Showing papers by "DECHEMA published in 2005"

Production of 2-phenylethanol and 2-phenylethylacetate from L-phenylalanine by coupling whole-cell biocatalysis with organophilic pervaporation.

Abstract: An integrated bioprocess for the production of the natural rose-like aroma compounds, 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEAc), from L-phenylalanine (L-phe) with yeasts was investigated. The hydrophobicity of the products leads to product inhibition, which can be compensated by in situ product removal (ISPR). An organophilic pervaporation unit, equipped with a polyoctylmethylsiloxane (POMS) membrane, was coupled via a bypass to a bioreactor and proved to be a suitable technique for the in situ removal of high-boiling products from culture broth. With batch cultures of the thermotolerant yeast Kluyveromyces marxianus CBS 600 in a standard medium at 35 degrees C, the use of pervaporation resulted in a double 2-PE concentration (2.2 g/L) and 1.3 g/L 2-PEAc, which only accumulated transiently in low concentrations during cultivation without ISPR. Using a previously optimized medium, the variation of the temperature from 30 degrees C to 40 degrees C caused an increase in the total conversion yield from 63% to 79%, corresponding to total product concentrations of 5.23 and 5.85 g/L, respectively. In the 40 degrees C batch experiment, the volumetric productivity (2-PE + 2-PEAc) during the exponential phase was 5.2 mmol/L h. While for 2-PE, there is still potential for further optimization, the more hydrophobic 2-PEAc was nearly completely removed from the aqueous culture broth (enrichment factor >400), resulting in highly aroma-enriched permeates. Due to the temperature-correlated performance of the pervaporation, the bioconversion was still efficient even at 45 degrees C (conversion yield: 69%). Surprisingly, at 45 degrees C, the molar ratio of the two products inverted and 2-PEAc turned out to be the main product (4.0 g/L), which opens easy control of the reaction's selectivity by external means. Retrofitting the process with interim heating and cooling equipment to use different temperature levels for cultivation and pervaporation resulted in a decreased yield and product concentration caused by multiple stress factors. The medium composition affected the pervaporation efficiency with molasses acting detrimental.

D-Mannitol formation from D-glucose in a whole-cell biotransformation with recombinant Escherichia coli

Abstract: Recently, we reported on the construction of a whole-cell biotransformation system in Escherichia coli for the production of D: -mannitol from D: -fructose. Supplementation of this strain with extracellular glucose isomerase resulted in the formation of 800 mM D: -mannitol from 1,000 mM D: -glucose. Co-expression of the xylA gene of E. coli in the biotransformation strain resulted in a D: -mannitol concentration of 420 mM from 1,000 mM D: -glucose. This is the first example of conversion of D: -glucose to D: -mannitol with direct coupling of a glucose isomerase to the biotransformation system.

Modelling oxide scale fracture

Abstract: In the present paper the approaches to modelling scale failure described in EPRI report FP 686 are compared to a more recent approach based on micromechanical considerations. The latter requires a ...

Oxidation behaviour of particle reinforced MoSi2 composites at temperatures up to 1700 °C: Part I: Literature review

Abstract: In the first part of this paper the results of a literature review are presented. An overview of the oxidation behaviour in air and in combustion environments of both pure MoSi 2 and MoSi 2 composites in the temperature range from 400 to 1650 °C is given. The second part of this paper reports about our results from oxidation tests with selected MoSi 2 composites (containing 15 vol.-% Al 2 O 3 , Y 2 O 3 , ZrO 2 , HfO 2 , SiC, TiB 2 , ZrB 2 , or HfB 2 , respectively) from different development stages at temperatures in the pest region as well as up to 1700 °C. The third part describes the oxidation behaviour of the optimised MoSi 2 composites developed on the basis of the results from part II.

Ion exchange properties and selectivity of PSS in an electrochemically switchable PPy matrix

Abstract: A composite of polypyrrole (PPy) and polystyrenesulfonate (PSS) exchanges cations and is a promising material for the technical application of water softening. The ion exchange properties of electrochemically prepared PPy(PSS) are studied by investigating the polymer using a electrochemical quartz crystal microbalance (EQCM) and by analysing the solution surrounding the polymer by atomic adsorption spectroscopy (AAS). The exchange of cations by PPy(PSS) is found to be caused by three driving forces: electrochemical oxidation/reduction of PPy; chemical oxidation of PPy by dissolved oxygen; gradients of cation concentration between polymer and solution. The ion selectivity of PPy(PSS) is investigated and ion exchange isotherms for the binary systems Ca2+/Na+ and Ca2+/Mg2+ are determined.

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

Abstract: Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 °C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic-martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe 2 Al 5 or FeAl phases were thus developed for deposition temperatures between 650 and 715 °C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe 2 Al 5 coatings at 550 °C. Furthermore, Si or codiffusion Al-Si coatings were developed at temperatures as low as 550 °C.

Gaseous corrosion of alloys and novel coatings in simulated environments for coal, waste and biomass boilers

Abstract: The reduction of emissions from power generation plants is a key part of the Kyoto Protocol Reduced emissions per unit of power produced can be achieved via increased thermal efficiency and this can be achieved by increasing steam parameters (ie temperature and pressure) Increased steam parameters in turn leads to accelerated corrosion of boiler components Biomass and solid waste fuels introduce a number of aggressive species into process environments that result in enhanced rates of boiler degradation This paper reports on studies, both theoretical and experimental, of the corrosion behaviour of high-alloy steels and Ni-base alloys as well as coatings for use in high efficiency coal and/or biomass- and waste-fired power plants Coatings produced within the SUNASPO project have been laboratory tested in gaseous atmospheres representative of coal combustion, biomass combustion and waste incineration Laboratory tests were carried out mainly in the temperature range 500 °C to 800 °C Initial results showed the poor performance of traditional uncoated low-alloy boiler steels P91 (9% Cr) and HCM12A (12% Cr), as well as the higher alloy steel, 17Cr/13Ni Results show the beneficial effects of coatings containing Al, Si, Al + Si, Al + Ti and Al + B in reducing the rate of corrosive attack In a combustion product gas containing 100 ppm HCl and 1000 ppm SO2, aluminizing affords corrosion resistance of low-alloy steels such as HCM12A and P91 similar to that of Alloy 800 over 1000 h of test The presence of Al inhibits internal, sometimes localized corrosion by promoting the formation of a protective surface oxide layer even at relatively low temperatures The results of experiments in simulated coal; biomass and waste atmospheres are presented and discussed in terms of both corrosion kinetics and mechanisms of degradation

Application of ion beam analysis for the control of the improvement of the oxidation resistance of TiAl at 900 °C in air by fluorine ion implantation and HF-treatment

Abstract: The oxidation resistance of TiAl at elevated temperatures >750 °C can be improved by the addition of small amounts of fluorine. The fluorine is applied in two ways: ion implantation and wetting with diluted HF. Using non-destructive Ion Beam Analysis the fluorine depth concentration profiles in the near surface region are determined before and after oxidation. The fluorine maximum is found to be at the metal/oxide interface, which supports the theoretical explanation of the fluorine microalloying effect. The time dependent behaviour of the fluorine content is characterized by a fast decrease of the fluorine concentration during the first hours of oxidation followed by a moderate decrease. The results offer the possibility for a technical application of the fluorine microalloying effect to improve the oxidation resistance of TiAl-alloys at temperatures >750 °C.

Steam oxidation and its potential effects on creep strength of power station materials

Abstract: The oxidation behaviour of several commercial alloys in simulated steam was investigated and compared with that of model alloys with systematic variations of selected alloying elements in the temperature range of 550' C to 650 °C Also, creep tests of specimens pre-oxidized in steam or in flue gas were carried out in order to study the interaction between creep and corrosion The corrosion products were characterised by optical microscopy, XRD, SEM/ EDX and Raman spectroscopy It was found that the oxidation resistance of the materials increased with increasing chromium content High chromium materials exhibited the best oxidation behaviour, whereas the low chromium materials formed thick, multilayered oxide scales, prone to spallation Anomalous temperature dependences were found in materials with intermediate chromium contents Creep tests showed a significant reduction in the creep strength of both alloys was caused by a 1000 h thermal exposure treatment at 650 °C for P92 and at 800 °C for Alloy 800 An additional, though much smaller reduction in strength was observed for the specimens that had been oxidized for 1000 h at 650 or 800 °C prior to testing Further testing is required for confirmation of this effect

The halogen effect for improving the oxidation resistance of TiAl-alloys

Abstract: Alloys based on TiAl intermetallics are potential candidates for high temperature applications in e.g. aero engines or automotive engines because of their low specific weight and good high temperature strength. To improve their oxidation resistance at temperatures up to 1000°C the halogen effect offers an innovative and cost-effective way. The addition of small amounts of halogens into the surface leads to the preferential formation of gaseous aluminium halides which are oxidised to aluminium oxide during their outward migration forming a dense, protective and slowly growing alumina scale on the surface. In this paper two methods were used to apply halogens to the surface, ion implantation (F and Cl) and a liquid phase process (F). Ion beam analysis with detection limits in the ppm-range was applied to quantify the needed amount of halogens to achieve the halogen effect. Thermocyclic oxidation experiments at 900°C were performed in laboratory air and wet air. Depth concentration profiles of fluori...

Oxidation behaviour of particle reinforced MoSi2 composites at temperatures up to 1700°C.

Abstract: The financial support of these investigations by the Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie (BMBF) (contract number 03 N 2015 C1) is gratefully acknowledged by the authors.

Performance and thermal stability of Pt-modified Al-diffusion coatings for superalloys under cyclic and isothermal conditions

Abstract: In this paper, the influence of the platinum content on the cyclic oxidation resistance at 1150°C of Pt-aluminide coatings deposited on a single crystal Ni-based superalloy is reported. The different coatings involve the well-known bi-phase (Ni,Pt)Al and PtAl2 as well as single phase (Ni,Pt)Al coatings with various compositions and microstructures. The results showed that the cyclic oxidation performance depends strongly on the average Pt-content present in the coating and, to a lesser extent, on the coating microstructure. Moreover, no relevant effect of the Al content could be evidenced. Surface deformation occurred during exposure and was attributed to phase transformations within the coating. This assumption was confirmed by isothermal experiments between 1050 and 1200°C. Post-experimental investigations of tested specimens were performed by optical and scanning electron microscopy, X-ray diffraction and EPMA.

The erosion‐corrosion resistance of uncoated and aluminized 12% chromium ferritic steels under fluidized‐bed conditions at elevated temperature

Abstract: In this paper, some results from a study of the erosion-corrosion resistance of uncoated and aluminized 12% chromium steel in a fluidized-bed rig are reported. The aims of the research are to establish and compare the erosion-corrosion resistance of these materials for possible applications as heat exchangers in future power plants, and to obtain an increased understanding on their behaviour and mutual superiority in a range of conditions. Damage to the uncoated 12% chromium steel occurs by an oxidation-affected erosion process under all the studied conditions, with spallation of scale being the primary mechanism of material wastage. At a temperature of 550 °C, the uncoated steel follows the typical angle-dependence of a brittle material, while, at temperatures above 550 °C, it follows an angle-dependence that is more typical of a ductile material. This change in the angle-dependence with temperature is related to characteristics, i.e. uniformity, adhesion and density, of the formed oxide scales. The rate of material wastage increases with increase in speed and temperature, due to the development of thicker, more uniform and more dense oxide scales, that promote more severe scale spallation. The erosion-corrosion behaviour of the aluminized 12% chromium steel changes in the temperature range from 600°C to 650 °C. This is due to a shift from a brittle-like to a ductile-like angle-dependence and to a more rapid oxide scale build-up at temperatures above 600 °C. At an impact angle of 30° and at 550 °C and 600 °C, the prevailing erosion-corrosion process for the aluminized steel is oxidation-affected erosion. At 650 °C and 700 °C for an impact angle of 90°, the primary erosion-corrosion mode is essentially erosion-enhanced oxidation. The results of the study have also demonstrated that the Al 5 Fe 2 coating deposited by pack aluminization offers enhanced protection against erosion-corrosion at shallow impact angles at 550 °C and 600 °C and at steeper impact angles at 700 °C.

Charme und Chancen der Weißen Biotechnologie

Abstract: Die Weise Biotechnologie ist keine neue Disziplin, sondern fasst nur ein Segment der Biotechnologie zusammen, um sie von den beiden anderen grosen Segmenten – der Roten und der Grunen Biotechnologie – abzuheben. Sie ist in den Fokus geraten, weil bahnbrechende Verfahren zur Analyse biologischer Systeme eine Neubetrachtung der Potenziale der Biotechnologie zur Folge haben. Neue Entwicklungen sind abzusehen, wie uber genombasierte Daten mit Hilfe der Bioinformatik, der Molekularbiologie und der Bioverfahrenstechnik Prozesse in ganzheitlicher Betrachtung optimiert werden. Wegen relativ einfacher biologischer Systeme, aber vielfaltiger Anwendungen wird die Weise Biotechnologie als Vorreiterdisziplin ins Feld gefuhrt. Durch die Forderung interdisziplinarer Ansatze zur integralen Prozessentwicklung sollte die biotechnologisch orientierte Industrie in weitem Mase profitieren. Dies gilt insbesondere fur das wissenschaftliche Umfeld und die kleinen und mittleren Unternehmen, die mehr und mehr vom Zugang zu den modernen Methoden der Biotechnologie abhangen. Im internationalen Rahmen ist gerade auf dem Gebiet der Weisen Biotechnologie eine konkurrenzfahige Situation in Deutschland festzustellen. Es bedarf jedoch einer nachhaltigen und langfristigen Unterstutzung, damit sowohl die Wissenschaft als auch die Industrie nicht den Anschluss an die internationale Entwicklung der Weisen Biotechnologie verlieren.

Oxidation behaviour of particle reinforced MoSi2 composites at temperatures up to 1700°C. Part II: Initial screening of the oxidation behaviour of MoSi2 composites

Abstract: The financial support of these investigations by the Bundes-ministerium fu¨r Bildung, Wissenschaft, Forschu ng und Tech-nologie (BMBF) (contract number 03 N 2015 C1) is gratefullyacknowledged by the authors.

The effect of water vapor in increasing growth stresses in the oxide scale on martensitic steam plant alloys

Abstract: Investigation of the oxidation behavior of 9% Cr steels at 650°C in dry air and air + 10% H2O have shown that oxide scale growth stresses may play a significant role in breakaway. For this reason, preliminary studies on the development and characteristics of growth stresses in oxides on these materials have begun. These studies include in situ acoustic emission (AE) for monitoring scale cracking, deflection testing in monofacial oxidation (DTMO) and in situ X–ray measurements. The measurements were complemented by detailed post-experimental metallographic investigations.From the DTMO measurements the stresses in the oxide on the specimens tested in humid environment are increased by about a factor of 5 compared to dry air at the beginning of oxidation for P91. In a humid environment the stresses decrease with oxidation time while in dry air they remain almost constant. Significant acoustic emission (AE) occurs in humid air for oxidation coupons while virtually no AE is observed for thin foils in a...

Potential-controlled chromatography for the separation of amino acids and peptides

Abstract: Potential-controlled chromatography is introduced as a new technique for the separation of amino acids and peptides. The principle of potential-controlled chromatography depends on the use of electrically conductive material as the stationary phase of the chromatographic column. Thus from an electrochemical point of view the packed column can be regarded as a packed-bed electrode. The electrical potential of this stationary phase can be controlled by a potentiostat. The separation of amino acid and peptide molecules during their migration through the column depends on their own electric charge on the one hand and on the electrical potential of the stationary phase on the other. The chromatographic separation of some amino acids could be demonstrated.

Fermentative production of aroma and/or flavor materials from amino acid in bioreactor, comprises forming Saccharomyces/Kluyveromyces two phase system having aqueous growth medium with water, which is not miscible with polypropylene glycol

Abstract: The glycol has a molecular weight of 1200-1800. The amino acid used is phenylalanine in a large quantity, which separates in the aqueous phase by bio converting reaction. Carbon source and vitamins for cell growth and minerals are added to the growth medium. The ratio of glycol is 1:1. The process further comprises separating the emulsion by constant agitating and centrifuging.

Verfahren zur Vermeidung oder Verminderung von Biofilmen auf einer Oberfläche

Abstract: Es wird ein Verfahren zur Vermeidung oder Verminderung von Biofilmen auf Oberflachen beschrieben, bei dem die Oberflache von Membranen oder anderen nicht elektrisch leitfahigen Oberflachen in wassrigen Losungen durch eine leitfahige Beschichtung polarisierbar wird.

Nitrogen Self-Diffusion in Polycrystalline Si3N4 Films: Isotope Heterostructures vs. Gas-Exchange

Abstract: The self-diffusion of nitrogen is investigated in polycrystalline thin silicon nitride films using a gas-exchange method (14N2/Si3 15N4) in comparison to Si3 14N4/Si3 15N4/Si3 14N4 isotope heterostructures. The films are produced by reactive r. f. magnetron sputtering. Depth profile analysis is carried out with secondary ion mass spectrometry (SIMS), secondary neutral mass spectrometry (SNMS), and nuclear resonant reaction analysis (NRRA). The nitrogen diffusivities determined with the use of isotope heterostructures follow an Arrhenius law in the temperature range between 1200 and 1700 °C with an activation enthalpy of DH = 4.9 eV and a pre-exponential factor of D0 = 1 x 10-6 m2/s, indicating a conventional diffusion mechanism via localized point defects. Using the gas-exchange method, the nitrogen diffusivities could be obtained only in the temperature range between 1600 and 1700 °C. This is due to the fact that at temperatures below 1600 °C the surface exchange process with its high activation enthalpy (about 10 eV) is rate limiting, leading to non detectable diffusion profiles. The application of the different methods of depth profiling leads to the same diffusivities within estimated errors.