Development of Betaine-Based Sustainable Catalysts for Green Conversion of Carbohydrates and Biomass into 5-Hydroxymethylfurfural

Article abstract of DOI:10.1002/cssc.201802342

Renewable and sustainable betaine-based catalysts (BX) derived from the betaine sugar industry or ChCl were developed for the production of 5-hydroxymethylfurfural (HMF) from various carbohydrates. The HMF yields in the BX-based media reached up to 88 %, 66 %, 37 % and 53 %, for the conversion of fructose, glucose, cellulose, and lignocellulosic biomass, respectively. In addition, choline-O-sulfate was synthesized and demonstrated to be an efficient catalyst for the conversion of fructose to HMF. From the perspective of green and sustainable chemistry, this work demonstrates benefits not only in the preparation of sustainable catalysts but also the green production of HMF from biomass.

Full text of DOI:10.1002/cssc.201802342

Accepted Article
Title: Development of betaine-based sustainable catalyst for
green conversion of carbohydrates and biomass into 5-
hydroxymethylfurfural
Authors: Yunchao Feng, Mengzhu Li, Zhebang Gao, Xin Zhang,
Xianhai Zeng, Yong Sun, Xing Tang, Tingzhou Lei, and Lu Lin
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To be cited as: ChemSusChem 10.1002/cssc.201802342
Link to VoR: http://dx.doi.org/10.1002/cssc.201802342
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ChemSusChem
10.1002/cssc.201802342
Communication
Development of betaine-based sustainable catalyst for green
conversion of carbohydrates and biomass into 5-
hydroxymethylfurfural
Yunchao Feng , Mengzhu Li , Zhebang Gao ，Xin Zhang , Xianhai Zeng*[a,b,c], Yong Sun[a,b,c], Xing
[
a]
[a]
[a]
[a]
Tang[a,b,c], Tingzhou Lei , Lu Lin[a,b,c]
[d]
This work develops renewable and sustainable betaine-based
catalysts (BX), which are derived from betaine sugar industry or
ChCl, for the production of 5-hydroxymethylfurfural (HMF) from
various carbohydrates. In particular, in these BX-based medium,
HMF yields reached up to 88%, 66%, 37% and 53%, when
conversing fructose, glucose, cellulose and lignocellulosic biomass
respectively. In addition, choline-O-sulfate (ChOS) was synthesized
and demonstrated as an efficient catalyst for the conversion of
fructose to HMF. From the perspective of green and sustainable
chemistry, this work demonstrates green benefits not only preparing
sustainable catalysts but also demonstrating green production of
HMF from biomass.
Introduction
Betaine (1-carboxy-N,N,Ntrimethylmethanaminium inner
salt), obtained as a natural by-product of the sugar beet
industry, has been widely used as animal feed supplement,
Fig. 1 The process of catalyst synthesis and the conversion of carbohydrates
enzyme stabilizer, pharmaceutical intermediate, cationic
to HMF. BX including B-S ( HSO
p-CH (C )SO ¯ ).
4 6 5 3
¯ ), B-B ((C H )SO ¯ ) , B-Cl ( X=Cl¯ ), B-P
[
1]
surfactants and personal care ingredient . At present, with
the rapid development of the betaine sugar industry, the
(
3
6
H
4
3
[
2]
accumulation of betaine has been continuously increasing .
To explore new applications of betaine embodies the
concept of sustainable development, recently, it has been
used as a novel raw material to prepare bio-based ionic
derived from biomass and biodegradable. Furthermore, the
biomass-based catalysis processes are milder and less waste
[
6]
discharge (i.e., humins) than conventional ones .
Recently, biomass based carboxylic acids such as oxalic acid,
citric acid, malic acid and betaine hydrochloride are typically
used as the biomass-based catalysts for the dehydration
2
liquids or as catalysts for hierarchical reduction of CO with
amines and hydrosilane or as a co-catalyst for biomass
valorization [ . In this work betaine was developed as a
biodegradable, harmless and cheap catalyst for the efficient
2-3]
[
7]
carbohydrates to HMF . These studies on HMF production were
mainly focus on costly fructose, which is a typical high-yield
feedstock for HMF production in the industrial scale. However,
dehydration
hydroxymethylfurfural (HMF).
HMF is versatile bio-based platform compound for
of
various
carbohydrates
to
5-
glucose is the principal candidate for this purpose with distinctive
a
advantages in sources and prices[
4d, 8]
. Furthermore, limited
synthesizing a series of value-added chemicals, especially for
transportation fuels and bulk polymer monomers, which can
transform the unsustainable economy based on fossil resources
studies has been conducted using cellulose and lignocellulosic
biomass as starting materials to produce HMF, yet they are the
most widely distributed and cheapest sources of carbohydrates,
[
4]
to a sustainable one based on renewable biomass . HMF is
mainly produced by the acid-catalyzed dehydration of
carbohydrates[ . In the prior art, catalysts for the dehydration of
carbohydrates to HMF are usually corrosive inorganic acids
and particularly, inedible resources[
5d, 9]
. With a view to the
present and future, performing a systematic study of the
conversion of various carbohydrates to HMF would be significant
for sustainable development.
In this work, we mainly prepared several betaine-based
renewable and sustainable catalysts for the conversion of
carbohydrates to HMF (Fig. 1). These catalysts, denoted by BX
4c]
(
such as hydrochloric acid, sulfuric acid, etc.), solid acid
catalysts with complicated preparation process and high cost, or
other metal catalysts with hazardous and environmentally
[5]
undesirable processes . Therefore, it is pressing to explore new
sustainable and renewable catalysts that are in line with the
concept of green chemistry to catalyze carbohydrates to prepare
HMF. In this case, biomass-based catalysts stand out as being
(
BX=B-B, B-P, B-S, B-Cl), were formed through the reaction of
the anhydrous betaine with Brønsted acids. Among BX, B-Cl
also can be directly obtained from beet. The conversion of
fructose to HMF using various betaine-based catalysts and the
mechanisms of reaction was evaluated. Moreover, the
coordination and activation of biomass-based co-catalyst ChCl
and the catalytic reactivity of CHOS was tested. Furthermore,
the reactivity of these catalysts was further studied for the
cheaper and more abundant glucose, cellulose and
lignocellulosic biomass, in combination with safe, recyclable and
inexpensive metal chlorides. It is expected that this research
would help promote the development of biomass-based
catalysts as a new direction for green chemistry.
[
a] Y. Feng, Meng. Li, Z Gao , X. Zhang, X. Zeng, Y Sun, X Tang, L Lin
College of Energy, Xiamen University, Xiamen 361102, China
E-mail: xianhai.zeng@xmu.edu.cn
[
[
[
b] X. Zeng, Y Sun, X Tang, L Lin
Fujian Engineering and Research Center of Clean and High-valued
Technologies for Biomass, Xiamen 361102, China
c] X. Zeng, Y Sun, X Tang, L Lin
Xiamen Key Laboratory of Clean and High-valued Utilization for Biomass,
Xiamen 361102, China
d] T. Lei
Henan Key Lab of Biomass Energy, Huayuan Road 29, Zhengzhou, Henan
450008, China
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ChemSusChem
10.1002/cssc.201802342
Communication
Results and Discussion
HMF was prepared with a classical biphasic reaction system,
where 0.15 g of fructose, 0.5 mL of deionized water, and 5 mL
of methyl isobutyl ketone (MIBK) were mixed in the sealed
environment in the presence of BX (0.05~ 0.25 g), subsequently
o
heated at 130 C for 60 min. HMF was extracted by MIBK and
quantified by GC. It can be seen from Fig. 2 that the HMF yield
firstly increased and then decreased with the increasing BX
content, with the maximum yields of 66%, 68%, 69% and 66%,
corresponding to B-S, B-B, B-Cl and B-P, respectively (Fig. 2).
Thus, it is demonstrated that the BX catalysts were efficient for
the dehydration of fructose to HMF. The lower amount of BX led
to a partial conversion of fructose while higher amount catalyst
resulted in the formation of byproducts, such as levulinic acid[10]
It must be noted that the catalyst dosages were different (B-S:
.1, B-Cl: 0.15, B-B: 0.15, B-P: 0.2) when the HMF yields
.
0
reached a maximum (Fig. 2). This difference may be ascribed to
their different acidities. Thus, the pH values (Table 1) of BX
solutions were tested. The expected acidity sequence (strong-to-
weak) of BX is B-S, B-Cl, B-B and B-P, which agreed with the
experimental results. The proposed mechanism was shown in
Fig. 3 Dehydration of fructose to HMF in BX/ChCl/H
2
O/MIBK systems.
Reaction conditions: fructose
=
0.15g,
H
2
O
=
0.5mL, MIBK 5mL,
=
temperature = 130 oC, time =60 min. ChCl: Vacuum drying for 12h.
-
+
3 3 2
Scheme 1, both anion (X ) and cation ((CH ) NCH COOH) )
played a key role in this process and they may have a
synergistic effect on the HMF yield. Firstly, due to the vigorous
stirring condition and the hydrogen bonding interactions between
Scheme 2 The proposed mechanism of stabilizing HMF by ChCl.
+
fructose and BX, the cation produced H (Scheme 1, route A),
which catalyzed fructose dehydration promoted by anion. Then,
BX would be formed immediately (Scheme 1, route B) with the
stronger acid HX. It has been reported that HMF yield was
influenced by anion, which participates in hydrogen bonds with
hydroxyl group of carbohydrates[ , while H dissociates from
cation to catalyze the formation of HMF. Cl¯ prefers to form
strong hydrogen bonds bridging structure OH…Cl…HO between
two adjacent –OH in fructose[ . So Cl¯ has stronger hydrogen
11]
+
12]
bonds formation ability than HSO
CH (C )SO ¯. In addition, Dumesic et.al.
that the partition coefficient (the ratio of the HMF
4
¯, CH
3
(C
6
13]
H
5
)SO
3
¯ and p-
[
3
6
H
4
3
also suggested
R
concentrations in the organic and aqueous phases) varies with
different anion. So, the effect of anion on the partition coefficient
R in biphasic systems was tested (Table 1). The sequence (high-
Fig. 2 Dehydration of fructose to HMF in BX-H
2
O/MIBK systems.
Reaction conditions: fructose = 0.15g, H
2
O = 0.5mL, MIBK = 5mL,
o
6 5 3 4 3 6 4 3
to-low) of R is Cl¯, (C H )SO ¯, HSO ¯ and p-CH (C H )SO ¯,
temperature = 130 C, time =60 min.
which was accorded with the experiment results when the BX
content was 0.15g (Fig 2). To further demonstrate the high
activity of BX, we investigated the dehydration of fructose with
inorganic or carboxylic acids in the identical conditions (Table
S1). It can be seen that the HMF yields were significantly lower
Scheme 1 The synergistic effect between anion and cation of BX in the
catalytic dehydration of fructose.
Table 1 pH value of BX in water and the effect of anion on the partition
coefficient R in biphasic systems
BX
Anion
B-S
B-B
)SO
0.72
4.3
B-Cl
Cl¯
0.68
6.5
B-P
(C
1.1
1.4
HSO
0.55
3.5
4
¯
(C
6
H
5
3
¯
p-CH
3
6
H
4 3
)SO ¯
a
pH
Rb
a
O. b Condition: 0.15g of BX, 0.5mL of
2
Fig. 4 Recycling of the B-S/H O/CHCl system
Condition: 0.15g of BX, 0.5mL of H
O, 4.5mL of MIBK.
2
H
2
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ChemSusChem
10.1002/cssc.201802342
Communication
than that of BX, which may attribute to their properties of weak
stronger than that between ChCl and fructose, which can
stabilize HMF by reducing susceptibility to nucleophilic attack
and minimizing undesirable hydration and humin-formation
reactions of HMF (Scheme 2). However, at higher ChCl
concentrations, more HMF remained in the reaction phase due
to strong molecular interaction between ChCl and produced
HMF. Therefore, the partition coefficient R became smaller, more
side reactions likely occurred and the HMF yield dropped as a
result. Therefore, the trend of initial increase in yield followed by
decline in yield of HMF was observed.
acidity (HCOOH, CH
3
COOH), Soluble in MIBK (HCOOH,
(C H4)SO H, (C6H5)SO H) and
CH COOH, SO p-CH
3
H
2
4
,
3
6
3
3
volatilization (HCl). These experiments suggested that the
synergic interactions between the anion and cation played an
important role in determining the high activity of BX in
dehydration of fructose. Moreover, compared with other
conventional Brønsted acids, BX stands out for the nature of
solid salt and immiscible with MIBK, which could be recycled by
evaporation or crystallization (Fig. S1 and S2).
Considering that the BX/ChCl/H
directly after HMF extracted with MIBK, recyclability of the
reaction phase was investigated. Herein, B-S as a
representative BX was used in the recycling experiments. As
shown in Fig. 4, HMF yield in Run 2 was more than that in Run
2
O mixture can be reused
Table 2 Synthesis of HMF from fructose by ChOS
c
Entry
Catalyst, g
ChOS, 0.05
ChOS, 0.1
ChOS, 0.15
ChOS, 0.2
ChOS, 0.15
ChOS, 0.15
Co-catalyst, g
Molar yield , %
1
2
3
4
5
6
0
22
45
62
61
64
65
0
1
due to the residual HMF and fructose in reaction phase. Note
0
0
that after 6 Runs, the HMF yields started to decline because of
the unavoidable accumulation of humins in the reaction medium.
It is worth noting that betaine can be also synthesized by the
NaCl, 0.2
b
ChCl , 0.2
a
b
Reaction conditions: fructose = 0.15g, H
2
O = 0.5mL, MIBK = 5mL.
O/MIBK systems a
x 2
Table 3 Dehydration of glucose to HMF in BX-MCl -H
ChCl: Vacuum drying for 12h. c Molar yield, based on GC analysis (external
d
Molar yield , %
standard).
metal chloride b,
pH c
Time,
min
Entry
B-Cl,g
g
HMF
LA
1
2
3
4
5
6
7
8
9
0.15
---
---
1.64
3.3
20
20
20
20
20
60
60
20
20
30
30
120
120
20
20
20
3
<4
<4
<4
4
CuCl
CuCl
2
.2H
.2H
2
O
O
O
O
19
22
26
29
4
0.15
---
2
2
0.55
1.55
0.5
FeCl
FeCl
3
.6H
.6H
2
2
0.15
---
3
5
MgCl
MgCl
2
.6H
.6H
2
O
3.76
0.65
0.57
0.41
1.72
0.58
0.67
0.67
0.58
0.63
0.65
<4
<4
10
12
<4
<4
5
0.15
---
2
2
O
26
27
25
58
64
37
39
14
12
18
SnCl
SnCl
4
.5H
.5H
2
O
0.15
---
4
2
O
10
11
12
13
14
15
16
AlCl
AlCl
NiCl
3
.6H
2
O
O
0.15
0.15
0.15
0.15
0.15
0.15
3
.6H
2
2 2
.6H O
LaCl
3
.nH
2
O
<4
<4
<4
<4
Scheme 3. Possible mechanism of dehydration of fructose to HMF by
ChOS
CaCl2.2H
2
O
MnCl
CoCl
2
.4H
2
O
ChCl,
a low-cost, biodegradable and safe quaternary
2
.6H
2
O
ammonium salt, also can be extracted from biomass, has the
ability to form a deep eutectic solvent (DES) system when
a
2
Reaction conditions: glucose = 0.9g, H O = 3mL, MIBK = 30mL, Temperature
= 170℃. metal chloride:1/6 the mass of glucose. c pH test: reaction phase. d
Molar yield, based on GC analysis (external standard).
b
combined with hydrogen donors such as carboxylic acids,
alcohols, and hexoses[14]. Therefore, ChCl-based DES systems
[
7a, 7b]
[15]
such as ChCl/oxalic acid, ChCl/citric acid
, ChCl/fructose
oxidation of ChCl in the presence of base[1c] (Scheme S2(1)),
which is another promising route to obtaine biomass-based
betaine. Whilst, it was also found that mixing ChCl with
concentrated sulfuric acid gives choline-O-sulfate (ChOS,
Scheme S2(2) ), which is widely distributed in plant species and
tissues[ . In this content, ChOS was prepared and applied for
the first time for the dehydration of fructose to HMF (Table 2).
This was perhaps the first attempt using ChOS as a catalyst.
Generally, the dehydration of fructose to HMF involves the use
of a Brønsted acid, and CHOS has no acid sites. Interestingly,
moderate to good HMF yields were obtained in a CHOS-based
biphasic system, ranging from 22% to 65% (Table 2, HMF was
identified by GC-MS, Fig. S3). Furthermore, CHOS is insoluble
in ethanol, even if 50% of concentration. So, ChOS can be
easily recycled and reused. The possible mechanism involved
for the dehydration of fructose to HMF was discussed (Scheme
and ChCl/glucose[16]
,
had been gradually studied, which
consuming significant amounts of ChCl. In an attempt to further
enhance the HMF yield, we investigated the effect of ChCl on
dehydration of fructose in ChCl aqueous solution (CAS), which
was applied for the first time for biomass valorization as we
knew so far (Fig. 3). For comparison, typical addition of NaCl,
was also investigated (Seeing Table S2). It was found that ChCl
as an additive significantly enhanced the HMF yield when
compared to BX alone and BX with NaCl. The results showed
that with increase in the amount of ChCl, the yield of HMF
initially improved and then slightly dropped. The maximum yields
were 87%, 85%, 85% and 88%, corresponding to B-S, B-B, B-Cl
17]
and B-P, respectively. The role of ChCl was similar to that of
NaCl in the dehydration of fructose, i.e., the key was Cl-
(
Scheme
S1).
In
addition,
the
reaction
phase
“
fructose/BX/H
2
O/ChCl” is a deep eutectic mixture, so there
3
), the catalytic performance of ChOS might stem from the
were complex intermolecular hydrogen-bonding interactions
involved.[
14]
valence unsaturation of S and the anion of O, which is
consistent with the catalytic mechanism of dehydration of
fructose by dimethyl sulfoxide (DMSO)[ . The sulfur atom of
Higher HMF yield was achieved when using ChCl
than NaCl as an additive, probably as the intermolecular
hydrogen-bonding interaction between ChCl and HMF was
18]
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ChemSusChem
10.1002/cssc.201802342
Communication
Table 4 Dehydration of glucose to HMF in BX or ChCl-AlCl
3
-H
2 3
OAlCl /MIBK
LaCl
CoCl
3
.nH
2
O. Furthermore, CaCl2.2H
2
O, MnCl
2
.4H
2
O
and
a
systems
2
.6H
2
O were also investigated as catalysts, and they
b
Molar yield , %
HMF
58
65
66
54
69
54
Entry
BX or ChCl, g
provided HMF yields of 14%, 12% and 18%, respectively. Note
that the effect of BX content and reaction time was described in
Table S3.
Next, other BX derivatives were also investigated for the
3 2
dehydration of glucose in the presence of AlCl .6H O (Table 4).
Large differences in activity were observed. With the addition of
B-B or B-P, the HMF yield improved from 58% to 65% and 66%,
respectively. However, the introduction of B-S led to a significant
decrease in HMF yield and a substantial increase in LA yield.
These results are likely due to the higher acidity of B-S when
compared to B-B and B-P. It can be concluded that an
LA
<4
<4
<4
8
<4
7
5
1
2
3
4
5
----
B-B
B-P
B-S
ChCl
ChCl
ChCl
b
6
c
7
70
a
Reaction conditions: glucose = 0.9g, BX or ChCl = 0.15g, H
30mL, Temperature = 170℃, Time = 30min, AlCl .6H O = 1/6 the mass of
glucose. Time = 60min. c ChCl = 0.45g. Molar yield, based on GC analysis
external standard).
2
O = 3mL, MIBK
=
3
2
b
b
(
appropriate augment in acidity to the biphasic system of AlCl
3
-
ChOS with respect to the hydroxyl oxygen of fructose is crucial
in the process of the ChOS-catalyzed dehydration of fructose to
HMF.
Compared to fructose, glucose is more attractive mainly
because of its low price, natural abundance and availability.
Hence, HMF produced from glucose was investigated. The
formation of HMF from glucose involves two steps, the
isomerization of glucose to fructose and the dehydration of
H
2
O/MIBK play a crucial role in conversion of glucose to HMF.
-
Considering that the introduction of Cl can also decrease the pH
of aqueous solution and ChCl can stabilize the HMF by
hydrogen-bond interaction, biomass-derived ChCl was also
selected as a catalyst. As expected, High HMF yield of 70% was
achieved in H
2
O/MIBK biphasic system (Table 4, entry 7), which
would be a promising way for the large-scale production of HMF.
glucose and fructose, which requires the presence of both Lewis
and Bronsted acid sites[19]. So, we sought to convert glucose to
Table 6 Dehydration of lignocellulosic biomass to HMF in BX-H
2
3
O/AlCl /MIBK
systems a
x
HMF combining BX and Lewis acid metal chlorides (MCl :
b
Molar yield , %
CuCl
NiCl
CoCl
2
.2H
.6H
.6H
2
O, FeCl
O, LaCl
3
.6H
2
O, MgCl
.nH O,
2
.6H
CaCl2.2H
2
O, SnCl
4
.5H
2
O, AlCl
MnCl
3
.6H
.4H
2
O,
O,
Entry
Biomass, g
BX
2
2
3
2
2
O,
2
2
HMF
Furfural
2
2
O).The carboxyl groups of BX are typical Bronsted
1
2
Bamboo powder
Bamboo powder
Bamboo powder
Bamboo powder
Bamboo powder
Corn stover
Corn stover
Corn stover
Corn stover
Corn stover
Wheat straw
Wheat straw
Wheat straw
Wheat straw
Wheat straw
Rice straw
--
26
37
40
41
39
31
48
52
53
52
27
36
42
43
41
38
47
48
51
51
47
53
59
59
55
39
45
51
52
52
33
38
42
43
43
47
55
61
64
66
acid, which can promote the dehydration of fructose to HMF or
the rehydration of HMF to LA[20]. Herein, B-Cl was also
investigated as a representative BX as it can be directly from
beet. In the absence of Lewis acid, HMF yield was only 3%
B-Cl
B-B
B-S
B-P
--
3
4
(
Table 3, entry 1), which clearly demonstrated that BX have no
obvious catalytic activity for glucose dehydration. The HMF
yields of 19%, 26%, 4%, 27% and 58% (Table 3, entries 2, 4, 6,
5
6
8
, and 10) were obtained in the presence of CuCl
2
.2H
.6H
2
O,
O,
7
B-Cl
B-B
B-S
B-P
--
FeCl .6H O, MgCl .6H O, SnCl .5H and AlCl
3
2
2
2
4
2
O
3
2
respectively. The addition of B-Cl resulted in an increase in HMF
yield when CuCl .2H O, FeCl .6H O and AlCl .6H O were used
as the catalysts. Moreover, a significant raise in yield from 4% to
6% (Table 3, entries 6-7) was also obtained using B-Cl and
MgCl .6H O, which is nearly 7.5 times the HMF yield obtained
8
2
2
3
2
3
2
9
2
10
2
2
1
1
2
without B-Cl. This vast improvement might be attributed to the
decrease in pH upon the addition of B-Cl (pH=0.65 versus 3.76)
and the increase in the number of Bronsted acid sites of
1
B-Cl
B-B
B-S
B-P
--
13
MgCl
dehydration of fructose and glucose to HMF. However, the HMF
yield showed decrease (Table 3, entries 8-9) when
SnCl .5H O was used as the catalyst with B-Cl as the additive.
This result might be due to the strong acidity of SnCl .5H O in
2
.6H
2
O
aqueous solution, which can promote the
1
4
5
1
a
4
2
16
4
2
1
7
8
Rice straw
B-Cl
B-B
B-S
B-P
aqueous phase (pH=0.57) and the fact that excess acid favors
the formation of LA. Moderate HMF yields of 37% and 39%
1
Rice straw
were obtained with B-Cl in the presence of NiCl
2
.6H
2
O and
19
Rice straw
Table 5 Dehydration of microcrystalline cellulose to HMF in BX-
20
Rice straw
a
H
2
O/AlCl
3
/MIBK systems
a
b
2
Reaction conditions: biomass = 0.45g, BX=0.1g, H O = 3mL, MIBK = 30mL,
BX
content, g
Molar yield , %
Entry
BX
Time, g
O = 1/3 the mass of glucose. b
Temperature = 180℃, Time = 30min, AlCl .6H
3 2
HMF
LA
<4
<4
6
1
2
---
B-Cl
B-Cl
B-Cl
B-Cl
---
---
30
30
30
60
30
30
30
30
30
30
30
28
35
37
33
22
22
30
35
37
38
24
Molar yield, based on GC analysis. Yields of HMF from bamboo powder, corn
stover, wheat straw and rice straw were based on hexose contents of 41%,
0.1
35%, 39%, and 35% by weight, respectively. Yields of furfural were based on
3
0.15
0.15
0.45
---
pentose contents of 28%, 27%, 37% and 23% by weight, respectively
(external standard) (1 mol hexose units = 162g, 1 mol pentose unit=132g).
4
13
15
<4
6
5
6 c
7 c
8
Cellulose is a promising raw material for the production of
HMF due to its low-cost, easy availability and inedible nature.
For this purpose, we firstly tested B-Cl additive in the presence
B-Cl
B-S
0.15
0.15
0.15
0.15
0.15
--
9
B-B
--
of AlCl
As expected, when the B-Cl content of 0.15g was added to the
AlCl -H O/MIBK biphasic system, the yield of HMF was
3 2
.6H O for the dehydration of microcrystalline cellulose.
1
0
B-P
ChCl d
--
11
<4
3
2
a
Reaction conditions: microcrystalline cellulose = 0.9g, H
2
O = 3mL, MIBK =
significantly improved from 28% to 37% (Table 5, entries 1, 3).
Hence, our biphasic system with B-Cl as additive is effective for
hydrolyzing microcrystalline cellulose. However, upon prolonged
reaction time, the HMF yield started to decrease and the
3
0mL, Temperature = 170℃, AlCl ·6H
3
2
O = 1/6 the mass of glucose. b Molar
yield, based on GC analysis (external standard) and hexose units (1 mol
c
hexose units = 162g). Microcrystalline cellulose was obtained by ball-milling.
d
Compared to BX
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ChemSusChem
10.1002/cssc.201802342
Communication
formation of LA clearly augmented from 6% to 13% (Table 5,
entries 3, 4). When the content of B-Cl was further increased
(
received. Lignocellulosic biomass was collected from the countryside
(
Xiamen, China). The general composition of lignocellulosic biomass
[
24]
considered in this work was based on published values
.
Table 5, entry 5), the HMF yield also declined, which was
Typical procedures for the synthesis of BX and CHOS
similar to the results obtained with glucose. Other additives,
such as B-S, B-B, and B-P were also studied, and they
displayed promising HMF yields of 35%, 37% and 38%,
BX: All betaine-based catalysts were prepared through a modified
[2]
version of the original method described by Journoux et al. . In this
modified procedure, betaine was mixed with 1.4 (mol) eq. of acid and
stirred for 2 h at room temperature (for p-toluenesulfonic acid, a small
amount of deionized water was added). Then, the obtained material was
washed three times with absolute ethanol. The product was further
purified by recrystallization using deionized water and absolute ethanol.
[
21]
respectively (Table 5, entries 8, 9, 10). Liu et al. reported that
the crystalline index of microcrystalline cellulose was decreased
after pretreatment processes such as ball-milling. Therefore, the
reactivity of microcrystalline cellulose after ball-milling was also
investigated here. The ball-milled microcrystalline cellulose
provided HMF yields of 22% and 30% (Table 5, entries 6-7),
which were lower compared to the microcrystalline cellulose
without pretreatment. This result suggests that the lower
crystalline index of microcrystalline cellulose does not increase
the yield of HMF, but adding B-Cl in this system can indeed
improve the HMF yield. It is noteworthy that the addition of ChCl
led to a decrease in HMF yield. This was probably because the
solubility of microcrystalline cellulose decreased in the presence
of DES system, which was formed by hydrogen-bond donors
o
Finally, the resulting white solid was filtered and dried at 60 C for 6 h.
2 4
CHOS: CHOS was prepared from ChCl and H SO using a modified
[25]
version of the original method of Stevens et al . After crystallization
from an ethanolic solution, the product was further purified by
recrystallization using deionized water and absolute ethanol. The
o
obtained white solid was filtered and dried at 60 C for 6 h.
Synthesis of HMF from fructose
In a typical experiment, 0.15 g of fructose, 0.5 mL of deionized water,
0.15 g of BX, 0.15 g of ChCl and 5 mL of MIBK were added into a 15 mL
glass bottle equipped with a Teflon screw top (Beijing Synthware Glass),
o
and heated at 130 C for 60 min (see the individual tables for specific
reaction conditions). The organic phase containing HMF was removed
and the aqueous phase was extracted with MIBK (2mL×3). The organic
phases was combined and analyzed by GC.
and acceptors such as ChCl, AlCl3.6H
2 2
O, H O and the produced
glucose, fructose and HMF[14a, 22]
.
Encouraged by all the above results, we then proceeded to
convert lignocellulosic biomass directly into HMF and furfural,
which would be a more cost-effective process. The yields of
HMF from bamboo, corn stover, wheat straw and rice straw were
Synthesis of HMF from glucose
In a typical experiment, 0.9 g of glucose, 3 mL of deionized water, 0.15
g of BX, 0.15 g of AlCl .6H O and 30 mL of MIBK were added into a 120
3 2
mL glass bottle equipped with a Teflon screw top (Beijing Synthware
o
Glass), and heated at 170 C for 30 min (see the individual tables for
2
6%, 31%, 27% and 38%, respectively, and the corresponding
furfural yields were 47%, 39%, 33% and 47% (Table 6, entries 1,
, 11, and 16). The yields of HMF from lignocellulosic biomass
were similar to the result (Table 5, entry 2) obtained from
microcrystalline cellulose in AlCl -H O/MIBK biphasic system,
specific reaction conditions). The organic phase containing HMF was
removed and the aqueous phase was extracted with MIBK (2mL×3). The
organic phases was combined and analyzed by GC.
Synthesis of HMF from microcrystalline cellulose
In a typical experiment, 0.9 g of microcrystalline cellulose, 3 mL of
6
3
2
deionized water, 0.15 g of BX, 0.15 g of AlCl
were added into a 120 mL glass bottle equipped with a Teflon screw top
3 2
.6H O and 30 mL of MIBK
and also agreed well with previous reports of HMF synthesis
from lignocellulosic biomass[5d, 23]. The structure of biomass is
o
(Beijing Synthware Glass), and heated at 170 C for 30 min (see the
more complex than that of microcrystalline cellulose. However,
the other biomass components, such as protein and lignin, are
not involved in reactions. By adding various BX catalysts, such
as B-Cl, B-B, B-S, and B-P, the yields of HMF and furfural were
improved by as much as 10%-20% and 5%-10%, respectively,
depending on the source of lignocellulosic biomass. Interestingly,
the HMF yields obtained from biomass were higherthan that
obtained from microcrystalline cellulose. This difference may be
attributed to the ratio of catalysts to hexose contents. That is,
higher ratio results in higher HMF yield. In summary, our BX-
individual tables for specific reaction conditions). The organic phase
containing HMF was removed and the aqueous phase was extracted with
MIBK (2mL×3). The organic phases was combined and analyzed by GC.
Synthesis of HMF from lignocellulosic biomass
In a typical experiment, 0.45 g of lignocellulosic biomass, 3 mL of
deionized water, 0.15 g of BX, 0.15 g of AlCl
3 2
.6H O and 30 mL of MIBK
were added into a 120 mL glass bottle equipped with a Teflon screw top
o
(
Beijing Synthware Glass), and heated at 180 C for 30 min (see the
individual tables for specific reaction conditions). The organic phase
containing HMF was removed and the aqueous phase was extracted with
MIBK (2mL×3). The organic phases was combined and analyzed by GC.
Product analysis
3 2
AlCl -H O/MIBK biphasic system provides high yields of both
HMF and furfural, and it is expected that higher yields can be
obtained in future studies.
HMF, LA and furfural were identified qualitatively by a Thermo-Fisher
Trace 1300 & ISQ LT GC–MS instrument equipped with a TR-5MS
column (15.0 m × 250 μm × 0.25 μm) and quantified by an Agilent 7890A
GC equipped with a DB-WAXetr column (30.0 m × 0.25 mm ×0.25 μm)
o
and a flame ionization detector (FID) which was operated at 270 C. In
this work, each experiment was tested at least for two times, and the
experiment results were all mean values. The yields of products were
calculated as follows:
Conclusions
(
1) Fructose and glucose as raw materials
Renewable and sustainable betaine-based catalysts (BX)
were prepared for the production of HMF from various
carbohydrates and biomass. We report here that fructose can be
HMF yield = moles of HMF produced/moles of starting materials
LA yield = moles of LA produced/moles of starting materials
2) Microcrystalline cellulose and lignocellulosic biomass as raw
(
materials
HMF yield = moles of HMF produced/moles of starting hexoses
conveniently dehydrated to HMF in
a BX-based biphasic
reaction system. The introduction of ChCl can significantly
improve the HMF yield. In addition, CHOS was also synthesized
and employed as a catalyst for the first time for the dehydration
of fructose to HMF. Moreover, satisfactory HMF yields were
attained from glucose, microcrystalline cellulose and biomass in
biphasic system with appropriate Bronsted acids (BX). From the
perspective of green and sustainable chemistry, this work
LA yield = moles of LA produced/moles of starting hexoses
Furfural = moles of furfural produced/moles of starting pentoses
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant Nos. 21506177; 21676223), the
Fundamental Research Funds for the Central Universities (Grant
Nos. 20720160087; 20720160077; 20720170062), and the
Natural Science Foundation of Fujian Province of China (Grant
No. 2016J01077), the Energy Development Foundation of the
College of Energy, Xiamen University (No. 2017NYFZ02).
provides
a promising approach for using biomass-derived
catalysts for biomass valorization effectively.
Experimental Section
Materials
HMF, LA and furfural were purchased from Sigma-Aldrich (St. Louis,
USA). Fructose, glucose, ChCl, and betaine were supplied by Aladdin
Chemical Technology Co. Ltd. (Shanghai, China). Microcrystalline
cellulose and other chemicals were purchased from Sinopharm Chemical
Reagent Co. Ltd. (Shanghai, China). All chemicals were used as
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ChemSusChem
10.1002/cssc.201802342
Communication
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