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 degreesC 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 degreesC 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 dioxide- and 1-butanol or 1-octanol. The carbon dioxide-1-butanol system exhibits type-1 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-1 curve at 60-120 degreesC, and shows liquid-liquid-vapor phase behavior at 40 degreesC. 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.