Poly(vinyl alcohol) / polyamide thin-film composite membranes.

[摘要] ENGLISH ABSTRACT: The aim of this study was to modify the surface of polyethersulfone (PES) ultrafiltration (UF)membranes to produce a more hydrophilic membrane by cross-linking poly(vinyl alcohol) (PVA) withsodium tetraborate (Na2B4O7.10H2O) (SB) on the surface. Key preparation factors were identified asPVA molecular weight, concentrations of the PVA and SB, cross-linking reaction time, number ofcoatings and the mode of coating. The effect of these factors on the membrane performance (saltretention and permeate flux) is discussed. These PVA-SB membranes typically had 11.46% retentionand 413.30 L/m2.h flux for a feed containing 2000 ppm NaCl (0.45 MPa, 20°C, 45 – 50 L/h). Thecoating was shown to be uniform and stable by Fourier transform infrared spectroscopy (FT-IR)analyses. Coating significantly increased hydrophilicity and a maximum flux increase of 500 L/m2.hwas reached. Measurements showed a reduced water contact angle and this confirmed the obviousenhancement of surface hydrophilicity.As a control, the role of the PVA base layer without cross-linking and the effects of its dryingand heating on the water permeability of the PES-UF membrane were also studied, in order toascertain maximum treatment conditions. Retention and permeate flux were determined (feedsolution: 2000 ppm NaCl, applied pressure 0.45 MPa, 25°C, 45 – 50 L/h). It was found that the heatinghad the largest effect on the reduction of water permeability and therefore 50°C was the limit fortreatment of this specific PES-UF membrane.Thin-film composite (TFC) membranes were prepared by an interfacial polymerization (IP)reaction between a polyfunctional amine and tri- or di-functional carboxylic chloride and thenevaluated for their reverse osmosis (RO) performance. The salt retention of the PVA-SB membraneswas improved when covering the cross-linked PVA gel sub-layer with a polyamide (PA) layer.However, the permeate flux decreased to below 30 L/m2.h (2000 ppm NaCl, 1 – 2 MPa, 20°C, 45 – 50L/h).Two TFC membranes made from trimesoyl chloride (TMC) with m-phenylenediamine (MPD)or 2,6-diaminopyridine (DAP) exhibited retentions of 96.71% to 89.65% and fluxes of 10.93 to 27.91L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (2 MPa,25°C, 45 – 50 L/h). Two TFC membranes made from a n ew 2,5-furanoyl chloride (FC) with MPD orDAP exhibited retentions of 34.22% to 58.54% and fluxes of 49.21 to 25.80 L/m2.h, depending on thetype of diamine used, when tested with a 2000 ppm NaCl solution (1 MPa, 25°C, 45 – 50 L/h).Novel PVA-SB-DAP-FC membranes made from the DAP with FC had the highesthydrophilicity value and exhibited >58.54% NaCl retention and 25.80 L/m2.h flux, and 75.08% MgSO4retention and 34.75 L/m2.h flux, when tested with (2000 ppm feed, 1 MPa, 25°C, 45 – 50 L/h).The effect of the chemical structures of the different amines and carboxylic chlorides used onthe RO performances of the TFC membranes prepared by two amines reacting with TMC or FC, onthe surfaces of the modified asymmetric PES-UF membranes, was investigated. FT-IR and watercontact angle determination were used to characterize the chemical structure, morphology andhydrophilicity of the PA layers of the composite membranes. The response surface methodology (RSM) was used to optimize the preparation conditionsthat had the largest effects on the RO performance of the PVA-SB-DAP-FC membranes. Goodmembrane performance could be realized particularly by manipulating three variables: DAPconcentration, FC concentration and polymerization time (PT). The regression equation between thepreparation variables and the performance of the composite membranes was established. Maineffects, quadratic effects and interactions of these variables on the composite membrane performancewere investigated.The membranes were characterized in terms of pure water permeation (PWP) rate, molecularweight cut off (MWCO), solute separation and flux. Mean pore size (μp) and standard deviation (σp) ofthe membranes were determined using solute transport data. The results revealed that PVA-SBmembranes have almost the same pure water permeation that PES-UF membranes have. The MWCOof the PES-UF membranes decreased from 19,000 to 13,000 Daltons when the membrane wascoated with PVA.

[发布机构] Stellenbosch University