The expanding grain model is used to describe the sulfation reaction rate involving sol-gel-derived copper-based sorbents and sulfur dioxide. The intrinsic reaction rate constant was estimated from the experimental data presented in Part 1 to be in the range of 0.014-0.0047 cm/min for the sorbents with copper content ranging from 11.2% (Cu-1) to 26.5% (Cu-5). The grain radius and the expansion factors were calculated from the physical and chemical properties of sol-gel-derived copper-based sorbents, such as the Brunauer-Emmett-Teller (BET) surface areas, particle porosities, and true densities, as well as chemical composition. The grain radius of the sorbents ranged from 8.89 to 9.14 nm, while the expansion factor ranged from 1.5 to 2.1. The model, which contained two adjustable parameters [i.e., the product layer diffusion (D-g) and the tortuosity parameter (alpha)], was shown to be capable of describing the experimental data of the sulfation reaction with excellent accuracy. On the basis of the model results, the optimum copper content of this type of the sol-gel-derived sorbent was determined to be 13.5%. The expanding grain model was also incorporated in a fluid-bed reactor model to describe the experimental data of the sorbent's performance in a batch fluidized-bed reactor with good accuracy.