Production of Medium-Chain Fatty Acids from Biorefinery Residue
When lignocellulosic biomass is used for ethanol or biofuel production, the resulting liquid residue (known as stillage) contains large amounts of organic material that may be further transformed into recoverable bioproducts. Lignocellulosic residue contains a high amount of chemical energy, approximately 100,000 mg/L as soluble chemical oxygen demand (sCOD). This amount of chemical energy, comparable to the amount recovered as ethanol or other fuel compounds, is in the form of unreacted polysaccharides and sugars, proteins and other complex plant materials not used by the alcohol-producing microorganisms.
In existing processes, lignocellulosic residue is often digested to produce biogas. Biogas is combusted in a combined heat and power generation process. A portion of the generated heat and power is used for operating facilities, and excess electricity can be sold. Alternatively, biogas can be converted to natural gas and injected into a natural gas pipeline. Given the high sCOD content of stillage, however, alternative uses are possible.
One route to potentially improve the economics of biorefining is to produce valuable co-products, such as medium-chain fatty acids (MCFA), from stillage. MCFAs are used in the production of rubbers, dyes, pharmaceuticals and antimicrobials. They also can be used as precursors for chemicals currently derived from fossil fuels.
UW–Madison researchers led by professors Daniel Noguera and Timothy Donohue have developed a method for converting unreacted chemical components in stillage to valuable medium-chain fatty acids, such as hexanoic and octanoic acids, using a mixture of microbes (e.g., anaerobic microbiome).
Operationally, a portion of the stillage stream is separated and fed to a bioreactor containing the mixture of microbes, which transforms a fraction of the stillage to MCFAs. The other fraction of the stillage can be sent on to the anaerobic digester to generate electricity (similar to existing biorefineries).
- Enables additional product stream
- Improves operational economics
- Does not detract from biogas production
Production of value-added chemicals from stillage
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