Claims
- 1. In a continuous process for the preparation of potassium dihydrogen phosphate by the steps involving the reaction of phosphate rock or solubilized form thereof with sulfuric acid, potassium hydrogen sulfate and recycle phosphoric acid at a temperature of about 40.degree.-90.degree.C. in a main reactor to form a resulting slurry containing KH.sub.2 PO.sub.4, H.sub.3 PO.sub.4 and precipitated calcium sulfate, removing the calcium sulfate solid from the mixture, precipitating KH.sub.2 PO.sub.4 from the resultant solution by addition of an organic solvent, recovering the KH.sub.2 PO.sub.4 from the phosphoric acid solution, removing the organic solvent from the phosphoric acid solution, and recycling at least a portion of the phosphoric acid solution to the main reactor, the improved steps which comprise:
- a. conducting the initial step of the reaction by initially charging a mixture of phosphate rock or solubilized form thereof, sulfuric acid and recycle phosphoric acid to a reactor and adding to the material at a controlled rate at 10-50 weight percent aqueous solution of KHSO.sub.4 until substantially complete reaction is obtained for the formation of filterable calcium sulfate crystals; and
- b. removing the calcium sulfate crystals to provide a filtrate and evaporating the resultant filtrate to obtain a solids concentration of greater than about 40 wt. percent prior to precipitation of the KH.sub.2 PO.sub.4.
- 2. A process according to claim 1 wherein the potassium hydrogen sulfate added to the main reactor is formed by the reaction of potassium chloride and sulfuric acid with removal of hydrogen chloride gas, the resulting potassium hydrogen sulfate is dissolved in water to attain about a 10 to 50 weight percent aqueous solution containing about 4 to 10 weight percent of sulfuric acid, and adding to the main reactor in a controlled manner.
- 3. A process according to claim 1 wherein the filtrate from step (b), after removal of the calcium sulfate, and prior to passing to the evaporator, is treated for sulfate reduction by contacting with a member selected from the group consisting of calcium oxide or equivalent calcium bearing material, phosphate rock and mixtures thereof to form a slurry, and separating the slurry to provide a solid and a filtrate.
- 4. A process according to claim 3 wherein the sulfate reduction step is carried out by passing the filtrate to a reactor maintained at a temperature of 40.degree. to 90.degree.C. and there is added thereto a molar quantity of calcium oxide substantially equal to the molar quantity of SO.sub.4.sup.= in the filtrate, the resulting mixture is sent to a separator, the calcium sulfate solids formed are removed therefrom and the filtrate is sent to said evaporator.
- 5. A process according to claim 3 wherein the sulfate reduction step is carried out by adding phosphate rock to the filtrate in a reactor maintained at a temperature of 40.degree. to 90.degree.C., the resulting solids are removed to said main reactor and the resulting filtrate is passed to the evaporator.
- 6. A process according to claim 1 wherein said phosphoric acid, after removal of the organic solvent is passed to a reactor where it is treated with calcium oxide or equivalent calcium-bearing material to form a calcium phosphate slurry and the resulting slurry is recycled to the main reactor for further conversion.
- 7. A process according to claim 6 wherein the resulting slurry, after treatment with the calcium oxide or equivalent calcium bearing material is passed to a separator to provide a resulting solid and a filtrate, said resulting solid is recycled to the main reactor and said filtrate is recycled as make-up water for the solution of KHSO.sub.4.
- 8. A process according to claim 1 wherein said solid potassium dihydrogen phosphate product is subsequently dried and polymerized by heating at a temperature of about 250.degree. to 850.degree.C. to provide a polymerized potassium phosphate product.
- 9. A process according to claim 1 wherein said recovered solid potassium dihydrogen phosphate product is contacted with water, any undissolved solids are removed in a separator to form a filtrate, the solids are withdrawn from the system and there is recovered a filtrate solution comprising potassium dihydrogen phosphate product.
- 10. A process according to claim 9 wherein sufficient water is evaporated from said filtrate to form a wet cake, and said wet cake is dried to provide a solid potassium dihydrogen phosphate product.
- 11. A process according to claim 9 wherein said filtrate is neutralized with calcium oxide to adjust the potassium to phosphorus ratio, the resulting mixture is separated to form a solid and a second filtrate, the recovered solid is removed, and the second filtrate, comprising an aqueous solution of a mixture of potassium phosphates, is recovered.
- 12. A process according to claim 11 wherein said second filtrate is evaporated to dryness to form a solid, and the solid is dried to provide a solid potassium phosphate product.
- 13. A process according to claim 12 wherein said dried product is polymerized by heating at temperatures of about 250.degree. to 850.degree.C. to provide a polymerized potassium phosphate product.
- 14. A process according to claim 1 wherein said potassium dihydrogen phosphate solid product is dissolved in water, the resulting aqueous solution is reacted with about 1 to 3 weight percent of ammonia, urea, NH.sub.4 NO.sub.3, or mixtures thereof, the resulting mixture is separated to form a solid and filtrate solution, said solid is removed, and said solution is recovered as a solution product containing values of nitrogen, phosphorus and potassium.
- 15. A process according to claim 1 wherein said solid potassium dihydrogen phosphate product is contacted with water to form solids and a solution, the solids are removed in a separator, said solution is treated with calcium oxide and ammonia, urea, NH.sub.4 NO.sub.3 or mixtures thereof, the mixture is separated to provide a solid and a solution, the solids are removed in a separator and the solution is recovered as a solution product containing values of nitrogen, phosphorus and potassium.
- 16. A process according to claim 1 wherein the filtrate from step (b), after removal of the calcium sulfate, is subjected to sulfate reduction by contacting with a member selected from the group consisting of calcium oxide, phosphate rock and mixtures thereof to form a slurry, separating said slurry to form a solid and a filtrate, contacting said filtrate with sufficient ammonia to neutralize to a pH of about 10.5 to 11.0 whereby a slurry is formed, separating said slurry to form a solid ammonium phosphate which is removed from the system and a filtrate solution, removing the ammonia from said filtrate solution and recycling to the ammonia neutralization step, evaporating about 10 to 50 percent of the liquid from said filtrate solution, and recovering a solution product containing nitrogen, potassium and phosphate values.
- 17. A process according to claim 16 wherein the filtrate solution is evaporated to dryness, the resulting product is dried at a temperature of about 100.degree. to 200.degree.C. to provide a solid product containing nitrogen, potassium and phosphate values.
- 18. A process according to claim 16 wherein the dried product is polymerized by heating at a temperature of about 250.degree. to 850.degree.C. to provide a solid polymerized product containing nitrogen, potassium and phosphate values.
- 19. A process according to claim 1 wherein said solid potassium dihydrogen phosphate product is contacted with water, the resulting slurry is separated to provide a solid and a filtrate solution, said solid is recycled to the main reactor, said filtrate solution is contacted with sufficient ammonia to neutralize to a pH of about 10.5 to 11.0 and form a slurry, said slurry is separated in a separator to form a solid ammonium phosphate which is removed from the system and a filtrate solution, the ammonia is removed from said filtrate solution and recycled to the neutralization step and there is recovered a filtrate solution containing nitrogen, potassium and phosphate values.
- 20. A process according to claim 19 wherein the filtrate solution is evaporated to dryness and the resulting product is dried at a temperature of about 100.degree. to 200.degree.C. to provide a solid product containing nitrogen, potassium and phosphate values.
- 21. A process according to claim 20 wherein the dried product is polymerized by heating at a temperature of about 250.degree. to 850.degree.C. to provide a solid polymerized product containing nitrogen, potassium and phosphate values.
- 22. A process according to claim 1 wherein said filtrate from step (b), after removal of the calcium sulfate, is evaporated to remove 20 to 50 weight percent of the water to provide a concentrate, said concentrate is contacted with a member selected from the group consisting of ammonia, urea, NH.sub.4 NO.sub.3 and mixtures thereof, the resulting slurry is removed to a granulator, the water is removed and the resulting mixture is granulated to provide a granulated product containing values of nitrogen, potassium and phosphates.
- 23. A process according to claim 3 wherein said filtrate from said sulfate reduction step is evaporated to remove 10 to 50 weight percent of the water and provide a concentrate, contacting said concentrate with a member selected from the group consisting of ammonia, urea, NH.sub.4 NO.sub.3 and mixtures thereof, removing the resulting slurry to a granulator, removing the water and granulating to provide a granulated product containing values of nitrogen, potassium and phosphates.
- 24. In a continuous process for the preparation of potassium dihydrogen phosphate by the steps involving the reaction of phosphate rock or solubilized form thereof with sulfuric acid, potassium hydrogen sulfate, and recycle phosphoric acid at a temperature of about 40.degree.-90.degree.C. in a main reactor to form a resulting slurry containing KH.sub.2 PO.sub.4, H.sub.3 PO.sub.4 and precipitated calcium sulfate, removing the calcium sulfate solid from the mixture, precipitating KH.sub.2 PO.sub.4 from the resultant solution by addition of an organic solvent, recovering the KH.sub.2 PO.sub.4 from the phosphoric acid solution, removing the organic solvent from the phosphoric acid solution, and recycling at least a portion of the phosphoric acid solution to the main reactor, the improved steps which comprise:
- a. conducting the initial step of the reaction by initially charging a mixture of phosphate rock or solubilized form thereof, sulfuric acid and recycle phosphoric acid to a reactor and adding to the material at a controlled rate a 10-50 wt. percent aqueous solution of KHSO.sub.4 until substantially complete reaction is obtained for the formation of filterable calcium sulfate crystals;
- b. continuously passing the resulting slurry to a first separator where the solid calcium sulfate precipitate is removed to leave a filtrate solution;
- c. continuously washing the solid in the separator with water and recycling the strong wash to the main reactor;
- d. removing the filtrate solution from said first separator and passing to a second reactor and reacting with a member selected from the group consisting of calcium oxide or equivalent calcium bearing material, phosphate rock, solubilized forms thereof and mixtures thereof, at a temperature of about 40.degree. to 90.degree.C.;
- e. passing the resulting slurry to a separator to provide solids and a filtrate, removing the resulting solids;
- f. passing the filtrate to an evaporator and evaporating to obtain a solids concentration of greater than about 40 weight percent;
- g. passing the resulting concentrated mixture to a solvent treatment precipitation step and contacting with a sufficient amount of an organic solvent selected from the group consisting of lower alkyl alcohols and lower alkyl ketones to precipitate solid potassium dihydrogen phosphate; and
- h. passing the slurry resulting form the organic solvent precipitation step to a separator to obtain solid potassium dihydrogen phosphate and an organic solvent solution, removing the solids and drying to provide a solid KH.sub.2 PO.sub.4 product, passing the solvent solution to a solvent recovery stage, removing the solvent and recycling to the precipitation step and recovering a solvent-free phosphoric acid solution suitable for recycle to the main reactor as recycle phosphoric acid.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to U.S. Application Ser. No. 755,699, now U.S. Pat. No. 3,600,152, and is a continuation in part of Application Ser. No. 81,280, filed Oct. 16, 1970.
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
739,119 |
Nov 1969 |
BE |
Non-Patent Literature Citations (1)
Entry |
Thompson, New Route Cuts Costs for Potassium Orthophosphates, Chemical Engineering, Apr. 5, 1971, pp. 83-85. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
81280 |
Oct 1970 |
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