The new Verenium plant is the first demonstration-scale cellulosic ethanol plant in the United States. It will be used to try out variations on the company's technology and is designed to run continuously. Verenium wants to demonstrate that it can create ethanol for $2 a gallon, which it hopes will make the fuel competitive with other types of ethanol and gasoline. Next year, the company plans to begin construction on commercial plants that will each produce about 20 to 30 million gallons of ethanol a year.
Until now, technology for converting nonfood feedstocks into ethanol has been limited to the lab and to small-scale pilot plants that can produce thousands of gallons of ethanol a year. Since these don't operate continuously, they don't give an accurate idea of how much it will ultimately cost to produce cellulosic ethanol in a commercial-scale facility.
Almost all ethanol biofuel in the United States is currently made from corn kernels. But the need for cellulosic feedstocks of ethanol has been underscored recently as food prices worldwide have risen sharply, in part because of the use of corn as a source of biofuels. At the same time, the rising cost of corn and gas have begun to make cellulosic ethanol more commercially attractive, says Wallace Tyner, a professor of agricultural economics at Purdue University. A new Renewable Fuels Standard, part of an energy bill that became law late last year, mandates the use of 100 million gallons of cellulosic biofuels by 2010, and 16 billion by 2022.
So far, however, there are no commercial-scale cellulosic ethanol plants in operation in the United States, although a number of facilities are scheduled to start production in the next few years. The Department of Energy is currently funding more than a dozen companies that will be building demonstration- and commercial-scale plants. One of these, Range Fuels, based in Broomfield, CO, plans to open a commercial-scale plant next year. It will have the capacity to produce 20 million gallons of ethanol and methanol a year.
Verenium will use a combination of acid pretreatments, enzymes, and two types of bacteria to make ethanol from the plant matter--called bagasse--that's left over from processing sugarcane to make sugar. It will also process what's called energy cane, a relative of sugarcane that's lower in sugar and higher in fiber. The high fiber content allows the plants to grow taller, increasing yield from a given plot of land.
The process begins when the cane is ground up and cooked under high pressure with a mild acid to hydrolyze the hemicellulose and separate it from the cellulose. The five-carbon sugars in hemicellulose are then fermented using genetically modified E. coli. The cellulose is broken down with enzymes and fermented with another type of bacteria called Klebsiella oxytoca. This bacteria does double duty, since it also produces enzymes that break down cellulose, reducing the amount of enzymes from outside sources by 50 percent. The dilute ethanol produced from fermentation of both types of sugar is then distilled to make fuel.
In addition to opening the demonstration plant, Verenium is also starting to grow energy cane and to work with local farmers to ensure a steady stream of material for its planned commercial plants. Short term, the company says that it can rely on leftover bagasse from sugar production, but eventually it will draw on energy cane grown specifically to make ethanol. Provisions in the Farm Bill, which was recently passed by the United States Congress, will help by providing farmers with incentives to plant energy crops, says Carlos Riva, Verenium's CEO. The incentives are important because it takes two to three years for energy cane, a perennial plant, to become established and reach ideal production levels. As a result, farmers will need to start planting the crops next year, before commercial plants are built and there is a market for these crops.
The opening of the demonstration plant, and the current construction of a number of other demonstration- and commercial-scale cellulosic ethanol plants, marks a turning point for the industry, Riva says. The development of improved enzymes and fermentation organisms means that no further scientific breakthroughs are needed to make cellulosic ethanol commercially successful, he says. "There's been a tremendous amount of background work in science and technology development," he says. "We've learned so much about the process that the really important thing now is to start to deploy the technology at a commercial scale."