Bioresource Technology 104 (2012) 737–742
Contents lists available at SciVerse ScienceDirect
Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech
Preparation and characteristics of bio-oil from the marine brown alga
Sargassum patens C. Agardh
Demao Li a,⇑, Limei Chen b, Dong Xu c, Xiaowen Zhang c, Naihao Ye c,⇑, Fangjian Chen a, Shulin Chen a
a
Tianjin Key Laboratory for Industrial Biological Systems and Bioprocessing Engineering, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
College of Agriculture, Liaocheng University, Liaocheng, China
c
Key Laboratory for Sustainable Utilization of Marine Fishery Resources, Yellow Sea Fisheries Research Institute, Qingdao, China
b
a r t i c l e
i n f o
Article history:
Received 22 July 2011
Received in revised form 1 October 2011
Accepted 2 November 2011
Available online 11 November 2011
Keywords:
Sargassum patens C. Agardh
Liquefaction
Bio-oil
a b s t r a c t
The marine brown alga, Sargassum patens C. Agardh, floating on the Yellow Sea, was collected and converted to bio-oil through hydrothermal liquefaction with a modified reactor. A maximum yield of
32.1 ± 0.2 wt.% bio-oil was obtained after 15 min at 340 °C, at a feedstock concentration of 15 g biomass/150 ml water, without using a catalyst. The bio-oil had a heating value of 27.1 MJ/kg and contained
water, lipid, alcohol, phenol, esters, ethers and aromatic compounds. The solid residue obtained had a
high ash and oxygen content. The results suggest that S. patens C. Agardh has potential as biomass
feedstock for fuel and chemical products.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Marine algae are a potential source of fuel and chemical compounds since their average photosynthetic efficiency is higher than
that of terrestrial plants (Huntley and Redalje, 2007; Kraan, 2010;
Li et al., 2010a,b, 2011; Ye et al., 2010). Various techniques have
been developed to utilize this biomass, including fermentation,
direct combustion, gasification, pyrolysis and hydrothermal liquefaction (Patil et al., 2009). With water as the reaction medium,
hydrothermal liquefaction is environmentally friendly, rapid, and
does not require drying of the biomass (Peterson et al., 2008). In
addition, hydrothermal reactions involve the elimination of oxygen
from the feedstock, which results in an increase in the H:C ratio of
the product (bio-oil) and therefore leads to more attractive fuels
(Peterson et al., 2008).
Studies on hydrothermal liquefaction of algae have primarily
focused on microalgae (Dote et al., 1994; Duan and Savage, 2011;
Minowa et al., 1995a; Sawayama et al., 1999; Yang et al., 2004;
Zou et al., 2010a,b), and only a few have investigated the potential
of macro-algae (Anastasakis and Ross, 2011; Aresta et al., 2005a,b;
Zhou et al., 2010), despite the fact that these alga are easy to
harvest and that mature culture technologies are in place.
⇑ Corresponding authors. Addresses: Key Laboratory for Sustainable Utilization of
Marine Fishery Resources, Yellow Sea Fisheries Research Institute, No. 106, Nanjing
Road, Qingdao, China. Tel.: +86 532 85822957 (N. Ye); Tianjin Key Laboratory for
Industrial Biological Systems and Bioprocessing Engineering, Tianjin Institute of
Industrial Biotechnology, Chinese Academy of Sciences, No. 32, XiQiDao, Tianjin
Airport Economic Park, Tianjin, China. Tel.: +86 22 84861932 (D. Li).
E-mail addresses: [email protected] (D. Li), [email protected] (N. Ye).
0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2011.11.011
The marine brown alga, Sargassum patens C. Agardh, has a high
biomass yield. It is capable of self-propagation in open sea water.
A large amount of raft-like S. patens C. Agardh was founded floating
in the Yellow Sea in April 2010. This indicated that it could potentially be developed for aquaculture as basis of a bioenergy industry.
In addition, the decay of large quantities of S. patens C. Agardh
biomass could be detrimental to the marine environment and
aquaculture (such as green tides) (Ye et al., 2011).
In the present study, the hydrothermal liquefaction characteristics of S. patens C. Agardh were studied and the products were
analyzed by elemental analysis, infrared spectroscopy (IR), gas
chromatography–mass spectrometry (GC–MS) and bomb calorimetry. The combustion characteristics of the bio-oil were evaluated
using a thermal analysis-mass spectrometry (TA-MS).
2. Methods
2.1. Raw materials
The S. patens C. Agardh was collected from the Yellow Sea,
Jiangsu Province, China, latitude 33.7843° north and longitude
120.6181° east. The algal material was sundried for 4 days (for the
preservation of the sample), pulverized in a plant disintegrator until
it passed through a 80 mesh sieve and stored in a desiccator.
2.2. Apparatus and experimental procedure
The hydrothermal liquefaction of S. patens C. Agardh was conducted in a modified cylindrical reactor (Fig. 1) based on previously
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D. Li et al. / Bioresource Technology 104 (2012) 737–742
Fig. 1. The experimental apparatus.
reported systems (Dote et al., 1994; Yang et al., 2004; Zhou et al.,
2010). The system is composed of a 1-L autoclave, an electrically
heated furnace, an agitator, a pressure gauge, two condensate pots,
two bio-oil recovery pots, a gas recovery pot, several valves and
two salt baths. The algal feedstock was placed into the autoclave
and placed under a N2 atmosphere at 3 MPa to avoid water evaporation. The autoclave was heated to the desired temperature (required time to reach desired temperature was about 1 h), and
held at that temperature (320–380 °C) for the desired amount of
time. The effects of temperature holding time was in the range of
15–90 min. The biomass to water ratio was in the range of
5–25 g/150 ml. Na2CO3 in the amount of 5% was used as catalyst.
After liquefaction, valve 1 was opened and the high temperature gas was released to the condensate pots 1 and 2, which were
pre-cooled to 5 and 15 °C, respectively. This process guaranteed
that the condensable gas was cooled quickly, avoiding the requirement for a long cool down period before the reactor could be
opened. The non-condensable gas was recovered in the gas recovery pot. After the autoclave had been cooled to room temperature,
the solid residue was removed. The separation process for the reaction products is illustrated in Fig. 2. The apparatus and the solid
and liquid reaction mixtures were washed with chloroform to recover the bio-oil, and the chloroform was then removed at 40 °C
using a rotary evaporator. Solid and liquid were separated by filtration through a membrane filter. The solid residue was dried at
105 °C until a constant weight was achieved. The aqueous phase
was evaporated at 60 °C for 16 h with a rotary evaporator to
remove water, and the residue was weighed.
2.3. Analysis and calculation methods
Moisture analysis was conducted according to ASTM E871 – 82
(E871-82, 2006). The ash content was determined according to
ASTM E1755 – 01 (E1755-01, 2007). The volatile matter content
was analyzed according to ASTM E872 – 82 (E872-82, 2006). The
fixed carbon was expressed as the 100%-ash content-volatile matter-moisture content. The higher heating value was measured
using a Parr 6100 (Parr Instrument Company, USA) bomb calorimeter. The C, H, S and N contents were measured using a Vario EL III
CHNS/O Elemental Analyzer. The oxygen content was calculated
using the equation O (wt.%) = 100 (ash + C + H + N) (wt.%). The
proximate analysis (received basis, wt.%) results and chemical content (elemental composition, wt.%) of S. patens C. Agardh are shown
in Table 1.
The yields of the products (gas, bio-oil, aqueous phase (AP) and
solid residue) were calculated according to the following equations
(wt.%):
Y Bio-oil ðwt:%Þ ¼ W Bio-oil =ðW Feedstock W moisture W ash Þ 100%
Y AP ðwt:%Þ ¼ W AP =ðW Feedstock W moisture W ash Þ 100%
Y solid residue ðwt:%Þ ¼ W solid residue =ðW Feedstock W moisture W ash Þ
100%
Y gas ðwt:%Þ ¼ ð100 Y Bio-oil Y WSP Y solid residue Þ 100%
where WBio-oil is the mass of bio-oil (g), Wfeedstock is the total
mass charged into the autoclave, including algae and catalyst
(where used), Wmoisture is the moisture content of the feedstock,
WAP is the mass of the water soluble residue, and Wsolid residue
is the mass of solid residue. YBio-oil, YAP, Ysolid residue and Ygas
refer to the yields of the products.
The components of the bio-oil were analyzed by a gas chromatography and mass spectrometry (GC–MS) (Agilent 6890N/5973
Table 1
Proximate analysis (received basis, wt.%) and chemical content (element composition,
wt.%) of the algal material.
Fig. 2. The separation process of the products.
Moisture
Ash
Volatile
Fixed carbon
HHV (MJ/kg)
14.38
C
40.18
17.77
H
5.22
55.49
N
2.00
12.36
S
0.98
15.47
O
33.85
D. Li et al. / Bioresource Technology 104 (2012) 737–742
with a HP-5 ms column) coupled system. Helium was used as the
carrier gas, at a flow rate of 20 ml/min. Two microliters of the chloroform/bio-oil solution (0.04 g/ml) were injected. The injector was
set to splitless mode, with an inlet temperature of 280 °C. The GC
oven temperature program was as follows: hold at 40 °C for
3 min, raise to 300 °C with a heating rate of 5 °C/min, and then hold
for 8 min. Compounds were identified by comparison with the National Institute of Standards and Technology (NIST) library of mass
spectra (Zhou et al., 2010).
The infrared spectrum of the bio-oil was determined using a
NICOLET NEXUS 470 instrument. The sample was placed in the
sample pool which was made from KBr. For each spectrum, a 32
scan adsorption interferogram was collected with a 4 cm1 resolution in the 4000–400 cm1 region at room temperature.
The thermal characteristics of the bio-oil were studied by
TA-MS (NETZSCH STA409PC-Aeolos QMS403C, Germany) with an
air atmosphere of 80 ml/min. The two pieces of equipment were
linked by a stainless steel capillary, which was heated to 260 °C.
For TG analysis of the bio-oil, the sample was heated from ambient
temperature to 800 °C, at a rate of 10 °C/min, until complete reaction was achieved. The sample mass used in each experiment was
15 ± 2 mg.
The micro-structure of the solid residue was determined by
scanning electron microscopy (SEM, Hitachi Tabletop Microscope,
TM-1000, Japan).
3. Results and discussion
3.1. Effects of reaction conditions on product yields
The important reaction conditions for product yield are known
to be temperature, holding time, catalyst dosage and feedstock ratio (Anastasakis and Ross, 2011; Yang et al., 2004). The yields of
bio-oil obtained under various conditions are summarized in Fig. 3.
The solid residue remaining in the reactor was composed of
inorganic salts and nonvolatile compounds. Aqueous products
(3.8–11.5%) were generally the least abundant. This result differs
from previous reports on Laminaria Saccharina, Botryococcus
braunii, Microcystis viridis and Enteromorpha prolifera treated under
approximately the same conditions. (Anastasakis and Ross, 2011;
Dote et al., 1994; Yang et al., 2004; Zhou et al., 2010). Losses incurred during the recycling of bio-oil and evaporation of the biooil with a rotatory evaporator, which resulted in inaccurate yield
measurements, especially for the gas products calculated by differences (see Section 2.3). Also, the incompletely evaporation of the
solvents (CHCl3 and water), which was inevitable with the standard evaporation procedure, might have caused an error.
Fig. 3A shows the effect of temperature on product yield. With
increasing temperature, the bio-oil yield increased, until it reached
a maximum at 340 °C, then it decreased at higher temperatures,
with the yield ranging from 22.1 ± 1.3% to 32.1 ± 0.2%. The solid residue and AP yields decreased with increasing temperature. The gas
yield first increased and then decreased between 320 and 340 °C,
and then increased with further increasing temperature. The feedstock in hot compressed water underwent hydrolysis and repolymerization (Yuan et al., 2009). The reactions processes were
assumed as follows. At lower temperatures, the polysaccharides
and proteins were degraded to small molecules, and dehydration,
deoxygenation and decarboxylation reactions occurred. At higher
temperature, the rate of hydrolysis decreased, while repolymerization was accelerated. With further increases in temperature to
340 °C, more solid residue was converted to bio-oil. When the temperature was increased further, however, the bio-oil decomposed
and the gas yield increased. During processing, the solid residue
yield decreased during the hydrolysis reaction.
739
The highest bio-oil yield was obtained at 340 °C for M. viridis
(same as this study) (Yang et al., 2004), 350 °C for L. saccharina
(Anastasakis and Ross, 2011), 350–395 °C for Chaetomorpha linum
(O.F. Muller) Kutzing (Aresta et al., 2005b) and 300 °C for E. prolifera (Zhou et al., 2010). These differences may be caused by differences in the feedstocks and the conditions used.
Reaction time also had an important effect on product yields, as
indicated in Fig. 3B. A holding time of 15 min was sufficient to
achieve the highest yield of bio-oil ((32.1 ± 0.2)%). With increasing
reaction time, the yield of solid residues decreased until 25 min
and increased at longer holding times. This tendency indicates that
the bio-oil was not formed completely, however, long reaction
time incurred decomposition of the bio-oil and promoted higher
yields of gas and solid residue. Therefore, a reaction time of
15 min was selected as optimal for the liquefaction of S. patens C.
Agardh with the modified reactor. Although a similar reaction time
was reported for the hydrothermal liquefaction of L. saccharina
(Anastasakis and Ross, 2011), the reaction times were different
due to the quick ramp down in temperature in the current study.
Other studies have found optimal reaction times that ranged from
30 to 60 min (Zhou et al., 2010; Zou et al., 2010a,b). Differences in
the reaction times for different feedstocks are likely responsible for
differences in optimal reaction times. The reactor set-up described
in the present study required similar ramp-up times as reactors
used in other studies (Anastasakis and Ross, 2011; Dote et al.,
1994; Yang et al., 2004; Zhou et al., 2010), the time required to cool
the reactor after operation was shorter than that required by the
other systems and thus allowed more accurate determination of
the reaction time. A benefit of the system described here is that
slow autoclave cooling was avoided by rapid cooling of the reaction, allowing reaction times to be more accurately measured
although the ramp up time was same with the previous studies.
The effect of the biomass to water ratio on bio-oil production is
illustrated in Fig. 3C. Increasing the biomass to water ratio led to a
decreased yield of bio-oil, from 38.0 ± 1.7% to 26.1 ± 1.0%. However,
the solid residue and gas yields increased with increasing biomass
to water ratio. With increasing biomass to water ratio, the biomass
content in the solvent decreased and the intermediate products
were estimated to have a tendency to undergo polycondensation.
Although the product yield ratio was high when a low biomass
to water ratio was used, the bio-oil weight was very low. This indicates that more water and heat was required when a higher biomass to water ratio was used. Thus, ratio of 15 g biomass/150 ml
of water was selected as optimal.
The effect of the catalyst on bio-oil production is illustrated in
Fig. 3D. A loading of 5% Na2CO3 catalyst resulted in a decreased yield
of bio-oil and solid residue, and increased yields of gas and aqueous
products compared to without catalyst. At a loading of 5%, Na2CO3
therefore reduced the formation of bio-oil and increased the aqueous solubility of the organic compounds produced. A similar phenomenon was observed when 0–100% KOH was used for
hydrothermal liquefaction of L. Saccharina (Anastasakis and Ross,
2011). Previous reports have indicated that sodium carbonate was
an effective catalyst for bio-oil production from garbage (Minowa
et al., 1995a) and cellulose (Minowa et al., 1998). It increased the
bio-oil yield in water and reduced the gas, bases and bicarbonates
formed, which can suppress the formation of char (Xu and Lad,
2007). This difference of the catalyst effect may be due to the large
quantities (17.77%) of ashes in S. patens C. Agardh (Zhou et al., 2010).
The effect of the catalyst was also observed in previous reports on
the liquefaction of Dunaliella tertiolecta (Minowa et al., 1995b).
3.2. Characteristics of the bio-oil
The bio-oil obtained at 340 °C (15 min) with 15 g biomass/
150 ml water was black and viscous. The results of its elemental
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D. Li et al. / Bioresource Technology 104 (2012) 737–742
Fig. 3. Effects of reaction condition on the product yields. A, effects of temperature with 15 g biomass/150 ml water for 15 min without catalyst; B, effects of reaction time at
340 °C with 15 g biomass/150 ml water without catalyst; C, effects of biomass and water ratio at 340 °C for 15 min without catalyst; D, effects of catalyst at 340 °C for 15 min
with 15 g biomass/150 ml water.
and HHV analysis are shown in Table 2. The C and H contents of the
bio-oil were greater after liquefaction compared with unreacted S.
patens C. Agardh, which indicates a significant increase in the HHV
of the bio-oil, but the contents are too high for a useful biofuel.
Therefore pretreatments such as catalytic hydrogenation and
esterification would be required. Similarly high O contents in
bio-oils were also observed with E. prolifera and D. tertiolecta (Zhou
et al., 2010; Zou et al., 2010b) as feedstock.
The IR spectrum of the bio-oil (supplemental Fig. 1, Table 3)
demonstrated the presence of water, lipids, alcohols, phenols, esters, ethers and aromatic compounds. GC/MS analysis allowed presumptive identification (>90% similarity with compounds in NIST
05 library) of 10 compounds of the 132 compounds detected in
the bio-oil (Table 4).
Ketones may have been formed by hydrolysis, dehydration and
cyclization of polysaccharides (Zhou et al., 2010), and alkenes by
the dehydration and hydrolysis of unsaturated fatty acids (Zhou
et al., 2010). Nitrogen containing heterocyclic compounds are typical products of the reaction of amines with sugars (Kruse et al.,
2006). The types of compounds identified above are consistent
with the products described in previous reports (Minowa et al.,
1995a,b; Xu and Lad, 2007; Yuan et al., 2009; Zhou et al., 2010;
Zou et al., 2010b).
Table 5 shows the characteristic temperatures of the bio-oil combustion and TG-DTG-DTA curves can be found in supplemental Fig. 2.
The bio-oil began to lose weight at low temperatures, and the highest
rate of weight loss was observed at 105 °C. An endothermic effect
Table 2
Elemental and high heat value analysis of the bio-oil and solid residue obtained at
340 °C for 15 min with 15 g biomass/150 ml water.
Bio-oil
Solid residue
C (%)
H (%)
N (%)
S (%)
O (%)
HHV (MJ/kg)
64.64
18.64
7.35
2.03
2.45
0.73
0.67
1.42
22.04
59.41
27.1
was observed during the initial stages of weight loss, suggesting volatilization of volatile compounds. An exothermic effect was observed when the temperature was increased above 108 °C. At this
stage, both volatilization and combustion occurred. The weight loss
rate decreased as the temperature was increased between 108 and
248 °C, indicating that volatile compounds were no longer present
and that the ignition point for most of the compounds had not yet
been reached. At temperatures higher than 248 °C, fluctuation in
the weight loss rate occurred, which suggested that combustion
had begun. Three weight loss peaks (temperature peaks of weight
loss rate at 360.7, 423.9 and 574.7 °C) were then observed in the
DTG curve, which corresponded with major exothermic peaks (temperature peak of heat exothermic effect at 560.4 °C). The weight loss
observed between 248 and 642 °C (temperature at which reaction
was deemed complete) was from 51.42% to 4.22%. About 47.2% of
the bio-oil compounds were burned and most of the heat was released during this stage.
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D. Li et al. / Bioresource Technology 104 (2012) 737–742
Table 3
Functional groups detected by infrared spectroscopy of bio-oil obtained at 340 °C for
15 min with 15 g biomass/150 ml water.
Wave
number
666.22
700.46
754.17
809.80
1109.77
1271.81
1378.22
1455.67
1514.13
1614.83
1698.18
2855.10
2925.89
2958.01
3363.24
Group
Table 6
The corresponding temperature to the release peak of the volatile compounds.
Characteristic temperature (°C)
Class of compound
Aromatic compounds Qian et al. (2007)
O–H bending
C–O stretching
C–H bending
Phenol, esters, ethers Qian et al. (2007)
Alcohol Zou et al. (2010a,b)
Fat Zou et al. (2010a,b)
–NO2 stretching
C@C stretching
C@O stretching
Nitrogenous compounds Qian et al. (2007)
Alkenes Qian et al. (2007)
Ketones, aldehydes, carboxylic acids Qian
et al. (2007)
Alkanes Zou et al. (2010b)
C–H stretching
O–H or N–H
stretching
–OH or N–H, water Matsui et al. (1997)
CO2
H2O
CO
C2H6
C2H6O
C3H6
C3H8O
C6H6
C7H8
1
2
3
366
223
104
571
129.3
159
142
218.7
163.3
575
374.7
571
–
575
433
437.7
591
437.7
–
504.3
–
–
–
566.7
–
‘–’ means no that temperature peak.
residual carbon was in the form of inorganic carboxylate salts. The
char maybe a potential fertilizer, but further investigation is required to confirm this possibility.
4. Conclusion
Table 4
Compounds identified by GC–MS in the bio-oil obtained at 340 °C for 15 min with
15 g biomass/150 ml water.
Retention time
(min)
Comparative
area (%)
Compound name
1.480
2.545
2.761
3.177
3.626
4.118
10.236
11.063
11.150
20.679
Total
8.31
3.21
8.52
6.59
3.52
2.62
2.55
0.52
0.67
0.49
37
Ethyl alcohol
Furan, 2,4-dimethyl2,5-Octadiene
7-Oxabicyclo[4.1.0]heptane,2-methyleneSpiropentane
Cyclononene
Indolizine, 2,7-dimethyl1H-Indole, 5,6,7-trimethyl2,3,7-Trimethylindole
1,5,9-Undecatriene, 2,6,10-trimethyl-,(Z)-
Table 5
Characteristic temperatures during combustion of the bio-oil obtained at 340 °C for
15 min with 15 g biomass/150 ml water.
Heat rate (°C min1)
Tb
Te
Tvm
Th
Thp
10
30.8
644
105
142
560.4
Tb, Te, Tvm, Th, and Thp denote the beginning temperature of the weight loss, the end
temperature of the weight loss, the maximum weight loss occurred temperature,
the beginning temperature of the heat liberation, and the maximum heat liberation
temperature, respectively.
A modified reactor (slow autoclave cooling was avoided by rapid cooling of the reaction) was used to study the liquefaction of
S. patens C. Agardh under different conditions. It has a high liquefaction yield and heating value. However, it contained a large
amount of O and N, which would have to be eliminated before it
could be used as a fuel. Also, a bio-refinery system shows promise
as a means to fully use the new algae biomass as a biofuel, and to
obtain other chemical products such as activated carbon and
fertilizer.
Acknowledgements
This work was financially supported by the National Basic Research Program (973 Program) of China (No. 2011CB200905), Tianjin special project (No. YOM2021171), National special fund for
transgenic project (2009ZX08009-019B), the Hi-Tech Research
and Development Program (863) of China (2009AA10Z106), Natural Science Foundation of Shandong Province (2009ZRA02075),
Shandong Science and Technology plan project (2011GHY11528),
National Natural Science Foundation of China (41176153), the National Science & Technology Pillar Program (2008BAD95B11) and
the Fundamental Research Funds for the Central Universities
(JUSRP21115).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.biortech.2011.11.011.
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