Carbonation of lime-based materials under ambient conditions for direct air capture

Carbonation of lime-based materials at high temperatures has been extensively explored in the processes for decarbonisation of the power and industrial sectors. However, their capability to capture carbon dioxide from air at realistic ambient conditions in direct air capture technologies is less explored. In this work, lime and hydrated lime samples are exposed to ambient air for prolonged durations, as well as to calcination/ambient-carbonation cycles, to assess their carbonation performance. It is shown that the humidity plays a key role in carbonation of lime under ambient conditions. Furthermore, faster weathering and higher conversions are demonstrated by hydrated lime, showing a carbonation conversion of 70% after 300 h. Importantly, it was found that there was a negligible difference in the carbonation conversions during five calcination/ambient-carbonation cycles, which can be explained by simultaneous reactivation of cycled material by moist air. These findings indicated that lime-based materials are suitable for carbon dioxide capture from ambient air employing cyclic processes, in a practical time-scale, and that humidity of air plays a key role.