KINETICS, MACROKINETICS AND DISSIPATIVITY SCALAR OF THE DECOMPOSITIONOF CO2 IN NONISOTHERMAL PLASMAS

Previous experimental investigations of electrical gas discharge syste ms led to the hypothesis that non-isothermal plasma chemical reactors have 'quasi-equilibrium' final states. Such equilibria are basic for a macrokinetic description of the gross reactions of the processes. Her e, we report on gaschromatographic measurements of glow discharge and silent discharge C/O systems in a closed vessel at gas pressure values between 0.3 kPa and 20 kPa. In the case of low power input empirical macrokinetic relations are supported. Based on a kinetic model of the decomposition of CO,, a clear mathematical definition of the 'Quasi-Eq uilibrium of Electronic Catalysis' and the 'Quasi-Equilibrium of Compl ete Decomposition' can be given and opposed to the state of 'Chemical equilibrium'. Asymptotically expanded versions of the kinetic differen tial equations are used to define different types of electronic activa tion which are called 'Electronic Catalysis' and 'Complete Decompositi on'. To have in hand a tool for checking the approach of the processes to quasi-equilibria or chemical equilibrium, respectively, we propose a definition of a 'Dissipativity Scalar', which generalizes the Onsag er bilinear form. This function can be used in the non-linear region f ar from thermodynamic equilibrium and is valid for one-side (non-rever sible) chemical reactions. In the neighbourhood of the thermostatic eq uilibrium it coincides with the entropy source density of the linear t hermodynamics of irreversible processes. A numerical evaluation of the dissipativity scalar indicates that the plasma chemical processes dur ing activation of the discharge have an initial period with almost con stant chemical dissipativity (reactivity) followed by a maximum dissip ativity at a time which varies from 1 ms to 1 s with the electron dens ity. In advanced stages of the passive relaxation processes of the dis charge, the dissipativity scalar obtains plateau values which correspo nd with the quasi-equilibrium.