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Progress and trends in CO2 capture/separation technologies: A review

Power-to-Methane is a concept that converts electrical into chemical energy using CO2 and H2O. The concept brings the possibility of connecting the power grid to different sectors, where CH4 is needed such as mobility and industry. In this review, a comprehensive overview of the state-of-the-art of Power-to-Methane is presented. The Power-to-Methane process chain is described in detail. Fundamentals of water electrolysis are highlighted and cell technologies are discussed and assessed. CO2 sources are pointed out, CO2 separation technologies are depicted and compared, and some separation projects worldwide are listed. Thermodynamics of methanation process is analyzed; catalysts and reactors used are descripted and evaluated. Finally, Power-to-Methane plants in operation and construction are addressed.

Power-to-Methane: A state-of-the-art review

Global warming and associated climate change has resulted in serious efforts towards reducing greenhouse gas emissions, primarily carbon dioxide through carbon capture. There are various technical options in pre- and post-combustion modes available viz., adsorption, absorption, membrane separation, chemical looping combustion with and without oxygen uncoupling and cryogenic separations. Among all these, absorption technology which could be deployed as a post-combustion option to be integrated with power plant, has been commercialized with amines as solvents long back. But there is a long way to go to improve this process in terms of economic viability due to large regeneration costs involved and to make it more environmental friendly with minimum toxic and corrosion problems due to solvents. In this review, absorption based carbon capture has been reviewed comprehensively and critically in terms of various aspects like solvents and their synthesis protocols, performance analysis of different solvent systems, contactors, kinetics and thermodynamics, modeling and simulation studies etc. Every section has been discussed in terms of the trends and developments observed including the contemporary status besides citing future challenges and prospects to improve the technology.

Carbon capture by absorption – Path covered and ahead

Modeling CO2 adsorption on amine-functionalized mesoporous silica: 1. A semi-empirical equilibrium model

Electrochemical CO2 capture technologies are gaining attention due to their flexibility, their ability to address decentralized emissions (e.g., ocean and atmosphere) and their fit in an electrified industry. In the present work, recent progress made in electrochemical CO2 capture is reviewed. The majority of these methods rely on the concept of “pH-swing” and the effect it has on the CO2 hydration/dehydration equilibrium. Through a pH-swing, CO2 can be captured and recovered by shifting the pH of a working fluid between acidic and basic pH. Such swing can be applied electrochemically through electrolysis, bipolar membrane electrodialysis, reversible redox reactions and capacitive deionization. In this review, we summarize main parameters governing these electrochemical pH-swing processes and put the concept in the framework of available worldwide capture technologies. We analyse the energy efficiency and consumption of such systems, and provide recommendations for further improvements. Although electrochemical CO2 capture technologies are rather costly compared to the amine based capture, they can be particularly interesting if more affordable renewable electricity and materials (e.g., electrode and membranes) become widely available. Furthermore, electrochemical methods have the ability to (directly) convert the captured CO2 to value added chemicals and fuels, and hence prepare for a fully electrified circular carbon economy.

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Electrochemical carbon dioxide capture to close the carbon cycle

The effect of the addition of weak acids into CO2-loaded solvents or rich solvents on the energy requirement of CO2 desorption was investigated experimentally. The commercially available CO2 solvent monoethanolamine (MEA) was used to absorb different amounts of CO2. Subsequently, a few weak acids such as suberic acid, phthalic acid, and oxalic acid were added into the solvents to study the effect of acid amount on the rate of CO2 release. It was found that CO2 could be released much faster and in much larger quantity with the addition of weak acids while the other desorption conditions were maintained the same. The amount of CO2 released was found to be proportional to the amount of acid added. Acid addition could be potentially used to reduce the energy requirement for CO2 desorption from solvent.

Bo Feng

Papers

Reduction of Energy Requirement of CO2 Desorption by Adding Acid into CO2-Loaded Solvent†