The Lee–Kesler method [1] allows the estimation of the saturated vapor pressure at a given temperature for all components for which the critical pressure Pc, the critical temperature Tc, and the acentric factor ω are known.

Equations

with

(reduced pressure) and (reduced temperature).

Typical errors

The prediction error can be up to 10% for polar components and small pressures and the calculated pressure is typically too low. For pressures above 1 bar, that means, above the normal boiling point, the typical errors are below 2%. [2]

Example calculation

For benzene with

  • Tc = 562.12 K[3]
  • Pc = 4898 kPa[3]
  • Tb = 353.15 K[4]
  • ω = 0.2120[5]

the following calculation for T=Tb results:

  • Tr = 353.15 / 562.12 = 0.628247
  • f(0) = -3.167428
  • f(1) = -3.429560
  • Pr = exp( f(0) + ω f(1) ) = 0.020354
  • P = Pr * Pc = 99.69 kPa

The correct result would be P = 101.325 kPa, the normal (atmospheric) pressure. The deviation is -1.63 kPa or -1.61 %.

It is important to use the same absolute units for T and Tc as well as for P and Pc. The unit system used (K or R for T) is irrelevant because of the usage of the reduced values Tr and Pr.

See also

References

  1. ↑ Lee B.I., Kesler M.G., "A Generalized Thermodynamic Correlation Based on Three-Parameter Corresponding States", AIChE J., 21(3), 510-527, 1975
  2. ↑ Reid R.C., Prausnitz J.M., Poling B.E., "The Properties of Gases & Liquids", 4. Auflage, McGraw-Hill, 1988
  3. 1 2 Brunner E., Thies M.C., Schneider G.M., J.Supercrit.Fluids, 39(2), 160-173, 2006
  4. ↑ Silva L.M.C., Mattedi S., Gonzalez-Olmos R., Iglesias M., J.Chem.Thermodyn., 38(12), 1725-1736, 2006
  5. ↑ Dortmund Data Bank
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