578
C. A. VAN GUNST,F. E. C. SCHEFFER AND G. A. M. DIEPEN
Vol. 57
ON CRITICAL PHENOMENA OF SATURATED SOLUTIONS I N BINARY SYSTEMS. I1 BY C. A. VAN GUNST,F. E. C. SCHEFFER AND G. A. M. DIEPEN Laboratory for Inorganic and Physical Chemistry at the Teclknical University, Dclfl, Holland Received September 69,1866
(1) Data are given for a number of binary systems, consisting of a volatile component (ethylene) and a slightly volatile substance (anthracene, hexamethylbenzene, hexaethylbenaene, stilbene, m-dinitrobenzene, hexachloroethane or naphtlialene). They all belong t o the type of system with an interrupted liquid-vapor critical locus. Measurement of the second critical end-point of the system ethylene-naphthalene is also reported. (2) For measurement of the solubility of mixtures of two solids in a fluid above the critical temperature, the system ethylene-naphthalene-hexachloroethane was chosen.
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5iK. ~
ethylene-naphthalene is considered extensively in some later publications.2 The purpose of the present investigation is to
CRITICAL PHENOMENA OF SATURATED SOLUTIONS IN BINARY SYSTEMS
June, 1953
579
t
160 140.
120 '
w
loo.
6 80
60
I
-10
-5
0
5
10
Fig. 3.-Pressure-temperature
were measured, with ethylene as the volatile component, and anthracene, hexamethylbenzene, hexaethylbenzene, stilbene, m-dinitrobenzene or hexachloroethane, as the slightly volatile component. A remeasurement of the system ethylene-naphthalene was performed to find the second critical endpoint. Experimental Method.-All pressure-temperature measurements were carried out in glass Cailletet tubes with electromagnetic stirring according to Kuenen. Temperatures were determined with calibrated Anschutz thermometers while pressures were read from regularly controlled Schaeffer and Budenberg precision pressure gages. A different supply of ethylene was used from that in the previous research. The material used here ~ was prepared from a commercial p r o d ~ c t . After washing it thoroughly first with ammoniacal Cu2Clzsolution and then with dilute sulfuric acid, it was dried by passing it over P205. Next the non-condensable gases were removed (controlled with Tesla-apparatus) and finally the ethylene was further purified by eliminating ten times the most volatile and the least volatile fraction during condensation. an indication of the Purity of the sample, severa1 Points were measured on the vapor Pressure curve using different volume ratios of vapor and liquid; no pressure differences were ( 5 ) Ohio Chemical and Manufacturing Co. 99.5% pure.
t
I
I
50 55 60 65 70 t, "C. projection of the system ethylene-naphthalene.
I
75
rioted at constant temperature. Measurements of the critical constants were found to be in good agreement with those of Maass and co-workers6 using the classical definition of critical point (t = 9.22'; p = 49.74 atm.). The values for the p-t line of ethylene differ slightly from those cited in an earlier pub1ication.l Experimental Results.-The measurements are summarized in the Tables I-VII. The curve SBL2-G of the system ethylene-hexachloroethane could not be measured, because the second component reacted with mercury at such high temperatures. Under 60" this reaction was unnoticeable. Only the measurements of the system ethylene-naphthalene are shown graphically in Fig. 3. Discussion of Results.-In all systems described, the three-phase line SB-L-G has two critical endpoints ICl and Kz. The pressure-temperature projections of the systems ethylene-anthracene, ethylene-hexaethylbenzene, ethylene-hexamethylbenzene, ethylenem-dinitrobenzene, ethylene-hexachloroethane and ethylene-stilbene are analogous to the one for ethylene-naphthalene (Fig. 3). Although metastable immiscibility could not be detected in any of these cases, it is probable, from the curvature of the three-phase lines SB-L-G, that they all belong to the systems with metastable immiscibility. Particularly in the case of ethylene(6) J. Dacey, R. McIntosh and 0. Maass. Can. J . Research, l T B , 206 (1939); S. M. Naldrett and 0. Maass, ibid., 18B, 118 (1940).
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C. A. VAN GUNST,F. E. C. SCHEFFER AND G . A. 7M. DIEPEN
VOl. 57
June, 1953
58 1
CRITICALPHEKOMENA OF SATCRATED SOLUTIOKS IN TERNARY SYSTEMS
naphthalene, where the two measured parts of the critical line do not seem to be parts of one curve without cusps, the metastable immiscibility is highly probable. In the same system it was possible to determine the second critical end-point by direct observation and by graphical extrapolation from the three-phase line SB-L~-G and the critical curve (Lz = G). At the second critical end-point, contrary t o the first critical end-point, a saturated solution which coexists with a gas phase becomes
critical by a slight temperature lowering. The system ethylene-hexachloroethane shows a maximum increment of the critical temperature, has a rather extended supercritical region, and gives a ternary system (with naphthalene) of the desired type which will be reported in another paper.3 Furthermore hexachloroethane easily can be determined quantitatively. Therefore hexachloroethane seems promising for use as a third component, together with ethylene and naphthalene, for measurements of the solubility of mixtures of solids in 8 supercritical fluid.
ON CRITICAL PHENOMENA OF SATURATED SOLUTIONS I N TERNARY SYSTEMS BY C. A.
VAN
GUNST,E”. E. C. SCHEFFER A N D G. A. M. DIEPEN
Contribution from the Laboratorg for Znorganic and Physical Chemistry at the Technical University, Delft, Holland Received September 88, 1958
Pressure-temperature measurements are given for the ternary system ethylene-naphthalene-hexachloroethane, including the critical phenomena of saturated solutions. Observations are discussed from the viewpoint of the theory of the phase equilibria in the critical region. The system shows a temperature range where solubility measurements can be made of two solids in a supercritical fluid.
Introduction The purpose of this investigation was to study the phase-equilibria of a ternary system which could be adapted for exact measurements of the solubility of mixtures of two solids in a supercritical fluid. To find such a system the necessary conditions must be traced. I n some p r e v i ~ u s l -papers ~ binary systems, consisting of a volatile component A and a slightly volatile component B showing an interrupted liquid-vapor critical locus with two critical end-points are described. In such systems a temperature range is noticed between the first and second critical end-points where, a t any pressure, only one fluid phase can coexist with solid B. Now we want to find a ternary system of a volatile component A and two slightly volatile components B and C which has a temperature range in which solids B and C can coexist only with a supercritical phase. Such a ternary system can be built from two binary systems A-B and A-C in which the three-phase lines SB-LG and Sc-L-G, respectively, cut the critical liquid-vapor curve. If we now consider the ternary univariant equilibrium : solid B, solid C, liquid and gas with increasing temperature, there will be the possibility, a t least if the solubility of B and C in liquid A is not too high, that this series of univariant equilibria ends in a first double critical end-point,S where the liquid (1) G. A. M. Diepen and F. E. C. Scheffer, J . Am. Chem. Soc., 7 0 , 4081 (1948). (2) C. A. van Gunst, F. E. C. Scheffer and G. A. M. Diepen, THIB JOURNAL, 6 7 , 5 7 8 (1953).
(3) G. A. M. Diepen and F. E. C. Scheffer, J . Am. Chem. Soc., 7 0 , 4085 (1948). (4) 0. A. M. Diepen and F. E. Scheffer, THISJOURNAL, 67, 575 (1953). (5) So denoted by A. Smits, Verslag Gewone Vergadering Wisen.Natuurk. Afd.; Nederland Akad. Welenschop. 21, 149 (1912); 24, 731 (19 15).
C.
and gas phase become identical. The four-phase line SB-Sc-L-G will appear again at the second double critical end-point and run to the correspunding quadruple point of the binary system B-C. The p-t projection of such a system is depicted in Fig. l. KIK1’ and K2K2‘ are the first and second critical end-points, respectively, of the two binary systems. Two critical lines run from these points to the ternary critical end-points p and q of the four-phase line XB-Sc-LG. On these lines the ternary critical points are found for liquids saturated with one of the solids.
$
L9
*
L,
E .*-*:::=:i::
1, “C. Fig. 1.-Pressure-temperature projection of a ternary system with a four-phase line SB-SC-L-G cut in two parts. Full drawn lines are univariant ternary curves, dotted lines are the univariant curves of the binary systems.
Between the temperatures of p and q there is's temperature range where together with solid B, C or both only one supercritical phase can coexist at all pressures. From Fig. 1 it follows that the eutectic temperature of the binary system B-C has to be well above the temperature of the critical point of A. If this eutectic temperature is too low, there will be a Possibility that the four-phase line SB-SC-L-G will not intersect the liquid-vapor critical locus.
