Oxyhydrogen reaction

An impressive example of the impact of miniaturization on the explosion limit has been given for the oxyhydrogen reaction [18]. For a conventional reactor of 1 m diameter, explosive behavior sets in at 420 °C at ambient pressure (10 Pa). An explosion occurs at about 750 °C, when the reactor diameter is decreased to about 1 mm. A further reduction to 100 pm shifts the explosive regime further to higher pressures and temperatures. 

Peschek, G. A. (1979b) Aerobic hydrogenase activity in Anacystis nidulans. The oxyhydrogen reaction. Biochim. Biophys. Acta, 548, 203-15. 

Above 550 °C the reaction occurs with flame propagation, explosion or detonation (oxyhydrogen reaction). The flame temperature is limited by the thermal dissociation of water vapor and attains a maximum of 2700 °C. 

Table 4.12 shows a comparison of safety-relevant thermo-physical and combustion properties of hydrogen with those of methane, propane and gasoline [26]. The flammability limits are affected by temperature, as shown in Figures 4.9 and 4.10, so that a preheated mixture has considerably wider limits for coherent flames [27]. An increase in pressures up to lOkPa has only a small effect. Water vapor has a strongly inhibiting influence on the oxyhydrogen reaction. 

There is an increased danger of explosions in the cooling chamber under the tundish due to possible oxyhydrogen gas reactions. These can lead not only to severe burns, but also to injuries of the tympanic membrane - the latter being possible even in the case of very minimal oxyhydrogen reactions, if an employee is standing very close to the source of the explosion. 

In Phormidium, respiration apparently provides anaerobiosis by taking over the role of the oxyhydrogen reaction. Further experiments are under way to obtain data as to what extent energy for nitrogenase is supplied by respiration. 

C05-0032. A reaction vessel contains H2 gas at 2.40 atm. If just enough O2 is added to react completely with the H2 to form H2 O, what will the total pressure in the vessel be before any reaction occurs (H2 and O2 can also be used as a torch. The flame produced in an oxyhydrogen torch is about 4000 K.)... 

W. G. Mixter 5 has recently investigated the combustion phenomena of several hydrocarbons by means of a weak electric spark discharge, and has proven among other things that ethylene can. also yield acetic acid besides carbonic acid. The pressure under which the gases react is important for the course of the experiment. Mixter sought to determine the relative reaction velocities as compared with that of an oxyhydrogen mixture, under equal conditions. 

This reaction is exothermic. The heat required to produce gaseous H2O and liquid H2O in this reaction at 25 °C and 1 atm is 242 and 286kJmol", respectively. This reaction proceeds spontaneously at temperatures above 500 °C. At temperatures lower than 500 °C this reaction occurs iu the presence of a snitable catalyst, such as Pt or Pd, or if activated by an electric spark or a flame. The combustion of hydrogen in oxygen prodnces flame temperatures as high as 2800 °C, a technique utilized in oxyhydrogen welding torches. 

The maximum velocity does. not therefore occur in the mixture which contains the gases in the proportion required for reaction. But it must be mentioned that Bunsen found very different values, e. g. 34 metres per second for oxyhydrogen mixture, as compared with 1 21 to 5 82 in the above experiments. 

A second phenomenon of propagation in mixtures or substances capable of reaction has only been made the subject of investigation in recent times. Although previously indications existed of a possible much greater velocity of propagation in explosives, it was first Berthelot and Vieille, and simultaneously Mallard and Le Chatelier, who followed out the phenomenon in question, and showed that besides the usual progressive combustion, which takes place in the oxyhydrogen mixture with a velocity of some metres per... 

This diver is using an oxyhydrogen torch. The energy released by the torch comes from a chemical reaction in which hydrogen and oxygen react to form water. 

This oxyhydrogen torch uses hydrogen as its fuel and oxidizes hydrogen to water in a vigorous combustion reaction. Like the torch, fuel cells also oxidize hydrogen to water, but fuel cells operate at a much more controlled rate. 

Procedure Introduce hydrogen gas into the combustion pipe, which contains copper oxide filled in a porcelain boat. If the oxyhydrogen test turns out to be negative, light the hydrogen on the exhaust pipe and heat the copper oxide with a burner. As soon as the reaction sets in, indicated by the formation of metallic copper, remove the burner. Cool down the combustion pipe under a continuous hydrogen stream before the hydrogen supply is turned off. 

The required ionization energy to form carbon ions in an oxyhydrogen flame mostly results from the high carbon oxidation energy released during the combustion reaction of carbon to carbon monoxide and carbon dioxide. The flame temperature itself is insufficient for a direct atom or molecule ionization. 

The final question to be addressed is why the Si02 formed is X-ray amorphous. It is obvious that Si02 formed in fractions of a second in an oxyhydrogen flame cannot be well ordered and crystalline. An equally amorphous product is formed if an oxygen stream loaded with SiCh passes a heating section of about 40 cm with a relatively small flow velocity. The thermolysis of Si20Cl6 in a closed system for several weeks also leads to amorphous products. This leads to the conclusion that the reaction time is not very important. In the discussion of the structures of the initially formed... 

This compound is synthesized by the method of Sliwinski in the apparatus shown in Fig. 243. Before the reaction the apparatus is flushed with dry Hg until free of ejqilosive oxyhydrogen mixture. Amorphous boron is placed in a Vycor tube and heated to a dull red. A stream of dry, COg-free HsS is passed over the boron. Molten boron sulfide condenses close to the point where the heat has been applied (point a, Fig. 243). Upon cooling, the material becomes transparent. Further downstream, at b, porcelainlike sulfide forms, while crystalline B3S3 forms at o. TTie sublimation zone should not be cooled or the ciystals will not be well formed. A steady stream of HgS is maintained throughout the entire reaction and controlled to give a flow of approximately 3 liters/hour. 

However, the situation changes as soon as gases are consumed or produced. We will look a little closer at an example, the reaction of oxyhydrogen (a mixture of hydrogen and oxygen gases) ... 

A process simulation software reports the enthalpy of a saturated liquid stream of 53kg/h of cyclohexane at 45 "C as -2.301 Gcal/h. Estimate this value using the data given in Appendices A and B and compare the results. How much heat per mol of water must be removed to reach a final temperature of T = 1000 K when the oxyhydrogen gas reaction... 

---