Fuel 81 (2002) 245±252 www.fuel®rst.com The characterization of coal macerals by diffuse re¯ectance infrared spectroscopy Helena Machnikowska a, Andrzej Krzton b, Jacek Machnikowski a,* a Institute of Chemistry and Technology of Petroleum and Coal, Wrocøaw University of Technology, GdanÂska 7/9, 50-344 Wrocøaw, Poland b Institute of Coal Chemistry, Polish Academy of Science, SowinÂskiego 5, 44-100 Gliwice, Poland Received 2 February 2000; revised 17 April 2001; accepted 12 July 2001 Abstract Diffuse re¯ectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0±91.5%C) using a centrifugal ¯oat±sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH2, and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CHar/CHal ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CHar/CHal and re¯ectance is observed up to vitrinite R0 value of 1.80%. For all macerals, the ratio CHar/CyC increases with re¯ectance, but at different rates. Structural parameters CHar/CHal and CHar/CyC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Coal macerals; Structure; Diffuse re¯ectance Fourier transform infrared 1. Introduction the study of coals, coal extracts and carbonization products [16±19]. It has also been successfully applied to character- Infrared spectroscopy is a method widely used for many ize coal blends [20] and to monitor oxidation of coals and years in the study of structure of coal and its derivatives. carbon materials [21,22]. Earlier works in the ®eld dealt mostly with the techniques Heterogeneity is one of the essential dif®culties in under- of specimen preparation and spectra recording, attributing standing the very complex constitution of coal. The study of absorption bands to corresponding functionalities and more homogeneous, microscopically distinguishable petro- determination\quad of extinction coef®cients [1±4]. graphic constituents of coal (macerals) is a possible way of The development of Fourier transform spectrometers, due decreasing the complexity. It is believed that on the basis of to improved sensitivity and accuracy of band position maceral composition and rank, it is possible to predict the measurement, allowed the semiquantitative evaluation of behaviour of whole coals during processing. Consequently, the contribution of various functional groups Ð hydroxylic maceral concentrates separated from different coals were [5±7], aromatic and aliphatic CH [5,8±10], carboxylic analysed to determine their chemical composition and relate COOH [11] and coal mineral matter [12]. FTIR method to the properties, which are relevant for different applica- was also proposed to study the type of hydrogen bonds in tions. These studies of macerals include different aspects of coal and coal extracts [13,14]. oxidation and combustion behaviour [23±26], graphitiz- In 1978, Fuller and Grif®ths [15] applied for the ®rst time ability [27], swelling properties [28,29], and liquefaction the diffuse re¯ectance Fourier transform infrared (DRIFT) behaviour [30,31]. spectroscopy to study various solids, including coal. Surprisingly, despite a good suitability of FTIR, espe- Currently, DRIFT technique is the most widely used in cially in DRIFT mode, relatively few works refer to maceral characterization using this technique. A large series of vitri- * Corresponding author. Tel.: 148-71-320-6350; fax: 48-71-322-1580. nites was studied using FTIR by Kuehn et al. [5] and Reisser E-mail address: machnikowski@nafta1.nw.pwr.wroc.pl et al. [10] to monitor the variation of distribution of hydro- (J. Machnikowski). gen between OH, aromatic CH and aliphatic CH groups. 0016-2361/02/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0016-236 1(01)00125-9 246 H. Machnikowska et al. / Fuel 81 (2002) 245±252 Table 1 Proximate and ultimate analyses of coals Coals Proximate analysis (wt%) Ultimate analysis (wt%, daf) a daf M A V C H N S Odiff Flame C31.1 13.6 4.8 40.6 77.0 4.9 1.2 0.9 16.0 Flame C31.2 9.1 5.4 35.6 79.3 4.5 1.3 0.8 14.1 Gas-¯ame C32 3.8 4.5 36.2 82.5 4.9 1.6 0.5 10.5 Gas C33 2.6 4.1 35.1 83.7 5.0 2.0 0.9 8.4 Gas-coking C34 1.2 9.3 35.1 85.6 5.4 1.7 0.9 6.5 Orthocoking C35.1 1.0 5.4 30.5 86.3 4.9 2.1 0.8 5.9 Orthocoking C31.2 0.8 4.4 22.0 89.5 5.2 2.0 1.0 2.3 Semicoking C37.1 1.7 7.8 21.8 89.4 4.0 1.5 0.7 4.4 Semicoking C37.1 1.5 6.9 20.0 90.6 3.7 1.9 0.5 3.3 Semianthracite C41 0.4 3.2 11.1 91.3 3.8 1.2 0.4 3.3 Anthracite C42 2.1 5.1 8.0 92.5 3.8 0.9 0.9 1.9 Results of Dyrkacz et al. [9] on concentrates of vitrinites, were adjusted individually for each sample. The ®nal liptinites and inertinites separated from low rank coals show separation products were dried in a vacuum oven at 608C. signi®cant differences in the chemical constitution both All the macerals obtained were analysed by proximate, between groups of macerals and within a given group. elemental and petrographic analyses and re¯ectivity The present work is an attempt in advanced structural measurement, according to Polish Standards. characterization of different macerals separated from wide rank coals from Polish basins using DRIFT technique. The 2.3. FTIR spectroscopy macerals studied include a series of vitrinites from the whole rank coals, liptinites which are distinguishable in Diffuse re¯ectance spectra were recorded with a FTS-165 the coal matrix, i.e. of subbituminous and high volatile Bio-rad spectrometer by co-adding 256 scans in the range bituminous coals and fusinites of different rank coals 4000±600 cm 21 at a resolution of 2 cm 21. The sample was provided that occurred in a form allowing the separation mixed with potassium bromide in the proportion 5/100 with a satisfactory purity. (% by weight). To linearize the relationship between concentration and spectral response, the Kubelka±Munk function was applied to the spectral data. The spectra were baseline corrected by subtracting the nonspeci®c back- 2. Experimental ground so that only the useful absorption bands of the 2.1. Coal characteristics analysed sample are visualized. The intensity and integral intensity of the bands were determined using local baseline. The macerals were isolated from 11 Polish coals of differ- ent rank, from subbituminous to anthracite, containing 3. Results and discussion 77.0±92.5%C. Proximate and ultimate analyses of coals are shown in Table 1. Anthracite C41 comes from Lower 3.1. Petrographic composition, proximate and ultimate Silesian Basin, whereas the others come from Upper Sile- analyses sian Basin. According to Polish classi®cation, the coals represent the types from ¯ame coal type 31.1 to anthracite The separated macerals are of high purity, except for type 42. liptinite (exinite) E34 that contains a considerable propor- tion of vitrinite (Table 2). The vitrinites and fusinites cover a 2.2. Maceral separation and analyses broad range of re¯ectivity, increasing with parent coal rank from 0.50 to 2.01% and from 1.29 to 3.73%, respectively. In the ®rst stage, lithotypes (vitrain, durain and fusain) R0 of vitrinites is inversely correlated with their V daf; however, were isolated from the parent coals by careful handpicking, there is no straight relationship with carbon content or H/C and then, the lithotypes were enriched by ¯oat±sink method ratio. Fusinites of higher rank coals have higher R0. There is using a mixture of toluene and carbon tetrachloride of suita- no correlation between R0 and elemental composition for ble density. Lithotypes, ground to the size of ,0.1 mm were the maceral, possibly due to a variable contribution of mixed with the liquid in the ratio of 1:10 and resulting semifusinite. Liptinites show distinctly lower re¯ectivity suspension was separated in centrifuge (20 min at (0.18±0.32) that slightly increases with parent coal rank 5000 rpm). The ef®ciency of separation was controlled by expressed by carbon or volatiles contents. microscopic analysis after each centrifugation step. Density Most of the separated macerals contain small amount of of the liquid and number of repetitive cycles of separation mineral matter (Table 3). The differences in elemental  H. Machnikowska et al. / Fuel 81 (2002) 245±252 247 Table 2 Petrographic analysis (% V/V, mmf) and re¯ectance (%) of macerals Sample Vitrinite Liptinite Fusinite Semifusinite Micrinite R0 Vitrinite V31.1 99.3 0.3 0.4 0.0 0.0 0.50 V31.2 98.4 1.0 0.3 0.0 0.3 0.58 V32 91.9 1.9 2.0 0.7 3.5 0.76 V33 97.6 1.1 0.7 0.2 0.4 0.87 V34 97.7 1.3 0.8 0.2 0.0 0.94 V35.1 96.6 1.4 1.1 0.6 0.3 1.14 V35.2 98.8 0.0 0.9 0.3 0.0 1.38 V37.1 94.7 0.0 3.6 0.9 0.8 1.30 V37.2 97.3 0.0 1.4 0.6 0.7 1.46 V41 95.1 0.0 3.9 0.0 1.0 1.81 V42 98.1 0.0 1.4 0.0 0.5 2.01 Liptinite (exinite) E31.1 1.4 93.1 5.5 0.0 0.0 0.18 E31.2 2.5 83.3 12.2 2.0 0.0 0.20 E33 6.2 72.2 17.6 4.0 0.0 0.27 E34 37.3 55.4 6.0 1.1 0.2 0.32 Fusinite F31.1 0.6 0.7 96.7 2.0 0.0 1.29 F31.2 4.5 0.8 91.0 3.6 0.0 1.73 F33 0.7 0.0 85.0 14.3 0.0 1.79 F34 2.8 0.5 87.8 8.9 0.0 2.39 F35.1 0.8 0.0 92.2 6.2 0.0 3.73 F42 13.4 0.0 83.1 3.4 0.0 3.69 Table 3 Proximate and ultimate analyses of macerals Sample Proximate analysis (wt%) Ultimate analysis (wt%, daf) M A V daf C H N S Odiff H/Cat Vitrinite V31.1 8.9 2.0 38.1 75.9 4.4 1.1 0.7 17.9 0.69 V31.2 5.4 1.0 35.7 78.1 4.6 1.3 0.6 15.3 0.70 V32 4.4 1.0 35.3 82.1 5.2 1.4 0.5 10.8 0.75 V33 3.0 0.4 34.3 83.4 5.2 2.2 0.3 8.9 0.74 V34 1.4 1.2 34.5 85.2 5.2 1.6 0.6 7.4 0.73 V35.1 1.6 1.3 29.8 87.6 5.3 2.3 0.6 4.2 0.72 V35.2 0.7 1.2 20.9 89.7 4.9 1.7 0.6 3.1 0.65 V37.1 1.1 1.5 23.8 86.9 4.8 1.5 0.7 6.1 0.66 V37.2 1.2 1.1 21.1 89.4 4.5 1.7 0.6 3.8 0.60 V41 0.4 0.1 11.4 89.6 4.4 1.3 0.4 4.3 0.58 V42 1.0 3.2 7.3 91.1 3.6 1.0 0.9 3.3 0.47 Liptinite (exinite) E31.1 4.0 1.1 64.8 76.6 6.5 1.4 1.0 14.5 1.01 E31.2 2.6 1.0 57.4 81.0 5.6 2.3 0.2 10.9 0.83 E33 3.0 0.3 53.0 86.7 6.1 2.0 0.3 4.9 0.84 E34 1.3 1.7 46.2 87.2 6.1 1.1 0.5 5.1 0.83 Fusinite F31.1 5.5 4.2 21.5 83.8 3.1 0.8 0.5 11.7 0.44 F31.2 4.7 3.6 19.1 84.6 3.6 1.6 0.4 9.8 0.51 F33 2.0 3.9 21.3 86.4 3.8 1.1 0.5 8.2 0.52 F34 0.5 7.1 11.8 92.8 3.3 1.2 0.4 1.1 0.41 F35.1 0.8 3.3 11.2 92.9 3.2 1.3 0.3 2.2 0.42 F42 0.9 0.8 5.3 93.0 2.5 0.8 1.4 2.3 0.32 248 H. Machnikowska et al. / Fuel 81 (2002) 245±252 Fig. 1. DRIFT spectra of vitrinites separated from different rank coals. composition between macerals of a given coal and within content suggests higher coali®cation degree of the macerals one maceral group with coal rank can be described as studied here. typical. For a given coal, the carbon content increases in the order: vitrinite , liptinite , fusinite; opposite to 3.2. Qualitative interpretation of infrared spectra the oxygen content. Volatile matter, hydrogen content and H/C atomic ratio increase in the order: fusinite , Representative DRIFT spectra of macerals are presented vitrinite , liptinite: in Figs. 1±3. The spectra of different rank vitrinites, lipti- Vitrinites separated for the study seem to be fairly repre- nites and fusinites contain the same characteristic absorp- sentative, in terms of elemental composition, of coals of a tion bands and differences in maceral composition and given rank. Slightly lower hydrogen content distinguishes rearrangement with coali®cation progress are re¯ected by vitrinites of high rank coals, compared to the data reported variation only in the position and intensity of peaks. in the literature [5,9,11,26]. Characteristic of the liptinites of the Polish coals is lower hydrogen content, when compared 3.2.1. Assignment of O±H stretching modes: region 3600± to the results of Dyrkacz et al. [9] and Milligan et al. [26]. 3100 cm 21 Very few data on elemental composition of fusinites are Vitrinites: The broad band in the range of 3600± available [9,26]. Higher carbon content and lower hydrogen 3100 cm 21 splits into two distinct peaks near 3600 and Fig. 2. DRIFT spectra of liptinites separated from different rank coals.  H. Machnikowska et al. / Fuel 81 (2002) 245±252 249 Fig. 3. DRIFT spectra of fusinites separated from different rank coals. 3500 cm 21 and somewhat overlapped bands near 3300 bands at 3697 and 3620 cm 21 in V37.2 spectrum can be and 3200 cm 21. According to Painter et al. [13], the band attributed to kaolinite [32]. near 3600 cm 21 can be attributed to free OH groups and the Liptinites: Intensity of absorption of OH groups of lipti- next to associated OH groups which form various types of nites E31.1 and E31.2 is comparable to that of correspond- hydrogen bonds: with p electrons of aromatic rings (OH± ing vitrinites, but for higher rank liptinites is distinctly p), coupled to ether oxygen (OH±ether O), and occurring in lower. IR spectra of liptinites show the same peaks as cyclic structure (cyclic OH), respectively. The spectra of were observed in the spectra of vitrinites. With the increas- vitrinites do not contain distinguishable band assigned to ing rank of liptinites, the intensity of absorption of OH self-associated OH groups at 3400 cm 21 and to acid-base groups decreases with a parallel increase in the contribution type bonds (OH±N) at 3150 cm 21, which were detected in of OH groups forming hydrogen bonds of OH±ether type. some coals and coal extracts [13,14]. In the case of low rank Intensity of absorption indicates that the contribution of OH vitrinites (up to V33), strong absorption at 3200 and groups decreases in the liptinites in the order: …OH cyclic 1 3300 cm 21 can cover the weaker band at 3150 cm 21. There- OH±N† . OH±ether O . OH±p . OH free: This trend is fore, the band near 3200 cm 21 should be considered as an the same as in low rank vitrinites. Comparison of absorption overlapped one derived from hydrogen bonded cyclic struc- pro®les in the OH region suggests that liptinites and vitri- ture of OH groups and, to lesser extent, OH±N bonds. nites from the same coal show similar content of hydrogen The intensity of absorption of OH groups decreases bonds of OH cyclic type; however, liptinites show lower distinctly up to V35.1 and varies slightly for higher rank content of OH±p bonds and free OH groups. As in the vitrinites, following closely the change of oxygen content. case of vitrinites, the spectra are lacking in the peak at The lowest rank vitrinites V31.1 and V31.2 show a strong 3400 cm 21. peak at 3200 cm 21 with shoulder near 3300 cm 21 and Fusinites: The spectra of F31.1 and F31.2 are comparable weaker at 3510 and 3605 cm 21. The evaluation of band to corresponding spectra of vitrinites. Based on the intensi- pro®le leads to the conclusion that contribution of different ties of bands, the contributions of associated OH groups OH groups decreases in the order: (OH cyclic 1 OH± in low rank fusinites (F31.1±F33) can be estimated as N) . OH±ether O . OH±p . OH free. With the increasing follows: (OH cyclic 1 OH±N) . OH±ether O . OH±p. carbon content and decreasing total OH content in vitrinites, As the fusinite rank increases, the intensity of OH bands the contribution of cyclic OH bonds decreases and that of diminishes as a result of decreasing oxygen content. Starting OH±ether and OH±p hydrogen bonds increases. In V34 from F34, only a weak shoulder indicates the presence of (85.2% C), the principal hydrogen bond is that of OH± associated OH±ether O groups. The band of OH free groups ether type; in higher rank vitrinites (up to V41), the main is overlapped by mineral matter peaks and determination of hydrogen bonds are of OH±p types. Cyclic hydrogen bonds the contribution of free OH groups in fusinite structure is are very rare in higher rank vitrinites and disappear in V41 dif®cult. (89.6% C). Contrary to the data of Chen et al. [14], the absorption band near 3500 cm 21 assigned to OH±p hydro- 3.2.2. Assignment of C±H stretching modes: region 3100± gen bond is observed in all vitrinites spectra. The same is 2800 cm 21 with band due to OH free hydroxyl. The absorption can be Vitrinites: In the region of stretching vibration of alipha- enhanced by mineral constituent contribution. Clearly, the tic CH group (3000±2800 cm 21) in vitrinite spectra appear 250 H. Machnikowska et al. / Fuel 81 (2002) 245±252 peaks at 2950, 2920 cm 21, attributed to asymmetric CH3 and asymmetric CH2 vibration and at 2870 cm 21, attributed to symmetric CH3 and CH2 vibrations. In addition, the band at 2980 cm 21, which is characteristic of low rank coal and assigned to methyls linked to oxygen groups [17], appears in the spectra of V31.1 and V31.2. The strong absorption of OH groups causes deformation of CH stretching bands in these vitrinites. The intensity of absorption of aliphatic groups varies in dependence on vitrinite rank. Up to V34, the band at 2950 cm 21 is stronger than that at 2920 cm 21, showing the great contribution of methyl groups. In higher rank vitrinites, the proportion of methyl groups decreases. The vitrinite from anthracite (V42) shows only a weak band at 2880 cm 21 that can be assigned to methine groups. The absorption band of aromatic CH stretching vibrations at 3050 cm 21 is very weak in the lowest rank vitrinites. Start- ing from V32, the peak at 3050 cm 21 is clearly distinguish- Fig. 4. Variation of intensity of 1600 cm 21 band of macerals with carbon able. Its intensity increases with vitrinite rank and for content. anthracite overcomes that due to aliphatic groups. Liptinites: Higher intensity of bands due to aliphatic CH bands derived from stretching vibrations of carbonyl groups and lowering of band due to aromatic CH basically dis- at 1695 cm 21 (V31.1 and V31.2) attributed to carboxylic tinguish spectra of liptinites from those of corresponding acids and at 1660 cm 21 (V31.2) attributed to conjugated vitrinites (Fig. 2). The differences between macerals almost ketones or quinones [11]. In the spectrum of V31.1, the disappear for medium rank coal C34. Spectra of liptinites band at 1695 cm 21 is very strong. Carbonyl group bands contain only two absorption bands attributed to aliphatic CH are observed as a weak shoulder in the spectra of V32± groups near 2930 and 2860 cm 21. It is characteristic that V41. Spectrum of V42 shows very weak absorption at their intensity is similar for all liptinites. The contribution 1677 cm 21 attributed to quinones. of CH2 modes is considerably higher than in corresponding Liptinites: Intensity of aromatic CyC band of liptinites is vitrinites. This is in agreement with the established view stable, independent of coal rank. Liptinites E31.1±E33 are on the chemical constitution of liptinites, implying the characterized by considerably higher absorption due to presence of longer aliphatic chains and naphtenic rings. carbonyl groups near 1700 cm 21 than corresponding vitri- The aromatic stretching band of liptinites at 3050 cm 21 is nites. For the liptinite E31.1, the band is stronger than that at very weak and in the spectra of low rank liptinites strongly 1600 cm 21 and its situation at 1709 cm 21 suggests a great overlapped by OH band. contribution of carboxylic groups. The intensity of car- Fusinites: The principal discrepancies between spectra of boxylic band decreases markedly with rank and for E33 is fusinites and vitrinites separated from the same coal are in threefold lower than for E31.1. The explanation of the beha- lower absorption from aliphatic CH groups and higher viour can be extensive decarboxylation characteristic of this absorption due to aromatic CH and CyC groups in the stage of coali®cation; however, taking account of a low case of fusinites. Spectra of fusinites show a weak band of content of oxygen in E33, the contribution of carbonyl aliphatic CH groups with maximum at 2950, 2920 and oxygen is remarkable and higher than that in vitrinite. 2860 cm 21. Their intensity decreases with an increase in Fusinites: The band at 1600 cm 21 is strongest in the spec- coali®cation and the band disappears in F42 spectrum. tra of fusinites isolated from low rank coals and intensity The intensity of aromatic CH bands at 3050 cm 21 is similar decreases with increasing carbon contents. It is interesting for fusinites up to F35 and decreases signi®cantly for F42 to note the similar intensity of the band of fusinites of the due to high condensation degree. same carbon content (F34, F35.1 and F42), despite their being separated of different rank coals. Spectra of F31.1, 3.2.3. Assignment of aromatic CyC and CyO stretching F31.2 and, to lower extent, that of F33 show relatively modes: region 1800±1550 cm 21 strong absorption due to carboxyl groups at 1705 cm 21. In Vitrinites: The band at 1600 cm 21 assigned to stretching this absorption range, spectra of fusinites are similar to the CyC groups in aromatic ring (n CyC) shows variable inten- spectra of liptinites. sity with a maximum for V33 (Fig. 4). Distinctly lower intensity of the band inV42 spectrum is due to weaker absorption of CyC groups in the condensed aromatic 3.2.4. Assignment of out-of-plane aromatic C±H vibration systems. The position of band maximum is slightly shifted modes: region 900±700 cm 21 to lower wave numbers with the increasing vitrinite rank. Vitrinites: All the spectra show the bands with a maxi- Characteristic of the low rank vitrinites is the presence of mum near 860, 815 and 750 cm 21, corresponding to isolated  H. Machnikowska et al. / Fuel 81 (2002) 245±252 251 CH groups, two or three neighbouring CH groups and four neighbouring CH groups, respectively. Up to V37.1, those near 860 and 815 cm 21 are stronger than that near 750 cm 21. In the spectra of anthracites, intensity of the band near 815 cm 21 is lower than that near 860 and 750 cm 21. The variation in the intensity with rank can be related to the substitution degree that is considerably higher for vitrinites V31±V33. The comparison of intensity of absorption in the aromatic CH out-of-plane region shows that there are two ranges of signi®cant increase in aromatic CH group content. The ®rst for low rank vitrinites (76± 82%C) is associated mostly with splitting of oxygen groups and the second in the range of highest rank vitrinites indi- cates a considerable increase in aromaticity within anthra- cites. In addition, in the spectra of V31.1 and V31.2, the bands assigned to aliphatic CH at 780 and 730 cm 21 [5] are Fig. 5. Variation of CHar/CHal ratio of macerals with carbon content. easily distinguishable. Low ash content in vitrinites allows the assumption that the absorption of mineral compounds is negligible. work [5]. It is interesting to note that the sharp increase in Liptinites: Three bands attributed to aromatic CH groups CHar/CHal ratio between V37.2 and V41 correlates well with near 860, 815 and 750 cm 21 are present in the spectra of re¯ectance value, as a measure of rank, but not with H/C liptinites. The weak shoulder at 730 cm 21 can be assigned to atomic ratio. CHar/CHal ratio of liptinites is lower than that aliphatic CH rocking mode. Aromatic CH bands are of of vitrinites and practically does not vary with carbon lower intensity than in corresponding vitrinites spectra. content. The ratio of CHar/CHal of fusinites is higher than The increase in the intensity of absorption bands in the that of vitinites from the same coal and increases relatively order: 860 cm21 , 815 cm21 , 750 cm21 can indicate a slowly with carbon content up to F35.1. Fusinite from lower contribution of isolated hydrogen, i.e. lower conden- anthracite is distinguishable from the former by distinctly sation degree of aromatic systems. higher aromaticity, despite very similar carbon content. Fusinites: The intensity of out-of-plane CHar deformation Liptinites and vitrinites show an increase in CHar/CHal bands near 875, 813 and 750 cm 21 varies irregularly, all ratio with their re¯ectance (Fig. 6). A linear correlation is bands being stronger than in corresponding vitrinites. The observed for vitrinites in the R0 range up to 1.81%. There is marked increase in intensity is observed in the range F31.1± no correlation between CHar/CHal ratio and re¯ectance of F33, and then, the changes are relatively smaller. In the fusinites. lowest rank fusinites (F31.1 and F31.2), the band intensity Fig. 7 presents the relationship between the ratio of CHar/ decreases, as in liptinites, in the order: 750 cm21 . CyC (integrated area of aromatic CH out-of-plane bending 813 cm21 . 875 cm21 : The band at 875 cm 21 predomi- to aromatic CyC stretching mode) and re¯ectance. For all nates in the higher rank. The spectra of F34 and F35.1 are macerals, the ratio CHar/CyC increases with re¯ectance, but most similar to those of corresponding vitrinites. at different rates. The strongest changes are observed in the The absorption pro®les in the aromatic CH region suggest distinct differences in condensation and substitution degree between maceral groups and, for vitrinites and fusinites, also within the groups. 3.3. Semiquantitative interpretation of DRIFT spectra Semiquantitative analysis of DRIFT spectra was used to calculate the structural parameters that allow the character- ization of the variation of maceral structure with increasing coali®cation degrees. CHar/CHal ratio, determined as a ratio of areas of absorp- tion bands at 3050 cm 21 to that between 3000 and 2800 cm 21, is plotted vs. carbon content and re¯ectivity of macerals, respectively, in Figs. 5 and 6. In the case of vitri- nites, CHar/CHal ratio increases at a low rate and linearly for carbon content between 78 and 89% and much rapidly for higher rank (Fig. 5). Similar trend was reported in an earlier Fig. 6. Variation of CHar/CHal ratio of macerals with re¯ectivity. 252 H. Machnikowska et al. / Fuel 81 (2002) 245±252 with coali®cation within low rank coals and anthracites. Aromatic units present in liptinites seem to be of lesser condensation/substitution degree than those of vitrinites and fusinites. The structural parameters CHar/CHal and CHar/CyC calculated from DRIFT spectra are very useful in monitor- ing the differences among macerals of a given coal and following structural rearrangement occurring with coal rank. References [1] Bent R, Brown JK. Fuel 1961;40:47. [2] Oelert HH. Brennst Chem 1967;48:331. [3] Durie RA, Shewchyk Y, Strenhell S. Fuel 1966;45:99. Fig. 7. Variation of CHar(900±700)/CyC ratio of macerals with re¯ectivity. [4] Fujii S, Osawa Y, Sugimura S. Fuel 1970;49:68. [5] Kuehn DW, Snyder RW, Davis A, Painter PC. Fuel 1982;61:682. [6] Solomon PR, Carangelo RM. Fuel 1982;61:663. case of liptinites, and the lowest in fusinites. The relation- [7] Tooke PB, Grint A. Fuel 1983;62:1003. ship is linear for liptinites, fusinites and for vitrinite in the [8] Solomon PR, Carangelo RM. Fuel 1988;67:949. range from the lowest rank to semianthracite …R0 ˆ 1:81%†: [9] Dyrkacz GR, Bloomquist CAA, Solomon PR. Fuel 1984;63:536. [10] Reisser B, Starsinic M, Squires E, Davis A, Painter PC. Fuel 1984;63:1253. 4. Conclusions [11] Starsinic M, Otake Y, Walker Jr PL, Painter PC. Fuel 1984;63:1002. [12] Painter PC, Coleman MM, Jenkins RG, Whang PW, Walker Jr PL. Evaluation of DRIFT spectra of macerals separated from Fuel 1978;57:337. [13] Painter PC, Sobkowiak M, Youtheff J. Fuel 1987;66:973. different rank coals shows that contribution of aromatic and [14] Chen C, Gao J, Yan Y. Energy Fuels 1998;12:446. aliphatic CH groups is the primary feature discriminating [15] Fuller MP, Grif®ths PR. Am Lab 1978;10:69. between constituents of a given coal. CHar/CHal ratio [16] Fuller MP, Hamadeh JM, Grif®ths PR, Lowenhaupt DE. Fuel enhances from liptinite through vitrinite to fusinite. The 1982;61:529. ratio does not vary with carbon content in liptinites, but [17] Wang SH, Grif®ths PR. Fuel 1985;64:229. [18] Cai MF, Smart RB. Energy Fuels 1994;8:369. increases in vitrinites and fusinites. In the case of liptinites [19] Krzton A, Cagniant D, Gruber R, Pajak J, Fortin R, Rouzaud JN. Fuel and vitrinites, a linear relationship between CHar/CHal and 1995;74:217. re¯ectance is observed up to vitrinite R0 value 1.8%. There [20] Frederiks PM, Kabayashi R, Osborn PR. Fuel 1985;64:229. is no correlation between the CHar/CHal ratio and re¯ectance [21] Pisupati SV, Scaroni AW. Fuel 1993;72:531. of fusinites. The CHar/CyC ratio increases with re¯ectance [22] Koch A, Krzton A, Finqueneisel G, Heintz O, Weber J-V, Zimny T. Fuel 1998;77:563. for all macerals, but at different rates. [23] Crelling JC, Hippo EJ, Woerner BA, West Jr DP. Fuel 1992;71:151. Lowest rank coal macerals (C31.1 and C31.2) are char- [24] Gryglewicz G, Boudou J-P, Boulegue J, Machnikowska H, JasienÂko acterized by comparable content of hydroxylic group that S. Fuel 1995;74:349. occurs as free and forms similar types of hydrogen bonds. [25] Hindmarsh CJ, Wang W, Thomas KM, Crelling LC. Fuel 1994; Associated groups that form OH±cyclic and/or OH±N 73:1229. [26] Milligan JB, Thomas KM, Crelling JC. Fuel 1997;76:1249. bonds are most abundant in the macerals. In the higher [27] JasienÂko S, Kidawa H. Chem Stos 1986;30:27. rank coals, vitrinites are richer in OH groups than liptinites [28] JasienÂko S, Machnikowska H, SÂwietlik U, Kaczmarska H. Proceed- and fusinites. Carbonyl groups appear mainly as coniugated ings of International Conference on Coal Science, Oviedo 1995. Coal ketones and quinones in low rank vitrinites, but as Science and Technology, vol. 24. 1995. p. 389. carboxylic groups in liptinites and low rank fusinites. [29] Milligan JB, Thomas KM, Crelling JC. Energy Fuels 1997;11:364. [30] King H-H, Dyrkacz GR, Winans RE. Fuel 1984;63:341. Evaluation of intensity of bands within 900±700 cm 21 [31] Machnikowska H, JasienÂko S. Proceedings of International Confer- suggests a considerable substitution/condensation of ence on Coal Science, Sydney, 1985. p. 673. aromatic ring in all vitrinites. Its degree strongly increases [32] Cooke NE, Fuller OM, Gaikwad RP. Fuel 1986;65:1254.