What are supercritical fluids and why are they gaining traction in various industries?

Supercritical fluids, a fourth state of matter besides solids, liquids, and gases, possess the properties of both liquids and gases, and offer exceptional efficiency and safety in extraction and separation processes. Supercritical fluids are utilized in a variety of industries, including food engineering, pharmaceuticals, cosmetics, and environmental engineering, and their importance and potential continues to grow.

 

Solids, liquids, and gases are familiar concepts that categorize the states of matter based on the arrangement of molecules. However, today’s engineers have discovered a fourth state of matter, the supercritical state, which has many applications in fields such as food processing.
To understand what a supercritical fluid is, imagine ice water. At first, the ice is light in density and floats on top of the water, making the boundary between ice and water clearly distinguishable. Over time, however, as the ice gradually melts, the boundary between ice and water disappears and the two phases mix, creating a new state called sherbet. The same is true for systems where liquids and gases coexist. Initially, the lighter-density gas is in the upper layer and the boundary between the two phases is clearly distinguishable. However, if the pressure and temperature are gradually increased so that the density difference between the liquid and gas becomes smaller, the boundary disappears and the liquid and gas mix. The temperature and pressure at the point where the boundary disappears is called the critical point, and the fluid at the point where the liquid and gas cannot be distinguished after the critical point is called supercritical fluid.

 

 

In the early days of research, supercritical fluids faced difficulties in commercialization due to the high energy consumption required for high temperature and pressure to create a supercritical state. However, when it was discovered that carbon dioxide exists in a supercritical state at a temperature close to room temperature of 31 degrees Celsius, supercritical fluids began to be used in extraction and separation processes, and are now widely used in food engineering. Typical examples of such processes include the extraction of caffeine from coffee to reduce the caffeine content, the extraction of active ingredients from hops to produce beer, the extraction of saponins from red ginseng, and the extraction of sesame oil. However, there are a growing number of other applications, such as non-thermal sterilization of food and laundry as an alternative to dry cleaning.
Furthermore, supercritical fluids are increasingly being used in a variety of industries, including pharmaceuticals, cosmetics, and environmental engineering. For example, supercritical fluids are used in the pharmaceutical industry to extract or purify the active ingredients of drugs, and in the cosmetics industry to extract and purify natural ingredients. In environmental engineering, the technology is being used to treat waste and clean up soil contamination. These diverse applications highlight the importance and potential of supercritical fluids.
So what are the advantages of supercritical fluids in these extraction and separation processes? The first thing to note is the superior physical properties of supercritical fluids. Like sorbets, supercritical fluids have partial properties of both liquids and gases. The solubility of liquids allows for the separation of products in the separation and extraction process, while the high permeability of gases increases the efficiency of the separation process. In other words, supercritical fluids are more permeable than traditional organic solvents, allowing them to reach the inside of the separator and completely dissolve the components you want to extract.
Supercritical fluids also offer cost savings in two ways. When using conventional liquid organic solvents, the extraction process involves dissolving the substance to be extracted into the solvent, followed by a final separation process to separate the solvent and the extracted component to produce the final product. However, in the case of supercritical fluids, when the pressure and temperature are changed to cause a phase change to the gas state, the solubility disappears and the gas and extractive components are automatically separated, which reduces the installation and operation costs of the separation process to produce the final product. In addition, supercritical fluids are easier to reuse than conventional organic solvents, so it is possible to reduce raw material costs among operating costs.
Finally, supercritical fluids are widely used in extraction and separation processes because they are safe for human health and the environment. In the case of conventional organic solvents, the separation process may destroy the unique flavor or nutritional components of the food, or the reaction may produce toxic intermediates, and even trace amounts of organic solvents can be toxic to humans, raising safety concerns. However, carbon dioxide used as a supercritical fluid has no effect on the human body, so even if the final food product contains carbon dioxide, there is no stability problem. In addition, the unique flavor and nutritional content of the food can be preserved, and the reaction process does not generate toxic intermediates, so the process is less risky and environmentally friendly.
As a result, supercritical fluids are being utilized in various industries as super critical solvents due to their superior properties, energy savings, stability, and environmental friendliness, and their importance is growing. This suggests that supercritical fluids will continue to be utilized in a wide variety of fields and will become more efficient and safe through continued research and development.