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Pyrolysis and catalytic upgrading of pine wood in a combination of auger reactor and fixed bed
Fuel 129 (2014) 61–67
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Pyrolysis and catalytic upgrading of pine wood in a combination of auger reactor and fixed bed Li Bosong, Lv Wei, Zhang Qi, Wang Tiejun, Ma Longlong ⇑ Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Pyrolysis and catalytic upgrading of
pine wood was studied in a combined system. The system included an auger pyrolysis reactor and a fixed-bed catalytic reactor. HZSM-5 catalyst was evaluated for catalytic cracking. HZSM-5 was suitable for converting pine wood to phenols and aromatics.
a r t i c l e
i n f o
Article history: Received 21 September 2013 Received in revised form 3 March 2014 Accepted 20 March 2014 Available online 5 April 2014 Keywords: Bio-oil Auger reactor Catalytic upgrading HZSM-5 Phenols
a b s t r a c t A combined system of auger pyrolysis reactor and fixed-bed catalytic reactor was designed and used for continuous pyrolysis and catalytic upgrading of pine wood in this paper. HZSM-5 (Si/Al = 38) catalyst was evaluated for catalytic cracking. The distributions of liquid and gaseous products at the pyrolysis temperatures of 400–600 °C and the catalytic cracking temperatures of 450–650 °C were determined. The results showed that HZSM-5 catalyst, at a catalytic temperature of 650 °C, was suitable for converting pine wood to phenols, aromatics and gaseous hydrocarbons. The phenols and aromatics increased from 6% (peak area) for non-catalytic pyrolysis to 41%. The decrease in oxygen content of bio-oil and the increase in alkenes and alkanes of gaseous products are desirable for the pyrolysis and catalytic upgrading of biomass. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The development of renewable energy as replacements for fossil-based fuels is rapidly progressing. Lignocellulosic biomass is being studied worldwide as a feedstock for producing liquid fuels and chemicals to replace petroleum because of its renewability and large availability [1–3]. Pyrolysis is one of the main methods ⇑ Corresponding author. Tel.: +86 20 87057790. E-mail address: [email protected] (L. Ma). http://dx.doi.org/10.1016/j.fuel.2014.03.043 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
from biomass to bio-oil production, and it has caused great attention and sparked interest extensively in recent years. However, bio-oil from biomass pyrolysis, is a mixture of more than 200 highly oxygenated compounds. Bio-oil is thermally unstable and must be upgraded if to be used as fuels. Various approaches have been applied to the improvement of bio-oil quality, including hydrodeoxygenation [4,5], catalytic cracking [6,7], emulsification [8,9], steam reforming [10], esterification [11], etc. One option for bio-oil upgrading is to use biomass-derived feedstocks in a petroleum refinery, such as catalytic cracking.
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Catalytic cracking of bio-oil is an upgrading process of deoxygenation, which can improve the quality of bio-oil. Various types of zeolite catalysts have been studied in the catalytic cracking of biomass in the past 20 years, such as ZSM-5, Beta, Y, Al-MCM-41, and SBA-15. Catalysts for bio-oil upgrading have been well reviewed by many researchers [12,13]. Among these catalysts, HZSM-5 performs as a good catalyst for catalytic conversion of biomass due to its moderate internal pore space and steric hindrance [14]. It has been found to dramatically change the composition of bio-oils by both reducing the amounts of oxygenated compounds via deoxygenation reactions and simultaneously increasing the aromatic species, producing a lighter faction, while decreasing the bio-oil molecular weight [15]. Several types of reactors have been used in catalytic pyrolysis/ upgrading of biomass [16–18]. In bench-scale reactors, currently only bubbling fluidized beds (BFBs) and circulating fluidized beds (CFBs) can be applied to continuous production, and there is mixing of solid biomass with the solid catalyst. There are two drawbacks on fluidized bed reactors. (1) The fluidized beds need large volumes of inert carrier gases, which dilute the pyrolytic gases and reduce the thermal efficiency of the process. (2) The presence of char (especially the ash in char) in the catalyst reduces the capability of the catalyst. Auger pyrolysis reactors, with/without the use of sand as a heat carrier, are among the most popular reactors being evaluated today [19,20]. These reactors do not require large volumes of carrier gases, and can produce pyrolysis vapors continuously. If a catalysis bed is connected to the auger pyrolysis reactors, the pyrolysis vapors will pass through the catalyst and there is no mixing of solid biomass with the solid catalyst, which called catalytic upgrading of pyrolysis vapors. Thus, the combined system of auger pyrolysis reactor and fixed-bed catalytic reactor can overcome the drawbacks of fluidized bed systems. In this paper, a combined system of auger pyrolysis reactor and fixed-bed catalytic reactor was applied to achieve biomass continuous pyrolysis and catalytic upgrading of pyrolysis vapors. HZSM-5 zeolite was evaluated for catalysis cracking upgrading using pine wood as feedstock. The reaction parameters were optimized with a focus on the effects of reaction temperatures. Furthermore, the properties and components were investigated before and after upgrading. 2. Experimental 2.1. Characterization of feedstock and catalysts The pine wood feedstock was from Guangdong province, China. Feedstock was ground and sieved to a particle size <1 mm. The pine wood samples were oven-dried overnight to 6–8% moisture content at 105 °C before tests. Elemental analyses of pine wood samples were carried out using a Vario EL cube. The ash content was determined according to ASTM D-482. Thermogravimetry (TG) analysis of feedstock was carried out under a nitrogen flow rate of 30 ml/min with STA 449 °C thermal analyzer (NETZSCH, Germany) by using 10 mg samples and a 30 °C/min temperature increase. HZSM-5 zeolite catalyst with a Si/Al ratio of 38 was from the Nankai University Catalyst Co. Ltd. (Tianjin, China). The shape of catalysts was cylindrical with the diameter of 3 mm and the length of 10 mm. Before using, the catalysts were calcined at 550 °C for 6 h in air. NH3 temperature-programmed desorption (NH3-TPD) analysis was carried out in a quartz tube reactor with a thermal conductivity detector (TCD). 200 mg of catalyst was pretreated in a flow of helium (25 ml/min) at 500 °C for 1 h, and after cooling to 120 °C, ammonia adsorption was carried out. Subsequently, excessive physisorbed ammonia was removed by purging with he-
lium at 100 °C for 1 h. Tests were carried out by increasing the temperature from 100 to 700 °C at a rate of 10 °C/min and a helium flow rate of 25 ml/min. 2.2. Pyrolysis and catalytic cracking upgrading Pine wood was pyrolysed and catalytic cracking upgrading using a combined system of auger pyrolysis reactor and fixedbed catalytic reactor as shown in Fig. 1. The dried biomass was introduced into the hopper of the feeder and fed into the auger reactor at a feeding rate of 25 kg/h. The pine wood was pushed through the hot zone of the reactor with an auger screw driven by a 1.5 kW variable speed motor. All the tests were conducted at auger speeds of 5 rpm which corresponds to a solid residence time inside the reactor of 8 min. Outside the auger screw, a stainless-steel tube with a length of 300 cm (heating zone was 240 cm) and a diameter of 16 cm was heated by a hot blast stove. A diesel burner (Riello 40 G3, Italy) was the heat resource of the hot blast stove. The temperature of the external wall in the pyrolysis reactor was recorded and maintained at set temperatures. The temperature of the pine wood sample pyrolysed was also quantified. Due to the structure of the reactor and the blowing direction of hot wind, the varied temperature values existed along the reactor’s axis. Owing to the relatively low heat transfer coefficient between the wall and the biomass moving bed, a significant temperature gradient was established between the biomass bed and the wall of the reactor. Fig. 2 shows the time–temperature profile for the pyrolysis of pine wood and the wall of the reactor. After pyrolysis, the charred particles were collected, left to cool for 2 h and weighed in a char pot. The pyrolysis vapors were sucked into a fixed-bed catalytic reactor which was loaded zeolite catalysts. The fixed-bed catalytic reactor (a stainless-steel tube with a length of 130 cm and a diameter of 78 cm) was heated by an electrical furnace to the desired temperature (450–650 °C) before experiments. After upgrading, the pyrolysis vapors were condensed in two condensation units. The first unit was a vertical tube with cooling water coils where pyrolysis vapors were cooled to approximately 25 °C. The second condensation unit consisted of two traps in series immersed in water cooled by ice. The pressure inside the reactor was kept by a Roots vacuum pump with a frequency converter. The Roots vacuum pump with a frequency converter to regulate the suction had two purposes: (1) helping to suck the pyrolysis vapors from the reactor, and (2) controlling the velocity of flow to adjust the residence time of vapors inside the pyrolysis reactor and catalyst bed. The yield of liquid was determined by weighing the first condenser and the traps. The non-condensable gases were calculated by difference. 2.3. Product analysis Gas chromatography mass spectroscopy (GC/MS) analysis of bio-oil was performed on a gas chromatograph (7890A, Agilent Technologies, USA) coupled with a mass spectrometer (5975C, Agilent Technologies, USA). A HP-INNOwax capillary column was used for the chromatographic separation of chemical components in bio-oil. The injector temperature was 260 °C, and a split ratio 20:1 was used. The GC oven temperature program was 2 min at 60 °C, and to 240 °C in a rate of 10 °C/min with a dwell time of 10 min. The mass spectrometer was operated in the electron impact mode at 70 eV. After a solvent delay of 2.8 min, full scan mass spectra were acquired from 12 to 500 m/z. The identification of the main peaks was made from NIST11 MS Library and previously published literatures. The water content of the bio-oil was determined by Karl Fischer titration (ASTM D 1744) with a Metrohm 787 KF Titrino. The analysis was carried out three times to confirm the
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Fig. 1. Scheme of a combination of auger pyrolysis reactor and fixed-bed catalytic reactor.
X gas ¼
massgas 100% masssample masschar massliquid masscoke
ð2Þ
Xgas – the total yield of gas released (wt.%) Yield of gas released (mol/kg biomass) was calculated based on the formula (3):
Yield of gas released ¼ P
X gas Sel:gas molecular mass Sel:gas
1000
ð3Þ
3. Results and discussion 3.1. Pine wood and HZSM-5 zeolite characterization
Fig. 2. Time–temperature profile for the pyrolysis of pine wood and the wall of the reactor.
reproducibility and average values were calculated for each identified product. Gas chromatography (GC) analysis of gas products was performed on a gas chromatograph (7890A, Agilent Technologies, U.S.A.). A series of columns were used the chromatographic separation of chemical components in gas, which were J&W GS-GASPRO, Agilent Mol. sieve 5A, and Agilent Hayesep Q. The injector temperature was 200 °C, and a split ratio 20:1 was used. The GC oven temperature program was 3 min at 60 °C, and 15 °C/min to 250 °C. Hydrocarbons were analyzed by a flame ionization detector (FID), CO2 and CO were analyzed by a thermal conductivity detector (TCD1), and H2 was analyzed by TCD2. The concentration of gas (vol.%) was calculated according to Eq. (1):
V gas Sel:gas ¼ P 100% V gas
The elemental composition of the pine wood used in the experiments was 45.29% C, 6.24% H, 0.20% N, 0.01% S, and 48.26% O. The ash content of pine wood was 2.60%. The TG and differential thermal gravity (DTG) curves (Fig. 3) were obtained for the pine wood pyrogenation under N2 at the heating rate of 30 °C/min. From Fig. 3, the TG curve of the pine wood pyrogenation shows that thermal reaction occurred over a wide temperature range. The pine wood sample had a char yield of 24.50 wt.% at the ending temperature of 600 °C. From the DTG curve, there was a primary peak of
ð1Þ
Sel.gas – the concentration of gas (vol.%); Vgas – the volume of gas (L). The total yield of gas released (wt.%) was calculated according to Eq. (2):
Fig. 3. TG and DTG curves for pine wood at a heating rate of 30 °C/min.
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mass loss at the temperature of 375.5 °C, and the temperature range of mass loss was from 215 °C to 430 °C. Thus, the pyrolysis temperature of 500 °C was enough to make sufficient pyrogenation for the pine wood sample. The pore structure properties of the HZSM-5 catalyst sample were that the specific surface areas were 325 m2/g, and the pore volume was 0.22 cm3/g. Fig. 4 shows the NH3-TPD curve of the HZSM-5 catalyst used in this study. It can be seen that two obvious desorption peaks occur over the HZSM-5 zeolite. The one at 230 °C could be attributed to weak adsorption of NH3 on the bronsted acid site and NH3 association with Si-OH, and the other peak at 440 °C could be ascribed to a strong description of NH3 adsorbed on the acidic Si–OH–Al group [21–24].
Table 1 The product distribution obtained under various pyrolysis and upgrading temperatures using the HZSM-5 catalyst. Data are the average of results from three experiments, the experimental error is 62.0%.
Sample temp. (°C) Catalyst bed temp. (°C) Char (wt.%) Gas (wt.%) Oil (wt.%) Water content (wt.% in oil)
Without catalyst
HZSM-5
400 – 45.1 24.7 30.2 40.2
500 450 30.0 37.5 32.5 50.4
500 – 30.3 35.7 34.0 45.6
600 – 25.2 41.7 33.1 60.5
500 550 30.2 39.8 30.0 60.2
500 650 30.5 42.5 27.0 70.8
3.2. Pyrolysis and catalytic upgrading of pyrolytic vapors from pine wood Table 1 shows the product distribution obtained under various pyrolysis and upgrading temperatures using the HZSM-5 catalyst. When pyrogenation without catalyst, a higher temperature caused more char to be converted into gases via secondary decomposition reactions, but the bio-oil yield maintained more or less unchanged. Based on this result and TG result, the pyrolysis temperature was set at 500 °C during the catalytic upgrading experiments. When the HZSM-5 catalyst was loaded in the catalytic upgrading bed, the bio-oil yield reduced due to catalytic cracking, which lead to an increased gas yield and an increased water content in bio-oil. The water content in the bio-oil increased obviously to 70.8% on increasing the catalytic cracking temperature to 650 °C. As mentioned above in NH3-TPD results, the strong acid sites existed in HZSM-5, which showed excellent cracking performances. This resulted in the deoxygenation of oxygenates in the bio-oil, which contained carbonyl and carboxyl groups, indicating that the catalytic upgrading improved the bio-oil quality [3]. The main deoxygenation pathway of bio-oil is dehydration, which can be used as a basis for the evaluation of bio-oil produced from lignocellulosic biomass [25]. 3.3. Chemical composition of upgraded bio-oils The GC–MS results of the bio-oil obtained from pyrolysis and catalytic upgrading are shown in Fig. 5. More than 50 compounds in bio-oil were identified by GC–MS. Compared with non-catalytic pyrolysis, the composition of the bio-oil from catalytic upgrading
Fig. 4. NH3-TPD profile of HZSM-5 catalysts.
Fig. 5. The GC–MS results of the bio-oil obtained from pyrolysis and catalytic upgrading. A: non-catalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C.
was changed obviously. However, not all the experimental conditions could change the composition of bio-oil effectively. When the catalyst bed temperature was lower (e.g. 450 or 550 °C), the peak curves were similar with the non-catalysis’ curves. This outcome may be related to the temperature of catalytic cracking because a higher temperature provides more energy, which favors the break of bonds in large molecules of bio-oil. The compositions of the bio-oil obtained from pyrolysis and catalytic upgrading are shown in Table 2. In the raw bio-oil, acids, ketones, phenolics and D-allose were shown to be the main products, while the distribution of products resulting from catalytic cracking over HZSM-5 at 650 °C was different. The primary products of upgraded bio-oil were mono-phenols, and the peak area percentage was more than 30%. Aromatics, such as xylene and indene, were also observed. With the use of catalysts, acetic acid decreased from 33% for non-catalytic pyrolysis to 13.8%, while phenols and alkyl phenols increased from 5.8% for non-catalytic pyrolysis to 34.4%. D-allose was not detected in the upgraded bio-oil. In this study, mono-phenols (phenol and alkyl phenols, not including guaiacol derivatives) and aromatics were regarded as desirable chemicals, and oxygenates were chosen as the criteria
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B. Li et al. / Fuel 129 (2014) 61–67 Table 2 The compositions of the bio-oil obtained from pyrolysis and catalytic upgrading. R.T./min
Name
Raw bio-oil/Area%
Upgraded bio-oila/Area%
4.19 6.03 6.51 7.26 7.42 8.50 8.73 8.98 9.41 9.46 9.66 11.11 12.10 12.31 12.39 13.02 13.32 13.38 14.37 14.47 14.84 14.87 15.56 15.62 16.49 17.31 18.06 19.92 20.70
p-Xylene Furan, 2,5-diethoxytetrahydro2-Propanone, 1-hydroxy2-Cyclopenten-1-one 2-Cyclopenten-1-one, 2-methylAcetic acid Furfural Indene Furan, 2,4-dimethyl2-Cyclopenten-1-one, 3-methylPropanoic acid 2-Furanmethanol 1H-Indene, 1-methylene2(5H)-Furanone 1,2-Cyclopentanedione 2-Cyclopenten-1-one, 2-hydroxy-3-methylNaphthalene, 1-methylPhenol, 2-methoxyPhenol, 2-methoxy-4-methylNaphthalene, 2,6-dimethylPhenol, 2-methylPhenol Phenol, 2,5-dimethylPhenol, 4-methylPhenol, 3-ethylPhenol, 2,6-dimethoxyBenzoic acid, 4-hydroxy-3-methoxyVanillin
– – 7.05 1.35 – 33.07 2.95 – – 1.32 1.90 1.55 – 1.17 – 2.48 – 1.88 1.39 – 1.01 2.79 – 2.03 – 4.17 2.61 1.02 7.21
5.46 4.75 5.69 3.59 1.40 13.79 1.36 1.77 1.13 – 2.40 – 2.81 – 1.84 2.95 2.56 3.35 – 1.79 4.36 11.67 2.28 11.71 1.24 1.33 – – –
D-Allose
Compounds listed are those represented by more than 1% of the total peak area. a Upgrading temperature condition: 650 °C.
species to assess the degree of deoxygenation. Changes in the biooil composition as a result of catalytic upgrading are shown in Fig. 6. In general, catalytic upgrading resulted in a reduction of the oxygen content and an increase in the phenols and aromatics contents, which were high value-added. In this study, with the HZSM-5 catalyst, at the higher temperature (650 °C), the main oxygenate compounds, such as acids, alcohols, carbonyls and carbohydrates, were removed effectively, while it was not effective at lower temperatures. Oxygenates decreased from 71% for noncatalytic pyrolysis to 48%, while phenols and aromatics increased from 6% for non-catalytic pyrolysis to 41%. It is concluded that HZSM-5 catalyst with micropores and strong acid were the most effective for removing oxygenates and producing phenols and
Fig. 6. Main chemical compounds in bio-oils. A: non-catalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C.
aromatics. This agrees with the results of other researches [3,26]. The high value-added condensables could be used as high quality aromatic fuel additives or chemicals after a distillation or extraction process. 3.4. Gas products The composition of gas products obtained by pyrolysis and catalytic upgrading is shown in Table 3. And Fig. 7 shows the yield of gas released at different experimental conditions. Compared with bubbling fluidized beds and circulating fluidized beds, there are no inert gases in the gas products by the combined system of auger pyrolysis reactor and fixed-bed catalytic reactor. CO and CO2 were the main gas products both in non-catalytic and catalytic pyrolysis, which took up 75–90 volume percentages. The formation of CO and CO2 is another well known pathway of the deoxygenation of biooil. Another interesting result was that employing a catalyst considerably increased the concentration and yield of C2+ alkenes, as well as water and CO. This observation suggests that HZSM-5 contains Brønsted acid sites and is a system of two perpendicularly intersecting channels. The larger of the two channels has a near circular pore structure with dimensions of 0.54 0.56 nm2. The smaller channels have a geometry of 0.51 0.54 nm2. The intersection of these channels which contains the proposed active site is approximately a 0.9 nm cavity [27]. Several reactions occur inside the zeolite including dehydration, decarboxylation, isomerization and decarbonylation thereby removing oxygen as water, carbon monoxide and carbon dioxide and converting the carbon and hydrogen into olefins and aromatics [1,17]. In addition, alkanes and hydrogen increased when catalytic upgrading. This result indicated that in the present of catalysts, the bonds in the side chains of bio-oil molecules broken up and released more gas molecules. Therefore, it is considered that HZSM-5 catalyst was effectual to produce alkenes and alkanes, which improved the quality of pyrolysis gases.
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Table 3 The composition of gas products obtained by pyrolysis and catalytic upgrading. Pyrolysis temp. (°C)
Catalyst bed temp. (°C)
500 500 500 500
– 450 550 650
The concentration of gas (vol.%) CH4
C2 + alkane
C2 + alkene
C6H6
CO2
CO
H2
6.17 6.17 4.89 9.64
0.83 0.83 0.78 1.54
1.26 1.26 2.14 9.80
0.11 0.11 0.02 0.33
46.74 46.74 51.16 37.43
43.75 43.75 39.92 37.95
1.14 1.14 1.08 3.32
the Cooperation Project of China–European Union Founded by MOST of China-China (246772).
References
Fig. 7. The yield of gas released at different experimental conditions. A: noncatalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C. Data are the average of results from three experiments, the experimental error is 62.0%.
4. Conclusions The general conclusion from this study is that the high value-added condensables and pyrolysis gases can be produced from biomass by a combined system of auger pyrolysis reactor and fixed-bed catalytic reactor. This means a significant development in the progress of continuous catalytic pyrolysis for the treatment of lignocellulosic biomass. The combined system can overcome the drawbacks of fluidized bed systems: No requirement of carrier gases and no mixing of solid biomass with the solid catalyst. HZSM-5 (Si/Al = 38) catalyst loaded in fixed-bed catalytic reactor shows high activity for biomass catalytic pyrolysis. Using HZSM-5 catalyst, the higher catalytic temperature (650 °C) is suitable for converting pine wood to phenols, aromatics and gaseous hydrocarbons. This work proves that the properties of bio-oil can be effectively improved and the oxygen content can be markedly reduced though continuous catalytic pyrolysis. The combined system of auger pyrolysis reactor and fixed-bed catalytic reactor used in this work must be viewed as a research prototype. Future work in this area will focus on two fields. The one is the efficiency analysis facing to the industry application. The other one is the stability and reaction–regeneration cycles of the catalysts.
Acknowledgements This research was sponsored by the National Natural Science Foundation of China-China (51106166), the National Science & Technology Pillar Program of China-China (2011BAD22B07), and
[1] French F, Czernik S. Catalytic pyrolysis of biomass for biofuels production. Fuel Process Technol 2010;91:125–32. [2] Adjaye JD, Bakhshi NN. Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part II: Comparative catalyst performance and reaction pathways. Fuel Process Technol 1995;45:185–202. [3] Park HJ, Park KH, Jeon JK, Kim J, Ryoo R, Jeong KE, et al. Production of phenolics and aromatics by pyrolysis of miscanthus. Fuel 2012;97:379–84. [4] Díaz E, Mohedano AF, Calvo L, Gilarranz MA, Casas JA, Rodríguez JJ, et al. Hydrogenation of phenol in aqueous phase with palladium on activated carbon catalysts. Chem Eng J 2007;131:65–71. [5] Fisk CA, Margan T, Ji Y, Crocker M, Crofcheck C, Lewis SA. Bio-oil upgrading over platinum catalysts using in situ generated hydrogen. Appl Catal A – Gen 2009;358:150–6. [6] Park HJ, Heo HS, Yim JH, Jeon JK, Ko YS, Kim SS, et al. Catalytic pyrolysis of Japanese larch using spent HZSM-5. Korean J Chem Eng 2010;27:73–5. [7] Carlson TR, Tompsett GA, Conner WC, Huber GW. Aromatic production from catalytic fast pyrolysis of biomass-derived feedstocks. Top Catal 2009;52: 241–52. [8] Chiaramonti D, Bonini M, Fratini E, Tondi G, Gartner K, Bridgwater AV, et al. Development of emulsions from biomass pyrolysis liquid and diesel and their use in engines Part 1: Emulsion production. Biomass Bioenergy 2003;25: 85–99. [9] Chiaramonti D, Bonini M, Fratini E, Tondi G, Gartner K, Bridgwater AV, et al. Development of emulsions from biomass pyrolysis liquid and diesel and their use in engines Part 2: Tests in diesel engines. Biomass Bioenergy 2003;25: 101–11. [10] Wang DN, Czernik S, Montané D, Mann M, Chornet E. Biomass to hydrogen via fast pyrolysis and catalytic steam reforming of the pyrolysis oil and its fractions. Ind Eng Chem Res 1997;36:1507–12. [11] Zhang Q, Chang J, Wang TJ, Xu Y. Upgrading bio-oil over different solid catalysts. Energy Fuels 2006;20:2714–7. [12] Butler E, Devlin G, Meier D, McDonnell K. A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading. Renew Sust Energy Rev 2011;15:4171–86. [13] Taarning E, Osmundsen CM, Yang X, Voss B, Andersen SI, Christensen CH. Zeolite-catalyzed biomass conversion to fuels and chemicals. Energy Environ Sci 2011;4:793–804. [14] Jae J, Tompsett GA, Foster AJ, Hammond KD, Auerbach SM, Lobo RF, et al. Investigation into the shape selectivity of zeolite catalysts for biomass conversion. J Catal 2011;279:257–68. [15] Lappas A, Iliopoulou E, Kalogiannis K. Catalysts in biomass pyrolysis. In: Crocker M, editor. Thermochemical conversion of biomass to liquid fuels and chemicals. RSC Publishing; 2010. p. 263–83. [16] Zhang HY, Xiao R, Jin BS, Shen DK, Chen R, Xiao GM. Catalytic fast pyrolysis of straw biomass in an internally interconnected fluidized bed to produce aromatics and olefins: Effect of different catalysts. Bioresour Technol 2013; 137:82–7. [17] Gayubo AG, Valle B, Aguayo AT, Olazar M, Bilbao J. Olefin Production by catalytic transformation of crude bio-oil in a two-step process. Ind Eng Chem Res 2010;49:123–31. [18] Zhang HY, Carlson TR, Xiao R, Huber GW. Catalytic fast pyrolysis of wood and alcohol mixtures in a fluidized bed reactor. Green Chem 2012;14:98–110. [19] Ingram L, Mohan D, Bricka M, Steele PH. Pyrolysis of wood and bark in an auger reactor physical properties and chemical analysis of the produced biooils. Energy Fuels 2008;22:614–25. [20] Liaw SS, Zhou S, Wu HW, Garcia-Perez M. Effect of pretreatment temperature on the yield and properties of bio-oils obtained from the auger pyrolysis of Douglas fir wood. Fuel 2013;213:672–82. [21] Hunger B, Hoffmann J, Heitzsch O, Hunger M. Temperature-programmed desorption (TPD) of ammonia from HZSM-5 zeolites. J Therm Anal 1990;36: 1379–91. [22] Chao KJ, Chiou BH, Cho CC, Jeng SY. Temperature-programmed desorption studies on ZSM-5 zeolites. Zeolites 1984;4:2–4.
B. Li et al. / Fuel 129 (2014) 61–67 [23] Lobree LJ, Hwang IC, Reimer JA, Bell AT. Investigations of the state of Fe in HZSM-5. J Catal 1999;186:242–53. [24] Jiang T, Zhang Q, Wang TG, Zhang Q, Ma LL. High yield of pentane production by aqueous-phase reforming of xylitol over Ni/HZSM-5 and Ni/MCM22 catalysts. Energy Convers Manage 2012;59:58–65. [25] Park HJ, Heo HS, Jeon JK, Kim JN, Ryoo R, Jeong KE, et al. Highly valuable chemicals production from catalytic upgrading of radiata pine sawdustderived pyrolytic vapors over mesoporous MFI zeolites. Appl Catal B – Environ 2010; 95:365–73.
67
[26] Li XY, Su L, Wang YJ, Yu YQ, Wang CW, Li XL, et al. Catalytic fast pyrolysis of Kraft lignin with HZSM-5 zeolite for producing aromatic hydrocarbons. Front Environ Sci Eng 2012;6:295–303. [27] Carlson TR, Tompsett GA, Conner WC, Huber GW. Aromatic production from catalytic fast pyrolysis of biomass-derived feedstocks. Top Catal 2009;52: 241–52.
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Fuel journal homepage: www.elsevier.com/locate/fuel
Pyrolysis and catalytic upgrading of pine wood in a combination of auger reactor and fixed bed Li Bosong, Lv Wei, Zhang Qi, Wang Tiejun, Ma Longlong ⇑ Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Pyrolysis and catalytic upgrading of
pine wood was studied in a combined system. The system included an auger pyrolysis reactor and a fixed-bed catalytic reactor. HZSM-5 catalyst was evaluated for catalytic cracking. HZSM-5 was suitable for converting pine wood to phenols and aromatics.
a r t i c l e
i n f o
Article history: Received 21 September 2013 Received in revised form 3 March 2014 Accepted 20 March 2014 Available online 5 April 2014 Keywords: Bio-oil Auger reactor Catalytic upgrading HZSM-5 Phenols
a b s t r a c t A combined system of auger pyrolysis reactor and fixed-bed catalytic reactor was designed and used for continuous pyrolysis and catalytic upgrading of pine wood in this paper. HZSM-5 (Si/Al = 38) catalyst was evaluated for catalytic cracking. The distributions of liquid and gaseous products at the pyrolysis temperatures of 400–600 °C and the catalytic cracking temperatures of 450–650 °C were determined. The results showed that HZSM-5 catalyst, at a catalytic temperature of 650 °C, was suitable for converting pine wood to phenols, aromatics and gaseous hydrocarbons. The phenols and aromatics increased from 6% (peak area) for non-catalytic pyrolysis to 41%. The decrease in oxygen content of bio-oil and the increase in alkenes and alkanes of gaseous products are desirable for the pyrolysis and catalytic upgrading of biomass. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The development of renewable energy as replacements for fossil-based fuels is rapidly progressing. Lignocellulosic biomass is being studied worldwide as a feedstock for producing liquid fuels and chemicals to replace petroleum because of its renewability and large availability [1–3]. Pyrolysis is one of the main methods ⇑ Corresponding author. Tel.: +86 20 87057790. E-mail address: [email protected] (L. Ma). http://dx.doi.org/10.1016/j.fuel.2014.03.043 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
from biomass to bio-oil production, and it has caused great attention and sparked interest extensively in recent years. However, bio-oil from biomass pyrolysis, is a mixture of more than 200 highly oxygenated compounds. Bio-oil is thermally unstable and must be upgraded if to be used as fuels. Various approaches have been applied to the improvement of bio-oil quality, including hydrodeoxygenation [4,5], catalytic cracking [6,7], emulsification [8,9], steam reforming [10], esterification [11], etc. One option for bio-oil upgrading is to use biomass-derived feedstocks in a petroleum refinery, such as catalytic cracking.
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Catalytic cracking of bio-oil is an upgrading process of deoxygenation, which can improve the quality of bio-oil. Various types of zeolite catalysts have been studied in the catalytic cracking of biomass in the past 20 years, such as ZSM-5, Beta, Y, Al-MCM-41, and SBA-15. Catalysts for bio-oil upgrading have been well reviewed by many researchers [12,13]. Among these catalysts, HZSM-5 performs as a good catalyst for catalytic conversion of biomass due to its moderate internal pore space and steric hindrance [14]. It has been found to dramatically change the composition of bio-oils by both reducing the amounts of oxygenated compounds via deoxygenation reactions and simultaneously increasing the aromatic species, producing a lighter faction, while decreasing the bio-oil molecular weight [15]. Several types of reactors have been used in catalytic pyrolysis/ upgrading of biomass [16–18]. In bench-scale reactors, currently only bubbling fluidized beds (BFBs) and circulating fluidized beds (CFBs) can be applied to continuous production, and there is mixing of solid biomass with the solid catalyst. There are two drawbacks on fluidized bed reactors. (1) The fluidized beds need large volumes of inert carrier gases, which dilute the pyrolytic gases and reduce the thermal efficiency of the process. (2) The presence of char (especially the ash in char) in the catalyst reduces the capability of the catalyst. Auger pyrolysis reactors, with/without the use of sand as a heat carrier, are among the most popular reactors being evaluated today [19,20]. These reactors do not require large volumes of carrier gases, and can produce pyrolysis vapors continuously. If a catalysis bed is connected to the auger pyrolysis reactors, the pyrolysis vapors will pass through the catalyst and there is no mixing of solid biomass with the solid catalyst, which called catalytic upgrading of pyrolysis vapors. Thus, the combined system of auger pyrolysis reactor and fixed-bed catalytic reactor can overcome the drawbacks of fluidized bed systems. In this paper, a combined system of auger pyrolysis reactor and fixed-bed catalytic reactor was applied to achieve biomass continuous pyrolysis and catalytic upgrading of pyrolysis vapors. HZSM-5 zeolite was evaluated for catalysis cracking upgrading using pine wood as feedstock. The reaction parameters were optimized with a focus on the effects of reaction temperatures. Furthermore, the properties and components were investigated before and after upgrading. 2. Experimental 2.1. Characterization of feedstock and catalysts The pine wood feedstock was from Guangdong province, China. Feedstock was ground and sieved to a particle size <1 mm. The pine wood samples were oven-dried overnight to 6–8% moisture content at 105 °C before tests. Elemental analyses of pine wood samples were carried out using a Vario EL cube. The ash content was determined according to ASTM D-482. Thermogravimetry (TG) analysis of feedstock was carried out under a nitrogen flow rate of 30 ml/min with STA 449 °C thermal analyzer (NETZSCH, Germany) by using 10 mg samples and a 30 °C/min temperature increase. HZSM-5 zeolite catalyst with a Si/Al ratio of 38 was from the Nankai University Catalyst Co. Ltd. (Tianjin, China). The shape of catalysts was cylindrical with the diameter of 3 mm and the length of 10 mm. Before using, the catalysts were calcined at 550 °C for 6 h in air. NH3 temperature-programmed desorption (NH3-TPD) analysis was carried out in a quartz tube reactor with a thermal conductivity detector (TCD). 200 mg of catalyst was pretreated in a flow of helium (25 ml/min) at 500 °C for 1 h, and after cooling to 120 °C, ammonia adsorption was carried out. Subsequently, excessive physisorbed ammonia was removed by purging with he-
lium at 100 °C for 1 h. Tests were carried out by increasing the temperature from 100 to 700 °C at a rate of 10 °C/min and a helium flow rate of 25 ml/min. 2.2. Pyrolysis and catalytic cracking upgrading Pine wood was pyrolysed and catalytic cracking upgrading using a combined system of auger pyrolysis reactor and fixedbed catalytic reactor as shown in Fig. 1. The dried biomass was introduced into the hopper of the feeder and fed into the auger reactor at a feeding rate of 25 kg/h. The pine wood was pushed through the hot zone of the reactor with an auger screw driven by a 1.5 kW variable speed motor. All the tests were conducted at auger speeds of 5 rpm which corresponds to a solid residence time inside the reactor of 8 min. Outside the auger screw, a stainless-steel tube with a length of 300 cm (heating zone was 240 cm) and a diameter of 16 cm was heated by a hot blast stove. A diesel burner (Riello 40 G3, Italy) was the heat resource of the hot blast stove. The temperature of the external wall in the pyrolysis reactor was recorded and maintained at set temperatures. The temperature of the pine wood sample pyrolysed was also quantified. Due to the structure of the reactor and the blowing direction of hot wind, the varied temperature values existed along the reactor’s axis. Owing to the relatively low heat transfer coefficient between the wall and the biomass moving bed, a significant temperature gradient was established between the biomass bed and the wall of the reactor. Fig. 2 shows the time–temperature profile for the pyrolysis of pine wood and the wall of the reactor. After pyrolysis, the charred particles were collected, left to cool for 2 h and weighed in a char pot. The pyrolysis vapors were sucked into a fixed-bed catalytic reactor which was loaded zeolite catalysts. The fixed-bed catalytic reactor (a stainless-steel tube with a length of 130 cm and a diameter of 78 cm) was heated by an electrical furnace to the desired temperature (450–650 °C) before experiments. After upgrading, the pyrolysis vapors were condensed in two condensation units. The first unit was a vertical tube with cooling water coils where pyrolysis vapors were cooled to approximately 25 °C. The second condensation unit consisted of two traps in series immersed in water cooled by ice. The pressure inside the reactor was kept by a Roots vacuum pump with a frequency converter. The Roots vacuum pump with a frequency converter to regulate the suction had two purposes: (1) helping to suck the pyrolysis vapors from the reactor, and (2) controlling the velocity of flow to adjust the residence time of vapors inside the pyrolysis reactor and catalyst bed. The yield of liquid was determined by weighing the first condenser and the traps. The non-condensable gases were calculated by difference. 2.3. Product analysis Gas chromatography mass spectroscopy (GC/MS) analysis of bio-oil was performed on a gas chromatograph (7890A, Agilent Technologies, USA) coupled with a mass spectrometer (5975C, Agilent Technologies, USA). A HP-INNOwax capillary column was used for the chromatographic separation of chemical components in bio-oil. The injector temperature was 260 °C, and a split ratio 20:1 was used. The GC oven temperature program was 2 min at 60 °C, and to 240 °C in a rate of 10 °C/min with a dwell time of 10 min. The mass spectrometer was operated in the electron impact mode at 70 eV. After a solvent delay of 2.8 min, full scan mass spectra were acquired from 12 to 500 m/z. The identification of the main peaks was made from NIST11 MS Library and previously published literatures. The water content of the bio-oil was determined by Karl Fischer titration (ASTM D 1744) with a Metrohm 787 KF Titrino. The analysis was carried out three times to confirm the
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Fig. 1. Scheme of a combination of auger pyrolysis reactor and fixed-bed catalytic reactor.
X gas ¼
massgas 100% masssample masschar massliquid masscoke
ð2Þ
Xgas – the total yield of gas released (wt.%) Yield of gas released (mol/kg biomass) was calculated based on the formula (3):
Yield of gas released ¼ P
X gas Sel:gas molecular mass Sel:gas
1000
ð3Þ
3. Results and discussion 3.1. Pine wood and HZSM-5 zeolite characterization
Fig. 2. Time–temperature profile for the pyrolysis of pine wood and the wall of the reactor.
reproducibility and average values were calculated for each identified product. Gas chromatography (GC) analysis of gas products was performed on a gas chromatograph (7890A, Agilent Technologies, U.S.A.). A series of columns were used the chromatographic separation of chemical components in gas, which were J&W GS-GASPRO, Agilent Mol. sieve 5A, and Agilent Hayesep Q. The injector temperature was 200 °C, and a split ratio 20:1 was used. The GC oven temperature program was 3 min at 60 °C, and 15 °C/min to 250 °C. Hydrocarbons were analyzed by a flame ionization detector (FID), CO2 and CO were analyzed by a thermal conductivity detector (TCD1), and H2 was analyzed by TCD2. The concentration of gas (vol.%) was calculated according to Eq. (1):
V gas Sel:gas ¼ P 100% V gas
The elemental composition of the pine wood used in the experiments was 45.29% C, 6.24% H, 0.20% N, 0.01% S, and 48.26% O. The ash content of pine wood was 2.60%. The TG and differential thermal gravity (DTG) curves (Fig. 3) were obtained for the pine wood pyrogenation under N2 at the heating rate of 30 °C/min. From Fig. 3, the TG curve of the pine wood pyrogenation shows that thermal reaction occurred over a wide temperature range. The pine wood sample had a char yield of 24.50 wt.% at the ending temperature of 600 °C. From the DTG curve, there was a primary peak of
ð1Þ
Sel.gas – the concentration of gas (vol.%); Vgas – the volume of gas (L). The total yield of gas released (wt.%) was calculated according to Eq. (2):
Fig. 3. TG and DTG curves for pine wood at a heating rate of 30 °C/min.
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mass loss at the temperature of 375.5 °C, and the temperature range of mass loss was from 215 °C to 430 °C. Thus, the pyrolysis temperature of 500 °C was enough to make sufficient pyrogenation for the pine wood sample. The pore structure properties of the HZSM-5 catalyst sample were that the specific surface areas were 325 m2/g, and the pore volume was 0.22 cm3/g. Fig. 4 shows the NH3-TPD curve of the HZSM-5 catalyst used in this study. It can be seen that two obvious desorption peaks occur over the HZSM-5 zeolite. The one at 230 °C could be attributed to weak adsorption of NH3 on the bronsted acid site and NH3 association with Si-OH, and the other peak at 440 °C could be ascribed to a strong description of NH3 adsorbed on the acidic Si–OH–Al group [21–24].
Table 1 The product distribution obtained under various pyrolysis and upgrading temperatures using the HZSM-5 catalyst. Data are the average of results from three experiments, the experimental error is 62.0%.
Sample temp. (°C) Catalyst bed temp. (°C) Char (wt.%) Gas (wt.%) Oil (wt.%) Water content (wt.% in oil)
Without catalyst
HZSM-5
400 – 45.1 24.7 30.2 40.2
500 450 30.0 37.5 32.5 50.4
500 – 30.3 35.7 34.0 45.6
600 – 25.2 41.7 33.1 60.5
500 550 30.2 39.8 30.0 60.2
500 650 30.5 42.5 27.0 70.8
3.2. Pyrolysis and catalytic upgrading of pyrolytic vapors from pine wood Table 1 shows the product distribution obtained under various pyrolysis and upgrading temperatures using the HZSM-5 catalyst. When pyrogenation without catalyst, a higher temperature caused more char to be converted into gases via secondary decomposition reactions, but the bio-oil yield maintained more or less unchanged. Based on this result and TG result, the pyrolysis temperature was set at 500 °C during the catalytic upgrading experiments. When the HZSM-5 catalyst was loaded in the catalytic upgrading bed, the bio-oil yield reduced due to catalytic cracking, which lead to an increased gas yield and an increased water content in bio-oil. The water content in the bio-oil increased obviously to 70.8% on increasing the catalytic cracking temperature to 650 °C. As mentioned above in NH3-TPD results, the strong acid sites existed in HZSM-5, which showed excellent cracking performances. This resulted in the deoxygenation of oxygenates in the bio-oil, which contained carbonyl and carboxyl groups, indicating that the catalytic upgrading improved the bio-oil quality [3]. The main deoxygenation pathway of bio-oil is dehydration, which can be used as a basis for the evaluation of bio-oil produced from lignocellulosic biomass [25]. 3.3. Chemical composition of upgraded bio-oils The GC–MS results of the bio-oil obtained from pyrolysis and catalytic upgrading are shown in Fig. 5. More than 50 compounds in bio-oil were identified by GC–MS. Compared with non-catalytic pyrolysis, the composition of the bio-oil from catalytic upgrading
Fig. 4. NH3-TPD profile of HZSM-5 catalysts.
Fig. 5. The GC–MS results of the bio-oil obtained from pyrolysis and catalytic upgrading. A: non-catalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C.
was changed obviously. However, not all the experimental conditions could change the composition of bio-oil effectively. When the catalyst bed temperature was lower (e.g. 450 or 550 °C), the peak curves were similar with the non-catalysis’ curves. This outcome may be related to the temperature of catalytic cracking because a higher temperature provides more energy, which favors the break of bonds in large molecules of bio-oil. The compositions of the bio-oil obtained from pyrolysis and catalytic upgrading are shown in Table 2. In the raw bio-oil, acids, ketones, phenolics and D-allose were shown to be the main products, while the distribution of products resulting from catalytic cracking over HZSM-5 at 650 °C was different. The primary products of upgraded bio-oil were mono-phenols, and the peak area percentage was more than 30%. Aromatics, such as xylene and indene, were also observed. With the use of catalysts, acetic acid decreased from 33% for non-catalytic pyrolysis to 13.8%, while phenols and alkyl phenols increased from 5.8% for non-catalytic pyrolysis to 34.4%. D-allose was not detected in the upgraded bio-oil. In this study, mono-phenols (phenol and alkyl phenols, not including guaiacol derivatives) and aromatics were regarded as desirable chemicals, and oxygenates were chosen as the criteria
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B. Li et al. / Fuel 129 (2014) 61–67 Table 2 The compositions of the bio-oil obtained from pyrolysis and catalytic upgrading. R.T./min
Name
Raw bio-oil/Area%
Upgraded bio-oila/Area%
4.19 6.03 6.51 7.26 7.42 8.50 8.73 8.98 9.41 9.46 9.66 11.11 12.10 12.31 12.39 13.02 13.32 13.38 14.37 14.47 14.84 14.87 15.56 15.62 16.49 17.31 18.06 19.92 20.70
p-Xylene Furan, 2,5-diethoxytetrahydro2-Propanone, 1-hydroxy2-Cyclopenten-1-one 2-Cyclopenten-1-one, 2-methylAcetic acid Furfural Indene Furan, 2,4-dimethyl2-Cyclopenten-1-one, 3-methylPropanoic acid 2-Furanmethanol 1H-Indene, 1-methylene2(5H)-Furanone 1,2-Cyclopentanedione 2-Cyclopenten-1-one, 2-hydroxy-3-methylNaphthalene, 1-methylPhenol, 2-methoxyPhenol, 2-methoxy-4-methylNaphthalene, 2,6-dimethylPhenol, 2-methylPhenol Phenol, 2,5-dimethylPhenol, 4-methylPhenol, 3-ethylPhenol, 2,6-dimethoxyBenzoic acid, 4-hydroxy-3-methoxyVanillin
– – 7.05 1.35 – 33.07 2.95 – – 1.32 1.90 1.55 – 1.17 – 2.48 – 1.88 1.39 – 1.01 2.79 – 2.03 – 4.17 2.61 1.02 7.21
5.46 4.75 5.69 3.59 1.40 13.79 1.36 1.77 1.13 – 2.40 – 2.81 – 1.84 2.95 2.56 3.35 – 1.79 4.36 11.67 2.28 11.71 1.24 1.33 – – –
D-Allose
Compounds listed are those represented by more than 1% of the total peak area. a Upgrading temperature condition: 650 °C.
species to assess the degree of deoxygenation. Changes in the biooil composition as a result of catalytic upgrading are shown in Fig. 6. In general, catalytic upgrading resulted in a reduction of the oxygen content and an increase in the phenols and aromatics contents, which were high value-added. In this study, with the HZSM-5 catalyst, at the higher temperature (650 °C), the main oxygenate compounds, such as acids, alcohols, carbonyls and carbohydrates, were removed effectively, while it was not effective at lower temperatures. Oxygenates decreased from 71% for noncatalytic pyrolysis to 48%, while phenols and aromatics increased from 6% for non-catalytic pyrolysis to 41%. It is concluded that HZSM-5 catalyst with micropores and strong acid were the most effective for removing oxygenates and producing phenols and
Fig. 6. Main chemical compounds in bio-oils. A: non-catalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C.
aromatics. This agrees with the results of other researches [3,26]. The high value-added condensables could be used as high quality aromatic fuel additives or chemicals after a distillation or extraction process. 3.4. Gas products The composition of gas products obtained by pyrolysis and catalytic upgrading is shown in Table 3. And Fig. 7 shows the yield of gas released at different experimental conditions. Compared with bubbling fluidized beds and circulating fluidized beds, there are no inert gases in the gas products by the combined system of auger pyrolysis reactor and fixed-bed catalytic reactor. CO and CO2 were the main gas products both in non-catalytic and catalytic pyrolysis, which took up 75–90 volume percentages. The formation of CO and CO2 is another well known pathway of the deoxygenation of biooil. Another interesting result was that employing a catalyst considerably increased the concentration and yield of C2+ alkenes, as well as water and CO. This observation suggests that HZSM-5 contains Brønsted acid sites and is a system of two perpendicularly intersecting channels. The larger of the two channels has a near circular pore structure with dimensions of 0.54 0.56 nm2. The smaller channels have a geometry of 0.51 0.54 nm2. The intersection of these channels which contains the proposed active site is approximately a 0.9 nm cavity [27]. Several reactions occur inside the zeolite including dehydration, decarboxylation, isomerization and decarbonylation thereby removing oxygen as water, carbon monoxide and carbon dioxide and converting the carbon and hydrogen into olefins and aromatics [1,17]. In addition, alkanes and hydrogen increased when catalytic upgrading. This result indicated that in the present of catalysts, the bonds in the side chains of bio-oil molecules broken up and released more gas molecules. Therefore, it is considered that HZSM-5 catalyst was effectual to produce alkenes and alkanes, which improved the quality of pyrolysis gases.
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Table 3 The composition of gas products obtained by pyrolysis and catalytic upgrading. Pyrolysis temp. (°C)
Catalyst bed temp. (°C)
500 500 500 500
– 450 550 650
The concentration of gas (vol.%) CH4
C2 + alkane
C2 + alkene
C6H6
CO2
CO
H2
6.17 6.17 4.89 9.64
0.83 0.83 0.78 1.54
1.26 1.26 2.14 9.80
0.11 0.11 0.02 0.33
46.74 46.74 51.16 37.43
43.75 43.75 39.92 37.95
1.14 1.14 1.08 3.32
the Cooperation Project of China–European Union Founded by MOST of China-China (246772).
References
Fig. 7. The yield of gas released at different experimental conditions. A: noncatalysis, B: catalytic temp. 450 °C, C: catalytic temp. 550 °C, D: catalytic temp. 650 °C. Data are the average of results from three experiments, the experimental error is 62.0%.
4. Conclusions The general conclusion from this study is that the high value-added condensables and pyrolysis gases can be produced from biomass by a combined system of auger pyrolysis reactor and fixed-bed catalytic reactor. This means a significant development in the progress of continuous catalytic pyrolysis for the treatment of lignocellulosic biomass. The combined system can overcome the drawbacks of fluidized bed systems: No requirement of carrier gases and no mixing of solid biomass with the solid catalyst. HZSM-5 (Si/Al = 38) catalyst loaded in fixed-bed catalytic reactor shows high activity for biomass catalytic pyrolysis. Using HZSM-5 catalyst, the higher catalytic temperature (650 °C) is suitable for converting pine wood to phenols, aromatics and gaseous hydrocarbons. This work proves that the properties of bio-oil can be effectively improved and the oxygen content can be markedly reduced though continuous catalytic pyrolysis. The combined system of auger pyrolysis reactor and fixed-bed catalytic reactor used in this work must be viewed as a research prototype. Future work in this area will focus on two fields. The one is the efficiency analysis facing to the industry application. The other one is the stability and reaction–regeneration cycles of the catalysts.
Acknowledgements This research was sponsored by the National Natural Science Foundation of China-China (51106166), the National Science & Technology Pillar Program of China-China (2011BAD22B07), and
[1] French F, Czernik S. Catalytic pyrolysis of biomass for biofuels production. Fuel Process Technol 2010;91:125–32. [2] Adjaye JD, Bakhshi NN. Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part II: Comparative catalyst performance and reaction pathways. Fuel Process Technol 1995;45:185–202. [3] Park HJ, Park KH, Jeon JK, Kim J, Ryoo R, Jeong KE, et al. Production of phenolics and aromatics by pyrolysis of miscanthus. Fuel 2012;97:379–84. [4] Díaz E, Mohedano AF, Calvo L, Gilarranz MA, Casas JA, Rodríguez JJ, et al. Hydrogenation of phenol in aqueous phase with palladium on activated carbon catalysts. Chem Eng J 2007;131:65–71. [5] Fisk CA, Margan T, Ji Y, Crocker M, Crofcheck C, Lewis SA. Bio-oil upgrading over platinum catalysts using in situ generated hydrogen. Appl Catal A – Gen 2009;358:150–6. [6] Park HJ, Heo HS, Yim JH, Jeon JK, Ko YS, Kim SS, et al. Catalytic pyrolysis of Japanese larch using spent HZSM-5. Korean J Chem Eng 2010;27:73–5. [7] Carlson TR, Tompsett GA, Conner WC, Huber GW. Aromatic production from catalytic fast pyrolysis of biomass-derived feedstocks. Top Catal 2009;52: 241–52. [8] Chiaramonti D, Bonini M, Fratini E, Tondi G, Gartner K, Bridgwater AV, et al. Development of emulsions from biomass pyrolysis liquid and diesel and their use in engines Part 1: Emulsion production. Biomass Bioenergy 2003;25: 85–99. [9] Chiaramonti D, Bonini M, Fratini E, Tondi G, Gartner K, Bridgwater AV, et al. Development of emulsions from biomass pyrolysis liquid and diesel and their use in engines Part 2: Tests in diesel engines. Biomass Bioenergy 2003;25: 101–11. [10] Wang DN, Czernik S, Montané D, Mann M, Chornet E. Biomass to hydrogen via fast pyrolysis and catalytic steam reforming of the pyrolysis oil and its fractions. Ind Eng Chem Res 1997;36:1507–12. [11] Zhang Q, Chang J, Wang TJ, Xu Y. Upgrading bio-oil over different solid catalysts. Energy Fuels 2006;20:2714–7. [12] Butler E, Devlin G, Meier D, McDonnell K. A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading. Renew Sust Energy Rev 2011;15:4171–86. [13] Taarning E, Osmundsen CM, Yang X, Voss B, Andersen SI, Christensen CH. Zeolite-catalyzed biomass conversion to fuels and chemicals. Energy Environ Sci 2011;4:793–804. [14] Jae J, Tompsett GA, Foster AJ, Hammond KD, Auerbach SM, Lobo RF, et al. Investigation into the shape selectivity of zeolite catalysts for biomass conversion. J Catal 2011;279:257–68. [15] Lappas A, Iliopoulou E, Kalogiannis K. Catalysts in biomass pyrolysis. In: Crocker M, editor. Thermochemical conversion of biomass to liquid fuels and chemicals. RSC Publishing; 2010. p. 263–83. [16] Zhang HY, Xiao R, Jin BS, Shen DK, Chen R, Xiao GM. Catalytic fast pyrolysis of straw biomass in an internally interconnected fluidized bed to produce aromatics and olefins: Effect of different catalysts. Bioresour Technol 2013; 137:82–7. [17] Gayubo AG, Valle B, Aguayo AT, Olazar M, Bilbao J. Olefin Production by catalytic transformation of crude bio-oil in a two-step process. Ind Eng Chem Res 2010;49:123–31. [18] Zhang HY, Carlson TR, Xiao R, Huber GW. Catalytic fast pyrolysis of wood and alcohol mixtures in a fluidized bed reactor. Green Chem 2012;14:98–110. [19] Ingram L, Mohan D, Bricka M, Steele PH. Pyrolysis of wood and bark in an auger reactor physical properties and chemical analysis of the produced biooils. Energy Fuels 2008;22:614–25. [20] Liaw SS, Zhou S, Wu HW, Garcia-Perez M. Effect of pretreatment temperature on the yield and properties of bio-oils obtained from the auger pyrolysis of Douglas fir wood. Fuel 2013;213:672–82. [21] Hunger B, Hoffmann J, Heitzsch O, Hunger M. Temperature-programmed desorption (TPD) of ammonia from HZSM-5 zeolites. J Therm Anal 1990;36: 1379–91. [22] Chao KJ, Chiou BH, Cho CC, Jeng SY. Temperature-programmed desorption studies on ZSM-5 zeolites. Zeolites 1984;4:2–4.
B. Li et al. / Fuel 129 (2014) 61–67 [23] Lobree LJ, Hwang IC, Reimer JA, Bell AT. Investigations of the state of Fe in HZSM-5. J Catal 1999;186:242–53. [24] Jiang T, Zhang Q, Wang TG, Zhang Q, Ma LL. High yield of pentane production by aqueous-phase reforming of xylitol over Ni/HZSM-5 and Ni/MCM22 catalysts. Energy Convers Manage 2012;59:58–65. [25] Park HJ, Heo HS, Jeon JK, Kim JN, Ryoo R, Jeong KE, et al. Highly valuable chemicals production from catalytic upgrading of radiata pine sawdustderived pyrolytic vapors over mesoporous MFI zeolites. Appl Catal B – Environ 2010; 95:365–73.
67
[26] Li XY, Su L, Wang YJ, Yu YQ, Wang CW, Li XL, et al. Catalytic fast pyrolysis of Kraft lignin with HZSM-5 zeolite for producing aromatic hydrocarbons. Front Environ Sci Eng 2012;6:295–303. [27] Carlson TR, Tompsett GA, Conner WC, Huber GW. Aromatic production from catalytic fast pyrolysis of biomass-derived feedstocks. Top Catal 2009;52: 241–52.