Structural Characterization of Carbonized Briquette Obtained From - DocsLib

sign in sign up

<<

Home , Briquette

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Journal of Analytical and Applied Pyrolysis

journal homepage: www.elsevier.com/locate/jaap

Structural characterization of carbonized briquette obtained from

anthracite powder

a a,∗ b,c a a

Yuqiong Zhao , Yongfa Zhang , Huirong Zhang , Qi Wang , Yunfei Guo

a

Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan, China

b

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, China

c

University of Chinese Academy of Sciences, Beijing, China

a r t i c l e i n f o a b s t r a c t

Article history: The structural characteristics of carbonized anthracite briquettes (CAB) obtained at different pyroly-

Received 12 June 2014

sis temperatures were studied by surface area measurements, scanning electron microscopy (SEM),

Accepted 13 January 2015

Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spec-

Available online xxx

troscopy. The results indicated that the pyrolysis of the anthracite briquette mainly included the following

three processes: drying, decomposition and bonding-repolymerization. The total pore volumes and sur-

Keywords: ◦

face areas of the CAB reached maximum values at 500 C and decreased at higher temperatures. The

Anthracite

side chains were removed during pyrolysis, leaving the CAB enriched with polyaromatics. The origi-

Pyrolysis

nal oriented anthracite crystallites were deposed, and the microcrystalline planar size La underwent a

Carbonized briquette ◦ ◦

prominent decrease before 700 C. When the pyrolysis temperature rose to 900 C, the higher pyrolysis

Structural characteristics

Raman spectroscopy temperature and more open structure of the briquette promoted the repolymerization of free radicals,

and the value of La increased from 9.03 to 14.60. The variation of La correlated well with the mechanical

strength of the CAB. The major change in La in the bonding-repolymerization process revealed stronger

interactions between the binder and the anthracite, which improved the quality of the CAB.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction briquettes. The atomic C/H ratio of the binders played an impor-

tant role in controlling the strength of carbonized briquettes, and

Fabrication of cokes consumes a large amount of coking coals binders with a C/H ratio greater than 1 were preferable. Taylor

that may strongly affect the quality of the product. Unfortunately, and C¸ oban [7] reported that the binder/coal ratio and coal parti-

the sources of these coals are being depleted, which signiﬁcantly cle size inﬂuenced the strength of carbonized briquettes. Under the

increases their price [1]. Low ash and low sulfur anthracite are used given addition of binder, the smaller coal particle size had a posi-

at low efﬁciency for burning. Using anthracite and lean coal as the tive effect on the bond between coal particles and binder. Wang [5]

raw materials to produce carbonized briquettes is an important noted that pressure in the range of 32–76 MPa could satisfactorily

technique. Thus, carbonized anthracite briquettes (CAB) could be meet the forming requirements of anthracite, while excess pressure

used for precision casting, which would efﬁciently utilize high rank promoted crack formation in the briquette during the carboniza-

coal and preserve quality coking coals for other uses [2–4]. tion process. Although numerous studies have been carried out,

Anthracite has a highly condensed aromatic structure and good many problems are still unsolved or not well solved, especially the

chemical stability; it does not soften or melt under the heating decrease of mechanical strength after high-temperature pyrolysis

condition of carbonization. In most anthracite carbonization tech- of anthracite briquettes [8,9]. To solve such problems, it is essen-

nologies, coal particles are bonded together in the presence of a tial to perform in-depth investigations on the pyrolysis behavior of

binder [4,5]. The present studies of this technique mainly investi- anthracite briquettes. Pyrolysis of bituminous coal has been exten-

gated the effects of process conditions (binder, particle distribution, sively studied, while minimal research has been conducted with

pyrolysis temperature, etc.) on the quality of the carbonized bri- anthracite briquettes [10–12].

quette. Sharma et al. [6] investigated the effect of various coal The pyrolysis of anthracite briquettes is an extremely complex

tar- and petroleum-based binders on the strength of carbonized process consisting of a series of stages, such as binder decom-

position, volatile precipitation, crystallite growth and carbonized

briquette generation. In our previous work, the gas-release prop-

∗

erties during the pyrolysis of anthracite briquette were investigated

Corresponding author. Tel.: +86 3516018676.

http://dx.doi.org/10.1016/j.jaap.2015.01.009

0165-2370/© 2015 Elsevier B.V. All rights reserved.

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

2 Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx

[4]. However, there is little comprehensive information on the

structural characteristics of carbonized briquettes, which have a

remarkable inﬂuence on the mechanical strength and other prop-

erties and should be a major research focus.

The structural characterization of coal and coal-derived prod-

ucts utilizes many different methods, such as SEM [13], FTIR

[14–16], XPS [17,18] and Raman spectroscopy [1,13,19] etc. SEM

and N2 adsorption techniques are often used to describe the mor-

phological characteristics and physical structure of coal-based

material. Pore volume and speciﬁc surface areas (SSA) are impor-

tant parameters for the characterization of carbonized briquettes

that may strongly affect their reactivity and other behaviors [20].

FTIR is a major technique used to probe the functional groups in coal

and chars [15,16]. It identiﬁes molecular vibration, both stretching

and bending, by the absorption of infrared radiation. The ener-

gies of stretching vibrations correspond to infrared radiation with

−1 −1

wave numbers between 1200 cm and 4000 cm , while bend-

−1

ing vibration is in the range of 500–1200 cm . This part of the

infrared spectrum is particularly useful for detecting the presence

of functional groups because these groups have characteristic and

invariant absorption peaks at these wavelengths. XPS has been Fig. 1. The preparation process of samples.

applied to quantitatively track carbon as well as other elements

in raw coal and coal-derived material due to surface sensitivity

The preparation of the carbonized briquette is shown in Fig. 1.

[21–23]. Raman is a powerful method for evaluating the degree

Prior to blending, the coal was crushed and screened to produce

of ordering and crystallinity of carbon-based materials due to its

four particle fractions, <0.45 mm, 0.45–1.00 mm, 1.00–2.00 mm and

remarkable sensitivity to structures that break the lattice transla-

2.00–3.00 mm. The asphalt blended with the modiﬁed coal was

tional symmetry. For coal and char structures, the Raman spectrum

used as a binder, which was denoted as AS. The preparation of the

−1 −1

generally presents two main bands at 1580 cm and 1357 cm .

modiﬁed coal was reported in detail in our previous study [32].

−1

The band at 1580 cm , often referred as the G band, represents

Subsequently, the mixing process was carried out with continuous

graphite E2g vibration and aromatic ring quadrant breathing. When

stirring to ensure good impregnation of the ﬁne anthracite with

defective graphites and disordered carbons are introduced, an addi-

the self-developed AS binder (a mixture of asphalt and modiﬁed

tional peak appears in the ﬁrst-order spectrum at approximately

coal). Then, the mixture was transferred into a 135-mm diame-

−1

1357 cm , which is usually called the D band (defected band).

ter mold and subjected to 60 MPa load. To ensure that the green

−1 −1

Other bands at 870 cm , 1230 cm and lower frequencies have

briquettes were formed under homogeneous pressure, 5 min were

also been reported, but the most interesting structural information

required to maintain after the ﬁnal pressure was reached. The form-

−1

on carbonaceous materials was produced between 1300 cm and

ing was followed by carbonization at the desired temperatures

−1

1650 cm [24–27]. Furthermore, the Raman spectral parameters ◦ ◦ ◦ ◦

(300 C, 500 C, 700 C or 900 C) with the temperature increasing

mentioned by Lespade et al. [28], mainly the position, intensity, ◦

at 3 C/min. Finally, the carbonized briquettes were obtained and

bandwidth and integrated intensity ration ID/IG, correspond to

denoted as ASt , where t represents the carbonization temperature.

structural changes and ordering degree. Since Tuinstral and Koenig

In addition, coal tar pitch and humic acid were used as binders for

[29] ﬁrst established an empirical correlation between the inten-

the preparation of reference samples denoted CPt and HAt . All sam-

sity ratio ID/IG and the crystallite size La, a number of studies on

ples were made with the same binder/coal weight ratio of 15:85.

carbon types as different as carbon ﬁbers, pitches, coals and chars

Fig. 2 is a picture of an AS900 carbonized briquette.

has been reported. Jawhari et al. [25] deconvoluted Raman spectra

to investigate the structure of carbon blacks that had a low crys-

2.2. Determination of mechanical strength

talline degree of graphitic carbons. Sme¸dowski et al. [1] obtained

many parameters calculated from Raman spectra to characterize ◦

The carbonized briquettes obtained at 900 C were crushed and

the ordered structures within cokes. These tools have the ability to

screened with a circular screen ( = 60 mm). Fifteen kilograms of

assess more information about the chemical structure and physical

samples whose diameter was above 60 mm were subjected to the

characteristics of CAB.

drum test at a rate of 25 r/min for 4 min. The mechanical strength

In this paper, SEM, FTIR, XPS, Raman and other testing methods

M40 was calculated by Formula (2.1)

were used to study the structural evolution that occurred during

m1

the pyrolysis of anthracite briquettes to investigate the pyrolysis M = × 100 (2.1)

40 m

behaviors of CAB and the effects of the structural characteristics on

the mechanical strength. where m is the weight of carbonized briquettes (g), and m1 is the

weight (g) of the samples whose diameter was larger than 40 mm

after the drum test.

2. Materials and methods 2.3. Sample characterization

2.1. Sample preparation Mercury intrusion and N2 adsorption techniques were used to

investigate the pore volumes, pore size distribution and surface

Jincheng coal was used in this experiment, and proximate and areas of samples. Pores larger than 6 nm were measured with a

ultimate analysis dates are given in Table 1. The sample was dem- Pascal 240 mercury porosimeter, while pores less than 6 nm were

ineralized to avoid the effect of mineral matter on the analysis and analyzed with a Sorptomatic1990 instrument using nitrogen as

improve the observation of coal structures [15,30,31]. adsorbed at 77 K.

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx 3

Table 1

The proximate and ultimate analysis of Jincheng coal.

Sample Proximate analysis/wt.%, ad Ultimate analysis/wt.%, daf

M A V FC C H O N S

Jincheng anthracite (JC) 3.99 9.47 7.51 79.03 92.21 2.11 2.39 0.92 0.28

Fig. 2. AS900 carbonized briquette.

SEM images of carbonized briquette were captured with a scan- pore structure was observed when the pyrolysis temperature was

◦

ning electron microscope (LEO-438VP). below 350 C. With increased pyrolysis temperature, the total pore

3 −1

The FTIR date collection was performed with a Bruker VER- volume of AS500 increased remarkably (from 0.24 to 0.87 cm g ),

−1 −1

TEX70. The spectral range was from 4000 cm to 400 cm using and the pore size distribution also changed. The volume fractions of

the KBr pellet technique. A total of 16 scans were performed with macropores and transitional pores decreased from 95.0% and 2.8%

−1

spectral resolution of 4 cm . to 90.9% and 2.8%, while the values of mesopores and micropores

X-ray photoelectron spectra were determined with an increased from 1.6% and 0.3% to 4.2% and 2.2%. Previous research

ESCALAB250 spectrometer using Al K non-monochromatic showed that breaking side chains in anthracite and binders pro-

◦

radiation. The X-ray source was operated at 200 W, and 60 eV pass duce partial ﬂuid and tar vapor at ca. 500 C [4], which could trap

energy was used for narrow scans. the released volatile gases in the solid–gel phase. Therefore, some

Raman analysis was conducted at room temperature using a new pores formed, and large pore might be divided into small

◦

Renishaw spectrometer equipped with a Si-based CCD-detector. pores, leading to an increase in total pore volumes. Over 600 C,

The 514.5 nm line of the argon laser was used for excitation with a the pyrolysis of anthracite briquettes enters into the solidiﬁcation

laser power of 20 mW. The spectra were recorded in the range of and shrinkage stage [4]. Because of pore coalescence [34], microp-

−1 −1

800 cm –1800 cm . For all spectra, a linear baseline correction ores in the carbonized briquette might collapse (from 2.2% to 0.8%),

was used, and peak analysis was performed with Origin-lab Pro7.5. and the SSA dropped to 4.88% from 28.80%. The total volume of the

The microcrystalline planar crystalline size La is given by follow- AS700 was almost the same as that of the AS500. However, the AS500

ing equation, which is valid for 400 nm <L < 700 nm as previously exhibited a higher speciﬁc surface area, which suggested that the

reported: micropores contributed the largest fraction of the total SSA.

−1 To acquire the surface morphology, representative samples

La = C(L)[ID/IG] (2.2)

were subjected to SEM. As shown in Fig. 3(a), no binder was found to

accumulate on the briquette after press molding, which indicated

C(L) ≈ C0 + LC1 (2.3)

the overall homogeneity of the mixed materials. The AS binder

−

where C(L) is the wavelength prefactor (C0 = 12.6 nm and had a strong afﬁnity for anthracite particles, which preferably wet

C1 = 0.033), and ID and IG are the intensity of the D and G bands, the coal surface and even penetrated the pores [35]. It was notice-

respectively [15]. able that the carbonized briquette had a relatively smooth surface

and less fragmentation at low pyrolysis temperatures (Fig. 3b).

◦

Increasing pyrolysis temperature up to 500 C (Fig. 3c) caused the

3. Results and discussion

micromorphology of the carbonized briquette to become more

and more irregular and demonstrated a large amount of leaﬂet

3.1. Pore structure and morphology analysis

textures that conglutinated with each other, resulting in the devel-

opment of porosity. Wang [5] reported that intense decomposition

The pore volumes and speciﬁc surface areas (SSA) of CAB

◦

of anthracite briquette occurred above 500 C, a higher tempera-

obtained at different pyrolysis temperatures are presented in

ture than that of conventional coking coal. When the temperature

Table 2. The pore diameter was divided into the following four

◦

was below 500 C, the pyrolysis process mainly involved dehydrox-

parts: micropore (<6 nm), transitional pore (6–50 nm), mesopore

ylation and removal of small-molecule gases absorbed among the

(50–400 nm) and macropore (>400 nm) [5]. As shown in Table 2,

aromatic lamella. The gases can be emitted through the natural

pores larger than 400 nm accounted for more than 90% in of all sam-

pores of the briquette, so no major morphological change could

ples. The pore structure parameters of AS20 and AS300 were almost

be observed. With increasing pyrolysis temperature, a great deal

the same. Xie [33] found variations in pore structure when vari-

◦

of volatile materials evacuated in a short time [4]. Meanwhile,

ous coals were heated from ambient temperature to 1200 C. The

the anthracite briquette did not produce colloids during pyrolysis,

results showed that the coals were mainly dried, and little change in

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

4 Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx

Table 2

Pore structure and speciﬁc surface area of AS carbonized briquettes.

3 −1 2 −1

Sample Pore size distribution/(cm g ) Speciﬁc surface area/(m g )

Vtotal V1(>400 nm) V2(400 ∼ 50 nm) V3(50 ∼ 6 nm) V4(6 ∼ 1.5 nm)

AS20 0.2392 0.2272 0.0039 0.0068 0.0007 4.30

95.0% 1.6% 2.8% 0.3%

AS300 0.2675 0.2525 0.0058 0.0072 0.0016 4.57

94.4% 2.2% 2.7% 0.6%

AS500 0.8791 0.7914 0.0372 0.0223 0.0191 28.80

90.9% 4.2% 2.5% 2.2%

AS700 0.8714 0.8052 0.0523 0.0142 0.0071 4.88

92.4% 6.0% 1.6% 0.8%

Fig. 3. SEM images of AS carbonized briquettes produced at different temperatures a: AS20.; b: AS300; c: AS500; d: AS700.

leaving the carbonized briquette enriched with pores and thin-

C=C & C=O C-H

ner lamellar after solidiﬁcation. However, the surface morphology C-H R.T

◦

became more compact when the temperature rose to 700 C. This

feature might be related to the polycondensation reaction and the 300℃

interaction between anthracite and binder, which led to the tight

aggregation of the turbostratic structure [3].

500℃

3.2. FTIR analysis 700℃

Absorbance

The FTIR spectra of AS carbonized briquettes produced at dif- 900℃

ferent pyrolysis temperatures are shown in Fig. 4. Compared to

bituminous coal, anthracite had less side chains and functional

500 1000 1500 2000 2500 3000 3500 4000 4500

groups due to the highly condensed structure [33]. Three obvi- -1

Wav enumber, cm

ous peaks were observed in spectra of all samples. The absorption

bands were assigned based on standard patterns. The peak at ca.

−1 Fig. 4. FTIR spectra of AS carbonized briquettes produced at different temperatures

2850 cm corresponds to the CH, CH2 and CH3 vibration. The

−1

peak at near 1620 cm belongs to C C/C O vibration, and the peak

−1

at 700–900 cm is attributed to the Car H vibration absorption loss of aliphatic C H bonds. The breaking of aliphatic C H bonds

◦

bands [36]. below 300 C may be attributed to the mild thermal decomposition

−1

The peak at 2850 cm showed a continuous decrease in inten- of the binder [37]. An obvious decrease in aromatic C H group con-

sity with increasing pyrolysis temperature because of the increased tent was observed when the pyrolysis temperature increased above

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx 5

Table 4

experiment Fitting parameters obtained from Raman spectra of AS carbonated briquettes

fit

Sample Position Intensity(area) Bandwidth I /I L (Å) C-C/C-H D G a

C-O AS20

C=O D 1344 133811 182 2.06 21.25

COO- D2 1580 41628 105

trons/a.u.

G 1598 65057 36 ec

AS300

toel

D 1350 103509 182 3.63 12.06 ho

P

D2 1588 53470 76

G 1604 28550 36

AS500

D 1349 33707 211 4.85 9.03

282 284 286 288 290 292 D2 1577 12319 112

1602 6955 45

Bind ing energy(BE)/eV G

AS700

Fig. 5. Deconvoluted X-ray photoelectron spectra (XPS) for C1s. D 1347 310021 207 3.66 11.96

D2 1588 100847 103

G 1604 84675 38

Table 3

Deconvolution analysis of XPS for C1s. AS900

D 1343 205843 191 3.00 14.60

E/eV Carbon form Content ω /%

mol D2 1583 71719 102

G 1603 68636 36

AS20 AS300 AS500 AS700 AS900

284.6 C C, C H 77.86 76.33 75.66 73.52 73.93

286.1 C O 5.42 5.88 9.62 11.98 12.21

binder. The number of these new bonds might be more than the dis-

287.6 C O 1.65 1.41 1.06 0.96 0.63

−

289.0 COO 15.07 16.38 13.66 13.54 13.23 rupted C H bonds. It indicated that the decomposition of radicals

leads to another aromatic condensation, resulting in the signiﬁcant

development of aromatic ring structure [40]. The C O concentra-

◦

500 C. It can be inferred that smaller aromatic rings were prefer- tion showed a general increase during carbonization, while the C O

entially consumed to increase the concentration of aromatic rings concentration demonstrated the opposite trend. Shinn [41] found

having six or more benzene rings during the briquette pyrolysis that the phenolic hydroxyl and ether oxygen bonds were the most

[19,33]. Therefore, large volumes of hydrogen would be released, stable organic carbon–oxygen functional groups because the lone

leaving the carbonized briquette enriched with condensed aro- pair electrons in combination with the aromatic ring could form a

matic rings. The behavior of these two functional groups was stable conjugated structure. As a result, the broken C O and C C

consistent with the hydrogen evolution during the pyrolysis of the bonds generated C O bonds, which increased the C O concentra-

carbonized briquette based on our previous work. The generation tion. It has also been noted that less carbonyl group content was

◦

of H2 began when the temperature exceeded 300 C, and the evo- found on the surface layer of char, and more existed at deeper

◦

lution rate increased at ca. 600 C [4]. The stretches caused by C O levels [33]. The carboxyl concentration of carbonized briquettes

◦

and C C groups in the carbonized briquette decreased signiﬁcantly increased at a pyrolysis temperature of 300 C. This behavior may

◦ ◦

at 300 C, denoting that they were thermally unstable above 300 C occur because active carbon could interact with oxygen to form a

and were removed in the pyrolysis process [38]. In the FTIR spectra COO functional group during the pyrolysis process. As the tem-

of AS900, the feature peaks in this region disappeared, indicating perature increased, the COO group decomposed into CO and CO2,

that the carbonized briquette prepared at a high temperature was resulting in a continual decrease in the carboxyl concentration [4].

composed of polyaromatics and few branched chains.

3.4. Raman spectroscopy analysis

3.3. XPS analysis

The Raman spectra of AS carbonized briquettes in the range of

−1

Deconvolution of X-ray photoelectron spectra allowed the iden- 1000–1800 cm are presented in Fig. 6. The spectra show that

−1 −1

tiﬁcation of various functional groups present on the AS carbonized two peaks appeared at approximately 1350 cm and 1600 cm ,

briquette surfaces [39]. The spectrum was deconvoluted into four corresponding to the D and G bands [42]. The bands of these

peaks, and the variation in the binding energy peak position was spectra were far broader than that recorded for highly oriented

±

0.2 eV according to literature values for C. A typical deconvo- carbonaceous materials, indicating a high degree of disorder in the

luted spectrum is depicted in Fig. 5. As shown in Fig. 5, these studied carbonized briquettes. To determine the precise spectro-

peaks occurred at 284.6, 286.1, 287.5 and 289.0 eV, primarily cor- scopic parameters such as peak position, bandwidth and integrated

responding to aromatic carbon and aliphatic carbon (C C, C H), intensity ration ID/IG, the Raman spectra were deconvoluted into

phenol carbon or aether carbon (C O), carbonyl (C O) and carboxyl three peaks (D, D2 and G) using Gaussian functions in Origin-lab

(COO ), respectively [17,18]. Pro7.5 according to the deconvolution proposed by Sonibare et al.

The XPS C1s dates of samples are shown in Table 3. There was a [15]. The D2 band making up the “overlap” between the G and D

small but clear trend in the reduction of C C/C H atomic percent- bands mainly represented amorphous sp2-bonded forms of carbon

age concentrations as the temperature increased. The aliphatic C H [15,25]. The spectroscopic parameters obtained after curve ﬁtting

◦

bonds of briquettes started to break at 300 C, which had been cer- are shown in Table 4.

tiﬁed by the FTIR results. Furthermore, the cleavage of C C bonds As can be observed from Table 4, no clear differences in the posi-

and aromatic C H bonds led to an obvious decrease in the C C/C H tion of the three peaks could be seen with the increase in pyrolysis

◦

concentration above 500 C. However, the value tended to be sta- temperature for these ﬁve samples. When comparing the band-

◦

ble when the temperature was over 700 C. This probably resulted width of the G and D bands, the carbonized briquette obtained at

◦

from the formation of new C C bonds between anthracite and 500 C exhibited the highest value. It is also known that the ratio of

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

6 Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx

Fig. 6. Raman spectrums of AS carbonated briquettes with the corresponding curve ﬁtted bands. a: AS20, b: AS300, c: AS500, d: AS700, e: AS900.

the intensities of the D band to the G band (ID/IG) is one of the most cals obtained by the reaction of the broken bonds of C C/C H and

important Raman parameters to study the degree of organization of the original free radicals in the anthracite were condensed aro-

carbon materials. A decrease in the ID/IG ratio is normally expected matic rings that had high thermal stability that would increase the

with increasing order because it is related to the microcrystalline difﬁculty in heat transfer and polycondensation reactions due to

planar size La [19]. For coking coal pyrolysis, the structural order- less available energy [3]. Furthermore, the pyrolysis of anthracite

ing degree and microcrystalline parameter La increasing through did not generate mesophase, which was unfavorable for increasing

the melting process and mesophase development [5]. However, the microcrystalline orderliness. Afterwards, the crystallite size La

the La value for the carbonized briquettes did not show the same increased with increasing temperature to reach a value of 14.60 at

◦

trend with increasing pyrolysis temperature. Many oriented crys- 900 C, indicating that the turbostratic structures of the anthracite

tallites formed during the coaliﬁcation of anthracite, which resulted rearranged after the decomposition reaction. This might be (1)

in the larger La value (21.25). When the pyrolysis temperature because the higher temperature increased the collision frequency

◦

reached 500 C, the La value decreased dramatically to 9.03. The between anthracite free radicals so as to promote the polyconden-

reasons for this phenomenon are that on one hand, the decom- sation reaction (see as FTIR analysis) and (2) because the structure

position of initial macromolecular structure occurred intensely at of anthracite became more open during the pyrolysis so that free

◦

500 C, and the cleavage of some crosslinks reduced the value of radicals of aromatic dense rings were bound together by free radi-

La [10]. On the other hand, most of the newly generated free radicals produced from AS binder pyrolysis, thereby forming the larger

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx 7

Table 5

of briquette became more open. The last was the bonding-

Effect of microcrystalline parameter on the mechanical strength of carbonated

repolymerization process, which resulted in the polycondensation

briquette.

of free radicals produced by the decomposition of binder and

Samples La(Å) La(Å) M40 anthracite.

The total pore volumes and surface areas of the carbonized

L (20) L (500) L (900)

a a a ◦

briquette reached maximum values at 500 C and decreased at

AS 21.25 9.03 14.60 6.57 86.77

higher temperatures. The aromatization process occurred above

CP 20.83 10.24 15.20 4.96 80.36

◦

HA 21.13 9.98 14.36 4.38 76.85 500 C and continued at higher temperatures, leaving the car-

bonized briquette enriched with polyaromatics. The original

*La = La(900) – La(500), where 900 and 500 present the carbonized briquettes

◦ ◦

oriented anthracite crystallites were deposed, and the microcrys-

obtained at the pyrolysis temperature of 900 C and 500 C, respectively.

talline planar size La underwent a remarkable decrease before

the bonding-repolymerization process. Afterwards, the value of La

microcrystalline structure. The change in La correlated well with

increased from 9.03 to 14.60. Moreover, the mechanical strength of

the behavior of the surface structure, which transformed from

the carbonized briquette was found to be dependent on the varia-

smaller fragments to larger lamella, revealing that La had a sig- ◦

tion of La. The larger change in La above 500 C indicated a stronger

niﬁcant effect on the surface structure of the carbonized briquette.

interaction between anthracite and binder, which promoted the

The variation in microcrystalline parameters affects the qual-

rearrangement of microcrystalline structures and improved the

ity of the carbonized briquette. For conventional coking coal, the

quality of the carbonized briquette.

larger the La value, the higher the strength of the coke [5,33].

Table 5 presents the microcrystalline parameter and mechanical

Acknowledgements

strength of three series of carbonized briquettes. The mechanical

strength of AS900 was higher than that of all other carbonized bri-

This work was supported by the National Natural Science

quettes. However, the La value of AS900 was smaller than that of

Foundation of China (Grant no. 51274147), National Science & Tech-

CP900, demonstrating that La was not the only factor that affected

nology Pillar Program (Grant no.2012BAA04B03) and 2014 Shanxi

the mechanical strength of the carbonized briquette. The experi-

Provincial Postgraduate Innovation program.

mental result, from the highest to the lowest mechanical strength,

was AS900 > CP900 > HA900, which was in accordance with the La of

samples. This phenomenon suggested that the change in La above References

◦

500 C was closely related to the mechanical strength. The larger

[1] Ł. Sme¸dowski, M. Krzesinska,´ W. Kwasny,´ Development of ordered structures

value of La indicated more intense polycondensation reactions of

in the high-temperature (HT) cokes from binary and ternary coal blends

smaller aromatic dense rings and more orderly rearrangement of studied by means of X-ray diffraction and Raman spectroscopy, Energy Fuel

the microcrystalline structure. It can be inferred that the interac- 25 (2011) 3142–3149.

[2] C. Wu, Y.F. Zhang, Y. Liang, Present situation and developing trend of

tions between the AS binder and anthracite were stronger, which

technology of carbonized coal processed from anthracitic powder, Shanxi

promoted the formation of a larger microcrystalline structure and

Energy Conserv. 3 (2009) 41–43.

improved the strength of the carbonized briquette. [3] Y.F. Zhang, Y.L. Sun, Study on the microcrystal structure of carbonated of

briquette made from anthracite powder, Coal Convers. 3 (2010) 19–22.

[4] Y.F. Zhang, H.R. Zhang, The characteristics of anthracite briquette

3.5. Pyrolysis behavior of anthracite briquette carbonization and the regularity of pyrolysis gas generation during

carbonization, J. China Coal Soc. 36 (2011) 670–675.

[5] Y.F. Wang, Study on Anthracite Briquetting and Formed Coke Technology,

Based on the preceding results, the pyrolysis of anthracite bri-

East China University of Science and Technology, Shanghai, 1998.

quette can be divided into three processes. The ﬁrst is the drying [6] A.K. Sharma, P.S. Das, B.P. Tripathi, Inﬂuence of properties of bituminous

◦

process (∼300 C), in which the briquette was dried and some of binders on the strength of formed coke, Fuel Process. Technol. 75 (2002)

201–214.

the lighter components started to decompose. Gases adsorbed in

[7] J.W. Taylor, A. C¸ oban, Factors affecting the strength of formed coke made from

the capillary pores were emitted from the natural pores of the

lignite char, Fuel 66 (1987) 1274–1280.

briquette, leading to little change in the pore structure. The sec- [8] Y.F. Wang, J.S. Gao, Study on coking mechanism of anthracite formed coke, J.

◦ Fuel Chem. Technol. 28 (2000) 216–220.

ond stage was decomposition, which commenced at ca. 500 C.

[9] Y.Q. Zhao, Y.F. Zhang, Y. Liang, Crack formation characteristic of ball structure

With the devolatilization of the briquette, the pore structure of

carbonized briquette, in: 30th Annual International Pittsburgh Coal

the CAB was much more developed, and obvious morphological Conference, Beijing, 2013.

[10] H. Marsh, Mechanisms of carbonization of coal to metallurgical coke and

changes could be observed. The original oriented anthracite crys-

inﬂuences of pitch additives upon coke properties, AIME Ironmaking Proc. 39

tallites were deposed due to cleavage of crosslinks and other bonds,

(1980) 266–273.

which opened up the coal structure and resulted in the genera- [11] F.E. Ndaji, I.M. Butterﬁeld, K.M. Thomas, Changes in the macromolecular

structure of coals with pyrolysis temperature, Fuel 76 (1997) 169–177.

tion of smaller microcrystalline structures. With the increase of

[12] K. Nishioka, A carbonization model based on a coking mechanism,

temperature, the pyrolysis of briquette entered the last phase –

Ironmaking Proc., Metall. Soc. AIME 42 (1983) 347–356.

bonding-repolymerization. The microstructure collapsed, and the [13] F. Jiménez, F. Mondragón, D. López, Structural changes in coal chars after

pressurized pyrolysis, J. Anal. Appl. Pyrolysis 95 (2012) 164–170.

surface morphology became more compact. High pyrolysis tem-

[14] Y.H. Bai, P. Wang, L.J. Yan, Effects of CO2 on gas evolution and char structure

perature and a more open structure of the briquette promoted the

formation during lump coal pyrolysis at elevated pressures, J. Anal. Appl.

repolymerization of free radicals produced by the decomposition Pyrolysis 104 (2013) 202–209.

of anthracite and binder. As a result, the microcrystalline planar [15] O.O. Sonibare, T. Haeger, S.F. Foley, Structural characterization of Nigerian

coals by X-ray diffraction, Raman and FTIR spectroscopy, Energy 35 (2010)

size La had a distinct increase, and the carbonized briquette was

5347–5353.

composed of polyaromatics.

[16] J. Ibarra, E. Munoz, R. Moliner, FTIR study of the evolution of coal structure

during the coaliﬁcation process, Org. Geochem. 24 (1996) 725–735.

[17] S. Kelemen, M. Afeworki, M. Gorbaty, Characterization of organically bound

4. Conclusions

oxygen forms in lignites, peats, and pyrolyzed peats by X-ray photoelectron

spectroscopy (XPS) and solid-state 13C NMR methods, Energy Fuel 16 (2002)

1450–1462.

The pyrolysis of anthracite briquette mainly included three

[18] H.Z. Chang, C.G. Wang, F.G. Zeng, XPS comparative analysis of coal macerals

processes. The ﬁrst was drying accompanied with the pyrolysis

with different reducibility, J. Fuel Chem. Technol. 34 (2006) 389–394.

of some light species. The second was decomposition, through [19] A. Guedes, B. Valentim, F. Prieto, A. Noronha, Raman spectroscopy of coal

macerals and ﬂuidized bed char morphotypes, Fuel 97 (2012) 443–449.

which smaller microcrystals were generated, and the structure

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

G Model

JAAP-3387; No. of Pages 8 ARTICLE IN PRESS

8 Y. Zhao et al. / Journal of Analytical and Applied Pyrolysis xxx (2015) xxx–xxx

[20] F. Min, M. Zhang, Y. Zhang, Y. Cao, An experimental investigation into the [31] M.J. Blesa, V. Fierro, J.L. Miranda, Effect of the pyrolysis process on the

gasiﬁcation reactivity and structure of agricultural waste chars, J. Anal. Appl. physicochemical and mechanical properties of smokeless fuel briquettes, Fuel

Pyrolysis 92 (2011) 250–257. Process. Technol. 74 (2001) 1–17.

[21] S.R. Kelemen, P.J. Kwiatek, Quantiﬁcation of organic oxygen species on the [32] D.L. Dong, Y.F. Zhang, Y.Q. Zhao, Improvement in the caking property of

surface of fresh and reacted argonne premium coal, Energy Fuel 9 (1995) lignite by hydromodiﬁcation in a CO subcritical water system, Chem. Lett. 43

841–848. (2014) 1470–1472.

[22] D.L. Perry, A. Grint, Application of XPS to coal characterization, Fuel 62 (1983) [33] K.C. Xie, Coal Structure and Its Reactivity, Science Press, Beijing, 2002.

1024–1033. [34] P. Fu, S. Hu, J. Xiang, Study on the gas evolution and char structural change

[23] B. Gong, P.J. Pigram, R.N. Lamb, Identiﬁcation of inorganic nitrogen in an during pyrolysis of cotton stalk, J. Anal. Appl. Pyrolysis 97 (2012) 130–136.

Australian bituminous coal using X-ray photoelectron spectroscopy (XPS) and [35] J.W. Taylor, L. Hennah, The effect of binder displacements during briquetting

time-of-ﬂight secondary ion mass spectrometry (TOFSIMS), Int. J. Coal Geol. on the strength of formed coke, Fuel 70 (1991) 873–876.

34 (1997) 53–68. [36] M. Ahmed, M. Blesa, R. Juan, Characterisation of an Egyptian coal by

[24] S. Vermaak, N. Maledi, N. Wagner, J. Van Heerden, J. Van Grieken, R. Potgieter, Mossbauer and FT-IR spectroscopy, Fuel 82 (2003) 1825–1829.

Raman spectroscopy for the analysis of coal: a review, J. Raman Spectrosc. 42 [37] B. Xu, D.Y. Guo, X.H. Zhang, Characteristics of coal-tar pitch

(2011) 123–129. pyro-condensation, J. Wuhan Univ. Sci. Technol. 1 (2004) 24–27.

[25] T. Jawhari, A. Roid, J. Casado, Raman spectroscopic characterization of some [38] M. Asadullah, S. Zhang, Z. Min, P. Yimsiri, C.-Z. Li, Effects of biomass char

commercially available carbon black materials, Carbon 33 (1995) structure on its gasiﬁcation reactivity, Bioresour. Technol. 101 (2010)

1561–1565. 7935–7943.

[26] A. Ferrari, J. Robertson, Interpretation of Raman spectra of disordered and [39] P. Rupper, S. Gaan, V. Salimova, Characterization of chars obtained from

amorphous carbon, Phys. Rev. B 61 (2000) 14095–14107. cellulose treated with phosphoramidate ﬂame retardants, J. Anal. Appl.

[27] X.J. Li, C.Z. Li, FT-Raman spectroscopic characterisation of chars from the Pyrolysis 87 (2010) 93–98.

pyrolysis of coals of varying rank, J. Fuel Chem. Technol. 33 (2005) 385–390. [40] J.H. Shinn, Investigation of resole, novalac and coal tar pitch blended binder

[28] P. Lespade, A. Marchand, M. Couzi, Caracterisation de materiaux carbones par for the production of metallurgical quality formed coke briquettes from coke

microspectrometrie Raman, Carbon 22 (1984) 375–385. breeze and anthracite, Fuel Process. Technol. 92 (2011) 631–638.

[29] F. Tuinstra1, J.L. Koenig, Raman spectrum of graphite, J. Chem. Phys. 53 (1970) [41] J.H. Shinn, From coal to single-stage and two-stage products: a reactive model

1126–1130. of coal structure, Fuel 63 (1984) 1187–1196.

[30] K.J. Li, R. Khanna, J.L. Zhang, The evolution of structural order, microstructure [42] R. Rajarao, I. Mansuri, R. Dhunna, R. Khanna, Characterisation of gas evolution

and mineral matter of metallurgical coke in a blast furnace: a review, Fuel 133 and char structural change during pyrolysis of waste CDs, J. Anal. Appl.

(2014) 194–215. Pyrolysis 105 (2014) 14–22.

Please cite this article in press as: Y. Zhao, et al., Structural characterization of carbonized briquette obtained from anthracite powder,

J. Anal. Appl. Pyrol. (2015), http://dx.doi.org/10.1016/j.jaap.2015.01.009

Web Analytics