Tetra-n-butyl Ammonium Bromide Semiclathrate Hydrate Research Articles

Semi-clathrate hydrate slurry as a cold energy storage and transport medium: Rheological study, energy analysis and enhancement by amino acid

Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate is an attractive phase change material for cold energy storage and transport. The high viscosity of hydrate slurry is a major challenge for process design and causes large pumping power consumption, not to mention the significant discrepancy of viscosity data observed in the literature. In this study, the discrepancy was clarified by studying the rheology of TBAB semi-clathrate hydrate slurry (SHS) using a rheometer with seed-induced in-situ formation of hydrate up to a high hydrate fraction (∼0.51). TBAB SHS exhibited a non-Newtonian shear-thinning behavior. Its apparent viscosity increased exponentially with the increase of hydrate fraction. Type B TBAB SHS was recommended due to its lower apparent viscosity than type A TBAB SHS. Energy analysis revealed that TBAB SHS with appropriate hydrate fractions could outperform chilled water to provide the same cooling capacity but consume less pumping power. Furthermore, to reduce the viscosity, an environmentally benign additive l-tryptophan was identified and employed for the first time. Addition of l-tryptophan up to 1.0 wt% in TBAB SHS significantly decreased the apparent viscosity and lead to a 68.7% reduction of pumping power consumption compared with chilled water. This work demonstrated the potential of TBAB SHS as a more efficient next-generation secondary refrigerant and the addition of a small dosage of l-tryptophan would considerably enhance its economic strength in cooling applications.

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.

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.

Separation processes for carbon dioxide capture with semi-clathrate hydrate slurry based on phase equilibria of CO2 + N2 + tetra-n-butylammonium bromide + water systems

The objective of this work was to assess multi-stage separation processes for CO2 capture based on semi-clathrate hydrate (SCH) adsorption media. Phase equilibria were determined for CO2+tetra-n-butyl ammonium bromide (TBAB), N2+TBAB and CO2+N2+TBAB SCH and correlated with a modified van der Waals–Platteeuw model. Experimental CO2 separation factors ranged from 5 to 10, whereas calculated values were all around 18 implying inhomogeneous absorption in the slurries. For simulation conditions, hydrate mass fractions less than 0.09 were estimated to prevent aggregation of the hydrate solids. A two-stage batch separation process allowed enrichment of CO2 to more than 90mol% from a 20mol% CO2 feed. A three-stage continuous countercurrent separation process allowed a CO2 recovery of about 90%. Separation performance of semi-clathrate hydrates ranked favorably among the CO2 separation methods, showing that SCH adsorption media have excellent potential for carbon capture applications.

Investigation of the kinetics of TBAB + carbon dioxide semiclathrate hydrate in presence of tween 80 as a cold storage material

Because of large cold storage capacity and suitable freezing temperature of hydrate slurries, these materials could be used as a medium to store the cold energy in air conditioning systems. Semiclathrate hydrates of tetra n-butylammonium bromide (TBAB) are favorable phase change materials (PCMs), due to their moderate hydrate formation conditions. The kinetics of carbon dioxide - TBAB semiclathrate hydrate formation in presence and absence of tween 80 as a non-anionic surfactant is investigated in this research. The experiments were performed in a 169 cm3 stirred batch reactor at initial pressure of 3.2 MPa and isothermal condition of 276.15 K. Aqueous solutions of TBAB with concentrations of 0–15 wt% in presence and absence of tween 80 with concentrations of 500 and 1500 ppm are tested. The results revealed that utilization of TBAB with concentrations of 5–15 wt%, inhibits the kinetics of formed hydrates. By increasing the concentration of TBAB the amount and rate of gas uptake and storage capacity (SC) of formed hydrates decreases. Tween 80 with a concentration of 500 ppm presented a slight positive effect on the kinetics of hydrate formation in presence and absence of TBAB. While 1500 ppm of this additive inhibited the kinetics of formed hydrates.

Morphology and kinetic investigation of TBAB/TBPB semiclathrate hydrates formed with a CO2 + CH4 gas mixture

This work presents a morphological and kinetic investigation of tetra-n-butyl ammonium bromide (TBAB) or tetra-n-butyl phosphonium bromide (TBPB) semiclathrate hydrates formed with a CO2 + CH4 gas mixture at the stoichiometric concentration (2.57 mol%). A 3-stage procedure was proposed and employed in the experiments. All experiments were performed at 2.8 MPa and a subcooling of 12 K was used as driving force for hydrate nucleation and growth. It was found that the shapes of hydrate crystals formed in TBPB and TBAB solutions were quite different. Besides, the TBPB semiclathrate hydrate grew laterally at gas/liquid interface and quickly covered the interface while the TBAB semiclathrate hydrate initially formed around the gas/liquid interface and then sank to the reactor bottom. As a consequence, gas uptake and the rate of hydrate growth obtained in TBAB solutions were higher than that in TBPB solutions. It was also found that CO2 content in hydrate phase, CO2 recovery, and separation factor obtained in TBAB solutions were higher than those obtained in TBPB solutions. Therefore, TBAB semiclathrate hydrate formed at the stoichiometric concentration and quiescent conditions will be a promising approach to improve the hydrate based CO2 separation from the CO2 + CH4 gas mixture.

Dissociation and Nucleation of Tetra-n-butyl Ammonium Bromide Semi-Clathrate Hydrates at High Pressures

The equilibrium pressure–temperature relations of the tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate were measured at pressures of up to 80 MPa by high-pressure differential scanning calorimetry. As a pressurizing medium, tetrafluoromethane (CF4), which cannot occupy any hydrate cages in the TBAB semiclathrate hydrate at the present experimental pressures, was used. The dissociation temperature of tetragonal TBAB semiclathrate hydrate (TBAB·26H2O) increases with the increase in pressure, whereas the dissociation enthalpy is (192 ± 3) J·g–1 and almost constant at pressures of up to 80 MPa. The temperature difference between formation and dissociation at the same pressure, that is, the maximum allowable degree of supercooling, is (17.7 ± 0.7) K and independent of the pressure.

Phase Equilibrium Data for Semiclathrate Hydrate of Synthesized Binary CO2/CH4 Gas Mixture in Tetra-n-butylammonium Bromide Aqueous Solution

Hydrate-based gas separation(HBGS) technology based on tetra-n-butyl ammonium bromide (TBAB) semiclathrare hydrate can be utilized in CO2 separation from biogas. The phase equilibria of semiclathrate hydrates are crucial for the successful industrial application of HBGS technology. In this work, the phase equilibrium data of TBAB semiclathrate hydrate with a synthesized binary CO2/CH4 mixed gas (0.5 CO2 and 0.5 CH4 in mole fraction) were reported at five different TBAB concentrations (0.001, 0.01, 0.05, 0.1, and 0.2 mass fraction). The experiments were conducted in the temperature range (278.1 to 292.6) K and pressure range (2.17 to 8.16) MPa using an isochoric method. The agreement between the experimental data and the data reported in the literature indicated the reliability of the apparatus and method. The results showed that there were no obvious thermodynamic promotion effects on the CO2/CH4 mixed gas hydrate phase equilibrium conditions when the mass fraction of TBAB was less than 0.01, while there ...

Separation of methane-ethylene via forming semi-clathrate hydrates with TBAB

The formation conditions of CH4-C2H4 hydrate in water and 10 wt% tetra-n-butyl ammonium bromide (TBAB) solution were measured in this work. On this basis, the equilibrium separation of CH4-C2H4 via TBAB semi-clathrate hydrate formation was conducted at constant temperature and pressure. The results show that the influence of TBAB on the formation of CH4-C2H4 hydrate changes with temperature. At low temperature, TBAB forms semi-clathrate hydrate and acts as a promoter for CH4-C2H4 hydrate. At high temperature, TBAB exists as a salt compound and behaves as an inhibitor for CH4-C2H4 hydrate. CH4-C2H4 can be efficiently separated via TBAB semi-clathrate hydrate formation under proper temperature and pressure. The results indicate that C2H4 can not be encased in the dodecahedral cages of TBAB hydrate. Therefore, the concentration of C2H4 in hydrate could be as low as 0.55 mol% and the recovery of C2H4 could reach 99.85% in equilibrium gas.

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.

Modeling the Dissociation Conditions of Carbon Dioxide + TBAB, TBAC, TBAF, and TBPB Semiclathrate Hydrates

The thermodynamic approach developed by Paricaud [J. Phys. Chem. B 2011, 115, 288–299] is applied to predict the dissociation conditions of semiclathrate hydrates made with tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl ammonium chloride (TBAC), tetra-n-butyl ammonium fluoride (TBAF), and tetra-n-butyl phosphonium bromide (TBPB). The SAFT-VRE equation of state is used to describe the properties of fluid phases, and a good description of osmotic and mean activity coefficients of electrolyte solution is obtained. The temperature–composition diagrams of water + tetra-n-alkylammonium/alkylphosphonium salt binary systems are well described by the model. Group contribution methods are proposed to predict the fusion enthalpies and the congruent melting points of semiclathrate hydrates. The van der Waals and Platteeuw theory is combined with the model to calculate the dissociation conditions of carbon dioxide semiclathrate hydrates. The liquid–vapor–hydrate three phase lines can be accurately described over...

Physicochemical properties of semi-clathrate hydrates as revealed by terahertz time-domain spectroscopy

The physical properties of semi-clathrate hydrates formed with tetra-n-butylammonium fluoride (TBAF) and tetra-n-butylammonium bromide (TBAB) in the temperature range of 83–263K were studied using terahertz time-domain spectroscopy (THz-TDS). From our measurements, the semi-clathrate hydrate of TBAF shows the general trend of slightly higher refractive indices than the TBAB semi-clathrate hydrate. Furthermore, significant differences in the absorption coefficients and dielectric constants between the TBAF and TBAB semi-clathrate hydrates are discovered. These originate from fundamental structural/compositional differences between the hydrates which are related to their gas storage capacities.

Measurement of pure hydrogen and pure carbon dioxide adsorption equilibria for THF clathrate hydrate and tetra-n-butyl ammonium bromide semi-clathrate hydrate

In this work, gas adsorption equilibria for H2 and for CO2 with THF clathrate hydrate particles and with tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate particles (250–355μm) were measured. The structures of the TBAB semi-clathrate hydrates were confirmed with Raman spectroscopy and with differential scanning calorimetry. The THF clathrate hydrate particles had the largest adsorption (ca. 13.7mmol-H2/mol-host) at 269K among all of the hydrates studied. H2 adsorption at 269K for 2.6mol% TBAB semi-clathrate hydrate (type-B rich) was ca. 6.9mmol-H2/mol-host and that for 3.7mol% TBAB semi-clathrate hydrate (type-A rich) was ca. 3.4mmol-H2/mol-host. For CO2, THF clathrate hydrate had higher adsorption capacity (ca. 68.5 mmol-CO2/mol-host) than type-A (ca. 16.3 mmol-CO2/mol-host) or type-B (ca. 29.0 mmol-CO2/mol-host) semi-clathrate hydrate. Type-B TBAB semi-clathrate hydrate had a larger Langmuir constant ratio (CCO2/CH2) than that of THF hydrate. The selectivity of type-B TBAB semi-clathrate hydrate implied by the Langmuir constant ratio can be expected to be large, however the results need to be confirmed with gas mixtures and other conditions including effect of semi-clathrate hydrate particle size.

Experimental Investigation of Methane Separation from Low-Concentration Coal Mine Gas (CH4/N2/O2) by Tetra-n-butyl Ammonium Bromide Semiclathrate Hydrate Crystallization

In this work, tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate was employed in a batch operation to separate CH4 from low-concentration coal mine methane (CMM) gas with a mole composition of 30% CH4, 60% N2, and 10% O2. TBAB semiclathrate hydrate formed from the low-concentration CMM gas has more favorable incipient equilibrium conditions than gas hydrates formed from the same gas mixture. The experiments were carried out at a fixed pressure of 4.0 MPa, three TBAB mole concentrations of 0.29, 0.62, and 1.38 %, and in the temperature range of 274.75–283.35 K. The effects of TBAB concentrations and subcoolings (ΔTsub) on CH4 separation from the low-concentration CMM gas were investigated. The results indicated that CH4 was preferentially incorporated into the hydrate crystals rather than N2 and O2 in the presence of TBAB. The experimental conditions of the TBAB concentration of 1.38%, 4.0 MPa, and ΔTsub = 7.0 K were most favorable for TBAB semiclathrate hydrate to separate CH4 from the low-concentration CMM gas. The CH4 recovery obtained at these conditions was approximately 27%. Compared with CH4 content in the low-concentration CMM gas, the mole fraction of CH4 in TBAB semiclathrate hydrate was increased to 41%.

Methane Separation from Coal Mine Methane Gas by Tetra-n-butyl Ammonium Bromide Semiclathrate Hydrate Formation

This work presents new data to further develop the hydrate-based process for the separation of CH4 from the low-concentration coal mine methane gas (30 mol % CH4/N2) through the formation of tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate. The TBAB semiclathrate hydrate formed from the 30 mol % CH4/N2 gas mixture has more favorable equilibrium conditions than the gas hydrate formed from the same gas mixture. The incipient equilibrium conditions at 0.17, 0.29, and 0.62 mol % TBAB were experimentally determined and reported. The experiments of forming TBAB semiclathrate hydrate from the 30 mol % CH4/N2 gas mixture were performed in both semibatch and batch operation under a fixed driving force of 3.5 MPa. The results indicate that CH4 is preferentially encaged into the TBAB hydrate. The use of a 0.29 mol % TBAB solution is preferred over the 0.17 and 0.62 mol % TBAB solutions. The semibatch operation is more effective than the batch operation for the separation of CH4 from the 30 mol % CH4/N2 ga...

Phase equilibrium measurements for semi-clathrate hydrates of the (CO2 + N2 + tetra-n-butylammonium bromide) aqueous solution systems: Part 2

Equilibrium pressures for dissociation of the carbon dioxide (CO2)+nitrogen (N2)+tetra-n-butylammonium bromide (TBAB)+semi-clathrate (sc) hydrates have been experimentally measured to determine the stability regions and dissociation conditions of mixed CO2+N2+TBAB semi-clathrate hydrates. Semi-clathrates have been formed with the addition of TBAB aqueous solutions with mass fractions of (0.05 and 0.30). The relative molar fractions of CO2 in the feed gas were (0.151, 0.399, and 0.749). Hydrate dissociation conditions have been measured using an isochoric pressure search method in the 275.1–291.0K temperature range and 0.67–19.07MPa pressure range. The obtained experimental clathrate hydrate dissociation data have been compared with the predictions of two thermodynamic models, namely CSMGem and HWHYD, available in open literature. Finally, the thermodynamic promotion effects of TBAB in aqueous solutions are discussed in terms of hydrate dissociation pressures and temperatures and consequently the most favorable operating conditions are proposed.

Equilibrium Conditions for Semiclathrate Hydrates Formed in the CH4 + N2 + O2 + Tetra-n-butyl Ammonium Bromide Systems

In the present work, phase equilibrium conditions for tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrates formed with the gas mixture (29.95 % CH4 + 60.0 % N2 + 10.05 % O2 in mole fraction) were measured. The experimental temperature, pressure, and mass fraction of TBAB ranged from (282 to 290) K, from (0.99 to 6.56) MPa, and from (0.05 to 0.20), respectively. For the gas mixture used in this work, the experimental results showed that at a given temperature, the pressure required to form TBAB semiclathrate hydrates is significantly lower than that required for forming gas hydrates from the same gas mixture. The formation pressure of TBAB semiclathrates formed with the gas mixture is reduced as TBAB concentration is increased in the solution at a given temperature.

Efficient Capture of CO2from Simulated Flue Gas by Formation of TBAB or TBAF Semiclathrate Hydrates

Capturing CO2 by forming hydrate is an attractive technology for reducing the greenhouse effect. The most primary challenges are high energy consumption, low hydrate formation rate, and separation efficiency. This work presents efficient capture of CO2 from simulated flue gas (CO2 (16.60 mol %)/N2 binary mixtures) by formation of semiclathrate hydrates at 4.5 and 7.1 °C and feed pressures ranging from 2.19 to 7.31 MPa. The effect of 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) and tetra-n-butyl ammonium fluoride (TBAF) on the hydrate formation rate, reactor space velocity, and CO2 separation efficiency was studied in a 1 L stirred reactor. The results showed the hydrate formation rate constant increased with increasing feed pressure and reached the maximum at 2.82 × 10−7 mol2/(s·J) with TBAB and 8.26 × 10−7 mol2/(s·J) with TBAF. The space velocity of the hydrate reactor increased with increasing feed pressure and reached a maximum of 13.46 h−1 with TBAB and 25.96 h−1 with TBAF. CO2 recovery was about...

Phase diagram, latent heat, and specific heat of TBAB semiclathrate hydrate crystals

Tetra- n-butyl ammonium bromide (TBAB) is a tetra-alkylammonium salt, that forms two types of semiclathrate hydrate. At atmospheric pressure, the melting points are between room temperature and freezing point of water. There are some useful applications of the semiclathrate, for example using as a heat transport medium and gas separator, but there are little knowledge about TBAB hydrates characteristics. In this paper, some thermal properties of TBAB semiclathrate hydrate are reported. We determined the phase diagram of semiclathrate hydrate nucleation under the condition of atmospheric pressure, latent and specific heats capacity of TBAB semiclathrate hydrate. From the phase diagram, the congruent melting points of two TBAB hydrates were determined. Using above results, we obtained the hydration numbers of two type TBAB hydrates.