Negative CO2 emissions technologies (NETs) are needed to remove decades of CO2 emissions that are driving global climate change. To this end, there have been recent research foci on developing sorbents and processes that capture CO2 from ambient air (direct air capture, DAC). However, nearly all published research on DAC has been conducted under indoor temperature conditions, i.e. 20 to 30 °C. In contrast, the future global implementation of DAC requires it to be operational across a wide expanse of geographical areas, of which the local temperatures can vary between -30 to 50 °C. Similarly, the absolute humidity can vary from ~0 to 84 g/m3 in various locations. Due to the massive amount of air that would be processed, it may be impractical to preheat or dehumidify the air before the CO2 separation. Therefore, it is important to develop DAC materials with good performance at realistic outdoor conditions, especially at sub-ambient conditions, i.e. -30 to 20 °C. In addition to material development, system-level studies at sub-ambient conditions are also needed for the DAC processes to reach optimal designs, which may be very different from those at ambient conditions. Here we demonstrate that MIL-101(Cr) materials impregnated with amines (TEPA, tetraethylenepentamine or PEI, poly(ethyleneimine)) offer promising adsorption/desorption behavior under DAC conditions both in the presence and absence of humidity under a wide range of temperatures (-20 to 25 oC). In particular, our results demonstrate that appropriately designed DAC sorbents can operate in a weak chemisorption modality at low temperatures, even in the presence of humidity. Significant energy savings may be realized via utilization of small temperature swings enabled by this weak chemisorption mechanism. This work suggests that significant work on DAC materials that operate at low, sub-ambient temperatures is warranted for possible deployment in temperate and polar climates.

Sub-ambient temperature direct air capture of CO2 : An overlooked but critical operational window

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.