1,720,966 research outputs found
Hydrogen emissions from an electrolysis unit
No full textHydrogen is expected to play a vital role as an energy carrier in the future decarbonized system. Currently, a large portion of the hydrogen produced comes from the steam reforming of methane present in natural gas, which produces significant amounts of carbon dioxide emissions. However, with the growing need to reduce greenhouse gas emissions, a shift from fossil fuels to renewable energy sources is required. As a result, there is a growing emphasis on green hydrogen, i.e., hydrogen generated using renewable power. Green hydrogen has been growing at an exponential rate since 2020 and is expected to account for the majority of hydrogen production by 2050. However, a few studies have recently suggested that hydrogen may indirectly contribute to global warming. It is believed that hydrogen delays the decomposition of methane, a strong greenhouse gas, and thus extends its lifetime in the atmosphere. If green hydrogen is to be the primary fuel in the energy transition, hydrogen emissions from an electrolysis unit should be investigated.This project focuses on identifying the sources of hydrogen emissions from an electrolysis unit. The goal is to comprehend the depth of this potential issue and investigate possible solutions. This project is carried out in collaboration with Worley, a market leader in the design, construction, and delivery of green H2 facilities. The leakage estimates for the green hydrogen alkaline electrolysis plant are based on Worley’s in-house data. Venting during startup and shutdowns when power is unavailable, as well as hydrogen crossover in the electrolyzer, have been identified as two major contributors to hydrogen emissions. Solutions such as flaring systems to combust the vented hydrogen and battery energy systems to reduce frequent shutdowns and startups are investigated. To reduce emissions from hydrogen crossover, a reactor is modeled to explore the catalytic recombination of hydrogen and oxygen. These solutions are subjected to a techno-economic analysis to determine their viability.Flare systems and battery energy systems are both deemed feasible. In the longrun, however, installing a battery energy system would be preferable to combusting the hydrogen product. In comparison to other battery technologies such as Li-ion and lead-acid batteries, vanadium redox flow battery systems have been found to provide the maximum incentives and highest optimal capacities at the lowest overall costs. To avoid emissions from hydrogen crossover in a low-pressure alkaline electrolysis unit, the most cost-effective design involves a single-stage compression followed by a scrubber, heater, and reactor. However, this design is still costly because the annualized costs are four times greater than the costs offset by emissions reductions per year. Governments can encourage the adoption of such solutions by providing financial incentives to businesses.Electrical Engineering | Sustainable Energy Technolog
Aqueous Phase Reforming of Maltose mediated by bimetallic nanostructured catalysts
Full text linkHydrogen is currently derived from nonrenewable natural gas and petroleum, but it could be generated from renewable resources such as biomass or water. Many manufacturing industries, such as breweries, have large waste streams which are mainly conditioned and returned to the environment, in fact, the beer production process generates from three to ten liters of wastewater per liter of beer. In this research the Aqueous Phase Reforming (APR) was studied as an approach to enhance H2 production from brewery wastewater, where maltose, a disaccharide made of two glucose molecules, constitutes most of the sugar made on the malting stage of the beer production and therefore it is one of the principal components of the wastewater. Aqueous phase reforming (APR) is the catalytic conversion at mild conditions of feedstock with organic compounds (e.g. biomass derived compounds) into valuable gaseous species from which H2 stands out. This reaction is mainly performed using monometallic and bimetallic catalysts made of nanoparticles. The preparation of metal nanoparticles could be a bit tricky due to the presence of some operating parameters which can modify the quality of the final product; for this reason, it's fundamental to have a good geometry and morphology control of these system and, consequently, that’s why it is the most treated topic in the chemical catalysis to obtain the desired material. In particular, in this research, the sol-immobilization method is used to synthetize nanostructured catalysts having metallic nanoparticles as active site, stabilized by polymers and deposited on a support. Then, the catalysts obtained are tested to perform the Aqueous Phase Reforming of Maltose, to see which one works better for the production of Hydrogen
Selective hydrogenation of CO2 to ethanol and higher alcohols using Li-supported Rh nanoparticles
Full text linkOne of the greatest and most complicated challenges of the 21st century for preventing even more disastrous effects on the habitability of our planet, is to minimize the increasing CO2 emissions representing the main cause of climate change. The focus of this thesis is the CO2 hydrogenation to higher alcohols. Particular attention is given to finding new catalysts and alternative catalyst synthesis methods that allow a good control over the structure of the catalyst involved in the CO2 hydrogenation reaction. Following both literature studies and previous results obtained by the research group, rhodium (Rh) nanoparticles (NPs) supported on mesosilica have been chosen as metal catalyst. An innovative hybrid method was developed, combining sol immobilization with impregnation. The best catalytic results showed 14.3% CO2 conversion for 1wt%Rh/meso-SiO2@Li10% and 5.8% of methanol selectivity for 1wt%RhFe/meso-SiO2@Li10% (both at 250°C, 80 bar, 20 mL/min of CO2/H2 with 1/3 ratio). Despite the low selectivity towards ethanol production, XPS spectra confirmed the presence of the desired species, and TEM and BET analysis a mesoporous structure with uniform dispersion of Rh NPs throughout all the surface. The efficacy of the synthesis strategy adopted was thus validated
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
Greener and facile synthesis of Cu/ZnO catalysts for CO<sub>2</sub>hydrogenation to methanol by urea hydrolysis of acetates
No full textCu/ZnO-based catalysts for methanol synthesis by COx hydrogenation are widely prepared via co-precipitation of sodium carbonates and nitrate salts, which eventually produces a large amount of wastewater from the washing step to remove sodium (Na+) and/or nitrate (NO3-) residues. The step is inevitable since the remaining Na+ acts as a catalyst poison whereas leftover NO3- induces metal agglomeration during the calcination. In this study, sodium- and nitrate-free hydroxy-carbonate precursors were prepared via urea hydrolysis co-precipitation of acetate salt and compared with the case using nitrate salts. The Cu/ZnO catalysts derived from calcination of the washed and unwashed precursors show catalytic performance comparable to the commercial Cu/ZnO/Al2O3 catalyst in CO2 hydrogenation at 240-280 °C and 331 bar. By the combination of urea hydrolysis and the nitrate-free precipitants, the catalyst preparation is simpler with fewer steps, even without the need for a washing step and pH control, rendering the synthesis more sustainable. This journal is </p
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
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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