| Acetic acid is an important organic chemical raw material which is widely used in basic organic synthesis, medicine, dyestuff, spices, pesticides, etc. Lots of acetic acid wastewater is produced in these paints. Acetic acid and water does not form azeotrope, but their relative volatility is small. Therefore, the recovery of acetic acid wastewater has been problems of processes related with acetic acid. Currently, azeotropic distillation, extraction and adsorption are often used to separate the acetic acid-water in industry. These typical processes for separating acetic acid wastewater are characterized with high energy consumption and low concentration of acetic acid. Therefore, researchers in both industry and academia are looking for a better solvent and separation process. The technology of liquid-liquid extraction coupled with azeotropic distillation is proposed in this paper for treatment of acetic acid wastewater by using sec-butyl acetate as an extractant and entrainer. The basic data of sec-butvl acetate in acetic acid wastewater treatment has not been reported in literature, therefore, basic researches of this liquid-liquid extraction coupled with azeotropic distillation process are carried out.The LLE and VLE data are important in liquid-liquid extraction coupled with azeotropic distillation. Firstly, the basic data were determined:(1) The kinetics data of the hydrolysis of sec-butyl acetate were studied because sec-butyl acetate could be hydrolyzed to acetic acid and sec-butyl alcohol. Kinetics model of hydrolysis reaction was established. The kinetics parameters of model equation were calculated by Particle Swarm Optimization method. (2) The Liquid-liquid equilibrium (LLE) data of the ternary system water+sec-butyl alcohol+sec-butyl acetate were determined at 298.15K-363.15K. The experimental data were correlated successfully with the NRTL and UNIQUAC equation. The quaternary system water+sec-butyl alcohol+sec-butyl acetate+acetic acid with reaction were also determined at 3O3.15K-333.15K. The thermodynamics model of this quaternary system with reaction was established. The experimental data were correlated with the NRTL and UNIQUAC model. The NRTL equation is suitable for describing the LLE of this quaternary system with reaction. (3) The saturation vapor pressure of sec-butyl acetate was measured by using modified Rose type and corrected by Antoine equation. The Antoine equation parameters were obtained. Isobaric vapor-liquid equilibrium (VLE) data of the binary system acetic acid +sec-butyl acetate and sec-butyl alcohol+sec-butyl acetateare determined by using the modified Rose type. The experimental data were correlated successfully with the NRTL and UNIQUAC equation. The quarternary system water+sec-butyl alcohol+sec-butyl acetate+acetic acid were also determined at 101.3kPa by using the modified Rose type. The experimental data were correlated with the NRTL and UNIQUAC equation. The NRTL equation is suitable for describing the VLE of this quaternary system with reaction.Secondly, the mass transfer behavior in the system of sec-butyl acetate-acetic acid-water was studied. (1)The optical contact angle measuring instrument was applied to observe the hydrodynamic instability of single drop. (2) The CFD software was employed to simulate the Marangoni effect driven by temperature difference. (3) Single drop method was used to determine the mass transfer coefficient. The effects of size of the drop, initial solute concentration and temperature were obtained on the mass transfer coefficient. The results show that the mass transfer coefficient is increased with the increasing of drop diameter and temperature, while decreased with the increasing of concentration in continuous phase. Moreover, the experiment data are fitted with the modified combined film mass transfer coefficient model. The result shows that the model is in a good agreement with experimental data. (4)The extraction treatment technology of acetic acid wastewater was investigated. The effects of operation conditions such as feed flow velocity, initial concentration of continues phase, phase ratio and temperature on the extraction process are discussed.Lastly, the simulation of the process of liquid-liquid extraction couple with azeotropic distillation was performed. Base on the phase equilibrium data determinated in the work, the liquid-liquid extraction and azeotropic distillation process was simulated in a tray tower for a PTA wastewater. The non equilibrium theory and heterogeneous models were used in the simulation of the azeotropic distillation. The suitable conditions were obtained for the system. The simulation results have important guiding significance for the design and reconstruction of recover process of the acetic acid wastewater. |
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