CROSS REFERENCE TO RELATED APPLICATIONS jOOOl] The present application claims priority to U.S. Provisional Application Serial Mo. 61/884,737, filed September 30, 2013, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION [0002] The present technology relates to the purification of phosphorus pentafluoride.

BACKGROUND OF THE INVENTION

[0003] High purity PF ₅ (phosphorus pentafluoride) is needed for many applications, including, for example, ion implantation, organic synthesis and LiPF ^' e (lithium

hexafluorophosphate) production.

[0004] LiPF _f , is an electrolyte often used in lithium ion batteries. Among commercially produced batteries, lithium ion batteries have one of the best energy-to- weight ratios, no memory effect, and a slow loss of charge when not in use. In addition to powering consumer electronics, lithium ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density. See, e.g., U.S. Publication No. 2012/0003138, which Is incorporated herein by reference in its entirety.

[0005] PF5 is often contaminated with HF (hydrogen fluoride), however, which can interfere with the use of F5 in the desired application. HF contamination can result from the particular way PF5 is produced or the reaction of PF5 with trace water impurities in the raw materials or manufacturing process. For example, some known methods for preparing PF5 include the treatment of polyphosphoric acid with excess HF to produce H^OPF _f ,

(hexafluorophosphonc acid), which then reacts with excess HF and fuming H ₂ S0 ₄ (sulfuric acid) to produce PF5. Another known method for preparing PF5 comprises the fluorination of PCI5 (phosphorus pentachlori.de) with HF to produce PF5 along with H.C1 (hydrogen chloride). [0006] Purifying PF ₅ to remove contaminating HF is often difficult. Because of the ease with which PF5 hydrolyzes, it is not possible, for example, to simply wash the PF5 gas stream with water or caustic solutions to remove HF impurities.

[0007] There remains a need for more effective ways to purify PF ₅ . The present invention addresses this need.

SUMMARY OF THE INVENTION

[0008] ^' The present invention provides a method of purifying PF5, which comprises the steps of (a) contacting a composition comprising PF ₅ and an impurity with a super absorbent polymer, and (b) removing the composition from the super absorbent polymer, wherein the amount of the impurity in the composition is reduced.

[ΘΘ09] In certain embodiments of the present invention, the impurity comprises HF. In other embodiments of the present invention, the impurity consists essentially of HF and the composition consists essentially of PF5. in other embodiments of the present invention, the amount of the impurity in the composition is reduced by more than about 80 % by weight. In other embodiments of the present invention, the amount of the impurity in the composition is reduced to about 5 vol % or less. In other embodiments of the present invention, the super absorbent polymer comprises or consists essentially of cross-linked polyacrylate- polyacrylamide copolymers. In other embodiments of the present invention, the super absorbent polymer has a molecular weight of from about 5,000 to about 5,000,000.

[0010] The present invention also provides a. composition comprising PF ₅ , HF and super absorbent polymer. In certain embodiments of the present invention, the super absorbent polymer in the composition comprises cross-linked polyacrylate-polyacrylamide copolymers. In certain non-limiting aspects, the weight ratio of HF to the super absorbent polymer is about or less than about 60: 1, in certain embodiments is about or less than about 10: 1, and in further embodiments is about or less than about 1 : 1.

[ΘΘ11] The present invention also provides a method of purifying PF ₅ , which comprises the steps of (a) contacting a composition comprising PF ₅ and an impurity with NaF, and (b) removing the composition from the NaF, wherein the amount of the impurity in the composition is reduced. [ΘΘ12] Tlie present invention also provides a composition comprising PF5, HF and NaF. In certain non-limiting aspects, the weight ratio of HF to NaF is about or less than about 1 : 1 , in certain embodiments is about or less than about 0.47: 1 , and in further embodiments is about or less than about 0.12: 1.

BRIEF DESCRIPTION OF THE DRA INGS

[0013] Figure 1 shows a scheme of the setup of a batch purification process using SAP. Crossed circles indicate valves.

[0014] Figure 2 shows a scheme of the setup of a. continuous flow purification process using SAP. Crossed circles indicate valves.

[0015] Figure 3 shows a scheme of the setup of a parallel flow purification process. Crossed circles indicate closed valves and open circles indicated open valves. In this case, bed A is being regenerated (the valves connecting it to the PF ₅ feed stream and the outflow are closed). N ₂ flows through the heated bed A to remove HF. Meanwhile, bed B is being used for the removal of HF from PF5. When bed B has reached capacity, the appropriate valves are opened and closed so that bed B is offline and regenerated and bed A is in operation.

[0016] Figure 4 shows the IR spectrum of material reco vered by static distillation after treatment of a PF5 TTF composition with SAP (superabsorbent polymer) (Example I).

[ΘΘ17] Figure 5 shows the IR spectrum of material recovered during the regeneration of used SAP absorbent by dynamic (heated) distillation (Example 1).

[ΘΘ18] Figure 6 shows the IR spectrum of material recovered by static distillation after treatment of a PF5/ITF composition with NaF (Example 3).

[0019] Figure 7 shows the IR spectrum of material recovered during the regeneration of used NaF absorbent by dynamic (heated) distillation (Example 3). DETAILED DESCRIPTION OF THE INVENTION

[0020] The inventors found thai HF impurities can be removed from crude PF5 by first contacting the HF/PF5 mixture with a suitable material (for example a chemical compound or an absorbent) that has a higher binding affinity for HF than for PF5, and then separating the purified PF5 from the suitable material to which HF is bound,

[0021] Non-limiting examples of materials suitable for the separation of HF and PF5 are NaF (sodium fluoride) and superabsorbent polymers (SAPs). The inventors found that organic SAP is, with respect to PF5, un-reactive and resistant to oxidation, and that it has a higher binding affinity for HF than for PF5, The invention was able to reduce the HF contamination in a PF5/HF mixture from about 75 vol % HF to about 0.3 vol % HF.

[0022] The present invention provides a method of purifying PF ₅ , wherein the method includes contacting a composition comprising PF ₅ and an impurity with a super absorbent polymer, and then removing the composition from the super absorbent polymer, thereby reducing the impurity in the composition.

[0023] The term super absorbent polymer (SAP) as used herein refers to any polymer or copolymer that has a higher binding affinity for HF than for PF5. Such polymers or copolymers may be crosslinked. Non-limiting examples of such SAPs are cross-linked copolymers comprising polyacrylaie and polyacrylamide monomer subunits. Such cross- linked polyacrylate-polyacrylamide copolymers are commercially available, for example, from Evonik Industries or one of its subsidiaries under the trade name Stockosorb* ^' , in particular Stockosorb^ M, Stockosorb^ CW, Stockosorb* ^'' FW, and Stockosorb^ SW.

[0024] The present invention provides a method of purifying PF ₅ , wherein the method includes contacting a composition comprising PF5 and an impurity with NaF, and then removing the composition from the NaF, thereby reducing the impurity in the composition. Within the scope of the present invention, any material that, provides a source of NaF may be used to practice the invention. A non-limiting example of such a material is NalTF?, which may be heated under vacuum to provide NaF.

[0025] The contacting of a composition comprising PF5 and an impurity with a SAP or other suitable material may be conducted in any of the ways usually practiced in the art. For example, the impurity-containing PF _¾ may be purified in batch mode or by using a continuous flow system.

[0026] Batch purifications of PF5/ITF mixtures employ a bed of SAP or other suitable material (Figure 1 ). The PF5 HF mixtures can be mixed with this bed and then left in contact with it for a reasonable amount of time, followed by the removal of the PF ₅ , possibly under vacuum. The purified material is then recovered, for example in a cold-trap.

[0027] Purification with a continuous flow system involves passing a continuous stream of a PF ₅ /HF mixture through a packed column of SAP or other suitable material (Figure 2). PF ₅ is then recovered using a cold trap or compressor; or it is introduced directly into a. process. In a continuous flow system, multiple packed beds may be used in series or in parallel. In parallel mode, one bed is continually used for purification operations while the other bed is regenerated offline. When the first bed nears saturation, it is taken offline for regeneration while the freshly regenerated bed is put on-line (Figure 3),

[0028] The above provided description of purification systems that may be used is not meant to be limiting and the use of any other system commonly practiced in the art is also contemplated to be within the scope of the present invention.

[ΘΘ29] The present invention is not limited to including PF5, the impurity and the super absorbent polymer or NaF in a particular weight ratio. Rather, the present invention encompasses any composition comprising PF5, the impurity and one or several super absorbent polymers and/or NaF. In certain non-limiting aspects, however, the weight ratio of the impurity to the super absorbent polymer is about or less than about 60: 1, in certain embodiments is about or less than about 10: 1, and in further embodiments is about or less than about 1 : 1. In further non-limiting aspects, the weight ratio of the impurity to NaF is about or less than about 1 :1 , in certain embodiments is about or less than about 0.47: 1 , and in further embodiments is about or less than about 0.12: 1.

[ 0030] As part of the present invention, the PFs-containing composition is removed from the super absorbent polymer, NaF or other suitable material The scope of the present invention is not limited to a particular method of facilitating this removal. Rather, any kind of method may be used. These methods are generally known in the art and therefore not repeated here. Non-limiting examples of methods that facilitate the removal of PF5 from the super absorbent polymer, aF or other suitable material include the application of heat, vacuum or pressure (e.g., in the form of an inert sweep gas like N ₂ ) to the composition comprising the PFj, the impurity (for example HF) and the super absorbent polymer, NaF or other suitable material.

[0031] In certain embodiments of the present invention, the impurity comprises or consists of HF. It should be noted that the removal of other impurities from PF5 is also contemplated to be within the scope of this invention. The present invention also

encompasses the removal of HF impurities where additional non-HF impurities are present. These non-HF impurities may be removed together with the HF impurities, separately or not at all. Non-HF impurities not removed together with the HF impurities may include nitrogen gas.

[0032] In certain embodiments of the present invention, the amount of the impurity in the composition is reduced or substantially reduced. While not necessarily limited thereto, in certain aspects, the terms "reduced" or "substantially reduced" mean a reduction of the impurity level by more than about 80 % by weight. In other embodiments, the amount of the impurity in the composition is reduced by more than about 85, 90, 95 or 99.7% by weight. The amount by which the impurity is reduced may be determined by any of the method commonly used in the art. A non-limiting example of such methods is IR (infrared) spectroscopy.

[0033] In certain embodiments of the present invention, the amount of the impurity in the composition is reduced or substantially reduced to about 0.3 vol % or less. In other embodiments, the amoun t of the impuri ty in the composition is reduced to about 5 vol % or less, about 4 vol % or less, about 3 vol % or less, about 2 vol % or less, about 1 vol % or less, or about 0.5 vol % or less. In even other embodiments, the amount of the impurity in the composition is reduced to from about 5 vol % to about 0.3 vol %. The amount of impurity present may be determined by any of the method(s) commonly used in the art. A non- limiting example of such methods is IR (infrared) spectroscopy. The term vol % as used herein refers to the relative amount in mole of a compound (e.g., of the impurity HF) present in a composition (e.g., a composition of PF ₅ ). These ranges refer to HF impurities specifically, as well as to impurities comprising other non-HF impurities. [0034] In certain embodiments of the present invention, the super absorbent polymer comprises or consists essentially of cross-linked polyacrylate-polyacrylamide copolymers. Such SAPs are commercially available, for example, from Evonik Industries or one of its subsidiaries under the trade name Stockosorb^. A number of different products are commercially available under this trade name, including, for example Stockosorb ^® M, Stockosorb ^® CW, Stockosorb ^® FW, and Stockosorb ^® SW. See, e.g., U.S. Patent Nos.

7,914,761 and 8, 153,096, which are incorporated herein by reference in their entirety. The use of all of these commercial products is considered part of this invention, as is the use of similar polymer products commercially available from the same or other companies.

Similarly, the use of similar polymer products not commercially available is also considered to be within the scope of this invention. ΘΘ35] The scope of this invention is not limited to copolymers with specific relative amounts and distributions of polyacrylate and polvacrylamide monomer subunits. Nor is the scope of this invention limited to copolymers with a specific degree and pattern of cross- linking. Furthermore, the present invention encompasses situations where two or more different cross-linked copolymers are used, or where cross-linked polyacrylate- polyacrylamide copolymers are used in conjunction with chemically different polymers or copolymers, which themselves may be cross-linked.

[0036] In certain embodiments of the present invention, the super absorbent polymer as a molecular weight of from about 5,000 to about 5,000,000 dalton. In other embodiments, the super absorbent polymer has a molecular weight of from about 5,000 to about 50,000, from about 50,000 to about 150,000, from about 150,000 to about 300,000, from about 3000,000 to about 1,000,000, or from about 1,000,000 to about 5,000,000 dalton.

[0037J The present invention also provides compositions comprising PF ₅ , HF and super absorbent polymer. The present invention is not limited to compositions including PF5, FIF and a super absorbent polymer in a particular weight ratio. Rather, the present invention encompasses any composition comprising PF5, HF and one or several super absorbent polymers. In certain non-limiting aspects, however, the weight ratio of the HF to the super absorbent polymer is about or less than about 60: 1 , in certain embodiments is about or less than about 10: 1 , and in further embodiments is about or less than about 1 : 1. [ΘΘ38] Similarly, the present invention also provides compositions comprising PF5, HF and NaF. The present invention is not limited to compositions including PF5, TF and NaF in a particular weight ratio. Rather, the present invention encompasses any composition comprising PF ₅ , HF and NaF. In certain non-limiting aspects, however, the weight ratio of the HF to NaF is about or less than about 1 : 1, in certain embodiments is about or less than about 0.47: 1, and in further embodiments is about or less than about 0.12: 1. ΘΘ39] The following examples further illustrate the invention, but should not be construed to limit the scope of the invention in any way.

EXAMPLES Example I

[ΘΘ40] PF5 and HF were separated by batch purification (Figure 1). A bed of about 2.5 g SAP (Stoekosorb*' M product, available from Evonik Industries) was loaded into a 300 ml stainless steel cylinder fitted with stainless steel valves. The cylinder was connected to a stainless steel vacuum manifold and was heated to about 150 °C under vacuum for about 1 hour prior to use to dry the polymer. The final weight of the SAP after heating was 21.7 g, which means that the original SAP before drying had a water content of about 13.2% by weight. The cylinder containing SAP was then loaded with 5.2 g of anhydrous FTF and 1 1.1 g of PF5 and was left standing at room temperature overnight.

[0041] The contents of the SAP-filled cylinder were then statically distilled at room temperature into a second stainless steel cylinder (50 cc), which was liquid nitrogen cooled and under vacuum. 10.7 g of material were recovered in this fashion. The remaining material in the SAP-filled cylinder was recovered by dynamically pumping the contents of the SAP-filled cylinder at 150 °C through a third stainless steel cylinder cooled with liquid nitrogen. 2.8 g of material were recovered in this fashion.

[0042] The material recovered by static distillation was analyzed by IR. The analysis of the IR- spectrum revealed that the recovered material consisted overwhelmingly of PF ₅ since the absorption spectmm showed only the PF ₅ -specifie absorption bands in the region between about 2000 and about 500 cm ^"1 (Figure 4), and that it contained only about 0.3 vol % HF (as determined by a calibration curve) when compared to a starting value of about 75 vol % HF which was initially loaded onto the SAP-filled cylinder.

[0043] The material which was recovered by dynamic distillation was also analyzed by IR spectroscopy. This analysis revealed that, the recovered material consisted mostly of HF since the spectrum showed primarily the HF -specific absoiption bands between about 4000 and about 3500 cm ^"1 (Figure 5).

[0044] The spectra (Figures 4 and 5) indicated that HF was effectively separated from PFs using SAP. Since the SAP used in this experiment had not previously been exposed to HF, about 2.4 g of the HF originally loaded into the SAP-filled cylinder irreversibly reacted with the SAP's cations and could not be recovered. This irreversible reaction between SAP and HF commonly occurs upon the initial exposure of SAP to HF.

Example 2

[0045] Example 1 was repeated using about 11 g of SAP, about 1 1 g of PFs and about 0.5 g of HF. After the removal of PFs and HF, the SAP was analyzed by ICP (inductively coupled plasma) spectroscopy and found to contain about 1 ,400 ppm of phosphoais. Since the SAP contained already about 500 ppm of phosphorus before the experiment was even conducted, the data indicated that PF ₅ irreversibly reacts with the SAP only to a. very limited degree.

Example 3

[0046] PFs and HF were separated by batch purification. A bed of about 10 g of NaHF ₂ was loaded into a 300 ml stainless steel cylinder fitted with a stainless steel valve. The cylinder was then slowly heated under dynamic vacuum to about 400 °C over a period of 5 hours. This yielded 6.70 g of NaF in the cylinder. The cy linder was then loaded with about 0.5 g of anhydrous HF and about 10.6 g of PFs and was left standing at room temperature overnight.

[0047] The contents of the aP --filled cylinder were then statically distilled at room temperature into a second stainless steel cylinder (50 cc), which was liquid nitrogen cooled and under vacuum. About 5.5 g of material were recovered in this fashion. The remaining material in the SAP-filled cylinder was recovered by dynamically pumping the material at 400 °C through a third stainless steel cylinder cooled with liquid nitrogen. About 4.7 g of material were recovered in this fashion.

[0048] The material recovered by static distillation and the material recovered dynamically were analyzed by IR. spectroscopy, as described in Example 1. The spectra (Figures 6 and 7) showed that not ail PF5 was recovered by static distillation and that the portion of the PF5 that could be recovered only dynamically was slightly more contaminated with HF (Figure 7; HF-speeific signals are increased by comparison to Figure 6). Therefore, NaF does remove HF from PF5, but is not as effective as SAP in separating HF from PF ₅ .

Example 4

[0049] Example 3 was repeated using about 10 g of NaHF ₂ , about 10.5 g of PF5 and about 0.5 g of HF. After the removal of PF5 and HF, the NaF pellets in the cylinder were analyzed by ICP (inductively coupled plasma) spectroscopy and found to contain about 17,000 ppm of phosphorus (1.7% by weight ). Since the original NaHF? was found to contain <25 ppm phosphorus before the initial exposure to the PF5/HF, the data indicated that PF5 reacts with NaF extensively and is thus not completely recoverable.

Example 5

[ΘΘ50] PF5 is purified using a continuous flow system. PF5 containing about 1 vol% of HF is flowed through a column of SAP and the purified PF ₅ analyzed by IR spectroscopy. The HF content is greatly reduced in the recovered PF5.

Example 6

[0051] Example 5 is repeated but the PF5 contains about 10 vol% of HF. The HF content is greatly reduced in the recovered PF ₅ .