Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1991-01-25
1992-12-08
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
423563, 502325, 502345, 502352, C01B 1716, C01B 3100, B01J 2300
Patent
active
051696126
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for gas purification, and more particularly to a regenerative process for removal of gasesous sulphides in hot gas streams. The invention further relates to a solid absorbent for use in such process.
Industrial gases, such as feed gases for chemical synthesis or off-gases from plant operation, often contain high levels of sulphur compounds which were part of the feed stock. Removal of sulphur compounds from sulphur-containing gases is necessary to meet environmental quality standards or to avoid damage of equipment.
BACKGROUND OF THE INVENTION
Conventionally used solid absorbents in desulphurization processes are activated carbon, iron oxide and zinc oxide.
A solid acceptor comprising supported platinum group metals in association with copper, germanium, rhenium or tin compounds is mentioned in GB Patent No. 1,592,378. The acceptor as described is used in the separation of sulphur dioxide from a gaseous mixture containing sulphur dioxide and oxygen.
Sulphur in sulphur-containing fuel, however, is available in many processes as gaseous sulphides such as hydrogen sulphide, carbonyl sulphide and carbon disulphide or related compounds, such as mercaptans.
Removal of gaseous sulphide-compounds is usually achieved by cold scrubbing processes with liquid absorbents, such as alkanolamines.
The known scrubbing methods disadvantageously require cooling of treated gases, resulting in thermally less efficient processes.
Certain drawbacks of the known scrubbing processes can be avoided by the use of solid gas purification systems including the use of solid sulphide absorbents like metal oxides, which operate at higher temperatures.
A process for removing hydrogen sulphide from gases is mentioned in EP Application No. 159,05. By this process a hydrogen sulphide containing gas is contacted at a temperature above 300.degree. C. with a solid absorbent comprising a mixture of zinc oxide and a zeolite. Spent absorbent is regenerated by passing an oxygen-containing gas over the absorbent at a temperature above 400.degree. C.
Several other absorbents based on zinc oxide are described in the literature. Thus, zinc ferrite was recently proposed as absorbent of this type. Zinc ferrite (ZnO.Fe.sub.2 O.sub.3) is a regenerative absorbent which works at high temperatures. During the gas desulphurization step the zinc and iron oxides are converted into the corresponding sulphides, which can be regenerated to the oxides by using oxidizing gases such as oxygen or air at elevated temperatures.
According to the following reactions: sintering of the absorption mass at elevated temperatures and in decreased desulphurization capacity of the absorbent caused by structural changes. To minimize sintering a proper control of the reaction temperature and atmosphere is necessary to stabilize the temperature within narrow ranges during the regeneration step. Lower temperatures, however, lead to a significant degree of zinc sulphate formation via the following reactions:
This is deleterious to the overall process in that the presence of sulphates not only reduces the sulphur capacity of the sorbent but also leads to the introduction of SO.sub.2 into the hot gas stream.
It is therefore an object of the present invention to provide a process for the purification of sulphide-containing gases without the disadvantages of the known processes.
According to the invention, there is provided a regenerative process for the removal of sulphides from a gas stream by using a solid absorbent comprising tin, tin oxides or mixtures thereof and optionally a stabilizing component, which process comprises the steps of contacting a sulphide-containing gas stream with the solid absorbent; sulphidizing the solid absorbent and desulphidizing the gas stream; and regenerating the sulphidized absorbent by contacting the sulphidized absorbent with a stream of steam.
In a preferred embodiment of the regenerative process according to the invention, the sulphide containing gas stream is contacted at a temperat
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Haldor Topsoe A/S
Straub Gary P.
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