Reaction Engineering Studies of Cold Plasma Partial Oxidation of Methane

Cold plasma is a partially ionized state of matter that unites high reactivity and mild conditions. Therefore, cold plasma reactors are intriguing for reaction engineering. In this work, a laboratory scale dielectric barrier discharge (DBD) cold plasma reactor was designed, set up, and used for studying the application of the technology for the partial oxidation of methane. Experiments were carried out near ambient conditions and in addition to the reactants the feed also contained the inert carrier gas argon. The product stream was split into a condensable fraction and the remaining gaseous fraction. The latter was analyzed at-line in a gas chromatograph equipped with a dual column and two carrier gases. The condensable fraction was analyzed by NMR spectroscopy, Karl Fischer titration, and sodium sulfite titration. In the product stream, 16 product components were identified and quantified: acetic acid, acetone, carbon dioxide, carbon monoxide, ethanol, ethane, ethene, ethylene glycol, formaldehyde, formic acid, hydrogen, methanol, methyl acetate, methyl hydroperoxide, methyl formate, and water. The conversion of the reactants and the selectivities to the products were measured varying the molar reactant ratio in the feed, the mole fraction of argon in the feed, the residence time in the reactor, and the electrical power input. The influence of the variation of the electrical power input, the residence time, and the argon mole fraction can be described well by lumping the three factors into a newly introduced specific energy input SEI*, such that the dependencies of conversions and selectivities can be described by using only the SEI* and the molar reactant ratio in the feed. The results from 43 experiments carried out in the present work and the sundry trends found in the comprehensive data set extend the available knowledge on DBD cold plasma partial oxidation of methane considerably and are useful for testing mechanistic models.