| The separation of acetic acid aqueous solution is a technical challenge which persecutes many enterprises. The investigation of the effective separation of acetic acid aqueous solution benefits both the economy and the society, which has important significance for industrial application. Extraction treatment of acetic acid wastewater with n-propyl acetate as extraction agent was studied. The research contents and results of this paper are as follows:(1) The extraction treatment technology of acetic acid wastewater was investigated. The effects of operation conditions such as feed flowrate, initial solute concentration of continuous phase, phase ratio and temperature on the extraction process were discussed. The results showed that the initial concentration of acetic acid should be between 20% and 40%. In addition, under the same phase ratio, the concentration of acetic acid in the raffinate phase increased at first and then decreased with the increase of the feed flowrate. And in the selected concentration range, the higher the initial concentration of continuous phase is, the phase ratio and temperature the better the extraction effect.(2) The process of mass transfer in w-propyl acetate/acetic acid/water system during the free rise of drops in a quiescent continuous phase was ascertained on the basis of single-drop extraction experiments. Mass transfer rate measurements were conducted for different drop sizes and initial solute concentrations. In all trials, mass transfer was directed from the continuous phase to the dispersed phase. The research results show that:① In n-propyl acetate/acetic acid/water system, the drops exhibited the Marangoni phenomena, and a cyclic and oscillatory motion when the drop diameter dp≥ 3.0 mm.② For a given initial solute concentration, the mass transfer rate increased in the case of smaller drops. For a given drop diameter, in the range of 0.05-0.15 g/ml, the mass transfer rate was controlled by the Marangoni convection, so it increased with the increase of the initial solute concentration. But in the range of 0.15-0.25 g/ml, the mass transfer rate decreased with the reduction of the Reynolds number for the stronger Marangoni convection could not compensate the decrease of the Reynolds number. The mass transfer rate reached its maximum value at an initial solute concentration of 0.15 g/ml. The results suggested that there existed a competing mechanism between reduction of velocity and mass transfer enhancement due to Marangoni effects. The data for different drop diameters fell on one curve if the values were plotted against the Fourier number.③A correction factor, α(ΔcA0), was introduced to a modified Newman model to account for the influence of the initial solute concentration on the mass transfer rate. The a term was fitted to the experimental data and the maximum value of a was obtained at an initial solute concentration of 0.15 g/ml, and so was R’, indicating that the initial solute concentration had a greater impact on the mass transfer rate under this condition.(3) Through applying the level set method, numerical simulation of the motion of the single drop was performed for the n-propyl acetate/acetic acid/water system. The results showed that the drop shape was gradually deviated from the sphere as the drop was rising or falling in the acetic acid aqueous solution. As the initial solute concentration became higher, the deformation of the drop was more evident and so was the case of the bigger drop, which showed the stronger Marangoni convection. For the higher concentration of acetic acid aqueous solution which was used as the dispersed phase or the continuous phase, the system showed a significant Marangoni phenomenon.The technological process and mass transfer process for the n-propyl acetate/acetic acid/water system was investigated in this thesis, and it was very important for understanding the mass transfer mechanism of extraction process and the design and scale-up of the extraction column. |
PDF Full Text Request