Rückgewinnung von Metallen aus niedrigkonzentrierten Lösungen

Recycling of metals from low concentrated solutions. A review is given of processes used for the separation of metals from aqueous solutions, especially low concentration waste waters. Purification processes for waste water used only to reach values set by law are compared with processes that allow recovery of metals. Precipitation with and without additives, adsorption, processes with ion exchange resins, solvent extraction and membrane processes, especially liquid membrane permeation, are described. As a result of these considerations, a qualitative comparison of all the described processes becomes possible. For the separation of zinc from a waste water stream, a special economic comparison is also shown between precipitation processes and the liquid membrane permeation process. Finally, the latest developments in the fields of solvent extraction and liquid membrane permeation are discussed.     

Hydrierende Vergasung von Kohle – Neuere Betriebsergebnisse

Hydrogasification of coal – recent operational results . The Rheinische Braunkohlenwerke AG has built and has been operating a semi-technical pilot plant for hydrogasification of coal in a fluidized bed. The objective is to develop a coal gasification process with hydrogen for producing directly substitute natural gas. Between 1976 and 1981, the semitechnical pilot plant having a capacity of 100 kg C/h was operated for about 22,900 h under test conditions, more than 9,500 h of which were under gasification conditions. During this time, approximately 1,400 metric tons of dry coal were gasified. The longest coherent operational phase under gasification conditions was 748 h in which 86.4 metric tons of dry lignite were gasified. Carbon gasification rates up to 82% and methane contents in the dry raw gas (free of N₂) up to 48 vol.-% were obtained. A detailed evaluation of the test results provided information on the influence of additional parameters on the efficiency dates of the gasifier and a considerable refining of the results obtained previously. Moreover, several components were tested for which no operational experience had previously been gained; these were newly developed devices, e. g. the inclined tube for feeding coal into the fluidized bed. Within the framework of scale-up work to large-scale coal gasification plants, a pilot plant having a capacity of approximately 6 t C/h will be commissioned in late 1982.     

What you get is what you see: revisiting the evaluator effect in usability tests

Usability evaluation is essential to user-centred design; yet, evaluators who analyse the same usability test sessions have been found to identify substantially different sets of usability problems. We revisit this evaluator effect by having 19 experienced usability professionals analyse video-recorded test sessions with five users. Nine participants analysed moderated sessions; 10 participants analysed unmoderated sessions. For the moderated sessions, participants reported an average of 33% of the problems reported by all nine of these participants and 50% of the subset of problems reported as critical or serious by at least one participant. For the unmoderated sessions, the percentages were 32% and 40%. Thus, the evaluator effect was similar for moderated and unmoderated sessions, and it was substantial for the full set of problems and still present for the most severe problems. In addition, participants disagreed in their severity ratings. As much as 24% (moderated) and 30% (unmoderated) of the problems reported by multiple participants were rated as critical by one participant and minor by another. The majority of the participants perceived an evaluator effect when merging their individual findings into group evaluations. We discuss reasons for the evaluator effect and recommend ways of managing it.     

Adsorption on activated carbon in countercurrent flow: An experimental study

The work describes adsorption experiments from aqueous solutions on activated carbon using a counter-current adsorber. Phenol and paranitrophenol were used for single component adsorption and molasses colour for multicomponent adsorption experiments. Isotherms were determined using simple equilibrium experiments. Three different techniques were used for determination of the kinetics. These were finite bath, infinite bath and fixed bed experiments. A mathematical model for countercurrent adsorption was tested. The model includes the effect of film diffusion and pore diffusion as well as surface diffusion, and can handle systems with a nonlinear isotherms. Kinetic data in the form of an average diffusivity in the carbon determined from the finite bath experiments and isotherm data did not predict the operation of the countercurrent column well. Data from the fixed bed experiments predicted countercurrent column operation much better. This is deemed to be due to inhomogeneities in the carbon used, resulting in a fairly quick initial uptake of the main part of the solute and a slower uptake of a minor amount.     

The manufacture of high-value carbon from coal-tar pitch

World-wide, 17 million ta^?1 of coal-tar are obtained as a by product in the chamber coking process for the production of metallurgical coke. Refining of this aromatic raw material yields coal-tar pitch which is the traditional coal-derived starting material for the manufacture of carbon precursors and carbon artefacts. Considerable progress has been made in the elucidation of the physical and chemical nature of this material by means of chromatography, n.m.r. spectroscopy, thermal analysis and chemical reactions schemes. The dominant fields of application of pitch are the manufacture of pitch coke and electrode binders. Delayed coking and horizontal chamber coking are the technologies currently used for the production of cokes with low sulphur and metal content, for anodes for the aluminium-refining industry and the electric steel process. Coal-tar pitch, low in quinoline-insolubles (QI), is an excellent raw material for the manufacture of needle-cokes with a low coefficient of thermal expension (CTE). The separation of inherent QI can be performed via gravity settling in aliphatic hydrocarbon mixtures, by centrifugation in a disc separator or by filtration. The possible co-carbonization with aromatic petroleum-derived residues yields premium coke suitable for the manufacture of UHP-electrodes. New developments in the production of coke from coal-tar pitch aim to improve coke yields and increase anisotropy (i.e. low CTE and high electrical conductivity values). Further technological progress has been made in the manufacture of hard pitch which can be used as a starting material for the production of pitch coke in the chamber coking process and for the production of electrode binders by means of a continuous flash process with optimized thermal and pressure treatment of pitch, thus facilitating the ‘tailored’ manufacture of binder pitches of different qualities.     

可记录DVD格式的在线生产控制

1引言:高级的可录DVD格式需要高级的测试设备 放眼当今市场,终端消费者已逐步接受可录DVD格式;展望不久的将来,可录DVD必将取代CD-R成为数据备份的标准存储媒体。因而盘片复制商、生产线制造商、测试设备提供商都越来越关注DVD-R。     

The Kinetics of the Thermal Decomposition of Thermoplastic Polyurethane Elastomers under Thermoplastic Processing Conditions

A theoretical approach to the kinetics of the thermal decomposition of molten thermoplastic polyurethane elastomers, under conditions of thermoplastic processing, is described. On the basis of these considerations, the thermal decomposition in different instruments (melt index analyser and measuring extruder) can be described quantitatively and the various results can be compared. As a result, identical conditions of decomposition of the melt can be defined accurately, thus opening up the possibility of combining experimental values from different instruments. The fundamental kinetic equation obtained for the kinetics of the thermal decomposition of thermoplastic polyurethanes describes the decomposition reaction and the reverse reaction (formation reaction) – which is dependent on the system of measurement and processing – as a function of the molar mass (end‐group concentration) of the original product, determined from the velocity constants for the decomposition reaction and back reaction. The consideration of the limiting value for t → ∞ is in agreement with the equilibrium constant. Consequently, the development of physical characteristic functions of thermoplastic polyurethane elastomers – independent of the system of measurement – is possible.

Experimental values and calculated curves for the thermal decomposition of PUR‐Et in a melt index analyser.     

Kinetics of Solid-State Reactions in Heterogeneous Catalysis from Time-Resolved X-Ray Absorption Spectroscopy

The potentials of X-ray absorption spectroscopy (XAS) (quantitative phase composition and average valence together with a short-range order structure analysis) combined with a time-resolution in the second range make time-resolved (TR-) XAS a powerful tool for investigating the reactivity of solids in catalysis and solid-state chemistry. General aspects of TR-XAS investigations are discussed (i.e., instrumentation, data analysis). In addition, some experiments illustrate how the kinetics of solid-state reactions in heterogeneous catalysis can be elucidated from TR-XAS studies.     

Application of K2CO3 catalysts in the coal gasification process using nuclear heat

Conventional gasification processes use coal not only as feedstock to be gasified but also for supply of energy for reaction heat, steam production, and other purposes. With a nuclear high temperature reactor (HTR) as a source for process heat, it is possible to transform the whole of the coal feed into gas. This concept offers advantages over existing gasification processes: saving of coal, as more gas can be produced from coal; less emission of pollutants, as the HTR is used for the production of steam and electricity instead of a coal-fired boiler; and a lower production cost for the gas. However, the process has the disadvantage that the temperature is limited to the outlet temperature (950 °C max) of the helium cooling gas of the HTR. Therefore the possibility of catalytic steam gasification was examined. Model calculations based on experimental results show that use of 3–4 wt% relative to coal of K²CO³ catalyst increases the throughput of a large scale nuclear gasification plant by ≈65%, while gas production costs decrease by ≈15%. Corrosion by catalysts is not significant at low concentration (< 5 wt%) and low temperature (< 900 °C).