Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1991-03-05
1996-01-09
Langel, Wayne
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
422203, 422225, C01G 2102
Patent
active
054826896
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The chemical basic reaction, on the basis of which red lead oxide is produced thermally on an industrial scale, reads
In contrast to the direct oxidation of metallic lead to form divalent oxide, this reaction proceeds rather slowly, so that diffusion processes in the solid matter are assumed to be rate-determining reaction steps. This is also borne out by the fact that the supplied oxide modification exerts a marked influence.
The long reaction times in the batch furnaces usually used were therefore frequently accepted as being a matter of course, although there was no lack of tests serving to improve the red lead oxide process:
It follows readily from the above-defined reaction equation that the reaction rate has to be proportional, among others, to the partial pressure of oxygen. Since the reaction proceeds slightly exothermally, the reverse reaction becomes increasingly stronger with rising temperature; however, the decomposition point for the red lead oxide may also be raised by increasing the partial pressure of oxygen in the ambient atmosphere, all other steps influencing the reaction being, of course, accelerated as well.
On the basis of these considerations various processes were developed in which either pure oxygen is supplied to the reaction instead of air or the process is carried out under increased total pressure, as shown e.g. by L. Holub, Bleioxide in der Vergangenheit und Gegenwart, Chemicke Listy 94 (1970), 10, pages 1009-1031, IT-PS 485,215 and DE-PS 633,620 and 590,481. Unfortunately, these references do not give any values showing the reaction rate and the energy consumption. It also seems that the corresponding processes have hardly gained ground in practice, although they were developed as early as around 1930.
Attempts were also made to accelerate the formation of red lead oxide by improving the contact between solid bulk material and atmosphere.
In this connection, reference is made particularly to DE-PS 633,620 where sand is added as a loosening agent and to ES-PS 238,670 in which the reaction is carried out in a ball mill. Also, these processes could not be introduced convincingly on an industrial scale, since the increased technical expenditure could obviously not be compensated by any sufficient different advantages.
In principle, the process described in IT-PS 485,215, in which an intimate contact is achieved between lead and oxygen by evaporating the lead, has to be counted among the latter processes as well. In this case, it was certainly due to the higher energy consumption that the otherwise very interesting process did not become common.
It follows from C.A., Vol. 54 (1960), No. 21671 h, that the oxidation of PbO to form Pb.sub.3 O.sub.4 is determined in the fluidized bed by the diffusion of oxygen and that a temperature increase to 560.degree. C. and an increase of the oxygen pressure to 1 atm could raise the reaction rate to 21/2 times its rate by a corresponding increase in the diffusion rate.
GB-PS 559,994 shows a reactor for red lead oxide, in which the lead oxide is kept in motion by a perpendicular stirrer and the preferably pre-heated oxidizing gases are fed into the reactor from below, so that they do not only chemically react with the material throughout their way up to the surface but also contribute to the fact that the temperature of the material is kept at a constant level. In this way, the oxidizing gases can also be supplied under pressure, which has a notable effect on the reaction rate. However, this is a batch reaction, a conversion into a material having 90% of Pb.sub.3 O.sub.4 taking 8 hours for a batch at approximately 480.degree. C. Formerly this took 20 to 30 hours.
U.S. Pat. No. 3,450,503 shows a process for the production of litharge which can be oxidized into red lead oxide in a second process step. The litharge is produced by spraying molten lead in a zone of high gas turbulence and oxidizing it with air or air enriched with oxygen, which may also be supplied at excess pressure, to form litharge. The finely dispersed PbO
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Chemical Abstracts 54:21671 (h) (1960).
Heubach & Lindgens GmbH & Co. KG.
Langel Wayne
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