636
Energy & Fuels 1989,3, 636-640
Separation of Mild Gasification Liquid Products Using Open-Column Chromatography S. Lamey,* P. Hesbach, and E. Childers Physical and Chemical Sciences Branch, Morgantown Energy Technology Center, US. Department of Energy, Morgantown, West Virginia 26505-0880 Received January 17, 1989. Revised Manuscript Received July 14, 1989 In order to predict potential fuel performance or estimate upgrading requirements, it is desirable to develop a relatively rapid and simple technique for determining the chemical properties of a fossil fuel and subsequently to be able to relate this chemical data to the required fuel properties. Described in this paper are the initial development steps of an open-column separation scheme that will separate liquids generated under mild coal gasification conditions into appropriate fractions for analysis primarily by gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS). Analysis of the data from both the chemical fractionation analyses and the characterization can then be used in appropriate equations to relate the chemical composition data to a number of liquid fuel properties.
Introduction Events of the past 15 years have created doubts concerning the constant availability of sufficient petroleum supplies. This has led to an increased interest in exploring the feasibility of converting fossil fuels, such as coal and shale, into liquid fuel stocks to supplement or replace those previously provided by petroleum. One possible application for these fossil fuel feedstocks is their use as highenergy dense fuels (high Btu/volume) for use in jet aircraft. Very stringent requirements have been set with regard to aircraft performance, fuel handling, and storage.' The fuel properties desired can be related to measured chemical and physical properties of the fossil fuels, with most of the key fuel properties being affected by chemical rather than physical properties. These chemical properties, in turn, are to a great degree determined by the composition of the fuel with reference to the quantities of the various classes of hydrocarbons such as paraffins, naphthenes, aromatics, and heteroatom-containing compounds present.2 A significant number of tars and oils from various sources have been separated by using open columns, usually packed with either alumina or silica gel. Separations conducted on columns packed with alumina have been reported frequently (see, for example, ref 3-6). The technique is reproducible and does give an acceptable fractionation of a sample into aliphatic, aromatic, acid, and base fractions. It is, however, somewhat weak in the properties needed to distinguish between different aliphatic compound types and in giving a distinct separation between aliphatic and light aromatic compounds. Since these types of compounds appear to be of major importance in assessing the quality of a high-energy dense fuel or fuel precursor, this open-column chromatographic method is of limited value for this particular application. Many separations of similar types of samples reported in the literature have utilized silica gel in some form as the (1) Hazlett, R. N.; Hall,J. M.; Solash, J. PTepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1976,21(6), 219-230. (2) Cookson, D. J.; Lloyd, C. P.; Smith, B. E. Energy Fuels 1987, 1 ,
438-447. (3) Later, D. W.; Lee, M. L.; Bartle, K. D.; Kong, R. C.; Vassillaroe, D. L. Anal. Chem. 1981,53, 1612-1620. (4) Selucky, M. L.; Chu, Y.; Ruo, T.; Strausz, 0. P. Fuel 1976, 55, 376-387. - . - - - ..
(5) Whitehurst, D. D.; Butrill, S. E., Jr.; Derbyshire, F. J.; Farcasiu, M.; Odoerfer, G. A.; Rudnick, L. R. Fuel 1982, 61, 994-1006. (6) Lucke, R. B.; Later, D. W.; Wright, C. W.; Chess, E. K.; Weimer, W. C. Anal. Chem. 1985,57,633-639.
sole or primary packing material with a number of schemes for elution of the sample via many variations of solvent
mixture^.^-'^ In assessing the upgrading potential of a mild gasification product to a high-energy dense fuel, the compounds of greatest interest, which are, thus, targeted for the most scrutiny, are the various classes of aliphatics (e.g., straight chain, cyclic, etc.) and the one-, two-, and three-ring aromatic components. This separation procedure, therefore, was directed at separation of these entities, while most literature reports using open-column chromatography are merely aimed at separations between the aliphatic and aromatic fractions. Two of the most difficult separations to achieve during this study were the cyclic aliphatics from the straight-chain and branched aliphatics and the single-ring aromatics from the cyclic aliphatics. Karam, McNair, and L a n m published an article in 1986 that was directed in many ways toward the separation goals desired in the present work.' The authors described their method as a general technique for characterization of alternate fuels. This method uses hexane as the initial eluting solvent and then progresses through a series of hexane and benzene mixtures until the polynuclear aromatics are eluted with 32% benzene in hexane. Although this method is somewhat similar to the one finally adopted and described in this report with regard to the solvent elution scheme, a satisfactory separation of a standard mixture could not be achieved in our laboratory with the volumes and solvent ratios of eluants as described in this paper. To reiterate, the main compounds of interest are the aliphatics and the one-, two-, and three-ring aromatics. Using the method of Karam et al., it was possible to easily separate the alphatic components from the aromatics and also satisfactorily separate the three-ring and higher aromatics from the one- and two-ring aromatics. However, it was not possible to achieve a significant separation of (7) Karm, H. S.; McNair, H. M.; Lan~aa,F. M. LC-GC 1987,5,41-48.
(8) Wallace, D.; Henry, D.; Pongar, K.; Zimmerman, D. Fuel 1987,66, 44-50. ._
(9) Farcasiu, M. Fuel 1977, 56, 9-14. (10) Meuzelaar, H. L. C.; McClennen, W. H.Tandem Mass Spectrometric Analysis (MSIMS) of Jet Fuels, Part I: ExperimentalProcedures and Qualitatiue Data Analysis; AFWAL-TR-85-2047;AFWALI POSF; Wright Patterson Air Force Base: Dayton, OH, 1986. (11) Farnum, S. A.; Farnum, B. W.; Bitzan, E. F.; Willson, W. G.; Baker, G. G. Fuel 1983,62, 799-805. (12) Farnum, S. A.; Farnum, B. W. Anal. Chem. 1982,54, 979-985.
This article not subject to U.S.Copyright. Published 1989 by the American Chemical Society
Separation of Liquid Products diethylbenzene from tetralin or tetralin from naphthalene in the standard mixture by using this technique. Because of the importance of these compound classes to potential upgrading, separation of these components was deemed necessary.
Discussion Several groups have reported the use of dual-packed columns with silica gel and a l ~ m i n a . ' ~ JThe ~ logic behind this combination is the incorporation of the ability of silica gel to separate aliphatic components and the aromatic ring size separation properties of alumina. However, tests incorporating these dual packings did not provide a satisfactory separation, especially among aromatic components. The use of charcoal in various forms has been reported previously for separation of many types of organic comp ~ u n d s . ' ~ JTrials ~ conducted in this study with charcoal as the sole packing showed that it provided a separation as good as any other packing tested. But the use of charcoal requires huge amounts of solvent to elute the larger aromatic compounds, and consequently, the separation requires a long period of time to complete. Silica gel produced a separation as good as any other packing under the same conditions, along with the inherent advantages of being cheap, easy to procure, and simple to use. A second observation noted was that pentane, toluene, and mixtures of these solvents were superior to any other eluant systems tested. Actually, the use of heptane rather than pentane in conjunction with toluene gave a slightly better separation but required a much longer time to elute. Experimental Section Solvents a n d Chemicals. Solvents used in this work, pentane and toluene, were HPLC grade purchased from J. T. Baker. Standard mild gasification model compounds, n-octane, cyclooctane, diethylbenzene, decalin, tetralin, naphthalene, and phenanthrene were purchased from Aldrich Chemical Co. and Chem Service Co. and were used without further purification. Instrumentation. The GC/MS system was a Hewlett-Packard Model 5985B equipped with a library search program. The capillary GC column was of fused silica, 30 m X 0.32 mm i.d., 0.25-wm f i i thickness, RTX-5 from Restek Corp. (Port Matilda, PA). The GC oven was held at 20 OC for 3 min and then temperature programmed a t 4 OC/min t o a final temperature of 280 OC and held for 5 min. Spitless injection was utilized for all fractions. The gas chromatograph for the model mixture and elution fraction monitoring was a Perkin-Elmer Model Sigma 1and for the kerosene and mild gasification sample analyses was a Perkin-Elmer Sigma 2000 with an LCI-100 integrator and 7500 computer. Both gas chromatographs were equipped with a flame-ionization detector and a capillary column of fused silica, 30 m X 0.32 mm i.d., DB-5 from J&W (Folsom, CA). Temperature programming was the same as with the GC/MS instrument. Column. A glass 50 cm X 11 mm chromatographic column fitted with a Telfon stopcock was used. Small pieces of glass wool were used to retain the packing material. The column was packed with 100-200 mesh Davidson 923 silica gel (Supelco, Bellefonte, PA) and 100-200 mesh chromatographic grade charcoal SK-4 (Alltech, Milwaukee, WI). For optimum separation, the charcoal comprised approximately 25% of the total packing material and was added to the column first. The remainder of the packing was silica gel, which was placed on top of the charcoal. The packings were added to the column slowly with continuous tapping of the column to insure a homogeneous sorbent bed. Samples of the model mixture and of kerosene were placed on the column via a 9-in. Pasteur pipet, which insured that the sample was placed (13)Hirsch, D. E.;Hopkins, R. L.; Coleman, H. J.; Cotton, F. 0.; Thompson, C. J. Anal. Chem. 1972,44, 915-919. (14)Tenney, H. M.;Sturgis, F. E. Anal. Chem. 1954, 26, 946-953. (15)Hirschler, A. E.US.Patent 2,472,250,1949. (16)Hirschler, A. E.US.Patent 2,559,157,1951.
Energy & Fuels, Vol. 3, No. 5, 1989 637 directly on top of the column packing. In all cases, the column was equilibrated prior t o sample addition by passing 40 mL of pentane through the packing. Sample Preparation. The kerosene sample used was a typical clear kerosene of the type used in home kerosene heaters and purchased locally. No further preparation was deemed necessary. The mild gasification liquid was produced at the United Coal Co. Research Corp.'s (UCCRC) mild gasification unit. This sample was filtered to remove particulate matter, but otherwise it was used as received. Mild gasification refers t o any of a number of relatively lowtemperature coal devolatilization processes. The process conditions, commonly 500-750 "C with pressure often as low as 1-2 atm., are designed to maximize the production of quality liquids that are potential precursors for transportation fuels. A desirable byproduct is marketable char, which can be used, for example, as metallurgical coke or in gas turbine applications. Higher temperature and pressure conditions are generally found t o be associated with processes that maximize gas production and have heavy tars as byproducts. The standard mixture of seven components, which was used to simulate the major classes of compounds of interest typically contained in mild gasification liquids, was prepared by weighing equal amounts of each and combining them. No solvent was necessary.
Quantitation and Peak Identification Quantitation by gas chromatography was accomplished by summing the areas of all the peaks in each fraction. The GC/MS was used only for identification. Compounds were initially identified by using the mass spectrometry library. Further identification, when necessary, was resolved through the use of standard compounds and a GC relative retention index program residing on the Perkin-Elmer dedicated computer, Model 7500. In order to determine the weight percentage of the composite fractions, each fraction was initially brought to exactly the same volume by addition of the methylene chloride solvent. Identical aliquots of each were then injected into the gas chromatograph, and the areas of all peaks in a fraction were added together. This value was taken to represent the relative amount of material in each fraction. Both the kerosene and mild gasification samples were run in duplicate. The components in each fraction were qualitatively virtually the same for both runs. There was, however, some slight variation in the relative amount^ of individual components in some of the fractions, but the total amount of material in each fraction was the same.
Results Mild Gasification Standard Mixture. A 0.35-g sample of the mild gasification standard mixture was placed on a column packed with 16 g of silica gel plus 5 g of charcoal. n-Octane, cyclooctane, and cis- and trans-decalin were eluted with 75 mL of pentane; diethylbenzene was eluted with an additional 75 mL of pentane; tetralin was then eluted with 70 mL of a 9:l mixture of pentane and toluene; naphthalene was eluted with 80 mL of a 3:l mixture of pentane and toluene; and phenanthrene was eluted with 150 mL of toluene. The adopted fractionation scheme achieved a separation of the standard mixture into the five classes of aliphatics, benzenes, tetralins, naphthalenes, and phenanthrenes, with an average class purity of 93%. Greater than 90% recovery of the standard compounds was achieved during each separation in which the fractions were quantitated. The eluting fractions were analyzed by GC and GC/MS. Fraction 1 contained only the four aliphatic standard components of the mixture (n-octane, cyclooctane, and the cis and trans isomers of decalin). Fraction 2 contained 93.3% diethylbenzene and 6.7% tetralin. Fraction 3 consisted of 11.6% diethylbenzene, 87.6% tetralin (a naphthene), and 0.8% naphthalene. Fraction 4 contained 7.1% tetralin and 92.9% naphthalene. Fraction 5 con-
Lamey et al.
638 Energy & Fuels, Vol. 3, No. 5, 1989
Minutes
(a) Original Kerosene
10
20
30
(b) Composite Fraction 1
Table I. Silica Gel/Charcoal Separation of Kerosene ComDonents of Column Fraction 1. ComDosite Fraction 1 n-nonane n-pentadecane n-decane n-hexadecane Cl-decanes (&-decane C2-nonanes Cz-undecanes C1-decenes Cg-cycloundecane C1-decalins Cz-dodecanes n-tridecane n-undecane C1-undecanes C1-tridecanes C6-cyclohexanes . tetradecene dodecene C2-tridecane n-tetradecane cyclodedecane Cz-decalin Cz-tetradecane n-dodecane
tot. relative area % of fraction 1: 84.63 % n-alkanes in fraction 1: 25.00 % branched cyclics in fraction 1: 59.63
+
Minutes
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20
(c) Composite Fraction 2 One Ring Aromatics
Minulcs
10
20
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(d) Composite Fraction 3 Two Ring Aromattcr
Figure 1. Open-column separation of kerosene. Fractions were analyzed by gas chromatography. sisted of 0.7% tetralin, 6.7% naphthalene, and 92.6% phenanthrene. Although naphthalene would gradually elute with pure pentane, a large volume of solvent was required. No phenanthrene was removed from the column without an addition of toluene to any of the several aliphatic elution solvents tried (pentane, hexane, or heptane). When toluene was only a minor solvent component, phenanthrene elution was very gradual and required large solvent volumes. Elution solvent volumes for the five fractions were chosen because they reproducibly maximize resolution while minimizing the number of fractions. The aliphatic compounds were found exclusively in fraction 1. Isolation of the aliphatic components was readily accomplished by nearly every separation scheme attempted. Taking a large number of small volume fractions achieved somewhat greater purity in certain aromatic fractions, but some overlap of the aromatic components was still unavoidable. One of the drawbacks of taking many small fractions was the large number of analyses required to characterize the separation process. In addition, the effective elution yield would be reduced if the less pure fractions were removed prior to any subsequent treatment such as product upgrading. Kerosene. The separation scheme was also performed with a kerosene sample weighing 0.35 g. (The gas chromatogram of this sample is shown in Figure la.) Column composition and elution solvents were identical with those of the mild gasification standard mixture. The order of fractions taken and the volumes of those fractions were unchanged from the standard separation, with the exception of the toluene fraction. Fraction 5 was enlarged and divided into fractions 5-7, containing 20,30, and 150 mL of toluene, respectively. Fraction 8, consisting of 50 mL of methanol, was added at the end of the kerosene separation to elute any polar constituents. Analyses performed on the eight fractions by GC and GC/MS enabled identification of all significant components. Fraction 1was composed entirely of aliphatic hydrocarbons. Among the 35 identified constituents of this fraction were the normal alkane series from n-nonane through n-hexadecane, branched alkanes in this molecular weight range, several alkenes, and some cyclic aliphatics, including alkyldecalins. These species were of the same broad class of aliphatics as the components of the first
fraction from the standard mixture separation. The six alkylbenzenes identified in fraction 2 of the kerosene separation correspond to the predominating diethylbenzene of the second fraction from the standard mixture. Fraction 3 contained 36 identified aromatic species, including tetralin and alkyltetralins, alkylbenzenes, and alkylindans, in addition to a tricyclic diene. The 11 identified components of fraction 4 were naphthalene, highly alkylated benzenes, and alkyltetralins. The principal components of the standard mixture’s third and fourth fractions, tetralin and naphthalene, respectively, were first detected in their corresponding kerosene separation fractions, but were found again in later fractions. The band broadening of the aromatic compound classes at the trailing edges resulted in greater overlap with earlier eluting classes in this complex fuel sample. The five identified components of fraction 5 were naphthalene, alkylnaphthalenes, and biphenyl. The same species comprised fraction 6. The sum of fractions 5 (20 mL) and 6 (30 mL) corresponds to the first one-third of the solvent volume of the fifth fraction (150 mL) from the standard mixture separation, in which phenanthrene was the principal constituent. Aromatic species as large as three rings were not found in this kerosene nor were any highly polar compounds; the large fraction 7 and the methanolic fraction 8 contained only solvent. The separation of an identical kerosene sample by the same chromatographic materials was performed by using identical elution solvents and solvent volumes. The compounds eluting in each fraction were unchanged, and the relative amounts of compounds within each fraction were very similar. The species found in fractions 2-4, when taken as a whole, are predominantly alkylbenzenes. Moreover, the trimethylene and tetramethylene bridges of the indans and tetralins, respectively, may be thought of as special subclasses of ortho disubstitution patterns involving methyl, ethyl, and propyl groups. The structural similarities between tetralin and 1,2-diethylbenzene or between indan and 1-ethyl-2-methylbenzene result in similarities in size and shape and in electronic properties. Thus, clean chromatographic resolution of such compound pairs will be difficult, and some overlap of the alkylated derivatives of these species is expected. The components of fraction 1 were entirely aliphatic, and aliphatic species were detected in no other fraction. This fraction clearly represents one major separation class of the total kerosene, hereafter designated as composite Fraction 1 (Figure I b and Table I). The separation fractions 2-4 contained almost exclusively monoaromatic compounds and were physically combined to give composite fraction 2 (Figure ICand Table 11). The identical
Separation of Liquid Products
Energy & Fuels, Vol. 3, No. 5, 1989 639
Table 11. Silica Gel/Charcoal Separation of Kerosene Components of Column Fractions 2-4, Composite Fraction 2 Cz-benzenes Cpzlihydroindenes C3-benzenes C6-benzenes C,-benzenes Cl-tetralins C&-benzenes octahydrobiphenylene tetralin Cs-indan naphthalene Cz-tetralins relative area % of composite fraction 2 13.80
(a) Naphthalenes
Table 111. Silica Gel/Charcoal Separation of Kerosene Components of Column Fractions 5 and 6, Composite Fraction 3 naphthalene biphenyl C1-naphthalenes C2-naphthalene relative area % of composite fraction 3: 1.57 Table IV. Silica Gel/Charcoal Separation of Mild Gasification Liquid Components of Column Fraction 4 relative area, % naphthalene 14.35 2-methylnaphthalene 10.03 1-methylnaphthalene 11.88 biphenyl 3.73
I
Minuter
I
I
I
I
10
20
30
40
;0
(b) Fluorenes F i g u r e 3. Open-column separation of mild gasification liquid (a) fraction 4; (b) fraction 5. Fractions were analyzed by gas chromatography.
t
-1J.-,i.
L G
40
50
.,,A
I_ 60
F i g u r e 2. Gas chromatogram of a mild gasification liquid.
set of diaromatic species was found in fractions 5 and 6, and these fractions were combined into composite fraction 3 (Figure I d and Table 111). Mild Gasification Liquid. This sample was so viscous that it was impossible to place the liquid on top of the packing material with a pipet as was done with the kerosene and standard mixture. In order to facilitate placement of this sample on the column, the following procedure was adopted. A 0.30-g quantity of a mild gasification liquid (United Coal Co. Research Corp.) was added to 1.0 g of silica gel. A slurry was prepared by stirring into this mixture 2.0 mL of methylene chloride. The solvent was allowed to evaporate slowly prior to addition of the silica gelfgasification liquid mixture to the top of a separation column. The gas chromatogram of this sample before separation is shown in Figure 2. The column composition and elution solvents were identical with those used in the previous separations. The order of fractions taken was unchanged from the standard and kerosene separations. The fraction volumes were identical with those used previously, with the exception of an expanded toluene fraction. In order to achieve a greater separation between the higher molecular weight classes of this aromatic-rich sample, a fraction 5 consisting of 70 mL of toluene was followed by fractions 6-9, each collected as 50-mL volumes. A final fraction 10 consisting of 50 mL of methanol was taken to elute polar constituents. Analyses were performed on the 10 fractions by GC/MS to identify significant components. Further GC analysis enabled relative quantification within fractions. Only solvent was detected in fractions 1-3, which contained aliphatics, alkylbenzenes, and tetralins, respectively, in the previous separations. The diaromatic fraction 4 (Figure 3a and Table IV) was approximately three-fourths naph-
(a) Phenanthrenes
Minutes
I 10
1
20
I
30
I 40
(b) Phenols
F i g u r e 4. Open-column separation of mild gasification liquid: (a) fractions 6-9; (b) fraction 10. Fractions were analyzed by gas chromatography. Table V. Silica Gel/Charcoal Separation of Mild Gasification Liauid ComDonents of Column Fraction 5 relative area, % 2-methylnaphthalene 6.54 1-methylnaphthalene 2.15 biphenyl 1.86 dimethylnaphthalenes 6.63 acenaphthylene 12.35 acenaphthene 2.93 dibenzofuran 16.03 phenalene 1.18 fluorene 26.57 10.75 methyldibenzofurans methylfluorenes 3.38 4.16 dibenzothiophene phenanthrene 4.81
thalene, with the balance being methylnaphthalenes and biphenyl. Fraction 5, shown in Figure 3b (Table V), consists primarily of aromatic compounds larger than naph-
Lamey et al.
640 Energy & Fuels, Vol. 3, No. 5, 1989 Table VI. Silica Gel/Charcoal Separation of Mild Gasification Liquid Components of Column Fractions 6-9 relative area, 70 3.12 acenaphthylene 3.58 dibenzofuran 2.54 fluorene 4.27 methyldibenzofurans 1.11 methylfluorene 2.85 dibenzothiophene 41.70 phenanthrene 20.07 anthracene 20.76 methylphenanthrenes and methylanthracenes Table VII. Silica Gel Charcoal Separation of Mild Gasification Liquid Components of Column Fraction 10 relative area, % 57.98 phenol 1.93 indene 18.50 methylphenols 6.80 phenanthrene 1.09 methylphenanthrene 1.72 methylanthracene 3.87 cyclopenta[deflphenanthrene 4.81 fluoranthene 3.20 pyrene
thalene but smaller than phenanthrene. The principal components of this fluorene fraction are fluorene, acenaphthylene, and dibenzofuran. Since the components of fractions 6 9 were the same, these fractions were combined. Figure 4a is a chromatogram of the combined fractions. Over 80% of the material was composed of phenanthrene, anthracene, and their methylated derivatives (Table VI). Very little material was eluted in fraction 9. Therefore, no additional toluene fractions were taken, even though some larger aromatic species remained on the column, in order to avoid any gradual elution of polar compounds prior to the methanol fraction. Fraction 10 (Figure 4b and Table VII) contained over 75% phenol and methylphenols, with some elution of three- to four-ring aromatics evident.
Conclusions Separation of a mixture of model compounds on a column packed with 16 g of silica gel and 5 g of charcoal gave a separation better than either packing material alone while maintaining a reasonable elution time. Good separations of a kerosene and a mild gasification liquid were achieved by using this packing. The method appears to be able to separate components over a wide boiling point range. Samples, not reported herein, have been successfully fractionated with aliphatic
components up to n-C, present and with aromatic entities up to five rings. An HPLC separation of the mild gasification liquid showed very little material larger than four rings, so complete separation of the aromatic portion of this sample should be attainable. The three kerosene fractions were analyzed by GC to measure the total area counts (excluding solvents) in each of these broad fractions. The GC area counts of the prominent n-alkanes (n-nonane through n-hexadecane) were taken from the aliphatic fraction. Relative percentages of the resulting four compound classes of this kerosene were determined to be as follows: n-alkanes, 25.00%; branched plus cyclic aliphatics, 59.63%; monoaromatics, 13.80%; and diaromatics, 1.57%. A summation of the latter two values yields the total aromatics, 15.37% . These values are within the observed range for the petroleum-derived kerosene fuels plotted by Cookson, Lloyd, and Smith within their triangular composition diagrams relating chemical composition to fuel properties.2 This kerosene is well within the specification domain for a commercial Jet A fuel, based on the findings of these workers. While this result is not surprising, it provides evidence that the separation and analysis procedures described here can be successfully applied to such an evaluation of a potential fuel. Since the mild gasification liquid is primarily composed to two- to three-ring aromatics, it is a possible candidate for upgrading to a high-energy dense fuel, especially if a light fraction of this material is used. Relating the composition of this sample to kerosene on a compositional diagram such as Cookson’s is not appropriate, not only due to the highly aromatic character of the former material but also because of the much more refined state of the latter. One method for evaluating the fuel potential of coal-derived liquids is the “average molecule” approach developed by Dorn and co-workers for synthetic kerosenes and diesel fuels.17 This NMR technique makes use of the average structural features of all molecules in a given fraction and relates these parameters to fuel properties. The utility of the described separation scheme has enabled the fractionation of fuel materials of widely differing composition by a simple preparatory-scale process. Characterization of fuel precursor fractions by NMR techniques as part of a larger fuel property correlation study is under way and will be described in a future publication. (17) Hazlett, R. N.; Dorn, H. C.; Glass, T. E. Introduction, Advanced Topics and Applications to Fossil Energy. In Magnetic Resonance; NATO AS1 Series 124C; Kluwer: Dordrecht, The Netherlands, 1984; pp 709-720.
