954
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
violet, and visible s p e r t r o w q y groups for analyses anti sprctral d a t a ; to the physical cheniiytry group who contributed vapor pressure data; and t o the macro- and microanalj-tical ]ahoratories for anal)-tical and microdistillation work. He also wiehes to thank D. J. Salley for kindly advice and courteous crit,icisms 2nd J. T. Thurston for support and encouragement. LITERATURE C I T E D
p, p., and ~ ~h ~ y,, . ~~ ~~chern,, ~ i20,753-6 l ~ , (19-18,. , (2) Edwards, F. I., and Hall, S. A., Ibid., 21, 1567 (1949). (3) Fletcher, ,J. I I . , Hamilton, J. Hechenbleikner. I., H o e d ) m . E. I., Sertl, B. J., and Cassaday, J. T., J . Am. Chem. S o c . , 72, (1)
c.,
2461-4 (1950). (4) Gore. R. C., "Infrared Spectra of Organic Thiophouphatr~."
Vol. 43, No. 4
presented a t Far:rday Soc. Symposium on Molecular S t r u c ture and Infrared Spectroscopy, at Cambridge, England, ~ Sept. , ? 25, ~ 8, 1950. ~ H i, , a~n d ~ atso ~ son, , F,A , , J . Chem. ,cot., 3514 (1948). (6) Iiirt, Jt. C., and C;isclard. .J. U.. A n a l . Chena., 23, 185 (1951). 4 . . Rec. trac. chinz.. 69, 649 (1950). ( 8 ) I'cck, D. It., Chenziatry R. Industry, 1948, 526, (9) Schriider, B., Office of Technical Services, Dept. Commerce. IZIOA Rept. 714 (1047). ( 1 o j Stanini, K. F.3 I N D . E E G . CHElI., - h a L . E D . , 17, 318 Cl945). (11) Witschonke. C ' . It.. Calco Chemical Division, A4mericanCyanamid Co.. private coi:imiinication. i12) ooii, 11, dcl,hysicalOptics,,33rd ed,, pp, 469-74, xew York, ATacniillai~,C o . , 1934. H E C E I V L D .\U!qISt
3 . 1950,
Properties of High Boiling Petroleum Products DISTILLATION STUDIES WITH RELATI05 TO POLY YUCLEAR AROMATIC COMPONENTS L. T. E B I ,
e. G. WANLESS, - 4 4JOHN ~~ REHNEK,
JK.
Esso Laboratories, Standard Oil Dweloprnent Co., Linden, JY.J . I)istillation studies h a t e been made with dilute solntions of polynuclear aromatic compounds in high boiling nonaromatic and aromatic petroleum oils. The purpose was to obtain more explicit information t h a n had heeu availahle on t h e distillation hehaiior of specifir t? pes of aromatics present i n such products. Representatite compounds ins estigated include p>rene, 3,4-henzop>renr. a n d 1,2,5,6-dihcnzanthracene, and t h e distillations were made in a straight-path still under near-equilibrium ronditioris. The relative tolatilities of the solutes were found t o he higher in nonaromatic t h a n in aromatic oils. ilinear relation v a s found between t h e atmospheric boiling point of a nonaromatic oil and t h e logarithm of the relative tnl'itility of a dissolted POI? nuclear aromatic compnund. O n
going from a i~onaromaticto a (hypothetical) completely aromatic oil, t h e relative volatility of t h e disfiolved compound is reduced to roughly one third its vnlue in t h e former oil. Corresponding to this reduction, i t is estimated that, in order to obtain equal amoiints of the solute in the distillate, the atmospheric distillation temperature required for the aromatic oil is a t least 50" F. higher than t h a t for the nonaromatir oil. 4 method is described for estimating the boiling point of a pol! rirrrlcar aromatic componnd from relatite volatilit! data on distillation frartions of an oil used a s the compound. The estimated hoiling solbent for snch poiri t c o f p? rene. 3,1-hendop? rene, and 1,2,5,6-dihenzanThese thraccne are 71.5". 860". and 870" F., respectitel!. talnes are regartied :IC tentatire.
I
h , ( i \ v c w i*:il,~ird out in an element.ai-\- fashionyiiilibriuni distillxtions were conducted with a straight-pat.11 1ahorator.y . M I operatecl under conditions very close So p l a t e or p c k i n g were employed in to one thenrcL?ic.al p1:it w iirop in thr latter wag thus kept low, and the ~ U I I R\ v c w n u d r at rrtiucrd prrswres in order to vaporize the largest jwssible : i i n i ~ i i n t of thc i - h a r p without appreciable cracking or ilc.c,ompo.i.itioii. T t i e niain objective sought was a better kriorvlc~igr (if the dial i1l:itic~nhchavior of polynuclear aromatic c.ompounds p i ' ( ' w r i t i i i high boiling products, rather than the condition. for ~nasiniiiiiifractionation efficiency.
X T H E course of an extensive series of experimental iiivrctiga-
'
tions on certain properties of high boiling petroleum products and fractions, carried out in tlicBse and cooperating Iaboratnrips during the past few years, it was found necessary to study t h e distillation behavior of such products with special elriphasis on the polynuclear aromatic componcwts that are usually prmcnt in varying degree. The purpose of t,his paper i-; to disc~lorthe, methods and results of these distillation Ftudies. The designat,ion "high boiling,'' as used here, I X ~ < T Srather broadly to a wide variety of pctroleiini refinery streams and products hailing above thc middle distillate range (roughly ahove 550" F.), and includes such diverse materials as heavy gas oils. cycle stocks, slurry oils, tars, asphalts, waxes, residua, and similar products derived mainly from thermal and catalytic cracking processes. T h e difficulties attending both distillation and chemical studies of such products, which present as hurdles not oiily high boiling ranges b u t also a wide variety of hydrocarbon types and an almost unlimited number of isomers, are too well laiown t o require comment. Tn order to obtain a basic pattern of distillation behavior, the
( 3 .
APPARATUS A S I ) PROCEDURE
Becniisr m o s t o f the distillations were performed with a 200gram charge, a 500-ml. borosilicate glass flask with a 34/45 stand:&-taper neck was used as the still pot. Figure 1 is a phot,ograph of the apparatus. Its design differs from thosc of similar
stills widely described in the literature only in one important respect--the arrangement for distilling waxy oils or materials that are normally solid at, room temperature but liquid at distillation tempcrn.tiires. The tube above the flask has an inside diameter
April 1951
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
955
Lvhether the distillation behavior of the systems investigated is subject t o a pressure effect under the conditions employed. Conversions to atmospheric boiling points were made with conversion charts similar to some recently published ( 6 ) . The apparatus a-as tested for plate efficiency a t a distillation rate of about. 1 gram per minute and a pressure of 0.035 mm. of mercury, using a mixture of diS-ethylhesyl sebacate and di2-ethylhexyl phthalate (7). The still was found to operate :it 1.05 plates (or 0.05 plate, if the one plate for the still pot is neglected), and thus functioned as an "equilibrium" still. The boiling point of the mixture was found to be the same as that reported by Perry and Fuguitt ( 7 ) . The major portion of the analytical work consisted in following the concentrations of certain added polynuclear aromatic conipounds, that had been dissolved in t,he various oils, during tlit. course of distillation. This was done by analyzing the distillation cuts for such compounds by ultraviolet absorption spectronietry. A Bcckman Model 1)U quartz spectrophotomcter W M used, and the samples were made up in a suitable grade of berizene or iso-octane as the solvent. In the least favorable case the minimum detect,able concentration of added hydrocarbon in the aromatic oil was estimated as 0.004%, while the accuracy of datection i. much greater than this in the nonaromatic oil. A COIIjervative alloFvance for error arising from possible mismatching between corresponding c u b of the original aromatic oil and the same oil containing the added hydrocarbon should raise the minimum detectable concentration to not more than 0.006%, which is well below the concentrations involved in later discue aion. PREPARATION OF MATERIALS
Since particular interest was focused on the distillation behavior of polynuclear aromatic components related to anthracene and pjrene, and containing four and five rings per molecule, the follo~vingsubstances kvere selected as typicd compounds for study as added solutes:
h"ms (&sellschitft fiir Teervenverturig). EsCimated purity, 997*. ~,~-HESZOPYREN (Bios E LaboiatorieP). Estimated purity, 100%. (l,Z-Benzopyrene, according to P:~tterson-Capell's"Ring Index.") 1 2 5 ( ~ - ~ ~ I R ~ ~ ~ , I N " H R . I C(Eastman). ~:S~, Estimated purity,
Figure 1. Straight-Path Laboratorj Still
of 28 mm. and is 140 mm. long from the bottom of the neck t o the collecting ring. To minimize radiation losses, the top of the flask and the tube are insulated with a heavy wrapping of asbestos cloth so that the thermometer bulb can see little but the hot cloth and hot still pot below it, nor can it see any appreciable amount of the take-off tube, as the cloth is srapped as high as the take-off ring. Bumping is eliminated a t low pressures by a magnetic stirrer, which serves t o kee satisfactory liquid-vapor equilibrium and makes possible smootg evaporation a t high rates and without appreciable entrainment. A n electric Glas-Col mantle (not shown) is used for heating. The vacuum line leading to the pump is located directly above the condenser, and the line t o the NcLeod gage is offset about 10 cm. These connections are large enough to eliminate any appreciable pressure drop between the thermometer and the point a t which the pressure is measured. A rotary-pig type of receiver is used in preference t o other types of fraction collectors, in order to eliminate pressure fluctuations during the distillation. The take-off tube of the still is jacketed down t o the tip located above the receivers. When necessary, warm or hot water is circulated in the jacket t o keep the fractions liquid. Graduated receivers collect fractions of de&red amount. Temperatures are measured with a mercury-in-glass therrnometer whose bulb is located just below thc collecting ring. It was calibrated t o an immersion depth of 3 inches ( i . 5 cm.) which corresponded closely to the vapor head ueually observed above the bulb level. The accuracy of the temperature readings for the range investigated is within about 2' F. Pressure measurements are made with a swivcl type of McLeod gage which %aschecked against a large 3lcLeod gage of standard design; good agreement in prcssure readings was obtained in the range of 0.01 t o 0.10 mm. mercury. In order to preclude compositional changes that might arise from prolonged heating, most distillations vere carried out a t pressures of 0.025to 0.040 mm. mercury, corresponding t o actual vapor temperatures of 180" to 350' F. A few comparable runs V~IP made at 10 0 mm. of nirrcurj-, with the aim of determining
%A' '
Several high boiling oils were used in the course of this work. Their preparation and description follow:
WHITE OILI was a highly refined mineral oil of U.S.P. grade. Its (atmospheric) boiling range, determined in the apparatua (Figure l ) , was about 620" to 907' F. It waa completely nonaromatic. WHITEOIL I1 was a highly refined mineral oil with a n (atmospheric) boiling range of about 570" to 800" F. It was completely nonaromatic. WHITEOILI11 was prepared by distilling white oil I1 in the above apparatus and selecting the first 83% of the overhead. Its (atniobpheric) boiling range was about 570" t o 780" F. The purpow of this separation was to prepare a completely nonaromatic oil whose distillation curve would match closely that of the aromatic oil described below and thus eliminate the difficulty of making comparisons that n-ould otherwise be introduced by that factor. BROAIATIC OIL was prepared from a heavy catalytic cycle stock containing about, 50% of aromatic hydrocarbons, as determined hy chroiiiatography on silica gel. Its (atmospheric) boiling range wa.s about 550" to 760" F. The original stock contained components with undesirably higli ultraviolet absorption in the 350 t o 400 n i p region. Since these would completely vitiate :malytical measurement of the polynuclear aromatic compound8 t o be dissolved in, and distilled from, the oil, the cycle stock was treated so as to reduce these interfering components. This waw done by heating the cycle stock with one fourth its weight of maleic anhydride for 7 hours a t 115' to 120" C. (2!8" I?.). Tho reaction products were hydrolyzed to form potassium salts, the latter were removed by water washing, and the residual oil was dried and iwovered in 95% yield. This product had a suitably low background absorption in the 350 to 400 mM spectral region. The high percentage recovery precluded more than a modest change in the original aromaticity. Table I gives distillation data for this oil in anticipation of later discussion, in order t o show how the aromaticity of the oil decreases in the coursc' of straight-path distillation.
INDUSTRIAL AND ENGINEERING CHEMISTRY
956
TABLE I. DISTILLATION I)AT.\ FOR Final
B.P.,
Fraction
O
Initial
F.
149 181 196 20 1 205 209 214 222 230 235 252 268
1 1
3
f 6
Q9 in 11
.
Residue
“ . \ R O ~ I A T I C 011.”
Refractive
Final .-it I l l .
Pressure, hlni. Hg
B.P., F.
0.11 0.05.5 0.05 0.043 0.038 0.040 0.040 0.030 0.028 0.030 0.031 0.040
541 61 1 639 648 660
~
684
672 895 708 713 737 7.51
..
.
~5 ; of Charge
.\Ioi,~
n ‘2
...
0 9 1 18 2 27 4 36.6: 45, I 54.6 63.6 72.3 81 1 89.6 98.3 99.3
1,‘52.24 1 5191 1 ,517% 1 51.53
272 278 290 305 312 327 340 350
1.5132 1.5110 1.5085
I Figure 2. Ijottcd
60
”/. OF CHARGE DISTILLED
80
-ZOO
Distillation of Solutions of 1,2,5,6-l)ihenz.anthracene in White Oil
C U N ~
is composite hoilinz point c u r v e for oil nncl three solutions
TETRIPHENYL SILICATE (.lndcrson 1,aborntories). This high boiling aromatic ester was uwd in sevrral runs to learn whethcr a given degree of aromaticity, produccd by niixing the polar ester with a nonaromatic oil, nould havc the Fame cffrct on the v o h tility of a dissolved polynuclvar aromatic hydrocarlmii as Ivoulil the samc degree of aromaticit?- oi petroleu~norigin Thc r,*t[,r as received was distilled in the :ipparntus, a n d a constant boiling cut was talirn xt 8 3 ” F. : i i i ( 1 0.15 mni. of niercury. L-ltrnviolct iibs(ir])tiF,ti(~* of the product a t 352 and 370 mp were’ fouiiii to he 0.00411 axid 0.00179, rcqcctivi~ly. Tlii’ (Englerj atmospheric boiling ]mint o i thc c’sti’r is reported to he 764@t o 766” F.(,-renedid not permit the attainment of the maxima
2 0.201 w
: I I
>
0.151
zg 1 ! a
t
0.101~
-
0
5
I
;
0.051-
1 J/-//
~~
0-
0.5
1.0
~
pound. Therefore, its volatility arid composition steadily change in tho course of distillation. ?;evertheless, the plots could be used for estimating approsimately the amount of a compound such as dibenzanthracene that would be distilled from a nonaromatic oil having a certain dibenzanthrarene ronc-rntratio~i and boiling range.
DE1’F:NDENCE OF VOLATILITY ON AROMATICITY O F OIL
3-I-
40
41 39
, . .
X
20
42
1’.4921
w
I(
40 4:i
1 4969
-
700
..
49
1,505; I . 5024
“00-
0‘
n-t.,yc l
hornatlcs
224 245 260 288
y/ i m
A,.~
I n d~e x ,
Wt,
Vol. 43, No. 4
1.5 2 .o 2.5 MOLE % DBA IN LIQUID
3.0
3.5
Figure 3 . \ apor-J,iquid Corriposi tion Ciirves f o r I .2,,6-Diheilzanthracenein White Oil Value.* iittaehecl to rt:r\cs rrpre-ent initial weight
pt:r
cent of added hydrocarbon
I
720
957
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1951
i
@ WHITE I OIL
0 AROMATIC
/
OIL
760
-0.5
-
I-
a
3
-0.4 c,
z
W
z
lAo
a
W
-0.301 > a
0.20
v)
#
X
w
,
560
,
-0.2
,\,@;kJ;/lloi a
m
i
0.05
WHITE OIL
a-D
5200
20
40
60
80
o/a OF CHARGE D I S T I L L E D
/"
looo
'
Figure 4. Distillation of 0.25% Solutions of 1,2,5,6Dibenzanthracene in Aromatic and Nonaromatic Oils
5200
Upper curve is composite boiling point curve for t w o oils
Figure 5.
20
in the concentration curves. Severtheless, the dependence of 3,4benxopyrene volatility on aromaticity of the solvent is readily apparent . The replotted curves of Figure 7 compare directly thc volatilities of 0.25w0 solutions of pyrene, 3,4benzopyrene, anti dibenzanthracene in the partially aromatic oil. The concentration of the added solute in the distillate increases as its boiling point is approached and then decreases, as it must, with progressively depleted concentration in the still pot. This is demonstrated for
80
CHARGE D I S T I L L E D
Distillation of 0.2570 Solutions of Pyrene in Aromatic and Nonaromatic Oils
pyrene, and can be assumed for 3,4benzopyrene and dibenzanthracenz. Associstionof the vapor concentration maxima with the boiling points of the additives will be further considered later.
690
IT>
-03
60
40
Ye OF
6S4
95
670
6,76
€93
691
7,OI
3 742
0.5-
0
r
PYRENE
v)
-0.4I-
3 0
z -0.3 2 -
N
m
a-0
c
/
Q W
8 0.2
-0.2
3,4-BENZOWRENE
:: 0.I
-0.1
OO 20
40
60
80
% OF CHARGE D I S T I L L E D Figure 6. Distillation of 0.25% Solutions of 3,4-Benzopyrene in Aroniatic and Nonaromatic Oils
20
60 80 % OF CHARGE D I S T I L L E D
Figure 7. Comparison of Volatilities of 0.25% Solutions of Pyrene, 3,4-Benzopyrene, and 1,2,5,6-Dibenzanthracene in Aromatic Oil
100
958
INDUSTRIAL AND ENGINEERING CHEMISTRY TaBLE
11. VOLATILITY OF
1,2,5,6-DIBESZ.4NTHR.iCENE IS WHITE ()IT., I S F L V E S C E D BY ADDITIOS O F T E T R A P H E K Y L sII,IC.kTE
evt‘r, a ronipariwii of coniparable boiling cuts on a Iveight basis, in the manner -1iown in Table 11, gives a c l o r all-
45
(Initial concentration of DBA = 0.23%) Av. Yo of Charge .IT..% oi Remaining DHA in ‘; IlI3.I i i i in Still Brill I‘rac tion
Vol. 43, No. 4
proximittion and s h o w that thc volat i l i t y of d i b e n z a n t h r a c e n e i n t h e /.,, / . ,, hynth~tic “aromatic oil” is roughl), half E’. , - i f K a o i i l t B I a n i.- obeyed. Hiid the above mixture may produce some if molar rather-than u-eight percentages are employed.) d Contains 63% tetraphenyl silicate. quantitative differences that would not e r o n t a i n s 69% tetraphenyl silicate. be predicted from mere comparisons of aromaticit) (4).This point, of course, is irrelevant as long as interest is restiicted to nonpolrir system3 entirely of petroleum origin. Fractions and Billvent Types
Atm. Boiling Range,
~
i;’:,!:
,,
,jf
I -
RELATIVE VOLATILITIES O F POLYNUCLEAR .iRO.\I.ITIC C O M P O U N D S IN O I L S
I
-0.7
-0.6
Although the distillation mixtures considered in this paper are niolecularly very complex, it is possible to treat them as quasibiriar?. systems, and to derive from t h c (lata v:~Iue.uof thv rvlative volatility, a, of the added polyniic~lear arumittic coiiipo.iii:I as defined b y the usual equation (I=
-0.5
(mole fraction of additive 111 vapor) X (mole fraction of additive in reqiduc) (mole fraction of oil in residue) iniole fraction of oil in v a a
v, I-
-0.4
2 z
a -0.3 8
-0.2
-0.1
I/,
5200
20
,
40 60
, 00
,
0
100
% OF CHARGE DISTILLED Figure 8. Distillation of 0.25% Solution of 1,2,5,6-Dibenzanthracene in a Mixture of Nonaromatic Oil and Tetraphenyl Silicate
However, it can be mentioned here that the agreemcmt I)c~tncsen the maximum and the boiling point is closcr, the m o w iicai.1)- thc system obeys Raoult’s IaLv, as is apparently the case for t l i c m o w aromatic oils. A further attempt to &udy the influence of aromatic components was made, using an equivoluminal mixture of whito oil I ani( tetraphenyl silicate as a synthetic “aromatic oil.” Figuro 8 shoivs distillation results for a0.2jwcsolution of c1ibcnzantlir:icene iii this mixture. The boiling range of the mixture \vas high eiiougll to provide a comparison of the behavior of dibenzanthracene in this system with that in white oil I alone. The best comparison could be made by determining from the original data value^ of rclative \-olatility on a mole fraction basis, in a manner to br. dr5rribed later. and to test the deviation from Raoult law behavior. How-
ivith wcoynition that the composition of the oil steadil). changes during the distillation process. Data werr obtained on the initial arid final boiling points, avcrage boiling point, arid refractive irides of each distillation fraction. In order to conserve space, most of these will not be reportr(1. -1single set of data and computed values arc given in typical illustration of the procedurr used i n finding relative volatility. The quantities dcsterniining CY for ewli fraction Jvr’re calculated as folloivs: The niolivxdar weight of the distilircl fraction \\-as obtained fi,oni thr. average boiling point and wt’ractive index hy means of established conversion ta1)les (2). Tlie mole fraction of additive in tile ,listillate fraction was calculated from the weight per cent of ahlditive present, its niolecwlar weight, and the molecular weight of the fraction. T h e weight of residuca a t the end of the cut was determined from thc original \\ caight o f the charge minus the accumulated weights of previously rrmovetf fractions. The n.eight of additive in the residue KHS detrrmined in like manner. These t n o values yielileti the ivcight per cent of additive in the rwitlue at the end of thc, cut.
’1
0
DISTILLATION AT 0.02-.03MM.HG
I
20
96 OF
40 60 CHARGE DISTILLED
80
J 100
Figure 9. Relative Yolatility of 1,2,5,6-Dibenzanthracene in Nonaromatic Oil and Effect of Distillation Pressure
April 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
:I ----O -"r
I e W H I T E OIL
959
1
m
.4
I
X
> I- - 0.1
a J0 I
>
40 >
J
w a
w
O"'
a
c
/
660
650
700 750 EXTRAP. ATM. B.P., OF.
800
1
Figure 11. Relative l'olatility us. Boiling Point for Solutions of Pyrene in Aromatic and Nonaromatic Oils
Figure 10. Relative Volatility us. Boiling Point for Solutions of 1,2,5,6-Dibenzanthracenein Various Oils
i
The average molecular weight of the residue a t the end of the cut d was determined, first by computing the weight average of the molc'rular weights of all fractions including the residue (this weight average being considered as the average molecular weight of the 4 "beginning residue" or initial charge). The average molecular 0 weight of the residue a t the end of each step in the distillation n-as > then calculated by determining the weight average of the molecular weights of the fractions removed after that point. The mole fraction of additive in the residue a t the end of each cut was V IL determined from the weight per rent of additive in the residue, WHITE O I L VAROMATIC OIL the molecular weight of the additive, and the average molecular weight of the residue. The average mole per cent of additive in I the still during the distillation of each fraction was determined 0.00,' ' 650 roo 750 800 from the average of the mole per cent of additive in the residue at EXTRAP. ATM. B.P.,'F. the end of the previous cut with that at the end of the specified Figure 12. Relative Volatility us. Boiling Point for Solucut. The mole per cent of oil in the distilled fraction was obtions of 3, %-Benzopyrenein Aromatic and Nonaromatic Oils tained kiy subtracting the mole per cent of additive in the fraction from 100. The average mole per cent of oil in the still during the rut wah calculated in a like manner from the average mole per cent of additive in the still during the cut. the crystals of this substance deposited in the take-off tube and Figure 9 s h o w how a for dibenzanthracene in white oil I varies were omitted from the last samples. as the oil is distilled. The results are given for two different disRelative volatility values 17ei-e determined for 0.1, 0.25, and tillation pressures, 0.02 to 0.03 and 10.0 mm. of mercury. T i t h i n 1.0% solutions of the polynuclear compounds in the various oils. this range there appears t o be no pressure effect; that is, the The results were found t o be independent of concentration, within dibenzanthracene undergoes the same degree of rectification a t the experimental error. The points for the 0.1 and 1.0% solutions tk%-opressures. were omitted from Figures 10 to 12 to avoid confusion. Figure 10 shows that log a increases linearly with the (atmosThe plot in Figure 10 appears, on first sight, to indicate that (Y pheric) boiling point for Polutions of dibenzanthracene in white oils for dibenzanthracene is the same, a t a given temperature, for white I and 111,regardlessof thrconcentration of dibenzanthracenein the oils as for the 50% aromatic oil. However, the concentrations of still during the distillation of the various fractions and regardless dibenzanthracene were too small to analyze in the latter case, until of the differences in boiling range of the two white oils. The same the distillation had reached an advanced stage; at,this point the olwervations apply to solutions of pyrene in these oils, as Figure 11 shows. I n t.he VOL4TILITY D ~ T FOR A 0.25% BENXOPYRESE I N W H I T E OIL 111 T.\BLE111. REI..ITIVE latter case. the a values suffer AV. 4V. in reliability above the boiling Mole % Mole % Mole To Final ResidMol. Oil. i n point of pyrene (about TOO" F.), Atln, ual lvt, of Healdue a t E n d of C u t i t ' z i i Residue since the concentratioiis of this B.P.. Wt., FracFracAv. TVt. % Mole % d u r i n g in during rraction F. Grains tion tion inol. w t . BzPy BzPy Cut Fraction Cut OI hydrocarbon become small a t Initial 573 200.00 ... 317 0.2600 0,314 the higher temperatures, as 99:9926 99.668 0.OZi 0.0074 322 0 . 2 7 3 8 0 350 0,'diZ 1 637 182.15 Pi5 already pointed out. illso, the 99.629 0.0341 0.371 99,9873 0,0127 323 0,3031 0.391 2 661 163.88 291 0.417 99.9833 99.583 0.0398 145 62 301 0.0167 328 0,3394 0.442 3 669 last two points shoivn in Fig99.526 0.0430 0.474 99.9795 127.54 308 0.0205 331 0,3831 0.506 -1 673 99.461 0,0455 99,9749 0,549 334 0.4463 0 . 5 9 1 109.23 312 0.0351 J 673 ure 10 for dibenzanthracene in 99.349 0.0544 99.9644 0.651 6 682 337 0,5306 0,710 90.80 318 0.0356 white oils diverge from the 99.304 0.0657 99.9510 0.696 73 00 320 0.0460 341 0 6518 0 . 6 8 2 7 686 99,083 0.0633 99.9415 0.917 5.5.11 324 0.0585 346 0.8461 1.151 8 695 correlation line. This is due 98.569 0.0803 99.8835 1 . 4 3 1 1 . 7 1 1 0,1165 353 1 . 2 2 2 9 704 36.83 333 730 18.25 341 0,321 366 2.226 3.237 2.474 99.670 97.526 0.127 t o anal)-tical error arising from 772 2.83 365 1.64 368 6.63 9.68 6.45 98,360 93.55 0 242 ... . . ... ... the low solubility of dibenz. . ... 368 ,.. .. ,.. . . 12 authracene in the oil; some of
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INDUSTRIAL AND ENGINEERING CHEMISTRY
oil fractions had become considerably more paraffinic (Table I) and no conclusions could be drawn. On the other hand, the lower curve in Figure 10 for the solution of dibenzanthracene in the mixture of white oil and tetraphenyl silicate shows that 01 for this system has an increasing tendency to fall below that for the white oil system &s the temperature is increased. Analysis of the fractions showed that, with increasing temperature of distillation, the fractions became progressively richer in their ester content or aromaticity. Because tetraphenyl silicate has a sharp boiling point, it is nearly completely removed late in the distillation, a t which point the relative volatility of dibenzanthracene rapidly reverts t o its value in white oil. This explains the abrupt discontinuity shown in Figure 10. Therefore it can be concluded that dibenzanthracene has a higher relative volatility in the nonaromatic oil than in a mixture of this with an aromatic compound, and the difference in volatilities increases with aromaticity. The above type of ambiguity does not appear in the pyrene ant1 3,&-benzopyrene plots shown in Figures 11 and 12. Here it is clearly seen that, in the earlier stages of distillation, a is considerably less for the aromatic oil. Later in the distillation, at which stage the fractions become less and less aromatic, the CY curves tend to merge with the corresponding a curves for white oil. I t follows from the figures that a for a completely aromatic oil will be roughly one third that for a completely nonaromatic oil. This means that, in order to distill a given amount of a dissolved polynuclear aromatic hydrocarbon, of the types considered, from the former oil, the (atmospheric) distillation temperature would have to be roughly 50' F. higher or perhaps morc'. depending on the error in the above ratio. BOILING POINTS OF POLYNUCLEAR ARO.MATIC COMPOUNDS
Scarcely any boiling point values can be found in the literat,urtL for aromatic compounds more complex than pyrene, even though such information would be of considerable usefulness to a better understanding of the distillation behavior of such compounds. In the absence of vapor pressure data for the latter, it is possiblc to estimate boiling point values from the a plots discussed above. If a line is drawn paraliel to the logarithmically plotted 01 line for whitc oil, but displaced below the latter by an amount equivalent to a reduction of tKo thirds in the value of a, the resulting graph should represent approximately the teniperature dependence of the volatility of the dissolved hydrocarbon in a completely aromatic oil, for reasons described above. Estrapolation of this line to a unit value of a should give a reasonably good boiling point value, unless there is a marked departure from Raoult's law for the hypothetical, completely aromatic system. The boiling point of pyrene thus obtained is i l 5 O F., compared with reported values ranging from 700" to 759' F. ( 1 , S , 8 ) . The boiling points of 3,&-benzopyrene and dibenzanthracene are similarly estimated to be 860" and 870" F., respectively. No comparable literature values are available for these two compounds; however, values higher than that for pyrene would be expected on the basis of larger ring number. Khile these limited examples will not permit a general recommendation of the method, the latter may prove
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useful for estimating boiling points in the many instances where directly measured values are either unavailable or difficult to determine by conventional means. Vapor pressure measurements currently being made in this laboratory on polynuclear hydrocarbons may serve to establish the degree of reliability of the indirect method. CONCLUSION s
The relative volatility of 1,2,5,6-dibenzanthracenein dilute solution in white oil is independent of the distillation pressure, a t least in the range from 0.03 to 10 mm. mercury. The relative volatilities of pyrene, 3,4-benzopyrene, and 1,2,5,6dibenzanthracene are higher in nonaromatic petroleum oils than in oils containing a substantial proportion of aromatic components. A linear relation is found between the (atmospheric) boiling point of a nonaromatic petroleum oil and the logarithm of the relative volatility of an added polynucleaz aromatic compound. The concentration of pyrene, 3,4benzopyrene, or 1,2,5,6dibeneanthracene in white oil distillation fractions can be estimated from established plots of relative volatility against boiling point, provided the boiling point and concentration of the polynuclear aromatic hydrocarbon in the mixture are known. As an approximation, the relative volatility of polynuclear aromatic: compounds of the above type is about half as large in an oil of 5070 aromaticity as in a nonaromatic oil; in a completely a r e matic oil the relative volatility is about one fourth to one third L L ~ large as in a nonaromatic oil. Corresponding to these reductions in reIative volatility it can be estimated that, in order to obtain equal amounts of the polynuclear compound in the distillates, the (atmospheric) distillation temperatures required are a t least 30" and 50' F. higher, respectively. Ak method is described for tentatively estimating the boiling point of a polynuclear aromatic compound from relative volatility data on distillation fractions of an oil used as the solvent for such a compound. The estimated boiling points of pyrene, 3,4-benzopyrene, and 1,2,5,6-dibenzanthracenewe 715', 860°, and 870" F., respectively. ACKNOWLEDGMENT
The authors are pleased to acknowledge the aid of R. C. Arnold and M. F. Maher, who carried out many of the distillations and analytical determinations. They are also grateful to H. G. 31. Fischer for his continued interest and valuable suggestions, and to a number of other associates for their comments. LITERATURE CITED
Decker, H., Ber., 67, 1636 (1934). Fenske, h l . R., private communication. Fittig, R., and Gebhard, F., Ber., 10, 2141 (1880). Hibshman, H. J., IND. ENCI.CHEW,41, 1366, 1369 (1949). ( 5 ) Johnston, L. H., U. S.Patent 2,335,012 (1943). (6) Maxwell, J. B., "Data Book on Hydrocarbons," p. 40, Ken. l-ork, D. Van Nostrand Co., 1950. (7) Perry, E. S.,and Fuguitt, R. E., IND.EKG.CHEY.,39, i s 2 (1947). (8) Pier, h f , , FIAT Report PB 74882.
(1) (2) (3) (4)
RECEIVED May 3, 1950.
* * * * * Some of the analytical methods used at the Esso Laboratories of the Standard Oil Co. in their work on the properties of high boiling petroleum products (page 934 of this ussue) will be described in "Physical and Chemical Characterization Studies with Relation to Polynuclear Aroniatic Components," by C. G. Wanless, L. T. Eby, and John Rehner, Jr., to be published in the 4pril issue of Analytical Chemistry. The characterJzatian methods are useful in studying refinery processes such as thermal and catalytic cracking, and physical and chemical methods for processing refinery streams containing high boiling products. They are also useful for examining the product behavior of tars, lubricating oils, asphalts, waxes, and residues. Both of these current papers are parts of a broad iniestigation of high boiling petroleum products which has been conducted by Esso Labot atories with the cooperation of other interested groups during the past several years.
