J. of Supercritical Fluids 34 (2005) 309–321 Phase equilibria of binary, ternary and quaternary systems for polymerization/depolymerization of polycarbonate V. Margon a , U.S. Agarwal a,∗ , C.J. Peters b , G. de Wit a , C. Bailly a , J.M.N. van Kasteren a , P.J. Lemstra a a Faculty of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands b Laboratory of Applied Thermodynamics and Phase Equilibria, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands Received 16 May 2004; received in revised form 1 September 2004; accepted 13 October 2004 Abstract Vapor–liquid phase equilibrium is studied for the systems composed of phenol, diphenyl carbonate (DPC), bisphenol A (BPA) and CO 2 . Bubble point pressures and vapor-phase compositions are measured at various temperatures (343.15–473.15K) for several compositions of the following systems: two binary systems DPC–CO 2 and BPA–CO 2 , three ternary systems phenol–DPC–CO 2 , phenol–BPA–CO 2 and DPC–BPA–CO 2 , and one quaternary system phenol–DPC–BPA–CO 2 . The Peng–Robinson equation of state (PR EOS) binary interaction parameters for the systems DPC–CO 2 and BPA–CO 2 are optimized by directly fitting to the corresponding experimental data. The PR EOS binary interaction parameters for phenol–DPC, phenol–BPA and DPC–BPA are obtained by fitting to experimental data of the ternary systems involving these constituents and CO 2 . The binary interaction parameters are then used to predict the phase equilibrium behavior of the quaternary system. A reasonable agreement with the experimental observations of this quaternary system indicates the predictive ability of the model in the range of our experimental measurements. © 2004 Published by Elsevier B.V. Keywords: Supercritical; Phase equilibrium; Polycarbonate; Phenol; DPC; BPA 1. Introduction Application of supercritical CO 2 is drawing increasing attention as a processing medium due to its non-toxicity, low cost, abundant availability in its pure form, easy removal, etc. An additional advantage of supercritical fluids is that its solvation characteristics are easily tailored by control- ling pressure, temperature and application of co-solvents, thereby providing an excellent medium for separation by extraction [1]. A reliable knowledge of relevant vapor–liquid equilibria (VLE) is required for successful development of industrial separation processes [2]. Such phase behavior of multicomponent systems is often described by equations of state (EOS). ∗ Corresponding author. Tel.: +31 40 2473079; fax: +31 40 2436999. E-mail address: u.s.agarwal@tue.nl (U.S. Agarwal). We are interested in developing a CO 2 -based system for extraction of components following the depolymerization of bisphenol A (BPA)-based polycarbonate. Such a system would be composed of BPA, diphenyl carbonate (DPC), phe- nol and CO 2 , perhaps along with oligomers of polycarbonate. In an earlier paper [3], we reported bubble point pressure mea- surements of the binary systems phenol–CO 2 and DPC–CO 2 . The phase behavior was described by the Peng–Robinson equation of state (PR EOS) using the quadratic mixing rules, and the involved binary interaction parameters were opti- mized. In the present work, we examine the VLE of the fol- lowing binary and ternary systems: DPC–CO 2 , BPA–CO 2 , phenol–DPC–CO 2 , phenol–BPA–CO 2 and DPC–BPA–CO 2 . The binary interaction parameters for the DPC–CO 2 and BPA–CO 2 systems are directly estimated from the exper- imental bubble point pressure and vapor-phase composi- 0896-8446/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.supflu.2004.10.008