375
Anal. Chen?. 1982, 54, 375-381
Table I. Results of Duplicate Separations of Various SRC Samples i SRC and in hydrotreated SRC --wt % m toluene pyridine solublesl solublesl n-hexane n-hexane toluene sample solubles insolubles insolubles a F-45 20.0 38.3 41.7 19.7 41.1 39.2 F-31 50.6 37.1 12.3 50.6 36.5 12.9 F-51 16.8 38.4 44.8 1K.5 39.6 43.9 F-36 28.6 4i.7 23.7 30.3 45.5 24.2 F-37 47.5 39.6 12.9 49.0 38.5 12.5 F-46 14.0 29.3 45.56 13.8 27.1 44.36 a Calculated by subtracting the sum of the wt % of n-hexane solubles and toluene solubles/iz-hexane insoluDetermined by weighing (high-ash SRC). bles from 100.
matter was retained on the Fluoropak column. According to our experience, an approximate time required for separation of a single SRC sample into three solvent-derived fractions is as follows: sample preparation, 0.5 h; coating
of Fluoropak, 1.0 h; elution of fractions, 1.0 h; solvent removal and weighing, 2.5 h; total, 5.0 h. However, several samples in various stages of analysis can be handled simultaneously. For example, six samples can be separated during one 8-hour working day by using six columns.
LITERATURE CITED (1) Pellpetz, M.; Kuhn. E M.; Friedman, S.; Storch, H. H. Ind. Eng. Chem. 1948, 40, 1259-1264. (2) Weller, S.; Pellpetz, M. G.; Friedman, S.; Storch, H. H. Ind. Eng. Chem. 1950, 42, 330-334. (3) Mima, M. J.; Schultz, H.; McKlnstry, W. E. in "Analytlcal Methods for Coal and Coal Products"; Karr, C.. Ed.; Academlc Press: New York, 1978; Vol. I , Chapter 19, pp 557-568. (4) Schwelghardt, F. K.; Thames, 8. M. Anal. Chem. 1978, 50, 1381. (5) Burke, F. P.; Winschel, R. A,; Wooton, D. L. Fue/ 1979, 58, 539. (6) Schwager, I.; Yen, T. F. Fuel 1978, 57. 100. (7) Steffgen, F. W.; Schroeder, K.T.; Bockrath, B. C. Anal. Chem. 1979, 57, 1164. (8) Schukz, H.; Mima, M. J. Prepr. Pap.-Am. Chem. Soc., Dlv. Fuel Chem. 1980, 25, 18, and references thereln. (9) Boduszynskl, M. M.; Hurtubise, R. J.; Sllver, H. F. Anal. Chem. W82, 54, 375. (10) Catalytlc, Inc., Wilsonville, AL, EPRI ProJectRP 1234-2, 1978. (11) Sllver, H. F.; Mlller, R. L.; Corry, R. T.; Hurtubise, R. J., presented at the 182nd Natlonal Meeting of the American Chemlcal Society, New York, Aug 1981. (12) Horvath, C. I n "The Practice of Gas Chromatography"; Ettre, L. S., Zlatkls, A,, Eds.; Wlley-Intersclence: New York, 1967; p 193.
RECEIVED for review June 8, 1981. Accepted November 16, 1981. Financial support was provided by the U. S. Department of Energy, Contract DE-AC22-79ET14874.
Separation of Solvent-Refined Coal into Compound-Class Fractions M. M. Boduszynskl" and R. J. Hurtulbise" Chemistry Department, The University of Wyoming, Laramle, Wyomhg 8207 1
H. F. Silver Chemlcal Engineering Department, The University of Wyoming, Laramle, Wyoming 8207 1
A separatlon method spleclflc for solvent-reflned coal (SRC) was developed. The niethod Is based on the use of SRCcoated Fluoropak-basic alumlna columns and can be applied In two ways. The flrst varlant Involves (a swltchlng column technlque and provldes; solublllty charaoterlstlcs and compound-class composltlon of SRC wlthout the need to evaporate solvents and redlseolve fractions. 'The second varlant permlts a rapld separation of SRC Into compound classes using a dual column system. Model compounds representing various compound classes were used to csvaluate the procedure. I n thls paper a low-ash Wyodak SRC was used to Illustrate the capablllty o f the method. However, the method was successfully used faw separatlon of varlous SRC sampler.
A detailed compound-class composition of coal-derived products is essential foir an indepth studly of the chemistry of coal liquefaction. In recent years, considerable progress has been made in developing methods o r separation and 0003-2700/82/0354-0375$01.25/0
characterization of coal liquids boiling below about 800 O F (427 "C) (1-8), Studies of the composition of solvent-refined coal (SRC), however, are much less advanced. SRC is defined as the pyridine-soluble coal-derived product boiling generally above about 800 O F (427 "C). SRC is particularly difficult to study because of its lack of solubility in solvents commonly used as mobile phases in liquid chromatography. A common approach used to separate SRC is time-consuming solvent extraction of the sample prior to further chromatographic separation. The major problem appears to be the difficulty in redissolving the solvent-derived fractions and the fractions usually contain some insoluble material. T o avoid this problem, chemists have developed separation procedures based on preadsorption of the total sample on top of a chromatographic column followed by a sequential elution of fractions with various solvents (9-11). The preadsorption of a sample on an adsorbent used for the separation can result in low recoveries due to irreversible adsorption of various components. In some cases, recoveries as low as 40% were 0 1982 American Chemical Society
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9
ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982
reported (9). Higher recoveries resulted ( 1 0 , I I ) when a sample was preadsorbed on less polar material (sand, glass beads) or when a partially deactivated adsorbent was used. However, the latter method, even though capable of yielding a good overview of the chemical composition of SRC, does not separate chemically unique fractions (12). A gradient elution chromatography method was also used to separate SRC into 12 fractions that were defined as “polar asphaltenes” (five fractions), “eluted asphaltenes”, ”polar resin”, “hard resin”, ”polynuclear aromatic soft resin”, “polynuclear aromatic oil”, “mono- and dinuclear aromatic oil”, and saturates (13). The fact that SRC comprises compounds of a broad molecular weight range from about 200 to about 1000 (14) has led to considerable interest in “size” separations. Gel permeation chromatography (GPC) has been used to achieve separation of SRC into fractions differentiated by molecular size (15-21). However, caution should be exercised when GPC is applied to separate a complex mixture such as SRC. In an ideal system, GPC separates according to the molecular size and shape (22,23). For SRC separation, however, the system is far from ideal due to the variety of highly polar, polycyclic aramatic structures containing heteroatoms (0,N, S). There are indications in the literature that the retention volume may be influenced by the type of hydrocarbon structure (e.g., peri-condensed aromatics give a calibration curve with a negative slope (24,25))and also by the adsorption of polar compounds on the polymer matrix. The effect of intermolecular association of polar compounds (even at very low concentrations) upon GPC results has been reported (26-29). The purpose of our work was to develop a separation method specific for solvent-refined coal (SRC) that would allow an integration of solvent extraction and liquid chromatography without the need to evaporate solvents and redissolve fractions for further separation. A method for rapid separation of SRC into solvent-derived fractions by utilizing a SRC-coated Fluoropak column was described previously (30). In this paper a method for further separation of SRC into major compound-class fractions of hydrocarbons, nitrogen heterocycles, hydroxyl aromatics, and polyfunctional compounds is presented. EXPERIMENTAL SECTION Material Studied. A low-ash Wyodak SRC sample (F-45)that was produced from a Wyoming subbituminous coal from the Canyon-Anderson seams in the Belle Ayr Mine of the Amax Coal Co. was used in this study. The SRC sample was supplied by Catalytic, Inc. from the Southern Company Services, Inc., SRC pilot plant located at Wilsonville, AL. The F-45 SRC sample represents low ash vacuum residue boiling above about 800 OF (427 OC). Apparatus and Chemicals. Precision bore glass columns 9 mm X 25 cm (Altex Scientific,Inc., Berkeley, CA) were used. Basic alumina AG 10 (BioRad Laboratories, Richmond, CA), activity I, pH 10.0-10.5,and 100-200 mesh, was used as received. Normal hexane 99+ mol % (Phillips Chemical Co., Bartlesville, OK), toluene (Mallinckrodt, Inc., Paris, KY), chloroform and methanol (VWR Scientific, Inc., San Francisco, CA), and pyridine (MCB Manufacturing Chemists., Inc., Cincinnati, OH), all reagent grade, were distilled prior to use. Tetrahydrofuran, unstabilized HPLC grade (Fisher ScientificCo. Fair Lawn, NJ), and methylene chloride HPLC grade (Burdick and Jackson Laboratories, Inc., Muskegon, MI) were used as received. Model Compounds. About 50 model compounds representing saturated, hydroaromatic, and polycyclic aromatic hydrocarbons, nonbasic and basic nitrogen heterocycles, hydroxyl aromatics, and other oxygen-containing compounds were used to evaluate the elution volume limits for major compound class fractions. Most of the model compounds were commercially available. Some compoundswere obtained from the U.S.Department of Energy’s Laramie Energy Technology Center. Approximately 10 mg of a model compound was used. Subfractions of 10 mL (void volume of the column) were collected
and the quantities of recovered samples were determined gravimetrically. The conditions of separation on basic alumina column were as follows: column, precision bore glass column 9 mm X 25 cm; stationary phase, basic alumina AG 10 (BioRad Laboratories) activity I, pH 10.0-10.5,100-200 mesh, about 13 g; mobile phases, n-hexane, 100 mL, t o (mobile phase strength) = 0.00,toluene, 100 mL, to = 0.29,chloroform, 100 mL, to = 0.40, back-flushed with chloroform-methanol 4:l v/v, 100 mL, to = 0.44, flow rate, 5 mL/& elution volume limits of compound-class fractions (fraction 1) (hydrocarbons) 0 - 130 mL, (fraction 2) (nitrogen heterocycles), 130-270 mL, (fraction 3) (hydroxyl aromatics), 270 - 400 mL. Separation Procedure. The system for separation of SRC into solvent-derived fractions was described previously (30). Further separation into compound-class fractions has been achieved by an integration of the SRC-coated Fluoropak column with a basic alumina columns and is described below. Variant I. Direct Separation of Solvent-Derived SRC Fractions into Compound Classes Using a Switching Column Technique. An accurately weighed sample of 0.3000 g of SRC was coated on the Fluoropak support material in the manner previously described (30). The SRC-coated Fluoropak column was connected to the liquid chromatographic system comprising three basic alumina columns (Figure 5). The system was kept under nitrogen gas, and the columns and fraction receivers were covered with black paper to minimize the risk of chemical alteration of the sample due to oxidation and exposure to light. A separation of SRC was achieved in four steps using a switching column technique. Step One. The elution was started with n-hexane which was pumped at a flow rate of 5 mL/min through the SRC-coated Fluoropak column. An n-hexane effluent of 100 mL was introduced directly into the first basic alumina column. Then, the Fluoropak column was switched to the second basic alumina column (see Step Two and Figure 5). The elution of the first basic alumina column was continued with 100 mL of toluene followed by 100 mL of chloroform. Finally, the material that still retained on the first basic alumina column was back-flushed with 100 mL of a mixture of chloroform and methanol 4:l (v/v). Subfractions of 10 mL were collected. Solvents were removed with a vacuum rotary evaporator and weights of recovered subfractions were plotted as a function of their elution volume. Step Two. The elution of the SRC-coated Fluoropak column was continued with toluene at a flow rate of 5 mL/min and 100 mL of toluene effluent was directly introduced into the second basic alumina column. Then, the Fluoropak column was switched to the third basic alumina column (see Step Three and Figure 5). The elution of the second basic alumina column was continued with 100 mL of chloroform. Then, the second basic alumina column was back-flushed with 100 mL of a mixture of chloroform and methanol 4:l (v/v). Subfractions of 10 mL were again collected. Solvents were removed and the subfractions weighed as described above. Step Three. The elution of the SRC-coated Fluoropak column was continued with chloroform at a flow rate of 5 mL/min and 100 mL of chloroform effluent was directly introduced into the third basic alumina column. The Fluoropak column effluent flow was stopped (see Step Four) and the third basic alumina column was back-flushed with 100 mL of a mixture of chloroform and methanol 4:l (v/v). Subfractions of 10 mL were again collected, solvents were removed, and the chromatogram was evaluated. Step Four. The elution of the remaining material on the Fluoropak column was achieved by pumping pyridine through the column at a flow rate of 5 mL/min. The effluent of 100 mL was collected without further separation. Pyridine was removed by use of a vacuum rotary evaporator. However, due to the problem of complete pyridine removal the weight percent of this SRC fraction (fraction 4) was determined by difference (30). Variant 11. Separation of SRC into Four Compound-Class Fractions Using the SRC-Coated Fluoropak-BasicAlumina Dual Column System. An accurately weighed sample of 0.3000 g of SRC was coated on the Fluoropak support material in the manner previously described (30). The SRC-coated Fluoropak column was connected in series with a basic alumina column. The system was kept under nitrogen gas and columns and fraction receivers were covered with black paper.
ANALYTICAL CHEMISTRY, VOL. 5
I ,
NO. 3, MARCH 1982
ov
PEAK I n-hexane
toluene
chloroform (4:l "/VI
(1.1 u/v)
cH3(cH21"cH3@ I
Ill
PEAK 3
PEAK 2
PEAK 5
0 & &
I I
377
PEAK 6
$& CH 3
II
I
I
PEAK 4
II
I
PEAK S
Ill
PEAK 9
IV
V
PEAK IO
CH-
ELUTION
VOLUME
(mll
Figure 1. Composlte elutlon curves of model compounds on basic alumina: (A) saturated and liydroaromatlc hydrocarbons, (6)polycyclic aromatic hydrocarbons, (C) basic nitrogen heteirocycles,(D) nonbasic nitrogen heterocycles, (E) oxygen-containing compounds, (F) hydroxyl aromatics. Note: Peak numbers and corresponding model compound
PEAK 12
PEAK 13
PEAK 17
I
PEAK IS
PEAK 16
PEAK 14
1
PEAK 19
I
I
O
0 PEAK 201
structures are given in Figure 2. Separation of SRC was achieved by pumping a sequence of n-hexane, toluene, and chloroform at a flow rate of 5 mL/min through the dual column eystem. Subfractions of 10 mL (100mL of each solvent effluent) were collected. Then, the basic alumina column was disconnected[ and material retained on the column was back-flushed with 100 mL of a mixture of chloroform and methanol 4 1 (v/v) and 10 mL subfractions were again collected. A portion of SRC that still remained on the Fluoropak column was eluted with 100 mL of pyridine. The pyridine effluent was collected directly from the Fluoropak column to produce fraction 4, polyfunctional compounds (pyridine soluble-chloroform insoluble). Solvents were removed from the subfractions with a vacuum rotary evaporator, and the recovered mateirial was weighed. Infrared Spectra. The infrared spectra of SRC fractions were recorded in methylene chloride using 0.5-mm NaCl cells. A Perkin-Elmer Model 621 ggating infrared spectrophotometer w13 used. The spectra of n-hexane soluble, andl toluene soluble-nhexane insoluble fractions were obtained at a concentration OS 50 mg/mL. The spectra of' compound-class fractions derived from n-hexane-soluble portion of SRC were obtained at a concentration of 25 mg/mL. Elemental Analysis. Elemental composition of the SRC sample was obtained by using conventionall methods. RESULTS AND DISCUSHION General Consideratiions. Earlier studies on the compo sition of SRC showed that a majority of' compounds comprising SRC contain heteroatoms (0,N, S) (14). Among heteroatom-containing compounds, hydroxyl and ether types and also nonbasic and basic nitrogen heterocycles were found to be most common (9, 10). A significant portion of SRC consists of polyfunctionid compounds. Hydrocarbons, predominantly polycyclic arlomatic and hydroaromatic types are present up to about 20 wt % of SRC (S1114). , Previously developed methods for separation of SRC used neutral alumina or silica gel as adsorbentsi (ell 13). , Compound class separation order on alumina and silica is generally similar. However, Schiller and Mathiason (9) stated that silica gel did not yield well-resolved fractions from SRC. Aromatic hydrocarbons which contain different numbers of aromatic carbon atoms are more easily separated on alumina than on silica (31). Also the preferential adsorption of weak acids (e.g., phenols) on alumina provides many separation possibilities for these compounds. In general, adsorbribility of nitrogen heterocycles on alumina is greater than thiat of their hydrocarbon analogues (32). An improved separation of certain heteroatom-containing compounds from hiydrocarbons may
Figure 2. Model compounds eluted from bask alumina column Key (see Figure 1): peak 1, (I) n-octadecane, (11) cholestane, (111) 1,2,3,4,5,6,7,8-0ctahydroanthracene, (IV) dodecahydrotriphenylene; peak 2, 1,2,3,6,7,8-hexahydropyrene; peak 3, (I) 9,lO-dihydrophenanthrene, (11) l-phenyl-3,4-dihydronaphthalene; peak 4, (I) 4b,5,6,10b,l1,12-hexahydrochrysene, (11) 9,10dihydroanthracene, (I1I) 5,124ihydrotetracen8, (IV) 5,6,7,8-tetrahydro-6-naphthyl-lnaphthylmethane, (V) 2,3dihydro-lHcyclopenta(l)phenanthrene;peak 5, 1,5-Dlmethylnaphthalene; peak 6: 1-phenylnaphthalene; peak 7: (I) 1,2diphenylbenzene,(11) fluorene, (111) phenanthrene, (IV) anthracene, (V) pyrene, (VI) chrysene, (VII) benzo[a]pyrene, ( V I I I )
coronene; peak 8, 2,6dl-p-tolylpyridine; peak 9, acridine; peak 10, 1,2-benzacrMine; peak 11, 3,4,5,6dibenzacrldine; peak 12, 5,6benzoquinoline; peak 13, 4-benzylpyridlne; peak 14, N-phenylcarbazole; peak 15, (I) 1,2,3,4-tetrahydrocarbazole, (11) tetraphenylpyrrole; peak 16, 1,2,7,8-dibenzocarbazole; peak 17, 2phenylidole; peak 18, carbazole; peak 19, dibenzofuran; peak 20, anthraquinone; peak 21, a-naphthoflavone; peak 22, (I) 1,2,3,4tetrahydro-I-naphthol, (11) 5,6,7,8-tebahydro-l-naphthol, (111) 1naphthol, (IV) o-phenylphenol, (V) p-phenylphenol, (VI) 9-phenanthrol, (VII) l-hydroxybenzo[c]phenanthrene,(VIII) o ,o'-biphenol (recovery about 30 wt %), (IX) 1,l'-bl-2-naphthol (recovery about 30 wt %). result when a nonneutral surface adsorbent is used (33). One important factor in the success of the separation is the acidity or basicity of the heteroatom-containing compounds. Hydroxyl aromatics are weakly acidic while nitrogen heterocycles are usually weakly acidic or basic. These properties can be utilized to improve the separation of hydrocarbons from heteroatom-containing compounds. With the above concepts in mind, we have developed a separation method which can isolate four major compound classes: hydrocarbons, nitrogen heterocycles, hydroxyl aromatics, and polyfunctional compounds. This goal was achieved by integrating the previously described SRC-coated Fluoropak column procedure (30) with a newly developed liquid chromatography procedure using basic alumina. Evaluation of the Compound-Class Separation Step Using Model Compounds. The detailed conditions of the separation are given in the Experimental Section. The model compounds were eluted from the same basic alumina column system as that used for a routine separation of SRC samples. The composite elution patterns of various compound classes are illustrated in Figure 1, and Figure 2 gives the corre-
378
ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982
Table I. Elemental Analysis of Low-Ash Wyodak SRC (F-45) component wt % component carbon hydrogen
nitrogen CI
84.8 6.1 1.4
wt %
sulfur
0.3
oxygena ash
0.5
6.9
By difference. ELUTiON
sponding peak numbers and structures. The results in Figure 1A show that saturates and also hydroaromatics containing only one aromatic ring (see Figure 1, peak 1) were eluted readily with n-hexane in the first void volume of the column (10 mL). Hydroaromatics containing more than one aromatic ring in a molecule (Figure lA, peaks 2,3, and 4) overlapped with polycyclic aromatics (Figure lB, peak 5,6, and 7). Some of these compounds (Figure lA, peak 4 and Figure lB, peak 7) were retained strongly on alumina and could not be eluted with n-hexane but were readily eluted with toluene. The results show that polycyclic aromatic hydrocarbons containing up to six condensed rings (coronene) were readily eluted with toluene. The presence of larger than six condensed aromatic ring systems in SRC is unlikely (14). It is also known that alkyl substitution of the aromatic ring has a minor effect on the retention on alumina. Thus, the results allow the assignment of the elution volume range for the first compound-class fraction, hydrocarbons, to be from 0 to 130 mL. The elution patterns (C) and (D) in Figure 1 show that nitrogen heterocycles can be well separated from hydrocarbons. However, overlap between hydrocarbons (Figure lA, peak 4 and Figure lB, peak 7) and nitrogen heterocycles may occur in some instances, for example, when steric hindrance prevents strong interaction of the nitrogen atom with the adsorbent (Figure lC, peak 8) or when ring substitution on the nitrogen prevents strong interaction with the adsorbent (Figure lD,peak 14). The elution volume range for the second compound-class fraction, nitrogen heterocycles, was determined to be from 130 to 270 mL. Among oxygen-containing compounds, ether and carbonyl types are a problem as these compounds were found in the entire elution volume range. Compounds such as dibenzofwan (Figure l E , peak 19) would overlap with the hydrocarbon fraction (Figure 1A,B,peaks 4,7). Anthraquinone (Figure lE, peak 20) would overlap with nitrogen heterocycles (Figure lC,D) while a-naphthoflavone (Figure lE, peak 21) would overlap with hydroxyl aromatics (Figure lF, peak 22). Thus, with the system developed, these compound types will overlap with the other compound-class fractions. The results in Figure 1F show that hydroxyl aromatics can be effectively separated from hydrocarbons and nitrogen heterocycles. The elution volume limits for the third compound-class fraction, hydroxyl aromatics, were determined to be from 270 to 400 mL. However, hydroxyl aromatics containing more than one hydroxyl group (e.g., polyphenols) such as o,o'-biphenol or l,l'-bi-2-naphthol retained very strongly on basic alumina and their recovery was only about 30 w t %. Also, polyfunctional compounds such as 8hydroxyquinoline are irreversibly adsorbed and cannot be eluted with the mobile phases used in this work. The elution volume data based on work with model compounds showed that a separation into three major compound classes, hydrocarbons, nitrogen heterocycles, and hydroxyl aromatics, can be achieved by using basic alumina. The results also imply that polyfunctional compounds should not be introduced onto the basic alumina column but rather should be collected directly from the Fluoropak column. Separation of SRC into Major Compound Classes. Experiments with an SRC sample were required to determine
VOLUME
(ml)
Figure 3. Elution of SRC from the Fluoropak column: (1) n-hexane soluble, (2) toluene soluble-n-hexane insoluble, (3) chloroform soluble-toluene insoluble, (4) pyridine soluble-chloroform insoluble.
c-c
C-H
ALIPHATIC
ca. 2900 cm-l
1600 cm-'
h
PYRROLIC -NH
3600
3200
2800
WAVENUMBER
. . 1700
1600 1500
(cm-')
Figure 4. Partial infrared spectra of the SRC solventderived fractions: (1) n-hexane soluble, (2) toluene soluble-n-hexane insoluble.
Tables. Weight Percent of Solvent-Derived Fractions in the Wyodak SRC F-45 solvent-derived fraction wt % n-hexane solubles toluene soluble-n-hexane insoluble chloroform soluble-toluene insoluble pyridine soluble-chloroform insoluble
19.9 40.8 10.6 28.7a
Determined by difference due to difficulty in complete pyridine removal. a
what portion of SRC could be separated on basic alumina without sacrificing recovery of the material. A low-ash Wyodak SRC F-45 sample was used for this purpose. Table I shows the elemental composition of the Wyodak SRC sample. A simple calculation using these data and an average molecular weight can illustrate hypothetical amounts of heteroatom-containing compounds in the SRC sample. For example, if the average molecular weight of the SRC is 500 (14), then calculations show that every average molecule of SRC contains about two oxygen atoms. In addition, every other average molecule contains a nitrogen atom and about one out of 20 average molecules contains a sulfur atom. The distribution of heteroatoms, however, is not known and could be different from that calculated for the average molecule. The data in Table I imply considerable amounts of oxygen- and nitrogen-containing compounds in the SRC sample. The SRC sample was separated into four solvent-derived fractions: (1)n-hexane solubles, (2) toluene solubles-n-hexane insolubles, (3) chloroform solubles-toluene insolubles, and (4) pyridine solubles-chloroform insolubles, using the previously described SRC-coated Fluoropak column procedure (30). This
ANALYTICAL CHEMISTRY, VOL. 54, NO. 3,MARCH 1982 379
p h flush
m
{
10 0
-F
tI
50
I
Figure 5. Experimental diagram of the separation of SRC Into corn-, pound-class fractions. Key: (A) SRC-coated Flluoropak column; (B)l basic alumina columns; (C) fraction receivers, ‘(1) n-hexane, (2) toluene, (3) chloroform, (4) chloroform-methanol 4:l (v/v) (back flush); (5) pyrldlne; (6) n -hexane soluble; (7) toluerie soluble-n -hexane insoluble; (8) chloroform soluble-toluene insoluble; (9) pyridine solu-
I
-
I
ble-chloroform Insoluble.
is illustrated in Figure 3. The weight percentages of solvent-derived SRC fractions are given in T,able 11. The first two solvent-derived fractions, representing “oils” and “asphaltenes”,were characterized using infrared spectrometry in order to identify major functional groups. The spectra of these two SRC fractions are shown in Figure 4. Spectra of the remaining two fractions, representing two portions of “preasphaltenes”, could not be obtained clue to insolubility of these materials in methylene chloride. The spectra in Figure 4 show similar patterns. The characteristic free phenolic -OH absorption bands are centered at about 3585 cm-l and characteristic pyrrolic -NH absorption bands are at about 3460 cm-l. In addition the spectrum of toluene soluble-nhexane insoluble fraction (asphaltenes) shlows a broad band at about 3200 cm-l resulting from intermlolecular hydrogen bonding. The major difference between the two spectra appears to be in the intensity of absorption bands at 1600 cm-’ and at about 2900 cm-l that are characteristic of aromatic ring vibrations and aliphatic C-H stretching, respectively. The asphaltenes appear to be much more aromtitic than oils. The presence of basic nitrogen heterocycles (e.g., pyridine, quinoline, acridine, etc.) could not be identified by infrared spectrometry because of the overlap with the absorption bands of aromatic C-C at 1600 cm-’. The infraired spectra of the two fractions provided evidence that considerable amounts of hydroxyl aromatics and nitrogen heterocycles presumably of carbazole types are present in SRC. Variant I of the separation procedure was used to separate solvent-derived SRC fractions into major compound classes. The experimental setup is illustrated in Figure 5. Three SRC fractions of n-hexane soluble (oils), toluene soluble-n-hexane insoluble (asphaltenes), and chloroform soluble-toluene insoluble (portion of preasphaltenes) were introduced from the SRC-coated Fluoropak column directly into respective basic alumina columns. The pyridine solublechlloroform insoluble portion of preasphaltenes was collected (directly from the Fluoropak column and was designated a&# fraction 4, polyfunctional compounds. The chromatograms of the three solvent-derived SRC fractions on basic alumina are shown in Figure 6. The first impression that emerges from the examination of these chromatograms is that all three solvent-derived SRC fractions contain nitrogen heterocycles and hydroxyl aromatics. In addition n-hexane solubles (Figure 6A) contain significant amounts of hydrocarbons. Infrared spectroscopy was used to determine which functional groups were represented in each compound-class fraction. The spectra of three compouind-class fractionsi derived from nhexane solubles are shown in Figure 7. The spectrum of
.
0
100
0
ELUTION
200
300
VOLUME
400
(ml)
Flgure 6. Chromatograms of SRC solventderived fractions on bask alumina: (A) n-hexane soluble; (B) toluene soluble-nhexane insoluble; (C) chloroform soluble-toluene insoluble. Key: (0)fraction 1, hydrocarbons; (@) fraction 2, nitrogen heterocycles; (0)fraction 3, hydroxyl aromatlcs. ca.
2900 cm-l
[ ALIPHATIC
WAVENUMBER
C- H
(om-’)
Flgure 7. Partial infrared spectra of the SRC compoundclass fractions derived from n-hexane solubles: (1) hydrocarbons, (2) nitrogen heterocycles, and (3) hydroxyl aromatics.
Fraction 1 (hydrocarbons) is virtually free of pyrrolic -NH and phenolic -OH absorption bands. The spectrum of fraction 2 (nitrogen heterocycles) shows a strong absorption band at 3460 cm-l that is characteristic of compounds having a pyrrolic -NH group. The spectrum of fraction 3 (hydroxyl aromatics) shows a very strong absorption band centered at 3585 cm-’ that is characteristic of compounds having a phenolic -OH group. The spectra in Figure 7 give strong support for the assignments of chemical classes present in the fractions. The infrared spectra of the two compound-class fractions derived from a toluene soluble-n-hexane insoluble fraction (asphaltenes) are not presented because of the similar pattern with the spectra of respective fractions derived from n-hexane solubles. The only difference was in intensity of absorption bands a t 1600 cm-l and at about 2900 cm-’ that are characteristic of aromatic ring vibrations and aliphatic C-H stretching, respectively. The fractions derived from asphaltenes were more aromatic than those from oils. The compound-class fractions derived from the chloroform solubletoluene insoluble portion of preasphaltenes (see Figure 6C) were not analyzed by infrared spectrometry due to the
380
ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982
Table 111. Weight Percent of Compound-Class Fractions in the Wyodak SRC F-45 compound-class fraction (wt % in SRC) fraction 2 fraction 4 solventfraction 1 nitrogen fraction 3 fraction polyfuncderived hydroheterohydroxyl total tional fractions separation approach carbons cycles aromatics (1 t 2 t 3) compds (wt % in SRC) variant 1" n-hexane soluble (oils) toluene soluble-n-hexane insoluble (asphaltenes) pyridine soluble-toluene insoluble (preasphaltenes) total
11.4 0.3
11.7
4.4 16.1
3.9 23.2
2.6
6.8
23.1
33.9
19.7 39.6 9.4c 68.7
19.7 39.6 31.3d
40.7
31.3
100.0
variant I I ~ SRC F-45 10.6 23.4 34.1 68.1 31.gd 100.0 Separation procedure using a switching column technique. Separation procedure using a dual column system. Chloroform soluble-toluene insoluble portion of preasphaltenes. Determined by difference to 100%.
(4 Iv/v) ,back flush
90 80.
-p g
70 60. 50-
P
$
40-
30-
ELUTION VOLUME
lml)
Figure 8. Chromatogram of the SRC chloroform solubies on bask alumina. Key: (0)fraction 1, hydrocarbons; (0)fractlon 2, nltrogen
heterocycles: (a)fraction 3, hydroxyl aromatics.
lack of solubility in methylene chloride. Variant I1 of the separation procedure rapidly separates the Wyodak SRC F-45 sample directly into four major compound-class fractions. The resulting chromatogram is illustrated in Figure 8. The three peaks in the chromatogram are represented by hydrocarbons, nitrogen heterocycles, and hydroxyl aromatics, respectively. The compound-class fraction 4 (polyfunctional compounds) was eluted directly from the Fluoropak column. The results of the separation of the Wyodak SRC sample using variant I and variant I1 are compared in Table 111. The data in Table 111show that variant I of the procedure provides weight percentages of the solvent derived fractions and their compound-class composition (columns 2 through 7). Variant I1 gives the overall compound-class composition of SRC. The total amounts of compound-class fractions obtained using both procedures remain in a very good agreement. Direct determination of recoveries of the material was not possible because of difficulty in a complete pyridine removal from fraction 4. Visual inspection of the basic alumina columns (variant I) showed that there was virtually complete recovery of the n-hexane soluble SRC fraction (first column). However, small amounts of material retained on the second and third basic alumina columns, indicating that some components of the toluene soluble-n-hexane insoluble SRC fraction (asphaltenes) and the chloroform soluble-toluene insoluble portion of preasphaltenes were irreversibly adsorbed. This implies that small amounts of polyfunctional compounds may be present in these solvent-derived fractions. It has been
shown previously (30) that a separation of SRC into solvent-derived fractions using only a SRC-coated Fluoropak column allows virtually complete recovery of a sample. Thus, approximate estimates of material losses due to irreversible adsorption on basic alumina were made by comparing the results of the SRC separation with and without a basic alumina column. The results in Table I1 which represent the recovered amounts of n-hexane solubles, toluene solubles-nhexane insolubles, and chloroform solubles-toluene insolubles can be compared with results of amounts recovered in Table 111, column 5, for the respective fractions. The sum of the first three fractions in Table I1 is 71.3 w t % of SRC while the results in Table 111, column 5, are 68.7 w t % (variant I) and 68.1 wt % (variant II), which corresponds to 96.3 and 95.5% recovery, respectively. The results also show that losses of the material are mainly due to irreversible adsorption of some components of toluene solubles-n-hexane insolubles (40.8 wt % in Table I1 and 39.6 wt % in Table 111 and chloroform solubles-toluene insolubles (10.6 wt % in Table I1 and 9.4 wt % in Table 111). According to our experience, an 8-h period is required to complete the separation of a single SRC sample using variant I. Variant I1 allows a complete duplicate separation in an 8-h period.
CONCLUSIONS The separation method described for solvent-refined coal can provide two levels of information, namely, compound-class composition and solubility characteristics of SRC. The method was devised to produce SRC fractions for further detailed studies. The compound-class fractions separated from SRC represent concentrates of major compound classes, e.g., hydrocarbons, nitrogen heterocycles, hydroxyl aromatics, and polyfunctional compounds. Other compound classes, for example, ether and carbonyl types, overlap with the major compound-class fractions and may require further separation steps for their isolation. Our separation system can be used in three different ways. A SRC-coated Fluoropak column alone can be used for a rapid separation of SRC into solvent-derived fractions (30). If compound-class fractions of SRC are preferred, variant I1 permits a rapid separation of SRC into four major compound-class fractions using the SRC-coated Fluoropak-basic alumina dual column arrangement. If solubility characteristics and compound-class composition is required a t the same time, the switching column technique (variant I) can be used. These features make the developed method particularly attractive for process monitoring. In the case of more detailed study, however, it is evident that the compound-class fractions, should be further
Anal. Cheni. 1982, 5 4 , 381-385
separated and analyzed. Work is in progress to obtain a detailed characterization of compound-class fractions and t o develop additional sep,aration methods.
ACKNO WLEDGMEMT We thank J. F. McKay of Laramie Energy Technology Center, U.S. Department of Energy, for providing several model compounds used in this study.
LITERATURE CITED (1) Aczel, T.; Williams, R. 8.; Chamberlain, N. F.; Lumpkln, H. E. Prepr., Dlv. Pet. Chem., Am. Chem. SOC. 1979, 24 (4), 955. (2) Scheppele, S. E.; Benson, P. A.; Greenwood, G. J.; Grindstaff, (2. Prepr., Dlv. Pet. Chem., Am. Chem. SOC. 1979, 24 (4), 963. (3) Cogswell, T. E.; Latham, D. R. Prepr. Dlv. Fuel Chem., Am. Chen?. SOC. 1978, 23 (2), 58. (4) Odoerfer. G. A.; Rudnlck. L. R.; Whltehurst, D. D. Prepr., Dlv. Fuel Chem., Am. Chem. SOC.1981, 26 (2). 89. (5) Burke, F. P.; Winscheil, R. A.; Pochapsky, T. C. Prepr., Div. Fuel Chem., Am. Chem. S I E . 1981, 26 (2), 68. (6) Schlller, J. E. Anal. Chlsm. 1977, 49, 2292. (7) Schabron, J. F.; Hurtubiise, R. J.; Slhrer, H. F. Anal. Chem. 1979, 51’,
1426. (8) Hurtublse. R. J.; Allen, T. W.; Hussain, A.; Silver, H. F. Prepr., Div. FuelChem., Am. Chern. SOC. 1981, 26(2), 55. (9) Schiller, J. E.; Mathlason, D. R. Anal. Chem. 1977, 49 (e), 1225. (IO) Farcaslu, M. Fuel 1977, 56, 9. (11) Mobil RBD Corp., EPRI AF-1296 Research Project 410 Final Report, “The Nature and Orlgln of Asphaltenes In Processed Coals”; Vol. 2, Dec 1979. (12) BETC US DOE, Quarterly Technlcal Progress Report QPR-80/3, Feb 1961. (13) Callen, R. B.; Simpson, C. A.; Bendoraltls, J. G. I n ”Analytlcal Chernlstry of Liquld Fuel Sources”; Uden, P. C., Silggla, S., Jensen, H. B., Eds.; American Chemical Society: Washington, DC, 1978; Chapter 21, pp 307-322; Adv. (;hem. Ser. No. 170. (14) Whltehurst, D. D.; Mitchell, T. 0.; Farcaslu, M. I n “Coal Llquefactlon”, Academic Press, New York, 1980.
381
(15) Coleman, H. M.; Wooten, D. L.; Dorn, H. C.; Taylor, J. T. J . Chromafogr. 1976, 123, 419. (16) Coleman, H. M.; Wooten, D. L.; Dorn, H. C.; Taylor, J. T. Anal. Chem. 1977, 49 (4), 533. (17) Wooten, D. L.; Coleman, H. M.; Taylor, J. T.; Dorn, H. C. Fuel 1978, 5 7 , 17. (18) Hausler, D. W.; Hellgeth, J. W.; McNair, H. M.; Taylor, L. T. J . Chromafogr. Scl. 1979. 17, 617. (19) Brown, R. S.; Hausler, D. W.; Taylor, J. T. Anal. Chem. 1980, 52(9), 1511. (20) Brown, R. S.; Hausler, D. W.; Taylor, J. T.; Carter, R. C. Anal. Chem. 1981, 53 (2), 197. (21) Curtis, C. W.; Hathaway, C. D.; Guin, J. A.; Tarrer, A. R. Fuel 1980, 59, 575. (22) Yau, W. W.; Malone, C. P.; Suchan, H., L. I n “Gel Permeation Chromatography”; Aitgelt, K. H., Segal, L., Eds.; Marcel Oekker: New York, 1971; pp 105-117. (23) Snyder, L. R.; Kirkland, J. J. “Introduction to Modern Liquid Chromatography”; 2nd ed.; Wlley: New York, 1979; p 491. (24) Oelert, H. H. ErdolKohle 1969, 22, 19. (25) Oelert, H. H.; Weber, J. H. ErdolKohle 1970, 2 3 , 484. (26) Cogswell, T. E.; McKay, J. F.; Latham, D. R. Anal. Chem. 1971, 4 3 , 645. (27) Brule, B. J . Llq. Chromatogr. 1979, 2, 165. (26) Such, C.; Brule, B. J . Llq. Chromafogr. 1979, 2 , 437. (29) Bcduszynski, M. M. I n “Chemistry of Asphaltenes”; Bunger, J. W., Li, N., Eds.; Amerlcan Chemical Society: Washington, DC, 1981; Chapter 7, pp 109-135; Adv. Chem. Ser., No. 195. (30) Bcduszynski, M. M.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1982, 54, 372. (3 1) Snyder, L. R. I n “Principles of Adsorption Chromatography”; Marcel Dekker: New York, 1968. (32) Klemrn, L. H.; Klopfensteln. C. E.; Kelly, H. P. J . Chromafogr. 1968, 23, 428. (33) Pop4 M.; Dolansky, V.: Mostecky, J. J . Chromafogr. 1972. 74. 51.
RECEIVED for review August 3, 1981. Accepted November 2, 1981. Financial support was provided by the U.S. Department of Energy, Contract No. DE-AC 22-79 ET14874.
Effect of Trace Metal Ions on the Analysis of Synthetic Fuel Samples Andrew D. Jorgensen Department of Chemlstt-y, Indiana State University-Evansville,
Evansville, Indiana 477 72
Joseph R. Stetter’ Argonne National Laboratory, 9700 South Cas$ Avenue, Argonne, Illinois 60439
Analysls of the organlc cmstltuents of synluel process Ilqulds Is extremely complex. Iinterpretatlon of thie results to obtaln an understandlng of the lprocess or to assess potentlal envlronmental and health effects Is even more eluslve. The heterogenelty of the sample materlals Is one source of concern. Process 011s In contact wlth an aqueous phase suffer potentlal alteratlon durlng sampllng or transportatlon. The lnteractlons between aqlueous Iron Ions (Fe2’, Fea+) and relevant synfuel organlo compounds are reported under modeled condltlons. These lnteractlons are Important for certaln organlc species and must be comsldered when reporting analytlcal results or attemptlng assessments uslng analytlcal data.
One of the most challenging problems facing the analytical chemist is the isolation and identification of hazardous compounds in environmentally relevant samples. Detectable levels of known and suspected carcinogens have been reported in coal tars, coal oils, and thte process and waste streams of coal 0003-2700/82/0354-038 1$0 1.25/0
gasification and liquefaction facilities, as well as of related energy processes for shale oils and tar sands (1-6). In analyzing trace levels of carcinogenic and mutagenic organic compounds in the real-world matrices where they are found, interference from other substances in the sample is often substantial. Research at Argonne National Laboratory (ANL) and other laboratories has been conducted to isolate and identify the wide variety of trace organics present in process and waste streams from emerging energy technologies. The resulting data provide part of the data base required for assessing the potential threat of these technologies to human health and the environment. A major consideration, therefore, is the relevance of analytical results to the actual concentration of the species in the environment or process stream. The problems affecting the relevance of the analytical data to field interpretations stem from the sampling, transportation, handling, and preparation of samples for analysis. All of these analytical stages must be considered in producing a fieldrelevant analytical study. However, little precise information on the effectiveness of methodologies at each of these stages 0 1982 American Chemlcal Society
