Fatty acids for nutraceuticals and biofuels from hydrothermal carbonization of microalgae

We used hydrothermal carbonization (HTC) of wet algal biomass to facilitate extraction of algal lipids that have value for both liquid biofuels and dietary supplements (i.e., nutraceuticals). HTC of the wet algal slurry produced a solid hydrochar that retained more than 85% of the fatty acids in the original biomass and more than 75% of the valuable omega-3 fatty acid eicosapentaenoic acid (EPA). The mass yield of hydrochar was a linear function of the logarithm of the reaction ordinate, which is a measure of the severity of the carbonization conditions. The retained fatty acids could be readily extracted using ethanol, a renewable and food-grade solvent. A total fatty acid recovery of 74% was achieved through this combination of HTC and ethanol extraction. Thus, we herein demonstrate a process for removing fatty-acid-containing lipids from wet algae using only water and a non-petroleum-derived solvent. The recovered lipids include both those suitable for making biodiesel or green diesel and those suitable for the human diet.