Kinetic measurements and in situ Raman spectroscopy study of the formation of TBAF semi-hydrates with hydrogen and carbon dioxide

The kinetics of formation of semi-clathrate hydrates of tetra n-butyl ammonium fluoride (TBAF) with hydrogen (H₂) and carbon dioxide (CO₂) were studied in order to elucidate their potential for H₂ storage as well as for CO₂ sequestration. The influence of pressure, TBAF concentration (1.8 mol% and 3.4 mol%) and formation method (T-cycle method and T-constant method) on the hydrate nucleation, hydrate growth and the amount of gas uptake were determined. The results showed that the kinetics of formation of H₂–TBAF semi-hydrates is favored at high pressures and TBAF concentrations. The TBAF concentration did not display a large influence on the kinetics of formation of CO₂–TBAF semi-hydrates and pressure only showed a major influence on the formation rate. Instead, the induction time and the amount of CO₂ consumed were favored at low temperatures. Additionally, in situ Raman spectroscopy was used to confirm the gas uptake in the hydrate structure and to observe structural changes.     

The synthesis of poly(butylene terephthalate) from terephthalic acid,part II: Assessment of the first stage of the polymerization process

The production of poly(butylene terephthalate) (PBT) struggles with the formation of substantial amounts of tetrahydrofuran (THF). When PBT is synthesized from terephthalic acid (TPA) instead of dimethyl terephthalate (DMT), even more THF is formed, mainly during the first stage of the melt polymerization process. Although a lot of literature reports on the existence of this side reaction in both processes, to the best of our knowledge, a comparison, which reveals the importance of the acidity and insolubility of TPA on the THF formation, was never described. Finally, an interesting study was performed on the THF formation during the synthesis of PBT from mixtures of DMT and TPA as well as from the completely soluble monomethyl terephthalate (MMT). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Flow pattern in a fluidized bed with a non-fluidized zone

The flow pattern of a fluidized bed with non-fluidized zones is investigated both experimentally and theoretically. Experiments were carried out in such a way that air was introduced only through part of the distributor. The results show a significant amount of air flowing to the zone where no air is introduced. However, once the gas velocity exceeds the minimum fluidization velocity in the zone where the air is introduced, the cross-flow hardly changes upon further increase of the gas velocity. A continuity equation and Ergun's equation are used to describe the flow pattern and pressure distribution over the bed. Very good agreement between the experimental and calculated results is achieved without any fitting parameter. The results are relevant to the understanding of heat transfer behaviour of a fluidized bed combustor (FBC) that is only partly fluidized to control its load.     

LESS: a model-based classifier for sparse subspaces

In this paper, we specifically focus on high-dimensional data sets for which the number of dimensions is an order of magnitude higher than the number of objects. From a classifier design standpoint, such small sample size problems have some interesting challenges. The first challenge is to find, from all hyperplanes that separate the classes, a separating hyperplane which generalizes well for future data. A second important task is to determine which features are required to distinguish the classes. To attack these problems, we propose the LESS (Lowest Error in a Sparse Subspace) classifier that efficiently finds linear discriminants in a sparse subspace. In contrast with most classifiers for high-dimensional data sets, the LESS classifier incorporates a (simple) data model. Further, by means of a regularization parameter, the classifier establishes a suitable trade-off between subspace sparseness and classification accuracy. In the experiments, we show how LESS performs on several high-dimensional data sets and compare its performance to related state-of-the-art classifiers like, among others, linear ridge regression with the LASSO and the Support Vector Machine. It turns out that LESS performs competitively while using fewer dimensions.     

Reference-material-based collaborative test of flame atomic absorption spectroscopic determination of calcium and magnesium in foods and biological materials

Summary A flame atomic absorption spectroscopic (FAAS) method is described for the determination of calcium and magnesium in a wide variety of foods and biological substrates. Results for reference materials (n=9) are presented that demonstrate the validity of the procedure. Samples are digested with nitric acid at 150° C in a pressure decomposition vessel, diluted and adjusted to pH 2 with ammonia. Lanthanum chloride solution is added to suppress phosphate interferences and the ionization of calcium and magnesium in the AAS flame. Additional dilutions are made as appropriate, whereupon the atomic absorption of calcium and magnesium is measured in an oxidizing air-acetylene flame. The wavelength settings for calcium is 422.7 nm and for magnesium 285.2 nm. The method was tested in a collaborative trial involving a milk powder practice sample and four test samples, all of which were reference materials. Participants were requested to carry out duplicate determinations exclusively. Results were obtained from 12 laboratories. However, the results of 3 laboratories had to be rejected for various reasons. The remaining set of data was statistically evaluated according to ISO 5725; the method of analysis proved to be precise and accurate. Coefficients of variation values for calcium ranged from 1.19% to 4.44% within laboratories (CV_r) and from 5.30% to 15.9% between laboratories (CV_R). For magnesium, the corresponding values were CV_r, 1.07% to 3.52% and CV_R, 3.07% to 5.99%. The method is recommended for the determination of calcium and magnesium at the levels considered in foods and biological substrates.

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Referenzmaterialien aus einem Ringversuch zur flammenatomabsorptions-spektroskopischen Bestimmung von Calcium und Magnesium in Lebensmitteln und biologischen Materialien

Zusammenfassung Es wird eine FAAS-Methode zur Bestimmung von Calcium und Magnesium in verschiedenen Lebensmitteln und biologischen Materialien beschrieben. An Hand von Ergebnissen für Referenzmaterialien (n=9) wird die Aussagekraft der Arbeitsweise erläutert. Die Proben werden mit Salpetersäure bei 150°C in einem Druckgefäß aufgeschlossen, verdünnt und auf pH 2 mit Ammoniaklösung gebracht. Lanthanchloridlösung wird zur Unterdrückung von Phosphatinterferenzen und Ionisation von Calcium und Magnesium in der AAS-Flamme zugesetzt. Je nach Bedarf wird weiter verdünnt und sodann die Atomabsorption von Calcium und Magnesium in einer oxidierenden Luft/Acetylenfiamme (Wellenlänge für Calcium 422,7 nm und für Magnesium 285,2 nm) gemessen. Die Methode wurde in einem Ringversuch erprobt, wobei ein Milchpulver als Übungsmaterial und vier Testproben benutzt wurden; alle Proben waren Referenzmaterialien. Alle Teilnehmer wurden aufgefordert, ausschließlich Doppelbestimmungen durchzuführen. Von zwölf Laboratorien wurden Ergebnisse erhalten, von dreien wurden die Ergebnisse aus verschiedenen Gründen nicht ausgewertet. Die übrigen Daten wurden nach ISO 5725 statistisch ausgewertet und zeigen, daß die Analysenmethode genaue und richtige Werte liefert. Die Variationskoeffizienten für Calcium betrugen 1,19–4,44% innerhalb der Laboratorien (CV_r; Wiederholbarkeit) und 5,30–15,9% zwischen den Laboratorien (CV_R; Vergleichbarkeit). Für Magnesium sind die entsprechenden Zahlen: CV_r 1,07–3,52% und CV_R 3,07–5,99%. Die Methode wird für die Calcium- und Magnesiumbestimmung in Lebensmitteln und biologischen Materialien in den angegebenen Konzentrationsbereichen empfohlen.

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This study was sponsored by the Commission on Food Chemistry (VI.1) of IUPAC (International Union of Pure and Applied Chemistry)     

On the influence of the processing conditions on the performance of electrically conductive carbon nanotube/polymer nanocomposites

We prepared multiwalled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites using a latex-based process, the main step of which consists of directly mixing an aqueous suspension of exfoliated MWCNTs and a PS latex, both stabilized by an anionic surfactant. After freeze drying and compression molding homogeneous polymer films with well-dispersed carbon nanotubes were produced as evidenced by scanning electron microscopy. Conductivity measurements performed on our nanocomposite films show that they have a low percolation threshold and exhibit high levels of electrical conductivity above this threshold. We observe that both these properties are influenced by the applied processing conditions, i.e., temperature and time, and provide a plausible explanation based on the diffusive motion of the MWNTs in the polymer melt during the compression molding stage.