Dry gas–solid carbonation in fluidized beds of Ca(OH)2 and nanosilica/Ca(OH)2 at ambient temperature and low CO2 pressure

This work presents a study on the chemisorption of CO2 by a bed of Ca(OH)2 powder subjected to the flow of a dry CO2/N2 gas mixture (1 vol.% CO2) at ambient temperature and atmospheric pressure. The amount of CO2 and vapor water in the effluent gas from the fluidized bed is analyzed by means of FTIR spectrophotometry. The results obtained indicate that, even in an almost dry atmosphere (RH ⪕ 0.01%), CO2 capture in the fluidized bed occurs by chemisorption on Ca(OH)2, as inferred from the rise of vapor water at the end of the fast carbonation phase. The use of nanosilica as an additive increases the gas–solids contact efficiency and, therefore, enhances CO2 chemisorption on Ca(OH)2 particles. This process is initially activated by free molecular water physisorbed on the material and becomes autocatalyzed by water produced from Ca(OH)2 carbonation. Accordingly, the addition of hydrophilic nanosilica, capable of retaining higher amounts of free molecular water, yields a further enhancement of the CO2 fast sorption capacity.

► Carbonation of Ca(OH)2 at ambient temperature is investigated in a dry fluidized bed.
► FTIR spectrometry has been used to measure the CO2 and H2O band intensities.
► CO2 chemisorption is inferred from our results as affected by the bed dynamical behavior.
► The use of nano-silica has a remarkable effect on enhancing fast carbonation.
► The use of hydrophilic silica serves to further enhance the fast CO2 capture efficiency.