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Showing papers by "DECHEMA published in 1981"


Journal ArticleDOI
J. Fischer1, Th. Lehmann1, Ewald Heitz1
TL;DR: In this article, the oxalic acid has been prepared on a preparative scale in an undivided cell with sacrificial anodes and an aprotic electrolyte, and the optimum current efficiencies have been obtained in cells with zinc anodes, stainless steel cathodes and acetonitrile with tetrabutylammonium perchlorate as the electrolyte.
Abstract: Oxalic acid has been prepared on a preparative scale in an undivided cell with sacrificial anodes and an aprotic electrolyte. Optimum current efficiencies (>90%) have been obtained in cells with zinc anodes, stainless steel cathodes and acetonitrile with tetrabutylammonium perchlorate as the electrolyte. Micro-pilot experiments revealed that a continuous electrochemical cell can be set up and that the reaction product can be removed by filtration. A complete process is designed by a combination of the oxalic acid production with a zinc electrolysis. No unwanted by-products appear, which is recently of increasing importance. Economic consideration shows that the process may become interesting in the future.

99 citations


Journal ArticleDOI
W. F. Chu1, A. Rahmel1
TL;DR: In this paper, the thermodynamic equilibria between chromium oxide, chromium carbide, and a CO-CO2 mixture were calculated for various conditions, and the conversion rate was low and was strongly dependent on the carbon activity.
Abstract: The thermodynamic equilibria between chromium oxide, chromium carbide, and a CO-CO2 mixture was calculated for various conditions. Experimental results on the rate of the Cr2O3 conversion to chromium carbide in CO-CO2 mixtures at 1200°C are reported. The conversion rate was low and was strongly dependent on the carbon activity.

39 citations



Journal ArticleDOI
TL;DR: In this article, the resolution in high-performance liquid affinity chromatography was studied using proteases as eluites and soy bean trypsin inhibitor immobilized on aminosilanized LiChrospher as a biospecific adsorbent.

31 citations


Journal ArticleDOI
W. F. Chu, A. Rahmel1
TL;DR: In this article, the scaling of an Fe-20Cr alloy was studied in H2-H2O-H 2S mixtures between 973 and 1223 K. The reaction followed a mixed rate law between linear and parabolic, indicating that the reaction rate at the scale-gas interface was comparable with the diffusion rate in the scale.
Abstract: The scaling of an Fe-20Cr alloy has been studied in H2-H2O-H2S mixtures between 973 and 1223 K. According to a simplified phase diagram, Cr2O3 and FeS should be the thermodynamically stable compounds in the gas mixtures chosen. The reaction followed a mixed rate law between linear and parabolic, indicating that the reaction rate at the scale-gas interface was comparable with the diffusion rate in the scale. At a constant H2/H2S ratio the scaling rate initially decreased slightly with increasing water-vapor pressure. A further increase of the water-vapor pressure resulted in localized sulfide formation, while the other parts of the surface were covered with a Cr2O3 film. Only Cr2O3 formed above a critical water-vapor content. Three zones could be distinguished when a sulfide scale is formed. The outer zone consisted of practically pure FeS; the intermediate zone was a solid solution of (Fe,Cr)S, partially decomposed to FeCr2S4 and metal during cooling; and the inner zone contained small Cr2O3 inclusions in an (Fe,Cr)S matrix.

15 citations


Journal ArticleDOI
K. Ledjeff, A. Rahmel1, M. Schorr1
TL;DR: In this paper, a fine-and coarse-grain 25Cr-20Ni steel was compared with a cast steel of similar composition in synthetic air between 900 and 1300°C and showed a strong influence of grain growth in the base metal on the oxidation behavior.
Abstract: Comparative oxidation tests with a fine- and a coarse-grain 25Cr-20Ni steel, and cast steel of similar composition in synthetic air between 900 and 1300°C reveal a strong influence of grain growth in the base metal on the oxidation behavior. Metal grain growth destroys the protective Cr2O3-rich scale, and promotes the formation of a scale rich in iron oxides. The result is a higher scaling rate, and a higher Cr depletion at the metal-scale interface of the fine-grain material which undergoes grain growth during oxidation.

14 citations


Journal ArticleDOI
TL;DR: In this paper, the distribution of non-metallic impurities, O, N, and C, and the phases which they form with the metallic constiturents as found by electron beam micro analysis and transmission electron microscopy are discussed.
Abstract: The preparation of magnets with energy products of up to 30 MGOe from Sm(Co, Cu, Fe, M)z alloys with M=Ti or Zr and z=6.8 or 7.25, respectively, as well as their magnetic properties and microstructures have already been reported on. We describe, in addition, the distribution of the non-metallic impurities, O, N, and C, and the phases which they form with the metallic constiturents as found by electron beam micro analysis and transmission electron microscopy. Ti, Zr, and C combine in forming the very stable carbides TiC and ZrC. The possible role of these carbides in regard to the magnetic properties is discussed.

4 citations


Journal ArticleDOI
Reiner Eckermann1
TL;DR: The DETHERM as discussed by the authors is a data bank for physical property data of chemical compounds and mixtures, which allows the retrieval of literature data, the algebraic manipulation of retrieved data, data calculations and estimations, data analysis, and connection with data processing systems.
Abstract: DETHERM, eine Datenbank fur thermophysikalische Daten chemischer Verbindungen und Gemische fur die Stoffdatenversorgung von Ingenieuren, wird beschrieben Damit sind Recherchen nach Literaturwerten, algebraische Datenmanipulationen und -umformungen, Datenberechnungen und -schatzungen, Datenanalysen sowie die Verknupfung mit Stoffdaten verarbeitenden Programmen moglich In der Datenbank sind numerische und bibliographische Daten gespeichert, die Art der Daten und Stoffe wird durch „Tags” gekennzeichnet A physical property data bank for chemical engineering DETHERM, a data bank for physical property data of chemical compounds and mixtures as required by chemical engineers is described, which allows the retrieval of literature data, the algebraic manipulation of retrieved data, data calculations and estimations, data analysis, and connection with data processing systems In the data bank both numerical and non-numerical data are stored, data and substances being labeled by „tags” which characterize the kind of stored data and substances

4 citations


Journal ArticleDOI
TL;DR: A model system is used to study the reaction engineering fundamentals of the biological waste gas scrubbing process, and some kinetic measurements of the biodegradation of pollutants dissolved in the absorbent are presented.
Abstract: A model system is used to study the reaction engineering fundamentals of the biological waste gas scrubbing process, and some kinetic measurements of the biodegradation of pollutants dissolved in the absorbent are presented.

3 citations


Journal ArticleDOI
J. Hessel1, H. E. Bühler1
TL;DR: In this article, a parametric analysis of creep tests under pressure and kind of failure in Thermoplastic Tubes under Chemical Load is presented, which proves that "weeping" takes place much earlier than total failure by rupture.
Abstract: Das Zeitstandverhalten von Thermoplastrohren unter mechanischer, thermischer und chemischer Belastung wird durch den Zeitstandinnendruckversuch gepruft. Dabei werden bei der Versuchsdurchfuhrung in der bisher ublichen Form wesentliche Versagenskriterien nicht erfast. In dieser Arbeit wird im Rahmen einer Parameteranalyse zum Zeitstandinnendruckversuch am Beispiel des Systems LDPE/H2SO4 nachgewiesen, das ein Versagen durch Medienaustritt („Schwitzen”) weit vor dem mechanischen Versagen der Prufkorper durch Bruch stattfindet. Die Betrachtung der Schadigungsmechanismen innerhalb der Rohrwand mit licht- und elektronenmikroskopischen Methoden zeigen, das die Ubertragbarkeit der an relativ kleinen Proberohren ermittelten Zeitstandwerte auf Rohre groserer Dimensionen nicht gegeben sein kann. Dies ist sowohl durch die werkstoffspezifischen Mikrostrukturen teilkristalliner Thermoplaste, als auch durch die herstellungsbedingten Makrostrukturen begrundet. Es werden Versuchsanordnungen vorgeschlagen, die es erlauben, das Versagen von innendruckbelasteten Rohrproben hinreichend zu erfassen. Parametric Analysis of Creep Tests under Pressur and Kind of Failure in Thermoplastic Tubes under Chemical Load Creep tests under pressure are a method to evaluate the long term behaviour of tubes under mechanical, thermic and chemical loading. However, this method does not enclude essential criteria of failure. In form of a parametric analysis this paper proves that “weeping” takes place much earlier than total failure by rupture. Investigations on the different kinds of damage within the tube material using light microscopy and electron scanning microscopy reveal- that it is not correct to transform results of creep tests with small and thin tubes to such of practically used dimensions. This is on the one hand based on the existance of different microstructures which are specific to the semicristalline material and on the macrostructure determined by production process on the other hand. In order to determine failure of tubes sufficiently new test methods are proposed.