Hydrogen explosion limits

Hydroxylamine sulfate is produced by direct hydrogen reduction of nitric oxide over platinum catalyst in the presence of sulfuric acid. Only 0.9 kg ammonium sulfate is produced per kilogram of caprolactam, but at the expense of hydrogen consumption (11). A concentrated nitric oxide stream is obtained by catalytic oxidation of ammonia with oxygen. Steam is used as a diluent in order to avoid operating within the explosive limits for the system. The oxidation is followed by condensation of the steam. The net reaction is... 

Many polymer films, eg, polyethylene and polyacrylonitrile, are permeable to carbon tetrachloride vapor (1). Carbon tetrachloride vapor affects the explosion limits of several gaseous mixtures, eg, air-hydrogen and air-methane. The extinctive effect that carbon tetrachloride has on a flame, mainly because of its cooling action, is derived from its high thermal capacity (2). 

The DMR process has no aqueous effluent, gives high purity products, and is less expensive. However, if hydrogen is produced, it has to be removed carefully and should not reach explosive limits. Not all metals are sufftcientiy reactive to be suitable for the DMR process. 

GP 11] [R 19] Based on an analysis of the thermal and kinetic explosion limits, inherent safety is ascribed to hydrogen/oxygen mixtures in the explosive regime when guided through channels of sub-millimeter dimensions under ambient-pressure conditions [9], This was confirmed by experiments in a quartz micro reactor [9],... 

During oxy chlorination of ethylene to 1,2-dichloroethane, excess hydrogen chloride is used to maintain the reaction mixture outside the explosive limits. 

There is a risk of generating hydrogen/chlorine/oxygen mixtures during electrolytic preparation from brine. An explosive limits diagram for this ternary system is given. 

The effects of the presence of 44 gaseous or volatile materials upon the upper explosion limits of hydrogen-air mixtures have been tabulated. 

The explosion limits have been determined for liquid systems containing hydrogen peroxide, water and acetaldehyde, acetic acid, acetone, ethanol, formaldehyde, formic acid, methanol, 2-propanol or propionaldehyde, under various types of initiation [1], In general, explosive behaviour is noted where the ratio of hydrogen peroxide to water is >1, and if the overall fuel-peroxide composition is stoicheiometric, the explosive power and sensitivity may be equivalent to those of glyceryl nitrate [2],... 

Explosive limits for this combination have been studied from 1 to 20 bar at 50°C. Hydrogen, Oxygen... 

A mixture of hydrogen and chlorine gas, eventually in combination with air, can be very explosive if one of the components exceeds certain limits. In chlorine production plants, based on the electrolysis of sodium chloride solutions, there is always a production of hydrogen. It is, therefore, essential to be aware of the actual hydrogen content of chlorine gas process streams at any time. There are several places in the chlorine production process where the hydrogen content in the chlorine gas can accumulate above the explosion limits. Within the chloralkali industry, mainly two types of processes are used for the production of chlorine—the mercury- and the membrane-based electrolysis of sodium chloride solutions (brine). 

Butler, M.A., Fiber optic sensor for hydrogen concentrations near the explosive limit, Journal of Electrochemical Society, 46(138), L46,1991. 

Anhydrous copper(II) sulfate, 7 773 Anhydrous ethanol, production by azeotropic extraction, 8 809, 817 Anhydrous gaseous hydrogen sulfide, 23 633 Anhydrous hydrazine, 13 562, 585 acid-base reactions of, 13 567-568 explosive limits of, 13 566t formation of, 13 579 vapor pressures of, 13 564 Anhydrous hydrogen chloride, 13 809-813 physical and thermodynamic properties of, 13 809-813 purification of, 13 824-825 reactions of, 13 818-821 uses for, 13 833-834... 

LEL the lower explosive limit of the gas (hydrogen) being transported this is reported to be approximately 18% by volume in air by NASA, NSS 1740.16. 

Many of the early contributions to the understanding of hydrogen-oxygen oxidation mechanisms developed from the study of explosion limits. Many extensive treatises were written on the subject of the hydrogen-oxygen reaction and, in particular, much attention was given to the effect of walls on radical destruction (a chain termination step) [2], Such effects are not important in the combustion processes of most interest here however, Appendix C details a complex modem mechanism based on earlier thorough reviews [3,4],... 

Figure 3.2 depicts the explosion limits of a stoichiometric mixture of hydrogen and oxygen. Explosion limits can be found for many different mixture ratios. The point X on Fig. 3.2 marks the conditions (773 K latm) described at the very beginning of this chapter in Fig. 3.1. It now becomes obvious that either increasing or decreasing the pressure at constant temperature can cause an explosion.

The higher-order hydrocarbons, particularly propane and above, oxidize much more slowly than hydrogen and are known to form metastable molecules that are important in explaining the explosion limits of hydrogen and carbon monoxide. The existence of these metastable molecules makes it possible to explain qualitatively the unique explosion limits of the complex hydrocarbons and to gain some insights into what the oxidation mechanisms are likely to be. 

There is, of course, a chemical effect in carbon monoxide flames. This point was mentioned in the discussion of carbon monoxide explosion limits. Studies have shown that CO flame velocities increase appreciably when small amounts of hydrogen, hydrogen-containing fuels, or water are added. For 45% CO in air, the flame velocity passes through a maximum after approximately 5% by volume of water has been added. At this point, the flame velocity is 2.1 times the value with 0.7% H20 added. After the 5% maximum is attained a dilution effect begins to cause a decrease in flame speed. The effect and the maximum arise because a sufficient steady-state concentration of OH radicals must be established for the most effective explosive condition. 

FIGURE 8.11 Approximate explosion limits for stoichiometric mixtures of hydrogen sulfide... 

Such reactions have been used to explain the three limits found in some oxidation reactions, such as those of hydrogen or of carbon monoxide with oxygen, with an "explosion peninsula between the lower and the second limit. However, the phenomenon of the explosion limit itself is not a criterion for a choice between the critical reaction rate of the thermal theory and the critical chain-branching coefficient of the isothermal-chain-reaction theory (See Ref). For exothermic reactions, the temperature rise of the reacting system due to the heat evolved accelerates the reaction rate. In view of the subsequent modification of the Arrhenius factor during the development of the reaction, the evolution of the system is quite similar to that of the branched-chain reactions, even if the system obeys a simple kinetic law. It is necessary in each individual case to determine the reaction mechanism from the whole... 

ZhFizKhim 5, 1459(1934) (Detonation in gaseous mixtures. Variation of the detonation wave velocity with pressure) 6) M.A. Rivin A.S. Sokolik, ZhFizKhim 7, 571 (1936) (The explosion limits of gaseous mixtures. Expln limits of hydrogen-air mixtures) 7) Ibid, 8, 767(1936) (Expln limits in carbon monoxide-methane mixts)... 

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