(587bb) Hexane Oil Extraction From Microalgae: Improving Rate and Reducing Hazard

Microalgae show significant large scale potential as feedstock in aquaculture to produce algae oil that can be used to produce biodiesel fuel and other valuable products such omega 3 fatty acids, eicosapentaemoic or EPA (a polyunsaturated fatty acid that tends to inhibit leukemia) and other healthy lipids. Significant research has been done to improve the algae growth and enhance the algae lipids/oil content. Extraction of oil/lipids from microalgae continues to be one of the major challenges in producing biodiesel and valuable healthy products. Oil extraction from microalgae is relatively energy-intensive, time-consuming and costly. Traditionally, hexane is the extraction solvent of choice. However hexane is also a toxic and flammable chemical. It is highly desirable to develop a faster and environmentally safer microalgae oil extraction technique. This paper presents an experimental study of the rate of oil extraction from microalgae and fitting the data to a kinetics model, and the use of a less toxic solvent, heptane, to enhance the oil extraction process and improve the bottom line.

The alternate algae oil extraction solvent selected was heptane, due to its structural similarities to heptane. Though heptane is less toxic than hexane, it is slightly more expensive. In terms of extraction effectiveness, roughly six times as much heptane as hexane is needed to extract the same mass of algae oil. The kinetics model adopted included two constants, K, representing a maximum lipid yield, and τ, a time constant. It was shown that when the volume of solvent and mass of algae were held constant, the value of the time constant for hexane was roughly double that for heptane. In addition, the maximum yield for hexane extractions was roughly 1.6 times that for heptane. These results demonstrate that while heptane extracts lipid material faster initially, the achievable lipid yield is lower for heptane. Use of heptane would require less energy in the extraction process, but more algae would need to be harvested to match hexane production. This is an optimization problem that requires a cost analysis of algae growth and dewatering versus extraction costs.