On-line process control of a fluidized bed reactor with non-catalytic gas/solid reaction

In a bench-scale, stainless steel reactor, experiments were carried out to investigate fluidized bed behavior by means of on-line process control. The non-catalytic thermal decomposition of sodium hydrogen carbonate to sodium carbonate, carbon dioxide and water was used a model reaction. The experimental equipment was provided with control systems and reulating units which were connected to a PDP 11/40 computer by means of suitable analogue and digital input/output interfaces. The operating conditions are highly influenced by the chemical reaction as well as by the fluid-dynamical behavior of the reactor. Several experiments were carried out to evaluate the kinetics of the model reaction. The fluid-dynamics was investigated by means of on-line experiments with and without chemical reaction. Based on the experimental results, a model was developed to describe the whole process so that model simulations should yield information on the process itself. With this model, strategies are tested before they are applied to the process computer for on-line process control.     

Modification of leather properties by grafting. I. Effect of monomer chain on the physico‐mechanical properties of grafted leather

Although leather has a number of desirable properties such as thermal stability and fire retardancey, in addition to high toughness, it has a few drawbacks such as weight, high water absorption, poor soil and rot resistance, and nonuniformity. If these defects are overcome, leather's usefulness would be further enhanced and its competitive position with respect to synthetics would increase. This study reports the physical and mechanical properties of buffalo leather after chemical graft copolymerization with ethyl acrylate, butyl acrylate, and 2‐ethyl hexyl acrylate using benzoyl peroxide as an initiator. The optimum conditions for grafting (e.g., monomer and initiator concentrations, temperature and time of grafting, and solvent leather ratio) were extensively investigated. The study achieved outstanding properties for buffalo leather in reduction of water uptake after grafting, especially on using 2‐ethyl hexyl acrylate and butyl acrylate monomers. FT‐IR and solid ¹³C‐NMR for leather before and after grafting confirmed the grafting process.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1478–1483, 2003     

Permittivite complexe de solutions electrolytiques non aqueuses

The complex permittivity * = ′ — j″ of ethanolic solutions of electrolytes has been measured between wavelengths 90 and 3·2 cm, at 25°C. Methods of measurement are briefly described. The results are interpreted by separating the conductivity and the dielectric losses. For solutions of LiClO₄, Mg(ClO₄) ₂, LiCl and LiI, a dielectric relaxation analogous to that of the solvent is observed, ie the dielectric loss factor passes through a maximum at a wavelength of about 30 cm. The ‘static’ permittivity, defined in terms of the relaxation spectrum, undergoes an important fall with increase of concentration. Solutions of (n-Bu)₄NI give more complicated behaviour, characterized by the probable existence of a new relaxation domain at longer wavelengths. The results are discussed in relation to data in the literature on the intermolecular structure of alcohols and the dielectric properties of electrolyte solutions in other types of solvent.

Zusammenfassung

Man ermittelte bei 25°C die komplexe Permittivität * = ′ — j″ verschiedener Elektrolytlösungen in Äthanol bei Wellenlängen zwischen 3,2 und 90 cm. Die Messmethoden werden kurz beschrieben. Die Ergebnisse werden interpretiert, indem die Leitfähigkeitsverluste von den dielektrischen Verlusten getrennt werden. Bei en Lösungen LiClO₄, Mg(ClO₄)₂, LiCl und LiI stellt man eine dem Lösungsmittel analoge dielektrische Relaxation fest, m.a.W.: der dilektrische Verlustfaktor geht bei Wellenlängen in der Nähe von 30 cm durch ein Maximum. Die “statische Permittivität”, welche aud dem Relaxationsspektrum definiert werden kann, nimmt mit zunehmender Konzentration stark ab. Lösungen von (n-Bu)₄NI zeigen ein komplizierteres Verhalten, welches möglicherweise durch das Auftreten eines neuen Relaxationsgebietes bei längeren Wellenlängen gekennzeichnet ist. Man diskutiert die Ergebnisse mit Bezug auf die Literaturdaten der intermolekularen Struktur von Alkoholen, und das dielektrische Verhalten von Elektrolylösungen in anderen Lösungsmitteln.     

Alkaline fuel cells: contemporary advancement and limitations

ZeTek Power recently introduced mass manufacturable and cost effective alkaline fuel cells on the market. Today's research is focused on further improvement both in terms of performance increase and cost reduction. This research is classically performed using small (4 cm²) experimental electrodes in the half-cell configuration. This allows the primary electrochemical losses in an anode or cathode to be determined independently. Additional performance losses occur when one integrates large electrodes into a module of 24 cells and in a stack comprised of many modules. By comparing the performance of half-cell experiments to that of modules, these losses can be distinguished and addressed. The information thus obtained, both for the small electrodes and in up-scaling is vital if one is to identify the key areas in which improvement is possible and where to focus future research. Furthermore, the identification of the losses in a module and system allows us to predict the final performance from half-cell measurements of a new laboratory scale experimental electrode.     

Redox chemistry of H2S oxidation by the British gas Stretford process part V: Aspects of the process chemistry

Stretford processes use air to oxidize H₂S in process and natural gases to elemental sulphur, by absorption in aqueous solution at about pH 9 and reaction of the resulting HS^– ions with dissolved oxygen, in the presence of anthraquinone disulphonates (AQDS) and vanadium (v) species, which act as catalysts. Kinetic measurements of the reactions (AQ27DS + HS^– ions), (V(v) + HS^– ions) and (AQ27DSH^– + O₂), primarily used stopped flow spectrophotometry, as reported here, following papers on the electrochemical behaviour of the individual redox couples in Stretford Processes. The course of reaction (AQ27DS + HS^– ions) was also followed with a gold bead indicator electrode, the potential of which was determined essentially by the AQ27DS/AQ27DSH^– couple as the former species were reduced to the latter. Attempts to use⁵¹V NMR to characterize aqueous vanadium-sulphur complexes were inconclusive. A possible mechanism for Stretford Processes is postulated, involving polysulphide (S _n ^2–) ions as intermediates, which are oxidized to elemental sulphur by another intermediate, H₂O₂, formed by reaction of AQ27DSH^– ions and dissolved oxygen.     

A Viscosity-Temperature Relation for Glass

A theory for the viscosity and structure of glass as a function of temperature and composition had been advanced, proposing that at a few critical temperatures silicate glasses undergo structural transformations. Between these transformation temperatures, the activation energy and lattice coefficient are constant. A series of special glasses were melted and viscosity was measured to test this theory. The results indicate that the viscosity-temperature behavior of glass does not conform to the previously proposed model. The activation energy appears to vary continuously over the entire temperature range studied. However, a critical temperature does exist at which the temperature coefficient of the activation energy changes. This discovery represents a more subtle change than that previously envisaged.     

Oxidative thermal decomposition of poly(vinyl chloride) compositions

“Pure” poly(vinyl chloride) resin and four compositions containing poly(vinyl chloride) were subjected to oxidative thermal degradation in air at &400°C both in a quiescent and a flow system. The volatiles formed were identified and quantitatively determined on a gram-per-gram basis. Hydrogen chloride was the main product found. The nature and relative concentration of the produced organic chlorinated species appeared to be dependent not only on the poly(vinyl chloride) constituent but also on the other ingredients. All the compositions contained phthalate ester plasticizers. In the dynamic system, these distilled largely unchanged, whereas under static conditions transformation into phthalic anhydride occurred.     

Role of P2O5 in TiO2-Opacified Porcelain Enamels

Phosphorus pentoxide is known to affect the reflectance and color of TiO₂-opacified porcelain enamels. It has been postulated that P₂O₅, impedes the anatase-to-rutile phase transformation. This hypothesis was tested by applying recently developed analytical procedures based on X-ray diffraction analysis to a typical porcelain enamel cover coat system. The inversion of anatase to rutile was not significantly affected by P₂O₅. Instead, in the range 0.5 to 4%, as P₂O₅ concentration was increased in the frit, the rate of crystallization of both anatase and rutile also increased, with the rate of increase of anatase being about twice that of rutile.     

Exploring single electrode reactions in polymer electrolyte fuel cells

Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway.     

Facile preparation of amphiphilic oxyethylene-oxypropylene block copolymers by selective triazine coupling

A novel synthetic route for preparing high molecular weight poly(oxyalkylene) block copolymers has been developed by using 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride, cc) as the coupling core. The coupling reaction involves the selective substitutions of oligo(oxyalkylene)-amines onto three chlorides of the triazine ring in a stepwise manner at 0, 25 and 130 °C. By judiciously selecting the starting amines and reaction conditions, one can tailor the copolymer structures with different block configurations (tri-block, multi-block, random and alternating block). The prepared copolymers can have a high molecular weight, up to 25,600 g/mol (GPC polydispersity=1.48), and also high thermal stability due to the presence of triazine functionalities. The copolymers with hydrophilic and hydrophobic oligo(oxyalkylene) blocks are of versatile properties in solubility (water soluble or water insoluble) and morphology (crystalline or amorphous). With a specific structure of alternating oligo(oxyethylene)/oligo(oxypropylene) blocks (2000 g/mol each block), the copolymer exhibits the property of self-association. It reduces the interfacial tension of toluene/water as low as 0.5 dyne/cm at the critical micelle concentration of 0.01 wt%.