Oxygenates production in a microfluidic dielectric barrier discharge device sustained in Ar/CH₄/O₂

Reforming of methane (CH₄) is a process to produce syngas (CO/H₂) and other value-added chemicals including oxygenates such as methanol (CH₃OH). Atmospheric pressure plasmas have the potential to be more energy efficient than traditional reforming methods as value-added chemicals can be synthesized directly in the plasma without requiring an additional step. In this paper, we discuss the results from a computational investigation of the formation of oxygenates by CH₄ oxidation in the presence of Ar, including CH₃OH and CH₂O, in a nanosecond pulsed dielectric barrier discharge. The plasma is formed in a microfluidic channel whose small dimensions are ideal for plasma formation at atmospheric pressure. The production and consumption mechanisms of dominant radicals and long-lived species are discussed in detail for the base case conditions of Ar/CH₄/O₂ = 50/25/25. CH₃OH is produced primarily by CH₃O reacting with CH₃O and CH₃O₂ reacting with OH, while CH₂O formation relies on reactions involving CH₃O and CH₃. The most abundant oxygenate formed is CO (produced by H abstraction from CHO). However, the greenhouse gas CO₂ is also formed as a by-product. The effects of gas mixture are examined to maximize the CH₃OH and CH₂O densities while decreasing the CO₂ density. Increasing the Ar percentage from 0% to 95% decreased the CH₃OH and CH₂O densities. At low Ar percentages, this is due to an increase in consumption of CH₃OH and CH₂O, while at high Ar percentages (>40% Ar), the production of CH₃OH and CH₂O is decreased. However, both CO and CO₂ reached peak densities at 70%–90% Ar. Changing the CH₄/O₂ ratio while keeping 50% Ar in the discharge led to increased. Authors: Meyer, Mackenzie [University of Michigan, Ann Arbor, MI (United States); US Naval Research Laboratory, Washington, DC (United States)] (ORCID:0000000221056690); Hartman, Ryan [New York University, NY (United States)] (ORCID:0000000253649933); Kushner, Mark J. [University of Michigan, Ann Arbor, MI (United States)] (ORCID:0000000174378573). DOE Contract: SC0020232. Subjects: 03 NATURAL GAS; 54 ENVIRONMENTAL SCIENCES; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; atmospheric pressure plasmas; dielectric barrier discharge; energy efficiency; greenhouse gases; methane conversion; methane oxygenation; microfluidics; microplasma; plasma chemical reactions; plasma devices; plasma production; plasma properties and parameters; reaction mechanisms