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Breakthroughs in Green Gasoline Production
Although significant investments have been made in technologies for the production of ethanol from corn, biodiesel from soybean oil or canola oil, and more recently for the conversion of nonfood biomass feedstocks into ethanol and biodiesel, to date, the technologies for producing hydrocarbon fuels such as gasoline, diesel and jet fuel from biomass seem to have been overlooked. This will likely change, however, with recent reports of advancements in green gasoline production from a research group at the University of Massachusetts, Amherst. In addition, scientists and engineers at the Pacific Northwest National Laboratory in Washington State, in collaboration with researchers at UOP LLC, a developer and licenser of process technologies and catalysts and the National Renewable Energy Laboratory, are preparing to scale-up their approach to the production of green gasoline in the next year or two.
«I think in the broadest sense, the significance of green gasoline is that it provides an alternative to ethanol,» explains Brent Shanks, a chemical engineer at Iowa State University who develops catalysts for the conversion of biomass to chemicals and fuels. «That's significant partially because, looking forward to biofuels, the key question is what is the right biofuel? Ethanol and biodiesel have been initially selected because the technology is known. As we go forward talking about second-generation biofuels, it's a broader picture we need to consider,» he says. «It is important as a country to have a portfolio of approaches for second-generation biofuels.»
The Washington workshop culminated in a recently released document, which was edited by George Huber, a chemical engineer at the University of Massachusetts, Amherst. The document provides a road map highlighting the novel process technologies being developed around the world for biofuels production. It is this transformational science that the workshop attendees believe will provide the foundation for future biorefineries.
In addition, the road map presents recommendations for research that will foster the development of a mature biofuels industry in the United States. The workshop and resulting road map focus on green hydrocarbon fuels because the workshop participants liken the growth of a biofuels industry as an accelerated version of the petroleum industry's development, defined by intensive research and driven by innovations and tools available today. This stems from the chemical similarities between fuels currently derived from petroleum and those hydrocarbon fuels derived from biomass. Since the fuels are essentially the same at the molecular level, green hydrocarbon fuels have the same energy content as the fuels consumers are using today. These renewable fuels can be used in existing infrastructures such as engines and pipelines, and the production of green hydrocarbon fuels could also be integrated into existing petroleum refineries. It's these characteristics that have piqued the interest of those in the oil industry. «All the big names are getting into this,» says Doug Elliott, a staff scientist at PNNL. «I think that's a key change.»
It's the infrastructure compatibility of green gasoline that is the primary draw. «These people are interested in using the facilities that they have to handle this type of material because it looks more like what they're used to working with,» Elliott explains. For example, ConocoPhillips announced in the spring of last year that it would establish an eight-year, $22.5 million research program at Iowa State University to advance technologies for the production of biofuels. At the center of this research is the development of a process called fast pyrolysis,
In this process, solid biomass is injected into some kind of reactor, typically a fluidized bed. The feedstock is heated to temperatures ranging from 400 to 600 degrees Celsius (752 to 1,112 degrees Fahrenheit) for short periods of time, typically less than 2 seconds, followed by rapid cooling. The products of the reaction include gases, char and a liquid bio-oil. The latter consists of water, oxygen and thermally cracked pieces of cellulose, hemicellulose and lignin from the original feedstock.
Bio-oils are mixtures of more than 300 compounds that must be upgraded in a catalytic process to a liquid transportation fuel. This process of upgrading bio-oil to gasoline is not a new process. In fact, Don Stevens, a senior program manager at PNNL, has a jar of green gasoline in his office that was made in the mid-1980s that has yet to evaporate. «Some of the ideas like green gasoline have been around for awhile and progress was made years ago,» Stevens says. But cheap petroleum-based fossil fuels made the production of a biobased alternative cost prohibitive. «Fortunately, the capability underlying [green gasoline production] is still around,» he says. «These days it's much more interesting.»
He explains that the early work into green gasoline production built off the advancements made in the catalytic refining of petroleum. The direct application of the petroleum industry's tricks was not appropriate for bio-oil, however, so modifications were made to reaction conditions and different catalysts were used. «It's complementary to the existing petroleum refining approach but it uses different catalysts and conditions,» Stevens explains.
«In the past three to five years, the pyrolysis community has made a lot of progress in the functional upgrading of biocrude to fuel products,» Stevens says. «We could do it in the past but we've gotten a lot better at it.»
This is not the only pathway to green gasoline. In a recent paper in the journal ChemSusChem, which features research at the interface of chemistry and sustainability with energy research, materials science, chemical engineering and biotechnology, Huber's team of chemical engineers reported a breakthrough in the process. In the new work, the researchers show that pure sugar feedstocks can be converted into certain components of gasoline in a single step. By adding a zeolite catalyst, a solid catalyst, which consists of aluminum and silicon, to the pyrolysis process, cellulose can be directly converted to aromatics that make up a quarter of the chemical components found in gasoline. With further treatment, a liquid can be produced that is indistinguishable from gasoline.
«This is a new concept to make sustainable biofuel-a new route,» Huber says. The process, however, features a catalyst common to petroleum refining. «We started working with these catalysts because they are already used in the petroleum refinery and they are very inexpensive,» he explains. «They work well for petroleum refining and work reasonably well for biomass feedstocks.»
Now the team is designing catalysts specifically for biomass conversion. Although the team is currently producing green gasoline on a milligram scale, the research objective over the next few years is to scale up. «Our goal is to be able to have a process that can produce 50 gallons of aromatics from 1 metric ton of biomass,» Huber says. «We anticipate that this technology will have a significantly lower capital investment than cellulosic ethanol and syngas conversion technologies.»
Although it might be some time before Huber's process is producing a significant amount of green gasoline, the approach PNNL, UOP and NREL have been working on is nearing that advancement. «We're at the stage now where we're [upgrading bio-oil] in several liter quantities,» Stevens explains. «It's still at the bench top but we believe that in another year or two we'll be at the position where if someone like the Department of Energy announced a demonstration-type solicitation, it would be time for us to do one of those.»
Picking one approach to reign now is shortsighted, however. «We're excited and enthusiastic about Dr. Huber's approach,» Stevens says. «All of these approaches are important. If we're going to get to our [mandated] 36 billion gallons of fuel by 2022, I think you have to consider multiple approaches, multiple fuels, and part of those have to be infrastructure compatible because if we try to do it all with ethanol we have to have a huge infrastructure investment.»
What's certain is that those invested in the domestic production of second-generation biofuels are ramping up their efforts. The road map edited by Huber sums up the current state of these efforts to produce fuels from nonfood biomass that are cost competitive with petroleum-based fuels: «At this stage, there are many more questions than answers but the tremendous potential for domestic production of essential fuels and products compels us to work diligently to develop the technologies necessary to realize this potential.»