Preparation of poly(vinyl alcohol)–silicone based hybrid membranes for the pervaporation separation of water–acetic acid mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle x-ray diffraction and differential scanning calorimetry. A remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen bonding and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as cross-linking agent. The membrane containing 1 : 2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10^?2kg/m²h at 30°C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values obtained, showing that water permeation is lower than that of acetic acid, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal because of the higher selective nature of membranes. The negative heat of sorption values (ΔH _s) for water in all the membranes suggests a Langmuir mode of sorption.     

Structural changes in Poly(lactic acid)–zeolite nanocomposites exposed to 60Co gamma rays

Poly(lactic acid) (PLA) nanocomposites containing 3%, 5% and 7% zeolite used in the present research study were prepared by solution casting. The PLA nanocomposites were structurally characterized by Scanning Electron Microscopy and Fourier-transform infrared spectroscopy. The effects of the gamma radiation at the absorbed doses of 10, 15 and 20?kGy on the structures and thermal properties of the nanocomposites were investigated in a tetrahydrofuran solvent. Thermodecomposition tests and analyses were carried within 30–500°C range at the rate of 10°C?min^?1 by thermogravimetric analysis (TG). The activation energies for thermal degradation of the nanocomposites were calculated from their TG data by Flynn–Wall–Ozawa method. The G values of the nanocomposites were calculated based on molecular weights which were measured by means of gel permeation chromatography before and after the gamma irradiation. The E_a and molecular weight results showed that addition of zeolite to the PLA affected the radiation resistance of the polymer.     

Surface-modified zeolite-filled chitosan membranes for pervaporation dehydration of ethanol

Surface-modified zeolite-filled chitosan (CS) membranes were prepared by incorporating 3-mercaptopropyltrimethoxysilane (MPTMS)-modified H-ZSM-5 zeolite into chitosan for pervaporation dehydration of aqueous ethanol solution. The physicochemical characterization by XPS, FT-IR, XRD, DMA and SEM showed that -SO₃H group was readily grafted on the surface of H-ZSM-5 with the mediation of MPTMS and hydrogen peroxide, and the accompanying ion-ion interaction between -SO₃H group on surface-modified H-ZSM-5 and -NH₃⁺ group on chitosan substantially eliminated the nonselective voids at the chitosan-H-ZSM-5 interface of the filled membranes. The experimental results also revealed that H-ZSM-5 exhibited desirable size-selective and preferential adsorption effects for aqueous ethanol solution. As a result, modified H-ZSM-5 filled membranes showed higher swelling degree and permeation flux, and improved selectivity for aqueous ethanol solution. In comparison between chitosan control membrane (permeation flux 54.18 g/(m² h) and separation factor 158.02 for 90 wt.% aqueous ethanol solution at 80 °C), the modified H-ZSM-5 filled membrane with 8 wt.% filling content exhibited a remarkably improved pervaporation performance with permeation flux 278.54 g/(m² h) and separation factor 274.46 under the identical experimental condition.     

Prediction of ortho substituent effect in alkaline hydrolysis of substituted phenyl benzoates in aqueous acetonitrile

The second‐order rate constants k (dm³mol^?1s^?1) for alkaline hydrolysis of meta‐, para‐ and ortho‐substituted phenyl esters of benzoic acid, C₆H₅CO₂C₆H₄‐X, in aqueous 50.9% (v/v) acetonitrile have been measured spectrophotometrically at 25 °C. In substituted phenyl benzoates, C₆H₅CO₂C₆H₄‐X, the substituent effects log k_X ? log k_H in aqueous 50.9% acetonitrile at 25 °C for para, meta and ortho derivatives showed good correlations with the Taft and Charton equations, respectively. Using the log k values for various media at 25 °C, the variation of the ortho substituent effect with solvent was found to be precisely described with the following equation: Δlog k_ortho = log k_ortho ? log k_H = 1.57σ_I + 0.93σ°_R + 1.08E_s^B ? 0.030ΔEσ_I ? 0.069ΔEσ°_R, where ΔE is the solvent electrophilicity, ΔE = E_S ? E_H20, characterizing the hydrogen‐bond donating power of the solvent. We found that the experimental log k values for ortho‐, para‐ and meta‐substituted phenyl benzoates in aqueous 50.9% acetonitrile at 25 °C, determined in the present work, precisely coincided with the log k values predicted with the equation (log k^X)_calc = (log k^H_AN)_exp + (Δlog k^X)_calc where the substituent effect (Δlog k^X)_calc was calculated from equation describing the variation of the substituent effect with the solvent electrophilicity parameter, using for aqueous 50.9% CH₃CN the solvent electrophilicity parameter, ΔE = ?5.84. In going from water to aqueous 50.9% CH₃CN, the ortho inductive term grows twice less as compared with the para polar effect. Copyright © 2013 John Wiley & Sons, Ltd.     

High resolution gamma-ray spectroscopy of the27Al(p,γ)28Si resonance reaction

High resolution gamma-ray spectra have been measured from the²⁷Al (p,γ)²⁸Si reaction for the resonances atE _p=2·482, 2·511 and 2·735 MeV at ϑ _pγ=0°, 30°, 55° and 90° using a Ge (Li) gamma spectrometer. From the spectra and the angular distributions the properties of the resonance states have been obtained. These states are the isobaric analogues of the levels at 4·69, 4·75 and 4·93MeV levels respectively in the parent nucleus A²⁸l.     

Instability of the lowest triplet state of benzene under environmental perturbations : zero-field splitting and radiative properties of the spin components

Coupling is considered between the lower ³ B _1u and ³ E _1u states of benzene under the combined influence of substituents and the crystal field. A model is derived in which the value of the E.S.R. parameter E, the orientation of the zero-field axes relative to the molecular frame and the radiative properties of the upper two spin components of the lowest triplet state are interpreted in terms of an electronic wavefunction.

With the model the reduced intensity of the 0-0 band relative to the 8₁ ⁰ band in the phosphorescence spectra of a number of benzene-like systems is explained. Further the radiative properties of the zero-field spin components of toluene in a benzene host are interpreted; in this system the angle between the in-plane zero-field axes and the molecular axes appears to be 74° (±6°).     

Solvent polarity scales: determination of new ET(30) values for 84 organic solvents

The solvent polarity parameter E_T(30) is newly measured from the solvatochromism of the betaine dye 30 for 84 solvents and re‐measured for 186 additional ones. The results are organized in a database. It is shown that the validity of linear solvation energy relationships used for the determination of secondary E_T(30) values is limited to non‐hydrogen‐bond donor solvents. Relationships with the chain length n are given for the determination of tertiary E_T(30) values of the homologous H(CH₂)_nY solvent series. The parameter E_T(30) is orthogonal to the function of the refractive index (n² ? 1) / (2n² + 1). For non hydrogen‐bond donor solvents, this allows to enter E_T(30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of the annealing temperature of thin Hf0.3Zr0.7O2 films on their energy storage behavior

With increasing annealing temperature (T_anneal), the magnitude of the electric fields for the antiferroelectric‐to‐ferro‐electric (E_AF) and ferroelectric‐to‐antiferroelectric (E_FA) transition of a 9.2 nm thick Hf_0.3Zr_0.7O₂ film decreased. The energy storage densities of the Hf_0.3Zr_0.7O₂ films crystallized at 400 °C, 500 °C, and 600 °C were as large as 42.2 J/cm³, 40.4 J/cm³, and 28.3 J/cm³, respectively, at the electric field of 4.35 MV/cm. The maximum dielectric constant of the Hf_0.3Zr_0.7O₂ film crystallized at 600 °C was the largest (～46) as it had the smallest E_AF and E_FA, whereas the leakage current density of the film crystallized at 400 °C was the smallest. The 400 °C of T_anneal was the optimum condition for energy storage application. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Investigation of the role of the projectile-target orientation angles on the evaporation residue production

The measured yield of evaporation residues in reactions with massive nuclei have been well reproduced by using the partial fusion and quasifission cross sections obtained in the dinuclear-system model. The influence of the orientation angles of the projectile- and target-nucleus symmetry axes relative to the beam direction on the production of the evaporation residues is investigated for the ⁴⁸Ca + ¹⁵⁴Sm reaction as a function of the beam energy. At the low beam energies only the orientation angles close to αP = 30° (projectile) and αP = 0°–15° (target) can contribute to the formation of evaporation residues. At large beam energies (about E _c.m. = 140–180 MeV) the collisions at all values of orientation angles αP and α _T of reactants can contribute to the evaporation residue cross section which ranges between 10–100 mb, while at E _c.m. > 185 MeV the evaporation residue cross section ranges between 0.1–1 mb because the fission barrier for the compound nucleus decreases by increasing its excitation energy and angular momentum.     

Membranes and films of zeolite and zeolite-like materials

An ideal structure of zeolite membrane should be a slice of a perfect zeolite crystal attached on a porous metal or ceramic support. To maximize the throughput, the zeolite layer must be very thin, limited only by the cell dimension of zeolite. Separation of a mixture may then be achieved based on the molecular sieving ability of zeolite, which allows only molecules smaller than a critical size to pass through. A variety of methods have been reported for the preparation of zeolite membranes, but so far a perfect epitaxial zeolite layer is still out of reach and only a polycrystalline zeolite membrane can be obtained. The first part of this review focuses on the permeation of gases and vapors through a polycrystalline zeolite membrane as a separation means. The effect of microstructure on permeance will also be discussed, as well as the preparation methods leading to different microstructures. In addition to the usage as a shape-selective membrane, thin films of zeolite and zeolite-like molecular sieves can also serve as hosts for the encapsulation and orientation of guest atoms and molecules and their clusters. In the second part of this review, the production of layers of aligned microporous molecular sieve crystals on supports and the fabrication of supported thin zeolite-like nanoporous silica films as well as their potential applications on the preparation of advanced materials are discussed.     

X‐ray fluorescence analysis of Co,Ni, Pd,Ag, and Au in the scrapped printed‐circuit‐board ash

A method for the quantitative analysis of Co, Ni, Pd, Ag, and Au in the scrapped printed‐circuit‐board ash by X‐ray fluorescence (XRF) spectrometry using loose powder was developed. The printed‐circuit‐board samples were converted to ash pyrolytically in porcelain crucibles by sequential heating using a gas burner and electric furnace, and then were ground with a ball mill. The calibrating standards were prepared by adding the appropriate amounts of NiO powder and aqueous standard solutions containing Co, Pd, Ag, and Au to the base mixtures of Al₂O₃ (5.0 mass%), SiO₂ (49 mass%), CaCO₃ (11 mass%), Fe₂O₃ (3.3 mass%), and CuO (30 mass%) as a matrix. Then, 10 g of the resulting mixtures were dried and homogenized for 90 min with a V‐type mixing machine. Specimens for XRF analysis were prepared from the so‐called loose‐powder method in which powder samples were compacted into a hole (12.0‐mm diameter and 5.0‐mm height) in an acrylic plate and covered with a 6‐µm thickness of polypropylene film. Matrix effects were corrected using the intensity value of Compton scattering for PdKα, AgKα, and AuLβ₂, and that of background scattering at 35.8° (2θ) for CoKα and NiKα. The detection limits corresponding to three times the standard deviation of the blank intensity were 2.5–45 µg g^?1. The proposed method was validated against the pressed‐powder‐pellet method by comparing the calibration curves. Moreover, the concentrations of Co, Ni, Pd, and Ag determined using the proposed XRF method were approximately the same as those resulting from an atomic‐absorption‐spectrometric analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Modeling Sorption Behavior for Ethanol/Water Mixtures in a Cross-linked Polydimethylsiloxane Membrane Using the Flory-Huggins Equation

The sorption behaviors of aqueous ethanol solutions in a polydimethylsiloxane (PDMS) membrane at 25°C were investigated in this study. The sorption isotherms for the ethanol and water binary mixtures were experimentally determined. The water uptake reached a maximum at a concentration of 80 wt% ethanol, and the partial water uptakes were even higher than the pure water solubility for 10–95 wt% ethanol solutions in the PDMS membrane, which implies the presence of a strong synergistic effect due to the ethanol copermeant. The Flory-Huggins equation was utilized to predict the sorption levels at various ethanol/water compositions. The binary Flory-Huggins interaction parameters obtained from pure solvent sorption experiments (χ_iM ) and the ethanol/water vapor liquid equilibrium data (χ ₁₂) were used in the construction of the model for predicting the partial penetrant solubilities. Using constant χ_ij parameters could not render satisfactory predictions; therefore, concentration-dependent expressions for either χ ₁₂ or χ_iM were employed to improve the prediction power. We found that constant or concentration dependent χ ₁₂ parameters had little impact on the predicted sorption, whereas the modified concentration-dependent χ_iM values greatly improved the modeling precision.     

Polarization Features of the 24Mg(2+) Nucleus Produced in the Reaction 27Al(p, α)24Mg(2+)

At the proton energy of E_p = 7.4 MeV, the double-differential cross sections for the reaction ²⁷Al(p, α₁γ)²⁴Mg were measured for 11 values of the alpha-particle emission angle in the range of θ_α = 30°–160°(lab). All even components of the density-matrix spin-tensors were reconstructed for the oriented ²⁴Mg nucleus in the 2⁺ state at 1.369 MeV, and the polarization features of this nucleus, including the populations of magnetic sublevels of the nucleus for all spin projections, multipole-moment orientation tensors, and the quadrupole and hexadecapole tensor polarizations, were determined. Relevant experimental results were compared with their counterparts calculated for the triton-pickup mechanism within the coupled-channel method and in the statistical limit of the compound-nucleus model.

     

On the structural stability and oxygen permeation behavior of inorganic SrCo0.8Fe0.2O3−δ membranes

The high oxygen permeability combined with reasonable structural stability of perovskite-type ABO_3−δ compounds is vital for their potential applications in gas separation, solid oxide fuel cells, sensors, etc. Hence, an attempt is made to develop SrCo_0.8Fe_0.2O_3−δ-based dense membranes with sol-gel-derived oxalates and study their phase stability and oxygen permeation. While X-ray diffraction confirms the presence of a perovskite-type cubic phase above 800 °C, X-ray photoelectron spectroscopy reveals the presence of cobalt and iron in 3+ and 4+ oxidation states with O₂ ²⁻, O₂ ⁻ and O⁻ species. The electrical conductivity increases up to a characteristic temperature and decreases slowly thereafter via pronounced carrier scattering. A 1.5-mm-thick membrane displays reasonable oxygen permeability of 1.05 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C but has inadequate stability. Partial substitution of iron with zirconium is shown to improve permeability and stability significantly. Thus, SrCo_0.8Fe_0.15Zr_0.05O_3−δ membrane shows promise for oxygen permeation purposes.

     

N.M.R. solid echoes in systems of dipolar-coupled inequivalent spins-1 or dipolar-coupled inequivalent pairs of spins-1/2

Proton solid-echo transverse relaxation functions for many thermotropic and lyotropic mesophases, mapped by measurement of the echo amplitude S_yx (t′ = τ) as a function of τ using a P_y (90°)-τ-P_x (90°)-t′ sequence, yield gaussian behaviour of the form exp [-½M ^E ₂τ²] for decays up to 20–30 per cent of the value at τ = 0. M ^E ₂, the second moment for the dipolar interactions between the spin-½ pairs, is related to the van Vleck second moment M ^VV ₂ through a factor f. Whilst experiments suggested a value of 0·70–0·72 for f = M ^E ₂/M ^VV ₂, simple models that ignored the non-equivalence of the dipolar-coupled spin-pairs had predicted f = 0·65. In this paper we derive an exact analytic expression for the spin response of a model of two dipolar-coupled inequivalent spins-1 to the pulse sequence P_y (90°)-τ-P _α(β)-t′, and show that the present model, with the quenching of the spin-flip terms of the dipolar hamiltonian, resolves the afore-mentioned discrepancy. We also reconcile the differences between the experimental and the earlier predicted values of f for deuteron N.M.R. spin echoes in perdeuterated solids.     

Improved stability of La0.5Sr0.5FeO3 by Ta-doping for oxygen separation membrane application

(La,Sr)FeO₃ mixed conducting perovskites are considered as interesting candidates for oxygen separation membranes but they suffer from limited structural stability in a large oxygen partial pressure (pO₂) gradient, because of their propensity for chemical expansion. Partial substitution of Fe with more stable elements tends to improve the stability while penalizing the electronic and ionic conductivities.In this study, we investigate the effect of 10% Ta substitution on the oxygen transport properties and stability of La_0.5Sr_0.5FeO₃. For this purpose, the material was evaluated as a membrane in a CPOX reactor. The oxygen permeation through a ~ 3 cm² pellet sample was first measured under air/Ar gradient in the temperature range of 800 to 1000 °C. The measured flux was 0.1 µmol cm^? 2 s^? 1 at 900 °C, which was a factor of 2 lower than for the Ta-free material. Methane was then introduced into the system and reacted in a catalytic bed with oxygen that has permeated through the membrane to form syngas (H₂, CO). As a result, the oxygen flux increased by a factor of 9, reaching 0.9 µmol cm^? 2 s^? 1 at 900 °C. The reactor was operated at 1000 °C for another 1000 h. During this time, the oxygen permeation flux decayed by ca. 4%/1000 h.The test was stopped after more than 2000 h of operation and the membrane analyzed by electron microscopy.     

The peierls energy and kink energy in fcc metals

In fcc crystals, dislocations are dissociated on the {111} glide plane into pairs of partial dislocations. Since each partial interacts individually with the Peierls potential and is coupled to its neighbour by a stacking fault, periodic variations in the separation distance d of the partials occur when dislocations running along closed packed lattice directions are displaced. This can drastically reduce the effective Peierls stress. By using the Peierls model the structure of 0°, 30°, 60° and 90° dislocations in a typical fcc metal with the elastic properties of Cu and a stacking-fault energy γ₀ in the interval 0.04?≤?γ₀?≤?0.05?J/m² was studied, and the magnitude of the Peierls energy ΔE _P and the resulting kink energies E _K were determined. Since the energies involved are of the order of 10^?3?eV/b or less, their magnitude cannot be asserted with high confidence, considering the simplifying assumptions in the model. The difference in the changes of the core configuration during displacement of dislocations of different orientations should, however, be of physical significance. It is found that a dissociated 60° dislocation generally has a higher effective Peierls energy than a screw dislocation, but the reverse is true for the kink energy, at least in Cu.     

The permeation of gases through symmetric and asymmetric (Loeb-Type) cellulose acetate membranes

Significant differences have been observed in the steady-state permeation of gases through symmetric and asymmetric (Loeb-type) cellulose acetate membranes. The studies were made with O₂, N₂, Ar, Kr, Xe, and CO₂ in the temperature range from -5 to 85°C and at subatmospheric pressures. The differences in permeation behavior may reflect structural differences between the symmetric membranes and the dense surface layer (“skin”) of the asymmetric membranes. The overall mechanism of gas permeation through the symmetric membranes appears to be one of “solution-diffusion,” similar to that observed with many other nonporous polymeric membranes. In the case of the asymmetric membranes, this mechanism is probably modified by the presence of micropores or other imperfections in the dense surface layer. Cellulose acetate exhibits two second-order transitions in the presence of the penetrant gases, one between 60 and 70°C and the other near 15°C. The transitions were observed with both types of membranes.     

Kinetics of radiation polymerization of vinyl benzoate

Abstract

Vinyl benzoate was polymerized by γ-radiation from a cobalt-60 source and the kinetics of polymerization were studied at several temperatures. The results showed that the rate of polymerization was proportional to I^0.66 , where I is the radiation dose rate. The net activation energy for the polymerization reaction, (E_p -1/2 E_t ), was found to be 3.62 kcal, where E_p and E_t are the activation energies for the propagation and termination stages of the reaction. The radical yield measured by the loss of DPPH in the solution after irradiation was G=5.0, while the G (Radical) effective in initiating polymerization was 0.94. The ratio of the rate constants, k² _p/k_t = 5.8 × 10^?4 at 60° and 1.59 × 10^?4 at 25° The rate of polymerization was higher than that of styrene but lower than that of vinyl acetate under comparable conditions.