Phase behavior of the carbon dioxide/toluene/poly(methyl methacrylate) ternary system

Carbon dioxide/organic polymer/solvent systems have several industrial applications, including supercritical polymerization. Various process parameters affect the phase behavior of these systems, thereby influencing the process design. Accordingly, the phase behavior of a carbon dioxide (CO 2 )/toluene (Tol)/poly(methyl methacrylate) (PMMA) ternary system was investigated in this study. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurement. Bubble points (vapor - liquid phase separation) were determined from changes in the piston displacement, whereas cloud points (liquid - liquid (LL) phase separation) were determined from changes in the turbidity The phase boundaries of CO 2 mass fractions ranging from 0.098 to 0.577 were measured by varying the Tol/PMMA ratio. The homogeneous phase area decreased when the ratio of PMMA to Tol increased, molecular weight of PMMA increased, and/or temperature decreased. These changes in the LL phase separation behavior were explained with reference to the free volume ( v f ) and solubility parameter ( delta ) estimated using the Sanchez - Lacombe equation of state. The estimation of v f and delta is expected to be helpful in comprehensively understanding the phase diagram and in predicting the phase behavior of CO 2 /organic solvent/polymer systems.