University of Michigan Pressure Cooks Algae Soup for Bio-oil
Researchers heat algae to 300 degrees Fahrenheit in a device that acts like a pressure cooker to turn the algae into a crude bio-oil. Photo courtesy of Nicole Casal Moore.
University of Michigan professors are working to improve a procedure that heats and squishes microalgae in a pressure cooker and examining the possibility of other new fuel sources, such as E. coli bacteria, that would feed on waste products from previous bio-oil batches.
"The vision is that nothing would leave the refinery except oil. Everything would get reused. That's one of the things that makes this project novel. It's an integrated process. We're combining hydrothermal, catalytic and biological approaches," said Phillip Savage, an Arthur F. Thurnau Professor in the university's department of chemical engineering and principal investigator on the $2-million National Science Foundation grant that supports this project. The grant is funded under the American Recovery and Reinvestment Act.
Microalgae are simple, floating plants that don't have leaves, roots or stems. They break down more easily than other potential biofuel source plants because they don't have tough cell walls, Savage said. Unlike fossil fuels, algae-based biofuels are carbon-neutral. The algae feed on carbon dioxide in the air, and this gets released when the biofuel is burned. Fossil fuel combustion puffs additional carbon into the air without ever taking any back.
The pressure-cooker method bucks the trend in algae-to-fuel processing. The conventional technique involves cultivating special, oily types of algae, drying the algae and then extracting its oil.
The hydrothermal process this project employs allows researchers to start with less-oily types of algae. The process also eliminates the need to dry it, overcoming two major barriers to large-scale conversion of microalgae to liquid fuels.
"We make an algae soup," Savage said. "We heat it to about 300 degrees and keep the water at high enough pressure to keep it liquid as opposed to steam. We cook it for 30 minutes to an hour, and we get a crude bio-oil."
The high temperature and pressure allows the algae to react with the water and break down. Not only does the native oil get released, but proteins and carbohydrates also decompose and add to the fuel yield.
Savage said, "The hard part is taking the tar that comes out of the pressure cooker and turning it into something you could put in your car, changing the properties so it can flow more easily, and doing it in a way that's affordable."
Savage and his colleagues are taking a broad and deep look at this process. They are investigating ways to use catalysts to bump up the energy density of the resulting bio-oil, thin it into a flowing material and also clean it up by reducing its sulfur and nitrogen content.
Furthermore, they're examining the process from a life-cycle perspective, seeking to recycle waste products to grow new source material for future fuel batches.
Other collaborators are: Gregory Keoleian, professor of sustainable systems in the School of Natural Resources and Environment and in the Department of Civil and Environmental Engineering; Adam Matzger professor in the Department of Chemistry; Suljo Linic, assistant professor in the Department of Chemical Engineering; Nina Lin, assistant professor in the departments of Chemical Engineering and Biomedical Engineering; Nancy Love, professor and chair of the Department of Civil and Environmental Engineering; and Henry Wang, professor in the departments of Chemical Engineering and Biomedical Engineering.