Deactivation by fouling of a new catalyst for the low temperature Claus process

Three samples of naturally occurring sepiolite from different deposits in Spain were used as catalysts for the Claus reaction 2nH2S+ nSO2→3n/xSx+ 2nH2O (ΔH = −109.2kJ mol−1) at low temperatures (< 400 K), to purify sulphur compounds (H2S and SO2) from tail-gas. The process was carried out in a fluidized bed reactor of the semicontinuous type on a semi-pilot scale. The sulphur produced in the reaction condenses on the solid surface contributing to its deactivation by fouling. Sulphur incorporation into the solid is governed by internal diffusion of the reactants in microdomains of the porous network, the factors affecting the latter being of capital importance in the occupation degree of the solid. The textural characteristics of the catalysts supports were studied by porosimetric techniques: nitrogen adsorption-desorption isotherms and mercury intrusion. Two pore-plugging mechanisms, the wedge layered (WLM) and the complete layered (MMM) mechanisms are described and applied to the porosimetric data of the sulphurized samples in order to ascertain the number of layers penetrating the system. Significant differences in the pore filling were observed by the application of the models which were related to factors affecting reactant diffusivity within the porous network: texture of the involved solids, working temperature (373–473 K) and reactant concentration (2–4% v/v H2S). Significant conclusions regarding the possibilities of sulphur recovery, in relation to the texture of the solids involved, may be reached in this study, but also, and more general, regarding parameters affecting catalyst deactivation by fouling.