Catalyst for the selective oxidation of sulfur compounds to elem

Details Catalyst for the selective oxidation of sulfur compounds to elem Catalyst for the selective oxidation of sulfur compounds to elem

1996-06-18

1998-09-29

Straub, Gary P.

Chemistry of inorganic compounds

Sulfur or compound thereof

Elemental sulfur

4235768, 502330, C01B 1704, B01J 2358

Patent

active

058142932

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a supported catalyst for the selective oxidation of sulfur compounds, in particular hydrogen sulfide, to elemental sulfur, a process for preparing such catalyst and a process for the selective oxidation of hydrogen sulfide to elemental sulfur.
The necessity of purifying gases which are further treated in chemical processes, supplied to buyers, or discharged to the atmosphere, from sulfur compounds, in particular hydrogen sulfide, is generally known. Accordingly, a number of processes are known which are directed to the removal of hydrogen sulfide from gas.
One of the best-known methods of converting hydrogen sulfide to non-harmful elemental sulfur is the so-called Claus process.
In the Claus process, however, the H.sub.2 S is not quantitatively converted to elemental sulfur, mainly as a result of the equilibrium character of the Claus reaction: not allowed to discharge H.sub.2 S-containing residual gas, and so the gas must be combusted, whereby the hydrogen sulfide and other sulfur compounds as well as the elemental sulfur present in the gaseous phase are oxidized to sulfur dioxide. As the environmental requirements are becoming stricter, this will not be allowed anymore because the resultant sulfur dioxide emission would be too high. It is therefore necessary to further treat the residual gas of the Claus plant, the so-called tail gas, in a so-called tail gas plant.
Tail gas processes are known to those skilled in the art. The best-known and to date most effective process for the treatment of tail gas is the SCOT process (See GB-A-1,461,070). In this process the tail gas, together with hydrogen, is passed over a cobalt oxide/molybdenum oxide catalyst applied to Al.sub.2 O.sub.3 as a support, whereby the SO.sub.2 present is catalytically reduced to H.sub.2 S. The total amount of H.sub.2 S is then separated in conventional manner by liquid absorption. One drawback of the SCOT process is that it requires a complicated plant. Another drawback is the high energy consumption involved in removing the hydrogen sulfide from the absorbent again.
Another option in converting hydrogen sulfide in tail gas to elemental sulfur is the so-called BSR Selectox process, disclosed in U.S. Pat. No. 4,311,683. According to this process, the H.sub.2 S-containing gas, mixed with oxygen, is passed over a catalyst containing vanadium oxides and vanadium sulfides on a non-alkaline, porous, refractory oxidic support.
An important drawback of both the SCOT process and the Selectox process is that in both cases the tail gas, after hydrogenation of the sulfur components present to H.sub.2 S, must first be cooled to remove the greater part of the water, because water greatly interferes with the absorption and the oxidation of H.sub.2 S. Due to the associated high investments involved, the costs of tail gas treatments according to these known methods are high.
Another process for the oxidation of H.sub.2 S to elemental sulfur is disclosed in U.S. Pat. No. 4,197,277. According to this publication, the hydrogen sulfide-containing gas is passed with an oxidizing gas over a catalyst which comprises iron oxides and vanadium oxides as active material and aluminum oxide as support material. Further, the support material, which has been impregnated with the active material, has a specific surface larger than 30 m.sup.2 /g and a pore volume of 0.4-0.8 cm.sup.3 /g, while at least 12.5% of the total pore volume is constituted by pores having a diameter greater than 300 .ANG.. It has been found that this catalyst gives rise to at least a partial Claus equilibrium, so that the formation of SO.sub.2 cannot be prevented. As a result, the effectiveness of this process is insufficient. The effectiveness with respect to the conversion of H.sub.2 S to elemental sulfur may generally be adversely affected by the occurrence of the following side reactions:
1. the continued oxidation of sulfur:
2. the reversed (or rather reversing) Claus equilibrium reaction: with the water vapor also present to form hydrogen sulfide and sulfur dioxide.

REFERENCES:
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patent: 5352422 (1994-10-01), Vanderbrink et al.
patent: 5366717 (1994-11-01), Dorshak et al.
"Catalytic Oxidation of Hydrogen Sulfide. Influence of Pore Structure and Chemical Composition of Various Porous Substances", Matt Steijns, et al, Ind Eng. Chem., Prod. Res. Dev., vol. 16, No. 1, 1977, pp. 35-41.
Chem. Abstracts, vol. 101, 1984, p. 109, 101:57159s, "Sulfur Production from Hydrogen Sulfide-Containing Gases from Petroleum Refineries Using Heterogeneous Catalysts".
Database WPI, Week 8713, Derwent Publications Ltd., London GB; AN 87-091266, A.M. Tsybulevsk, et al, "Catalyst for Sulphur Production in Claus Process, etc." and SU,A, 1 248 648 (Gas Processing Res.) 7 Aug. 1986 .

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