Extraction of Algae Oil for Biodiesel Production
There are three well-known methods to extract the oil from oilseeds, and these methods should apply equally well for algae too. These are Expeller or Press and Solvent extraction.
Expression / Expeller Press: When algae is dried, it retains its oil content, which then can be "pressed" out, with an oil press. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil. While more efficient processes are emerging, a simple process is to use a press to extract a large percentage (70-75%) of the oils out of algae.
Hexane Solvent Method: Algae oil can be extracted using chemicals. Benzene and ether have been used, but a popular chemical for solvent extraction is hexane, which is relatively inexpensive. The downside to using solvents for oil extraction is the inherent dangers involved in working with the chemicals. Benzene is classified as a carcinogen. Chemical solvents also present the problem of being an explosion hazard.
Hexane solvent extraction can be used in isolation or it can be used along with the oil press / expeller method. After the oil has been extracted using an expeller, the remaining pulp can be mixed with cyclo hexane to extract the remaining oil content. The oil dissolves in the cyclo hexane, and the pulp is filtered out from the solution. The oil and cyclo hexane are separated by means of distillation. These two stages (cold press & hexane solvent) together will be able to derive more than 95% of the total oil present in the algae.