Tetrahydrofuran Hydrate Formation Research Articles

Simulation of tetrahydrofuran-water hydrate formation with a combined cellular automata method and finite difference

The present work simulates the formation of Tetrahydrofuran hydrate considering a reactor under atmospheric pressure. Heat transfer by conduction and convection were considered as the governing mechanisms. The simulation approach based on the cellular automata method (CA) and finite differences was developed to simulate the THF-water hydrate formation and calculate the temperature in the whole range, including the solution and hydrate phases. The finite difference method was used to calculate the temperature of both phases within the reactor during each time step. The model CA contains several transition rules that define the state of the cells (solid or liquid) during each time step and estimate the probability of phase change from liquid to solid (hydrate formation) or vice versa (hydrate dissociation). The simulation method was applied to study the effects of the temperature of the copper plate on the left and right sides and the initial temperature of the THF-water solution on the thickness of the hydrate layer, the number of hydrate cells formed during the growth process, and the temperature distribution in the hydrate and liquid phases. The simulation results were in good agreement with the experimental data.

Effect of nano-SiO2 particles on THF hydrate induction time and its distribution

Clathrate hydrate has been studied for a few decades as a potential alternative energy source and gas storage medium. The direct engineering application of hydrate is still struggling due to the slow formation rate and the ambiguity of induction time. To understand the effect of nanoparticles on the hydrate nucleation induction time, we used different amounts and magnitude sizes of nano-SiO2 particles as promoter to observe the Tetrahydrofuran (THF) hydrate induction time under repeated experiments. We conducted a statistical analysis method based on Kolmogorov-Smirnov (K–S) test and probability-probability plot (P–P plot) test for the analysis of induction time. The results showed that the logarithmic normal distribution can be used to describe the distribution of THF hydrate induction time with addition of nano-SiO2 under repeated experiments. The expected value and variance of induction time vary with particle sizes of different magnitudes at different mass concentrations, showing different effects of nano-SiO2 on hydrate formation and dispersion of induction time. There is a critical condition (with different sizes or mass concentrations) for the influence of nano-SiO2 particles on the THF hydrate induction time, which determines the promoting or inhibiting effect of nano-SiO2 particles on THF hydrate formation.

The pore-structure characteristics of foraminiferal shells and their relations with natural gas hydrate formation in the marine sediments

Many marine hydrate reservoirs exhibit significant foraminifera abundance. These foraminifera alter the original properties of the sediments, potentially affecting the formation and accumulation of hydrates. This present study analyzed the pore-structure characteristics of foraminifera-containing sediments from the South China Sea and their influences on the hydrate formation process by using microscopic imaging techniques. Scanning electron microscopy (SEM) and X-ray computed tomography (X-CT) reveal the unique dual-porosity characteristics of these sediments, characterized by matrix pores and foraminiferal pores. These two types of pores diverge significantly in their size distribution, morphological attributes, connectivity, and other aspects. Further experiments show the formation and occurrences of tetrahydrofuran (THF) hydrate under different sedimentary conditions and solution concentrations. Foraminiferal shells are found to promote the formation of hydrate by increasing the volume fraction of hydrate-favoring pores, which is more pronounced under conditions of low hydrate saturation. These findings obtained may contribute to global hydrate resource assessments and enhance understanding of hydrate reservoirs.

Probing the effect of amino acid-based ionic liquids on the CO2 (sI) and THF (sII) hydrate formation

In the present work, four acetyl glycinate-based ionic liquids (ILs) with distinct cations, namely 1-alkyl-3-methylimidazolium acetyl glycinate [C2mim][AcGly], ammonium acetyl glycinate [NH4][AcGly], N-(2-hydroxyethyl)-N,N,N-trimethyl ammonium N-acetylglycinate [N111(2OH)][AcGly] ≈ [Ch][AcGly], and N-Butyl-N,N-dimethyl-N-(2-hydroxyethyl) ammonium N-acetylglycinate [N411(2OH)][AcGly] ≈ [C4Ch][AcGly], were synthesized and tested for their effect on the formation of CO2 hydrates at elevated pressures and tetrahydrofuran (THF) hydrate formation at atmospheric pressure. The phase behaviour of the CO2 hydrates, sI type, was studied in the presence of the selected ILs using the isochoric pressure search method. The ILs shifted the phase boundary towards lower temperatures indicating a thermodynamic inhibition characteristic. The constant cooling method was used to determine the onset nucleation temperature of CO2 hydrates in the presence and absence of additives. The isothermal method was used to determine the induction time of CO2 hydrates in the presence of additives. The pressure drops in both experiments indicate the hydrate growth in the absence/presence of additives. Later, the THF hydrate crystal growth experiments at atmospheric pressure were carried out to understand the effect of additives on the sII-type hydrate growth. The crystal morphology also points out the mode of action of the tested additives on hydrate formation and growth. The extensive testing using the same additives at identical concentrations revealed the importance of the method and conditions, which become crucial in the absence of a standard screening procedure for kinetic hydrate additives.

Morphologies, kinetics and structures of methane hydrate in the system containing tetrahydrofuran and cyclopentane

The morphologies of methane (CH4) hydrate formation in the system containing different mole ratios of tetrahydrofuran (THF) and cyclopentane (CP) at two different temperatures are systematically studied in this work. The results showed that for all cases conducted at 274.2 K, a hydrate film quickly covers the entire interface between the oil (CP) and the THF solution phase after gas loading, and then a hydrate layer forms, thereby significantly decreasing the following gas-liquids mass transfer efficiency. Raman spectrum shows this hydrate layer is caused mainly by pure THF hydrate. Interestingly, as the temperature increase to 278.2 K, the hydrate layer breaks. This is because, after hydrate layer formation, hydrate still grows at the contact interface of the metal, gas, and liquid phase, and then moves upward. In this process, liquids are gradually transported to the reaction front to form hydrate by capillary force and the hydrate layer’s downward curvature gradually increases as the consumption of liquid until rupture. Besides, typical reaction kinetics shows that there are three stages of hydrate formation in the THF + CP + CH4 system at 278.2 K. (1) hydrate layer formation (pure THF hydrate formation); (2) CP-CH4 hydrate formation; (3) large amount of THF-CH4 hydrate formation (after hydrate layer rupture). Further, this work also confirmed that after the hydrate layer rupture, the CH4 occupancy in 512 cages of sII at the same temperature and promoter’s mole fractions is independent of the type of promoters (CP, THF, and CP + THF) used in the system.

Effect of the Temperature and Tetrahydrofuran (THF) Concentration on THF Hydrate Formation in Aqueous Solution

The knowledge of the mechanism of clathrate hydrate formation is crucial for studying the formation of a natural gas hydrate and developing hydrate-based technologies. In this study, low-field nuclear magnetic resonance (NMR) is applied to observe the processes of tetrahydrofuran (THF) hydrate formation from the solutions with different THF concentrations, and from the analysis of the NMR transverse relaxation time (T2) of hydrates and solutions, the formation mechanism of THF hydrate is discussed. A quantitative relationship between the NMR T2 spectral area and the mass of THF hydrate is established, and it is applied to estimate the hydrate amount in the formation process of THF hydrate. The results obtained show that T2 of THF solution is controlled by the temperature and THF concentration: longer at a higher temperature and shorter at a higher THF concentration. Moreover, the initial THF concentration does not affect the final concentration of the remaining solution after hydrate crystallization, and the formation of THF hydrate from solution follows the thermodynamics of solution reaction, with the THF concentration of the solution ending at the phase line after hydrate crystallization. The kinetics of THF hydrate formation is affected by the temperature and THF concentration: a higher formation rate in the solution with stoichiometric composition (19.06 wt % THF) of THF hydrate than either THF-rich or water-rich solution and a lower formation rate at a higher temperature.

Supercooling suppression in the tetrahydrofuran clathrate hydrate formation

The addition of silver(ii) oxide effectively diminishes the degree of supercooling in the tetrahydrofuran hydrate formation.

Effects of Halide Anions on Water Desalination based on Crystallization Methods: Freezing and Tetrahydrofuran Hydrate formation

In this study, the water desalination was performed using the freezing method and Tetrahydrofuran hydrate formation in a stationary reactor. The experimental setup includes two coaxial cylinders, which ice crystals deposit outside the cool inner cylinder; thus the salt concentration increases in the residual brine. In order to evaluate the performance of these methods, the removal percentage of salt was measured by the electrical conductivity instrument. The results show that the removal efficiency decreases with an increasing salt concentration in the freezing method while the different trend is observed in the hydrate formation method. As an important result, the salt removal efficiency of the hydrate formation method was higher than the freezing process. Also, to investigate the effect of the anionic size on the salt removal efficiency, the experiments were performed with NaCl, NaBr, NaF, and NaI, which have the same cations. The results show that the performance of desalination improves by increasing anionic radius. So the dissolved mineral components are removed in the following order. The removal of salts with a higher size is further by the hydrate-based and freezing desalination.

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.

Effects of Glycine, L-Arginine and their Complexation with Polyvinylpyrrolidone on Tetrahydrofuran Hydrate Formation

Hydrophilic amino acids as a new type hydrate inhibitor is a hot topic for scholars. In this paper, the influence of glycine and L-arginine, and their complexation with polyvinylpyrrolidone (PVP) on hydrate formation were clarified by tetrahydrofuran (THF) hydrate formation simulation experiments, and the intrinsic influence mechanism was revealed by many experimental methods. The results show that glycine has a strong inhibitory effect on water molecules because of its strong disturbance to water molecules, and the inhibitory effect is the best when the addition of glycine is 1.0 wt%. Due to the disturbance and binding of hydrophilic amino acids to water molecules, the effect of PVP on the semi-cage structure of water molecules as well as the adsorption and encapsulation of hydrate crystal particles, the combination of glycine and L-arginine and PVP has synergistic inhibitory effect on the formation of THF hydrate. When the total amount of hydrate inhibitor is 1.0 wt%, the synergistic inhibition ability of glycine and PVP is stronger. The results obtained in this paper provide an experimental and theoretical basis for the research and development of new hydrate inhibitors.

Changes in Physical Properties of Hydrate Deposit during Hydrate Formation and Dissociation

The microscopic distribution pattern of hydrates in pores is closely related to the accuracy of seismic data and acoustic data in the exploration of hydrate resources, and has important influence on the permeability and mechanical stability of reservoirs during mining. This study performed macro-micro experiments of tetrahydrofuran (THF) hydrate formation and dissociation in solution and pore space. Dissociation characteristics of pore hydrate with different saturation and distribution pattern were observed, 2D and 3D models were built, fluid and quartz particle migration, channel blockage and reformation were captured and analysed. Results demonstrated that, as the concentration of THF in the solution increases from 19%, 24% to 29%, the main distribution pattern of the hydrate formed in the pores gradually changes from pore filling, particle cementation to skeleton supporting, while the dissociation behaviour of pore hydrate mainly happened at the pore filled area, particle surface and the particle connection area. As the saturation increases, the amount of water generated by dissociation increases, the more obvious the water migration, the greater the impact on the stability of the particles, and the more the formation of channels and blockages. During field methane recovery, controlling the dissociation rate of hydrates and fluid migration rate are helpful to maintain reservoir mechanical stability. Therefore, when temperature and pressure conditions are relatively stable, increasing the drainage channel can effectively reduce the turbulent oscillation, the impact on particle stability and blockage of sand production channel.

The effects of graphene oxide nanosheets and Al2O3 nanoparticles on the kinetics of methane + THF hydrate formation at moderate conditions

Gas hydrates, as a novel technology for storage and transportation of natural gases, have attracted many researchers. High pressures and low-temperatures demand, and slow kinetics of hydrates formation are the two critical challenges. In this study, mixed tetrahydrofuran (THF) and aluminum oxide nanoparticles (Al2O3) or graphene oxide (GO) nanosheets solutions were prepared, and their effects on the kinetics of methane hydrate formation were investigated. Also, the mechanism of hydrate formation in the presence of these nanoparticles is discussed. The concentrations in the systems were 5 and 15 wt% for THF, 100, 300, and 400 ppm for GO, and 0.2, 0.4, and 0.6 wt% for Al2O3. It is concluded that 15 wt% THF solutions decline the induction time, and promote the mole of consumed gas, rate of gas uptake, apparent rate constant of hydrate growth, storage capacity, and water to hydrate conversion comparing to 5 wt% systems. In addition, adding the nanoparticles to THF solutions declines the induction time, enhances the gas consumption during the initial minutes, and increases the rate of gas consumption, and the apparent rate constant of hydrate growth; however they have no significant effect on the final mole of gas consumed, storage capacity, and water to hydrate conversion.

Experimental study on the formation and agglomeration of tetrahydrofuran hydrate under flowing condition

The microscopic morphology and agglomerating characteristics of hydrate particles play an important role in the flow assurance as well as heat transfer in refrigeration systems. The formation process of tetrahydrofuran (THF) hydrate was studied by using a visual reactor with stirring. The microscopic morphology of THF hydrate could be divided into single crystal type, flat plate type, and agglomerate type and each experimental condition includes these three types. However, there is a large difference in the proportion of the three morphological particles and the average particle size. The larger the initial concentration of the THF solution, the larger the average size of the particles, and the higher the proportion of agglomerate-type particles. An increase in the stirring speed causes breakup of the agglomerate-type particles, and the proportion of the single crystal-type particles increases. Moreover, the agglomeration of hydrate particles is related to the content of THF in the liquid phase. A microscopic model indicated the evolution mechanism of the microscopic morphology in THF hydrate formation and agglomeration process was presented. These research results provide a theoretical basis for the application of hydrate technology in refrigeration systems.

Effect of a weak electric field on THF hydrate formation: Induction time and morphology

The kinetics of bulk hydrate formation is of crucial importance in the application of hydrate-based technique involving energy storage, desalination and flow assurance. Various procedures have been found to significantly impact the kinetics of hydrate formation; yet with few studies touching the effects of a weak electric field. A voltage across the solution could likely affect the activity and orientation of the molecules inside, thereby playing a potential role in the hydrate nucleation, crystal growth and even diffusion of water and guest molecules. In this study, the effect of a weak electric field on the induction time, bulk surface characteristics and growth rate of THF (tetrahydrofuran) hydrate were investigated by controlling the voltage across the two electrodes placed on the two sides of the reactor. The results showed that an increasing voltage intensity could result in a longer induction time of hydrate formation. The memory effect was fading at an increasing voltage intensity, indicating that the relic components helping the fast formation could be destroyed by the electric field. The following formation under the electric field can be identified by a neat zigzag surface of hydrate generated from the periphery of the reactor. The formation rate of THF hydrate was found to increase with a rising voltage intensity during the hydrate growth period. The results could be of help in the application of hydrate-based techniques in industries where a fast and successive hydrate growth is expected.

Kinetic mechanism of hydrophilic amino acid inhibiting the formation of tetrahydrofuran (THF) hydrate

Hydrophilic amino acid, as a new kind of hydrate inhibitor, is the hot spot of domestic and foreign relevant studies. At present, however, its intrinsic mechanism influencing the formation of hydrate is not figured out, and the understandings on its synergistic inhibition mechanism with other kinetic hydrate inhibitors (KHIs) are still controversial. In this paper, the influence laws of glycine, l-arginine and its combination with polyvinylpyrrolidone (PVP) on the formation of hydrate were clarified by experimentally simulating the formation of tetrahydrofuran (THF) hydrate, and the intrinsic mechanism was revealed by virtue of various experimental methods. And the following research results were obtained. First, glycine has such a strong disturbance action on water molecules that it has stronger inhibition on the formation of hydrate. And when its dosage is 1.0%, its inhibition effect is the best. Second, l-arginine has a stronger binding action on water molecules, so it has stronger inhibition on the formation of hydrate. And in the range of lower dosages, its inhibition on the formation of hydrate increases gradually with the increase of its dosage. Third, the combination of hydrophilic amino acid and PVP has synergistic inhibition on the formation of hydrate. And the synergistic inhibition ability of combined glycine and PVP K90 is stronger when the total dosage of inhibitors is 1.0%. In conclusion, the research results provide experimental data and a theoretical basis for the research and development of new hydrate inhibitors.

Quantitative determination of pore‐structure change and permeability estimation under hydrate phase transition by NMR

AbstractQuantitatively characterizing the seepage features is critical important for multi‐fluid flow in gas hydrate accumulations; however, limited researches concern water permeability during hydrate phase transition. In this work, nuclear magnetic resonance (NMR) measurement is employed to observe the in situ formation and dissociation of tetrahydrofuran (THF) hydrate in porous media. Results indicate that the relative free water and bound water consumption during hydrate phase transition can affect the seepage features of sediments. In addition, we investigate the growth habits of THF hydrate in quartz glass sand and find the growth pattern of the hydrate transforms from suspension to cementation when its saturation exceeds approximately 35%. The Tokyo model shows that the hydrate are heterogeneous distribution of pore‐filling and likely to evolve in larger pores; The findings clearly show that NMR is an efficient and direct technique for investigating the seepage characteristics during hydrate phase transition as well as pore fluid distribution in sediments.

Improving THF hydrate formation in the presence of nonanoic acid

Numerous experiments of tetrahydrofuran (THF) hydrate formation are conducted to investigate the potential of nonanoic acid, which is an organic phase change material, as a kind of novel promoters for hydrate formation. The mixture of THF + nonanoic acid + H2O was stirred using an ultra-sonication bath to prepare emulsion. Nonanoic acid forms a series of small crystal particles when the temperature of the emulsion is lowered. These small crystal particles of organic phase change material promote THF hydrate nucleation and growth. The induction time of THF hydrate formation reduces and the rate of hydrate growth increases with the increase of the mass fraction of nonanoic acid when nonanoic acid mass fraction is <3 wt%. However more additives of nonanoic acid do not further promote THF hydrate formation. The average induction time of THF hydrate formation is the smallest with 3 wt% nonanoic acid in this work. The conversion degree of THF hydrates formed with 3 wt% nonanoic acid is about 82.9% at 0.2 °C under static conditions. The experimental results also show that the nucleation of THF hydrate is a stochastic process but nonanoic acid improves the scatter of hydrate induction time. THF hydrate can form within 73 min under 0.2 °C with 3 wt% nonanoic acid in quiescent conditions. The induction time of THF hydrate formation reduces and the rate of hydrate growth increases with the decrease of experimental temperature.

Innovative Approach To Enhance the Methane Hydrate Formation at Near-Ambient Temperature and Moderate Pressure for Gas Storage Applications

The solidified natural gas (SNG) technology via hydrates is a promising and potential method for storing natural gas. It offers a compact mode of natural gas storage with high degree of safety. In this work, we present the synergistic effects of tetrahydrofuran (THF), hollow silica (HS), and sodium dodecyl sulfate (SDS) in enhancing the kinetics of mixed methane–THF hydrate formation at 6 MPa and 293.2 K in an unstirred reactor configuration. HS at the low loading of 0.5% w HS/v in 5.56 mol % THF solution used in the current study is an innovative approach to improve the surface contact area resulting in kinetic enhancement at moderate conditions (low driving force). However, the mixture of 0.5% w HS/v in 5.56 mol % THF solution resulted in a long induction time (about 400 min), which is not favorable for the SNG technology. Addition of SDS decreased the induction time and increased the hydrate formation rate under similar experimental conditions. The induction time significantly decreased with the increase in the SDS concentration. Additionally, the presence of SDS played a key role in influencing the temperature profile and the hydrate morphology during mixed hydrate formation. The methane gas uptake was 0.0591 (±0.0007) and 0.0615 (±0.0023) mol of methane/mol of water without and with SDS, respectively. Thermal stimulation with ΔT = 15 K was employed to recover methane from hydrates. A recovery of 96–98% of the stored methane gas from the hydrates formed with and without SDS was demonstrated. Interestingly, the presence of HS was effective in preventing the foam generation during hydrate dissociation in the presence of SDS.

The effect of sodium halide salts on the kinetics of tetrahydrofuran hydrate formation by using a differential scanning calorimetry method

In this study, the effect of sodium halide salts including Sodium Fluoride, Sodium Iodide, Sodium Bromide, and Sodium Chloride was investigated on the kinetics of tetrahydrofuran hydrate formation by using a differential scanning calorimetry setup. It was found that the anions of salts can destroy hydrogen bonding between the water molecules and prevent the growth of gas hydrate. The fluorine with the smallest ionic radius and the highest enthalpy of hydration was the most effective material to decrease the hydrate growth rate. According to the results, the formation kinetics of hydrate changes with the concentration of salts in a different manner. Results show that the hydrate formation rate decreases with increasing the concentration of salts up to 0.6 wt%, while it increases when the concentration is at a range of 0.6 to 1.2 wt%. The rate begins to decrease by the concentration of >1.2 wt%. It was found that the parameters such as the hydration effect and the activity coefficients of salt solutions can affect the kinetics of tetrahydrofuran hydrate formation.

Spontaneous Formation of Tetrahydrofuran Hydrate in Ultrahigh Vacuum

Clathrate hydrates (CHs) typically nucleate under high-pressure conditions, but their existence in ultrahigh vacuum (UHV) is an open question. Here, we report the formation of tetrahydrofuran (THF)...