Performance Of Thin-film Composite Membrane Research Articles

Novel interfacially-polymerized polyamide thin-film composite membranes: Studies on characterization, pervaporation, and positron annihilation spectroscopy

To improve the pervaporation performance of thin-film composite membranes, novel thin-film composite membranes were prepared via interfacial polymerization by reacting 5-nitrobenzene-1,3-dioyl dichloride (NTAC) or 5-tert-butylbenzene-1,3-dioyl dichloride (TBAC) with triethylenetetraamine (TETA) on the surface of a modified polyacrylonitrile (mPAN) membrane (TETA-NTAC/mPAN and TETA-TBAC/mPAN). The effect of the acyl chloride monomers chemical structure on the pervaporation separation of an aqueous ethanol solution was investigated. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, surface roughness and hydrophilicity of the polyamide active layer of the composite membrane. To correlate the variations in the free volume of the polyamide active layers with the pervaporation performance, positron annihilation spectroscopy (PAS) experiments were performed with a variable monoenergetic slow positron beam. From the results of the PAS and XPS experiments, the S parameter, o-Ps annihilation lifetime τ 3 (corresponding to free volume size) and its intensity I 3 (corresponding to free volume concentration), the τ 3 and I 3 of TETA-NTAC polyamide layer (positron incident energy of 1–1.7 keV) were both higher than those of TETA-TBAC polyamide layer. The S parameter for TETA-NTAC polyamide layer was also higher than that of the TETA-TBAC polyamide layer even though the former was more crosslinking than that of the latter. In the aqueous ethanol solution dehydration experiments, the TETA-NTAC/mPAN membrane produced both a higher permeation rate and water concentration in the permeate than the TETA-TBAC/mPAN membrane.

High Performance Thin-Film Composite Forward Osmosis Membrane

Recent studies show that osmotically driven membrane processes may be a viable technology for desalination, water and wastewater treatment, and power generation. However, the absence of a membrane designed for such processes is a significant obstacle hindering further advancements of this technology. This work presents the development of a high performance thin-film composite membrane for forward osmosis applications. The membrane consists of a selective polyamide active layer formed by interfacial polymerization on top of a polysulfone support layer fabricated by phase separation onto a thin (40 mum) polyester nonwoven fabric. By careful selection of the polysulfone casting solution (i.e., polymer concentration and solvent composition) and tailoring the casting process, we produced a support layer with a mix of finger-like and sponge-like morphologies that give significantly enhanced membrane performance. The structure and performance of the new thin-film composite forward osmosis membrane are compared with those of commercial membranes. Using a 1.5 M NaCl draw solution and a pure water feed, the fabricated membranes produced water fluxes exceeding 18 L m(2-)h(-1), while consistently maintaining observed salt rejection greater than 97%. The high water flux of the fabricated thin-film composite forward osmosis membranes was directly related to the thickness, porosity, tortuosity, and pore structure of the polysulfone support layer. Furthermore, membrane performance did not degrade after prolonged exposure to an ammonium bicarbonate draw solution.

Study on a novel polyester composite nanofiltration membrane by interfacial polymerization of triethanolamine (TEOA) and trimesoyl chloride (TMC): I. Preparation, characterization and nanofiltration properties test of membrane

A novel thin-film composite (TFC) membrane for nanofiltration (NF) was developed by the interfacial polymerization of triethanolamine (TEOA) and trimesoyl chloride (TMC) on the polysulfone (PSf) supporting membrane. The active surface of the membrane was characterized by using FT-IR, XPS and SEM. The performance of TFC membrane was optimized by studying the preparation parameters, such as the reaction time of polymerization, pH of aqueous phase and the concentration of reactive monomers. It is found that the membrane performance is related to the changes of the monomer content in the aqueous phase rather than in the organic phase. Furthermore, the nanofiltration properties of the TFC membrane were tested by examining the separating performance of various salts at 0.6 MPa operating pressure. The rejection to different salt solutions decreased as per the order of Na 2SO 4 (82.2%), MgSO 4 (76.5%), NaCl (42.2%) and MgCl 2 (23%). Also, streaming potential tests indicated that isoelectric point of the TFC membrane is between pH 4 and 5. Moreover, the investigation of the flux for NaCl solution at different pH showed that the polyester NF composite membrane is also particularly suitable for treating acidic feeds: the flux increased from 8.4 to 11.5 L/m 2 h when pH of the feed decreased from 9 to 3. Additionally, the TFC membrane exhibits good long-term stability.

Gas permeation in amine functionalized silicon rubber membranes

Silicon rubber (SR) based thin film composite (TFC) membranes find increasing applicability in various industrial separations owing to its excellent thermal and chemical stability. The functionalization of SR would provide enhanced separation characteristics for certain separation applications. The present research focuses on gas permeation properties of dense and thin film composite membranes based on amine substituted silicon rubber (ASR) and unsubstituted silicon rubber (SR). The dense membrane sorption analysis indicated that presence of amine functionality in ASR increased pressure dependant CO 2 sorption capacity. Owing to this, an elevation of CO 2 permeability by 15% and CO 2 based selectivities by 22–34% in comparison to that of unsubstituted SR was observed. The TFC membranes with SR and ASR as the selective layer on the top of different ultrafiltration (UF) supports with varying properties based on polyacrylonitrile and polysulfone were prepared. The effects of crucial parameters that affected TFC membrane performance, viz., coating solution concentration, UF support membrane porosity and nature of materials were investigated. The preparation of ASR based TFC membranes was demonstrated with a simple crosslinking agent—glutaraldehyde while analyzing effects of crosslinking time on their permeation properties. Polyacrylonitrile (PAN) was found to be better support layer material for ASR based TFC formation than polysulfone (PSF). Thin defect free coating layer can be obtained by appropriate combination of coating solution concentration and support UF membrane porosity. The analysis of effective skin layer thickness of TFC membranes indicated that careful optimization of these parameters is necessary to achieve defect free TFC membranes possessing a good combination of permeance and selectivity.

Synthesis and characterization of interfacially polymerized polyamide thin films

A homologous series of thin film composite (TFC) membranes was made by interfacial polymerization (IP) of trimesoyl chloride (TMC) and m-phenylenediamine (MPD). Membrane flux and rejection as well as the chemical and mechanical properties of the unsupported IP film were evaluated as a function of monomer concentration. The surface characteristics of the IP films were determined using electron-spectroscopy-for-chemical-analysis (ESCA) and contact angle measurements, and the mechanical properties were obtained using pendant drop mechanical analysis (PDMA) and surface profilometry. Results indicate that the TMC concentration has a more pronounced effect on the IP film properties than the MPD concentration. Higher TMC concentration leads to a pronounced increase in the IP film thickness and surface hydrophilicity. In contrast, the thickness increase is smaller and surface hydrophilicity decreases when the MPD concentration is increased. Water flux was determined to depend mainly upon the IP film thickness and surface hydrophilicity whereby these two parameters have counterbalancing effects. Consequently, the decrease in water flux with increasing MPD concentration is pronounced, but a corresponding increase in the TMC concentration has a smaller effect. These studies provide an improved basis for understanding the factors that govern TFC membrane performance.

Study of reverse osmosis separation and permeation rate for sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) membranes of different ion exchange capacities

AbstractThe reverse osmosis performance of thin‐film composite membranes prepared from sulfonated polyphenylene oxide polymer with different ion‐exchange capacities was studied using various electrolyte solutes. The effect of the solvent used for the preparation of the polymer solution for surface coating was also studied. It was found that the preparation of thin‐film composite membranes with high selectivities and high fluxes was possible by adjusting properly the ion‐exchange capacity and the solvent. It was also found that the membrane performance was governed primarily by the ion‐exchange reaction between the solute cation and the proton in SO3H and the Donnan equilibrium. © 1995 John Wiley & Sons, Inc.