Phase Transitions in Mixed Gas Hydrates:  Experimental Observations versus Calculated Data

Schicks, Judith M.; Naumann, Rudolf; Erzinger, J.; Hester, Keith C.; Koh, Carolyn A.; Sloan, E. Dendy

doi:10.1021/jp0612580

Cited by 89 publications

(110 citation statements)

References 13 publications

(19 reference statements)

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“…This allows a visual observation of the phases present in the cell as well as the collection of Raman spectra during formation, decomposition or transformation processes of the gas hydrate crystals. For further details regarding the experimental setup the reader is directed to the publication of Schicks et al [17].…”

Section: Methodsmentioning

confidence: 99%

Systematic kinetic studies on mixed gas hydrates by Raman spectroscopy and powder X-ray diffraction

Luzi

Schicks

Naumann

et al. 2012

The Journal of Chemical Thermodynamics

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This study presents results from systematic time-resolved experiments regarding the guest molecule geometry. The in situ observations of formation and dissociation processes of multicomponent hydrates were performed by means of Raman spectroscopy and a newly designed experimental setup including powder X-ray diffraction (PXRD) whose capabilities will be presented here in more detail. Both experimental setups allow investigating hydrate kinetics as a function of pressure, temperature and feed gas composition. The unique feature of both setups is the continuous gas flow providing a constant composition of the gas phase during the whole experiment. This is crucial for the formation of mixed hydrates formed from feed gas mixtures that contain one or more components in low concentrations. The formation of structure II hydrates including C 3 H 8 , iso-C 4 H 10 , n-C 4 H 10 or neo-C 5 H 12 besides CH 4 was analysed according to a multi-step model. For the initial phase it turned out that hydrates grown from the gas mixture containing 2% n-C 4 H 10 and 98% CH 4 have the highest formation rate at defined p,T conditions in comparison to other hydrates formed from gas mixtures containing about 2 vol% of the above mentioned hydrocarbons besides CH 4 . But the reaction mechanisms for each hydrate system emerged to be different. Fur-2 thermore, time-resolved Raman and PXRD experiments were performed to study the formation of structure H hydrates with a low-concentrated large hydrocarbon guest molecule. In case of a gas mixture containing 1% iso-C 5 H 12 and 99% CH 4 the formation of a simple structure I CH 4 hydrate was observed at first. Later on, structure H CH 4 + iso-C 5 H 12 hydrate was formed resulting in a coexistence of both structures.

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Section: Methodsmentioning

confidence: 99%

Systematic kinetic studies on mixed gas hydrates by Raman spectroscopy and powder X-ray diffraction

Luzi

Schicks

Naumann

et al. 2012

The Journal of Chemical Thermodynamics

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“…For Raman spectroscopic investigation CH 4 hydrate was synthesized in situ from 150 µL deionised water at 275.15 K and 3 MPa. The procedure and experimental set up are described elsewhere in detail [38,39]. When microscopic investigations and Raman spectra indicate a complete transformation of the liquid water into CH 4 hydrate, the gas phase was changed to CO 2 .…”

Section: Conversion Of Ch 4 /Hydrocarbon Hydrates To Co 2 Hydratesmentioning

confidence: 99%

“…The advantages of these system are short detection times and the gain of additional information regarding the crystallinity of the sample. More details regarding the pressure cells and the experimental set up can be found elsewhere [38,39,41].…”

Section: Raman Spectroscopy and Powder X-ray Diffractionmentioning

confidence: 99%

New Approaches for the Production of Hydrocarbons from Hydrate Bearing Sediments

et al. 2011

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Abstract:The presence of natural gas hydrates at all active and passive continental margins has been proven. Their global occurrence as well as the fact that huge amounts of methane and other lighter hydrocarbons are stored in natural gas hydrates has led to the idea of using hydrate bearing sediments as an energy resource. However, natural gas hydrates remain stable as long as they are in mechanical, thermal and chemical equilibrium with their environment. Thus, for the production of gas from hydrate bearing sediments, at least one of these equilibrium states must be disturbed by depressurization, heating or addition of chemicals such as CO 2 . Depressurization, thermal or chemical stimulation may be used alone or in combination, but the idea of producing hydrocarbons from hydrate bearing sediments by CO 2 injection suggests the potential of an almost emission free use of this unconventional natural gas resource. However, up to now there are still open questions regarding all three production principles. Within the framework of the German national research project SUGAR the thermal stimulation method by use of in situ combustion was developed and tested on a pilot plant scale and the CH 4 -CO 2 swapping process in gas hydrates studied on a molecular level. Microscopy, confocal Raman spectroscopy and X-ray diffraction were used for in situ investigations of the CO 2 -hydrocarbon exchange process in gas hydrates and its driving forces. For the thermal stimulation a heat exchange reactor was designed and tested for the exothermal catalytic oxidation of methane. OPEN ACCESSEnergies 2011, 4 152 Furthermore, a large scale reservoir simulator was realized to synthesize hydrates in sediments under conditions similar to nature and to test the efficiency of the reactor. Thermocouples placed in the reservoir simulator with a total volume of 425 L collect data regarding the propagation of the heat front. In addition, CH 4 sensors are placed in the water saturated sediment to detect the distribution of CH 4 in the sample. These data are used for numerical simulations for up-scaling from laboratory to field conditions. This study presents the experimental set up of the large scale reservoir simulator and the reactor design. Preliminary results indicate that the catalytic oxidation of CH 4 operated as a temperature controlled, autothermal reaction in a countercurrent heat exchange reactor is a safe and promising tool for the thermal stimulation of hydrates. In addition, preliminary results from the laboratory studies on the CO 2 -hydrocarbon swapping process in simple and mixed gas hydrates are presented.

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“…1 Due to the crucial roles played by NGHs, many experimental and theoretical efforts have made to study these systems. [12][13][14][15][16][17][18] Experimentally, Raman, NMR, and other spectroscopic tools are the regular means to study NGHs. Especially, Raman spectroscopy has been used to identify the type of crystal phase, [19][20][21] type of guest molecule, 19 cage occupancy, 21 and hydration number, [21][22] to monitor the nucleation and growth processes in real-time, 23 to study phase transformations, [24][25] and to detect the location of NGH deposits.…”

Section: Introductionmentioning

confidence: 99%

C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

Liu

Ojamäe

2014

J. Phys. Chem. A

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Abstract:The presence of specific hydrocarbon gas molecules in various types of water cavities in natural gas hydrates (NGHs) are governed by the relative stabilities of these encapsulated guest molecule ─ water cavity combinations. Using molecular quantum-chemical dispersion-corrected hybrid density functional computations, the interaction energies (ΔEhost-guest) and cohesive energies (ΔEcoh), enthalpies and Gibbs free energies for the complexes of host water cages and hydrocarbon guest molecules are calculated at the ωB97X-D/6-311++G(2d,2p) level of theory. The zero point energy effect of ΔEhost-guest and ΔEcoh is found to be quite substantial. The energetically optimal host-guest combinations for seven hydrocarbon gas molecules (CH4, C2H6, C3H6, C3H8, C4H8, i-C4H10, and n-C4H10) and various water cavities (D, ID, T, P, H and I) in NGHs are found to be CH4@D, C2H6@T, C3H6@T, C3H8@T, C4H8@T/P/H, i-C4H10@H, and n-C4H10@H, as the largest cohesive energy magnitudes will be obtained with these host-guest combinations. The stabilities of various water cavities enclosing hydrocarbon molecules are evaluated from the computed cohesive Gibbs free energies: CH4 prefer to be trapped in a ID cage; C2H6 prefer T cages; C3H6 and C3H8 prefer T and H cages; C4H8 and i-C4H10 prefer H cages; and n-C4H10 prefer I cages. The vibrational frequencies and Raman intensities of the C-C stretching vibrational modes for these seven hydrocarbon molecules enclosed in each water cavity are computed. A blue shift results after the guest molecule is trapped from gas phase into various water cages due to the host-guest interactions between the water cage and hydrocarbon molecule. The frequency shifts to the red as the radius of water cages increases. The model calculations support the view that C-C stretching vibrations of hydrocarbon molecules in the water cavities can be used as a tool to identify the types of crystal phases and guest molecules in NGHs.2

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Phase Transitions in Mixed Gas Hydrates: Experimental Observations versus Calculated Data

Cited by 89 publications

References 13 publications

Systematic kinetic studies on mixed gas hydrates by Raman spectroscopy and powder X-ray diffraction

Systematic kinetic studies on mixed gas hydrates by Raman spectroscopy and powder X-ray diffraction

New Approaches for the Production of Hydrocarbons from Hydrate Bearing Sediments

C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

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