Abstract
The direct capture of CO2 from air (DAC) has been shown a growing interest for the mitigation of greenhouse gases but remains controversial among the engineering community. The high dilution level of CO2 in air (0.04%) indeed increases the energy requirement and cost of the process compared to carbon capture from flue gases (with CO2 concentrations around 15% for coal power plants). Until now, solid sorbents (functionalized silica, ion exchange resins, metal–organic frameworks, etc.) have been proposed to achieve DAC, with a few large-scale demonstration units. Gas-liquid absorption in alkaline solutions is also explored. Besides adsorption and absorption, membrane processes are another key gas separation technology but have not been investigated for DAC yet. The objective of this study is to explore the separation performances of a membrane unit for CO2 capture from air through a generic engineering approach. The role of membrane material performances and the impact of the operating conditions of the process on energy requirement and module production capacity are investigated. Membranes are shown to require a high selectivity in order to achieve purity in no more than two stages. The specific energy requirement is globally higher than that of the adsorption and absorption processes, together with higher productivity levels. Guidelines on the possibilities and limitations of membranes for DAC are finally proposed.
Highlights
Drastic reductions in CO2 emissions are urgently needed in order to face climate change concerns (Field and Mach, 2017)
Carbon Capture and Storage (CCS) consists of first capturing CO2 from concentrated sources that typically emit around 1 million tons of CO2 per year or more per site
CCS is actively investigated through numerous R&D (Research & Development) projects, with a strong emphasis on the capture step, which accounts for 60–80% of the cost of the overall CCS chain (Steeneveldt et al, 2006)
Summary
Drastic reductions in CO2 emissions are urgently needed in order to face climate change concerns (Field and Mach, 2017). Among the portfolio of strategies that can be deployed to mitigate greenhouse gases in the atmosphere, Carbon Capture and Storage (CCS) is considered a key technology (Lackner, 2003). CCS consists of first capturing CO2 from concentrated sources (power plants, cement factories, blast furnaces, refineries) that typically emit around 1 million tons of CO2 per year or more per site. An energy-efficient capture process is of major importance, in order to minimize the impact of secondary carbon emissions; a maximum of 2 GJ per ton of recovered CO2 (thermal basis) is often taken as the target (Figueroa et al, 2008). A broad range of capture processes has been investigated for CCS. Absorption in a chemical solvent is usually considered the best available technology today, with several pilot units installed and tested
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