Experimental Investigation of the Reactivity of Sodium Bicarbonate toward Hydrogen Chloride and Sulfur Dioxide at Low Temperatures

The use of sodium bicarbonate (NaHCO3) as a solid reactant for the removal of acid pollutants in industrial flue gas streams is a simple and effective process solution. Nonetheless, despite its technological maturity, the industrial application of NaHCO3-based flue gas treatment is still highly empirical. A better knowledge of the heterogeneous reaction process could allow process optimization, resulting in a reduction both in the consumption of reactants and in the generation of solid waste products. In the present study, the reactivity of NaHCO3 toward HCl and SO2 was investigated in the temperature range between 120 and 300 °C. The key role of thermal activation in determining the reactivity of the sorbent was confirmed. The choice of the optimal temperature for acid gas sorption results from a trade-off: higher temperatures increase the reaction kinetics, but induce the sintering of the activated sodium carbonate. The occurrence of sintering is particularly detrimental for high removal efficiency toward SO2, possibly due to the role of the sodium sulfite layer originated by SO2 sorption. As a consequence, the optimal operating temperature resulted as 150 °C for SO2 and 210 °C for HCl. The choice of operating temperature in industrial dry sorbent injection units for acid gas abatement is discussed in view of the present findings.