Dialysis Coefficient Research Articles

Imidazolium functionalized anion exchange membrane blended with PVA for acid recovery via diffusion dialysis process

Anion exchange silica precursor (AESP) was prepared by alkylation of 3-chloropropyltriethoxysilane (CPTS) to 1-methyl imidazole and then the corresponding anion exchange membranes were obtained through sol–gel process of AESP with polyvinyl alcohol (PVA) in the presence of tetraethoxysilane (TEOS). The obtained anion-exchange membranes showed water uptakes (WU) in the range of 44.11–118.86% and ion-exchange capacities (IEC) of 1.34–1.86mmol/g. The presence of alkoxy-silane groups influenced the membrane properties as they exhibited moderate thermal stability and excellent mechanical properties. When applied for acid recovery through diffusion dialysis process, the membranes exhibited excellent acid flux. The H+ dialysis coefficients (UH) are in the range of 1.87–4.83×10−2m/h greater than commercial membrane DF-120 (9×10−3m/h). The obtained separation factors (S) 12.72–52.5 are also greater than that of commercial membrane DF-120 (18.5). Hence, the results of this study suggest that the imidazolium functionalized AEMs can be potentially applied in diffusion dialysis process for acid recovery.

Preparation of diffusion dialysis membrane for acid recovery via a phase-inversion method

Herein, the preparation of anion exchange membrane (AEM) from brominated poly(2,6-dimethyl 1,6-phenylene oxide) BPPO and dimethylaniline (DMA) by phase-inversion process is reported. Anion exchange membranes (AEMs) are prepared by varying the DMA contents. Prepared AEMs show high thermal stability, water uptake (WR) around 202% to 226%, dimensional change ratios of 1.5% to 2.6% and ion exchange capacities (IECs) of 0.34 mmol/g to 0.82 mmol/g with contact angle of 59.18° to 65.15°. These membranes are porous in nature as confirmed by SEM observation. The porous property of membranes are important as it could reduce the resistance of transportation of ions across the membranes. They have been used in diffusion dialysis (DD) process for recovery of hydrochloric acid (HCl) from the mixture of HCl and ferrous chloride (FeCl2). Presence of ¯N+(CH3)2C6H5Br &$175;as a functional group in membrane matrix facilitates its applications in DD process. The dialysis coefficients of hydrochloric acid (UH) of the membranes are in range of 0.0016 m/h to 0.14 m/h and the separation factors (S) are in range of 2.09 to 7.32 in the HCl/FeCl2 system at room temperature. The porous membrane structure and presence of amine functional group are responsible for the mechanism of diffusion dialysis (DD).

Diffusion dialysis membranes with semi-interpenetrating network for acid recovery

Semi-interpenetrating polymer networks (sIPN) based on anion exchange membranes (AEMs) for acid recovery process were fabricated by immobilizing polyvinyl chloride (PVC) in dimethylaminoethyl methacrylate (DMAM) and divinylbenzene (DVB) copolymer (P(DMAM-co-DVB)). Prepared membranes were fully characterized in terms of FTIR, TGA, ion exchange capacity (IEC), water uptake (WR), etc. Membrane structure and performance can be tuned by varying the content of PVC and dosage of cross-linking agent as well. Consequence of PVC content plus the cross-linking degree on ion permeability and selectivity was discussed in brief. Results revealed that the prepared membranes possess excellent thermal and acid stability due to the incorporation of chemically stable PVC matrix and the formation of sIPN morphology. Acid dialysis coefficients (UH) appeared in the range of 0.012–0.040m/h and separation factors (S) ranged from 36 to 61 at 25°C. These obtained values are much higher than that of commercial membrane DF-120 (0.009m/h for UH, 18.5 for S). This methodology can be effortlessly scaled up and the obtained membranes could be an encouraging candidate for the acid recovery process via diffusion dialysis.

Novel Pendant Benzene Disulfonic Acid Blended SPPO Membranes for Alkali Recovery: Fabrication and Properties.

To reconcile the trade-off between separation performance and availability of desired material for cation exchange membranes (CEMs), we designed and successfully prepared a novel sulfonated aromatic backbone-based cation exchange precursor named sodium 4,4'-(((((3,3'-disulfo-[1,1'-biphenyl]-4,4'-diyl)bis(oxy)) bis(4,1-phenylene))bis(azanediyl))bis(methylene))bis(benzene-1,3-disulfonate) [DSBPB] from 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3,3'-disulfonic acid [BAPBDS] by a three-step procedure that included sulfonation, Michael condensation followed by reduction. Prepared DSBPB was used to blend with sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) to get CEMs for alkali recovery via diffusion dialysis. Physiochemical properties and electrochemical performance of prepared membranes can be tuned by varying the dosage of DSBPB. All the thermo-mechanical properties like DMA and TGA were investigated along with water uptake (WR), ion exchange capacity (IEC), dimensional stability, etc. The effect of DSBPB was discussed in brief in connection with alkali recovery and ion conducting channels. The SPPO/DSBPB membranes possess both high water uptake as well as ion exchange capacity with high thermo-mechanical stability. At 25 °C the dialysis coefficients (UOH) appeared to be in the range of 0.0048-0.00814 m/h, whereas the separation factor (S) ranged from 12.61 to 36.88 when the membranes were tested for base recovery in Na2WO4/NaOH waste solution. Prepared membranes showed much improved DD performances compared to traditional SPPO membrane and possess the potentiality to be a promising candidate for alkali recovery via diffusion dialysis.

Novel quaternized aromatic amine based hybrid PVA membranes for acid recovery

For the first time this study reports novel quaternized aromatic amine based anion exchange membranes (AEMs) with polyvinyl alcohol (PVA) acting as a binder and tetraethoxysilane (TEOS) as a crosslinker for acid recovery via diffusion dialysis. Physiochemical properties and electrochemical performance of prepared membranes can be tuned by varying the dosage of quaternized 4,4′-(1,1′-biphenyl-4,4′-diyldioxy)dianiline (QBAPB). All the thermo-mechanical properties like dynamic mechanical analysis (DMA) and thermo-gravimetric analysis (TGA) were investigated along with water uptake (WR), ion exchange capacity (IEC), dimensional stability etc. The effect of quaternary ammonium group and crosslinking agent (TEOS) was discussed in brief related to acid recovery and ion conducting pathway. The QBAPB/PVA membranes showed the water uptake (WR) values ranging between 23.7% and 37.9%, ion exchange capacity (IEC) between 0.65 and 1.12mmol/g, initial decomposition temperatures (IDTs) of 222–241°C, tensile strength of 16.6–18.3MPa and elongation at break of 332–403%. The dialysis coefficients (UH) for different nanocomposite membranes are found to be in the order of 0.0172–0.0252m/h, while the separation factors (S) varied from 14 to 21 at 25°C. The obtained values are much higher than that of commercial membrane DF-120B (0.004m/h for UH, 24.3 for S). The membranes reported in this manuscript could be a promising candidate for acid recovery via diffusion dialysis.

PVA–PSSS membranes for alkali recovery through diffusion dialysis: effect of alkoxysilanes

Poly(sodium-p-styrene-sulfonate) (PSSS) is synthesized by the method of ARGET ATRP, then mixed with polyvinyl alcohol (PVA), and cross-linked with different alkoxysilanes, that is, tetraethoxysilane (TEOS), 3-aminopropyltriethoxysilane (APTS), or γ-glycidoxypropyltrimethoxysilane (GPTS). The obtained flexible cation-exchange membranes have water uptakes (WR) of 46.8–120.7% and ion-exchange capacities (IEC) of 1.03–1.64 mmol/g. The category of the alkoxysilanes strongly influences the membrane properties. The membrane from GPTS has the highest thermal stability with Td (temperature at 5% weight loss) of 267.4°C, the highest IEC, and the lowest swelling degree in 65°C water, which is due to the dual cross-linking of Si–O–Si and C–O–C between GPTS and PVA. When applied for diffusion dialysis (DD) process of NaOH/Na2WO4 mixture, the membranes exhibit excellent alkali flux. The OH− dialysis coefficients (UOH) are in the range of 0.0072–0.0208 m/h, higher than PVA blank membrane (0.0077 m/h) or commercial poly(2,6-dimethyl-1,4-phenylene oxide)-based membrane (0.004 m/h) (Tianwei Membrane Co., Ltd., Shandong of China). The separation factors (S) are in the range of 16.8–25.7, higher than PVA–PSSS membrane cross-linked with formaldehyde (S = 8.0). Hence, the membranes can be potentially applied in DD process for alkali recovery.

Diffusion dialysis for separating acidic HCl/glyphosate liquor

Acidic HCl/glyphosate liquor is produced largely during the production of glyphosate herbicide, which contains 2.5–3.0molL−1HCl, 1.1–1.5molL−1 glyphosate and 34–35wt% other organic components. The acidic liquor is traditionally neutralized to pH 1.5 by alkali (NaOH) for the maximum crystallinity of glyphosate. Here the acidic liquor is separated by commercial anion exchange membrane 9010 through batch diffusion dialysis (DD). The DD process shows the advantages including recovery of HCl, crystallization of glyphosate, and low dosage or avoidance of alkali. The DD performances are evaluated by acid concentration, dialysis coefficients of HCl (UH) and separation factor (S) with respect to the time.DD running 12h shows that the acid concentration decreases from 3.57 to 2.60molL−1 for the acidic liquor, and the UH values are in the range of 0.0048–0.0062mh−1. The relatively low UH values are attributed to the existence of other organic components in the acidic liquor. DD running 24h shows that most of HCl can be recovered, the concentration of recovered acid is in the range of 0.29–0.78molL−1, and the separation factors are in the range of 53–66. Moreover, 53.2% glyphosate can be recovered and thus 62% NaOH can be saved. DD running 36h shows reduced performance due to the decreasing acid concentration and the water osmosis. Hence, DD performances can be optimized to separate the acidic liquor for producing glyphosate.

The effects of multi-functional groups from PVA and ternary multisilicon copolymer on diffusion dialysis

Ternary multisilicon copolymers are prepared from copolymerization of acrylic acid, sodium styrene sulfonate and γ-methacryloxypropyl trimethoxy silane, from which functional groups of –Si(OCH3)3, –COOH and –SO3Na are obtained respectively. The acidic –COOH groups may induce gel during copolymerization, and thus sufficient solvent needs to be used. The –Si(OCH3)3 groups can crosslink with polyvinyl alcohol (PVA) to yield cation exchange hybrid membranes.The membranes have the ion exchange capacity of 1.01–2.26mmol/g, water uptake of 39.1–59.7%, swelling degrees of 108–339% in 65°C water after 192h, and swelling degrees of 254–344% in 65°C alkaline solution after 60h. Membrane with proper ratios of multi-functional groups can sorb 1.4mol/L NaOH in 1.0mol/L NaOH solution. The membranes are used in diffusion dialysis (DD) process for alkali recovery from NaOH/Na2WO4 solution. The dialysis coefficients of NaOH (UOH) are in the range of 0.013–0.021m/h at room temperature, with the separation factors of 15–23. The high UOH values indicate the superiority of multi-functional groups. The –OH, –COOH and –SO3Na groups from PVA and multisilicon copolymer chains may have coupling effects on the transport of both Na+ and OH− ions.

Facile and cost effective PVA based hybrid membrane fabrication for acid recovery

A new route for a hybrid anion exchange membrane was proposed for diffusion dialysis (DD) using polyvinyl alcohol (PVA) and glycidyl trimethyl ammonium chloride (EPTAC) as starting materials and aminopropyltriethoxysilane (KH550) as crosslinking agent. A series of membranes were prepared by varying the content of EPTAC. The obtained membranes were characterized with ion exchange capacity (IEC), water uptake (WR), linear expansion ratio (LER), tensile strength (TS), elongation at break (Eb), thermal decomposition temperature (Td) and initial decomposition temperature (IDT), etc. Their diffusion dialysis (DD) performance was conducted with a simulated feed containing 0.81M HCl+0.18M FeCl2. The results show that the membranes not only have good chemical/thermal stability, but possess high DD performance. The dialysis coefficients (UH) are in the range of 0.011–0.018m/h and the separation factors (S) are in the range of 18.5–21 at 25°C, both are higher than those of the commercial DF-120 membrane (0.009m/h for UH, 18.5 for S) determined at the same conditions. Considering its low cost and easy fabrication, the route for hybrid anion exchange membranes provides better candidates in DD process for acid recovery.

Separation of NaOH and NaAl(OH)4 in alumina alkaline solution through diffusion dialysis and electrodialysis

Alkaline solution containing NaOH and NaAl(OH)4 is produced largely during extracting aluminum from aluminum ore. Conventionally alkali and alumina-bearing components in the solution are separated by purification, filtration and precipitation, so that gibbsite precipitation is obtained and the alkaline liquor can be returned to the circuit. The feasibility of membrane separation, including diffusion dialysis (DD) and electrodialysis (ED), is investigated by batch DD and ED running with total 6.15×10–4m2 and 2.865×10–3m2 membranes, respectively. The DD running shows that the dialysis coefficient of OH− (UOH−) is at a low level (0.0028–0.0031m/h), mainly because of the hydrophobic nature of the membrane matrix and absence of a pressure difference or an electrical field as the driving force. The OH− recovery ratio is 6.3%, the Al(OH)4− leakage ratio is 0.6%, and the caustic ratio (αk) can reach up to 17.8 after 4h. As for ED running, the OH− recovery ratio is substantially enhanced, while the Al(OH)4− leakage and αk value can still meet the industrial requirements. The OH− recovery ratio, Al(OH)4− leakage ratio and αk are 48.0%, 12.6% and 7.9, respectively, when OH− concentration is ~1.55mol/L in the feed chamber, and the ED current density is 350.0mA/cm2. The current efficiency is 62.5% and the energy consumption is 12.43kWh/kg, relatively high because of use of a 0.01m plexiglas spacer between two neighboring membranes, the increase of the solution temperature which is caused by the high current density. Overall, the ED process is a more effective approach to treat the alumina alkaline solution. Much higher alkali concentration and recovery ratio can be achieved in a short time because of the higher permeability, leading to higher treatment capacity for ED device. The DD process, on the other hand, has advantages of low energy consumption, low membrane fouling and environmental friendliness.

Preparation of cation-exchange hybrid membranes with multi-functional groups and their performance on alkali recovery

Cation-exchange hybrid membranes have been prepared via the blending of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) with poly(vinyl alcohol) (PVA), which is cross-linked with multisilicon copolymer of poly(acrylic acid-co-γ-methacryloxypropyl trimethoxy silane) (poly(AA-co-γ-MPS)). The SPPO phase, PVA phase, and multisilicon copolymer can provide the membranes with functional groups of –SO3Na, –OH and –COOH, respectively. Hence, multi-functional groups are formed within the hybrid membranes. The hybrid membranes have a short-term thermal stability of 234–260°C, tensile strength (TS) of 12–13 MPa, and elongation at break of 27–49%. Membrane stability in alkaline solution is much affected by the content of SPPO. The membranes are potentially applied in diffusion dialysis (DD) for alkali recovery (NaOH/Na2WO4). The dialysis coefficients of NaOH (UOH) are in the range of 0.0075–0.032 m/h, which are higher than those of commercial membranes and reported membranes. The separation factor can reach up to 21.2 at 25°C for the membrane containing 10 wt% SPPO. Meanwhile, the membrane shows relative stability during long-term DD process. Hence, the multi-functional groups are effective for the diffusion dialysis process.

Anion exchange membranes used in diffusion dialysis for acid recovery from erosive and organic solutions

Diffusion dialysis (DD) is a process that the solutes pass through the ion exchange membrane from the feed side to water side. Some solutes such as HCl–FeCl2 may be erosive on membrane structure during practical DD process. The erosion effects are investigated by four anion exchange membranes, including commercial membranes DF-120 and 9010, and our previous membranes based on quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) and polyvinyl alcohol (PVA). Besides, the membranes are also used to separate organic solution containing HCl and glyphosate, which is produced largely during the preparation of glyphosate pesticide.The membrane structures are damaged and their performances are reduced after the erosion of HCl–FeCl2, which are mainly attributed to the loss of –N+(CH3)3Br− and –OH groups. The weight loss percent is in the range of 10–21%, the ion exchange capacity decreases but the swelling degree increases. The dialysis coefficient of HCl (UH-1) and separation factor (S1) reduce to 0.006–0.010mh−1 and 13.9–15.5 for commercial membranes, and 0.016–0.024mh−1 and 33.2–47.6 for QPPO/PVA membranes, correspondingly. Besides, the membranes without erosion are used to separate organic solution containing HCl and glyphosate. The UH-2 is in the range of 0.0040–0.0062mh−1 for commercial membranes, and 0.0094–0.0104mh−1 for QPPO/PVA membranes. The UH-2 values are generally stable within 10h, and the acid concentration in the feed side decreases from 5.82 to 3.16molL−1. Hence, the QPPO/PVA membranes can be potentially applied in DD process to recover acid from organic solution containing HCl and glyphosate.

A preliminary study on electrically assisted diffusion dialysis

Additional weak-electric field is adopted to improve the performance of diffusion dialysis (DD) process for the first time. Anion exchange membrane DD was taken as an example, and Na2SO4+H2SO4 waste solution was selected as a model system. Firstly, mode of applying electric field was discussed, and results showed the mode that anode contacted with dialysate compartment was more effective, and results were explained through Nernst-Plank equation. Secondly, effect of electric field on odd pieces of membranes DD was studied, results illustrated that the more the pieces of membranes, the weaker the effect of electric field on DD performance. Thirdly, effect of electric field on even pieces of membranes DD was investigated, results revealed that overall dialysis coefficient has almost nothing to do with electric field. At last, energy consumption and current efficiency were investigated, and differences between electrically assisted diffusion dialysis (EADD) and electro-electrodialysis (EED) were stated.

Facile surface modification of anion-exchange membranes for improvement of diffusion dialysis performance

In this study, a facile membrane modification method by spin-coating of pyrrole (Py) monomers dissolved in a volatile solvent followed by an interfacial polymerization is proposed. The surface of a commercial anion-exchange membrane (i.e., Neosepta-AFX, Astom Corp., Japan) was successfully modified with polypyrrole (Ppy) to improve the acid recovery performance in diffusion dialysis (DD). The result of DD experiments revealed that both the acid and metal ion transports are significantly influenced by the surface modification. The metal crossover through the membranes was largely reduced while mostly maintaining the acid permeability by introducing a thin Ppy layer with excellent repelling property to cations on the membrane surface. As a result, the anion-exchange membrane modified with the optimum content of Py monomer (5vol.%) exhibited excellent acid dialysis coefficient (KAcid) and selectivity (KAcid/KMetal) which is approximately twice as high as that of the pristine membrane.

Diffusion dialysis membranes with semi-interpenetrating network for alkali recovery

Cation exchange membranes based on semi-interpenetrating network (sIPN) are prepared for diffusion dialysis (DD) using poly(vinylidene difluoride) (PVDF) and sodium p-styrenesulfonate (SSS) as starting materials. Five membranes have been prepared by varying the content of PVDF and dosage of cross-linking agent. Ion exchange capacity (IEC), water uptake (WR), swelling resistance and mechanical property of the membranes have been measured. These membranes show excellent thermal and alkali stability due to the high-performance PVDF matrix and sIPN morphology. The membranes have been successfully applied to alkali recovery. The base dialysis coefficients (UOH) are in the range of 0.0008–0.0061m/h and the separation factors (S) in the range of 12.0–90.3 at 25–65°C. Effect of PVDF content and cross-linking degree on ion permeability and selectivity has been discussed.

Porous BPPO-based membranes modified by multisilicon copolymer for application in diffusion dialysis

Brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)-based hybrid membranes are produced from phase inversion, partial hydrolysis, modification with multisilicon copolymer of poly(MA-co-γ-MPS) and quaternization processes. The membranes have a porous structure, as revealed by SEM observation and water flux measurement. The modification by poly(MA-co-γ-MPS) introduces 3Si3O3Si network in the BPPO matrix, and hence the membrane swelling resistance in 65°C water is enhanced.The membranes are taken for diffusion dialysis (DD) process to recover HCl from HCl/FeCl2 solution. The dialysis coefficients of HCl (UH) are in the range of 0.020–0.025m/h at 25°C and the separation factor (S) can reach up to 45.5. The high permeability and selectivity are due to the unique membrane structure and the presence of different functional groups.

Non-charged PVA–SiO2 hybrid membranes for potential application in diffusion dialysis

Non-charged PVA–SiO2 hybrid membranes are prepared from the sol–gel reaction of polyvinyl alcohol (PVA) and methacryloxypropyl trimethoxy silane (γ-MPS) or poly(γ-MPS). As the polymerization degree increases from γ-MPS to poly(γ-MPS), the sol–gel solution becomes turbid or generates precipitation, while the formed silica particles in the hybrid membranes become smaller from 1.0–3.4μm to 0.1–0.2μm or disappear. The membrane tensile strength (TS) generally increases from 35MPa to 44MPa, while the elongation at break (Eb) decreases from 318% to 141%.Three deductions are proposed according to the structure of poly(γ-MPS), membrane swelling behaviors in 65–85°C water and 65°C alkaline solution, and the diffusion dialysis (DD) performance. (1) As poly(γ-MPS) contains no ion-exchange groups like the multisilicon copolymer [1], it tends to become inhomogeneous during sol–gel process, which reduces its crosslinking ability. (2) The membrane structure is generally stable in 65°C water with the swelling degrees of 140–347%, but is damaged in 85°C water or 65°C alkaline solution. (3) Non-charged hybrid membranes can be potentially applied in DD process. The dialysis coefficient of NaOH (UOH) is in the range of 0.0069–0.0127m/h, and the separation factor (S) is in the range of 19–92. The OH− ions may be transferred in the hybrid membranes through PVA-OH groups and interstices between organic and inorganic phases, according to the mechanisms of adsorption–desorption and free diffusion, correspondingly.

Polyelectrolyte complex/PVA membranes for diffusion dialysis

Polyelectrolyte complexes (PECs)/polyvinyl alcohol (PVA) membranes are prepared from PVA, anion exchange and cation exchange multisilicon copolymers, which contain plenty of functional groups of OH, N+(CH3)3/Si(OCH3)3, and SO3Na/Si(OCH3)3, respectively. The OH and Si(OCH3)3 groups can undertake sol–gel reaction to form crosslinking structure, while the N+(CH3)3 and SO3Na groups can be combined through electrostatic interaction.The PECs/PVA membranes exhibit improved thermal stability, swelling resistance and flexibility as compared with single anion or cation exchange hybrid membranes. The PECs/PVA membranes have the water uptakes (WR) of 25.3–70.4%, initial decomposition temperatures (IDTs) of 246–285°C, tensile strength of 23.1–33.8MPa, and elongation at break of 3.5–13.1%. The membranes can be potentially applied for both acid and alkali recovery through diffusion dialysis (DD) process. The separation factor (S) for HCl/FeCl2 mixture can reach up to 89.9, which is about five times higher than that of commercial DF-120 membrane (18.5 at 25°C). The dialysis coefficients of NaOH (UOH) are in the range of 0.014–0.019m/h, around 7–9 times higher than the value of commercial SPPO membrane (0.002m/h at 25°C). The membranes also show potential usefulness for industrial acidic and alkali wastes treatment.

Ureidoarene–heteropolysiloxane as alkali transport promoter within hybrid membranes for diffusion dialysis

Alkali transport promoter is designed from 3-(ureidoarene)propyltriethoxysilane (UPTS), which takes sol–gel process to form ureidoarene–heteropolysiloxane (UHPS) within polyvinyl alcohol (PVA). Hence PVA-based hybrid membranes are obtained for diffusion dialysis (DD) application. Besides, sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) is used as reference to compare the formation of alkali transport promoter within different polymer matrix.The micro-aggregation of UHPS within PVA leads to loose structure, while within SPPO leads to plenty of clusters within 0.1–0.5μm. The membrane swelling resistance is improved but the alkaline stability is reduced in the presence of UHPS. The PVA-based membranes have the tensile strength (TS) of 19–52MPa, and the elongation at break (Eb) of 343–534%. DD results show that the dialysis coefficients of OH− (UOH) are in the range of 0.01–0.022m/h in the presence of UHPS, which are about 2–5times higher than the blank PVA or SPPO membranes. The separation factors (S) are in the range of 26–32, which are also higher than the blank membranes. Hence, UHPS can act as alkali transport promoter for DD process. The effect of UHPS is affected by the membrane matrix and micro-aggregation degree.

A simple and green preparation of PVA-based cation exchange hybrid membranes for alkali recovery

Here, a novel and green route for preparing cation exchange hybrid membranes is presented via polyvinyl alcohol (PVA) and 3-trihydroxysilyl-1-propanesulfonic acid (THOPS), during which aqueous media instead of organic solvents is used and sulfonation process is avoided. The resulting hybrid membranes have the water uptake (WR) of 38–86%, ion exchange capacities (IECs) of 0.70–1.56mmol/g, initial decomposition temperature (IDT) of 224–231°C, tensile strength (TS) of 13.3–40.7MPa, and favorable elongation at break (Eb) of 177–571%. The linear expansion ratio (LER) is in the range of 15–25% in water, while in the range of 18–27% in 1.0M alkali solution. Diffusion dialysis (DD) of NaOH/Na2WO4 system shows that the dialysis coefficients of NaOH (UOH) are in the range of 0.011–0.022m/h, with the separation factors (S) of 11.6–20.6. Consequently, apart from endowing the resulting hybrid membranes with desirable DD performances, the method employed herein is simple and environment-friendly particularly due to the avoidance of organic solvents and hazardous sulfonation agents.