Thin-film Composite Layer Research Articles

Evolution of surface damage of thin film composite (TFC) reverse osmosis (RO) membranes under controlled hygro-mechanical conditions

Limited attention has been given to understanding how failure to the selective layer of reverse osmosis (RO) membranes develops and accumulates during operation; and to integrating this response into membrane fabrication. While the integrity of the selective layer is crucial for the separation process, available studies are limited to simple loading conditions and use failure of the entire membrane at rupture to represent its mechanical integrity. This work aims to investigate the evolution of surface damage to the selective layer under controlled interrupted mechanical tests under dry and wet conditions. AFM, SEM, and contact angle are used to characterize the selective layer integrity. Wet membranes exhibited lower strain at rupture (10.3%) than that of dry membranes (12.3%). However, interrupted tests revealed that the failure of the selective layer occurred at much lower strains than the rupture strain. Stretching and thinning in the TFC layer were observed at strain limits as low as 5%, which developed into localized deformation and cracks at higher strain limits (i.e., 8%). These findings can explain why membranes fail to perform before rupture occurs. By understanding how the selective layer's surface damage evolves during operation, membrane fabrication can be improved to enhance membrane performance and durability.

Hybrid nanofiltration thin film hollow fiber membranes with adsorptive supports containing bentonite and LDH nanoclays for boron removal

This study focused on removal of boron from water via hybrid nanofiltration (NF) thin film composite (TFC) hollow fiber (HF) membranes. To do so, nanocomposite polyvinyl chloride (PVC) HF membranes containing bentonite and layered double hydroxide (LDH) nanoparticles as natural and synthetic adsorbents were fabricated as the adsorptive support layers with high efficiency in boron removal. The phase inversion behavior of dope solutions and mechanical strength of the adsorptive nanocomposite PVC HF membranes were investigated and the results showed that LDH interacts better with PVC polymeric chains than bentonite. It was found that LDH with smaller pores and better adsorption capability in comparison with bentonite results in more hydrophilic membranes with better performance. On the other hand, bentonite tends to become agglomerated at above 1.5 wt%. Moreover, the fabricated membranes containing LDH have lower MWCO and more uniform pore size distribution which make them better options as support for the TFC layer formation to fabricate NF TFC membranes. The selective TFC layer was then fabricated via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5- benzenetricarbonyl trichloride (TMC) on the outer layer of the nanocomposite PVC HF membranes. Boron removal, and recovery and reusability of the fabricated NF TFC membranes were investigated by Na₂CO₃ solution. It was found that the NF TFC membranes containing LDH with boron removal of more than 83.6% and water flux of 16.1 L/m2.h at 4 bar operational pressure exhibit better performance than the NF TFC membranes containing bentonite.

Thin film composite solvent resistant nanofiltration membrane via interfacial polymerization on an engineered polyethylene membrane support coated with polydopamine

In this work, a thin film composite (TFC) membrane possessing outstanding properties for solvent resistant nanofiltration (SRNF) membrane application was fabricated. For this purpose, high density polyethylene (HDPE)-polystyrene (PS)-styrene-ethylene-butylene-styrene (SEBS) blends were fabricated in the first step with different compositions by using an internal mixer machine and hot press technique, respectively. Then, the fabrication of a novel HDPE support was conducted by etching the PS phase out of the as-prepared HDPE-PS-SEBS blends through solvent extraction method (Etched HDPE). In the next step, the prepared Etched HDPE membrane support was dipped in a dopamine solution, by which auto-oxidization and self-polymerization of dopamine monomers onto the Etched HDPE membrane supports surface was done, leading to the formation of an ultrathin polydopamine (PDA) layer with a strong chemical binding force. By the formation of the polydopamine layer, hydrophilic functional groups were introduced onto the HDPE membranes surface, causing the attraction of m-phenylenediamine (MPD) monomers onto the membrane surface and the formation of a uniform ultrathin PA top layer. Finally, the TFC layer was formed on the as-prepared membrane supports with different m-phenylenediamine and trimesoyl chloride (TMC) concentrations. The performance and properties of the prepared TFC-PE@PDA membrane was investigated for rejection of different dyes including Reactive Red, Direct Yellow, Methyl Blue, Rhodamine B, Crystal Violet and Methyl Orange in SRNF applications, based on which outstanding separation performance (dye rejections of 99.8, 99.5, 99.2, 98.5, 96.8 and 94.4 for RR, DY, MB, RDB, CV and MO, respectively, under the pressure of 9 bar), methanol flux as high as 1.8 L/m2 h bar along with excellent methanol flux as high as 3.7 L/m2 h bar after Dimethylformamide activation, were obtained. Furthermore, it is noteworthy that an outstanding solvent resistance (dye rejections of more than 99.2, 98.8, 98.5, 97.9, 96 and 93.8% for RR, DY, MB, RDB, CV and MO, respectively, being dipped in Dimethylformamide at 70 °C for 90 days) was also shown by the prepared TFC-PE@PDA membrane.

Interaction study between M-Phenylenediamine, Trimesoyl Chloride and Nylon 66 using Molecular Dynamic Simulation

The thin film composite (TFC) membrane is a porous membrane layered by a polyamide active layer. In the experimental work, the polyamide active layer prepared by the interaction between monomers, m-phenylenediamine (MPD) and trimesoyl chloride (TMC) which deposited on a membrane support. Considering the possibility of producing a loose TFC membrane and affect the separation performance, this study enlightens the interaction between monomers with Nylon 6 6 (N66) support membrane using simulation - molecular dynamic (MD). Different simulation system has been investigated with varying the ratio molecule of MPD to TMC where, TFC1 (1:1), TFC2 (3:1) and TFC3 (3:2) to the tertiary system of N66/MPD/TMC. The simulation was set for a COMPASS force field, where the equilibrium phases in a microcanonical (constant volumes and total energy) (NVE) followed by run-production stage (constant pressure and temperature ensembles) (NPT) ensembles. The temperature and pressure were set at 323.15 K and 1atm respectively. The polyamide TFC was found to be formed by the main interactions between nitrogen (N) from MPD group to the carbon, (C) from TMC main chain at ranges of 4.25Å. Overall interaction can be observed between N from TFC layer with O atom from the substrate layer. All of the intermolecular interactions take place at 3.25Å distance. The best interaction in N66 to MPD and TMC system to the weakest is in the arrangement of TFC2 > TFC3 > TFC1. The highest intensity was obtained by the TFC2, indicating the best ratio of 3:1 of MPD molecules to TMC molecule with support polymer when fully polymerized occurred. This study suggests that ratio N66 to MPD and TMC in TFC2 is the best to interaction between TFC layer and substrate for fabrication of the TFC membrane.

Radial Distribution Function Analysis of the Polyamide Thin Film Composite formation using Trimesoyl Chloride and Piperazine

Polyamide thin film composite (TFC) membranes are well known for their performance and strength which normally applied in pervaporation dehydration and reverse osmosis field. TFC is produced by the rapid reaction between aqueous and organic monomer. However, the interaction between monomers is not well discussed at the atomic level and there is no precise tool to measure the effectiveness of the selection of organic with the aqueous monomer to form a stable TFC layer. Thus, this paper aims to analyze the interaction between aqueous monomer and organic monomer using the Molecular Dynamic (MD) simulation to form the TFC membrane. This work was done by using Piperazine (PIP) as the aqueous monomer with the combination of Trimesoyl Chloride (TMC) as the organic monomer in the binary systems. The simulation involved the setting of Ewald Summation Method, COMPASS force field, equilibrium phase by microcanonical, NVE (constant volumes and total energy) and run-production stage by NPT (constant pressure and temperature). Analysis by the Radial distribution function (RDF) explicates the intermolecular interfacial of 5.75 Å between the bonding of N (Amine) - C (TMC) atoms at the distance of 1.0 Å. This study suggested that the TFC formed by the interaction between TMC - PIP is very much stable based on the higher interaction in a very short distance.

Performance Enhancement of PA-TFC RO Membrane by Using Magnesium Silicate Nanoparticles

This study focuses on to the change of the execution of polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane utilizing surface alteration by MgSiO3 nanoparticles. This has been an expert by means of holding of the practical grafting of PA layer with magnesium silicate nanoparticles (MgSiO3) in the presence of 2-acylamido 2-methyl propane sulphonic acid (AMPS) as condensing monomer. To confirm the presence of MgSiO3 nanoparticles and to inspect the morphology of the TFC nanoparticles layer SEM, FT-IR, XRD, TGA and DMA analysis were used. The outcomes demonstrated that the AMPS are effectively joined on the TFC film surface with an upgrade in thermal and mechanical decencies contrasted with pristine TFC layer. Besides, the contact angle estimations demonstrate an increase in the hydrophilicity of the thin film surface by the addition of nanoparticles. The water flux and salt rejection of the modified membranes were 25 L/m2 h and 95.5%, respectively.

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

Outer‐selective thin‐film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer‐selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect‐free polyamide film. A new simplified method to fabricate outer‐selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular‐sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m−2 h−1 bar−1. Outer‐selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well‐attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active‐to‐draw (i.e., the active layer facing the draw solution) and active‐to‐feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20‐min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil‐water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491–4501, 2015

Hydroxyl functionalized polytriazole-co-polyoxadiazole as substrates for forward osmosis membranes.

Hydroxyl functionalized polytriazole-co-polyoxadiazole (PTA-POD) copolymers have been synthesized and cast as promising highly thermally stable, chemically resistant, and antiorganic/biological fouling porous substrates for the fabrication of thin-film composite (TFC) forward osmosis (FO) membranes. The roles of PTA/POD ratios in the membrane substrates, TFC layers, and FO membrane performance have been investigated. This study demonstrates that the substrate fabricated from the copolymer containing 40 mol % PTA is optimal for the TFC membranes. Compared to the POD-TFC membrane, the 40 mol % PTA-TFC membrane exhibits a remarkable decrease in structural parameter (S) of more than 3.3 times. In addition, the 40 mol % PTA-TFC membrane is characterized by high water fluxes of 24.9 LMH and 47.2 LMH using 1 M NaCl as the draw solution and DI water as the feed under FO and pressure retarded osmosis (PRO) modes, respectively. Compared to a polysulfone (PSU) supported TFC-FO membrane under similar fabrication conditions, the 40% mol PTA-TFC membrane shows better FO performance and enhanced antifouling properties on the support (lower protein binding propensity and improved bacterial inhibition). Moreover, the performance of the 40 mol % PTA supported TFC-FO membrane can be improved to 37.5 LMH (FO mode)/78.4 LMH (PRO mode) and potentially higher by optimizing the support morphology, the TFC formation, and the post-treatment process. Hence, the use of newly developed hydroxyl functionalized polytriazole-co-polyoxadiazole copolymers may open up a new class of material for FO processes.

Design of robust hollow fiber membranes with high power density for osmotic energy production

This study highlights the design strategy of highly asymmetric hollow fiber membranes that possess both characteristics of high flux and high mechanical strength to effectively reap the osmotic energy from seawater brine with an ultrahigh power density. An advanced co-extrusion technology was employed to fabricate the polyethersulfone (PES) hollow fiber supports with diversified structures from macrovoid to sponge-like. The microstructure of the supports is found critical for the stability and water permeability of the thin film composite (TFC) membranes. A high porosity in the porous layer is needed to reduce internal concentration polarization, while a thick and relatively dense skin layer underneath the TFC layer is required to maintain good mechanical stability and stress dissipation. The pore size of the supporting layer underneath the TFC layer must be small with a narrow pore size distribution to ensure the formation of a less-defective, highly permeable and mechanically stable TFC layer. The newly developed hollow fiber comprising high asymmetry, high porosity, and a thick skin layer with a small and narrow pore size distribution underneath the TFC layer produces a maximum power density of 24.3W/m2 at 20.0bar by using 1M NaCl as the concentrated brine and deionized (DI) water as the feed. The proposed design strategy for ultrahigh power density membranes clearly advances the osmotic energy production close to commercialization with a quite cost-effective and practicable approach.

Outer-Selective Pressure-Retarded Osmosis Hollow Fiber Membranes from Vacuum-Assisted Interfacial Polymerization for Osmotic Power Generation

In this paper, we report the technical breakthroughs to synthesize outer-selective thin-film composite (TFC) hollow fiber membranes, which is in an urgent need for osmotic power generation with the pressure-retarded osmosis (PRO) process. In the first step, a defect-free thin-film composite membrane module is achieved by vacuum-assisted interfacial polymerization. The PRO performance is further enhanced by optimizing the support in terms of pore size and mechanical strength and the TFC layer with polydopamine coating and molecular engineering of the interfacial polymerization solution. The newly developed membranes can stand over 20 bar with a peak power density of 7.63 W/m(2), which is equivalent to 13.72 W/m(2) of its inner-selective hollow fiber counterpart with the same module size, packing density, and fiber dimensions. The study may provide insightful guidelines for optimizing the interfacial polymerization procedures and scaling up of the outer-selective TFC hollow fiber membrane modules for PRO power generation.

Effects of free volume in thin‐film composite membranes on osmotic power generation

For the first time, the effects of free volume in thin‐film composite (TFC) membranes on membrane performance for forward osmosis and pressure retarded osmosis (PRO) processes were studied in this work. To manipulate the free volume in the TFC layer, a bulky monomer (i.e., p‐xylylenediamine) was blended into the interfacial polymerization and methanol immersion was conducted to swell up the TFC layer. Results from positron annihilation lifetime spectroscopy (PALS) show that p‐xylylenediamine blending and methanol induced swelling enlarge and broaden the free volume cavity. In addition, the performance of TFC membranes consisting of different free volumes were examined in terms of water flux, reverse salt flux, and power density under high pressure PRO operations. The TFC‐B‐5 membrane (i.e., a TFC membrane made of blending monomers) with a moderate free volume shows the highest power density of 6.0 W/m2 at 9 bar in comparison of TFC membranes with other free volumes. After PRO operations, it is found that the free volume of TFC layers decreases due to high pressure compression, but membrane transport properties in terms of water and salt permeability increase. Interestingly, the membrane performance in terms of resistance against high pressures and power density stay the same. A slow positron beam was used to investigate the microstructure changes of the TFC layer after PRO operations. Compaction in free volume occurs and the TFC layer becomes thinner under PRO tests but no visible defects can be observed by both scanning electronic microscopy and PALS. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4749–4761, 2013

Deformation and reinforcement of thin-film composite (TFC) polyamide-imide (PAI) membranes for osmotic power generation

To understand the deformation of thin-film composite (TFC) membranes in high-pressure pressure retarded osmosis (PRO) processes, TFC membranes have been fabricated by interfacial polymerization upon Torlon® polyamide-imide (PAI) porous substrates. Experimental results show that reinforcements can be achieved by controlling the chemistry and morphology of the substrate and TFC polyamide layer. The PAI substrate exhibits reinforced properties and performance by pre-compression and polydopamine (PDA) cross-linking modification, while the interfacial properties between the substrate and TFC layer are improved by the adhesive PDA cushion layer. The responses of the modified PAI substrate under high pressures have been examined in terms of structural compaction and permeation decline. When subjected to a hydraulic pressure of 14bar for periods up to 1600min, the PDA modified substrate exhibits a better mechanical stability and less deformation. The PDA modified substrate shows a steady-state water permeability that doubles the steady-state value of the unmodified substrate. In addition, casting membranes on polyester fabrics and post-treatments by chloride and ethanol show positive effects on membrane performance in PRO processes. As a result, the modified TFC membrane achieves a 3-fold increment in water flux and a 16-fold rise in power density (2.84W/m2 vs. 0.16W/m2) as compared with the unmodified TFC membrane. Positron annihilation spectroscopy (PAS) has been employed to investigate membrane morphological changes after high pressure PRO processes. The high hydraulic pressure mainly deforms the porous substrate but has little effect on the TFC dense layer. These results may provide important insights into the hydraulic characteristics of TFC membranes and are essential to the design of PRO membranes for osmotic power generation.

Molecular design of thin film composite (TFC) hollow fiber membranes for isopropanol dehydration via pervaporation

Abstract High performance hollow fiber membranes consisting of a thin film composite (TFC) polyamide layer and a porous Torlon® polyamide-imide substrate have been fabricated via interfacial polymerization for pervaporation dehydration of isopropanol. The effects of substrate characteristics on the formation of the thin polyamide layer and the pervaporation performance are investigated. It is found that the resultant TFC membranes show superior separation performance if the substrates have a fine surface pore size and desirable sub-structural morphology. The effects of amine monomers, i.e., m-phenylenediamine (MPD) and hyperbranched polyethyleneimine (HPEI), for interfacial polymerization with trimesoyl chloride (TMC) on separation performance are also compared. The TFC membrane prepared from HPEI exhibits a higher pervaporation flux than that from MPD possibly due to the fact that the former has higher amine content than the latter. As a consequence, the polyamide selective layer of the former has a greater hydrophilicity than the latter. X-ray photoelectron spectroscopy (XPS) and contact angle measurements have confirmed the hypothesis. The molecular weight of HPEI also affects the pervaporation performance of the resultant TFC membranes. With the optimal interfacial polymerization conditions, the TFC membrane fabricated from HPEI with a molecular weight of 2 kg/mol shows the best separation factor of 624 with a flux of 1282 g/m2-h and a permeate water concentration of 99.1 wt% using a feed composition of 85/15 wt% IPA/water at 50 °C. After post methanol treatment, the flux can be enhanced to 1920 g/m2-h with a slightly decrease in permeate water concentration to 98.4 wt%. The mechanism of flux enhancement has been examined by slow beam positron annihilation spectroscopy (PAS). It is found that the removal of the excess amine from the TFC layer during the methanol treatment is the main cause.

Application of response surface methodology in describing the performance of thin film composite membrane

The thin film composite layer (TFC), on a polysulfone support was formed using an interfacial polymerization reaction between aqueous and organic phases. In order to identify the important interfacial reaction factors, which influence the membrane performance, a systematic experimental design based on the response surface methodology (RSM) is used. The factors considered were the composition of the aqueous phase, which includes the ratio of m-phenyldiamine (MPDA) to hydroquinone (HQ) as monomer ratio, percent of tetrabutylammonium bromide (TBAB) as a catalyst and percent of sodium hydroxide (NaOH) as an acid acceptor. The performance of the TFC membranes in terms of the rejection and flux were the response variables investigated. The experiment plan was based on the central composite design (CCD). The acid acceptor is found to be the most significant factor that influences the rejection rate of the TFC membranes and this is followed by the ratio of monomer, and the interaction of acid acceptor and ratio of monomer. The results also revealed that catalyst provided secondary contribution to the rejection rate. In the case of flux, the catalyst and the second order effect of ratio of monomer provided principle effect, whilst acid acceptor, the ratio of monomer and the second order effect of acid acceptor and the catalyst provided the secondary effect. The experimental results also indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors being investigated.