Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1996-09-03
1999-07-27
Lewis, Michael L.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502342, 502 38, B01J 2372
Patent
active
059289856
DESCRIPTION:
BRIEF SUMMARY
This invention relates to copper catalysts. Copper catalysts are widely employed in reactions involving hydrogen. Thus they are employed for hydrogenations, including the hydrogenation of carbon oxides to organic oxygen-containing compounds, such as alcohols, e.g. methanol, and for the shift reaction where carbon monoxide is reacted with steam to form carbon dioxide and hydrogen. They may also be used for the reverse of the shift reaction.
Such copper catalysts usually have the copper in finely dispersed form, and usually incorporate a support or stabiliser such as silica, alumina, chromia, magnesia, and/or zinc oxide to maintain the copper in that finely dispersed form. The catalysts are often supplied as oxidic precursors which require reduction, e.g. with hydrogen, to the active state. This reduction step is often relatively lengthy and consumes a considerable amount of reducing gas, e.g. hydrogen, which in some cases has to be imported to effect the reduction. It is not normally possible to supply copper catalysts in the reduced state as such reduced catalysts tend to be pyrophoric and so present handling difficulties.
After a period of use the catalyst will tend to lose its activity: eventually the activity will have been lost to such an extent that it is necessary to discharge the catalyst and to fill the catalytic reactor with a fresh charge of catalyst. Again, as a result of the pyrophoric nature of the reduced catalysts, special measures have to be taken to effect the discharge of the catalysts. Generally it is necessary to oxidise the copper, under carefully controlled conditions, before discharge is effected. This oxidation step is generally quite time consuming. An alternative discharge method involves displacing an inert atmosphere, e.g. of nitrogen, in the catalyst bed with water: the catalyst can then be discharged together with the water and allowed to weather. However this presents environmental problems as the water tends to be contaminated with copper dust and so disposal of the water after separation from the discharged catalyst presents problems.
The problems of both the lengthy reduction of fresh oxidic copper catalyst precursors and the discharge of spent copper catalysts can be overcome by effecting passivation of the reduced copper. Thus the copper surface is oxidised to a state at which the catalyst can be safely handled. Thus catalysts which have been reduced to the active state and then passivated by the catalyst manufacturer can be supplied without incurring handling problems to the customer who need only effect re-reduction of the oxidised surface layers. Thus the amount of reduction that need be effected by the customer is decreased. Likewise passivation of reduced copper catalysts to a readily handleable state can assist discharge of the catalysts from reactors.
Stabilisation of copper catalysts by passivation is described in GB-A-1319622. In this reference it is proposed that the reduced catalyst is contacted with an inert gas, e.g. nitrogen, and then a small concentration of oxygen, e.g. air, is introduced at such a rate as to keep the temperature below 150.degree. F. (66.degree. C.). The oxygen concentration is gradually increased until the oxygen content is at least 5% by volume: in the example, it is indicated that, despite the passivation treatment. 93% of the copper was still in the elemental state.
We have devised an improved stabilisation method involving passivation. In the present invention the passivation is effected with carbon dioxide as well as oxygen, e.g. air. We have found that the use of carbon dioxide as well as oxygen confers significant benefits.
The aforesaid GB-A-1319622 discloses that an oxidic copper catalyst precursor can be reduced by passing a stream of inert gas over the catalyst to heat the precursor to 350-375.degree. F. (177-191.degree. C.) and then introducing hydrogen to effect the reduction. Upon completion of the reduction, passivation can be effected by purging the hydrogen with inert gas, cooling to 100.degree. F. (38.degree. C.) and th
REFERENCES:
patent: 4062899 (1977-12-01), Laurer et al.
patent: 4863894 (1989-09-01), Chinchen et al.
Ghyka Alexander G.
Imperial Chemical Industries plc
Lewis Michael L.
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