(544cz) Reaction Conversion of Gases in Plasma Reactors

Electrical discharges in gases, or plasmas, are capable of breaking molecular bonds leading to conversion of stable molecules such as methane or nitrogen at relatively low temperatures. For a steady-state plasma reactor, reaction conversion is believed to depend on process parameters such as reactor volume and gas flow rate similar to other chemical reactors, and applied power. Here, using a combined experimental and modeling study where we independently varied reactor volume, gas flow rate, and power, we show that pure methane conversion depends only on power and gas flow rate and is independent of reactor volume. Experimentally, the variation of these process parameters was achieved by setting up a confined dielectric barrier discharge where the reactor volume remained constant with varying power and could be varied independently. In support of the experimental results, we carried out simulations using a segmented 1-D model consisting of filamentary volume segments and afterglow volume segments that allowed calculations to be performed at steady state. Both experimental and simulation results showed that the reaction conversion follows a master curve that only depends on energy density which is equivalent to power divided by flow rate. The lack of volume dependence is contrary to traditional chemical processes where conversion depends on residence time, which is equivalent to volume divided by flow rate. We will also discuss application of similar approaches to nitrogen fixation.