Phase behavior of carbon dioxide/dioctyl phthalate and trioctyl trimellitate systems

Abstract

Phthalate plasticizers, which are widely used as general-purpose plasticizers for polyvinyl chloride (PVC), have been identified as harmful to human health. This has created a pressing need to separate these substances from PVC products. In addition, the potential contamination of trioctyl trimellitate (TOTM), an alternative to phthalate plasticizers, with dioctyl phthalate (DOP) cannot be overlooked. Supercritical carbon dioxide (scCO₂) has been proposed as a solvent for extracting and separating these compounds; therefore, understanding the phase behavior of these systems is critical for optimizing the process design. This study investigated the phase behavior of CO₂/DOP and CO₂/TOTM binary systems using a synthetic method combined with a laser displacement technique to measure the movement of the piston in a high-pressure vessel. The phase boundaries were determined over temperature and CO₂ mole fraction ranges of (313–373) K and (0.2–0.9), respectively. The vapor–liquid equilibria of the two experimentally obtained binary systems were correlated using the Sanchez-Lacombe equation of state. The one- and two-parameter mixing rules were tested, with better correlation over a wide composition range achieved using the two-parameter mixing rule. The results of this study imply that while separating DOP and TOTM using scCO₂ may be challenging, scCO₂ shows great potential as an extraction solvent for both plasticizers.