Reactivity of poly-, di-, and monosaccharides in their hydrolysis in subcritical water

Article abstract of DOI:10.1134/S0023158412010028

The reactivity of the water-soluble sodium salt of carboxymethyl cellulose (CMC), sucrose, glucose, and fructose in subcritical water at 120-320°C is reported. A mathematical model is suggested to describe the variation of the CMC molar mass during hydrolysis at various temperatures and reaction times. Kinetic parameters of the conversions of CMC, sucrose, glucose, and fructose in subcritical water are presented. High temperatures and short reaction times are favorable for the formation of monosaccharides from CMC. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0023158412010028

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2012, Vol. 53, No. 1, pp. 19–24. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.G. Khudoshin, A.Yu. Goryainov, V.V. Lunin, V.I. Bogdan, 2012, published in Kinetika i Kataliz, 2012, Vol. 53, No. 1, pp. 21–26.
Reactivity of Polyꢀ, Diꢀ, and Monosaccharides in Their Hydrolysis
in Subcritical Water
,
b
,
A. G. Khudoshina , *, A. Yu. Goryainova, V. V. Lunina, and V. I. Bogdanb **
a Faculty of Chemistry, Moscow State University, Moscow, 119991 Russia
b Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
eꢀmail: *khudoshin@kge.msu.ru; **vibogdan@gmail.com
Received October 19, 2010
Abstract—The reactivity of the waterꢀsoluble sodium salt of carboxymethyl cellulose (CMC), sucrose, gluꢀ
cose, and fructose in subcritical water at 120–320°C is reported. A mathematical model is suggested to
describe the variation of the CMC molar mass during hydrolysis at various temperatures and reaction times.
Kinetic parameters of the conversions of CMC, sucrose, glucose, and fructose in subcritical water are preꢀ
sented. High temperatures and short reaction times are favorable for the formation of monosaccharides from
CMC.
DOI: 10.1134/S0023158412010028
Cellulose is a linear monosaccharide consisting of yields a multicomponent mixture of oligoꢀ and
Dꢀglucose monomer units joined together by ꢀ1,4ꢀ
β
monosaccharides and furfural derivatives [3, 9].
glycosidic linkages. Native celluloses can be considꢀ
ered in terms of an amorphous–crystalline structural
model with a twoꢀphase crystalline component [1, 2].
Cellulose monomers, oligomers, and deep conversion
products (oligosaccharides, glucose, furfurals, and
others) are valuable substance usable in the production
of food, medicines, etc. The most promising way of
obtaining these nonꢀmacromolecular products is celꢀ
lulose hydrolysis.
For selective synthesis of the most valuable prodꢀ
ucts, namely, nonꢀmacromolecular sugars, it is pertiꢀ
nent to hydrolyze soluble polymers or oligomers at
lower temperatures, using subcritical water. In order to
optimize the process conditions—as will be demonꢀ
strated below, not only the reaction temperature, but
also the reaction time needs optimization—it is necꢀ
essary to have kinetic data for the process. Determinaꢀ
tion of kinetic parameters of the hydrolysis reactions
in scꢀH2О is usually based on measuring the variation
of the substrate weight or the total amount of carbon in
cellulose and glucose oligomers [11, 12]. This circumꢀ
stance makes it fairly difficult to compare the reactiviꢀ
ties of nonꢀmacromolecular, oligomeric, and polyꢀ
The presentꢀday wood hydrolysis technology
employs mineral acids and alkalis as catalysts. For creꢀ
ating new, environmentally friendly technologies for
this important process, it is essential to study reactions
of cellulose in subcritical and supercritical water (scꢀ
H2O). The results of such studies might provide scienꢀ
tific foundations for sustainable processing of celluꢀ meric carbohydrates. As a consequence, it is difficult
loseꢀcontaining raw materials, including technogenic
formations and agricultural and wood processing
waste [3]. The physical and chemical properties of
water change significantly as its temperature and presꢀ
sure are raised. In particular, subcritical water shows
pronounced properties of an acid–base catalyst, and
this important circumstance makes it possible to carry
out hydrolysis in the absence of conventional catalysts,
such as acids and alkalis [4–6].
to optimize the reaction conditions for obtaining valuꢀ
able products. Depending on the degree of polymerꢀ
ization, the same total mass of reacting carbohydrates
may contain different numbers of key reaction sites,
specifically, glycosidic ether linkages.
Here, we report a comparative estimate of the reacꢀ
tivities of the polymeric substrate and products of its
hydrolysis in subcritical water. This estimate is based
on the changes in the molar mass of the polymer subꢀ
jected to hydrothermal treatment. However, it is techꢀ
nically difficult to directly monitor cellulose converꢀ
sion in scꢀH2О, because cellulose is insoluble in water.
For this reason, we studied the conversion of model
substrates, namely, the water soluble sodium salt of
carboxymethyl cellulose (CMC) and monoꢀ and disꢀ
The main cellulose conversion pathways in subcritꢀ
ical and supercritical water were determined in earlier
studies [3, 7–12]. Cellulose crystal structure disrupꢀ
tion yielding soluble oligomers and oligomer fragmenꢀ
tation occur in scꢀH2О at a high rate, and so do secꢀ
ondary glucose conversions, such as dehydration,
isomerization, and retroꢀaldol condensation. As a
consequence, glucose conversion in scꢀH2О usually accharides (glucose, fructose, and sucrose).
19

20
KHUDOSHIN et al.
Electric
furnace
The glucose, fructose, and sucrose concentrations
in the reaction mixture were determined by HPLC on
an Agilent 1100 chromatograph (Kromasil 100
Highꢀpressure
pump
Backꢀflow
regulator
Valves
Å
5 μm
NH2 column, acetonitrile : water = 70 : 30 mobile
phase, 190 nm UV detector).
Condenser
The changes in the molar mass as a result of CMC
hydrolysis at 35 0.1°С was estimated by measuring
Vessel with
solution
the viscosity of solutions at different CMC concentraꢀ
tions by capillary viscometry on a VPZhꢀ4 viscometer
with a capillary 0.62 mm in diameter. The solvent flow
time was at least 100 s, and this obviated the need to
apply kinetic energy corrections [13]. The flow time in
each case was measured at least five times, and the disꢀ
crepancy between measurements did not exceed 0.2–
Product
collector
Fig. 1. Experimental setup for investigation of plyꢀ and
monosaccharide hydrolysis in subcritical and supercritical
water.
0.3 s. Reduced viscosity ηsp/C was determined as
ηsp/С
7
tf t0 −1
(1)
ηsp C =
,
C
where
flow time, and
solution. Characteristic viscosity [
t
f is the CMC solution flow time, t0 is the solvent
6
5
4
3
2
1
C
is the CMC concentration in the
] was determined
η
by extrapolating reduced viscosity to infinite dilution
(Fig. 2):
η
⎛
⎜
⎝
⎞
⎟
⎠
sp
(2)
[η] = lim
.
C
C→0
The viscosityꢀaverage molar mass
М
was calculated
using the Kuhn–Mark–Houwink equation [14]:
α
(3)
is a facꢀ
tor depending on the temperature, polymer nature,
and solvent; and is the constant characterizing the
conformation of the macromolecule in the solution.
For CMC, = 1.23 = 0.91 [15].
10–2 ml/g and
[η] = KM ,
where [ К
] is characteristic viscosity (cm3/g);
η
0
2
4
6
8
, g/l
α
C
K
×
α
Fig. 2. Characteristic viscosity
CMC concentration in the solution.
η
/C as a function of the
sp
The density of subcritical water was calculated
using the WaterSteamPro software package (http://
www.wsp.ru).
EXPERIMENTAL
Because the density of water decreases with increasꢀ
ing temperature, the reaction time
τ
depends not only
The conversions of glucose and fructose under subꢀ
on the reactor volume Vr and volumetric feed flow rate
critical conditions were studied in aqueous solutions at
a monosaccharide concentration of 20 g/l, and the
conversions of disaccharides and polysaccharides were
studied using solutions of sucrose (20 g/l) and CMC
(15 g/l).
but also on the temperature and pressure
,
P
:
v
VrρT
(4)
τ =
,
ρ25v
where ρ25 and ρT is the density of water at 25
temperature
son of experimental data, we used the quantity Vr
The rate constants of chemical reactions were calcuꢀ
lated using values determined via formula (4).
°C
and at
T, respectively. For convenient compariꢀ
The process was carried out using the laboratory
setup schematized in Fig. 1. The setup can include
several reactors with a volume of Vr = 0.11–4.4 ml.
The reactor temperature was controlled with a Miniꢀ
v.
/
τ
term 400.31 regulator with an accuracy of 2.0°C.
The liquid reactants were fed into the system at a high
pressure with a Gilson 307 pump, which is employed
in highꢀperformance liquid chromatography (HPLC).
A pressure of up to 220 atm at the reactor outlet was
maintained using a Tescom backꢀpressure regulator.
RESULTS AND DISCUSSION
Hydrolysis of Carboxymethyl Cellulose
Figure 3 and Table 1 present experimental data
characterizing the variation of the viscosityꢀaverage
molar mass
The acid hydrolysis of the ether linkages in sucrose
sible to use the plugꢀflow reactor model in the kinetic and starch, the latter consisting of glucose monomer
description of the reaction. units bonded by ether linkages, occurs as a firstꢀorder
M of CMC in subcritical water.
The solution feed flow rate (
v
) was 1.0 ml/min. Since
the solution flow was laminar (Re < 1000), it was posꢀ
KINETICS AND CATALYSIS Vol. 53
No. 1
2012

REACTIVITY OF POLYꢀ, DIꢀ, AND MONOSACCHARIDES
21
reaction with respect to the substrate [16, 17]. It can,
M
2.5
2.0
1.5
1.0
0.5
×
×
×
×
×
105
therefore, be assumed that the hydrolysis of CMC,
which is a waterꢀsoluble ether of cellulose, is also a
firstꢀorder reaction.
The viscometry technique employed in this study
was used earlier in the kinetic study of cellulose ether
conversion under mechanochemical treatment [18].
The variation of the molar mass of hydroxyethyl celluꢀ
lose was fitted in that study to the firstꢀorder equation
105
105
105
104
0
1
d(M∞ − M) M∞
k(M − M∞)
(5)
=
,
3
2
dt
M∞
where
polymer at the point in time
mass, and is the rate constant of the reaction.
M
is the viscosityꢀaverage molar mass of the
t,
M∞ is the limiting molar
k
100
150
200
250 T, °C
The CMC hydrolysis kinetics in subcritical water
can be considered in the same way. This approach
seems to be quite correct since one polymer molecule
has a multitude of reaction sites, specifically, glycoꢀ
sidic linkages. It is most likely that the hydrolysis reacꢀ
tions of different macromolecules are independent of
one another. Therefore, the rate of conversion of the
polymeric substrate should be proportional not to the
molecule concentration, but to the “concentration”
of reaction sites in the polymer molecule, which is
related to the molar mass of the polymer.
Fig. 3. Molar mass of CMC as a function of temperature at
= ( ) 9, ( ) (50), and ( ) 264 s. The points represent
experimental data, and the curves represent calculated
data.
V
/
v
1
2
3
r
as furfural and 5ꢀhydroxymethylfurfural. Upon CMC
hydrolysis in subcritical water above 250 at V / =
°C
v
r
264 and 50 s, the solution indeed acquires the brown
color characteristic of furfural derivatives. For this reaꢀ
son, in order to optimize the process parameters for
obtaining valuable products with high selectivity, it is
necessary to compare the reactivities of CMC and the
monoꢀ and disaccharides under similar experimental
conditions.
Equation (5) can be rewritten as
d(M1 − M)
(6)
= k(M − M1),
dt
is the viscosityꢀaverage molar mass of CMC
at the point in time and M1 is the molar mass of the
where
M
t
monomer unit of CMC. After integration of Eq. (6),
the dependence of the molar mass of CMC in subcritꢀ
ical water on the reaction time will appear as
Conversions of Sucrose, Glucose, and Fructose
Tables 2–4 list experimental data on sucrose, gluꢀ
cose, and fructose conversions in subcritical water at
different temperatures.
M = (M0 − M1)e−kτ + M1,
(7)
where M0 is the molar mass of the initial CMC. To
determine the rate constant, we will represent Eq. (7)
in the following form:
Table 1. CMC conversion at various temperatures and Vr
ratios
/
v
⎛M0 − M1 ⎞
1
τ
(8)
k = ln
.
⎜
⎟
M ,
10–5
g/mol
×
M − M
1
⎝
⎠
T
,°C
Vr
/
v
, s
k
, s–1
–
The M0 value derived from experimental viscosity data
for the initial CMC (Fig. 2) using Eqs. (2) and (3) is
25
120
161
170
197
200
124
170
200
234
170
200
235
265
2.19
2.12
1.35
1.14
0.95
0.24
2.19
1.77
1.62
1.14
1.96
1.95
1.49
1.38
2.19 ×
105 g/mol.
264
264
264
264
264
50
50
50
50
9
1.3 × 10–4
2.0 × 10–3
2.7 × 10–3
3.6 × 10–3
9.6 × 10–3
–
4.6 × 10–3
6.9 × 10–3
1.6 × 10–2
1.4 × 10–2
1.5 × 10–2
5.2 × 10–2
6.6 × 10–2
Table 1 lists the rate constants of CMC hydrolysis
in subcritical water according to Eq. (8) under differꢀ
ent experimental conditions (V / and T).
v
r
From the temperature dependence of the rate conꢀ
stant of CMC hydrolysis (Table 1), we graphically
derived the activation energy and preexponential facꢀ
tor: Eа = 63.6 kJ/mol and log
lated dependences of the molar mass
A
= 5.0 [s–1]. The calcuꢀ
on the reacꢀ
M
tion temperature and time, derived using the above
kinetic parameters, the Arrhenius equation, and
Eq. (7), are plotted in Fig. 3.
According to the literature [3, 9, 19], the solution
in which cellulose hydrolysis occurs at high temperaꢀ
tures may contain sugar decomposition products, such
9
9
9
KINETICS AND CATALYSIS Vol. 53
No. 1
2012

22
KHUDOSHIN et al.
Table 2. Sucrose conversion in subcritical water at various
temperatures
The main products of sucrose hydrolysis are gluꢀ
cose and fructose, whose concentrations pass through
a maximum as the temperature is raised (Table 2).
Concentration
×
102, mol/l
Complete sucrose decomposition is attained at 255 C,
°
T
,°C
ρ
, kg/m3
k
, s–1
with the fructose yield 11% lower than the glucose
yield. The inequality of the fructose and glucose yields
in the hydrolysis of the disaccharide can be due to the
further conversion of the monosaccharides, for frucꢀ
tose is more reactive than glucose, other conditions
being equal. This is indicated by our data on glucose
and fructose decomposition in subcritical water
sucrose glucose fructose
215
225
235
245
255
265
280
856
844
831
817
803
787
762
4.5
3.1
2.4
0.8
0
1.4
3.2
3.3
5.2
5.9
4.6
4.5
1.1
2.6
2.8
4.4
5.3
3.7
3.4
0.048
0.117
0.166
0.371
–
(Tables 3, 4). At 260 C, the glucose conversion is only
°
0
–
~10% (Table 3), while the fructose conversion under
the same conditions is 26% (Table 4).
0
–
Since the kinetics of the diꢀ and monosaccharide
conversions in subcritical water, like the kinetics of the
same processes in “ordinary” water [16, 20–23], can
be described in terms of a firstꢀorder rate equation, the
sucrose, glucose, and fructose conversion rate conꢀ
stants were determined using the equation
–2
* The initial sucrose concentration is 5.9
× 10 mol/l. Glucose
v
and fructose are absent at the beginning of the reaction.
V
/ =
r
6.6 s;
P = 140 atm.
Table 3. Glucose conversion in subcritical water at various
temperatures
(9)
is the
is the
k = −1 τln C C0 ,
where C0 is the initial substrate concentration,
outlet concentration of the substance, and
Concentration
glucose
×
102, mol/l
fructose
C
T
,°C
ρ
, kg/m3
k
, s–1
τ
reaction time. The sucrose, glucose, and fructose
decomposition rate constants determined using this
equation are presented in Table 2–4. As was demonꢀ
strated above, the sucrose conversion rate constant
refers to the hydrolysis of the glycosidic linkage of
sucrose. According to the literature, glucose and frucꢀ
tose decomposition in scꢀH2O is a complicated comꢀ
bination of reactions including dehydration, isomerꢀ
ization, and retroꢀaldol condensation [3, 10, 11]. The
temperature dependences of the rates of these reacꢀ
tions in the Arrhenius coordinates are shown in Fig. 4.
The activation energies and preexponential factors for
these reactions are listed in Table 5.
200
230
260
290
320
874
838
795
744
676
11.3
11.0
10.5
7.8
0
0.006
0.011
0.021
0.082
0.276
0
0.2
0.6
0.5
3.4
The initial glucose concentration is 0.117 mol/l. Fructose is absent
at the beginning of the reaction. = 6.6 s; = 140 atm.
V
/
v
P
r
Table 4. Fructose conversion in subcritical water at various
temperatures
The activation energies for the disaccharides
sucrose (Table 5) and cellobiose [22] are similar. Difꢀ
ferent values of the apparent activation energy of conꢀ
version in subcritical water have been reported for
fructose (158 kJ/mol [21] and 96 kJ/mol [23] and gluꢀ
cose (119 kJ/mol [20]).
Fructose
concentration
T
,°C
ρ
, kg/m3
k
, s–1
×
102, mol/l
200
230
260
320
874
838
795
676
11.5
11.2
8.6
0.003
0.008
0.058
0.286
3.1
The initial fructose concentration is 0.117 mol/l;
140 atm.
V
/
v
= 6.6 s;
P
=
Comparing the Reactivities of Polyꢀ, Diꢀ,
and Monosaccharides
r
The purpose of this study was to estimate the reacꢀ
tivities of CMC and of the products of its hydrolysis in
subcritical water and to optimize the process condiꢀ
tions (temperature and reaction time) for obtaining
sugars. Because the kinetic equation (7) describes the
decrease in the molar mass of CMC rather than the
formation of glucose monomers and dimers, this comꢀ
parison cannot be carried out by the conventional
method, comparing the rate constants of reactions at a
fixed temperature. Nonꢀmacromolecular sugars form
only at the latest stages of polymer hydrolysis. Thereꢀ
fore, for optimizing the sugar synthesis conditions, it is
Table 5. Activation energies and preexponential factors for
the CMC, sucrose, cellobiose, glucose, and fructose conꢀ
versions in subcritical water
Substrate
CMC
Sucrose
Cellobiose [13] 320–400
Glucose
Fructose
T
,°C
E
a, kJ/mol
log
A
[s–1
5.0
]
120–265
200–245
64
134
123
89
12.9
10.1
7.0
200–320
200–320
88
7.1
KINETICS AND CATALYSIS Vol. 53
No. 1
2012

REACTIVITY OF POLYꢀ, DIꢀ, AND MONOSACCHARIDES
23
necessary to determine the “polymer depolymerizaꢀ
6
5
4
3
2
1
0
tion time,” τd, defined as the minimum reaction time
required for CMC hydrolysis to nonꢀmacromolecular
products at a given subcritical water temperature.
An analysis of kinetic equation suggests that τd can
be determined as follows. Substituting the condition
2
3
M
= 2M1 into Eq. (8), we obtain
1
⎛
⎞
M0 − M1
τd = ln
[kCMC(T)]−1,
(10)
⎜
⎝
⎟
⎠
M1
where kCMC
temperature
tion. The condition
son that, at M1, which means “total depolymerꢀ
ization,” in Eq. (7) tends to infinity.
(
T
T
) is the CMC hydrolysis rate constant at
determined using the Arrhenius equaꢀ
= 2M1 was chosen for the reaꢀ
M
0.0017 0.0018 0.0019 0.0020 0.0021 0.0022
1/
, K–1
M
=
T
τ
Fig. 4. Arrhenius plot of the rate constant of the conversion
of ( ) sucrose, ( ) glucose, and ( ) fructose.
The stability of the cellulose hydrolysis products
can be estimated as the glucose, fructose, and sucrose
1
2
3
conversion (
α
) at the reaction time τd. The necessity of
α
this estimate is dictated by the high polydispersity of the
1.0
polymer solutions and by the roughness of the
condition.
M
= 2M1
1
Let us represent Eq. (9) as
3
0.8
0.6
0.4
0.2
0
C
(11)
α = 1 − = 1 − exp[−τksug(T)],
2
C0
where ksug
charide conversion in subcritical water at temperature
, determined using the Arrhenius equation. Combinꢀ
ing Eqs. (10) and (11) yields
(T) is the rate constant of monoꢀ and disacꢀ
T
⎡
⎛
⎞
⎤
M1
α = 1 − exp ln
CMC(T)−1ksug(T) .
(12)
k
⎥
⎜
⎝
⎟
⎠
1
⎢
⎣
M − M
⎦
0
Equation (12) describes the temperature dependence
of the sugar conversion in subcritical water at the
reaction time equal to the CMC depolymerization
time τd. The value of is the upper estimate of the
α
100
150
200
T, °C
250
300
α
actual conversion of the CMC hydrolysis products.
Fig. 5.
(1) Sucrose, (2) glucose, and (3) fructose converꢀ
sions as a function of temperature at the reaction time
equal to the CMC depolymerization time at the correꢀ
sponding temperature.
Figure 5 plots the temperature dependences of the
sugar conversions calculated via Eq. (12) using the
Arrhenius equation and the kinetic parameters of
CMC, glucose, fructose, and sucrose hydrolysis (Table 5)
at the reaction time equal to τd. The
with increasing temperature (Fig. 5). At low temperaꢀ
tures of 100–115 , the conversion of sucrose, a
model dimer, is low ( < 0.15). Evidently, under the
α
values increase
good agreement with the above experimental and literꢀ
ature data.
°
C
α
Thus, we have developed a kinetic model for CMC
hydrolysis in subcritical water. The dependence of the
CMC molar mass on the hydrolysis time is satisfactoꢀ
rily described by a firstꢀorder kinetic equation. Rate
constants have been determined for CMC and sucrose
hydrolysis and glucose and fructose conversions in
subcritical water at different temperatures. The apparꢀ
ent activation energies of these reactions have been
estimated. Sucrose hydrolysis in subcritical water can
proceed selectively to yield monosaccharides throughꢀ
out the temperature range examined. Kinetic data
have been used to analyze the temperature effect on
the qualitative composition of the CMC conversion
CMC hydrothermal conversion in this temperature
range, as well as at reaction times shorter than τd, it is
possible to obtain products of partial CMC hydrolysis,
namely, dimers and trimers.
Between 165 and 190
close to unity and the glucose conversion is comparaꢀ
tively low ( < 0.6). These temperatures are favorable
°
C, the sucrose conversion is
α
for obtaining the monosaccharides. The data preꢀ
sented in Fig. 5 demonstrate that, by conducting
CMC hydrolysis in subcritical water above 210 C, it is
°
difficult to obtain nonꢀmacromolecular sugars in high
yield and the reaction mixture is dominated by deep
sugar decomposition products. This conclusion is in products in subcritical water.
KINETICS AND CATALYSIS Vol. 53
No. 1
2012

24
KHUDOSHIN et al.
12. Rogalinski, T., Liu, K., Albrecht, T., and Brunner, G.,
ACKNOWLEDGMENTS
J. Supercrit. Fluids, 2008, vol. 46, p. 335.
This study was supported by the Russian Foundaꢀ
13. Rafikov, S.R., Budtov, V.P., and Monakov, Yu.B.,
Vvedenie v fizikokhimiyu rastvorov polimerov (Introducꢀ
tion to the Physical Chemistry of Polymer Solutions),
Moscow: Nauka, 1978, p. 192.
tion for Basic Research (grant nos. 11ꢀ03ꢀ12126 and
11ꢀ03ꢀ12190).
14. Tsvetkov, V.N., Eskin, V.E., and Frenkel, S.Ya., Strukꢀ
tura makromolekul v rastvorakh (Structure of Macroꢀ
molecules in Solution), Moscow: Nauka, 1964.
REFERENCES
1. Aleshina, L.A., Glazkov, S.V., Lugovskaya, L.A., Podoꢀ
inikova, M.V., Fofanov, A.D., and Silina, E.V., Khim.
Rastit. Syr’ya, 2001, no. 1, p. 5.
2. Kovalenko, V.I., Usp. Khim., 2010, vol. 79, p. 261.
3. Ehara, K. and Saka, Sh., Cellulose, 2002, vol. 9, p. 301.
4. Bandura, A.V. and Lvov, S.N., J. Phys. Chem. Ref. Data
2006, vol. 35, p. 15.
5. Watanabe, M., Aizawa, Yu., Iida, T., Levy, C.,
Aida, T.M., and Inomata, H., Carbohydr. Res., 2005,
vol. 340, p. 1931.
15. Baumgärtel, M. and Willenbacher, N., Rheol. Acta.
1996, vol. 35, p. 168.
,
16. Lebedev, S.Yu., Khizhnyak, T.A., and Kulish, A.S.,
Vestn. Sum. Gos. Univ., Ser. Tekh. Nauki, 2008, no. 1,
p. 112.
17. Yarovenko, V.L., Tekhnologiya spirta (Ethanol Producꢀ
tion Technology), Moscow: Kolos, 2002, p. 177.
18. Chen Rong, Yi Chuanbin, Wu Hong, and Guo Shaꢀ
,
oyun, Carbohydr. Polym., 2010, vol. 81, p. 188.
19. Aida, T.M., Sato, Yu., Watanabe, M., Tajima, K., Nonꢀ
6. Watanabe, M., Aizawa, Yu., Iida, T., Aida, T.M.,
Levy, C., Sue, K., and Inomata, H., Carbohydr. Res.
2005, vol. 340, p. 1925.
7. S nag, A., Gülbay, S., Uskan, B., and Güllü, M.,
J. Supercrit. Fluids, 2009, vol. 50, p. 121.
8. Matsunaga, M., Matsui, H., Otsuka, Y., and Yamaꢀ
moto, S., J. Supercrit. Fluids, 2008, vol. 44, p. 364.
9. Ehara, K. and Saka, Sh., J. Wood Sci., 2005, vol. 51,
,
aka, T., Hattori, H., and Arai, K., J. Supercrit. Fluids
2007, vol. 40, p. 381.
20. Qi Jing and Lu Xiuyang, Chin. J. Chem. Eng., 2008,
vol. 16, p. 890.
21. Bicker, M., Hirth, J., and Vogel, H., Green Chem.
2003, vol. 5, p. 280.
,
ι
,
p. 148.
22. Sasaki, M., Furukawa, M., Minami, K., Adschiri, T.,
and Arai, K., Ind. Eng. Chem. Res., 2002, vol. 41,
p. 6642.
10. Sasaki, M., Fang, Zh., Fukushima, Y., Adschiri, T., and
Arai, K., Ind. Eng. Chem. Res., 2000, vol. 39, p. 2883.
11. Zhao Yan, Lu Wenjing, and Wang Hongtao, Chem. 23. Hirth, J., Ph.D. Dissertation, Darmstadt: Darmstadt
Eng. J., 2009, vol. 150, p. 411.
Univ. of Technology, 2002.
KINETICS AND CATALYSIS Vol. 53
No. 1
2012