100 Proceedings Spring 2025 CHEMICAL O F T H E Q UA R T E R Diluted Bitumen by BeNedette adewaLe, ph.d. Research Physical Scientist, Research and Development Center U.S. Coast Guard The growth in North American oil production is par- tially due to the increase in the production and distribu- tion of Canadian oil sands products (OSP), like diluted bitumen, or dilbit, an OSP transported from Canada to the United States. Recent dilbit events have demon- strated that these OSPs generally behave differently than conventional crude oil during a spill. What is Bitumen? Extracted from natural oil sands, bitumen is a semisolid form of petroleum that is sticky and highly viscous, meaning it does not easily flow or pour, which makes it difficult to transport through pipelines. What is Dilbit? Dilbit is typically composed of 70% to 80% bitumen and 20% to 30% dilutant. The dilutants can include gas condensates, synthetic crude oil, synthetic naphtha— petroleum—and added butane (C4) or pentane (C5) com- pounds. The purpose of the dilutant is for easy transport and handling through pipelines or in tanks. Though typ- ically conveyed by rail or pipeline, dilbit is also trans- ported by barges or tank ships. Each method carries an inherent risk of spillage. What has the Coast Guard done about it? The Coast Guard’s Great Lakes Oil Spill Response and Cleanup Activities Assessment to Congress, pub- lished November 21, 2018, identified knowledge gaps in the behavior of dilbit in the freshwater environment. Specifically, it stated less is known about the transport and fate of dilbit pollution in the Great Lakes in compari- son to other navigable U.S. waters. In 2021, the U.S. Coast Guard Research and Development Center (RDC) performed an in-depth literature review of dilbit research to determine addi- tional knowledge gaps and identify research areas to improve dilbit spill response.1 This resulted in the RDC performing three experiments at the U.S. Army Engineer Research and Development Center Cold Regions Research and Engineering Laboratory facilities in Hanover, New Hampshire, to further characterize the behavior of dilbit products in freshwater. The experi- ments assessed the physical and chemical properties of two common dilbit products, Western Canadian Select and Cold Lake Blend, using varied seasonal environ- mental conditions—temperature and solar exposure and waterbody sediment concentration—to determine their impact on spilled dilbit. Guidance for Planners and Responders The RDC’s literature review and experiments found that dilbit generally floats after initial release into freshwater. When conditions are calm with no agitation or sediment in the water, dilbit may generally stay afloat for six to 10 days in both freshwater and saltwater. The same contain- ment and recovery tools used for medium to heavy crude oil can be used on dilbit when floating. However, by com- parison to traditional crude oil, dilbit weathers rapidly in freshwater. As the dilutant evaporates, the density and viscosity increase, and the remaining oil exhibits behavior similar to heavy oil. The fate of spilled dilbit depends on the type of diluted bitumen products, whether its Western Canadian Select or Cold Lake Blend, its characteristics, the environmen- tal conditions during and after a spill, and the nature of the waterbody—the amount of suspended sediment. Response plans should focus on containing and remov- ing the surface slick before it becomes more difficult to collect with skimmers or weathers sufficiently to sink. About the author: Benedette Adewale, Ph.D., is a research physical scientist and project manager at the Coast Guard Research and Development Center. She earned a Master of Science degree in chemistry from the City Univer- sity of New York, City College of New York and a Doctor of Philosophy degree in chemistry from Stony Brook University. She is a member of American Chemical Society. Endnotes: 1. Adewale, B., Cisternelli, M., Gonin, I., Wurl, M., and Tusia, M. (2021). Literature Review of Diluted Bitumen (dilbit), USCG Research and Development Center, Report No. CG-D-03-21, June 2021.
