Ind. Eng. Chem. PIOcess Des. Dev. 1983, 22, 298-305
298
Jewel, D. M.;Weber, J. H.; Bunger. J. W.; Planchet‘, H.; Latham, D. R. Anal. Chem. 1972, 44, 1391. L a b . W. R.; Petrakls, L.; Qates, 8. C., to be publbhed. Munday, M. A.; Eaves, A. “Procedngs, Fifth World Petroleum Congress”, Sectlon V, Paper 9, New York, 1959. Petrakls. L.; Young, D. C.; Ruberto, R. G.; Gates, 8. C. Ind. Eng. Chem. procesS Des. &v. 198% fdlowing paper In this Issue. Ruberto, R. G.; Jewell, D. M.: Jensen, R. K.;Cronauer, D. C. Chapter 3 In Adv. Chem. Ser. 1978. No. 151.
Suatonl, J. “Chromatography In Petroleum Analysh”: Vol. 11. Ait~eit.K. H.; (kuw, T. H., Ed.; Marcel Dekker: New York, 1979; Chap* 6. Scheppele, S. E.; Aczel, T.; Beneon, P. A.; Greenwood, 0. J.; Orkrdetaff, Q.; Bleber. B. Repr. ACSDlv. Pet. Chem. 1979, 24(4), 963.
Received for review July 15, 1981 Revised manuscript received May 20, 1982 Accepted September 29,1982
Catalytic Hydroprocesdng of SRC-I I Heavy Distillate Fractions. 2. Detaiied Structural Characterizations of the Fractions LeonMas Petrakis;
Donald C. Young, and Raffaek 0. Ruberto
Gulf Science and Technobgy Company, Piftsbwgh, Pennsylvanla 15230
Bruce C. Gates’ Center for Cata&tlc Science and TechnObgy, Department of Chemhl Englneerlng, University of Delaware, Newah, Delaware 1071 1
One kilogram of SRCII heavy dlstl#ete has been separated into nine fractkns by pmparative liquid chromatography. The fractions (strong, weak, and very weak bases; strong, weak, and very weak acids; neutral resins; and asphaltenes) have been characterized in detail by elemental analysis, ’H NMR at 80 and 600 MHz, 13C NMR, IR, mass spectrometry, vapor phase osmometry, and other techniques. The results have been used as a basis for postulating representative molecular structures of each fraction. The fractions are to be used individually in high-pressure microreactor studies of catalytic hydroprocessing.
Introduction As part of a project to establish reaction networks and kinetics of hydroprocessing of coal-derived liquids, 1 kg of SRC-I1 heavy distillate has been separated into nine fractions by column chromatography, and the methods are described in an accompanying paper (Petrakis et al., 1983). These fractions are being used individually as feeds to a high-pressure microreactor. The elucidation of reaction networks and kinetics requires analytical profiles of each feed fraction and the catalytic reaction products. In this paper we present the results of characterization of the fractions by ‘H NMR a t 80 and 600 MHz, 13C NMR, infrared spectroscopy (IR),vapor-phase osmometry (VPO), mass spectrometry, and other techniques. Experimental Procedures The fractionation of the SRC-I1 heavy distillate provided the samples characterized by the following techniques. NMR spectra were obtained with samples dissolved in CDC13. The 600.02-MHz proton spectra were obtained with a high-field instrument a t Mellon Institute, Pittsburgh, PA. This instrument was operated in the correlation mode with homonuclear (TMS) lock and an ambient probe temperature of about 20 OC. Proton-NMR spectra a t 79.542 MHz were obtained with a Varian FT-80A Fourier transform spectrometer. The spectra of CDC13 solutions of the fractions were obtained at about 32 OC from the Fourier transformation of a free induction decay. The following standard conditions were applied: pulse width = 5 ps (90° pulse = 50 ps); acquisition time = 1.027 s; sweep width = lo00 Hz;number of data points = 2048. Neither zero filling nor exponential smoothing was employed.
13Cspectra at 20.00 MHz were obtained with a Varian FT-8OA spectrometer, with samples in 5- or 10-mm tubes under conditions of square-wave modulated broadband proton decoupling. The following standard conditions were applied: pulse width = 4 pus (90° = 21 ps for 10-mm and 11ps for 5-mm tubes); pulse delay = 1 s both for 5-mm and for 10” tubes; sweep width = 4000 Hz; number of data points = 8092. A variety of exponential smoothing factors were used; none broadened the lines by more than 1 Hz. No zero filling was employed. In addition to the proton and 13C NMR techniques, a variety of other standard techniques were applied to provide detailed profiles of the fractions. Included in the array of analyses were the following: (1)C, H, N, S, 0 elemental analyses; (2) Fourier transform infrared spectroscopy; (3) mass spectrometric group-type analyses of saturates (ASTM D2786) and aromatics (Swansiger et al., 1974); (4) gel permeation chromatography; ( 5 ) further separation of aromatics according to the number of aromatic rings in the molecule (Suatoni, 1980); (6) simulated distillation of saturate fractions (ASTM D2887); (7) grouptype NMR analyses [“average molecule’’ calculations (Clutter et al., 1972)];and (8) ESR determination of free radicals. Results and Discussion Neutral Oils. The neutral oils constituted 73.5% of the SRC-I1 heavy distillate sample. They were expected to contain only saturated and aromatic hydrocarbons with nearly nonpolar heteroatom-containing compounds such as ethers and thioethers. The elemental analysis (Petrakis et al., 1983) indicates that the neutral oils contained almost no nitrogen and only
0196-4305/83/1122-0298$01.50~0 0 1983 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 299
Table 11. Hydrogen Distribution from 80-MHz NMR Data hydrogen type" ~~
fraction saturates aromatics oils very weak bases weak bases strong bases neutral resins very weak acids weakacidsbiC strong acids Figure 1. Simulated distillation of saturates (ASTM D2887). Carbon numbers of n-alkane peaks are labeled. Table I. Average Molecular Formulas of the Fractions fraction formula neutral oils very weak bases weak bases strong bases neutral resins very weak acids weak acids
~18.~~17.4~0.11~0.~ c1~.9H17.2N0.2~01.1s0.~ C29.0H19.5N1.2402.29S0.31 c19,1H1~.~2N0.~00.~s0.~
c~5,~H1~.4N0.~30~.~s0.01 ~ 1 3 . 8 ~ 1 7 . 1 ~ 0 . 0 3 ~ 1 . 1 2 ~ 0 . ~ 1
C13.5H15.101.20S0.01
0.72% oxygen. The sulfur content of the oils (0.62%) exceeded that of the total heavy distillate (0.44%). The
IR spectrum of the oils is typical of a highly aromatic hydrocarbon mixture. The absence of bands due to N-H, 0-H, and C=O group indicates that polar heteroaromatic structures were absent and confirms the effectiveness of the separation procedure. To obtain a better characterization of the oils, a small sample was separated into saturates and aromatics by the techniques of Suatoni (1980). The aromatics were further separated into mono-, di-, tri-, and polyaromatics. The yield data are summarized elsewhere (Petrakie et al., 1983). Saturated Hydrocarbons. The saturates comprise about 6% of the neutral oils (or about 4 % of the original SRC-11 heavy distillate sample). Their mass spectrometric analysis indicates that they are made up of about 43 vol % alkanes, the remainder being 1-6-ring cycloalkanes, principally 2-, 3-, and 4-ring structures. The gas chromatogram (Figure 1) shows the presence of long-chain hydrocarbons ranging from CIS(or smaller) to Cw These hydrocarbon peaks appear as large, sharp spikes over a large envelope which is indicative of cycloalkanes. The smaller peaks between the large peaks in Figure 1 are indicative of isoparaffms. The chromatogram shows a maximum at about Cia. Assuming that this is the carbon number of the average molecule, we calculate a molecular weight of 254, which is in good agreement with the average molecular weight of the total oils as determined by VPO, namely, 243. VPO molecular weight data and the elemental analyses of all the fractions have been used to calculate the average molecular formula of each fraction (Table I). The molecular formulas are to be used only as a guide. Certainly the formulas reflect the correct average molar ratios of the elements in each fraction. The NMR spectra of the saturate fraction (not shown) yielded the following results. Treatment of the 80 MHz proton data according to methods described by Tominaga et al. (1977) gives the information listed in Tables I1 and 111. Table I1 is a summary of the hydrogen distribution
Ar
AI
0.39 0.43 0.28 0.42
0.22 0.31 0.18 0.29
N 0.10 0.49 0.28 0.07 0.45 0.26 0.07 0.52 0.23 0.04
B M OH het 0.64 0.26 0.10 0.06 0.16 0.07 0.10 0.06 0.04 0.02
0.09 0.14 0.06 0.12 0.14 0.21 0.08 0.08
0.10 0.06 0.01 0.07 0.01 0.16 0.01 0.02 0.04 0.06 0.03
0.58 0.22 0.03 0.08 0.04 0.03 0.45 0.32 0.11 0.03 0.08
Ar = aromatic, A1 = alpha to aromatic, N = naphthenic, B = p to aromatic, M = terminal methyl at least y to aromatic, OH = hydroxyl, het = protons on carbon LY to heteroatom. Fractions from analytical separaOH included in aromatics due to strong overlap. tion. Table 111. Carbon Distribution from Proton Data carbon typea fraction saturates aromatics total oils very weak bases weak bases strong bases neutral resins very weak acids weak acids strong acids bpc
CA
cs
cn
CI
0.77 0.75 0.81 0.74 0.74 0.67 0.71 0.79 0.80
1.00 0.23 0.25 0.19 0.26 0.26 0.33 0.29 0.21 0.20
0.60 0.61 0.61 0.51 0.56 0.38 0.70 0.77 0.54
0.17 0.20 0.20 0.23 0.18 0.29 0.01 2.0 0.26
a CA = aromatic carbon, C, = saturate carbon, C, = peripheral carbon, CI = internal carbon. Calculated,by method of Tominaga et al. (1977). From analytical CA is overestimated because of contribution from run. OH to aromatic area.
data for all the fractions, Le., the fractional area contained in the various parts of the proton spectrum. Table 111gives the carbon-type distributions calculated from the proton data. All the NMR spectra show a predominance of normal and branched paraffins. The 80-MHz proton spectrum shows a distorted triplet with some extra structure at 0.88 ppm and a major singlet at 1.27 ppm, with a significant shoulder centered about 1.6 ppm. The expanded 600-MHz spectrum is somewhat better resolved and shows a distinct triplet at 0.88 ppm, with an upfield shoulder. The major resonance is at 1.262 ppm, and it gives a downfield shoulder at 1.30 ppm, which is not resolved at 80 MHz. There are, however, apparently real resonances between 1.2 and 0.9 ppm, and these provide a direct indication of methyl-substituted cycloparaffins. The '3c data provide further evidence of cycloparaffins while giving the appearance of a branched-alkane spectrum. First, the area under the main-chain CH2 peak a t 30.01 ppm is about five times the average area of the peaks at 14.16,22.90, 29.64, and 32.21 ppm. This result indicates an average straight-chain length of about 18 carbons. Further, the areas under the peaks near 39.6 and 37.5 ppm indicate one branch per 15.6 carbon atoms. The relative areas under the 39.6-ppm peak (methyl branch carbon) and 37.5-ppm peak (indicating branches with groups other than methyl) indicate that about 25% of the branches are methyl. However, the branch methyl carbon area near 20 ppm is that which would be expected if 83% of the
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a
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d
1
8
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Figure 2. NMR of total neutral aromatic fraction: (a) 80-MHz 'H spectrum; (b) 6OO-MHz 'H spectrum; (c) 20-MHz I3C spectrum.
branches were methyl. We may resolve the apparent discrepancy by taking account of the distinct peaks near 24-26 ppm and the ill-defined but significant intensity above 40 ppm and suggesting that many of the methyl groups could be associated with a variety of substituted cycloparaffins. Assuming that all the ill-defined regions of the spectrum are indicative of cycloparaffins, we calculate a maximum of 30% cycloparaffin carbon from the 13Cspectrum. In summary, we estimate that the saturates are made up of about 43% alkanes (ranging from CI4to C%), 54% cycloalkanes, and about 3% monoaromatics (by mass spectrometry). The cycloalkanes contain from one to six condensed rings, but only 30% of the total carbon is incorporated in the rings. Aromatic Hydrocarbons. The aromatic fraction comprises the largest portion of the sample, about 94% of the oils or 69% of the SRC-I1heavy distillate. The mass spectral analysis shows that this fraction is made up mostly of 3- and 4-ring aromatic and hydroaromatic molecules, with smaller amounts of &ring compounds. The molecular
10.0
5.0
0
CHEMICAL SHIFT-PPM VS T Y S
Figure 3. The 80-MHz protpn NMR of aromatic subfractions: (a) monoaromatics; (b) diaromatics; (c) triaromatics; (d) polynuclear aromatics.
weights range from about 200 to 300. VPO molecularweight data were not obtained for the separated aromatic oil fraction, but the molecular weight of 243 for the total neutral oils is consistent with the finding of mass spectrometry. The aromatics were further fractionated into mono-, di-, tri-, and polyaromatics by high-pressure liquid chromatography (HPLC) (Petrakis et al., 1983). The total aromatics were analyzed by 13Cand 80- and 6W-MHz 'H NMR (Figure 2); the fractions were analyzed only by 80 MHz 'H NMR (Figure 3). The method of Clutter et al. (1972) was used to generate the average molecular parameters of the aromatic fractions in Table IV. This method is applicable to fractions containing three or fewer condensed aromatic rings, and it gives further structural in-
Ind. Eng. Chem. Process Des, Dev., Vol. 22, No. 2, 1983 301
Table IV. Average Molecular Parameters for Aromatic Fractions from 80-MHz 'H NMR fraction total mono di tri average molecular weight average formula aromaticity % monoaromatics % diaromatics % triaromatics % nonbridge aromatic carbons % substitution of
nonbridge aromatic carbon % saturate carbon alkyl substituents/molecule no. of carbons/ substituent H/C atom ratio of substituents % naphthenic carbon naphthene rings/ molecule
161.4
228.3
177.9
192.5
C12.4H12.5 0.76 28.7 57.2 14.1 62.2
Cl,HZ,. 2 0.38 90.5 9.5 0.0 36.5
Cl3.7Hl3.2 0.77 6.6 73.4 20.0 60.3
C,,HlZ.l 0.88 1.6 14.8 83.6 64.2
20.8
54.7
21.9
13.0
24 1.6
62.4 3.4
23.1 1.8
11.5 1.2
1.9
3.2
1.8
1.4
2.12
2.00
2.12
2.12
2.0
29.4
7.4
1.7
0.1
1.4
0.3
0.1
formation about the fractions of uniform ring size. For example, a molecule containing two noncondensed aromatic rings would appear as monoaromatic by NMR but diaromatic by HPLC. The total aromatic fraction has an NMR-calculated molecular weight of 161. This value is low compared with the results of other methods, because some monoaromatics (by NMR) are actually associated with diaromatics or larger molecules. The monoaromatic analysis is believed to provide a close approximation to the real composition (Table IV). The spectrum (Figure 3a) shows only a small contamination due to diaromatic molecules. An average molecular structure consistent with the parameters in Table IV is given below. "
-
"
~
"
c
-
"
y c
L
The diaromatic fraction contains a small amount of triaromatics, as shown by the resonances between 8.5 and 8.0 ppm (Figure 3b). The molecular weight seems to be low for this fraction, but the existence of triaromatic molecules prevents a clear basis for reassessment. It is apparent that the frequency of substitution is much less for this fraction than for the monoaromatics (Figure 3b). The substitution is limited almost entirely to methyl groups and hydroaromatic ring structures. The triaromatic fraction (Table IV and Figure 3c) contains a considerable amount of diaromatics, as indicated by NMR analysis. However, it is apparent from the spectrum that no substituent longer than methyl appears and that there are few hydroaromatic rings. By comparing the relative intensity a t 2.9-2.7 ppm and that at 1.7-1.5 ppm, we infer that those hydroaromatic rings present are either highly substituted in the /3 position or reside between aromatic rings. Most hydrogen a to the aromatic rings is in CH2groups (70%),with the rest being distributed about equally between CH3 and CH groups. As was the case for the diaromatic fraction, the molecular weight found by NMR is low compared with that determined by VPO of the whole neutral oils fraction.
Average molecule analysis of the polynuclear aromatic fraction is not included because the method is not applicable to molecules with more than three condensed aromatic rings. The appearance of the spectrum indicates relatively long substituents on the hydroaromatic structure of these molecules. The broad spectral lines of this fraction are an indication that the molecules are larger than those of other aromatic fractions. Free radicals present could also contribute to line broadening. The 6OO-MHz spectrum of the total aromatic fraction (Figure 2b) shows much higher spectral resolution than the 80-MHz spectrum. For example, doublets ( J 8.0 Hz) centered about 7.8 and 7.3 ppm associated with diaromatic molecules having nonequivalent protons now satisfy the A6/J condition for a first-order spectrum. The aliphatic region shows several interesting features. First, it clearly separates two types of methyl groups: one, a triplet at 0.848 ppm, is probably a short-chain terminator with at least two groups between it and the aromatic part of the molecule; the other is a doublet a t 0.936 ppm and probably indicates methyl substitution on the @-carbonof a hydroaromatic ring. A further doublet a t 1.192 ppm probably is due to methyl substitution at the a-carbon of a hydroaromatic ring. This latter resonance partially obscures a fairly well defiied quartet of doublets, which may be due to the corresponding CH2 groups. The region from 2.0 to 1.4 ppm contains either broad, ill-defined resonances or highly split patterns of relatively low intensity. The upfield range of these is probably due to a variety of overlapping /3-CH2groups in hydroaromatic rings (the broad resonances) and methines bonded to /3 positions of hydroaromatic rings (the highly structured patterns). Further downfield, highly structured peaks are probably due to 8-CH in hydroaromatic rings. The region from 2.0 to nearly 2.5 ppm includes a series of single sharp peaks with only little indication of any coupling structure. This part of the spectrum indicates mainly methyl groups substituted on mono- and diaromatic rings. Between about 2.5 and 3.0 ppm, the spectrum becomes a combination of highly split and broad peaks. Broad resonances near 2.7 and 3.0 ppm are due to a-CH2and CH groups in hydroaromatic rings, and the highly structured peaks are probably due to CH2 groups, a to mono- and diaromatic rings. Beyond 3 ppm, the spectrum degenerates into a series of single peaks superposed on some relatively ill-defined structures. The single peaks must be equivalent protons in bridges between condensed aromatic rings or methyl groups on condensed aromatic rings, with three or more rings in the structure. The broader, ill-defined resonances are in positions attributable to methine protons on carbons a to aromatic rings. The 6OO-MHz spectrum indicates several types of single resolved peaks below 3.3 ppm, which are assigned to methyl groups on condensed rings. Ordinarily, methyl substitution would appear farther upfield; thus, the resolution of the 600-MHz spectrum allows assignment of these peaks, which would not be possible from the 80-MHz spectrum of the total fraction. A check of the 80-MHz spectra of the various aromatic fractions indicates that most of the intensity in the 3.3 ppm region and below is in the triaromatic fraction. The 13C spectrum is shown in Figure 2c. Overall structure parameters could be derived from this spectrum as well as from the proton spectra. Several structural features are present which c o n f i i or augment those found by proton NMR. We believe that the proton spectra are
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302 Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983
the more reliable. The aromaticity calculated from the carbon spectrum is 0.71, compared with 0.76 calculated from the proton spectrum. Peaks between 0 and 22 ppm make up about one-third of the aliphatic carbon area and are assignable to methyl Substituentson aromatic rings. Those near 14 ppm might usually be aeeigned to terminal methyls on longer chains, especially since they occur in conjunction with absorption at 22.7 ppm. However, we prefer to assign these peaks to positions two carbons away from oxygen in benzofuran-like structures, since there is little intensity near 36-39 ppm, where the peaks representing a-carbons of longer chains should appear. The region 31-22 ppm represents carbons in tetralin-like structures. These are important because they have potentially transferable hydrogen (Seshadri et d., 1978) to aid in coal liquefaction. A calculation shows C, = 9.3% and I-& = 0.49%, based on the total heavy distillate. These values are in the low range for donor solvents. The aromatic region is typical of a mixture of aromatic hydrocarbons. No phenolic groups are noted, but peaks near 111 and 157 ppm are associated with benzofuran-like structures. Molecules having this functionality represent 1-270 of all the aromatic carbons. Other structural parameters, such as the average number of condensed rings per molecule and the percentage of alkyl-substituted aromatic carbons, are highly sensitive to experimental conditions; we have therefore inferred this kind of information from the proton spectrum rather than the carbon spectrum. The Bases. The three base fractions combined account for about 10% of the total sample. Because they contain significant amounts of nitrogen, these fractions are major targets for catalytic upgrading. They are much more difficult to characterize in detail than the neutral oils, but some useful information is, nonetheless, obtainable. Very Weak Bases. The very weak bases are expected to contain structures which are inherently weakly basic or which exhibit acid-base behavior modified by hydrogen bonding. The spectroscopic data are consistent with this expectation, as shown in Figure 4. The IR spectrum (not shown) shows -OH and -NH functionalities. The proton NMR spectrum is about the same at the two fields. The -OH, -NH peak is better separated from the aromatic proton region at 80 MHz, only because of concentration differences. The ratio of oxygen to nitrogen moieties is expected to be about 6 from the elemental analyses (7.12% 0 , 1 . 2 7 % N). Nearly all the oxygen is present in structures like phenol or benzofuran. The 13C spectrum (Figure 4c) demonstrated this result clearly by the presence of peaks in the 150-157 ppm and 110-115 ppm regions. Oxygen associated with saturated carbons is absent, as shown by the lack of intensity in the 60-72 ppm region of the spectrum. The nitrogen-containing groups are less apparent in the 13Cspectrum. Very small amounts of aromatic amines or indoles are indicated by intensity near 104 ppm. The bulk of the nitrogen appears to be associated with saturated parta of these molecules. This result is indicated by the tailing of the 13C spectrum downfield of 50 ppm in the saturate region, and it is also indicated by the resonances downfield of 3.3 ppm in the proton spectrum. Assuming that most of the oxygen is present in -OH groups and moat of the nitrogen is present in -NH2 groups, we calculate that the area downfield of 3.3 ppm (the assumed average of CH2) accounts for more than enough nitrogen (namely, O/N = 4/1, rather than the 6/1 found from elemental
a
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200
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Figure 4. Spectral data for very weak bases: (a) 80-MHz 'H NMR spectrum; (b) 6W-MHz IH NMR spectrum; (c) 20-MHz 13C NMR spectrum.
analysis). We infer that a significant amount of oxygen is present in furan structures, or alternatively, that the nitrogen is highly methyl substituted. Nonetheless, it seems safe to assign most of the nitrogen to aliphatic structures. Both the proton and 13Cspectra indicate the major carbon substituent to be a methyl group; many of these are ortho to OH substituents (- 15 ppm). From the intensity at 2.7 ppm and 1.7 ppm in the proton spectra, a sizeable amount of hydroaromatic ring structure is inferred. We infer that the @-carbonin these rings is highly substituted because the intensity near 1.7 ppm is less than that at 2.7 ppm. The Weak Bases. From the acid-base behavior of the weak-base fraction, hydroxypyridines or indoles would be expected. The weak bases contain twice as much nitrogen (3.65%) as the very weak bases and about the same amount of oxygen (8.93%). The solubility of this fraction in CDC1, is less than that of any other fraction, and therefore only an inferior 13CNMR spectrum was obtained (and no 600 MHz spectrum was obtained because of experimental difficulties). The NMR spectra are shown in Figure 5. The molecular weight of this fraction measured by VPO is about 60% higher than those of the other base fractions. The IR spectrum indicates the presence of -NH and -OH groups. The proton spectrum shows the presence of hydrogen-bonded -OH or -NH functionalities and also shows absorption in the 3.3-4.0 ppm range (the sharp peak
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 303
a
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C
I1
CHEMICAL SHIFT-PPM VS TMS
Figure 5. Spectral data for weak bases: (a) 80-MHz 'H NMR spectrum; (b) 20-MHz 13C NMR spectrum.
at -5.3 ppm is due to a trace of methylene chloride which had not been completely removed in an earlier solubility test). There is no strong evidence for N or 0 associated with the saturate region in the 13Cspectrum, but any such evidence would be obscured by the low signal-to-noise ratio. The general shape of the carbon-13 aromatic region is more suggestive of pyridine-like structures than that of the very weak bases. Only 60% of the carbon is aromatic in this fraction by carbon-13 NMR; thus there is more saturate carbon than in the very weak bases. The difference seems to be mainly in the length of the a-alkyl chains (average = C2rather than C,) or in the frequency of methyl substitution p to N or to 0. Some hydroaromatic character is definitely present. The Strong Bases. The strong-base fraction (Figure 6) is expected to contain pyridines (or quinoline or more highly condensed analogues) and anilines. The IR spectrum shows the presence of -NH and -OH moieties but at much reduced levels relative to the other base fractions. No -NH, -OH absorption is evident in the proton spectra, nor are characteristic peaks at 157 or 104 ppm present in the carbon spectrum. The elemental analysis (4.85% N, 1.8% 0) implies that there are three times more nitrogen-containing functional groups than oxygen-containing groups; the types of oxygen-containing groups cannot be determined from the NMR spectrum. There is a hint of absorption near 58 ppm in the carbon spectrum, which would indicate aliphatic nitrogen. However, the most probable position for the nitrogen is, indeed, in pyridinelike structures, having proton resonances farther downfield than those of the corresponding aromatic hydrocarbons.
200
100 CHEMICAL SHIFT-PPM V S TMS
0
Figure 6. Spectral data for strong bases: (a) 80-MHz 'H NMR spectrum; (b) 600-MHz 'H NMR spectrum; (c) 20-MHz 13C NMR spectrum.
As with most of these fractions, the major substituent on the aromatic rings is the methyl group. The 600-MHz spectrum indicates this result because of very little coupling on the resolved peaks in the region 2.0-3.0 ppm. Although methyls would ordinarily appear only in about the first third of this range, the effect of nitrogen in the ring would be to move the resonances of these substituents downfield. The other regions of this spectrum are much like those described for the previously discussed fractions. The Neutral Resins. The neutral resins constitute about 1% of the heavy distillate. This fraction contains about 7% oxygen and 0.8% nitrogen. The 13C NMR spectrum (Figure 7) is dominated by several sharp peaks, mainly in the saturate region of the spectrum. A corresponding pattern was present in the 6OO-MHz 'H NMR. The infrared spectrum shows a strong carbonyl absorption. The spectra indicate the presence of di-2-ethylhexylphthalate,which is a plasticizer commonly found in plastic tubing. Since pains were taken to avoid this contamination in the separation procedures and since the plasticizer could not be found in representative
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spectrum.
Figure 8. Spectral data for very weak acids: (a) 80-MHz 'H NMR spectrum; (b) 6OO-MHz 'H NMR spectrum; (c) 20-MHz 13C NMR spectrum.
1-L samples of the solvents used in this project, we conclude it must have been a contaminant in the heavy distillate sample as received. The phthalate impurity in the neutral resins constitutes about 15% of this fraction, but it is only about 0.15% of the total heavy distillate sample. The phthalate should have been concentrated in the neutral resins by the separation procedure; the result confirms the efficiency of the separation procedure. The comparison of the 600- and 80-MHz proton spectra shows the effects of high field. The AA'BB' pattern for the aromatic phthalate proton is simplified, as expected, at 600 MHz. In contrast, the pattern near 4.3 ppm is a doublet at the low field but a quartet of doublets at the high field. The high field has emphasized the magnetic nonequivalence of the -CH,-CH group and has turned a simple A2X pattern into an ABX pattern. Other portions of the phthalate spectrum are well-resolved at the high field but not to the extent of allowing us to resolve %ew" nonequivalences. The coal liquid products in this fraction are probably hydrogen-bonded phenolics. Protons characteristic of phenol show up in the 'H spectrum, and the range of
aromatic 13C chemical shifts is indicative of phenol and aromatic ethers. The aliphatic portions of the spectra are obscured by the phthalate peaks, and the calculated aromaticity (-50%) is much less than a realistic value. If the phthalate resonances are deleted, the spectra appear to indicate highly aromatic structures. No clear evidence of other carbonyls such as quinones, aldehydes, or ketones is present. The Acids. The Very Weak Acids. The very weak acid fraction is expected to be highly phenolic in character because of its very weakly acidic properties. It contains 9% 0 and only 0.2% N. Indeed, the IR spectrum shows free and hydrogen-bonded-OH groups; the proton NMR spectrum shows phenolic -OH groups, and the 13Cspectrum shows a pattern indicative of phenols (Figure 8). The only apparent inconsistency between the carbon and proton spectra is the presence of a saturated CH, bonded to a heteroatom in the proton spectrum and the absence of such a group in the carbon spectrum. The 600-MHz NMR spectrum shows the presence of more CH, CH2 groups relative to CH3 groups than in the fractions discussed above. This result is borne out by the 13Cspectrum,
Figure 7. Spectral data for neutral resins: (a) 80-MHz 'H NMR spectrum; (b) 600-MHz 'H NMR spectrum; (c) 20-MHz 'H NMR
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 2, 1983 905 V E R Y WEAK BASES
R-0:::
R
WEAK BASES
W
Q-OH
R
n Hydroxypyr,dines R
Indoles R
R
STRONG BASES NH2 pyr,dines
VERY W E A K ACIDS
Anilines
don
&R Phenols
STRONG A C I D S
Outnolines
Nophthofs
R ~ c o o H &--COOH
R3COOH
Eenzoics
Afiphntics
Naphlhoics
NEUTRAL RESINS
A
R
Corbozoles
NEUTRAL OILS
CnHpnt2
,
Eenzocorbozolss Phenazines Cnnzn
( d i ) b e n z o f u r a n , ( d i ) benrothiophenes
Figure 9. Suggested structures representative o f the SRC-I1 heavy distillate fractions.
which indicates that much of the saturate area is in hydroaromatic rings. The aromatic rings are methyl-substituted, but the substituents are less likely to be ortho to -OH groups. This result is shown by a major peak at 21.3 ppm, which is about three times larger than that a t 15.34 ppm. The sharpness of the 13C lines indicates that the molecules are relatively small. They must be highly hydrogen bonded to appear in the heavy distillate. The aromaticity is 0.72, and about 9% of all the aromatic carbons are bonded to oxygen in some manner. The Weak Acids. The weak-acid fraction amounts to about 2% of the heavy distillate sample, contains almost no nitrogen, only little sulfur, and about 10% oxygen, and it is also made up of phenolic type compounds. The IR spectrum shows only free and bonded OH, and no carbonyl bands. The weak acids are very similar in spectral detail and molecular weight to the very weak acids. The IR spectra are essentially indistinguishable, as are the 13C NMR spectra. Our instrumental probes do not show a clear difference between the weak acids and the very weak acids. Thus, the only differences must be the arrangement of
various functional groups to cause subtle polarity and pK, differences. The Strong Acids. The strong-acid fraction presents some problems in analysis. IR and NMR data verify the presence of carboxylic acids, but we are surprised by the simplicity of the 13CNMR spectrum. Such a simple 13C spectrum ordinarily indicates a single component and is highly unusual considering the heterogeneity of the other fractions. The impurity which contaminated the acid fractions was removed prior to spectrum analysis. Nonetheless, there is some doubt about the origin of this fraction. We have not been able to identify the compound (if it is a single compound); nor have we been able to preclude its existence in the heavy distillate sample. The Asphaltenes. The pentane-insoluble, toluenesoluble portion of the heavy distillate was also examined spectroscopically. Although this fraction accounted for about 8% of the total sample, its broad NMR lines and indistinct spectral features make it less tractable than the other fractions. Further characterization of the asphaltenes will be presented elsewhere (Ladner et al., to be published). Conclusions Coal liquid fractions derived from SRC-I1 heavy distillate have been characterized with spectroscopic techniques in combination with VPO, GPC, and elemental analysis. The 600-MHz 'H NMR spectra were especially useful in providing assignments and augmenting the 13C results. A collection of representative structures expected to appear in each fraction on the basis of polarity and acid-base properties is given in Figure 9. Not all of these structures were found by our spectroscopic probes. Acknowledgment We thank Kuoshin Lee of Carnegie-Mellon University for obtaining the 6OO-MHz NMR spectra. This work was supported by the US. Department of Energy. Literature Cited Annual Book of ASTM Standards, Part 24, Amerlcan Soclety for Testing and Materials, Philadelphia. 1980. Clutter, D. R.; Petrakls, L.; Stenger, R. L.; Jensen, R. K. Anal. Chem. 1972, 44, 1395. Ladner, W. R.; Petrakls, L.; Qates, B. C., to be published. Petrakls, L.; Ruberto, R. 0.; Young, D. C.; Qates, B. C. Ind. Eng. Chem. Process Des. Dev. 1983. precedlng paper in thls Issue. Seshadrl, K. S.; Ruberto. R. G.; Jewell. D. M.; Melone, H. P. Fuel 1978, 57, 549. Suatoni, J. C., Qulf Research and Development Company, private communlcation, 1980. Swansiger, J. T.; Dlckson, F. E.; Best, H. T. Anal. Chem. 1974, 45, 730. Tomlnaga, H.; Seijl, I.; Yashiro, M. Bull. Jpn. Pet. Inst. 1977, 79, 50.
Received for review July 15, 1981 Revised manuscript received May 20, 1982 Accepted September 29, 1982
