The Study Of Thermodynamic Consistency Check Method For Vapor-Liquid-Liquid Phase Equilibrium Of The Associating System

The process design and reform of heterogeneous azeotropic distillation requires vapor-liquid-liquid equilibrium(VLLE) data. But, isobaric vapor-liquid-liquid equilibrium data is hard to come, the vapor temperature will oscillate and one liquid phase will disappear since the difficulty of keeping the liquid phases properly mixed, this is the main reason for the lack of the VLLE data. In addition, vapor-liquid-liquid equilibrium system, special in the associating system, has high non-ideal degree, lack of general and applicable data calculation and thermodynamic consistency check method. At present, there has no applicable thermodynamic consistency check method applied for vapor-liquid-liquid equilibrium system containing the associating components.In this paper, the existing thermodynamic consistency check method and the characteristics of associating system has been studied. Combined with the Hayden-O'connell method and Wisniak method, after introduced fugacity coefficient to fix vapor phase's non-ideal degree, a thermodynamic consistency check method applied for vapor-liquid-liquid equilibrium system containing the associating components has been established. 8 group binary VLE systems have been checked by the new consistency check method and the Herington area method, the results indicate that all of 8 group systems are consistent with the two methods. The water-acetic acid-methyl ethyl ketone VLE system and the Water-isopropenyl acetate-acetic acid VLLE system have been checked by this new consistency method. The results indicate, in addition to a azeotropic point of water-acetic acid-methyl ethyl ketone system, all the rest are consistent to the new method. The reason that the data is not consistent to the thermodynamic consistency is given, and points out the applicable scope of the new method.According to the binary liquid phase's mixing effect in the existing VLLE device is not ideal, based on the analysis of the existing mixing mechanism and equipment, the pressure drop and mixing effect of the static mixer has been studied. The results indicate the static mixer can be introduced to the phase equilibrium devices. Based on the analysis of the VLE and VLLE apparatuses, a new VLLE apparatus has been built, then the apparatus has been checked by previous literature. The results indicate that the data obtained from the experiment are consistent with the previous literature, the new apparatus is accurate and reliable to measure VLLE data.Combined with the requirement of removing acetic acid in the process of purified acrylic acid, the water-acetic acid-cyclohexane system in 101.3 kPa has been measured to solve the lack of the water- acetic acid-entrainer system data in 101.3 kPa, then the results has been checked by the new consistent check method. The results indicate that all the values of D are less than 3, the data are consistent with the consistency check method and can be used as basic data for the process improvement of removing acetic acid.