Lipid Identification and Extraction Techniques - Biotechnological Applications of Microalgae - page 93

Dried algae biomass

Oil extraction methods

Mechanical extraction Chemical extraction

Solvent Method

Oil expeller

Hydraulic press Supercritical fluid extraction

FIGURE 7.1 Classification of oil extraction methods used for dried algae biomass.

7.3.1.1 Oil Expeller
The first successful, continuously operating mechanical expeller was invented and
patented by Anderson in the year 1900. An oil expeller is also called a screw press.
The screw press is well suited for feedstocks having more than 30% oil content. The
working principle of this machine is introducing pressure for crushing and break-
ing the cells, followed by squeezing out the algal oil. An oil press is the simplest
method used for oil extraction from algae biomass (Popoola and Yangomodou,
2006; Demirbas, 2009). The oil cake obtained from a screw press may contain some
amount of residual oil (4% to 5% by weight). The oil extraction efficiency improves
with applied pressure in a particular range, but too much pressure leads to less lipid
recovery, more heat generation, and choking problems. Increased heat produced due
to excessive pressure applied inside the screw press leads to darkening of the oil
and a low-quality oil cake. The major drawbacks of this method are the high energy
consumption, high maintenance cost with low capacities, labor intensiveness, long
extraction time and less efficiency than other methods.

7.3.2 C heMiCal e xtraCtion

7.3.2.1 Solvent Extraction
The process of extracting oil from oil-containing materials using a suitable solvent is
called solvent extraction . It is well suited for lipid recovery from materials with low
oil content, and it produces oil cake with low residual oil content (<1% by weight)
(Erickson et al., 1984; Hamm and Hamilton, 2000). Algae cell walls are made of
multiple layers and they are more recalcitrant than those of other microorganisms
(Sander and Murthy, 2009). Some species having an additional trilaminar sheath
(TLS) containing an algaenan component are resistant to degradation (Allard et al.,
2002; Versteegh and Blokker, 2004).