Pure Liquid Ammonia Research Articles

A hybrid forces Quantum Mechanical Charge Field Molecular Dynamics of Cs+ ion in aqueous ammonia: A solvation lability, “structure breaking” phenomenon and hydrogen bond properties

AbstractThe dynamics and structure of Cs+ solvation in an aqueous ammonia solution have been investigated using the Quantum Mechanical Charge Field Molecular Dynamics (QMCF‐MD) simulation method. The system contained 18.6% ammonia in aqueous solution at 298.15 K. The QM region was set to a radius of 7.0 Å to include the first and second solvation shells. The Hartree‐Fock (HF) level was applied to calculate the ion‐ligand and ligand–ligand interactions in the QM region using the LANL2DZ‐ECP basis set for the ion and DZP‐Dunning for the ligands. The radial distribution revealed only one solvation shell, indicating a labile solvation structure. The various coordination number of ligands suggests an instant exchange between them. The mean residence times of 1.29 and 0.9 ps were less than in the pure water and liquid ammonia system, indicating higher mobility ligands of the aqueous ammonia system. The preferential factor 0.55 supports the hypothesis that the Cs+ ion prefers to be dissolved in water. As the ligands moves further away from the ion, the observed number of hydrogen bonds increases, revealing the “structure‐breaking” property of the Cs+ ion. The minimum angle ligand‐ion‐ligand tends to be higher near the ion, confirming this phenomenon.

Can’t we negotiate the importance of electron correlation? HF vs RIMP2 in ab initio quantum mechanical charge field molecular dynamics simulations of Cu+ in pure liquid ammonia

The impact of electron correlation in quantum mechanical charge field molecular dynamics (QMCF MD) simulations of Cu+ in pure liquid ammonia has been investigated by comparing the results obtained at the Hartree–Fock (HF) level and via resolution-of-identity second order Møller–Plesset perturbation theory (RIMP2). To achieve a manageable computational demand, a rigid-body solvent model was employed to describe the NH3 molecules. The solvation structures observed in both cases have similar characteristics in which tetrahedral [Cu(NH3)4]+ dominates with average CuN distances of 2.24 (HF) and 2.12 (RIMP2) Å, respectively. The ligand dynamics in the first solvation shell of the RIMP2 simulation are notably higher than in the HF case and resulted in the formation of an intermediate [Cu(NH3)3]+ complex along the sampling period. Electron correlation effects were found to mainly impact the solvent–solvent hydrogen bonding interaction, thereby providing a more accurate description of the structural properties in terms of the average CuN distances along with greatly enhanced ligand exchange dynamics occurring between the first and second solvation shell.

Liquid ammonia spray combustion in two-stage micro gas turbine combustors at 0.25 MPa; Relevance of combustion enhancement to flame stability and NOx control

The development of liquid ammonia spray combustion technology is expected to reduce the cost and size of gas turbines otherwise fueled with gaseous ammonia. However, successful studies on this topic are scarce due to the difficulty in flame stabilization. In this study, the flame stability and emissions control in liquid ammonia spray combustion is studied for the first time for input thermal power up to 230 kW using novel two-stage gas turbine combustors with and without slot film cooling at 0.25 MPa. The experiments were conducted in a micro gas turbine combustor test facility originally developed for gaseous ammonia combustion. The results show that the injection of liquid ammonia spray into a methane-air flame encouraged rapid cooling of the combustor liner head, enhancing flame blowoff. The blowoff limit based on ammonia fraction in the fuel showed a strong dependence on the combustor temperature, hence the combustor without slot film cooling extended the blowoff limit allowing the successful stabilization of pure liquid ammonia spray flame. Result of emissions analysis showed that two-stage rich-lean combustion is effective in controlling emissions from the flames, however, requires further enhancement of the flame in the primary combustion zone. An increase in combustor inlet temperature and a decrease in combustor wall heat loss, both of which enhanced the combustion of the liquid spray, resulted in a decrease in the emissions of NO, NO2, N2O, NH3, HCN and CO from liquid ammonia co-fired with methane. Conversely, pure liquid ammonia spray combustion resulted in higher emissions of NH3, NO and N2O than did the co-combustion with methane, encouraged by inhomogeneity in droplets distribution and larger heat transfer to the liquid droplets.

Theoretical insight on the solvation properties of Zn2+ in pure liquid ammonia: A quantum mechanical molecular charges field molecular dynamics (QMCF-MD) study

In this work, the structural and dynamical properties of Zn2+ in pure liquid ammonia have been investigated via a quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach. The average equilibrium Zn–N distance in the first solvation shell resulting from the radial distribution analysis is 2.15 Å. Even though the complex displays a high rate of ligand exchange compared to Zn2+ in aqueous solution, the result imply that NH3 is the preferred ligand compared to H2O. This result of this simulation studies provide a fundamental understanding of the characteristic of this metal ion in pure liquid ammonia, which is inter alia essential in the development of applications for CO2 capture based on Zn2+-containing NH3 solutions.

Carbon dioxide in liquid ammonia: An ab initio Quantum Mechanical/Molecular Mechanical Molecular Dynamics Thermodynamic Integration (QM/MM MD TI) simulation study on structure, dynamics and thermodynamics of solvation

In this work, the first investigation of the structural, dynamical and thermodynamical properties of solvated CO2 in liquid ammonia using a recently developed Quantum Mechanical/Molecular Mechanical Molecular Dynamics Thermodynamic Integration (QM/MM MD TI) approach has been carried out. The correlated resolution-of-identity Møller-Plesset Perturbation Theory (RI-MP2) ab initio level of theory has been applied to treat CO2 and its entire first solvation shell. In contrast to aqueous CO2, a negative value for the absolute solvation free energy of −25.9 ± 1.5 kJ/mol was found. This latter value reflects that the solute-solvent interaction is more favorable in liquid ammonia solution. In order to obtain a detailed structural characterisation of solvated CO2, the evaluation of radial distribution functions was performed in conically restricted regions with respect to the main axis of the CO2 molecule. The presented data provides detailed information on the solvation properties of CO2 in pure liquid ammonia. Since knowledge about the latter is a key prerequisite to understand CO2-capture in ammonia solutions, the simulation results can be expected to act as a valuable reference.In addition, the detailed analysis of the individual QM/MM energy contributions showed that the overall potential energy is not affected by artificial contributions, which might influence the determination of solvation free energy.

Co3+ and Ir3+ in pure liquid ammonia: Structure and dynamics from ab initio quantum mechanical charge field molecular dynamics

Abstract The solvation properties of Co3+ and Ir3+ in pure liquid ammonia have been investigated via ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations. During the simulation time of 20 ps, octahedral [Co(NH3)6]3+ and [Ir(NH3)6]3+ complexes were formed in the first solvation shell without the occurance of ligand exchange. The respective average first shell ion distance of Co3+ and Ir3+ were found to be 2.07 and 2.18 A, respectively. The solvation properties in the first shells of each system are found in excellent agreement with experimental data. A number of ligands were exchanged between the second solvation shell and the bulk phase in both systems along the simulation. The associated mean residence times of NH3 ligands in the second shell are 3.06 and 2.47 ps for Co3+ and Ir3+, respectively.

Reactive dyeing of ramie yarn washed by liquid ammonia

The washing efficiency of water, nonionic soap solution, reflux solution, pure liquid ammonia (99.99%), and solvated liquid ammonia was studied on dyed ramie yarns. The ramie yarn samples were dyed with a 2% on weight of fiber (o.w.f) shade with five types of reactive dye by the classical exhaustion method. The washing performances of these solvents were quantified by the dye removal rate, the color uniformity, and the color fastness properties (washing, rubbing, and lightness). Furthermore, the influence of these wash methods on the physical properties of the final yarn samples including shrinkage, tensile strength, and elongation was schematically examined. The results of these measurements revealed that the dye removal rates during the washing in pure liquid ammonia and solvated liquid ammonia were lower than the yarn washed in water, soap solutions, or reflux solutions. The color uniformity (expressed as the standard deviation of K/S values for all dyed ramie yarns) was within the acceptable limits with the satisfactory color fastness levels. The shrinkage values of yarns that were washed in the pure liquid ammonia and the solvated liquid ammonia were both similar (9.0%) and considerably higher than the samples washed in water (1.8%), soap solution (2.4%), or reflux solution (2.6%). The tensile strength and the elongation of the resultant yarns improved significantly when the samples washed in pure liquid ammonia. The yarns that were washed in the solvated liquid ammonia solutions had decreased tensile strength and elongation. The cause of the decrease was determined by the XRD measurements, which confirmed that the crystallinity, and the orientation of these fibers decreased dramatically after being washed in the ammonia system solutions. The samples that were washed in the liquid ammonia had a smoother surface morphology than the other washing processes.

Lignin Depolymerisation and Lignocellulose Fractionation by Solvated Electrons in Liquid Ammonia.

We explored the depolymerisation of several lignins in liquid ammonia at relatively high temperatures and pressures (120 °C and 88 bar). Five different lignins were tested: Indulin AT kraft, Protobind 1000 soda, wheat straw organosolv, poplar organosolv and elephant grass-milled wood lignin (EG MWL). In pure liquid ammonia, all lignins underwent slow incorporation of nitrogen into their structure, resulting in higher molecular weight and polydispersity index. Subsequently, we show a reductive depolymerisation by solvated electrons at room temperature by adding sodium metal to the liquid ammonia without any external hydrogen donor. The netto yields of bio-oil are low for technical lignins (10-23 %), but with higher yields of alkylphenols. In the case of native EG MWL, netto yields of 40 % bio-oil were achieved. Finally, when the room temperature method was applied to poplar wood fibre, we observe improved delignification upon the addition of sodium compared to poplar wood fractionation in pure liquid ammonia.

Lipase catalysed conversion of triglycerides to amides in liquid ammonia

AbstractImmobilised lipase B (Candida antarctica lipase B) is, perhaps unexpectedly, catalytically active in liquid ammonia and exhibits chain length selectivity in the ammonolysis of triglycerides. Using glycerol triacetate as the substrate, the ammonolysis of only the first ester linkage is catalysed by the enzyme, whereas for glycerol tributyrate, the cleavage of all three ester groups is catalysed and converted to the corresponding amide. These observations represent the first example of the use of enzymes in pure liquid ammonia, exemplifying both catalysis and selectivity. Glycerol trioleate is relatively stable in liquid ammonia but, with Candida antarctica lipase B present, readily undergoes ammonolysis to give oleamide and glycerol even at 25 °C. There is no enzyme‐catalysed ammonolysis with the native lipase as it is insoluble in liquid ammonia. The solvolysis of triglycerides in liquid ammonia occurs by a stepwise conversion of the triester to diester to monoester to glycerol with one equivalent of carboxylic acid amide produced at each stage. The pseudo first‐order rate constants for each of the three steps of the uncatalysed ammonolysis of triglycerides in liquid ammonia decrease with increasing alkyl chain length in the carboxyl residue as expected from a small steric effect. Copyright © 2016 John Wiley & Sons, Ltd.

Lignin solubilisation and gentle fractionation in liquid ammonia

It's definitely not water! The complete dissolution of lignin in pure liquid ammonia opens opportunities for converting this abundant yet stubborn biopolymer to useful aromatics under moderate conditions.

Solid sorption cycles: A short history

Adsorption cycles for heat pumping or refrigeration might seem like a relatively new and minor interest in refrigeration research. Fig. 1 from the International Web of Science shows the numbers of papers published over a 30-year period to 2008. It would appear that there was no work done before 1978, but this is not the case. The history of solid sorption systems is long, dating from Faraday (1823). He used the adsorption of large amounts of ammonia into silver chloride as the basis of a thermal compressor to obtain and study liquid ammonia. With the ammoniated silver chloride in one leg of a sealed bent glass tube, upon heating he could repeatedly drive out and condense pure liquid ammonia in the other leg. Although his purpose was to study the liquid, he noted, “When the chloride of silver is allowed to cool, the ammonia immediately returns to it, combining with it, and producing the original compound. During this action a curious combination of effects takes place: as the chloride absorbs the ammonia, heat is produced, the temperature rising up to nearly 100°, whilst a few inches off, at the opposite end of the tube, considerable cold is produced by the evaporation of the fluid”. The practical significance was noted and a range of refrigerating machines was developed over the remainder of the century.

Stability of InP oxide versus solvated electrons in liquid ammonia

Abstract In alkaline aqueous medium (pH 9), potassium ferricyanide was used as an oxidizing agent on InP. This electroless process was successfully controlled by capacity measurements, AFM and XPS analyses. For the first time, the chemical stability of the oxide has been studied against the strongest reducing agent in liquid ammonia (−50 °C): the solvated electron. It was obtained in two ways; an electroless process which involved the addition of metallic potassium and by cathodic galvanostatic treatment on InP in neutral medium. As a first result, the electroless process required a strong rinsing step of the surface by pure liquid ammonia. As a second result, the galvanostatic process gave also promising results. A significant decrease of the amount of oxide was evidenced by capacity measurements, AFM and XPS analyses.

The structure of Co 2+ in liquid ammonia: Monte Carlo simulation including three-body correction

The solvation structure of Co 2+ in liquid ammonia was investigated by the Monte Carlo simulation method. The simulation was carried out for a system containing one Co 2+ and 215 NH 3 molecules with ab initio generated pair and three-body corrected potentials, with the experimental density of pure liquid ammonia at 240 K and 1 atm. of 0.682 g cm −3, corresponding to a periodic cubic of side length 20.86 Å. The results prove the pair potential approximation to fail in predicting correct structural properties of the system. Consideration of the three-body effects reduces the first-shell solvation number of Co 2+ in liquid ammonia from 8 to 6. The arrangement of ammonia ligands in the first solvation shell shows a rather distorted octahedron with average Co–N distance of 2.24 Å.

The role of nonadditive effects in the first solvation shell of Na+ and Mg2+ in liquid ammonia: Monte Carlo studies including three-body corrections

The solvation structure of Na+ and Mg2+ in liquid ammonia has been investigated using the Metropolis Monte Carlo scheme. Simulations have been carried out for four systems namely, one Na+ in 201 NH3 and one Mg2+ in 201 NH3 with and without three-body corrections. With the experimental density of pure liquid ammonia at 277 K and 1 atm of 0.9893 g cm−3, a periodic cubic volume of side length 20.99 Å was yielded. The Na+–NH3 and Mg2+–NH3 pair potentials as well as the corresponding three-body correction functions have been newly developed based on ab initio calculations with a basis set of double zeta quality. The results indicate the failure of the pair approximation in predicting structural properties of both systems: the three-body corrections reduce the first shell coordination number of Na+ and Mg2+ in liquid ammonia from 9 to 8 and from 10 (two of them lying in small peak beyond the first maximum) to 6, respectively.

A Molecular Dynamics Simulation of the Structure of Sodium Ion in Liquid Ammonia

The structural properties of Na1/ammonia solution have been studied by means of a molecular dynamics simulation, the experimental density of pure liquid ammonia being used. In contrast to the previous study for the lithium ion in liquid ammonia, a free orientation of the ammonia molecules in the first solvation shell of the sodium ion has been found. The effects of elevated temperature on the structure function of the cationic solvation shell could be observed clearly i.e., an increase in temperature leads to significant changes in molecular orientation and an increase in the average dipole moment of solvated ammonia. The intramolecular geometry changes of an ammonia molecule relative to the pure liquid were similar to those reported for Li1/ammonia solution.

Ultraviolet absorption by metal–ammonia solutions

BY pulse radiolysis of aqueous solutions at room temperature, new absorption bands for H, OH, D, OD and eaq− in the ultraviolet region down to 188 nm have been observed1,2 and recently confirmed3. The favoured interpretation was a redshift of the absorption band of water caused by perturbation by the solutes (H, D, eaq−) similar to the β-band displacement in alkali halide crystals1. It was also suggested that such a band may exist in liquid ammonia, implying that it is a general phenomenon associated with the solvated electron. Furthermore, the transient spectrum obtained by pulse radiolysis of pure liquid ammonia (−45 °C) shows, in addition to the broad infrared absorption of the solvated electron, two unidentified bands in the ultraviolet region4. To study optical properties in this range, we chose metal–ammonia solutions which are relatively stable although their decomposition leads to the amide ion which itself absorbs strongly in the same region. Our findings strongly support the hypothesis, though amide and hydrogen are the only products and have been thoroughly studied.

Dielectric constant of liquid ammonia from -35 to + 50.deg. and its influence on the association between solvated electrons and cation

The dielectric constant of pure liquid ammonia was measured from -35 to +50$sup 0$C. In addition previous works were reviewed so as to allow the estimation of a best value for the dielectric constant anywhere between -75 and +50$sup 0$C. Anomalies had been reported in the temperature coefficient of the association between solvated electrons and cations. They are explained in the light of these new measurements. (auth)

Specific rates of some reactions of the solvated electron in liquid ammonia measured by pulse radiolysis at 23°C

An experimental procedure is described for measurement by nanosecond pulse radiolysis of specific reaction rates of e − am with solutes in liquid ammonia at 23°C. The measured specific rates, in units of dm 3mol −1s −1, follow in parentheses after each solute: anthracene (3·5×10 11), nitrobenze (2·8×10[su11]), phenanthrene (2·3×10 11), naphthalene (1·5×10 9), acetone (1·7×10 8) and (1·1 × 10 11), dichloromethane (1·2 × 10 11), 1,2-dichloroethane (1·5 × 10 9, acetone (1·7 × 10 8) and 1-chloropropane (1·1 × 10 7). For 18 other solutes an upper limit for the specific rate is given. The upper limit for reaction of e am - with NH 4 + at zero ionic strength is estimated to be 1·6 × 10 8 dm 3 mol −1 s −1. Application of the Smoluchowski-Debye equation for diffusion-controlled reactions to reactions of e am - with a univalent positive ion (model ion NH 4 +), a univalent negative ion (model ion NO 3 -), and a neutral species (assumed radius 3·5 Å) gives 1·4 × 10 12, 2·9 × 10 9 and 2·9 × 10 11 dm 3 mol −1 s −1, respectively, for the specific rates at 25°C. The transient absorption spectrum induced in neat (pure) liquid ammonia at 23°C by nanosecond pulse radiolysis is given for the wavelength range 0·25–1·93 microm. A transient absorption with a peak at 0·38 microm grows for 60 ns after the pulse, and is ascribed to a product of a non-homogeneous process. The absorption spectrum for phenanthrene negative ion in liquid ammonia at 23°C, in the wavelength range 0·38–0·55 microm, is given and calculation of the extinction coefficient at 0·447 microm, wavelength of maximum absorption, gives 8·60 × 10 2 m 2 mol −1.

Liquid ammonia solutions—VIII

Abstract The electronic spectra of aniline, toluidine, anisidine, P-chloroaniline, 2,5-dichloroaniline, N,N-dimethyl-P-phenylenediamine, p-acetamido-N-N-dimethylaniline, and acetanilide have been determined in pure liquid ammonia and in KNH2-liquid ammonia solutions. In the latter solutions, the N-H moieties were converted into the corresponding conjugate bases. An interpretation of the spectra observed is given in terms of the solvent and electronic effects of the substituents on the π → π∗ and N → π∗ transitions of the parent aniline.

Liquid ammonia solutions. IX. An acidity scale for liquid ammonia

LIQUID AMMONIA SOLUTIONS. IX. AN ACIDITY SCALE FOR LIQUID AMMONIA J. H. Takemoto and J. J. Lagowski Department of Chemistry, The University of Texas at Austin Austin, Texas, 78712 ~Reeeived 30 J a n ~ 1970) Since the work of Conant and Wheland (i) and McEwen (2), the subject of the acidities of weak hydrocarbon and nitrogen acids in various nonaqueous solvent systems has been an area of expanding interest (3). There have been numerous qualitative examples of the use of liquid ammonia as a reaction medium in which extremely basic species could exist (4) as well as attempts to establish relative scales of acidities involving a variety of compounds (5-8). Quantitative estimates of the extent of ionization of weak acids in ammonia have been made using potentiometric (9, I0) and spectrophotometric (ii, 12) data. The purpose of this communication is to suggest a method of linking the quantitative results recently obtained on carbon acids using spectroscopic data (ii) to the relative acidities of an extensive series of substituted anilines obtained from nmr measurements (5). As was pointed out earlier (5), the lower acidity limit of the nmr method occurs for compounds with acidities that lie between toluene and diphenylmethane. The spectroscopic method (ii) which depends upon establishing the concentrations of the weak acid, its conjugate base, and amide ion from a quantitative analysis of the spectra of mixtures of these species is not amenable to acids as strong as the anilines for which the nmr method was used. Acids which undergo partial ionization in pure liquid ammonia have been studied spectroscopically (12), however these are much more acidic than the anilines. Thus, the relative acidities of the