Think of the chemical reactions that turn wood into sustainable biofuel as the brackets for March Madness. And think of the molecules produced by those chemical reactions as the teams inside the brackets. Until now, chemical engineers couldn’t even chart the brackets, much less fill in the teams. All those reactions were so complex that engineers didn’t have a clue what was happening inside a biomass reactor. Now a team of chemical engineers from the University of Massachusetts Amherst has developed a brilliant new tool that will allow researchers for the first time to study the reactions inside a biofuel reactor, track the molecules produced by those reactions, and adjust the reactor to produce the highest possible grade of bio-oil.
This new experimental technique for studying high-temperature biomass chemistry is called “thin-film pyrolysis.”
“What we have invented here is the basic tool necessary to optimize biofuel reactors,” says Paul Dauenhauer, the leader of this research team from the UMass Chemical Engineering Department.
When the high temperatures in a bioreactor break down wood, multiple reactions produce a cascade of molecules, a complicated process that until now has never been understood. “If you heat a piece of wood, you want to predict all the vapors that come off,” explains Dauenhauer, “because that’s what we turn into biofuels.”
This new technique gives researchers a method for separating all the myriad individual reactions and understanding what is happening so they can then make the whole pyrolysis process more efficient and economical.
“Once you have an understanding of all the reactions,” says Dauenhauer, “you can use computer simulations to optimize the process.” Until now, the only way to optimize production was by cumbersome trial and error.
The breakthrough was reported in an article entitled “Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates,”which was published by Energy & Environmental Science, Issue 1, 2012, the number-one-ranking journal in the world for its subject matter. The article was considered so significant that it was also highlighted in another prestigious journal, Nature Chemistry, whose impact factor is first among all primary research journals in chemistry.
“It’s a critical step in the evolution of biofuel production,” notes Dauenhauer. “Petroleum reached a similar stage about 20 years ago, when they first developed these models to optimize their refineries for each specific mixture of petroleum, and it has proven incredibly valuable.” That development has triggered a fortune in savings for the industry each year.
The Holy Grail of biofuel production would be the equivalent of what the petroleum industry calls “light sweet crude oil,” which contains a disproportionately high percentage of molecules used to process gasoline, kerosene, and high-quality diesel. The term "sweet" originated because the low level of sulfur provides the oil with a mildly sweet taste and pleasant smell.
“Bio-oil can be really nice to work with, or it can be really gunky, really heavy, full of molecules you don’t want,” says Dauenhauer. “So we want to make the equivalent of ‘light sweet crude’ for biomass that’s easy to process in our fast pyrolysis reactors. To do that we need to know how all these hundreds of molecules are made to optimize the reactor for it. You can’t do it by trial and error, because there are just too many variables.”
Now, with this new technique, researchers can start to model the fast pyrolysis reactor process and predict all the different reactions and the molecules they produce.
“Once we have that kinetic model, we can change the parameters of the reactor process and make the highest value bio-oil,” says Dauenhauer. “It will lead to us making very precise adjustments to optimize the reactor and get rid of undesirable molecules.” Dr. Dauenhauer’s website is located at www.ecs.umass.edu/~dauenhauer/. (February 2012)