Correlation of Azeotropic Data

The following relations define a system of azeotropes involving an azeotropic agent with members of a homolo- gous series: (a) the azeotrope boiling p...
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INDUSTRIAL AND ENGINEERING CHEMISTRY

442

NOMENCLATURE

LITERATURE CITED

a = constant, varying inversely with T raised to a power A = constant y

T z

= activity coefficient = atmospheric boiling temperature in = mole fraction

X = abscissa for Figure 3 = 56

O

Kelvin

( F ) ~- ( T T - T L ) + K 340

\

Y

1.9

/

ordinate of Figures 1 and 2 = T?(?” - T s )

=

Vol. 40, No. 3

100,000

Subscripts H = hydrocarbon or halogenated hydrocarbon L = low boiling component S = solvent (nonhydrocarbon component) T = high boiling component Z = azeotrope

(1)

Cailson and Colburn, IND.EXG.CHEM.,34,551 (1942).

( 2 ) Ewell, Harrison, and Berg, Ibid., 36,871 (1944). (3) Ewe11and Welch, J . Am. Chem. Soc., 63,2475(1941).

(4) Hildebrand, J. H., “Solubility,” A.C.S. Monogiaph No. 17, New York, Reinhold Pub. Corp., 1936. ( 5 ) Horsley, L. H., IND. ESG.CHEM.,AKAL.ED , 19, 505 (1947). (6) Lecat, M . “L’Azeotropisme,” Brussels, 1918; Ann. SOC.Sci. Britzelles, Vol. 45,47B,48B,49B,50B,55B,56B,(1926-37). (7) hIair, Glasgow, and Rossini, J . Research S a t l . Bur. Standards, 27, 39-63 (July 1941; R.P. 1402). (5) Porter, C. W., Trans. Faraday SOC.,16,336 (1921). RECEIVED June 24, 1946.

Correlation of Azeotropic Data HERMAN SKOLSIK Hercules Powder Company, Wilmington, Del

T h e following relations define a system of azeotropes involving a n azeotropic agent with members of a homologous series: (a)the azeotrope boiling point as a function of the logarithm of the mole per cent of the azeotropic agent in the azeotrope; (b) the azeotrope boiling point as a function of the boiling point of the pure hom,olog; a n d ( c ) the boiling point of the pure homolog as a function of the logarithm of the mole per cent of the azeotropic agent in the azeotrope. Relations a and b are straight-line functions from which relation c is immediately derivable. These three relations are employed for t h e correlation of the azeotropic data of the systems: benzene-saturated hydrocarbons, benzene-alcohols, and ethanol-hydrocarbons. Interpolations can be carried out o n the straight-line relations a and b which permit predictions of azeotropic behavior w-ith more certainty than previous methods. The term “relative azeotropic effect” is introduced as a measure of the azeotropic effect of an azeotropic agent in various systems compared to the azeotropic effect of benzene on saturated hydrocarbons.

B

ECAUSE the theory of azeotropisin is little developed,

several empirical methods have been employed for the analysis and interpretation of azeotropic systems. Of these, the graphical method introduced by Mair, Glasgow, and Rossini ( I d ) is the most useful. I t consists of plotting on rectangular coordinates the azeotrope composition as a function of the azeotrope boiling point, and drawing tie lines between the boiling point of each pure hydrocarbon on the ordinate and its azeotropic point on the smooth curve. This relation is illustrated in Figure 1for the system benzene-saturated hydrocarbons, as plotted from the data of Marschner and Cropper ( I S ) . Figure 1 provides an over-all picture of the homologous series of saturated hydyocarbons whose azeotropes with benzene are known. The solid smooth curve represents the azeotropes of both the normal and the branched alkanes, which are differentiated into their respective homologous series by the slopes of their tie lines, the slope being greater for a branched than for a normal alkane (compare the slopes of the tie lines for n-heptane and 2,2,Ctrimethylpentane), The branched alkanes are further broken down into two series according t o the number of alkyl branches (compare the slopes of the tie lines of 2,4-dimethylpentane and 2,2,3-trimethylbutane), although the difference in

I

slope is so slight that this dichotomy may be unwarranted. The saturated alicyclic hydrocarbons are represented by the brokenline curve. I n terms of the fractionation of a hydrocarbon mixture containing benzene, normal alkanes, branched alkanes, and saturated alicyclics, Figure 1 shows the order of separation and the approximate hydrocarbon boiling point range a ithin which benzene azeotropes will be encountered. The prediction of an azeotrope is made n i t h Figure 1 by interpolating on the plot a tie line between the boiling point of the pure hydrocarbon, whose system has not been studied, and the smooth curve, estimating the slope of the tie line relative t o the slopes of neighboring tie lines of homologous compounds whose systems are known and desclibed. The intersection of the estimated tie line with the smooth azeotrope curve gives the composition and boiling point of the unknown azeotrope. The disadvant a g e s of t h i s graphical method are: the relation between the azeotrope boiling point and the azeotrope composition is a smooth curve and not a straight-line function; and the tie lines do not have a constant slope, but progressively increase in slope as the boiling poiQt increases. These two objections are particularly serious when only ID 20 i o b. i o $0 70 810 i o a few points deMOLE PER CENT BENZENE scribe a system. Figure 1. Correlation of AzeoFor example, it is tropes of Benzene with Saturated open t o question Hydrocarbons by Mair-Glasgowwhether a smooth Rossini Method

4

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INDUSTRIAL AND ENGINEERING CHEMISTRY

W

dI

3-

2-

I.

Figure 2.

Correlation of Azeotropes of Benaene with n-Paraffins

I

Figure 3.

Correlation of Azeotropes of Benzene with Naphthenes

Line A , azeotrope composition us. azeotrope boiling point; curve A', azeotrope composition us. boiling point of pure paraffin hydrocarbon

Line B, azeotrope compomition us. azeotrope boiling point; curve E ' , azeotrope composition us. boiling point of pure naphthene

curve can be drawla through the two points for hexane and heptane. Also, since the slopes of the tie lines for normal alkanes and branched alkanes indicate two homologous groups, it is reasonable to anticipate that their smooth curves will 'be somewhat different. In the case of the alicyclic hydrocarbon curve, the fact that both points defining it are equidistant from the solid smooth curve makes the accuracy of this curve doubtful, inasmuch as the alicyclic curve should converge towards the solid smooth curve and become coincident with it a t the pure azeotropic agent point. Furthermore, when only a few points are plotted, any inaccuracy must be appreciable before it becomes obvious. Because there is no constancy in the slopes of the tie lines, the time consumed in making predictions and the accuracy of the predictions are dependent upon the accuracy and number of known points plotted.

and C for the s y s t e m benzene-normal alkanes, benzene-saturated alicyclics, and benzene-branched alkanes, respectively. Since this is a straight-line function, the data fit the equation: log z = A (273.1 = mole

viherez

In connection with a program for the study of azeotropic systems, it was found desirable t o investigate other relations for the correlation of azeotropic data which would overcome the disadvantages of the Mair-Glasgow-Rossini method. This paper describes a method based on the relations between (a)the azeotrope boiling point and the logarithm of the azeotrope composition; (b) the azeotrope boiling point and the boiling point of the pure components of the azeotrope; and ( c ) the boiling points of the pure components of the azeotrope and the logarithm of the azeotrope composition. The data published by Marschner and Cropper (IS) are employed in this paper t o illustrate the new method and to compare it with the method of Mair, Glasgow, and Rossini (1%). RELATION a. The plot of the boiling point of the azeotrope a s a function of the logarithm of the mole per cent of the aeeotropic agent is shown in Figures 2, 3, and 4 by the straight lines A , B,

+ T a p )+ B

(1)

% of azeotropic agent (benzene) in azeo-

trope

T,, = boiling point of azeotrope, " C. A , B = constants The equations for the straight lines of Figures 2, 3, and 4 are, 'respectively:

+ Tsz) - 37.14 log z = 0.1054 (273.1 + TaZ)- 35.22 log z = 0.07091 (273.1 + !Pa,,) - 23.05

log z = 0.1108 (273.1

NEW METHOD

*

I

I

(2) (3)

(4)

Inasmuch as the straight, line for each of these three systems terminates a t the point representing pure benzene (loo%, 80.0" C.), only one accurately determined azeotrope is needed t o describe this relation. RELATION b. The rectangular coordinate plot of the relation between the boiling point of the azeotrope and the boiling point of the pure saturated hydrocarbon is shown in Figure 5. This curve appears to be exponential and asymptotic t o some line D, and therefore would fit the following equation: log ( D where D

T,,

T

E, F

- TsB)=

E

-F

(273.1

+ T)

= asymptoticline = azeotrope boiling point, O C. = boiling point of pure saturated hydrocarbon, = constants

(5)

O

C.

INDUSTRIAL AND ENGINEERING CHEMISTRY

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Vol. 40, No. 3

Prima fucie, line D should be the line representing the boiling point of the pure azeotropic agent; this value is 80.0" C. for benzene. However, on calculation by both Equation 6 and by the method of approximation (data for cyclohexane were not used), D is found to be 81.1' C. Substituting this calculated value in Equation 5 and solving for constants E and F , the following equation is obtained:

i I I

log (81.1 - Tsz')= 14.11 0.03804 (273.1

I

+ T)

(7)

As D is not identical with the boiling point of pure benzene, its significance, if any, must await further investigation. If Equation 7 is correct, the plot of log ($1.1 - TaZ) with the boiling point of the pure hydrocarbon should be a straight line. This is shown to be the case in Figure 6. (Cyclow '0hexane is not included as it was not used for the z 9w I calculation of D.) N 8z R E ~ A T I Oc.X The relation between the boiling w 7m of the pure saturated hydrocarbon and point 1 +z 6 the logarithm of the mole per cent of benzene in the azeotrope is equivalent to the tie line con50 struction of Figure 1. This relation is shown by [I w 4 the curved lines A', B', and C' for the three a homologous series of saturated hydrocarbons in W Figures 2, 3, and 4. 3I If sufficient data are available, this relation 2 may be plotted directly. For the homologous I series shown in Figures 2, 3, and 4,A' is repre2sented by two points; B' by one (the data for I cyclohexane and methylcyclopentane apparently are not in agreement); and C' by four points (two of which are in close proximity). Thus, 0OlLlNG POINT OF [ BENZENE-2.2these three curves cannot be drawn with any DIMETHYLPENTANE I I I degree of accuracy with the lrnown data. They I AZEOTROPE are therefore constructed by means of Figure 5 or 6 or Equ'ations 7 and 2-4. The most accurate procedure is that employing the straight-line reFigure 4. Correlation of Azeotropes of Benzene with Branched Paraffin lation. Substitute values for Tin Equation 7 and solve for the corresponding values of T,,, which, L i n e C, a z e o t r o p e c o m p o s i t i o n US. a z e o t r o p e boiling p o i n t ; c u r v e C', a z e o t r o p e c o m p o s i t i o n US. boiling point of pure b r a n c h e d paraffin when substituted in Equations 2, 3, and 4, will give the corresponding values of composition. From these calculated values curves A', B' (based on only methyloyclopentane), and C' of Figures 2, 3, and 4 can In the solution of this equation the value for D is first determined. Two points [TI, ( T 4 and [ T2,(T.,)z] are chosen on ' be accurately drawn. t h e curve in Figure 5, and a third point is chosen on the curve such that T3 = 1/2 ( T t T2)from which the value of (Ts.), HYDROCARBON -4ZEOTROPES TABLEI. PREDICTED BENZENE-SATURATED is measured. D then is calculated from Azeotropes Predicted the folloiying equation:

I I

I

I

z

I I

I

-

0'

I

I

I

+

Compound 2,2-Dimethylpentane 3.3-Uimethvlpentane 2-llethylhexane 3-Methylhexane 3-Ethylpentane 1,l-Dimethylcyclopentane trans-l,3-Dimethylcyclopentane trans-l,Z-Diinethylcyclopentane

1.

'

However, the accuracy of the calculatcd value of D by this procedure is subject to the errors inherent in any relation represented by a curve. Although in the present case a sufficient number of points define the curve in Figure 5, the occasion may arise when there are fewer d:tt;t. Iir this event the method of approxiinat ion is recommended in which values of /I are chosen until the plot o f log ( D - Tat) us. T is a straight fine.

2. 3. 4. 5, 6. 7.

8.

Hydrocarbon B P. C. (760 k m . ) 79.2

hlarschner and Cropper B.p.," C. Mole 70 (760 mm.) benzene 75.7 48.0

From Fig. 2, 3, & 4 B.p.,O C. Mole % (760 mm.) benzene 75.8 50.0

86.1

78.7

72.0

78.4

76.0

90.1 92.0 93.5 87.5

79.9 80.0 80.0 80.0

86.0 92.0 96.0 94.0

79.2 29.4 ('9.6 78.8

85.2a 89.3 gl.9 72.0

90.0

None

None

79.2

80.3

91.9

None

Xone

79.3

85.7

Literature B.p., C. (760 mm.) 75.85

... .. .. .. .. .. .. ... ...

Value Mole ?& benzene 52.5(8(

... 84.0a

89.5)

.. .. ..

... ...

If Egloff's ( 3 ) value of 89.7" C. is taken for t h e hydrocarbon boiling point, the mole % benzene ia predicted t o be 84.3. b AIarschner and Cropper (19) gave the composition for benzene in the 2-methylhexane and 3-methylhexane azeotropes as 76 and 84 volume %, resp. T h e mole % was calculated using the following oon= 0.6787; 3-methylhexane d:' = 0.6900. stants (3): benzene d z n = 0.87866; 2-methylhexane d:O Q

.

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i

I

100

2,2,4-TRIMETHYLPENTANE

loot

2,J-DIMETHYLPENTANE

-

Q

tl

e 2 , 22,4-DIMETHYLPENTANE ,3-TRIMETHYLBUTANE

I-

z

x

\

eo-

0

z

2

s

METHYLCYCLOPENTANE

70

1 60

ASYMPTOTE D,CALCULATED

1

I

I

70

80

...

-

-

HEXANE-

\

'

I

BOILING POINT OF AZEOTROPE, OC. Figure 5 (Above). Curve of Relation between Boiling Point of Pure Saturated Hydrocarbon and Boiling Point o f Its Azeotrope with Benzene for Determination of Asymptote

Figure 6 (Upper Right). Straight-Line Relation of Boiling Point of Pure Saturated Hydrocarbon and Boiling Point of Its Azeotrope with Benzene

0.0 0.1

0.2

0.3

04

0.5

LOG (81.1-BOILING

I IO

i

0.6

0.7

a0

0.9

0.1

1.1

1.2

P O I N T OF AZEOTROPE PC.)

h

2-METHYL- I - PROPANOL

Figure 7 (Right). Correlation of Azeotropes of Benzene with Alcohols by Mair-Glasgow-Rossini Method A , primary alcohols; B , secondary alcohols; C, tertiary alcohols

A convenient and rapid method for plotting curves A', B', a n d C' of Figures 2, 3, and 4 is through the use of Figure 5. . Intervals of 5' or 10" in the boiling point of the pure saturated )hydrocarbons are chosen for which the corresponding azeotrope boiling points are determined from the curve in Figure 5. From curves A , B, and C of Figures 2, 3, and 4, the compositions corresponding t o the respective boiling points of the azeotrope end pure saturated hydrocarbon are obtained. These data are then used for plotting curves A', B', and C'. PREDICTION OF AZEOTROPES.Azeotropes are predicted simply and accurately by means of Figures 2, 3, and 4. The method is illustrated best by an example. 2,2-Dimethylpentane boils a t 79.2" C. a t 760 mm. What is the composition and boiling point .of its azeotrope with benzene? A straight edge is placed so that it connects the boiling point of 2,2-dimethylpentane on the abscissa with the smooth curve of Figure 4. The ordinate a t the intersection gives the mole per cent of benzene in the benzene-2,2-dmethylpentane azeotrope. To obtain the boiling point of the azeotrope, the straight edge is placed so that it connects the point representing mole per cent of benzene on the straight-line relation with the abscissa. This process is shown in Figure 4 by the dotted lines. The prediction may also be accomplished by the use of Equations 7 and 4.

2-METHYL-2 -PROPANOL 2-PROPANOL

50t

40t 30c)

IO 20 30 40 50 60 70 80 90 I M O L E PER C E N T B E N Z E N E IN AZEOTROPE

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INDUSTRIAL AND ENGINEERING CHEMISTRY

Vol. 40, No. 3

if these two naphthenes can be classified as homologs of methvlcyclopentane. Their frac9( tionation test mixture unfortunately did not 2-BUTANOL contain sufficient benzene to indicate whether 8C i-PROPANOL-d/ azeotropes for t,a~zs-l,2-dimethylcyclopentane and trans-l,3-dimeth~.lc~~clopentane exist. 7c RANGEOF AZEOTROPEFORMITION.By definition, the boiling point of a minimum azeotrope must be lower than the boiling point of 6C either component of the azeotrope. Inspection of Equation 7 discloses that it contains two limits: a minimum and a maximum boiling 5c W point for saturated hydrocarbons below and a above which no azeotrope will be formed with Ibenzene. The maximum boiling point is calcu4c lated by substituting the boiling point of pure benzene, 80.0" C., for T,, in Equation 7 , and I solving for T which is found t o be 98' C. The W minimum boiling point is the temperatuie a t W N which the azeotrope boiling point and the 5 3c saturated-hydrocarbon boiling point become m c identical, and is calculated by substituting the z W same temperature value for T,, and 1' in u Equation 7 until both sides of the equation a are equal. The value calculated in this way is E w 65O c. ds 2 c That there is an indicated minimum and maximum boiling point for any homologous series (the condition of miscibility being imposed) means that the smooth curves in Figures 2, 3,and 4 must intersect or become identical with the 100yGbenzene line and the corresponding straight-line relation a t these points DISCUSSION.The outstanding advantage of this new method is that azeotropic data may be correlated and plotted %ith two straight-line functions, and that an azeotropic system, suck I I I I I I as compound A with homologs of B, can be de1% 60 70 80 90 IO0 I10 scribed when relatively few data are known. BOILING POINT .OC. Provided that compounds A and B are not asFigure 8. Correlation of Azeotropes of Benzene with Alcohols by sociated, relation a may be plotted with only one New Method accurately determined azeotrope (azeotrope Azeotrope composition 1;s. azeotrope boiling p o i n t for: A , primary alcohols; B . secondboiling point and composition). Relation b ary alcohols; C, tertiary alcohols; D , azeotropic composition US. boiling point of pure primary, secondary, a n d tertiary alcohols requires the boiling point determination of at least three A-B azeotropes and the boiling point determination of the pure compounds (which usually are k n o m ) . Relation c is immediately derivable Table I compares the azeotropes predicted by Marschner and from relations a and 6. Cropper (13) and the azeotropes predicted by the neiv method An error or discrepancy i n experimental data is readily made for a group of saturated hydrocarbons whose azeotropic behavior evident in this new method by virtue of the straight-line funcwith benzene had not been described a t the time the predictions tions. Furthermore, homologous groups are more clearly dewere made. In the literature column values are given for the fined. Whereas the lair-Glasgow-Rossini plot places methyldata which have been reported since the predictions were made. cyclopentane and cyclohexane on the same homolog curve, this The agreement between the predicted azeotrope boiling points new method indicates t,hat these two naphthenes probably have as determined by Figures 1, 2, 3, and 4 is good for compounds 1, different azeotropic properties with benzene, assuming, of course, 2, and 5 ; for compoundq 3, 4, and 6 the agreement is fair. The that the experimental data are correct. It is not unreasonable two methods, however, differ widely in the predicted composition. to expect different azeotropic properties for these two naphThe predictions by the new method are more closely in agreement with the few literature values than are the predictions by Marschner and Cropper. For 2,2-dimethylpentane both methTABLE IT. BESZESE-~~LCOHOL A l ~ ods predict closely the azeotrope boiling point; however, the predicted composition is 4.5 and 2.5 mole 70low by the old and Compound hzeotloPe B.P., C. B.P., C. hlole % Literature new methods, respectively. The composition predictions by Compound (760 M m ) (760 mm.) benzene Citation hfarschner and Cropper for 2-methylhexane and 3-methylhexane ... 80.1 Benzene ... 83.3 99.5 1. 2-Butanol 78.8 azeotropes are, respectively, 2.0 and 2.5 mole Yo high; the com86.5 101.8 80.0 2. 2-ILlethyl-2-butanol 55.2 position predictions by the new method for these two azeotropes 68.2 3. Ethanol 78.5 38.5 58.3 2. Methanol 64.7 lo^. are, respectively, 1.2 mole % high and 0.2 mole 7G 79.1 77.1 a. 1-Propanol 97.3 90.3 79.8 6. 2-Methyl-1-propanol 107.9 Marschner and Cropper predicted no azeotropes for trans60.6 71.9 82.4 7. 2-Propanol 1,3-dimethyIcyclopentane and t~nns-1,2-dimethylcyclopentane, 82.6 74.0 62.7 8. 2-hlethyl-2-propanol whereas this new method predicts the formation of azeotropes IO(

2-METHYL-I-PROPANOL

C

-1

ij

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

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above the boiling point of pure benzene). D cannot be calculated from either curves B or C, since a minimum of three points is required, as already pointed out. Therefore, it was assumed that their asymptotes also would be 88.2" C. That this assumption is probably justified is shown by Figure 10, in which the relations for the three homologous groups are parallel. The asymptote value for this system when substituted in Equation 5, yields the following equations for benzene with primary, secondary, and tertiary alcohols, respectively: log (88.2

- TSE)=

log (88.2

-

5.80 0.0128 (273.1 5.75 0.0128 (273.1

+ T) + T) log (88.2 - Tan)= 5.71 0.0128 (273.1 + T) I

/

L

I

I

60

70

I

ao

BOILING POINT OF AZEOTROPE ,OC.

(9A) (9B) (9C)

An anomaly which is made evident in both Figures 7 and 8 appears t o be present in this system. Whereas both curves should terminate at the point representing the boiling point of pure benzene on the 1 0 0 ~ obenzene line, the curve in Figure 7 ends a t 81.2" C., and all three straight-line functions in Figure 8 end a t 82.5" C. In Figure 7, curves A, B, and C cross the true boiling-point line of benzene a t 92.0, 89.5, and 86.7 mole % benzene, respectively; in Figure 8, curves A, B, and C cross the line a t 90.3, 88.9, and 87.0 mole yobenzene, respectively. That relation a does not terminate a t the true boiling point of benzene is probably caused by the association of the alcohol molecules through hydrogen bonding. Consequently, it appears that the system benzene-alcohols is affected by all four factors contributing to the condition of nonideality-namely, internal pressure, polarity, length and complexity of analogous groups, and association of a component, the last factor possibly being the most important. On the other hand, the system benzene-saturated hydrocarbons is probably affected by only internal pressure and molecular size.

C-2-METHYL-2-PROPANO

ETHANOL-.o

Tas) =

Figure 9. Curves of Relation between Boiling Point of Pure Alcohol and Boiling Point of Its Azeotrope with Benzene for Determination of Asymptote

CORRELATION OF SYSTEM ETHANOL HYDROCARBONS

Similar curves are 'drawn for the azeotropic systems of ethanol with paraffinic, olefinic, A , primary alcohols; B , secondary alcohole; C, tertiary alcohols saturated cyclic, mono-olefinic cyclic, diolefinic cyclic, and aromatic hydrocarbons, and are shown in Figures 11, 12, and 13. The data for this system are shown in Table 111. thenes since the ring structures are inherently different in terms Relation a equations for the azeotropes of ethanol with parafof strain and carbon valency forces. finic, saturated cyclic, mono-olefinic cyclic, diolefinic cyclic, aroPredictions of unknown azeotropes are made with greater acmatic, and olefinic hydrocarbons are, respectively: curacy by the new method than by the Rlair-Glasgow-Rossiniplot. (loa) log x = 0.02525 (273.1 T) - 6.875

+

log x = 0.02524 (273.1 +:I")

CORRELATION OF SYSTEM BEN ZENE-ALCOHOLS

In the system benzene-alcohols (the data for which are shown in Table 11) both the Mair-Glasgow-Rossini plot and the new method (Figures 7 and 8) classify the alcohols into the homologous series: primary alcohols, secondary alcohols, and tertiar alcohols. Mathematical treatment of relation a gives the fogowing equations for benzene-primary alcohols, benzenesecondary alcohols, and benzene-tertiary alcohols, respectively:

+ T) - 4.232 log x = 0.02145 (273.1 + T ) - 5.628 log x = 0.02329 (273.1 + T) - 6.287

log x = 0.01752 (273.1

(8A) (8B)

(8C) In Figure 8, curve D is an average of the three individual curves which would represent the three alcohol homologs. Because the three individual curves were very close together, only one curve was drawn t o avoid difficulty in reading the graph. Figure 9 is the rectangular coordinate plot of relation b for this system. The three homologous groups are represented by three curves. Curves B and C are estimated relative t o curve A , since they are defined by data for only two points. Curve A was used l o r the calculation of asymptote D, which is 88.2' C. (8.1' C.

- 6.872

(10B)

TABLE 111. ETHANOL-HYDROCARBON ~LZEOTROPES Compound Ethanol 1. Benzene 2. 3-Methyl-1,Z-butadiene 3. 2-Methylbutane 4. 3-Methyl-I-butene 6. 2-Methyl-%butene 6. Cyclohexane 7. Methylcyclohexane 8. Heptane 9. 1,5-Hexadiene 10. Hexane 11. Octane 12. Pentane 13. Toluene 14. 2,5-Dimethylhexane 15. Isoprene 16. 1,3-Cyclohexadiene 17. Cyclohexene

Compound B.P., "C. (760 Mm.) 78.3 80.1 40.8 28.0 22.5 37.2 80.8 101,l 98.6 60.2 69.0 125.6 36.3 110.8 109.2 34.3 80.4 82.7

Azeotrope B.P., O C . Mole % (760 mm.) ethanol

...

...

68.2 38.2

44.8 8.6

26.8 21.9 35.3 64.9 72.0 70.9 53.5 68.7 77.0 34.3 76.7 73.6 32.7 66.7 66.7

5.4 3.0 5.96 48.6 68.9 67.6 21 .o 33.2 89.8 7.6 80.9 78.1 4.37 47.8 47.9

Literature Citation

(l,i,'jl) ( 9 , 11)

INDUSTRIAL AND ENGINEERING CHEMISTRY

448

Vol. 40, NO. 3

*30'l O H 0 3 l V 3Hnd 3 0 1 N l O d 3 N l l l O B

\

\

+ T ) - 7.681 + T ) - 7.105 log x = 0.03422 (273.1 + T ) - 10.03

log x = 0.02755 (273.1

(IOC)

log x

(10D)

=

0.02591 (273.1

log x = 0.02804 (273.1 f T )

- 7.856

(IoE)

(10~) In Figure 11, the curves for the azeotropes of ethanol with satursted cyclic, mpno-olefinic cyclic, diolefinic cyclic, and aromatic

hydrocarbons were omitted as they are very close together and would not permit easy reading. The division of the homologous groups is the same as specified by the older method. It is probable that the olefinic group, composed of a t least two separate homologous groups, would be more clearly differentiated by more exact data. However, even then it majr be that these groups are close enough t o be considered practically as one. Curve A , Figure 12, was used for the calculation of the asynip-

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The solution of Equation 11A for minimum

and maximum boiling points indicates that no paraffinic or olefinic hydrocarbon boiling below approximately 20" C., or above approximately 133" C., should form an azeotrope with ethanol. I40

~

RELATIVE AZEOTROPIC EFFECT

I

It is customary to regard the spread of the boiling range of the compounds which form azeotropes with an azeotropic agent as a measure of the azeotropic effect of the agent. Accordingly, ethanol is considered to be a stronger azeotropic agent than benzene with hydrocarbons, as the spread of the boiling pdnts of the hydrocarbons forming azeotropes is 3.5 times greater for ethanol (from 22.5' C. for 3-methyl-1-butene to 125.6' C. for octane) than for benzene (from 69" C. for hexane to 98" C. for heptane). A more convenient and accurate measure of the azeotropic effect is possible by employing the slope of the straight line of relation a, which is the value of A in Equation 1. If the slope of the benzenenormal alkane system is arbitrarily taken as the basis for comparison, relative azeotropic effects may readily be obtained by calculating the quotient: A for benzene-normal alkane system divided by A for any other system. Table IV lists the relative azeotropio values of the systems discussed in this paper. The advantage of this procedure for comparing azeotropic effects is that entire ranges need not be known. The value of A can be determined by only one known point. The straight-line

II10 2Ol

2 0 1 , ~ - ~ ~ ~ ~ ! ~ - ~ - ~I u ~ ~ ~ 1 ~ , I 20 30 40 50 60 70 BOILING POINT OF AZEOTROPE ?C.

I

80

Figure 12. Curves of Relation between Boiling Point of Pure Hydrocarbon and Boiling Point of Its Azeotrope with Ethanol for Determination of Asymptote A , aliphatic hydrocarbons (saturated and unsaturated); B , saturated cyclic hydrocarbons; C, mono-olefinic cyclic hydrocarbons; D , diolcfinic cyclic hydrocarbone; E , aromatic hydrocarbons

tote value, which is 87.6" C. It was assumed that this value is the same for curves B, C, D, and E, each of which is defined by only one or two points. Figure 13 shows that this assumption is probably justified, inasmuch as the relations for aromatic, saturated cyclic, and paraffinic and olefinic hydrocarbons are parallel. The two relations for unsaturated cyclic hydrocarbons were drawn through the single points parallel to the other relations. The asymptote value, when substituted in Equation 5, yields the following equations for curves A , B, and E, respectively: log (87.6

- TBs) = 4.099

-

+ 7') log (87.6 - TaZ)= 4.192 0.007985 (273.1 + 7') log (87.6 - TaZ)= 4.168 0.008155 (273.1 + T ) 0.007707 (273.1

\

130-

\YNE

ie0c

\

(11A) (11B) (11C)

TABLEIV. RELATIVE AZEOTROPIC EFFECT (Comparison of azeotropic behavior of various azeotrope systems with system benzene-normal alkanes) A (for BenzeneNormal Alkane)/A (for Other Azeotropic Agent-Other Component System) 1. Benzene-normal alkane 1.00 2. Benzene-saturated cyclic hydrocarbon 1.05 1.56 3. Benzene-branched alkane 4. Benzene-primary alcohol 6.32 5. Benzene-secondary alcohol 5.17 6. Benzene-tertiary aloohol 4.76 , 7. Ethanol-alkane 4.39 8. Ethanol-saturated cyclic hydrocarbon 4.39 9. Ethanol-mono-olefinic cyclic hydrocarbon 4.02 10. Ethanol-diolefinic cyclic hydrocarbon 4.28 11. Ethanol-aromatic hydrocarbon 3.23 12. Ethanol-olefinic hydrocarbon 3.95

40 ISOPRENE

3-METHYL-2-BUTENE

20

01 0.8

'

I

1

1

1

1

1

1

1

I

I.o

1.2 1.4 I.6 1.8 LOG (876-BOILING P O I N T OF AZEOTROPE YC.)

l

l

2.0

Figure 13. Straight-Line Relation of Boiling Point of Pure Hydrocarbon and Boiling Point of Its Azeotrope with Ethanol A , alkanes and olefine; B , saturated cyclic hydrocarbons; C, cyclic mono-olefins$ D , cyalic diolefins; E, aromatic hydrocarbons

450

INDUSTRIAL AND ENGINEERING CHEMISTRY

relation passes through it and the pure azeotropic agent point, provided there is no association, in which case two points must be known. Consequently, the search for the best azeotropic agent for the separation of the constituents of a mixture is simplified and made less time-consuming. ACKNOWLEDGMEhT

The author wishes to thank A. L. Glasebrook of this laboratory for his interest and helpful cooperation in the preparation of this article. LITERATURE CITED

(1) Atkins, W. R. G., Nature, 151,4 4 9 (1943). (2) Birch, S. F., Collis, C. B., and Lom-ry, R. A., Ibid., 158, 60 (1946). (3) Egloff, G., “Physical Constants of Hydrocarbons,” Vol. I, p. 42

Yol. 40, No. 3

(1939), Vol. 111, p. 25 (1946), A.C.S. Monograph 78, 1st ed., New York, Reinhold Pub. Corp. (4) Kolosovskii, N. A., and Alimov, A,, BuTZ. soc. chim., [ 5 ] 2, 6 8 6 (1935). (5)

Kolosovskii, N. A , , and Teodorovich, R. L., I b i d . , [ 5 ] 2, 692

(1935). (6) Lecat, R.1. $., Ann. S O C . sci. Bruzelles, 48B ( I ) , 54 (1928). (7) I b i d . , 48B (11),1 0 5 (1928). (8) I b i d . , 50B, 21 (1930). (9) Lecat, XI. A,, “L’Azeotropisrne,”Brussels, Maurice Lamertin, 1918. (10) Lecat, 31.A , , Rec. trac. chim., 45, 620 (1926). (11) I b i d . , 47, 13 (1928). (12) Mair, B. J., Glasgow, A. R., Jr., and Rossini, F. D., J . Research ATatLatl. Bur. Standards. 27. 39 (1941). (13) Marschner, R. F., and Cropper, JV. P., IND.ENG.CHEM., 38, 262 (1946).

RECEIVED October 17, 1947.

Chlorine and So ium Pentaehlorohenate as in Sea W. J . TURNER,

JR., D. RI. REYIOLDS, AND A. C. REDFIELD

Woods Hole Oceanographic Institution, Woods Hole, Mass.

Continuous chlorination with residual concentrations as low as 0.25 part per million prevents the attachment and growth of slime bacteria and macroorganisms in sea waEer circulating systems. Some adult mussels and anemones may survive 10 days of intermittent chlorinatien with residual concentrations as high as 10.0 parts per million even when the periods of treatment are as long as 8 hours per day. Sodium pentachlorophenate prevents the attachment and growth of macroorganisms but is ineffective in eliminating slime w-hen concentrations as low as 1.0 part per million are maintained continuously. The relative merits of chlorine and sodium pentachlorophenate are discussed.

and conduits used to transport sea water in ships and P I Pindustrial F S power plants are frequently subject to marine fouling. Such growths reduce the efficiency of cooling systems, and when they occur in fire mains, they create serious hazards. The design of the system must provide for periodic cleaning, and cleaning operations with their attendant shutdowns are themselves expensive. Dobson (1) recently reviewed the various methods which have been tried or suggested for the control of such fouling. He concluded that the most promrsing treatment is the injection of chlorine into the sea water. Such treatment appears to be quite effective against slime-forming organisms which directly interfere with heat transfer in condensers. In somP cases it has given promise of controlling the growth of niacroorganisms in pipe systems. Although a number of installations have been made for the control of fouling by means of chlorine, there appears to be no published record of studies designed t o determine experimentally the concentrations and periods of treatment which are required t o prevent fouling efficiently. Such experiments have been conducted recently by the Woods Hole Oceanographic Institution. T h e results of these experiments are reported here. They give

some indication of what may be expected from various methods of treatment and also suggest an explanation of failures which sometimes occur in industrial practice. The antifouling properties of an organic toxic, sodium pentachlorophenate, were also investigated t o determine if this material could be used where chlorine might be unsuitable. EXPERIMEYTS WITH CHLORISE

ISTERMITTENT TREATYENT. The first experiment,, performed a t Woods Hole, Mass., determined the killing power of various concentrations of chlorine when applied both intermittently and continuously to adult organisms ( 4 ) . Battery jars containing organisms of representative species were subjected to the following treatment : One jar, serving as a control, was circulated continuously with fresh sea water. Four jars were irrigated periodically with sea water containing chlorine in a residual concentration of 10 parts per million on a schedule of 1, 2, 4, and 8 hours each day. The rest of the time the jars were circulated with untreated sea water. The sixth jar was flushed continuously with the chlorinat,ed water. (Chlorine was applied as a solution of calcium hypochlorite, introduced int,o the sea water main by means of a proportionating pump.) After 10 days of this treatment, the organisms in all six jars were flushed continuously for 10 more days v i t h unchlorinated sea water to allow for delayed effects t,o develop. The results of this experiment are given in Table I. Intermittent, exposures for periods as long as 8 hours per day with 10 p.p.m. chlorine were ineffective against mussels and ar:emones, and the 4-hour periods did not completely eliminat’eall the barnacles. The tunicates and bryoxoa were all killed by exposure for 1 hour per day. This short treatment was sufficient t o prevent the formation of slime on the sides of the jars. CONTINUOUSTREATMEST. Since int,ermittent treat’ment with daily exposures as long as 8 hours per day was ineffective against some forms, an experiment was performed t o determine