Phase Relations i n the Nitric Acid-Nitrogen Dioxide-Water System a t Physicochemical Equilibrium WEBSTER 6 . KAY
and
MANOJ D. SANGHVI Columbus, Ohio
T h e Ohio State University,
I n orevious papers (1, 2), the phase relations of nitric acid and'of b i n a j h i x t u r e s of nitric acid and nitrogen dioxide and of nitric acid and water were presented. T h e range of concentration covered w a s up to 15 weight 5% of nitrogen dioxide and 5 weight S, of water. It w a s found that t h e high physicochemical equilibrium pressure, observed in t h e c a s e of nitric acid, i s reduced considerably by the addition of either nitrogen dioxide or water. T h e work h a s been continued with a study of the phase relations of ternary mixtures of nitric acid, nitrogen dioxide, and water. A limited study h a s a l s o been made of binary mixtures of nitric acid and nitric oxide. Measurements of the phase relations were made a t temperatures between 85' and 150'C. and for t h e ratios of vapor volume to total volume, ( V G / V ) , from 0.8 to near zero, the bubble point of t h e mixture. T h e results are summarized in t h e present article. Reamer, Corcoran, and Sage (5) have reported measurements on four compositions in the ternary system nitric acid-nitrogen dioxide-water, but their measurements were made primarily, in a region of lower specific volume than those covered in the present investigation.
OF M A T E R I A L S N i t r i c Acid. Yitric acid w a s prepared (1) by reaction of 100% sulfuric acid with anhydrous potassium nitrate a t D O C . in the complete absence of air, and t h e acid w a s collected a s a solid a t liquid nitrogen temperature. T h e acid showed, by chemical analysis, a total acidity of 99.98 f0.05% HNO,, with no trace of nitrogen dioxide or sulfur trioxide., Nitrogen Dioxide. Nitrogen dioxide w a s prepared (2) by t h e thermal decomposition of pure, dry lead nitrate according to t h e equation
PREPARATION
Pb(NO,),(s) = PbO(s)
+ 2N0, +
1/2 0, ( 9 )
( 1)
T h e gaseous nitrogen dioxide-oxygen mixture w a s dried over phosphorus pentoxide and subsequently t h e nitrogen dioxide was frozen out in a trap cooled with a dry ice-acetone mixture. T h e nitrogen dioxide w a s purified by contact in t h e liquid phase with oxygen g a s to oxidize the lower oxides, and by repeated sublimation under high vacuum. N i t r i c Oxide. Commercial nitric oxide g a s having a
Table I. Experimental Data on Phase Relations in Nitric Acid-Nitragen
Dioxide-Water
System at Physicochemical Equilibrium
(All pressures are in pounds per square inch absolute)
Initial Compn., Weight % HNO,
Molal Ratio.
Snec. Vol..
NO1
90.00
0.00
10.00
0: 1
0.01363
70.00
30.00
0.00
1:0
0.01363
94.70
4.69
0.61
1.5:l
0.01363
84.56
13.66
1.78
1.5: 1
0.01363
79.22
18.37
2.41
1.5:l
0.01363
Press. VG/V Press. VG/V
Press. VG/V Press. VG/V Press. VG/V
72.37
24.44
3.19
1.5:l
0.0 1363
Press.
72.37
24.44
3.19
1.31
0.02371
Press.
vG/v
VG/V
86.05
11.71
2.24
1:1
0.01363
Press. VG/V
81.29
15.65
3.06
1:1
0.01363
Press.
76.61
19.56
3.83
1:1
0.01363
95.00
3.59
1.41
0.5: 1
0.01363
95.00
3.59
1.41
0.51
0.01762
Press. VQ/V Press. VG/V Press.
95.00
3.59
1.41
0.5:l
0.02389
90.00
7.18
2.82
0.5: 1
0.01363
90. 00
7.18
2.82
0.5: 1
0.02371
Press. VG/V Press. VG/V Press.
85.00
10.77
4.23
0.5:l
0.01363
Press.
85.a)
10.77
4.23
0.5:l
0.02371
Press.
vc/v
vo/v
vo/v
VG/V VG/V
80.00
14.36
5.64
0.5: 1
0.01363
Press. VG/V
22
85
95
147 0.149 229 0.217 654 0.187 178 0.190 82 0.195 80 0.196 79 0.561 176 0.185 78 0,186 72 0.205 580 0.182 340 0.375 232 0.538 222 0.194 134 0.535 80 0.176 70 0.533 58 0.178
177 0.138 300 0.204 732 0.175 231 0.178 122 0.183 113 0.183 111 0.55 7 218 0.174 114 0.175 105 0.193 653 0.169 389 0.368 272 0.533 270 0.181 170 0.529 114 0.166 99 0.526 84 0.167
Temoerature. 105 115
216 0.125 391 0.187 832 0.162 307 0.164 177 0.169 160 0.176 158 0.549 299 0.161 165 0.161 147 0.180 746 0.156 450 0.359 323 0.527 343 0.171 217 0.524 161 0.153 138 0.522 118 0.153
265 0.114 499 0.169 939 0.148 395 0.151 245 0.154 217 0,161 212 0.543 384 0.147 228 0.147 200 0.166 85 1 0.142 522 0.350 385 0.521 418 0.156 275 0.518 221 0.140 190 0.515 168 0.140
C. 125
135
150
327 0.101 635 0.148 1076 0.133 509 0.135 340 0.138 294 0.145 287 0.53 7 494 0.132 315 0.132 272 0.151 969 0.128 615 0.340 458 0.516 520 0.142 348 0.513 302 0.124 256 0,509 232 0.125
406 0.088 80 3 0.121 1235 0.114
559 0.0 64
... ...
461 0.118 396 0.127
... ...
...
...
1540 0.082
... ...
721 0.086
..* ... ... ...
... ... 655 0.084 ... ... ... ... ... ... ... 728 942 0.329 0.312 ... ... ... ... 644 884 0.100 0.128 ... ... ... ...
627 0.115 428 0.115
e . .
407 0.108
... ... ... ...
616 0.081
... ... ... ...
JOURNAL O F CHEMICAL AND ENGINEERING DATA
purity of 98.0% or better w a s admitted t o a purification train from which a l l a i r had been removed and w a s passed, first through a trap cooled by dry i c e and acetone, then through a drying tube 5 feet long, packed loosely with g l a s s wool upon which phosphorus pentoxide w a s suspended, and finally w a s condensed and frozen in a trap cooled with liquid nitrogen. T h e solid w a s pumped for 10 to 1 5 minutes, then sublimed under a pressure of about 50 a m . of mercury and pumped again. T h i s ‘was repeated four times. T h e solid w a s stored a t liquid nitrogen temperature until used. Wator. P u r e water w a s obtained by t h e double distillation of an acidified aqueous solution of potassium permanganate.
0
4
Weight
Ratio
NOp
e
12
16
Weiqht
20
PREPARATION OF MIXTURES Ternary Uixtures of Nitric Acid-Nitrogen
28
24
Oioxide-Water.
Samples of ternary mixtures of nitric acid-nitrogen dioxide and water for the study of their phase relations were prepared by measuring each component separately in an apparatus free from any trace of air, and then transferring t h e s e quantities by distillation to the experimental tube to make a mixture of known composition. T h e apparatus and procedure were similar to those described for t h e preparation of binary mixtures of nitric acid-nitrogen dioxide and nitric acid-water (2). Mixtures of any composition t o within 0.02 weight %, and of any specific volume to within 0.1 % could b e prepared,
0
8
4
I2
Welqht
percent o d d i t i v e
16
20
24
percent oddltlve
Figure 3.
Relation between equilibrium pressure and composition a t c o n s t a n t specific volume (0.01363 CU. f t l l b . ) for ternary m i x t u r e s c o n t a i n i n g NO, and H,O i n proportion of 2.55 t o 1 by weight
Figure 1. Relation between equilibrium pressure and composition at constant specific volume (0.01363 cu. ft./lb.) for ternary mixtures containing NO, and H,O in proportion o f 7.66 t o 1 by weight
600ci+W/qhl
Specific
volum N Oe p = tip0 0 02378 : 2 5c 5 u 10ft/lb
I
500 I
0
n
400
: c4
u
k 300 E
2 P
5, 200
E I00
I
0
4
8 Weight
12
16 20 percent additive
24
Figure 2 Relation between equilibrium pressure ond composition a t constant specific v o l u m e (0.01363 CU. ft./lb.) for ternary m i x t u r e s Containing NO, and H,O i n the proportion of 5.11 t o 1 by weight VOL. 4, NO. 1, JANUARY 1959
0
4
8 Weiqht
I2
16
20
24
percent a d d i t i v e
Figure 4.
Relation between equilibrium pressure and composit i o n a t constant specific volume (0.02378 CU. fts/lb.) for ternary mixtures c o n t a i n i n g NO, and H,O i n proportion of 2.55 t o 1 by weight
23
1
=
NO,
359%
I
I
0
1 014
012
I 016
I
1
1
018
020
022
024
S p e c i f i c volume cu f t / I b
Figure 5. Relotian+ between equilibrium pressure and V C / V rotio at different temperatures for ternary mixtures contoining initiolly 95.00% HNO,, 3.59% NO,, and 1.41% H , 0
I
I
1 20
8 I2 16 Weight percent oddittve
Figure 7. Relotions between equilibrium ressure and initio1 composition for various volues of VcPV at 85'C. for ternary mixtures containing NO, ond H,O i n proportion of 2.55 to 1 by weight
10001
I n l t i o l composition
I
4
I
I
1
1
I
I
I
I
( b y wcqhtl
400
320
f
80 ---=-e-
I
1
85.7"
I
Mixtures of Nitric Acid and Nitric Oxide. A mixture of known composition of nitric acid and nitric oxide w a s prepared by transferring a measured amount of nitric acid to t h e experimental tube, then condensing a measured amount of the nitric oxide on top of t h e acid. T h e nitric oxide w a s measured by confining a sample of t h e g a s a t constant temperature and under a known pressure, i n a bulb of known volume. T h e volumetric bulb w a s s e a l e d directly to t h e trap i n which t h e nitric oxide w a s stored. Attached to a s i d e ann of t h e bulb w a s a mercury manometer. To prepare a mixture of given specific volume and given composition, t h e pressure of the nitric oxide g a s in t h e bulb, necessary to give t h e desired amount of nitric oxide, w a s computed for a reference temperature of O°C. by means of t h e perfect g a s law, and the c r o s s hairs of the c a t h e tometer were s e t accordingly on the manometer. T h e g a s w a s then admitted to t h e bulb which w a s maintained a t O°C. by a n i c e bath, until the pressure w a s slightly greater
24
than that computed. A stopcock on top of t h e volumetric bulb w a s then opened cautiously, and t h e g a s was pumped off until t h e mercury level in t h e manometer coincided exactly with the c r o s s hairs of the cathetometer. T h e remainder of t h e procedure w a s exactly t h e same a s employed in t h e s t u d i e s of binary and ternary mixtures of nitric acid, nitrogen dioxide, and water. It i s estimated that the composition of the prepared mixture w a s known to within 0.01%. A P P A R A T U S AND P R O C E D U R E
For t h e measurement of the equilibrium pressure of nitric acid-nitrogen dioxide-water mixtures, a sample, prepared a s described, w a s maintained under isochoric condiJOURNAL OF CHEMICAL AND ENGINEERING DATA
tions a t a constant temperature and w a s stirred continuously with a magnetic stirrer until physicochemical equilibrium w a s reached, a s indicated by t h e constancy of t h e pressure exerted by t h e sample. T h e temperature w a s then changed and t h e experiment w a s repeated a t t h e new temperature. T h e apparatus and procedure were t h e same as for similar measurements on initially pure nitric a c i d (2). T h e temperature of t h e sample w a s kept constant t o within 0.05°C. and w a s measured by a calibrated mercury
L
3
n YI
u Temperature * 85% Specific volume = 001363 cu f t l l b
E 7
P
io00
3
W 0
I
I
I
I
I ?
I
I
I
1
100 110 Temperature, *t
I
I
I20
i
100%addltlve-
I
WATER;
11.
I
Figure 10. Comporiron of effect of odding NO, ond H,O in different proportions on the equilibrium pressure of the mixture of vorious temperotures in the HNOJ-NO,-HIO system
theraometer marked in 0.l"C. divisigns. T h e pressure w a s indicated by a 0 to 2000 p.s.i. precision Rourdon-type gage with a 16-inch dial, hand-marked in 2-pound divisions. T h e gage was t e s t e d a t 20-pound intervals with a precision dead weight gage tester. P r e s s u r e s were read to 1.0 pound per square inch. T h e volume of the vapor p h a s e of the sample w a s determined from the length of the tube occupied by the vapor, t h e length having been related to the volume by a previous calibration of t h e tube. A cathetometer reading to 0.05 mm. w a s used for measurement of t h e lenzth. From a knowledge of the vapor volume and the total volume of t h e
Figure 9. Relotion between equilibrium pressure ond proportion of woter in the additive ot 85OC. in the HNO,-NO,-HIO system
Figure
1
90
PERCENT BY
WEIGHT
Equilibrium pressures in the nitric acid-nitrogen
dioxide-water
system
Temperature = 8 5 O C . , V G / V = 0.15
VOL. 4,
NO. 1,
JANUARY 19S9
25
sample section of t h e experimental tube, the V G / v ratio w a s calculated. T h e accuracy was estimated to be within 0.1% of t h e true value of t6e ratio. A s in t h e c a s e of the binary mixtures, the t i m e required to reach equilibrium at a given temperature, a s judged by the constancy of pressure, w a s dependent on the initial composition and the V c / V ratio. Equilibrium was approached rapidly for a l l mixtures except t h o s e of nitric acid and water containing 10% of water. For the latter, equilibrium w a s not attained even after 4 5 hours at 85'C. In this c a s e , the pressure w a s recorded a s a function of time and a large s c a l e plot w a s prepared of the pressure versus the reciprocal of time. By extrapolation t o infinite time, t h e value of the equilibrium pressure w a s obtained graphically. Fquilibrium at higher temperatures w a s attained much more rapidly. RESULTS
To establish t h e relations among pressure, volume, temperature, and initial composition in t h e nitric acid-nitrogen dioxide-water system, in t h e region of high concentration of nitric acid, a total of 11 compositions associated with three restricted ternary s y s t e m s containing nitrogen dioxide and water in t h e ratio of 7.66:1.0, 5.11: 1.0, and 2.55:1.0, were studied. In addition, one composition each of t h e binary systems nitric acid-nitrogen dioxide and nitric acidwater was studied in order to extend t h e range of binary mixtures already investigated (2). Three mixtures of nitric acid with nitric oxide w e r e a l s o studied. T h e range of concentration covered w a s from 70 to 97.5% of nitric acid, 0 to 30% of nitrogen dioxide, 0 t o 10% of water, and 0 t o 3% of nitric oxide. 3 e c a u s e for each experimental run t h e specific volume and t h e V G / V ratio were fixed, i t w a s necessary t o study several mixtures of t h e same composition in order to determine t h e relation of t h e s e variables with the equilibrium pressure. For each of the mixtures the equilibrium pressures and V G / V ratios w e r e determined under isochoric conditions at 10'C. intervals from 85' t o 125OC.
and in some c a s e s at 135' and 150'C. T h e experimental data a r e presented in T a b l e I and shown graphically in Figures 1 through 4. VOLUMETRIC EQUILIBRIUM RELATIONS
T h e isothermal relations between t h e equilibrium press u r e and the initial composition for the three restricted ternary systems a r e shown in Figures 1 through 4. T h e composition h a s been expressed a s the weight p e r cent of the additive, which i s defined a s the sum of the weight per cents of nitrogen dioxide and water in t h e mixture. T h e data points a t 5.30 and 15.40% of the additive i n Figure 1 were obtained from measurements on mixtures prepared by adding nitric oxide t o nitric acid. Nitric oxide r e a c t s with nitric acid according to the equation
2 HNO, + NO
+ H,O
(2)
PERCENT
BY
WEIGHT
12 Equilibrium pressures in the nitric acid-nitrogen dioxide-water s y s t e m Temperature = 85'C.,
26
3 NO,
0.00
WATER,
Figure
I
to give nitrogen dioxide and water in the weight ratio of 7.66 to 1. Mixtures so prepared were found t o have t h e same properties a s if the nitrogen dioxide and water in the same amounts had been added directly t o t h e acid. Figures 5 and 6 exhibit the effect of the V G / V ratio on the equilibrium pressure when the temperature and initial composition a r e held constant. Figure 7 shows the relation between equilibrium pressure and weight per cent of additive with V G / V a s the parameter. T h e relations depicted by the a w e s in Figures 1 through 7 are similar t o those for the binary mixtures of "0,-NO, and "0,-H,O (2). T h e equilibrium pressure is markedly decreased by the addition of nitrogen dioxide and water and reaches a minimum value between 20 and 28 weight % of the additive, depending on t h e temperature and t h e ratio of
V G / V = 0.35 JOURNAL OF CHEMICAL AND ENGINEERING DATA
nitrogen dioxide t o water. A comparison of t h e curves i n F i g u r e s 1, 2, and 3 indicates that, on t h e b a s i s of equal amounts of t h e additive, the mixtures containing t h e greater amounts of water exhibit t h e lower equilibrium pressure. This difference between nitrogen dioxide and water, i n t h e i r effectiveness to reduce the equilibrium pressure, is brought out by t h e c u r v e s i n F i g u r e s 8 and 9. Figure 1 0 indicates that t h e s a m e relations hold at higher temperatures. A s in t h e case of the binaries, t h e equilibrium pressures of mixtures of high acid content a r e s e n s i t i v e t o the V G / V ratio, but t h i s sensitivity diminishes with a d e c r e a s e i n acid content and becomes insignificant below about 80% of nitric a c i d at 85OC. At higher temperature, t h i s concentration will b e somewhat l e s s than 80%. CORRELATION O F
EXPERIMENTAL D A T A
T h e relations among t h e equilibrium pressure, initial composition, V G / V ratio, and temperature, exemplified by t h e curves in F i g u r e s 1 through 10, have been correlated and a r e expressed graphically by t h e triangular diagrams of F i g u r e s 11 through 22. Each triangular diagram shows t h e isobaric curves of the equilibrium pressure a t regular press u r e intervals, in t h e i r relation t o the initial composition a t a given temperature and V G / V ratio. Diagrams were prepared for t h e temperatures S o ,1OSo, 1 2 S 0 , and 150°C. for e a c h of t h e V G / V ratios 0.15, 0.35, and 0.60. T h e s p e c i f i c volumes of the heterogeneous mixtures i n cubic feet per poi nd for the conditions s t a t e d i n Figures 11 through 22 were correlated with the initial composition by the generalized empirical chart (Figure 23). To determine t h e s p e c i f i c volume of a mixture of any given initial com-
position, t h e value of the specific volume of t h e equilibrium mixture, resulting from t h e dissociation of pure nitric acid a t t h e s a m e temperature and V G / V ratio, is multiplied by the composition factor read from t h e generalized chart (Figure 23). T h e specific volume of the equilibrium mixture for pure nitric acid t o be used i n the calculation, is given in T a b l e 11. T h e generalized chart i s based on the assumption that l i n e s of constant liquid density at 25OC.
Table
II. Relotion omong V G / V , Temperature, and Specific Volume for I n i t i a l l y Pure Nitric Acid ot Physicochemical Equilibrium
Specific Volume, Cu. Ft./Lb. Temp., OC.
V G / V = 0.15
V G / V = 0.35
V G / V = 0.60
85 105 125 150
0.01300 0.0 1341 0.01382 0.01433
0.01678 0.0 1729 0.01781 0.0 1845
0.02625 0,02707 0.02788 0.02890
for t h e nitric acid-nitrogen dioxide-water system a r e a l s o l i n e s of constant specific volume of t h e heterogeneous sample a t a given temperature and V G / V ratio. T h e curves were constructed using t h e experimental d a t a given in T a b l e I and t h e density data of Stern and Kay (7), Klemenc and Rupp (3), Sprague and Kaufman (6), and Mason, Petker, and Vango (4). T h i s method of estimating t h e equilibrium specific volume, when applied to che mixtures listed in T a b l e I, gave values which agreed t o within 1% of t h e experimental values. ACKNOWLEDGMENT
T h e authors wish to thank S. A. Stern for many helpful suggestions and Lillian Golub for a s s i s t a n c e with calculations and preparation of t h e manuscript. T h a n k s a r e a l s o due t o the many students who helped in t h e taking of t h e data. (LiteratureCited on page 32)
WATER, Figure
PERCENT BY
WEIGHT
13. Equilibrium pressures in the nitric acid-nitrogen dioxide-water system Temperature = 8SoC., @/V
VOL. 4, NO. 1, JANUARY 1959
= 0.60
27
Figure 14. Equilibrium pressures i n the nitric acid-nitrogen dioxide-water system
Temperature = 1 0 S o C , VG/V = a15
WATER,
PERCENT BY WEIGHT
Figure 15. Equilibrium pressures i n h e nitic acid-nitrogen dioxide-water system
Temperature = l0SoC., V Q / V = 0.35
WATER,
28
PERCENT BY WEIGHT JOURNAL O F CHEMICAL AND ENGINEERING DATA
Figum
16, Equilibrium pressures
i n the n i t r i c acid-nitmgm dioxidcwater s y s t m
Temperature = 10Soc,
V % V = 0.60
22 WATER, PERCENT BY WEIGHT
Figum
17. Equilibrium pressures in the nitric acid-nitrogm d i o x i d r w a t e r systrm
Temperature = 12S°C., V c / V = 0.15
P WATER, PERCENT fN WEIGHT
va.
4, NO. 1,'JANUARY 1959
29
Figure
18. Equilibrium pressures i n thenitric ocid-nitmgen dioxide-water system
Temperature = 12SoC., V o / V = 0.35
WATER,
Figure 19.
PERCENT B Y WEIGHT
Equilibrium pressures i n the nitric acid-nitrogen dioxide-woter system
Temperature = 12S°C., V G / V = 0.60
WATER,
30
PERCENT BY WEIGHT JOURNAL OF CHEMICAL AND ENGINEERING DATA
Figure
20. Equilibrium pressures in the nitric acid-nitrogen dioxide-woter
system
Temperature = 150°C., V G / V = 0.15
22
2
0
Figure
4
6
8 IO 12 14 WATER, PERCENT BY WEIGHT
16
ia
20
78 22
21.
WATER, PERCENT BY
VOL. 4, NO. 1, JANUARY 1959
WEIGHT
31
Figure
2 2 Equilibrium plrssuros in the nitric ocid-nitrogen dioxide-water
system
Temperature = 150°C., f l / V = 0.60
WATER.
PERCENT
ev
WEIGHT
LITERATURE CITED (1) Kay, W. E., Stern, S. A., Ind. Eng. Chem. 47, 1463 (1955); Am. Doc. Inst, Library of Congress, Doc. 4507, Washington, D. C (2) Kay, W. B ., Stern. S b, Ssnghvi, M. K. D., Ind. EN. Chem, Chem. Eng. Data Ser. 2, 2 1 (1957). (3) Klemenc, L,Rupp, J., 2. anorg. U. allgem. Chem. 194, 5 1 (1930). (4) Mason, D. M., Petker, 1, Vango, S P., .I. Phye. Chem. 59, 511 (1955). ., Sage, B. H.. Ind. Eng. Chem. (5) Reamer, It It, Cormran, W. H Chem. Eng. Data Ser. 1. (1956). (6) Sprague, R W., Kaufmpn, E. I n d Eng. C h e n 47, 458 (1955). (7) Stern, S 11, Kay, W. B.. .I. Am. Chem. SOC.76. 5353 (1954). Received for review December 14, 1957. Accepted May 8, 1958. Bosed on work performed under Contract AI 33(038)10381 with Wright Air Development Center, Wright-Patterson Air Force Bane.
bL
22/
0
v
!J 2
vvvvvvvvvvvv vvvv 4
6
8
IO
I2
)4
16
Figure
23, C.noraIixod relation botwom spocific volume a d a n p o s i t i o n at c o n s t a t tomp.rature a d constant vC/V ratio
vv
WATER, PERCENT EY WEIGHT
32
JOURNAL O f CHEMICAL AND ENGINEERING DATA
