Clathrate Formation Research Articles

Uptake and accommodation of water clusters by adamantane clusters in helium droplets: interplay between magic number clusters.

We report an experimental study of water clusters as guests in interactions with clusters of adamantane (Ad) as hosts that occur in doped helium droplets at extremely low temperatures. Separate experiments with pure water as dopant showed ready formation of a distribution of water clusters (H2O)mH+ that peaks at m = 11 and extends beyond m = 100 with local maxima at m = 4, 11, 21, 28 and 30 with (H2O)21H+ being the most anomalous and showing the greatest stability with respect to clusters immediately adjacent in water content. When adamantane is also added as a dopant, extensive hydration is seen in the formation of water/adamantane clusters, (H2O)mAdn+; magic number clusters (H2O)21Adn+ are seen for all the adamantane clusters. Other magic numbers for water clusters attached to adamantane, (H2O)mAdn+, are as for pristine protonated water, with m = 28 and m = 30. The icosahedral shell closure of pure adamantane at n = 13 and 19 appears to be preserved with (H2O)21 replacing one adamantane. (H2O)21Ad12+ and (H2O)21Ad18+ stand out in intensity and demonstrate the interplay of magic number water clusters with magic number adamantane clusters, observed perhaps for the first time in gas-phase cluster chemistry. There was no clear evidence for the formation of clathrate hydrates in which adamantane is trapped within structured water.

Guest Partitioning and Metastability of the Nitrogen Gas Hydrate

Gas clathrate hydrates or gas hydrates are made of H-bonded water molecules forming cages, within which gaseous (guest) molecules are encapsulated. The formed clathrate structures, which may be metastable, depend on the nature and on the partitioning of the guest molecules in the water cage. This work focuses on the structural and vibrational properties of nitrogen hydrate in its two clathrate forms (namely, SI and SII) in the thermodynamic ranges 50–200 bar and 150–270 K, together with a comprehensive analysis of the transformation from SI to SII of this gas hydrate. The thermal expansion of both structures has been measured at 1 bar, and the melting of the nitrogen hydrate has been measured at ca. 210 K at 1 bar. Moreover, the SI structure is metastable in the studied pressure region: from time-dependent neutron powder diffraction analysis, it is shown that the SI structure transforms over time to the SII structure with a rate of (1.37 ± 0.17) × 105 s–1 at 100 K and at 1 bar. The transformation is also ...

Morphological Studies of Mixed Methane Tetrahydrofuran Hydrates in Saline Water for Energy Storage Application

Solidified natural gas (SNG) in the form of clathrate hydrates has been considered one of the most promising technologies for natural gas storage and transportation because it is safe and economically feasible compared to liquefied natural gas (LNG) and compressed natural gas (CNG). In this direction, we recently observed that mixed methane tetrahydrofuran hydrates had the ability to store a significant amount of methane gas close to ambient temperature conditions. To further improve the economic feasibility of methane gas storage and transportation process, utilization of saline water was recommended. In the present work, we investigate the morphology of mixed CH4/THF hydrate formation and dissociation in presence of NaCl for the first time. Morphology changes observed during the nucleation, hydrate growth and dissociation of mixed hydrates at two different operating conditions are presented. All the experiments were performed with a stoichiometric concentration of THF (5.56 mol% THF). More over, the gas uptake was also measured and compared with non-salt experiments.

Role of the global water ocean on the evolution of Titan’s primitive atmosphere

During the accretion of Titan, impact heating may have been sufficient to allow the global melting of water ice and the release of volatile compounds, mainly constituted of CO2, CH4 and NH3. The duration and efficiency of exchange between the primitive massive atmosphere and the global impact-induced water ocean likely play a key role in the chemical evolution of the early Titan’s atmosphere. To investigate the atmospheric composition of early Titan for a wide range of global (atmosphere + ocean) composition in volatils, we first developed a gas–liquid equilibrium model of the NH3–CO2–H2O system, where the non-ideal behavior of both gas and liquid phases, and the speciation of volatiles dissolved in the aqueous phase are taken into account. We show that the relative abundance of CO2 and NH3 determine the composition of Titan’s atmosphere. For CO2/NH3 ≤ 1, CO2 is massively dissolved in the ocean. On the contrary, for CO2/NH3 > 1, CO2 is the main constituent of Titan’s primitive atmosphere while the NH3 atmospheric content is dramatically decreased. We then investigate the conditions for the formation of CH4-rich clathrates hydrates at Titan’s surface that could be the main reservoir of methane for the present-day atmosphere. In absence of reliable experimental data in the CH4–CO2–NH3–H2O system, the dissolution of methane in water is included using a simplified Henry’s law approach. We find that if the concentration of CH4 in Titan’s building block was higher than ∼ 0.1 mol kg−1 and CO2/NH3 < 3, a large fraction of methane may be stored in the primordial crust, which would form at temperature below ∼ 10 °C.

Understanding Carbon Dioxide Solubility in Ionic Liquids by Exploring the Link with Liquid Clathrate Formation.

The solubilities of the quadrupolar molecules benzene and CO2 in various ionic liquids (ILs) are compared in order to determine the connection between aromatic liquid clathrate formation and CO2 dissolution in ILs. It was found that both CO2 Henry's law constants and benzene solubility are remarkably well correlated with each other and with IL molar volume, suggesting both phenomena depend more on the strength of interionic interactions between the ions of an IL rather than the identity of either ion. However, IL ion-quadrupole interactions were found to have an effect for dicyanamide ([N(CN)2 ]- ), where solubility of CO2 and benzene are affected by destabilizing and stabilizing interactions with [N(CN)2 ]- , respectively. The results suggest both solubility phenomena are related to the incorporation of the solute into an IL host network. Aromatic liquid clathrate formation thus has potential as a facile experimental probe for predicting the relative ability of ILs to physisorb CO2 .

Effect of vanadium compounds on the sulfonation of carbon materials

The synthesis of sulfonated carbon materials (SCMs) via the direct sulfonation of carbon nanofibers with sulfuric acid in the presence of vanadium compounds is studied. An efficient sulfiding system (98% H2SO4–NaVO3) providing a high sulfur content in a carbon material without oleum is proposed. It is established that the introduced sulfur exists in samples in the form of sulfo groups located predominantly on the surface. No intrusion of sulfuric acid residues between graphene layers with the formation of clathrates is revealed. It is shown that the surface of a carbon material is partially oxidized with the formation of carbonyl and carboxyl groups. The kinetic activity of the synthesized SCMs in the liquid-phase reaction of acetic acid esterification with ethanol is studied.

New Insights on Gas Hydroquinone Clathrates Using in Situ Raman Spectroscopy: Formation/Dissociation Mechanisms, Kinetics, and Capture Selectivity.

Hydroquinone (HQ) is known to form organic clathrates with different gaseous species over a wide range of pressures and temperatures. However, the enclathration reaction involving HQ is not fully understood. This work offers new elements of understanding HQ clathrate formation and dissociation mechanisms. The kinetics and selectivity of the enclathration reaction were also investigated. The focus was placed on HQ clathrates formed with CO2 and CH4 as guest molecules for potential use in practical applications for the separation of a CO2/CH4 gas mixture. The structural transition from the native form (α-HQ) to the clathrate form (β-HQ), as well as the reverse process, were tracked using in situ Raman spectroscopy. The clathrate formation was conducted at 323 K and 3.0 MPa, and the dissociation was conducted at 343 K and 1.0 kPa. The experiments with CH4 confirmed that a small amount of gas can fill the α-HQ before the phase transition from α- to β-HQ begins. The dissociation of the CO2-HQ clathrates highlighted the presence of a clathrate structure with no guest molecules. We can therefore conclude that HQ clathrate formation and dissociation are two-step reactions that pass through two distinct reaction intermediates: guest-loaded α-HQ and guest-free β-HQ. When an equimolar CO2/CH4 gas mixture is put in contact with either the α-HQ or the guest-free β-HQ, the CO2 is preferentially captured. Moreover, the guest-free β-HQ can retain the CO2 quicker and more selectively.

Determination of polycyclic aromatic hydrocarbons in infant formula using solid state urea clathrate formation with gas chromatography – tandem mass spectrometry

An analytical method has been developed for the quantitative determination of the 16 EU priority polycyclic aromatic hydrocarbons (PAHs) in infant formula. Prior to analysis infant formula is subjected to sample preparation including the extraction of PAHs from the sample, transesterification of the triglyceride content of the extract to fatty acid methyl esters (FAMEs), and solid state urea clathrate formation to remove the FAMEs. Measurements were carried out with gas chromatography – tandem mass spectrometry. The developed method has been evaluated in terms of trueness, precision (repeatability), limit of detection (LOD), limit of quantification (LOQ), selectivity, sensitivity and linearity. Measurement range of 200–1500ngkg−1 was selected in accordance with the limit values set by the European Commission (835/2011/EC). LOD values were 75ngkg−1 for dibenzo(a,e)pyrene, dibenzo(a,i)pyrene and dibenzo(a,h)pyrene while 50ngkg−1 for the rest of the PAHs (benzo(c)fluorene, benzo(a)anthracene, cyclopenta(cd)pyrene, chrysene, 5-methylchrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(j)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene, dibenzo(a,l)pyrene), LOQ was 200ngkg−1 for all 16 PAHs. Trueness ranged between –29.7 and 29.8% while precision values were between 0.5 and 24.7% (RSD, n=3).

Effect of Biofriendly Amino Acids on the Kinetics of Methane Hydrate Formation and Dissociation

Solidified natural gas (SNG) is a promising option to store natural gas in the form of clathrate hydrates because of several benefits offered that include high degree of safety, eco-friendliness, high volumetric storage capacity, and the relative ease of gas recovery. Environmentally benign amino acids have been reported as promising kinetic promoters for enhancing methane hydrate formation. In this work, we examine in detail the effect of three different types of amino acids—tryptophan (nonpolar, hydrophobic amino acid with aromatic side chain), histidine (polar, basic amino acid with aromatic side chain), and arginine (polar, basic amino acid with aliphatic side chain)—on the kinetics of methane hydrate formation. The effect of amino acid concentration on the hydrate formation kinetics was investigated in two reactor configurations, namely, stirred and unstirred tank reactors. Amongst the amino acids studied, the best kinetic promotion for methane hydrate formation (in both stirred and unstirred reactor...

Properties of CO2clathrate hydrates formed in the presence of MgSO4solutions with implications for icy moons

There is evidence to suggest that clathrate hydrates have a significant effect on the surface geology of icy bodies in the Solar System. However the aqueous environments believed to be present on these bodies are likely to be saline rather than pure water. Laboratory work to underpin the properties of clathrates in such environments is lacking. We fill this gap by carrying out a laboratory investigation of the physical properties of CO$_2$ clathrates produced in weak aqueous solutions of MgSO$_4$. We use synchrotron X-ray powder diffraction to investigate clathrates formed at high CO$_2$ pressure in ice that has formed from aqueous solutions of MgSO$_4$. We measure the thermal expansion, density and dissociation properties of the clathrates under temperature conditions similar to those on icy Solar System bodies. We find that the sulphate solution inhibits the formation of clathrates by lowering their dissociation temperatures. Hysteresis is found in the thermal expansion coefficients as clathrates are cooled and heated; we attribute this to the presence of the salt in solution. The density derived from X-ray powder diffraction is temperature and pressure dependent. When comparing the density of CO$_2$ clathrates to that of the solution in which they formed, we conclude that they sink in the oceans in which they form. We also find that the polymorph of ice present at low temperatures is Ih rather than Ic, which we attribute to the presence of the MgSO$_4$. We 1) conclude that the clathrate density has implications for their behaviour in satellite oceans as their sinking and floating capabilities are temperature and pressure dependent, 2) conclude that the presence of MgSO$_4$ inhibits the formation of clathrates and in some cases may even affect their structure and 3) report the dominance of Ih throughout the experimental procedure despite Ic being the stable phase at low temperature.

2-2-5 コールベッドメタンと随伴水のクラスレートハイドレート化に関する実験的研究(2-2 資源2,Session 2 天然ガス・メタンハイドレート等,研究発表)

2-2-5 コールベッドメタンと随伴水のクラスレートハイドレート化に関する実験的研究(2-2 資源2,Session 2 天然ガス・メタンハイドレート等,研究発表)

IR spectrometric studies of thin film cryovacuum condensates of methane and methane-water mixtures

The results of IR spectrometric studies of thin film cryovacuum condensates of methane and methane-water mixtures in the 16–36 K temperature range. The condensation pressure was P = 10−4 Torr, and the thickness of the samples varied from 1 to 5 μm. For pure methane cryocondensate, a relationship between the position of the deformation vibration absorption band and the α–β phase transition in solid methane is established. The stretching of the transition with respect to temperature and time is explained by the temperature dependence of the spin-nuclear relaxation time in methane molecules. The results of studying both 20% methane-water mixture and bilayer methane-water samples have demonstrated that in the 27–31 K temperature range there are abrupt changes to the position and amplitude of the deformation vibration absorption band ν = 1300 cm−1, which may be due to the activation of the interaction between the methane molecules and the water. A displacement of the absorption band minimum in comparison to pure methane (νm = 1306 cm−1 for the mixture versus νm = 1300 cm−1 for pure methane) is detected, which can be associated with the processes of methane clathrate formation. The transformations taking place in the film in the 27–32 K interval serve as evidence of either the continuation of the cluster formation process in the film, or of thermally stimulated structural changes already in the clustered sample.

Xenon-Water Interaction in Bacterial Suspensions as Studied by NMR

Xenon is a perspective gas for creation of oxygen free environment for different applications of biomaterials. To use xenon in suspensions and products properly it is necessary to know the molecular mechanisms of its interactions with water and cells. This work reports the study of bacterial suspensions of Escherichia coli in the presence of xenon using nuclear magnetic resonance (NMR). The work studied how the spin-lattice relaxation times of water protons in suspension change under xenon conditions. Xenon is able to form clathrate hydrates with water molecules at a temperature above the melting point of ice. The work studied NMR relaxation times which reflect the rotation freedom of water molecules in suspension. Lower relaxation times indicate reduced rotational freedom of water. Single exponential behavior of spin-lattice relaxation of protons in the suspensions of microorganisms has been registered. A recovery of longitudinal magnetization in cell suspensions with xenon clathrates has been characterized by two peaks in T1-distribution. Fast relaxing T1-component was related to the intracellular water and depended on the amount of xenon clathrates. The obtained results elucidate how the NMR method can monitor the process of clathrate formation and how the xenon atoms and hydrates interact with cells.

Breaking the Tetra‐Coordinated Framework Rule: New Clathrate Ba8M24P28+δ (M=Cu/Zn)

A new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba8 M24 P28+δ (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra common to clathrates along with a unique 22-vertex polyhedron with two hexagonal faces capped by additional partially occupied phosphorus sites. This is the first example of a clathrate compound where the framework atoms are not in tetrahedral or trigonal-pyramidal coordination. In Ba8 M24 P28+δ a majority of the framework atoms are five- and six-coordinated, a feature more common to electron-rich intermetallics. The crystal structure of this new clathrate was determined by a combination of X-ray and neutron diffraction and was confirmed with solid-state 31 P NMR spectroscopy. Based on chemical bonding analysis, the driving force for the formation of this new clathrate is the excess of electrons generated by a high concentration of Zn atoms in the framework. The rattling of guest atoms in the large cages results in a very low thermal conductivity, a unique feature of the clathrate family of compounds.

Breaking the Tetra‐Coordinated Framework Rule: New Clathrate Ba8M24P28+δ (M=Cu/Zn)

AbstractA new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba8M24P28+δ (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra common to clathrates along with a unique 22‐vertex polyhedron with two hexagonal faces capped by additional partially occupied phosphorus sites. This is the first example of a clathrate compound where the framework atoms are not in tetrahedral or trigonal‐pyramidal coordination. In Ba8M24P28+δ a majority of the framework atoms are five‐ and six‐coordinated, a feature more common to electron‐rich intermetallics. The crystal structure of this new clathrate was determined by a combination of X‐ray and neutron diffraction and was confirmed with solid‐state 31P NMR spectroscopy. Based on chemical bonding analysis, the driving force for the formation of this new clathrate is the excess of electrons generated by a high concentration of Zn atoms in the framework. The rattling of guest atoms in the large cages results in a very low thermal conductivity, a unique feature of the clathrate family of compounds.

Separation of CO2 and CH4 from Biogas by Formation of Clathrate Hydrates: Importance of the Driving Force and Kinetic Promoters

This paper relates to the upgrading of model biogas mixtures, typically 60/40 CH4/CO2, by clathrate (gas) hydrates, which have recently been considered as a safe alternative to high-pressure or liquefied gas storage, and as an economic, chemical-free process for the separation of gas mixtures. Several factors affecting the driving force to hydrate formation are considered, such as the degree of overpressurization and the presence of chemical promoters. Promoters used were several anionic and zwitterionic surfactants which are demonstrated to affect the hydrate-forming ability of water. Some lignin derivatives were also tested. Promoted hydrates were also compared to hydrate-based separation starting from nonpromoted water. Separation experiments were conducted under pressures of 4 and 2.5 MPa at 274 K, under either pressure-dropping or constant pressure conditions. Results show that the separation ability of clathrate hydrates as determined by the separation factor S is highest when no promoters are added...

Physicochemically modified peat by thermal and oxidation processes as an active material for purification of wastewaters from certain hazardous pollutants

The physicochemical modification of peat through thermal and oxidation processes was carried out, in order to obtain new, inexpensive and active material for purification of different types of waters. During the modification, surface chemical compounds of Shilov type were formed. Batch adsorption properties and suitability of physicochemically modified peat (PCMP) for odor removal were tested in aqueous solutions of H2S and colloidal sulphur. Additionally, PCMP was tested in the removal of As(V) which is hazardous ingredient in contaminated waters. Possible mechanisms of pollutants binding include interactions, which lead to formation of adducts and clathrates. All these processes are elucidated in detail. The results showed that the obtained material can be used for the removal of sulphide, colloidal sulphur and As(V) from different types of waters.

Experimental Investigation To Elucidate Why Tetrahydrofuran Rapidly Promotes Methane Hydrate Formation Kinetics: Applicable to Energy Storage

Methane storage as SNG (solidified natural gas) in the form of clathrate hydrates is an emerging, economically feasible and environmentally benign technology for large scale storage. Mixed tetrahydrofuran (THF)–methane (CH4) hydrates offer a paradigm shift to milder storage conditions and faster hydrate formation kinetics, providing a promising scenario to scale up the SNG technology. In this work, we synthesize mixed THF–CH4 hydrates in a high pressure microdifferential scanning calorimeter (HP μ-DSC) to elucidate the two-step hydrate formation mechanism of mixed THF–CH4 hydrate identifying the synergism between THF and CH4. Heat flow change during hydrate formation and dissociation of mixed THF–CH4 hydrates formed in the presence of 5.56 mol % THF (stoichiometric composition) were monitored. The two step-mechanism of mixed THF–CH4 hydrate formation was further confirmed by the pressure–temperature profile and visual observations with a sample volume scale-up of about 350 times that of μ-DSC experiments.

Thermal resistances in stirred-tank and tubular reactors for clathrate-hydrate formation: Estimating their reactor-scale dependences

Efficient formation of clathrate hydrates is the primary condition for establishing the hydrate-based technology for various industrial applications such as the natural gas storage/transport, the capture of CO2 from industrial flue gases, etc. Because hydrate formation is an exothermic process, the heat discharge from the inside of hydrate-forming reactors can be one of the major rate-controlling processes. The thick stainless-steel walls encasing such reactors configured for high-pressure operations may provide significant resistances to the heat transfer across them. Based on the conventional schemes for calculating the hoop stress in pressure-vessel walls and the convective/conductive heat transfer in cylindrical systems, this paper demonstrates how the thermal resistances to the heat discharge from the inside of each stirred-tank or tubular reactor vary depending on the geometric scale (i.e., the diameter) and the design pressure of the reactor. In general, the thermal resistance to the conductive heat transfer in the reactor wall becomes increasingly significant, relative to the resistance to the convective heat transfer inside the reactor, not only with an increase in the design pressure, but also with an increase in the reactor diameter.

Combined cluster and discriminant analysis: An efficient chemometric approach in diesel fuel characterization

Combined cluster and discriminant analysis (CCDA) as a chemometric tool in compound specific isotope analysis of diesel fuels was studied. The stable carbon isotope ratios (δ13C) of n-alkanes in diesel fuel can be used to characterize or differentiate diesels originating from different sources. We investigated 25 diesel fuel samples representing 20 different brands. The samples were collected from 25 different service stations in 11 European countries over a 2 year period. The n-alkane fraction of diesel fuels was separated using solid-state urea clathrate formation combined with silica gel fractionation. The stable carbon isotope ratios of C10–C24 n-alkanes were measured with gas chromatography–isotope ratio mass spectrometry (GC–IRMS) using perdeuterated n-alkanes as internal standards. Beside the 25 samples one additional diesel fuel was prepared and measured three times to get totally homogenous samples in order to test the performance of our analytical and statistical routine.Stable isotope ratio data were evaluated with hierarchical cluster analysis (HCA), principal component analysis (PCA) and CCDA. CCDA combines two multivariate data analysis methods hierarchical cluster analysis with linear discriminant analysis (LDA). The main idea behind CCDA is to compare the goodness of preconceived (based on the sample origins) and random groupings. In CCDA all the samples were compared pairwise.The results for the parallel sample preparations showed that the analytical procedure does not have any significant effect on the δ13C values of n-alkanes. The three parallels proved to be totally homogenous with CCDA.HCA and PCA can be useful tools when the examining of the relationship among several samples is in question. However, these two techniques cannot be always decisive on the origin of similar samples. The initial hypothesis that all diesel fuel samples are considered chemically unique was verified by CCDA. The main advantage of CCDA is that it gives an objective index number about the level of similarity among the investigated samples. Thus the application of CCDA supplemented by the traditionally used multivariate methods greatly improves the efficiency of statistical analysis in the CSIA of diesel fuel samples.