- Email: [email protected]
Synthesis and its characterization of pitch from pyrolyzed fuel oil (PFO)
G Model
JIEC 2836 1–5 Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1 2 3 4 5 6 7 8
Synthesis and its characterization of pitch from pyrolyzed fuel oil (PFO) Q1 Jong
Gu Kim a,b, Ji Hong Kim a,d, Byung-Jin Song a, Chul Wee Lee a,c, Ji Sun Im a,c,*
a
Division of Green Chemistry & Engineering Research, Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600, Republic of Korea Department of Applied Chemistry and Biological Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea c University of Science and Technology (UST), Daejeon 305-333, Republic of Korea d Department of Chemical and Biological Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Republic of Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 January 2016 Received in revised form 28 January 2016 Accepted 16 February 2016 Available online xxx
Pitch synthesis from pyrolyzed fuel oil (PFO) was conducted to understand the empirical synthesis tendency as a function of reaction temperature. Additionally, the chemical and physical characteristics of PFO and produced pitch are identified using X-ray diffraction analysis, thermogravimetric analysis, softening point analysis, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis. The produced pitch exhibited an enhanced stacking height (LC) value and C/H ratio, which is related to the formation of graphitic structure, according to the increased reaction temperature. The carbon residue yield obtained at 900 8C showed a gradually increased value of up to 42.58% in the sample synthesized at the temperature of 410 8C, depending on the increased reaction temperature. The molecular weight distribution of the produced pitches exhibited noticeable variation during the thermal reaction via MALDI-TOF analysis. The variation of the molecular weight fraction is assumed based on the pitch synthesis mechanism, e.g., polymerization, condensation and cracking reaction. ß 2016 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: Pyrolyzed fuel oil Pitch Thermal reaction MALDI-TOF TG analysis
9 10
Introduction
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Pitch is a representative precursor for the manufacturing of carbon materials [1]. Petroleum residues are generally used as a feedstock to produce the pitch by thermal and catalytic reaction [2]. The pitch characteristic is an important factor because the properties of carbon materials (carbon fiber, artificial graphite, etc.) are determined by the chemical and physical characteristics of pitch, which are classified as mesophase contents, solubility by solvents (hexane, toluene, quinolone etc.), softening point, chemical compositions, and molecular weight distribution (MWD) [3,4]. For example, carbon fiber for the aerospace industry requires a type of the mesophase (anisotropic) pitch that can improve the Young’s modulus of fiber [5]. Artificial graphite block demands well-refined pitch that has low levels of impurities, such as metal and ash, because of the expansion on carbon layer structure during the graphitization process over 2000 8C.
Q2 * Corresponding author at: Division of Green Chemistry & Engineering Research, Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600,
Q3 Republic of Korea. Tel.: +82 42 860 7366; fax: +82 42 860 7388. E-mail address: [email protected] (J.S. Im).
Petroleum residues can be typically categorized as fluid catalytic cracking decant oil (FCC-DO), pyrolyzed fuel oil (PFO), and vacuum residue (VR), which have different chemical composition, viscosity, and impurities (metal, ash) according to the refining operation condition, such as distillation temperature, refinery unit process and type, inducing the catalyst. Furthermore, those by-products have undefined chemical components consisting of more than thousands polycyclic aromatic hydrocarbon (PAH) species and a broad MWD. As mentioned above, various petroleum residues have been used as a precursor for pitch synthesis [6–8]. However, undefined chemical components of petroleum residues make controlling the pitch properties difficult during the pitch synthesis reaction. It is well known that the pitch synthesis mechanism includes condensation, polymerization, volatilization, aromatization and cracking reaction [1,9,10]. In the case of pitch synthesis from single-chemical components, such as naphthalene and anthracene, the pitch having a narrow MWD can be produced by aromatization and condensation with the introduction of a Bronsted acid type catalyst [3]. Alternatively, the pitch synthesis derived from petroleum residues is accompanied by complicated chemical reactions due to the chemical components of the feedstock. Briefly, light compounds are removed during the thermal cracking and
http://dx.doi.org/10.1016/j.jiec.2016.02.014 1226-086X/ß 2016 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
2
49 volatilization, and heavy compounds are condensed and polymer50 ized during the thermal reaction. 51 Finally, selection of the feedstock for pitch synthesis is an 52 important factor that determines the properties of the pitch and 53 carbon materials. Various researchers have studied pitch synthesis 54 from petroleum residues. Eser and Wang considered the high55 Q4 sulfur FCC-DO as feedstock for needle coke production [11]. Yoon 56 et al. studied the carbon fiber production from the isotropic pitch 57 derived from naphtha cracked oil [12]. Mochida et al. evaluated the 58 spinnability of mesophase pitch derived from FCC-DO based on 59 Q5 structural characterizations [13]. Xiong et al. developed a new 60 route for producing the high-value pitch-based carbon fiber from 61 catalytic slurry oil using various treatment processes [14]. 62 Among the petroleum residues, PFO, which is by-product of the 63 naphtha cracking process, is produced at a high level (with over 64 100 million metric ton per annum produced in the South Korea 65 refinery industry [15]) and is used as plant fuel because of the 66 difficulty of the re-treatment process and the low utilization. 67 Nevertheless, the abundant aromatic contents and low impurities 68 of PFO are an attractive advantages to utilize as a feedstock for 69 producing the pitch. 70 In this study, pitch derived from PFO was synthesized by 71 thermal reaction as a function of reaction temperature in the range 72 of 390–410 8C. The empirical reaction tendency of the pitch 73 derived from PFO was determined with chemical and physical 74 characterization. The produced pitches and feedstock were 75 analyzed to understand the MWD variation using matrix-assisted 76 laser desorption/ionization-time of flight analysis (MALDI-TOF) 77 analysis. In addition, a chemical reaction was suggested that 78 describes the changes of each molecular weight fraction during the 79 thermal reaction. Softening point and thermogravimetric (TG) 80 analyses supported the physical characteristics of pitch related to 81 the thermal properties. 82
Experimental
83
Materials
84 85 86 87 88
PFO (Yeochun NCC CO. LTD., produced by NCC (Naphtha Cracking Center, South Korea)) was used as a feedstock for synthesis of the petroleum based pitch. 7,7,8,8-tetracyanoquinodimethane (TCNQ, 98%, CAS Number 1518-16-7, Sigma-Aldrich) was used as matrix for the MALDI-TOF analysis.
89
Procedure of PFO based pitch
90 91 92 93 94 95 96 97 98 99
The pitch synthesis reaction was conducted using a 1L scale batch type autoclave reactor. The reaction temperature was carefully controlled because the pitch properties could be affected by a drifting temperature. The experimental error range of the controlled temperature was within 2 8C using a PID controller system. The reaction procedure was as follows: (1) 500 g of PFO was placed in the 1L vessel of the reactor; (2) 200 cc/min of N2 gas was injected into the vessel to produce an inert gas state atmosphere for 30 min; (3) after the N2 purging step, the furnace was heated according to the programmed temperature step using a Yokogawa
control system (UT35A, UT32A). The details on the reaction conditions and sample names are presented in Table 1.
100 101
Analysis of the pitch and the feedstock
102
The elemental analysis was conducted to confirm the C, H, N, and S contents and the C/H ratio of the feedstock and the produced pitches using a Thermo Scientific FLASH EA-2000 Organic Elemental Analyzer. The X-ray diffraction (XRD) analysis was performed to determine the crystallinity of the pitch using a Rigaku Ultima IV diffractometer with a Cu-Ka radiation. The softening point of the produced pitches was measured using a softening point analyzer (DP-70, Mettler Toledo) according to ASTM D3416. The heating rate was 4 8C/min in an N2 atmosphere. TG analysis was conducted at a heating rate of 10 8C/min, and at temperatures of up to 900 8C in an N2 atmosphere. The sample for MALDI-TOF analysis was prepared in accordance with the Mark method [16,17]. Briefly, the pitch was finely ground in a grinding mill and then mixed with TCNQ. The mixture was then transferred to the MALDI target-plate cell using the waterspotting method. To remove all water, the entire sample was allowed to dry over a 12-h period. The MALDI-TOF analysis was conducted over a range of 0–1500 m/z using a Bruker Daltonics Autoflex MALDI-TOF mass spectrometer.
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123
Results and discussion
124
Temperature effects of the thermal reaction of PFO
125
The experimental condition of thermal synthesis reaction was considered to understand the empirical pitch synthesis tendency from real feedstock (PFO) because each of the petroleum residues showed a different tendency due to the origin and chemical composition of each residue [11–14]. The pitch yield and volatile matter were measured as listed in Table 1. The pitch yield was found to gradually decrease with increasing reaction temperature. The minimum pitch yield was 25.4%, which was observed for the P-410 sample. The amount of volatile matter was inversely dependent on the reaction temperature. Both pitch yield and volatile matter were found to be correlated with reaction temperature. In addition, PFO was found to have a high volatile content under the boiling point of 400 8C, despite the fact that PFO is a by-product of naphtha catalytic cracking process in the temperature range of 400–500 8C. Thus, a catalyst for polymerization of light components may be needed to increase the pitch yield. Elemental analysis was conducted to identify the C, H, N, and S contents and the C/H ratio, which are listed in Table 2. The carbon contents were found to slightly increase with decreasing hydrogen content, depending on the reaction temperature. The C/H ratio was also increased by 1.29 in the P-410 sample. Increasing the C/H ratio indicates that aromatic contents are being formed at increased reaction temperature.
126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
Table 1 Experimental conditions of the thermal reaction. Sample name
P-390 P-400 P-410
Reaction condition Temp. (8C)
Time (h)
Pressure (bar)
N2 flow (cc/min)
Pitch yield (%)
Volatile matter (%)
Loss (%)
390 400 410
1 1 1
1 1 1
100 100 100
28.9 26.5 25.4
67.5 68.3 69.2
3.6 5.2 5.4
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx Table 2 Bulk properties of the pitch prepared by the thermal reaction. Sample name
PFO P-390 P-400 P-410
Softening point (8C)
– 104.30 123.00 132.20
TGA yield (%, at 900 8C)
13.71 34.85 38.47 42.58
Elemental analysis (%) C
H
N
S
C/H
91.60 92.30 92.60 92.70
7.90 6.40 6.10 6.00
N.D N.D N.D N.D
0.10 0.83 0.79 0.78
0.97 1.20 1.27 1.29
150
Crystallinity of the pitch
151 152 153
XRD analysis was conducted to confirm the crystallinity of the prepared pitch. The stacking height (LC) of the samples was calculated by following equation [18].
154 LC ¼ 0:89l=BC cos ’C 157 156 155 158 159 160 161 162 163 164 165 166 167 168 169 170
3
showed an increased trend, with values of 8.9 (P-390), 15.2 (P-400) and 21.2 (P-410). This result indicates that increased reaction temperature affects the growth of the graphitic structure in the pitch synthesis. Furthermore, these trends from the XRD analysis correspond to the C/H ratios related to the aromatic contents.
171 172 173 174 175
Thermal properties of the pitch
176
The thermal properties of produced pitches were analyzed using TG and softening point analyses. The TG curve showed a similar pattern in the all of the samples, as shown in Fig. 2(a). The final carbon residue yield of the produced pitches was calculated from the TG curve at 900 8C. These yields were increased according to the increasing reaction temperature; the P-410 sample presented the maximum value of 42.58%, which was threefold the value of PFO (13.71%). The weight loss of all samples was ceased at approximately 600 8C. The flat pattern of the TG curve over 600 8C corresponds to coke formation [19]. As shown in Fig. 2(b), the DTG curve of PFO showed the two peaks of the
177 178 179 180 181 182 183 184 185 186 187
Where l is the wavelength of the X-rays, BC is the full width at half maximum of the (002) peak, and wC is the corresponding scattering angle. As shown in Fig. 1, the pitches exhibited an amorphous peak at approximately 58–308; 2-theta peaks of (002) were measured at 24.268, 24.628, and 25.238 in the samples of P-390, P-400, and P410, respectively. Although all of the peaks of (002) did not reach a graphitic carbon peak at 26.58, these peaks of (002) were gradually shifted to a higher 2-theta region, depending on the reaction temperature, indicating the formation of a graphitic carbon structure. In addition, the values of the full width at half maximum of (002) were also measured as 9.00, 5.29, and 3.8 in the samples of P-390, P-400, and P-410, respectively. These values were found to decrease with increasing reaction temperature. The calculated LC
Fig. 1. Crystalline analysis by XRD of the prepared pitch.
Fig. 2. TG analysis of the prepared pitch and PFO. (a) TG curve, (b) DTG, and (C) DTA.
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
4
Fig. 4. Diagram of the molecular weight fraction divided by the pseudo-component.
Fig. 3. MALDI-TOF spectrum of the prepared pitch and PFO.
188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205
maximum rate of weight loss at approximately 150 8C and 370 8C, whereas the produced pitches showed only one peak at approximately 350–550 8C; this result highlighted the complicated patterns that indicate the chemically complexity of the pitch derived from PFO. A similar result was reported by Pe´rez et al. [20]. They found that the range of 350–550 8C corresponds to the weight loss associated with cracking/polymerization reactions. The DTA curve confirmed the endothermic characteristic in the same temperature range (350–550 8C), as shown in Fig. 2(c). The endothermic peak is well known as a representative peak of volatilization and the cracking reaction [21]. Because the pitch is complicated mixture derived from petroleum residue, the softening point is generally used as an indicator instead of the melting point. The softening point of produced pitches was also increased, depending on the increased reaction temperature, as listed in Table 2. The increased softening point is the result of the polymerization or condensation of each of the components that occurred during the thermal reaction.
206
Molecular weight distribution analysis of the samples
207 208 209
MWD variation of the prepared pitches during the thermal reaction was identified using the MALDI-TOF analysis, as shown in Fig. 3. It was confirmed that noticeable variation of MWD occurred
from the PFO to pitch by thermal reaction. PFO had a MWD in the range up to 600 m/z. After thermal reaction in the temperature range of 390–410 8C, the MWD of the pitch samples was expanded by approximately 1400 m/z. Considering the pitch synthesis reaction, the condensation and polymerization reaction was predominantly affected by the thermal reaction. As shown in Fig. 3, the three samples of pitch displayed similar patterns of MWDs in the MALDI-TOF spectra. However, each molecular fraction area separated by pseudo components showed a different tendency related to the pitch synthesis mechanism. To divide the area fraction, anthracene was selected as a pseudocomponent because a standard material is required to separate the molecular weight area. The area fraction was divided as follows: fraction 1 (1–178 m/z), fraction 2 (178–356 m/z), fraction 3 (356–534 m/z), fraction 4 (534–712 m/z), fraction 5 (712–890 m/z), fraction 6 (890–1068 m/z), fraction 7 (1068–1246 m/z), and fraction 8 (1246–1424 m/z) (Table 3). Q6 The pitch synthesis reaction was considered with the MWD variation relative to the area fractions, as shown in Fig. 4. Comparing PFO and the produced pitches, fractions 1 and 2 showed significant MWD variations. The area fraction of PFO in fraction 1 was 19.8%; however, the values of the prepared pitches decreased to less than 1%. This result indicates that low boiling point compounds were emitted due to volatilization during the thermal reaction or converted to the high molecular weight area fraction by means of the condensation and polymerization reaction. Comparing the produced pitches, a specific MWD variation was investigated. In fractions 2 and 3, the area fraction of the produced pitches was found to increase with increasing reaction temperature. However, fractions 5–8 showed an opposite trend compared with fractions 2 and 3. In fractions 2 and 3, each area fraction was increased by a maximum of 16.6% and 34.4% in the P-410 sample, respectively. The value of fraction 3 occupied the largest area fraction. This result indicated that the main compounds in the
Table 3 Integrated area fraction of the MALDI-TOF spectrum separated by the pseudo-component. Sample name
PFO P-390 P-400 P-410
Area fraction (%) Fraction 1
Fraction2
Fraction3
Fraction 4
Fraction 5
Fraction 6
Fraction 7
Fraction 8
19.8 0.5 0.3 0.5
48.8 11.0 12.8 16.6
17.3 29.5 32.7 34.4
6.8 26.2 26.7 24.4
2.8 16.2 14.8 13.1
1.6 8.7 7.0 6.2
1.4 4.9 3.5 3.1
1.3 3.0 2.0 1.8
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
245 246 247 248 249 250 251 252 253 254 255
produced pitches are in range of 356–534 m/z due to conversion of the components by means of polymerization and cracking during the thermal reaction. In fractions 5–8, the area fraction was found to decrease with increasing reaction temperature. This finding indicates that condensate molecules are converted to lower molecular weight fraction species due to the cracking reaction with increasing reaction temperature. Fraction 4 showed a variable tendency, with no correlation with the reaction temperature. Apparently, this fraction is at the border between condensation and the cracking reaction.
256
Conclusion
257 258 259 260 261 262 263 264 265 266 267 268 269 270
Pitch derived from PFO was synthesized by thermal reaction. Increasing the reaction temperature in range of 390–410 8C, the pitch yield was found to decrease, and the amount of volatile matter was found to increase. The minimum pitch yield was 25.4% at 410 8C. The C/H ratio of the produced pitches was also increased by 1.29, indicating the formation of aromatic contents, which corresponded to the XRD result. The thermal properties were determined by softening point and TG analyses. The produced pitches exhibited a complicated pattern on the DTG curve in the range of 350–550 8C. In addition, an exothermic peak was observed in the DTA curve. MALDI-TOF analysis was conducted to identify the MWD change of the produced pitches. Fractions 2 and 3 (178–534 m/z) exhibited increased area fractions, suggesting the polymerization and condensation reaction, whereas, fractions 5–8
5
(712–1424 m/z) showed the decreasing tendency attributed to the cracking reaction. Finally, the empirical pitch synthesis reaction from PFO was carried out to reveal the physical and chemical characteristics of the feedstock and the produced pitch.
271 272 273 274
References
275
[1] I. Mochida, Y. Korea, C.H. Ku, F. Watanabe, Y. Sakai, Carbon 38 (2000) 305. [2] H. Song, X. Chen, X. Chen, S. Xhang, H. Li, Carbon 41 (2003) 3037. [3] I. Mochida, K. Shimizu, Y. Korai, Y. Sakai, S. Fujiyama, H. Toshima, T. Hono, Carbon 30 (1992) 55. [4] J.G. Kim, J.H. Kim, B.J. Song, Y.P. Jeon, C.W. Lee, Y.S. Lee, J.S. Im, Fuel 167 (2016) 25. [5] S. Chand, J. Mater. Sci. 35 (2000) 1303. [6] K. Subhash, S. Manoj, Carbon Lett. 16 (2015) 171. [7] J. Zhu, S.W. Park, H.I. Joh, H.C. Kim, S. Lee, Carbon Lett. 14 (2013) 94. [8] C.J. Ahn, I.S. Park, H.J. Joo, Carbon Lett. 11 (2010) 304. [9] X. Cheng, Q. Zha, X. Li, X. Yang, Fuel Process. Technol. 89 (2008) 1436. [10] R. Moriyama, H. Kumagaia, J. Hayashia, C. Yamaguchi, J. Mondorib, H. Matsui, T. Chiba, Carbon 38 (2000) 749. [11] S. Eser, G. Wang, Energy Fuels 21 (2007) 3573. [12] B.J. Kim, Y. Eom, O. Kato, J. Miyawaki, B.C. Kim, I. Mochida, S.H. Yoon, Carbon 77 (2014) 747. [13] I. Mochida, H. Toshima, Y. Korai, T. Varga, J. Mater. Sci. 25 (1990) 3484. [14] P.P. Li, J.M. Xiong, M.L. Ge, J.C. Sun, W. Zhang, Y.Y. Song, Fuel Process. Technol. 140 (2015) 231. [15] H.Y. Kim, Monthly Energy Statistics, Korea Energy Economics Institute, 2015. [16] W.F. Edwards, L. Jin, M.C. Thies, Carbon 41 (2003) 2761. [17] W.A. Burgess, M.C. Thies, Carbon 49 (2011) 636. [18] B. Manoj, A.G. Kunjomana, Int. J. Electrochem. Sci. 7 (2012) 3127. [19] M. Dumont, G. Chollon, M.A. Dourges, R. Pailler, X. Bourrat, R. Naslain, J.L. Bruneel, M. Couzi, Carbon 40 (2002) 1475. [20] M. Pe´rez, M. Granda, R. Garcı´a, R. Santamarı´a, E. Romero, R. Mene´ndez, J. Anal. Appl. Pyrolysis 63 (2002) 223. [21] L.M. Manocha, M. Patel, S.M. Manocha, C. Vix-Guterl, P. Ehrburger, Carbon 39 (2001) 663.
276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
JIEC 2836 1–5 Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1 2 3 4 5 6 7 8
Synthesis and its characterization of pitch from pyrolyzed fuel oil (PFO) Q1 Jong
Gu Kim a,b, Ji Hong Kim a,d, Byung-Jin Song a, Chul Wee Lee a,c, Ji Sun Im a,c,*
a
Division of Green Chemistry & Engineering Research, Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600, Republic of Korea Department of Applied Chemistry and Biological Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea c University of Science and Technology (UST), Daejeon 305-333, Republic of Korea d Department of Chemical and Biological Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Republic of Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 January 2016 Received in revised form 28 January 2016 Accepted 16 February 2016 Available online xxx
Pitch synthesis from pyrolyzed fuel oil (PFO) was conducted to understand the empirical synthesis tendency as a function of reaction temperature. Additionally, the chemical and physical characteristics of PFO and produced pitch are identified using X-ray diffraction analysis, thermogravimetric analysis, softening point analysis, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis. The produced pitch exhibited an enhanced stacking height (LC) value and C/H ratio, which is related to the formation of graphitic structure, according to the increased reaction temperature. The carbon residue yield obtained at 900 8C showed a gradually increased value of up to 42.58% in the sample synthesized at the temperature of 410 8C, depending on the increased reaction temperature. The molecular weight distribution of the produced pitches exhibited noticeable variation during the thermal reaction via MALDI-TOF analysis. The variation of the molecular weight fraction is assumed based on the pitch synthesis mechanism, e.g., polymerization, condensation and cracking reaction. ß 2016 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: Pyrolyzed fuel oil Pitch Thermal reaction MALDI-TOF TG analysis
9 10
Introduction
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Pitch is a representative precursor for the manufacturing of carbon materials [1]. Petroleum residues are generally used as a feedstock to produce the pitch by thermal and catalytic reaction [2]. The pitch characteristic is an important factor because the properties of carbon materials (carbon fiber, artificial graphite, etc.) are determined by the chemical and physical characteristics of pitch, which are classified as mesophase contents, solubility by solvents (hexane, toluene, quinolone etc.), softening point, chemical compositions, and molecular weight distribution (MWD) [3,4]. For example, carbon fiber for the aerospace industry requires a type of the mesophase (anisotropic) pitch that can improve the Young’s modulus of fiber [5]. Artificial graphite block demands well-refined pitch that has low levels of impurities, such as metal and ash, because of the expansion on carbon layer structure during the graphitization process over 2000 8C.
Q2 * Corresponding author at: Division of Green Chemistry & Engineering Research, Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600,
Q3 Republic of Korea. Tel.: +82 42 860 7366; fax: +82 42 860 7388. E-mail address: [email protected] (J.S. Im).
Petroleum residues can be typically categorized as fluid catalytic cracking decant oil (FCC-DO), pyrolyzed fuel oil (PFO), and vacuum residue (VR), which have different chemical composition, viscosity, and impurities (metal, ash) according to the refining operation condition, such as distillation temperature, refinery unit process and type, inducing the catalyst. Furthermore, those by-products have undefined chemical components consisting of more than thousands polycyclic aromatic hydrocarbon (PAH) species and a broad MWD. As mentioned above, various petroleum residues have been used as a precursor for pitch synthesis [6–8]. However, undefined chemical components of petroleum residues make controlling the pitch properties difficult during the pitch synthesis reaction. It is well known that the pitch synthesis mechanism includes condensation, polymerization, volatilization, aromatization and cracking reaction [1,9,10]. In the case of pitch synthesis from single-chemical components, such as naphthalene and anthracene, the pitch having a narrow MWD can be produced by aromatization and condensation with the introduction of a Bronsted acid type catalyst [3]. Alternatively, the pitch synthesis derived from petroleum residues is accompanied by complicated chemical reactions due to the chemical components of the feedstock. Briefly, light compounds are removed during the thermal cracking and
http://dx.doi.org/10.1016/j.jiec.2016.02.014 1226-086X/ß 2016 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
2
49 volatilization, and heavy compounds are condensed and polymer50 ized during the thermal reaction. 51 Finally, selection of the feedstock for pitch synthesis is an 52 important factor that determines the properties of the pitch and 53 carbon materials. Various researchers have studied pitch synthesis 54 from petroleum residues. Eser and Wang considered the high55 Q4 sulfur FCC-DO as feedstock for needle coke production [11]. Yoon 56 et al. studied the carbon fiber production from the isotropic pitch 57 derived from naphtha cracked oil [12]. Mochida et al. evaluated the 58 spinnability of mesophase pitch derived from FCC-DO based on 59 Q5 structural characterizations [13]. Xiong et al. developed a new 60 route for producing the high-value pitch-based carbon fiber from 61 catalytic slurry oil using various treatment processes [14]. 62 Among the petroleum residues, PFO, which is by-product of the 63 naphtha cracking process, is produced at a high level (with over 64 100 million metric ton per annum produced in the South Korea 65 refinery industry [15]) and is used as plant fuel because of the 66 difficulty of the re-treatment process and the low utilization. 67 Nevertheless, the abundant aromatic contents and low impurities 68 of PFO are an attractive advantages to utilize as a feedstock for 69 producing the pitch. 70 In this study, pitch derived from PFO was synthesized by 71 thermal reaction as a function of reaction temperature in the range 72 of 390–410 8C. The empirical reaction tendency of the pitch 73 derived from PFO was determined with chemical and physical 74 characterization. The produced pitches and feedstock were 75 analyzed to understand the MWD variation using matrix-assisted 76 laser desorption/ionization-time of flight analysis (MALDI-TOF) 77 analysis. In addition, a chemical reaction was suggested that 78 describes the changes of each molecular weight fraction during the 79 thermal reaction. Softening point and thermogravimetric (TG) 80 analyses supported the physical characteristics of pitch related to 81 the thermal properties. 82
Experimental
83
Materials
84 85 86 87 88
PFO (Yeochun NCC CO. LTD., produced by NCC (Naphtha Cracking Center, South Korea)) was used as a feedstock for synthesis of the petroleum based pitch. 7,7,8,8-tetracyanoquinodimethane (TCNQ, 98%, CAS Number 1518-16-7, Sigma-Aldrich) was used as matrix for the MALDI-TOF analysis.
89
Procedure of PFO based pitch
90 91 92 93 94 95 96 97 98 99
The pitch synthesis reaction was conducted using a 1L scale batch type autoclave reactor. The reaction temperature was carefully controlled because the pitch properties could be affected by a drifting temperature. The experimental error range of the controlled temperature was within 2 8C using a PID controller system. The reaction procedure was as follows: (1) 500 g of PFO was placed in the 1L vessel of the reactor; (2) 200 cc/min of N2 gas was injected into the vessel to produce an inert gas state atmosphere for 30 min; (3) after the N2 purging step, the furnace was heated according to the programmed temperature step using a Yokogawa
control system (UT35A, UT32A). The details on the reaction conditions and sample names are presented in Table 1.
100 101
Analysis of the pitch and the feedstock
102
The elemental analysis was conducted to confirm the C, H, N, and S contents and the C/H ratio of the feedstock and the produced pitches using a Thermo Scientific FLASH EA-2000 Organic Elemental Analyzer. The X-ray diffraction (XRD) analysis was performed to determine the crystallinity of the pitch using a Rigaku Ultima IV diffractometer with a Cu-Ka radiation. The softening point of the produced pitches was measured using a softening point analyzer (DP-70, Mettler Toledo) according to ASTM D3416. The heating rate was 4 8C/min in an N2 atmosphere. TG analysis was conducted at a heating rate of 10 8C/min, and at temperatures of up to 900 8C in an N2 atmosphere. The sample for MALDI-TOF analysis was prepared in accordance with the Mark method [16,17]. Briefly, the pitch was finely ground in a grinding mill and then mixed with TCNQ. The mixture was then transferred to the MALDI target-plate cell using the waterspotting method. To remove all water, the entire sample was allowed to dry over a 12-h period. The MALDI-TOF analysis was conducted over a range of 0–1500 m/z using a Bruker Daltonics Autoflex MALDI-TOF mass spectrometer.
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123
Results and discussion
124
Temperature effects of the thermal reaction of PFO
125
The experimental condition of thermal synthesis reaction was considered to understand the empirical pitch synthesis tendency from real feedstock (PFO) because each of the petroleum residues showed a different tendency due to the origin and chemical composition of each residue [11–14]. The pitch yield and volatile matter were measured as listed in Table 1. The pitch yield was found to gradually decrease with increasing reaction temperature. The minimum pitch yield was 25.4%, which was observed for the P-410 sample. The amount of volatile matter was inversely dependent on the reaction temperature. Both pitch yield and volatile matter were found to be correlated with reaction temperature. In addition, PFO was found to have a high volatile content under the boiling point of 400 8C, despite the fact that PFO is a by-product of naphtha catalytic cracking process in the temperature range of 400–500 8C. Thus, a catalyst for polymerization of light components may be needed to increase the pitch yield. Elemental analysis was conducted to identify the C, H, N, and S contents and the C/H ratio, which are listed in Table 2. The carbon contents were found to slightly increase with decreasing hydrogen content, depending on the reaction temperature. The C/H ratio was also increased by 1.29 in the P-410 sample. Increasing the C/H ratio indicates that aromatic contents are being formed at increased reaction temperature.
126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
Table 1 Experimental conditions of the thermal reaction. Sample name
P-390 P-400 P-410
Reaction condition Temp. (8C)
Time (h)
Pressure (bar)
N2 flow (cc/min)
Pitch yield (%)
Volatile matter (%)
Loss (%)
390 400 410
1 1 1
1 1 1
100 100 100
28.9 26.5 25.4
67.5 68.3 69.2
3.6 5.2 5.4
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx Table 2 Bulk properties of the pitch prepared by the thermal reaction. Sample name
PFO P-390 P-400 P-410
Softening point (8C)
– 104.30 123.00 132.20
TGA yield (%, at 900 8C)
13.71 34.85 38.47 42.58
Elemental analysis (%) C
H
N
S
C/H
91.60 92.30 92.60 92.70
7.90 6.40 6.10 6.00
N.D N.D N.D N.D
0.10 0.83 0.79 0.78
0.97 1.20 1.27 1.29
150
Crystallinity of the pitch
151 152 153
XRD analysis was conducted to confirm the crystallinity of the prepared pitch. The stacking height (LC) of the samples was calculated by following equation [18].
154 LC ¼ 0:89l=BC cos ’C 157 156 155 158 159 160 161 162 163 164 165 166 167 168 169 170
3
showed an increased trend, with values of 8.9 (P-390), 15.2 (P-400) and 21.2 (P-410). This result indicates that increased reaction temperature affects the growth of the graphitic structure in the pitch synthesis. Furthermore, these trends from the XRD analysis correspond to the C/H ratios related to the aromatic contents.
171 172 173 174 175
Thermal properties of the pitch
176
The thermal properties of produced pitches were analyzed using TG and softening point analyses. The TG curve showed a similar pattern in the all of the samples, as shown in Fig. 2(a). The final carbon residue yield of the produced pitches was calculated from the TG curve at 900 8C. These yields were increased according to the increasing reaction temperature; the P-410 sample presented the maximum value of 42.58%, which was threefold the value of PFO (13.71%). The weight loss of all samples was ceased at approximately 600 8C. The flat pattern of the TG curve over 600 8C corresponds to coke formation [19]. As shown in Fig. 2(b), the DTG curve of PFO showed the two peaks of the
177 178 179 180 181 182 183 184 185 186 187
Where l is the wavelength of the X-rays, BC is the full width at half maximum of the (002) peak, and wC is the corresponding scattering angle. As shown in Fig. 1, the pitches exhibited an amorphous peak at approximately 58–308; 2-theta peaks of (002) were measured at 24.268, 24.628, and 25.238 in the samples of P-390, P-400, and P410, respectively. Although all of the peaks of (002) did not reach a graphitic carbon peak at 26.58, these peaks of (002) were gradually shifted to a higher 2-theta region, depending on the reaction temperature, indicating the formation of a graphitic carbon structure. In addition, the values of the full width at half maximum of (002) were also measured as 9.00, 5.29, and 3.8 in the samples of P-390, P-400, and P-410, respectively. These values were found to decrease with increasing reaction temperature. The calculated LC
Fig. 1. Crystalline analysis by XRD of the prepared pitch.
Fig. 2. TG analysis of the prepared pitch and PFO. (a) TG curve, (b) DTG, and (C) DTA.
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
4
Fig. 4. Diagram of the molecular weight fraction divided by the pseudo-component.
Fig. 3. MALDI-TOF spectrum of the prepared pitch and PFO.
188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205
maximum rate of weight loss at approximately 150 8C and 370 8C, whereas the produced pitches showed only one peak at approximately 350–550 8C; this result highlighted the complicated patterns that indicate the chemically complexity of the pitch derived from PFO. A similar result was reported by Pe´rez et al. [20]. They found that the range of 350–550 8C corresponds to the weight loss associated with cracking/polymerization reactions. The DTA curve confirmed the endothermic characteristic in the same temperature range (350–550 8C), as shown in Fig. 2(c). The endothermic peak is well known as a representative peak of volatilization and the cracking reaction [21]. Because the pitch is complicated mixture derived from petroleum residue, the softening point is generally used as an indicator instead of the melting point. The softening point of produced pitches was also increased, depending on the increased reaction temperature, as listed in Table 2. The increased softening point is the result of the polymerization or condensation of each of the components that occurred during the thermal reaction.
206
Molecular weight distribution analysis of the samples
207 208 209
MWD variation of the prepared pitches during the thermal reaction was identified using the MALDI-TOF analysis, as shown in Fig. 3. It was confirmed that noticeable variation of MWD occurred
from the PFO to pitch by thermal reaction. PFO had a MWD in the range up to 600 m/z. After thermal reaction in the temperature range of 390–410 8C, the MWD of the pitch samples was expanded by approximately 1400 m/z. Considering the pitch synthesis reaction, the condensation and polymerization reaction was predominantly affected by the thermal reaction. As shown in Fig. 3, the three samples of pitch displayed similar patterns of MWDs in the MALDI-TOF spectra. However, each molecular fraction area separated by pseudo components showed a different tendency related to the pitch synthesis mechanism. To divide the area fraction, anthracene was selected as a pseudocomponent because a standard material is required to separate the molecular weight area. The area fraction was divided as follows: fraction 1 (1–178 m/z), fraction 2 (178–356 m/z), fraction 3 (356–534 m/z), fraction 4 (534–712 m/z), fraction 5 (712–890 m/z), fraction 6 (890–1068 m/z), fraction 7 (1068–1246 m/z), and fraction 8 (1246–1424 m/z) (Table 3). Q6 The pitch synthesis reaction was considered with the MWD variation relative to the area fractions, as shown in Fig. 4. Comparing PFO and the produced pitches, fractions 1 and 2 showed significant MWD variations. The area fraction of PFO in fraction 1 was 19.8%; however, the values of the prepared pitches decreased to less than 1%. This result indicates that low boiling point compounds were emitted due to volatilization during the thermal reaction or converted to the high molecular weight area fraction by means of the condensation and polymerization reaction. Comparing the produced pitches, a specific MWD variation was investigated. In fractions 2 and 3, the area fraction of the produced pitches was found to increase with increasing reaction temperature. However, fractions 5–8 showed an opposite trend compared with fractions 2 and 3. In fractions 2 and 3, each area fraction was increased by a maximum of 16.6% and 34.4% in the P-410 sample, respectively. The value of fraction 3 occupied the largest area fraction. This result indicated that the main compounds in the
Table 3 Integrated area fraction of the MALDI-TOF spectrum separated by the pseudo-component. Sample name
PFO P-390 P-400 P-410
Area fraction (%) Fraction 1
Fraction2
Fraction3
Fraction 4
Fraction 5
Fraction 6
Fraction 7
Fraction 8
19.8 0.5 0.3 0.5
48.8 11.0 12.8 16.6
17.3 29.5 32.7 34.4
6.8 26.2 26.7 24.4
2.8 16.2 14.8 13.1
1.6 8.7 7.0 6.2
1.4 4.9 3.5 3.1
1.3 3.0 2.0 1.8
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244
G Model
JIEC 2836 1–5 J.G. Kim et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx
245 246 247 248 249 250 251 252 253 254 255
produced pitches are in range of 356–534 m/z due to conversion of the components by means of polymerization and cracking during the thermal reaction. In fractions 5–8, the area fraction was found to decrease with increasing reaction temperature. This finding indicates that condensate molecules are converted to lower molecular weight fraction species due to the cracking reaction with increasing reaction temperature. Fraction 4 showed a variable tendency, with no correlation with the reaction temperature. Apparently, this fraction is at the border between condensation and the cracking reaction.
256
Conclusion
257 258 259 260 261 262 263 264 265 266 267 268 269 270
Pitch derived from PFO was synthesized by thermal reaction. Increasing the reaction temperature in range of 390–410 8C, the pitch yield was found to decrease, and the amount of volatile matter was found to increase. The minimum pitch yield was 25.4% at 410 8C. The C/H ratio of the produced pitches was also increased by 1.29, indicating the formation of aromatic contents, which corresponded to the XRD result. The thermal properties were determined by softening point and TG analyses. The produced pitches exhibited a complicated pattern on the DTG curve in the range of 350–550 8C. In addition, an exothermic peak was observed in the DTA curve. MALDI-TOF analysis was conducted to identify the MWD change of the produced pitches. Fractions 2 and 3 (178–534 m/z) exhibited increased area fractions, suggesting the polymerization and condensation reaction, whereas, fractions 5–8
5
(712–1424 m/z) showed the decreasing tendency attributed to the cracking reaction. Finally, the empirical pitch synthesis reaction from PFO was carried out to reveal the physical and chemical characteristics of the feedstock and the produced pitch.
271 272 273 274
References
275
[1] I. Mochida, Y. Korea, C.H. Ku, F. Watanabe, Y. Sakai, Carbon 38 (2000) 305. [2] H. Song, X. Chen, X. Chen, S. Xhang, H. Li, Carbon 41 (2003) 3037. [3] I. Mochida, K. Shimizu, Y. Korai, Y. Sakai, S. Fujiyama, H. Toshima, T. Hono, Carbon 30 (1992) 55. [4] J.G. Kim, J.H. Kim, B.J. Song, Y.P. Jeon, C.W. Lee, Y.S. Lee, J.S. Im, Fuel 167 (2016) 25. [5] S. Chand, J. Mater. Sci. 35 (2000) 1303. [6] K. Subhash, S. Manoj, Carbon Lett. 16 (2015) 171. [7] J. Zhu, S.W. Park, H.I. Joh, H.C. Kim, S. Lee, Carbon Lett. 14 (2013) 94. [8] C.J. Ahn, I.S. Park, H.J. Joo, Carbon Lett. 11 (2010) 304. [9] X. Cheng, Q. Zha, X. Li, X. Yang, Fuel Process. Technol. 89 (2008) 1436. [10] R. Moriyama, H. Kumagaia, J. Hayashia, C. Yamaguchi, J. Mondorib, H. Matsui, T. Chiba, Carbon 38 (2000) 749. [11] S. Eser, G. Wang, Energy Fuels 21 (2007) 3573. [12] B.J. Kim, Y. Eom, O. Kato, J. Miyawaki, B.C. Kim, I. Mochida, S.H. Yoon, Carbon 77 (2014) 747. [13] I. Mochida, H. Toshima, Y. Korai, T. Varga, J. Mater. Sci. 25 (1990) 3484. [14] P.P. Li, J.M. Xiong, M.L. Ge, J.C. Sun, W. Zhang, Y.Y. Song, Fuel Process. Technol. 140 (2015) 231. [15] H.Y. Kim, Monthly Energy Statistics, Korea Energy Economics Institute, 2015. [16] W.F. Edwards, L. Jin, M.C. Thies, Carbon 41 (2003) 2761. [17] W.A. Burgess, M.C. Thies, Carbon 49 (2011) 636. [18] B. Manoj, A.G. Kunjomana, Int. J. Electrochem. Sci. 7 (2012) 3127. [19] M. Dumont, G. Chollon, M.A. Dourges, R. Pailler, X. Bourrat, R. Naslain, J.L. Bruneel, M. Couzi, Carbon 40 (2002) 1475. [20] M. Pe´rez, M. Granda, R. Garcı´a, R. Santamarı´a, E. Romero, R. Mene´ndez, J. Anal. Appl. Pyrolysis 63 (2002) 223. [21] L.M. Manocha, M. Patel, S.M. Manocha, C. Vix-Guterl, P. Ehrburger, Carbon 39 (2001) 663.
276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303
Please cite this article in press as: J.G. Kim, et al., J. Ind. Eng. Chem. (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.014