Ammonia simulation

In this paper we review the results of our systematic work on the catalytic and adsorptive properties of transition metal carbides (titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and iron). We focus our attention on the oxidation of hydrogen, carbon monoxide, ammonia, and the oxidative coupling of methane. The first two reactions are examples of complete (non-selective) oxidation, while the oxidation of ammonia simulates a selective oxidation process. The reaction of oxidative coupling of methane is being intensively explored at present as a means to produce higher hydrocarbons.5 10... 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

The relative susceptibHity of several commercial aHoys is presented in Table 8. The index used is a relative rating based on integrating performance in various environments. These environments include the harsh condition of exposure to moist ammonia, Hght-to-moderate industrial atmospheres, marine atmosphere, and an accelerated test in Mattsson s solution. The latter testing is described in ASTM G30 and G37 (35,36) and is intended to simulate industrial atmospheres. The index is linear. A rating of 1000 relates to the most susceptible and zero designates immunity to stress corrosion. 

Figure 6. A complete ammonia plant process flow diagram. (Used with permission of Simulation Sciences Inc.)...

Armrmanto, R., Schwenk, C.F. and Rode, B.M. (2004) Gold(I) in Liquid Ammonia Ab Initio QM/MM Molecular Dynamics Simulation. Journal of the American Chemical Society, 126, 993—99354. 

Ammonia oxidation was a prototype system, but subsequently a number of other oxidation reactions were investigated by surface spectroscopies and high-resolution electron energy loss spectroscopy XPS and HREELS. In the case of ammonia oxidation at a Cu(110) surface, the reaction was studied under experimental conditions which simulated a catalytic reaction, albeit at low... 

Figure 5.2 Oxygen states present at the ends of -Cu-O-Cu-O- chains are established as the active sites in ammonia oxidation at Cu(110) from a Monte Carlo simulation of the growth of the oxygen adlayer. The reactivity (the experimental curve) is best fitted to the atoms present at chain ends. (Reproduced from Ref. 7).

Follow-up investigations of the earlier spectroscopic studies6 were designed to simulate a catalytic reaction, albeit at low pressures, with both chemical and structural information available from XPS and STM, respectively. With a 30 1 ammonia-to-oxygen ratio imide strings were formed11 at 290 K running in the... 

The development of an SCR system for vehicle applications requires precise calibration of the amount of urea injected as a function of the quantity of NO emitted by the engine, exhaust temperature and catalyst characteristics. Although model simulations can help in the control, it is necessary to use specific NO sensors which, however, still have problems of sensitivity and transient response. Installing a clean-up catalyst for ammonia would provide more latitude and obtain higher NO conversion ratios without re-emission of ammonia into the atmosphere. 

As already mentioned, hydrogen cyanide is formed in simulation experiments using reducing primeval atmospheres. CN was discovered in interstellar space as early as 1940 by optical spectroscopy (Breuer, 1974), and later HCN itself (from measurements using millimetre wavelengths). Only a few years after the Miller-Urey experiments, Kotake et al. (1956) obtained HCN in good yields by reacting methane with ammonia over aluminium-silicate contacts ... 

Marchi, M. Sprik, M. Klein, M. L., Calculation of the free energy of electron solvation in liquid ammonia using a path integral quantum Monte Carlo simulation, J. Phys. Chem. 1988, 92, 3625-3629... 

The reaction of ammonia and hydrogen chloride in the gas phase has been the subject of several studies in the last 30 years [56-65], The interest in this system is mainly that it represents a simple model for proton transfer reactions, which are important for many chemical and biological processes. Moreover, in the field of atmospheric sciences, this reaction has been considered as a prototype system for investigation of particle formation from volatile species [66,67], Finally, it is the reaction chosen as a benchmark on the ability, of quantum chemical computer simulations, to realistically simulate a chemical process, its reaction path and, eventually, its kinetics. 

SHERLOCK, R.R. and GOH, K.M. (1984). Dynamics of ammonia volatilisation from simulated urine patches and aqueous urea applied to pasture. I. Field experiments. Fertilizer Research 5,181-196. 

Hydrogen sulfide (H2S), hydrogen chloride (HCl) and ammonia (NH3) are impurities typically found in coal gas. Some of these substances may be harmful to the performance of SOFCs. Recent experiments (35) have used a simulated oxygen-blown coal gas containing 37.2% CO/34.1% H2/0.3% CH4 /14.4% C02/13.2% H2O/0.8% N2. These experiments have shown no... 

We first considered applications of this approach within process engineering. Steady-state flowsheeting or simulation tools are the workhorse for most process design studies the application of simultaneous optimization strategies has allowed optimization of these designs to be performed within an order of magnitude of the effort required for the simulation problem. An application of this strategy to an ammonia synthesis process was presented. Currently, flowsheet optimization is widely available commercially and has also been installed on the FLOWTRAN simulator for academic use. 

Aqueous solutions of ammonium sulfate and ammonium bisulfate were deposited on Fluoropore filters, placed in the direct insertion probe, and analyzed in the chemical ionization mode (H2O reagent) gas. The samples were heated from 100°C to 330 C at 15 C/minute. No sample ions were observed under these anlaysis conditions, even when several micrograms of ammonium salts were analyzed. The thermal decomposition of ammonium salts of sulfate has been the subject of many studies. (29,30) Some pathways include sulfuric acid production at one stage of the decomposition while others suggest ammonia, SO2 and SO3 are the products. None of these accurately simulate the conditions (temperature, pressure, gas flow) present in our chemical ionization source. However, no sulfuric acid ions (H3SO4+, etc.) were ob-served... 

Tronconi et al. [46] developed a fully transient two-phase 1D + 1D mathematical model of an SCR honeycomb monolith reactor, where the intrinsic kinetics determined over the powdered SCR catalyst were incorporated, and which also accounts for intra-porous diffusion within the catalyst substrate. Accordingly, the model is able to simulate both coated and bulk extruded catalysts. The model was validated successfully against laboratory data obtained over SCR monolith catalyst samples during transients associated with start-up (ammonia injection), shut-down (ammonia... 

The same model was applied to the simulation of typical transients occurring during the operation of industrial SCR monolith reactors in large power plants. In all cases it was found that the change in NO outlet concentration is considerably delayed with respect to the variation of the inlet NH3 concentration. This is unfavorable for a feedback control system using the ammonia feed as the control variable and makes... 

The chloride exchange reaction in water is modeled in Monte Carlo simulations using the same approach as that described for the proton transfer reaction between ammonium ion and ammonia. The potential of mean force for the Sn2 reaction of C f + CH3C1 —> C1CH3 + C f obtained with the HF/6-31 G(d)... 

Compared with the surprising variety of biochemical compounds that can be readily synthesized in Miller-type one-pot simulation experiments, the suite of organics produced under the conditions proposed by Wachtershauser is quite limited. However, the impressive demonstration that the FeS/H2S combination can reduce nitrogen to ammonia shows that considerable attention should be given to the reducing power of pyrite formation. Primordial life may have not been autotrophic, but should we hesitate to accept the idea that the primitive soup was formed from both extraterrestrial sources and endogenous synthesis in which pyrite production played a role After all, a spicy, thick bouillon is always tastier than a bland, diluted broth. 

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