280 research outputs found
Physicochemical Properties of Ionic Clathrate Hydrates
No full textIonic clathrate hydrates are known to be formed by the enclathration of hydrophobic cations or anions into confined cages and the incorporation of counterions into the water framework. As the ionic clathrate hydrates are considered for their potential applicability in various fields, including those that involve solid electrolytes, gas separation, and gas storage, numerous studies of the ionic clathrate hydrates have been reported. This review concentrates on the physicochemical properties of the ionic clathrate hydrates and the notable characteristics of these materials regarding their potential application are addressed.close201
Preparation of oligonucleotide arrays with high-density DNA deposition and high hybridization efficiency
No full textIn DNA microarray produced by DNA-deposition technology, DNA-immobilization and -hybridization yields on a solid support are most important factors for its accuracy and sensitivity. We have developed a dendrimeric support using silylated aldehyde slides and polyamidoamine (PAMAM) dendrimers. An oligonucleotide array was prepared through a crosslinking between the dendrimeric support and an oligonucleotide. Both DNA-immobilization and -hybridization yields on the solid support increased by the modification with the dendrimers. The increase of the immobilization and hybridization efficiency seems to result from a three-dimensional arrangement of the attached oligonucleotide. Therefore, our dendrimeric support may provide a simple and efficient solution to the preparation of DNA microarrays with high-density DNA-deposition and high hybridization efficiency
CH4 recovery and CO2 sequestration using flue gas in natural gas hydrates as revealed by a micro-differential scanning calorimeter
No full textThe CH4-flue gas replacement in naturally occurring gas hydrates has attracted significant attention due to its potential as a method of exploitation of clean energy and sequestration of CO2. In the replacement process, the thermodynamic and structural properties of the mixed gas hydrates are critical factors to predict the heat flow in the hydrate-bearing sediments and the heat required for hydrate dissociation, and to evaluate the CO2 storage capacity of hydrate reservoirs. In this study, the C-13 NMR and gas composition analyses confirmed that the preferential enclathration of N-2 molecules in small 5(12) cages of structure I hydrates improved the extent of the CH4 recovery. A high pressure micro-differential scanning calorimeter (HP mu-DSC) provided reliable hydrate stability conditions and heat of dissociation values in the porous silica gels after the replacement, which confirmed that CH4 in the hydrates was successfully replaced with flue gas. A heat flow change associated with the dissociation and formation of hydrates was not noticeable during the CH4-flue gas replacement. Therefore, this study reveals that CH4-flue gas swapping occurs without structural transitions and significant hydrate dissociations. (C) 2015 Elsevier Ltd. All rights reserved.close2
Phase Equilibria and Thermodynamic Modeling of Ethane and Propane Hydrates in Porous Silica Gels
No full textIn the present study, we examined the active role of porous silica gels when used as natural gas storage and transportation media. We adopted the dispersed water in silica gel pores to substantially enhance active surface for contacting and encaging gas molecules. We measured the three-phase hydrate (H)-water-rich liquid (L-W)-vapor (V) equilibria of C2H6 and C3H8 hydrates in 6.0, 15.0, 30.0, and 100.0 nm silica gel pores to investigate the effect of geometrical constraints on gas hydrate phase equilibria. At specified temperatures, the hydrate stability region is shifted to a higher pressure region depending on pore size when compared with those of bulk hydrates. Through application of the Gibbs-Thomson relationship to the experimental data, we determined the values for the C2H6 hydrate-water and C3H8 hydrate-water interfacial tensions to be 39 +/- 2 and 45 +/- 1 mJ/m(2), respectively. By using these values, the calculation values were in good agreement with the experimental ones. The overall results given in this study could also be quite useful in various fields, such as exploitation of natural gas hydrate in marine sediments and sequestration of carbon dioxide into the deep ocean.The authors acknowledge funding from
the Korea Ministry of Knowledge Economy (MKE) through
“Energy Technology Innovation Program”. This research is also
financially supported by Changwon National University in 2008
and partially supported by the Brain Korea 21 project
Structural Transformation from Semi- to True Clathrate Hydrates Driven by External Methane Molecules
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No full textDepartment of Urban and Environmental Engineering (Environmental Science and Engineering)This dissertation investigated the synergistic inhibition effect of gas hydrate inhibitors, newly designed gas hydrate inhibitors, and gas hydrate remediation method development for the field of production chemistry of flow assurance. In order to perform above research topics, fundamental experimental studies of thermodynamic stability, structural analysis, gas uptakes, cage-filling molecular behaviors in the presence inhibitors were examined with computational methods and tried to synthesize eco-friendly and innovative gas hydrate inhibitors. The sigma (??) profiles of inhibitor molecules obtained from the Conductor-Like Screening Model for Real Solvents (COSMO-RS) software were used to estimate inhibitor???water interactions for the pre-screening of potential inhibitors. From the ?? profile results, candidates for thermodynamic hydrate inhibitor (THI) and kinetic hydrate inhibitor (KHI) were selected. In addition, the stability conditions in the presence of various inhibitors show that thermodynamic inhibition effect is related to molecular interaction between water and inhibitor. As is well known, intrinsic properties and the number of inhibitors are the biggest factors influencing the thermodynamic inhibition effect. Thus, even if two or more inhibitors mixed, it is hard to observe thermodynamic synergistic inhibition effect. Moreover, inhibitors hard to enclathrated in the gas hydrate structure because their sizes are too large (van der Waals radius values), so they reside on the outside of the cages or are partly involved in cages to disrupt the water-water networks. Furthermore, kinetic analyses were conducted to observe kinetic inhibition effect regarding onset temperature, growth rates and conversion of water into gas hydrates. It was confirmed that different results of onset temperature, growth rates and conversion of water into gas hydrates are shown according to types of inhibitor and inhibitor mixtures. Therefore, density functional theory (DFT) calculation, quantum theory of atoms in molecules (QTAIM) calculation, fourier-transform infrared (FT-IR) spectroscopy, and in-situ Raman spectroscopy were used to demonstrate inhibition mechanisms of each inhibitor. The DFT and QTAIM calculations indicated that each inhibitor has different interaction energy with cage, and the smaller negative interaction energy means that inhibitor significantly retards gas hydrate formation. The FT-IR was used to investigate the interaction sites of inhibitors toward water and find the peak shifts to observe the hydrogen bonding sites. In particular, in-situ Raman analysis verified inhibition mechanisms of inhibitors during nucleation and formation process, thus delaying behaviors of cages could be observed directly. The overall experimental and computational results in this dissertation provide invaluable information of THI and KHI, thus can contribute to the opening up a new field for flow assurance in oil and gas industries and CO2 storage process.ope
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No full textDepartment of Urban and Environmental Engineering (Environmental Science and Engineering )This study investigated thermodynamic and microscopic characteristics of various F-gas hydrates to examine the feasibility of gas hydrate-based F-gas separation process and to demonstrate the newly discovered F-gas hydrates. Thermodynamic phase equilibria were measured to determine the thermodynamically stable region of each F-gas hydrate, while powder X-ray diffraction was conducted to identify the gas hydrate crystal structure and lattice parameter. In addition, 13C & 19F NMR and insitu Raman spectroscopy were utilized to confirm the hydrate structure and observe cage-filling guestmolecular behavior. Lastly, the gas and hydrate phase compositions were analyzed via gas chromatography to examine the separation efficiency by gas hydrate formation process. From the experimental results, the thermodynamic stability range of pure CHF3 and CHF3 + N2 gas hydrates demonstrated that CHF3 can be captured in hydrate phase with high separation efficiency, while they form sI hydrate regardless of CHF3 concentrations used in this study. On the other hand, pure C2F6 and C2F6 + N2 gas mixture formed sII hydrates, and since C2F6 + N2 + water system showed an azeotropic behavior at high temperature range, restricting the gas hydrate-based separation process only applicable at specific temperature and pressure range. Lastly, the fundamental thermodynamic and spectroscopic properties of pure NF3 hydrate were obtained to estimate the feasibility for gas hydrate-based separation process. This study also made important discoveries on two F-gases (c-C4F8 and C3F8) which form sH hydrate in presence of suitable guest molecules. Since C3F8 and c-C4F8 molecules have large molecular sizes, those molecules have not been expected to be enclathrated in sI or sII hydrate cages. However, this study discovered that c-C4F8 molecules can be enclathrated in sH large (51268) cages in presence of CH4 as help gas, which was demonstrated through PXRD and 13C NMR spectroscopy. In addition, C3F8 was found to act as a dual hydrate former between sH and sII hydrates according to help gas molecules. Via 13C NMR and Raman spectroscopy, C3F8 was confirmed to form sH hydrate with CH4, while forming sII hydrate in presence of SF6. The discovery of c-C4F8 and C3F8 as sH hydrate former is very meaningful, since there have been no gas-phase sH hydrate former investigated until present. The overall results obtained in this study provide invaluable information of various properties of F-gas hydrates, and are expected to be useful sources for gas hydrate application fields in the future.clos
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No full textDepartment of Urban and Environmental Engineering (Environmental Science and Engineering)Gas hydrates are crystalline inclusion compounds that consist of well-defined hydrogen-bonded water frameworks (host cages) into which guest molecules are incorporated. As water is the main component
required for gas hydrate formation, gas hydrates are considered environmentally benign. Therefore, gas hydrates have been applied to various energy and environmental fields. This study deals with two main
topics as hydrate application technology.
In Topic 1, guest replacement and hydrate dissociation/reformation behavior during injection of CO2 and flue gas into NGH layer were comprehensively observed through an experimental method. we investigated CH4 - CO2 replacement behavior according to the experimental conditions or changes in the injected gas. Firstly, the time-dependent behavior during CH4 - CO2 replacement was quantitatively examined via a multi-methodological approach, which is a combination of PXRD analysis and in-situ Raman measurement, demonstrated that a significant guest exchange in the large 5 126 2 cages had a greater effect on the extent of replacement. Secondly, dissociation behavior of CH4 hydrate after N2 gas injection was confirmed. Time-dependent Raman spectra confirmed that the N2 molecules began to be captured in the hydrate cages immediately after the N2 gas injection at certain conditions, and the extent of N2 incorporation in the hydrate phase increased at a higher N2 gas injecting pressure, which indicates that N2 molecules revealed the dual functional roles of inhibitor for hydrate dissociation and external guest for guest replacement. Next, condition-dependent CH4 - CO2 + N2 replacement behavior was observed in terms of reaction kinetics and extent of replacement. At a higher temperature, the extent of replacement did not change, but CO2/N2 ratio in the replaced hydrates decreased slightly. An increase in the pressure led to an accelerated CO2 inclusion rate in the large (5126 2) cages at the initial stage and an enhanced N2 inclusion in the small (512) cages at the final stage. In case of injecting different composition of CO2 + N2 mixed gas, the extent of replacement was increased as N2 composition in the injecting gas increased at same partial pressure of injecting CO2, but the CO2 storage was decreased, which was due to the additional participation of N2 occurred in both large and small cages. In addition, the CO2 enclathration behavior in various mixed gas conditions are observed for CO2 sequestration. The presence of NaCl shifted the equilibrium conditions of CO2 + N2 hydrates to the higher-pressure or lower-temperature region, whereas it increased thermodynamic CO2 selectivity at a specified
temperature and pressure. In situ Raman spectroscopic measurements demonstrated that CO2 was kinetically selective at the early stage of CO2 + N2 hydrate formation and that kinetic CO2 selectivity was more noticeable in the saline water system. In case of CH4 + CO2 + N2 mixed hydrates, the CO2/CH4 ratio in the hydrate phase was not changed in different additional N2 compositions in same CO2/CH4 ratio of injecting gas.
In Topic 2, we focused on an evaluation of hydrate-based desalination efficiency from gaseous hydrate formers (propane, R134a, R152a, and R22). The thermodynamic stability, crystallographic information, dissociation enthalpy, and kinetic growth behavior of various hydrate formers were experimentally measured. The Hu-Lee-Sum (HLS) correlation was employed to predict the equilibrium shift and hydrate depression temperature. A novel approach to examine the maximum achievable salinity and maximum water yield using the HLS correlation was introduced. The theoretical HBD efficiency increased as the initial salinity decreased, the operating pressure decreased, and the initial subcooling temperature increased. In addition, theoretical HBD efficiency was employed as a quantitative standard for evaluating the kinetic performance of the HBD. At a fixed initial subcooling (2 K), R134a gave faster formation kinetics in the early stage, but R22 eventually offered highest hydrate conversion. At a fixed temperature (272 K), R152a showed fastest formation kinetics and highest HBD efficiency due to its milder hydrate equilibrium conditions. In addition, the estimation of theoretical desalianiton efficiency was also conducted on the liquid phase-hydrate former, cyclopentane (CP). The operating condition-dependent cooling demand for the process was simply examined from a thermodynamic point of view. The study provides a valuable theoretical foundation for the further development of gas hydrate-based desalination technology.ope
Semiclathrate-based post- and pre-combustion CO2 capture: thermodynamic and spectroscopic analyses
No full textDepartment of Urban and Environmental Engineering(Environmental Science and Engineering)The accumulation of CO2 and other greenhouse gases in the atmosphere has led to global warming. These climate changes are threatening the earth and its inhabitants. So, the clathrate hydrates formation application is interesting to many researchers and experts.This research is focused on minimizing CO2 capture using clathrate hydrates formation because CO2 is attributed to a large portion of global warming.
Clathrate hydrates are are non-stoichiometric crystalline compounds formed by a physical reaction between small guest molecules and host water molecules at low temperature and high pressure conditions. Water molecules form a framework while the guest molecules are trapped. These two different molecules are mechanically intermingled but not chemically. Clathrate hydrates have many technological applications, such as separation processes, natural gas storage/transportation and carbon dioxide sequestration. These clathrate hydrate-based technologies are expected to be an innovative method for solving energy and environmental issues. However, the major drawback of the clathrate hydrate-based technologies is that they require the maintenance of a specific temperature and pressure for storing or capturing gas molecules in the hydrate cages.
Clathrate hydrates can be divided into true and semi clathrate hydrates. These hydrates have many similar physical and chemical properties, but the main difference between the two is that there exists a chemical interaction between the host and guest molecules. The chemical interaction between semiclathrate hydrates is not yet fully understood. Recently, semi-clathrate hydrates have been reported to be formed by the existence of a hydrate promotor such as quaternary ammonium salts (QASs), amines, and alcohols. The presence of a hydrate promotor forms semiclathrate hydrates under a higher temperature and lower pressure conditions when compared with the pure hydrate systems. Semi-clathrate hydrates have unoccupied cages which can be applied to gas separation/sequestration for capturing CO2. Quaternary ammonium salts (QASs) form semiclathrate hydrates under higher temperature and lower pressure conditions when compared with the pure hydrate systems. These semi-clathrate hydrates have vacant small cages which can be used for capturing small-sized gas molecules, while the large cages are occupied by the TBA cation.
The main purpose of this study is to develop an innovative energy-efficient and eco-friendly CO2 separation method using semiclathrate hydrates formation, formed by quaternary ammonium salts (QASs). This research is based on selective partitioning of the CO2 and N2 (or H2) gases during hydrates formation. CO2 has a higher occupancy in the hydrate phase, even though both gases can form hydrates, since CO2 has a larger molecular diameter and more thermodynamic stability than N2 (or H2). The feasibility of the semiclathrate hydrates based CO2 capture method will be examined with a focus on the macroscopic phase behavior and microscopic analytical methods such as NMR, and Raman spectroscopy to investigate the guest gas enclathration behavior. In addition, thermal properties will also be measured using a high pressure micro differential scanning calorimeter (HP ??-DSC) in order to provide heat of formation and dissociation values of semiclathrate hydrates.
??? In this study, clathrate-based CO2 capture from flue and fuel gas was investigated in the presence of quaternary ammonium salts (QASs) as a semiclathrate former (tetra-n-butyl ammonium bromide (TBAB), chloride (TBAC), and fluoride (TBAF)), tetrahydrofuran (THF) as a water-soluble sII hydrate former, and cyclopentane (CP) as a water-insoluble sII hydrate former. The clathrate stabilities of the CO2 (20%) + N2 (80%) + promoter systems and the CO2 (40%) + H2 (60%) + promoter systems were measured using an isochoric method. The clathrate equilibrium pressures at a specified temperature were significantly reduced in the presence of these thermodynamic promoters. Gas storage capacity and CO2 composition analysis in both vapor and clathrate phases were conducted using gas chromatography. The CO2 in flue gas mixtures was found to be enriched approximately 61% in semiclathrate phase. In addition, the 5.6 mol% THF solution showed the largest gas storage capacity during the clathrate formation, but it demonstrated the lowest CO2 concentration (35%) in the clathrate phase after the completion of clathrate formation. In addition, the CO2 in fuel gas mixtures was found to be enriched approximately 95% in semiclathrate phase after the completion of semiclathrate formation. The inclusion of CO2 in the clathrate phase was also confirmed via Raman spectroscopy. The overall experimental results are useful for the clathrate-based CO2 capture process from flue and fuel gas.ope
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