The goal of the project is to develop enzymatic biocatalysts that are active in the oil phase and functional at moderate temperatures of 50-80° C.

Oak Ridge National Laboratory
Oak Ridge, TN

Heavy crudes are commonly recalcitrant for conventional methods of refining. This recalcitrance is imparted largely by polyaromatic linkages composed of polyaromatic hydrocarbons (PAHs) and sulfur and nitrogen heterocycles. Polyaromatic structures stabilize asphaltenic groups and protect metals from thermochemical and biological removal. The same structures are substrates for oxidase enzymes. Previous work has shown the capability of these oxidative enzymes to attack polyaromatic compounds. This transformation may be the first step in the carbon-carbon bond cleavage reactions; it thus may lead to a decrease in the molecular weight of the oil and render sulfur, nitrogen, nickel, and vanadium groups more susceptible to further biological or conventional treatment. It is a common practice to use elevated temperatures during recovery of heavy oils. A combination of thermal tolerance and resistance to inactivation in oil can be ideal properties for an oil processing biocatalyst. This project will investigate development of a catalyst to carry out the initial oxidation of PAH molecules and evolve it to be operational at 50-80° C. while remaining active in the organic media.

The work conducted in this project will allow more-efficient refining of heavy crudes.

A thermophilic peroxidase from an archaea/bacteria with optimum activity at 50-90°C will be used as a starting point for the development of enzymatic biocatalysts.

The objective is to evolve the functionality (allowing conversion of oil compounds) of the enzyme while improving temperature stability (temperature tolerance). In the researcher's previous work, it was shown that the reactions of interest cease to occur in a predominantly organic media such as oil. To activate the enzymes in the oil phase, the enzymes have been modified via molecular genetic techniques called Directed Evolution, resulting in catalysts that are stable and functional in oil. In order to allow conversion using enzymes as catalysts, it is important to know the partitioning of the enzyme between the oil and the aqueous phase. This was investigated using the oxidase enzyme peroxidase. The capability to operate at higher temperatures is useful in thermal recovery and reduces the need for heat exchange equipment in the refining process. Oxidative transformation of the polyaromatics were investigated as a strategy for biorefining heavy crudes, with particular emphasis on lowering molecular weight, decreasing viscosity, and rendering increased availability of sulfur, nitrogen, nickel, and vanadium to further refining technologies.

The enzyme P450 from P. putida is known to have some activity for PAH conversion. Another P450 enzyme-from Sulfolobus solftaricus, a thermophilic organism-is capable of operation at elevated temperatures (80° C.); however, it does not oxidize PAH compounds. In order to produce a thermostable PAH-oxidizing enzyme, a hybrid of these two enzymes was produced.

The project is complete.

$300,000

$30,000 (9% of total)

NETL - Kathleen Stirling (kathy.stirling@netl.doe.gov or 918-699-2008) 
ORNL - Abhijeet Borole (borolea@ornl.gov or 865-576-7421)