Researchers at the National Renewable Energy Laboratory (NREL) in Golden, Colorado, have successfully modified a microorganism to produce a useful intermediate from sugar fermentation, which can then be upgraded into valuable biobased fuels and chemicals. NREL’s modified microorganism, a world-class cellulosic ethanol fermentation organism (Zymomonas mobilis), can now exclusively produce 2,3-butanediol (2,3-BDO)—a versatile fermentation intermediate that can be catalytically upgraded to a variety of hydrocarbon fuel precursors and valuable chemical co-products from six-carbon and five-carbon cellulosic sugars. NREL scientists have known the benefits of Z. mobilis, also known as Zymo, for years, and the bacteria can be used in the fermentation process for breaking down sugar for biofuels more efficiently than yeast.
NREL collaborated on this project with Oak Ridge National Laboratory (ORNL), which showed several catalytic upgrading pathways can convert 2,3-BDO to produce a range of fuels and co-products. Techno-economic modeling performed by NREL indicates a strong potential to cost-effectively produce diesel- and jet fuel–range molecules while diverting a portion of the 2,3-BDO intermediate to a wide range of large-market co-product applications, including solvents, polymers, and chemical feedstocks. Producing bioproducts, including biobased chemicals, alongside biofuels will bring down the price per gallon, allowing biofuels to be price-competitive.
The first key breakthrough occurred when NREL’s microorganism strain development team identified and implemented the needed genetic modifications to the ethanol-producing Z. mobilis microorganism in order to route sugar metabolism pathways to also produce 2,3-BDO. At this point, the microorganism produced a mixture of ethanol and 2,3-BDO—while useful in being able to produce a variety of fuel and chemical products, the mixed intermediates cause significant process separations and upgrading challenges that are quite costly. Completely eliminating the ethanol pathways was a step toward exclusively producing 2,3-BDO.
While ORNL’s catalytic upgrading system can work with either a mixture of ethanol and 2,3-BDO or just 2,3-BDO exclusively, the process is greatly simplified and the economics are greatly improved when it is recovering and upgrading a single product. ORNL is exploring additional modifications to achieve further process simplifications and cost savings.
As BETO’s mission involves facilitating the development of advanced hydrocarbon biofuels and bioproducts, this success represents a simplified process configuration with wide-ranging flexibility and cost-effectiveness. NREL verified the fermentation process, which is being further developed on actual sugar-rich hydrolysates produced from engineering-scale pretreatment and saccharification operations on biomass feedstocks. Future catalytic upgrading activities will use fermentation broths directly produced from these hydrolysates. BETO’s support of such early-stage process development and integration is essential to enable industry to verify these technologies and subsequently take them towards the market.
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