Bioresource Technology 108 (2012) 258–263
Contents lists available at SciVerse ScienceDirect
Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech
Characterisation of the products from pyrolysis of residues after acid hydrolysis
of Miscanthus
F. Melligan a, K. Dussan a, R. Auccaise b, E.H. Novotny b, J.J. Leahy a, M.H.B. Hayes a, W. Kwapinski a,⇑
a
b
Carbolea Research Group, Department of Chemical and Environmental Sciences, University of Limerick, Ireland
Embrapa Solos, RuaJardimBotânico 1024, Brazil
a r t i c l e
i n f o
Article history:
Received 9 August 2011
Received in revised form 19 December 2011
Accepted 20 December 2011
Available online 28 December 2011
Keywords:
Biorefinery
Biochar
Bio-liquid
Pyrolysis
Acid hydrolysis
a b s t r a c t
Platform chemicals such as furfural and hydroxymethylfurfural are major products formed during the
acid hydrolysis of lignocellulosic biomass in second generation biorefining processes. Solid hydrolysis
residues (HR) can amount to 50 wt.% of the starting biomass materials. Pyrolysis of the HRs gives rise
to biochar, bio-liquids, and gases. Time and temperature were variables during the pyrolysis of HRs in
a fixed bed tubular reactor, and both parameters have major influences on the amounts and properties
of the products. Biochar, with potential for carbon sequestration and soil conditioning, composed about
half of the HR pyrolysis product. The amounts (11–20 wt.%) and compositions (up to 77% of phenols in
organic fraction) of the bio-liquids formed suggest that these have little value as fuels, but could be
sources of phenols, and the gas can have application as a fuel.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Second generation biofuels are produced from non-food crops.
This involves the utilisation of lignocellulosic materials, such as agriculture and forestry residues, some industrial waste materials, and
also dedicated lignocellulose crops. Acid hydrolysis processes are
amongst the promising methods for converting such feedstocks into
platform chemicals and energy. The process involves the hydrolysis
of the cellulose and hemicellulose components in lignocellulose into
individual sugar monomers, and these are then converted into a
range of platform chemicals. This process involves dehydration of
the hexoses to hydroxymethylfurfural (HMF) and rehydration of
the HMF to levulinic acid (LA) and formic acid (FA, in equimolar
amounts), and dehydration of the pentoses in hemicelluloses to furfural, which can also be transformed to LA. LA is an excellent platform chemical that can also be transformed into fuel additives
such as ethyllevulinate, butan-2-ol, methyl tetrahydrofuran and cvalerolactone (Hayes et al., 2005). The FA when decarboxylated
can be used as a source of hydrogen (Bulushev and Ross, 2011).
The solid residual material in the hydrolysis process is derived
mainly from lignin (Sharma et al., 2004), which resists hydrolysis,
and cutin, cutan, and waxy materials in biomass, and also from condensation reactions that involve reactive intermediates (such as
HMF) in the degradation processes. Despite the highly recalcitrant
nature of the lignin, it can be broken down to low molecular weight
⇑ Corresponding author.
E-mail address: [email protected] (W. Kwapinski).
0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2011.12.110
compounds (lignols) through a variety of routes (de Wild et al.,
2009).
Mullen and Boateng (2010), Caballero et al. (1996), Baumlin
et al. (2006), Liu et al. (2008) and Shen et al. (2010), amongst others, have looked at pyrolysis as a method of processing lignin for
the production of both energy and platform chemicals. Lignin,
when pyrolysed yields much higher quantities of char than both
cellulose and hemicelluloses. There are several research papers
(e.g. Bridgwater et al., 2002; Tange and Drohmann, 2005) that
point out how pyrolysis can be more attractive than combustion
or gasification. The biggest advantages of pyrolysis are the value
added products it provides such as char (which can be used as a
sequester of carbon, as a soil conditioner, an adsorbent, and as a
higher energy density fuel), and bio-oil (which can be used as a
source of chemicals). In addition, the heat produced in the case
of combustion must be used immediately as it cannot be stored,
and also the amount of waste gases from combustion is much
higher. Char, when applied to soil is usually known as biochar. It
can have a large surface area and porosity, and therefore have possible uses as an adsorbent, and as a soil conditioner. Because of its
resistance to microbial attack, and because of its low content of
volatiles, the carbon in biochar when added to soil can be regarded
as sequestered carbon (Kwapinski et al., 2010).
Vapours in pyrolysis processes give rise to syngas, and some vapours condense to give bio-oil. Bio-oil has a number of unfavourable properties, such as low pH, instability, high water and
oxygen contents, and thus it will have low heating value. Hence
the usefulness of the bio-oil is limited. Because some valuable
F. Melligan et al. / Bioresource Technology 108 (2012) 258–263
Table 1
Reaction parameters for the production of the hydrolysis residue materials.
Sample
HR1
HR2
HR3
HR4
Temperature
(°C)
Pressure
(atm)
Time
(min)
Acid
concentration
(wt.%)
Residue
(wt.%)
200
200
200
175
23
23
23
11
120
10
10
10
5
1
0.5
1
33.5
36.6
36.6
37.6
platform chemicals can be extracted from bio-oil, it is important to
know how pyrolysis parameters will affect its chemical composition. Caballero et al. (1996) found that with an increase in pyrolysis
temperature the yields of methane, ethylene, propylene, propane,
benzene, C4 hydrocarbons, and water increased. The polyphenolic
structure of lignin means that it is a rich source of phenolic compounds. de Wild et al. (2009) achieved up to 20 wt.% of a phenolic
fraction in the bio-oil from the continuous fast pyrolysis of granit
lignin (lignin prepared from a mixture of hardwoods via the Alcell
organosolv process), and 9 wt.% could be considered as low molecular weight phenolic compounds.
The work reported here investigates the pyrolysis of solid residues (HRs) from the acid hydrolysis of a lignocellulosic substrate
under conditions that simulate biorefining processes. These residues can be regarded as models for biorefinery residuals (BRs).
The study investigates the properties of the pyrolysis products
and the potential usefulness of the products obtained.
2. Methods
2.1. Preparation of hydrolysis residue
Miscanthus x giganteus (M) samples, of particle size between 5
and 10 mm were subjected to acid hydrolysis under the conditions
described in Table 1, and the solid hydrolysis residual materials
(HR) were recovered. The hydrolysis processes differ in the concentrations of sulphuric acid used, and in the reaction time, temperature and pressure of the hydrolysis process. The acid hydrolysis
was carried out in an aqueous medium. As the reaction temperature increased the pressure also increased. The acid to solid ratio
used was 9:1.
The liquid phase after the acid treatment was a mixture of compounds derived from the cellulose and hemicellulose components
259
of the biomass. That mixture contained platform chemicals, and
are not dealt with in this manuscript.
2.2. Pyrolysis process
Pyrolysis of M and of the HR samples (HR1, HR2, HR3 and HR4)
was carried out in a fixed bed tubular reactor (5 cm i.d.) at temperatures of 600 °C with a heating rate of 70 °C/min and residence
time of 10 min. Pyrolysis at 600 °C was conducted for 30 and
60 min in the cases of M and HR1. HR1 was also pyrolysed at
400 and 500 °C, with heating rates of 65 and 70 °C/min, respectively, and a residence time of 10 min. A constant flow of N2
(50 cm3/min) was passed through the reactor. The pyrolysis vapour
passed through a condenser cooled to 10 °C, and the bio-liquid
condensate was collected for analysis and stored in air tight sample
bottles. At the end of the run the solid residue (char) was allowed
to cool to ambient temperature before recovery, and it was then
stored in air tight sample containers prior to analysis. The non-condensable vapours were collected in gas sample bags for analysis.
Each experiment was carried out at least three times, and the average values are displayed in the figures and tables. The maximum
error for the bio-oil, char, and gas yields was less than 3%; however,
the error was less than 1% for all the other measurements (elemental analysis, volatiles, ash, moisture, cellulose, etc.). The analytical
procedures used are summarised in Table 2.
2.3. Plant growth trials
Plant growth trials were carried out using 3 wt.% char in 500 g
of soil. For each type of biochar five different pots were used, and
10 corn (Zea mays L.) seeds were planted in each pot. Five control
pots were also used. All pots were then placed in a growth chamberat 20 °C and exposed to 12 h of light per day. Water (50 cm3 per
pot) was added to every pot twice a week for the duration of the
trial. After 10 days the five weakest plants were removed from
each pot, and all remaining plants were harvested after 21 days.
The green parts of plants were dried to constant weight in an oven
at 60 °C.
3. Results
3.1. Characterisations of pyrolysis products of hydrolysis residues and
of Miscanthus biomass
Fig. 1 shows the thermogravimetric (TGA) and differential thermogravimetric (DTG) analysis of the pyrolysis products of the HRs
Table 2
Methods used for determinations of some properties and compositions of biomass and bio-oil.
Property
Method
Moisture content of biomass
The moisture contents of the feedstocks were measured by placing the sample in an oven at 105 °C and weighing until a constant
value was reached. Acc. ASTM d4442
These analyses were carried out using an Elemental Vario el Cube analyser. Sulphanilamide was used as a standard. Oxygen was
determined by difference
Acc. ASTM E1758-01 ‘‘Standard method for the Determination of Carbohydrates by HPLC’’
C, H, N, S, O contents
Cellulose, hemicellulose and
lignin content
HHV
Water content in bio-oil
pH
Chemical composition of bioliquid
Gas composition
Volatile matter
The HHV was determined using the oxygen bomb calorimeter 6200 No. 442 m Parr company. Benzoic acid was used as a standard.
Acc. ASTM d240
The water contents of the samples were determined using a Karl–Fischer titration and a Mettler Toledo dl 31. The samples were
titrated using hydranal Composite 5, and methanol-chloroform (3:1) was used as the solvent. Acc. ASTM D95
The pH was determined at 25 °C using a pH meter, type Orion 420
Agilent 7890a GC 5975c MS (GC/MS) instrument with an ion-trap detector was used for bio-oil analysis. GC was carried out using a
Varian capillary column (30 m and i.d. 0.25 mm, 0.25 lm film thickness). To prepare samples for the GC/MS the bio-oil was first
filtered (0.45 lm filter), then acetone was added to give a 6% sample solution
Agilent micro-GC
Volatile material associated with the biochar was determined from weight loss on heating for 7 min at 900 °C, according to the
standard procedure CEN/TS 15148:2005
260
F. Melligan et al. / Bioresource Technology 108 (2012) 258–263
Table 4
Some properties of Miscanthus before and after acid hydrolysis.
Biochar source
HHV (MJ kg
C (wt.%)
H (wt.%)
N (wt.%)
O (wt.%)b
1
)
Miscanthus
HR1
HR2
HR3
HR4
ALMa
18.7
46.6
6.36
0.41
46.63
21.4
62.6
3.37
0.23
33.80
25.9
65.1
5.29
0.58
29.03
25.8
64.8
5.32
0.61
29.27
20.2
55.7
4.75
0.37
39.18
n.d.
62.05
5.95
n.d.
32.00
n.d. = not determined.
a
Results from Nowakowski et al. (2010).
b
By difference.
Fig. 1. TGA of hydrolysis residue feedstocks.
of M biomass. The heating rate for the TGA was 10 °C/min. The initial weight loss is primarily due to the evaporation of residual
water. The broad peak at 180–220 °C on the DTG plot for HR4 is
attributable to the decomposition of glucose. HR4 was subjected
for 10 min to a lower pressure (11 atm) and temperature (175 °C)
and complete hydrolysis of the cellulose may not have taken place
under these reaction conditions. The glucose content (14.5%, Table
3), and the carbon (Table 5) contents for HR4, indicate incomplete
hydrolysis of the cellulose compared with less than 0.5% glucose
content for HR1 (Table 3). The peak at 180–220 °C was not evident
for the pyrolysis products of the other HR samples, further suggesting that most, or all of the cellulose and hemicelluloses were removed when the hydrolysis process was carried out at
temperatures of 200 °C or greater. Characteristically hemicelluloses decompose at a relatively low temperature (Yang et al.,
2007). The rapid weight loss between 200 and 600 °C is due to
the breakup of inter-unit linkages and evaporation of monomeric
phenol units (Wörmeyer et al., 2011). Ferdous et al. (2001) found
a linear transformation from about 28% to 60% for a temperature
rise from 350 to 650 °C, and a heating rate of 15 °C/min. They
showed that for a heating rate of 10 °C/min lignin conversion
was 60 wt.%. The conversion was 64 wt.% at 800 °C for a heating
rate of 15 °C/min. Hence, the heating rate has a small impact on
the overall lignin conversion. Above 600 °C the weight loss was
small (Fig. 1), and the weight remained relatively constant above
650 °C. Heo et al. (2010) contend that the temperature range for
the decomposition of lignin is very wide (150–900 °C). However,
although the lignin would continue to decompose up to a temperature of 900 °C and beyond (Yang et al., 2007), the rate of degradation above 600 °C would be slow, as can be seen from the TGA data.
From both the elemental analyses (Table 4) and the TG analysis
of the hydrolysis residues it can be concluded that the acid concentration has a lesser effect than the reaction temperature on the
composition of the residual material. The data in Table 4 show that
an increase of over 10% is obtained in the carbon content for a temperature increase of 25 °C. However, when the acid concentration
was increased from 0.5% to 5% and the temperature remained constant, the difference in the carbon content was only about 2%.
Lenihan et al. (2010) observed that an increase in the reaction
temperature for acid hydrolysis of potato peelings caused both
the sugar production and decomposition reaction rates to increase
significantly. When account is taken of the acid concentration and
reaction temperature (Table 1) it can be deduced from comparisons of the data for HR2 with HR4 in Table 3, that increasing the
reaction temperature decreases the sugar yield.
3.2. Pyrolysis
In a separate set of experiments, pyrolysis of HR1 was carried
out at 400 °C with a heating rate 65 °C/min and residence time
10 min, and the percentages measured of char, gas, and of bio-liquid were of the order of 73, 23 and 4 wt.%, respectively. With
the increase in temperature from 400 to 600 °C the amount of solid
product decreased by almost 20 wt.%, and the volatile product
gradually increased.
Fig. 2 presents results for the pyrolysis for 10 min at 600 °C of
Miscanthus and of the HR products. Pyrolysis of the HRs yielded very
low quantities of condensed liquid products and high levels of char
when compared to the Miscanthus feedstock. Data from Nowakowski et al. (2010) in the same figure show that the pyrolysis product
of ALM (an Asian Lignin Manufacturing India Pvt. Ltd. sulphur-free
lignin) gave a gas, bio-liquid, and char distribution similar to that
for HR4, and along the lines of the distributions for HR2 and HR3.
ALM is a very stable lignin material (Nowakowski et al., 2010), and
the similarities with the relative abundances in the HR pyrolysis
products highlights the importance of lignin as the major component of the HR products of the M used in the present study. The
ALM lignin was pyrolysed in a batch reactor at 480 °C.
3.3. Biochar
Table 5 gives some of the properties of the biochar from the four
different HRs and from M, produced at 600 °C, and with the
residence time variously set at 10, 30 and 60 min, from the four
Table 3
Biomass composition.
Biomass type
Moisture (wt.%)
Cellulose
Miscanthus
HR1
HR2
HR3
HR4
ALMa
6.21
15.4
n.d.
0.2
Glucose (wt.%)
8.82
37.1
5.98
0.36
5.67
0.38
5.49
1.4
Hemicellulose
Xylose (wt.%)
Rhamnose (wt.%)
17.84
0.19
0.1
0.08
n.d.
n.d.
n.d.
n.d.
Lignin
Ash (wt.%)
Volatile matter (wt.%)
Klason lignin (wt.%)
20.1
3.55
79.4
85.5
1.92
56.3
95.5
1.58
57.1
93.6
1.59
56.9
0.11
0.17
76.2
1.86
59.2
2
94
<4
n.d.
n.d. = not determined.
a
Results from Nowakowski et al. (2010); ALM lignin, manufactured by Asian Lignin Manufacturing India Pvt. Ltd., is a sulphur-free lignin obtained from annually harvested
non-woody plants (wheat straw and sarkanda grass (Saccharum munja)).
F. Melligan et al. / Bioresource Technology 108 (2012) 258–263
Fig. 3.
Fig. 2. Product distribution from the pyrolysis at 600 °C for 10 min of Miscanthus
and HR materials, and of lignin (in a different reactor type). Results from
Nowakowski et al. (2010).
different HRs and from M. In order to produce biochar with optimum value for soil amendments and for carbon sequestration it
is necessary to have relatively high temperatures and residence
times. The residence time does not influence the elemental composition of HR char, but it does the surface area which increases with
the time of pyrolysis (see data for HR1, Table 5). This is similar to
the results of Sharma et al. (2004). These show that the aromaticity
and the carbonaceous nature of the char increase with reaction
temperature. This also holds for an increase in the residence time,
as evident from Fig. 3.
Solid state NMR provides an excellent spectroscopic procedure
for following the changes in the compositions of biomass and of
biochars that take place during pyrolysis. Kwapinski et al. (2010)
have presented a 13C NMR DP/MAS spectrum that demonstrates
aliphatic, aromatic, phenolic, methoxyl, and carbohydrate functionalities for M. The solid state NMR spectrum in Fig. 3A clearly
shows the aliphatic hydrocarbon (10–45 ppm) and the aromatic
(110–140 ppm) resonances in the HR4 sample, but there is no
definitive evidence for carbohydrate components. The resonance
for methoxyl at about 56 ppm, and the ‘shoulder’ at 140–
150 ppm indicate resonances for lignin, or lignin alteration products. The Gaussian shape of the spectrum shown in Fig. 4(b) is
characteristic of the fused aromatic structures (centred around
130 ppm) of biochars, and with no indications of the aliphatic
and phenolic-type structures indicated in spectrum for HR4.
The process of pyrolysis maintains a large amount of the structural architecture of the starting plant material, and a definite
13
261
C DP/MAS NMR spectra of A – HR4; B – char from HR4.
‘honeycomb structure’ is preserved (Melligan et al., 2011) that is
characteristic of the plant cell structure, and the surface area is increased (Kwapinski et al., 2010). The acid hydrolysis process results in a breakdown of the cell structure and the absence of the
well defined ‘honeycomb structure’ is lost, as is evident in
Fig. 4(a). The evident differences between the SEMs in Fig. 4 are
to be expected. The hydrolysis process removes a large amount
of cellulose, which in combination with the hemicellulose and lignins are predominantly responsible for the structural integrity of
the biomass. Hydrolysis conditions for HR1 were more energy
intensive than those for HR4 (Table 1). In the case of HR4, the
Table 5
Yields and some properties of biochars from pyrolysis at varying reaction times.
a
Char source
M
HR1
HR1
HR1
HR2
HR3
HR4
Pyrolysis time (min)
Temperature (°C)
Surface area
(m2 g 1)
HHV (MJ kg 1)
C (wt.%)
H (wt.%)
N (wt.%)
O (wt.%)a
Volatile matter
(wt.%)
60
600
161
10
600
151
30
600
171
60
600
260
10
600
131
10
600
157
10
600
277
32.5
85.1
2.40
0.55
11.95
24.8
27.9
87.5
2.15
0.34
10.01
19.1
27.9
87.7
2.12
0.379
9.80
13.6
27.7
88.4
1.99
0.323
9.29
16.5
29.3
84.0
3.12
0.84
12.04
18.9
28.6
89.5
2.14
0.94
7.42
19.1
26.1
79.4
2.18
0.66
17.76
24.1
By difference.
Fig. 4. SEM of (a) char from HR1 (600 °C and 10 min); (b), char from HR4 (600 °C
and 10 min).
262
F. Melligan et al. / Bioresource Technology 108 (2012) 258–263
hydrolysis was carried out at a lower pressure and temperature,
and incomplete removal of the cellulose had taken place (Table
3), and aspects of the honeycomb structure were preserved
(Fig. 4). The data in Table 5 show that the pyrolysis time is important in determining the surface area of the biochar.
3.3.1. Biochar as a fertiliser and soil ameliorant
It has been well documented that the application to soil of biochar from the pyrolysis of lignocellulosic feedstocks can be a key
component for sustainable biomass to bioenergy production systems (Chan and Xu, 2009). There is abundant evidence to show
that applications of biochar to soil can promote plant growth. Biochar increases the activity of soil symbiotic microorganisms and
enhances soil water retention (Yamato et al., 2006). In addition,
during pyrolysis a large proportion of the nutrients required for
healthy plant growth, such as Ca, Mg, K and P are concentrated
in the char, and also about half of the N and S remain in the char
(Laird et al., 2010). The char loses both hydroxyl and aliphatic
groups and the aromatic character increases quite rapidly above
450 °C (Sharma et al., 2004). Therefore most of the nutrients can
be returned to the soil. Due to the highly aromatic nature of the
biochar it will potentially remain in the soil for millennia.
Fig. 5 compares the growth of maize (Zea mays L.) in soil
amended with 3 wt.% HR1, with char from HR1, and with char from
M. Char produced from the M feedstock has a greater influence on
plant growth than that from HR. The M char was shown to increase
plant productivity by up to 60% over a 21 day period, whereas that
from HR increased plant growth by about 10% during the same period. Despite the fact that the growth promoting potential of char
from HR materials is decreased, the biochars will, because of their
high carbon, low oxygen, and volatile matter contents, and their
predominant fused aromatic structures, have potential as stable
long lasting soil conditioners, and will sequester carbon. Thus, even
though the HR char was seen to be inferior to that from the parent
M material for promoting plant growth it will have value in
sequestering carbon, in providing a habitat for soil microorganisms, in the retention of water, and in lowering the leaching losses
of nutrients.
3.4. Gas
The gas composition obtained from pyrolysis of HR at 600 °C
was H2: 0.3–2 vol.%; CO: 13–28 vol.%; CO2: 14–24 vol.%; methane:
12–20 vol.%; ethane: 0.1–5 vol.%; ethylene: 0.1–1.8 vol.%. As the
carrier gas for the pyrolysis process was nitrogen, it was assumed
that any nitrogen detected by the micro GC was not from biomass.
Therefore the nitrogen content was subtracted and the concentra-
Fig. 5. Growth of maize after 21 days in soil amended with 3 wt.% biochar from
Miscanthus and HR1 before and after pyrolysis under various conditions.
tion of the remaining gases was then calculated on a dry base. The
major components of the gas produced are CO and CO2. Shen et al.
(2010) also found that CO and CO2 were the main gaseous product
from the pyrolysis of wood lignin. They also found a high level of
methane, along with small amounts of some light hydrocarbons,
such ethane and ethylene were obtained. The hydrocarbons can
make up over 20 vol.% of the gas, resulting in an estimated heating
value of between 7 and 9 MJ/N m3.
3.5. Bio-liquid
The vapour condensate from the pyrolysis of HRs formed a twophase liquid. The bottom dark brown layer was only about 4% of
the total volume. The physical properties of the upper layer, the
bio-liquid produced from HRs at 600 °C in 10 min, are presented
in Table 6, and these are compared with the upper phase from
the pyrolysis of M. Results from the pyrolysis of lignin in an international collaboration study by Nowakowski et al. (2010) also
show a high water content for some of the bio-oil samples. One
of the most notable differences between the bio-liquid from M
and that from its HR is the high water content and the low carbon
content in the product from the HR materials. The high water contents, in all bio-liquid from pyrolysis of HRs can explain their similar physical properties. However, some differences can be seen in
the levels of the organic compounds present (Fig. 6). The bars in
Fig. 6 represent normalised amounts, and the values on the bars
are absolute yields of components with respect to the initial quantity of M. The absolute yields of organic compounds for HR4 were
more than were obtained for HR1 as the result of the incomplete
acid hydrolysis in the case of the former. As expected, phenol
and phenol derivatives were major organic products from the thermal decomposition of the HRs. These results have similarities with
those of Shen et al. (2010), which show that methoxy phenols are
Table 6
Physical properties of bio-liquid produced at 600 °C in 10 min.
Bio-liquid source
M
HR1
HR2
HR3
HR4
Water content (wt.%)
pH
Density (g/cm3)
C (wt.%)
H (wt.%)
N (wt.%)
36
2.5
1.09
43.1
5.73
0.28
74.0
5.1
1.01
3.09
10.3
0.73
65.5
n.d.
1.01
4.86
11.0
0.65
63.8
n.d.
1.01
5.11
10.7
0.72
n.d.
n.d.
1.00
8.34
11.1
0.34
n.d. = not determined.
Fig. 6. Distribution of functional groups in bio-liquid detected by GC/MS. All bioliquid samples were produced with in a reaction time of 10 min. The numbers
displayed on chart correspond to the approximate yields of the different groups
with respect to the initial mass of Miscanthus.
F. Melligan et al. / Bioresource Technology 108 (2012) 258–263
the most characteristic products of lignin pyrolysis, and phenol-2methoxy, phenol-2,6-dimethoxy, and their derivatives including
alkyl guaiacol, eugenol, catechol-methoxy, vinyl guaiacol, alkylsyringol, and vinylsyringol, are the most abundant products. The
GC/MS results in Fig. 6 show that an increase in reaction temperature results in an increase in the phenol contents. This is due to the
secondary cracking of alkyl guaiacol and alkyl syringol (Shen et al.,
2010). There is a definite decrease in the level of hydrocarbons and
of organic acids as the reaction temperature increases. The bio-liquid has little or no value as a fuel because of its high water content and a very small organic composition. However, the liquid can
be a source for the isolation of components such as phenols.
Changing a pretreatment method from high temperature and acid
concentration (HR1) to lower temperature and acid concentration
(HR4) results in the production of lower amounts of phenols and
of higher amounts of oxygenates. Therefore it is possible to alter
the reaction parameters to influence the formation of certain phenol derivatives.
4. Conclusions
Pyrolysis, yielding bio-liquid, gas, and biochar provides a method for utilising the residue from Miscanthus from hydrolysis biorefining processes. The biochar is, arguably, the most useful product.
It has high carbon content, an almost entirely fused aromatic structure, and a large surface area. These properties are appropriate for
applications as a soil conditioner, and for carbon sequestration.
There are limitations in the usefulness of the bio-liquid as a fuel.
The organic fraction is primarily composed of phenols, which could
be isolated. About 35% of the feedstock is converted to gas with a
heating value of 7–9 MJ/nm3.
Acknowledgements
We acknowledge financial support of Science Foundation Ireland under Grant number 06/CP/E007, and European Community’s
Seventh Framework Programme (FP7/2007-2013) under Grant
agreement number 227248-2.
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