Residual gases/vapors

The rich oil from the absorber is expanded through a hydrauHc turbiae for power recovery. The fluid from the turbiae is flashed ia the rich-oil flash tank to 2.1 MPa (300 psi) and —32°C. The flash vapor is compressed until it equals the inlet pressure before it is recycled to the inlet. The oil phase from the flash passes through another heat exchanger and to the rich-oil deethanizer. The ethane-rich overhead gas produced from the deethanizer is compressed and used for produciag petrochemicals or is added to the residue-gas stream. 

Entry into a tank that has contained any chlorinated or any easily evaporated solvent requires special procedures to ensure worker safety. The heavier vapors tend to concentrate in unventilated spaces. The proper tank entry procedure requires positive ventilation, testing for residue solvent vapor and oxygen levels, and the use of respiratory equipment and rescue harness. Monitoring the tank from outside is also important. The use of an appropriate gas mask is permissible in vapor concentrations of less than 2% and when there is no deficiency of atmospheric oxygen, but not for exposures exceeding one-half hour. Skin exposure to 1,1,1-trichloroethane can cause irritation, pain, bHsters, and even burning. Eye exposure may produce irritation, but should... 

The cleaning and gas freeing of tanks containing flammable residues Chlonne vaporizers... 

There is another method that has been sometimes employed in the vapor phase growth of eiystals. This method uses an evacuated eapsule as shown in 6.12.4., given on the next page. The eapsule is generally made from quartz, although platinum is sometimes used. Tlie capsule needs to be evacuated to remove any residual gas before heating is started. Otherwise, the internal pressure would build until the eapsule would explode. 

The central transport chamber is an 80-cm-diameter stainless steel vessel, and is pumped by a 1000-1/s turbomolecular pump, which is backed by a small (501/s) turbomolecular pump to increase the compression ratio for hydrogen, and by a 16-m /h rotating-vane pump. UHV is obtained after a bake-out at temperatures above 100°C (measured with thermocouples at the outside surface) of the whole system for about a week. A pressure in the low 10 " -mbar range is then obtained. With a residual gas analyzer (quadrupole mass spectrometer, QMS) the partial pressures of various gases can be measured. During use of the system, the pressure in the central chamber is in the low 10 -mbar range due to loading of samples. Water vapor then is the most abundant species in the chamber. 

An extensive and detailed coverage of the MS of expls in general has been documented (Ref 163). Volatile constituents of Comp A-3, Comp B, pressed TNT and cast TNT were surveyed with a residual gas analyzer MS (Ref 40). The mass spectra of all possible TNT (except for 3,4,5-TNT) and DNT isomers in the vapor phase were obtained as a function of ionizing voltage (Refs 65 84). The use of membrane inlet systems for the separation of TNT vapor in trace vapor detection is described and an analysis of the membrane inlet system for quadrupole mass spectroscopy is presented (Refs 95 113). Estimations of the vapor pressure of TNT were made mass spectrometrically in the range of 50—... 

Precooling, Water Removal. The raw gas is cooled and residual water vapor is removed to prevent subsequent icing. The... 

In the case of the counter-flow/sweep membrane module illustrated in Figure 4.18(c) a portion of the dried residue gas stream is expanded across a valve and used as the permeate-side sweep gas. The separation obtained depends on how much gas is used as a sweep. In the calculation illustrated, 5 % of the residue gas is used as a sweep even so the result is dramatic. The concentration of water vapor in the permeate gas is 13 000 ppm, almost the same as the perfect counter-flow module shown in Figure 4.18(b), but the membrane area required to perform the separation is one-third of the counter-flow case. Mixing separated residue gas with the permeate gas improves the separation The cause of this paradoxical result is illustrated in Figure 4.19 and discussed in a number of papers by Cussler et al. [16]. 

Figure 4.19(b) shows an equivalent figure for a counter-flow module in which 5 % of the residue gas containing 100 ppm water vapor is expanded to 50 psia and introduced as a sweep gas. The water vapor concentration in the permeate gas at the end of the membrane then falls from 1900 ppm to 100 ppm, producing a dramatic increase in water vapor permeation through the membrane at the residue end of the module. The result is a two-thirds reduction in the size of the module. 

A mixture of N2, NO, and NO2 was analyzed by selective absorption of the oxides of nitrogen. The initial volume of the mixture was 2.74cm3. After treatment with water, which absorbed the NO2, the volume was 2.02 cm3. A solution of FeSOq in water was then shaken with the residual gas to absorb the NO, after which the volume was 0.25 cm3. All the volumes were measured at the same pressure. Neglecting water vapor, what was the volume percentage of each gas in the original mixture ... 

Vacuum Contamination of the A1 layer by residual gas components (mainly water vapor) affects the barrier substantially good vacuum (<5 x 104 mbar) in the evaporation chamber is therefore required for barrier applications. Contamination from the evaporation material and the evaporators must also be avoided as much as possible. 

The reactant mixture, consisting of 1 mole % o-xylene in air was raised to a temperature of 105-110°C by a vaporizer located up-stream of the reactor, before entering the top of the bed. The gas stream leaving the reactor passed to a condenser where the phthalic anhydride sublimated. The residual gas was conveyed to a stripper where the Organic material was washed out before being vented to atmosphere. 

The analysis of the products called for supplementary data on the decreases in vapor pressure produced by low temperature baths. After removal of hydrobromic acid, ethylene and unsaturated compounds the residual gas was subjected in different cooling baths to the temperatures listed in Table V and the cor-... 

Another effect, "surface contamination", must also be taken into account This may arise from residual gas and small leaks in the vacuum system, but a further possible source should not be overlooked, namely the following Polymers are capable of entrapping appreciable amounts of gas in their free volume, and these molecules are released under the effect of vacuum and of particle bombardment. In the present experiments the polymers were deliberately not degassed before plasma treatment, as such a pretreatment would not likely be economical in an industrial plasma process. The released molecules, primarily air and water vapor, evidently can participate chemically during plasma treatment by intermixing with the feed gas molecules. 

Secondary contamination is common and personnel should wear aprons, mbber gloves, and masks as needed. Contaminated items can be washed in cold water (hot water will cause residual gas to vaporize) with soap or allow nonwashable items to air out for a few days. Most lacrimators dissipate quickly, but CS may be micronized and mixed with an antiagglomerant agent (CSl) which remains active for up to 5 days. A similar formulation mixed with silicone (CS2) remains in the environment for up to 45 days (Hu et al, 1989). 

Nonflammable, but high concentrations of trichloroethylene vapor in high-temperature air can be made to bum mildly if plied with a strong flame. Though such a condition is difficult to produce, flames or arcs should not be used in closed equipment that contains any solvent residue or vapor. Reacts with alkali, epoxides, e.g., 1-chloro-2,3-epoxypropane, 1,4-butanediol mono-2,3-epoxypropylether, 1,4-butanediol di-2,3-epoxypropylether, 2,2-bis[(4(2, 3 -epoxypropoxy)phenyl)propane] to form the spontaneously flammable gas... 

On the other hand, some studies on shock-induced devolatilization produced results inconsistent wiOt the above conclusion. Mukliin et al. [70J examined tlie effect of laser-pulse heating on meteorite materials and silicates in order to simulate the vaporization that occurs during impacts and to stud the chemical composition of the gases produced. The experimental results showed tliat the residual gas mixture consisted of both oxidized and reduced components CO, CO2, SO2, H2O, H2, N2, H2S, COS, CS2, various hydrocarbons from Ci to Ce, HCN, and CH3CHO. They emphasized that the gas mixtures formed by vaporization of silicates provide favorable conditions for abiotic synthesis of organic materials. 

This process involves a chemical reaction between the evaporated constituent and the residual gas atmosphere. The technology of reactive evaporation is applied in all cases where direct evaporation of a chemical compound is not possible because of thermal dissociation or very low vapor pressnre. Stoichiometric oxide films can be obtained with a relatively high controlled oxygen partial pressnre and a slow metal atom condensation rate. 

Quite aside from physical or chemical reactions, an important function served by high vacuum is the provision of collision-free space, such as required in radio and television tubes, and particle accelerators. In these applications, charged particles must travel relatively long distances before reaching their target. Obviously, their path will be unimpeded only when the probability of collision with residual gas molecules is very low. A similar function is served in vacuum coating, where metal vapor is condensed on a suitable substrate some distance from an evaporation source. 

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