Asphaltenes biodegradation from heavy crude oils by the yeast Yarrowia lipolytica.

Abstract

Heavy crude oil reserves are characterized by their high viscosity and density, largely due to significant quantities of asphaltenes. The removal of asphaltene precipitates from oil industry installations is crucial, as they can contaminate catalysts and obstruct pipelines. Therefore, this study aimed to bio-transform heavy oil asphaltenes into smaller molecules using the yeast Yarrowia lipolytica, known for its ability to efficiently degrade hydrophobic substrates. For this purpose, asphaltenes were extracted from crude oil samples, and yeast growth was assessed in a mineral medium containing 2, 5, or 10 g L^-1 of asphaltenes. After 168 h of incubation, liquid-liquid extraction was conducted on samples from the Yarrowia lipolytica growth medium using chloroform. The extracted fractions were then quantified by gas chromatography. The results indicated that the yeast could utilize the asphaltenes as a carbon source for growth, though there was a delay in growth compared to the control (glucose as the carbon source), with a maximum biomass concentration of 2.26 g L^-1 achieved at 144 h. From the experimental design, it was determined that a higher concentration of aromatic compounds was achieved under the conditions of 115 rpm, 2 g L^-1 of asphaltenes, and 0.5 g L^-1 of cell inoculum. Conversely, to obtain a higher concentration of saturated compounds, the optimal conditions were 160 rpm, 5 g L^-1 of asphaltenes, and 1.0 g L^-1 of cell inoculum. Molecular docking results indicated that asphaltenes have a high affinity for cytochrome P450, laccase, and Lip2, with interactions observed with their catalytic triads, suggesting a significant role for these enzymes in asphaltene bioconversion.