Energy & Fuels 1990,4, 28-33
28
Comparison of the Structure and Reactivity of a Kansk-Achinsk Basin (USSR)Coal with Those of a Latrobe Valley (Australia) Coal Peter J. Redlich* and W. Roy Jackson Department of Chemistry, Monash University, Clayton, Victoria, Australia 3168
Frank P. Larkins Department of Chemistry, University of Tasmania, GPO Box 252C, Hobart, Tasmania, Australia 7001
Alan L. Chaffee CSIRO Division of Fuel Technology, Research Laboratories, Private Mail Bag 7, Menai, New South Wales, Australia 2234
Andrei A. Krichko, Evgeniya A. Grigoryeva, and Sergei N. Shatov Institute of Fossil Fuels, U S S R Ministry of Coal Industry, 29 Leninsky Prospect, Moscow, U S S R Received June 28, 1989. Revised Manuscript Received September 22, 1989 Samples of coals from two of the largest brown coal deposits in the world, the Kansk-Achinsk Basin in Siberia, USSR, and the Latrobe Valley in Victoria, Australia, have been studied by a range of spectroscopic and chemical techniques. Three such coals, with similar atomic H/Cratios, show the same reactivity in hydrogenation reactions, but an analysis of the structure of the products from these reactions and spectroscopicmeasurements on the coals reveal significant differences in their chemical structure. The aliphatic content of the Australian coals is, to a large extent, in the form of long-chain material, loosely retained in a macromolecular, lignin-based polymer, whereas the aliphatic component of the Soviet coal consists of short chains that are much more firmly bound to the aromatic macromolecular network.
Introduction Earlier studies1i4 found that, when the effect of inorganics and minerals was minimized, coal conversion and oil yield under typical liquefaction conditions a t 400 O C for a wide range of coals could be related to the elemental analysis of the coal, without any large independent contributions from chemical-structural characteristics. The generality of this conclusion for low-rank coals was doubtful, because all the low-rank coals studied were of similar structure. Previous papers in our series have described the characterization of a suite of Australian their conversion characteristics toward reactions in hydrogen: and structural data concerning the products of these readions.'W This three-pronged approach has been shown to give valuable information on the structure of the coals and some insight into their reactivity patterns. Similarly the Soviet group in the Institute of Fossil Fuels has studied extensively the structure-reactivity relationships of a series of coals from the USSR.*11 (1)Redlich, P.; Jackson, W. R.; Larkins, F. P. Fuel 1985, 64, 1383-1390. ( 2 ) Redlich, P. J.; Jackson, W. R.; Larkins, F. P.; Rash, D. Fuel 1989,
m. 222-2311 ._ --I
(3)Lynch, L. J.; Sakurovs, R.; Webster, D. S.; Redlich, P. J. Fuel 1988, 67,1036-1041. (4)Redlich, P. J.; Jackson, W. R.; Larkins, F. P. Fuel 1989, 68, 231- -227 ___ .. (5)Supaluknari, S.;Larkins, F. P.; Redlich, P.; Jackson, W. R. Fuel Process. Technol. 1988,18, 147-160. (6)Part 16. Redlich, P. J.; Jackson, W. R.; Larkins, F. P.; Chaffee, A.; Liepa, I. Submitted for publication in Fuel. (7)Part 17. Redlich, P. J.; Jackson, W. R.; Larkins, F. P. Submitted for publication in Fuel. (8)Part 18. Redlich, P. J.; Jackson, W. R.; Larkins, F. P.; Chaffee, A.; Liepa, I. Submitted for publication in Fuel.
0887-0624/90/2504-0028$02.50/0
In this paper the above strategy is applied to coals from two of the world's most significant brown coal depositsthe Kansk-Achinsk Basin in Siberia, USSR,and the Latrobe Valley in Victoria, Australia. Both of these very large deposits contain coal with low sulfur and mineral contents and with low overburden to coal ratios. Both are the subject of pilot-plant-scale investigations for the production of liquid fuels by direct liquefaction. It is thus important to compare and contrast the structure and reactivity of these important coals. To this end the Soviet coal from the Irsha-Borodino deposit in the Kansk-Achinsk Basin was compared with two coals from the Latrobe Valley, a Loy Yang bore 1276 sample2and a Rosedale bore sample No. 7.2 The coals were chosen on the basis of similar atomic H/C ratios.2
Experimental Section Coal Preparation and Chemical Analysis. Coals were taken from as mined core samples. They were ground to -60 mesh (250
pm) and acid washed according to previously described procedures.2 Reaction Conditions. The liquefaction experiments on the acid-washed coal and host lv4 components were conducted in 70-mL rocking autoclaves, for 1h under the following sets of conditions: (1)3 g of dry coal, 6 MPa initial hydrogen pressure, with tetralin at a 3:l solvent coal ratio at 405 O C ; (2) 9 g of dry coal, 10 MPa
(9) Grigor'eva, E. A.; Zharova, M. N.; Zimina, E. S.; Krichko, A. A.; Lesnikova, E. B.; Titova, T. A.; Shulyakovskaya, L. V.; Yashina, T. N. Khim. Tuerd. Topl. (Moscow)1983,No.I, 114-120. (IO) Grigor'eva, E. A.; Lesnikova, E. B.; Artemova, N. I.; Chizhewkaya, V. R.; Klinkova, V. V.; Egorova, T. F.; Dement'eva, 0. A. Khim.Tuerd. Topl. (Moscow)1985,No.2,5642. (11)Krichko, I. B.;Khrenkova, T. M. Khim.Tuerd. Topl. (Moscow) 1985,NO.5,53-57.
0 1990 American Chemical Society
Energy & Fuels, Vol. 4, No. 1, 1990 29
Kansk-Achinsk Basin and Latrobe Valley Coals Table I. Comparison between Maceral Composition and Volatile Matter Contents of ABR1/3 and IB Coals volatile maceral analysis, matter vol % content, w t huminite liptinite % dmif ABRl (Loy Yang 1276) 98.8 1.2 45.7 ABR3 (RosedaleNo. 7) 93.2 6.4 51.1 IB (Irsha Borodinsk) 96.6 3.4 46.0
Table 111. Oxygen Functional Group Distribution for ABR1/3 and IB Coals functional group distribn, wt % dmif COOH 0 phenolic 0 nonacidic 0 ABRl 6.9 6.5 12.8 ABRB 7.0 6.1 14.0 IB 5.0 5.0 11.1
il/
Table 11. Chemical Characteristics of IB and ABR1/3 Coals elemental composition, wt % dmif C H N S 0" H/C f,b ABRl 68.4 4.50 0.50 0.39 26.2 0.79 0.62 ABRB 67.4 4.64 0.55 0.28 27.1 0.83 0.53 IB 71.7 4.94 0.91 1.30 21.1 0.83 0.71 By difference. *Solid-state13C NMR. initial hydrogen pressure with no solvent, but in the presence of 1 mol/kg dry coal of stannic oxide at 405 "C; (3) 3 g of dry coal, 6 MPa initial nitrogen pressure with decalin at a 2:l solvent coal ratio at 320 O C ; (4) as in 3 but in the absence of solvent. Full details of the experiments have been reported elsewhere: The products were separated into oils, asphaltenes, and residues by a solvent separation scheme based on 40-60 "C bp petroleum (Shell X4) and dichloromethane: Analyses. Elemental analyses of the coals were carried out by the Herman Research Laboratory of the State Electricity Commission of Victoria and by the Institute of Fossil Fuels, Moscow. Acidity measurements on the coal and reaction products were carried out by a nonaqueous titration technique.2 Spectral Analyses. Solid-state 13C NMR spectra of coals, hydrogenation residues, and asphaltenes were recorded on a Bruker CXP 200 spectrometer at a carbon frequency of 50.33 MHz. Samples were spun at 3 kHz in a zirconia rotor. The magic angle was set with internal KBr. The following parameters were used to obtain spectra: relaxation delay 2 s, contact time 1.5 ms, 'H 90" pulse width 6 ps, spectral width 30 KHz. 'H NMR spectra were recorded on a Bruker AM 300 MHz NMR spectrometer. Samples were dissolved in CDC13, and tetramethylsilane was used as an internal standard. Fourier transform infrared (FTIR) spectra were recorded on a Digilab FTS-2OE spectrometer which was internally calibrated by use of a He-Ne laser. All spectra were referenced against a standard 100-mg KBr pellet. Solution 13CNMR spectra of oils were obtained at 50.33 MHz using inverse gated techniques with a relaxation delay of 10 s and a 90" pulse flip angle (16 ps). The sample was diluted (40-50 wt %) with deuteriochloroform and contained 0.7 wt % tris(acetylacetonato)chromium(III), Cr(acac)3,used as relaxation agent. Gas chromatography-mass spectrometric (GC/MS) analyses of oils were carried out on a JEOL DX-300 system coupled to a JEOL DA-5000 data system. Typical spectrometer conditions used were ionizing potential, IO eV; accelerating voltage, 3.0 kV; mass range scanned, 35-600 amu; scan speed, 1scan/s; filament current, 250 PA; ion source temperature, 250 "C. Gas-liquid chromatography was carried out on a 36-m fused silica capillary column (BP-5, SGE Scientific Pty. Ltd.). Neat coal liquids (approximately 1 pL) were injected (300 "C) in the split mode (approximately 50/1) onto the column which was held at 10 "C (2 min) and then programmed upward at 4 OC min-' to 300 "C, where it was held until the conclusion of each analysis.
Results and Discussion Coal Characteristics. The Irsha-Borodino (IB) coal is significantly older, being of Jurassic origin, than the two Victorian brown coals, which were deposited during the Miocene Epoch. The IB coal was laid down in strata that have only been weakly metamorphosed12 and were never (12) Nalivkin, D. V. Geology of the U.S.S.R.(English ?'rad.); Oliver and Boyd: Edinburgh, UK, 1973; p 243.
'd- i.
/'+
v
300
30
200
100
0
PPM
Figure 1. Solid-state 13CNMR spectra of (a) ABRl coal; (b) IB coal. +, aromatic spinning sidebands. deeply buried. For these reasons it is of similar rank to Victorian brown coal. A comparison of the analysis of the coals is given in Tables I and 11, with results expressed on a dmif (dry mineral inorganic free) basis. The coals have similar maceral concentrations and volatile matter contenta (Table I) and the same atomic H/C ratio (Table 11). The IB coal contained more carbon and less oxygen than ABRl and ABR3 (Table 11),having a carbon content similar to that of Victorian brown coals with H/C ratio 1.0 or above. Table I11 shows that values for all three classes of oxygen-containing functional groups were reduced for IB coal relative to ABR3. The fraction of aromatic carbon (fa) of the coals was determined by solid-state 13C NMR. The IB coal contained slightly more aromatic carbon than ABRl and ABRB as seen in Table 11. The actual NMR spectra (Figure 1) of IB and ABRl showed a significant difference in the aromatic area. In all other coals previously studied in this work2J3the aromatic area was partially resolved into two main peaks which were attributed to (1) aromatic C-C (130 ppm) and (2) aromatic C-0 (150 ppm), e.g., phenol and ether. The aromatic area of the IB coal was resolved into three peaks. The extra peak can be attributed to a n unusually large quantity of benzylic carbon atoms resulting from a very high number of side chains bound to aromatic rings.14 There was no significant difference between the FTIR spectra of the coals (see Figure 2). (13) Part 19. Redlich, P. J.; Jackson, W. R.; Larkins, F. P.; Carr, R. M.; Chaffee, A. L.; Liepa, I. Submitted for publication in Fuel. (14) Snape, C. E.; Ladner, W. R.; Bartle,K. D. Anal. Chem. 1979,51,
2189-2198.
Redlich et al.
30 Energy & Fuels, Vol. 4, No. 1, 1990
"000
3500
3600
2S00
Cm-1
2660
is00
la00
50B
Figure 2. FTIR spectra of (a) ABRl coal; (b) ABR3 coal; (c) IB coal. Table IV. Conversion Characteristics of ABR1/3 and IB Coals with Tetralin under Hydrogen at 405 OC yields, wt % dmif total conv asph oil" H 2 0 C02/C0 HC gas 1.8 9.4/1.0 20.0 23.1 8.7 ABRl 62.9 9.6/1.1 1.8 66.6 20.5 25.0 8.6 ABRB 6.9/0.7 1.6 25.7 24.0 6.7 IB 65.6 a
By difference.
Reaction under Hydrogen with Tetralin. The reactivity of IB coal under the ~tandard'.~ liquefaction conditions with tetralin as solvent as described previously was almost identical with that of the Victorian coals as seen in Table IV. This was particularly the case for the two conversion parameters that are most strongly related to atomic H/C ratio of the coal, the total conversion and the oil yield. Therefore, the IB coal falls almost exactly on the main trends of reactivity versus atomic H / C exhibited by the 29 Australian coals studied previously by There were, however, minor differences in the product distributions between IB coal and ABR1/3. The lower yield of COz, CO, and H 2 0 for the IB coal can be directly attributed to its lower total oxygen content. Another difference was the higher asphaltene yield from IB coal. Residues. Comparisons between elemental analyses, f a determined by solid-state 13C NMR, and nonaqueous titration results for the reaction residues are given in Table V, and 13C NMR spectra are shown in Figure 3. The elemental composition of the IB residue showed that it contained less oxygen than ABR1/3 residues but the phenolic content of all the residues was similar. However, the IB residue had a higher H/C ratio and lower f a than the ABR1/3 residues. A qualitative comparison of the aliphatic carbon region of the NMR spectra of ~
5
.
~
9
L
I
I
I
250
I
150
1
1
50
0
PPM ~
Figure 3. Solid-state 13C NMR spectra of residues derived from reaction of coals with tetralin and hydrogen at 405 O C : (a) ABRl residue; (b) ABR3 residue; (c) IB residue. +, aromatic spinning sidebands.
ABR1/3 and IB residues (Figure 3) suggests the differences were due to the greater CH, content of the IB residue (15 ppm resonance). Asphaltenes. The asphaltenes were analyzed by 'H NMR as well as by the techniques used for the residues and coals (Table V). The pattern seen in the residues was also seen in the asphaltenes in that the IB asphaltene contained less oxygen and had a higher atomic H/C ratio and lower f a value than ABR1/3 asphaltenes. The lower fa value (determined from a solid-state '3c NMR spectrum) was clearly associated with an increase in the absorption due to aliphatic groups in the IB asphaltene (Figure 4).
Table V. Chemical Characteristics of Residues (A) and Asphaltenes (B) Derived from Reaction of ABR1/3 and IB Coals with Tetralin under Hydrogen at 405 OC 'H NMR data elemental composition, wt % hydrogen distribn Brown-Ladner param dmif phenolic 0, C
H
N
O+S"
H/C
ABRl ABRB IB
84.1 82.1 84.8
4.15 4.32 4.84
1.1
1.0 1.3
10.7 12.6 9.1
0.59 0.63 0.69
ABRl ABRB IB
80.9 80.6 81.9
5.81 5.83 6.22
NA' NA' 1.2
11.5d 12.6d 10.7
0.86 0.87 0.91
w t % dmif
f,b
H,
H,
H,
H,
fa
0
0.38 0.40 0.44
0.20 0.21
0.04 0.03
0.19
0.04
0.73 0.72 0.70
0.50 0.47 0.47
H,/C,
A. Residues 5.4 0.86 5.5 0.89 5.0 0.78 B. Asphaltenes 0.38 10.8 0.74 0.36 9.0 0.73 0.32 0.67 9.5
By difference unless otherwise stated. *Solid-state I3C NMR. cNot available.
By direct measurement.
0.82 0.81 0.83
Energy & Fuels, Vol. 4,No. 1, 1990 31
Kansk-Achinsk Basin and Latrobe Valley Coals
1000
3000
2000
4000
5000
I
IC
I _ I
I
250
-
1
150
I
50
-
I
Figure 4. Solid-state 13C NMR spectra of asphaltenes derived from reaction of coals with tetralin and hydrogen at 405 "C: (a) ABRl asphaltene; (b) ABR3 asphaltene; (c) IB asphaltene. +, aromatic spinning sidebands. Table VI. Conversion Characteristics of ABRl and IB Coal from Reaction with SnOl and Hydrogen at 405 OC in the Absence of Solvent yields, wt % dmif H/C total of coal conv asph oila H20 C02/C0 HC gas
By
0.79 0.83
41.6 43.5
2.4 4.5
12.4 11.0 13.0/1.0 15.5 10.6 9.8/0.8
t
B
2000
3000
4000
1.8 2.3
difference.
Phenols were the predominant oxygen functional group as for most asphaltenes produced under these condition~.','~ The 'H NMR spectra showed only minor variations between the asphaltenes. Small differences in H, are consistent with H/C and solid-state I3C NMR data (Table V). Conversion Results from Reactions of Coal with Hydrogen in the Presence of Stannic Oxide (Sn02) but No Solvent. The conversion results for these reactions are given in Table VI. Only the ABRl coal was used in these experiments, which were designed to give oil products not contaminated with large amounts of reaction ~olvents.~~~J~ Analysis of Oils from Sn02-No Solvent Reactions by GC/MS. The total ion chromatograms of the oils from ABRl and IB are shown in Figure 5. The most obvious difference between them is in the relative abundance of
SCAN
NO.
0
PPM
ABRl IB
1000
SCAN NO.
Figure 5. Total ion chromatograms of oils derived from reaction of coals with stannic oxide and hydrogen at 405 OC: (a) IB oil; (b) ABRl oil; (c) ABRl host oil. Peaks: A, phenol; B, cresol; C, alkylcresols; D, naphthalene; E, methylnaphthalenes; F, C2-alkylnaphthalenes; G, C3-alkylnaphthalenes;I, C5-alkylnaphthalenes; J, C2-alkyltetralins (or C3-indans); K, C3-alkyltetralins (or C,indans); L, C4-alkyltetralins(or C5-indans);M, C5-alkyltetralins (or C6-indans); N, C2-alkylbenzenes; 0, CB-alkylbenzenes; T, phenanthrene; U, C2-phenanthrene;V, hydroxyphenol; W, C1hydroxyphenols; X, pyrene; Y, decalins; Z, phthalates; a, diasterenes; i followed by integer number, isoprenoid alkane of corresponding carbon number; integer number, n-alkane of corresponding alkane number. n-alkanes; IB oil has a much lower concentration than ABRl oil. The alkane distributions also differ significantly (Figure 6). Both oils exhibit broad (C8-C35, at least) unimodal distributions, but the positions of the distributional maxima are different (C25for ABRl oil and C16for IB oil). The ABRl oil exhibits a predominance of odd carbon chain lengths, whereas no such predominance occurs in the IB oil. The n-alkane distribution of IB oil is thus similar to those observed for oils derived from higher rank bituminous coals and prepared by the same method (refer to ABL3 and ABL6 in Redlich et a18). Examination of the C12-Cmregion of the chromatograms shows that the IB oil distribution contains higher relative concentrations of the isoprenoid alkanes. Other worked5 have examined the distribution of n-alkanes from the chloroform extracts of a range of Soviet coals including a sample from the IB deposit. A distribution of n-alkanes (maximum = C15) similar to that reported by us was noted for the IB coal extract and significant amounts of isoprenoid alkanes were (15) Gulyaeva, N. D.; Arefev, 0. A.; Sokolov, V. L.; Khim. Tuerd. Topl. (Moscow) 1976, No. 1, 106-110.
Petrov, A.
A.
32 Energy & Fuels, Vol. 4 , No. 1, 1990
R e d l i c h et al.
Table VII. Chemical Characteristics of Oils Derived from Reaction of ABRl Coal, ABRl Host, and IB Coal with SnOz and Hydrogen at 405 "C in the Absence of Solvent elemental composition, wt % dmif 'H NMR data, hydrogen distribn phenolic 0,
C ABRl IB ABRl host a
84.5
85.0 86.6
By difference.
H 9.0
N
O+Sn
H/C
0.5
7.8 7.5
1.2 1.4
6.0 6.0 4.5
1.27 1.10 1.04
* Solution 13C NMR.
wt % dmif
4.5 3.9
NA'
f,b
HaI
Ha
H,
H,
0.63 0.66 0.73
0.23 0.28 0.35
0.27 0.35 0.31
0.40 0.28
0.10 0.09 0.06
0.28
'Not available. Table VIII. Conversion Characteristics of ABRl and IB Coals in Decalin and Nitrogen at 320 OC vields. wt % dmif total conv asph oiln HzO HC gas COz ABRl 11.0 1.4 5.4 0 0.03 4.1 IB 10.6 1.4 4.4 1.3 0.03 3.4
la
By difference.
Table IX. Chemical Characteristics of Residues (Host) from Reaction of ABRl and IB Coals in Decalin and Nitrogen at 320 OC elemental composition, wt % dmif C H N O+S" H/C f.b 0.66 0.72 4.06 0.8 21.3 ABRl 73.8 IB 76.3 4.65 1.0 18.0 0.73 0.70 *By difference.
I000
2000
3000
4000
5000
SCAN NO.
Figure 6. Single ion chromatograms ( m / z 71) of oils in Figure 5a,b, indicating their respective alkane distribution. (See Figure 5 legend for identification of peaks.)
also observed. The extracts from Soviet low-rank coals from two other basins showed similar n-alkane distributions. The fraction bp 180-360 "C from an oil obtained by hydrogenating a Kansk-Achinsk Basin coal (Borodino deposit) also showed a similar distribution of n-alkanes.16 The other notable difference between the ABRl and IB oils is the presence of diasterenes in the latter (a, Figure 5 ) . One CZ8and four C29 isomers were recognized. Two of the CZ9isomers together with other stearanes and triterpenes were identified in the hexane extract from another coal from the Kansk-Achinsk Basin." Although diasterenes have been previously identified in extracts of Victorian brown coal,18analysis of the characteristic single ion chromatogram ( m / z 257) showed that they were not present in the ABRl oil. The data indicate that they are stable under liquefaction conditions, yet they have not been identified in significant quantities in any of the other liquefaction oils that have been investigated in our extensive s t ~ d y . ~ Diasterenes -~J~ are formed by backbone rearrangement of sterenes19during sedimentary diagenesis. Clearly steroidal compounds must be present in significant quantities among the biomass contributing to all coals. Hence, their absence (and the absence of their diagenetic products) in most oils we have examined is, in some ways, more surprising than their abundance in the present case. (16) Yulin, M. K.;Sokolova, I. M.; Berman, S. S.; Eremina, A. 0. Khim. Tuerd. Topl. (Moscow) 1987, N o . I , 56-60. (17) Vorob'eva, N. S.;Zemskova, Z. K.; Petrov, A. A. Khim. Tuerd. Topl. (Moscow) 1984, No. 5, 40-48. (18) Chaffee, A.L.Ph.D. Thesis, University of Melbourne, Melbourne, Australia, 1981. (19) Rubinstein, I.; Sieskind, 0.; Albrecht, P. J.Chem. Soc., Perkin Trans. I 1975, No. 19,1833-1836.
Solid-state I3C NMR.
The relative abundance and distribution of other major molecular classes in the oils (e.g., phenols, naphthalenes) are remarkably similar, although not identical (see peaks A-I, Figure 5). Analysis of Oils from Sn02-No Solvent Reactions by Other Techniques. Results from other techniques are in agreement with the differences in oil structure noted above. The hydrogen distribution in the oils determined by 'H NMR (Table VII) showed that the IB oil contained a significantly lower proportion of hydrogen in the H, form and higher proportions as H , and H, than ABRl oil. The relative intensity of the 30 ppm aliphatic resonance in the solution 13C NMR spectrum of ABRl oil was higher than in the spectrum of IB oil, indicating a higher concentration of long-chain n-alkane material in the former. The elemental analysis of the two oils (Table VII) showed that the H/C ratio of the IB oil was lower than that of ABRl oil. The fraction of aromatic carbon content of the two oils was similar. The phenolic oxygen content of ABRl oil was higher than that of IB oil. Comparison between ABRl Host Oil and IB Coal Oil. The ABRl coal was heated in decalin a t 320 "C in order to remove the (aliphatic) guest material.'j4J3 The host (residue after extraction) was then reacted with hydrogen at 405 "C in the presence of SnOz in the absence of solvent. A t first sight, the oil obtained from this reaction of ABRl host shows greater similarity to the IB oil than the ABRl total oil (Figure 5c). Also, the hydrogen content, atomic H/C ratio, and H, value of IB total oil were closer to those of ABRl host oil than to those of ABRl total oil (see Table VII). However, upon closer examination of the product distributions (Figure 5 ) it can be seen that the ABRl host oil contains a lower abundance of higher molecular weight products generally, and n-alkanes in particular, than the IB total oil. The distributions within individual molecular classes also differ significantly. For example, the C3 and higher naphthalene homologues (G and I) are nearly absent in the host oil, yet are significant components of both ABRl and IB total oils. From this qualitative perspective IB total oil is more similar to ABRl total oil than to ABRl
Energy & Fuels, Vol. 4, No. 1, 1990 33
Kansk-Achinsk Basin and Latrobe Valley Coals
1000
1000
20-00
3000
4000
5000
2000
3000
4000
5000
SCAN NO.
SCAN NO.
Figure 7. (a) Total ion chromatogram of oil (guest) derived from reaction of IB coal at 320 "C with nitrogen; (b) single ion chromatogram ( m / z 71) of oil of (a). (See Figure 5 legend for identification of peaks.)
host oil. The only significant differences between the former two oils, as outlined above, are in the relative abundances and distributions of alkanes and diasterenes. Low-Temperature Reactions and Product Analyses. The IB coal was reacted under Nz a t 320 "C in both the presence and absence of decalin, and the products were analyzed (Tables VI11 and IX). The conversion results were similar to those for ABRl even though the IB coal had a slightly higher H/C ratio and gave a significantly higher conversion figure a t 405 "C. The amount of asphaltene (polar 0i1)ls4was less than 2%,and the polar oil is not discussed further. GC/MS analysis of the IB 320 "C oil (guest oil) (Figure 7a) again showed a relatively low concentration of alkanes compared to that of the guest oils derived from Victorian brown coals.6 The n-alkane distribution (Figure 7b) also differed, being unimodal with a maximum a t C19 and without odd carbon chain predominance. The abundance of isoprenoid alkanes and alkenes (especially pristenes) relative to n-alkanes is particularly notable. The concentration of phenolic homologues in this oil is extremely high. All 320 "C oils examined in our previous studies have had negligible concentrations of these comp o n e r ~ t s . ~ For , ~ J ~these components to be extracted in such large amounts under such mild conditions, they must have been present in the coal as free phenols (adsorbed on the coal surface). Comparison of the elemental composition and fa values of 320 "C residues of the two coals (Table IX) showed that the IB residue, with a higher H/C ratio and a slightly lower fa value than ABRl residue, contained a higher concentration of aliphatic material.
Summary and Conclusion The IB and Victorian coals studied in this paper had chemical structures significantly different from each other, as summarized below, but similar elemental compositions, so that the similarity of conversion and oil yield found for these coals strongly supports the earlier findings.
Therefore in this respect conversion and oil yield at 400 "C resemble such coal properties as volatile matter and specific energy.20 The main difference in structure is that in the IB coal the atomic H/C ratio of 0.83 arises not because of the presence of long-chain aliphatic molecules in the coal, but because of a relatively high number of short aliphatic side chains attached to the aromatic ring system. Evidence for this conclusion is most clearly seen in the comparison of the total ion chromatograms of the coal-derived oils, the solid-state 13CNMR spectra of the coals, and the relatively high H/C ratio of the residues and asphaltenes produced from liquefaction reactions a t 405 "C. At 320 "C the structural differences between IB and Victorian coals become important in determining their reactivity; for example, the explanation of the reactivity and atomic H/C ratio of a Victorian brown coal in terms of the relative concentration of host and guest material cannot be extended to IB coal. Although IB coal gave a higher conversion than ABRl for a reaction a t 405 "C in tetralin, in agreement with its higher atomic H/C ratio, a comparable, if not slightly smaller, amount of "guest" material was extracted at 320 "C from IB coal than from ABRl (Table VIII). The difference in the type of aliphatic materials in the two coals can perhaps be attributed to two main geological/geochemical reasons. First, the type of plant source material may have been significantly different in that the IB coal is considerably older (Jurassic) than Victorian brown coal (Miocene). Second, the original plant material may have been similar but the long-chain aliphatics have been degraded by either chemical oxidation and/or biochemical attack.21 The latter explanation could be of importance for the following reason. Significant long-chain material (Cl&.z) is seen in most Australian coal oils. The parent coal origins range from Permian age to the Miocene Epoch. Lower concentrations of long-chain aliphatic material are seen only in very high rank coals.8 Coals from an international subsuite originating from the Carboniferous Period also give long-chain aliphatic material.13 Furthermore, the position of the IB coal, close to the surface for such long periods, would enhance the possibility of aerobic degradation leading to smaller amounts of n-alkanes with generally shorter chain lengths. Similar results have been obtained for other Soviet low-rank c0a1s.l~ The origin of the relatively large amounts of short-chain aliphatic residues attached to the main aromatic structure of IB coal is not clear, but it could have arisen by alkylation reactions involving degradation products of long-chain material. Diasterenes in the IB oil may also be indicative of postdepositional microbiological activity in the coal.
Acknowledgment. We thank Mr. I. Liepa, CSIRO Division of Fuel Technology, Lucas Heights for GC/MS data; Dr. D. Cookson and Dr. P. Lloyd, BHP Melbourne Research Laboratories for 13C NMR data; Dr. D. Brockway, SECV Herman Research Laboratory for advice on analytical techniques; and Dr. M. Marshall, Monash University, for expert help and assistance. We thank the Coal Corporation of Victoria for financial support. (20) Neavel, R. C.; Smith, S. E.; Hippo, E. J.; Miller, R. N. Fuel 1986,
65, 312-320.
(21) Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence; Springer-Verlag: Berlin, FRG,1978; p 343.
