In the quest to produce affordable biofuels, poplar trees are one of the Pacific Northwest’s best bets — the trees are abundant, fast-growing, adaptable to many terrains and their wood can be transformed into substances used in biofuel and high-value chemicals that we rely on in our daily lives.

But even as researchers test poplars’ potential to morph into everything from ethanol to chemicals in cosmetics and detergents, a commercial-scale processing plant for poplars has yet to be achieved. This is mainly because production costs still are not competitive with the current price of oil.

A 91±¬ÁÏ team is trying to make poplar a viable competitor by testing the production of younger poplar trees that could be harvested more frequently — after only two or three years — instead of the usual 10- to 20-year cycle. These trees, essentially juveniles compared with fully grown adults, are planted closer together and cut in such a way that more branches sprout up from the stump after each harvest, using the same root systems for up to 20 years. This method is called “,” and the trees are known as poplar coppice.

This video shows the speed with which young poplar can be harvested. Video provided by Rick Stonex/GreenWood Resources, Inc.

The team is the first to try converting the entire young tree — including leaves, bark and stems — into bio oil, a biologically derived oil product, and ethanol using two separate processes. Their results, published this summer in two papers — one in and the other in — point to a promising future for using poplar coppice for biofuel.

“Our research proved that poplar coppice can be a good option to meet the cheap, high-volume criteria of biofuel feedstock,” said lead author on both papers, a doctoral student in the 91±¬ÁÏ’s . “Our findings are significant for the future biofuel industry, and the ultimate goal is to make poplar coppice biofuel a step closer to the pump.”

Poplar woodchips from older trees have been the focus of most research, mainly because wood parts contain the highest concentration of sugar, which is important for making ethanol and chemicals. Earlier studies show that poplar woodchips are a viable biofuel source, but costs still don’t pencil out, especially since trees are cut just once every 10-plus years. Additionally, other tree parts go to waste when only the trunk is used, making the process more inefficient and wasteful.

However, if poplar were planted close together like an agriculture crop, and whole trees were harvested on a much quicker cycle, it could make sense from a cost perspective and offer a short return on investment — and be more attractive for farmers.

Alternative fuels must make economic sense, the researchers stress, for biofuels to make a dent in the petroleum-driven market.

“We have the environmental incentives to produce fuels and chemicals from renewable resources, but right now, they aren’t enough to compete with low oil prices. That’s the problem,” said , a 91±¬ÁÏ associate professor in the School of Environmental and Forest Sciences and the senior author.

Bura’s research is part of the funded by U.S. Department of Agriculture’s National Institute of Food and Agriculture. The project, directed by 91±¬ÁÏ professor , is a consortium of universities and industries led by the 91±¬ÁÏ whose goal is to lay the foundation for a Pacific Northwest biofuels and bio-based industry based on poplar feedstock. For this study, trees in Jefferson, Oregon — one of the four study sites — were planted in rows close together in spring of 2012 and harvested less than two years later before the leaves had fallen.

The 91±¬ÁÏ team first tested whether entire young poplar trees could be converted into sugar by a process that uses high temperature, pressure and enzymes to break down the wood materials into sugar. From there, it is possible to make ethanol, acetic acid, lactic acid and other valuable chemicals by fermenting the sugar.

After processing the trees, the researchers found that leaves are poor performers and lowered the overall sugar output, not just because leaves are naturally low in sugar, but they also contain other chemicals that impede the sugar-releasing process. When scaled up to a commercial operation, leaves should be removed and may be used for other purposes, such as feed for animals.

They also tested whole poplar trees from the same plot in another conversion process that uses much higher heat — upwards of 500 degrees Celsius — to transform the tree materials directly to bio oil in a process called “.” Research is underway to convert this dark brown oil to a transportation fuel that resembles gasoline or diesel.

In the experiment, the researchers found that including leaves didn’t make a big difference to the quality of the resulting bio oil. When scaled up, producers could ultimately save time and money by not separating leaves from branches to achieve similar quality oil.

Future poplar production plants could leverage both methods, weighing factors like the current cost of materials or the dollar value of the products being made to determine which method makes more financial sense, Dou explained.

The young poplars used in the study have similar properties to shoots that would sprout from a stump in a true coppicing operation. Using that cutting method, it is possible to harvest trees every two years for up to 20 years without the added effort and cost of pulling up roots, preparing the soil and planting new trees that is required in usual planting regimes.

Ultimately, the researchers say that coppice poplar is likely the best balance of cost and reliability for Pacific Northwest growers to produce biofuel.

“Currently, we are looking at how we can grow poplar for monetized ecosystem services,” Bura said. “In the future, we envision a bio-based industry that will provide multiple environmental benefits, will invigorate rural communities and will serve as a bridge to a fully developed biofuels industry.”

Other co-authors on the papers are Fernando Resende, a 91±¬ÁÏ assistant professor of environmental and forest sciences; Devin Chandler, a 91±¬ÁÏ graduate student in the Bioresource Science and Engineering program; Wilian Marcondes, a 91±¬ÁÏ exchange student from the University of São Paulo-Brazil; and Jessica Djaja, a 91±¬ÁÏ undergraduate student.

The research was funded by a grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

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For more information, contact Bura at renatab@uw.edu and Dou at changdou@uw.edu.

Grant information:

Agriculture and Food Research Initiative Competitive Grant No. 2011-68005-30407

A five-year, $40 million study is laying the foundation for a Pacific Northwest industry that converts sustainably produced poplar feedstock into fuels and chemicals.

The research, led by the 91±¬ÁÏ, will seed the world’s first wood-based cellulosic ethanol production facility. The handful of other cellulosic ethanol factories use agricultural waste to convert feedstock into sustainable transportation fuels.

The U.S. Department of Agriculture-funded project is in its final year, and the consortium of 10 academic institutions and private companies will gather at the 91±¬ÁÏ Sept. 8-10 to share results and finalize research projects. They identified hybrid poplars as a beneficial feedstock because of the tree’s fast growth, year-round availability and wood that is readily broken down to fermentable sugars.

ZeaChem, a Colorado-based biofuels company and one of the industry partners in this study, is moving ahead with plans to build a commercial production facility in Boardman, Oregon, in 2016 that will produce fuel-grade ethanol and bio chemicals.

“We’ve established that poplar is a viable and sustainable feedstock for the production of fuels and bio-based chemicals,” said , a 91±¬ÁÏ professor of bioresource science and engineering, who leads the project. “We’ve provided fundamental information that our industry partners can use to convince investors that production of fuels and chemicals from poplar feedstock is a great investment.”

The research team, called , set up five demonstration tree farms with different varieties of poplar. None of the trees is genetically engineered, but instead researchers bred them to thrive in different environments and to grow fast. The trees can gain up to 20 feet a year, allowing for a harvest every two or three years.

“They grow like mad,” Gustafson said. “The production growth rate of these trees has just been phenomenal.”

When a poplar tree is cut, its stump naturally sprouts new shoots and the next generation of trees grow out of the parent stumps. Each tree can go through about six cycles of this regrowth before new poplars must be planted, Gustafson said.

A number of 91±¬ÁÏ faculty members and students, mainly in the 91±¬ÁÏ’s , have contributed to different aspects of this broad research project. They explored the pros and cons of processing whole trees verses using clean wood chips, developed catalysts to convert ethanol to jet fuel, examined the efficacy of endophytes — microorganisms — that live within the trees that provide benefits such as nitrogen fixation, assessed the social impact on potential landowners, and looked at available land for poplar tree farms and the impact climate change may have on growing them.

The 91±¬ÁÏ team also has refined the process of converting the poplar trees to fuel.

In this process, sugars are extracted from the poplar tree using a combination of thermal/chemical pretreatment and enzymatic reactions. The pretreatment step is performed in a high-pressure reactor to efficiently extract some of the sugars and to open the wood structure to enable enzymes to access carbohydrates remaining in the wood.

These sugars can then be fermented to different products including ethanol and acetic acid. Poplar is ideal for this process because they grow quickly and have relatively accessible carbohydrates in the wood.

Process improvements developed on the laboratory scale at the 91±¬ÁÏ can be tested at a demonstration scale at ZeaChem’s demonstration biorefinery in Boardman and then applied at a commercial scale once that facility is constructed.

“Advanced Hardwood Biofuels is more than a big research program,” Gustafson said. “We are setting the stage for a new, sustainable enterprise for the Pacific Northwest.”

Project collaborators and reporters interested in this project can take a tour of the 91±¬ÁÏ biorefinery pilot plant and laboratory facilities on campus Sept. 8 as part of the team’s annual meeting.

The other institutions involved are Washington State University, University of California, Davis, University of Idaho, Oregon State University, the Agriculture Center of Excellence, Greenwood Resources, Inc. and the Rocky Mountain Wildlife Institute.

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For more information, contact Gustafson at 206-543-2790 or pulp@uw.edu.