The Study Of Extraction Of Acetic Acid From Aqueous Solutions

For a long time, separation of acetic acid aqueous solution is a technical challenge whichpersecutes many enterprises. Study on the effective separation of acetic acid aqueous solution notonly benefits economy and society, but also plays an important role in the disciplinedevelopment such as chemical engineering separation and environmental protection.The coupling treatment method of liquid-liquid extraction and azeotropic distillation wasproposed on the basis of summary of treatment methods of acid wastewater in this paper.Extraction treatment of acetic acid wastewater with sec-butyl acetate as extraction agent wasstudied. The research contents and results of this paper are as follows:(1) The extraction treatment technology of acetic acid wastewater was investigated.Theeffects of operation conditions such as feed flow velocity, initial concentration of continuesphase, phase ratio and temperature on the extraction process were discussed. The results showedthat under the same phase ratio, the larger the feed flow velocity, the more quickly the processbecame steady.And the extraction effect became better then worse with the increasing feed flowvelosity.The higher the initial concentration of continues phase,phase ratio and temperature thebetter the extraction effect.(2) The mass transfer behavior in the system of sec-butyl acetate-acetic acid-water wasstudied. Firstly, mass transfer coefficient was measured and fitted. Single drop method was usedto determine the mass transfer coefficient while solute acetic acid transferring from aqueoussolution to drops of sec-butyl acetate under various conditions. Parameter variations were thedrop size, initial solute concentration and temperature. The results showed that overall dispersedphase mass transfer coefficient remarkably increased with increasing drop diameter andtemperature, while decreased with the solute concentration in continuous phase. Moreover, theexperiment data was fitted with the modified combined film mass transfer coefficient model, andgood agreement was observed between the calculated values and the experiment data.Secondly, experimental study of interfacial instability characteristics accompanying withinterphase mass transfer was carried out.The shadowgraph optical technique was utilized toobserve the Marangoni convection with interphase mass transfer between two planar liquidlayers. It was found that the interfacial cellular convection appeared when the acetic acidconcentration in aqueous solution reached25%. Besides, optical contact angle measuringinstrument was applied to observe the hydrodynamic instability of single drop. In the case of acetic acid transferring from drop of water to sec-butyl acetate, the instability occurred when thesolute concentration was greater than15%. The instability dominated by Rayleigh-Taylorinstability when solute concentration is lower than25%.While it reaches25%,the instability iscontrolled by the combined impact of Rayleigh-Taylor instability and Marangoni effect. With theincreasing solute concentration, the drop oscillated more intensely. In the opposite mass transferdirection the instability arises due to Rayleigh-Taylor instability.(3) Numerical simulation of the Marangoni effect was performed. On one hand, CFDsoftware was employed to simulate the Marangoni effect driven by temperature difference. Thesimulation result suggested that the physical coupling between the temperature and the velocityfield was visible when the temperature difference was higher than0.05K. And the Marangonieffect occured. The Marangoni effect became more pronounced as the temperature differenceincreased. On the other hand, a level set method was applied for simulating the moving processof single drop in an immiscible liquid, calculating the drop deformation in two-dimensional andthree-dimensional space. Evolution of the Marangoni convection in the cases of acetic acidaqueous solution was the disperse phase and the continuous phase separately were performed fordifferent initial solute concentrations varied from25%to50%. And the drop shape changedrulelessly. The numerical calculation results were consistent with the experimental results.