Microalgae Cultivation in Bioreactors for CO2 Mitigation from Power Plants Flue Gas and Fuel Production by Supercritical CO2 Extraction
Maoqi Feng, Div. of Chemistry and Chemical Engineering, Southwest Research Institute, 6220 Culebra Rd, San Antonio, TX 78238
Microalgae can consume CO2 gas as a carbon source for growth. After the flue gas from power plants is recovered, CO2 is separated. Part of the CO2 can be used as a carbon source for microalgae cultivation. Cultivation of microalgae by photosynthesis in bioreactors utilizes CO2 from power plant flue gas and solar energy as the energy source to produce microalgae, which can be used for biofuel production. Optimizing the culture conditions can increase CO2 fixation rates. Biofuels from microalgae are similar to vegetable oils, and can thus be considered as potential substitute for fossil oil. There are several different ways for biofuel production from microalgae: supercritical CO2 extraction, organic solvents extraction, pyrolysis, gasification, liquefaction, and anaerobic fermentation, etc. The utilization of scCO2 as solvent for biofuel extraction appears more economic than organic solvent extraction, as the captured CO2 from power plant flue gas can be used for this application. The process is solvent-free, thus avoiding the production of waste solvents. Fuel production from microalgae by scCO2 extraction is more energy efficient than direct thermochemical liquefaction, which operates at high temperature (300 °C –350 °C) and under catalyst, e.g., sodium carbonate. However, scCO2 extraction can also be combined with liquefaction to make the whole process more efficient.