Oil Extraction

Oil extraction from algae is a hotly debated topic currently because this process is one of the more costly processes which can determine the sustainability of algae-based biodiesel.

In terms of the concept, the idea is quite simple: Harvest the algae from its growth medium (using an appropriate separation process), and extract the oil out of it. Extraction can be broadly categorized into two methods:

1. Mechanical methods

The mechanical methods are further classified into:

• Expression/Expeller press
• Ultrasonic-assisted extraction

1. Chemical methods

The chemical methods are further classified into:

• Hexane Solvent Method
• Soxhlet extraction
• Supercritical fluid Extraction 

Each of these methods has drawbacks: 

1. The mechanical press generally requires drying the algae, which is energy intensive
2. The use of chemical solvents present safety and health issues
3. Supercritical extraction requires high pressure equipment that is both expensive and energy intensive. 

Many manufacturers of algae oil use a combination of mechanical pressing and chemical solvents in extracting oil.

source :

http://www.oilgae.com/algae/oil/extract/extract.html