Enhanced CO2 adsorption capacity of bi-amine co-tethered flue gas desulfurization gypsum with water of hydration

An alcoholamine, 2-[2-(dimethylamino)ethoxy]ethanol (DMAEE), was co-tethered with pentaethylenehexamine (PEHA) on the surfaces of the flue gas desulfurized gypsum (FGDG) carriers to synthesize a solid bi-amine adsorbent. The effects of temperature, loading of the blended amines, mass ratio of DMAEE to PEHA, CO 2 partial pressure on the CO 2 adsorption performance were discussed. The water of hydration contained in the FGDG carriers promoted the CO 2 adsorption capacity of the bi-amine adsorbent. Both the breakthrough time and the saturation adsorption capacity of the bi-amine adsorbent were distinctly higher than the DMAEE or PEHA singly tethered adsorbents. The adsorption capacity of the bi-amine adsorbent decreased by only 1.86% over twelve cycles. The isosteric heat of adsorption Q s t and the mean free energy of adsorption E f e was determined and both the values indicated that the adsorption was primarily chemisorption. In the kinetics analysis, Avrami model fitted best with the measured adsorption capacity. With the aid of the 13 C–NMR quantitative analysis results, the CO 2 adsorption mechanism of the bi-amine adsorbent in the presence of the water of hydration was revealed. For the bi-amine adsorbents supported on some porous carriers, FGDG particles were testified to replace up to 7 wt.% of montmorillonite clay or 7 wt.% of MCM–41 zeolite or 10.5 wt.% of ZSM–5 zeolite without any decrease in the CO 2 adsorption capacity.