Selective conversion of methane to synthetic fuels using dielectric barrier discharge contacting liquid film

Abstract

This paper presents the reaction mechanism of single-step methane partial oxidation to methanol at room temperature using non-thermal plasma microreactor. Macroscopic quantities of hydrogen peroxide (H 2 O 2 ) and methyl hydroperoxide (CH 3 OOH) are produced when methane is partially oxidized at room temperature (about 5 °C). CH 3 OOH is known to be the principle intermediate of incomplete methane oxidation product such as CH 3 OH and HCHO, but has not been demonstrated experimentally so far. H 2 O 2 promotes post-plasma oxidation of oxygenates in the condensed plasma-synthesized liquid. At an early stage of in-liquid oxidation, H 2 O 2 oxidizes HCHO into HCOOH preferentially; subsequently, HCOOH is fully oxidized to CO 2 and H 2 O. Depending upon the concentration of oxygenates and H 2 O 2 , electrical conductivity of the plasma solution dramatically increased, which detrimentally influences plasma properties. Methane partial oxidation with air was also investigated from a practical viewpoint. Generation of active nitrogen species (ANS) is the key to promoting overall methane conversion in the presence of oxygen; however, fragile oxygenates were also decomposed by ANS, thus selectivity for useful oxygenates was degraded in the presence of nitrogen. When oxygen is fully consumed, CH 4 conversion is also terminated and water gas shift reaction (CO + H 2 O = CO 2 + H 2 ) becomes predominant.