March 1952
’
INDUSTRIAL AND ENGINEERING CHEMISTRY
with the present measurements, except possibly as to the mole fraction of n-butane associated with the aqueous liquid phase, and this showed reasonable agreement at the lower temperatures. Apparently at the higher temperatures the presence of methane in the aqueous liquid phase influenced the distribution of the n-butane between the aqueous liquid and hydrocarbon liquid phases. Because of the absence of a basis for a direct comparison, no attempt has been made to evaluate the agreement between the measurements of McKetta and Katz and the present data. Again it is emphasized t h a t the information presented here leaves much t o be desired in the way of completeness and is of limited accuracy, but nevertheless it adds to the available knowledge of the influence of water upon the phase behavior of hydrocarbon systems. ACKNOWLEDGMENT
This paper is a contribution from the American Petroleum Institute Research Project 37. R. H. Olds gave material assistance in connection with the preparation of the data for publication. Betty Kendall and Virginia Berry helped with the calculations. NOMENCLATURE
constant of pro ortionality fugacity, poun& per square inch f pressure, pounds per square inch absolute P P” vapor pressure, pounds per square inch absolute R universal gas constant T thermodynamic temperature, R. molal volume, cu. feet per pound“mo1e V residual molal volume, cu. feet per pound mole V X = mole fraction in a hydrocarbon liquid phase Y = mole fraction in a gas phase 2 = mole fraction in an aqueous liquid phase = = = = = = = =
p
N
Subscripts g = gas phase
= ideal solution = liquid phase = water
i 1
H 4
615
LITERATURE CITED (1) Amagat, M. E. H., Ann. chim. phys., 29, 505-74 (1893). (2) Bartlett, E. P., J. Am. Chem. Soc., 49, 65-78 (1927). (3) Beattie, J. A., Simard, G. L., and Su, G.-J., Ibid., 61, 24-6 (1939). (4) Bridgman, P. W., Proc. Am. Acad. Arts Sci., 48, 310-62 (191213). (5) Dodson, C. R . , and Standing, M. B., “API Drilling and Production Practice,” pp. 173-9, New York, American Petroleum Institute, 1944. (6) Kay, W. B., IND. ENG.CHEM.,32, 358-60 (1940). (7) Keenan, J. H., and Keyes, F. G., “Thermodynamic Properties of Steam,” New York, John Wiley & Sons, 1936. (8) Keyes, F. G., Smith, L. B., and Gerry, H. T., Mech. Eng., 56, 87-92 (1934). (9) Laulhere. B. M.. and Briscoe. C. F.. Gas. 15, No. 9. 2 1 4 (1939). (10) Lewis, G. N., J . Am. Chem. Soc., 30, 668-83 (1908). (11) Lewis, G . N., and.Randal1, M., “Thermodynamics and the Free
Energy of Chemical Substances,” New York, McGraw-Hill Book Co., 1923. (12) McKetta, J. J., Jr., and Katz, D. L., IND.ENG. CHEM.,40, 853-63 (1948). (13) Olds, R. H., Reamer, H. H., Sage, B. H., and Lacey, W. N., Ibid., 36, 282-4 (1944). (14) Olds, R. H., Sage, B. H., and Lacey, W. N., Ibid., 34, 1223-7 (1942). (15) Poynting, J. H., PhiE. Mag., (5) 12, 32 (1881). (16) Reamer, H. H., Olds, R. H., Sage, B. H., and Lacey, W. N , IND. ENQ.CHEM.,35, 79&3 (1943). (17) Ibid., 36, 381-3 (1944). (18) Reamer, H. H., Sage, B. H., and Lacey, W. N., American Documentation Institute, Washington, D. C., Document 3328 (1950). (19) Roberts, 0. L., Brownscombe, E. R., and Howe, L. S., Oil Gas J., 39. NO. 30. 37-40 11940). (20) Sage; B. H., ’and Lacey, W. N., Trans. Am. Inst. Mining Met. Engrs., 136, 136-57 (1940). (21) Smith, L. B., and Keyes, F. G., Proc. Am. Acad. Arts. Sci., 69, 285-312 (1934). (22) Villard, P., Compt. rend., 106, 1602-3 (1888). (23) Ibid., 107, 395-7 (1888). (24) Wilcox, W. I., Carson. D. B.. and Katz. D. L., IND. ENG.CHEM., 33, 862-5 (1941). RECEIVED for review July 23, 1951. ACCEPTEDOctober 31, 1951. For material supplementary to this article order Dooument 3328 from American Documentation Institute, 1719 N St., N.W., Washington 6, D. C., remitting $1.00 for microfilm (images 1 inch high on standard 35-mm. motion picture film) or $2.70 for photocopies (6 X 8 inches) readable without
n-butane
Superscript = pure substance
optical aid.
O
Vapor Pressure of Phosphoric Acids EARL H. BROWN AND CARLTON D. WHITTI Tennessee Valley Authority, Wilson Dum, Ala.
D
ATA in the literature on vapor pressures in the system P401o-HzO pertain chiefly to solutions of orthophosphoric acid (72.4% P&) in water. Elmore, Mason, and Christensen ( 9 ) determined the vapor pressures over phosphoric acid in concentrations from 1.2 t o 63.7% P4OlOa t 25” C. by the isotonic method described by Robinson and Sinclair (7). A static method was used by Kablukov and Zagvozdkin (6) for determining the vapor pressures a t 25 O , 40 O, 60 O, and 80 O C . of orthophosphoric acid solutions that contained 4.1 to 63.1% P401a,and by Zagvozdkin, Rabinovich, and Barilko (10) for determining the vapor pressures at 150 O, 200 ’, 250 O, and 300’ C. of acids that contained 63.4 t o 88.7’% P4O10. Britake and Pestov ( 2 ) determined the boiling points of acids that contained 9.1 to 71.0% PaO10.
The present paper describes the determination of the pressure 1
Present address, The Chemstrand Corp., Decatur. A l a .
and composition of the vapor over phosphoric acid containing from 61.6 to 92.7% P4O10. The vapor densities of four of the acids also were determined. The data should be useful in the design and operation of phosphoric acid plants and of plants in which the acids are used as catalysts. The results also have utility in thermodynamic calculations involving the acids. YAPOR PRESSURE MEASUREMENTS
The acids were re ared by heating mixtures of reagent grade phos horic oxide &4&) and 85% orthophosphoric acid in a gold vessef. The P4010contents of the acids were determined through double precipitation as magnesium ammonium phosphate with subsequent ignition to and weighing as magnesium pyrophosphate. The vapor pressure for each acid was measured by determining the boiling point at several reduced pressures in an apparatus, shown in Figure 1, similar t o that described by Mack and France (6). The acids that contained more than 797$ P4010 were heated
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
616
in a tube constructed of Hastelloy B and were stirred by means of a magnetic lift pump; the less concentrated acids were heated in a borosilicate glass tube and were stirred by means of a Cottrell pump. The maximum temperature that remained constant for 10 minutes a t each pressure was taken as the boiling point. To ensure continuous active refluxing, the temperature of the furnace was held about 60” C. above the boiling point of the acid.
SURGE
BOTTLE
Vol. 44, No. 3
The vapor over boiling phosphoric acids w-as collected and analyzed in the present work. Samples of vapor from the more dilute acids were obtained from B borosilicate glass still. The acids of higher P4010 content wore boiled in Hastelloy B or platinum vessels. J\’ith the exception of small holes for the tip of the sampling bulb and the therrnocouplc, the metal boilers were covered. ~. .. ~ .~. . Samples of vapor from the metal boilers were taken in B tared 500-ml. evacuated glass bulb that was fitted with a capillary tube and a stopcock. T o minimize thc collection of spray with the vapor, a 6-em. length of shell tubing was close-connected t o the capillary by means of a short rubber sleeve. The oncn end of the shell tubing was held about 2 em. a b o k the surface of the liquid, and the sample was withdrawn a t a rate considered to be slow enough to avoid the entrainment; of droplets, yet fast enough to minimize the effect of fractional ronden5ation in the shell tuhing The shell tubing and rubber sleeve then were removed, and liquid clinging to them was discarded. The raugc of compositions shown a t the right of Table I11 reA the difficulty of obtaining samples representative given boiling point. ~
TO VAC
e&(-
)(-
A temperature-c>omposition diagram for the R ) btciii P40i~-H~ is 0presented as Figure 4. The diagi am A ab constructed from the vapor compositions in Table 111, the boiling points in Table 11, and the boiling pointh reported by Britzke and Pestov (2). Figure 4 also includes values ( 4 ) representing the subliniation point of the solid H-form and the boiling point of the liquid 0’-form of P4010 The relationships indicate that the syatem is azeotropic and that a composition containing about 92% PaOlc has the highest boiling point in the P,01~-IX20syatem. These observations are in agreement r5ith those of Tarbutton :inti Deming (8). MOLECULAR SPECIES IN VAPOR PHASE
/
Figure 1. Apparatus for Determining Vapor Pressures in System P~O~O-H~O
The results are listed in Table I and are plotted in Figure 2 as the logarithm of the pressure against the reciprocal of the absolute temperature. Equations for the straight portions of the curves were derived by the method of averages. The equations, together with boiling points and apparent heats of vaporization calculated from the eauations, are summarized in Table II. The approximate relation of the heat of vaporization to the concentration of the acids is shown in Figure 3, which includes two values reported by Kablukov and Zagvozdkin (6). The relation shown in Figure 3, although somewhat inexact, should be useful in engineering calculations.
Tilden and Barnett (9) deteiniined the vapor density of three preparations of “metaphosphoric acid” a t “bright red heat” by the Victor Meyer method in platinum apparatus. The samples contained about 91% phosphoric oxide, which is significantly more than the phosphoric oxide content (88.75%) of metaphosphoric acid. The vapor dmvities indicated molecular weights of 138 to 156, and Tilden and Barnett conthe cluded that metaphosphoric acid exists in the vapor state as the dimeric molecule, (HPOa)2. Tilden and Barnett’s measurements of the vapor density of phosphoric oxide in the same apparatus, however, were about 15% higher than the accepted value. A similar error in their experiments on “metaphosphoric acid vapor” would indicate an apparent molecular weight of the order of 130 for the vapor over phosphoric acid with a P4Om content of about 91% a t bright
COMPOSITION OF VAPOR
Zagvozdkin, Rabinovich, and Barilko (10) found no phosphorus compounds in the vapor over acids containing 63.4 t o 88.7% P4010 a t 150” to 300” C. Britzke and Pestov (2) determined the orthophosphoric acid content of vapor condensed from acid boiling in a quartz tube; over a range of boiling points from 219’ to 739’ C., the ILPOa content of the condensates ranged from 0.006 to 2.8101,.
1000/sK
Figure 2.
Vapor Pressure in the System P~OIO-HZO
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1952
617
OF PHOSPHORIC ACIDS TABLE I, VAPORPRESSURE
GLASSAPPARATUS 61.6%
t=
pb
85.5 96 104 111.5 120 130.5 154
53.3 89.2 124.9 170.2 234.7 344.0 752.0
115 123.5 129 138 150.5 160 166 193
63.7%
Pi010
t 87 93 103 111.6 115 127 138 161 69.0%
45.6 71.7 93.3 134.2 216.6 294.6 347.5 755.0
Pa010
P 41.5 57.8 89.9 134.4 156.2 242.8 350.9 752.1 P4010
1
P
120 138.5 156 173 177.5 207
39.3 86.5 166.2 293.6 356.7 755.0
66.9% P4Oie . t P 105.5 39.2 9 0.3 123 130.5 1 1 9 . 3 181.2 142 150 240.9 161.5 343.9 188 757.0
70.3% Pa010 t P 132.5 30.9 147 63.6 156 94.3 162.5 129.9 184 243.0 195 339.3 224 758.9
72.4% P4010 t P 166 32.2 175 59.7 183 88.6 195.5 131.4 211 223.5 227 356.1 256 758.9
78.7% t
204 223 233.5 245, 257 276 301
41.8 87.8 121.5 173.1 231.9 384.3 755.2
276 284 291 326
226.1 287.0 349.9 750
HASTELLOY APPARATUS
66.1% Pa010 t P 104 52.1 93.3 117 128.9 126 137.5 199.4 147 286.8 154 352.6 177 750.0
267 278 295 310.5 327 344 380
78.2%
Pa010
t
P
85.9% PaOio t P
79.7% t 341 357 370 383 392 399 408 412 419 428
P4010
88.5%
P40io
t
P 109.3 168.6 231.0 317.1 380.2 436.6 527.2 581.8 645.4 746.7
P
F83 ,098 GI3 624 634 a t = temperature, C. b p = pressure, mm. of mercury.
P4010
P 35.0 56.8 92.2 163.7 250.2 363.3 753.0
81.5% P4Olo t P
83.7% P d h t P 99.3 148.1 202.5 265.9 335.2 399.4 455.8 529.8 591.8 646.0 749.1
91.9% PlOlo
92.7% PnOio . t P 88.0 135.3 190.1 254.8 317.0 414.3 483.1 568.4 656.9 754.7
t
P
117.9 195.2 237.2 318.7 365.5 499.3 566.4 672.1 752.7
TABLE 11. VAPORPRESSURE EQUATIONS AND HEATSOF VAPORIZATION FOR PHOSPHORIC ACIDS
61.6 63.7 66.1 66.9 68.5 69.0 70.3 72.4 76.3 76.3 78.2 78.7 79.7 81.5 83.7 85.9 88.6 91.9 92.7
0.8 1.2 2.9 1.5 2.5 6.2 5.1 2.6 4.0 3.5 3.3 1.6 4.0 4.0 4.2 6.2 7.7 4.6 6.9
0.4 0.8 1.2 0.5 1.8 0.3 2.4 1.8 2.9 2.4 1.3 1.2 2.2 1.6 1.4 3.1 2.4 1.8 2.0
-
a Equations of the form, log pmm. = A B/T,derived from the data doscribing Ytraight lines in Figure 2. b Calculated from the vapor pressure equations (760 mm.). 0 Calculated from the vapor pressure equations.
Pd01oCONTENT OF ACID, WEIGHT
$ :
Figure 3. Heat of Vaporization in the System P~OIG-H~O
TABLE 111.
COMPOSITION O F VAPOR OVER
ACIDS
Borosilicate Glass Still P4oio in Temp. of boiling acid, C. 221-228 0.009 228-234 0.014 234-241 0.02 241-250 0.03 250 0.02 250-259 0.05 259-268 0.08 268-273 0.12 273-281 0.16 281-290 0.29 290-301 0.47 301-308 0.64 308-316 0.89 320 1.20 350-362 1.62 362-385 1.96 410 6.10
3%
BOILING PHOSPHORIC
Hastelloy B or Platinum Boiler Temp. of PdOm in boilip vapor, acid, C. wt. % 350 1.59, 1.85, 2.36 400 5.3 4 6 5 4 449 9.2: 915: 9 : 8 548 19.5, 18.7, 22.7 647 34.5, 36.9, 34.1 696 31.5 30.0 32.9 744 40 0' 38 8' 38.6 47:3: 45:6: 50.6' 793 54.8, 71.8, 53.9 840 62.9, 66.0, 66.4
Figure 4.
Temperature-Composition Diagram for the: System P ~ O N - H ~ O
618
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE Iv
APPARENT L\IOLECUL,AR FYEIGHTB SYSTEM I’,Oio-HsO
PlOio in Liquid, Wt. % 61. 5Q
Apparent Mol. 1% t. of Vapor Experimental values Average 43.8,44.7,45.8,44.8 44.8 58.7, 5 0 . 0 , 5 9 . 2 56.0 108.7, 108.4, 1 1 1 . 8 109.6 1 3 2 . 0 ,123.5, 135.5, 132.2 137.0, 133.0, 130.2, 134.0
72.46 88.0C 92.0d
a
OF
VAPOR
I N THE
~~~~~i~~ Calcd. Mol.vapo; Wt. is PaOn HzO 42.4 56.0 102.4 130.0
+
The apparent molecular weights derived from the vapor density measurements were compared with those calculated from assumptions that the vapor consisted of various binary combinations of H20, P4010,H3P04,Hapgo?,HPO,, (HPO&, and (HPO&. The striking agreement of the measured values with the values calculated on the basis of the P& and HpO combination (Table IV) leaves little doubt t h a t the vapor over phosphoric acids of high P4010content a t 1020” C. consists of a mixture of P,O,Oarid H 2 0 molecules.
HaPOa, 85%.
b HsP04. d
Vol. 44, No. 3
LITERATURE CITED
Approximate1.y (HPOdn doeotropic mvrture.
red heat. The lower value ~ o u l d mean that the vapor consisted of Ppoto and HzO molecules instead of H2P206 molecules. D a t a reported by Balareff (1) indicate that the meta acid dissociates upon vaporization. Balareff distilled metaphosphoric acid in a gold vessel and found that the vaporized product, as n-ell as the residue, contained less water than the theoretical content of 11.25%. H e concluded that the rate of loss of water from metaphosphoric acid and the eventual composition of the acid are dependent upon the temperature and dyration of heating and upon the partial pressure of water vapor in the system. I n the present work, the density of the vapor over four acids (61.5, 72.4, 88.0, and 92.0% P401o)was determined by the Victor Meyer method in platinum apparatus. The measurements were made a t 1020’ C. to ensure rapid and complete volatilization of the acids, although i t was recognized that the molecular species found in the vapor a t this temperature would not necessarily be the same as would exist at lower temperatures.
Balareff, D., 2. anorg. u. allgem. Cham.,102, 34-40 (1917). Britzke, E. V., and Pestov, N. E., Trans. Sci. I n s t . Feitilizers (U.S.S.R.), NO. 59, 5-160 (1929). Elmore, K. L., Mason, C. M., and Christensen, J. €I., J . Am. Chem. Soc., 6 8 , 2528-32 (1946).
Farr, T. D., “Phosphorus. Properties of the Element and Some of Its Compounds,” Tenn. Valley Authority, Chem. Eng. Rept. No. 8, 1950.
Kablukov, I. A., and Zagvozdkin, K. I., Z. anorg. u. allgem. Chem.,224, 315-21 (1935). ‘
Mack, Edward, Jr., and France, W. G., “A Laboratory Manual of Elementary Physical Chemistry,” 2nd ed., p. 77, New York, D. Van Xostrand Go., 1934. Robinson, R. A,, and Sinclair, D. A , , J . Am. Chem. Soc., 56, 1830-5 (1934).
Tarbutton, G., and Deming, M. E., Ibid., 72, 2086 8 (1950). Tilden, W. A., and Barnett, R. E., Trans. Chem. Soc. (London), 69, 154-60 (1896).
Zagvozdkin, K. I., Rabinovich, Yu. hI., and Batilko, N. A., J . A p p l i e d Chem. (U.S.S.R.), 13, 29-36 (1940). A c c r p r m October 17, 1951. RECEIVED for review J u l y 5, 1951. Presented at the Southwide Chemical Conference, Wilmn Dam, Ala.. Octoher 1951.
LiquidHEPTADECANOL-WATER-ACETIC ACID AND HEPTADECANOLWATER-ETHANOL JAMES C . UPCHURCHI AND MATTHEW VAN WINKLE University of Texas, Austin, Tex.
S
UCCESSFUL development of liquid-liquid extraction systems and the design of the necessary equipment is extremely difficult without a knowledge of the phase equilibrium relations for the constituents involved. A knowledge of these data alloivs the prediction of the applicability of the process and permits a mathematical analysis of the extraction method used. The systems investigated in this study include the acetic aridheptadecanol-water system, a t 25’ and 50’ C., and the ethanolhrptadecanol-water system a t 25“ C MATERIALS
The heptadecanol used in this investigation was obtained from Union Carbide and Carb?n Chemicals Corp. The glacial acetic acid was secured from Allied Chemical and Dye Corp. and was obtained as a 99.5% pure compound. The 100% ethanol wah obtained from U. S. Industrial Chemicals, Inc. All water used in this investigation was distilled, and the water used in the arid systems was also boiled t o remove any carbon dioxide present. 1
Present addreas. Carbide and Carbon Chemicals Corp., Texas C i t y , Tex.
PROCEDURE
There are various experimental procedures for the determination of ternary equilibrium data. The methods of Othmer ( d ) , Taylor ( 5 ) , and Othmer el al. ( 4 ) are probably the most widely used. The latter method was used in this investigation since the techniques involved were considered more adaptable t o the systems investigated. In this method the mutual solubility curve and the tie line data are dptermined separately in the analyses of ternary equilibrium, I n the determination of the solubility curve a known amount of solvent was measured into a flask from a calibrated buret. This made possible the calculation of the weight quantity present. The diluent was then added t o the solvent in a dropwise manner, with constant agitation of the flask, until the solution became turbid. This indicated t h a t the solvent phase was then saturated with diluent. The recorded volumes were then converted by means of the known weight per volume delivered calibrations to weight percentages. This particular point represented the solubility of the diluent in the solvent since no solute was present. To this turbid mixture a known amount of the solute was added, and because of its consolute effect a clear solution resulted. This addition
