'Mini-cellulose' discovery may maximize thermochemical processes

By Bryan Sims | February 23, 2012

In thermochemical processes such fast pyrolysis or gasification, the breakdown of biomass into solid biopolymers—in particular cellulose, a polysaccharide that consists of long chains of tightly linked sugar subunits that must be broken down into simple sugars before they can be processed into biofuel or biobased chemicals—involves reactions that occur at such a rapid rate and are often so complicated in nature. The reactions are so fast and complex that current technology doesn’t allow operators to devise or employ reliable computer modeling systems to track and decipher the myriad of complex reactions of biomass in the process all the way to the chemical vapor products, most notably furans, an important precursor for the production of biofuels and biochemicals.

But a team of chemical engineers at the University of Massachusetts Amherst have discovered a small molecule, called α-cyclodextrin, which behaves the same as cellulose when it’s converted into biofuel. Coined the “mini-cellulose” molecule, according to Paul Dauenhauer, assistant professor of chemical engineering and leader of the UMass Amherst research team, it reveals for the first time the chemical reactions that take place in wood or prairie grasses during high-temperature conversion into biofuels. Dauenhauer and his team’s discovery was reported in the January 2012 issue of the journal Energy & Environmental Science and highlighted in Nature Chemistry.

“It’s like a scientific tool,” Dauenhauer explained to Biorefining Magazine, adding that he and his team made a video simulating how cyclodextrin acts as a surrogate molecule for cellulose converted into a furan molecule.

“The reason we can do that is because the mini-cellulose behaves identical to cellulose, but it’s small enough that we can do this with a computer simulation,” Dauenhauer said. “For example, if you took real cellulose and you tried to do a computer simulation with it, it would take thousands of years, but [with the mini-cellulose] we can do this in a couple weeks to a month. Now, we can actually just watch the molecule and see what reactions it does because then we know the reactions that happened in wood or grasses when you put them in a pyrolysis reactor.”

He continued: “What’s so exciting about this is we can now make a mathematical model that tells us the reactions that occur in anybody’s reactor, and then we can apply that model to any type of pyrolysis or gasification system and tell you what the chemicals will be coming out of it.”

Upon making the discovery of the mini-cellulose molecule, Dauenhauer and his colleagues used a novel experimental technique for studying high temperature biomass chemistry called thin-film pyrolysis where cellulose is processed into very thin layers, about a thousandth of a millimeter thick, which enables rapid heat transfers and rapid diffusion of volatile products.

“You apply that to a really fast heating rate and that’s how you can study the chemistry,” he said.

The discovered reactions occurring within wood, according to Dauenhauer, will serve as the basis for designing current and future pyrolysis and/or gasification reactors. By creating reaction models of wood conversion, scientists are now able to optimize specific reactions dialed into the desired production of biofuels, thereby maximizing furan content in resulting pyrolytic bio-oil while helping minimize carbon dioxide.

Dauenhauer joined UMass Amherst in 2009 and conducts his research as part of the Catalysis Center for Energy Innovation in collaboration with the University of Delaware and funded by the U.S. DOE. Dauenhauer’s research team includes Dion Vlachos and graduate students Matt Mettler, Alex Paulsen and Samir Mushrif.

Dauenhauer has received several high-profile grants to support the ongoing research, including a five-year $800,000 Early Career Award in Basic Energy Sciences from the DOE in May 2011. The grant provides support for his research on understanding the catalysts involved that control the process of breaking down biomass into biobased chemical and fuel byproducts. In February 2011, he was awarded a one-year $80,000 grant from the National Science Foundation to conduct basic research on pyrolysis. Additionally, in 2011, he was awarded a three-year Young Faculty Award from 3M Corp.

“This is a scientific discovery,” Dauenhauer said, “but it’s led to a couple of technologies that are currently under development.”