Sub-atmospheric pressures

Edmister, W.C. and K.K. Okamoto (1959), Applied hydrocarbon thermodynamics. Part 13 equilibrium flash vaporization for heavy oils under sub-atmospheric pressures . Petroleum Refiner, Vol. 38, No. 9, p. 271. 

Pyrolysis of chlorodifluoromethane is a noncatalytic gas-phase reaction carried out in a flow reactor at atmospheric or sub atmospheric pressure yields can be as high as 95% at 590—900°C. The economics of monomer production is highly dependent on the yields of this process. A significant amount of hydrogen chloride waste product is generated during the formation of the carbon—fluorine bonds. 

Vacuum measurement spans the range from 10 Pa (atmospheric pressure) to pressures that are less than 10 orders of magnitude. Sub atmospheric pressures are divided into six regions for convenience (9) ... 

This equation can be used for an orifice plate introduced into pipework as a measuring, throttling or balancing device, and for a jet discharging gas into the injector of a burner at atmospheric or sub-atmospheric pressure. 

This reaction normally takes place at 700°C and at low pressure ( < 1 Torr). Doping is accomplished by the addition of arsine, diborane, or phosphine. The addition of ozone (O3) to Reaction (6) at atmospheric pressure or sub-atmospheric pressures provides films with excellent properties. H ]... 

B. Sub-atmospheric pressure allows for the hazard of air leakage into equipment. It is only applied for pressure less than 500 mmHg (9.5 bara). 

The production of vacuum (sub-atmospheric pressure) is required for many chemical engineering processes for example, vacuum distillation, drying and filtration. The type of vacuum pump needed will depend on the degree of vacuum required, the capacity of the system and the rate of air inleakage. 

Hydrogen is a stable gas in seclusion, but in air, is very unstable. The flammability properties of such a mixture are well-known at atmospheric pressure, yet little is known about the hydrogen-air mixture at sub-atmospheric pressures. In order to determine the hydrogen reaction limits within a vacuum, a number of experiments were performed and analyzed. The results were used to design a vacuum furnace system and processes with safeguards to protect against a severe hydrogen reaction. 

Air separation by PSA on a large scale is today dominated by machines in which the pressure swing may be from near atmospheric to substantially sub-atmospheric pressure. The industry typically calls these machines vacuum swing adsorption (VSA) separators. A second sub-class in air separation is the machines that use a pressure swing the ranges from somewhat super-atmospheric to sub-atmospheric and these may be called trans-atmospheric PSA. The distinctions made here have implications as to equipment specifications and performance limitations in both bed size factor and O2 recovery. 

From the discussion in the previous section, it is clear that, above all, NO2, and then NO, are the principal oxidizers produced in the flames of nitrate esters. The reaction of NO2 with aldehydes plays an important role in the combustion of nitrate esters, since these molecules are the major decomposition products of these materials in the first stage of combustion. Pollard and Wyatt studied the combustion process of HCHO/NO2 mixtures at sub-atmospheric pressures.They found that the reaction occurs very rapidly at temperatures above 433 K, the NO2 being reduced almost quantitatively to NO, and the aldehyde being oxidized to CO, COj, and H2O. The order of reaction was found to be one with respect to both reactants. The same result has been reported by McDowell and Thomas.I ] jgg proposed reaction steps are ... 

In the simplest type of PSA system, an adsorber separates the desired product from the feed mixture at feed pressure and ambient temperatures. When the adsorbent bed has been saturated with impurities, it is depressurized to a lower pressure and in a direction countercurrent to the feed flow direction. The depressurization (blowdown) causes desorption and removal of much of the impurities from the adsorbent. The bed is then purged, also countercurrently to the feed flow direction, with product gas to complete the removal of impurities to a low residual level. Alternately, the bed may be evacuated to a sub-atmospheric pressure to remove impurities. The adsorber is then pressurized with product gas and it is put back on line to begin the adsorption step once again. 

Today, most multiple-wafer MOCVD systems are operated at sub-atmospheric pressure, in the 20-300 Torr (2.6 10 kPa) range to improve the uniformity of the epi-... 

ADN and compositions of ADN have been shown to be able to undergo self-sustained combustion with higher burn rates than the commonly used oxidizer AP. A basic study showed that the bum rate for compressed ADN was 7.4 mm/s at the sub-atmospheric pressure of 0.2 MPa and 54 mm/s at 6 MPa. Since ADN has a surplus of oxygen, its burn rate increases if a carbon source is added. The low-pressure burning is then expanded down to 0.02 MPa. The burn rate for a mixture of ADN and paraffin in the ratio 90 10 has been determined to be 50 mm/s at 7 MPa with a burn rate coefficient of 0.8 and a flame temperature of 2960 [17]. 

Isolation of a common group of olefin isomers has now been accomplished, charging olefins from C.-C.Q over HZSM-5 at sub-atmospheric pressure. Conditions usea were ... 

The common product distribution as established above at sub-atmospheric pressures is evidence that a similar common distribution also occurs at higher pressure, explaining the similarity of final products. 

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