Antoine Constant

Antoine constant is the empirical coefficients used in the Antoine equation, a widely accepted correlation for representing the relationship between the vapor pressure of a pure substance and temperature.  The pressure and temperature units must correspond to the units used in the parameter regression.  These constants are determined by fitting experimental vapor–liquid equilibrium data over a specified temperature range.

From an engineering standpoint, Antoine constants are used extensively in thermodynamics, chemical process design, and separation calculations.  They enable practical estimation of saturation pressure for pure components in operations such as distillation, evaporation, and condensation.  The correlation is valid only within the temperature range over which the constants were derived; outside that range, deviation from measured data can be significant.

The Antoine equation is empirical rather than derived from first principles.  Therefore, the constants have no independent physical meaning outside the regression context.  Multiple sets of Antoine constants may exist for the same substance, each applicable to a different temperature interval.  This is standard practice in chemical engineering thermophysical property databases.

For Water, the Antoine Constants Depend on the Temperature Range

Here are two common sets of constants for water  -

• For the temperature range 1°C to 100°C (or 273.15 °K to 373.15 °K)  -
  
  • \(A \;=\; 8.07131\)
    
  • \(B \;=\; 1730.63\)
    
  • \(C \;=\; 233.426\)
    

• For the temperature range 99°C to 374°C (or 372.15 °K to 647.15 °K)  -

  • \(A \;=\; 8.14019\)
    
  • \(B \;=\; 1810.94\)
    
  • \(C \;=\; 244.485\)