Insight into contraction dynamics of microwave plasmas for CO₂ conversion from plasma chemistry modelling

Abstract

This work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO2 conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo flux (MCF) simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO2 and O2 at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10−5 to 10−4. These factors are shown to be fundamental to drive contraction in the CO2 microwave discharge.

Advances in non-equilibrium $$\hbox {CO}_2$$ plasma kinetics: a theoretical and experimental review

“…In practice, VT relaxation appears quite important in both MW plasmas (at (sub)atmospheric pressure) and GA plasmas, explaining their high gas temperature (3000 K or higher). For this reason, the CO 2 conversion proceeds mainly by thermal reactions in MW and GA plasmas at practical operating conditions, as demonstrated by several models [271,294,[298][299][300][301][302]. However, Pietanza et al recently studied in detail the kinetics vs thermodynamics effects on CO 2 dissociation in high-temperature MW plasmas, with a self-consistent model of the vibrational kinetics of CO 2 , CO and O 2 , and the electron Boltzmann equation, and they concluded that the assumption of thermodynamic equilibrium in MW CO 2 high temperature plasmas has to be considered with caution, as there are still non-equilibrium effects at play, even at temperatures of 3500-5500 K [271].…”

“…Despite the fact that the power was initially mainly deposited into the vibrational levels, fast VT transfer caused significant gas heating, and the CO 2 dissociation was revealed to be mainly thermal. Viegas et al applied a 0D model to describe the plasma chemistry in the core of a vortex-stabilized MW CO 2 plasma, focusing on the pressure-dependent contraction dynamics, in the pressure range between 45 and 225 Torr and temperature range between 3000 and 6500 K [301]. The authors self-consistently coupled the plasma chemistry model with Monte Carlo flux simulations to describe the electron kinetics.…”

Sorption-Enhanced Water-Gas Shift Reaction for Synthesis Gas Production from Pure CO: Investigation of Sorption Parameters and Reactor Configurations

“…The Kerogreen project aims to investigate an advanced PtL conversion route from water and captured CO 2 to carbon neutral jet fuel powered by renewable energy sources [3]. In this project, the crucial step of CO 2 activation is tackled by means of CO 2 plasma splitting into CO and O 2 [4,5]. To circumvent product recombination, O 2 is separated by a solid oxide electrolyte cell.…”

Benchmarking of Monte Carlo flux simulations of electrons in CO2

“…In this framework, MCF can potentially be considered as a reference method, faster than conventional MC approaches, for benchmarking popular Boltzmann solvers that are based on the two-term approximation, with the caveat that, as we have shown, each method must operate with its most appropriate optimized set of cross sections. This model has been integrated in a 0-D model for plasma chemical kinetics in [92].…”