Сhemistry

zation of nuclear power: Collector of articles of industrial scientific 8. Kuritskiy B.Ya. Search for optimal solutions by means of Excel 7.0. and technical conference. – Seversk: SSTI, May 20–23, 2003. – – St. Petersburg: BHV – St. Petersburg, 1997. – 384 p., ill. P. 58–61. 9. Boyarinov A.I., Kafarov V.V. Optimization technique in chemical 6. Applied electrochemistry / Ed. by D.E. professor A.P. Tomilov. – 3d engineering. – Moscow: Khimiya, 1969. – 556 p. edition, revised. – Moscow: Khimiya, 1984. – 520 p., ill. 7. Kurin N.P., Shashkin B.F Ionic forms concentration in melted sy stem KFHF // The VIIth allUSSR symposium on chemistry of Received on 07.12.2006 inorganic fluorides: Theses of the report. – Moscow: Nauka, 1987. – P. 222.

UDC 544.344

PHASE EQUILIBRIUM LIQUIDVAPOR IN THREECOMPONENT SYSTEM UF6IF5BrF3 AT COMPLETE MUTUAL COMPONENTS SOLUBILITY I.I. Zherin, V.F. Usov, R.V. Ostvald, V.V. Shagalov, I.V. Gayday, Z.M. Tyulyubaev Tomsk Polytechnic University Email: [email protected] The results of studying phase equilibrium liquidvapor at 353,15 K in the system of uranium hexafluoride, iodine pentafluoride, bromine trifluoride have been presented. The dependences of saturated vapor pressure on condensed phase composition, the results of analysis of studied system deviation from errorfree behavior, the data on equilibrium vapor phase are given.

Applying halogenfluorides in processing materials of concentrations xIF5 to xBrF3 remains constant along the nuclear power engineering is of great importance. Use of whole secant and expressed by the coefficient аi: halogenfluoride mixture for fluoridation of uranium x IF5 containing compounds is rather actual. Applying gaseous ai ==const, xBrF mixture BrF3IF7 for these purposes allows fluoridating 3 uranium compounds at low temperatures and pressures where i is the number of the plane. in contrast to elemental fluoride [1]. In this case multi component systems are formed. They contain uranium Thus, each secant may be presented in the form of hexafluoride and halogenfluorides which should be se pseudobinary system in which uranium hexafluoride is one of the components and another one is the mixture parated for extracting pure UF6 and regeneration of fluo ridating agents. Besides, using halogenfluorides and of iodine pentafluoride and bromine trifluoride at con their mixtures at processing nuclear fuel improves signifi stant ratio of the components cantly process variables and reduces production string According to the experimental data of the depen and decreases considerably waste volumes. dence of saturated vapor pressure on solution composi Thermodynamics of phase equilibrium liquidvapor tion at constant temperature the dependence of satura ted vapor pressure on liquid and vapor phases composi of threecomponent system UF6IF5BrF3 at tempera ture 353,15 К was studied. As the given system at the tion was calculated on the basis of Wilson equation [6]. specified temperature has unlimited reciprocal com The dependences of saturated vapor pressure on liquid ponents solubility [2, 3] heterogeneous equilibrium phase composition for the system UF6IF5BrF3 by the between liquid and vapor was studied. secants with corresponding values of the coefficient аi are given in Fig. 2. For researching phase equilibriums in threecom ponent systems the selection of changing technique of One of the peculiarities of the system UF6IF5BrF3 threecomponent system composition is of great impor is different character of deviations form Raoult law in tance [4, 5]. We selected the technique of composition binary system constituents. In threecomponent sy changing by secant planes passing through the top meeting stems it should be taken into consideration that factors uranium hexafluoride. The triangle of GibbsRosebum influencing the character of deviation from the ideal behavior act simultaneously in solution therefore the compositions of threecomponent system UF6IF5BrF3 indicating secants by which the compositions of conden deviations observed in threecomponent systems are the sed system were changed is presented in Fig. 1. result of overlapping deviations opposite in sign which are introduced by each component. As it was stated in The composition was changed adding uranium he the work [5] very often simultaneous action of opposite xafluoride to the mixture of iodine pentafluoride and factors and deviation character are mainly defined by bromine trifluoride the content of which in the mixture condensed system composition. decreases at hexafluoride addition. However, the ratio of

45 Bulletin of the Томsк Pоlytеchnic University. 2007. V. 311. № 3

(η>1) then real pressure in the system exceeds the ideal one and deflection in the system is positive, at η<1 the de flection from ideal behavior in the system is negative.

The deflection coefficient η for the system UF6IF5BrF3 was calculated by the equation: Content UF Px000⋅⋅+⋅⋅+⋅γγ Px P x ⋅ γ η = UF666 UF UF IF 555 IF IF BrF 3 BrF 3 BrF 3,(*) Px000⋅+⋅+⋅ PxP x UF66 UF IF 55 IF BrF 3 BrF 3

6 , molar fractions 0 0 0 where P UF6, P IF5, P BrF3 are elasticity of pure UF6, IF5 , molar fractions 3 and BrF3 vapors; xUF6, xIF5, xBrF3 is the content of UF6, IF5 and BrF3 in liquid phase, molar fractions; γUF6, γIF5, γBrF3 are the activity factors of UF6, IF5 and BrF3. Content BrF It is necessary to keep in mind that the deflection co efficient η is the characteristic of one of the set of points in the field of compositions of the system UF6IF5BrF3.

Content IF5, molar fractions therefore for the equation (*) it is necessary to fulfill the condition: xxx++ =1. Fig. 1. Secants at the triangle of compositions of the system UF65 IF BrF 3 UF6IF5BrF3 at a: 1) 0,13; 2) 0,23; 3) 0,29; 4) 0,47; Dependence of deflection coefficient η logarithms 5) 0,61; 6) 0,78; 7) 1,08; 8) 2,12; 9) 3,76; 10) 5,25 from three component mixture composition at 353,15 К for all ten secants is presented in Fig. 3. The existence domain of negative deflection in the system UF6IF5BrF3, Fig. 3 (I), and existence domain of posi tive deflection from Raoult law are seen from Fig. 3. In this case at uranium hexafluoride dominance in con densed phase in the system UF6IF5BrF3 the positive deflection is observed. Transition from positive deflec tion to the negative one is stipulated by halogen fluori des dominance in the system UF6IF5BrF3 therefore properties of tree component system in this region are close to the properties of the system IF5BrF3. The regularity is well seen from Fig. 3: changing the composition of the system UF6IF5BrF3 from binary sy stem UF6BrF3 to the system UF6IF5 (increasing аi), de

Saturated gas pressure, mm Hg flection coefficient η decreases. In this case the peak ty pical for the system UF6BrF3 (x(UF6)=0,11 molar frac tions, Fig. 3) adding iodine pentafluoride to the system UF6IF5BrF3 shifts to the peak in the system UF6IF5

Content UF6, molar fractions (x(UF6)=0,32 molar fractions, Fig. 3). This phenomenon may be explained in the following way. Molecules of bro Fig. 2. Dependence of saturated vapor pressure on liquid compo sition in treecomponent system UF IF BrF by secants mine trifluoride and iodine pentafluoride interact diffe 6 5 3 rently with molecules of uranium hexafluoride. So incre General deviation from Raoult law in the system asing iodine pentafluoride content in liquid phase of the UF6IF5BrF3 was estimated in the following way. Devia system UF6IF5BrF3 forces of intermolecular interac tion from the ideal behavior observed in any real systems tions in solution increase that results in decrease of posi when studying phase equilibriums in isothermal condit tive deflection of the system from the ideal behavior. ions may be expressed as the ratio of saturated vapor As it was stated before factors influencing the charac pressure observed in the studied system to the pressure of ter of deflections from the ideal behavior act simultan ideal saturated vapor calculated by Raoult law and addi eously in solution therefore, deflections observed in real tive Dalton law [5, 7]. Thus, denoting system deviation systems are the result of overlapping the deflection of op in the whole from the ideal behavior by coefficient η it posite signs which are introduced by each component. may be expressed by the equation: The numerator of the equation (*), which describes Ð η = , total deflection of the system UF6IF5BrF3 from the ide Ð′ al behavior consists of three members. Each of them inc where Р is the saturated vapor pressure observed in real sy ludes elasticity of pure component vapor – the constant, stem; P' is the saturated vapor pressure observed in ideal component concentration in solution and activity coeffi system, calculated by Raoult law. In this case it is obvious cient of the same component. The latter depend on solu that if the deflection coefficient is greater than a unit tion composition and their changes are given in Fig. 4.

46 Сhemistry from the ideal behavior from 3 BrF 5 IF 6

Region of maximum shift of system UF

the function lgη=f(xUF6) depen ding on enriching solution with

– Decimal algorithm of deflection coefficient the iodine pentafluoride

η lg UF6 content in the system, molar fractions

Fig. 3. Dependence of lgη on content of UF6 in condensed system UF6IF5BrF3 at secants a: 1) 0,13; 2) 0,23; 3) 0,29; 4) 0,47; 5) 0,61; 6) 0,78; 7) 1,08; 8) 2,12; 9) 3,76; 10) 5,25. X, Y – dependence of lghη fon content of UF6 in systems UF6IF5 and UF6BrF3 It is seen from Fig. 4 that logarithm values of activi which activity coefficient logarithm of this component ty coefficients of uranium hexafluoride are greater than has the highest negative values and the region of negati zero in the whole region of compositions of three com ve values lgγ BrF3 is close to the system UF6IF5. ponent system UF6IF5BrF3. It is also seen from Fig. 4 that it is in the system For iodine pentafluoride (Fig. 4, б) there is a number of UF6IF5BrF3 when opposite factors act simultan concentrations in the system UF6IF5BrF3, at which loga eously. Deflection which is observed in the system in rithm of its activity coefficients has negative values and they whole is the result of imposition of deflections opposi appear to the greatest degree when increasing bromine tri te in sign. fluoride concentration that is shifting concentration in the To analyze the distillation system separation the da system UF6IF5BrF3 to the binary system UF6BrF3. ta on system component content in vapor phase are ne For bromine trifluoride (Fig. 4, в) there is also a ran cessary. For this purpose the graphical interpolation of ge of concentrations in the system UF6IF5BrF3, at the obtained experimental and calculated data by phase

Fig. 4. Dependences of activity coefficient logarithms of UF6 (Fig. 4, а), IF5 (Fig. 4, б) and BrF3 (Fig. 4, в) on composition of the sy stem UF6IF5BrF3

47 Bulletin of the Томsк Pоlytеchnic University. 2007. V. 311. № 3

equilibrium liquidvapor in the system UF6IF5BrF3, yyyUF++ IF BrF =1. given above was carried out. 65 3 The technique of graphical interpolation of the ex The obtained diagram, Fig. 6, describes the change perimental data consists in the following. To plot the li of saturated vapor composition depending on liquid nes of constant content of uranium hexafluoride in va composition. The given diagram may be used not only por phase the diagram of dependence of uranium hexa for calculation of separation processes of the system fluoride in vapor on its content in liquid is plotted for all UF6IF5BrF3 by distillation techniques but also for cal secants stated above (Fig. 5). culation of other technological processes where the da ta on vapor phase composition being in equilibrium with the condensed system UF6IF5BrF3 of any com 6 position are required. Crosssections

IF

5 сontent, molar fractions

olar fractions

Vapor composition, molar fraction UF composition, Vapor сontent, m 3

BrF

UF6 сontent, molar fractions Liquid composition, molar fractions UF6 Fig. 6. Lines of UF6 and IF5 constant content in vapor phase of Fig. 5. Dependence of UF6 content in vapor on its content in liq the system UF6IF5BrF3 uid in the system UF6IF5BrF3 As a result of investigations of phase equilibrium in Then by these magnitudes the UF6 content in liquid the system UF6IF5BrF3 at 353,15 К the dependences phase at its constant content in vapor phase for all se of saturated vapor pressure on composition of conden cants is determined and these data are plotted to the tri sed and vapor phase of the system were obtained, the angle of concentrations. The lines of constant content character of system deflection from the ideal behavior of uranium hexafluoride in vapor phase are drawn was analyzed, lines of constant content of uranium he through the obtained points. xafluoride and iodine pentafluoride in vapor phase were

The lines of constant content of vapor for UF6 and plotted. All obtained data may be used for calculation IF5 are shown in Fig. 6. Content of the third com and design of separation processes of the system ponent, BrF3, may be determined from the condition: UF6IF5BrF3 by distillation techniques.

REFERENCES 4. Karapetyants M.H. Chemical thermodynamics. – Moscow: Khimi 1. Zherin I.I., Amelina G.N., Rudnikov A.I. et al. Phase equilibrium in ya, 1975. – 360 p.

systems on the basis of UF6, BrF3, IF5, HF // Collected scientific pa 5. Kogan V.B. Heterogeneous equilibrium. – Moscow: Khimiya, 1968. pers: Khimicheskaya Tekhnologiya i Avtomatizatsiya Predpriyatiy – 432 p. Yadernogo Toplivnogo Tsikla / Ed by B.M. Kerbel. – Tomsk: TPU 6. Machine computation of vaporliquid equilibrium of multicom STI, 1999. – P. 39–43. ponent mixtures: Translated from English / Ed by V.M. Platonov. – 2. Zherin I.I., Amelina G.N., Kalaida R.V. Descriptions of components Moscow: Khimiya, 1971. – 216 p. solubility in the systems UF6IF5 and IF5BrF3 // First Intern. Siberi 7. Khala E., Pik I., Frid V., Vilim O. Liquid and vapor equilibrium / Ed an Workshop (ISIF2003). – Novosibirsk, 2003. – P. 14–17. by A.G. Morachevsky. – Moscow: Foreign Languages Press, 1962. – 3. Fischer J., Vogel R.C. Phase Equilibrium in the Condensed Systems 438 p. Uranium hexafluoride – Bromine Trifluoride and Uranium hexa fluoride – Bromine Pentafluoride // J. Amer. Chem. Soc. – 1954. – V. 76. – № 19. – P. 4829–4832. Received on 07.12.2006

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