| Membrane permeation extraction connected with liquid-liquid extraction is a new membrane separation technology,which is often used for separation of volatile organic compounds and mixtures of low boiling point.The theory and applied research of membrane extraction technology in wastewater treatment is very active,the technology in the treatment of high salinity and high concentration organic wastewater has the advantages of low energy consumption,convenient operation etc.Recently,the application of membrane extraction technology is mainly focused on the silicone rubber membrane,but its application is limited due to its poor acid and alkali resistance.Ethylene propylene dinne monomer membrane(EPDM)can effectively make up for the lack of silicone rubber membrane with good resistance of acid and alkali and physical and mechanical properties.In this paper,9 aromatic acids were selected as the target pollutants,and the influence of the structure parameters of aromatic acids on the extraction characteristics was studied by static experiments.P-aminobenzoic acid(PABA)was selected as the target pollutant,a novel membrane permeation extraction system was constructed by EPDM membrane through dynamic experiment,the removal/permeation rate and permeation flux were improved by optimizing the operating conditions of the influent flow rate,the pH value of the extraction phase,the temperature,the concentration of NaCl and the initial concentration of feed solution.As for the mas transfer character of liquid film boundary layer,membrane and support layer,mass transfer mechanism and process of aromatic acid through EPDM membrane were investigated.Descriptions of mathematical models of the process were developed respectively.According to the mass transfer resistance model,the main factors affecting the mass transfer process of were measured.The research results show that the EPDM membrane has good chemical compatibility with PABA.The number,type and position of the substituent of aromatic acids are the important factors affecting the removal efficiency,the removal rate and the structure parameters have strong correlation for aromatic organic acids with the same substituents.The removal characteristics of aromatic acids by EPDM membrane are determined by the structural parameters.Structural parameters are available to predict the effect of EPDM membrane on the removal of aromatic acids.When the influent flow rate is 1.5ml/min,the removal rate can reach more than 40% with the extension of the running time.The removal rate of PABA increases from 32% to 38% by increasing the pH of extraction phase and the transmittance increases significantly.The removal rate decreases with the increase of initial concentration of feed solution,while mass flux increases.The concentration of salt can improve the removal rate of PABA by 10%.Removal rate rises with the increasing temperature.Under the optimized experimental conditions with temperature of 30℃,the influent flow rate of 5.5ml/min and pH was 12,the salinity of 150g/L,the removal rate of PABA and the transmittance both increased about 12% and the permeate flux was increased from 5.91mg/m2·h to 21.66mg/m2·h.The mass transfer resistance of the boundary layer on liquid side accounts for about 5%-11% of the total mass transfer resistance.With the increase of Re,the mass transfer resistance of the boundary layer in the liquid side become smaller to the total mass transfer resistance.The total mass transfer coefficient increases with the increase of the concentration,and the mass transfer flux increases linearly with the increase of the concentration.There is a strong correlation between the total mass transfer coefficient and the concentration of salt ion.The quadratic equation can be used to express the relationship.The membrane resistance plays a decisive role in the mass transfer process and NaOH has a significant effect on the mass transfer coefficient in the extraction phase.The total mass transfer coefficient of PABA on the membrane increases with the increase of temperature,the permeability coefficient(P)and temperature(T)have the relationship with the Arrhnius equation.Under the optimized experimental conditions,the total mass transfer resistance decreased compared with the original mass transfer resistance.However,there is no change on the order of magnitude of membrane resistance,and the ability of experimental conditions to change the resistance of the membrane is limited. |
