Hydrothermal synthesis of calcium aluminium hydrate-based adsorbent for the removal of CO2

Abstract

In this paper, the influence of Al2O3 on the formation of calcium aluminium hydrate under hydrothermal conditions and the capture of CO2 by Al-based CaO adsorbent, which was prepared from natural calcined lime and synthetic calcium aluminium hydrate, was investigated. It has been determined that, in CaO–Al2O3–SiO2–H2O system, the main synthesis product was calcium aluminium hydrate and the quantity of Al2O3 additive in the primary mixtures affected the amount of formed CAH. It has been observed that the largest absorbed heat (~290 J g−1) of calcium aluminium hydrates was obtained after 8 h of hydrothermal treatment, in the mixtures with a higher amount of Al2O3. It has been estimated that synthetic calcium aluminium hydrates are stable till 225 °C and at a higher temperature are recrystallized to mayenite, while the basic diffraction maximum intensity of mayenite significantly increases in the temperature range of 650–900 °C and the solid-state reactions occurred at the temperature higher than 850 °C. A high value of CO2 capture will be characteristic to formed Al-based CaO adsorbent, and the uptake of CO2 by this adsorbent only slightly decreases from 0.358 at the first cycle to $$0.337{\text{g}}_{{({\text{CO}}_{{\text{2}}} {\text{)}}}} {\text{g}}_{{({\text{ads)}}}}^{{ - 1}}$$ at the eighth cycle.