1,720,956 research outputs found
Calculating the products yield and their vapor-liquid equilibrium in the low-temperature Fischer-Tropsch synthesis
No full textThe ultimate goal of this paper is the assessment of the yield of liquid hydrocarbons formed in the low-temperature Fischer-Tropsch synthesis over a representative cobalt-based catalyst at relevant process conditions. To achieve this goal, a set of steady-state Fischer-Tropsch runs has been carried out in a lab-scale reactor loaded with a 20 wt.% Co/Al2O3 catalyst, investigating the effects of the main process conditions (temperature, H 2/CO inlet ratio, content of inert gas in the feed, syngas space velocity) on the reactants conversion and on the C1-C50 product selectivity. Then, a CO conversion kinetic model and a product distribution model have been developed and have been jointly adopted to describe the product yields in the reactor as a function of the process conditions. Product yields have been finally used as input for an isothermal and isobaric non-ideal vapor-liquid equilibrium calculation. It has been found that, at the typical low-temperature Fischer-Tropsch synthesis process conditions, more than 95 mol.% of the C1-C30 hydrocarbons, that in general represent more than 99 mol.% of the hydrocarbon products, are in the vapor phase
Development and validation of an integrated model for the description the products yield and their vapour/liquid repartition in the Fischer-Tropsch synthesis
No full textLow-Temperature Fischer-Tropsch synthesis: products yieldand their vapor-liquid equilibrium
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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
Fischer-Tropsch synthesis over Al2O3- supported cobalt catalysts
No full textThe low temperature Fischer-Tropsch synthesis (FTS) is a CO hydrogenation process applied to produce synthetic long chain hydrocarbons and oxygenates that can be marketed as high added value fuels (gasoil, kerosene) or chemicals (base oils, normal paraffins, naphta).
Several aspects have been addressed in this work. A model for the prediction of the yields of vapor and liquid hydrocarbon species formed during the low-temperature Fischer-Tropsch synthesis over a representative cobalt-based catalyst at industrially relevant process conditions has been developed in this work. At the typical process conditions more than 95 mol.% of the C1-C30 hydrocarbons are in the vapor phase the most abundant product in the liquid phase formed in the reactor is the heptacosane, whose liquid fraction represents more than 78% of the total amount of C27 formed in the reactor.
A kinetic model able to describe the distribution of FTS products, not only in terms of hydrocarbon products, but also of oxygenates, including carbon dioxide has been developed. Given that the Co-based FTS does not produce many oxygenated species, it has been decided to group the alcohols with more than five carbon atoms into a single pseudo component. The developed model accurately predicts the reactants conversions and the hydrocarbon products distribution, distinguishing between n-paraffins and -olefins. In particular this model is able to describe the linear hydrocarbon product distribution typical of the polymerization reactions like the FTS. Furthermore, the same model is able to properly describe the distribution of oxygenated products and the carbon dioxide selectivity.
Mass transfer limitations may affect the net rate of reactants conversion and the product distribution. This work addresses indeed the effect of internal diffusive limitations on the reactivity of Co/Al2O3 catalysts for the FTS. In order to study the effects of diffusive limitations tests were carried out on two catalytic systems having the same composition but different particle size, and operating at different temperatures. Both catalyst systems were tested at different temperatures, so as to be able to estimate the activation energy of the reaction as a function of the catalyst particle size. The effects observed pointed out that, upon increasing the temperature the CO conversion increases, the selectivity to heavy products (especially C25+) decreases, while the light species (CH4 in particular) increases, the olefin content in the products is reduced the CO2 selectivity increases.
In order to prevent the onset of mass transfer limitations, it is also possible to choose a catalytic system of egg-shell type, constituted by particles in which the catalytically active phase is arranged on a thin layer which constitutes the outer part of the granule. Adoption of these catalyst systems enables a compromise between pressure drop and diffusive limitations. With the developed method eggshell catalysts based on cobalt and supported on alumina. An activity test is carried out to demonstrate the ability of the catalyst to be active at the FTS.The low temperature Fischer-Tropsch synthesis (FTS) is a CO hydrogenation process applied to produce synthetic long chain hydrocarbons and oxygenates that can be marketed as high added value fuels (gasoil, kerosene) or chemicals (base oils, normal paraffins, naphta).
Several aspects have been addressed in this work. A model for the prediction of the yields of vapor and liquid hydrocarbon species formed during the low-temperature Fischer-Tropsch synthesis over a representative cobalt-based catalyst at industrially relevant process conditions has been developed in this work. At the typical process conditions more than 95 mol.% of the C1-C30 hydrocarbons are in the vapor phase the most abundant product in the liquid phase formed in the reactor is the heptacosane, whose liquid fraction represents more than 78% of the total amount of C27 formed in the reactor.
A kinetic model able to describe the distribution of FTS products, not only in terms of hydrocarbon products, but also of oxygenates, including carbon dioxide has been developed. Given that the Co-based FTS does not produce many oxygenated species, it has been decided to group the alcohols with more than five carbon atoms into a single pseudo component. The developed model accurately predicts the reactants conversions and the hydrocarbon products distribution, distinguishing between n-paraffins and -olefins. In particular this model is able to describe the linear hydrocarbon product distribution typical of the polymerization reactions like the FTS. Furthermore, the same model is able to properly describe the distribution of oxygenated products and the carbon dioxide selectivity.
Mass transfer limitations may affect the net rate of reactants conversion and the product distribution. This work addresses indeed the effect of internal diffusive limitations on the reactivity of Co/Al2O3 catalysts for the FTS. In order to study the effects of diffusive limitations tests were carried out on two catalytic systems having the same composition but different particle size, and operating at different temperatures. Both catalyst systems were tested at different temperatures, so as to be able to estimate the activation energy of the reaction as a function of the catalyst particle size. The effects observed pointed out that, upon increasing the temperature the CO conversion increases, the selectivity to heavy products (especially C25+) decreases, while the light species (CH4 in particular) increases, the olefin content in the products is reduced the CO2 selectivity increases.
In order to prevent the onset of mass transfer limitations, it is also possible to choose a catalytic system of egg-shell type, constituted by particles in which the catalytically active phase is arranged on a thin layer which constitutes the outer part of the granule. Adoption of these catalyst systems enables a compromise between pressure drop and diffusive limitations. With the developed method eggshell catalysts based on cobalt and supported on alumina. An activity test is carried out to demonstrate the ability of the catalyst to be active at the FTS.DIPARTIMENTO DI CHIMICA, MATERIALI E INGEGNERIA CHIMICA GIULIO NATTA25LIETTI, LUCAFARAVELLI, TIZIAN
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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