9–2. Methane Conversion into Acetylene in Non-Equilibrium Plasma Conditions . Co
ID: 2303823 • Letter: 9
Question
9–2. Methane Conversion into Acetylene in Non-Equilibrium Plasma Conditions.
Compare relations (9–14) and (9–15) to estimate the relative accuracy of logarithmic approximation (9–15) for calculations of the CH4 dissociation rate coefficient at Tv > T0. Why can’t the logarithmic approximation be applied to describe methane conversion into acetylene in strongly non-equilibrium plasma-chemical system, when the vibrational temperature significantly exceeds the translational one?
9.2.5. Non-Equilibrium Kinetics of Methane Conversion into Acetylene Stimulated by Vibrational Excitation The kinetics of dissociation of polyatomic molecules, in particular CH4, stimulated by vibrational excitation in conditions of not very high non-equilibrium parameters y(Tv To)/ To has been analyzed by Kuznetsov (1971). The CH4 dissociation (9-13) proceeds through vibrational excitation of CH4 molecules at any parameters ? = (T,-T)/ T-The vibrational energy distribution is an essentially non-Boltzmann distribution in this case, and it is characterized by both temperatures, Ty and To, even when Tv > To. The rate coefficient kn(To, T.) of the methane dissociation (9-13) in non-equilibrium conditions (T, > T) can be expressed as follows (Kuznetsov, 1971): @do) expLE"(To)·Tx-. To ) where kRo (To) is the rate coefficient of methane dissociation (9-13) in quasi-equilibrium conditions; (Tv) and Q(To) are relevant partition functions; E*(To) is the vibrational energy of a CH4 molecule when the VT relaxation rate becomes equal to that of vibrational vibrational exchange (see Section 3.4.4). For calculations at low values of the parameter y -(Tv -To)/To, expression (9-14) can be simplified: (9-15) where the parameter A E"(T)/T, is slowly changing with temperature. The CH, dis- sociation rate coefficient recalculated to the first kinetic order is shown in Fig. 9-7 as a function of translational temperature and the non-equilibrium parameter ? = (Tv-To)/ To (Babaritsky et al., 1991). To compare, the quasi-equilibrium reaction rates of the Kassel scheme (9-9)-(9-12) are also presented in the figure. Results of the non-equilibrium kinetic calculations of the energy cost of C2H2 production from methane as function of the specific energy input Ev and the non-equilibrium parameter y (Tv To)/To (Babaritsky et al 1991) are also presented in Fig. 9-6 for the case ofgas pressure of 80 Torr. These calculations take into account the acceleration by vibrational excitation of the only reaction of CH4 dis- sociation, (9-13) other reactions are considered as in Section 9.2.3. These non-equilibrium kinetic calculations are in a good agreement with experimental results achieved in the non- equilibrium microwave discharge (Section 9.2.2, especially assuming the non-equilibrium parametery(T - To)/To- 0.5. As seen from Fig. 9-6, the minimum energy cost value 02Explanation / Answer
The reason why the logarithmic approximation be describe methane conversion into acetylene because it strongly convert the particles into other and no chance of reaction Is possible.
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