WAVE LENGTH,
Figure 4.
The n a v e length a t which the transmittance is 10% is recommended since a small shift in the cut-off wave length is more important analytically than a small change in actual transmittance values, and specification of larger transmittance values might permit undesirable variations in the cutoff point if the shape of the curve changes slightly from melt to melt. Even if it is not desirable to duplicate the filters exactly, the spectra shown are very useful to show what filters are available and exactly how they differ
mp
Transmittance spectra of Wratten gelatin filters
from each other to facilitate the best choice for a given analytical procedure. The filters that are actually used should then be characterized exactly as described above to be sure that the analytical results can be duplicated. The yellow and red glasses show strong fluorescence when irradiated by light of the proper wave length. Since the fluorescence is emitted a t \T-ave lengths longer than the corresponding absorption band, a nonfluorescent blue or green component will absorb much of the fluorescent radiation and reduce
its contribution to the fluorescence being measured if it is placed between the yellow or red filter and the detector. LITERATURE CITED
(1) Corning Glass Works, Corning, N. Y.,
Glass Color Filters, 1948. ( 2 ) Eastman Kodak Co., Rochester, N. Y., Kodak Wratten Filters, 18th ed. (3) Sill, C. W.,ANAL. CHEM.33, 1579
(1961).
RECEIVED for review January 3, 1961. Accepted July 12, 1961.
Investigation of the Structure of Petroleum Asphaltenes by X-Ray Diffraction TEH FU YEN, J. GORDON ERDMAN, and SIDNEY S. POLLACK Mellon Institute, Pittsburgh, Pa.
b The aromaticity and crystallite parameters have been determined for eight petroleum asphaltenes, a petroleum resin, a gilsonite asphaltene, and an asphaltene prepared from a visbreaker tar. The aromaticity values for these macromolecules were obtained from the integrated areas of the y- and (002) x-ray bands after necessary corrections were applied. The values for the aromaticity of the petroleum asphaltenes and the gilsonite asphaltene gave an inverse correlation with oxidation rate as
previously determined b y permanganate titration. The characteristic pattern of a petroleum asphaltene could be reproduced b y blending a polyethylene (chains) and a carbon black (condensed aromatic sheets); and, conversely, the x-ray pattern of the aromatic portion of an asphaltene compares with that of a blend of condensed aromatic compounds of known structure where the maximum diameter of the sheets i s approximately 14 A.
T
asphaltene fraction of crude oils and refinery bottoms is a brown-toblack, amorphous, powdery, solid material, insoluble in n-pentane and ether but soluble for the most part in solvents such as benzene, pyridine, and carbon disulfide. Except for small amounts of hydrocarbons carried along by adsorption or occlusion, petroleum asphaltenes are nonhydrocarbons, containing, in addition to carbon and hydrogen, nitrogen, oxygen, and sulfur. Investigation of the structure of asphaltenes prepared from refinery fracHE
VOL. 33,
NO.
11, OCTOBER 1961
1587
tions using infrared (11) and nuclear magnetic resonance (46) indicates the presence of both aromatic and alkyl structure. No naphthenic is reported although the possibility of a small amount is not excluded. Molecular weight values vary widely depending upon the method of measurement ( I S , 21, 48), probably indicating a considerable degree of association in the solvents used. Statistical constitution analysis (49), spectroscopic ( I C ) , and chemical (15) studies carried out in this laboratory indicate that the native petroleum asphaltene fraction of a crude oil consists of molecules of similar structure, but having a wide molecular weight range. The similarity in the properties of solvent fractions suggests that characteristic structural groups tend to repeat themselves in the large molecules. The objective of this paper is to characterize those structural features of the asphaltenes which tend to repeat themselves in the fabric and hence can be detected by x-ray diffraction. Powder photographs usually show only a few diffuse halos, and the data therefrom are necessarily limited. The x-ray diffractometer, on the other hand, provides quantitative intensity curves, and it is from shape as well as position of the peaks, that structural parameters can be obtained. Finally as means become available for the determination of structural features, more meaningful comparisons can be made between the asphaltene fractions of crude oils, other bitumens, and processed fractions such as refinery asphalts. An extensive review of early diffraction studies of amorphous carbons and coals has been prepared by Ergun and Tiensuu (17). It was Warren (45) who first developed the theory of diffraction in random layer lattices and correlated the position, form, and intensity of the bands in terms of layer dimension. Petroleum asphaltenes were shown by Labout (29) to yield a powder x-ray pattern characteristic of amorphous substances. Nellensteyn (34) first observed a band corresponding to 3.5 A. and pointed out the similarity of this feature of petroleum asphaltics and amorphous carbons. Later Williford (47) studied a number of paving asphalts and reported single spacings varying from 4.7 to 5.3 A. For an asphaltene fraction, however, he observed two spacings a t 3.53 and 4.76 A. Alexarian and Louis (3) reported that as many as 11 to 14 bands could be detected in the powder patterns of a few asphaltenes. Since no description of sample preparation was given, it is possible that sonic of these bands may nave stemmer f r n v mineral impurities Thr x-ray phttvrl of gilsorute wa5 studied by Y L W I ~(60) who described it as a “one nrir type in contrast tcl
1588
ANALYTICAL CHEMISTRY
the “two ring” type of albertite and grahamite. Most recently Padovani, Berti, and Prinetti (36) reported bands corresponding to 4.4 to 4.5, 3.6, and 2.1 A. for asphaltene from Bachaquero (Venezuela) crude oil. In general a thoroughgoing attempt to interpret the x-ray pattern of petroleum asphaltenes and related substances in terms of their structure has been lacking. Eight asphaltenes, prepared from crude oils of widely different geographic origin were used. To preserve continuity of study, these asphaltenes were the same as those reported upon in previous papers from this laboratory. For contrast the nonhydrocarbon portion of the gross resin fraction of one of these crude oils; the native bitumen, gilsonite; and an asphaltene, prepared from a visbreaker tar, were studied also. The gross resin fraction of a crude oil represents that portion soluble in npentane, but insoluble in propane a t ambient temperatures and consists largely of nonhydrocarbons; this truly resinous portion is generally similar in structure to asphaltenes (43) but is thought to be of lower molecular weight. Gilsonite is a hard, black, organic solid found in veins in some parts of the western United States, notably Utah. Although its origin geologically is in dispute ( 7 ) , recent studies of its rate of oxidation indicate a close chemical similarity to petroleum asphaltenes (15). A visbreaker tar is the distillation residue of a petroleum bottom which has been subjected t o a mild thermal cracking. EXPERIMENTAL
Preparation of Samples. The preparation of the petroleum asphaltenes, gilsonite asphaltene, and the asphaltene from a Kuwait visbreaker tar is described in a previous paper by Erdman and Ramsey (15). The hydrogen to carbon atom ratios were obtained by micro combustion analysis. The resin sample was prepared by passing the n-pentane-soluble and propaneinsoluble fractions of the crude oil, dissolved in pentane, through a chromatographic column comprised of Whatman No. 1 powdered paper, medium grade. The fraction which exhibited brown fluorescence when exposed to ultraviolet light was collected, concentrated, transferred to benzene, and freeze-dried a t low temperature. The polyethylene of low crystallinity was a copolymer derived from diazomethane and diazobutane. Infrared measurements showed 8% n-propyl side chains. Using the correlation of Smith (41) the crystallinity was estimated to be approximately 5 to 10%. The x-ray pattern revealed one crystalline reflection, a very weak (200pband at 3.7 A. The rarbon black sample was Statex R of the Columbia Carbon Co The carbon black-polyethylene blend
was niised by the gradual addition of the carbon black to the polyethylene in a hydraulic rubber press. This blended specimen was passed 15 times under 10,000 p.s.i., each pass of S to 15 minutes’ duration a t 100” C. The blend of polynuclear compounds was prepared by dissolving equal parte of violanthrone, isoviolanthrone, flayanthrone, indanthrene olive green BW’, and pyranthrone in hot 97% sulfuric acid. The violanthrones were manufactured (since discontinued) by Imperial Chemical Industry, Ltd., London; the flavanthrone and pyranthrone, by Du Pont, and the indanthrene olive green BWP, by the General Dyestuff. After filtration, an ice water mixkure was added to the clear filtrate, thereby precipitating the dissolved dyes. The resulting black, gel-like substance, after being thoroughly washed, was dried at 100” C. in vacuo. X-Ray Technique. The x-ray techniques used in this study are those of Alexander and Sommer @) and Pollack and Alexander (37), used previously in studies of carbon blacks, pitches, and cokes. The powdered samples were packed into aluminum holders, each of which was mounted in a Xorelco goniometer, and the x-ray intensiti;s measured over the range 2 0 = 8 to 100 . Ross balanced filters (24,33), consisting of cobalt and of nickel, were used to achieve highly monochromatic Cu K, radiation. The differences in counting rates, I , illustrated in Figure 1, were measured with a xenon-filled proportional counter and the values n ere then corrected for polarization. This corrected experimental curve was normalized to electron units, A , by fitting it to the independent scattering curve of carbon over the range (sin 0)/X = 0.080.50. The incoherent scattering, C, was then subtracted from the normalized curve t o give the coherent scattering. Dividing this coherent scattering by the independent coherent scattering, E , yields finally the reduced intensity, 1‘, i.e., - C 1’ = A E
the curve foi n lilch is shown in Figure 2. Interpretations regarding the various structural features of the asphaltenes and related substances are based on this curve rather than on the directly measured intensity curve. The peak in the low angle region, i.e., (sin B)/h = 0.05- 0 20
encompasses both the y- and the (002)bands which must be resolved into the individual peaks. To simphfy the process, it was assumed that the peaks are symmetrical. The high angle side of the broad peak was used as a guide to delineate the unresolved slopr or thc (OO2)-band M o s t of thr intensitx remaining was attributed t o t h e v-ban6 The areas under the two banas ~ r measured aith a poiar planmiPtrr anr
.
0
20
40
28
28 60 80 100
2 o 10 1
20
30
I
40
50
60
70
80
I
I
I
l
l
90
100
II
Baxterville asphaltene
I .o
Laqunillos aspholtene
Raguso asphaltene
Baxterville resin
d
Gilsonite aspholtene
1.0
2.0
01 05
A
1
I
15
.IO
,
I
I
25
20
,
I
40
35
30
M
45
(sin @ / A
Figure 2. X-ray diffraction patterns from Figure 1 replotted on basis of reduced intensities
(sin 8)/A
Figure 1. X-ray diffraction patterns for several petroleum asphaltenes, a petroleum resin, a gilsonite asphaltene, and an asphaltene prepared from a visbreaker tar
Dashed llner show resolved y and (002)-bands
28
20
IO
,
30
40
50
_.-_. Corm
the areas were taken as representing the intensities. Separation of the y- and (002)bands in the above manner to determine aromaticity, f., involves three potential sources of error. Fortunately, in this study each of these could be dealt with in a reasonably satisfactory manner. The first of these possible errors arises from small angle scattering which tends t o increase the intensity on the low angle side of the yband. Khere peaks are broad, as in case of the substances under study, this type of scattering is hard to detect there being no discrete lines, only decreasing intensity with increasing angle. Assuming an approximately symmetrical y-band, it was possible to attribute some of the intensity on the low angle side of the band to small angle scattering and hence to exclude it from the calculation of fo. The excluded intensity was approximately 10 to 15y0of the intensity in the unresolved band. The second factor is that the intensity of a (002)-band due to a seven-layered unit of approximately 24-A. thickness, for example, would exhibit an intensity 1.17 times that of the band for a two-layered unit of approximately 7-11. thickness. Thus, a variation in size distribution of the repeat units from sample to sample would result in an error in f a . Fortunately, the substances under study have about the same L, and width-athalf maximum of the y-band, indicating a similar size distribution. The third
60
70
80
90
,
1"
-Pdyelhyltne Block-Slaler R
b -Composite
Represenling a I I Summation of the Polyelhylene ond the Corbon Block
Figure 3. X-ray diffraction patterns of lowcrystallinity polyethylene, a carbon black, and blends of the two
..... h o f m *b-l bspholtene
Blends of the Polyethylene and Catban B 8 0 c i
-1 I Mixture by Weight
...... I I Mixture Bosed
=t
01% Carbon
Contenl
91
ob
I
1
i i I
. 005
0'10
0'15 020 025
--1-J
030
035
040
045
050
055
lsin B)/i
factor is the assumption of symmetrical peaks. Only after division by (4) 0.0606 ( 2 sin e7 --2 )
is the (002)-band truly symmetrical while the exact shape of the y-band is not known. Actually the error involved over the range of angle under consideration is small, as can be seen from the nearly symmetrical curves for the carbon black and polyethylene in Figure 3A. This of course, assumes that the y-band has a shape similar t o amorphous polyethylene. RESULTS AND DISCUSSION
The x-ray diffraction patterns of several of the native asphaltenes, a petroleum resin, and the asphaltene
fractions of a ,visbreaker tar, and of gilsonite are shown in Figures 1 and 2. In Figure 1, the intensity scale is shown in counts per second, and in Figure 2, as reduced intensity expressed in arbitrary units. The curves are qualitatively similar, exhibiting unsymmetric, or saw-toothed peaks in the high angle region, which can be indexed as the (10)-reflection, Le., 2 6 = 43O, d = 2.13 A,, and the (11)-reflection, Le., 2 0 = 78", d = 1.23 A. Aromaticity, fa. The resin and asphaltene fractions of the Baxterville crude oil provide an interesting pair of samples for a detailed consideration of the relationship of aromatic t o aliphatic structure. If assumptions made previously are correct (15, 16, @), these fractions should be similar VOL. 33, NO. 1 1 , OCTOBER 1961
1589
with respect to the type of structural unit, but different with respect to the molecular weight ranges of the natural polymer comprised of these units. While the two curves are generally similar in the wide angle scattering region, they differ markedly in the medium angle region below (sin 6')/A = 0.2, where the intensities of the members of the doublet are reversed. Resolution of the doublets into pairs of approximately symmetrical peaks places the two maxima at 2 e = 18' or d = 4.8 A,, and 2 e = 26' or d = 3.5 A. The former is designated as the yband and the latter as the (002)-band. The (002)- spacing, which appears in carbon blacks (40), graphite pitch and coke (37)) and coals (17)) is accepted as representing the spacing between the layers of a condensed aromatic system. The true significance of the y-band has been the subject of considerable discussion. Kasatochkin (29) states that it represents the
(a),
Table I. Comparisoh of Calculated Values of Aromatic to Saturated Carbon Ratios and of Aromaticities with Known Values from Make-up of Polyethylene-Carbon Black Blends
Values Determined From CA/CS
fa
Blends, 1: 1 Mixture Based on Bv carbon weight content
Calcd. Make-up
0.93 1.17
0.76 1.00
Calcd. Make-up
0.48 0.54
0.43 0.50
packing distance of aliphatic chains. Ergun and Wender (19), on the other hand, believe that it might equally well represent layers of condensed saturated rings. Whatever the interpretation, the y-band almost certainly represents saturated structure in contrast to the (OO2)-band, which represents aromatic structure. Accordingly, it appears that the resin fraction contains proportionately more saturated than aromatic structure. It is possible that this finding may be due to occluded waxy material. On the other hand, if the asphaltic polymer consists of islands of condensed aromatic rings tied together with chains or saturated rings, then as the islands become smaller, the proportion of saturated structures around the aromatic islands might reasonably be expected to increase. To investigate the origin of the yband, two experiments were performed. Both were aimed a t producing an asphaltene-like x-ray diffraction curve from constituents of known structure. For these experiments, a low crystallinity polyethylene was chosen to represent a slightly branched but ringfree saturated hydrocarbon; and Statex R, a carbon black, was chosen to provide sheets of aromatic rings, Le., graphitelike platelets of very small size. As is shown in Figure 3 A , the curve for the polyethylene shows a strong y-band a t 2 6' = 18' but no (002)-band; while the curve for the carbon black shows a strong (002)-band a t 2 0 = 26' but no y-band. The first experiment consisted of weight summing the curves for the polyethylene and the carbon black in
Table II. Aromaticity and Crystallite Parameters for some Petroleum Asphaltenes, a Petroleum Resin, a Gilsonite, and an Asphaltene Prepared from a Visbreaker Tar ( d M , dr, d y l , and L, are expressed in Angstroms)
L,Basedon (Schemer's Equation) Number Petroleum asphaltenes 1 Baxterville 2 Lagunillas 3 Burgan 4 Wafra, No. A-1 Mara 5 6
Wafra. No. 17
7 8
Rauddata-in Ragusa Petroleum resin Baxterville Gilsonite asphaltene Tabor vein Refinery asphaltene Visbreaker tar
9 10 11
1590
(10)- (11)-
L, Based on (Diamond's Method) (11)-
j,,
dx
dr
dr'
L, band band
band
0.53 0.41 0.38 0.37 0.35 0.35 0.32 0.26
3.57 3.57 3.55 3.57 3.57 3.60 3.60
4.7 4.7 4.6 4.6 4.7 4.8 4.6 4.8
5.7 5.7 5.6 5.6 5.7 5.9 5.7 5.9
19 17 19 18 18 19 18 19
10 10 12 12 16 14 13 12
13 9.7 9.7 11 15 9.1 11 12
0.22
3.70
4.7
5.7
16
12
0.14
3.5Ci
4.9
6.0
20
15
0.59
3 57
4.7
5.7
18
12
ANALYllCAL CHEMISTRY
3.57
15 11 11 12 17 10 12 14 9.6 10 9.;
8.5 9.1
8.6
such a way as to achieve the best match with a curve for a petroleum asphaltene, prepared in this case from a Wafra crude. The best match was obtained when the weighting factor was approximately l:,l. In Figure 3B, the constructed curve for the composite is compared with the experimental curve for the asphaltene. Approximately the same degree of match could have been achieved Kith any of the other petroleum asphaltenes. The second experiment consisted of the preparation of two blends of the polyethylene and the carbon black, with subsequent determination of the x-ray patterns. The curves for these blends are shon-n in Figure 3C and can be seen to resemble the curves for the natural bitumens shown in Figure 2 For a series of similar amorphous substances, the integrated areas under the curves for the y- and (002)-bands can be correlated with the numbers of saturated and aromatic carbon atoms, respectively, provided the assumption is made that, for each substance considered, the fraction of the aromatic layers which are associated is constant. The relations are as follows: Ar = CS = Aoap
( c- CA) CA
and
where A represents the areas under the respective peaks; CS, C A , and C, the number of saturated, aromatic, and total carbon atoms per structural unit, and fa, the aromaticity. Table I compares the calculated values of the aromatic to saturated carbon ratios and of the aromaticities with the known values from the make-up of two blends of a polyethylene (pure aliphatic structure) and a carbon black (pure aromatic structure). The good agreement obtained between the calculated and known values is taken as further evidence that y- and (OOZ)-bands reflect quantitatively as well as qualitatively the respective contents of saturated and aromatic structures. Values of the aromaticity for the 11 materials studied are listed in Table 11. For the eight asphaltenes prepared from crude oils, the values of the a r e maticity vary by more than a factor or two. The resin fraction from a crude oil and the gilsonite exhibit low values. The asphaltene from the visbreaker tar, on the other hand, exhibits a relatively high value, suggesting that during thermal cracking aliphatic groupings art split off as low molecular weight hy. drocarbons. Eilers (14) has reported an apparent decrease in the ratio of the intensitieF of the (002)- and the 7-bands, Le., a
in Figure 5; thus they differ as a class
055
0 30
0.8 0
c
Values of the intercept assuming 71 W b o n atoms per unit, as judgedfrom the average La values for the a s p h r n t m s
,
-
from native petroleum asphaltenes and gilsonite. Whether, when aromaticityoxidation rate data for coals become available, a similar correlation will be observed and, whether the curves foi petroleum asphaltenes and coals will intersect are a t present unknown. In the oxidation study, it was pointed out that for some asphaltenes the rate was nearly as slow as that for graphite The observation was interpreted as indicating that the carbon skeleton rather than the functional groups was ratecontrolling. The correlation between oxidation rate and aromaticity also supports this concept. Further, the fact that the correlation is inverse is consistent with a still earlier conclusion of Erdman, Ramsey, and Hanson (16) based on the work of Randall, Benger, and Grocock (58), that the aliphatic portion of the asphaltene would be oxidized by permanganate more rapidly than the aromatic portion. Crystallite Parameters, d ~ d,y , L,, and L.. From the x-ray diffraction patterns of gilsonite, the asphaltenes, and the resin, additional crystallite parameters can be determined. These are the interlayer distance, d M ; the interchain distance, d y ; the diameter of the aromatic clusters perpendicular to the plane of the sheets, L,; and the diameter of the aromatic sheets, La. The structural significance of these parameters may be visualized more easily from the cross-sectional view of the asphaltene model, as shown in Figure 6. The repeat distance indicated by the maximum of the (002)-band was calculated by the Bragg relation.
N.
>
.z.- 0.6 -
\
c
+ 0
\
\
E
0.4
-
0.2 -
0-PetroleJm
asphaltenes
\
v-Resin A-Gilsonite
\
visbreaker t a r
0-Asphaltene from
(For key t o t h e i u r r b e r s see T a b l e
\
\
osphaltene
\ \
'\
\
I)
\,
Pure unbranched oaroffin
\
-
Pure peri condensed naphtixnic'?
,
I
0
',.
o1
-
0.5
1.0 H/,C
I : O
I55
Figure 4. Plot of aromaticity vs. H/C ratio for some petroleum asphaltenes, a petroleum resin, a gilsonite asphaltene, and an asphaltene prepared from visbreaker tar
decrease in aromaticity, with increasing hydrogen-to-carbon ratio. Since petroleum asphaltenes are not true hydrocarbons but contain nitrogen, oxygen, and sulfur as well as hydrogen and carbon, this relationship does not necessarily follow. In Figure 4, the values of the aromaticity for the substances listed in Table I1 are plotted against the values of the hydrogen-carbon ratio and the best straight line through the points determined by the method of least squares. The present data also show the correlation between aromaticity and H/C ratio suggested by Eilers. The dashed lines in the figure represent the general limits within which any hydrocarbon of comparable size must fall. The intercepts with the horizontal axes, f,, equal to 0 and 1, represent the five structural extremes, i.e., pure periand kata-condensed naphthenic, pure nparaffin, pure peri-condensed aromatic, and pure kata-condensed aromatic. The comparable intercepts of the line through the points for the asphaltenes represent the extents of condensation within the aromatic and saturated portions of the asphaltene structures,
assuming that the perturbations due to the presence of nitrogen, oxygen, and sulfur are minor. In Figure 5, the values of the aromaticity for the compounds studied are plotted against the oxidation rates as determined by Erdman and Ramsey (16). Of the asphaltenes, those prepared from crude oils show an inverse correlation. The asphaltene from the visbreaker tar does not correlate well, but this material cannot be considered as a fraction from a natural bitumen. The fact that gilsonite falls reasonably close to the curve is interesting in that it adds support to a conclusion, previously reached by the above authors on the basis of oxidation rate alone, that there is a close geochemical relationship between gilsonite and crude oils. X-ray determinations of aromaticity of coals thus far have not been made. It is evident, however, from the oxidation rate data (16) and known H/C values, that coals will not fall on the aromaticity-oxidation rate curve shown
The values for &, representing layer spacing of the aromatic sheets, are provided in Table 11. The value of d M is related to the flatness and size
-
Sheet
08-
B.Petroleum aspholtenes A. Giison8te aspholiene 0 -Aiphoitene f r o m virbreoker t o r (For Ley Io numbers I I L ToblC I I
X*,Y
-L.8.5-15
A
d, 5.5-
O x i d a t i o n Rate x 10'
represents the rig-zag conliguralion
Figure 5. Relation between aromaticity and oxidation rate for some petroleum asphaltenes, a gilsonite asphaltene, and an asphaltene prepared from a visbreake. tar
Figure
6.
m a i n or IWSE vet
tit
naphthen
01
0
saturalad carmn
rem\
reorrsents lhe edge of llat sheel) of rondenseo aromatir
r no'
Cross-sectionai view of asphaltene rnoaa, VOL. 35, NO. 1 1 , OCTOBER 1901
1591
28
Table 111. lnterlayer Distances, d M in Certain Coals, Pitch Binder, Coke, and Carbon Blacks with Some Aromatic Hydrocarbons
Substance
d u , A. 3.64 3.54 3.43
20
3.6 I
40
I
I
0.10
0.15
60
00
I
I
I
100
'
LhA
1 0.45
0.50
'
120
'
140 160
I I I I I
Reference
(21) Coal, 80.1% (2.2) Coal. 87.39% Coal; 94.1% iwj Pitch, electrode binder (U. S. Steel) 3.52-3.60 (37) Coke 3.48-3.52 (37) . . Channel black, 3.62 (4) Spheron 3, Cabot Furnace black, Vulcan SC, Cabot 3.54 (4) Graphite, natural 3.34 (6) Ovalene 3.45 (44) Pyrene 3.52 (44) Table IV. Calculated lnterchain Distances, dr, of Crystalline Saturated Chain and Ring Compounds Based on Crystallographic Data
Compound Polyethylene Polypropylene oxide Poly-3-methyl-1-butene Ergosterol f HzO Dihydroergosterol Ergosterol-B8 Vitamin Dt Pyrocalciferol Suprasterol I Lumisterol
dn A.
Reference (9) (33) (32) (8)
4.10
4.26 4.75 4.95 4.1
(8)
4.5
(8) (8) (8) (8)
5.0 5.2
(8)
4.5 4.5
Table V. lnterchain Distances of Amorphous Long Chain Compounds
Compound Polyethylene Polyethylene (178" C.) Polypropylene Polyisobutylene Poly-1-butene Poly-1-pentene Poly-1-methyl-1-per& ene Poly-1-hexane Polytrifluorochloroethylene Natural rubber Polymethyl acrylate Polystyrene Poly(viny1 acetate) Octacosane (150" C.) a Present work.
dr, A.
dl,
A.
Reference
4.5 . . . 4.9 . . . 5.4 . . . 6.3 . . . 4.5 6.9 4.5 8.8
(31) (31)
4 . 5 9.4
(6)
1
(18) (30)
(SO)
0.20
0.25
0.30
higher values for the Raudhatain and Ragusa samples may not be significant. In contrast t o the petroleum asphaltenes, data from the literature listed in Table I11 show that coals, pitch binder, coke, and carbon blacks together with polynuclear aromatic hydrocarbons exhibit a considerably wider range of dM values. The repeat distance represented by the y-band was calculated in similar manner by the relation. d7
=
x 2 sin e
The values of d y are listed in Table 11. For this application, it has been shown that a more precise relation might be
4 . 5 9 . 8 (30)
5.5 . . . (16)
4.8 . . . a 4 . 1 7.0 (26')
4.6 9.2
a
4 . 0 7.2 4.8
. . . (28)
ANALYTICAL CHEMISTRY
I I 0.35 0.40 (sin @)A
1
0.55
0.60
a65
Figure 7. Theoretical diffraction patterns for randomly oriented perfect aromatic molecules of various sizes plotted from data published b y Diamond
(31)
of the aromatic sheets (20, 4 2 ) . Imperfections in the aromatic hexagonal net such as saturation or inclusion of heteroatoms lead to bulges or bends in the sheets preventing close approach. Similarly, aliphatic and naphthenic edge groups tend to hold the sheets apart. As the sheets become larger, however, the effect becomes smaller, allowing the distance between the sheets to approach the limit of 3.34 A. observed in graphite. The range of values exhibited by the eight petroleum asphaltenes is small; in fact, the slightly
1592
0
0.05
For contrast, values of dr' are also listed in Table 11. Actually, theoretical calculations have been made (1, 56) both for isolated particle-like cylindrical rods and for aggregates of parallel rods with regard to x-ray scattering for linear chains. Since the quantity, k, defined by k =4
T
(sin e)/x
for y-band is 1.33, the diameter for the bundle according to Oster and Riley (36) is 7.7 A,, and the bundle size of parallel line scatters according t o Alexander and Michalik (1) is 5.3 A. The latter value is very close to the dr' values as listed in Table 11. Although the low angle region was examined, no repeat distances between 5 and 40 A. could be detected. The values of d y , 4.5 to 4.90 A,, compare to those reported in the literature and listed in Table IV, for several crystal-
line chain polymers and condensed naphthenic compounds to which are attached short aliphatic chains. In Table V are provided the spacings observed for a series of amorphous chain polymers ranging from straight chain to those with extensive branching. The fact that in the asphaltenes the primary d y values are small, and that no secondary spacings comparable to the d 2 spacings of the highly brandied substances in Table V are observed, argues for the concept that branching beyond methyl or ethyl is not extensive. If, on the other hand, the variation in d , values for the petroleum asphaltenes represents the degree of short branching in aliphatic chains, or variation in the paraffin-to-naphthene ratio, a correla'ion might be expected with the same parameters in the hydrocarbon portion of the crude oils. This possibility will be investigated. Theoretically both the average size and size distribution (2, 37) of the aromatic clusters perpendicular to the plane of the sheet can be calculated from the shape of the (002)-band. Owing to the fact that the precise shape of the band is difficult to resolve, the study was limited to the calculation of average size, L,, using the Scherrer crystallite size formula 0.9 X 045 Lc = _ _ = - ( 8 6 ) COS e B~~~ which requires only the determination of the width of the band a t half maximum, i.e., of w expressed in degrees, as 2 B or of B ~ /in L terms of (sin @/A. The values of L, are listed in Table I1 and show no simple relationship to the aromaticity as listed in the same table. From the values of L, and d.W it is possible to calculate the effective num-
0L 0
1
002
I
008
006
504
P
(a 1
,IO-
0 0
07
3 4
ROld
Figure 8. Calibration curve of corrected diameter of aromatic sheets based on width at half maximum of ( 1 1 )-band of curves calculated by Diamond
ber of aromatic sheets associated in a stacked cluster, Le.,
For the petroleum asphaltenes, this value is about 5. Values of M, for a number of carbons as reported in the literature are listed in Table VI for comparison. The tendency of the aromatic sheets to stack or cluster is believed by the authors to be an important factor in the tendency of asphaltic molecules to associate when dissolved in hydrocarbon solvents of low polarity. The last parameter listed in Table I1 is the average layer diameter of the sheets, La. This value also can be calculated by the Scherrer crystallite size formula from the width of either the (10)- or the (11)-bands, Le.,
work of Cartz and Hirsch (IO) which has shown reasonable agreement between the fo values calculated for coal from L, and molecular weight and those obtained from infrared spectrosCOPY * Since the average diameter of the aromatic sheets is perhaps the most critical feature of the petroleum asphalterie molecule, the quantitative relationship between the La values as calculated by the Scherrer formula and actual aromatic sheet diameter was examined critically, several approaches being taken. In his paper, Diamond (12) computed the intensity of x-rays diffracted from randomly oriented perfect aromatic molecules of various sizes using the Debye radial distribution function. The complete tabulated data from this paper were plotted on a common scale to yield the curves shown in Figure 7 . From the (11)-band of each theoretical curve, the quantity Bl,z,the width a t half maximum in terms of (sin @ / A was measured and compared with the true L, value of the particular size of aromatic. This fact is shown in Figure 8. As will be seen, the Diamond method gives a much better approximation than the Scherrer formula. 0
iiwoianthrone
indanlhrenr olive green B w P
La = 1.84h = 0.92 . ~~
COS
e
E?~,~
Of the two sets of values, those calculated from the (10)-band are considered less reliable owing to the partial overlap with the (004)-band and possible overlap of the second band of the paraffins. Again, no correlation with any of the other parameters is evident. Thus far it has been assumed that the sheets are formed completely of condensed aromatic rings. It is not unlikely that heteroatoms replace some of the carbons in the sheets and that some rings may be partially or completely saturated (18). Further the dimensions of the sheet may be considered to include the a carbons of side chains which also are restricted to the plane of the sheet. That such factors probably are second order is indicated by the fact that van Krevelen (27) has obtained satisfactory agreement for coals between values of L, and those of the laminar diameters of aromatic nuclei obtained by refractometric vnstitution analysis. Still further evid e n w is provided bv the more recent
violanthrone
0
pyranthrona
Figure 9. Five polynuclear aromatic compounds used to prepare amorphous blend to test the Scherrer crystallite size formula
To test the above, an amorphous blend of the five polynuclear aromatic compounds, shown in Figure 9, containing aromatic nuclei of approximately equal size, was prepared. The x-ray pattern was determined, and an La value of 15 A. was obtained. This value was in good agreement with the long dimension of the aromatic clusters; whereby L, based on the Scherrer formula will yield a higher value, 17 A. Thus, for the asphaltenes and other asphaltic substances listed in Table 11, the La values in the last column obtained from the curve of Figur? 8 are believed to provide a
Table VI. Estimated Average Number of Layers Per Aromatic Cluster, Me,for Various Carbonized Materials As Reported in Literature
Material Saran char Sugar char Polyvinyl chloride ch2r Petroleum coke, 1000 to 1700' C. Graphitized coking coal Pitch Coke
Asphaltenes a Present work.
M,
Refer ence
2.0-7.7 ( 2 0 ) 2.4-5.4 (goj 4.5-33 ( 2 0 )
4.1-33 12 3.2-4.0 4.5-5.5 5
(20) (80)
(57) (37) 0
reasonably accurate average of the sheet size of the aromatic clusters in these substances. Earlier it was shown that a 1:I blend by weight of a carbon black and a polyethylene gave an x-ray diffraction pattern resembling a petroleum asphaltene. The carbon black was chosen because the La value approximated that in the asphaltenes. The preparation of the amorphous blend of polynuclear aromatic compounds provided a means of comparing the x-ray scattering of the aromatic clusters in the asphaltenes with clusters of known structure. To accomplish this objective. the previous procedure was reversed, namely, the x-ray pattern of polyethylene was subtracted from the pattern of the asphaltene, the weight factor being one part by weight polyethylene to two parts of the asphaltene. The resulting solid line curve in Figure 10 is believed, therefore, to represent approximately the x-ray diffraction pattern of the aromatic clusters in the asphaltene. The dashed line curve in the same figure represents the experimental curve for the blend of the five aromatic compounds shown in Figure 9. Correlation between the two curves is very close.
IY~UV~
Figure 10. Comparison of x-ray dif. fraction pattern computed for aromatic clusters in petroleum asphaltene with experimental pattern for blend of five polynuclear aromatic compound. of known structure VOL 33, NO. 1 1 , OCTOBER 1961
1593
ACKNOWLEDGMENT
The authors gratefully acknowledge the technical advice of Leroy E. Alexander of the Fundamental Research Group of Mellon Institute, and also thank M. J. Richardson, visiting Fellow at Mellon Institute for a sample of low-crystallinity polyethylene, and Leslie Reggel of the U. S. Bureau of Mines, Pittsburgh, Pa., for the samples of the violanthrones. LITERATURE CITED
(1) Alexander, L. E., Mkhalik, E. R., Acta Cryst. 12, 105 (1959). (2) Alexander, L. E., Sommer, E. C., J . Phys. Chem. 60,1646 (1956). (3) Alexarian, C;, Louis, M., Compt. rend. 231,1233 (1950). (4) Austin, A. E., PTOC. 3rd Conf. Carbon Buffalo, N. Y., 1957, published 1959, p. 389. (5) Bacon, G. E., in “Industrial Carbon and Graphite,” p. 183, Society of Chemical Industry, London, 1958. (6) Bailey, W. J., Yates, E. T., Preprints, p. 65, Division of Polymer Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960. (7) Barb, C. F., Ball, J. O., Quart. Colo. School Manes 39, No. 1, 11 (1944). (8) Bernal, J. D., Crowfoot, D., Frankuchen, I., Trans. Roy. SOC. (London) A239, 135 (1940). (9) Bum, C. W., Trans. Faraday SOC. 35,482 (1939). (10) Cartz, L., Hirsch, P. B., Trans Rou. SOC.(London)A252,857 (1960). (11) Chelton, H. M., Traxler, R. N., World Petrol. 6th Congr., New York, Section V, Paper 19 June 1959. (12) Diamond, R., Acta Cryst. 10, 359 (1957). (13) Eckert, G. W., Weetman, B., Znd. Eng. Chem. 39, 1512 (1947).
(14) Eilers, H., J. Phys. & Colloid Chem. 53, 1195 (1949). (15) Erdman, J. G., Ramsey, V. G., Preprints, Symposia 5, No. 4, A51, ACS, New York, September 1960. (16) Erdman, J. G., Ramsey, V. G., Hanson, W. E., Ibid., 3, No. 2, A73, ACS, San Francisco, April 1958. (17) Ergun, S., Tiensuu, V. H., Fuel 38,64 (1959). (18) Ereun. S.. Tiensuu. V. H.. Nature . 183, a 6 8 (1959). (19) Ergun, S., Wender, I., Fuel 37, 503 (19581. ~_.__,.
(20) Franklin, R. E., Proc. Roy. SOC. (London)209, 196 (1951). (21) Greenfeld, S. H., J . Res. Natl. Bur. Stand. 64C, 287 (1960). (22) Hirsch, P. B., Proc. Roy. SOC. (London)A226, 143 (1954). (23) Kasatochkin,\V.I., Izuest. Akad. Nauk S.S.S.R. Otdel Tekh. Nauk 1951,1321. (24) Kirkpatrick, P., Rev. Sci. Instr. 15, 223 (1944). (25) Klug, H. P , Alexander, L. E., “X-ray Diffraction Procedure,” p. 538, Wiley, New York, 1954. (26) . . Klug, H. P., Alexander, L. E., Ibid., pp. 63fL3. (27) Krevelen, D. W. van, Schuyer, J., “Coal Science.” D. 177. Elsevier. New York, 1957. (28) Krimm, S., Tobolsky, _ . A. V., Teztik . Res. J. 21; 805 (1951). (29) Labout, J. W., in J. P. Pfeiffer, “The Properties of Asphaltic Bitumen,” p. 24, Elsevier, New York, 1950. (30) Natta, G., Rubber & Plastics Age 38,495 (1957). (31) Natta, G., Corradini, P., Ricerca sci. suppl. 25A, 695 (1955). (32) Natta, G., Corradini, P., Bassi, I. W., Atti accad. naz. Lincei 19, No. 8, 404 (1955). (33) Natta, G., Corradini, P., Dall’asta, G.. Zbid.. 20. No. 8. 408 (1956). (34) ‘Nellenst&n, F.’ J., d “The Science of Petroleum,” Vol. IV, p. 2760, Oxford University Press, London, 1938. I
_
(35) Oster, G., Riley, D. P., Acta Cryst 5,272 (1952). (36) Padovani, C., Berti, V., Prinetti, A., World Petrol. 6th Congr. New York, Section V, Paper 21, June 1959. (37) Pollack, S. S., Alexander, L. E., J. Chem. Eng. Data 5,88 (1960). (38) Randall, R. B., Benger, M., Grocock, C. M., Proc. Roy. Soc. (London) A165, 432 (1938). (39) Ross, P. A., Phys. Rev. 28,425 (1926). (40) Sack, H. A., Trillat, J. J., Compt. rend. 224. 15n2 (1047),. (41) Smith.‘ I:). C.. Ind. Ena. Chem. 48. ‘ lis1 (1956). ’ (42) Steward, E. G., Davidson, H. W., I”-
\*“A.
in “Industrial Carbon and Graphite,” p. 207, Society of Chemical Industry, London, 1958. (43) Stewart, J. E., J . Res. Natl. Bur. Stand. 58,265 (1957). (44) Ubbelohde, A. R., Lewis, F. A.,
Graphite and Its Crystal Compounds,”
p. 8, Oxford University Press, London, 1960. (45) Warren, B. E., Phys. Rev. 59, 693 (1941). (46) Williams, R. B., iy, Thornton, E., Thompson, H. W., Conference on Molecular Spectroscopy,” p. 26, Pergamon Press, New York, 1959. (47) Williford, C. L., Bull. Agr. Mech. College Tezas 73, 1 (1943). (48) Winniford, R. S., Preprints, Symposia 5, No. 4, All, ACS, New York, September 1960. (49) Yen, T. F., Erdman, J. G., Hanson, W. E., Preprints, 9. 69, Division of Gas and Fuel Chemstry, 137th Meeting ACS, Cleveland, Ohio, April 1960. (50) koung, R. S., Bull. Am. Assoc. Petrol. Geol. 38, 2017 (1954). RECEIVEDfor review March 13, 1961. Accepted August 7, 1961. Division of Petroleum Chemistry, 139th Meetin ACS, St. Louis, Mo. March 1961. W O ~ sponsored b the Research & De-
60. ddf
velopment as part of the research program of the Multiple Fellowship on Petroleum.
Spectrophotometric Determination of Total Erythrocyte Copper HAROLD MARKOWITZ, G. S. SHIELDS,’
W. H. KLASSEN, G. E. CARTWRIGHT, and M. M. WINTROBE
Department of Medicine, University of Utah College of Medicine, Salt lake City, Utah
b The determination of erythrocyte copper concentration with oxalyldihydrazide as the colorimetric reagent is described. As little as 0.1 pg. of copper can be accurately determined. Complete color development occurs over a pH range of 8.6 to 10.3. Recoveries of copper range
1 Present address, Department of Internal Medicine, University of Cincinnati School of Medicine, Cincinnati 29, Ohio.
1594
0
ANALYTICAL CHEMISTRY
from 9 2 to 103% with a mean difference between duplicates of 3.9%. The erythrocyte copper content of 20 normal subjects is 89.1 11.4 pg. of Cu per 100 ml. of packed red blood cells. The variation of erythrocyte copper in a given individual over a 2-hour period was on the order of *6% of the mean. The variation observed in erythrocyte copper in a given individual from week to week was as great as the variation among individuals.
*
D (Y),
studies on the copper components of human erythrocytes a sensitive and accurate method for the determinaton of the total amount of copper in erythrocytes was necessary. The previously described method for determining erythrocyte copper with the colorimetric reagent sodium diethyldithiocarbamate (1, 9, 6) was unsatisfactory because of the low molar absorbance of the copper-carbamate complex and because of the developURING
