Carbon dioxide supply and scaling constraints on direct air capture using calcium oxide powder

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S0959652625019857

Authors: Lance Dostie, Ian M. Power, Kwon Rausis

24 September 2025

https://doi.org/10.1016/j.jclepro.2025.146635

Highlights

•0.5, 1.0, and 1.5 cm CaO achieved average CO2 removal rates of 32–35 kg CO2/m2/yr

•CO2 diffusion was limited through ≥0.5 cm thick CaO powder

•Ca(OH)2 carbonation rates exponentially increased from 100 ppm to 450 ppm CO2

•The fastest Ca(OH)2 carbonation rate was 5.2 wt% CaCO3/h at 450 ppm CO2

•CO2 supply was readily limited for CaO powder, suggesting small plots are efficient

Abstract

Calcium oxide (CaO; lime) looping is a carbon dioxide (CO2) removal technology that can mitigate carbon emissions. However, scaling this technology requires a thorough understanding of the rate-limiting effects of CO2 supply on CO2 removal rates at and below atmospheric CO2 concentration levels, as well as with various CaO thicknesses and plot areas. Here, we show that carbonation is readily limited by CO2 supply even under high flow rates (e.g., 25 mmol CO2/h over 100 g CaO). Subsequently, the CO2 capture efficiencies using CaO and Ca(OH)2 powders were investigated under ambient CO2 concentrations (397–490 ppm) to 100 ppm. Ca(OH)2 carbonation rates increased exponentially with increasing CO2 concentrations, e.g., 2.1 wt% CaCO3/h at 100 ppm compared to 5.2 wt% CaCO3/h at ambient CO2 concentrations, thereby demonstrating the impact of CO2 concentrations on carbonation efficiency. Column experiments determined CO2 diffusion limitations for CaO deposits ≥0.5 cm, yielding 64 ± 2 wt% CaCO3 and an average CO2 removal rate of 32 kg CO2/m2/yr (24 days; 85–95% RH). Finally, the CO2 removal efficiency of CaO plot areas was estimated, revealing the importance of scaling CO2 supply in concert with increasing CO2 removal that results from greater thicknesses and masses.

Source: ScienceDirect