Antoine Vapor Pressure

What Antoine is for

Antoine gives the equilibrium vapor pressure of a pure liquid at a given temperature. Direct uses:

• Boiling point at altitude: T_bp = boiling at given P_atm. Mt. Everest at 250 mmHg → water boils at 71°C.
• Distillation column design: relative volatility α₁₂ = P_sat,1 / P_sat,2 across the column.
• Tank breathing losses: gasoline tank at 30°C → P_sat,gasoline determines vapor space concentration.
• Solvent selection: pick a solvent whose P_sat at process conditions is appropriate (low for evaporative loss prevention, high for fast removal).
• Pump NPSH: NPSH_a depends on vapor pressure of the pumped fluid at fluid temperature.

Antoine coefficient sources

• NIST WebBook: webbook.nist.gov — most accurate, multiple formulations
• Yaws' Handbook of Vapor Pressure: Yaws (2007), Gulf Publishing, ch. 1
• Perry's Chemical Engineers' Handbook: Perry & Green, 9th ed., ch. 2
• DIPPR Database: industry standard for chemical properties

Always check the temperature range for which the coefficients are valid. Antoine is a 3-parameter polynomial fit and extrapolates poorly outside the calibrated range. Some compounds use multiple coefficient sets for different temperature ranges.

Limits of Antoine

Antoine works well from triple point to ~70% of critical temperature. For:

• Near critical: use Wagner equation (4-parameter, asymptotic to T_c)
• Multi-component liquid: Antoine is for pure compounds. Use Raoult's law: P_sat,solution = Σ x_i × P_sat,i for ideal mixtures, or activity-coefficient models (NRTL, UNIQUAC) for non-ideal.
• Dissolved gas in water: use Henry's law instead of Antoine.
• Solid → vapor (sublimation): separate Antoine fit, applies below triple point.

Inverse — finding boiling point at a given pressure

Solve for T given P_sat: T = B / (A − log10(P_sat)) − C. The equation is closed-form invertible because of the simple log-linear structure. For Wagner equation, inverse requires Newton-Raphson iteration.

Coefficient examples (mmHg basis)

Reference: Antoine, C. (1888). "Tensions des vapeurs." C. R. Acad. Sci., Paris, 107: 681. NIST Chemistry WebBook (current). Reid, R.C., Prausnitz, J.M., Poling, B.E. (1987). The Properties of Gases and Liquids, 4th ed., McGraw-Hill.