Oxygen atmospheric residence time

An Equilibrium Model for the Sea Abstracting from the complexity of nature, an idealized counterpart of the oxic ocean (atmosphere, water, sediment) may be visualized. Oxygen obviously is the atmospheric oxidant that is most influential in regulating (with its redox partner, water) the redox level of oxic water. It is more abundant—within the time span of its atmospheric residence time—in the atmosphere than in the other accessible exchange reservoirs. It is chemically and biologically reactive its redox processes (photosynthesis... 

The 0XC0 reactions are being studied using several laboratory-scale reactors to determine the influence of process variables such as oxygen level, residence time, temperature and pressure on metnane conversion and selectivity to products. Methane conversion is definea as the percentage of input methane converted to total products, ano selectivity as the amount of methane converted to a particular product expressed as a percentage of the total methane converted. The results presented here were obtained in a fixed-bed reactor (20 mm i.d. x 39 mm 17.3 g catalyst) which was operated at 770°C and atmospheric pressure. 

The majority of thermal polymerizations are carried out as a batch process, which requires a heat-up and a cool down stage. Typical conditions are 250—300°C for 0.5—4 h in an oxygen-free atmosphere (typically nitrogen) at approximately 1.4 MPa (200 psi). A continuous thermal polymerization has been reported which utilizes a tubular flow reactor having three temperature zones and recycle capabiHty (62). The advantages of this process are reduced residence time, increased production, and improved molecular weight control. Molecular weight may be controlled with temperature, residence time, feed composition, and polymerizate recycle. 

Stabilizers counter the effect of the high temperatures and the oxygen rich atmosphere experienced by the resin during the rotational molding process. Since some rotational molded parts require up to one hour of residence time in the oven, such stabilizers are essential. Without them, the polymer would lose its inherent properties, becoming unfit for the final application. 

Results of an experimental program in which aluminum particles were burned with steam and mixtures of oxygen and argon in small-scale atmospheric dump combustor are presented. Measurements of combustion temperature, radiation intensity in the wavelength interval from 400 to 800 nm, and combustion products particle size distribution and composition were made. A combustion temperature of about 2900 K was measured for combustion of aluminum particles with a mixture of 20%(wt.) O2 and 80%(wt.) Ar, while a combustion temperature of about 2500 K was measured for combustion of aluminum particles with steam. Combustion efficiency for aluminum particles with a mean size of 17 yum burned in steam with O/F) / 0/F)st 1-10 and with residence time after ignition estimated at 22 ms was about 95%. A Monte Carlo numerical method was used to estimate the radiant heat loss rates from the combustion products, based on the measured radiation intensities and combustion temperatures. A peak heat loss rate of 9.5 W/cm was calculated for the 02/Ar oxidizer case, while a peak heat loss rate of 4.8 W/cm was calculated for the H2O oxidizer case. 

However, formaldehyde can be rapidly destroyed through radical reactions or even decomposed by oxygen at very short residence times. This is one of the main reasons why formaldehyde selectivity is low at high conversions. Apart from this, it is difficult to compare the gas-phase and heterogenous reactions because there is a pressure gap and temperature gap, i. e., moderately high pressure and low temperatures in the purely gas-phase oxidation and high temperature and atmospheric pressure in the heterogenous oxidation. 

In this paper, we summarize results from a small scale methane direct oxidation reactor for residence times between lO and lO seconds. For this work, methane oxidation (using air or oxygen) was studied over Pt-10% Rh gauze catalysts and Pt- and Rh-coated foam and extruded monoliths at atmospheric pressure, and the reactor was operated autothermally rather than at thermostatically controlled catalyst temperatures. By comparing the steady-state performance of these different catalysts at such short contact times, tiie direct oxidation of methane to synthesis gas can be examined independent of the slower reforming reactions. 

Catalytic tests of n-pentane oxidation were carried out in a laboratory glass flow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst diluted with inert material. Feed composition was 1 mol% n-pentane in air residence time was 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. The products were collected and analyzed by means of gas chromatography. A FlP-l column (FID) was used for the separation of C5 hydrocarbons, MA and PA. A Carbosieve Sll column (TCD) was used for the separation of oxygen, carbon monoxide and carbon dioxide. 

The influence of the reactor temperature on the conversion of methane was examined during pulsed operation. The heat performance of the foil heater was slowly increased while the reactor was continuously supplied with gas pulses consisting of pure oxygen at 129.5 ml min-1 together with a flow of methane (0.5 ml min-1). The volume flow of the carrier gas nitrogen was adjusted to 130 ml min-1 at atmospheric pressure, delivering a residence time in the coated spiral of 0.4 s. The cat-... 

Given that the flow of oxygen into and out of the Earth s atmosphere is 3 x 1014 kg/year, what is the residence time of oxygen in the Earth s atmosphere ... 

Strategy. Because we are given the flow into and out of the compartment (the Earth s atmosphere), we need to know the stock (M) so that we can divide one by the other and get a residence time (r = M/F). Although we do not know the stock, we do know the concentration of oxygen in the atmosphere (21%). Thus, to calculate the stock of oxygen in the Earth s atmosphere, it is convenient to use the volume of the atmosphere at 15°C and at 1 atm pressure, which we figured out above to be 4.3 x 1021 L, and to multiply that by the concentration. Then, we just have to convert units to calculate the mass of oxygen in kg. 

Instead of using an inert purge gas to blanket the polymer in the chamber the chamber atmosphere can also be evacuated to remove air/oxygen. Pyrolysis under vacuum reduces the incidence of secondary reactions in the gas phase in contrast to pyrolysis at atmospheric pressure. Under vacuum, the residence time of the pyrolysis products is short and so the secondary reactions are limited. 

As described previously pyrolysis is a process that thermally degrades organic waste at high temperatures in absence of air and oxygen. This process can be carried out in a rotary kiln reactor or in a fluidized bed. In a rotary kiln process the feed material is conveyed through a rotating drum (i.e. reactor) and is then pyrolysed in the hot atmosphere into gas and solid residues. The residence time of the reaction is dependent on the rotating... 

Volatilization of selenium from volcanoes, soils, sediments, the oceans, microorganisms, plants, animals, and industrial activity all contribute to selenium in the atmosphere. Natural background concentrations of selenium in nonvolcanic areas are only around 0.01-1 ngm , but the short residence time, usually a matter of weeks, makes the atmosphere a rapid transport route for selenium. Volatilization of selenium into the atmosphere results from microbial methylation of selenium from soil, plant, and water, and is affected by the availability of selenium, the presence of an adequate carbon source, oxygen availability, and temperature (Frankenberger and Benson, 1994 Jacobs, 1989). 

The build-up of the original, photosynthetically-generated oxygenated atmosphere resulted from an evolutionary lag between the event of photosynthesis and that of the oxidative respiration that followed. Its maintenance, however, throughout the latter eons was essential to keep the organic cycle operative. Because the residence time of O2 in the present atmosphere is relatively short in the geological sense (6000 y Holland,... 

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