Modification And Experimental Study On Surfactant Resistance Model Of Emulsion Liquid Membrane

The surfactant is indispensable for the stability of emulsion liquid membrane,but the adsorption of surfactant on the interface raise the interface resistance in emulsion liquid membrane which draws much attention in recent years,and the models considering the increased interface resistance due to surfactant were proposed.However,because the surfactant adsorption is dynamic and the process of surfactant adsorption on the external interface of the emulsion liquid membrane is simultaneous with the separation process,the adsorption rate of the surfactant would have some effects on the mass transfer in emulsion liquid membrane especially the surfactant with lower adsorption rate.But the models considering the increased interface resistance due to surfactant at present neglected this effects which would cause some deviation of the theory result from the actual process. Considered the factors mentioned above and based on the present models which considering the increased interface resistance due to surfactant,the improved model which considering the effects of adsorption rate of the surfactant on the external interface of the emulsion liquid membrane was proposed.First,to detect the effects of emulsions preparation parameters and operating conditions on mass transfer in emulsion liquid membrane,the emulsion liquid membrane with LIX 84-Ⅰas carrier,T161 as surfactant,kerosene as membrane phase and the sulfuric acid solution as inner phase was prepared and used to extract copper from water,and the influencing factors which include the pH value of inner phase,the membrane phase behavior,the surfactant in the membrane phase,the stirred speed and the temperature was investigated.The results show that the pH value of inner phase has no effect on copper(Ⅱ) extraction by emulsion liquid membrane if the concentration of hydrogen ions is more than 1.0mol/L;there are some effects on mass transfer in emulsion liquid membrane when system temperature and the stirred speed increased from 10℃to 50℃and 250r/min to 450r/min respectively;the difference of extraction rate between kerosene and liquid paraffin as membrane phase respectively is noteworthy.It's also worth mentioning that there is obvious difference on extraction rate between the emulsion liquid membrane with Span 80 and T161 as surfactants respectively, especially during the extraction time from 20s to 120s;but the difference is small at first 20s in the extraction process,the reason of which would be related to the surfactant adsorption rate. In the end,tracer method was used for detection of the breakage rate of emulsion liquid membrane,the result shows that the breakage rate of emulsion liquid membrane is lower than 0.4%and can be ignored.Second,based on the experiment results and fact that the effect of emulsion liquid membrane breakage could be neglected,the present model considering the increased interface resistance due to surfactant as well as the theory that the amount of surfactants adsorbed on the interface is a gradual increase process,the improved mass transfer model for emulsion liquid membrane is proposed which considering the continuous-phase resistance,the interfacial resistance,the permeation through a composite emulsion globule,and more important,the effect of surfactant adsorption rate on external interface of emulsion liquid membrane on mass transfer.The parameters in the model are obtained by experiment and the model equations are solved by MATLAB software.The experiment results of extraction of copper from water by emulsion liquid membrane with LIX 84-Ⅰas carrier and T161 as surfactant indicate that the agreement between the experiment date and calculated results are satisfactory.Compared to the other models which neglect different factors,the theory result of the developed model in this thesis has better agreement with the experiment result,especially at the first 20s in the separation process;what is more,the surfactants with low adsorption rate has important effects on mass transfer in emulsion liquid membrane especially when the adsorption time is similar with the separation process.Because emulsion liquid membrane has much higher extraction rate at the beginning of the separation process,the better interpretation of this would be of more significance.