Oxidation Pressure

Dual-Pressure Process. Dual-pressure processes have a medium pressure (ca 0.3—0.6 MPa) front end for ammonia oxidation and a high pressure (1.1—1.5 MPa) tail end for absorption. Some older plants still use atmospheric pressure for ammonia conversion. Compared to high monopressure plants, the lower oxidation pressure improves ammonia yield and catalyst performance. Platinum losses are significantiy lower and production mns are extended by a longer catalyst life. Reduced pressure also results in weaker nitric acid condensate from the cooler condenser, which helps to improve absorber performance. Due to the spHt in operating conditions, the dual-pressure process requires a specialized stainless steel NO compressor. 

Oxydehydrogenation of /i-Butenes. Normal butenes can be oxidatively dehydrogenated to butadiene in the presence of high concentration of steam with fairly high selectivity (234). The conversion is no longer limited by thermodynamics because of the oxidation of hydrogen to water. Reaction temperature is below about 600°C to minimise over oxidation. Pressure is about 34—103 kPa (5—15 psi). 

Additive Oxidizer Pressure, torr C2H2 Air 760 C2H2 Oxygen 4 Order of Dependencea C2H4 Oxygen 4... 

Oxidative pressure acid leaching is also applied to copper-nickel mattes. Nickel recoveries of >99% are obtained when leaching is carried out at 135-160 °C at oxygen partial pressures of 140-350 kPa,... 

Parker, E.G., "Oxidative Pressure Leaching of Zinc Concentrates", Fifth Annual District Six Meeting of CIMM, Kimberley, B.C.,... 

Arsenic is oxidised, mainly to arsenious oxide, when heated in nitrous oxide 8 the reaction becomes appreciable at 250° to 270° C. and ignition occurs at 400° to 450° C. This reaction takes place specifically between arsenic and the nitrous oxide and is not due to reaction with oxygen after thermal decomposition of the nitrous oxide, as such decomposition does not occur below 400° C. and is very slight at 460° C. Nor does the reaction resemble that which occurs in oxygen, except that, like the reaction in the dark with the latter gas (see p. 47), it is a surface reaction. No chemi-luminescence is observed, however, and there is no upper critical oxidation pressure. At 360° C. the product contains at least 99 per cent, of pure arsenious oxide, and at 420° C. it contains about 5-8 per cent, of arsenic pentoxide. 

At high NO pressures quenching of Hg 6(3Pi) atoms by NO becomes important. Under such conditions, NO(4II) molecules are formed, and these species are capable of directly decomposing the alkane molecule. This type of reaction is very probably responsible for the observed decrease in the relative yields of normal radicals at high nitric oxide pressures. 

Appropriate parameters should follow linear Arrhenius behavior as a function of temperature (69). The model must demonstrate oxidant pressure dependence (78), memory effects as a function of growth temperature (83), and substrate doping effects on oxidation (84). 

Arulsamy, N. et al., J. Amer. Chem Soc., 2001, 123(44), 10860 Reaction of acetone with nitric oxide in presence of alkali alkoxides gives various diazene A-oxide- A -hydroxylate salts (RN(0)=N0Met, also called diazenediolates), such as the disodium methanebis- or trisodium methanetris- compounds according to nitric oxide pressure. Potassium alkoxides behaved similarly, but lithium only formed a bis- compound. These compounds are explosive. The sodium bis- hydrate shattered a DSC apparatus. 

A second problem with nitrous oxide was its property of cooling dramatically when allowed to expand very rapidly on going from high pressure to low pressure. This resulted frequently in ice formation on the cylinder head, and poor gas flow stability. To avoid the consequential loss in precision, cylinder heads were often warmed, or a ballast tank at an intermediate pressure could be used as a stabilizer.9 Most modern AAS instruments employ quite high oxidant pressures and flow rates in the interests of safety, in spite of the greater cost, and this problem is less common than it used to be. 

Low Pressures.—The velocity of oxidation of phosphorus vapour at low pressures has been further investigated by Semenoff,4 who found that an inert gas increases the reaction velocity and lowers the lower critical oxidation pressure. The subject was taken up at this point by Melville.5... 

Oxidation (pressurized oxygen) 10mg/2mL with pressurized oxygen in closed headspace vial (80-300psi), protect from light. 1, 2, and 3 days... 

FIGURE 9.26 Time dependence of permeability coefficients for the mixture of gases CH4/C2H4/C2H6 (71%/19%/10% mol) for the membrane based on poly-2,6-dimethyl-l,4-phenylene oxide (pressure of the mixture 5x10 Pa, 7= 298 K). (From Lapkin, A.A., Roschupkina, O.P., and Dinitch, O.M., J. Membr. Sci., 141, 223, 1998.)... 

In most practical combustion installations there are two separate parts of the equipment system (1) the burner itself and (2) all of the peripheral equipment necessary to control the burner operation efficiently and safely. The control equipment includes fuel and oxidant pressure and flow controls automatic shutoff controls flame supervision equipment furnace purge equipment and other related devices. The safety issues of the burner are significantly different in character as compared with the safety issues of the control equipment. In many ways, these two safety issues are diametrically opposed. Within the burner, fire is a desired condition, whereas within the control system and surrounding environment, fire is to be avoided entirely. 

Colloc h, N., Sopkova-de Oliveira Santos, J., et al. (2007). Protein crystallography under xenon and nitrous oxide pressure Comparison with in vivo pharmacology studies and implications for the mechanism of inhaled anesthetic action. Biophysical Journal, 92(1), 217-224. 

Ruhr-Zinc GmbH (the first zinc smelter in Europe) defined a concept, which eliminated these two problems (Veltman and Weitz 1982). It used sulfuric acid, oxidizing pressure-leaching of zinc sulfide, with which Fe(III) ions take over a catalytic role by constant oxidation with oxygen. The resulting elementary sulfur can be produced in either liquid or solid form by further pressure-leaching of the residues. Pyrite (FeS) can also be used for meeting the sulfuric... 

Because of manufacturing demands for lower process temperatures, interest in two alternative oxidation techniques has been rekindled. One technique is high pressure oxidation. From the L-P model we can see that an increased oxidant pressure will accelerate transport across the growing film and thereby increase the rate. This technique was identified in the 1960 s (27) but was ahead of... 

Substrate Temperature (°C) Catalyst Co Mn Br (mol mohmol) Oxidant Pressure Time (bar) (h) Condi- Substrate Yieid tions concentration (%) Selectivity Refere nces ... 

Charged atom Physisorption Surface oxidation Pressure... 

Pressure-reducing valves two gauge, two-stage pressure regulators to maintain fuel and oxidant pressures somewhat higher than the controlled operating pressures of the instrument. 

---