low dodecane concentration region. However, t h e remainder of t h e experimental y v a l u e s for butyl carbitol and a l l v a l u e s for n-dodecane a g r e e very well with t h e van L a a r equation r e s u l t s , a s shown in Figure 4. F o r t h e naphthalene-butyl carbitol system, values of y above and below 1.0 were found for butyl carbitol (Figure 6), and i t w a s impossible t o correlate t h i s s y s t e m with t h e van L a a r equation. An unsuccessful effort w a s made t o correlate t h i s system by means of t h e Margules equation. Figure 1 s h o w s a n azeotrope a t approximately 67% naphthalene and 140.2 OC. for t h e naphthalene-n-dodecane system. Figure 3 s h o w s a n azeotrope a t approximately 65% n-dodecane and 142.6OC. for the n-dodecane-butyl carbitol system. Figure 5 i n d i c a t e s that the naphthalene-butyl carbitol system exkibits a slight tendency toward azeotrope formation a t high naphthalene concentrations. A s in t h e ndodecane-butyl carbitol system, t h i s binary s h o w s unusual behavior, in that activity coefficients above and below 1.0 a r e found for butyl carbitol. T h i s system could not b e correlated using t h e van L a a r equations. T h i s peculiar behavior h a s b e e n noted before (3, 9, 2 4 ) . It c a n possibly b e explained through molecular association a t low concentrations of t h e higher aromatic in t h e binary.
NOMENCLATURE A = c o n s t a n t of van L a a r solution of Gibbs-Duhem equation B = c o n s t a n t of van L a a r solution of Gibbs-Duhem equation b = c o n s t a n t of Margules s o l u t i o n of Gibbs-Duhem equation c = c o n s t a n t of Margules solution of Gibbs-Duhem equation d: = density a t 20 ‘C. f = fugacity fn = fugacity of pure component a t total p r e s s u r e n b = index of refraction a t tcmperature t , using sodium D l i g h t P , = vapor p r e s s u r e of component 1 a t temperature of s o l u t i o n , mm. Hg x1 = mole fraction of component 1 i n liquid p h a s e
x 2 = mole fraction of component 2 i n liquid p h a s e y = mole fraction of component in vapor p h a s e ‘n = total p r e s s u r e of s y s t e m , mm. Hg a b s o l u t e
v = fugacity coefficient y = activity coefficient
Subscripts BC D exptl N TC
= b u t y l carbitol = n-dodecane = experimental = naphthalene = thermodynamically c o n s i s t e n t
LITERATURE C I T E D (1) Carlson, H. C., Colbum, A. P . , Ind. Eng. Chem. 34, 581-9 (1942). (2) Dreisbach, R. R., “ P h y s i c a l P r o p e r t i e s cf Chemical Subs t a n c e s , ” Dow Chemical Co., Midland, Mich., 1953. (3) Haynes, Steward, Jr., Van Winkle, M., Ind. Eng. Chem. 46, 334-7 (1954). (4) Hougen, 0. A., Watson, K. M., “Chemical P r o c e s s P r i n c i p l e s , P a r t E,” Wiley, New York, 1954. (5) International C r i t i c a l T a b l e s , vol. I., p. 279, McGraw-Hill New York, 1926. (6) Kirk, R. E . , Othmer, D. F., “Encyclopedia of Chemical Technology,” Vol. 7, p. 251, I n t e r s c i e n c e Encyclopedia, New York, 1951. (7) L a n g e , A. L., ed., “Handbook of Chemistry,” 6th ed., Handbook Publishers, Sandusky, Ohio, 1946. (8) Lydersen, A. L., Univ. Wisconsin, Eng. Expt. Sta. Rept. 3 (1955). (9) Martin, W. L., Van Winkle, M., Ind. E n g . Chem. 46, 1477 (1954). (10) Redlich, Otto, Kister, A. T . , I b i d . , 40, 345 (1948). (11) Robinson, C. S., Gilliland, E. R . , “ E l e m e n t s of F r a c t i o n a l Distillation,” pp, 39-65, McGraw-Hill, New York, 1950. (12) R o s s i n i , F. D., others, “Selected V a l u e s of P h y s i c a l and Thermodynamic P r o p e r t i e s of Hydrocarbons a n d R e l a t e d Compounds,” API R e s e a r c h P r o j e c t 44, December 1952. (13) Stull, D. R., Znd. Eng. Chem. 39, 5 1 7 4 0 (1947). (14) Ward, S. H., Van Winkle, M., I b i d . , 46, 338-49 (1954). R e c e i v e d for review October 22, 1956. Accepted April 15, 1957.
Some Volatility Characteristics of Aircraft Jet Fuels IRWIN POLITZINER Continental Oil Co., Ponca City, Okla.
To
aid in t h e design of a combustion system for j e t engines, certain information regarding t h e volatility of the various potential fuels is required. U s e of t h e fuel a s a heat sink i n supersonic aircraft introduces considerable preheat before injection into t h e combustion chamber. T h e preheat and/or t h e pressure drop a c r o s s t h e nozzle c a u s e a certain portion of t h e fuel t o vaporize. T h e final ratio of vapor t o liquid depends on many factors, including t h e initial pressure, initial temperature, final pressure, and h e a t losses or influx from or to t h e fuel. Considerable vapor-liquid equilibrium d a t a h a v e been recorded for binary and ternary hydrocarbon s y s t e m s (2), but relatively l i t t l e work h a s b e e n done o n multicomponent systems. Work in t h i s field h a s been limited t o mixtures of
16
INDUSTRIAL AND ENGINEERING CHEMISTRY
known composition p l u s some scattered data obtained by various petroleum companies on their own refinery streams (3). Several methods of calculating flash equilibrium data from ASTM distillation data h a v e been proposed (3, 4, 7). None of t h e s e is t o o satisfactory, a s t h e deviations from t h e mean range from 12’ t o 40° F. a t atmospheric pressure and a r e s t i l l higher a t elevated pressures. T h e present work w a s undertaken in order t o obtain flash equilibrium data on commercial j e t fuels a t pressures and temperatures characteristic of t h o s e to b e expected i n engine operation. T h e flash equilibrium data were obtained i n a laboratory flash equilibrium s t i l l . T h e s t i l l design w a s adapted from that s u c c e s s f u l l y u s e d by several other investigators to obtain flash equilibrium data (6, 8). Standardization runs VOL. 2, NO. I
T a b l e I.
P h y s i c a l Properties of T e s t F u e l s
Gravity, 'API Distillation, ASTM D-86, 70recovered
IBP 5 10 20 30
40 50 60 70 80 90 95 EP
70 recovered
70r e s i d u e % loss
Sample A, JP-4
Sample
49.4
~
JP-4
Sample C, JP-4
Sample D, JP-5
55.9
48.2
42.7
B,
,(pRGE
STOCK
RELIEF
VALVE
4 ' OF 3 / 8 " T U B I N G
JACKET CONNECTION
123 202 240 285 302 327 347 367 3 90 419 449 470 486
152 200 217 236 252 2 66 278 2 92 304 319 334 348 378
124 214 251 277 290 300 3 14 340 367 40 5 450 484 514
2 74 325 347 3 68 3 82 404 420 434 451 4 70 496 515 542
98.5 1.0 0.5
98.0 1.0 1.0
98.8 0.9 0.3
98.0 1.2 0.8
/-
TO OVERHEAD CONDENSER
' '
T T T
, l 6 ' OF I" PIPE
-THERMOWELL
-T2
-FLASH
were made by charging a toluene-iso-octane blend t o t h e s t i l l and comparing t h e r e s u l t s with published d a t a for t h i s s y s t e n (5). In t h i s equilibrium study, data were recorded under isothermal conditions; and i s e n t h a l p i c data were calculated by h e a t and material balances. T h e s e data represent t h e two thermal extremes. T h e engine designer c a n then provide for t h e most s e v e r e conditions and estimate for any intermediate thermal condition. A family cf equilibrium curves for p r e s s u r e s from 5 pounds per s q u a r e inch a b s o l u t e t o 20 atm. w a s obtained for e a c h of t h e three f u e l s meeting JP-4 specifications and one fuel meeting JP-5 specifications. T h e s e fuels repres e n t t h e extremes of volatility of commercial production of JP-4 and a typical JP-5. A typical JP-4 (sample A) w a s u s e d t o develop t h e detailed procedure. A manufacturer of
THERMOCOUPLE LOCA-TIONS
ZONE
-TI
TO BOTTOM
11-
REG. Figure 2. F l a s h equilibrium s t i l l
aircraft j e t e n g i n e s made a v a i l a b l e for extension of t h i s work t h e following samples: 1. A J P - 4 representing t h e most volatile commercial product ( s a m p l e B). 2. A J P - 4 intended to r e p r e s e n t t h e l e a s t v o l a t i l e commercial A c t u a l l y t h i s sample w a s s l i g h t l y more product (sample C). v o l a t i l e than s a m p l e A.
SEE FIG. i b
\\ I40
OVERHEAD
BOTTOMS
F i g u r e 1. Schematic diagram o f flash equilibrium s t i l l
1957
CHEMICAL AND ENGINEERING DATA SERIES
17
VOLUME
Figure 6. ASTM
Figure 4. Equilibrium data for toluene-iso-octane Mole fraction iso-octane V S . boiling point
3. A typical commercial JP-5.Only one sample was needed to define the JP-5volatility range, a s there are only five suppliers of this product; t n d the spread of distillation range among these five is only 25 t o 30' F. One sample in the middle of this distillation spread was obtained (sample D).
T a b l e 1 g i v e s t h e physical properties of t h e four f u e l s studied.
EQUIPMENT T h e equipment c o n s i s t e d of a continuous flash equilibrium s t i l l shown in F i g u r e s 1 and 2. T h e s t i l l w a s designed t o allow a maximum opportunity for equilibrium to b e attained. Charge s t o c k w a s pumped a t a constant rate of 1 liter per hour through a n extended preheating s e c t i o n
I
I
I8 2
m
1
WEIQHT
38.0
1
8
1
70 6
which consisted of 4 feet of 3/8-inch 18-gage tubing. In order to provide room for expansion a n d reduce t h e pressure drop a s t h e fuel began t o vaporize, i t w a s expanded into a l d f o o t length of 1-inch s c h e d u l e 40 pipe. T h e equilibrium mixture of liquid and vapor tangentially entered the flash z o n e which w a s composed of 6 i n c h e s of 6-inch schedule 40 pipe. T h e vapors were withdrawn overhead through a 2-foot length of 3-inch pipe, and t h e liquid w a s withdrawn a t t h e bottom. T h e entire s t i l l system exposed to t h e j e t fuel stream w a s constructed of T y p e 304 s t a i n l e s s steel. T h e preheater and t h e flash z o n e were a l l enclosed in a heating jacket made of 12-inch pipe. T h e heating medium w a s circulated a s a vapor through t h e j a c k e t by means of a n external boiler, t h u s a l w a y s employing a condensing vapor to heat the s t i l l . Steam w a s used for temperatures up t o 365' F. and s u i t a b l e Dowtherms were used for higher temperatures. Temperatures were measured in t h e jacket by three thermocouples p l a c e d a t different heights a s shown in F i g u r e s 1 and 2. A Milton Roy MiniPump w a s used to meter
66
eo
KXJ
E R CENT
Figure 5. F l a s h equilibrium and isenthalpic curves for sample A
18
VAPORIZED
and gravity for sample A
~
seo
40VDLUME 8 VbWRlZED
PER GENT
D-86 distillotion
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 7. F l a s h equilibrium and isenthalpic curves for sample B
VOL. 2, NO. I
m
40
O'
Figure 8. ASTM
VOLUME
mn
CENT
100
VA&zED
D-86 d i s t i l l a t i o n and
gravity for sample
0
20
40
B
t h e charge stock. Nitrogen w a s u s e d t o provide t h e back p r e s s u r e for superatmospheric operation.
EXPERIMENTAL E a c h run w a s made a t c o n s t a n t temperature and pressure. Temperatures were read t o 1' F., and t h e maximum s p r e a d among t h e t h r e e i n d i c a t e d temperatures w a s held to l oF. T h e s e temperatures were not permitted t o vary more than f 1" F. during a run. Variations in p r e s s u r e were held to .t 0.5 inch of mercury for subatmospheric runs, jk 1 pound per s q u a r e inch for p r e s s u r e s from 1 to 5 atm., and t 5 pounds per s q u a r e inch for p r e s s u r e s from 10 t o 20 atm. Volume per c e n t overhead w a s measured by collecting 10-minute samples of overhead and bottoms until three s u c c e s s i v e s a m p l e s yielded r e s u l t s with a maximum spread of 1%. T h e a v e r a g e of t h e s e three readings w a s recorded a s the per c e n t vaporized. T h e length of time required for s t e a d y - s t a t e conditions t o
Figure 10. A S T M
D-86 distillation
STAN DARDl ZATlON In order t o determine whether equilibrium conditions could b e produced i n t h e s t i l l , two standardization runs were made a t carefully controlled conditions. A l l three j a c k e t temperatures were identical, and no d e t e c t a b l e variation in any of t h e temperatures w a s permitted during the c o u r s e of t h e run. T h e data obtained were checked a g a i n s t t h o s e a v a i l a b l e from t h e literature (5). T h e toluene-isooctane system w a s c h o s e n b e c a u s e t h e components and the literature data were readily available. Nitration grade toluene and ASTM reference fuel grade iso-octane, both over 99% pure, were used. T h e literature data were plotted a s refractive index and temperature vs. t h e mole fraction of isc-octane (Figures 3 and 4). A s t h e s e data were reported a t a p r e s s u r e of 760 mm. and t h e standardization work w a s done a t t h e prevailing barometric p r e s s u r e (733 mm.), t h e recorded s t i l l temperatures were corrected by t h e foll?wing e q u a t i o n s (1):
Toluene.
Figure 9. F l a s h equilibrium and isenthalpic curves for sample C
and gravity for sample C
b e a t t a i n e d varied from 30 to 60 minutes after t h e temperature and p r e s s u r e became constant. T h e e x i s t e n c e of s t e a d y - s t a t e conditions w a s determined by the method of c o l l e c t i n g s u c c e s s i v e s a m p l e s as described above.
Iso-octane. log p = 6.81189
1957
60
VOLUME P E R CENT VAPORIZED
l o g p = 6.95464
-
1257.840
t
+ 220.735 1344.800
t + 219.482
Figure 11. Flash equilibrium curves a t atmospheric pressure Various jet fuels
CHEMICAL AND ENGINEERING DATA SERIES
19
where p is t h e a b s o l u t e p r e s s u r e in millimeters of mercury and t is t h e boiling point in d e g r e e s centigrade. T h e temperature corrections were c a l c u l a t e d a s 1.273 C. for iso-octane and 1.268' C. for toluene. A s t h e difference between t h e s e corrections w a s less than t h e experimental error, a n a v e r a g e v a l u e of 1.27OoC. (2.3' F . ) w a s used. During t h e s t i l l run s a m p l e s of charge, overhead, and bottoms were obtained. T h e refractive i n d i c e s were measured; a n d from F i g u r e 3, t h e concentrations of iso-octane in e a c h stream were determined. T h e measured s t i l l temperat u r e s were corrected by adding 2.3' F., and from Figure 4 t h e concentrations of iso-octane that should b e in t h e overhead and bottoms were determined. T h e r e s u l t s obtained by analyzing t h e s t r e a m s and t h e expected results obtained from F i g u r e 4 a r e compared in T a b l e 11. T h e comparison of t h e data i n d i c a t e s that under t h e operating conditions u s e d , equilibrium w a s c l o s e l y approximated in the still, and that c l o s e approximations t o true temperatures were measured, although t h e thermocouples were in t h e j a c k e t rather than i n t h e still.
RESULTS After t h e standardization work w a s completed, d a t a were obtained for s e v e r a l JP-4 j e t fuels. A family of flash vaporization curves w a s obtained under isothermal condit i o n s for sample A at p r e s s u r e s ranging from 5 pounds per s q u a r e inch a b s o l u t e to 20 atm. C u r v e s were obtained a t p r e s s u r e s of 5 and 10 pounds per s q u a r e inch a b s o l u t e and T h e curve a t atmospheric a t 1, 2, 3, 5 , 10, and 20 atm. p r e s s u r e w a s carefully defined by obtaining a l a r g e number of p o i n t s along i t s length. A s t h e c u r v e s belong to a family, only four or five p o i n t s were needed to define t h e c u r v e s a t other pressures. Complementary i s e n t h a l p i c curves were c a l c u l a t e d by h e a t a n d material b a l a n c e s for t h e temperature and p r e s s u r e ranges. T h e families of flash vaporization and i s e n t h a l p i c curves a r e shown in F i g u r e 5. A s t h e original d a t a were reported in volume per c e n t and the c a l c u l a t i o n s were on a weight b a s i s , d a t a from a n Engler t y p e distillation (Figure 6) were u s e d to c a l c u l a t e t h e weight per c e n t comparable with volume per cent. T h e other two s a m p l e s of JP-4 j e t fuel (samples B and C) were similarly i n v e s t i g a t e d throughout t h e temperature and p r e s s u r e ranges. T h e c u r v e s for t h e s e s a m p l e s a r e shown in F i g u r e s 7 to 10. T h e s e three j e t fuels effectively covered t h e range of volatilities normally found in commercial JP-4's. F i g u r e 11, which s h o w s t h e flash equilibrium d a t a a t atmospheric p r e s s u r e for a l l t h e fuels, illustrates t h e range of volatilities investigated. P o i n t s on the i s e n t h a l p i c c u r v e s were c a l c u l a t e d by t h e following procedure.
Figure 12. F l a s h equilibrium and isenthalpic curves far sample D
A temperature representing t h e bubble point of t h e liquid is s e l e c t e d . T h i s liquid is then expanded to some lower pressure. At t h i s point, a trial and error calculation is n e c e s s a r y t o determine t h e final temperature. After a final p r e s s u r e is chosen and a final temperature assumed, t h e experimental flash vaporization curves a r e u s e d to obtain t h e p e r cent vaporized. When t h e initial and final condit i o n s a r e t h u s e s t a b l i s h e d , enthalpy d a t a (7) a r e u s e d t o c a l c u l a t e t h e e n t h a l p i e s of t h e liquid and vapor. If t h e correct final temperature h a s been a s s u m e d , the two ent h a l p i e s (feed and expanded product) will be equal. A difference in t h e s e e n t h a l p i e s requires additional t r i a l s until t h e b a l a n c e is obtained. A similar family of c u r v e s w a s obtained for a typical s a m p l e of JP-5 jet fuel. T h e s e data a r e given in F i g u r e s 1 2 and 13.
DISCUSSION OF RESULTS T h e s h a p e s of t h e f l a s h c u r v e s a r e similar t o t h e corresponding ASTM distillation curves, although t h e equilibrium
~~
Table
II.
Experimental Standordisation D a t a for Toluene-lso-octone
Base Stocks Toluene Iso-octane Blend
R.L
Mole Fraction Iso-octane, Figure 3
1.4968 1.3920 1.4658
0.202
-
Overhead Temperature, OF. Recorded Corrected
22 1 222
223.3 224.3
Mole Fraction Iso-octane
Mole Fraction Iso-octane
RI. ExptLa Lit.b R.L ExptLa Lit.b 1.4611 0.239 0.246 1.4718 0.160 0.167 1.4628 0.227 0.212 1.4740 0.142 0.141
aFrom Figure 3. bFrom Figure 4.
20
Bottoms
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOLUME PER CUI1 OVLRHCAD
Figure 13. A S T M D-86 distillation and gravity for sample D
VOL. 2 , NO. I
tion a t a given temperature; however t h i s becomes l e s s pronounced a t elevated pressures. For example, in t h e c a s e of s a m p l e A a n i n c r e a s e in t h e p r e s s u r e from 1 to 3 atm. h a s approximately t h e s a m e effect on vaporization a s an itlc r e a s e from 10 to 20 atm. T h u s , a t 390’ F. (see Figure 5), increasing t h e pressure from 1 t o 3 atm. d e c r e a s e s t h e volume per c e n t overhead from 100 to 28; while a t 595: F. increasing t h e pressure from 10 t o 20 atm. results in an almost identical d e c r e a s e in overhead of 99 t o 24.
ACKNOWLEDGMENT T h e author w i s h e s t o e x p r e s s h i s appreciation to H. E. L u n t z a n d J. W. Conwell for their many helpful suggestions concerning the obtaining, calculation, and presentation of the d a t a included in t h i s paper and to Continental Oil Co. for permission t o publish t h i s work.
LITERATURE C I T E D Figure
14. ASTM D-86 distillation
Am. Petroleum Inst., “Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds,” API Project 44, Carnegie P r e s s , Pittsburgh, 1953. Chu, J. C., “Distillation Equilibrium Data,” Reinhold, New York, 1950. Chu, J. C . , Staffel, E. J., J . Inst. Petroleum 41, 92 (1955). Edmister, W. C . , Pollock, D. H . , Chem. Eng. Progr. 44, 905 (1948). Gelus, E . , Marple, S., Jr., Miller, M. E . , Ind. Eng. Chem. 41, 1757 (1949). Johnson, P. H., Mills, K. L., Ibid., 44, 1624 (1952). Maxwell, J. B . , “Data Book on Hydrocarbons,” Van Nostrand, New York, 1950. Smith, R. B., Dresser, T.,Hopp, H. F . , Paulsen, T. H., Ind. Eng. Chem. 43, 766 (1951).
and flosh equilibrium data
at atmospheric pressure for sample A
curve is flatter. Figure 14, showing a plot of both t h e ASTM D-86 distillation curve a n d t h e f l a s h equilibrium curve a t atmospheric p r e s s u r e for s a m p l e A, illustrates t h i s point. T h i s is i n accord with t h e expected r e s u l t s for t h e s e t y p e s of data (3, 4, 7 ) . On t h e flash curve, t h e point corresponding to t h e ASTM initial boiling point is high b e c a u s e of t h e s u p p r e s s i n g effect of t h e heavy ends. T h e reduced s l o p e a n d lower end point a r e c a u s e d by t h e partial p r e s s u r e effect of t h e light ends. T h e effect of p r e s s u r e is, of course, to reduce vaporiza-
Received for review July 2, 1956.
Accepted October 26, 1956.
Phase Relations of Nitric Acid-Nitrogen Dioxide and Nitric
Acid -W a te r M ixt u res at P hy s icoc hem ic a I E q uiIib r ium WEBSTER B. KAY, S. ALEXANDER STERN’, AND MANOJ D. SANCHVI’ The Ohio State University, Columbus, Ohio
T h e volumetric p h a s e relations of liquid nitric acid a t p h y s i c a l and chemical equilibrium h a v e been presented (5). I t w a s shown t h a t t h e pure a c i d is u n s t a b l e a t temperatures above i t s melting point (-41.59OC.) and t h a t i t d e v e l o p s a high g a s p r e s s u r e when stored i n a c l o s e d container if t h e ratio of t h e vapor s p a c e t o t h e total volume of t h e container is small. As t h e concentrated nitric a c i d of commerce cont a i n s e x c e s s water and nitrogen dioxide, i t i s of i n t e r e s t in connection with t h e storage and handling of t h e acid to know t h e effect of t h e s e additives on i t s equilibrium pressure. To obtain t h e required data, a n investigation of t h e volumetric p h a s e relations of t h e s y s t e m nitric acid-nitrogen ‘Present address, Linde A i r Products C o . , Tonawanda, N. Y. ’Present address, Standard Oil Co. (Indiana), Whiting, Ind.
1957
dioxide-water i s necessary. A s a preliminary s t e p t o such an investigation, t h e p h a s e relations of nitric acid-nitrogen dioxide mixtures containing up t o 15% by weight of nitrogen dioxide and of nitric acid-water mixtures containing up t o 5% by weight of water were determined under conditions of physicochemical equilibrium. T h e s e l e c t e d concentration range i s of particular interest in t h e field of liquid rocket propellants. T h e measurements were made between 85 and 15OoC. and for t h e ratios of t h e vapor volume to total volume, ( V c / V ) , between 0.8 and near t h e bubble point. T h e r e s u l t s are summarized here. Corcoran, Reamer, Duffy, and Sage (1, 2) h a v e investigated t h e volumetric and p h a s e behavior of t h e nitric acidnitrogen dioxide and t h e nitric acid-water systems, but their CHEMICAL AND ENGINEERING D A T A SERIES
21
