The Applications of Supercritical Carbon Dioxide

Dear Colleagues,

Supercritical-fluid-based knowledge is involved in a wide-ranging diversity of industrial applications, which have shown a notable evolution in recent years. Although water and others supercritical solvents, such as methanol, ethanol, propane, and ethane, have increase their importance in emblematic fields of application to various industrial sectors, the use of supercritical CO₂ (Tc = 31 °C, Pc = 74 bar) as an extraction solvent for natural products is the oldest and most established process on an industrial scale, with notable applications in the food industry.

The strong variation of the solvation power of CO₂, which arises by varying operating conditions (temperature and pressure), is the basic principle of this technique. This allows to selectively extract molecules according to their chemical natures. CO₂ is an excellent solvent of nonpolar or small polar molecules in supercritical conditions. Moreover, the use of a polar co-solvent can extend the supercritical power extraction of CO₂ to obtain more polar compounds.  In principle, different materials, such as plants, wood, and plastics, can be submitted to supercritical fluid extraction in order to recover valuable compounds (essential oils, oils, pigments, etc.) or undesired constituents (pollutants, residual solvents, etc.).

Supercritical-fluid-based developments include extraction, impregnation, formulation, particle formation, sterilization, cleaning, chemical reactions, energy, and waste treatment, among others. In all circumstances, the supercritical fluid is used as an alternative to traditional organic liquid solvents, and, in many processes, with the use of supercritical CO₂, it is possible to significantly eliminate or decrease solvent residues, contributing to environmentally-friendly chemical routes and technical innovations to achieve green chemical processes.

Prof. Jose Augusto Paixao Coelho
Guest Editor

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