Excess enthalpies of {x(CH3)2CO+(1–x)C6H14} in the supercritical region

Abstract

Excess molar enthalpies H_m^E of acetone–n-hexane mixtures have been measured at the critical temperature 493.2 K of the x= 0.5 mixture, and at the supercritical temperatures 510.2, 523.2 and 548.2 K. The H_m^E measurements for {x(CH₃)₂CO+(1–x)C₆H₁₄} were made at fixed mole fractions x at pressures up to 7.94 MPa. At 510.2 K measurements were made at x= 0.25, x= 0.50 and x= 0.75, but at all other temperatures the measurements were made at x= 0.50 only. The H_m^E values measured at 493.2 K have been combined with the enthalpies of acetone and n-hexane to obtain the enthalpy vs. pressure isotherm at the critical temperature T_c(x= 0.5) of the mixture. The H_m^E values in the supercritical region exhibit double maxima similar to those observed for carbon dioxide–ethane mixtures at supercritical temperatures. The double maxima fade as the temperature increases. The shape of the H_m^E against p graphs is well reproduced by the Patel–Teja equation of state using k₁₂= 0.14 in the combining rule a₁₂=(1 –k₁₂)(a₁₁a₂₂)^1/2. Density-dependent local composition mixing rules were found not to improve the fit to the measurements. The Patel–Teja equation has been used to explore the shape of the H_m^E(x,p,T) surfaces in the supercritical region. The surfaces are similar to those for carbon dioxide–ethane mixtures.