280
R. Halim
however, are expensive and have low biodegradability. The high temperature requirement for their operation (> 100 °C) can potentially be detrimental to the integrity
of targeted pigments and other valuable components in the microalgal biomass
(e.g. protein) (Desai et al. 2016; Praveenkumar et al. 2015; Rodrigues et al. 2018).
Ionic liquids are classified as either aprotic (which includes imidazolium and pyridine cations) or protic (which includes ethylammonium cations) (Desai et al. 2016;
Praveenkumar et al. 2015; Rodrigues et al. 2018). Rodrigues et al. (2018) found
protic ionic liquids to be more effective than standard sodium phosphate buffer in
extracting phycobiliprotein from Spirulina platensis (Table 12.5). They attributed
the high extraction efficiency to the liquid’s high diffusional power and strong interaction with the pigment molecules. Desai et al. (2016) used ionic liquids as an agent
to permeabilise Haematoccous pluvialis cell wall before subjecting the biomass to
ethyl acetate extraction for astaxanthin recovery (Table 12.2).
12.3.4 Supercritical Carbon Dioxide (SCCO 2 ) Extraction
When carbon dioxide is subjected to temperature and pressure beyond their critical values (T c at 31.1 °C and P c at 72.9 atm), it is transformed into a supercritical fluid that exhibits physical properties intermediate between a liquid and a gas
(Cuellar-Bermudez et al. 2015; Halim et al. 2011, 2012a; Rammuni et al. 2019; Reyes
et al. 2014; Soh and Zimmerman 2011). Supercritical carbon dioxide or SCCO 2 is a
highly effective extraction solvent because of its transitional properties, such as high
diffusivity and adjustable solvating power.
SCCO 2 has a high diffusivity which enables it to rapidly penetrate cellular matrix
and complete extraction within a shorter timeframe. The fluid’s solvating power is a
direct function of its density and can thus be tailored to the targeted pigment through
pressure and temperature adjustments (Cuellar-Bermudez et al. 2015; Halim et al.
2011, 2012a; Rammuni et al. 2019; Reyes et al. 2014; Soh and Zimmerman 2011).
In addition to being a powerful extraction solvent, SCCO 2 is non-toxic, produces a
solvent-free pigment extract (no additional solvent recovery step is needed—refer
to operational description below) and operates at a moderate temperature range
which minimises degradation of thermally sensitive pigments (Cuellar-Bermudez
et al. 2015; Halim et al. 2011, 2012a; Rammuni et al. 2019; Reyes et al. 2014; Soh
and Zimmerman 2011).
The main disadvantages of SCCO 2 extraction are the high capital cost of its infrastructure and the high energy cost associated with biomass drying step prior to the
extraction (Cuellar-Bermudez et al. 2015; Halim et al. 2011, 2012a; Rammuni et al.
2019; Reyes et al. 2014; Soh and Zimmerman 2011). Since SCCO 2 is generally
assumed to have a limited capacity to interact with solutes in wet biomass, lipid
extraction using the fluid has almost always been carried out on dried (or freeze
dried) biomass. This introduces the need for an energy-intensive dehydration step
before the extraction and significantly inflates the operational energy requirement
of the extraction process. In their study investigating SCCO 2 extraction from wet
R. Halim
however, are expensive and have low biodegradability. The high temperature requirement for their operation (> 100 °C) can potentially be detrimental to the integrity
of targeted pigments and other valuable components in the microalgal biomass
(e.g. protein) (Desai et al. 2016; Praveenkumar et al. 2015; Rodrigues et al. 2018).
Ionic liquids are classified as either aprotic (which includes imidazolium and pyridine cations) or protic (which includes ethylammonium cations) (Desai et al. 2016;
Praveenkumar et al. 2015; Rodrigues et al. 2018). Rodrigues et al. (2018) found
protic ionic liquids to be more effective than standard sodium phosphate buffer in
extracting phycobiliprotein from Spirulina platensis (Table 12.5). They attributed
the high extraction efficiency to the liquid’s high diffusional power and strong interaction with the pigment molecules. Desai et al. (2016) used ionic liquids as an agent
to permeabilise Haematoccous pluvialis cell wall before subjecting the biomass to
ethyl acetate extraction for astaxanthin recovery (Table 12.2).
12.3.4 Supercritical Carbon Dioxide (SCCO 2 ) Extraction
When carbon dioxide is subjected to temperature and pressure beyond their critical values (T c at 31.1 °C and P c at 72.9 atm), it is transformed into a supercritical fluid that exhibits physical properties intermediate between a liquid and a gas
(Cuellar-Bermudez et al. 2015; Halim et al. 2011, 2012a; Rammuni et al. 2019; Reyes
et al. 2014; Soh and Zimmerman 2011). Supercritical carbon dioxide or SCCO 2 is a
highly effective extraction solvent because of its transitional properties, such as high
diffusivity and adjustable solvating power.
SCCO 2 has a high diffusivity which enables it to rapidly penetrate cellular matrix
and complete extraction within a shorter timeframe. The fluid’s solvating power is a
direct function of its density and can thus be tailored to the targeted pigment through
pressure and temperature adjustments (Cuellar-Bermudez et al. 2015; Halim et al.
2011, 2012a; Rammuni et al. 2019; Reyes et al. 2014; Soh and Zimmerman 2011).
In addition to being a powerful extraction solvent, SCCO 2 is non-toxic, produces a
solvent-free pigment extract (no additional solvent recovery step is needed—refer
to operational description below) and operates at a moderate temperature range
which minimises degradation of thermally sensitive pigments (Cuellar-Bermudez
et al. 2015; Halim et al. 2011, 2012a; Rammuni et al. 2019; Reyes et al. 2014; Soh
and Zimmerman 2011).
The main disadvantages of SCCO 2 extraction are the high capital cost of its infrastructure and the high energy cost associated with biomass drying step prior to the
extraction (Cuellar-Bermudez et al. 2015; Halim et al. 2011, 2012a; Rammuni et al.
2019; Reyes et al. 2014; Soh and Zimmerman 2011). Since SCCO 2 is generally
assumed to have a limited capacity to interact with solutes in wet biomass, lipid
extraction using the fluid has almost always been carried out on dried (or freeze
dried) biomass. This introduces the need for an energy-intensive dehydration step
before the extraction and significantly inflates the operational energy requirement
of the extraction process. In their study investigating SCCO 2 extraction from wet