Fractionation and biocatalitic demetallation of asphaltenes from Castilla crude oil

Asphaltenes obtained from a crude oil rich in heavy metals (Castilla crude oil) were fractioned by adsorption chromatography. These asphaltenes were partially characterized in order to determine Ni and V content by High-pressure liquid chromatography (HPLC) UV-visible spectroscopy and atomic absorption. Petroporphyrin contents and molecular weight in the fractions were also determined. The results indicated that Ni and V were not uniformly distributed in asphaltene fractions. Bio catalytic modifications by chloro peroxidase (CPO) of these petroporphyrins were evaluated in both aqueous buffer and organic solvents. The reactions were carried out in both aqueous buffers and ternary systems of toluene: isopropanol: water with petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary system than in the aqueous buffer systems. CPO-mediated reactions were effective in eliminating the Soret peak in both aqueous and organic solvent systems. The effect of CPO-mediated reaction on the release of the metals complexed with the porphyrins and asphaltenes was determined. Chloro peroxidase was able to modify components in the heavy fractions of petroleum and remove 57 % of total heavy metals Ni and V and 23 % of asphaltenes from petroporphyrin-rich fractions