Algae oils for biofuels: Chemistry, physiology, and production

Microalgae are attractive as sources of renewable biofuels not only because of their high lipid and/or sugar content and high areal productivity, but also because they can be grown on land using saline water and on land that is not suitable for agriculture. Algae-based biofuels are also expected to reduce CO2 emissions. The great diversity of microalgae provides opportunities for the selection of species and strains with particular fatty acid profiles with advantages for the production of biofuel with specific properties. In the longer term, microalgae present the option of genetic modification to enhance lipid productivity and/or modify the fatty acid profile. The total oil and fat content of microalgae ranges from about 1% to 70% of ash-free dry weight. Microalgae lipids are generally esters of glycerol and fatty acids with a chain-length of C14 to C22; they may be saturated or unsaturated. Biodiesel is prepared from algal lipids by esterifying free fatty acids or transesterifying triacylglycerol fatty acids by reacting them with an alcohol, usually methanol or ethanol; other alcohols, such as propanol, butanol, isopropanol, tert-butanol, branched alcohols, and octanol, can be used