Ethane, decomposition

Hase W L 1972 Theoretical critical configuration for ethane decomposition and methyl radical recombination J. Chem. Rhys. 57 730-3... 

Ethane, C2H , dissociates into methyl radicals by a first-order reaction at elevated temperatures. If 250. mg of ethane is confined to a 500.-mL reaction vessel and heated to 700°C, what is the initial rate of ethane decomposition if k = 5.5 X 10 4 s-1 in the rate law (for the rate of dissociation of C2H6) ... 

Structure Sensitivity of Ethane Decomposition to Surface Carbon During Hydrogenolysis... 

Many mechanistic implications have been discussed, but we will concentrate here only on the most important structures in the context of dihydrogen-cation complexes. Deuterium-labeled methane and methyl cations were employed to examine the scrambling and dissociation mechanisms. The protonated ethane decomposition yields the ethyl cation and dihydrogen. Under the assumption that the extra proton is associated with one carbon only, a kinetic model was devised to explain the experimental findings, such as H/D scrambling. ... 

Laboratory experiments, confirmed by data from large scale operations, have shown that ethane decomposition is a homogeneous first order reaction, the rate constant (s ) being given by the equation in SI units 6 ... 

The ethane decomposition reaction is in fact reversible, but in the first instance, to avoid undue complication, we shall neglect the reverse reaction a more complete and satisfactory treatment is given below. For a simple first-order reaction, the rate equation is ... 

Calculation with reversible reaction. At 900°C the equilibrium constant Kr for ethane decomposition FoHtfWPciH, is 3.2 bar using the method described in Example 1.1 the equilibrium conversion of ethane under the conditions above (i.e. 1.4 bar, 0.5 kmol steam added) is 0.86. This shows that the influence of the reverse reaction is appreciable. 

Thermal data on ethane decomposition are not as clear as those dealing with hot ethane formed by recombination reactions. We consider the latter, first. Chemically activated ethane has been formed in experimental work by three different reactions ... 

These models were used to evaluate the necessary sums, densities, and moments of inertia, and eqs. (22) and (27) were integrated numerically to give k, (Fig. 12) and the calculated values of Table XVI. As was mentioned earlier in connection with ethane decomposition, we believe the thermally activated ethyl radical decomposition at 600°C. to be well into the fall-off region at pressures below atmospheric. In fact, comparison of Tables XII and XVI indicates that the fall-off behavior at 600°C. is very similar in its pressure dependence for ethyl and ethane, i.e., k, is a closely similar function of energy in both cases as shown explicitly... 

The inhibition of the ethane decomposition by NO has been studied by a number of workers.There seems to be a maximum inhibition of the reaction somewhere in the range 2 to 10 per cent (NO). The effect is least at higher temperatures and also at higher total pressures. In addition the effect seems to be greatest on the initial rate, the inhibited reaction appearing to follow the normal reaction after several per cent decomposition. 

More detailed evidence of the same kind was obtained for the ethane decomposition by Rice and Varnerin who decomposed C2D6 in the presence of CH4 and investigated the rate of production of the mixed methanes. The mixed product CH3D, for example, is formed in the following sequence of reactions... 

Calculations with a = 0.8 A-1 (curve 1) were performed, in addition to a = 1 A 1, because the choice for the potential energy surface interpolation parameter although reasonable is somewhat arbitrary. Hase27 used a = 0.82 A 1, based on a fit of ethane decomposition rates to the experimental data. 

Plasma Catalysis of Hydrogen Production by Direct Decomposition (Pyrolysis) of Ethane. Interpreting the plasma-catalytic effect of ethane decomposition and hydrogen production illustrated in Fig. 10-10, explain why the application of thermal plasma results in an increase of gas temperature, while application of non-equilibrium plasma results in gas cooling and additional hydrogen production. Compare the thermodynamics of these systems with that of refrigerators and heat pumps. 

The acetaldehyde decomposition occurs in the first reactor, since ethane decomposition is thermodynamically negligible at that operating condition. On the other hand, ethane decomposition takes place in the second reactor. These components should be included into the global balance. 

The kinetics of the reactions is known. The acetaldehyde decomposition is of second order at variable volume and the ethane decomposition is of first order according to the unit of the rate constants. 

Ethane decomposition is also a chain reaction, and the main features have now been elucidated. The initiation process is the dissociation of the ethane molecule into two methyl radicals ... 

For example, chain carriers of ethane decomposition, C2H. and H., can be oxidized as indicated in the following scheme ... 

Probably the principal cause for the abnormally low ethane decomposition at 100 mm. is the pressure sensitivity of k3 This has also been documented previously (2-4) though it is hard to quantify. 

Constancy of Initiation Reaction, Despite the variation in the over-all rate constant at a particular temperature of nearly an order of magnitude, depending on the pressure and dilution, the rate constant for the initiation reaction is remarkably constant. This is illustrated by Table III, which gives rate constants ki for 675°C. Relatively minor corrections for secondary methane were necessary at this low temperature—the ethane decomposition never... 

---