Efficient conversion of biomass-derived furfuryl alcohol to levulinate esters over commercial α-Fe2O3

Article abstract of DOI:10.1039/c5ra24319j

An efficient process for the production of levulinate esters from biomass-derived furfuryl alcohol in liquid alcohol over commercial α-Fe₂O₃ was firstly investigated. Among the catalysts we tested, α-Fe₂O₃, a cheap, commercially available and environmentally benign catalyst, exhibited a remarkable catalytic performance for the transformation and gives levulinate esters in good yield compared to the previous studies. The corresponding esters such as methyl levulinate, ethyl levulinate and butyl levulinate were obtained in high yields under optimized reaction conditions. Several influence factors for the formation of levulinate esters were also discussed. A plausible reaction mechanism for the formation of levulinate ester from furfuryl alcohol was proposed. From the viewpoint of practice and economy, the present study provides a potential application for the efficient synthesis of fine chemicals from biomass-derived compounds over cheap, commercially available and environmentally benign catalysts.

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Efficient conversion of biomass-derived furfuryl alcohol to
levulinate esters over commercial α-Fe2O3
Received 00th January 20xx,
Accepted 00th January 20xx
Dezhang Ren, Jun Fu, Lu Li, Yunjie Liu, Fangming Jin and Zhibao Huo*
An efficient process for the production of levulinate esters from biomass-derived furfuryl alcohol in liquid alcohol over
commercial α-Fe2O3 was firstly investigated. Among the catalysts we tested, α-Fe2O3, a cheap, commercially available and
environmentally benign catalyst, exhibited a remarkable catalytic performance for the transformation and gives levulinate
esters in good yield compared to the previous studies. The corresponding esters such as methyl levulinate, ethyl levulinate
and butyl levulinate were obtained in high yields under optimized reaction conditions. Several influence factors for the
formation of levulinate esters were also discussed. A plausible reaction mechanism for the formation of levulinate ester
from furfuryl alcohol was proposed. From viewpoint of practice and economy, the present study provided a potential
application for the efficient synthesis of fine chemicals from biomass-derived compounds over cheap, commercially
available and environmentally benign catalyst.
DOI: 10.1039/x0xx00000x
www.rsc.org/
solid acid catalysts have been developed and studied, such as
acidic ion-exchange resins 14, organic-inorganic hybrid solid
1. Introduction
16,
acid 15, aluminosilicate acid
17, carbon or organosilica
Petroleum oil which promotes the development of human
society is diminishing at an alarming rate during the past
century. Its over-consumption leads to a host of energy crisis
issues and environmental problems. Biomass and its
material 18-20. Moreover, acidic ionic liquid (ILs) is another good
choice, Several groups reported good selectivity of production
of ethyl levulinate and γ-valerolactone (GVL) from FA and
ethanol using sulfonic acid functionalized ILs 21, 22. However,
the above-mentioned catalysts or catalytic processes still
existed several defects. For example, expensive and poor
thermal stability, low yield of LEs, the complex preparation of
catalyst and the synthetic process of feedstock for preparation
of catalyst or ILs itself with possible environmental risks and
pollution 23. Therefore, development of cheaper, greener and
efficient catalyst is imperative.
derivatives are warmly welcomed since they are a kind of
1-3
abundant, renewable and clean organic carbon resources
.
To some extent, their effective utilization can relieve the
overdependence on petroleum resources 4.
Over the past decade, reports on the acid-catalyzed
conversion of carbohydrate biomass to levulinate esters (LEs),
one of the important compounds, were published at an
increasing rate 5-7. LEs can be used as solvent, flavoring agent,
fuel additive and intermediates for the synthesis of the value-
added chemicals and fuels 8-11. In recent years, the production
of LEs from furfuryl alcohol (FA), obtained easily via
hydrogenation of biomass-derived furfural (FAL), has been
increasingly noticed. Acid catalyst is considered as the key
point for LEs production. Strong mineral acids or metal salts as
24-26
27
Previously, our group
and other groups
reported
some interesting results on the conversion of biomass to fuel
and industrial chemicals catalyzed by metal and metal oxides.
Iron oxides and iron salts are known to have widespread
applications, including photocatalytic water-splitting, Fischer-
28,
Tropsch synthetic hydrocarbons
29, due to its abundant,
cheap, easily obtained, low or nontoxicity and environmentally
friendly nature. Recently, iron (III) acetylacetonate as catalyst
was investigated to produce LEs from FA 30. However, this
process used toxic solvent CCl4, and formed corrosive HCl as
the reaction progress, and the formed HCl was considered as a
real catalyst to prompt the FA conversion. Therefore, to
develop a new cleaner route with iron-contain substance as
catalyst is a promising option.
homogeneous catalysts to prompt this reaction were
12, 13
investigated at early stage
.
However, theses
homogeneous catalysts lead to some problems like difficulties
in treatment and separation of highly toxic mixture liquid,
inevitable reaction container corrosion. To avoid that, various
Herein, we report a greener and efficient approach for the
conversion of FA to LEs in liquid alcohol mediated by
commercial α-Fe2O3 (hematite), one of the important iron
oxides and widely distributed in the earth crust. The
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Journal Name
O
ꢀꢁꢂꢃ ꢄꢅꢆꢇꢈ ꢈꢇꢄꢉꢆꢊꢋꢀ, ꢌꢌꢋꢍ
ꢎꢏ ꢊꢀ ꢆℎꢇ ꢊꢀꢊꢆꢊꢄꢍ ꢆꢊꢌꢇ, ꢌꢌꢋꢍ
OH
Yield, % =
× 100 %
α
Cat. -Fe2O3
O
ꢀ
O
R
ROH
+
O
Furfuryl alcohol (FA)
Levulinate esters (LEs)
3. Results and discussion
3.1 Catalyst screening
Scheme 1. Conversion of furfuryl alcohol into levulinate esters
over α-Fe2O3.
Initially, we screened the catalysts for the alcoholysis of FA in
ethanol in the production of ethyl levulinate (EL). All
experiments were conducted in the presence of catalysts in 10
mL ethanol at 250 oC for 60 min, the results are summarized in
Table 1. It can be seen that the target product (EL) did not
appear when no catalyst was used (entry 1). We first tested
Fe(acac)3, which is an effective catalyst for the alcoholysis of
FA according to the previous report, and no reaction took
place, even all the FA was exhausted (entry 2). A magnetic
CuFe2O4 containing Cu and Fe atoms did not give the desired
product EL (entry 3) either. Interestingly, α-Fe2O3 exhibited an
excellent catalytic activity for the transformation and provided
a good yield of 73% (entry 4). In Figure SI-1, it is clear that the
peak of product EL (m/z = 144.1) by GC/MS spectrum was
observed. The catalytic role of α-Fe2O3 has been confirmed by
XRD patterns and SEM images in Figure SI-2 and Figure SI-3. It
can be seen clearly that α-Fe2O3 did not change before and
after the reaction. However, the presence of other catalysts,
such as Fe3O4, ZrO2 and CuO, did not produce the desired EL,
the conversion of FA was also low (entries 5-7). In order to
improve the yield of EL, various catalysts were also
investigated and no desired products EL were obtained (see
Table SI-1 in Supporting Information). Based on the obtained
results, the acidity of commercial α-Fe2O3, CuFe2O4 and Fe3O4
was investigated by NH3-TPD analysis. The result found the
acid amount of commercial α-Fe2O3 is 0.1mmol/g while
CuFe2O4 and Fe3O4 did not show the acidity. It indicated that
commercial α-Fe2O3 acted as acidic catalyst for the
reaction.However, the acidity of α-Fe2O3 after repeat reaction
was investigated and found that the acid amount was
decreased from 0.1 mmol/g to 0.06 mmol/g and yield was
decreased to 38%. This indicated that decreasing the acidity of
α-Fe2O3 might lead to the low yield and also reduce its recycle
ability.
corresponding esters such as methyl levulinate, ethyl
levulinate and butyl levulinate have been effectively obtained
in high yields. Several formed key intermediates during the
reaction were also discussed (Scheme 1).
2. Experimental
2.1 Experimental Materials and Procedure
Furfuryl alchohol (≥ 98.5%), methanol (≥ 99.5%), ethanol (≥
99.7%), n-butanol (≥ 99.5%), ethyl levulinate (99%) and metal
powder or oxides including Ni (≥ 99.5%), Co (≥ 99%), Cu (≥
99.7%), Cr (≥ 99%), Fe (≥ 98%), Pd/C (5%), ZrO2 (≥ 99%), Al2O3
(AR), SiO2 (AR), TiO2 (≥ 98%), Cu2O (≥ 90%), CuO (≥ 99%), Fe3O4
(≥ 98%), α-Fe2O3 (≥ 99%), FeCl3·6H2O (AR), Fe(NO3)3·9H2O (AR)
were purchased from Sinopharm Chemical Reagent (China).
Fe(acac)3 (AR), Methyl levulinate (99.0%, GC) was purchased
from J&K Scientific Ltd. Butyl levulinate (98%) was obtained
from Aladdin Chemical Reagent. CuFe2O4 was prepared
according to the literature 31
.
Most of the experiments were performed in a Teflon-lined
stainless steel batch reactor with an inner volume of 30 mL.
Typical procedure for the synthesis of levulinate esters was as
follows. The catalyst, solvent and furfuryl alcohol were added
into reactor, respectively. Before the reactor sealed, the
loaded reactor was purged by nitrogen for excluding the effect
of air. Then, the reactor was placed into a preheated oven.
After a stipulated time, the reactor was taken out from the
oven and cooled down to room temperature. The reaction
time was defined as the time when the oven temperature was
up to 250 oC after the reactor placed.
In this study, 0.23 mmol furfuryl alcohol as starting material
was used in all experiments. Due to the limiting temperature
In view of the good result of used α-Fe2O3, the effect of the
amount of α-Fe2O3 on the production of EL was checked as
shown in Figure 1a. The experiments were conducted in 10 mL
ethanol at 250 oC for 60 min in the amount of catalyst range of
2.5-12.5 mmol. All the FA was exhausted quickly. The yield of
EL increased remarkably with the amount of α-Fe2O3 raising
from 2.5 to 7.5 mmol. The maximum EL yield of 83% was
achieved when the amount of α-Fe2O3 up to 7.5 mmol.
However, the yield of EL decreased with the amount of α-
Fe2O3 increasing from 7.5 to 12.5 mmol. The decreasing yield
might be attributed to the polymerization of FA during the
reaction when the amount of α-Fe2O3 was excessive. The detail
discussion of polymerization will be given later.
o
of the Teflon container was 250 C, the SUS 316 reactor was
used when the experiment was performed at 300 oC in this
study.
2.2 Product analysis
The liquid samples were collected via a filter procedure and
analyzed by gas chromatography (Agilent GC7890A, with flame
ionization
detector)
and
gas
chromatograph-mass
spectrometer (Agilent GC7890A-MS5975C), both of which
equipped with HP Innowax capillary column (30 m × 0.25 mm ×
0.25µm). The solid samples were collected and analyzed by X-
ray diffraction (XRD).
The yield of LEs was calculated on the basis of the following
equation.
2 | J. Name., 2012, 00, 1-3
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Table 1. Catalyst screening for the production of EL from FA.a
It is generally known that both reaction temperature and time
are also important factors on the reaction efficiency and
product yield. Figure 1c shows the influence of temperature in
the range of 100 oC to 300 oC in presence of 7.5 mmol α-Fe2O3
in 10 mL ethanol for 60 min. The yield of EL was rather low
(1%) when the reaction was carried out at 100 oC and the
conversion of FA was 11.8%, indicating that the reaction for
the formation of EL was difficulty happened at low
temperature. As the temperature raised from 100 oC to 250 oC,
the yield of EL increased significantly from 1 to 83% and the
conversion of FA also increased quickly. However, the yield of
FA Conv. EL Yield
Entry
Catalyst
Alcohol
(%)
0
(%)
0
1
none
ethanol
ethanol
ethanol
ethanol
ethanol
ethanol
ethanol
2
Fe(acac)3
CuFe2O4
α-Fe2O3
Fe3O4
100
9.9
100
0.5
0
0
3b
4
0
73
0
5
6
ZrO2
0
7
a
CuO
4
0
Reaction condition: 0.23 mmol FA, catalyst 5 mmol, ethanol
10 mL, 250 oC, 60 min. b 2.5 mmol CuFe2O4 was used.
o
EL decreased rapidly at 300 C and only a 15% yield of EL was
obtained, many undetermined peaks were observed on the
gas chromatogram. This results indicated that side reactions of
FA might take place at a higher temperature.
Consideration of the potential polymerization of FA at a
higher temperature, the experiment at lower temperature was
o
carried out at 130 C with the reaction time changed from 2 h
to 12 h. The results in Figure SI-4 showed that FA was
consumed within 2 h, the EL yield raised as the reaction time
increased, and the maximum value of EL was 82% at 10 h
o
which is similar to the highest yield of EL at 250 C at 60 min.
From the observation above, it is thought that the
temperature from 130 oC to 250 oC for the polymerization
process of FA did not give a significant influence. However, a
higher reaction temperature can effectively shorten the
reaction time.
The influence of the reaction time from 10 to 80 min on the
production of EL was shown in Figure 1d by keeping other
conditions constant (α-Fe2O3 7.5 mmol, ethanol 10 ml, 250 oC).
The yield of EL increased as the reaction time prolonged to 60
min, and the maximum yield of 83% was obtained. When the
time up to 80 min, the yield of EL decreased gradually. To
investigate whether the produced EL was decomposed and
Figure 1. Effect of parameters: (a) Amount of α-Fe2O3 (0.23 mmol
FA, 10 mL ethanol, 250 oC, 60 min); (b) Volume of ethanol (0.23
mmol FA, 7.5 mmol α-Fe2O3 , 250 oC, 60 min); (c) Temperature (0.23
mmol FA, 7.5 mmol α-Fe2O3 , 10 mL ethanol, 60 min); (d) Time (0.23 gave reduced yield at longer time or not, the experiment using
mmol FA, 7.5 mmol α-Fe2O3 , 10 mL ethanol, 250 oC).
EL as feedstock was carried out with 7.5 mmol α-Fe2O3 in 10
mL ethanol at 250 oC for 80 min. The concentration of EL
decreased from 14.1 mmol/L before reaction to 13.3 mmol/L
3.2 Effect of the volume of ethanol
after reaction. Hence, this evidence supports that a longer
The concentration of substrate is a key factor for most of
chemical reactions. In general, polymerization of FA to
oligomeric compounds will occur at a high concentration.
Thus, the effect of the volume of ethanol for the conversion of
FA into EL was investigated. The experiments were carried out
in the presence of 7.5 mmol α-Fe2O3 at 250 oC for 60 min with
the volume range of ethanol from 4.5 to 15 ml as shown in
Figure 1b. The conversion of FA was 100% with ethanol range
from 4.5 to 15 ml. The yield of EL increased gradually when the
ethanol volume changed from 4.5 mL to 7.5 mL. The highest
yield of EL reached 83% when the ethanol volume was 7.5 mL.
Between 7.5 mL and 10 mL, of EL decreased from 83% at 10
mL to 76% at 15 mL. This might be because higher ethanol
volume caused higher pressure to accelerate the
decomposition of EL.
reaction time, to certain extent, can be negative for the
production of EL.
3.4 Scope of various alcohols
With optimized reaction condition in hand, we next assessed
the substrate scope of the reaction. The results are
summarized in Table 2. The reaction of FA and methanol,
instead of ethanol, gave the methyl levulinate (ML) in 73%
yield (entry 1). The substrate n-butanol also proceeded well
and obtained the corresponding n-butyl levulinate (BL) in 86%
yield (entry 3).
3.5 Intermediates study and proposed mechanism
The mechanism of the conversion of FA to LEs is still not clear
for the identification of the different intermediates separated
during the alcoholysis processes of FA, and several plausible
reaction pathways were proposed in previous studies 15, 16, 32
.
3.3 Effect of the temperature and time
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Table 2. Reaction of FA with different alcohols to produce
levulinate esters.a
1, EMF;
2, Compound 1;
3, EL;
4, FA;
EtOH
3
Entry
1b
Alcohol
FA Conv. (%)
100
100
Yield (%)
300
200
100
0
5, Compound 2
methanol
ethanol
n-butanol
73
83
86
2c
3d
100
1
2
5
50 min
a Reaction condition: 0.23 mmol FA, 7.5 mmol α-Fe2O3, 10 mL
o
b
c
20 min
10 min
alcohol, 250 C, 40 min. 7.5 mL methanol was used. Time
was 60 min. d Time was 80 min.
4
In general, the intermediates can contribute to understand
the reaction pathway. As shown in Figure 2, the time profile of
the reaction of FA monitoring by GC. From Figure 2, the
completely conversion of FA occurred within 20 min. Peaks of
three possible intermediates formed within the first 10 min
were observed, which then became smaller and disappeared
completely at the end. However, it is obvious that the peak
area of product EL increased continuously during the reaction.
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
Retention time (min)
Figure 3. Gas chromatogram of liquid samples (0.23 mmol FA,
7.5 mmol α-Fe2O3, 10 mL ethanol, 250 oC).
obtained as shown in Figure SI-6. The yield of EL decreased
quickly from 73% without water (entry 4, Table 1) to 36% with
This observation indicated that the intermediates including (2- water in the presence of α-Fe2O3 (entry 2, Table 3). Catalysts
1 and 2 were
(ethoxymethy)furan (EMF), compounds
converted gradually to product EL after 10 min.
ZrO2 and Cu2O gave lower yield in ethanol/water system
(entries 3-4). These results indicate that large amount of water
15, 33, 34
Figure 3 also shows the same changes of peaks of FA, EL,
and three possible intermediates. With the time increased,
peaks of FA, EL and three intermediates can be observed at
the first 10 min and then peaks of FA and three intermediates
became smaller and smaller until disappeared completely from
10 min to 50 min, only peak of EL could be observed at last.
Mass spectrum informations of three possible intermediates
by GC/MS are described in Figure SI-5. EMF was identified
is favoured for the side reactions and polymerization
similar to appearances observed by Dumesic and coworkers 32
.
However, it is still debatable whether produced trace
amount of water as a reactant participates in the alcoholysis
process of FA or not 15, 32. Two reactions by using drying agents
were conducted to identify. 4 Å molecular sieve (MS), which
has been reported as drying agent used to remove water in
organic reaction 35, was added into ethanol system to
investigate the influence of the trace amount of water. The
yield of 30% was obtained (entry 5). When molecular sieve was
used in the absence of α-Fe2O3, no reaction took place and no
based on the comparison of the mass spectra between our
16
result and previous report
considered to be
. 2-(alkoxymethy)furan was
a
first-step intermediate during the
alcoholysis of FA 15. However, other two intermediates with
the probable molecular weight of 203 or 173 g/mol were hard
to be identified.
desired product was obtained (entry 6). The presence of α-
Fe2O3+molecular sieve or -Fe2O3 only gave 30% (entry 5) and
α
83% yield (best result obtained in this study), respectively.
These results indicated that molecular sieve could not catalyze
this reaction and αꢀFe2O3 acted as an efficient catalyst for EL
production. These observation indicate that trace amount of
water plays an important role and can promote the alcoholysis
process as a reactant.
As we know, water is produced in the alcoholysis process of
FA which will cause the dehydration reaction to form diethyl
ether 16, 32 and 2-(ethoxymethy)furan. Next, the effect of water
and its amount on the alcoholysis of FA was further discussed.
Herein, we carried out the experiments of the alcoholysis of FA
with added large amount of water at first (Table 3). As a result,
interestingly no catalyst also gave a lower 5% yield of EL (entry
1). It might be because water acted as an acid catalyst to affect
the alcoholysis of FA 4. However, its selectivity was low and
mixtures, such as EMF, EL, FA and other by-products, were
Table 3. Influence of water on the alcoholysis process of FA.a
FA
EL
Entry Catalyst Alcohol
Additive
Conv. Yield
(%)
96
(%)
5
1b
2
none
ethanol+water
-
300
α-Fe2O3 ethanol+water
-
100
100
100
36
21
15
3
ZrO2
ethanol+water
ethanol+water
-
EMF
Compound 1
EL
200
4
Cu2O
-
Molecular
sieve
5c
α-Fe2O3 ethanol
100
30
FA
Compound 2
100
Molecular
sieve
6c
none ethanol
100
0
a Reaction condition: FA 0.23 mmol, catalyst 5 mmol, ethanol
o
or ethanol/water (v/v = 1/1) 10 mL, 250 C, 60 min. b FA 1.157
0
0
10
20
30
40
50
mmol, 200 oC. c 1 g molecular sieve was used.
Time (min)
Figure 2. The peaks area change of FA, EL and possible
intermediates at different time (0.23 mmol FA, 7.5 mmol α-
Fe2O3, 10 mL ethanol, 250 oC).
4 | J. Name., 2012, 00, 1-3
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OH
OC2H5
-C2H5OH
+
O
5
J. Hegner, K. C. Pereira, B. DeBoef and B. L. Lucht,
+
O
O
O
C2H5OH
C2H5OH
C2H5O
Tetrahedron Lett., 2010, 51, 2356-2358.
- H2O
1,4-addition
6
J. J. Bozell and G. R. Petersen, Green Chem., 2010, 12,
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1
2
3
539-554.
O
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H shift
C2H5
O
- H+
+ H2
O
O
C2H5
C2H5
5
EL
O
4
OH
8
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Scheme 2. A possible pathway of the alcoholysis process of FA
to EL.
2012, 4, 1230-1237.
9
M. Chia and J. A. Dumesic, Chem. Commun., 2011, 47,
Based on the observation above, a plausible mechanism of
the alcoholysis process of FA to EL is presumably similar to the
previous reports 15, 32. As is illustrated in Scheme 2, FA first
12233-12235.
10
11
12
H. J. Bart, J. Reidetschlager, K. Schatka and A. Lehmann,
Ind. Eng. Chem. Res., 1994, 33, 21-25.
reacted with ethanol to produce intermediate
subsequent loss of ethanol to give . Next, the obtained cation
underwent nucleophilic conjugate 1,4-addition of ethanol to
give species . Species was formed by a hydrogen shift from
. Finally, H2O as nucleophile attacked species to produce
1, and
Y. Yang, C. Hu and M. M. Abu-Omar, Bioresour.
Technol., 2012, 116, 190-194.
2
2
WO8002423-A1;
BE883067-A;
WO8002423-A;
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4
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A; CA1140579-A; IT1141938-B, 1980.
3
4
5,
and then isomerization to obtain desired EL.
13
14
15
16
Y.-B. Huang, T. Yang, M.-C. Zhou, H. Pan and Y. Fu,
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J. P. Lange, W. D. van de Graaf and R. J. Haan,
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We explored an efficient method for the production of
levulinate esters by the alcoholysis process of biomss-derived
furfuryl alcohol over commercial α-Fe2O3. Among the alcohol
substrates test, the highest yield of 73%, 83% and 86% of
corresponding methyl levulinate, ethyl levulinate and n-butyl
levulinate were achieved, respectively under optimal reaction
conditions. On the basis of the investigation of intermediates
and the role of water and its amount, a plausible mechanism
was proposed. The present study provides a fast, efficient and
environmentally friendly method for the conversion of
biomass-based compounds to value-added chemicals.
4
Rocha and A. A. Valente, Catal. Today, 2013, 218-219
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76-84.
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Acknowledgements
6
The authors gratefully acknowledge the financial support from
the State Key Program of National Natural Science Foundation
of China (No. 21436007). Key Basic Research Projects of
Science and Technology Commission of Shanghai
(14JC1403100). The Program for Professor of Special
Appointment (Eastern Scholar) at Shanghai Institutions of
Higher Learning (ZXDF160002). We thank the all reviewers and
editors for reviewing the manuscript and providing valuable
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DOI: 10.1039/C5RA24319J
Efficient conversion of biomassꢀderived furfuryl alcohol to
levulinate esters over commercial αꢀFe2O3
Dezhang Ren, Jun Fu, Lu Li, Yunjie Liu, Fangming Jin and Zhibao Huo*
Graphic abstract