Issue Date: November 2, 2009
Cellulosic Test Bed
At Coskata's site in Madison, Pa., workers in hard hats, surrounded by loud mechanical humming, walk through a towering maze of reactors, tanks, pipes, and gauges. This hustle and bustle makes a point: Cellulosic ethanol has escaped the lab.
The biofuels start-up is producing ethanol from wood chips in a semicommercial plant sited at a Westinghouse complex. On a recent tour for reporters, Coskata executives were on hand to show how far they've come and to explain how they plan to scale up the company's process to make cellulose-based ethanol that is price-competitive with gasoline.
Most cellulosic ethanol companies on the cusp of commercialization—a list that includes Poet, Iogen, Verenium, Mascoma, and Range Fuels—use either thermochemical or biochemical processes to break down cellulose and transform it into ethanol. Coskata, in contrast, has selected one of each: gasification to break down the carbon feedstock and microbial fermentation to turn it into ethanol.
"What we've tried to do is take the best of both," explained Coskata's chief executive officer, William Roe, during the tour. "A thermal front end gives us feedstock flexibility combined with a biological conversion step that gives us very high yields." He identified Coskata's ability to take in multiple feedstocks such as wood chips and agricultural, municipal, and construction waste as the company's most important competitive advantage.
Among the investors in Coskata are two blue-chip names: General Motors and venture capital powerhouse Khosla Ventures. Both of them, though, are hedging their bets on the best route to cellulosic ethanol. GM has also partnered with Mascoma, which uses yeast and bacteria to digest and ferment cellulose. And Khosla is funding Mascoma, Range Fuels, and waste-gas conversion firm LanzaTech.
The first of the new breed of cellulosic ethanol facilities to go on-line will be a Range Fuels plant in Soperton, Ga. Scheduled to begin production in the second quarter of 2010, the facility will use gasification followed by chemical catalysis to create ethanol and methanol from wood chips (C&EN, April 27, page 10).
Because technologies vary, success for Range Fuels won't mean success for others—and that's a problem for firms trying to raise funds. "Everyone's technology is either a little different or a lot different. That presents major challenges," points out David Woodburn, a green technology analyst at investment adviser ThinkEquity. "It's a catch-22—you can't test your scale-up without capital, and right now it's hard to get capital if you don't have data at scale."
Getting believable data is the point of Coskata's plant. Codenamed "Lighthouse," it can produce tens of thousands of gallons of ethanol, or about 0.1% of a full-scale commercial plant. The design mimics full-scale processes, which is why the largest bioreactor is 65 feet tall: It is the same height, although skinnier, as a reactor in a full-sized plant. The facility is "of sufficient size that the engineering and design work here and the knowledge we gather here allow us to translate to a full-scale facility," Roe said.
The next step for Coskata is to build that commercial facility. The company has not disclosed its planned location but says it has selected a site in the southeastern U.S. The firm is aiming for a capacity of 50 million to 100 million gal per year and an opening date in late 2012.
Meanwhile, Coskata is running the Lighthouse facility 24 hours a day, seven days a week to show off the efficiency of its microbes and to demonstrate how much it will cost to produce the ethanol. Information from the plant will also help measure CO2 savings and energy and water usage.
Converting feedstock to ethanol at the plant is a three-step process. The tour group observed wood chips being sucked out of a 500-lb bag and into a feed handler and then being sent to a gasifier. Coskata has chosen a plasma gasifier made by Westinghouse Plasma and originally developed for the National Aeronautics & Space Administration. Ionized gases at temperatures of up to 2,500 °C vaporize the feedstock into a synthesis gas composed primarily of carbon monoxide and hydrogen.
The syngas is then cleaned and cooled; waste heat from the hot gas is used to turn a turbine and provide electricity to the plant. The cooled gas is piped to a series of bioreactors, where specially designed microbes feast on it and excrete ethanol. The microbes are a type of Clostridia bacteria that have been selected to produce only two-carbon alcohols, meaning Coskata does not have to separate ethanol from methanol.
In the final step, Coskata separates the ethanol from water by distillation to obtain fuel-grade ethanol. In the future, the firm plans to investigate membrane separation to save energy. The water is recycled and reused in the bioreactors. Coskata has been sending a portion of the ethanol output to GM for quality tests. Early indications look positive, Roe said.
In addition, Roe noted, the Lighthouse project will show that the fuel produced in the scaled-up process will emit 96% less greenhouse gas throughout its life cycle than regular gasoline. To do that, Coskata's microbes consume 90–95% of the carbon monoxide and hydrogen in the syngas, producing 100 gal of ethanol for each dry ton of feedstock. During the plant tour, Roe declined to confirm a cost per gallon.
ThinkEquity's Woodburn warns scale-up can bring surprises. "As a former engineer I can tell you, you haven't really scaled up until you've scaled up. You can model, but there will be interactions you weren't expecting—they can be positive, but normally they are not," he says. However, strong data from Lighthouse can only help Coskata in its quest for funding. "If things look really good factoring in feedstock cost and conversion yield, that can be very promising," Woodburn says.
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