Studies On Preparation And Performance Of Cellulose Acetate Forward Osmosis Membrane

As one of osmosis-driven membrane technologies developed in recent years,forward osmosis （FO） membrane process has many advantages, such as low energyconsumption, high separation efficiency, low membrane fouling, and so on. It hasgood application prospect in many fields. This paper is based on the preparation ofhigh performance forward osmosis membrane, using cellulose acetate （CA） formembrane materials and polyester mesh for the support materials. The effect of thedifferent conditions on membrane structure and performance were studied. Differenttest conditions were also employed to study the effect of test conditions on the reversesolute flux of draw solution; In the laboratory conditions, the concentration of orangejuice was studied to evaluate the further application of FO membranes, and themembrane fouling in the application were also studied.The effects of polymer content in polymer solution, humidity, the temperature ofcoagulate bath and annealing, the proportion of CA and CTA on the membraneperformance （the water flux and the rejection for NaCl） were investigated. The resultsshowed that different polymer concentration played an important role on the hole sizeof the membrane. When the increasing of the concentration of polymer, water fluxdecreased and the rejection rose; Environment humidity also had certain effect on CAforward osmosis membrane. With the humidity increase, at first water flux increased,and then reduced. Therefore, there was a best humidity. When the humidity was70%,water flux reached5.0Lm^-2h^-1or so; the increase of coagulation bath temperature canmake water flux lower. At0℃, the water flux was highest,which reached5.3Lm^-2h^-1;Annealing can make cellulose acetate membrane structure tend to be more stable state,also contraction of membrane hole. With the annealing temperature rising, the fluxgradually reduced and rejection rose; CTA was blended into CA, which improved theperformance of the membrane. The membranes which were prepared of proportion ofCA and CTA for1:1,3:1,5:1, and the pure CA were tested, and it was found that with the increase of the content of CA, water flux increased at first and then reduced, andrejection increased. The optimal preparation conditions were that CA concentrationwas10.4%¹3.9%（volume fraction）, evaporated30s in the environment athumidity of70%, coagulate bath temperature in0¹5℃, annealing temperature in50⁶0℃. In addition, when theproportion of CA and CTA was3:1, water flux ofmembrane was the highest.Reverse solute diffusion phenomenon in the forward osmosis process wasstudied. The results indicated that different draw solutes make membraneperformance different, and when bivalent salt was draw solute, the reverse solutefluxes was lower than monovalence salt; Membrane orientation also had certain effecton water flux. In PRO mode, water flux was higher,8.0Lm^-2h^-1or so, and reversesolute fluxes lower, only0.4molm^-2h^-1; The concentration of draw solution had aclosely matter with water flux and the reverse solute flux. With the increase ofconcentration of draw solution, osmosis driving force increased, so water fluxincreased from5.0Lm^-2h^-1to9.2Lm^-2h^-1, and reverse solute flux also from0.5molm^-2h^-1to1.9molm^-2h^-1.Self-made forward osmosis membrane of cellulose acetate was used inconcentration of orange juice, and the effect of different draw solution, membraneorientation on concentration process and also membrane fouling phenomenon werestudied in the concentration process. The results showed that when the3mol/Lglucose+2mol/L NaCl solution was used as draw solution, the water flux of FOmembrane was higher, and the reverse solute flux reduced significantly. After14h,the total soluble solids increased from11.5to40.5°Brix. It was also found that, theeffect of concentrated internal concentration polarization in PRO mode less thandiluted internal concentration polarization in FO mode on the water flux. In theconcentration process, there was little membrane fouling, and after cleaning, flux wasrecovered mostly. The FO membrane was cleaned by pure water once every6h. After25h concentrating, total soluble solids increased from11.5to48.0°Brix.