| In this paper, the dynamic LBL polyion composite membranes were prepared by depositing polyacrilic acid and polyethyleneimine alternatively on the ultrafiltration support membrane under a certain pressure. The polyion composite membranes were evaluated by the pervaporation separation of water-ethanol mixture.In this study, the suitable preparation conditions were experimentally determined. The support membrane is polyethersulfone ultrafiltration membrane, the concentration of polyacrylic acid was selected at 0.05wt%, a suitable PAA/PEI ratio was 1/5-1/10 with a number of 4 bilayers. The molecular weight of PAA was 4 000 000. The corresponding filtration time of the first PAA layer range was 10 minutes while the reaction time was 20 minutes. Given these conditions, the separation factor and the permeate flux were about 1207 and 140 g/(m2·h) (40℃), respectively. Comared with static LBL process, dynamic LBL could shorten preparative duration and simplyfiy the preparative procedure. By varying the temperature and ethonal concentration of the feed solutions, the sepraration performance agreed with conventional pervaporation law, the suitable operating temeratue is determined at 40℃.The mechanism of composition of polyanion and polycation was characterized by IR and SEM. The surface of polyion composite membranes was uniform while the cross-section micrograph showed the separation layer was cross-linked with the support membrane very well. A mathematical model for continuous cross-flow ethanol-water pervaporation process was developed. Under the given operating conditions, the caculation data of water content in permeate agreed well with the experimental data. These contrast can be used to optimize the operating conditions. In addition, the regression equations of permeate flux was developed to optimize the operating conditions. These equations could potentially be used to predict permeate flux in the pervaporation separation of water-ethanol mixture. |
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