December 1949
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Table XIV. Predictions of Azeotropes between Thiols and Hydrocarbons Using Figurea 18 and 19 B.P. of Component,
Properties of Azeotropes Thiol in azeotro e, mole
0 C.“ System 1-Butanethiol 98.58 86.071 3 3-Dimethylpentane ... 87.84 1:l-Dimethylcyclopentana 91.7 91.87 trans-1 2-Dimethylcyolopentane 91.7 91.9 cis-l,3-’Dimethylcyclopentane 92.8 93.468 3-Ethylpentane 106.30 97.8 > 2 3 3-Tetramethylbutane 98.5 109,432 $4~6imethylhexane 98.55 909,844 2,2,3-Trimethylpentane Z-Butanethiol 85.15 2 2 %Trimethylbutane 80.871 79.9 3’3:Dimethylpentane 86.071 82.7 t~ans-1,2.Dimethyloyclopentane 91.87 84.9 cis-l,3-Dimethylcyclopentane 91.9 84.9 3-Ethylpentane 93,488 85.2 %Methyl-1-propanethiol 3 3-Dimethylpentane 2:Methylhexane trans-1,2-Dimethylc clopentane cis-1,3-Dimethyloyo~opentane 3-Ethylpentane Boiling points taken from A.P.I. Research Project 44.
...
w
1
B
2 2 18 18 31 80.5 92 93.4 32.3 55
Table XV. Predictions of Azeotropic Constants of Straight-Chain Thiols with Paraffins B.P. of Entrainer,
Entrainer
0
c.
Maximum Minimum B.P. of B.P. of HydroHydrocarbon, carbon, 0
c.
0
c.
Boiling Range, 0
c.
Relative Aeeotropir Effect
Table XVI. Predicted Azeotropes between Paraffins and Me thanethiol
86
86 88
2737
Cornponents
B.P. of Component, C .
Methanethiol 2-Methylpropane n-Butane 2,P-Dimethylpropane 2-Methylbutane
6.5 -11.73 -0.50 9.503 27.854
Properties of Azeotropes Thiol in areoC. trope, mole %
B.P.,
-16.5 -4 0.6 6.3
12.5 37.0 58.0
97.0
( 5 ) Coulson and Herington, J . Chem. Soc., 150, 597 (1947).
The straight-line relationship for each thiol can be drawn on the slopeFigure 18 from a knowledge of thc boiling range-+., and the fact t h a t a hydrocarbon with the same boiling point as the thiol forms a n azeotrope having a composition of 51.5 mole % thiol. Similarly, the line on Figure 19 that can be drawn for its slope is equal to the relative aeeotropic effect divided by the value of constant A for benzene-n-paraffins-i.e., 0.1108-while its exact position is fixed because it passes through the boiling point of the thiol a t 100% composition. From these two lines, predictions can now be made of the properties of azeotro es with paraffins of suitable boiling point. This has been $one for methanethiol (Table XVI). Future experimental work will serve t o show how far these predictions are true and whether the suggested procedure for obtaining them is a sound one.
LITERATURE CITED (1) Birch, Collis, and Lowry, Nature, 158,60 (1946).
(2) Bjorkman, Suensk Kern. Tids., 59,211 (1947). ENG.CHEM.,34,581 (1942) (3) Carlson and Colburn, IND. (4) Collis, Nature. 157,845 (1946).
(6) Ewell, Harrison, and Berg, IND.ENG.CHEM.,36,871 (1944) (7) Ewell and Welch, J . Am. Chem. SOC.,63,2475 (1941). (8) Fenske, “Science of Petroleum,” Vol. 11, p. 1629, London Oxford University Press, 1948. (9) Glasstone, “Textbook of Physical Chemistry,” 1st ed., p. 4.50 New York, D.Van Nostrarid Co., 1940. (10) Horsley, Anal. Chem., 19, 508 (1947). (11) Zbid., p. 603. (12) Jones, Schoenborn, and Colburn, INIJ.ENQ.CHEM.,35, 666 (1943). (13) Lecat, Bull. classe sci., Acad. roy. Belg., 33, 160-82 (1947) (14) Licht and Denzler, Chem. Eng. Progress, 44,627 (1948). (15) Mair, Glasgow, and Rossini, J . Research Natl. Bur. Standarh 27,39 (1941). (16) Marschner and Cropper, IND.ENG.CEEM.,38, 262 (19461 (17) Meissner and Greenfeld, Ibid., 40,438 (1948). (18) Othmer, Ibid., 35, 614 (1943). (19) Rheinboldt, Mott, and Motzkus, J . prakt. Chem., 134,257 (1932) (20) Rossini, J . Research Natl. Bur. Standards, 35, 355 (194.5) (21) Rossini et al., Ibid., 35, 219 (1945). (22) Skolnik, IND.ENQ.CHEM.,40,442 (1948). (23) Taylor and Layng, J . Chem. Phys., 1, 798 (19.73). RECEIVED
April 18, i9hy.
Thermodynamic Properties of Some Sulfur Compounds GORDON M. BARROW
AND
KENNETH S. P I T Z E R ’ ,
T
HE purpose of this paper is to present the available thermo-
chemical data on sulfur compounds of petroleum interest. Some values are taken directly from the literature; others are calculated by statistical methods where the necessary molecular data are available. Methods of estimation are given for the changes in these values on substitution of larger organic radicals. Binder (2)very recently has published some thermodynamic functions for methyl mercaptan and dimethyl sulfide which agree fairly well with those presented here. The molecular data necessary for the accurate calculation of t h e thermodynamic properties of methyl mercaptan (methane1
Present address. Atomic Energy Commission, Washington 25, D. C.
University of California, Berkeley, Calif.
thiol) and dimethyl sulfide are available. The fundamental vibrations for these two compounds are given by Thompson and Skerrett (I?, 18). The moments of inertia and the barrier t o internal rotation, 1460 calories per mole, for methyl mercaptan were taken from Russell, Osborne, and Yost (I,?). T h e moments of inertia of dimethyl sulfide were calculated from t h e structural parameters as measured by electron diffraction (3). The barrier t o internal rotation of the methyl groups has been determined t o be 2000 calories per mole (9). Using these barriers the contribution of internal rotation was obtained from t h e tables of Piteer and Gwinn (If). The thermodynamic functions for these compounds are prpsented in Tables I t o IV.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2738
Vol. 41, No, 12
A summary of the available or readily calculated thermodynamic properties has been prepared for some sulfur compounds of interest to petroleum chemistry. Included are mercaptans, sulfides (thioethers), disulfides, sulfoxides, and sulfones, in addition to the reference substances sulfur, hydrogen sulfide, sulfur dioxide, and sulfur trioxide. In each case data are given for the methyl compound and in some cases for the ethyl compound. Extension of values to larger organic radicals is discussed. The entropies and heat capacities have been calculated by statistical methods where the necessary molecular data
are available. In other cases these quantities are obtained by the addition of increments calculated for the several parts of the molecule. The heats of formation come largely from the classical studies of Thomsen. Although somewhat lacking in precision, these heat values are found to be consistent with the directions of chemical reactions, where known. The equiIibrium constants calculated for several reactions are uncertain to one or two powers of 10 but are the best now available. Finally. this paper should serve to point out the need for thermochemical data of organic sulfur compounds.
For ethyl mervaptan the vibi htioiial assigiiiiieiit of Troltei and Thompson (20)was used. The moments of inertia were calculated assuminga tetrahedral C--C--S angle and C-S arid S--H distances, as in methyl mercaptan (19). Because the barriels i ( i internal rotation of the rotating methbl arid 9-H groups are r i o t known, they were taken a5 equal to t h P barriws found in propanr and methyl mercaptan, respectively. Inasmuch O S these barriers are rather uitcertairr. wheii uwd 171
ethyl mewaptail, ihe thcrmod~-narur~ iumdiona, not includilik the contribution of internal rotation, aia pesented, in addition t ( 7 the total functions. in Tables I to IV. The therniod? naniic functions (ti ethyl mercaptan, etll: I mercaptan, arid iiiethyl sulfide ai I h hoiling points arc prrjented in Table The fundamental vibrations of diriiethyl disulfide (20) indicatt that the vibrational contribution to t h P thermodynamic propcv ties is essentially that of dimethyl sulfide with the addition of t h c frequencies 243 and 512 em.--] and ail internal rotation of thc 9-CH3 group. The barrier to rotation of thiy group is unlrnowii and waR taken i o be such as to give, at 298" K., an entropj oi 1 calorie per degree mole less than that cosiesyouding to free rotation. This leads t o a barrier of 2200 calories. The moments OI inertia were calculated using the structural parameters of Stevwbon and Reach ( 1 6 )and assuming thal the two planes containing the C--S--S a t o m make an angle of 106' i ) found ~ in dimethl I trisulfide ( 4 ) . For dimethyl 5uXfoxidr and diinetlij 1 S i i l l r i i w , tht. thcrmodj mainic furwtions &ere calculated bx I I I C H I ~ L o f the folloniirrr rel~tion5:
~
Entropy So
Table I.
Temperature, K. -__ 500 600 700 8U0 905 I000 Cal./Degree Mole 68.11 71.18 74.02 76 65 79 12 81.44 98.57 78.61 83.11. 87 84 91.31 9 5 . 0 2 81.4 101.9 86.2 94.7 90.6 98.6 73.31 77.46 81.39 85.11 88.64 91,74 68.36 71.35 74.03 76.46 78.69 80.75 64.72 66.79 68.62 70 26 71.74 73.09 .53.30 54.97 6 6 , 40 57.73 58.96 59 81
----__~-_____I__-
400
2Y8.16
Compound CHaSH (CHdz8 CzHsSH CzH6SHa
______
__
60.91 64 78 68.30 73 I75 70.6 76.4 64 34 69.08 61.24 65.07 808 59.40 62.32 so2 49.15 51.36 H2S Without internal rotation. ~
~
~
~
~
~
Table 11. Free Energy Function -Fa
Colllyound
__
......
__ H : ,
T
Cal.,lDegree Mole
Table
CHIS€€ (CHp)zS CzHjSH CzHsSH" SO8
2.90 3.73 3.6 2.92 2.77 SO? 2.52 H2S 2.38 Without internal
62.631 68.?0 71.31 71.0 74.1 65.22 67.49 6 1 , 2 3 62.98 58.71 60.05 4 8 ~ 1 3 49,27 60.80
634.33 73.72 76.6 69.63 64,61 61.27 50.30
66.12 62.39 b l 24
13,31 19.16 19.7 17.11 12.67 9.42 7.78
15,52 22.51 22.9 20.05 14.63 10.70 8,8!
5.22 ,3.64 5.6 4.58 6.10 3.53 3.13
79.0 7P,69
7.42 10.2Y 10.5 8.77 7,22 6.73
5.74 7.81 7.9 6.48 5.60 4.61 3.9Y
2,8!J
9.25 13.04 13.4 11.32 8.96 6.94 5,X2
11.22 15.99 16.5 14,11
10.78 8.17 6,78
rotation.
..
400 .__.-__.I
r1, he terrria ill bracker rtpreserrt a g i ~ ~ athrriiiodynamic ii furit tion, and the symme corrections, in paientheses, weie uwti only for the free energy and entropy functions. The thermodynamic functions for all the compounds discww:. nre shown graphically in Figures I to 4, For higher alkyl derivatives of these ~1111pIecompounds t h e thermodynamic functions can be calculated by adding incwmrn t obtained from the corresporiding hydrocarbons (10). The functions for sulfur dioxide and .ulfui trioxide ale yiveii b\ Kelley ( 7 )and Stockmeyei, Kavanagh, and Mickley ( l o ) ,resprctiveIy. Values foi ~ulfurdioxide have a l w heeri given by X ) n ning and Hurd (IS). Hydrogen sulfide hac been discussc4 t y KeIWrp ( 7 )and h j h e h a
($11.
Heat Capacity
Temperat,ure, ~ _X. . _ 500 600 700 800 900 C;, Cttl./Lkpree Mole l_l
Colllpound CHaSH (CHdaS CzHsSH
6.?.Y> 76.01
III. Heat Content Function
Table IV. 298.16
- ......
.......
E51,18 54.21 56.66 ,58,83 55.79 59.64. 6 2 . 9 8 65.97 58.4 62.3 65.6 68.7 54.56 57.63 60.34 6 2 , 8 6 51.94 54.81 57,17 5Y,31 50.95 53.49 55,50 ,57 21 HzS 41.18 43.53 4 5 , 3 4 -1H,83 a Without internal rotation.
CHzSH (CMs)zS CiHsSH CzHsSH" SO8
1 2 . 1 2 14.09 15.95 17.15 20.36 23.32 21.4 24.8 17.6 C2H&Ha 13.88 17.80 2 1 . 2 6 SO, 12.10 1 4 , 0 5 15.66 SO2 9.52 10.37 11.08 H2S 8.14 8.48 8.81. Without internal rotation.
____-._
20.37 21.52 30.76 32.65 31.9 33.6 29.00 30.92 18.61 1 9 . 2 2 1 2 . 1 0 12.43 1 2 . 6 9 9.47 9.81 10.1.4
17,60 19.07 28.58 30.0 26.99 17.85
26.11
27.4 24.24 16.89 i1.m 9.14
..........
1000
Table V. Thermodynamic Functions a t Boiling Point
. 42,54
34.38 35.2 32.55 19.75 12.89 10.47
CHaSH 279.12 60.16 (CH3)ZS 291.06 67.87 CzHsSH 307,8 71,1 CzHsSHa ..i, 64.78 IL Withoul; internal rotation.
60,6(' .:5.42 08.8 54.8':
2.67 3.62 3.77 3.05
11.70 16 95 ~
18.0 14,26
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949
I
1
I
I
300
400
SO0
600
2739
I
1
700
BW
I
I
8(10
a00
I
TEMR 'K
Figure 2. Free Energy Function i n the Gaseous State against Temperature
For sulfur, the functioris for gaseous S2 from 298'to 1000°K. and for rhombic sulfur at 298" K. and a t the temperature of transition t o monoclinic sulfur, 368.6" K., are given in Table VI. Further consideration of the sulfur equilibria will not be made, as the subject has been discussed in considerable detail by Kelley (7).
Table VI. Thermodynamic Properties of Sulfur
S O
(FO
-HE)
T
Cal./beCal./DeTemp., wee Mole gree Mole K. da (gas) 298.16 54.41 47.24 400 56.78 49.38 500 58.60 51.05 600 60.10 52.44 700 61.38 53.64 800 62.51 54.69 900 63.51 55.63 56.48 64.42 1000 7.63 3.12 Y (rhombio)a 298.16 8.83 4.10 368.6 For S(rh) = 1/z S, (gas), AH: = 15.80 koal.
w
n
-
Ho HZ, Ca Koal./ Cal.yDeMole gree Mole 2.14 7.76 2.96 8.15 3.77 8.38 4.60 8.54 5.42 8.65 6.26 8.73 7.09 8.78 7.94 8.82 1.34 5.44 1.74 5.88
L
I
300
I
I
400
SO0
1 1 6W 700 TEMP. X
I
I
6W
9M
I /mO
Figure 3. Heat Content Function in the Gaseous State against Temperature
HEAT OF FORMATION AND FREE ENERGY OF FORMATION The heats of formation of the mercaptans and the sulfides, except propyl mercaptan, are taken from the work of Thomsen (19). The heat of formation of propyl mercaptan has been obtained by Barr and Keyes ( I ) from equilibrium measurements. The heat of oxidation of dimethyl sulfide to dimethyl sulfoxide and to dimethyl sulfone has been measured by Douglas (6). This, together with Thomsen's data on dimethyl sulfide, and a n estimation of the heat of sublimation of dimethyl sulfone at 298' I
