The goal of this project is to evaluate the biodesulfuriztion/hydrodesulfurization process to determine how to meet current Environmental Protection Agency (EPA) diesel standards (15 ppm sulfur concentration) most efficiently. Specific objectives are to 1) develop a biocatalyst that will remove a large portion of the sulfur in diesel fuel at commercially acceptable rates and 2) develop design specifications and a cost estimate for a 5,000 barrel-per-day biodesulfurization demonstration unit.

Petro Star Inc.
Anchorage, AK

Petro Star, Inc., a subsidiary of Arctic Slope Regional Corporation, runs two small refineries in Alaska. These refineries produce kerosene, diesel, and jet fuels. Because of concerns over air pollution, the EPA has imposed limits on the sulfur concentrations in diesel fuel nationwide. Even relatively complex refineries will have some difficulty meeting the required level, but small refineries without hydrotreating capability face even more challenges. There is not a readily identified, economical process that can help them achieve the low-sulfur levels that soon will be required.

Petro Star has developed a biodesulfurization process that it believes will help reduce the sulfur content in their diesel.

Hydrotreated Petro Star diesel has been generated for use in the characterization of biocatalyst strains. Both moderate (300-500 ppm sulfur concentration) and deep (10-50 ppm sulfur concentration) hydrotreated diesels were generated.

As part of the project, Petro Star has contracted the hydrotreatment of its diesel to PARC Technical Services. A pilot plant for hydrotreating diesel generated the following products:

• 12.5 gallons of 43 ppm diesel.
• 11.5 gallons of 418 ppm diesel.
• 14 gallons of 1,746 ppm diesel.

This work helps determine the exact components needed to treat and evaluate the amount of hydrotreating necessary to reach low sulfur levels. This can be used in the economic evaluation of the work that is being done.

Petro Star has subcontracted to Diversa Corporation to develop a bioprocess it can use to reduce sulfur in diesel fuel, either before or after mild hydrotreatment, to <10 ppm sulfur concentration. As a first step, Diversa is to develop enzymes that can reduce sulfur at commercially viable rates. The subcontractor also is to develop a host for the enzymes.

Several biocatalysts have been tested for their activity in partially treated diesel fuel. The fractions containing dibenzothiophene (DBT) are generally the hardest to remove with hydrotreating, so these compounds have been the focus of the research. Researchers have found that virtually all of the DBTs can be removed after 22 hours of hydrotreating. However, other sulfur species survive both treatments.

Hydrotreated Petro Star diesel has been generated for use in the characterization of biocatalyst strains. A bioprocess has been developed that can reduce sulfur in diesel fuel. Several biocatalysts have been tested for their activity in partially hydrotreated diesel fuel. This work is expected to develop a biodesulfurization/hydrodesulfurization process to cost-effectively meet EPA sulfur content requirements.

The biodesulfurization/hydrodesulfurization developed in this project is expected to reduce the sulfur compounds most resistant to hydrotreating, thereby allowing less-severe processing conditions to be used to meet the EPA's 15 ppm sulfur concentration requirement.

Several biocatalysts have been tested for their ability to reduce sulfur concentrations in partially treated diesel fuel. Catalyst testing and development is in progress.

$5,295,075

$1,323,769 (20% of total)

NETL - Kathy Stirling (kathy.stirling@netl.doe.gov or 918-699-2044)
Petro Star - James Boltz (jfboltz@petro-star.com or 907-339-6614)