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This article is from the In-Depth Report New Solutions for Clean Energy

Building a Better Biofuel: A New Carbon-Neutral Approach Turns Carbohydrates into Hydrocarbons

Turning plant sugars into gasoline with heat, pressure and catalysts
virent-biofuel-and-sugar-cane



Courtesy of Virent

When Randy Cortright of the University of Wisconsin found an aromatic fluid floating in his beaker that smelled just like gasoline, he thought he had a problem. After all, the chemical engineer wanted to make fuel from plants for the hydrogen economy that was supposed to boom about now. Instead, when he put the fluid in a chromatograph, he found it had all the hydrocarbon components of a high-octane gasoline.

"We're making hydrocarbons that look just like the hydrocarbons from fossil fuels," such as heptane, isooctane and others, Cortright says. And with a barrel of oil costing more than $80 per barrel, making gasoline from the carbohydrates in plants rather than much-touted hydrogen is proving a better business opportunity for Cortright and Virent Energy Systems, the Madison, Wisc.-based company he founded to commercialize the technology.

Just as a typical oil refiner cracks petroleum into a mixture of hydrocarbons ranging from ethane to jet fuel, Virent transforms sugars into a fuel that has a 102 octane rating. "Instead of feeding in crude oil, we're feeding in sugar water," Cortright explains. The fuel also delivers roughly 115,000 British thermal units per gallon, close to conventional gasoline's 125,000. That's because Virent's biogasoline does not have oxygen molecules along for the ride, unlike ethanol (the oxygen simply takes up space without adding much in the way of fuel, hence ethanol's lower energy density). And their new facility has already churned out in trial runs 2,000 liters of the carbon-neutral fuel—deemed as such because the CO2 absorbed from the atmosphere by the plant is the same CO2 released to the atmosphere when the fuel is burned—and started making 2,000 liters more to enable further testing on April 9.

Virent can make a batch of fuel in one hour rather than the days required for fermentation of plant sugars into ethanol or the eons to produce natural petroleum, though it employs the same tricks as nature: heat and pressure. The real key to the process is catalysis, which enables and speeds up the necessary chemical reactions. Or as physicist Steven Koonin, undersecretary of science at the U.S. Department of Energy told the recent ARPA-e conference, "During my time at BP, I came to understand that catalysis is more of a black art than science."

That's because much of what happens when a catalyst affects a given chemical reaction is unknown. DOE and others are working to change that but Virent is simply harnessing it. Cortright and chemical engineer James Dumesic discovered in their university lab back in 2001 that by starting with water and various carbohydrates from plants—basically, carbon, hydrogen and oxygen compounds—and using catalysts, heat and pressure, they could start creating CO2 and hydrogen and then use that hydrogen to eliminate the oxygen as water (the process produces more water than it consumes). "If we didn't make H2 we started making these nonoxygenated hydrocarbons, losing the H2 into methane, ethane and gasoline components," Cortright explains.

The process requires platinum, rhenium and ruthenium catalysts, in the shape of sand or gravel pellets, all of which are expensive and rare. "They also use these types of catalysts in an oil refinery," Cortright notes. "It's been done in the oil business for 50 years." None of the catalysts are consumed and the reaction is actually exothermic, meaning it produces heat. "The catalytic reactions in total generate sufficient heat to sustain the process without the requirement of additional energy input," says Lee Edwards, Virent's CEO.

In fact, the "green" gasoline can be made at temperatures ranging from 175 to 300 degrees Celsius and pressures of as much as 90 atmospheres and delivers nearly all of the underlying plant's embedded energy into the resulting mix, though roughly 50 percent of the carbon is lost as CO2 or waste products. That mix is then subjected to acid or base condensation as well as distillation to create and separate the gasoline and jet fuel. The waste products are burned as fuel to drive the process.

That means the limits to this process are the prices and available quantities of the sugars used. But the process can use almost any sugar, whether direct sucrose from sugarcane or the polysaccharides derived from breaking down cellulose in water. "We're not dependent on a particular sugar; we can run a mixture of sugars," Cortright says. "We can switch from sugar to sugar within the same plant."

And there's a lot of spare sugar to be found in the cellulosic materials left behind in crops. "In the U.S. alone, from current activities in agriculture and forestry, 1.5 billion tons of cellulosic material are generated every year and none of that goes into liquid transportation," noted microbiologist Tim Donohue, director of the Great Lakes Bioenergy Research Center, during a tour of the center in Madison, Wisc., this past October. Converting 1 billion tons of that into liquid fuel could replace 30 percent of our fossil fuel use, Donohue said.

Such fuels will need to be tested in actual engines, however, though the molecules are the same as the premium gasoline sold today. "It's drummed and shipped to the Shell [research and development] facilities outside Manchester, U.K.," Edwards says of the biogasoline produced to date. "We're getting ready to do blending studies." Virent has also partnered with Honda and Cargill to address its challenges on the engine side as well as on the feedstock side. "The biofuel Virent has produced is similar in composition to reformate components produced by the platforming of naphtha feeds during normal refinery operations," says technology manager Grahame Buss of Shell. "Our tests indicate that gasolines containing the bio-components may be blended at high ratios within the existing specifications."

Of course, other companies are doing something similar. Longtime oil refiners UOP have a new refining process that turns plant oils into jet fuel—that has, in turn, been used to power everything from a commercial jet to an F/A-18, dubbed the "Green Hornet." And biotechnology companies such as Amyris and LS9 are generating genetically engineered microbes that can churn out specific hydrocarbon molecules.

But Virent has added its process to the list of tools to convert plants into fuel, joining fermentation, Fischer-Tropsch and pyrolysis, and thinks it can compete with fuel from fossil oil at prices at or above $70 per barrel. The technology can also fit into existing infrastructure, such as corn mills or refineries.

The company will likely tackle diesel and jet fuel next, and it may have a significant advantage. Because the process makes a blend of hydrocarbons, it does not lack the aromatic compounds that seal aircraft engines, like the biojet fuel produced from camelina oil by UOP. But, for now, Virent is happy to harvest the gasoline that floats to the top in its process. "The gasoline floats on top of water," Cortright says. "We can design a plant that is completely self-sufficient where you do not need to bring in any other fossil fuels to help you."

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