Anal. Chem. 1981,
in nonbuffered methanol solutions, but they are concentration independent -solvent composition dependent in methanolphosphate buffer mixtures. From the foregoing discussion, solutes in groups I and I11 can be eliminated as suitable for use in determining the column void volume. Discrimination between the group I1 solutes, sodium nitrate and potassium dichromate, can be made on the basis of the elution order for equimolar quantities of these solutes in buffered eluent. That solute which undergoes a greater pore penetration of the silica gel backbone is expected to have a greater elution volume, e.g., sodium nitrate. Therefore, according to eq 2, sodium nitrate more nearly represents the case of C#I = 1 than does potassium dichromate.
CONCLUSIONS On the basis of the evidence presented for the solutes examined, acetone, N,N-dimethylformamide, methanol, and uracil appear to be unsuitable for determining column void volume on hydrocarbonaceous stationary phases. When buffered methanol eluents are used, the injection of any detectable amount of sodium nitrate produces a good estimate of the column void volume in RPHPLC. In unbuffered aqueous methanol, the column void volume can be estimated by an injection of approximately 3 x 10+ mol or greater of sodium nitrate. Perhaps the most important conclusion is that the identity and concentration of the solute used to determine the column void volume must accompany all reported k'data in RPHPLC studies.
53, 1345-1350
1345
Horvah, Csaba; Lin, HungJye J . Chromafogr. 1976, 726,401-420. Scott, R. P. W.; Kucera, P. J . Chromafogr. 1977, 725, 251-263. Scott, R. P. W.; Kucera, P. J . Chromafogr. 1877, 742, 213-232. McCormick,.R. M.; Karger, 8. L. Anal. Chem. 1980, 52, 2249-2257. Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Ch8m. 1978, 50, 1911-1917. Roumeliotis, P.; Unger, K. K. J. Chromafogr. 1978, 749, 211-224. Melander. Wayne R.; Chen, Bor-Kuan; Horvath, Csaba J . Chromatogr. 1979, 785, 99-109. Karger, Barry L.; Gent, J. Russel; Hartkopf, Arleigh; Weiner, Paul H. J. Chromafogr. 1978, 728, 65-78. Gant, J. R.; Dolan, J. W.; Snyder, L. R. J . Chromfogr. 1979, 785, 153- 177. Baker, John K.; Ma, Cheng-Yu J . Chromatogr. 1979, 769, 107-115. Johnson, Howard J., Jr.; Cernosek, Stanley F., Jr.; GutierrezCernosek, Rose Mary J . Chromafogr. 1979, 777, 297-311. Unger, Stefan H.; Feuerman, Tony F. J . Chromatogr. 1979, 776, 426-429. Bakalyar, Stephen R.; Mcliwrick, Rod; Roggendorf, Elizabeth J . Chromatogr. 1977, 742, 353-365. Bakalyar, Stephen R.; Henry, Richard A. J . Chromafogr. 1976, 726, 327-345. Schoenrnakers, P. J.; Billlet, H. A. H.; Tijssen, R.; de Galan, L. J . Chromatogr. 1978, 749, 519-537. Lochmuiler, C. H.; Wilder, D. R. J . Chromafogr. Scl. 1979, 77, 574-579. Horvath, Csaba; Melander, Wayne; Molnar, Imre J . Chromafogr. 1976, 725, 129-156. Hemetsberger, H.; Maasfeld, W.; Ricken, H. Chromafographie 1978, 9 , 303-310. Hemetsberger, H.; Kelierman, Marlene; Ricken, H. Chromafographie 1977, 10, 726-730. Neddermeyer, P. A.; Rogers, L. B. Anal. Ch8m. 1969, 41, 94-102. Buvtenhuvs. F. A.; van der Maeden, F. P. B. J . Chromatoor. 1978. 749, 489-500. Krejci. M.; Kourilova, D.;Vespalec, R.; Slais. K. J . Chromafogr. 1980, 191 . - . , 3-7 - .. Berendsen, a r t E.; Schoenmakers, Peter J.; de Galan, Leo; Vigh, Gyula; Varga-Puchony, ZRa; Inczedy, Janos J . Llq. Chromafogr. 1980, 3 , 1669-1686.
LITERATURE CITED (1) Haftmann, Erich "Chromatography: A Laboratory Handbook of Chromatographic and Electrophoretic Methods"; Van Nostrand Reinhold: New York, 1975; p 49. (2) Colin, Henri; Ward, Norman, Guiochon, Georges J . Chromfogr 1978, 749, 169-197.
RECEIVED for review December 29, 1980. Accepted April 27, 1981. We sincerely appreciate the support of the American Foundation for Pharmaceutical Education Silas M. Burroughs Memorial Fellowship for M. J. M. Wells.
Preparative Liquid Chromatography for Fractionation of Petroleum and Synthetic Crude Oils James W. Vogh' and Jane S. Thomson Barflesville Energy Technology Center, U S . Deparlment of Energy,
P.0. Box 1398, Bartlesville,
The procedures for routine preparative liquid chromatographic separation of hydrocarbon classes in high boiling petroleum and coal liquid samples have been improved by use of highperformance liquid chromatography techniques. Separations were carried out on alumina and silica gel to produce sample fractions equivalent to those obtained with older methods. The columns are reusable foilowing suitable solvent backwashing and provide stable performance and good hydrocarbon class resolution over an extended series of runs. The complete operating time, including regeneration to starting conditions, is 80 min for the alumina column and 25 min for the silica gel column. Capacity ranges from 1 to 6 g of sampie, depending on its composition.
One of the primary steps in the detailed characterization of petroleum and similar materials has been the adsorption column separation of hydrocarbon classes. The principal methods have been the silica-alumina gel procedure developed
Oklahoma 74003
under the API-60 program or variations of this procedure (1). The subsequent steps through gel permeation and characterization by mass spectrometric and other methods depend largely on the success of the adsorptioii column separation. The silica-alumina procedure in common use is a conventional open column chromatographic method. It was developed through a procedure of step gradient displacements of a series of model compounds. This became a set procedure depending on the dimensions of the column, the quality and activation of the adsorbants, and the volumes and flow rate of the eluting solvents. Sample capacity varied from 4 to 15 g depending on the amount or nature of the more strongly adsorbed components. The procedure does not permit an easy change of scale of equipment unless the column is coupled to a liquid chromatography monitor. The silica-alumina column method usually provides a good separation of the hydrocarbon classes; however, there are difficulties and inconvenient aspects in this procedure. As a method conceived for routine use, the most severe problem is the requirement for an unbroken 50-h operation. Other
This article not subject to U.S. Copyright. Published 1981 by the American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 9, AUGUST 1981 n-
n
soldered
1/8"SS Tube
b
Flgure 1. Column end fitting prepared by modification of Swagelok
cap
SS-2000-C.
problems in the method are associated with lack of a detection system. Overloading of the column may not be detected until succeeding separations or characterizations are carried out. There is a large background of information on alumina column chromatography, especially in procedures developed by Snyder ( 2 ) ,based on water deactivated alumina for separations of petroleum samples and many hydrocarbon classes. Detailed studies of structural and other effects in separations on alumina were carried out (3), and it was shown that deactivation of alumina results both in improved column efficiency and in increased linear capacity. The latter effect is particularly important in preparative chromatography. Other studies ( 4 ) on deactivated alumina have shown the effects of molecular shape, alkylation, and acid-base interactions of a large variety of hydrocarbons. A routine for adsorbant activity control has been worked out (5). Highly active alumina is infrequently used in high-performance liquid chromatography separations, but it has been applied in gradient mode for analyses of lubricant base oils (6). In this method, the column was reactivated for the succeeding run at 250 "C while purging with nitrogen. There is some inconvenience in maintaining a fixed level of deactivation with water or in holding a highly active state by thermal activation. I t has been shown that various polar solvents may be used in place of water ( 2 ) so that it seemed desirable to select a solvent combination that would allow more convenient control of the alumina activity level. Alumina can separate saturate from monoaromatic hydrocarbons only in the highly activated state. Silica is more satisfactory for this separation since it provides good resolution without need for high activation. In addition, it has a much higher sample capacity than does activated alumina. Generally, the group separation obtained with the silicaalumina column has been satisfactory when carried out properly, and these adsorbants were retained as the basis of the separation method in the development of an improved procedure. Continued use of group separation by alumina and silica gel adsorption also allows the other separation and characterization procedures to be continued without change. The major change sought in the improved procedure was development of efficient, high-speed, reusable preparative columns. Current techniques of liquid chromatography provide the basis for the development of this type of column.
EXPERIMENTAL SECTION The column tubing and fittings were prepared from conventional stainless steel pipe and Swagelok fittings. Tubing was 30-cm lengths of 3.18 cm (1.25 in.) 0.d. and 2.75 cm i.d. pipe, and the interior of the tubing was polished by means of a cylinder hone. The end fitting is shown in Figure 1. These were Swagelok 1.25 in. caps, type SS-2OOO-C,machined to a flat interior base leaving an end wall about 7 mm thick. A length of 0.125-in. 0.d. stainless tubing was silver soldered through the center of the end wall. A slurry packing reservoir of 150-cm length was prepared from the 1.25-in. pipe and was attached t o the column by a drilled out Swagelok union. Columns and the reservoir were tested at 2000
psi before the columns were packed. A disk of porous polyethylene (Bel Art, Pequannock, NJ, 35 fim) was cut to fit tightly in the end of the column by means of a sharp-edged punch prepared from the tubing stock. Stainless steel screen (150 mesh, Small Parts, Inc., Miami, FL) and polytetrafluoroethylene filter element (Millipore, Bedford, MA, type FHLP, 0.5-pm porosity) were cut to approximately the outer diameter of the column and were placed in the end fitting. The Millipore element was placed against the polyethylene frit. Adsorbants were prepared from thin-layer grade materials (Merck alumina 60 PF-254, type E, and Merck silica gel H, type 60, EM Laboratories, Inc., Elmsford, NY). These adsorbants are not suitable for column chromatography as received and must be processed to remove the very small particle material. For refining of the silica gel, about 200 g of the adsorbant was suspended in 2 L of 0.04 N NH40H,the mixture was dowed to settle about 5 min, and the supernatant suspension was siphoned off. This was repeated three or four times with the last rinse being carried out with deionized water. The silica was dried and activated at 110 "C. The alumina was first soaked in ethyl acetate a minimum of 48 h, with occasional stirring, for removal of binder material. It was then washed with successive portions of ethyl acetate and acetone and finally with deionized water. Fine particulates were removed by suspension, first in 0.04 N acetic acid and subsequently in deionized water. The supernatant suspension was siphoned off after 30 min of settling. Typically, seven t o eight rinses with deionized water were used. Drying and activation were at 200 "C. All column packing was done by a pressurized viscous slurry technique. The slurry was prepared as a suspension of about 215 mL of the adsorbant (about 20% excess of the column volume) in about 500 mL of pharmaceutical-grade mineral oil plus 25-60 mL of pentane. The pentane causes a substantial reduction in the viscosity of the mineral oil slurry. The amount added should not be sufficient to allow visible settling of the adsorbant but should be enough to make the mixture quite fluid. About 25 mL of mineral oil was placed in the column, the slurry was introduced, and the remaining space in the reservoir was filled with pentane. The slurry was forced into the column under the pressure of pentane from a Haskel (Burbank, CA) air driven pump, Model 28645. About 1600 psi pressure was applied by the pump during the packing and about 20-60 min were required for completion of the packing. Two liters of pentane were then pumped rapidly through the packing assembly. After the slurry packing was completed, the column and reservoir tubes were carefully separated to avoid excessive disturbance of the adsorbant bed. The exposed adsorbant was scraped out of the end of the column t o allow insertion of a polyethylene frit. The column was closed with a fitting including a wire gauze and Millipore filter in the same manner as the opposite end. After packing and closure of the columns they were washed with about 500 mL of pentane, allowed to stand for 18-24 h, and again washed with more pentane. This procedure was found to be necessary for complete removal of the mineral oil. After the second washing the silica column was ready for use in examination of samples. The alumina column required washing with 10% (vol) of ethyl ether in pentane. About 2-4 L of this mixture was passed through the column followed by about 500 mL of 1% (vol) ether in pentane to prepare it for use. Figure 2 shows the schematic flow system used when the columns were operated in the preparative mode by gradient elution. For solvent gradient operation a pair of 500-mL mixing vessels (Glenco, Houston, TX, type 3130) were used. Linear gradients were formed in this system. The system included a Fluid Metering, Inc., Oyster Bay, NY, solvent pump (Model RPSDSS). This pump was capable of pumping up to 110 mL min-' at pressures up to 200 psi. Refractive index (Waters Associates, Milford, MA, Model R401) and ultraviolet (254 nm, Waters) detectors were used with the silica column. Effluent from the silica column was split, with the major part of the flow going to waste or sample receivers and the minor part of those detectors. This splitting of the solvent stream prevented development of excessive back-pressure in these analytical-type detectors. A flow-through cuvette-type cell of 1.5-mmpath length (Helma CeUs,
ANALYTICAL CHEMISTRY, VOL. I
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53, NO. 9, AUGUST 1981
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.-
I Gradient
I
9co'"mnb I8 Detector
Pump
B' m valve
A Sample
Syringe and sample valve
Receiver
Figure 2. Schematic of preparative liquid chromatography system.
Jamaica, NY, Model 176.52) was used in an ultraviolet-visible spectrophotometer (Beckman Instruments, Fullerton, CA, Model 25) as detector for the alumina column. No signifciant backpressure was developed by this flow-through cell so that solvent stream splitting was not needed. Large sample introduction and column back-flushing were accomplished with Altex four-way slider valves. The alumina column was commonly operated in the solvent gradient elution mode. In the usual preparative separation routine, the sample was introduced in the stop-flow mode by syringe injection through the slider valve. It was then washed onto the column with 150 mL of I vol% of ethyl ether in either pentane, hexane, or heptane. This was followed by 800 mL of 1-10% ether linear gradient and back-washing with 400-800 mL of 20% ether in the same hydrocarbon solvent. To prepare the column for further use, it was then washed in the forward direction with 400-600 mL of 1%ether solution. Cut points for fraction collection were taken at the chromatogram minima, if these were evident and at the beginning of the backflush. Complex or unusual samples that did not show the typical hydrocarbon class chromatograms were cut at points determined from model compound studies. Prior to preparative separations, an analytical size sample of the particular oil was chromatographed on the alumina column to aid in location of exact cut points and to detect any unusual character of the oil. The first cut from the alumina column contains both saturate and monoaromatic hydrocarbon classes. This sample cut was concentrated to a suitable volume for introduction to the silica column for further separation. The following cuts from the alumina column contained diaromatic and polyaromatic-polar classes and were not subjected to silica column separation. The silica gel column was operated in a similar forward and backflush manner but without solvent gradient. Pentane was the commonly used solvent, and no regeneration of the column was required before a succeeding run. The forward and backwash volumes for the silica column were determined by the detector response to the saturate and monoaromatic hydrocarbon classes. In some cases it was found desirable to carry out preparative separations at elevated temperatures. For this purpose the column was placed in a regulated-temperature water bath. The upper temperature limit was set at the boiling point of the solvent in the column. Hydrocarbon solvents (Phillips Petroleum Co., Bartlesville,OK, commercial and pure grades) were distilled and passed through columns of activated 3A molecular sieve. Anhydrous, alcohol-free ethyl ether (Fisher Scientific,Pittsburgh, PA) was used as received. Tetrahydrofuran was used in mixtures with pentane or heptane for displacement of strongly held materials or for occasional regeneration of the columns. Hydrocarbon model compounds listed in the discussion were used as received. Petroleum and coal liquid samples from characterization studies were examined for comparison with previous separation results.
RESULTS AND DISCUSSION Figure 3 shows a chromatogram of some model compounds at analytical levels on an alumina column. This run was made under the conditions described earlier of gradient elution and backwash. On the time axis of Figure 3, the zone A-B was
6.1
1
A
B
IO
20
-
JO
43
53
MINJTES C
Figure 3. Chromatogram of hydrocarbons on preparative alumina column: (1) toluene, (2) 2,6dimethylnaphthalene, (3) acenaphthene, (4) pyrene. UV detection, flow rate, 28 mL/min. The solvent gradient zones are as follows: A-B, 1 % ether in hexane; 6-C, 1-10% ether linear gradient; C (backflush), 2 0 % ether.
W l
Figure 4. Chromatogram of hydrocarbons on preparative silica column: (1) cyclohexane, (2) 2-methyI-l-pentene, (3) toluene, (4) 6-methyltetralin. Refractive index detection, pentane solvent, flow rate, 28 mL/min.
the initial isocratic stage of 1% ethyl ether in hexane and zone B-C the linear gradient stage of 1-10% ether in hexane. At C the flow direction was reversed to backflush remaining material from the column with 20% ether in hexane. The point B was selected for development of a well-resolved chromatogram and was not related to fraction collection. C, however, represents the initial collection of the backflush on polar class fraction. Figure 4 shows a similar chromatogram for the silica column. This chromatogram was prepared with forward flow only and without gradient. It is evident that the performance of these columns in the analytical mode is not that of the best LC systems. However, it can be useful in preliminary analytical examination of samples as well as in the preparative separations. Figure 5 shows a chromatogram from the alumina column of a 1-g sample of the 370-535 "C distillate of Gach Saran crude. This chromatogram was carried out in the conventional gradient and backflush manner described for Figure 3. The zones of aromatic hydrocarbon classes for this as well as other oil samples appear somewhat earlier than expected on the basis of model compound studies. This is not an overload effect since the chromatograms are not altered if analytical size samples are injected. The first peak in this chromatogram is the UV response for monoaromatic hydrocarbonsq Saturate hydrocarbons elute before and with the monoaromatics so that this fraction must be resolved later on the silica column. The alumina column in this procedure could not be maintained in a sufficiently active state to provide a useful separation of
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 9, AUGUST 1981
Table I. Capacity Factors ( K ' )of Hydrocarbons on Silica and Alumina Columns silicaa alumina b dotriacontane isopentane pristane cyclohexane deca1in cyclododecane perhydroanthracene 7-tetradecene 1-hexadecene 2-hexene 2-methyl-1-pentene 4-methylcyclohexene nonadecylbenzene tridecylbenzene a Pentane solvent. values.
0.00
0.00
0.05 0.06 0.10 0.10 0.10 0.10
0.20 0.23 0.39 0.43 0.47 1.06 1.19
silicaa
but ylbenzene benzylcyclohexane ethylbenzene toluene cyclohexylbenzene 1,3,5-trimethylbenzene p-xylene indan tetralin 6-methyltetralin tetrahydroacenap h t hene naphthalene 1,2,4,54etramethylbenzene dodecahydrotriphenylene hexamethylbenzene
aluminab
1.51 1.63
1.74 0.67
1.98
2.14
2.19
2.26 2.55 2.12 2.88 2.92 3.24 3.29 4.30 4.75
0.80 1.26 4.55 1.05 2.51 2.94
Hexane, 1%ether solvent. Capacity factors were determined only for compounds with listed .
E E
0 6-
t-
a
W
I
04/
A
B
C
Flgure 5. Chromatogram of Gach Saran crude distillate, 370-535 "C, 1-01 g, on alumina column. For conditions see Figure 3.
saturate from monoaromatic hydrocarbons. The columns were ordinarily operated a t a flow rate of about 28 mL min-', which was about as fast as possible for convenient sample collection. If an automated, detectorcoupled, sample collection apparatus was available, columns should operate well a t much higher flow rates. Figure 6 shows the trend of plate height (HETP) with flow rate for toluene and 2-butylbiphenyl on alumina. The column was at 25 "C, and the solvent was 1%ether in heptane. Figure 6 also shows the same trend for cyclohexane and toluene on silica at 25 "C with pentane solvent. It is apparent that both columns will give useful separation and stable behavior at flow rates to 80 mL m i d . At the time of this H E T P rating, both of these columns were several months old and had been subjected to backflush operation so that these results represent the properties of well-stablized columns. The apparent low resulution of the chromatogram in Figure 5 compared to the other chromatograms is due the complexity of that high-boiling sample rather than any failure of the column to resolve individual compounds efficiently. Variation of capacity factors for model compounds in a class is discussed below. Because of this, class separations do not benefit very much from high plate numbers and should be only slightly less complete when carried out at high flow rates. Table I shows capacity factors for a variety of saturate and aromatic hydrocarbons on the silica gel column. There is a slight retention of some cyclic saturates, but it is not sufficient to provide useful separation in this class. Alkenes are sufficiently resolved from saturates to allow their detection in
02-
-a 0
I 20
1
40
1 60
-
80
FLOW, m l / m i n u t e s
Trends of plate helght (HETP) with flow rates. Upper two lines represent alumina column, 1% ether in heptane solvent: (W) 2-butylblphenyl, (0)toluene. Lower two lines represent silica column, pentane solvent: (0)toluene, (A) cyclohexane. Flgure 6.
analytical samples. For preparative separations of alkenes from saturates, the column must be cooled to -10 "C or lower to increase retention sufficiently to offset the peak blending effect of large sample volumes. If large amounts of normal paraffins are present in the sample, they will tend to crystallize from solution at this temperature and interfere with flow through the column. In this situation, a procedure based on a mixed fluorinated solvent and aliphatic solvent system (7) might be preferable. That procedure was not examined in this work, however. Capacity factors of monoaromatic hydrocarbons show the same general patterns that have been observed in other work (8,9). The monoaromatic hydrocarbon class is well separated from the saturates but tends to overlap the diaromatic hydrocarbons. For this reason, the silica gel column is used mainly for separation of saturate from monoaromatic hydrocarbons in mixtures containing only these two classes. Table I1 shows the effect of temperature and solvent on capacity factors of the silica column. Most of this effect is due to temperature. Ordinarily no special benefit is gained by operating at elevated temperature, but waxy samples may
ANALYTICAL CHEMISTRY, VOL. 53, NO. 9, AUGUST 1981
Table 11. Influence of Temperature and Solvent on Capacity Factors Silica Column, Isocratic Mode capacity factors room temp 44 "C pentane heptane nonadecylbenzene pentyl benzene toluene cyclohexylbenzene tetralin
1.06 1.42 1.98 2.14 2.72
0.70 1.05 1.35 1.35
1.59
Alumina Column, Gradient Mode capacity factors 1-10% 1-10% ether in ether in 1-10% hephepether in tane, tane hexane, 35 "C 22 "C 22 "C 2-butylbiphenyl naphthalene 2,6-dimethylnaphthalene l-phenylnaphthalene fluorene 2,6-dimethylanthracene a
2.2 3.5 4.3
3.4 3.7
5.5
4.9
4.5
BFa BF
BF BF
7.2 BF
1.8
1.8 3.1
3.4
Backflush.
Table 111. Capacity Factors ( K ' ) of Hydrocarbons on the Alumina Columna 2-butylbiphenyl 1-butylnaphthalene naphthalene hexahydropyrene
2.19 3.08 3.54 3.79
l12-diphenylethane l15-dimethy1naphthalene biphenyl acenaphthene
4.1 6 4.24 4.36 5.00
1-phenylnaphthalene fluorene 2-phenylnaphthalene 2,6-dimethylanthracene phenanthrene chrysene
BF BF
pyrene
BF
Gradient mode, 1-10% ether in hexane.
5.46 B F ~
BF BF
Backflush.
require higher temperature for adequate solubility. Table I contains capacity factors for some model compounds in the mono- and diaromatic hydrocarbon classes on the
1349
alumina column. These capacity values were determined in isocratic mode operation with 1% ether in hexane, that is, without gradient operation. Although resolution efficiency is less for the alumina than for the silica gel column, the separations of aromatic hydrocarbon classes are more satisfactory on alumina since the capacity factors of members of an aromatic class are less dispersed than on silica gel. The last three monoaromatic hydrocarbons in this list would elute after naphthalene on the silica column but are well retained in the monoaromatic class on alumina. These retention values follow the same patterns that have been observed in other work ( 4 ) . Table I11 shows capacity factors of a number of diaromatic and polyaromatic hydrocarbons on alumina under gradient operation. Most of the diaromatics elute between capacity factor values of 3 and 5. Only the sterically crowded 2-butylbiphenyl falls significantly outside this range. The tri.. aromatic 1-phenylnaphthalene elutes just after the diaromatic zone and much before any other model triaromatic compound. This is expected since the hydrogens of the 2-phenyl and 8-naphthyl positions of this compound crowd each other. The other polyaromatics examined all elute at essentially the same zone in the backflush. Table I1 shows the effect of temperature and solvent on capacity factors on alumina under gradient operation. Alumina shows less sensitivity than silica, but the appearance of fluorene in the forward wash near the end of the solvent program at 35 "C indicates a possible effect on sample fraction composition. A number of samples originating from petroleum, coal liquids, and shale oil sources have been processed by this system. Each of the samples was first introduced to the alumina column at analytical level. Sample size was then increased until the chromatogram showed signs of overloading as indicated by smearing or substantially early appearance of the peaks. The acceptable quantities varied among the different samples and fell in the range of 1-6 g per injection. It seemed in several cases that the polar and polyaromatic materials could occupy a sufficient fraction of the column capacity so that the diaromatic and earlier polyaromatic hydrocarbons were crowded forward in the chromatogram at the overload condition. For this reason, the usual overload rating based on HETP at increasing single compound injection (IO) was not used. Some of the samples studied were duplicates of those run by the API-60 method ( I ) either in that program or in later residue or coal liquid studies at the Bartlesville Energy Technology Center. The first of these is the 370-535 "C
Table IV. Recovery of Hydrocarbon and Polar Class Fractions
fraction saturate monoaromatic diaromatic diaroma tic-second
Gach Saran crude 370-535 "C dist (acid and base free) API-60 method" this report 51.03 17.72 12.32
48.81 20.64 10.42 5.86 12.1 7
South Swan Hills crude 370-535 "C dist (acid and base free) API-60 method this report 65.94 12.55 6.27
64.75 13.65 6.67 3.02 9.99 .26
Utah coal syncrude 200-370 "C dist API-60 methodC this reportd 28.1 30.0 14.7
27.32 28.85 16.89 2.67 3.49 0.65 10.47 5.50
18.93 10.82 5.2 BF (THF)b 0.00 acids 10.8 bases 0.6 solids 3.4 (total) 100.00 97.90 95.58 98.34 92.8 95.84 " Data had been normalized to 100%. Backflush with tetrahydrofuran. Acid and base materials were extracted from the initial PAP fraction. In the extraction procedure, solids amounting to 3.4% of total sample were also recovered. Acid and base materials were extracted from the distillate. PAP-back flush
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Table V. Comparison of Mass Spectrometric Saturate Class Analysis, South Swan Hills, 370-535 "C
O-ring 1-ring 2-ring 3-ring 4-ring 5-ring 6-ring monoaromatic
MI-60 method
this report
28.8 31.1 14.6 9.2 8.1 4.5 3.8 0.0
29.5 28.3 17.1 9.3 8.1 4.6 3.2 0.0
distillate of Gach Saran (Iran) crude (11)shown in Table IV. Both runs were carried out on acid- and base-free material. Yields from the two methods are in reasonable agreement for the saturate, monoaromatic, and diaromatic classes. In this and the following samples, the eluant following the diaromatic zone was collected separately from the backflush (PAP) material. The yield of this (DA-2, Diaromatic-Second) plus the backflush (BF) approximates the PAP fraction of the API-60 method. In several samples the yield of the DA-2 fraction was fairly substantial in comparison to the backflush fraction. Since the DA-2 appears by mass spectrometric examination to be largely diaromatic, characterization of it apart from the polar components of the backflush material should improve analytical results. Analysis of the saturate fraction by mass spectrometry showed it to correspond well to the old saturate fraction. The Gach Saran sample was a fairly typical high-boiling distillate of petroleum crude. It responded well to both separation processes and, according to the yields shown in Table IV, produced well-defined hydrocarbon concentrates. The second part of Table IV shows the yields from separation of the 370-535 "C distillate of South Swan Hills (Alberta, Canada) crude (12). Both runs were carried out on acida d base-free material. Again the yields of the saturate, monoaromatic, and diaromatic concentrates are in good agreement. The combined DA-2 and backflush yields are somewhat greater than the PAP yield of the old method, which probably indicates improved sample recovery by the backflush operation. The South Swan Hills distillate is somewhat higher in saturates than the usual crude. It separated to the several concentrates by both methods without difficulty. The analysis of the saturate fractions of both the old and new separations of South Swan Hills distillate is shown in Table V. The MS analysis of the old fraction was repeated concurrently with the analysis of the new sample. The last part of Table IV shows results obtained on a coal liquid. This was the 200-370 "C distillate of a Utah syncrude (13) produced by the COED process from Utah A-seam coal and supplied by FMC Co. (Chicago, IL). This was a fairly complex material containing a relatively large amount of polar material. Also, the hydrocarbon material was highly aromatic. The sample processed by the API method did not have acids and bases removed before the hydrocarbon class separation; therefore, these as well as some solids were recovered from the PAP fraction. The sample processed in this work was treated by extraction for removal of acids and bases before the column separations. Despite the considerable difference in sample handling, the hydrocarbon class yields for the Utah Syncrude are quite comparable for the two methods. The low overall yields by both methods may be partly due to loss of the more volatile components boiling near 200 "C. The experience gained in processing a number of samples has shown the advantages as well as the need for certain
cautions. Solvent mixtures more polar than 10% tetrahydrofuran in heptane should probably not be used in the alumina column. Both pure tetrahydrofuran and methanol in heptane appear to have been damaging to alumina and should be avoided if possible. The need for washing alumina with strongly polar solvents arises when the column has been used for an extended series of highly polar samples. In this condition, the column will show diminished capacity and retention volume. Ordinarily, extended recycle washing with 10% tetrahydrofuran with a tube of conventional activated alumina in line will correct this problem. Solvents and samples should be free of water if possible, but washing with 10% tetrahydrofuran will reactivate the column. Particulate matter in the samples either may be caught on the polyethylene frit or may be passed through and lodged on the end of the adsorbent bed. This may be repaired without harm to the column by removing the frit, scraping out the particulate and a small amount of the packing, and replacing with a new frit. Silica appears to be immune to these problems. The silica column prepared originally for this study is still in use. Several advantages have been achieved by use of this separation procedure. An obvious advantage is the saving of time. At the flow rates used in most of this work, the alumina column requires 80 min for a complete cycle and the silica column about 25 min. Samples equal in size to those processed in the old, open-column method can be prepared in a series of runs scheduled at convenient times, rather than in a continuous 50-h run. Small samples may be processed in a lesser number of runs with proportional saving of time, whereas the open-column run time cannot be shortened. The use of the columns to produce a reference analytical chromatogram has been helpful in identifying unusual composition of samples and problems that may result. For example, comparison of chromatograms prepared during preparative runs with the reference analytical chromatogram can indicate possible overload conditions. Both the silica and alumina columns are reusable and stable through an extended series of sample separations. The reusable chracter of the columns saves a considerable amount of time activating adsorbents and cleaning and repacking columns. More important than the saving of time is the reliably good resolution and repeatability of the columns. Column reproducibility over a long time period has been important in the development of an efficient separation procedure.
LITERATURE CITED (1) Htsch, D. E.; Hopkins, R. L.; Coleman, H. J.; Cotton, F. 0.; Thompson, C. J. A d . C b m . 1972, 44, 915-919. (2) Snyder, L. R.; sunders, D. L. "Chromatography in Petroleum Analysis"; Altgett, K. H., Gouw, T. H.. Eds.; Marcel Dekker: New York, 1979; Chapter 10. (3) Snyder, L. R. "Principles of Adsorption Chromatography"; Marcel Dekker: New York, 1968; Chapters 10, 11. (4) Popl, M.; Dolansky, V.; Mostecky, J. J. Chromtogr. 1974, 91, 649-058. (5) Engelhardt, H.; Wledemann, H. Anal. Chem. 1073, 45, 1641-1646. (6) Mabunaga, A.: Yagi, M. Anel. Chem. 1078, 50, 753-756. (7) Suatonl, J. C.; Swab, R. E. J. Cbfomtogf. S d . 1980, 18, 375-378. (8) Snyder, L. R. J. Cbromtogr. 1983, 11, 195-227. (9) Popl, M.; Dolansky, V.; Mostecky, J. J. Chromtogr. 1978, 117, 117-127. (10) DeStefano. J. J.; Beachell, H. C. J . Chromtogr. So/. 1972, 10, 654. (11) Dooley, J. E.; Hopkins, R. L.; Hlrsch, D. E.; Coleman, H. J.; Thompson, C. J. Bureau of Mines Report of Investigations R I 7770; Bartlesvllle Energy Technology Center: Bartlesville, OK, 1973. (12) Dwley, J. E.; Hirsch, D. E.; Coleman, H.J.; Thompson, C. J. Bureau of Mines Report of Investigations R I 782 1; Bartlesvllle Enegy Technology Cmter: Bartlesvllle, OK, 1973. (13) Dwley, J. E.; Sturm, G. P., Jr.; Woodward, P. W.; Vogh, J. W.; Thompson, C. J. BERC/RI-75/7; Bartlesvllle Energy Technology Center: Bartlesvllle, OK, 1975.
RECEIVED for review November 20, 1980. Accepted May 11, 1981.
