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

Abstract

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, CO2 partial pressure on the CO2 adsorption performance were discussed. The water of hydration contained in the FGDG carriers promoted the CO2 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 Qst and the mean free energy of adsorption Efe 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 13C–NMR quantitative analysis results, the CO2 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 CO2 adsorption capacity.