The oxidation of benzene under conditions encountered in waste incinerators

The oxidation of benzene was studied as a function of residence time (τ_res=0–2.5 s), temperature (850–960 K), and oxygen concentration (O₂=0.2–2.3%) in a heated laminar flow reactor at atmospheric pressure. Nitrogen, doped with 350 ppm benzene, was injected downstream of the burned gas from a near stoichiometric flame of methane + air. Gas samples were taken at different heights up the reactor and analyzed using GC-FID/TCD and HPLC techniques. Phenol and partially oxidized hydrocarbons such as acetaldehyde, formaldehyde, and acrolein were found with concentrations up to 50 ppm. At relatively low temperatures, the conversion of benzene was observed to proceed considerably more slowly at higher oxygen concentrations. Measured concentration profiles were modeled using detailed reaction schemes. A modified mechanism for the oxidation of benzene called BenWas was constructed from the mechanism of Zhang and McKinnon (Combust. Sci. Technol. 107 (1995) 261) by incorporating a submechanism for benzoquinone (OC₆H₄O) and by updating and enlarging the reaction scheme of cyclopentadiene (C₅H₆). The agreement between observed and predicted concentration profiles, e.g., of phenol (C₆H₅OH), acetylene (C₂H₂), and carbon monoxide (CO), was considerably improved by the use of the BenWas mechanism for rich and lean conditions, mainly due to the introduction of an additional pathway for phenyl oxidation (C₆H₅ + O₂ = OC₆H₄O + H) and due to the changed kinetics of the oxidation of cyclopentadienyl (C₅H₅) in C₅H₅ + O₂ = C₅H₄O + OH. The measured retardation of benzene oxidation with higher amounts of oxygen can be explained by the formation and reactions of peroxy radicals.     

Hydrodynamische Einlauflänge und Widerstandsgesetz von reibungsmindernden kationschen Tensidlösungen

Zusammenfassung Durch Zugabe geeigneter Tensidsysteme in Wasser kann der Str?mungsdruckverlust in geraden Rohren erheblich gesenkt werden. Die diesem Effekt zugrunde liegenden Mechanismen wurden in früheren Arbeiten eingehend diskutiert. In dieser Arbeit werden neue Ergebnisse vorgestellt, die sowohl die Bestimmung der hydrodynamischen Einlaufl?nge als auch die Ermittlung der Widerstandsbeiwerte im ausgebildeten Str?mungszustand erm?glichen. Für den Bereich der ausgebildeten Rohrstr?mung wird eine neue Berechnungsgleichung vorgeschlagen. Durch Erweiterung der bisherigen Modellvorstellungen ergibt sich ein Widerstandsgesetz für den gesamten Wirkungsbereich des Tensids. Die Ergebnisse stützen sich auf Untersuchungen mit zwei verschiedenen Additivsystemen, bei denen die Parameter Str?mungsgeschwindigkeit, Temperatur und Einsatzkonzentration variiert wurden.     

Conversion of ethane on modified zsm-5 zeolites: A study of aromatization as a function of reaction media

Ethane was converted into aromatic hydrocarbons on H-ZSM-5 and Zn-ZSM-5 at 773 K in a flow reactor system using nitrogen and hydrogen as carrier gases. Residence time was varied by changing catalyst weights to obtain information about primary and secondary reaction steps. On H-ZSM-5 ethane conversion proceeds via formation of ethene and subsequent oligomerization. Oligomers undergo fast isomerization, cracking and cyclization leading to a broad spectrum of aromatics. Methane is a secondary product. Dehydrogenation reactions proceed irreversibly. Introduction of zinc species significantly enhances the aromatization activity of H-ZSM-5 on the one hand and causes a change of reaction mechanism on the other. Oligomerization of olefinic intermediates can take place at zinc sites. In nitrogen, aromatization of C₆ olefins is faster than isomerization and cracking of these oligomers. Dehydrogenation steps proceed reversibly. On using hydrogen as the carrier gas over Zn-ZSM-5, the conversion of ethane as well as the formation of aromatics decrease. Furthermore, aromatics richer in hydrogen (especially C₈ aromatics) are then formed preferentially.     

Lachnumon and lachnumol a, new metabolites with nematicidal and antimicrobial activities from the ascomycete Lachnum papyraceum (Karst.) Karst. II. Structural elucidation

The structures of two new biologically active chlorinated metabolites isolated from submerged cultures of the ascomycete Lachnum papyraceum have been elucidated by NMR and mass spectroscopy. The compounds, lachnumon (1) and lachnumol A (2), which structurally are related with mycorrhizin A that also is produced by the fungus, contain an unusual chlorinated epoxide group.     

The striatins--new antibiotics from the basidiomycete Cyathus striatus (Huds. ex Pers.) Willd

Three crystalline antibiotics which we named striatins A, B, and C were isolated from the mycelium of the basidiomycete Cyathus striatus strain No. 12. The striatins are highly active against fungi imperfecti and a variety of Gram-positive bacteria, as well as against some Gram-negative bacteria. The molecular formulas as determined by mass spectrometry are C27H36O7 for striatin A, C27H36O8 for striatin B, and C25H34O7 for striatin C.     

Eigenschaften von extrudierten Holz-Kunststoff-Werkstoffen auf Basis von Refiner-(TMP-)Fasern und Hanffasern

At present, wood particles (wood flour) with a low aspect ratio are mostly used as fillers in wood-plastic composites (WPC). Reinforcement of WPC and improved strength properties may be achieved by using real wood fibres with a high aspect ratio. WPC based on 70% (wt.) refiner (TMP) wood fibres and mechanically processed hemp fibres were extruded in a two-step process. Eleven compounds based on the two natural fibre types were prepared using a thermokinetic mixer and extruded in a conical, counter-rotating twin-screw extruder. Additional formulation components were polypropylene fibres, maleic anhydride-modified polypropylene (MAPP) and lubricant. It was determined that compounding in a thermokinetic mixer is a useful step for processing of WPC with refiner and hemp fibres as little fibre damage occurred. However, during extrusion, both natural fibre types were severely shortened due to strong shear forces, and homogeneous dispersion of fibres in the matrix was not achieved. WPC based on hemp fibres displayed the best strength properties of the formulations tested. Current extruder screw and die configurations need to be modified to achieve improved fibre reinforcement and to create new, structurally demanding applications for WPC. Using dynamic mechanical analysis, fibre-matrix adhesion of WPC was investigated, and activation energies for glass transition of selected formulations were calculated. Activation energy for formulations containing MAPP was higher than for WPC without MAPP. This indicates that better fibre-matrix adhesion was achieved in formulations with MAPP.     

Quantitative Evaluation of Thermal Inactivation Kinetics of Free-Floating Versus Surface-Attached Listeria innocua Cells

Surface pasteurization is one of the decontamination treatments that can contribute to better preservation of meat products retaining most of their quality characteristics relatively intact if compared with the raw products. The current research compares the kinetics of free-floating and surface attached Listeria innocua cells by using integrated microbial and heat transfer modelling approaches. Surface pasteurization treatments are applied on a (abiotic) Teflon® model system in a novel steam surface decontamination rig. The experimental set-up prevented following four technological aspects to occur, (1) cold purge migration to the surface during the heating process, (2) inactivation kinetics of a cocktail of microbes, (3) protective effect of food components, and (4) physical distribution of bacteria throughout the depth of the product skin. Microbial load predictions are performed based on the inactivation parameters obtained during free-floating cell experiments. These predictions, when compared with the microbial data of the surface treatments, prove that the surface attached cells were much more heat resistant, despite the experimental set-up preventing the aforementioned (technological) events to occur. Indeed, surface attached cells can have different physiological/phenotypical/genetical characteristics, such as cell aggregations, colony formations, presence of flagella. In a final step, three techniques are implemented to evaluate mathematically the kinetics of the surface attached cells. Overall, this research’s significance is lying in the quantitative assessment of microbial heat resistance. The technological reasons underlying the increased microbial heat resistance on biotic and abiotic surfaces should be reevaluated, taking into account possible physiological/phenotypical/genetical characteristics.     

Supercharged Proteins and Polypeptides

Electrostatic interactions play a vital role in nature. Biomacromolecules such as proteins are orchestrated by electrostatics, among other intermolecular forces, to assemble and organize biochemistry. Natural proteins with a high net charge exist in a folded state or are unstructured and can be an inspiration for scientists to artificially supercharge other protein entities. Recent findings show that supercharging proteins allows for control of their properties such as temperature resistance and catalytic activity. One elegant method to transfer the favorable properties of supercharged proteins to other proteins is the fabrication of fusions. Genetically engineered, supercharged unstructured polypeptides (SUPs) are just one promising fusion tool. SUPs can also be complexed with artificial entities to yield thermotropic and lyotropic liquid crystals and liquids. These architectures represent novel bulk materials that are sensitive to external stimuli. Interestingly, SUPs undergo fluid–fluid phase separation to form coacervates. These coacervates can even be directly generated in living cells or can be combined with dissipative fiber assemblies that induce life-like features. Supercharged proteins and SUPs are developed into exciting classes of materials. Their synthesis, structures, and properties are summarized. Moreover, potential applications are highlighted and challenges are discussed.