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.     

Bestimmung der partikulären Eigenschaften von aufbereiteten Sekundärrohstoffen aus Wärmedämmverbundsystemen

In recent decades, the proportion of external thermal insulation composite systems (ETICS) installed in the Federal Republic of Germany has increased significantly due to energy requirements. Currently, there is a significant increase in ETICS waste, for which there is no established recycling strategy. For this reason, in this work ETICS waste was processed in the sense of the circular economy in order to make the secondary raw materials obtained industrially usable. In order to enable targeted recycling and to close the material cycle of ETICS in the long term, particulate properties such as the comminution ratio, sphericity, dispersity as well as the flowability and compressibility of the recyclates were investigated.     

Strategien zum Schließen der Stoffkreisläufe beim Recycling von Fluorpolymeren

In fluoropolymers, a large portion or even all of the hydrogen atoms in a polymer chain are replaced by fluorine, which results in a number of special properties such as high chemical and temperature resistance. As a result of this combination of properties, these high-performance polymers are not replaceable, or only with difficulty, for some applications. The recycling of polymers and the associated closing of material loops is an essential development task for the entire polymer industry. Materials such as fluoropolymers have a special position due to their chemical composition and their low market volume, as they cannot be recycled together with other bulk polymers at the end of their life cycle. This paper discusses different processes in terms of their technical maturity and suitability to allow fluoropolymers to be fully recycled.     

Werkstoffliche Aufbereitung von Wärmedämmverbundsystemen

Due to increasing energy requirements for buildings, thermal insulation composite systems (TICS) have been used to insulate building facades since the 1970s. In view of the longevity of these composite materials, there has been an increased amount of TICS waste in recent years. Since there is no current recycling concept for these systems, an enormous resource efficiency potential remains unused. Due to the complexity of composite materials this study focuses on the pretreatment and discusses different processing steps in detail.     

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.     

Die Stabilität von Rohrreaktoren

The present paper deals with the stability analysis of tubular reactors for the case of rapid exothermic reactions in the homogeneous gas phase. The investigation is based on a non-steady volume reaction, whose reaction velocity satisfies an equation of very general form. Starting from the balance equations of the tubular reactor, using purely analytical methods, the characteristic equation is derived that determines the stability behaviour of this reactor type.     

Durchgangswiderstand von partikulären Systemen

The electrical properties of particles especially the volume resistance of bulk particles have decisive implication on a multitude of processes in the process engineering such as, product qualification or fire and explosion protection. Since the charge transport in a disperse system and a homogeneously solid is different, the product properties of the particles and the fluid are crucial for the volume resistance. In this work the dependence of the volume resistance on the internal structure of the bed, the relative humidity, the conditioning time at different climates and the average particle size was investigated. All measurements were carried out in a concentric measuring cell.     

Potenziale und Grenzen der Sekundärrohstoffgewinnung – Ergebnisse der r4-Begleitforschung

The socio-economic and ecological impacts of selected projects of the BMBF funding program “r⁴ – Innovative Technologies for Resource Efficiency – Research for the Provision of Raw Materials of Strategic Economic Importance” are presented. Many, but not all, research projects indicate a potential improvement of the supply situation in Germany. In some cases, the provision of secondary raw materials is unprofitable or ecologically detrimental. These cases require a balancing between security of supply and other economic and ecological objectives.     

Synthese von Dithiocarbamidsäureestern des Pyrazols

Synthesis of Pyrazolyldithiocarbonates The reaction of 3-amino-pyrazole 1 with carbondisulfide and alkylating agents in basic conditions to yield different dithiocarbonates 2 – 8 was studied. The dithiocarbonates 2a react with isocyanates to form 1-acyl-5-acylamino-pyrazoles 9 – 10 . Acyl migrations were observed depending on the reaction temperature and the isocyanates. The results obtained enable us to correct some confusions in the literature about thioureas of pyrazoles.     

Charakterisierung und Qualitätssicherung von Oberflächenvorbehandlungen auf Kunststoffbauteilen

With the aim of increasing wetting, adhesion, and long-term stability usually surface pretreatments are carried out on plastic surfaces for subsequent painting and bonding processes. Depending on the treatment methods, materials and subsequent processing steps, a variety of characterization methods are available. An overview is given of established characterization options for activated plastic surfaces, which are suitable for adjusting processes or quality assurance. In addition, new promising research approaches for two-dimensional and non-destructive quality control of activated plastic surfaces are discussed.     

Regenerationspotenzial von Alginit zur Abreicherung von organischen Schadstoffen aus Abwässern

Endocrine-disrupting chemicals (EDC) in wastewater are receiving increasing attention as studies have confirmed the harmful effects on living organisms' hormonal systems. So far, activated carbon has been used in sewage treatment plants to adsorb the pollutants. The rock alginite as a new type of adsorbent is also suitable for a cleaning process as a 4th cleaning stage due to the good depletion rates for EDC and the low purchase costs. Investigations have shown that repeated loading and regeneration cycles are possible while maintaining a high loading capacity.     

Phosphorrecycling durch Mitverwertung von Klärschlammaschen bei der Phosphorsäureherstellung

The approach of recycling phosphorus from sewage sludge ash by co-processing in conventional phosphoric acid production was investigated. Lab-scale experiments with real ashes and simulated industrial conditions showed that mixing of ash and phosphate rock prior to processing resulted in several disadvantages. As a solution the novel concept of return acid extraction is presented, which overcomes some of the identified shortcomings of direct mixing.     

Demontage von Komposit-Bauteilen – Potenzial energetischer Materialien zur Demontage von Rotorblättern

Rotor blades of wind turbines are a challenge for recycling due to the composite materials used and their large-volume construction. The article presents a new approach for the disassembly of composite components with energetic materials. The results illustrate the different disassembly effects of detonating cords and cutting charges as well as the dependence on the material fractions, the material thickness, the layer structure or even the fibre architecture.     

Sauergasbasierte stoff- und energieautarke Trocknung von Klärschlamm und Gärresten

During the processing of biomass as well as during waste water treatment, residual materials with a high water content are produced. They must therefore be dried prior to thermal utilization. Classical drying processes often use fossil raw materials to generate the necessary energy. With sour gas-based drying based on carbon dioxide-air mixtures, an alternative is presented that considers CO₂ as a valuable raw material (second life) and uses it in the process for drying sewage sludge and fermentation residues. Especially in the drying of fermentation residues, significant differences in dry substance content (DS) were measured, which in individual cases amounted to up to 35 % DS with the same drying time. This is expressed, among other things, in a higher carbon content of 0.42 wt % (wf) in the dry material, accompanied by a heating and calorific value that is more than 1 MJ kg⁻¹ higher.     

Porositätsmessungen durch absorption von röntgenstrahlen

A new method of porosity measurements is discussed in our paper, and namely an X-ray method applied to the porous nickel electrode.The porosity measurements described in the literature, based on the absorption of K_α radiation fail in case of samples whose thickness is of the order of 1 mm, and in case of large mass absorption coefficients. This difficulty is overcome in our method by the use of a continuous spectrum of an X-ray tube. In this spectrum a suitable wavelength λ is chosen by means of a spectrograph, so that absorption measurements can be carried out for every sample under the best conditions.The relative error of the measurement is not larger than ±5 per cent. The determination lasts not more than 4 min.     

Feinstzerkleinerung von CFK-Abfällen und Charakterisierung der Zerkleinerungsprodukte

The comminution of carbon fiber reinforced plastics (CFRP) is a central process step for almost all recycling processes. Size reduction creates a specific surface that serves as a measure in particular of the size reduction success of fines. The article shows the comminution from 1 m edge length in the feed material down to a target product size of less than 100 µm by means of three-stage comminution. The challenges of granulometric characterization of the comminution products and the associated evaluation of the comminution success are specifically addressed.