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Algae to Crude Oil: New Slurry Process Findings Published

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Photo courtesy Pacific Northwest National Laboratory Photo courtesy Pacific Northwest National Laboratory

RICHLAND, Wash. – Engineers have created a continuous chemical process that produces useful crude oil from harvested algae in less than an hour.

According to a press release from the Department of Energy's Pacific Northwest National Laboratory, engineers published their research findings in the journal Algal Research. Utah-based Genifuel Corp., a biofuels company, has licensed this new technology and hopes to build a pilot plant with an industrial partner.

In the PNNL process, a slurry of wet algae -- a green paste with the consistency of pea soup -- pumps in the front end of a chemical reactor. Once the system is up and running, crude oil emerges in less than an hour.  Additionally, water and a byproduct stream of material containing phosphorus come out as well.  A plant can use these byproducts to grow more algae.

Conventional refining can convert the crude algae oil into aviation fuel, gasoline or diesel fuel. When the resulting waste water receives further processing, it yields burnable gas and substances like potassium and nitrogen.  These byproducts, along with the cleansed water, can also be recycled to grow more algae.

"Cost is the big roadblock for algae-based fuel," said Douglas Elliott, the laboratory fellow who led the PNNL research team. "We believe that the process we've created will help make algae biofuels much more economical."

PNNL scientists and engineers simplified the production of crude oil from algae by combining several chemical steps into one continuous process. Because the new PNNL process works with an algae slurry containing as much as 80 to 90 percent water, a potential producer would recognize a sizable cost savings compared with most current processes.

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," said Elliott. "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."

The PNNL system also runs continuously, processing about a half gallon of algae slurry in the research reactor per hour. While that doesn't seem like much -- a working continuous system demonstrates a greater potential required for large-scale commercial production.

Additionally, the new PNNL system also eliminates another step required in today's most common algae-processing method.  It does not require complex processing with solvents like hexane to extract the energy-rich oils from the rest of the algae. Instead, the PNNL team's process 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.

"It's a bit like using a pressure cooker, only the pressures and temperatures we use are much higher," said Elliott.  The system runs at around 662 degrees Fahrenheit (350 degrees Celsius),  at a pressure of around 3,000 PSI.  It combines processes known as hydrothermal liquefaction and catalytic hydrothermal gasification. Elliott says such a high-pressure system is not easy or cheap to build.  While that proves one drawback to the technology, the cost savings on the back end more than makes up for the investment.

Elliott has worked on hydrothermal technology for nearly 40 years, applying it to a variety of substances, including wood chips and other substances. Because of the mix of earthy materials in his laboratory, and constant chemical processing, he jokes that his laboratory sometimes smells "like a mix of dirty socks, rotten eggs and wood smoke."

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.

In addition to Elliott, authors of the paper include 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, all at PNNL.