Understanding the pore size distribution of Ca(OH)2 for effective desulfurization under low-to-medium temperatures

The pore size distribution plays a crucial role in the gas-solid desulfurization reaction of Ca(OH)2, yet its impact on desulfurization performance is not fully understood, especially in low-to-medium temperature range (100–400 °C). This study examined the diffusion and adsorption characteristics of SO2 in Ca(OH)2 pores with different sizes by Monte Carlo Simulation and Molecular Dynamics Methods. The reaction kinetics of desulfurization for samples with different pore structures were analyzed based on TGA data and linear regression. It is found that the adsorption of SO2 on Ca(OH)2 was mainly induced by electrostatic interaction. Pores with the size of 5–15 nm were most favorable for SO2 adsorption, with the maximum adsorption heat of 464.83 kJ/mol at 5 nm. When the pore size increased, the diffusion of SO2 was improved, but the distribution of SO2 became more scattered, resulting in an adverse effect on the desulphurization reaction. The desulphurization process can be divided into the surface reaction controlled stage and product layer diffusion controlled stage. The desulphurization ability was primarily contributed by the reaction controlled stage, in which Ca2+ migration resistance was the least. Pore structure was a crucial factor in determining the duration of the reaction controlled stage. The presence of 15–30 nm pores was of significant importance for this stage. Yet in the diffusion controlled stage, pores size of ≥30 nm was much more important than other sizes to improve the Ca2+ diffusion. This study shows that a reasonable pore size combination facilitates the diffusion of SO2 and its reaction with Ca2+.