(112c) Modeling Sulfidation Kinetics and Understanding Sulfidation Equilibrium in Packed Bed Desulfurizers

After external mass transfer and pore diffusion, sulfidation of porous zinc oxide sorbent with hydrogen sulfide can be described in five steps. They are surface adsorption of hydrogen sulfide gas on zinc oxide sorbent and dissociation of the gas molecule on the sorbent surface, followed by reversible surface reactions, sulfide ion migration under the surface, and sulfidation penetration into the solid crystallite. Based on this understanding of chemistry, an empirical rate law for the intrinsic kinetics of sulfidation process was derived in this study. Kinetics modeling results using this reversible, adsorption, and ion migration (RAIM) model were applied to select experiments of single particle sulfidation and compared with several well-defined sulfidation models from the literature. In modeling the sulfidation with zinc oxide pellets, the saturated sulfur capacity and effective pore diffusivity of gaseous hydrogen sulfide in pellets were calculated using the gPROMS (general PROcess Modelling System) modeling. In modeling the sulfidation in full-scale packed desulfurizers, the gPROMS distributed reactor model was used. Case studies were presented for hydrogen sulfide removal from natural gas in a simulated fuel processing train. Finally, a new understanding on the sulfidation equilibrium in packed bed was proposed.