| Hollow fiber renewal liquid membrane(HFRLM) is a novel liquid membrane process.The main characteristic of HFRLM,which different from other liquid membrane processes,is that the flow in the tube-side is a liquid-liquid two-phase.In the flow fields,the dispersion phase(liquid membrane phase) renews the flow liquid membrane and so enhances the transport rate.In this thesis,a study on the mechanism of HFRLM mass transfer process is investigated using Cr(Ⅵ) as the main experimental system.The extraction efficiency of Cr(Ⅵ) by tri-n-butyl phosphate(TBP) and the stripping efficiency of complex by NaOH were studied by means of solvent extraction experiments.The extractive and stripping reactions were confirmed.The transport performance of Cr(Ⅵ) through bulk liquid membrane(BLM) process using TBP as mobile carrier was evaluated.A kinetic model was developed assuming that the Cr(Ⅵ) transport through BLM can be explained by a irreversible first-order reaction.The mass transfer behavior of Cr(Ⅵ) in BLM process was analyzed and the effect of the distribution coefficient on the mass transfer process was discussed.With the help of digital microscope camera technique,the liquid-liquid two-phase flow in the hollow fiber was investigated and a large of visual information was obtained.The existence of the droplets and the flow liquid membrane in the hollow fiber was proved.The correctness of the HFRLM basic theory was confirmed.According to the video,the flow pattem of the two-phase in the hollow fiber was divided into 6 kinds and a flow pattern diagram was drawn,which would be help for the determination of the operation parameters.Make reference to the molecule collision theory as well as the study of the droplet coalescence/breakage behavior,a mathematic model was proposed to describe the collision and coalescence between the droplet and the flow liquid membrane.This model provides a theory basis for the quantitative calculation of the mass transfer intensification and the deep investigation of HFRLM mass transfer mechanism.On the basis of the resistance-in-series model,the mass transfer process in the tube-side was divided into 3 steps:(1) the transport between the flow liquid membrane and the droplet,(2) the transport in the droplet and(3) the transport out of the droplet.In view of the complexity of the non-ideality in the shell side,both theory analysis and experimental verification were used to determine the appropriate shell side mass transfer correlation.Inside of the hollow fiber,the surface-renewal-stretch model was used to describe the mass transfer intensification phenomena caused by the collision between the droplets and the flow liquid membrane.Higbie permeation theory was used to describe the mass transfer process out of the droplet.The modeling study of HFRLM,would be helpful for the deep analysis of the mass transfer mechanism,and also give guidance to the HFRLM scaling up design and industrial application.The stability of the HFRLM was studied by monitoring the leakage of the tracer.Results show that the stability of the HFRLM was good and the leakage is less than 0.01%.Under the guidance of the mathematical model,the mass transfer behavior of various systems(such as Cr(Ⅵ),Cu(Ⅱ) and PG) through the HFRLM was studied systematically.The mechanism of the liquid membrane mass transfer process was analyzed from the point of view of the resistance and the driving force.The extraction/stripping distribution coefficient play an important role in the liquid membrane process.They affect the type and the rate of the transport,and even determine whether it will take place or not.The contribution of the individual mass transfer resistance to the overall resistance was affected greatly by the mixing method.HFRLM was used for chromium(Ⅵ)-containing wastewater treatment, which had advantages of rapidness and excellent treatment.The removal efficiency of chromium(Ⅵ) is bigger than 99.8%,and the Cr(Ⅵ) concentration in the treated outlet wastewater is less than 0.5 mg·L-1,which is lower than national discharge standards.No second-pollution in the whole treatment process,and the concentrated solution could be reused.HFRLM and has obvious economic and environmental benefits.HFRLM can be widely used in treatment of chromium(Ⅵ)-containing industrial wastewater. |
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