Electrolysis of sodium chloride using composite poly(styrene-co-divinylbenzene) cation exchange membranes

Composite cation exchange membranes are prepared from cross-linked styrene-divinylbenzene copolymers for the electrolysis of sodium chloride to produce sodium hydroxide and chlorine by selective removal of sodium ions. It is prepared from a syrup of the polymer using dual initiating system and is modified with chloroacetic acid to introduce acid functional groups (COO⁻) on its surface. The effect of the modification is confirmed by FTIR, SEM, contact angle, water content, and ion exchange capacity measurements. The performance of the membrane has been evaluated in terms of current efficiency and power consumption and the effect of current density, salt concentration and flow rate on efficiency has been studied. Our membrane has an ion exchange capacity of 0.833 meq./g which is close to that of the commercially available Nafion-117 membrane having an ion exchange capacity 0.9 meq./g. The Nafion-117 used for electrodialysis of sodium sulfate has a current efficiency of around 90% and specific energy consumption of 0.1 kW/mol at 2N concentration of the salt at 1000 A/m². Our membrane used for electrodialysis of sodium chloride has a current efficiency of 93% and a power consumption of around 0.3122 kW/mol at the same concentration of salt and at a current density of 254 A/m². The two-dimensional space-charge model in cylindrical coordinates has been solved semi-analytically to obtain the effective wall potential and pore size of the membrane which are difficult to measure directly. The experimentally obtained solute flux and current density have been fitted to the model and optimum values of effective wall potential and pore diameter have been determined to be 98.5 mV and 0.8 nm, respectively.     

Mitigated membrane fouling in an SMBR by surface modification

Fouling is a major obstacle in membrane processes applied in membrane bioreactor. To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes (PPHFMMs) in a submerged membrane bioreactor (SMBR), the PPHFMMs were surface modified by NH₃, CO₂ plasma treatment, photoinduced graft polymerization of acrylamide and acrylic acid. The structural and morphological changes on the membrane surface were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR) and field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The results of XPS and FT-IR/ATR clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously. The antifouling characteristics of the modified membranes in an SMBR were evaluated. The modified membranes showed better filtration performances in the submerged membrane bioreactor than the unmodified one, and the acrylic acid-grafted membrane presented the best antifouling characteristics. The results demonstrated that (1) the surface carboxyl-containing membranes were better than the surface amido-containing membranes; (2) surface-grafted membranes were better than the plasma-treated membranes.     

Proton conductive thin films prepared by plasma polymerization

Proton conductive membranes were prepared as thin films of about 10 μm thickness by an ion beam assisted plasma polymerization process. Argon ions were generated in a high frequency plasma and accelerated towards a PTFE target where CF fragments were released as a consequence of the ion impact. Various sulfur components (SO₂, CF₃SO₃H or ClSO₃H) were added to achieve proton conductivity by the formation of sulfonic acid groups. The CF fragments combined with the sulfur components to form a coherent thin film on a substrate. Mass spectrometric investigations revealed, however, that sulfur oxygen compounds were extremely delicate towards reduction to sulfur carbon compounds like CS₂ or SCF₂. The best membrane conductivities (>10⁻⁴ S/cm) and highest ion exchange capacities (0.15 mmol/g) were achieved with chlorosulfonic acid involved in the plasma polymerization process. Ultra-thin layers of these of these plasma polymers (ca. 300 nm) were subsequently deposited onto Nafion^® membranes in order to suppress methanol permeation for a potential application in a direct methanol fuel cell (DMFC). The ratio of proton conductivity and methanol diffusion coefficient was employed for an assessment of the transport characteristics of the coated membrane. Diffusion coefficients were determined in a flow cell coupled to a mass spectrometer. The plasma polymer coating decreased both the methanol permeation and the proton conductivity. With a proton conductive plasma polymer coating the decrease of methanol diffusion could outweigh the loss of proton conductivity. Plasma coating offers a way to suppress methanol crossover in DMFCs and to maintaining the proton conductivity.     

Surface modification of non-woven fabric by DC pulsed plasma treatment and graft polymerization with acrylic acid

Direct-current pulsed plasma treatment (DPPT) followed by thermal-induced graft polymerization with acrylic acid (AA) was used to modify poly(ethylene terephthalate)/polyethylene (PET/PE) non-woven fabric (NWF) in this study. The water contact angle of plasma modified NWF decreased sharply with DPPT time in 4 s. The water content of the NWF increased with DPPT time and levelled off after 30 s. Chemical analysis by X-ray photoelectron spectroscopy (XPS) indicated that the surface property of modified NWF could be maintained for more than 8 months under ambient conditions and could be further improved by grafting with acrylic acid. The concentration of AA in PET/PE-g-AA NWF increased both with the monomer concentration and the plasma treatment time. The maximum grafting density was 1.17 μmol/cm² with 40 s DPPT and 20% (w/w) AA. Improved biocompatibility of the modified NWF was confirmed with 3T3 fibroblast cells where cell viability was analyzed by MTT assays. More cells were found to attach to the modified NWF with higher growth rates, indicating that an improvement in surface properties by DPPT followed by graft polymerization of AA is beneficial for cell attachment and growth. A much more uniform cell distribution was found within the modified NWF from confocal laser scanning microscope observations.     

PREPARATION AND CHARACTERIZATION OF ION EXCHANGE MEMBRANES BASED ON POLYVINYLIDENE FLUORIDE

 A new ion exchange membrane based on polyvinylidene fluoride (PVDF) and sulfonated poly(styrene- divinylbenzene) was prepared by in-situ polymerization. The incorporation of sulfonic groups into the polyvinylidene fluoride composite membrane was confirmed by infrared spectroscopy (IR), ion exchange capacity (IEC) and energy dispersive X-ray analysis (EDAX). Area resistance, IEC and water uptake of the treated membrane were evaluated. When 20% of the crosslinked membrane was sulfonated at 80°C for 22 h, the PVDF ion exchange membrane can attain 0.8 Ω·cm²area resistance in NaCl aqueous solution at 25℃, IEC is as high as 2.43 millimoles per gram of the wet membrane. The hydrophilicity of PVDF membrane is also significantly improved after treatment. When 60% of crosslinked membrane was sulfonated at 80 ℃ for 6 h, water uptake of the treated membrane can attain 64.7%.     

Studies on synthesis and property of novel acid-base proton exchange membranes

Sulfonated poly(phthalazinone)s (SPPENK, SPPESK and SPPBEK) were prepared by direct polymerization reaction from sulfonated monomers. The novel acid-base membranes were composed of sulfonated polymers as the acidic compounds, and polyetherimide (PEI) as the basic compounds, casting from their N-methylpyrrolidone (NMP) solution directly onto clean glass plates at 60℃ aiming at enhancing membrane toughness and other relative properties. The resulted acid-base composite membranes had excellent resistance to swelling, thermo-stability, hydrolysis resistance and oxidative resistance properties with highly ion-exchange capacity (IEC).     

Isolation of lysozyme from hen egg albumen using glass fiber-based cation-exchange membranes

In this study, porous glass fiber membranes were coated with monophenyl trimethoxysilane (MPh) and then sulphonated by chlorosulphonic acid to prepare the cation-exchange membranes with sulphonic acid groups. Different MPh-coating times were tested and the properties of the resulting membranes such as contact angle, FTIR spectrum, conductivity, and ion-exchange capacity were measured. It was found that the optimal MPh-coating time was 60 min and the related ion-exchange capacity was 49.5 μequiv./disc. The modified membrane under the optimal MPh-coating condition was adopted for lysozyme isolation. The results were compared with those for the commercial cation-exchange membrane with sulphonic acid groups (ICE 450 unsupported membrane). Although the prepared membrane exhibited less adsorption capacity than ICE 450 unsupported membrane in the batch lysozyme adsorption experiment, it showed lower non-specific binding ratio under higher salt concentration. In the flow process isolating lysozyme from hen egg albumen, the purification effectiveness obtained using the prepared cation-exchange membrane was superior to the ICE 450 unsupported membrane.     

Study on the separation of amino acids in modified poly(dimethylsiloxane) microchips

A mixture of five amino acids including arginine, histidine, phenylalanine, serine and glutamic acid was successfully separated in microchip capillary electrophoresis and detected with laser-induced fluorescence (LIF) detector. These amino acids were labeled with 5-(4, 6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF). The analyses were performed on two kinds of modified poly(dimethylsiloxane) (PDMS) microchips. One kind of chip was simply treated with oxygen plasma (OP-chip), and the other was further modified by coating double layers of non-ionic polymer poly(vinyl alcohol) (PVA) after plasma oxidization (PVA-chip). The derivatization condition of amino acids by DTAF was optimized. The properties of the two modified PDMS microchips were studied and separation conditions, such as the buffer pH, buffer concentration and separation voltage, were also optimized. The column efficiencies of the two microchips were in the range of 193,000–1,370,000 plates/m. The DTAF-labeled amino acids were sufficiently separated within 50 s and 90 s in 2.5 cm channels on OP-chip and PVA-chip, respectively.     

Preparation of High‐capacity,Monodisperse Polymeric Weak Cation Exchange Packings Using Surface‐initiated Atom Transfer Radical Polymerization and Its Chromatographic Properties

A novel stationary phase for weak cation exchange (WCX) chromatography was prepared by "grafting from" strategy. Surface initiated atom transfer radical polymerization (ATRP) of acrylic acid (AA) was conducted in toluene medium, starting from the macromolecule initiators of poly(4‐vinylbenzyl chloride‐co‐divinylbenzene) (P_CMS/DVB) beads. The amounts of poly(acrylic acid) grafted chains with different ATRP formulations were calculated based on the elemental analyses. The poly(acrylic acid) grafted beads obtained with different ATRP formulations were tried as chromatographic packings in the separation of proteins by ion‐exchange chromatography. The effect of the poly(acrylic acid) grafted chain lengths on P_CMS/DVB beads for the separation of proteins was investigated in details. Simultaneously, characterization of the column was investigated as ion chromatographic stationary phase for the separation of inorganic cations. The results show that poly(acrylic acid) grafted columns had excellent performance for separation of proteins and inorganic cations. The highest of the dynamic capacity of the column was 35.55 mg/mL. The columns were provided with high column efficiency.     

Preparation and characterization of sulfated zirconia (SO4/ZrO2)/Nafion composite membranes for PEMFC operation at high temperature/low humidity

Fine particle superacidic sulfated zirconia (SO₄²⁻/ZrO₂, S-ZrO₂) was synthesized by ameliorated method, and composite membranes with different S-ZrO₂ contents were prepared by a recasting procedure from a suspension of S-ZrO₂ powder and Nafion solution. The physico-chemical properties of the membranes were studied by ion exchange capacity (IEC) and liquid water uptake measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, thermogravimetry–mass spectrometry (TG–MS) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that the IEC of composite membrane increased with the content of S-ZrO₂, S-ZrO₂ was compatible with the Nafion matrix, the incorporation of the S-ZrO₂ could increase the crystallinity and also improve the initial degradation temperature of the composite membrane. The performance of single cell was the best when the S-ZrO₂ content was 15 wt.%, and achieved 1.35 W/cm² at 80 °C and 0.99 W/cm² at 120 °C based on H₂/O₂ and at a pressure of 2 atm, the performance of the single cell with optimized S-ZrO₂ was far more than that of the Nafion at the same condition (e.g. 1.28 W/cm² at 80 °C, 0.75 W/cm² at 120 °C). The 15 wt.% S-ZrO₂/Nafion composite membrane showed lower fuel cell internal resistance than Nafion membranes at high temperature and low relative humidity (RH).     

CuPc(COOH)8-SA/CuTAPc-CS双极膜的制备及表征

分别用八羧基铜酞菁[CuPc(COOH)₈]和四氨基铜酞菁(CuTAPc)改性海藻酸钠(SA)阳膜层和壳聚糖(CS)阴膜层, 制备了CuPc(COOH)₈-SA/CuTAPc-CS双极膜. 实验结果表明, 经八羧基铜酞菁和四氨基铜酞菁改性后, 促进了双极膜中间层水的解离, 增大了阳离子交换膜层和阴离子交换膜层的离子交换容量及H⁺和OH^-的透过率. 与Fe³⁺改性的Fe-SA/mCS双极膜相比, CuPc(COOH)₈-SA/CuTAPc-CS双极膜的阻抗、电阻压降(即IR降)和溶胀度降低. 当电流密度高达120 mA/cm²时, CuPc(COOH)₈-SA/CuTAPc-CS双极膜的IR降仅为0.9 V.     

Aqueous-phase synthesis of PAA in PVDF membrane pores for nanoparticle synthesis and dichlorobiphenyl degradation

This paper deals with bimetallic (Fe/Pd) nanoparticle synthesis inside the membrane pores and application for catalytic dechlorination of toxic organic compounds form aqueous streams. Membranes have been used as platforms for nanoparticle synthesis in order to reduce the agglomeration, encountered in solution phase synthesis which leads to a dramatic loss of reactivity. The membrane support, polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase. Subsequent steps included ion exchange with Fe²⁺, reduction to Fe⁰ with sodium borohydride and Pd deposition. Various techniques, such as STEM, EDX, FTIR and permeability measurements, were used for membrane characterization and showed that bimetallic (Fe/Pd) nanoparticles with an average size of 20–30 nm have been incorporated inside of the PAA-coated membrane pores. The Fe/Pd-modified membranes showed a high reactivity toward a model compound, 2,2′-dichlorobiphenyl and a strong dependence of degradation on Pd (hydrogenation catalyst) content. The use of convective flow substantially reduces the degradation time: 43% conversion of dichlorobiphenyl to biphenyl can be achieved in less than 40 s residence time. Another important aspect is the ability to regenerate and reuse the Fe/Pd bimetallic systems by washing with a solution of sodium borohydride, because the iron becomes inactivated (corroded) as the dechlorination reaction proceeds.     

Preparation and basic characterization of heterogeneous weak acid cation exchange membrane

The goal of this article is focused on the preparation and the basic characterization of heterogeneous weak acid cation exchange membranes. The six weak cation exchange resins were chosen for the preparation of the membranes. The strong acid cation exchange membrane was prepared for the comparison of properties and preparation parameters. Heterogeneous membranes were prepared in the several steps. The last operations were the extrusion and hydraulic hot-pressing. The torque and pressure in the extrusion head were observed while the extrusion of heterogeneous membranes. According to the type of the ion exchange resin, parameters varied greatly. The strong acid cation exchange membrane and weak acid cation exchange membranes with carboxylic groups had the lowest values of the torque and pressure while the homogenization and extrusion. All membranes were characterized. Electrochemical (permselectivity, ion exchange capacity, resistance), physical (relative water content, swelling in the different solutions), and mechanical properties were measured. Properties varied distinctly according to the type of the ion exchange resins. Swelling dimensional changes of ion exchange membranes in sodium hydroxide and water were bigger than changes in hydrochloric acid. Ion exchange capacity of membranes related with ion exchange capacity of used ion exchange resins. Weak acid cation exchange membranes with carboxylic functional groups compared to the strong membrane had the best specific and areal resistance.     

The influence of H2SO4 electrolyte concentration on proton transfer resistance of membrane/solution interface

The proton transfer resistance of membrane/solution interface is investigated in this paper by employing H₂SO₄ aqueous solution with different concentration. Two commercial cation exchange membranes, Nafion1135 and PE01 membranes with different ion exchange capacity were selected as test membranes; Proton transfer resistance measurements were made by A.C impedance techniques. The proton transfer resistance of membrane/solution interface increases quickly from 0.059 to 2.22 Ω with the decrease of H₂SO₄ concentration from 2.0 to 0.05 mol/L. The ion exchange capacity of the membrane, or more exactly, the surface charge of the membrane has obviously effect on the membrane/solution resistance due to the formation of electrical double layer (EDL). The effect of electrolyte concentration on membrane/solution interface resistance can be explained by the electrical interactions between ions and charged groups of the membrane: high concentration of ions in the medium can compress the EDL and reduce the electrical interactions between ions and charged groups of the membrane.     

Oxygen permeation study in a tubular Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxygen permeable membrane

Dense tubular Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) membranes were successfully prepared by the plastic extrusion method. The oxygen permeation flux was determined at different oxygen partial pressures in the shell side and different temperatures between 700 and 900 °C. The oxygen vacancy diffusion coefficients (D_v) at different temperatures were calculated from the dependence of oxygen permeation flux on the oxygen partial pressure term based on the surface current exchange model. No unsteady-state of oxygen permeation flux was observed at the initial stage in our experiments. The reason is the equilibrium time is too short (less than 10 min) to observe the unsteady-state in time. The increase of the helium flow rate can increase the oxygen permeation flux, which is due to the decrease of the oxygen partial pressure in the tube side with increasing of the helium flow rate. The oxygen permeation flux can also be affected by the air flow rate in the shell side when the air flow rate is lower than 150 ml/min. But the oxygen permeation flux is insensitive to the air flow rate when the air flow is higher than 150 ml/min. The membrane tube was operated steadily for 150 h with oxygen permeation flux of 1.12 ml/(cm² min) at 875 °C. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis showed that both the surface exposed to air and the surface exposed to helium of the BSCFO membrane tube after permeation for 150 h are similar to the fresh membrane tube in composition and structure. These results indicated that the membrane tube exhibits high structure stability.     

Comparison of fuel cell performance of selected fluoropolymer and hydrocarbon based grafted copolymers incorporating acrylic acid and styrene sulfonic acid

Fuel cell tests have been carried out on ion exchange membranes produced by the radiation grafting of either acrylic acid or styrene monomers (followed by a sulphonation reaction) onto selected hydrocarbon and fluoropolymer films. Relationships between the membranes' intrinsic properties, composition, ion exchange capacity and equilibrium water content and their respective fuel cell performance have been established. Copyright © 2002 John Wiley & Sons, Ltd.     

Surface Modification of Ultra-high Molecular Weight Polyethylene Membranes Using Underwater Plasma Polymerization

Ultra-high molecular weight polyethylene membranes were modified and subsequently polymer coated using the underwater plasma produced by glow discharge electrolysis. This plasma pretreatment generated various O-functional groups among them OH groups have dominated. This modified inner (pore) surface of membranes showed complete wetting and strong adhesion to a hydrogel copolymerized by glow discharge electrolysis also. The deposited hydrogel consists of plasma polymerized acrylic acid crosslinked by copolymerization with the bifunctional N,N′-methylenebis(acrylamide). Tuning the hydrogel hydrophilicity and bio-compatibility poly(ethylene glycol) was chemically inserted into the copolymer. Such saturated polymer could only be inserted on a non-classic way by (partial) fragmentation and recombination thus demonstrating the exotic properties of the underwater plasma. The modification of membrane was achieved by squeezing the reactive plasma solution into the pores by plasma-induced shock waves and supported by intense stirring. The deposited copolymer hydrogel has filled all pores also in the inner of membrane as shown by scanning electron microscopy of cross-sections. The copolymer shows the characteristic units of acrylic acid and ethylene glycol as demonstrated by infrared spectroscopy. A minimum loss in carboxylic groups of acrylic acid during the plasma polymerization process was confirmed by X-ray photoelectron spectroscopy. Additional cell adhesion tests on copolymer coated polyethylene using IEC-6 cells demonstrated the bio-compatibility of the plasma-deposited hydrogel.     

Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid-catalyzed crosslinking for proton exchange membrane fuel cells

Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01–0.19 S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H₂/O₂ fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm² (Pd/C) exhibited a peak power density of 220.3 mW/cm², which was close to that of Nafion 212 (214.0 mW/cm²) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.     

Modified carrageenan 3. Synthesis of a novel polysaccharide-based superabsorbent hydrogel via graft copolymerization of acrylic acid onto kappa-carrageenan in air

A novel biopolymer-based superabsorbent hydrogel was synthesized through chemically crosslinking graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC), in the presence of a crosslinking agent and a free radical initiator. A proposed mechanism for κC-g-polyacrylic acid was suggested and the affecting variables onto graft polymerization (i.e. the crosslinker, the monomer and the initiator concentration, the neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Maximum water absorbency of the optimized final product was found to be 789 g/g. The swelling capacity of the synthesized hydrogels was also measured in various salt solutions. The time-temperature profile of the polymerization reaction, in order to investigate the effect of molecular oxygen was conducted in terms of the absence and presence of the atmospheric oxygen. The overall activation energy (E_a) of the graft polymerization reaction was found to be 2.93 KJ/mol.