| Supported liquid membrane (SLM) separation technology combines the characteristics of solvent extraction and solid membrane separation, which realizes the inner coupling of extraction and back extraction. Moreover it has some advantages such as high separation efficiency, none addition of surfactant, little use of organic phase and ease of operation. However due to its instability and relative short lifetime, there is still not industrial application of SLM. The study of mass transfer process and instability mechanisms of SLM is imperfect so far. Therefore the mass transfer process and instability of phenol extraction system and copper (â…¡) ion extraction system were studied in this thesis. The main results are summarized as follows.(1) A liquid-liquid equilibria cell was used to determine the distribution ratios of phenol between organic phase (TBP in kerosene) and aqueous phase. Moreover a model was established for the distribution ratios, which took the complexation effect between TBP and water and physical extraction effect of kerosene into account. Mass transfer process of phenol from feed phase into stripping phase through SLM using Celgard2500 flat-sheet membrane as supports and tributyl phosphate (TBP) dissolved in kerosene as carrier was studied. A model based on two-film theory was used to describe the process.(2) The extraction equilibria of copper (â…¡) ion between aqueous solution and organic solution (LIX984N in kerosene) were discussed. The mass transport of copper (II) ion through SLM was studied and a model for this process based on two-film theory was also built. According to the variation of separate mass transfer coefficient in SLM, km it was easy to find out that the carrier concentration in SLM was gradually decreasing as the mass transfer proceeded.(3) Electrochemical impedance spectrometry (EIS) was employed to study the ML loss during the mass transfer process of SLM. The obtained EIS diagrams were analyzed by the equivalent circuit method. Furthermore, the electrical characteristic of a partially decayed SLM was analyzed from its physical properties. In order to find out the governing mechanisms of SLM instabilities, two SLM systems, phenol transport and copper (â…¡) ion transport were studied by the EIS method. The results showed that:shear induced emulsion formation should be the main reason for ML loss, and conditions facilitating emulsion such as high carrier concentration, fast stirring speed, low salt concentration in aqueous solution and high HLB value of membrane liquid all accelerated the ML loss; in a practical operation especially long term operation more than one mechanism worked together to provoke the instability and shorten the lifetime of SLM.(4) Combining the measurement and characterization of physical properties the instability mechanisms of SLM were discussed deeply. The results showed that emulsion formation was the main mechanism for ML loss. With the addition of external energy the ML would lose to the adjacent aqueous solutions through emulsion droplet. The vacant space would be filled in by the ML from the same pores or connected pores and the interface of ML and aqueous solution would penetrate into the pores from the other side, which resulted in a total loss of SLM.In summary, SLM is a very efficient separation method, but the loss of carrier from the membrane liquid would result in a quick decrease of mass transfer coefficient; EIS method provides a new, real time and accurate method to determine the status of membrane liquid loss; The governing instability mechanism of SLM is emulsion formation provoked by the addition of external energy but other mechanisms, such as solubility and the pores gradually wetted by aqueous solution also accelerate the degradation of SLM. |
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