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Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor
Journal Pre-proof Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor Jae-Yong Jeong, Chang-Won Yang, Uen-Do Lee, Soo-Hwa Jeong
PII:
S0165-2370(19)30633-3
DOI:
https://doi.org/10.1016/j.jaap.2019.104708
Reference:
JAAP 104708
To appear in:
Journal of Analytical and Applied Pyrolysis
Received Date:
14 August 2019
Revised Date:
8 October 2019
Accepted Date:
8 October 2019
Please cite this article as: Jeong J-Yong, Yang C-Won, Lee U-Do, Jeong S-Hwa, Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor, Journal of Analytical and Applied Pyrolysis (2019), doi: https://doi.org/10.1016/j.jaap.2019.104708
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Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor
Jae-Yong Jeonga,b, Chang-Won Yanga,b,c, Uen-Do Leea,b,c,**, and Soo-Hwa Jeongb,c,*
a
Department of Green Process and System Engineering, University of Science and
b
ro of
Technology(UST), 89 Yangdaegiro-gil, Ipjang, Cheonan, Chungnam 331-822, South Korea Thermochemical Energy System R&D Group, Korea Institute of Industrial Technology
(KITECH), 89 Yangdaegiro-gil, Ipjang, Cheonan, Chungnam 331-822, South Korea
Future Energy Plant Convergence Research Center, Korea Institute of Energy Research
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c
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(KIER), Daejeon 305-343, South Korea
[email protected]
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* Corresponding author: Tel: +82-41-589-8576. Fax: +82-41-589-8323. E-mail:
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** Co-corresponding author: Tel: +82-41-589-8574. Fax: +82-41-589-8323. E-mail:
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[email protected] Highlights
Bio-oil obtained from the pyrolysis of palm kernel cake (PKC) was characterized PKC can reduce production costs and increase the yield and quality of bio-oil The maximum yield of bio-oil was 63 wt.% at a reaction temperature of 401 °C High nitrogen in the bio-oil requires extra treatment before use as a clean fuel
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ABSTRACT Palm kernel cake (PKC) was pyrolyzed in a bench-scale pyrolysis plant equipped with a bubbling fluidized bed reactor, char separation system, and bio-oil recovery system under various reaction temperatures. Experiments were conducted to evaluate the effects of reaction temperature and observe the behavior of nitrogen in pyrolysis products. The maximum yield of bio-oil from PKC was approximately 63 wt.% at a reaction temperature of 401 °C. The main chemical compounds of bio-oils obtained from PKC were acetic acid, levoglucosan,
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nitrogen-containing compounds, and fatty acids such as dodecanoic acid, octanoic acid, tetradecanoic acid, and oleic acid. At reaction temperatures above 401 °C, the nitrogen
content of bio-oils does not depend on reaction temperature. It is suggested that the resulting
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bio-oil requires additional treatment for use as a clean fuel.
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Keywords: Pyrolysis, Fluidized bed, Bio-oil, Palm kernel cake (PKC), Nitrogen
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1. Introduction
As an abundant and environmentally friendly energy source, biomass is increasingly being used as a renewable alternative to fossil fuels. Raw biomass can be used directly but is more
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effective after appropriate thermochemical conversion processes and when transformed into liquid or gaseous form. Fast pyrolysis is the best way to produce bio-oil [1]; this liquid fuel
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has many advantages over solid fuel in terms of storage, transport, handling, and diversity of
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applications. Bio-oil is generally used as fuel for boilers but can be employed in engines and turbines after certain upgrading processes [2]. Another application of bio-oil is to produce bio-chemicals through catalytic pyrolysis, which can improve the yield of specific chemicals in the bio-oil by utilizing the selectivity of the catalyst [3]. Biochar is another important product of the pyrolysis process, which can be used as a high quality solid fuel as well as a soil improvement agent. Application of bio-char to soil is an
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attractive method of effectively sequestering C in soils. It is also able to improve soil fertility, enhance plant growth, retain nutrients, and provide habitats for microorganisms [4]. Several companies are already promoting the commercialization of fast pyrolysis technology in the bio-energy sector; however, it is still challenging to achieve economic feasibility without government subsidies [5]. Therefore, the feed material price and pretreatment process should be reduced in order to reduce the overall production cost. Palm fruit is mainly produced in Malaysia and Indonesia, with approximately 317 million
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tons produced in 2017 [6]. Approximately 10 % of the palm fruit is extracted as oil and approximately 90 % is palm residues [7]. Among the palm residues, palm kernel cake (PKC) has predominantly been used in livestock feed; however, as the production of PKC increases
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(approximately 2.59 million tons were produced in Malaysia in 2018) [8], it is necessary to find other applications. For example, using PKC as a raw material of fast pyrolysis has
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various advantages [9]. The production of PKC is concentrated in palm oil processing plants,
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so it can be supplied in large quantities with lower transportation costs. Its low water content and oil component properties (the residue after palm oil extraction) contribute to the improved yield and quality of pyrolysis oil. In addition, as the size of PKC is small and
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uniform, it can be applied directly to the fast pyrolysis process without pretreatment. Therefore, it is regarded as the most suitable raw material in terms of bio-oil production
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through fast pyrolysis. Some studies have been conducted on the pyrolysis of PKC for
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producing bio-oil. Razuan et al. pyrolyzed PKC in a fixed bed reactor and reported that the maximum liquid yield (~42.8 wt.%) was attained at a reaction temperature of 700 °C with a heating rate of 10 °C/min [10]. Ngo et al. performed fast pyrolysis of PKC in a fluidized bed reactor and reported that the maximum bio-oil yield (~50 wt.%) was obtained at a reaction temperature of 500 °C. They also reported that the main compounds of bio-oil were 1,2-
3
benzenedicaboxylic acid-bis (2-ethylhexyl) ester, β-D-allose, and fatty acids [11]. These studies were carried out using a small fixed and fluidized bed reactor. It should be noted that the nitrogen content in PKC can be a disadvantage because the nitrogen content of gas, liquid, and solid pyrolysis products is proportional to the nitrogen content of the feedstock. The nitrogen content in the PKC originates from proteins (14–16 %) composed of nitrogen in the form of amino acids (generally 16 % in the protein) [12,13]. In this study, PKC was pyrolyzed using a bench-scale fluidized bed reactor equipped with
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a char separation system. The aim of this study was to determine the influence of reaction temperature on the characteristics of the resulting bio-oil. In addition, the behavior of
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nitrogen in the pyrolysis products was investigated.
2. Materials and methods
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2.1. Feed material
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The PKC used in this study was obtained from Indonesia. Unlike other biomass, PKC is produced in powder form in the manufacturing process; thus, it has the advantage of not requiring a powder process. Before using the PKC, it was sieved to obtain a size of 0.4–0.8
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mm and dried in an oven at 110 °C for 24 h to remove moisture. Then, proximate analysis and ultimate analysis were conducted following ASTM D3172 and ASTM D3176,
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respectively, the properties of which are presented in Table 1.
Table 1 Properties of the feed material. Proximate analysisa
wt.%
Ultimate analysis
wt.%
Volatile matter
89.3
C
50.8
Na
43.0
Fixed carbon
7.0
H
6.1
K
6678.0
Ash
3.7
N
3.1
Mg
2789.0
S
0.2
Ca
4068.0
Metal analysis
ppm
4
HHV (MJ/kg)
20.5
Ob
39.8
a: air dry basis b: by difference
The proximate analysis was calculated on a dry basis and the ultimate analysis of oxygen was calculated by the difference. According to the proximate analysis, the predominant component of the PKC is volatile matter with a value of 89.3 wt.%, which is higher than that of other biomass (62.9–88.2 wt.%) [14]. According to the ultimate analysis, the nitrogen
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content of PKC is approximately 3 wt.%, which is much greater than that of woody biomass (< 1 wt.%) [15]. The sulfur content is 0.2 wt.%, which predominantly originates from sulfurcontaining amino acids such as methionine and cysteine in the feed material [16]. The metal
considerably greater than those of other biomass.
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2.2. Pyrolysis plant
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analysis showed that all alkali and alkali earth metal contents, except for potassium, are
Experiments were conducted in a bench-scale pyrolysis plant composed of a feeding
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system, fluidized bed reactor, char separation system, and bio-oil recovery system. A
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schematic diagram of the pyrolysis plant is shown in Figure 1.
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Fig. 1 Schematic diagram of the pyrolysis plant.
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The feeding system was composed of a silo and two screw feeders. The purging gas was supplied to the feeding system in order to prevent backflow by the fluidizing gas and an air jacket was installed at the inlet of the reactor to prevent any thermal degradation of the feed
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material by heat transfer from the reactor. The pyrolyzer, a fluidized bed reactor, was made of a 316SS tube with an inner diameter and height of 160 mm and 610 mm, respectively. It was
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indirectly heated by two electric heaters. The reaction temperature was determined by the
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average value of the second and third thermocouples from the bottom. The char separation system was composed of two cyclones heated by a heating tape to 350 °C in order to prevent condensation of the pyrolysis gas. The fine char was removed from the char separation system and the excess char in the bubbling fluidized bed was removed by a char pot. The biooil recovery system was composed of three condensers, two impact separators, and an electrostatic precipitator for more efficient recovery. The condensers were made of 316SS,
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which were water-cooled to 5–10 °C. The non-condensable gas was circulated by a diaphragm pump and used as a fluidizing medium. The excess gas was sampled for analysis or burned in a flare stack. 2.3. Thermogravimetric analysis Thermogravimetric analysis was performed using a thermogravimetric analyzer (TGA Q50, TA Instruments) to confirm the decomposition behavior of the feed material. Approximately 10–20 mg of the feed material was used, and the temperature was increased from 30–800 °C
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at a rate of 10 °C /min. Nitrogen gas was used as a carrier gas for the balance and furnace. The thermogravimetry (TG) and differential thermogravimetry (DTG) curves of PKC are
shown in Figure 2 and compared with those of an earlier study with palm kernel shell (PKS)
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[17,18].
0.10
0.9
0.09
0.8
0.08
0.6 0.5 0.4 0.3
0.06 0.05 0.04
0.2 0.1
ur
0.0 0
100
200
300
400
DTG (dX/dt)
0.07
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0.7
0.03
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Normalized mass to initial mass
PKC PKS
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1.0
0.02 0.01 0.00 500
600
700
800
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Temperature (℃ )
Fig. 2 TG and DTG curves for samples of palm kernel cake (PKC) and palm kernel shell
(PKS).
Initially, the weight of PKC gradually decreased over 100 °C due to evaporation of moisture. Subsequently, major weight loss occurred in the temperature range of 200–380 °C,
7
potentially due to weight loss of the hemicellulose in the fibers, which typically occurs from 100–365 °C [19]. According to Jo et al., the chemical composition of PKC determined by TAPPI methods was 16.4% cellulose, 49.4% hemicellulose, and 34.2% lignin [20]. Compared to PKC, two clear shoulder peaks appeared on the DTG curve of PKS, which was attributed to differences in the chemical composition of the raw material. After approximately 380 °C, weight loss of both feed materials slowly occurred until 800 °C due to the degradation of lignin.
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2.4. Reaction conditions In this study, the only reaction parameter was the reaction temperature (Table 2), which is
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most important for determining the yields and properties of products.
Run1
Run2
Reaction temperature (°C)
349
401
Flow rate (NL/min)
76
Fluidizing medium
Product gas
Run3
Run4
Run5
Run6
450
501
557
603
61
58
54
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Parameters
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Table 2 Reaction parameters of the pyrolysis experiments.
66
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70
In all experiments, 1,500 g and 5,600 g of feed material and quartz sand were used,
ur
respectively. Based on the results of the TGA experiments, the experiments were conducted
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in the temperature range from 350–600 °C. The minimum fluidization velocity that was calculated using the Ergun equation was maintained at 3 umf [21]. To achieve reliable results, all experiments were conducted twice. 2.5. Analysis of pyrolysis products The recovered pyrolysis products were separated into three fractions: oil, gas, and char. The bio-oils were reliably separated into two phases in the bio-oil recovery system: an aqueous
8
phase (AP) and a viscous phase (VP). AP was recovered with condensers and VP was recovered with impact separators, connection tubes, and an electrostatic precipitator. The separated bio-oils were analyzed for each phase. Moreover, the bio-oil was subjected to elemental analysis using an elemental analyzer (Flash Smart, Thermoscientific). The water content was analyzed by Karl Fisher titration (Metrohm 870, KF Titrino). HYDRANAL Composite 5K and methanol were used as the titration reagent and the titration solvent, respectively. A GC-MS (5975C, 7890A, Agilent) was used for qualitative analysis of the bio-
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oils, which indicated that only peaks with an area of 0.1 % or higher were confirmed. The higher heating value (HHV) was calculated by Dulong's equation. The gas produced during
the experiments was sampled three times and analyzed using GC-TCD (6890N, Agilent) and
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FID (7890A, Agilent). TCD analyzed hydrogen, nitrogen, carbon monoxide, carbon dioxide,
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and methane and FID analyzed C1 – C8 hydrocarbons.
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3. Results and Discussion 3.1. Mass balance
The mass balance was established by measuring the weight of the pyrolysis products.
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Figure 3 shows the mass balance for each condition. The yield of bio-oils was calculated by measuring the weight of the recovery system before and after the experiments. The yield of
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gas was obtained by measuring the gas volume of the experiments and calculating the gas
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density from the gas composition. The yield of product char was calculated from the difference. For PKC, the maximum bio-oil yield of 63.0 wt.% was obtained at a reaction temperature of 401 °C. The bio-oil yield was the lowest at reaction temperature of 603 °C. This phenomenon may be because the main reaction ended at 380 °C, as discussed in Section 2.3. As the reaction temperature increased, the yield of gas rapidly increased. This is probably
9
due to secondary cracking of the pyrolysis vapor. Conversely, the yield of char gradually decreased. This may be due to volatilization of unconverted biomass in the reactor.
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Oil Char Gas
60
Yield (wt.%)
50 40 30
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20 10 0 349
401
450
501
557
603
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Reaction temperature (oC)
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Fig. 3 Distribution of pyrolysis products according to reaction temperature.
3.2. Pyrolysis oil
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The main properties of the bio-oils produced in the experiments are shown in Table 3. After pyrolysis, the bio-oils were separately into two phases (Section 2.5). The weight ratio
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(wt./wt.%) of both AP and VP in bio-oils was approximately 6:4. According to the proximate analysis, the bio-oils produced were almost entirely composed of carbon and oxygen. The
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oxygen content of AP occupied approximately 70 wt.% with the carbon occupying a very small amount of less than 19 wt.%. Conversely, the oxygen content of VPs was less than 23
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wt.% and the carbon content was greater than 63 wt.%. The nitrogen contents of AP and VP were 1.3–2.5 wt.% and 2.0–6.7 wt.%, respectively. A detailed discussion on nitrogen behavior is given in Section 3.5. The water content of APs was greater than 19.6 wt.%, while the water content of VP was less than 2.2 wt.%. Because of these characteristics, the HHV of APs (5–8 MJ/kg) was very low and that of VPs (29–39 MJ/kg) was high. The HHVs of bio-
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oils were calculated by Dulong's equation. Considering the HHVs, the VPs in bio-oil could be used as fuel oil or an energy source in a pyrolysis plant.
Runs
Run1
Run2
Run3
Run4
Run5
Run6
Reaction temperature (°C)
349
401
450
501
557
603
Phase
AP
VP
AP
VP
AP
VP
AP
C
11.8
67.2
18.6
68.9
16.1
66.9
13.4
65.1
10.4
65.9
13.4
63.3
H
8.2
10.1
9.2
7.0
8.5
8.6
8.6
8.3
8.6
7.9
8.6
7.5
N
1.3
2.1
2.2
2.0
2.0
3.2
2.0
4.2
2.5
4.9
2.0
6.7
S
0.1
-
-
-
-
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Table 3 Main properties of the bio-oils.
-
0.1
0.1
-
-
-
-
Oa
78.6
20.6
70.0
22.2
73.4
21.3
75.9
22.3
78.5
21.2
75.9
22.5
Water content (wt.%)
23.5
2.2
24.8
1.9
19.6
0.7
24.1
1.7
23.1
2.2
21.3
1.8
HHV (MJ/kg)
5.7
33.7
6.2
38.4
5.1
33.3
6.4
30.9
6.7
25.0
5.5
24.4
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VP
AP
VP
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a: by difference
AP
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Elemental analysis (wt.%)
VP
3.3 Chemical components of bio-oils
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The major components of the bio-oils analyzed by GC-MS are listed in Table 4, where the
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area% values only present values greater than 0.5 area% (i.e., detectable amounts). The main components observed in the bio-oils were acetic acid, levoglucosan, nitrogen-containing compounds, and fatty acids such as dodecanoic acid, octanoic acid, tetradecanoic acid, and oleic acid. Acetic acid is produced during breakaway from the acetyl group bound to the xylose unit, which is one of the constituents of hemicellulose [22]. In all experiments, the yields of acetic acid in bio-oils were concentrated in the APs due to high solubility in water.
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The levoglucosan predominantly originated from thermal degradation of cellulose and can be used as a precursor to various chemicals such as diols, surfactants, and pharmaceutical additives [23]. In Run2 (401 °C), higher yields of levoglucosan (~25 area% in AP and ~18 area% in VP) were observed in the bio-oils than in other Runs. Above a reaction temperature of 500 °C, the yield of levoglucosan was significantly decreased. The main compounds of fatty acid observed in the bio-oils were decanoic acid, tetradecanoic acid, oleic acid, and hexadecanoic acid, which resulted from the degradation of residual palm oil substances [11].
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PKC generally contains between 7 % and 10 % fatty acids [24]. The main nitrogencontaining compounds identified in the bio-oils were pyridine and acetamide. They appeared to originate mainly from alanine-containing proteins and glycine-containing proteins,
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respectively [25]. Furfuryl alcohol was also found in the bio-oils, originating from the
degradation of hemicellulose in the fibers. The concentrations of phenol and phenolics
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compounds, which were degradation products of lignin, were smaller than those of other
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palm residues [17,18].
Run1
Reaction temperature (°C)
349
Phases
Aqueous
Viscous
Run2
Run3
Run4
Run5
Run6
401
450
501
557
603
Aqueous
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Runs
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Table 4 Chemical components of the bio-oils determined by GC-MS.
Viscous
Aqueous
Viscous
Aqueous
Viscous
Aqueous
Viscous
Aqueous
Viscous
Components (area%) Acetic acid
1.20
8.83
1.14
10.41
0.85
11.95
1.08
20.92
1.24
12.41
0.79
-
+
3.69
0.73
4.13
0.68
4.91
0.69
-
0.53
-
+
Propanoic acid
0.64
+
-
+
1.52
+
1.71
+
-
0.44
1.66
+
2-Propenoic acid
-
-
-
-
-
-
-
-
1.62
-
2.36
-
Furfuryl alcohol
2.46
1.39
2.32
0.89
2.07
0.61
1.98
0.59
1.04
+
0.97
+
Butanoic acid
-
-
-
-
-
-
-
-
0.86
-
+
-
Butyrolactone
+
-
+
-
+
-
+
-
0.66
-
+
-
2(5H)-Furanone
0.71
-
1.06
-
0.65
-
0.65
-
+
-
-
-
Phenol
0.78
1.15
1.17
0.82
1.16
1.04
0.99
1.31
1.06
1.36
1.02
2.55
Indene
-
+
-
+
-
+
-
+
-
+
-
0.66
Cresols
-
0.80
-
+
-
0.62
-
0.88
-
1.08
-
1.57
Cyclobutanol
-
0.96
-
0.79
-
+
-
0.53
-
-
-
-
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Acetol
9.57
12
-
-
-
-
-
+
-
0.53
-
0.58
-
0.50
Corylon
0.63
-
0.75
-
0.94
-
0.76
-
+
-
+
-
Glycerin
+
1.86
3.98
2.42
6.26
+
5.10
0.69
3.52
0.52
2.62
+
Maltol
1.56
0.92
1.57
0.68
1.21
+
0.66
+
2.10
0.33
3.09
+
Xylenols
-
-
-
-
-
-
-
+
-
0.81
-
0.84
Ethyl 2-butenoate
1.71
-
2.00
-
2.18
-
0.99
-
0.80
-
0.73
-
Naphthalene
-
0.55
-
0.90
-
+
-
0.54
-
1.00
-
2.21
Benzoic acid
0.88
1.42
1.13
1.47
0.85
1.50
0.72
1.56
1.41
1.90
1.37
1.89
Methylnaphthalenes
-
-
-
-
-
-
-
+
-
+
-
0.99
Coumaran
-
+
-
+
-
+
-
0.85
-
+
-
-
Cyclobutanol
0.55
-
0.83
-
1.05
-
0.84
-
0.68
-
+
-
Resorcinol
-
+
-
0.69
-
-
-
+
-
0.69
-
+
Syringol
+
+
0.59
0.56
+
-
0.91
-
+
-
+
-
Decanoic acid
3.87
2.22
4.70
2.69
5.63
2.13
6.64
2.07
-
1.04
-
0.58
Isoeugenol
-
+
-
0.54
-
+
-
-
-
+
-
+
2-Tridecanone
-
+
-
+
-
+
-
0.60
-
+
-
+
Levoglucosan
15.10
10.92
24.82
18.02
20.41
3.31
8.85
2.15
5.12
1.83
0.71
-
Dodecanoic acid
-
17.92
-
10.52
-
22.18
-
20.41
-
15.97
-
10.20
Octanoic acid
-
1.15
-
0.52
-
0.87
-
1.06
-
0.80
-
1.04
Methoxyeugenol
-
1.16
-
1.91
-
0.73
-
0.66
-
0.72
-
0.69
Tetradecanoic acid
10.82
9.63
5.45
10.86
4.35
12.92
10.81
13.86
10.78
12.11
23.43
6.36
Oleic Acid
18.24
26.18
7.16
21.59
6.47
29.43
Hexadecanoic acids
9.48
7.72
7.34
7.01
7.55
9.66
N-compounds
1.37
0.18
2.06
0.18
2.82
0.27
20.41
13.78
19.65
-p 27.47
5.46
25.09
9.07
26.21
11.73
8.42
14.37
6.09
18.07
3.49
3.40
0.39
5.89
0.63
2.08
0.67
11.88
22.95
23.29
19.63
36.75
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5.98
10.69
20.23
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Others 20.53 10.69 (+): Less than 0.5 area%; (-): Not detected
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Undecanes
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3.4. Gas products Figure 4 shows the main gas compositions and HHVs of the gas according to reaction temperature. More than 80 wt.% of the product gas was composed of carbon monoxide and carbon dioxide. As the reaction temperature increased, the concentration of carbon dioxide decreased whereas that of carbon monoxide increased. This phenomena is due to the fact that higher temperature favors the Boudouard reaction (CO2 + C ↔ 2CO), enhancing the
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production of carbon monoxide [26,27]. The concentration of methane increased continuously with reaction temperature up to 14.6 wt.%. Methane is generally produced by
secondary cracking of hydrocarbons [28]. Moreover, methane and carbon monoxide have a
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substantial influence on the heating value of the gases. As can be seen in Figure 4, the
product gas obtained from Run6 (14.6 wt.% of methane and 38.1 wt.% of carbon monoxide)
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had the highest HHV with a value of 20.1 MJ/kg. Therefore, the gas produced with high
100 90
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80
60 50 40 30
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20
20
16
12
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Yield (wt.%)
70
24
8
HHV (MJ/kg)
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HHV could be reused as a heat source in the pyrolysis process.
Hydrogen Methane Carbon monoxide Carbon dioxide C₂ - C₃ hydrocarbons Others HHV
4
10
0
349
0 401
450
501
557
603
Reaction temperature (oC)
Fig. 4 Distribution of gas composition and higher heating value (HHV) according to reaction temperature.
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3.5. Nitrogen balance of pyrolysis products The nitrogen distribution of the pyrolysis products is shown in Figure 5. The nitrogen contents of each product (bio-oil and char) were calculated by elemental analysis. The nitrogen content of the produced gases was calculated using the difference. Generally, HCN and NH3, which is the main nitrogen compound in the gas, are generated by decomposition of pyrrole and pyridine during the pyrolysis of biomass [29]. These gases are very harmful to human health but are produced less during pyrolysis than during combustion [30]. In Run1
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(349 °C), the nitrogen content predominantly remained in the char (Figure 5). With increasing reaction temperature, the nitrogen content in the char decreased, whereas nitrogen in the bio-oil and gas increased. This result is attributed to a decrease in the yield of char with
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increasing reaction temperature, which resulted in the nitrogen in the char converting to gas. In particular, when the reaction temperature reached 450–501 °C (Run3 and Run4), the
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amount of nitrogen in VP increased significantly. In Run4 (501 °C), the nitrogen content of
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bio-oil accounted for more than half of the nitrogen content in all products.
100
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80 70 60
40 30 20
Char Bio-oil (VP) Bio-oil (AP) Gas
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50
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Nitrogen mass balance (wt.%)
90
10
0
349
401
450
501
557
603
Reaction temperature (oC)
Fig. 5 Nitrogen distribution of products according to reaction temperature.
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The presence of nitrogen in the bio-oil is a crucial problem, which causes the fuel to generate NOx during combustion. This nitrogen can be removed directly from the bio-oil using a hydrothermal or catalytic process. For example, Du et al. employed hydrothermal pretreatment to reduce the nitrogen content in bio-oil. They investigated the effects of both reaction temperature (200–225 °C) and time (30–60 min) and found that the pretreated feed material had 6–42 % less nitrogen than the untreated feed material [31]. Gao et al. investigated the catalytic pyrolysis of natural algae using MgAl-LDO/ZSM-5 as catalysts,
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which revealed that the nitrogenous compounds of the bio-oil obtained by catalytic pyrolysis decreased from 50.9 % to 45.3 % [32].
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4. Conclusions
Fast pyrolysis of the PKC was conducted in a bench-scale fluidized bed pyrolysis plant to
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investigate the characteristics of the pyrolytic products at different reaction temperature. The
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maximum bio-oil yield of approximately 63 wt.% was obtained at 401 °C. The HHV of VPs was more than 24 MJ/kg, indicating that VPs were sufficient for use as fuel. As for their potential applications as fuel oil for combustion, the pyrolysis oils obtained from PKC had a
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problematically high nitrogen content. Therefore, the bio-oil requires additional upgrading
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before being used as a clean fuel.
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Acknowledgements
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20183010092830).
16
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5. J. Lehto, A. Oasmaa, Y. Solantausta, M. Kytö, D. Chiaramonti, Review of fuel oil quality and combustion of fast pyrolysis bio-oils from lignocellulosic biomass. Appl. Energy 116 (2014) 178–190. 6. Food and Agriculture Organization of the United Nations (FAO), FAOSTAT. Data. Oil palm fruit, World+(Total), http://www.fao.org/faostat/en/#data/QC/visualize/; 2017 (accessed 12 April 2019).
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12. K.L. Ng, M.K. Ayob, M. Said, M.A. Osman, A. Ismail, Optimization of enzymatic hydrolysis of palm kernel cake protein (PKCP) for producing hydrolysates with antiradical capacity. Ind. Crops Prod. 43 (2013) 725–731. 13. H.H. Mitchell, R.J. Block, Some relationships between the amino acid contents of proteins and their nutritive values for the rat. J Biol. Chem. 163 (1946) 599–620. 14. J. Parikh, S.A. Channiwala, G.K. Ghosal, A correlation for calculating elemental composition from proximate analysis of biomass materials. Fuel 86 (2007) 1710– 1719.
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15. L. Cuiping, W. Chuangzhi, H. Haitao, Chemical elemental characteristics of biomass fuels in China. Biomass Bioenerg. 27 (2004) 119–130. 16. S.W. Yeong, Amino acid availability of palm kernel cake, palm oil sludge and sludge fermented product (Prolima) in studies with chickens. MARDI Res. Bull. 11 (1983) 84–88. 17. S.J. Kim, S.H. Jung, J.S. Kim, Fast pyrolysis of palm kernel shells: influence of operation parameters on the bio-oil yield and the yield of phenol and phenolic compounds. Bioresour. Technol. 101 (2010) 9294–9300. 18. J.Y. Jeong, U.D. Lee, W.S. Chang, S.H. Jeong, Production of bio-oil rich in acetic acid and phenol from fast pyrolysis of palm residues using a fluidized bed reactor: Influence of activated carbons. Bioresour. Technol. 219 (2016) 357–364.
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19. Z. Ma, D. Chen, J. Gu, B. Bao, Q. Zhang, Determination of pyrolysis characteristics and kinetics of palm kernel shell using TGA–FTIR and model-free integral methods. Energy Convers. Manage. 89 (2015) 251–259. 20. Y.J. Jo, H.V. Ly, J. Kim, S.S. Kim, E. Lee, Preparation of biopolyol by liquefaction of palm kernel cake using PEG# 400 blended glycerol. J. Ind. Eng. Chem. 29 (2015) 304–313.
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29. P. Zhou, S. Xiong, Y. Zhang, H. Jiang, Y. Chi, L. Li, Study on the nitrogen transformation during the primary pyrolysis of sewage sludge by Py-GC/MS and PyFTIR. Int. J. Hydrog. Energy 42 (2017) 18181–18188. 30. D. Czajczyńska, L. Anguilano, H. Ghazal, Krzyżyńska, R., A.J. Reynolds, N. Spencer, H. Jouhara, Potential of pyrolysis processes in the waste management sector. Therm. Sci. Eng. Prog. 3 (2017) 171–197. 31. Z. Du, M. Mohr, X. Ma, Y. Cheng, X. Lin, Y. Liu, W. Zhou, P. Chen, R. Ruan, Hydrothermal pretreatment of microalgae for production of pyrolytic bio-oil with a low nitrogen content. Bioresour. Technol. 120 (2012) 13–18.
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32. L. Gao, J. Sun, W. Xu, G. Xiao, Catalytic pyrolysis of natural algae over Mg-Al layered double oxides/ZSM-5 (MgAl-LDO/ZSM-5) for producing bio-oil with low nitrogen content. Bioresour. Technol. 225 (2017) 293–298.
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PII:
S0165-2370(19)30633-3
DOI:
https://doi.org/10.1016/j.jaap.2019.104708
Reference:
JAAP 104708
To appear in:
Journal of Analytical and Applied Pyrolysis
Received Date:
14 August 2019
Revised Date:
8 October 2019
Accepted Date:
8 October 2019
Please cite this article as: Jeong J-Yong, Yang C-Won, Lee U-Do, Jeong S-Hwa, Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor, Journal of Analytical and Applied Pyrolysis (2019), doi: https://doi.org/10.1016/j.jaap.2019.104708
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor
Jae-Yong Jeonga,b, Chang-Won Yanga,b,c, Uen-Do Leea,b,c,**, and Soo-Hwa Jeongb,c,*
a
Department of Green Process and System Engineering, University of Science and
b
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Technology(UST), 89 Yangdaegiro-gil, Ipjang, Cheonan, Chungnam 331-822, South Korea Thermochemical Energy System R&D Group, Korea Institute of Industrial Technology
(KITECH), 89 Yangdaegiro-gil, Ipjang, Cheonan, Chungnam 331-822, South Korea
Future Energy Plant Convergence Research Center, Korea Institute of Energy Research
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c
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(KIER), Daejeon 305-343, South Korea
[email protected]
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* Corresponding author: Tel: +82-41-589-8576. Fax: +82-41-589-8323. E-mail:
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** Co-corresponding author: Tel: +82-41-589-8574. Fax: +82-41-589-8323. E-mail:
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[email protected] Highlights
Bio-oil obtained from the pyrolysis of palm kernel cake (PKC) was characterized PKC can reduce production costs and increase the yield and quality of bio-oil The maximum yield of bio-oil was 63 wt.% at a reaction temperature of 401 °C High nitrogen in the bio-oil requires extra treatment before use as a clean fuel
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1
ABSTRACT Palm kernel cake (PKC) was pyrolyzed in a bench-scale pyrolysis plant equipped with a bubbling fluidized bed reactor, char separation system, and bio-oil recovery system under various reaction temperatures. Experiments were conducted to evaluate the effects of reaction temperature and observe the behavior of nitrogen in pyrolysis products. The maximum yield of bio-oil from PKC was approximately 63 wt.% at a reaction temperature of 401 °C. The main chemical compounds of bio-oils obtained from PKC were acetic acid, levoglucosan,
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nitrogen-containing compounds, and fatty acids such as dodecanoic acid, octanoic acid, tetradecanoic acid, and oleic acid. At reaction temperatures above 401 °C, the nitrogen
content of bio-oils does not depend on reaction temperature. It is suggested that the resulting
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bio-oil requires additional treatment for use as a clean fuel.
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Keywords: Pyrolysis, Fluidized bed, Bio-oil, Palm kernel cake (PKC), Nitrogen
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1. Introduction
As an abundant and environmentally friendly energy source, biomass is increasingly being used as a renewable alternative to fossil fuels. Raw biomass can be used directly but is more
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effective after appropriate thermochemical conversion processes and when transformed into liquid or gaseous form. Fast pyrolysis is the best way to produce bio-oil [1]; this liquid fuel
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has many advantages over solid fuel in terms of storage, transport, handling, and diversity of
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applications. Bio-oil is generally used as fuel for boilers but can be employed in engines and turbines after certain upgrading processes [2]. Another application of bio-oil is to produce bio-chemicals through catalytic pyrolysis, which can improve the yield of specific chemicals in the bio-oil by utilizing the selectivity of the catalyst [3]. Biochar is another important product of the pyrolysis process, which can be used as a high quality solid fuel as well as a soil improvement agent. Application of bio-char to soil is an
2
attractive method of effectively sequestering C in soils. It is also able to improve soil fertility, enhance plant growth, retain nutrients, and provide habitats for microorganisms [4]. Several companies are already promoting the commercialization of fast pyrolysis technology in the bio-energy sector; however, it is still challenging to achieve economic feasibility without government subsidies [5]. Therefore, the feed material price and pretreatment process should be reduced in order to reduce the overall production cost. Palm fruit is mainly produced in Malaysia and Indonesia, with approximately 317 million
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tons produced in 2017 [6]. Approximately 10 % of the palm fruit is extracted as oil and approximately 90 % is palm residues [7]. Among the palm residues, palm kernel cake (PKC) has predominantly been used in livestock feed; however, as the production of PKC increases
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(approximately 2.59 million tons were produced in Malaysia in 2018) [8], it is necessary to find other applications. For example, using PKC as a raw material of fast pyrolysis has
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various advantages [9]. The production of PKC is concentrated in palm oil processing plants,
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so it can be supplied in large quantities with lower transportation costs. Its low water content and oil component properties (the residue after palm oil extraction) contribute to the improved yield and quality of pyrolysis oil. In addition, as the size of PKC is small and
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uniform, it can be applied directly to the fast pyrolysis process without pretreatment. Therefore, it is regarded as the most suitable raw material in terms of bio-oil production
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through fast pyrolysis. Some studies have been conducted on the pyrolysis of PKC for
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producing bio-oil. Razuan et al. pyrolyzed PKC in a fixed bed reactor and reported that the maximum liquid yield (~42.8 wt.%) was attained at a reaction temperature of 700 °C with a heating rate of 10 °C/min [10]. Ngo et al. performed fast pyrolysis of PKC in a fluidized bed reactor and reported that the maximum bio-oil yield (~50 wt.%) was obtained at a reaction temperature of 500 °C. They also reported that the main compounds of bio-oil were 1,2-
3
benzenedicaboxylic acid-bis (2-ethylhexyl) ester, β-D-allose, and fatty acids [11]. These studies were carried out using a small fixed and fluidized bed reactor. It should be noted that the nitrogen content in PKC can be a disadvantage because the nitrogen content of gas, liquid, and solid pyrolysis products is proportional to the nitrogen content of the feedstock. The nitrogen content in the PKC originates from proteins (14–16 %) composed of nitrogen in the form of amino acids (generally 16 % in the protein) [12,13]. In this study, PKC was pyrolyzed using a bench-scale fluidized bed reactor equipped with
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a char separation system. The aim of this study was to determine the influence of reaction temperature on the characteristics of the resulting bio-oil. In addition, the behavior of
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nitrogen in the pyrolysis products was investigated.
2. Materials and methods
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2.1. Feed material
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The PKC used in this study was obtained from Indonesia. Unlike other biomass, PKC is produced in powder form in the manufacturing process; thus, it has the advantage of not requiring a powder process. Before using the PKC, it was sieved to obtain a size of 0.4–0.8
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mm and dried in an oven at 110 °C for 24 h to remove moisture. Then, proximate analysis and ultimate analysis were conducted following ASTM D3172 and ASTM D3176,
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respectively, the properties of which are presented in Table 1.
Table 1 Properties of the feed material. Proximate analysisa
wt.%
Ultimate analysis
wt.%
Volatile matter
89.3
C
50.8
Na
43.0
Fixed carbon
7.0
H
6.1
K
6678.0
Ash
3.7
N
3.1
Mg
2789.0
S
0.2
Ca
4068.0
Metal analysis
ppm
4
HHV (MJ/kg)
20.5
Ob
39.8
a: air dry basis b: by difference
The proximate analysis was calculated on a dry basis and the ultimate analysis of oxygen was calculated by the difference. According to the proximate analysis, the predominant component of the PKC is volatile matter with a value of 89.3 wt.%, which is higher than that of other biomass (62.9–88.2 wt.%) [14]. According to the ultimate analysis, the nitrogen
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content of PKC is approximately 3 wt.%, which is much greater than that of woody biomass (< 1 wt.%) [15]. The sulfur content is 0.2 wt.%, which predominantly originates from sulfurcontaining amino acids such as methionine and cysteine in the feed material [16]. The metal
considerably greater than those of other biomass.
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2.2. Pyrolysis plant
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analysis showed that all alkali and alkali earth metal contents, except for potassium, are
Experiments were conducted in a bench-scale pyrolysis plant composed of a feeding
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system, fluidized bed reactor, char separation system, and bio-oil recovery system. A
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schematic diagram of the pyrolysis plant is shown in Figure 1.
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Fig. 1 Schematic diagram of the pyrolysis plant.
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The feeding system was composed of a silo and two screw feeders. The purging gas was supplied to the feeding system in order to prevent backflow by the fluidizing gas and an air jacket was installed at the inlet of the reactor to prevent any thermal degradation of the feed
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material by heat transfer from the reactor. The pyrolyzer, a fluidized bed reactor, was made of a 316SS tube with an inner diameter and height of 160 mm and 610 mm, respectively. It was
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indirectly heated by two electric heaters. The reaction temperature was determined by the
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average value of the second and third thermocouples from the bottom. The char separation system was composed of two cyclones heated by a heating tape to 350 °C in order to prevent condensation of the pyrolysis gas. The fine char was removed from the char separation system and the excess char in the bubbling fluidized bed was removed by a char pot. The biooil recovery system was composed of three condensers, two impact separators, and an electrostatic precipitator for more efficient recovery. The condensers were made of 316SS,
6
which were water-cooled to 5–10 °C. The non-condensable gas was circulated by a diaphragm pump and used as a fluidizing medium. The excess gas was sampled for analysis or burned in a flare stack. 2.3. Thermogravimetric analysis Thermogravimetric analysis was performed using a thermogravimetric analyzer (TGA Q50, TA Instruments) to confirm the decomposition behavior of the feed material. Approximately 10–20 mg of the feed material was used, and the temperature was increased from 30–800 °C
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at a rate of 10 °C /min. Nitrogen gas was used as a carrier gas for the balance and furnace. The thermogravimetry (TG) and differential thermogravimetry (DTG) curves of PKC are
shown in Figure 2 and compared with those of an earlier study with palm kernel shell (PKS)
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[17,18].
0.10
0.9
0.09
0.8
0.08
0.6 0.5 0.4 0.3
0.06 0.05 0.04
0.2 0.1
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0.0 0
100
200
300
400
DTG (dX/dt)
0.07
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0.7
0.03
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Normalized mass to initial mass
PKC PKS
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1.0
0.02 0.01 0.00 500
600
700
800
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Temperature (℃ )
Fig. 2 TG and DTG curves for samples of palm kernel cake (PKC) and palm kernel shell
(PKS).
Initially, the weight of PKC gradually decreased over 100 °C due to evaporation of moisture. Subsequently, major weight loss occurred in the temperature range of 200–380 °C,
7
potentially due to weight loss of the hemicellulose in the fibers, which typically occurs from 100–365 °C [19]. According to Jo et al., the chemical composition of PKC determined by TAPPI methods was 16.4% cellulose, 49.4% hemicellulose, and 34.2% lignin [20]. Compared to PKC, two clear shoulder peaks appeared on the DTG curve of PKS, which was attributed to differences in the chemical composition of the raw material. After approximately 380 °C, weight loss of both feed materials slowly occurred until 800 °C due to the degradation of lignin.
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2.4. Reaction conditions In this study, the only reaction parameter was the reaction temperature (Table 2), which is
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most important for determining the yields and properties of products.
Run1
Run2
Reaction temperature (°C)
349
401
Flow rate (NL/min)
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Fluidizing medium
Product gas
Run3
Run4
Run5
Run6
450
501
557
603
61
58
54
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Parameters
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Table 2 Reaction parameters of the pyrolysis experiments.
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70
In all experiments, 1,500 g and 5,600 g of feed material and quartz sand were used,
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respectively. Based on the results of the TGA experiments, the experiments were conducted
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in the temperature range from 350–600 °C. The minimum fluidization velocity that was calculated using the Ergun equation was maintained at 3 umf [21]. To achieve reliable results, all experiments were conducted twice. 2.5. Analysis of pyrolysis products The recovered pyrolysis products were separated into three fractions: oil, gas, and char. The bio-oils were reliably separated into two phases in the bio-oil recovery system: an aqueous
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phase (AP) and a viscous phase (VP). AP was recovered with condensers and VP was recovered with impact separators, connection tubes, and an electrostatic precipitator. The separated bio-oils were analyzed for each phase. Moreover, the bio-oil was subjected to elemental analysis using an elemental analyzer (Flash Smart, Thermoscientific). The water content was analyzed by Karl Fisher titration (Metrohm 870, KF Titrino). HYDRANAL Composite 5K and methanol were used as the titration reagent and the titration solvent, respectively. A GC-MS (5975C, 7890A, Agilent) was used for qualitative analysis of the bio-
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oils, which indicated that only peaks with an area of 0.1 % or higher were confirmed. The higher heating value (HHV) was calculated by Dulong's equation. The gas produced during
the experiments was sampled three times and analyzed using GC-TCD (6890N, Agilent) and
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FID (7890A, Agilent). TCD analyzed hydrogen, nitrogen, carbon monoxide, carbon dioxide,
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and methane and FID analyzed C1 – C8 hydrocarbons.
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3. Results and Discussion 3.1. Mass balance
The mass balance was established by measuring the weight of the pyrolysis products.
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Figure 3 shows the mass balance for each condition. The yield of bio-oils was calculated by measuring the weight of the recovery system before and after the experiments. The yield of
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gas was obtained by measuring the gas volume of the experiments and calculating the gas
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density from the gas composition. The yield of product char was calculated from the difference. For PKC, the maximum bio-oil yield of 63.0 wt.% was obtained at a reaction temperature of 401 °C. The bio-oil yield was the lowest at reaction temperature of 603 °C. This phenomenon may be because the main reaction ended at 380 °C, as discussed in Section 2.3. As the reaction temperature increased, the yield of gas rapidly increased. This is probably
9
due to secondary cracking of the pyrolysis vapor. Conversely, the yield of char gradually decreased. This may be due to volatilization of unconverted biomass in the reactor.
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Oil Char Gas
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Yield (wt.%)
50 40 30
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20 10 0 349
401
450
501
557
603
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Reaction temperature (oC)
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Fig. 3 Distribution of pyrolysis products according to reaction temperature.
3.2. Pyrolysis oil
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The main properties of the bio-oils produced in the experiments are shown in Table 3. After pyrolysis, the bio-oils were separately into two phases (Section 2.5). The weight ratio
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(wt./wt.%) of both AP and VP in bio-oils was approximately 6:4. According to the proximate analysis, the bio-oils produced were almost entirely composed of carbon and oxygen. The
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oxygen content of AP occupied approximately 70 wt.% with the carbon occupying a very small amount of less than 19 wt.%. Conversely, the oxygen content of VPs was less than 23
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wt.% and the carbon content was greater than 63 wt.%. The nitrogen contents of AP and VP were 1.3–2.5 wt.% and 2.0–6.7 wt.%, respectively. A detailed discussion on nitrogen behavior is given in Section 3.5. The water content of APs was greater than 19.6 wt.%, while the water content of VP was less than 2.2 wt.%. Because of these characteristics, the HHV of APs (5–8 MJ/kg) was very low and that of VPs (29–39 MJ/kg) was high. The HHVs of bio-
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oils were calculated by Dulong's equation. Considering the HHVs, the VPs in bio-oil could be used as fuel oil or an energy source in a pyrolysis plant.
Runs
Run1
Run2
Run3
Run4
Run5
Run6
Reaction temperature (°C)
349
401
450
501
557
603
Phase
AP
VP
AP
VP
AP
VP
AP
C
11.8
67.2
18.6
68.9
16.1
66.9
13.4
65.1
10.4
65.9
13.4
63.3
H
8.2
10.1
9.2
7.0
8.5
8.6
8.6
8.3
8.6
7.9
8.6
7.5
N
1.3
2.1
2.2
2.0
2.0
3.2
2.0
4.2
2.5
4.9
2.0
6.7
S
0.1
-
-
-
-
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Table 3 Main properties of the bio-oils.
-
0.1
0.1
-
-
-
-
Oa
78.6
20.6
70.0
22.2
73.4
21.3
75.9
22.3
78.5
21.2
75.9
22.5
Water content (wt.%)
23.5
2.2
24.8
1.9
19.6
0.7
24.1
1.7
23.1
2.2
21.3
1.8
HHV (MJ/kg)
5.7
33.7
6.2
38.4
5.1
33.3
6.4
30.9
6.7
25.0
5.5
24.4
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VP
AP
VP
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a: by difference
AP
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Elemental analysis (wt.%)
VP
3.3 Chemical components of bio-oils
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The major components of the bio-oils analyzed by GC-MS are listed in Table 4, where the
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area% values only present values greater than 0.5 area% (i.e., detectable amounts). The main components observed in the bio-oils were acetic acid, levoglucosan, nitrogen-containing compounds, and fatty acids such as dodecanoic acid, octanoic acid, tetradecanoic acid, and oleic acid. Acetic acid is produced during breakaway from the acetyl group bound to the xylose unit, which is one of the constituents of hemicellulose [22]. In all experiments, the yields of acetic acid in bio-oils were concentrated in the APs due to high solubility in water.
11
The levoglucosan predominantly originated from thermal degradation of cellulose and can be used as a precursor to various chemicals such as diols, surfactants, and pharmaceutical additives [23]. In Run2 (401 °C), higher yields of levoglucosan (~25 area% in AP and ~18 area% in VP) were observed in the bio-oils than in other Runs. Above a reaction temperature of 500 °C, the yield of levoglucosan was significantly decreased. The main compounds of fatty acid observed in the bio-oils were decanoic acid, tetradecanoic acid, oleic acid, and hexadecanoic acid, which resulted from the degradation of residual palm oil substances [11].
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PKC generally contains between 7 % and 10 % fatty acids [24]. The main nitrogencontaining compounds identified in the bio-oils were pyridine and acetamide. They appeared to originate mainly from alanine-containing proteins and glycine-containing proteins,
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respectively [25]. Furfuryl alcohol was also found in the bio-oils, originating from the
degradation of hemicellulose in the fibers. The concentrations of phenol and phenolics
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compounds, which were degradation products of lignin, were smaller than those of other
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palm residues [17,18].
Run1
Reaction temperature (°C)
349
Phases
Aqueous
Viscous
Run2
Run3
Run4
Run5
Run6
401
450
501
557
603
Aqueous
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Runs
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Table 4 Chemical components of the bio-oils determined by GC-MS.
Viscous
Aqueous
Viscous
Aqueous
Viscous
Aqueous
Viscous
Aqueous
Viscous
Components (area%) Acetic acid
1.20
8.83
1.14
10.41
0.85
11.95
1.08
20.92
1.24
12.41
0.79
-
+
3.69
0.73
4.13
0.68
4.91
0.69
-
0.53
-
+
Propanoic acid
0.64
+
-
+
1.52
+
1.71
+
-
0.44
1.66
+
2-Propenoic acid
-
-
-
-
-
-
-
-
1.62
-
2.36
-
Furfuryl alcohol
2.46
1.39
2.32
0.89
2.07
0.61
1.98
0.59
1.04
+
0.97
+
Butanoic acid
-
-
-
-
-
-
-
-
0.86
-
+
-
Butyrolactone
+
-
+
-
+
-
+
-
0.66
-
+
-
2(5H)-Furanone
0.71
-
1.06
-
0.65
-
0.65
-
+
-
-
-
Phenol
0.78
1.15
1.17
0.82
1.16
1.04
0.99
1.31
1.06
1.36
1.02
2.55
Indene
-
+
-
+
-
+
-
+
-
+
-
0.66
Cresols
-
0.80
-
+
-
0.62
-
0.88
-
1.08
-
1.57
Cyclobutanol
-
0.96
-
0.79
-
+
-
0.53
-
-
-
-
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Acetol
9.57
12
-
-
-
-
-
+
-
0.53
-
0.58
-
0.50
Corylon
0.63
-
0.75
-
0.94
-
0.76
-
+
-
+
-
Glycerin
+
1.86
3.98
2.42
6.26
+
5.10
0.69
3.52
0.52
2.62
+
Maltol
1.56
0.92
1.57
0.68
1.21
+
0.66
+
2.10
0.33
3.09
+
Xylenols
-
-
-
-
-
-
-
+
-
0.81
-
0.84
Ethyl 2-butenoate
1.71
-
2.00
-
2.18
-
0.99
-
0.80
-
0.73
-
Naphthalene
-
0.55
-
0.90
-
+
-
0.54
-
1.00
-
2.21
Benzoic acid
0.88
1.42
1.13
1.47
0.85
1.50
0.72
1.56
1.41
1.90
1.37
1.89
Methylnaphthalenes
-
-
-
-
-
-
-
+
-
+
-
0.99
Coumaran
-
+
-
+
-
+
-
0.85
-
+
-
-
Cyclobutanol
0.55
-
0.83
-
1.05
-
0.84
-
0.68
-
+
-
Resorcinol
-
+
-
0.69
-
-
-
+
-
0.69
-
+
Syringol
+
+
0.59
0.56
+
-
0.91
-
+
-
+
-
Decanoic acid
3.87
2.22
4.70
2.69
5.63
2.13
6.64
2.07
-
1.04
-
0.58
Isoeugenol
-
+
-
0.54
-
+
-
-
-
+
-
+
2-Tridecanone
-
+
-
+
-
+
-
0.60
-
+
-
+
Levoglucosan
15.10
10.92
24.82
18.02
20.41
3.31
8.85
2.15
5.12
1.83
0.71
-
Dodecanoic acid
-
17.92
-
10.52
-
22.18
-
20.41
-
15.97
-
10.20
Octanoic acid
-
1.15
-
0.52
-
0.87
-
1.06
-
0.80
-
1.04
Methoxyeugenol
-
1.16
-
1.91
-
0.73
-
0.66
-
0.72
-
0.69
Tetradecanoic acid
10.82
9.63
5.45
10.86
4.35
12.92
10.81
13.86
10.78
12.11
23.43
6.36
Oleic Acid
18.24
26.18
7.16
21.59
6.47
29.43
Hexadecanoic acids
9.48
7.72
7.34
7.01
7.55
9.66
N-compounds
1.37
0.18
2.06
0.18
2.82
0.27
20.41
13.78
19.65
-p 27.47
5.46
25.09
9.07
26.21
11.73
8.42
14.37
6.09
18.07
3.49
3.40
0.39
5.89
0.63
2.08
0.67
11.88
22.95
23.29
19.63
36.75
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5.98
10.69
20.23
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ur
na
lP
Others 20.53 10.69 (+): Less than 0.5 area%; (-): Not detected
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Undecanes
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3.4. Gas products Figure 4 shows the main gas compositions and HHVs of the gas according to reaction temperature. More than 80 wt.% of the product gas was composed of carbon monoxide and carbon dioxide. As the reaction temperature increased, the concentration of carbon dioxide decreased whereas that of carbon monoxide increased. This phenomena is due to the fact that higher temperature favors the Boudouard reaction (CO2 + C ↔ 2CO), enhancing the
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production of carbon monoxide [26,27]. The concentration of methane increased continuously with reaction temperature up to 14.6 wt.%. Methane is generally produced by
secondary cracking of hydrocarbons [28]. Moreover, methane and carbon monoxide have a
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substantial influence on the heating value of the gases. As can be seen in Figure 4, the
product gas obtained from Run6 (14.6 wt.% of methane and 38.1 wt.% of carbon monoxide)
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had the highest HHV with a value of 20.1 MJ/kg. Therefore, the gas produced with high
100 90
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80
60 50 40 30
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20
20
16
12
ur
Yield (wt.%)
70
24
8
HHV (MJ/kg)
lP
HHV could be reused as a heat source in the pyrolysis process.
Hydrogen Methane Carbon monoxide Carbon dioxide C₂ - C₃ hydrocarbons Others HHV
4
10
0
349
0 401
450
501
557
603
Reaction temperature (oC)
Fig. 4 Distribution of gas composition and higher heating value (HHV) according to reaction temperature.
14
3.5. Nitrogen balance of pyrolysis products The nitrogen distribution of the pyrolysis products is shown in Figure 5. The nitrogen contents of each product (bio-oil and char) were calculated by elemental analysis. The nitrogen content of the produced gases was calculated using the difference. Generally, HCN and NH3, which is the main nitrogen compound in the gas, are generated by decomposition of pyrrole and pyridine during the pyrolysis of biomass [29]. These gases are very harmful to human health but are produced less during pyrolysis than during combustion [30]. In Run1
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(349 °C), the nitrogen content predominantly remained in the char (Figure 5). With increasing reaction temperature, the nitrogen content in the char decreased, whereas nitrogen in the bio-oil and gas increased. This result is attributed to a decrease in the yield of char with
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increasing reaction temperature, which resulted in the nitrogen in the char converting to gas. In particular, when the reaction temperature reached 450–501 °C (Run3 and Run4), the
re
amount of nitrogen in VP increased significantly. In Run4 (501 °C), the nitrogen content of
lP
bio-oil accounted for more than half of the nitrogen content in all products.
100
na
80 70 60
40 30 20
Char Bio-oil (VP) Bio-oil (AP) Gas
ur
50
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Nitrogen mass balance (wt.%)
90
10
0
349
401
450
501
557
603
Reaction temperature (oC)
Fig. 5 Nitrogen distribution of products according to reaction temperature.
15
The presence of nitrogen in the bio-oil is a crucial problem, which causes the fuel to generate NOx during combustion. This nitrogen can be removed directly from the bio-oil using a hydrothermal or catalytic process. For example, Du et al. employed hydrothermal pretreatment to reduce the nitrogen content in bio-oil. They investigated the effects of both reaction temperature (200–225 °C) and time (30–60 min) and found that the pretreated feed material had 6–42 % less nitrogen than the untreated feed material [31]. Gao et al. investigated the catalytic pyrolysis of natural algae using MgAl-LDO/ZSM-5 as catalysts,
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which revealed that the nitrogenous compounds of the bio-oil obtained by catalytic pyrolysis decreased from 50.9 % to 45.3 % [32].
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4. Conclusions
Fast pyrolysis of the PKC was conducted in a bench-scale fluidized bed pyrolysis plant to
re
investigate the characteristics of the pyrolytic products at different reaction temperature. The
lP
maximum bio-oil yield of approximately 63 wt.% was obtained at 401 °C. The HHV of VPs was more than 24 MJ/kg, indicating that VPs were sufficient for use as fuel. As for their potential applications as fuel oil for combustion, the pyrolysis oils obtained from PKC had a
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problematically high nitrogen content. Therefore, the bio-oil requires additional upgrading
ur
before being used as a clean fuel.
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Acknowledgements
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20183010092830).
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