Fly the Poplar Skies: Research teams developing processes for carbon-negative renewable jet fuel, higher poplar yields
The Dumesic Lab's catalytic process for producing GVL and converting into liquid transpotration fuels
In Wisconsin and Maryland, a pair of teams are working independently on processes that, when paired, may lead to the direct conversion of poplar trees into jet fuel as well as other high-density biofuels. One project is just getting underway in Maryland — a project to radically improve the nitrogen efficiency of poplar by discovering, defining and enhancing the switching mechanisms in the poplar genome nitrogen cycle thereby improving the plant’s already considerable reputation for fast growth.
A second project in Wisconsin is now reporting results in Science magazine, the direct conversion (in two steps) of cellulose to jet fuel via an old fuel pathway — GVLs — that have now been made radically more efficient at Jim Dumesic’s lab at the University of Wisconsin.
What is a GVL? It’s found in fruits and is widely used as a food additive.
To envision it, first think about biodiesel, and how that is produced from virgin or waste oils by a process called transesterification. It’s a process found in nature — and if you’ve ever had a ripe Gouda cheese, one of the flavoring components is a product called a lactone, ultimately formed from milk but specifically a transesterification of a hydroxy fatty acid.
Lactones, like milk products, are many in number and wide in uses. They are divided by the number of carbon molecules — and generally speaking, the more carbon, the more dense a fuel made from them. A five-carbon lactone is valerolactone (now you know where Valero got its name), and one type of valerolactone is gamma-valerolactone (GVL) referring to the location of carbon in its molecular chain.
GVL first came on the radar as a potential biofuel about two years ago, when according to a Treehugger report, “A team of researchers, led by Eötvös University’s István T. Horváth, examined GVL’s properties as a sustainable fuel additive or outright alternative, concluding that its physical and chemical properties made it an attractive candidate for liquid transportation fuels,” in an issue of Green Chemistry. More on that report.
What Dumesic’s team has come up with is a catalytic process that dos not require what others have not been able, heretofore, avoid: an external source of a lot of hydrogen.
Generally speaking, the relative scarcity of cheap hydrogen — even though it is the most abundant element in the universe by a long shot — is an even more annoying stumbling block in biofuels than the scarcity of cheap sugars. For example, it is the bugaboo that plagues the development of hydrogen fuel cell technology.
The novel approach: turn a problem into a pathway. The team noted the tendency of sugars to break down too easily into levulinic acid and formic acid — acids that previously had not been utilized as a base for fuel production.
The Dumesic lab’s biomass is fed through a series of catalytic conversions, and produces both condensable alkenes of gasoline or jet-fuel weights, plus a pressurized stream of CO2 that can be captured and sequestered, or otherwise used in other processes that require CO2, such as the cultivation of algae.
It raises the potential of something even more interesting than a carbon-neutral fuel — as all biofuels are (except for carbon emissions from their actual production and distribution). With CO2 sequestration that is possible from this process, there is the potential of a carbon-negative fuel — that is, a fuel that scrubs CO2 from the atmosphere rather than simply recycling.
But as Steve Jobs is wont to say…one more thing. Note that Dumesic’s team are using a catalytic process to produce a jet fuel from biomass. No need to add hydrogen in to upgrade a virgin oil. No messing around with microbes — which, as living organisms generally are not least their human brethren, always “high maintenance” and occasionally unruly. Keep in mind that one of the 50 Hottest Companies in Bioenergy — Virent — uses a chemical process called bioforming to produce renewable diesel from simple sugars – that’s a technology that also emerged from discoveries in Dumesic’s lab.
A lab demonstration is a ways down the road from affordable fuel on the street — in this case, the cost of producing the GVL is still prohibitively high, and other researchers have noted that the cost lies in the pesky number of steps involved in conversion. But the Dumesic breakthrough is compelling enough to put this one on the radar quite early in its development.
The Science magazine article (fee-based) and free downloads of tables and charts, is here.
Meanwhile, researchers at the University of Maryland and Bowie State University have landed a $3.2 million grant from the National Science Foundation’s Plant Genome Research Project. Using the recently completed poplar genome, the researchers are focusing on ways to improve the tree’s nitrogen processing capability, which will enhance its growth rate and feasibility for use in fuel production. According to lead researcher and associate professor Gary Coleman, “both the growth in the spring and regrowth from roots after the stems are harvested depend on the availability of stored nitrogen,” says Coleman. “The data we collect will allow us to understand mechanisms of nitrogen cycling, determine how to increase the rates of the cellular reactions, and identify the genes that play a crucial role in the process. Eventually, we should be able to breed a variety of poplar with a more efficient nitrogen process, optimized for growth and rapid maturity.”
The research team are examining how the thousands of genes in poplar are being switched on and off during the nitrogen storage cycle, measuring the rates of dozens of chemical reactions and studying the many proteins that facilitate all of the activity.
“What we’re looking for is the most efficient way for these plants to process nitrogen,” explained Ganesh Sriram, assistant professor of chemical and biomolecular engineering at the University of Maryland. “It’s like dealing with traffic. Imagine you’ve got cars on a road, each can only hold one passenger, and that can’t be changed. If you want more people to get to a destination in a certain amount of time, you can increase the speed limits, add more traffic lanes, reroute the cars onto parallel roads, avoid delays, or change the timing of the traffic lights. That’s what we’re doing on a genetic and molecular level for poplar.”
The research has been enabled by the recent publication of the poplar tree’s genome, a map of its complete genetic structure.
More on the poplar project at the University of Maryland.
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