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Catalytic copyrolysis of cork oak and bio-oil distillation residue
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Catalytic copyrolysis of cork oak and bio-oil distillation residue Yejin Lee a , Daejun Oh a , Young-Min Kim a,b , Jungho Jae c,d , Sang-Chul Jung e , Jong-Ki Jeon f , Sang Chai Kim g , Young-Kwon Park a,∗ a
School of Environmental Engineering, University of Seoul, Seoul 02504, Republic of Korea Frontier Laboratories Ltd., Fukushima 963-8862, Japan Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea d Department of Clean Energy and Chemical Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea e Department of Environmental Engineering, Sunchon National University, Suncheon 57922, Republic of Korea f Department of Chemical Engineering, Kongju National University, Cheonan 31080, Republic of Korea g Department of Environmental Education, Mokpo National University, Muan 58554, Republic of Korea b c
a r t i c l e
i n f o
Article history: Received 31 March 2017 Received in revised form 4 June 2017 Accepted 13 June 2017 Available online xxx Keywords: Catalytic copyrolysis Cork oak Distillation residue HZSM-5 Aromatic hydrocarbons
a b s t r a c t The atmospheric distillation residue (ADR) of cork oak (CO) pyrolysis oil was used as the co-feeding material for the catalytic pyrolysis of CO over HZSM-5 catalysts to improve the formation of aromatic hydrocarbons. Although the non-catalytic copyrolysis of CO and ADR did not improve the formation of aromatic hydrocarbons, the catalytic copyrolysis of CO and ADR promoted the synergistic formation of aromatic hydrocarbons. HZSM-5(30), having a lower SiO2 /Al2 O3 (30), showed better performance for the formation of aromatic hydrocarbons than HZSM-5(80) because of its higher acidity. The catalytic copyrolysis of CO and ADR also decreased the formation of coke. The largest quantity of aromatic hydrocarbons was obtained from the catalytic copyrolysis of CO and ADR over HZSM-5 (30) at 600 ◦ C, whereas the lowest coke yield was achieved at 700 ◦ C. When the catalyst to sample ratio was increased from 2:1 to 5:1, the synergistic formation of aromatic hydrocarbons was limited, resulting in a lower experimental yield of aromatic hydrocarbons than the theoretical yield. A lower coke yield was also achieved at a high catalyst to sample ratio (5:1). © 2017 Elsevier B.V. All rights reserved.
1. Introduction Zeolites have attracted considerable interest as versatile catalysts for biomass conversion [1,2]. In particular, zeolites are effective in the selective deoxygenation of biomass pyrolysis vapors, resulting in the formation of aromatics and effectively increasing the C/O ratio. Zeolites, particularly those with high acidity and low Si/Al ratios, promote the cracking reaction in the initial pyrolysis reactions [3–7]. Among the various types of zeolites, HZSM-5 has been used in many studies because it can produce many useful materials, such as aromatics and aliphatic unsaturated hydrocarbons (olefins) during the catalytic pyrolysis of biomass. On the other hand, even with its high activity, the catalytic cracking of woody biomass over HZSM-5 still has low carbon efficiency and produces huge amounts of undesirable char and coke. The low yield of aromatic hydrocarbons and the large amount of coke formation is related to the inherent hydrogen-deficient and oxygen-rich
∗ Corresponding author. E-mail address: [email protected] (Y.-K. Park).
nature of biomass feedstock. The effective hydrogen to carbon ratio (H/Ceff ) of biomass was reported to be a good parameter for predicting the conversion efficiency of biomass to bio-fuels via pyrolysis or catalytic pyrolysis [8–13]. A biomass sample with a high H/Ceff can produce large amounts of aromatic hydrocarbons with a low coke yield. On the other hand, a sample with a low H/Ceff produces a large amount of coke during catalytic pyrolysis, resulting in fast catalyst deactivation and reduced catalyst lifetime [14]. The catalytic co-pyrolysis of biomass and the feedstock with a high hydrogen content was suggested to be one option for overcoming the low conversion efficiency in the catalytic pyrolysis of biomass [15]. To date, many plastics have been used as co-feeding materials for the catalytic pyrolysis of biomass because they have a high H/Ceff [16–19]. Although other materials also have a high H/Ceff , there have been few studies using other materials. One of the possible hydrogen-rich co-feeding materials for the catalytic copyrolysis of biomass is the distillation residue of biomass pyrolysis oils because the distillation of bio-oil can be used as a proper method to separate valuable fuel oils and chemical feedstock from bio-oil, leaving residue after the distillation process. The use of residue as a cofeeding material for the catalytic biomass was reported to be more
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economical than plastics. In addition, no substance is discarded in the entire distillation process [20–22]. In this study, the catalytic co-pyrolysis of cork oak (CO) and atmospheric distillation residue (ADR) of CO pyrolysis oils were investigated to determine the feasibility of ADR as a co-feeding material. HZSM-5 catalysts with different Si/Al ratios were used as the catalysts to examine the effects of the catalyst acidity on the catalytic copyrolysis of CO and ADR. The effects of the reaction temperature were also investigated to determine the optimal temperature for the formation of aromatic hydrocarbons.
Table 1 Physicochemical properties of CO and ADR.
C H N Ob Moisture Volatile matters Fixed carbon Ash
Ultimate analysis (wt.%)
Proximate analysis (wt.%)
a b
COa
ADRa
46.27 5.94 0.37 47.42 2.50 81.05 15.10 1.35
73.48 4.88 0.62 21.01 2.46 40.18 57.26 0.11
Dry base. By difference.
2. Experimental 2.1. Samples CO, which was supplied by the National Institute of Korea Forest Science, was cryo-milled, sieved to make a particle size smaller than 500 m, and dried at 100 ◦ C for 3 h. CO pyrolysis oil, which was obtained from the pyrolysis of CO at 500 ◦ C, was distilled by atmospheric distillation. A 10 g sample of bio-oil in a round bottom flask was heated from ambient temperature to 350 ◦ C at a heating rate of 10 ◦ C/min and maintained at the final temperature for 15 min. The steam generated during the distillation of CO pyrolysis oil was collected in the cooling condenser at −30 ◦ C and analyzed by gas chromatography/mass spectrometry (GC/MS, 7890A/5975C inert, Agilent Technology). The ADR remaining in the flask after distillation was dried in an oven at 150 ◦ C for 12 h to remove all the moisture and sieved to less than 500 m for pyrolysis. Ultimate and proximate analyses of CO and DR were carried out to determine their physicochemical properties. Thermogravimetric analysis (TG, Pyris 1, Perkin Elmer) was also performed by heating a 6.0 mg sample of CO, ADR, and their mixture (CO-ADR) from ambient temperature to 900 ◦ C at a heating rate of 30 ◦ C/min under 50 mL/min of nitrogen gas to determine their non-isothermal pyrolysis behavior.
Table 2 Physicochemical properties of HZSM-5 catalysts. Catalyst
SiO2 /Al2 O3
BET surface area (m2 /g)
HZSM-5(30) HZSM-5(80)
30 80
400 425
2.2. Catalyst Commercial HZSM-5 catalysts (SiO2 /Al2 O3 = 30 and 80), which were purchased from Zeolyst International, were calcined at 550 ◦ C for 3 h. NH3 TPD was performed to compare the acidic properties of the two types of HZSM-5. The detailed methods can be found elsewhere [23].
2.3. Ex-situ catalytic pyrolysis The catalytic co-pyrolysis of CO and ADR and product analysis were performed simultaneously using a pyrolyzer (Py, EGA-Py3030D, Frontier Laboratories)-GC/MS. For this, CO-ADR (1 mg) with a CO to ADR mixing ratio of 4: 1 was loaded first onto the bottom of a deactivated SUS sample cup. Glass wool and 2 mg of catalyst were placed on top of the CO-ADR in turn to make the ex-situ catalytic pyrolysis. The sample cup was free fallen into a preheated pyrolyzer heater (500 ◦ C) and the emission vapor was transferred to a GC separation column (UA-5, 30 m length × 0.25 mm inner diameter x 0.25 m film thickness) and cryo-focused at the front part of the column by liquid nitrogen (–195 ◦ C) supplied from a MicroJet Cyro-Trap (MJT-1035E, Frontier Laboratories) for 3 min. After 3 min cryo focusing time, the product chemicals were separated using a GC oven temperature program, from 40 ◦ C to 320 ◦ C at a heating rate of 10 ◦ C/min, and detected by a MS. The total and column flow of helium were set to 100 and 1 mL/min, respectively. The MS peaks on the total ion chromatogram were identified by the NIST 05th library and F-Search library (Frontier Laboratories)
Fig. 1. NH3 TPD of HZSM-5 catalysts. Table 3 Chemical composition of pyrolysis oil and distilled pyrolysis oil (Unit: area%). Compound
Pyrolysis oil
Distilled pyrolysis oil
Acetic acid Phenolics Esters Aldehydes Ketones Furans Alcohols Cyclic compounds Levoglucosans Other oxygenates
32.57 28.32 5.16 1.14 10.29 6.92 6.94 2.54 4.19 1.93
54.57 8.16 5.31 1.04 21.44 7.19 0.00 0.90 0.00 1.91
3. Results and discussion 3.1. Physicochemical properties of samples and catalysts Table 1 lists the ultimate and proximate analysis results of CO and ADR used in this study. More than 90% of CO consisted of carbon (46.27%) and oxygen (47.72%). ADR contained 73.48% carbon and 21.01% oxygen. The calculated H/Ceff of ADR (0.35) was higher than that of CO, which suggests that a smaller amount of coke from catalytic pyrolysis can be produced using ADR as a co-feeding material of CO. Compared to CO, ADR had a smaller amount of volatile matter (40.18%) and larger amount of fixed carbon (57.26%) than those of
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Fig. 2. TG and DTG curves of CO, ADR, and the mixture of CO and ADR.
CO because most of the volatile matter in bio-oil had already been extracted during its distillation. Table 2 lists the physicochemical properties of the HZSM-5 catalysts. HZSM-5 is the best catalyst having high selectivity toward aromatic hydrocarbon during biomass catalytic pyrolysis because of its strong acidity and proper pore size [23]. The HZSM-5 catalyst with a lower SiO2 /Al2 O3 ratio had higher concentrations of both weak and strong acid sites, demonstrating its stronger acidity, as shown in Fig. 1. Therefore, its strong acidity makes it highly active for various catalytic reactions, such as cracking, deoxygenation, decarboxylation, cyclization, aromatization, isomerization, alkylation, oligomerization, and polymerization [7]. 3.2. Distillation of cork oak pyrolysis oil After the atmospheric distillation of cork oak pyrolysis oil at 350 ◦ C, 37 wt.% of cork oak (63 wt.% of pyrolysis oil) was obtained
as ADR. Although similar types of organic compounds with pyrolysis oil have been obtained from the oil distilled from pyrolysis oil, their relative composition ratios were different (Table 3). Cork oak pyrolysis oil contained acetic acid (32.57%), phenolics (28.32%), and other oxygen-containing chemicals (39.11%). On the other hand, the relative contents of acetic acid (54.57%) and phenolics (8.16%) of distilled oil were different, indicating that pyrolysis oil likely undergoes secondary reactions during distillation. Zhang et al. shows a range of decomposition pathways of woody biomass components that can occur during the pyrolysis and/or distillation process [20]. Light oxygen-containing compounds, such as acetic acid, are formed not only by the decomposition of hemicellulose and cellulose, but also by the depolymerization of lignin. Furfural is also generated by the decomposition of hemicellulose, cellulose, and lignin. Levoglucosan, a primary decomposition product of cellulose, can produce furans and ketones via the dehydration and other secondary reactions [24]. Therefore, high contents of ketones and the
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Table 4 Chemical compositions of the pyrolysis product obtained from the Py-GC/MS analysis of CO, ADR, and their mixture. (Unit: area%).
CO2 Acids Oxygenates BTEXs PAHs Phenolics Hydrocarbons
CO
ADR
Mixture of CO and ADR
7.01 17.61 49.72 0.00 0.00 25.49 0.17
37.22 1.51 16.30 3.97 6.76 33.55 0.68
13.51 16.56 38.60 0.32 0.57 30.16 0.28
lack of levoglucosan in distilled oil can be the result of the additional cleavage of levoglucosan [20]. 3.3. TGA
Fig. 3. Chemical compositions of the pyrolysis product obtained from the catalytic Py-GC/MS analysis of CO and ADR over HZMS-5 catalysts. (Unit: area%).
Fig. 2 presents the TG and DTG curves of CO and ADR. CO decomposed mainly at temperatures between 300 and 400 ◦ C. In contrast, ADR underwent decomposition over a wide temperature range from 200 to 900 ◦ C. On the other hand, the amount of solid residue obtained after the TGA of ADR was much larger than that of CO. The mixture of CO and ADR showed a similar TG curve with CO, even though it has a larger amount of solid residue than that of CO due to the contribution from ADR. The first DTG peaks at below 150 ◦ C can be assigned to the vaporization of water. The second and third DTG peaks of CO and a mixture of CO and ADR at 200–400 ◦ C correspond to the typical DTG peaks of woody biomass, which are related to the decompositions of hemicellulose, cellulose, and lignin [25]. The DTG curve of ADR had only two peaks at approximately 200 and 500 ◦ C, respectively. 3.4. Non-catalytic co-pyrolysis of CO and ADR Table 4 lists the Py-GC/MS results obtained from the thermal decomposition of CO, ADR, and the mixture of CO and ADR. Both CO and ADR produced light gas, acids, oxygenates, phenolics, and hydrocarbons via pyrolysis reactions. CO pyrolysis oil consisted of oxygenates (49.72%), phenolics (25.49%), and acids (17.61%). In addition, the pyrolysis of ADR produced a large amount of carbon dioxide (37.22%) together with phenolics (33.55%) and oxygenates (16.30%) as the major liquid products. BTEXs (3.97%) and poly aromatic hydrocarbons (PAHs, 6.76%) were also produced from the pyrolysis of ADR. The relative amounts of aromatic hydrocarbons (BTEXs and PAHs) obtained from the non-catalytic co-pyrolysis of CO and ADR were similar to the calculated values. This suggests that there is no synergistic effect on the formation of aromatic hydrocarbons. Therefore, the use of a catalyst is required to increase the yields of aromatic hydrocarbons together with the decrease in oxygen containing compounds. 3.5. Catalytic co-pyrolysis of CO and ADR Fig. 3 presents the Py-GC/MS results obtained from the thermal and catalytic co-pyrolysis of CO and ADR at 500 ◦ C. The contents of mono aromatic hydrocarbons (MAHs) and PAHs increased with decreasing concentration of acids, phenolics, and other oxygenates. Between the two HZSM-5 catalysts, HZSM-5(30), having higher acidity, produced larger amounts of MAHs (39%) and PAHs (20%) than those of MAHs (38%) and PAHs (12%) over HZSM-5(80), as shown in Fig. 3. The synergistic formation of aromatic hydrocarbons via the catalytic co-pyrolysis of CO and ADR over both HZSM-5(30) and HZSM-5(80) was also evaluated in comparison with the theoretical yield, as shown in Fig. 4. The theoretical yields of aromatic hydrocarbons were calculated using the yields obtained from the
Fig. 4. Theoretical and experimental aromatic formations obtained from the catalytic Py-GC/MS analysis of CO and ADR over both HZSM-5 catalysts. (Unit: wt.%).
experimental aromatic yields of the individual CO and ADR at their mixing ratio (4:1). The experimental yield of aromatic hydrocarbons (4.39 wt.%) obtained from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) was higher than its theoretical yield (3.66 wt.%). The catalytic co-pyrolysis of CO and ADR over HZSM5(80) also produced a larger amount of aromatic hydrocarbons (3.58 wt.%) than its theoretical value (2.85 wt.%). This shows that the catalytic co-pyrolysis of CO and ADR over both HZSM-5 catalysts have a synergistic effect on the formation of aromatic hydrocarbons. Fig. 5 presents the chemical compositions of bio-oils obtained from the catalytic co-pyrolysis of CO and ADR at different reaction temperatures (500, 600, and 700 ◦ C) over HZSM-5(30). The catalytic pyrolysis of CO over HZSM-5(30) produced gas, acids, oxygenates, phenolics, MAHs, PAHs, and hydrocarbons, whereas that of ADR over HZSM-5(30) generated large amounts of gas, MAHs, and PAHs along with small amounts of acids, oxygenates, phenolics, and hydrocarbons. The catalytic co-pyrolysis of CO and ADR also produced large amounts of gas, MAHs, and PAHs together with small amounts of acids, oxygenates, phenolics, and hydrocarbons. The MS peak area% of gas, MAHs, and hydrocarbons obtained from the catalytic pyrolysis of the individual CO and ADR, and the co-pyrolysis of CO and ADR over HZSM-5(30) increased with increasing reaction temperature. At a high reaction temperature of 700 ◦ C, the MS peak area% of gas, MAHs, and hydrocarbons were increased to 16%, 40%, and 4%, respectively, when the mixture of CO and ADR was pyrolyzed over HZSM-5(30), as shown in Fig. 5. This result is in accordance with the results reported elsewhere [19] in that a high reaction temperature accelerates the formation of hydrocarbons because the diffusion of pyrolysis vapors into the pore of
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Fig. 5. Chemical compositions of bio-oils obtained from the catalytic pyrolysis of CO, ADR, and their mixture over HZSM-5(30) at 500, 600, and 700 ◦ C.
Fig. 6. Theoretical and experimental yields of aromatic hydrocarbons and coke produced from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at different temperatures.
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Fig. 7. Theoretical and experimental yields of aromatic hydrocarbons and coke produced from the catalytic co-pyrolysis of CO and ADR over 5 mg of HZSM-5(30) at 600 ◦ C. (catalyst: sample = 5: 1).
the zeolites can be enhanced. In addition, the relative content of phenolics decreased significantly from 12% to 7% with increasing reaction temperature from 500 to 700 ◦ C. More phenolics may be converted to aromatic hydrocarbons at high temperatures without coke formation. Therefore, the effect of the reaction temperature on coke formation needs to be investigated in future work because it is related directly to the lifetime of the catalyst. Fig. 6 presents the theoretical and experimental yields of aromatic hydrocarbons and coke obtained from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at different temperatures. The experimental yields of aromatic hydrocarbons produced from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at all temperatures were much higher than their theoretical yields. Among them, the largest amounts of aromatic hydrocarbons (5 wt.%) were obtained from the catalytic co-pyrolysis of CO and ADR at 600 ◦ C. The amount of coke formed decreased with increasing reaction temperature from 500 to 700 ◦ C. At all reaction temperatures, the experimental coke yields were lower than the theoretical coke yields, which indicates that catalytic co-pyrolysis also suppress the formation of coke. A decrease in coke yield during the catalytic co-pyrolysis of CO and ADR can be explained by hydrogen transfer from the pyrolyzates of ADR with the high H/Ceff value to the pyrolyzates of CO. Biomass pyrolyzates, which consist mainly of hydrogen-deficient and highly oxygenated molecules, have been reported to be converted easily to coke via condensation and oligomerization reactions [26]. On the other hand, coke formation can be alleviated if hydrogen is supplied from the hydrogen-rich pyrolyzates of the co-feeding materials, such as plastics [14]. In these experiments, the pyrolyzates of ADR may act as a hydrogen donor, reducing the formation of coke from biomass pyrolyzates together with synergistic aromatic formation. Fig. 7 presents the theoretical and experimental yields of aromatic hydrocarbons and coke obtained from the catalytic co-pyrolysis of CO and ADR over larger amounts of HZSM-5(30) catalyst (i.e., catalyst to sample ratio of 5 to 1) at 600 ◦ C. Although the experimental coke yield was smaller than the theoretical yield by increasing the catalyst to sample ratio to 5 to 1, the experimental yield of aromatic hydrocarbons was smaller than the theoretical value, indicating that the synergistic formation of aromatic hydrocarbons is limited at high catalyst to sample ratios.
4. Conclusions The catalytic copyrolysis of CO and ADR over HZSM-5 catalysts produced a higher yield of aromatic hydrocarbons than the theoretical values. This shows that ADR is a promising co-feeding material for the catalytic pyrolysis of biomass for enhancing the production of valuable aromatic hydrocarbons on account of its high H/Ceff . A comparison of HZSM-5(30) and HZSM-5(80) catalysts revealed HZSM-5(30) to produce larger amounts of aromatic hydrocarbon owing to its higher acidity. The optimal temperature for the formation of aromatic hydrocarbons was found to be 600 ◦ C, but the lowest coke yield was obtained at 700 ◦ C. The synergistic formation of aromatic hydrocarbons was alleviated at a high catalyst to sample ratio (i.e., 5:1), indicating that the positive effect of the cofeeding of ADR can be maximized when a small amount of catalyst is applied to the catalytic copyrolysis of CO and ADR. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1A2A2A11001193). References [1] H. Lee, Y.M. Kim, I.G. Lee, J.K. Jeon, S.C. Jung, J.D. Chung, W.G. Choi, Y.K. Park, Korean J. Chem. Eng. 33 (2016) 3299. [2] X. Zhao, L. Wei, J. Julson, Z. Gu, Y. Cao, Korean J. Chem. Eng. 32 (2015) 1528. [3] A.A. Lappas, M.C. Samolada, D.K. Iatridis, S.S. Voutetakis, I.A. Vasalos, Fuel 81 (2002) 2087. [4] H.J. Park, J.I. Dong, J.K. Jeon, K.-S. Yoo, J.H. Yim, J.M. Sohn, Y.K. Park, J. Ind. Eng. Chem. 13 (2007) 182. [5] A. Aho, N. Kumar, K. Eränen, T. Salmi, M. Hupa, D.Yu. Murzin, Fuel 87 (2008) 2493. [6] R. French, S. Czernik, Fuel Process. Technol. 91 (2010) 25. [7] D.J. Mihalcik, C.A. Mullen, A.A. Boateng, J. Anal. Appl. Pyrolysis 92 (2011) 224. [8] S. Yi, X. He, H. Lin, H. Zheng, C. Li, C. Li, Korean J. Chem. Eng. 33 (2016) 2923. [9] Y. Long, H. Zhou, A. Meng, Q. Li, Y. Zhang, Korean J. Chem. Eng. 33 (2016) 2638. [10] R. Soysa, Y.S. Choi, S.K. Choi, S.J. Kim, S.Y. Han, Korean J. Chem. Eng. 33 (2016) 603. [11] Y.-T. Cheng, G.W. Huber, Green Chem. 14 (2012) 3114. [12] C. Dorado, C.A. Mullen, A.A. Boateng, Appl. Catal. B-Environ. 162 (2015) 338. [13] H. Zhang, R. Xiao, J. Nie, B. Jin, S. Shao, G. Xiao, Bioresour. Technol. 192 (2015) 68.
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Catalytic copyrolysis of cork oak and bio-oil distillation residue Yejin Lee a , Daejun Oh a , Young-Min Kim a,b , Jungho Jae c,d , Sang-Chul Jung e , Jong-Ki Jeon f , Sang Chai Kim g , Young-Kwon Park a,∗ a
School of Environmental Engineering, University of Seoul, Seoul 02504, Republic of Korea Frontier Laboratories Ltd., Fukushima 963-8862, Japan Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea d Department of Clean Energy and Chemical Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea e Department of Environmental Engineering, Sunchon National University, Suncheon 57922, Republic of Korea f Department of Chemical Engineering, Kongju National University, Cheonan 31080, Republic of Korea g Department of Environmental Education, Mokpo National University, Muan 58554, Republic of Korea b c
a r t i c l e
i n f o
Article history: Received 31 March 2017 Received in revised form 4 June 2017 Accepted 13 June 2017 Available online xxx Keywords: Catalytic copyrolysis Cork oak Distillation residue HZSM-5 Aromatic hydrocarbons
a b s t r a c t The atmospheric distillation residue (ADR) of cork oak (CO) pyrolysis oil was used as the co-feeding material for the catalytic pyrolysis of CO over HZSM-5 catalysts to improve the formation of aromatic hydrocarbons. Although the non-catalytic copyrolysis of CO and ADR did not improve the formation of aromatic hydrocarbons, the catalytic copyrolysis of CO and ADR promoted the synergistic formation of aromatic hydrocarbons. HZSM-5(30), having a lower SiO2 /Al2 O3 (30), showed better performance for the formation of aromatic hydrocarbons than HZSM-5(80) because of its higher acidity. The catalytic copyrolysis of CO and ADR also decreased the formation of coke. The largest quantity of aromatic hydrocarbons was obtained from the catalytic copyrolysis of CO and ADR over HZSM-5 (30) at 600 ◦ C, whereas the lowest coke yield was achieved at 700 ◦ C. When the catalyst to sample ratio was increased from 2:1 to 5:1, the synergistic formation of aromatic hydrocarbons was limited, resulting in a lower experimental yield of aromatic hydrocarbons than the theoretical yield. A lower coke yield was also achieved at a high catalyst to sample ratio (5:1). © 2017 Elsevier B.V. All rights reserved.
1. Introduction Zeolites have attracted considerable interest as versatile catalysts for biomass conversion [1,2]. In particular, zeolites are effective in the selective deoxygenation of biomass pyrolysis vapors, resulting in the formation of aromatics and effectively increasing the C/O ratio. Zeolites, particularly those with high acidity and low Si/Al ratios, promote the cracking reaction in the initial pyrolysis reactions [3–7]. Among the various types of zeolites, HZSM-5 has been used in many studies because it can produce many useful materials, such as aromatics and aliphatic unsaturated hydrocarbons (olefins) during the catalytic pyrolysis of biomass. On the other hand, even with its high activity, the catalytic cracking of woody biomass over HZSM-5 still has low carbon efficiency and produces huge amounts of undesirable char and coke. The low yield of aromatic hydrocarbons and the large amount of coke formation is related to the inherent hydrogen-deficient and oxygen-rich
∗ Corresponding author. E-mail address: [email protected] (Y.-K. Park).
nature of biomass feedstock. The effective hydrogen to carbon ratio (H/Ceff ) of biomass was reported to be a good parameter for predicting the conversion efficiency of biomass to bio-fuels via pyrolysis or catalytic pyrolysis [8–13]. A biomass sample with a high H/Ceff can produce large amounts of aromatic hydrocarbons with a low coke yield. On the other hand, a sample with a low H/Ceff produces a large amount of coke during catalytic pyrolysis, resulting in fast catalyst deactivation and reduced catalyst lifetime [14]. The catalytic co-pyrolysis of biomass and the feedstock with a high hydrogen content was suggested to be one option for overcoming the low conversion efficiency in the catalytic pyrolysis of biomass [15]. To date, many plastics have been used as co-feeding materials for the catalytic pyrolysis of biomass because they have a high H/Ceff [16–19]. Although other materials also have a high H/Ceff , there have been few studies using other materials. One of the possible hydrogen-rich co-feeding materials for the catalytic copyrolysis of biomass is the distillation residue of biomass pyrolysis oils because the distillation of bio-oil can be used as a proper method to separate valuable fuel oils and chemical feedstock from bio-oil, leaving residue after the distillation process. The use of residue as a cofeeding material for the catalytic biomass was reported to be more
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economical than plastics. In addition, no substance is discarded in the entire distillation process [20–22]. In this study, the catalytic co-pyrolysis of cork oak (CO) and atmospheric distillation residue (ADR) of CO pyrolysis oils were investigated to determine the feasibility of ADR as a co-feeding material. HZSM-5 catalysts with different Si/Al ratios were used as the catalysts to examine the effects of the catalyst acidity on the catalytic copyrolysis of CO and ADR. The effects of the reaction temperature were also investigated to determine the optimal temperature for the formation of aromatic hydrocarbons.
Table 1 Physicochemical properties of CO and ADR.
C H N Ob Moisture Volatile matters Fixed carbon Ash
Ultimate analysis (wt.%)
Proximate analysis (wt.%)
a b
COa
ADRa
46.27 5.94 0.37 47.42 2.50 81.05 15.10 1.35
73.48 4.88 0.62 21.01 2.46 40.18 57.26 0.11
Dry base. By difference.
2. Experimental 2.1. Samples CO, which was supplied by the National Institute of Korea Forest Science, was cryo-milled, sieved to make a particle size smaller than 500 m, and dried at 100 ◦ C for 3 h. CO pyrolysis oil, which was obtained from the pyrolysis of CO at 500 ◦ C, was distilled by atmospheric distillation. A 10 g sample of bio-oil in a round bottom flask was heated from ambient temperature to 350 ◦ C at a heating rate of 10 ◦ C/min and maintained at the final temperature for 15 min. The steam generated during the distillation of CO pyrolysis oil was collected in the cooling condenser at −30 ◦ C and analyzed by gas chromatography/mass spectrometry (GC/MS, 7890A/5975C inert, Agilent Technology). The ADR remaining in the flask after distillation was dried in an oven at 150 ◦ C for 12 h to remove all the moisture and sieved to less than 500 m for pyrolysis. Ultimate and proximate analyses of CO and DR were carried out to determine their physicochemical properties. Thermogravimetric analysis (TG, Pyris 1, Perkin Elmer) was also performed by heating a 6.0 mg sample of CO, ADR, and their mixture (CO-ADR) from ambient temperature to 900 ◦ C at a heating rate of 30 ◦ C/min under 50 mL/min of nitrogen gas to determine their non-isothermal pyrolysis behavior.
Table 2 Physicochemical properties of HZSM-5 catalysts. Catalyst
SiO2 /Al2 O3
BET surface area (m2 /g)
HZSM-5(30) HZSM-5(80)
30 80
400 425
2.2. Catalyst Commercial HZSM-5 catalysts (SiO2 /Al2 O3 = 30 and 80), which were purchased from Zeolyst International, were calcined at 550 ◦ C for 3 h. NH3 TPD was performed to compare the acidic properties of the two types of HZSM-5. The detailed methods can be found elsewhere [23].
2.3. Ex-situ catalytic pyrolysis The catalytic co-pyrolysis of CO and ADR and product analysis were performed simultaneously using a pyrolyzer (Py, EGA-Py3030D, Frontier Laboratories)-GC/MS. For this, CO-ADR (1 mg) with a CO to ADR mixing ratio of 4: 1 was loaded first onto the bottom of a deactivated SUS sample cup. Glass wool and 2 mg of catalyst were placed on top of the CO-ADR in turn to make the ex-situ catalytic pyrolysis. The sample cup was free fallen into a preheated pyrolyzer heater (500 ◦ C) and the emission vapor was transferred to a GC separation column (UA-5, 30 m length × 0.25 mm inner diameter x 0.25 m film thickness) and cryo-focused at the front part of the column by liquid nitrogen (–195 ◦ C) supplied from a MicroJet Cyro-Trap (MJT-1035E, Frontier Laboratories) for 3 min. After 3 min cryo focusing time, the product chemicals were separated using a GC oven temperature program, from 40 ◦ C to 320 ◦ C at a heating rate of 10 ◦ C/min, and detected by a MS. The total and column flow of helium were set to 100 and 1 mL/min, respectively. The MS peaks on the total ion chromatogram were identified by the NIST 05th library and F-Search library (Frontier Laboratories)
Fig. 1. NH3 TPD of HZSM-5 catalysts. Table 3 Chemical composition of pyrolysis oil and distilled pyrolysis oil (Unit: area%). Compound
Pyrolysis oil
Distilled pyrolysis oil
Acetic acid Phenolics Esters Aldehydes Ketones Furans Alcohols Cyclic compounds Levoglucosans Other oxygenates
32.57 28.32 5.16 1.14 10.29 6.92 6.94 2.54 4.19 1.93
54.57 8.16 5.31 1.04 21.44 7.19 0.00 0.90 0.00 1.91
3. Results and discussion 3.1. Physicochemical properties of samples and catalysts Table 1 lists the ultimate and proximate analysis results of CO and ADR used in this study. More than 90% of CO consisted of carbon (46.27%) and oxygen (47.72%). ADR contained 73.48% carbon and 21.01% oxygen. The calculated H/Ceff of ADR (0.35) was higher than that of CO, which suggests that a smaller amount of coke from catalytic pyrolysis can be produced using ADR as a co-feeding material of CO. Compared to CO, ADR had a smaller amount of volatile matter (40.18%) and larger amount of fixed carbon (57.26%) than those of
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Fig. 2. TG and DTG curves of CO, ADR, and the mixture of CO and ADR.
CO because most of the volatile matter in bio-oil had already been extracted during its distillation. Table 2 lists the physicochemical properties of the HZSM-5 catalysts. HZSM-5 is the best catalyst having high selectivity toward aromatic hydrocarbon during biomass catalytic pyrolysis because of its strong acidity and proper pore size [23]. The HZSM-5 catalyst with a lower SiO2 /Al2 O3 ratio had higher concentrations of both weak and strong acid sites, demonstrating its stronger acidity, as shown in Fig. 1. Therefore, its strong acidity makes it highly active for various catalytic reactions, such as cracking, deoxygenation, decarboxylation, cyclization, aromatization, isomerization, alkylation, oligomerization, and polymerization [7]. 3.2. Distillation of cork oak pyrolysis oil After the atmospheric distillation of cork oak pyrolysis oil at 350 ◦ C, 37 wt.% of cork oak (63 wt.% of pyrolysis oil) was obtained
as ADR. Although similar types of organic compounds with pyrolysis oil have been obtained from the oil distilled from pyrolysis oil, their relative composition ratios were different (Table 3). Cork oak pyrolysis oil contained acetic acid (32.57%), phenolics (28.32%), and other oxygen-containing chemicals (39.11%). On the other hand, the relative contents of acetic acid (54.57%) and phenolics (8.16%) of distilled oil were different, indicating that pyrolysis oil likely undergoes secondary reactions during distillation. Zhang et al. shows a range of decomposition pathways of woody biomass components that can occur during the pyrolysis and/or distillation process [20]. Light oxygen-containing compounds, such as acetic acid, are formed not only by the decomposition of hemicellulose and cellulose, but also by the depolymerization of lignin. Furfural is also generated by the decomposition of hemicellulose, cellulose, and lignin. Levoglucosan, a primary decomposition product of cellulose, can produce furans and ketones via the dehydration and other secondary reactions [24]. Therefore, high contents of ketones and the
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Table 4 Chemical compositions of the pyrolysis product obtained from the Py-GC/MS analysis of CO, ADR, and their mixture. (Unit: area%).
CO2 Acids Oxygenates BTEXs PAHs Phenolics Hydrocarbons
CO
ADR
Mixture of CO and ADR
7.01 17.61 49.72 0.00 0.00 25.49 0.17
37.22 1.51 16.30 3.97 6.76 33.55 0.68
13.51 16.56 38.60 0.32 0.57 30.16 0.28
lack of levoglucosan in distilled oil can be the result of the additional cleavage of levoglucosan [20]. 3.3. TGA
Fig. 3. Chemical compositions of the pyrolysis product obtained from the catalytic Py-GC/MS analysis of CO and ADR over HZMS-5 catalysts. (Unit: area%).
Fig. 2 presents the TG and DTG curves of CO and ADR. CO decomposed mainly at temperatures between 300 and 400 ◦ C. In contrast, ADR underwent decomposition over a wide temperature range from 200 to 900 ◦ C. On the other hand, the amount of solid residue obtained after the TGA of ADR was much larger than that of CO. The mixture of CO and ADR showed a similar TG curve with CO, even though it has a larger amount of solid residue than that of CO due to the contribution from ADR. The first DTG peaks at below 150 ◦ C can be assigned to the vaporization of water. The second and third DTG peaks of CO and a mixture of CO and ADR at 200–400 ◦ C correspond to the typical DTG peaks of woody biomass, which are related to the decompositions of hemicellulose, cellulose, and lignin [25]. The DTG curve of ADR had only two peaks at approximately 200 and 500 ◦ C, respectively. 3.4. Non-catalytic co-pyrolysis of CO and ADR Table 4 lists the Py-GC/MS results obtained from the thermal decomposition of CO, ADR, and the mixture of CO and ADR. Both CO and ADR produced light gas, acids, oxygenates, phenolics, and hydrocarbons via pyrolysis reactions. CO pyrolysis oil consisted of oxygenates (49.72%), phenolics (25.49%), and acids (17.61%). In addition, the pyrolysis of ADR produced a large amount of carbon dioxide (37.22%) together with phenolics (33.55%) and oxygenates (16.30%) as the major liquid products. BTEXs (3.97%) and poly aromatic hydrocarbons (PAHs, 6.76%) were also produced from the pyrolysis of ADR. The relative amounts of aromatic hydrocarbons (BTEXs and PAHs) obtained from the non-catalytic co-pyrolysis of CO and ADR were similar to the calculated values. This suggests that there is no synergistic effect on the formation of aromatic hydrocarbons. Therefore, the use of a catalyst is required to increase the yields of aromatic hydrocarbons together with the decrease in oxygen containing compounds. 3.5. Catalytic co-pyrolysis of CO and ADR Fig. 3 presents the Py-GC/MS results obtained from the thermal and catalytic co-pyrolysis of CO and ADR at 500 ◦ C. The contents of mono aromatic hydrocarbons (MAHs) and PAHs increased with decreasing concentration of acids, phenolics, and other oxygenates. Between the two HZSM-5 catalysts, HZSM-5(30), having higher acidity, produced larger amounts of MAHs (39%) and PAHs (20%) than those of MAHs (38%) and PAHs (12%) over HZSM-5(80), as shown in Fig. 3. The synergistic formation of aromatic hydrocarbons via the catalytic co-pyrolysis of CO and ADR over both HZSM-5(30) and HZSM-5(80) was also evaluated in comparison with the theoretical yield, as shown in Fig. 4. The theoretical yields of aromatic hydrocarbons were calculated using the yields obtained from the
Fig. 4. Theoretical and experimental aromatic formations obtained from the catalytic Py-GC/MS analysis of CO and ADR over both HZSM-5 catalysts. (Unit: wt.%).
experimental aromatic yields of the individual CO and ADR at their mixing ratio (4:1). The experimental yield of aromatic hydrocarbons (4.39 wt.%) obtained from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) was higher than its theoretical yield (3.66 wt.%). The catalytic co-pyrolysis of CO and ADR over HZSM5(80) also produced a larger amount of aromatic hydrocarbons (3.58 wt.%) than its theoretical value (2.85 wt.%). This shows that the catalytic co-pyrolysis of CO and ADR over both HZSM-5 catalysts have a synergistic effect on the formation of aromatic hydrocarbons. Fig. 5 presents the chemical compositions of bio-oils obtained from the catalytic co-pyrolysis of CO and ADR at different reaction temperatures (500, 600, and 700 ◦ C) over HZSM-5(30). The catalytic pyrolysis of CO over HZSM-5(30) produced gas, acids, oxygenates, phenolics, MAHs, PAHs, and hydrocarbons, whereas that of ADR over HZSM-5(30) generated large amounts of gas, MAHs, and PAHs along with small amounts of acids, oxygenates, phenolics, and hydrocarbons. The catalytic co-pyrolysis of CO and ADR also produced large amounts of gas, MAHs, and PAHs together with small amounts of acids, oxygenates, phenolics, and hydrocarbons. The MS peak area% of gas, MAHs, and hydrocarbons obtained from the catalytic pyrolysis of the individual CO and ADR, and the co-pyrolysis of CO and ADR over HZSM-5(30) increased with increasing reaction temperature. At a high reaction temperature of 700 ◦ C, the MS peak area% of gas, MAHs, and hydrocarbons were increased to 16%, 40%, and 4%, respectively, when the mixture of CO and ADR was pyrolyzed over HZSM-5(30), as shown in Fig. 5. This result is in accordance with the results reported elsewhere [19] in that a high reaction temperature accelerates the formation of hydrocarbons because the diffusion of pyrolysis vapors into the pore of
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Fig. 5. Chemical compositions of bio-oils obtained from the catalytic pyrolysis of CO, ADR, and their mixture over HZSM-5(30) at 500, 600, and 700 ◦ C.
Fig. 6. Theoretical and experimental yields of aromatic hydrocarbons and coke produced from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at different temperatures.
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Fig. 7. Theoretical and experimental yields of aromatic hydrocarbons and coke produced from the catalytic co-pyrolysis of CO and ADR over 5 mg of HZSM-5(30) at 600 ◦ C. (catalyst: sample = 5: 1).
the zeolites can be enhanced. In addition, the relative content of phenolics decreased significantly from 12% to 7% with increasing reaction temperature from 500 to 700 ◦ C. More phenolics may be converted to aromatic hydrocarbons at high temperatures without coke formation. Therefore, the effect of the reaction temperature on coke formation needs to be investigated in future work because it is related directly to the lifetime of the catalyst. Fig. 6 presents the theoretical and experimental yields of aromatic hydrocarbons and coke obtained from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at different temperatures. The experimental yields of aromatic hydrocarbons produced from the catalytic co-pyrolysis of CO and ADR over HZSM-5(30) at all temperatures were much higher than their theoretical yields. Among them, the largest amounts of aromatic hydrocarbons (5 wt.%) were obtained from the catalytic co-pyrolysis of CO and ADR at 600 ◦ C. The amount of coke formed decreased with increasing reaction temperature from 500 to 700 ◦ C. At all reaction temperatures, the experimental coke yields were lower than the theoretical coke yields, which indicates that catalytic co-pyrolysis also suppress the formation of coke. A decrease in coke yield during the catalytic co-pyrolysis of CO and ADR can be explained by hydrogen transfer from the pyrolyzates of ADR with the high H/Ceff value to the pyrolyzates of CO. Biomass pyrolyzates, which consist mainly of hydrogen-deficient and highly oxygenated molecules, have been reported to be converted easily to coke via condensation and oligomerization reactions [26]. On the other hand, coke formation can be alleviated if hydrogen is supplied from the hydrogen-rich pyrolyzates of the co-feeding materials, such as plastics [14]. In these experiments, the pyrolyzates of ADR may act as a hydrogen donor, reducing the formation of coke from biomass pyrolyzates together with synergistic aromatic formation. Fig. 7 presents the theoretical and experimental yields of aromatic hydrocarbons and coke obtained from the catalytic co-pyrolysis of CO and ADR over larger amounts of HZSM-5(30) catalyst (i.e., catalyst to sample ratio of 5 to 1) at 600 ◦ C. Although the experimental coke yield was smaller than the theoretical yield by increasing the catalyst to sample ratio to 5 to 1, the experimental yield of aromatic hydrocarbons was smaller than the theoretical value, indicating that the synergistic formation of aromatic hydrocarbons is limited at high catalyst to sample ratios.
4. Conclusions The catalytic copyrolysis of CO and ADR over HZSM-5 catalysts produced a higher yield of aromatic hydrocarbons than the theoretical values. This shows that ADR is a promising co-feeding material for the catalytic pyrolysis of biomass for enhancing the production of valuable aromatic hydrocarbons on account of its high H/Ceff . A comparison of HZSM-5(30) and HZSM-5(80) catalysts revealed HZSM-5(30) to produce larger amounts of aromatic hydrocarbon owing to its higher acidity. The optimal temperature for the formation of aromatic hydrocarbons was found to be 600 ◦ C, but the lowest coke yield was obtained at 700 ◦ C. The synergistic formation of aromatic hydrocarbons was alleviated at a high catalyst to sample ratio (i.e., 5:1), indicating that the positive effect of the cofeeding of ADR can be maximized when a small amount of catalyst is applied to the catalytic copyrolysis of CO and ADR. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1A2A2A11001193). References [1] H. Lee, Y.M. Kim, I.G. Lee, J.K. Jeon, S.C. Jung, J.D. Chung, W.G. Choi, Y.K. Park, Korean J. Chem. Eng. 33 (2016) 3299. [2] X. Zhao, L. Wei, J. Julson, Z. Gu, Y. Cao, Korean J. Chem. Eng. 32 (2015) 1528. [3] A.A. Lappas, M.C. Samolada, D.K. Iatridis, S.S. Voutetakis, I.A. Vasalos, Fuel 81 (2002) 2087. [4] H.J. Park, J.I. Dong, J.K. Jeon, K.-S. Yoo, J.H. Yim, J.M. Sohn, Y.K. Park, J. Ind. Eng. Chem. 13 (2007) 182. [5] A. Aho, N. Kumar, K. Eränen, T. Salmi, M. Hupa, D.Yu. Murzin, Fuel 87 (2008) 2493. [6] R. French, S. Czernik, Fuel Process. Technol. 91 (2010) 25. [7] D.J. Mihalcik, C.A. Mullen, A.A. Boateng, J. Anal. Appl. Pyrolysis 92 (2011) 224. [8] S. Yi, X. He, H. Lin, H. Zheng, C. Li, C. Li, Korean J. Chem. Eng. 33 (2016) 2923. [9] Y. Long, H. Zhou, A. Meng, Q. Li, Y. Zhang, Korean J. Chem. Eng. 33 (2016) 2638. [10] R. Soysa, Y.S. Choi, S.K. Choi, S.J. Kim, S.Y. Han, Korean J. Chem. Eng. 33 (2016) 603. [11] Y.-T. Cheng, G.W. Huber, Green Chem. 14 (2012) 3114. [12] C. Dorado, C.A. Mullen, A.A. Boateng, Appl. Catal. B-Environ. 162 (2015) 338. [13] H. Zhang, R. Xiao, J. Nie, B. Jin, S. Shao, G. Xiao, Bioresour. Technol. 192 (2015) 68.
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