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The effect of carbon black on reforming of pyrolysis fuel oil for a binder pitch
Fuel 206 (2017) 58–63
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
The effect of carbon black on reforming of pyrolysis fuel oil for a binder pitch Kyung Hoon Kim, Sangmin Lee, Min-Il Kim, Young-Seak Lee ⇑ Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Pitch was reformed from PFO by
Carbon black was added to PFO to increase the QI content of the reformed pitch by serving as nuclei for the growth of QI particles.
adding carbon black to increase its QI content. Carbon black in the pitch served as nuclei for the growth of QI particles. QI content of pitch increased and its SP decreased on the addition of carbon black.
a r t i c l e
i n f o
Article history: Received 1 March 2017 Received in revised form 11 April 2017 Accepted 16 May 2017
Keywords: Petroleum Pyrolysis fuel oil Binder Pitch Carbon black
a b s t r a c t Pyrolysis fuel oil (PFO) has been reformed to increase the quinoline-insoluble (QI) content by adding carbon black for use as a binder pitch because petroleum-based pitch generally has a low QI content. The prepared pitch was analyzed for its aromaticity (fa), QI content, molecular weight distribution, coking value (CV), softening point (SP), and carbonization yield. The QI content of the reformed pitches increased from 0.4% to 14.1%, whereas the average molecular weight of only quinoline-soluble content decreased by increasing the carbon black content. These results indicate that carbon black adsorbs lowmolecular-weight compounds and serves as nuclei for the growth of QI particles. For these reasons, the SP and carbonization yield showed a decreasing tendency, but increased when QI sharply increased. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Binder pitches are used as a binder in the manufacture of artificial graphites because cokes, which are a main precursor of arti-
⇑ Corresponding author. E-mail address: [email protected] (Y.-S. Lee). http://dx.doi.org/10.1016/j.fuel.2017.05.056 0016-2361/Ó 2017 Elsevier Ltd. All rights reserved.
ficial graphite, have little coking power [1]. The binder pitches are divided into coal-tar pitch and petroleum pitch on the basis of their precursors [2–4]. The binder pitches from coal tar are commonly used because their quinoline-insoluble (QI) content is higher than that of petroleum pitches. However, the coal-tar pitches have a higher content of impurities such as sulfur, nitrogen and ash compared to the petroleum pitches. These impurities cause puffing during heat treatment, which reduces the mechanical strength of
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K.H. Kim et al. / Fuel 206 (2017) 58–63
the artificial graphite. Therefore, a purification process is needed in the manufacture of the coal-tar-based pitches prior to their use as binders. However, petroleum pitches have few impurities compared to coal-tar pitch; they therefore exhibit reduced puffing during the heat treatment. However, the QI content of the petroleum pitches is very low, typically less than 1% [5–10]. The extent to which the QI content can be increased using heat treatment is limited; thus, an alternative method is required to increase the QI content [11–13]. In the preparation of artificial graphite and cokes, the influence of the QI content of the binder pitch on the structure and properties has been extensively studied. The QI content reduces the optical texture size of the cokes and improves the mechanical strength of the artificial graphite and cokes. The QI increases the viscosity of the binder pitch; thus, an appropriate QI content is required. The binder pitch for the synthesis of artificial graphite typically contains 10–15 wt% QI. In this study, to prepare petroleum-based binder pitch with high QI content, we reformed PFO using heat treatment by adding amorphous carbon black as an additive as an alternative method to control the QI content in the reformed pitch. The effect of the presence of the carbon black during the reforming of the PFO on the growth of the QI particles was investigated. On the basis of the results of this study, we evaluated the suitability of the reformed pitches as a binder pitch. 2. Experimental 2.1. Materials In this study, PFO (Yeochun NCC Co. Ltd., produced by NCC (Naphtha Cracking Center), Republic of Korea) was used as a precursor for the binder pitch without any further purification. Carbon black (Chezacarb AC-60; Unipetrol RPA, Litvinov, Czech Republic) was used as an additive for the binder pitch. 2.2. Reforming of PFO
Fisher Scientific Inc., USA) was used to analyze the chemical structure of the components in the reformed pitches. The aromaticity values were calculated from the elemental analysis results and FT-IR spectra according to the following equations [15,16]
Fa ¼ 1
H=C X 0 ð1 þ ðHa =Hs ÞÞ
ð1Þ
Ha =Hs ¼
D3030 1 D2920 eA =eS
ð2Þ
where X0 is the average number of hydrogen atoms combined with non-aromatic carbon atoms, generally assumed to be 2; H/C is the atomic ratio between hydrogen and carbon; Ha/Hs is the hydrogen combining ratio of aromatic and aliphatic compounds; eA =eS is 0.5 times the absorptivity coefficient; and D3030/D2920 is the ratio between the peak intensities of the aromatic CAH bond (D3030) and the aliphatic CAH bond (D2920). The molecular weight distribution was investigated using a matrix-assisted laser-desorption ionization time-of-flight mass spectrometer (Voyager-DE STR Biospectrometry workstation, Life Technologies Co., CA) with DHB (2,5-dihydroxybenzoic acid) as the matrix. The coking value (CV) and QI of the reformed pitches were measured according to standard methods ASTM D 2416 and ASTM D 4746, respectively. To investigate thermal properties of the reformed pitches, thermogravimetric analysis (TGA; SDT Q600, TA Instruments Ltd., USA) was conducted at heating rate of 10 °C/min and at temperature of up to 1000 °C under N2 atmosphere, and carbonization yield of the pitch was based on the TGA result at 1000 °C [17]. The softening point (SP) was investigated using a softening-point apparatus (FP90, Mettler Toledo International Inc., Switzerland) following ASTM 3104 standard. A ring-shaped mold was filled with the prepared pitch, then placed in the SP apparatus and was heated at a rate of 2 °C/min until the pitch is flowing down to the bottom.
3. Results and discussion
The reforming process is based on a reported procedure involving heat treatment and distillation in a 1.2 L reactor [14]. The reforming was conducted by heat treatment in the presence of different concentrations of carbon black in PFO (0, 0.5, 1.0 and 1.5 wt %; the total weight of the mixture was 500 g). The mixture was reformed from room temperature to 340 °C at a heating rate of 2 °C/min under a 4 L/min N2 gas flow and a 200 rpm agitation rate. The samples were maintained at 340 °C for 4 h and naturally cooled to room temperature. The reformed pitches were labeled as PCB-X, where X is the concentration of the carbon black in the PFO as shown in Table 1.
3.1. Chemical properties
Elemental analysis of the reformed pitches was conducted using an elemental analyzer (EA; EA1112, CE Instrument, Italy). Fourier transform infrared spectroscopy (FT-IR; Nicolet 6700, Thermo
Table 2 shows the elemental analysis results of the carbon, hydrogen and other element content in the reformed pitches [18]. The hydrogen content of the reformed pitches increases with the amount of carbon black, whereas the carbon content shows no clear tendency. However, the H/C mole ratio of the reformed pitches is little changed among PCB-0, PCB-0.5 and PCB-1.0, then slightly increase at PCB-1.5 during the reforming process because of the increase in aliphatic compounds or the reduction of aromatic compound size. Fig. 1 presents the FT-IR spectra of the reformed pitches with different carbon black content. The FT-IR spectra show adsorption bands for aliphatic CAH bonds at approximately 2920 cm1 and aromatic CAH bonds at approximately 3030 cm1. Adsorption bands associated with aromatic CAHAH bonds and C@C bonds appear at 700–900 cm1 and 1600 cm1, respectively [19–21].
Table 1 Reforming conditions of the pitches.
Table 2 Elemental content of the reformed pitches.
2.3. Characterization
Sample name
PCB-0 PCB-0.5 PCB-1.0 PCB-1.5
Reforming conditions
Sample name
Temp. (°C)
Time (h)
PFO (g)
Carbon black (g)
340 340 340 340
4 4 4 4
500.0 497.5 495.0 492.5
0 2.5 5.0 7.5
PCB-0 PCB-0.5 PCB-1.0 PCB-1.5
Elemental content (wt%) C
H
Other elements
92.10 92.73 92.54 92.25
6.65 6.68 6.68 6.73
1.25 0.59 0.78 1.02
H/C (mol ratio)
0.867 0.864 0.866 0.875
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slightly increases with increasing carbon black content. It is attributed that the volatile compounds (low-molecular-weight) in PFO was prevented to be distillated because carbon black adsorbs volatile compounds at the initial reforming step [25]. The yield of PCB0, PCB-0.5, PCB-1.0 and PCB-1.5 is 25.8, 28.9, 31.2 and 34.1%, respectively. As evident from the yield and the molecular weight distribution results, the increase of the yield is attributed to the low-molecular-weight compounds being less volatilized because they were adsorbed onto the carbon black. 3.3. Quinoline-insoluble content
Fig. 1. Fourier transform infrared spectra of the reformed pitches.
The aromaticity (fa) and H/C molar ratio of the reformed pitches are shown in Fig. 2. The aromaticity of the reformed pitches increases from 0.71 to 0.74 with increasing amount of carbon black. This result indicates that PCB-1.5 was composed of more aromatic carbon compounds than PCB-0, PCB-0.5 and PCB-1.0; this increase is attributed to the increase of small-sized aromatic compounds because of the tendency of H/C mole ratio. Therefore, reforming by adding carbon black can be an effective method for increasing the aromatic compound content. 3.2. Molecular weight properties Fig. 3 presents the MALDI-TOF spectra of the PFO and the reformed pitches. The molecular weight distributions only consider the quinoline-soluble content because the QI content of the prepared pitches does not ionize. The molecular weight of the PFO and the reformed pitches are 100–400 m/z and 215–715 m/z, respectively. The molecular weight distribution of PCB-0 range from 306 to 715 m/z, and those of PCB-0.5, PCB-1.0 and PCB-1.5 are 282–648, 216–552 and 215–434 m/z, respectively. The molecular weight distributions enable the compounds to be classified as a monomer (210–388 m/z), dimer (388–645 m/z), trimer (645–895 m/z) or tetramer (895–1120 m/z) [22–24]. According to this classification, the PFO is mainly composed of monomer compounds, whereas the reformed pitches are composed of monomer and dimer compounds. As shown in Fig. 3, the average molecular weight decreases and the intensity of the peaks in the mass spectra
Fig. 2. H/C molar ratio and aromaticity of the reformed pitches.
The QI content and CVs of the reformed pitches are presented in Fig. 4. The QI content and CV of PCB-0, PCB-0.5, PCB-1.0 and PCB1.5 are 0.4, 5.3, 7.8 and 14.1% and 44.3, 45.2, 46 and 46.3%, respectively. Both the QI content and the CV of the reformed pitches increase with increasing amount of carbon black. The amount of carbon black added to the PFO in PCB-0, PCB-0.5, PCB-1.0 and PCB-1.5 is only 0, 2.5, 5.0 and 7.5 g, respectively. Nevertheless, the increase in the QI content in PCB-0.5, PCB-1.0 and PCB-1.5 is 12.3, 18.5 and 34.3% compared to that of PCB-0. These increases are substantial compared to the amount of carbon black added. We speculate that the carbon black serves as nuclei for QI particle growth, as supported by previous research showing that carbon black serves as nuclei for the growth of mesophase pitch [25– 27]. The carbon black adsorbs low molecular weight compounds in PFO before reforming process and it is nuclei for formation of QI particle. Some low molecular weight compounds and other aromatic compounds on the carbon black converted to QI particle during heating process up to 340 °C. Then they are converted more to QI particle and the carbon black with QI particle agglomerate together during heating process at 340 °C for 4 h. We suggest a mechanism concerning the formation and growth of QI particles driven by carbon black during the reformation of PFO, as shown in Fig. 5. The CV of the reformed pitches tends to increase with increasing carbon black content, and this tendency is similar to that of the QI. As shown in Fig. 5, the coking values of the reformed pitches with added carbon black (PCB-0.5, PCB-1.0 and PCB-1.5) are increased by approximately 2–4.5% compared to that of PCB-0. We presume that the increase in the QI content led to the increased CV. 3.4. Thermal properties The thermal properties of the reformed pitches were analyzed using TG and SP analyses. The weight loss fractions of the reformed pitches were measured using TGA under a N2 atmosphere at temperature up to 1000 °C, as shown in Fig. 6. The initial decomposition temperature of the reformed pitches decreases with increasing carbon black content because of the increase in the low-molecular-weight compounds by carbon black as shown at MALDI-TOF results. As shown in Fig. 7, the carbonization yield has a tendency to decrease with increasing carbon black content until carbon black added 1.0 wt%; PCB-0: 40%, PCB-0.5: 37.8% and PCB-1.5: 37.4%. When carbon black added 1.5 wt%, however, the carbonization yield increases 10% compared to that of PCB1.0. It is attributed that the QI content in PCB-1.5 with the highest QI value among the reformed pitches affect to increase the carbonization yield, because the QI content of the pitches has affected to increase of fixed carbon fractions generally. The SP of PCB-0, PCB-0.5, PCB-1.0 and PCB-1.5 is 198, 167, 134 and 143 °C, respectively and the change tendency of the SP are similar to that of carbonization yield, as shown in Fig. 7. This result concerning decrease of SP with increasing carbon black content until 1.0 wt% is attributed to volatile compounds (low-molecular-
K.H. Kim et al. / Fuel 206 (2017) 58–63
61
Fig. 3. Matrix-assisted laser desorption/ionization spectra of (a) PFO, (b) PCB-0, (c) PCB-0.5, (d) PCB-1.0 and (e) PCB-1.5.
the QI content because it is mainly composed with highmolecular-weight compounds.
4. Conclusions
Fig. 4. Quinoline-insoluble content and coking value of the reformed pitches.
weight compounds) resulting from adsorption of low-molecularweight compounds such as light oil fractions and BTX (benzene, toluene and xylene) by the carbon black during the initial reforming process. The SP of PCB-1.5 increase slightly compared to that of PCB-1.0. it is attributed that the QI content of PCB-1.5, which is the highest QI value in this study, affected to increase the SP because
In this study, we used a heat treatment to reform PFO by adding carbon black to increase the QI content in the reformed binder pitch and subsequently evaluated its properties. The aromaticity (fa) and H/C mole ratio were observed to increase with increasing carbon black content, which is indicating that carbon black has helped to form small-sized aromatic compounds. The average molecular weight of the reformed pitches, which are only quinoline-soluble content, decrease and the yield of the reformed pitches increase with increasing carbon black content. We attributed these results to low-molecular-weight compounds being adsorbed by the carbon black so that low-molecular-weight compounds are less volatilized. The QI content of the reformed pitches increase and the grown QI content which except carbon black content also increase according to increase of carbon black content. Thus, carbon black serves as nuclei for the growth of QI particles in the binder pitch. Since MALDI-TOF and QI results had an effect on the SP and carbonization yield simultaneously, they decrease with increase of carbon black content and then slightly increase
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Fig. 5. The formation and growth mechanism for QI particle by carbon black as nuclei.
Acknowledgements This work was supported by the Technology Innovation Program (10048941, Development of preparation technology in petroleum-based pitch and needle/isotropic cokes) funded by the Ministry of Trade, Industry & Energy (MI, Korea). References
Fig. 6. TG curves of the reformed pitches under N2 atmosphere.
Fig. 7. Softening point and carbonization yield of the reformed pitches.
when the QI sharply increase. In conclusion, the PFO reforming process using heat treatment by adding the amorphous carbon black is a facile method as an alternative means to increase the QI content in petroleum-based binder pitch.
[1] Mochida I, Oyama T, Korai Y. Formation scheme of needle coke from FCCdecant oil. Carbon 1988;26:49–55. [2] Marvin LD, Thomas MOG. Petroleum derived carbon. In: Erle I, Shorbert II, editors. Carbon Materials in Large Volume Applications. Philadelphia: American Chemical Society; 1976. p. 91–109. [3] Alcaniz-Monge J, Cazorla-Amoros D, Sinares-Solano A, Oya A, Saknoto A, Hoshi K. Preparation of general purpose carbon fibers from coal tar pitches with low softening point. Carbon 1997;35:1079–87. [4] Mayani SV, Mayani VJ, Lee JY, Ko SH, Lee SK, Kim SW. Preparation of multi metal–carbon nanoreactors for adsorption and catalysis. Adsorption 2012;19:251–7. [5] Dong W, Liu H-C, Park S-J, Jin F-L. Fracture toughness improvement of epoxy resins with short carbon fibers. J Ind Eng Chem 2014;20:1220–2. [6] Greinke RA, O’connor LH. Determination of molecular weight distributions of polymerized petroleum pitch by gel permeation chromatography with quinoline eluent. Anal Chem 1980;52:1877–81. [7] Mayani VJ, Mayani SV, Lee Y, Park S-K. A non-chromatographic method for the separation of highly pure naphthalene crystals from pyrolysis fuel oil. Sep Purif Technol 2011;80:90–5. [8] Mora E, Blanco C, Santamaria R, Granda M, Menendez R. A novel method to obtain a petroleum-derived mesophase pitch suitable as carbon fiber precursor. Carbon 2003;41:445–52. [9] Shin HK, Seo MK, Bang YH, Park SJ. Effects of heat treatment time on aromatic yield of pyrolysis fuel oil-derived pitches. Carbon Lett 2016;19:104–6. [10] Kumar S, Srivastava M. Meliorate optical textures and mesophase contents by promising approach of deasphalting of petroleum residues. J Ind Eng Chem 2017;48:133–41. [11] Figueiras A, Granda M, Casal E, Bermejo J, Bonhomme J, Menendez R. Influence of primary QI on pitch pyrolysis with reference to unidirectional c/c composites. Carbon 1998;36:883–91. [12] Ball DR. The influence of the type of quinoline insolubles on the quality of coal tar binder pitch. Carbon 1978;16:205–9. [13] Matzinos PD, Patrick JW, Walker A. Coal tar pitch as a matrix precursor for 2D C/C composites. Carbon 1996;34:639–44. [14] Lee Y-S, Basova YV, Edie DD, Reid LK, Newcombe SR, Ryu S-K. Preparation and characterization of trilobal activated carbon fibers. Carbon 2003;41:2573–84. [15] Yamada Y, Honda H, Abe T. Production of binder pitch from petroleum vacuum residue. J Jpn Petrol Inst 1975;18:758–64. [16] Jung M-J, Jung J-Y, Lee D, Lee Y-S. A new pitch reforming from pyrolysis fuel oil by UV irradiation. J Ind Eng Chem 2015;22:70–4. [17] Kim JG, Kim JH, Song B-J, Lee CW, Im JS. Synthesis and its characterization of pitch from pyrolyzed fuel oil (PFO). J Ind Eng Chem 2016;36:293–7. [18] Hwang J-S, Lee C-H, Cho K-H, Kim M-S, Kim C-J, Ryu S-K, et al. Preparation of anisotropic/isotropic pitches from NCC-PFO. Korean Chem Eng Res 1995;33:551–8. [19] Chiono V, Carmagnola I, Gentile P, Boccafoschi F, Tonda-Turo C, Ballarini M, et al. Layer-by-layer coating of photoactive polymers for biomedical applications. Surf Coat Technol 2012;206:2446–53.
K.H. Kim et al. / Fuel 206 (2017) 58–63 [20] Wazir AH, Kakakhel L. Preparation and characterization of pitch-based carbon fibers. New Carbon Mater 2009;24:83–8. [21] Kim B-H, Kim J-H, Kim J-G, Bae M-J, Im JS, Lee CW, et al. Electrochemical and structural properties of lithium battery anode materials by using a molecular weight controlled pitch derived from petroleum residue. J Ind Eng Chem 2016;41:1–9. [22] Cervo EG, Thies MC. Control of molecular weight distribution of petroleum pitches via multistage supercritical extraction. J Supercrit Fluids 2010;51:345–52. [23] Kim JG, Kim JH, Song B-J, Jeon YP, Lee CW, Lee Y-S, et al. Characterization of pitch derived from pyrolyzed fuel oil using TLC-FID and MALDI-TOF. Fuel 2016;167:25–30.
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[24] Kim JG, Kim JH, Song B-J, Lee CW, Lee Y-S, Im JS. Empirical approach to determine molecular weight distribution using MALDI-TOF analysis of petroleum-based heavy oil. Fuel 2016;186:20–3. [25] Dornath P, Fan W. Dehydration of fructose into furans over zeolite catalyst using carbon black as adsorbent. Microporous Mesoporous Mater 2014;191:10–7. [26] Menendez R, Fernandez JJ, Bermejo J, Cebolla V, Mochida I, Korai Y. The role of carbon black/coal-tar pitch interactions in the early stage of carbonization. Carbon 1996;34:895–902. [27] Korai Y, Wang YG, Yoon SH, Ishida S, Mochida I, Nakagawa Y, et al. Effects of carbon black addition on preparation of meso-carbon microbeads. Carbon 1997;35:875–84.
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
The effect of carbon black on reforming of pyrolysis fuel oil for a binder pitch Kyung Hoon Kim, Sangmin Lee, Min-Il Kim, Young-Seak Lee ⇑ Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Pitch was reformed from PFO by
Carbon black was added to PFO to increase the QI content of the reformed pitch by serving as nuclei for the growth of QI particles.
adding carbon black to increase its QI content. Carbon black in the pitch served as nuclei for the growth of QI particles. QI content of pitch increased and its SP decreased on the addition of carbon black.
a r t i c l e
i n f o
Article history: Received 1 March 2017 Received in revised form 11 April 2017 Accepted 16 May 2017
Keywords: Petroleum Pyrolysis fuel oil Binder Pitch Carbon black
a b s t r a c t Pyrolysis fuel oil (PFO) has been reformed to increase the quinoline-insoluble (QI) content by adding carbon black for use as a binder pitch because petroleum-based pitch generally has a low QI content. The prepared pitch was analyzed for its aromaticity (fa), QI content, molecular weight distribution, coking value (CV), softening point (SP), and carbonization yield. The QI content of the reformed pitches increased from 0.4% to 14.1%, whereas the average molecular weight of only quinoline-soluble content decreased by increasing the carbon black content. These results indicate that carbon black adsorbs lowmolecular-weight compounds and serves as nuclei for the growth of QI particles. For these reasons, the SP and carbonization yield showed a decreasing tendency, but increased when QI sharply increased. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Binder pitches are used as a binder in the manufacture of artificial graphites because cokes, which are a main precursor of arti-
⇑ Corresponding author. E-mail address: [email protected] (Y.-S. Lee). http://dx.doi.org/10.1016/j.fuel.2017.05.056 0016-2361/Ó 2017 Elsevier Ltd. All rights reserved.
ficial graphite, have little coking power [1]. The binder pitches are divided into coal-tar pitch and petroleum pitch on the basis of their precursors [2–4]. The binder pitches from coal tar are commonly used because their quinoline-insoluble (QI) content is higher than that of petroleum pitches. However, the coal-tar pitches have a higher content of impurities such as sulfur, nitrogen and ash compared to the petroleum pitches. These impurities cause puffing during heat treatment, which reduces the mechanical strength of
59
K.H. Kim et al. / Fuel 206 (2017) 58–63
the artificial graphite. Therefore, a purification process is needed in the manufacture of the coal-tar-based pitches prior to their use as binders. However, petroleum pitches have few impurities compared to coal-tar pitch; they therefore exhibit reduced puffing during the heat treatment. However, the QI content of the petroleum pitches is very low, typically less than 1% [5–10]. The extent to which the QI content can be increased using heat treatment is limited; thus, an alternative method is required to increase the QI content [11–13]. In the preparation of artificial graphite and cokes, the influence of the QI content of the binder pitch on the structure and properties has been extensively studied. The QI content reduces the optical texture size of the cokes and improves the mechanical strength of the artificial graphite and cokes. The QI increases the viscosity of the binder pitch; thus, an appropriate QI content is required. The binder pitch for the synthesis of artificial graphite typically contains 10–15 wt% QI. In this study, to prepare petroleum-based binder pitch with high QI content, we reformed PFO using heat treatment by adding amorphous carbon black as an additive as an alternative method to control the QI content in the reformed pitch. The effect of the presence of the carbon black during the reforming of the PFO on the growth of the QI particles was investigated. On the basis of the results of this study, we evaluated the suitability of the reformed pitches as a binder pitch. 2. Experimental 2.1. Materials In this study, PFO (Yeochun NCC Co. Ltd., produced by NCC (Naphtha Cracking Center), Republic of Korea) was used as a precursor for the binder pitch without any further purification. Carbon black (Chezacarb AC-60; Unipetrol RPA, Litvinov, Czech Republic) was used as an additive for the binder pitch. 2.2. Reforming of PFO
Fisher Scientific Inc., USA) was used to analyze the chemical structure of the components in the reformed pitches. The aromaticity values were calculated from the elemental analysis results and FT-IR spectra according to the following equations [15,16]
Fa ¼ 1
H=C X 0 ð1 þ ðHa =Hs ÞÞ
ð1Þ
Ha =Hs ¼
D3030 1 D2920 eA =eS
ð2Þ
where X0 is the average number of hydrogen atoms combined with non-aromatic carbon atoms, generally assumed to be 2; H/C is the atomic ratio between hydrogen and carbon; Ha/Hs is the hydrogen combining ratio of aromatic and aliphatic compounds; eA =eS is 0.5 times the absorptivity coefficient; and D3030/D2920 is the ratio between the peak intensities of the aromatic CAH bond (D3030) and the aliphatic CAH bond (D2920). The molecular weight distribution was investigated using a matrix-assisted laser-desorption ionization time-of-flight mass spectrometer (Voyager-DE STR Biospectrometry workstation, Life Technologies Co., CA) with DHB (2,5-dihydroxybenzoic acid) as the matrix. The coking value (CV) and QI of the reformed pitches were measured according to standard methods ASTM D 2416 and ASTM D 4746, respectively. To investigate thermal properties of the reformed pitches, thermogravimetric analysis (TGA; SDT Q600, TA Instruments Ltd., USA) was conducted at heating rate of 10 °C/min and at temperature of up to 1000 °C under N2 atmosphere, and carbonization yield of the pitch was based on the TGA result at 1000 °C [17]. The softening point (SP) was investigated using a softening-point apparatus (FP90, Mettler Toledo International Inc., Switzerland) following ASTM 3104 standard. A ring-shaped mold was filled with the prepared pitch, then placed in the SP apparatus and was heated at a rate of 2 °C/min until the pitch is flowing down to the bottom.
3. Results and discussion
The reforming process is based on a reported procedure involving heat treatment and distillation in a 1.2 L reactor [14]. The reforming was conducted by heat treatment in the presence of different concentrations of carbon black in PFO (0, 0.5, 1.0 and 1.5 wt %; the total weight of the mixture was 500 g). The mixture was reformed from room temperature to 340 °C at a heating rate of 2 °C/min under a 4 L/min N2 gas flow and a 200 rpm agitation rate. The samples were maintained at 340 °C for 4 h and naturally cooled to room temperature. The reformed pitches were labeled as PCB-X, where X is the concentration of the carbon black in the PFO as shown in Table 1.
3.1. Chemical properties
Elemental analysis of the reformed pitches was conducted using an elemental analyzer (EA; EA1112, CE Instrument, Italy). Fourier transform infrared spectroscopy (FT-IR; Nicolet 6700, Thermo
Table 2 shows the elemental analysis results of the carbon, hydrogen and other element content in the reformed pitches [18]. The hydrogen content of the reformed pitches increases with the amount of carbon black, whereas the carbon content shows no clear tendency. However, the H/C mole ratio of the reformed pitches is little changed among PCB-0, PCB-0.5 and PCB-1.0, then slightly increase at PCB-1.5 during the reforming process because of the increase in aliphatic compounds or the reduction of aromatic compound size. Fig. 1 presents the FT-IR spectra of the reformed pitches with different carbon black content. The FT-IR spectra show adsorption bands for aliphatic CAH bonds at approximately 2920 cm1 and aromatic CAH bonds at approximately 3030 cm1. Adsorption bands associated with aromatic CAHAH bonds and C@C bonds appear at 700–900 cm1 and 1600 cm1, respectively [19–21].
Table 1 Reforming conditions of the pitches.
Table 2 Elemental content of the reformed pitches.
2.3. Characterization
Sample name
PCB-0 PCB-0.5 PCB-1.0 PCB-1.5
Reforming conditions
Sample name
Temp. (°C)
Time (h)
PFO (g)
Carbon black (g)
340 340 340 340
4 4 4 4
500.0 497.5 495.0 492.5
0 2.5 5.0 7.5
PCB-0 PCB-0.5 PCB-1.0 PCB-1.5
Elemental content (wt%) C
H
Other elements
92.10 92.73 92.54 92.25
6.65 6.68 6.68 6.73
1.25 0.59 0.78 1.02
H/C (mol ratio)
0.867 0.864 0.866 0.875
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slightly increases with increasing carbon black content. It is attributed that the volatile compounds (low-molecular-weight) in PFO was prevented to be distillated because carbon black adsorbs volatile compounds at the initial reforming step [25]. The yield of PCB0, PCB-0.5, PCB-1.0 and PCB-1.5 is 25.8, 28.9, 31.2 and 34.1%, respectively. As evident from the yield and the molecular weight distribution results, the increase of the yield is attributed to the low-molecular-weight compounds being less volatilized because they were adsorbed onto the carbon black. 3.3. Quinoline-insoluble content
Fig. 1. Fourier transform infrared spectra of the reformed pitches.
The aromaticity (fa) and H/C molar ratio of the reformed pitches are shown in Fig. 2. The aromaticity of the reformed pitches increases from 0.71 to 0.74 with increasing amount of carbon black. This result indicates that PCB-1.5 was composed of more aromatic carbon compounds than PCB-0, PCB-0.5 and PCB-1.0; this increase is attributed to the increase of small-sized aromatic compounds because of the tendency of H/C mole ratio. Therefore, reforming by adding carbon black can be an effective method for increasing the aromatic compound content. 3.2. Molecular weight properties Fig. 3 presents the MALDI-TOF spectra of the PFO and the reformed pitches. The molecular weight distributions only consider the quinoline-soluble content because the QI content of the prepared pitches does not ionize. The molecular weight of the PFO and the reformed pitches are 100–400 m/z and 215–715 m/z, respectively. The molecular weight distribution of PCB-0 range from 306 to 715 m/z, and those of PCB-0.5, PCB-1.0 and PCB-1.5 are 282–648, 216–552 and 215–434 m/z, respectively. The molecular weight distributions enable the compounds to be classified as a monomer (210–388 m/z), dimer (388–645 m/z), trimer (645–895 m/z) or tetramer (895–1120 m/z) [22–24]. According to this classification, the PFO is mainly composed of monomer compounds, whereas the reformed pitches are composed of monomer and dimer compounds. As shown in Fig. 3, the average molecular weight decreases and the intensity of the peaks in the mass spectra
Fig. 2. H/C molar ratio and aromaticity of the reformed pitches.
The QI content and CVs of the reformed pitches are presented in Fig. 4. The QI content and CV of PCB-0, PCB-0.5, PCB-1.0 and PCB1.5 are 0.4, 5.3, 7.8 and 14.1% and 44.3, 45.2, 46 and 46.3%, respectively. Both the QI content and the CV of the reformed pitches increase with increasing amount of carbon black. The amount of carbon black added to the PFO in PCB-0, PCB-0.5, PCB-1.0 and PCB-1.5 is only 0, 2.5, 5.0 and 7.5 g, respectively. Nevertheless, the increase in the QI content in PCB-0.5, PCB-1.0 and PCB-1.5 is 12.3, 18.5 and 34.3% compared to that of PCB-0. These increases are substantial compared to the amount of carbon black added. We speculate that the carbon black serves as nuclei for QI particle growth, as supported by previous research showing that carbon black serves as nuclei for the growth of mesophase pitch [25– 27]. The carbon black adsorbs low molecular weight compounds in PFO before reforming process and it is nuclei for formation of QI particle. Some low molecular weight compounds and other aromatic compounds on the carbon black converted to QI particle during heating process up to 340 °C. Then they are converted more to QI particle and the carbon black with QI particle agglomerate together during heating process at 340 °C for 4 h. We suggest a mechanism concerning the formation and growth of QI particles driven by carbon black during the reformation of PFO, as shown in Fig. 5. The CV of the reformed pitches tends to increase with increasing carbon black content, and this tendency is similar to that of the QI. As shown in Fig. 5, the coking values of the reformed pitches with added carbon black (PCB-0.5, PCB-1.0 and PCB-1.5) are increased by approximately 2–4.5% compared to that of PCB-0. We presume that the increase in the QI content led to the increased CV. 3.4. Thermal properties The thermal properties of the reformed pitches were analyzed using TG and SP analyses. The weight loss fractions of the reformed pitches were measured using TGA under a N2 atmosphere at temperature up to 1000 °C, as shown in Fig. 6. The initial decomposition temperature of the reformed pitches decreases with increasing carbon black content because of the increase in the low-molecular-weight compounds by carbon black as shown at MALDI-TOF results. As shown in Fig. 7, the carbonization yield has a tendency to decrease with increasing carbon black content until carbon black added 1.0 wt%; PCB-0: 40%, PCB-0.5: 37.8% and PCB-1.5: 37.4%. When carbon black added 1.5 wt%, however, the carbonization yield increases 10% compared to that of PCB1.0. It is attributed that the QI content in PCB-1.5 with the highest QI value among the reformed pitches affect to increase the carbonization yield, because the QI content of the pitches has affected to increase of fixed carbon fractions generally. The SP of PCB-0, PCB-0.5, PCB-1.0 and PCB-1.5 is 198, 167, 134 and 143 °C, respectively and the change tendency of the SP are similar to that of carbonization yield, as shown in Fig. 7. This result concerning decrease of SP with increasing carbon black content until 1.0 wt% is attributed to volatile compounds (low-molecular-
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Fig. 3. Matrix-assisted laser desorption/ionization spectra of (a) PFO, (b) PCB-0, (c) PCB-0.5, (d) PCB-1.0 and (e) PCB-1.5.
the QI content because it is mainly composed with highmolecular-weight compounds.
4. Conclusions
Fig. 4. Quinoline-insoluble content and coking value of the reformed pitches.
weight compounds) resulting from adsorption of low-molecularweight compounds such as light oil fractions and BTX (benzene, toluene and xylene) by the carbon black during the initial reforming process. The SP of PCB-1.5 increase slightly compared to that of PCB-1.0. it is attributed that the QI content of PCB-1.5, which is the highest QI value in this study, affected to increase the SP because
In this study, we used a heat treatment to reform PFO by adding carbon black to increase the QI content in the reformed binder pitch and subsequently evaluated its properties. The aromaticity (fa) and H/C mole ratio were observed to increase with increasing carbon black content, which is indicating that carbon black has helped to form small-sized aromatic compounds. The average molecular weight of the reformed pitches, which are only quinoline-soluble content, decrease and the yield of the reformed pitches increase with increasing carbon black content. We attributed these results to low-molecular-weight compounds being adsorbed by the carbon black so that low-molecular-weight compounds are less volatilized. The QI content of the reformed pitches increase and the grown QI content which except carbon black content also increase according to increase of carbon black content. Thus, carbon black serves as nuclei for the growth of QI particles in the binder pitch. Since MALDI-TOF and QI results had an effect on the SP and carbonization yield simultaneously, they decrease with increase of carbon black content and then slightly increase
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Fig. 5. The formation and growth mechanism for QI particle by carbon black as nuclei.
Acknowledgements This work was supported by the Technology Innovation Program (10048941, Development of preparation technology in petroleum-based pitch and needle/isotropic cokes) funded by the Ministry of Trade, Industry & Energy (MI, Korea). References
Fig. 6. TG curves of the reformed pitches under N2 atmosphere.
Fig. 7. Softening point and carbonization yield of the reformed pitches.
when the QI sharply increase. In conclusion, the PFO reforming process using heat treatment by adding the amorphous carbon black is a facile method as an alternative means to increase the QI content in petroleum-based binder pitch.
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