Tetrahydrofuran Clathrate Hydrate Research Articles

Probing the critical nucleus size in tetrahydrofuran clathrate hydrate formation using surface-anchored nanoparticles

Controlling the formation of clathrate hydrates is crucial for advancing hydrate-based technologies. However, the microscopic mechanism underlying clathrate hydrate formation through nucleation remains poorly elucidated. Specifically, the critical nucleus, theorized as a pivotal step in nucleation, lacks empirical validation. Here, we report uniform nanoparticles, e.g., graphene oxide (GO) nanosheets and gold or silver nanocubes with controlled sizes, as nanoprobes to experimentally measure the size of the critical nucleus of tetrahydrofuran (THF) clathrate hydrate formation. The capability of the nanoparticles in facilitating THF clathrate hydrate nucleation displays generally an abrupt change at a nanoparticle-size-determined specific supercooling. It is revealed that the free-energy barrier shows an abrupt change when the nanoparticles have an approximately the same size as that of the critical nucleus. Thus, it is inferred that THF clathrate hydrate nucleation involves the creation of a critical nucleus with its size being inversely proportional to the supercooling. By proving the existence and determining the supercooling-dependent size of the critical nucleus of the THF clathrate hydrates, this work brings insights in the microscopic pictures of the clathrate hydrate nucleation.

Thermodynamic modeling for ternary clathrate hydrates of carbon dioxide, nitrogen and tetrahydrofuran

Hydrate-based CO2 separation technology is one of research hotspots in the field of Carbon Capture, Utilization, and Storage. However, thermodynamics, such as phase temperature and pressure, are very important for CO2 separation. In this study, a thermodynamic model was developed for calculating the temperature, pressure, separation efficiency and separation factor of the CO2-N2-THF/H2O system at the three-phase equilibrium of vapor–liquid-hydrates (V-L-H). The Chen-guo model was applied for the hydrate phase and the Patel-Teja equation of state (EOS) was used for the vapor phase. The Wilson activity coefficient model was employed for the liquid phase and the solubility of CO2 in solution was calculated using Henry's law. The average absolute deviation of the equilibrium pressure and temperature compared to the experimental data are 10.441% and 0.343%, respectively, which showed that the predicted three-phase equilibrium pressure and temperature were in good agreement with the experimental results. The three-phase equilibrium temperature and pressure of CO2 and N2 gas mixture in pure water and in THF aqueous solutions were compared. The results showed that THF had a promotion effect in reducing temperature and pressure of CO2 hydrate formation.

Ultralow thermal conductivity in tetrahydrofuran clathrate hydrate

The detailed knowledge of the low thermal conductivity of host–guest compounds is essential to improve our fundamental understanding of heat conduction in complex solids and develop high-performance thermoelectric materials. In this Letter, the intrinsic ultralow thermal conductivity (0.44 ± 0.06 W m−1 K−1 in 140–190 K) of the tetrahydrofuran (THF) clathrate hydrate is characterized by the time-domain thermoreflectance technique. The underlying heat conduction mechanism is further investigated by non-equilibrium molecular dynamics simulations. We find that trapped THF molecules do harmonic motions and behave as parts of a crystalline structure, thus playing negligible roles in thermal conductivity reduction. The large unit cell and complex cage-like host structure dominate the low thermal conductivity of the THF hydrate.

Clathrate Hydrate Inhibition by Polyisocyanate with Diethylammonium Group.

Polymers containing amide groups have been used as kinetic hydrate inhibitors (KHIs). The amide group has good performance for hydrate nucleus adsorption, resulting in inhibition of hydrate growth. Polyisocyanates composed of an amide backbone can be KHI candidates; however, the use of polyisocyanates as KHIs has not yet been reported. Herein, we prepared water-soluble poly[3-[[2-(diethylamino)ethyl]thio]-1-propyl isocyanate-ran-hexyl isocyanate] (P(DETPIC-ran-HIC)) to investigate the ability of polyisocyanates to inhibit hydrate formation. In the tetrahydrofuran (THF) clathrate hydrate crystal growth inhibition tests, P(DETPIC-ran-HIC) showed better performance than the polyamide, poly(N-vinylpyrrolidone) (PVP).

CO2 capture from CH4–CO2 mixture by gas–solid contact with tetrahydrofuran clathrate hydrate

This study evaluated the CO2 separation characteristics for gas–solid contact between CH4 and CO2 mixtures and stoichiometric tetrahydrofuran (THF) hydrate to elucidate system temperature and pressure effects on clathrate hydrate gas separation performance. The CO2 molecules in the system were incorporated selectively into the hydrate phase during the gas–solid contact at lower temperatures. The CO2 selectivity for gas uptake was higher at higher-pressure conditions at a constant temperature. Results suggest that greater driving force for gas uptake to stoichiometric THF hydrate crystals contributes to improved CO2 selectivity from the CH4–CO2 mixture. Effects of the driving force on CO2 separation from CH4–CO2 mixture contrasted against those of gas–liquid systems using THF aqueous solution or liquid water. The different effects are expected to derive from differences in gas uptake process between gas–solid and gas–liquid systems and differences in cages for competition for gas uptake.

Universal temperature dependence of the thermal conductivity of clathrate compounds, molecular crystals, and glasses at low temperatures

A new approach is used to analyze the experimental data on the temperature dependence of low-temperature thermal conductivity κ(T) of some typical disordered complex crystals: clathrate hydrates (tetrahydrofuran, methane, xenon), Sr8Ga16Ge30 and p-type Ba8Ga16Ge30 clathrate compounds, YSZ ceramics, molecular structural glasses of 1-propanol, glycerol and D-ethanol exhibiting glass-like behavior of κ(T), and some representatives of regular complex crystals: tetrahydrofuran clathrate hydrate, n-type Ba8Ga16Ge30 clathrate compound, CsDy(MoO4)2 layered crystal, 1-propanol, and D-ethanol. A universal approach to normalizing low-temperature thermal conductivity is proposed, based on the theoretical model of hybridized Klinger–Kosevich excitations. The low-temperature universal behavior of the thermal conductivity of both crystalline and amorphous solids is shown to be a result of the same phenomenon: the hybridization of acoustic and low-lying optical branches.

Molecular Dynamic Simulations of Clathrate Hydrate Anomalous Preservation: The Effect of Coating Clathrate Hydrate Phases

In this work, the effect of cyclopentane (CP) clathrate hydrate on the anomalous preservation of tetrahydrofuran (THF) hydrate under conditions outside its stability region is studied by using molecular dynamics simulations. The decompositions of pure structure II THF and CP clathrate hydrate, and also THF hydrate coated by CP hydrate, all with outer (001) surfaces exposed to vacuum, were simulated at different temperatures and characterized by the potential energy, the F3 order parameter, and visual inspection of snapshots of the hydrate system at different times. The upper bounding melting points of THF and the CP hydrate with the employed force fields were predicted to be 270 and 290 K, respectively, which were close to the experimental values of 277.5 and 281 K. To study the origins of anomalous preservation and superheating effects in hydrates, we placed layers of the higher-decomposition point CP hydrate as a coating on bulk THF hydrate to study the possible superheating of the THF hydrate. Whereas ...

Spectroscopic fingerprints in the low frequency spectrum of ice (Ih), clathrate hydrates, supercooled water, and hydrophobic hydration reveal similarities in the hydrogen bond network motifs.

Solid phases of water, such as ice (Ih) and clathrate hydrates, form characteristic hydrogen bond network motifs, such as hexagonal ice, pentagons, and dodecahedrons. The same motifs might be present in supercooled water and in the hydration structure around hydrophobes. Here, we present the characteristic low frequency fingerprints of ice (Ih), tetrahydrofuran (THF) clathrate hydrates, and tetrabutyl-ammonium bromide (TBAB) semiclathrate close to their melting point, as well as supercooled water at 266.6 K and aqueous alcohol solutions. Interestingly, we find in all these cases two characteristic resonances in the THz frequency range: at least, one intensive band in the frequency range between 190 cm-1 and 220 cm-1 which is a characteristic of a tetrahedral hydrogen bond network configuration and a second band in the frequency range between 140 cm-1 and 170 cm-1, indicating a component with weaker hydrogen bonds. For solvated alcohols, we find spectroscopic fingerprints of a clathratelike structure at 164 cm-1 as well as a tetrahedral network structure at 194 cm-1, which is close to one of ice (Ih) at 192 cm-1. We propose that in the hydration shell of hydrophobes, both structural motifs are present. In the case of supercooled water-unlike ice-only one peak was found in the frequency range between 190 cm-1 and 220 cm-1. Interestingly, the latter peak center-frequency (204 cm-1) corresponds to the average of those of the two peaks observed for ice Ih (191 cm-1 and 215 cm-1). This indicates a homogeneous intermediate hydrogen bonding, providing no evidence for any heterogeneity in two high-density and low-density phases.

Elucidation of the pressure induced amorphization of tetrahydrofuran clathrate hydrate.

The type II clathrate hydrate (CH) THF·17 H2O (THF = tetrahydrofuran) is known to amorphize on pressurization to ∼1.3 GPa in the temperature range 77-140 K. This seems to be related to the pressure induced amorphization (PIA) of hexagonal ice to high density amorphous (HDA) ice. Here, we probe the PIA of THF-d8 · 17 D2O (TDF-CD) at 130 K by in situ thermal conductivity and neutron diffraction experiments. Both methods reveal amorphization of TDF-CD between 1.1 and 1.2 GPa and densification of the amorphous state on subsequent heating from 130 to 170 K. The densification is similar to the transition of HDA to very-high-density-amorphous ice. The first diffraction peak (FDP) of the neutron structure factor function, S(Q), of amorphous TDF-CD at 130 K appeared split. This feature is considered a general phenomenon of the crystalline to amorphous transition of CHs and reflects different length scales for D-D and D-O correlations in the water network and the cavity structure around the guest. The maximum corresponding to water-water correlations relates to the position of the FDP of HDA ice at ∼1 GPa. Upon annealing, the different length scales for water-water and water-guest correlations equalize and the FDP in the S(Q) of the annealed amorph represents a single peak. The similarity of local water structures in amorphous CHs and amorphous ices at in situ conditions is confirmed from molecular dynamics simulations. In addition, these simulations show that THF guest molecules are immobilized and retain long-range correlations as in the crystal.

Kinetic inhibition effect of Type I and III antifreeze proteins on unidirectional tetrahydrofuran hydrate crystal growth.

Experiments were performed to evaluate the kinetic inhibition effect of Type I and Type III antifreeze proteins (AFPs), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) on the growth of tetrahydrofuran (THF) clathrate hydrate crystals using the unidirectional growth technique. The crystal growth interface shifted under an applied temperature gradient over a given time. Type I AFP was the most effective kinetic inhibitor, followed by PVP, Type III AFP and PVA. The morphology of the THF hydrate was affected significantly by the concentration of Type I AFP. At low concentrations of Type I AFP, a large hexagonal plate-like crystal formed. At high concentrations, the growth interface became relatively flat. Conversely, at low concentrations of Type III AFP, the morphology of the THF hydrate crystal was unaffected by the additive.

A Second Glass Transition in Pressure Collapsed Type II Clathrate Hydrates.

Type II clathrate hydrates (CHs) M·17 H2O, with M = tetrahydrofuran (THF) or 1,3-dioxolane, are known to collapse, or amorphize, on pressurization to ∼1.3 GPa in the temperature range 77-140 K. On heating at 1 GPa, these pressure-amorphized CH states show a weak, stretched sigmoid-shaped, heat-capacity increase because of a glass transition. Here we use thermal conductivity and heat capacity measurements to show that also type II CH with M = cyclobutanone (CB) collapses on isothermal pressurization and undergoes a similar, weak, glass transition upon heating at 1 GPa. Furthermore, we reveal for both THF CH and CB CH a second, much more pronounced, glass transition at temperatures above the thermally weak glass transition on heating in the 0.2-0.7 GPa range. This result suggests the general occurrence of two glass transitions in water-rich (94 mol %) pressure-collapsed CHs. Because of a large increase in dielectric permittivity concurrently as the weak heat capacity increase, the first glass transition must be due to kinetic unfreezing of water molecules. The thermal features of the second glass transition, measured on isobaric temperature cycling, are typical of a glass-liquid-glass transition, which suggests that pressure-amorphized CHs transform reversibly to liquids.

Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

Gas hydrates have long been of interest to the petrochemical industry, but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host–guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work, we have shown that it is possible to use muon spin spectroscopy to characterize H atom like muonium and muoniated free radicals formed in clathrate hydrates. Muonium (Mu) forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro derivatives form radicals. The current work extends studies to clathrates hydrates of other five-membered heterocycles: thiophene, pyrrole, and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to furan, two distinct radicals are formed when Mu reacts with thiophene and pyrrole. However, only one muoniated radical was detected from isoxazole. Muon, proton, and nitrogen hyperfine constants were determined and compared with values predicted by DFT calculations to aid the structure assignments. The results show that Mu adds preferentially to the carbon adjacent to the heteroatom in thiophene and pyrrole and to the carbon adjacent to oxygen in isoxazole. The same radicals are formed in clathrates, but the spectra have broader signals, suggesting slower tumbling. Furthermore, additional signals in the avoided level-crossing spectra indicate anisotropy consistent with restricted motion of the radicals in the clathrate cages.

2-2-2 一方向凝固法による動的インヒビタの成長抑制および分解速度に与える影響の評価

2-2-2 一方向凝固法による動的インヒビタの成長抑制および分解速度に与える影響の評価

Thermodynamic aspects of freeze-drying

Aqueous solutions of glycine and tetrahydrofuran (THF) were frozen under variable conditions and subsequently annealed. The phases that resulted from this process were studied by X-ray diffraction, DSC and cryotemperature SEM. Under conditions achieved in common laboratory freeze-dryers, the THF clathrate hydrate of cubic structure II was formed in near-quantitative yields. The temperature–composition state diagram for the THF–water–β-glycine systems suggests that the critical temperature of the primary drying stage is the temperature of the four-phase peritectic reaction (269 K), and not the temperature of the congruent melting of the THF hydrate in the THF–water system (278 K). Freeze-drying is shown to go much faster if aqueous solutions are substituted for THF–water solutions. This finding is of great importance for practical applications, including pharmaceutical drug formulation.

Experimental investigations of clathrate hydrate inhibition in water based drilling fluid using green inhibitor

Formation of hydrate plugs in drilling fluid is a serious problem in oil and gas industries. Recently, interest in the development of green hydrate inhibitors increased which can be used as substitutes for available low dosage hydrate inhibitors (LDHIs). In this research paper the effect of porcine pancreatic lipase on the formation of tetrahydrofuran (THF) clathrate hydrate was studied by determining the time for nucleation of hydrate crystals (induction time). Pancreatic lipase inhibits the formation of clathrate hydrate and its growth by adsorbing to different hydrate crystal faces. The ability of pancreatic lipase to eliminate or extends the “memory effect” was also studied and compared with polyvinylpyrrolidone (PVP). Pancreatic lipase found to be a better inhibitor than PVP and also suppresses the “memory effect” more efficiently. The effect of pancreatic lipase on the rheology of drilling fluid was studied as rheological characteristics of drilling fluid are most crucial for safe drilling operations. It was found that drilling fluid performs satisfactorily in terms of rheology at different concentrations of pancreatic lipase. This research paper shows that pancreatic lipase can be effectively used in drilling fluid as a green hydrate inhibitor.

Micro-Tomographic Investigation of Ice and Clathrate Formation and Decomposition under Thermodynamic Monitoring.

Clathrate hydrates are inclusion compounds in which guest molecules are trapped in a host lattice formed by water molecules. They are considered an interesting option for future energy supply and storage technologies. In the current paper, time lapse 3D micro computed tomographic (µCT) imaging with ice and tetrahydrofuran (THF) clathrate hydrate particles is carried out in conjunction with an accurate temperature control and pressure monitoring. µCT imaging reveals similar behavior of the ice and the THF clathrate hydrate at low temperatures while at higher temperatures (3 K below the melting point), significant differences can be observed. Strong indications for micropores are found in the ice as well as the THF clathrate hydrate. They are stable in the ice while unstable in the clathrate hydrate at temperatures slightly below the melting point. Significant transformations in surface and bulk structure can be observed within the full temperature range investigated in both the ice and the THF clathrate hydrate. Additionally, our results point towards an uptake of molecular nitrogen in the THF clathrate hydrate at ambient pressures and temperatures from 230 K to 271 K.

Energy-dissipation of OH-stretching in tetrahydrofuran clathrate hydrate by Raman spectroscopy and DFT calculation

Temperature dependences of a Raman spectrum of a tetrahydrofuran clathrate hydrate (THF-CH) and an ice Ih are measured in 2800–3500cm−1 from 4 to 250K. A quality factor (Q factor) of a main peak at 3100cm−1, which is assigned as an OH-stretching mode of H2O molecules, is discussed. An energy-dissipation of H2O molecules in the THF-CH is larger than that of the ice Ih for all temperatures in this study, since the THF-CH has the lower Q factor than the ice Ih. Molecular orbitals of a “THF-CH-like cluster” are calculated by density-functional theory to confirm a guest-host interaction in the THF-CH. HOMOs of the THF molecule and H2O molecules almost filled inside of a water-cage. This means that the THF interacts directly with H2O molecules of the water-cage. From the experimental and theoretical results, it is concluded that the direct guest-host interactions are the extra energy-dissipation channel of the OH-stretching mode in THF-CH.

Mechanism of Slow Crystal Growth of Tetrahydrofuran Clathrate Hydrate

Tetrahydrofuran (THF) clathrate hydrate has been frequently used in experimental studies instead of gas hydrates because it forms at a temperature higher than the ice point under ambient pressure. In this paper, we compare the crystal growth rates of THF hydrate and ice using molecular dynamics simulations. It is demonstrated that the crystal growth of THF hydrate is much slower than that of ice. The growth rates of THF hydrate significantly deviate from a standard kinetic model known as the Wilson–Frenkel model, whereas it reproduces the temperature dependence of the growth rate of ice. The slow crystal growth and the deviation from the Wilson–Frenkel model are attributed to the trapping of THF molecules in open small cages at the hydrate surface. We calculate the free energy profile of a THF molecule transferring from the bulk solution phase to the hydrate surface using the umbrella sampling technique. It is shown that a THF molecule trapped in an open small cage needs to cross one or two free energy ba...

Effects of Empty Cages on Lattice Distortion of Tetrahydrofuran Clathrate Hydrate

Tetrahydrofuran (THF) clathrate hydrate has been studied as a new storage system for H2. To investigate effects of empty cages on lattice distortion, molecular dynamics calculations of THF clathrate hydrate were performed. The results show that the hexakaidecahedral cages shrink due to absence of THF from the cages, whereas the surrounding dodecahedral cages expand. The vibrational density of states indicates that the O–H symmetric stretching mode shifts to lower frequency with decreasing cage occupancy. The results suggest that the average strength of the hydrogen bonds increases with decreasing cage occupancy. It is concluded that a small number of empty cages can affect not only the local structures, but also the macroscopic properties of the crystal. The effects of empty cage may be an important factor governing the efficiencies of storage and release of H2 in THF clathrate hydrate.

Evaluation of the performance of kinetic inhibitors for clathrate hydrate using unidirectional growth apparatus

We study the formation of tetrahydrofuran (THF) clathrate hydrate from polyvinylpyrrolidone (PVP) aqueous solution as a function of growth rate V and adsorbed PVP concentration c using the unidirectional growth technique.