Supercritical Fluid Extraction
4.6 Economic importance and industrial challenges
Table 4.3 Examples of supercritical fluid extraction of agricultural wastes
Raw material Application Process Reference
Sunflower leaves Bioactive compounds 10–50 MPa and 308–333 K and different cosolvents
Casaset al., 2005, 2007, 2008, 2009, 2010 Sunflower leaves Allelopathy 10–50 MPa and 308–333 K El Marsniet al., 2011
Grape pomace Resveratrol 10–40 MPa and 308–333 K
with ethanol as cosolvent
Casaset al., 2010 Mango leaves Phenolic
compounds-Antioxidants
Carbon dioxide at 10–40 MPa and 313–333 K and subcritical water at 10 MPa and 353 K
Fernandez-Ponceet al., 2011
Eucalyptus leaves Antioxidants 20 MPA and 323 K Fadel, 1999
Olive leaves Tocopherols 25–45 MPa and 313–333 K Daukˇsaset al., 2002 Tomato paste waste Pigments 20–30 MPa and 308–338 K Baysalet al., 2000 Red grape pomace Anthocyanin 10–50 MPa and 313–333 K
with methanol as cosolvent
Mantellet al., 2003
functions as diesel oil while having the added benefit of reduced particulate, CO2, and hydrocarbon emissions (Miao and Wu, 2006; Xuet al., 2006; Chisti, 2007). The content in an algal oil can vary from 15 to 75% depending on the variety. The possibility of developing an extensive cultivation of the raw material means that production per hectare is 10 to 20 times higher than that of palm oil (the plant that represents the highest oil production per hectare). Likewise, microalgae grow extremely rapidly, doubling in biomass every 24 hours, and the oil produced by microalgae does not compromise food derived from seed production.
Supercritical fluid technology provides interesting alternatives for the extraction of substances from microalgae, as these are efficient and selective methods. The application of this extraction technique with supercritical carbon dioxide has been widely studied in recent years due to the clear advantages of carbon dioxide as a solvent—advantages that include low toxicity, low cost, and ease of separation of the extracted product (Merceret al. 2011).
Numerous studies have been undertaken on the supercritical fluid extraction of wide varieties of com-pounds from different microalgae and these are summarized in Table 4.4. Hydrocarbons, carotenoids, lipids, fatty acids, and bioactive compounds can all be obtained with high extraction yields from microalgae using this technique. In many cases, it is necessary to add a small amount of modifier to the carbon dioxide to increase the extraction yields. Methanol is very efficient in removing large quantities of compounds in extraction processes but it is toxic to humans and, as a result, ethanol is usually selected as the cosolvent.
Table 4.4 Examples of supercritical fluid extraction of microalga
Varieties Application Process Reference
Botryococcus braunii Hydrocarbons 313 K and pressure up to 30 MPa
Palavraet al., 2011 Chlorella vulgaris Carotenoids 313 K and 35 MPa Palavraet al., 2011 Chlorella sp. Biodiesel production 15–30 MPa and
313–333 K with hexane/methanol as cosolvent
Charet al., 2011
Scenedesmus dimorphus
Lipids for biodiesel production
16–48 MPa and 323–373 K
Soh and Zimmerman, 2011
Schizochytrium limacinum
Lipid—DHA 35 MPa and 313 K with
ethanol as cosolvent
Tanget al., 2011 Chlorococcum sp. Oil for biodiesel
production
10–50 MPa and 333–353 K
Halimet al., 2011 Chlorella vulgaris Active compounds 30 MPa and 323 K and
H2O/ethanol as cosolvent
Wanget al., 2010
Nannochloropsis oculata
Bioactive compounds SFE and anti-solvent purification
Liauet al., 2010 Scenedesmus
almeriensis
Lutein 20–60 MPa and
305–333 K
Mac´ıas-S´anchez et al., 2010 Crypthecoodinium
cohnii
Lipids/PUFAs 20–30 MPa and
313–323 K
Coutoet al., 2010 Chlorcoccum
littorale
Carotenoids 33 K and 30 MPa—ethanol
as cosolvent
Otaet al. 2009
Cholrella vulgaris Pigments 50 MPa and 353 K Kitadaet al., 2009
Dunaniella salina Carotenoids and chlorophyll
10–50 MPa and 313–333 K
Mac´ıas-S´anchez et al., 2009b Various microalgae
and cyanobacterial species
Phenolic compounds Combinations of solid-phase/supercritical-fluid extraction
Klejduset al., 2009
Haematococcus pluvialis
Astaxanthin 343 K and 40 MPa with vegetable oil as cosolvent
Krichnavaruket al., 2008
Various microalgae Carotenoids and chlorophyll
20–50 MPa and 313–333K with ethanol as cosolvent
Mac´ıas-S´anchez et al., 2008 Synechococcus sp. Carotenoids and
chlorophylls
10–50 MPa and 313–333 K
Mac´ıas-S´anchez et al., 2008 Spirulina platensis Vitamin E 8–36 MPa and 300–356 K
with ethanol as cosolvent
Mendiolaet al., 2008 Spirulina platensis Compounds with
antioxidant and antimicrobial activities
22–32 MPa and 328 K with 10% of ethanol
Mendiolaet al., 2007
Chaetoceros muelleri Compounds with antimicrobial activity
25 MPa and 333 K with ethanol as cosolvent
Mendiolaet al., 2007 Chlorella vulgaris Carotenoids and fatty
acids
30 MPa and 313 K Gouveiaet al., 2007
Table 4.4 (continued)
Varieties Application Process Reference
Schizochytrium sp. Lipids—PUFAs Experimental design and mathematical modeling
Zinnaiet al., 2006
Asthrospira maxima Lipids—GLA 323–333 K and
25–35 MPa with ethanol as cosolvent
Mendeset al., 2006
Haematococcus pluvialis
Astaxanthin and other carotenoids
20–30 MPa and 313–333 K with 10%
ethanol as cosolvent
Nobreet al., 2006
Spirulina platensis Lipids—PUFAs 25–70 MPa and 313–328 K
Andrichet al., 2006 Nannochloropsis sp. Bioactive
compounds—PUFAs
40–70 MPa and 313–328 K
Andrichet al., 2005
Synechococcus sp. Carotenoids 10–50 MPa and
313–333 K
Monteroet al., 2005 Nannochlorpsis
gaditana
Carotenoids and chlorophylls
10–50 MPa and 313–333 K
Mac´ıas-Sanchez et al., 2005 Spirulina platensis Antioxidant compounds 22 MPa and 238 K with
10% ethanol as cosolvent
Mendiolaet al., 2005 Various microalga Compounds with
pharmaceutical importance
12.5–30 MPa and 313–333 K
Mendeset al., 2003
Hematococcus pluvialis and Spirulina maxima
Astaxantine and phycocyanine
30 MPa and 333 K with ethanol as cosolvent
Valderramaet al., 2003
Cholrella vulgaris Carotenoids and other lipids
35 MPA and 313–328 K Mendeset al., 1995
because the materials are processed at moderate temperatures so that their properties are not altered.
In the extraction of flavorings and fragrances, samples can undergo hydrolysis when subjected to distillation with steam, whereas the organoleptic properties are virtually unchanged when samples are processed by SFE. Similarly, Wagner and Eggers (1996) compared the refinement of oils by classical methods with those obtained by supercritical extraction and concluded that SFE allows the omission of several refinement steps after extraction with carbon dioxide, thus reducing the consumption of alkali and minimizing the loss of neutral lipids.
• There is no need for the separation of the solvent from the extract, a factor that reduces costs since the SFE is completely removed into the separator.
• Supercritical processes allow environmental problems to be solved, such as the reduction of emissions of volatile organic compounds and the replacement of conventional halogenated solvents used in wool, paints and metal, and textile drying and cleaning.
• Supercritical technology enables the production of various products from which it is difficult to remove traditional solvents (e.g. extracts of ginger, pepper and paprika) and other completely new products, such as so-called drug-distribution systems, a recent application in the pharmaceutical industry.
• The rapid rate of SFE processes in comparison to classical separations makes operation times far lower, a factor that significantly decreases staff costs. This is due to two factors: the SCF penetrates the solid
matrix more rapidly than liquid solvents and, secondly, a concentration stage is not required after the extraction.
In addition to the advantages outlined earlier, other— mainly economic—factors have impeded the rapid dissemination of supercritical technology. The systems operate at high pressures and this requires high investment costs for equipment. Currently, supercritical processes compete with traditional extraction processes when they are applied to high value-added products (polyunsaturated fatty acids, essential oils, vanillin extracts, etc.) or when large volumes of materials are processed, for example for coffee and tea, hops, the manufacture of paint, and the treatment of waste, among others. However, the increasingly strict regulations in relation to effects on the ozone layer, the discharge of volatile organic compounds, and waste concentrations in the final product for the protection of consumers and the environment, facilitate the development of supercritical extraction and fractionation processes, thus making them more competitive.