AUGUST 1947
603
CA. B
C/‘A
//./
e/
a U
0
-1
AZEOTROPIO A T A L L P R E S S U R E S
AZEOTROPE DISAPPEARS AT P AND P ’ . COX
Figure 2.
SCALE
I/(T°C.+230)
Schematic Diagram of Vapor Pre-snrc Curbes of Binary Azeotropes
curves of the coniponent s. This is indicated schematicall) ill Figure 2 where A and B are vapor pressure curves of the components and C is the vapor pressure of the azeotrope. If curve C crosses either 3 or B , the azeotropic vapor pressure is no longer greater or less than any of the components and the system will become nonazeotropic at the point of intersection. On the other hand, if the azeotropic curve is parallel to the other curvps the system \vi11 he azeotropic up t o the critical pressure. The method ha6 bren successfully applied to numerous systems, four of whirh are shown in Figure 1. The azeotrope methanol-niethyl ethyl ketone became nonazeotropic a t 3000 mm. of mercury after it was predicted that this would occur at 2000 to 4000 mm. The azeotrope methanol-acetone was studied in detail after it was predicted that the azeotropism would disappear a t both low and high pressures. This system is nonazeotropic below 200 mm. of mercury and above 15,000 mm. compared to predicted limits of 200 to 500 mm. and 10,000 to 20,000 mni. While this is the only azeotropic system known to become nonazeotropic a t
hulh lo\\. aiid high pressures, there are indications that the phciiomenon occurs in several othcr systems, contrary to the conclusions of Lecat that such systems probably do not exist ( 3 ) . Caution should he used in extrapolating curves to very low pressures because of the possibility of curvature in the vapor pressure lilies over a manyfold range of pressures. In cases where only the normal azeotropic boiling point is knoxvn, it is possible to predict the effect of pressure on the systt’m by dran-ing the azeotrope curve through the normal boiling point with a slope equal to the average slopes of the component vapor pressure curves. This procedure will permit a fairly accurate prediction of rvhether the azeotrope will cease to exist below the critical pressure. LITERATURE CITED
( 1 ) Cox, I d . Eng. Chem., 15, 592 (1923). ( 2 ) Lecat, Ann. SOC. sci. Bruzelles, 49B,261-333 (1929). (3) Lecat, “Trait6 de Chimie Organique,” Vol. 1, p. 139, Paris, Grigtiard. Mason et Cie., 1935.
Graphical Method for Predicting Azeotropism and Effect of Pressure on Azeotropic Constants L. H. HORSLEI , The Dow Chemical Company, Midland, Mich.
L
E C h T (2) has devised an analytical method for determining azeotropic boiling points and compositions for certain related groups of binary systems. The method is based on the fact that the composition and boiling point of an azeotrope are related to the relative boiling points of the two components. 1,rcat thus obtained a series of equation. of the foriii
+ I A I b + A2c L‘ = d + Ae + Azf
difference in boiling point of azeotrope and the lower boiling component u, b, . . . . f = constants for a given series of related azeotropes such as methanol-hydrocarbons S o t e that A may be positive or negative; I A 1 is always positive. .- - ___ ---___ _ _ _ _ ~ 6
=
Table I.
8 = n
Pressure
M m . Hg
where A
1A C
(boiliiig point of component A ) - (boiling point of component B ) = difference in boiling point of d and B (absolute value of A) = azeotropic coniposition in weight percent d =
~
200 400 760 6,000 11,000 -~
Effect of Pressure
Boiling Point Methanol Benzene
C. 35 50 65 130 153
O
~
C 43 61 80
162 193
A
C. -9 -12 -15 -35 -44 O
Azeotropic Boiling Point Calcd. Found O C. C. 23 26 39 42 55 57 125 124 150 149
C Calcd. Found W e i g h t 70 30 34 33 36 39 40 54 55 64 63
_ _ _ ~ _ ~ _ _ _ _
V O L U M E 19, NO. 8
604 I6
16
12
12
12
8
8
8
4
4
4
0
0
0
0
20
40
60
100IAl 120
60
40
20
0
c
l
l
I
60
l
/
80
I 1
40
40
0
-120 -80
-40
0
l
1
-EO 18
12
6
12
8
4
8
4
2
4
IO
20
30
40
50 lA1 60
0
-80
-40
0
40
80 A I20
1
8
0
50 1 ~ 60 1
~
16
0
40
1
80 A 120
40
30
I
I 1
1
20
I
1
i
0.
IO
'
\,+
I
100 80
0
- WDROCARBONS
E+A+OLS
100
1001A,120
80
0 IO
0
20
30
0
t0
N)
30
40
M lA1 60
-60
-40
-20
0
20
40 A 60
IO
20
30
40
50 lAl 60
-20
-10
0
IO
50 ~I 60
40
IO0
too
80
80
4
40
I D -60 -40
-20
0
40 A 80
20
I
I
I
I l u , l
I
I
I 0
A 80
-60
-40
-20
0
20
40
0
20
40
80
80
100,A1120
32 24
16 8
I I
1x1 I
I
I
I
I
0
0
20
40
60
80
100,N120
0
100 80
100
80 40
40
40
IO0
0
-m
80
0 -80
Figure 1.
-40
0
C-A and
40
80 A 120
-120
-80
-40
0
40
80 A 120
0 -30
20
~
30
Curves for Alcohol-Hydrocarbon, Glycol-Hydrocarbon, and Phenol-Hydrocarbon Systems C.
Azeotropic composition in weight
96 first component
8 . Boiling point of lower boiling component minus aEeotropic boiling point \ A / . Absolute difference in boiling points of components A. Boiling point of first component minus boiling point of seeond eompment
AUGUST 1947
605
16
16
I6
12
12
I2
8
8
8
4
4
4
0
0
too
100
100
80
80
80
40
40
40
0
-20
-30
-0
0
IO
0
0
20 A X ,
-30
-20
0
-10
20 A 30
IO
0
0
0
-20
-10
0
IO
20 A 30
-60 -40
-20
0
20
40 A 80
IO
20
30
40
50 lA160
-40
-20
0
M)
40 A 6 0
-30
32
16
16
24
12
12
16
8
8
94
~
0 0
l
l
20
40
-40
-20
l
I'
l
60
80
0
20
~
l
~
l
K)OlAl12O
0
l 20
IO
30
50 lA1 60
40
IO0 80 40
0 -80
40 A 60
16 . I S I
I I I I I I I i I I I
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8
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IO
20
30
40
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0
IO
20
30
40
50 lA160
0
I00
100
100
80
80
80
40
40
40
0 -60 -40
Figure 2.
-20
0
20
40 A 6 0
0 -60
0 -40
-20
0
20
40
-60
C-A and &!AI Curves for Phenol-Hydrocarbon, iicid-Hydrocarbon, and .4lcohol-Halitle Hydrocarbon Systems
V O L U M E 19, NO. 8
606 16
I6
16
12
12
12
8
8
4
4
0
0 0
IO
20
30
40
50 lA1 60
0
!
l
C
c
j
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15
20
25 lA1 30
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5
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l PENTdN0-S
*-
HALldE
I 100
100
80
80
1 : P . ( I
40
40
40
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I
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20
40
60
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30
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20
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32
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1
CRkSC/LS.- HALItE $YDkOCA~Or;JS
12
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20
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l
l
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16
8
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100 '
10
20
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1
30
40
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60
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0 -60
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20
40 A 60
16
12 8
8
4
4
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0 0
IO
20
30
40
50 1A160
0
20
40
60
80
1OOlA1120
100
I00
80
80
80
40
40
40
0 -30
-20
Figure 3.
-10
0
IO
20
30
0 -60
0 -40
-20
0
20
40 A 60
60
C-A and 8-1A Curves for Alcohol-Halide Hydrocarbon, Glycol-Halide Hydrocarbon, Phenol-Halide Hydrocarbon, and Acid-Halide Hydrocarbon Systems
601
A - U G U S T 1947 16
S
I2
t A ~ ~O -L Eb ~ T L R S
~
12
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1
8
8
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20
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50 IAl 60
40
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100
80
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40 A 60
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16
16
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30
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1
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20 A 30
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BJTAN~SI-E~TERS
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5
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BUTANOLS t ElbTEkS
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C GLYCERINE
/-
1
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100-
80
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Figure 4.
-20
0
20
40
60
C-1 and 8-111 Curies for
l A 160
, c
1
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l P $ E N O L ~- E S T T E R ~
I
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1
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608
V O L U M E 19, NO. 8 16
16
I2
12
8
8
4
4
0
0 10
0
20
30
50 l A 1 6 0
40
I
I
C
IO0
100
80
80
40
40
0 -30 - 2 0
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20 A 30
0 -60
I6
16
12
12
16
8
8
8
4
4
0 1 1 1 l I y Y l l l 0 0 20 40 60 80 100IAl120
0
I
s -
24
I
w
TER 7 ESHEPs,
ACETALS I
0 0
20
40
60
80
10OlA1 120
4or\rd -60
-40
-20
0
20
40
60
16
12
12
8
8
4
4
0
0
20
40
5
IO
I5
20
25 u13U
-0
0
IO
20
80
40
0 -60
16
20
100
40
0
0
A 60
4 0
-40
-20
0
20
40
SO
0 -30
QO
I5
20
25 lA1 30
0
5
IO
IS
20
25
-40
+20
0
20
40
A
A
30
0 0
5
IO
I5
20
25 lA1 30
5
0
IO
c ! I i l ' AIJOVO$S
100
100
-t
I KET+E$
I
,
100
80
80
40
40
0 -30
0
-20
Figure 3.
-10
0
IO
20
30
-60
-40
-20
0
20
40 A 60
-SO
C-A and 8-13 CurFes for Alcohols-Ethers, Glycols-Ethers, Water-Ethers, Acids-Ethers, AlcoholsKetones, Glycol-Ketones, Alcohols-Phenols, and Phenols-Ketones
609
A U G U S T 1942
From a practical standpoint, for determining the azeotropic constants of a system, the plots of the above equations have been found 100 more useful and are given in Figures 1 to 5 100 80 80 for forty-five systems for which data are available. Up to this time only the curve for ethanol-halide hydrocarbons has been 40 40 published (I). A h o t h e ruse for this set of curves is for esti0 0 -GO -80 -40 0 40 80 A I20 -60 -40 -20 0 20 40 A 60 mating the aaeotropic boiling point and composition at pressures other than atmospheric. Consider the azeotrope methanol-benzene. Since the vapor pressure curves of methanol and benzene are known, the difference in boilIO0 100 ing point, A, can be obtained a t any pressure. 80 80 From this value of 1 and the C-S curve for methanol-hydrocarbons the azeotropic 40 40 qoncentration C a t that prcssure can be determined. For example, the effect of pressure 0 0 on the methanol-benzene azeotrope is show1 -120 -80 -40 0 40 80 A 120 -60 -40 -20 0 20 40 A 60 in Table I. .1plot of A as a function of C from this table IC1 I I! I! I! 1! I ! , I! I# I ! I I is shown in Figure 6. The experimental data I ! ! arc rcpresented by the five points n-bile the smooth curve is identical with the methanolhydrocarbon curve in Figure 1. Similar curves and data for other systems over the pressure range indicated are also 40 shown. I n each case the curve is the same as the general curves of Figures 1 to 5 , while the *;'t\ 0 0 esperimental points are for the particular -40 -20 0 20 40 60 A 80 system and for the pressure range indicated. In the same Kay, the 6- 1 A 1 curves of Figures Figure 6 . C - 1 CurFes for Alcohol-Hydrocarbons, Alcohol-Halide Hydro1 to 5 can be used to determine 6 and the carbons, and Alcohols-Ketones azeotropic boiling point at any pressure from Showing agreement with experimental data at various pressures C. Weight % alcohol hydrocarbon the value of I A I a t that pressure. A. Boiling point of alcohol halide ' hydrocarbon Khile the agreement between predicted minus boiling point \ketone and experimental values is far from perfect, the method has served as a valuable guide in LITERATURE CITED estimating effect of pressure on azeotropic systems. (1) Lecat. A n n . S O C . sci. Bruxelles. 55B. 43 (19363. It is reconnized that it would be more convenient to be able to i2) Lecat, Compt. rend., 183, 880 (1926) ; 184, 816 (1927) ; 189, 990 plot pressur; instead of A as a function of C and 6. However, this (1929); Ann. SOC. sci. BruseZles, 47B,39, 87 (1927); 48B, 1, would require a separate curve for each azeotrope, whereas the 105 (1928); 49B,28, 119 (1929); 55B, 43, 253 (1935); 56B, above method permits use of a single curve for a large group of 41 (1936) ; Atti accad. nail. Lincei, ( 6 ) 9,1121 (1929) : 2.a n m g . allgem. Chem., 186, 119 (1930) systems. ~
\&
B
1
Colorimetric Determination of Uranium with Thiocyanate J. E. CURRAH AND F. E. BEAMISH Department of Chemistry, University of Toronto, Toronto, Ontario, Canada A method has been de~elopedfor the rapid estimation of small quantities of hexatalent uranium in the presence of relatively large amounts of thorium and small amounts of iron and copper. The determination is based on the estimation of the color produced with thiocyanate and uranyl. This method permit5 the estimation of 0.05 to 0.80 mg. of uranium in the presence of at least 1.23 grams of thorium, 2 mg. of iron, and 50 mg. of copper per 25 ml. of solution. The ,interferenceof iron is eliminated by reduction with stannous chloride.
A
METHOD \!-as required for the determination of uranium in concentrations as low as 2 or 3 parts per million in the
presence of approximately ten thousand times as much thorium. Low concentrations of iron and copper were to be considered as possible interfering elements. Becaux a rapid and simple method was desired, one that would require no preliminary separations was thought most suitable,
A number of colorimetric methods for the estimation of uranium, such as the fluorescence method, and the diethyldithiocarbamate, ferrocyanide, peroxide, salicylate, and tannic acid determinations are well known ( 2 ) . However, these methods have a poor sensitivity or require a preliminary separation to remove the interfering iron or copper. A preliminary investigation of possible new color reactions of
