Study On Preparation And Performances Of Cellulose Acetate Forward Osmosis Membranes

In this dissertation,cellulose acetate(CA)positive osmosis(FO)membranes were prepared by phase inversion with 1,4-dioxane and acetone as solvents.Maleic acid,methanol and polyvinylpyrrolidone(PVP)were used as additives.Concentration experiments of anthocyanin solution were carried out by using CA FO membrane.The effects of different composition of casting solution on permeation flux,porosity and rejection rate of CA FO membrane were studied by orthogonal experiment.The optimum composition ratio of casting solution was selected.The effects of coagulation bath temperature,membrane thickness,membrane evaporation time,draw solution concentration,membrane orientation and liquid flow velocity on both sides of the membranes on flux and rejection rate of forward osmosis membranes were investigated.The experimental results showed that the optimum composition of casting solution was obtained with 13%CA,45%1,4-dioxane,31%acetone,2%maleic acid,3%PVP and 6%methanol.At this time,the forward osmosis membrane had a good concentration effect on anthocyanin solution:2.04 L·m-2·h-1 flux and 98.61%rejection rate.By changing the relevant factors,the optimum concentration conditions were obtained as follows:the thickness of the membrane was 100 ?m,the temperature of the coagulation bath was 16?,the evaporation time was 30 s,The draw solution was saturated sucrose solution,the orientation of the membrane was mode ?,and the flow velocity of liquid on both sides of the membrane was 0.70 mL·s-1.The phenomenon of reverse diffusion of NaCl solution was also studied with NaCl solution as draw solution.The membrane fouling and cleaning experiments were also carried out.In addition,zeta potential of membrane surface was also measured.The fouling of dye contaminants with different charges on the membrane and the recovery rate of water flux after the polluted membrane was emphatically investigated.The experimental results showed that there was a reverse diffusion phenomenon when NaCl solution was used as the draw solution for the study of solute reverse diffusion.The reverse flux increased with the increase of NaCl concentration,which affected the change trend of the forward water flux.Membrane fouling experiments were carried out with anthocyanin solution and four dye solutions as feed solution in the process of membrane fouling and cleaning.The magnitude of water flux and interception rate was related to the charge and relative molecular mass of the solute in the feed solution.The zeta potential of FO membrane was-63.90 mV,which can attract cationic dyes and repel anionic dyes.The smaller the relative molecular weight of solute,the easier it was to enter the draw solution through the pore of the membrane,and the lower the rejection rate.Therefore,the dye contaminants with smaller molecular weight cations were more likely to pass through the membrane pore and entered the extracting solution,which made the rejection rate lower.Therefore,the rejection rate of eosin Y was higher,while that of methylene blue was the smallest.Reverse water rinsing was beneficial to the cleaning of CA FO membranes,and the recovery rate of water flux of dyes could be explained by solubility parameters.The more similar the solubility parameters of dyes and CA were,the better the compatibility and fastness of dyes and CA were.The stronger the dyes adhered to CA,the less easily they could be washed out by reverse water rinsing,and the lower the recovery rate of water flux.