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).