Preparation of new composite membranes for water desalination using electrodialysis

The use of polyethersulfone (PES), an excellent but highly hydrophobic thermoplastic, as a matrix material for ion-exchange membranes was investigated. To make PES ion-exchangeable, sulfonate groups were introduced to the polymer chains by sulfonation reaction with chlorosulfonic acid. The degree of sulfonation of sPES was estimated to be 21%. Preliminary experiments investigated the effect of polyethylene glycol (PEG) and Pluronic F127 as fillers to improve the hydrophilicity of the membranes. Moreover, a lab scale electrodialysis cell has been designed and set up to evaluate the performance of these novel membranes compared to the benchmark of commercial membranes. The results show promising properties of ion-exchange capacity, water uptake, conductivity and hydophilicity from blended membranes, comparable to commercial membranes, though the performance of the prepared membranes did not exceed the commercial one. Further characterization of the transport properties of ion-exchange membranes need to be investigated to be able to understand the effects of the fillers on the performance of the membranes in ED application

Novel Organic-Inorganic Nanocomposite Membranes for Electrodialysis Application in Water Recovery

Water shortage has become one of the major global concerns and has led to great efforts towards the search and utilization of an alternative water supply such as from abundant salt rich brackish water and sea water. Desalination by membrane separation process becomes an important technology for global population by producing fresh water out of saline water. Membrane is the key element in the membrane separation processes that determines to a large extent the performance, process efficiency, energy consumption and water production cost of the desalination. Up to date, the majority of existing commercial membranes is polymer based membranes which still require further modifications to achieve high desalination efficiency and low energy consumption. The key target of this work is to synthesize a new class of ion-exchange membranes applicable for electrodialysis desalination process by utilizing a new concept of composite membrane design. Organic-inorganic composite membranes have recently gained increasing attention due to their hybrid functionalities derived from organic and inorganic phases that may offer a variety of important applications. Fortunately, the composite design concept can provide enormous opportunities to control membrane structure and properties by simply tuning material components, compositions, and functionalities. Introducing metal oxide nanoparticles into the polymer matrix is expected to improve conductivity and transport properties of the polymer membranes while still keeping favorable mechanical and thermal stability. Polyethersulfone (PES), an inexpensive and high performance polymer with excellent mechanical, thermal and chemical stability, was selected as a main organic matrix in this work. The PES was first chemically modified by sulfonation reaction to introduce charged functional groups into polymer backbones to form sulfonated polyethersulfone (sPES) for use as ion-exchangeable polymer matrix. High surface area mesoporous silica was also chemically modified with sulfonate groups and used as an inorganic filler. A series of composite membranes containing sPES and sulfonated mesoporous silica (SS) have been prepared via a number of membrane preparation techniques. Systematic material synthesis and characterizations have been applied to elucidate the crucial links among synthesis conditions, membrane structure and properties and their desalination performance. It is well-known that the properties and performance of the membranes depends highly on their structure which in turn is affected by membrane preparation conditions. In the first part of this work, the relationship among membrane fabrication condition, membrane structure and property is the main focus for establishing an optimized membrane preparation procedure. The membranes prepared by different phase inversion techniques offered different structures and distinct properties. The preparation conditions in the ternary system of solvent/nonsolvent/polymer in the phase inversion were carefully investigated. It was found that the combination of two commonly-used phase inversion techniques, namely wet and dry phase inversion, was an effective tool for preparing membranes with adjustable structure, pore size and porosity. The structure and porosity of the prepared sPES membranes can be easily controlled by tuning ageing periods of membrane formation in the steps of dry and wet phase inversions. The properties of polymer matrix membrane are further improved by incorporating surface functionalized mesoporous silica. In the second part of this thesis, the influence of inorganic fillers with different sizes and shapes on the membrane structure and properties was investigated. It was found that by incorporating small amount of inorganic additive, the membrane properties such as water content, conductivity, and transport number were significantly enhanced while the membranes still maintain their mechanical and thermal stabilities. The desalination results by a custom-designed lab-scale electrodialysis (ED) cell of the composite membranes also exhibited good performances with high current efficiency over 80%, which is compatible to a benchmark membrane (FKE, FumaTech). The newly developed membranes can thus be considered as excellent candidates for ion-exchange membranes in desalination application. The findings from this project will generate a suite of new knowledge that underpins both fundamental understanding of membrane design and their applications in ED desalination. The outcomes are expected to lead to the development of new alternative composite ion-exchange membranes which may open up cost-effective and less energy consumption desalination application

Evaluating Post-Treatment Effects on Electrospun Nanofiber as a Support for Polyamide Thin-Film Formation

Poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) electrospun nanofiber (ENF) was used as the support for the formation of polyamide (PA) thin films. The ENF support layer was post-treated with heat-pressed treatment followed by NaOH hydrolysis to modify its support characteristics. The influence of heat-pressed conditions and NaOH hydrolysis on the support morphology and porosity, thin-film formation, surface chemistry, and membrane performances were investigated. This study revealed that applying heat-pressing followed by hydrolysis significantly enhances the physicochemical properties of the support material and aids in forming a uniform polyamide (PA) thin selective layer. Heat-pressing effectively densifies the support surface and reduces pore size, which is crucial for the even formation of the PA-selective layer. Additionally, the hydrolysis of the support increases its hydrophilicity and decreases pore size, leading to higher sodium chloride (NaCl) rejection rates and improved water permeance. When compared with membranes that underwent only heat-pressing, those treated with both heat-pressing and hydrolysis exhibited superior separation performance, with NaCl rejection rates rising from 83% to 98% while maintaining water permeance. Moreover, water permeance was further increased by 29% through n-hexane-rinsing post-interfacial polymerization. Thus, this simple yet effective combination of heat-pressing and hydrolysis presents a promising approach for developing high-performance thin-film nanocomposite (TFNC) membranes

MCM-41/PVA Composite as a Separator for Zinc–Air Batteries

Membrane separators are one of the critical components in zinc–air batteries (ZABs). In the control of mass transfer, and hence, electrochemical reaction, membrane separators have an important role to play. This work addresses the issue of battery performance in a ZAB via a new composite membrane separator based on polyvinyl alcohol (PVA). To enhance the electrolyte uptake and ionic conductivity, mesoporous Mobil Composition of Matter No. 41 (MCM-41) is incorporated as a filler in the membrane while maintaining its integrity. The presence of MCM-41 is seen to reduce the number of cycles of secondary ZABs due to the uninvited drawbacks of increased zincate crossover and reduced triple phase boundary at the air cathode, which is pivotal for oxygen reduction reaction. Overall, results suggest that the application of the MCM-41/PVA composite has the potential for use as a separator in high-capacity primary ZABs

Preparation and characterization of sulfonated polyethersulfone for cation-exchange membranes

Polyethersulfone (PES) was sulfonated by chlorosulfonic acid and then used as the polymer matrix for cation-exchange membranes (CEM). The sulfonation reaction was conducted at room temperature and the degree of sulfonation was easily controlled by varying the ratios of reaction reagents. The morphology, physical properties, electrochemical properties, mechanical and thermal stabilities of the membranes were characterized to evaluate the properties of sulfonated polyethersulfone (sPES) as a cation-exchange membrane. Membranes with 40% degree of sulfonation were found to have the optimal properties, with good water uptake, ion-exchange capacity (IEC: similar to 1.44 mequivg(-1)) and conductivity while maintaining excellent mechanical stability and thermal stability. These membranes can be considered as excellent candidates suitable for water desalination by electrodialysis. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved

Tuning the selectivity of thin film composite forward osmosis membranes: Effect of co-solvent and different interfacial polymerization synthesis routes

status: publishe

Preparation of porous ion-exchange membranes (IEMs) and their characterizations

Ion-exchange membranes consisting of sulfonated polyether sulfone with controllable porosities and structures were prepared via a two-step phase inversion procedure. The porosity of membranes has been deliberately controlled by adjusting drying conditions. It was experimentally evidenced that membranes with high porosities possessed excellent conductivity; they also had poor selectivity and mechanical stability, while non-porous membranes exhibited much better selectivity and mechanical strength at the cost of lower conductivity. Porous membranes with 2.11 mequiv cm(-3) of fixed charged density, 0.33 mS cm(-1) of conductivity, 0.9 of transport number and similar to 500 MPa of Young's modulus were obtained by carefully controlling the two-step phase inversion preparation process. The results from this work lead to better understanding of the relationship among the formation conditions in water/dimethylformamide (DMF)/sulfonated polyether sulfone (sPES) system, structures and properties of membranes, which may shed light on advanced membrane design for appropriate applications. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved

Aminosilane-Functionalized Zeolite Y in Pebax Mixed Matrix Hollow Fiber Membranes for CO₂/CH₄ Separation

Due to their interfacial defects between inorganic fillers and polymer matrices, research into mixed matrix membranes (MMMs) is challenging. In the application of CO2 separation, these defects can potentially jeopardize the performance of membranes. In this study, aminosilane functionalization is employed to improve the nano-sized zeolite Y (ZeY) particle dispersion and adhesion in polyether block amide (Pebax). The performance of CO2/CH4 separation of Pebax mixed matrix composite hollow fiber membranes, incorporated with ZeY and aminosilane-modified zeolite Y (Mo-ZeY), is investigated. The addition of the zeolite filler at a small loading at 5 wt.% has a positive impact on both gas permeability and separation factor. Due to the CO2-facilitated transport effect, the performance of MMMs is further improved by the amino-functional groups modified on the ZeY. When 5 wt.% of Mo-ZeY is incorporated, the gas permeability and CO2/CH4 separation factor of the Pebax membrane are enhanced by over 100% and 35%, respectively

Synthesis of composite ion-exchange membranes and their electrochemical properties for desalination applications

A new type of composite ion-exchange membrane of sulfonated polyethersulfone (sPES) and sulfonated mesoporous silica (SS) was synthesized by dispersing inorganic SS nanoparticles as the fillers in the organic polymer matrix. Physical and electrochemical properties of the composite membranes were investigated in order to evaluate their key parameters as electromembrane candidates in their application in electrodialysis (ED) water purification. The results revealed that incorporating small amounts of SS enhanced the properties of the ion-exchange membranes with negligible influence on their thermal and mechanical properties. Membranes with 0.5 wt% SS were found to have the optimal properties, with good water uptake, ion-exchange capacity (IEC similar to 1.1 mequiv g(-1)), transport properties and excellent permselectivity while maintaining excellent mechanical and thermal stability. These newly-developed membranes can be considered as excellent candidates suitable for water desalination by ED