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News Article

Researchers develop improved method of producing bio-oil from dead trees

Fast-pyrolysis technique found to be more efficient and cost effective

A team of researchers from the University of Washington have made significant progress on a solution to remove trees that have been killed by the mountain pine beetle and use them to make high value chemicals as well as renewable transportation fuels.  They have refined the technique to process larger pieces of wood than ever before, which could save time and money for commercial applications in the future.

In the western United States, the mountain pine beetle (Dendroctonus ponderosae) has destroyed over 40 million acres of forest.  The beetles carry spores of the blue stain fungus (Ceratocystis minor) in structures in their heads that resemble pouches.  As the adult beetles chew through the bark, the spores are dislodged and begin to germinate in the sapwood, preventing nutrients and water from travelling within the tree.  The beetles also lay their eggs under the bark, and the feeding larvae help kill the trees, often within a just few weeks of the attack.  The dead trees can then fall at any time or add fuel to a wildfire.  The infestation stains the wood and causes the tree to crack on the inside, which means that the wood cannot be harvested for lumber.  However, this new study has found a way to transform these dead trees into a useful product.  

“We came up with a different way of converying wood into oil, that’s really the main accomplishment of this project,” said senior author and assistant professor Fernando Resende, from the UW School of Environmental and Forest Sciences.

“Not only do we want to reduce the costs, but we are hoping to increase the value of what we produce so we have a better chance of making it commercial.”

Researchers around the country are exploring the method of “fast pyrolysis”, which involves heating the wood in an oxygen-free chamber to about 500°C, until the material turns to vapour. As the vapour rises and moves into other chambers, it cools and becomes a dark brown liquid fuel, known as “bio-oil”.  These researchers, including the UW team are currently testing whether or not it is possible to upgrade this oil by adding catalysts, which would thereby convert the bio-oil into transportation fuel resembling diesel and gasoline.

Once the trees have been killed following an infestation, they become extremely dry.  This is useful in that drying the wood prior to the fast-pyrolysis process is not required.

“If you can extract the wood and process it using fast pyrolysis , not only will you free up space and safety hazards in the forest, but you also have the organic liquid that could potentially be used for products,” explains Resende.

Some fast-pyrolysis systems must use small wood pieces measuring 1-2 millimetres long, which can often add an extra step to grind larger pieces down to the approximate size necessary before converting them into bio-oil.  The system developed by the UW team can effectively break down woodchip sized pieces, though the team have successfully turned an entire log into bio-oil.

Their method involves placing the woodchips on a rotating surface and a hot stainless steel plate then crushes the wood.  The woodchips are hot from the contact with the metallic surface and the chemical transformation from solid to vapour begins.

According to the researchers, this method can be used in mobile pyrolysis units, so that dead trees can be processed on site.  This would save on transportation costs associated with removing large pieces of wood from the forest.   While these units are already being used for standard wood-to-oil processing, the changes proposed by the team could make the process more cost-effective and efficient.

Journal reference

Guanqun Luo, Devin S. Chandler, Luiz C.A. Anjos, Ryan J. Eng, Pei Jia, Fernando L.P. Resende. Pyrolysis of whole wood chips and rods in a novel ablative reactorFuel, 2017; 194: 229 DOI: 10.1016/j.fuel.2017.01.010

Further information on the mountain pine beetle (Dendroctonus ponderosae) is available on CABI’s open access Invasive Species Compendium

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 11 May 2017
  • Source
  • University of Washington
  • Subject(s)
  • Forest products