Einfluß von Mischungsvorgängen auf den Umsatz bei der Äthylenhydrierung in Fließbetten

Using the hydrogenation of ethylene by a copper catalyst the strong influence of mixing- and/or segregation-processes on chemical conversion existing in fluidized beds was investigated for the range of dense phase fluidization. The catalyst was used in three sizes (0–42, 42–60, 60–90 μ) in three fluidized bed reactors with different height-to-diameter ratios (21,5 : 10 ;35,5 : 7,5 ; 80 : 4,8 cm). Conversion was measured between 100 and 150°C in dependence of the gas velocity. Mixing processes were measured by taking residence time distributions of a tracer gas at two different distances from the entrance of the gas. Concentration fluctuations of the solid particles and bubble diameters, estimated from these, could be determined during reaction by X-ray absorption. With increasing gas velocity the conversions observed in the fluidized beds departed more and more from those existing in an ideal piston-flow reactor, and approached conversions valid for an ideal back-mix reactor; in some cases they were even lower. These observations depended on particle size and reactor geometry. They could only in part be explained by the already known diffusion and two-phase models. A better understanding is possible by the proposed two-zone model, which considers important differences of mixing, density and gas velocity between the wall region and the central region of the fluidized bed.     

Alkalische Aktivierung und Reaktivierung von Sekundärrohstoffen der Bau- und Abbruchindustrie

The present work deals with the production of geopolymers from brick flour and mixed rubble using an alkaline activator solution. The study aims to investigate whether these geopolymers can be reactivated several times without having to add new starting material, and how the number of reactivations affects the structure and material properties. The results show that geopolymers can be made from a mixture of brick flour and mixed rubble and can be ground up and reactivated up to three times.     

Jahreszeitliche Schwankungen in der Zusammensetzung von Klärschlamm bei der Betrachtung eines Klärwerks

By evaluating sewage sludge analysis data from a large German sewage treatment plant (>1 million population equivalents), seasonal fluctuations in the composition of the sewage sludge could be identified. These fluctuations include a periodic decrease in carbon content and an increase in ash content in the middle of the year. Various wastewater and sludge treatment processes as well as climatic influences could be identified as causes for this trend. The investigation of the contents of various heavy metals and trace elements in the sewage sludge also showed partly strong fluctuations in the course of the year, which can have an influence on the utilization possibilities of the sewage sludge.     

Notwendigkeit und Vermarktung von Flexibilitätsoptionen im Energiesystem der Zukunft

Demands on production, distribution and consumption of electrical energy change fundamentally with the energy revolution. Energy purchasing costs for inflexible consumers are rising and proceeds of inflexible producers are sinking. Companies are able to reduce costs by marketing operational flexibility options. This article sets out the need of flexibility in the energy system and the new marketing options. Flexibility potentials within infrastructure plants of a chemical park are analyzed, evaluated regarding marketing and activated in the presented research project FlexChemistry.     

Die simultane Abhängigkeit der Reaktionsgeschwindigkeitskonstante von Druck und Temperatur

It is shown that under certain conditions an equation which has general validity and resembles the law of Arrhenius can be established to express the specific influence of very high pressures on the reaction velocity of chemical conversions:

This equation expresses the simultaneous dependence of the reaction velocity constant on pressure and temperature. The specific influence of pressure may accordingly be considered either in terms of the reaction velocity constant as a function of pressure or in terms of the activation energy as a function of pressure. The magnitude of the pressure influence may be defined by the following characteristic expression:

which shows the relationship between pressure influence and temperature influence.     

Vorteile von Open-Source-Ansätzen bei der Etablierung einer automatisierten wirkungsbezogenen Analytik

The determination of toxic compounds in wastewater is perfomed using thin layer chromatography. For automation of effect-directed analytics, an existing technical solution was adapted as an open-source hardware approach in combination with additive manufacturing. The system is flexibly applicable to specific issues of automated determination of environmentally relevant compounds and makes a valuable contribution to the digitalization and automation of high-performance thin-layer chromatography systems.     

Filtrationsmembranen und spezifische Adsorber auf der Basis von maßgeschneiderten selbst-organiserenden Blockcopolymeren

Due to their ability to form self-assembled structures, block copolymers offer various possibilities for material separation. Flat and hollow filament membranes with regularly arranged pores of the same diameter and high pore number density can be produced from self-assembling block copolymers. The pore sizes and functionalities of these membranes and thus their application possibilities in the material separation can be adjusted in different ways, whereby the setting of these parameters on finished membrane structures is particularly interesting. Furthermore, tailor-made amphiphilic block copolymers can be used for the specific extraction of substances from aqueous (hydrophilic) solutions to organic (hydrophobic) solutions.     

Der einfluβ der konzentration stabiler oberflächenoxide auf die intensität der oxydation von Ruβ durch sauerstoff-I. Oxydation bei konstantbleibender ruβoberfläche

A carbon black, preoxidized and subsequently heat-treated at 1100°C, was re-exposed to oxygen and its reaction intensity was measured at temperatures ranging from 267° to 416°C. The reaction occurred in a range of burn-up within which there was no significan't change in surface area. Both the intensity of formation of stable surface oxide and the intensity of carbon consumption could be represented as the sum of two Elovich functions with respect to the surface oxide concentration. This becomes plausible if there are assumed to exist on the surface two types of active centres, which after being occupied by oxygen will give rise to two different surface oxides. The Elovich function can be interpreted by the assumption of an energetically inhomogeneous carbon surface. Apparently, the carbon consumption is due mainly to oxygen-free carbon atoms. The temperature dependence of the Elovich coefficients suggests a decreasing influence of the surface oxide concentration on the intensity of carbon consumption as temperature increases. As temperature is lowered, however, the surface oxide concentration secures much more significance, so that finally no constant reaction intensities can be obtained within reasonable times. The inhomogeneity of the carbon surface then seems to represent a predominant property relevant to chemical kinetics.     

Unstete Überströmung bei der Crossflow-Mikrofiltration und ihr Einfluss auf auftretendes Fouling

The main disadvantage of crossflow microfiltration processes is the occurrence of fouling, which impedes its application and economic efficiency. Unsteady crossflow, e.g., due to pulsatile or alternating operating mode, can reduce the formation of a deposit layer and therefore prevent strong flux decay and retention of solutes. With this technique, especially processes run at low crossflow velocity or high transmembrane pressure can be significantly improved. The degree of improvement also largely depends on the fouling propensity of the fluid to be filtered.     

Die Änderung der inneren Energie von Pulvern bei der Herstellung am Beispiel des ZrN und MgO

In view of the significance of surface and mixing energy for the reactivity of powders, both of these interdependent energies have been investigated as a function of the conditions of formation, using ZrN and MgO. Since for both powders two different methods of formation exist, for ZrN the inclusion of nitrogen in the metal lattice conversion from body-centred cubic to face-centred cubic, and for MgO thermal decomposition of the salt via an X-ray amorphous phase, the relationships of surface energy to mixing energy are different for each. The curves of these energies in relation to the conditions of formation are shown.     

Einfluss der Holzalterung auf die Brennstoffqualität und die Verbrennungschemie in einem Scheitholzofen

The study investigates the impact of decomposition processes of beech and pine wood on the fuel quality and the combustion chemistry in a wood-burning stove. Especially, when considering the volume of wood fed, the burning time and energy output decrease with the stage of decomposition. The gaseous emissions as well as the total dust emissions do not change, depending on the decomposition processes. However, at the experiments carried out here, the combustion of softwood generally showed lower gaseous emissions than hardwood.     

Zur kinetik der anodischen passivierung von eisen,kobalt und nickel—III. Der einfluss von sulfat- und perchlorationen auf die passivierungsgeschwindigkeit von eisen in saurer lösung

Rates of passivation have been measured by means of anodic current/potential curves obtained at constant potential with a rotating disk electrode of Armco iron. In acid solution sulphate and perchlorate ions accelerate the passivating reaction     

Porendimensionen und Oberflächenkapazität von Braunstein

The BET area of battery manganese dioxide lies between 5 and 10 m²/g, while the electrically active area appears to be definitely smaller. In the present paper some idealized assumptions are shown to lead to certain conclusions concerning the number and the dimensions of the pores. Pore diameters of 23 to 200 Å are obtained; in a single grain 10⁶ to 10⁷ pores are to be expected. Measurements of the surface capacity and of the polarization of polished, massive pieces of electrolytically prepared manganese dioxide yield values of 10⁻⁵ S/cm² at a polarization of 22 mV for the polarization conductance and of 25 μF/cm² for the capacity. Both values are referred to the area of the electrically active surface. On this basis electric models can be set up which make it possible to explain why it frequently happens that only a small portion of the BET area participates in the electric phenomena. These models show also that the re-establishment of polarization tensions must occur with relatively long time constants. Measurements of these time constants gave 1·6 sec in contrast with a prediction of 2·5 sec. Moreover, a slow decay with a time constant of 100 to 150 sec remains to be explained.In the investigation of the electrode/kinetics by means of impedance measurements there are three significant limiting frequencies. A first one, which corresponds to the expansion of the concentration wave in the fission between the grains, has already been examined. In the present work there appear two new limiting frequencies below or above which, respectively, the whole BET area or only the geometric area of the grains is electrically active. In many cases the pores of the grains are so narrow that no ions can penetrate them. In this case also only the geometric area is effective.     

Beziehungen zwischen der Korngrößenverteilung und der Beanspruchungsenergie bei der Einzelkornprallzerkleinerung

Investigations are reported concerning single impact crushing of irregularly shaped rock-salt particles. It is shown that with constant initial grain size not only the probability of fracture as function of the mass-related load energy follows a logarithmic normal function, but that the same relation also applies to the size-distribution function of the product being crushed for any undersize at any mesh aperture. The distributions resulting with different impact energies are thus functionally interconnected.By comparison with the results of other authors it can be shown that other substances also reveal the same behaviour with the most different initial grain sizes. Only glass spheres deviate from it.Further relations between initial size, load energy, and grain-size distribution function are indicated for rock-salt particles.     

Über den einfluss des ohmschen widerstandes und der doppelschichtkapazität auf den spitzenstrom in der wechselstrompolarographie

The well-known fact that with increasing frequency the height of the peak current decreases after reaching a maximum, was hitherto explained by assuming that the electrode reaction could not follow the rapid changes in potential. The decrease of the peak current also occurs, however, in the case of reversible reactions. This can be attributed to the fact that on keeping the applied alternating potential constant, the effective alternating potential at the electrodes decreases with increasing frequency. Mathematical treatment of the problem shows that the ohmic resistance of the circuit and the double-layer capacity of the electrode are responsible for this decrease in the peak current.In square wave polarography the impedance of the measuring circuit determines the time constant and is therefore responsible for the degree of eliminating the capacity current.     

Ausgleich der Volatilität der Erneuerbaren Energien mittels Wärmespeichern auf Salzbasis

To compensate for the volatility of renewable energies, solutions beyond fossil reserve power plants are needed. One approach is salt-based heat storage with phase change materials (PCM). In order to achieve economic efficiency, ambitious targets are required. A sensible and latent heat storage system for the temperature range around 400 °C based on salts and thermal oils with high development potential is presented.