Comparison of the group V and VI transition metal carbides for methane dry reforming and thermodynamic prediction of their relative stabilities

The DME‐SCR activity was suppressed upon exposure of a γ-alumina catalyst to SO₂, in contrast to methanol‐SCR, which remains active at the same surface sulphate coverage. This difference in behaviour is attributed to the limited availability of surface methoxy, which may be regarded as a prerequisite for NOx- reduction over γ-alumina under lean conditions, in the case of dimethyl ether in the presence of SO₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Free Radical Chemistry. Part 9.1 Approaches to Fluorinated Polyethers—Model Compound Studies

Using peroxide, γ-, and UV-irradiation, free radical addition reactions of hexafluoropropene to diethers and to 18-crown-6 have been investigated and mono-, di-, and poly-adducts have been obtained. Factors influencing these additions, especially polar characteristics of intermediate radicals, have been elucidated. Adducts of 18-crown-6 retain a capacity to complex to alkali-metal ions.     

Dielectric Drying

ABSTRACT

Dielectric heating is a term which covers both radio frequency (RF) and microwave systems. It has been used for industrial drying for many years because it has a number of advantages over other drying processes. These advantages include the volumetric dissipation of energy throughout a product, and the ability to automatically level any moisture variation within it. It is generally true to say that these techniques can only be justified in processes involving material of “high” value being processed in modest quantities but when combination with other fuel fired techniques there may be opportunities to broaden the range of applications. In addition to a desciption of current industrial applications, the theory of dielectric heating, the similarities and differences between RF and microwave are discussed together the effects of the dielectric roperties of a product on the design of the equipment     

Charring rates for double beams made from laminated veneer lumber (LVL)

This paper examines charring rates for different cross‐sections of single and double timber beams made from laminated veneer lumber, with nailed, screwed or glued connection types for the double beams. Charring rates and burning characteristics were examined both in a small furnace and in a larger pilot furnace. The bottom charring rates were sometimes greater than the side charring rates for very narrow beams dominated by corner effects and for double beams where the two components could separate during the fire exposure. The nail‐connected double laminated veneer lumber beams experienced the largest separation, leading to charring between the two components. The best performance was from the glued connection, which showed similar charring rates as a solid timber beam. Both the large‐scale and small‐scale testing showed that suitably placed screws (preferably full‐length threaded) can be used to give almost the same performance as a glued connection. Experimental findings were compared with results from a finite element analysis. There was reasonable agreement while the char layer was small, but less agreement in later stages as the char layer increased in thickness. Experimental findings were used to modify a spreadsheet design tool that predicts the fire resistance of a timber–concrete composite floor. Copyright © 2012 John Wiley & Sons, Ltd.     

High Temperature Interactions Between Residual Oil Ash and Dispersed Kaolinite Powders

The potential use of sorbents to manage ultrafine ash aerosol emissions from residual oil combustion was investigated using a downfired 82 kW laboratory-scale refractory-lined combustor. The major constituents were vanadium (V), nickel (Ni), iron (Fe), and zinc (Zn). The overall ash content of residual oil is very low, resulting in total ash vaporization at 1725 K with appreciable vaporization occurring at temperatures as low as 1400 K. Therefore, the possibility of interactions between ash vapor and sorbent substrates exists. Kaolinite powder was injected at various locations in the combustor. Ash scavenging was determined from particle size distributions (PSDs) measured by a Scanning Mobility Particle Sizer. Impactor samples and X-ray fluorescence (XRF) analyses supported these data. Injection of kaolinite sorbent was able to capture up to 60% of all the ash in the residual fuel oil. However, captures of ～ 30% were more common when sorbent injection occurred downstream of the combustion zone, rather than with the combustion air into the main flame. Without sorbent addition, baseline measurements of the fly ash PSD and chemical composition indicate that under the practical combustion conditions examined here, essentially all of the metals contained in the residual oil form ultrafine particles (～0.1 μ m diameter). Theoretical calculations showed that coagulation between the oil ash nuclei and the kaolinite sorbent could account for, at most, 17% of the metal capture which was always less than that measured. The data suggest that kaolinite powders reactively capture a portion of the vapor phase metals. Mechanisms and rates still remain to be quantified.     

Interactions between fat crystal networks and sodium caseinate at the sunflower oil-water interface

A Couette-type torsion wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of pH 7 (I=0.05 M) buffered solutions of sodium caseinate in contact with sunflower oil. The sunflower oil contained 1% fat crystals in either the β or β′ polymorphic form, or was crystal free. In all cases, the fat crystals increased the interfacial shear viscosity synergistically, with the β′ crystals causing the biggest increase. Substituting the protein for a small-molecule surfactant (Tween-40) showed that this was not simply due to the protein lowering the interfacial tension. Sedimentation studies of the different fat crystal slurries suggested that the extent of the interfacial shear viscosity increase was related to the strength of crystal-crystal interactions in the oil phase. It seems likely that when protein is present at the interface, it fixes the adsorbed layer of fat crystals to the cross-linked protein film at the interface. When this film was sheared, the strength of the crystal-crystal interactions in the oil phase became important. However, when Tween-40 was in the aqueous phase instead of the protein, the crystal-crystal interactions were not relevant, presumably because the Tween-40 interfacial film simply flowed around the adsorbed crystals     

An analytical index for evaluating manufacturing cost and performance of low-pressure hollow fibre membrane systems

Water and waste-water treatment through the use of the membrane filtration technology is one of the processes utilized currently to meet the growing demand for water. While new technologies can harness water from various non-traditional sources such as oceans, there remains the possibility of making drinking water more expensive through the use of costly water treatment equipment. To prevent this and ensuing catastrophes in the world, the water industry needs a strategy that keeps the price of water and price of products aiding the treatment of water controlled in to the future.     

Thermodynamically consistent modeling of elementary electrochemistry in lithium-ion batteries

This paper is particularly concerned with the elementary reactions and transport processes that are responsible for Li-ion battery performance. The model generally follows the widely practiced approach developed by Newman and co-workers (e.g., Doyle et al., J. Electrochem. Soc. 140 (1993) 1526 [1]). However, there are significant departures, especially in modeling electrochemical charge transfer. The present approach introduces systems of microscopically reversible reactions, including both heterogeneous thermal reactions and electrochemical charge-transfer reactions. All reaction rates are evaluated in elementary form, providing a powerful alternative to a Butler-Volmer formalism for the charge-transfer reactions. The paper is particularly concerned with the influence of non-ideal thermodynamics for evaluating reversible potentials as well as charge-transfer rates. The theory and modeling approach establishes a framework for extending chemistry models to incorporate detailed reaction mechanisms that represent multiple competitive reaction pathways.     

Global Optimization of Adsorbate–Surface Structures While Preserving Molecular Identity

As the complexity of atomistic simulations in catalysis and surface science increases, the challenge of manually finding the lowest-energy adsorbate–surface geometries grows significantly. In the current work, a global optimization approach that preserves adsorbate identity is applied to enable the automated search for optimized binding geometries. This technique is based on the minima hopping method developed by Goedecker, but is modified to preserve the molecular identity of adsorbates by the application of a new class of Hookean constraints. These constraints are completely inactive when the adsorbate identity is preserved, but act to restore the adsorbate structure via a Hookean force when the bond length exceeds a threshold distance. Additionally, a related Hookean constraint has been developed to prevent adsorbates (particularly such adsorbates as CO and CH₂O that have stable gas-phase forms) from volatilizing during the molecular dynamics portion of the minima hopping technique. This combination, referred to herein as the constrained minima hopping method, was tested for its suitability in finding the minimum-energy binding configuration for a set of 17 C _x H _y O _z adsorbates on a stepped Cu fcc(211) surface and in all cases found the global minima in comparable or fewer steps than the previous brute force methodologies. It is expected that methods such as this will be crucial to finding low-energy states in more complex systems, such as those with high coverages of adsorbed species or in the presence of explicit solvent molecules.