Ramon Gonzalez and Syed Shams Yazdani have identified the metabolic processes and conditions that allow a known strain of Escherichia coli to convert glycerin into ethanol through an anaerobic fermentation process. Gonzalez is currently the William Akers assistant professor in chemical and biomolecular engineering at Rice University, and Yazdani is a postdoctoral research associate.
In a comparison of feedstock and operating costs, Gonzalez found that ethanol from glycerol is 39 cents cheaper to produce than ethanol from corn. Feedstock costs per gallon were 53 cents for corn, versus 30 cents for glycerol. Per gallon operating costs were 52 cents for corn and just 36 cents for glycerol. "The main reason for the difference in costs is that there is no preprocessing," Gonzalez says. In feedstock operations, the corn must be ground and cooked, and the sugar extracted. "It is a process that is both capital and process intensive," he says. "You need to work all the way from the corn grain until you get sugar, and then you start fermentation." Meanwhile, glycerin doesn't require those steps because it comes preprocessed. This means no enzymes to buy and less equipment.
The implications of this research are so promising that the process may be commercialized before cellulosic ethanol. Gonzalez partnered with Paul Campbell, who researches, develops and markets blends of microbes for industrial, agricultural and environmental purposes, to form Glycos Biotechnologies Inc. The company, which was funded by Houston-based venture capital fund DFJ Mercury, expects to complete its pilot plant in early 2008. "Once we have the pilot running and working properly, [commercialization] is a matter of months," Gonzalez says, noting that the pilot plant is being designed to be one step away from a commercial-scale plant. Gonzalez couldn't say how big the pilot plant will be, but he says it would be capable of fermenting at least 10,000 liters (2,641 gallons). Glycos Biotechnologies will not develop and sell the technology, Gonzalez says. Instead, the company plans to form partnerships with those already in the biodiesel, glycerin and ethanol industries, he says. The company's Houston location lends itself well to working with biodiesel producers, as there are several in the region.
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Gonzalez says this process could be collocated with either an ethanol or biodiesel facility, and there are advantages to each. If collocated with a biodiesel plant, costs to transport glycerin would be saved. At least initially, this will be the most likely deployment of the company’s technology.
Glycerol is the principal component of glycerin, a clear, odorless, viscous liquid. It is found in animal fats, vegetable oils or petrochemical feedstocks, and is derived through soap production and the transesterification process, in which fatty acids and alcohol are mixed. Although glycerin has more than 1,000 uses, including many applications as an ingredient or processing aid in cosmetics, toiletries, personal care, drugs and food products, it is typically used in a highly refined and purified form. Refined glycerin is mostly pure glycerol, with the salt, methanol and free fatty acids removed.
The rapid growth of the biodiesel industry changed the glycerin market. In fact, it was cited as the reason that Dow Chemical Co., which produced synthetic glycerin, exited the glycerin production business in North America in 2006. "The increased supply of glycerin in North America due to biodiesel production, which caused prices to drop, was a factor in that decision," says Catherine Maxey, business public affairs director for Dow Chemical. "However, we continue to produce synthetic glycerin in Europe for sales into specialized markets such as pharmaceutical, personal care and food applications, among others, where high quality is the major requirement. The high purity at constant quality levels of Dow's synthetic glycerin presents distinct advantages over natural glycerin in these specialized end applications."
Maxey's point about glycerin quality is important when considering the market for the biodiesel byproduct. Biodiesel production yields unrefined glycerin. Biodiesel producers will usually then boil the glycerin to recover the methanol. This results in what is called crude glycerin, which is the form of glycerin most biodiesel producers sell. "[In most commercial applications], the quality of the glycerin must be high," Gonzalez says. "It can't be the nasty thing that comes out of biodiesel plants. If you use a feedstock that is not pure oil in biodiesel production, the glycerin is not very nice." His technology, however can use the "nasty" glycerin—both unrefined and crude.
The Process
Gonzalez became interested in glycerol while he was an assistant professor at Iowa State University in Ames. His initial research philosophy was to develop a microbial fermentation process for converting a low-cost, high-carbon feedstock into something with a higher value—not necessarily ethanol. Glycerol was targeted as the carbon source because it is the byproduct of an established and growing industry.
Gonzalez and Yazdani coauthored a report entitled “Anaerboic fermentation of glycerol: a path to economic viability for the biofuels industry,” which was printed in Current Opinion in Biotechnology. According to the report, glycerol is competitive with sugar used in the production of chemicals and fuels via microbial fermentation at its current price, which ranges from 5 to 10 cents per pound. Additionally, glycerol has yield advantages over sugar due to the highly reduced nature of carbon atoms. “One pound of sugar gives you a half-pound of ethanol and a half-pound of useless carbon dioxide,” Gonzalez explains. “On the other hand, one pound of glycerol gives you a half-pound of ethanol and a half-pound of formic acid. Since formic acid is as valuable as ethanol, and also has a fuel value (in fuel cells), the use of glycerol as a carbon source doubles the overall product yield.”
Once glycerin's advantages as a feedstock were established, Gonzalez set forth to find a product. "Once we decided on glycerol, we had to see what we could do with it," Gonzalez says. He knew it could be fermented, and indeed, that it could be fermented into ethanol. This is not the first time that glycerin has been successfully fermented into ethanol. It was first done in 1877, using fungi as the agent. In his report, Gonzalez says many microorganisms are able to metabolize glycerol in the presence of external electron acceptors, but few are able to do so fermentatively. Gonzalez discovered one microorganism that could—E. coli. In previous studies, researchers had been unable to successfully convert glycerol to ethanol with the bacteria. "The major find is that we found conditions that enable a native, nonpathogenic strain of E. coli to [ferment glycerol to ethanol] without oxygen," Gonzalez says. "We don't need to do much genetic engineering to have ethanol as the main product."
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