Research

277 KiB

Open AccessArticle

Experimental Investigation into the Transmembrane Electrical Potential of the Forward Osmosis Membrane Process in Electrolyte Solutions

by Lixia Bian, Yanyan Fang and Xiaolin Wang

Membranes 2014, 4(2), 275-286; https://doi.org/10.3390/membranes4020275 - 19 Jun 2014

Cited by 6 | Viewed by 6010

Abstract

The transmembrane electrical potential (TMEP) in a forward osmosis membrane process with a single electrolyte solution as the draw and feed solutions was investigated by experiments. The effects of membrane orientation, the electrolyte species (KCl, NaCl, MgCl₂, and CaCl₂), [...] Read more.

The transmembrane electrical potential (TMEP) in a forward osmosis membrane process with a single electrolyte solution as the draw and feed solutions was investigated by experiments. The effects of membrane orientation, the electrolyte species (KCl, NaCl, MgCl₂, and CaCl₂), concentration and concentration ratio of solutions at both sides of membrane on water flux and TMEP were investigated. The results showed that the TMEPs at different membrane orientation cannot completely coincide, which confirmed the effect of membrane asymmetry. The ion diffusion coefficients significantly affected the TMEP across the membrane, with different patterns for different electrolytes and concentrations. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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1863 KiB

Open AccessArticle

The Effect of Chain Structures on the Crystallization Behavior and Membrane Formation of Poly(Vinylidene Fluoride) Copolymers

by Wenzhong Ma, Haoge Yuan and Xiaolin Wang

Membranes 2014, 4(2), 243-256; https://doi.org/10.3390/membranes4020243 - 19 May 2014

Cited by 37 | Viewed by 9359

Abstract

The crystallization behaviors of two copolymers of PVDF were studied, and the effect of copolymerized chains on the crystallization behavior was investigated. The results indicated that both copolymers had a lowered crystallization temperature and crystallinity. The crystallization rate was improved by the copolymer [...] Read more.

The crystallization behaviors of two copolymers of PVDF were studied, and the effect of copolymerized chains on the crystallization behavior was investigated. The results indicated that both copolymers had a lowered crystallization temperature and crystallinity. The crystallization rate was improved by the copolymer with symmetrical units in PVDF chains, but hindered by asymmetrical units, compared with the neat PVDF. The symmetrical units in PVDF chains favored the β-crystals with fiber-like structures. According to the solubility parameter rule, methyl salicylate (MS) can be chosen as a diluent for PVDF copolymers. Both diluted systems had liquid-liquid (L-L) regions in the phase diagrams, which was due to the lowered crystallization temperature. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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516 KiB

Open AccessArticle

Effect of Cross-Linking on the Mechanical and Thermal Properties of Poly(amidoamine) Dendrimer/Poly(vinyl alcohol) Hybrid Membranes for CO₂ Separation

by Shuhong Duan, Teruhiko Kai, Takashi Saito, Kota Yamazaki and Kenichi Ikeda

Membranes 2014, 4(2), 200-209; https://doi.org/10.3390/membranes4020200 - 08 Apr 2014

Cited by 20 | Viewed by 7601

Abstract

Poly(amidoamine) (PAMAM) dendrimers were incorporated into cross-linked poly(vinyl alcohol) (PVA) matrix to improve carbon dioxide (CO₂) separation performance at elevated pressures. In our previous studies, PAMAM/PVA hybrid membranes showed high CO₂ separation properties from CO₂/H₂ mixed gases. [...] Read more.

Poly(amidoamine) (PAMAM) dendrimers were incorporated into cross-linked poly(vinyl alcohol) (PVA) matrix to improve carbon dioxide (CO₂) separation performance at elevated pressures. In our previous studies, PAMAM/PVA hybrid membranes showed high CO₂ separation properties from CO₂/H₂ mixed gases. In this study, three types of organic Ti metal compounds were selected as PVA cross-linkers that were used to prepare PAMAM/cross-linked PVA hybrid membranes. Characterization of the PAMAM/cross-linked PVA hybrid membranes was conducted using nanoindentation and thermogravimetric analyses. The effects of the cross-linker and CO₂ partial pressure in the feed gas on CO₂ separation performance were discussed. H₂O and CO₂ sorption of the PAMAM/PVA hybrid membranes were investigated to explain the obtained CO₂ separation efficiencies. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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3481 KiB

Open AccessArticle

Preparation of Sulfobetaine-Grafted PVDF Hollow Fiber Membranes with a Stably Anti-Protein-Fouling Performance

by Qian Li, Han-Han Lin and Xiao-Lin Wang

Membranes 2014, 4(2), 181-199; https://doi.org/10.3390/membranes4020181 - 08 Apr 2014

Cited by 15 | Viewed by 6799

Abstract

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as [...] Read more.

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDF membrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDF membranes was significantly enhanced and the polyMPDSAH-g-PVDF membrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDF membrane, the polyMPDSAH-g-PVDF membrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDF membrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDF membrane could be maintain without any chang; however, the polyMEDSA-g-PVDF membrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDF membrane for a stable anti-protein-fouling performance via the two-step polymerization method. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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817 KiB

Open AccessArticle

Solidification Behavior of Polymer Solution during Membrane Preparation by Thermally Induced Phase Separation

by Toru Ishigami, Yoko Nii, Yoshikage Ohmukai, Saeid Rajabzadeh and Hideto Matsuyama

Membranes 2014, 4(1), 113-122; https://doi.org/10.3390/membranes4010113 - 28 Feb 2014

Cited by 26 | Viewed by 7910

Abstract

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed [...] Read more.

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed on a stage, is moved upwards and the surface of the polymer solution contacts a sphere attached to the tip of a needle. The displacement of a blade spring attached to the needle is then measured by a laser displacement sensor. Different phase separation modes, such as liquid-liquid (L-L) phase separation and solid-liquid (S-L) phase separation (polymer crystallization) were investigated. In the case of S-L phase separation, the stiffness of the solution surface began to increase significantly just before termination of crystallization. In contrast, L-L phase separation delayed solidification of the solution. This was because mutual contact of the spherulites was obstructed by droplets of polymer-lean phase formed during L-L phase separation. Thus, the solidification rate was slower for the L-L phase separation system than for the S-L phase separation system. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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909 KiB

Open AccessArticle

Preparation of Polyvinylidene Fluoride (PVDF) Hollow Fiber Hemodialysis Membranes

by Qinglei Zhang, Xiaolong Lu and Lihua Zhao

Membranes 2014, 4(1), 81-95; https://doi.org/10.3390/membranes4010081 - 27 Feb 2014

Cited by 56 | Viewed by 11781

Abstract

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDF membrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was [...] Read more.

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDF membrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was found that membrane thickness and PEG content affected both the structure and performance of hollow fiber membranes. The tensile strength and rejection of bovine serum albumin (BSA) increased with increasing membrane thickness, while the Ultrafiltration flux (UF) flux of pure water was the opposite. The tensile strength, porosity and rejection of BSA increased with increasing PEG content within a certain range. Compared with commercial F60S membrane, the PVDF hollow fiber membrane showed higher mechanical and permeable performance. It was proven that PVDF material had better hydrophilicity and lower BSA adsorption, which was more suitable for hemodialysis. All the results indicate that PVDF hollow fiber membrane is promising as a hemodialysis membrane. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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728 KiB

Open AccessArticle

A Pervaporation Study of Ammonia Solutions Using Molecular Sieve Silica Membranes

by Xing Yang, Thomas Fraser, Darli Myat, Simon Smart, Jianhua Zhang, João C. Diniz da Costa, Audra Liubinas and Mikel Duke

Membranes 2014, 4(1), 40-54; https://doi.org/10.3390/membranes4010040 - 17 Feb 2014

Cited by 40 | Viewed by 9215

Abstract

An innovative concept is proposed to recover ammonia from industrial wastewater using a molecular sieve silica membrane in pervaporation (PV), benchmarked against vacuum membrane distillation (VMD). Cobalt and iron doped molecular sieve silica-based ceramic membranes were evaluated based on the ammonia concentration factor [...] Read more.

An innovative concept is proposed to recover ammonia from industrial wastewater using a molecular sieve silica membrane in pervaporation (PV), benchmarked against vacuum membrane distillation (VMD). Cobalt and iron doped molecular sieve silica-based ceramic membranes were evaluated based on the ammonia concentration factor downstream and long-term performance. A modified low-temperature membrane evaluation system was utilized, featuring the ability to capture and measure ammonia in the permeate. It was found that the silica membrane with confirmed molecular sieving features had higher water selectivity over ammonia. This was due to a size selectivity mechanism that favoured water, but blocked ammonia. However, a cobalt doped silica membrane previously treated with high temperature water solutions demonstrated extraordinary preference towards ammonia by achieving up to a 50,000 mg/L ammonia concentration (a reusable concentration level) measured in the permeate when fed with 800 mg/L of ammonia solution. This exceeded the concentration factor expected by the benchmark VMD process by four-fold, suspected to be due to the competitive adsorption of ammonia over water into the silica structure with pores now large enough to accommodate ammonia. However, this membrane showed a gradual decline in selectivity, suspected to be due to the degradation of the silica material/pore structure after several hours of operation. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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685 KiB

Open AccessArticle

Effect of Preparation Methods on Crystallization Behavior and Tensile Strength of Poly(vinylidene fluoride) Membranes

by Jie Liu, Xiaolong Lu and Chunrui Wu

Membranes 2013, 3(4), 389-405; https://doi.org/10.3390/membranes3040389 - 21 Nov 2013

Cited by 85 | Viewed by 8576

Abstract

Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDF membranes was investigated. Fourier transform infrared [...] Read more.

Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDF membranes was investigated. Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD) were employed to examine the crystal form of the surface layers and the overall membranes, respectively. Spherulite morphologies and thermal behavior of the membranes were studied by polarized light optical microscopy (PLO) and differential scanning calorimetry (DSC) separately. It was found that the crystallization behavior of PVDF membranes was closely related to the preparation methods. For membranes prepared by the NIPS method, the skin layers had a mixture of α and β phases, the overall membranes were predominantly α phase, and the total crystallinity was 60.0% with no spherulite. For melt spinning membranes, the surface layers also showed a mixture of α and β phases, the overall membranes were predominantly α phase. The total crystallinity was 48.7% with perfect spherulites. Whereas the crystallization behavior of solution-cast membranes was related to the evaporation temperature and the additive, when the evaporation temperature was 140 °C with a soluble additive in the dope solution, obvious spherulites appeared. The crystalline morphology of PVDF exerted a great influence on the tensile strength of the membranes, which was much higher with perfect spherulites. Full article

(This article belongs to the Special Issue Selected Papers from AMS8 Conference (July 2013, Xi’an, China))

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