Supercritical Fluids

What is a Supercritical Fluid?

Supercritical Fluids (SCFs) are compounds at a temperature and pressure beyond their critical point. Carbon dioxide is the most widely used SCF owing to its reasonable critical point (304.1 K and 7.38 MPa), low cost, inert and non-toxic character.

SCFs are a single phase with properties that lie between the properties of typical gases and that of typical liquids. Gaseous carbon dioxide (at 298 K and 1 atm) has a density of 1.8 kg/m³. Liquid carbon dioxide (at 298 K and 10 MPa) has a density of 818.88 kg/m³. Supercritical Carbon Dioxide’s density can be tuned (at 350 K and 8 MPa it is 164 kg/m³ while at 305 K and 30 MPa it is 941 kg/m³). This density shift over narrow temperature and pressure changes is key to many of the opportunities associated with SCF applications.

SCF property tunability extends well beyond density. Density, enthalpy, entropy, diffusivity, viscosity, solubility and more depend on the selected SCF and on the operating conditions of temperature and pressure. This tunability presents an opportunity for the development of a wide range of applications.

Carbon Dioxide Phase Diagram

Advantages of Carbon Dioxide

Environmentally Friendly

Carbon Dioxide is considered a green solvent and is recycled in the process.

Worker Friendly

Carbon Dioxide is considered non-toxic and non-flammable.

Economically Friendly

Carbon Dioxide is inexpensive and readily available.

Solubility in Supercritical Carbon Dioxide

Supercritical Fluids have many unique advantages. The dependence of solubility on temperature and pressure is the most important.

Oil

At Supercritical conditions, oil (e.g. diesel) is quite soluble in Carbon Dioxide. Whereas, at lower temperatures and pressures, solubilities are quite low.

The main advantage of Supercritical Carbon Dioxide over other conventional solvents is that the oil can easily be recovered from the Supercritical fluid by simple depressurization rather than an expensive distillation process for conventional solvents. This feature presents many opportunities in different industries to remove an oil-based product such as diesel.

Caffeine

Supercritical Carbon Dioxide has the potential to extract caffeine from various solid matrices such as coffee beans, coffee waste, tea leaves, cocoa beans, etc.

One of the earliest industrial applications of Supercritical Fluid Extraction using Carbon Dioxide has been the extraction of caffeine from coffee beans.

Caffeine extraction using Supercritical Carbon Dioxide is a selective process. In other words, based on operating conditions, only the caffeine compound can be extracted, but not the other precursors present in the bean (such as carbohydrates and peptides).

Lycopene

Lycopene is a type of carotenoid and is considered an anti-oxidant. It is widely found in fruits and vegetables, specifically those that have a pink to red colour.

Supercritical Carbon Dioxide has the potential to extract Lycopene from food containing this valuable anti-oxidant.

Extraction of Lycopene using Supercritical Carbon Dioxide does not damage the structure of Lycopene and does not present any toxicity. This feature presents many opportunities to safely extract and use Lycopene, which has application in the nutraceutical industry and food industry.

Palladium Acetylacetonate

Palladium Acetylacetonate is considered a metal chelate and used as a catalyst precursor and reagent.

Palladium Acetylacetonate is soluble in Supercritical Carbon Dioxide, hence it is used for the fabrication of catalysts and nano-functional materials.

Other than this application (i.e. product context), we envisage extraction of Palladium Acetylacetonate with Supercritical Carbon Dioxide from waste streams to be a future application.

Solubility Calculation in Supercritical Carbon Dioxide

SCFVirtual has developed an application (for macOS) to calculate solubility in Supercritical Carbon Dioxide for Binary Systems and Ternary Systems. For more information and download, visit the website.

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