Pervaporation separation of acetic acid-water mixtures using modified membranes. I. Blended polyacrylic acid (PAA)-nylon 6 membranes

Membranes consisting of ionically crosslinked polyacrylic acid (PAA) and Nylon 6 were prepared and tested for the pervaporation separation of acetic acid-water mixtures. The polyacrylic acid (PAA) membranes were crosslinked in aluminum nitrate aqueous solution while the polyacrylic acid (PAA)-Nylon 6 blends were cast from homogeneous PAA-Nylon 6 mixtures to appropriate thicknesses and then crosslinked in aqueous aluminum nitrate solutions. Optimum pervaporation results were obtained from blends of Nylon 6 and PAA in the weight ratio of 60–75 wt% Nylon 6 and 25–40 wt% PAA which have separation factors (water/acetic acid) of over 60 and flux rates higher than 100 g/m² h at 15°C for the separation of acetic acid-water mixtures. The flux rates and separation factors could be altered by changing the blend composition of the membrane. The effects of the feed composition on the separation factors were investigated.     

Actions of wetting agents on coal dust

The rate of wetting of coal dust by aqueous solutions of surface active agents (surfactants) has been studied. It has been shown that surfactant is adsorbed onto the coal surface during the wetting process. Rates of wetting by solutions of the widely used sodium salt of di(2-ethylhexyl)sulphosuccinic acid (Aerosol OT) are strongly influenced by low concentrations (1–2 mg/l) of dipositive metal ions. After wetting, electron spectroscopy for chemical analysis (ESCA) has been used to show the presence of these metal ions and the surfactant on the surface of the particles of coal dust.     

聚丙烯酸复合铝改性膨润土制备及其对Cr(VI)的吸附

为改善膨润土对Cr(VI)的吸附性能,用铝、丙烯酸聚合及十六烷基三甲基溴化铵改性合成聚丙烯酸复合铝改性膨润土。采用X射线衍射、红外光谱和扫描电子显微镜对天然膨润土和改性膨润土进行表征。结果表明,在25℃、溶液pH=5~6时,0.5 g吸附剂对200 mL浓度为20 mg/L Cr(VI)的平衡吸附量为1.996 mg/g,平衡吸附时间为130 min,且固液分离容易。吸附过程较好地符合Lagergren二级吸附动力学方程和Freundlich等温吸附方程,颗粒状吸附剂对Cr(VI)的吸附以络合吸附为主。     

Application of Fourier transform infrared spectroscopy to study the interactions of poly(acrylic acid) and mixtures of poly(acrylic acid) and polyacrylamide with bone powders and hydroxyapatites

Fourier transform infrared (FTIR) spectroscopy was used to study the interactions of aqueous solutions of poly(acrylic acid) (PAA) and mixtures of aqueous solutions of PAA and polyacrylamide (PAAm) with chemically and thermally treated bone powders (BPs) and two commercial hydroxyapatites (HAs). An analysis of the spectra of the precipitates that resulted from the mixtures of PAA and the chemically treated samples of BP revealed that the spectra exhibited three new bands at 1544, 1552, and 1661 cm^?1. The first band was attributed to the formation of calcium–polycarboxylate resulting from the interaction between the carboxylic acid groups of PAA and the calcium ions of BP. The appearance of the other two bands, in addition to the disappearance of the band corresponding to the absorption of the acid groups of PAA, provided strong evidence for the existence of other interactions between the carboxylic acid groups and the amide groups of the organic matrix of BP. On the other hand, the FTIR spectra of the samples that resulted from the mixture of PAA and thermally treated BP and the two commercial HAs showed only a new absorption band at 1544 cm^?1. The interactions of mixtures of the aqueous solutions of PAA and PAAm, adjusted at low or high pH values, with the different BPs and HAs were examined. The mixtures of the aqueous solutions of PAA and PAAm interacted with the different BPs and two HAs, resulting in the formation of ternary PAA–BP–PAAm and PAA–HA–PAAm complexes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis of calcium carbonate–chitosan composites via biomimetic processing

The crystal growth of calcium carbonate on a chitosan substrate was achieved using a supersaturated calcium carbonate solution, at different concentrations of polyacrylic acid (PAA) as an additive. Several techniques have been employed to characterize the systems. The pH of the solution as the one of indices was used to monitor the crystallization. In the absence of polyacrylic acid, the pH of the solution changed from 6.00 to 8.50 during the crystallization; meanwhile, sporadic nucleation and crystallization was observed via optical microscopy. By introducing polyacrylic acid to the systems, positively charged protonated nitrogen and negatively charged carboxylate ions were produced by reaction between the amino group in chitosan and the carboxyl group in polyacrylic acid, which were detected by ATR-IR and XPS techniques. These charges induced calcium carbonate nucleation of calcite and vaterite crystals on the chitosan-film surface. The average size of the vaterite phase was about 15 nm, determined by XRD. The pH of the solution changed from 5.80 to 9.25 during the crystallization; moreover, the crystals showed spherical morphology, which consisted of a large number of small particles with a diameter of about 0.2 μm. © 1995 John Wiley & Sons, Inc.     

Improvement of the electrospinnability of Polyvinyl alcohol via dialysis and complexation pretreatment

The electrospinnability of polyvinyl alcohol (PVA) aqueous solutions for two samples (HS and FL) was carried out. FL solutions produced nanofibers in electrospinning process, whereas HS solutions showed poorer electrospinnability accompanying dropping and electro-spraying. The analysis of the spinning solution properties indicated that the electric conductivity and viscosity of both FL and HS solutions demonstrated similar behaviors, however, the surface tensions of FL solutions were slightly decreased while the surface tension presented U-shaped curves for HS solutions with the increase of polymer concentration. The NMR spetra and DSC results implied that HS had higher degree of saponification. The metal element analysis results meant that HS contained high concentrations of calcium and aluminum ions while FL much less. The dosage of calcium chloride into FL aqueous solutions indicated that electrospinnability was significantly aggravated. The electrospinnability of HS was substantially improved both by dialysis and complexation. It was the high degree of saponification and it was intramolecular crosslinking and intermolecular crosslinking occurred between PVA chain and the metal ions that coined the abnormal behaviors in surface tension and thus deteriorated electrospinnability.     

Effect of Organic Additives on Electrochemical Surface Precipitation and Polymorphism of CaCO3

The inhibition effect of three organic additives on the precipitation and polymorphism of CaCO₃ deposited on gold surfaces was investigated using electrochemical and microscopic techniques. Additives, two polyacrylic acid (PAA) polymers with different molecular weights (Mw 2100, Mw 30,000), and 1,2,4,5‐benzenetetracarboxylic acid (BTCA), were either added to the solution before or during deposition. In the presence of 100 ppm of one of the three additives in solution, almost no scale was observed on the surface for at least 24 hours. In the presence of lower concentrations of PAA Mw 2100, only distorted calcite crystals were obtained while with PAA Mw 30,000 the polymorph was spherical vaterite. A mixture of calcite and vaterite was observed with the BTCA additive. Addition of the polymers inhibits further nucleation and growth even if added after partial deposition of CaCO₃ while BTCA has no effect once nucleation has started. The results indicate that the inhibit ion effect of the PAA polymers is due to adsorption on the electrode surface while the effect of BTCA is related to chelation of calcium ions in solution.     

Factors affecting improvement in the flexural modulus of polyacrylic acid-modified crystalline films

When high-molecular weight polyacrylic acid (PAA) macromolecules are incorporated into phosphating solutions, they significantly increase the stiffness and ductility of zinc phosphate conversion crystal films deposited on metal substrate surfaces. The degree of improvement in these mechanical properties depends primarily on the thickness and fineness of the highly dense PAA-complexed zinc phosphate crystals that are formed. The presence of this complexed PAA polymer at the outermost surface sites on the crystal layer plays an essential role in promoting adhesion with polymeric topcoats by the formation of polymer—polymer chemical bonds. The use of low-molecular weight PAA results in a poor interfacial adhesion because of a high degree of alternation in chain conformation caused by charge-transfer reactions between the proton-donating COOH groups and the nucleophilic Zn²⁺ ions in the acidic aqueous medium. In addition, the protective polymer topcoat overlayed on the complex precoat surfaces increases the flexibility of the crystalline precoat itself. The most important factors controlling the flexibility of the precoat were low elastic modulus, high tensile strength, and elongation of the topcoat systems. These characteristics are more important than the magnitude of interfacial adhesive bonds at topcoat/precoat joints.     

Synthesis and characterization of salep sulfate and its utilization in preparation of heavy metal ion adsorbent

A multicomponent polysaccharide obtained from dried tubers of certain natural terrestrial orchids was chemically modified by sulfonation using chlorosulfonic acid–dimethylformamide (HClSO_3–DMF) complex as a reagent. For a structural characterization of salep sulfate ¹H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectra, and Thermogravimetric analysis (TGA) curves were recorded. The sulfate content of modified salep was determined using elemental analysis. This modified biopolymer was used to prepare a new environment‐friendly heavy metal ion adsorbent, salep sulfate‐graft‐polyacrylic acid hydrogel (SS‐g‐PAA). Swelling rate and equilibrium water absorbency in various pH and saline solutions were investigated to study the effect of salep sulfate on swelling behavior of the hydrogel. In addition, the effect of sulfate content on heavy metal ion adsorption from aqueous solution was investigated. The results show that SS‐g‐PAA can effectively remove heavy metal ions (Co²⁺, Zn²⁺, Cu²⁺) from aqueous solution and swelling behavior of the hydrogels highly dependent on the amount of sulfate group on corresponding modified polysaccharide. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3001–3008, 2013     

金属离子掺杂硅胶吸附剂的性能与结构表征

以陶瓷纤维纸为基材,钴盐、铝盐或钛盐为改性剂,顺次经水玻璃、酸性盐溶液浸渍共沉积制得金属离子掺杂硅胶吸附剂。采用扫描电镜、多孔介质空隙分析仪、光电子能谱仪表征改性吸附剂组成、表面形貌、孔径大小及分布;用程序升温脱附谱,热失重分析仪等检测材料的脱附性能及热稳定性。结果表明:金属离子掺杂硅胶均匀分布在陶瓷纤维纸表面及其空隙中;经掺杂后的硅胶,其吸附性能、Brunauer-Emmett-Teller(BET)比表面积、孔容、平均孔径明显增加。改性硅胶的BET表面积、饱和吸附量及热稳定性按照铝掺杂硅胶、钛掺杂硅胶、钴掺杂硅胶及硅胶的顺序递减。     

Pervaporation separation of ethanol–water mixtures using ionically crosslinked blended polyacrylic acid (PAA)–nylon 6 membranes

The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m² h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.     

Transient Analysis of Mass-Transfer Rate in Recovering Metal Ions Using a Microporous Hollow Fiber Membrane and a Water-Soluble Chelating Polymer

ABSTRACT

Microporous hollow fiber membranes were used with a water-soluble chelating) polymer (polyacrylic acid) to recover and concentrate metal ions [copper(H)] from a solution. The polymer (chelator) solution was pumped through the bore of the fibers which was immersed in the metal ions solution. In this process the metal ions diffuse through the fiber porous space into the bore side and react with the chelator passing in the bore of the fiber. The transient change in concentration of metal ions at the outlet of the fiber were measured. The experimental data were well fitted by a one-dimensional convection equation which was derived with relatively simple assumptions and a steady-state theory, and reasonable values for the dispersion coefficient and an overall mass transfer coefficient were obtained.     

Polarographic studies of cadmium(II) ions binding in aqueous polyelectrolyte solutions

Polarographic behaviour of cadmium(II) ions in aqueous solutions of polyacrylic acid with and without indifferent electrolyte (potassium chloride) has been examined. Data for polyacrylic acid were compared with those for the monomer. The diffusion current of polarographic reduction of cadmium(II) ions in the range 0 ? [KCl] < 0.2 N in the presence of polyelectrolytes depends upon the concentration and degree of polymer neutralization and also upon the nature of cation (Na⁺, K⁺) in the polyacrylate salt.     

Binary and ternary polymer–strontium complexes and the capture of radioactive strontium‐90 from the polluted soil of the Semipalatinsk Nuclear Test Site

The interaction of poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG) with strontium ions and the binding of strontium ions by equimolar interpolymer complexes (IPCs) of PAA and PEG were studied. The stability constants of binary polymer–metal complexes were determined. Aqueous solutions of IPCs of PAA and PEG were applied as soil structuring agents in model and real experiments. The ability of IPCs to capture radioactive strontium ions from the polluted soil of the Semipalatinsk Nuclear Test Site was established. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 759–764, 2003     

Formation of a glass-ionomer cement based on an lon-leachable glass and polyacrylic acid

The chemistry of the cement-forming reaction between a fluorine-containing calcium aluminosilicate glass and aqueous solutions of poly(acrylic acid) has been studied using infrared spectroscopy and classical chemical procedures. It was concluded that calcium, aluminium and fluoride ions were leached from the glass leaving a relict of silica gel. These ions migrated into the polyelectrolyte phase where the cations cross-linked polyanionic chains causing the system to gel. Initial set, which takes place within 10 minutes, was attributed to the formation of the calcium salt, the aluminium salt forming later and contributing to the hardening of the cement. Reactions continued for at least 48 h. The role of ion-binding in the reaction is discussed.     

聚丙烯酸改性凹土对Pb2+、Ni2+和Cr3+的选择性吸附

通过凹土的表面功能化开发高性能低成本的吸附材料,采用溶液聚合法在其表面接枝聚丙烯酸,制备出聚丙烯酸/凹土吸附材料(PAA/ATP),系统考察了PAA/ATP对Pb²⁺、Ni²⁺和Cr³⁺三元混合体系的吸附性能。结果表明:PAA/ATP复合吸附材料的有机物接枝率为14.1%,其结构中出现聚丙烯酸的特征官能团;PAA/ATP吸附Pb²⁺的动力学符合拟二级动力学,即化学吸附是速率控制步骤,说明PAA/ATP对Pb²⁺的吸附是一个有化学作用的过程,吸附过程与Pb²⁺和吸附剂PAA/ATP表面官能团之间的电子转移或电子共用有关;PAA/ATP对Pb²⁺的吸附符合Langmuir吸附等温模型;PAA/ATP对Pb²⁺、Ni²⁺和Cr³⁺的竞争吸附能力依次为Pb²⁺ > Cr³⁺ > Ni²⁺,即对Pb²⁺具有较好的选择性吸附。     

Chemical investigations on the leaching of sulphur from sulphur infiltrated concretes

Sulphur-infiltrated concretes have been treated with aqueous solutions of acid, base and salt. From the ESCA decomposition products were identified and using ultraviolet spectroscopy it was possible to identify thionates and polysulphides as intermediates. Thiosulphates were also found in the leachate but the final product was a mixture of calcium sulphate, sulphite and elemental sulphur. Decomposition in salt solutions is significantly slower than in water.     

Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)

Ultra-fine polyelectrolyte fibers have been generated from electrospinning of poly(acrylic acid) in aqueous and DMF solutions. The fiber diameters ranged from 80 to 500 nm and increased with increasing solution concentrations and electrospinning voltages. The fibers generated from the aqueous solutions were more homogeneous in sizes, especially when NaCl or NaOH was added. Higher voltages in electrospinning of the aqueous solutions also resulted in fibers with larger heat capacity in the glass transition region, and higher dehydration temperatures. These polyelectrolyte fibers could be rendered water-insoluble by incorporating β-cyclodextrin (at 20 wt% of PAA) in the aqueous solution, then heat-induced crosslinking was performed at 140 °C for 20 min. The resulting hydrogel fibers showed strongly pH-responsive swelling behaviors.     

Electrochemical behaviour of polyacrylic acid coated gold electrodes: An application to remove heavy metal ions from wastewater

An efficient and low cost preparation method (Diazonium-Induced Anchoring Process) to graft polyacrylic acid (PAA) on the gold substrate has been reported. IR, XPS and AFM techniques were used to characterize the obtained polymer film. The interfacial electrochemistry of the PAA coated gold electrodes was studied by means of impedance spectroscopy and cyclic voltammetry transition techniques. The ability of PAA-grafted onto a gold electrode to reversibly bind or release metal ions was confirmed. As a broad-range chelating material, PAA is able to capture several heavy metal ions at low concentration. The release of those metal ions from the grafted PAA film was obtained under electro-induced-acidification by applying an anodic potential at the electrode to promote a localized water electrolysis. Application of electrochemical-pH-switchable PAA films can be considered within the field of heavy metal waste treatments.     

Chelation and Foam Separation of Metal Ions from Solutions

Abstract

An experimental study was conducted on the chelation and foam separation of trace amounts of cadmium, zinc, and lead from their water solutions. The chelation agents ethylenediaminetetraacetate (sodium salt), sodium diethyl-dithiocarbamate, and citric acid were used with sodium dodecylsulfate (SDS) as a foam-producing agent. The chelation agents did not produce metal complexes that were very surface active. The foam-producing agent produced metal ion complexes that were surface active and resulted in appreciable separation of the metal ions. The use of 100 ppm SDS resulted in separation of 90% of the zinc ions from solution containing 2 to 20 ppm zinc. At concentrations below and above this, the removal efficiency dropped significantly