Process for purifying phosphorus pentafluoride
A method for obtaining high-purity phosphorus pentafluoride (PF 5 ), which is industrially useful in the fields of semiconductors and batteries, from PF 5 containing a gas mixture of HCl, HF, and so on. Specifically, provided is a process for purifying phosphorus pentafluoride including ( 1 ) an immobilization step in which phosphorus pentafluoride containing a mixture is brought into contact with a metal fluoride (MF n ; M is an n-valent metal) having a specific surface area of 1.0 m 2 /g or more at 40° to 150° C. to immobilize phosphorus pentafluoride in the form of a hexafluorophosphate (M(PF 6 ) n ), ( 2 ) a separation step in which the mixture remaining in the gas phase is expelled out of the reaction system to separate the mixture from the hexafluorophosphate, and ( 3 ) a heat-decomposition step in which the hexafluorophosphate freed of the mixture is heated at 150° to 400° C. under a pressure of −0.1 to 0.1 MPa·G to give phosphorus pentafluoride.
1. A process for purifying phosphorus pentafluoride comprising (1) an immobilization step in which phosphorus pentafluoride (PF 5 ) containing an impurity is brought into contact with a metal fluoride MF n , wherein M is an n-valent metal having a specific surface area of 1.0 m 2 /g or more, at 40° to 150° C. to form a reaction system to immobilize phosphorus pentafluoride in the form of a hexafluorophosphate (M(PF 6 ) n ), (2) a separation step in which the impurity remaining in a gas phase is expelled out of the reaction system to separate the impurity from the hexafluorophosphate, and (3) a heat-decomposition step in which the hexafluorophosphate freed of the impurity is heated at 150° to 400° C. under a pressure of −0.1 to 0.1 MPa·G to give phosphorus pentafluoride.
2. The process according to claim 1 , wherein the impurity in the phosphorus pentafluoride (PF 5 ) used in (1) the immobilization step contains at least one of HF, HCl, F 2 , Cl 2 , CO 2 , SO 3 , POF 3 , SO 2 , H 2 S, PF 3 , NO 2 , NO 3 , and NH 3 .
3. The process according to claim 1 , wherein the contact in (1) the immobilization step is carried out at a contact temperature of 40° to 150° C. under a pressure of 0 to 1.5 MPa·G.
4. The process according to claim 1 , wherein the metal fluoride (MF n ) used in (1) the immobilization step is a monovalent metal fluoride, the metal being at least one member selected from the group consisting of lithium, sodium, potassium, and cesium.
5. The process according to claim 1 , wherein (2) the separation step is carried out by expelling the impurity remaining in the gas phase out of the reaction system to separate the impurity from a solid M(PF 6 ) n .
6. The process according to claim 1 , wherein (3) the heat-decomposition step is carried out by evolving phosphorus pentafluoride with a reduced content of the impurity under a pressure of −0.1 to 0.1 MPa·G and selectively discharging the evolved phosphorus pentafluoride from the reaction system.
7. The process according to claim 1 , wherein (3) the heat-decomposition step further comprises separating the metal fluoride (MF), and the metal fluoride (MF n ) separated in (3) the heat-decomposition step is reused in (1) the immobilization step.
8. The process according to claim 2 , wherein the contact in (1) the immobilization step is carried out at a contact temperature of 40° to 150° C. under a pressure of 0 to 1.5 MPa·G.
9. The process according to claim 2 , wherein the metal fluoride (MF n ) used in (1) the immobilization step is a monovalent metal fluoride, the metal being at least one member selected from the group consisting of lithium, sodium, potassium, and cesium.
10. The process according to claim 3 , wherein the metal fluoride (MF n ) used in (1) the immobilization step is a monovalent metal fluoride, the metal being at least one member selected from the group consisting of lithium, sodium, potassium, and cesium.
11. The process according to claim 2 , wherein (2) the separation step is carried out by expelling the impurity remaining in the gas phase out of the reaction system to separate the impurity from a solid M(PF 6 ) n .
12. The process according to claim 3 , wherein (2) the separation step is carried out by expelling the impurity remaining in the gas phase out of the reaction system to separate the impurity from a solid M(PF 6 ) n .
13. The process according to claim 4 , wherein (2) the separation step is carried out by expelling the impurity remaining in the gas phase out of the reaction system to separate the impurity from a solid M(PF 6 ) n .
14. The process according to claim 2 , wherein (3) the heat-decomposition step is carried out by evolving phosphorus pentafluoride with a reduced content of the impurity under a pressure of −0.1 to 0.1 MPa·G and selectively discharging the evolved phosphorus pentafluoride from the reaction system.
15. The process according to claim 3 , wherein (3) the heat-decomposition step is carried out by evolving phosphorus pentafluoride with a reduced content of the impurity under a pressure of −0.1 to 0.1 MPa·G and selectively discharging the evolved phosphorus pentafluoride from the reaction system.
16. The process according to claim 4 , wherein (3) the heat-decomposition step is carried out by evolving phosphorus pentafluoride with a reduced content of the impurity under a pressure of −0.1 to 0.1 MPa·G and selectively discharging the evolved phosphorus pentafluoride from the reaction system.
17. The process according to claim 5 , wherein (3) the heat-decomposition step is carried out by evolving phosphorus pentafluoride with a reduced content of the impurity under a pressure of −0.1 to 0.1 MPa·G and selectively discharging the evolved phosphorus pentafluoride from the reaction system.
18. The process according to claim 2 , wherein (3) the heat-decomposition step further comprises separating the the metal fluoride (MF n ), and the metal fluoride (MF n ) separated in (3) the heat-decomposition step is reused in (1) the immobilization step.
19. The process according to claim 3 , wherein (3) the heat-decomposition step further comprises separating the metal fluoride (MF n ), and the metal fluoride (MF n ) separated in (3) the heat-decomposition step is reused in (1) the immobilization step.
20. The process according to claim 4 , wherein (3) the heat-decomposition step further comprises separating the metal fluoride (MF n ), the metal fluoride (MF n ) separated in (3) the heat-decomposition step is reused in (1) the immobilization step.