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Introduction to the technique of supercritical CO2 fluid extraction

Date: Apr 12, 2024

In recent years, the development of supercritical carbon dioxide fluid extraction technology has advanced rapidly, achieving a leap from theoretical research to large-scale production. This technology is widely used in industries such as environmental engineering, pharmaceuticals, and food processing. A supercritical fluid refers to a special state of matter that exists above its critical temperature and critical pressure. Supercritical fluids exhibit several unique properties, such as high density, low viscosity, low surface tension, and strong solubility. Furthermore, the solubility of a supercritical fluid changes with pressure, making the extraction and separation process more efficient. Owing to these distinctive properties, supercritical fluids are becoming a popular choice for green extraction solvents. Many substances can be used as supercritical fluid extraction agents, including carbon dioxide, ammonia, nitrous oxide, ethane, ethylene, propane, etc. Among these, carbon dioxide is the most widely used due to its critical temperature being close to room temperature, and its colorless, odorless, non-toxic, inert, non-flammable nature, as well as its widespread availability and low cost.

1. Principle of the supercritical CO2 fluid extraction technique

The principle of supercritical CO2 fluid extraction technology lies in the variable solubility of supercritical fluids, which changes with their density. By altering the pressure or temperature, the density of a supercritical fluid can be significantly changed, thereby modifying its solubility. In the supercritical state, CO2 fluid fully contacts and dissolves the substances to be separated. Then, by changing the temperature or pressure, the solubility of supercritical CO2 changes accordingly. This allows for selective extraction based on the polarity and boiling points of the extractables. The process of reverting supercritical CO2 back to a gaseous state, either by reducing pressure or increasing temperature, causes the extracted substances to precipitate completely, thus achieving separation and extraction. Therefore, the supercritical CO2 fluid extraction process consists of both extraction and separation phases. The relationship between supercritical fluid and solid, liquid, and gas states can be illustrated in a diagram, with the supercritical region indicated by a shaded area.


Supercritical fluids exhibit the dual characteristics of gases and liquids, combining the favorable solubility of liquid solvents with the excellent fluidity and strong permeability of gases, without phase boundary effects. Consequently, they achieve better extraction results compared to conventional liquid solvents. Below is a comparative table of the physical properties of supercritical fluids, gases, and liquids:


2.The characteristics of supercritical CO2 extraction technology

Common supercritical fluids such as carbon dioxide, ethane, ethylene, propane, and ammonia have their own critical parameters. It is known from the table that CO2's critical temperature is close to room temperature, its critical pressure is not high, and it is inert and non-toxic, making it the most ideal supercritical fluid. The solubility of supercritical fluids changes with pressure and temperature, so by adjusting the temperature or pressure of the extraction, the desired extract can be obtained. This allows for good selectivity and high efficiency without the need for solvent extraction.


3.The advantages of supercritical CO2 fluid extraction technology are summarized as follows:

1). The extraction temperature of supercritical CO2 is low (around 35°C), which can effectively protect the thermosensitive components in the extracted substances from damage.

2). The supercritical CO2 extraction process is clean. It does not require organic solvents throughout the process, thus not producing substances harmful to humans and the environment.

3). Supercritical CO2 extraction is more efficient. It is a technology that combines extraction and separation processes. When the temperature or pressure changes, the CO2 fluid becomes gaseous, allowing for quick separation from the extract, characterized by high extraction efficiency and low energy consumption.

4). Supercritical CO2 extraction has high safety. Carbon dioxide is a chemically inert inert gas, making the extraction process safe, stable, non-toxic, colorless, and odorless.

5). Supercritical CO2 extraction has low cost. Carbon dioxide gas is widely available, easy to produce, inexpensive, and recyclable, thereby reducing usage costs.

6). The supercritical CO2 extraction process is simple. Different extraction effects can be achieved by adjusting temperature or pressure parameters, making the extraction steps simple and offering good extraction selectivity.

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