The oxidation and self-heating of metal sulphides as an electrochemical corrosion phenomenon

Experiments with a representative number of technically interesting metal sulphides trace out hydrogen peroxide as the reactive intermediate of sulphide oxidation. It is formed through an electrochemical reduction of molecular oxygen. The formation of sulphur or sulphate as the final state of oxidation is determined by consecutive reactions which are critically dependent on the catalytical properties of the surface and the solution for hydrogen peroxide decomposition. The individual steps of the reaction are discussed in some detail. Conclusions with respect to a possible control of the autogeneous heating are drawn.     

Hybrid systems in seawater desalination—practical design aspects, present status and development perspectives

Ever since seawater desalination has been applied on an industrial scale, and particular in the countries of the Arabian Gulf, the application of desalination processes in dual-purpose facilities—water and power—as a hybrid configuration has been discussed in many feasibility investigations and also planning concepts. It is above all the combination of reverse osmosis with thermal processes that has found increasing interest with the aim of ensuring, as economically as possible, uniform water supplies under the specific, greatly varying load conditions in the Gulf countries. Such design concepts for hybrid configurations encompass straightforward structures with a low degree of coupling between membrane and thermal desalination processes, but range up to very complex configurations with strong interconnections on both the water side and thermally, as well as with several desalination processes connected in series or in parallel. Classical hybrid concepts in which the permeate from an RO desalination component is mixed with distillate from thermal desalination have already been implemented in Saudi Arabian dual-purpose plants, like Jeddah and Yanbu-Medina. Although hybrid systems of greater complexity have been addressed in many design studies and publications, up to now none has been brought to fruition. Coming into consideration asthe design basis for determining the capacity shares of the various desalination processes operated in a hybrid configuration are: arrangement of thermal cycle of the power plant component; water/power ratio of the dual-purpose seawater desalination and power plant; provision of undiminished water production of the desalination plant as electricity generation varies; provision of a specified drinking water quality with regard to composition and salt content; combination of all these aspects. Also gaining in importance are concerns of environmental pollution and sustainable development when selecting seawater desalination and power plant configurations, as well as their optimization when considering desalination and electricity generation as a whole. In the practical design of hybrid membrane and thermal systems, aspects come to light, though, that restrict linking of the two systems and joint utilization of facilities, as conceived in studies and conceptual design investigations. This applies both for common utilization of intakes and the use of heated up cooling water from thermal processes as a feed stream for the RO part of the desalination process. Additionally, requirements of drinking water composition, particularly chloride content, TDS and compliance with a specific residual content of boron, influence specifically the design of the membrane process part and its share in the total desalination capacity. Such practical aspects have greatly influenced the design and configuration of the Fujairah hybrid plant for which, from a total desalination capacity of 100 MIGD (454,600 m³/d), the share of 37.5 MIGD (170,500 m³/d) makes its seawater RO plant the biggest currently being constructed anywhere in the world. From the findings of the engineering of this plant and the idea that, by increasing interconnection between the two processes on the water side, it is possible to advance a hybrid configuration of this type with regard to cost optimization in the membrane installation, but also by joint utilization of the intake equipment, perspectives result for applied research efforts over the near and long terms, for example: long-term behavior of membranes at elevated temperatures; tendency for biofouling in membrane process with common utilization of cooling water and brine; influences of such interconnections on the overall availability of the facility. But also for the operation and maintenance organization of such large facilities, consequences can be foreseen for the future development of hybrid plants, particularly for operation management and organisation of the interplay of the different power plant and desalination systems, monitoring of SWRO membrane replacement and cleaning, as well as controlling water quality.     

Characterization of Precursor-Derived Silicon-Carbon-Nitrogen Ceramics after Creep Testing

Precursor-derived Si-C-N ceramics after creep testing in air were characterized using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the crept Si-C-N ceramics were covered by an α-cristobalite layer. TEM observations revealed that the precipitated nanocrystallites in the crept Si-C-N ceramics were β-SiC. Between α-cristobalite and crept Si-C-N ceramic, there was an intermediate zone in which Si₂N₂O nanocrystallites were distributed homogeneously. Moreover, Si₂N₂O nanocrystallites were often found covering the surface of nanosized gas channels in the crept Si-C-N ceramics, where no α-cristobalite phase was detected. Based on these observations, a two-step oxidation mechanism of Si-C-N ceramics during creep testing in air was proposed.     

Identification of the state of palladium in various hydrogenation catalysts by XPS

Various commercial supported palladium hydrogenation catalysts were studied by XPS and treated at ambient pressure with hydrogen and air. Unused catalysts exhibit a significant fraction of divalent Pd (oxide) which is reduced by hydrogen treatment at room temperature. Exposure to air in systems with carbonate, alumina, silica or active carbon as support causes the formation of a solid solution of oxygen in Pd characterized by a Pd 3d chemical shift of ca. + 0.4 eV. The absolute binding energy of Pd depends strongly on the matrix, indicating a significant contribution of extra-atomic screening, which prevents a direct comparison of reference samples and supported catalysts. Using the oxidation of CO to CO₂ at 300 K as in situ chemical probe it was confirmed that Pd supported on carbonate, silica and alumina exists in the same metallic state which could be activated for the test reaction irrespective of the variation in XPS binding energies.     

A Complete and Highly Effective Mothproofing Agent Comprising a Pyrethroid and a Hexahydropyrimidine

Pyrethroids, considered as a general class of compounds, have been shown to provide effective protection from the larvae of the keratin-digesting insects Tineola bisselliella H., Tinea pellionella Linn., Hofmannophila pseudo-spretella Station and Attagenus piceus Oliv. The position regarding the susceptibility of the furniture carpet beetle to pyrethroids is less clear, however. It has been reported that both deltamethrin and permethrin are effective against Anthrenus flavipes Le Conte, whilst permethrin is also reported elsewhere to be effective against the same species. Results obtained in our laboratory, however, have indicated that pyrethroids may offer inadequate protection against Anthrenus vorax Waterh. [1, 2]. This latter species is identical to Anthrenus flavipes var. seminiveus Casey, a colour variety of Anthrenus flavipes Le Conte. The 1,3-disubstituted5-phenylcarbamoyl-2,4,6-trioxo- and 4,6-dioxo-2-thione-hexahydropyrimidine derivatives described in this paper exhibit a surprisingly high and selective toxicity to the Anthrenus species. Thus, a combination of an appropriate hexahydropyrimidine with a suitable pyrethroid, e.g. permethrin, provides complete control of a wide range of commonly encountered textile insect pests. The influence of substituents on the mothproofing activity is discussed.     

Syntheses and reactions of urethanes of cellobiose and cellulose-containing uretdione groups

Urethanes of cellobiose and cellulose-containing uretdione groups are synthesized by the reaction of aliphatic and aromatic diisocyanate uretdiones with the saccharides. The syntheses are performed as a heterogeneous reaction in dimethyl acetamide using dibutyl tin dilaurate as a catalyst, as well as a homogeneous reaction in dimethyl acetamide-lithium chloride. Thus, Semisynthetic prepolymers are formed that offer the reactivity of (blocked) isocyanate groups. To demonstrate their reactivity, ring opening of the uretdiones is performed by the addition of a secondary amine to yield the corresponding ureas.     

An axisymmetric model for thread forming in polycarbonate and polypropylene screw and boss fasteners

Plastic boss and screw fasteners are an economical means of securing automotive components, such as instrument or body panels. However, new materials and/or suboptimal design present challenges to the boss/screw effectiveness. Failure of a boss/screw can result is loss of functional performance or increased squeak and rattle. Failure is often controlled by what occurs during the initial thread‐forming process. Thus, the goal of this paper is to develop an FEA model to elucidate the thread‐forming process so that we can facilitate subsequent design and/or process optimization, and understand potential failure modes. The FEA must accommodate nonlinear couplings, such as large strain and heat transfer. Heat generation is present in the forms of interfacial shear heating and plastic work associated with the large deformation of the interface between the boss and screw. Strain rate‐dependent materials are included using the Eyring theory for plastic flow of polymeric materials. Results of the model are presented and compared to experimentally determined torque curves and temperatures. Polym. Eng. Sci. 44:1498–1508, 2004. © 2004 Society of Plastics Engineers.     

Produktionsintegrierter Umweltschutz – Verwertung von Reststoffen

Production-integrated environmental protection – Utilization of residues . Chemical plants as well as coal-fired powerstations utilize chemical reactions in order to produce materials or energy. Most of these reactions additionally produce gaseous, liquid, or solid residues. It is the main objective of production-integrated environmental protection to use these residues as suitable feedstocks in order to reduce environmental pollution and lower the consumption of raw materials. Several examples from the BASF Group will show how, by crossing the borders of the respective plant, reasonable solutions for material, or at least energetic, utilization of residues can be achieved. As a result of permanent efforts in production-integrated environmental protection over many years and despite increasing outputs the emissions of the chemical industry have been continuously reduced.