Compositional Studies of a High-Boiling 370-535°C Distillate from Prudhoe Bay, Alaska, Crude Oil H. J. Coleman, J. E. Dooley, D. E. Hirsch, and C. J. Thompson Bartlesville Energy Research Center, Bureau of Mines, U. S. Department of the Interior, Bartlesville. Okla. 74003
I n addition to providing some of the general characteristics of the Prudhoe Bay, Alaska, crude oil as determined by the Bureau of Mines routine method of analysis, this paper presents a comprehensive analytical characterization of a high-boiling 370-535 "C distillate. Following distillate preparation by several distillation steps in special distillation equipment, careful separating procedures with ion-exchange resins, coordination-complex formation of neutral nitrogen compounds with ferric chloride, and dual silica-alumina gel adsorption provided suitable concentrate fractions for further study. Subdivision of aromatics into three major aromatic types-monoaromatics, diaromatics, and polyaromatics-polar-greatly simplified subsequent separation and characterization studies. Monoaromatic, diaromatic, and polyaromatic-polar concentrates combined represent a large portion (45.5%) of the 370-535 OC boiling range distillate of the Prudhoe Bay, Alaska, crude oil, the importance of which justified detailed determinations of the number of rings involved, the relative aromaticity, and the degree of condensation of aromatic, naphthene, or heterocyclic rings. Further analytical separations by GPC, followed by determination of mass and NMR spectral data on the resulting GPC subfractions, provided a basis for determining a m u c h more intelligible and reasonable understanding of compound type distributions for this specific high-boiling 370-535 "C Prudhoe Bay, Alaska, crude oil distillate. The end result is a scheme of sample preparation, analysis, and characterization that should be applicable to similar high-boiling distillates from other crude oils and of value to the petroleum industry in studies related to the origin of petroleum as well as its production, processing, storage, and usability.
Knowledge of the types and distribution of major structural and functional groups in the residual fractions of petroleum is needed for petroleum technology. To obtain such information and to develop suitable analytical methods, the Bureau of Mines is studying the higher boiling fractions of five crude oils of different chemical and geological origin. In 1969 and 1970, Hinds ( I , 2) provided reasons for the cooperative study and background information and pointed out limitations of the methods available. Later, Haines and others ( 3 ) ,provided preliminary data on several selected crude oils and some refinements in the analytical mcthods. This report is prompted by interest, both by the industry and the public, in the extremely large potential production from the North Slope and the dearth of data on oils from that area. In addition to the compositional data presented, the development and application of new and (1) G. P. Hinds, Jr., Proc.. Arner. Petrol. Inst.. Sect. 3. 49, 147 ( 1 9 6 9 ) . ( 2 ) G . P. Hinds, Jr.. Proc.. Amer. Petrol. lnst., Sect. 3. 50, 279 ( 1 9 7 0 ) . ( 3 ) W. E. Haines, C. C. Ward, and J. M. Sugihara, Proc., Arner. Petrol. Inst., Sect. 3, 51,375 ( 1 9 7 1 ) .
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improved separation and characterization methods applicable to high-boiling petroleum fractions are described. These include distillation techniques, dual silica gel-alumina gel adsorption chromatography, chemical treatment, gel permeation chromatography, and spectral studies.
SAMPLE SOURCE This crude oil sample originated in the Prudhoe Bay area of the Alaskan North Slope. As obtained from the Atlantic Richfield-Humble Sag River State No. 1, 2637 ft from the west line, and 866 f t from the north line, 4-10n15e, UM, Alaska, this oil represents an intermediate age production from the Sadlerochit formation of the Triassic and Permian sandstone with interbedded shales and siltstone a t a production depth of about 9000 ft. The production test a t the time of sampling was 2747 barrels of oil per day with a 753: 1gas-oil ratio. Sample analysis by the Bureau of Mines method for routine crude oil analysis provided the experimental data of Table I and the derived data of Table 11.
PREPARATION OF HIGH-BOILING DISTILLATES Figure 1 shows the sequence of steps used in processing approximately 50 gallons (168.45 kg) of Prudhoe Bay, Alaska, crude oil to yield the desired high-boiling distillates. The initial steps consisted of passing the crude oil through an all-glass, falling-film flash still ( 4 ) heated to 100 "C. Thus, with a crude oil input of roughly 40 ml/ min, a sample contact time on the rotating glass drum of less than 30 sec, and a helium sweep rate of 9 l./min, this isothermal still a t atmospheric pressure removed a lowboiling (38-165 "C) distillate representing 11.3% of the original crude oil. A secon'd pass through the isothermal still a t approximately 6 mm of pressure removed an additional 6.2% of the original crude oil and effectively topped the Prudhoe Bay crude oil to above 200 "C without introducing any thermal hazards. The use of an Asco (Arthur F. Smith Co.) 4-in. RotaFilm (wiped wall) still under vacuum a t successively lower pressures and higher temperatures shown in Figure 1 removed distillates having boiling ranges of roughly 225-315, 315-370, 370-535, and 535-675 "C. The conditions of sample topping used throughout included short residence time in the heated zone measured in seconds, vacuum operation for exclusion of air and reduction of operating temperatures, and an inert system consisting only of glass, Teflon (Du Pont), stainless steel, and carbon; these conditions were such as to avoid any measurable sample decomposition, commonly called "cracking." The separations obtained with the Rota-Film still were quite good. For rough topping, a charge rate can be as high as 1000-1200 ml/hr. However, to obtain a high-boiling distillate of specific boiling range with minimum overlap, as in the case of the 370-535 "C ( c a . 700-1000 "F) boiling range, the charge rate was but 600 ml/hr. For the (4) H. T. Rall, R. L. Hopkins. C. J. Thompson, and H. J. Coleman, Proc.. Amer. Petrol. lnsf..Sect. 8, 42, 46 ( 1 9 6 2 ) .
ANALYTICAL CHEMISTRY, VOL. 45, NO. 9, AUGUST 1973
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~~
Table I. Data from Routine Analysis of Prudhoe Bay, Alaska, Crude Oila Distillation, Bureau of Mines Routine Method Stage 1. Distillation at atmospheric pressure, 741 mm, first drop, 81'F
Fraction No.
cut temp. "F
1 2 3 4 5 6 7 8 9 10
SP gr, 60/60 "F
OAPI, 60 "F
Per cent
Sum, %
CI
122 167 21 2 257 302 347 392 437 482 527
...
...
...
...
...
2.1 2.6 3.5 3.6 3.7 3.5 4.3 4.8 5.0
2.1 4.7 8.2 11.8 15.5 19.0 23.3 28.1 33.1
0.693 0.723 0.752 0.773 0.790 0.801 0.818 0.836 0.851
72.7 64.2 56.7 51.6 47.6 45.2 41.5 37.8 34.8
...
11 12 13 14 15
392 437 482 527 572
Residuum
...
2.8 6.5 6.8 6.0 7.4 36.3
35.9 42.4 49.2 55.2 62.6 98.9
Refractive index, nD at 20 "C
Specific dispersion
1.38591 1.40312 1.41922 1.43082 1.43922 1.44626 1.45528 1.46565 1.47467
127.9 139.0 141.9 147.0 149.6 152.1 154.7 157.0 160.5
1.48218 1.48650 1.49477
161.5 168.6 169.4
SU visc, I
23 27 30 31 30 33 36 38
Cloud test, OF
100 "F .
...
.
...
... ...
40 45 58 93 176
10 30 50 70 90
...
Stage 2. Distillation continued at 40 mmb
0.873 0.881 0.897 0.91 0 0.919 0.990
30.6 29.1 26.2 24.0 22.5 11.4
45 45 49 52 53
...
Approximate Summary Per cent
SP 9'
'API
Viscosity
4.7 19.0 4.3 18.4 11.0 8.1 1.8 36.3 1.1
0.710 0.762 0.818 0.860 0.887-0.91 1 0.91 1-0.922 0.922-0.924 0.990
67.9 54.2 41.5 33.1 28.0-23.9 23.9-22.0 22.0-21.6 11.4
...
Light gasoline Total gasoline and naphtha Kerosine distillate Gas oil Nonviscous lubricating distillate Medium lubricating distillate Viscous lubricating distillate Residuum Distillation loss
...
... ... 50-1 00 100-200 Above 200
...
General characteristics: gravity, specific, 0.893; gravity, "API, 27.0: pour point, "F 15; sulfur, % 0.82; color, brownish black; viscosity. Saybolt U n i versal at 77 O F 11 1 sec, at 100 "F 84 sec. nitrogen, YO,0.230. Carbon residue, Conradson; residuum, 11.6°/0; crude, 4.7%.
Table It. Supplemental Data on Prudhoe Bay Crude Oil Analysis Cut point Fraction no.
"C
"F
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
50 75 100 125 150 175 200 225 250 275 308 336 364 392 420
122 167 212 257 302 347 392 437 482 527 587 637 687 737 78 7
Residue Crude oil
...
...
...
...
Vol % of crude
Aromatics, %
Naphthenes. %
Paraffins, %
PN. %
Sulfur, %
Nitrogen, %
...
...
...
...
...
...
...
2.1 2.6 3.5 3.6 3.7 3.5 4.3 4.8 5.0 2.8 6.5 6.8 6.0 7.4 36.3
3.4 11.3 14.0 19.6 23.0 25.0 27.1 26.9 26.6 27.6 32.9
23.1 22.3 38.5 39.1 36.3 29.4
73.5 66.3 47.5 41.3 40.8 45.6
... ...
...
...
...
...
... ... ...
...
... ... ... ...
... ...
...
...
0.10 0.01 0.01 0.01 0.02 0.03 0.07 0.13 0.23 0.27 0.54 0.78 0.97 1.06 1.36 0.82
...
... ... ...
96.6 88.7 86.0 80.4 77.0 75.0 72.9 73.1 73.4 72.4 67.1
.
I
.
...
... ... ...
...
...
highest-boiling range of 535-675 "C (ca. 1000-1250 OF), the charge rate was reduced to 450 to 500 ml/hr. Although the high-boiling distillate of specific interest in this report is the 370-535 "C distillate, Table I11 provides analytical data on all distillates and on the final residue produced in the series of distillation steps. The boiling point overlap of adjacent distillate fractions proved to be quite limited. For such high-boiling distillates, true boiling range assessments can be achieved only
...
... ...
... ... ... I
.
.
... ... ... ...
... ...
... ... ... 0.468 0.230
by simulated distillation ( 5 ) data obtained by programmed high-temperature gas-liquid chromatography (GLC). Figure 2 shows such a GLC chromatogram and resultant simulated distillation data for the Prudhoe Bay, Alaska, 370-535 "C boiling range distillate. The GLC column used for this particular experiment was a %,j-in. by 6-ft stainless steel tube packed with high-temperature (5) J. C. Worman and L. E. Green, Anal. Chern., 37,1620 (1965).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 9, A U G U S T 1973
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Table 111. Analytical Data on Prudhoe Bay, Alaska, Fractions
CRUDE OIL
Approximate boiling range,
Irothermd Dirtilldim, 100. C
Fraction
"C
Weight Yo of crude
1 st isothermal distillate 2d isothermal distillate
38-165 165-225 225-31 5 315-370 370-535 535-675 >675
11.30 6.23 16.30 15.72 21.63 11.90 15.55
I
1st Rota-Film distillate
Isothermal Distilldim 100' C, 6 mm 143. 16 kg
DISTILLATE 6.23%
2d Rota-Film distillate 3d Rota-Film distillate 4th Rota-Film distillate
Residue
RESIDUE
io. 19 kg
81.10%
132.59 kg
0.23%
Rot-Film Distilldim 251' C, 10 mm 67. I 9 kg
DISTILLATE m . 8 9 kg
Rote-Film Distillotion 245' C, co 4 p 50.45 kg
I DISTILLATE 22.23 kg
28.22 kg
Rac-Film Distillation 3x)' c, ca 511 26.35 kg
DISTILLATE
Figure 1. Flow chart showing distillation of Prudhoe Bay, Alaska, crude oil Dexsil-300 stationary phase on 80 to 100 mesh, acidwashed and silanized, "Chromasorb G" solid support, in a Perkin-Elmer Model 900 gas chromatograph. The sample was introduced through an injection block heated to 350 "C, the column temperature was programmed from 210 to
1
'371.C400.C429.C455.C-
1
1
!I
I
700.F
32%
751.F 804.F 85I.F
I I 4% 205% 2 1 7%
Sulfur
Nitrogen
0.746 0.810 0.853 0.893 0.939 0.972 1.037
0.06 0.06 0.30 0.75 1.17 1.60 2.38
0.020 0.016 0.017 0.064 0.191 0.397 0.745
SEPARATION OF HIGH-BOILING DISTILLATES INTO FRACTIONS
I
21.63%
601 60 F
380 "C at 4 "C/min, and the flame ionization detector was operated a t 350 "C. These conditions provided adequate boiling range coverage and detection with no stationary phase "bleeding" problems. The table in the upper left portion of Figure 2 shows this high-boiling distillate to be quite well placed within the general boiling range of 370-535 "C.
I
16.30 kg
The Bureau of Mines-AP1 Research Project 60 is developing a standardized separation scheme ( 3 ) for high-boiling distillate samples. Presently this analytical separation scheme (Figure 3) includes the use of an anion resin to remove acids, a cation resin to remove bases, ferric chloride treatment to remove neutral nitrogen compounds, and silica-alumina adsorption to separate the remainder of the material into four distinct compound type concentrates: namely, saturates, monoaromatics, diaromatics, and polyaromatics-polar. Figure 3 illustrates the application of several separation and analytical procedural steps to a high-boiling (370-535 "C) Prudhoe Bay, Alaska, crude oil distillate. It also shows interpretative hydrocarbon-type data developed from mass spectrometric analysis of the concentrates. This particular boiling range distillate represented 21.63% of the original crude oil and contained 1.17% sulfur and 0.191% nitrogen. Percolation of a 150-g sample of this distillate, using dilution and elution techniques, through a 50-cm section of 5-cm i.d. glass pipe filled with a synthetic anion-exchange resin (Rohm & Haas Amberlyst A-29), removed petroleum acids representing 2.84% of the original distillate. Cation-exchange resin (Rohm & Haas Amber-
I
VG
0 '
>:
I
538.C- I.OO0'F 538'C- 1.000'F
Figure 2. Simulated distillation by gas-liquid chromatography of a high-boiling Prudhoe Bay, Alaska, crude oil distillate 1726
Weight %
0 . 3 !q
Rac-Film Distiilotia 180' c, io m m 91.29 kg
15.R%
Specific gravity,
ANALYTICAL C H E M I S T R Y , VOL. 4 5 , NO. 9 , A U G U S T 1973
370.535-
c
2 1 b 3 i s 06 C r v d d '
I Liquid s l i d Chromdogophy Through Cotion Resin (Amberlyd-A- I S )
n BASES 0 . 5 3 % (2.46%)
Chemical Treatment with Ferric Chlaidc
I
Freed
DISTILLATE Acids, BOIFI,
d
md
N e u t r c l Nitropen Compounds
20 29"-
I
Elution niith ?ti% Dinthy E r h r , 23% k n z e n , to% ~ t k d
Elution W i t h r r P s n t ~ r r
I
I 10.45'0 14a.31~ 0.t89L 8, 0 . 0 1 4 % N
'- _ _ _ _ Sarier
-12
Figure 3. Flow chart of
2.58% 1.52"c!,
3. 10% 5. 0,01041, h
Wf.
PCf.
'
,11.9141,) '.025%N
3 59%
'16.60%)
Series
0.65% L 1 7 . W
-12,-25,-16S -14,-45,-165
- I4
. S i % [15.0*1
-16
.38% 110.3%l
-16
-1s
. 2 5 % [ 6.7Ok1
- 18
-6,-20.~108
,5341, [14.4%l
-2O,-I0S
-8,-22,-125
.MY5 [17.54hl
-22,-125
-10,-14S
,679- [ 1 8 . 3 W
-24.01.
- I45
separation procedures and related analyses for a 370-535 "C Prudhoe Bay distillate
lyst A-15) treatment of the acid-free distillate removed petroleum bases representing 2.46% of the original distillate. The resin column in this instance was a 75-cm section of 5-cm i.d. glass pipe. The third preparatory sampletreatment step consisted of chromatographing the essentially acid- and base-free distillate through a 4.5-cm 1.d. by 80-cm glass column filled with ferric chloride impregnated pumice for removal of neutral nitrogen compounds by coordination-complex formation. This distinct fraction amounted to 0.90% of the original distillate, so the combined three preliminary sample-treatment steps removed a total of 6.20% of the 370-535 "C boiling range distillate. Admittedly, such sample pretreatments are not 100% effective in removing acids, bases, and neutral nitrogen compounds, but the types and quantities of compounds removed significantly simplifj any add:tional frat I mation and characterization procedures. Sulfur balances for the various subfractions are good and their further discussion appears later in the text. However, the nitrogen data are less than desirable because of inherent inaccuracies of the Kjeldahl method for trace quantities and small sample size. The next procedural step, liquid-solid chromatography with a dual-packed adsorption column containing both
silica gel and alumina gel, represents a most recent Bureau of' Mines-AP1 Research Project 60 development (6) for separating high-boiling petroleum distillates into four major and distinct compound type concentrate fractions with but a single operational step. The adsorption column was a 2.5-cm 0.d. by 240-cm long glass tube (ea. 960-ml capacity), fitted with a 600-ml eluant reservoir a t the top and a Teflon bore stopcock a t the bottom. The principal adsorption development was the use of fully activated (16 hr a t 260 "C) silica gel (Davison grade 12) in the top half of the column and fully activated (16 hr a t 400 "C) alumina gel (Alcoa F-20) in the bottom half of the column, followed by proper sample size charging and gradient elution with proper quantities of given solvents. Best results for such a adsorption step dictate the use of a sample-to-gel ratio no greater than 1 g of aromatics and polar compounds per 100 g of gel, which in this instance allowed a charge of roughly 15 g of the 370-535 "C Prudhoe Bay distillate. This 15-g sample was diluted with ten volumes of n-pentane, introduced to the adsorption column full of n-pentane prewet gel, and followed by appro(6) D. E. Hirsch. R. L. Hopkins, H. J. Coleman, Thornpson,Ana/ Chem., 4 4 , 9 1 5 (1972).
F. 0. Cotton, and
ANALYTICAL CHEMISTRY, VOL. 45, NO. 9 , AUGUST 1973
C. J.
1727
5
9
I3
4n '
17
FRACT8Ohl N'JURE'1 21 25 29
3%
37
4,
45
49
~
I
Figure 4. Gel permeation chromatograms of monoaromatic, diaromatic, and polyaromatic-polar concentrates previously separated by adsorption from Prudhoe Bay, Alaska, 370-535 "C distillate
priate quantities and kinds of eluting solvents. The use of a continuous solvent stripper (7) attached to the bottom of the column provides solvent-free fractions. Thus, by employing an approximate 200 ml/hr flow rate out of the bottom of the column, (1) elution with 2500 ml of n-pentane removed a saturate concentrate fraction, (2) elution with 3000 ml of 570 benzene-95% n-pentane removed a monoaromatic concentrate fraction, (3) elution with 3000 ml of 15% benzene-85% n-pentane remove? a diaronatic fraction, and (4) elution with 500 ml of 60% methanol20% diethylether-20% benzene followed by 1000 ml of methanol completely desorbed a polyaronatic-polar cnmpound fraction. The concentrate fractions separated by liquid-solid chromatography (see Figure 3) showed the following compound-type distributions based on the original distillate: 48.31% saturates, 16.98% monoaromatics, 11.91% diaromatics, and 16.60% polyaromatics-polar.
CHARACTERIZATION OF FRACTIONS Preliminary sulfur, nitrogen, and mass spectral data on the individual concentrate fractions provided considerable insight into sample composition. High-voltage mass spectral data of the saturate fraction, with an assist from gasliquid chromatography, established the carbon number range to be roughly CZZto C42. Applicable mass matrices (8) provided a basis for determining the major compound 17) R. L. Hopkins, Ind. Eng. Chem., 43, 1456 (1951) (8) A . Hood and M.J. O'Neal, Advan. MassSpectrom., 1, 175 (1959).
1728
types within this saturate fraction to be 27.7% normal and isoparaffins, 22.3% mononaphthenes, 15.8% dinaphthenes, 12.2% trinaphthenes, etc., to a low of 3.6%for the hexanaphthenes. The presence of only 0.7% monoaromatics in the saturate concentrate indicated excellent separation of saturates and monoarornatics. The chromatogram of Figure 2 shows very small n-paraffin peaks in the entire distillate, thus suggesting the 27.7% subdivision of normal and isoparaffins to be largely isoparaffins. Preliminary low-voltage mass spectral analysis for the three remaining silica-alumina adsorption concentrate fractions of Figure 3 provided an important initial indication of compound type structures within each concentrate. Such advantageom preliminary mass series data can be derived readily from raw, low-ionizing voltage (11 eV) spectral information without concern for corrections involving sensitivity differences or isotope contributions. Thus, the monoaromatic concentrate fractions appeared to be roughly alkylbenzenes and naphthenologs thereof (formed by addition of 1 to 7 naphthene rings to the alkylbenzene structure). Similarly, the diaromatik concentrate fraction appeared to be predominantly alkylnaphthalenes and naphthenologs thereof, and the polyaromatics-polar fractions appeared to be much more complex because of sulfur compounds (3.92% sulfur), nitrogen compounds (0.21% nitrogen), plus diverse aromatic ring structures, combined with naphthene rings in various numbers and degrees of condensation so as not to exceed six total rings. To simplify these individual concentrate fractions further and to resolve some important quantitative relationships, not only within each concentrate but also for the overall Prudhoe Bay 3i0-53
