Slow combustion

In a study of the slow combustion of the three xylenes, it was observed that OX is much mote reactive toward oxygen than MX and PX (18). 

Oxidation of Hydrocarbons. Ethanol is one of a variety of oxygen-containing compounds produced by the oxidation of hydrocarbons. Ethanol is reported to be obtained in a yield of 51% by the slow combustion of ethane (158,159). When propane is oxidi2ed at 350°C under a pressure of 17.2 MPa (170 atm) (160,161), 8% of the oxygen is converted to ethanol. Lower conversions to ethanol are obtained by oxidi2ing butane. Other oxidation systems used to produce ethanol and acetaldehyde (162—164) and methods for separating the products have been described in the patent Hterature. 

L. Landau. On the theory of slow combustion. Acta Physicochimica URSS, 19 77-85,1944. 

Plewinsky, B. et al., Thermochim. Acta, 1985, 94, 33-43 Safety aspects of the combustion of various materials in an amosphere of pine oxygen under the conditions prevailing in oxygen bomb calorimetry were investigated experimentally. The combustion of a stable substance (benzoic acid, used to calibrate bomb calorimeters) in oxygen gives a relatively slow combustion, with a low rate of pressure increase of 17 bar/s to a maximum of 64 bar in 2.3 s, for... 

CA 29, 8335 (1935) (A slow combustion fuse compn is prepd by mixing with alcohol to form a thick paste K nitrate 5, pulverized sulfur 4and charcoal 3.5 parts after thor ough blending the mass is dried)... 

In cases of vivid, as distinguished from slow combustion, the heat and light scorn to he evolved from the... 

The slow combustion reactions of acetone, methyl ethyl ketone, and diethyl ketone possess most of the features of hydrocarbon oxidation, but their mechanisms are simpler since the confusing effects of olefin formation are unimportant. Specifically, the low temperature combustion of acetone is simpler than that of propane, and the intermediate responsible for degenerate chain branching is methyl hydroperoxide. The Arrhenius parameters for its unimolecular decomposition can be derived by the theory previously developed by Knox. Analytical studies of the slow combustion of methyl ethyl ketone and diethyl ketone show many similarities to that of acetone. The reactions of methyl radicals with oxygen are considered in relation to their thermochemistry. Competition between them provides a simple explanation of the negative temperature coefficient and of cool flames. 

Figure 5. Effect of addition of formaldehyde on slow combustion of 40 mm. of diethyl ketone and 40 mm. of oxygen at 400°C. (1)...

Methyl ethyl ketone is unique, in that long and irreproducible induction periods were observed on occasion, reaction ensued only after 7 hours and then was completed within 10 minutes. During the long induction period the only detectable product was methanol. No convincing reason can be advanced to account for this anomalous behavior. The virtual absence of ethylene from the products of the low temperature slow combustion of methyl ethyl ketone strongly suggests that the low-temperature mechanism proceeds almost exclusively by further oxidation of the radicals produced by hydrogen abstraction from the parent ketone. 

Figure 6 shows the variation of peroxide concentration in methyl ethyl ketone slow combustion, and similar results, but with no peracid formed, have been found for acetone and diethyl ketone. The concentrations of the organic peroxy compounds run parallel to the rate of reaction, but the hydrogen peroxide concentration increases to a steady value. There thus seems little doubt that the degenerate branching intermediates at low temperatures are the alkyl hydroperoxides, and with methyl ethyl ketone, peracetic acid also. The tvfo types of cool flames given by methyl ethyl ketone may arise from the twin branching intermediates (1) observed in its combustion. 

For the low temperature slow combustion of acetone (21), kb has been obtained by this method at four temperatures. The corresponding Arrhenius plot is a good straight line with the equation ... 

The complicated situation in which methyl radicals participate in the equilibrium with oxygen and methylperoxy and the methylperoxy radicals can react further by at least two alternative routes, is capable of explaining many of the features of acetone slow combustion. Similar arguments, with appropriate modifications, can be developed for the combustion of other fuels. 

T Talogen compounds promote slow combustion (1, 5, 11, 16, 17), and yet they strongly inhibit flame processes (4, 6, 7, 8, 10, 18). These effects have intrigued many investigators, but it is still not clear at what stage and how the effect changes from promotion to inhibition. 

It was the late Professor Callender (12), who as an outcome of experiments upon the slow combustion of hexane which resulted in the formation of valeraldenyde, acetaldehyde, and fonnaldehyde without any detectable initial hexyl alcohol, CeHi3OH, first suggested that the initial oxidation of a hydrocarbon in air more probably involves the formation of an alkyl peroxide by the direct incorporation of the oxygen molecule in the hydrocarbon molecule after the collision which subsequently decomposes into aldehydes and water thus... 

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