Enhanced Process for the Extraction and Purification of Oils from Microalgae Using CO2 as a Solute

One of the principal technical and cost barriers to successful commercialization of algal biofuels as an alternative energy source is the inability to extract the useful oil components from the algae in an economical and environmentally sound fashion. Indeed, the DOE announcement for this proposal specifically notes topic areas (5d) regarding methods for extracting oils from microalgae as goal of research and development. The announcement further recognizes the critical barriers that impact cost and performance: oil extraction systems for wet algal biomass and further purification of neutral lipids. Current processing methods for algal oil require large investments in costly and energy intensive centrifuges and distillation equipment using environmentally unfriendly solvents such as hexane due to the difficulty in isolating oil components from residual biomass and water. Alternative strategies are urgently needed to purify the valuable oil components from algae that can be subsequently processed into useful biodiesel. The objective of this Phase I/Phase II project is to implement a novel chemical processing strategy that applies carbon dioxide as a solute to alter the physical properties of lipids including density, viscosity, and solubility such that algal oil is more readily separated from the remaining biomass and water. Our CO2 solute enhanced lipid isolation is fundamentally different from supercritical extraction, which uses CO2 as a solvent and requires much greater volumes of CO2 and high capital costs. During Phase I, we measured the effects of CO2 on the physical properties of oil, water, and algal biomass in a series of laboratory experiments. Significant CO2 solute dissolves primarily in oil as a single phase at elevated pressures to alter the density and viscosity of oil and facilitates the separation of oil from separate phases of algal biomass and water. Therefore, the aim of the proposed Phase II project is to translate this knowledge of physical properties of CO2 solute in oil into a complete chemical process for purifying oil from biomass and water at laboratory scale. During year 1, optimal process operating parameters will be specified for the specific unit operations in order to reduce the water content following algal growth, solubilize CO2 solute in oil, purify oil from biomass and water, then recycle the CO2 and water. The second year of the Phase II project will integrate these individual unit operations into a continuous process and to design an economical process for scale up in Phase III. The Phase III project, if approved, will implement a pilot project at 200-to 2,000-fold higher scales that demonstrates the commercial feasibility of CO2 solute based processing for oil purification from algal biomass and water. Commercial Applications & amp; Other Benefits: The commercial benefits will be a substantial reduction in processing costs for purifying oil from algal biomass. As processing the algal species represents the single highest capital cost component of algal biofuels, methodologies that reduce these costs will have a significant impact towards making algal biofuels including biodiesel and other products economically viable. Given the expanding number of algal growth companies in the US, the implementation of complementary technologies to process the algae to oil and residual biomass represents an equally important goal towards the development of a commercially viable renewal algal biofuels source to replace current fossil fuels.