Regeneration of zinc particles for zinc–air fuel cells in a spouted-bed electrode

Fuel cells wherein zinc particles form a negative electrode and a gas-diffusion electrode (air electrode) is the positive electrode, are under development. Such cells are dependent on the regeneration of the zinc particles (and electrolyte). This paper describes experiments on electrolytic cells equipped with spouted bed cathodes for use in this application. Experiments have been carried out on laboratory scale cells to determine the operability of cells for growing 'seed particles in the range from 0.4 to 1 mm to measure cell voltage and current efficiency (and thereby energy consumption rate), and to identify a suitable material that could be used as a diaphragm (separating the spouted bed from the oxygen evolving anode). A larger cell, capable of producing up to 10 kg Zn per day, was designed and built. The larger cell was run successfully fifteen times and showed cell voltages and energy consumption rates comparable with those of smaller cells.     

A study of PtRuO2 catalysts thermally formed on titanium mesh for methanol oxidation

Platinum-based catalysts, for the electro-oxidation of methanol, have been made by thermal decomposition of chloride precursors onto titanium mesh. The catalysed electrodes were successfully operated in acidic methanol electrolytes. Electrochemical characterisation has been carried out using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarisations. A complete analysis of the electrochemical results showed that the preliminary performance of the catalysed titanium mesh was comparable to that achieved with carbon-supported PtRu catalysts. The catalysts formed on titanium mesh by thermal decomposition also exhibited dimensional stability. Catalysed titanium mesh therefore appears to be a promising alternative to carbon-supported catalysts for certain fuel cell applications.     

Hydrolytic aging of polypropylene studied by X‐ray photoelectron spectroscopy

X‐ray photoelectron spectroscopy (XPS) was used to study the hydrolytic aging of polypropylene according to the pHs of degrading buffer solutions and the time of aging. The study was concentrated over periods of 3, 6, and 9 months for values of pH close to the real environments of use of the material (pH of 6, 7, and 8). The polypropylene underwent an oxidation of its polymeric matrix, independently of the range of pH values, by the production of C? OH, C?O, and O?C? O groups. These chemical functions were observed in high resolution XPS spectra around C1s and O1s peaks. Beginning with these results and from mechanisms of (photochemical, thermal, and others) aging proposed in the literature, it was then possible to propose mechanisms of hydrolytic ageing of polypropylene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3830–3838, 2004     

Anisotropy in mechanical and dynamic properties of composites based on carbon fiber filled thermoplastic elastomeric blends of natural rubber and high density polyethylene

The effects of short carbon fibers on static and dynamic properties of thermoplastic elastomeric blends of natural rubber (NR) and high density polyethylene (HDPE) have been studied. Both mechanical and dynamic properties are dependent on fiber concentration. The fiber aspect ratio ranges from 20 to 30. Adhesion between fiber and matrix is evident from the SEM photomicrographs of the failed composites and from variation of relative damping properties. Fiber orientation occurring during processing causes anisotropy in the physical properties. In composites with longitudinally oriented fibers, tensile failure occurs by both fiber pullout and breakage, while in composites with transversely oriented fibers, matrix failure dominates. The incorporation of fibers into the matrix lowers the tan δ_max value, but no change in glass transition temperature is observed.     

Effect of water on HDS of DBT over a dispersed Mo catalyst using in situ generated hydrogen

A novel process was developed for the bitumen emulsion upgrading, wherein emulsion breaking and upgrading occurred in the same reactor using H₂ generated in situ from the water in the emulsion via the water gas shift reaction (WGSR). In this study, dibenzothiophene (DBT) was chosen as a model compound to investigate the effect of water and in situ H₂ on hydrodesulfurization (HDS). All the experiments were performed in a 1-L autoclave reactor at temperatures between 300 and 380 °C using in situ H₂ and ex situ H₂ (externally supplied H₂) over a dispersed Mo catalyst formed from phosphomolybdic acid (PMA). At very low water content, water was found to promote the HDS reaction in the ex situ H₂ run probably because it facilitates the formation of more active dispersed MoS_x species. At higher water content, however, water inhibits every individual reaction in the reaction network in the HDS of DBT, blocking the hydrogenation pathway more than the hydrogenolysis pathway. The relative reactivity of the in situ and ex situ H₂ depends on the water content present in the reaction system. At an optimized mole ratio of H₂O:CO (1.35), higher HDS activity was observed in the in situ H₂ run compared to ex situ H₂ run, and particularly, the hydrogenation pathway was promoted in the in situ H₂ run.     

Phenolic compounds from vacuum pyrolysis of wood wastes

Various softwood and hardwood bark residues, primary sludges and softwood sawdust residues were processed by vacuum pyrolysis in a laboratory scale batch reactor. The pyrolysis oil, water, charcoal, and gas were recovered and analyzed. The pyrolysis oils were analyzed in details for their content in phenolic compounds after derivatization to their acetyl derivatives. The influence of temperature, heating rate, feedstock bed thickness, particle size and feedstock water pretreatment on the yield of phenols was investigated. The highest yield of phenols was obtained when hardwood bark was soaked in water for 48 hours and pyrolyzed at a temperature of 450°C and a heating rate of 10°C/min. Pyrolysis performance was evaluated in terms of total phenolic yield and composition.     

Prediction of minimum velocity and minimum bed pressure drop for gas-solid fluidization in conical conduits

Experimental investigations have been carried out for spherical and non-spherical particles using beds comprised of single-sized particles and mixtures in the size and particle density ranges of 439 to 1524 μm and 1303 to 4948 kg/m³, respectively. Five conical fluidizers with varying apex angles of 8.86, 14.77, 19.60, 32.0 and 43.2 degrees were used. Experimental values of minimum velocity and bed pressure drop with air as the fluidizing medium have been compared with their respective values obtained from different models available in the literature. Deviations for each chosen model have been presented.     

Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Numerical simulations of drop impact and spreading on horizontal and inclined surfaces

The phenomenon of drop spreading is important to several process engineering applications. In the present work, numerical simulations of the dynamics of drop impact and spreading on horizontal and inclined surfaces were carried out using the volume of fluid (VOF) method. For the horizontal surfaces, the dynamics of impact and spreading of glycerin drops on wax and glass surfaces was investigated for which the experimental measurements were available [Šikalo, Š., Tropea, C., Ganic, E.N., 2005a. Dynamic wetting angle of a spreading droplet. Experimental Thermal and Fluid Science 29, 795-802; Šikalo, Š., Tropea, C., Ganic, E.N., 2005b. Impact of droplets onto inclined surfaces. Journal of Colloid and Interface Science 286, 661-669]. The influence of surface wetting characteristics was investigated by using static contact angle (SCA) and dynamic contact angle (DCA) models. The dynamics of drop impact and spreading on inclined surfaces and the different regimes of drop impact and spreading process were also investigated. In particular, the effects of surface inclination, surface wetting characteristics, liquid properties and impact velocity on the dynamics of drop impact and spreading were investigated numerically and the results were verified experimentally. It was found that the SCA model can predict the drop impact and spreading behavior in quantitative agreement with the experiments for less wettable surfaces (SCA>90^°). However, for more wettable surfaces (SCA<90^°), the DCA observed at initial contact times were order of magnitude higher than SCA values and therefore the DCA model is needed for the accurate prediction of the spreading behavior.     

CO2 gasification of wood charcoals derived from vacuum and atmospheric pyrolysis

The gasification of biomass derived char obtained via vacuum and atmospheric pyrolysis of Populus tremuloides has been studied in the ranges of 725–960°C and 0.1 to 6 MPa. CO₂ was used as the oxidizing gas. The results show that char reactivity is influenced by the preheating rates and that pressure effects are significant between 850°C and 950°C. A correlation based on the expression: df/dt = k₀{exp(-E/RT)}(1 - f)^af^βP^yCO₂ was used to fit the experimental data. In general, vacuum pyrolysis derived char showed a higher reactivity than atmospheric pyrolysis chars. An explanation based on a higher oxygen content of the vacuum pyrolysis char is suggested.