- Email: [email protected]
Preparation and carbonization behavior of cinnamaldehyde modified coal tar pitch
Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
Contents lists available at SciVerse ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Preparation and carbonization behavior of cinnamaldehyde modified coal tar pitch Wenjuan Zhang ∗ , Tiehu Li, Heguang Liu, Alei Dang, Cuiling Hou, Tingkai Zhao, Guangming Li Department of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, PR China
a r t i c l e
i n f o
Article history: Received 14 July 2011 Accepted 16 November 2011 Available online 25 November 2011 Keywords: Cinnamaldehyde Coal tar pitch Thermal analysis Carbonization
a b s t r a c t In this paper, coal tar pitch (CTP) was modified with cinnamaldehyde (CMA) in the presence of p-toluene sulfonic acid. The parent CTP and CMA modified CTP were characterized by 1 H nuclear magnetic resonance spectroscopy, elemental analysis and scanning electron microscopy. Carbonization behaviors of CMA modified CTPs were studied by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction techniques. The results show that the carbonization behaviors of parent CTP and CMA modified CTPs are much different. The modification of CTP with CMA results in an increase in carbonization yield by 3.46–5.08% when 100 g CTP was modified with 5–15 ml of CMA. During the carbonization process, methyl and methylene groups of the CMA modified CTP gradually disappear while increasing temperature and its chemical structures change greatly when the temperature is higher than 400 ◦ C. In addition, the modification with CMA is beneficial for increasing graphitizability of CTP. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Coal tar pitch (CTP) is a kind of complex material consisting of aromatic compounds with a broad molecular weight distribution [1]. It has been employed extensively in production of carbon materials and carbon–carbon composites for its low cost and the ability to generate graphitizable carbons [2]. However, the present techniques for preparing carbon–carbon composites are inefficient, time-consuming and, consequently, expensive. Therefore, it is of great importance to simplify the preparation procedure and reduce production costs [3]. It is well known that the carbon yield of CTP can be improved by physical separation and chemical modification. Physical separation (i.e., fractional distillation and solvent extraction) can be used to separate components with different average molecular weights from CTP [4]. On the other hand, chemical modifications are involved in chemical reactions between CTP and silicon compounds, polystyrene, rosin, polyvinylpyridine, iodine, phenolic resin, divinylbenzene, polyacrylonitrile, lignin/silica hybrid, etc. [5–13]. Compared to physical separation, chemical modification is superior in saving resources, reducing waste disposal and simplifying the preparation procedure, therefore, it has been the typical approach to improve the carbonization yield of CTP. Cinnamaldehyde (CMA) is a major bioactive compound isolated from the leaves of Cinnamomum osmophloeum kaneh [14]. It is a ␣,
∗ Corresponding author. Tel.: +86 29 88492870; fax: +86 29 88492870. E-mail address: zhangwj [email protected] (W. Zhang). 0165-2370/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2011.11.005
-unsaturated aldehyde, in which the benzene ring is conjugated with C O and C C groups. So, it is a potential natural cross-linking agent [15] and hydrogenation reactions can take place in both the C O and C C groups [16,17]. In addition, the aldehyde group, in the presence of acid, can react with small molecules in CTP to form large molecules [18], and there is an aldehyde group in the chemical structure of CMA. Hence, in this paper, CMA was used to modify CTP in the presence of p-toluene sulfonic acid (PTS). The purpose of this paper is to study the characterization and carbonization behavior of CMA modified CTP.
2. Experiment 2.1. Materials CTP was purchased from the Steel Co. Ltd. (Wuhan, China). CMA and PTS were of analytical grade. Some properties of the CTP are included in Table 1.
2.2. Procedures 2.2.1. Modification of CTP 100 g CTP and 7 g PTS were mixed in a 500 ml round bottom three-neck flask equipped with a motor driven stirrer. It was started at 100 ◦ C at 90 rpm and CMA was added slowly into the flask. The speed of the stirrer was raised to 200 rpm at 150 ◦ C and held for 3 h under a nitrogen flow of 50 ml min−1 . The four pitches used in this study are parent CTP (M0 ), the CTP modified with 5 ml of CMA (M5 ),
64
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
Table 1 Main characteristics of different pitches. Pitches
SPa (◦ C)
CVb (wt.%)
TSc (wt.%)
QId (wt.%)
M0 M5 M10 M15
120 116 112 90
57.75 59.71 65.02 60.20
44.05 44.23 48.46 52.24
7.90 9.35 11.24 12.06
a b c d
Softening point. Coking value. Toluene solubles. Quinoline insolubles.
the CTP modified with 10 ml of CMA (M10 ) and the CTP modified with 15 ml of CMA (M15 ), respectively. 2.2.2. Carbonization Carbonization of samples was carried out in a tube furnace. About 1 g sample was heated to designated temperature at a rate of 10 ◦ C min−1 and kept at this temperature for 2 h. The N2 stream was introduced into the tube furnace throughout the carbonization. The products are denoted as Cx , where x is the final carbonization temperature. 2.3. Analysis 2.3.1. Characteristics of CTP and CMA modified CTPs The compositions of CTP and CMA modified CTPs were analyzed using the following standard methods: softening point (SP), ring and ball method, ASTM D36-66; coking value (CV), ISO 6998; toluene insolubles (TI), ISO 6376-96; quinoline insolubles (QI), ISO 6791-81. 2.3.2. Measurements Thermogravimetric analysis (TGA) was performed on a MettlerToledo thermal analyzer under N2 atmosphere with a heating rate of 10 ◦ C min−1 . 1 H nuclear magnetic resonance (NMR) spectroscopy was recorded on a Bruker AV 300 NMR spectrometer by dissolving the samples of pyridine solubles of CTP and CMA modified CTP (M10 ) in CDCl3 using tetramethyl-silane as internal standard. Elemental analysis of C, H, N, and S was performed on a Vario EL-III analyzer. The morphologies of parent CTP and CMA modified CTP (M10 ) were examined using FEI Sirion 200 scanning electron microscopy (SEM). Fourier transform infrared (FT-IR) spectroscopy was acquired on a Bruker Tenser-27 FT-IR spectrometer with thin films of KBr in the range 4000–400 cm−1 . X-ray diffraction (XRD) was carried out on the Panalytical X-Pert PRO X-ray diffraction ˚ radiation at 40 kV and 35 mA. instrument with CuK␣ ( = 1.5406 A)
Fig. 1. TG curves of parent CTP and CMA modified CTPs.
3.2. TGA analysis TGA consists of TG and DTG. Here, TG is used in combination with DTG to study the transitions of CMA modified CTPs at different carbonization temperatures. It can be observed in Fig. 1 that both parent CTP and CMA modified CTPs decompose in one single mass loss stage in the temperature range of 25–800 ◦ C. The weight loss is mainly due to the removal of gases and light compounds generated via thermal polymerization and cracking of side chains of aromatic rings [1]. The carbonization yields of M0 , M5 , M10 and M15 are 41.04%, 44.50%, 46.12% and 45.53%, respectively, indicating that the carbonization yield of CTP can be improved by adding CMA. It could be rationalized as follows: first, in the presence of acid, CMA can react with small molecules in parent CTP. So, large molecules can be formed via the reaction between CMA and the small molecules in CTP [18], which decreases the removal of light compounds and increases the carbonization yield. Second, PTS is an oxidation catalyst. It can partly oxidize CTP material [20], and thus results in the formation of black spots shown in Fig. 3. This would lead to formation of more thermal resistant material and increases the carbonization yield of CTP. The analysis of the DTG curves (Fig. 2) show that parent CTP and CMA modified CTPs are losing mass at varying rate related to the cross-linking degree of modification by CMA. The profile of parent CTP is characterized by a single peak centered at 362 ◦ C, which indicates that the mass loss rate at this temperature reaches the
3. Results and discussion 3.1. Characteristics of parent CTP and CMA modified CTPs Table 1 lists the main characteristics of parent CTP and three different CMA modified CTPs. The modified CTPs (M5 , M10 and M15 ), compared with parent CTP, have lower SP, higher toluene solubles (TS) and QI content with increasing CMA content. An important difference between the CMA modified CTPs is their coking values. It can be observed in Table 1 that CMA modified CTPs have higher coking values than that of parent CTP. However, the coking value does not increase with the increasing content of CMA, as indicated by that the coking value of M10 is 65.02% but that of M15 is 60.20%. A possible reason for this is that the CMA dosage is excessive when 15 ml of CMA is added to 100 g parent CTP. The excessive CMA may self-polymerize and the resultant product has poor heat-resistance [19], which would lead to the decrease of the coking value.
Fig. 2. DTG curves of parent CTP and CMA modified CTPs.
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
65
Table 2 Results of elemental analysis and 1 H NMR. Elemental analysis (wt.%)
M0 M10
N
C
H
S
2.50 0.64
93.07 90.82
4.09 3.99
0.66 1.72
C/H
Har %
Ha %
H+␥ %
Har /Hal
1.89 1.90
90.34 72.36
2.76 15.76
6.90 11.89
9.35 2.62
Har , aromatic hydrogen; Hal , aliphatic hydrogen; H˛ , aliphatic hydrogen in the ␣-position; H+␥ , aliphatic hydrogen in the - and ␥- positions.
Fig. 3. SEM images of parent CTP (a) and CMA modified CTP (M10 ) (b).
maximum value. However, there are two peaks in the DTG profile of the CMA modified CTPs (M10 and M15 ) at around 350 ◦ C, which indicates the formation of different phases. In addition, the small peaks observed at around 500 ◦ C, which are related to the thermal polymerization reactions at this temperature [21], are more obvious in CMA modified CTPs than in parent CTP. All the above indicates the carbonization behaviors of parent CTP and the CMA modified CTPs are different. 3.3.
1H
NMR and elemental analysis
CMA modified CTP (M10 ) is mainly studied in the subsequent work for its high carbonization yield in modified CTPs. Elemental analysis of parent CTP and CMA modified CTP (M10 ) is shown in Table 2. It is observed that the content of N in CMA modified CTP (M10 ) is much lower than that in parent CTP, which may be attributed to the removal of N2 at low temperature during the process of modification. The increased content of S in CMA modified CTP (M10 ) is caused by the introduction of PTS to CMA modified CTP (M10 ). In addition, the C/H ratio of CMA modified CTP (M10 ) (1.90) is almost the same as that of parent CTP (1.89). 1 H NMR spectra can directly characterize distribution of protons differing in chemical environments, i.e., aromatic protons, olefinic, and protons in ␣-, - and ␥-positions in aliphatic substituents on aromatic ring system [22]. To characterize the distribution of protons in parent CTP and CMA modified CTP (M10 ), 1 H NMR measurements were performed. The results are shown in Table 2. The proton in the respective chemical shift windows: 6.3–9.5 ppm are aromatic protons (Har ); 2.0–4.5 ppm are protons at ␣ positions in aliphatic substituents on aromatic ring (H␣ ) as well as 0.5–2 ppm at  and ␥ positions (H+␥ ), respectively [23]. The distribution of all the hydrogen atoms was determined by digital integration of Har , H␣ , H and H␥ band intensities normalized over the complete spectrum. As shown in Table 2, CMA modified CTP (M10 ) has much lower Har and Har /Hal than parent CTP. In addition, the modification leads to high increase of protons in methyl and methylenes (␣-position) attached to aromatic rings. Although CMA modified CTP (M10 ) has much lower Har and Har /Hal than parent CTP, the C/H values of parent CTP and CMA modified CTP (M10 ) are similar.
It seems contradictory but it is reasonable because the different objects are detected: the object of 1 H NMR experiment is pyridine soluble, but the object of elemental analysis experiment is the total CTP, which contains both pyridine solubles and pyridine insolubles. 3.4. SEM analysis SEM images of parent CTP and CMA modified CTP (M10 ) are shown in Fig. 3. The surface of parent CTP is loose, with few black spots (Fig. 3(a)). Nevertheless, major surface changes appear when the parent CTP is modified with CMA. Fig. 3(b) shows the SEM image of CMA modified CTP (M10 ). Some black spots, which are the products of oxidized material, distribute on the surface of the CMA modified CTP (M10 ). Therefore, these black spots are partly responsible for the higher carbonization yield of CMA modified CTP (M10 ).
Fig. 4. FT-IR spectra of CMA modified CTP (M10 ) carbonized at different temperatures.
66
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
Fig. 5. XRD patterns of parent CTP and CMA modified CTP (M10 ) carbonized at different temperatures.
3.5. FT-IR analysis To recognize the structure changes of CMA modified CTP (M10 ) during the pyrolysis process, the products of CMA modified CTP (M10 ) carbonized at different temperatures are prepared and characterized with FT-IR spectra, which are shown in Fig. 4. The spectra show the following regions of interest. The peaks at 3030 and 2915 cm−1 are due to aromatic C–H stretching vibration and aliphatic C–H stretching vibration, respectively [24]. The peak at 1600 cm−1 is attributed to aromatic C C stretching vibration and the peak at 1441 cm−1 is attributed to C–H bending vibration of methyl and methylene. In addition, the peaks at 1226, 1180, 1126, 1035 and 567 cm−1 are attributed to –SO3 H [25]. From Fig. 4, it can be observed that methyl and methylene groups (see the peak at 2915 cm−1 ) of the CMA modified CTP (M10 ) gradually disappear while increasing temperature, which is caused by demethylation of methyl and methylene. In addition, the peaks of C200, C300 and C400 in the range of 500–1000 cm−1 are different from that of C500, C600 and C700. This indicates the chemical structures of the CMA modified CTP (M10 ) change greatly when the temperature is higher than 400 ◦ C. 3.6. XRD analysis XRD patterns of parent CTP and CMA modified CTP (M10 ) carbonized at different temperatures are shown in Fig. 5. All the samples exhibit two diffraction peaks centered at 25◦ and 43◦ in wide angle region, which can be generally indexed to (0 0 2), (1 0 0) diffraction of graphite [26]. Furthermore, it can be observed that the two peaks become sharp when the pitches are heated to temperature higher than 400 ◦ C, which is caused by the formation of mesophase. This agrees with the fact that the mesophase can be considered as a liquid crystal [27]. Table 3 shows the XRD parameters of parent CTP and CMA modified CTP (M10 ). It is worthwhile to note that the 2 angle increases with increasing carbonization temperature, consequently, the dspacing of carbonized CTPs decrease when the carbonization
Table 3 XRD parameters of parent CTP and CMA modified CTP (M10 ). Parent CTP ◦
C200 C300 C400 C500 C600 C700
CMA modified CTP (M10 )
2 0 0 2 ( )
d0 0 2
24.5 24.8 25.1 25.5 25.7 25.8
3.63 3.59 3.55 3.49 3.46 3.45
˚ (A)
2 0 0 2 (◦ )
˚ d0 0 2 (A)
24.8 24.9 25.3 25.7 25.8 25.9
3.59 3.57 3.52 3.46 3.45 3.44
temperature increases. In addition, the d002 values of CMA modified CTP (M10 ) are smaller than the corresponding data of parent CTP, indicating the CMA modified CTP (M10 ) is easier to be graphitized than parent CTP. 4. Conclusions The modification of CTP with CMA has great effect on its characteristics and carbonization behavior. The CMA modified CTPs, compared with parent CTP, have lower SP, higher TS and QI content with increasing CMA content. In addition, the modification with CMA results in an increase in carbonization yield by 3.46–5.08% when 100 g CTP was modified with 5–15 ml of CMA. During the carbonization process, methyl and methylene groups of the CMA modified CTP gradually disappear while increasing temperature and its chemical structures change greatly when the temperature is higher than 400 ◦ C. Furthermore, the modification with CMA is beneficial for increasing graphitizability of CTP. Acknowledgements This research was supported by the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20096102120016), the Natural Science Foundation of Shaanxi Province (No. 2009GM6001-1), the Foundation for Fundamental Research of Northwestern Polytechnical University (No. JC201030), the Innovation Foundation of China Aerospace Science and Technology (Grant No. CASC200906) and the Graduate Starting Seed Fund of Northwestern Polytechnical University (No. Z2011005). References [1] M. Pérez, M. Granda, R. Santamaría, T. Morgan, R. Menéndez, A thermoanalytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch, Fuel 83 (2004) 1257–1265. ´ Use of coal tar pitch in carboncarbon composites, Fuel 66 (1987) [2] V. Markovic, 1512–1515. [3] V. Prada, M. Grandda, J. Bermejo, R. Menéndez, Preparation of novel pitches by tar air-blowing, Carbon 37 (1999) 97–106. [4] J.J. Fernández, A. Figueiras, M. Granda, J. Bermejo, R. Menéndez, Modification of coal-tar pitch by air-blowing — I. Variation of pitch composition and properties, Carbon 33 (1995) 295–307. [5] O.S. Efimova, G.P. Khokhlova, Y.F. Patrakov, Thermal conversion of coal-tar pitch in the presence of silicon compounds, Solid Fuel Chem. 44 (2010) 5–11. ´ ´ J. Zielinski, T. Brzozowska, Thermal treatment of pitch–polymer [6] W. Ciesinska, blends, J. Therm. Anal. Calorim. 95 (2009) 193–196. [7] Q.L. Lin, W. Su, Y. Xie, Effect of rosin to coal-tar pitch on carbonization behavior and optical texture of resultant semi-cokes, J. Anal. Appl. Pyrolysis 86 (2009) 8–13. [8] B. Grzyb, J. Machnikowski, J.V. Weber, Mechanism of co-pyrolysis of coal-tar pitch with polyvinylpyridine, J. Anal. Appl. Pyrolysis 72 (2004) 121–130. [9] N. Miyajima, T. Akatsu, T. Ikoma, O. Ito, B. Rand, Y. Tanabe, E. Yasuda, A role of charge-transfer complex with iodine in the modification of coal tar pitch, Carbon 38 (2000) 1831–1838.
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67 [10] T.Q. Li, X.J. Liu, C.Y. Wang, H. Wang, Structural characteristics of mesophase spheres prepared from coal tar pitch modified by phenolic resin, Chin. J. Chem. Eng. 14 (2006) 660–664. [11] Q.L. Lin, T.H. Li, C.Z. Zheng, Y. Zhao, S.H. Song, Carbonization behavior of coaltar pitch modified with divinylbenzene and optical texture of resultant semicokes, J. Anal. Appl. Pyrolysis 71 (2004) 817–826. [12] B. Grzyb, J. Machnikowski, J.V. Weber, A. Koch, O. Heintz, Mechanism of copyrolysis of coal-tar pitch with polyacrylonitrile, J. Anal. Appl. Pyrolysis 67 (2003) 77–93. [13] Q.L. Lin, H.Y. Tang, C.H. Li, L.Q. Wu, Carbonization behavior of coal-tar pitch modified with lignin/silica hybrid and optical texture of resultant semi-cokes, J. Anal. Appl. Pyrolysis 90 (2011) 1–6. [14] S.S. Cheng, J.Y. Liu, K.H. Tsai, W.J. Chen, S.T. Chang, Chemical composition and mosquito larvicidal activity of essential oils from leaves of different Cinnamomum osmophloeum provenances, J. Agric. Food Chem. 52 (2004) 4395–4400. [15] M.P. Balaguer, J.G. Estaca, R. Gavara, P.H. Munoz, Functional properties of bioplastics made from wheat gliadins modified with cinnamaldehyde, J. Agric. Food Chem. 59 (2011) 6689–6695. [16] F. Delbecq, P. Sautet, Competitive C C and C O adsorption of ␣--unsaturated aldehydes on Pt and Pd surfaces in relation with the selectivity of hydrogenation reactions: a theoretical approach, J. Catal. 152 (1995) 217–236. [17] Th. Vergunst, F. Kapteijn, J.A. Moulijn, Kinetics of cinnamaldehyde hydrogenation-concentration dependent selectivity, Catal. Today 66 (2001) 381–387. [18] Q.L. Lin, T.H. Li, Y.B. Ji, W.Z. Wang, X.X. Wang, Study of the modification of coal-tar pitch with p-methyl benzaldehyde, Fuel 84 (2005) 177–182.
67
[19] G. Battistuzzi, S. Cacchi, G. Fabrizi, An efficient palladium-catalyzed synthesis of cinnamaldehydes from acrolein diethyl acetal and aryl iodides and bromides, Org. Lett. 5 (2003) 777–780. [20] N. Noroozi-Pesyan, A.H. Dabbagh, p-Toluenesulfonic acid a useful and selective reagent for the oxidation of benzoins to benziles under solvent-free condition, J. Iran. Chem. Res. 1 (2008) 123–127. [21] C. Blanco, V. Prada, R. Santamaría, J. Bermejo, R. Menéndez, Pyrolysis behaviour of mesophase and isotropic phases isolated from the same pitch, J. Anal. Appl. Pyrolysis 63 (2002) 251–265. [22] A.A. Herod, M.J. Lazaro, M.Domin, C.A. Islas, R. Kandiyoti, Molecular mass distributions and structural characterisation of coal derived liquids, Fuel 79 (2000) 323–337. [23] M.D. Guillén, C. Díaz, C.G. Blanco, Characterization of coal tar pitches with different softening points by 1 H NMR Role of the different kinds of protons in the thermal process, Fuel Process. Technol. 58 (1998) 1–15. ˜ [24] J. Alcaniz-Monge, D. Cazorla-Amorós, A. Linares-Solano, Characterisation of coal tar pitches by thermal analysis, infrared spectroscopy and solvent fractionation, Fuel 80 (2001) 41–48. [25] F. Selampinar, U. Akbulut, E. Yildiz, A. Güngör, L. Toppare, Synthesis of a novel poly(arylene ether ketone) and its conducting composites with polypyrrole, Synth. Met. 89 (1997) 111–117. [26] A.H. Lu, W.C. Li, E.L. Salabas, B. Spliethoff, F. Schüth, Low temperature catalytic pyrolysis for the synthesis of high surface area, nanostructured graphitic carbon, Chem. Mater. 18 (2006) 2086–2094. [27] J.D. Brooks, G.H. Taylor, The formation of graphitizing carbons from the liquid phase, Carbon 3 (1965) 185–193.
Contents lists available at SciVerse ScienceDirect
Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Preparation and carbonization behavior of cinnamaldehyde modified coal tar pitch Wenjuan Zhang ∗ , Tiehu Li, Heguang Liu, Alei Dang, Cuiling Hou, Tingkai Zhao, Guangming Li Department of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, PR China
a r t i c l e
i n f o
Article history: Received 14 July 2011 Accepted 16 November 2011 Available online 25 November 2011 Keywords: Cinnamaldehyde Coal tar pitch Thermal analysis Carbonization
a b s t r a c t In this paper, coal tar pitch (CTP) was modified with cinnamaldehyde (CMA) in the presence of p-toluene sulfonic acid. The parent CTP and CMA modified CTP were characterized by 1 H nuclear magnetic resonance spectroscopy, elemental analysis and scanning electron microscopy. Carbonization behaviors of CMA modified CTPs were studied by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction techniques. The results show that the carbonization behaviors of parent CTP and CMA modified CTPs are much different. The modification of CTP with CMA results in an increase in carbonization yield by 3.46–5.08% when 100 g CTP was modified with 5–15 ml of CMA. During the carbonization process, methyl and methylene groups of the CMA modified CTP gradually disappear while increasing temperature and its chemical structures change greatly when the temperature is higher than 400 ◦ C. In addition, the modification with CMA is beneficial for increasing graphitizability of CTP. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Coal tar pitch (CTP) is a kind of complex material consisting of aromatic compounds with a broad molecular weight distribution [1]. It has been employed extensively in production of carbon materials and carbon–carbon composites for its low cost and the ability to generate graphitizable carbons [2]. However, the present techniques for preparing carbon–carbon composites are inefficient, time-consuming and, consequently, expensive. Therefore, it is of great importance to simplify the preparation procedure and reduce production costs [3]. It is well known that the carbon yield of CTP can be improved by physical separation and chemical modification. Physical separation (i.e., fractional distillation and solvent extraction) can be used to separate components with different average molecular weights from CTP [4]. On the other hand, chemical modifications are involved in chemical reactions between CTP and silicon compounds, polystyrene, rosin, polyvinylpyridine, iodine, phenolic resin, divinylbenzene, polyacrylonitrile, lignin/silica hybrid, etc. [5–13]. Compared to physical separation, chemical modification is superior in saving resources, reducing waste disposal and simplifying the preparation procedure, therefore, it has been the typical approach to improve the carbonization yield of CTP. Cinnamaldehyde (CMA) is a major bioactive compound isolated from the leaves of Cinnamomum osmophloeum kaneh [14]. It is a ␣,
∗ Corresponding author. Tel.: +86 29 88492870; fax: +86 29 88492870. E-mail address: zhangwj [email protected] (W. Zhang). 0165-2370/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2011.11.005
-unsaturated aldehyde, in which the benzene ring is conjugated with C O and C C groups. So, it is a potential natural cross-linking agent [15] and hydrogenation reactions can take place in both the C O and C C groups [16,17]. In addition, the aldehyde group, in the presence of acid, can react with small molecules in CTP to form large molecules [18], and there is an aldehyde group in the chemical structure of CMA. Hence, in this paper, CMA was used to modify CTP in the presence of p-toluene sulfonic acid (PTS). The purpose of this paper is to study the characterization and carbonization behavior of CMA modified CTP.
2. Experiment 2.1. Materials CTP was purchased from the Steel Co. Ltd. (Wuhan, China). CMA and PTS were of analytical grade. Some properties of the CTP are included in Table 1.
2.2. Procedures 2.2.1. Modification of CTP 100 g CTP and 7 g PTS were mixed in a 500 ml round bottom three-neck flask equipped with a motor driven stirrer. It was started at 100 ◦ C at 90 rpm and CMA was added slowly into the flask. The speed of the stirrer was raised to 200 rpm at 150 ◦ C and held for 3 h under a nitrogen flow of 50 ml min−1 . The four pitches used in this study are parent CTP (M0 ), the CTP modified with 5 ml of CMA (M5 ),
64
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
Table 1 Main characteristics of different pitches. Pitches
SPa (◦ C)
CVb (wt.%)
TSc (wt.%)
QId (wt.%)
M0 M5 M10 M15
120 116 112 90
57.75 59.71 65.02 60.20
44.05 44.23 48.46 52.24
7.90 9.35 11.24 12.06
a b c d
Softening point. Coking value. Toluene solubles. Quinoline insolubles.
the CTP modified with 10 ml of CMA (M10 ) and the CTP modified with 15 ml of CMA (M15 ), respectively. 2.2.2. Carbonization Carbonization of samples was carried out in a tube furnace. About 1 g sample was heated to designated temperature at a rate of 10 ◦ C min−1 and kept at this temperature for 2 h. The N2 stream was introduced into the tube furnace throughout the carbonization. The products are denoted as Cx , where x is the final carbonization temperature. 2.3. Analysis 2.3.1. Characteristics of CTP and CMA modified CTPs The compositions of CTP and CMA modified CTPs were analyzed using the following standard methods: softening point (SP), ring and ball method, ASTM D36-66; coking value (CV), ISO 6998; toluene insolubles (TI), ISO 6376-96; quinoline insolubles (QI), ISO 6791-81. 2.3.2. Measurements Thermogravimetric analysis (TGA) was performed on a MettlerToledo thermal analyzer under N2 atmosphere with a heating rate of 10 ◦ C min−1 . 1 H nuclear magnetic resonance (NMR) spectroscopy was recorded on a Bruker AV 300 NMR spectrometer by dissolving the samples of pyridine solubles of CTP and CMA modified CTP (M10 ) in CDCl3 using tetramethyl-silane as internal standard. Elemental analysis of C, H, N, and S was performed on a Vario EL-III analyzer. The morphologies of parent CTP and CMA modified CTP (M10 ) were examined using FEI Sirion 200 scanning electron microscopy (SEM). Fourier transform infrared (FT-IR) spectroscopy was acquired on a Bruker Tenser-27 FT-IR spectrometer with thin films of KBr in the range 4000–400 cm−1 . X-ray diffraction (XRD) was carried out on the Panalytical X-Pert PRO X-ray diffraction ˚ radiation at 40 kV and 35 mA. instrument with CuK␣ ( = 1.5406 A)
Fig. 1. TG curves of parent CTP and CMA modified CTPs.
3.2. TGA analysis TGA consists of TG and DTG. Here, TG is used in combination with DTG to study the transitions of CMA modified CTPs at different carbonization temperatures. It can be observed in Fig. 1 that both parent CTP and CMA modified CTPs decompose in one single mass loss stage in the temperature range of 25–800 ◦ C. The weight loss is mainly due to the removal of gases and light compounds generated via thermal polymerization and cracking of side chains of aromatic rings [1]. The carbonization yields of M0 , M5 , M10 and M15 are 41.04%, 44.50%, 46.12% and 45.53%, respectively, indicating that the carbonization yield of CTP can be improved by adding CMA. It could be rationalized as follows: first, in the presence of acid, CMA can react with small molecules in parent CTP. So, large molecules can be formed via the reaction between CMA and the small molecules in CTP [18], which decreases the removal of light compounds and increases the carbonization yield. Second, PTS is an oxidation catalyst. It can partly oxidize CTP material [20], and thus results in the formation of black spots shown in Fig. 3. This would lead to formation of more thermal resistant material and increases the carbonization yield of CTP. The analysis of the DTG curves (Fig. 2) show that parent CTP and CMA modified CTPs are losing mass at varying rate related to the cross-linking degree of modification by CMA. The profile of parent CTP is characterized by a single peak centered at 362 ◦ C, which indicates that the mass loss rate at this temperature reaches the
3. Results and discussion 3.1. Characteristics of parent CTP and CMA modified CTPs Table 1 lists the main characteristics of parent CTP and three different CMA modified CTPs. The modified CTPs (M5 , M10 and M15 ), compared with parent CTP, have lower SP, higher toluene solubles (TS) and QI content with increasing CMA content. An important difference between the CMA modified CTPs is their coking values. It can be observed in Table 1 that CMA modified CTPs have higher coking values than that of parent CTP. However, the coking value does not increase with the increasing content of CMA, as indicated by that the coking value of M10 is 65.02% but that of M15 is 60.20%. A possible reason for this is that the CMA dosage is excessive when 15 ml of CMA is added to 100 g parent CTP. The excessive CMA may self-polymerize and the resultant product has poor heat-resistance [19], which would lead to the decrease of the coking value.
Fig. 2. DTG curves of parent CTP and CMA modified CTPs.
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
65
Table 2 Results of elemental analysis and 1 H NMR. Elemental analysis (wt.%)
M0 M10
N
C
H
S
2.50 0.64
93.07 90.82
4.09 3.99
0.66 1.72
C/H
Har %
Ha %
H+␥ %
Har /Hal
1.89 1.90
90.34 72.36
2.76 15.76
6.90 11.89
9.35 2.62
Har , aromatic hydrogen; Hal , aliphatic hydrogen; H˛ , aliphatic hydrogen in the ␣-position; H+␥ , aliphatic hydrogen in the - and ␥- positions.
Fig. 3. SEM images of parent CTP (a) and CMA modified CTP (M10 ) (b).
maximum value. However, there are two peaks in the DTG profile of the CMA modified CTPs (M10 and M15 ) at around 350 ◦ C, which indicates the formation of different phases. In addition, the small peaks observed at around 500 ◦ C, which are related to the thermal polymerization reactions at this temperature [21], are more obvious in CMA modified CTPs than in parent CTP. All the above indicates the carbonization behaviors of parent CTP and the CMA modified CTPs are different. 3.3.
1H
NMR and elemental analysis
CMA modified CTP (M10 ) is mainly studied in the subsequent work for its high carbonization yield in modified CTPs. Elemental analysis of parent CTP and CMA modified CTP (M10 ) is shown in Table 2. It is observed that the content of N in CMA modified CTP (M10 ) is much lower than that in parent CTP, which may be attributed to the removal of N2 at low temperature during the process of modification. The increased content of S in CMA modified CTP (M10 ) is caused by the introduction of PTS to CMA modified CTP (M10 ). In addition, the C/H ratio of CMA modified CTP (M10 ) (1.90) is almost the same as that of parent CTP (1.89). 1 H NMR spectra can directly characterize distribution of protons differing in chemical environments, i.e., aromatic protons, olefinic, and protons in ␣-, - and ␥-positions in aliphatic substituents on aromatic ring system [22]. To characterize the distribution of protons in parent CTP and CMA modified CTP (M10 ), 1 H NMR measurements were performed. The results are shown in Table 2. The proton in the respective chemical shift windows: 6.3–9.5 ppm are aromatic protons (Har ); 2.0–4.5 ppm are protons at ␣ positions in aliphatic substituents on aromatic ring (H␣ ) as well as 0.5–2 ppm at  and ␥ positions (H+␥ ), respectively [23]. The distribution of all the hydrogen atoms was determined by digital integration of Har , H␣ , H and H␥ band intensities normalized over the complete spectrum. As shown in Table 2, CMA modified CTP (M10 ) has much lower Har and Har /Hal than parent CTP. In addition, the modification leads to high increase of protons in methyl and methylenes (␣-position) attached to aromatic rings. Although CMA modified CTP (M10 ) has much lower Har and Har /Hal than parent CTP, the C/H values of parent CTP and CMA modified CTP (M10 ) are similar.
It seems contradictory but it is reasonable because the different objects are detected: the object of 1 H NMR experiment is pyridine soluble, but the object of elemental analysis experiment is the total CTP, which contains both pyridine solubles and pyridine insolubles. 3.4. SEM analysis SEM images of parent CTP and CMA modified CTP (M10 ) are shown in Fig. 3. The surface of parent CTP is loose, with few black spots (Fig. 3(a)). Nevertheless, major surface changes appear when the parent CTP is modified with CMA. Fig. 3(b) shows the SEM image of CMA modified CTP (M10 ). Some black spots, which are the products of oxidized material, distribute on the surface of the CMA modified CTP (M10 ). Therefore, these black spots are partly responsible for the higher carbonization yield of CMA modified CTP (M10 ).
Fig. 4. FT-IR spectra of CMA modified CTP (M10 ) carbonized at different temperatures.
66
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67
Fig. 5. XRD patterns of parent CTP and CMA modified CTP (M10 ) carbonized at different temperatures.
3.5. FT-IR analysis To recognize the structure changes of CMA modified CTP (M10 ) during the pyrolysis process, the products of CMA modified CTP (M10 ) carbonized at different temperatures are prepared and characterized with FT-IR spectra, which are shown in Fig. 4. The spectra show the following regions of interest. The peaks at 3030 and 2915 cm−1 are due to aromatic C–H stretching vibration and aliphatic C–H stretching vibration, respectively [24]. The peak at 1600 cm−1 is attributed to aromatic C C stretching vibration and the peak at 1441 cm−1 is attributed to C–H bending vibration of methyl and methylene. In addition, the peaks at 1226, 1180, 1126, 1035 and 567 cm−1 are attributed to –SO3 H [25]. From Fig. 4, it can be observed that methyl and methylene groups (see the peak at 2915 cm−1 ) of the CMA modified CTP (M10 ) gradually disappear while increasing temperature, which is caused by demethylation of methyl and methylene. In addition, the peaks of C200, C300 and C400 in the range of 500–1000 cm−1 are different from that of C500, C600 and C700. This indicates the chemical structures of the CMA modified CTP (M10 ) change greatly when the temperature is higher than 400 ◦ C. 3.6. XRD analysis XRD patterns of parent CTP and CMA modified CTP (M10 ) carbonized at different temperatures are shown in Fig. 5. All the samples exhibit two diffraction peaks centered at 25◦ and 43◦ in wide angle region, which can be generally indexed to (0 0 2), (1 0 0) diffraction of graphite [26]. Furthermore, it can be observed that the two peaks become sharp when the pitches are heated to temperature higher than 400 ◦ C, which is caused by the formation of mesophase. This agrees with the fact that the mesophase can be considered as a liquid crystal [27]. Table 3 shows the XRD parameters of parent CTP and CMA modified CTP (M10 ). It is worthwhile to note that the 2 angle increases with increasing carbonization temperature, consequently, the dspacing of carbonized CTPs decrease when the carbonization
Table 3 XRD parameters of parent CTP and CMA modified CTP (M10 ). Parent CTP ◦
C200 C300 C400 C500 C600 C700
CMA modified CTP (M10 )
2 0 0 2 ( )
d0 0 2
24.5 24.8 25.1 25.5 25.7 25.8
3.63 3.59 3.55 3.49 3.46 3.45
˚ (A)
2 0 0 2 (◦ )
˚ d0 0 2 (A)
24.8 24.9 25.3 25.7 25.8 25.9
3.59 3.57 3.52 3.46 3.45 3.44
temperature increases. In addition, the d002 values of CMA modified CTP (M10 ) are smaller than the corresponding data of parent CTP, indicating the CMA modified CTP (M10 ) is easier to be graphitized than parent CTP. 4. Conclusions The modification of CTP with CMA has great effect on its characteristics and carbonization behavior. The CMA modified CTPs, compared with parent CTP, have lower SP, higher TS and QI content with increasing CMA content. In addition, the modification with CMA results in an increase in carbonization yield by 3.46–5.08% when 100 g CTP was modified with 5–15 ml of CMA. During the carbonization process, methyl and methylene groups of the CMA modified CTP gradually disappear while increasing temperature and its chemical structures change greatly when the temperature is higher than 400 ◦ C. Furthermore, the modification with CMA is beneficial for increasing graphitizability of CTP. Acknowledgements This research was supported by the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20096102120016), the Natural Science Foundation of Shaanxi Province (No. 2009GM6001-1), the Foundation for Fundamental Research of Northwestern Polytechnical University (No. JC201030), the Innovation Foundation of China Aerospace Science and Technology (Grant No. CASC200906) and the Graduate Starting Seed Fund of Northwestern Polytechnical University (No. Z2011005). References [1] M. Pérez, M. Granda, R. Santamaría, T. Morgan, R. Menéndez, A thermoanalytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch, Fuel 83 (2004) 1257–1265. ´ Use of coal tar pitch in carboncarbon composites, Fuel 66 (1987) [2] V. Markovic, 1512–1515. [3] V. Prada, M. Grandda, J. Bermejo, R. Menéndez, Preparation of novel pitches by tar air-blowing, Carbon 37 (1999) 97–106. [4] J.J. Fernández, A. Figueiras, M. Granda, J. Bermejo, R. Menéndez, Modification of coal-tar pitch by air-blowing — I. Variation of pitch composition and properties, Carbon 33 (1995) 295–307. [5] O.S. Efimova, G.P. Khokhlova, Y.F. Patrakov, Thermal conversion of coal-tar pitch in the presence of silicon compounds, Solid Fuel Chem. 44 (2010) 5–11. ´ ´ J. Zielinski, T. Brzozowska, Thermal treatment of pitch–polymer [6] W. Ciesinska, blends, J. Therm. Anal. Calorim. 95 (2009) 193–196. [7] Q.L. Lin, W. Su, Y. Xie, Effect of rosin to coal-tar pitch on carbonization behavior and optical texture of resultant semi-cokes, J. Anal. Appl. Pyrolysis 86 (2009) 8–13. [8] B. Grzyb, J. Machnikowski, J.V. Weber, Mechanism of co-pyrolysis of coal-tar pitch with polyvinylpyridine, J. Anal. Appl. Pyrolysis 72 (2004) 121–130. [9] N. Miyajima, T. Akatsu, T. Ikoma, O. Ito, B. Rand, Y. Tanabe, E. Yasuda, A role of charge-transfer complex with iodine in the modification of coal tar pitch, Carbon 38 (2000) 1831–1838.
W. Zhang et al. / Journal of Analytical and Applied Pyrolysis 94 (2012) 63–67 [10] T.Q. Li, X.J. Liu, C.Y. Wang, H. Wang, Structural characteristics of mesophase spheres prepared from coal tar pitch modified by phenolic resin, Chin. J. Chem. Eng. 14 (2006) 660–664. [11] Q.L. Lin, T.H. Li, C.Z. Zheng, Y. Zhao, S.H. Song, Carbonization behavior of coaltar pitch modified with divinylbenzene and optical texture of resultant semicokes, J. Anal. Appl. Pyrolysis 71 (2004) 817–826. [12] B. Grzyb, J. Machnikowski, J.V. Weber, A. Koch, O. Heintz, Mechanism of copyrolysis of coal-tar pitch with polyacrylonitrile, J. Anal. Appl. Pyrolysis 67 (2003) 77–93. [13] Q.L. Lin, H.Y. Tang, C.H. Li, L.Q. Wu, Carbonization behavior of coal-tar pitch modified with lignin/silica hybrid and optical texture of resultant semi-cokes, J. Anal. Appl. Pyrolysis 90 (2011) 1–6. [14] S.S. Cheng, J.Y. Liu, K.H. Tsai, W.J. Chen, S.T. Chang, Chemical composition and mosquito larvicidal activity of essential oils from leaves of different Cinnamomum osmophloeum provenances, J. Agric. Food Chem. 52 (2004) 4395–4400. [15] M.P. Balaguer, J.G. Estaca, R. Gavara, P.H. Munoz, Functional properties of bioplastics made from wheat gliadins modified with cinnamaldehyde, J. Agric. Food Chem. 59 (2011) 6689–6695. [16] F. Delbecq, P. Sautet, Competitive C C and C O adsorption of ␣--unsaturated aldehydes on Pt and Pd surfaces in relation with the selectivity of hydrogenation reactions: a theoretical approach, J. Catal. 152 (1995) 217–236. [17] Th. Vergunst, F. Kapteijn, J.A. Moulijn, Kinetics of cinnamaldehyde hydrogenation-concentration dependent selectivity, Catal. Today 66 (2001) 381–387. [18] Q.L. Lin, T.H. Li, Y.B. Ji, W.Z. Wang, X.X. Wang, Study of the modification of coal-tar pitch with p-methyl benzaldehyde, Fuel 84 (2005) 177–182.
67
[19] G. Battistuzzi, S. Cacchi, G. Fabrizi, An efficient palladium-catalyzed synthesis of cinnamaldehydes from acrolein diethyl acetal and aryl iodides and bromides, Org. Lett. 5 (2003) 777–780. [20] N. Noroozi-Pesyan, A.H. Dabbagh, p-Toluenesulfonic acid a useful and selective reagent for the oxidation of benzoins to benziles under solvent-free condition, J. Iran. Chem. Res. 1 (2008) 123–127. [21] C. Blanco, V. Prada, R. Santamaría, J. Bermejo, R. Menéndez, Pyrolysis behaviour of mesophase and isotropic phases isolated from the same pitch, J. Anal. Appl. Pyrolysis 63 (2002) 251–265. [22] A.A. Herod, M.J. Lazaro, M.Domin, C.A. Islas, R. Kandiyoti, Molecular mass distributions and structural characterisation of coal derived liquids, Fuel 79 (2000) 323–337. [23] M.D. Guillén, C. Díaz, C.G. Blanco, Characterization of coal tar pitches with different softening points by 1 H NMR Role of the different kinds of protons in the thermal process, Fuel Process. Technol. 58 (1998) 1–15. ˜ [24] J. Alcaniz-Monge, D. Cazorla-Amorós, A. Linares-Solano, Characterisation of coal tar pitches by thermal analysis, infrared spectroscopy and solvent fractionation, Fuel 80 (2001) 41–48. [25] F. Selampinar, U. Akbulut, E. Yildiz, A. Güngör, L. Toppare, Synthesis of a novel poly(arylene ether ketone) and its conducting composites with polypyrrole, Synth. Met. 89 (1997) 111–117. [26] A.H. Lu, W.C. Li, E.L. Salabas, B. Spliethoff, F. Schüth, Low temperature catalytic pyrolysis for the synthesis of high surface area, nanostructured graphitic carbon, Chem. Mater. 18 (2006) 2086–2094. [27] J.D. Brooks, G.H. Taylor, The formation of graphitizing carbons from the liquid phase, Carbon 3 (1965) 185–193.