Fractionation and Characterization of Low Molecular Weight Asp ha1tic Hydroca rbons D.
E. WETMORE,' C. K. HANCOCK,
and R. N. TRAXLER
Chemistry Department, Texas A&M University, College Station, Tex. The fractions of lower molecular weight were isolated from three commercial road-building asphalts. The first step was precipitation of the asphaltenes with n-pentane. Pentane solutions of the petrolenes were then treated twice with 85% sulfuric acid, followed by chromatography of the sulfuric acid-insoluble material on Florisil. Finally the product eluted from the Florisil by n-pentane was separated into ten fractions by thermal diffusion. The resulting 30 thermal diffusion fractions were investigated by physical constant-structure correlation procedures and by ultraviolet, infrared, and nuclear magnetic resonance spectral methods. Of these procedures, nuclear magnetic resonance spectrometry offers the most promising approach to the type of materials encountered. The fractions obtained from a solvent-refined asphalt were somewhat more aromatic than from those produced solely by distillation. Hypothetical molecular structures are presented for some of the low molecular weight hydrocarbons present in the three asphalts.
M
investigations of asphaltic constituents have been directed toward establishing relationships between service characteristics and measurable parameters. Among the comprehenqive investigations directed toward the elucidation of asphalt chemistry are those of O'Donnell (28), Gardner and coworkers @ I ) , and Yen and Erdman (41). The work described here is concerned with the hydrocarbons of relatively low molecular weight, which comprise only a portion of the petrolenes, Fractions from three different asphalts were investigated to determine whether differences in the gross asphalts were reflected in the hydrocarbon fractions of low molecular weight and, if so, to evaluate the magnitude of these reflected differences. The fractions were characterized by elemental analyses, molecular weights, indices of refraction, densities, ultraviolet spectra, infrared spectra, and nuclear magnetic 1
ANY
Present address. Sun Oil Co., Marcus
resonance spectra. The results of several of these methods are compared and their effectiveness is evaluated. EXPERIMENTAL
Asphalts Used. Three 135 penetration grade asphalt cements were obtained by Texas Highway Department personnel in 1959 a t paving sites in the state of Texas. The asphalts are designated by code numbers 1-4, 3A, and 6A. Asphalts 1A and 3X are straight-run asphalts, while 6A is a solvent-refined product. Analytical data are given in Table I. Physical and rheological properties are shown in Table 11. Fractionation Procedures. The asphaltenes were precipitated with 40 volumes of n-pentane, the supernatant petrolene solution was decanted, and the asphaltenes were washed with an additional 20 volumes of solvent. The recovered asphaltenes were washed further in a large Soxhlet extractor with n-pentane until the washings were almost colorless. The extracted petrolenes were conibined and completely stripped of solvent. Basic materials were then removed from the petrolenes by extraction with sulfuric acid. This acid has been utilized in several fractionation schemes (19,S I ) . The extractions were made a t 15' C. to minimize oxidation and sulfonation. Fifty grams of petrolenes were added to 2.5 liters of n-pentane in a 3-liter flask. The mixture was stirred until the petrolenes had dissolved and then cooled to approximately 15' C. Then, with stirring, 100 ml. of 85% sulfuric acid were added dropwise over a period of 5 minutes and the reaction mixture placed in an icebox overnight. The supernatant n-pentane solution was decanted and the sulfuric acid solution washed with three 250-ml. portions of n-pentane. The combined washings and filtrate were evaporated to a volume of 2.5 liters and the extrac-
Table 1.
tion process was repeated. The acidinsoluble material from the second acid treatment was dried in n-pentane over sodium hydroxide pellets for 15 minutes and filtered and the n-pentane was evaporated. The nonbasic nitrogen compounds in the sulfuric acid-insoluble portion of the petrolenes were removed by adsorption onto a Florisil (activated magnesium silicate) column. The nonnitrogenous compounds were then desorbed with n-pentane. This technique has been used by others (17, 22, 52) to remove nitrogen compounds from petroleum materials. Florisil (60- to aOO-mesh, The Floridin Co., Hancock, W. Va.) was dried a t 150' C. for 24 hours and cooled to room temperature under vacuum. The Florisil was then run, in a slow stream, into a 5- X 85-em. chromatographic column full of anhydrous n-pentane. After the column was filled, a plug of glass wool was placed on the Florisil surface, and a 2-liter separatory funnel was attached to the top of the column. The column was heated to approximately 100" C. for 4 hours under a slow stream of dry nitrogen. The column was cooled while the nitrogen flow was maintained. The weight of the Florisil in the column varied between 0.9 and 1.1 kg. After the column was prepared, 50 grams of the sulfuric acid-insoluble material was dissolved in 1 liter of anhydrous n-pentane and adsorbed onto the column. The column was eluted (under 20- to 30-mm. pressure of dry nitrogen) with 15 liters of anhydrous n-pentane. The eluate was collected and the solvent removed to yield a predominantly hydrocarbon fraction. This residue is referred to as the "base material" of the particular asphalt. The base materials were then fractionated by thermal diffusion. This method, a separation based on shape differences (2, 2.4, has been used in the investigation of many petroleum fractions, including lubricating oils (27) and asphalt fractions (13, 2 1 ) .
Analytical Data of Asphalts
AS-
Per cent, Asphalt 1A 38 6A
C
H
85.44 84.07 87.05
10.35 9.81 10.95
0 1.06 0.40 0.73
S 2.74 4.46 1.00
N 0.65 0.45 0.50
H/C ratio
phaltene content,
1.44 1.39 1.50
70
11.0 17.5 1.0
Hook, Pa.
VOL. 38, NO. 2, FEBRUARY 1966
225
Prior to filling, the thermal diffusion column (186 cm. long, 27-ml. capacity) was thoroughly flushed with dry nitrogen. The column was filled by a syringe fitted with an adaptor which screwed onto the bottom port. The outer wall of the column was preheated to approximately 50' C. and the charge introduced through the syringe. The column was considered full when a steady stream of material emerged from the top port. The outer wall of the diffusion column was heated electrically and maintained a t 90" C. Water at 40' C. was circulated through the inner tube. After 200 hours the 10 fractions were drained from the equally spaced ports into nitrogen-flushed containers and stored in the dark. The thermal diffusion fractions are designated by asphalt source and
column port, 1 through 10, bottom to top. Analytical Procedures. Elemental analyses were obtained for all of the fractions. Oxygen was determined directly, not by difference. Molecular weights of asphalt fractions have been determined by viscosity measurements (30) and ebullioscopic (13, $20)and cryoscopic techniques (18). In this investigation molecular weights of the thermal diffusion fractions were determined by the osmometric method (10, 36). 411 measurements were made on a Mechrolab 301 Osmometer. A calibration curve was constructed from three readings a t each of ten concentrations (0.01 to 0.10M) of recrystallized trimyristin in Spectrograde chloroform. Solutions of each thermal diffusion fraction were made up
Table
Code No.
ASTM penetration at 77" F., 100 g . / 5 sec.
R&B softening point, "F.
1A 3A 6A
132 142 133
111 111 111
II.
Physical and Rheological Properties
Flash COC, OF. 560 540 600
a t two concentrations (approximately 50 and 25 grams per liter). Triplicate readings were taken on each solution and the two molecular weight values averaged to yield a mean number average molecular weight for the fraction. The average deviation of the values for a given fraction was 2.1%. Refractive indices were measured a t 70" i 0.03' C. with a Bausch and Lomb Abbe-56 refractometer, calibrated before use with the test piece supplied by the manufacturer. Because of the small amount of material in each thermal diffusion fraction, densities were determined by direct weighing. Several test tubes made from a semimicroburet were hung on a line suspended from the stirrup hook of a balance through a hole in the pan and balance case and about two
+
Sp'ogr'J 77 F.
Viscosity at 77' F., poises"
Viscosity of hardened sampleb at 77' F., poises
Relative viscosity of hardened samplee
0.999 1.024 0.985
0.59 X loe 0.54 X lo6 0.36 X lo6
2 . 5 X lo6 2 . 2 x 106 0 . 9 x 106
4.2 4.1 2.5
Viscosity obtained in thin film (sliding plate) viscometer and calculated a t 5 X sec.-l rate of shear. F. Viscosity of hardened film measured a t same temperature and rate of shear as original asphalt. c Quotient obtained by dividing viscosity of hardened asphalt by that of original bitumen. a
* Fifteen-micron films on glass plates heated in dark oven for 2 hours a t 225' Table 111.
Fraction
cJ%
Hj 97,
N,%
Properties of Asphalt Fractions OJ%
' J
%
Molecular weight
H/C ratio
Index of refraction
Density
802 752 769 762 806 793 864 863 871 795 760
1.72 1.73 1.76 1.79 1.80 1.84 1.86 1.88 1.93 1.95
...
1.4726 1.5060 1.4963 1.4890 1.4852 1.4784 1.4714 1,4683 1,4634 1,4578 1.4488
0.8903 0.9047 0.9017 0.8927 0.8829 0.8795 0.8744 0.8728 0.8583 0.8497 0.8411
776 772 779 833 805 698 661 816 777 784 630
1.70 1.72 1.75 1.84 1.82 1.83 1.90 1.85 1.95 1.96
...
1,4787 1.4987 1.4982 1.4865 1,4807 1.4803 1.4750 1,4646 1.4567 1.4540 1,4445
0.8720 0.9007 0.8921 0.8793 0.8695 0.8660 0.8648 0.8603 0.8631 0.8451 0.8423
915 797 955 887 942 782 756 747 769 742 666
1.61 1.68 1.67 1.68 1.71 1.84 1.84 1.86 1.98 1.98
...
1.4743 1.5137 1.5051 1.4982 1.4915 1.4845 1.4773 1.4718 1.4659 1.4382 1.4485
0.8841 0.9206 0,9081 0.9027 0,8966 0.8881 0.8792 0.8717 0.8603 0.8399 0,8413
Asphalt 1A BM 1 2 3 4 5 6 7 8 9 10
85.52 86.19 86.16 85.90 85.98 85.50 85.64 85.15 85.27 85.31 85.42
12.96 12.45 12.48 12.72 12.95 12.94 13.22 13.21 13.42 13.83 14.00
0.16 0.17 0.14 0.25 0.31 0.27 0.28 0.30 0.25 0.22 0.23
0.44 0.49 0.84 0.82 0.72 0.71 0.72 1.32 0.74 0.35 0.20
BM 1 2 3 4 5 6 7 8
85.38 86.44 86.22 86.18 85.65 85.87 85.67 85.03 85.65 85.35 85.33
13.31 12.32 12.46 12.63 13.25 13.13 13.13 13.54 13.30 13.95 14.01
0.95 0.21 0.07 0.10 0.21 0.00 0.03 0.71 0.06 0.15 0.11
0.42 0.21 0.00 0.18 0.19 0.00 0.13 0.07 0.00 0.00 0.00
86.01 85.58 85.66 85.73 85.79 85.69 84.48 84.72 84.65 84.48 84.42
13.06 11.59 12.05 12.00 12.10 12.33 13.06 13.06 13.22 14.06 14.06
0.11 0.14 0.07 0.14 0.14 0.15 0.20 0.34 0.24 0.17 0.16
0.26 0.00 0.26 0.04 0.16 0.26 0.62 0.14 0.04 0.00 0.00
0.60 1.02 0.87 0.47 0.50 0.57 0.44 0.42 0.55 0.56 0.44
Asphalt 3A
9
10
1.01 0.71 1.02 0.76 0.82 1.05 1.08 0.63 0.86 0.6Q 0.62
Asphalt 6A B Il.I 1 2 3 4 5
6 7 8 9 10
226
ANALYTICAL CHEMISTRY
0.79 1.66 1.94 1.96 1.74 1.68 1.79 1.90 1.82 1.53 1.41
1
Figure 2. fraction 1
Figure 1. fraction
2
3
2
3
4
5 6 FRACTION
7
8
9
1
0
Relative absorption at 718 ern.-' vs.
4 5 6 FRACTION
Relative absorption at 1725 crn.-l
thirds submerged in a dibutyl phthalate bath maintained a t 70" + 0.03" C. The tubes were half-filled with distilled water and weighed. The exact liquid levels in the tubes were determined through interpolation between graduations on the tubes by a cathetometer. From these data, the true volume of each tube was correlated with its graduations. This technique was used to determine the densities of the thermal diffusion fractions. Triplicate determinations (with triplicate weighings and cathetometer readings on each) were made for each sample. Ultraviolet spectra (210 to 360 mk) were obtained for all the thermal diffusion fractions as 10-5~f solutions in cyclohexane. The solvent, purified by distillation and percolation through silica gel, was transparent from 750 to 215 mp. Infrared spectra were recorded on a Beckman IR-8 spectrophotometer using 0.50-mm. sodium chloride cavity cells. Commercial Spectrograde chloroform and cyclohexane purified as described above were used as solvents. Two concentrations (30 and 0.625y0) were chosen. At 30 weight %, peaks other than those arising from carbon-hydrogen and carbon-carbon bonds were visible, while dilution to 0.625 weight yo was necessary to reduce the carbon-hydrogen absorptions to less than 1 0 0 ~ o . Suclear magnetic resonance has been used to investigate asphaltenes (21, 40, 41), various asphalt fractions ( I @ , and petrolenes (21). Suclear magnet'ic reSonance spectra of the fractions obtained by thermal diffusion were recorded on a Varian Model A-60 spectrometer. Spectra were obtained for the fractions both pure and as 70 volume yo solutions in carbon tetrachloride. Tetramethylsilane was used as an internal standard. Spectra were recorded a t 500 and 1000 c.p.s. RESULTS
Correlation of Physical Properties. Properties of the three base materials charged to the thermal diffusion column and of the fractions obtained therefrom are shown in Table 111. Several methods have been developed for the empirical correlation of properties and structure in petroleum chemistry (16, 23, 25). The correlations
vs.
O'
; ;
b
4
;i
FRACTION
Figure 3. fraction
Relative absorption at
+
v
A b Ib
696 ern.-' vs.
proposed by Waterman (57') and Corarea contains distinctive patterns pebett (14) were used. Waterman's culiar to different types of aromatic method was suitable for only a limited substitution (48). The spectra of the number of the fractions because the thermal diffusion fractions show a 1,2,heterocyclic content often exceeded the 3,&tetra-substituted aromatic pattern limits he had established. a t 1725 em.-' (Figure 1). To exclude Corbett's method, while designed the possibility of carbonyl absorption, a specifically for asphalts and some fraction which absorbed strongly in this asphalt fractions, proved unsatisfactory in this case as conjugated olefins were present and the fraction of the carbon in aromatic rings was much less than Table IV. Molar Extinction Coeffithe 0.25 required by the Corbett method cients ( X 10-5) in Ultraviolet in the presence of naphthenic rings (55). FracUltraviolet Spectra. The ultration 230 mp 233 mp 260 mp violet spectra of the fractions (Table Asphalt 3A IV) indicate the presence of monoBM 28.5 0.0 6.8 cyclic aromatic compounds and con1 0.0 49.8 21 .o jugated olefins in asphalts 1-4 and 3A. 2 0.0 54.7 20.0 The spectra of the fractions from these 3 0.0 68.3 22.5 4 0.0 74.0 25.0 two asphalts have two peaks, one a t 5 0.0 38.9 12.0 230 to 233 mp and a smaller peak a t 16.5 6 0.0 53.0 260 mp. These peaks, and the lack of 30.5 0.0 7 7.9 well defined absorption minima, are 8 3.8 18.1 0.0 consistent with the assumption that the 30.9 0.0 9 7.2 10 9.5 0.0 0.1 unsaturation in the fractions from these two asphalts consists mainly of monoAsphalt 1A cyclic aromatics and conjugated olefins B11 21.8 0.0 6.8 (34). The fractions from asphalt 6-4 0.0 5.5.5 1 22.8 have only a 230-mp peak, indicative of 2 0.0 37.5 15.0 3 24.8 0.0 7.8 the presence of thionaphthenes (9). 4 23.0 8.0 0.0 In all cases, all but the lower fractions 5 12.1 35.0 0.0 are completely transparent from 270 to 2.0 6 12.1 0.0 26.0 0.0 360 mp, showing the lack of condensed 7 7.1 19.5 8 0.0 3.0 aromatic systems. 9 20.1 0.0 4.2 Infrared Spectra. Interpretation 10 6.0 0.0 0.0 of the infrared data is complicated by Asphalt 6A the intense paraffinic hydrocarbon absorption bands appearing through the Bhl. 7.5 0.0 0.0 1 10.0 0 .0 0.0 spectra. T o utilize the spectra for 2 1 5 . 1 0 . 0 0.0 detection of other than carbon hydro3 10.5 0.0 0.0 gen absorptions, it was necessary to 4 16.5 0.0 1.0 use concentrated solutions (30%). 5 6.5 0.0 0.0 6 8.8 0.0 0.0 In general, the 4000- to 2000-~m.-~ 7 10.0 0.0 0.0 region contains only extremely strong 8 12.2 0.0 2.8 methyl and methylene stretching peaks 9 3.8 0.0 0.0 (3). In the absence of fundamental 10 0.0 0.0 0.0 carbonyl peaks, the 2000- to 1650-cm.-l ~~
VOL. 38, NO. 2, FEBRUARY 1966
227
9-
i
8-
7-
I
0 6-
58
c
4-
3-
Figure 5.
Branchiness index vs. fraction
2.
I-
FRACTION
Figure 4.
Alpha-hydrogen (na) vs. fraction
area was reduced with sodium borohydride. The reduction product showed no diminution in this absorption. An aromatic double bond stretch pattern, consisting of a weak peak a t 1600 cm.-l with a shoulder a t 1575 cm.-l (6) is noted in some of the lower fractions. The 2000- to 1000-cm.-l area also contains paraffinic deformation peaks a t 1460 and 1370 cm.-l (3), a peak a t 1270 cm.-', possibly a carbon-carbon stretch coupled with a methylene wagging vibration ( 5 ), and aromatic
Table V.
substitution peaks a t 1118 and 1070 cm.-' (8). The 1000- to 650-cm.-l region contains three areas of interest: a series of broad, ill-defined peaks in the 800- to 720-cm.-l area, again indicating aromatic substitution patterns (Y), a peak a t 718 cm.-1 arising from a chain of four or more methylene groups (4) (Figure 2) , and an aromatic carbon-hydrogen deformation peak at 696 cm.-* (33) (Figure 3). From the infrared spectra it would
Normalized NMR Absorptions
Fraction
hAr
4 5 6 7 8 9 10
0.010 0.015 0 IO09 0,010 0.013 0.008 0.008 0.008 0.005 0.003
0.073 0.055 0.031 0.037 0.035 0.041 0.037 0.040 0.033 0.037
0.007 0.006 0.009 0.007 0.012 0.012 0.008 0.007 0.006 0.004
0.069 0.041 0.077 0.086 0.059 0.065 0.064 0.026 0.038 0.068
0,007 0.017 0.020 0.018 0.027 0,018 0.017 0.011 0.009 0.012
0,092 0.091 0.078 0,080 0.063 0.031 0.020 0.024 0.062 0,011
ha
hN
hR
Asphalt 1A 0.162 0.139 0.115 0.127 0.130 0.122 0.115 0.119 0,099 0.101
0.493 0.509 0.618 0.597 0.614 0.634 0.672 0.677 0.684 0.710
0.262 0.282 0.227 0.229 0.208 0.195 0.168 0.156 0.179 0.149
0.496 0.471 0.553 0.568 0.633 0.652 0.710 0.791 0.767 0.721
0.295 0.334 0.234 0,212 0.188 0.174 0.30 0.114 0.129 0.140
0.513 0.524 0.563 0.579 0.623 0.658 0.713 0.734 0.723 0.807
0.222 0.221 0.211 0.214 0.196 0.179 0.156 0.163 0.140 0.106
Aspha1t 3A 1
2 3 4 5 6 7 8 9 10
0.113 0.148 0.127 0.127 0.108 0.097 0.068 0.062 0.060 0.067
Asphalt 6A 1
2 3 4 5 6 7 8 9 10
228
ANALYTICAL CHEMISTRY
0.166 0.147 0.128 0.109 0.091 0.116 0.094 0.068 0.066 0.064
appear that the base material from asphalt 1h contains a large number of tetra-substituted aromatic systems, concentrated in the middle thermal diffusion fractions (Figure I). In the base material from asphalt 3A, the aromatic ring content decreases as the total ring content decreases and the molecules become not only smaller with total decreasing ring content, but more paraffinic. The base material from solventrefined asphalt 6 h is more chemically homogeneous throughout the thermal diffusion fractions than the base materials from the two straight-run asphalts. Nuclear Magnetic Resonance. Many heavier petroleum fractions (11, 12, 21, 38, 39) have been studied by nuclear magnetic resonance. Yen and Erdman (41) integrated suitable portions of the XMR spectrum t o determine the amounts of aromatic protons, H A R ,protons alpha to aromatic nuclei, H a , naphthenic protons, H N , aliphatic methylene protons, H R , and methyl protons not alpha or beta to aromatic systems, H B Y ~ . These areas of the KMR spectra of the thermal diffusion fractions were measured with a planimeter. Replicate determination of the larger areas agreed within lyo,while measurements of the smaller areas differed by no more than 4%. After division of each area by the spectrum amplification for that particular spectrum, the areas were corrected to 1OOyo concentration of the asphalt fraction and then divided by the total proton absorption for that fraction. The resulting normalized areas, designated by h, are given in Table V. Multiplication of the total percentage of hydrogen in a fraction by the normalized area of a particular form of hydrogen gives the percentage of hydrogen in that particular form. The ultraviolet spectra indicate that a large percentage of the aromatics are mononuclear, while the infrared spectra indicate the presence of 1, 2, 3, 5-tetrasubstituted systems. This gives a value of 4/6, or 0.66 for ja, the fraction of available aromatic positions which are substituted. ,4n expression from NMR
data containing this value and the number of alpha-hydrogens takes the form :
where na is the number of alphahydrogens on each alpha-carbon atom. The nu values corresponding to an fa of 0.66 are given in Table VI and Figure 4. The high values of n are due to a decrease in fa, which, in the lower fractions, is due to the presence of condensed aromatic systems, and in the higher fractions to small amounts of mono-, di-, and tri-substituted monoaromatic molecules. X variety of assumptions have been made concerning the structures of the naphthenic molecules of asphalt (14, 16, 23, 26, 37). If the naphthenic molecules are considered to be six-membered, ortho-condensed systems, they have the general formula CZ+ 4R"e + 6RN where RN is the number of rings in the system. The number of six-membered rings is related to the percentage of naphthenic hydrogen by the expression
% HN = 1.008 (6 -I- ~ R N X) 102/M.W.
(2)
which leads to an expression for R N :
The branchiness index, BI, is the ratio of methyl groups (not alpha or beta to an aromatic nucleus) to the aliphatic, acyclic methylene groups. It was calculated from the formula BI
=
(hme/hR) (2/3)
(5)
where the' factor of z/3 was introduced to transform the 3 : 2 methyl hydrogenmethylene hydrogen absorption ratio to a 1 : l methyl carbon-methylene carbon ratio. The branchiness indices are shown in Figure 5 . The structural parameters derived from the KMR data confirm the conclusions drawn from the other data and also give reliable quantitative results. From an examination of polymers of known composition, it was found that the structural parameters derived from NMR data were closer to the true values than those derived from infrared data (41). Consequently, where the NMR and infrared data conflict, the NMR data are assumed to be more reliable. The parameters concerning the aromatic portions of the fractions are the least reliable, as the peak areas were relatively small, giving rise to spurious peaks (low signal-to-noise ratio) and errors in peak area measurement.
R N = { (%O")(M.W.)/ 6.048 X lo2)
-1
The average number of six-membered rings in naphthenic systems is shown in Table VII. Form the general form of a paraffin, C,H2, + 2, the number of carbon atoms in the average paraffinic chain can be calculated from the following expression
+ %,Hsu,)
=
DISCUSSION
(3)
(M.W.)/
2.016 X lo2} - 1
(4) Table VI11 gives the number of carbon atoms in the average paraffinic chain in each fraction.
The ultraviolet spectra show that the aromatic material from base materials 1A and 3 h is predominantly mononuclear. The aromatic content of base material 6A is extremely low. I n base material 6d the ultraviolet spectra indicate that the sulfur is present as thionaphthenes. The aromatic absorptions in the fractions from base materials 1A and 3-4 overlap the thionaphthene absorption, and do not permit identification of the sulfur compounds in these base materials. The na values for the middle fractions
46
of base materials 1A and 6A corroborate the evidence of the infrared spectra for the presence of 1,2,3,5-tetrasubstituted benzenes. There are wide variations in aromatic type in the fractions from 3A base material. In the lower fractions of all three base materials these anomalous
Table VI. Average Number of AlphaHydrogen per Alpha-Carbon Atom
Fraction
Asphalt 1A
Asphalt 3A
Asphalt 6A
1 2 3 4 5 6 7 8 9 10
3.65 1.83 1.72 1.85 1.35 2.56 2.31 2.50 3.30 6.18
4.92 3.42 4.28 6.14 2.46 2.71 4.00 1.86 3.16 8.50
6.57 2.68 1.95 2.22 1.17 0.86 0.59 1.09 3.44 0.46
Table VII. Average Number of SixMembered Rings in Naphthenic Systems
Frac- Asphalt tion
1A
Asphalt 3A
Asphalt 6A
1 2 3 4 5 6 7 8 9 10
1.507 1.205 0.843 1.190 1.208 1.304 1.167 1.299 0.799 0.776
0.776 1.374 1.208 1.239 0.636 0.391 0.242 0.059 0.085 -0.022
1.535 1.796 1.252 1.054 0.450 0.893 0.516 0.143 0.138 -0.009
Table VIII. Average Number of Carbon Atoms in Paraffinic Acyclic Systems
Fraction
Asphalt 1A
Asphalt 3A
Asphalt 6A
1 2 3 4 5 6 7 8 9 10
34.06 32.84 39.62 41.76 40.83 45.97 46.50 47.29 446.06 4.33
36.31 38.80 40.06 40.27 36.32 34.56 .. 46.12 45.38 36.69 47.60
32.67 41.52 39.86 43.83 38.17 39.84
~~
4i.05
44.23 41.40 43.65
44 42 c
N
I 40
5
.E 38 5
36
34 32 FRACTION
Figure 6. Average number of carbon atoms in paraffinic, acyclic systems v5. fraction
FRACTION
Figure 7.
Molecular weight vs. fraction VOL. 38, NO. 2, FEBRUARY 1966
229
values are caused by the presence of polycyclic aromatics and of less substituted benzenes in the upper fractions. Both effects would appear to occur throughout the entire fraction range of base material 3A. The NRIR values indicate a steady decrease in the average number of sixmembered rings in naphthenic systems, and, assuming only six-membered rings, a decrease in the total number of naphthenic rings as the fraction number is increased. The branchiness index is a function of both the degree of branching and the size of the molecule. However, as the size increases, its effect on the branchiness index decreases. The difference in the branchiness indices of n-hentriacontane (n-C31H64)and n-octatetracontane (n-C48H98)is 0.023, and is too large to be ignored in the values obtained for the base material fractions, which range from 0.473 to 0.088 (Table VIII). The general decrease in the branchiness indices for the fractions from all the base materials (Figure 5) cannot, however, be attributed only to size variations, as the range of the branchiness indices is 0.385, much greater than 0.023, and the value for the largest member of the series, n-C48HOg,if normal, would be 0.067. The average number of carbon atoms in paraffinic systems varies widely from fraction to fraction, but a comparison of figures shows that the paraffinic carbon atom plot (Figure 6) is, for the m o d part, an exaggerated form of the molecular weight plot (Figure 7 ) . This would indicate that in all cases the majority of the fraction average molecule is paraffinic. The chemical shift pattern of the methyl groups indicates that a majority of the paraffinic chains terminate in -(CH2).CH3 groups, where n > 1 (I). CONCLUSIONS
Nuclear magnetic resonance spectrometry appears to offer the most promising approach to the characterization of the asphaltic components studied. With materials predominantly hydrocarbon-like in nature, information about hydrogen distribution aiso provides much information concerning carbon distribution and the structure of the material. X survey of all the data obtained in this study allows some general conclusions to be drawn about the chemical make-up of the different base materials. Base material 6-1 is much less aromatic than those froin asphalts I d and 3A. Base materials 3-1 and 6.1 are similar in their naphthenic content, while base material 1A is more naphthenic than the other two. The lower fractions of all three base materials are similar in the amount of acyclic material prezent. In 230
ANALYTICAL CHEMISTRY
the lighter fractions, differing amounts of acyclic material are present, but no trends of difference are evident. The degree of branchiness is similar for all the fractions. On the basis of data accumulated for each fraction, one is able to construct hypothetical structures for the average molecule from each fraction. Such hypothetical structures for the top and bottom thermal diffusion fractions for each base material are presented in Figure 8. These structures are not intended to represent the actual chemical structure of a specific compound in the fraction, but rather to illustrate the general nature of the compounds present in that fraction. They are hypothetical structures which fairly closely fit the data accumulated for the fraction average molecule.
IA-I
P IA-IO
+ 3A-I
ACKNOWLEDGMENT
Asphalts were supplied by the Texas Highway Department. The thermal diffusion column was loaned by Texaco, Inc. Alfred Danti made possible the application of nuclear magnetic resonance spectrometry. In addition, the authors thank their associates who contributed aid and encouragement during the investigation.
3A-IO
LITERATURE CITED
(1) Bartz, K. W., Chamberlain, E. F., AKAL.CHEM.36, 2151 (1964). ( 2 ) Begeman, C. R., Cramer, P. L., Ind. Eng. Chem. 47, 202 (1955). ( 3 ) Bellamy, L. J., “The 1nfl;Y-Red Spectra of Complex hlolecules, 2nd ed., p. 13, Wiley, New York, 1962. ( 4 ) Ibid., p. 27. ( 5 ) Ibid., p. 29. ( 6 ) Zbid., p. 71. ( 7 ) Ibid., p. 75. ( 8 ) Ibid., p. 81. ( 9 ) Bestougeff, &I., World Petrol. Congr., 5th Proc., N . Y . 5, 143 (1959). (10) Brady, A. P., Huff, H., McBain, J. W., J . Phys. Chem. 55, 304 (1951). (11) Brown, J. K., Ladner, W. R., Fuel 39, 87 (1960). (12) Brown, J. K., Ladner, W. R., Sheppard, N., Ibid., 39, 79 (1960). (13) Chelton, H. RI., Traxler, R. N., World Petrol. Congr., 5th Proc., N . Y . 5, 247 (1959). (14) Corbett. L. W.. ANAL. CHEM.36, ‘ 1967 (1964). 1 1 5 ) Corbett. L. W.. Swarbrick. R. E.. Proc. dssbc. Asphalt Paving Technologists 27, 107 (1958). (16) Deanesly, K. bl.,Carleton, L. T., IND. E K G .CHEM.,ANAL.ED. 14, 220 (1942). (17) Dinneen, G. U., Cook, G. L., Jensen, H. B., ANAL.CHEM.30, 2026 (1958). (18) Eckert, G. W., Weetman, B., Ind. Eng. Chem. 39, 1512 (1947). (19) Fernandez, RI., Bol. Inform. Petrol. (Rvpno.s .4ires’i 19. 79 11942): C.A. - - - -~ 38, 50658 (1944); ‘ (20) Fischer, K. A,, Schram, A., World Petrol. Congr., 5th Proc., N. Y . 5, 259 (1959). (21) Gardiier, R. A., Hardman, H. F., Jones, A. L., Williams, R. B., J . Chem. Eng. Data 4 , 155 (1959). \
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Figure 8. Hypothetical structures for top and bottom thermal diffusion fractions for each of three base materials
(22) Helm, R. V., Latham, D. lE., Ferrin, C. R., Ball, J. S.,Ind. Eng. Chem., Chem. Eng. Data Ser. 2, 95 (1957). (23) Hersh, R. E., Fenske, bl. R., Boozer, E. R., Koch, E. F., J . Inst. Petrol. 36, 624 (1950). (24) Kramers, H., Broeder, J. J., Anal. Chzm. Acta 2, 687 (1948). (25) Lipkin, SI. R., Martin, C. C., IND. ENG.CHEM.,ANAL.E D . 19, 183 (1947). (26) Mair, B. J., Rossini, F. D., Ind. Eng. Chcm. 47, 1062 (1955). (27) RIelpolder, F. W., Brown, R. -4., Washall, T. A., Doherty, W., Young, W. S., ANAL.CHEM.26, 1904 (1954). (28) O’Donnell, G., Ibid., 23, 894 (1951). (29) Phillips, J. P., “Spectra-Structure Correlation,” p. 42, Academic Press, New York, 1964. (30) Romberg, J. W.,Nesmith, S. D., Traxler. R. N.. J . Chem. Ena. Data 4, 159 (1959). ‘ (31) Rostler, F. S., White, R. AI., Ind. Eng. Chem. 46, 610 (1954). (32) Smith, J. R., Smith, C. R., Jr., Dinneen, G. U., ANAL.CHEM.22, 867 (1950).
(33) St. C. Flett, M:,
“Characteristic Frequencies of Chemical Groups in the Infra-Red,” p. 33, Elsevier, New York,
1963. (34) Stevenson, D. P., McConnell, H. M., Spectrochim. Acta 12, 262 (1958). (35) van Krevelen, D. W., Chermin, H. A. G., Fuel 33, 338 (1954). (36) Wagner, R. H. in “Physical Methods
of Organic Chemistry,” A. Weissberger, ed., p. 547, Vol. I, Part 1, Interscience, New York, 1949. (37) Waterman, H. I., ‘Correlation be-
tween Physical Constants and Chemical Structure,” pp. 3-26, Elsevier, New York, 1958. (38) Williams, R. B., Spectrochim. Acta 14, 24 (1959). (39) Williams, R. B., Chamberlain, N. F., World Petrol. Congr., 6th PTOC.,Frankfurt, West Germany 5 , 217 (1963). (40) Winniford, R . S., Bersohn, M., Di-
vision of Fuel Chemistry, Am. Chem. Soc., Preprints, Vol. 1, p. 21, Atlantic City, 1962.
(41) Yen, T. F., Erdman, J. G., Division
of Petroleum Chemistry, Am. Chem. SOC.,Pre rints, Vol. 7, No. 3, p. 99, Atlantic &y, 1962. (42) Young, C. W., DuVall, R. B., Wright, N., ANAL.CHEM.23, 709 (1951). RECEIVEDfor review June 28, 1965. Accepted November 22, 1965. Work supported by a Petroleum Research Fund Grant (No. 591-AI) to R. N.
Traxler.
Isolation and Identification of to C,, AI kylna phthalenes, AI kylbiphenyls, and Alkyldibenzofurans from the 275” to 305” C. DinucIear Aromatic Fraction of Petroleum c 1 3
FOCH FU-HSIE YEW and BEVERIDGE J. MAlR Petroleum Research laboratory, Carnegie Institute of Technology, Pittsburgh 7 3, Pa. A substantially complete analysis in terms of the amounts of the individual components in the dinuclear aromatic portion of petroleum boiling in the range from 275’ to 305’ C. was achieved. Twenty-nine compounds were isolated or identified. These include eight C13 alkylnaphthalenes, seven CI4 alkylnaphthalenes, five C14 alkylbiphenyls, four C,a alkylbiphenyls, four dibenzofurans, and fluorene. Methods were developed for identifying individual alkylnaphthalenes from their NMR spectra in those cases where synthetic samples and reference spectra were not available.
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the API Research Project 6 has concentrated its efforts on investigating the composition of the aromatic portion in the gas oil range of its reference petroleum. Preceding investigations have covered the trinuclear aromatic fractions of the heavy gas oil and light lubricating distillate, 305’ to 405’ c. (12) ; the mononuclear aromatic material in the light gas oil range, low refractive index portion, 230’ to 305’ C. (10) ; and the dinuclear aromatics in the light gas oil r~+nge,230’ to 275’ C. (11). The present research continues the program on the dinuclear aromatics in the light gas oil range, 275’ to 305’ C. Analysis in terms of the amounts of the individual compounds was substantially complete. Some compounds within this range have not yet been synthesized; therefore, their physical and spectrometric propURING THE PAST FEW YEARS,
Volume in l i t e r s Figure 1.
Results of the azeotropic distillation of Portion 5A
Numbers near the bottom of the figure indicate parts which were investigated additionally
erties are not available. For this reason, it became necessary to develop spectrometric methods of identification from basic principles and a knowledge of the spectra of model compounds; these methods are applicable to other similar problems. PROCEDURE
The method used to separate the dinuclear aromatic material from the light gas oil fraction of petroleum and the results of the subsequent distillation have been described previously (11). Portions 5 and 6 of the distillate, illus-
trated in Figures 1 and 2 of Reference (11) constituted the starting material for this investigation. Some of the distillate fractions near the middle of Portion 5 contained crystalline material which was subsequently identified as 2,3,&trimethylnaphthalene. After the removal of most of this compound by crystallization, the mother liquors, designated Portion 5 4 were azeotropi d l y distilled with dimethoxytetraethylene glycol. Portion 6 was azeotropically distilled with triethylene glycol. Results are given in Figures 1 and 2. The numbers at the bottom of each figure indicate the portions of the distillate which were investigated in detail. VOL. 38, NO. 2, FEBRUARY 1966
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