The Vapor-liquid-liquid Phase Equilibrium For Water-cyclohexane-acrylic Acid System

The refining process of acrylic acid needs to remove the impurities such as water and acetic acid.Special rectification process are needed in industrial production for acrylic acid,such as heterogeneous azeotropic distillation and extractive distillation.All these processes are involved with VLLE,which means the shortage of VLLE data for acrylic acid may have a great influence in design and calculation for these technological processes.Thus the study of our work designed and built an VLLE experimental facility for Water-Cyclohexane-Acrylic Acid system.The phase equilibrium data of the system has been measured and some thermodynamic models has been selected and regressed.The study of our work solve the problem of lacking VLLE data for system with acrylic acid under the low pressure condition and also provide infallible data for further study of thermodynamic fundamentals.The key to VLLE determination is mixing,we analyzed the mechanism of interphase transfer in VLLE process and add the magnetic matrix mixer into the experimental apparatus.The structure of samplings are also redesigned to solve the difficulties of sampling under the low pressure.The new VLLE experimental facility can determined the equilibrium data under the low pressure conditions,and passed the reliability inspection which means it can be used in our work.Considering the actual production conditions of acrylic acid’s refining,we took 200 mmHg as the pressure condition and determined the VLLE data for Water-Cyclohexane-Acrylic Acid system.In order to solve the problem of lacking thermodynamic model for acrylic acid system.We based on the definition of thermodynamic models and the characteristic of acrylic acid,selected NRTL,NRTL-HOC,UNIQUAC-HOC models to correct the non-ideality for the system.The binary interaction parameters in these models were regressed with experimental data.After that,these models were used to predict the equilibrium behavior for the system.The comparative result between prediction and experimental indicated that the NRTL-HOC has the precisely prediction result than other thermodynamic models,the mean mole deviations for vapor-liquid-liquid phases are 0.0045,0.0232,and 0.0093.