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Received for review June 8, 1981 Revised manuscript received February 1, 1982 Accepted May 3, 1982
Lanthanum Oxide-Based Catalysts for the Claus Process Joseph A. Bagllo,’ Thomas J. Susa,’ David W. Wortham, Elizabeth A. Trlckett, and Thomas J. Lewis’ GTE Laboratories Incorporated, Waltham, Massachusetts 02254
The application of sulfided lanthanum/transition metal based catalysts to the Claus process, with particular emphasis on COS and CS, oxidations by SO, is discussed. Experimental results demonstrate that a sulfided lanthanum
oxide-based material is an effective first stage catalyst, and there is no advantage in adding a transition metal “promoter”. It is also demonstrated that a suwided transition metal based catalyst without the addiin of lanthanum is a more effective catalyst under final air oxidation conditions. The deactivation and regeneration of these catalysts are also discussed.
Introduction Sulfur removal is an essential part of petroleum refining, coal liquefaction, coal gasification, and natural gas processing. Large quantities of hydrogen sulfide are produced from the desulfurization processes that are commonly used. This hydrogen sulfide is subsequently oxidized to sulfur and water in a Claus plant. The combined environmental and economic constraints that are imposed on these plants require that the hydrogen sulfide oxidation process be driven to almost 100% completion. For example, some tail gas treatment processes must limit H2S emissions to less than 10 ppm/vol with emissions of total sulfur, expressed as SO2 equivalent to 1300 ppm/vol. The SO2 equivalent is equal to the combined emissions of H2S,SO2, COS, 2CS2 and sulfur vapor.
serious reactor instabilities. Oxygen-induced poisoning, as well as condensation of sulfur within the pores of the catalyst, is also responsible for making the optimum recovery process impractical. Reaction 1is, therefore, usually carried out in a furnace at -1000 “C to produce a stoichiometric amount of SO2(2HzS/SO2)while reducing the H2S level by -75% (see Table I). Before entering the succeeding catalytic stages and between catalytic stages, sulfur and water are condensed from the gas stream to prevent sulfur condensation on the catalyst bed and to improve the equilibrium yield (Kerr, 1976). The HzS concentration is then further reduced by the reaction 2H2S + SO2 = 2H20 + ( S / n ) S , (2)
Claus Reaction-General The design of a typical Claus plant can be described by the thermodynamic equilibrium calculations for the basic reaction 2H2S + (1 + a)O2 = 2Hz0 + [(2 - a ) / n ] S , + aSO2 (1)
which is carried out catalytically in three or more subsequent stages. As with the thermal stage, the oxidation of H2S by SOz is thermodynamically favored at lower temperatures. Unfortunately, COS and CS2 are formed in significant quantities (0.05 to 1.5 mol %) in the thermal stage by the reaction of CH4 or CO (formed from traces of organic compounds) with sulfur. The reactions are of the type (Grancher, 1978)
where a = 0 to 2 and n = 2 to 8. Under typical conditions, the theoretical degree of conversion of H2S approaches 100% at temperatures
