The products of the PNNL process are:

• Crude oil, which can be upgraded via catalytic hydrotreating (applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude) to form liquid hydrocarbon fuel. In the team’s experiments, generally more than 50% of the algae’s carbon is converted to energy in crude oil—sometimes as much as 70%.

• Clean water, which can be re-used to grow more algae.

• Fuel gas, which can be burned to make electricity or cleaned to make natural gas for vehicle fuel in the form of compressed natural gas.

• Nutrients such as nitrogen, phosphorus, and potassium—key nutrients for growing algae.

While algae has long been considered a potential source of biofuel, and several companies have produced algae-based fuels on a research scale, the fuel is projected to be expensive. The PNNL technology harnesses algae’s energy potential efficiently and incorporates a number of methods to reduce the cost of producing algae fuel.

Cost is the big roadblock for algae-based fuel. We believe that the process we’ve created will help make algae biofuels much more economical.

—Douglas Elliott, the laboratory fellow who led the PNNL team’s research

PNNL scientists and engineers simplified the production of crude oil from algae by combining several chemical steps into one continuous process. The most important cost-saving step is that the process works with wet algae. Most current processes require the algae to be dried—a process that takes a lot of energy and is expensive. The new process works with an algae slurry that contains as much as 80 to 90 percent water.

Not having to dry the algae is a big win in this process; that cuts the cost a great deal. 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.

—Douglas Elliott

While a few other groups have tested similar processes to create biofuel from wet algae, most of that work is done one batch at a time. The PNNL system runs continuously, processing about 1.5 liters of algae slurry in the research reactor per hour.

The PNNL system also eliminates another step required in today’s most common algae-processing method: the need for complex processing with solvents such as hexane to extract the energy-rich oils from the rest of the algae. Instead, the PNNL team works with the whole algae, subjecting it to very hot water under high pressure to tear apart the substance, converting most of the biomass into liquid and gas fuels.

Elliott has worked on hydrothermal technology for nearly 40 years, applying it to a variety of substances, including wood chips and other substances. Genifuel Corp. has worked closely with Elliott’s team since 2008, licensing the technology and working initially with PNNL through DOE's Technology Assistance Program to assess the technology.

This has really been a fruitful collaboration for both Genifuel and PNNL. The hydrothermal liquefaction process that PNNL developed for biomass makes the conversion of algae to biofuel much more economical. Genifuel has been a partner to improve the technology and make it feasible for use in a commercial system. It’s a formidable challenge, to make a biofuel that is cost-competitive with established petroleum-based fuels. This is a huge step in the right direction.

—James Oyler, president of Genifuel

The recent work is part of DOE’s National Alliance for Advanced Biofuels & Bioproducts, or NAABB. This project was funded with American Recovery and Reinvestment Act funds by DOE’s Office of Energy Efficiency and Renewable Energy. Both PNNL and Genifuel have been partners in the NAABB program.

Resources

• Douglas C. Elliott, Todd R. Hart, Andrew J. Schmidt, Gary G. Neuenschwander, Leslie J. Rotness, Mariefel V. Olarte, Alan H. Zacher, Karl O. Albrecht, Richard T. Hallen and Johnathan E. Holladay (2013) “Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor,” Algal Research doi: 10.1016/j.algal.2013.08.005