(Table V). These weights are not affected by solution association problems (compare Belridge VPO and electron microscope weights). Micelle Molecular Weights. Association between particles to form micelles was seen in the electron micrographs. The micelles are 100-300 A in diameter and correspond to a molecular weight equivalent of 37,000-10,000,000. The ultracentrifuge work here has, to date, followed Witherspoon’s method (5) and results are very similar. For Baxterville asphaltene, a molecular weight of 34,000 was obtained. More interesting is the observation, also reported by Witherspoon, that a very heavy fraction moves rapidly to the bottom of the centrifuge tube. Some preparatory scale work was started here in an effort to separate the fast moving material. On resuspension of the pellet and recentrifugation, it was noted that there was little difference in the supernatant liquid; it was again highly colored. It might be postulated that this represents dissociation of the largest micelles into smaller units and indicates some sort of equilibrium between associated particles (11). Micelles have previously been observed by Altgelt (12) who reported a molecular weight equivalent to 40,000 by GPC. Under the experimental conditions of the present work this peak was not found. The low angle x-ray diameter (50 A) may represent a micelle also. If it does, its molecular weight would be 46,000. However, the alternate explanation (2) that this diameter represents an unfolded particle in contrast to the compact electron microscope particle continues to be a possibility. (11) M. Wales and M. Van der Waarden, ACS, Div. Petroleum Chem., Preprmts, 9 (2), B21, (1964). (12) K. H. Altgelt, bbid., 10 (3), 29 (1965).
Macrostructure of Asphaltic Material. Figure 1, referred to previously, is a compilation of present knowledge about the macrostructure of the asphaltics. Of course, the structures pictured represent only some of the possible combinations of unit sheets, and specific features may vary among the fractions, particularly association in the resin fraction. In addition to structures discussed in this paper, Le., unit sheets (Figure 1, 4, intercluster association (Figure 1, G), particles (Figure 1, C) and micelles (Figure 1, E)), other features from previous work are shown. Metals (Figure 1, L), for example, can be an aid to micelle association. Similarly, petroporphyrins (Figure 1, K) can be associated with the crystallites (Figure 1, A), or defect centers (Figure 1, F), or attached through weak links (Figure 1, E). The defect centers could also be areas which would stabilize free radicals. ACKNOWLEDGMENT
The authors acknowledge the assistance of the following persons from Research Services, Mellon Institute: Stephen J. Ondrey, in the preparation of samples and calculations; Robert E. Rhodes, on mass spectral work; Robert E. Callahan, for VPO data; Linn A. Pittman, on the ultracentrifuge work; and Sidney S. Pollack, on small angle x-ray studies. The authors also acknowledge the assistance of Nancy D. Maranowski, Physical Sciences Division, Gulf Research & Development eo., on high angle x-ray studies. RECEIVED for review June 8, 1967. Accepted June 28, 1967. Work sponsored by Gulf Research & Development Co. as part of the research program of the Multiple Fellowship on Petroleum.
nverse Gas-Liquid Comparison wit
tudies of Asphalt ractionat ion
T. C. Davis and J. C. Petersen Laramie Petroleum Research Center, Bureau of Mines,
U.S . Department of Interior, Laramie, Wyo.
Results of analysis of asphalts by inverse gas-liquid chromatography (GLC) have been compared with results of analyses by the Kleinschmidt chromatographic fractionation and the Rostler and Sternberg sulfuric acid precipstation procedures. Relationships between the two fractionation techniques are indicated. The combined asphaltease and asphaltic resin content from the Kleinschmidt fractionation of each asphalt studied was found to be proportional to the GLC retention behavior of the test compound formamide determined on the whole asphalt. A common compositional factor between the asphaltenes and asphaltic resins was indicated. After oxidation of the asphalts within the GLC column, correlative trends were found between the inverse GLC retention behavior of the test compounds phenol and propionic acid, and measures of asphalt durability proposed by Rostler and White.
test compounds and chemical functionality in an asphalt, The asphalt serves as the stationary phase in a GLC column and is analyzed by observing the retention behavior of volatile test compounds. The asphalt may be analyzed either as-received or after an oxidation procedure which is performed within the column. Approaches extensively used in the characterization of asphalts involve the separation of the asphalts into fractions based on such properties as solubility, adsorption chromatography, or chemical reactivity. Two of the more recent fractionation techniques are the solvent precipitation-chromatographic separation of Kleinschmidt (5) and the sulfuric
THEABILITY of inverse gas-liquid chromatography (GLC) to indicate differences in the chemical composition of asphalts without the necessity of prior fractionation has been demonstrated previously (1-4). Briefly, the inverse GLC technique measures functional group interactions between volatile
Highway Research Board, National Research Council, 1-7
185%
e
ANALYTICAL CHEMISTRY
(1) T. C. Davis, J. C. Petersen, and W. E. Haines, ANAL.CHEM., 38, 241 (1966). (2) T. C. Davis and J. C. Petersen, Highway Res. Rec. No. 134, (1966). (3) T. C. Davis and J. C. Petersen, ANAL.CHEM., 38, 1938 (1966). (4) T. C. Davis and J. C . Petersen, Proc. Assoc. of Asphalt Paving Technologists, 36, in press, 1967. (5) L. €3.Kleinschmidt, J. Res. Nut. Bur. Srd., 54,163 (1955).
D i g e r I I it h] n-pentane solution fillrotion Asphallener
E l u t e through fuller's e u r l h with n - p t n t s n s
,
Eluate
I
,
Residue i n Eiutelwilh melhylene chloride
@
1-1
Residue i n
Elute'with methyl ethyl ketone
column Elute w i l k acetone chloroform mixture I
Asphallic
, Acetone chloroform
Figure 1. Kleinschmidt method of asphalt fractionation acid fractional precipitation of Rostler and Sternberg (6, 7). Flow diagrams of the two methods are shown in Figures 1 and 2. These methods have been compared previously (8, 9). The various fractions identified by the Kleinschmidt and the Rostler-Sternberg separations have differences in chemical composition and should, therefore, exhibit differences in molecular association forces. These forces should influence GLC retention data. Significant relationships may, therefore, exist between inverse GLC test compound retention data obtained on whole asphalt and the fractional composition as determined by the separation methods. Inverse GLC data were obtained on a number of asphalts and results were compared with the fractional composition. Rostler and White (7) have reported a correlation between results of the Rostler-Sternberg analysis and durability as measured in the laboratory by their pellet abrasion test. Inverse GLC retention data on asphalts oxidized in the column have shown a correlation with Weather-Ometer durability (2, 3) and road service (4). Therefore, a comparative study of inverse GLC data obtained on the same asphalts analyzed by Rostler and White was undertaken. Correlations were developed between test compound retention behavior on these asphalts after oxidation and compositional data obtained by Rostler and White. EXPERIMENTAL
Apparatus and Procedure. GLC data were obtained on a Beckman GC-2 gas chromatograph. The GLC column was prepared from '/(-inch by 13-foot aluminum tubing packed (6) F. S. Rostler and H. W. Sternberg, Ind. and Eng. Chem., 41, 598 (1949). (7) F. S. Rostler and R. M. White, Proc. Assoc. of Asphalt Paving Technologists, 31, 35 (1962). (8) F. S. Rostler and R. M. White, Am. Sac. Testing Materials Special Tech. Publ. No. 277, 64 (1959). (9) F. S. Rostler, "Bituminous Materials: Asphalts, Tars, and Pitches," Vol. 2, Part I, A. J. Hoiberg, Ed., Interscience, New
York, 1965, p. 196.
Figure 2. Rostler-Sternberg method of asphalt group analysis with one part of asphalt on 10 parts by weight of Fluoropak 80 and conditioned for a minimum of 6 hours using a helium inlet gage pressure of 15 psi and an instrument operating temperature of 130" C (normal testing conditions). After conditioning, 0.1-111 quantities of the test cornpounds were introduced individually, and retention times were determined as previously described ( I ) . The asphalt was then oxidized for 24 hours at 130" C within the column by replacing the helium carrier gas with filtered air using the technique previously reported (2, 3). After the oxidation step, retention data were again obtained for the test compounds. Previous studies ( 2 ) have shown that exposing the asphalts to the test compounds prior to the oxidation step does not alter the retention data obtained later on the oxidized columns. Analytical data from the Kleinschmidt procedure were obtained in our laboratory; analytical data from the RostlerSternberg procedure were taken from the literature (7). The apparatus and procedure for the Kleinschmidt separation have been described (5). In the Kleinschmidt determination reported in this study the acetone-chloroform desorbed fraction (see Figure 1) was small, usually about 1 and was added to the asphaltic resins fractions for data comparison. Materials. Three groups of asphalts were used in this study. The first group consisted of 14 asphalts selected from 119 highway asphalts studied previously by Welborn and Halstead ( I O ) and by Rostler and White (7). These asphalts were representative of 85-1 00 penetration grade asphalts available in various regions of the country in the late 1950's and were furnished through the courtesy of the Bureau of Public Roads. This group was used in the inverse GLC comparisons with both Kleinschmidt and Rostler-Sternberg analyses. The remaining two groups of asphalts were used in the Kleinschmidt comparisons only. One group consisted of five asphalts used in the original inverse GLC studies ( I ) and are prefixed "L" in the present paper. The other group comprised six coating-grade asphalts studied previously by Greenfeld and Wright ( 1 1 ) and were supplied through the courtesy of the National Bureau of Standards. The Greenfeld and Wright asphalts are prefixed "GW".
z,
(10) J. Y. Welborn and W. J. Halstead, Proc. Assoc. of Asphalt Paving Technologists, 28, 242 (1959). (11) S . H. Greenfeld and J. R. Wright, Materials Reseurch and Srundurds, 2 , (9) 738 (1962). VOL. 39, NO. 14, DECEMBER 1967
o
1853
Table I. Compositional Data as Determined by the Kleinschmidt Chromatographic Method Asphalt White oils
n0.a
29.2 25.7 20.3 21.9 24.9 22.2 28.0 28.8 26.2 26.5 26.1 30.4 28.5 21.7 21.4 19.9 19.8 20.7 18.5 21.4 13.6 13.0 12.2 23.7
1
2 4 13 19 24 28 32 52 61 63 82 91 99 GW-2 GW-3 GW-5 GW-9 GW-19 GW-22 G1 L-2 L-3 L-4 L- 5
18.0
Composition, wt. Asphaltic Dark oils resins 27.9 27.3 31.1 30.7 33.7 31.9 31.1 31.1 33.3 34.4 30.4 27.9 31.3 34.2 30.8 23.1 27.7 24.2 27.8 26.2 40.3 38.6 32.8 29.3 35.5
15.5 25.0 19.4 19.8 15.4 18.0 18.0
17.6 18.8 22.0 18.8 17.6 27.1 22.6 11.2 12.4 14.6 12.8 15.5 12.4 17.8 21.2 44.7 34.2 22.8
Asphaltenes 27.4 22.0 29.2 27.6 26.0 27.9 22.9 22.5 21.7 17.1 24.7 24.1 13.1 21.5 36.6 44.6 37.9 42.3 38.2 40.0 28.3 27.2 10.3 12.8 23.7
a Numbers without prefixes identify Welborn and Halstead asphalts (IO); numbers prefixed GW identify Greenfeld and Wright asphalts (11); numbers prefixed L identify Davis, Petersen, and Haines asphalts ( I ) .
Table 11. Inverse GLC Test Compound Data on As-Received Asphalts Asphalt noa 1 2 4 13 19 24 28 32 52 61 63 82 91 99 GW-2 GW-3 GW-5 GW-9 GW-19 GW-22 L-1 L-2 L-3 L-4 L-5 a
Interaction coefficient Urn) Propionic DMSO Formamide Phenol acid 114 132 123 119 108 114 121 109
108 112 113 108 132 114 117
131 116 128 117 120 110 Ill 145 127 108
132 150 145 142 124 137 126 122 127 123 129 124 135 133 133 152 136 149 141 141 127 132 164 145 128
See footnote of Table I.
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ANALYTICAL CHEMISTRY
121 139 138 126 125 123 133 99 122 120 119 121 122 129 io8
126 117 137 110 129 118 120 147 125 106
78 90 89 83 68 83 86 60
77 78 82 84 87 85 65 87 71 96 66 81 73 83 136 99 63
Properties of all three groups of asphalts are given in the references cited. Twenty test compounds were used in the inverse GLC studies. Among the types used were acids, alcohols, amines, aromatics, cycloparaffins, esters, olefins, and sulfur compounds. Calculation of the Interaction Coefficient (ZJ. The interaction coefficient (Zp)is a term devised for expressing inverse GLC data. It is obtained by first determining on the asphalt the corrected retention volumes ( Y E o ) for a series of n-paraffins covering the molecular weight range of the test compounds. The logarithms of the VRo's for the n-paraffins are then plotted as a function of their molecular weight. The 1, for a given test compound on the asphalt column is then defined as 100 times the difference between the logarithm of the YR' of the test compound and the logarithm of the YRO of a hypothetical n-paraffin (obtained from the above plot) of the same molecular weight as the test compound (I). The interaction coefficient is thus a measure of the interaction of chemical functionality in the test compound with chemical functionality in the asphalt. RESULTS AND DISCUSSION
Comparison of Inverse GLC Data with the Kleinschmidt Analysis. The Kleinschmidt method separates asphalts into four principal fractions-asphaltenes, white oils, dark oils, and asphaltic resins-and a small fifth fraction. In the present study the fifth fraction (usually about 1%) was combined with the asphaltic resin fraction. Compositional data, as determined by the Kleinschmidt chromatographic method, are shown in Table I. Table I1 shows the inverse GLC data on the as-received asphalts for four of the test compounds. One good relationship was evident between the inverse GLC data on as-received asphalts and the Kleinschmidt compositional data. This correlation, shown in Figure 3, was between the Zp for formamide and the summation of the per cent asphaltenes and asphaltic resins. The initial data obtained are plotted in the upper half of the figure. Examination of this plot and the asphalt properties shown in Table I11 revealed that those asphalts deviating considerably above the line had higher nitrogen content and/or higher acid numbers than the average values for all the asphalts. The reverse was true for those deviating considerably below the line. This suggested an influence of the nitrogen and acid content of the deviations of the formamide Zp. An attempt was made to correct for the effect of the nitrogen and acid content by the following empirical equation :
Zp formamide (corrected) = Zp formamide + 12.5 ( A - B) + 4.2 (C - 0) where
A
average per cent nitrogen for all asphalt samples studied, B = per cent nitrogen for the asphalt under test, C = average acid number for all asphalt samples studied, and D = acid number for the asphalt under test. =
The successful application of the preceding equation is shown in the lower half of Figure 3. Even the atypical, high-nitrogen shale-oil residue, sample L-3, and the highnitrogen Wilmington (Calif.) asphalt, L-4, are made to conform well in the correlation. The lack of a correlation of the per cent nitrogen and/or acid number with the per cent asphaltenes plus asphaltic resins is further evidence that
160
Table 111. Asphalt Property Data
I
Asphalt no.=
u
130
I20
w
i
B - I3Ot
0.76 1.15
1 2 4 13 19 24 28 32 52 61 63 82 91 99 GW-2 GW-3 GW-5 GW-9 GW-19 GW-22 L-1 L-2 L-3
: : 150 w
I
I
I
I
1
I
ASPHALTENES t ASPHALTIC R E S I N S , Y iKleinschmidl1
Figure 3. Relationship between the interaction coefficient for formamide and asphaltenes plus asphaltic resins
neither the nitrogen nor the acid content play a significant role in determining the correlation in Figure 3. The functionality in the asphalt detected by formamide, which relates to the asphaltene plus asphaltic resin content, is as yet unknown. Neither the asphaltenes nor asphaltic resins by themselves correlate with the Zp’s for formamide. This suggests that the components interacting with formamide are split between the asphaltene and pentane sohble fractions during the pentane precipitation of the asphaltenes. The fact that only the sum of the asphaltenes and asphaltic resins correlates with the I , for formamide suggests a close chemical similarity between these two asphaltic fractions, at least as far as the chemical functionality being detected by formamide is concerned. Similarities in the retention behavior of test compounds on asphaltenes and polar resin fractions have been shown previously (1) for a chromatographically separated Wilmington (Calif.) asphalt. Those polar resin fractions not eluted from a modified fuller’s earth column by carbon tetrachloride, benzene, or chloroform, but eluted with methanol and with pyridine, had formamide Zp’s of 206 and 180, respectively, The corresponding asphaltenes from the initial sample had a formamide IDof 193. The different types of asphalts tested add significance to the plot in Figure 3. The asphalts grouped on the left side of the plot are paving-grade asphalts from a variety of sources. The asphalts on the right side of the plot (prefixed “GW”) are air-blown coating-grade asphalts, again from a variety of sources. The latter show both higher Ip’s and asphalteneasphaltic resin contents. This suggests that components which interact with formamide are produced during the oxidative blowing process and are associated with the formation of asphaltenes and asphaltic resins. Comparison of Inverse GLC Data with the Rostler-Sternberg Analysis. Rostler and White made an extensive study
0.87 3.34 1.65 1.33 1.33 1.40 1.48 1.57 0.85 0.95 0.72 1.26 1.57 0.62 0.62 5.96 0.40
0.80 0.80
L-4
032
Acid no.
Nitrogen, wt.
L- 5 Average a See footnote for Table I.
0.48 0.75 0.64 0.60 0.70 0.76 0.58 0.49 1.06 0.68 0.54 0.94 0.49 0.92 0.50 0.56 0.55 0.67 2.42 1.12 0.63 0.78
1.00
0.56 0.83 0.12 0.30 0.49 1.86 0.12 1.05
Table IV. Composition and Abrasion Loss Data as Determined by Rostler and Whiten
Asphalt no. 1 2 4 13
19 24 28 32 52 61 63 82 91 99
A 27.6 22.9 28.7 28.8 25.9 28.3 21.5 20.1 19.6 15.8
22.0 23.0 11.6 22.4
z
Fractions, wt. N AI Az 22.0 31.3 22.4 22.5 14.2 20.3 19.2 16.7 24.4 24.8 19.0 14.2 36.7 23.2
20.8 15.0 24.1 23.0 20.5 24.7 21.9 22.2 22.6 16.4 19.4 19.3 17.0 26.0
21.7 18.8 17.9 18.9 27.5 19.4 25.0 28.9 23.2 26.1 26.7 28.9 20.9 20.8
I’ 7.9 12.0 6.9 6.8
11.9 7.3 12.4 12.1 10.2 16.9 12.9 14.6 13.8 7.6
Abrasion loss N + A I average P Az wt. zb
+
1.44 1.50 1.87 1.77 0.88 1.69 1.10
0.95 1.41 0.96 0.97 0.77 1.55
1.73
47 75 38.5 38.5 17 51 9 1
26 15
6 23.5 46 63
From reference 7.
* Average of as-mixed and aged values. Q
of the original 119 paving asphalts collected and characterized by Welborn and Halstead and were able to develop a relationship between the chemical composition of the asphalts, as determined by the Rostler-Sternberg fractional chemical analysis, and durability of the asphalts (7). An average of the abrasion resistance of asphalt-Ottawa sand pellets, before and after aging (8), was used as the criterion for durability. The compositional and abrasion loss data, as determined by Rostler and White (9, are shown in Table IV. Rostler and White based their durability predictions upon VOL. 39, NO. 14, DECEMBER 1967 e
1855
170
Tab& V. Inverse GLC Test Compound Data after Column Oxidatiow
c
Interaction coefficient (I,) Phenol Propionic acid
Asphalt no. 1 2 4
154 161 169 168
13
91
151
19 24 28
A
160 147
32
133
52 61 63 82
151 130 142 141 142 164
91 99 5
I
I
4
1
1.5
1.7
1.9
NtAI
P+A~-(before
Figure 4. P
2.1
aqinq, data from raf.71
Relationship between interaction coefflcients and
column oxidation showed correlative trends with two test AI)/ compounds, phenol and propionic acid, and the (N (P Az) ratios. The inverse GLC data after column oxidation for these two test compounds are shown in Table V. Plots of the correlations are shown in Figure 4. Although there is some scatter in the data, a relationship is evident between the Rostler and White durability factor and the phenol and propionic acid interaction coefficients. The asphaltenes are not included in the durability factor; however, if the asphaltenes are considered as a reactive component, the ratio ( A + N + AS/(P Az) also gives an equally good relationship with both the phenol and propionic acid interaction coefficients. These two test compounds, particularly phenol, have shown correlations with Weather-Ometer durability and actual road performance (2,-4). Both the inverse GLC and Rostler-Sternberg analyses techniques are based on the chemical reactivity of asphalt. It is unlikely, however, that the same chemical functional groups are being measured, particularly those which react with the aqueous acid in the Rostler-Sternberg technique as opposed to those formed on
+
+
++ Az values +
the ratio obtained by dividing the per cent N AI (more reactive components) by the per cent P A2 (less reactive components). In the inverse GLC technique the retention behavior of the test compounds after column oxidation of asphalt is used as a measure of the susceptibility of asphalt to oxidative changes, Examination of the test compound data after
+
u
8 0
2
70-
I
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ANALYTICAL CHEMISTRY
102
Column oxidation for 24 hours, 130" C, 15-psi inlet pressure.
+
1.3
94 106 104 105 88 102 88 76 92 81 87 85 100
I
I
I
oxidation which interact with phenol in the inverse GLC technique. The precursors of the factors formed on oxidation of the asphalt which interact with phenol may well be concentrated in the Rostler-Sternberg N and A1 fractions. The I p values after oxidation of the asphalts for the test compounds phenol and propionic acid were also compared with the average abrasion loss data which had been obtained by Rostler and White. The Ip’s for the test compound propionic acid showed a better correlation with the average abrasion loss data than the Ip’s for the test compound phenol. The plot of the propionic acid-abrasion loss data is shown in Figure 5 . The better correlation between the propionic acid Ip’s and the abrasion loss is in contrast with the better correlation between the phenol Ip’s and durability (cited previously) as measured by the Weather-Ometer and road service performance. However, different measures of durability were used. In the propionic acid-abrasion loss correlation, poor performance is measured by abrasion loss from the sand pellet; in the phenol-durability correlations, cracking of the asphalt is a measure of poor performance. The better correlations of the propionic acid Ip’s with the asphalt-Ottawa sand pellet abrasion test data suggest that this test compound is more sensitive to chemical groups produced in asphalt on oxidation which relate to abrasion resistance than is the test compound phenol. Inverse GLC model compound studies suggest that the difference in phenol and propionic acid response on oxidized asphalts is largely a result of the stronger afiinity of propionic acid for carboxylic acid groups. Phenol may indicate the formation of functional groups more related to failure by cracking. Thus both test compoundspropionic acid and phenol-are probably contributing significant information about performance-related chemistry of the asphalt. Asphalts 2, 4, 13, and 82 were reported by Rostler and
White (7) to show anomalous behavior and were not used by them in establishing the correlation between the durability ratio and the abrasion loss. The inverse GLC data obtained in the present study do not justify omitting these asphalts in establishing the correlations with the Rostler and White parameters shown in Figures 4 and 5. CONCLUSIONS
The individual per cent of asphaltenes and asphaltic resins obtained by the Kleinschmidt fractionation procedure did not correlate with inverse GLC data, but the sum of these two fractions showed a good correlation with the Interaction Coefficient for the test compound formamide, as determined on the whole asphalt. The correlation was considerably improved by taking into account the effect of the nitrogen and acid content of the asphalt on the Ip’s. A relationship was found between the ratio of reactive to nonreactive components, as defined by the Rostler-Sternberg analysis, and the Ip’s determined on oxidized asphalts for the test compounds phenol and propionic acid. The Zp’s for propionic acid also showed a correlation with the asphaltOttawa sand pellet abrasion test developed by Rostler and White and used by them as a measure of asphalt durability. The poor correspondence of the test compound phenol (which correlated with Weather-Ometer durability) and abrasion loss values suggest that the pellet abrasion test and the Weather-Ometer test are measuring different parameters of asphalt durability. RECEIVED for review July 14, 1967. Accepted October 18, 1967. Work done under cooperative agreements between the Bureau of Mines, U. S . Department of Interior, and the University of Wyoming. Reference to specific commercial materials or models of equipment is made for identification only and does not imply endorsement by the Bureau of Mines.
VOL. 39, NO. 14, DECEMBER 1967
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