Gas solubility in low-volatility liquids : applications for carbon capture and separation

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2022-05

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Primary energy production from renewable resources has been and is projected to increase dramatically in the coming years. However, as these technologies are developed and in order to meet energy demand, we continue to rely on energy production from fossil fuel resources. As the use of these carbon-intensive technologies continues, there is a growing recognition of the importance of developing energy-efficient carbon capture strategies to minimize the environmental impact of CO₂ emissions. Current industrial technology for carbon dioxide separation include absorption by aqueous amine solutions as well as membrane separations. Low-volatility liquids could decrease the energy requirement of solvent regeneration. Here we focus on ionic liquid (IL) and liquid polymer absorbents. While the CO₂ solubility in ILs has been researched extensively, the solubilities of non-target gases, such as N₂, have not. We present the high-pressure solubility of nitrogen in 12 ionic liquids and relate the solubility to IL molar volume and functionalization. Other promising physical absorbents are liquid polyethers such as the commercial Selexol™. However, there has been little report of CO₂ solubility in liquid poly(ethers) other than poly(ethylene oxide) (PEO). This work reports the solubility of CO₂ in a series of poly(glycidyl ethers) in comparison to PEO. Although the CO₂/N₂ selectivity in physical absorbing ILs is reasonable compared to industrial absorbents like Selexol™, it has been previously suggested that blending ILs could further improve the selectivity while providing additional tunability of thermophysical properties. This work characterizes and reports the gas solubility in binary IL/IL mixtures. Composite materials incorporating polymers and ILs have been gaining interest for gas separation applications such as liquid blend absorbents, supported ionic liquid membranes, composite membranes, and liquid-filled capsules. The design of such composite materials is dependent upon the fundamental phase behavior between the polymer and IL. This work reports the phase behavior between ionic liquids and poly(glycidyl ether) materials we identified as promising CO₂ absorbents in previous work.

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