1,720,967 research outputs found
Intensification of TSA processes using a microwave-assisted regeneration step
No full textThe energy consumption in the temperature swing adsorption (TSA) process is essentially due to the heating of the purge gas used in the regeneration of the adsorbent bed. The use of microwave (MW) irradiation, replacing the traditional heating technique, can result in process acceleration and energy costs reduction: the electromagnetic energy is directly converted into thermal energy inside the adsorbent bed, all the resistances to the heat transfer are overcome, and the heat flow becomes the opposite of the conventional one. In this work, the innovative MW-assisted regeneration of zeolites bed is investigated. A dedicated laboratory plant was set up, and the optimal operating conditions were studied and determined. The results highlighted (i) the heating of the zeolites up to 300°C, (ii) an energy efficiency of 75 % (due to a more uniform heat transfer to the adsorbent) and (iii) the consecutive tests showed a perfect repeatability of the results in terms of CO2 adsorption and desorption, so evidencing that no modification occurred in zeolites after MW irradiation. In addition, both the adsorption and desorption steps were modelled through a simulation tool specifically realized in Air Liquide, and the results showed a good agreement between the predicted and experimental values
Main hydrogen production processes: An overview
No full textDue to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use
Adsorption of N2O using Fe-13X zeolites - A Possibility to Make a Process Intensification by Using Microwaves for the Regeneration Step
No full textNitrous oxide is an effective greenhouse gas, which also greatly contributes to the depletion of the stratospheric ozone. Among the most common abatement methods, the capture of N2O by adsorption and the consequent reutilization appears as the best technique. In this work, the adsorption - regeneration cycle of N2O on 13X zeolites has been intensified by electrification of the process. More in detail, the regeneration step has been conducted in an innovative way, by employing a microwave heating. For the adsorption step, a concentrated stream consisting of 40 %vol N2O has been used, while the regeneration one was carried out using a stream of 100 %vol Ar and a power of 500 W for microwave heating. Each complete adsorption - regeneration cycle has been repeated several times, considering both wet and dry conditions for the gas mixture to be adsorbed, to prove the repeatability of the process. The results of the tests revealed that microwaves allowed to regenerate the solid adsorbent bed, by obtaining a significant reduction in the purge gas consumption and a recovery of 100 %. Therefore, employing a microwave-assisted regeneration step led to a process intensification, with respect to a conventional Temperature Swing Regeneration
Development of Innovative Structured Catalysts for the Catalytic Decomposition of N2O at Low Temperatures
No full textNitrous oxide (N2O), produced from several human activities, is considered a greenhouse gas with significant environmental impacts. The most promising abatement technology consists of the catalytic decomposition of N2O into nitrogen and oxygen. Many recently published papers dealing with N2O catalytic decomposition over Ni-substituted Co3O4 are related to the treatment of N2O concentrations less than 2 vol% in the feed stream. The present work is focused on developing catalysts active in the presence of a gaseous stream richer in N2O, up to 20 vol%, both as powder and in structured configurations suitable for industrial application. With this aim, different nickel-cobalt mixed oxides (NixCo1−xCo2O4) were prepared, characterized, and tested. Subsequently, since alumina-based slurries assure successful deposition of the catalytic species on the structured carrier, a screening was performed on three nickel-cobalt-alumina mixed oxides. As the latter samples turned out to be excellent catalysts for the N2O decomposition reaction, the final catalytic formulation was transferred to a silicon carbide monolith. The structured catalyst led to the following very promising results: total N2O conversion and selectivity towards N2 and O2 were reached at 510 °C by feeding 20 vol% of N2O. It represents an important achievement in the view of developing a more concretely applicable catalytic system for industrial processes
MW‐Assisted Regeneration of 13X Zeolites after N2O Adsorption from Concentrated Streams: A Process Intensification
No full textN2O has a global warming potential about 300 times higher than CO2, and even if its contribution to the greenhouse effect is underrated, its abatement in industrial production’s tail gas has become imperative. In this work, we investigate the feasibility of the microwave (MW)‐assisted regeneration of a 13X zeolite bed for N2O capture from tail gases. Several consecutive adsorption– desorption cycles were performed to verify the microwave heating effect on the zeolite’s adsorption properties. The results of the experimental tests, performed at N2O concentrations of 10, 20 and 40% vol, highlighted that (i) the steps are perfectly repeatable in terms of both adsorbed and desorbed amount of N2O, meaning that the MWs did not damage the zeolite’s structure, (ii) the presence of both H2O and O2 in the feed stream irreversibly reduces the adsorbent capacity due to nitrites and nitrates formation, and (iii) the presence of H2O alone with N2O still reduces the adsorbent capacity of the zeolites, which can be recovered through MW‐assisted regeneration at 350 °C. Moreover, the MW‐assisted TSA assured an energy and purge gas saving up to 63% and 82.5%, respectively, compared to a traditional regeneration process, resulting in effective process intensification
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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