共查询到20条相似文献,搜索用时 703 毫秒
1.
Structure I (sI) and H (sH) hydrates containing methane were synthesized and characterized with PXRD, DSC, NMR, and Raman spectroscopy. Three well-known large molecule guest substances (LMGSs) were selected as sH hydrate formers: 2,2-dimetylbutane (NH), methylcyclohexane (MCH), and tert-butyl methyl ether (TBME). The solid phase analysis confirmed the presence of sH hydrate whenever a LMGS was present. The presence of a non-hydrate former (n-heptane) did not affect the methane hydrate structure or cage occupancies. Ice to hydrate conversion was limited when the LMGS amount was less than stoichiometric and synthesized at low methane pressure, but nearly complete conversion was achieved with temperature ramping and excess LMGS. The methane occupancies were found to depend on the type of LMGS and increased with pressure. The hydrate with TBME was found to have the smallest methane content followed by the hydrates with NH and MCH. Both NMR and Raman identified methane and LMGS signals from the hydrate phase, however, the cage occupancy values of sH hydrate can only be obtained from NMR spectroscopy. The hydrate structures, ice to hydrate conversion, gas content in hydrate and cage occupancy from the various measurements are consistent with each other. 相似文献
2.
13C NMR spectra were obtained for pure CH4, mixed CH4+THF, and mixed CH4+Neohexane hydrates in order to identify hydrate structure and cage occupancy of guest molecules. In contrast to the pure
CH4 hydrates, the NMR spectra of the mixed CH4+THF hydrate verified that methane molecules could occupy only the small portion of 512 cages because the addition of THF, water-soluble guest component, to aqueous solution prevents the complete filling of methane
molecules into small cages. Furthermore, from these NMR results one important conclusion can be made that methane molecules
can’t be enclathrated at all in the large 51264 cages of structure II. In addition, gas uptake measurements were carried out to determine methane amount consumed during
pure and mixed hydrate formation process. The moles of methane captured into pure CH4 hydrate per mole of water were found to be similar to the full occupancy value, while the moles of methane captured into
the mixed CH4+THF hydrate per moles of water were much lower than the ideal value. The overall results drawn from this study can be usefully
applied to storage and transportation of natural gas. 相似文献
3.
Compositional and structural identification of natural gas hydrates collected at site 1249 on ocean drilling program leg 204 总被引:2,自引:0,他引:2
Do-Youn Kim Tae-Won Uhm Huen Lee Young-Joo Lee Byong-Jae Ryu Ji-Hoon Kim 《Korean Journal of Chemical Engineering》2005,22(4):569-572
In 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. The13C 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. 相似文献
4.
Sukjeong Choi Kyuchul Shin Jong-Ho Cha Huen Lee 《Korean Journal of Chemical Engineering》2008,25(6):1397-1400
We demonstrate the spectroscopic observation of H2 migration in the binary structure-I (sI) clathrate hydrate. The H2 molecules captured into sI small cage (sI-S) at lower temperature migrate to sI large cage (sI-L) through shared pentagonal
face of 51262 cage. The hexagonal faces of 51262 cage provide the windows essential for creating continuous diffusion paths for H2 molecules. It is essential to realize that the vacant channels formed by the linkage of specific cages can play an important
role in guest diffusion pathways and occupancy occurring in a complex clathrate hydrate matrix. 相似文献
5.
Toshiyuki Nakamura 《Chemical engineering science》2004,59(1):163-165
It has been regarded that the limit of the largest cage occupancy for the structure-H hydrate is between the 1,2-dimethylcyclohexane stereo-isomers, because the cis-isomer is able to generate the structure-H hydrate in the presence of methane while the trans-isomer is not. In the present study, gas hydration of trans-1,2-dimethylcyclohexane in the presence of methane and cis-1,2-dimethylcyclohexane is found from stability boundaries for the structure-H hydrate system. 相似文献
6.
7.
Sun-Hwa Yeon Jeasung Park Youngjune Park Sukjeong Choi Kyuchul Shin Jiwoong Seol Minjun Cha Huen Lee 《Korean Journal of Chemical Engineering》2008,25(1):154-157
Clathrate compounds are crystalline materials formed by a physical interaction between host and relatively light guest molecules.
Various types of nano-sized cages surrounded by host frameworks exist in the highly unique crystalline structures and free
guest molecules are entrapped in an open host-guest network. Recently, we reported two peculiar phenomena, swapping and tuning,
naturally occurring in the hydrate cages. Helium, one of the smallest light guest molecules, must be the challengeable material
in the sense of physics and moreover possesses versatile applications in the field of superconductivity technology and thermonuclear
industry. In this regard, we attempted for the first time to synthesize helium hydrates at moderate temperature and pressure
conditions. According to inclusion phenomena, helium itself normally cannot form clathrate hydrates due to being too small
molecularly without the help of hydrate former molecules (sI, sII, and sH formers). In this study, the hydrate equilibria
of the binary clathrate hydrate containing tetrahydrofuran, helium, and water were determined at 2, 3, 5.56 THF mol%. Direct
volumetric measurements were also carried out to confirm the exact amount of helium captured in the hydrate cages. Finally,
the crystalline structure of the formed mixed hydrates was identified by powder X-ray diffraction, resulting in structure
II. 相似文献
8.
Yuuki Matsumoto Hiroshi Miyauchi Takashi Makino Takeshi Sugahara Kazunari Ohgaki 《Chemical engineering science》2011,(12):2672
Methane+ethane+1,1-dimethylcyclohexane+water system was investigated by using Raman spectroscopy and isothermal phase equilibrium measurements under four-phase (gas+aqueous+large guest species+hydrate phases) equilibrium conditions at 288.15 K. The results suggest that three kinds of hydrate structures emerge at 288.15 K in the methane+ethane+1,1-dimethylcyclohexane+water system. The hydrate structure for this system changed from structure-H to structure-I via structure-II with increase in the mole ratio of ethane to methane. 相似文献
9.
Takeshi Sugahara 《Chemical engineering science》2005,60(6):1783-1786
Four mixtures of 1,1-, cis-1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes (hereafter abbreviated DMCH) including H2O and Xe have been investigated in a temperature range over 274.5 K and a pressure range up to 2.7 MPa. The 1,1-DMCH and cis-1,2-DMCH generate the structure-H hydrate in the temperature range up to 295.2 and 280.2 K, respectively. Especially, very large depression of equilibrium pressure has been observed in the structure-H 1,1-DMCH hydrate system. On the other hand, neither trans-1,2-DMCH nor cis-1,4-DMCH generates the structure-H hydrate in the present temperature range. It is an important finding that the cis-1,4-DMCH does not generate the structure-H hydrate in the presence of Xe, while the mixture of cis-1,4-DMCH and methane generates the structure-H hydrate. 相似文献
10.
Alcohols are frequently used in hydrate communities as thermodynamic hydrate inhibitors, but some alcohol molecules are also known to be hydrate formers with a help gas. In this study, the crystal structures of binary 1-propanol+methane hydrates at various temperatures were identified using neutron powder diffraction analysis with Rietveld refinement. Characteristic behaviors of the guest molecules in the hydrate structure were also analyzed to verify possible host-guest interactions from the refinement results. The results showed that the thermal factors of host water and guest methane increased continuously as the temperature increased. However, the isotropic thermal factors (B values) of 1-propanol were abnormally high compared to those of methane in the small cages of structure II (sII) hydrates, which could be because the 1-propanol molecules were off-centered in the large cages of sII hydrates. This implies that hydrogen bonding interactions between host and guest molecules can occur in the large cages of sII hydrates. The present findings may lead to a better understanding of the nature of guest-host interactions that occur in alcohol hydrates. 相似文献
11.
LEI Huaiyan LIU Zhihong FAN Shuanshi XU Maoquan GUAN Baocong 《化工学报》2003,54(Z1):41-46
As we know, there are three structures-sⅠ, sⅡ, and sH, with hydrocarbonate gas hydrate. Because of those special structures characteristics and potentail large fossil energy resource, gas hydrate play an important role in natural carbonate cycle system. In this paper, CH_4, CO_2, C_3H_8, and CH_4 CO_2 system have been experimental performed in order to model hydrate formation and discomposition and to obtain hydrate stability conditions of tempreature and pressure. The results from laboratory using Raman spectra show that Raman spectrascopy is a effective tool to identify hydrate structure. Raman spectra of clathrate hydrate guest molecules are presented for two structure (sⅠ and sⅡ) in the following systems: CH_4, CO_2, C_3H_8. Relatively occupancy of CH_4 in the large and small cavities of sⅠ were determined by deconvoluting the v_1 symmetric bands, resulting in hydration numbers of 6.04±0.03. The freqyuency of the v_1 bands for CH_4 in structures Ⅰ and Ⅱ differ statistically. The large cavities were measured to be almost fully occupied by CH_4 and CO_2, whereas only a small fraction of the small cavities are occupied by CH_4. No CO_2 was found in the small cavities. 相似文献
12.
Ji-Ho Yoon 《Korean Journal of Chemical Engineering》2012,29(12):1670-1673
This work presents a theoretical prediction of the cage occupancy of CH4 in small cages and the heat of dissociation for THF-CH4 hydrate using the predictive Soave-Redlich-Kwong group contribution method combined with the UNIFAC model. The predicted cage occupancy of CH4 gradually increases with increasing pressure, indicating that the CH4 molecules could readily be encaged in the small 512 cages of the sII hydrate framework stabilized by THF molecules. The molar enthalpy of encagement of CH4 in the small 512 cages of the sII clathrate hydrate is estimated to be 26.7±1.7 kJ mol?1. 相似文献
13.
Toshiyuki Nakamura 《Chemical engineering science》2003,58(2):269-273
The four-phase coexistence curves for the structure-H hydrates of methylcyclohexane and cis-1,2-dimethylcyclohexane in the presence of methane are measured in the temperature range 274.09- and pressure range 1.42-. Very large pressure reductions from the pure methane hydrate are observed by forming structure-H hydrates. The present investigation on the trans-1,2-dimethylcyclohexane system reveals that the limit of the largest-cage occupancy for the structure-H hydrate is laid between the 1,2-dimethylcyclohexane stereo-isomers. 相似文献
14.
A calibration protocol to quantify the compositional information of gas hydrates using Raman spectroscopy is proposed. Structure I pure CH4‐, CO2‐ and C2H6‐hydrates in their deuterated and hydrogenated forms with known cage occupancies were investigated by Raman spectroscopy. Raman scattering cross sections of CH4 in the large and small cages were found to be very similar, but not identical. Some C2H6 bands of C2H6‐hydrate were tentatively reassigned or newly reported and assigned. Our results show that the relative cross sections of guest vibrational modes in the deuterated hydrate are in agreement with those in the hydrogenated hydrate, whereas they are considerably different from those in fluid phase. Using our Raman quantification factors, the relative cage occupancies can now be determined more reliably in CH4‐hydrates. Moreover, with additional assumptions, the absolute cage occupancies, the bulk guest composition and hydration number of pure or mixed gas hydrates become accessible by Raman spectroscopy. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2155–2167, 2013 相似文献
15.
The changes in the dynamic structure during temperature-induced phase transition in D2O/ethanol solutions of poly(vinyl methyl ether) (PVME) were studied using NMR methods. The effect of polymer concentration and ethanol (EtOH) content in D2O/EtOH mixtures on the appearance and extent of the phase separation was determined. Measurements of 1H and 13C spin-spin and spin-lattice relaxations showed the presence of two kinds of EtOH molecules: besides the free EtOH expelled from the PVME mesoglobules there are also EtOH molecules bound in PVME mesoglobules. The existence of two different types of EtOH molecules at temperatures above the phase transition was in solutions with polymer concentration 20 wt% manifested by two well-resolved NMR signals (corresponding to free and bound EtOH) in 13C and 1H NMR spectra. With time the originally bound EtOH is slowly released from globular-like structures. From the point of view of polymer-solvent interactions in the phase-separated PVME solutions both EtOH and water (HDO) molecules show a similar behaviour so indicating that the decisive factor in this behaviour is a polar character of these molecules and hydrogen bonding. 相似文献
16.
Acyclic Stereochemical Analysis. III. Estimation of the Preferred Conformers of Substituted γ-Chloropropyl-methyl Ethers by NMR Spectroscopy and Molecular Modelling The conformers of the various stereoisomers of a series of γ-chloropropyl methyl ethers 1–4 with 1, 2 and 3 chiral centres have been estimated by Molecular Modelling (MOBY) and the results compared with the data of previous 1H and 13C NMR studies. The calculations corroborate former NMR results and the remarkable potential of both NMR spectroscopy and Molecular Modelling to assign even four diastereomers of acyclic molecules with three chiral centres. 相似文献
17.
Rajnish Kumar Peter Englezos Igor Moudrakovski John A. Ripmeester 《American Institute of Chemical Engineers》2009,55(6):1584-1594
Gas hydrates from a (40/60 mol %) CO2/H2 mixture, and from a (38.2/59.2/2.6 mol %) CO2/H2/C3H8 mixture, were synthesized using ice powder. The gas uptake curves were determined from pressure drop measurements and samples were analyzed using spectroscopic techniques to identify the structure and determine the cage occupancies. Powder X‐ray diffraction (PXRD) analysis at ?110°C was used to determine the crystal structure. From the PXRD measurement it was found that the CO2/H2 hydrate is structure I and shows a self‐preservation behavior similar to that of CO2 hydrate. The ternary gas mixture was found to form pure structure II hydrate at 3.8 MPa. We have applied attenuated total reflection infrared spectroscopic analysis to measure the CO2 distribution over the large and small cavities. 1H MAS NMR and Raman were used to follow H2 enclathration in the small cages of structure I, as well as structure II hydrate. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
18.
四氢呋喃水合物(THF)是典形的笼形水合物,目前有关其热导率的报道较少,且都存在测量样品不是单一相、测量过程水合物发生分解等问题。采用基于飞秒脉冲激光的时域热反射法(TDTR)测量THF热导率。根据样品常温下是流体的特点,设计了可同时适用样品制备及TDTR测量的温控台,实现THF热导率非接触原位测量。获得THF热导率为0.6 W/(m?K),Al/THF界面热导为90.3 MW/(m2?K)。该实验结果有助于理解并完善固体水合物微观导热机理,明晰水分子笼子和客体分子的耦合关系。 相似文献
19.
Dongsheng Bai Bei Liu Guangjin Chen Xianren Zhang Wenchuan Wang 《American Institute of Chemical Engineers》2013,59(7):2621-2629
Systematic molecular dynamics simulations have been performed to illustrate the roles of guest molecules played in the process of hydrate growth at vapor‐liquid interfaces. In our simulations, guest molecules are represented by a commonly used single‐site Lennard–Jones model, and the roles of guest molecules on hydrate growth have been investigated separately from the effect of water–guest molecule attractive interaction ε and that of molecular size σ, respectively. Our simulation results demonstrate that the water‐guest molecule attraction regulates the pathway and rate of nucleus growth, whereas the size of guest molecules determines the dynamically preferable structure. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2621–2629, 2013 相似文献
20.
1 INTRODUCTION Gas hydrates are serious problems in the petroleum and petrochemical industries since it may cause the plugging of production facilities and trans- portation pipelines during gas and oil production. It is known to all that gas hydrates have three poten- tial hydrate formation structures: structure- structure- and structure-H (SH). The two for- mer structures have been studied extensively and their phase equilibrium conditions are well characterized. For a long time, molecu… 相似文献