Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1996-09-04
1998-12-29
Wu, David W.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
423230, 423232, 42324401, 4232451, 502345, 502346, 502415, 208246, C01B 1716
Patent
active
058536817
DESCRIPTION:
BRIEF SUMMARY
This invention relates to absorbents and in particular to compositions containing copper compounds for the absorption of sulphur compounds, such as hydrogen sulphide, which are often present as impurities in gases and liquids such as hydrocarbon streams, e.g. natural gas.
There have been numerous proposals of using composition containing copper compounds for the absorption of such sulphur compounds: in many of the previous proposals the copper is present in the composition as an oxide, often together with other components such as zinc oxide and/or alumina. Often the copper oxide is reduced to the corresponding metal before use, or is used for treating gas streams containing a reducing gas such as carbon monoxide or hydrogen at such an elevated temperature that reduction of the oxide will occur in situ.
In our EP-A-0 243 052 we demonstrate that certain compositions, containing certain copper compounds, in the form of agglomerates, e.g. granules, as opposed to moulded tablets or pellets, have superior sulphur absorption characteristics and can be used without a reduction step and have good absorption characteristics at low temperatures. The agglomerates were formed by mixing the composition containing the copper compounds with a cement binder and with a little water, insufficient to form a slurry, and then causing the composition to agglomerate into roughly spherical granules. Alternatively the granules could be made by extruding the wetted composition. In that reference, the composition contained zinc or aluminium compounds, preferably both, in addition to the copper compounds and the cement binder. Preferably zinc atoms formed 10-40% of the total number of copper, zinc, and aluminium atoms. Specifically we described the production of agglomerates using a copper-compound containing composition produced by mixing co-precipitated copper and zinc basic carbonates, ie a zinc-substituted malachite, with a zinc aluminate precipitate. We described that such agglomerates, which had been dried but which had not been calcined at a temperature high enough to decompose the basic carbonates, were useful for absorbing hydrogen sulphide at low temperatures, and were superior to agglomerates that had been calcined.
U.S. Pat. No. 4,582,819 discloses the use of agglomerates formed by extruding a mixture of alumina and basic copper carbonate, e.g. malachite, followed by calcination, for the absorption of sulphur compounds. Under the calcination conditions disclosed, viz heating to above 500.degree. F. (260.degree. C.), the malachite will decompose to copper oxide. The agglomerates of this reference contain substantial amounts (above 25% by weight) of alumina.
The amount of sulphur that can be absorbed from a gas stream depends on the absorption capacity of the absorbent, the amount of absorbent employed, and the absorption profile given by a bed of the absorbent. The absorption capacity of an absorbent is the theoretical amount of sulphur that can be absorbed by a given weight of an absorbent.
Thus 1 kg of an absorbent composed of copper oxide or zinc oxide and containing 10% by weight of non-absorbent material, eg alumina, has a theoretical capacity to absorb about 350-360 g of sulphur; on the other hand 1 kg of an absorbent of malachite, or zinc-substituted malachite, again containing 10% by weight of non-absorbent material, has a theoretical sulphur absorption capacity of only about 250-260 g.
It is generally not possible for the full theoretical capacity of the absorbent bed to be realised: thus some sulphur compounds will be detected in the product stream leaving the bed before the theoretical capacity has been realised. The reason for this is that the sulphur absorption front in the bed is not sharp: the sharper the absorption front, the closer the theoretical capacity can be approached.
We have found that despite their lower theoretical capacity compared to copper oxide or copper metal, absorbents made from copper carbonate, basic copper carbonate, or copper hydroxide in fact can give a greater actual sulphur capacity.
REFERENCES:
patent: 4582819 (1986-04-01), Miller et al.
patent: 4983367 (1991-01-01), Denny et al.
Carnell Peter John Herbert
Denny Patrick John
Williams Brian Peter
Wood Peter
Woodroffe Cathy Anne
Imperial Chemical Industries plc
Wu David W.
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