Phase behavior of diisobutyl adipate–carbon dioxide mixtures

Phase equilibrium data are reported for diisobutyl adipate (DiBA) in CO₂ at temperatures from 25 to 150 °C. This system exhibits a continuous mixture-critical curve with a maximum near 200 °C and 260 bar. The phase behavior of the DiBA–CO₂ system is well characterized and modeled with the Peng–Robinson equation of state using a single, fixed binary interaction parameter, k_ij. The DiBA–CO₂ data are compared to other solute–CO₂ systems with structures similar to DiBA to demonstrate the impact of the diester end groups in DiBA, which enhance DiBA solubility in CO₂ at low temperatures, relative to a single (ethyl laurate) or no ester end groups (tetradecane), and a single acid end group (tetradecanoic acid). DiBA–CO₂ data are also compared to data for two compounds each with diester groups but one containing an interior aromatic group (dibutyl phthalate) and the other containing the same number of interior carbon groups but with two less carbon groups at either end of the chain (divinyl adipate).