Separation and Composition of a Lubricating Oil Distillate

i”

Separation and Composition of a Lubricating Oil Distillate M. R. FENSKE AND R. E. HERSH The Pennsylvania State College, State College, Penna.

The systematic separation of a lubricating oil distillate by selective solvent extraction and fractional distillation into portions comprising 0.6 to 1.4 weight per cent of the original oil allowed the construction of three-dimensional diagrams incorporating yield, viscosity index, and molecular weight or viscosity. Such diagrams permit an estimation of the distribution of oil fractions with respect to molecular size and molecular type. Used in connection with graphs of boiling-point and aniline-point isotherms superimposed on the composition diagram, methods for the segregation of any portion of the oil are suggested. Comparison of the physical properties of the fractions with those of synthetic hydrocarbons indicates that the oil fractions, while perhaps far from being separated into pure compounds, are segregated into groups ranging from monocyclic naphthenes (C,H2,) to polycyclic aromatics (CmH2,- 18).

in accordance with the relative solubility or the type of chemical compounds present in the original oil. By the proper combination of these two processes, therefore, an efficient procedure could be utilized to yield fractions in which similar molecules with respect to both size and type had been concentrated. The numerous variables that may be adjusted in the two processes allow maximum flexibility in controlling any desired separation or in making the separation conform to actual production-scale operations. In the course of such an extensive study of the composition of mineral oils and the physical and chemical characteristics of the derived fractions, a large quantity of a dewaxed distillate stock was systematically separated by selective extraction and fractional distillation into portions averaging from 0.6 to 1.4 per cent of the original oil. This distillate was obtained from a Pennsylvania crude by commercial distillation and represented approximately 8 per cent from the viscous portion of the crude. It was dewaxed to a 20’ F. pour point and clay-filtered lightly to about a 3l/1 A. S. T. M. color, but was not otherwise treated or refined for specific use as a commercial product such as engine lubricating oil. The physical properties of the over-all distillate stock are given in Table I, together with the hydrocarbon-type analysis determined by the method of Vlugter, Waterman, and van Westen (17).

TABLE I. PROPERTIES OF THE ORIGINAL DISTILLATH Gravity, OA. P. I. Density, dz0 Viscosity Saybolt 6ea. (centistokes) At 100’ F. At 210.O F: Kinematic vieoosity index Gravity index Viscosity-gravity aonstant Pour point, F. Refractive index at 20° C. (68O F,), n l n Sp. refraction at 20° C.. r q = (l/d)(nz Exptl. mol. weight hthalene) Sp. dispersion E t 20 (104)( m nc)/d Aniline point C. (O F.) Waterman adalysis: Aromatic rings, wt. % Naphthene rings, wt. % Para511 ohains, wt. Yo No. of rings per mol. In general formula CnHtn+z Value for n Value for s

H E study of the composition of the high-molecularT weight portion of petroleum has been undertaken by a number of investigators 13, 14, but seldom (11,

16),

with the definite purpose of establishing practical and useful relations. It is obvious that a more complete and compre‘hensive knowledge of the components of viscous oil would be of material benefit both to the research worker and to the refiner for purposes of devising methods for improving quality and for producing new or specialty products. The physical and chemical properties of constituent fractions separated from a mineral oil should be extremely advantageous in obtaining an exact analysis of the type of compounds that is present in the raw stock and may also suggest methods or procedures for eliminating certain undesirable constituents from the finished lubricant. However, to obtain the maximum usefulness from such data, the fractions must have been prepared by a practical and readily duplicated procedure. Probably the best practical methods available for effecting the comprehensive separation of hydrocarbon oils are fractional distillation and selective solvent extraction. As is commonly known, distillation separates petroleum hydrocarbons according to their relative boiling points or molecular size, while selective extraction performs the separation more

pa. 2,

-

-

30.3 0.8710 176 (37.86) 44.7 (5.76) 103 08 0.820 20 1.4841 0.3286 406 110 99.6 (211.3)

+

9 16 76 1.7 29.2 -4.6

Separation Procedure The separation technique employed was first t o extract the oil into various portions of successively decreasing solubility and then to distill these portions in a vacuum fractionating unit. This procedure, rather than first distilling and then extracting, was selected largely because of the facilities for handling a large quantity of oil. With an initial charge of 43 gallons of oil the extraction was conducted in a discontinuous batch process utilizingreflux of extract the procedure being similar to that described in the literature (Bj. To ensure thorough mixing of the solvent with the large quantity of oil, an auxiliary contacting zone or 331

332

INDUSTRIAL AND ENGINEERING CHEMISTRY

leaching section was employed between the main leaching section and the countercurrent tower. A flow diagram of the process is shown in Figure 1. The solvent used was 98-99 per cent acetone. Briefly, the operation consists of pumping the solvent from receiver E t o the bottom of a 4-inch diameter auxiliary tower t o which the oil, saturated with solvent, is pumped from receiver D at a rate greatly in excess of that governed by the solubility in the solvent. The solvent passes through the oil and flows from the top of the auxiliary tower t o the bottom of the 30-foot contacting zone by the same pump pressure. This tower consists of a 1.62-inch i. d. steel tube packed with '/*-inch carbon Raschig rings, the entire length being jacketed in order to control the temperature. From the top of this tower the solvent layer is led directly to a vaporizer or still, where the solvent is removed by distillation and then returned to the storage reservoir. The extract, substant,ially free of solvent, flows to receiver A , where the product is removed and the balance is returned as reflux to the top of the 30-foot countercurrent contacting section. The oil phase forming at the bottom of this tower is automatically exhausted through a solenoid valve operated by a suitable interface control device (8) and flows back t o the oil reservoir. Similarly, the oil level in the 4-inch auxiliary tower is automatically maintained about 8 inches from the top, the excess oil also being returned t o the oil reservoir through a line from the bottom of the auxiliary section. A recycle gear pump is used to circulate and mix the oil in the reservoir. At the start of the extraction the temperature in the tower was controlled at about 60" F., and total reflux of the extract was maintained until the system became stabilized; then the product was removed and the reflux returned in the proportion of 1 to 6-4. e., O / P = 6/1. As the solubility of the extract decreased, the temperatures of the auxiliary tower and the bottom section of the 30-fOOt column were increased to maintain a reasonable throughput. Temperature gradients were employed t o assist in maintaining reflux. A t the end of the extraction (70 per cent removed) the temperatures were: top 10-foot section of ao-foot tower, 85" F.; middle 10-foot section, 106' F.; bottom section, 133" F. The extracts ryere removed as 125 one-quart fractions which were later blended in consecutive groups for further separation by distillation andjor re-extraction after the properties of the individual fractions were correlated t,o expedite the blending. The first portion, blend 1-40, representing 23.44 per cent of the original oil, was re-extracted in a small-scale apparatus (9) which operated in a similar manner to that described; a mixture of acetone and methanol was used as the solvent to obtain a more efficient and uniform separation of this very soluble portion.

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Subsequent portions, blends 4140, 61-80, 81-102, 103-125, and the raffinate, corresponding to 11.07, 11.04, 12.06, 12.89, and 29.50 per cent of the original oil, res ectively, were fractionally distilled at reduced pressure in a 5-gaton unit operating at about 0.2 mm. mercury absolute pressure at the top of the column; the pressure drop through the 9-foot fractionating section was about 1.5 to 2.0 mm. mercury at a reflux ratio of 5 to 1. This column has the equivalent of seven to ten theoretical plates. The boil-up is 6 to 8 liters (6.3 to 8.5 quarts) per hour. The boiling point spread in a simple distillation of the overhead fractions between the initial and 50 per cent points averaged about 5" C. (9" F.) a t 1 mm. mercury absolute pressure. A sample of the raffinate portion was also re-extracted in the smaller extraction apparatus (9) with acetone as the solvent for the purpose of completing the extraction data on the over-all oil. A diagram summarizing the treatment given the original oil and the subsequent fractions is presented in Figure 2. Physical properties and other characterization constants of the final extraction and distillation fractions were determined. For the most part hysical measurements were made in conformity to the procezures designated by the American Society of Testing Materials (1). Aniline points were determined by using 3 cc. each of the oil and freshly distilled aniline, and noting the temperatures of the disappearance and appearance of cloudiness. Values recorded were the average of two such determinations, between which the difference was not more than 0.2' C. (0.36' F.). Refractive indices and specific dispersions were obtained with a Spencer Abbe-type refractometer. Specific refractions were calculated by the Lorenz-Lorentz relation. Correlations based on experimental data were used for calculating the viscosity index ( 7 ) , gravity index (IB), and viscosity-gravity constant ( I O ) . The molecular weights were determined by a cryoscopic method using naphthalene as the solvent on selected fractions throughout each distillation and extraction. From a graph of the molecular weight us. the weight per cent separated, the intermediate values were interpolated, a smooth and uniform relation being assumed for the individual separations. The method outlined by Vlugter, Waterman, and van Westen ( 1 7 ) for indicating the chemical nature of hydrocarbon oils was adopted for this work. From their established relations between the molecular weight, specific refraction, and aniline point, the average weight per cent of aromatic rings, naphthene rings, and paraffin chains and the average number of rings per molecule were computed. Values of n and x in the empirical formula * C,H,,+, were then calculated on the assumption that the rings in the molecules were present as condensed six-carbon-atom rings. The boiling point data were obtained in modified Cottrell units (6) operating at reduced pressures and containing a solenoid stirrer to ensure thorough mixing in the boiler and to reduce bumping. Initial vapor pressure relations over a range from 1 to 10 mm. of mercury absolute pressure and the equilibrium boiling points up to 50 per cent distilled at 1 mm. pressure were obtained on various fractions.

Graphical Summary of Constants Representation of the separation and the variation in some

of the physical properties can be accomplished readily by

DIAGR.4EII FIGURE 1. FLOW

OF THE EXTRACTION PROCESS

several graphs. I n Figure 3 the viscosity indices of the fractions are plotted against the cumulative weight per cent of the original oil. The relative proportions and the locations of each fraction with respect to the over-all oil are thus illustrated. Re-extraction of the first blend (blend 1-40) of extracts from the initial exbraction having a viscosity index of 30 is here shown t o be separated into component fractions increasing from - 122 to +113. Distillation of successive blends of extracts shows decreases in the viscosity indices of the fractions as the molecular weight or the viscosity increases during each distillation. The spread or range in viscosity index, however, decreases with consecutive blends of extracts until with the raffinate the separation, as measured by the change in viscosity index, is not markedly different in the case of either the extraction or distillation of this portion. This may be due in part to the characteristics of the solvent employed, but is probably also related to the homogeneity of the sample. In general, therefore, it is indicated t h a t the process of distillation also has acted t o separate the blends according to types of molecules. The heavy aromatic-type materials which were not segregated in the initial extraction procedure have been concentrated in the heavier distillation fractions.

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333

4.3 GuA.

I

"

I

FIGURE 2. TREATMENT OF THE DISTILLATD FRACTION

In other words, the initial extraction tended to separate the Composition Diagrams material roughly according to type, but covering the entire range in molecular size, and the distillation of these extracts The proportions of the over-all oil of definite molecular then separated the blends according to molecular size and, size and type can be best illustrated by three-dimensional to some extent, according to molecular type. diagrams. In F w r e 5 the height of blocks above the base The boiling point data for the various fractions are sumrepresents the relative amounts of portions between definite marized in Figure 4,where the equilibrium boiling points a t limits in viscosity index and viscosity. The limits of the 1 mm. mercury absolute pressure are plotted against the over-all distillate also are thus indicated. The greater portion cumulative weight per cent of the over-all oil separated by of the oil is relatively high in viscosity index. Although the extraction and distillation. The initial and the 50 per cent original over-all oil has a viscosity a t 100" F. of 176 Saybolt boiling points are indicated, and in practically all cases interUniversal seconds (S. U. S.) and a viscosity index of 103, mediate points lie on a straight line joining them, similar to about GO per cent of the oil has a viscosity index above 100 the curve shown for the over-all oil. At the beginning of the and about 67 per cent has a viscosity a t 100" F. less than separation the boiling points of the extraction fractions do 230 Saybolt seconds (50 centistokes), as shown by the supnot change appreciably from one fraction to another, although plementary scales on the base which are merely the cumulathe Cottrell spread between the initial boiling point and the tive addition of the individual percentages, starting from 50 per cent point is relatively high, averaging about 45" F. (25" C.). The distillation fractions show little spread in themselves, averagingabout 9" F. (5" C.)between initial and 50 per cent point, but the range in boiling points of the fractions from the extraction blends taken for distillation vary from about 170" F. (95" C.) for blend 41-60 to about 110"F. (61" C.) for blend 103-125. For the raffinate portion, fractions from both the extraction and the distillation covered a range of about 140" F. (78"C.), which again indicated the similarity in the separation effected by the different processes. The lines labeled "Initial B. P." and "50% Points" refer to the Cottrell boiling points of the individual extraction fractions; the curve connecting the solid points relates to the initial and 50 per cent Cottrell boiling points (shown as paired points) for the distillation fractions of this portion. On the curves closely paired points represent the initial and 50 per cent 0 P PI ID 53 m W m W XD boiling points in a simple distillation W&h+ Per cent pc ong/m/e/ (Cottrell apparatus) of the designated FIGURE3. VISCOSITY INDICES OF FRACTIONS SEPARATED BY DISTILLATION fractions. AND EXTRACTION *)

334


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conforms with the expected distribution for the original distillate, there is an absence of low-viscosity-index material of high-molecular weight. Sufficient work was done on heavier fractions and residua to determine that the absence of such material was not a peculiarity of the particular oil investigated or the procedure employed. Extending the size of the crude fraction appears merely to extend the corresponding molecular weight ranges without changing the general shape of the outline. It seems, therefore, that the very high-molecular-weight substances present in this oil always have high values of viscosity index, irrespective of chemical type. This is not untenable with the conclusions of Mikeska (16) that saturation of the aromatic rings produces little change in the viscosity index, and that aromatic hydrocarbons, or the corresponding naphthenes, with one or two rings attached to long paraffin chains have high visBOILING-POINT DATAON THE VARIOUS FRACTIONS cositv indices. FIQURE 4. EQUILIBRIUM SEPARATED BY DISTILLATION AND EXTRACTION TGat the boundaries of the composition diagram for the over-all distillate are in reasonable agreement with what could be expected from the commercial preparation of the distillate studied can the rear edges. Small amounts of the distillate, however, be seen in Figure 8, where the constituents having constant are very viscous and very low in viscosity index. The maboiling points a t 1 mm. mercury absolute pressure are terial of lower viscosity index than -300, and of higher vislocated on the plan view of the composition diagram. cosity a t 100’ F. than 2310 seconds (500 centistokes) has It is indicated, therefore, that distillation accounts for been grouped to avoid undue extension of Figure 5 . the general outline of the plan view and that it separates A somewhat similar representation of the composition is the neutral mainly according to molecular weight. Also given in Figure 6, except that here the molecular weight is included on this graph are lines showing the average values used to represent molecular size instead of viscosity. This for the extraction fractions that were prepared and used in scale is also supplemented with an equivalent one for the the separation procedure. average number of carbon atoms per molecule (n). Likewise, since definite relations usually exist between the constants that are characteristic of the chemical types present in a given oil, equivalent scales have been included for the kinematic viscosity index (K. V. I,),weight per cent aromatic rings per moleoule, and the value of z in the general formula C,H2,+.; the latter two were determined with the aid of the Waterman procedure (17). Scales labeled “Cum. Wt.%” are also included to show the cumulative addition of all the material between any coordinate line, or vertical plane through that line, and the corresponding rear edge. For example, 50.3 weight per cent of the original oil have molecular weights less than 400, or between 280 and 400, and 86.9 weight per cent have kinematic viscosity indices above 0, or between 0 and 140. Sections through any part likewise can be obtained by subtraction; e. g., 47.3 per cent have molecular weights between 400 and 600. As will be emphasized later, such sections roughly represent distillation fractions when they exist between molecular weight limits, and extraction fractions when they lie between viscosity index limits. I n the construction of these diagrams the data obtained on the individual fractions were used as a basis. However, since the separation cross-sectioned the over-all oil a t least partially, both according to chemical type and molecular size (that is, by extraction and distillation, respectively), it was possible t o plot series of curves representing the projection of surfaces of the three-dimensional model from which complete interpolations of the quantities within definite ranges could be made. The proportions of the individual groups of constituents and the over-all limits of the distillate stock are illustrated also in the plan view of the composition diagram shown in Figure 7. The general outline of the cDmposition is of interest FIGURE 5 . AMOUNTSOF CONSTITUENTS HAVINGDEFINITE LIMITSOF VISCOSITYAND VISCOSITYINDEX since it shows that, although the low-molecular-weight side

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March, 1941

E E R I N G C H EM IST R Y

335

A similar graph was made to illustrate the effect of separating the oil by extraction. I n Figure 9 the aniline point isotherms are superimposed on the plan view of the composition diagram. Since the aniline points signify the relative solubility of the constituents in a selective solvent, these isotherms indicate the approximate manner in which solvent extraction would tend to separate the oil; this appears to be roughly according to chemical type. The amounts of material within definite ranges or limits of aniline point are also included. Only a small proportion of the oil had very low values, and about 57 per cent of the over-all oil had aniline points above 100" C. (212" F.). The average separation lines for the initial extraction fractions are also included, together with data on some of the properties of the raffinates remaining after the removal of each extract.

Chemical Constitution

FIGURE 6. GRAPHICAL ISOMETRIC REPRESENTATION OF THE COMPOSITION

-."

While the diagrams and charts so far discussed afford a convenient means of presenting the large quantity of data obtained on the various fractions and serve to depict the general nature of the over-all oil in a reasonably quantitative manner, little is known about the actual chemical composition of the various constituents. The Waterman hydrocarbon-type procedure permits some estimate to be made of the aromatic and naphthenic rings and the paraffin chains and of the general formula for the fractions, but it is of interest also to supplement these data with comparisons of the physical properties of the individual fractions and those of different types of hydrocarbons. The existence of ring compounds, which account for the hydrogen deficiency from the empirical formula C,Han+2, has been fairly well established by

CUYULATIVE WEIGHT PER CENT OF ORIGINAL O

O ;

J 1-

f

u~ r

t n

oT

T 5 E ~ ? 1 Y T ~ 3 T ? 4 3 n . * m S S O R X P P % 3 P X f i f f E f i X ! % g

~

~

260 0

300

0.9

340

13.6

4.75 25.8 380

58. I

50.3 420

2

61 -25 70.7

c

"0 I-

78.5

460 I

84.9

5

88.9

500

1

91.9 93.9

540

95.4 96.6

580

2 2 g-

I

r2

1 I

*

97.6 620

98.3

660

99.3

98.9 99.7 160

120

80

40

0

-40 -80 -120 -160 KIWEWATIC V I S C 0 8 I T Y INDEX

-200

-240

-280

-(o

IO0

COMPOEITION DIAQRAM FIG- 7. PLANVmw OF TFDJTHREE-DIMENSIONAL Numbers in squares refer to weight per cent of neutrsl oil having indioated ranges of molecular weight and visoosity index.

1

3

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FIGURE 8. BOILING-POINT ISOTHERMS SUPERIMPOSED O N THE PLAN VIEW OF THE COMPOSITION DIAGRAM

FIGURE9. ANILINE-POINT ISOTHERMS DRAWN ON THE PLANVIEW OF THE COMPOSITIOS DIAGRAM

Temperatures are initial equilibrium boilinq points determined at 1 mm. mercury absolute pressure. Broken lines lndlcate averages for the extraotion fractions taken for distillation. Amounts of the original oil having boiling points lower than the indicated values are as follows:

Broken lines indicate the separation obtained with acetone during the initial extraction. Amounts of the original oil having aniline points below the indicated values are a8 follows:

F. 340 360 380 400 420

c.

Wt. %

F.

171 I82 193 204 216

4.3 12.2 23.0 40.2 58.5

440 460 480 500

0

c.

227

249 238 260

Wt. % 70.6 76.7 88.1 93.6

the investigations of Mabery (11), Mair, Willingham, and Streiff ( I d ) , Vlugter, Waterman, and van Westen ( l 7 ) , etc. The deficiency of hydrogen may be attributable to the presence of naphthene and/or aromatic rings. Further, the work of Mikeska (15) on synthetic hydrocarbons shows that the physical properties are affected by the proportions of these groups sometimes in an unexpected manner. A comparison of some of the physical constants of the oil fractions with those of high-molecular-weight synthetic hydrocarbons, therefore, may serve as additional aid in extending the knowledge on the composition of the oil fractions under investigation. The boiling points of the various fractions were indicated in Figure 4 with respect to the relative position of the fraction during separation of the over-all oil. I n Figure 10 the initial boiling points a t 1 mm. mercury absolute pressure are plotted against the number of carbon atoms per molecule. The ranges in boiling point and molecular size of the different separation blends are thus illustrated, and the boiling points increase as the number of carbon atoms per molecule increase for all the fractions in about the same order. The boiling points of the normal paraffin hydrocarbons, as reported in the literature (Z), are also included in Figure 10, but these values coincide with those of the oil fractions only in the low-molecular-weight range, between about 22 and 26 carbon atoms per molecule. This, however, does not imply conformity of chemical structure, since even a cursory examination of the literature shows that the boiling points of the hydrocarbons are dependent on the length, branching, and number of the side chains, presence of aromatic or naphthenic rings, and degree of unsaturation. For example, the normal paraffins usually have higher boiling points than the corresponding isoparaffins or naphthene derivatives; the polynuclear naphthenes have lower boiling

"C.

O F .

_in_ 20

68

30 40 50 60 70

104 122 140 158

5n "-

86

Wt. % _2 _2 3.6 5.4 7.9 10.7 14.1 18.4

O

C.

OF.

R n _.

176 194 212 230 266 248

90

100 110

130 120

W t . 7% 23.8 30.9 42.9 72.3 98.3 90.5

points than the aromatic hydrocarbons of corresponding number of carbon atoms. A more useful correlation with respect t o classification of constituents is shown in Figure 11, where the aniline points of some of the fractions are compared with the values for synthetic hydrocarbons having the same number of carbon atoms per molecule. The curves for the aniline points of the

Number of Curbon Atoms ,berMo/ecff/e FIGURE10. BOILINGPOINTS O F FRACTIONS SEPARATED BY DISTILLATION AXD EXTRACTION WITH RESPECT TO MOLECULAR SIZE

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331

Number of Carbon Afoms per Mo/ecu/e FIGURE 11. ANILINE POINTS OF VARIOUS TYPESOF HYDROCARBONS AND OF SEVERAL OIL FRACTIONS AS A FUNCTION OF THE NUMBER OF CARBON ATOMS

pure hydrocarbons are constructed from the data of Evans (3) on the light hydrocarbons and from the values reported by the National Bureau of Standards (14) and by Mikeska (16) for the high-molecular-weight compounds. The extraction fractions from blend 1-40 apparently range from polycyclic aromatic to naphthenic type compounds, but it must be remembered that these fractions are not particularly homogeneous and that a t best the relation can give only an approximation of the average composition of the fractions. The distillation fractions, however, are somewhat more uniform, except possibly the residues. The aniline points of the fractions from the distillation of the raffinate coincide with the values for monocyclic naphthene hydrocarbons which have the general formula C,Hh. From the data obtained on the raffinate fractions, it was noted that the values of x in the general formula CnHPn++ averaged about -0.4, some of the heavier fractions being slightly higher. This would indicate either some unsaturation or contamination with aromatic compounds, but since the values are within the reliability limits of the analytical procedures, further conclusions must be corroborated by additional data. The aniline point data for the distillation fractions of blend 41-60, the group of fractions immediately following extraction fractions from blend 1-40, are also included in Figure 11. The data indicate a range of compounds from bicyclic naphthenes to bicyclic aromatics or higher polycyclic naphthenes. This is in agreement with the values of x obtained for the fractions, which range from -2.3 to -14.0 (excluding the residue) in the corresponding order. The aniline points for the other fractions are not included on the graph, but it is sufficient to say that the values for the distillation fractions from blends 61-80, 81-102, and 103-125 lie intermediate to the curves outlined by the data for the distillation fractions of blend 41-60 and the raffinate, and approximately equally spaced in corresponding order. As an additional aid in summarizing the extent of the data in this connection, however, the proportions of the over-all oil having definite limits in molecular size are also shown in Figure 11; the height and width of the blocks represent the percentage of the original oil and the range in number of carbon atoms, respectively. The majority of the fractions, comprising about 78 per cent of the original oil, have between 22 and 32 carbon atoms per moleoule.

FIGURE12. KINEMATIC VISCOSITY OF HYDROCARBONS AT 100" F. US. NUMBER OF CARBON PER MOLECULB ATOMS

A somewhat similar graph (Figure 12) was prepared t o correlate the viscosities of the various fractions and synthetic hydrocarbons with the number .of carbon atoms per molecule. The curves for the different types of pure hydrocarbons were constructed from the data of Doss @), Evans (I and ), Mikeska (16). Viscosity values for the fractions from the extraction of blend 1-40 and the distillation of the raffinate are plotted on the figure for comparison. Again i t is indicated that the first extract portions are polynuclear aromatics or mixtures of such complex molecules. The final raffinate fractions, however, are indicated to have viscosity characteristics resembling those of the naphthalene homologs, but this is probably of no significance since the data on the synthetic hydrocarbons are inconsistent in this region. A further interesting comparison can be made between the specific dispersions of synthetic hydrocarbons and some of the petroleum fractions. Some data on the high-molecular-weight hydrocarbons are available from the work of Mikeska (16), Ward and Kurtz (18), Mair, Willingham, and Streiff (Id), and von Fuchs and Anderson (B), and the specific dispersions of various types of hydrocarbons were plotted against the number of carbon atoms per molecule; the average curves are shown in Figure 13. The experimental values for some of the oil fractions, determined on an Abbe-type refractometer, are also included for comparison. The first extracts have dispersions resembling those of polynuclear aromatics but varying as the extraction proceeds to values comparable to the naphthene hydrocarbons. The next series of fractions from the distillation of blend 41-60, also indicates a range of compounds from bicyclic to monocyclic aromatics, although the latter may be a mixture of benzene and naphthene homologs. Specific dispersions of the distillation fractions of the raffinate are slightly higher than the average for naphthene hydrocar-

338


bons, indicating some unsaturation or admixture with benzene or Tetralin derivatives. Considering both the data obtained by the Waterman analysis on the number of rings per molecule and the empirical formula, and the comparisons of certain physical properties with those of synthetic hydrocarbons, it appears that the composition of the particular oil investigated ranges from a small amount of polynuclear aromatics with few side chains to considerably larger quantities of monocyclic naphthenes with long paraffinic side chains. The separate fractions studied cannot be considered as individual chemical components, for while the oil was separated into fractions comprising 1 per cent or less of the original distillate, they are still undoubtedly mixtures of hydrocarbons, even though well segregated according to type and size.

Practical Aspects The separation accomplished in this investigation, while probably insufficient for strict chemical analysis of components, serves to yield some valuable theoretical and practical information. The knowledge of the physical and chemical characteristics of the narrow fractions of any oil naturally should be of some assistance to the technologist or refiner in obtaining a better understanding of the raw materials available and of methods for producing any possible product from them. The behavior of an oil in service is related t o the composition or the combination of individual constituents. In order to study the effects of the components alone or in combination with one another, it is necessary to have them separated, and from a practical standpoint, a t least, it is preferable to perform the separation by simple established procedures that are readily available and adaptable t o the refiner. It is unnecessary to conduct the initial separation on so large a scale as the present one, where large-size final samples were desired for further study. When collecting data for the construction of a composition diagram representing the proportions of the various type fractions, such as shown in Figure 6, from 3 to 10 gallons of oil are ample. Obviously the laboratory distillation and extraction should be commensurate with the anticipated or available plant processes to obtain maximum usefulness. If extraction is first employed in the separation sequence,

Vol. 33, No. 3

$

additional useful information can be obtained /IO by sampling p /OO the raffinate remaining after B& 200 /90 r e m o v a l of $‘ /80 successive ext r a c t s . Final 170 samples, how/so e v e r , c a n be $ /50 blended back t o 460 obtain similar results. Using \ 450 Q . the latter $440 method, for ex4 430 ample, the 2 420 physical prop4/0 erties that may be expected for 400 different yields 0 /O 10 30 40 50 60 70 80 90 100 Weight Per Cent HWd o f Rqffihu#e of raffinate as produced by FIGURE14. PROPERTIES OF RAFFIthe particular NATE AS A FUNCTION OF EXTRACTION YIELD extraction procedure described a r e shown in Figure 14. Varying the extraction technique or the solvent may produce somewhat different relations.

* B

/20

4

3

Acknowledgment Credit should be given to the entire staff of the Petroleum Refining Laboratory for their services in operating the equipment and obtaining the analytical data. The authors wish to express their appreciation to A. H. Caser for assistance in assembling and correlating the data, to Stephen Lawroski and James D. Hegy for valuable suggestions in the construction of the composition diagrams, and to R. A. Rusk for constructing most of the equipment. Grateful acknowledgment is made to the Pennsylvania Grade Crude Oil Association for their generous support and cooperation in this study.

Literature Cited (1) Am. Soc. Testing Materials, Standards on Petroleum Products

Number o f Carbon Atoms per Mo/ecde FIGURE 13. SPECIFIC DISPERSIONS OF PETROLEUM FRACTIONS AND SYNTHETIC HYDROCARBONS

and Lubricants, Philadelphia, 1939. (2) Doss, M. P., “Physical Constants of the Principal Hydrocarbons”, New York, Texas Co., 1939. (3) Evans, E. B., J.I n s t . Petroleum Tech., 23, 220 (1937). (4) Ibid., 24, 321-37, 537-53 (1938). (5) Fenske, M. R., “Science of Petroleum”, p. 1634, London, Oxford Univ. Press, 1938. (6) Fuchs, G. H. yon, and Anderson, A. P., IND. ENG.CHmr., 29, 319-25 (1937). (7) Hersh, R. E., Fisher, E. K., and Fenske. & R., !IIbid., . 27, 1441-6 (1935). ( 8 ) Hersh, R. E., Fry, E. &I., and Fenske, M. R., Ibid., 30, 363-4 (1938) (9) Hersh. R. E.. Varteressian, K. A , , and Fenske, M. R., IND.ENQ. CHEM.,Anal. Ed., 10, 86-91 (1938). (10) Hill, J. B., and Coats, H. B., IXD.ENG.CHEM.,20, 641 (1928) (11) Maybery, C. F., IND.ENG.CHEM.,15, 1233 (1923): 18, 814 (1926). (12) MoCluer, W7.B., and Fenske, & R., I.I b i d . , 24, 1371-4 (1932). (13) Mair, B. J., and Willingham, C. B., J . Research N a t ? . B u r . Standards, 17, 923-42 (1936). (14) Mair. B. J., Willingham, C. B., and Streiff, A. J., Ibid., 21, 581607 (1938); IND. ENG.CHEM.,30, 1256-68 (1938). (15) Mikeska, L. A., Ibid., 28, 970-84 (1936). (16) Smith, H. M., U. 9. Bur. Mines, Tech. Paper 428 (1928). (17) Vlugter, J. C., Waterman, H. I., and Westen, H. A. van, J. Inst. Petroleum Tech., 21, 661 (1935). (18) Ward, A. L., and Kurta, S. S.,Jr., IXD. ENQ.CHEM.,Anal. Ed., 10, 559-76 (1938).

Separation and Composition of a Lubricating Oil Distillate

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