INDUSTRIAL AND ENGINEERING CHEMISTRY
1624
Lamb. H., "Hydrodynamics," 6th ed., p. 588, CambIidge, England, The University Press, 1932. Mason, W. P., J . Colloid Sei., 3, 147 (1948). Mason, W.P., private communication. Mason, W.P., T m n s . A m . Soc. Mech. Engrs., 69, 359 (1947) Mason, W.P., et al., J . -4pplied Phys., 73, 1074 (1948).
LITERATURE CITED
(1)
(2) (3) (4) (5) (6)
(7) (8) (9)
(10) (11) (12) (13) (14)
Alfrey, T., "Mechanical Behavior of High Polymers," S e w York, Interscience Publishers, Inc., 1948. Andrade, E. N. da C . , Phil. M a g . , 17, 497, 698 (1934). Askew, F. A , , Paint Technol., 9, S o . 106, 217 (1944). Bekk, J., Deut. Drucker, 44, No. 256, 450 (1938). Bikerman, J. J., Palra Packaging Bzdl. 2 (1945). Bowles, R. F., P a i n t Technol., 9 , Yo. 106, 213 (1944). De Bruyne, S . X.. Ibz'd., 9 , S o . 106, 211 (1944). Derjaguine, B., Beitr. ongew. Geophys., 4, 452 (1934). Deryagin, B. W,,and Poretskaya, A. P., "The PhysicalChemical Fundamentals of the Printing Process," Moscow, The Graphic Institute, 1937 (in Russian). Ferry, J. D., Ann. AT.1'. Acad. Sci., 44, 313 (1943). Ferry, J. D., J . Am. Chem. Soc., 64, 1323 (1942). Gilkey, H. J., et al., "Materials Testing," New York, 5IcGran-Hill Publishing Co., 1941. Green, H., IND.ENG.CHEM.,AS.IL. ED., 13, 632 (1941). Josefowitz, D., and Mark, H., I t i d i u Rubbw W o l l d , 106, 33 (1942).
Vol. 43, No. 7
(22) (23) (24) (25) (26) (27) (28)
(29) (30) (31) (32) (33)
Ibid., 75, 936 (1949). Maxwell, J. C., Phil. Tians. Royal SOC.,157, 49 (1867). Mill, C. C., et al., Patra J., 3, 215 (1940). Poisson, S. D., J . dcole polytech., 20, 139 (1831). Ramati, C. V., et aZ., h i a t w e , 143, 198 (1939). Reed, R . F., Am. Ink Maker, 17, No. 12, 27 (1939). Reynolds, O., Trans. Royal Soc. London, 177, 190 [1886). Sjodahl, L. H., Modern Lithography, 17, 85 (1949). Stefan, J., Sitz. her. A k a d . Wiss.Wien, Math. naturw. Klasss, 69, 713 118741. Toe:; i., Am.Ink Maker, 18, S o . 3, 27 (1940). Ibid., 23, No. 10, 65 (1945). Ibid., 27, No. 2, 27 (1949). Ibid., S o . 6, p. 31. Voet, A, J . Phys. &: Colloid G h m . , 51, 1037 (1947).
RECEIYED March 2 , 1960,
Vapor-Liquid Equilibrium of Antimony Pentafluoride-Hydrogen Fluoride PROPERTIES OF ANTIMONY PENTAFLUORIDE ROBERT C. SHAIR' .4ND W. FRED SCHURIG Polytechnic I n s t i t u t e of Brooklyn, Brooklyn 2, hi. Y . Antimony pentafluoride is used as a fluorinating agent. The process for its manufacture consists of interacting antimony pentachloride with hydrogen fluoride to form the pentafluoride. A necessary step in the purification of the product is separation of the excess hydrogen fluoride by distillation. For design of a suitable distilling column, vapor-liquid equilibrium data on the binary system and information on some of the physical properties of the compounds are necessary. Vapor-liquid equilibrium data for the binary system, antimony pentafluoride-hydrogen fluoride, are reported at 1 atmosphere pressure. The system is very far from ideal.
The vapor pressure of antiinony pentafluoride is reported from 50" C. to its normal boiling point, which was determined to be 142.7" C. The specific gravity is 3.145 at 15.5"/15.5' C.; its latent heat of vaporization is estimated I O be 10,370 calories per gram-mole at the normal boiling point. The results add to the Itnowledge of the physical properties of antimony pentafluoride and are of significance in process equipment design. The work further develops the techniques of the use of an Othmer-type recirculation still for vapor-liquid equilibrium, specifically a metal modification where internal visual observations are limited.
&-TIMONY pentafluoride is used as a fluorinating agent, and is especially applicable in many instances because it is a liquid. In the manufacture of antimony pentafluoride, antimony pentachloride is treated with hydrogen fluoride in excess to interact the halogens. A necessary step in the preparation is separation of the excess hydrogen fluoride from the antimony pentafluoride by distillation. It was desired to determine the vaporliquid equilibrium data requiied for designing the distillation equipment.
impurities \vere found, the antimony pentafluoride was concluded to be 100% pure. The hydrogen fluoride used was a commercial grade of 99.8% purity.
PREPARATION OF MATERIALS
Hydrogen fluoride mas bubbled into antimony pentachloride in excess to form antimony pentafluoride (7). The crude antimony pentafluoride was distilled and the middle fraction collected and redistilled. The middle cut of this second distillation was collected and analyzed for all possible impurities, since the only analytical method available for antimony pentafluoride was not found reliable. The only possible impurities in the antimony pentafluoride were aluminum fluoride, antimony pentachloride, antimony trifluoride, water, and hydrogen fluoride. \Then no 1
Present address, Stauffer Chemical Co., New Y o l k 17 N. Y .
ANALYTICAL METHOD
Antimony pentafluoride has a specific gravity of about 3. Hydrogen fluoride has a specific gravity of about 1. This difference enables an accurate analysis of mixtures of the two compounds by density. With ordinary care, using a calibrated pycnometer, specific gravity could be determined to t0.002. For a spread in specific gravity from 3.000 to 1,000, which rppresented 100 weight yo in composition, a determination of *0.002 was equivalent to an analysis precise to *O.l weight %. It is probable that for solutions containing low hydrogen fluoride percentages, the precision was reduced to +0.5 weight yo. Two pycnometers similar in principle to the specific gravity bottle were specially made of aluminum and calibrated. Mixtures of known composition of hydrogen 5uoride and antimony pentafluoride were carefully made up and their specific gravities measured to give the specific gravity-composition relationship ehown in Table I and Figure I .
July 1951 TABLE
INDUSTRIAL AND ENGINEERING CHEMISTRY
I. SPECIFIC GRAVITY-COMPOSITION RELATIONSHIP Wt.
9'
Hydrogen fiuoride
0.00 15.00 28.40 44.41 02.60 74.84 100.00
Specific Gravity e t
15.5O C. 15.5" C. 3.145 2.571 2.120 1.689 1.342 1.173 0,982
DESCRIPTION OF APPARATUS
The equilibrium still developed by Othmer has become standard for such studies ( 2 , 3, 5, 6). A modified Othmer still was designed and built for the determination of vapor-liquid equilibria. Previously, Carey and Lewis ( 1 ) modified the still to be made of copper. Aluminum was found to be a satisfactory material of construction since the fluorides react with the aluminum to form a thin coatin of aluminum fluoride, which is impervious to further attack by &y fluorides. Chlorotrifluoroethylene was found to be a satisfactory transparent material for visual observation of the condensate rate. The equipment is shown in Figure 2. All parts were made of pieces of aluminum tubing welded together, except where specified. HEATERS.A semimicro gas burner directly beneath the bottom of the still pot was used as the main heater. To prevent reflux in the vapor passageway, a 100-watt electric heater was wired along the side of the main pot from just above the liquid sampling tube up to the top and for about 3 inches along the vapor line. The entire 3-inch pipe section, top and bottom and the vapor line up to the total condenser, were lagged with asLestos and plaster of Paris, except for a 1-inch opening in the bottom for the burner. CONDENSERS.The original specifications called for a reflux condenser only, but subsequent investigations revealed that for solutions having components with widely different boiling points, such an arrangement \?-as unsatisfactory. Vapors containing a
Figure 2.
high fraction of the more volatile component a t the boiling point of the solution condensed in the reflux condenser to a liquid of relatively low boiling point. This liquid traveled down the condenser but was met by the hot uncondensed vapors, and flashed. Liquid condensate could not get t o the condensate chamber and accuinulated in the condenser; therefore, a total condenser was added on the vapor pipe. An auxiliary cooling jacket of sheet copper was fitted around the condensate chamber. It cooled the condensate t o prevent flashing upon reentering the main still pot, and to condense the antimony pentafluoride Figure 1. s p y i f i c Gravity of Mixu,hich were tures of Antimony Pentafluoride so dense in the conand Hydrogen Fluoride densate chamber that thev fogned __ the peep sight. PEEPSIGHTS. The gastight peep sights were arranged as shown in the auxiliary view of Figure 2. Extending perpendicular
-Modified Othmer Still
e m a t e l y '/a actual size 1. all temperature thermocouple well 2. Vapor temperature thermocouple well 3. Sloping shelf to drain off any condensed liquid above the vapor passageway 4. Vapor passageway 5. Liquid sampling tube 6. Liquid temperature thermocouple well 7. Main still pot, capacity 125 cc. 8. Vapor condensate return line 9. Copper pan through which water circulated to cool the condensate chamber and vtqmr return line.
1625
The peep sight extended through notches in the walls of the pan.
10. Peep sight 11. Pressure equalizing tube 12. Total condenser on the vapor line
13.
Reflux condenser
14. Atmospheric vent
15. Transparent plastic peep sight 16. Vapor sampling tube A-A. Condensate chamber and peep sight viewed in direction of arrows B-B. Condensate chamber viewed from above. Capacity of eondensate chamber, 37 CO.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1626
to the sides of the ll/a-inch pipe condensate chamber were two l'/g-inch pieces of 1/4-inch pipe. Two l/a-inch caps were drilled with 1/8-inch holes and held two small circles of chlorotrifluoroethylene plastic sheet, as shown. A light held near one of the aights illuminated the inside of the condensate chamber, permitting observation of the condensate drop rate through the other.
Vol. 43, No. 7
course of obtaining the data. Each time the still was thoroughly cleansed and dried. EQUILIBRIUM. Equilibrium conditions between vapor and liquid were realized when the vapor temperature, liquid temperature, and wall temperature were equal and unchanged for 15 minutes; the condensate drop rate as seen through the peep sight was about 100 drops per minute. Approximately 1 hour was required t o reach this steady state during which time the three temperatures were recorded periodically and the main and auxiliary heaters adjusted accordingly. The pressure was adjusted to 760 mm. by blowing air into or sucking air out of the surge chamber, and the system was closed off with a pinch clamp. SAMPLING.After equilibrium conditions had been attained, the main supply of heat source was stopped. Boiling and recycling rapidly ceased. The sampling tube on the liquid side waa opened e s t , and a sample of the hot liquid quickly pipetted out and immediately transferred to a chilled pycnometer and further chilled. The vapor sample was removed as quickly as possible and transferred to its chilled pycnometer. The samples were analyzed by specific gravity. EXPERIMENTAL EQUILIBRIUnl DATA
0
10
20
30
40
50
60
70
SO
90
4
100
WEIGHT % HF
Figure 3. Boiling Point-Composition Relationship for Binary System Antimony Pentafluoride Anhydrous Hydrogen Fluoride
TEMPERATURE MEASUREMEXTB. Temperature measurements were made a t three points: in the liquid and vapor lines and a t the outer wall of the still pot. Three calibrated iron-constantan thermocouples were used with a Leeds & Northrup Type K potentiometer. The electromotive force (e.m.f.) was read t o 10.005 mv., corresponding to a temperature sensitivity of *0.l0 C. DRYING TUBE.A glass drying tube filled with calcium sulfate was attached to the atmospheric vent. The dryer served two functions; it kept moisture away from the hygroso ic compounds in the equipment, and turned red on contact witK hydrogen fluoride, indicating any losses due to flashing. PRESSURE RESERVOIRAND REGULATOR.A 5-gallon surge chamber and manometer were connected to the apparatus to keep the pressure constant a t 760 mm. After the binary mixture had been boiling steadily and the inert gases were flushed from the equipment, the surge chamber was ronnected a t the drying tube and closed off a t a pressure of 760 mm. of mercury. For the determination of vapor pressure, a Gilmont-type Cartesian manostat was connected between a water aspirator and the surge chamber to keep the ressure constant a t the desired level. SAMPLIKG. d m p l i n g of liquid and vapor was done through the capped openings leading into the respective sections of the still. Samples were withdrawn with aluminum pipets.
Experimental equilibrium data are given in Table I1 and plotted in Figures 3 and 4. The pressure was 760 mm. For binary solutions the components of which have very different boiling points, as is the case with antimony pentafluoride (boiling point, 142.7' C.), and hydrogen fluoride (boiling point, 19.5' C.), it would be expected that the vapors coming off from a solution containing any more than just a few per cent of the more volatile component would contain almost 100% of the more volatile component. Equilibrium data, however, showed an unexpectedly large amount of antimony pentafluoride in the vapors when the hydrogen fluoride content in the liquid was as high as 10 to 15 weight %. Ruff, in his work on antimony pentafluoride
VAPOR-LIOUID
EOUILIBRIUM
/
ILOPERATING PROCEDURE
CHARGING.The still pot was charged through the liquid sampling tube with 150 cc. of the pvrified, 100% antimony pentafluoride, and 10 ml. of liquid hydrogen fluoride (99.8% HF). For each run about 10 to 20 ml. each of liquid and vapor were removed for analysis and 20 to 40 ml. of liquid hydrogen fluoride were added t o the contents of the still pot. Thus the composition of the liquid was shifted with increasing hydrogen fluoride content for each run. Three separate fresh charges of pure antimonypentafluoride were put into the equilibrium equipment during the
Figure 4
( 8 ) ,also noted when distilling a mixture of antimony pentafluoride and hydrogen fluoride that the vapors coming over a t 100" C. contained an unexpectedly large amount of antimony pentafluoride?. He suspected the formation of an azeotrope. This work revealed no azeotrope but pointed out the nonideality of the system.
* 1627
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
~~
TABLE111. EXPERIMENTAL VALUES OF VAPOR PRESSCRE
TABLE11. EXPERIMENTAL EQUILIBRIUM DATA Temp.,
Run S o . Pure SbFa 15 17 16 18 6 1 5 21 2 20 19 22 8 23 7 10 13 11 12 14 Pure H F
C. 142.7 127.7 121.3 120.1 114.6 112.0 110.3 105.0 100.5 99.4 96.2 95.8 92.0 90.8 87.1 85.1 73.3 64.1 54.3 41.4 30.7 19.4 O
€IF in Liquid
Wt. %
Mole %
0
...
...
0.9 0.7 1.5 1.4 1.5 2.5 3.0 4.1 5.0 4.8 6.0 6.2 7.5 8.1 11.2 15.4 21.5 36.1 58.2 100
0
9.0 7.1 14.2 13.3 14.2 21.7 25.1 31.7 36.2 35.3 40.8 41.8 46.7 48.8 57.6 66.4 74.7 85.9 93.7 100
H F in Vapor Wt. % Mole % 0 0
2.2 4.2 4.5 5.8 8.8
19.6 32.2 33.8 40.0
12.3 17.0 18.6 22.5 23.5 30.4 33.5 41.1 47.7 65.6 78.2 88.4 96.2 98.8 100
60.3
...
T, C . 49.6 59.2 68.5 77.5 88.5 106.1 123.9 133.4 143.2
51 1
...
68.9 71.2 75.9 77.5 82.5 84.8 88.2 90.9 95.3 97.4 98.8 99.7 99.8 100
P, Mm. H g 16.2 26.4 42.3 66.3 108.5 218.9 407.1 560.4 762.9
sure of water has a slope of 1.131. The slope of this line is equal to the ratio of the molar latent heat of vaporization of antimony pentafluoride to the molar latent heat of vaporization of water at the same temperature (6). The heat of vaporization of water a t 142.7' C. is 9172 calories per gram mole, and the heat of vaporization of antimony pentafluoride was calculated to be 10,370 calories per gram mole, or 48.3calories per gram.
The nonideality of the system was attributed to the several factors listed below. REL.4TIVE SIZE O F THE MOLECULES. Antimony pentafluoride has a molecular weight of 216.8 compared to 20.0 for hydrogen fluoride. The molecular volumes are rather different, and there is probably a large intermolecular force of attraction between the two molecules making separation more difficult. Antimony pentafluoride is known to COMPLEX FORMATION. form a solvate with five molecules of hydrogen fluoride (8) which decompose a t temperatures above 70" C. ASSOCIATION. Data on hydrogen fluoride show that a t 10% temperatures and moderate pressures hydrogen fluoride exists in the vapor state as associated molecules which have both linear and cyclic structures. Equilibrium between the associated molecules and the monomer is rapidly shifted in the direction of the associated forms a t temperatures below 70' C. HYDROGEN BOND, The presence of the hydrogen bond accounts for the molecular association of hydrogen fluoride with itself. Since the fluorine atom is highly electronegative, it is probable that there is also h drogen bonding between hydrogen fluoride and antimony pentadoride. A thermodynamic correlation of the data could not be worked out because the system was so far from ideal and sufficient data on antimony pentafluoride were not available t o calculate accurate activity coefficients.
I
2 VAPOR
PROPERTIES OF ANTIMONY PENTAFLUORIDE
The vapor pressure of antimony pentaVAPORPRESSURE. fluoride from 50' C. up to its normal boiling point was determined dynamically using the modified Othmer still equipped with a pressure regulating system. Boiling temperatures corresponding to various pressures were observed. A correction was applied to the manometer to give the pressure in millimeters of mercury a t 0" C. Experimental values of vapor pressure are tabulated in Table 111,and plotted in Figure 5,using the logarithmic reference substance plot of Othmer ( 4 ) . Close agreement with the usual straight line indicates consistent experimental results. A plot of log pressure (millimeters of mercury) versus the reciprocal of the temperature (' K.) gives the equation log p = 8.567 -
2364.1
T
Figure 5.
30 40
3 4 5 678910 20 PRESSURE OF WATER. FSIA.
Plot of Antimony Pentafluoride us. Water
SPECIFICGRAVITY.Three independent measurements of the specific gravity of pure antimony pentafluoride gave 3.143, 3.144, 15.5' C., which is in close and 3.148. The average value is 3.145____ 15.5" C. 23" C. agreement with the literature value of 2.99 -
4'
c.
*
ACKNOWLEDGMENT
Appreciation is gratefully expressed to H . G. McCann, U. S. Public Health Service, Bethesda, Md., for his helpful interest and numerous suggestions. LITERATURE CITED
In the region from 55 to 760 mm. the equation is precise to *0.370. NORMAL BOILINGPOINT.The normal boiling point of antimony pentafluoride, as determined from the above vapor pressure plot, is 142.7' C., and it is probably more reliable than the literature value of 149' to 150" C. determined about 50 years ago, apparently from a direct measurement of the temperature a t which a sample boiled. LATENTHEAT OF VAPORIZATION. The Othmer plot of the vapor pressure of antimony pentafluoride against the vapor pres-
(1) Carey, V. S.,and Lewis, W. K., IND. ENG.CHEM.,24, 882 (1932). (2) Othmer, D. F., Anal. Chem., 20, 763 (1948). (3) Othmer, D. F., IND. ENQ.CHEM.,20,743 (1928). (4) Ibid., 32, 841 (1940). (5) Ibid., 35, 614 (1943). (6) Othmer, D. F., IND. ENG.CHEM.,ANAL.ED.,4, 232 (1932). (7) Perkins, M. A., and Irwin, C. F., U. S. Patent 2,410,358 (1946). (8) Ruff, O., Ber., 39, 4310 (1906). RECEIVED July 25, 1950. Presented before the Metropolitan Long Island Croup of the AMERICANCHEMICAL SOCIETY, March 17. 1950.
