Fabrication Of Reverse Osmosis Membranes Research Articles

Molecular heterostructured interlayer for fabrication of high-performance thin film composite reverse osmosis membranes

To solve the scarcity of fresh water, reverse osmosis (RO) technology for seawater desalination and wastewater reuse has been developed rapidly. However, the performance of RO is limited by poor selectivity towards certain harmful small molecule constituents (e.g., boron in seawater and N-nitrosodimethylamine in wastewater) and the permeability-selectivity trade-off. Herein, a metal polyphenol network interlayer including both hydrophobic zone and monomer adsorption zone is proposed to optimize interfacial polymerization (IP) process for fabrication of RO membrane. This heterogeneous characteristic is endowed by well-chosen phenol (i.e. TTSBI) and metal (Ni). The physicochemical properties of the substrate are also optimized. An ultra-selective RO membrane with thinner separation layer, higher crosslinking degree and larger surface area is obtained. The RO membranes exhibit separation performance beyond the upper selectivity limit for NaCl and hazardous small molecules. The membrane water permeance is 3.50 L m−2h−1bar−1while the NaCl rejection is 99.5 %. Meanwhile, the mechanism of the interlayer influencing IP process is investigated by combining molecular simulation and experimental methods. Our work provides a novel design direction of substrate used for fabricating RO membrane with outstanding performance.

Ionic Liquid-Mediated Interfacial Polymerization for Fabrication of Reverse Osmosis Membranes.

This study revealed the effects of incorporating ionic liquid (IL) molecules: 1-ethyl, 1-butyl, and 1-octyl-3-methyl-imidazolium chlorides with different alkyl chain lengths, in interfacial polymerization (IP) on the structure and property (i.e., permeate-flux and salt rejection ratio) relationships of resulting RO membranes. The IL additive was added in the aqueous meta-phenylene diamine (MPD; 0.1% w/v) phase, which was subsequently reacted with trimesoyl chloride (TMC; 0.004% w/v) in the hexane phase to produce polyamide (PA) barrier layer. The structure of resulting free-standing PA thin films was characterized by grazing incidence wide-angle X-rays scattering (GIWAXS), which results were correlated with the performance of thin-film composite RO membranes having PA barrier layers prepared under the same IP conditions. Additionally, the membrane surface properties were characterized by zeta potential and water contact angle measurements. It was found that the membrane prepared by the longer chain IL molecule generally showed lower salt rejection ratio and higher permeation flux, possibly due to the inclusion of IL molecules in the PA scaffold. This hypothesis was supported by the GIWAXS results, where a self-assembled surfactant-like structure formed by IL with the longest aliphatic chain length was detected.

Ionic Liquid-Mediated Interfacial Polymerization for Fabrication of Reverse Osmosis Membranes

Ionic Liquid-Mediated Interfacial Polymerization for Fabrication of Reverse Osmosis Membranes

Regulating solvent activation by the mechanical force for the fabrication of reverse osmosis membranes with high permeability and selectivity

Solvent activation before heat treatment is an effective way to fabricate a more permeable polyamide (PA) reverse osmosis (RO) membrane. However, this method usually induces a decrease in selectivity due to the excessive swelling and dissolution of PA. A facile strategy of regulating solvent activation by the mechanical force was proposed in this work. With this strategy, the mechanical force was applied to the partial region of membrane surface before solvent activation to strengthen the interactions between the PA fragments and the PA, which would reduce the dissolution of partial PA fragments and alleviate the swelling of PA during activation for higher selectivity; while the region of membrane surface without applying mechanical force would be activated by solvent normally for high permeability. The desalination performances of the RO membranes for both brackish water and seawater were evaluated. The results verified that the membrane prepared by regulating solvent activation had a higher rejection and a comparative flux compared to the membrane activated by solvent directly. This work provides a facile way to fabricate the advanced RO membrane by regulating solvent activation.

Composite reverse osmosis membrane with a selective separation layer of double-layer structure for enhanced desalination, anti-fouling and durability properties

High performance membrane is crucial for energy-efficient desalination of salty water and reclamation of wastewater. Commercially available reverse osmosis membranes manufactured by interfacial polymerization or phase inversion techniques usually face the obstacle of “trade-off” effect between water permeation ability and salt rejection capability. In this work, a novel approach of constructing selective separation layer of double-layer structure was proposed to break through the difficulty of fabrication of reverse osmosis membrane with both high water permeation and salt rejection capabilities. Selective separation layer comprising loose polyamide (PA) sub bulk and dense hydroxypropyl methylcellulose (HPMC)-modified polyvinyl alcohol (PVA) top skin was constructed by the technique of interfacial polymerization followed with surface coating and cross-linking. The double-layer selective separation layer was found to possess an enhanced balance in water and salt permeations and endow the composite membrane with both high water flux and salt rejection. The desired membrane with an optimized selective layer of PA2/PVA + HPMC0.2 achieved 99.4% salt rejection and 37.9 kg/m2 h MPa water permeance to brackish water, which were higher than those of commercial membrane BW30. Furthermore, the desired membrane also exhibited better separation and antifouling performances in reclamation of secondary industry effluent when compared with the state-of-the-art antifouling membrane BW30FR.

Precise assembly of a zeolite imidazolate framework on polypropylene support for the fabrication of thin film nanocomposite reverse osmosis membrane

Polypropylene (PP) has been widely used in the fields of lithium battery separators, proton exchange membranes, membrane bioreactors and polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membranes owing to its excellent mechanical strength, chemical durability and low cost. Nevertheless, its inherent strong hydrophobicity and low surface porosity severely limit its in-depth development in the field of polyamide TFC membranes. Herein, we propose a general strategy for the precise assembly of ZIF-8 nanoparticles on PP support for the fabrication of RO membrane. By this method, position induced nanoporous surface (PINS) was introduced via in-situ synthesis of ZIF-8 assisted by diazonium-induced anchoring process (DIAP) on PP support, and it would achieve precise repair of non-porous regions of PP support, thereby increasing its surface porosity and hydrophilicity of PP support. Subsequently, a high-performance ZIF-8 hybrid reverse osmosis (HPP-ZIF-8-RO) membrane was fabricated by conventional interfacial polymerization (IP) on modified commercialized PP support for the first time. The optimal rejection of HPP-ZIF-8-RO for NaCl is ~99%, and the water flux is up to 50 kg m−2 h−1 under the operating pressure of 1.55 MPa. In addition, the HPP-ZIF-8-RO membrane has a superior chemical stability after the solvent resistance test. To prove the university of DIAP and PINS, we have successfully fabricated other types of HPP-MOF-RO (HPP-ZIF-67-RO, HPP-HKUST-1-RO) which also show enhanced desalination performance. Hence, DIAP and PINS could provide a convenient and versatile method for precise repairing the defect area of the hydrophobic porous substrates.

Fabrication of Reverse Osmosis Membrane with Enhanced Boron Rejection Using Surface Modification

Fabrication of Reverse Osmosis Membrane with Enhanced Boron Rejection Using Surface Modification

Preparation of poly(vinyl chloride) (PVC) ultrafiltration membranes from PVC/additive/solvent and application of UF membranes as substrate for fabrication of reverse osmosis membranes

ABSTRACTUltrafiltration (UF) membranes were prepared from poly(vinyl chloride) (PVC) as main polymer, poly(vinyl pyrrolidone) (PVP) as additive, and 1‐methyl‐2‐pyrrolidone (NMP) as solvent using Design Expert software for designing the experiments. The membranes were characterized by SEM, contact angle measurement, and atomic force microscopy. The performance of UF membranes was evaluated by pure water flux (PWF) and blue indigo dye particle rejection. In addition, the molecular weight cutoff of UF membranes was determined by poly(ethylene glycol) (PEG) rejection. The UF membranes were used as substrates for fabrication of polyamide thin film composite (TFC) reverse osmosis (RO) membranes. The results showed that the model had high reliability for prediction of PWF of UF membranes. Also, increment in PVC concentration caused reduction of PWF. Moreover, at constant PVC concentration and if the concentrations of PVC was lower than 10 wt %, the PWF reduced by increasing the concentration of PVP. However, at PVC concentration higher than 11 wt %, increment in PVP concentration showed increment and reduction of PWF. The PEG rejection results showed that the prepared membranes had UF membranes properties. Finally, the NaCl rejection tests of RO membranes by PVC as substrates indicated that the performance of RO membranes were lower than commercial membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46267.

Effects of polymerization conditions on hydrophilic groups in aromatic polyamide thin films

For polyamide used in reverse osmosis (RO) membranes, the content of pendant acid groups is critical to its performance. In this work, FTIR was used to analyze the acid contents in the polyamide films prepared via interfacial polymerization of trimesic acid trichloride (TMC) in hexane and 1,3-phenylenediamine (MPDA) in water, and the effects of reaction conditions, including monomer concentrations, time, and temperature, were studied. It was found that more pendant acid groups are present in the polyamide film at higher TMC concentrations or lower MPDA concentrations, and longer reaction times and lower temperatures also favor the formation of the free acids. These results can be explained by the monomer diffusion in the interfacial polymerization process. This work may help the design and fabrication of RO membranes with different hydrophilicity and target performance.

THE FABRICATION AND PERFORMANCE OF CELLULOSE REVERSE OSMOSIS MEMBRANES

A method for the fabrication of reverse osmosis membranes made from cellulose material is reported along with their performance data with respect to the separation of single electrolyte solutes from their aqueous solutions. The separation depends on the charge and the valence of the ions involved as well as the porosity of the membrane. The larger rejection for electrolytes involving negative ions of higher valence is attributed to a net negative charge on the surface of the membrance. Further, it was found that the solute separation decreases with an increase of feed solute concentration, which is also attributable to the charge on the membrane surface.