Experimental investigation of CO₂ conversion in Boudouard reaction driven by an atmospheric-pressure microwave plasma torch

Abstract

An atmospheric-pressure microwave plasma torch (APMPT) is employed to drive Boudouard reaction [C(s)+CO2(g) 2CO(g)] to convert CO2 into CO with storable chemical energy, which is available from the renewable electric energy, such as wind and solar power. In this experiment, the solid carbon is placed in the downstream of the afterglow of CO2 plasma produced by APMPT, which is enclosed in reaction chamber, thereby the reaction occurs in the environment with a plenty of the active species and the large enthalpy. The conversion rate and energy efficiency are experimentally determined by measuring the change of the gas composition, which is analyzed with a Fourier transformation infrared spectrometer (FTIR) and Gas Chromatograph (GC). The variations of conversion rate and energy efficiency are investigated with respect to the plasma state, which is tuned by changing microwave power, gas flow rate, and argon-to-CO2 mixture ratio, and the different forms of carbon material. Furthermore, the high conversion efficiency is obtained with use of the herbaceous type of biomass as carbon material and by increasing microwave power, however, the large percentage of CO2 in carrier gas and increasing gas flow rate impose a negative influence on CO2 conversion.

CO2 conversion to CO via plasma and electrolysis: a techno-economic and energy cost analysis

“…For these reasons, recent investigations have proposed a novel approach for removing O 2 from the outlet streams of plasma reactors by utilising embedded carbon beds. 32,33,36,37 The mechanism incorporates a solid carbon source, such as activated charcoal or biochar, into a basket inside the reactor and next to the stream outlet. The O atoms and O 2 molecules generated after initial CO 2 dissociation reaction (CO 2 -CO + O, or CO 2 -CO + 1 2 O 2 ) react with the incorporated carbon to form additional CO product…”

“…Moreover, the overall performance has not improved drastically when comparing the review of Snoeckx and Bogaerts (2017) 16 to the recent work of Vertongen and Bogaerts (2023). 18 They suggest other routes for improvement beyond the plasma reactor, such as a carbon bed [32][33][34][35][36][37] and quenching in the post-plasma zone. 38 However, the typical lab-scale experiments remain insufficient to draw conclusions on the economic feasibility of plasma technology at an industrial scale.…”

Combined ns pulsed-RF excitation and impedance matching considerations for the production of moderate E/n atmospheric pressure discharges for gas conversion

“…The presence of the C 2 swan bands can provide insight into the properties of the atmospheric pressure CO 2 RF plasma by comparing the spectra in figure 12 to that of other sources operating in similar conditions. The presence of C 2 lines is quite typical of warm plasma sources such as atmospheric pressure MW discharges in CO 2 [29][30][31]. Alternatively, in highly nonequilibrium sources under similar conditions (such as DBD plasmas powered by HV-AC sources), the C 2 lines typically do not dominate [25,32].…”

“…The production of C atoms can be produced through neutral processes, provided that the discharge maintains a high degree of vibrational excitation and/or high gas temperatures [29]. Equations ( 11)-( 13) show a set of reaction pathways where collisions of vibrationally excited CO molecules can produce C 2 O, and in turn, react to form excited C 2 species [31] CO (ν 1 ) + CO (v 2 ) → CO 2 + C ( 11)…”

“…In a pure Ar mixture, ionization and electronic excitation are the only allowable inelastic collisions with energy thresholds of 15.76 and 11.55 eV, respectively. Below these energy thresholds, energy pooling via electron collisions with Ar create metastable states, and this continues until the ionization and/or electronic excitation are achieved [31,38,39]. Introducing CO 2 into the mixture provides an additional energy sink as energy thresholds for electronic excitation, dissociation and vibrational excitations are low (6.23, 5.52 and 0.08 eV, respectively) in comparison to ionization and electronic excitation for Ar [38].…”