Isothermal vapor-liquid equilibrium measurement of isobutanol + isooctane/N-heptane binary mixtures at temperatures range of 303.15-323.15 K

The addition of alcohol as an oxygenated compound in gasoline blends may increase the vapor pressure of gasoline mixture. As a result, the study of vapor-liquid equilibrium for gasoline component and alcohol is necessary. In this study, the vapor-liquid equilibrium of isobutanol - isooctane/n-heptane blends were obtained experimentally at temperatures in the range 303.15 to 323.15 K using modified simple quasi-static ebulliometer. The apparatus was validated by comparing the vapor pressure of pure isobutanol, isooctane, and n-heptane with the published data and giving average absolute deviation (AAD) between experimental and calculated ones with magnitude less than 1.0%. The addition of isobutanol with the mole fraction range from 0.2 to 0.6 would increase the vapor pressure of the isooctane and n-heptane up to 12% and 14% respectively. The vapor pressure of binary mixtures was correlated with the Wilson, Non-random two-liquid (NRTL), and Universal quasi-chemical (UNIQUAC) equations with AAD 1.6%, 1.5%, and 1.7%, respectively for isobutanol + isooctane system and 1.8%, 1.7%, and 2.0%, respectively for isobutanol + n-heptane system. The systems studied show positive deviation from Raoult’s Law.