Effect of Solvent Extraction on Aromaticity of Lubricating Oils The importance of aromaticity as a characteristic oil property is discussed. It is suggested that the progressive improvement attained on solvent extraction may be measured by the change in aromaticity. For rapid determination of aromaticity the specific dispersion, a function of optical dispersion and specific gravity, is proposed. The principle and the advantages of this constant are discussed, and specific dispersion values are correlated with chemical constitution, viscosity index, carbon residue, and oxidation stability of successive extraction stages on several types of oils. 0.H. V O N FUCHS A N D A. P. ANDERSON HE chemical constitution fore, a characteristic property of Shell Petroleum Corporation, Wood River, 111. of petroleum lubricating oils an oil. The purpose of this paper is to describe a rapid means of deis regarded as being made termining aromaticity and to show its relation to other oil up of three types of hydrocarbons-paraffinic, naphthenic, properties, particularly in connection with the measurement and aromatic. The difference between various types of oils of the improvement attainable on solvent extraction. is due not to different types of constituents but to variations ~in their relative ratio. The aim of solvent extraction is to Aromatics by Usual Methods change this ratio, separating the less desirable from the desirable constituents- by physical means. The conventional analytical methods of determining aroFor identification and classification of lubricating oils, the matics, involving repeated extraction with sulfuric acid or present practice is to use gravity, viscosity index (5), vissome solvent such as furfural, require considerable skill, cosity-gravity constant (6), viscosity slope number (W), reconsume an excessive testing time, and are not very accurate. fractive index, etc. These properties are more or less unrelated Moreover, they are entirely empirical and do not allow of a to each other and are a t best only of empirical value. A discrimination between purely aromatic molecules and molephysical constant related t o the chemical constitution mould, cules of a mixed type. therefore, be of great value as a characteristic of lubricating The critical solution temperature in aniline (aniline point) oils. is a widely used rapid method for estimating aromatic conAmong chemical constituents, the aromatics are the least tent. However, the aniline point is affected not only by arodesirable and the ones most generally removed on refining. matics but, in a lesser degree, also by naphthenes and by the The term “aromaticity” is used here to indicate the nature average molecular weight of all constituents, including paraffins. Because of unavoidable and unpredictable changes in and extent of the aromatic character of a lubricating oil. On refining, the aromatic content of an oil decreases in procharging stock, the aniline point of the raffinate will also flucportion to the improvement attained. Aromaticity is, theretuate, making the whole test uncertain or even meaningless.
T
319
320
INDUSTRIAL AND ENGINEERING CHEMISTRY
In the Waterman method (11) the percentage of carbon atoms present as members of aromatic rings is determined. This is done either (a) by hydrogenating the oil tested to convert all aromatic rings into naphthenic rings, determining the aniline points before and after hydrogenation, and multiplying their difference in degrees Centigrade by an empirical factor, or ( b ) by estimating the rise in aniline point upon hydrogenation by means of a chart based on the correlation between molecular weight, aniline point, and specific refraction. Both methods are slow and require considerable sliill.
VOL. 29, KO. 3
influences the value of the specific refraction and since the molecular weight changes on extraction, the method is not generally applicable.
Aromatics by Specific Dispersion
The difference between the specific refractivities for lights of different wave lengths is called the “specific dispersive power” or “dispersivity.” The value of this constant depends on the two wave lengths chosen but is practically independent of temperature and molecular weight. According to Bruhl (3), dispersivity is preeminently a constitutive property. Conjugated double bonds, for instance, raise the specific dispersion above that calculated from TABLEI. PHYSICAL PROPERTIES AND CHEMICAL COMPOSITION OF VARIOUS OIL the dispersive constants for the two double bonds. TYPESSOLVENT-EXTRACTED TO THE SAME AROMATIC CONTENT This exalting effect of structure on specific disOil 8. A. E. 40a -Oil S. A. E.20”persion is remarkably great in case of the aro1 2 3 4 5 2 3 4 5 matic compounds. Cr., A. P. I. 29.4 28.8 28.6 23.8 23.0 31.4 29.9 26.7 25.4 Darmois (4) pointed out the difference which 627 581 793 948 183 Viscosity, 100’ F. 666 196 192 170 71 65 72.6 64.0 45.0 43.9 44.1 43.1 Viscosity, 210’ F. 76 exists between the specific dispersion values of 99 86 107 Viscosity index 54 33 85 92 67 33 Viscosity-gr. condifferent groups of hydrocarbons. 0,800 0.806 0.810 0.843 0.853 0.803 0.816 0.839 0.860 stant The s a t u r a t e d (paraffinic and naphthenic) 260 228 235 274 247 263 257 Viscosity slope No. 269 278 Sp. gr., 20/4” C. 0.8761 0.8807 0.8832 0.0069 0.9117 0.8654 0.8730 0.8906 0.8980 hydrocarbons have nearly the same specific disRefractive index, persion values which are independent of the 1.4856 1.4862 1.4870 1.4968 1.4990 1.4779 1.4810 1.4881 1.4917 200 c. 0.3275 0.3261 0.3256 0.3225 0.3221 0.3270 0.3260 0.3236 0.3229 Sp. refraction molecular weight and of structural differences. 115.9 110.3 107.8 98.9 94.0 102.0 95.8 89.7 86.0 Aniline point 494 450 463 406 378 Mol. weight 358 336 327 311 The introduction of one double bond or several 24 29 32 44 47 29 35 48 48 Rings % conjugated bonds increases the specific dispersion 2.5 3.0 3.0 Rings7mol. 2 0 2.5 1.8 2.0 2.5 2.5 Aromatic rings/ values stepwise. 0.3 0 4 0.3 0.3 mol. 0.4 0.2 0.2 0.2 0.2 Darmois also reported the specific dispersion Para5ns, % 76 71 69 56 53 71 65 55 62 26 40 Naphthenes % 20 26 43 26 31 41 44 of benzene to be very high and showed the 5 4 Aromatics, % 4 4 4 3 4 4 4 systematic decrease of this value for the higher a 1, Pennsylvania: 2, Midcontinent; 3, West Texas; 4, California; 5, Gulf Coastal. benzene homologs, but no data for condensed ring systems were shown. It is interesting to commre mecific dimereion The viscosity index, viscosity slope, or viscosity-gravity data and the data on u1trav;olet absbrptiLn. Accorhing to constant is affected not only by the aromatic content but also the theory of dispersion, a relation should exist between them, by the amount and tjhenature of the naphthenic and paraffinic the increase of refractive index (dispersion) pointing to an components of the oil and by the molecular weight. They approach to an absorption band. The paraffins and naphare, therefore, unsatisfactory unless the source of the crude thenes, both of which have a low dispersion, only show aband the approximate viscosity are known. There is also no sorption very far in the ultraviolet (wave length smaller than direct relation between these properties and the stability to about 2000 i.). oxidation, as is evident when we compare an unrefined Benzene and its derivatives, however, show a system of abPennsylvania type oil with a refined oil of a lower viscosity sorption bands in the range from 2300 to 2700 e., much index. nearer to the visible-and this is accompanied by a steeper Among optical methods, the refractive index is most comincrease of the refractive index-i. e., by a higher dispersion. monly used. This constant is, however, also influenced both Polynuclear aromatics show other systems of bands nearer by naphthenes and aromatics and, furthermore, by the to the visible spectrum and again much higher dispersions. temperature and the molecular weight of the oils. Table I Ward and Fulweiler (14) used specific dispersion to difshows the difference in refractive index for different types of ferentiate between different series of hydrocarbons and sugoils extracted to the same aromatic content. The extremes gest the use of specific dispersion as a check on other methods. for S. A. E. 40 oils show a difference of 0.0134 unit of refractive Vlugter (9) and Waterman (16) used the specific dispersion index, and for S. A. E. 20 oils, a difference of 0.0138 unit. to determine whether, on hydrogenation, all aromatic rings The differences between the same crudes for S. A. E. 40 and were completely converted into naphthenic rings, and recently 20 oils average 0.0076 unit, showing the effect of viscosity published with van Westen an article (12) dealing with the alone. The other properties, such as aniline point, etc., also properties of this physical constant. The constant is applied give wide variations. The chemical composition of these to determining the absence of aromatics in white oils and in oils was determined by the Waterman method (11). hydrogenated oils. The specific refraction as calculated from the refractive Since two of the constituents of lubricating oil (paraffinic index and the specific gravity, either by the Gladstoneand naphthenic) have nearly identical specific dispersion Dale (n)formula or from the Lorenz-Lorentz (n2)formula is values, and since unsaturated compounds are, for practical useful in connection with the molecular weight to estimate purposes, absent, the specific dispersion could be used to the ratio of paraffins and naphthenes in oils free from aroestimate the aromatic constituents of lubricating oils. This matics. I n the Waterman method (IO), the Lorenz-Lorentz method has been used by the writers for some time. or n2 formula is used. The specific refraction of both the The formula n/d generally used for the specific dispersion paraffins and aromatics is high, while that of the naphthenes is derived from the Gladstone-Dale or n equation for specific is low. Removal of aromatics (with their paraffinic side refraction as follows: chains) increases the ratio of the naphthenes and lowers the n - 1 y=specific refraction. On successive extractions the specific d nB-1 ne-1 nB-ne=pn refraction should pass through a minimum value at the time ‘6 ra = ____ d all the aromatics are extracted. Since the molecular weight d d d L
-
w.4.
,
MARCH, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
where rg, ra = sp. refraction values ng, nu = refractive indices for p and a lines of the hydrogen spectrum d = density at temperature at which refractive indices were determined I n order to obtain more convenient figures, the value of the specific dispersion is multiplied by lo4. While theoretically the difference between the refractive indices of any two spectrum lines could be used, in order to obtain comparable figures, the refractive indices of either the p and a or of the y and a lines of the hydrogen spectrum are used. Since the hydrogen y line (G’) cannot always be seen clearly even when only light yellow substances are being investigated (8), in more recent research work the hydrogen p (F) spectrum line has often been substituted and, consequently, He - Ha(ng - ne) taken as a measure of dispersion. The dispersion tables of the Abbe refractometer are based on these latter two spectrum lines. The approximate difference of the two refractive indices for hydrogen p and a lines can be estimated with the Abbe refractometer. The limit of accuracy of the Abbe refractometer is two units in the fourth decimal of the refractive index and three dispersion units. Its advantage is that white light can be used. The dispersion is estimated from the relative angle of the two Amici prisms a t which the color fringe of the line of total reflection disappears. For more accurate dispersion measurements, it is necessary to determine the refractive indices corresponding to the two spectrum lines chosen and to take the difference of the two determinations. This necessitates the use of a hydrogen Geissler tube. The Pulfrich refractometer is generally used for making dispersion measurements. The accuracy of this instrument is one-tenth of a specific dispersion unit. I n the case of dark oil, where the hydrogen p line (F) could not be seen, measurements were made for the hydrogen a line (C), the sodium D or helium d line, and the mercury e line, a,nd the np value estimated by means of a chart based on the Cauchy formula ( I S ) :
321
factory. A microscope eyepiece lense focuses the light on a Pulfrich capillary vessel containingthe oil sample. The capillary vessel is fastened with a trace of a-bromonaphthaleneto the horizontal surface of the Abbe refracting prism. An adjustable mirror reflects the refracted spectrum lines into the telescope of a Zeiss dipping refractometer. The Amici prism of the telescope is removed. With the adjustable reflecting mirror, the blue spectrum line is brought to the zero point of the telescope scale. The position
I
n = A + -
B x2
Such extrapolated values were accurate to within one specific dispersion unit for extracted oils of low aromaticity. I n the case of higher aromatic content, the deviation between measured and extrapolated values was proportionally greater, the extraVIEW OF SCALE polated values being generally low. I: HYDROGEN TUBE Dispersion measurements 2. CONDENSING LENS on the Pulfrich refractome3. CAPILLARY TUB€ ter require considerable skill. 4 PRISM Consequently, for extraction 5: ADJUSTABLL- M/t?EOR plant control, a dispersometer was constructed, using parts of the Abbe, Pulfrich, and Dipping refractometers. Figure 1 shows the new instrument and Figure 2 its optical train: As light source a h y d r o gen Geissler t u b e made of quartz is used, but a mercury sunlight lamp is also satis-
FIQURE1. DISPERSOMETER of the red line is then noted. The respective scale reading is
proportional to the angular difference measured by the micrometer adjustment of the Pulfrich refractometer for the same two spectrum lines. Strictly speaking, this correlation exists only when the mirror remains stationary. However, within the refractive index range of raffinates made from the same charging stock, the correlation is sufficiently accurate. For measurements made on extraction-dant raffinate oil. the instrument is calibrated against thePulfrich refractometer by means of known raffinate samples. The relation thus established is used for converting scale readings directly t o dispersion values. For plant control work the instrument is enclosed within a box t o shield it from stray light. Operation is rather simple, the only part moved being the adjustable mirror. The accuracy of the dispersometer is within one unit of the specific dispersion.
Specific Dispersion of Hydrocarbon Types Calculated specific dispersion values for pure hydrocarbons are given in Table 11. The data for these calculations were
taken from Beilstein, Landolt-Bornstein, International Critical Tables, and actual measurements. Most of the hydrocarbons listed are below the lubricating oil range, because of the diftjculty of obtaining pure compounds in that range. However, the regularity of the available data seems to warrant extrapolation. This is also confirmed by FIGURE 2. OPTICAL TRAINOF DISPERSOMETERtests on lubricating oils.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE 11. SPECIFIC DISPERSION OF HYDROCARBONS Mol. Weight
86.1 86.1 86.1 86.1 86.1 100.1 100.1 100.1 114.1 114.1 114.1 114.1 114.1 128.2 128.2 128.2 142.2 142.2 142.2 142.2 142.2 142.2 142.2 142.2 226.3 240.3 254.3 254.3 254.3 282.3 282.3 282.3 296.3 332.4 450.1
n-Hexane 2-Methylpentane 3-Methylpentane 2 2-Dimethylbutane rjiisopropyl n-Heptane 3-Ethylpentane 2,2,3-Trimethylbutane n-Ortann -. .... ~.
n-Octane 4-Methylheptane 2,5-Dimethylhexane 2-Ethvlhexane n-Nonane 4-Ethylheptane 3-Propylhexane %-Decane Isodecane 2-Methylnonane 2 6-Dimethyloctane 2:7-Dimethvloctane Ijiisoamyl Diisoamyl Tripropylmethane 3-Ethyltetradecane n-Heptadecane n-Octadecane 2-Methylheptadecane n-Nonadecane Eicosane 2-Methylnonadecane Ethyloctadecane Heneicosane Trioosane Dotriacontane
Cyclohexane Cyclohexane Meth ylc yclohexane 1 1-Dimethylhexane ly2-Dimethvlhexane 1;Z-Dirneth?lhexane 1 3-Dimethylhexane 1’4-Dimethylhexane 1:4-Diniethylhexane 1.2.4 Trimethylcyclo hexane 1,2,4 Trimethylcyolo hexane 1,3,5 Trimethylcyclo hexane 1.3.5 Trimethylcyclo hexane 1-Methyl - 3 -isopropyloyclopentane Menthane Tetrahydroterpene Deoahy dronaphthalene
-
Benzene Benzene Toluene Toluene Toluene o-Xylene o-Xylene +Xylene m-Xylene m-Xylene pXylene p-Xylene
-
-
Temp.
c.
Paraffins 20
... ... ... ...
23
...
15 17.6 20.6
... ... ...
,..
ii:s 14.9 15.1 15.1 20.2 18.1 13.1 18.1 15.2 14.2
... ... 15.6 .. . ...
18.1 15.5
... ,.. ...
Nauhthenes 13.5 84.1 44.6 84.1 15.5 98.1 112.1 17.0 112.1 17.9 112.1 112.1 2018 112.1 15.7 112.1
-
Dispersion Sp. Sp. Gr. H e H , Dispersion
Weight Mol.
Temp. O
0.6603 0.654 0.668 0.649 0.666 0.6809 0.670 0.695 0.7046 0.7019 0.722 0.693 0.717 0.718 0.741 0.7307 0.7278 0.7279 0.728 0.7289 0.7278 0.7290 0.7278 0.7396 0.7829 0.778 0.7718 0.7836 0.7760 0.7715 0.7876 0.7959 0,775 0.7570 0.775
0.00651 0.0065 0.0065 0.0064 0.6654 0.0091“ 0.0068 0.0068 0.00695 0.00693 0.0070 0.0080a 0.0070
.....
0.0071 0.00713 0.0072 0.00722 0.0072 0.00712 0.00720 0.00723 0.00720 0.00720 0.00768 0.0076 0.0075 0.00774 0.0076 0.0075 0.00778 0.00784 0.0076 0.0075 0.0077 Average
98.6 98.9 99.4 98.6 97 6 129.2b 101.4 97.8 98.6 98.7 97.0 115.46 97.6
...
0.7843 0.7550 0.7773 0.7851 0.7809 0.779 0.7707 0.7722 0.769
0.00754 0.00729 0,0075 0.0078 0.00772 0.0076 0.00771 0.00767 0.0076
96.1 96.6 96.5 99.4 99.0 97.6 97.8 99.1 98.8
126.1
16.7
0.7848
0.0078
99.4
126.1
16.9
0.7799
0.0077
98.7
126.1
13.1
0.7777
0.0079
101.6
126.1
15.7
0.7744
0.0078
100.7
126.1 140.2 140.2 138.1
15.2 19.9 17.4 18.0
0.7799 0.7904 0.7943 0.8952
0.0077 0.00776 0.00773 0.00849 Averaae
Aromatics: Benzene Homologs 78.1 25 0.8736 78.1 20 0.8791 92.1 14.7 0.8707 92.1 1 6 . 4 0.8684 92.1 15.0 0.87160 106.1 14.1 0.8852 106.1 15.5 0.8837 106.1 20.0 0.8812 106.1 14.9 0.8686 106.1 1 5 . 7 0,8688 106.1 14.7 0.8659 106.1 1 6 . 2 0.8624
0.01654 0.01664 0.0160 0.01602 0.01624 0.0160 0,01592 0.0158 0.01580 0.0158 0.0154 0.01577
98.7 98.2 97.3 94.9 98.3 189.3 189.3 183.8 184.5 186.3 180.7 180.2 179.3 181.9 181.9 177.9 178.7
Sp. Gr. Dispersion H e - H , Dispersion Sp.
Aromatics: Benzene Homoloes - (Cont . Ethylbenzene 106.1 14.5 0.8748 E t h lbenzene 106.1 14.5 0.8708 118.1 21.4 0.9595 rindene ( C ~ H I D ) $&indene (CoHm) 118.1 0.957 120.1 1 9 . 6 0.8949 1 2 3-Trimethylbenzene 15.3 0.8794 120.1 1’2’4-Trimethylbenzene 14.7 120.1 0.8829 1’2’4-Trimethylbenzene 120.1 7.6 0.87397 1:3:5-Trimethylbenzene 1 4 . 6 0.86486 120.1 1,3,5-Trimethylbenaene 17.1 120.1 0.8646 1 3 5-Trimethylbenzene 15.7 120.1 0.8841 oiEthyltoluene 1 7 . 9 1 2 0 . 1 0.8690 m-Ethyltoluene 22.8 120.1 0.8597 p-Ethyltoluene 8 . 3 0.8719 1 2 0 . 1 n-Propylbenzene 12.3 0.8681 120.1 n-Propylbenzene 16.8 0.8662 120.1 Isopropylbenzene 7.9 0.8727 120.1 Isopropylbenzene 1 , 2 , 3 4 Tetrahydro 17.8 0,9732 132.1 naphthalene 1, 2, 3, 4 Tetramethyl16.0 0.9044 benzene 134.1 1, 2 4 5 Tetramethyl81.3 0.8380 bbnLene 134.1 1 Methyl 2 -propyl 1 5 . 7 0 8775 benzene 134 1 1 Methyl 3 propyl 17.0 0.8648 benzene 134.1 1 Methyl 4 propyl 134.1 15.4 0.8642 benzene 1 -Methyl -2 -Isopropylbenzene 134 1 16 0.8789 1- Methyl-3 -Isopropylbenzene 134 1 17 0.8628 1-Methyl-4-Isopropyl7.9 0.86700 benzene 134 1 1 Methyl-4-Isopropylbenzene 134.1 13.4 0.8822 1 Methyl-4-IsopropYb 134.1 13.7 0,86192 benzene 1 Methyl- 4 -Isopropylbenzene 134.1 20 0.8569 134.1 1 6 . 3 0.8678 1,CDiethylbenzene 1&Diathylhenzene 134.1 18.2 0.8645 0 87620 134.1 7.9 Isobutylbenaene Isobutylbenzene 134.1 1 4 . 5 0.87183 Dhenvlcyclopentane 146.1 25 0.9432 i,3;5-- irrimethyl 2 148.1 16.4 0.8885 ethylblenzene 1,2,4 Trimethyl 5 ethylbenzene 148.1 15.9 0.8866 Pentamethylbenzene 148.1 107.2 0.8472 uUuyI1 -Methyl-.l-ter’C -I-.-&--’ 148.1 13.3 0.8667 benzene 162.1 15.6 0.8708 2-Ethylcymene 176.2 15 0.8685 2-Propylcymene 218.2 20.3 0.8983 Pentaethylbenzene 218.2 107.9 0.8336 Pentaethylbenzene Hexaethylbenzene 246.2 130.4 0.8305
...
...
95.8 97.6 98.9 99.2 98.9 97.7 98.9 99.2 98.9 97.4 98.1 97.7 97.2 98.8 97.9 97.2 98.8 98.5 98.1 99.1 99.4 98.4
c.
-
-
-
-
-
-
.
-
-
-
-
-
-
-
- -
-
’a 0.0154 0.01530 0.01679 0.0168 0.0157 0.0158 0.0154 0.01536 0.0147 0,01533 0.0154 0.0151 0.01496 0.01462 0.01454 0.01476 0.01462
176.1 175.7 175.0 175.6 175.4 179.7 174.4 175.8 170.0 177.3 174.2 173.8 173.6 167.7 167.5 166.5 167.5
0.0169
173.7
0.0157
173.6
0.01473
175.8
0.0145
165.3
0,0148
171.1
0.0148
172.4
0.0146
166.1
0.0143
165.7
0.01441
166.2
0.0143
165.9
0.0140
162.4
0.01370 0.0149 0.01441 0.01399 0.0140 0.0148
159.9 171.7 166.7 159.7 160.6 156.9
0.0154
173.3
0.0151 0.01448
170.3 170.9
0,0139 0.01384 0.01351 0.01430 0 01327 0.01329
160,4 158.9 155.0 159.6 159.2 160.0
I
Polynuclear Aromatics 182.1 182.1 168.1 210.1
14.7 133 11 15
0.9991 0.9066 1,0126 0,9776
0.02003 0.01806 0.02077 0.02038
200.5 199.0 205.1 208.5
210.1 244.2 154.1 154.1
20
73 77.1
0.9676 1.014 0,9919 0.9896
0.0209 0,0219 0.02647 0.02648
216.0 216.0 266.9 267.6
156.1
16.6
1.025
0.0288
281.0
1.016 1.025 1.029 1.028 1.145 1.0017 0.9940
0,0296 0.0303 0.0289 0.0294 ‘0.0287 0.04661
291.3 295.6 280.9 286.0 297.6 465.3 187.0
...
Apparently out of line. On actual determination on heptane the epecific dispersion was found to be 95.6. The two values marked b are dlsregarded as belng obvlously In error.
lene 1,4 Dimethylnaphthalene a-Methylnaphthrtlene ,&Methylnaphthalene Acena hthene Naphtxalene Mesoisortmylanthracene Dihydroamylanthracene
I n compiling the list of hydrocarbons, all such paraffins, naphthenes, and aromatics were included whose refractive indices for the hydrogen p and a (F and C) spectrum lines or their difference (He - Ha)could be found in the literature. In case several sets of data were available for one hydrocarbon, they are all listed. Whenever the temperature is not given in Table 11, it was assumed that the specific gravity and the dispersion were determined a t the same temperature. The specific dispersion of thirty-four paraffinic hydrocarbons are given (Table 11). Of these, thirty-two show satisfactory agreement, considering the fact that the data used for
these calculations were contributed by a large number of investigators. Two of the samples (n-heptane and 2,5-dimethylhexane) are obviously in error and are included only for the sake of completeness. The heptane data, as determined by Gladstone, were checked with n-heptane from the California Chemical Corporation and were found to be in error (95.6 was found as against Gladstone’s 129.2). Also, t h e specific dispersions of isooctane, pure dodecane, tetradecane, hexadecane, and octadecane (Eastman Kodak Company) were found to be 96.7, 97.6, 97.9, 97.7, and 96.0, respectively, which agree well with the calculated average for paraffins
5
b
-
156.1 142.1 142.1 154.1 128.1 248.1 250.1
... ... ...
98.8 99.6 71.7 44.4
0.01860
MARCH, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
323
visible side. I n other monoalkyl benzenes little further change (98.4). Dicetyl with a molecular weight of 450, which is well of the benzene nucleus takes place. Such homologs can be within the lubricating oil range, was found to have a specific regarded as homologs of toluene rather than of benzene. dispersion of 97.5, showing practical independence of molecuThe polysubstituted benzene ring has a somewhat higher lar weight. specific dispersion than a monosubstituted ring with the Seventeen naphthenes are listed, and their average specific same number of nonbenzenoid (side-chain) carbon atoms. dispersion value (98.3) is almost identical with that of the This too is in accordance with absorption spectra. paraffins (98.4). Unfortunately only one condensed six-ring naphthene (decahydronaphthalene) could be given. These experiments include cyclohexane, methylcyclohexane, and TABLE111. SPECIFIC DISPERSION OF BENZENE HOMOLOGS decahydronaphthalene. The calculated as well as the experimentally determined Specifio Dispersion --Calcd.specific dispersion values for paraffinic and naphthenic hydroFound Aa Bb carbons show remarkable uniformity-in the neighborhood Benzene 189.3 ... Toluene 183.8-186.3 l76:3 of 98. This figure was confirmed in later experiments using Ethylbensene 175.7-176.1 166.6 aromatic-free medicinal oil samples and a paraffinic polyn-Propylbensene 167.5-167.7 159.0 166.7 Is0 ropylbenzene 166.5-167.5 159.0 166.7 merization product of very high molecular weight (about Iso!utylbenzene 159.7-160.6 152.9 159.9 2500). * a From the ratio of benzenoid t o nonbenzenoid carbon atoms. The aromatic hydrocarbons are listed in Table I1 in two b Assuming the compounds to be side-chain-substituted toluene homologs (specific dispersion of nonbenzenoid side chain oarbon atoms, 98.4). separate groups, the first containing the benzene homologs and the second the polynuclear aromatics. The specific dispersion of benzene (189.3) is nearly twice Remarkable is the behavior of the polynuclear aromatics. that of the nonaromatics, the difference being 91 units. Naphthalene and its homologs have specific dispersions The benzene homologs show a gradual decrease with increasing about three times as great as those of the saturated hydrolength and number of side chains. The reducing effect of carbons; the specific dispersions of diphenylmethane and its the side chains is, however, not strictly proportional to the homologs are only about twice those of the saturated hydronumber of nonaromatic carbon atoms in the molecule. In carbons and only slightly higher than that of benzene. I n the case of one side chain, the carbon atom next to the arodiphenylmethane there is a nonbenzenoid carbon atom matic ring has practically no lowering effect (Table 111). between the two rings; that is, the rings do not touch a t any The absence of a decrease in specific dispersion upon inpoint. Diphenyl has a much higher specific dispersion since troduction of a CH, group in benzene is in accordance with the benzene rings touch a t one point. the fact that the absorption of toluene I n naDhthalene the rings is higher than that of benzene. and the - touch at DISTILLATION AND HEATEXCHANGE two pdints. spectrum is displaced somewhat to the OF THE EQUIPMENT (FOREGROUND) EXTRACTION PLANT
\
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IKDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 29, NO. 3
c to 340 ( 7 ) . T h e In other words, a p p r o x i m a t e exan unbroken contrapolated specific n e c t i o n of c o n dispersion value of jugated double p y r e n e would be bonds is a sign of a about 550. high specific disperThis exalting sion. This is again effect of the polys u p p o r t e d by the n u c l e a r aromatics analogy b e t w e e n on the specific disabsorption spectra persion is very and dispersive f o r t u n a t e for the properties. p r e s e n t purpose, Continuing t h i s since the exaltation line of t h o u g h t , is in the direction of a n t h r a c e n e (or greater aromaticity phenanthrene) and the results should have a spedo not indicate cific d i s p e r s i o n merely the aromatic about four times that c o n t e n t but take of the saturated hyinto account strucdrocarbons. Since ture differences. anthracene is highIt is well known m e l t i n g and only that p o l y n u c l e a r sparingly soluble in rings are less stable most solvents, a 5 than benzene and per cent solution of i t s homologs. anthracene in Anthracene is more methylnaphthalene easily oxidized (conwas tested (at 65" C.) and showed a verted to anthrasix-point i n c r e a s e quinone) or p o l y merized than naphover that of methylt h a l e n e which, in naphthalene, which turn, is more reacvalue extrapolated tive than bennene. would give a specific T h e s e compounds dispersion of over are also less soluble 400 for anthracene. in normal lubricatMesoisoamylan ing oil and, on oxithracene has a EXTRACT/ON STAG&.S dation, tend to specific dispersion form more sludge. of 465. DihydroFIGURE 6 ( T o p ) . EFFECTOF IMT h e r e f o r e , it is mesoisoamylanthraPROVEMENTS IN SLUDGINGTIME (INDIANA OXIDATION TEST) ON desirable to know cene has a specific SOLVENT EXTRACTION the nature of the dispersion of 187aromatic comt h a t is, slightly FIGURE7 (Bottom). EFFECT OF REDUCTION IN VISCOSITYINCREASE pounds as well as lower than benzene (INDIANA OXIDATIONTEST)ON SOLthe amount. (189). I n the anVEKT E X T R a C T I O N On s o l v e n t exthracene ring structraction, the more ture there are seven complex' aromatic compounds are extracted first and, conseconjugated double quently, the improvement is most pronounced in the first bonds; on hydrostages of extraction. Comparing compounds of similar mog e n a t i o n a comlecular weights, a benzene homolog will have a much longer pound is obtained paraffinic side chain and will behave more like a paraffin containing two hydrocarbon than would an anthracene derivative. The benzene nuclei last few per cent of aromatic content of an extracted oil will which are separated be most difficult to remove but is also less significant than by saturated carbon the same small aromatic content in an unextracted oil. atoms. FIGURE3 ( T o p ) . DECREASEIN AROMATICITY ON SOLVENT EXTRACPy r e n e ( C I Q H ~ Therefore, the specific dispersion method of estimating TION AS MEASUREDBY SPECIFIC aromatic content, while not giving the same proportion of is a polyaromatic DISPERSION aromatics, is nevertheless superior to other methods since hydrocarbon made FIGURE 4 (Center). EFFECTOF IN- up of four interit takes into account aromaticity. For following the course CREASE IN VISCOSITY INDEX ON SOLof a solvent extraction, the method is invaluable. locked a r o m a t i c VENT EXTRACTION rings. T e n per FIGURE 5 (BOtlOm). EFFECT O F cent of pyrene disSolvent Extraction DECREASE IN CARBON RESIDUE ON solved in quinoline SOLVENT EXTRACTION The most important properties of a lubricating oil which sol(C9H7N)raises the vent extraction is meant to improve are viscosity-temperature dispersion of this characteristics, stability toward oxidation, and carbon residue. compound from 309
INDUSTRIAL AND ENGINEERING CHEMISTRY
MARCH, 1937 0
105240
M/D- CONT/N€NT RfSIDUE WEST TEXAS DIST/LLATL
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0 VISCOSITY INCRfASE IN SfCONDS
BETWEEN AROMATICITY AND SLUDGING (Left). RELATIONS TIME (INDIANA OXIDATIONTEST) FIGURE 9 (Right). RELATION BETWEEN AROMATICITY AND VrsCOSITY INCREASE (INDIANA OXIDATIONTEST)
FIQURE 8
The improvement of these properties is accomplished almost entirely by the extraction of aromatics. Figure 3 shows the decrease in aromaticity on solvent extraction as measured by the specific dispersion of several sets of successive stage samples from five typical stocks, and including experimental as well as commercial operations with different solvents. Figure 4 shows the viscosity index (Dean and Davis) plotted against the same stage samples. The corresponding curves in Figures 3 and 4 are very similar. The drop in specific dispersion is proportional to the increase in viscosity index for each stock presented the are not interchangeable for the different stocks. Figure 5 shows the carbon residue values (A. 8. T. M. method D184-30) of two residual stocks and a distillate of high aromaticity plotted against extraction stages. The curves again follow the general shape of the corresponding curves of the specific dispersion. Figures 6 and 7 show the sludging time and viscosity inby the IndianaOxidation test ( I ) plotted against the stages. The relation between aromaticity and oil improvement on
325
solvent extraction is further demonstrated in Figures 8 to 11; a direct and nearly straight-line relation exists between specific dispersion and such oil properties as Indiana oxidation test, carbon residue, and viscosity index, for each individual stock. If raffinates from different types of crudes are compared, the numerical values in these relations will have to be established for each stock. If widely varying fractions of the same stock or their blends are compared, the specific dispersion values will not necessarily correspond to identical values for other characteristics. Bright-stock blends, for example, will increase in stability with increased bright-stock content, although the specific dispersion also tends to increase. The stability toward oxidation exhibited by a solvent-extracted oil will naturally be influenced by variations in the finishing treatment the oil receives after the extraction process. Avoidance of superheating, oxidation and contamination, and properly applied clay treatment will all contribute toward making a stable oil. I
Summary
On solvent extraction of any given stock, the information required is: T o what extent have the undesirable materials been removed? This amounts to determining the aromaticity of the oil. Since specific dispersion is a direct and rapid measure of aromaticity, the extent of extraction can readily be determined. Further uses of the specific dispersion in petroleum refining operations include all those where aromatics and/or unsaturates play a part.
Literature Cited (1) Barnard, Barnard, Rogers, Shoemaker, and Wilkin, 8. A . Journal, 34,5, 167 (1934). (2) Bell and Sharp, Oil Gas J., 32 (13), 13 (1933). (3) Brlihl, Z . p h w i k . Chem., 7. 140 (1891).
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(9)
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~ ~ ~ ~ ~~ ~ dt . 36, c ( 618 ~ ~ (1929) ~ ~~ ~ Davis, ; ~ Lapeyrouse, and Dean, Oil Gas J., 30, 46, 92 (1932). Hill and Coats, IND.EXQ.CHEM.,20, 641 (1928). International Critical Tables, V d . VII, p. 107, New York, McGraw-Hill Book Co., 1930. Nernst, “Theoretical Chemistry,” p. 366, London, Maomillan Co., 1923. Vlugter, dissertation, Delft, 1932. (10) Vlugter, Waterman, and van Westen, J. Inst. Petroleum Tech., 18, 735 (1932). (11) Ibid., 21, 661 (1935). (12) Ibid., 21, 701 (1935). (13) Ibid., 21, 706 (1935). (14) Ward and Fulweiler, IND.ENG.CHEM.,Anal. Ed., 6, 396 (1934). (15) Waterman, Proc. World Petroleum Congr., London, 1933. 2, 332; Waterman, Kruijff, Schonlau, end Tulleners, J . Inst. Petroleum Tech., 20, 159 (1934).
RECEIVED September 26, 1936. Presented before the Division of Petroleum Chemistry st the 92nd Meeting of the American Chemical Sooiety, Pittsburgh, Pa., September 7 t o 11, 1936.
CARBON RfSIDUf
VISCOSITY INDEX
BETWEEN AROMATICITY AND CARBON RESIDUE FIGURE 10 (Left). RELATION
FIGURE 11 (Right). RELATION BETWEEN AROMATICITY A N D VISCOSITY INDEX
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