Effect of Torrefaction Temperature on Product Distribution from Two

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Effect of Torrefaction Temperature on Product Distribution from Two-Staged Pyrolysis of Biomass Anqing Zheng,†,‡ Zengli Zhao,*,†,‡ Sheng Chang,†,‡ Zhen Huang,†,‡ Fang He,†,‡ and Haibin Li†,‡ †

Guangzhou Institute of Energy Conversion, Chinese Academy of Science, Guangzhou 510640, People's Republic of China Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Science, Guangzhou 510640, People's Republic of China

‡

ABSTRACT: Two-staged biomass pyrolysis process consisting of torrefaction and subsequent fast pyrolysis is proposed to obtain high quality bio-oil. The purpose of this study is to evaluate the effect of torrefaction temperature on yield, composition, and physical properties of the liquid of torrefaction and bio-oil. Torrefaction of pine was conducted on an auger reactor at 240− 320 °C with a residence time of 40 min to produce liquid of torrefaction and torrefied pine. Then, the torrefied pine was fast pyrolyzed in a bubbling fluidized bed reactor at 520 °C to produce bio-oil. Torrefied pine was characterized by chemical composition analysis and Fourier transform infrared (FTIR) spectroscopy. The liquid of torrefaction was determined by gas chromatography (GC); bio-oil was characterized by gas chromatography mass spectroscopy (GC-MS) and 13C nuclear magnetic resonance spectrometry (NMR). The experimental results show that water content in liquid of torrefaction and water and acetic acid content in bio-oil decreased with elevated torrefaction temperature, while the yield of liquid of torrefaction, aromaticity, higher heating value, and density of bio-oil increased. However, the yield of total liquid (sum of liquid of torrefaction and bio-oil) decreased significantly with elevated torrefaction temperature because of the cross-linking and carbonization of torrefied pine. carried out at temperatures ranging from 240 to 320 °C for liberating water and releasing volatile organic compounds through the devolitization of primarily the hemicelluloses.24 Water in bio-oil is mainly from original moisture and the dehydration reaction of biomass. Acetic acid in bio-oil is mainly derived from the deacetylation reaction of hemicellulose.25 Accordingly, two-stage biomass pyrolysis process consisting of torrefaction and subsequent fast pyrolysis is proposed to obtain chemicals and high quality bio-oil with lower content of water and acetic acid (as shown in Figure1). Currently, torrefaction of biomass has been well studied by many researchers. Most of them have focused on the mechanical properties, composition, structure, and reactivity change of torrefied biomass;26−30 some of them have investigated the composition distribution of liquid and gas product from biomass torrefaction.31,32 The effect of torrefaction on combustion or gasification of torrefied biomass has also been investigated.27,33,34 However, to our knowledge, less attention has been paid to the effect of torrefaction on the yield and quality of bio-oil. In this work, torrefaction of pine was conducted on an auger reactor at 240−320 °C with a residence time of 40 min. Fast pyrolysis of torrefied pine was performed on a bubbling fluidized bed reactor at 520 °C to produce bio-oil. The process conditions of the whole system were keep constant, except for torrefaction temperature. The effect of torrefaction temperature on the yield, composition, structure, and physical properties of bio-oil were studied. In addition, the product distribution of pine torrefaction was also investigated.

1. INTRODUCTION Due to diminishing petroleum resources and economic, environmental, and political concerns regarding petroleumbased economy, it is imperative to develop new process for the renewable fuels and chemicals.1−5 Biomass is the only renewable energy source that can be converted into fuels and chemicals through thermochemical and biochemical processes. Among various processes, fast pyrolysis of biomass has attracted great attention as a result of its highest yield of liquid product and lowest costs.6−9 Fast pyrolysis of biomass can produce the liquid product known as bio-oil with yield as high as 80 wt %, dry feed basis.10 In addition, it has been shown to be two or three times cheaper than biomass gasification and fermentation processes.1,9 Bio-oil obtained by fast pyrolysis of biomass could be used either as a potential substitute for fuel oil in boilers, furnaces, turbines, and engines, or as a feedstock for chemicals.11,12 However, the bio-oil is a complex mixture of several hundreds of oxygenated organic compounds that has the characterization of high acid content, high water content, and low heating value. High acid content leads to the instability of bio-oil and the corrosion of transport pipes, storage tanks, and thermal devices.13,14 High water content lowers its heating value and may cause phase separation of bio-oil; moreover, it increases ignition delay and reduces combustion rates and adiabatic flame temperatures during the combustion process.12−14 These drawbacks have limited the broad application of bio-oil. The quality of bio-oil can be improved through several approaches such as chemical pretreatment of biomass and15,16 optimization of the process conditions of fast pyrolysis and catalytic upgrading. 17−23 In addition to these routes, torrefaction could also be a candidate for improving the quality of bio-oil. Torrefaction is a low temperature pyrolysis process © 2012 American Chemical Society

Received: November 29, 2011 Revised: April 2, 2012 Published: April 4, 2012 2968

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Figure 1. Schematic flowsheet of biomass two-staged pyrolysis system.

Table 1. Ultimate and Chemical Component Analysis of Pine (wt %, Dry Basis) ultimate analysis

a

chemical composition analysis

sample

C

H

Oa

N

S

extractive

hemicellulose

cellulose

lignin

pine

49.86

5.33

42.74

0.02

2.04

2.67

21.38

46.36

27.29

The oxygen content was calculated by difference.

Figure 2. Torrefaction system. The reaction residence time was controlled with a motor to maintain a 40 min residence time. Nitrogen flow was used to keep the inert and remove volatile products from the reactor. The nitrogen flow rate was 7 L/min. The volatile products were cooled to collect the liquid product in two condensers at −5 °C. The volume of noncondensable gas was determined by a wet gas meter. Each experiment was repeated twice under the same conditions to ensure its repeatability, and the mass balance for all of the experiments was in the range from 93 to 99%. 2.3. Fast Pyrolysis System. The schematic diagram of the 10 kg/ h fast pyrolysis system used in this study is shown in Figure 3. This system included a bubbling fluidized bed section, two gas−solid cyclones in series for char separation, followed by a heat exchanger cooled by circulating glycol jackets maintained at around −10 °C, and two gas−liquid cyclones for bio-oil collection. The uncollected aerosol was absorbed by cotton in the end of this system. The reaction temperature was fixed at 520 °C, the temperature at which highest yield of bio-oil can been obtained from pine. Silica sand was used for bed material, and its static height was 12 cm. Nitrogen was used as fluidized gas with a flow rate of 12 N m3/h. Total liquid products included the collected liquids by the heat exchanger and gas−liquid cyclones and the weight increase of the cotton filter. The char products involved the char collected by the two gas−solid cyclones and the char in the bed material. The gas yield was calculated according to the

2. MATERIALS AND METHODS 2.1. Biomass Sample Preparation and Analysis. The feedstock used in this study was pine chips provided by a local wood chipping plant in Guangzhou. The pine chips were ground and sieved to the particle size range 0.20−0.45 mm. The particles were dried at 105 °C for 8 h before the experiment. The moisture of pine is around 8%. The ultimate analysis and chemical composition analysis are shown in Table 1. The elemental analysis of pine was performed on a Vario EL. The chemical composition analysis of pine was determined according to the corresponding Chinese national standards (GB). Extractive content analysis was made according to GB/T 2677.6-1994. Holocellulose content was determined based on GB/T 2677.101995. Cellulose content was determined by nitric acid-ethanol method.35 Hemicellulose content was calculated by difference. Lignin content was analyzed as acid-insoluble Klason lignin by GB/T 2677.81994. 2.2. Torrefaction System. The schematic diagram of the torrefaction system is presented in Figure 2. This system consisted of a hopper, an auger reactor, a char collection bin, and two condensers. The auger reactor had an outer diameter (o.d.) of 100 mm and a length of 0.6 m; it was heated by an 3.5 kW electrical furnace, the temperature of which was controlled by a temperature control unit. The reaction temperature was set to 240, 260, 280, 300, or 320 °C. 2969

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Figure 3. Fast pyrolysis system. nitrogen balance between the inlet and outlet gases of the fast pyrolysis system. Each experiment was performed twice under the same conditions to ensure its repeatability, and the mass balance for all of the experiments was in the range from 92 to 98%. 2.4. Characterization of Pyrolysis Products. The Fourier transform infrared (FTIR) spectroscopy analyses of torrefied pine were carried out on a Bruker TENSOR27 to characterize the main functional group of the torrefied pine. All liquid products were kept in a freezer at 0 °C before analysis because of their instability. Eleven compounds in liquid of torrefaction were quantitatively analyzed by gas chromatography (GC) by a GC HP 4890 equipped with a flame ionization detector (FID) using external standard method. The GC column used was a DB-1701 60 m × 0.25 mm, 0.25 μm film thickness. The oven was programmed to hold at 45 °C for 5 min, then increase at 5 °C/min to 280 °C, and hold there for 5 min. The injector temperature was 250 °C. Helium was used as carried gas. The standard chemicals were supplied by Sigma-Aldrich. The gas chromatography mass spectroscopy (GC-MS) analysis of bio-oil obtained from fast pyrolysis was performed on an Agilent 7890 GC instrument followed by an Agilent 5973 mass selective detector (MSD). The GC column used was HP-INNOWax 30 m × 0.25 mm, 0.25 μm film thickness. The oven was programmed to hold at 50 °C for 2 min, increase at 10 °C/min to 90 °C, then increase at 4 °C/min to 120 °C, finally increase at 8 °C/min to 230 °C, and hold there for 10 min. Helium was used as carrier gas. The injector temperature was 250 °C. The injector split ratio was set at 20:1. The ion source temperature was 240 °C for the mass spectrometer detector. The mass spectrometer was set at an ionizing voltage of 70 eV with mass range (m/z) of 33−500 u. The compounds were identified by comparison with National Institute of Standards and Technology (NIST) mass spectral data library. Due to their higher relative peak area in GC-MS analysis results, 16 compounds were chosen for quantitative analysis by GC using an external standard method. 13C nuclear magnetic resonance spectrometry (NMR) analyses were performed for quantitative analysis of the main functional group of bio-oil. Solution-state (acetone-d6) NMR spectra of bio-oil were recorded on a Bruker DRX 400 NMR spectrometer operating at 9.4 T with a 5 mm BBO BB-1H probe at room temperature. The relaxation delay was 2 s. The acquisition time varied between 4 and 8 h. The physical properties of bio-oil were determined based on the American Society for Testing and Materials (ASTM) standard methods or GB. The water content of bio-oil was analyzed by a general Karl Fischer titrimetry (787KF Titrino, Metrohm). The higher

heating value of bio-oil was determined using an isoperibol oxygen bomb calorimeter (WZR-IT-C). The pH of bio-oil was analyzed by a pH meter (PHS-3C, SPSIC). The dynamic viscosity was determined using viscometer (DR-KF) at 20 °C. The solid content of the bio-oil was defined as acetone-insoluble material retained on the Millipore filter (0.1 μm pore size, o.d. 37 mm). Each test was repeated three times under the same conditions to ensure repeatability. 2.5. Methods of Data Processing. The product yields of twostaged pyrolysis system was defined as follows:

yield of torrefied pine mass of torrefied pine obtained in pine torrefaction = × 100% mass of original pine (wet basis) yield of liquid of torrefaction mass of liquid of torrefaction obtained in pine torrefaction = mass of original pine (wet basis) × 100% yield of bio‐oil mass of bio‐oil collected in fast pyrolysis of torrefied pine = mass of original pine (wet basis) yield of char mass of char collected in fast pyrolysis of torrefied pine = mass of original pine (wet basis)

3. RESULTS AND DISCUSSION 3.1. Effect of Torrefaction Temperature on Pine Torrefaction. 3.1.1. Product Yield of Pine Torrefaction. After pine torrefaction, The solid, liquid, and gas products, known as torrefied pine, liquid of torrefaction, and noncondensable gas, respectively, were obtained. The effects of torrefaction temperature on product yield of pine torrefaction are shown in Figure 4. As the torrefaction temperature raised from 240 to 300 °C, the yield of torrefied pine decreased gradually from 93.59% to 62.21%, whereas the yield of liquid of torrefaction increased from 3.92% to 16.14% and the yield of noncondensable gas increased from 1.09% to 19.33%. It 2970

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Table 2. Quantification of Some Compounds in the Liquid of Torrefaction Obtained at Different Torrefaction Temperatures (wt %, Based on the Liquid of Torrefaction) torrefaction temps (°C) cmpd water

group

240

260

280

300

water 75 72 64 56 Hemicellulose/Cellulose-Derived Compounds (wt %) acetic acid acid 5.89 7.28 8.53 9.54 2-cyclopenten-1ketone 0.08 0.07 0.15 0.20 one 1-hydroxy-2ketone 2.00 2.21 2.63 4.07 propanone propionic acid acid 0.17 0.19 0.27 0.34 furfural furan 0.99 1.31 1.40 1.44 2-furanmethanol furan 0.69 0.60 0.78 1.12 Lignin-Derived Compounds (wt %) phenol phenol 0.01 0.01 0.01 0.02 phenol, 4-ethylphenol 0.07 0.02 0.05 0.17 2-methoxyguaiacol phenol 0.10 0.13 0.21 0.39 rugenol phenol 0.01 0.01 0.02 0.06 isoeugenol phenol 0.02 0.01 0.14 0.36 vanillin phenol 0.08 0.09 0.09 0.15

Figure 4. Effect of torrefaction temperature on products yield of pine torrefaction.

indicates the increasing decomposition of pine with elevated torrefaction temperature. 3.1.2. Composition of Liquid of Torrefaction. Liquid of torrefaction could be used as feedstock for chemicals. The liquid of torrefaction contains hundreds of compounds. It is hard to quantify all the compounds. Therefore, 12 compounds were selected and quantified using GC due to their higher relative peak area in GC-MS analysis. As the torrefaction temperature increased, the water content of the liquid of torrefaction decreased from 75% to 54%. Water was a major product released in two different mechanisms during torrefaction. It was derived mainly from the evaporation of the moisture in pine and partially from the dehydration reaction of pine. The decrease of water content with increasing temperature could be due to greater decomposition of pine. The acetic acid content first increased from 5.89% at 240 °C to 9.54% at 300 °C and then dropped to 6.78% at 320 °C. The same variation trends were observed for 1-hydroxy-2propanone and furfural. These compounds were mainly derived from the decomposition of hemicellulose. The decrease in their content at 320 °C could be due to the initial serious decomposition of cellulose and lignin at this temperature. The phenols in the liquid of torrefaction were predominantly from lignin pyrolysis. As can be seen from Table 2, the most of phenolic compounds contents increased gradually with the increasing torrefaction temperature. It indicates greater decomposition of lignin with increasing torrefaction temperature. 3.1.3. Characterization of Torrefied Pine. The effects of torrefaction temperature on the chemical composition of torrefied pine are listed in Figure 5. The main changes in pine during torrefaction involve decomposition of hemicelluloses and the partial depolymerization of cellulose and lignin. With the increase of the torrefaction temperature from 240 to 320 °C, the hemicellulose content of torrefied pine dropped from 17.35% to 1.14%. In other words, the hemicellulose was the major decomposed component while pine torrefied at 240 to 320 °C. The cellulose content changed slightly. The cellulose content first increased from 46.70% at 240 °C to a maximum of 51.31% at 260 °C, and then, it decreased to 36.42% at 320 °C. The result indicates that the cellulose started to partially depolymerize at 280 °C. The content of lignin increased gradually, although lignin might

320 52 6.78 0.18 3.33 0.25 1.12 0.92 0.02 0.23 0.41 0.07 0.47 0.08

Figure 5. Chemical composition analysis of torrefied pine (wt %).

have been partially depolymerized. Lignin is known as the most stable components of biomass. In addition, the carbonization of hemicellulose and cellulose was also a major cause of increasing lignin content. These results were accordance with the literature.36 During torrefaction, the color of torrefied pine changed from white to dark brown. This indicates that carbonization of pine was happening. In Figure 6, the FTIR spectra of torrefied pine at 320 and 280 °C are compared with that at 240 °C. The higher intensity of the C−O−C asymmetric stretching in cellulose at 1156 cm−1 could be attributed to the cross-linking of cellulose. The broader or higher intensity of the aromatic skeletal vibrations at 1510 cm−1 and 1630 cm−1 can be seen as a consequence of the splitting of aliphatic side chains in lignin and cross-linking formation by condensation reactions of lignin.37,38 The condensation structure indicates the carbonization of pine after torrefaction. 3.2. Effect of Torrefaction Temperature on Fast Pyrolysis of Torrefied Pine. 3.2.1. Product Yield of Fast 2971

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3.2.2. Chemical Characterization of Bio-oil. Chemical characterization of bio-oil has been a challenging undertaking because of its complex nature. Bio-oil includes about 40 wt % medium-polar monomers detectable by GC, 12 wt % polar monomers detectable by high pressure liquid chromatography (HPLC), 20 wt % oligomeric material (pyrolytic lignin), and 28 wt % water. Only a fraction of bio-oil can be identified and quantified by GC or HPLC.39,40 However, the NMR spectroscopy can be used for the quantitative analysis of the total chemical structure of bio-oil.40 Consequently, we used GC to quantify some major components in bio-oil and 13C NMR to quantify the chemical structure composition of the whole biooil. 3.2.2.1. Quantification of Some Compounds in Bio-oil. As shown in Table 3, 17 compounds were identified and quantified in bio-oil. With the increasing torrefaction temperature, the water content in bio-oil decreased from 30% to 19% because of the removal of moisture content and dehydration of pine during torrefaction. The acetic acid content decreased from 4.88% at 240 °C to 3.26% at 320 °C because of the reducing hemicellulose content of torrefied pine with increasing torrefaction temperature. The decrease of furfural contents were caused the same way. These compounds were mainly derived from hemicellulose and cellulose. The lignin-derived compounds are less than 1%, except for 2-methoxy-4-methylphenol and isoeugenol. The maximum contents of these two compounds were 1.02% and 1.12%, respectively, at the torrefaction temperature of 320 °C. This could be due to the increasing lignin content of torrefied pine with elevated torrefaction temperature. 3.2.2.2. 13C NMR Analysis of Bio-oil. The 13C NMR spectra of bio-oil are shown in Figure 8. The integrated spectra were divided into seven general chemical shift ranges for analysis:41 0−45 ppm (alkyl carbon), 45−65 ppm (methoxyl and N-alkyl carbon), 65−90 ppm (O-alkyl carbon), 90−110 ppm (Di-Oalkyl carbon), 110−145 ppm (aryl and unsaturated carbon), 145−165 ppm (O-aryl carbon), 165−190 ppm (carbonyl carbon and amide carbon), and 190−215 ppm (aldehyde and ketone carbon). The integration values of each chemical shift region are tabulated in Figure 9. These values indicate the distributions of different types carbon as a percentage of the total carbon in bio-oil. As shown in Figure 9, the alkyl carbon presented in 0−45 ppm decreased from 22.78% to 19.50% as the torrefaction temperature increased from 240 to 320 °C. The maximum content of O-alkyl carbon and Di-O-alkyl carbon presented in 65−110 ppm was 43.05%, at the torrefaction temperature of 240 °C. This indicates that the greater cleavage of O-alkyl carbon and Di-O-alkyl carbon in pine torrefaction with elevated torrefaction temperature. The aryl carbon presented in 110−145 ppm increased from 16.63% to 23.90% with elevated torrefaction temperature. The aryl carbon in bio-oil was mainly in the form of phenols and pyrolytic lignin. The increase of aryl carbon was due to the increasing lignin content and carbonization of torrefied pine. The content of total aliphatic carbon presented in 0−110 ppm decreased with elevated torrefaction temperature. On the contrary, the content of total aromatic carbon presented in 110−165 ppm enhanced with increasing temperature. Therefore, the aromaticity of bio-oil increased from 25.29% to 40.86%. 3.2.3. Physical Properties Analysis of Bio-oil. As shown in Table 4, the higher heating value and kinematic viscosity of biooil increased gradually with elevated torrefaction temperatures.

Figure 6. FTIR spectra of torrefied pine after torrefaction at different temperatures.

Pyrolysis of Torrefied Pine. The process conditions of the whole system were keep constant, except for the torrefaction temperature. The effect of torrefaction temperature on bio-oil yield, char yield, and noncondensable gas yield are presented in Figure 7. The bio-oil and char yields were based on original

Figure 7. Effect of torrefaction temperatures on product yields of fast pyrolysis of torrefied pine.

pine, wet basis. The noncondensable gas yield was calculated by difference. The total liquid yield was the sum of bio-oil and liquid of torrefaction. As can be seen from the figure, the bio-oil yield decreased significantly from 54.87% at 240 °C to 22.72% at 320 °C, and the total liquid yield decreased from 58.79% at 240 °C to 38.88% at 320 °C, while the char yield increased gradually from 17.37% to 23.28%. The noncondensable gas yield first increased from 18.63% at 240 °C to 21.26% at 260 °C and then decreased to 11.83% at 320 °C. The decrease in biooil yield was a result of devolitization, cross-linking, and carbonization of pine during torrefaction. The decrease of total liquid yield was only attributed to the cross-linking and carbonization of torrefied pine. The cross-linking and carbonization of pine can increase the char and gas yield from fast pyrolysis of torrefied pine. The decrease in the noncondensable gas yield at 260 °C could be due to the serious carbonization of torrefied pine, which could result in the higher char yield. 2972

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Table 3. Quantification of Some Compounds in Bio-oil (wt %, Based on the Bio-oil) torrefaction temp. (°C) cmpd water acetic acid 2-propanone,1-hydroxy2-cyclopenten-1-one furfural 2-furanmethanol 5-(hydroxymethyl)-2-furancarboxaldehyde phenol, 2-methoxyphenol, 2-methoxy-4-methylphenol 4-methyl-phenol 3-methyl-phenol 4-ethyl-phenol vanillin isoeugenol eugenol 2-methoxy-4-vinylphenol

group

240

260

280

water 30 26 Hemicellulose/Cellulose-Derived Compounds (wt %) acid 4.88 4.32 ketone 3.23 2.84 ketone 0.51 0.47 furan 0.57 0.51 furan 0.10 0.11 furan 0.16 0.52 Lignin-Derived Compounds (wt %) phenol 0.43 0.54 phenol 0.48 0.73 phenol 0.27 0.29 phenol 0.06 0.10 phenol 0.02 0.03 phenol 0.09 0.11 phenol 0.17 0.21 phenol 0.55 0.26 phenol 0.45 0.06 phenol 0.34 0.45

300

24

320

21

19

3.79 2.81 0.54 0.51 0.12 0.48

3.57 2.88 0.45 0.46 0.12 0.44

3.26 2.49 0.54 0.40 0.12 0.47

0.60 0.88 0.34 0.12 0.06 0.14 0.18 0.76 0.47 0.48

0.59 0.90 0.36 0.15 0.19 0.07 0.24 0.92 0.31 0.39

0.67 1.02 0.40 0.11 0.16 0.12 0.27 1.12 0.38 0.47

Table 4. Effect of Torrefaction Temperature on Physical Properties of Bio-oil physical properties of bio-oil 240 °C 260 °C 280 °C 300 °C 320 °C high heating value MJ (kg) pH kinematic viscosity at 20 °C (cSt) solid content (wt %)

15.61 2.49 4.65

16.73 2.52 7.46

17.14 2.81 8.59

17.86 2.74 13.56

18.58 2.69 28.63

0.38

0.43

0.46

0.57

0.72

content of bio-oil increased from 0.38% to 0.72% because of the higher char yield caused by the increasing lignin content, crosslinking, and carbonization of torrefied pine. It is worth noting that the pH of bio-oil first increased from 2.49 at 240 °C to 2.81 at 280 °C and then decreased to 2.69 at 320 °C. The pH was mainly affected by the content of organic acids, phenols, and water in bio-oil.

Figure 8. Effect of torrefaction temperature on 13C NMR spectra of bio-oil.

This could be explained by the decrease of water content and the increase of pyrolytic lignin content of bio-oil. The solid

4. CONCLUSIONS Two-stage biomass pyrolysis was performed on auger reactor and bubbling fluidized bed reactor, respectively. The operating conditions of whole system were kept constant besides the torrefaction temperature. The effect of torrefaction temperature on bio-oil yield and quality was investigated. In addition, the liquid of torrefaction was also investigated. The results show that the liquid of torrefaction and bio-oil quality improved with elevated torrefaction temperatures, in addition to the kinematic viscosity and solid content of bio-oil. However, the total liquid yield decreased significantly with elevated torrefaction temperature. This could be caused by the cross-linking and carbonization of torrefied pine. We note that the bio-oil quality improved but not dramatically, and the cross-linking and carbonization of pine resulted in the decrease of total liquid yield. Therefore, low torrefaction temperature, residence time, and improvement of heat transfer efficiency to limit the cross-linking and carbonization of biomass in torrefaction are preferred in next study.

Figure 9. Percentage of carbon distribution from 13C NMR spectra of the bio-oil influenced by torrefaction temperature. 2973

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AUTHOR INFORMATION

Corresponding Author

*Email:[email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the National 863 Hi-Tech R&D Program of China (No. 2007AA05Z456) for financial support of this work.

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NOTE ADDED AFTER ASAP PUBLICATION This article published April 18, 2012 with an error in the nitogen flow rate noted in the Material and Methods section. The correct version reposted April 18, 2012.

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dx.doi.org/10.1021/ef201872y | Energy Fuels 2012, 26, 2968−2974