Claus process catalyst deactivation

Reverse-flow operation for Sulfur Production over Bauxite Catalysts by the Claus Reaction has been considered in Refs 9 and 31. The rate of H2S oxidation by SO2 on bauxite catalysts is very high even at ambient gas inlet temperature, but sulfur condensing at low temperatures blocks the active catalyst surface, and the reaction stops because of catalyst deactivation. In a reverse-flow reactor the periodic evaporation of condensed sulfur from the outlet parts of the catalyst bed occurs. Although it is difficult to remove all the sulfur condensed within the catalyst pellets at the bed edges, after a certain time a balance between the amount of sulfur condensed and evaporated is attained. Using a reverse-flow reactor instead of the two-bed stationary Claus process provides an equal or better degree of... 

Extent of deactivation is a basic criterion determining the efficiency of industrial catalysts. In the case of alumina catalysts widely used in the Claus process the main reason for their deactivation is sulfation (refs. 1,2) The poisoning by sulfates leads to a reduction in life of Claus catalysts, which usually does not exceed ilixee years ... 

Considering industrial operational features of the Claus process, we have suggested that deactivation of Claus catalysts may occur nonuniformly through the catalyst bed. In this paper, results are presented of an investigation of samples of the industrial alumina Claus catalyst after three years of use obtained by means of a specially designed device from four different bed heights of a Claus converter. 

Figure 2c ilustrates the influence of the sulphation on the activity of NaX zeolite in the Claus reaction.The sulphation by method A results in a very high increase in the zeolite activity. NaX sulphated by method B is also more active than pure zeolite but the growth of the activity is lower than after sulphation by method A. Such a high increase of the activity is not observed for NaY sulphated samples- According to the above discussed IR and X-ray results, one can state that hydrogen sulphite and sodium sulphate species, easily formed during NaX sulphation, cause the rise in the Claus activity. Both species react with H25 (refs.2,5,6 10). The third species i.e. aluminium sulphate seems to deactivate the catalyst- This species was observed not only after sulphation process but also after the Claus reaction on pure NaX and NaY. Sulphate ions adsorb on aluminium poison the basic sites in zeolites required in the Claus reaction. 

In practice, it is the sum of all these different processes that leads to deactivation of Claus catalysts. 

The method developed for layer-by determination of extent of deactivation for Claus catalysts has universal application and may be used in other industrial processes with a stationary catalyst bed. 

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