Oxygen in the gas phase

Measurements of oxygen in the gas phase are based on its paramagnetic properties. Any change in the mass concentration of 02 affects the density of a magnetic field and thus the forces on any (dia- or para)magnetic material in this field. These forces on, for example, an electrobalance can be compensated electrically and the current can be converted into mass concentrations further conversion into a molar ratio, e.g. % 02, requires the knowledge of total pressure (Fig. 8). 

Analysis of 02 as well as C02 in exhaust gas is becoming generally accepted and is likely to be applied as a standard measuring technique in bioprocessing. It is possible to multiplex the exhaust gas lines from several reactors in order to reduce costs. However, it should be taken into account that the time delay of measurements with classical instruments is in the order of several minutes, depending on the efforts for gas transport (active, passive) and sample pretreatment (drying, filtering of the gas aliquot). 

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Nickel sulfate also is made by the reaction of black nickel oxide and hot dilute sulfuric acid, or of dilute sulfuric acid and nickel carbonate. The reaction of nickel oxide and sulfuric acid has been studied and a reaction induction temperature of 49°C deterrnined (39). High purity nickel sulfate is made from the reaction of nickel carbonyl, sulfur dioxide, and oxygen in the gas phase at 100°C (40). Another method for the continuous manufacture of nickel sulfate is the gas-phase reaction of nickel carbonyl and nitric acid, recovering the soHd product in sulfuric acid, and continuously removing the soHd nickel sulfate from the acid mixture (41). In this last method, nickel carbonyl and sulfuric acid are fed into a closed-loop reactor. Nickel sulfate and carbon monoxide are produced the CO is thus recycled to form nickel carbonyl. 

Stable intermediates are those where concentration and lifespan are comparable to those of stable reactants and products. An example is the reaction between methane and oxygen in the gas phase at 700 K and 1 atmosphere. The overall reaction is ... 

Gas and liquid systems are explained by solubility. The solubility of oxygen at room temperature is about 10 ppm therefore the concentration of oxygen is 10 ppm (oxygen flux, Na). The solubility of oxygen at 0 °C is double that at 35 °C. Also, the solubility decreases if the electrolyte concentration is increased. The concentrations of oxygen in the gas phase and liquid phase are related to each other by the Raoult-Dalton equilibrium law. 

As a first approximation, suppose that the concentration of oxygen in the gas phase changes instantly from 20.9% oxygen to 100% oxygen. Then a j will change instantly from 0.219 to 1.05mol/m, and the gas-phase balance is not required. The parameter k , = 0.1 s was specified in Example 11.1 so the only unknown parameter is the liquid holdup, VijV. A typical value for a mechanically agitated tank is 0.9. The liquid-phase balance becomes... 

The effect of oxidizing atmospheres on the reduction of NO over rhodium surfaces has been investigated by kinetic and IR characterization studies with NO + CO + 02 mixtures on Rh(lll) [63], Similar kinetics was observed in the absence of oxygen in the gas phase, and the same adsorbed species were detected on the surface as well. This result contrasts with that from the molecular beam work [44], where 02 inhibits the reaction, perhaps because of the different relative adsorption probabilities of the three gas-phase species in the two types of experiments. On the other hand, it was also determined that the consumption of 02 is rate limited by the NO + CO adsorption-desorption... 

Figure 9.14. Precision and accuracy of the instrument at various concentrations of oxygen as compared to a standard oxygen analyzer (Servomex). The fiber optic sensor monitored the concentration of oxygen in saline solution (continuous stair) in equilibrium with various nitrogen-oxygen gas mixtures monitored by the gas analyzer (dotted staircase). The absolute concentration of oxygen in the gas phase is about 60 times larger than the corresponding equilibrium concentration in the liquid phase. The bath temperature was 37 C For the purpose of comparison both measurements have been scaled to percent oxygen. (From Ref. 21 with permission.)...

Q mall amounts of aliphatic amines profoundly affect the reactions be- tween simple organic molecules and oxygen in the gas phase. Inhibition occurs in the slow oxidation region and, at higher temperatures, ignition is either delayed or prevented. 

The nitrosyldioxyl radical has largely been ignored in the chemical literature because it is relatively unstable in air. Nitrosyldioxyl radical is approximately 4.8 kcal/mol less stable than nitric oxide and oxygen in the gas phase less than 0.1% of the nitric oxide will combine with oxygen under standard conditions in the gas phase. Although present in low concentrations, the infrared spectrum of nitrosyldioxyl radical has been reported in the gas phase (Guillory and Johnston, 1965) and ab initio quantum mechanics calculations have been performed (Boehm and Lohr, 1989). 

Surface reaction between adsorbed reactant and oxygen in the gas phase k k c c A mA React - 02 React 1 React React R —02 1 1 — S —S —... 

The existence of the latter has been recognized for many years, since Wagner (20) applied his thermodynamic theory of defect oxides to the system zinc oxide-oxygen (21). According to this scheme, at sufficiently high temperature an equihbrium sets in between zinc oxide and oxygen in the gas phase, whereby excess zinc (Zn ) can be accommodated in interstitial positions of the lattice ... 

Butadiene is available commercially as a liquefied gas underpressure. The polymerization grade has a minimum purity of 99%, with acetylene as an impurity in the parts-per-million (ppm) range. Isobutene, 1-butene, butane and cis-l- and Zrc//7.s-2-butcnc have been detected in pure-grade butadiene (Miller, 1978). Typical specifications for butadiene are purity, > 99.5% inhibitor (/c/V-butylcatecliol). 50-150 ppm impurities (ppm max.) 1,2-butadiene, 20 propadiene, 10 total acetylenes, 20 dimers, 500 isoprene, 10 other C5 compounds, 500 sulfur, 5 peroxides (as H2O2), 5 ammonia, 5 water, 300 carbonyls, 10 nonvolatile residues, 0.05 wt% max. and oxygen in the gas phase, 0.10 vol% max. (Sun Wristers, 1992). Butadiene has been stabilized with hydroquinone, catechol and aliphatic mercaptans (lARC, 1986, 1992). 

In experiments using oxygen as a ligand, it is the partial pressure of oxygen in the gas phase above the solution, p02, that is varied, because this is easier to... 

Carlier fundamental studies of autoxidations of hydrocarbons have concentrated on liquid-phase oxidations below 100 °C., gas-phase oxidations above 200°C., and reactions of alkyl radicals with oxygen in the gas phase at 25°C. To investigate the transitions between these three regions, we have studied the oxidation of isobutane (2-methylpropane) between 50° and 155°C., emphasizing the kinetics and products. Isobutane was chosen because its oxidation has been studied in both the gas and liquid phases (9, 34, 36), and both the products and intermediate radicals are simple and known. Its physical properties make both gas- and liquid -phase studies feasible at 100°C. where primary oxidation products are stable and initiation and oxidation rates are convenient. 

Results of screening tests with different catalysts in the absence of oxygen in the gas phase. Conditions T = 230°C, 6.0 g of catalyst, 2.9 g of 1 was passed through the catalyst bed within 20-25 min. The catalyst was preheated 30 min prior to its use. 

The initial experiments discussed in this section were performed without oxygen in the gas phase. Figures la and lb show conversion of i and selectivity towards 2 and 3 as a function of time, respectively. Initially, the conversion (65%) as well as the selectivity were stable. However, after 6 hours on stream the catalyst started to be deactivated. The decrease in conversion was accompanied by a decrease in selectivity towards the unsaturated diketone 2 and an increase in that for the saturated diketone 3. The ratio of the hydroxy ketone isomers 1 and 4 was not influenced by the deactivation. 

Further experiments were therefore carried out with oxygen in the gas phase in order to maintain a high concentration of lattice oxygen in the solid phase. In fig.2 conversion vs time plots are shown for experiments in which the molar ratio 02/l was lower than 0.5. After each experiment (2a and 2b) the catalyst (l.Og of H-Cu-0203T) was reactivated in an Oz-He gas stream which restores its initial activity. 

In Figure 5 are shown the concentration profiles of oxygen in the gas phase during various times in the cycle. These curves were obtained from the same bed as the one used for the pressure data. As would be expected, the S-shaped curve moves toward the... 

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