# Patent

## Title
Method of producing sulfur tetrafluoride from uranium tetrafluoride

## Abstract

A method for converting depleted uranium tetrafluoride (UF4) to triuranium octaoxide (U3O8), and producing sulfur tetrafluoride, using a two step process. The first step uses heat and a mixture of the uranium tetrafluoride and an alkaline compound, either an alkaline oxide or an alkaline hydroxide, to produce U3O8 and a water-soluble metal halide. The second step uses heat, sulfur and a halogen to produce sulfur tetrafluoride and triuranium octaoxide.

## Background
PRIORITY/CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 61/279,999 filed Oct. 29, 2009, the disclosure of which is incorporated by reference.


TECHNICAL FIELD
The presently disclosed and claimed inventive concept(s) generally relates to a method for making triuranium octaoxide and more particularly to a method of making uranium-free sulfur tetrafluoride, and triuranium octaoxide from uranium tetrafluoride.
BACKGROUND
The current state-of-the-art in depleted uranium processing requires that DUF6 tailings be converted into DUF4 (depleted uranium tetrafluoride), which can be processed into metallic inorganic fluoride gases, like GeF4, SiF4, and BF3. Pearlhill Technologies has just proved it is feasible to develop nonmetallic inorganic fluorides from uranium tetrafluoride (NIFUT) to produce sulfur tetrafluoride (SF4) gas and triuranium octaoxide (U3O8) from depleted UF4. Producing SF4 opens the door to a whole range of metallic inorganic fluoride gases with established commercial markets. This project will contribute to uranium tailing management in the Excess Uranium Inventory Management Plan of the United States Department of Energy, by achieving viable large scale fluorine recovery for civilian market.
Currently, conversion processes involve either (i) hydrolysis of DUF6 to produce U3O8, along with anhydrous hydrogen fluoride (HF); or (ii) using the fluorine extraction process (FEP) to produce commercially valuable metal fluorides, such as BF3, GeF4, SiF4, and U3O8. This technology (i) is economically unviable; and the FEP technology for production of metallic fluorides, such as BF3, GeF4, and SiF4, appears to be viable for production of very expensive high purity gas product grades that are priced to pay for the high cost of production. While the FEP is profitable for production of expensive, limited-volume specialty products like GeF4, it is still to be proven viable for bulk gases BF3, and SiF4, respectively.
Meanwhile, DOE has 700,000 metric tons of UF6 that can be recovered into useful marketable fluorinated products. United States Enrichment Corporation (USEC), Louisiana Energy Services (LES), AREVA Inc., and General Electric (GE) have all either announced plans to build, or are building new nuclear fuel enrichment facilities in the United States. When these facilities are completed, at their initial stated capacity, they will produce approximately 60 million pounds of DUF6 tails each year. DUF6 cannot be disposed of directly, but must be converted into disposable waste forms. There are very few facilities in the U.S. today that can convert depleted DUF6 tails. This patent presents the most effective and economically viable alternative technology for fluoride recovery from UF6.
SUMMARY
The innovation is an energy efficient, two-step process for production of uranium free SF4 from UF4, called nonmetallic inorganic fluoride from uranium tetrafluoride (NIFUT) technology. The uranium byproduct of the processes in this technology is pure U3O8 and a water-soluble metal halide. It produces uranium-free SF4 gas from a room temperature reaction that can be operated for large scale production of commercially valuable SF4, at a competitive cost with the alternative current industrial. NIFUT technology can produce high quality SF4, to be used by manufacturers of active pharmaceutical ingredients (APIs), agrochemicals, inorganic chemicals, and fluoropolymers.
The invention is a method for converting depleted uranium tetrafluoride (UF4) to uranium free sulfur tetrafluoride (SF4) and triuranium octaoxide (U3O8). This method starts with the first step which is heating a mixture of uranium tetrafluoride and an alkaline compound. These two reagents can be heated at various temperatures, with 350° C. to 650° C. being a typical range. The two reagents are heated in a reaction chamber for 60-240 minutes. The reaction chamber is flushed with dry air from a gas reservoir. Off gases from the reaction of the first step occur, and are passed through a filter to prevent particulate uranium from escaping from the reaction chamber.
The next step is allowing a mixture of the uranium containing product from the first step, combined with sulfur (S) and a halogen to be place in the same reactor. This process is operated at a temperature of approximately 25-80° C., for varying times including 96 hours to 120 hours. The heating of the uranium containing product along with sulfur (S) and a halogen produces sulfur tetrafluoride (SF4) gas, and solid byproducts of a metal halide salt and U3O8 has to be at temperatures below 400° C. that is favorable for re-fluorination of U3O8 to produce UF6.
The reactant defined above as an alkaline compound can take the form of either an alkaline oxide or an alkaline hydroxide. The alkaline oxides which have proven favorable for this reaction include cesium oxide, calcium oxide, and potassium oxide. An alkaline oxide for use in the reaction above can be selected from the group consisting of calcium oxide, cesium oxide, and potassium oxide. The preferred halogen is chlorine, although bromine is also a suitable and a preferred halogen.
One version of the method described above utilizes cesium fluoride (CsF) to combine with sulfur, and a halogen reagent to produce tetrafluoride (SF4) in the second step. The second step of this version of the reaction could utilize bromine or chlorine, with chlorine being preferred. This version of the reaction can be conducted at 25-80° C. for 96-120 hours.
Another embodiment of the method of the invention utilizes cesium hydroxide and uranium tetrafluoride in a reaction chamber at 350-650° C., for 60-240 minutes in the first step. The second step of this version of the reaction preferably utilizes chlorine with bromine also being suitable as a halogen.
Among the alkaline hydroxides which may be utilized for step one of this method are potassium hydroxide and cesium hydroxide.
Another embodiment of the method of the invention utilizes cesium carbonate and uranium tetrafluoride in a reaction chamber at 350-650° C., for 60-240 minutes in the first step. The second step of this version of the reaction preferably utilizes chlorine with bromine also being suitable as a halogen.
Among the alkaline carbonates which may be utilized for step one of this method are potassium carbonate and cesium carbonate.
The method can be operated using the reagents potassium hydroxide and chlorine, potassium hydroxide and bromine, cesium hydroxide and chlorine, or cesium hydroxide and bromine.
Similarly, sodium oxide, potassium oxide, cesium oxide potassium carbonate, and cesium carbonate can be utilized with either chlorine or bromine.
The method can be conducted at various temperatures and times including 400-600° F. Step two of the method can also be conducted at 80° C. or less for less than 10 hours utilizing bromine as the halogen.
The atmosphere in which the heating step of step one is conducted would typically be dry air, which flushes the reaction chamber and causes off gases to go to a KOH scrubber. Step two of the method utilizes a cryogenic condenser to collect the SF4 gas.
The purpose of the Abstract is to enable the public, and especially the scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection, the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the inventive concept(s) of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the inventive concept(s) in any way.
Still other features and advantages of the presently disclosed and claimed inventive concept(s) will become readily apparent to those skilled in this art from the following detailed description describing preferred embodiments of the inventive concept(s), simply by way of illustration of the best mode contemplated by carrying out the inventive concept(s). As will be realized, the inventive concept(s) is capable of modification in various obvious respects without departing from the inventive concept(s). Accordingly, the drawings and description of the preferred embodiments are to be regarded as illustrative in nature, and not as restrictive in nature.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of NIFUT production of nonmetallic fluoride gases from DUF4 and other available alternative technologies for fluoride recovery from DUF4.
FIG. 2 shows uses of SF4 combined with carboxylic acids in pharmaceuticals and agrochemicals.
FIG. 3 shows uses of SF4 combined with ketones, aldehydes, or alcohols in pharmaceuticals and agrochemicals.
FIG. 4 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample after stoichiometric mixture of Na2O—Na2O2 (80:20) and UF4 were heated at 600° C. for one hour.
FIG. 5 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample after stoichiometric mixture of CaO and UF4 were heated at 600° C. for one hour.
FIG. 6 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample after stoichiometric mixture of MgO and UF4 were heated at 600° C. for one hour.
FIG. 7 shows XRD pattern for UF4 as reference for identification of uranium by products of steps 1 and 2.
FIG. 8 shows XRD pattern for U3O8 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 9 shows XRD pattern for UO3 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 10 shows XRD pattern for UO2 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 11 shows a summary of logarithms of equilibrium constants listed in Table 6.
FIG. 12 shows a summary of logarithms of equilibrium constants listed in Table 6.
FIG. 13 is a diagram of the laboratory scale apparatus for SF4 production for step one.
FIG. 14 is a diagram of the laboratory scale apparatus for SF4 production, for step two.
FIG. 15 is a graph of FTIR absorbance spectrum of 30% SF4.



DETAILED DESCRIPTION OF THE PREFERRED AND EXEMPLARY EMBODIMENTS
While the presently disclosed inventive concept(s) is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the inventive concept(s) to the specific form disclosed, but, on the contrary, the presently disclosed and claimed inventive concept(s) is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the inventive concept(s) as defined in the claims
A preferred embodiment of the method is the production of sulfur tetrafluoride (SF4) from uranium tetrafluoride by a two-step process. This process results in nonmetallic inorganic fluorides from uranium tetrafluoride (NIFUT) to produce sulfur tetrafluoride (SF4) gas and triuranium octaoxide (U3O8) from depleted UF4. This process is shown in FIG. 1. The production of sulfur tetrafluoride is commercially valuable because when SF4 is combined with carboxylic acids, many products useful in pharmaceuticals and agrochemicals can be made, as shown in FIG. 2. When SF4 is combined with ketones, aldehydes, or alcohols, many products useful in pharmaceuticals and agrochemicals can be made, as shown in FIG. 3.
Step One: The first step of this particular embodiment of the method is to combine a mixture of uranium tetrafluoride (UF4, a green solid) and an alkaline compound, such as sodium oxide or cesium oxide (Na2O—Na2O2 or Cs2O, white solids). An alkaline oxide, alkaline carbonate, or an alkaline hydroxide can be used, such as sodium oxide, sodium hydroxide, cesium carbonate, cesium oxide, cesium hydroxide, potassium oxide, potassium carbonate, or potassium hydroxide. The next step is heating to 400° C. with sufficient air present, for 15 hours. Heating to 600° C. produced complete conversion of UF4 within 4 hr. The reaction at 400° C. achieves about 70% conversion after 15 h. The products of the reaction are, and will have, an orange-grey and grey color, respectively. The uranium byproduct of the processes in this technology is pure U3O8 and a water-soluble metal halide.
The quantities of uranium tetrafluoride and alkali metal oxide, as an example, can be in the range of 314 g of uranium tetrafluoride to mass equivalent of 1 mole of alkali metal oxide
In the preferred embodiment, heat is applied to the stainless steel reactor or other suitable container using a Lindberg Blue heater, a Parr heater, or other suitable heating apparatus and methods can be used.
An alternative preferred embodiment involves the reaction of uranium tetrafluoride and cesium hydroxide (CsOH) or potassium hydroxide (KOH) at 450° C. in the presence of air, and over 12 h, resulted in the production of corresponding anhydrous fluoride salts, i.e. CsF and KF, and U3O8 as the uranium byproduct
A preferred production apparatus for carrying out the method 10 is shown in FIGS. 13 and 14, and would be scaled up for large scale production, with equivalent equipment to the equipment shown in the laboratory scale embodiment. Shown in FIG. 13 is a 304 or 316 L stainless steel cylinder 14 which serves as a crucible or reaction vessel, and a heat source 16. A thermocouple 18 is present to monitor the temperature of the reaction chamber 14.
Attached to the stainless steel cylinder 14 is a T coupling, with the T coupling in the laboratory scale version being a 1 inch stainless fitting with a 1 inch top opening 22, and a 1 inch side opening 24. Inserted into the top opening 22 is a gas line 26, in this case made of stainless steel, although Hastelloy C, Monel, or other suitable material could be utilized for the gas line 26.
The gas line 26 extends to a dry air source 28, with an inline valve 30, pressure regulator 32, and mass flow meter 34 being present on the gas line 26. The dry air source supplies air to flush the gases from the reaction chamber 14.
Attached to the side opening 24 is a 1 inch outflow line 36, with a gauge 38, a valve 40, and a filter 42. The material of the outflow line is preferably stainless steel in the laboratory scale setup, but could also be Teflon, Hastelloy C, or Monel, or any suitable material in a larger production model. The purpose of the filter 42 is to prevent any particulate uranium from leaving the reaction vessel 14, and a suitable filter is a 0.3 micrometer Pall's Gaskleen V filter, although other suitable filters may be used.
Gas passing through the filter 42 is routed through the online gas cell 44 which is located in analytical instrumentation 46 to test for the composition of volatile effluents. Effluents pass through the gas cell 44, to either a cryogenically cooled condenser or a KOH scrubber 48, and are vented from the KOH scrubber 48 through a vent 50. In the laboratory scale setup, the preferred analytical instrumentation is a Fourier Transform Infrared (FTIR) spectrometer, or a gas chromatograph (GC). The KOH scrubber is approximately 5 L in volume, and contains 1-5 M KOH, and would be scaled up for larger production.
The reactivity's of MgO, CaO, or Na2O with UF4 were determined over a wide range of temperature. The process involved addition of stoichiometric quantities of each oxide with UF4, and heating to 600° C. for 30 minutes. The physical look of the products vs. starting materials were photographed, showing color change from white (metal oxide, MOx) or green (UF4) to grey final color. In the case of 80:20 Na2O—Na2O2, there was a separate yellow-red colored product that stayed on top of the grey powder. Powder X-Ray diffraction (XRD) data confirm that the reaction of UF4 was rapid and complete, producing U3O8, and the respective metal fluorides.
However, the effort to produce SF4 from the reaction of (i) NaF/S/Br2, (ii) MgF2/S/Br2, or (iii) CaF2/S/Br2 at room temperature was unsuccessful. The computerized study evaluation of thermodynamic feasibility of conversion of the metal fluorides to SF4 was undertaken using the HSC 7.0 software. The results are summarized in Tables 1 to 7 as in FIGS. 11 and 12. The results showed that the best candidates were CsF and KF.
The most practicable commercial approach to producing KF or CsF from UF4 involved dehydration of the mixture of the metal hydroxide and UF4 at 600° C., with flowing air. The only byproducts are dry U3O8 and the respective metal fluoride (MFn). When this product has been sufficiently dehydrated, the MFn represents the best chemical reagent for production SF4, in the presence of U3O8; and resulting in <10,000 ppm of SOF2 and HF.

4M-OH+3UF4+O2→4MFn+U3O8+6H2O

U3O8+4MFn+S+2Cl2→SF4(g)+4MCl+U3O8 

Early investigation of this approach produced encouraging results. When the mixtures of (i) CsF/S/Cl2, ad (ii) CsF/S/Br2 were allowed to sit at room temperature, 75%, and 60% conversion of S/Cl2 to SF4 had occurred within 72 h. Although, these two processes resulted in the production of SF4, the byproduct from CsF/S/Br2 was a messy brown viscous liquid! This will complicate the clean up of U3O8, a make the process an uncomfortable task because of the presence of residual bromine. On the other hand, the gas-solid process of CsF/S/Cl2 produced SF4 and light yellow CaCl/CsF solid mixture, which changed to white on standing in the hood. Thus, on the basis of the kinetic advantages, better thermodynamic feasibility, and less complex byproducts stream, the CsF/S/Cl2 process was selected for study of the U3O8—CsF/S/Cl2 and U3O8—KF/S/Cl2 systems. The progress of the reaction can be monitored by Fourier Transform infrared (FTIR) spectrometer. The yield of the process was studied by recording the pressure in batch processes at (a) RT; and (b) 80° C./8 h. The general balanced equation shows that the product (SF4) pressure will be half as much as the reagent gas (Cl2) pressure.
A successful process must prevent the conversion of U3O8 to UF6. SF4 reacts with UO2, UO3, and U3O8 to produce UF6 at 100, 300 and 400° C., respectively. Therefore, the ideal commercial process must operate at or below 100° C. The KOH/UF4, CsOH.H2O/UF4, and the resultant U3O8—KF/S/Cl2 and U3O8—CsF/S/Cl2 processes were assembled according to the set up in FIGS. 13 and 14. Kinetic information was obtained by recording changes in pressure periodically. The reaction of cesium hydroxide (CsOH) and UF4 to produce CsF/U3O8 is thermodynamically favored (see Table 1), and was carried out at 600° C. to ensure complete dehydration of CsF produced.
FIG. 4 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample “J” after step 1 of the method, after stoichiometric mixture of Na2O—Na2O2 (80:20) and UF4 were heated at 600° C. for one hour.
FIG. 5 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample “K” after step 1 of the method, after stoichiometric mixture of CaO and UF4 were heated at 600° C. for one hour.
FIG. 6 shows the presence of U3O8 in the X-Ray diffraction (XRD) pattern of a sample “L” after step 1 of the method, after stoichiometric mixture of MgO and UF4 were heated at 600° C. for one hour.
FIG. 7 shows XRD pattern for UF4 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 8 shows XRD pattern for U3O8 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 9 shows XRD pattern for UO3 as reference for identification of uranium byproducts of steps 1 and 2.
FIG. 10 shows XRD pattern for UO2 as reference for identification of uranium byproducts of steps 1 and 2.
Step Two: The second step of the two-step process involves adding powdered sulfur (S) and a halogen, such as bromine (Br2) or chlorine (Cl2), to the mixture of U3O8—CsF or U3O8—KF (from step 1); and stirring this in a reactor at room temperature for 3 hrs to 200 hrs, with 120 hours being typical, to produce sulfur tetrafluoride (SF4) gas in quantitative conversion, with the solid byproducts being alkaline halide, and U3O8.
Stoichiometric quantities of sulfur (S) and a halogen such as bromine (Br2) or chlorine (Cl2) are added to the mixture of U3O8—CsF (from step 1) at the rate of 3 mass parts S, 15 mass parts Cl2 (for instance) and 36-38 mass parts U3O8—CsF.
At this temperature, SF4 (produced from step 2) did not react with U3O8 (from step 1). SF4 has a vapor pressure of 145 PSIG at 21° C., and is compressible as liquid in the reactor. The gas can be removed from the reactor at room temperature by passing the >99% pure SF4 product through a 0.3 micrometer Pall's Gaskleen V filter to prevent any particulate uranium from leaving the reactor. While a description of the Batch process has been given, this process can be adapted for continuous flow process
The reaction of cesium hydroxide (CsOH) and UF4 to produce CsF/U3O8 is thermodynamically favored (see Table 1), and was carried out at 600° C. to ensure dehydration of CsF produced. The reaction of potassium hydroxide and UF4 was previously studied by others.







TABLE 1







12 CsOH + 3 UF4 + O2 (g) → 12 CsF + U3O8+ 6 H2O












T
H
S
G




C
Kcal
cal/K
Kcal
K
Log(K)















100.000
−295.014
−3.790
−293.600
9.385E+171
171.972


200.000
−293.680
−0.655
−293.370
3.311E+135
135.520


300.000
−305.976
−25.725
−291.232
1.148E+111
111.060


400.000
−311.765
−36.289
−287.337
1.980E+093
93.297


500.000
−303.628
−25.033
−284.274
2.310E+080
80.364


600.000
−294.667
−14.143
−282.318
4.679E+070
70.670









Table 1 shows equilibrium constant (K) as indication of thermodynamic feasibility of quantitative fluoride recovery from UF4 to form cesium fluoride (CsF).
Stoichiometric quantities of sulfur (S) and a halide such as bromine (Br2) or chlorine (Cl2) are added to the mixture of U3O8/CsF (from step 1) at the rate of 3 parts S, 15 parts Cl2 (for instance) and 36-38 parts U3O8/CsF.
The temperature-dependent thermodynamic equilibrium constant (K) data in Tables 1 and 2 below show that using CsF/S/Cl2 or CsF/S/Br2 to produce SF4 gas will be the most thermodynamically feasible approach, when compared to conventional methods of KF/S/Br2/25-70° C. (Tables 3) or NaF/S/Cl2/92° C. (Table 4). The reactions in Tables 1 and 2 produced yields of 95-100% at 25° C./24 h or 70° C./5 h (Table 5).







TABLE 2







S + 2Cl2 (g) + 4 CsF → SF4 (g) + 4 CsCl












T
H
S
G




C
Kcal
cal/K
Kcal
K
Log(K)















25.000
−72.658
−35.562
−62.055
3.102E+045
45.492


50.000
−72.704
−35.709
−61.164
2.342E+041
41.370


100.000
−72.877
−36.192
−59.372
5.975E+034
34.776


150.000
−73.445
−37.640
−57.517
5.119E+029
29.709


200.000
−73.751
−38.325
−55.618
4.923E+025
25.692









Table 2 shows equilibrium constant (K) as indication of thermodynamic feasibility of using the reactivity of sulfur (S) and chlorine (Cl2) for quantitative fluoride transfer from CsF to produce SF4 and cesium chloride (CsCl) as byproducts.







TABLE 3







S + 2 Br2 (g) + 4 CsF → SF4 (g) + 4 CsBr












T
H
S
G




C
Kcal
cal/K
Kcal
K
Log(K)















25.000
−52.338
−35.011
−41.899
5.196E+030
30.716


50.000
−52.400
−35.211
−41.022
5.568E+027
27.746


100.000
−52.615
−35.814
−39.251
9.790E+022
22.991


150.000
−53.225
−37.368
−37.413
2.111E+019
19.325


200.000
−53.565
−38.128
−35.525
2.572E+016
16.410









Table 3 shows equilibrium constant (K) as indication of thermodynamic feasibility of using the reactivity of sulfur (S) and chlorine (Cl2) for quantitative fluoride transfer from CsF to produce SF4 and cesium chloride (CsCl) as byproducts.







TABLE 4







S + 2 Br2 (g) + 4 KF → SF4 (g) + 4 KBr












T
H
S
G




C
Kcal
cal/K
Kcal
K
Log(K)















25.000
−30.923
−26.030
−23.162
9.535E+016
16.979


50.000
−30.947
−26.110
−22.510
1.678E+015
15.225


100.000
−31.071
−26.452
−21.201
2.618E+012
12.418


150.000
−31.563
−27.710
−19.837
1.764E+010
10.247


200.000
−31.753
−28.135
−18.441
3.300E+008
8.519





Winter, R; Cook, P. W., In A simplified and efficient bromine-facilitated SF4-preparation method, J. Fluorine Chem. 2010, 131, 780-783






Table 4 shows equilibrium constant (K) and thermodynamic feasibility of using the reactivity of sulfur (S) and bromine (Br2) for quantitative fluoride transfer from potassium fluoride (KF) to produce SF4 and potassium chloride (KCl) as byproducts.







TABLE 5







S + 2Cl2 (g) + 4 NaF → SF4 (g) + 4 NaCl












T
H
S
G




C
Kcal
cal/K
Kcal
K
Log(K)















25.000
−24.197
−23.411
−17.217
4.184E+012
12.622


50.000
−24.186
−23.374
−16.632
1.777E+011
11.250


100.000
−24.251
−23.547
−15.465
1.143E+009
9.058


150.000
−24.696
−24.687
−14.250
2.293E+007
7.360


200.000
−24.846
−25.022
−13.007
1.019E+006
6.008





1. Tullock, C. W.; Fawcett, F. S.; Smith, W. C.; Coffman, D. D., In The Chemistry of Sulfur Tetrafluoride. I. The Synthesis of Sulfur Tetrafluoride, J. Amer. Chem. Soc. 1960, 82, 539-542


2. Appel, R; Gilak, A., In Process for the production of sulfur tetrafluoride, U.S. Pat. No. 3,950,498, 1976


3. Oda; Y., Otouma; H., Uchida; K., Morikawa; S., Ikemura; M., In Producing sulfur tetrafluoride using amine/hydrogen fluoride complex, U.S. Pat. No. 4,372,938, 1983






Table 5 shows equilibrium constant (K) and thermodynamic feasibility of using the reactivity of sulfur (S) and chlorine Cl2 for quantitative fluoride transfer from sodium fluoride (NaF) to produce SF4 and Sodium chloride (NaCl) as byproducts.







TABLE 6





Logarithm of equilibrium constants (log K) for the reactions of


alkaline/alkaline earth metal fluorides and 


chlorine for production of SF4 as an indication of


thermodynamic feasibility







S + 2Cl2 (g) + 4 MFn → SF4 (g) + 4 MCln









Table 6 shows Logarithm of equilibrium constants (log K) for the reaction of alkaline/alkaline earth metal fluorides and chlorine for the production of SF4 as an indication of thermodynamic feasibility.
X-Axis:

    
    
        1=25° C.
        2=50° C.
        3=100° C.
        4=150° C.
        5=200° C.
        6=N/A
    
    













Metal
Temperature












fluoride
25° C.
50° C.
100° C.
150° C.
200° C.















NaF
12.62
11.25
9.06
7.36
6.01


KF
36.03
32.77
27.55
23.55
20.37


CsF
45.49
41.37
34.78
29.71
25.69


RbF
40.65
37.05
31.30
26.87
23.36


MgF2
−41.62
−38.87
−34.48
−31.14
−28.53


CaF2
−23.20
−21.82
−19.61
−17.96
−16.68
















TABLE 7







Logarithm of equilibrium constants (log K) for the reactions of


alkaline/alkaline earth metal fluorides and bromine for production 


of SF4 as an indication of thermodynamic feasibility


S + 2Br2 (g) + 4 MFn → SF4 (g) + 4 MCln








Metal
Temperature












fluoride
25° C.
50° C.
100° C.
150° C.
200° C.















NaF
−10.81
−10.31
−9.51
−8.93
−8.48


KF
16.89
15.23
12.42
10.25
8.52


CsF
30.72
27.75
22.99
19.33
16.41


RbF
23.90
21.66
18.07
15.29
13.09


MgF2
−71.27
−66.19
−58.06
−51.88
−47.02


CaF2
−51.55
−47.98
−42.28
−37.96
−34.57









Table 7 shows Logarithm of equilibrium constants (log K) for the reaction of alkaline/alkaline earth metal fluorides and bromine for the production of SF4 as an indication of thermodynamic feasibility. These values are shown in graph form in FIG. 12.
Overall, determination of the feasibility of producing SF4 from CsF/U3O8 at room temperature has established that:

    
    
        NIFUT Technology will produce high quality SF4 at a cost competitive process vs. conventional processes
        Production of SOF2, a typical byproduct in the production of SF4, is minimized to <2%
        Large scale (e.g. ton scale) production of SF4 can be carried out in batch process, over several days
        Since SF4 vapor pressure is 145 PSIG at 70° F., and the gas is condensable, it can be separated from the solid/solid reaction phase
        At reaction temperature, U3O8 (produced in step 1) does not react with SF4. Reaction of U3O8/SF4 has been reported at 300° C.
    
    


Example Embodiments
While certain exemplary embodiments are discussed in this disclosure, it is to be distinctly understood that the presently disclosed inventive concept(s) is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the disclosure as defined by the following claims.
Example 1
Reaction of Uranium Tetrafluoride and Potassium Hydroxide




Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (International Bio-Analytical Laboratories Inc, Boca Raton, Fla.) and 22.5 g (0.402 mol) crushed potassium hydroxide pellets (Sigma Aldrich Co.) were placed in a 300 cc stainless steel cylinder that was then fitted into a set up illustrated in FIG. 13. A PALL Gaskleen V filter was placed in the outlet of the continuous flow of 550 standard cubic centimeter (sccm) dry air through the cylinder reactor. The supply of dry air is carefully controlled through online regulator and mass flow meter. The heater is powered on, and controlled to 600° C. for 4 h. During this period, droplets of water from the reaction were noticeable in the hose that connects the vent to the KOH scrubber. Any residual water was removed by vacuum of the isolated reactor, through the Gaskleen filter. Flow of dry air continued after heater power was turned off, until the temperature dropped to 100° C. Powder X-Ray diffraction of the resulting byproduct of this process showed that all UF4 had reacted, and that U3O8 was the only uranium byproduct. Based on reaction stoichiometry, 3.6 g water should be eliminated from the reactor in a quantitative conversion, and weight loss of 7.2 g was confirmed. Thus, the reactor would contained 23.3 g (0.402 mol) KF, and 31.56 g (0.034 mol) U3O8.




Step Two: The reactor was opened under inert atmosphere, and then 3.0 g (0.094 mol) sulfur was added to the content of the stainless steel cylinder before it was sealed (see FIG. 14). Afterwards, 14.9 g (0.210 mol) chlorine gas was carefully condensed in the stainless steel cylinder reactor—and the pressure at room temperature was 39 PSIG. The reactor was left to stand undisturbed at room temperature, and conversion to SF4 gas was achieved after 120 h. This is confirmed by decrease of the initial pressure from 39 PSIG to 33 PSIG, the FTIR spectrum of the gaseous content of the reactor, and gravimetric weight of cryogenically condensed product. Powder XRD analyses show that the byproducts of this process are U3O8 and KCl. A determination of the uranium content of the SF4 gas was obtained by analyzing the aliquot from impinging the gas into water on an inductively coupled mass spectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction is reported as experiment #4 in Table 8.
Example 2
Reaction of Uranium Tetrafluoride and Potassium Hydroxide




Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (International Bio-Analytical Laboratories Inc, Boca Raton, Fla.) and 22.5 g (0.402 mol) crushed potassium hydroxide pellets (Sigma Aldrich Co.) were placed in a 300 cc stainless steel cylinder that was then fitted into a set up illustrated in FIG. 13. A PALL Gaskleen V filter was placed in the outlet of the continuous flow of 550 standard cubic centimeter (sccm) dry air through the cylinder reactor. The supply of dry air is carefully controlled through online regulator and mass flow meter. The heater is powered on, and controlled to 600° C. for 4 h. During this period, droplets of water from the reaction were noticeable in the hose that connects the vent to the KOH scrubber. Any residual water was removed by vacuum of the isolated reactor, through the Gaskleen filter. Flow of dry air continued after heater power was turned off, until the temperature dropped to 100° C. Powder X-Ray diffraction of the resulting byproduct of this process showed that all UF4 had reacted, and that U3O8 was the only uranium byproduct. Based on reaction stoichiometry, 3.6 g water should be eliminated from the reactor in a quantitative conversion, and weight loss of 7.2 g was confirmed. Thus, the reactor would contain 23.3 g (0.402 mol) KF, and 31.56 g (0.034 mol) U3O8.




Step Two: The reactor was opened under inert atmosphere, and then 3.0 g (0.094 mol) sulfur was added to the content of the stainless steel cylinder before it was sealed. Afterwards, 15.0 g (0.212 mol) chlorine gas was carefully condensed into the stainless steel cylinder reactor—and the pressure at room temperature was 40 PSIG. The reactor was heated with thermostat regulation at 80° C. for 8 h. Upon cooling, the pressure has dropped to BB PSIG, indicating that CC % conversion to SF4 gas was achieved. Further evidence was obtained from the gravimetric weight of cryogenically condensed product, that is, 10.1 g (99.8% of theoretical possible). Powder XRD analyses show that the byproducts of this process are U3O8 and KCl. A determination of the uranium content of the SF4 gas was obtained by analyzing the aliquot from impinging the gas into water on an inductively coupled mass spectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction is reported as experiment #6 in Table 8.
Example 3
Reaction of Uranium Tetrafluoride and Cesium Hydroxide




Step One: 35.1 g (0.112 mol) Uranium tetrafluoride (International Bio-Analytical Laboratories, Inc, Boca Raton, Fla.) and 74.5 g (0.442 mol) cesium hydroxide monohydrate (CsOH.H2O) powder (Sigma Aldrich Co.) were placed in a 300 cc stainless steel cylinder that was then fitted into a set up illustrated in FIG. 13. A PALL Gaskleen V filter was placed in the outlet of the continuous flow of 550 sccm dry air through the cylinder reactor. The supply of dry air is carefully controlled through online regulator and mass flow meter. The heater is powered on, and controlled to 600° C. for 4 h. During this period, droplets of water from the reaction were noticeable in the hose that connects the vent to the KOH scrubber. Any residual water was removed by vacuum of the isolated reactor, through the Gaskleen filter. Flow of dry air continued after heater power was turned off, until the temperature dropped to 100° C. X-Ray diffraction of the resulting byproduct of this process showed that all UF4 had reacted, and that U3O8 was the only uranium byproduct. Based on reaction stoichiometry, 4.7 g water should be eliminated from the reactor in a quantitative conversion, and weight loss of 9.2 g was confirmed. Thus, the reactor contained 67.14 g (0.442 mol) anhydrous CsF, and 34.70 g (0.037 mol) U3O8.




Step Two: The reactor was opened under inert atmosphere, and then 3.0 g (0.094 mol) sulfur was added to the content of the stainless steel cylinder before it was sealed (see FIG. 14). Afterwards, 14.9 g (0.210 mol) chlorine gas was carefully condensed into the stainless steel cylinder reactor—and the pressure at room temperature was 40 PSIG. The reactor was left to stand undisturbed at room temperature, and 100% conversion to SF4 gas was achieved after 120 h. This is initially confirmed by decrease of the initial pressure from 41 PSIG to 20 PSIG—a confirmation that 2 mole equivalent Cl2 is required to produce 1 mole equivalent SF4 gas, according to the balanced stoichiometric equation. Further evidence was obtained from the FTIR spectrum of the gaseous content of the reactor, and gravimetric weight of cryogenically condensed product, that is 10 g (98.8% of theoretical possible). Powder XRD analyses show that the byproducts of this process are U3O8 and KCl. A determination of the uranium content of the SF4 gas was obtained by analyzing the aliquot from impinging the gas into water on an inductively coupled mass spectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction is reported as experiment #5 in Table 8.
Example 4
Reaction of Uranium Tetrafluoride and Cesium Hydroxide Monohydrate




Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (International Bio-Analytical Laboratories, Inc, Boca Raton, Fla.) and 74.6 g (0.443 mol) cesium hydroxide monohydrate (CsOH.H2O) powder (Sigma Aldrich Co.) were placed in a 300 cc stainless steel cylinder that was then fitted into a set up illustrated in FIG. 13. A PALL Gaskleen V filter was placed in the outlet of the continuous flow of 550 sccm dry air through the cylinder reactor. The supply of dry air is carefully controlled through online regulator and mass flow meter. The heater is powered on, and controlled to 600° C. for 4 h. During this period, droplets of water from the reaction were noticeable in the hose that connects the vent to the KOH scrubber. Any residual water was removed by vacuum of the isolated reactor, through the Gaskleen filter. Flow of dry air continued after heater power was turned off, until the temperature dropped to 100° C. X-Ray diffraction of the resulting byproduct of this process showed that all UF4 had reacted, and that U3O8 was the only uranium byproduct. Based on reaction stoichiometry, 4.7 g water should be eliminated from the reactor in a quantitative conversion, and weight loss of 9.7 g was confirmed. Cesium hydroxide is extremely hygroscopic, and the difference in amount of water lost is a reflection of moisture absorbed during the transfer of the CsOH.H2O into the reactor cylinder. Thus the reactor contained 67.29 g (0.443 mol) anhydrous CsF, and 34.70 g (0.037 mol) U3O8.




Step Two: The reactor was opened under inert atmosphere, and then 3.0 g (0.094 mol) sulfur was added to the content of the stainless steel cylinder before it was sealed (see FIG. 14). Afterwards, 15.1 g (0.213 mol) chlorine gas was carefully condensed into the stainless steel cylinder reactor—and the pressure at room temperature was 40 PSIG. The reactor was heated with thermostat regulation at 80° C. for 8 h. Upon cooling, the pressure has dropped to 19 PSIG, indicating that 100% conversion to SF4 gas was achieved. Further evidence was obtained from the gravimetric weight of cryogenically condensed product, that is, 10.1 g (99.8% of theoretical possible). Powder XRD analyses show that the byproducts of this process are U3O8 and KCl. A determination of the uranium content of the SF4 gas was obtained by analyzing the aliquot from impinging the gas into water on an inductively coupled mass spectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction is reported as experiment #6 in Table 8.







TABLE 8





Production of SF4 from UF4 by two-step NIFUT technology and directly from MFn








 








 


4 KF (w/U3O8) + S + 2 Cl2 → SF4 (g) + 4 KCl


4 CsF (w/U3O8) + S + 2 Cl2 → SF4 (g) + 4 CsCl


















Reagent composition
















Ex-


Equiv.
Equiv.






peri-
UF4

M—F
U3O8
H2O
Sulfur
Halogen
Process


ment
Added
M—OH
added
byproduct
removed
added
added
condition





















1
—
—
6.4 
g
—
—
0.67 
g
4.4 
g
Batch,



















CsF


0.021 
mol
Cl2
RT/72 h




















0.042 
mol



0.062 
mol



















2
—
—
12.5 
mol
—
—
1.3 
g
22.5 
g
Batch,



















CsF


0.041 
mol
Br2
RT/72 h




















0.082 
mol



0.141 
mol























3
35.0 
g
22.5 
g
23.3 
g
31.56 
g
7.2 
g
3.0 
g
14.9 
g
Batch,




















0.112 
mol
KOH
KF
0.034 
mol
0.4
mol
0.094 
mol
Cl2
RT/120 h




















0.402 
mol
0.402 
mol



0.210 
mol























4
35.2
g
22.5 
g
23.3 
g
31.56
g
9.0
g
3.0
g
15.0
g
Batch,




















0.112 
mol
KOH
KF
0.034
mol
0.5
mol
0.094
mol
Cl2
80° C./8 h






















0.402 
mol
0.402 
mol



0.212
mol























5
35.1
g
74.5
g
67.14
g
34.70
g
9.2
g
3.0
g
15.1
g
Batch,




















0.112
mol
CsOH•H2O
CsF
0.037
mol
0.511
mol
0.094
mol
Cl2
RT/120 h






















0.442
mol
0.442
mol



0.213
mol























6
35.2
g
74.6
g
67.29
g
34.70
g
13.8
g
3.0
g
15.0
g
Batch,




















0.112
mol
CsOH•H2O
CsF
0.037
mol
0.767
mol
0.094
mol
Cl2
80° C./8 h






















0.443
mol
0.443
mol



0.212
mol























Products




















Ex-


Analysis of products







peri-
SF4
M—Cl/M—Br
Gas (FTIR)







ment
collected
byproduct
Solid (XRD)
























1

√
SF4, 90%, SOF2,
—










5%, Cl2, 20%,








2


HF, 5%










√
SF4, 70%, SOF2,
—










5%, Cl2, 20%,








3


HF, 5%










√
SF4, 99%, SOF2,
U3O8,










0.5%, HF, 0.5%
KCl







4

√
SF4, 99%, SOF2,
U3O8,










1%, HF, 0.5%
KCl







5

√
SF4, >99%, SOF2,
U3O8,










0.4%, HF, 0.5%
KCl







6

√
SF4, >99%, SOF2,
U3O8,










0.4%, HF, 0.5%
KCl





1XRD spectra of post-react solid byproducts of experiments 5 and 6 are shown in FIGS. 11 and 12.


2U3O8 prepared from step 1 was preserved intact through the process conditions of experiments 1-6.


No evidence of any reaction with SF4.

## Claims

1. A method for converting depleted uranium tetrafluoride (UF4) to uranium free sulfur tetrafluoride and triuranium octaoxide (U3O8), comprising the steps of:
heating in a first step a mixture of uranium tetrafluoride and an alkaline compound in a first step at 350 degrees C. to 650 degrees C. in a reaction chamber for 60 minutes to 240 minutes to produce a mixture of the respective alkaline fluoride and U3O8;
continuously flushing said reaction chamber with dry air during heating;
filtering reaction offgases to prevent particulate uranium from escaping from said reaction chamber;
heating in a second step the mixture of the respective alkaline fluoride and U3O8 from said first step, combined with sulfur (S) and a halogen, at a temperature of 25 degrees C. to 80 degrees C., for 6 hours to 120 hours; to produce sulfur tetrafluoride (SF4) gas, and solid of the corresponding metal halide and U3O8 as byproducts.

2. The method of claim 1 in which said alkaline compound comprises an alkaline oxide.

3. The method of claim 1 in which said alkaline oxide is cesium oxide.

4. The method of claim 2 in which said alkaline oxide is selected from the group consisting of sodium oxide, cesium oxide, and potassium oxide.

5. The method of claim 1 in which said halogen is bromine.

6. The method of claim 1 in which said halogen is chlorine.

7. A method for converting depleted uranium tetrafluoride (UF4) to uranium free sulfur tetrafluoride and triuranium octaoxide (U3O8), comprising the steps of:
heating in a first step a mixture of tetrafluoride and cesium oxide in a first step at 350 degrees C. to 650 degrees C. in a reaction chamber for 60 minutes to 240 minutes to produce a mixture of cesium fluoride and U3O8;
continuously flushing said reaction chamber with dry air during heating;
filtering reaction off gasses to prevent particulate uranium from escaping from said reaction chamber;
heating in a second step the mixture of cesium fluoride and U3O8 from said first step, combined with sulfur (S) and chlorine, at a temperature of 25 degrees C. to 80 degrees C., for 6 hours to 120 hours; to produce sulfur tetrafluoride (SF4) gas, and solid byproducts of cesium chloride (CsCl) and U3O8.

8. A method for converting depleted uranium tetrafluoride (UF4) to uranium free sulfur tetrafluoride and triuranium octaoxide (U3O8), comprising the steps of:
heating in a first step a mixture of uranium tetrafluoride and cesium hydroxide in a first step at 350 degrees C. to 650 degrees C. in a reaction chamber for 60 minutes to 240 minutes chamber to produce a mixture of cesium fluoride and U3O8;
continuously flushing said reaction chamber with dry air during heating;
filtering reaction offgases to prevent particulate uranium from escaping from said reaction;
heating in a second step the mixture of cesium fluoride and U3O8 from said first step, combined with sulfur (S) and chlorine, at a temperature of 25 degrees C. to 80 degrees C., for 96 hours to 120 hours; to produce sulfur tetrafluoride (SF4) gas, and solid byproducts of cesium chloride (CsCl) and U3O8.

9. The method of claim 1 in which said alkaline compound comprises an alkaline hydroxide.

10. The method of claim 4 in which said alkaline hydroxide is selected from the group consisting of Sodium hydroxide, potassium hydroxide and cesium hydroxide.

11. The method of claim 1 in which said halogen is selected from the group consisting of bromine and chlorine.

12. The method of claim 9 in which alkaline hydroxide is potassium hydroxide and said halogen is chlorine.

13. The method of claim 9 in which alkaline hydroxide is potassium hydroxide and said halogen is bromine.

14. The method of claim 9 in which alkaline hydroxide is cesium hydroxide and said halogen is bromine.

15. The method of claim 2 in which alkaline oxide is sodium oxide and said halogen is bromine.

16. The method of claim 1 in which alkaline oxide sodium oxide and said halogen is chlorine.

17. The method of claim 2 in which alkaline oxide is potassium oxide and said halogen is bromine.

18. The method of claim 1 in which alkaline oxide potassium oxide and said halogen is chlorine.

19. The method of claim 1 in which said heating step in said first step is heated to 400 degrees C.-600 degrees C.

20. The method of claim 1 in which further comprises a heating step with stirring in step two at 80° C. or less for less than 10 hours, and in which said halogen is bromine.

21. The method of claim 1 in which said heating step of step one include heating in inert atmosphere.

22. The method of claim 1 in which said heating step in step two is for less than 24 hours, and further comprises a stirring step two at 80° C. or less for less than 10 hours, and in which said halogen is bromine.

23. The method of claim 1 in which said heating step in step one is at room temperature for approximately 24 hours, and said heating step in step two is for less than 24 hours, and further comprises a stirring step two at 120° C. or less for less than 10 hours, and in which said halogen is chlorine.

24. The method of claim 1 which further comprises a cryogenic condensation step of gasses produced from step two.