Sulfate Ion → Calcium Sulfate, Hemihydrate
Reaction equation
[S:1]([O-:5])([O-:4])(=[O:3])=[O:2].[S:6](=[O:10])(=[O:9])([OH:8])[OH:7].[Ca:11].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[F-].[Ca+2].[Ca+2].[Ca+2].[Ca+2].[Ca+2]>>[OH2:2].[S:6]([O-:10])([O-:9])(=[O:8])=[O:7].[Ca+2:11].[Ca+2:11].[S:1]([O-:5])([O-:4])(=[O:3])=[O:2]Participants
Procedure
The present invention is directed to the manufacture of phosphoric acid by the wet process. The hemihydrate, or as it is sometimes called the semihydrate, process is employed to produce wet process phosphoric acid from phosphate rock and sulfuric acid. Phosphate rock and phosphoric acid are added to a first reaction vessel which contains a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate, sulfuric acid and phosphoric acid. The phosphate rock is substantially converted into monocalcium phosphate, phosphoric acid and calcium sulfate hemihydrate in the first reaction vessel. The soluble sulfate content of the first slurry in the first reaction vessel is maintained at a concentration of about +0.7% to about -4%. Sulfuric acid is added to the second reaction vessel which contains a second slurry comprising calcium sulfate hemihydrate, monocalcium phosphate, sulfuric acid and phosphoric acid. The sulfuric acid reacts with the phosphate rock and the monocalcium phosphate producing calcium sulfate hemihydrate and phosphoric acid. The soluble sulfate concentration of the second slurry is maitained at a value of about +0.7% to about +4.5%; provided that the soluble sulfate content of the second slurry is about +1.0% or greater when the soluble sulfate content of the first slurry is +0.7%. Sulfuric acid is added in amounts such that the sulfate content of the added acid and the sulfate content of the added rock is equivalent to about 90% to about 100% of the stoichiometric amount of sulfate required to react with calcium added in the phosphate rock to form calcium sulfate hemihydrate. In order to maintain the desired soluble sulfate concentration in the first reaction vessel and in the second reaction vessel, circulation between the two reaction vessels is initiated. A first portion of the first slurry from the first reaction vessel is circulated through a first conduit into the second reaction vessel, and a first portion of the second slurry from the second reaction vessel is circulated through a second conduit into a first reaction vessel. This circulation is continuous. In order to better disperse the added phosphate rock and the added sulfuric acid within the slurry of the first and the second reaction vessels respectively and to better disperse the incoming slurry with the slurry present in the given reaction vessel, a second portion of the first slurry and a second portion of the second slurry is circulated within the first and second reaction vessels respectively each through its own draft tube at a rate equal to at least 50% of the volume of the slurry in a given reaction vessel per minute. This inter- and intra- vessel circulation disperses the reactants within the slurry in the respective reaction vessels. A third portion of the second slurry is removed from the reaction system so as to separate the liquid and solid components from the said slurry.
Sources & evidence
- ORD record
- ord-b91aecf209f445148626a7f8179be456
- Source dataset
- uspto-grants-1979_01
- Patent number
- US04132760
Reaction notes
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