Ethane thermal decomposition

Table 1. Calculated DDEs (kcal/mol) for methane and ethane thermal decomposition...

Finally, Fig. 2.22 illustrates the kinetic curve behaviour for the source reactant and the end product of ethane thermal decomposition. The calculations assume that the process proceeds at a temperature of 1,100 K and at an initial pressure of the gas mixture 2 atm. One should remember that, in this case, it is considered an approximate solution obtained in the framework of the approximation about a steady-state course of the process. 

H. Bockborn and co-workers, "Production of Acetylene ia Premixed Flames and of Acetylene—Ethylene Mixtures," Chem. Ing. Pechnol. 44(14), 869 (1972). "Thermal Decomposition of Ethane ia a Plasma Jet," Rogyo Kagaku Zasshil4(9), 83 (1971). 

The preparation of semiconductors by thermal decomposition would appear to be impossible because of the high amount of energy required to break all of the metal-carbon bonds before the atomic species could be formed. However, the thermal method is successful because the reaction to form free methyl radicals, which combine to form ethane, lowers the energetic requirements for the formahon of gallium, for example, according to the equation... 

The proposed polymerization mechanism is shown in Scheme 9.12. Thermal decomposition of the hexasubstituted ethane derivative yields hindered tertiary radicals that can initiate polymerization or combine with propagating species (primary radical termination) to form an oligomeric macroinitiator. The addition of the diphenylalkyl radicals to monomer is slow (e.g. k[ for 34 is reported as KT M"1 s l at 80 °C84) and the polymerization is characterized by an inhibition period during which the initiator is consumed and an oligomeric macroinitiator is formed. The bond to the Cl I formed by addition to monomer is comparatively thermally stable. 

Thermal Decomposition. The therm decompn was studied betw 380 and 430° and found to be homogeneous and apparently 1st order. The products were complex and included nitric oxide, methane, carbon monoxide, and w plus small amts of ethane, ethylene, and nitrous oxide (Ref 23)... 

It has been generally accepted that the thermal decomposition of paraffinic hydrocarbons proceeds via a free radical chain mechanism [2], In order to explain the different product distributions obtained in terms of experimental conditions (temperature, pressure), two mechanisms were proposed. The first one was by Kossiakoff and Rice [3], This R-K model comes from the studies of low molecular weight alkanes at high temperature (> 600 °C) and atmospheric pressure. In these conditions, the unimolecular reactions are favoured. The alkyl radicals undergo successive decomposition by [3-scission, the main primary products are methane, ethane and 1-alkenes [4], The second one was proposed by Fabuss, Smith and Satterfield [5]. It is adapted to low temperature (< 450 °C) but high pressure (> 100 bar). In this case, the bimolecular reactions are favoured (radical addition, hydrogen abstraction). Thus, an equimolar distribution ofn-alkanes and 1-alkenes is obtained. 

In their original paper, Ayscough and Steacie42 claimed that the photolysis was very simple and that only carbon monoxide and hexa-fluoroethane were formed as a result of a reaction of type B. Subsequent work has thrown some doubt on this simple interpretation, nevertheless, the ratio of the quantum yields of carbon monoxide and hexafluoro-ethane was close to unity for a temperature range of 25-300°C. (above which temperature, thermal decompositions become important) and at wavelengths of 3130 A. and 2537 A. No trace of perfluorobiacetyl was found, nor any other product which could arise from the reactions of the trifluoroacetyl radical. 

In earlier work, acetylene was not considered as an intermediate in the combustion proper, but, rather, as a product of thermal decomposition occurring as a side reaction due to the heat released by oxidation of part of the hydrocarbon. Egloff, Schoad, and Lowry (21) suggested, for example, the following scheme of reactions for ethane ... 

Refining petroleum involves cracking large hydrocarbon molecules into smaller, more volatile pieces. A simple example of hydrocarbon cracking is the gas-phase thermal decomposition of butane to give ethane... 

The fragmentation patterns of a number of phosphine-metal carbonyl complexes have been reported 164). Complexes of bis(diphenylphos-phino)ethane (diphos) appear to lose ethylene to give ions of the type (Ph2P)2Mo+. In contrast to thermal decomposition by loss of phosphine,... 

The thermal decomposition of (CH3)5As at 100°C leads to quantitative yields of trimethylarsine, methane, and ethylene, as followed by gas chromatography. Only traces of ethane were detectable. It is, therefore, assumed that the compound is decomposed via the ylide, which is known to be unstable under these conditions ... 

The Thermal decomposition of ethane to ethylene, methane, butane, and hydrogen can be expressed by the following mechanism. 

The possible extent to which free radical chains may account for the thermal decomposition of organic molecules in the gas phase was first emphasized by Rice and Herzfeld.26 They gave three examples showing how all the known facts in the decomposition of acetone, acetaldehyde and ethane could be explained by chain reactions involving free radicals. Their calculations showed that the first order character of the reaction could be maintained under proper conditions and they estimated reaction rates and temperature coefficients in agreement with the facts. 

The presence of methane in the decomposition products together with the fifty per cent of carbon monoxide indicates a reaction more complicated than (1) or (4) and favors reaction (2) or (5). Rice and Herzfeld32 have proposed a series of chain reactions for the thermal decomposition of acetone which would give both methane and ethane. The recombination of CH3 and CH3CO according to (2) might account for the low quantum yield. 

The photochemical dissociation of di-(-butyl peroxide appears to proceed in a very similar way to the thermal decomposition. Dorfman and Salsburg47 photolyzed di-(-butyl peroxide using 2537 and 2650 A. radiation between 25 and 75°C. They found that the main products were ethane and acetone in relative yields of 1 2. With low intensity radiation, some methane was obtained and, even though acetone was removed to prevent its reactions becoming appreciable, (-butanol was produced. The evidence is therefore very strong that di-f-butyl peroxide decomposes by the usual breaking of the peroxide 0—0 bond and the (-butyl radicals then rapidly decompose to give acetone and methyl radicals, i.e.,... 

Fig. 2a and b. Relationships between AG (300 °C) of thermal decomposition of sym-hexyalkyl-ethanes and... 

Hydrogen, metliane, and ethylene are also at tunes to be fomid amongst the products of oxidation, without, however, any carbon being liberated. Their appearance is believed to be due to the purely thermal decomposition of ethane, formaldehyde, and acetaldehyde.3 Thus ... 

Example The gas-phase thermal decomposition of one mole of di-tert-butyl peroxide, in a constant volume apparatus, yields two moles of acetone and one mole of ethane. If life reaction obeys first-order kinetics, develop expression the rate-constant as a function of time, initial pressure and total pressure. 

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