Intrinsic reaction selectivity between gaseous HCl and SO2 over ethanol-hydrated CaO adsorbent in coal-fired flue gas dechlorination

The reaction selectivity between HCl and SO2 on Ca-based adsorbents has attracted increasing concern for coal-fired flue gas HCl removal, while previous studies have not reached a convincing consensus. To address this knowledge gap, the reaction selectivity of HCl and SO2 over a newly-developed ethanol-hydrated CaO adsorbent was studied under series of experimental conditions. Essential factors of temperature, SO2 concentration, and products layers on the HCl reaction selectivity were revealed and the reaction pathways, thermodynamic and kinetic characteristics and turnover frequency were elucidated using DFT calculations. The results show that HCl has superior priority over SO2 to active sites. Though the opponent SO2 has thermodynamic advantage in terms of Gibbs free energy and adsorption ratios in equilibrium state, the reaction selectivity highly depends on the kinetics, where the dechlorination reaction shows larger chemical reaction rate than desulfurization reactions. The in-situ FTIR spectra indicates that HCl reacts with the desulfurized products, which exhibits the cleaning effect of sulfide product layers and benefits the high selectivity of the dechlorination reaction. The findings of competitive reaction mechanism of HCl and SO2 on Ca-based adsorbents provide a good foundation for flue gas dechlorination in commercial applications.