Phase behavior and modeling of the poly(methyl methacrylate)-CO2-methyl methacrylate system

Cloud-point data for the system poly(methyl methacrylate) (PMMA)-CO2-methyl methacrylate (MMA) are measured in the temperature range of 26 to 170 degrees C, to pressures as high as 2500 bar, and with cosolvent concentrations of 10.4, 28.9, and 48.4 wt.%. PMMA does not dissolve in pure CO2 to 255 degrees C and 2550 bar. The cloud-point curve for the PMMA-CO2-10.4 wt.% MMA system exhibits a negative slope that reaches 2500 bar at 105 degrees C. With 28.9 wt.% MMA the cloud-point curve remains relatively flat at similar to 900 bar for temperatures between 25 and 170 degrees C. With 48.4 wt.% MMA the cloud-point curve exhibits a positive slope that extends to 20 degrees C and similar to 100 bar. pressure-composition isotherms are also reported for the CO2-MMA system at 40.0, 80.0, 105.5 degrees C. This system exhibits type-I phase behavior with a continuous mixture-critical curve. The Peng-Robinson (PR) and SAFT equations of state model the CO2-MMA data reasonably well without any binary interaction parameters, although the PR equation provides a better representation of the mixture-critical region. It is not possible to obtain even a qualitative fit of the PMMA-MMA-CO2 data with the SAFT equation of state. The SAFT model qualitatively shows that the cloud-point pressure decreases with increasing MMA concentration and that the cloud-point curve exhibits a positive slope for very high concentrations of MMA in solution. (C) 1999 Elsevier Science B.V. All rights reserved.