Kinetics of the reduction of wüstite by hydrogen and carbon monoxide for the chemical looping production of hydrogen

Hydrogen of very high purity can be produced via the steam-iron process, in which steam oxidises metallic Fe in 3/4Fe + H2O→1/4Fe3O4 + H2. It is then advantageous to oxidise Fe3O4 in air to Fe2O3, an oxygen-carrier. This higher oxide of Fe is then reduced to regenerate metallic iron by reacting with synthesis gas, producing metallic Fe and possibly some wüstite (FexO, 0<x<1). In this three-stage process, the reduction of FexO to Fe is the slowest reaction. This paper is concerned with the kinetics of the reduction of wüstite (FexO) by reaction with CO, and, or H2. Starting with pure (99 wt%) wüstite, the intrinsic kinetics of its reduction to metallic iron were measured in fluidised beds at different temperatures. The reaction was found to have 3 distinct stages, (i) the removal of lattice oxygen in wüstite, (ii) rate increasing with conversion of solid and (iii) rate decreasing with conversion of solid. A random pore model was used to simulate the latter stages of the reduction of wüstite by either H2 or CO or a mixture of the two. It was found that the intrinsic rate of reduction in H2 is substantially faster than with CO, whereas the resistances to diffusion of H2 and CO through the product layer of Fe are comparable; these factors account for differences in the overall rates observed with these gases.This is the final published version. It is also available from the publisher at: http://www.sciencedirect.com/science/article/pii/S000925091400428X

The continuous combustion of glycerol in a fluidised bed

It is difficult to burn a liquid fuel inside a fluidised bed. For the first time, liquid glycerol has been burned, when continuously injected into the bottom of an electrically heated bed of alumina particles (sieved to 355 – 425 μm), fluidised by air. The temperature in the bed was held at 700, 800 or 900oC; usually (U/Umf) was 2.5. The bed’s depth was varied, as also were (U/Umf) and the ratio of fuel to air supplied to the bed. Measurements were made of the concentrations of CH4, O2, CO and CO2, and also of the temperature, in the freeboard well above the bed. On entering the bed, the liquid glycerol, rapidly formed bubbles of vapour, which quickly decomposed thermally, yielding mostly CO and H2. These gases then mixed with the other gases in the bed. It appears that the diffusive H2 mainly burns between the fluidised particles. With the bed at 700 – 900oC, no CO was detected far downstream of the bed, provided the equivalence ratio, θ, was below 0.7, i.e. with more than 43 % excess air. Under these fuel-lean conditions, all the carbon in the glycerol was oxidised to CO2. However, in a more fuel-rich situation, with θ > 0.7, CO was detected well above the bed, particularly with a deeper bed, at a lower temperature and operating more fuel-rich. Thus, with the bed at 900oC, CO was mostly oxidised inside the bed, but occasionally some CO burned on top of the bed. When a fuel-rich bed was below 850oC, not all the CO burned in the bed. Achieving complete combustion inside a fluidised bed is partly a problem of mixing the products of glycerol’s thermal decomposition with the fluidising air, which on entry exists mainly in bubbles. Consequently, increasing (U/Umf) promoted both mixing and combustion in a bed. In addition, in-bed combustion requires the bed to be sufficiently deep, hotter than 850oC and θ to be less than a critical value. The effects of other variables are discussed

Intronic Cis-Regulatory Modules Mediate Tissue-Specific and Microbial Control of angptl4/fiaf Transcription

The intestinal microbiota enhances dietary energy harvest leading to increased fat storage in adipose tissues. This effect is caused in part by the microbial suppression of intestinal epithelial expression of a circulating inhibitor of lipoprotein lipase called Angiopoietin-like 4 (Angptl4/Fiaf). To define the cis-regulatory mechanisms underlying intestine-specific and microbial control of Angptl4 transcription, we utilized the zebrafish system in which host regulatory DNA can be rapidly analyzed in a live, transparent, and gnotobiotic vertebrate. We found that zebrafish angptl4 is transcribed in multiple tissues including the liver, pancreatic islet, and intestinal epithelium, which is similar to its mammalian homologs. Zebrafish angptl4 is also specifically suppressed in the intestinal epithelium upon colonization with a microbiota. In vivo transgenic reporter assays identified discrete tissue-specific regulatory modules within angptl4 intron 3 sufficient to drive expression in the liver, pancreatic islet β-cells, or intestinal enterocytes. Comparative sequence analyses and heterologous functional assays of angptl4 intron 3 sequences from 12 teleost fish species revealed differential evolution of the islet and intestinal regulatory modules. High-resolution functional mapping and site-directed mutagenesis defined the minimal set of regulatory sequences required for intestinal activity. Strikingly, the microbiota suppressed the transcriptional activity of the intestine-specific regulatory module similar to the endogenous angptl4 gene. These results suggest that the microbiota might regulate host intestinal Angptl4 protein expression and peripheral fat storage by suppressing the activity of an intestine-specific transcriptional enhancer. This study provides a useful paradigm for understanding how microbial signals interact with tissue-specific regulatory networks to control the activity and evolution of host gene transcription

ICAR: endoscopic skull‐base surgery

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Stakeholder communication in 140 characters or less: a study of community sport foundations

Community sport foundations (CSFs), like other non-profit organizations, are increasingly employing social media such as Twitter to communicate their mission and activities to their diverse stakeholder groups. However, the way these CSFs utilize social media for communicating such practices remains unclear. Through a mixed-method approach of content analysis of tweets from 22 CSFs established by English professional football clubs and interviews with key individuals within these CSFs (n = 7), this study examines the extent to which CSFs’ core activities are being communicated through Twitter and identifies the strategies employed for doing so. Reflecting the target audiences CSFs are seeking to reach through Twitter and the challenges associated with communication about projects involving marginalized groups, tweets largely concern programs related to sports participation and education. The most frequently employed communication strategy is to inform, rather than interact or engage with stakeholders. However, CSFs with higher organizational capacity attempt to go beyond mere informing towards engaging with stakeholder groups that relate to their social agenda, highlighting the importance of trained and dedicated social media personnel in optimizing CSFs’ use of Twitter for communication

Oscillatory and nonoscillatory behavior of a simple model for cool flames, Sal'nikov's reaction, P → A → B, occurring in a spherical batch reactor with varying intensities of natural convection

When cool flames, or indeed any exothermic chemical reaction, occur in a fluid inside an unstirred vessel, the heat from the reaction often induces temperature gradients and consequently motion, i.e., natural convection. The intensity of the resulting flow is governed by the Rayleigh number (Ra). This work simulates numerically the behavior of Sal'nikov's reaction, P → A → B, under the influence of natural convection in an unstirred spherical reactor. This reaction is the simplest to exhibit the thermokinetic oscillations characterizing cool flames. The behavior of this system can be represented on a three-dimensional regime diagram, whose axes are ratios of the characteristic timescales (τ) for chemical reaction, diffusion (of both heat and mass), and natural convection. Previous work has identified a region of oscillations on this diagram in the purely diffusive limit, when Ra = 0. This work extends this analysis to the general 3D space, where diffusion and natural convection are both important. A region in which oscillations are observed has been found for fixed values of the first-order rate constants for Sal'nikov's reaction. There is a distinct change in the shape of the region of oscillations around the critical value of Ra ∼ 500, when natural convection becomes important. When diffusion dominates transport (Ra 500), the oscillations occur over a wider range of parameters than is the case for a diffusive system. The presence of natural convection also leads to various, more complex behaviors than are seen in the diffusive or well-mixed limits. A region in the regime diagram was found where the oscillations in temperature and the concentration of A have small amplitudes and a frequency that is quite different from those generated in a well-mixed system. It is possible that these oscillations are caused by natural convection, i.e., are not thermokinetic oscillations produced by the chemical reaction. It was also found that sometimes the oscillations in the temperature and the concentration of A are in phase; more generally they are in anti-phase. The evolution of nonoscillatory behavior with relatively small increases in temperature was found to be always fairly similar, regardless of the intensity of natural convection. The shape of the temperature profile along the vertical axis of the reactor did, however, change with the intensity of natural convection. Finally, the nonoscillatory solutions with a large rise in temperature in the presence of natural convection were found to be very much like those seen in the purely diffusive limit for small times, due to the relatively long induction time (∼3.5 s in a vessel with diameter 0.1 m) for the onset of natural convection. © 2008 The Combustion Institute

Oscillatory and nonoscillatory behavior of a simple model for cool flames, Sal'nikov's reaction, P → A → B, occurring in a spherical batch reactor with varying intensities of natural convection

When cool flames, or indeed any exothermic chemical reaction, occur in a fluid inside an unstirred vessel, the heat from the reaction often induces temperature gradients and consequently motion, i.e., natural convection. The intensity of the resulting flow is governed by the Rayleigh number (Ra). This work simulates numerically the behavior of Sal'nikov's reaction, P → A → B, under the influence of natural convection in an unstirred spherical reactor. This reaction is the simplest to exhibit the thermokinetic oscillations characterizing cool flames. The behavior of this system can be represented on a three-dimensional regime diagram, whose axes are ratios of the characteristic timescales (τ) for chemical reaction, diffusion (of both heat and mass), and natural convection. Previous work has identified a region of oscillations on this diagram in the purely diffusive limit, when Ra = 0. This work extends this analysis to the general 3D space, where diffusion and natural convection are both important. A region in which oscillations are observed has been found for fixed values of the first-order rate constants for Sal'nikov's reaction. There is a distinct change in the shape of the region of oscillations around the critical value of Ra ∼ 500, when natural convection becomes important. When diffusion dominates transport (Ra 500), the oscillations occur over a wider range of parameters than is the case for a diffusive system. The presence of natural convection also leads to various, more complex behaviors than are seen in the diffusive or well-mixed limits. A region in the regime diagram was found where the oscillations in temperature and the concentration of A have small amplitudes and a frequency that is quite different from those generated in a well-mixed system. It is possible that these oscillations are caused by natural convection, i.e., are not thermokinetic oscillations produced by the chemical reaction. It was also found that sometimes the oscillations in the temperature and the concentration of A are in phase; more generally they are in anti-phase. The evolution of nonoscillatory behavior with relatively small increases in temperature was found to be always fairly similar, regardless of the intensity of natural convection. The shape of the temperature profile along the vertical axis of the reactor did, however, change with the intensity of natural convection. Finally, the nonoscillatory solutions with a large rise in temperature in the presence of natural convection were found to be very much like those seen in the purely diffusive limit for small times, due to the relatively long induction time (∼3.5 s in a vessel with diameter 0.1 m) for the onset of natural convection. © 2008 The Combustion Institute