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Univ. Assoc. Professor Roman Ostvald, PhD
Chair of the rare elements chemical engineering
E-mail: [email protected]
Ljubljana, Slovenia 2010
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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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
BrF3 3.
- Fast-soluble metals Ag, Au, Ru, Ir, Os.
- Slow-soluble metals Pt, Pd, Rh.
1. A. G. Shar pe and H. J. Emeleus, J. Chem. Soc., 2135 (1948)
2 . V. Mitk in, J. Anal. Chem., 118-142 (2001)
3. V. Mitk in, S. Zayak ina , V. Tsim bali st , J. Anal. Chem., 22-33 (2003).
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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.
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1. V. Mitk in, S. Zayak ina , V. Tsim bali st , J. Anal. Chem., 22-33 (2003).
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Liquid-phase fluorination method, by the interaction
between potassium fluoride and liquid bromine trifluoride
KF + BrF3 → KBrF4
Fluorescent
spectrometer Quant`X
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
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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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Scheme of the experimental installation
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Analogous principle was used by
Japanese scientists Tsutomu
Sakurai and Matae Iwasaki for
kinetic research of fluorination
UF4 by vapours of BrF3 1.
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1. Tsutom u Sak urai and Matae Iwasak i, J. Phys. Chem., 1491-1497 (1968).
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Scheme of the experimental installation
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Time dependence of the temperature and mass of KBrF4
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KBr before
fluorination
Time dependence of mass KBr at fluorination.
The temperature is 70 °C
products after
fluorination
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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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3KBrF4 + 5H2O → HBrO3 + Br2 + O2 + 9HF + 3KF 1
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1. A. G. Shar pe and H. J. Emeleus, J. Chem. Soc., 2135 (1948)
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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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tg Θ = Ea where Ea is activation energy
Ea = 23 kJ
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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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Rotary drum-type furnace
Disadvantage:
- Insufficient conversion degree,
- Conglutination of product in homogeneous
mass,
- Looses of gaseous bromine
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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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Screw reactor
Preliminary test was successful, KBrF4 was obtained
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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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Thermal analytical data of
KBrF4, synthesized by
liquid phase method
Thermal analytical data
of KBrF4, synthesized by
gaseous phase method
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Dispersed structure,
flaked kind of powder
Average size near 0.25 mm
Specific surface area of powder
3120 ± 500 cm2/g
Bulk density
0.75 ± 0.05 g/cm3
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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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- 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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- Technological regimes working-off on the
industrial phototype,
- Test of new powders in the fluorination
technology of rare elements.
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Univ. Assoc. Professor Roman Ostvald, PhD
Chair of the rare elements chemical engineering
E-mail: [email protected]
Ljubljana, Slovenia 2010