Showing papers by "DECHEMA published in 1998"

Electrochemical measurements of the ion conductivity, permselectivity and transference numbers of polypyrrole and polypyrrole derivatives

Abstract: Electrochemical dc and ac measurements were carried out on free-standing polypyrrole (ppy) membranes to study the ion conductivity and permselectivity of the polymer as a function of the oxidation state. The membranes were prepared by electropolymerisation and mounted in a two-compartment cell, where the oxidation state of the ppy membrane could be adjusted by potentiostatic polarisation and the ion conductivity and permselectivity of the polymer could be measured in a symmetrical electrolyte/membrane/electrolyte configuration. Combining constant current permeation experiments with solution analysis using ion chromatography (IC) and atomic absorption spectroscopy (AAS), it was demonstrated that ppy exhibits not only an appreciable ion conductivity but also a distinct permeability and selectivity for anions in the oxidised state. Incorporation of immobile anions like dodecylsulfate or copolymerization with a modified pyrrole monomer like N-sulfopropyl-pyrrole carrying a sulfonate group leads to modified membranes which exhibit distinct cation permselectivity in the reduced state. Such a membrane can be switched dynamically between anion and cation permeability through electrochemical oxidation and reduction of the polymer backbone.

Dynamic modelling of gas hold-up in different electrolyte systems

Abstract: In measurements of gas hold-up of oxygen and hydrogen as a function of the gas flow rate it was found that the gas hold-up epsiv(ug0) depends on the type of electrolyte and its concentrations as well as on the type of gas. Using an ultrasonic Doppler velocimeter, bubble rise velocities were investigated. It was observed that the single bubble rise velocity in electrolyte solutions depended strongly on the concentration. A model, developed to take into account the impediment to coalescence by electrolytes, was used to evaluate the dependence of gas hold-up on electrolyte concentration. An almost linear correlation between the system specific parameter, epsivmax, of this model and the ionic strength was found. However, this correlation is not too accurate and can only be seen as a rough approximation. Experimental results indicate that another mechanism is responsible for the dependence of the gas hold-up on electrolyte concentration. Thus, a new model was derived, which incorporated results of measurements of bubble rise velocities. This model was also applied to describe the gas hold-up in different electrolyte solutions as a function of gas flow rate. It also includes a system-specific parameter. The dependence of this parameter on the concentration of electrolytes was found to be in accordance with current theories on the bubble coalescence.

Electrochemical Study of NO Conversion from Fe(II)‐EDTA‐NO Complex on Pt Electrodes

Abstract: The Fe(II)-ethylenediaminetetraacetic acid (EDTA)-NO complex formed by interaction of gaseous nitrous oxide (ca. 200 ppm) and Fe(II)-EDTA in aqueous solution was found to be convert3ed electrochemically on platinum electrodes at potentials below ca. {minus}0.6 V{sub SCE}, indicating the cathodic reduction of NO. In addition to the previous studies by which the indirect conversion of NO with dithionite as a redox mediator was confirmed, the present results should elucidate the possibility of the direct electrochemical conversion of NO in mediator-free solutions. To clearly separate this process from other reactions in the system, the electrochemical behavior of Fe(II)-EDTA and Fe(III)-EDTA was studied over a wide potential range at different pH values. Five electrode reactions could be identified, which include the oxidation/reduction of Fe{sup 2+}/Fe{sup 3+} in the EDTA complex, the reduction of EDTA, the reduction of protons, the cathodic deposition of iron, and the anodic decomposition of EDTA. The electrochemical deposition of iron from Fe(II)-EDTA at potentials E < {minus}1.0 V{sub SCE} was confirmed by electrochemical quartz crystal microbalance measurements and energy-dispersive x-ray analysis.

Numerische Untersuchungen zur optimalen Wärmeleitfähigkeit in Mikrowärmeübertragerstrukturen

Abstract: Proposition d'une modelisation du transfert de chaleur dans les micro-echangeurs de chaleur

Application of an alloy from aluminium and titanium

Abstract: of EP0906967An alloy of aluminum and titanium is used as a high temperature corrosion resistant coating material of heat resistant steels in installations with process gases which have a very low partial pressure of oxygen and, as consequence of carbon compounds in their composition, possess a high carbon activity. The claimed coating material has an atomic aluminum content amounts to 22-56 %.

Eine Querschnittstechnologie drängt zum Markt: Die Möglichkeiten der modernen Biotechnologie†

Abstract: Any attempt to explain the term modern biotechnology and to distinguish it from classical biotechnology soon reveals that the boundary is anything but distinct and frequently disappears in a terminological fog. Things only become easy when modern biotechnology can be defined as using the methods and processes of genetic engineering. This is indeed often the case, but not always. Modern biotechnology embraces advances in process engineering as well as new developments in equipment ; it depends on monoclonal antibodies and new cell culture techniques, it benefits from advances in embryonal transfer in the animal kingdom and also from cloning; it is taking over large areas of environmental engineering. This list could be continued. Processes of classical biotechnology are always involved in the production of a modern biotechnological product. It is ultimately irrelevant to the engineer whether a fermenter contains genetically engineering microorganisms or not; or to the farmer whether the potatoes he grows are genetically modified or not. There can be no modern biotechnology without classical biotechnology - and the reverse will soon also be true.

Protective Coatings for High Temperatures and High Sulphur-Low Oxygen Environments

Abstract: Different coatings based on MoSi{sub 2}, TiAl or FeSi were applied by air plasma spraying (APS) to low alloy steel and tested at 700 C in an atmosphere of pS{sub 2} = 10{sup {minus}6} bar and pO{sub 2} = 4.2 {times} 10{sup {minus}27} bar which is representative for atmospheres in certain industrial gasification processes. Tests were run isothermally and with thermal cycling for times up to 1000 hrs. In particular coatings based on TiAl provide a significant improvement of sulfidation resistance.

Spalten von Vakuumgasöl an mikro- und mesoporösen Katalysatorsystemen†

Abstract: Cf Article en Anglais dans Chemical Engineering & Technology, 1998, Vol 21, No 5, pp. 401-403.