Chemistry of inorganic compounds – Phosphorus or compound thereof – Halogen containing
Reexamination Certificate
1999-08-17
2001-11-27
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Phosphorus or compound thereof
Halogen containing
Reexamination Certificate
active
06322764
ABSTRACT:
BACKGROUND FOR THE INVENTION
1. Field of the Invention
This invention relates to the preparation of anhydrous high purity phosphorus pentafluoride in high yield.
2. Description of the Prior Art
Known processes for the production of phosphorus pentafluoride include:
1. A phosphorus pentachloride halogen exchange reaction with arsenic trifluoride,
3PCl
5
+5AsF
3
→3PF
5
+5AsCl
3
;
2. The chlorination of phosphorus trifluoride,
5PF
3
+3Cl
2
→3PF
5
+2PCl
3
;
3. Phosphoryl fluoride reacting with hydrogen fluoride,
POF
3
+2HF→PF
5
+H
2
O;
4. Heating a metal fluoride, a phosphoric acid or monofluoro-phosphoric acid and sulfur trioxide;
2H
3
PO
4
+6SO
3
+6 CaF
2
→PF
5
+HPF
6
.2H
2
O+HF 7+6 CaSO
4
;
5. Phosphorus pentachloride reaction with hydrogen fluoride,
PCl
5
+5HF→PF
5
+5HCl.
The first three processes are described in U.S. Pat. No. 3,584,999 to Wiesboeck. The halogen exchange and the chlorofluorination processes require extensive fractionation to separate mixed halides (PClF
4
, PCl
2
F
3
), HCl, inter alia from the desired end product, phosphorus pentafluoride. The last process is disclosed in U.S. Pat. No. 3,634,034 to Nickerson and Wiesboeck, which produces along with phosphorus pentafluoride, hexafluorophosphoric acid and calcium sulfate. Separation problems and disposal of large amounts of calcium sulfate are problems which must be addressed with this process. Finally, the reaction involving phosphorus pentachloride and hydrogen fluoride (equation 5) also requires special techniques of separation for undesirable by-products.
Therefore, there exists a need to provide high purity phosphorus pentafluoride in a simple and economical procedure without the need for extensive fractionation or high pressure equipment and not to have extensive acid gases present which require special disposal.
SUMMARY OF THE INVENTION
In accordance with the present invention, high purity phosphorus pentafluoride can be produced in high yield without resorting to complex process operations. The critical feature of the present invention is effecting the reaction of hexafluorophosphoric acid with a sulfur based acid reactant selected from the group consisting essentially of fuming sulfuric acid (oleum), sulfur trioxide per se, fluorosulfonic acid and mixtures thereof in a reaction medium comprising hydrogen fluoride to form high purity phosphorus pentafluoride in yields of 65 to 100 weight percent (based on contained phosphorus). The yield based on fluoride content is also calculated to be about 90 to 99 percent. Preferably the process is conducted under a dry atmosphere, at autogenous pressures and moderate temperatures.
In one preferred embodiment the process involves a two step process: first preparing hexafluorophosphoric acid by effectively reacting phosphoric acid with a stoichiometric excess of anhydrous hydrogen fluoride and then in the second step, effectively reacting the so formed hexafluorophosphoric acid with fuming sulfuric acid or sulfur trioxide in a reaction medium comprising the unreacted excess hydrogen fluoride from the first reaction step. All fluoride containing compounds other than the phosphorus pentafluoride product may be recycled to the reactor.
More specifically in a preferred embodiment, the process for producing phosphorus pentafluoride according to the invention comprises the steps of:
a) adding an excess of anhydrous hydrogen fluoride above a stoichiometric amount to polyphosphoric acid to effect reaction in a preferably dry atmosphere to form hexafluorophosphoric acid in the unreacted excess of hydrogen fluoride; and then
b) reacting the hexafluorophosphoric acid with fuming sulfuric acid while in contact with the unreacted excess of hydrogen fluoride to form substantially pure phosphorus pentafluoride; and
c) recovering phosphorus pentafluoride, hydrofluoric acid and sulfuric acid.
Optionally, the recovered hydrofluoric acid may be recycled or added to supplement the amount of hydrogen fluoride to be used in the next preparation batch in the first step of the process or as the reaction medium in the second step.
Alternatively, in another preferred embodiment, hexafluorophosphoric acid can be used as the starting material and effectively reacted with a stoichiometric amount or less than a stoichiometric amount required of a sulfur based acid reactant selected from the group consisting essentially of sulfur trioxide, fuming sulfuric acid, fluorosulfonic acid and mixtures thereof in a reaction medium of hydrogen fluoride to produce high purity phosphorus pentafluoride in high yield.
It is, therefore, an object of the present invention to provide an improved process for the preparation of high purity phosphorus pentafluoride in high yield.
Another related object of the present invention is to provide a process which is highly efficient and economical.
A further object of the present invention is to provide a process which produces a minimum amount of hydrofluoric acid by-product.
An associated object of the present invention is to provide a process which results in an industrial grade sulfuric acid which can be recycled.
Further objects and embodiments of the process of this invention will be more readily apparent from the following description of the accompanying drawing and detailed description.
REFERENCES:
patent: 2488298 (1949-11-01), Lange
patent: 3584999 (1971-06-01), Wiesboeck
patent: 3634034 (1972-01-01), Nickerson
patent: 4202867 (1980-05-01), Cannon
McCloskey Joel
Smith W. Novis
Griffin Steven P.
John Lezdey & Assoc
Lithdyne LLC
Medina Maribel
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