Longevity Demonstration of Methane to C2 via a Nonthermal Plasma Microreactor

Hydrocarbon processing using plasmas has tremendous potential, yet there still exist many uncertainties pertaining to practical operation over long durations. Previously, it has been demonstrated that a nonthermal plasma operating in a DC glow regime can transform methane into C2 species (acetylene, ethylene, ethane) in a microreactor. Using a DC glow regime in a microchannel reactor allows for lower power consumption, at the expense of greater consequence of fouling. Since biogas can be a source of methane, a longevity study was undertaken to understand how the microreactor system would change over time with a feed mixture of simulated biogas (CO₂, CH₄) and air. Two different biogas mixtures were used, one of which contained 300 ppm H₂S, while the other had no H₂S. Potential difficulties observed from previous experiments included carbon deposition on the electrodes, which could interfere with the electrical characteristics of the plasma discharge as well as material deposition in the microchannel, which could affect gas flow. It was found that raising the temperature of the system to 120 °C helped prevent hydrocarbon deposition in the reactor. Purging the reactor periodically with dry air was also found to have positive effects as it removed carbon buildup on the electrodes themselves. Successful operation over a 50 h time period without any significant deterioration was demonstrated.