gas hydrate - CCOP

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same crystalline structure directly after its replacement with CO 2, this not only enables the ocean floor to remain stable even after recovering the CH 4 gas, but also makes the swapping process more viable by enhancing its economical efficiency. Although numerous hydrate studies, involving both macroscopic and microscopic approaches, have recently been conducted for a variety of purposes, and to a certain extent have yielded notable success, little attention has been paid to cage dynamics in exploring guest distributions within the sensitive host-guest networks. Moreover, the complex hydrate behavior occurring under strong attacks by external guest molecules on the existing cages has not yet been fully considered, and no detailed study exists even at a very fundamental level. In a previous study, we explored the replacement mechanism of CH 4 hydrate with CO 2 using spectroscopic methods and found that when a CH 4 hydrate is exposed to gas mixtures containing CO 2 , CH 4 is replaced by CO 2 in mainly the large cages (Lee, 2003). If the CH 4 hydrates could be converted into CO 2 hydrates, they would serve doubly as CH 4 sources and CO 2 storage sites. Here, we further extend our investigations to consider the occurrence of CO 2 replacement phenomena on sII hydrate, which is thought to exist in the seabed. From this point of view, we present an interesting conclusion reached by inducing a structure transition. A microscopic analysis is conducted in order to examine the real swapping phenomena occurring between CO 2 guest molecules and sII hydrate through spectroscopic identification, including solid-state Nuclear Magnetic Resonance (NMR) spectrometry and FT-Raman spectrometry. More importantly, we also investigate the possibility of the direct use of binary N 2 and CO 2 gas mixture for recovering CH 4 from the hydrate phase, which shows a remarkably enhanced recovery rate by means of the cage-specific occupation of guest molecules due to their molecular properties. RESULTS AND DISCUSSION Direct sequestration of CO 2 and N 2 Mixtures into sI CH 4 hydrates In the preceding work we verified that the CH 4 amount that could be recovered by replacing sI CH 4 hydrate with CO 2 could reach around 64% of the hydrate composition. CO 2 molecules only preferably replaced CH 4 in large cages, while CH 4 molecules in small cages remain almost intact (Lee, 2003). Due to such a preferential cage occupation of guest molecules, the recovery rate of CH 4 is limited to the maximum value of 64 %. a CO 2 in sI-L b CH 4 in sI-L CH 4 in sI-S 250 200 150 100 50 0 Chimecal shift (ppm) 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 Chem ical shift (ppm ) Figure 1. The N 2 + CO 2 mixture consists of 20 mol% CO 2 and balanced N 2 . 13 C NMR spectra of CH 4 hydrates replaced with N 2 + CO 2 : blue line – before replacement, red line – after replacement. (a) 13 C CP NMR spectra for identifying replaced CO 2 molecules in CH 4 hydrates. (b) 13 C MAS NMR spectra for identifying residual CH 4 molecules in CH 4 hydrates. 98 New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane
This swapping process, accomplished by the direct attacks of external guests, is considered to be a favorable method for long-term storage of CO 2 . It also enables the ocean floor to remain stable even after recovering the CH 4 gas, because the sI CH 4 hydrate maintains the same crystalline structure directly after its replacement with CO 2 . Is it possible to completely achieve the spontaneous exchange by extracting CH 4 molecules and substituting any other guest molecules to most of the small cages already existing in sI CH 4 hydrate We first attempted to examine the real swapping phenomenon occurring between binary guest molecules of N 2 and CO 2 and crystalline sI CH 4 hydrate through spectroscopic identification. In accordance with the idealized cage-specific pattern of multiple guests, N 2 molecules attack CH 4 molecules occupying small cages (sI-S) and eventually occupy the sites, while CO 2 molecules specifically play an active role in replacing most of the CH 4 molecules in large cages (sI-L). Such unique cage occupancy behavior might be attributed to molecular details of the participating guests. CO 2 has a molecular diameter almost identical with the small cage diameter of sI hydrate, and thus only a slight degree of distortion in small cages need exist to accommodate CO 2 molecules. Accordingly, we expect that CO 2 molecules could be more stably encaged in sI-L under a favorable host-guest interaction. On the other hand, N 2 is known as one of the smallest hydrate formers and its molecular size almost coincides with CH 4 . Although N 2 itself forms pure sII hydrate with water (Sloan, 1998), the relatively small size of N 2 molecules leads to the preference of sI-S over other cages and, moreover, the stabilization of the overall sI hydrate structure when N 2 directly participates in forming the hydrate. Accordingly, CH 4 and N 2 are expected to compete for better occupancy of sI-S, while CO 2 preferentially occupies only sI-L without any challenge from other guests. Thus, the capacity of these two external guests, N 2 and CO 2 , in extracting original CH 4 molecules would make it possible for diverse CO 2 streams to be directly sequestrated into natural gas hydrate deposits. To verify several key premises mentioned above, we identified the ternary guest distribution in cages by means of Raman and 13 C NMR spectra. The NMR spectrum as shown in Figure 1a provides clear evidence that CO 2 molecules are distributed only in sI-L, while CH 4 molecules remained in both sI-S and sI-L even after completion of replacement as shown in Figure 1b. Qualitative information of cage dynamics in sI-S and sI-L concerning CO 2 molecules could be obtained by analyzing the 13 C CP NMR spectral shape of the mixed hydrate. For CO 2 entrapped in hydrate cages, an anisotropic chemical shift is induced by asymmetry in the immediate environment of molecules and is sensitively affected by the guest distribution in hydrate cages (Ripmeester, 1988). As the sI-S produces pseudospherical symmetry, which causes molecular motions to be isotropic, only a sharp peak at an isotropic chemical shift of about 123 ppm is observed for CO 2 (Seo, 2004: Kim 2005). For hydrate samples prepared after replacement, no clear isotropic line appeared and thus CO 2 molecules were not observed in sI-S, as can be seen in Figure 1a. A powder pattern having an anisotropic chemical shift of -55.8 ppm was observed, and this spectral shape reflects the anisotropic motion of CO 2 molecules in asymmetric sI-L. However, for CH 4 molecules, the 13 C MAS NMR spectra (Figure 1b) were taken at conditions before/after replacement and two peaks were clearly identified as representing CH 4 in sI-S and sI-L, respectively. Here, we note that the CH 4 in sI-S was replaced mainly with N 2 , while CO 2 replaced CH 4 in sI-L. However, further spectroscopic evidence might be required before the pattern of N 2 cage occupancy is more definitively established. New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 99
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Coordinating Committee for Geoscien
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Thematic Session on New Energy Reso
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CONTENTS Page OPENING REMARKS……
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OPENING REMARKS by Chen Shik Pei Di
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WELCOME ADDRESS by Tai-Sup Lee Pres
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WELCOME ADDRESS by Keun-Pil Park Di
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CONGRATULATORY ADDRESS by David Pri
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PART I GAS HYDRATE: EXPLORATION, RE
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Partial differential equations for
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RESULTS AND DISCUSSION In the follo
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REFERENCES Berner R. A. (1980) Earl
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features of the seabed than those o
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secure the stability of the solutio
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trends depending on the following f
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Organic carbon in sediments is of i
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Sedimentological and Geochemical As
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Figure 3. Sedimentation rate of the
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Marine Gas Hydrate off W. Canada an
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Several methods for computing the Q
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0.035 0.03 Amplitude 0.025 0.02 0.0
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60 50 Amplitude 40 30 20 10 0 0 50
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REFERENCES Dallimore, S.R. and T.S.
Page 46 and 47: Frequency % 20 16 12 8 HAMA #5, MV=
Page 48 and 49: Figure 3. Experimental procedures f
Page 50 and 51: Figure 7 shows two cases of the com
Page 52 and 53: Seismic Characteristics of Gas Hydr
Page 54 and 55: Purpose The purpose of this paper i
Page 56 and 57: The dissociation zone created by th
Page 58 and 59: hydrate that forms near the wellbor
Page 60 and 61: dissociation, composite thermal con
Page 62 and 63: Figure 9. The Advanced Light Source
Page 64 and 65: Experimental Studies and Developmen
Page 66 and 67: Natural gas hydrate exploitation an
Page 68 and 69: Natural gas Free gas layer Figure 5
Page 70 and 71: Figure 7. One-dimensional developme
Page 72 and 73: Temper at ur e 2 1 0 -1 -2 -3 -4
Page 74 and 75: From the above discussion, the heat
Page 76 and 77: INTRODUCTION Clathrate hydrates are
Page 78 and 79: MATHEMATICAL MODEL The mathematical
Page 80 and 81: Where the hydrate-aqueous radius of
Page 82 and 83: REFERENCES Brooks, R.H., and A.T. C
Page 84 and 85: 86 New Energy Resources in the CCOP
Page 86 and 87: In this paper, an overview of the M
Page 88 and 89: The brief tasks in the Phase I are:
Page 90 and 91: In "Development of the dissociation
Page 92 and 93: Figure 5. Preparation equipment. AN
Page 94 and 95: Other recent research subjects in t
Page 98 and 99: Another important aspect of the pre
Page 100 and 101: a + CO 2 CH 4 C 2 H 6 b CH 4 in sII
Page 102 and 103: REFERENCES Collett, T.S. and Kuuskr
Page 104 and 105: Figure 1. Physiographic and crust m
Page 106 and 107: Figure 3. Seismic profile showing s
Page 108 and 109: Figure 7. Distribution of echo char
Page 110 and 111: Figure 10. Seismic profile and its
Page 112 and 113: In the early stage of back-arc open
Page 114 and 115: PART II COALBED METHANE (CBM)
Page 116 and 117: Supply and demand infrastructure of
Page 118 and 119: Amisan, Jogyeri, Baegunsa, and Seon
Page 120 and 121: PROPERTIES OF ANTHRACITE The coals
Page 122 and 123: Table 4. Average chemical compositi
Page 124 and 125: CONCLUSIONS 1. Most of the coals em
Page 126 and 127: INTRODUCTION Coal (total reserves 2
Page 128 and 129: ีีีีีีีีี ั ิ
Page 130 and 131: RESULTS By Government: The outcomes
Page 132 and 133: The gas composition (12 samples ana
Page 134 and 135: Table 4. Coal Depth Interval Hole N
Page 136 and 137: The results of studies made on 11 c
Page 138 and 139: CONCLUSION CBM is still hoped to be
Page 140 and 141: The Government of Indonesia through
Page 142 and 143: The Berau basin is a major coal pro
Page 144 and 145: PP: CBM - 1 Rambutan (GOI Sponsor)
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Overview of Project for CO 2 Seques
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The organic geochemistry research g
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3.5 25 3.0 20 Ar(%) C O 2(%) 2.5 2
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20 8 10 0 6 δ13C of CO2(‰) -10 -
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Figure 1. Index map of Akabira Coal
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ORIGIN OF AKABIRA CBM In Akabira mi
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