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Iron promoted activated alumina for scavenging free oxygen in claus converters Bedrossian, Sevan

Abstract

The Claus process is used to remove H2S from acid gas streams and is widely practiced in industry. The most common Claus catalyst in sulphur recovery units is activated alumina (γ- Al2O3). However, it is well documented that excessive free oxygen in the Claus process stream deactivates the alumina catalyst. O2 surface reactions with SO2 lead to sulphation of the alumina surface, thereby inhibiting the conversion of H2S and CS2. One approach to minimizing deactivation by sulphate formation is to use a dual bed reactor configuration, where part of the conventional alumina catalyst is replaced with a catalyst that will promote oxygen consumption and thereby limit sulphate formation. In the present study, Fe catalysts supported on alumina have been examined for oxygen removal. The catalysts were prepared by impregnating a commercial alumina support with solutions of Fe (NO3) 3.9H2O. Catalysts were characterized using XRD (X-ray Diffraction Spectroscopy) and DRIFT (Fourier Transmission Infrared Spectroscopy) as well as BET surface area measurement. The stable phase of Fe on the alumina in the relatively rich H2S reaction gas, typical of Claus process streams, was verified to be FeS2- The effect of catalyst pre-treatment conditions on oxygen removal kinetics is also reported. Experiments showed that O2 consumption occurred on Fe2O3 sites based on the reaction (a) and on FeS2 sites based on the sequential reaction (a) and (b). (a) [Chemical Equation] (b) S + 02 > SO2. It was also concluded that the FeS2/γ-Al2O3 catalyst is bifunctional due to activity of the alumina support towards the Claus reaction. Further study of the O2 removal kinetics was therefore conducted on bulk FeS2 without support. By assuming the stoichiometric order for reactants, the reaction rate constants on bulk FeS2 were determined using the HYSYS simulator and the rate of reaction (b) faster than reaction (a). Hence, FeS2 provides an overall faster rate of O2 consumption than Fe2O3. Also, a mechanism was postulated and the rate limiting steps that were consistent with the rate data were identified.

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