- Email: [email protected]
Case study of igneous intrusion effects on coal nitrogen functionalities
International Journal of Coal Geology 86 (2011) 291–294
Contents lists available at ScienceDirect
International Journal of Coal Geology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j c o a l g e o
Case study of igneous intrusion effects on coal nitrogen functionalities Bruno Valentim ⁎, Alexandra Guedes, Sandra Rodrigues, Deolinda Flores Centro de Geologia e Departamento de Geociências, Ambiente e Ordenamento do Território da Faculdade de Ciências, Universidade do Porto, 4169-007-Porto, Portugal
a r t i c l e
i n f o
Article history: Received 16 February 2011 Accepted 19 February 2011 Available online 26 February 2011 Keywords: Bukit Asam coal Natural coke Nitrogen XPS
a b s t r a c t This study presents the results of the nitrogen XPS analysis performed on a set of four Bukit Asam (Indonesia) low-rank coals and on a related natural pyrolysis product formed after an igneous intrusion. Low-rank coal nitrogen XPS sub-peak is dominantly pyrrolic, with subordinate quaternary and pyridinic. Dike intrusions are responsible for transformation of these nitrogen forms nitrogen to “graphitic” quaternary nitrogen. The transformation of nitrogen is similar to that exhibited by laboratory prepared pyrolysis products of other coals. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Whatever the maceral composition, coal nitrogen is mostly organic and dominantly presented as pyrrolic, pyridinic, and quaternary nitrogen functional groups within the carbon matrix (Boudou et al., 2008; Gammon et al., 2003; Kelemen et al., 1994; Kelemen et al., 2007; Pels et al., 1995). Over a wide coal rank range (carbon 65–95 wt. %, daf), the nitrogen functional forms are generally composed of 50%– 80% pyrrole (N-5), 20%–40% pyridine (N-6), and 0%–20% quaternary (N-Q) (Mitra-Kirtley et al., 1993; Thomas, 1997); however, their amounts appear to vary with coal rank. The effects of igneous intrusions on coal nitrogen have been studied by infra-red spectroscopy (e.g. Fredericks et al., 1985), but there have been no reports on coal nitrogen transformations during natural pyrolysis processes using X-ray photoelectron spectroscopy (XPS). In this work, we examined five fresh samples of four coals from the Bukit Asam coal mine and the pyrolysis product by the igneous intrusion. 2. Methods The samples were obtained at the Bukit Asam coal mines complex situated near Tanjung Enim town in South Sumatra. The coal belongs to the Miocene Muara Enim Formation of South Sumatra Basin and locally was altered by igneous intrusions of Plio-Pleistocene age (ICCP, 2006). Chemical and petrographic compositions of the samples are given in Tables 1–3. Petrographic analyses were performed on coal pellets prepared according to ASTM D2797-04 (2004) using a Leitz Orthoplan microscope equipped with a high resolution digital camera and a ⁎ Corresponding author at: Rua do Campo Alegre, 687, 4169-007 Porto, Portugal. Tel.: +351 220402489; fax: +351 220402490. E-mail address: [email protected] (B. Valentim). 0166-5162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2011.02.008
Diskus–Fossil software. The maceral compositions and mean random reflectance of huminite and pyrolysis product were determined following ISO standard procedures, ISO 7404-3 (1994) and ISO 7404-5 (2009), respectively. Maceral nomenclature and coal classification are in accordance with the International Committee for Coal and Organic Petrography (ICCP, 1971, 2001; Sýkorova et al., 2005) and ISO 11760 (2005), respectively. To avoid bias originated by oxidation, samples were crushed in air to 212 μm in an agate mortar to expose new fresh surfaces immediately before XPS analysis and then pressed at 8 t/cm2. XPS analysis was performed using an ESCALAB 200A – V.G.SCIENTIFIC system equipped with a dual-anode Al X-ray source and a hemispherical analyser. The energy intensity is 15 keV. The photoelectron spectrum was taken with 20 eV pass energy. The software XPSPEAK was used in the spectra curve resolution and data treatment. Pyrrolic (N-5), pyridinic (N-6) and quaternary nitrogen (N-Q) were observed as assigned by Boudou et al. (2008 and references therein) on other samples. The proximate and ultimate analysis (Table 1) and petrographic data (Table 2) show that the samples are low-rank A coals (subbituminous) with low-ash yields and sulfur contents. Nitrogen content (wt.%, daf) is within the nitrogen range found in other coals with the same rank (van Krevelen, 1993). Petrographically, the coals are huminite-rich with ca. 10% minerals. However, funginite and resinite are also very common in these coals (Fig. 1A), and their occurrence may be related to funginite– resinite associations due to incorporation of fungus into resinite as described by Hower et al. (2010). 3. Results and discussion Coal intruded by igneous rocks is not an uncommon occurrence (Finkelman et al., 1998; Golab and Carr, 2004). Igneous intrusions not only elevated inorganic trace elements and minerals in coal (Dai and
292
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
Table 1 Proximate and ultimate analysis (wt.%) and atomic ratios of H/C, O/C, and N/C. Sample
Moisturea.r.
Ash
TE_59 TE_63 TE_67 TE_70 Nat. coke
18.7 10.5 8.6 1.5 0.4
3.9 1.8 1.1 1.2 6.5
d
VMdaf
Cdaf
Hdaf
Ndaf
Odaf
Sdaf
H/C
O/C
N/C
46.5 45.0 44.4 45.0 nd
62.4 69.0 72.0 78.1 79.9
6.0 5.6 5.8 5.6 1.5
1.4 1.1 1.2 1.2 0.9
29.6 24.0 20.8 14.3 17.3
0.6 0.3 0.2 0.8 0.3
1.14 0.98 0.97 0.86 0.23
0.36 0.26 0.22 0.14 0.16
0.02 0.01 0.01 0.01 0.01
VM: volatile matter; a.r.: as received basis; d: dry basis; daf: dry and ash-free basis.
Table 2 Petrographic composition (vol.%; mineral matter free) and mean random reflectance (Rr,%) of the studied samples. Sample
Rr %
Huminite
Inertinite
Liptinite
TE_59 TE_63 TE_67 TE_70 Nat. coke
0.33 0.31 0.41 0.36 6.02*
68 75 83 74 nd
26 21 12 16 nd
7 5 5 10 nd
Rr: huminite and vitrinite (*) mean random reflectances; nd: not determined.
Table 3 XPS N (1s) total nitrogen, nitrogen XPS sub-peaks, and nitrogen functionality ratios. Sample
Total N (N per 100 °C)
TE_59 TE_63 TE_67 TE_70 Nat . coke
1.59 0.90 1.04 0.96 0.58
Nitrogen functionalities (mol%)
Nitrogen functionality ratio
N-6
N-5
N-Q
N-6/N-5
N-6/N-Q
13 20 19 23 32
55 54 56 53 28
32 26 25 24 41
0.23 0.37 0.34 0.43 1.15
0.41 0.77 0.76 0.93 0.78
N-6: pyridinic nitrogen; N-5: pyrrolic nitrogen; N-Q: quaternary nitrogen.
Ren, 2007; Dai et al., 2011; Finkelman et al., 1998; Stewart et al., 2005), but also affected organic matter (Cooper et al., 2007; Rimmer et al., 2009). Igneous dike intrusions locally pyrolysed some of the coal
of this study (Fig. 1B), and also other samples geographically nearby (Susilawati and Ward, 2006), due to the very high temperatures derived from igneous intrusions in these zones (Barker et al., 1998; Guedes et al., 2005). The effects of igneous intrusions on coal described by Susilawati and Ward (2006) include the elevated coal rank (vitrinite reflectance up to at least 4.17%), volatile matter loss, and thermal metamorphism of minerals. The sample of the pyrolysis products in this study has a high random reflectance (Fig. 1C and D; Table 2) corresponding, at least, to meta-anthracite and semi-graphite (Kwiecinska and Petersen, 2004). Not surprisingly the pyrolysis product no longer exhibits low-rank coal microstructure (Fig. 1A) but is characterized by intercalations of mosaics material with “metaanthracite”-like material (Fig. 1C, D). Funginite is the only recognizable maceral in the product, probably due to its low-reactivity (Fig. 1C). The elemental contents of the pyrolysis product are characterized by low-carbon, low-nitrogen, and high-oxygen (wt.%, daf). Most probably, the heat from igneous intrusions, the introduction of hot fluids, and the moisture remobilized from the original low-rank coal (Susilawati and Ward, 2006) caused the decrease of graphitic carbon content, which was lost as CH4 and CO2 (Barker et al., 1998), organic nitrogen, or/and NH4+, HCN, NH3, and N2 (Aho et al., 1993; Boudou and Espitalié, 1995; Johnsson, 1994). The N-5 sub-peak intensity is the highest of all coals of this study (Table 3; Fig. 2). This is in agreement with results published on other low-rank coals (Friebel and Köpsel, 1999; Kelemen et al., 2006) and corresponds to pyrrolic nitrogen mainly resulted from convertion/
Fig. 1. (A) Abundance of funginite in low-rank coal (TE-59 sample; reflected light, oil immersion); (B) Natural coke associated with Plio-Pleistocene igneous intrusions in Bukit Asam coalfield; (C) Natural coke (Nc), meta-anthracite like (Ma), funginite (F) (reflected polarized light, oil immersion); (D) Pyrolytic carbon on the edges of natural coke (Nc) and meta-anthracite (Ma) (reflected polarized light, oil immersion).
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
293
The thermal rupture of both pyrrole and pyridine nitrogen could in part explain the decrease of these aromatic rings containing nitrogen heteroatoms. However, during the nitrogen transformation path, it is more likely that several other mechanisms also occurred, leading to the increase of pyridinic nitrogen by: (i) “ring expansion” whereby the 5-membered ring is opened and incorporates another C atom (Pels et al., 1995), and (ii) transformations of amide, amine and protonated pyridinic (quaternary nitrogen) structures (Kelemen et al., 1994, 2006). However, the considerable increase in the N-Q peak observed in the pyrolysis product cannot be directly explained by these transformations, but may be explained by pyridine nitrogen transformation to “graphitic” quaternary nitrogen, following thermal reactions and hot fluids interaction with the coals. The results are consistent with laboratory studies of pyrolysis. Studies of products formed at 800–900 °C in inert atmosphere revealed the appearance of significant levels of quaternary nitrogen associated with the development of larger polynuclear aromatic carbon structures (Friebel and Köpsel, 1999; Kelemen et al., 1999). Less stable nitrogen structures abundant in low-rank coals, such as pyrrolic nitrogen, are gradually transformed to more stable structures, such as pyridine (Pels et al., 1995). At severe heating conditions, pyridine is preferentially transformed to quaternary nitrogen (Kawashima et al., 2002; Stanczyk, 2004). For example, during condensation of the carbon matrix, nitrogen atoms are incorporated in the graphene layers, and then replace carbon
cyclization of amide nitrogen in peats due to thermal stress (Kelemen et al., 2006). The intensities of the N-Q and N-6 sub-peaks (Fig. 2) are considerably lower than that of the N-5 sub-peak. The N-Q sub-peak has a slightly higher intensity peak than the N-6 sub-peak, except for sample Te-59, where a marked difference is present. Similar peaks were also observed in low rank coals (Friebel and Köpsel, 1999; Kelemen et al., 2006) and in low maturity type I and II kerogens (Kelemen et al., 2007). Although XPS cannot distinguish quaternary nitrogen between amide and amine nitrogen forms (at 401.6 ±0.3 eV), it is believed that, in low rank coals, pyridinic nitrogen results from the transformations of amide, amine, and the elimination of oxygen from pyridones (Geng et al., 2009; Kelemen et al., 1994, 2006; Mitra-Kirtley et al., 1993). The N-Q sub-peak in the XPS spectra of the samples studied are thus assigned to protonated pyridinic forms (Pels et al., 1995), which were possibly derived from the interaction between pyridinic nitrogen and neighbouring phenolic groups (Friebel and Köpsel, 1999; Kelemen et al., 1994). The relative abundance of the nitrogen forms of Bukit Asam coal samples and the natural pyrolysis product is compared. Table 3 and Fig. 2 show that (i) in the pyrolysis product the N-5 value is approximately one half of the coals studied and is no longer the dominant type; (ii) N-6 increases moderately; and, (iii) N-Q increases considerably and became the dominant form.
TE59
Relative intensity
TE63
394
N-6 N-5 N-Q
396
398
400
402
404
406 394
396
398
400
402
404
406
400
402
404
406
TE67
Relative intensity
TE70
394
N-6 N-5 N-Q
396
398
400
402
404
406 394
396
398
Relative intensity
Binding Energy (eV)
394
Natural coke
N-6 N-5 N-Q
396
398
400
402
404
406
Binding Energy (eV) Fig. 2. XPS nitrogen (1s) spectra and curve resolution of fresh samples from Bukit Asam coal and Bukit Asam natural coke.
294
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
atoms and form quaternary nitrogen as organic nitrogen N-C3 atoms (Furimsky and Ohtsuka, 1997). Acknowledgements The authors thank the Fundação para a Ciência e a Tecnologia (Portugal) and FEDER (UE) for financing the Projects POCI/CLI/60557/ 2004 and PPCDT/CLI/60557/2004. We are grateful to Dr. Shifeng Dai, Professor Michael Wilson and two anonymous reviewers for helping us improve this paper. References Aho, M.J., Hämäläinen, J.P., Tummavuori, J.L., 1993. Conversion of peat and coal nitrogen through HCN and NH3 to nitrogen oxides at 800 °C. Fuel 72, 837–841. ASTM D2797-04, 2004. Standard practice for preparing coal samples for microscopical analysis by reflected light. American Society for Testing and Materials, Philadelphia, USA. 4 pp. Barker, C.E., Bone, Y., Lewan, M.D., 1998. Fluid inclusion and vitrinite-reflectance geothermometry compared to heat-flow models of maximum paleotemperature next to dikes, western onshore Gippsland Basin, Australia. International Journal of Coal Geology 37, 73–111. Boudou, J.P., Espitalié, J., 1995. Molecular nitrogen from coal pyrolysis: kinetic modelling. Chemical Geology 126, 319–333. Boudou, J.P., Schimmelmann, A., Ader, M., Mastalerz, M., Sebilo, M., Gengembre, L., 2008. Organic nitrogen chemistry during low-grade metamorphism. Geochimica et Cosmochimica Acta 72, 1199–1221. Cooper, J.R., Crelling, J.C., Rimmer, S.M., Whittington, A.G., 2007. Coal metamorphism by igneous intrusion in the Raton Basin, CO and NM: implications for generation of volatiles. International Journal of Coal Geology 71, 15–27. Dai, S., Ren, D., 2007. Effects of magmatic intrusion on mineralogy and geochemistry of coals from the Fengfeng-Handan Coalfield, Hebei, China. Energy and Fuels 21, 1663–1673. Dai, S., Ren, D., Chou, C.-L., Finkelman, R.B., Seredin, V.V., Zhou, Y., 2011. Geochemistry of trace elements in Chinese coals: a review of abundances, genetic types, impacts on human health, and industrial utilization. International Journal of Coal Geology. doi:10.1016/j.coal.2011.02.003. Finkelman, R.B., Bostick, N.H., Dulong, F.T., Senftle, F.E., Thorpe, A.N., 1998. Influence of an igneous intrusion on the inorganic geochemistry of a bituminous coal from Pitkin County, Colorado. International Journal of Coal Geology 36, 223–241. Fredericks, P.M., Warbrooke, P., Wilson, M.A., 1985. A study of the effect of igneous intrusions on the structure of an Australian high volatile bituminous coal. Organic Geochemistry 8, 329–340. Friebel, J., Köpsel, R.F.W., 1999. The fate of nitrogen during pyrolysis of German low rank coals – a parameter study. Fuel 78, 923–932. Furimsky, E., Ohtsuka, Y., 1997. Formation of nitrogen-containing compounds during slow pyrolysis and oxidation of petroleum coke. Energy and Fuels 11, 1073–1080. Gammon, W.J., Kraft, O., Reilly, A.C., Holloway, B.C., 2003. Experimental comparison of N(1s) X-ray photoelectron spectroscopy binding energies of hard and elastic amorphous carbon nitride films with reference organic compounds. Carbon 41, 1917–1923. Geng, W., Kumabe, Y., Nakajima, T., Takanashi, H., Ohki, A., 2009. Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS). Fuel 88, 644–649. Golab, A.N., Carr, P.F., 2004. Changes in geochemistry and mineralogy of thermally altered coal, Upper Hunter Valley, Australia. International Journal of Coal Geology 57, 197–210. Guedes, A., Noronha, F., Prieto, A.C., 2005. Characterisation of dispersed organic matter from lower Palaeozoic metasedimentary rocks by organic petrography, X-ray
diffraction and micro-Raman spectroscopy analyses. International Journal of Coal Geology 62, 237–249. Hower, J.C., O´Keefe, J.M.K., Volk, T.J., Watt, M.A., 2010. Funginite–resinite associations in coal. International Journal of Coal Geology 83, 64–72. ICCP (International Committee for Coal and Organic Petrology), 1971. International handbook of coal petrography, International Committee for Coal Petrography2nd ed. Centre National de la Recherche Scientifique, Academy of Sciences of the URSS, Paris. ICCP (International Committee for Coal and Organic Petrology), 2001. The new inertinite classification (ICCP System 1994). Fuel 80, 459–471. ICCP (International Committee for Coal and Organic Petrology), 2006. Field trip guide to Bukit Asam coal mine, Tanjung Enim. Indonesia Center for Geological Resources. 58th meeting of the ICCP, Bandung (West Java, Indonesia) 3 – 9 September 2006, and Asia Pacific Symposium on Lower Rank Coal – integrating lower rank coals with industrialization in the 21st century. International Organization for Standardization (ISO), 1994. Methods for the petrographic analysis of bituminous coal and anthracite – Part 3: Method of determining maceral group composition. ISO 7404–3, Geneva, Switzerland. 4 pp. International Organization for Standardization (ISO), 2005. Classification of coals. ISO 11760, Geneva, Switzerland. 9 pp. International Organization for Standardization (ISO), 2009. Methods for the Petrographic Analysis of Coals – Part 5: Method of Determining Microscopically the Reflectance of Vitrinite. ISO 7404–5, Geneva, Switzerland. 4 pp. Johnsson, J.E., 1994. Formation and reduction of nitrogen oxides in fluidized-bed combustion. Fuel 73, 1398–1415. Kawashima, H., Wu, Z., Sugimoto, Y., 2002. Change of nitrogen functionality of 15N-enriched condensation products during pyrolysis. Fuel 81, 2307–2316. Kelemen, S.R., Gorbaty, M.L., Kwiatek, P.J., 1994. Quantification of nitrogen forms in Argonne Premium coals. Energy and Fuels 8, 896–906. Kelemen, S.R., Freund, H., Gorbaty, M.L., Kwiatek, P.J., 1999. Thermal chemistry of nitrogen in kerogen and low-rank coal. Energy and Fuels 13, 529–538. Kelemen, S.R., Afeworki, M., Gorbaty, M.L., Kwiatek, P.J., Sansone, M., Walters, C.C., 2006. Thermal transformations of nitrogen and sulfur forms in peat related to coalification. Energy and Fuels 20, 635–652. Kelemen, S.R., Afeworki, M., Gorbaty, M.L., Sansone, M., Kwiatek, P.J., Walters, C.C., Freund, H., Siskin, M., Bence, A.E., Curry, D.J., Solum, M., Pugmire, R.J., Vandenbroucke, M., Leblond, M., Behar, F., 2007. Direct characterization of kerogen by X-ray and solid-state 13C nuclear magnetic resonance methods. Energy and Fuels 21, 1548–1561. Kwiecinska, B., Petersen, H.I., 2004. Graphite, semi-graphite, natural coke, and natural char classification – ICCP system. International Journal of Coal Geology 57, 99–116. Mitra-Kirtley, S., Mullins, O.C., Branthaver, J.F., Cramer, S.P., 1993. Nitrogen chemistry of kerogens and bitumens from X-ray absorption near-edge structure spectroscopy. Energy and Fuels 7, 1128–1134. Pels, J.R., Kapteijn, F., Moulijn, J.A., Zhu, Q., Thomas, K.M., 1995. Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis. Carbon 33, 1641–1653. Rimmer, S.M., Yoksoulian, L.E., Hower, J.C., 2009. Anatomy of an intruded coal, I: effect of contact metamorphism on whole-coal geochemistry, Springfield (No. 5) (Pennsylvanian) coal, Illinois Basin. International Journal of Coal Geology 79, 74–82. Stanczyk, K., 2004. Temperature–time sieve – a case of nitrogen in coal. Energy and Fuels 18, 405–409. Stewart, A.K., Massey, M., Padgett, P.L., Rimmer, S.M., Hower, J.C., 2005. Influence of a basic intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, Illinois. International Journal of Coal Geology 63, 58–67. Susilawati, R., Ward, C.R., 2006. Metamorphism of mineral matter in coal from the Bukit Asam deposit, south Sumatra, Indonesia. International Journal of Coal Geology 68, 171–195. Sýkorova, I., Pickel, W., Christanis, K., Wolf, M., Taylor, G.H., Flores, D., 2005. Classification of huminite – ICCP System 1994. International Journal of Coal Geology 62, 85–106. Thomas, K.M., 1997. The release of nitrogen oxides during char combustion. Fuel 76, 457–473. van Krevelen, D.W., 1993. COAL: Typology – Physics – Chemistry – Constitution, Third, completely revised edition. Elsevier, Amsterdam. London. New York. Tokyo. 979 pp.
Contents lists available at ScienceDirect
International Journal of Coal Geology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j c o a l g e o
Case study of igneous intrusion effects on coal nitrogen functionalities Bruno Valentim ⁎, Alexandra Guedes, Sandra Rodrigues, Deolinda Flores Centro de Geologia e Departamento de Geociências, Ambiente e Ordenamento do Território da Faculdade de Ciências, Universidade do Porto, 4169-007-Porto, Portugal
a r t i c l e
i n f o
Article history: Received 16 February 2011 Accepted 19 February 2011 Available online 26 February 2011 Keywords: Bukit Asam coal Natural coke Nitrogen XPS
a b s t r a c t This study presents the results of the nitrogen XPS analysis performed on a set of four Bukit Asam (Indonesia) low-rank coals and on a related natural pyrolysis product formed after an igneous intrusion. Low-rank coal nitrogen XPS sub-peak is dominantly pyrrolic, with subordinate quaternary and pyridinic. Dike intrusions are responsible for transformation of these nitrogen forms nitrogen to “graphitic” quaternary nitrogen. The transformation of nitrogen is similar to that exhibited by laboratory prepared pyrolysis products of other coals. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Whatever the maceral composition, coal nitrogen is mostly organic and dominantly presented as pyrrolic, pyridinic, and quaternary nitrogen functional groups within the carbon matrix (Boudou et al., 2008; Gammon et al., 2003; Kelemen et al., 1994; Kelemen et al., 2007; Pels et al., 1995). Over a wide coal rank range (carbon 65–95 wt. %, daf), the nitrogen functional forms are generally composed of 50%– 80% pyrrole (N-5), 20%–40% pyridine (N-6), and 0%–20% quaternary (N-Q) (Mitra-Kirtley et al., 1993; Thomas, 1997); however, their amounts appear to vary with coal rank. The effects of igneous intrusions on coal nitrogen have been studied by infra-red spectroscopy (e.g. Fredericks et al., 1985), but there have been no reports on coal nitrogen transformations during natural pyrolysis processes using X-ray photoelectron spectroscopy (XPS). In this work, we examined five fresh samples of four coals from the Bukit Asam coal mine and the pyrolysis product by the igneous intrusion. 2. Methods The samples were obtained at the Bukit Asam coal mines complex situated near Tanjung Enim town in South Sumatra. The coal belongs to the Miocene Muara Enim Formation of South Sumatra Basin and locally was altered by igneous intrusions of Plio-Pleistocene age (ICCP, 2006). Chemical and petrographic compositions of the samples are given in Tables 1–3. Petrographic analyses were performed on coal pellets prepared according to ASTM D2797-04 (2004) using a Leitz Orthoplan microscope equipped with a high resolution digital camera and a ⁎ Corresponding author at: Rua do Campo Alegre, 687, 4169-007 Porto, Portugal. Tel.: +351 220402489; fax: +351 220402490. E-mail address: [email protected] (B. Valentim). 0166-5162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2011.02.008
Diskus–Fossil software. The maceral compositions and mean random reflectance of huminite and pyrolysis product were determined following ISO standard procedures, ISO 7404-3 (1994) and ISO 7404-5 (2009), respectively. Maceral nomenclature and coal classification are in accordance with the International Committee for Coal and Organic Petrography (ICCP, 1971, 2001; Sýkorova et al., 2005) and ISO 11760 (2005), respectively. To avoid bias originated by oxidation, samples were crushed in air to 212 μm in an agate mortar to expose new fresh surfaces immediately before XPS analysis and then pressed at 8 t/cm2. XPS analysis was performed using an ESCALAB 200A – V.G.SCIENTIFIC system equipped with a dual-anode Al X-ray source and a hemispherical analyser. The energy intensity is 15 keV. The photoelectron spectrum was taken with 20 eV pass energy. The software XPSPEAK was used in the spectra curve resolution and data treatment. Pyrrolic (N-5), pyridinic (N-6) and quaternary nitrogen (N-Q) were observed as assigned by Boudou et al. (2008 and references therein) on other samples. The proximate and ultimate analysis (Table 1) and petrographic data (Table 2) show that the samples are low-rank A coals (subbituminous) with low-ash yields and sulfur contents. Nitrogen content (wt.%, daf) is within the nitrogen range found in other coals with the same rank (van Krevelen, 1993). Petrographically, the coals are huminite-rich with ca. 10% minerals. However, funginite and resinite are also very common in these coals (Fig. 1A), and their occurrence may be related to funginite– resinite associations due to incorporation of fungus into resinite as described by Hower et al. (2010). 3. Results and discussion Coal intruded by igneous rocks is not an uncommon occurrence (Finkelman et al., 1998; Golab and Carr, 2004). Igneous intrusions not only elevated inorganic trace elements and minerals in coal (Dai and
292
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
Table 1 Proximate and ultimate analysis (wt.%) and atomic ratios of H/C, O/C, and N/C. Sample
Moisturea.r.
Ash
TE_59 TE_63 TE_67 TE_70 Nat. coke
18.7 10.5 8.6 1.5 0.4
3.9 1.8 1.1 1.2 6.5
d
VMdaf
Cdaf
Hdaf
Ndaf
Odaf
Sdaf
H/C
O/C
N/C
46.5 45.0 44.4 45.0 nd
62.4 69.0 72.0 78.1 79.9
6.0 5.6 5.8 5.6 1.5
1.4 1.1 1.2 1.2 0.9
29.6 24.0 20.8 14.3 17.3
0.6 0.3 0.2 0.8 0.3
1.14 0.98 0.97 0.86 0.23
0.36 0.26 0.22 0.14 0.16
0.02 0.01 0.01 0.01 0.01
VM: volatile matter; a.r.: as received basis; d: dry basis; daf: dry and ash-free basis.
Table 2 Petrographic composition (vol.%; mineral matter free) and mean random reflectance (Rr,%) of the studied samples. Sample
Rr %
Huminite
Inertinite
Liptinite
TE_59 TE_63 TE_67 TE_70 Nat. coke
0.33 0.31 0.41 0.36 6.02*
68 75 83 74 nd
26 21 12 16 nd
7 5 5 10 nd
Rr: huminite and vitrinite (*) mean random reflectances; nd: not determined.
Table 3 XPS N (1s) total nitrogen, nitrogen XPS sub-peaks, and nitrogen functionality ratios. Sample
Total N (N per 100 °C)
TE_59 TE_63 TE_67 TE_70 Nat . coke
1.59 0.90 1.04 0.96 0.58
Nitrogen functionalities (mol%)
Nitrogen functionality ratio
N-6
N-5
N-Q
N-6/N-5
N-6/N-Q
13 20 19 23 32
55 54 56 53 28
32 26 25 24 41
0.23 0.37 0.34 0.43 1.15
0.41 0.77 0.76 0.93 0.78
N-6: pyridinic nitrogen; N-5: pyrrolic nitrogen; N-Q: quaternary nitrogen.
Ren, 2007; Dai et al., 2011; Finkelman et al., 1998; Stewart et al., 2005), but also affected organic matter (Cooper et al., 2007; Rimmer et al., 2009). Igneous dike intrusions locally pyrolysed some of the coal
of this study (Fig. 1B), and also other samples geographically nearby (Susilawati and Ward, 2006), due to the very high temperatures derived from igneous intrusions in these zones (Barker et al., 1998; Guedes et al., 2005). The effects of igneous intrusions on coal described by Susilawati and Ward (2006) include the elevated coal rank (vitrinite reflectance up to at least 4.17%), volatile matter loss, and thermal metamorphism of minerals. The sample of the pyrolysis products in this study has a high random reflectance (Fig. 1C and D; Table 2) corresponding, at least, to meta-anthracite and semi-graphite (Kwiecinska and Petersen, 2004). Not surprisingly the pyrolysis product no longer exhibits low-rank coal microstructure (Fig. 1A) but is characterized by intercalations of mosaics material with “metaanthracite”-like material (Fig. 1C, D). Funginite is the only recognizable maceral in the product, probably due to its low-reactivity (Fig. 1C). The elemental contents of the pyrolysis product are characterized by low-carbon, low-nitrogen, and high-oxygen (wt.%, daf). Most probably, the heat from igneous intrusions, the introduction of hot fluids, and the moisture remobilized from the original low-rank coal (Susilawati and Ward, 2006) caused the decrease of graphitic carbon content, which was lost as CH4 and CO2 (Barker et al., 1998), organic nitrogen, or/and NH4+, HCN, NH3, and N2 (Aho et al., 1993; Boudou and Espitalié, 1995; Johnsson, 1994). The N-5 sub-peak intensity is the highest of all coals of this study (Table 3; Fig. 2). This is in agreement with results published on other low-rank coals (Friebel and Köpsel, 1999; Kelemen et al., 2006) and corresponds to pyrrolic nitrogen mainly resulted from convertion/
Fig. 1. (A) Abundance of funginite in low-rank coal (TE-59 sample; reflected light, oil immersion); (B) Natural coke associated with Plio-Pleistocene igneous intrusions in Bukit Asam coalfield; (C) Natural coke (Nc), meta-anthracite like (Ma), funginite (F) (reflected polarized light, oil immersion); (D) Pyrolytic carbon on the edges of natural coke (Nc) and meta-anthracite (Ma) (reflected polarized light, oil immersion).
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
293
The thermal rupture of both pyrrole and pyridine nitrogen could in part explain the decrease of these aromatic rings containing nitrogen heteroatoms. However, during the nitrogen transformation path, it is more likely that several other mechanisms also occurred, leading to the increase of pyridinic nitrogen by: (i) “ring expansion” whereby the 5-membered ring is opened and incorporates another C atom (Pels et al., 1995), and (ii) transformations of amide, amine and protonated pyridinic (quaternary nitrogen) structures (Kelemen et al., 1994, 2006). However, the considerable increase in the N-Q peak observed in the pyrolysis product cannot be directly explained by these transformations, but may be explained by pyridine nitrogen transformation to “graphitic” quaternary nitrogen, following thermal reactions and hot fluids interaction with the coals. The results are consistent with laboratory studies of pyrolysis. Studies of products formed at 800–900 °C in inert atmosphere revealed the appearance of significant levels of quaternary nitrogen associated with the development of larger polynuclear aromatic carbon structures (Friebel and Köpsel, 1999; Kelemen et al., 1999). Less stable nitrogen structures abundant in low-rank coals, such as pyrrolic nitrogen, are gradually transformed to more stable structures, such as pyridine (Pels et al., 1995). At severe heating conditions, pyridine is preferentially transformed to quaternary nitrogen (Kawashima et al., 2002; Stanczyk, 2004). For example, during condensation of the carbon matrix, nitrogen atoms are incorporated in the graphene layers, and then replace carbon
cyclization of amide nitrogen in peats due to thermal stress (Kelemen et al., 2006). The intensities of the N-Q and N-6 sub-peaks (Fig. 2) are considerably lower than that of the N-5 sub-peak. The N-Q sub-peak has a slightly higher intensity peak than the N-6 sub-peak, except for sample Te-59, where a marked difference is present. Similar peaks were also observed in low rank coals (Friebel and Köpsel, 1999; Kelemen et al., 2006) and in low maturity type I and II kerogens (Kelemen et al., 2007). Although XPS cannot distinguish quaternary nitrogen between amide and amine nitrogen forms (at 401.6 ±0.3 eV), it is believed that, in low rank coals, pyridinic nitrogen results from the transformations of amide, amine, and the elimination of oxygen from pyridones (Geng et al., 2009; Kelemen et al., 1994, 2006; Mitra-Kirtley et al., 1993). The N-Q sub-peak in the XPS spectra of the samples studied are thus assigned to protonated pyridinic forms (Pels et al., 1995), which were possibly derived from the interaction between pyridinic nitrogen and neighbouring phenolic groups (Friebel and Köpsel, 1999; Kelemen et al., 1994). The relative abundance of the nitrogen forms of Bukit Asam coal samples and the natural pyrolysis product is compared. Table 3 and Fig. 2 show that (i) in the pyrolysis product the N-5 value is approximately one half of the coals studied and is no longer the dominant type; (ii) N-6 increases moderately; and, (iii) N-Q increases considerably and became the dominant form.
TE59
Relative intensity
TE63
394
N-6 N-5 N-Q
396
398
400
402
404
406 394
396
398
400
402
404
406
400
402
404
406
TE67
Relative intensity
TE70
394
N-6 N-5 N-Q
396
398
400
402
404
406 394
396
398
Relative intensity
Binding Energy (eV)
394
Natural coke
N-6 N-5 N-Q
396
398
400
402
404
406
Binding Energy (eV) Fig. 2. XPS nitrogen (1s) spectra and curve resolution of fresh samples from Bukit Asam coal and Bukit Asam natural coke.
294
B. Valentim et al. / International Journal of Coal Geology 86 (2011) 291–294
atoms and form quaternary nitrogen as organic nitrogen N-C3 atoms (Furimsky and Ohtsuka, 1997). Acknowledgements The authors thank the Fundação para a Ciência e a Tecnologia (Portugal) and FEDER (UE) for financing the Projects POCI/CLI/60557/ 2004 and PPCDT/CLI/60557/2004. We are grateful to Dr. Shifeng Dai, Professor Michael Wilson and two anonymous reviewers for helping us improve this paper. References Aho, M.J., Hämäläinen, J.P., Tummavuori, J.L., 1993. Conversion of peat and coal nitrogen through HCN and NH3 to nitrogen oxides at 800 °C. Fuel 72, 837–841. ASTM D2797-04, 2004. Standard practice for preparing coal samples for microscopical analysis by reflected light. American Society for Testing and Materials, Philadelphia, USA. 4 pp. Barker, C.E., Bone, Y., Lewan, M.D., 1998. Fluid inclusion and vitrinite-reflectance geothermometry compared to heat-flow models of maximum paleotemperature next to dikes, western onshore Gippsland Basin, Australia. International Journal of Coal Geology 37, 73–111. Boudou, J.P., Espitalié, J., 1995. Molecular nitrogen from coal pyrolysis: kinetic modelling. Chemical Geology 126, 319–333. Boudou, J.P., Schimmelmann, A., Ader, M., Mastalerz, M., Sebilo, M., Gengembre, L., 2008. Organic nitrogen chemistry during low-grade metamorphism. Geochimica et Cosmochimica Acta 72, 1199–1221. Cooper, J.R., Crelling, J.C., Rimmer, S.M., Whittington, A.G., 2007. Coal metamorphism by igneous intrusion in the Raton Basin, CO and NM: implications for generation of volatiles. International Journal of Coal Geology 71, 15–27. Dai, S., Ren, D., 2007. Effects of magmatic intrusion on mineralogy and geochemistry of coals from the Fengfeng-Handan Coalfield, Hebei, China. Energy and Fuels 21, 1663–1673. Dai, S., Ren, D., Chou, C.-L., Finkelman, R.B., Seredin, V.V., Zhou, Y., 2011. Geochemistry of trace elements in Chinese coals: a review of abundances, genetic types, impacts on human health, and industrial utilization. International Journal of Coal Geology. doi:10.1016/j.coal.2011.02.003. Finkelman, R.B., Bostick, N.H., Dulong, F.T., Senftle, F.E., Thorpe, A.N., 1998. Influence of an igneous intrusion on the inorganic geochemistry of a bituminous coal from Pitkin County, Colorado. International Journal of Coal Geology 36, 223–241. Fredericks, P.M., Warbrooke, P., Wilson, M.A., 1985. A study of the effect of igneous intrusions on the structure of an Australian high volatile bituminous coal. Organic Geochemistry 8, 329–340. Friebel, J., Köpsel, R.F.W., 1999. The fate of nitrogen during pyrolysis of German low rank coals – a parameter study. Fuel 78, 923–932. Furimsky, E., Ohtsuka, Y., 1997. Formation of nitrogen-containing compounds during slow pyrolysis and oxidation of petroleum coke. Energy and Fuels 11, 1073–1080. Gammon, W.J., Kraft, O., Reilly, A.C., Holloway, B.C., 2003. Experimental comparison of N(1s) X-ray photoelectron spectroscopy binding energies of hard and elastic amorphous carbon nitride films with reference organic compounds. Carbon 41, 1917–1923. Geng, W., Kumabe, Y., Nakajima, T., Takanashi, H., Ohki, A., 2009. Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS). Fuel 88, 644–649. Golab, A.N., Carr, P.F., 2004. Changes in geochemistry and mineralogy of thermally altered coal, Upper Hunter Valley, Australia. International Journal of Coal Geology 57, 197–210. Guedes, A., Noronha, F., Prieto, A.C., 2005. Characterisation of dispersed organic matter from lower Palaeozoic metasedimentary rocks by organic petrography, X-ray
diffraction and micro-Raman spectroscopy analyses. International Journal of Coal Geology 62, 237–249. Hower, J.C., O´Keefe, J.M.K., Volk, T.J., Watt, M.A., 2010. Funginite–resinite associations in coal. International Journal of Coal Geology 83, 64–72. ICCP (International Committee for Coal and Organic Petrology), 1971. International handbook of coal petrography, International Committee for Coal Petrography2nd ed. Centre National de la Recherche Scientifique, Academy of Sciences of the URSS, Paris. ICCP (International Committee for Coal and Organic Petrology), 2001. The new inertinite classification (ICCP System 1994). Fuel 80, 459–471. ICCP (International Committee for Coal and Organic Petrology), 2006. Field trip guide to Bukit Asam coal mine, Tanjung Enim. Indonesia Center for Geological Resources. 58th meeting of the ICCP, Bandung (West Java, Indonesia) 3 – 9 September 2006, and Asia Pacific Symposium on Lower Rank Coal – integrating lower rank coals with industrialization in the 21st century. International Organization for Standardization (ISO), 1994. Methods for the petrographic analysis of bituminous coal and anthracite – Part 3: Method of determining maceral group composition. ISO 7404–3, Geneva, Switzerland. 4 pp. International Organization for Standardization (ISO), 2005. Classification of coals. ISO 11760, Geneva, Switzerland. 9 pp. International Organization for Standardization (ISO), 2009. Methods for the Petrographic Analysis of Coals – Part 5: Method of Determining Microscopically the Reflectance of Vitrinite. ISO 7404–5, Geneva, Switzerland. 4 pp. Johnsson, J.E., 1994. Formation and reduction of nitrogen oxides in fluidized-bed combustion. Fuel 73, 1398–1415. Kawashima, H., Wu, Z., Sugimoto, Y., 2002. Change of nitrogen functionality of 15N-enriched condensation products during pyrolysis. Fuel 81, 2307–2316. Kelemen, S.R., Gorbaty, M.L., Kwiatek, P.J., 1994. Quantification of nitrogen forms in Argonne Premium coals. Energy and Fuels 8, 896–906. Kelemen, S.R., Freund, H., Gorbaty, M.L., Kwiatek, P.J., 1999. Thermal chemistry of nitrogen in kerogen and low-rank coal. Energy and Fuels 13, 529–538. Kelemen, S.R., Afeworki, M., Gorbaty, M.L., Kwiatek, P.J., Sansone, M., Walters, C.C., 2006. Thermal transformations of nitrogen and sulfur forms in peat related to coalification. Energy and Fuels 20, 635–652. Kelemen, S.R., Afeworki, M., Gorbaty, M.L., Sansone, M., Kwiatek, P.J., Walters, C.C., Freund, H., Siskin, M., Bence, A.E., Curry, D.J., Solum, M., Pugmire, R.J., Vandenbroucke, M., Leblond, M., Behar, F., 2007. Direct characterization of kerogen by X-ray and solid-state 13C nuclear magnetic resonance methods. Energy and Fuels 21, 1548–1561. Kwiecinska, B., Petersen, H.I., 2004. Graphite, semi-graphite, natural coke, and natural char classification – ICCP system. International Journal of Coal Geology 57, 99–116. Mitra-Kirtley, S., Mullins, O.C., Branthaver, J.F., Cramer, S.P., 1993. Nitrogen chemistry of kerogens and bitumens from X-ray absorption near-edge structure spectroscopy. Energy and Fuels 7, 1128–1134. Pels, J.R., Kapteijn, F., Moulijn, J.A., Zhu, Q., Thomas, K.M., 1995. Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis. Carbon 33, 1641–1653. Rimmer, S.M., Yoksoulian, L.E., Hower, J.C., 2009. Anatomy of an intruded coal, I: effect of contact metamorphism on whole-coal geochemistry, Springfield (No. 5) (Pennsylvanian) coal, Illinois Basin. International Journal of Coal Geology 79, 74–82. Stanczyk, K., 2004. Temperature–time sieve – a case of nitrogen in coal. Energy and Fuels 18, 405–409. Stewart, A.K., Massey, M., Padgett, P.L., Rimmer, S.M., Hower, J.C., 2005. Influence of a basic intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, Illinois. International Journal of Coal Geology 63, 58–67. Susilawati, R., Ward, C.R., 2006. Metamorphism of mineral matter in coal from the Bukit Asam deposit, south Sumatra, Indonesia. International Journal of Coal Geology 68, 171–195. Sýkorova, I., Pickel, W., Christanis, K., Wolf, M., Taylor, G.H., Flores, D., 2005. Classification of huminite – ICCP System 1994. International Journal of Coal Geology 62, 85–106. Thomas, K.M., 1997. The release of nitrogen oxides during char combustion. Fuel 76, 457–473. van Krevelen, D.W., 1993. COAL: Typology – Physics – Chemistry – Constitution, Third, completely revised edition. Elsevier, Amsterdam. London. New York. Tokyo. 979 pp.