ARTICLE pubs.acs.org/EF
Development of Ordered Structures in the High-Temperature (HT) Cokes from Binary and Ternary Coal Blends Studied by Means of X-ray Diffraction and Raman Spectroscopy y. Sme-dowski,*,† M. Krzesinska,†,‡ W. Kwasny,§ and M. Kozanecki|| †
)
Institute of Physics, Centre for Science and Education, Silesian University of Technology (SUT), Krzywoustego 2, PL-44100 Gliwice, Poland ‡ Centre of Polymer and Carbon Materials, Polish Academy of Sciences, Marii Curie-Skzodowskiej 34, PL-41819 Zabrze, Poland § Institute of Engineering Materials and Biomaterials, Silesian University of Technology (SUT), Konarskiego Street 18a, PL-44100 Gliwice, Poland _ Department of Molecular Physics, Technical University of yodz, Zeromskiego 116, PL-90924 yodz, Poland ABSTRACT: The aim of this work was to characterize ordered structures within cokes produced from single bituminous coals and from their blends. Three Polish coals of varying rank and caking ability were collected from the Krupinski, Szczygzowice, and Zofiowka mines, respectively. These coals were used for preparation of 19 blends: single (trivial blends), binary, and ternary ones. Cokes were manufactured in a laboratory scale using an apparatus with a Jenkner’s retort with a charge of 1000 g and heat-treatment temperature of 1000 °C. The X-ray diffraction (XRD) and Raman spectroscopy were used for the study. To determine the kind and size of ordered structures, the following parameters were discussed: interlayer spacing, d002, crystallite stack height, Lc, obtained from the XRD studies as well as the fractional contribution of ordered elements to all kinds of structures, and ratio of the amount of graphite structures (G type) to the amount of D2-type structures (less ordered than graphite), determined with Raman spectroscopy. The cokes produced from blends were treated as a compound system dependent upon properties of its components, single coal cokes. Additivity of the structural parameters of the cokes from blends was verified by the series model. Well-ordered structures, including the graphite-like ones, were found in all cokes studied. The highest degree of ordering was found in the single coke from very good caking Zofiowka coal. A similar structure was found in the cokes from binary and ternary blends of medium content of this coal of about 3050 wt %. The preparation of cokes with well-ordered structures from blends of considerable lower concentration of the Zofiowka coal is promising, because the cost of these coke productions is lower than that of single coke from the Zofiowka coal. Discrepancy between the experimental data and those obtained from the series model confirmed mutual interactions between coals in a blend that affects forming of well-ordered structures in the cokes. This interaction was found to be the strongest in the blends with the content of the Zofiowka coal equal to 3050 wt %.
1. INTRODUCTION Bituminous coal is one of the most important natural resources that is exploited by humanity.1 Both coal and its derivatives, e.g., coke, are used on a large scale in various branches of industry. Cokes manufactured at high temperatures (HTs) are used in the steel industry for the reduction of iron ore to pig iron in blast furnaces. Fabrication of such HT cokes, called metallurgical cokes, needs a large amount of very good coking coals because the very good quality of this product is required. Unfortunately, sources of these coals are running low, which strongly increases their price. Thus, efficiency of very good caking coal exploitation is an important task for both users and researchers. Some solution of the problem is using low-quality coking coals instead of a part of expensive good coals. Good coking coal and one or two coals with lower caking ability are mixed to create a blend and next are pyrolyzed in a coking chamber. Components heated to HTs affect each other in many different ways, dependent upon their content in a blend and values of their fluidity parameters: fluidity, Fmax, softening temperature, T1, temperature of maximal fluidity, Tmax, and resolidification temperature, T3.2,3 Mutual interactions of coals in a blend are very complex. r 2011 American Chemical Society
Coals contain volatile matter that can be moved from the first softening coal in a blend and stored in pores of the other coals of higher softening temperature, T1. Captured volatiles from lowquality coking coals may plasticize other components of a blend, which results in the growing of ordered, graphite-like objects within the coke structure.2 Because of the relationships between the degree of ordering of a coke structure and coke quality, it is clear that the latter also depends upon these interactions between coals in a blend. Summarizing, cokes produced from blends could be characterized by similar structure and quality as those of the cokes manufactured from only good coking coals. It is clear that production of cokes from blends is cheaper, because a less amount of expensive, good coking coal is needed. Unfortunately, to this day, a universal rule concerning proportions and types of each component in a blend was not elaborated. Products of coal pyrolysis were studied by means of many different methods.48 It is well-known that the application of Received: April 18, 2011 Revised: May 29, 2011 Published: June 07, 2011 3142
dx.doi.org/10.1021/ef200609t | Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
ARTICLE
Table 1. Basic Technological Parameters of Initial Coals: Zofi owka, Szczygzowice, and Krupi nskia technical analysis (wt %) coal
Wa
Ad
Vdaf
elemental analysis (wt %) Cdaf
Std
Hdaf
Ndaf
coke-making indices RI
CRI
Fmax
CSR
SI
Ba
Bb
Zofiowka
1.02
7.15
24.03
0.53
88.66
5.40
1.89
77
25.5
62.0
478
8
30
143
Szczygzowice
1.14
5.01
30.34
0.64
86.21
5.46
2.21
63
53.7
24.5
1825
7
30
55
Krupi nski
1.38
7.73
35.20
0.72
82.67
5.99
2.47
24
58.7
23.8
434
6
30
15
a
W, moisture; A, ash; V, volatile matter; Std, sulfur; C, carbon; H, hydrogen; N, nitrogen; RI, Roga index; CRI, coke reactivity index; CSR, coke strength after reaction; Fmax, fluidity; SI, swelling index, Ba, contraction, Bb, dilatation; a, air basis; d, dry basis; and daf, dry and ash-free basis. The data are quoted from ref 3.
Table 2. Composition of Blends Containing Various Amounts of the Zofi owka Coal concentration of coal in a blend (wt %) coal
Z100
Z70K30
Z50S50
Z50K50
Z30K70
S70K30
S50K50
S100
Zofiowka Szczygzowice
100 0
70 0
50 50
50 0
30 0
0 70
0 50
0 100
0 0
0
30
0
50
70
30
50
0
100
Krupi nski
K100
concentration of coal in a blend (wt %) coal
Z80S10K10
Z60S20K20
Z50S10K40
Z40S50K10
Z40S30K30
Z40S20K40
Z30S40K30
Z20S20K60
Z20S40K40
Z10S40K50
Zofiowka
80
60
50
40
40
40
30
20
20
10
Szczygzowice
10
20
10
50
30
20
40
20
40
40
Krupi nski
10
20
40
10
30
40
30
60
40
50
physical methods, such as X-ray diffraction (XRD) and Raman spectroscopy, allows us to study the coke structure in detail.912 Cokes contain various structures of different degrees of ordering: the graphite fragments of a perfect structure with the same value of interlayer spacing as that in a graphite single crystal, structures with some distortion (turbostratic structures), and completely not ordered objects (amorphous structures). The XRD method supports information about objects of the graphite single crystal ordering (“crystallites”) with typical graphite parameters: the interlayer spacing between adjacent graphene planes (d002), average height of crystallites (Lc), and average lateral dimension of aromatic planes (La).12,13 Discrepancy between the values of d002 measured for a coke and d002 = 3.35 Å characteristic for a graphite single crystal is a measure of distortion of graphene layers in the turbostratic structure. The remaining kinds of structures of lower ordering are evaluated by the Raman spectroscopy.14 Using this method, it is possible to determine the proportions of the types of structures mentioned above. A discussion of the data performed using both the XRD and Raman analyses for the same samples of cokes gives complete information about the ordering structure of a coke. However, to our knowledge, there are not any studies concerning using these methods simultaneously for cokes produced from different coal blends in the same conditions of pyrolysis. The aim of this work was to characterize ordered structures that form cokes obtained from single coals and their binary and ternary blends with an increasing content of very good caking coal from 0 to 100 wt %. To obtain full information about ordering of the coke structure, both the XRD and Raman analyses were used in the study. The second aim of this work was to verify the effect of both the strongly caking coal concentration in a blend and a blend kind on the structure ordering degree. It was expected
that the results could indicate types and proportions of lowquality coals that should be added to a blend with good coking coal to produce very good-quality coke of the most developed ordered structure.
2. EXPERIMENTAL SECTION 2.1. Samples. Three Polish coals were used in different proportions to make binary and ternary blends. These coals differ in rank (88.66, 86.21 and 82.67 wt % carbon content) and caking ability (strong, moderate, and weak); their basic technological parameters are presented in Table 1. The samples are named after mines from which they were collected: Zofi owka, Z; Szczygzowice, S; and Krupi nski, K. Obtained blends with composition shown in Table 2 were carbonized in an apparatus with a Jenkner’s retort. Details of the coking process are described in ref 15. Cokes from the single original coals (SC) and binary (BBC) and ternary (TBC) coal blends were analyzed using two methods: XRD and Raman spectroscopy. 2.2. XRD. The XRD analysis of powdered coke samples of a grain dimension less than 3 μm was carried out with a Panalytical X’Pert Pro, with cobalt KR radiation (wavelength λ = 0.1789 nm). The spectra were recorded in the 2θ range of 15110°. For each sample, diffraction curves were carried out. On the basis of these curves, interlayer spacing, d002, and average dimension of crystallites, Lc, were calculated using the Bragg16 and Sheerer12 equations, respectively. 2.3. Raman Spectroscopy. The Raman analysis was carried out with a Jobin Yvon T64000 spectrometer. A microscope equipped with a lens of magnification 50 was used to focus the excitation laser beam (Ar laser with a wavelength of 514.5 nm) on randomly selected areas of each coke sample and to collect the Raman signal in a backscattered direction. The Ar-laser power at the sample surface was controlled at about 0.5 mW. The laser spot diameter reaching the sample was about 1 μm, much larger than the size of carbon microcrystallites in the cokes 3143
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
ARTICLE
Figure 1. Diffractograms obtained for the single coal cokes Z100, S100, and K100 in the 2θ range of ∼20110°. Three characteristic peaks of (002), (100), and (110) are assigned. studied. Therefore, the Raman microprobe actually provided averaged information of a large number of randomly distributed microcrystallites. The spectra were recorded in the range of 9001900 cm1, covering first-order bands with two bands, i.e., the G band (graphite) and the D band (disordered), that are characteristic for carbon materials.17 The acquisition time for each spectrum was 120 s. Each Raman spectrum was decomposed into five bands related to different structures that form carbon materials:14,18 (1) the G band at 1580 cm1, stretching vibration mode in the aromatic layers of crystallite; (2) the D1 band at 1350 cm1, defects or heteroatoms in graphitic lattices; (3) the D2 band at 1620 cm1, vibrations analogous to that of the G band but involving layers, which are not directly localized between other layers; (4) the D3 band at 1530 cm1, amorphous forms of carbon; and (5) the D4 band at 1180 cm1, very poorly organized materials. The G band is attributed to a perfect graphite structure, while the bands D1 and D2 show the graphite structure with some defects. The bands D3 and D4 correspond to poor organized structures. In the literature, there are a lot of different parameters calculated from the Raman spectra that were discussed to characterize the structure of various carbon materials.1824 To compare structure ordering expected to occur in three various groups of cokes, we chose two parameters based on the Raman bands: (1) SG + D2/Sall, ratio of the integrated area of the G and D2 bands together to the area of all bands. This parameter presents the contribution (fractional) of ordered elements, i.e., the degree of the structure ordering, including the turbostratic structure. (2) IG/ID2, ratio of the intensity of the G band to the intensity of the D2 band. This parameter presents the ratio of the amount of graphite structures (G band) to the amount of D2-type structures (less ordered than graphite). This parameter shows the contribution of perfect ordering within less ordered structures.
3. RESULTS AND DISCUSSION The structural parameters of the cokes from blends, such as interlayer spacing, d002, crystallite stack height, Lc, contribution of well-ordered structures within all structures, SG + D2/Sall, and ratio of perfect graphite structures to graphite structures with some
Figure 2. Diffractograms obtained for (a) BBC and (b) TBC. The data of SC are also shown.
defects, IG/ID2, were discussed using the data from the XRD and Raman analyses made for the same samples. The diffraction curves with three peaks characteristic for carbon materials are shown in Figure 1 for the single coal cokes. The peaks (002), (100), and (110) are located at 2θ equal to 30°, 55°, and 95°, respectively. In comparison to curves shown in Figure 1, it can be seen that the Z100 coke has the most intensive (002) peak of the narrowest fwhm, where fwhm is the full width at half-maximum of the diffraction (002) peak expressed in radians. Intensities of the (002) peaks for both cokes S100 and K100 are lower and similar to each other. On the base of these observations, we can conclude that the Z100 coke from very good caking coal has the best organized structure in comparison to that of cokes K100 and S100 manufactured from worse caking coals. For all of the binary blend cokes (BBC) and ternary blend cokes (TBC), the peak (110) of inconsiderable height is located on a similar position as in the case of single coal cokes (SC). Therefore, Figure 2 shows the diffraction spectra in the shortened 2θ range, i.e., between ∼20° and 60°. It can be seen from Figure 2 that, in the case of BBC and TBC, peaks for the samples with a higher content of the Z coal are generally more distinctive 3144
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
ARTICLE
Figure 4. Decomposition of the Raman spectrum into five characteristic bands for the Z100 coke.
Each spectrum was decomposed into five bands according to the procedure described in ref 14. Figure 4 shows exemplary decomposition of the Raman spectrum for the Z100 sample. The D1 band responsible on well-ordered structures with some defects (located at about 1350 cm1) was found to be the most intensive band in this coke. It is distinctly larger than that of the G band, indicating a perfectly ordered structure (graphite). The G and D2 bands distinguished from the Z100 spectrum have relatively low fwhm values; therefore, we can suppose that the degree of ordering of structures that are represented by these two bands is very high. The G band is higher than the D2 band; therefore, graphite-like structures dominate over turbostratic structures in this coke. A coke produced from a coal blend can be treated as a compound system dependent upon properties of its components, single coal cokes. Generally, a multi-component system, C, can be represented in the form of a combination of components Cn coupled consecutively (series) or in parallel26 C¼
∑n ϕnCn
1 ¼ C
∑n Cnn
for series model
ð1Þ
for parallel model
ð2Þ
Figure 3. Raman spectra for the cokes with (a) well-developed and (b) poor-developed ordered structures. Two characteristic bands (G band and D band) are assigned.
and
from the background; i.e., they have better developed (002) peaks than those of the samples with a lower content of the Z coal. The samples Z30S40K30, Z40S30K30 (TBC), and Z50K50 (BBC) are also characterized by more distinctive (002) peaks, although they contain a medium concentration of good caking coal in a blend. The typical two bands, the G band (graphite band) and D band (disorder band), were detected in the first-order region for all samples studied. Figure 3 shows the exemplary Raman spectra obtained for the coke with a well-ordered structure (Figure 3a) and for the coke with a poor-ordered structure (Figure 3b). It is clear that coke with a well-ordered structure has a better developed G band than coke with a poor-ordered structure. It is well-known from the literature that the ratio of intensity of the D band to that of the G band, ID/IG, is inversely proportional to the in-plane crystalline size, La, if the La values are contained between 25 and 3000 Å.25 It was observed that the ID/IG ratio decreases with an increasing Z coal content in a blend. It suggests that the in-plane crystallite size, La, in the cokes studied increases with an increasing content of a strongly caking coal in a blend.
where Φn is the concentration of the nth component Cn. To evaluate mutual interactions between components in a blend, for all structural parameters, the experimental data of the cokes from blends were compared to theoretical values calculated using the series model with the data of Z100, S100, and K100. If experimental data are equal to those calculated with the assumption of additivity of the coal properties, the coals in a blend do not interact. It was observed that the contribution of well-ordered structures presented by the Raman parameter SG + D2/Sall generally increases with an increasing concentration of very good coking coal Z in a blend (Figure 5). The SG + D2/Sall parameter is the highest for the single Z coal coke of the best ordered structure among all cokes studied. When the experimental data are compared to those calculated with eq 1, we can conclude that the contribution of well-ordered structures within all kinds of structures is additive for BBC (Figure 5a), while this conclusion is not pertinent for TBC (Figure 5b). TBC with a lower Z coal content is characterized by higher SG + D2/Sall values, unlike TBC with a medium Z coal content in a blend; they have lower SG + D2/Sall values. The highest contribution of well-ordered structures of 3145
ϕ
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
Figure 5. Fractional contribution of well-ordered structures, SG + D2/Sall determined from the Raman spectra for (a) BBC and (b) TBC. Light columns are attributed to the data calculated using the series model. Straight lines show the trend.
over 0.20 (or over 20%) was found, beside Z100, in three BBC (Z30K70, Z50S50, and Z70K30) as well as five TBC (Z20S40K40, Z30S40K30, Z40S30K30, Z60S20K20, and Z80S10K10). High values of SG + D2/Sall in cokes with a high content of very good caking coal are obvious, but well-ordering in the case of cokes poor in content of Z coal in a blend is surprising. We suppose that this difference is caused by some interactions between coals in blends. When they are very intensive, there are good conditions to ordered objects forming. Contribution of graphite structures, i.e., the ratio of G-type ordered structures to D2-type structures, IG/ID2, is not the same for the cokes studied; it depends upon a kind of blend. There is not any relationship between IG/ID2 and the Z coal content for BBC (Figure 6a), while some proportion is visible for TBC (Figure 6b). Six cokes are characterized by high contribution (IG/ID2 of over 2) of perfectly ordered structures, i.e., of the graphite structures: Z100, Z80S10K10, Z60S20K20, Z50K50, Z40S30K30, and Z30S40K30. In the case of Z100, it is clear, because very good coking coals of the lowest number of crosslinks are known as materials able to graphitize. Similarly, as in the case of the well-ordering degree of coke structures, a high share of graphite structures in cokes with a high content of very good caking coal is obvious but perfect ordering in the case of cokes poor in content of Z coal in a blend is surprising. A considerable
ARTICLE
Figure 6. Ratio of the amount of G-type structures to the amount of D2-type structures, IG/ID2, determined from the Raman spectra for (a) BBC and (b) TBC. Light columns are attributed to the data calculated using the series model. Straight lines show the trend.
discrepancy between the experimental data and calculated ones with the series model provides evidence of the important role of mutual interactions in a blend on the creation of perfect structures in cokes from blends. The distance between graphene layers, d002, was found to be generally dependent upon the content of strongly caking coal in a blend; the higher the Z coal content in a blend, the lower the d002 value and the higher ordering of graphene layers (Figure 7). It can also be seen from this figure that the d002 parameter is approximately additive for BBC, unlike in the case of TBC. For the latter group, distinct discrepancy between experimental data and those calculated from the series model was observed. The lower values of d002 of about 3.45 Å were found for the cokes Z100, Z80S10K10, Z40S30K30, Z30S40K30 and Z50K50 in the case of BBC. These cokes can be treated as materials with the smallest distortion of graphene layers among the cokes studied. A discrepancy between the data and trend shown in Figure 5b provides evidence of the strong interaction between components in TBC, which results in better ordering (lower d002) or worse ordering (higher d002). Averaged height of crystallites, Lc, determined in the cokes studied was discussed in relation to the very good coking coal content in a blend (Figure 8). It can be seen that the Lc parameter does not depend upon the contribution of the Z coal clearly in 3146
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
Figure 7. Interlayer spacing, d002, determined from the XRD curves for (a) BBC and (b) TBC. Light columns are attributed to the data calculated using the series model. Straight lines show the trend.
both BBC and TBC. Single coke produced from Z coal is characterized by the high value of Lc. This means that the coke Z100 is mainly formed by the graphite structures of large dimensions. Figure 8a shows that the Lc value of Z50K50 is higher than that suggested by the content of this blend. Moreover, this coke is characterized by predomination of graphite structures (Figure 6a). This observation suggests that the structure of Z50K50 is almost similar to that of the Z100 coke. Figure 8b shows the plot of Lc versus the Z coal content for TBC. Samples from two groups that differ with values of Lc. The cokes Z80S10K10, Z40S30K30, and Z30S40K30 have high values of Lc of over 22 Å, while the other cokes are characterized by Lc of 1317 Å. Distinct deviation from the series model is explained by specific interactions between components in a blend. As described in ref 3, the K coal reaches a maximum of fluidity at a lower temperature than that of the Z coal. The K coal has a great amount of volatile matter, which is released from this coal to the Z coal at the moment when the latter coal does not reach its maximum fluidity. Volatiles from the K coal are supposed to plasticize softening Z coal, which results in better conditions of crystallites growing. Probably for the proportions of coals in the blends Z50K50, Z80S10K10, Z40S30K30, and Z30S40K30, this effect is the strongest, and for that reason, these cokes are characterized by very well-developed crystallites.
ARTICLE
Figure 8. Average height of crystallites, Lc, determined from the XRD curves for (a) BBC and (b) TBC. Light columns are attributed to the data calculated using the series model. Straight lines show the trend.
The Raman parameter, IG/ID2, was related to both XRD parameters, i.e., interlayer spacing, d002, and crystallite stack height, Lc (Figure 9). The lowest distance between two adjacent graphene layers was found to be 3.440 Å for the coke Z80S10K10. It is higher than that of a perfect graphite single crystal with d002 = 3.354 Å, and therefore, the name “graphite-like” is more justifiable than “graphite” for the notation of the G-band structures. The ratio of the amount of graphite-like structures (G band) to the amount of well-ordered ones (D2 band) found in both kinds of cokes depend upon d002 and Lc distinctly. Graphite-like structures occurring in a great amount in both BBC and TBC are characterized by the lowest values of d002 below 3.455 Å, while in the case of the cokes with a distinctly lower volume of graphitelike structures, the d002 values are higher up to 3.557 Å. This means that, in the cokes with a smaller amount of graphite-like structures, these structures are more distorted. Panels c and d of Figure 9 show the plot of IG/ID2 versus the average height of crystallites for both kinds of cokes. Generally, the IG/ID2 parameter is proportional to Lc. This means that the growth of volume of graphite-like structures is the result of the increase of the height of crystallites. The cokes, such as Z50K50, Z80S10K10, Z40S30K30, and Z30S40K30, of unusual values of the parameters studied, which were shown as a discrepancy from 3147
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
ARTICLE
Figure 9. Plots of the Raman parameter, IG/ID2, versus the structural parameters calculated from XRD, i.e., (a and b) d002 and (c and d) Lc. The data for BBC are shown in panels a and c, while the data for TBC are shown in panels b and d. (b) SC, (9) BBC, and (2) TBC.
the series model, are characterized by long crystallites of the lowest interlayer spacing close to the spacing of a perfect graphite crystal. These structures are best ordered among all kinds of structures evaluated in both BBC and TBC. A way of growing of the crystallite volume in cokes studied is similar to that presented by Oberlin for all carbon materials.27
4. CONCLUSION Well-ordered structures including graphite-like structures of cokes produced from the binary and ternary coal blends were investigated using the XRD and Raman spectroscopy. The results are summarized as follows: (1) Well-ordered structures were found in all of the cokes studied. Some of them have features characteristic for graphite-like crystallites. (2) The highest degree of ordering characterizes the single coke from very good caking Zofi owka coal (Z100). Ordered structures that build Z100 are mainly graphite-like of high Lc. A similar structure also characterizes the cokes of a lower content of this coal, i.e., the cokes Z50K50, Z40S30K30, and Z30S40K30. (3) A discrepancy between the experimental data and those obtained from the series model confirms mutual interactions between coals in a blend that affects the forming of well-ordered structures in the cokes. This interaction was found to be the strongest in the blends with amedium content of very good caking Zofiowka coal of about 3050 wt % (the cokes Z50K50, Z40S30K30, and Z30S40K30). (4) The presence of the well-ordered structures in the cokes of considerable lower concentration of the Zofiowka coal is a very important observation, because the cost of production
of the coke from these blends is lower than that from the single Zofiowka coal, while the structure of these cokes (and quality) is similar to that of Z100.
’ AUTHOR INFORMATION Corresponding Author
*Telephone: +48-32-237-2017. Fax: +48-32-237-2057. E-mail:
[email protected].
’ ACKNOWLEDGMENT This study was partially financed by the Ministry of Education and Science (Poland) under Grant 3378/B/T02/2010/38. Samples of the cokes were fabricated under Grant 4 T12B 044 29, financed by the Ministry of Education and Science (Poland). ’ REFERENCES (1) van Krevelen, D. W. Coal: TypologyPhysicsChemistry Constitution; Elsevier: Amsterdam, The Netherlands, 1993. (2) Sakurovs, R. Fuel 2003, 82, 439–450. (3) Krzesi nska, M.; Szeluga, U.; Czajkowska, S.; Muszy nski, J.; Zachariasz, J.; Pusz, S.; Kwieci nska, B.; Koszorek, A.; Pilawa, B. Int. J. Coal Geol. 2009, 77, 350–355. (4) Takagi, H.; Maruyama, K.; Yoshizawa, N.; Yamada, Y.; Sato, Y. Fuel 2004, 83, 2427–2433. (5) Tsafnat, N.; Tsafnat, G.; Jones, A. Fuel 2008, 87, 2983–2987. (6) Marques, M.; Suarez-Ruiz, I.; Flores, D.; Guedes, A.; Rodrigues, S. Int. J. Coal Geol. 2009, 77, 377–382. (7) Kelemen, S. R.; Fang, H. L. Energy Fuels 2010, 15, 653–658. 3148
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
Energy & Fuels
ARTICLE
(8) Gornostayev, S.; Kerkkonen, O.; Harkki, J. Steel Res. Int. 2009, 80, 390–395. (9) Diamond, R. Philos. Trans. R. Soc. London 1960, 252, 193–223. (10) Lu, L.; Sahajwalla, V.; Kong, C.; Harris, D. Carbon 2001, 39, 1821–1833. (11) Lin, Q.; Guet, J. Fuel 1990, 69, 821–825. (12) Feret, F. Analyst 1998, 123, 595–600. (13) Matsuoka, K.; Akahane, T.; Aso, H.; Sharma, A.; Tomita, A. Fuel 2008, 87, 539–545. (14) Sheng, Ch. Fuel 2007, 86, 2316–2324. (15) Koszorek, A.; Krzesinska, M.; Pusz, S.; Pilawa, B.; Kwieci nska, B. Int. J. Coal Geol. 2009, 77, 363–371. (16) Kittel, Ch. Introduction to Solid State Physics; PWN: Warsaw, Poland, 1975 (in Polish). (17) Sekine, Y.; Ishikawa, K.; Kikuchi, E.; Matsukata, M.; Akimoto, A. Fuel 2006, 85, 122–126. (18) Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Poschl, U. Carbon 2005, 43, 1731–1742. (19) Kwiecinska, B.; Suarez-Ruiz, I.; Paluszkiewicz, C.; Rodriques, S. Int. J. Coal Geol. 2010, 84, 206–212. (20) Wang, W.; Thomas, K.; Poultney, R.; Willmers, R. Carbon 1991, 33, 1525–1535. (21) Lee, Y. J. J. Nucl. Mater. 2004, 325, 174–179. (22) Zhu, X.; Sheng, Ch. Energy Fuels 2010, 91, 837–842. (23) Li, Ch. Z. Fuel 2007, 86, 1664–1683. (24) Tay, H. L.; Li, Ch. Z. Fuel Process. Technol. 2010, 91, 800–804. (25) McCulloch, D. G.; Prawer, S.; Hoffman, A. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 5905–5917. (26) Krzesinska, M.; Pusz, S.; Sme-dowski, y. Int. J. Coal Geol. 2009, 78, 169–176. (27) Oberlin, A. Carbon 1984, 22, 521–541.
3149
dx.doi.org/10.1021/ef200609t |Energy Fuels 2011, 25, 3142–3149
