The solid–liquid equilibrium, excess molar volume and refractive deviation properties of binary systems containing dimethyl carbonate, anisole and phenol
Introduction
Polycarbonate (PC) is an important engineering thermo-plastic material known for its superior features, such as its high impact resistance, and its excellent electrical and heat resistance properties [1]. The market for aromatic PCs has grown by more than 10% annually since the late 1990s. The current worldwide PC production capacity exceeds 1.5 million t/year, and the expectation is that new plants capable of producing PC will continue to be constructed [2], [3]. However, the process by which PC is currently synthesized is not only environmentally unfriendly, but also a safety and health hazard. The primary commercial method for the synthesis of PC involves the interfacial polycondensation reaction of bisphenol A (BPA) with phosgene, a highly toxic gas, a process that requires the use of copious amounts of dichloromethane, a volatile and potentially harmful liquid, as the solvent [3], [4]. Increasing demands for safer and cleaner chemical processes have therefore prompted attempts to improve or essentially replace the process based on phosgene by more environmentally friendly or compatible processes [5]. Polycarbonate is typically produced by polymerizing diphenyl carbonate (DPC), a compound that has traditionally been synthesized by reacting phenol with phosgene. However, several approaches for producing DPC without using phosgene have since been explored [4], [6], of which the trans-esterification of dimethyl carbonate (DMC) with phenol has proven to be the most attractive and commercially promising route. This route consists of two reaction steps, enabling the achievement of a good separation between the reactants and products such as methanol, dimethyl carbonate (DMC), phenol, anisole and DPC. The purity of DPC directly influences the quality of the PC, with high-purity DPC being critical for producing PC that meets the requirements of optical media applications [7]. For this reason, an effective high-yield procedure for the isolation of the DPC product from the synthetic mixture is very important. Crystallization, could serve as an energy-saving separation method, and the development of a feasible process, would require knowledge of the solid–liquid equilibrium (SLE) data. However, to date relatively few studies have examined these phase equilibria and the properties of the pure components of the mixtures, knowledge of both of which would contribute to the understanding of the separation process.
Therefore, this research examined the binary SLE of the following systems analytically at atmospheric pressure: {DMC + anisole}, {DMC + phenol} and {anisole + phenol}. The measured SLE data were correlated with the non-random two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) models. Furthermore, the excess molar volumes (VE) and deviations in the refractive indices (ΔR) at 323.15 K were calculated using the directly determined density (ρ) and refractive index (nD) for the same binary mixtures, properties which provided insight into the molecular interactions in the non-ideal systems and assisted with the design of the separation process. The calculated binary VE and ΔR data were fitted to the Redlich–Kister polynomial.
Section snippets
Materials
Anisole was supplied by Junsei Chemical Co. Ltd (Japan). Dimethyl carbonate (DMC) was obtained from Sigma–Aldrich (USA). Phenol and methanol were supplied by Samchun Chemical (Korea). Anisole, DMC, and methanol were dried using molecular sieves with a pore diameter of 0.3 nm. The water content of the chemicals, which was determined using a Kar-Fischer titrator (Metrohm 684 KF-Coulometer), was less than 65 ppm. Before experimentation, the purities of the above chemicals were periodically confirmed
Solid–liquid equilibrium
The SLE of a eutectic system can be calculated by relating information about the system's real behavior in the liquid phase to the physical properties of the pure components of the system (i.e. the melting point, enthalpy of fusion, transition temperature, and enthalpy of transition) using Eq. (1), which can be derived from the iso-fugacity criterion [14]:where xi is the mole fraction in the liquid phase, γi is the activity coefficient in the
Conclusions
Each of the solid–liquid equilibrium curves for the binary systems {DMC + anisole}, {DMC + phenol} and {anisole + phenol} presented a simple eutectic point. The experimental equilibrium temperature obtained from these plots is well-correlated with the values that were calculated using the NRTL and UNIQUAC models, as confirmed by the RMSD values of the equilibrium temperature that were found to be less than ca. 0.5.
The VE data at 323.15 K for the binary {DMC + phenol} and {anisole + phenol} systems showed
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