Supercritical Carbon Dioxide Extraction of Algal Lipids for the Biodiesel Production

Abstract

Biodiesel production from algae is a promising technique. Microalgae are able to accumulate fatty acids up to 50% of their dry weight when submitted to nitrogen defaults. They are then expected to be a new potential renewable source of biodiesel. Efficiently extracting algae oil from microalgae plays an important role in the development of microalgae biofuel. Algae bio-oil is traditionally obtained using thermal liquefaction or pyrolysis, and they may be obtained after an extraction using organic solvents as hexane. Such methods have some drawbacks like inherent toxicity, poor selectivity, difficult separation of the contaminants as well as solvents from the desired product, energy consuming and pollutant. Supercritical carbon dioxide extraction is a promising green technology that can potentially displace the use of traditional organic solvents for lipid extraction. The supercritical fluid extraction has several advantages when compared to traditional extraction method (hexane, petroleum ether, chloroform/ethanol) used for obtaining lipids from algae, in which supercritical extraction provide higher selectivities, shorter extraction time and do not use toxic organic solvents. This study examines the performace of supercritical carbon dioxide extraction of lipids from Botryococcus braunii for biodiesel production. The experiments were conducted at temperatures of 50 – 80 °C, pressure from 200 to 250 bar. The evolution of the process was followed by gas chromatography, determining the concentration of the fatty acids at different reaction times. For supercritical carbon dioxide extraction, lipid yield was found to decrease with temperature and to increase with pressure. Relatively high recovery of polyunsaturated fatty acids and essential fatty acids in supercritical fluid extracted algal lipids were observed. The optimum operating conditions for a supercritical extraction were pressure between 220-250 bar and temperature of 50 °C. This research is part of a wider experimental project involving the supercritical carbon dioxide extraction of lipids from microalgae to contribute to the development of algal lipids into a variable energy source by optimizing lipid extraction techniques for efficiency, sustainability, decreased hazard, and selectivity, focusing on the use of supercritical fluids as alternative green solvents.