Investigation Of Phase Equilibria For Binary Supercritical Carbon Dioxide And Polymer Systems

The PC-SAFT equation of state (EOS) is used to investigate the vapor-liquid equilibria for supercritical carbon dioxide (SC-CO₂) and hydrocarbon binary mixtures. The binary interaction parameters (k_ij) are regressed by using the experimental data. When the carbon number n in each hydrocarbon ranges from 1 to 20, the regressed k_ij increases monotonously with the increase of n. However, when n is greater than 20, there is a unique binary interaction parameter (k_ij=0.16) that can well describe the vapor-liquid phase equilibria for CO₂-C₂₀H₄₂, CO₂-C₂₈H₅₈, CO₂-C₃₆H₇₄ and CO₂-C₄₄H₉₀ binary mixtures.Investigation shows that SC-CO₂ has excellent dissolving capacity for small organic molecules. However, for long chain n-alkanes, only under the conditions of high temperatures and high pressures can they be well dissolved by SC-CO₂. Moreover, for long chain polymers with m ranging from 30 to 50, only when segmental diameter ranges from 0.2 to 0.4nm, energy parameter ranges from 195 to 200K and the temperature is above 773.15K, can they be well dissolved.