December 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
creases. Since less surface in proportion to the volume of reactants is available in the longer flames, less oxygen diffuses into the outer cone and the smoking point fuel-air ratio decreases.
POINT
LIQUID BENZENE
(calmin) SMOKING SMOKING SMOKING CARBONFORMING
0
a Q
280
-
0
0.24 .33 .46 .24, 3 3 AND .46
200-
a
L
14
A
4b0
*bo "I:m
A
h
ISOO"
2doo
SECONDARY AIR FLOW RATE,
;loo
JOO
cc,/min.
Figure 8. Influence of Secondary Air Flow Rate on Carbon-Forming and Smoking Points of Benzene-Air Flames Burner tube diameter, 0.6 om.
SECONDARY AIR. The heated and jacketed burner tube was removed from the benzene-air mixer and a simple apparatus for burning the flame in a protective jacket, or duct, was installed in its place (Figure 2, c). With this apparatus, the amount of air surrounding the flame could be controlled. The effect of air flow variation was determined for three fuel flow rates. The results are shown in Figure 8. Here again, change in secondary air flow rate had no effect on the carbon-forming fuel-air ratio. I n the range of higher values of secondary air flow (beyond the scale in Figure 8), the variation in secondary air flow had no appreciable effect on the smoking point fuel-air ratio. It remained substantially the value for a flame burning in open air with a protective chimney. I n the lower range of secondary air flow rates shown in the figure, the smoking point occurred a t increasingly leaner fuel-air ratios as the secondary air flow rate was decreased,
2789
Flames of all flow rates became unstable and extinguished a t a smoking point fuel-air ratio of approximately 164% of stoichiometric. This value was approached from the opposite direction by igniting a lean flame, either without flowing secondary air or with nitrogen substituted for secondary air. The flames were stable up t o a fuel-air ratio of 140% of stoichiometric a t room temperature. From 140 to 164% of stoichiometric fuel-air ratio, incandescent carbon filled the upper portion of the flame as a faint haze. At this upper value the flame extinguished. No smoke was given off up to a value of 164% of stoichiometric. If the premixed benzene and air were preheated to near their ignition temperature and burned in the absence of air, or in nitrogen, the carbon-forming point and the smoking point would both occur a t approximately 164% of stoichiometric. The stoichiometric equation for the reaction of benzene and oxygen indicates that complete conversion to carbon monoxide and water occurs a t 167% of stoichiometric. Flames burning in the absence of oxygen are stable and do not smoke to a value of approximately 164% of stoichiometric. Since no smoke is formed, the products under these conditions must be almost wholly carbon monoxide and water, since the oxygen present under these conditions would allow only one half conversion to carbon dioxide. Apparently, a t room temperatures, the incandescent carbon forming a t 140% of stoichiometric reacts further up in the flame with the oxygen which has preferentially diffused out of the flame tip, for the flame does not smoke, even though incandescent yellow carbon is visible in the outer cone. LITERATURE CITED
(1) Arthur, J. R., Trans. Faraday Soc., 47,164-78 (1951). (2) Institution of Petroleum Technologists, London, "Standard
Method of Testing Petroleum and Its Products," 3rd ed., pp. 133-6,1935.
(3) Lewis, B., and Von Elbe, G., "Combustion, Flames and Explosions of Gases," pp. 277-8, New York, Academic Press, Inc.,
1951.
ACCEPTED September 11, 1953. REOEIVED for review April 14, 1953. Presented a8 part of the Symposium on Chemistry of Combustion before the Division of Gas and Fuel Chemistry a t the 122nd Meeting of t h s A M ~ R I CAN CHEMICAL SOCIETY, Atlantic City, N. J.
Isopycnics and Twin Density Lines SYSTEMS WITH TWO LIQUID PHASES ALFRED W. FRANCIS Research and Development Department, Socony-Vacuum Oil Co., Paulsboro, N . J .
I
I
T OFTEN happens that for one tie line in a ternary system
+
the two liquid phases in equilibrium have identical densities. This tie line, sometimes denoted by a straight dashed line (a), is called an isopycnic (equal densities), and is readily located with precision. Compositions within the binodal area but near each side of the curve are identified as points on the isopycnic when droplets of the smaller phase fail to rise or fall with appreciable speed (provided they have already coalesced t o macroscopic size). This is a convenient method for accurate location of one tie line. Isopycnics have considerable practical importance in solvent extraction since with compositions in their vicinity settling of the layers is extremely slow. Some otherwise suitable solvents or conditions may be thus disqualified. At least 95 of the published ternary systems have isopycnics. These are listed in Table I with the page reference in Seidell's book (3). The systems are arranged nearly in order of increasing number of carbon atoms.
However, very few of the isopycnics are noted in the original papers (indicated by footnotes), and none are called by that name. Mondain-Monval and Quiquerez (7) listed three binary and 15 ternary systems with inversions of density, and gave experimental data for two of each group. In three other published systems an inversion tie line is indicated. I n a few other papers density observations on the two phases make clear the existence of an isopycnic without showing its exact location. It is hoped that future publications of systems having isopycnics will have them marked. One system has two isopycnics. I n the water-propionic acido-toluidine system of Figure 1 (a, p. 961) a liquid phase changes in position (upper or lower layer) five times in progressing around the binodal curve, at the plait point, and a t each end of each isopycnic. The portions of the curve are marked U for upper and L for lower layer. Isopycnics occur either with a free binodal curve (a bite out of
INDUSTRIAL AND ENGINEERING CHEMISTRY
2790
Vol. 45, No. 12
TABLEI. TERKARY SYSTEMSWITH ISOPYCNICS Components
Page Number in Seidell ( 3 )
Components
Aqueous Systems
Aqueous Systems 84 1 842 843 843 843-4', 844a
Carbon disulfide Chloroacetic acid Acetone 1-Propanol Isobutyl alcohol
84ja 84Sa 846 847
Formic acid o-Nitrotoluene
85Sa
Methanol Benzene Toluene o-Toluidine (above 24.5" C.) m-Toluidine o-Xylene m-Xylene p-Xylene m-Xylidine Mesitylene Butyltoluene Trichloroacetic acid n-Amyl alcohol Isoamyl alcohol
Page Iiumber in Seidell (3)
1039'
865b,a
868b 869 869 b 871 871b 87 1 8716 872" 872 b
Glycerol Aniline Benzyl alcohol
975 976
Z-Butanone (methyl ethyl ketone) Trichloroethylene Trich loroethane Chlorobenzene
981-2 982 982
n-Butyric acid Aniline o-Toluidine m-Toluidine
988 989 989
Furfural E t h y l acetate 3Iethyl isobutyl ketone Toluene Isoamyl acetate
lOlOa lOlOa
Isovaleric acid E t h y l bromide h-itrobenzene o-Nitrotoluene
1016 1016 1016
Chlorobenzene Dichloroacetic acid n-Butylamine
981je
1
f
876 876
Tetrachloroethane Isobutyl alcohol
Benzene Phenol Aniline m-Cresol
1024 1024
879
Chloroacetic acid Nitrobenzene o-Iiitrotoluene
Nitrobenzene Sulfuric acid
10205
883a 883
Acetic acid o-Toluidine
897
Phenol Hydrogen chloride Phosphorous acid Phosphoric acid n-Amyl alcohol Aniline (above 77O C.) Triethylamine Toluene Xylene Thymol
1025" 10265 102tIa 1017a 1027 1029 1030 1031 1032a
Aniline Toluene
10340
Caproic acid Methyl iodide Xitrobenzene Bromobenzene .Inisole (below 1 3 O C . )
1039" 1039Q 103ga 103ga
E t h y l alcohol Benzene (below 19O C.) Toluene o-Toluidine (above 24.5') Methylaniline Methyl salicylate o-Xylene m-Xylene p-Xylene Phenetol Mesitylene Benzyl ethyl ether Anethole Pinene Butyltoluene Kerosine Cottonseed oil
935 937 937 9385 939 9396 940a 941a
Acetone Phenol Aniline Anethole
952-3 953a 957Q
Propionic acid Aniline (above 5 0 O C.) o-Toluidine m-Toluidine
960a 961 9616
920-2b 927-8d 929b 929 9320
933
933d 934
1023
Nonaqueous Systems 1065a 1069a 1070h 1083
cetane
1117
a laopycnics not indicated in Seidell ( 3 ) .
Listed b y Mondain-Xlonval and Quiquerez ( 3 ,b u t without data. Barbaudy ( I ) . D a t a b y Mondain-XIonval and Quiquerez ( 7 ) . Conway and Philip ( 2 ) . b u t no isopycnic indicated. f Peake and Thompson ( 8 ) , but no isopycnic indicated. 0 Smith and Drexel (9). h Janecke (6). b C
1-Propanol Chloroform Bromobenzene
862 965
2-Propanol Aniline o-Toluidine Butyltoluene Cottonseed oil
970b 974b 974b 974a
one side of the triangle) or with the ba.nd-type binodal area. With temperature change an isopycnic may gradually drop on the diagram and disappear at the base line at the hinary isopycnic temperature, discussed below. Or it may rise and disappear at the plait point,. Thus, the system water-ethanol-benzene (3, pp. 920-2) has an isopycnic near the plait point at lorn- temperature. It disappears above 19" C. because the preference of ethanol for the aqueous layer is no longer sufficient t'o lower its density to that of t,he benzene layer. An isopycnic may occur in an island curve, that of water-acetone-phenol at temperatures of 66" C. to about 80" C . (3, pp. 952-3). An isopycnic mag even lie found in t,he two-phase area. of a system with three liquid phases, that of formamide-nitro-
d e
benzene+-hexane (3,p. 1070; 6 ) . A modification of t,hat system w-ith additional components was found t)>- the author of this paper, so that all three phases have the same density, 1.15. It, consists of aniline, carbon tetrachloride. formamide, n-hexadecane, and nitrobenzene. Holyever, since this system cont,ains morc than three components, the compositions of the three phases are not uniform, as they are in a ternary system. The inversion of the layers on crossing the isopycnic could result in confusion in identity of the two layers, especially if both are colorless. In fact, there are indications that such an inadvert'ent interchange of the phases has actually been made at compositions above the isopycnic in one or two published systems. The author has prepared for demonstration purposes a large
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1953
PROPIONIC KID
279 1
dicated. Other binary iso-optics occur with methyl sulfate*heptane, formamide-chloroform, ethanolamine-carbon tetrachloride, and benzene-hydroxyethylethylenediamineover limited temperature ranges. These binary coincidences in properties are less common than those in ternary systems. TWIN DENSITY LINES
0-TOLUIDI NE
WATER
Figure 1. Ternary System with Two Isopycnics ii
U
Temp., 20° C. L =, Lower layer
= Upper layer
sealed tube containing an isopycnic of water-methanol-bensene. The aqueous layer is colored bright blue with a trace of copper ammonium nitrate, and the benzene layer is colored bright red with a trace of an azo dye. The gradual resolution of the phases caused by s u r f a c e t e n s i o n makes it an interesting toy. On agitation it forms a purple emulsion. W i t h i n a few minutes the droplets coalesce to large red drops surrounded by blue liquid and blue drops surrounded by red liquid. Finally, the red drops gather into a large shapeless mass WATER ANILINE (shmoo) if the tube is vertical. Figure 2. Binary If it is horizontal, they gather Isopycnic into the shape of deep red boats U = Upper layer in a blue sea, sometimes with L = Lower layer blue spherical drops within them. A binary isopycnic is illustrated in Figure 2 for water-aniline a t 77” C. ( 7 ) . Other binary isopycnics with water occur with methylaniline at 2” C., m-toluidine at 7” C., o-toluidine a t 24.5’ C. ( 7 ) , benzonitrile a t 34” C., fluorobenzene a t 48’ C., benzyl cyanide a t 60” C., and nicotine ( 7 ) and acetophenone a t 96” C. (last four temperatures approximate), A nonaqueous binary isopycnic is that of carbon disulfide and glycerol a t about 20’.
If one component of a nominally ternary system is a mixture like lubricating oil, the locus of compositions separating into two liquid layers of equal densities is not a tie line; i t is not even straight; and the equal densities are not uniform. When a small oil phase is almost dissolved, it has a lower density than that of the whole oil because the heavier and more soluble constituents of the oil have been mostly extracted. The line fails to satisfy the dictionary definition of an isopycnic, a line “passing through points a t which the density is equal” ( I O ) . A more accurate term for such an example would be “didymopycnic” (twin densities). But since this name might be confusing, the English expression “twin density line” is suggested when the pair of densities are equal to each other but do not have the same value in different parts of the graph. A similar expression, “twin density surface,” is used in another paper (4) for a surface under similar conditions. The term “isopycnic” will be retained for those twin density lines in which the density is uniform (three component systems). These lines are straight. Figure 5 illustrates a twin density line observed on an actual system. The lubricating oil was a Rodessa oil, dzo 0.8770, ng 1.4869, molecular weight 352, aromatic hydrocarbons 27.4%. U and L indicate upper and lower layers, respectively. The light sloping straight lines are tie lines, which were observed by noting the distribution of nitrobenzene between the methanol and oil layers. They have a steeper slope than the dashed twin density line, ANILINE
I s0-0pT1cs
4
If the refractive indices of two liquid layers in equilibrium are equal (and their dispersions different), this fact becomes apparent because of a bright colored opalescence in the emulsion on shaking (5). This appearance is distinct from the pearly colorless opalescence observed near the plait point. The color may be fairly permanent, and the composition need not be even close to that of the plait point. In fact, the phenomenon may appear in a system with a band-type binodal curve which has no plait point, as in Figure 3. By observing the compositions giving an indigo color, for example, with a small solvent layer and with a small hydrocarbon layer, respectively, an “indigo” tie line is located. Purple, magenta, red, and yellow tie lines are located similarly, giving a substantial group of such lines. These “is-optics” are encountered almost daily in the author’s own researches on solvent extraction. Figure 3 shows a system with an isopycnic and a complete set of iso-optics. A binary system with iso-optics is shown in Figure 4 (6). Any horizontal line across the binodal curve is a tie line of the color in-
/ METHANOL
Figure 3.
/ DECALIN
System with Isopycnic and Set of Iso-optics
The latter is nearly straight for most of its length, but is curved downward at each end. At the right end it seems to be asymptotic to a tie line. This would indicate that with less than 25% total solvent in the system not enough aromatic hydrocarbon is extracted from the oil to affect its density appreciably. With larger amounts of solvent the residual oil contains a steadily decreasing concentration of aromatics, and so has a lower density. The matching density of the solvent mixture corresponds t o lower tie lines. At the left end the twin density line curves downward sharply because the last few drops of undissolved oil are highly paraffinic. Theoretically, the curve could even intersect the base line if the
INDUSTRIAL AND ENGINEERING CHEMISTRY
2Z92 nominal oil “component” consisted of two or more constituents, some lighter and some heavier than the primary solvent and also more soluble in it. However, this is unlikely in an actual case because the solvents lighter than oil, such as methanol and acetonitrile, usually lack the requisite selectivity for each type of hydrocarbon. The choice of components in Figure 5 is not very critical. Methanol could be replaced with acetonitrile or other liqiud
Vol. 45, No. 12
benzene (d:’ 0.859) to one volume of n-hexadecane or cetane (d:’ 0.7737). The density of the mixture was 0.832. The solid line is a phase boundary curve, and no tie lines are shown. They would not terminate on the phase boundary curve. The twin density line intersects it just above the base line a t each side. If any component of a nominally ternary system is impure, as in the last system of Table I, an isopycnic is not rigorously straight.
c
E g
\
I 80” 70; 65 55 O
LAVENDER MAGENTA RLD AMBER
45O
YELLOW
25 O
YELLOW
60”
NTTROBENZENC:
PURPLE
U-UPPER LAYER L -LOWER LAYER
CETANE +
METHANOL
Figure 6.
20588
T w i n Density Line for System w i t h I m p u r e Component
NITROBENZEN
LITERATURE CITED
Barbaudy, J., Compt. rend., 182, 1279 (1926). (2) Conway, J. B., and Philip, J. B., IND.ENG.CHEM.,45, 1083 (1)
(1953). (3) Francis, A. W., in “Solubilities of Inorganic and Organic Compounds,” A. Seidell and W.Linke, eds., Suppl. t o 3rd ed., New York, D. Van Nostrand Co., 1952. (4) Francis, 9.W,, IND. ENG CHEM., in press. ( 5 ) Francis, A. W., J . Phys. Chem., 56, 510 (1952). (6) Janecke, J., 2. physik. Chem., 184,71-5 (1939). (7) Mondain-Monval, P., and Quiquerea, J., Bull. SOC. chini., 7, 240-53 (1940). (8) Peake, J. S., and Thompson, K. E., Jr., IND.ENG.CHEV., 44, 2439 (1952). (9) Smith, J. C., and Drexel, R. E., Ibid., 37, 601 (1945). ( I O ) Webster’s New International Dictionary, p. 1318, Springfield, Mass., C. C llerriam Co., 1946. RECEIVED for review J u n e 6, 1953. ACCEPTED August 7, 1953. Presented before the Division of Chemical Education a t the 124th Meeting the AMERICAN CHEMICAL SOCIETY, Chicago, I11
Figure 5. Twin Density Line o f S y s t e m w i t h Lubricating Oil portion of it. Similarly, the less soluble hydrocarbon in the oil layer, which is more paraffinic, dissolves less methanol than does the whole oil. The equilibrium mixture curve (not shown) forms the ends of these tie lines, but is indefinite, since it would vary in position with the relative volumes of the solvent and oil layers. This fuzziness of a binodal curve always results when one component is made t o represent more than one actual substance. As with the twin density lines, the twin index lines (marked with names of colors in Figure 5 ) of a lubricating oil system are not quite the same as tie lines. They have a different slope, and they are presumably slightly curved at their ends, although their precise determination is more difficult because of the color in the oil sample. Another system with a curved twin density line is illustrated in Figure 6. The same two solvents are used, but the hydrocarbon oomponent consists of a mixture of two volumes of di-secbutyl-
Kinetics of Carbon Gasification by Steam-Correction I n the article on ‘(Kineticsof Carbon Gasification by Steam” ENG.CHEM.,45, 2586 (1953)] on page 2587, the sixth and seventh lines of the first column should read: “the curves of Figures 1 and 2.” On page 2589, the first line of the sixth paragraph should read: “It is clear from 1 , 2 , and 4,” as these numbers refer to the paragraphs above and not to literature cited. GEOFFREYE. GORING [IN&
Atmospheric Pollution-Correction Atmospheric Pollution column, November 1953, page 109 A, first paragraph, address of Grindle Corp. is Markham, Ill.
