1. Hydrothermal dissolution of willow in hot compressed water
as a model for biomass conversion
R. Hashaikeh a
, Z. Fang a
, I.S. Butler b
, J. Hawari c
, J.A. Kozinski a,*
a
Energy and Environmental Research Laboratory, McGill University, 3610 University Street, Wong Building, Rm. 2160, Montreal, QC, Canada H3A 2B2
b
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, QC, Canada H3A 2K6
c
Biotechnology Research Institute, National Research Council, McGill University, 6100 Royalmount Avenue, Montreal, QC, Canada H4P 2R2
Received 21 October 2005; received in revised form 6 October 2006; accepted 2 November 2006
Available online 29 November 2006
Abstract
Biomass has wide applications as a source of clean energy and as a raw material for different chemical stocks. Dissolution of willow as
a model system for biomass conversion has been investigated in the 200–350 °C temperature range. The dissolution process was studied
using a batch-type (diamond-anvil cell) and a continuous flow process reactor. A 95% dissolution of willow was achieved. The lignin and
hemicellulose in willow were fragmented and dissolved at a temperature as low as 200 °C and a pressure of 10 MPa. Cellulose dissolved in
the 280–320 °C temperature range. A dissolution mechanism is proposed, which involves a rapid fragmentation and hydrolysis of lignin,
hemicellulose and cellulose to form oligomers and other water–soluble products, such as glucose. The re-condensation behavior of the
dissolved oligomers is the main challenge for efficient dissolution. A continuous flow process is more effective and simpler in this regard
than is a batch process. The results of this work show that hot, compressed water affords a viable alternative to corrosive chemicals and
toxic solvents, thereby facilitating the utilization of biomass as a source of renewable fuel and chemical feedstocks.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Hydrothermal; Biomass; Willow
1. Introduction
Besides their use as a source of fuels [1], there is
increased interest in converting biomass materials into glu-
cose and other useful derivatives. At the present time, enzy-
matic and acid hydrolysis processes are the main ones
being used to convert biomass. Yet, these two processes
are quite restricted in their applications. The enzymatic
hydrolysis process is complicated and focuses on the cellu-
lase complex isolated from the fungus Trichoderma reesei
[2]. There are still many obstacles to overcome, particularly
when treating lignocellulosic materials. The major problem
is that the structure of the cellulose present in lignocellu-
loses inhibits access of the cellulase enzymes to the cellulose
[3]. On the other hand, acid hydrolysis is a process that
requires corrosion-resistant materials and acid recovery
cycles. Moreover, during the time needed for acid hydroly-
sis, the glucose formed can be degraded severely [4].
Recently, hot, compressed water (super- and sub-criti-
cal) has been shown to have a high ability to hydrolyze
cellulose and other highly polymeric materials [5]. The
use of hot, compressed water is considered to be unique,
because it utilizes water as a solvent and as a reactant at
the same time. It is seen as a promising path for ‘green
chemistry’ by providing alternatives to corrosive acids
and toxic solvents. It is also seen as a way to optimize
energy usage, since it does not require extra energy for a
subsequent water evaporation step.
Fang and Kozinski [6] have shown that several materials
such as rubber and cellulose can be converted in supercrit-
ical water (SCW) into one homogeneous phase. Since bio-
mass is a solid material that requires conversion into liquid
0016-2361/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fuel.2006.11.005
*
Corresponding author.
E-mail address: janusz.kozinski@videotron.ca (J.A. Kozinski).
www.fuelfirst.com
Fuel 86 (2007) 1614–1622

2. and gas products, the homogenization characteristics of
hot compressed water are really attractive. In the case of
heterogeneous catalytic processing, the fact that the bio-
mass material and the catalyst are solids is the main limita-
tion in using this process for biomass feedstock conversion.
When biomass is converted to a homogeneous phase with
water, however, it becomes accessible to the active sites
of the catalyst.
The moisture content in biomass is the main limitation
in designing energy-efficient systems based on biomass. In
the case of direct combustion and thermal gasification, a
large amount of energy (compared to the biomass energy
content) is consumed in order to evaporate the water con-
tent. On the other hand, in a hydrothermal treatment with
hot compressed water, the water content does not present a
problem. Instead, it is useful, since water is also employed
as a reactant.
The accessibility of water to biomass increases with
increasing pressure [7]. This situation is advantageous
because of the structural arrangement of biomass (highly
crystalline cellulose covered and surrounded with both lig-
nin and hemicellulose). The accessibility restriction is a
major problem in the enzymatic treatment of biomass.
The main objective of the earlier studies of hydrother-
mal dissolution of biomass feedstock was the production
of chemical feedstock [8] and/or a pretreatment in the fer-
mentation process to produce ethanol [9]. These studies
showed that cellulose could be dissolved completely in
hot compressed water at elevated temperatures of 290–
400 °C. The studies that focused on biomass feedstocks,
such as sugar bagasse [9], corn fiber [10], sugar cane [12]
and several woody and herbaceous biomass species [11],
have revealed that 50–60% of the biomass can be dissolved
(mainly the lignin and hemicellulose portions). This disso-
lution occurs at temperatures of 180–240 °C. Complete dis-
solution could not be achieved, however, mainly because of
recondensation of soluble components originating from lig-
nin [10].
Recently there has been an increased interest in using
biomass as a source of hydrogen fuel. Several researchers
[13–15] have investigated hydrothermal gasification of bio-
mass. Most of these studies have used glucose as a model
compound, chiefly because it is the main building block
of biomass and because it is water soluble. Cortright
et al. [15] have demonstrated that hydrogen can be
produced from sugars at temperatures near 227 °C in an
Thermocouples
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Fig. 1. Diamond-anvil cell (DAC).
Fig. 2. Schematic and picture of the semi-continuous flow reactor (SCFR) for willow dissolution.
R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622 1615

3. aqueous-phase reforming process using a platinum-based
catalyst. Several biomass-derived materials that are soluble
in water have been used for the aqueous hydrogen genera-
tion process. Since hydrothermal gasification of biomass to
hydrogen necessitates using catalytic materials, it is impor-
tant to produce water–soluble products from biomass so
that these products will be compatible with the heteroge-
neous catalytic gasification.
The focus of the work reported here was to establish the
ideal operating conditions under which lignocellulosic
biomass materials can be dissolved in a homogenous
phase with water as a liquefaction step prior to further
processing.
2. Experimental
A diamond-anvil cell (DAC) system (W. Bassett, Cor-
nell University) [17,18] and a flow-type, semi-continuous
reactor were used to study the liquefaction process of wil-
low. Willow is a woody biomass material that is mainly
composed of lignin (22.7%), hemicellulose (26.7%) and cel-
lulose (49.6%) [16].
2.1. DAC experiments
Visual observations at high pressures and temperatures
were conducted using the DAC. The experimental set-up
and procedures were similar to those described in previ-
ously published work [19]. The DAC, Fig. 1, is a batch
reactor that consists of two opposing diamond-anvils. An
Inconel gasket (250-lm thick) is located between the faces
of the two diamond-anvils. At the point where the two dia-
monds meet, the Inconel has had a hole of 508-lm ID
drilled into it. This arrangement affords a closed, cylindri-
a-
b-
c-
d-
0
50
100
150
200
250
300
350
400
450
500
0 5 10 15 20 25 30
Time (min)
TemperatureC
Fig. 3. DAC observation and temperature profile of the DAC chamber for (willow + water) system.
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
TOC
3 ml/min
8 ml/min
5 ml/min
Fig. 4. TOC profile in the liquid residue obtained during willow treatment
at different flow rates and a dissolution temperature of 215 °C.
1616 R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622

4. cal chamber with a volume of 50 nL. Since the DAC has
two diamond faces, the interior of the chamber can be
monitored easily. Both visible and IR light can be used
with the DAC. An optical microscope (Olympus SZ11),
at a magnification of 110X, was used for the optical obser-
vations. Images were recorded with a Panasonic 3CCD
camera (AW-E300). Three different systems were studied
in the DAC: (1) willow + water, (2) lignin + water and
(3) cellulose + water. The chamber was heated by two elec-
tric micro-heaters and the temperature was measured at
several locations in the DAC with the aid of a Strawberry
Tree data acquisition unit.
2.2. Semi-continuous flow reactor (SCFR) experiments
The reactor is illustrated in Fig. 2. A 3-g sample of wil-
low was loaded inside a stainless-steel tube reactor (40-cm
long tube, 9.525-mm OD, 7.874 mm ID, 316 SS). Distilled
water, preheated to the desired temperature (200–320 °C),
was pumped through the reactor using a high performance
liquid chromatography (HPLC) pump at a flow rate of 3–
8 mL/min. The reactor temperature was maintained at the
preheater outlet temperature using the tube furnace. The
pressure in the system was controlled at 10 MPa using a
back-pressure regulator. The flowing stream was passed
through a high-pressure filter (Millipore, 25 mm) cooled
and depressurized. The residues remaining in the reactor
were collected and dried for analysis. The liquid samples
from the filtered stream were analyzed for carbon concen-
tration. Selected samples were also analyzed for glucose
concentration. The solid residues produced from the
hydrothermal treatment process of willow were analyzed
for their chemical composition and structure using a
DMAX-III Rigaku rotating anode diffractometer (Rigaku,
Japan). X-ray diffraction patterns were collected for the
green (untreated) willow and compared with those of the
residue products.
3. Results and discussion
Fig. 3 shows selected images of the reactive phase behav-
ior of willow in the DAC. Willow begins to dissolve at
$200 °C, as indicated by the color change to yellow1
as
well as by the shrinkage of the willow particles (Fig. 3b).
An increase in temperature did not result in an increase
in dissolution, but it did initiate pyrolysis of the willow,
as indicated by the darkening color (Fig. 3d). By the end
of the test, a partial (40–60%) dissolution of the willow
had been achieved.
In the second series of tests, the semi-continuous flow
reactor was used. Willow samples were dissolved at both
215 and 230 °C. The time required for complete reaction
was evaluated by measuring the total organic carbon
(TOC) concentration of the liquid residue as a function
of time, as shown in Figs. 4 and 5. The solid residues
remaining in the reactor were filtered, dried and weighed
to estimate the % dissolution of willow. Fig. 4 shows that
the willow dissolution time varied with water flow rate.
Such a behavior indicates that the dissolution process
occurring within the tube reactor is diffusion controlled.
The dissolution time (20 min at 8 mL/min, 25 min at
5 mL/min and 40 min at 3 mL/min) is markedly affected
by the ability to remove the products formed during the
hydrothermal treatment process. It is noteworthy that an
increase in temperature did not affect the dissolution time
(Fig. 5). At a constant flow rate of 5 mL/min, the dissolu-
tion took 25 min for all the temperatures studied. Gener-
ally, an increase in temperature in a chemical reaction
results in an increase in its reaction rate. But, since the dis-
solution process is diffusion controlled, the effect of temper-
ature was not apparent. On the other hand, temperature
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
TOC
230 C,
215 C,
300 C,
5 ml/min
Fig. 5. TOC profile in the liquid residue obtained during willow treatment at different temperatures and a water flow rate of 5 ml/min.
1
For interpretation of color in Figs. 3, 7–9 the reader is referred to the
web version of this article.
R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622 1617

5. effects were significant when comparing dissolution effi-
ciency. Table 1 shows the dissolution of willow as a
function of temperature using the SCFR equipment. Rea-
sonable dissolutions in the 60–65% range were achieved
at a relatively low temperature (215–230 °C). Contrary to
expectations, increasing the temperature decreased the
dissolution of willow. At 300 °C, 50% of the willow had
dissolved, while 65% had dissolved at 230 °C. Any further
increase in temperature (T > 230 °C) resulted in blockage
of the tube reactor indicating increased willow pyrolysis.
Instead of being hydrolyzed and dissolved, the biomass
material tended to dehydrate and form solid products,
which remained in the reactor. Such behavior is also appar-
ent from Fig. 3d where a black solid precipitate is the main
product obtained when willow is treated at high tempera-
tures (>300 °C).
Fig. 6 shows the X-ray diffraction patterns of untreated
willow and the residue obtained from the semi-continuous
flow reactor (SCFR) treatment at 230 °C. The untreated
willow has a broad diffraction pattern, which indicates
the presence of both amorphous and crystalline material.
The three peaks observed are those of cellulose. After the
hydrothermal treatment, the X-ray diffraction pattern of
the residue shows the presence of highly crystalline cellu-
lose compared to that of willow. This observation is clear
indication that the amorphous part of willow (lignin and
hemicellulose) is reacting at the operating conditions
(215–230 °C).
The 60% dissolution obtained when willow was treated
at 200 °C corresponds to a higher level than the possible
chemical composition of both lignin and hemicellulose
combined together in the willow (lignin 22.7%, hemicellu-
lose 26.7%). Therefore, it seems that some of the cellulose
has dissolved at the 215–230 °C temperature range. The
dissolution of cellulose at such low temperature is
explained by the fact that not all of the cellulose is crystal-
line and part of it is amorphous.
The glucose concentration in the water–soluble portion
was equivalent to 53 ppm (0.6% carbon based). Traces of
acetic acid (153 ppm = 1.7% carbon based) were also
detected. The low glucose concentration is reasonable since
the building block of lignin is not glucose, but it is mainly
phenyl-propanes [20]. The liquid residue was milky-like
Table 1
Dissolution efficiency of willow at different operating temperatures
Temperature (°C) Dissolution (wt%)
215 63
230 65
300 52
Treated willow
Willow
Pure cellulose
0
2000
4000
6000
8000
10000
12000
5 10 15 20 25 30 35 40
2 θ
Intensity
Fig. 6. X-ray diffraction pattern of green willow and the residues out of
treating willow at 230 °C in pressurized water (10 MPa).
Fig. 7. Visual observation of cellulose decomposition in compressed water up to 350 °C in the DAC: (A) heating rate = 1 °C/s and (B) heating
rate = 5 °C/s [1].
1618 R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622

6. and contained solid fraction of small particles (0.5–0.6 lm).
It is likely that the lignin polymer underwent a fraction-
ation process, resulting in the formation of these solid
particulates. In addition, soluble products of lignin and
hemicellulose tend to react and re-condense to form solid
precipitates [21].
It is worth pointing out that even though cellulose and
hemi-cellulose have similar chemical compositions, cellu-
lose is more stable at higher temperature and hemicellulose
is much more reactive than cellulose. This particular situa-
tion has to do with the fact that hemicellulose is amor-
phous, while cellulose is not.
Even though previous research [1,22–24] has shown that
cellulose can be dissolved completely in SCW (Fig. 7), the
cellulose in willow did not dissolve in our experiments. The
fact that willow, and particularly the cellulose in willow,
underwent pyrolysis rather than hydrolysis can be
explained by the fact that the initial products of the disso-
lution reactions undergo various isomerization, dehydra-
tion, fragmentation and condensation reactions [25]. Such
re-condensation reactions have been reported by other
researchers [21]. In the case of willow, lignin and hemicel-
lulose start dissolving much earlier than does cellulose.
When working at higher temperatures (>300 °C), the re-
condensation reaction rates increase with temperature
resulting in precipitation of the re-condensation products
on the surface of cellulose. These precipitates form an
arrangement that inhibits access of water to the cellulose,
thus resulting in cellulose pyrolysis rather than hydrolysis
and dissolution.
3.1. Lignin behavior studied in the DAC
There is no pure lignin available as a commercial prod-
uct. Instead, lignin is usually separated from lignocellulosic
biomass by specific solvents. The one used in this work was
an organo-solvent-lignin, purchased from Aldrich Chemi-
cal Co. Fig. 8 shows selected observations of the reactive
0
50
100
150
200
250
300
350
400
450
0 5 10 15 20 25
Time (min)
TempC
a
b-
c-
e
f-
d
Fig. 8. DAC observation and temperature profile of the DAC chamber for (lignin + water) system.
R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622 1619

7. phase behavior of lignin in the DAC. In the 150–180 °C
temperature range, Fig. 8b and c, lignin begins to accumu-
late in a sintering-like behavior to form a spherical mass of
accumulated particles. A melting behavior was sub-
sequently observed at 180 °C. The melted droplets of
lignin formed were not miscible in the hot, compressed
water in the DAC environment. A further increase in the
temperature to 200 °C resulted in the dissolution of lignin
into water–soluble products (Fig. 8d and e). Some precipi-
tates were also formed on the surface of the diamonds
(Fig. 8f).
As a result of the above observations, a two-step disso-
lution process was employed. Lignin and hemicellulose
were first dissolved and separated from willow at an oper-
ating temperature of 230 °C using the SCFR equipment.
The residues generated in this step were then tested for
dissolution using both the SCFR and the DAC under the
dissolution conditions established previously from experi-
ments with pure cellulose (Fig. 7). Following such a proce-
dure resulted in nearly complete dissolution of willow. A
95% conversion was achieved at 310 °C in the SCFR.
The glucose concentration in the water–soluble portion
was equivalent to 20% (carbon-based). The other products
present in the water–soluble phase were identified as: cello-
biose, fructose, erythrose, glyceraldehydes, and 5-hydrox-
ymethylfuraldehyde (5-HMF).
Fig. 9 illustrates visually the phase behavior of the
treated willow using the DAC. The treated willow starts
dissolving at around 250 °C (Fig. 9b), as indicated by the
color change to yellow. Gas bubbles resulting from the gas-
ification of the dissolution products started to form at the
surface of the Inconel gasket edges (Fig. 9c). The tempera-
ture was maintained at 280 °C when a significant amount
of the willow was dissolved.
0
50
100
150
200
250
300
350
400
450
0 10 20 30 40 50 60 70 80 90
Time (min)
TempC
a
b
c
d
e
f
Fig. 9. DAC observation and temperature profile of the DAC chamber for treated willow.
1620 R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622

8. The schematic shown in Fig. 10 presents a proposed
mechanism for lignocelluloses dissolution based on our
work. Willow, as a lignocellulosic material, is composed
of lignin, hemicellulose and cellulose. These components,
which have different chemical natures, are arranged in a
complex structure within the biomass cell wall. When trea-
ted with hot, compressed water at 200–230 °C (path A),
water attacks the vulnerable amorphous phase (lignin
and hemicellulose). The materials are fragmented and dis-
solved from the cell wall into the water stream. The
untreated cellulose remains. Treatment of this cellulose
with hot compressed water at T > 300 °C resulted in disso-
lution of the cellulose into various water–soluble compo-
nents, such as glucose and fructose. On the other hand,
path B, i.e., the direct treatment of lignocellulosic materials
with hot compressed water at T > 300 °C had negative
effects on the dissolution process. When treated at such
temperatures, the lignin and hemicellulose dissolution
kinetics are both fast and the dissolution reactions termi-
nate with the formation of precipitates. These precipitates
deposit on the cellulose chains, thereby blocking access
of water to them. The cellulose is then dehydrated with
the formation of char-like solid residues as a result of
pyrolysis.
4. Summary and conclusions
Biomass is available in solid forms. In order to gasify
biomass materials successfully into hydrogen, catalytic
materials are required. The biomass needs to be available
in a homogenous phase for the heterogeneous catalyst
active sites to function. The liquefaction and conversion
process of willow (a model compound for biomass) into
water–soluble products has been studied. As any typical
woody biomass material, willow is composed of lignin,
hemicellulose and cellulose. These compounds differ in
1,6-anydroglucose,
erythrose,
glycolaldehyde,
glyceraldehydes,
dihydroxyacetone,
pyruvaldehyde, 5-
(hydroxymethyl)-
furaldehyde (5-
HMF), and
furaldehyde.
Cellohexaose, cellopentaose,
cellotetraose, cellotriose,
cellobiose
glucose, fructose
precipitates
Structural arrangement
of lignocellulose cell wall
Lignin and hemicellulose Cellulose
Fragmentation and
Dissolution products out of
lignin and hemicellulose
Fragmentation
Dissolution
Direct treatment with hot
compressed water at
temperature > 300 ºC
Treatment at 200-230ºC
Treatment at 300-340º C
Path A
Path B
Fig. 10. The mechanism of lignocelluloses dissolution.
R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622 1621

9. their chemical structure and are arranged in a complex
manner within the wood cell wall. Any hydrothermal disso-
lution (liquefaction) process will be dramatically affected
by these two factors. Fragmentation and dissolution of
the amorphous phase (lignin and hemicellulose) of willow
was achieved easily at temperatures as low as 200 °C. At
temperatures above 230 °C, however, the dissolution pro-
cess of lignin and hemicellulose slows down as a result of
re-condensation reactions. These re-condensation reactions
result from the fact that the dissolution products of lignin
and hemicellulose tend to react internally and precipitate
within the willow mass. As a result of these various precip-
itation and re-condensation reactions, the cellulose mate-
rial is blocked and water does not have access to it.
Cellulose then tends to dehydrate and form char-like pre-
cipitates inside the reactor. This problem was solved by
using a two-step dissolution process. This procedure takes
advantage of the flowing system and the fact that the amor-
phous phase is preferentially removed at lower tempera-
tures than is the crystalline phase. The amorphous phase
in biomass could be dissolved and removed in a semi-con-
tinuous flow reactor at a temperature of 230 °C. The crys-
talline cellulose was then dissolved at 310 °C. An overall
95% dissolution of willow was achieved in the end.
Acknowledgements
This research was supported by discovery, strategic and
equipment grants from the NSERC (Canada) and the
FQRNT (Quebec).
References
[1] Hashaikeh R, Fang Z, Butler IS, Kozinski JA. Sequential hydro-
thermal gasification of biomass to hydrogen. Proc Combust Inst
2005;30:2231–7.
[2] Reczey K, Szengyel Z, Zacchi G. Cellulase production by T. Reesei.
Bioresour Technol 1996;57:25–30.
[3] Hiler E, Stout B. Biomass energy: a monograph, TEES monograph
series. USA; 1985.
[4] Walker J, Butterfield B. Primary wood processing: principles and
practice. London: Chapman & Hall; 1993.
[5] Fang Z. Phase behavior and oxidation of organic wastes in
supercritical water, PhD thesis, McGill University; 2003.
[6] Fang Z, Kozinski JA. Phase behavior and combustion of hydrocar-
bon-contaminated sludge in supercritical water at pressures up to
822 MPa and temperatures up to 535 °C. Proc Combust Inst
2000;28:2717–25.
[7] McHardy J, Sawan S. Supercritical fluid cleaning – fundamentals,
technology, and applications. New Jersey, Westwood: Noyes Publi-
cations; 1998.
[8] Ehara K, Saka S. A comparative study on chemical conversion of
cellulose between the batch-type and flow-type systems in supercrit-
ical water. Cellulose 2002;9:301–11.
[9] Laser M, Schulman D, Allen S, Lichwa J, Antal M, Lynd L. A
comparison of liquid hot water and steam pretreatments of sugar
cane bagasse for bioconversion to ethanol. Bioresour Technol
2002;81:33–44.
[10] Allen S, Schulman D, Lichwa J, Antal M, Laser M, Lynd L. A
comparison between hot liquid water and steam fractionation of corn
fiber. Ind Eng Chem Res 2001;40:2934–41.
[11] Mok W, Antal M. Uncatalyzed solvolysis of whole biomass hemi-
cellulose by hot compressed liquid water. Ind Eng Chem Res
1992;31:1157–61.
[12] Allen S, Kam L, Zemann A, Antal M. Fractionation of sugar cane
with hot, compressed, liquid water. Ind Eng Chem Res
1996;35:2709–15.
[13] Yu D, Aihara M, Antal M. Hydrogen production by steam reforming
glucose in supercritical water. Energy Fuels 1993;7:574–7.
[14] Xu X, Matsumura Y, Stenberg J, Antal M. Carbon-catalyzed
gasification of organic feedstocks in supercritical water. Ind Eng
Chem Res 1996;35:2522–30.
[15] Cortright R, Davda R, Dumesic J. Hydrogen from catalytic reform-
ing of biomass-derived hydrocarbons in liquid water. Nature
2002;418:964–7.
[16] Fengel D, Wegener R. Wood, Berlin: De Gruyter; 1989. cited in:
Bobleter O. Hydrothermal degradation of polymers derived from
plants. Prog Polym Sci 1994;19:797–841.
[17] Bassett W, Shen A, Bucknum M. A new diamond anvil cell for
hydrothermal studies to 2.5 GPa and from À190 to 1200 °C. Rev Sci
Instrum 1993;64:2340–5.
[18] Dunstan D, Spain I. The technology of diamond anvil high-pressure
cells: I. Principles, design and construction. J Phys E Sci Instrum
1989;22:913–23.
[19] Fang Z, Kozinski JA. Proc Combust Inst 2000;28:2717–25.
[20] McKendry P. Energy production from biomass (Part 1): Overview of
biomass. Bioresour Technol 2002;83:37–46.
[21] Bobleter O, Concin R. Cell Chem Technol 1979;13:583–93.
[22] Sasaki M, Adschiri T, Arai K. Kinetics of cellulose conversion at
25 MPa in sub- and supercritical water. AIChE 2004;50:192–202.
[23] Boon J, Pastorova I, Botto R, Arisz P. Structural studies on cellulose
pyrolysis and cellulose chars by PYMS, PYGCMS, FTIR, NMR and
by wet chemical techniques. Biomass Bioenergy 1994;7:25–32.
[24] Sasaki M, Fang Z, Fukushima Y, Adschiri T, Arai K. Dissolution
and hydrolysis of cellulose in subcritical and supercritical water. Ind
Eng Chem Res 2000;39:2883–90.
[25] Antal M, Allen S, Schulman D, Xu X. Biomass gasification in
supercritical water. Ind Eng Chem Res 2000;39:4040–53.
1622 R. Hashaikeh et al. / Fuel 86 (2007) 1614–1622