Experimental Study And Kinetic Simulation Involving In Methane Cracked And Converted To C₂ Hydrocarbons In Cold Plasma

In this paper the kinetics of methane cracked and converted to C2 hydrocarbons in cold plasma was investigated. The kinetic models were founded on the base of the different characteristics of RFD (radio frequency discharge) and DBD (dielectric barrier discharge) plasma, and the rate constants were gained to simulate the set of kinetic equations. Because the set of stiff ordinary equations couldn't converge computed by means of the gear method, it was integrated by means of a new small parameter method. The dependence of the conversion efficiency of methane and the yields of C2 hydrocarbons on operating pressure, electron density, electron temperature or discharge voltage was studied. The results of the simulation and the experiment were in good agreement. On the base of the simulation the kinetic analysis was carried out and the main reactions forming products were picked out.This paper consisted of the theoretical and experimental studies. In the experimental study, the effects of the input power, operating pressure and Ar partial pressure on reactions were researched by using the built RFD setup. The result showed that the higher the input power was and the lower operating pressure was, the higher the conversion efficiency of methane and the yields of C2 hydrocarbons were; the largest conversion efficiency of methane approached 51.05% and the mass yields of ethane, ethylene and acetylene were 36.42%, 4.27%and 5.95% with the input power of 96W and the pressure of 200Pa respectively. By DBD plasma, the largest conversion efficiency of methane approached 19% and the mass yields of ethane, ethylene and acetylene were 11.4%, 2.3%and 3.8﹪ with the discharge voltage of 28kV respectively.The theoretical study derived the rate constants of dissociation reactions for different reaction systems. For RFD plasma, the relation between electron temperature and rate constants was calculated through Boltzmann distribution and collision theory, and for DBD plasma, the relation between electron temperature and discharge voltage was calculated through the distributive principle of the free journey. The kinetic models of methane converted in RFD plasma and DBD plasma were founded on the base of radical reaction mechanism. The result of the kinetic simulation showed that the conversion efficiency of methane and the yields of C2 hydrocarbons increased in the different degree with electron density, electron temperature or discharge voltage increasing at the different operating pressure. At the same pressure, when electron density or electron temperature was lower the conversion efficiency of methane is lower with the ethane as the main equilibrium product, and when electron density or electron temperature was higher, the conversion efficiency of methane was higher and the selectivity of the product changed with acetylene and ethane as the main equilibrium products. The conversion efficiency of methane and the yields of C2 hydrocarbons increased with the pressure reducing for the same electron density and electron temperature.The result of simulation was in good agreement with that of the experiment and the kinetics of the methane conversion was analyzed with the main reactions affecting the main product by combining the two results. The kinetic analysis indicated that the methane cracked was mainly by means of electron collision, the formations of acetylene and ethylene were mainly by radical transfer, and the formation of ethane was mainly by radical transfer together with the combination of methyl radical at the beginning of reactions then mainly by radical transfer with reactions going on. Moreover, the conversion of methane and the formation of each C2 hydrocarbons were affected by several main radical reactions, which showed that the process of reaction was quite complicated. The study of this paper showed that methane cracked and converted to C2 hydrocarbons in cold plasma was feasible and the distribution of the products could be changed by changing the structure of the reactor and operating conditions, a...