Phase behavior and modeling of the systems CO2-acetonitrile and CO2-acrylic acid

Pressure-composition isotherms are obtained for the CO2-acetonitrile (ACN) system at 35, 55, and 75 degrees C and for the CO2-acrylic acid (AA) system at 45, 65, 85, and 100 degrees C. Also a portion of the CO2-AA critical mixture curve is determined near the critical point of pure CO2. These two CO2-polar solute systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of CO2 and AA or ACN. The experimental data are modeled using both the statistical associating fluid theory (SAFT) and the Peng-Robinson equation of state. The Peng-Robinson equation of state accurately models the pressure-composition isotherms for these two systems only if two temperature-independent mixture parameters are used for each system. In contrast, the SAFT equation with no adjustable mixture parameters gives a reasonable fit the data. A good fit of the data are obtained with SAFT using one adjustable parameter for the CO2-ACN system and two adjustable parameters for the CO2-AA system.