Phase Behavior of Binary Mixtures Containing Succinic Acid or Its Esters

This work provides experimental data and thermodynamic modeling on phase equilibria of binary mixtures that are relevant for esterification reactions. The components under investigation include water, succinic acid (SA), ethanol (EtOH), 1-butanol (1-BuOH), and the diesters of SA, namely, diethyl succinate (DES) and dibutyl succinate (DBS), respectively, as well as the organic solvents acetonitrile (ACN) and tetrahydrofuran (THF). Liquid–liquid equilibria (LLE) of water/DBS were measured at ambient pressure for temperatures between 313 and 353 K. Isobaric vapor–liquid equilibria (VLE) were measured for the binary systems ACN/DES, ACN/DBS, 1-BuOH/DBS, and THF/DBS at pressures of 10 or 20 or 30 kPa. Temperature ranges for the isobaric VLE varied between 300 and 500 K. The measured data and phase equilibria reported in literature were accurately modeled using perturbed-chain statistical associating fluid theory (PC-SAFT). For this purpose, pure-component PC-SAFT parameters, which were not already reported in the literature, were adjusted to experimental literature pure-component data. Applying binary interaction parameters allowed precise phase-equilibrium modeling results of the binary systems under investigation. Two different association schemes for water were used (“2B” and “4C”). Both schemes appeared to be suitable to describe phase equilibria of aqueous mixtures; however, a binary parameter for the Wolbach–Sandler mixing rule was required for aqueous mixtures modeled with the 4C scheme. For LLE modeling the 2B scheme was found to give better modeling results. In general, the 4C association scheme for water yields better results for mixtures with two self-associating components while the 2B association scheme for water should be preferred if mixtures are considered with water and a non-self-associating component. Further, the modeling concept of “induced association” has been investigated and discussed. Especially for mixtures with esters, which are of main importance for esterification mixtures, the induced-association approach turned out to be a more accurate modeling strategy compared to the nonassociative approach.