Azeotrope Formation' between Sulfur Compounds and Hydrocarbons I
D. H . DESTT
F. A. FIDLER
Reseurch Stcction. inglo-lrunian Oil Co., L t d . , Szcnbrcry-on-Thames, Middlesex, England
Becar,-e on fractionation of a petroleunl naphtha, the sulfur compounds distill oFer a t column head teniperatures which do not correspond with their true boiling points, the azeotropes formed between sulfur Compounds and hydrocarbons were studied. Azeotrope formation betw-een alkane thiols and h)drocarbons has already been described and the present paper extends the work to coier alkane sulfides and disulfides, thiophenes, and a cyclic sulfide. Sixtj -three azeotropes have been prepared and their properties and compositions determined. The results h a l e been correlated in a manner similar to t h a t prebiously adopted for thiols and h?drocarbons and the same relationships shown to exist. A s a result of this wark, it is now possible in m a n j cabei to predict whether azeotrope formation between a specific hydrocarbon and sulfur compound boiling in the gasoline range will occur and, if i t does, to gile the boiling point and composition of the azeotrope. I n addition, a comparison has been made of the strength of azeotrope formation for the barious classes of sulfur compounds. From this, i t appears probable t h a t azeotrope formation with hydrocarbons m a t be used as a means of separating individual sulfur compounds from mixtures such as ma) be isolated from petroleuni distillates.
niary of the physical properties of the sulfur compounds used for the preparation of the azeotropes described in this paper is given in Table 11.
I
T-\RLE I. PHYSIC ' i PROPERTIES ~ OF HYDROCARBOXS GSEDFOR
Iu T H E previous paper ( 2 )a considerable number of azeotropes, formed between thiols and hydrocarbons boiling in the gaeoline range, Tvere examined and their physical properties deterhon-n t h a t certain simple relationships mined. As a result, it I exist between the conip on of the azeotrope, the boiling points of the azeotropes, and the boiling points of the pure hydrocarbon^. Using these correlations, it \vas possible to state, merely from its boiling point, whether a h)-drocarl>on \voultI form an azeotrope with any particular thiol and if it did, t o predict the lioiling point' and composition of the azeotropr. It was of interest t o determine whether the relntionships so established for thiols Tyere applicable t o azeotrope formation between other types of sulfur compounds and hydrocarbons and also to compare the azeotrope-forming tendencies of the various classes of sulfur compounds which are knonm t o occur in petroleum distillates. T h e present paper contains information on the properties of azeotropes formed betIveen hydrocarbons and alkane sulfides, alkane disulfides, thiophenes, and a cyclic sulfide.
DETERMINATION OF PHYSICAL PROPERTIES
T h e physical properties of the components and azeotropes were measured as in the previous work ( 2 ) . T h e compositions of the azeotropes were determined in most cases b y the bracketingblends method, which consists of making u p a number of synthetic hlends of composition approximating the one being :malyzed. T h e refract,ive indeses of the blends are then measured and a refractive index-composition curve is drawn. From this, the coniposition of the unknown can be read from its refractive index by interpolation. In a few instances, however, where the refractive indexes of the azeotropes were close to those of the hydrocarbons, the compositions were calculated From determinations of the sulfur contents. P R E P A R 4 T I 0 4 O F 4ZEOTROPES
The azeotropes viere prepared generally from the suliur compounds listed in Table I1 b y fractionating appropriate mivturea with hydrocarhons in 50- or 100-plate columns. T h e only r v c e p
;\ZEOTROPE\
€1,-drocarbon 2-1Iethyl-1-hutene 2-lIethi.1-2-butene 1-Herene 1,1,2-Trirnethylcyclopentane 2-llethylheptane trans-l.R-Dimethi.1cyclohexane
n-Octane
Ethylcyclohexane n-Nonane 3-Nethyl-3-ethyIheptane
31.25 38.60 63.50
1.3777 1.3871 1,3880
0.6504 0.6619 0.6730
...
113.75 117.70
1.4229 1.3950
0,7722 0 6977
-21.95
...
99.92
120.30 126.70 131.85 150.65
1.4233 1.3971 1.4332 1.4053
0.7667 0.7025 0.7881 0.7176
-56180
99:98
-53.55
99181
163,OO
1,4208
0,7501
... ...
...
TABLE 11. PHYS~CAL PROPERTIES OF SULFCRCOMPOUXDS USED FOR AZEOTROPES Sulfur Compound Sulfides 2-Thiapropane 2-Thiahutane 3-Thiapentane 2-Thiapentane 3-llethyl-2-thiabutane Disulfides 2,3-Dithiabutane 3,4-Dithiahexane Thiophenes Thiophene 3-llethylthiophene 2-llethylthiophene
MATERIALS EMPLOYED
T h e hydrocarbons employed in the present work were available as the result of syntheses carried out over many years, and Table I gives the physical properties of those used in this F o r k which were not given in the previous paper. T h e majority of the sulfur compounds were synthesized in the laboratories of the Anglo-Iranian Oil Co. and papers giving complete details of their preparation and physical properties have been written. T h e three thiophenes were prepared b y fractionation of samples hindly donated by the Socony-Vacuum Oil Co. h sum-
Cyclir sulfide Thiacyclopentane
905
B,P,at Refractive 760011m.. Index, C. n ;2
Density, d2'
Estimated Purity, l l o l e Vo
37.32 66.61 92.07 95.47 84.iG
1.4353 1 4103 1.4427 1.4442 1.4392
0.8483 0 8422 0.8363 0.8291
99.95 99 90 99.8 39.96 93.8
109.44 151.11
1.5259 1,5072
1.0623 0,9933
99.96 99.8
83.97 114.96 111.92
1.5286 1.5201 1,3201
1.0642 1.0203 1.0794
9Q:95
120.79
1.5047
0.9998
99.7
0.8424
...
906
Vol. 43, No. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY I
7
175
*ISOPARAF FINS *
E-PARAFFINS -tNAPHTHENES
-
I50
B . P O F PURE
m V
125
z
0
m
a
4 100 V
100
0 U
a
>
r
g
75
15
50
50
25
25
I-
z0
a
0
5
=!
0
m
DISULFIDES A N D ALKANE SULFIDES 0
0
I
20
I
40
I
60
T H IO P HEN ES
CYCLIC S U L F I D E I
I
I
100 0 20 40 20 40 60 80 IO M O L E PER C E N T S U L F U R COMPOUND I N AZEOTROPE
80
Figure 1. Boiling Points of Hydrocarbons
TS.
tions nere the azeotropes of hj-tiromrbons n ith disulhtlts-, 111 which case the metal packing normally employed in the 5O-l)l:it t? column a as replaced b y glass helices in order t o atuid deconipoiition of the disulfide. As a result, the column efficicncy \\:I\ rcduced t o the order of 15 to 20 plates. RESULTS
Sisty-three definite azeotropes v-ere prepared between sulfur compounds and hydrocarbons and their properties werr cletcrmined. Most of these were with naphthenes or paraffins, but three olefin-sulfide azeotropes were also isolated. Detailed result? are given in Tables 111, IV, V, and 1-1. I n the previous work with thiols, no azeotrope formation coulcl be detected betneen benzene and any of the thiols employed. T h e same inability to form azeotropes was ohserved n.ith t h o alkane sulfides and benzene and, even n h e n 2-methyl-3-thial)erltane v a s distilled with toluene, no azeotrope formation betn-een these tn-o compounds could b e detected, although the builiiig point difference between t,hein is only 3.5' C. Simil:idy, no azeotropes were formed between thiophene and benzene nnti thiacyclopentane and toluene. [The absence of azeotrope furmation between benzene and thiophene agrees with the findings of Coulson, Hales, and Heringt,on ( 1 ) .j However, in the case of 2,3dithiabutane and toluene, which have a boiling point difference of only 1.4"C., a definite azeotrope was formed. This lvas shown b>the fact t h a t all the fract,ions from the distillation boiled at slightly lon-er temperatures than the boiling points of eithcr of the two components. A sharp separation of this azeotrope from the component in escess, in this case toluene, was not obtained liecause the presence of a disulfide made it necessary t o use ~t column of relatively low efficiency. T h e composition of the azeotrope has therefore not been determined. This is the only
I
I
60
80
I
?
hlole Per Cent Sulfur Cornpollrid in Azeotropes :izeotrope which has been detccted in this work between a sulfur compound and an aromatic hydrocarbon. CORRELATION OF DATA
'1'11e eqx~rinieritaldata have been plotted in essctly the saine iiiariner as for t,lie thiol. and h~-drocarl,owand, in every case, the c:iiiit: straight-line relationships have lieen shon-n t o hold. For iiwt:inm, ill I l g u r e 1 the lmiling poiiits oi thc pure hydrocarbons :ire plottcvt ng:iinst the compositions of the azeotropes. Straightliiic, wlationships arc produced mi(1 the ,slopes of t h e lines for rc slightly less than for thow or' paraffins with the, *mi(>sull'ur c-ompound.. Froin theye lines the boiling point, rangt-. which arc the diffcwncca I)etn.een the maximum and iiiininiiiiii boiling poiiitx of hydrocarbons forming azeotropes with 1~acIiindividual sulfur compound, have been determined for all the sysfe1ii.s esamined and are given in Table VII. The same general rules lvere found t o hold for the systems deFrribetl here as for the thiol-hydrocarbon systems. Increasing inolecular weight in a homologous series of sulfur compounds gave a narroiver hoiling point range, while in every case where I)oth paraffins and naphthenes were esamined with the same sulfur compound, the former had a wider boiling point range than the latter. Finally, branching of the carbon chain tended to give a narrower boiling point range Chnn the corresponding straight chain. I n the only case where substitut,ionin a ring vias investigatedi.e., vith the thiophenes--the same tendency for a narroxer boiling point range was found with increasing molecular weight. IIoivever, it appeared t h a t the position of the substituent group in the ring might also have some effect, as was seen b y comparing the ranges for 2-methyl- and for 3-methylthiophene. -At the moment,, there are insufficient d a t a t o shorn vliether this difference continues t o hold for higher homologs in the series.
April 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
907
-
slooes for the several svstems investigated-i.e.. AZEOTROPES OF HYDROC~RBOXS the constants -4,where -4 is given by the equation WITH -ILKLXE SULFIDES log :I. - B Properties of Azeotropes '4 = ______ R . P . oi RefractireSulfide in (273.1 TAZ) c'om-
PROPER TIE^ T ~ B I . E 111. PHYSICAL
OF
+
ponent. Components
2-Thiaprcpanp 9-Methylbutane n-Pentane 2,2-Dinietlrylbutane Cyclopentane 2-Met hyl-1-butene 2-SIethyl-2-butene
c.
3;. 32 27.90 36.15 49.70 49.33 31.2.5 38.60
2-Thiahutane 66.61 2,3-L)itnethylbut~n~ .58.10 68.7: n- Hexane 2,?-Diiiietliy11~entane 79.20 .\fetliylcyrloi~entan~ 71.85 Cyclohexane K O . 8.3 1-IIexene 63.50 ii-Thiapentane 92.07 2.4-Dimethylpentana 80.55 2.3-Diiiieths-igentane 89.i40 3-11ethvlhe\-ane Rl.60 2,,".4-Tritiiethylpentane !IY.30 Cyclohexane 80.85 l,l-Diineth3-1cyclor,~ntane 87 90 ~ ~ a n s - 1 . 3 - l ) ~ 1 i 1 e t l i y l c ~ - c i o p e n c a n90 ~ 80 ~Iethylcsclol~e~ai?e 101 0.; Benzene 80.10 2-Thiapentane 95 4 7 2,3-Diiriet hylrxntane 89.90 8-Methylheuane 91.60 ~.2,4-'~riiiiethsipentane YY.30 9.2-Diiiiethylhexane 106.8: 1,l-Dimethylcyclopentane 87.90 f r a n s - 1 , 3 - D i m e t h y l c y ~ l o ~ e n t a n e 90.80 11ethylcyclohexane 101.05 E t hylcyciopentane 103.4.; 3-1Iethyl-2-tliiabutane 84.76 2,,%-L)iinetIiylpentane 79.20 2.4-Dimethylpentane 80.55 2,3-Diniethvl~entnne 89.90 :3-.\Iethylhexane 21.60 I 1.83 Methylcyclopentane Cyclohexane 80.85 1,l-Diinethylcyclopentane 37.90 tranu-1.3-Diinethylcyclopentane UO.80
B.p..
Density,
3C
index, n ko
16.62 31.80 36.50 37.09 30.64 34.33
1.3671 1.3840 1.4154 1,4290 1.3862 1,4086
0.6237 0.705.5 0.7908 0.8294 0 68013 0,7470
57,41 63.94 66.37 65.59
1.38-11 0.6878 1.4057 0.7484 1.4306 0.8165 i.4282 0.8081 Sonazeotropic 1.4002 0.713~
62.71 80.53 87.R3 89.19 91.44 86.98 88.89 92.10
d20
1.3826 0.67.59 1,4080 0.7408 1.4104 0.7491 1.4287 0,7970 Sonazeotropio 1.4194 0.7721 1.4206 0.7784 1.4410 0.8325 Pionazeotropic
0.7222 0.7288 0.7776 0,8313 0.7615 0.7647 0.8235 0.8336
89.10 90.53 94.00 95.42 87.66 90.11 95.06 95.41
1.4014 1.4032 1.4213 1.4405 1.4158 1.4158 1.4385 1.4413
28.40 (9.39 83.93 84.38
1.392i 0.1035 1.3950 0.7111 1.4230 0.7856 1.4275 0 7984 Sonazeotropic 1.4281 0.7900 1.4279 0.7991 1.4317 0.8099
79.76 83.62 84.38
azeotrope, mole
are quoted in Table VII. It is suggested that a modification be made i l l 27.9 the use of these constants for the direct indicatir.)ri 50.3 84.4 of the relative power of a compound to form azeo88., 18.7 tropes with different homologous series. Skol56.6 nik, in his paper, calculates the "relative azeotroI,i(. effect" of a system by comparing the values of thr, 20.6 59.6 constant -1for a n unknown system xvith tho value, 90.8 66.5 of .4 for the system "benzene-n-alkanes," whicli he adopts as standard. T h e same method of coni31.6 parison \vas also adopted for the different thiol2.5 hydrocarbon systems discussed in the previow 41.2 50.9 p:iper in this series (2). I t has since been m i l 80.9 ized that t,he choice of this particular standard is 27.8 not entirely satisfactory, because the accuracy oi 43.0 95.3 the value of -4 as calculated for thc hcnzene - I / allmie system is open to some doubt. The o n l ~ , n-alkanes which form azeotropes with beiizcno arv 24.i 35.3 n-hexane and n-heptane, and, as shown b y llarscli67.6 95.5 ner and Cropper ( d ) , these azeotropes are a t th(, 10.6 estrenie ends of the range. a result, the coni24.8 r9.6 plete separation of the azeotropes from the close 91.5 boiling components is extremely difficult, which 25.2 means t h a t the accuracy of the figures is not i o 31.9 high as when dealing TJ-ith azeotropes in the miti74.8 83.8 dle of the composition range. I n addition, as :tI38.6 ready pointed out (Z),the plot of the boiling point 66.7 of the azeotrope against its composition (Figure 2 ) 81.8 is unreliable when the mole per cent of the conipound being plotted on the graph is below 10, as is the case with n-hexane and benzene. Evidence of the unsatisfact,ory nature of the benzene--/dliatit~ system as a standard is seen by studying thc relative azeotropic effects for the various systems quoted by Skolnik. It, appears from his calculations t h a t n-alkanes are different from branchid alkanes in their tendency t o form azeotropes with benzene and ill fact are very similar t o the saturated cyclic hydrocarbons. From the present work, carried out ivith the various t,ypes of sulfur compounds and hydrocarbons, this seems extremely unlikely, inasmuch as normal and branched alkanes are usually similar i i i their azeotrope-forming tendencies. As might be expected, there appears t o be an approximate relationship in the majority of cases between relative azeotropic effect and the boiling point range of azeotrope formation, b u t the values for the benzene-nalkane system do not fit in with this generalization. The boiling point range for this s)-stem is of the order of 30" C., which is almost, the same as t h a t for l-propanethiol with paraffins-i.t.., 32' C.---indicating a similarity between the two systems. C h i
The only example rvhich ran be given for azeotrope formation Iwtwecn olefins and a sulfide is with 2-thiapropane, and in this in..t:ince the boiling point range is considerably narrower than for Ilaraffins n-ith the mine sulfide. If a value for the boiling point range for nsrphthenes with 2-thiapropnne could have been determined, this n-oulil almost certainly have been intermediate between the ranges for pnrafins and olefiris. The order of ease of azeotrope form:ition of hJ-drocarbons with alkane sulfides noultl thus appear to be paraffins > naphthenes > olefins. With the exception of 2,3-dithiat)utane, the lines for naphthenes and paraffins cross. The reason for this exception is not clear. \\-ith the thiol-hydrocarbon azeotropes, it n-as found that the boiling points of the pure thiols intercepted the lines a t 51.5 mole yo thiol. T h e same is not exactly true in all the examples considered here, but, the boiling points of the pure sulfur compounds which are indicated by the arrows on Figure l do, in general, intercept the lines a t 51 * 3 mole %. The second correlation which has been plotted is the relation of the boiling point of the azeotrope to t,he logarithm of the mole per cent of the sulfur compound in the azeotrope (Figure 2). Again, as TABLE .'\I PHYSICAL PROPERTIES O F .kZEOTROPES O F HYDROCARBONS was found for thiols, linear relationships occur for WITH ALKASEDISULFIDES the various sulfur compound-hydrocarbon sysProperties of Azeotropes B.P. of tenis. A4spointed out by Skolnik ( 5 ) , the slopes ComRefractive Disulfide in ponent, index, Density, azeotrope, of the lines, which can be represented by equations Components c. $ ' n dzo mole 7, of the form, 2,3-Dithiabutane 109.42
:.E:,
log z = A (273.1
+ TAZ)+ B
where x = mole yosulfur compound in azeotrope, TAZ= boiling point of azeotrope, and d and B are constants, give a n indication of the power of the various compounds to form azeotropes with the different hydrocarbon classes. Values of these
n-Heptane 2,5-Dimethylhexane 2-Methylheptane Methylcyclohexane trans-1,3-Dimethylcyclohexane Toluene 3,4-Dithiahexane n-Nonane 3-Methyl-3-ethylheptane
98.40 109.15 117.70 101.05 120.30 110.85 154.11 150.65 163.00
96.44 102.84 106.22 98.92 107.22 108.93
1.4112 1,4406 1.4682 1.4431 1,4886
0.7528 0,8314 0.8984 0.8299 0,9595 Azeotropic
27.5 53.2 73.3 29.3 76.7
148.62 153.02
1.4381 1.4843
0.8066 0.9311
42.3 82.5
INDUSTRIAL AND ENGINEERING CHEMISTRY
908
the other hand, the relative azeotropic effect for the latter systen: is 1.54, indicating a dissimilarity. Moreover, the value of 1.54 is almost identical with the value determined by Skolnilr for benzenebranched alkanes. This discrepancy can be resolved if i t is assumed t h a t the value for the benzene-n-alkane system is in error and t h a t all three systems have similar relative azeotropic effects. This then means t h a t normal and branched alkanes would be expected t o be sinlilar in their power to form azeotropes with benzene. As a n alternative t o Skolnik’s relationship, it is suggested t h a t a better relative order would be given by merely using the reciprocal of the slope, or 1/A, as a guide t o the “relative azeotrope-forming power” of a system. Values of this factor for the various systems of sulfur compounds and hydrccarbons, including those for thiols and hydrocarbons, are given in Table \TI. This method has the advantage t h a t no standard is needed, and the value for the relative azeotrope-forming power is always greater than unity. This basis can be used for the comparison of any azeotropic systems and need not be confined t o sulfur compounds or hydrocarbons. With the aid of Figures 1 and 2, i t is now possible, as vias the case with thiols, to say whether a paraffin or a naphthene will form a n azeotrope Lvith a n y of the sulfur compounds examined and, if it does, t o predict the boiling point and composition of the azeotrope formed. Thiol-hydrocarbon systems have been shown (2) t o give straight-line relationships n hen the log-
TABLE V. PHYSICAL PROPERTIES OF AZEOTROPES OF HYDROCARBOXS WITH THIOPHEXES B.P. of Component.
Components
3
2-Xethylthiophene n-Heptane ”2-Dimethylhexane 2,s-Dimethylhexane 2-Methylheptane
1‘ARI.E;
VI,
1’ilVSICAL
-4-N A P H T H E N E S
c.
83.97 68.75 80.5.5 89.90 98.40 71 8.5 80.83 90.80 80.10
Thiophene n-tlexane 2,4-Diinethylpentane 2,3-Dimethylpentane n-Heptane lilethylcyclopentane Cyclohexane trans- 1,3-Dimeihylcyclopentane Benzene
Properties of Azeotropes Thiqphene Refractive in index, .‘o” Density, azeotrope, d20 mole %
B.$:, 68.46 76.58 80. 90 83.09 71.47 77,90 82 00
1.3851 0.6870 1,4262 0,7957 1.4622 0.8893 1.4917 0.9685 1.4202 0.7778 1,4570 0.8691 1.4772 0.9311 Sonazeotroiic
114.96 98.40 109.15 117.70 125.70 103.45 113.75 120.30
107.12 111.86 114.15 102.82 110.47 113.17
~onaaeotropic 1.4210 0.7693 1.4.540 0.8333 1,4882 0.9404 1.4228 0.7733 1.4.562 0.8696 1.4783 0.9143
35.1 62.4 84.0 3.9 46.5 69.0
111.92 98.40 106 85 109.15 117.70
97.77 104.62 106.12 109.97
1.3898 1.4231 1.4305 1.4662
2.2 35.7 43.3 71.1
0.6892 0.7742 0.7931 0.8846
WITH A
CTCIJCSULFIDE Propertie. of Azeotropes ThiacycloRefractive pentane in irides* Density, azeotrope, n ‘D” d20 mole yo
B . P . of COW
ponent, Cumponentb
0
Tliiaiyclopentane 2,5-Dimethylhexane 2-Methylheptane n-Octane t ra ~i s-1,3-Dimethylcyclohexane Eihylcycloherane Toluene
c.
120.79 109.15 117.70 123. 70 120.30 131.85 110.85
B.P.. C.
3
1 0 i . 9.5 113.96 117.79 115.90 120 46
1.4066 0.7319 1.4281 0.7019 1.4823 0.8372 1.4534 0.8539 1.4876 0.9517 Sonazeotropic
I
4175
I-
ALKANE
0
I
IO
20
SULFIDES I
I
I
30 40 50
l
l
70
MOLE
Figure 2.
I
CYCL-IC SULFIDE
IO
20
I
1
I
1
PER CENT
-I25
DISULFIDES AND I
I
I
I
30 40 50
SULFUR
I
l
l
L
70 IC
COMPOUND
11.3 -17.0 68.1 85.5 14.0 41.2 10.9
PROPERTIES OF .kEOTROPES O F HYDROChRROSS
t
ISOPARAFFINS
n - PA R A F F INS
Vol. 43, No. 4
IO
20
30 40 50
m
IN A Z E O T R O P E
Boiling Points of Azeotropes us. i\lole Per Cent Sulfur Compound in Azeotrope
100
20.7 44.6 66.3 49.0 84.1
April 1951
909
INDUSTRIAL AND ENGINEERING CHEMISTRY
-0- T H l O L S --f-ALKANE S U L F l D E S 60
+DISULFIDES
+THIOPHENES
50 A
$401
1 % 4 30
\
50
100
I50
i
3
0
50
100
200
150
B O I L I N G P O I N T OF S U L F U R C O M P O U N D
Figure 3.
Azeotropic Constants of Sulfur Compounds with Paraffins
arithms of either the boiling point ranges or the relative xzeotropic effects for the straight-chain t,hiols with paraffins !\-ere plotted against the boiling points of the thiols. I n Figure 3, the logarithms of the boiling point ranges and relative azeotrope-forming porvers for the straight-chain sulfides, disulfides, and thiophenes with paraffins, as given in Table 1-11>have also been plotted against the boiling points of the sulfur compounds; similar st,raight-lirie relationships appear t o hold. These correlation? are most useful, for not only is it possible t o predict the azeotropic constants of other sulfur compounds of each particular class, h u t the azeotrope-forming potvers of t h e various types of sulfur compounds can also be compared. I n order t o include the thiols in this comparison, the azeotropic constants of the straight-chain thiols with paraffins have also been plotted in Figure 3. T h e plots of azeotropic constants shon- t h a t , within any one class of sulfur compound, these constants are proportional t o the boiling point of the sulfur compound. T h e most satisfactory method of comparing the different types is, therefore, to corisider the relative values of these constants for each class a t the same temperature. Consequently. as only one cyclic sulfide-thiacyclopentane-was investigatcd, the azeotropic constmte of the other four types have been obtained from Figure 3 for a temperature of 120.79' C.-the boiling point of thiacyclopentane-and these values are given in Table S'III. T h e tn-o groups of aliphatic compounds-the straight-chain thiols and sulfides-are of the same order, the sulfides Ixing the weakest of the fire classes examined. Kext come the two types of cyclic sulfur compound, the thiophenes and cyclic sulfide, and finally the disulfides, these latter being the strongest group of azeotrope formers with hydrocarbons. T h e boiling range of paraffins which will form azeotropes with disulfides is more than twice the range for straight-chain sulfides of similar boiling points. Although the figures in the talde refer only to paraffins. the same
relative order also applies to naphthenes, because in every sy;itc.m investigated the naphthenes are slightly less pot! erful thaii paraffins with the same sulfur compound. This variation in tendency of the various sulfur c o ~ n p o u n t lt ~ o
TABLE VII.
VALUES O F CONSTAXT A , RELATIVE AZEOTROPE BOILINGP O I N T RANGES FOR dULFrJR COXPOCXDS A N D HYDROCARBOXS
F o R \ f r N o POWERS, .4XD
Group of Binary Systems Thiols Ethanetbiol with 3 paraffins 1-Propanethiol with 7 paraffins 2-Propanethiol with 4 paraffins 1-Butanethiol with 8 Daraffins 4 naphthenes 2-Butanethiol with 5 paraffins 3 naphthenes 2-Methyl-1-propanethiol with 7 paraffins 5 naphthenes 2-,\Ieth3-l-2-propanetli~olwith 4 paraffins Sulfides 2-Thiapropane x i t h 3 paraffin? 2 olefins 2-Thiahutane with 3 paraffins 3-Thiapentane with 4 paraffins 3 naphthenes 2-Thiapentane with 4 paraffins 3-Methyl-2-thiabutane 4 naphthenes with 4 paraffins
3 naphtheries Disulfides 2,3-Dithiahutane with 3 paraffins 3,&Dithiahexane with 2 naphthenes paraffins Thiophenes Thiophene with 4 paraffins 3 naphthenes 3-Lfethylthiophene with 3 paraffins 3 naphthenes 2-llethylthiophene with 4 paraffins Cyclic sulfide Tliiacyclopentane with 3 paraffins 2 naphthenes
A 0,04!# 0.072 0.066 0.087 0.101 0.084 0.111
Relative AzeotropeForining Power
Boiling Point Range 39 32 28.6 27 23
0.117 0.095
20.5 14 15 11.5 10 12 0 10 8,5 10.5
0 052 0.108 0.074 0.091 0 108 0.095 0.118 0 099 0.128
10.5 9.5 13.5 11 9.5 10.5 8.5 10 8
0.043 0,050 0.071
23.5 20 14
42 40.5 30
0.048 0.071 0.059 0.069 0.063
21 14 17 14.5 16
41 33 33.5 26 30.5
0.054 0.067
18.5 15
34.5 32
0.097
22.5
18.5 24,6 21 20 38,h 1Y
30.5 23.5 19. 5 23
19 21 18
INDUSTRIAL AND ENGINEERING CHEMISTRY
9 10
TABLELrIII. REL.4TIVE AZEOTROPICCONSTANTS FOR YARIOW TYPES OF SULFUR C O X P O U N D S WITH PARAFFINS AT 120.79' c'. Type of Sulfur Conipound
Relative Azeotrope Forming Power, 1 'A
Boiling P2int Range, C.
Straight-chain sulfides Straight-chain thiols Thiophenes Cyclic sulfide Straight-chain disulfides
8 9 15.3
18.5 23.5 30.2 34 3 38 .i
18.5
2 0 . ,i
fomi azeotropes x i t h 1iytirov:irl)ous offers proiiiisc for the sep:ir:itioii of mixtures of sulfur coiiipounds as obtained from petrolcrini distillates. I n exactly the ssmc manner as Iiossini arid hi. I'Oworkers have eniployed extensively polar entrainem t o si:p:irni I , close boiling hydrocarbons, particularly naphthenes ant1 pnraffiii,~, it n o w appears possible t h a t hydrocarhiis may he u trainers to separate c1o.i~ boiliiig sulfur compounds o classes. This is a lmsiblc alternative to silica gel at1aoq)tioii for I)ringing about such a separation ( 3 ) rind may prove a niorc~us,~i'iil technique than the latter in t h e higher boiling ranges \vliertl t lit' strength of adsorption on silica gel is generally reduced. Furt l 1 f ' i ' more, the order of azeotrope-forming tendencies of tiit, v n y i t l i i . classes of sulfur compounds is different from t h e order 01' i l i o i i . relative adsorbability on silica gP1. AZEOTROPE FORA1.ATION BETWEER- SULFUR CO\lI'OUSI)S
A l l the data XT-hich have been presented refer to the azeotrope? formed between mixtures of sulfur compounds and h>-drocarhoii~. s n d from the experimental r e d t s i t has been possible t,o ulitniii :L rrlative order for azeotrope formation for the different cl ;iuliur compounds. T h e n c r t step was t o determine whether iulfur compounds of different types b u t similar boiling points woultl theniselves form azeotropes and whether the relative order givclii in Table VI11 applied t o these. Distillations were carried out on :I number of binary mixtures of sulfur compounds and it WAS soon obvious t,hat, even if azeotrope? were formed, the power of forinntion was ext,rernely weak. -1s a result, it was necessary t o choose pairs of compounds which boiled as close together as possible, I)[>cause the boiling range over which azeotropes would be fornieti would be limited. T h e pairs of compounds which were exnminc~tl are shown in Table I X . It appears from Tables VI11 and I S t h a t azeotrope iormntiun hetween the sulfur compounds is a function of the difference l w tween their azeotrope-forming tendencies with hydrocarbons i n t h a t azeotropes are not formed between compounds whose azeotrope-forming tendencies are similar. For instance, alkane sulfides and thiols, which are both relatively weak in their tenrlency t o form azeotropes with hydrocarbons, do not appear to form azeotropes with each other, Tyhile disulfides and thiophenes.
TABLEIx.
Vol. 43, No. 4
AZEOTROPES FORMED BETWEEN VARIOCS c L I \ , l \ O F SULFUR COMPOUNDS
--
Properties of
which t i o t h forin :motropes fairly rc;itlily rritli hyclrocarl~ons. also do not forni Lizeotropcs v i t h c w h other as shown by 2,:G tlithinl~utaiicand 2-nieth!-ltl~iopheri(,Iieing noii:tzeotropic. IIon.ever, :I. disulfide and a cj-clic sulfide liot,li forni azeotropes xit,h LLII :illiniic> sulfide, n n t l i t is seen from Table \ T I 1 that these XI'I, \videly ililfc,rent in their power of forinirig :tzeotropes with hydrur;irl)oii?, Hecause it is neceswry t o have the two component. boiling ciosc+together hefore azeotropes can be obtained, it ivas n u t Iiwsililta 1 o s t u d y nzeotrope formation bet,n-een sulfur conip~uriils 011 tiit, s:itii(: extensive scale as F i t h hydrocarbons. Ilowcver, t h c n w i l t s in T:ible I S are sufficient t o give a n idea of the type oi :tzcotropes t o be espected and to indicate t h a t when a rnirture of piraffin arid naphthcne hydrocarbons and sulfur compounds, such as are fouiitl in petroleum, is distilled, the azeotropes formed are morc likely t n conqist of mixtures of hydrocarbons and sulfur cnmpouii(1s th:i n of mifur compounds alone. .ICKNOWLEDG.\IE.YT
The authors rvish to thank R . IT. Killnughhy for xssistancc i n coiiic of t h c cupcrimentd \vork. LITERATURE CITED (1) C,'oui~oii, E. --I., Hales, ,J. L., arid Herington, E. E'. G., Trails. F a r n d n g S n c . , 44, 63G (1948).
( 2 I Denycr, R. L., Firller, F. A , , and I,owry, 11. -I.,ISD. ESG. CHEXf.. 41, 2727 (1949). ( 3 ) Haresnape, D., Fidler, F.*L, a n d Lowry, R. .I.,I bid., 41, 2691 (1840). (4) l l n r s c h r i e r . R. F., a n d Cropper, V. P.. I b i d . , 38, 262 (1946). (5) Skolnik, H., I b i d . , 40, 442 (1948).
RECEIVED July 29, 1950. Presented before the Division of Petroleum CheinS O C I E T Y , Chicago, 111. iqtry a t the 118th XIeeting of the AXERICAXCHE\IIC.AL
* * * * * v
When the AMERICANCHEMICAL SOCIETY'S Division of Petroleum Chemistry meets in Cleveland on April 8, first on its order of business will be the presentation of a symposium on the composition of petroleum and its hydrocarbon derivatives. In the general session of the meeting, following the symposium, P. T. White, D. G. Bernard-Smith, and F. A. Fidler of the Anglo-Iranian Oil Co., Sunbury-on-Thames, Middlesex, England, will rep o r t their work on vapor pressure-temperature relationships of sulfur compounds related to petroleum. Fidler also is eo-author of the preceding paper in this issue (page 905) on azeotrope formation between sulfur compounds and hydrocarbons.
A second symposium programmed by the Division of Petroleum Chemistry includes thirty-three papers on combustion chemistry; this is a joint presentation with the Division of Gas and Fuel Chemistry.
