Plasma-stimulated processes

The exothermic plasma-stimulated process of partial oxidation of kerosene can be represented as... 

Plasma-stimulated processes are usually characterized by low productivities, since low pressures (<100Torr) are used, and enhanced energy consumption compared to the microwave processes. 

In this relation, g and e are statistical weights and energies of corresponding states. A statistical approach can be applied in a consistent way for reactions (3-28) if the non-thermal plasma stimulation of the process is limited to the electronic excitation of a single state (energy E, ). The population of the excited state can be expressed then by 5-function and Boltzmann factor with an effective electronic temperature T ... 

The non-equilibrium effect is much stronger than the equilibrium effect. Numerical values of the coefficient of selectivity for different plasma-chemical processes of isotope separation stimulated by vibrational excitation are presented in Fig. 3-13. A detailed consideration of the Treanor-effect isotope separation can be found in Akulintsev, Gorshunov, and Neschi-menko (1977,1983) for nitrogen and carbon monoxide isotopes and in Eletsky and Zaretsky (1981) and Margolin, Mishchenko, and Shmelev (1980) for hydrogen isotopes. 

Energy Efficiency of Plasma-Chemical Processes Stimulated by Vibrational Excitation of Molecules... 

Mechanisms of stimulation of plasma-chemical reactions by electronic excitation were discussed in Section 2.5.5. No one of the four kinetic factors mentioned in Section 3.6.2 can be apphed in this case therefore, energy efficiency is relatively low, usually below 20-30%. Plasma-chemical processes through electronic excitation can be energy effective if they initiate chain reactiorrs. Such a situation takes place, for example, in NO synthesis, where the Zeldovich mechanism can be effectively initiated by dissociation of molecular oxygen through electronic excitation (see Section 6.1.2). 

The critical vibrational temperature corresponds to equality between the rates of vibrational excitationby electron impact and vibrational relaxation (see Chapter 3, and Section 5.3 for a similar case involving plasma-chemical CO2 dissociation). Stimulation of plasma-chemical processes by vibrational excitation becomes effective when The total... 

The CO-to-H2 shift reaction (5-3) in plasma imposes strong limitations on mixture composition (see Fig. 5-62). Nevertheless, the plasma-chemical shift reaction (5-3) in the presence of O2 - that is, CO-O2-H2O plasma chemistry - has been analyzed (Bochin et al., 1978a,b Legasov et al., 1980). Chemical processes in the CO-O2-H2O mixture can be plasma-stimulated in three different regimes. The first regime, which does not produce hydrogen, corresponds to the branched-chain explosion of CO-O2 (see Fig. 5-62 and, for example, Benson, 1960), which takes place without any significant involvement of water molecules ... 

The energy efficiency of this plasma-chemical process can be high, because it ean be effectively stimulated in non-equilibrium discharges by vibrational excitation of CO2 molecules. A relatively high process efficiency was achieved in experiments with non-thermal microwave discharge at moderate pressures (Garsky, Givotov, Ivanov, 1981). 

Figure 6-46. Plasma-cliemical process in S -P CO2 mixture at atmospherie pressure. Energy cost of CO production as function of specific energy input (1) ideal quenching in thermal plasma conditions (2) super-ideal quenching in thermal plasma conditions (3) non-equilibrium process stimulated by vibrational excitation of CO2 molecules.

Similar characteristics are achieved in non-equilibrium plasma stimulation of elimination reactions (Suhr, 1973). In the elimination processes, plasma provides selective cutting of some specific functional groups from initial hydrocarbon molecules, which is illustrated by Table 9-5. For example, the non-thermal plasma treatment of phthalic anhydride is characterized by a high conversion degree (70%) and selectivity, which means that almost 90% of the products are di- and triphei lene. Such conversion and selectivity characteristics of the non-equilibrium plasma systems allow them to be used in preparative organic chemistry. 

This plasma-chemical process is promoted in strongly non-equihbrium conditions, when the vibrational temperature of CO2 molecules significantly exceeds their translational gas temperature (TV To). Vibrational excitation of CO2 molecules stimulates the chain reaction of methanol production ... 

Plasma-Stimulated Partial Oxidation of Liquid Fuel into Syngas (CO- H2). Explain why the total energy efficiency of syngas production by partial oxidation of liquid fuels is always less than 100%, even in the ideal plasma process (for example, the efficiency is 65% for diesel fuel conversion see Section 10.2.4). A fraction of energy is always converted into heat in the processes. Calculate the maximum energy efficiency for conversion of kerosene... 

Use relation (10-54) to estimate the front velocity of solid-state (coal) oxidation at low temperatures. How does the oxidation front velocity depend on temperature Which effects determine the temperature limit for acceleration of the oxidation front In which way does nonequilibrium plasma stimulate the process ... 

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