1,720,977 research outputs found
Experimental and Modeling Analysis of the Thermal Behavior of an Autothermal C3H8 Catalytic Partial Oxidation Reformer
No full textIn this work, a spatially resolved sampling technique is applied to characterize the performance of a C3H8 CPO reformer and to compare it with that of a CH4 reformer. The case of Rh-coated honeycomb catalysts is examined. The axial profiles show that higher temperatures are reached in C3H8 CPO, especially at the reactor inlet. Surface hot-spot temperatures around 950 °C lead the catalyst to rapid loss of activity. A detailed model analysis is also applied to better understand the reasons for the observed differences of the thermal behavior. On one hand, the heat release via oxidation reactions is controlled by O2 mass transfer rate and thus proportional to O2 inlet concentration, which is 20% higher in the C3H8/air mixture at equal C/O ratio. On the other hand, while CH4 steam reforming is partly chemically controlled, C3H8 steam reforming is mainly limited by gas–solid diffusion. Thus, a less efficient balance between exo- and endothermic reactions occurs in the case of C3H8 CPO, and this results in much higher hot-spot temperatures. As a consequence, specific strategies for the optimization of the thermal behavior are required depending on the fuel. Modeling of the C3H8 CPO results shows that an increased catalyst load or a suitable aspect ratio of the reactor, combined with a decrease of the flow rate, produces a beneficial moderation of the hot-spot temperature of the catalytic wall
Catalytic partial oxidation of ethanol over Rh/Al2O3: Spatially resolved temperature and concentration profiles
No full textThe catalytic partial oxidation (CPOX) of ethanol was studied over rhodium/alumina-coated monoliths. An in situ sampling technique was used for ethanol CPOX, yielding spatially resolved temperature and concentration profiles. Molar C/O ratios from 0.65 to 0.85 were studied. Catalytic and blank experiments were both performed. The investigations clearly showed two zones inside the catalytic channel, an oxy-reforming zone as long as oxygen is present, with total oxidation and steam reforming as prevalent reactions, and a reforming zone, with steam reforming as the dominating reaction. Moreover, homogeneous gas-phase reactions, leading mainly to acetaldehyde and water, were observed in front of the catalyst. This was confirmed by blank experiments, which showed that homogeneous conversion of ethanol by oxidative dehydrogenation may occur in absence of a catalyst at temperatures higher than 640 K. Additionally, axial profiles were collected at a fixed C/O ratio in three catalytic channels, which were differently located across the monolith. A radial heat loss from the center to the outer channels of the monolith was observed, which led to variations in the axial concentration profiles across the honeycomb
Optimization of the thermal behavior of an adiabtic reformer for the catalytic partial oxidation of CH4 at short contact time
No full textHierarchical refinement of microkinetic models: assessment of the role of WGS and r-WGS pathways in CH4 Partial Oxidation on Rh
Full text linkIn this article, we demonstrate how first-principles calculations can be effectively employed in the development of microkinetic models for practical catalysis, despite material gaps and calculation uncertainties. In particular, we develop a hierarchically refined microkinetic model for the conversion of CH4 to syngas on Rh/alumina that incorporates peculiar insights from first-principles modeling. This model is able to correctly describe the behavior of the reacting system under significantly different conditions and also exhibits consistency between the predicted catalytic cycle and the observed reaction orders. We show that consistency between the kinetic parameters of all of the elementary steps included in the microkinetic model is of utmost importance in achieving full predictivity of the model. As a consequence, the information from various levels of theory needs to be integrated in an underlying framework that accounts for coverage effects and thermodynamic and kinetic consistencies. Within this scope, we performed a detailed microkinetic analysis of kinetic experiments in an annular reactor to hierarchically modify the reaction parameters guided by first-principles analysis. Then, to further assess the capabilities of the refined microkinetic model, we performed a microkinetic analysis of spatially resolved CH4 partial oxidation experiments on foams at different conditions of H2O and CO2 cofeed. The insights derived from first-principles calculations and included in the semiempirical microkinetic model were found to be pivotal for explaining the roles of the WGS and r-WGS in catalytic partial oxidation experiments. On the whole, this contribution provides a clear demonstration of the current possibilities and potentialities of first-principles machinery in developing microkinetic models for complex catalytic processes and represents the first practical example of the full application of the first-principles hierarchical refinement of a microkinetic model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Optimal Design of a CPO-Reformer of Light Hydrocarbons with Honeycomb Catalyst: Effect of Frontal heat Dispersions on the Temperature Profiles
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