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Tuning the hydrophilic/hydrophobic nanophase-separated morphology to enhance the conductivity is a considerable challenge in the field of anion exchange membranes (AEMs). Here, a series of novel aliphatic-aromatic copolymer AEMs were designed by embedding flexible alkyl chains of different lengths into rigid main chain of poly(ether sulfone). Compared to traditional aromatic polymer, the aliphatic-aromatic copolymers had more flexible main chains and longer hydrophobic segments, both of which promoted the nanophase separation and the formation of ionic clusters. Increasing aliphatic chain length made the ionic clusters larger and more interconnected, but too long aliphatic chain led to the formation of smaller ionic clusters because the ionic groups were far away from each other. An optimum length of the aliphatic chain (8 C) existed for the nanophase-separated morphology with the biggest ionic clusters (around 8 nm), with which the membrane showed the highest conductivity. A peak power density of 159 mW cm −2 was obtained for the cell incorporating the 8 C membrane. Based on these, this study reveals a new direction to create a tunable nanophase-separated morphology for high-performance AEMs. [ABSTRACT FROM AUTHOR]

A novel amphoteric membrane was prepared using imidazolium-functionalized polysulfone (ImPSf) as the base polymer and sulfonated poly (ether ether ketone) (SPEEK) as the acid polymer for vanadium flow battery applications. The introduction of the ImPSf effectively resists the migration of vanadium ions owing to the Donnan repelling effect of the imidazolium cations on the vanadium ions and the low swelling ratio of the amphoteric membranes due to the ionic cross-linked interactions between the imidazolium and sulfonic groups. The amphoteric membrane with an ImPSf mass ratio of 17% shows a vanadium permeability of 1.5 × 10 −8 cm 2 s −1 that is much lower than that of Nafion212 (21 × 10 −8 cm 2 s −1 ). Having a high IEC of 2.04 mmol g −1 , it also exhibits a low area resistance of 0.48 Ω cm −2 that is comparable to that of Nafion212 membrane (0.41 Ω cm −2 ). As a result, the VFB cell with the amphoteric membrane exhibits high performances even at high current densities, i.e. at a current density of 200 mA cm −2 , and the amphoteric membrane achieves a coulombic efficiency of 97.5% and an energy efficiency of 77.3%, both of which are higher than those of Nafion212 (92.4% and 73.4%). These results indicate that the ImPSf/SPEEK amphoteric membrane is promising for VFB applications. [ABSTRACT FROM AUTHOR]

Heavy metal ions (HMIs) in wastewater can be removed by polyethyleneimine (PEI) adsorption, however, it is difficult to recycle PEI macromolecules from their mixture with suspended particles in wastewater. A novel HMIs adsorption technique with renewable PEI-grafted porous membranes was developed. PEI molecules were dispersed with high specific area and structured morphology, which allowed HMIs and suspended particles to be retained separately at different locations of the membrane, with the former adsorbed in matrix and the latter rejected on surface. The membranes with the optimized PEI loading ratio of 30 k wt % behaved excellently with microsphere rejection and Co(II) adsorption reaching 98.5% and 51.0 mg/g, respectively. They successfully decreased Co(II) concentration from 3.0 mg/L to the allowable discharge standard (0.5 mg/L), even with an enhanced flux of 6200 L/m2/h at 0.12 MPa under the cyclic tests. Overall, PEI-grafted membrane adsorption is highly efficient for removing HMIs and suspended particles simultaneously from wastewater. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4541-4548, 2017 [ABSTRACT FROM AUTHOR]

Hydroxide exchange membrane fuel cells (HEMFCs) are attracting growing interest owing to their advantages such as low cost and high power density. However, their applications are hindered due to the poor stability of the membrane. Here, we proposed a novel strategy to improve the alkaline stability of hydroxide exchange membranes (HEMs) using the interactions between strongly polar nitrile groups and side-chain functional cations. A poly(ether nitrile) (PEN) was synthesized by the polycondensation of bisphenol A and 2,6-difluorobenzonitrile, and then imidazolium and morpholinium functional groups were integrated by the typical chloromethylation-functionalization method. The existence of the interactions between nitrile groups and cation groups i.e. imidazolium and morpholinium, was proved by the density functional theory calculations. The interactions have two positive effects that contribute to the improvement of the alkaline stability of the PEN based membranes. On the one hand, they increase the LUMO energies of the functional groups; and on the other hand they reduce the free volume around hydrated cationic groups. As a result, PEN based membranes showed much better alkaline stabilities compared to the membrane based on commercial polysulfone that has a similar chemical structure. In addition, given similar swelling ratios, PEN based membranes exhibited higher hydroxide conductivities than simple polysulfone based ones. [ABSTRACT FROM AUTHOR]

A series of soluble quaternized polyetherimides (QAPEIs) have been successfully synthesized by homogeneous quaternization in trimethylamine aqueous solution. 1H NMR spectra confirm the successful synthesis of QAPEI. The QAPEIs exhibit good solubility in membrane-preparation solvents, making it possible to prepare the QAPEI composite membrane. Novel composite hydroxide exchange membranes have been prepared by incorporating QAPEIs with polytetrafluoroethylene (PTFE) membranes. The SEM images, gas permeation measurements and FTIR spectra show that the QAPEI is successfully filled in PTFE membrane and the resulted composite membrane is dense and smooth. The ion exchange capacity of composite membranes ranges from 0.35 to 0.58 mmol g−1. The composite membranes have appropriate water uptake (≤154%) and moderate swelling ratio (≤42%) even at 60 °C. The hydroxide conductivity of the composite membrane reaches 11.9 mS cm−1 at 20 °C that increases to 35.2 mS cm−1 at 60 °C. TGA curve shows that the composite membrane possesses high thermal stability (T OD: 210 °C). All these properties indicate that the QAPEI/PTFE composite membranes are good candidates for use as HEMs in HEM fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: Water sorption, water transport and ion transport are compared for polyether–ether ketone polymers functionalized with sulfonic acid, quaternary amine hydroxide, and imidazolium hydroxide. Water sorption in all three ionomers increases modestly with increasing water activity up to a w =0.6 and then increases more rapidly between 0.60.6. The increase in ion conductivity with increasing water activity is 10 times greater for the proton exchanged polymer compared to the hydroxide exchanged polymers. Water permeation from partially saturated vapor streams is primarily diffusion limited for all three ionomers and the permeation rates were approximately the same. Water pervaporation from liquid water appeared to be interfacial transport limited for membranes<120μm thick; the pervaporation rates at 40 and 60°C were independent of membrane thickness. Water sorption and transport show little dependence on the mobile ion while the ion transport appears to depend on both ion size and hydrophilicity of the fixed ion. [Copyright &y& Elsevier]

A high performance of anion exchange membranes (AEMs) is highly demanded in anion exchange membrane fuel cells (AEMFCs) and has been extensively studied. However, the poor ionic conductivities and the alkaline stability might limit their applications. Herein, we developed a novel strategy to improve the ionic conductivity and alkaline stability of AEMs by introducing hydrophilic oligo(ethylene glycol)(OEG) groups. Continuous ion-conducting channels were efficiently formed thanks to the dynamic aggregation of water molecules assisted by the hydrophilic side chains. The resultant AEMs with low IEC values showed significant enhancement in hydroxide conductivity compared to the AEMs functionalized by the conventional 1,2-dimethylimidazolium (PSf-Im), as the hydroxide conductivity of PSf-2 membrane with an IEC of 1.05 mmol g −1 was 59.5 mS·cm −1 at 60 °C while the hydroxide conductivity of PSf-Im membrane with an IEC of 1.27 mmol g −1 was 36.7 mS·cm −1 . In addition, the alkaline stability and the mechanical properties of the resultant AEMs were improved remarkably. The density functional theory (DFT) study showed that the introduction of OEG part can significantly increase the LUMO energy of functional group and then enhance the alkaline stability. [ABSTRACT FROM AUTHOR]

This is a continuation of the development of polyimide membrane for tetrafluoroethylene (TFE) recovery [Sep.Purif.Technol.124(2014)89–98]. A industrial membrane plant has been designed and constructed after cryogenic acetone absorption to enhance TFE recovery for the first time. Specific to the 10-kt/a TFE synthesis plants, the nominal process capacity is set as 20 Nm 3 /h. The vacuum mode (−0.08 MPaG) is executed for the permeate side to increase the feed/permeate pressure ratio and enhance separation performance under low feed pressure. In response to the drastic fluctuation in feed flow rate and composition, owing to the unsteady cracking reaction, the adaptive control of membrane area is customized technically for the operation strategy. In detail, one or two modules can be shut down by the automatic response while the stream into membrane plant is lower in flow rate or higher in TFE content, and vice versa. In comparison to the ordinary mode under inflexible operation, whose TFE recovery ratio is about 84.5%, the adaptive control strategy behaved better with the recovery ratio up to 87.6%. According to the three-month running result, the membrane recovery plant with adaptive membrane area control can efficiently decrease TFE loss from 130 to 17 t/a, and the annual gross profit was about 1.264 million US dollar, with the payback period less than 4 months. It is undoubted that the polyimide membrane plant is practicable and cost-efficient for TFE recovery in the synthesis. [ABSTRACT FROM AUTHOR]

In polyelectrolyte membranes, hydrated protons and proton conductive channels have cooperative effect on proton conductivity, the mechanism of which is believed to involve the structure of hydrated proton being deformed to adapt the confining channel. To investigate the dependence of the structural and dynamical properties of hydrated protons in Hyfion ® perfluorosulfonic acid membranes with various water uptake values on the channel size, a series of molecular dynamics simulations based on an all-atom force field were conducted. The water uptake dependence of the hydrated proton diffusivity determined from our simulations was consistent with the experimental results in literature, which verified the simulation systems. A probability distribution of the hydrated proton complex is proposed to characterize the confinement effect of the proton conductive channel on the hydrated proton structure in the membranes with different morphologies. By means of local structural properties and pair-potential energies, a reasonable hydrogen bond criterion was employed to characterize the structures of the hydrated proton complexes. It was found that the nanochannels confined the structure of the hydrated proton complex and that confined complexes of H 9 O 4 + , H 7 O 3 + and H 5 O 2 + were dominant. Weakening the confinement by increasing the channel size was beneficial for the formation of the H 9 O 4 + complex, the probability distribution of which gradually became plateau. Thus, H 9 O 4 + can be considered the stable structure of the confined hydrated proton complex in polymer electrolyte membranes. This work is helpful in understanding the relationship between the structure of the confined hydrated proton and the proton conductive channel. It also provides potential guidance for improving the membrane performance in fuel cell. [ABSTRACT FROM AUTHOR]

Fluoroform (HFC-23), the unavoidable byproduct of chlorodifluoromethane (HCFC-22) synthesis, is one of the most potent greenhouse gases. The general approach to incinerate the vent gas, though avoids the adverse environmental impacts, is a waste of HFC-23, which is valuable as refrigerant and plasma etchant. In this work, membrane process was coupled with distillation to separate high purity HFC-23 from the vent gas economically. Theoretical analysis and experimental tests were conducted to find the applicable membrane materials. The results indicated that the rubbery PDMS, with higher selectivity and gas permeation coefficients, was superior to the glassy PI for HFC-23 separation. PDMS thin-film composite membranes were prepared and characterized. In the actual permeation tests with industrial vent gas at 30 °C and 0.55 MPa, the as-prepared PDMS composite membranes behaved with selectivity α F22/F23 = 3.2 and permeation rate J F22 = 661 GPU, respectively. Afterwards, the cascaded membrane systems with different stage number were studied by process simulation and their economic feasibility was analyzed. Briefly according to the economic data, the 4-stage cascade structure is the optimal configuration to couple with distillation unit. For a 50 kt/a synthesis plant, the 4-stage process can efficiently refine HFC-23 to a purity as high as 99.5 mol%, with a specific cost of 70 USD t −1 and an extra gross profit of 3.8 × 10 6 USD a −1 . However, taking the process complexity into account, the 3-stage cascaded process, although exhibited slightly lower economic performance, is more suitable in industry. Overall, our studies have revealed that coupling PDMS membrane unit with distillation is a feasible and promising technique to separate high purity HFC-23 efficiently and economically in the HCFC-22 synthesis industries. [ABSTRACT FROM AUTHOR]

Abstract: The different states of water in a series of SPPESK membranes, including sulfonated poly (phthalazinone ether sulfone ketone) (SPPESK) membrane, cross-linked (XL) SPPESK membrane and SPPESK/polyacrylic acid (PAA) semi-interpenetrating polymer network (sIPN) membrane were investigated by low temperature differential scanning calorimetry (DSC) measurements. Only one melting peak was observed for each DSC curve, therefore the free water cannot be distinguished from freezing bound water in the experimental condition. The melting temperature of the freezable water was found to decrease when the content of the freezable water reduced. The content of non-freezing bound water decreased with the increase in total water uptake in each type of the membranes. It indicates that the total water uptake cannot exactly reveal the ability of tight water retention of the membranes. As compared with SPPESK/PAA membrane, SPPESK and XL-SPPESK membranes presented a higher ability of water retention because of higher content of non-freezing bound water measured. A schematic structural model is given to explain the interrelation of distribution of ionic groups (hydrophilic groups) and structure of polymers to the content of non-freezing bound water. [Copyright &y& Elsevier]