1. Tomsk Polytechnic University
Production of the Potassium Tetrafluorobromate in the Horizontal Screw Reactor: Feasibility Study
Univ. Assoc. Professor Roman Ostvald, PhD Chair of the rare elements chemical engineering
Ljubljana, Slovenia 2010

2. Purpose of the Research
To evaluate the feasibility of the KFBr4 synthesis by means of fluorination by elementary fluorine, compare this method to the liquid phase fluorination technique and investigate the applicability of this synthesis technique for industrial aims.
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3. Application of the KBrF4
KBrF4 is a complex compound of BrF3 with KF, which was recently proposed for the use as alternative to BrF3. At room temperature KBrF4 is a stable powder and has much lower chemical and corrosive activity therefore it is much more convenient for the work and storage and is much safer to handle compared to liquid BrF3 1, 2. Due to it high oxidizing capacity BrF3 can fully oxidize noble metals. The noble metals could be divided into two groups on the relative kinetic propensity to oxidation of BrF Fast-soluble metals Ag, Au, Ru, Ir, Os. - Slow-soluble metals Pt, Pd, Rh.
1. A. G. Sharpe and H. J. Emeleus, J. Chem. Soc., 2135 (1948)
2. V. Mitkin, J. Anal. Chem., (2001)
3. V. Mitkin, S. Zayakina, V. Tsimbalist, J. Anal. Chem., (2003).
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4. Application of the KBrF4
Metalls of the first group interact in a complex multistage mechanism through the formation of coordinating fluorides. In general there are following reaction schemes 1: 6 Ag + 8 BrF3 → 6 Ag[BrF4] + Br2, 2 Au + 4 BrF3 → 2 [BrF2+][AuF4-] + Br2, 6 Me + 16 BrF3 → 6 [BrF2+][MeF6-] + 5 Br2, where Ме is Ru, Os, Ir.
1. V. Mitkin, S. Zayakina, V. Tsimbalist, J. Anal. Chem., (2003).
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5. Methods of KBrF4 Synthesis
Liquid-phase fluorination method, by the interaction between potassium fluoride and liquid bromine trifluoride
KF + BrF3 → KBrF4
Spectrum of potassium tetrafluorobromate
Characteristic lines
K Kα=3,04 keV, Кβ=3,9 keV
Br Kα=11,92 keV, Кβ=13,29 keV, L3=1,54 keV
Constructive materials
Ni Kα=7,47 keV, Кβ=8,26 keV, L1=1,01 keV
Cu Kα=8,04 keV, L3=0,85 KeV
Fluorescent spectrometer Quant`X
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6. Methods of KBrF4 Synthesis
Gaseouse fluorination method by the interaction of potassium bromide with elementary fluorine
KBr + F2 → KBrF4
As in this case the stage of BrF3 recovery is absent, therefore this method could be more promising for the industrial production of KBrF4
First test experiment of KBr fluorination
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7. Kinetic Research of Potassium Bromide Fluorination process
Scheme of the experimental installation
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8. Kinetic Research of Potassium Bromide Fluorination process
Analogous principle was used by Japanese scientists Tsutomu Sakurai and Matae Iwasaki for kinetic research of fluorination UF4 by vapours of BrF3 1.
1. Tsutomu Sakurai and Matae Iwasaki, J. Phys. Chem., (1968).
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9. Kinetic Research of Potassium Bromide Fluorination process
Scheme of the experimental installation
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10. Kinetic Research of Potassium Bromide Fluorination process
Time dependence of the temperature and mass of KBrF4
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11. Kinetic Research of Potassium Bromide Fluorination process
KBr before fluorination
products after fluorination
Time dependence of mass KBr at fluorination. The temperature is 70 °C
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12. Presumable Mechanism of the Reaction
2KBr + F2 → 2KF + Br2
Br2 + F2 → 2BrF
Br2 + 3F2 → 2BrF3
Br2 + 5F2 → 2 BrF5
KBr + F2 → KF + BrF
KBr + BrF → KF + Br2
KF + BrF3 → KBrF4
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13. Qualitative reaction of KBrF4 hydrolysis
3KBrF4 + 5H2O → HBrO3 + Br2 + O2 + 9HF + 3KF 1
1. A. G. Sharpe and H. J. Emeleus, J. Chem. Soc., 2135 (1948)
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14. Kinetic Research of Potassium Bromide Fluorination process
temperatures, ° C
Fluorination process kinetics data were fitted by linear equation f(x)=1-2/3α-(1- α)2/3 where α – conversion degree
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15. Kinetic Research of Potassium Bromide Fluorination process
tg Θ = Ea where Ea is activation energy Ea = 23 kJ
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16. Search for the industrial reactor prototype
Horizontal type reactor with stationary layer of the material Disadvantage: -Conversion degree was not sufficient, due to the stationary layer of the material -Losses of gaseous bromine
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17. Search for the industrial reactor prototype
Rotary drum-type furnace Disadvantage: - Insufficient conversion degree, - Conglutination of product in homogeneous mass, - Looses of gaseous bromine
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18. Search for the industrial reactor prototype
Reactor hindered falling Disadventage: - High temperatures at the point of KBr supply, - Sticking of mass at the point of KBr supply
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19. Search for the industrial reactor prototype
Screw reactor Preliminary test was successful, KBrF4 was obtained
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20. Design of Screw Reactor
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21. Design of Screw Reactor
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22. Dependance of the Conversion Degree from Time at Difference Temperatures
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23. Testing of Screw Reactor
Thermal analytical data of KBrF4 synthesized in screw reactor at 80 °C
Residence time 15 min
Residence time 23 min
Residence time 70 min
Residence time 35 min
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24. Comparison of KBrF4 Obtained by Two methods
Thermal analytical data of KBrF4, synthesized by liquid phase method
Thermal analytical data of KBrF4, synthesized by gaseous phase method
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25. Comparison of KBrF4 Obtained by Liquid Phase Method
Dispersed structure, flaked kind of powder Average size near 0.25 mm
Specific surface area of powder ± 500 cm2/g
Bulk density ± 0.05 g/cm3
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26. Comparison of KBrF4 Obtained by Gaseous Phase Method
Macro-crystalline structure, Average size of crystals near 1 mm
KBrF4 was obtained on the surface of the KBr crystals Specific surface area of powder 373 ± 60 cm2/g Bulk density 0.97 ± 0,05 g/cm3
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27. Conclusion
- Possibility of KBrF4 production by means of KBr fluorination was shown, formation mechanism of KBrF4 was suggested, rate constant and total reaction activation energy were calculated, - The proposed screw horizontal reactor was constructed and tested as an industrial prototype of the technological equipment, - Comparison of powders obtained by two different methods was performed.
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28. Future Research Plans
- Technological regimes working-off on the industrial phototype, - Test of new powders in the fluorination technology of rare elements.
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32. Tomsk Polytechnic University
Production of the Potassium Tetrafluorobromate in the Horizontal Screw Reactor: Feasibility Study
Univ. Assoc. Professor Roman Ostvald, PhD Chair of the rare elements chemical engineering
Ljubljana, Slovenia 2010