Applications of glycerol

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Production of high-value chemicals from biodiesel by-products: To improve the economic viability of biodiesel refining, chemical engineers at Rice University have developed a technology that can convert difficult-to-manage biodiesel waste into sellable chemicals. The latest research findings were published in the Journal of Metabolic Engineering. This article, along with other articles published earlier this year, describes this transformation process. During fermentation, Escherichia coli and other gut bacteria convert glycerol, the main by-product of biodiesel production, into valuable organic acids such as formic acid and succinic acid. Biodiesel producers used to sell glycerin, but as biodiesel production increased sharply, there was an excess supply of glycerin, forcing producers to spend money to dispose of the surplus. 1 ton of glycerin is produced for every 10 tons of biodiesel manufactured. The United States produced approximately 450 million gallons of biodiesel in 2007, and this figure was expected to reach 1.2 billion gallons by 2010. Gonzalez’s research team announced last year a method for producing ethanol from glycerol using E. coli. The new fermentation technology is highly efficient; its cost is about 40% lower than that of ethanol produced from corn. It enables the production of chemicals with high added value such as formic acid and succinic acid, which generate higher profits than ethanol. Scientists previously believed that bacteria capable of producing 1,3-propanediol in metabolic pathways could ferment glycerol, yet neither E. coli nor yeast can produce 1,3-propanediol. Gonzalez’s research revealed a previously unknown metabolic pathway for glycerol fermentation that can utilize 1,2-propanediol. The chemical structure of 1,2-propanediol is similar to that of 1,3-propanediol, and it can be produced by Escherichia coli. The reason this metabolic pathway had not been discovered before was that it could only be activated when a number of conditions were met simultaneously. Once this fermentation pathway was identified, Gonzalez’s team began to use metabolic engineering techniques to create a new strain of E. coli capable of producing various high-value products. For example, the control strain could produce only a small amount of succinic acid when fermenting glycerol, whereas the yield of succinic acid in the newly developed strain increased by 100 times. Succinic acid is a commonly used raw material in the chemical industry; it can be used to manufacture corrosion-resistant airport de-icing devices, non-toxic plastics, pharmaceuticals, and food additives. Most succinic acid today comes from non-renewable fossil fuels. Gonzalez has also successfully developed engineered E. coli strains for the production of formic acid and lactic acid. Their goal is not to use it merely to produce this one product, but to use this technology as a platform for manufacturing various high-value green chemical products. Glycos Biotechnology in Houston has been granted permission to use this technology, and the company plans to put the first demonstration units into use within 12 months. This research was supported by the U.S. Department of Agriculture, the U.S. **Science Center, Rice University, and Glycos Biotechnology.