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Sulfonated poly(ether ether ketone) (SPEEK), synthesized for use as a cation exchange polymer, and aminated polysulfone (APSf), synthesized for use as an anion exchange polymer, were applied to commercial carbon electrodes through direct coating. Then the flow pattern was investigated using a computational fluid dynamics (CFD) analysis to find any occurrence of dead zones in the existing cell. On the basis of the CFD analysis, new capacitive deionization (CDI) cells were designed to minimize the dead zones. Next, a comparison between the old and newly designed cells was conducted through CDI experiments to determine the ability of the newly designed cells equipped with SPEEK and APSf coated electrodes to separate NaCl, MgCl2, CaCl2, and MgSO4 under a variety of experimental conditions. Under the given experimental conditions, a salt removal efficiency (SRE) of 100% was generally obtained at cell voltages above 1.2 V. For single component seed solutions of NaCl, MgCl2, CaCl2, and MgSO4, the SRE was determined in the order of NaCl > MgCl2 > CaCl2 > MgSO4. In a case of city tap water, even with a low feed concentration of 70 mg/L, we were able to obtain an SRE of 92.3%, and this result was attributed to the larger number of multivalent metal ions in the feed compared with the number of monovalent ions.

Clean water is an absolute necessity to sustain life on Earth; thus, research and development in water management and disinfection processes are necessary. As an effective method to disinfect water, dilute solutions containing hypochlorous acid and hypochlorite ions are often utilized. Herein, we report a newly designed hypochlorite ion generation process, which involves installation of cation exchange membranes (CEMs) to conventional electrolysis cell to enhance stability and controllability, and addition of Cl2 recovery stream to increase the production rate and efficiency of hypochlorites generation. Electrolysis cells with SPEEK, Nafion 115, and Nafion 324 are evaluated and compared with a cell without CEM, which resulted in up to 17% enhancement of the production rate. In addition, increased energy efficiency and controllability of the electrolysis process are achieved when SPEEK is used as the membrane. The CEM installed electrolysis combined with Cl2 recovery stream, which enables enhancement of stability and performances of the electrolysis-based hypochlorite generation, opens a new possibility for an efficient in-situ water disinfection system.

In this study, computational fluid dynamics (CFD) analysis was conducted to investigate the flow pattern and to find the occurrence of dead zones in an existing capacitive deionization (CDI) cell. Newly designed cells—specifically designed to avoid dead zones —were analyzed by CFD in accordance with the flow rates of 15, 25 and 35 ml/min. Next, the separation performances between the existing and newly designed cell were compared by conducting CDI experiments in terms of salt removal efficiency at the same flow rates. Then, the computational and experimental results were compared to each other. The salt removal efficiencies of the hexagon flow channel 1 (HFC1) and hexagon flow channel 2 (HFC2) were increased 88-124% at 15 ml/min and 49-50% at 25 ml/min, respectively. There was no difference between the existing cell and the foursquare flow cell (FFC) at 35 ml/min.

In this study, to improve the water flux of porous hydrophobic membranes, various water-soluble polymers including neutral, cationic and anionic polymers were adsorbed using 'salting-out' method. The adsorbed hydrophobic membrane surfaces were characterized mainly via the measurements of contact angles and scanning electron microscopy (SEM) images. To enhance the durability of the modified membranes, the water-soluble polymers such poly(vinyl alcohol) (PVA) were crosslinked with glutaraldehyde (GA) and found to be resistant for more than 2 months in vigorously stirred water. The water flux was much more increased when the ionic polymers used as the coating materials rather than the neutral polymer and in this case, about 70% of 0.31 L/m2·h (LMH) to 0.50 LMH was increased when 300 mg/L of polyacrylamide (PAAm) was used as the coating agents. Among the cationic coating polymers such as poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA), poly(acrylic acid-comaleic acid) (PAM) and poly(acrylic acid) (PAA), PSSA_MA was found to be the best in terms of contact angle and water flux. In the case of PSSA_MA, the water flux was enhanced about 80%. The low concentration of the coating solution was better to hydrophilize while the high concentration inclined to block the pores on the membrane surfaces. The best coating condition was found: (1) coating concentration 150 to 300 mg/L, (2) ionic strength 0.15, (3) coating time 20 min.

The sulfonated polyether ether ketone (SPEEK) as a cation exchange polymer and aminated polysulfone (APSf) as an anion exchange membrane (AEM) were synthesized to prepare bipolar membranes (BPMs) through hot pressing. The water splitting electrodialysis (WSED) experiments were conducted to produce acids and bases by using the resulting SPEEK/APSf BPM. For comparative performance evaluation of the commercialized ASTOM membrane and the newly synthesized membranes in our lab, the acid/base production rate and the voltage changes according to the constant current were measured. The acid and base formation rates of the commercialized membrane from ASTOM were 2.3 and 2.7 g/L/h, respectively, whereas the rates of the membranes we developed were 1.0–2.4 and 1.5–2.7 g/L/h, respectively, depending on the amine contents in the AEM. The performance of the synthesized BPM in our lab was equivalent or higher than that of the commercialized membrane from the viewpoint of the acid/base production rates.

In this study, polysufone (PSf) was used as a base polymer to synthesize sulfonated polysulfone (SPSf) and aminated polysulfone (APSf) as cation and anion exchange polymers, respectively. Then the ion exchange polymers were coated onto the surface of commercial carbon electrodes. To compare the capacitive deionization (CDI) and membrane capacitive deionization (MCDI) processes, the pristine carbon electrodes and ionic polymer coated electrodes were tested under various operating conditions such as feed flow rate, adsorption time at fixed desorption time, and feed concentration, etc., in terms of effluent concentration and salt removal efficiency. The MCDI was confirmed to be superior to the CDI process. The performance of MCDI was 2-3 times higher than that of CDI. In particular, the reverse desorption potential was a lot better than zero potential. Typically, the salt removal efficiency 100% for 100 mg/L NaCl was obtained for MCDI at feed flow rate of 15 ml/min and adsorption/ desorption time of 3 min/1 min and applied voltages 1.0 V for adsorption and -0.3 V for desorption process, and for 500 mg/L, the salt removal efficiency 91% was observed.

In this study, blended and cross-linked poly(vinyl alcohol) (PVA) with sulfur succinic acid (SSA) and poly(styrene sulfonic acid- co -maleic acid) (PSSA_MA) (PVA/PSSA_MA/SSA) was synthesized for use as a cation exchange polymer and aminated polysulfone (APSf) was synthesized for use as an anion exchange polymer. Then the ion exchange polymers were coated onto the surface of commercial carbon electrodes. Membrane capacitive deionization (MCDI) performance using these coated electrodes was tested in terms of effluent concentration and salt removal efficiency under various operating conditions such as feed flow rate, adsorption time at fixed desorption time, feed concentration, and desorption voltages for NaCl, CaSO 4 and MgCl 2 , mixed feed solutions of the three salts at concentrations of 100 ppm and 300 ppm, and finally city tap water. Both the effluent concentration and salt removal efficiency were found in the sequence of NaCl > CaSO 4 > MgCl 2 for a single feed component at the typical experimental conditions because of the stronger electrostatic force of multivalent ions than that of monovalent ions. For the mixed feed solution, similar results were observed except that salt removal efficiency was lower at 95% than the 96.7–100% values for single feed solutions. For the city tap water, salt removal efficiency was lowered further to 87.3% even for a lower feed concentration of 85 ppm; it is speculated that this is because of multiplicative metal ions in tap water.

폴리페닐렌옥사이드(PPO)와 폴리에테르이미드(PEI)에 대해 각각 설폰화(SPPO) 및 아민화(APEI) 반응이 이루어졌다. SPPO와 APEI의 특성평가를 위하여 FTIR, 열무게분석(TGA), 팽윤도, 이온교환용량(IEC) 및 이온전도도 등에 대한 측정을 하였다. 표면불소화를 실시한 후 표면불소화된 SPPO와 APEI 막과 불소화하지 않은 막과의 차이점을 알아보기 위하여 위에서 실시한 특성평가를 다시 수행하여 비교하였다. SPPO막의 이온교환용량을 고정시킨 후 APEI의 이온교환용량을 변경하면서 전체적으로 3개 유형의 바이폴라막을 제조하였고, 이를 차염소산 발생을 위하여 여러 전류밀도 하에서 저농도 및 고농도 소금용액에 적용하였다. 표면불소화된 막의 차염소산 생성 농도는 APEI의 이온교환용량에 의존하며 80 mA/m 2 에서 차염소산 농도 491-692 ppm의 결과를 얻었으며, 5 mA/m 2 에서 18-28 ppm의 차염소산 농도를 나타내었으며 내구성이 매우 상승된 것을 보여 주었다.

In this study, sulfonated poly(phenylene oxide) (SPPO) and aminated polysulfone (APSf) were synthesized for use as a cation exchange polymer and an anion exchange polymer respectively. The resulting ion exchange capacities of SPPO and APSf of 0.93 and 1.0 respectively were almost equivalent to each other. Then the ion exchange polymers were coated onto the surface of commercial carbon electrodes. Membrane capacitive deionization (MCDI) performance using these coated electrodes was tested under various operating conditions such as adsorption/desorption time, feed flow rate, and feed NaCl concentration and compared with capacitive deionization (CDI) under the same conditions. The experimental results indicate that the effluent concentration during desorption becomes higher with increased adsorption time and a lower feed flow rate. Also it was shown that the introduction of both cation and anion exchange polymers was effective in preventing the “co-ion” effect. With MCDI, a salt removal efficiency of 100% was obtained under the conditions of 5 min/1 min adsorption/desorption time and 23 mL/min feed flow rate, while with CDI the salt removal efficiency was less than 40% under the same conditions. Open image in new window

In this study, poly (phenylene oxide) (PPO) and poysulfone (PSf) were sulfonated and aminated respectively. Both sulfonated poly (phenylene oxide) (SPPO) and aminated polysulfone (APSf) were characterized via the measurement of FT-IR, swelling degree, ion exchange capacity (IEC), and ion conductivity. Then the surfaces of these membranes were modified by surface fluorination using 2000 ppm F2 gas against N2 gas for 1 h at room temperature. The surface fluorinated SPPO and APSf membranes were characterized again to determine any differences between the pristine and fluorinated membranes. In total, 3 types of bi-polar membranes were prepared by varying the IEC of the APSf and having a fixed value for the IEC of the SPPO. The hypochlorite concentration generated by using the surface fluorinated membranes was dependent on the IEC of the APSf and ranged from 683 to 826 ppm, while there was a considerable improvement in the durability of the surface fluorinated membranes as they remained intact even after operating for 4 h.

A new technique is introduced for the preparation of composite membranes based on the salting-out effect. The concept of this new technique consists of three parts: (i) polymer precipitation by the salting-out effect, (ii) blocking the pore structure by pressurizing the precipitated polymer particles (polyelectrolyte), and (iii) deposition of opposite charged polyelectrolyte through ionic cross-linking (polyelectrolyte complex). The pore blocked polyelectrolyte has the role of a membrane, and we called this membrane preparation technique by forced fouling induction “precipitated solute pressurization” (PSP). In this study, water-soluble polymers that are all polyelectrolytes were used as coating materials, namely polyethylenimine (PEI), poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA), and poly(vinyl sulfonic acid) (PVSA). The polymer particles formed by the addition of Mg(NO3)2·6H2O were pressurized and flown to the surface of microporous polyvinyledene fluoride (PVDF) to prepare composite membranes under varying conditions of polyelectrolyte concentration, ionic strength of salt, pressure, annealing temperature, etc. The resulting membranes were characterized in terms of the flux and rejection for 100 ppm NaCl at 4 atm to determine their suitability for application in a household water purifier. A combination of PVSA and PEI polyelectrolyte complex produced by the PSP method showed the best performance of flux of 43 LMH and salt rejection rate of 83%, and this performance was maintained without loss of flux or rejection rate in a durability test carried out for 10 days.

The surfaces of the reverse osmosis (RO) membranes prepared by an interfacial polymerization method on the polysulfone supports in our lab were modified by the adsorption of the three hydrophilic polymers, poly(vinyl sulfonic acid) (PVSA), poly(ethylenimine) (PEI) and poly(vinyl alcohol) (PVA). Using the ‘salting-out effect’, these polymers, representative of anionic, cationic and neutral polymers, respectively, were used to investigate which adsorbed polymer is the most resistant to chlorine attack. The surface properties of the adsorbed RO membranes were characterized to confirm the adsorption by using contact angle measurement and scanning electron microscopy (SEM). The performance of chlorine-resistance RO membranes was measured through their evolution, before and after hypochlorite exposures in 3,450 ppm NaOCl solution for desired time points. This was determined in terms of pure water permeability and salt rejection. In order to determine the most dominant factor contributing to chlorine resistance, experiments were carried out under several conditions. The candidate factors included coating time, concentration of coating solution, ionic strength, and salt types. In general, as the coating time and concentration increased, the chlorine resistance increased for any salt used. Among the three materials, PVSA showed the greatest chlorine resistance of ca. 62,000 ppm·h, under the determined conditions, ionic strength (IS)=0.2 Mg and coating time of 60 s. The order of chlorine stabilities for the coating materials was determined to be PVSA, PEI, and PVA. It was found that the chlorine resistance of any polymer-coated membrane is superior to the pristine RO membrane.

In this study, polyvinylamine (PVAm), poly(vinyl sulfonic acid) (PVSA), and poly(styrene sulfonic acid) (PSSA) were physically adsorbed, using the ‘salting-out’ effect, onto hydrophobic membrane surfaces such as polysulfone (PSf), polyvinylidene fluoride (PVDF), and polyethylene (PE), commonly used as ultrafiltration (UF) and microfiltration (MF) membranes. The physical adsorption of such hydrophilic polymers were monitored as a function of concentration, time, type of salt, and ionic strength, and the resulting adsorbed membranes were characterized using a contact angle measurement, a gravimetric analysis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In most cases, with increasing the adsorption time, the wettability of surface-modified membranes was significantly improved. Physical adsorption of hydrophilic polymers on hydrophobic membrane surfaces, facilitated by the salt-out effect, was almost achieved within a few minutes. Typically, a contact angle of 47° was observed at ionic strength (IS)=0.1Mg(NO3)2·6H2O and PVAm 2,000 ppm for a PSf membrane. The weight changes by adsorption were varied with adsorption time in the cases of PVSA and PSSA, while the weight change for PVAm approached the equilibrium rapidly after the initial adsorption time. Open image in new window