Clarification of a wheat straw‐derived medium with ion‐exchange resins for xylitol crystallization

BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry     

Influence of confinement on conformational entropy of a polymer chain and structure of polymer-nanoparticles complexes

Behaviour of a polymer chain in the presence of fixed obstacles has been studied by the static Monte Carlo simulations. A modified self-avoiding walk on a cubic lattice has been used to model the polymer in an athermal solution. The statistical counting method has been applied to calculate the conformational entropy of the chain, assumed to be grafted to an obstacle. Different chain lengths and obstacle curvatures have been examined. Some implications of the confinement induced changes in the conformational entropy of polymer chains to the structure of complexes composed of long polymer chains and nanoparticles are discussed.     

Recovery of uranium and other valuable metals from substrates and waste from copper and phosphate industries

ABSTRACT

Recovery of heavy metals and other useful materials from industrial waste is crucial because it reduces the environmental impact of the production facilities. The selective separation of uranium from such waste might be very important in the context of future energy production and the still essential role of nuclear power in the energy mix. The copper ores, waste from the copper industry, phosphate rocks and phosphogypsum were considered as sources of uranium in these studies. Apart from uranium, these materials also contain other valuable metals, e.g. rare earth elements. In the present work the procedures of extraction of uranium and accompanying metals designed for specific materials – the potential sources of metals, were reported.     

Thermal characterization of screen printed conductive pastes for RFID antennas

Thermal resistance is an essential aspect of electronic circuits designing. It leads to unexpected changes in electronic components during their work. In this study, new materials for screen printed RFID tag's antennas were characterized in terms of their resistance to thermal exposure. Polymer materials containing silver flakes, silver nanopowder, carbon nanotubes or conductive polymer PEDOT:PSS were elaborated and used for antenna printing on flexible materials. In order to verify their long term susceptibility to damages caused by the changing environmental conditions, the temperature cycling test was used in three different temperature ranges: +65 °C, −12 °C, −40 °C/+85 °C (3 h in each temp., dwell time 1 h). The highest durability to thermal exposure exhibited the paste with carbon nanotubes dispersed in poly(methyl methacrylate) PMMA and the lowest one – the paste with conductive polymer PEDOT:PSS.     

Spectral calibration of radiometric detectors using tunable laser sources

This paper describes the analysis of laser-based responsivity measurements using the Tunable Lasers in Photometry setup at the Physikalisch-Technische Bundesanstalt. An approach based on digital signal analysis is proposed to remove interference-caused oscillations in highly resolved spectral data from laser-based measurements, yielding an improved reproducibility and comparability of results. Digital filters are used to selectively suppress the frequency components of interference fringes visible in the measurement data. We describe the algorithm used and discuss the associated uncertainty components of laser-based measurements. Finally, we give examples of the calibration of different detectors with and without interference effects.     

Effect of the Morphological Types in Grinding of Iron-Ore Products

The iron-ore products are characterized in order to investigate the effect of the mineralogical features on the grinding results into pelletizing plant. The studied materials are from four mines of the different regions of Iron Quadrangle, processed by flotation, magnetic separator and produced from screening with P₈₀ in 8 mm. In this study, we apply for the first time the novelty of electron backscatter diffraction technique for the iron ore phase identification and quantification of the microstructural parameters. The mineralogical and microstructural parameters were introduced as a base in the specific grinding test applied in the industrial routine. Each sample was characterized based on the mineral shape, pores, fractures, polycrystalline hematite, and aggregate of hematite with goethite. The test results demonstrate that there is a strong relationship between the gain of the specific surface area, represented by the K-factor, and the morphological types.