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Formation kinetics of propane hydrates
No full textPropane hydrates are rarely considered by scientists. Despite the narrow borders of the formation region, they can form during storage and transportation of the liquefied petroleum gases. Therefore, it is important to know the induction time for solid hydrate formation. The present paper has considered the formation both from melting ice (at 1 °C and 4 bar) and from water (at 2 °C and 3.6-4.8 bar) in a stirred vessel. The formation from ice was quite instantaneous, while the production from water took about 15 h to start (and about 3 days to be completed) and depended on the pressure: in fact, it was slower at low pressure. All hydrates contained a high amount of ice (75-80%). The modulated differential scanning calorimetry was used for hydrate characterization: the reversing (heat-capacity) curves permitted one to quickly distinguish between hydrate and ice, also allowing a semiquantitative evaluation of the hydrate content
Characterization of gas hydrates by Modulated Differential Scanning Calorimetry
No full textModulated Differential Scanning Calorimetry (MDSC) has been applied to the study of methane, ethane, and propane hydrates at different hydrate and ice concentrations. The reversing thermodynamical component of the MDSC curves, makes it possible to characterize such hydrates. Methane and ethane hydrates show the melting-decomposition peak at a temperatures higher than the ice contained in the sample, while propane hydrate melts and decomposes at a lower temperature than the ice present in the sample. The hydrate peaks tend to disappear if the hydrate is stored at atmospheric pressure. Guest size and cavity occupation fix the heat of dissociation and stability of the hydrates, as confirmed by parallel tests on tetrahydrofurane hydrates
Dissociation Rate of THF-methane Hydrates
No full textA number of papers and research projects suggest that stranded natural gas can be transported in a solid hydrate state at higher temperatures or lower pressures compared to conventional transportation systems (LNG and CNG). The self-preservation effect of methane hydrate can probably be improved by the use of a third component besides CH4 and water. Tetrahydrofuran (THF) is a promoter that greatly reduces the required formation pressures. In the present work the influence of THF on the decomposition kinetics of mixed THF-CH4 hydrates was studied to evaluate the THF stabilization effect. The experimental work, carried out with the help of a reaction calorimeter, has revealed that the dissociation rate of mixed THF hydrates is lower (on average by one order of magnitude) than that of simple methane hydrates. Mixed hydrates can also be stored for short periods at temperatures over 0ıC. However, the best preservation conditions (among the experimented ones) are realized at 1ıC and 3 MPa. (about 66 days required for complete dissociation)
CO2 sequestration from coal fired power plants
No full textThe paper takes into consideration a new approach for CO2 capture and transport, based on the formation of solid CO2 hydrates. Carbon dioxide sequestration from power plants can take advantage of the properties of gas hydrates. The formation and decomposition of hydrates from various N2-CO2 mixtures has been studied experimentally in a 2 l reactor, to determine the CO2 separation in terms of hydrate composition and residual CO2 content in the reacted gas. Carbon dioxide acts as a co-former for the production of hydrates containing nitrogen, besides CO2. The mixed hydrates that are obtained are less stable than simple CO2 hydrates. When CO2 content in the flue gas is higher than 30% by volume, the hydrates formed at 5 MPa are sufficiently concentrated (about 70% CO2) and carbon dioxide reduction in the reacted gas is acceptable. The application of a process based on hydrate formation could be especially interesting (for CO2 capture and transport) when connected to an oxy-coal combustion process; in this case the CO2 content in the flue gas is very high and the hydrate formation is greatly facilitated. © 2009 Elsevier Ltd. All rights reserved
CO2 hydrate: Formation and dissociation compared to methane hydrate
No full textFor CO2 disposal in the form of hydrate it is important to know the decomposition kinetics at moderate pressures and temperatures, similar to those that could be realized in the storage systems. This paper has considered the preservation of CO2 hydrate containing different quantities of CO2, at pressures between 0.1 and 0.3 MPa and temperatures between -3 and 0 degrees C. At the conditions (P, T) of this work, CO2 hydrate does not present any anomalous self-preservation effect, and its dissociation is not affected by subcooling before storage. More than pressure, which is very important for methane hydrate, temperature affects the preservation. The temperature of -3 degrees C assures a good stability at atmospheric pressure, providing that CO2 saturation into the hydrate is not too high CO2 hydrate is generally more stable than CH4 hydrate due to the different activation energy of decomposition
Modulated DSC for gas hydrates analysis
No full textModulated DSC has been applied to the study of methane, ethane and propane hydrates at different hydrate and ice concentrations. The reversing component of the TMDSC curves, makes it possible to characterize such hydrates. Methane and ethane hydrates show the melting-decomposition peak at a temperatures higher than the ice contained in the sample, while propane hydrate melts and decomposes at lower temperature than the ice present in the sample. The hydrate peaks tend to disappear if the hydrate is stored at atmospheric pressure. Guest size and cavity occupation fix the heat of dissociation and stability of the hydrates, as confirmed by parallel tests on tetrahydrofurane hydrates
Formation and Dissociation of CO2 and CO2-THF Hydrates Compared to CH4 and CH4-THF Hydrates.
No full textThis work is part of a research project sponsored by the Italian Electricity Agency for CO2 disposal in form
of hydrate. The dissociation behavior of CH4 hydrate was taken as a reference for the study of the CO2
hydrate preservation. The formation and dissociation of CO2 and CO2–THF mixed hydrates, compared to
CH4 and CH4 – THF mixed hydrates, has been considered.
The experimental tests were performed in a 2 liter reaction calorimeter at pressures between 0.1 and 0.3
MPa. The dissociation has been followed at temperatures from -3 °C to 0 °C for CO2 and CH4 hydrates,
and from -3 °C to 10 °C for THF mixed hydrates.
More than pressure, which is very important for methane hydrates, temperature affects the preservation of
CO2 and CO2–THF mixed hydrates. Subcooling after formation is important for methane hydrate
preservation, but it does not substantially affect CO2 hydrate stability. In the studied P, T range, CO2
hydrate does not present any anomalous self-preservation effect. The mixtures containing more ice show a
slower dissociation rate. Methane hydrate requires less energy to dissociate than CO2 hydrate and,
therefore, is less stable. On the contrary, the mixed CO2 – THF hydrates are less stable than the mixed
methane hydrates. Modulated differential scanning calorimetry (MDSC) has been used for hydrate
characterization: both CH4 and CO2 hydrates include two decomposition peaks, the first due to the melting
of the ice and the second to the decomposition of the hydrate. The higher temperature of the decomposition
peak of CO2 hydrate confirms its higher stability respect to CH4 hydrate
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
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