Understanding the chemical kinetics for plasma in liquid: Reaction mechanism of ethanol reforming in microwave discharge

Toward understanding the chemical nature of fuel reforming in liquid phase discharge, a novel kinetic model with being governed by both mass and energy equations was developed for the first time. The model reliability was verified by experimental results for ethanol reforming with water by microwave discharge plasma in liquid (MDPL). The reaction kinetics of ethanol in MDPL were revealed quantitatively. It illustrated that the key reactive species in the MDPL were H, OH, HCO, C and CxHy radicals, which induced the productions of H2, CO and hydrocarbons (CH4 and C2H2). The rate determining steps for ethanol conversion were identified as dehydrogenizing ethanol to C2H5O firstly, and then splitting to CH2O and CH3 radicals. Those two species of CH2O and CH3 governed the formation of CO and hydrocarbons respectively. In addition, the kinetic control mechanism for ethanol reforming in MDPL determined that ethanol was converted by mixed routes of pyrolysis and steam reforming at low initial ethanol molar concentration in liquid (CLeth <50%), and it was converted via only pyrolysis route at CLeth >50%. Water in the liquid supplied OH radical promoting the conversion of CxHy to CO, thereby it regulated the reaction pathway transition between pyrolysis and steam reforming. The energy transfer pathway for discharge power to chemical energy, very important but never discussed for plasma reforming in liquid, was also simulated. It revealed that a very competitive energy efficiency of-85% for ethanol reforming was achieved in the MDPL.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

A novel kinetic model was developed to understand the chemical nature of fuel reforming in liquid phase discharge. The model was verified by experimental results for ethanol reforming in microwave discharge plasma in liquid. The key reactive species in the liquid phase discharge were identified, and the rate determining steps for ethanol conversion were revealed. The kinetic control mechanism for ethanol reforming in liquid phase discharge was determined, and the energy transfer pathway for discharge power to chemical energy was simulated. A competitive energy efficiency of -85% for ethanol reforming was achieved in the liquid phase discharge.