Design and characterization of a solar-enhanced microwave plasma reactor for atmospheric pressure carbon dioxide decomposition

Abstract

The decomposition of carbon dioxide (CO 2 ) is a primary step in carbon re-utilization approaches aimed to fulfill fuels and chemicals demands and mitigate environmental emissions. Plasmachemical CO 2 decomposition processes can be highly efficient; however, their reliance on electrical energy can limit their economic viability and sustainability advantage. In contrast, solar thermochemical CO 2 decomposition approaches can have limited efficiency, but their direct use of the most abundant form of renewable energy affords them the greatest sustainability potential. Solar-enhanced microwave plasma (SEMP) chemical synthesis, based on the direct interaction between microwave plasma and concentrated solar radiation, is investigated as a novel approach to combine the advantages of plasmachemical and solar thermochemical processes. SEMP is motivated by the potential for synergistic effects between solar photons and plasma species, implied by the markedly greater spectral absorption of nonequilibrium CO 2 plasma compared to that of equilibrium CO 2 , to lead to enhanced chemical decomposition. The design, development, and characterization of a SEMP reactor for atmospheric pressure CO 2 decomposition is presented. The reactor is powered by a 1.25 kW magnetron and by up to 525 W of incident radiative power from a high-flux solar simulator. Experimental results reveal that the microwave plasma absorbs up to 20% of concentrated solar radiation at a solar-to-electrical power ratio of 0.5, and that relative absorption decreases with increasing solar input power. However, conversion efficiency and plasma energy efficiency increase with increasing solar power, up to 9% and 25% respectively, for a solar-to-electrical power ratio of 0.75. The enhanced process performance appears to be a consequence of the greater power density in the plasma caused by the direct absorption of solar radiation.

Computational modeling of CO2 conversion by a solar-enhanced microwave plasma reactor

“…SEMP chemical conversion aims to combine the advantages of solar thermochemical and microwave plasma processes. The SEMP CO 2 conversion system developed by Mohsenian et al (2019a) is schematically depicted in figure 1. The reactor was designed to operate with up to 1250 W of electric power from a 2.45 GHz magnetron and up to 525 W of concentrated solar power (effective incident power from a 6.5 kW high-flux solar simulator), using as feedstock CO 2 diluted in argon or nitrogen.…”

“…In SEP processes, the amount of electric power to sustain the plasma is greater than the solar input power, whose role is to augment plasma-driven chemical reactions. A distinct implementation of a SEP process is the conversion of CO 2 using the Solar-Enhanced Microwave Plasma (SEMP) reactor devised by Mohsenian et al (2019aMohsenian et al ( ), (2019b. The SEMP reactor was designed to operate with up to 1250 W of microwave power (MP) at 2.45 GHz and up to 525 W of concentrated solar power at atmospheric pressure conditions with argon-CO 2 and nitrogen-CO 2 mixtures.…”

“…The present work constitutes the first computational study of solar-plasma CO 2 conversion in a SEMP reactor. Specifically, this study focuses on unveiling characteristic features of solar-plasma CO 2 conversion, particularly the role of solar radiation, during operation of the SEMP reactor under the conditions experimentally investigated in Mohsenian et al (2019a) and(2019b). The computational solar-plasma reactor model couples a microwave plasma flow model, based on previously-reported models (i.e.…”

Multi-dimensional modelling of a magnetically stabilized gliding arc plasma in argon and CO2

“…For instance, the influence of discharge power, gas flow rate and Ar dilution on the CO 2 decomposition was studied in a packed-bed plasma [2]. A solar-enhanced microwave plasma was designed to enhance the decomposition of CO 2 at atmospheric pressure [3]. The CO 2 reaction kinetics, especially the vibrational-translational processes in microwave plasma reactors, was studied using a 1D plug flow model [4].…”

Effect of gas temperature on CO2 + ion transport in CO2

“…Consequently, the mobility of the main ions, including of course CO2 + , affects, in multiphysical plasma models, not only the ion density itself, but also the results for the electric field and, through its effect on plasma resistivity, the plasma temperature. Now, since most CO2 plasma sources are characterized by strong temperature variation and temperature gradients (e. g. strong gas cooling like in the case of supersonic expansion [2,16] and strong gas heating like in the case of tangential gas injection with microwave heating [6,7,17,18]), one would expect that the mobility of CO2 + in its parent gas and CO2-bearing gas mixtures had been carefully characterized in the past. Surprisingly, this is not the case, and most recent papers [15] still include the effect of the gas temperature by using the approximate, phenomenological approach of McDaniel and Mason [19].…”