Non-Thermal Plasma Conditions

Kinetics of Hydrazine (N2H4) Synthesis from N2-H2 Mixture in Non-Thermal Plasma Conditions 

In the case of the discharge in the N2-H2 mixture, the effective direct dissociation of Itydrogen essentially affects the plasma-chemical synthesis. When the initial dissociation degree of hydrogen in the discharge is 1%, the yield of ammonia exceeds the yield of hydrazine by about 10-fold. The effect is mostly due to recombination of NH2 radicals with atomic hydrogen  

Kinetic competition of the three-body recombination processes (6-126) and (6-127) requires about 10-fold excess nitrogen over hydrogen atoms for effective hydrazine synthesis. This effect can be clearly seen from the kinetic curves presented in Fig. 6-43. Atomic hydrogen also shifts the yield of the process in the direction of ammonia because of the reaction sequence  

The contribution of reaction (6-128) is especially important when generation of H atoms in the discharge is delayed with respect to the formation of N atoms. Such a kinetic delay can be due to a more effective N2 dissociation through vibrational excitation and contribution of dissociative attachment and electronic excitation to dissociation of hydrogen molecules. 

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NO Synthesis in Non-Thermal Plasma Provided by Positive Ions and Electronically Excited Molecules. Estimate the energy cost of NO molecule formation in air at non-thermal plasma conditions produced by each of the three following processes (1) dissociation of molecular nitrogen through its electronic excitation by direct electron impact (2) electron-ion recombination of positive molecular nitrogen ion and (3) ion-molecular reactions of... 

Co-production of NO and CN can be accomplished in the CO-N2 mixture in both thermal and non-thermal plasma conditions. The endothermic plasma-chemical process can be presented as... 

Somewhat similarly to the aforementioned synthesis of formaldehyde, the oxidation of methane in non-thermal plasma conditions can be optimized for the production of methanol ... 

These processes were demonstrated in different non-equihbrium plasma-chemical systems (Hemptinne, 1897 Losanitch Jovitschitsch, 1897 Lob, 1906 Losanitch, 1911 Lind, 1923 Briner Hoefer, 1940). It is interesting to compare hydrogenization of carbon dioxide (9-59) with that of carbon disulfide (CS2), which has been done in non-thermal plasma conditions and leads to the production of acetylene and strlfur ... 

Methane and acetylene can be effectively produced from syngas (CO-H2) in non-thermal plasma conditions. Syngas-based production of methane is an exothermic process ... 

At present the most effective available after-treatment techniques for NO, removal under lean conditions are ammonia selective catalytic reduction (SCR) [1-3] and NO, storage reduction (NSR) [4—6]. Indeed, three-way catalysts (TWCs) are not able to reduce NO, in the presence of excess oxygen, because they must be operated at air/ fuel ratios close to the stoichiometric value. Also, non-thermal plasma (NTP) and hydrocarbon-selective catalytic reduction (HC-SCR) are considered, although they are still far from practical applications. 

Electron energy distribution functions (EEDFs) in non-thermal discharges can be very sophisticated and quite different from the quasi-equilibrium statistical Boltzmann distribution discussed earlier, and are more relevant for thermal plasma conditions. EEDFs are usually strongly exponential and significantly influence plasma-chemical reaction rates. 

ICP discharges at moderate to high pressures usually generate thermal plasma, whereas the RF-CCP discharges in the same conditions can generate non-thermal plasma. 

CO2 conversion in non-equilibrium plasma conditions can significantly exceed conversion at thermodynamic quasi equilibrium, which is, for example, equal to a = 1.6% and a = 3.6% at Tq = 2000 K and pressures p = 2 atm and p = 50 Torr, respectively (Maltsev, Eremin, Ivanter, 1967). To compare, in addition to the non-thermal discharges considered earlier, the CO2 conversion degree in corona discharge reaches a = 28% at a gas temperature Tq not much above room temperature. 

Heating of N2O in conventional chemical or thermal plasma-chemical systems leads mostly to N2O dissociation and reduction of molecular nitrogen. The selective oxidation of N2O (5-178) becomes possible in non-equilibrium plasma conditions by means of oxygen dissociation and by the following exothermic reactions of NO formation ... 

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.

The reaction of methane and carbon dioxide in thermal plasma conditions leads mostly to the production of syngas. While non-thermal plasma can also be apphed for effective conversion of the CH4-CO2 mixture into syngas (see Chapter 10), non-equihbrium plasma conditions can also lead to the direct formation of methanol in the following process (Rusanov Fridman, 1984) ... 

Specific Conditions and Results of Non-Thermal Plasma Treatment of Textiles... 

Effect of Non-Thermal Atmospheric Pressure Air Plasma Contacting Water Surface on the Water Acidity. Analyzing reactions (12-2-8) describing interaction of electrons and ions of air plasma with water, explain why the non-thermal plasma treatment of water usually decreases pH and makes the water slightly acidic. Find out conditions, when plasma treatment does not make the water acidic or at least stabilizes the plasma-stimulated decrease of pH. 

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