Effect of the storage condition of microalgae on hydrochar lipids and direct esterification-transesterification of hydrochar lipids for biodiesel production

Abstract

The hydrochar product from the hydrothermal carbonization (HTC) of microalgae contains most of fatty acids (FAs) in the original microalgae. In the hydrochar, FAs exist in both types of bound fatty acids (BFAs) and free fatty acids (FFAs). Besides, when the microalgae paste is stored at the room temperature (25 °C) for one day, there is an increase of total fatty acids (TFAs) and free fatty acids (FFAs) in microalgae. The hydrochar from this microalgae paste was proved to have a higher amount of TFAs and a higher percentage of FFAs/TFAs compared to the ordinary hydrochar (without the additional storage step) in this research. Both of these factors favor for the subsequent acid catalyzed esterification-transesterification reaction of hydrochar lipids. In summary, a process based on a combination of the storage of fresh microalgae, the HTC of microalgae paste, and the direct esterification-transesterification of the hydrochar has been developed for biodiesel production. With the additional storage step of fresh microalgae, the total biodiesel yield has been improved of 19.3% in the optimum condition.

Keywords

• microalgae
• hydrothermal carbonization
• hydrochar
• fatty acid
• esterification
• transesterification