Iranian Journal of Chemical Engineering (IJChE)

Abstract The droplet size distribution in the column is usually represented as the average volume to surface area, known as the Sauter mean drop diameter. It is a key variable in the extraction column design. A study of the drop size distribution and Sauter-mean drop diameter for a liquid-liquid extraction column has been presented for a range of operating conditions and three different liquid-liquid systems. The effects of rotor speed, and dispersed and continuous phase velocities on drop size are investigated. Drop size distribution are appropriately described using the normal and log-normal probability density functions. The mathematical approach is used to determine the constant parameters in these functions and to provide the fit of the experimental data with them. and empirical expressions are derived to predict the parameters of the distribution curve as a function of operating variables, and physical properties of the systems. Good agreement between the prediction and experiments was achieved for all investigated operating conditions. An empirical correlation is also proposed to predict the Sauter-mean drop diameter with mean deviation of 9.8%.

Abstract Mass transfer coefficients of rising drops in spray and packed columns with random and structured packing in a liquid-liquid extraction operation were experimentally measured and the results compared. In this work, a high interfacial tension chemical system of toluene-acetic acid-water in a structured packed column is investigated. Results of random and structured packing show that random types are effective only for a drop size less than 9 mm, while the structured ones are shown to have a positive effect on mass transfer coefficient in a wide drop size range. Furthermore, structured packing proved to be slightly more effective than random packing in improving the mass transfer coefficient. The effect of drop size on mass transfer coefficient has also been studied in this work and the results showed that when the drop diameter increases, the mass transfer coefficient increases too. Finally, new correlations for the prediction of the mass transfer coefficient in both a random and structured packed column have been introduced which are in better agreement with the experimental data in comparison with those resulted from Newman, Kronig-Brink and Handlos-Baron models.

Abstract The effects and influences of various operational parameters on the efficiency of mixer-settlers are thoroughly studied in this paper. One of the most important factors in designing a mixer-settler is to obtain an optimum operational extraction and overall efficiency. These two factors are dependent on various parameters such as impeller shape, size and speed of impeller, baffle size, residence time, volumetric flow rates and the ratio of heavy to light phases. In this paper, the effect of impeller speed and volumetric flowrates of two phases on efficiency are studied. Also, the effect of hold-up of each stage upon stage efficiency is studied. According to the above experiments and achieved results, it can be concluded that in general, an increase in impeller speed and solvent amount results in an increase in extraction efficiency. Also, when hold-up of the dispersed phase decreases, the stage efficiency usually increases up to a certain point.