THF Hydrate Research Articles

Influence of non-stoichiometric solutions on the THF hydrate growth: chemical affinity modelling and visualization

Influence of non-stoichiometric solutions on the THF hydrate growth: chemical affinity modelling and visualization

Formation and Transformation of Clathrate Hydrates under Interstellar Conditions.

ConspectusContinuing efforts by many research groups have led to the discovery of ∼240 species in the interstellar medium (ISM). Observatory- and laboratory-based astrochemical experiments have led to the discovery of these species, including several complex organic molecules (COMs). Interstellar molecular clouds, consisting of water-rich icy grains, have been recognized as the primordial sources of COMs even at extremely low temperatures (∼10 K). Therefore, it is paramount to understand the chemical processes of this region, which may contribute to the chemical evolution and formation of new planetary systems and the origin of life.This Account discusses our effort to discover clathrate hydrates (CHs) of several molecules and their structural varieties, transformations, and kinetics in a simulated interstellar environment. CHs are nonstochiometric crystalline host-guest complexes in which water molecules form cages of different sizes to entrap guest molecules. CHs are abundant on earth and require moderate temperatures and high pressures for their formation. Our focus has been to form CHs at extremely low pressure and temperature as in the ISM, although their existence under such conditions has been a long-standing question since water and guest molecules (CH4, CO2, CO, etc.) exist in space. In multiple studies conducted at ∼10-10 mbar, we showed that CH4, CO2, and C2H6 hydrates could be formed at 30, 10, and 60 K, respectively. Well-defined IR spectroscopic features supported by quantum chemical simulations and temperature-programmed desorption mass spectrometric analyses confirmed the existence of the 512 (for CH4 and CO2) and 51262 (for C2H6) CH cages. Mild thermal activation for long periods under ultrahigh vacuum (UHV) allowed efficient molecular diffusion, which is crucial for forming CHs. We also explored the formation of THF hydrate (a promoter/stabilizer for binary CHs), and a spontaneous method was found for its formation under UHV. In a subsequent study, we observed a binary THF-CO2 hydrate and its thermal processing at 130 K leading to the transportation of CO2 from the hydrate cages to the matrix of amorphous water. The findings imply that such systems possess a dynamic setting that facilitates the movement of molecules, potentially accounting for the chemical changes observed in the ISM. Furthermore, an intriguing fundamental phenomenon is the consequences of these CHs and their dynamics. We showed that preformed acetone and formaldehyde hydrates dissociate to form cubic (Ic) and hexagonal (Ih) ices at 130-135 K, respectively. These unique processes could be the mechanistic routes for the formation of various ices in astrophysical environments.Other than adding a new entry, namely, CHs, to the list of species found in ISM, its existence opens new directions to astrochemistry, observational astronomy, and astrobiology. Our work provides a molecular-level understanding of the formation pathways of CHs and their transformation to crystalline ices, which sheds light on the chemical evolution of simple molecules to COMs in ISM. Furthermore, CHs can be potential candidates for studies involving radiation, ionization, and electron impact to initiate chemical transformations between the host and guest species and may be critical in understanding the origin of life.

Evaluation of the Xanthan Gum, Gum Acacia, and Their Graft Copolymers with Acrylamide as Low-Dosage Hydrate Inhibitors for Their Application in the Drilling of Gas Hydrate Reservoirs

Hydrate formation is a significant issue while drilling into deep-water reservoirs containing gas hydrates. They may form in the drilling fluid flowlines, wellbore annulus, and ram cavities of blowout preventers. The natural gums, i.e., xanthan gum (XG) and gum acacia (GA), and their two graft copolymers with acrylamide (AAm), i.e., XG-g-PAAm and GA-g-PAAm, have been synthesized and tested as low-dosage hydrate inhibitors using THF hydrate systems via temperature-augmented visual method. XG-g-PAAm and GA-g-PAAm have shown better inhibition efficiencies and higher induction times than XG and GA. All of these inhibitors are then tested as drilling fluid additives to the formulated water-based drilling fluid systems (WBDFs). The formulated WBDFs contained 0.4 w/v % of each carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), and 5 w/v % of potassium chloride (KCl). The rheology of the formulated WBDFs has been tested at an ambient temperature (293 K) and low temperature (275 K). The rheological parameters of WBDFs obtained from the experiments are within permissible limits with an inhibitor concentration of 0.5 w/v %. The rheological data are then fitted to the Bingham–Plastic (B–P) model and Herschel–Bulkley (H–B) model. The coefficient of determination’s (R2) upper and lower limits for the B–P model is 0.9715–0.9969 for 0.5 w/v % GA- and 0.5 w/v % XG-g-PAAm-containing WBDF systems. Again, for the H–B model, the range for R2 is from 0.9891 to 0.9980 for 0.5 w/v % GA- and 0.5 w/v % XG-containing WBDFs. Hence, the R2 showed a better agreement with the H–B model than with the B–P model. These observations suggest that XG, GA, XG-g-PAAm, and GA-g-PAAm may be used as hydrate inhibitors in the formulated WBDFs while drilling into gas hydrate reservoirs.

Molecular Insights into the Effect of Nitrogen Bubbles on the Formation of Tetrahydrofuran Hydrates.

In this work, a molecular dynamics simulation was conducted to study the microscopic mechanism of how nitrogen bubbles affect the formation of THF hydrates at the molecular level. The results obtained reveal that the nitrogen bubble can promote the formation of THF hydrates. In the system with a nitrogen bubble, more THF-filled cages were generated, and the crystal structure was more orderly. The promotion of nitrogen bubbles on hydrate crystallization comes from the dissolution of nitrogen molecules. Some of dissolved nitrogen molecules can be enclosed in small hydrate cages near the nitrogen bubble, which can serve as stable sites for hydrate crystal growth, resulting in the fact that THF-filled cages connected with N2-filled cages are much more stable and have a long lifetime. The results in this work can help to understand the promotion effect of micro- and nano-air bubbles on the crystallization of THF hydrates.

Effect of surface structure on the kinetic of THF hydrate formation

The most important aim of this study is to check the surface effect on THF/H2O hydrate formation by the volumetric method [Asadi et al. J. Mol. Liq., https://doi.org/10.1016/j.molliq.2019.111200]. A wide variety of experiments have been conducted to investigate effective parameters on hydrate formation. Suitable additives and operational conditions have been already studied while the effect of other parameters including surface efficacy has not been considered. Hence, the experiments have been done at atmospheric pressure in a cell that has a prefabricated surface. Therefore, the modified surfaces used here are 304 stainless steel specimens with specific roughness which have been coarsened through laser. Since the roughness and wettability of metallic plates play a critical role in hydrophobicity or hydrophilicity of surfaces, the contact angles have been measured between 123.00 and 23.47°changing the speed of laser radiation. It is demonstrated, increasing radiation speed forms a hydrophilic surface. Moreover, hydrate nucleation and growth have been rapidly recorded via volume changes of solution. Subsequently, the most effective surface has been recognized according to induction and relaxation time as well as the rate of hydrate formation. The results show that developing a hydrophilic surface, the rate of THF hydrate formation is highly increased. Therefore, this study can provide a new viewpoint in the relation of surface structure and the kinetics of THF/H2O hydrate formation.

Significance of wettability of porous media and its implication for hydrate-based pre-combustion CO2 capture

Gas hydrate-based pre-combustion CO2 capture is considered a promising technology for CO2 separation. To further improve hydrate-based CO2 capture from gaseous mixtures (i.e., CO2 + H2) generated from pre-combustion processes, it is necessary to enhance the hydrate thermodynamic stability and formation kinetics. Surfactants and interstitial pore materials have been suggested to enhance formation kinetics, but the optimum confined space and wettability of the porous media, which are the key factors affecting kinetic performance, have not been fully determined when using thermodynamic promoters. In this study, the thermodynamic stability and formation kinetics (e.g., induction time, formation rate, gas composition, and gas uptake) of THF (5.56 mol%) hydrates of CO2 (40%) + H2 (60%) mixtures in the presence of SDS (0, 100, or 500 ppm) were evaluated in silica gels of various hydrophobicities. The results revealed that the hydrophobicity of the porous media significantly affects both the thermodynamic phase equilibria and kinetic properties. Interestingly, the weak hydrophobic silica gel enhanced the thermodynamic stability, induction time, formation rate, and gas uptake with 96% CO2 composition. The SDS (particularly 500 ppm) also improved the kinetic properties of the hydrate. The present findings provide a new guideline for designing the optimum hydrophobicity of porous media to enhance the thermodynamic stability and formation kinetics for hydrate-based pre-combustion CO2 capture.

Growth rate and morphology study of tetrahydrofuran hydrate single crystals and the effect of salt

Single crystals of sII THF hydrate grown using a seed/template method demonstrated an increase in growth rates. With 3.5 wt% NaCl, the growth rates are lower, resulting in a morphology of parallel intergrowths of octahedral crystals.

Influence of Rock Wettability on THF Hydrate Saturation and Distribution in Sandstones

Natural gas trapped in hydrate deposits is a potentially enormous source of energy which can in principle be extracted from the underground reservoir structures. These reserves can potentially also catastrophically release very large quantities of greenhouse gases to the atmosphere. One key parameter which is well known to strongly influence fluid distribution, saturation, and production is rock wettability. However, the effect of wettability on gas hydrate in sediments has not been investigated yet. We thus used nuclear magnetic resonance (NMR) spectrometry to measure relaxation times (T2 and T1) and the corresponding surface relaxivity of tetrahydrofuran hydrate during the formation and dissociation in water- and oil-wet Bentheimer sandstones. We also measured the NMR porosities and hydrate saturations at different temperatures during hydrate formation/dissociation for both water-wet and oil-wet sandstones. Significantly higher hydrate saturation was observed in the water-wet sandstone (when compared to the oil-wet sandstone) at all stages of hydrate formation and dissociation. Furthermore, the T2 spectra moved from the lower relaxation domain (before hydrate formation) to the fast relaxation domain (after hydrate formation) in both water-wet and oil-wet sandstones. However, the water-wet sandstone generally had a T2 relaxation range due to the higher water affinity to the water-wet rock and the associated faster demagnetization of the water molecules. These results demonstrate that low-field NMR can be used to quantify the rock wettability and observe hydrate behavior in geologic sediments. This fundamental information thus aids in the development of gas extraction from hydrate reservoirs and the assessment of potential greenhouse gas emissions from such reservoirs into the atmosphere.

Experimental study and kinetic modeling on THF hydrate formation under a static electric field

Hydrate formation has drawn wide-ranging research attention because of its applications in natural gas storage and transportation, refrigeration technology, seawater desalination, gas separation, capturing greenhouse gases, and energy storage. Also, THF hydrate has been widely investigated in terms of its kinetics, thermophysical properties, and suitability as a replacement for CH4 hydrates in experimental studies. In this work, the kinetics of THF hydrate formation under the impact of an electric field is studied by performing a chemical affinity model. Hence, the effect of an electric field on the chemical affinity model variations involving nucleation temperature and time duration to attain equilibrium needs to be studied from the model point of view. Then, the chemical affinity model under the effect of an electric field is performed for three THF-H2O systems involving solutions containing 10 wt% THF, 19 wt% THF, and 30 wt% THF, and one THF–H2O–SDS system containing 19 wt% THF and 100 ppm SDS. Based on the results, imposing an electric field with a strength of 4.3 × 105 V/m for the mentioned systems causes the nucleation temperature and the hydration reaction time to reach equilibrium to increase. Herein the change in THF consumption versus time in the process of formation and growth of THF hydrate is analyzed by using the chemical affinity model.

Rapid Formation of Hydrogen-Enriched Hydrocarbon Gas Hydrates under Static Conditions

This work introduces a “hydrate seed solution”, a surfactant solution containing pre-constructed structure II (sII) hydrate crystals, for the rapid formation of hydrogen-enriched hydrocarbon mixed hydrates. We observed the instantaneous nucleation and fast growth of mixed gas hydrates for both CH4–H2 and C2H6–H2 mixtures with the cyclopentane (CP) hydrate seed. The CP hydrate seed, which is immiscible with water, dominantly induces the growth of CH4–H2 and C2H6–H2 mixed gas hydrates with thermodynamically favorable sI structure. However, the THF hydrate seed, which is miscible with water, induced the formation of seed-templated sII CH4–H2 or C2H6–H2 hydrate, and the overall reaction was much slower than the CP hydrate seed case. For the C2H6–H2 gas mixture, C2H6 molecules could not occupy the small cage of hydrates, but H2 mainly occupied the small cage. The THF hydrate seed provided a higher storage ratio of H2 than the CP hydrate seed because the seed-templated sII C2H6–H2 gas hydrates have a larger number of small cages than does the structure I (sI) hydrate. As the CP hydrate seed concentration decreased from 2.78 to 0.278 mol %, the growth of the mixed gas hydrates was extremely accelerated, and the overall conversion was completed within 1 h. The growth kinetics of hydrogen-enriched hydrocarbon mixed hydrates in the non-stirred system was much faster than that in prior agitation-applied studies. These findings suggest a way forward to an enhanced formation of hydrogen–natural gas clathrates for sustainable energy gas storage.

Enhanced methane storage in clathrate hydrates induced by antifreezes

• Antifreezes such as methanol and ammonia can enhance methane uptake ability of binary clathrate hydrates. • Methanol can be encaged in the distorted 5 12 cages of TBAB clathrate hydrate. • Methanol can accelerate the structural transformation of TBAB clathrate hydrate. • Methanol and ammonia can be key materials for hydrate-based gas storage systems. Antifreezes are widely used in preventing hydrate formation in oil and gas flowlines. Recent studies have revealed that methanol and ammonia can be incorporated into clathrate hydrate phases along with a more hydrophobic guest such as THF or propane and that these antifreezes act as catalysts for methane hydrate formation from ice. In this work, we demonstrated that these antifreezes can enhance the methane storage content of binary clathrate hydrates, namely those of THF and TBAB. THF + methane and TBAB + methane binary hydrates with/without methanol or ammonia were synthesized and analyzed with 13 C NMR spectroscopy and X-ray diffraction (XRD) methods. In the THF hydrate system, 84% and 81% of the 5 12 small cages were occupied by methane in the presence of methanol and ammonia respectively, while only 44% of the small cages were occupied in the absence of these antifreezes. In the TBAB-H 2 O system, the powder XRD (PXRD) patterns of 1TBAB:38H 2 O samples without antifreeze both before and after methane introduction showed mostly tetragonal structures. On the other hand, it was confirmed that methanol can easily induce TBAB hydrates to form the orthorhombic structure which is more suitable for methane storage than the tetragonal structures of TBAB hydrates. The single crystal XRD analysis of a crystal grown from the 1TBAB:1CH 3 OH:38H 2 O solution at 277 K showed that methanol was present in the 5 12 cage of the orthorhombic TBAB hydrate phase. The 13 C NMR spectra of TBAB + methane hydrates also showed an enhanced methane content in the presence of methanol. The present findings on the enhancement of methane storage induced by antifreezes suggest that methanol can be a key material for hydrate-based methane storage systems.

Enhancing Hydrogen Cluster Storage in Clathrate Hydrates via Defect-Mediated Lattice Engineering

Can we create even more “plenty of room at the bottom” of the confined nanospaces in clathrate hydrates by tuning the complex interactions between the host water frameworks and guest molecules? Because the lattice of the clathrate hydrate is stabilized by van der Waals forces between the host and guest, irradiating the lattice of the clathrate hydrate with energetic particles is anticipated to introduce artificial defects on the host water molecules, resulting in creating a better occupation of guest molecules. Here, we explored the effects of proton irradiation on the intermolecular hydrogen and intramolecular polar covalent bonds in the host frameworks of THF hydrates. The distinct roles of the secondary guest molecules in the lattice elongation of the proton irradiated THF hydrates were examined experimentally. Conclusively, multiple occupations of H2 in small cages was observed at moderate pressure and temperature conditions following H2 reloading of the lattice elongated THF hydrate.

The experimental study and molecular dynamic simulation of THF hydrate growth kinetics in the presence of Arabic and Guar gum: New approaches in promotion of THF hydrate formation

The effect of two natural polymers, Guar gum and Arabic gum, on tetrahydrofuran hydrate formation kinetics was examined and simulated in the present investigations. The experiments were conducted under atmospheric pressure in a batch reactor. The induction time and growth rate of the hydrate formation were measured and the results of two gums were compared together. Both of the gums dramatically promoted the hydrate formation nucleation and growth rate at very low concentrations; overally Guar gum was better and at best it decreased the induction time (delay time) of the hydrate formation by 11 times. This is most likely the first report of edible molecules that promote the rate of THF/H2O hydrate formation. The molecular dynamic simulation showed that the presence of gums causes a greater tendency to order the water molecules around the THF molecules for forming the hydrate cages. Although there is a greater probability of hydrogen bonding between Arabic gum and water molecules, Guar gum has a better effect on the hydrate growth rate compared to the Arabic gum. After all, in addition to promote the THF hydrate formation rate, the most important property of these natural polymers is that they are edible and environmentally-friendly, so they can be considered as a novel candidate for the future of clathrate hydrate science and storage of H2 and He through the THF hydrate.

Revealing the Growth of H2 + THF Binary Hydrate through Molecular Simulations

The use of H₂ as an ideal fuel is restricted by storage and transportation. It is proposed that THF is a promising promoter for storing H₂ in the form of hydrates under mild conditions. However, the molecular-level details of the formation of H₂ + THF binary hydrate are still unclear. In the present work, molecular simulations were conducted for two sets of temperature and pressure conditions to investigate the growth of H₂ + THF binary hydrate. We find that H₂ as a kinetic promoter can significantly accelerate the growth of a pure THF hydrate at 250 K and 50 MPa. Our results indicate that the evolution of the growth rate of H₂ + THF binary hydrate with temperature and pressure is similar to that of the pure THF hydrate, where the growth rate is the maximum at 260 K and a fixed pressure of 50 MPa; pressure has a negligible impact on the growth rate of the binary hydrate at pressures of 10–110 MPa and a fixed temperature of 250 K. This means that THF molecules control the growth process of H₂ + THF binary hydrate at our conditions except that the rearrangement of water molecules dominates the growth process at 230 K and 50 MPa. Increasing temperature and pressure can lower the percentage of empty cages in the newly formed binary hydrate, thus improving the occupancy of 5¹² cages by H₂. The occupancy rate of 5¹²6⁴ by H₂ at different temperatures is correlated with the growth rate of the binary hydrate. As a result, H₂ storage capacity is associated with the trend of the growth rate. Moreover, increasing pressure will increase the average number of H₂ molecules in each 5¹²6⁴ cage, and triple H₂ clusters begin to fill 5¹²6⁴ at 110 MPa and 250 K, which dramatically enhances the H₂ storage capacity in the binary hydrate.

Formation characteristics of THF hydrate within media under a temperature gradient detected by multi-layer NMR

Formation characteristics of THF hydrate within media under a temperature gradient detected by multi-layer NMR

Effect of Micro- and Nanobubbles on the Crystallization of THF Hydrate Based on the Observation by Atomic Force Microscopy

The air micro- and nanobubbles on a silicon wafer surface, generated by ethanol–water exchange method in THF solution, are found with anomalous small contact angles on the gas side due to the pinni...

Hydrate formation under static and pulsed electric fields

For the first time, numerous experiments were carried out to evaluate the effect of electric field (EF) on the mechanism of naturally occurring THF hydrate formation. The Statistical Package for the Social Sciences (SPSS) software was utilized to analyze the experimental data. First, the effect of static electric field (SEF) strength on nucleation temperature (T-nuc) and growth time (t-growth) studied. Based on the statistical results, increasing the intensity of SEF induces nucleation at a relatively high temperature. Furthermore, the completion of solidification takes a longer time than the same process in the absence of SEF. The notable point is that by switching a SEF to a pulsed electric field (PEF) of equal voltage, the EF effectiveness on the two mentioned kinetic parameters significantly reduces. The other point is that applying EF heightens the enthalpy of fusion of THF hydrate.

Epoxycyclopentane hydrate for sustainable hydrate-based energy storage: notable improvements in thermodynamic condition and storage capacity.

We suggest epoxycyclopentane (ECP) as a novel guest compound for hydrate-based energy storage. All of the key properties of the ECP hydrate, including the thermodynamic stability, storage capacity, and formation condition, are notably superior to those of hydrates containing tetrahydrofuran (THF) and cyclopentane (CP), currently considered to be the most powerful promoters.

Investigation of THF hydrate formation kinetics: Experimental measurements of volume changes

The present study is based on the investigation of hydrate formation and growth of THF through an online and direct method. In fact, the volume rise associated with hydrate formation has been used for kinetics studies. This procedure which is called volumetric method is more precise than the conventional method based on temperature variation. Monitoring the hydrate nucleation using the deviation of volume can be carried out more rapidly, compared to doing so using the temperature variation, especially in the initial hydrate nucleation point. Furthermore, the mole of formed hydrate can be easily estimated by this method. According to this approach, the effect of MCM-41 nanoparticles with a mass/volume fraction of 0.004%, 0.016%, 0.04% and 0.2% on ambient pressure has been studied applying THF hydrate former. The results of temperature and volume variation indicated that the growth of hydrate was enhanced by an increase in the concentration of nanofluid to the specific concentration. Moreover, it was approved that, the volumetric method is more appropriate to identify the kinetics of hydrate nucleation and growth in the presence of additives.

Study the kinetics and thermodynamics conditions for CO2 hydrate formation in orange juice concentration

Abstract In this study, for concentration of orange juice, two laboratory systems were used; one for CO2 hydrate formation at high-pressure system, another for formation of THF hydrate at atmospheric pressure system. In the high-pressure system, the kinetic parameters of CO2 hydrate formation in orange juice were investigated in comparison with pure water, in constant temperature and volume. Also the effect of the initial pressure (20, 30 and 35 bar), temperature (2, 3 and 4 °C) and brix (10, 13 and 16) were investigated on hydrate formation conditions. The results showed that, with increasing the pressure and lowering temperature, the initial rate of formation CO2 hydrate is increased and the relaxation time is decreased. With increasing the brix, the initial rate of CO2 hydrate formation is decreased and the relaxation time is increased. The maximum relaxation time of 1230 s was reached at 20 bar, 4 °C and 16 brix. It was determined that the content of orange juice plays as an inhibitor in hydrate formation. In the atmospheric system, the effect of brix (7, 10, 13, 16 and 20) on kinetics of THF hydrate formation was investigated in orange juice. After the separation of the formed crystals, the secondary brix was measured; the highest concentration in the initial brix of 7 was obtained about 200%., with increasing the brix, the induction time was increased, while it had no effect on the relaxation time.