Highly efficient conversion of microcrystalline cellulose to 5-hydroxymethyl furfural in a homogeneous reaction system

Article abstract of DOI:10.1039/c5ra22129c

The development of novel methods to obtain biofuels and chemicals from biomass has been an immediate issue in both academic and industrial communities. The present work introduces a new route to synthesize 5-hydroxymethyl furfural (5-HMF) in a one-vessel system through a tandem pathway involving decrystallization, depolymerization and conversion of microcrystalline cellulose (MCC) in a molten hydrate solution. A 71.62 wt% ZnCl₂ aqueous solution was employed as the reaction media and methylisobutylketone (MIBK) as the extracting solvent in the reaction system. A yield of 80.6 mol% of 5-HMF was obtained at 150 °C with a HCl concentration of 0.2 mol L^-1 in the solution for 40 min. The aqueous phase can be reused without significant loss of catalytic activity.

Full text of DOI:10.1039/c5ra22129c

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Highly efficient conversion of microcrystalline
cellulose to 5-hydroxymethyl furfural in
a homogeneous reaction system
Cite this: RSC Adv., 2016, 6, 21347
a
a
b
ab
Yan-Ru Zhang, Nan Li, Ming-Fei Li and Yong-Ming Fan*
The development of novel methods to obtain biofuels and chemicals from biomass has been an immediate
issue in both academic and industrial communities. The present work introduces a new route to synthesize
5
-hydroxymethyl furfural (5-HMF) in
decrystallization, depolymerization and conversion of microcrystalline cellulose (MCC) in a molten
hydrate solution. A 71.62 wt% ZnCl aqueous solution was employed as the reaction media and
methylisobutylketone (MIBK) as the extracting solvent in the reaction system. A yield of 80.6 mol% of
a one-vessel system through a tandem pathway involving
Received 22nd October 2015
Accepted 16th February 2016
2
DOI: 10.1039/c5ra22129c
ꢀ
ꢁ1
5
-HMF was obtained at 150 C with a HCl concentration of 0.2 mol L in the solution for 40 min. The
www.rsc.org/advances
aqueous phase can be reused without significant loss of catalytic activity.
well known that ionic liquids, DMF, and dimethyl sulfoxide
DMSO) are promising solvents in dissolving cellulose and have
1
. Introduction
(
13
In view of the irreversible consumption of fossil fuels and the been used as a reaction media in the production of 5-HMF.
serious concerns with global climate, lignocellulosic biomass, Despite their effectiveness toward 5-HMF production, ionic
14
as a renewable and sustainable resource, has received signi- liquids is too expensive to be used in commercial scale. DMSO
1
cant attention. So far, efforts have been devoted to chemical and DMF also have to face the similar challenges for the cost-
and biological conversion of lignocellulosic biomass into bio- liness in the separation of 5-HMF from the solvent due to their
2
fuels and chemicals.
high boiling point. Therefore, further studies are still necessary
Among a variety of biomass-derived chemicals, 5-hydrox- to develop new green systems for the conversion of natural
ymethyl furfural (5-HMF) has been regarded as an important cellulose into 5-HMF.
platform chemical which can be the substitute for
Zinc chloride hydrate has been considered a low-toxic and
petroleum-based building blocks in making polymers or other inexpensive solvent compared with ionic liquids in the disso-
3
15
materials and biofuels. As presented in Scheme 1, the subse- lution of cellulose. Lv et al. reported that 68 wt% ZnCl
quent transformation of 5-HMF into a multitude of high-value aqueous solution could dissolve cotton cellulose to prepare
2
16
added bio-based chemicals, such as 2,5-dimethyl furan homogenous solution. Lu and Shen found that ZnCl $4H O
2 2
4
5
(DMF),
2,5-furan dicarboxylic acid (FDCA),
5-chlor- (65.43 wt%) could be used as swelling agent for bacteria cellu-
6
7
omethylfurfural (CMF), 5-ethoxymethylfurfural (EMF), levu- lose while ZnCl
2
$3H
2
O (71.62 wt% ZnCl
2
) can efficiently
8
9
linic acid (LA) and g-valerolactone (gVL) has been explored dissolve bacteria cellulose with a maximal concentration of 5.5
using 5-HMF as a starting substrate.
wt% in the solution. This inexpensive solvent not only exhibits
There are emerging interests in producing 5-HMF from good solubility for celluloses, but also can promote the
biomass-based sugars and polysaccharides at present. Although conversion of glucose, fructose, maltose, sucrose, cellulose and
10
11
12
high yield of 5-HMF from pure fructose and glucose can be starch. Recently, attentions have been paid on zinc chloride
obtained, large scale and sustainable production of 5-HMF hydrate as a reaction media in the conversion of lignocellulosic
17
requires cellulosic biomass as the feedstock. But it is still materials. Wang et al. found that 21.9% of 5-HMF yield could
challenging to efficiently convert cellulose into 5-HMF because be obtained from GlcNH
of the rm crystal structure. Dissolution and depolymerization 120 C without co-catalyst. Deng et al. produced 40% of 5-HMF
2
in 67 wt% ZnCl
2
aqueous solution at
ꢀ
12
of cellulose could be the good choice to solve the problem. It is from carbohydrate using a two-phase system in concentrated
2
aqueous ZnCl solution.
In this work, an efficient conversion process for the
production of 5-HMF from cellulose in 71.62 wt% ZnCl2
a
MOE Engineering Research Center of Forestry Biomass Materials and Bioenergy,
Beijing Forestry University, Beijing, 100083, China. E-mail: fanym@bjfu.edu.cn; Tel:
aqueous solution with
a
low-boiling point solvent
+
b
86-185-15301003
methylisobutyl-ketone (MIBK) as organic phase was investi-
Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing,
gated, the effect of HCl concentration, reaction time,
1
00083, China
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Scheme 1 5-HMF production and its use for making many value added chemicals.
temperature and the reusing of aqueous phase on conversion 2.4 Analytical methods
was discussed.
The reaction sample was diluted with the eluent used for HPLC,
then the solid products, if present, were separated by centrifu-
gation and ltration. Sugars in aqueous layers were analyzed
with an Agilent Technologies HPLC system equipped with an
Aminex HPX-87H column (Biorad) and a refractive index (RI)
detector, and 0.005 M H SO as mobile phase with owing rate
of 0.5 mL min . Products in organic layers were analyzed by
HPLC equipped with a QuikSep UV-100D detector and an
Inertsil ODS-C18 column at 298 K, using methanol–water
2. Experimental section
2.1 Materials
Analytical grade ZnCl
2
, MIBK, MCC (DP ¼ 162), cotton ber
2
4
ꢁ
1
(
DP ¼ 1024), HCl (36.5%), glucose, fructose and 5-HMF were
purchased from Beijing ZKKA Biotechnology Co., Ltd. (Beijing,
China) and used without further purication. Deionized water
was used for all reactions.
(40 : 60) as eluents. The rate of conversion, yield, and selectivity
of the products were calculated as follows:
m
cellulose;t¼0 ꢁ mcellulose;t¼t
Conversion of MCC ð%Þ ¼
ꢂ 100%
2.2 The dissolution of cellulose
m
cellulose;t¼0
The dissolving process was observed under a polarizing
microscope (Leica DMLP; Leica Microsystems, Wetzlar, Ger-
ꢀ
many) equipped with a hot plate at 70 C. Cotton ber was used
m
HMF=126
Yield of 5-HMF ðmol%Þ ¼
ꢀ
ꢂ 100%
in the observation. The dissolution experiment of MCC was
conducted by charging 0.2 g of MCC into 5 mL of 71.62 wt%
m
cellulose;t¼0 162
ꢀ
ZnCl
2
aqueous solution in a 20 mL glass reaction bottle at 90 C.
m
HMF=126
Selectivity of 5-HMF ðmol%Þ ¼
ꢀ
ðmcellulose;t¼0 ꢁ mcellulose;t¼tÞ 162
2.3 Conversion of MCC into 5-HMF
ꢂ 100%
Reactions in homogeneous reaction system were conducted in
a 20 mL autoclave lined with Teon and heated in a tempera-
ture-controlled oil bath equipped with an electronically
controlled magnetic stirrer (Zhengzhou Great Wall Scientic
3
. Results and discussion
Industry and Trade Co., LTD). MCC solution (0.2 g) in 71.62 wt%
ꢀ
3.1 The solubility of cellulose in ZnCl aqueous
2
ZnCl
2
(9.8 g, 5 mL) was prepared at 90 C and then hydrochloric
acid was charged into autoclave to the preset concentrations. To make the dissolving process easy to be observed, cotton ber
The mixture was saturated with 0.5 g of NaCl. 10 mL of MIBK was employed. The pictures for the dissolving process in
was used as an extraction solvent. The mixture was heated to the 71.62 wt% ZnCl was recorded with a polarization microscope at
2
ꢀ
preset temperature and stirred at 1200 rpm. Aer reactions, the 70 C. As shown in Fig. 1, we can clearly see the whole cellulose
autoclave was immediately cooled to room temperature in the ber before the dissolution starting because the crystallized
water bath.
cellulose ber can reect the polarized light beam. Aer a while,
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for example, 35 s and 75 s, fractures could be found owing to its
decrystallization. Gradually, the light fade away, which signied
the complete dissolving of crystallized cellulose ber. This
process nished in couple of minutes for cotton ber. There-
fore, we have the reason to believe that MCC will also behave the
same way for the dissolution.
The dissolution process of MCC in 71.62 wt% ZnCl
2
was
ꢀ
observed at 90 C and shown in Fig. 2. The MCC suspension at
ꢀ
2
5 C (Fig. 2a) was turned into a transparent and viscous liquid
solution in the solvent system (Fig. 2b). This is correlated well
18
with the results in the literature. This indicates that 71.62 wt%
ZnCl is an effective solvent for cellulose, which will make the Fig. 2 The dissolution of MCC in 71.62 wt% ZnCl aqueous solution.
2
2
reaction system homogeneous.
promoted the dissolution of MCC, isomerization of hydrolyzed
glucose into fructose, and conversion to 5-HMF through acidic
catalyzed dehydration.
3
.2 Conversion of MCC into 5-HMF
It is generally accepted that three steps are required for the
conversion of cellulose to 5-HMF: (1) decrystallization and
hydrolysis of cellulose to glucose; (2) isomerization of glucose to
fructose; (3) dehydration of fructose to 5-HMF (Scheme 2). In
this work, 5-HMF was produced in a single step starting from
MCC solution in ZnCl
conditions on conversion was explored by varying concentration
of ZnCl , HCl concentration, reaction time and temperature.
As shown in Fig. 3, with the increase of the concentration of
ZnCl solution from 0 wt% to 71.62 wt%, 5-HMF yield increased.
We found that, without ZnCl in the system, only 31.3 mol% of
In this system, the Brønsted acid offered hydrogen ions
which catalyzed both the hydrolysis of MCC into glucose
1
9
20
monomer and the conversion to 5-HMF. The effect of the HCl
concentration on the conversion of 5-HMF was investigated and
the results were shown in Table 1. It indicated that the
concentration of hydrochloric acid played an important role in
2
aqueous solution. The effect of reaction
2
the conversion. Without HCl in the conversion system, only
ꢀ
2
8.5 mol% of 5-HMF yield was obtained aer 40 min at 150 C,
2
ꢁ1
while it increased to 80.6 mol% with 0.2 mol L
of HCl
2
concentration. However, excess use of HCl would deteriorate
the conversion. For example, the 5-HMF yield of 28.6 mol% was
5-HMF was yielded and trace amount of fructose was found. This
suggested the synthesis of 5-HMF mainly followed the mechanism
ꢁ1
obtained under 1 mol L of HCl concentration in the aqueous
2
0
directly from glucose, which was suggested in the report. ZnCl
as a Lewis acid catalyst, can catalyze the isomerization of aldoses
glucose) to ketose (fructose), which made acidic dehydration
2
,
phase even if the MCC was completely conversed (100%). This
suggested that high concentration of hydrogen ions will
promote the further decomposition of the 5-HMF, which will
increase the formation of humins and the production of levu-
(
21
catalyzed reactions more efficient for the production of 5-HMF.
For example, the yield of 5-HMF increased from 31.3 mol% to 43.1
mol% with 0 wt% and 10 wt% ZnCl respectively at 150 C in 60
min in this biphasic reaction system. 5-HMF yield of 80.6 mol%
could be obtained at 150 C in just 40 min with 71.62 wt% ZnCl in
the reaction system by using MIBK as extracting solvent, which was
higher than that reported 53% in ionic liquids. This suggests that
the production of HMF mainly follows the mechanism of acidic
dehydration of fructose. It can be seen in Fig. 3d that the
production of fructose in the system with high concentration is
much more than that with low concentration, which offered the
support for the expectation. In this homogenous reaction system
23
linic and formic acids.
ꢀ
2
The effect of reaction temperature on 5-HMF selectivity and
MCC conversion was investigated in this homogenous reaction
system (Fig. 4). 5-HMF selectivity of 54 mol% was observed at
ꢀ
2
ꢀ
1
40 C aer 40 min. 5-HMF selectivity of 81 mol% was obtained
22
ꢀ
when the reaction mixture was heated to 150 C. Over elevated
temperature would result in the rehydration of 5-HMF to form
levulinic acid and formic acid and accelerate the production of
23
humins.
The effect of reaction time on the conversion was investi-
gated under the optimized reaction temperature. As shown in
Fig. 3a, the yield of 5-HMF in 71.62 wt% ZnCl2 solution
with high concentrated ZnCl solutions, the formation of the
coordination between Zn and hydroxyl groups in cellulose chains
2
2+
2
Fig. 1 The dissolution of cotton fiber in 71.62 wt% ZnCl aqueous solution.
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Scheme 2 Schematic representation of cellulose conversion into 5-HMF with acid catalysts.
Table 1 Conversion of MCC to 5-HMF in biphasic system with various
a
hydrochloric acid concentrations
HCl loading
Yield
(mol%)
Conversion
(%)
Selectivity
(mol%)
ꢁ
1
Entry
(mol L
)
1
2
3
4
5
6
0
28.5
35.6
64.5
80.6
55.4
28.6
71.7
78.9
83.9
99.6
100
39.7
45.1
76.8
81.0
55.4
28.6
0.03
0.1
0.2
0.3
1.0
100
a
Reaction conditions: MCC, 0.2 g; ZnCl
0 mL; NaCl, 0.5 g; 150 C; 40 min.
2
, 71.62 wt%, 9.8 g (5 mL); MIBK,
ꢀ
1
2
To elucidate the effect of recycling of ZnCl aqueous solution
on the conversion in this biphasic reaction system, four
consecutive runs were carried out. First, the organic layer con-
taining the produced 5-HMF was removed. Then the aqueous
phase were centrifuged to separate humins before being reused.
Aer that, 0.2 g of MCC was charged into the recycled aqueous
ꢀ
phase and the dissolution of MCC was performed at 90 C and
5
min on a hot plate. Finally the fresh MIBK (10 mL) was
charged into the autoclave. The steps aerward followed the
method and conditions previously described. The results were
Fig. 3 Conversion of MCC into 5-HMF in ZnCl
conditions: MCC, 0.2 g; ZnCl , 5 mL (71.62 wt%, 9.8 g; 10 wt%, 5.49 g;
wt%, 5 g); MIBK, 10 mL; NaCl, 0.5 g; HCl concentration, 0.2 mol L
2
solution. Reaction
2
ꢁ1
0
;
ꢀ
1
50 C. ZnCl
wt%; b:
0 wt%,
2
concentration: a:
71.62 wt%, 10 wt%,
0 wt%; d: 71.62 wt%,
71.62 wt%,
0 wt%; c:
10 wt%,
10 wt%,
0
71.62 wt%,
0 wt%.
1
increased remarkably from 30.3 mol% to 80.6 mol% upon
increasing the reaction time from 20 min to 40 min. Aerward,
5
-HMF yield decreased gradually. This suggested that 5-HMF is
Fig. 4 Synthesis of 5-HMF from MCC at different reaction tempera-
an unstable product and subjected to the further conversion
into other products. Based on the overall yield of conversion,
the reaction time should be limited to about 40 min.
ture. Reaction conditions: MCC, 0.2 g; ZnCl
MIBK, 10 mL; NaCl, 0.5 g; HCl concentration, 0.2 mol L ; 40 min.
2
, 71.62 wt%, 9.8 g (5 mL);
ꢁ1
5-HMF selectivity;
conversion.
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This work was supported by Special Fund for Beijing Common
Construction Project, the Fundamental Research Funds for the
Central Universities (No. YX2015-01) and the Natural Science
Foundation of China (31110103902).
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