer system; thus, mass transfer limit ed the reactions. These substrates were more soluble in the ternary sy stem and the reactions were more complete, yielding decreases in metal recovery associated with the methylene chloride-soluble porphyrin-con taining material. These decreases were: 93% of the Ni from nickel octa ethylporphine, 53% of the V from vanadyl octaethylporphine, and 20% of the total Ni and V from the asphaltene fraction. This work clearly de monstrated that an extracellular enzyme, chloroperoxidase, can alter c omponents in the asphaltene fraction of petroleum. Because of the requ irement for chloride, the enzyme-mediated reactions likely yield chlor inated products which would be undesirable in a refinery feedstock if this enzymatic process was used for the demetallation of petroleum.