Energy 66 (2014) 162e171

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Energy
journal homepage: www.elsevier.com/locate/energy

Application of biomass fast pyrolysis part I: Pyrolysis characteristics

and products
S.I. Yang a, *, M.S. Wu a, C.Y. Wu b, **
a
Department of Power Mechanical Engineering, National Formosa University, Yunlin County 63202, Taiwan
b
Department of Mechanical and Automation Engineering, Kao Yuan University, Kaohsiung, Taiwan

a r t i c l e i n f o a b s t r a c t

Article history: In the present study, the thermal decomposition behavior of three common biowastes in Taiwan (cedar
Received 28 January 2013 sawdust, coffee bean residue, and rice straw) upon fast pyrolysis was studied. Products were determined
Received in revised form by gas chromatographyemass spectrometry. The composition of the resulting bio-oils was also quanti-
16 October 2013
fied. TGA (thermogravimetric analysis) results indicate that thermal degradation of the biowaste samples
Accepted 27 December 2013
Available online 27 January 2014
occurs through four steps, namely, start of decomposition of extractives (<490 K), hemicellulose
decomposition (490e650 K), cellulose and lignin decomposition (650e780 K), and lignin decomposition
(>780 K). The temperature for thermochemical conversion was 700 K. Maximum rates of bio-oil pro-
Keywords:
Biomass
duction (51, 48, and 28 wt% for cedar sawdust, coffee bean residue, and rice straw, respectively) were
Fast pyrolysis observed when the flow rate of carbon dioxide was 30 L/min. Char production decreased with increased
Bio-oil reaction temperature, and increased with the increase in flow rate of carbon dioxide. Hence, char pro-
TGA (thermogravimetric analysis) duction was highly correlated with fluidization of the fluid bed. Bio-oil contained two phases, namely,
GCeMS (gas chromatographyemass the oily phase from lignin and cellulose, and the aqueous phase from cellulose and hemicellulose. The
spectrometry) water content of the oily phase was relatively low and consisted mainly of extractives and low- and high-
molecular-weight lignins. Extractives included hexane-soluble compounds consisting mainly of hydro-
carbons. The oily phase was composed of hexane-soluble aliphatic, aromatic, and polar fractions. The
aqueous phases of bio-oils derived from the three biowaste samples had compositions that were very
similar, and most contained significant amount of aromatics and oxygenated compounds such as car-
boxylic acids, phenols, and ketones. When CO2 was utilized as fluidization gas, the vented gas produced
by pyrolysis of the three biowaste samples contained roughly 95.3 vol% CO2, and biomass pyrolysis
produced around 4.6 vol% CO2. The vented gases had compositions that were similar, and consisted
mostly of CO2 (nearly 48.2e51.3 vol%) and CO (about 44.2 vol%).
Crown Copyright Ó 2014 Published by Elsevier Ltd. All rights reserved.

1. Introduction followed by coal (over 40%). Taiwan emitted approximately

113 million tons of CO2 in 1990 (i.e., 5.5 tons per capita), and in
Human economic activities have resulted in overconsumption of 2005, the country’s CO2 emissions reached 270 million tons (i.e.,
fossil fuels. Coal and petroleum are fossil fuels that are used in the 11.74 tons per capita). The rise in total emissions was more than
largest quantities. Because of fluctuations of fossil fuel prices and 110%, which was four times greater than the increase in global
anomalies in the global climate, the discovery of an alternative emissions. Consequently, biomass energy development has become
source of clean energy has become an important area of research in one of Taiwan’s critical energy policies.
recent years. In particular, numerous countries have made an effort Biomass is a renewable energy source that can alleviate the
to develop application technologies for biomass energy. According problems of global energy consumption and greenhouse gas
to statistics provided by the International Energy Agency [1], the emissions; therefore, it has been analyzed in numerous studies [2e
major source of global electricity in March 2012 was petroleum, 5]. It can be utilized in various application technologies. It contains
three major components, namely, cellulose, hemicellulose, and
lignin, and it minor constituents comprise other extractives and
minerals. Thermochemical conversion of biomass to obtain various
* Corresponding author. Tel.: þ886 5 631 5432; fax: þ886 5 631 2110. solid, liquid, and gas products may be performed through pyrolysis,
** Corresponding author. Tel.: þ886 7 607 7293; fax: þ886 7 607 7906.
a method in which the organic matrix undergoes direct thermal
E-mail addresses: ianyang@nfu.edu.tw, shouyang@gmail.com (S.I. Yang),
chihyungwu@gmail.com (C.Y. Wu). decomposition in the absence of oxygen. Previous studies have

0360-5442/$ e see front matter Crown Copyright Ó 2014 Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.energy.2013.12.063
 S.I. Yang et al. / Energy 66 (2014) 162e171 163

examined three major distributions of pyrolysis components to 0.5e1, 0.3e0.9, and 2e5 mm, respectively (Table 1). As the milling
further understand pyrolysis reactions. Ferdous et al. [6] conducted process of rice straw was rather laborious, reducing it to a smaller
TGA (thermogravimetric analysis) to investigate the pyrolysis of particle size was difficult. All samples were oven-dried for 5 h and
lignin on a fixed bed. They identified strong relationships among subjected ASTM E1756-08 standard procedures to reduce their
the kinetic parameters, the type and origin of lignin, and the water content [13].
equipment used for the pyrolysis reactions. Yang et al. [7] con- The samples were subjected to proximate, ultimate, and
ducted TGA of the pyrolysis characteristics of lignin, hemicellulose, composition analyses (results are given in Table 2). During the
and cellulose, and found that hemicellulose and cellulose are experiment, all results from tests on the biowaste samples were
related to environmental characteristics. Wang et al. [8] performed analyzed on the basis of dried samples. Oxygen levels in the sam-
TGA on sawdust to determine the influence of various compositions ples subjected to ultimate analysis were calculated by a difference
of lignin, hemicellulose, and cellulose on syngas produced at method. Lignocellulosic compositions of the samples affected the
various heating rates. Raveendran et al. [9] conducted TGA to study distribution of the fast-pyrolysis products. Among the three sam-
the product compositions corresponding to various biomass com- ples, cedar sawdust contained the most lignin, Rice straw contained
positions and operating parameters for a fixed bed. Notably, their the most cellulose and hemicelluloses.
research revealed that ash in biomass influences the characteristics
biomass pyrolysis and product compositions. A number of studies 2.2. TGA measurement
also examined the relationship between heat or thermal mass and
composition [10] and between pyrolysis products and biomass To examine the thermal decomposition behavior of the three
compositions. Bassilakis et al. [11] used thermogravimetric anal- biowaste samples at various temperatures and to provide a refer-
ysiseFourier transform infrared spectrometry to examine differ- ence for operational parameters of fast pyrolysis, changes in the
ences in products caused by differing biomass sources and molecular weights of the samples and temperatures under various
temperatures. Mehrabian et al. [12] employed TGA data to establish heating rates (1, 5, 10 K/min) were observed on a thermogravi-
a thermal conversion model. Another work also revealed that the metric analyzer (SDT-Q600 Simultaneous TGA/DSC, TA In-
lignin and inorganic compound compositions in biomass are struments). Each sample was around 10e20 mg, and the purging
related to the quality and stability of pyrolysis products [13]. gas was CO2, which was introduced at a flow rate of 100 mL/min.
Furthermore, many studies [14e18] have examined reactors and The correlation between time and weight of each sample was
biomass pyrolysis reactions. For example, Lappas et al. [19] adopted recorded.
a circulating fluid bed to consecutively produce pyrolysis oil and to
upgrade oil quality by using catalysts, and obtained 70% oil yield. 2.3. Fast-pyrolysis system
Lédé et al. [20] utilized a cyclone reactor to produce oil by fast
pyrolysis, and analyzed the water or moisture content rate, particle The 1 kg/h feedstock system used biomass fast pyrolysis (Fig. 1).
residue, viscosity, and pH values of the oil. Ohmukai et al. [21] It consisted of a fluidization gas supply, gas heater, screw feeder,
adopted a countercurrent flow reactor to analyze the pyrolysis fluidized bed reactor, cyclone separator, two atomizing condensers,
characteristics of a mixture of biomass and plastics and to establish and vented gas combustor. Carbon dioxide was used as the fluid-
a kinetic model for the pyrolysis. Chen et al. [22] examined the ization gas. A flow control valve was employed to control the flow
characteristics and reaction models for pyrolysis of sucrose in a rate of fluidization gas, which was passed through a heater to bring
tubular reactor. the CO2 to the temperature of the fluidized bed reactor before in-
According to the aforementioned literature, operational pa- jection of the fluidization gas into the fluidized bed. The fluidized
rameters of the thermochemical conversion and thermal decom- bed reactor, which was made from stainless 316, had an inner
position behavior of various biomasses have an effect on the diameter of 40 mm and a height of 400 mm. Preheated fluidization
compositions of bio-oil and its production rate. TGA is a common gas was provided from below the fluidized bed reactor through the
technique for analyzing the thermal decomposition behavior as sintered-metal perforated plate to allow fluidization of the medium
well as the chemical kinetics of complex reactions of thermo- in the reactor. Operating parameters and conditions are listed in
chemical conversion of various biomasses. Alternatively, GCeMS Table 1.
(gas chromatographyemass spectrometry) is used for quantifica- The fluidized bed reactor was covered by an insulation device
tion analysis of the bio-oil compositions; its data can then be and an electrical heating system with three thermocouples
applied to TGA to examine the chemical kinetics of complex re- installed separately on fluid beds at various heights: TC1, TC2, and
actions of biomass pyrolysis. In the present study, the impact of TC3, which are located 80, 200, and 320 mm from the bottom of the
operational parameters of thermochemical conversion on the reactor, respectively (Fig. 1). The thermocouples were used to
compositions of cedar sawdust, coffee bean residue, and rice straw monitor the temperature of the fluid beds, and the electrical
and bio-oil were investigated. As fluidization gas has little effect on heating system and fluidization gas provided heat required by the
the thermal decomposition behavior and chemical kinetics of reactions. During the reaction, TC2 was used as the reactor tem-
complex reactions, the study was done through TGA, fast pyrolysis, perature. The temperature difference, which was less than 20 K
and GCeMS of bio-oil by using CO2 as fluidization gas. The obtained between thermocouples, was used as the operational indicator of
results may serve as reference for applications of bio-oil in diesel
engines [23]. Table 1
Experimental conditions.
2. Materials and methods
Feedstock Cedar Coffee bean Rice
sawdust residue straw
2.1. Feedstock preparation
Feed size (mm) 0.5e1 0.3e0.9 2e5
Feedrate (g/min) 5e15
The effects of various compositions of cedar sawdust, coffee Fluidizing medium Ceramic ball
bean residue, and rice straw, which are three common biowastes in Reactor temperature (K) 600e800
Taiwan, on their thermal decomposition behavior were examined. Fluidization gas Carbon dioxide
Fluidization gas flow rate (L/min) 5e20
The biowaste samples were milled and sieved to particle sizes of
164 S.I. Yang et al. / Energy 66 (2014) 162e171

Table 2 Table 3
Results of proximate, ultimate, and composition analysis of biomass. Physical properties of ceramic particles and quartz grains.

Cedar sawdust Coffee bean residue Rice straw Fluidizing medium Ceramic ball Quartz sand

Proximate analysis (wt.%) Bulk density (kg/m3) 1550 2850

Moisture 7.7 9.4 8.5 Particle density (kg/m3) 1300e1400 2600e2800
Volatile matter 81.2 82.5 83.8 Particle size (mm) 4e5 1e2
Fixed carbon 1.9 1.4 1.6 Specific heat capacity (J/kgK) 628e700 800
Ash 2.1 6.7 6.1
HHV (MJ/Kg) 19.45 18.32 17.21
Ultimate analysis (dry, wt.%)
Carbon 45.12 44.43 43.24 2.4. GCeMS measurement
Hydrogen 5.25 5.31 5.58
Nitrogen 1.14 0.92 1.33 Fluids of the two bio-oil phases were quantified by GCeMS to
Sulfur 0.03 0.05 0.21
determine their compositions and to examine the effects of bio-
Oxygen 48.46 49.29 49.64
Composition of lignocellulosic material (wt.%) waste on the chemical kinetics of pyrolysis reactions. Operational
Cellulose 48.34 19.72 36.78 temperatures for pyrolysis and interface in the pyrolyzer (Double-
Hemicellulose 11.3 30.32 31.67 shot PY-2020D) were 500 and 300 K, respectively, when 0.5e1.0 mg
Lignin 31.45 30.92 12.66
of bio-oil was injected into the microfurnace. The vapor produced
from this step was injected into a HewlettePackard HP 6890 GC gas
chromatograph equipped with an HP 5973 mass-selective detector
the reactor. Hollow ceramic balls, the bed material, were inserted and a column from Agilent Technologies. The HP-5ms hl opera-
into the bed (Table 3). These balls have lower particle and bulk tional parameters were as follows: injector temperature, 300 K;
densities and greater fluid cross-sectional areas than those of carrier gas, helium; flow rate, 1 mL/min (constant flow); and oven
quartz sand, which is commonly used for fluidized beds. temperature program, 40 K for 5 min and then increase to 300 K at
The biomass was conveyed into the fluidized bed reactor by a 20 K/min. Operational parameters of the mass spectrometer de-
screw feeder. Upon interaction with the fluidized bed material, tector were as follows: type, quadruple mass filter; scan range, 29e
the biowaste sample underwent pyrolysis reactions and pro- 550 Da; source temperature, 230 K; ionization mode, electron
duced bio-oil, gases, and char. Most of the char was separated by impact; ionization voltage, 70 eV.
a cyclone separator, and biogases were condensed by two
atomizing condensers into bio-oils of various condensation
3. Results and discussion
temperatures. The inner widths and heights of these atomizing
condensers were 200 and 300 mm, respectively. Each atomizing
The three biowaste samples processed under various operating
condenser recycled bio-oil inside the column by pressing the oil
conditions were used for the bio-oil production experiments.
through an atomizer with a pump, thereby producing vaporized
Operating conditions are summarized in Table 1.
high-temperature bio-oil vapor, which was then cooled by
circulating atomized cooling. The condensers were covered by a
water jacket to remove heat from the bio-oil vapor. The retention 3.1. TGA of biomass
time of the biowaste, that is, the time from entering the fluid bed
to the fuel tank, was less than 2 s. Gases products of pyrolysis that Fig. 2 shows the TGA thermogram and the mass loss rates of the
could not be condensed were directed to the vented gas samples at three heating rates. As shown in Fig. 2aec, most samples
combustor for heat-energy recycling to reduce the energy con- began to lose mass at 500 K rather than at 400 K. This behavior may
sumption of the pyrolysis process. be due to the oven-drying of the samples to remove moisture. The

Fig. 1. Biomass fast-pyrolysis system: screw feeder, fluidized bed reactor, cyclone, condenser, and porous burner.
 S.I. Yang et al. / Energy 66 (2014) 162e171 165

mass of the samples decreased significantly at 500 and 700 K [24], Zone I: <490 K, decomposition of extractives
which was the temperature range at which thermal decomposition Zone II: 490e650 K, decomposition of substances composed
of cellulose and hemicellulose began [9,24], whereas the thermal predominantly of hemicellulose
decomposition for the lignin occurred at a wider temperature range Zone III: 650e780 K, decomposition of substances composed
(500e1200 K). Thus, whether the mass changes in the samples chiefly of cellulose and lignin
were caused by cellulose or hemicellulose could not be determined. Zone IV: >780 K, decomposition of substances composed chiefly
However, mass changes above 700 K were caused by lignin of lignin
decomposition, which was slow compared with the decomposition
between 500 and 700 K [24]. In summary, behaviors of the three No obvious change in mass of the three samples at low heating
samples varied with temperature. These behaviors may be cate- rate (1 K/min) was observed, whereas responses in Zone II were
gorized into four zones [9]: found to be stronger. Upon increase in the heating rate to 5 K/min,

Fig. 2. TGA of biomass under various heating conditions: (a) cedar sawdust, (b) coffee bean residue, and (c) rice straw.
166 S.I. Yang et al. / Energy 66 (2014) 162e171

mass changes were significantly concentrated in Zone II. Several 3.3. Product yields of biomass pyrolysis
reactive regions were concentrated in Zone III (a, b), but for all
samples except rice straw. When the heating rate was elevated to Cellulose, hemicellulose, and lignin in biomass undergo pyrol-
10 K/min, regions of mass reduction were concentrated in Zone II, ysis in a heated environment with insufficient oxygen, producing
although the mass reduction for rice straw was insignificant. char and condensable or noncondensable products. Factors that
However, the reaction rate of cedar sawdust in Zone III decreased influence biomass pyrolysis characteristics include temperature,
with increased heating rate, whereas that of coffee bean residue particle size, heating rate, feed rate, and biomass composition. Ef-
increased. These results show that the decomposition rate of fects of various fluidization gas temperatures and flow rates on
hemicellulose in the samples was maximal between 550 and 650 K products of biomass pyrolysis are discussed below.
and increased with heating rates. Hemicellulose was the major
substance that was decomposed during biomass pyrolysis. An
increased heating rate reduced the reaction rate of cedar sawdust in 3.3.1. Effects of pyrolysis temperatures
Zone III but increased that of coffee bean residue because the The TGA results indicate that various temperatures for biomass
decomposition temperatures in Zone III had the greatest effects on pyrolysis affect the rates of mass loss. The present study produced
cellulose, and because coffee bean residue contained more cellulose bio-oil and bio-char through fast-pyrolysis on a fluidized bed.
than did cedar sawdust. Rice straw showed reactions that were Previous studies [25e32] suggest that a temperature between 700
significantly different from coffee bean residue and cedar sawdust, and 800 K for biomass fast pyrolysis maximizes the bio-oil yield.
and exhibited differing effects due to temperature. Crushing of rice Temperatures above this range initiate a volatile secondary reaction
straw is complex. Thus, this study adopted a more common process that decreases the rate of bio-oil production. Three temperatures of
to crush rice straw to particles of 2e5 mm size. The relationship the fluidized bed (between 550 and 800 K) were used for tests on
between thermal conduction between the biomass and reaction the product distribution of the biowaste samples at a CO2 flow rate
gas and the particle size affecting the area for thermal conduction of 10 L/min (Fig. 4). The amount of char residue of the cedar
influenced the temperature response to and thus biomass pyrolysis sawdust declined from 48 (550 K) to 30 wt% (800 K), and that of the
during TGA. Furthermore, an increased heating rate concentrated coffee bean residue declined from 40 (550 K) to 17 wt% (800 K).
the mass loss in Zone II. Consistent with the TGA results, the rice straw had the most char
residue because the crushing process could not easily break rice
straw into smaller sizes char residue declined from 60 (550 K) to
3.2. Physical properties of the bio-oil 48 wt% (800 K). Therefore, pyrolysis analysis of rice straw was done
by using only large particle sizes (2e5 mm), which led to smaller
After the three samples were crushed and dried, they were and more uneven heated areas on the fluidized bed compared with
conveyed into the biomass fast-pyrolysis system at various gas those for the other two samples. Structural pyrolysis of rice straw
flow rates and reaction temperatures. Pyrolysis of coffee bean was, therefore, also less likely to occur.
residue to oil used CO2 as fluidization gas (10 L/min flow rate) and Variations of the oil yield over time for both phases are shown in
a temperature of 500 K for the fluidized bed reactor. Fig. 3 shows Fig. 4. The oily-phase yield increased at temperatures greater than
the appearance of the produced oil. The oil consisted of two 550 K, reached a maximum at 700 K, and then decreased as the tem-
phases, namely, the oily and aqueous phases (Fig. 3). The former perature exceeded 700 K, whereas the aqueous-phase yield was
was a viscous and opaque black liquid (Fig. 3a), and the latter had inversely proportional to temperature. The yield of the oily-phase was
lower viscosity and higher transparency (Fig. 3b). The first greater than that of the aqueous-phase. Total yield of the two phases
condenser (condensation temperatures ¼ 380e400 K) produced a was highest with cedar sawdust followed by coffee bean residue and
liquid that was mostly in the oily phase, whereas the second then rice straw. The oil yield for the three biomass sources seems to be
condenser (condensation temperatures ¼ 300e330 K) produced a consistent with results in previous research, in which the oil yields
liquid that was chiefly in the aqueous phase. This result implies from pyrolysis of rice straw, sugarcane bagasse, and coconut shell were
that different condensation temperatures oil production by less than 14 wt% [26], and that of rapeseed was between 13 and 17 wt%
biomass pyrolysis lead to different oil composition, as discussed in [28]. In another study, rice straw with 43 wt% water had an oil yield of
the next section. 57 wt% [33]. An experiment by Nokkosmaki et al. [34] showed that

Fig. 3. Two phases of the pyrolysis oil produced from the coffee bean residue.
 S.I. Yang et al. / Energy 66 (2014) 162e171 167

Fig. 4. Influence of temperature on the product distribution of pyrolyzed biowaste samples: (a) cedar sawdust, (b) coffee bean residue, and (c) rice straw.

pine sawdust with 20 wt% water yielded 66 wt% oil upon pyrolysis. use of biomass with appropriate particle size contributed to an
These results indicate that oil yields were related to biomass compo- evenly mixed and heated bed material, which resulted in enhanced
sition, especially to the proportions of cellulose and hemicellulose. In pyrolysis. In addition, the biomass crushing process affected the
the present study, the maximum yield was attained at 700 K, which overall cost of using biomass as energy source.
was similar to previous research results.
The temperatures in the present study (i.e., 550e800 K) influ- 3.3.2. Effects of flow rate of fluidization gas
enced the cellulose, hemicellulose, and lignin levels, and led to The flow rate of fluidization gas is related to the fluidization ef-
conversion of most of the biomass into condensable and noncon- fects on the fluidized bed, the thermal or heating effects on biomass,
densable gases. The char yields were related to biomass size. The and the residence time of the biomass. At a reactor temperature of

Fig. 5. Influence of flow rate of fluidized gas on product distribution of pyrolyzed biowaste samples: (a) cedar sawdust, (b) coffee bean residue, and (c) rice straw.
168 S.I. Yang et al. / Energy 66 (2014) 162e171

Table 4
Characteristics of the oily and aqueous phases of pyrolysis oil.

Oily phase Aqueous phase

Cedar sawdust Coffee bean residue Rice straw Cedar sawdust Coffee bean residue Rice straw

Element analysis
Carbon (wt.%) 44.8 42.56 39.76 22.85 23.54 23.16
Hydrogen (wt.%) 4.76 4.32 4.51 5.14 5.41 5.49
Nitrogen (wt.%) 0.25 0.62 0.08 0.72 0.77 0.56
Oxygen (wt.%) 43.22 46.19 49.85 65.56 66.31 67.29
Water content (wt.%) 25 22 25 77 87 84
pH 3.6 3.6 3.4 2.71 3.6 2.4
Viscosity@40  C, cP 231 221 210 0.73 0.75 7
LHV (MJ/Kg) 21.78 21.59 20.41 9.18 8.32 7.21

*Obtained at pyrolysis temperature of 700 K, carbon dioxide flow rate of 10 L/min, and condensation temperature of 350 K and 300 K, respectively.

700 K, the flow rates of fluidized gases were adjusted to investigate conduction characteristics of the biomass and reactor, leading to
the relationships between these characteristics (Fig. 5). In addition, distribution differences in the biomass pyrolysis products.
flow rate is one of the factors that influence the product distribution Reaction temperature and flow rate of the fluidized CO2 influ-
in biomass fast pyrolysis. The results show that the char yield of the enced the yield and characteristics of the bio-oil. Sipila et al. [35]
three samples increased with the flow rate of the fluidization gas. found that liquids in the aqueous phase are chiefly composed of
Their bio-oil yield reached a maximum at 10 L/min. The oily phase water from biomass, volatile acids, alcohols, and sugar, and
was influenced more significantly by the flow rate than was the amounts of these liquids may be affected by carbohydrates (i.e.,
aqueous phase. Reduced flow rate could not support fluidization of cellulose and hemicellulose) in the biomass. In the present study,
the bed material, resulting in conditions that resemble those in a the largest amount of bio-oil was produced by cedar sawdust fol-
fixed-bed reactor. Consequently, continuous feeding of the feed- lowed by coffee bean residue and then rice straw. Because the oily
stock resulted in biomass accumulation and influenced the pyrolysis phase primarily consisted of lignin-derived materials [25,34,35],
reaction rates. Although no significant difference was observed be- higher proportions of high-molecular-weight compounds
tween the compositions of the three biowaste samples, the biomass increased the viscosity of this phase, causing its dark appearance.
size and residence time on the fluidized bed changed the thermal Properties of the bio-oils are discussed in the next section.

Fig. 6. GCeMS chromatogram of the oily phase of the pyrolysis oil from (a) cedar sawdust, (b) coffee bean residue, and (c) rice straw.
 S.I. Yang et al. / Energy 66 (2014) 162e171 169

Fig. 7. GCeMS chromatogram of the aqueous phase of the pyrolysis oil from (a) cedar sawdust, (b) coffee bean residue, and (c) rice straw.

3.4. Chemical properties of bio-oils as 2-cyclopenten-1-one and 2,6-dimethoxy-phenol, and that the
aqueous phase was composed mainly of acetone, acetic acid, propi-
After stabilization through extended storage, properties of the onic acid, and a substantial amount of water.
two phases were analyzed (Table 4). The oily and aqueous phases The aforementioned results indicate that bio-oil consisted of the
differed in terms of carbon content (the oily-phase oil contained products of lignocellulosic decomposition, and that their compo-
approximately 39.76e44.80% carbon), water content, heating sitions do not meet standards for common fossil fuel. In addition,
value, shape, and color. The hydrogen content in the oily phase was components of the bio-oil could not be easily isolated by common
approximately 4.32e4.76 wt%, and that in the aqueous phase was conversion techniques because numerous oxygen-containing,
5.14e5.49 wt%. The nitrogen content of both phases was small reactive functional groups caused unstable heating values of the
(0.08e0.77 wt%). The oily and aqueous phases contained approxi- bio-oil. The oily and aqueous phases contained higher proportions
mately 43.22e49.85 wt% and 65.56e67.29 wt% oxygen, respec- of water, carboxylic acids, carbohydrates, and lignin-derived sub-
tively. Such difference in oxygen content led to differences in pH stances [35]. Furthermore, bio-oil gases were produced during fast
values of the two phases. Significant differences in viscosity were pyrolysis by decomposition in a high-temperature environment,
caused by difference in oil compositions, which were examined and lignin was incompletely depolymerized because of the short
using GCeMS analysis. residence time [36e38]. In summary, the pyrolysis products varied
Organic compounds in the bio-oil phases produced by fast py- with storage environment and time, and biomass compositions and
rolysis were examined GCeMS. Figs. 6 and 7 show the GCeMS temperature of pyrolysis condensation influenced the composition
chromatograms of the oily and aqueous phases, respectively. Since a and quantity of the oily and aqueous phases.
mixture standard was not available for calibration of the mass Differences in the two bio-oil phases resulted from differences
spectrometer detector, most of the organic compounds in the bio-oil in the condensation temperatures, which influenced the water
could not be identified, and are therefore not discussed of this paper. content, compounds, and bio-oil properties. The oily phase was
Table 5 shows the tentative compounds of the bio-oil, which are the collected mainly at higher condensation temperatures. Since the
index compounds that could be identified by using the MS search file. condenser with higher temperature retained bio-oil gas, the resi-
In addition, the areas of each peak were calculated. Analytical results dence time for the water in the gases was shorter and the oily phase
show that the oily and aqueous phases contained similar constitu- contained less water and higher-molecular-weight compounds. In
ents regardless of the composition of the biowaste material, differing contrast, the aqueous phase required lower condensation temper-
only in the amounts of components. The bio-oil contained numerous atures and therefore contained more water and low-molecular-
aromatic and oxygenated compounds such as carboxylic acids, weight compounds.
phenols, and ketones. Comparison between the GCeMS chromato- The compositions of lignin and carbohydrates (i.e., cellulose and
grams showed that the oily phase was composed of compounds such hemicellulose) of the biowaste samples influenced the formation of
170 S.I. Yang et al. / Energy 66 (2014) 162e171

Table 5
List of GCeMS area percentages of compounds in pyrolysis oil.

Peak no. tRb (min) Component Area, %

Cedar sawdust Coffee bean residue Rice straw

OP AP OP AP OP AP

1 1.3 Water 1.35 4.19 0.61 15.29 1.43 13.91

2 1.6 Acetone 0.18 1.56 0.14 0.99 0.63 1.54
3 1.8 Hydroxy-acetaldehyde 0.09 0.19 0.08 0.27 0.09 0.30
4 1.9 Acetic acid 0.25 0.39 0.16 2.10 0.18 2.92
5 2.6 1-Hydroxy-2-propanone 0.80 0.61 0.16 1.72 0.35 0.98
6 3 Propionic acid 0.42 0.52 0.21 0.64 0.38 1.43
7 3.9 Pyridine 0.07 0.12 0.11 0.24 0.07 0.17
8 4.6 1-Hydroxy-2-butanone 0.09 0.14 0.06 0.17 0.09 0.35
9 5 2-Hydroxytetrahydrofuran 0.06 0.13 0.05 0.13 0.06 0.14
10 5.2 Cyclopentanone 0.08 0.11 0.06 0.16 0.08 0.21
11 5.4 Butyric acid 0.07 0.13 0.08 0.17 0.08 0.33
12 6.3 2-Cyclopenten-1-one 0.23 0.14 0.05 0.24 0.11 0.22
13 6.8 Furfuryl alcohol 0.38 0.20 0.23 0.88 0.29 0.71
14 7.7 Butyrolactone 0.52 0.39 0.24 0.71 0.39 0.61
15 8.4 3-Methyl-2-cyclopenten-1-one 0.45 0.20 0.17 0.32 0.28 0.40
16 8.7 Phenol 1.08 0.43 0.52 0.53 0.74 0.96
17 9.2 2-Hydroxy-3-methyl-2-cyclopenten-1-one 0.68 0.32 0.34 0.72 0.60 0.58
18 9.3 2,3-Dimethyl-2-cyclopenten-1-one 0.46 0.19 0.21 0.33 0.34 0.34
19 9.4 Cresol 0.87 0.27 0.38 0.37 0.73 0.42
20 9.8 2-Methoxyphenol 2.56 0.69 1.05 1.78 2.20 1.68
21 10.8 Pyrocatechol 4.39 1.31 1.52 2.32 3.85 2.21
22 11.3 Hydroquinone 0.47 0.25 0.35 0.47 0.55 0.28
23 11.5 Methyl benzenediol 2.52 0.59 0.92 1.07 1.74 0.91
24 11.9 2.6-Dimethoxy-phenol 1.14 0.28 0.42 0.44 0.94 0.54
25 12.5 Levoglucosan 0.77 0.22 0.39 0.61 0.75 0.35
26 15 Caffeine 0.35 0.61 1.51 1.57 0.66 0.40
27 15.1 Hexadecanenitrile 0.32 0.21 0.85 0.33 0.59 0.32
28 15.4 Palmitic acid 0.33 0.22 6.22 0.42 0.98 0.38
29 16.2 Linoleic acid 0.17 0.14 1.63 0.22 0.38 0.23
30 16.4 Stearic acid 0.22 0.19 1.66 0.29 0.47 0.31

*OP: oliy phase; AP: aqueous phase.

the oily and aqueous phases, respectively. A substantial portion of cracking of cellulose, CO2 was produced by carboxyl-containing
the oily phase is produced by decomposition of biomass lignin, and compounds in the cracking and reforming of hemicellulose.
is therefore also known as pyrolytic lignin [7]; 22%e28% of this Because the intermediates of cracking were not prone to oxida-
phase is produced from the biomass lignin [39]. The oily phase tion, pyrolysis produced less CO2 and more H2 and CO. Therefore,
produced in this study appeared heavy, oil-like, and sticky (Fig. 3a). the use of CO2 as fluidization gas increased the concentration of
It was composed of extractives, low-molecular-weight lignin, and CO and H2 in the vented gases. In the present study, the vented
high-molecular-weight lignin compounds. The extractives were gases were mixed with a small amount of propane/air mixture to
hexane-soluble compounds that chiefly consisted of hydrocarbons. fully utilize the heating values of the vented gases, to reduce odors
In several studies on the pyrolysis of lignocellulosic materials, the of the vented gas, and to complete combustion and heat recycling
hexane-soluble compounds in oily-phase bio-oil are categorized of the vented gas.
into aliphatic, aromatic, and polar fractions. Relevant results show
that the polar fraction is the major component in hexane-soluble 4. Conclusions
compounds [39e41]. Furthermore, measurements in this study
showed that the aqueous bio-oil phases from the three biomass The present study subjected three biowaste samples (cedar
samples were extremely similar in composition, and that most of sawdust, coffee bean residue, and rice straw) to fast pyrolysis to
them contained numerous aromatics and oxygenated compounds produce bio-oil. TGA was conducted to investigate variations in the
such as carboxylic acids, phenols, and ketones. samples under various heating conditions. GCeMS was performed
to examine the compositions of the oily and aqueous phases of the
3.5. Vented gas produced by pyrolysis oil produced by pyrolysis and to identify the influence of pyrolytic
conditions and biomass compositions.
Bio-oil gases produced by high-temperature pyrolysis of
biomass were converted into char and two gases (condensable 1. TGA results suggest that the thermal decomposition of the
and uncondensable gases) by using a cyclone separator and con- biowaste could be divided into four steps, namely, decomposi-
densers, respectively. Compositions of the vented bio-oil gas tion of extractives (<490 K), decomposition of hemicellulose
produced through biomass pyrolysis were calculated. Vented (490e650 K), decomposition of cellulose and lignin (650e
gases from the three biowaste samples were similar in composi- 780 K), and decomposition of lignin (>780 K).
tion. CO2 (approximately 48.2e51.3 vol%) and CO (44.2 vol%) 2. During the optimized process of fast pyrolysis, bio-oil produc-
comprised the major fractions of the vented gases. Wang et al. tion of the three biomasses reached maximum when the py-
[37] utilized a bubbling fluidized bed reactor and N2 as fluidiza- rolysis temperature was 700 K and the flow rate of fluidization
tion gas to process beech, which produced vented bio-gases with gas was 30 L/min. Bio-oil production of cedar sawdust, coffee
58.5 vol% CO2. Yang et al. [38] observed that when CO was pro- bean residue, and rice straw was around 51, 48, and 28 wt%,
duced by carbonyl- and carboxyl-containing compounds during respectively.
 S.I. Yang et al. / Energy 66 (2014) 162e171 171

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