Researchers at the Department of Energy’s Pacific Northwest National Laboratory pumped a slurry of wet algae into a chemical reactor, which then subjects the biological material to very hot water under high pressure to tear it apart and convert it into liquid and gas fuels.
The resulting crude oil can then be conventionally refined into aviation fuel, gasoline or diesel fuel, the researchers reported in the journal Algal Research.
The team’s experiments converted more than 50 percent of the algae’s carbon into crude oil, sometimes up to 70 percent, in about one hour and created nothing more hazardous than an odor of dirty socks, rotten eggs and wood smoke from the processed biological material.
In fact, the leftover water and nutrients such as nitrogen, phosphorus and potassium can be recycled to grow more algae.
Algae has long been considered a potential source of biofuel and has been produced by several companies on a research scale, but the fuel was projected to be prohibitively expensive.
However, the recently developed technology uses a number of methods to reduce costs and has been licensed by the Utah-based Genifuel Corp., which is building a pilot plant with an industrial partner.
The process works an algae slurry that contains up to 90 percent water, unlike most current processes that used dried algae, and cuts costs significantly by eliminating the need for time and energy used to dry out the biomaterial.
“Not having to dry the algae is a big win in this process; that cuts the cost a great deal,” said Douglas Elliott, who led the PNNL research team. “Then there are bonuses, like being able to extract usable gas from the water and then recycle the remaining water and nutrients to help grow more algae, which further reduces costs.”
Other groups have tested similar processes, but most of that work was done one batch at a time.
The PNNL system runs continuously and processes about 1.5 liters of algae slurry per hour in the laboratory reactor, and scientists think this can be accomplished on a commercial scale.
The method also eliminates the need for complex processing with solvents such as hexane to extract energy-rich oils from the algae.
The system runs at more than 660 degrees Fahrenheit at about 3,000 pounds per square inch, combining processes known as hydrothermal liquefaction and catalytic hydrothermal gasification.
The system isn’t easy or cheap to build, but Elliott said cost savings later in the process justified the investment.
“It’s a bit like using a pressure cooker, only the pressures and temperatures we use are much higher,” Elliott said. “In a sense, we are duplicating the process in the Earth that converted algae into oil over the course of millions of years. We’re just doing it much, much faster.”
Watch this video report about the process posted online by PNNLgov:
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