1. Technical Overview 

Carbon dioxide supercritical fluid extraction (CO2 SCFE) is free of the defects inherent in the methods otherwise employed to extract nutrients from algae – solvent extraction and pyrolysis. These leave behind solvent residues in the extract while also causing its thermal degradation [1]. 

Figure 1: Spirulina tablets
Image credits: Perdita at English Wikipedia 

Algae are a whole range of aquatic organisms that produce food by absorbing sunlight [2]. They can be multicellular or unicellular, but they inhale carbon dioxide, exhale oxygen, and contain essential vitamins, minerals, and nutrients [3]. Commonly known algae include kelp, phytoplankton, algal blooms, and pond scum [2]. 

Pressure is the most important parameter during CO2 SCFE of algae. Generally, yields rise and extraction time drops with pressures climbing up. The effect of temperature on yield depends on pressure. Pre-treatments such as centrifugation, drying, and crushing (in that order) provide better yields [4]. 

Carotenoids: Solvent extraction of carotenoids from seaweeds and microalgae is prone to limitations such as impurity, inefficient yields, lengthy durations, and excessive solvent consumption. 

Efficiency of carotenoid extraction rises when the pressure and temperature of carbon dioxide is increased in the CO2 SCFE process [5]. For better recovery of β-carotene, lutein, astaxanthin, and zeaxanthin, co-solvents such as ethanol, vegetable oil, and acetone are often used. Crushed algae yield more carotenoids and lipids via CO2 SCFE than whole ones [6]. 

Antioxidants: Lutein, asthaxanthin, and fatty serve as valuable antioxidants for the cosmetic and neutraceutical industry. CO2 SCFE on the microalgae Haematococcus pluvialis is able to recover considerable fractions of astaxanthin, lutein, and fatty acids [7].  

Fatty Acids: Extraction of fatty acids from microalgae is a part of the biodiesel production process. CO2 SCFE for separating fatty acids from algae offers greater selectivity and shorter process durations. Pyrolysis or thermal liquefaction followed by solvent (hexane) extraction is the conventional segregation method. Not selective in separating fatty acids, the method presents issues when separating the extract from the solvent. Besides, it is polluting, toxic, and energy intensive [1]. 

Sterols: CO2 SCFE offers an effective and eco-friendly way to extract phytosterols that are free of solvents and, therefore, safe for use in foods, beverages, and functional foods. Researchers point to the need of integrating CO2 SCFE with chromatographic techniques to precisely measure phytosterol yields [8]. 

2. Global Algae Extract Market 

Algae product global market is forecasted to reach $6.09 billion by 2026 [9]. Apart from being a storehouse of natural nutrients that provide a more than viable alternative [10] to nutrients extracted from animals, algae are increasingly acknowledged as an excellent carbon sink, fuel energy source, and water nutrient filter [9]. 

Following is a list of drivers:

  • Greater investment in algae production [10].
  • Rising awareness on the merits of products including natural ingredients such as those sourced from algae [9]. 
  • Growing demand for algae-sourced bio-fuels for generation of non-conventional energy [10] and development of technology that makes such energy generation viable [3]. 
  • Increasing number of mergers and acquisitions in the algae product industry [10].
  • Booming global populations [9]. 
  • Formulation of useful algae-based products by manufacturers. 

Extracts from algae can be [9]:

  • Carotenoids and Pigments
  • Antioxidants
  • Fatty Acids
  • Peptides
  • Sterols 

Sources of algae [9]:

  • Blue-green algae
  • Green algae
  • Red algae
  • Brown algae

Algal extracts find application in a wide range of industries [9]:

  • Neutraceutical & Diet Supplements
  • Food-Beverage
  • Feed for Animals and Aquaculture 
  • Fuels
  • Paints-Colorants
  • Personal Care
  • Pharmaceuticals
  • Chemicals
  • Pollution control 

3. Supercritical Fluid Extraction (SCFE) & Carbon dioxide (CO2) SCFE

3.1. Why SCFE Use is Rising?

Regulations on toxicity, quality, safety, and residues in consumer products are getting stricter as consumers demand products with more natural ingredients in food-beverage, pharmaceutical, neutraceutical, and personal care products. SCFE is safer, more eco-friendly, and leaves behind zero or less toxic residues in the final product. 

Alternative methods have drawbacks: 

  • Solvent Extraction: uses toxic organic solvents whose residue cannot be completely separated from the extracted ingredient [11]. Some solvents deplete the ozone layer and create environmental issues [12]. 
  • Hydrodistillation: employs heat which can thermally degrade the ingredient [13].  

3.2. What are Supercritical Fluids & How do they Assist with Extraction?

A fluid at above its critical pressure and temperature is a supercritical fluid. The phase boundary between its liquid and vapour phase disappears and its properties can be customized by changing the pressure and temperature.

Roughly, supercritical fluids with higher density possess greater solvent power. And because altering pressure and temperature substantially varies their density, supercritical fluids make exceptional solvents. 

Figure 2. Triple Point Parameters

Supercritical fluids are excellent solvents because of their [14]:

  • Higher, Liquid-like Density: boosts solvent power.
  • Low, Gas-like Viscosity: improves mass transfer and diffusion inside porous solids.
  • Low, Gas-like Surface Tension: enables greater seepage inside porous solids. 

3.3. Why Supercritical Carbon dioxide (CO2) Makes an Excellent SCFE Solvent? 

Carbon dioxide and water are the most popularly utilized supercritical fluids [15]. Supercritical (CO2) is an ideal solvent for SCFE because it [14]:

  • Has a critical temperature of 31.10C, which is around the ambient temperature. Relatively low temperatures for CO2 SCFE avoid thermal degradation.
  • Has a more manageable critical pressure of 73.9 bar.
  • Is non-flammable and non-toxic.
  • Has a customizable density to upgrade its solvent power.
  • Is available in ample quantities and in pure form.
  • Has a comparatively low cost.

Although CO2 is a greenhouse gas (GHG), the SCFE process using CO2 becomes eco-friendly if the gas is captured from the atmosphere, reused, and recycled. 


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Contact us at +91 20 6790 9600 or sales.automation@cybernetik.com and witness unrivalled customer delight.

References

  1. https://www.sciencedirect.com/science/article/pii/S1877705812029761
  2. https://www.livescience.com/54979-what-are-algae.html
  3. https://www.alliedmarketresearch.com/algae-products-market
  4. https://pubs.acs.org/doi/abs/10.1021/ie102297d
  5. https://www.mdpi.com/1660-3397/14/11/214/pdf
  6. https://www.sciencedirect.com/science/article/pii/0308814695957947
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6163853/
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515614/
  9. https://www.researchandmarkets.com/reports/4753171/algae-products-global-market-outlook-2017-2026
  10. https://www.techsciresearch.com/report/algae-products-market/2719.html
  11. https://www.sciencedirect.com/topics/immunology-and-microbiology/solvent-extraction
  12. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/organic-solvent
  13. http://www.florajournal.com/archives/2019/vol7issue1/PartA/7-3-34-739.pdf
  14. https://www.chemengonline.com/supercritical-co2-a-green-solvent/?printmode=1
  15. https://en.wikipedia.org/wiki/Supercritical_fluid