Surfactant-Enhanced dewatering of algae with supercritical CO2

• Supercritical CO 2 dewaters algae at sub-boiling temperatures at high energy efficiency. • Inexpensive surfactants added at < 1 % of dry biomass increase water removal by an additional 50% by stabilizing water in the CO 2 phase. • The spent CO 2 can be partially expanded after each cycle to drop out its carried water and can then be recompressed for reuse. Supercritical CO 2 (sCO 2 ) dewaters wet algal suspensions at sub-boiling temperatures at a much higher energy efficiency than that provided by a spray dryer. The process is sensitive to temperature, but relatively less so to pressure. Water removal is threefold higher than the value expected from solubility considerations alone, which implies that the water is both dissolved and emulsified in the sCO 2 phase. A key finding is that inexpensive surfactants at < 1 % of dry biomass increase water removal by up to an additional 50 % by stabilizing the water emulsions in the sCO 2 phase. Extraction of a unit of water from twenty to ninety percent solids requires about eighty units of CO 2 . The spent CO 2 can be partially expanded after each cycle to drop out its carried water and then recompressed for reuse. In addition to contributing to carbon reuse, the sCO 2 process uses much less energy and has lower emissions as compared to spray drying. It is also expected to apply to other types of biomass. Overall, sCO 2 dewatering of algae is a less energy intensive approach with a lower environmental impact as compared to conventional spray drying.