High pressure phase behavior for carbon dioxide-1-butanol and carbon dioxide-1-octanol systems

Pressure-composition isotherms are obtained for binary mixtures of carbon dioxide-1-butanol and carbon dioxide-1-octanol systems at 40, 60, 80, 100, and 120 °C and pressures up to 220 bar. The accuracy of the experimental apparatus was tested by comparing the measured phase equilibria data of the carbon dioxide-1-butanol system at 40 °C with those of Ishihara et al. 1996]. The solubility of 1-butanol and 1-octanol for the carbon dioxide-1-butanol and carbon dioxide-1-octanol systems increases as the temperature increases at constant pressure. The carbon dioxide-1-butanol and carbon dioxide-1-octanol systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of carbon dioxideand 1-butanol or 1-octanol. The carbon dioxide-1-butanol system exhibits type-I phase behavior, characterized by a continuous critical line from pure carbon dioxide, to the second component with a maximum in pressure. Also, the carbon dioxide-1-octanol system exhibits type-I curve at 60–120 °C, and shows liquid-liquid-vapor phase behavior at 40 oC. The experimental results for the carbon dioxide-1-butanol and carbon dioxide-1-octanol systems have been modeled by the Peng-Robinson equation of state. A good fit of the data is obtained with the Peng-Robinson equation by using two adjustable interaction parameters for the carbon dioxide-1-butanol system and a poor fit using two adjustable parameters for the carbon dioxide-1-octanol mixture.