Isotopic Experimental and Modelling Study of Acetylene Formation in a Plasma Reactor Using an A.c Corona Discharge

The mechanism of C2 formation in methane conversion using plasma discharge has been studied by researchers around the world with ambiguous conclusions. Motivated by this challenge, this paper discusses the pathway of acetylene formation based on experimental results using deuterium isotope. Methane was fed with deuterium with a ratio of 1 to 5. Ethane and acetylene were also fed with deuterium at the same ratio (1 to 5) to study the composition of acetylene products. Experimental results suggest that ethane, C2H6, was formed from the coupling of CH3 radicals; C2H4 was formed from the coupling of CH2 or CH and CH4; C2H2 formed involving C and C2 radicals. Secondary dehydrogenation may also account for some production of ethylene and acetylene from ethane and ethylene, respectively, and is insignificant compared to the radical coupling mechanism. A modeling study was done to try comparing and explaining the experimental work, particularly in C2 selectivity and acetylene formation. C2 selectivity of methane conversion by non-thermal plasma has been found to be a function of the specific power input. At low power, ethane is the major product; while at high power, acetylene is mainly produced. However, in some cases even at low specific energy input (low temperature) and low electron density such as corona discharge, acetylene is still the main product. There are two parts of the model: plasma physics and free radical chemistry, the results showed that all C2 products are produced simultaneously from CHx(x=0-3) radical’s reactions at low temperature. The free radical distribution created initially from direct methane electron impact reactions depends on the applied reduced electric field strength (E/N): CH3 radicals are the most abundant species at low E/N while C, CH, CH2 radicals are present at high E/N (precursors of C2 radicals).