Hydrothermal carbonization of microalgae II. Fatty acid, char, and algal nutrient products

Steven M. Heilmann, Lindsey R. Jader, Laurie A. Harned, Michael J. Sadowsky, Frederick J. Schendel, Paul A. Lefebvre, Marc G. von Keitz, Kenneth J. Valentas

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127 Scopus citations


A process for isolation of three products (fatty acids, chars and nutrient-rich aqueous phases) from the hydrothermal carbonization of microalgae is described. Fatty acid products derived from hydrolysis of fatty acid ester groups in the microalgae were obtained in high yield and were found to be principally adsorbed onto the char also created in the process. With the highest lipid-containing microalga investigated, 92% of the fatty acids isolated were obtained by solvent extraction of the char product, with the remaining 8% obtained by extraction of the acidified filtrate. Obtaining the fatty acids principally by a solid-liquid extraction eliminates potential emulsification and phase separation problems commonly encountered in liquid-liquid extractions. The aqueous phase was investigated as a nutrient amendment to algal growth media, and a 20-fold dilution of the concentrate supported algal growth to a level of about half that of the optimal nutrient growth medium. Uses for the extracted char other than as a solid fuel are also discussed. Results of these studies indicate that fatty acids derived from hydrothermal carbonization of microalgae hold great promise for the production of liquid biofuels.

Original languageEnglish (US)
Pages (from-to)3286-3290
Number of pages5
JournalApplied Energy
Issue number10
StatePublished - Oct 2011

Bibliographical note

Funding Information:
Financial assistance was provided by the BioTechnology Institute of the University of Minnesota and the Initiative for Renewable Energy and the Environment (IREE) and is gratefully acknowledged. We thank Mr. Timothy Montgomery for providing artistic support in the creation of the figures. Dr. Jack Richmond is thanked for helpful discussions regarding the NMR analytical method and obtaining the NMR spectra. A gift of high-lipid microalga from Dr. Mark Ferguson of Inspired Fuels was greatly appreciated.


  • Algal oil
  • Char
  • Hydrothermal carbonization
  • Hydrothermolysis


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