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:
Mechanical methods
The mechanical methods are further classified into:
Expression/Expeller press
Ultrasonic-assisted extraction
Chemical methods
The chemical methods are further classified into:
Hexane Solvent Method
Soxhlet extraction
Supercritical fluid Extraction
Each of these methods has drawbacks:
The mechanical press generally requires drying the algae, which is energy intensive
The use of chemical solvents present safety and health issues
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.
Apart from these, there are some other methods which are not well-known. This includes the following:
Enzymatic extraction - Enzymatic extraction uses enzymes to degrade the cell walls with water acting as the solvent, this makes fractionation of the oil much easier. The costs of this extraction process are estimated to be much greater than hexane extraction.
Osmotic shock - Osmotic Shock is a sudden reduction in osmotic pressure, this can cause cells in a solution to rupture. Osmotic shock is sometimes used to release cellular components, such as oil.
CHALLENGES IN OIL EXTRACTION FROM ALGAE:
Microscopic algae suspended in water are virtually indestructible
Cell wall has a high elasticity modulus
Even when free water has been removed, wet biomass retains sufficient interstitial water to act as lubricant
Rupture of cell wall through mechanical friction and steam explosion is only possible when dry
BREAKTHROUGHS IN OIL EXTRACTION FROM ALGAE:
a.Single-Step Extraction:
The OriginOil’s algae Single-Step oil extraction process is simpler and more efficient than current systems, without requiring chemicals or significant capital expenditure for heavy machinery.
- See more at: http://www.oilgae.com/algae/oil/extract/extract.html#sthash.Swwle5fM.dpuf