In recent years, scientific research and the industrial world have shown growing interest in extracting solvents, extractive fluids in general, and technological innovations that allow replacing organic solvents, commonly used in traditional extraction processes of solutes from plant matrices, ensuring greater advantages as we will see in this article.
Supercritical Carbon Dioxide
Supercritical fluids, due to their chemical-physical properties, can be defined as “very dense gases”. They can diffuse inside solid matrices like gases but, at the same time, have solvent power similar to that of liquids, thanks to their high density.
In most applications, the choice of extracting solvent falls on supercritical carbon dioxide (CO2), because it has several advantages:
- it is non-toxic;
- it is non-flammable;
- it is odorless and tasteless;
- it is inert;
- it is available at high purity;
- it has a relatively low cost.
Moreover, it is possible to reduce its environmental impact if used in a closed system; it is suitable for processes involving thermolabile compounds, since its critical temperature is close to room temperature and it can be used with easily oxidizable compounds, being a non-oxidizing species.
Finally, it is a fluid recognized as GRAS (Generally Recognized as Safe) by the FDA (Food and Drug Administration) and EFSA (European Food Safety Authority).
The main drawback is its non-polar nature. Therefore, it is poorly selective towards hydrophilic compounds, but this can be resolved by using, in small percentages, polar co-solvents such as methanol and ethanol.
Applications of supercritical fluids
What can be the industrial-scale applications of supercritical fluids?
Some are:
- extraction of oils from plant matrices (seeds, fruits, leaves, and flowers);
- refining and fractionation of oils;
- production of hop extracts for the brewing industry;
- decaffeination of tea and coffee;
- production of non-alcoholic beverages;
- extraction of spices for the food industry and natural substances for the pharmaceutical and cosmetic industries.
Hydrofluorocarbons as extracting solvents
Other extracting solvents, which in recent years have found wide use in industry, are some refrigerant fluids, hydrofluorocarbons, used under subcritical conditions.
These have no effect on the ozone layer and, although characterized by a very high Global Warming Potential (GWP), they can be considered completely eco-friendly solvents when used in closed systems without any atmospheric emissions.
Moreover, like supercritical CO2, they are non-toxic, non-explosive, and non-flammable and are available at contained costs.
Finally, due to their chemical-physical properties, hydrofluorocarbons behave very similarly to supercritical fluids while operating at much milder temperature and pressure conditions.
Therefore, they can also be advantageously used under subcritical conditions, maintaining all the positive aspects of the supercritical process but at the same time allowing reduced initial investment capital and operating costs.
Hydrofluorocarbons have some affinity with water, allowing the treatment of wet matrices, thus reducing the costs of pre-drying the matrix, sometimes necessary upstream of all traditional and non-traditional extraction processes.
For this reason, they also promote the recovery of polar compounds without the use of organic co-solvents.
Conclusions
Over the years, the experience and knowledge acquired in the sector through projects with national and international partners and clients have enabled us to use the most appropriate extracting solvents according to client needs. Indeed, a solvent cannot always fit every situation, and sometimes, a wrong choice can cause serious damage to the company (both economic and to the final products).
If you want to deepen the topic and discover how to use solvents in your industrial processes, you can contact us.
