Tetra-n-butyl Ammonium Bromide Aqueous Solution Research Articles

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.

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%.

Effects of Graphene Oxide Nanosheets and Al2O3 Nanoparticles on CO2 Uptake in Semi‐clathrate Hydrates

AbstractGas hydrate/clathrate hydrate formation is an innovative method to trap CO2 into hydrate cages under appropriate thermodynamic and/or kinetic conditions. Due to their excellent surface properties, nanoparticles can be utilized as hydrate kinetic promoters. Here, the kinetics of the CO2 + tetra‐n‐butyl ammonium bromide (TBAB) semi‐clathrate hydrates system in the presence of two distinct nanofluid suspensions containing graphene oxide (GO) nanosheets and Al2O3 nanoparticles is evaluated. The results reveal that the kinetics of hydrate formation is inhibited by increasing the weight fraction of TBAB in aqueous solution. GO and Al2O3 are the most effective kinetic promoters for hydrates of (CO2 + TBAB). Furthermore, the aqueous solutions of TBAB + GO or Al2O3 noticeably increase the storage capacity compared to TBAB aqueous solution systems.

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.

Thermal property, charging and discharging characteristics study on tetra-n-butyl ammonium bromide semi-clathrate hydrates for air-conditioning cold storage and secondary refrigerant applications

In this study, the heat of dissociation of tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrates (SCH) together with thermal conductivity and specific heat of both TBAB aqueous solution (AQS) and solidified AQS (SAQS) was measured for various weight fractions of AQS (wTBAB) ranging from (0.050 to 0.400). AQS and SAQS properties were measured by varying temperature from (283.2 to 308.2) K and (243.2 to 283.2) K, respectively. Thermal properties of AQS, SAQS, SCH, and clathrate hydrates slurry (CHS) have been reported. Subsequently charging and discharging characteristics of 0.400 wTBAB was studied in (42, 51, and 64) mm diameter spherical enclosures. Effect of diameter and wall temperature on charging characteristics were investigated, and the effect of diameter on discharging characteristics was explored. All the properties of AQS along with thermal conductivity of SAQS are influenced more by a change in wTBAB than by a change in temperature whereas, the reverse trend is observed for specific heat of SAQS. Thermal conductivity of SAQS and specific heat of AQS showed minimal variation while changing temperature, whereas specific heat of SAQS showed minimal variation while altering the wTBAB. Supercooling property of SCH had a significant effect on charging performance, and supercooling degree of SCH depend on wall temperature. Change in diameter does not affect the supercooling degree of SCH. In a spherical enclosure, SCH melts eccentrically. Charging and discharging rate of SCH increases with an increase in diameter. Based on this, it is found that a higher diameter capsule provides better charging and discharging performance.

Calorimetric and small-angle X-ray scattering studies on the memory effect in the tetra-n-butylammonium bromide semiclathrate hydrate system

Abstract The solution structures in the tetra-n-butylammonium bromide (TBAB) aqueous solution relate closely with the memory effect. In the present study, the behavior derived from the existence of the residual solution structures after TBAB semiclathrate hydrate (TBAB SCH) decomposition was investigated with two methods. One is a high-precision differential scanning calorimetry. The heat capacity of a TBAB aqueous solution with memory effect was slightly larger than that after the memory effect disappeared. The larger heat capacity implies the existence of solution structures. The other is a small-angle X-ray scattering (SAXS). In the first cooling process, strong scattering derived from rapid crystallization was observed at 263.6 K. In the second cooling process where the TBAB aqueous solution exhibited the memory effect, the scattering intensity gradually increased and became remarkably strong at a temperature (approximately 277 K) higher than 263.6 K. In the second cooling process, the invariant Q, which corresponds to electron density fluctuation, increased gradually until crystallization, whereas, in the first cooling process, the change of the invariant Q was quite small until crystallization. The increase of invariant Q implies the existence of 10–100 nm density fluctuation, which is consistent with the cluster size (10–20 nm) previously observed with electron microscopy in the same system.

Study on TBAB hydrate nucleating activity of electrode products due to DC voltage application

The effect of the products obtained by applying a direct current (DC) voltage to electrodes on the nucleation of tetra-n‑butyl ammonium bromide (TBAB) hydrate was investigated experimentally. Six kinds of materials were used as electrodes and the products were generated by applying a DC voltage to the electrodes in a TBAB aqueous solution at a normal temperature. The nucleating activities of the products were estimated by measuring the freezing probability of the TBAB aqueous solution containing the products. High probabilities of freezing were obtained for the Zn, Cu, and Ag electrodes. Moreover, the insoluble products were separated from the TBAB solution after a DC voltage was applied to the Zu, Cu, and Ag electrodes. The products were placed in a clear TBAB aqueous solution and the freezing probability of the TBAB solution was measured. The products had a high nucleating activity for TBAB hydrate.

Hydration numbers and thermal properties of tetra-n-butyl ammonium bromide semiclathrate hydrates determined by ion chromatography and differential scanning calorimetry

Abstract The hydration numbers and thermal properties of tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate crystals formed from TBAB aqueous solutions with TBAB mole fractions (x) in the range of (0.0060–0.0360) were investigated by ion chromatography and differential scanning calorimetry (DSC). The hydration numbers of TBAB hydrates can be estimated from combined ion chromatography and DSC. The hydration number (n) and dissociation enthalpy of orthorhombic TBAB hydrate are constant at n = 38 and ΔHdiss ≈ 220 kJ mol−1, respectively, for x = (0.0060–0.0120). The hydration numbers and the enthalpies of tetragonal TBAB hydrates gradually increase from n = 26.0 and ΔHdiss = 149 kJ mol−1 at x = 0.0360 to n = 28.2 and ΔHdiss = 160 kJ mol−1 at x = 0.0150, respectively. The dissociation enthalpies of tetragonal TBAB hydrates linearly increase from n = (26 to 32), which indicates that the enthalpies increase because of an increasing number of hydrogen bonds forming the TBAB hydrates. The dissociation temperatures of tetragonal TBAB hydrates decrease with increasing hydration number, and crystals with higher hydration numbers are thermodynamically unstable.

Solubility of Nitrogen Gas in Aqueous Solution of Tetra-n-Butylammonium Bromide

Semiclathrate hydrates are water-based host-guest compounds formed from aqueous solutions of ionic guest substances. These materials can greatly moderate formation pressures and temperatures from canonical gas hydrates. This is a significant advantage for industrial applications such as gas separation and storage. $$\hbox {N}_{2}$$ gas is a major component contained in various flue gases and is usually mixed with $$\hbox {CO}_{2}$$ . Semiclathrate hydrates can separate these gases under moderate thermodynamic conditions. Tetra-n-butylammonium bromide (TBAB) is a widely used ionic guest substance. To develop the application technologies and their theoretical models, solubility data of $$\hbox {N}_{2}$$ gas in TBAB aqueous solutions are required. In this study, we report $$\hbox {N}_{2}$$ gas solubility measured by an absolute gravimetric method for the semiclathrate hydrate formation system of $$\hbox {TBAB} + \hbox {H}_{2}\hbox {O} + \hbox {N}_{2}$$ . The measurement pressures, temperatures and TBAB mass fractions were 3 MPa, 5 MPa and 7 MPa, 292.15 K, 302.15 K and 307.15 K, and 0 (pure water), 0.10, 0.20, 0.32 and 0.40, respectively. The uncertainties were 0.056 MPa, 0.44 K and 0.00012 in mole fraction. Although the technical difficulty lays on measurements of small $$\hbox {N}_{2}$$ gas solubility by the absolute gravimetric method, our data implied the unique gas dissolution property of aqueous TBAB solution depending on the TBAB concentration. The aqueous TBAB solutions with mass fractions of 0.10 and 0.20 had similar $$\hbox {N}_{2}$$ gas solubility as that in pure water. With higher mass fractions, 0.32 and 0.40, the $$\hbox {N}_{2}$$ gas solubility slightly increased from that in pure water, which implies the salting-in effect of TBAB.

Conjugated heat and mass transfer during flow melting of a phase change material slurry in pipes

PCS (phase change materials slurries) are very useful for thermal energy storage. TBAB (tetra-n-butyl ammonium bromide) CHS (clathrate hydrate slurry) is a promising PCS, which is composed of TBAB hydrate crystal and TBAB aqueous solution. In the present study, the flow melting characteristics of TBAB CHS through pipes were numerically investigated. The solid–liquid two-phase nature of TBAB CHS was numerically investigated using the Eulerian–Eulerian multiphase model. And the interphase heat and mass exchange between TBAB hydrate crystals and TBAB aqueous solution was numerically modeled by considering the phase change phenomenon. Moreover, the diffusion of TBAB salt (solute) in TBAB aqueous solution was also numerically investigated. The numerical results showed that the liquid temperature increased more quickly than the solid temperature because of the latent heat involved. Moreover, the local heat transfer coefficient decreased in the thermally fully-developed region because of the increasing temperature difference between the wall and fluid. When the solid particles were almost fully melted, the fluid temperature increased more quickly than the wall temperature due to the absence of phase change, resulting in the increase of the local heat transfer coefficient.

Theoretical and experimental study of phase equilibrium of semi-clathrate hydrates of methane + tetra-n-butyl-ammonium bromide aqueous solution

In this study, the phase stability conditions of semi-clathrate hydrate of methane + tetra-n-butyl-ammonium bromide (TBAB) + water system is investigated. New experimental data on the hydrate–liquid–vapor equilibrium conditions of this system is measured. The measured data is for the pressure range of 2.88–14.1 MPa, temperature range of 285.6–295.9 K and TBAB mass fractions of 0.05, 0.15 and 0.3. A thermodynamic model is also developed to predict the phase stability conditions of hydrate for this system. In the developed model, the phase equilibrium of the hydrate of pure TBAB in water is predicted based on the Gibbs free energy minimization technique. This model is then combined with the statistical thermodynamic model of van der Waals–Platteeuw (vdW–P) to predict the phase stability conditions of semi-clathrate hydrate of methane with TBAB in aqueous solution. Binding mean spherical approximation (BiMSA) electrolyte model is used for aqueous phase properties prediction and modified Peng–Robinson equation of state (PR-EoS) is used for calculation of the gaseous phase properties. The results show that the developed model satisfactorily predicts the experimental data with Average Absolute Relative Deviation (AARD) of 12%. Moreover, the model is able to predict the different types of pure TBAB semi-clathrate hydrates and also the inhibition and promotion effects of this salt. The results also show that considering the association effect in the electrolyte model, can improve the predictions of the developed thermodynamic model for hydrate phase equilibrium of methane in the presence of TBAB aqueous solution.

Surface tension between CO2 gas and tetra-n-butylammonium bromide aqueous solution

This paper reports experimental values of the surface tension between CO2 gas and tetra-n-butylammonium bromide (TBAB) aqueous solution measured by the pendant drop method. The experimental conditions were pressures from 1.00MPa to 4.00MPa, temperatures from 288.15K to 303.15K and wTBAB from 0.10 to 0.40, where wTBAB denotes the mass fraction of TBAB in the aqueous solution. These pressure–temperature-composition conditions partially fall into the stability zone of (CO2+TBAB) semiclathrate hydrate but all data were obtained without any hydrate in the system. Surface tension decreased with increasing wTBAB and pressure but temperature dependency was not observed. Compared to the air–TBAB aqueous solution system and CO2–water system, the values of the surface tension were smaller.

Measurement of Latent Heat of Tetra-n-Butyl Ammonium Bromide Hydrate and Specific Enthalpy of Its Slurry

The specific heat of a tetra-n-butyl ammonium bromide (TBAB) aqueous solution, the latent heat of a TBAB hydrate, and the specific enthalpy of a TBAB hydrate slurry were measured to understand the thermal storage characteristics of TBAB hydrate slurry. A solution sample and the hydrate slurry were heated, the change in temperature was measured, and the specific heat of the TBAB aqueous solution and the specific enthalpy of the hydrate slurry were obtained from the change in temperature. Two types of TBAB hydrate form. Therefore, the hydrates were separated from the hydrate slurry formed from TBAB aqueous solution having several initial concentrations. The hydrate crystals were placed into solution, and the latent heats were obtained from the temperature change of the solution. The specific enthalpy of the hydrate slurry was estimated from the latent heats of the hydrate crystals and the specific heat of the solution under phase equilibrium conditions, and the measured and estimated values were compared.

Experimental and modeling study on the phase equilibria for hydrates of gas mixtures in TBAB solution

Accurate calculation of equilibrium formation conditions of hydrates is important for gas storage and separation based on hydrate technology. In this work, the hydrate formation conditions of a synthesized gas mixture in tetra-n-butyl ammonium bromide (TBAB) aqueous solution were measured at temperature ranging from 278.1 to 286.2K. An inflection point in the P–T curve of hydrate phase equilibria was found. It is suggested that the hydrate structures transformed from semiclathrate hydrates to pure structure I hydrates with an increase in formation temperature. Then a thermodynamic model was proposed for calculating formation conditions of the semiclathrate hydrates formed from the gas mixtures+TBAB aqueous solution. The Patel–Teja equation of state was used to calculate the fugacity of gaseous hydrate former and several correlations were used to calculate the properties of TBAB. Ethylene molecules are supposed not to be able to occupy the dodecahedral small cages in the TBAB semiclathrate hydrates under the experimental P–T conditions. The presented model results show good agreement with the experimental data and the literature data.

Kinetics of Hydrate Formation in the CO2+TBAB+H2O System at Low Mass Fractions

In the present study, CO2 gas and tetra-n-butyl ammonium bromide (TBAB) is adopted to form CO2+TBAB double hydrate at mass fractions w = 0.05 and 0.10. The moles of CO2+TBAB double hydrate are calculated by the variation of pressure of CO2 gas from initial pressure at about 4.03 MPa and the solubility of CO2 in TBAB aqueous solution at various subcoolings of 2.0–5.0 K. In addition, the formation characteristics of CO2+TBAB double hydrate are observed by the visualization, and it is verified to be a type B double hydrate. The kinetics of CO2+TBAB double hydrate formation at w = 0.05 and 0.10 is determined by the normalized rate of hydrate formation in the hydration process.

Experimental and Modeling Study on Phase Equilibria of Semiclathrate Hydrates of Tetra-n-butyl Ammonium Bromide + CH4, CO2, N2, or Gas Mixtures

Tetra-n-butyl ammonium bromide (TBAB) is most-widely used as a hydrate promoter in the separation of flue gases and CO2 sequestration. Because of the complicacy of semiclathrate hydrate formed by TBAB aqueous solution and gases, few researchers have investigated the thermodynamic modeling of phase equilibria of semiclathrate hydrates. In this work, the CH4–N2 hydrate dissociation conditions were determined in TBAB solution first, and then a thermodynamic model for gas hydrate proposed by Chen and Guo was extended for semiclathrate hydrates of gas mixtures in TBAB aqueous solution. The Patel-Teja equation of state (PT EoS) was used for calculation of the fugacity of the gas phase. To evaluate the activity of water and activity coefficients of TBAB in TBAB aqueous solution, a correlation on the basis of existing osmotic coefficient and activity coefficient values is employed. For modeling the hydrate phase, parameters for sII hydrates proposed in the Chen–Guo hydrate model were used to calculate the fugacit...

Crystallization of tetra-n-butyl ammonium bromide clathrate hydrate slurry and the related heat transfer characteristics

Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is a promising phase change material slurry for cold storage and transport in air-conditioning system. This slurry can be generated from the supercooled TBAB aqueous solution. In the present study, TBAB CHS was generated under different thermal conditions, i.e. different initial mass concentrations of TBAB aqueous solution and different supercooling degrees. The crystallization of TBAB CHS and the overall heat transfer coefficient under different thermal conditions were clarified. It was concluded that the crystallization characteristics of TBAB hydrate crystals mainly depended upon the thermal condition of the supercooled TBAB aqueous solution. In addition, the dropping of pre-produced TBAB CHS into supercooled TBAB aqueous solution could immediately induce the crystallization of TBAB hydrate crystals, and the initial type of TBAB hydrate crystals was only related to the status of the supercooled TBAB aqueous solution regardless of the type of the dropped TBAB CHS. Furthermore, the overall heat transfer coefficients before crystallization and during crystallization were also measured. It was found that more hydrate crystals would adhere to the vessel wall at larger supercooling degree and higher mass concentration of aqueous solution, which would deteriorate the heat transfer significantly. Moreover, images of TBAB hydrate crystals under different thermal conditions were recorded in order to help clarifying the crystallization characteristics.

A comparative study of different methods for the generation of tetra-n-butyl ammonium bromide clathrate hydrate slurry in a cold storage air-conditioning system

A cold storage air-conditioning system using tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) as cold storage medium was built to investigate the high-efficiency method of TBAB CHS generation. In the present study, four kinds of different TBAB CHS generation methods were experimentally investigated and compared, and these methods included continuously cooling, turning off refrigerator while crystals appearing, supercooling release and accession of TBAB CHS into supercooled TBAB aqueous solution. The results showed that continuously cooling would lead to severe adhesion of crystal to the heat exchanger wall, and supercooling release took place with a big stochastic characteristic, hence the first and third method were concluded not reliable. Both the second and fourth methods could maintain the temperature of heat exchanger wall at a relatively higher level, therefore the crystal adhesion to the heat exchanger wall would be reduced significantly, which led to higher coefficient of performance (COP). In addition, accession of TBAB CHS into TBAB supercooled solution could shorten the time of supercooling release, resulting in about 21.8–35.4% shorter generation time than other methods. Moreover, the influence of flow rate on the CHS generation process was investigated, and the results showed that higher flow rate generally resulted in higher system COP.

Thermodynamic Equilibrium Conditions for Simulated Landfill Gas Hydrate Formation in Aqueous Solutions of Additives

This work presents the thermodynamic study of separating CH4 and CO2 from the simulated landfill gas (LFG) [CO2 (0.45) + CH4 (0.55)] based on hydrate crystallization in the presence of tetra-n-butyl ammonium bromide (TBAB), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and their mixtures. The mole fractions of TBAB, THF, and DMSO aqueous solutions were fixed at 0.0234, 0.0556, and 0.0165, respectively. The equilibrium hydrate formation conditions were measured by T-cycle method in the temperature range of (274.15 to 294.95) K and the pressure ranges up to 6.72 MPa. The gas phase in the crystallizer at the equilibrium points was also sampled and analyzed. For the additives with the fixed concentrations studied in this work, it was found that both TBAB and THF can remarkably reduce the equilibrium hydrate formation pressure of LFG mixture gas, but the effect of THF is better than that of TBAB in the high temperature region, while DMSO have no obvious pressure drop effect on the equilibrium hydrate formation conditions but can promote the solubility of CO2 in the solution. However, the mixture additives of TBAB + DMSO and THF + DMSO can not only remarkably promote the solubility of CO2 but also remarkably reduce the equilibrium hydrate formation pressure of CO2 + CH4 + H2O hydrate. Moreover, the pressure drop effect of THF + DMSO is better than that of TBAB + DMSO on the CO2 + CH4 + H2O equilibrium hydrate formation in the high temperature region.