Effect of pH on the performance of polyamide/polyacrylonitrile based thin film composite membranes (original) (raw)
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Journal of Membrane Science, 2011
A novel TFC NF membrane was prepared on a polyacrylonitrile (PAN) supporting film using interfacial polymerization with the 3,3 ,5,5 -biphenyl tetraacyl chloride (mm-BTEC) monomer and piperazine (PIP). In the interfacial polymerization process, organic solvents were changed from cyclohexane to toluene, which increased the diffusion rate and solubility of PIP in the organic solvent. The diffusion of PIP and its solubility both influence the structure, morphology and thickness of TFC membranes. The streaming potential of TFC NF membranes was measured at various pHs. The results demonstrate that the surface of the membrane is positive charged. Permeation experiments were employed to evaluate the salt rejection and water flux performance of the membranes. These new NF films exhibited interesting performance properties as compared with commercial nanofiltration membranes in terms of their retention and relative flux for positively charged inorganic compounds. The salt rejection of the mm-BTEC/PIP membranes corresponding to different types of feed solutions are CaCl 2 > MgCl 2 > NaCl > Na 2 SO 4 . The flux and rejection of CaCl 2 (500 ppm) were 50.8 L/m 2 h and 95.1%, respectively, under 0.4 Mpa. In addition, the NF membranes exhibited enhanced water permeability and salt rejection compared with those prepared from trimesoyl chloride (TMC).
Journal of Membrane Science, 2011
Nanofiltration polyamide membranes obtained by interfacial polymerization possess skin layers containing amine and carboxylic acid groups that are distributed in an inhomogeneous fashion, leading to a bipolar fixed charge distribution (i.e. the sign of the surface charge density changes over the skin layer thickness). In this work we have modified the standard NF model (based on steric/Donnan exclusion and the extended NernstPlanck equation) so as to account for the spatial variations of the fixed charge inside pores. The retention performances 1 of NF membranes having bipolar charge distributions that capture the main electrostatic features of polyamide membranes have been investigated by considering 12, 21 and 11 electrolytes. In the range of volume fluxes usually obtained with NF polymer membranes, calculations show that the theoretical retention sequence of polyamide membranes for the abovementioned electrolytes is 12 > 21 > 11, in agreement with experimental data available in the literature. This retention sequence has been shown to be specific of membranes with bipolar charge distributions since both homogeneously charged membranes and membranes with unipolar charge distributions (i.e. the concentration of charged surface groups can vary over the skin layer thickness but the sign of surface groups remains the same) would be more permeable to asymmetric electrolytes having divalent counterions than to symmetric monomonovalent electrolytes.
Polymers, 2017
Membrane support properties influence the performance of thin-film composite nanofiltration membranes. We fabricated several polysulfone (PSf) supports. The physicochemical properties of PSf were altered by adding polyethylene glycol (PEG) of varying molecular weights (200-35,000 g/mol). This alteration facilitated the formation of a thin polyamide layer on the PSf surface during the interfacial polymerization reaction involving an aqueous solution of piperazine containing 4-aminobenzoic acid and an organic solution of trimesoyl chloride. Attenuated total reflectance-Fourier transform infrared validated the presence of PEG in the membrane support. Scanning electron microscopy and atomic force microscopy illustrated that the thin-film polyamide layer morphology transformed from a rough to a smooth surface. A cross-flow filtration test indicated that a thin-film composite polyamide membrane comprising a PSf support (TFC-PEG20k) with a low surface porosity, small pore size, and suitable hydrophilicity delivered the highest water flux and separation efficiency (J = 81.1 ± 6.4 L•m −2 •h −1 , R Na2SO4 = 91.1% ± 1.8%, and R NaCl = 35.7% ± 3.1% at 0.60 MPa). This membrane had a molecular weight cutoff of 292 g/mol and also a high rejection for negatively charged dyes. Therefore, a PSf support exhibiting suitable physicochemical properties endowed a thin-film composite polyamide membrane with high performance.
Journal of Membrane Science, 2011
A novel thin-film composite polyamide nanofiltration membrane was prepared through interfacial polymerization of polymeric polyamine polyvinylamine (PVAm) with isophthaloyl chloride (IPC) on a polysulfone supporting film. The composite membranes were prepared under different conditions and characterized in terms of chemical and morphological structures, surface zeta potential, pure water permeability, and rejection to different solutes including electrolytes and sucrose. The results showed that the membrane performance was significantly affected by the content of amine units of PVAm and the concentrations of PVAm and IPC. The increase of the content of amine units of PVAm and the concentration of IPC resulted in an augment in salt rejection and a decrease in permeability, while the increase of PVAm concentration led to enhancement in both the salt rejection and water flux. The obtained membranes were positively charged at pHs lower than 6.5 and negatively charged at pHs higher than 7.0. The rejection order of the membrane changed from MgCl 2 > MgSO 4 > NaCl > Na 2 SO 4 at pH 3.0 to MgSO 4 > Na 2 SO 4 > MgCl 2 > NaCl at pH 7.5. The decrease of feed pH from 7.5 to 3.0 resulted in an over 35.0% augment in permeability. Furthermore, the novel nanofiltration membrane is of good performance stability and particularly suitable for treating acidic feed.
Solvent resistant thin film composite nanofiltration membrane: Characterization and permeation study
Applied Surface Science, 2013
The present investigation reports the fabrication of thin film composite nanofiltration (TFC-NF) membranes using interfacial polymerization technique for desalination. Ethylene diamine (EDA) and terephthaloyl chloride (TPC) were employed as aqueous and organic phase monomers, respectively to develop polyamide thin layer on the surface of Celgard 2400. The prepared membranes were characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The molecular weight cutoff of TFC-NF membranes was estimated to be below 342 Da using dextrose, sucrose and raffinose solutions. A low cost dead end NF Cell was designed and manufactured domestically to conduct permeation experiments. The effect of different reaction conditions including concentration of monomers, residence time in each monomer and curing temperature on the membrane performance (water flux and MgCl 2 rejection) was also studied. The water flux was augmented linearly at higher applied pressure while MgCl 2 rejection was remained constant. The obtained water flux and MgCl 2 rejection were measured 33 L/m 2 h and 90%, respectively at 7 bar applied pressure. Beside this, membrane stability was analyzed, which confirmed the excellent constancy of ethanol and n-hexane fluxes even after an extended period. Hagen-Poiseuille equation was applied to estimate the TFC-NF membrane pore size ∼0.45 nm.
Preparation and Characterization of Nanofiltration Membrane for Water Treatment
2012
Thin-film composite (TFC) nanofiltration (NF) membranes were developed by terephthaloyl chloride (TPC) crosslinked the hydroxyl ended groups of hyperbranched polyester (HPE) on polyacrylonitrile (PAN) support. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that a thin layer of crosslinked HPE molecules were deposited on PAN porous membrane surface successfully. The preparation conditions were also optimized. The separation performance of PAN-HPE-TPC NF membranes are mainly related with the concentration of monomer in the aqueous phase rather than that in the organic phase. Water permeability and salts rejections of the membranes were measured. The flux and rejection of these NF membranes for Na 2 SO 4 (1 g/L) reached 11.43 L/m 2 h and 96.5% under 0.6 MPa, respectively. At the same time, the nanofiltration properties were compared with other membranes prepared with hyperbranched polymers. All NF membranes prepared with hyperbranched polymers showed relative high permeate flux.
Journal of Membrane Science, 2016
Polyethyleneimine (PEI) is cheap low-toxic polymer and is used for the preparation of thin film composite (TFC) nanofiltration (NF) membranes. Nevertheless, one serious problem with most of the reported high salt rejecting (ca. 90% divalent cation) PEI-based TFC membrane is the low permeate flux and low average monovalent to divalent anion selectivity. There is also no comparative study of antifouling property of the PEI TFC membranes with conventional poly(piperazineamide) TFC membrane. Herein, we report an approach for in situ manipulation of permeation behavior and antifouling property of PEI-based TFC NF membrane. The approach was based on the use of dextran (Dex) conjugate of PEI (PEI-Dex) as a new monomer or co-monomer for the interfacial polymerization (IP) with trimesoyl chloride (TMC). Particularly, membranes prepared with mixture of PEI-Dex (2.5%, w/v)+PEI (0.25%, w/v) showed ca. 86 Lm-2 h-1 MPa-1 pure water permeate flux and 84%, 85% and 37% rejections of Na 2 SO 4, MgCl 2 and NaCl respectively. On the other hand, membrane prepared with PEI (0.25%, w/v) alone gave much lower permeate flux (37 Lm-2 h-1 MPa-1). The membrane prepared with PEI-Dex (3%, w/v) gave permeate flux as high as 163 Lm-2 h-1 MPa-1 with ca. 71%, 72% and 10% rejections of Na 2 SO 4, MgCl 2 and NaCl respectively under similar experimental conditions. All the PEI-based membranes prepared under suitable experimental conditions showed high average monovalent to divalent ions (cation and anion) selectivity. The active layer thickness decreased with increasing proportion of added PEI-Dex into the aqueous bath. This is the reason for the enhancement of permeate flux of the PEI-Dex membranes. On the other hand, low membrane surface charge at neutral feed pH is responsible for the higher average monovalent to divalent ions selectivity. The PEI-based membranes exhibited much improved antifouling/antiscaling properties compared to that of conventional poly(piperazineamide) TFC NF membranes. These types of membranes are suitable for long-term water softening without frequent cleaning step.
Fabrication and characterisation of novel nanofiltration polymeric membrane
Materials Today Communications, 2019
A novel composite membrane was obtained by combining the products of ion-tracking and electrospinning processes. Swift heavy ions generated from a cyclotron were used to irradiate polyethylene terephthalate (PET) polymer film of thickness 23 µm to create latent tracks which were then chemically etched in an alkaline solution, to produce track-etched membrane. Magnetron sputtering was then used to deposite titanium (Ti) on the membrane to produce PET-TM with Ti thickness of ~45 nm. Polyamide 6 nanofibres (PA6-nfs) or polyacrylonitrile nanofibres (PAN-nfs) were directly electrospun upon the Ti coated PET-TM using an electrospinning process. The average fibre diameter of PA6-nfs or PAN-nfs was 52±9.8 nm or 354±40 nm, respectively. The track-etched membrane, the nanofibres and the novel composite membrane were characterised using SEM, TEM, TGA, ATR-FTIR and adsorption/desorption of nitrogen techniques. The results confirmed the fabrication of nanofibre coated track-etched composite membrane.
Preparation of nanofiltration membranes from polyacrylonitrile ultrafiltration membranes
Journal of Membrane Science, 2006
Polyacrylonitrile (PAN) membranes display some unusual features for ultrafiltration (UF). The meso-macropores of PAN UF membranes can be easily reduced into the range of micro-mesopores by taking advantage of surface tension forces within the capillary pores during heat treatment in the presence of ZnCl 2 . Asymmetric PAN nanofiltration (NF) membranes with controlled highly dense pore surface functional groups were prepared by hydrolysis of the nitrile groups with NaOH. The combined effects of heat treatment and the presence of ZnCl 2 on the formation of nanofiltration membranes were investigated. In addition, membrane post-treatment with NaOH was studied.
Journal of Applied Polymer Science, 2019
Hollow-fiber (HF) membranes have the advantage of a higher packing density compared to flat-sheet and spiral-wound configurations. However, the low pressure tolerance of HF membranes limits their applications in nanofiltration (NF). In this study, reinforced thin-film composite (r-TFC) HF NF membranes were fabricated and evaluated in tests with water containing different salts and organic matter. Reinforced polysulfone ultrafiltration membranes were used as a support for a polyamide layer prepared from piperazine and trimesoyl chloride monomers. The interfacial polymerization conditions were optimized via selection of the trimesoyl chloride reaction time that gave the highest membrane performance. A specific permeate flux of 5.1 L m-2 h-1 bar-1 , an MgSO 4 rejection of 69%, and an NaCl rejection of 26% at a transmembrane pressure of 6 bars were obtained with the optimized r-TFC membranes. Performance studies with water characterized by synthetic solution demonstrated removals of the total organic carbon, ultraviolet absorbance at 254 nm, and turbidity in excess of 65, 80, and 90%, respectively. The results of this study illustrate the feasibility of manufacturing r-TFC HFs and using them in water-treatment applications.