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.
Keywords: Acidic hydrothermal treatment; Chlorella vulgaris; Microalgal biodiesel; Surfactant partitioning; Wet oil extraction.