Abstract
The purpose of this study is to enhance the efficiency of lipid extraction from Chlorella vulgaris for biodiesel precursor by supercritical CO2 (scCO2) pretreatment, CO2-expaneded alcohol extraction and optimization of extraction. Supercritical CO2 pretreatment was used to disrupt the cell wall of microalgae to enhance the extracted lipid yield; however, scCO2 pretreatment was ineffective when it was operated at a temperature range of 313 to 353 K and at a high pressure of 20.3 MPa. The CO2-expanded methanol (CXM) was a superior solvent to methanol, ethanol, pressurized methanol and ethanol, and CO2-expanded ethanol for lipid extraction from the microalga Chlorella vulgaris (a total lipid content of 20.7% of the dried biomass was determined by Soxhlet extraction with methanol at 373 K for 96 h) in continuous mode. The effects of operation variables, such as temperature, pressure and CO2 flow rate, on extraction performance were examined using response surface and contour plot methodologies. The optimal operating conditions were a pressure of 5.5 MPa, a temperature of 358 K, a methanol flow rate of 1 mL/min and a CO2 flow rate of 3.0 mL/min, providing an extracted lipid yield of 84.8 wt% over an extraction period of 30 min. Compared with PM, CXM was safer and more energy efficient for lipid extraction from Chlorella vulgaris.