in the food or pharma industries), or for special products that could not be produced at ambient pressures (e.g. Additional advantages of high-pressure processes are their low environmental impact, economic feasibility, and sustainability for certain high-value products (e.g.
The relatively new use of high pressure as a tool may lead to the production of completely new products with special characteristics that are impossible to obtain in any conventional way. subcritical fluid or SCFs, can also be used for integrated extraction and in situ formulation, like impregnation of solid particles, for formation of solid powderous emulsions, particle coating, etc. The unique thermodynamic and fluid dynamic properties of different gases used as dense fluids, e.g. However, the most commonly investigated process where SCFs are used as solvent media is the supercritical fluid extraction (SFE) process ( Oman et al., 2013). SCF can be used as solvents for precipitation and micronization (PGSS ®, RESS, etc.), as a reaction medium, as a mobile phase for chromatography (supercritical fluid chromatography-SFC), and so on. Typical thermophysical properties of SCFs are low viscosity, high diffusivity, density, and the dielectric constant of SCF, which can easily be changed by varying the operating pressure and/or temperature. Other advantages of SCFs include health and safety ( Knez, 2016). The most important SCFs, such as SC CO 2 and SC H 2O, are nontoxic, non-flammable, non-carcinogenic, non-mutagenic, and also thermodynamically stable. The use of most supercritical (SC) fluids in industrial processes can replace far more damaging conventional solvents.
Using SCFs in numerous processes may lead to the production of completely new products with certain characteristics having a very low impact on the environment, such as low energy consumption during the process, along with health and safety benefits. Several smaller industrial units are also in operation for extraction of spices for the food industry and natural substances for use in cosmetics ( Luetge et al., 2007). Typical applications, operated by means of supercritical fluids (SCFs), are the extraction of hop constituents, decaffeination of tea and coffee, and the separation of lecithin from oil, all of which are high-pressure processes, which are performed on a large industrial scale. Meanwhile, several hundred supercritical extraction plants have been designed to operate at extremely high pressures (up to 2000 bar) worldwide.
Research in supercritical extraction technology started about two decades ago. The pressures used in high-pressure industrial processes range from 50 bar (in particle formation processes) to over 200000 bar (conversion of graphite to diamond) ( Knez, 2016). Nowadays, the demand for new products has increased, and it has thus become necessary to find ways to shift technological processes towards high pressure. On Earth, this pressure ranges from 0.25 bar, on the highest mountain, up to almost 1000 bar at the bottom of the ocean. Most commonly, the industrial technologies for producing different products were operated at atmospheric pressure.
In recent times, the design of new products with certain characteristics or the design of environmentally friendly processes has presented a challenge for engineers. Separation, fractionation, extraction, value-added products, green solvents Introduction