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Separation and Characterization of Components of Catalytic Cracker Feed Using Centrifugal Partition Chromatography Randy A. Menges, Larry A. Spina,? and Daniel W. Armstrong' Department of Chemistry, University of Missouri-Rolla, Rolla, Missouri 65401-0249
Centrifugal partition chromatography (CPC)was used to fractionate a catalytic-cracking feedstock (Le., catalytic cracker feed) into 16 separate fractions in the descending mode and 5 fractions in the inverse or ascending mode. Each fraction was analyzed by UV, fluorescence, and synchronous luminescence (SL) spectroscopy as well as by gas chromatography/mass spectrometry (GC/MS). It appeared that CPC can be used to fractionate larger samples of this type and with a greater degree of selectivity than previously reported preparative HPLC approaches. The SL spectra tended to be much more useful and informationrich for these complex mixtures as compared to UV or fluorescence spectra. GC/MS of each fraction allowed identification of specific components. In this way the selectivity of the CPC separation could be accessed. It was found that CPC effectively separated catalytic cracker feed into fractions by polarity, aromaticity, and alkyl substitution patterns. In addition, fractionation by heteroatom type and of homologues was observed. The aromatic content found by gravimetry after CPC separation matched well with the aromatic content measured by UV spectrometry.
INTRODUCTION Crude oils and other related products such as coal and shale are by nature very complex mixtures. Initial refining yields light petroleum products and heavy distillates and residues. Heavy distillates are valuable materials that can be converted to useful fuel products.' It is well-known that the percentage and composition of the heavy residue in crude petroleum, for example, varies with its origin. With the increased use of heavier crude petroleum reserves and the development of nonconventional fossil fuels such as shale and coal oil, and withthe increaseddemand for light petroleum products, it is necessary to convert these heavy residues into light petroleum products in more economical, efficient, and environmentally friendly ways. This conversion is performed by either a thermal or catalytic cracking process that chemically breaks or %acks" higher molecular weight molecules into lighter fragments. Studies have shown that different classes of compounds typically found in heavy residues react differently in the cracking process.2 In order to better understand and improve the cracking process, it is important to thoroughly characterize these residues. Typically, the analysis consists of physicochemicalmeasurements
* To whom correspondence should be sent.
+ Shell Development Co., Westhollow Research Center, Houston, TX.
(1) McKay, J. F.; Amend, P. J.; Harnsberger, P. M.; Cogswell, T. E.; Latham, D. R. Fuel 1981,60,14. (2) Bollet, C.; Escalier, J. C.; Souteyrand, C.; Caude, M.; Rosset, R. J. Chromatogr. 1981,206, 289. 0003-2700/93/0365-2873$04.00/0
such as density, viscosity, elemental analysis, and asphalt and ash content. Unfortunately these basic measurements yield little information that can be used to optimize the refining process.2 Much more useful information may be elicited through spectroscopic analysis, but only after preparative separation of the complex petroleum materials.%' Preparative high-performance liquid chromatography (HPLC) has been used to separate the components of heavy residues and crude oil samples into various classes. In a separation technique called SARA (for saturate, aromatic, resin, and asphaltene), the asphaltenes are removed by extraction with hexane or heptane, and then the saturates, aromatics,and resins are separatd by HPLC.8 Other schemes separate components according to functionality (Le., acid, base, and neutral) followed by chemical group-type fractionation (saturate, aromatic, and polar) or chromatographic separation by aromatic ring number (saturate, mono-, di, tri-, and polyaromatic, and polar).6 Analyses are subject to many limitations with these preparative techniques, including low sample-masscapacity, irreversible retention, poor selectivity, tailing, and considerable sample preparation.6 Much attention has been given to the detailed study of molecular structure and substituent effects on the retention characteristics of aromatic hydrocarbonson various stationary phases such as alumina, chemically bonded silica-NH2, and silica-R(NHz)2.6 All of the stationary phases reported for this use had very low capacities. Consequently, it was necessary to use very large columns. Alumina stationary phases showed excellent selectivity for aromatic-ring-containing molecules but not for alkanes or cycloalkanes.9 Heteroatom-containingcompounds (polar components)often were irreversibly adsorbed on the alumina stationary phase. Also, alumina stationary phases needed extensive equilibration or reactivation times and suffered from poor reproducibility due to varying levels of alumina activity.9 Silica stationary phases in conjunction with alumina wereused for the separation of alkanes and cycloalkanes from aromatic hydrocarbons, but polar components still irreversibly adsorbed to the stationary phase.1° Silica-NHz and dualfunctional alkylaminealkanenitrile bonded stationary phases facilitated the elution of many of the polar components, retained roughly equivalent selectivity, and eliminated the extensive equilibration times.2J1 Silica-NHzstationary phases are commercially available and well characterized; however, they still lack the high capacity necessary for preparativescale separations. (3) Radke, M.; Willsch, H.; Welte, D. H. Anal. Chem. 1984,52,406. (4) Radke, M.; W a c h , H. Welte, D. H. Anal. Chem. 1984,56,2538. (5) Grizzle, P. L.; Sablotny, D. M. Anal. Chem. 1988,58,2389. (6) Grizzle, P. L.; Thomson, J. S. Anal. Chem. 1982,54, 1071. (7) Dark, W. H.; McFadden, W. H.; Bradford, D. L. J. Chromatogr. Sci. 1977, 15, 454. (8) Jewell, D. M.; Albaugh, E. W.; Davis, B. E.; Ruberto, R. C. Znd. Eng. Chem. Fundam. 1974,13,278. (9) Matsunga, A.; Yagi, M. Anal. Chem. 1978,50, 753. (10)Vogh, J. W.; Thomson, J. S.Anal. Chem. 1981,53, 1345. (11) Miller, R. Anal. Chem. 1984,54, 1742. (12) Armstrong, D. W. J. Liq. Chromutogr. 1988,11, 2433. 0 1993 American Chemlcal Society
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Centrifugal partition chromatography (CPC) is a form of countercurrent chromatography that has been used for preparative-scale separations of natural products.1slS CPC has a liquid stationary phase free of solid support. There are several characteristics that make CPC ideal for preparative applications, such as its large stationary-phase to mobilephaae volume ratio.19 This characteristic gives it the capacity to accommodate large samples. The liquid stationary phase eliminates irreversible retention and allows strongly retained samples to be recovered by flushing the system or using dualmode elution. Also, column efficiency for the CPC improves with increased flow rates.20v21 This trend is opposite that found in other forms of chromatography and is ideal for preparative-scale applications. The cost of operating the CPC is less than other forms of preparative chromatography because a new stationary phase for the CPC (fresh solvent) is relatively inexpensive when compared to silica gel-based column packings.19 Synchronous luminescence (SL) spectroscopy was first described by Lloyd22 and further developed by Vo-Dinh23.24 as a selective tool for quantitative multicomponent analysis of complex mixtures. By simultaneously scanning the excitation and emission monochromators, keeping a fixed wavelength increment, AX, SL can create a bandwidthnarrowing effect and reduce spectral overlap.23 Featureless emission spectra of complex mixtures can be resolved into a series of narrow peaks, each representing an individnal component. Synchronous luminescence has been used in a variety of applications including the determination of the origin of crude oils of spills25 and the identification of polynuclear aromatics in environmental air samples.26 Synchronous luminescence also has been used in conjunction with liquid chromatography.8 When used with mass spectrometry data, SL was useful in identifying the number of condensed rings and determining the skeletal structure of aromatic molecules in fractions from liquefied coal separated by reversed-phase HPLC.28 In this paper we describe the use of CPC to fractionate catalytic cracker feedstock using a nonlinear methanol/ aqueous gradient and a hexane stationary phase. Fractions were collected and analyzed by UV absorption, fluorescence, synchronous luminescence spectroscopy, and mass spectrosCOPY.
Nine cartridges, Model 250W, composed the column (a total column volume of 180 mL). Two LC pumps, Shimadzu Model LC-GA, and a Shimadzu system controller SC-6A were used to develop mobile-phase flow gradients. The pumps and controller were capable of pumping both linear and nonlinear gradients. Detection was by UV absorption using a variable-wavelength Shimadzu, Model SPD-6A detector. The recorder was a Linear, Model 1200. The UV absorption spectra of collected fractions were measured with a Hitachi, Model U-2OOO UV spectrophotometer. A Perkin-Elmer, Model LS-5 fluorescence spectrophotometer recorded the emission, excitation, and synchronous luminescence spectra. HPLC-grademethanol and hexanewere purchased from Fisher and filtered through a 0.45-pm nylon membrane (Alltech)prior to use. The water was distilled, passed through a Barnstead D8922 cartridgeto trap any residualorganics,and fiitered through a 0.45-pm nylon membrane to remove any particulate matter. The catalytic cracker feedstock was provided by Shell Development Co., Houston, TX. Procedure. The catalytic cracker feed samples were prepared byaddingapproximately0.5mLofhexaneto 1.2-1.6gofcatalytic cracker feed to reduce the viscosity of the sample and give a total sample volume of approximately 2 mL. The sample was shaken for 1 min and then directly injected without filtration (sample loop volume was 1.9 mL). The initial mobile phase was 75% methanol and 25% water and the final was 95% methanol and 5 % water. Both the initial and final mobile phases were saturated with stationary phase by stirring, and the stationary phase was saturated with the initial mobile phase in a similar manner. The column was prepared by fillingthe empty cartridges with stationary phase in the descending mode. Then, in the ascending mode, with the centrifuge spinning at 700 rpm, approximately 95 mL of stationary phase was displaced by the initial mobile phase at a flow rate of 4.0 mL/min. In this way all chambers in all cartridges contain both stationary-phase and mobile-phase s ~ l v e n t s . * The ~ J ~mode ~ ~ was then switched to descending, and the column was equilibrated for 45 min at a flow rate of 4.0 mL/min with the initial mobile phase. During this time period the system can be checked for baseline stability, leaks, etc. Also, a dead volume marker such as aqueous NaI can be injected to determine the amount of mobile phase and stationary phase in the system. Detection in the descending mode was at 254 nm. The concentration of the methanol, C ( t ) ,in the mobile-phase gradient is described by the equations C(t) = Ci
t5d
EXPERIMENTAL SECTION Equipment and Materials. The centrifugal partition chromatograph used was a Model CPC-NMF, Sanki Laboratories, Inc., Cherry Hill,PA. This instrumentwas described previously.m (13)Berthod,A.;Armstrong, D. W.J.Liq. Chromatogr. 1988,11,1187. (14)Alveraz, J. G.; Cazes, J.; Touchstone, J. C.; Grob, R. L. J. Liq. Chromatogr. 1990,13,3603. (15)Marston, A,; Slacanin, I.; Hostettmann, K. J. Liq. Chromatogr. 1990,13,3615. (16)Glinski, J. A,; Caviness, G. 0.; Mikell, J. R. J. Liq. Chromatogr. 1990,13,3625. (17)Okuda, T.;Yoshida, T.; Hatano, T.; More, K.; Fukuda, T. J. Liq. Chromatogr. 1990,13,3637. (18)Armstrong,D. W.;Menges,R.A.; Wainer,I. W.J.Liq.Chromatogr. 1990,13,3571. (19)Cazes, J. Am. Lab. 1992,(Feb), 66. (20)Berthod, A.; Armstrong, D. W. J. Liq. Chromatogr. 1988,11,567. (21)Armstrong,D. W.;Bertrand, G. L.; Berthod, A. Anal. Chem. 1988, 60,2513. (22)Lloyd, J. B. F. Nature (London) 1971,231,64. (23)Vo-Dinh, T. In Modern Fluorescence Spectroscopy; Wehey, E. L., Ed.; Plenum: New York, 1981;Vol. 4,pp 167-192. (24)Vo-Dinh, T.Anal. Chem. 1978,50,396. (25)John, P.;Soutar, F. Anal. Chem. 1976,48,520. (26)Abbott, D. W.; Moody,R. L.; Mann, R. M.; Vo-Dinh, T. Am. Znd. Hyg. Assoc. J . 1986, 47, 379. (27)Spino, L.A.;Armstrong,D. W.; Vo-Dinh,T. J. Chromatogr. 1987, 409, 147. (28)Katon, T.;Yokoyana, S.;Sanada, Y. Fuel 1980,59,845.
for convex gradients,
for concave gradients, and
for linear gradients, C(t)=C,
t>T+d
where Ci is the methanol concentration in the initial mobile phase, Ct is the methanol concentration in the final mobile phase, y is the curve of the nonlinear gradient, t is time, d is the gradient delay time, T is the total time length of the gradient, and 0 < t < T. The spin rate was increased as the experiment progressed to stabilize the pressure and the stationary phase. After a period of time, approximately 400 min, the mobile-phase flow in the descending mode was stopped. The mobile phase was then changed to hexane, and the retained components were eluted at a flow rate of 1.0mL/min in the ascendingmode with UV detection at 320 nm. Fractions were collected and analyzed in both the descending and ascending modes. In this technique, as in any chromatographic method, internal standards can be employed if desired or needed.
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Flgue 1. CPC descendingmode chromatogramshowingthe separation of catalylic cracker feed. The flow rate was 4.0 mL/min, the stationary phase was hexane, and the UV detection wavelength was 254 nm. Gradient elution was used (seeExperimental Section for details). The arrows indicate where thecollection of one fractionended and the next
one began.
Recovery of injected material was measured gravimetrically. Sixty 30-mLjam were heated in a vacuum oven at 55 O C overnight. The jars were removed, cooled in a desiccator for 1 h, and then weighed. The solvent was reduced to 1-2 mL from the CPCcollected fractions by heating on a steam bath with a gentle nitrogen stream passing over the open containers. The catalytic cracker fractions were quantitatively transferred to the tared jars with three washes of 10 mL each of heptane. Excess heptane was removed by evaporation on a steam bath. The jars were placed in a vacuum oven at 55 "C for 3.5 h and then removed and cooled in a desiccator. Of the original 1.1209g of catalyticcracker feed used in the CPC experiment, 1.1047 g was recovered gravimetrically. This gave a 98.6% recovery rate for this procedure. A portion of each collected fraction was diluted (1:l) with 2-propanol, and the UV absorption spectrum was recorded over the range of 190-400 nm. The excitation, emission, and synchronous luminescence spectra also were measured using the diluted fraction. The emission spectra were measured using 230 nm as the &=dhtiOnover the range of 250-700 nm with a scan speed of 60nm/min and excitationand emissionslit width settings of 15 and 3 nm, respectively. The emission wavelength for the excitation spectra was X, -, as determined by the emission spectra. X, mu was in the range of 340-375 nm. The excitation spectra scan speed was 30 nm/min, and the slit width settings were 3 and 5 nm for the excitation and emission slits,respectively. The synchronous luminescence spectra were recorded by scanning simultaneouslythe excitation and emission monochromators with a slit width setting of 3 nm for both the emission and excitation slits. The excitation monochromatorwas scanned from 230 to 700 nm at a rate of 30 nm/min. AX settings of 5,10, 20, 30, and 40 nm were used to synchronize the emission monochromator with AX of 20 nm generally giving the greatest spectral information. The emission scale was set automatically by the instrument for each luminescencemeasurement by setting the maximum emission to 90% full scale. For the synchronous luminescencespectra, the monochromatorswere adjusted to &x -I and X, -, and the emission was set at 90% of full scale. Mass spectral information of the CPC fractions was obtained on a Finnigan 4535 mass spectrometer after gas chromatograph (GC) separation from a Hewlett-Packard Model 5880 GC. The GC was equipped with a 30-m, 250-~m4.d.boiling point capillary column with a 0.25-m film thickness. Interpretation of spectra was based upon positive ion electron impact MS data.
RESULTS AND DISCUSSION Figures 1 and 2 show the CPC chromatograms for catalytic cracker feedstock. Figure 1 is the descending mode chromatogram and illustrates the separation of the catalytic cracker feed into 16 peaks with a shoulder clearly present on the first peak. The ninth and fifteenth peaks also show the presence of shoulders. Seventeen fractions, which correspond
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Flgure 2. CPC ascending mode chromatogram showing addkionai fractionationof catalytic cracker feed. The flow rate was 1.O mL/min, the stationary phase was hexane, and the detection wavelength was
320 nm. The arrows indicate where the collection of one fraction ended and the next one began.
to these major peaks and shoulders, as shown by the arrows in Figure 1, were collected and analyzed. Figure 2 depicts the ascending mode elution of the retained components. The ascending mode elution profile indicates that there is somewhat less selectivity in this mode than in the descending mode, but there is some fractionation present. This trend is to be expected because strongly retained Components in the descending mode partition mainly to the new mobile phase and interact very little with the new stationary phase. Five fractions were collected in the ascending mode, as depicted by the arrows in Figure 2. Solvent remaining in the CPC chambers after separationwas collected and analyzed as well. Mobile-phase gradient parameters were varied to optimize the separation in terms of peak shape and stationary-phase stability. For the separation in Figure 1, the curve of the gradient, y, was -3, the length of the gradient, T, was 300 min, and the delay time, d, was 30 min. These conditions optimized efficiency and column stability. y values of 3,0, and -4 were also used. The smallest curve value (y = -4) produced more efficient peaks in the middle portion of the chromatogram (75-150 min); however, greater increases in the methanol concentration in the mobile phase from the smaller gradient curve made the stationary phase unstable and caused it to be washed from the column by the mobile phase in approximately 150-175 min. Efficiency of the earlyeluting peaks decreased when y = 3. Also,this extended the elution times for middle-eluting peaks, resulting in a further decrease in efficiency. The delay time of the gradient, d, and the length of the gradient, T, were varied with y held equal to 0 (linear gradient). Efficiency appeared to increase for earlier startingtimes (d < 30 min) and shorter gradient lengths (T< 300 min); however, stationary-phase instability was observed. UV absorption, emission and excitation fluorescence, and SL spectra were measured for each of the collected fractions shown in Figures 1 and 2. The UV absorption and emission fluorescence spectra were generally diffuse and featureless. The spectra of fractions 3-17 showed strong absorption below 250 nm and weaker absorption at wavelengths greater than 330 nm. The emission spectra of all the fractions showed maxima between 360 and 375 nm, some with shoulders and smaller peaks between 250 and 480 nm, but with little structure present. Many of the excitation spectra of fraction 1-17 showed structure. Figure 3 illustrates the excitation spectra of fractions 1, 5, and 13. The spectral distribution and intensity of SL spectra are functions of the wavelength increment, AA, and an important aspect of this technique is determining the optimum wavelength increment. Figure 4 shows the SL spectra of fraction 1 using AX of 5,10,20, and 40 nm. From these observations it was noted that generally a AX value of 20 nm produced the most highly resolved structure for fractions 1-17 and a AX
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Figuro 9. Excltatlon spectra of (A) fraction 1, (8)fractlon 5, and (C) fractkn 13 from theseparationrepresentedby Figure 1. The A emission was 365 nm, the scan speed was 30 nm/mln, and the slit wldths were 3 and 5 nm for the excltatlon and emission monochrometers,
respectively.
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Figure 4. Illustration of theeffect of AX on synchronous luminescence spectra. The AX were (A) 5, (8)10, (C) 20, and (D) 40 nm. The scan speed was 20 nm/mln and the slit wldths were 3 nm.
value of 30 or 40 nm was optimum for fractions Al-A5. Figure 5 shows the SL spectra of fractions 1, 11, and 16. Figure 6 shows the SL spectra of fractions A2-A4. The spectral changes in successive CPC fractions are easily seen with SL but not with normal UV or fluorescence spectra. SL also provides some structural information. Generally, synchronousluminescence bands shift to higher wavelengths when more condensed aromatic rings are present. Katon et al. used PAH standards to assign regions of the synchronous luminescence spectra to the number of condensed aromatic rings in a molecule.% They found that emissions between 270 and 310 nm could be attributed to molecules with single aromatic rings (there may be more than one ring in the molecule), 31&340 nm for molecules with two condensed aromatic rings, and greater than 340 nm for molecules with three or more condensed aromatic rings. Of course, this will vary according to the number and type of substituents attached to the aromatic ring. From these data, it was concluded that all of the fractions analyzed have components containing two and three or more condensed aromatic rings. Fractions 1-3 contain components with one, two, and three or more condensed aromatic rings. Fractions 3-9 contain few components with single aromatic rings. Also, the reverse fractions, Al-A5, do not seem to have any components with single aromatic rings. Although there are distinct emission bands for each fraction analyzed, there is not sufficient information to identify individual compounds present in the
catalytic cracker feed. More detailed informationconcerning individual species can be obtained by using GUMS. Hundreds of components were found to be present in this particular catalytic cracker feed using GC/MS. Although identifying every compound would be exceedingly difficult (and beyond the scope of this work), it is apparent that CPC fractionates homologous series of compounds. Pertinent examples are cited in Table I. For instance fractions 1and 2 contain mostly polar materials, such as phenols, substituted phenols, similar pyrroles, and benzamines. These fractions make up only0.6 wt 5% of the catalytic cracker feed. Fractions 3-10 contain most of the nitrogenous polynuclear aromatics such as the carbazoles, phenanthridines, and acridines. It was found that the nitrogen species were separated by increasing alkyl and/or aryl substitution. Fraction 4 contains mostly methyl-substituted components, fraction 5 contains mostly ethyl-substituted components, fraction 6 contains mostly propyl and isopropyl substituted components, etc. Gravimetrically, fractions 3-10 contain 3.6 wt 5% of the catalytic cracker feed components. Sulfur-containingaromatic compounds (substituted thiophenes) are contained in CPC fractions 11and 12 along with three- or four-ring polynuclear aromatic hydrocarbons (PNAs). Fractions 11-17 contain the bulk of the PNA species, making up 11.2 wt 5% of the catalytic cracker feed. These include pyrene, chrysene, anthracene, biphenyl, and other fused polycyclic compounds includingisomeric analogues and their alkyl-substituted analogues. Like the previous fractions containing the heterocylic compounds, the CPC separation of fractions 11-16 showed an increasing degree of alkyl substitution. However, the alkyl substitution does not seem as straightforward. Some fractions contain ethyl- as well as propyl-substituted PNAs. For example,fraction 14 contains ethyl-substituted biphenyl and propyl-substituted fluorene. Fractions Al-A5 of the CPC separation (done in the ascending or inverse mode) contains the bulk of the catalytic cracker feed, (84.55% 1. These components were identified mostly as saturated alkanes and cyclic compounds, including alkyl-substituted cyclic components. Table I1gives examples of these compounds. At the end of the descending and ascending CPC separations, the remaining solvent trapped in the instrument was removed and found to contain 0.2 wt 5% of materials from the catalytic cracker feed. The species identified by GC/MS were those of relatively higher molecular weight saturates or highly alkyl substituted aromatics,giving an overall paraffinic character to these components. Most petroleum products are classified and separated into major constituent fractions by precipitation and/or by adsorption chromatography. Typically, six to nine major fractions from a catalytic cracker feed are obtained in this way. This, of course, depends on the nature of the feed, the chromatographic conditions, etc. UV spectrometry also is used to quantify the aromatic content.29 For the catalytic cracker feed used in this study, the total aromatics measured by UV spectrometry were found to be 16.6 wt %. Total aromatics found by gravimetry after CPC separation were found to be slightly higher, but not exactlyquantifiable, since there are some aromaticcompounds with high degrees of alkyl substitution found in the fractions from the ascendingmode.
CONCLUSIONS Centrifugal partition chromatography can be used for the preparative-scale separation of heavy distillates such as catalytic cracker feed. It has several advantages over preparative HPLC in similar applications, including sample capacity, which is at least 10 times greater. Also there is no (29) Zerlia, T.;Pinelli, G.Riv. Combwt. 1988, 42, 145.
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Figure 5. Synchronous luminescence spectra of fractlons 1 (A), 11 (B), and 16 (C) from the separation represented by Figure 1. The AX was 20 nm, the scan speed was 20 nm/min, and the slit widths were 3 nm.
Table 11. Typical Components Identified by GC/MS from the Fractions Collected i n the Ascending or Reverse CPC Mode fraction no. wt% representative compounds
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Figure 8. Synchronous luminescence spectra of fractions A2-A4 from the separation represented by Figure 2. The AX was 20 nm, the scan speed was 20 nm/mln, and the slit widths were 3 nm.
Table I. Typical Components Identified by GC/MS from the Fractions Collected in the Descending CPC Mode fraction representative compounds no. % 1 2 3
4 5 6 7 8 9 10 11 12 13 14 15 16 17
0.29 alkyl-substituted benzamines 0.27 alkyl-substituted benzamines 0.21 carbazole, 5H-indeno[1,2-b]pyridine, 2-fluoranthenamine 0.17 methylcarbazole, methyl 2,3-phenylcarbazole 0.37 ethylcarbazole, ethyl 2,3-phenylcarbazole 0.41 propylphenanthridine, propylcarbazole 0.42 butylphenanthridine, 1-methyl 9-phenyltetrahydroquinoliie 0.55 pent ylphenanthridine 0.71 hexylcarbazole,hexylphenanthridine 0.72 heptylcarbazole, heptylphenanthridine 0.80 anthracene, pyrene, fluoranthene, tryphenylene 0.88 methylanthracene, methyldibenzothiophene 1.17 ethylanthracene, ethyldibenzothiophene 1.43 propylanthracene, propylpyrene 1.67 2,3-dihydro-l-methyl-3-phenyl-lH-indene, tetramethvhhenanthrene 2.11 tetramethyldidhenyl, trimethylpropenylnaphthalene 3.12 pentyldibenzothiophene, 4-pentylbiphenyl
irreversible retention when CPC is used. The cost of the stationary phase (a solvent in CPC) is only a fraction of that for HPLC. A greater number of distinct fractions (peaks) were found for CPC than has been reported for preparative
1A 2A
0.29 63.24
3A
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unidentified paraffins octahexane and higher alkanes (normaland branched) 4-,6-, 6-, and 7-ring naphthenes, alkyl-substituted tetracyclic alkanes alkyl- and/or cycloalkyl-substituted tetralins alkyl- and/or cycloalkyl-substituted fluorenee alkyl- and/or cycloalkyl-substituted fluorenee
HPLC on analogous samples. This study also shows that nonlinear gradients may be used to optimize efficiency in CPC. Mass spectrometric analysis of each CPC fraction showed that this particular catalytic cracker feed material can be classified into four major groups: polars, nitrogenousspecies, polynuclear aromatics,and saturates. Although this is similar to current group classificationby liquid chromatography,the described CPC fraction afforded significant subgroup separation from these major groups as well as rendering enough quantity of material for further study. This was particularly useful for studying the nitrogenous heterocyclic compounds, the sulfur-containing heterocyclic compounds, and the polynuclear aromatic hydrocarbons. Furthermore this CPC system appears to be able to separate homologues of most of the major groups of compounds. Because no solid support is necessary for CPC, all materialsinjected into the instrument can be fully recovered. This was confirmed by mass balance measurements and calculations.
ACKNOWLEDGMENT Support of this work bv the Department of Eneray, Office of Basic Sciences (Grant DE FGo2 88ER13819) andxhe Shell Development Co., Houston, TX, are gratefully acknowledged. RECEIVED for review M~~ 12, 1993. Accepted jUly 19, 1993." Abstract published in Advance ACS Abstracts, September 1,1993.
