Tetra-n-butyl Ammonium Bromide Hydrate Research Articles

Morphological Study of Tetra-n-Butylammonium Bromide Semi-Clathrate Hydrate in Confined Space

Tetra-n-butylammonium Bromide (TBAB) finds extensive use in diverse applications. An in-depth investigation into the effects of the formation conditions on TBAB hydrate is necessary to optimize the application process. This work focuses on examining the influence of the mass concentration of TBAB solution and the cooling rate on TBAB hydrate formation through optical microscopy and Raman spectroscopy. The TBAB hydrate formation process occurs in a confined space created by an optical sheet with a 0.03 mm deep groove. Four TBAB solutions of 13. 8 wt%, 18 wt%, 32 wt%, and 40 wt% are investigated, and the supercooling required for hydrate nucleation increases with concentration at a cooling rate of 0.5 K/min. Notably, Type A TBAB hydrate preferentially forms in all of the solutions, although type B hydrate is thermodynamically stable in the two dilute solutions. At a larger cooling rate of 2 K/min, two distinct crystal growth patterns are observed: one controlled by mass transfer and the other regulated by heat transfer. Increasing the cooling rate not only alters the optical morphology, but also reduces the supercooling due to a decrease in the Gibbs free energy barrier caused by a larger temperature gradient. This is beneficial for practical applications as it helps to alleviate the supercooling degree.

Nucleation-promoting effect of mixed Zn and ZnO particles on tetra-n-butylammonium bromide hydrate

Tetra-n-butylammonium bromide (TBAB) hydrate is an ionic semi-clathrate hydrate, and it can be used as an energy-storage and gas-separation medium. Nucleation of TBAB hydrate is unlikely to occur and this characteristic causes problems in the refrigeration system due to the need for excessive cooling and delays in gas separation due to the slow formation. Therefore, a technique for rapid formation of TBAB hydrate is required. In a previous study, it was found that addition of mixed and ground Zn and ZnO particles (Zn–ZnO) to TBAB aqueous solution significantly promoted nucleation of TBAB hydrate. Since the nucleation of TBAB hydrates was effectively promoted by the very simple addition of Zn–ZnO, this technique can be easily applied to conventional systems. However, the nucleation-promoting mechanism have not been clarified. The clarification of the nucleation-promoting effect of Zn–ZnO on TBAB hydrates is important to elucidate the nucleation-promoting mechanism of clathrate hydrates by the addition of substances. Therefore, the objective of the present study was to investigate the nucleation-promoting mechanism of Zn–ZnO on TBAB hydrate. Experimental results showed that immersion of Zn–ZnO in TBAB aqueous solution reduced the nucleation-promoting effect, but a decrease in the nucleation-promoting effect was not observed when Zn–ZnO was immersed in water. Microscopy observation confirmed that immersion of Zn–ZnO in TBAB aqueous solution had little effect on its surface morphology, but X-ray diffraction and X-ray photoelectron spectroscopy indicated formation of solid TBAB on Zn–ZnO. Zn–ZnO did not show a significant nucleation-promoting effect on tetrahydrofuran hydrate, which is a non-ionic clathrate hydrate. This suggest that Zn–ZnO has properties that attract tetra-n-butylammonium and Br ions, and that the proximity of these ions may promote formation of TBAB hydrate. It was also suggested that the mechanism of nucleation promotion by the addition of substances is different for ionic clathrate hydrates and non-ionic clathrate hydrates.

Crystal growth of tetra-n-butylammonium bromide hydrate nucleated from metallic particles

Nucleation of tetra-n-butylammonium bromide (TBAB) hydrate is unlikely to occur; thus, nucleation promotion is required to nucleate TBAB hydrate. In a previous study, it was found that addition of specific metallic particles effectively promotes nucleation of TBAB hydrate. TBAB hydrate is known to have two stable crystal structures (type A and type B). It is expected that the type of TBAB hydrate crystals that initially grow will differ depending on the molecular structure of the precursor liquid phase influenced by the added metallic particles. In this study, the correlation between the type of added metallic particles and the crystal structure of the formed TBAB hydrate was experimentally investigated. Addition of Ag, Ag–AgBr, Zn, and Zn–ZnO particles promoted nucleation of TBAB hydrate. When Ag or Ag–AgBr was added, type-A TBAB hydrate crystals formed from 10 wt% TBAB aqueous solution, where type-B TBAB hydrate should preferentially be formed. In contrast, when Zn or Zn–ZnO was added, only type-B TBAB hydrate crystals formed from 10 wt% TBAB aqueous solution. These results suggest that Ag and Ag–AgBr affect the molecular structure of the liquid phase, facilitating formation of type-A TBAB hydrate crystals.

Experimental study on visualization of TBAB hydrate formation in confined small channels

Hydrate crystals' microscopic characteristics and agglomerating morphologies play an important role in the hydrate reaction equipment's flow assurance and heat transfer. In order to study the formation process of hydrate, experimental quartz tubes with small diameters were selected, and a fully visualized flow loop system was established. The study investigated the effects of supercooling, solution concentration, tube diameter, and flow rate on hydrate blockage time and agglomeration morphology. The results show that under the same supercooling conditions, the density of single crystal hydrate formed in 10 wt%-20 wt% TBAB (Tetra-n-butylammonium bromide) hydrate solution is low, and the crystal front appears needle-like or sword-like, which is conducive to mass and heat transfer. High concentration TBAB solution(30 wt%-40 wt%) can form dense hydrate crystals, and the tip effect was significantly weakened. For low concentration TBAB solution, the increased flow rate can accelerate the formation of new nuclei and inhibit the growth of large crystals. Grout solutions with different particle sizes can be obtained by adjusting the flow rate. It was found that the initial morphology of TBAB hydrate crystals included spherical and cylindrical shapes, and the morphological evolution process of a single hydrate crystal was similar. Finally, a microscopic physical model of the TBAB hydrate growth and aggregation process was established.

Molecular Dynamics Simulation to Evaluate the Stability of Tetra-n-butyl Ammonium/Phosphonium Bromide Semiclathrate Hydrates in the Presence and Absence of Methane, Carbon Dioxide, Methanol, and Ethanol Molecules

Stability of tetra-n-butyl ammonium bromide (TBAB) and tetra-n-butyl phosphonium bromide (TBPB) semiclathrate hydrates with a hydration number of 38 is studied by the molecular dynamics (MD) simulation in the absence and presence of methane, carbon dioxide, methanol, and ethanol molecules. All of the simulation runs are performed under NVT (constant number of atoms, volume, and temperature) and NPT (constant number of atoms, pressure, and temperature) conditions using optimized potentials for liquid simulations-all-atom (OPLS-AA) force field with nonpolarizable water models (including SPC, TIP3P, TIP4P, and TIP4P/Ice), where the operating conditions include a temperature range of 250–350 K and pressures of 0.1 and 50 MPa. The potential energy and structural analysis, mean square displacement (MSD), diffusion coefficient, radial distribution function (RDF), lattice parameter, and the average number of hydrogen bonds between water–water molecules are evaluated by employing MD strategy. According to the potential energy results, the order for the water models in both TBAB and TBPB hydrate stabilities is as follows: TIP4P/Ice > TIP4P ≈ SPC > TIP3P. This order agrees well with the previous studies of gas hydrates and ices. In the absence and presence of methane and carbon dioxide guest molecules, the height of the peaks in the RDF of oxygen–oxygen atoms decreases with lowering pressure and increasing temperature; greater MSD, diffusion coefficient, and lattice parameter values are also achieved. Thus, in the absence and/or presence of guest gas molecules, the stability of TBAB and TBPB hydrate cages decreases with increasing temperature and reducing pressure. A good match is noticed between the results of MD simulation and previous experimental and theoretical studies, confirming the accuracy and validation of the simulation method. Reduction of the hydrogen bond balance between water molecules and formation of new hydrogen bonds between the water and the hydroxyl groups of methanol and/or ethanol molecules in the cages indicate that methanol and ethanol molecules have an inhibitory effect on TBAB and TBPB hydrates. Due to different hydrophilic versus hydrophobic behaviors of alcohols, the extent of disruption of hydrogen bonds between water–water molecules of TBAB and TBPB hydrates in the presence of methanol is larger than that in the presence of ethanol, which is consistent with the MD simulation results of clathrate hydrate. This study can help to further understand the semiclathrate hydrate stability or dissociation conditions at a molecular scale for better design and operation of corresponding processes.

Effect of polyvinyl alcohol on aggregation and flow characteristics of tetra-n-butylammonium bromide and tetra-n-butylphosphonium bromide semi-clathrate hydrate slurries formed under CO2 bubbling

The rheological properties of tetra-n-butylammonium bromide (TBAB) and tetra-n-butylphosphonium bromide (TBPB) semi-clathrate hydrate (SCH) slurries with polyvinyl alcohol (PVA) were measured using a viscometer to evaluate the anti-agglomeration effect of PVA. The TBAB and TBPB hydrate slurries exhibited a stronger dilatant trend with yield stress and more aggregates with increasing solid fraction. Only TBPB had plate-like crystals, and the frictional force between particles and aggregability in TBPB hydrate slurries were higher than those in TBAB hydrate slurries. The appropriate degree of polymerization (DP) of PVA was 1000, and the appropriate PVA (DP of 1000) concentrations were 0.53 wt% for TBAB hydrate and 1.8 wt% for TBPB hydrate among the SCH solid fractions examined. CO2 bubbling weakens the anti-agglomeration effect of PVA by promoting particle aggregation and enhancing the interactions between plate-like particles. However, adding PVA changed the rheological properties of slurries to a Bingham fluid even under CO2 bubbling conditions.

Nucleation probability of Type-A tetra-n-butyl ammonium bromide semi-clathrate hydrate via the memory effect

The memory effect in clathrate hydrates is known to produce recrystallization under milder conditions than those needed for the initial nucleation. Tetra-n-butyl ammonium bromide (TBAB) forms tetragonal (type A) as well as orthorhombic (type B) semi-clathrate hydrate in aqueous solution. Here we investigate the nucleation probability for recrystallization of type A TBAB hydrate via the memory effect. Using optical microscopy, we observed recrystallization in situ under various concentrations of aqueous solution. After their initial nucleation, the hydrate crystals were dissociated by raising the temperature and then cooled to slightly below the equilibrium temperature while measuring the nucleation probability and induction times for recrystallization. We found the nucleation probability to be highest at about 20 wt%, which is about half of the stoichiometric weight fraction of 40 wt%, and found the shortest induction time at about 30 wt%. These results suggest the importance of free water in solution to nucleate TBAB hydrate crystal with the memory effect. We also found that the nucleation occurred near the location of prior dissociation and the nucleation probability decreased when we increased the temperature of dissociation. Both of these findings support the concept that there exists a residual water structure from the dissociated hydrate that promotes nucleation.

An electrical resistivity-based method for measuring semi-clathrate hydrate formation kinetics: Application for cold storage and transport

Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate has a large latent heat and suitable phase transition temperatures to be used as a phase change material for cold energy storage and transport. The mass fraction of hydrates in the semi-clathrate hydrate slurry is a key parameter determining the cold carrying capacity and flow properties. We developed a new experimental methodology based on electrical resistivity to quantify the hydrate fraction in semi-clathrate hydrate slurry during hydrate formation. Relationship between electrical resistivity and hydrate fraction of semi-clathrate hydrate slurry was established based on Bruggeman’s effective-medium approximation. After validation, this method was employed to quantitatively investigate the effect of temperature on TBAB hydrate formation from 20 wt% TBAB/water system. As the temperature was lowered from 278.2 K to 274.2 K, the induction time was reduced by 97.8% and the hydrate growth rate was enhanced by over 2.5 times. At 274.2 K and 276.2 K, type A hydrates were preferentially formed followed by a structural transition to type B. At 278.2 K, only type A hydrates were observed. Furthermore, given an appropriate concentration, amino acid L-tryptophan was identified to be a good kinetic promoter for TBAB hydrate formation. The presence of 500 ppm L-tryptophan reduced the induction time by 60% and boost the hydrate growth rate by more than 32%. The electrical resistivity-based method developed in this work has shown simplicity, low cost, high accuracy, and repeatability. It would enable precise investigation of semi-clathrate hydrate kinetics in the future for cold energy applications and beyond.

Visual Observation of Tetra-n-butylammonium Bromide Ionic Semiclathrate Hydrate Formation: A Laboratory Experiment

A laboratory experiment was performed using tetra-n-butylammonium bromide (TBAB) ionic semiclathrate hydrate, a crystalline compound. Ionic semiclathrate hydrates have unique properties, and hence, novel technologies utilizing the ionic semiclathrate hydrates have been proposed to date. Thus, students could learn fundamentals of functional materials through ionic semiclathrate hydrates from chemical and engineering points of view. In the experiment, formation of the TBAB hydrate was observed at fixed temperature and under atmospheric pressure by using TBAB aqueous solutions having TBAB mass fractions of wTBAB = 0.10, 0.20, 0.30, 0.40, and 0.50. There are no serious safety hazards. In addition, the experiment can be performed using inexpensive equipment and materials. The amount of the formed TBAB hydrate and its crystal morphology depended on the concentration of the aqueous solution. The students needed to submit a laboratory report describing fundamentals of the ionic semiclathrate hydrates, a relationship between equilibrium conditions and the amount of the formed TBAB hydrate, and an adequate crystal morphology of the TBAB hydrate crystals as a thermal storage material. Most students understood the experiment well, and the average score of the reports was approximately 80%.

Experimental and theoretical investigation on hydrate nucleation in TBAB droplets

The efficient and rapid formation of natural gas hydrate is of great significance for its large-scale industrial application, which is inseparable from the intensive study of hydrate formation mechanism. Most of the previous studies focused on the growth of hydrate crystals and the effects of different factors on the morphology. However, the research specifically on the nucleation and theoretical analysis of tetra-n-butylammonium bromide (TBAB) hydrate has not been reported. In this work, the nucleation of TBAB hydrate in 2 μL droplets was studied using high-speed photography. Combined with the classical nucleation theory, a model for calculating the Gibbs free energy required for TBAB hydrate nucleation by fugacity is proposed. Through this model and combined with macro experimental phenomena, it is calculated for the first time that the maximum critical nucleation size of A-type TBAB hydrate is about 29(±6) Å and that of B-type TBAB hydrate is about 15.6(±6) Å. This work has great significance for further study of hydrate formation kinetics.

The Effect of DC Voltage on Solidification of Tetrabutyl-Ammonium Bromide (TBAB) Aqueous Solution

This study aimed to investigate the nucleation process of 23 wt% tetra-n-butyl ammonium bromide (TBAB) aqueous solution due to DC voltage. TBAB hydrate is an example of a thermal energy storage system with a phase change temperature of around 0–12 °C. The commonly sold copper electrodes are inserted into the sample to supply the voltage continuously. The diameter of the electrodes was 1 mm, and the gap was approximately 0.5 mm. The applied voltage varied as the experimental parameter is in the range of 0 to 30 V. Two repetitive freezing-thawing experiments are performed to ensure data repeatability. The experimental results showed that the TBAB hydrate would not form until a minimum value of 20 V of DC voltage was applied. The increase of the voltage used led to higher solidification temperature and reduction of the supercooling degree.

The effect of sodium dodecyl sulfate and dodecyltrimethylammonium chloride on the kinetics of CO2 hydrate formation in the presence of tetra-n-butyl ammonium bromide for carbon capture applications

Tetra-n-butyl ammonium bromide (TBAB) is a commonly used promoter to moderate CO2 hydrate phase equilibrium. However, it decreases CO2 gas uptake. In this work, the effects of anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant dodecyltrimethylammonium chloride (DTAC) on the kinetics of CO2–TBAB hydrate formation are investigated. Experiments in a batch reactor at the same initial pressure of CO2/N2 gas mixtures are conducted in systems of 10-wt% TBAB and varied SDS concentrations of 0–1500 ppm and DTAC concentrations of 0–0.6 wt%. Induction time, normalized gas uptake, split fraction and separation factor are the metrics to study in this paper. The results show that the hydrate formation is most accelerated with the addition of SDS, and the best CO2 separation performance is achieved in the presence of DTAC. 10-wt%TBAB with 0.1-wt% DTAC is found to be the optimum recipe, and it leads to the same amount of CO2 uptake at 283.15 K as that in a pure water system at 276.45 K under the same initial pressure. CO2 uptake is also found to increase with a higher subcooling. Furthermore, the intensive uptake period of different systems is determined for practical applications of hydrate-based carbon capture.

Comments on Effect of Salts on TBAB Semi Clathrate Hydrate Formation: Application to Produced Water Desalination

In the paper titled “Effect of Salts on TBAB Semi Clathrate Hydrate Formation: Application to Produced Water Desalination” by Aziz Alhejaili, Ponnivalavan Babu, and Nagu Daraboina [Energy Fuels 2020, 34 (10), 12810–12821, DOI: 10.1021/acs.energyfuels.0c02091], the authors emphasized the possibility of tetra-n-butylammonium bromide (TBAB) semiclathrate hydrate desalination and concluded that TBAB hydrate formation is a favorable means of desalination in comparison to ice, suggesting the thermodynamic effectiveness of TBAB as a hydrate former. However, there is some incorrect and missing points, which led to the wrong analysis. The possible effect of other co-existing anions to form different semiclathrates was not considered.

Effect of metal particles on promoting the nucleation of tetra-n-butylammonium semiclathrate hydrate

Abstract The formation of tetra-n-butylammonium bromide (TBAB) hydrate from a TBAB aqueous solution tends to show a supercooling phenomenon, which is non-ideal for the practical use of TBAB hydrate. However, as reported in the literature, the products obtained from the use of metal electrodes for the application of an electric field can accelerate the nucleation of the hydrate. Herein, we investigated the role of metal particles (Ag, AgBr, Zn, and ZnO) and their mixed forms (Ag–AgBr and Zn–ZnO) on promoting the nucleation of TBAB semiclathrate hydrate. The nucleation-promoting effect was most significant for the mixed metal particles when prepared by simultaneous grinding of the metal particle components. The changes in the physicochemical properties of the mixed metal particles as a result of grinding were believed to accelerate the nucleation of TBAB hydrate.

Kinetic study of semiclathrate hydrates formed with CO2 in the presence of tetra-n-butyl ammonium bromide and tetra-n-butyl phosphonium bromide

The kinetics of semiclathrate hydrates formation with CO2 in the presence of tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl phosphonium bromide (TBPB), and TBAB + TBPB were investigated. The experiments were conducted at the stoichiometric concentration of TBAB hydrate (2.57 mol%) and three subcoolings (ΔT = 6 K, 9 K, and 12 K) with the initial pressure fixed at 2.8 MPa. It was found that adding TBPB into the TBAB solution can promote hydrate nucleation, and this promotion effect at a lower subcooling (ΔT = 6 K) was stronger compared to that at higher subcoolings (ΔT = 9 K and 12 K). The gas consumption obtained in TBAB, TBPB, and TBAB + TBPB solutions decreased with the increase of subcooling, despite the increase of the rate of hydrate growth. At a given subcooling, gas consumption (CO2 uptake) in TBAB + TBPB solutions was greater than that in TBAB and TBPB solutions, indicating that hydrate formation kinetics and the CO2 storage capacity were improved in the TBAB + TBPB solution. The largest gas consumption was obtained at ΔT = 6 K in the TBAB + TBPB solution, which was 28.7% and 17.2% larger than those obtained in TBAB and TBPB solutions, respectively. Therefore, a mixture of TBAB + TBPB is a promising option to improve the kinetics of semiclathrate hydrate formation with CO2.

Carbon dioxide hydrate separation from Integrated Gasification Combined Cycle (IGCC) syngas by a novel hydrate heat-mass coupling method

A novel hydrate heat-mass coupling separation (HHMCS) method was studied to reduce the energy consumption of CO2 hydrate separation from Integrated Gasification Combined Cycle (IGCC) syngas in this work. Tetra-n-butyl ammonium bromide (TBAB) is used as a hydrate promoter and pure TBAB hydrate is used as a phase change heat-mass coupling additive. The heat-mass coupling effect, CO2 separation characteristics and influence factors were studied by continuous separation experiments in a bubble column reactor. Compared to conventional gas hydrate separation method, the HHMCS process exhibits a higher energy-saving potential, less temperature and TBAB concentration fluctuation due to pure TBAB hydrate phase change. Increase inlet gas rate, the accumulated gas consumption decreased slightly, but the average gas consumption rate increased. Increase operating pressure and decrease gas phase volume increased the average gas consumption rate and CO2 separation efficiency. After continuous separation of simulated syngas, the average CO2 concentration in H2-rich gas decreased to 17.45 mol%, and that in CO2-rich gas increased to 86.44 mol%. The CO2 split fraction and separation factor reached 0.80 and 8.15, respectively. The work provided a new idea to integrally utilize the phase change enthalpy, improve the operating flexibility and heat transfer in large device.

Application of tetra-n-butyl ammonium bromide semi-clathrate hydrate for CO2 capture from unconventional natural gases

In this study, tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate was employed for CO2 capture from unconventional natural gases exploited by supercritical CO2 injection. The TBAB hydrate formation kinetics and CO2 separation efficiency were studied under different TBAB concentrations and subcoolings using a stirred tank reactor. Optimum experimental conditions were obtained (2.8 MPa, ΔT = 6 K, 2.57 mol% TBAB), and the synergetic effect of sodium dodecyl sulfate (SDS) and TBAB on CO2 separation from CH4 + CO2 was investigated under these conditions. The results indicate that gas consumption and CO2 selectivity declined with the increase of subcooling, and the best CO2 selectivity was obtained at 2.57 mol% TBAB. The kinetics of TBAB hydrate nucleation and growth were promoted when adding SDS into the TBAB solution, but the CO2 separation efficiency was reduced. The CO2 selectivity obtained at 2.57 mol% TBAB was significantly improved as compared to the THF, THF/SDS, and TBPB systems. Therefore, TBAB is a prospective promoter for hydrate-based CO2 capture from CH4 + CO2. Continued efforts are required in the future to increase the gas consumption without sacrificing the CO2 separation efficiency.

Thermodynamic properties of tetra-n-butylammonium 2-ethylbutyrate semiclathrate hydrate for latent heat storage

The quaternary onium salt-based semiclathrate hydrates have been investigated in many kinds of fields such as latent heat storage materials and gas separation media. In the present study, equilibrium (temperature−composition) relations in the tetra-n-butylammonium 2-ethylbutyrate (TBA-2 EB) semiclathrate hydrate system have been measured. In addition, thermodynamic and spectroscopic properties of TBA-2 EB semiclathrate hydrate were analyzed. The maximal equilibrium temperature and stoichiometric concentration of TBA-2 EB semiclathrate hydrate was 283.22 ± 0.05 K and x1 = 0.0281 ± 0.0007, respectively. The crystal lattice of TBA-2 EB semiclathrate hydrate, determined by the single crystal X-ray diffraction, was tetragonal. Other properties, not only Raman spectrum but also the maximum allowable degree of supercooling, in the TBA-2 EB semiclathrate hydrate system were similar to those in the tetra-n-butylammonium bromide (TBAB) hydrate. The TBA-2 EB semiclathrate hydrate would be an alternative to TBAB hydrate as a halogen-free semiclathrate hydrate system.

Insights into the phase behaviour of tetra-n-butyl ammonium bromide semi-clathrates formed with CO2, (CO2 + CH4) using high-pressure DSC

This work investigated the phase behaviour of tetra-n-butyl ammonium bromide (TBAB) semi-clathrates formed with CO2, and (CO2 + CH4) gas mixture using high-pressure differential scanning calorimetry (HP DSC). The phase equilibrium data of TBAB semi-clathrate formed with (40% CO2 + 60% CH4) in mole fraction were obtained at four TBAB molar concentrations (0.29%, 0.62%, 1.38%, and 2.57%). It was found that (TBAB + CO2 + CH4) mixed hydrate formed at 2.57% TBAB was more stable than that formed at 0.29%, 0.62%, and 1.38% TBAB, and two types of TBAB semi-clathrate (type A and type B) formed at the same time in the presence and absence of the (CO2 + CH4) gas mixture. The dissociation enthalpy of TBAB hydrate formed at 0.62% TBAB was higher than those obtained at 0.29%, 1.38%, and 2.57% TBAB. Besides, the phenomenon of liquid CO2 evaporation was confirmed in the (TBAB + CO2) hydrate formation system with the pressure varying from 3 MPa to 5 MPa. The endothermic heat of liquid CO2 evaporation was found to be much larger than that for the dissociation of (TBAB + CO2) semi-clathrate hydrate.

Investigation of the Growth Kinetics of Tetra-n-butylammonium Bromide Hydrate Formation in Small Spaces

The kinetics of tetra-n-butylammonium bromide (TBAB) hydrate formation orientated within the space of a small dimensional tube is investigated through microscopic experiments in the temperature range of −5.5 to −9.7 °C. Based on the experimental data, a kinetic model in a small dimensional space is proposed to describe the formation process. Hydrate crystals are observed uniformly growing in the small dimensional space. The experimental results show that the nucleation time of TBAB hydrate increases from 9 to 25 min and the linear growth rate decreases from 16.36 to 9.66 μm/s with the increasing temperature. Crystal morphologies show that the tube wall has less effect on the inner crystal growth when the temperature is lower. Furthermore, the number of nucleation sites increases under even lower temperatures. The varying degree of brightness of the crystals indicates that there is a variation of facets of hydrate crystals formed at different temperatures. Hydrate crystals under lower temperatures exhibit ...