Tetra-n-butyl Ammonium Chloride Research Articles

Experimental measurement and thermodynamic modeling of hydrate stability conditions in the methane + cyclopentane + tetra-n‑butyl ammonium chloride (TBAC) aqueous solution system

The present study investigates hydrate dissociation conditions in methane + cyclopentane (CP) and tetra-n‑butyl ammonium chloride (TBAC) aqueous solution. The experimental work was done using an isochoric vessel with varying compositions of the promoters in the pressure and temperature ranges of (1.42 to 4.90) MPa and (291.2 to 298.9) K, respectively. The methane hydrate dissociation pressure was predicted by the Gibbs minimization method. The findings denote that adding CP to the TBAC-containing system shifts the hydrate dissociation temperature of methane to higher values. The results also show an average increase of 12, 9, 5, and 3 K in hydrate dissociation temperature for 5, 10, 20, and 30 wt% TBAC in aqueous solution within the pressures. These results can be caused by the existence of more dodecahedral cages that are inhabited by methane. Thus, it makes hydrates more stable and increases the temperature of hydrate dissociation. On the other hand, adding TBAC to CP containing system has an inhibitor effect. The methane hydrate dissociation temperature was not changed sensibly when a 5 wt% TBAC was added to CP containing system. When the addition of the TBAC weight percentage to CP containing system is increased to 10, the average hydrate dissociation temperature decreases by 1 K within the pressures. When adding 20 and 30 wt% TBAC to CP containing system an average decrease of 2 K and 3 K in the hydrate dissociation temperature is resulted, respectively, within the pressures. The reduction in the hydrate dissociation temperatures can be attributed to salting-out and ion clustering. The experimental data and modeling results for the hydrate dissociation pressures exhibit an AARD of 2.4 %.

Semiclathrate-based CO2 capture from pre-combustion fuel gas using tetra-n-butylammonium chloride: A thermodynamic, kinetic, and spectroscopic study

The primary objective of this study was to investigate the feasibility of pre-combustion CO2 capture using tetra-n-butylammonium chloride (TBAC) semiclathrate in a fuel gas mixture comprising CO2 (40%) + H2 (60%), with a primary focus on examining the thermodynamic, kinetic, and spectroscopic aspects of this process. Phase equilibria measured at various TBAC concentrations revealed that the CO2 + H2 + TBAC semiclathrates exhibited maximum thermodynamic stability at a stoichiometric concentration (3.3 mol%). CO2 concentrations in both the vapor and semiclathrate phases, along with gas consumption during and after semiclathrate formation, were measured to assess CO2 selectivity and gas uptake in the semiclathrate phase. Notably, CO2 enrichment was approximately 90% in the semiclathrate phase. In-situ Raman spectroscopy provided clear confirmation of the enclathration of both CO2 and H2 in the semiclathrate lattices, while powder X-ray diffraction analysis revealed the tetragonal (P42/m) structure of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate. Furthermore, a high-pressure micro-differential scanning calorimeter was used to measure the dissociation enthalpies of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate at various pressures. The comprehensive results obtained in this study strongly support the potential use of TBAC semiclathrate as a material for pre-combustion CO2 capture.

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid-Based Copolyesters.

To synthesize high molecular weight poly(phenolic ester) via a living ring-opening polymerization (ROP) of cyclic phenolic ester monomers remains a critical challenge due to serious transesterification and back-biting reactions. Both phenolic ester bonds in monomer and polymer chains are highly active, and it is difficult so far to distinguish them. In this work, an unprecedented selectively bifunctional catalytic system of tetra-n-butylammonium chloride (TBACl) was discovered to mediate the syntheses of high molecular weight salicylic acid-based copolyesters via a living ROP of salicylate cyclic esters (for poly(salicylic methyl glycolide) (PSMG), Mn =361.8 kg/mol, Ð<1.30). Compared to previous catalysis systems, the side reactions were suppressed remarkably in this catalysis system because phenolic ester bond in monomer can be selectively cleaved over that in polymer chains during ROP progress. Mechanistic studies reveal that the halide anion and alkyl-quaternaryammonium cation work synergistically, where the alkyl-quaternaryammonium cation moiety interacts with the carbonyl group of substrates via non-classical hydrogen bonding. Moreover, these salicylic acid-based copolyesters can be recycled to dimeric monomer under solution condition, and can be recycled to original monomeric monomers without catalyst under sublimation condition.

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid‐Based Copolyesters

AbstractTo synthesize high molecular weight poly(phenolic ester) via a living ring‐opening polymerization (ROP) of cyclic phenolic ester monomers remains a critical challenge due to serious transesterification and back‐biting reactions. Both phenolic ester bonds in monomer and polymer chains are highly active, and it is difficult so far to distinguish them. In this work, an unprecedented selectively bifunctional catalytic system of tetra‐n‐butylammonium chloride (TBACl) was discovered to mediate the syntheses of high molecular weight salicylic acid‐based copolyesters via a living ROP of salicylate cyclic esters (for poly(salicylic methyl glycolide) (PSMG), Mn=361.8 kg/mol, Ð&lt;1.30). Compared to previous catalysis systems, the side reactions were suppressed remarkably in this catalysis system because phenolic ester bond in monomer can be selectively cleaved over that in polymer chains during ROP progress. Mechanistic studies reveal that the halide anion and alkyl‐quaternaryammonium cation work synergistically, where the alkyl‐quaternaryammonium cation moiety interacts with the carbonyl group of substrates via non‐classical hydrogen bonding. Moreover, these salicylic acid‐based copolyesters can be recycled to dimeric monomer under solution condition, and can be recycled to original monomeric monomers without catalyst under sublimation condition.

Methane and Carbon Dioxide Separation Characteristics of Quaternary Ammonium Salt Hydrates for Biogas Upgrading under Static Conditions of Gas–Solid Contact

This report describes the methane and carbon dioxide separation characteristics of stoichiometric quaternary ammonium salt (QAS) hydrates for gas–solid contact with simulated biogas (CH4, 0.613 mol fraction; CO2, 0.387 mol fraction). Tests for elucidating the separation characteristics were conducted using tetra-n-butylammonium fluoride (TBAF), tetra-n-butylammonium chloride (TBAC), and tetra-n-butylammonium bromide (TBAB) hydrates as solid phases. To ascertain system temperature and pressure effects on their gas separation performance, the tests were conducted at 253–293 K under the initial fed pressures of 3.0 and 0.9 MPa. The gas–solid contact between the simulated biogas with 0.387 mol fraction of CO2 and the QAS hydrates reduced CO2 in the gas phase to 0.26–0.37 mol fraction and enriched CO2 in the hydrate phases to 0.54–0.89 mol fraction. All QAS hydrates showed selective incorporation of carbon dioxide into the hydrate phase. Under all comparable conditions, TBAC hydrate exhibited the highest separation factor (15.2 ± 3.0 under initial pressure of 3.0 MPa at 253 K and 13.9 ± 2.5 under initial pressure of 0.9 MPa at 253 K), indicating that TBAC hydrate had the highest CO2 separation performance for biogas upgrading among the QAS hydrates we examined. At the same initial pressure, high gas separation performance was shown for low-temperature ranges. The separation factors of the QAS hydrates were maintained or improved by lowering the initial pressure at the same contact temperature, suggesting that the separation performance of the QAS hydrates, even at lower pressures, was nearly equal to or better than that achieved at higher pressures. The results contrasted against those reported for tetrahydrofuran hydrate, for which the separation factor decreases with lower initial pressure. The use of the QAS hydrates is expected to lower a system’s operating pressure without compromising separation performance.

Phase equilibria of methane/TBAC mixed hydrates in the presence of produced water

AbstractProduced water (PW) is a by‐product and one of the major pollutants from the oil and gas industry. PW contains various pollutants and must be treated as per environmental regulations before its disposal or reuse. Thus, it presents a substantial economic and ecological problem in the oil and gas industry. Currently, there is ongoing research on various methods to treat PW efficiently. Hydrate‐based water desalination is one of the promising technologies. There is a continuing effort to identify a suitable hydrate former that can enhance the commercial feasibility of the process. This study investigates tetra‐n‐butyl ammonium chloride (TBAC) + methane as a potential clathrate former. The hydrate equilibrium temperatures of the mixed hydrates (TBAC + methane) are significantly higher at a given pressure than methane hydrates, suggesting the suitability of mixed hydrates for process development. There was a significant increase in the phase equilibrium temperature at 5 wt.% TBAC in the presence of PW compared to deionized water (DI), but the effect faded away as TBAC concentration increased in the solution. This can be attributed to a higher amount of chloride ions as the TBAC concentration is increased. These results elucidate the necessity to optimize the TBAC concentrations to develop an efficient hydrate desalination process for higher saline concentrations.

Abnormal structural transformation of tetra-n-butyl ammonium chloride + Xe clathrates and its significance for clathrate-based Xe capture and storage.

Tetra-n-butyl ammonium chloride (TBAC) is a semi-clathrate former that can be used for clathrate-based gas capture and storage since TBAC semi-clathrate has vacant small cages available for entrapping gas molecules under mild conditions. In this study, the phase equilibria and structural information of TBAC + Xe + water systems were experimentally investigated at two different TBAC concentrations (1.0 and 3.3 mol%). The slopes of the three-phase (clathrate [H] - liquid [L] - vapor [V]) equilibrium lines for the TBAC + Xe + water systems altered at one or two points as the pressure and temperature changed, which indicates that this slope change might be caused by the structural transformation of the clathrates that were formed. The powder X-ray diffraction (PXRD) patterns, in situ Raman spectra, and 129Xe nuclear magnetic resonance (NMR) spectra demonstrated that the clathrate structure of the TBAC + Xe + water systems changed from tetragonal (P42/m) or orthorhombic (Pmma) to cubic (Pm3̄n) as the pressure increased. Surprisingly, in the higher-pressure region, TBAC acted as a thermodynamic inhibitor without being enclathrated in the clathrate lattices. The thermodynamic and structural information of the TBAC + Xe clathrates will be helpful for conceptualizing and designing the clathrate-based noble gas or radioactive gas capture and storage process.

Donor-acceptor complex formation in tetra-n-butylammonium chloride: n-decanoic acid deep eutectic solvent.

Complex formation between pyrene (Py) and N,N-dimethylaniline (DMA) is presented in a deep eutectic solvent constituting of tetra-n-butylammonium chloride (TBAC) and n-decanoic acid (DA) in a 1:2 mol ratio, respectively, named TBAC:DA. The addition of DMA to a Py solution of TBAC:DA results in the formation of a fluorescent Py-DMA charge-transfer complex, which is manifested via a broad structureless bathochromically shifted band centered at 550(±2) nm. The solvatochromic nature of the Py-DMA fluorescent complex indicates the solvent polarity of TBAC:DA to be higher than that of methanol. The absence of a negative pre-exponential factor in the intensity decay at 550 nm combined with the excitation scans implies the presence of weak interaction between Py and DMA in the ground-state, leading to the rapid formation of a Py-DMA complex possibly at a sub-nanosecond time scale. The Stern-Volmer quenching constant (KSV) varies from 53(±2) to 96(±1) M-1, and the bimolecular quenching rate constant (kq) varies from 3.0(±0.4) × 108 to 8.8(±1.3) × 108 M-1 s-1 by increasing the temperature (T) from 283.15 to 313.15 K, implying efficient deactivation of electron-acceptor Py in the excited-state induced effectively by the electron-donor DMA within TBAC:DA. ln kq varies linearly with 1/T with an activation energy (Ea) of 26.4(±0.4) kJ mol-1. The linear behavior between kq and 1/η suggests conformity to the Stokes-Einstein relationship within TBAC:DA. The Py-DMA complex formation efficiency increases with an increase in T and reaches maxima at 298.15 K before decreasing with a further increase in T. The initial reduction in η favors Py-DMA complex formation; this effect is overcome by preferential thermal deactivation of the Py-DMA fluorescent complex as compared to that of pyrene.

Determination of CO2 gas hydrates surface tension in the presence of nonionic surfactants and TBAC

The gas hydrates formation, in spite of its disadvantages, has some advantages such as separating, transferring and storing gas. Therefore, determining the appropriate promoters for the gas hydrates’ formation is as important as selecting an appropriate inhibitor. One of the effective promoters is tetra-n-butyl ammonium chloride (TBAC). Due to TBAC non-destructive environmental effects and its extraordinary effect on the thermodynamics of gas hydrates, this salt is one of the most widely used promoters. TBAC was discussed in the context of hydrate structure formation and Alkyl Poly Glucoside (APG) as a nonionic surfactant, because of its characteristics like biodegradability, emulsifiers and reasonable prices. In this study, the surface tension between Co2 hydrates was determined at constant temperatures and pressures with different concentrations. For this purpose, the classical nucleation theory has been used. The experimental data show that at constant temperature, the induction time is reduced by increasing TBAC concentration and adding APG. Also, the surface tension value reduces significantly due to adding APG, which this reduction has led to an upward trend with increasing temperature. Finally, the surface tension values obtained from the developed method were compared by presented correlations.

Thermal properties of tetragonal tetra-n-butyl ammonium bromide + tetra-n-butyl ammonium chloride mixed semiclathrate hydrates based on hydration numbers and guest mole fraction rates

In this study, we investigated variations in the thermal properties of tetragonal tetra-n-butyl ammonium bromide (TBAB) + tetra-n-butyl ammonium chloride (TBAC) mixed semiclathrate hydrates by ion chromatography and differential scanning calorimetry; these variations were assessed both in terms of their hydration numbers and the guest mole fraction rates of the hydrates. TBAB mole fraction rates in mixed hydrate crystals (yTBABh) are lower than those in mixed aqueous solutions; therefore, as Cl− has a smaller size difference to a water molecule, it is more easily incorporated into the host frameworks of hydrates than Br−. The melting points of mixed hydrates were observed at 286–289 K, and the maxima are around yTBABh = 0.1–0.3 in each hydration number. The increase in melting points largely depends on decreasing yTBABh rather than increasing hydration numbers. It is suggested that the combinations of TBAB and TBAC optimize the crystal structures, and melting points of TBAB + TBAC mixed hydrates become anomalously higher than those of the pure TBAC hydrates. Dissociation enthalpies per mass increase from 193 J g−1 to 215 J g−1, primarily with decreasing yTBABh, whereas those per guest moles increase from 154 kJ mol−1 to 188 kJ mol−1, primarily with increasing hydration numbers rather than yTBABh.

Chloride-mediated co-formation of 3-monochloropropanediol esters and glycidyl esters in both model vegetable oils and chemical model systems

3-Monochloropropanediol esters (3-MCPDEs) and glycidyl esters (GEs) with high toxicity have drawn global concerns due to their widespread occurrence in refined oils and oil-based foods. The effect mechanisms of organic chlorine compound lindane, inorganic chlorine compounds tetra-n-butylammonium chloride (TBAC) and sodium chloride (NaCl) on the formation of 3-MCPDEs and GEs were investigated in model oils and chemical models at 240 °C. Results showed that 3-MCPDEs contents increased with the addition of lindane and TBAC, whereas, surprisingly, GEs presented the same tendency as the results of 3-MCPDEs. This suggested that although chlorine compounds were not involved in the formation reaction of GEs, they could also promote GEs formation. Chemical model experiments confirmed that the presence of chlorine compounds led to the transformation of GEs to 3-MCPDEs and conversely 3-MCPDEs could also transform to GEs. The latter transformation rate from 3-MCPDEs to GEs was higher than the former, which might account for the fact that chlorine compounds promoted GEs formation. Additionally, it was also observed that solid NaCl did not induce the increase of 3-MCPDEs and GEs levels in chemical models, suggesting that the chlorine in NaCl, different from lindane and TBAC, was not available for 3-MCPDEs formation. The present findings give novel insights into the interactions between 3-MCPDEs and GEs formation mechanisms, which offer the theoretical basis for efficient and simultaneous inhibition of 3-MCPDEs and GEs.

Statistical Analysis of the Effects of Aluminum Oxide (Al2O3) Nanoparticle, TBAC and APG on Storage Capacity of CO2 Hydrate Formation

In this study, the effect of various concentrations of alkyl polyglycoside (APG), aluminum oxide nanoparticles (Al2O3), and tetra-n-butyl ammonium chloride (TBAC) on the storage capacity of CO2 hydrate formation are investigated. For this aim, a laboratory system is developed. The experiments are carried out in the pressure range of 25 to 35 bar and the temperature range of 275.15 K to 279.15 K. The Experimental results showed that by increasing the system pressure at constant temperature, the storage capacity increased by 48% in average. Decreasing the system temperature at constant pressure increased the storage capacity by 23% in average. Adding APG to the system at constant temperature and pressure increases the storage capacity by 75% in average, while adding nanoparticles of aluminum oxide increases the storage capacity by 5% and TBAC 38% in average. For statistical analysis of laboratory data, Design Expert software and Response Surface test design method and Quadratic model are employed and a mathematical relationship is developed with R2 = 0.9987 to estimate CO2 storage capacity in hydrates. The optimum amount of storage capacity equal to 137.476 has been reached at 34.558 bar, 276.085 K, 2.825 Wt% of TBAC, 956.733 ppm APG, 2.436 Wt % Al2O3.

Evaluation of the Effect of Nonionic Surfactants and TBAC on Surface Tension of CO2 Gas Hydrate

Given that most of the gaseous constituents of industrial chimneys are usually carbon dioxide which is one of the most important greenhouse gases. It seems that the hydration process is one of the newest methods for the separation of this gas from gaseous mixtures. In the gas hydrate formation industry, in addition to disadvantages, there are some advantages such as gas separation, transmission, and storage. Therefore, it is important to determine the appropriate promoter for the formation of gaseous hydrates as well as to find the inhibitor. In this study, the effect of tetra-n-butyl ammonium chloride (TBAC) (which is a thermodynamics promoter) and alkyl poly glucoside (APG) as a nonionic surfactant on the surface tension of carbon dioxide hydrate formation process have been studied. The experiments were carried out in a 218 cm3 batch reactor. The surface tension of CO2 hydrate has been determined at different concentrations and different temperatures and pressures. The nucleation classical theory has been used for this purpose. Designing the experiments performed by Design-Expert software. The results show that increasing the APG and temperature leads to decreasing the surface tension and in contrast, induction time decreases, and the experimental model of the effect of these parameters on surface tension presented as R2 = 0.9898.

Effect of Adding Lithium Chloride on Tetra-n-butyl Ammonium Chloride Semiclathrate Thermal Stability at Atmospheric Pressure

Tetra-n-butyl ammonium chloride (TBAC) is an organic salt known to form semiclathrate complexes in the presence of water. Previous studies using differential scanning calorimetry have shown that the addition of either NaCl or KCl can affect these semiclathrate structures. In this work, the effect of adding LiCl to aqueous TBAC solutions on the melting points of these semiclathrate structures was determined and compared to the effects of adding either NaCl or KCl. Ternary TBAC–LiCl–H2O systems were created by adding LiCl to 1, 1.5, 2, 3, and 4 m TBAC–H2O solutions to give ionic strength fractions of TBAC (YTBAC) from 0.25 to 1. It was found that the melting points of TBAC–H2O semiclathrate were unaffected with the addition of LiCl as long as there were sufficient amounts of free, bulk water present to solvate the salt at concentrations less than 2 m TBAC where free, bulk water can exist. However, at lower ionic strength fractions of TBAC, when the system runs out of free, bulk water, LiCl was found to disrupt the TBAC–H2O semiclathrate structures. At concentrations above 2 m TBAC, the situation is more complex as there is no free, bulk water in the TBAC–H2O system. Adding LiCl disrupted the normal TBAC–H2O semiclathrate complex, forming new TBAC–LiCl–H2O semiclathrate structures at high ionic strength fraction of TBAC that were disrupted upon increasing the relative concentration of LiCl.

Optimization of determination of CO2 gas hydrates surface tension in the presence of non-ionic surfactants and TBAC

The gas hydrates formation, in spite of its disadvantages, has some advantages such as separating, transferring and storing gas. Therefore, determining the appropriate promoters for the gas hydrates’ formation is as important as selecting an appropriate inhibitor. One of the effective promoters is Tetra-N-Butyl ammonium chloride (TBAC). Due to TBAC'snon-destructive environmental effects and its extraordinary effect on the thermodynamics of gas hydrates, this salt is one of the most widely used promoters. TBAC was discussed in the context of hydrate structure formation and Alkyl Poly Glucoside (APG) as a nonionic surfactant due to biodegradability, emulsifiers, and reasonable prices. In this study, the surface tension between CO2hydrates was evaluated at constant temperatures and pressures with different concentrations. For this purpose, the classical nucleation theory has been used. The experimental data show that at constant temperature, the induction time was reduced by increasing the TBAC concentration and adding APG. Also, the surface tension value reduced significantly by adding APG, led to an upward trend with increasing temperature. Finally, the surface tension values obtained from the developed method were compared by presented correlations. The results of the developed model are in satisfactory agreement with literature data.

Semi-clathrate hydrate phase equilibria of carbon dioxide in presence of tetra-n-butyl-ammonium chloride (TBAC): Experimental measurements and thermodynamic modeling

The promotion effect of TBAC on the dissociation condition of the studied system is determined under the present experimental data. A combination of the van der Waals–Platteeuw solid solution theory, binding mean spherical approximation electrolyte model and modified Peng–Robinson equation of state is used for calculation of the hydrate, aqueous solution and gaseous phases properties, respectively. The results are also compared with the experimental data for other salts such as tetra-n-butyl-ammonium bromide (TBAB) and tetra-hydro furan (THF). A good agreement between the model predictions and experimental data is found with an absolute average relative deviation of 13.1%.

Effect of Adding Potassium Chloride on Tetra-n-butyl Ammonium Chloride Semiclathrate Thermal Stability at Atmospheric Pressure

Tetra-n-butyl ammonium chloride (TBAC) is known to form semiclathrate complexes with water. In this work, the melting points and latent heats of fusion of these semiclathrate structures were determined using Differential Scanning Calorimetry (DSC). A phase diagram was created for binary TBAC-H2O from 0 to 7.775 molal TBAC at atmospheric pressure. Below 2 molal TBAC, the semiclathrate is in equilibrium with free, bulk water. At approximately 2 molal TBAC a congruent melting point at 286.96 K is observed in this phase diagram. Beyond this composition, there is no free, bulk water present, and there are multiple forms of the TBAC-H2O semiclathrate complexes with varying amounts of water. Ternary TBAC-KCl-H2O systems were created by adding KCl to 1, 1.5, 2, 3, and 4 molal TBAC solutions to give ionic strength fractions of TBAC (YTBAC) from 0.25 to 1. It was found that the melting points of the TBAC-H2O semiclathrate were unaffected as long as there was a sufficient amount of free, bulk water at concentrations less than 2 molal TBAC. However, at greater concentrations, adding KCl disrupted the normal TBAC-H2O semiclathrate complex, and KCl was incorporated into new, TBAC-KCl-H2O complexes that melted at higher temperatures than previously reported for similar TBAC-NaCl-H2O complexes.

Thermodynamic and crystallographic properties depending on hydration numbers in tetra-n-butylammonium chloride semiclathrate hydrates

Tetra-n-butylammonium chloride (TBAC) semiclathrate hydrate crystals with hydration numbers n = (26.4–33.2) were prepared from TBAC aqueous solutions over the range of TBAC mole fractions (0.0060–0.0500). The thermodynamic and crystallographic properties of the TBAC hydrates were then investigated via ion chromatography, powder X-ray diffraction (PXRD), and differential scanning calorimetry. The crystal system of the TBAC hydrates with n = (26.4–33.2) was tetragonal, while the crystal structures (PXRD patterns) slightly varied with the hydration numbers. The dissociation enthalpies per guest mole (TBAC) gradually varied with the hydration numbers, from ~149 kJ mol−1 at n = 26.4 to ~187 kJ mol−1 at n = (33.1–33.2). These results suggest that the enthalpies per TBAC increased with greater hydrogen-bond formation in the TBAC hydrate crystals. The dissociation temperatures and dissociation enthalpies per H2O of the TBAC hydrates suggest that the hydrate crystals were most thermally stable at around n = 30 and slightly unstable with higher/lower hydration numbers.

Phase equilibrium data for semiclathrate hydrates formed with tetra-n-butylammonium (bromide or chloride) and tetra-n-butylphosphonium (bromide or chloride) under hydrogen + carbon dioxide pressure

Semiclathrate hydrates are host–guest materials that can be used for CO2 capture due to their unique gas selectivity. CO2 capture from H2 + CO2 mixed gas is possible by semiclathrate hydrates formed by tetra-n-butylammonium (TBA) and tetra-n-butylphosphonium (TBP) salts. TBA bromide (TBAB), TBA chloride (TBAC), TBP bromide (TBPB) and TBP chloride (TBPC) are widely available ionic substances for semiclathrate hydrate formation. In order to understand their gas capture properties, phase equilibrium data of these materials are necessary. Here we report experimental three phase (gas–hydrate–aqueous phase) equilibrium data measured in (TBAB, TBAC, TBPB or TBPC) + H2 + CO2 + H2O systems. The comparison with the literature data suggested that H2 can be incorporated in the TBAB and TBAC hydrates together with CO2, but TBPB and TBPC hydrates reject H2. The hydrate phases were identified by single crystal X-ray diffraction analyses. The TBAB, TBPB and TBPC form the same or similar hydrate phases, i.e., orthorhombic and hexagonal phases. The TBAC formed the tetragonal hydrate phase. The present results suggest that different CO2 capture properties are obtained by these semiclathrate hydrates.

Experimental measurement and thermodynamic modeling of hydrate dissociation conditions for (CO2 + TBAC + cyclopentane + water) system

In this communication, experimental data of hydrate dissociation conditions for (CO2 + tetra n-butylammonium chloride (TBAC) + cyclopentane (CP) + water) system is reported in the temperature range of (286–293) K, the pressure range of (0.97–3.51) MPa, and at various concentrations of TBAC (0.05, 0.10, 0.18 and 0.25 mass fractions). The experiments were carried out using an isochoric pressure-search method to obtain the experimental data and the method validity was checked by re-generating (CO2 + TBAC) hydrate data reported in literature. A thermodynamic model was developed to estimate the experimental hydrate dissociation conditions, which employs e-NRTL activity coefficient model and PR equation of state to model the liquid and the vapor/gas phases and van der Waals – Platteeuw (vdW-P) theory to model the hydrate phase. Experimental hydrate dissociation conditions at 0.05, 0.10 and 0.25 TBAC mass fractions were used to obtain the parameters of the thermodynamic model. Using the obtained parameters, the hydrate dissociation conditions at 0.18 mass fraction of TBAC were predicted. The predicted values are in a reasonable agreement with the experimental data demonstrating the success of modeling. The average absolute relative deviation (AARD %) for the model is about 3.5%.