Study On Pervaporation For Removal Of Dilute Organic Compounds From Water With Hollow Fiber Composite Membrane

Wastewater containing organic compounds,if is emitted directly,can cause pollution on the environment.For example,if ethyl acetate content in wastewater is too high,it can be a direct impact on the Chemical Oxygen Demand(COD)value of water,and reduce the efficacy of water treatment reagent,even lead to wastewater treatment reagent poisoned.Therefore,the discharge of ethyl acetate in wastewater must be strictly controlled. Pervaporation is suitable for removal of dilute organic compounds from wastewater.The hollow fiber membrane with the advantages of high unit volume density,large surface areas and self-supporting,are paid more attention to recently.In this study,the composite membranes have been prepared by coating polydimethylsiloxane(PDMS)on polyvinylidene fluoride(PVDF)hollow fiber membrane in laboratory.The effects of feed temperature,flow rate and feed concentration on the performance of the composite membrane for the separation of ethyl acetate/water,methyl acetate/water,propyl acetate/water, ethanol/water and acetone/water systems were studied.The result shows that these hollow fiber composite membranes have better pervaporation performance.The effects of operating conditions such as operating temperature,feed concentration and flow rate on the permeating performance were investigated by pervaporation of ethyl acetate/water with PDMS/PVDF composite membranes.It is shown that the increase of the feed concentration,flow rate and feed temperature is in favor of the permeation flux,and that the separation factor increases with the feed concentration at first and then decreases, increasing with the raising of feed temperature as well as flow rate.By means of the Willson plot method,the membrane resistance was determined, furthermore,the mass transfer coefficient of liquid phase and mass transfer correlation were obtained.The results indicate that the mass transfer process of pervaporation is controlled dominantly by mass transfer in the feed.The PDMS/PVDF composite membrane was used in methyl acetate/water and propyl acetate/water separation.The comparison of pervaporations performance for methyl acetate/water and ethyl acetate/water was carried out.It is shown that their peravporation behaviors correspond to ordinary rules,the methyl acetate permeating flux is larger than that of ethyl acetate at the same operating condition,and the relation of their selectivity is complex.The ethanol/water and acetone/water were separated by PDMS/PVDF composite membrane.The comparison of pervaporations performance for ethyl acetate/water,acetone/water and ethanol/water was studied.It is shown that their peravporation behaviors correspond to ordinary rules,the permeating flux and selectivity at the same operating condition decrease in the following order:ethyl acetate＞acetone＞ethanol.The results are in accordance with the principles of solubility parameter and inter-dissolution with similar polarity.