­­Chemical reaction mechanisms accompanying pulsed electrical discharges in liquid methanol

Abstract

The primary goal of this study was to explore the fundamental chemical processes occurring during a pulsed electrical discharge in liquid methanol. To this end, advanced analytical techniques were used to identify and, when possible, quantify gas and liquid methanol decomposition products. The effects of applied voltage, voltage polarity, and presence of water on the reaction stoichiometry and the selectivity for the identified gas products were also studied. Density Functional Theory (DFT) simulations were used to determine the most feasible thermal reaction pathways between 300 and 4000 K responsible for the formation of experimentally identified gas and liquid products. From these results, the key chemical reaction pathways were theorized and a reaction mechanism was developed. Gas products of plasma‐induced decomposition of methanol that were detected and quantified include hydrogen, carbon monoxide, carbon dioxide, methane, acetylene, ethylene, and ethane. The reaction selectivity was the highest for the former two compounds regardless of the applied voltage, discharge polarity or presence of water in the starting solution. Results also showed that the applied voltage, discharge polarity and presence of water had no effect on the types of reaction products. Liquid methanol decomposition products that where identified include ethanol, ethylene glycol, formaldehyde, acetic acid, allyl alcohol, 1‐propanol, 3‐buten‐1‐ol, 3‐butyn‐1‐ol, glycolaldehyde, and methyl glycolate. The chemical reaction mechanism that was proposed to explain the formation of the experimentally verified gas products offers specific pathways for the production of carbon monoxide and short‐chained hydrocarbons. In contrast, the reactions leading to the formation of hydrogen, carbon dioxide, and liquid products appear to be random. In general, recombination reactions of direct methanol decomposition products are largely responsible for the formation of C1 and C2 liquid products. Step‐wise reactions of those compounds with single or multiple carbon‐based radicals grow the molecular chain length to up to four carbon atoms thereby producing C4 compounds.