(368c) Multiple Greenhouse Gases Mitigation (MGM): Process Intensification to Mitigate Non-CO2 Gases and CO2 from Air

The Paris Agreement is an important milestone that brought together 196 countries to agree upon climate targets through emission reduction. Although the main focus has been on mitigating CO₂ in the IPCC’s 1.5 °C report [1], mitigating non-CO₂ greenhouse gases like CH₄ and N₂O will have a significantly higher climate impact. Majority of these non-CO₂ GHGs are from the agricultural and farming sector, accounting for 39% and 72% of CH₄ and N₂O emissions worldwide in 2017 [2, 3]. One of the main challenges with these emissions is that they are very diverse and dilute. However, the confidence gained through development of Direct Air Capture (DAC) technology for CO₂ capture from air [4] presents opportunities to mitigate CH₄ and N₂O emissions. The scope of this paper is to provide an insight into an intensified process that can mitigate multiple GHGs (CH₄, N₂O and CO₂) from air in a single system. The proposed process concept is termed as Multiple Greenhouse Gas Mitigation (MGM) and can accelerate achieving negative emissions. The envisioned process technology can be first applied to mitigate GHGs from air closer to animal ventilation stables, that contains CH₄ (2-300 ppm).

Two types of approaches have been studied to mitigate CH₄ and/or N₂O from air i) gas separation, capture and regeneration, and ii) catalytic conversion/decomposition. In the first approach, CH₄ and N₂O are generally adsorbed over porous zeolites and metal-organic frameworks (MOFs) [5, 6]. However, these processes have challenges with presence of CO₂ and moisture in air [7]. The second approach is to convert CH₄ and N₂O over a catalyst surface (thermal or photocatalyst). Thermal catalyst can convert CH₄ and N₂O only at temperatures above 300 °C [8-10]. It is worth noting that the studies didn’t include results for simultaneous CH₄ and N₂O mitigation. However, photocatalyst have potential to convert both CH₄ and N₂O at room temperatures [11, 12]. Based on this concept, a solar chimney power plant (SCPP) [11] was proposed that can convert CH₄ and N₂O while generating electricity from solar panels. However, there is still a gap in science with respect to mitigating all the three major GHGs (CH₄, N₂O, CO₂) in one single system.

This paper presents a first-of-its-kind process intensification concept to mitigate all the three major GHGs (CH₄, N₂O, CO₂) from air. A simple schematic of the process is shown in Figure 1. Photocatalytic surface is used to convert the CH₄ into CO₂ and H₂O, and N₂O into N₂ and O₂, followed by DAC of CO₂. The captured CO₂ can be then compressed, transported and utilized or stored. The proposed concept can advance the development of DAC technologies and can have greater impact by mitigating CH₄ and N₂O that have higher global warming potential (28 and 265 respectively, following fifth assessment report AR5). In this paper, we propose the intensified process and present analysis with respect to the energy consumed per ton of CO₂-equivalent mitigated.

Methods

A 0D model for the photocatalytic converter is modelled using MATLAB. The 0D model incorporates the thermodynamic and kinetic data, and radiation transport equation to predict the conversion of CH₄ and N₂O in air. 0D model does not consider the shape of the catalytic converter nor the flow profiles. The remainder of the process is modelled using commercial simulation software tools like Aspen Plus. The energy consumed in the process for blowers and regeneration of sorbent is estimated. The energy consumed in the DAC of CO₂ is considered as the reference. The typical amine‑impregnated oxide-based DAC for CO₂ [4] technology is considered in this study.

The key performance indicator in this study is the energy consumed per ton of CO₂-equivalent mitigated. The tons of CO₂-equivalent includes the tons of CO₂ and tons of CH₄ and N₂O multiplied by their global warming potential.

Results

The results from this study mainly compares the estimation of the conversion, material and energy requirements in the process against the DAC for CO₂. We will also make a comparison of the results against the process where each gas would been separately mitigated. The amount of greenhouse gases mitigated and the energy consumed per ton of CO₂-equivalent mitigated will be calculated. The DAC for CO₂ capture consumes 12 GJ/ton-CO₂ for a technology that uses amine impregnated oxide‑based DAC. Preliminary results show that the energy consumed per ton of CO₂-equivalent mitigated will be 4 GJ in the MGM concept. A detailed process analysis, with material (catalyst and sorbent) and energy consumed, quantum yield (as we consider photocatalysts) and amount of greenhouse gases mitigated will be presented in the final paper.

Acknowledgements

The work is part of the project “Energieffektiv negativa utsläpp frÃ¥n jordbrukssektorn” (project number 50340-1) funded by Energimyndigheten (Swedish Energy Agency). The authors would like to thank the collaborators in the project from KTH Royal Institute of Technology (Stefan Grönkvist), Uppsala University and Swedish University of Agricultural Sciences for their contributions through discussions within the project. This work is also financially supported by the Swedish governmental initiative StandUp for Energy.

References

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