Researchers improve bio-oil refining, aim for carbon negative production system

A team of University of Georgia (UGA) researchers has improved the processing of bio-oil (pyrolysis oil) into biofuels that can be mixed with diesel. Unlike previous pyrolysis fuels derived from wood, the new and still unnamed fuel can be blended directly with biodiesel and petroleum diesel to power conventional engines.

The group's findings [*abstract] are detailed in the early online edition of the American Chemical Society journal Energy and Fuels. Tom Adams, author and director of the UGA Faculty of Engineering outreach service, explains that scientists have long been able to derive oils from wood, but they had been unable to process it effectively or inexpensively so that it can be used in conventional engines. The researchers have developed a new chemical process, which they are working to patent, that inexpensively treats the oil so that it can be used straight in unmodified diesel engines or blended with biodiesel and petroleum diesel.

"The exciting thing about our method is that it is very easy to do. We expect to reduce the price of producing fuels from biomass dramatically with this technique. [...] This research will really benefit the citizens of the state, and that fits perfectly into the mission of a land grant institution. Georgia has 24 million acres of forested land, and we could see increased employment and tax revenues based on this research. Another huge benefit is that this fuel would reduce the amount of fuel we import from other states and from other countries." - Tom Adams, director of the UGA Faculty of Engineering

The new process works as follows: wood chips and pellets - roughly a quarter inch in diameter and six-tenths of an inch long - are heated in the absence of oxygen at a high temperature, a process known as pyrolysis. Up to a third of the dry weight of the wood becomes charcoal, while the rest becomes a gas. Most of this gas is condensed into a liquid bio-oil and chemically treated. When the process is complete, about 34 percent of the bio-oil (or 15 to 17 percent of the dry weight of the wood) can be used to power engines. The researchers are currently working to improve the process to derive even more oil from the wood.

Towards carbon-negative biofuels
Adams points out that the pyrolysis system offers an opportunity to make biofuels radically carbon-negative, meaning that they do not merely reduce heat-trapping carbon dioxide in the atmosphere, but actually take more of it out than they release (see: "Biochar soil sequestration and pyrolysis most climate-friendly way to use biomass for energy"). As long as new trees are planted to replace the ones used to create the fuel, the biofuel is carbon-neutral. But if the charcoal fraction obtained from pyrolysis is stored as a fertilizer in soils, then the biofuel becomes carbon-negative:
bioenergy :: biofuels :: energy :: sustainability :: wood :: biomass :: pyrolysis :: bio-oil :: biochar :: charcoal :: terra preta :: carbon sequestration :: carbon-negative ::

The researchers have created test plots to explore whether the charcoal can indeed be used as a fertilizer. If the economics work for the charcoal fertilizer, going carbon negative becomes a very green option.

"You're taking carbon out of the atmosphere when you grow a plant, and if you don't use all of that carbon and return some of it to the soil in an inert form, you're actually decreasing the amount of carbon dioxide in the atmosphere. We're optimistic because in most types of soil, carbon char has very beneficial effects on the ecology of the soil, its productivity and its ability to maintain fertility."

The idea of storing "bio-char" or "carbon black" into soils is thousands of years old. Scientists working in the Amazon and in the West African rainforest found that native populations had been using the technique of sequestring charcoal in soils for millennia. Such "terra preta" or "dark earth" plots are surprisingly fertile compared to non-treated soils (earlier post). The technique is currently receiving a lot of attention from the renewable energy community and from climate scientists alike, because it promises to offer a reliable and affordable method to reduce carbon dioxide emissions. The process could be implemented on a vast scale in low-fertility and problematic soils across the tropics and the subtropics.

But more research is needed. As Adams says, although the new biofuel with carbon negative potential has performed well, further tests will allow the researchers to assess its long-term impact on engines, its emissions characteristics and the best way to transport and store it. "It's going to take a while before this fuel is widely available", Adams said. "We've just started on developing a new technology that has a lot of promise."

The research was funded by the U.S. Department of Energy, the Georgia Traditional Industries Pulp and Paper Research Program and the State of Georgia upon the recommendation of the Governor's Agriculture Advisory Committee.

More information:
Manuel Garcia-Perez, Thomas T. Adams, John W. Goodrum, Daniel P. Geller, and K. C. Das, "Production and Fuel Properties of Pine Chip Bio-oil/Biodiesel Blends" [*abstract], Energy and Fuels, May 18, 2007, ASAP Article 10.1021/ef060533e S0887-0624(06)00533-0.

University of Georgia: New biofuel from trees developed at UGA: Still-unnamed fuel can be blended with biodiesel, petroleum diesel - May 18, 2007.