V. H. THOUTNEH.
1356
VOl. 63
PHASE RELATIONSHIPS I N MIXTURES OF THE SIMPLE POLYPHENYLS AND CONDENSED RING AROMATICS. A SURVEY OF ORGANIC REACTOR COOLANT MIXTURES BY V. H. TROUTNER Reactor and Fuels Research and Development Operation, Hanford Laboratories Operation, Richland, Washington Received December 8,1968
Solid-liquid-vapor phase diagrams are determined and discussed for the binary, ternary, quaternary end quinary mixtures of biphenyl, o-terphenyl, m-terphenyl, naphthalene and phenanthrene. The suitability of these mixtures as reactor coolants is discussed.
I n recent years, considerable interest has been shown in the possible use of an organic material as a coolant for nuclear reactors. Organic materials offer the advantages over aqueous systems of operstion at high temperatures (up to 400") with relatively low pressures and virtually no corrosion problems. It was the purpose of this work to investigate the possible organic compounds and mixtures which might be used as a reactor coolant and to select the most promising system based on certain physical criteria. Restrictions imposed by reactor considerations narrowed the possible coolants down to five most promising compounds and their mixtures. The restrictions imposed were, (a) that the organic material must have good pyrolytic and radiolytic stability, (b) it should have a low melting point and high boiling point, and (c) it should be relatively non-toxic and safe to handle. The stability conditions are best met by the simple polyphenyls and condensed ring aromatics. The presence of aliphatic side chain substitutions reduces the stability markedly and these substituted compounds were not considered in this study. Imposing the arbitrary limitation that compounds to be considered must have a melting point of 100" or less, and eliminating benzene because of the hazardous nature and low boiling point, the materia,ls to be studied were limited to the five shown in Table I. TABLE I ORGANIC COOLANT MATERIALS Compound
'
Biphenyl o-Terphenyl m-Terphenyl Naphthalene Phenanthrene
mp.,
oc.
69 56 87 80 100
B.P., OC.
254 336 371 217 340
sidered. The composition of the vapor phase in equilibrium with the liquid mixture must be of such a composition that when condensed it is also liquid. This requirement was mentioned by Bowen and Groot3in their theoretical treatment of some of the binary and ternary mixtures. An optimum coolant mixture may be defined by the criteria: (1) it must have good pyrolytic and radiolytic stability; (2) it must be liquid a t 2 5 " ; (3) it must have a high boiling point; (4) the vapor in equilibrium with the mixture must be of such a composition that it is liquid when condensed at 25". Strictly speaking, this set of criteria defines a "25' optimum mixture." In general, optimum mixtures may be referred to other base temperatures. The objectives of this study were, (a) to examine the solid-liquid-vapor phase relationships of all mixtures of the compounds biphenyl, o-terphenyl, m-terphenyl, naphthalene and phenanthrene, (b) to compare the experimentally determined phase diagrams with those based on theoretical considerations and (c) to determine the temperatures and compositions of optimum coolant mixtures. Summary and Conclusions Melting point diagrams were determined for all the binary and ternary mixtures of biphenyl, oterphenyl, m-terphenyl, naphthalene and phenanthrene. Wide ranges of solid solubility were found and consequently they differed significantly from the calculated theoretical diagrams of French and Epstein2 which were based on ideality and the assumption that the solid phases are in every case the pure components. Boiling point and vapor composition diagrams were calculated for all of these mixtures. Some experimental melting point data were obtained for the quaternary and quinary mixtures. It was shown that no combination of the five compounds formed optimum mixtures which melted below 35". Experimental
It is clearly desirable that a coolant material be liquid a t room temperature, 25". All five of the compounds included in this study are solid at 25'. Based on theoretical considerations, French and Epstein2 have shown that mixtures of these comorganic materials used in this investigation were of pounds are possible which melt below 25". How- theThe highest purity obtainable. They had a capillary melting ever, there is an important additional requirement point range of one degree centigrade or less, and were nomiwhich must be met if low melting mixtures are con- nally 99 .% pur:.
+
(1) R. 0. Bolt and J. G. Carroll, "Organics as Reaotor ModeratorCoolants: Some Aspects of Their Thermal and Radiation Stabilities," Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva, August, 1955, Vol. 7, p. 546. (2) N. E. French and L. F. Epstcin, "Preliminary Considerations of Phase Relations in Systems of Diphenyl with Terphenyls and Other Aromatic Hydrocarbons," Knolls Atomic Power Laboratory, KAPLM-NEF-I, October, 1956.
The melting point diagrams were determined using mixtures which were weighed out to give incremental mole per cent. compositions. Five mole per cent. intervals were used for the binary systems and 10 mole % intervals were used for the ternary systems. These mixtures were sealed in (3) H. C. Bowen and C. Groot, "Boiling Points, Vapor Compositions and Freezing Points for Some Aromatic Hydrocarbon Mixtures," Hanford Atomic Products Operation, HW-48427,February, 1957.
4'
SURVEY OF ORGANICREACTOR COOLANT MIXTUIWS
Sept., 1959
1357
glass ampoules and placed in a constant temperature bath, whose temperature was increased in steps of one degree every two hours. The temperatures at which melting began and a t which they were completely melted were recorded. The procedure of cooling melted mixtures until the first crystals were observed could not be used because of the strong tendency of these systems to supercool. Some vapor composition data were obtained experimentally with an Othmer equilibrium still4 which had additional heaters for use a t high temperatures. The equilibrium liquid and vapor samples were analyzed by gas chromatography.
Discussion Vapor Composition.-Only a limited amount of experimental vapor composition data was obtained because of difficulties encountered in the operation of the equilibrium still a t high temperatures (300" and above). These data were used to calculate the activity coefficients of the components in the variniis mixtures as defined by 7'-
PtNv PvNl
0
w
a 3 i-
U
a
w
B
T w
where
i-
activity coefficient of the given component Pt = total pressure (1 atm. in this case) Nv = mole fraction of the given component in the vapor NI = mole fraction of the given component in the liquid Pv = vapor pressure of t,he given component a t the b.p. of the mixture P, was calculated using the following vapor pressure equations where P , is in atmoepheres and t is in centigrade degrees Biphenyl: 2213.3 l O g P = 4.576 - t 230 Nanhthalene : 1962.4 logP 4.394 - ___ t 230 o-Terphenyl: 2680.1 log P = 4.7338 - t 230 m-Terphenyl: 2848.2 log P = 4.7337 t 230 Phenanthrene : y =
60
40
I
+
-
20
Mixture composition Biphenyl o-Terphenyl Biphenyl o-Terphenyl Biphenyl o-Terphenyl Phenanthrene o-Terphenyl m-Terphenyl o-Terphenyl rn-Terphenyl o-Terphenyl Biphenyl Phenanthrene o-Terphenyl m-Terphenyl m-Terphenyl o-Terphenyl Biphenyl Phenanthrene
+
log P = 26.6669 - 4743 ' - 6.7893 log T
T
t
+ 278.13
These vapor equations are those used by Bowen and Groot.3 The experimental vapor composition and boiling point data are given in Table I1 along with the calculated activity coefficients. The activity coefficients appeared to be randomly scattered about unity and those determined from runs of high reliability (runs in which no experimental troubles occurred) were very close to unity. It was decided, therefore, t o assume activity coefficients of one and to use the foregoing vapor pressure equations and Raoult's law to calculate all the desired vapor compositions and boiling points. Accordingly Pp = NIP, = NvPt or log N , = log N I log P, when Pt = 1 atm. where P p = partial pressure of the given compo-
+
nent. (4) D. F. Othmer, Anal. Chem., 20, 763 (1948).
I
80
IO0
TABLE I1 VAPORCOMPOSITION DATA
+
=
I 60
MOLE PERCENT 0-TERPHENYL. Fig. 1 .-0-Terphenyl :biphenyl.
+
T
I 40
Z.P., C. 261 261 269 269 278 278 337 337 352 352 301 301 301 346 346 346 316 316 316 31G
Nv 0.961 ,039 .925 ,075 ,845 ,155 ,502 ,498 ,352 ,648 ,087 ,191 ,722 .401 ,411 ,189 .086
,171 ,451 ,292
NI 0.779 ,221 ,675 ,325 ,496 .504 .493 .507 ,541 ,459 ,376 ,332 ,292 ,321 ,319 .370 240 ,227 .169 .364
pv I atm. 1.17 0.188 1.38 0.231 1.66 0,287 0.957 1.016 0.G92 1.340 0.235 0.486 2.501 1.127 1.205 0.616 0.329 0.669 3.334 0.641
a Non-equilibrium caused by heater failure. tquilibrium caused by leaky fittings.
r 1.05 0.94 0.99 1.00 1.03 1.07 1.06 0.97 0.94 1.05 0.99 1.19 0.97 1.14a 1 .07a 0 . 83n 1.09a
1 ,13b 0.80' 1 , 25b
Non-
€
Binary Systems.-A typical binary diagram is shown in Fig. 1. The lowest melting optimum mixture is shown by the dotted line. It contains 78 mole yoo-terphenyl and 22 mole yobiphenyl and melts a t 45.5'. The vapor in equilibrium with this mixture contains 39 mole Yo o-terphenyl and 61 mole yo biphenyl. The condensed vapor will
1358
V. H. TROUTNEI~
Vol. G3
TABLE I11 BINARY SYSTEMS I .-,
Eutectic--OptimuinMole % of 1st Component
Afixture
o-Tcrphenyl: biphenyl o-Terphenyl:naphthalene o-Terphenyl:phenanthrene o-Terphenyl :m-terphenyl Biphenyl :naphthalene
na-Terphenyl :biphenyl m-Terphenyl:naphthalene Phenanthrene:naphthalene
Phenanthrene:m-terphenyl Phenanthrene:biphenyl
m.p.,
57.5 (61.0) (59.8) 63.0 70 0 75.0 55 0 (56) (60) (55) 35.5 (45.0) 41.0 43.0 (45.8) (42.7) (45.0) (41.8) 50.0 30.0
OC.
hlole % of 1 s t Coinponent n1.p. 'C.
29.5' (22.8) (27.5) 31.5 39.0 39.0 39.5 (39.4) (38.0) (39.5) 45.5 (41.5) 49.5 52.0 (47 5) (51.0) (48.0) (54.0) 56.5 58.5
78 0
4G
0-35,75-100
58.5 37.5 39.0 36.0
52 43 49 50
-16,76-100 -30,85-100 -63,82-100 -30,70-100
I
57.0
64.5
-22,52-100
76.0 35.5
75 74
-10,55-100 -27,61-100
$1.0
64.5 64.5
$7.0
NAPHTHALENE EUTECTIC AT 32 M X BIPHENYL 4 2 MY. o-TERPHENYL 2 6 M X NAPHTHALENE
5 65
BIPHENYL
60
55
50
45
4 0 35 30 35 4 0
45
50 55 o - TERPHENYL
Fig. 2.-Biphenyl: o-terphenyl: naphthalene melting point diagram.
begin to freeze at 45.5'. Although mixtures exist which melt a t lower temperatures, their condensed vapors begin to freeze a t higher temperatures. The binary data are summarized in Table 111 along with the existing values available in the lit(5) V. H . Troutner, "Phase Relationships in Mixtures of the Simple Polyphenyl6 and Condensed Ring Aromatics," Hanford Atomic Products Operation, HW-57431, 1958, Available from the O s e e of Technical Service, U.5 . Dept. of Commerce, Washington 25, D. C. (6) 8. Nakayato and R . H. J. Gercke. "Organic In-Pile Loop, NAA18." Atomics International, NAA-SR-1592, 19613. (7) K. Anderson. "Engineering Properties of Diphenyl," Argonne National Laboratory, ANL-5121, August, 1953. ( 8 ) E. W. Washburn and J. W. Read, Proc. Nat. h a d . Sci., 1, 191, (1915). (9) C. M . Mason, B.W. Rosen and R. M. Swift, J . Chsm. Educ., 18, 473 (1941). (10) H. H. Lee and J. C. Warner, J . Am. Chem. SOC.,6 7 , 3 1 8 (1935). (11) E. Rudolf?, 2. phyaik. Chem.,66, 705 (1909). (12) V. M. Kravchenko, Ukrain., Khim. Zhur., 18, 473 (1952). (13) A. Miolati, 2. phusik. Chsm., 9, A49 (1892). (14) Yu. F. Kloohko-Zhovnir. Zhur. P d d a d . Khim.. 22, 848 (1949).
Solid solubility regions (mole % of 1st component)
-38, 65-100 0-100
Source
This work.6 Figure 1 Nakayato and Gerckes Anderson? This work6 This work6 This work6 This works Washburn and Reads Mason, et al.9 Lee and Warner10 This work6 Anderson7 This work6 This works Rudolfi" I
