Subcritical Water

Why Subcritical H2O

There is a great demand for environmentally friendly extraction procedures that eliminate the need for toxic organic solvents. Supercritical carbon dioxide is one and has been highlighted here. However, one can also use water in some innovative ways.

Water can be held in a liquid state above its normal boiling temperature (100°C) by increasing the pressure. This process is demonstrated using a simple pressure cooker. Water above its normal boing point but below its supercritical temperature (374°C), is “subcritical” water.

Water can be used as an alternative to toxic organic solvents because the dissolving power of water can be changed by changing its temperature. Water can be physically altered to become “subcritical” water

Polar
Water at room temperature has a high dielectric constant - dissolving polar and ionic compounds.
More Non-Polar
Water at high temperatures has a lower dielectric constant - dissolving non-polar organic compounds

  • Substitute for ethanol & polar solvents
  • Lower energy than steam distillation
  • All-natural processing platform - complimentary with SC-CO2
  • Non-toxic
  • Inexpensive
  • Readily obtained
  • Easily disposed of
  • Sample does not need to be dried
  • Variable polarity (e)
  • Subcritical Water and Supercritical CO2 in ONE System

Viscosity and surface tension decrease

  • Viscosity and surface tension decrease with increasing temperature
  • Solubility of solutes increases
  • Solute diffusion increases, decreasing time to solubilize

Replace alcohol with subcritical water

  • Since the dielectric constant of water decreases significantly as it is heated, it can behave like alcohol

Subcritical water may be used to extract many organic molecules

  • Eliminate the use of conventional organic solvents.