2,100 research outputs found
Enthalpies of dissociation of clathrate hydrates of carbon dioxide, nitrogen, (carbon dioxide plus nitrogen), and (carbon dioxide plus nitrogen plus tetrahydrofuran)
No full textA calorimetric technique is described for measuring the enthalpy of dissociation liberated from solid hydrates. In this study, the enthalpies of dissociation were determined at T = 273.65 K and p = 0.1 MPa for simple and mixed hydrates of carbon dioxide, nitrogen, (carbon dioxide + nitrogen), and (carbon dioxide + nitrogen + tetrahydrofuran) using an isothermal microcalorimeter. The addition of tetrahydrofuran (THF) promoted hydrate stability and increased the number of guest molecules encaged in the small and large cavities of the hydrate lattice, resulting in lower enthalpy of dissociation, compared with structure It hydrate. The composition ratio of guest molecules did not affect the enthalpy of dissociation, which was found to be nearly constant for the same mixture. (C) 2001 Academic Press.This work was supported by grant No. 98-0502-04-01-3 from the Basic Research program
of the KOSEF and also partially by the Brain Korea 21 Project
Hydration number and two-phase equilibria of CH4 hydrate in the deep ocean sediments
No full text[1] The aqueous solubilities of CH4 in the two-phase (hydrate (H)-liquid water (L-w)) region, which is very close to the deep sea floor condition, were measured at various ranges of temperature and pressure. The hydration number determined via Raman spectroscopy at 10.0 MPa and 274.15 K was found to be 6.00 that is a little higher than 5.75 of the ideal one. The solubility of CH4 in liquid water largely increased with a small increase of temperature, but slightly decreased with increasing pressure in the two-phase (H-L-w) region. This solubility behavior was experimentally confirmed to be completely different from that occurring in the three-phase (H-L-w-V) boundary. The present results might be valuable as the fundamental data for estimating the amount of in situ gas hydrate and understanding the unique feature of hydrate formation/dissociation mechanism and the hydrate stability in the deep ocean sediments
Phase equilibria of R22 (CHClF2) hydrate systems in the presence of NaCl, KCl, and MgCl2
No full textThe three-phase (hydrate-aqueous liquid-vapor) equilibria of the R22 (CHClF2 = chlorodifluoromethane) hydrate forming systems in aqueous solutions containing NaCl, KCl, and MgCl2 were measured at pressures ranging from 0.140 to 0.790 MPa, temperatures between 273.9 and 287.8 K, and several compositions of each electrolyte. The upper quadruple points (hydrate-liquid R22-aqueous liquid-vapor) were also measured at each electrolyte concentration. The addition of electrolytes to the aqueous solutions caused inhibition of the hydrate formation. A thermodynamic model that predicts the three-phase hydrate equilibria was developed. The inhibiting effect of electrolytes was accounted for using a Pitzer model. A van der Waals and Platteeuw model and Redlich-Kwong-Soave equation of state with a modified Huron-Vidal mixing rule were used. The calculated results were found to be in good agreement with the experimental data.This work was supported by Grant 98-0502-04-01-3 from the Basic
Research program of the KOSEF and also partially by the Brain
Korea 21 Project
FE based preliminary thermal analysis to evaluate the curing efficiency of heating elements in mass concrete
No full textS-H hydrate equilibria of (methane plus water plus 2-methylbutane plus magnesium chloride), (methane plus water plus 2,2-dimethylbutane plus magnesium chloride), and (methane plus water plus methylcyclohexane plus magnesium chloride)
No full textFour-phase (S-H hydrate + water-rich liquid + hydrocarbon-rich liquid + vapour) structure H (S-H) hydrate equilibria of (methane + water + 2-methylbutane + magnesium chloride), (methane + water + 2,2-dimethylbutane + magnesium chloride), and (methane + water + methylcyclohexane + magnesium chloride) were measured in the temperature range from T = 271.55 K to T = 284.65 K, and the pressure range from p = 1.47 MPa to p = 9.75 MPa. The results for three ternary hydrates were found to be in good agreement with those in the literature. The addition of MgCl2 exerted a substantial inhibition effect on hydrate formation. The hydrate equilibrium temperature and pressure were predicted by the Redlich-Kwong-Soave equation of state (RKS-EOS) using the Huron-Vidal second-order (MHV2) mixing rule incorporated with the modified UNIFAC model and Aasberg-Petersen et al.'s model. Good agreement was observed between the predicted conditions and experimental results. A small deviation was found as the system pressure increased. (C) 1999 Academic Press
Stabilization Effect of THF, Propylene Oxide, 1,4-Dioxane and Acetone on Methane and Nitrogen Hydrates : Experimental Data adn Thermodynamics Model
No full textTTF-1, a homeodomain-containing transcription factor, participates in the control of body fluid homeostasis by regulating angiotensinogen gene transcription in the rat subfornical organ
No full textCompositional and structural identification of natural gas hydrates collected at Site 1249 on Ocean Drilling Program Leg 204
No full textIn contrast to the structural studies of laboratory-grown gas hydrate, this study has been performed on naturally grown clathrate hydrates from the sea floor. The PXRD pattern of natural gas hydrate shows that the sample had a structure I hydrate. The C-13 NMR spectrum was obtained for the natural gas hydrate sample in order to identify the cage occupancy of guest molecules and determine the hydration number. The NMR spectrum reveal that the natural gas hydrates used in this study contain only methane with no noticeable amount of other hydrocarbons. The existence of two peaks at different chemical shifts indicates that methane molecules are encapsulated in both large and small cages. In addition, Raman spectroscopic analysis is also carried out to identify natural hydrates and compared with the NMR results. Investigating the composition and structure of natural gas hydrates is essential for applying natural gas hydrates as a novel energy source.This research used samples provided by the Ocean Drilling Program
(ODP). ODP is sponsored by the U.S. National Science Foundation
(NSF) and participating countries under management of Joint
Oceanographic Institutions (JOI), Inc. Funding for this research was
provided by K-IODP in KIGAM (Korea Institute of Geoscience
and Mineral Resources). 400 MHz Solid-state NMR study was supported
by Korea Basic Science Institute (KBSI)
Thyroid transcription factor 1, a homeodomain containing transcription factor, contributes to regulating periodic oscillations in GnRH gene expression.
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