Showing papers by "DECHEMA published in 1982"

Relation Between Mass Transfer and Corrosion in a Turbulent Pipe Flow

Abstract: Electrochemical measurements of mass transfer in a turbulent pipe flow are presented. In particular the effect of flow obstacles, such as orifices and circumferential slots with varying diameter and axial length, has been studied. The results also include measurements of mass transfer downstream, a sudden expansion or reduction of the tube diameter. The experiments were performed at a Schmidt number of 1460 and Reynolds numbers ranging between and . The work presented in this paper is a part of a project aiming to study the relation between corrosion and mass transfer at high flow rates with particular emphasis on disturbed turbulent pipe flow.

Optimal design of packed bed cells for high conversion

Abstract: In connection with the electrochemical purification of metal containing waste waters, the realization of a high concentration decrease per pass is one of the goals of design optimization. For a packed bed cell with crossed current and electrolyte flow directions high conversion in conjunction with a large space time yield requires limiting current conditions for the whole electrode. For establishing the concentration profiles in the direction of flow a plug flow model is used. These considerations result in a new packed bed electrode geometry for which an analytical bed depth function is derived. The basic engineering equations of such packed bed electrodes are given, and design equations for different arrangements are developed. The reliability of this scaling-up method is shown by comparison of theoretically predicted and experimental performance data of two cells. Engineering aspects such as easy matching of cells to waste water properties and parametric sensitivity are discussed. Some technical applications are reported.

Reaction engineering parameters for immobilized biocatalysts

Abstract: The article concentrates on those biochemical engineering parameters of immobilized biocatalysts which are considered important with respect to their application in industrial processes Thus swelling behaviour, mechanical stability, pressure drop and abrasion are stressed The effectiveness is discussed in the context of external mass transfer, pore diffusion and enzyme kinetics, including systems with two substrates and two enzymes Properties which affect the operational stability are summarized Selected data from the recent literature are included New concepts directed towards an optimized catalyst design are discussed, emphasizing the effectiveness and productivity

The influence of electrode potential on the corrosion of gas turbine alloys in sulfate melts

Abstract: The influence of the electrode potential on the corrosion behavior of a series of nickel- and cobalt-base gas turbine alloys has been investigated in a (mole %) 53Na2SO4+7CaSO4+40MgSO4 melt at 1073 and 1173 K and in a 90Na2SO4+10K2SO4 melt at 1173 K. Only acidic fluxing is observed in the (Na2,Ca, Mg)SO4 melt at positive potentials while a protective scale rich in MgO is formed on all alloys at negative potentials. This scale prevents basic fluxing because MgO is insoluble in neutral and basic melts. The breakthrough potential for acidic fluxing is a function of the material composition. Increasing chromium content of the alloys extends the potential range of protective film formation. Acidic and basic fluxing are observed in the (Na, K)2SO4 melt. Acidic fluxing occurs at positive and basic fluxing at negative potentials. A protective scale is formed in an intermediate (neutral) potential range on the high-chromium alloys IN-597 and IN-738 LC. Here, too, the breakthrough potentials for acidic and basic fluxing are influenced by the composition of the alloys.

Raman Scattering: Fast Axial Rotation of Methylhalides and Acetonitrile in the Liquid State

Abstract: The temperature dependence of the degenerate methyl stretching Raman profiles of CH3CN, CH3I, CD3I, CH3Cl, and CH3F and, further, for CH3CN the pressure dependence are investigated. The Raman bands are analysed in terms of the small angle diffusion and the J-diffusion model both with and without Coriolis interaction. The comparison with the small angle diffusion model is carried out in the frequency domain. For the analysis in terms of the J-diffusion model, first experimental orientational correlation functions are calculated. Then, by following theoretical arguments, the overall correlation function is decomposed into two partial correlation functions g(2)1(t) and g(2)2(t). There is limited agreement with previous magnetic relaxation studies on the fast axial spinning motion. In particular, it is found that the partial correlation function g(2)2(t) shows little temperature and pressure dependence, which cannot satisfactorily be accounted for by the existing models.

Effects of immobilization on intrinsic kinetics and selectivity of trypsin

Abstract: There is few information available on effects of covalent coupling on the intrinsic kinetics of an enzyme excluding the interference of adsorption and transport phenomena. We present clear evidence for significant shifts in association constants for substrates and inhibitors due to covalent binding onto a rigid support. KM and KI values were changed by factors up to 6 and relative affinities were also different as compared to the native enzyme. Interference by other phenomena like adsorption or diffusion has been excluded. Protection of the enzyme by very strong inhibitors during binding can avoid such alterations. The effect of pH on KI/KM was not observed showing that there is no apparent effect of the solution pH on the relative affinities between pH-values 7 and 9. Similar findings were obtained for the maximal reaction rates.

Mechanisms of Hot Corrosion

Abstract: This paper reviews the results of hot corrosion mechanisms research carried out in Round 2 of COST 50 and sets it in relation to contemporary research outside COST 50.

The identification of the sulfide NaCrS2 in nickel-base superalloys during corrosion in sulfate melts

Abstract: The sulfide NaCrS2 has been identified in the internal corrosion zone of several nickel-base superalloys under basic fluxing conditions at very negative potentials in a 90% Na2SO4-10% K2SO4 melt at 1173 K. It can also be formed in the presence of carbon-contaminated sulfate. NaCrS2 can dissolve some Ti, Al, Ni, and Co; other elements, e.g., K, Mo, W, Nb, Ta, and Zr, could not be detected.

Corrosion in the polluted environment

Abstract: Natural and man-made pollution of the environment significantly affects the corrosion behaviour of structural materials and non-metallic coatings. Of the natural environments atmosphere, water, and soil, the atmosphere has been chosen to discuss the effects of typical groups of pollutants on the corrosion of unalloyed steels and on the behaviour of organic coatings. Finally, the enhanced deterioration of works of art due to air pollution is briefly discussed.