| Membrane separation technology is a new method to treat oily wastewater.And it has attracted wide attention because the effectiveness in the separation of oil-water mixture.But the treatment of the oil-water emulsion containing emulsifiers by membrane,because of the interaction between the emulsifier and oil,water,the membrane,has complex separation mechanisms to separate difficultly.Therefore,the study of membrane separation of oil-water emulsion containing emulsifiers is necessary.Ceramic tube membrane was applied to the separation of oil-in-water emulsion by crossflow microfiltration.Effects of three industrially used emulsifiers,cetyltrimethyl ammonium bromide?CTAB?,sodium dodecyl sulfate?SDS?and Tween 80 were investigated.Firstly,Orthogonal rest technique was employed with concentration of oil,temperature and flow as well as operating pressure selected as affecting factors in this paper.Orthogonal experiment results showed that the maximum steady permeate flux was existed under operating conditions of 0.5 g?L-1?50??60 L?h-1?0.16MPa.Then,under the optimum experimental conditions,the effect of different kind and concentration of emulsifiers on the the separation of oil-water system containing three kinds of emulsifier by the stable flux and emulsifier evaluation index?EE?,to the separation result and the membrane fouling,were studied.The results showed that the response degree of the seperation of the emulsions containing 1 g?L-1 emulsifier to pressure,flow,temperature and concentration from big to small order was CTAB>tween 80>SDS.And the membrane pollution degree had the contrary regular.At low concentrations,CTAB and Tween 80 for influence of oil-water separation is greater than SDS.At high concentration,the regular was contrary.Based on the experiment of oil-water separation,the process mechanism of oil-water separation was discussed theoretically by the modeling method.Research showed that process of the seperation of emulsion of SDS was in accordance with partial blockage model,while CTAB and Tween 80conformed to cake layer filtration model in pre filtration the separation.The order of demulsification effect of three kinds of emulsifiers was Tween 80>CTAB>SDS,but the order of steric effect was CTAB>tween 80>SDS.When the oil content of the permeate side was the same,if the stronger the effect of demulsification was and the weaker the effect of steric was,the greater the average oil droplet size and the poorer the membrane separation effect was.The theory of molecular level was also discussed.The molecular simulation method was adopted to study the stability of emulsifier in oil-water interface under different conditions.Relations of oil-water interface formation energy?E?and interface diffusion coefficient?D?of emulsifier with species,number and temperature were analyzed.Simulative results showed that the order of E and D about three emulsifiers was CTAB>SDS>Tween 80.And E was increased first and then decrease with the number of emulsifier rising,while D was opposite.The This simulation result explain the experimental phenomenon that the permeation flux was increased first and then decreased with the increase of the concentration of Tween 80.With temperature rising,E and D gradually increased and Tween 80 might result in emulsion breaking.In summary,the simulation results explain demulsification mechanism on the microscopic molecular level,in a certain extent,which can explain the results of oil-water separation.The results of research can provide the basis for the industrial application of membrane. |
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