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

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

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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

The influence of inorganic filler particle size on composite ion-exchange membranes for desalination

In this work, we report a new class of organic inorganic nanocomposite ion-exchange membranes containing a sulfonated functionalized polymer (sulfonated polyethersulfone) and sulfonated mesoporous silica (SS). The effect of SS filler size (20 and 100 nm) on membrane structures and properties has been investigated. The results revealed the significant impact of filler sizes on macroscopic properties, such as morphologies, physico-electrochemical performance, and mechanical and thermal stabilities of the resultant composite membranes. The appropriate amount of smaller-sized SS fillers (20 nm diameter) led to better overall properties of the composite membranes with a conductivity up to 2.7 mS cm(-1), a permselectivity of 98% (around 640% and 16% improvement of conductivity and permselectivity compared with the pristine membranes, respectively), and high thermal and mechanical stability due to intimate polymer inorganic filler interaction. The performance of the composite membranes in the desalination of a NaCl solution was evaluated by a lab-scale electrodialysis cell in comparison with a benchmark membrane, FKE. The results revealed that the optimized composite with 0.5 wt % inorganic SS additive with a smaller particle size (20 nm diameter) exhibited an overall desalination performance comparable to that of FKE. Moreover, the energy consumption of the composite membrane was brought down to nearly a half compared to that of the pristine polymer membrane

Preparation of porous composite ion-exchange membranes for desalination application

Via a two-step phase inversion technique, composite membranes with controllable porosity and a significant improvement of electrochemical properties were successfully prepared. The presence of surface functionalized mesoporous silica (SS) as inorganic fillers in the sulfonated polyethersulfone (sPES) polymer matrix was proved to have a great impact on the resultant membrane structure, which subsequently led to significantly enhanced ionic conductivity of the membranes. The correlation among inorganic fillers, composite structures, electrochemical properties and desalination performance by electrodialysis (ED) was discussed in detail. The optimal membrane was the composite with 0.2 wt% SS loading, which possessed a good ionic conductivity of 5.554 mS cm(-1), a high selectivity with 0.95 transport number while maintaining good mechanical strength and thermal stability. Moreover, the performance of this membrane in ED was comparable to a commercial membrane (FKE), exhibiting a current efficiency of 0.84 and 3.82 kW h kg(-1) of salt removed

Pebax/Modified Cellulose Nanofiber Composite Membranes for Highly Enhanced CO₂/CH₄ Separation

This work explored the use of biomass-derived cellulose nanofibers as an additive to enhance the separation performance of Pebax membranes for the removal of CO2 from biogas. Succinate functional groups were modified on the cellulose nanofiber (SCNF) to incorporate more CO2-attracting functional groups before they were added to the polymer matrix. A small addition of SCNF up to 0.5 wt % had no significant impact on the polymer chain packing of Pebax but significantly enhanced the tensile strength and separation performance in both CO2 permeability and CO2/CH4 selectivity. On the other hand, increasing the SCNF addition amount above 1 wt % resulted in a slight alternation of membrane microstructure, i.e., lowering crystallinity, stiffer structure, and reduced tensile strength. At high loading, the CO2 permeability and CO2/CH4 selectivity of the composite membrane were, however, found to decline. This behavior is explained by a greater propensity for interaction among the CO2-attracting functional groups of SCNF and Pebax at elevated SCNF loadings, leading to fewer functional groups available for CO2 sorption. The optimal 0.5% SCNF loading (Pebax/SCNF-0.5) demonstrated a CO2 permeability of 263.8 Barrer and selectivity of 19.9 under 4 bar pressure and an operating temperature of 30 °C. These separation performances increased by 29.69% permeability and 39.04% selectivity compared with those of pure Pebax. These highly impressive results corresponded to the increases in the levels of CO2 dissolution and diffusion via hydrophilic SCNF nanofillers in Pebax. This work could strongly advance the research and development of gas separation technology based on polymeric membranes with the utilization of biobased nanofillers for energy and environmental sectors

Inclined forward osmosis module system for fouling control in sustainable produced water treatment using seawater as draw solution

Produced water (PW) generated from oil and gas production is a threat to the environment if not treated properly. Conventional methods for PW treatment are often accompanied by a series of treatments to fulfill the discharge standard. Forward osmosis (FO) is a promising option due to its high solute retention, less irreversible fouling, low energy footprint and potentially used as a standalone unit. However, FO still suffers from the low flux and fouling when treating highly contaminated feeds. This study investigated fouling control in the FO system for concentrating PW by using seawater as a draw solution (DS). A multi-stage filtration system (via via replenishments of the DS) with an aeration and module inclination for fouling mitigation was proposed to improve concentration factor (CF) and flux. Results showed that the multi-stage concentration offered higher fluxes range of 1.72–15.48−1.72 L/(m2h) (LMH) and four times of CF than the single-stage one with fluxes range of 0.39–9.49 LMH corresponding to CF of 1.75. The aeration was effective to enhance the water flux and suppress the fouling, and showed a significant impact at the rate of 0.4 L/min, reaching flux increment by 11 times at a rate of 1 L/min. The impact of aeration was enhanced by inclining the filtration cell up to 5 times at the inclination angle (θ) of 90° due to the improved contacts of air bubbles with the membrane surface. The contribution of the aeration and cell inclination on the water flux can be explained through the forces acting on moving air bubbles