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.