ChemCalc calculates saturation vapor pressure P* for 129 pure components using the Peng-Robinson equation of state and IAPWS water saturation where applicable. The result feeds directly into VLE bubble/dew-point calculations, McCabe-Thiele distillation, and flash calculations.
Antoine Equation (Classic Form)
| Form | Expression |
|---|
| log₁₀ form (common) | log₁₀(P*) = A − B / (C + T) |
| ln form (NIST/DIPPR) | ln(P*) = A − B / (C + T) |
| Extended Antoine | ln(P*) = A + B/T + C·ln(T) + D·TE |
P* is typically in mmHg, bar, or kPa depending on the source; T in °C or K. Always verify the units and temperature range of the Antoine constants you use.
Why ChemCalc Uses PR EOS Instead of Antoine
| Aspect | Antoine equation | PR EOS (ChemCalc) |
|---|
| Accuracy near Tc | Degrades rapidly above ~0.85 Tr | Uses pure-component critical properties and acentric factor |
| Water (steam) | Constants vary widely by source | IAPWS water saturation model |
| Mixture VLE | Requires separate mixing rule assumption | Cubic EOS directly handles fugacity for mixtures |
| Parameters needed | 3 fitted constants per component | Tc, Pc, ω (acentric factor) — widely tabulated |
Supported Components (129 total)
Water
Light hydrocarbons C1–C10
Aromatics (benzene, toluene, xylenes)
Alcohols (methanol, ethanol, propanol)
Ketones and esters (acetone, MEK, ethyl acetate)
Common gases (N₂, O₂, CO₂, H₂, H₂S, NH₃)
Refrigerants (R134a, R22, propylene)
Applications
| Application | How vapor pressure is used |
|---|
| Bubble-point calculation | ∑ yᵢ = ∑ xᵢ · Pᵢ*(T) / P = 1; solve for T or P |
| Dew-point calculation | ∑ xᵢ = ∑ yᵢ · P / Pᵢ*(T) = 1 |
| McCabe-Thiele / FUG distillation | Relative volatility αᵢⱼ = Pᵢ* / Pⱼ* (Raoult's law baseline) |
| Flash (isothermal / adiabatic) | K-values Kᵢ = Pᵢ* / P for ideal VLE |
| NPSH available | Pv = P*(Tliquid) subtracted from static head |
| Safety valve sizing | Rupture disc / relief valve latent heat and two-phase relief |
Related Calculators
← Back to ChemCalc — 44 engineering modules