Money doesn’t grow on trees, but gasoline might

In 2003, University of Wisconsin–Madison graduate student George Huber and colleagues made hydrogen from plant sugars using nickel-tin alloy catalysts in the lab of Chemical and Biological Engineering Professor James Dumesic. 

In 2005, the team made a diesel-like fuel from plants.

Today, University of Massachusetts Amherst Assistant Professor of Chemical Engineering George Huber has graduate students of his own. 

Reporting in the cover article of today’s issue of "Chemistry & Sustainability, Energy & Materials," Huber’s team announced the first direct conversion of plant cellulose into gasoline components. This "green gasoline" can be created from sustainable biomass sources like switchgrass and poplar trees.

In the same issue, Dumesic and his team at UW–Madison announced an integrated process for creating chemical components of jet fuel using a green gasoline approach. While Dumesic’s group had previously demonstrated the production of jet-fuel components by combining separate catalytic steps, its current work shows that these steps can be integrated together and run sequentially, without complex separation and purification processes between reactors.

While it may be five to ten years before these green fuels arrive at the pump or power a jet, these breakthroughs have bypassed significant hurdles to bringing biofuels to market.

"It is likely that the future consumer will not even know that they are putting biofuels into their car," says Huber. "Biofuels in the future will most likely be similar in chemical composition to gasoline and diesel fuel used today. The challenge for chemical engineers is to efficiently produce liquid fuels from biomass while fitting into the existing infrastructure today."

For their new approach, the UMass researchers rapidly heated cellulose in the presence of solid catalysts, materials that speed up reactions without sacrificing themselves in the process, and then rapidly cooled the products to create a liquid that contains many of the compounds found in gasoline.

The entire process was completed in less than two minutes by using relatively moderate amounts of heat. The compounds that formed in that single step, like naphthalene and toluene, make up one fourth of the suite of chemicals found in gasoline. The liquid can be further treated to form the remaining fuel components or can be used "as is" for a high-octane gasoline blend.

"Green gasoline is an attractive alternative to bioethanol since it can be used in existing engines and does not incur the 30 percent gas mileage penalty of ethanol-based flex fuel," says John Regalbuto, who directs the Catalysis and Biocatalysis Program at the National Science Foundation (NSF) and supported this research.

"In theory, it requires much less energy to make than ethanol, giving it a smaller carbon footprint and making it cheaper to produce. Making it from cellulose sources such as switchgrass or poplar trees grown as energy crops, or forest or agricultural residues such as wood chips or corn stover, solves the life-cycle greenhouse gas problem that has recently surfaced with corn ethanol and soy biodiesel," Regalbuto adds.

Beyond academic laboratories, both small businesses and Fortune 500 petroleum refiners are pursuing green gasoline. Companies are designing ways to hybridize their existing refineries to enable petroleum products including fuels, textiles, and plastics to be made from either crude oil or biomass and the military community has shown strong interest in making jet fuel and diesel from the same sources.

"Huber’s new process for the direct conversion of cellulose to gasoline aromatics is at the leading edge of the new ‘Green Gasoline’ alternate energy paradigm that NSF, along with other federal agencies, is helping to promote," states Regalbuto.

Not only is the method a compact way to treat a great deal of biomass in a short time, Regalbuto says that the process, in principle, does not require any external energy. "In fact, from the extra heat that will be released, you can generate electricity in addition to the biofuel," he adds. "There will not be just a small carbon footprint for the process; by recovering heat and generating electricity, there won’t be any footprint."

The latest pathways to produce green gasoline, green diesel, and green jet fuel are found in a report released this month and sponsored by NSF, the Department of Energy and the American Chemical Society entitled "Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels: Next Generation Hydrocarbon Biorefineries." In the report, Huber, Dumesic and a host of leaders from academia, industry and the government present a plan for making green gasoline a practical solution for the impending fuel crisis.

"We are currently working on understanding the chemistry of this process and designing new catalysts and reactors for this single step technique. This fundamental chemical understanding will allow us to design more efficient processes that will accelerate the commercialization of green gasoline," says Huber.