One-pot preparation of methyl levulinate from catalytic alcoholysis of cellulose in near-critical methanol

Article abstract of DOI:10.1016/j.carres.2012.07.002

One-pot preparation of methyl levulinate (MLA) from cellulose in near-critical methanol was studied. Acids containing SO₃H group were proven to be effective catalysts for the production of MLA from cellulose's catalytic alcoholysis. The effects of different reaction conditions, such as an initial cellulose concentration of 10-30 g/L, a temperature range from 170 to 190 °C, and a sulfuric acid concentration of 0.01-0.03 mol/L, on the production of MLA were investigated. The results showed the reaction temperature and acid concentration significantly affected the process of cellulose alcoholysis and the yield of MLA. A high yield of up to 55% MLA was achieved at 190 °C for 5 h, using 0.02 mol/L H₂SO₄ as a catalyst.

Full text of DOI:10.1016/j.carres.2012.07.002

Carbohydrate Research 358 (2012) 37–39
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
One-pot preparation of methyl levulinate from catalytic alcoholysis
of cellulose in near-critical methanol
⇑
⇑
Xiaoyu Wu, Jie Fu , Xiuyang Lu
Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China
a r t i c l e i n f o
a b s t r a c t
Article history:
One-pot preparation of methyl levulinate (MLA) from cellulose in near-critical methanol was studied.
Acids containing SO3H group were proven to be effective catalysts for the production of MLA from
cellulose’s catalytic alcoholysis. The effects of different reaction conditions, such as an initial cellulose
concentration of 10–30 g/L, a temperature range from 170 to 190 °C, and a sulfuric acid concentration
of 0.01–0.03 mol/L, on the production of MLA were investigated. The results showed the reaction temper-
ature and acid concentration significantly affected the process of cellulose alcoholysis and the yield of
MLA. A high yield of up to 55% MLA was achieved at 190 °C for 5 h, using 0.02 mol/L H2SO4 as a catalyst.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 20 February 2012
Received in revised form 29 June 2012
Accepted 4 July 2012
Available online 14 July 2012
Keywords:
Cellulose
Methyl levulinate
Near-critical methanol
Alcoholysis
One-pot preparation
1. Introduction
used fine chemical intermediate and polymer monomer,11 making it
an ideal platform chemical from cellulose. Tominaga et al.12 devel-
Cellulose is a renewable and alternative source for the produc-
tion of chemicals and fuels. Various conversion processes from cel-
lulose to useful chemicals, such as acid hydrolysis,1 enzymatic
hydrolysis,2 pyrolysis,3 and decomposition in supercritical liquid,4
have been developed to obtain platform chemicals like ethanol,
lactic acid, 5-hydroxymethylfurfural, and levulinic acid.5 However,
all these methods have some limitations such as low conversion
efficiency, device corrosion, high energy consumption, and compli-
cated processes.5,6 Thus, there is considerable scope for the devel-
opment of a novel and more effective method.
Near-critical catalytic methanol alcoholysis is a promising alter-
native method for the conversion of cellulose to new platform
chemicals.4,7–9 Methanol is a good solvent for the products from cel-
lulose and lignin with relatively high molecular weight (HMW), as
well as a methylating agent in chemical reactions. This allows for
the conventional multi-steps process from cellulose to platform
chemicals to be achieved in a facile one-pot procedure.4,10
oped a mixed acid system, employing a Lewis acid and Bronsted acid
to catalyze cellulose to MLA with a 75% yield. Although the yield of
MLA is high, the catalytic system of mixed acids is expensive, and
hard to be applied to industry. Therefore, a low-cost catalytic sys-
tem needs to be explored.
In this article, the catalytic activities of several kinds of acid
catalysts for the alcoholysis of cellulose to MLA in near-critical
methanol were evaluated to develop an efficient and low-cost
method. Kinetics on the catalytic alcoholysis of cellulose to MLA
were investigated using the following reaction conditions: initial
cellulose concentration of 10–30 g/L, reaction temperature range
from 170 °C to 190 °C, and catalyst sulfuric acid concentration of
0.01–0.03 mol/L. The results provide insights on an efficient and
low-cost approach to produce MLA from cellulose.
2. Experimental
Microcrystalline cellulose with 50 lm average particle size was
Cellulose can be decomposed efficiently in supercritical metha-
obtained from Acros Organics, England. Other chemicals were pur-
chased from Sinopharm Chemical Reagent Co. Ltd, China, and were
all of analytical reagent grade.
All the catalytic alcoholysis reactions of cellulose were carried
out in a 316L stainless steel batch reactor with a capacity of
13.5 mL. The reactor was constructed in three parts (tube, stopper,
and cap), and can be directly heated in a steel box furnace. The fur-
nace could handle up to 12 reactors at a time. The designed
maximum pressure and temperature for the batch reactor were
20 MPa and 290 °C, respectively.
nol (350 °C), with the main products being methyl
a- and b-D-gluco-
pyranoside.4 With the addition of acidic catalysts, a 50–60% yield of
methyl-D-glucopyranoside could be obtained with a relative mild
reaction condition (6220 °C).8,9 There was also a low yield (<10%)
of methyl levulinate (MLA) detected in the reaction. MLA is a widely
⇑
Corresponding authors. Tel.: +86 515 2949007; fax: +86 515 2942689 (J.F.);
tel./fax: +86 571 87952683 (X.L.).
E-mail addresses: jiefu@iastate.edu (J. Fu), luxiuyang@zju.edu.cn (X. Lu).
0008-6215/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2012.07.002

38
X. Wu et al. / Carbohydrate Research 358 (2012) 37–39
A pre-determined amount of cellulose was first added into the
than Fe2O3, CuO, and TiO2 possibly due to good solubility of PMA and
FeCl3 in methanol. Amberlyst 35W (A-35W) exhibited strong cata-
lytic activity because of the high density of the SO3H group in its
structure. The synthesis of dimethyl ether could be accelerated un-
der acid catalysis. Heteropolyacids and solid acids were more effec-
tive at catalyzing the dimethyl ether formation due to their Lewis
acidity, allowing them to easily accept the lone pair electron in the
nucleophilic oxygen atom in methanol.14 With the formation of
more dimethyl ether, the reactor pressure also increased, especially
when the reactor was cooled down because of decreased dimethyl
ether solubility in methanol.
batch reactor, followed by 10 mL of methanol solution containing
a certain amount of acid catalyst. The reactor was then sealed
and put into steel box furnace for pre-selected condition. These
experiments took place under the methanol saturation vapor pres-
sure at each reaction temperature. After a pre-set reaction time
period (allow extra reactor heating up time of 20 min), the reactor
was removed from the furnace and immediately placed in water to
quench the reaction.
An Agilent 1790 GC and an Agilent 6890 GC/5973 MSD were
used in quantifying the liquid samples from the cellulose catalytic
alcoholysis process. GC operation conditions were as follows: col-
Based on above analysis, both sulfuric acid and p-toluenesul-
fonic acid were very good catalysts for the cellulose alcoholysis
process. Sulfuric acid was inexpensive, therefore it was selected
as the catalyst of cellulose alcoholysis for further study.
umn with FFAP 30 m  0.32 mm  0.4
lm; Column temperature
at 90 °C; Inject temperature at 200 °C; Detector temperature at
200 °C. Quantification was achieved by comparing the peak area
to that of the internal standard, n-octanol. Reaction products were
identified through comparison of individual retention time with
those pure compounds’ standard solutions, and further confirmed
with GC–MS (Agilent 6890 GC/5973 MSD).
3.2. Kinetics study on cellulose alcoholysis to MLA
Microcrystalline cellulose is insoluble in methanol at room tem-
perature, so mass transfer resistance has a significant impact on
this solid–liquid reaction. However, production rates of MLA were
similar at different initial concentrations at a reaction temperature
of 170 °C and a sulfuric acid concentration of 0.02 mol/L (Fig. 2).
The results suggested that cellulose was rapidly decomposed to
methylated cellotriose, methylated cellobiose, and other oligosac-
charides which possessed a certain degree of solubility in methanol
at high temperature.4 Figures 3 and 4 illustrate the influence of sul-
furic acid concentration and reaction temperature on MLA yield,
respectively. The results showed the production rate and equilib-
rium yield (the average of almost invariant yields) of MLA were
dependent on sulfuric acid concentration and reaction tempera-
ture. As sulfuric acid concentration increased, equilibrium yield in-
creased from 27% (0.02 mol/L) to 32% (0.03 mol/L). In addition, the
equilibrium yield increased by 17% when the temperature rose
from 170 °C to 180 °C, which indicated the reaction temperature
had a more significant effect on the production of MLA than sulfu-
ric acid concentration. The highest MLA yield (55%) was achieved
at 190 °C for 5 h using 0.02 mol/L H2SO4 as the alcoholysis catalyst.
A literature survey4,8 indicated the cellulose decomposition
mechanism in near-critical methanol consists of two steps: the
conversion of cellulose to methyl-glucopyranoside by methylation,
followed by the degradation to MLA with the acid catalysis. To
determine which step is the rate limiting step, separate glucose
alcoholysis experiments were carried out at 170 °C with sulfuric
acid concentration of 0.02 mol/L. The results indicated that glucose
was completely consumed in near-critical methanol within the
first 10 min, and the reaction product was mainly methyl-glucopy-
ranoside. Therefore, the glucose alcoholysis process can be
The yield of MLA was calculated by the following formula: MLA
yield (%) = amount of the MLA (mol) produced/amount of C6H10O5
units in cellulose (mol) Â 100%.
3. Results and discussion
3.1. Catalytic activity of acid catalyst on alcoholysis of cellulose
Degradation of cellulose to small molecular compounds is an
acid-catalyzed process.7,8 Under a reaction temperature of 180 °C,
a reaction time of 4 h, and without using catalyst, an MLA yield
of only 3% was observed. The catalytic performances of various di-
lute inorganic and organic acids were tested. These acids included
sulfuric acid (H2SO4), p-toluenesulfonic acid (PTSA), phosphoric
acid (H3PO4), formic acid, and acetic acid, all with [H+] at
0.04 mol/L. Figure 1 shows the effect of inorganic and organic acid
catalysts on MLA yield. The results suggested that H2SO4 and PTSA
provided a significant MLA yield increase (both over 40%), while
only 7% yield was achieved by using H3PO4 as catalyst. The reason
is probably the relatively stronger acidity (pKa) of H2SO4 and PTSA
contributing to their higher catalytic activity.8 On the other hand,
the organic acids, such as formic acid and acetic acid were not that
effective as catalysts in cellulose catalytic alcoholysis process. It
has been reported that subsidiary reaction of acids esterification
with methanol at high temperature was the main reason.13
Several types of heteropolyacids and solid acids with a concen-
tration of 10 g/L were also examined and the results are summarized
in Figure 1. From the data, we concluded that phosphomolybdic acid
hydrate (PMA) and ferric trichloride (FeCl3) were much more active
60
50
40
35
30
25
20
30
20
15
10
20
10
5
30
10
0
10(GLU)
0
0
50
100
150
200
250
300
350
Time, min
Figure 2. Effect of initial microcrystalline cellulose concentration (g/L) on MLA
Figure 1. Effect of different acid catalysts on MLA yield.
yield.

X. Wu et al. / Carbohydrate Research 358 (2012) 37–39
39
45
40
process of cellulose to methyl-glucopyranoside more significantly
than methyl-glucopyranoside alcoholysis to MLA, and also improve
the reaction selectivity to methyl-glucopyranoside.
0.01
0.02
35
30
25
20
15
10
0.03
0.03(GLU)
4. Conclusion
Acid catalysts are essential for the cellulose alcoholysis process.
Various acids including inorganic acids, organic acid, and solid
acids were evaluated for their catalytic activities. Sulfuric acid
was determined to be the best catalyst overall with good catalytic
activity for the cellulose alcoholysis process. The highest MLA yield
of 55% was achieved using 0.02 mol/L H2SO4 as a catalyst at 190 °C
for 5 h. The results of the kinetic study on cellulose alcoholysis to
MLA suggested that reaction temperature had a great influence
on cellulose catalytic alcoholysis and the MLA formation rate. Sul-
furic acid concentration variations had greater impact on forma-
tion of methyl-glucopyranoside. The results provide insights on
an efficient and low-cost approach to produce MLA from cellulose.
5
0
0
50
100
150
200
250
300
350
Time, min
Figure 3. Effect of sulfuric acid concentration (mol/L) on MLA yield with 20 g/L
cellulose at 170 °C.
60
170
50
40
30
20
180
190
Acknowledgments
180 (GLU)
This work was supported by the National Natural Science Foun-
dation of China (No. 20976160, 21176218), and the National High
Technology Research and Development Program of China (863 Pro-
gram, No. 2012AA040211).
10
0
References
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200
250
300
350
1. Camacho, F.; Gonzalez-Tello, P.; Jurado, E.; Robles, A. J. Chem. Technol.
Biotechnol. 1996, 67, 350–356.
2. Elkins, J. G.; Raman, B.; Keller, M. Curr. Opin. Biotechnol. 2010, 21, 657–662.
3. Yanik, J.; Kornmayer, C.; Saglam, M.; Yüksel, M. Fuel Process. Technol. 2007, 88,
942–947.
Time/min
Figure 4. Effect of temperature on MLA yield at 0.02 mol/L H2SO4 and 20 g/L
cellulose.
4. Ishikawa, Y.; Saka, S. Cellulose 2001, 8, 189–195.
5. Bozell, J. J.; Petersen, G. R. Green Chem. 2010, 12, 539–554.
6. Huber, G. W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044–4098.
7. Minami, E.; Saka, S. J. Wood Sci. 2005, 51, 395–400.
8. Deng, W. P.; Liu, M.; Zhang, Q. H.; Tan, X. S.; Wang, Y. Chem. Commun. 2010, 46,
2668–2670.
9. Deng, W. P.; Liu, M.; Zhang, Q. H.; Wang, Y. Catal. Today 2011, 164, 461–466.
10. Yoshihiro, T.; Hiroyuki, H.; Atsushi, S.; Satoshi, Y.; Takeshi, F.; Katsuto, O. Ind.
Eng. Chem. Res. 2008, 47, 704–709.
11. Macdonald, S. F. Can. J. Chem. 1974, 52, 3257–3258.
12. Tominaga, K.; Mori, A.; Fukushima, Y.; Shimada, S.; Sato, K. Green Chem. 2011,
13, 810–812.
13. Pöpken, T.; Götze, L.; Gmehling, J. Ind. Eng. Chem. Res. 2000, 39, 2601–2611.
14. Blaszkowski, S. R.; Van Santen, R. A. J. Phys. Chem. B 1997, 101, 2292–2305.
regarded as alcoholysis of methyl-glucopyranoside. Compared to
glucose alcoholysis, MLA formation from cellulose is much slower
under the same reaction conditions of initial feed concentration
(Fig. 2) and reaction temperature (Fig. 4), which is mainly attrib-
uted to the shorter decomposition pathway of glucose alcoholysis.
However, the production rates of MLA were almost identical from
either cellulose alcoholysis (equilibrium yield of 43%) or glucose
alcoholysis (equilibrium yield of 44%) under the same sulfuric acid
concentration and the same reaction temperature. This phenome-
non indicated that sulfuric acid could accelerate the alcoholysis