The most expensive stage of biofuel production is pre-treatment of the plant material involved. Typically, high temperatures and pressures are needed to break up the lignin and hemicellulose polymers that surround the all-important cellulose fibers.
But how do these essential pre-treatment processes actually change the plant structures involved? It's a question that has kept researchers at the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL), Oak Ridge, Tenn., busy for some time.
However, in an article published in Green Chemistry the researchers outline the results of an investigation that integrates experimental techniques such as neutron scattering, X-ray analysis and supercomputer simulations in an effort to provide some answers.
"While pre-treatments are used to make biomass more convertible, no pre-treatment is perfect or complete," says ORNL coauthor Brian Davison. "Whereas the pre-treatment can improve biomass digestion, it can also make a portion of the biomass more difficult to convert. Our research provides insight into the mechanisms behind this 'two steps forward, one step back' process."
On the surface, what Davison and his coworkers found makes little sense — as the biomass heats up, the fiber bundles dehydrate. "This is very counterintuitive because you are boiling something in water, but simultaneously dehydrating it. It's a really simple result, but it's something no one expected," says ORNL researcher Paul Langan.
This dehydration causes the cellulose fibers to move closer together and become more crystalline, which makes them harder to break down.
The researchers then describe how they carried out a second part of the study to analyze lignin and hemicellulose. According to the team's experimental observations and simulations, the two polymers separate into different phases when heated during pre-treatment.
"Lignin is hydrophobic so it repels water, and hemicellulose is hydrophilic," Langan explains. "Whenever you have a mixture of two polymers in water, one of which is hydrophilic and one hydrophobic, and you heat it up, they separate out into different phases."
Gaining a better understanding of how the physical processes of dehydration and phase separation play out during pre-treatment could lead to improved manufacturing techniques and ultimately bring down the cost of biofuel production.
"Our insight is that we have to find a balance which avoids cellulose dehydration but allows phase separation," Langan notes. "We know now what we have to achieve — we don't yet know how that could be done, but we've provided clear and specific information to help us get there."
Meanwhile, other researchers at ORNL have been studying root microbiomes and have come up with insights that could enable making biofuels-feedstock plants grow stronger and more quickly.
These researchers investigated cottonwood poplars and described their work in PLOS One, an online scientific journal published by the Public Library of Science, on October 16, 2013.
In it, a team led by Christopher Schadt of ORNL's biosciences division investigated two naturally occurring riverbank populations of cottonwood poplars in Tennessee and North Carolina. The study collected data to understand the genotypic and environmental origins of variation in the root-associated microbiome. They found that bacterial and fungal microbiomes varied across habitat niche, space, and, often, season. Depending on given space, weather and location, the microbiomes inside the trees' roots could work in different ways — and could, with further study, be manipulated to do much more.
"We found that the microbes in the plant roots are dramatically different from those outside the roots just millimeters away," Schadt says. "This implies the host is selecting its microbial associates."
Many of these microbes have been implicated in promoting plant growth, but based on the team's discovery, it's possible these microbiomes could be manipulated to promote plant growth, which could increase productivity, stress resistance and efficiency.
"Knowing this information could have a number of implications for forestry practices, carbon cycling and biomass production for biofuels," Schadt notes. "In response to changes in the global environment due to fossil fuel use, each of these areas faces unique challenges and opportunities that could potentially benefit from a better understanding of beneficial plant-microbe interactions."
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at firstname.lastname@example.org.