Research On Composite Nanofiltration Membranes Based On Sodium Carboxymethyl Cellulose, Sodium Alginate And Phosphorylated Chitosan

Sodium carboxymethyl cellulose （CMC）, sodium alginate （ALG） andphosphorylated chitosan （PCS） were explored as the active layer materials forcomposite nanofiltration （NF） membranes in this study. A series of negatively chargedcomposite NF membranes were prepared through coating the casting solution ontoPSF matrix, and then cross-linked with glutaraldehyde （GA）, epichlorohydrin （ECH）,or CuSO4, repectively. The membranes were characterized by scanning electronmicroscopy （SEM）, attenuated total reflection infrared spectroscopy （ATR-IR） andatomic force microscopy （AFM）. Effects of membrane making conditions,low-molecular-weight organic additives in the casting solution and operatingconditions on performance of the composite membranes were also investigated.A negatively charged composite NF membrane was prepared using CMC assurface active layer, PSF matrix as support layer, cross-linked with GA. The resultsindicated that the composite membrane with excellent rejection performance shouldbe prepared while CMC concentration1%, GA concentration0.5%, cross-linking time2h at30℃. At room temperature, the contact angle is57.85°, degree of swelling44.26%, and its molecular weight cut-off is520Da. At1MPa and40L·h^-1feed flow,the rejections of the composite membrane to1000mg·L^-1K₂SO₄, Na₂SO₄, KCl, NaCl,MgSO4and MgCl₂were98.3,98.0,62.5,59.1,54.4and24.6%, with a flux of10.0,10.1,15.2,15.8,13.7and16.5L· m^-2· h^-1, respectively. The rejection rate of themembrane to different electrolyte solutions decreased in the order of Na₂SO₄, NaCl,MgSO4and MgCl₂.A blend composite NF membrane was prepared using CMC and ALG blend assurface active layer, PSF as support layer, cross-linked with ECH at pH=10. Thecomposite membrane with excellent rejection performance should be prepared whileALG/CMC proportion1:3, ECH concentration2%, cross-linking time18h at50℃. At1MPa and30L·h^-1feed flow, the rejections of the composite membrane to1000mg·L^-1 K₂SO₄, Na₂SO₄, KCl, NaCl, MgSO4and MgCl₂were97.4,97.1,58.9,55.1,51.6and24.6%, with a flux of17.1,17.3,16.9,17.2,16.0and16.6L· m^-2· h^-1, respectively. Theresults indicate that the composite NF membrane has different rejection ratio todifferent kinds of inorganic salts. Similar to other negative charged membranes, therejection performance of the composite membrane depends on the electrostatic forcebetween the charged membrane and ions of electrolyte.The water soluble PCS with D.C. of0.78was prepared through a modified andhomogeneous method. A novel kind of composite NF membrane was prepared usingPCS as surface active layer, PSF as support layer, cross-linked with ECH. Themembrane preparation techniques on the performance of the composite membranewere investigated. The results suggest that the composite membrane with excellentrejection performance should be prepared while PCS concentration1.5%, ECHconcentration1%, cross-linking time22h at60℃. The structure and morphology ofthe resulting membrane were characterized by ATR-IR, SEM, and AFM. At1MPa and40L·h^-1feed flow, the rejections of the NF membrane to1000mg·L^-1Na₂SO₄andNaCl were89.2and20.8%, respectively. The flux were6.9and7.4L· m^-2· h^-1. Therejections of the membrane to different electrolyte solutions decreased in the order ofNa₂SO₄, MgSO4, NaCl and MgCl₂.The PCS/PSF composite NF membrane was prepared using PCS as surfaceactive layer, PSF as support layer, cross-linked with GA. The results suggest that thecomposite membrane with excellent rejection performance should be prepared whilePCS concentration2%, GA concentration0.5%, cross-linking time1.5h at50℃.At1MPa and40L·h^-1feed flow, the rejection and flux of the NF membrane to1000mg·L^-1Na₂SO₄was87.6%and8.3L· m^-2· h^-1, respectively. The rejections of thiskind of membrane to the electrolyte solutions decreased in the order of Na₂SO₄,MgSO4, NaCl and MgCl₂. The preparation techniques on the performance of thecomposite membrane were investigated. At room temperature, the contact angle is56.20°, degree of swelling44.07%, and its molecular weight cut-off510Da.A novel PCS/PSF composite membrane was prepared using PCS as surfaceactive layer, PSF as support layer, cross-linked with CuSO4. The composite membranewith excellent rejection performance should be prepared while PCS concentration1.5%, CuSO4concentration4%, cross-linking time2h at40℃. At1MPa and40L·h^-1feed flow, the rejection and flux of the NF membrane to1000mg·L^-1Na₂SO₄was85.5%and7.4L· m^-2· h^-1, respectively. The contact angle is58.46°and molecular weight cut-off580Da.The GA cross-linked PCS/PSF composite membrane was used in reclaimedwater treatment of a waste water plant. The permeate flux and the removalefficiencies in color, CODCr, TP, NH3and conductivity were investigated in relationto the driving pressure, the feed flow, and the operation time. At the pressure of1MPaand40L·h^-1feed flow, the removal efficiencies for color, CODCr, TP, NH3andconductivity were100,76.2,85.2,69.8and33.2%, respectively. After membraneprocess treatment, all the indexes of permeate reached A level standard ofGB18918^-2002.