Study On Preparation And Properties Of CMCNa/PEI Hollow Fiber Composite Forward Osmosis Membrane

As a novel membrane separation technique developed over the recent years, forwordosmosis (FO) has exhibited its promising potential application in seawater desalination, foodprocessing, drug release and waster water treatment due to its adventages of lower energyconsumption、lower fouling tendency and higher water recovery rate. The performance of theforward osmosis membrane separation process is manily determined by the membrane used,which attracts the attentions of many membrane researcheres.In this study, CMCNa/PEI hollow fiber thin-film composite forward osmosis membranewas fabricated by method of dip-coating using polypropylene (PP) hollow fiber as support,polyvinyl alcohol (PVA) as hydrophilic modification material, sodium carboxymethyl cellulose(CMCNa) and polyethyleneimine (PEI) as functional materials, glutaraldehyde (GA) as cross-linking agent, respectively. The hydrophilic modification of PP hollow fiber membrane and thepreparation parameters of the active separation layer including the concentrations of CMCNa,PEI and GA, the coating time of CMCNa, PEI and GA were systematically investigated to obtainthe optimum preparation condition for the composite FO membranes. Surface properties of theresulted membranes were characterized through ATR-FTIR, FE-SEM, Zeta potential analysesand contact angle measurement. The effects of operating conditions on the forward osmosisperformance of the developed CMCNa/PEI composite membranes were also systematicallyinvestigated through forward osmosis experiments. Furthermore, the chemical stability of the FOmembrane was studied through soking tests and the antifouling property was also investigatedthrough osmosis experiments with the model foulants of bovine serum albumin (BSA), cetyltrimethylammonium bromide (CTAB) and tween-80(TW-80), respectively. The conclusionsobtained were showed below:(1) The results of ATR-FTIR and FE-SEM showed that an active separation layer has beensuccessfully deposited on the out side surface of PP hollow fiber membrane through thereactions of CMCNa, PEI and GA. The active skin layer of the formed thin-film was smooth andcompact, and usually had a thickness of less than0.5μm. The surface of the membrane waspositively charged under pHs within the scope of3~9.(2) Hydrophilization of the PP hollow fiber membrane with polyvinyl alcohol (PVA) couldeffectively improve the performance of the CMCNa/PEI composite forward osmosis membrane.Under the same conditions, the water permeation flux (JV), salt permeation flux (JS) and thevalue of JS/JVof the composite membrane with a support of unmodified PP membrane were13.2 L/m2.h、15.8g/m2.h and1.2g/L, respectively, while for the composite membrane with a supportof modified PP membrane, the water permeation flux (JV), salt permeation flux (JS) and JS/JVwere26.4L/m2.h,17.4g/m2.h and0.66g/L, respectively.(3) The performance of CMCNa/PEI composite membrane was mainly determined by thepreparation parameters of the contents of CMCNa, PEI, and GA, the coating times of CMCNa,PEI and GA. The optimal preparation parameters were as follows: CMCNa concentration=0.05w/v%, dip-coating time of CMCNa=20min, PEI concentration=1.5w/v%, dip-coating time ofPEI=5min, GA concentration=2.1w/v%, dip-coating time of GA=2min. The desiredmembrane exhibited a water permeation flux of29.1L/m2.h and salt rejection of92.8%to500mg/L MgCl2aqueous solution at0.3MPa,25℃and pH=6.8. In FO process with the active layerfacing draw solution, distilled water as feed solution and0.5M MgCl2as draw solution, theresulted membrane possessed a water flux of30.7L/m2.h and a reverse salt flux of17.9g/m2.h at25℃.(4) The FO performance of the CMCNa/PEI composite membrane was affected by themembrane orientation, flow rates of feed and draw solutions, as well as the concentration of thedraw solution. In FO process with the active layer facing draw solution, distilled water as feedsolution and0.5M MgCl2as draw solution, the composite FO membrane had a water flux (JV) of22L/m2.h, a reverse salt flux (JS) of117g/m2.h and a relatively high value of JS/JVof5.3g/L.While for the FO process with the active layer facing feed solution, the JV,JSand JS/JVat25℃were30.7L/m2.h,17.9g/m2.h and0.58g/L, respectively. Increasing the flow rates of feed anddraw solutions could reduce concentration polarization and thereby improving the water flux. Asthe rate of draw solution increased from0.005to0.04L/min, the water flux increased by17.9L/m2.h and the reverse salt flux increased from5.0to17.9g/m2.h. With increasing the rate offeed solution from0.3to1.8L/min, the water flux increased from21.0to30.7L/m2.h, while thereverse salt flux reduced by12.0g/m2.h. As the concentration of the draw solution increasedfrom0.5to2.0M, the water flux increased linearly and then changed slightly for futher increaseof draw solution concentration, while the salt flux increased linearly with the draw solutionconcentration.(5) The results of soaking tests revealed that the composite FO membranes developedpossessed good chemical stability. After soaking in0.5M H2SO4or NaOH solution for168hours, the performance of the membrane changed slightly.(6) FO experiment with the1000mg/l model foulant of bovine serum albumin (BSA), cetyltrimethylammonium bromide (CTAB) or tween-80(TW-80), respectively, showed that the CMCNa/PEI composite membrane possessed good anti-fouling property to CTAB and TW-80solutions. After operation of3.0h, the fluxes of the membrane to CTAB and TW-80solutionsvaried slightly, while to the BSA solution, the flux decreased by39.1%.