13 Process Intensification Aspects of Extraction …
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13.3 Extraction Processes for Pigment Recovery
13.3.1 Organic Solvent Extraction
The most common method used for recovery of pigments is organic solvent extraction process which employs an organic solvent to extract pigments from disrupted
microalgae cells. Microalgae cells are firstly disrupted via homogenisation, ball
milling, colloidal milling or sonication processes and are further subjected to organic
solvent extraction. Using cell disruption is a very important step in deciding overall
recovery. In a study performed by Simon and Helliwell on chlorophyll pigment
extraction, only 25% pigment recovery was reported by solvent extraction performed
without cell disruption (Simon and Helliwell 1998). Parameters like time of extraction, type and loading of organic solvent, time span of microalgae storage and cycles
of extraction also play a major role in optimisation of this process. Organic solvents
generally used are ethanol, methanol, acetone and dimethyl formamide (DMF) with
ethanol and methanol typically giving better results as compared to acetone, while
DMF is reported to be effective but its toxic nature limits the further usage. There
have been some modifications in the overall processing of microalgae reported to
enhance the yield of pigments. For example, boiling of organic solvent at its boiling
point for a time period of 3 to 5 min has been reported to result in increased pigment
yield after 24 h extraction process (Sartory and Grobbelaar 1984). It is also reported
that freezing microalgae at lower temperatures after filtration helps in cell disruption
with further increased yields of pigments from solvent extraction process (Schumann et al. 2005). High solvent consumption, selectivity and extraction efficiency
are, however, the major limitations of conventional solvent extraction process.
13.3.2 Supercritical Fluid Extraction (SFE)
Supercritical fluids have same densities as fluids but their viscosity is similar to
gas which helps them in diffusing into cells under higher pressures with enhanced
mass transfer rates and selective extraction of desired products (Guedes et al. 2013).
Carbon dioxide is one of the most preferred solvents as it can attain supercritical
state easily and has advantages like high purity and low flammability, toxicity and
cost. Supercritical carbon dioxide results in non-polar environment and its polarity
can be varied using co-solvents like ethanol. Extraction efficiency of SFE is typically
reported to increase up to an optimal CO 2 pressure and temperature values and can
vary based on combined effect of pressure and temperature under different conditions.
In one of the study, pressure and temperature were varied in range of 40–60 °C
and 100–500 bar, respectively and the highest yield of 1.51 μg/mg pigments from
Synechococcus sp. was reported to be obtained at 50 °C and 200 bar pressure reported
as optimum with further variation resulting in decreased yield (Macías-Sánchez et al.
2007). Another study performed by Macias-Sanchez et al. (2010) on Scenedesmus
313
13.3 Extraction Processes for Pigment Recovery
13.3.1 Organic Solvent Extraction
The most common method used for recovery of pigments is organic solvent extraction process which employs an organic solvent to extract pigments from disrupted
microalgae cells. Microalgae cells are firstly disrupted via homogenisation, ball
milling, colloidal milling or sonication processes and are further subjected to organic
solvent extraction. Using cell disruption is a very important step in deciding overall
recovery. In a study performed by Simon and Helliwell on chlorophyll pigment
extraction, only 25% pigment recovery was reported by solvent extraction performed
without cell disruption (Simon and Helliwell 1998). Parameters like time of extraction, type and loading of organic solvent, time span of microalgae storage and cycles
of extraction also play a major role in optimisation of this process. Organic solvents
generally used are ethanol, methanol, acetone and dimethyl formamide (DMF) with
ethanol and methanol typically giving better results as compared to acetone, while
DMF is reported to be effective but its toxic nature limits the further usage. There
have been some modifications in the overall processing of microalgae reported to
enhance the yield of pigments. For example, boiling of organic solvent at its boiling
point for a time period of 3 to 5 min has been reported to result in increased pigment
yield after 24 h extraction process (Sartory and Grobbelaar 1984). It is also reported
that freezing microalgae at lower temperatures after filtration helps in cell disruption
with further increased yields of pigments from solvent extraction process (Schumann et al. 2005). High solvent consumption, selectivity and extraction efficiency
are, however, the major limitations of conventional solvent extraction process.
13.3.2 Supercritical Fluid Extraction (SFE)
Supercritical fluids have same densities as fluids but their viscosity is similar to
gas which helps them in diffusing into cells under higher pressures with enhanced
mass transfer rates and selective extraction of desired products (Guedes et al. 2013).
Carbon dioxide is one of the most preferred solvents as it can attain supercritical
state easily and has advantages like high purity and low flammability, toxicity and
cost. Supercritical carbon dioxide results in non-polar environment and its polarity
can be varied using co-solvents like ethanol. Extraction efficiency of SFE is typically
reported to increase up to an optimal CO 2 pressure and temperature values and can
vary based on combined effect of pressure and temperature under different conditions.
In one of the study, pressure and temperature were varied in range of 40–60 °C
and 100–500 bar, respectively and the highest yield of 1.51 μg/mg pigments from
Synechococcus sp. was reported to be obtained at 50 °C and 200 bar pressure reported
as optimum with further variation resulting in decreased yield (Macías-Sánchez et al.
2007). Another study performed by Macias-Sanchez et al. (2010) on Scenedesmus