Ambrose-Walton method

The Ambrose-Walton method is a method for estimating the vapor pressure of pure substances. The method is based on the theorem of the coincident states and uses the critical temperature , the critical pressure and the acentric factor . It is a further development of the Lee-Kesler method .

Determining equations

${\displaystyle \ln {\frac {P}{P_{\mathrm {c} }}}=f^{(0)}+\omega \cdot f^{(1)}+{\omega }^{2}\cdot f^{(2)}}$

${\displaystyle f^{(0)}={\frac {-5{,}97616\cdot \tau +1{,}29874\cdot \tau ^{1{,}5}-0{,}60394\cdot \tau ^{2{,}5}-1{,}06841\cdot \tau ^{5}}{T_{\mathrm {r} }}}}$

${\displaystyle f^{(1)}={\frac {-5{,}03365\cdot \tau +1{,}11505\cdot \tau ^{1{,}5}-5{,}41217\cdot \tau ^{2{,}5}-7{,}46628\cdot \tau ^{5}}{T_{\mathrm {r} }}}}$

${\displaystyle f^{(2)}={\frac {-0{,}64771\cdot \tau +2{,}41539\cdot \tau ^{1{,}5}-4{,}26979\cdot \tau ^{2{,}5}+3{,}25259\cdot \tau ^{5}}{T_{\mathrm {r} }}}}$

with and ${\displaystyle \quad T_{\mathrm {r} }={\frac {T}{T_{\mathrm {c} }}}}$ ${\displaystyle \tau =1-T_{\mathrm {r} }}$

${\displaystyle T}$: Absolute temperature

${\displaystyle T_{\mathrm {c} }}$: Critical temperature

${\displaystyle P}$: Vapor pressure

${\displaystyle P_{\mathrm {c} }}$: Critical pressure

${\displaystyle \omega }$: Acentric factor

Sample calculation

For acetone ( ) at a temperature of 329 Kelvin, the following calculation results : ${\displaystyle T_{\mathrm {c} }=508\,\mathrm {K} ,P_{\mathrm {c} }=4700\,\mathrm {kPa} ,\omega =0{,}309}$ ${\displaystyle T}$

With and surrender ${\displaystyle T_{\mathrm {r} }={\frac {329\,\mathrm {K} }{508\,\mathrm {K} }}=0{,}6476}$ ${\displaystyle \tau =1-T_{\mathrm {r} }=0{,}3524}$

${\displaystyle f^{(0)}=-2{,}9097}$

${\displaystyle f^{(1)}=-3{,}0571}$

${\displaystyle f^{(2)}=-0{,}0309}$

${\displaystyle \ln {\frac {P}{P_{\mathrm {c} }}}=-2{,}9097+0{,}309\cdot (-3{,}0571)+0{,}309^{2}\cdot (-0{,}0309)=-3{,}8573}$

${\displaystyle P=e^{-3{,}8573}\cdot 4700\,\mathrm {kPa} =99{,}2870\,\mathrm {kPa} }$

329 Kelvin is about the normal boiling point temperature of acetone, i.e. the point at which acetone becomes gaseous at normal pressure ( ). ${\displaystyle \approx 101\,\mathrm {kPa} }$

literature

1. ↑ Ambrose D., Walton J., "Vapor Pressures up to Their Critical Temperatures of Normal Alkanes and 1-Alkanols", Pure Appl. Chem. , 61, 1395-1403, 1989
2. ↑ Lee BI, Kesler MG, "A Generalized Thermodynamic Correlation Based on Three-Parameter Corresponding States", AIChE J., 21 (3), 510-527, 1975