15.2 Supercritical fluid properties and applications

Supercritical fluids exist above a substance's critical temperature and pressure, combining liquid-like density with gas-like diffusivity. This unique state allows for high solubility, rapid mass transfer, and tunability, making them versatile solvents for various applications.

Supercritical fluids, especially CO2, are used in extraction processes, offering advantages over traditional methods. They align with green chemistry principles, promoting sustainable and environmentally friendly industrial processes by reducing hazardous chemicals and minimizing waste.

Supercritical Fluid Properties

Unique Characteristics of Supercritical Fluids

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• Supercritical fluids exist above the critical temperature and critical pressure of a substance
• Exhibit liquid-like density, allowing for high solubility and extraction efficiency
  • Density can be up to 100 times greater than gases
• Possess gas-like diffusivity, enabling rapid mass transfer and penetration into porous materials
  • Diffusivity is typically 100 times higher than liquids
• Lack a distinct liquid or gas phase, resulting in a single homogeneous phase

Solvent Power and Tunability

• Supercritical fluids have high solvent power, dissolving a wide range of compounds
  • Solvent power is dependent on fluid density, which can be adjusted by changing temperature and pressure
• Tunability of supercritical fluids allows for selective extraction and separation processes
  • Properties can be fine-tuned by manipulating temperature and pressure near the critical point
  • Enables optimization of extraction conditions for specific target compounds
• Solvent power and tunability make supercritical fluids versatile solvents in various applications (pharmaceuticals, natural product extraction)

Applications of Supercritical Fluids

Supercritical Extraction Processes

• Supercritical extraction utilizes supercritical fluids to extract valuable compounds from materials
  • Common applications include decaffeination of coffee and tea, extraction of essential oils and flavors
• Offers advantages over traditional extraction methods (liquid-liquid extraction, Soxhlet extraction)
  • Higher efficiency, selectivity, and faster extraction times
  • Eliminates the need for toxic organic solvents
• Supercritical CO2 is widely used due to its low critical temperature (31.1°C), non-toxicity, and easy removal from extracted products

Green Chemistry and Sustainable Processes

• Supercritical fluids align with the principles of green chemistry, promoting sustainable and environmentally friendly processes
  • Reduce the use of hazardous chemicals and solvents
  • Minimize waste generation and energy consumption
• Supercritical CO2 is considered a green solvent, as it is non-toxic, non-flammable, and readily available
  • Can replace harmful organic solvents in various industrial processes (cleaning, dyeing, polymer processing)
• Supercritical fluid technology enables the development of cleaner and more efficient manufacturing processes (pharmaceuticals, food, materials)