Phase Equilibrium And Separation Process Simulation Of Dilute Acetic Acid Extraction-azeotropic Distillation System

Acetic acid is a very important basic chemical product and plays an extremely significantly role in the industry production.Acetic acid can be used as a raw material for chemical synthesis,and it is also an excellent organic solvent.As a solvent,acetic acid would become weak acetic acid through the production process.If the acetic acid wastewater is discharged directly,it is very harmful to the environment.The treatment of acetic acid wastewater has been a biggest problem to many chemistry companies for a long time.The energy consumption of dilute acetic acid recovery process is relatively high,and the proportion of the production cost is very high.The study on efficient separation of acetic acid and water not only benefits the economy and society,but also plays an important role in the whole production operation and environmental protection.On the basis of summarizing separation method of acetic acid-water system,we studied the azeotropic distillation process of acetic acid-water system,preferred process operation parameter.In the experimental study,the liquid-liquid phase equilibrium data of acetic acid-isopropyl acetate were measured at different temperatures in the atmospheric pressure firstly.The results show that the selectivity coefficient increaseed with the decrease of temperature.And NRTL model was used to correlate the experimental data.The phase diagrams under the two temperatures are drawn and analyzed systematically.Second,vapor-liquid equilibrium(VLE)data for water-acetic acid,acetec acid-isopropyl acetate and water-acetic acid-isopropyl acetate systems were measured at 101.33 kPa by using an improved equilibria cell.In the aspect of process simulation,the steady-state model of acetic acid dehydration process is put forward on the basis of the existing steady state model of dilute acetic acid dehydration azeotropic distillation column.According to the characteristics and separation requirements of dilute acetic acid,the comparison of the extraction of acetic acid was made by different azeotropic agent.Acetic acid isopropyl ester was selected as the extractant of dilute acetic acid extraction azeotropic distillation,and isopropyl alcohol was used as auxiliary extractant.The distillation problem of acetic acid was discussed,such as,the influence of the number of extraetion tower,the feed composition and extractor with different concentration in the process.Isobutyl acetate and N-butyl acetate was screened from the entrainers by observing their ability of entraining water.Acetic acid dehydration process via azeotropic distillation was established by using them separately.During the designing of the azeotropic column,the equation which could calculate the reflux flow was found.This equation brought a lot of conveniences in the designing process.Finally,an optimum proeess conditions is seleeted.Compared with azeotropic distillation,the final recommended proeess is extraetion-azeotropic distillation proeess.Second,the model of the flow process which was industrialized was set up using chemical software tool.The factors of extraction temperature,extractant ratio,extraction order,the reflux ratio,the feed position,the bottom of the column heater heat load were considerated during the distillation process.The results showed that with the increase of the extraction temperature,the water content in the raffinate increases linearly.Increasing the ratio of isopropyl alcohol was helpful to improve the extraction efficiency.When the feed plate is low,it could result in the increase of the azeotropic dose required for the heating evaporation at the bottom of the tower.With the increase of the number of the feed tray,the heat load at the bottom of the column decreased firstly and then increases.The best process parameters of practical significance were obtained by optimization of process conditions.The process of dilute acetic acid extraction azeotropic distillation was simulated.The temperature distribution in tower,the flow rate and the composition distribution were obtained under t the best process parameters.Through the above research,the optimum technological conditions of dilute acetic acid extraction azeotropic distillation were obtained,which will provide the technical support for the development of the process amplifying design of azeotropic distillation and the practical production of distillation process.