Determination and correlation of binary molten solid-liquid equilibria of tetramethyl biphenyl isomers

Abstract Three binary molten phase diagrams of three isomers of tetramethyl biphenyl (TMB) were constructed by differential scanning calorimetry (DSC) at 101.3 kPa. Our results reveal that the tetramethyl biphenyl isomers binary system presents a eutectic behaviour that lays a solid foundation for its separation technology. Meanwhile, the thermodynamic model such as Wilson, NRTL and Ideal model were employed to correlate the phase equilibrium data of the tetramethyl biphenyl isomers. The results show the ideal model can describe two binary phase behaviour of 2,2',3,3'-Tetramethyl biphenyl (TMB1) + 3,3',4,4'-Tetramethyl biphenyl (TMB3) well while it isn't suitable for TMB1+2,3',3,4'-Tetramethyl biphenyl (TMB2) and TMB3+ TMB2 systems. The best correlation of the solid-liquid equilibrium data has been obtained by the NRTL equation. Besides, the mixing thermodynamic properties were calculated by NRTL model to gain more insights into the phase behaviour of the binary melt eutectic systems. Then, we discuss the co-effect of temperature and low melting point components on the binary phase melting mechanism. At last, non-linear enthalpy-entropy compensation analysis indicated different dissolution mechanism with the variation in mixtures composition.