Study On The Interphase Mass Transfer Of Liquid-liquid Extraction Using The System Of Chloroform-DMF-water

With the development of polyurethane synthetic leather,pesticide and pharmaceuticals industry,large amounts of wastewater bring difficulty in recycling DMF technically.The separation of DMF aqueous solution benefits from reducing the pollution and lowering the cost,which has significant importance for industrial application.Base on the separation of wastewater containing DMF,study on the extraction process using the system of chloroform-DMF-water was conducted.The research contents and results of this study are indicated as follows:(1)Single drop experiment on the system of chloroform-DMF-water with special propertiey of high density difference was carried out to measure the overall mass transfer coefficients under different conditions.Chloroform-ethanol-water was also applied to make the mass transfer model more suitable.Then the effects of the initial solute concentration,drop diameter and temperature on the overall mass transfer coefficients were studied.The research results showed that:?In both systems,same results were obtained for the effect of various parameters.First,the overall mass transfer coefficients became higher with the rise of temperature.When the initial concentration increases,the overall mass transfer coefficient decreases where the effect of competition between Marangoni convection enhancement and drop diameter dreasing exists.Then due to the effect of shape deformation and internal oscillation,the overall mass transfer coefficients tended to be higher when the drop diameter increases.?Based on the Whitman two-film theory,the overall mass transfer coefficient of drops under the same condition was calculated when the drops can be seen as rigid sphere.Then,a mass transfer enhancement factor F was introduced to express the effect of shape deformation and internal circulation or oscillation on the mass transfer.The F term was calculated with experimental data,and then was correlated to be a function of several dimensionless numbers,such as Reynolds number,Weber number,density ratio and Sc number.The correlation showed good agreement with experimental data.(2)Experimental study of interfacial instability accompanying with interphase mass transfer was conducted.The OCA20 optical contact angle measuring instrument was used to observe the instability phenomenon of hanging drops with the system of chloroform-DMF-water.In addition,the influence of initial solute concentration and drop diameter on the instabilities of drops was discussed.The results showed that:under the same initial solute concentration,larger drops showed more violent Marangoni convection.And when the initial solute concentration increases,Marangoni convection in smaller drops could be observed.(3)The VOSET method was applied to catch the interface between the two phases.Numerical simulation on single drop with the system of chloroform-DMF-water was performed.The simulation results suggested that drop deformation would become more remarkable when the concentration of the single drop increases.Then the rise velocity was obtained.The results indicated that drops with larger diameter or higher solute concentration would experience more intense oscillation on the rise velocity,where exists greater influence of Marangoni convection on mass transgfer.(4)The extraction treatment technology of DMF wastewater with chloroform being extraction agent was investigated.The effects of operation conditions such as feed flow rate,initial solute concentration of dispersed phase,phase ratio on the extraction process were discussed.The result showed that the extraction ratio became better then worse with the increasing feed flow rate under the same phase ratio.The suitable flow rate tended to be 7mL/min.Then the extraction ratio increases when the flow ratio decreases.And the initial solute concentration should be about 10%wt.