Presence Of Tetra-n-butyl Ammonium Bromide Research Articles

Modeling Dissociation Pressure of Semi-Clathrate Hydrate Systems Containing CO2, CH4, N2, and H2S in the Presence of Tetra-n-butyl Ammonium Bromide

Abstract In this study, the phase equilibria of semi-clathrate hydrates of methane (CH4), carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S) in an aqueous solution of tetra-n-butyl ammonium bromide (TBAB) were modeled using a correlation based on a two-stage formation mechanism: a quasi-chemical reaction that forms basic semi-clathrate hydrates and adsorption of guest molecules in the linked cavities of the basic semi-clathrate hydrate. The adsorption of guest molecules was described by the Langmuir adsorption theory and the fugacity of the gas phase was calculated by Peng–Robinson (PR) equation of state (EOS). The water activity in the presence of TBAB was calculated using a correlation, dependent on temperature, the TBAB mass fraction, and the nature of the guest molecule. These equations were coupled together and form a correlation which was linked to a genetic algorithm for optimization of tuning parameters. The results showed an excellent agreement between model results and experimental data. In addition, an outlier diagnostic was performed for finding any possible doubtful data and assessing the applicability of the model. The results showed that more than 97 % of the data were reliable and they were in the applicability domain of the model.

Experimental Investigation of CO2 Hydrate Formation in the Water Containing Graphite Nanoparticles and Tetra-n-butyl Ammonium Bromide

The effects of tetra-n-butyl ammonium bromide (TBAB) and graphite nanoparticles (GN) on phase equilibrium curves, gas consumption, induction time, and ratio of water to hydrate conversion were investigated in this work. Aqueous solutions of the mixture of TBAB and GN with three concentrations of 0.04%, 0.06%, 0.08%, and 0.1% were tested in a stirred reactor. The graphite nanoparticles with a concentration of 0.08% showed the highest hydrate formation rate, revealing that 0.08% is the optimal concentration for the hydrate formation in this study. Comparing the induction time of the pure TBAB system with that of various concentrations of GN, a decrease by 16.6% of induction time at 0.08% GN concentration was observed, while the value decreased by 31.62% at a GN concentration of 0.1%. The final water to hydrate conversion reached the maximum value of 50.75% at a GN concentration of 0.08%. The concentration effect of graphite nanoparticles on the phase equilibrium curve in the presence of TBAB was also studie...

Experiment on the separation of tail gases of ammonia plant via continuous hydrates formation with TBAB

We used hydrate separation method in this paper to recover H2 and N2 from tail gases of ammonia plant in the presence of tetra-n-butylammonium bromide (TBAB). The formation condition of H2/N2/CH4/TBAB hydrates was measured by pressure search method. Then the continuous separation of H2/N2/CH4 via hydrates formation was conducted in the presence of TBAB, and a two-stage separation process was proposed to increase the recovery of H2 and N2. The influences of experimental pressure, temperature and gas flow on the separation results were investigated. The results show that the total concentration of H2 and N2 in the unhydrated gas (recovered gas) is 95.28 mol%, and the total recovery of H2 and N2 is more than 90%. This work supplies the preliminary ideas and fundamental data for the industrial application of hydrate separation method.

High-efficiency separation of a CO2/H2 mixture via hydrate formation in W/O emulsions in the presence of cyclopentane and TBAB

CO2/H2 mixtures, such as integrated gasification combined cycle (IGCC) syngas, were separated via hydrate formation in water-in-oil (W/O) emulsions. The oil phase was composed of diesel and cyclopentane (CP). Span 20 was used to disperse the aqueous phase or hydrate in the oil phase, and tetra-n-butyl ammonium bromide (TBAB) was added to produce a synergistic effect with CP. The experimental results show that the presence of TBAB can remarkably increase the separation ability and improve the flow behavior of the hydrate slurry. The most suitable contents of TBAB in the aqueous phase and water in the emulsion were determined to be 0.29 mol% and 35 vol%, respectively. The maximum separation factor of CO2 over H2 was 103, which is much higher than the literature values for separating CO2/H2 gas mixture via hydrate formation. After a two-stage separation, hydrogen was enriched from 53.2 to 97.8 mol%. The influence of temperature, pressure, and the initial gas–liquid volume ratio on the separation ability and hydrate formation rate were investigated in detail. In addition, a criterion for choosing the suitable operation conditions was suggested based on both phase equilibrium and kinetic factors. Based on this criterion, the suitable operation temperature, pressure, and gas–liquid volume ratio for the separation of CO2/H2 are approximately 270.15 K, 3–5 MPa, and 80–100, respectively.

Enhanced Selectivity of the Separation of CO2from N2during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions

CO2 mitigation is crucial environmental problem and a societal challenge for this century. CO2 capture and sequestration is a route to solve a part of the problem, especially for the industries in which the gases to be treated are well localized. CO2 capture by using hydrate is a process in which the cost of the separation is due to compression of gases to reach the gas hydrate formation conditions. Under pressure, the water and gas forms a solid that encapsulates preferentially CO2 . The gas hydrate formation requires high pressures and low temperatures, which explains the use of thermodynamic promoters to decrease the operative pressure. Quaternary ammoniums salts represent an interesting family of components because of their thermodynamic effect, but also because they can generate crystals that are easily handled. In this work, we have made experiments concerning the equilibrium of (CO2 , N2 ) in presence of Tetra-n-Butyl Ammonium Bromide (TBAB) which form a semi-clathrate hydrate. We propose equilibrium data (pressure, temperature) in presence of TBAB at different concentrations and we compare them to the literature. We have also measured the composition of the hydrate phase in equilibrium with the gas phase at different CO2 concentrations. We observe that the selectivity of the separation is dramatically increased in comparison to the selectivity of the pure water gas clathrate hydrate. We observe also a benefice on the operative pressure which can be dropped down to the atmospheric pressure.

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%.

Preparation and characterization of monodisperse porous silica microspheres with controllable morphology and structure

AbstractA novel method for the preparation of monodisperse porous silica microspheres with controllable morphology and structure is reported. The starting porous polymer microspheres were first functionalized with ethylenediamine (EDA) to generate amino groups. Subsequently, silica nanoparticles were deposited in the porous polymer microsphere to form polymer/silica hybrid microspheres via a modified sol‐gel process in the presence of tetra‐n‐butylammonium bromide (TBAB) or tetramethyl ammonium hydroxide (TMAH). Upon calcination of the polymer/silica hybrid microspheres, the porous silica microspheres were obtained. The morphology, inner structure, and properties of the porous silica microspheres were studied by field emission scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, and mercury intrusion method. The results show that the presence of TBAB or TMAH in the process not only prevents the agglomeration of the hybrid microspheres, but also governs the controllable morphology from a porous inner structure to a hollow‐cage structure. The obtained porous silica microspheres exhibit no shrinkage from the polymer microspheres with a yield of around 98%. These porous silica microspheres have potential applications in the fields of chromatography, catalyst, and biology. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Phase Equilibria of Semiclathrate Hydrate for Nitrogen in the Presence of Tetra-n-butylammonium Bromide and Fluoride

Semiclathrate hydrate phase equilibria for N2 + TBAB (tetra-n-butylammonium bromide) + water mixtures were measured in the temperature range of (280 to 290) K and in the pressure range of (4.0 to 9.2) MPa at TBAB, w (weight fraction) = 0.05, 0.20, 0.40, and 0.60. Also, semiclathrate hydrate phase equilibria for N2 + TBAF (tetra-n-butylammonium fluoride) + water mixtures were measured in the temperature range of (293 to 302) K and in the pressure range of (2.0 to 9.7) MPa at TBAF, w = 0.10, 0.20, 0.34, and 0.45. The equilibrium dissociation temperatures for each pure TBAB and TBAF semiclathrate were also measured at the same concentrations under atmospheric conditions. The presence of TBAB or TBAF remarkably shifted the equilibrium conditions of the double semiclathrates to higher temperature and lower pressure regions when compared with those of the pure N2 hydrate. The highest stabilization effect was observed at the stoichiometric concentrations of each semiclathrate (TBAB, w = 0.40; TBAF, w = 0.34).

Phase equilibrium and dissociation enthalpy for semi-clathrate hydrate of CO 2 + TBAB

The present work investigates equilibrium conditions and dissociation enthalpy of hydrates formed from CO 2–TBAB (tetra- n-butylammonium bromide)–water mixtures. Differential Thermal Analysis (DTA) was used for hydrate–liquid–vapour (H–L–V) equilibrium condition determination in a TBAB concentration range from 4.43 to 9.01 wt% and in a CO 2 pressure range from 0.3 to 2.5 MPa. The results showed that the presence of TBAB allowed decreasing the formation pressure of CO 2 hydrate by approximately 74 and 87% at 283 and 279 K, respectively. Moreover, pressure reductions were dependent on the TBAB concentration. The dissociation enthalpy and the composition of double hydrate formed from 9.01 wt% TBAB solution were determined by both the DTA and Clapeyron equation. The DTA method resulted in 313.2 kJ kg −1 of hydrate for the dissociation enthalpy and 2.51CO 2 ·TBAB ·38H 2O for composition of the double hydrate. For the use of Clapeyron equation, the volume change was defined by taking into account the gas solubility in the liquid phase. The calculation results showed a discrepancy with the experimental data obtained by DTA, suggesting the limited application of Clapeyron equation in the CO 2–TBAB–water system.

Tris[(2‐oxazolinyl)phenolato]manganese(III) as Catalyst for Mild and Efficient Oxidation of Sulfides to Sulfones with Oxone®.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tris[(2-oxazolinyl)phenolato]manganese(III) as catalyst for mild and efficient oxidation of sulfides to sulfones with Oxone®

Tris[(2-oxazolinyl)phenolato]manganese(III), Mn(phox) 3 , catalysed oxidation of dialkyl, diaryl, dibenzyl, and alkyl aryl sulfides to the corresponding sulfones is carried out by Oxone® in biphasic conditions (CH 2 Cl 2 /H 2 O), in the presence of tetra n-butylammonium bromide as phase transfer agent at room temperature in very short reaction times (5 min.) with quantitative yields.

Effect of salt and solvents on the ionic solvation of p-toluidinonaphthalene sulfonate

Fluorescence properties of p-toluidinonaphthalene sulfonate (TNS) are studied in the presence of tetra-n-butylammonium bromide (TBBr) in different solvents. In the presence of TBBr, in solvents of low polarity (tetrahydrofuran, THF), the fluorescence decay of TNS at the blue end (395 nm) is distinctly faster than that at the red end (500 nm). This is attributed to the formation of ionic aggregates involving negatively charged TNS and positively charged tetrabutylammonium ions. From the difference in the lifetimes at the red and blue ends, the ionic relaxation rates are obtained. In solvents of moderately high polarity (dimethylformamide, DMF) no such aggregates are detected and the decay at the red end is very similar to that at the blue end. In highly polar aqueous media, however, micellar aggregates of TBBr are formed, but there is no difference in the decay at the red and blue ends. The micellar aggregates in aqueous media remain unaffected in the presence of 3 mol dm–3 urea.