H2S adsorption on a sulfided CoMo/Al2O3 catalyst under flow and pressure conditions: a thermodynamic and modelization study

The amount of H2S adsorbed on a sulfided CoMo/Al2O3 hydrotreating catalyst has been measured under flow conditions using a high pressure thermogravime tric technique. The measurements have been performed under a wide range of conditions: at 313-573 K with a mixture of H2S and CH4 (0.015-0.35 MPa) obt ained from the decomposition of dimethyldisulfide diluted in H-2 (1.8-3.8 M Pa). Five isotherms determined at temperatures below, near, and above the c ritical temperature of H2S, were established from isobaric measurements. Th e adsorbed phase was found to consist essentially of H2S. The thermodynamic s of H2S sorption was studied in order to obtain information about the stat e of the adsorbed phase and the mutual interaction between adsorbed H2S mol ecules or dissociated H2S species, and about the homogeneity or the heterog eneity of the catalyst surface. The experimental isotherms were compared to 15 isotherm models featuring mobile adsorption and localized molecular or dissociative adsorption on a single-, two- and multi-site surface. Discrimi nation among rival models was based on statistics and theory. Two models we re retained: the generalized Freundlich model featuring adsorption of H2S m olecules on a patch-wise distribution of sites, and the Langmuir model char acterized by the dissociative chemisorption of H2S on dual-sites on both Co Mo sulfide phases and alumina. Using the latter model, the amount of adsorb ed H2S on the supported CoMo sulfide phases was determined under conditions close to industrial practice. (C) 2001 Elsevier Science B.V. All rights re served.