Scientists find new way to break down woody wastes

Source: Amanda Peterka, E&E reporter • Posted: Friday, November 7, 2014

Scientists have announced the discovery of new way to break down the woody waste left after the manufacture of plant-based fuels, opening the door for potential new products that could make biorefineries more profitable.

University of Wisconsin, Madison, researchers exposed lignin, the complex polymer that gives plants structure, to oxygen and then added an acid under mild conditions. The treatment left behind building blocks that could one day be further processed to replace hydrocarbon aromatics in chemical manufacturing.

“It’s a messy polymer, a waste product, and we have to do something valuable with it” to make advanced biofuels production profitable, said Shannon Stahl, a senior author of the study and a chemistry professor. “We’re essentially coming up with a chemically insightful way of deconstructing lignin.”

The study was published Sunday in the journal Nature and received funding from the Department of Energy’s Great Lakes Bioenergy Research Center.

Up to now, lignin has been mostly viewed as an obstacle in cellulosic biofuels production. It’s difficult to release a plant’s component sugars from lignin’s grasp at the front end of the biofuels process. At the back end, biofuel companies view lignin as a waste product and typically burn it off for fuel, largely because there’s nothing better to do with it.

But biofuels scientists think lignin has big commercial potential if it could be deconstructed economically. Lignin contains chains of six-carbon rings called aromatics that could be used as substitutes for hydrocarbon versions.

Aromatics are found in plastic soda bottles, Kevlar, pesticides and pharmaceuticals, among other valuable products (Greenwire, May 20).

“Everybody’s been focusing on let’s get the sugars, let’s get the sugars,” Stahl said. “If we keep treating lignin like that, we’re never going to get its full value.”

The research team members from UW think they may have found the key to deconstruction with the two-step process laid out in their study.

Adding oxygen to lignin weakens the links in the chain. After oxidation, the polymer is amenable to being broken down by an acid under “incredibly mild conditions,” according to Stahl. It requires the temperature of boiling water to work and doesn’t require any other expensive components like precious metals.

“Under these conditions, the aromatics formed in significantly higher yields than anyone has observed previously,” said Alireza Rahimi, a UW postdoctoral researcher and lead author of the study, in a statement.

The technology is not ready for prime time at the three major cellulosic ethanol companies that are opening plants this year in the Midwest, Stahl acknowledged.

The research team plans to focus future research both on refining the process and on looking for uses for the lignin components.

“We’re the first to recognize this two-step technology. It’s not itself ready to put into a plant,” Stahl said. “We’ve got new strategies to take advantage of the concepts we established in this study, new and tandem technologies that build on the concepts. We have a two-pronged focus on where to go now, with the molecules that will be accessible and how to make those in a scalable way.”