Showing papers by "DECHEMA published in 2001"
TL;DR: In this article, the authors discuss two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst.
Abstract: Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide. Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year. Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation, is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst. Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water. The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.
467 citations
TL;DR: In this article, the ion exchange behavior and capacity of electrochemically and chemically prepared polypyrrole (PPy) in dependence on the incorporated counterions are characterized using an electrochemical quartz crystal microbalance and cyclovoltammetry.
107 citations
TL;DR: In this article, the preparation and modification of conducting polymer films as electrocatalysts for anodic hydrogen oxidation was investigated, and the catalytic activity of the modified films was derived from polarisation curves of hydrogen oxidation using rotating disk electrode technique.
104 citations
TL;DR: The catalytic activity of polypyrrole films prepared in different ways was studied for the methanol oxidation reaction in this paper, where the platinum load, film thickness and potential of platinum deposition were found to be important parameters.
Abstract: The catalytic activity of platinum modified polypyrrole films prepared in different ways was studied for the methanol oxidation reaction. Surprisingly, no catalytic activity was observed for films modified with colloidal platinum particles incorporated into the film during its synthesis or for the film synthesised with tetrachloroplatinate complex as a nucleophilic counter-ion, which was subsequently cathodically reduced. On the other hand, high catalytic activity was observed for platinum deposited onto pre-synthesised polypyrrole film. The platinum load, film thickness and potential of platinum deposition were found to be important parameters. High electrocatalytic activity was also observed for platinum layers deposited directly onto the glassy carbon (GC) support. However, in the latter case the stability of the electrocatalytic activity was lower when compared with the polypyrrole film modified by cathodically deposited Pt.
75 citations
TL;DR: The crystal structure of Cellosyl from S. coelicolor exhibits a new lysozyme fold and represents a new class of polysaccharide-hydrolyzing β/α-barrels.
67 citations
TL;DR: By circumventing inhibiting product concentrations and thus intensifying aroma production, total yield of aroma compounds produced is higher in an IBP compared with batch cultivation and permeates obtained from pervaporation consist of highly enriched mixtures of produced flavors and fragrances.
60 citations
TL;DR: In this paper, high-temperature permeation tests (350-650°C) were carried out to determine the permeation properties as well as the thermal and mechanical stability of the prepared membranes.
53 citations
TL;DR: In this article, a catalytic membrane contactor for selective hydrogenation of nitrate in water to nitrogen is discussed as a promising new approach to develop a technically feasible catalytic process for nitrate reduction from ground and surface water.
38 citations
TL;DR: In this article, a modified four-point bending test is described, which allows a quantitative determination of the mechanical properties of oxide scales on metallic substrates at temperatures from ambient to 900°C.
Abstract: In this paper, a modified four-point bending test is described, which allows a quantitative determination of the mechanical properties of oxide scales on metallic substrates at temperatures from ambient to 900°C. Scale failure is detected by acoustic emission. By combining deformation data with the physical defect-structure values for the scales, fracture toughnesses have been evaluated for the cases of through-scale cracking and delamination/spalling. The test was applied to NiO scales on pure nickel and to the oxide scales on an intermetallic TiAl alloy at room temperature and 900°C, respectively. The fracture-toughness values determined in these investigations correspond to the order of magnitude expected from the rare literature data. The test itself can also be applied to a variety of brittle coatings on more-or-less ductile substrates.
29 citations
TL;DR: In this paper, the authors provide an overview of the materials that are suitable for long term service in oxidizing atmospheres at temperatures of 1500 °C and higher, and provide a sufficient stability against the surrounding environment, low vapor pressure of the material or reaction product formed and sufficient creep resistance.
Abstract: In the first part of this paper the results of a literature review are presented. Here we provide an overview of the materials that are suitable for long term service in oxidizing atmospheres at temperatures of 1500 °C and higher. Criteria are a sufficient stability against the surrounding environment, low vapor pressure of the material or the reaction product formed and sufficient creep resistance. A further aspect is that reactions between contacting materials of different compositions should not lead to the formation of low melting eutectics at the contact areas. The second part reports about results from thermogravimetric measurements on the oxidation resistance of several potential materials. The third part deals with the experimental investigations concerning the contact-corrosion of selected high-temperature resistant materials (Al 2 O 3 , ZrO 2 , CeO 2 , La 2 O 3 , Y 2 O 3 , HfO 2 , and the Spinel (MgO.Al 2 O 3 )) in direct contact with a SiO 2 -scale forming material (MoSi 2 ) at 1600 °C in air, since most of the potential materials for such high temperatures are silica formers. Parts II and III will appear in the next 2 issues of this journal.
27 citations
TL;DR: In this paper, the authors described the key mechanical properties of oxide scales with regard to model equations and investigation methods and introduced a universal mechanical properties diagram, which describes fracture and creep behavior of the oxide scales.
Abstract: The present paper describes the key mechanical properties of oxide scales with regard to model equations and investigation methods. Modified test methods are introduced for the determination of values describing scale failure, growth stresses in oxides and creep of the scales. Furthermore, a summary of scale fracture data from the literature is given. As a conclusion it is discussed that failure strains of oxide scales can be estimated from the model equations and using basic mechanical property data like fracture toughness and geometrical scale parameters as physical defect size, interface roughness, scale thickness etc. without complicated mechanical tests. In the end a universal mechanical properties diagram is introduced, which describes fracture and creep behavior of the oxide scales.
TL;DR: In this article, two types of sensor applications using polypyrrole (PPy) as the active material will be considered, i.e., measurement of the pH or detection of iron in aqueous solutions.
Abstract: In this study two types of sensor applications using polypyrrole (PPy) as the active material will be considered. The fisrt part deals with the development of a new type of pH glass electrode, where PPy is used as a mixed electron/ion conductor, to replace the conventional liquid junction reference electrode in a buffer electrolyte solution by an all-solid-state contact interface. The second part deals with PPy as an ion-sensitive material for the development of a potentiometric sensor, e.g. for the measurement of the pH or the detection of iron in aqueous solutions.
Patent•
11 Oct 2001TL;DR: The use of a liquid solution of hydrogen fluoride to treat the surface of aluminum and titanium alloys to improve the oxidation resistance of the alloys between 800-1100 deg C is new as discussed by the authors.
Abstract: Use of a liquid solution of hydrogen fluoride to treat the surface of aluminum and titanium alloys to improve the oxidation resistance of the alloys between 800-1100 deg C is new
TL;DR: The formation of biofilms in a waste paper medium was studied in a pilot plant by analysing the redox potential in the biofilm by applying miniaturised redox electrodes at the reactor wall/biofilm phase boundary.
Abstract: The formation of biofilms in a waste paper medium was studied in a pilot plant by analysing the redox potential in the biofilm. Miniaturised redox electrodes were applied at the reactor wall/biofilm phase boundary. With this measurement set-up, it was possible to demonstrate the effectiveness of biocides and thus to avoid under- and over-doses with these agents. The redox signals measured were correlated with reference methods, such as colony-forming units and dehydrogenase activity.
TL;DR: In this paper, a literature survey had been performed leading to the conclusion that either particle or fiber reinforced MoSi 2-based materials or RSiC coated with a MoSi2-based layer are suitable for applications at such high temperatures.
Abstract: The topic Materials for temperatures above 1500 °C in oxidizing atmospheres is discussed in a 3 part publication. In the first part a literature survey had been performed leading to the conclusion that either particle or fiber reinforced MoSi 2 -based materials or RSiC coated with a MoSi 2 -based layer are suitable for applications at such high temperatures. In the present part such material systems are investigated experimentally at 1500 and 1600 °C with respect to their oxidation resistance in air. Particular interest was given to the influence of the Mo 5 Si 3 content in MoSi 2 and the influence of second phase particles in MoSi 2 consisting of ZrB 2 and SiC. Furthermore, the oxidation resistance of several dip-coatings on RSiC which were manufactured from a polysiloxane precursor by subsequent pyrolysis were also investigated. Part III which reports about contact corrosion between different materials at these temperatures will follow in the next issue.
Patent•
22 May 2001TL;DR: In this paper, a Verfahren zur biotechnologischen erzeugung von Duft-and/oder Aromastoffen vorgeschlagen, umfassend eine Bioreaktoreinrichtung, an der in einer Flussigphase infolge mikroorganismen- und/oder enzymindierter Stoffumwandlungsprozesse die Duft and/oder aromastoffebgereicherte Phase darstellt,
Abstract: Es wird ein Verfahren zur biotechnologischen Erzeugung von Duft- und/oder Aromastoffen vorgeschlagen, umfassend eine Bioreaktoreinrichtung, an der in einer Flussigphase infolge mikroorganismen- und/oder enzyminduzierter Stoffumwandlungsprozesse die Duft- und/oder Aromastoffe erzeugt werden, sowie eine angeschlossene Pervaporationseinrichtung, in der die Zielprodukte kontinuierlich oder sequentiell aus der Flussigphase isoliert werden, wobei das Retentat, das die duft- und/oder aromastoffabgereicherte Phase darstellt, wenigstens teilweise in die Bioreaktoreinrichtung zuruckgefuhrt wird. Das Verfahren wird bei Prozestemperaturen > 25° C unter Verwendung thermotoleranter und/oder thermophiler Mikroorganismen und/oder Enzymen durchgefuhrt.
TL;DR: In this article, the contact reactions of MoSi 2 with 10 other high temperature oxide based structural materials were investigated at 1600 °C in air and the results are mainly documented by microprobe investigations with respect to the contact reaction products formed.
Abstract: The topic Materials for Temperatures above 1500 °C in Oxidizing Atmospheres is discussed in a 3 part publication. In the first part [1] a literature survey had led to two potential material systems consisting either of particle reinforced MoSi 2 or of a MoSi 2 based oxidation resistant coating on creep resistant RSiC. Both systems were verified experimentally in a second publication [2] including the development of optimum oxidation resistant MoSi 2 composite materials and of an optimum coating system on RSiC. The present part deals with the contact corrosion behavior of these silica formers if other refractory materials are used in combination with these material systems as it is often the necessity in practical applications. Therefore, the contact reactions of MoSi 2 with 10 other high temperature oxide based structural materials were investigated at 1600 °C in air. The results are mainly documented by microprobe investigations with respect to the contact reaction products formed. It was found that only two material combinations are conceivable for long-term use in contact with MoSi 2 . The results are in agreement with the considerations discussed in part one of this publication [1].
Journal Article•
01 Jan 2001
TL;DR: Of all the arguments to be considered when choosing a biotechnical process, improving the process economy is the most important one.
Abstract: Biotechnological processes or process steps can substitute traditionally applied techniques. Of all the arguments to be considered when choosing a biotechnical process, improving the process economy is the most important one.
Patent•
05 Jul 2001TL;DR: In this paper, an elektrochemische Messzelle zur bestimmung der Zellzahl und Aktivitat von biologischen System beschrieben, die mit einer Anode, einer Kathode, deren elektrischen Ableitungen und mit Vorrichtungen zur Messung der Spannung and des Stromflusses ausgerustet ist, wobei das zu untersuchende biologische System zusammen mit e
Abstract: Es wird eine elektrochemische Messzelle zur Bestimmung der Zellzahl und Aktivitat von biologischen System beschrieben, die mit einer Anode, einer Kathode, deren elektrischen Ableitungen und mit Vorrichtungen zur Messung der Spannung und des Stromflusses ausgerustet ist, wobei das zu untersuchende biologische System zusammen mit einem Redoxmediator in einem aus einem Gel bestehenden Tragergerust immobilisiert ist
01 Jan 2001
TL;DR: This study presents the program structure and features, and also test cases on technically relevant reactions, of a program developed to predict the feasibility of applying microreaction technology for a specific synthesis in a microreactor.
Abstract: The practical applicability of microreaction technology is an unsolved problem. A program has been developed for potential users of microreaction technology to predict the feasibility of applying this technology for a specific synthesis in a microreactor. The program consists of two parts. In the first part basic process equations and parameters and a simplified model of the microreactor are used to obtain preliminary information on the applicability of the microreactor. The second part provides a more detailed consideration of the potential of applying a microreactor, using a detailed microreactor model (CPU intensive). This study presents the program structure and features, and also test cases on technically relevant reactions.