Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Patent
1986-03-03
1987-06-16
Carter, H. T.
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
423619, 423620, C01G 2102, C01G 2120, C01G
Patent
active
046735615
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the manufacture of hydrated lead oxides in the bivalent state which may be used commercially as the starting point in the making of all lead chemicals.
More particularly these hydrated lead oxides are useful in the plastic industry to produce stabilizers for polyvinyl chloride resins against thermal and ultraviolet degradation. Typical derivatives are tri-basic lead sulphate, tetra-basic lead silico sulphate, lead silicon sulphate, dibasic lead phosphite, lead phthalate, dibasic lead stearate and lead stearate.
The hydrated lead oxides are also useful in the paint and pigment industry.
BACKGROUND ART
The stabilizers aforementioned are presently manufactured by a process which involves the production of litharge by blowing air through molten lead at very high temperatures. The litharge so produced is slurried with water and then with sulphuric acid under controlled conditions to cause the tri-basic lead sulphate to precipitate. This precipitate is separated and dried ready for use as a stabilizer. It is found that this process causes a high degree of atmospheric pollution, and that the final product contains an undesirably high concentration of unreacted lead. For instance in U.S. Pat. No. 3,323,859 dibasic lead salt stabilizers for PVC are manufactured by reacting litharge with dilute acetic acid, and the dibasic lead acetate so formed is reacted with sodium sulphate.
Various approaches have been taken to avoid the use of litharge in the production of stabilizers. In U.S. Pat. No. 452,386, metallic lead is converted to lead acetate by subjecting it to the alternate action of dilute acetic acid and of atmospheric air, then reacting the lead acetate with sulphuric acid.
DISCLOSURE OF THE INVENTION
It is the principal object of the present invention to provide a process for the manufacture of hydrated lead oxides in the bivalent state, which minimizes pollution and yields a product which may be utilized in the paints and pigment industries and also to avoid the use of litharge in the production of PVC stabilizers.
Accordingly there is provided a process for the manufacture of hydrated lead oxides in the bivalent state characterized by the steps of (1) reacting metallic lead with acetic acid at a temperature up to 200.degree. C. under an atmosphere of an oxygen containing gas of between 1 and 10 atmospheres absolute pressure to form lead acetate, then (2) reacting the lead acetate with a source of ammonium ion under an absolute pressure between 1 and 5 atmospheres up to 100.degree. C. to precipitate hydrated lead oxides.
The acetic acid may be present in concentrations of up to 50% wt., preferably up to 25% wt. and if added as ammonium acetate concentrations of up to 50% wt., preferably 35% wt. should be used.
In a preferred embodiment of the invention the process may include the additional step of adding sulphuric acid and/or ammonium sulphate to the hydrated lead oxides to produce tri- or tetra-basic lead sulphate. Additionally the tri- or tetra-basic lead sulphate can be separated and dried.
In a particularly preferred form of the invention is a process for the manufacture of tri- and tetra-basic lead sulphates, characterized by the steps of (1) reacting excess metallic lead with an aqueous solution containing between 5% and 30% by weight of ammonium acetate at a temperature between 50.degree. C. and 200.degree. C. under an atmosphere of oxygen of between 1 and 10 atmospheres absolute pressure to form lead acetate, then (2) reacting the lead acetate so formed with ammonia under an absolute pressure between 1 and 5 atmospheres at a temperature between 15.degree. C. and 100.degree. C., preferably 60.degree. C. to 90.degree. C., to precipitate lead oxides, then (3) adding to the lead oxides so precipitated sulphuric acid in the stoichiometric amount to produce tri- or tetra-basic lead sulphate, then (4) separating and drying the tri- or tetra-basic lead sulphate so formed.
Preferably in step (1) the concentration of the aqueous solution of ammonium acetate is be
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Carter H. T.
Gasohol Energy Pty. Ltd.
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