Cavitation Enhanced Subcritical Water Extraction of Wet Algae for Phytol and Lipids Recovery

The full utilization of algae as a source for fuels and products requires process optimization of many key steps and the economical recovery of useful materials. A potentially high value chemical produced by photosynthetic algae is phytol which is formed during the hydrolysis of Chlorophyll A. It is used as a pharmaceutical, a fragrance, a component in surfactants, and biodegradable plastics. It can also be used directly as a fuel with a cetane number of 42, similar to diesel. Phytol has been recovered when algae cells are lysed in water by us and others. It has been measured in concentrations of 30%-60% of the total lipids recovered from several species of algae, and therefore would increase potential fuel production. HOW THIS PROBLEM IS BEING ADDRESSED: In this proposed Phase I SBIR project, we will investigate the feasibility of using hydrodynamic cavitation in the subcritical fluid not only to enhance extraction efficiency and reduce the operating temperatures and pressures, but to also recover phytol, a potentially valuable compound. The algae cells will be lysed by the rapid pressure fluctuations and fluid shear produced by cavitation. The collapse of the bubbles generated during cavitation will create transient regions of high temperature and pressures where the solvent properties of the subcritical water will be non-polar without the need for higher operating temperatures in the entire reactor. We will investigate the use of subcritical water to produce high-value compounds such as phytol. The concept will then be applied to pilot scale systems and scaled up. WHAT IS TO BE DONE IN PHASE I: In Phase I, we will design and construct a subcritical water reactor with specially designed rotating blades capable of generating cavitation in pressurized water at relatively low pressures and temperatures to demonstrate efficient extraction of wet algae paste. Cavitating bubbles will form in the fluid on the blades, expand explosively, and then collapse abruptly creating regions of high temperature and pressure within the fluid near the surface of the algae cells. These blades will be designed to generate cavitation efficiently with low energy input. Thus, using cavitation to enhance subcritical water extraction will be more economical than increasing the temperature and pressure of the entire reactor. The reactor and process design will be helped with numerical simulations of the reactor flow field and of bubble / particle interactions in the wet algae paste. COMMERCIAL APPLICATION AND OTHER BENEFITS: Improving the energy efficiency of subcritical water extraction of biomass with high water content will decrease the production costs for renewable chemicals and fuels produced from algae. This will reduce the barriers to bringing this technology to commercial scale. The extraction technology developed in this SBIR would also have applications in other fields such as methane production by anaerobic digestion, natural product recovery, and chemical production.