­­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 plasmainduced 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.

Plasma-enabled catalyst-free conversion of ethanol to hydrogen gas and carbon dots near room temperature

“…S1). It is well known that compared to the corona discharge, spark discharges in liquid have longer discharge channels and higher partial discharge intensity; while by contrast with reactive arc discharge, they usually require lower energy input, making themselves more suitable for inducing reactions in liquids [22,23]. Clearly, in the initial discharge state at a lower discharge power of 4 W, a purple-coloured plasma (Fig.…”

“…When plasma is introduced into the system, reactions related to ethanol conversion can take place at room temperature, resulting in the production of gas-phase chemicals, including H2, CO, CH4 and other gases like CO2, C2H4 and C2H2, with hydrogen being the major product [2,[22][23][24]. The total gas flow rate as a function of discharge time (the first 60 min) in these three kinds of discharge modes is presented in Fig.…”

“…For these reasons, NTP-based strategies are emerging as an economically-viable family of technologies for various types of material conversion, including ethanol reforming [2,[20][21][22]. Compared to conventional SR, H2 production from NTP-induced ethanol conversion operates at a significantly lower temperature ( < 100°C) and results in a higher conversion rate (with a H2 flow rate of several and even more than ten litres per minute) [23,24]. However, the conversion usually has unsatisfactory H2 selectivity (< 70% v/v) since the reactions initiated by plasma are usually lack of controllability due to the diversity and high reactivity of plasma-generated species [22][23][24].…”

Special issue: Plasma and Liquids

“…The two different configurations of gas‐liquid plasma reactors allow for compact operation and characterization of the chemical and physical processes inside the reactor. Other papers in this issue include analysis of direct underwater discharges (Yang et al and Kozakova et al), study of pollutant treatment (Magureanu et al, Kozakova et al, Tampieri et al), determination of the fundamental species formation for plasma formed in contacting with a liquid water stream (X. Zhang et al, Tarabova et al, and Wandell et al), and analysis of plasma with organic liquids (Rezaei et al and Franclemont et al) . Of particular importance for chemical oxidation is the determination of hydroxyl radical, ·OH, concentrations and production using chemical probes (M. Zhang et al and X. Zhang et al), and in the case of an air plasma contacting the liquid the determination of nitrogen containing species and their interactions with species such as hydrogen peroxide (Tarabova et al) is necessary.…”

“…Franclemont et al utilized density function theory, DFT, and experiments to analyze the reaction mechanisms of liquid methanol with plasma discharge . This work contributes to the growing field of plasma for chemical processing in the energy field .…”