Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

Analysis of Fe species in zeolites by UV–VIS–NIR, IR spectra and voltammetry. Effect of preparation, Fe loading and zeolite type

Three procedures were employed for the preparation of Fe-zeolites with ZSM-5 (MFI), ferrierite (FER) and beta (BEA) structures: ion exchange from FeCl₃ solution in acetyl acetonate and solid-state ion exchange from FeCl₂ using an oxygen or nitrogen stream. A combination of UV–VIS–NIR spectra, IR spectra of skeletal vibrations and of adsorbed NO, as well as voltammetry provided information on the type of Fe species introduced. Single Fe(III) ion complexes (Fe(H₂O)_6−xOH_x) in hydrated zeolites were reflected in the charge-transfer bands at 33 100, 37 300 and 45 600 cm⁻¹. The single Fe(II) ions at cationic sites in evacuated zeolites yielded (through perturbation of framework T–O bonds) characteristic bands (910–950 cm⁻¹) in the region of the skeletal window. These Fe(II) ions with adsorbed NO were also reflected in vibrations at 1880 cm⁻¹. Dinuclear Fe–oxo complexes yielded the Vis band at 28 200 cm⁻¹. Voltammetry indicated the presence of Fe oxides (hematite) through the reduction peak at −0.7 V. Such oxide-like species were also reflected in the absorption edge at 19 800 cm⁻¹, and a doublet at 11 000 and 11 800 cm⁻¹ in the Vis spectra. Fe(II)–NO vibrations at 1840, 1810 and 1760 cm⁻¹ belonged to the undefined exposed Fe cations, probably originating from supported oxides. Using an ion exchange procedure, employing FeCl₃ in acetyl acetonate, exclusively Fe ions at cationic sites could be introduced at low concentrations (Fe/Al < 0.1). At higher Fe loadings, dinuclear Fe–oxo complexes were formed preferably in Fe-ZSM-5, but were absent in Fe-beta. Exclusively single Fe species could not be prepared at Fe concentrations above Fe/Al > 0.2; all three types of Fe species, single Fe ions, dinuclear Fe–oxo complexes and Fe oxides were formed.     

Effect of temperature on the structure and density of ammonium chloride particles

The structure and density of individual ammonium chloride particles formed at 0 and −20°C by homogeneous nucleation were studied using electron microscopy and X-ray diffraction. The crystal size apparently increased at the lower temperature and many of the particles formed at −20°C were single crystals or had an oriented polycrystalline structure. These results differ from those reported previously for particles formed at room temperature (23–26°C), which showed an amorphous or randomly-oriented fine crystal structure. Coagulation was more frequently observed as the temperature decreased and the porosity present in the particles appeared to be much finer and more uniform. The density of these particles decreased from about 0.26 g cm⁻³ for particles of size 0.1–0.2 μm to approximately 0.1 g cm⁻³ for particles slightly smaller than 1 μ.     

Selective reduction of nitric oxide with propene over platinum-group based catalysts: Studies of surface species and catalytic activity

The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO₂, ZnO, ZrO₂, and Al₂O₃ has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523–673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900–3080 cm⁻¹), isocyanate (2180, and 2232–2254 cm⁻¹), cyanide (2125 cm⁻¹), nitrosonium (1901 cm⁻¹), CO₂ (2343–2357 cm⁻¹), CO (2058 cm⁻¹) and carbonate (1300–1650 cm⁻¹) species. In the case of rhodium containing catalysts, when supported on Al₂O₃, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.     

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm⁻¹ were identified in the region of the CH overtones (5200–6200 cm⁻¹). Among them, two bands at 5810 (aliphatic) and 6010 cm⁻¹ (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm⁻¹), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm⁻¹ (free-end) can be observed.     

Preparation and characterization of mesoporous γ-Ga2O3

Mesoporous γ-Ga₂O₃ was prepared by calcination (at 773 K) of a gallia gel obtained by adding ammonia to an ethanolic solution of gallium nitrate. The corresponding powder X-ray diffraction pattern was found to be similar to that of γ-alumina; all diffraction lines could be indexed by assuming a cubic spinel-type structure having a lattice parameter a₀=0.830 nm. Nitrogen adsorption–desorption at 77 K showed the material to have a BET surface area of 120 m² g⁻¹ and a most frequent pore radius of 2.1 nm. The surface chemistry was studied by FTIR spectroscopy of adsorbed carbon monoxide at liquid nitrogen temperature. Partially hydroxylated γ-Ga₂O₃ gave main O–H stretching bands at 3692 and 3637 cm⁻¹. These hydroxyl bands were significantly perturbed by adsorbed CO, thus showing a Brønsted acid character. Lewis acidity was monitored by analyzing the C–O stretching mode of carbon monoxide adsorbed on coordinatively unsaturated Ga³⁺ ions; main IR absorption bands of Ga³⁺CO adducts were found at 2220 and 2193 cm⁻¹.     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia powder from sucrose derived organic precursors

An organic precursor synthesis of 8 mol% yttria stabilized zirconia (YSZ) powder from Zr–Y composite nitrate solution and sucrose has been studied. Oxidation of sucrose in Zr–Y composite nitrate solution containing excess nitric acid in situ generates hydroxy carboxylic acids that forms a white sol which showed peaks at 1640 cm⁻¹ and 1363 cm⁻¹ in IR spectrum corresponding to hydroxy carboxylic acid complexes of Zr and Y. Precursor mass obtained by drying the sol on calcinations at 600 °C produced loosely agglomerated particles of cubic YSZ. Deagglomerated YSZ contain submicron particles with D₅₀ value of 0.5 μm and the particles are aggregates of nanocrystallites of nearly 10 nm size. Compacts prepared by pressing the YSZ powder sintered to 96.7% TD at 1450 °C. The sintered YSZ ceramic showed an average grain size of 2.2 μm.     

Study of the changes in i.r. spectra bands of coal after reductive alkylation

Depolymerization reactions of a Spanish bituminous coal, such as reductive hydrolysis and alkylation, and O-alkylation, were investigated by Fourier transform infrared spectroscopy (FT-i.r.). The spectra show that the reductive hydrolysis increases the phenolic hydroxyl groups, whereas these decrease by alkylation. These changes in the OH group content were studied in relation to variations in the absorbances at 3800–2000, 1700, 1600 and 1112 cm⁻¹, and some linear correlations were found, which seem to indicate a clear contribution of the OH groups to the intensity of the broad band near 1600 cm⁻¹. The influence of the phenolic OH groups on the C=O vibration frequency at 1700 cm⁻¹ was also studied.     

High-pressure synthesis and characterization of diamond from a sulfur–carbon system

Diamond crystallization in the sulfur–graphite system has been studied at P=7 GPa and T=1750–1850°C in experiments with a duration up to 7 h. It has been found that diamond nucleation and crystallization occur both at the interface between the graphite and sulfur melt and directly within the carbon–saturated sulfur melt. Diamond crystals with maximum size up to 500 μm were synthesized. The crystals had cube–octahedral morphology with minor faces of trapezohedron. Goniometric measurements revealed that crystallographic indexes of the trapezohedron faces are {411} and {944}. Spectroscopic characterization of sulfur–synthesized diamonds by means of infrared absorption microscopy and cathodoluminescence has been made for the first time. It was found that crystals contain nitrogen impurity in the form of A aggregates with concentration up to approximately 700 at. ppm. An absorption band with a maximum at 1050 cm⁻¹, whose origin is not clear, was observed in the IR spectra. The cathodoluminescence spectra of these diamonds were found to comprise of the well-known H3 and 575-nm systems as well as a broad emission band.     

Electrochemical reduction of thermally prepared oxides of iron and iron-chromium alloys studied by in situ Raman spectroscopy

Pure Fe and Fe/Cr alloys (3% and 12% Cr) were oxidized at 250–260°C and subsequently electrochemically reduced in borate buffer, pH 8.4. The reduction was followed by in situ Raman spectroscopy as well as chronopotentiometric and chronoamperometric measurements. At several time intervals ex situ Raman control investigations and ESCA analyses were undertaken. Although at −0.7 V vs sce partial reduction of the oxide film was observed, -Fe₂O₃ remained unchanged and reduced at −0.9 V. A mixture of spinel structured oxide, possibly Fe₃O₄, and a ferrous deposit were observed when the oxide film was galvanostatically reduced at 100 μA cm⁻²; after prolonged reduction the bare metal resulted. The thermally created oxide of the Cr alloy possessed an inner Cr rich layer which during the galvanostatic reduction of the oxide film at 50 μA cm⁻² is most likely responsible for an increase in the overpotential of more than 80 mV.     

Low-density, microcellular polystyrene foams

Numerous applications have been identified for low-density, microcellular, polymeric foams. In this paper the authors describe a general technique to produce foams of this type with organic-soluble polymers, in particular polystyrene. Open-celled polystyrene foams have been developed with densities of 0.02–0.2 g cm⁻³ and uniform cell sizes of 1–20 μm. By using well-characterized polymers the authors have related form morphology to the phase diagram of the polymer/solvent system employed.     

The interaction of alumina with HCl: An infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering study

The interaction of HCl with an η-alumina catalyst has been investigated by a combination of diffuse reflectance infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering (INS) spectroscopy. Infrared spectra provide evidence for dissociative adsorption of HCl and for a process in which hydroxyl groups terminally bound to Al are replaced by chlorine. Temperature-programmed desorption experiments show HCl to desorb over the temperature range 350–>970 K, indicating dissociative HCl adsorption to occur on a wide range of active sites. INS experiments show the residual alumina hydroxyl groups to exhibit an out-of-plane deformation feature, γ(OH), at ca. 200 cm⁻¹, while the in-plane deformation mode, δ(OH), is seen at ca. 1000 cm⁻¹. The formation of new surface hydroxyl groups via the adsorption of hydrogen chloride yields a δ(OH) feature that can be resolved into two bands at 990 and 1050 cm⁻¹. Hydrogen bonding within the alumina/HCl system is responsible for the observation of an Evans transmission window in the infrared spectrum, that occurs via a Fermi resonance interaction between (i) the ν(OH) mode of hydrogen bonded hydroxyl groups and chemisorbed water with (ii) the overtone of the δ(OH) mode of surface hydroxyl groups. The INS technique is able to discriminate among different hydroxyl group bonding geometries on the basis of the local symmetry of the active sites.     

MEASUREMENTS OF THE NEAR INFRARED OPTICAL PROPERTIES OF COAL SLAGS

The spectral complex refractive index has been measured over the wavelength range of 1 μm to 12 μm for three coal ash samples. The measurements were conducted by making spectral transmittance and near-normal reflectance measurements on thin, homogeneous slag wafers prepared from the ash samples. The imaginary part of the refractive index k exhibits a large peak near 9 μm, attributable to Si-O vibrational absorption. Three smaller peaks in the k spectra were observed at 1·2μm, 1·8 μm, and 2·8 μm, which have been identified as due to absorption by the ferrous iron ion Fe²⁺ and the hydroxyl group OH. The dependence of the ash optical properties on ferrous iron content in the wavelength range of 1 μm to 5 μm suggests that both the total iron content of the ash and the ash oxidation state may affect the contribution of ash to radiative heat transfer in coal combustion systems.     

Effects of oxygen concentration on the electrical properties of ZnO films

In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N₂ and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10²¹ and mid 6 × 10¹⁷ cm⁻³ and resistivity at 10⁻³–10⁻¹ Ω cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at −10¹⁷ cm⁻³ and resistivity at 10 Ω cm.     

A new tantalum sulfur compound as electrode material for non-aqueous alkali metal batteries

Polycrystalline (PbS)_1.14(TaS₂)₂, a misfit layer sulfide, was used as cathodic material for lithium secondary battery. One molar LiClO₄ in propylene carbonate (PC) was used as electrolyte. The cell could be galvanostatic discharged down to x = 4.6 [Li_x(PbS)_1.14(TaS₂)₂] when the current density was 65 μA cm⁻² and the cell was cycled more than 100 times between 3.5 and 1.5 V at a current density of 260 μA cm⁻². Lattice expansion increased linearly with lithium content and was less than that reported for the Li/TaS₂ system. Chemical diffusion coefficients were determined by a modified version of the galvanostatic intermittent titration technique and they were fairly constant in the composition range 0.2 < x < 1, and an average value of 8.1 × 10⁻¹¹ cm² s⁻¹ was calculated. Sodium intercalation was also accomplished, but the uptake of this ion resulting in a significant lattice expansion compared with that observed for lithium ions. Moreover, a similar dependence of the sodium chemical diffusion coefficient on the composition was observed with an average value of 1.4 × 10⁻¹⁰ cm² s⁻¹, somewhat higher than that of lithium ion. We believe that differences in lattice expansion may be responsible for the differences found in the chemical diffusivity values.     

Aerosol measurement by laser doppler spectroscopy—II. Operational limits, effects of polydispersity, and applications

The theoretical basis and the results of a computer simulation are presented which describe the operational limits of size and concentration for aerosol sizing by laser Doppler spectroscopy LDS,. This analysis suggests that a state of the art LDS system has the capability of sizing 0·03 μm diameter particles when the number concentration is 10⁸ cm⁻³ or greater and 0·2 μm diameter for coocentrations as low as 100 particles cm⁻³. An evaluation of the effect on the laser Doppler spectroscopy measurements of a polydisperse aerosol having a log normal size distribution is presented and methods for combining these measurements with other averaged measurements to determine both count median diameter (CMD) and geometric standard deviation (δ_g) are proposed. For aerosols having log normal distributions with 0·3 < CMD < 3 μm and 1·0 < δ_g < 2·0, laser Doppler spectroscopy is able to measure the surface area median diameter within ± 15 per cent, independent of polydispersity. Applications of LDS to aerosol sizing are evaluated and its advantages and disadvantages relative to other sizing methods are discussed.     

Infrared spectroscopic study of the acid properties of dealuminated BEA zeolites

A series of HBEA samples were prepared by dealumination through three different methods (steaming, treatments with hydrochloric acid and ammonium hexafluorosilicate (HFS) solutions) of a parent sample with total and framework Si:Al ratios of 12.5 and 33, respectively, constituted of 20 nm crystallites. The samples were characterized by XRD, nitrogen adsorption and pyridine adsorption–desorption followed by IR spectroscopy. Whereas the three dealumination treatments have practically no effect on crystallinity and nitrogen adsorption properties, they cause large changes in the ranges of the O–H bond stretching modes (3300–3800 cm⁻¹) and of the most intense IR absorption of pyridine (1400–1700 cm⁻¹). Treatments with HCl or HFS cause the most significant changes: disappearance of the 3662 and 3782 cm⁻¹ bands corresponding to extraframework Al species and to tricoordinated Al species partially connected to the framework, respectively, appearance of additional bands at 1603 and 1446 cm⁻¹ ascribed to a new type of pyridine species coordinated to Lewis sites (PyL₂) and for desorption temperatures above 350 °C, of a band at 1462 cm⁻¹ generally ascribed to iminium ions, apparently at the expense of the PyL₂ band. In agreement with this formation of iminium ions, desorption at high temperatures causes the complete disappearance of pyridinium ions without complete restoration of the acidic bridging hydroxyl band. PyL₂ species are proposed to be pyridine molecules coordinated to Lewis sites and interacting through hydrogen bond with protonic sites.     

In situ FTIR study on NO reduction by C3H6 over Pd-based catalysts

The reaction mechanism of the reduction of NO by propene over Pd-based catalysts was studied by FTIR spectroscopy. It was observed that the reaction between NO and propene most probably goes via isocyanate (2256–2230 cm⁻¹), nitrate (1310–1250 cm⁻¹) and acetate (1560 and 1460 cm⁻¹) intermediates formation. Other possible intermediates such as partially oxidized hydrocarbons, NO₂, and formates were also detected. The reaction between nitrates and acetates or carbonates reduced nitrates to N₂ and oxidized carbon compounds to CO₂. In situ DRIFT provides quick and rather easily elucidated data from adsorbed compounds and reaction intermediates on the catalyst surface. The activity experiments were carried out to find out the possible reaction mechanism and furthermore the kinetic equation for NO reduction by propene.     

Characterization of Pd-based FCC CO/NOx control additives by in situ FTIR and extended X-ray absorption fine structure spectroscopies

Pdⁿ⁺/Ceⁿ⁺/Na⁺/γ-Al₂O₃-type materials used as FCC additives for CO/NO_x control were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and in situ FTIR. The EXAFS data indicate that in freshly prepared samples palladium is present in the form of highly dispersed PdO species. Reduction with H₂ at 500 °C leads to the formation of small Pd clusters incorporating on average approximately six to eight metal atoms at a Pd−Pd bond distance of 2.76 Å. All components of these materials can interact with NO and promote the formation of nitrate/nitrite species, essentially “trapping” NO_x species on the catalyst surface. However, the Na⁺ species dominate the surface chemistry and readily form sodium nitrates with a characteristic IR band at 1370–1385 cm⁻¹. Finally, hydroxyls from the support are also actively participating in the formation of HNO_x type compounds with characteristic stretching vibrations in the 3500–3572 cm⁻¹ region.     

Ion conduction in crosslinked β-cyclodextrin gels

Gels of crosslinked β-cyclodextrin have been prepared using dimethylacetamide containing lithium, sodium and potassium triflate salts.

Compositions were adjusted to produce materials with dry surfaces that showed no evidence of solvent leakage. Alternating current conductivity (σ) measurements of ion transport in these systems were made over the temperature range 290–360 K. Systems containing KCF₃SO₃ exhibited the best range of conductivity values from σ=10⁻⁴ S cm⁻¹ (293 K) to σ=1.8×10⁻³ S cm⁻¹ (360 K). These systems also show a linear dependence of log conductivity on 1/temperature, with activation energies for ion transport in the range 32–48 kJ mol⁻¹.