Direct air capture by membranes

Reducing CO₂ emissions alone will not suppress global warming, and it is necessary to capture the CO₂ that has been cumulatively emitted into the atmosphere as well. For this reason, negative CO₂ emission technology, a technology to capture CO₂ from the atmosphere, is considered essential. Especially, direct capture of CO₂ from the air, so-called direct air capture (DAC) has attracted much attention as one of promising technologies, because of the high potential capacity of CO₂ capture. In general, absorption, adsorption, and membrane separation are known as representative CO₂ capture technologies, and DAC is basically based on these technologies. In particular, DAC using absorption and adsorption methods has already reached the level of plant scale, but the desorption process of captured CO₂ from the absorbent or adsorbent consumes a large amount of heating energy and water. On the other hand, membrane separation is generally considered as a most cost- and energy-efficient process among these capture technologies, but DAC by membrane separation has not been considered at all due to the immaturity of the membrane performance for CO₂ capture, especially CO₂ permeance. However, recent developments in membrane technology have brought the possibility that membrane processes can be considered as a new approach to DAC. In this article, the potential of membrane technologies as DAC is discussed and future technology target is proposed. Graphical abstract: [Figure not available: see fulltext.]