Binary Solid-liquid Equilibria Of Xylene Isomers

With the increasing awareness of the energy conservation, using crystallization technology for purification of p-xylene has been received much attention. Since the phase diagram is the basis for the separation process, the subject of this thesis mainly focuses on the solid-liquid equilibria of three xylene isomer binary systems.Based on the principle of the minimum Gibbs energy, the solid-liuqid equilibria of the three binary systems are calculated using Thermo-calc software. In the calculation, the solid phase is chosen as the reference staste, and the regular solution model is used to calculate the excess Gibbs energy of the system. Thermodynamic properties of pure components, theoratical estimation or experimental, from different literatures are used for the assessment of their sensitivity on the calculation. In general, the results of o-xylene/p-xylene system are better then the rest of the three isomer binary systems.In addition, Tween-80 is chosen as surfactant, and 1,2-propanediol as co-surfactant, the phase diagram of pseudo-ternary of Tween-80/p-xylene/l,2-propanediol aqueous system at 25℃ is studied. The phase diagram is divied into three regions, the microemulsion region, the two phase region and the emulsion region. The microstructure of the microemulsion is determined by conductivity measurement. Water-in-oil, bicontinous and oil-in-water structure are identified. Meanwhile, the microemulsion region is investigated at different temperature and different 1,2-propanediol/water ratio. The results show that the microemulsion region increases with the increasing of the 1,2-propanediol/water ratio. The oil-in-water microemulsion region decreases as the temperature increases.