Energy & Fuels 1992,6, 702-708
702
Pyrolysis-Field Ionization Mass Spectrometry of Extracts Separated from a Gas Coal and Its Macerals Using N-Methyl-2-pyrrolidinone D. Cagniant,' R. Gruber, and C. Lacordaire-Wilhelm Laboratoire de Chimie Organique, PICS Carbochimie PAN-PIRSEM-CNRS, Universit6 de Metz, Ile du Saulcy, 57045 Metz Cedex, France
H.-R. Schulten Department of Trace Analysis, Fachhochschule Fresenius, Dambachtal, 20-6200 Wiesbaden, Germany Received November 26,1991. Revised Manuscript Received July 16, 1992
The characterization by pyrolysis-field ionization mass spectrometry (Py-FIMS) of the N-methyl2-pyrrolidinone (NMP) extracts of several coals (gas coal, flame coal, orthocoking coal) has recently been described. This study is now extended to the NMP extracts of the macerals, i.e., vitrinite, exinite, and inertinite, after separation from the gas coal sample. The Py-FI mass spectrum of the original gas coal is also reported. The contribution of each maceral to the extractible phase was estimated from the petrographic analysis and from the yields of NMP extraction. The thermogram patterns are characteristicfor eachmaceral extract. A great similarity was observed between vitrinite (the main maceral) and the parental coal extracts. In this case the two maxima displayed by the thermograms have approximately the same area. Conversely, the exinite and inertinite groups are mainly retained in the extraction residues. Their thermograms are strikingly different from the one of vitrinite. The extractible phases, obtained in low yields, as mostly made of easily distillable components. All the three macerals contribute to the formation of hydroxylated compounds in the high-temperaturedevolatilizationstep. No major distinction between the aromatic structures of the maceral and the parental coal extracts can be evidenced.
Introduction The characterization of pyrolysis-field ionization mass spectrometry (Py-FIMS) of the extracts obtained from four bituminous coals, by means of N-methyl-2-pyrrolidinone (NMP), was described in the preceding study.' The good properties of NMP in coal solvolysis were previously r e p ~ r t e d . ~Indeed, -~ NMP acts only on noncovalent interactions, without cleavage of covalent bonds by chemical reactions. In the conditionsapplied,two devolatilizationsteps were established on the basis of the thermograms. The first step corresponded to a sequentialdistillationprocess giving rise to alkylaromatics and hydroaromatics as well as homologous series of paraffins. Hydroxylated compounds (mainly alkylphenols)appeared during the second step (t > 450 OC), owing to a pyrolysis process. It was concluded that the NMP extracts are made up of easily distillable components (t < 450 "C)and by larger entities considered as "oligomeric" parts of the coal structure, which by pyrolysis at temperature over 450 "C give rise to hydroxylated structures and mainly to alkylphenolicderivatives. The total devolatilization occurs below 750 "C. (1) Cagniant, D.; Gruber, R.; Lacordaire-Wilhelm, C.; Schulten, H.-R. Energy Fuels, preceding paper in this issue. (2) Lacordaire-Wilhelm, C. Doctoral Thesis, University of Metz, 22 Oct. 1990. (3) Cagniant, D.; Gruber, R.; Lacordaire-Wilhelm, C.; Jasienko, S.; Machnikowska, H.; Salbut, P. D.; Bimer, J.; Puttmann, W. Fuel 1990,69,
902. (4) Iino, M.; Takanohashi, T.; Ohsuga, H.; Toda, K. Fuel 1988 67, 1639.
It was interesting to carry on this study by investigating, under the same conditions, the NMP extracts of coal macerals. Little has been published in the particular field of PyFIMS applied to separated macerals or maceral extracts. Indeed, the structural studies of macerals were mainly carried out by using FT/IR and NMR spectroscopies.5~~ In the course of the characterization of the "distillable phase" of coals by Py-FIMS, Meuzelaar et al?+ interpreted the formation of hydroxylated compounds (alkylphenols and dihydroxybenzenes) in the high-temperature devolatilization step to the pyrolysis of uitrinite-like components. Several arguments were proposed to support this interpretation: (i) Vitrinite is the main maceral(85% of Pittsburgh No. 8 coal). (5) Choi, C.; Wang, S.; Stock, L. M. Energy Fuels 1988,2, 37. (6) Totino, E. Doctoral Thesis, University of Metz, 1986.
(7) Meuzelaar, H. L. C.; Yun,Y.;Simmleit, N.;Schultan, H.-R. Prepr. Pap-Am. Chem. SOC., Diu.Fuel Chem. 1989,34,693. (8) Yun, Y.;Meuzelaar, H. L. C.; Simmleit, N.; Schultan, H.-R. In Recent Advances in Coal Sciences: A Symposium in Remembrance of P. H. Given; Schobert, H. H., Bartle, K. D., Lynch, L. J., Eds.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991; 89-110.
(9)Yun,Y.;Meuzelaar, H. L.C.; Simmleit, N.; Schulten, H.-R. Energy -. Fuels 1991, 5 , 22. (10)Meuzelaar, H. L. C.; Harper, A. M.; Pugmire, R. J.; Karas, J. Inst. J. Coal Geol. 1984, 4, 143. (11) Chakravarty, I.; Windig, W.;HiIl, G .R.;Meuzelaar,H.L. C.Energy Fuels 1988,2, 400. (12) Jasienko, S.; Kidawa, H.; Kowalik, H. Chem. Stosow. 1969, 13, 263.
0887-0624/92/2506-0702$03.00/00 1992 American Chemical Society
Energy & Fuels, Vol. 6, No. 6,1992 703
Py-FIMS of NMP Extracts of Coals
Table 111. NMP Extraction Yields (wt %) gas coal vitrinite exinite inertinite
Table I. Proximate and Ultimate Analyses Coal Sample GC and Its Macerals G
proximate analyses moisture ash (wt % dry) volatile matter MV (wt % daf) ultimate analyses (wt % daf) C
H N 0
H/Catomic ratio O/C atomic ratio a
C
V
E
I
2.6 4.1 35.1
3.0 0.4 34.3
3.0 0.3 53.0
2.0 3.9 21.3
84.3 5.2 1.6 9.3" 0.73 0.08
83 4.8 1.4 10.7b 0.69 0.10
87.2 5.9 1.2 5.Sb 0.81
88.1 3.8 0.7 7.4b 0.52 0.06
0.05
27.7 (28.8)a a
24.1
15.2
8.0
Previous yield from 10 g of coal.
By direct determination. By difference. Table 11. Petrographic Analyses (vol % ) a vitrinite exinite
bb
inertinite mineral Fu S-Fu Mi matter
gascoal 69.6 6.9 23.0 8.8 10.3 3.9 3.3 vitrinite 97.5 1.1 1.3 0.7 0.2 0.4 0.1 exinite 6.2 72.0 21.6 17.6 4.0 0.2 inertinite 0.7 98.5 84.3 14.2 0.8 Data from Poland. b = fusinite (Fu) + semifusinite (S-Fu) + micrinite (Mi).
(ii) In Curie-point Py-LVMS studies of maceral concentrates, vitrinite moieties were shown to be the main source of the hydroxyaromatic components.1° (iii) Chakravarty et al." consideredthe exinite group as "the main pyrolysis event that can be deconvoluted into at least three overlapping events involving vitrinite moieties,in addition to alginite/cutinite-likeand sporinitelike components". From these observations, the authors7v8also concluded that the nonmobile phase, rather than the mobile phase, was the main source of the phenols. This hypothesis was substantiated by the fact that pyridine extracts of Pittsburgh No. 8 coal, known to contain colloidal matter,' also gave phenols, whereas THF extracts (free of colloidal material) produced no phenols. All these hypotheses or conclusions will be discussed in comparison with our own results related to the Py-FIMS characterization of the NMP extracts of macerals.
Experimental Section 1. Maceral Samples. From among the four coals studied,l the gas coal (GC)was selected for this study. It is a high-volatile bituminous coal from Silesia. The macerals (vitrinite V, exinite E, and inertinite I) were separated at the Institute of Chemistry and Technology of Wroclaw, Poland, in a two-step procedure:1*-13(a) separation of the lithotypes by hand picking; and (b) separation of the macerals from lithotypes by the sink-float technique with a density gradient obtained with a mixture of CC4-toluene. Five iterative treatments (0.5-1 L of CCL-toluene by run) were necessary to obtain sufficient purity (except in the case of exinite, as seen below). During these operations, about 10% of losses were observed (mechanical losses and evaporation of some organic material). The proximate, ultimate, and petrographic analyses are reported in Tables I and 11. The purity of each maceral can be evaluated from the data in Table 11. It was difficult to obtain exinite with a high rate of purity, starting from a coal of low content of this maceral. On the contrary, vitrinite and inertinite groups were obtained with a 97-98% purity rate. (13)Jaeienko, S.; Kidawa, H. Chem. Stosow. 1985, 29, 315. (14)Xiangming, W.; Marzec, A.; Schulten, H.-R. Fresenius 2.Anal. Chem. 1989,333, 793.
m/z
D
Figure 1. Integrated pyrolysis-FI mass spectrum of the initial gas coal (GC) obtained by heating 100 pg of the coal sample from 50 to 750 "C at 1 "C/s. All substances evolved in this heating program are considered, disregarding the kind of physical or chemical bond in the authentic material. The thermogram (upper right, full line) shows a plot of the total ion intensity (abscissa) versus the temperature (ordinate). In addition, the number in daltons) of the thermally evolved average molecular weight (Mn, products is displayed as a function of temperature (dashed line). Approximately 35% of the starting material is volatilized. 2. Solvent Extraction. The procedure of extraction with NMP'@ is recalled in the first part of this study.1 It was first applied to 10g of coal, then adapted to lesser amounts of macerals (0.2-1 g), and, for comparison, repeated for the same amount of the GC sample.2 The extraction yields are reported in Table 111. The yields of extraction for macerals vary according to the sequence vitrinite > exinite > inertinite as in the case of the macerals separated from the other coal samples studied.' This trend follows the properties of NMP which extracts aromatic and hydroaromatic compounds in preference to long-chain alkyl hydrocarbons. The high condensation of aromatic hydrocarbons can account for the drop in yield in the case of inertinite. 3. Pyrolysis-Field Ionization Mass Spectrometry. The conditions are the same as described.' The mass spectra and the relevant thermograms (intensity of the FI signalsvs temperature) were recorded respectively for the NMP extracts of gas coal and its macerals. The fractionated mass spectra were selected in relation to the thermograms.
Results 1. Volatilization of the Gas Coal before Extraction (Figure 1). To the best of our knowledge, Figure 1shows the first FI mass spectrum of the pyrolysis products of a coal up to a mass range of 1500 Da. However, the signals in the high mass range are observed with low relative abundances, e.g., mlz 1340with 0.059%. In total, together with the low-mass signals between m/z 18 and m/z 100, approximately 1500 nominal masses are occupied. Concerningdifferent elemental compositionsand isomers,this complex pattern represents probably many thousands of thermally released chemical species. It is clear, therefore, that the assignment to chemical substances can only be preliminary, tentative approach. It is interesting to compare the curve of the total ion current (TII) with the curve of the number of average molecular weighta (M,) of the evolving pyrolysis products. Both TI1 (full line) and M,,(dashed line) are contrasted in the same temperature frame and show very clearly how the increase of thermal
Cagniant et al.
704 Energy & Fuels, Vol. 6,No.6,1992
"1
I
Table IV. Thermograms Devolatilization Stepsa
II
low-temp step range Mi
GC
v
E
F a
Figure 2. Mass spectra and thermograms of the gas coal (a), vitrinite (b), exinite E (c), and inertinite I (d) extracts. energy degrades the gas coal mainly between 250 and 620 O C . The temperature maxima are 415 O C for TI1 and 465 "C for Mn, which is explained by the fact that generally products of higher mass are generated with increasing temperature. However, at the same time (in particular above 450 OC), thermally induced mass spectrometric fragmentation occurs and leads to a decrease in M , due to low mass fragments. In the 500-600 OC temperature range an equilibrium is established between this mass spectrometric fragmentation and the still continuing production of chemical substances of higher masses. The various gradients in the TI1 and M , curves should reflect the bond strengths of the thermal products and the mass (or size) of the coal subunits. This means that, in the initial phase of thermal coal degradation (e.g., 250-400 OC for GC), a linear heating rate and a quasi-linear increase of Mn in this temperature range is accompanied by a rapid increase in the average weight of the chemical species cleaved from the coal macromolecule. 2. Volatilization of the Maceral Extracts. The integrated FI mass spectra of the maceral extracts and of the parental gas coal (Figure 2) display molecular ions in the mass ranges mlz = 50-600, if we consider only significant masses. Each even and odd nominal mass is detected in this range with main mass distributions ranging, as a rule, between 200 and 475, as discussed hereafter for each sample. 3. Thermograms. The thermograms are shown in Figure 2 (in seta) for the extracts of GC (a),and its macerals V (b), E (c), and I (d). The main features discussed hereafter are summarized in Table IV.
100-380 100-430 100-200
320 380 165
205-350
225 290 322 224 333 392
100-260 260-460
Ranges and maxima in
high-temp step range Mz
380-700 430-700
480 478
350-600
369
460-700
481
OC.
4. Mass Spectra Recorded in SelectedTemperature Ranges. Several basic series of homologous ions were selected to offer a reference to compare the samples, as previously explained,' but, by no means, with the aim of making structural identifications: series A, starting from mlz = 128 typical for the first terms of naphthalenes and mainly paraffinic compounds; series B, starting from mlz = 178,180, and 182 typical, for example, for the first terms, of phenanthrene (or anthracene) and their hydro derivatives; series C, starting from mlz = 228,230, and 232, typical in the same way for the first terms of four-ringedaromatic compounds and hydro derivatives; and series D, starting from mlz = 94, corresponding to phenolic derivatives. Some example of series A, B, and D are plotted on each fractionated mass spectra, correspondingto specific parts of the thermograms, as indicated in Figures 3-6.
Discussion The discussion is focused on the comparison between the three maceral extracts accordingto (i) the mass ranges of the molecular ions, (ii) the thermograms, and (iii) the fractionated mass spectra. In each case, reference will be made to the parental gas coal extract. During the discussion,we should have the petrographic composition of samplesin mind (Table 11). Only vitrinite and inertinite have a high purity rate (98% 1, whereas exinite is contaminated by about 22% of inertinite. Consequently, several similarities between these two macerals (see hereafter) could be due to this contamination, which will bias the results. (i) As for the mass range of the molecular ions, if we except some typical signals and the low m/z values in the range 50-200, the coal and maceral extracts give almost bell-shaped distributions with mlz values ranging from 200 to 550 (the mlz values above 550 having less significant FI signal intensity). The mlz ranges of the main signal distributions are somewhat different from one sample to another. In the case of the vitrinite extract, the maximum of the mass distribution (mlz = 300-475) is shifted toward higher values, in comparison to the parental coal extract (mlz = 235-400). A narrower distribution is observed with inertinite (mlz = 275-425) and a wider distribution with exinite (mlz = 225-450), with, in the latter case, almost equal intensity of the FI signals. From mlz = 50 to 200, the low relative intensities of the FI signals increase according to the following sequence: inertinite < vitrinite = gas coal < exinite
Energy & Fuels, Vol. 6, No. 6,1992 706
Py-FIMS of NMP Extracts of Coals 310
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Figure 4. Homologous ions starting from mlz 178 (-) and m/z 182 (+ - +) Series B (mass ranges mlz 150-500) Py-FIMSof vitrinite extract (b.1). Partial mass spectra of selected temperature ranges 255-427 O C (b.2)and 444-717 O C (b.3).
& '
5bOm/z
Figure 3. Homologous ions starting from m/z = 128,series A, gas coal (a),vitrinite (b),exinite E (c), inertinite I (d) extracts.
(ii) Concerning the thermograms, two steps of devolatilization were pointed out as in the case of the gas coal extract. The first one ( t < 450 "C) corresponds to vacuum desorption and distillation processes, the second one ( t > 450 "C) gives rise to pyrolysis reactions, and the temperatures of total devolatilization (below 700 "C) are in the same range as with nonextracted coals (refs 7-9 and 14 and Figure l), and with parental gas coal extract.' Nevertheless, the thermograms (Figure 2, insets) are strikingly different (cf. Table IV) and are characteristic of eachmaceralextract, if we consider the low-temperature devolatilization steps and the relative area corresponding to the two steps. Agreat similarity is observed between the thermograms of vitrinite and of the parental gas coal. Nevertheless, in the case of vitrinite, a shift of the f i s t maximumM1toward higher temperatures, in relation to a shift of the ml2 maximum distribution toward higher masses, accounts for a high content of heavy structures which also requires a greater input of thermal energy, for their devolatilization in the first step, than in the case of coal extract. The two maxima displayed by the thermograms are of ~ 1with approximatelythe same area (area ratio M 1 / M = coal and 1.2 with vitrinite).
The low-temperature devolatilization steps of exinite and inertinite extracts are characterized by a sequence of several maxima corresponding probably to the devolatilization of specificgroups of components. The f i s t of these partial maxima occur a t low temperatures and correspond to very easily distillable components (160 "C for exinite and 225 OC for inertinite). A clearcut imbalance between the areas corresponding to the low- and high-temperature devolatilization steps is observed, particularly with inertinite: the major part of the components extracted by NMP are thermodistillable below 400 "C, without pyrolysis. Only a small part of the extracts corresponds to the high-temperature step, with the occurrence of pyrolysis at t > 450 "C. Then, not only the main part of inertinite group remains in the residue of NMP extraction,but the extract consists mostly of easily distillable components. The same holds true for exinite, though the extraction yield was greater than for inertinite. This disproportion in the areas can account for the shift of the maximum M Itoward a lower temperature (320"C) in the case of gas coal extract, as compared to the one of vitrinite (380"C), owing to its content in the exinite (7% ) and inertinite groups (23%). In all cases, the hightemperature devolatilization steps correspond to the occurrence of hydroxylated compounds, mainly alkylphenols, due to pyrolysis. In this respect, all the macer&, and not only vitrinite as was claimed in the literature, contribute to the formation of alkylphenols.
Cagniant et 01.
706 Energy &Fuels, Vol. 6, No. 6,1992 178
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500
364 224
Figure 6. Homologous ions starting form m / z = 94, series D
468-646°C
500
Figure 5. Homologous ions starting from m/z 178 (-) and m/z
182 (+ - +). Series B (mass ranges m/z 150-500) Py-FIMS of inertinite extract (c). Partial mass spectraof selected temperature ranges 94-261 "C (c.l), 268-450 "C (c.2), and 468-646 "C (c.3).
(iii) As in the case of coal extracts,' it is interesting to follow the development of the fractionated mass spectra correspondingto homologous ion series,as the temperature increases. Some particular features of maceral extracts were put forward. Homologous Ions Starting from mlz = 128 (Series A). The corresponding homologous ions are plotted on each mass spectrum of GC (a), V (b), E (4,and I extracts (d) (cf. Figure 3). Generally speaking, the conclusions established in the first part of this study' for coal extracts, can be extended to the maceral extracts: The FI signals of very low intensity up to mlz = 198 could Correspondto the CnH2n-12 family,naphthalene and its C1 to Cg derivatives.lJ5 The main FI signals could correspond mainly to the CnH2n+2homologous ions. They give rise to two unequal distributions: (a) the lower one centered around the term (15) Simmleit, N.;Schulten, H.-R.; Yun, Y.; Meuzelaar, H.L. C. Advances in Spectroscopy;Meuzelaar, H.L. C., Ed.;Plenum Press: New York, 1992.
in C16 and even less significant in the case of inertinite; and (b) the higher one centered around the terms in C22 (GO, c24-c26 (V),C21428 (E), and c23426 (I). The same range (carbon number) and the same distribution of m/z values for these n-paraffins were also evidenced in the hydropyrolysis tars (600 OC) of Westerholt coal vitrinite and exinite.16 The development of these distributions as the temperature increasesis followed on the fractionated mass spectra (not recorded here). In all cases, the second distribution predominates during the low-temperaturedevolatilization steps, the FI signalscorrespondingto the fiist distribution being of very low intensity. Contrary to this, in the hightemperature devolatilization step, when the pyrolysis process occurs, we observe an increasing proportion and even the predominance of the terms of CU. As in the case of other coal extracts,' this fact was put down to the cracking of alkylaromatic hydrocarbons. Homologous Ions Starting from m/z178,180, and 182 (Series B). T w o examples were selected vitrinite (b.1) and its fractionated mass spectra (b.2, b.3) and inertinite (c) and its fractionated mass spectra (c.1, c.2, c.3). These mass spectra are presented respectively in Figures 4 and 5, for the series starting from 178 and 182. The first terms could correspond to phenanthrene (or anthracene) and alkyl derivatives (starting from 178)and their hydro derivatives(starting 180and 182),but as stated above, many other structures are ala0 possible. The maceral extracts can be divided into two groups: (a) Vitrinite (Figure 41, whose mass spectrum b l presents a bimodal distribution (D1 and Dz), the point of differentiationbeing locatedat mlz = 300. The three series (starting from mlz = 178, 180, and 182) follow approxi~~
(16) Cagniant, D.;Wilhelm, J. C.; Katoh, T.;Van Heek,K. H.;Wanzl, W. Fuel 1990 69,1496.
Py-FIMS of NMP Extracts of Coals mately the same trend, with an inversion in the relative abundance over mlz = 300 (predominance of the series starting from mlz = 178 up to mlz = 300 and the other way round from mlz = 300onwards). The distribution Dz is the main one in the first devolatilization step (mass spectrum b2), and the two distributions D1 and D2 are nearly equal in the second step (mass spectrum b3). The same trends are observed in the case of the GC extract, though some differences appeared owing to the presence of the other macerals (Le., predominance of the distribution D1 in the first devolatilization step). ( b )Inertinite and exinite gave similar mass spectra that were strikingly different from that of vitrinite. The case of inertinite is reported in Figure 5. Except for some individual FI signals (see below), the homologous ion patterns display a Gaussian distribution from mlz = 225 to mlz = 550 (maximum for mlz = 250450). Furthermore, the mass spectra were characterized by individual FI signals of great relative abundance: in the caw of inertinite, mlz = 178,probablydue tophenanthrene (or anthracene); in the case of exinite, a very important signal at mlz = 208, in addition to the above signal m / z = 178. The developmentof these homologousion distributions, when temperature increases (cf. Figure 5, mass spectra c.1, c.2, c.3), shows that there is (i) a displacement of the maximum of the Gaussian distribution toward higher mlz values (mass spectra c.1, c.2), and (ii) a predominance of the signal mlz = 178 (mass spectra c.1) at the beginning of the first devolatilization step ( t < 225 "C). At the end of this step (c.2) ( t < 450 "C), there is a drop of this signal and a characteristic rise of the one at mlz = 192 (C1 derivative of phenanthrene (or anthracene)). In the second devolatilization step (massspectrum c.3),these two signals disappear. The signal mlz = 208 (hexahydrofluorantheneor pyrene, or dimethyldihydrophenanthrene, for example), found only in the exinite extract, predominates in the parts 1 and 2 of the thermogram (t < 350 OC). Taking into account the presence of inertinite in the exinite sample, we can assume that phenanthrene (or anthracene) and the C1derivativeare mostly characteristic of inertinite, but the signal at mlz = 208 seems to be characteristic of only exinite. Though no explanation can be offered at that stage about the origin of these typical compounds, all chances of accidental pollution being discarded,they could not be caused by the pyrolysisprocess considering that they are absent at t > 460 "C (mass spectrum 12.3). Homologous Ions Starting from 228,230, and 232 (Series C). All the discussion presented concerning coal extracts' also applies to maceral extracts and will not be repeated here, except for the outstanding features. Specifically,the characteristic mlz values 232,246,260, 274, and 288, present in coal extracts (assignedto steranesa phenylnaphthalene~~ or cyclopenta[deflphenanthrene15 in the case of nonextracted coal), are also predominant in the mass spectra of the maceral extracts and in the fractionated mass spectra of the low-temperature devolatilization step. For instance, they are the main signals of the part 1of the thermogram ( t < 240 "C) of vitrinite. As in coal extracts,' it is interesting to follow up the development of the mlz 232-288 series in relation to the temperature; these homologous ions are predominant at
Energy & Fuels, Vol. 6, No. 6,1992 707 t < 260 "C (part 1of the thermogram), less intense in part 2 (268< t < 450 "C),and, once again,stronglypredominant in part 3 ( t > 460 "C), when pyrolysis reactions occur. This development is in agreement with our previous conclusion,' considering that the components giving the homologous 232-288 ions could be present in the extract in the form of easily volatilizable molecules, but could also be released from larger entities by pyrolysis, at t > 450 "C, with the simultaneous formation of alkylphenols (see series D). These structural characteristics of series C are found whatever the macerals. Homologous Ions Starting from mlz = 94 (Series D).The homologous ions mlz 94,108,122,136,150, and 164reported in Figure 6 for somefractionated mass spectra of V, E, and I extracts correspond to alkylphenols. As previously stated,' they appeared in the whole mass spectra and only in the end part of the thermogramscorresponding to the high-temperature volatilization step and to the occurrence of pyrolysis. It is obvious that, contrary to literature data,7-11 the alkylphenols (and also, in lesser amounts, other hydroxy derivativessuch as hydroxynaphthalenes,hydroxyindenes) are not produced "only by vitrinite moieties"and we cannot accept the conclusions presented by these authors. Furthermore, we have no evidencethat "the nonmobile phase, rather than the mobile phase, was the main source of the ~ ~ ~ The series D and phenols", as was ~ l a i m e d .Remark: B overlap from mlz = 178 as can be seen by comparing mass spectra a (Figure 6) and b.3 (Figure 41, and mass spectra c (Figure 6) and c.3 (Figure 5 ) . Conclusions
As in the case of coal NMP extracts, the Py-FIMS analyses emphasizethe great heterogeneity of the maceral NMP extracts. As vitrinite is the main maceral of gas coal (about 70%), it is not surprising that the mass spectraand thermograms are quite similar. The main discrepancyconcerns a higher amount of heavy structures in vitrinite, as shown by the shift of the maximum M I and of the mlz maximum distribution toward, respectively, the higher temperatures and the higher masses. Then, the conclusions presented in case of coal extracts' applied also to the vitrinite extract. The most striking difference between vitrinite and the two other macerals, exinite and inertinite, appears in their thermograms and in selected series of homologous ions, series A, B, and C, particularly in the low-temperature devolatilization steps. In respect with series A, if the main homologous ions could correspondto paraffms, the analogybetween vitrinite and inertinite is in agreement with previous observations;5 the authors suggested, on the basis of experiments on ruthenium tetroxide oxidation, that the aromatic structures in the three maceral groups are similar and the differences between inertinite and vitrinite arise from variations in concentration with similar types of aromatic and hydroaromatic structures. Indeed, we observed also an analogy between the homologous ion series starting from mlz 178 and mlz 182, presented in b2 and c2, and b3 and c3 (Figures 4 and 5), respectively, for vitrinite and inertinite extracts. It can be assumed that the large polynuclear aromatic clusters in inertinite undergo noncovalent aromatic-
Cagniant et al.
708 Energy 13Fuels, Vol. 6, No. 6, 1992
aromatic interactions" which decrease the solubility in NMP. Only small free molecules (like phenanthrene) and smaller macromolecules, bound by noncovalent interactions in the sol can be extracted and account for the lowtemperature devolatilization step. But there are no main differences in the types of aromatic functionalities. In the case of exinite, the conclusions are more doubtful as this maceral is contaminated by inertinite. Nevertheless, the main part of the NMP extract is volatilizedbelow 450 "C, and even partly below 200 OC, in successive steps as proved by the presence of several maxima in the thermogram. Interestingly,the homologous ions starting from m/z 94 (seriesD) are found in the Py-FI mass spectra of the three macerals as the result of pyrolysis process (t > 450 OC), as mentioned bef0re.l Assumingthat the extractible phases play an important role in the formation of the plastic stage during the process (17)Nishioka, M.;Larsen, J. W.Energy Fuels, 1990,4, 100.
of coal softening, this study shows how each maceral provides a specific contribution according to ita weight (petrographic analysis of coals), ita content in the extractible phases (yields of NMP extraction), and the thermodistillable properties of this phase as evidenced by Py-FIMS analyses.
Acknowledgment. This work is apart of a cooperative research program (PICS) between the Polish Academy of Sciences (PAN) and the French Centre National de la Recherche Scientifique (CNRS). The financial support granted to H.R.S. by the Deutsche Forschungegemeinschaft, Bonn-Bad Godesberg, Germany (Project Schu 416/ 15-1) is gratefullyacknowledged. We thank the PIRSEMCNRS for the financial support granted by PICS "Carbochimie" (PAN-CNRS) and Professor S. Jasienko (Wroclaw) for a gift of a gas coal sample and ita macerals. Registry No. NMP, 872-50-4.
