Steam activation of biochar for CO2 capture

https://doi.org/10.1016/j.ccst.2022.100059

“Steam activation is another typical modification method for aiding devolatilization and the development of a crystalline phase as well as removing contaminants such as incomplete combustion products Rajapaksha et al., 2016). Steam gasification of biochar is typically carried out at temperatures ranging from 500 to 850 °C, with treatment times ranging from 1 to 7 h (Xie et al., 2022). During the modification process, oxygen from water molecules is exchanged to the free active centers on the carbon surface(Eq. (1)), while the hydrogen produced combines with the carbon on the surface of the biochar to form surface hydrogen complexes. (Eq. (2)–(3) Consequently, thus incomplete combustion products from the pyrolysis process are removed and the formation of crystalline carbon are promoted in the biochar (Wang and Wang, 2019). The total pore volume of steam-activated biochar is higher compared to CO₂-activated biochar. This may be attributed to the fact that the size of water molecules is smaller than that of CO₂, thus facilitating the diffusion of steam into the pores and the formation of more O-containing functional groups on the surface of the biochar. Therefore, steam-activated biochar is usually more useful than CO₂-activated biochar during CO₂ capture (H. Zhao et al., 2018).”