Solubility determination and thermodynamic modeling of bis-2-hydroxyethyl terephthalate (BHET) in different solvents

Abstract Studies on the degradation process of waste polyethylene terephthalate (PET) have become increasingly mature, but there are relatively few studies on the separation of degradation products. The products contain many components and the separation of which is difficult. Therefore, the study on phase equilibrium thermodynamics of bis-2-hydroxyethyl terephthalate (BHET) is of great theoretical significance and practical value to provide basic data for the BHET crystallization separation. In this work, the degraded products were purified and characterized. The solubility of BHET in methanol, ethanol, ethylene glycol, water and the mixture of ethylene glycol+water were determined by static method. The experimental results were correlated with different models, such as IS model, λh equation, Apelblat equation and NRTL model. Based on the Van't Hoff equation, the mixing Gibbs energy, enthalpy and entropy were calculated. From this work, the basic data which can be used to guide the crystallization process of BHET were obtained, including solubility data, correlation model and thermodynamic properties