In Situ Raman Spectroscopy Study on Catalytic Pyrolysis of a

Subscriber access provided by University of Florida | Smathers Libraries

Article

In-situ Raman spectroscopy study on catalytic pyrolysis of a bituminous coal Huaili Zhu, Guangsuo Yu, Qinghua Guo, and Xingjun Wang Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 02 May 2017 Downloaded from http://pubs.acs.org on May 6, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

In-situ Raman spectroscopy study on catalytic pyrolysis of a bituminous coal

2

Huaili Zhu, Guangsuo Yu*, Qinghua Guo, Xingjun Wang*

3

Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education

4

East China University of Science and Technology, Shanghai, 200237 (PR China)1

5

Abstract: How different catalysts would affect the evolution of char structure with increasing temperature in

6

pyrolysis of coal is fundamentally important for coal clean utilization. In this study, we applied in-situ Raman

7

spectroscopy and a fixed-bed reactor to characterize the evolution of char structure and product gas formation

8

behavior. The results showed that the formation curves of main gases presented two stages and the catalyst

9

enhanced the pyrolysis significantly. The Raman spectra were fitted with a combination of 4 Lorentzian bands (D1,

10

D2, D4, G) and 1 Gaussian band (D3) in the first-order region. Spectral parameters, such as band position, full

11

widths at half maximum (FWHM) and band area ratio, were used to characterize char structure. The D1 and G

12

band FWHM, band area ratios ID1/IG, ID3/IG and ID4/IG increased with increasing temperature while the D1 and G

13

band positions and IG/IAll decreased indicating a decrease in the ordering of char structure. The addition of catalyst

14

led to a lower degree of char structure order. A thermogravimetric analysis (TGA) was also used to measure the

15

reactivity of char derived from pyrolysis and the results showed a good correlation between reactivity indexes and

16

IG/IAll.

17

Keywords: coal pyrolysis; char structure; in-situ Raman spectroscopy; gasification reactivity

18

1 Introduction

19

Gasification has been an efficient technology for coal clean utilization. The whole process of coal

20

gasification involves two main steps: coal pyrolysis and char gasification. As the prior step of char gasification,

*Corresponding authors. Tel.: +86-21-64252974; Fax: +86-21-64251312. E-mail: [email protected](Guangsuo Yu); [email protected](Xingjun Wang)

ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

21

pyrolysis or devolatilization of coal is essential and has been extensively studied over the past decades.1-3 Good

22

understanding of the mechanism of pyrolysis and decomposition reactions of coal would help clarifying the char

23

structure evolution. Pyrolysis conditions, such as heating rate, temperature and catalyst, have dramatically

24

influence on the evolution of char structure which affects the gasification reactivity of char.

25

In pyrolysis process, coal is devolatilized with the production of char, gas and tar. In initial time, temperature

26

is low and the weak non-covalent bonds such as hydrogen bond are cracked and reduced.4 With rising temperature,

27

bridge bonds begin to be cleaved, resulting in the formation of free radical groups and a large amount of CO and

28

CO2. Meanwhile, the residue char undergoes further condensation reactions, which has been recognized as one of

29

the primary reasons responsible for the low reaction rate in the later stage of char gasification.5 Considerable

30

literatures have reported that metal-based catalyst, such as alkalis (K),6-8 alkaline earths (Ca)9-11 and transition

31

metals (Fe),12 can significantly improve the pyrolysis and gasification reactivity of carbon materials, which is

32

partially due to catalytic effect on chemical structure of char in pyrolysis process. Therefore, investigating how a

33

catalyst would affect coal pyrolysis behavior and char structure evolution is fundamentally important for coal

34

clean utilization technologies.

35

In the past decades, considerable works have been done on carbon materials, such as soot, coal and biomass,

36

by using different experiment apparatuses combined with Raman spectroscopy analytical technique. Li13-15 and his

37

coworkers worked on Victorian brown coal using fluidized-bed/fixed reactor and found correlations between char

38

structure and pyrolysis/gasification behaviors. Effect of bio-char structure on its gasification reactivity was also

39

studied by using a novel quartz reactor and the results showed that the structure of bio-char played a more

40

dominant role in the char intrinsic combustion reactivity.16 Thermo gravity analysis (TGA) combined with Raman

41

spectroscopy was applied in investigation of effect of char structure on combustion reactivity and the results

42

showed that the increase of char microstructural order under heat treatment could be characterized by Raman


Page 2 of 34

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

43

parameters and the combustion reactivity of the chars from demineralized coals was found to have good

44

correlations with band area ratios.17 A gas-fired drum pyrolyser18 and drop tube furnace (DTF)19 were also been

45

used as experiment apparatuses to study the evolution of biomass/coal char structure.

46

Numerous analytical techniques, such as X-ray diffraction (XRD),20, 25-29

21

Fourier transform infrared

47

spectroscopy (FTIR),22-24 Raman spectroscopy

and transmission electron microscopy (TEM),19, 30 have been

48

used to characterize the evolution of char structure, and good correlations between analytical parameters and char

49

structure have been established. XRD technique provides information about stacking structure of aromatic layers

50

as well as a size of layers, while TEM illustrates the change of carbon crystal structure. FTIR spectroscopy is used

51

to record the chemical information such as C-H bond of aromatic/aliphatic and oxygen-containing groups, but

52

some useful information such as molecular structure is still unachievable by FTIR.31 For carbon materials,

53

however, Raman spectroscopy is a more suitable technique to illustrate the carbon structure for its sensitive not

54

only to crystal structures but also to molecular structures.27

55

However, the off-line data collected from different experiments using Raman spectroscopy analytic technique

56

cannot directly reflect the changes of coal structure during heating process；While the in-situ Raman spectroscopy

57

can achieve the purpose of reflecting the changes of char structure directly. In-situ Raman spectroscopy has not

58

been widely used on coal pyrolysis/gasification but has been developed rapidly on graphene32 and other research

59

areas.33 In this work, in-situ Raman spectroscopy was used to investigate the catalytic pyrolysis process of a

60

Chinese bituminous coal under isothermal heating condition. Three different catalysts, Fe2O3, Ca(OH)2 and

61

K2CO3, were chosen in the experiments. A fixed-bed reactor and TGA were also used to characterize the

62

microstructure changes and gasification reactivity of char derived from coal pyrolysis. The objective was to apply

63

in-situ Raman spectroscopy to characterize the evolution of coal char microstructure directly under different

64

temperature in heating process and to investigate the correlation between char chemical structure and pyrolysis


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

65

behavior as well as the gasification reactivity of char.

66

2 Experimental

67

2.1 Materials

68

Raw materials used in the study were a Chinese bituminous coal named Shenfu coal (SF) and three kinds of

69

catalysts (K2CO3, Ca(OH)2 and Fe2O3). In this study, all catalysts, including K2CO3 (purity >99.0%), Ca(OH)2

70

(purity >99.0%), and Fe2O3 (purity >99.0%), were obtained from Sinopharm Chemical Regent Co., Ltd. Before

71

experiments, the raw coal was dried at 105℃ under N2 atmosphere for 24 h and then pulverized and sieved to

72

obtain a fraction sample of particle sizes range from 80 to 120 µm. The characteristic analysis data of coal are

73

summarized in Table 1 and Table 2.

74

The catalyst loading was 10 wt% in this study, 6 which is the weight percent of the metal atoms referenced to

75

the amount of dry coal. The method of catalyst loading was a solution impregnation method. The procedure of

76

impregnating was as follows: a certain amount of catalyst powders were completely dissolved in 100 ml of

77

deionized water to form solution, and then 10 g sample was added into the solution; this mixture was stirred at

78

70–80℃ under N2 atmosphere using a magnetic stirrer until the liquid was transformed into a thickened mass.

79

Finally, this thickened mass was dried at 105 ℃ in a vacuum oven for 24 h. The dried samples were ground,

80

mixed uniformly, and sieved to a size range between 80 - 120 µm before experiments. The samples with different

81

catalysts were denoted as SF-Fe, SF-Ca and SF-K, respectively.

82

2.2 Product gas release measurement

83

A fixed-bed reactor6 was used to pyrolyze coal samples in this study. The system is primarily composed of

84

four parts: gas feeding, reactor, controlling units, and analysis units. The reactor (0.05 m i.d. and 1.0 m height) is

85

made of a special heat-resistant Inconel 625 alloy, designed to maintain up to 1223 K and 6 MPa. Metal supports

86

and quartz sand were first added to the reactor, followed by an alundum tube (50 cm height), and 5 g samples in


Page 4 of 34

Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

87

each run were placed in the middle area of the reactor. With the use of quartz and the alundum tube, the samples

88

were not in direct contact with the metal tube, avoiding catalytic effect of the metal tube on the pyrolysis of coal

89

samples.

90

The furnace was heated at a rate of 25 K/min until it reached to predetermined temperature. Meanwhile, the

91

flow rate of outlet gas was measured by a flow meter, and the major gaseous products, such as methane, hydrogen,

92

carbon monoxide and carbon dioxide, were quantitatively determined using an online non-dispersive infrared flue

93

gas analyzer (Gasboard-3100). At the end of each experiment, pure N2 was purged into the reactor until the reactor

94

was cooled to room temperature. The remaining chars were collected for further analysis. Each experiment was

95

repeated at least three times.

96

2.3 Reactivity measurement in TGA

97

The reactivity of char reacting with CO2 was measured using a TGA (made by NETZSCH, STA449F3

98

Jupiter). The sample (about 15 mg) was placed in an alumina crucible and heated at the rate of 25 K/min to 105℃

99

and held for 30 min to drive off the moisture in sample; then heated at the rate of 25 K/min to 1000℃ under a

100

stream of N2. Once the temperature reached to predetermined temperature, gasification started isothermally at

101

atmospheric pressure by sweeping CO2 into the reactor. The final mass was then taken as the mass of ash. The

102

reactivity index (Rs) of char was calculated using the following equation: 34

103

ܴ‫= ݏ‬

ଵ

(1)

ఛబ.ఱ

104

where ߬଴.ହ is the time required for the conversion to reach 50%.

105

2.4 In-situ Raman spectroscopy measurement

106

The evolution of char structure in pyrolysis was measured by an in situ Raman spectroscopy system. The

107

system is mainly composed of four parts: a Renishaw inVia Raman spectrometer, a heating stage (TS1500,

108

Linkam), a temperature controller and an online computer system gathering sample spectrogram during different


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

109

reaction phases continuously. The schematic diagram of the in-situ Raman spectroscopy system is shown in Fig. 1.

110

About 2 mg of corresponding sample was placed on the center surface of heating stage which was heated at 25

111

K/min to 105 ℃ and held for 30 mins to drive off the moisture in sample. Then the system was heated at the rate

112

of 25 K/min to prescribed temperature (800 ℃) under a continuous nitrogen flow of 100 mL/min. The Raman

113

signal was collected at 20 ℃, 200 ℃, 400 ℃, 500 ℃, 600 ℃ and 800 ℃, respectively. The ex-situ data

114

(spectra of chars derived from pyrolysis at different temperatures) were also collected as a comparison.

115

A microscope equipped with a 50*lens was used to focus the excitation laser beam (514.5 nm exciting line of

116

a Spectra Physics Ar-laser) on sample and to collect the Raman signal in the backscattered direction. The beam

117

was controlled to reach on the surface of char particles with a final laser power of ~2 mW and a spot diameter of 1

118

µm. The laser spot was much larger than the size of carbon micro-crystallites, ensuring the collection of the

119

average information from a large number of the micro-crystallites of char. The spectra were recorded in the

120

wavenumber range of 1000–1800 cm-1 covering the first-order region. The acquisition time for each spectrum was

121

30 s. For the accuracy of experimental results, each experiment was repeated three times as well.

122

3 Results and discussion

123

3.1 Product gases release behavior

124

Release behavior of main product gases were investigated in a fixed-bed reactor with an online non

125

dispersive infrared flue gas analyzer (Cube, Gasboard-3100) which can record the percentage change of gases

126

every second, and then the formation rates of main gases can be calculated. Fig. 2 presents the formation rates of

127

main gases of the four samples under the same pyrolysis conditions.

128

Compared to raw coal, the catalysts-loading samples show high pyrolysis reactivity. It is found that the main

129

gases released in pyrolysis are CO, CO2, CH4 and H2, and the devolatilization does not start until the temperature

130

reached to 300 ℃. CO2 and CO release firstly followed by CH4, CnHm and H2, which indicates that oxygen


Page 6 of 34

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

131

containing functional groups crack first to produce CO2 and CO and then the aromatic and aliphatic groups crack

132

at higher temperature to produce CH4, CnHm and H2, which is consistent with those literatures.24, 35, 36 The oxygen

133

containing functional groups usually contain C=O groups in esters, quinones, carboxylic acids and carbonyl

134

compounds. At low temperature, CO and CO2 are mainly derived from the decomposition of carboxylic acids and

135

carboxyl compounds. At high temperature, the more stable oxygen-contained groups such as C=O groups in esters

136

and quinones decompose with the release of CO and CO2.37 When the temperature rises up to 400℃, a large

137

amount of H2 with a few of CH4 and CnHm appear. It can be seen in Fig. 2a that H2 shows high formation rate, a

138

wide curve peak starts at approximate 400 ℃ and reaches maximum at 800 ℃. For SF-Fe sample, the curve

139

peak of H2 formation rate shows a wider peak width indicating high value of total H2 yield than SF sample (Fig.

140

2b). H2 formation rates of SF-Ca and SF-K sample are enhanced quickly and reach maximum values at the

141

temperature below 700 ℃ (Fig. 2c and Fig. 2d), which means a better catalytic effect of Ca/K-based catalyst than

142

Fe2O3. H2 derives from the decomposition of aromatic structures and heterocyclic compounds at high

143

temperature.3 The CH4 formation rate curves show highly similarity for the four samples and start at about 400 ℃

144

and then reach a maximum at temperature between 400 ℃ and 500 ℃.

145

It is obvious that the pyrolysis process is divided into two stages and the second stage starts at the

146

temperature varied from approximate 600 ℃ to 700 ℃, and the gas formation rate is enhanced again. Fig. 2b

147

and Fig. 2c show that the second stage is extremely enhanced by catalysts and the Ca-based catalyst has a greater

148

catalytic effect than a Fe-based catalyst for H2 and CO production. The CO2 formation rate is enhanced relative to

149

that for the other catalyst-impregnated samples while the CO formation is inhibited and there is nearly no CO

150

released at the first stage, which may be caused by the high content of carbonate in the initial time. The probable

151

reactions are as follows: 6

152

K2CO3+C-O→K2O2-C+CO2

(2)


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

153 154

K2CO3+C=O→K2O2-C+CO2

Page 8 of 34

(3)

where K2O2-C is an intermediate produced at low temperature.

155

For SF-Ca and SF-Fe sample, CO formation rate is dramatically enhanced at the second stage, which is

156

probably caused by the improved decomposition of esters and quinones under the effect of Ca/Fe- based catalysts.

157

3.2 In-situ Raman spectroscopy study

158

Fig. 3 shows the baseline-corrected Raman spectra of samples gathered at different temperatures. It can be

159

found that the Raman intensity decreases with increasing temperature for all samples and there are two

160

characteristic peaks at 1350 cm-1 (D band or “defect” band) and 1580 cm-1 (G band or “Graphite” band) in each

161

spectrum. The intensity of G band is stronger than that of D band. The variations of G and D bands intensity

162

reflect the change of char structure in pyrolysis process. It is reported that both Raman scattering ability and the

163

light absorptivity of the samples can affect Raman intensity,38 and the structural change affects the light

164

absorptivity.

165

Furthermore, for getting more spectral information such as peak position, the full width at half maximum

166

(FWHM) and integrated area (I) of each band and better understanding of char structure evolution in pyrolysis

167

experiments, a curve fitting software, Origin8.5/Peak Fitting Module, was used to resolve Raman spectra into 4

168

Lorentzian bands (G, D1, D2 and D4) and 1 Gaussian band (D3 band) (Fig. 4). The D1 band is commonly called

169

the defect band and appears at ~ 1350 cm-1 and can be attributed to the in-plane imperfections such as defects and

170

heteroatoms and corresponds to a graphitic lattice vibration mode with A1g symmetry.27, 39, 40 The D2 band at

171

~1620 cm-1 is always appearing as a shoulder on the G band, which represents the vibration mode of disordered

172

graphitic lattices and corresponds to a graphitic lattice mode with E2g symmetry.25 41 The D3 band, at ~ 1500 cm-1,

173

is suggested to originate from a sp2 band form of amorphous carbon including organic molecules and fragments

174

of functional groups26 and the D4 band at ~ 1200 cm-1 is still under debate for its attribution and is tentatively


Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

175

attributed to sp2-sp3 bonds or C–C and C=C stretching vibrations of polyene-like structures.27, 42, 43 The G band or

176

‘‘Graphite’’ band (~ 1580 cm-1) corresponds to an ideal graphitic lattice vibration mode with E2g symmetry.25, 44

177

3.2.1 FWHM and peak position of bands

178

Fig. 4 shows curve-fitted results of SF coal in the first-order region at room temperature. It provides typical

179

information about the microstructure of SF bituminous coal. The raw spectrum in the first-order region has two

180

obvious bands at ~1350 cm-1 and ~1580 cm-1. It can be found that the G and D2 band are sharp and have narrow

181

FWHM, while the D1, D3 and D4 band have wider FWHM indicating the poor order of SF coal.

182

The spectral parameters, peak position and FWHM, have been widely studied for characterizing the structure

183

of carbon materials and good correlation between Raman spectral parameters and the degree of carbon structure

184

order has been discovered.45-47 The variations of D1 and G band FWHM and position with the increasing

185

temperature in pyrolysis process are shown in Fig. 5

186

The results show that the D1 band FWHM of the four samples increase with increasing temperature, while

187

the G band FWHM increases initially and then decreases at 600 ℃. The D1 band FWHM of SF-Fe has the

188

maximum increase range and increases from 172 cm-1 at 20℃ to 220 cm-1 at 800 ℃, while the D1 band FWHM

189

of SF increases from 161 cm-1 at 20 ℃ to 185 cm-1 at 800 ℃. Fig. 5b reveals that the crystalline components

190

increase at first stage and decrease at second stage and the final values of G bands FWHM indicate that the carbon

191

structure order decreases at high temperature, which may be caused by the thermal crack of carbon at high

192

temperature. The wider G bands FWHM of SF-Ca and SF-K samples also suggest that the Ca/K-based catalysts

193

play an important role in cracking carbon at high temperature.

194

Fig. 5c shows that D1 band positions of all samples decrease with increasing temperature reflecting the

195

fracture of large aromatic ring systems and the formation of heteroatom groups, which is consistent with Fig. 5a.

196

The different D1 band positions of four samples in initial time indicate that the catalyst loading process at 105 ℃


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

197

has influence on char structure. The G band positions are shift to low wavenumber with the increase of

198

temperature as shown in Fig 5d.

199

The band position and band FWHM were often used to characterize char structure order.48 However, because

200

Raman measurements only yield relative spectra, the band parameters, particularly the FWHMs, depend to some

201

extent on the recorded intensities (i.e. count points) of each spectrum.49 Fig. 5 shows that both band position and

202

FWHM vary with temperature and parameters of different chars have no obvious trend. So simply using band

203

position or FWHM is not enough to represent the evolution of char structure. The band area ratio, including D1,

204

D2, D3 and D4 band to G band (denoted as ID1/IG, ID2/IG, ID3/IG, ID4/IG) and G band to the integrated area (denoted

205

as IG/IAll), is a parameter combined two parameters and is widely used to characterize the char structure.

206

3.2.2 Band area ratios

207

The results of band area ratios variation with increasing temperature are showed in Fig. 6. It can be seen that

208

ID1/IG, ID3/IG and ID4/IG increase with increasing temperature significantly while ID2/IG has a decrease trend. As

209

reported by Tuinstra in 1970s,50 the ratio ID1/IG is inversely proportional to the microcrystalline planar size, so the

210

increase of ID1/IG with increasing temperature represents the decrease of the graphitic microcrystalline planar size,

211

as shown in Fig. 6a. It is also can be found that the ID1/IG of SF-Ca and SF-K samples are higher than that of

212

SF-Fe and SF samples at high temperature indicating considerable effect of Ca and K on cracking the graphitic

213

microcrystalline planar. It is noted that the ID1/IG ratio as well as ID3/IG and ID4/IG of SF-Fe is lower than that of SF

214

sample, which may be caused by the comprehensive effects of devolatilization and catalytic. In the

215

devolatilization process, the char structure is condensed caused by the release of volatile, thus leading the decrease

216

of ID1/IG.17 Meanwhile, the catalyst reacts with carbon with the cracking of the carbon structure leading the

217

increase of ID1/IG. For SF-Fe sample, the comprehensive effects of Fe2O3 leading the lower ID1/IG than that of SF.

218

The ID2/IG shows an opposite trend that decreases with increasing temperature as shown in Fig. 6b. As stated


Page 10 of 34

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

219

above, the D2 band represents the disordered graphitic lattices at the surface of graphitic crystal. In pyrolysis

220

process, those surface structures are broken leading the diminishing of ID2/IG value. The obviously different ID2/IG

221

ratios of four samples in initial time suggest that catalyst loading process at 105 ℃ also has significantly impact

222

on the surface structures of coal.

223

The evolution of the amorphous carbon structure of samples with increasing temperature can be

224

characterized by ID3/IG ratio as shown in Fig. 6c. Similar trends of ID3/IG ratio curves are observed in Fig. 6c

225

indicating the increase of amorphous carbon structure. As temperature rising, the ID4/IG ratios increase

226

simultaneously (Fig. 6d), which is caused by the cracking of larger aromatic rings. The high ID4/IG ratio is

227

attributed to the abundance of sp3 or sp2–sp3 mixed structures. It can be found that the SF sample has the highest

228

value of ID4/IG ratio at high temperature, which may be caused by the less consumption of carbon and

229

oxygen-contained groups in initial time as reported by Chabalala.51

230

Fig. 6e shows the variations of IG/IAll ratios of four samples with increasing temperature. For samples of SF

231

and SF-Fe, the IG/IAll ratios increase firstly and then decrease, while the IG/IAll ratios of SF-Ca and SF-K samples

232

decrease immediately. But the final values of IG/IAll ratios are lower than that in initial time indicating the reducing

233

of graphite structure in char. Combined with the results in Fig. 5, it can be inferred that the degree of char

234

structure at high temperature is lower than that at normal temperature and catalysts have effects on carbon

235

cracking, thus making the catalyst-loading samples obtain lower degree of carbon structure order than raw coal.

236

The catalytic effects of the three catalysts can be ranked as K2CO3>Ca(OH)2>Fe2O3.

237

3.2.3 Ex-situ Raman spectra

238

For comparison, the spectra of chars prepared ex-situ at different temperatures were measured. The results

239

(800 ℃ for instance) of in-situ and ex situ spectra are shown in Fig.7. It can be found that ex-situ spectra of all

240

samples are different from in-situ spectra significantly. Raman intensities of ex-situ spectra are higher than of


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

241

in-situ spectra for the reason of chemical structural change at high temperature. G and D band position of in-situ

242

spectra are shift to low wavenumber meaning the fracture of char structure. For getting more information about

243

char structural change, band area ratios of ID1/IG and IG/IAll variations with temperatures are shown in Fig. 8. The

244

trends of band area ratios of ID2/IG, ID3/IG, ID4/IG are similar to that of ID1/IG and not shown here.

245

Fig. 8 shows that ID1/IG increases and IG/IAll decreases with increase temperature, which means that all chars

246

transformed to disordered structure. Compared with in-situ results in Fig. 6, it can be found that ID1/IG ratios are

247

lower and IG/IAll ratios are higher than that of in-situ spectra. In heating process, highly ordered char structure is

248

partially thermal cracked making char structure order decrease, and the reactions between catalyst and carbon also

249

make ordered char structure decrease. Therefore, ID1/IG and IG/IAll ratios of ex-situ spectra at the same condition

250

are significantly different from that of in-situ spectra. It can be inferred that catalyst reacts with carbon at high

251

temperature with producing more disordered char structure which not exist in chars at normal temperature.

252

3.3 Relationship between Raman parameters and char reactivity

253

The gasification reactivities of four different chars derived from pyrolysis experiments are shown in Fig. 9.

254

Fig. 9a shows the variations of char conversion with gasification time and Fig. 9b shows the reactivity indexes of

255

different samples. It is obvious that the SF-K char has the highest reactivity followed by SF-Ca and SF-Fe chars

256

and the SF char has the lowest reactivity, which is consistent with the results of in-situ Raman spectroscopy.

257

In catalytic gasification process, a part of catalyst combines with carbon and transforms to active

258

intermediate which would react with CO2 in the follow step. Through this transformation, the catalyst affects the

259

evolution of char structure and further affects the gasification reactivity of char. Besides, the true densities of chars

260

have been measured and the results are shown in Fig. 10. True density refers to the density of solid matter after

261

removing the internal pore or space between particles and is connected to porosity and represents the physical structure

262

of char. It can be found that true densities of chars with catalysts are higher than that of non-catalyst because of the


Page 12 of 34

Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

263

release of more volatiles. SF-Ca char and SF-Fe char, which have higher true densities compared to SF char, have

264

higher reactivities. It can be inferred that the physical structure is not the main factor influencing on the reactivity

265

of char and the different reactivity is attributed to the chemical characteristics.

266

The relationship between IG/IAll ratio at 800 ℃ and reactivity index of char is shown in Fig. 11. It can be

267

seen that good correlation is obtained (correlation coefficients better than 0.9489). With the increase of IG/IAll ratio,

268

the reactivity of char decrease linearly. The good correlation confirms that the strong connection between char

269

structure reflected by the in-situ Raman spectra and gasification reactivity. Therefore, the reactivity of different

270

chars derived from catalytic pyrolysis can be predicted by in-situ Raman spectroscopy technique.

271

4. Conclusion

272

In-situ Raman spectroscopy was used in this work for better understanding the evolution of char structure

273

with increasing temperature directly and clarification of catalytic effects of different catalysts on pyrolysis of a

274

bituminous coal. The conclusions were achieved as follows:

275

(1) The main product gases emission behaviors of different samples were studied in a fixed-bed reactor. The

276

results showed that CO2 and CO released first at the temperature above 300 ℃ followed by CH4, H2

277

and CnHm at the temperature above 400 ℃. With the addition of catalyst, the pyrolysis reactivity was

278

enhanced. The formation rates curves of main gases suggested that the pyrolysis process presented two

279

stages.

280

(2) Raman spectra of four samples at different temperatures were used to characterize the evolution of char

281

structure during pyrolysis. The increased D1 and G band FWHM, ID1/IG, ID3/IG and ID4/IG as well as the

282

decreased D1 and G band positions and IG/IAll at high temperature indicated the decrease of the carbon

283

structure order degree. With the addition of catalysts, the char obtained lower degree of carbon structure

284

than that of raw coal. The rank of the three catalysts is K2CO3>Ca(OH)2>Fe2O3.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

285

(3) Good correlation between IG/IAll ratios and reactivity indexes of chars derived from pyrolysis was found.

286

With the increase of IG/IAll ratio, the reactivity of char decreased linearly. Therefore, the in-situ Raman

287

spectroscopy could be a useful technique to predict the char reactivity in pyrolysis of coal.

288 289

Acknowledgements This work is partially supported by National Nature Science Foundation of China (Grant 21176078).

290

References

291

(1) Li, X.; Hayashi, J.; Li, C., FT-Raman spectroscopic study of the evolution of char structure during the

292

pyrolysis of a Victorian brown coal. Fuel 2006, 85, (12-13), 1700-1707.

293

(2) Amin, M. N.; Li, Y.; Razzaq, R.; Lu, X.; Li, C.; Zhang, S., Pyrolysis of low rank coal by nickel based zeolite

294

catalysts in the two-staged bed reactor. Journal of Analytical & Applied Pyrolysis 2016, 118, 54-62.

295

(3) Shi, L.; Wang, X.; Zhang, S.; Wu, X.; Yuan, L.; Tang, Z., A new in-situ pyrolytic time-of-flight mass

296

spectrometer instrument for study on coal pyrolysis. Journal of Analytical and Applied Pyrolysis 2016, 117,

297

347-353.

298

(4) Lin, X.; Wang, C.; Ideta, K.; Jin, M.; Nishiyama, Y.; Wang, Y.; Yoon, S.; Mochida, I., Insights into the

299

functional group transformation of a chinese brown coal during slow pyrolysis by combining various experiments.

300

Fuel 2014, 118, 257-264.

301

(5) Miura, K.; Hashimoto, K.; Silveston, P. L., Factors affecting the reactivity of coal chars during gasification,

302

and indices representing reactivity. Fuel 1989, 68, (11), 1461-1475.

303

(6) Zhu, H.; Wang, X.; Zhang, J.; Yao, K.; Yu, G.; Wang, X., Investigation of K2CO3-Catalyzed Pyrolysis and

304

Steam Gasification of Coal Char. Energy Technol-Ger 2015, 3, (9), 961-967.

305

(7) Skodras, G., Catalysis and compensation effect of K 2 CO 3 in low-rank coal — CO 2 gasification. Central

306

European Journal of Chemistry 2013, 11, (7), 1187-1200.


Page 14 of 34

Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

307

(8) Kopyscinski, J.; Rahman, M.; Gupta, R.; Mims, C. A.; Hill, J. M., K 2 CO 3 catalyzed CO 2 gasification of

308

ash-free coal. Interactions of the catalyst with carbon in N 2 and CO 2 atmosphere. Fuel 2014, 117, (1),

309

1181-1189.

310

(9) Jie, H.; Liu, L.; Cui, M.; Jie, W., Calcium-promoted catalytic activity of potassium carbonate for gasification

311

of coal char: The synergistic effect unrelated to mineral matter in coal. Fuel 2013, 111, (9), 628–635.

312

(10) Chen, S. G.; Yang, R. T., Mechanism of alkali and alkaline earth catalyzed gasification of graphite by CO 2

313

and H 2 O studied by electron microscopy. Journal of Catalysis 1992, 138, (1), 12-23.

314

(11) Matsuoka, K.; Yamashita, T.; Kuramoto, K.; Suzuki, Y.; Takaya, A.; Tomita, A., Transformation of alkali and

315

alkaline earth metals in low rank coal during gasification. Fuel 2008, 87, (6), 885-893.

316

(12) Gong, X.; Guo, Z.; Wang, Z., Variation of Char Structure during Anthracite Pyrolysis Catalyzed by Fe2O3

317

and Its Influence on Char Combustion Reactivity. Energ Fuel 2009, 23, (3), 4547-4552.

318

(13) Li, X.; Li, C., Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the

319

pyrolysis and gasification of Victorian brown coal. Part VIII. Catalysis and changes in char structure during

320

gasification in steam. Fuel 2006, 85, (10-11), 1518-1525.

321

(14) Li, X.; Hayashi, J.; Li, C., Volatilisation and catalytic effects of alkali and alkaline earth metallic species

322

during the pyrolysis and gasification of Victorian brown coal. Part VII. Raman spectroscopic study on the changes

323

in char structure during the catalytic gasification in air. Fuel 2006, 85, (10-11), 1509-1517.

324

(15) Zhang, S.; Hayashi, J.-i.; Li, C.-Z., Volatilisation and catalytic effects of alkali and alkaline earth metallic

325

species during the pyrolysis and gasification of Victorian brown coal. Part IX. Effects of volatile-char interactions

326

on char–H2O and char–O2 reactivities. Fuel 2011, 90, (4), 1655-1661.

327

(16) Asadullah, M.; Zhang, S.; Min, Z.; Yimsiri, P.; Li, C. Z., Effects of biomass char structure on its gasification

328

reactivity. Bioresource Technol 2010, 101, (20), 7935-43.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

329

(17) Sheng, C., Char structure characterised by Raman spectroscopy and its correlations with combustion

330

reactivity. Fuel 2007, 86, (15), 2316-2324.

331

(18) McDonald-Wharry, J.; Manley-Harris, M.; Pickering, K., Carbonisation of biomass-derived chars and the

332

thermal reduction of a graphene oxide sample studied using Raman spectroscopy. Carbon 2013, 59, 383-405.

333

(19) Yoshizawa, N.; Maruyama, K.; Yamashita, T.; Akimoto, A., Dependence of microscopic structure and

334

swelling property of DTF chars upon heat-treatment temperature. Fuel 2006, 85, (14–15), 2064-2070.

335

(20) Liu, H.; Xu, L.; Jin, Y.; Fan, B.; Qiao, X.; Yang, Y., Effect of coal rank on structure and dielectric properties

336

of chars. Fuel 2015, 153, 249-256.

337

(21) Lu, L.; Sahajwalla, V.; Kong, C.; Harris, D., Quantitative X-ray diffraction analysis and its application to

338

various coals. Carbon 2001, 39, (12), 1821-1833.

339

(22) Xiao, J.; Zhong, Q.; Li, F.; Huang, J.; Zhang, Y.; Wang, B., Modeling the Change of Green Coke to Calcined

340

Coke Using Qingdao High-Sulfur Petroleum Coke. Energ Fuel 2015, 29, (5), 3345–3352.

341

(23) Solomon, P. R.; Carangelo, R. M., FTIR analaysis of coal. 1. techniques and determination of hydroxyl

342

concentrations. Fuel 1982, 61, (7), 663-669.

343

(24) Murakami, K.; Shirato, H.; Nishiyama, Y., In situ infrared spectroscopic study of the effects of exchanged

344

cations on thermal decomposition of a brown coal. Fuel 1997, 76, (7), 655-661.

345

(25) Cuesta, A.; Dhamelincourt, P.; Laureyns, J.; Martínez-Alonso, A.; Tascón, J., Raman microprobe studies on

346

carbon materials. Carbon 1994, 32, (8), 1523-1532.

347

(26) Jawhari, T.; Roid, A.; Casado, J., Raman spectroscopic characterization of some commercially available

348

carbon black materials. Carbon 1995, 33, (11), 1561-1565.

349

(27) Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U., Raman microspectroscopy of soot and

350

related carbonaceous materials: Spectral analysis and structural information. Carbon 2005, 43, (8), 1731-1742.


Page 16 of 34

Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

351

(28) Daniel M. Keown; Xiaojiang Li; Junichiro Hayashi; ChunZhu Li, Characterization of the Structural Features

352

of Char from the Pyrolysis of Cane Trash Using Fourier Transform−Raman Spectroscopy. Energy Fuels 2007, 21,

353

(3), 1816-1821.

354

(29) Tay, H. L.; Kajitani, S.; Shuai, W.; Li, C. Z., A preliminary Raman spectroscopic perspective for the roles of

355

catalysts during char gasification. Fuel 2014, 121, 165-172.

356

(30) Oberlin, A., Application of dark-field electron microscopy to carbon study. Carbon 1979, 17, (1), 7-20.

357

(31) Li, K.; Khanna, R.; Zhang, J.; Barati, M.; Liu, Z.; Xu, T.; Yang, T.; Sahajwalla, V., A Comprehensive

358

Investigation on Various Structural Features of Bituminous Coals using Advanced Analytical Techniques. Energ

359

Fuel 2015, 29, (11), 7178-7189.

360

(32) Kalbac, M.; Kong, J.; Kavan, L.; Farhat, H.; Janda, P.; Dresselhaus, M. S., Raman Spectroscopy and in Situ

361

Raman Spectroelectrochemistry of Bilayer C-12/C-13 Graphene. Nano Letters 2011, 11, (5), 1957-63.

362

(33) Lee, J. M.; Cho, S. J.; Lee, J. D.; Linga, P.; Kang, K. C.; Lee, J., Insights into the Kinetics of Methane

363

Hydrate Formation in a Stirred Tank Reactor by In Situ Raman Spectroscopy. Energy Technol-Ger 2015, 3, (9),

364

925-934.

365

(34) Heek, K. H. V.; Mühlen, H. J., Aspects of coal properties and constitution important for gasification. Fuel

366

1985, 64, (10), 1405-1414.

367

(35) Ibarra, J.; Muñoz, E.; Moliner, R., FTIR study of the evolution of coal structure during the coalification

368

process. Organic Geochemistry 1996, 24, (6–7), 725-735.

369

(36) Niu, Z.; Liu, G.; Yin, H.; Wu, D.; Zhou, C., Investigation of mechanism and kinetics of non-isothermal low

370

temperature pyrolysis of perhydrous bituminous coal by in-situ FTIR. Fuel 2016, 172, 1-10.

371

(37) Heek, K. H. V.; Hodek, W., Structure and pyrolysis behaviour of different coals and relevant model

372

substances. Fuel 1994, 73, (6), 886-896.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

373

(38) Sforna, M. C.; Zuilen, M. A. V.; Philippot, P., Structural characterization by Raman hyperspectral mapping of

374

organic carbon in the 3.46 billion-year-old Apex chert, Western Australia. Geochimica Et Cosmochimica Acta

375

2014, 124, (1), 18–33.

376

(39) Ferrari, A. C.; Robertson, J., Interpretation of Raman spectra of disordered and amorphous carbon. Physical

377

Review B Condensed Matter 2000, 61, (20), 14095-14107.

378

(40) Wang, Y.; Alsmeyer, D. C.; Mccreery, R. L., Raman spectroscopy of carbon materials: Structural basis of

379

observed spectra. Chemistry of Materials; (United States) 1990, 2:5, (5), 557-563.

380

(41) Beyssac, O.; Goffé, B.; Petitet, J. P.; Froigneux, E.; Moreau, M.; Rouzaud, J. N., On the characterization of

381

disordered and heterogeneous carbonaceous materials by Raman spectroscopy. Spectrochimica Acta Part A

382

Molecular & Biomolecular Spectroscopy 2003, 59, (10), 2267-76.

383

(42) Dippel, B.; Heintzenberg, J., Soot characterization in atmospheric particles from different sources by NIR FT

384

Raman spectroscopy. Journal of Aerosol Science 1999, 30, S907–S908.

385

(43) Zaida, A.; Bar-Ziv, E.; Radovic, L. R.; Lee, Y. J., Further development of Raman Microprobe spectroscopy

386

for characterization of char reactivity. Proceedings of the Combustion Institute 2007, 31, (2), 1881-1887.

387

(44) Al-Jishi, R.; Dresselhaus, G., Lattice-dynamical model for graphite. Physical Review B 1982, 26, (8),

388

4514-4522.

389

(45) Tay, H.-L.; Li, C.-Z., Changes in char reactivity and structure during the gasification of a Victorian brown

390

coal: Comparison between gasification in O2 and CO2. Fuel Processing Technology 2010, 91, (8), 800-804.

391

(46) Zhang, L.; Kajitani, S.; Umemoto, S.; Wang, S.; Quyn, D.; Song, Y.; Li, T.; Zhang, S.; Dong, L.; Li, C.-Z.,

392

Changes in nascent char structure during the gasification of low-rank coals in CO2. Fuel 2015, 158, 711-718.

393

(47) Tsaneva, V. N.; Kwapinski, W.; Teng, X.; Glowacki, B. A., Assessment of the structural evolution of carbons

394

from microwave plasma natural gas reforming and biomass pyrolysis using Raman spectroscopy. Carbon 2014,


Page 18 of 34

Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

395

80, (1), 617-628.

396

(48) Yoshida, A., Kaburagi, Y., Hishiyama, Y., Full width at half maximum intensity of the G band in the first

397

order Raman spectrum of carbon material as a parameter for graphitization. Carbon 2006, 44, 2333–2344.

398

(49) Sheng, C., Char structure characterised by Raman spectroscopy and its correlations with combustion

399

reactivity. Fuel 2007, 86, 2316-2324.

400

(50) Tuinstra, F.; Koenig, J. L., Raman Spectrum of Graphite. Journal of Chemical Physics 1970, 53, (3),

401

1126-1130.

402

(51) Chabalala, V. P.; Wagner, N.; Potgieter-Vermaak, S., Investigation into the evolution of char structure using

403

Raman spectroscopy in conjunction with coal petrography; Part 1. Fuel Processing Technology 2011, 92, (4),

404

750-756.

405


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

406 407 408 409 410 411 412 413 414 415 416 417 418

Figure captions Fig. 1. Schematic diagram of in-situ Raman spectroscopy Fig. 2. Gas formation rates of four samples Fig. 3. Baseline-corrected Raman spectra of four samples at different temperatures. Fig. 4. Curve-fitting for SF coal of Raman spectra in the first-order region. Fig. 5. Variations of D1 and G band FWHM and position with increasing temperature Fig. 6. Variations of band area ratio with increasing temperature Fig. 7. Baseline-corrected Raman spectra of ex-situ and in-situ at 800℃. Fig. 8. Band area ratios of chars ex-situ prepared at different temperatures Fig. 9. a: Variations of char conversion with gasification time; b: Reactivity indexes of different chars Fig. 10. True densities of coal and chars prepared at 800℃ Fig. 11. Correlation between reactivity index and band area ratio of IG/IAll


Page 20 of 34

Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

419 420 421

Fig. 1. Schematic diagram of in-situ Raman spectroscopy


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

422

423 424 425

Fig. 2. Gas formation rates of four samples


Page 22 of 34

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

426

427 428 429

Fig. 3. Baseline-corrected Raman spectra of four samples at different temperatures.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

430 431

Fig. 4. Curve-fitting for SF coal of Raman spectra in the first-order region.

432 433


Page 24 of 34

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

434

435 436 437 438

Fig. 5. Variations of D1 and G band FWHM and position with increasing temperature, a: D1 band FWHM; b: G band FWHM: c: D1 band position; d: G band position


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

439

440

441 442 443

Fig. 6. Variations of band area ratio with increasing temperature


Page 26 of 34

Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

444

445 446 447

Fig. 7. Baseline-corrected Raman spectra of ex-situ and in-situ at 800℃ ℃.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

448 449 450

Fig. 8. Band area ratios of chars ex-situ prepared at different temperatures


Page 28 of 34

Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

451 452 453

Energy & Fuels

Fig. 9. a: Variations of char conversion with gasification time; b: Reactivity indexes of different chars


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

454 455

456 457 458 459

Fig. 10. True densities of coal and chars prepared at 800℃ ℃


Page 30 of 34

Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

460 461 462

Energy & Fuels

Fig. 11. Correlation between reactivity index and band area ratio of IG/IAll


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table captions

463 464

Table 1. Proximate analysis and ultimate analysis of SF coal

465

Table 2 Ash compositions of SF coal

466 467


Page 32 of 34

Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

468 469

Table 1 Proximate analysis and ultimate analysis of SF coal Proximate analysis wd /%

Ultimate analysis wd /%

Sample

SF

V

FC

A

C

H

O

N

S

33.29

58.65

8.06

74.20

4.21

11.93

0.97

0.63

470 471


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

472

Page 34 of 34

Table 2 Ash compositions of SF coal Constituent

Sample SF

w/%

Al2O3

CaO

Fe2O3

SiO2

SO3

NaO

K2 O

MgO

17.21

13.85

11.78

44.52

6.53

1.89

1.35

1.55

473 474


In Situ Raman Spectroscopy Study on Catalytic Pyrolysis of a

Recommend Documents