SELECTIVE PHOSPHATE EXTRACTION

Abstract

The invention relates to a process for the production of phosphoric acid, phosphoric acid obtainable by the process, the production of ammonium phosphate salts, and to the use of ammonium salts. A process for the production of phosphoric acid, comprising: i) reacting a phosphorus-containing material with an acid, without organic solvent, thereby forming a reaction mixture comprising phosphoric acid, wherein said acid has a pKa of 3.5 or lower, and ii) extracting phosphoric acid from the reaction mixture by adding organic solvent to the reaction mixture, thereby forming a phosphoric acid solution, wherein 20 wt. % or less of free water is added to the reaction mixture, based on the total weight of the reaction mixture, and the phosphorus-containing material comprises secondary raw material comprising phosphate.

Claims

1. A process for the production of phosphoric acid, the process comprising: i) reacting a phosphorus-containing material with an acid, without organic solvent, thereby forming a reaction mixture comprising phosphoric acid, wherein said acid has a pKa of 3.5 or lower, and ii) extracting phosphoric acid from the reaction mixture by adding at least one organic solvent to the reaction mixture, thereby forming a phosphoric acid solution, wherein 20 wt. % or less of free water is added to the reaction mixture, based on the total weight of the reaction mixture, and the phosphorus-containing material comprises secondary raw material comprising phosphate.

2. The process according to claim 1, wherein the phosphorus-containing material and the acid combined comprise an amount of 20 wt. % or less of free water by their combined total weight.

3. The process according to claim 2, wherein the phosphorus-containing material and the acid combined comprise an amount of 10 wt. % or less of free water by their combined total weight.

4. The process according to claim 1, wherein 10 wt. % or less of free water is added to the reaction mixture.

5. The process according to claim 1, wherein the reaction mixture comprises at least 30 wt. % of water originating from crystalline frameworks by total weight of the reaction mixture.

6. The process according to claim 1, wherein the organic solvent is added to the reaction mixture having a temperature below a boiling point at atmospheric pressure of the organic solvent.

7. The process according to claim 1, wherein the phosphorus-containing material comprises one or more of: apatite, calcium phosphate, struvite, vivianite, sewage sludge ash, meat and bone meal ash.

8. The process according to claim 1, wherein the phosphorus-containing material comprises struvite.

9. The process according to claim 1, wherein the phosphorus-containing material comprises sewage sludge ash.

10. The process according to claim 1, wherein said acid has a pKa of 2.2 or lower.

11. The process according to claim 1, wherein said acid comprises one or more inorganic acids.

12. The process according to claim 1, wherein the at least one organic solvent is water-miscible.

13. The process according to claim 1, wherein the organic solvent comprises one or more alcohols, ethers, nitriles or ketones.

14. The process according to claim 1, wherein the organic solvent comprises one or more of: acetone, methanol, ethanol, isopropanol, and diisopropyl ether.

15. The process according to claim 1, wherein the at least one organic solvent comprises acetone.

16. (canceled)

17. The process according to claim 1, wherein a molar ratio between said acid, calculated as protons, and phosphorus in the phosphorus-containing material, calculated as P, is 1:1 or more.

18. The process according to claim 17, wherein the molar ratio is 3:1 to 12:1.

19. The process according to claim 1, further comprising at least one of: a) adding phosphoric acid to at least one of step i) and step ii); b) ammoniating the phosphoric acid solution to form an ammonium phosphate salt; and c) removing the at least one organic solvent from the phosphoric acid solution.

20.-24. (canceled)

25. The process according to claim 11 said one or more inorganic acids comprises one or more of: sulfuric acid, phosphoric acid, nitric acid and hydrochloric acid.

Description

EXAMPLES

[0067] Synthesis of Phosphoric Acid from Struvite with No Added Free Water

[0068] 294.5 g dried struvite (1.2 mol) was added to a blender, after which 100.5 ml H.sub.2SO.sub.4 (96%, 1.88 mol) was added slowly. The reactants were blended for 1-2 mins and during the process, the temperature of the reaction mixture increased to 85-98 C. (depending on the insulation level of the blender). A syrupy, semi-transparent liquid was obtained. The blender was stopped and the blender cup cooled in ice until less than 40 C. 600 ml acetone was added to the partly solidified cooled reaction mixture and blended for 1 min to extract phosphoric acid to the organic solvent. The mixture was transferred to a 3.5 liter reactor and mixed at 600 rotations per minute. An additional 400 ml acetone was added to the blender, mixed and transferred to the reactor. The resulting reaction mixture contained solid residues and phosphoric acid dissolved in acetone. The solid residues were separated from the solvent via filtration. Additional 500 ml and 200 ml acetone were successively added to the reactor and filtered, as further extraction and washing steps. The combined filtrates from all the filtration steps yielded a total of 6.5% H.sub.3PO.sub.4in acetone. Acetone was evaporated on a solvent evaporator to obtain pure solvent-free phosphoric acid. The total yield of the pure phosphoric acid was 96% (calculated as phosphorus based on the phosphorus content in the starting material).

Synthesis of Phosphoric Acid from Struvite with a Small Amount of Water Added

[0069] 294.5 g dried struvite (1.2 mol) was added to a blender. 17.7 ml H.sub.2O (0.98 mol) was first added, after which 100.5 ml H.sub.2SO.sub.4 (96%, 1.88 mol) was added slowly. The reactants were blended for 1-2 mins and during the process, the temperature of the reaction mixture increased to 80-95 C. (depending on the insulation level of the blender). The blender was afterwards cooled in ice until less than 40 C. 600 ml acetone was added to the partly solidified cooled reaction mixture and blended for 1 min to extract phosphoric acid to the organic solvent. The mixture was transferred to a 3.5 liter reactor and mixed at 600 rotations per minute. An additional 400 ml acetone was added to the blender, mixed and transferred to the reactor. The resulting reaction mixture contained solid residues and phosphoric acid dissolved in acetone. The solid residues were separated from the solvent via filtration. Additional 500 ml and 200 ml acetone were successively added to the reactor and filtered, as further extraction steps. The combined filtrates from all the filtration steps yielded a total of 5.8% H.sub.3PO.sub.4 in acetone. Acetone was evaporated on a solvent evaporator to obtain a more concentrated phosphoric acid. The total yield of the pure phosphoric acid was 98% (calculated as phosphorus based on the phosphorus content in the starting material).

Extraction Using Different Solvents

[0070] Phosphoric acid extraction after the acidulation process was carried out using different types of solvents (Table 1). In all the experiments, 294.5 g dried struvite (1.2 mol) was added to a blender. 17.7 ml H.sub.2O (0.98 mol) was first added, after which 100.5 ml H.sub.2SO.sub.4 (96%, 1.88 mol) was added slowly. The reactants were blended for 1-2 mins and during the process, the temperature of the reaction mixture increased to 80-95 C. (depending on the insulation level of the blender). The blender was afterwards cooled in ice until less than 40 C. 600 ml organic solvent was added to the partly solidified cooled reaction mixture and blended for 1 min to extract phosphoric acid to the solvent. The mixture was transferred to a 3.5 liter reactor and mixed at 600 rotations per minute. An additional 400 ml solvent was added to the blender, mixed and transferred to the reactor. The resulting reaction mixture contained solid residues and phosphoric acid dissolved in the solvent. The solid residues were separated from the solvent via filtration. Additional 500 ml and 200 ml solvent were successively added to the reactor and filtered, as further extraction steps. The filtrates from the filtrations steps were combined and the results are given in table 1.

TABLE-US-00001 TABLE 1 Phosphoric acid extraction with different solvents. Solvent Yield Acetone 98 Isopropanol 91 Isopropanol azeotrope (12.2 vol. % water) 93