Phase Diagrams and Supercritical Fluids

Phase Diagrams

• Phases of Elements: Solid, liquid, and gas.
• Phase Diagrams: Illustrate the boundaries of different phases based on temperature and pressure.
• Dividing Lines: Indicate physical processes like melting and boiling.
• Phase Fusion Example: Ice melting, water boiling.

Key Points on Phase Diagrams

• Triple Point:
  • Intersection of all three phases.
  • Temperature and pressure where solid, liquid, and gas coexist in equilibrium.
  • Particles are loosely arranged.
• Critical Point:
  • Endpoint of phase equilibrium between liquid and gas.
  • Beyond this, forms a supercritical fluid.

Supercritical Fluids

• Behavior: Acts like a gas but dissolves like a liquid.
• Utility: Allows for the extraction of one substance from another.
• Dissolution Process:
  • Dissolve a substance in supercritical fluid.
  • Lower pressure to turn fluid into gas.
  • Dissolved particles fall for collection.

Advantages of Supercritical Fluids

• Flow more easily than liquids.
• Can reach areas inaccessible to regular fluids due to lack of surface tension.

Applications

• Decaffeination of Coffee:
  • Previously used dichloromethane, a carcinogen.
  • Now uses supercritical CO2, which leaves beans' oil intact and reclaims caffeine.
• Extraction of Compounds:
  • Proteins (e.g., diterpenes, tetraterpenes).
  • Vitamin E from fruits and vegetables.
  • Floral fragrances from flowers.

Critical Opalescence

• Phenomenon: Rapid fluctuation between liquid-like and vapor-like volumes near the critical point.
• Appearance: Causes substance to appear cloudy.
• Recent Research:
  • Observed in CO2 and recently in liquid helium by Brown University scientists.
  • Demonstrates potential universality of the phenomenon.

Case Study: Liquid Helium Experiment

• Heated at 4.2 K, observed boiling until reaching supercritical phase at 5 minutes.
• Critical opalescence occurs at around 5.23 K.
• Phase separation observed as temperature drops, supporting Einstein’s theory on opalescence.