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Characteristics of rice husk tar pyrolysis by external flue gas
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 5 ) 1 e8
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Characteristics of rice husk tar pyrolysis by external flue gas Ming Zhai*, Xinyu Wang, Yu Zhang, Peng Dong, Guoli Qi School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China
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abstract
Article history:
Biomass tar is a major problem in both pyrolysis and gasification of biomass. Considering
Received 5 June 2015
the process and conditions of tar formation, an external flue gas pyrolysis system for rice
Received in revised form
husk tar pyrolysis was designed. The characteristics of rice husk tar pyrolysis by external
9 July 2015
flue gas were investigated. The GCeMS analysis was applied to analyze the composition of
Accepted 11 July 2015
rice husk tar and its distillate. TGA was carried out to investigate the properties of rice husk
Available online xxx
tar and its distillate. Results show that when the temperature is below 500 C, the liquid product of rice husk pyrolysis is rice husk oil; when the temperature reaches about 700 C,
Keywords:
PAHs increase significantly and the liquid product is tar; when the temperature reaches
Biomass pyrolysis
800 C, a large amount of charcoal liquid is produced. There are many similarities between
Rice husk oil
rice husk tar and its distillate. After distillation, the content of the primary compounds like
Rice husk tar
naphthalene, anthracene, phenol and its derivative increases, while the content of fluo-
Tar distillate
rene and phenanthrene decreases. Temperature plays an active role in the pyrolysis of rice
External flue gas
husk oil and tar, and the proportion of compounds in the pyrolysis product. The weight
Tar cracking
loss of rice husk tar distillate can be divided into three regions, and it reaches a maximum at about 160 C. The experimental data provide a reference to the optimization of the operating conditions for rice husk pyrolysis and tar cracking. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Biomass pyrolysis is an extremely complex process. The essence of pyrolysis phenomenon is a series of complex chemical reactions including organic macromolecules cracking successively and forming volatile matter and solid product at specific temperatures. The pyrolysis of biomass can be regarded as a linear superposition of the pyrolysis of cellulose, hemicelluloses and lignin [1]. Cellulose and hemicelluloses mainly produce volatile substance [2]. Lignin can be cracked into char, tar, wood vinegar and gaseous product. The
product yield depends on several factors, such as chemical composition, heating rate, the final temperature of the reaction and the structure of the reactor [3]. Biomass tar is a complex mixture of all organic contaminants that are produced by the process of pyrolysis and gasification [4]. Tar can potentially condense as liquid or solid at operation condition of vaporizer, gas transmission pipeline and gas generator. There are different definitions on the tar, but it is usually believed that the tar is mainly composed of large molecular aromatic hydrocarbon material. The most appropriate one is defined by Milne et al.: The organics, produced under thermal or partial oxidation regimes of any
* Corresponding author. Tel.: þ86 18646218082. E-mail address: [email protected] (M. Zhai). http://dx.doi.org/10.1016/j.ijhydene.2015.07.045 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Zhai M, et al., Characteristics of rice husk tar pyrolysis by external flue gas, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.07.045
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organic material, are called tar [5]. Under the thermal regime of biomass, the amount of tar produced is mainly determined by temperature. For common biomass, the amount of tar produced reaches a maximum at around 500 C while it declines as temperature increase or decrease. There are thousands of compounds in biomass tar, and more than 100 have been analyzed, but it is still hard to analyze all of them. The composition of tar produced varies with types of biomass. Besides, limited by analytical instruments and analytical methods, there are different results, but it can be confirmed that the primary compounds are no less than 20, most of which are derivatives of benzene and PAHs [6]. Biomass tar is a major problem in both pyrolysis and gasification of biomass. It is a high viscous liquid condensed that blocks and contaminates the pipelines. Hence, tar is strongly undesirable. Tar composition and amount depend on several factors, such as the fuel properties, the operating conditions (temperature, pressure, residence time), the type of gasifier, the gasification agents, the use of catalysts, and the method of tar sampling and analysis. Tar removal technologies include treatment inside the reactor and gas cleaning after the reactor [7]. Several methods are well known, such as physical treatment, thermal cracking, plasma cracking, and catalytic reforming [8,9]. These include modification of operating conditions such as temperature [1011], pressure [12], gasification agents [13], residence time [14], design of the gasifier [15], secondary oxidization [16] and addition of catalysts [11, 17]. Postgasification tar reduction usually employs washing, but this process contaminates water heavily. The preferred option for tar reduction is through process control in the gasifier and the use of additives and catalysts to modify operation conditions [18]. Three groups of catalysts are reported: natural catalysts, alkali-based catalysts and metal-based catalysts [19]. In general, produced gas with low tar content can be obtained at hightemperature. Primary tars are formed during the early stages of biomass pyrolysis inside the particles at temperatures between 200 and 300 C [20]. As temperature increases the total tar content gradually decreases [21] due to tar cracking and steam reforming [22]. Therefore, high-temperature thermal cracking is considered as the most promising one for tar reduction in large-scale applications due to its fast reaction rate, and high reliability [2325]. However, it may have a negative impact on the heating value of the produced gas as a result of increasing the temperature by means of more combustion [26]. Conventional biomass pyrolysis and gasification reactors like fix-bed reactors and fluidize beds use the flue gas and heat produced by partial combustion of the biomass itself for pyrolysis and gasification. Since the heating value of biomass is low, the temperature of the flue gas produced is fairly low. Therefore, the tar content in the product gas is considerably high. To reduce the tar content, we proposed a scheme that uses an external burner to produce high-temperature anaerobic flue gas and heat by combustion of part of the produced gas for pyrolysis and gasification. The pyrolysis and gasification were separated in the reactor, and the heat self-sustain was achieved by using 15.4%e20.5% of the total produced gas for combustion [27]. Although the produced gas was diluted by the flue gas, more tar content converted to non-condensable hydrocarbons, and the heating value of the gas may not be affected much. To verify the scheme experimentally, it is necessary to conduct an
in-depth study on the characteristics of biomass tar pyrolysis and the physicochemical properties of the tar. Considering the process and conditions of tar formation, an external flue gas pyrolysis system for rice husk tar pyrolysis was designed. The characteristics of rice husk tar pyrolysis by external high-temperature anaerobic flue gas and heat such as yield of pyrolysis products, composition of the liquid product, and properties of rice husk tar were investigated. Propane was used as the fuel in combustion for producing external flue gas because it was easy to control the composition and the temperature of the flue gas, but it could be replaced by produced gas from pyrolysis and gasification. The aim of this study is to provide the experimental data of the yield of the rice husk pyrolysis products, composition of the tar and the properties of the tar for the reference to the optimization of the operating conditions.
Material and methods Rice husk is selected as the material for pyrolysis. The Proximate and ultimate analysis of rice husk is shown in Table 1. The external flue gas is illustrated in Fig. 1 which mainly consists of an external burner, a fix-bed reactor for pyrolysis, and a condenser. Considering high-temperature flame was generated in the burner, stainless steel mesh was wired on the inner wall, and refractory concrete and construction aggregate were applied inside. Thermal insulation material was covered outside the burner. Propane and supplied in the burner was tangential. An observation window was set on the end face of the burner for observing the ignition and burning condition. The fix-bed reactor was for rice husk pyrolysis. Stainless steel featured by refractory concrete was installed on its inner wall. Rice husk was fed to the grid plate initially, and valve 17 was open and valve 16 was closed. Propane and air sufficiently combusted in the burner. The flue gas analyzer was used to measure the oxygen content of the flue gas and adjust the proportion of propane and air to ensure there was no extra oxygen in the flue gas. When the temperature at the exit of the burner was stable, valve 16 was opened and valve 17 was closed so that the high-temperature flue gas produced from the burner entered the fix-bed reactor for the pyrolysis of rice husk. Then, the mixture of volatile matter and high-temperature flue gas entered into the condenser. The condensed tar flew into the deposition tank, and the non-condensable gas was discharged. The tar condensed in the condensing tube of the condenser was dissolved by acetone solution and collected and calculated to determine the total mass of the tar condensed. The operating condition is shown in Table 2. The GCeMS analysis was applied to analyze the composition of rice husk tar and its distillate. TGA was carried out to investigate the properties of rice husk tar and its distillate.
Results and discussion Yield of pyrolysis products Fig. 2 shows the yield of the pyrolysis products. The gas yield varies little as the temperature increases below 500 C. When
Please cite this article in press as: Zhai M, et al., Characteristics of rice husk tar pyrolysis by external flue gas, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.07.045
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Table 1 e Proximate and ultimate analysis of rice husk. Moistureada (%) Volatilead (%) Ashad (%) Fixed Carbonad (%) Cdafb (%) Hdaf (%) Odaf (%) Ndaf (%) Sdaf (%) Qnet,dc (kJ/kg) 5.08 a b c
63.05
14.98
16.89
46.18
6.08
45.02
2.62
0.10
14,556
ad: air-dry basis. daf: dry, ash free basis. d: dry basis.
Fig. 1 e External flue gas pyrolysis system. the temperature exceeds 500 C, the gas yield rises rapidly with temperature because rice husk oil converts to the noncondensable gas after pyrolysis. Above 800 C, the gas yield slows down significantly, but it is still on the rise as few tar cracks into non-condensable gas. The solid product decreases with the increase of temperature and reaches a certain value above 800 C. It is because volatile matter completely precipitates out at this temperature. The value of residue solid carbon also reaches a certain value. Therefore, the solid product will finally reach close to the value of fixed carbon plus ash. With the increase of temperature, the liquid product experiences a process from increasing to decreasing. The liquid product increases significantly when the temperature is from 400 to 500 C, as such temperature range is most suitable for the generation of rice husk oil. Above that temperature range, with the increase of temperature, the yield of liquid product declines. Especially above 650 C, the output yield declines significantly. It is because the organic matter of rice husk converts into light hydrocarbons. It declines sharply above 800 C, as the generation of macromolecule tar has
resulted in that the liquid product is hard to cracks into noncondensable gas.
Composition of the liquid product The recognizable compounds and their contents (the ones greater than 1% are selected) at different temperatures are shown in Tables 3e7. In Table 3, the maximum contents of the recognizable compounds are furans and acids. The liquid
Table 2 e Operating conditions of the system. Feeding amount Exit temperature of the burner Exit temperature of tar condenser Reaction temperature of fix-bed reactor
1.5e2.0 kg 400e1300 C 30e40 C 400e800 C
Fig. 2 e The yield of the pyrolysis products.
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Table 3 e The recognizable compounds in the liquid product at 400 C. No.
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
1 2 3 4 5 6 7 8 9 10 11
3.616 4.812 5.600 5.721 6.183 6.515 6.679 7.472 8.592 8.635 9.285
C2H4O2 C10H8O C9H12O2 C5H8O C6H6O C7H16O C6H8O C5H12O C5H10O2 C8H16O C6H10O3
60 122 152 84 94 116 152 88 102 128 130
2.151 9.697 1.392 1.700 1.297 1.477 8.898 2.108 3.795 1.191 2.151
12 13 14 15
9.444 10.043 10.244 11.659
Acetic acid 4-ethyl-phenol 4-ethyl-2-methoxy-phenol 1-acrolein Phenol 1-propoxy-butane 2,5-dimethyl-furan 2,2-dimethyl-1-propyl alcohol Valeric acid 3,3-dimethyl-cyclohexanol 1-hydroxymethyl-1-methyl ester cyclopropane carbonic acid Valine hexanoic acid 1-butyl-dihydro-2(3H)-furanone Dodecenoic acid
C5H9NO2 C6H12O2 C8H14O2 C12H22O2
117 116 142 198
1.186 2.987 3.804 1.877
product at this temperature can be considered as rice husk oil. It is also defined as wood vinegar, which proves that rice husk only produce biomass oil at low temperatures. In Table 4, the recognizable compounds are still organic matter with low molecular weight. Compared with Table 3, furans organic matter has larger relative content while acids decrease significantly due to acids converting to alkanes as the increase of temperature. In general, there is no obvious difference in the liquid components when the temperature is below 500 C and the liquid product belongs to biomass oil. In Table 5, naphthalene and biphenyl appear in the recognizable compounds, indicating that with the increase of temperature, the conversion gradually starts to change. However, the phenols are still regarded as the primary compounds. In Table 6, the product featured with tar property, such as fluorene, phenanthrene, and anthracene start to appear in the recognizable compounds. The relative content of naphthalene increases remarkably. Therefore, with the rise of temperature, the rice husk oil will gradually be replaced by rice husk tar. In Table 7, such PAHs as dibenzofuran, fluoranthene, and pyrene begin to appear in the recognizable compounds. The content of phenol further decreases, while charcoal liquid compounds, like metoxyphenol and eugenol, increase significantly. These compounds are difficult to crack unless the higher temperature and longer residence time are provided for cracking. On the whole, when the temperature is below 500 C, the liquid product is biomass oil, and its essential components are organic acid, furan, and low molecular weight aromatic compounds. With the increase of temperature, thermal cracking occurs. The molecular weight of each component increases significantly, and a tiny amount of naphthalene and fluorene is produced at 600 C. When the temperature reaches 700 C, PAHs like naphthalene, fluorene, phenanthrene, anthracene, and fluoranthene increase significantly, while organics containing oxygen decreases to some extent. When the temperature reaches 800 C, a large amount of charcoal liquid is produced. Fig. 3 displays the variation of the number of compounds in the liquid product. From 400 C to 600 C, with the increase of temperature, the number of compounds in liquid decreases gradually from 246 to 204. When the temperature is higher
than 600 C, the number of compounds in liquid product declines sharply from 204 to 94, indicating that temperature plays an active role in the pyrolysis of rice husk oil and tar. It also proves that temperature will also significantly influence the proportion of compounds in pyrolysis product.
Properties of rice husk tar The rice husk tar produced at 800 C was selected for analysis. Table 8 is the elemental composition of rice husk tar and Table 9 is the properties of the distillate of rice husk tar.
Composition of rice husk tar distillate Acetone was used to dissolve the rice husk tar, and sodium sulfate anhydrous was used to remove its moisture. The tar distillate was obtained by distillation. Moreover, sodium sulfate anhydrous was used to remove its moisture. The compounds that are recognizable in the tar distillate and the relative content are shown in Table 10. Compared with Tables 7e10, tar distillate and tar have many similarities in composition, such as naphthalene, phenol and their derivatives, phenanthrene, anthracene, fluorine, were detected in both tar and tar distillate. More specifically, in the distillate, the content of naphthalene, anthracene, phenol and their derivatives increases, while the content of fluorine and phenanthrene decreases. The growing content of phenol and its derivatives is because the ringeopening reaction occurs between naphthalene and anthracene, which combine other free radical to form phenol and its derivatives. The decreasing content of fluorine and phenanthrene is because they are cracked into naphthalene and anthracene. The increasing content of naphthalene and anthracene is because the crack of naphthalene and anthracene is lower than production. Further, the number of compounds in the tar and that in the distillate increase from 45 to 147. The reason is the increasing species of free radical contribute to producing more compounds.
TGA for rice husk tar and its distillate Fig. 4 shows the TG and DTG curves of the tar vary with the different heating rate at N2 atmosphere. With the increase
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Table 4 e The recognizable compounds in the liquid product at 500 C. No. 1 2 3 4 5 6 7 8 9
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
5.311 7.398 8.292 9.531 10.257 11.157 11.369 11.397 12.947
1-hydroxy-2-butene 2,5-dimethyl furan Propanoic acid Phenol 4-methylphenol 5-methylfufural 2,5-dimethyl-phenol 4-ethyl-phenol 4,5-dimethyl-resorcinol
C4H8O2 C6H8O C3H6O2 C6H6O C7H8O C6H6O2 C8H10O C8H10O C8H10O2
88 96 74 94 108 110 122 122 138
5.215 11.417 1.249 4.652 1.017 3.391 3.633 1.787 2.647
Table 5 e The recognizable compounds in the liquid product at 600 C. No. 1 2 3 4 5 6 7 8 9 10
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
6.126 8.525 9.567 10.992 11.835 12.092 12.789 13.110 13.147 14.932
Acetol cyclopentane 2-methyl-1,3-pentanedione Naphthalene 4-ethyl-2-methoxy-phenol 4-ethyl-phenol Eugenol Diphenyl Biphenyl 2-methoxy-4-(1-propenyl)-(E)-phenol Fluorene
C7H12 C6H8O2 C10H8 C9H12O2 C8H10O C10H12O2 C12H10 C12H8 C10H12O C13H10
96 112 128 152 122 164 154 152 164 168
3.603 1.048 2.235 1.102 2.156 1.246 1.645 1.847 1.490 3.603
of heating rate, TG curves shift to the higher temperature side below 360 C and shift to the lower temperature side above 415 C. The reason is the rice husk tar generates a kind of material that is difficult to pyrolyze from 360 C to 415 C. Moreover, the content of such material increases with the decline of heating rate. Such material accumulates gradually, as it is difficult to be cracked. The phenomenon is shown in DTG curves when the temperature reaches 415 C.
The weight-loss of the tar with high heating rate at the same temperature is still higher than that of the tar with low heating rate, or the DTG curve with high heating rate is above that with low heating rate. The materials detected are naphthalene and its derivatives. The difference is small in TG and DTG curves with different heating rates, indicating that heating rates influence the cracking of the tar little.
Table 6 e The recognizable compounds in the liquid product at 700 C. No. Retention time (min) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
9.297 9.554 9.698 10.101 10.964 11.190 11.467 12.057 13.271 14.121 14.695 14.922 16.231 16.435 17.144 17.246 18.460 18.873 18.961 19.066 19.948 20.446 20.501
Name 4-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 2,3-dihydrobenzofuran 4-ethyl-2-methoxy-phenol 1-methyl-naphthalene 2-methoxy-4-vinyl-phenol Eugenol 2-methoxy-4-(1-propenyl)-(Z)phenol Dibenzofuran 3-tert-butyl-4-hydroxyl Fluorene 2,6-dimethoxy-4-(2-propenyl)-phenol 1-butyl-2-ethylbutane Phenanthrene Anthracene 4-cyclopentane-2,4,6-trienephenol n-hexadecanoic 3-isopropyl-4-methyl-12-1-en-4-alcohol 2-phenl-naphthalene Fluoranthene Pyrene Benzo[b]naphtha[1,2-d]furan
Molecular formula Molecular weight Relative content (%) C8H10O C10H8 C9H12O3 C8H8O C9H12O2 C11H10 C9H10O2 C10H12O2 C10H12O2 C12H8O C14H21NO3 C13H10 C22H26O6 C10H20 C14H10 C14H10 C14H12O2 C16H32O2 C14H28O C16H12 C16H10 C16H10 C16H10O
122 128 168 120 152 142 150 164 164 168 251 166 386 140 178 178 212 256 212 204 202 202 218
1.609 2.292 1.031 1.412 1.614 2.344 1.331 1.370 5.638 1.219 1.059 1.193 1.317 1.825 2.530 1.149 1.324 2.722 1.003 1.140 1.267 1.414 1.183
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Table 7 e The recognizable compounds in the liquid product at 800 C. No.
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
9.298 9.556 9.702 10.103 10.965 11.191 11.467 12.057 13.269 14.122 14.922 16.231 16.436 17.144 18.461 18.874 19.948 20.449 20.502 24.951
4-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 2,3-dihydrobenzenofuran 4-ethyl-2-methoxy-phenol 2-methyl-naphthalene 2-methoxy-4-vinyl-phenol 2-methoxy-3-(2-propenyl)-phenol 2-methoxy-4-(1-propenyl)-(E)-phenol Dibenzofuran Fluorene 2,6-dimethoxy-4-(2-propenyl)-dimethoxyphenol 1,1,2-trimethyl cycloundecane Phenanthrene Methyl palmitate n-hexadecanoic acid Fluoranthene Fyrene 4-(p-N,N-Dimethylaminoimine)-(Z)-2-amyl alcohol 2-(3,4-dimethoxy)-7-hydroxyl-4H-1-pyran-4-1
C8H10O C10H8 C9H12O3 C8H8O C9H12O2 C11H10 C9H10O2 C10H12O C10H12O C12H8O C13H10 C22H26O6 C14H28 C14H10 C17H34O2 C16H32O2 C16H10 C16H10 C13H18N2O C20H18O9
122 128 168 120 152 142 150 164 164 168 166 386 196 178 270 256 202 202 218 402
2.102 2.030 1.059 1.592 1.767 2.391 1.378 1.239 6.181 1.227 1.233 1.227 1.372 2.677 1.801 2.915 1.166 1.419 1.320 1.026
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Fig. 5 shows the TG and DTG curves of the tar distillate. The weight loss of rice husk tar distillate can be divided into three regions. In the first region, moisture in tar evaporates, so there is a massive weight loss below 105 C. However, some weight loss has already existed below 100 C, indicating that there is light distillate. The second region is from 105 C to 240 C. Most thermal weight loss occurs in this region. The weight loss reaches a maximum at about 160 C. The third region is from 240 C to the final temperature, indicating the residue of the distillate cannot be further cracked.
Conclusions
Fig. 3 e Variation of the number of compounds in the liquid product.
Table 8 e Elemental composition of rice husk tar. Moisture (wt.%) Ash (wt.%) C (wt.%) H (wt.%) Oa (wt.%) 16.5 a
0.06
33.21
6.09
44.14
By difference.
Table 9 e Properties of rice husk tar distillate. Density Viscosity PH value Flash Fire point HHV at 20 C at 20 C point ( C) (MJ/kg) ( C) (g ml1) (mm2 s1) 1.031
120
4.4
49
54
17.10
(1) The liquid product of rice husk pyrolysis increases significantly when the temperature is from 400 to 500 C. Above that range, it declines, and especially above 800 C, the liquid product is hard to be convert into non-condensable gas. (2) When the temperature is below 500 C, the liquid product of rice husk pyrolysis is rice husk oil. When the temperature reaches about 700 C, PAHs increase significantly and the liquid product is tar. When the temperature reaches 800 C, a large amount of charcoal liquid is produced. (3) There are many similarities between tar and its distillate. After distillation, the content of the primary compounds like naphthalene, anthracene, phenol and its derivative increases, while the content of fluorene and phenanthrene decreases. (4) Temperature plays an active role in the pyrolysis of rice husk oil and tar, and the proportion of compounds in the pyrolysis product. (5) The weight loss of rice husk tar distillate can be divided into three regions. The weight loss reaches a maximum at about 160 C.
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Table 10 e The recognizable compounds of rice husk tar distillate. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
4.267 5.294 5.421 5.902 6.076 6.223 6.269 6.569 6.729 6.868 6.992 7.072 7.343 7.408 7.502 7.745 7.868 8.052 8.285 8.827
Phenol 4-methyl-phenol 2-methoxy-phenol 2, 4-dimethyl-phenol 3-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 1-ethyl-4-methoxy-benzene 2, 6-dimethyl anisole 4-ethyl-2-methoxy-phenol 1-methylnaphthalene 2, 3-dihydro-3, 3-dimethyl-1H-indene N,N,N0 ,N0 -tetramethyl-1,4-phenylenediamine 2-vinyl-naphthalene 2-methoxy-4-propyl-phenol 2, 6-dimethyl-naphthalene 3- methoxy-4-(1-propenyl)-, (E)-phenol Pentadecane Dibenzofuran 4-methyl-dibenzofuran
C6H6O C7H8O C7H8O2 C8H10O C8H10O C10H8 C9H12O3 C9H12O C9H12O C9H12O C11H10 C9H8O C20H36N2 C12H10 C10H12O2 C12H22O2 C10H12O2 C15H32 C12H8O C13H10O
94 108 124 122 122 128 168 136 136 136 142 132 304 154 164 188 164 212 168 182
2.147 2.686 2.198 1.679 3.181 2.392 1.708 1.792 2.770 2.134 1.719 1.574 1.571 2.073 1.792 1.958 1.877 2.098 1.810 2.085
references
Fig. 4 e TG and DTG curves of the tar vary with different heating rate.
Fig. 5 e TG and DTG curves of the tar distillate.
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Characteristics of rice husk tar pyrolysis by external flue gas Ming Zhai*, Xinyu Wang, Yu Zhang, Peng Dong, Guoli Qi School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China
article info
abstract
Article history:
Biomass tar is a major problem in both pyrolysis and gasification of biomass. Considering
Received 5 June 2015
the process and conditions of tar formation, an external flue gas pyrolysis system for rice
Received in revised form
husk tar pyrolysis was designed. The characteristics of rice husk tar pyrolysis by external
9 July 2015
flue gas were investigated. The GCeMS analysis was applied to analyze the composition of
Accepted 11 July 2015
rice husk tar and its distillate. TGA was carried out to investigate the properties of rice husk
Available online xxx
tar and its distillate. Results show that when the temperature is below 500 C, the liquid product of rice husk pyrolysis is rice husk oil; when the temperature reaches about 700 C,
Keywords:
PAHs increase significantly and the liquid product is tar; when the temperature reaches
Biomass pyrolysis
800 C, a large amount of charcoal liquid is produced. There are many similarities between
Rice husk oil
rice husk tar and its distillate. After distillation, the content of the primary compounds like
Rice husk tar
naphthalene, anthracene, phenol and its derivative increases, while the content of fluo-
Tar distillate
rene and phenanthrene decreases. Temperature plays an active role in the pyrolysis of rice
External flue gas
husk oil and tar, and the proportion of compounds in the pyrolysis product. The weight
Tar cracking
loss of rice husk tar distillate can be divided into three regions, and it reaches a maximum at about 160 C. The experimental data provide a reference to the optimization of the operating conditions for rice husk pyrolysis and tar cracking. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Biomass pyrolysis is an extremely complex process. The essence of pyrolysis phenomenon is a series of complex chemical reactions including organic macromolecules cracking successively and forming volatile matter and solid product at specific temperatures. The pyrolysis of biomass can be regarded as a linear superposition of the pyrolysis of cellulose, hemicelluloses and lignin [1]. Cellulose and hemicelluloses mainly produce volatile substance [2]. Lignin can be cracked into char, tar, wood vinegar and gaseous product. The
product yield depends on several factors, such as chemical composition, heating rate, the final temperature of the reaction and the structure of the reactor [3]. Biomass tar is a complex mixture of all organic contaminants that are produced by the process of pyrolysis and gasification [4]. Tar can potentially condense as liquid or solid at operation condition of vaporizer, gas transmission pipeline and gas generator. There are different definitions on the tar, but it is usually believed that the tar is mainly composed of large molecular aromatic hydrocarbon material. The most appropriate one is defined by Milne et al.: The organics, produced under thermal or partial oxidation regimes of any
* Corresponding author. Tel.: þ86 18646218082. E-mail address: [email protected] (M. Zhai). http://dx.doi.org/10.1016/j.ijhydene.2015.07.045 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Zhai M, et al., Characteristics of rice husk tar pyrolysis by external flue gas, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.07.045
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organic material, are called tar [5]. Under the thermal regime of biomass, the amount of tar produced is mainly determined by temperature. For common biomass, the amount of tar produced reaches a maximum at around 500 C while it declines as temperature increase or decrease. There are thousands of compounds in biomass tar, and more than 100 have been analyzed, but it is still hard to analyze all of them. The composition of tar produced varies with types of biomass. Besides, limited by analytical instruments and analytical methods, there are different results, but it can be confirmed that the primary compounds are no less than 20, most of which are derivatives of benzene and PAHs [6]. Biomass tar is a major problem in both pyrolysis and gasification of biomass. It is a high viscous liquid condensed that blocks and contaminates the pipelines. Hence, tar is strongly undesirable. Tar composition and amount depend on several factors, such as the fuel properties, the operating conditions (temperature, pressure, residence time), the type of gasifier, the gasification agents, the use of catalysts, and the method of tar sampling and analysis. Tar removal technologies include treatment inside the reactor and gas cleaning after the reactor [7]. Several methods are well known, such as physical treatment, thermal cracking, plasma cracking, and catalytic reforming [8,9]. These include modification of operating conditions such as temperature [1011], pressure [12], gasification agents [13], residence time [14], design of the gasifier [15], secondary oxidization [16] and addition of catalysts [11, 17]. Postgasification tar reduction usually employs washing, but this process contaminates water heavily. The preferred option for tar reduction is through process control in the gasifier and the use of additives and catalysts to modify operation conditions [18]. Three groups of catalysts are reported: natural catalysts, alkali-based catalysts and metal-based catalysts [19]. In general, produced gas with low tar content can be obtained at hightemperature. Primary tars are formed during the early stages of biomass pyrolysis inside the particles at temperatures between 200 and 300 C [20]. As temperature increases the total tar content gradually decreases [21] due to tar cracking and steam reforming [22]. Therefore, high-temperature thermal cracking is considered as the most promising one for tar reduction in large-scale applications due to its fast reaction rate, and high reliability [2325]. However, it may have a negative impact on the heating value of the produced gas as a result of increasing the temperature by means of more combustion [26]. Conventional biomass pyrolysis and gasification reactors like fix-bed reactors and fluidize beds use the flue gas and heat produced by partial combustion of the biomass itself for pyrolysis and gasification. Since the heating value of biomass is low, the temperature of the flue gas produced is fairly low. Therefore, the tar content in the product gas is considerably high. To reduce the tar content, we proposed a scheme that uses an external burner to produce high-temperature anaerobic flue gas and heat by combustion of part of the produced gas for pyrolysis and gasification. The pyrolysis and gasification were separated in the reactor, and the heat self-sustain was achieved by using 15.4%e20.5% of the total produced gas for combustion [27]. Although the produced gas was diluted by the flue gas, more tar content converted to non-condensable hydrocarbons, and the heating value of the gas may not be affected much. To verify the scheme experimentally, it is necessary to conduct an
in-depth study on the characteristics of biomass tar pyrolysis and the physicochemical properties of the tar. Considering the process and conditions of tar formation, an external flue gas pyrolysis system for rice husk tar pyrolysis was designed. The characteristics of rice husk tar pyrolysis by external high-temperature anaerobic flue gas and heat such as yield of pyrolysis products, composition of the liquid product, and properties of rice husk tar were investigated. Propane was used as the fuel in combustion for producing external flue gas because it was easy to control the composition and the temperature of the flue gas, but it could be replaced by produced gas from pyrolysis and gasification. The aim of this study is to provide the experimental data of the yield of the rice husk pyrolysis products, composition of the tar and the properties of the tar for the reference to the optimization of the operating conditions.
Material and methods Rice husk is selected as the material for pyrolysis. The Proximate and ultimate analysis of rice husk is shown in Table 1. The external flue gas is illustrated in Fig. 1 which mainly consists of an external burner, a fix-bed reactor for pyrolysis, and a condenser. Considering high-temperature flame was generated in the burner, stainless steel mesh was wired on the inner wall, and refractory concrete and construction aggregate were applied inside. Thermal insulation material was covered outside the burner. Propane and supplied in the burner was tangential. An observation window was set on the end face of the burner for observing the ignition and burning condition. The fix-bed reactor was for rice husk pyrolysis. Stainless steel featured by refractory concrete was installed on its inner wall. Rice husk was fed to the grid plate initially, and valve 17 was open and valve 16 was closed. Propane and air sufficiently combusted in the burner. The flue gas analyzer was used to measure the oxygen content of the flue gas and adjust the proportion of propane and air to ensure there was no extra oxygen in the flue gas. When the temperature at the exit of the burner was stable, valve 16 was opened and valve 17 was closed so that the high-temperature flue gas produced from the burner entered the fix-bed reactor for the pyrolysis of rice husk. Then, the mixture of volatile matter and high-temperature flue gas entered into the condenser. The condensed tar flew into the deposition tank, and the non-condensable gas was discharged. The tar condensed in the condensing tube of the condenser was dissolved by acetone solution and collected and calculated to determine the total mass of the tar condensed. The operating condition is shown in Table 2. The GCeMS analysis was applied to analyze the composition of rice husk tar and its distillate. TGA was carried out to investigate the properties of rice husk tar and its distillate.
Results and discussion Yield of pyrolysis products Fig. 2 shows the yield of the pyrolysis products. The gas yield varies little as the temperature increases below 500 C. When
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Table 1 e Proximate and ultimate analysis of rice husk. Moistureada (%) Volatilead (%) Ashad (%) Fixed Carbonad (%) Cdafb (%) Hdaf (%) Odaf (%) Ndaf (%) Sdaf (%) Qnet,dc (kJ/kg) 5.08 a b c
63.05
14.98
16.89
46.18
6.08
45.02
2.62
0.10
14,556
ad: air-dry basis. daf: dry, ash free basis. d: dry basis.
Fig. 1 e External flue gas pyrolysis system. the temperature exceeds 500 C, the gas yield rises rapidly with temperature because rice husk oil converts to the noncondensable gas after pyrolysis. Above 800 C, the gas yield slows down significantly, but it is still on the rise as few tar cracks into non-condensable gas. The solid product decreases with the increase of temperature and reaches a certain value above 800 C. It is because volatile matter completely precipitates out at this temperature. The value of residue solid carbon also reaches a certain value. Therefore, the solid product will finally reach close to the value of fixed carbon plus ash. With the increase of temperature, the liquid product experiences a process from increasing to decreasing. The liquid product increases significantly when the temperature is from 400 to 500 C, as such temperature range is most suitable for the generation of rice husk oil. Above that temperature range, with the increase of temperature, the yield of liquid product declines. Especially above 650 C, the output yield declines significantly. It is because the organic matter of rice husk converts into light hydrocarbons. It declines sharply above 800 C, as the generation of macromolecule tar has
resulted in that the liquid product is hard to cracks into noncondensable gas.
Composition of the liquid product The recognizable compounds and their contents (the ones greater than 1% are selected) at different temperatures are shown in Tables 3e7. In Table 3, the maximum contents of the recognizable compounds are furans and acids. The liquid
Table 2 e Operating conditions of the system. Feeding amount Exit temperature of the burner Exit temperature of tar condenser Reaction temperature of fix-bed reactor
1.5e2.0 kg 400e1300 C 30e40 C 400e800 C
Fig. 2 e The yield of the pyrolysis products.
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Table 3 e The recognizable compounds in the liquid product at 400 C. No.
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
1 2 3 4 5 6 7 8 9 10 11
3.616 4.812 5.600 5.721 6.183 6.515 6.679 7.472 8.592 8.635 9.285
C2H4O2 C10H8O C9H12O2 C5H8O C6H6O C7H16O C6H8O C5H12O C5H10O2 C8H16O C6H10O3
60 122 152 84 94 116 152 88 102 128 130
2.151 9.697 1.392 1.700 1.297 1.477 8.898 2.108 3.795 1.191 2.151
12 13 14 15
9.444 10.043 10.244 11.659
Acetic acid 4-ethyl-phenol 4-ethyl-2-methoxy-phenol 1-acrolein Phenol 1-propoxy-butane 2,5-dimethyl-furan 2,2-dimethyl-1-propyl alcohol Valeric acid 3,3-dimethyl-cyclohexanol 1-hydroxymethyl-1-methyl ester cyclopropane carbonic acid Valine hexanoic acid 1-butyl-dihydro-2(3H)-furanone Dodecenoic acid
C5H9NO2 C6H12O2 C8H14O2 C12H22O2
117 116 142 198
1.186 2.987 3.804 1.877
product at this temperature can be considered as rice husk oil. It is also defined as wood vinegar, which proves that rice husk only produce biomass oil at low temperatures. In Table 4, the recognizable compounds are still organic matter with low molecular weight. Compared with Table 3, furans organic matter has larger relative content while acids decrease significantly due to acids converting to alkanes as the increase of temperature. In general, there is no obvious difference in the liquid components when the temperature is below 500 C and the liquid product belongs to biomass oil. In Table 5, naphthalene and biphenyl appear in the recognizable compounds, indicating that with the increase of temperature, the conversion gradually starts to change. However, the phenols are still regarded as the primary compounds. In Table 6, the product featured with tar property, such as fluorene, phenanthrene, and anthracene start to appear in the recognizable compounds. The relative content of naphthalene increases remarkably. Therefore, with the rise of temperature, the rice husk oil will gradually be replaced by rice husk tar. In Table 7, such PAHs as dibenzofuran, fluoranthene, and pyrene begin to appear in the recognizable compounds. The content of phenol further decreases, while charcoal liquid compounds, like metoxyphenol and eugenol, increase significantly. These compounds are difficult to crack unless the higher temperature and longer residence time are provided for cracking. On the whole, when the temperature is below 500 C, the liquid product is biomass oil, and its essential components are organic acid, furan, and low molecular weight aromatic compounds. With the increase of temperature, thermal cracking occurs. The molecular weight of each component increases significantly, and a tiny amount of naphthalene and fluorene is produced at 600 C. When the temperature reaches 700 C, PAHs like naphthalene, fluorene, phenanthrene, anthracene, and fluoranthene increase significantly, while organics containing oxygen decreases to some extent. When the temperature reaches 800 C, a large amount of charcoal liquid is produced. Fig. 3 displays the variation of the number of compounds in the liquid product. From 400 C to 600 C, with the increase of temperature, the number of compounds in liquid decreases gradually from 246 to 204. When the temperature is higher
than 600 C, the number of compounds in liquid product declines sharply from 204 to 94, indicating that temperature plays an active role in the pyrolysis of rice husk oil and tar. It also proves that temperature will also significantly influence the proportion of compounds in pyrolysis product.
Properties of rice husk tar The rice husk tar produced at 800 C was selected for analysis. Table 8 is the elemental composition of rice husk tar and Table 9 is the properties of the distillate of rice husk tar.
Composition of rice husk tar distillate Acetone was used to dissolve the rice husk tar, and sodium sulfate anhydrous was used to remove its moisture. The tar distillate was obtained by distillation. Moreover, sodium sulfate anhydrous was used to remove its moisture. The compounds that are recognizable in the tar distillate and the relative content are shown in Table 10. Compared with Tables 7e10, tar distillate and tar have many similarities in composition, such as naphthalene, phenol and their derivatives, phenanthrene, anthracene, fluorine, were detected in both tar and tar distillate. More specifically, in the distillate, the content of naphthalene, anthracene, phenol and their derivatives increases, while the content of fluorine and phenanthrene decreases. The growing content of phenol and its derivatives is because the ringeopening reaction occurs between naphthalene and anthracene, which combine other free radical to form phenol and its derivatives. The decreasing content of fluorine and phenanthrene is because they are cracked into naphthalene and anthracene. The increasing content of naphthalene and anthracene is because the crack of naphthalene and anthracene is lower than production. Further, the number of compounds in the tar and that in the distillate increase from 45 to 147. The reason is the increasing species of free radical contribute to producing more compounds.
TGA for rice husk tar and its distillate Fig. 4 shows the TG and DTG curves of the tar vary with the different heating rate at N2 atmosphere. With the increase
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Table 4 e The recognizable compounds in the liquid product at 500 C. No. 1 2 3 4 5 6 7 8 9
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
5.311 7.398 8.292 9.531 10.257 11.157 11.369 11.397 12.947
1-hydroxy-2-butene 2,5-dimethyl furan Propanoic acid Phenol 4-methylphenol 5-methylfufural 2,5-dimethyl-phenol 4-ethyl-phenol 4,5-dimethyl-resorcinol
C4H8O2 C6H8O C3H6O2 C6H6O C7H8O C6H6O2 C8H10O C8H10O C8H10O2
88 96 74 94 108 110 122 122 138
5.215 11.417 1.249 4.652 1.017 3.391 3.633 1.787 2.647
Table 5 e The recognizable compounds in the liquid product at 600 C. No. 1 2 3 4 5 6 7 8 9 10
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
6.126 8.525 9.567 10.992 11.835 12.092 12.789 13.110 13.147 14.932
Acetol cyclopentane 2-methyl-1,3-pentanedione Naphthalene 4-ethyl-2-methoxy-phenol 4-ethyl-phenol Eugenol Diphenyl Biphenyl 2-methoxy-4-(1-propenyl)-(E)-phenol Fluorene
C7H12 C6H8O2 C10H8 C9H12O2 C8H10O C10H12O2 C12H10 C12H8 C10H12O C13H10
96 112 128 152 122 164 154 152 164 168
3.603 1.048 2.235 1.102 2.156 1.246 1.645 1.847 1.490 3.603
of heating rate, TG curves shift to the higher temperature side below 360 C and shift to the lower temperature side above 415 C. The reason is the rice husk tar generates a kind of material that is difficult to pyrolyze from 360 C to 415 C. Moreover, the content of such material increases with the decline of heating rate. Such material accumulates gradually, as it is difficult to be cracked. The phenomenon is shown in DTG curves when the temperature reaches 415 C.
The weight-loss of the tar with high heating rate at the same temperature is still higher than that of the tar with low heating rate, or the DTG curve with high heating rate is above that with low heating rate. The materials detected are naphthalene and its derivatives. The difference is small in TG and DTG curves with different heating rates, indicating that heating rates influence the cracking of the tar little.
Table 6 e The recognizable compounds in the liquid product at 700 C. No. Retention time (min) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
9.297 9.554 9.698 10.101 10.964 11.190 11.467 12.057 13.271 14.121 14.695 14.922 16.231 16.435 17.144 17.246 18.460 18.873 18.961 19.066 19.948 20.446 20.501
Name 4-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 2,3-dihydrobenzofuran 4-ethyl-2-methoxy-phenol 1-methyl-naphthalene 2-methoxy-4-vinyl-phenol Eugenol 2-methoxy-4-(1-propenyl)-(Z)phenol Dibenzofuran 3-tert-butyl-4-hydroxyl Fluorene 2,6-dimethoxy-4-(2-propenyl)-phenol 1-butyl-2-ethylbutane Phenanthrene Anthracene 4-cyclopentane-2,4,6-trienephenol n-hexadecanoic 3-isopropyl-4-methyl-12-1-en-4-alcohol 2-phenl-naphthalene Fluoranthene Pyrene Benzo[b]naphtha[1,2-d]furan
Molecular formula Molecular weight Relative content (%) C8H10O C10H8 C9H12O3 C8H8O C9H12O2 C11H10 C9H10O2 C10H12O2 C10H12O2 C12H8O C14H21NO3 C13H10 C22H26O6 C10H20 C14H10 C14H10 C14H12O2 C16H32O2 C14H28O C16H12 C16H10 C16H10 C16H10O
122 128 168 120 152 142 150 164 164 168 251 166 386 140 178 178 212 256 212 204 202 202 218
1.609 2.292 1.031 1.412 1.614 2.344 1.331 1.370 5.638 1.219 1.059 1.193 1.317 1.825 2.530 1.149 1.324 2.722 1.003 1.140 1.267 1.414 1.183
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Table 7 e The recognizable compounds in the liquid product at 800 C. No.
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
9.298 9.556 9.702 10.103 10.965 11.191 11.467 12.057 13.269 14.122 14.922 16.231 16.436 17.144 18.461 18.874 19.948 20.449 20.502 24.951
4-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 2,3-dihydrobenzenofuran 4-ethyl-2-methoxy-phenol 2-methyl-naphthalene 2-methoxy-4-vinyl-phenol 2-methoxy-3-(2-propenyl)-phenol 2-methoxy-4-(1-propenyl)-(E)-phenol Dibenzofuran Fluorene 2,6-dimethoxy-4-(2-propenyl)-dimethoxyphenol 1,1,2-trimethyl cycloundecane Phenanthrene Methyl palmitate n-hexadecanoic acid Fluoranthene Fyrene 4-(p-N,N-Dimethylaminoimine)-(Z)-2-amyl alcohol 2-(3,4-dimethoxy)-7-hydroxyl-4H-1-pyran-4-1
C8H10O C10H8 C9H12O3 C8H8O C9H12O2 C11H10 C9H10O2 C10H12O C10H12O C12H8O C13H10 C22H26O6 C14H28 C14H10 C17H34O2 C16H32O2 C16H10 C16H10 C13H18N2O C20H18O9
122 128 168 120 152 142 150 164 164 168 166 386 196 178 270 256 202 202 218 402
2.102 2.030 1.059 1.592 1.767 2.391 1.378 1.239 6.181 1.227 1.233 1.227 1.372 2.677 1.801 2.915 1.166 1.419 1.320 1.026
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Fig. 5 shows the TG and DTG curves of the tar distillate. The weight loss of rice husk tar distillate can be divided into three regions. In the first region, moisture in tar evaporates, so there is a massive weight loss below 105 C. However, some weight loss has already existed below 100 C, indicating that there is light distillate. The second region is from 105 C to 240 C. Most thermal weight loss occurs in this region. The weight loss reaches a maximum at about 160 C. The third region is from 240 C to the final temperature, indicating the residue of the distillate cannot be further cracked.
Conclusions
Fig. 3 e Variation of the number of compounds in the liquid product.
Table 8 e Elemental composition of rice husk tar. Moisture (wt.%) Ash (wt.%) C (wt.%) H (wt.%) Oa (wt.%) 16.5 a
0.06
33.21
6.09
44.14
By difference.
Table 9 e Properties of rice husk tar distillate. Density Viscosity PH value Flash Fire point HHV at 20 C at 20 C point ( C) (MJ/kg) ( C) (g ml1) (mm2 s1) 1.031
120
4.4
49
54
17.10
(1) The liquid product of rice husk pyrolysis increases significantly when the temperature is from 400 to 500 C. Above that range, it declines, and especially above 800 C, the liquid product is hard to be convert into non-condensable gas. (2) When the temperature is below 500 C, the liquid product of rice husk pyrolysis is rice husk oil. When the temperature reaches about 700 C, PAHs increase significantly and the liquid product is tar. When the temperature reaches 800 C, a large amount of charcoal liquid is produced. (3) There are many similarities between tar and its distillate. After distillation, the content of the primary compounds like naphthalene, anthracene, phenol and its derivative increases, while the content of fluorene and phenanthrene decreases. (4) Temperature plays an active role in the pyrolysis of rice husk oil and tar, and the proportion of compounds in the pyrolysis product. (5) The weight loss of rice husk tar distillate can be divided into three regions. The weight loss reaches a maximum at about 160 C.
Please cite this article in press as: Zhai M, et al., Characteristics of rice husk tar pyrolysis by external flue gas, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.07.045
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 5 ) 1 e8
Table 10 e The recognizable compounds of rice husk tar distillate. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Retention time (min)
Name
Molecular formula
Molecular weight
Relative content (%)
4.267 5.294 5.421 5.902 6.076 6.223 6.269 6.569 6.729 6.868 6.992 7.072 7.343 7.408 7.502 7.745 7.868 8.052 8.285 8.827
Phenol 4-methyl-phenol 2-methoxy-phenol 2, 4-dimethyl-phenol 3-ethyl-phenol Naphthalene 2-methoxy-4-methyl-phenol 1-ethyl-4-methoxy-benzene 2, 6-dimethyl anisole 4-ethyl-2-methoxy-phenol 1-methylnaphthalene 2, 3-dihydro-3, 3-dimethyl-1H-indene N,N,N0 ,N0 -tetramethyl-1,4-phenylenediamine 2-vinyl-naphthalene 2-methoxy-4-propyl-phenol 2, 6-dimethyl-naphthalene 3- methoxy-4-(1-propenyl)-, (E)-phenol Pentadecane Dibenzofuran 4-methyl-dibenzofuran
C6H6O C7H8O C7H8O2 C8H10O C8H10O C10H8 C9H12O3 C9H12O C9H12O C9H12O C11H10 C9H8O C20H36N2 C12H10 C10H12O2 C12H22O2 C10H12O2 C15H32 C12H8O C13H10O
94 108 124 122 122 128 168 136 136 136 142 132 304 154 164 188 164 212 168 182
2.147 2.686 2.198 1.679 3.181 2.392 1.708 1.792 2.770 2.134 1.719 1.574 1.571 2.073 1.792 1.958 1.877 2.098 1.810 2.085
references
Fig. 4 e TG and DTG curves of the tar vary with different heating rate.
Fig. 5 e TG and DTG curves of the tar distillate.
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Please cite this article in press as: Zhai M, et al., Characteristics of rice husk tar pyrolysis by external flue gas, International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.07.045