Chemistry of inorganic compounds – Phosphorus or compound thereof – Oxygen containing
Reexamination Certificate
1999-08-25
2001-02-06
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Phosphorus or compound thereof
Oxygen containing
C423S157200, C423S157300, C423S157400, C423S311000, C423S312000
Reexamination Certificate
active
06183712
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for the manufacture of calcium hydrogenphospate from calcium phospate. It also relates to methods for the manufacture of monocalcium phosphate fertilizer, edible monocalcium phosphate and edible dicalcium phosphates.
BACKGROUND OF THE INVENTION
Tricalcium orthophosphate, Ca
3
(PO
4
)
2
, commonly known as calcium phosphate, occurs in nature as rock phosphate ore, for example and is used as such as a source of fertilizer. It can also be converted with sulphuric acid to a mixture of calcium sulphate and phosphoric acid, or it can also be converted with sulphuric acid to a mixture of calcium sulfate and monocalcium phosphate, Ca(H
2
PO
4
)
2
, the latter also being known as calcium dihydrogen phosphate. Calcium phosphate has a relatively low phosphorous content (20% m/m) while monocalcium phosphate, while having a much higher phosphorous content (26.5% m/m), is difficult to manufacture, and also expensive mainly because one of the by-products of the reaction by means of which it is so prepared, calcium sulphate, has to be discarded as a waste product.
Dicalcium phosphate, CaHPO
4
, also known as calcium hydrogenphosphate, has a relatively high phophorous content (22.8% m:m) and may be used as a fertilizer. It is also used in animal licks as well as in the manufacture of certain toothpastes.
Therefore, there is a need in the art for an economical method of producing calcium hydrogenphosphate from calcium phosphate. There is a further need in the art for an economical method of producing monocalcium phosphate fertilizer from calcium phosphate and further producing edible products from the resultant fertilizer.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, a method of producing dicalcium phosphate from calcium phosphate comprises the following steps:
a) reacting the calcium phosphate with a suitable mineral acid to form the corresponding calcium salt and phosphoric acid;
b) hydrolyzing the calcium salt produced by step a) to form the corresponding calcium alkali and the mineral acid of step a), or its salt;
c) if the salt of the mineral acid is formed in step b), electrolyzing said salt to form the corresponding mineral acid together with an alkali;
d) recycling the mineral acid of steps b) or c) to step a);
e) reacting the calcium alkali of step b) with the phosphoric acid of step a) to form dicalcium phosphate.
In accordance with another aspect of the invention, the invention comprises a method of producing monocalcium phosphate (“MCP”) fertilizer comprising the steps of:
(a) reacting ore containing calcium phosphate with sulfuric acid to produce MCP, calcium sulfate and water;
(b) reacting the MCP with oxalic acid to produce calcium oxalate and phosphoric acid;
(c) reacting additional ore containing calcium phosphate with the phosphoric acid produced in step (b) to produce MCP.
The monocalcium phosphate or MCP may be further processed in accordance with this second aspect of the invention to produce fluorine-free edible MCP, or fluorine-free dicalcium phosphate, or fluorine-free dicalcium phosphate dihydrate.
REFERENCES:
patent: 852372 (1907-04-01), Bergmann
patent: 1788952 (1931-01-01), Holz
patent: 2728635 (1955-12-01), Miller
patent: 3391993 (1968-07-01), Cutter
patent: 4012491 (1977-03-01), Hauge
Derwent Publications Ltd., London, G.B.; AN 94-208026, XP002102469 & SU 1 810 319 A (Caspian Area Ore Metall Prodn Assoc), Apr. 23, 1993.
Ullmann's Encyclopedia of Industrial Chemistry, Fifth Edition, vol. A19, pp. 498-499 XP002102468.
Bennett Jones LLP
Griffin Steven P.
Medina Maribel
LandOfFree
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