Torrefaction of Various Biomass Feedstocks and Its Impact on the

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Biofuels and Biomass

Torrefaction of various biomass feedstocks and its impact on the reduction of tar produced during pyrolysis Supatchaya Konsomboon, Jean-Michel Commandre, and Suneerat Fukuda Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04406 • Publication Date (Web): 13 Mar 2019 Downloaded from http://pubs.acs.org on March 24, 2019

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Torrefaction of various biomass feedstocks and its impact on the reduction of tar produced during pyrolysis Supatchaya Konsomboon1, Jean-Michel Commandré2, Suneerat Fukuda1* 1The

Joint Graduate School of Energy and Environment, Center of Excellence on Energy Technology and

Environment, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand 2CIRAD,

UPR BioWooEB, F-34398 Montpellier, France

*Corresponding author. Tel.: +66 2 470809 Ext 4148; Fax: +66 2 8726978 E-mail address: [email protected]

ACS Paragon Plus Environment

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Abstract The aim of this study is to investigate the reduction of tar produced during biomass pyrolysis by torrefaction pretreatment. In this study, various biomass feedstocks (pine, ash wood, miscanthus, and wheat straw) with different particle sizes were torrefied at 280°C. The results indicated that both particle size and biomass composition have a significant effect on the yield and properties of the torrefied products. With increasing particle size, the yield of solid product increased, while the yield of condensable liquid and non-condensable gases decreased. The raw biomasses and torrefied biomasses were then subjected to pyrolysis at 500°C. The results clearly showed that torrefaction had a significant effect on the yield and composition of tar generated during subsequent pyrolysis. For all biomasses, the tar yields of biomasses after torrefaction were 42% to 62% lower compared to direct pyrolysis of raw biomasses. However, when considering the condensable liquid produced combining torrefaction and pyrolysis, the total yield of condensable liquid produced were decreased 3% to 12% lower compared to the direct pyrolysis. This suggests that not only some volatiles were released during the torrefaction process, but the thermal pretreatment also transformed the biomass structure to less favor tar production in subsequent pyrolysis step.

Keywords: torrefaction; tar; biomass composition; particle size; pyrolysis


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1. INTRODUCTION In recent years, the interest in biomass has been growing fast as a renewable resource to substitute fossil fuels in energy production. Biomass conversion by thermochemical process is considered as a promising alternative for the purpose of energy production [1]. Pyrolysis of biomass plays an important role in thermal conversion process as the first step of gasification and when the primary tar forms [2]. Especially in gasification, if the formed tar is not completely converted into gaseous products, it can cause many problems in the downstream process equipment especially gasification resulting in the decreased overall process efficiency and reliability. During pyrolysis, the release of primary tar which is a mixture of compounds derived from thermal degradation of cellulose, hemicellulose or lignin starts to occur and is later subject to the secondary reaction to form tertiary tar, which is more resistant to cracking [3]. Thus, it is important to study the pyrolysis behavior to form primary tar and the reduction of tar during the pyrolysis process. Tar reduction can be achieved by both post-treatment of tar after the process and pretreatment of biomass prior to use as a fuel in the processes. Biomass pretreatment can be classified into four methods, including i) physical pretreatment, ii) thermal pretreatment, iii) chemical pretreatment and iv) biological pretreatment. Each process has its own advantages and disadvantages. Torrefaction is one of the commonly used pretreatment methods for upgrading raw biomass into a solid fuel that is suitable for utilization in the thermal conversion process, given that it is of high energy density, hydrophobic, low oxygen-to-carbon (O/C) ratio, compactable, grindable, and reduce the formation of tar [4,5]. Effects of torrefaction on the pyrolysis behavior and its products have been reported by a group of researchers. Chen et al. [6,7] reported that the pretreatment of biomass by torrefaction influencing the yield and


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properties of pyrolysis products by reducing the yield of condensable liquid (or tar) and increasing the yield of biochar and non-condensable gases. A decrease in tar yield after torrefaction possibly due to the release of volatile matter, which is the main source of tar. Generally, torrefaction is performed in the temperature ranges of 200-300°C at atmospheric pressure in the inert atmosphere. Its performance is affected by many factors. Although the reaction temperature and residence time are the most crucial parameters, the particle size also affected the yield and properties of torrefaction products [8]. Peng et al. [9] studied the effect of particle size on biomass torrefaction and concluded that particle size had an influence on the torrefaction rate especially at high temperatures. Bates and Ghoniem [10] used a one-dimensional model to investigate the effect of particle size on the torrefaction performance and found that the mass loss during torrefaction decreased with increasing particle size. Torrefaction is a complex process related to various phenomena, i.e. chemical reactions and thermal transfer. Some previous studies have reported that for small particles (< 2 mm), torrefaction is free from heat and mass transfer limitations [8,11]. However, because of the considerable amount of energy required to grind raw biomass, large particles are preferred for operation in industrial scale torrefaction. Although there have been investigations of the particle size effect on torrefaction, only the small size ranges, i.e. < 2 µm were covered in those studies [12,13]. A variety of biomass feedstocks have been used for the energy production purposes. The biomass composition affects both the yield and properties of thermal products [14-16]. It is known that the constituents in biomass mainly consist of hemicellulose, cellulose, lignin with trace amounts of extractives and inorganic minerals. The conversion performances of biomass strongly depend on the thermal degradation behavior of these components [17]. Among the three


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major constituents of biomass, hemicellulose is the least stable polymer at the temperature range of 200-300°C. Cellulose degrades at higher temperature but within a narrow temperature range, i.e. 270-350°C. For lignin, it starts to soften at the temperature 80-90°C but its degradation occurs only in the temperature range of 250-500°C. The previous researches [18,19] concluded that the tar yield was proportional to the cellulose content during biomass pyrolysis. Hosoya et al. [20] investigated the secondary reactions of primary tar from pure cellulose and lignin, and found that unsaturated side chain and phenolic compounds were the primary tar-derived from lignin. Therefore, the understanding how biomass compositions impact the yield and properties of thermal products is necessary in order to develop and optimize the conditions for efficient thermal conversion. In this study, the effects of particle size and feedstock type on the torrefaction performance and consequent tar reduction during subsequent pyrolysis were investigated. The particle size of biomass was varied from less than 500 µm to 10,000 µm. Four kinds of biomass sample, i.e. pine, ash wood, miscanthus, and wheat straw were selected for the experiment as representative of four biomass families, softwood, hardwood, energy crop, and agricultural residue, respectively. The torrefaction of various biomass feedstocks was conducted at 280°C, and the torrefied biomasses were pyrolyzed at 500°C in the subsequent experiment. The products from the pyrolysis of torrefied biomass focusing on the amount and composition of tar were analyzed and compared with those from the raw biomass under the same pyrolysis conditions. The results obtained from this study provide information helping for the development of thermochemical biomass conversion processes, as well as expand of the range of biomass used at industrial scale.


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2. EXPERIMENTAL SECTION 2.1 Biomass feedstocks Four kinds of biomass, which represent four different biomass families, i.e. pine (softwood), ash wood (hardwood), miscanthus (energy crop) and wheat straw (agricultural residue) were used in the test to investigate the influence of biomass composition on the torrefaction behavior and pyrolysis products. All biomasses were crushed and ground by a knife mill. Pine and ash wood were collected in Aveyron (South West of France) and received in chip form, while miscanthus and wheat straw were collected in Montans (South West of France) and received as pellets. Three particle size ranges of biomass according to the following categories were applied in this study: small ( 500 m), medium (500-5,000 m) and large (5,000-10,000 m). Fig. 1 shows the four biomass feedstocks with the particle sizes in the range of this study. All biomass samples were dried at 105°C for 24 h before the experiments.

Figure 1 Pine, ash wood, miscanthus and wheat straw with three particle sizes range: < 500 µm, 500-5,000 µm and 5,000-10,000 µm


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2.2 Torrefaction and pyrolysis experiment The torrefaction and pyrolysis experiments were performed in a lab-scale fixed bed reactor. The schematic diagram of the system is shown in Fig. 2. The reactor system consists of four main parts: (1) sample feeding chamber, (2) fixed-bed reactor, (3) liquid quenching unit, and (4) gas analyzer. The reactor was made of a stainless steel tube, with a length of 600 mm and a diameter of 50 mm. Since the oven had a single heating zone, an external resistive heater was added at the end of the reactor to prevent the condensation of the condensable species. Nitrogen was used as the carrier gas and the nitrogen flow rate was controlled by a mass flow meter (Brooks 5850s).

Fig. 2 Schematic diagram of torrefaction/pyrolysis experiment (1) sample feeding chamber (2) fixed-bed reactor (3) liquid quenching unit (4) gas analyzer

The torrefaction and pyrolysis experiments were performed at temperature 280°C and 500°C, respectively. In each experiment, the reactor was purged with nitrogen to remove the remaining oxygen in the system. The oven was pre-heated to 140C to allow the final torrefaction/pyrolysis temperature to be reached quickly. The biomass sample was loaded into a sample container (hereafter called “cradle”), which was placed in the cold zone during the thermal stabilization of the reactor and rapidly inserted into the hot zone of the reactor once the temperature reached 140C to start the torrefaction/pyrolysis. About 5±0.1 g of raw biomass was


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used for the torrefaction experiment. In the subsequent pyrolysis experiment, about 2±0.1 g of solid torrefied product was used. The sample was then heated at 10C/min until reached the final reaction temperature and maintained at this temperature for 45 minutes. A continuous flow of nitrogen at 0.5 L/min was supplied for both torrefaction and pyrolysis experiment. The condensable liquid and non-condensable gases produced during torrefaction or pyrolysis passed through the two glass condensers, which were cooled to -20C in a cryostat containing a mixture of ethylene glycol and water. The non-condensable gas species were analyzed online by the micro-gas analyzer (micro-GC, Agilent Technologies, Varian CP-4900). Once the torrefaction/pyrolysis finished, the cradle was returned to the cold zone and the heater was switched off. When the cradle reached the room temperature, the solid product was weighed and kept in the desiccator. The biomass sample, fittings, connector tubes and condensers were weighed before and after each experiment to determine the yield of solid and condensable products. The condensable products were collected by rinsing with acetone (Honeywell, purity 99.5%), and stored in a refrigerator for further analysis. Each experiment was conducted at least in duplication. 2.3 Analytical method 2.3.1 Analysis of solid products The analysis of moisture content was performed according to the NF EN 14774-1. The proximate analysis including that from the volatile matter and ash content was performed according to the XP CEN/TS 15148 and XP CEN/TS 14775 standard, respectively, while the fixed carbon was defined by difference. The ultimate analysis (C, H, and N) was analyzed according to the standard XP CEN/TS 15104 using an elemental analyzer (Elementar, vario


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MACRO cube), while the O content was determined by difference. The heating value of biomass was measured according to the XP CEN/TS 14918 using a bomb calorimeter (Parr 6200). 2.3.2 Analysis of condensable products The water content of condensable products was analyzed by Karl-Fischer titration (Mettler Toledo, Karl Fischer V20) according to the ASTM E203-80 standard. Since acetone itself contains some water, a sample of acetone used during rinsing of condensers was kept, and the water content in acetone was also measured to subtract its water content from those of condensable products. The condensable species were analyzed by a gas chromatography-mass spectrometry (GC-MS, Agilent 6890 chromatograph coupled with an Agilent 5975 mass spectrometer). The GC column was DB1701, 60 m long, 0.25 mm diameter with a film thickness of 0.25 m. Helium was used as carrier gas with a constant flow rate at 1.9 mL/min. Analysis with GC-MS was carried out with two modes (split and splitless mode). For the split mode, the split ratio was 10:1, and the column oven temperature was programmed from 45C to 120C at 3C/min, then increased to 270C at 20C/min. A similar program was applied for the splitless mode but held at 270C for 60 min. The transfer line was maintained at 270C. The mass spectrum was acquired using a quadrupole with an electron voltage of 70 eV. The quadrupole temperature was 150C and the ion source temperature was 230C. A sample volume of 2 mL of condensable species was filtered through a 0.45 m nylon microfilter (Agilent) prior to the analysis to remove the contaminants. Then, 1 mL of sample was transferred to a vial and mixed with a known concentration of 4 deuterated compounds used as internal standards (acetic acidd4, phenol-d6, toluene-d8, and phenanthrene-d10) for quantification. For analysis, 1 L was injected and then analyzed. The compounds were identified by comparing their spectrum with those in the NIST database.


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2.3.3 Analysis of non-condensable gas The non-condensable gases were analyzed online by the micro-gas analyzer (micro-GC, Agilent Technologies, Varian CP-4900). The concentration of N2, O2, H2, CH4, CO, CO2, C2H4 and C2H6 were determined. The content of N2, O2, H2, and CO was detected with the Molsieve 5A column, while CH4, CO2, C2H4, and C2H6 were detected with the Poraplot Q column. The mass of non-condensable gases was calculated from the flow rate of N2, which remained constant at 0.5L/min at STP throughout the experiment. 3. RESULTS AND DISCUSSION 3.1 Fuel characterization Table 1 shows the basic properties of biomass feedstocks including that of proximate and ultimate analysis and lower heating value (LHV). The characteristics of all biomass samples are quite similar, i.e. high volatile matter but low fixed carbon content. The carbon, hydrogen and oxygen contents in biomasses varied between 44.7-51.5 wt.%, 5.3-5.8 wt.%, and 40.5-43.2 wt.%, respectively with small amounts of nitrogen content (i.e. < 1 wt.%). The major difference among the biomass samples studied is the ash content. For example, woody biomasses (i.e. pine and ash wood) have the low ash contents (0.3-1.5 wt.%), while wheat straw shows the highest ash content closed to 9 wt.%. The low heating values of biomasses varied around 16.6-19.2 MJ/kg (dry basis).


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Table 1 Moisture content, Proximate, Ultimate and Heating value analyses Pine

Ash wood

Miscanthus

Wheat straw

Proximate analysis (wt.%, db) Volatile matter

83.3±0.1

80.2±0.1

78.5±0.2

72.7±0.1

Ash content

0.3±0.1

1.5±0.1

2.9±0.1

8.6±0.1

Fixed carbon

16.4±0.1

18.3±0.1

18.6±0.2

18.7±0.2

Ultimate analysis (wt.%, db) Carbon (C)

51.5±0.3

49.6±0.7

48.3±0.7

44.7±0.9

Hydrogen (H)

5.8±0.2

5.4±0.5

5.6±0.6

5.3±0.3

Nitrogen (N)

0.2±0.06

0.3±0.05

0.3±0.04

0.9±0.07

Oxygen (O)

42.3±0.1

43.2±0.7

43.0±0.6

40.5±0.5

19.2±0.3

18.4±0.7

17.9±0.7

16.6±0.7

LHV (MJ/kg, db)

The structural components in biomass feedstocks and sugar compositions in hemicellulose varied among the type of biomasses. Table 2 shows the structural components in biomass and sugar compositions in hemicellulose. Details for the characterization of structural components and sugar compositions in hemicellulose are presented in Alonso et al. [21]. Cellulose is a major constituent in biomasses. Among the different biomasses used in this study, cellulose contents vary between 34-46 wt.%. The contents of hemicellulose vary between 22-26 wt.%, while the contents of lignin vary between 21-28 wt.%. Pine has the greatest hemicellulose content compared with other biomass feedstocks. Considering the lignin content, woody biomasses (i.e. pine and ash wood) contain a higher lignin proportion, i.e. over 25 wt.%, while non-woody biomasses (i.e. miscanthus and wheat straw) contain around 20 wt.% of lignin. The analysis of sugar compositions in hemicellulose showed that xylan is the major composition in


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all biomass feedstocks except pine. The major sugar composition in hemicellulose of pine is mannan. Table 2 Structural components and sugar compositions in hemicellulose Pine

Ash wood

Miscanthus

Wheat straw

Structural component (wt.%) Cellulose

36.7

39.0

45.7

33.8

Hemicellulose

26.1

21.9

22.8

21.7

Lignin

27.5

26.3

20.2

20.5

Extractives

8.4

10.0

8.6

15.7

Sugar composition in hemicellulose (wt.%) Acetyl

1.7

3.6

2.6

1.7

Mannan

10.3

1.2

0.3

0.4

Xylan

5.0

14.3

17.2

16.0

Galactan

1.7

0.6

0.4

0.9

Arabinan

1.0

1.6

1.9

2.3

Other sugars

6.4

0.6

0.4

0.6

3.2 Effects of particle size and biomass composition on torrefaction 3.2.1 Product distribution through torrefaction As the particle size of biomass is one of the important parameters affecting the yield and properties of torrefied products, experiments were conducted by varying the particle size in the range of < 500 µm to 10,000 µm. During torrefaction, biomass is subjected to mass loss. This is mainly caused by the thermal degradation of the chemical components in biomass [22]. The initial biomass is converted mainly into solid (torrefied biomass), condensable (water and dry condensable species), and non-condensable gases (mainly CO and CO2). Fig. 3 shows the


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product yield of various biomasses during torrefaction at 280°C as a function of particle size. The product mass balance closes rather well with values between 95-99 wt.%. The loss during torrefaction was assumed to be mainly from the recovery of condensable fractions as some parts of condensable product condensed on the reactor wall, which could not be removed and directly weighed. Solid was the main product from torrefaction, varying in the range of 59-76 wt.% depending on the particle size and feedstock type. It was obviously found that particle size had a significant effect on the thermal degradation behavior during torrefaction which could affect the yield and properties of torrefied products. With increasing particle size, the solid product increased due to the lower volatile released. It was reported that the heat and mass transfer during torrefaction is controlled by the size of biomass [9, 23]. The heat required during the process depends on both of the convective and conductive heat transfer from the reactor to the biomass and within the biomass particle. Biomass with larger particle size would have less surface area per unit of mass than the smaller size, thus, reducing the rate of the convective heat transfer. In addition, larger particle sizes of biomass take longer time during the heat up process due to the higher resistance to heat and mass transfer, therefore it is likely to have a shorter time at the reaction temperature [10,24]. Water was the main volatile product released during torrefaction, accounting for around one-third of the total volatile products on average. Water is mainly released during the dehydration reactions between organic molecules [25]. CO2 was found as the main non-condensable gas species, which is released by the decarboxylation of acid groups in hemicellulose [26]. The formation of CO can be likely attributed to the mineral matters in biomass, which act as a catalyst in the reaction of CO2 and steam with porous char to produce CO [27].


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Fig.3 Product distribution of torrefaction experiments at 280°C As shown by Alonso et al. [21] and Thành et al. [28], the (dry) condensable species composition is related to the chemical structure of biomass. The details of (dry) condensable species released during experiments are presented in Section 3.2.3. Feedstock type is one of the crucial parameters influencing the torrefaction product yields. As presented in Fig. 3, pine had the greatest solid mass yield for all particle sizes in the range of the study, while wheat straw showed the lowest one. This observation is in accordance with the result from the previous study which reported that the solid to liquid conversion of agricultural residues is higher than that of wood under the same torrefaction conditions [29]. The difference in torrefaction behavior could be explained by the difference in lignocellulosic structures and properties of biomass among cellulose, hemicellulose, and lignin. It is well known that hemicellulose is strongly active at torrefaction temperature range. Thus, the torrefaction


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performance of biomass depends on the thermal degradation of these biomass polymers. Hemicellulose degradation occurs over the range of torrefaction temperature, while cellulose and lignin are slightly or rarely affected [30, 31]. Among all biomasses studied, pine showed the highest solid mass yield, while wheat straw showed the lowest one. This can be explained by the different reactivity of sugar components in hemicellulose. Pine had the highest mannan content, which is a stable sugar in hemicellulose [32]. On the contrary, the lowest solid mass yield of wheat straw is attributed to the high content of xylan, which is the most reactive component of hemicellulose within the torrefaction temperature range and it degrades faster than any other solid components of the biomass [23]. Also, the high ash content of wheat straw especially potassium element, which is typically found in wheat straw, is expected to promote the mass loss during torrefaction. The effect of potassium to promote the mass loss during torrefaction was confirmed by Macedo et al. [33]. 3.2.2 Chemical properties of torrefied biomass Table 3 shows the chemical properties including that from proximate and ultimate analyses, LHV and energy yield of torrefied biomasses as a function of particle size compared with those values of the raw biomasses. After torrefaction, the moisture content in biomasses decreased to 3.5-4.2 wt.%. Thành et al. [28] reported that the moisture content of torrefied biomass could reduce up to 0 wt.% just after torrefaction at 280C, but this moisture will increase with time until stabilization. However, the presence of moisture in the current study is interesting to show that torrefied biomass is quite resistant to water as it can absorb only 3-4 wt.% of moisture even if the torrefied biomass was kept in the atmosphere for a long time. As some volatiles have been liberated during torrefaction, fixed carbon and ash content increased compared to raw biomasses. The ultimate analysis results revealed that after torrefaction the


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carbon content significantly increased, while the oxygen content decreased so that the atomic ratio of oxygen to carbon (O/C) decreased compared to that of the raw biomass. The hydrogen and nitrogen contents remained slightly constant from raw biomass to torrefied biomass. The decrease in oxygen confirms that the oxygen is released into functional groups in biomass such as water, CO2, CO and some oxygen-containing compounds (i.e. acetic acid and methanol) during torrefaction. Among all biomasses studied, torrefaction of wheat straw showed the greatest change in carbon and oxygen content for all particle sizes studied, while the smallest change in carbon and oxygen was observed in the case of pine. Undergoing torrefaction, moisture is naturally removed during the drying step and the products become more hydrophobic. However, re-absorption of moisture is possible depending on the degree of torrefaction. As expected, the moisture content was present at similarly low level and the particle size does not have any significant influence on the residual moisture content in torrefied product. Regardless of biomass type, the volatile matter gradually increased with an increase in particle size; the fixed carbon and ash content exhibited the opposite trend. The elemental analysis results revealed that with the increase in particle size, the carbon content decreased, while the oxygen and hydrogen content showed the opposite trend. Through these results, it can be confirmed that particle size has an influence on the chemical properties of torrefied biomass. It was observed that the LHV of biomasses after torrefaction at 280C increased around 2.4-4.8 MJ/kg (or 12.3-28.6 %) compared to that in the case of raw biomass feedstocks. The increased heating value of torrefied biomass may have the advantage for utilization as a fuel in the thermal conversion process. As the LHV of biomass is always correlated to the carbon content, thus, the greatest change in the increment of LHV was observed in the torrefied wheat


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straw. However, the LHV seems not to be influenced by particle size, but the trend is increasing with decreasing particle size. Energy yield is one of the important parameters in determining the torrefaction performance of biomass. The energy yield, which is the ratio of energy in the torrefied solid on the energy available in raw biomass, was calculated according to Equation (1). As presented in Table 3, the energy yield increased with an increase in particle size. Among all biomass samples studied, pine had the highest energy yield, while wheat straw had the lowest one. Energy yield (%) = Mass yield × (LHVt/LHV0) ----- (1) Where LHVt is the LHV of torrefied biomass (dry basis) and LHV0 is the LHV of raw biomass (dry basis).


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Table 3 Moisture content, Proximate and ultimate analysis, low heating value (LHV) and energy yield of raw and torrefied biomasses Moisture

Proximate analysis

Ultimate analysis

LHV

Energy

(wt.%)

(wt.%, db)

(wt.%, db)

(MJ/kg,

yield (%, db)

Volatile

Ash

matter

Fixed

C

H

N

O

O/C

db)

carbon

Pine Raw

83.3±0.1

0.3±0.1

16.4±0.1

51.5±0.3

5.8±0.2

0.2±0.06

42.3±1.1

0.8±0.7

19.2±0.3

Torrefied < 500 µm

3.5±0.7

73.1±0.5

1.2±0.1

25.7±0.1

57.8±0.6

5.6±0.4

0.2±0.06

35.1±0.3

0.6±0.5

22.1±0.5

82.7±0.7

Torrefied 500-5,000 µm

3.5±0.4

74.9±0.1

0.6±0.1

24.6±0.7

57.2±0.4

5.7±0.3

0.1±0.09

36.5±0.3

0.6±0.5

21.8±0.4

84.0±0.5

Torrefied 5,000-10,000 µm

3.6±0.1

75.9±0.2

0.4±0.3

23.8±0.2

56.6±0.6

5.6±0.2

0.2±0.03

37.2±0.2

0.7±0.2

21.6±0.4

85.2±0.3

80.2±0.1

1.5±0.1

18.3±0.1

49.6±0.7

5.4±0.5

0.3±0.05

43.2±0.7

0.9±0.5

18.4±0.7

Ash wood Raw Torrefied < 500 µm

3.4±0.5

64.6±0.7

4.6±0.9

30.8±0.2

58.7±0.5

5.0±0.5

0.4±0.07

31.2±0.3

0.5±0.4

22.4±0.3

81.3±0.5


3.5±0.4

69.6±0.1

1.7±0.1

28.7±0.1

58.1±0.5

5.1±0.3

0.2±0.10

34.9±0.3

0.6±0.4

22.1±0.4

84.8±0.6


3.6±0.4

70.3±0.2

1.6±0.3

28.1±0.2

58.0±0.6

5.2±0.7

0.3±0.03

34.9±0.3

0.6±0.4

22.1±0.4

85.9±0.6

78.5±0.2

2.9±0.1

18.6±0.2

48.3±0.7

5.5±0.6

0.3±0.04

43.0±0.6

0.9±0.5

17.9±0.7

Miscanthus Raw Torrefied < 500 µm

3.5±0.5

61.3±0.1

5.1±0.3

33.6±0.4

58.6±0.4

5.1±0.6

0.4±0.06

30.9±0.3

0.5±0.3

22.4±0.9

82.4±0.3


4.0±0.1

62.3±0.3

4.1±0.1

33.6±0.3

58.2±0.4

5.2±0.3

0.3±0.06

32.2±0.3

0.6±0.4

22.2±0.6

84.7±0.6


4.2±0.1

63.7±0.3

3.7±0.3

32.5±0.3

56.3±0.5

5.2±0.4

0.3±0.03

34.4±0.3

0.6±0.4

21.9±0.4

85.4±0.4

Wheat straw Raw

72.7±0.1

8.6±0.1

18.7±0.2

44.7±0.9

5.3±0.3

0.9±0.07

40.5±0.5

0.9±0.2

16.6±0.7

Torrefied < 500 µm

4.1±0.3

49.9±1.1

16.4±0.8

33.7±0.3

56.7±0.5

4.4±0.4

1.4±0.03

21.1±0.4

0.4±0.3

21.4±0.6

75.2±0.5


4.1±0.4

52.6±0.7

13.6±0.6

33.8±0.9

56.1±0.6

4.5±0.4

1.2±0.04

24.5±0.4

0.4±0.6

21.1±0.6

78.2±0.5


4.2±0.1

53.1±0.3

13.3±0.1

33.6±0.6

55.9±0.5

4.6±0.4

1.2±0.07

25.0±0.2

0.5±0.4

21.0±0.7

80.2±0.7


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Energy & Fuels

3.2.3 Dry condensable products Fig. 4 shows the composition of some major (dry) condensable species quantified by GCMS. It was observed that particle size does not affect the composition of the (dry) condensable species. Acetic acid was the major organic species found in all types of biomass except pine. Since acetic acid mainly released from the degradation of hemicellulose via the hydrolysis of acetyl group in xylan [34]. this difference could be explained by the sugar compositions of hemicellulose in pine. Formaldehyde was found in all biomasses studied except wheat straw. Glycolaldehyde and 2-propanone-1-hydroxy were found in all biomasses studied. Among all biomasses studied, wheat straw showed the least glycolaldehyde content, but the highest content of 2-propanone-1-hydroxy. The release of anhydrosugar, i.e. LAC (3,6 dioxabicyclo [3.2.1] octan-2-one,1-hydroxy-,(1R)) was also observed during torrefaction. Pine is the only biomass that produces the significant content of LAC, whereas the others showed the insignificant LAC content. The release of anhydrosugar was reported as the result of cellulose depolymerization, which occurs between 240 and 350°C [35].


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 4 Composition of (dry) condensable species during torrefaction at 280°C

3.3 Effect of torrefaction on pyrolysis products 3.3.1 Product distribution through the pyrolysis of raw and torrefied biomasses The results from the previous section led to the conclusion that torrefaction condition had a significant effect on the yield and properties of torrefied products. The opportunity of reduction of grinding energy obtained by torrefaction encourages industries to use the large-size biomass feedstocks and grind them after torrefaction instead of using biomass ground to small particle size [10]. In addition, since the analysis results of torrefied biomasses in the range of 500-5,000 µm were found attractive in term of the improved fuel properties and energy yield that were retained in the biomasses, the pyrolysis experiments focused on this range of particle size. Fig. 5 shows the distribution of product yield during pyrolysis of raw and torrefied biomasses at 500°C in the nitrogen atmosphere. During pyrolysis, large complex molecules are decomposed into


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Energy & Fuels

several smaller molecules. Products consist of solid (hereafter called char), condensable liquids (or tar), and non-condensable gases. The closure of product distribution was in the range of 97100 wt.%. Similarly to the previous section, the losses during pyrolysis were assumed to be from the recovery of condensable liquid fractions. It was observed that torrefaction had a significant effect on the yield of pyrolysis products. Regardless the biomass type, the char yield of torrefied biomass was higher, while the yield of tar was significant lower, compared to those of the raw biomass. Slightly lower gas yield was observed in the pyrolysis of torrefied biomass. The change in pyrolysis product yields is primarily attributed to the change in chemical compositions of biomass by torrefaction and to the release of some volatiles during torrefaction. The char yield from pyrolysis of raw biomasses increased from 22.0-32.9 wt.% to 32.4-52.2 wt.% after torrefaction. The higher char yield of torrefied biomass could be explained by the increase in relative ash and lignin content after torrefaction. During torrefaction, the volatile matter was released while mineral matters remained so the relative ash content in solid char product increased. This resulted in a higher char yield in the case of pyrolysis of torrefied biomass as compared to raw biomass. The decrease in tar yield after torrefaction could be explained by the decrease in oxygen content of biomass after torrefaction (referred to Table 3), which reduced the crosslinking reaction during pyrolysis to form volatiles [36]. For all biomasses studied, the tar yields obtained from pyrolysis of torrefied biomasses were 42% to 62% lower compared to pyrolysis of raw biomasses. CO2, CO and CH4 were the main gas species released during pyrolysis at 500°C (results not show). The other gases (i.e. H2, C2H4 and C2H6) were also detected but their concentrations were quite small especially H2. It was observed that the yield of CO2 and CO decreased after torrefaction, while the yield of CH4 slightly increased. The decrease in CO2 and CO after torrefaction is attributed to the


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

decomposition of hemicellulose during torrefaction. The increase in CH4 is attributed to the demethoxylation during the degradation of lignin, which was enhanced after torrefaction.

Fig. 5 Product distribution during pyrolysis of raw and torrefied biomasses at 500C

3.3.2 Analysis of tar from pyrolysis of raw and torrefied biomass The condensable liquid products (or tar) consisted of water and (dry) condensable species. Table 4 shows the water and (dry) condensable species content in tar from pyrolysis of raw and torrefied biomasses at 500°C. The water content from pyrolysis of raw biomasses varied in the range of 18.0-23.4 wt.%, among which wheat straw had the highest water content. The water in tar was resulting as a product mainly from the dehydration occurred during pyrolysis [37]. Compared to the pyrolysis of raw biomasses, the water fraction significantly dropped to 11.8-12.9 wt.% due to the dehydrating effect of torrefaction and the reduced production of water in the subsequent step. The yield of (dry) condensable species from pyrolysis of raw to torrefied


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Energy & Fuels

biomasses decreased from 33.8 to 28.7 wt.%, 27.4 to 19.4 wt.%, 21.1 to 16.9 wt.%, and 15.9 to 12.2 wt.% in the experiment of pine, ash wood, miscanthus, and wheat straw, respectively.

Table 4 Yield (wt.%, db) of water and (dry) condensable species from pyrolysis of raw and torrefied biomasses Pine

Ash wood

Miscanthus

Wheat straw

Raw

Torrefied

Raw

Torrefied

Raw

Torrefied

Raw

Torrefied

Water

18.2±0.4

12.0±0.6

19.8±1.7

12.9±1.0

18.0±1.0

11.8±0.8

23.4±0.8

12.3±0.7

(Dry) condensable

33.8±1.4

28.7±1.3

27.4±1.0

19.4±0.3

21.1±0.4

16.9±1.3

15.9±0.9

12.2±0.7

species

Fig. 6 shows the composition of (dry) condensable species from pyrolysis of raw and torrefied biomasses quantified by GC-MS. These organic compounds can cause a severe problem in downstream processing, especially gasification, a reduction of these tar species before being utilized in the future process is important. For the GC-MS analysis, several organic compounds were observed on the chromatogram and grouped into 9 major chemical functional groups. It was observed that the nature of biomass feedstocks influenced the yield and composition of (dry) condensable species. For pyrolysis of raw biomasses, ketone, furan, guaiacol, and phenol were the major organic species found in all types of biomass, accounted around 73-81% of the (dry) organic compounds. Ketone and furan are principally derived from the thermal degradation of cellulose [38]. Ketone was the major organic species found in wheat straw. The high content of ketone in wheat straw, especially acetol, could be explained by the effect of minerals in ash as wheat straw had the highest ash content among all biomasses studied. It was reported that the mineral contents in biomass, especially potassium, favored the production of low molecular weight compounds such as acetol by promoting the decomposition of glycosidic units in


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cellulose through the heterolytic mechanism [39]. Furan contents were found to be similar for all biomasses and varied in the range of 11.5-13.6 % of (dry) organic compounds. Guaiacol and phenol are generally released from the thermal degradation of lignin [40], however, the lignin structure from different biomasses differs somewhat, mainly in methoxy substitution and the degree of carbon-carbon linkage between phenyl groups [41]. Guaiacol was the major organic species in all biomasses except wheat straw, while phenol content in non-woody biomasses was higher than that of woody biomasses. (Dry) condensable species of woody biomasses contained higher sugar content than that of non-woody biomasses. The sugar content in pine was two times higher than that of ash wood. It was clearly observed that torrefaction had an important effect on the (dry) condensable components. As presented in Fig. 6, regardless of the biomass type, the content of alcohol, aldehyde, ketone, acid, furan, and guaiacol from torrefied biomass is lower than from raw biomass, while sugar, phenol, and PAH content were noticeably higher. As a large proportion of hemicellulose and some parts of cellulose had been decomposed during torrefaction, alcohol, aldehyde, ketone, acid, furan, and guaiacol contents in (dry) condensable products were lower for torrefied biomass than for raw biomass. On the contrary, an increase in sugar and phenol content in (dry) condensable products could be explained by an increase in relative cellulose and lignin content by torrefaction. For the pyrolysis of wheat straw, a significant increase in PAH content was observed after torrefaction. The presence of PAH might be generated from the aromatic structure of lignin [42], which was enhanced after torrefaction.


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Energy & Fuels

Fig. 6 Composition of (dry) condensable species from pyrolysis of raw and torrefied biomasses at 500°C

3.4 Comparison on tar yield from the direct pyrolysis and integrated pyrolysis with torrefaction Since the effect of torrefaction was focused on the reduction of tar, the comparison on the amount of tar yields produced from the direct pyrolysis and from the integrated pyrolysis with torrefaction were made. Fig. 7 shows the comparison of condensable products yield (tar) from the direct pyrolysis (without torrefaction) of raw biomass on one hand, and the integrated pyrolysis process consisting of torrefaction and subsequent pyrolysis of various torrefied biomass feedstocks on the other hand. For the integrated pyrolysis including torrefaction, the tar yields in the pyrolysis step were converted into the raw biomass basis. As presented in the schematic diagram, for an example, direct pyrolysis of 1 kg pine generated 0.52 kg of tar, while the integrated pyrolysis with torrefaction generated 0.50 kg of tar when considering the condensable products released during torrefaction and pyrolysis stage. Thus, 0.02 kg of all the


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

condensable liquids were reduced (or around 4% reduction). For other biomass types, the integrated pyrolysis with torrefaction can decrease all the condensable products by 12 % in the experiment of ash wood and 3 % in the experiment of miscanthus and wheat straw compared with the direct pyrolysis. The decrease in all the condensable products from the integrated pyrolysis with torrefaction is attributed to the structural change of biomass after torrefaction. The difference in reduction performance of condensable products from different biomass species may be explained by the difference in structural composition of biomass. The change in chemical structure of biomass during torrefaction can affect the tar yield during pyrolysis. However, in the current study, we did not analyze the structural change in each biomass after torrefaction. Thus, future work should be focused on the analysis of structural change after torrefaction for each biomass. This result shows that integrated pyrolysis with torrefaction is an effective method to minimize the tar yield from the pyrolysis process. Similarly, recovery of condensable liquids into two different steps (after torrefaction and after pyrolysis) can be considered as a first chemical separation of tar products. It is interesting for a chemical valorization afterwards of these condensable species if a valorization as chemical bioproducts is considered. For the integrated pyrolysis process with torrefaction, torrefaction is an energy consuming process which means that an external heat source is required during the process. The heat requirements for torrefaction are small due to the low temperature operated. However, an energetic integration of torrefaction in the whole process by recovering energy of the pyrolysis step for torrefaction step should be done in future work.


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Fig. 7 Schematic diagram for the comparison on tar yield during direct and integrated pyrolysis with torrefaction

4. CONCLUSIONS The impact of torrefaction on tar reduction was investigated. Different particle sizes of biomasses were torrefied at 280°C, and then the torrefied biomasses were subsequently pyrolyzed at 500°C. The results showed that increasing particle size resulted in an increased


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

yield of solid torrefied biomass, while the yield of condensable and non-condensable gases decreased. The mass loss during torrefaction was attributed to the reactivity of sugar component in hemicellulose and inorganic matters in biomass. Xylan was the most reactive sugar, while mannan was the most stable one. The torrefied biomasses were subsequently pyrolyzed at 500°C. The results showed that the tar yield of torrefied biomasses significantly dropped as some volatile matters had been released. The analysis of tar components indicated that after torrefaction the content of alcohol, aldehyde, ketone, acid, furan, and guaiacol decreased; while sugar, phenol, and PAH increased. For all biomasses studied, the tar yields of biomasses after torrefaction were 42 % to 62 % lower compared with direct pyrolysis of raw biomasses. However, when considering the overall tar reduction, the pretreatment of fuels with torrefaction prior to pyrolysis can decrease the total condensable liquid yield by 3 % to 12 %, compared with the direct pyrolysis.

ACKNOWLEDGEMENTS The authors gratefully acknowledge the Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) PhD Program (PHD/0007/2556) and the Franco-Thai Scholarship Program (French Government Grants from the French Embassy in Thailand) for the financial support.


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REFERENCES [1] Bridgwater, A.V. Renewable fuels and chemicals by thermal processing of biomass. Chem. Eng. J. 2003, 91 (2-3), 87-102. [2] Dufour, A.; Masson, E.; Girods, P.; Rogaume, Y.; Zoulalian, A. Evolution of aromatic tar composition in relation to methane and ethylene from biomass pyrolysis-gasification, Energy Fuels. 2011, 25(9), 4182-4189. [3] Morf, P.; Hasler P.; Nussbaumer, P. Mechanisms and kinetics of homogeneous secondary reactions of tar from continuous pyrolysis of wood chips, Fuel, 2002, 81, 843-853. [4] Kirsanovs, V.; Zandeckis, A. Investigation of biomass gasification process with torrefaction using equilibrium model. Energy Procedia. 2015, 72, 329-336. [5] Chen, D.; Zheng, Z.; Fu, K.; Zeng, Z.; Wang, J.; Lu, M. Torrefaction of biomass stalk and its effect on the yield and quality of pyrolysis products. Fuel. 2015, 159, 27-32. [6] Chen, D.; Cen, K.; Jing, X.; Li, C.; Ma, Z. An approach for upgrading biomass and pyrolysis product quality using a combination of aqueous phase bio-oil washing and torrefaction pretreatment. Bioresour. Technol. 2017, 233, 150-158. [7] Chen, D.; Mei, J.; Li, H.; Li, Y.; Lu, M.; Ma, T.; Ma, Z. Combined pretreatment with torrefaction and washing using torrefaction liquid products to yield upgraded biomass and pyrolysis products. Bioresour. Technol. 2017, 228, 62-68. [8] van der Stelt, M.J.C.; Gerhauser, H.; Kiel, J.H.A.; Ptasinski, K.J. Biomass upgrading by torrefaction for the production of biofuels: A review. Biomass Bioenergy. 2011, 35 (9), 37483762. [9] Peng, J.; Bi, H.T.; Sokhansani, S.; Lim, J.C. A study of particle size effect on biomass torrefaction and densification. Energy Fuels. 2012, 26(6), 3826-3839.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[10] Bates, R.B.; Ghoniem, A.F. Modeling kinetics-transport interactions during biomass torrefaction: The effects of temperature, particle size, and moisture content. Fuel. 2014, 137(1), 216-229. [11] Chen, W.H.; Peng, J.; Bi, X.T. A state-of-the-art review of biomass torrefaction, densification and applications. Renew. Sust. Energ. Rev. 2015, 44, 847-866. [12] Wang, Z.; Lim, C.J.; Grace, J.R.; Li, H.; Parise, M.R. Effects of temperature and particle size on biomass torrefaction in a slot-rectangular spouted bed reactor. Bioresour. Technol. 2017, 244, 281-288. [13] Wang, M.J.; Huang, Y.F.; Chiueh, P.T.; Kuan, W.H.; Lo, S.L. Microwave-Induced torrefaction of rice husk and sugarcane residue. Energy. 2012, 37(1), 177-184. [14] Tsalidisa, G.A.; Tsekos, C.; Anastasakis, K.; Jong, W. The impact of dry torrefaction on the fast pyrolysis behavior of ash wood and commercial Dutch mixed wood in a pyroprobe. Fuel Process. Technol. 2018, 177, 255-265. [15] Hlavsová, A.; Corsaro, A.; Raclavská, H.; Vallová, S.; Juchelková, D. The effect of feedstock composition and taxonomy on the products distribution from pyrolysis of nine herbaceous plants. Fuel Process. Technol. 2016, 144, 27-36. [16] Arias, B.; Pevida, C.; Fermoso, J.; Plaza, M.G.; Rubiera, F.; Pis, J.J. Influence of torrefaction on the grindability and reactivity of woody biomass. Fuel Process. Technol. 2008, 89(2), 169-175. [17] Ma, Z.; Chen, J.; Gu, B.; Bao, B.; Q, Zhang. Determination of pyrolysis characteristics and kinetics of palm kernel shell using TGA-FTIR and model-free integral methods. Energy Convers. Manag. 2015, 89, 251-259.


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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[18] Yu, H.; Zhang, Z.; Li, Z.; Chen, D. Characteristics of tar formation during cellulose, hemicellulose and lignin gasification. Fuel. 2014, 118, 250-256. [19] Fagbemi, L.; Khezami, L.; Capart, R. Pyrolysis products from different biomasses: application to the thermal cracking of tar. Appl Energy. 2001, 69, 293-306. [20] Hosoya, T.; Kawamoto, H.; Saka, S. Secondary reactions of lignin-derived primary tar components. J. Anal. Appl. Pyrolysis. 2008, 83, 78-87. [21] Alonso, E.R.; Dupont, C.; Heux, L.; Perez, D.D.; Commandré, J.M.; Gourdon, C. Study of solid chemical evolution in torrefaction of different biomasses through solid-state 13C crosspolarization/magic angle spinning NMR (nuclear magnetic resonance) and TGA (Thermogravimetric analysis), Energy. 2016, 97, 381-390. [22] Poudel, J.; Ohm, T.I.; Oh, S.C. A study on torrefaction of food waste. Fuel. 2015, 140, 275281. [23] Prins, M.J.; Ptasinski, K.J.; Janssen, F.J.J.G. Torrefaction of wood: Part 1. Weight loss kinetics. J. Anal. Appl. Pyrolysis. 2006, 77(1), 28-34. [24] Basu, P.; Rao, S.; Dhungana, A. An investigation into the effect of biomass particle size on its torrefaction. Can. J. Chem. Eng. 2013, 19, 466-474. [25] Bridgeman, T.G.; Jones, J.M.; Shield, I.; Williams, P.T. Torrefaction of reed canary grass, wheat straw and willow to enhance solid fuel qualities and combustion properties. Fuel. 2008, 87(6), 844-856. [26] Chen, Y.; Yang, H.; Wang, X.; Zhang, S.; Chen, H. Biomass-based pyrolytic polygeneration system on cotton stalk pyrolysis: Influence of temperature. Bioresour. Technol. 2012, 107, 411418.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[27] Prins, M.J.; Ptasinski, K.J.; Janssen. F.J.J.G. Torrefaction of wood: part 2. Analysis of products. J. Anal. Appl. Pyrolysis. 2006, 77(1), 35-40. [28] Thành, K.L.; Commandré, J.M.; Valette, J.; Volle, G.; Meyer, M. Detailed identification and quantification of the condensable species released during torrefaction of lignocellulosic biomasses. Fuel Process. Technol. 2015, 139, 226-235. [29] Bergman, P.C.A.; Boersma, A.R.; Zwart, R.W.R.; Kiel, J.H.A. Torrefaction for biomass cofiring in existing coal-fired power stations, Energy Res. Cent. Neth. 2005. ECN-C-05-013. [30] Chen, W.H.; Kuo, P.C. Torrefaction and co-torrefaction characterization of hemicellulose, cellulose and lignin as well as torrefaction of some basic constituents in biomass. Energy. 2011, 36(2), 803-811. [31] Rousset, P.; Aguiar, C.; Labbé, N.; Commandré, J.M. Enhancing the combustible properties of bamboo by torrefaction. Bioresour. Technol. 2011, 102(17), 8225-8231. [32] Moreira, L.R.S.; Filho, E.X.F. An overview of mannan structure and mannan degrading enzyme systems. Appl. Microbiol. Biotechnol. 2008, 79, 165-178. [33] Macedo, L.A.; Commandré, J.M.; Rousset, P.; Valette, J.; Petrissans, M. Influence of potassium carbonate addition on the condensable species released during torrefaction of lignocellulosic biomasses. Fuel Process. Technol. 2018, 169, 248-257. [34] Degroot, W.F.; Pan, W.P.; Rahman, M.D.; Richards, G.N. First chemical events in pyrolysis of wood. J. Anal. Appl. Pyrolysis. 1988, 13(3), 221-231. [35] Mohan, D.; Pittman, C.U.; Steele, P.H. Pyrolysis of wood/biomass for bio-oil: A critical review. Energy Fuels. 2006, 20(3), 848-889. [36] Zheng, A.; Zhao, Z.; Chang, S.; Huang, Z.; Wang, X.; He, F.; Li, H. Effect of torrefaction on structure and fast pyrolysis behavior of corncobs. Bioresour. Technol. 2013, 128, 370-377.


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Energy & Fuels

[37] Zheng, Y.; Tao, L.; Yang, X.; Huang, Y.; Liu, C.; Gu, J.; Zheng, Z. Effect of the torrefaction temperature on the structural properties and pyrolysis behavior of biomass. BioResources. 2017, 12(2), 3425-3447. [38] Zhao, C.; Jiang, E.; Chen, A. Volatile production from pyrolysis of cellulose, hemicellulose and lignin. J. Energy. Inst. 2017, 90(6), 902-913. [39] Nowakowski, D.J.; Jones, J.M.; Brydson, R.M.D.; Ross, A.B. Potassium catalysis in the pyrolysis behaviour of short rotation willow coppice. Fuel. 2007, 86(15), 2389-2402. [40] Qu, T.; Guo, W.; Shen, L.; Xiao, J.; Zhao, K. Experimental study of biomass pyrolysis based on three major components: hemicellulose, cellulose, and lignin. Ind. Eng. Chem. Res. 2011, 50(18), 10424-10433. [41] Demirbas, A. Estimating of structural composition of wood and non-wood biomass samples. Energy Source. 2005, 27, 761-767. [42] Wu, C.; Wang, Z.C.; Huang, J.; Williams, P.T. Pyrolysis/gasification of cellulose, hemicellulose and lignin for hydrogen production in the presence of various nickel-based catalysts. Fuel, 2013, 697-706.


Torrefaction of Various Biomass Feedstocks and Its Impact on the

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