Bioresource Technology 243 (2017) 85–92
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Fast pyrolysis of durian (Durio zibethinus L) shell in a drop-type fixed bed reactor: Pyrolysis behavior and product analyses Y.L. Tan, A.Z. Abdullah, B.H. Hameed ⇑ School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
h i g h l i g h t s Fast pyrolysis of durian shell was studied using a drop-type fixed bed reactor. Effects of reaction temperature and biomass size on product yield were studied. Chemical compositions of bio-oil produced at different temperatures were compared.
a r t i c l e
i n f o
Article history: Received 9 April 2017 Received in revised form 28 May 2017 Accepted 4 June 2017
Keywords: Biomass Pyrolysis Bio-oil Characterization
a b s t r a c t Durian shell (DS) was pyrolyzed in a drop-type fixed-bed reactor to study the physicochemical properties of the products. The experiment was carried out with different particle sizes (up to 5 mm) and reaction temperatures (250–650 °C). The highest bio-oil yield was obtained at 650 °C (57.45 wt%) with DS size of 1–2 mm. The elemental composition and higher heating value of the feedstock, bio-oil (650 °C), and biochar (650 °C) were determined and compared. The compositions of product gases were determined via gas chromatography with thermal conductivity detector. The chemical composition of bio-oil was analyzed by gas chromatography–mass spectrometry. The bio-oil produced at lower temperature yields more alcohols, whereas the bio-oil produced at higher temperature contains more aromatics and carbonyls. Bio-oil has potential to be used as liquid fuel or fine chemical precursor after further upgrading. The results further showed the potential of bio-char as a solid fuel. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Recently, the utilization of lignocellulosic biomass as a renewable source for fuels and chemicals has been addressed by many researchers because of its favorable property of potential energy (Huang et al., 2016). Thermochemical methods, such as pyrolysis, gasification, liquefaction, and combustion are widely used for the conversion of biomass into energy and chemical products (Meesuk et al., 2012). Among the techniques, pyrolysis is effective and widely adopted in thermal decomposition for converting biomass waste into useful products in an oxygen-free atmosphere at relatively low temperatures (Fan et al., 2015). During pyrolysis, the biomass components are turned into light gases (volatiles), liquids (bio-oil), and solid char. All light gases, bio-oil, and char products are effective fuel sources because of their high heating values (Damartzis et al., 2011). Moreover, bio-oil contains various organic
⇑ Corresponding author. E-mail address:
[email protected] (B.H. Hameed). http://dx.doi.org/10.1016/j.biortech.2017.06.015 0960-8524/Ó 2017 Elsevier Ltd. All rights reserved.
compounds that can be used as chemical feedstock (Huang et al., 2014). Pyrolysis can be divided into three types, namely, slow, fast, and flash pyrolysis, based on the heating rate and vapor residence time. Furthermore, upgraded pyrolysis, such as microwave (Dai et al., 2017) and solar pyrolysis (Zeng et al., 2017), were introduced to optimize the quality and quantity of the products. Operating parameters, such as types of feedstock, biomass particle size and temperature, are important factors that will affect the product distribution and properties. These factors play important roles in the heat and mass transfer resistance that affect the volatilization of the biomass and the secondary reactions of primary volatiles (Hasan et al., 2017). Larger biomass particles tend to have greater temperature gradients from its center to the outer surface, thereby enhancing the intra-particle secondary reactions that increase the char yield (Shen et al., 2009). In general, maximum bio-oil yield can be obtained at the temperature range of 400–550 °C, and then the bio-oil and char are further decomposed into gases with further heating to temperatures higher than 600 °C because of secondary cracking reactions (Kan et al., 2016).
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Durian (Durrio zubethinus Linn), a member of the Bombaceae family, is one of the most popular fruit in Southeast Asia, especially in Malaysia, Indonesia, Thailand, and the Philippines (Amid and Mirhosseini, 2012). The tree grows to approximately 25–50 m in height with a typical buttressed trunk and oblong or elliptic leaves of 3–7 cm in length and dark green in color (Foo and Hameed, 2012). The fruit is oval with weight from 1–3 kg with an average length of 30 cm and a diameter of 15 cm based on its types. In Malaysia, the production of durian fruit is approximately 320,164 MT in 2013 according to the Malaysia Ministry of Agriculture and Agro-Based Industry statistical crop data (Manshor et al., 2014). Only 15%–30% of the entire fruit weight is edible, and the remaining shell and seeds are discarded as wastes, thereby causing an environmental problem if not disposed properly. The improper disposal of durian wastes may cause respiratory diseases, pungent smell, and water pollution (Prakongkep et al., 2014). Durian fruit shell (DS) consists of 60.5% cellulose, 13.1% hemicellulose, and 15.45% lignin (Masrol et al., 2015). This high cellulosic composition makes it a highly attractive source for value-added products, which are useful in various applications (Aditiya et al., 2016). Durian shell is a biomass produced in Southeast Asia that contains high volatile matters and carbon content. Previous works mainly concerned the preparation of activated carbon using durian shell but the pyrolysis vapor is ignored. The main purpose of this work is to study the effects of pyrolysis parameters on product distribution and properties by fast pyrolysis of DS in a drop-type fixed bed reactor. The reactions were completed at different temperatures (250–650 °C) with different particle sizes (up to 5 mm), and the products were collected and characterized. 2. Materials and methods 2.1. Preparation of DS sample DSs were collected from a local market in Malaysia and used as a raw material for pyrolysis. The collected samples were washed repeatedly with distilled water to remove dust and dirt, dried in an oven at 105 °C overnight to remove moisture, grinded into smaller pieces and sieved into sizes <0.5, 0.5–1, 1–2, and 2– 5 mm before the experiment was performed. The samples were stored in an airtight container before use. 2.2. Fast pyrolysis by drop-type fixed bed reactor Drop-type fixed bed pyrolysis reactor was used for the fast pyrolysis study of DS. This reactor consists of a cooling zone jacketed with tap water, a feeding system, a pyrolysis reactor, a condensation system, a carrier gas flow controller, and a temperature controller, which is modified from the reactor reported by Fermoso et al. (2016). Three grams of sample was purged with nitrogen gas in the wire mesh sample basket at cooling zone when the furnace was heated to the preset experimental temperature to remove the residual oxygen and ensure an inert experimental atmosphere for the pyrolysis reaction. A thermocouple was placed to touch the biomass and determine the actual temperature of biomass sample instead of the reactor temperature. Once the reactor reached the targeted temperature, the sample basket was pushed to the heating zone, and the temperature of the biomass was recorded. The sample was kept at the target temperature for 10 min. At the same time, the condensable vapor was quenched immediately in the condensation system. The temperature of the cooling agent (ethylene glycol–water mixture) was decreased to 4 °C by the chiller and pumped continuously to the cooling coil that surrounded the condenser tube to ensure that all the condensable volatiles can be condensed into liquid form.
The solid and liquid products were weighed while the quantity of the gas product was calculated by difference based on mass balance. The condensed liquid product was kept inside a dark sample bottle while the incondensable light gases were sampled in a gasbag to analyze the gas composition. The experiments were repeated at least thrice to calculate the standard deviation of each experiment. The solid, liquid, and gas products were analyzed. The effects of particle size and temperature on the product yield distributions were studied. 2.3. Analyses of raw materials and products The lignocellulosic content of the raw biomass was determined following the reported methods in the publication of Li et al. (2004). The proximate analysis was done using the Perkin Elmer Pyris TGA1 based on the ASTM methods: E871-82 to determine moisture content, E1755-01 to determine ash content, D3172-02 to determine volatile matter, and E870-82 to determine the fixed carbon in the biomass sample. Approximately 5 mg of sample was purged with N2 gas at a flow rate of 20 mL/min and heated to 850 °C at a heating rate of 20 °C/min. The nitrogen gas was then switched to air/oxygen to determine the ash content by the combustion of fixed carbon. Elemental analysis was conducted with Perkin Elmer 2400 Series II CHNS/O Elemental Analyzer to reveal the weight percentages of carbon, hydrogen, nitrogen, and sulfur in the samples. The oxygen content was measured by difference. Bomb calorimeter Model IKA C 200 was used to determine the heating values of feedstock, bio-oil, and bio-char based on German standard method DIN 51900. Water content was measured by Karl-Fischer titration using Metrohm 870 KF Titrino Plus titration device according to ASTM method E203. The properties of DS are listed in Table 1. The chemical composition of liquid product was identified by GC–MS analysis performed on a Perkin Elmer Clarus 600/600T with a fused silica capillary column HP–INNOWAX. The samples were diluted with acetone with 1:10 ratio. The chemical components were identified by comparing the retention time and major mass fragments in the detectable peaks with those of the authentic standards from NIST mass spectral library installed in the computer. An Agilent 7890A gas chromatography (GC) equipped with thermal conductive detector (TCD) was used to quantify the composition of gas products. A carbon molecular sieve column (Carboxen1010 PLOT Capillary GC Column) was used to separate the permanent gases (carbon monoxide, carbon dioxide, and methane) and light hydrocarbons (C2–C3) in the same analysis. Helium was used as the carrier gas with a flow rate of 3 mL/min. The inlet and detecTable 1 Properties of durian shell. Proximate analysis (wt% on dry basis) Moisture content 4.96 Volatile matters 70.28 Fixed carbon 21.65 Ash 3.11 Ultimate analysis (wt% on dry and ash-free basis) Carbon 40.98 Hydrogen 4.44 Nitrogen 1.31 Sulfur 0.34 Oxygen (by difference) 52.93 H/C molar ratio 1.30 O/C molar ratio 0.97 HHV (MJ/kg) 13.79 Chemical composition (wt% on dry basis) Extractives 11.09 Hemicellulose 13.01 Cellulose 60.45 Lignin 15.45
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tor temperatures were set to 200 °C and 250 °C, respectively. The oven temperature was held at 50 °C for 2 min, increased to 140 °C at a heating rate of 6 °C/min, raised to 200 °C at a heating rate of 10 °C/min, and then maintained at 200 °C for 14 min.
and condensate are more likely to form. Thus, no ideal biomass particle size fits all the reactions; it can only be found experimentally. In this work, DS with size 1–2 mm was used for the following experiment because it provided the highest bio-oil yield.
3. Results and discussion
3.1.2. Effect of reaction temperature The effect of reaction temperature on the pyrolysis yield distribution was also investigated (Fig. 2). The liquid yield increased from 26.05 wt% at 250 °C to 57.45 wt% at 650 °C, whereas the char yield decreased from 39.25 wt% at 250 °C to 23.51 wt% at 650 °C. The pyrolysis temperature enhances the cracking of the lignocellulosic materials, such as fragmentation and hydrolysis, and causes the recombination of volatiles (Aysu, 2015b). Pyrolysis can be classified into four stages: removal of moisture when temperature is less than 200 °C, hemicellulose breakdown at a temperature range of 220–315 °C, cellulose decomposition at 315–400 °C, and lignin decomposition at 160–900 °C (Yang et al., 2010). At low temperatures, the biomass was partially pyrolyzed; thus, the solid yield was high. When the pyrolysis temperature is increased, the primary decomposition of lignocellulosic structure or even the secondary decomposition of volatiles on primary char are dominant and generate more condensable and non-condensable vapor (Angın, 2013). In addition, higher pyrolysis temperature will increase the volatilization rate of organic compounds, such as extractives and proteins, in the biomass sample that contributes to the liquid and gas yields (Al-Wabel et al., 2013). In this work, the highest bio-oil yield was obtained at 650 °C, which is inconsistent with the study by Kan et al. (2016) that stated that the liquid yield decreased at temperature above 600 °C because of secondary cracking reactions. However, the liquid yield might be contributed from the water removed by cracking reactions because the liquid products include both an organic and an aqueous phase which is 38.16 wt% and 19.29 wt%, respectively. Mazlan et al. (2015) pyrolyzed rubber and Meranti wood dust in a fixed bed drop-type pyrolyzer at different temperatures. The highest bio-oil yield was produced at 550 °C for rubber wood dust (33.0 wt%) and 600 °C for Meranti wood dust (33.7 wt%). The reaction temperatures were different for each type of material; this might be attributed to the different material density of the biomass. They suggested that the decrease of char yield when the temperature was increased might be attributed to the dominance of the volatilization reaction at higher temperatures.
3.1. Product yields of DS fast pyrolysis
3.2. Properties of liquid products The elemental analysis of bio-oil produced at 650 °C is listed in Table 2. The carbon content of bio-oil is much higher than that of
100
100
80
80 Yield (wt%)
Yield (wt%)
3.1.1. Effect of particle size The effect of particle size on product yields was investigated at a temperature of 550 °C with the same amount of DS. Fig. 1 displays the comparative distribution of pyrolysis product yield by DS with different sizes. The solid char yield of DS sample was in the range of 26–28 wt%, liquid yield in the range of 44–46 wt%, and the gas product yield in the range of 25–29 wt%. The DS with size of 1.0–2.0 mm produced the highest amount of solid char (28.30 wt%) and liquid product (46.29 wt%) among all the samples, while the biomass with size less than 0.5 mm obtained the highest yield (29.21 wt%) of gaseous product. No significant effect on the liquid yields was observed when the particle size was changed. The particle size of biomass can affect the pyrolysis behavior of biomass. The gas yield in particles with smaller sizes (<0.5 mm) might increase because the heat and mass transfer resistances are lower than those in larger particles. This phenomenon leads to a faster heating rate across the particles, and it favors the fragmentation of biomass into smaller volatiles over recombination into solid char (Luo et al., 2010). A slight increase of char yield occurs from DS with size <0.5 mm to DS with size 1–2 mm. Shen et al. (2009) suggested that the char yield of larger particles is higher because of the greater intra-particle mass transfer resistance, thereby hindering the volatiles to escape from the particles. Then, larger reactive molecules reaggregate into solids. These results are in good agreement with those reported in previous studies. Bennadji et al. (2014) found that the effect of varying particle size was consistent yet minimal. They noticed that the char yield of smaller particles was on average 7% lower than that of the large particles. Aysu (2015a) found that the change in particle size does not significantly influence the product yield. However, a trend shows that bio-char yield increased with increasing particle size, whereas the liquid yield decreased at large particle size (0.85– 0.425 mm) because of the insufficient heat and slow intraparticle mass transfer. As discussed above, smaller particles provide higher bio-oil yield because of the low mass and heat transfer resistances. However, smaller particles have higher surface area and faster heating rate compared with larger particles (Luo et al., 2010). When heating rate is higher, light gases and thus, less char
60 40
60 40 20
20
0
0 <0.5
0.5-1 1-2 Average particle size (mm) Char
Bio-oil
2-5
Gas
Fig. 1. Product yields of the pyrolysis of DS with different sizes. (Condition: N2 gas flow = 200 mL/min; Temperature = 550 °C; Mass = 3 g).
250
350
Char
450 550 Temperature (°C) Bio-oil
650
Gas
Fig. 2. Product yields of the pyrolysis of DS at different temperatures. (Condition: N2 gas flow = 200 mL/min; Size = 1–2 mm; Mass = 3 g).
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Table 2 Ultimate analysis of bio-oil and bio-char produced at 650 °C.
a b
Ultimate analysisa
Bio-oil
Bio-char
Carbon Hydrogen Nitrogen Sulfur Oxygenb H/C molar ratio O/C molar ratio Water content (wt%) Higher heating value (MJ/kg)
66.72 9.29 4.49 0.66 18.84 1.67 0.21 19.29 25.76
70.94 3.02 0.73 0.16 25.15 0.51 0.27 – 23.29
Weight percentage dry and ash-free basis. By difference.
raw feedstock, which also accounts for the higher heating value of bio-oil. Bio-oil has lower oxygen content compared with raw DS and bio-char, indicating its potential as fuel source, because high oxygen content is not favorable for transportation fuel. Furthermore, the higher hydrogen content in bio-oil might be attributed to the volatile matter released during pyrolysis containing a high amount of hydrogen. Although this bio-oil has higher H/C molar ratio and lower O/C molar ratio compared with the literature reported by Moralı and Sensöz (2015), the energy value of the bio-oil (25.76 MJ/kg) is still much lower than that of the petroleum fuel (40 MJ/kg). The oxygen content in biodiesel is usually higher
than petroleum diesel, which is around 10 wt% –12 wt% (Singh and Singh, 2010). In this study, the oxygen content of bio-oil is 18.84 wt%, indicates the possibility to further reduce this value by catalytic pyrolysis. In addition, the water content in bio-oil was 19.29 wt% (Table 2), which is in good agreement with the work by Yin et al. (2013) that stated the bio-oil usually contains 15–30 wt% water. The compositions of bio-oil were identified by using GC–MS. Bio-oil is a very complex mixture that contains hundreds of chemical compounds in a wide range of molecular weights. In this study, only the main peaks with higher area percentages were presented. Fig. 3 shows the comparison of the GC–MS spectra of bio-oil produced at 250 °C and 650 °C. The retention time of compounds in bio-oil produced at 250 °C mainly appeared after 50 min, whereas the retention time of compounds in bio-oil produced at 650 °C are well distributed in the range of 5 min to 35 min. This finding indicates that the compounds in bio-oil (250 °C) have higher molecular weights than bio-oil (650 °C). This observation might be attributed to the partial degradation of biomass components that provides bigger molecules, such as sugar derivatives, which is consistent with the results shown in Table 3. This result is in good agreement with those of Meesuk et al. (2012), which stated that the average molecular weight of bio-oil decreased with increasing reaction temperature because of the thermocracking reactions. The bio-oil obtained at 250 °C contains lower sugar derivatives than the biooil obtained at 350 °C and 550 °C. This might due to the degrada-
Fig. 3. Total ion chromatograms of bio-oil produced at (a) 250 °C and (b) 650 °C. (The labeled number is the compound number listed in Table 3).
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Y.L. Tan et al. / Bioresource Technology 243 (2017) 85–92 Table 3 Chemical composition of the bio-oil from DS detected by GC–MS. No.
Types
Compound
250 °C
350 °C
450 °C
550 °C
650 °C
Acids
Total Pentanedioic acid, 2,2-dimethyl-, dimethyl ester Cyclopropanecarboxylic acid, 1-amino2-Butenoic acid, 2-methoxy-3-methyl-, methyl ester 9-Hexadecenoic acid Cyclopropanedodecanoic acid, 2-octyl-, methyl ester 2-Butenedioic acid (Z)Hexanoic acid, 4-methyl Nonanedioic acid, dibutyl ester Sulfurous acid, cyclohexylmethyl undecyl ester
2.51 0.70 0.68 0.43
14.73
–
12.33
1.53
Total 1-Tetracosanol 10-Nonadecanol 2-(Propylamino)ethanol 3-Dodecen-1-ol, (Z)(S)-3,4-Dimethylpentanol 1,3-Propanediol, 2-(hydroxymethyl)-2-methyl1,3-Pentanediol, 2,2,4-trimethyl1-Hexacosanol 1-Hexanol, 3,5,5-trimethyl5-Hexen-1-ol DL-2,3-Butanediol
64.57 51.53 9.22 2.10 0.62
Total
–
1 2 3 4 5 6 7 8 9 Alcohols 10 11 12 13 14 15 16 17 18 19 20 Benzene and derivatives
% Area
0.13 0.57
22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Carbonyls
Total 16-Octadecenal Hexanal, 4-methyl1-Hexyn-3-one 1-Oxetan-2-one, 4-methyl-3-methylene2-Hexenal, 5-(1-ethoxyethoxy)-, [R*,S*-(E)]-(.±.)2-Pentanone, 3-ethyl2-Propenal 4-Heptenal, (E)Cyclohexanone, 3-ethylMethanetricarboxaldehyde 2-Hexanone
40 41
2-Pyrrolidinone, 1-ethenyl Cyclobutanone, 2-methylFurans
6.61 2.09 32.51
11.70
0.83
1.64 1.44
0.50
32.51
46.17
3.06 2.15 3.41
0.33
–
4.44
16.04
0.98 5.78
2.83 2.31 0.63 3.50 1.65
1.61
7.92 1.54 3.95 0.32
4.31
0.65 0.65
18.42
12.45
53.40
3.72 0.12 0.25 18.42 0.22
2.54 1.50 1.14 1.62 1.46 1.80 1.31 1.08
1.07
35.98 15.67 0.68 2.66 1.74 0.41 0.51
1.85
Guaicols
Total Guaicol-á-d-glucopyranoside, pentakis(O-trimethylsilyl)-
–
10.67 10.67
Hydrocarbons
Total 1-Tridecene Cyclohexane 1,2-Butadiene 1-Hexacosene 1-Hexene, 3,4,5-trimethyl1-Hexyne, 5-methyl1-Pentene, 3,4-dimethyl2-Heptyne 2-Methyl-2-octene 4-Decene, 2,2-dimethyl-, (E)Cyclopentane
10.91 5.02 5.35
11.75
48 49 50 51 52 53 54 55 56 57 58 59 60
Eicosane, 2-cyclohexylHeptadecane, 9-hexyl-
47
46.17
0.12
Total Isoxazole, 4,5-dimethyl1H-Pyrazole, 3-ethyl-4,5-dihydroFuran, 2,5-dihydro-3-methylà-Amino-2,5-dihydro-5-methyl-2-furanaceticacid Cytidine, 20 -deoxy-
42 43 44 45 46
1.13
2.98
[2,60 -Bi-2H-1-benzopyran]-4(3H)-one, 30 ,40 -dihydro-3,5,7-trihydroxy-50 -methoxy-20 ,20 dimethyl-, (2S-trans)Benzenamine, 4-ethylBenzene, [3-(2-cyclohexylethyl)-6-cyclopentylhexyl]Benzoic acid Nerbowdin, 3-acetyl Nitrobenzene-D5 o-Toluidine p-Xylene
21
3.63 5.83 5.92
–
5.81
1.39 0.85
1.40 2.36 2.05
0.54
–
–
–
29.15
17.24
18.26
7.45 1.01
0.35
1.85
1.95 7.28
0.14
1.28 3.36 1.01 1.04 8.44 3.10
0.40
7.93 0.99 1.53
0.53 (continued on next page)
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Table 3 (continued) No.
Types
Compound
% Area 250 °C
61 Nitrogencontaining 62 63 64 65 66 67 68 69 Others
0.66
–
6.25
9.09
6.43
1.11 0.55 6.25 1.74 0.66 4.14 1.80 6.18
Phenols
Total 1,4-Naphthalenedione, 3,5-dihydroxy-2-methyl-
–
–
–
1.74 1.74
0.16 0.16
Pyrans
Total Butanal, 4-[(tetrahydro-2H-pyran-2-yl)oxy]2H-Pyran-2-one, tetrahydro-3,5-dimethyl-
–
0.85
–
2.59 2.59
1.81 1.28 0.53
11.59
–
76
11.01
0.14
2.56
0.14
0.85
Total Naringenin-7-O-glucoside, tmsMaltose, octakis(trimethylsilyl)á-D-Glucopyranose, 2,3,4,6-tetrakis-O-(trimethylsilyl)-, 1-(trimethylsilyl)-1H-indole-3acetate à-D-Glucopyranoside, 1,3,4,6-tetrakis-O-(trimethylsilyl)-á-D-fructofuranosyl 2,3,4,6tetrakis-O-(trimethylsilyl)D-Fructose, 3-O-[2,3,4,6-tetrakis-O-(trimethylsilyl)-à-D-glucopyranosyl]-1,4,5,6-tetrakis-O(trimethylsilyl)D-Glucose, 2-O-[6-deoxy-2,3,4-tris-O-(trimethylsilyl)-à-L-mannopyranosyl]-3,4,5,6tetrakis-O-(trimethylsilyl)Galactopyranose, 1,2,3,4,6-pentakis-O-(trimethylsilyl)-, á-dHexopyranose, 1,2,3,4,6-pentakis-O-(trimethylsilyl)l-Mannopyranose, 6-deoxy-1,2,3,4-tetrakis-O-(trimethylsilyl)-
tion of cellulose that occurred at higher temperature (315–400 °C). At higher temperature, unstable intermediates formed in a faster rate. These unstable intermediates tend to recombine into more stable compounds and this explains the phenomenon of sugar derivatives in bio-oil produced at 550 °C is higher than the biooil produced at 250 °C and 450 °C. Durak and Aysu (2015) also stated that the number and types of compounds increased with increasing temperature because of the incomplete degradation of lignin in the biomass. Thus, more observable peaks are found in the spectrum of bio-oil (650 °C), indicating the existence of a greater variety of compounds. Table 3 indicates the identified compounds and the total area percentage of each type of chemicals in the bio-oil. Every compound in Table 3 has been grouped into acids (e.g.: 4-methylhexanoic acid), alcohols (e.g.: DL-2,3-butanediol), benzene derivatives (e.g.: o-toluidine), carbonyls (e.g.: 2-propenal), furans (e.g.: 1(2-furanyl)-3-methyl-3-butene-1,2-diol), guaiacols (e.g.: pentakis( O-trimethylsilyl)-guaiacol-á-D-glucopyranoside), hydrocarbons (e.g.: 1,2-butadiene), nitrogen-containing compounds (e.g.: N-iso butylidene-cyclopropylamine), other compounds (e.g.: ether and silane compounds), phenols (e.g.: 3,5-dihydroxy-2-methyl-1,4-na phthalenedione), pyrans (e.g.: tetrahydro-3,5-dimethyl-2H-pyran2-one) and sugars (e.g.: glucose and mannopyranose derivatives). Table 3 shows that alcohol is the major product for the pyrolysis of DS at 250, 350, and 450 °C, such as 1-hexacosanol, DL-2,3butanediol, and 1-tetracosanol. The area percentage of alcohol for bio-oil produced at 250, 350, and 450 °C are 64.57%, 32.51%, and 46.17%, respectively. The bio-oil produced at 350 °C contains more
–
8.45
Bufotalin Sugars
83 84 85
Total
–
74 75
82
650 °C
8.05 7.69 0.13 0.23
73
81
550 °C
Total Dimethallyl ether 1-Ethoxy-5,5-dimethyl-2-hexene 2-Butyne, 1,1-dimethoxySilane, (1,2-dimethylpropoxy)trimethyl-
72
80
450 °C 29.15
1-Hexyl-2-nitrocyclohexane 1H-Imidazole, 4,5-dihydro-2-methyl1-Propanol, 2-aminoAziridine, 1,2,3-trimethyl-, trans2-Butanamine, N,N-dimethylCyclopropylamine, N-isobutylideneFormamide, N,N-bis(2-cyanoethyl)Propanenitrile, 3,30 -iminobis-
70 71
77 78 79
350 °C
Neopentane
6.33 4.29 0.93
21.20
–
4.01 0.13
3.54
1.91
6.92 0.56
5.86
0.16 0.26
0.87
5.40 3.18 1.10
undecomposed sugar (21.20%) and oxygenates, which are 32.51% alcohol and 14.73% acids. The bio-oil produced at 450 °C also contains a high percentage of oxygenates, which are 46.17% alcohol and 18.42% carbonyls, but it has a comparatively high amount of hydrocarbons (29.15%). The chemical distribution of bio-oil produced at 550 °C is more even compared with that of the others, which contains 17.24% hydrocarbons, 12.33% acids, 11.70% alcohols, and 11.59% sugar. Although the bio-oil produced at 650 °C contains a high amount of oxygenated compounds (53.40% carbonyls), it also contains 16.04% benzene derivatives and 18.26% hydrocarbons with greater HHV. The compounds in bio-oil are affected by the biomass component composition, the cracking pathway, and the secondary decomposition of volatiles on primary char. As mentioned above, hemicellulose and cellulose are decomposed at 250 °C. The cellulose is degraded into anhydrocellulose (partially depolymerized cellulose) and levoglucosan by the cracking of glycosidic bonding between the monomer units. Levoglucosan is the precursor for secondary reactions, such as decarbonylation and repolymerization, to form secondary products, such as pyran and light oxygenated compounds (Wang et al., 2012). Thus, bio-oil produced at 250 °C contains high concentration of oxygenates, such as alcohols. Hemicellulose has a more complex structure than cellulose because it is composed of different polysaccharides, such as mannose, galactose, and glucose. The monomers have different compositions; thus, the products may be varied. The products, such as 2O-[6-deoxy-2,3,4-tris-O-(trimethylsilyl)-à-L-mannopyranosyl]-3,4 ,5,6-tetrakis-O-(trimethylsilyl)-D-glucose and 1,2,3,4,6-pentakis-O
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3.3. Ultimate analysis of solid product The elemental composition of solid char is shown in Table 2. The carbon content in char increased from 40.98 wt% to 70.94 wt %, whereas the hydrogen content dropped from 4.44 wt% to 3.02 wt%. The H/C molar ratio of sample decreased from 1.30 (raw) to 0.51 (char) after pyrolysis at 650 °C, which is consistent with the results in the study by Moralı and Sensöz (2015), which revealed that the H/C ratio of hornbeam sawdust was decreased from 1.75 to 0.54 after pyrolysis. In addition, the heating value of the char produced at 650 °C is 23.29 MJ/kg, which is 68.89% higher than that of raw DS (13.79 MJ/kg). The heating value of DS char is comparable with other solid fuels, such as commercial charcoal briquettes with heating values of 20–25 MJ/kg and bituminous coal with heating values of 15–25 MJ/kg (Ward et al., 2014), indicating that its potential as solid fuel. 3.4. Analysis of gas products Fig. 4 shows the gas product compositions determined by GC– TCD. The gas product at 250 °C totally contained CO2. When the temperature increased to 350 °C, a small amount of CO (25.43%) was produced. The amount of CO (29.44%) increased as the temperature further increased to 450 °C without the production of light hydrocarbon gases. CH4 (5.07%) was released when the pyrolysis temperature reached 550 °C, while C2H4 (2.14%) and C2H6 (1.58%) were produced when the reaction temperature was 650 °C. As the temperature increased, the percentage of CO2 decreased, whereas the percentage of other gases, such as CO, CH4, C2H4, and C2H6 increased. The gases are produced by the fragmentation of the lignocellulosic structure (hemicellulose, cellulose, and lignin). As described earlier, the thermal decomposition of biomass is divided into four stages, and the pyrolysis of each biomass component provides different major product gases. For example, the decomposition of lignin gives CO2 > H2 > CH4 > CO > C2+ because of the cracking and deformation of aromatic rings, whereas the decomposition of hemicellulose and cellulose provides more CO and CO2 because of the cracking of carbonyl groups. The decomposition of hemicellulose gives CO > CO2 > CH4 > C2+ > H2, whereas the decom-
100 80 Yield (v/v%)
-(trimethylsilyl)-,á-d-galactopyranose, are formed by the degradation of hemicellulose. Lignin consists of methoxylated phenylpropane structure that degrades across a wide range of temperature from 200 °C to 600 °C. Degradation of lignin contributes to the formation of benzene derivatives, phenols, and methoxy-phenols, such as guaiacols and syringols (Quan et al., 2016). Across the temperature range of 200 °C–600 °C, incondensable gases, such as CO and CO2, are the main gas products. Light hydrocarbons C1AC3 are formed at higher temperature (550 °C) because of the cracking of CAC bonds in the alkyl substituent of aromatic rings. When the degradation of lignin reach a maximum rate, benzene derivatives are produced at maximum rate as well (Cao et al., 2013). The high yield of benzene derivatives and phenols at 650 °C indicates that the degradation rate of lignin is optimum at that temperature. Numerous reports about the bio-oil composition from different feedstock and types of reaction have been published (Damartzis et al., 2011; Mourant et al., 2013). Quan et al. (2016) studied the thermal decomposition of biomass component and the bio-oil compounds. The most prominent products for the pyrolysis of each biomass component at 500 °C are as follows: furan (16.14%) for cellulose, such as furfural and 5-methyl-furfural; nitrogen-containing oxygenated compounds (20.3%) for hemicellulose, such as 2-methy liminoperhydro-1,3-oxazine and ethyl carbonocyanidoate; and guaiacols (32.06%) for lignins, such as 2-methoxyphenol and 2methoxy-4-vinylphenol.
60 40 20 0 250
350
450 Temperature (°C)
Carbon monoxide
Methane
Ethylene
Ethane
550
650
Carbon dioxide
Fig. 4. Gas product compositions of the pyrolysis of DS at different temperatures. (Condition: N2 gas flow = 200 mL/min; Size = 1–2 mm; Mass = 3 g).
position of cellulose gives CO2 > CO > CH4 > C2+ > H2 (Quan et al., 2016). In this work, the DS sample used contains of 11.09 wt% extractives, 13.01 wt% hemicellulose, 60.45 wt% cellulose, and 15.45 wt% lignin. The decomposition of hemicellulose producing only CO2 at 250 °C shows that the decarboxylation of ACOOH is more preferable than the decarbonylation of CAOAC and C@O at low temperature. This explanation can be proven when the CO gas concentration increased after the temperature increased to 350 °C and 450 °C. Huang et al. (2014) investigated the gas composition produced by fast pyrolysis of sewage sludge at different temperatures. The main gas product was CO2 at temperature below 500 °C, which is consistent with the result of the present work. However, it shows opposite result when they reported that more CO and light hydrocarbon gases are more likely to be produced at temperatures ranging from 500 °C to 700 °C because of the secondary cracking or primary volatiles. In this study, CO2 is still major in gas product though its volume percentage decreased with increasing temperature. This shows that decarboxylation is the major cracking reaction for DS pyrolysis. 4. Conclusions The highest bio-oil yield (57.45 wt%) was obtained at 650 °C with DS size of 1–2 mm. The liquid yield increased with temperature, whereas the effect of particle size on liquid yield is not significant. CO2 is the major gas product and light hydrocarbon gases were only formed at temperatures 550 °C. In bio-oil, light oxygenates are formed at low temperature while aromatic compounds are formed at 550–650 °C. The HHV of bio-char is comparable to charcoal briquettes (20–25 MJ/kg) but the HHV of bio-oil is lower than fossil fuels (40 MJ/kg) indicate the potential as fuel precursor prior to catalytic upgrading. Acknowledgements The authors acknowledge the research grants provided by the Universiti Sains Malaysia – Malaysia, under Research University (RU) grant (Project No: 1001/PJKIMIA/814227) that resulted in this article. References Aditiya, H.B., Chong, W.T., Mahlia, T.M.I., Sebayang, A.H., Berawi, M.A., Nur, H., 2016. Second generation bioethanol potential from selected Malaysia’s biodiversity biomasses: a review. Waste Manage. 47, 46–61. Al-Wabel, M.I., Al-Omran, A., El-Naggar, A.H., Nadeem, M., Usman, A.R.A., 2013. Pyrolysis temperature induced changes in characteristics and chemical
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