INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1948
zation from 1.0 down t o 0.07 weight % sulfur is believed to involve the hydrogenation and splitting of heterocyclic rings containing sulfur; the analyses indicate t h a t the proportion of aromatic rings decreased from 15 to 11 weight yo without a corresponding increase in naphthene rings. Destruction of rings is likely t o be more effective than saturation in improving the cetane number of Diesel fuel (Table V). It is anticipated t h a t added hydrogenation of the West Texas gas oil t o saturate the remaining aromatics would give only a further small increase in cetane number. The relatively high bromine numbers of the virgin feed and hydrogenated product are believed due in large part to addition of bromine t o aromatic nuclei rather than t o the presence of olefinic linkages.
1273
CONCLUSIONS
Diesel fuels in the range of 80 cetane number having pour points of 25' F. may be produced from paraffin wax feedstock by high pressure hydrogenation. Petrolatum, petroleum foots oil, virgin paraffinic gas oils and synthetic (Fischer-Tropsch process, iron catalyst) gas oils may also be used as feedstocks t o the hydroKenation process for the manufacture of Diesel fuels having 70 t o 80 cetane number. Destructive hydrogenation is shown t o be superior to either thermal or catalytic cracking for the production of Diesel fuels from paraffinic feedstocks. LITERATURE CITED
TABLE VI. COMPOSITION CHANGES DURING HYDROGENATION OF (1) Am. Soo. Testing Materials, Designation D613-43T, tentative WEST TEXAS LIGHTGASOIL Untreated Cetane No. (estd.) Gravity 'A.P.1. F. Aniline boint Bromine No.,' cg./g. Refractive index, ny Specific dispersion (F-C) Aromatio rings wt. % Naphthene rinks. wt. % Acyolioa and side chains, wt. 7% Carbon wt. % Hydroien, wt. % Sulfur, wt. %
Hydrogenated
127 15 16
,'
117 11 17 72 86.4 13.3 0.07
09
86.0 13.0 1.0
CETANE NUMBER AGAINST POUR POINT
Figure 3 illustrates the pour point characteristics of several types of Diesel fuels in relation to their estimated cetane number values. It is clearly indicated from the results plotted in the figure t h a t the product derived by hydrogenation of crude scale wax is superior in quality to the Diesel fuel made by thermally cracking the same feed stock. The Diesel fuel produced by hydrogenation of petrolatum is above 70 cetane number at the 25 O F. pour point level, but is not as good as either the hydrogenated or thermally cracked fuel made from crude scale wax. This is attributed t o the fact t h a t the petrolatum feedstock is higher in oil content than the crude scale wax and may contain some naphthene hydrocarbons which would adversely affect the cetane number.
standard, issued 1941, revised 1943,1947.
(2) Blackwood, A. J., and Cloud, G. H., SOC.Automotive Engrs.
Trans., 46,49-53 (1940). (3) Brown, C. L., and Tilton, J. A,, OiZ Gas J., 36, No. 46, 74-7 (1938). (4) Brown, C. L., Voorhies, A,, Jr., and Smith, W. M., IND. ENG. CHEM., 38,136 (1946). (5) Burk, F. C., Cloud, G. H., and Aug, W. F., S.A.E. Trans., 53, 166-76 (1945). (6) Deanesly, R. M., and Carleton, L.T., IND.ENQ.CHEM., ANAL. ED., 14,220-6 (1942). (7) Griep, E.F., andGoddin, C. S., S.A.E. Trans.,54,436-48 (1946). (8) Keith, P. C., Oil GasJ., 45, No. 6,102, 105, 107, 108, 111, 112 11946). (9) Mur'phree, E. V., Brown, C. L., and Gohr, E. J., IND. ENG. CHEM., 32,1203 (1940). (10) Murphree, E. V., Gohr, E. J., and Brown, C. L., Ibicl., 31, 1083 (i939). (11) Petrov, A. D., BUZZ. Aca. Sci. (U.R.S.S.), 145, 533 (1941); Universal Oil Products, SFPL, T346 (1942). (12) Shoemaker, F. G., and Gadebusch, H. M., S.A.E. Trans., 54, 339-46 (1946). (13) Small, L. F., S.A E. Trans., 52, No. 8, 17-19 (1944). (14) Ibid., p. 198-201, 224. (15) Vlugter, J. C., Waterman, H. I., and Van Westen, H. A., J . Inst. Petroleum Technol.,21,661 (1935). (16) Voorhies, A., Jr., Smith, W. M., and Hemminger, C. E., IND. ENQ.CHEM.,39, 1104-7 (1947). RECEIVED May 3, 1947. Presented before the Division of Petroleum Chemistry a t the 111th Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantio City, N. J.
Physical Properties of BenzeneMethanol Mixtures G . C. WILLIAMS, S. ROSENBERG, AND H. A. ROTHENBERG University of Louisville, Louisville, Ky. Data and curves are presented for densities, refractive indices, boiling points, specific heats, heats of mixing, and enthalpies of boiling liquid and saturated vapor for the azeotropic eystem, benzene-methanol. Results approximately confirm the reported position of the azeotrope, but indicate that the maxima and minima for other properties are at other compositions.
F
OR a cynsiderable period of time, numerous data, correlations, and statistical methods for predicting physical property values of pure liquids and solutions have been recorded in the literature. This compilation is a laudable and necessary function of the literature, and its value i s recognized by all technical men. However, frequently the specific data most
urgently needed for normal problems that arise i n scientific investigations either have been neglected or are sketchy and incomplete. This condition was encountered by the authors when an azeotropic mixture was sought with its physical properties already completely described. Because no such information was available, the opportunity and need for $he experimental determination were presented. The azeotropic system benzene-me thanol employs a oyclio hydrocarbon and a n aliphatic alcohol. These substances differ so much from one another in nature t h a t normal rules of true solutions may be completely disregarded,' and experimental determinations of physical properties are almost a necessity. Discontinuities, maxima, minima, and inversions may be expected; and the system has been reported t o have an azeotropic point at around 38.6 mole % benzene (9).
INDUSTRIAL AND ENGINEERING CHEMISTRY
1214
Vol. 40, No. 7
154
1.50
x
g 1.46
-z
$ 1.42
+
::
a 1.38 U
w
0:
1.34
0 PER CENT BENZENE
Figure
1. Densities of RenzeneMethanol Mixtures
I3'O
20 40 60 00 PER GENT BENZENE
Figure 3. Refractive Indices Benzene-Methanol IIixtures
100
100
of
W
z
:80
Curve A is the derived relationship which may be obtained by the use of Figure 2, volume us. mole compositions of benzene-methanol mixtures, and presents the density us. mole per cent of benzene. The volume vs. mole relationship for the benzene-methanol mixtures (Figure 2) was used frequently for conversions.
vs. volume per cent benzene.
2
w m
5 60 w
0
$40 n
w
4 20
REFRACTIVE I ~ D I C E S
A
0
> ' 0
20 40 60 80 100 MOL PER CENT BENZENE Figure 2. Volume os. Mole Compositions of Benzene-Methanol Mix tures RAW MATERIALS
BENZENE. The benzene was of reagent grade, thiophene-free, and water-white. I t was subjected to three successive distillations in a glass-packed Pyrex laboratory column, and in each of the distillations 20% of the charge was discarded in head and tail cuts. The final liquid was retained in a Pyrex bottle closed with a foil-wrapped cork stopper. METHAKOL.The methanol was of C.P. grade and water-white. It was purified by successive distillations similar t o those used with benzene, and was held in a Pyrex bottle closed with a cleaned rubber stopper. The final products in each case had a boiling point range of less than 0.05 C. and were considered to be of high purity. DENSITIES
A Westphal balance was used for the determination of these data. Mixtures were made up in 0 to 100 volume per cent, in 100cc. samples, and were held in a 25" C. thermostatic bath both prior to and during the density determinations.
The samples prepared for the density data xere further analyzed with an Abbe refractometer. The temperature of the refractometer was maintained a t 25" C., and readings were made of successive samples until three were obtained within 0.0003 unit. The arithmetic averages of the three values &re reported in Table I, and are presented graphically i n Figure 3. Curve B gives refractive indices a t 2.5' C. zs. volume per cent benzene, and curve A gives the value as a function of mole per cent benzene. BO1 LING POINT DIAGRAM
The boiling point diagram was determined by a combination of methods, each used i n the range where it would give the highest degree of accuracy. The Othmer apparatus (4)was employed for the major portion of the data (Table 11, -4) and was used for the full range of compositions; but i t was evident that in the high benzene regions, the shape of the dew point curve made a high degree of accuracy improbable by this technique. Over this portion of the diagram, therefore, a differential dibtillation procedure was used and a vapor temperature cs. condensate composition relationship was obtained which was highly reproducible.
Data are presented in Table I and shown graphically in Figure 1. Curve B is that obtained from the original data-i.e., density
INDICES OF BENZENETABLE I. DENSITIESAND REFRACTIVE METHANOL MIXTURES Volume yo Benzene 0 10 20 30 40 50 60 70 80 90 100
kola
Vo
Benzene 0 4.81 10.21 16.29 23.28 31.25 40.60 51.50 64.50 80.10
100
Density at 25' C.
Average nn at 2 5 O C.
0.78G5 0,7960 0,8040 0.8128 0,8230 0,8320 0.8410 0,8495 0,8576 0.8683 0.8724
1.3264 1,3429 1.3595 1.3765 1,3942 1.4121 1.4296 1.4471 1 ,4640 1.4809 1.4967
0
Figure 4.
MOL PER C E N T B E N Z E N E Boiling Point Diagram of Benzene-Methanol 3Iixtures
July 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
1273
EQUILIBRIUM DATAFOR BENZENETABLE 11. LIQUID-VAPOR METHANOL MIXTURES Temp., "C.
Average n of VaporD
78.00 77.60 67.20 -. 62.85 62.80 60.80 59.80 59.30 59.20 58.70 58.60 58.50 58.30 58.00 57.80 57.70 57.50
1.4931 1.4791 1.4557 1.3450 1.4429 1.4395 1.4285 1.3952 1.3978 1.4359 1.4349 1.4069 1.4340 1.4311 1.4280 1.4160 1.4216
A. *
a
B.
Figure 5.
78.6 78.5 78.3 78.0 77.6 77.1 76.1 74.4 72.4 69.7 67.1 63.1 61.4 58.0
Equilibrium Diagram for BenzeneMethanol System
Average n of LiquidD
Mole % Benzene in Vapor
Mole % Benzene in Liquid
B y Othmer Apparatus
*
1.4972 1.4970 1.4947 1.3301 1.4908 1,4880 1.4564 1.3570 1.3610 1,4861 1.4910 1.3740 1.4830 1.4660 1.4770 1.3957 1.4190
95.5 79.0 57.7 8.0 47.5 50.5 43.0 26.5 28.0 44.3 42.5 31.5 43.0 41.5 42.8 36.1 39.0
By Di fferential Distill ation Method
... ... ... *.. ... ... ... ... ...
... ...
... ... ...
...
... ... ... .
.
... ...
I
... ...
...
TABLE111. SPECIFIC HEAT DATA FOR BENZENEMETHANOL MIXTURES Temp., OC 30
Concentration,
Specific Heat Cal./G., C.'
vel. % C6H6
10 10 10 20 20
0 PER CENT BENZENE BY VOLUME
..
50 30 40 50 30 40 50 30 50 30 40
Figure 6. Effect of Temperature and Composition on Specific Heats of Benzene-Methanol Mixtures
Two liters of benzene-rich charge were placed in a jacketed flask, heated by a hot water bath, and the solution was brought to a slow steady boil under total reflux. Product was then removed at a slow but steady rate and a t intervals 1-cc. samples were caught and analyzed, while the temperature was noted. It was previously established that a removal of this volume of distillate was accompanied by no noticeable increase in temperature. When the volume of still pot liquor decreased to 1950 ml. or when the removal of 5 cc. of dttillate increased the temperature by over 0.1 C., the experiment was stopped and a new mixture made. Data as presented in Table II,B, represent the results of six independent runs. This procedure can establish only the position of the dew point curve, but the g-140 bubble point curve is adequately fixed by the I Othmer apparatus data. a Figures 4 and 5 relate liquid and vapor compositions on both the normal boiling point diagram and the conventional X-Y equilibrium relationship.
50
30 40 50
40 40 40 50 50 50 60 60 60 70 70 80
0.643 0 525 0.561 0.605 0.534 0 555 0 574 0.480 0.556 0.483
80 80 90 90 90
0.502 0.530 0.444 0.473 0.491
w p-'oo v)
5- 6 s
SPECIFlC HEATS
Specific heat data were obtained on mixtures of the benzene-methanol system by a method involving heating the mixtures in an vatuum bottle with a n electrical resistance source of
0
Figure 7.
IO
20
30 40 50 60 MOL PER CENT BENZENE
70
80
, 90
100
Heat Evolved in Isothermal Preparation of 1 Mole of Benzene-Methanol Mixture at 25' C.
1276
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. '7
obtained were the enthalpies of 1 mole of mixture as boiling liquid, above a datum plane of the same mixture a t 25" C. These values were calculated by a graphical integration of the specific heat LS. temperature curves for the mixtures between the 25' C. datum plane and the boiling point for the specific mixture. The series of curves used for these calculations are shown in Figure 8, although they were enlarged for the measurements. The values, as calories per gram of solution were converted t o a basis of a mole of solution, and are plotted as curve B i n Figure 9. Curve A represents the conversion of the datum plane t o that of pure liquids at 25" C. by the inclusion of the heat of mixing data.
TEMPERATURE-
OC.
Figure 8. Construction Curves for Enthalpies of Benzene-Methanol Mixtures
heat supply ( 5 ) . The data for the pure substances were taken from the literature ( d ) and the pure substances were used in the calibration of the apparatus. The complete data are presented i n Table 111; the results are shown i n agreement with themselves, and follow the extrapolated points for the pure substances very well. The accuracy is indicated also by the manner in which t h e smoothed data from Figure 6 fit into a family of curves used subsequently for enthalpy calculations i n Figure 8. The specific heats of the mixtures are not arithmetic averages of those of the components on either a volume, mole, or weight per cent basis, although closer to t)he mole relationship than to the others. HEAT OF MIXING
When benzene and methanol are mixed, the reaction is endothermic, although t o a relatively small degree. The heat of mixing-i.e., heat evolved on mixing--for this system wan measured by mixing the ingredients t o a n approximate total volume of 150 ml. i n a calorimeter, and measuring the amount of electrical energy necessary t o make the system regain i t s original temperature. All ingredients were a t 25" C. The heat of mixing, per mole of mixture, is given i n Figure 7, and experimental points are included. The maximum heat effect is not in the vicinity of the azeotropic point, although the data are insufficient t o place the point, with extreme accuracy. ENTHALPY
The enthalpies of the benzene-methanol mixtures were calculated from the data previously presented by employing some assumptions which are normally acceptable. The first values
ab 60 710 60 PER CENT BENZENE I
Godo Figure 9.
Ib
20
30
MOL
40
90
A0
Molal Enthalpies for Boiling Mixtures o f Benzene-Methanol
Enthalpies per mole of mixture as saturated vapor at the boiling point and relative t o the pure liquids at 25' C. are presented in Figure 10. These values were obtained by the method suggested by Dodge ( I ) wherein the assumption was made that the specific heats of the gaseous mixtures were an arithmetic average of the molal values for the two components, and that the values were constant over a range of 20" C. near the boiling points. This is a valid assumption, as i t has been shown (3)that the materials normally act as almost perfect gases in this range. It is noticed that the minimum in the enthalpy curve €or the gaseous mixtures is close to the azeotropic composition. This condition could not have been predicted by the boiling liquid enthalpy curves and the relative latent heats of vaporization for the two components. Latent heats of vaporization for mixtures niay be obtained by subtracting the corresponding vapor and liquid enthalpy curve values. ACKNOWLEDGMENT
The authors wish t o thank T. M. Clapham for his laboratory assistance on the heatv of mixing for t,his project. LITERATURE CITED
(1) Dodge, B. I?.,
"Chemical Engineering Thermodynamics," pp. 651-2, New York, McGraw-Hill Book Co., 1944. (2) International Critical Tables, New York, McGraw-Hill Book Co., 1933. (3) MacDougall, F. H., "Physical Chemistry," p. 88, New York, Macmillan Co., 1944. (4) Othmer, D. F., IND.ENG.CEIEM., 20, 743
MOL PER CENT BENZENE
Figure 10.
Molal E n t h a l p i e s f o r S a t u r a t e d M e t h a n o l Mixtures
(1928). (5) Williams, G. C., Ibid., 40, 340 (1948).
Vapor of BenzeneRECEIVED February 24, 1947.
