Mixture Of NH3 Research Articles

Absorption of ammonia into water-in-oil microemulsion in a rotor-stator reactor

Absorption of NH3 into water-in-oil (W/O) microemulsion in a rotor-stator reactor (RSR) was investigated in this work. The microemulsion comprised triton X-100, 1-pentanol, cyclohexane and water while the gas phase was a mixture of NH3 and N2. Experiments were performed to study the mass transfer process between the gas and the microemulsion. The effects of water content on the physical properties of the microemulsion as well as the influences of operating conditions including water content of the microemulsion, rotation speed, liquid volumetric flow rate and gas volumetric flow rate on the mass transfer coefficient (Kya) were investigated. The results showed that the density and viscosity of the microemulsion increased with an increasing water content whereas the Henry’s constant of the NH3-microemulsion system decreased. Kya increased with an increase in water content of the microemulsion, rotation speed, liquid volumetric flow rate and gas volumetric flow rate. A comparison of the Kya of NH3 in the RSR and in a packed tower showed that the Kya of NH3 in the RSR was 65% higher than that in the packed tower under the same operating conditions, thus, revealing that the RSR has higher mass transfer efficiency than the packed tower.

Performance analysis of a low pressure discharge thermal energy combined desalination unit

This study proposes a novel steam recovery cogeneration system, which is based on the low temperature thermal desalination (LTTD) system and named Low Pressure-Discharge Thermal Energy Combined Desalination (LP-DTECD). This technology includes open water and closed power cycles. Utilizing discharged thermal energy from a waste steam in an ammonia plant to cogenerate water and power is one significant of this system. Also, using an eductor instead of a steam jet ejector or a rotary vacuum pump to save valuable steam and make a convenient operation is another merit of the proposed technology. The mixture of NH3–H2O is utilised as working fluid for its closed Rankin cycle. A 28% improvement in the exergy flow was noted as in comparison with the energy waste of the base case. Utilising the LP-DTECD system is economical and demonstrates an improved CO2 emission reduction by 7%.

Investigation of plasma parameters in an active screen cage-pulsed dc plasma used for plasma nitriding

Active screen cage-pulsed dc plasmas are widely used in the material processing applications such as plasma nitriding, carburizing and nitrocarburizing. Specifically for plasma nitriding applications, a H2–N2 mixture is used. In this article, a study of the electron number density (ne), atomic nitrogen density ([N]), electron temperature and the excitation temperature is reported in the presence of an active screen cage-pulsed dc plasma. The ne and are determined here by a triple Langmuir probe, while [N] and are estimated by optical emission spectroscopy (OES). The two temperatures and their ratio are compared for different input parameters (such as applied power, gas pressure and H2 percentage). This study is useful in active screen cage plasma nitriding applications where only few plasma diagnostic measurements have been reported.

Initial growth, refractive index, and crystallinity of thermal and plasma-enhanced atomic layer deposition AlN films

The authors have studied and compared the initial growth and properties of AlN films deposited on Si(111) by thermal and plasma-enhanced atomic layer deposition (ALD) using trimethylaluminum and either ammonia or a N2-H2 mixture as precursors. In-situ spectroscopic ellipsometry was employed to monitor the growth and measure the refractive index of the films during the deposition. The authors found that an incubation stage only occurred for thermal ALD. The linear growth for plasma-enhanced ALD (PEALD) started instantly from the beginning due to the higher nuclei density provided by the presence of plasma. The authors observed the evolution of the refractive index of AlN during the growth, which showed a rapid increase up to a thickness of about 30 nm followed by a saturation. Below this thickness, higher refractive index values were obtained for AlN films grown by PEALD, whereas above that the refractive index was slightly higher for thermal ALD films. X-ray diffraction characterization showed a wurtzite crystalline structure with a (101¯0) preferential orientation obtained for all the layers with a slightly better crystallinity for films grown by PEALD.

The role of NH3 and hydrocarbon mixtures in GaN pseudo-halide CVD: a quantum chemical study.

The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons-NH3-Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located π-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis.

ChemInform Abstract: Crystal Structure of Ammonium Divanadium(IV,V) Tellurium(IV) Heptaoxide.

Abstract(NH4)(VIVO2)(VVO2) (TeO3) is obtained by solvothermal processing of a mixture of V2O5, TeO2, NH3, and H2O (pH 8.5, autoclave, 438 K, 3 d).

Novel recipe for double-hybrid density functional computations of linear and nonlinear polarizabilities of molecules and nanoclusters.

Double-hybrid (DH) density functionals are now among the most applied methods for quantum chemical calculations within density functional theory (DFT). In this work, a new DH density functional is developed for linear and nonlinear optical properties of molecules and hydrogen-bonded nanoclusters. The proposed functional, denominated as PBEDH-P (-P stands for polarizability), is based on Perdew-Burke-Ernzerhof (PBE) exchange and correlation functionals and includes 68% Hartree-Fock exchange and 31% correlation from second-order Møller-Plesset perturbation theory (MP2). From the obtained results, PBEDH-P is shown to be accurate for the calculations of hyperpolarizability, isotropic and anisotropic polarizabilities, and dipole moment of molecules and hydrogen-bonded nanoclusters of H2O (neutral, protonated, and deprotonated), NH3, HF, and binary mixtures of HF-H2O. This novel DH functional not only reveals a considerable improvement in comparison to the recently proposed parameter-free and parametrized DHs but also seems to be superior to the MP2 method in some cases. Moreover, we find that using only contributions of electron pairs with opposite spin for the perturbative part within scaled opposite-spin scheme does not represent a great improvement over PBEDH-P. On the whole, our study nominates PBEDH-P as a promising model for the calculations of electric response properties, where the DH density functionals again come into play and further evidence of the quality of these approximations are highlighted.

Investigation of simultaneous removal of ammonia and hydrogen sulphide from producer gas in biomass gasification by titanomagnetite

A novel hot gas cleaning process using titanomagnetite for the simultaneous removal of ammonia (NH3) and hydrogen sulphide (H2S) from a producer gas in biomass gasification has been developed. In a hot reactor operated at 500–800°C and under atmospheric pressure, NH3 is removed by a decomposition reaction to N2 and H2, whereas H2S is removed by an adsorption reaction. Titanomagnetite was tested using three different gas streams, namely 2000ppmv NH3 in Ar, 2000ppmv NH3 and 230ppmv H2S in Ar, and 2000ppmv NH3 and 230ppmv H2S in a simulated biomass producer gas. From the experimental results, it was discovered that ferrite (α-Fe) was readily formed by the H2 reduction of titanomagnetite and that almost complete decomposition of NH3 (100%) was achieved in Ar gas at 700 and 800°C. The presence of H2S in a gas mixture of NH3 and Ar slightly reduced the catalytic activity for NH3 decomposition at 700 and 800°C (>96%), and H2S adsorption of greater than 98% could be achieved in the same temperature range. Under the coexistence of a simulated biomass producer gas, the NH3 decomposition rate and H2S adsorption rate were decreased at 800°C, which could be due to the high content of H2 (45vol%) in the feed gas that favours the reverse reaction of NH3 decomposition and H2S adsorption, the increased surface coverage of the active α-Fe phase by adsorbed hydrogen, and the competition of α-Fe for the reverse water–gas shift reaction. Moreover, it was discovered that temperature significantly affected the removal of NH3 and H2S in the simulated biomass producer gas and thus the operation temperature needs to be optimised.

A Plausible Simultaneous Synthesis of Amino Acids and Simple Peptides on the Primordial Earth

AbstractFollowing his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH4, NH3, and H2O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine‐containing dipeptides, and 3 glycine‐containing diketopiperazines were detected. Miller’s experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory.

A plausible simultaneous synthesis of amino acids and simple peptides on the primordial Earth.

Following his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH4, NH3, and H2O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine-containing dipeptides, and 3 glycine-containing diketopiperazines were detected. Miller's experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory.

Experimental and modeling study of the effect of elevated pressure on lean high-hydrogen syngas flames

New laminar burning velocity measurements of 85:15% (by volume) H2–CO and H2–N2 mixtures with O2–He oxidizer are reported at lean conditions and elevated pressures (1–10atm). Experiments are conducted using the heat flux method at initial temperature of 298K. In this technique a near adiabatic flame is stabilized by balancing the heat loss from the flame to the burner with heat gain to the unburnt gas mixture such that no net heat loss to the burner is observed. A new facility was designed for such high pressure burner stabilized flame experiments. The results obtained are compared with five chemical kinetic schemes from literature for syngas mixtures at elevated pressures. Large differences are observed between the kinetic schemes and the experiments which can be attributed to certain key chemical reactions. A study of the kinetics is performed through reaction rate and sensitivity analysis which indicate that a high uncertainty still remains in important reactions that drive the production and consumption of species such as H, HO2 and OH. For lean mixtures the reaction H+O2(+M)=HO2(+M) contributes significantly to the deviation of models from the experiments. The present analysis in the lean mixture regime suggests the need for further studies in assessment and modification of rate constants for this reaction.

Determination of Primary Amine Content in Bonding Agent Used in Composite Solid Propellants

AbstractThe primary amine content in tetraethylenepentamine (TEPA) and TEPAN, a bonding agent used in composite solid propellants, was determined by near infrared (NIR) spectroscopy and the results were compared to those obtained by potentiometry. The band at 4930 cm−1, which showed to be influenced only by primary amine groups, was chosen as the analytical band. The calibration curves based on isopropylamine (IPA) and isopropylamine/dibutylamine (IPA/DBA) mixtures proved to be suitable for determining the NH2 content of TEPA or of samples containing mixtures of NH and NH2 groups. It was found that TEPA contains 26.4 % of NH2 and 25.7 % of NH, and that TEPAN contains 0.5 % of NH2, confirming the low content of primary amine of this bonding agent. The lowest amine equivalent of TEPA is 31.1±0.3 g/eq, as determined by potentiometry, was found because this technique measures the total hydrogen content, including primary and secondary amines. The literature value of 62.6 g/eq for TEPA ACROS obtained by potentiometry in a non aqueous medium and related to the first inflection of the primary amine, validates the value obtained by NIR in this work for a similar type of amine. The equivalent weight obtained by NIR spectroscopy (62.7 g/eq) allowed to calculate the molar mass of TEPA of 195.6 g mol−1, which is close to the typical value of 200 g mol−1.

Hydrogen bonding induced proton exchange reactions in dense D2-NH3 and D2-CH4 mixtures.

We have investigated high-pressure behaviors of simple binary mixtures of NH3 and D2 to 50 GPa and CH4 and D2 to 30 GPa using confocal micro-Raman spectroscopy. The spectral data indicate strong proton exchange reactions occur in dense D2-NH3 mixture, producing different isotopes of ammonia such as NH3, NH2D, NHD2, and ND3. In contrast, the proton exchange process in dense D2-CH4 mixture is highly limited, and no vibration feature is apparent for deuterated methane. The vibrational modes of H2 isotopes in D2-NH3 are blue shifted from those of pure H2 isotopes, whereas the modes of D2-CH4 show overall agreement with those in pure D2 and CH4. In turn, this result advocates the presence of strong repulsion and thereby internal pressure in D2-NH3 mixture, which are absent in D2-CH4. In fact, the bond length of hydrogen molecules in D2-NH3, calculated from the present spectral data, is shorter than that observed in pure hydrogen - supporting the enhanced intermolecular interaction in the mixture. Comparing the present spectral results with those previously observed in D2-H2O mixtures further suggests that the strength of repulsive interaction or the magnitude of internal pressure in the mixtures is proportional to the strength of hydrogen bonding in H2O, NH3, and CH4 in decreasing order. Hence, we suggest that the proton exchange is assisted by hydrogen bonding in these molecules.

An exact calculation of the N2+ and H2+ influx at cathode surface in N2–H2 discharges

An exact calculation of N2+ and H2+ influx, at cathode surface in N2–H2 discharge, has been derived using electron impact ionization cross-section at plasma sheath boundary. The analytical formula is very convenient in practical applications. Through the analysis of experimental parameters for glow discharge plasma nitriding, the formula explains, why treatment in an N2–H2 mixture with H2 percentage ∼70% gives most enhanced result.

The formation of carbamate ions in interstellar ice analogues

Carbon dioxide and ammonia are two of the most abundant species in astrophysical media, where they can react in the solid phase under certain conditions. This contribution presents a study of this reaction both in the presence of water and for anhydrous samples. It is shown that after deposition at 15 K, the reaction can start by warming the deposit, and the process continues on up to a temperature of 220 K. Reaction products are studied using infrared spectroscopy and mass spectrometry. For anhydrous samples, a 2 : 1 stoichiometry mixture of NH3 : CO2 gives the highest yield of products. The reaction is favored when a small amount of water is present, which enables ammonia and carbon dioxide molecules to collide within the pores and channels of the amorphous water solid. Large concentration of water, on the other hand, hampers such collisions. The main reaction product is found to be ammonium carbamate, but also carbamic acid is formed, and, in the presence of water, ammonium bicarbonate is produced as well. Theoretical calculations are carried out to provide the basis for the assignment of the spectra. Some of the experiments presented in this contribution consist of the generation of a compact water ice matrix where the carbamate and ammonium ions are embedded. If such a system was found in astrophysical media, it is shown that the ammonium ion could not be detected, whereas two infrared features of the carbamate ion in the 1040 to 1115 cm(-1) (9 to 9.6 μm) region could enable the observation of this species.

Reduction Behaviors of Pellets Under Different Reducing Potentials

Owing to the change of gas composition in top gas recycling-oxygen blast furnaces compared with traditional blast furnace, many attentions are attracted to the research on iron oxide reduction again. In order to study the influence of H2 and CO on the reduction behavior of pellets, experiments were conducted with H2-N2, CO-N2 or H2-CO gas mixtures at 1173 K by measuring the mass loss, respectively. It was found that the reduction degree increased with increasing the ratio of H2 or CO in the gas mixture, but the reduction with hydrogen was faster than that with carbon monoxide. The reduction degree could reach 96. 72% after 65 min for the reduction with 50% H2 + 50% N2, while it is only 53. 37% for the reduction with 50% CO+ 50% N2. The addition of hydrogen to carbon monoxide will accelerate the reduction because the hydrogen molecules are more easily chemisorbed and reacted with iron oxide than carbon monoxide. A scanning electron microscope was used to characterize the structures of reduced samples. Dense structure of iron was obtained in the reduction with hydrogen while the structure of iron showed many small fragments for the reduction with carbon monoxide. At the later stage of reduction with the gas mixtures containing carbon monoxide, the reduction curves showed a descending trend because the rate of carbon deposition caused by the thermal decomposition of carbon monoxide was faster than the rate of oxygen loss. Compared with the reduction with CO-N2 and H2-CO gas mixtures, H2 gas could enhance the carbon deposition while N2 gas would reduce this phenomenon. The results of X-ray diffraction and chemical analysis demonstrated that the carbons are mainly in the form of cementite (Fc3C) and graphite in reduced sample.

Enhanced mass diffusion phenomena in highly defective doped ceria

The densification and grain growth of the solid state ionic conductor material Ce0.9Gd0.1O1.95−δ (i.e. GDC10, gadolinium-doped ceria, with Gd 10mol.%) are analysed for nanometric and fine powders of various particle sizes, both in air and in a 9vol.% H2–N2 mixture. Due to a dominant solute drag effect in aliovalent highly doped ceria, the starting morphology of the powders controls the diffusion mechanisms of the material in air. Conversely, highly enhanced densification and grain growth are achieved by firing the materials at reduced temperatures (800<T<1200°C) in low oxygen activity atmospheres (pO2<10−12atm). Solute drag is not the rate-limiting step in highly defective GDC and the densification mechanisms are nearly independent of the starting powder properties. Fast diffusion is activated under low oxygen activity with high grain boundary mobility (e.g. Mgb∼10−10m3N−1s−1 at 1100°C). The change of the dominant sintering mechanisms under low oxygen activity is attributed to the formation of a large concentration of oxygen vacancies (VO¨), electronic defects (CeCe′, i.e. Ce3+) and reduced Gd/Ce cation mismatch. High densification and electric conductivity are achieved in Ce0.9Gd0.1O1.95−δ at low temperatures (∼1000°C) and low oxygen activity, preserving the mechanical integrity of the material.

2D-THIN LAYER CHROMATOGRAPHY (2D-TLC) FLASH TEST OF 17α-ETHINYLESTRADIOL AND RELATED STEROIDS DETECTED BY FLUORESCENCE DENSITOMETRY

We present a two dimensional (2D) planar chromatographic separation of ethinyl steroids on cyanopropyl phase. A mixture of nine steroids was separated by using a cyanopropyl-coated silica gel plate (Merck, 1.16464) with the solvent mix of dichloromethane, methanol, cyclohexane (95 + 5 + 60, v/v) in the first direction and with a mixture of water, acetonitrile, ethanol, dioxane, and NH3 (25%) (8 + 2 + 1 + 1 + 0.05, v/v) in the second direction. Both developments were carried out over a distance of 70 mm. The steroids were catalytically transformed into fluorescent compounds that can be sensitively detected. The fluorescence was measured by a simple 8-bit CCD-camera. The range of linearity covers two magnitudes of power using the extended Kubelka-Munk expression for data transformation. This separation method is inexpensive, fast, and reliable and can be used to quantify 17α-ethinylestradiol (EE2) in the effluents of waste water treatment plants at an LOD of 2 ng per spot. Using a solid phase extraction pretreatment procedure achieves an LOD of 2 ng L−1 water.

A numerical study on the effects of H2 addition in non-premixed turbulent combustion of C3H8–H2–N2 mixture using a steady flamelet approach

This study has been implemented in two sections. At first, the turbulent jet flame of DLR-B is simulated by combining the k–ε turbulence model and a steady flamelet approach. The DLR-B flame under consideration has been experimentally investigated by Meier et al. who obtained velocity and scalar statistics. The fuel jet composition is 33.2% H2, 22.1% CH4 and 44.7% N2 by volume. The jet exit velocity is 63.2 m/s resulting in a Reynolds number of 22,800. Our focus in the first part is to validate the developed numerical code. Comparison with experiments showed good agreement for temperature and species distribution. At the second part, we exchanged methane with propane in the fuel composition whilst maintaining all other operating conditions unchanged. We investigated the effect of hydrogen concentration on C3H8–H2–N2 mixtures so that propane mole fraction extent is fixed. The hydrogen volume concentration rose from 33.2% up to 73.2%. The achieved consequences revealed that hydrogen addition produces elongated flame with increased levels of radiative heat flux and CO pollutant emission. The latter behavior might be due to quenching of CO oxidation process in the light of excessive cold air downstream of reaction zone.

Effect of thickness on the photoluminescence of silicon quantum dots embedded in silicon nitride films

In this work, the effect of film thickness on the photoluminescence (PL) spectra of Si quantum dots embedded in silicon nitride films is investigated experimentally and theoretically. The films were deposited by remote plasma enhanced chemical vapor deposition using the same SiH2Cl2/H2/Ar/NH3 mixture and deposition conditions, in order to obtain films with similar composition and approximately equal average size (∼3.1 nm) of Si quantum dots. Only the deposition times were varied to prepare five samples with different thicknesses ranging from ∼30 nm to 4500 nm. Chemical characterization by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy were carried out in order to check that the composition in all films was the same. The structure, average size, and size distribution of the Si quantum dots were deduced from High-Resolution Transmission Electron Microscopy. The thickness of the films was determined by ellipsometry and interferometry of UV-Vis transmission spectra. It was found experimentally that the increase of the thickness above a few hundreds of nanometers produces significant distortions of the PL spectra of the films, such as peak shifts and the appearance of shoulders and multiple peaks suggesting interference effects. Comparing the experimental results with theoretical simulations, it is shown that these distortions are mainly due to interference effects and not to intrinsic changes in the films. The approximation used to simulate the PL spectra as a function of film thickness allows improving the fitting between simulated and experimental spectra by changing some optical parameters and can be helpful to further investigate the intrinsic optical properties of the films.