Ammonia/oxygen ratio

The ammoxidation of isobutene has not received much attention. The only contribution in this field is by Onsan and Trimm [2.44] for a rather unusual catalyst, a mixture of the oxides of Sn, V and P (ratio 1/9/3) supported on silica. At 520 C, a maximum selectivity to methacrylonitrile + methacrolein of 80% was reached with a Sn—V—P oxide catalyst (ratio 1/9/3), an isobutene/ammonia/oxygen ratio of 1/1.2/2.5 and a contact time of 120 g sec l ]. The kinetics are very similar to those for the pro-pene ammoxidation. Again, the data are initially analysed by means of (parallel) power rate equations, for which the parameters were calculated, while a more detailed analysis proves that a Langmuir—Hinshelwood model with surface reaction as the rate-controlling step provides the best fit with regard to the two main products. At 520° C, the equation which applies for the production of methacrolein plus methacrylonitrile is... 

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... 

Having validated the mechanism on ammonia-oxygen flames, the yield of NO from nitrogen doped CH4-air flames was examined. Both NH3 and NO doping were investigated. Only post-flame NO concentrations were measured. These are compared with calculations of the full kinetics and with adiabatic equilibrium calculations. The calculated profiles indicate the complexity of the NO dynamics in these flames. The temperature and major species profiles in the undoped flames had been studied in earlier work( ). Three near stoichiometric methane-air flames having initial equivalence ratios(0) of 0.8, 1.0 and 1.2 are diluted with less than 5 volume percents of NH3 or NO. In this section NO concentration is expressed both as a mole fraction and as a fraction of the total nitrogen concentration ... 

For instance, when the degree of ammonia decomposition is only 29.4%, the yield to acrylonitrile is 58.9% at 93.1% propane conversion, with a feed composition propane/ammonia/oxygen/inert equal to 1.0 1.2 3.0 14.8, at 420 °C and W/F 0.5 g s cc . When the same active phase is diluted in silica by means of the spraydrying procedure, the best yield to acrylonitrile achieved is 52.7% at 430 °C [29e], but the addition of a dopant (Yb, Er, Dy, Nd, etc.) increases the yield up to 55-56%. Dopants also allow the feed of a lower ammonia/propane ratio, for example, 0.8 instead of the stoichiometric 1.0, while reaching in high yield to acrylonitrile with respect to ammonia, and minimizing ammonia combustion [29h]. 

Selective Catalytic Reduction (SCR) SCE is a process to reduce NO, to nitrogen and water with ammonia in the presence of a catalyst between 540-840 F (282-449 C). Ammonia is usually injected at a 1 1 molar ratio with the NOx contaminants. Ammonia is used due to its tendency to react only with the contaminants and not with the oxygen in the gas stream. Ammonia is injected by means of compressed gas or steam carriers. Efficiencies near 90% have been reported with SCR. See Exxon Thermal DeNO. ... 

Autotrophic activity. Because of the low C N ratio and its declining value as carbonaceous residues are degraded there is substantial ammonification. With all mean treatment times greater than the doubling time of Nitrobacter sp. nitrification will occur provided that oxygen is not limiting. Smith and Evans (19) found that with DO levels above 15% of saturation, nitrification continued until the culture was limited by a fall in pH level. Up to 40% of the slurry ammonia was oxidised. The autotrophic activity never achieved steady state and cycled between periods of activity when the pH value was above about 5.5 and periods of inactivity when the pH value fell below 5.5. Complete nitrification of all ammonia only occurred if the pH value was controlled at about 7 by the addition of alkali. When the DO level was held within the range of 1 to 15% of saturation a system of simultaneous nitrification and denitrification was established. The reduction of nitrate allowed the pH value to remain above 6 and nitrification to continue. Thus more than 70% of the ammonia was oxidised. If the DO level was held below 0.1% of saturation, nitrification was inhibited (unpublished). 

The first clue to the existence of the SrnI mechanism came from product studies both in aliphatic and aromatic cases. It was noticed that in the reaction of benzyl and substituted benzyl chlorides with the 2-nitropropane anion, oxygen alkylation, yielding the oxime and then the aldehyde, occurs exclusively in the case of benzyl chloride and 3-nitrobenzyl chloride, whereas, with 4-nitrobenzyl chloride, the yield of aldehyde is only 6% and the carbon-alkylated (104) product is obtained in 92% yield (Kornblum, 1975). This was interpreted as the result of a competition between 8, 2 (O-alkylation) and S l (C-alkylation) reactions. In the aromatic case, it was observed that the reaction of 5- and 6-halopseudocumenes with KNHj in liquid ammonia (Kim and Bunnett, 1970) forms the 5- and 6-pseudocumi-dines in a ratio which is the same whether the starting compound is the 5- or 6-isomer in the case of the chloro- and bromo-derivatives, as expected from an aryne mechanism (Scheme 9), whereas much more non-rearranged... 

At present the most effective available after-treatment techniques for NO, removal under lean conditions are ammonia selective catalytic reduction (SCR) [1-3] and NO, storage reduction (NSR) [4—6]. Indeed, three-way catalysts (TWCs) are not able to reduce NO, in the presence of excess oxygen, because they must be operated at air/ fuel ratios close to the stoichiometric value. Also, non-thermal plasma (NTP) and hydrocarbon-selective catalytic reduction (HC-SCR) are considered, although they are still far from practical applications. 

Oxidation of cobalt(ll) to cobalt(lll) by oxygen in the presence of N-hydroxyethylethylenediamine and carbon produces large amounts of ethylenediamine. Other products are formaldehyde, formic acid, and ammonia. The sum of the moles of ethylenediamine and ammonia produced is equal to the total number of moles of cobalt(ll) oxidized. A steady-state concentration of Co(ll)-Co(lll) is established in which the ratio Co(lll)/ Co(ll) = 1.207. Thus cobalt ion behaves as a true catalyst for cleavage of the N-hydroxyethyl-ethylenediamine. The total amount of cobalt(ll) oxidized per unit time, X, was calculated from the derived equation X = 3.8 + 7.0 k2 T — 3.8e-2-2k 1, where k2 = 0.65 hr.—1 The observed rate of formation of ethylenediamine plus ammonia also follows this equation. It is proposed that the cobalt ion serves as a center where a superoxide ion [derived from oxidation of cobalt-(II) by oxygen] and the ligand are brought together for reaction. 

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