Behavior of Surfactants in Oil Extraction by Surfactant-Assisted Acidic Hydrothermal Process from Chlorella vulgaris

The feasibility of surfactants for enhancement of extraction efficiencies in wet oil extraction through an acidic hydrothermal process was evaluated. Three different types of surfactants were tested: anionic (SDBS and SDS), cationic (CTAB and MBC), and non-ionic (IGEPAL CA-210 and Tween 60). The total fatty acid content of Chlorella vulgaris was 291.0 mg/g cell. Under the no-surfactant condition, the oil-extraction yield of the acidic hydrothermal extraction was 75.5%. The addition of SDBS and MBC at the 0.4% concentration showed enhanced oil-extraction performance, 85.4 and 85.7% yields, respectively. CTAB and Tween 60 showed low extraction yields, less than 43.0%. SDS and IGEPAL CA-210 showed high oil-extraction yields, higher, in fact, than the initial fatty acid content, due to surfactant partitioning into microalgal oil. With increasing surfactant concentration, the oil-extraction yields of CTAB decreased, those of IGEPAL CA-210 gradually increased, and those of SDBS increased and then decreased again. The best performance, an oil-extraction yield of 95.6%, was observed under the 0.2% SDBS, 120 °C, 1 h condition. Although IGEPAL CA-210 showed the high net oil-extraction yield of 98.3% at the 0.6% surfactant concentration, 61.2% of surfactant was partitioned into oil. Graphical abstract