INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
vcstigation. Their partial pressures of m t e r vapor over 5 and 1 0 7 solutions are considerably loJrer than those calculated by Raoult'. law. They apparently did not attain saturation of the carrier g:is by passing i t over a static surface of solution. The numericd clata reported by t,hem give neither straight lines nor ~ m o o t hcurves Trlien plotted as the logarithm of pressure against the reciprocal of absolute temperature. The pirtial prchsures of hydrogen fluoride at 25' C. reported by Frcdenhngen a n d Kellmnnn (4)are npprosimately tn-ice the correspondiiig vnlues obtained in the present study. Fredenhagen and Wcllrnann calculated, but did not measure, the partial prei,cures of water w p o r . Tht ilso passed a carrier gas over a atatic surface of solution; hence seems t h a t their rcxsults n-ould tend t o 1)elow rather t h n high. They absorbed the hydrogen fluoride from the carrier gns and dctermiiied the amount conductometrirally rather than by direct anal! In the short range of o v e i h p between the preeent dntn nnd the vapor pwsiure t1:ita presented graphically by the General Cheniical Company (5),the trro s e t s of data are in fnir agreement.
427
ACKNOULEDGXIEhT
The authors acknowledge the assistance of John ;i.Brabson and .hits Darron-, v h o prepared the silica-free hydrofluoric acid used in the study. LITERATURE CITED
(1) Berkeley, E a r l o f , a n d H a r t l e y , E. G. J., Proc. R o y . Soc. ( L o n d o n ) .
A77, 156-89 ( 1 9 0 6 ) . (2) B i c h o w s k y , F. R., and Rossini, F. D.. " T h e r m o c h e m i s t r y of The C h e m i c a l S u b s t a n c e s " , Xew York, Reinhold P u b . Corp.. 1936. (3) D a r i s , D. S.," E m p i r i c a l E q u a t i o n s a n d Somography", S e w I-ork, M c G r a w - H i l l Book Co., I n c . , 1043. (4) F r e d e n h a g e n , K., and TT'ellmann, >I., Z. p h y s i k . C h e m . , A162, 451-66 ( 1 9 3 2 ) . ( 5 ) G e n e r a l C h e m i c a l Co., Tech. Seraice BuU. 30A (1945). (6)H o f f m a n , ,J. I., a n d L u n d e l l , G. E. F., Bur. Standaids J . Resecrrch, 3, 5s1-05 (1929). ( 7 ) K h a i d u k o r , S . ,L i n e t s k a y a , Z., a n d Bognol-arov, d.,J . ilplili'erl Chem. ( U . S . S . R . ) , 9, 439-45 (1936) (S) L a n g e , S . A , . H a n d b o o k of C h e m i s t 4 t h Ed., Gandusky, Ohio, H a n d b o o k P u h l i s h e r s , Inc., 1941. (9) TYashburn, E. IT-.. and H e u s e , E. O., J . --im. C h r m . S u r . . 37, w 21 (1915).
HYDROFLUORIC ACID-WATER and
HYDROFLUORIC ACID-HY DROFLUOSlLlClC ACID-WATER *
Paul A. Munter, O t t o T. Aepli, and Ruth A. Kossatz PENNSYLVANI4 S 4 L T hI4NUFACTURING CO., WVYNDVOOR, Pi.
I
OI'ERATIOY O F EQUILIB THE liquid-yapor equilibria of the binar! system HF-Hz0 RlC3I STILL and of the ternary system HF-HZSiFa-II20 have been deIlling basic d a t a relative The equilibrium still emto tlic industrial production of termined a t atmospheric pressure over a considerable ployed for the measurement? range of composition. The azeotropic mixture of the pure arihydrous hydrofluoric was constructed of pure silver system HF-H20 was found to have a composition of 38.26% acid, it was found t h a t only sheet (B. 8: S. gage 18) ami hydrofluoric acid and a boiling point of 112.0" C . at 750.2 meager information on the tubing joined with "hard" mm. pressure. A constant-boiling solution was found in \,oiling points and the related silver solder (Figure 1). It the ternary system HF-HaSiFs-HzO a t the composition liquid and vapor composic o n s i s t e d e s s e n t i a i l y of : 1Oc/c hydrofluoric acid, 36Yo hydrofluosilicic acid, 54$?'0 tions for the systems HFboiler A with chnrging port water, which boiled a t 116.1" C. at 759.7 mm. pressure. H,O and HF-H2SiF6-H20 is B and heater well C, whicli The all-silver equilibrium still employed for these deteravailable in the literature. was surrounded by bafflc minations is described. For the system HF-H20, plate D to ensure good mixing most of the reported data of the return condensate witli :ire for the constant-boiling the boiliiig solution : columri E supporting thermocoupit mixture and are summarized later in Table 11'. I n addition, well F , which extended to just below the surface of the boilFrederihagen and Wellmann (4)determined the boiling poiiiting liquid; condenser G; and sampler H with auxiliary coilliquid composition curve, a t atmospheric pressure, for the denser J , condensate return line K , and rotatable sampling system HF-H?O over the composition rnnge from 0 to 100'; tube assembly L. T h e silver charging-port cover and the' hydrofluoric acid. sampling tube assembly were sealed by clamping Tvith bras? S o measurements have been reported on the liquid-vapor unions. Figure 2 is a photograph of the still assembly. equi1ibri:i a t the normal boiling points for the ternary system The heater unit vias constructed b y winding Sichrome wire tIF-II&F6-H20. Some Jvork was done on the binary system (Alloy V, B. 8: S.gage 12, 1 w/foot) on a porcelain thermocouplP IIiSiF6-Hn0 by Baur ( I ) , Truchot ( I I ) , and Jacobson ( 6 ) . n-ire insulntor (Std. 723, Leeds & Korthrup). The windings Irere Beyolid indicating the dissociation of hydrofluosilicic acid in the insulated by covering with Insalute cement t o such a diameter ah vapor phase and the probable existence of an azeotropic mixture to permit the heater to slip readily into the heater vie11 of t h r i l l the system H2SiFs-HQ0, these studies provide little information still when required. The rate of heating rras regulated by :I relative t o the liquid-vapor equilibria. Variac transformer so t h a t not more than 1 to 2 grams of mateThe present research was carried out to supplement these rial distilled over per minute. meager d a t a ; it covers measurements, over a wide range of coniThe t,emperature of the boiling solution was measured t o positions, of the boiling points and related liquid and vapor com* 0 . l o C. by a calibrated iron-constantan thermocouple which positions, at atmospheric pressure, on the binary system HFextended t o the bottom of the thermocouple well. ,4 little H 2 0 and the ternary system HF-H2SiFsH20.
S TIIE course of assem-
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE I.
(:.lLIRRATIOS
Jtniidard Methanol Benzene \T-a t e r Toluene
I 1
IC 1
Figure 1. Diagram of Silver Equilibrium Still
Figure 2.
Silver Equilibrium Still
O F h'1I.L
Vol. 39, No. 3
THERMOCOUPLE IS O f E R . A T I o N
Sorrnal Bailing P o i n t , ' C Literature Observed (cor.) 64.45 64.5 80,09 80.1 100.0 100.3 110.8 110.7
nnphthnleiie 01' toluene was Elaced in the bott'om of this well t o improve thermal contact. The electromotive force of the thermocouple ivaa measured to =t1 microvolt by a Rribicon Type €3 potentiometer and spotlight galvanometer. The behavior of t,lie tliermocouple duririg operation was checked by determining the boiling poiiits in tlie equilibrium still of tmice-distilled samples of \\-:itcir, nictli:iiiol, lmizeiie, arid toluene: Table I gives results Of t1iCSt t The condensers of t h e still assembly were cooled I)?. forceti cii,culwtioii of either ice n-ater (0' C.) or R ~ a t e r - e t h y l m c gl?-col mixture (-20" C ) ,depending on the probable boiling ~ ~ i i i of n t tlie coiideiisnte. To :ivoid refliiziiig of tlir vapors in the upper boiler arid the coluniri during opcxitiun, the still assembly, escept for the condenser and sampler, \vas enclosed in a transite air oveii (Figure 3). The temperature of the oren was maintained at bevernl degrees above tlie boiling point of the liquid in the boiler. The still was charged with approsimately 175 grams of t'he solution under test. After the charging port was sealed and the sampling tube clamped in the u p position, which permitted the condensate t o return t o the boiler and also vented the still to the atmosphere, the heater \\-as inserted and the boiler heated gradually until t,lie temperature of the boiling solution became practically constant. The temperature of the transit'e air oven surrounding the still was simultaneously raised to several degrees above the boiler temperature. When constant temperature had been maintained for 15 t o 30
Figure 3.
Transite .4ir Oven and Still
TABLE11. LIQUIDAND V A P O R COMPOSITIOSS POIKTS OF SYSTEM HF-H,O Compn,, n-t,7o HF '
Liquid 5.47 10.1 20.6 24.7 30.1 36.2 36.8 37.6
Vapor 0.87 2.03 7.06 11.6 19 4 32 8 34.4 36.4
38.22 38.27 39.2 42.2 47.0 49 2 52.9 54.8
38.15 38.26 41.1 50.1 65.7
58.6 60.7 64.1 66.2 72.0 81.4 89.0
1
BOILIXG
Sormal Boiliy Point, C.
0 inches I 2
429
9
101.6 102.8 106.8 108.4 110.3 111.7 112 0 112.1
82.6 87.4
112 112 111 111 108 106 101 98
0 9 5 3 7 3 5
i54.9 750.2 756.1 762.6 i51.7 757.1 749.8 749.6
112.3 112 4 112,l 111.4 108.7 106.8 101.7 98.9
92.9 97.3 99.0 98.7 98.8 99.3 99 5
90 86 78 74 61 44 33
7 1 5 0 6 9 3
i54 4 747.1 748.4 i45.9 i46.2 753.4 754.5
90 9 86.6 79.0 74.6 61.6 45.1 33.5
Figure i. Diagram of Weighing Bottle Construction
LIQUID POI ST^
Liquid Compn , \\-t, e; HF H ~ S I FHzO ~ 0.22 24.1 75.7 0 76 29 7 69.5 0 85 3 3 . 2 65.9 1 . 8 9 36 2 61.9 2.69 38.3 59.0 4 . 4 0 26 0 69.6 4 . 6 0 38 0 57.4 5.60 3 3 . 7 60.7 6 33 37.9 55.8 6 . 5 1 38 5 55.0
0 16 2 55 0 16 5.33 0 17 9.75 0.19 18.0 0 27 2 5 . 9 1 3i 3.32 0 06 3 0 . , 5.19 12.3 0 98 3 9 . 1 0 24 4 6 . 3
55 1
7 . 5 6 37 3 7 86 37 2
9i 3 94.5 RO 1 81.8 i3.8 95.3 69.2
82,s 59 ? 53 o
10.8
37.9 36.7 38 1 25.8 36.0 :34 2
54.9 55.1 69 0 53.2 54 2 52.6 64 4 53 9 55 0
3.61 5 45 5.43 5.98 3 46 7 76 3.65 8.55 9.84 12.8
39.3 57 1 36 4 58 1 36 5 58 1 0.46 93.5 50.2 46.3 36 1 06 1 51.8 44 5 0 40 01 0 36 0 54.2 27.4 59.8
12.5 12.9 15.4 15.6 17.3 18.6 18.6 19.6 22.9 a3.9
33.0 34.4 31.6 29 8 32.9 16.4 29.0 17.2 38.7 24.5
54 5 02 7 53 0 54 6 49 8 65 0 52 4 53 2 38 4 51 6
18.3 16.7 25.6 26.9 26.7 14.3 33.7 35.4 5.18 44.8
23.3 35.4 23.4 14.1 36.8 0.59 19.9 11.8 93.2 12.0
58 4i 51 59 36 85 46 52 1 43
25.3 26.1 26.7 27.6 28.3 29.8 33.0 33 6 36.3 37.2
5.25 32.4 14.9 15 3 ii.6 16.1 36.0 26.0 20.7 16.7
69.4 41.5 58.4 54.1 31.0 40.4 43.0 46.1
17.3 37.3 36.4 40.4 35.0 49.9 0.61 57.6 74.6 71.6
0.11 58.2 1.21 1.63 0.10 2.38 98.4 36.7 13.9 8.87
39.1 40 5 45.7 49.2 53.1 54.1 60.0 60.7 69.6 70.6 92.0
5.04 2 i 5 12.0 18.6 25 3 16.5 17.1 8.96 9.31 11.9 0.69
55.9 32 0 42.3 32.2 21.6 29 4 22.9 30.3 21.1 17.5 7.3
1 5 7 6 0 92 63 0 26 3 92 2 43.3 5 97 77 4
i.3; ;;p
10.1
.4ND
Observed Barometric Boiling Pressure, P o i n t , C. 1 I m . Hg (Cor.) 100.8 740.5 102.2 745.1 106 8 i59 7 107 8 i47 2 110.1 i54.6 111.6 757.0 111 9 758.4 112.2 i62 i
...
TABLE111.
8.88 9.13 9.28 9 83
-
I N D U S T R I A L A N D E N G I N E E R I N GI C H E M I S T R Y
March 1947
57 1
60.i
54 26 Si 66
104 4 107.3 108.8 111.2 112., 108 1 114 3 113.1 115 2 115.5
749.3 758 9 753.5 z53.9 io0 2 763 2 757.2
753 1 i55.8 758 4
115 3 115.3 115.7 108.4 115.2 115.~ 115.2 113 5 116.1 115.9
750.1 752 6 752.2 744 1 744 4 759.7 759 8
82.6 4.5 62.4 58 0 64.9 47.7 1.0 5.7 11.5 19.5
110.0 100.9 113 2 113.2 112.5 111.9 62.5 95.9 100 1 104.4
757 755 762 761 752 745 750 759 754 761
0 . 4 1 45 5 72.6 0 9 3.98 8 3 32 2 1 1 96.0 J 1 35.1 73.0 2.10 5 7 56 2 0 5 93.6 0 4 0 8 21.8
111 2 70 1 94 0 76 2 33 7 63 8 46 9 67 1 46 6 32 7 25 5
758.1 744.3 758.3 757.5 749.6 755 1 756.9 756.9 760.1 749.1 750.6
A:
747.0
-748 - - i9 135
Figure 3.
Photograph of U eiphing Bottle
4 9 0 0 5 1 4 8 6 2 3 9 1 0 8 4 8 0 1
0
TABLE IV. AZEOTROPIC MIXTUREO F SYSTEM HF-H,O Compn., W t . 70 HE' 35.37 37.0 48.17 43.2 35.4 38.18 38.26
Boiling Point, ' C. 120 120 126
iii
115.2 110.8 112.0
Pressure, M m . Hg Atin. Atm. Atm. 7 50 Atill. 732 750
Investigator Bineau ( 2 ) Roscoe (8) Deussen ( 3 ) Fredenhagen ds Kellmann hIuehlberger ( ? ) This investigation
(4)
Weight c6 of H F 111 Liquid ( I ) and Vapor ( 8 ) Figure 6. Boiling Points and LiquidVapor Compositions of the System
HF-HzO
430
INDUSTRIAL AND ENGINEERING CHEMISTRY
minute., the +,impling tube n as uiiclainpd a i d t r i i i i c d t o tlic don-n positioii for sampliiig the condensate. A conveiiieiit weight of condensate \vas collected for analysis after the first fen- drops vere discarded. T h e atmospheric pressure and temperature vere recorded :it the same time. Immediately after tlie condciisate was sampled, t h e heaters were shut oft', thc btill n-ni dizmounted and cooled in water, and a sample of the boilcr liquid was poured o u t through the charging port for arinl~ The condensate nnd boiler liquid were sampled in a doublenalled weighing bottle of about 20 ml. capacity, fitted ~ i t ha ground stopper. T h e bottle and the stopper n-ere cast from Asplit cement, a n acid-proof resin cement. A small amount of crushed ice TTRS generally included in the n-eighing bottle t o avoid \.apor losses during collection of thc sample. Tlic doublen-all coiistruction prevented the condeiisatioii of Iiioiqture oil tlie outsidc during weighing of the chillrti coiiteiit+.
.it.
0
---
+ .....,. Y
-1 -
Vol. 39, No. 3
Foi .,impliiig distillates high 111 acid content ( > 4 0 r c ) , the lid of the weighing bottle was modified by inserting through its center a tight-fitting silver tube which extended within 0.5 em. of the bottom of the weighing bottle. T h e internal diameter of tliis tube was such t h a t i t fitted snugly over the silver tubc of the still sampling assembly; the result was an essentially closed path from condeiiser to sampling bottle. During the mighings, the silver tube of the sampling bottle was closed by a small silver plug. Figures 4 and 5 how details of the sampling hottlc c o n struction.
Tlie :ic.id boliitioiic w i ' e prepared when fensible, from 48% Ilytlrofluoi,ic :icicl (Ualtcr's xpecial, c.11. grade) and frunl 30Yc liydrofluo~ilicicacid ( l k k c r ' s :innlyzed, C . P . grade). Oiily lots of hydrofluoric ncid containing 1e:s than 0.05cc liydroflrio~ilicic
Ternary constant boiling point Liquid composition, weight 90' Vapor composition, weight 70 Tie lines Liquid isotherms Vapor pressure trough Constant boiling point of system HF-HzO Approximate constant boiling point of system IIzSiF~-IlzO
March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
acid were used. T h e more concentrated acid solutions Tvere prepared in pure silver beakers from anhydrous hydrofluoric acid (Pennsylvania Salt Manufacturing Co.) b y dilution and by reaction with powdered silica (Baker's analyzed, C.P. grade). T h e hydrofluoric acid solutions were analyzed by titration with standard sodium hydroxide solutions (silica- and carbonatefree), using phenolphthalein as indicator. T h e hydrofluoric and hydrofluosilicic acid mixtures were analyzed by a method of cold and hot titrations with standard sodium hydroxide, using phenolphthalein as indicator, according to the procedure described by Scott ( 0 ) and Sherry et al. ( 1 0 ) . DISCUSSIOS OF RESCLTS
Table I1 presents the liquid and vapor compositions and related boiling points as determined for the 5ystem HF-HZO. T h e normal boiling points in column 5 were cnlculated from the experimental d a t a on the assumption of a n average entropy of vaporization of 23 calories per degree-mole for these solutions. The liquid and vapor compositions, in veight per cent, and the normal boiling points are plotted in Figure 6. Table 111 lists t h e boiling points and related liquid and vapor compositions as determined for t h e ternary system HF-H2SiFsHs0. These data are plotted in Figure 7 along with the approsimate liquid isotherms. T h e constant-boiling mixture of the system HF-H20 T K I ~ found to have a composition of 3 8 . 2 6 5 hydrofluoric acid and a boiling point of 112.0" C. a t 750.2 mm. pressure. These values are compared with previously published d a t a in Table IV and are in good agreement with results secured by Muehlberger ( 7 ) . T h e boiling point curve for the system HF-H,O as determined in thi. work is a t considerable variance TTith t h a t determined hy Fredenhagen and Wellmann ( d ) , except in the regions approaching the pure components. Lacking suitable corrohorntive dat:i, i t is concluded t h a t the boiling point curve as determined in this work is the more reliable in view of: (a) the agreement secured between the boiling points of the test liquids as determined in the still (Table I) Kith the published values, ( b ) the good agreement of t h e d a t a for the constant-boiling mixture with those secured b y Muehlberger, and (c) the smooth curve given b y the boiling points and t h e close extrapolation of this curve t o the boiling point of pure hydrofluoric acid. In the ternary system HF-H2SiF6-H20, a masimum boiling point was found having a cornposition of 10yc hydrofluoric acid, 36% hydrofluosilicic acid, and 54% Kater, and a boiling point of 116.1" C. a t 759.7 mm. pressure. This point lies in a vapor pressure trough which extends across the phase sy=tem from the
43 1
L3zeotropic mixture of HF-H20 to t h a t of H2SiF6-H&. as indicated by the dotted line on Figure 7. The composit,ion ( 4 1 5 !iydrofluosilicic acid and 59% water) and the boiling point, 111.5" C.) indicated for the aaeotropic mixture of the system HzSiF6-H20 are only approximate values; attempts t o determine these d a t a accurately were unsuccessful, because of the tendency of such solutions with lon- free hydrofluoric acid content to deposit silica in the boiler or in the condenser of the still d u r ing distillation. T h e boiling point ridge divides the phase diagram into two regions so t h a t a solution of a composition lying in one region cannot be distilled under normal pressure to yield ,z condensate having a composition lying in t h e other region. T h e results secured for the liquid and vapor compositions of solutions in the more acid regions of the ternary system (that ib, for solutions containing over 60% free hydrofluoric acid or over 30"' free hydrofluoric and 30% free hydrofluosilicic acids) are not equilibrium values since t h e still condenser did not condense all the vapor phase. Severt'heless, since in t,he method of sampling employed, practically all of the vapor and the eondensate y e r e collected for analysis, it was concluded t h a t the compositions found gave a reliable approximation of tlir liquid-vapor equilibria of such solutions. .iCBSOW LEDGhI E S T
The authors hereby express their thank5 to the PenwylvLtniu Salt llanufncturing Co. for permission t o puhlilh these esperimental data. An nclinowledgmeiit is made of the :issistance of R.H. Rnlston in sume preliminary studies on the subject systems. LlTERATURE CITED
Baur. E., Z . phuaik. Chem., 48, 453 (1904). Bineau, -L,Ann. chim. phys., [3] 7 , 257 (1843). Deussen. E., 2.anorg. Chem., 49, 297 (1906). Fredenhagen, IC., and Wellmann, M., 2.p h y s i k . Cheni., A162, 454 (1932). ( 5 ) Gore, G., Landolt-Bornstein Tabellen, p. 273 (1905). (6) Jacobson, C. X., J . Phus. Chern., 27, 577, 761 (1923): 28, 506 (1942). (7) hluehlberger, C. IT., Ibid., 32, 1858 (1928). (8) Roscoe, H., J . Chem. SOC.,13, 162 (1860); - i n n . Chern. 1 1 . Pharrn., 116, 218 (1860). (9) Scott, TI'. W,, "Standard Methods of Chemical .lnalysis", 5th ed., Vol., 11, p. 2209, New York, D. Van Nostrand Co., 1939. (10) Sherry, W.B., Swinehart, C. F., Dunphy, R. A., and Oghum S. C., IXD. ENG.CHEM.,ANAL.ED.,16,483 (1044). (11) Truchot, C., Compt. rend., 98, 821 (1884). PRESESTEO before the Symposium on Fluorine Cheniistry as paper 93. Division of Industrial a n d Engineering Chemistry, 110th Meeting of tlie .$\IEHIC.4\. C H E \ l I C h t SOCIETY, Chicago, 111.
HYDROGEN-FLUORINE TORCH Homer F. Priest and Aristid V. Grossel WAR R E S E i R C H LABORATORIES, COLU\IB14 U \ I \ ERSITY. A E W YORB, N. Y .
A
S SOOK as the problem was solved of Dtoriiig fliiori:it=
under pressure ( 5 ) , the means was avrtilable for studying fluorine flames and constructing a fluorine torch. Since fluorine is the most reactive element known, we expected it t o produce the highest possible flame temperatures. This follows for two interdependent reasons: First,, reactions n.ith fluorine show the highest molar heat evolution, and second, because of the high strength of fluorine bonds, t h e dissociation of the reaction products is curtailed. The first point is illustrated by a comparison of the heat of 1 Present
address, Houdry Process Corporation, Marcus H o o k . Pa.
combustion ( f ) of one mole of hydrogen in fluorine and in oxygen, as shon-n below:
+ F: +2HF(,,,) + 128.0 lig.-cd. Hz + HnO(,ss, + 57.8 kg.-cal. H?
1,1202 -t
(1) (2)
Thus, in the case of fluorine the heat generated, for the sam(> volume of hydrogen, is 2.2 times greater than for oxygen. Similarly, tlie heats of combustion of methane or acetylene with fluorine are tTTice :IS high as those with oxygen, for
CH4
+ iF, --+
CF4
+ 4 H F + 415 1rg.-cal.
(3,
