Esterification of levulinic acid to ethyl levulinate over bimodal micro-mesoporous H/BEA zeolite derivatives

Article abstract of DOI:10.1016/j.catcom.2013.10.006

A series of bimodal micro-mesoporous H/BEA zeolite derivatives were prepared by the post-synthesis modification of H/BEA zeolite by NaOH (0.05 M-1.2 M) treatment. Samples were characterized by powder XRD, low temperature nitrogen adsorption/desorption, temperature programmed desorption of ammonia and ICP. The mesopore formation was found to play a crucial role in liquid phase esterification of levulinic acid with ethanol. The enhanced catalytic activity of a bimodal micro-mesoporous H/BEA zeolite derivative (H/BEA_0.10) prepared by treatment with 0.1 M NaOH can be mainly attributed to the high mesoporosity coupled with better preserved crystallinity and acidic properties.

Full text of DOI:10.1016/j.catcom.2013.10.006

Catalysis Communications 43 (2014) 188–191
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Esterification of levulinic acid to ethyl levulinate over bimodal
micro–mesoporous H/BEA zeolite derivatives
C.R. Patil, P.S. Niphadkar, V.V. Bokade, P.N. Joshi ⁎
Catalysis & Inorganic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune 411008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 June 2013
Received in revised form 11 September 2013
Accepted 8 October 2013
Available online 17 October 2013
A series of bimodal micro–mesoporous H/BEA zeolite derivatives were prepared by the post-synthesis modification
of H/BEA zeolite by NaOH (0.05M–1.2M) treatment. Samples were characterized by powder XRD, low temperature
nitrogen adsorption/desorption, temperature programmed desorption of ammonia and ICP. The mesopore
formation was found to play a crucial role in liquid phase esterification of levulinic acid with ethanol. The enhanced
catalytic activity of a bimodal micro–mesoporous H/BEA zeolite derivative (H/BEA0.10) prepared by treatment with
0
.1M NaOH can be mainly attributed to the high mesoporosity coupled with better preserved crystallinity and acidic
Keywords:
H/BEA zeolite
Post-synthesis modification
Mesoporosity
properties.
© 2013 Elsevier B.V. All rights reserved.
Esterification
Ethyl levulinate
1
. Introduction
Synthesis of levulinate esters from biomass is one of the avenues
of catalysts are some of the challenges that exist for the further improve-
ment in productivity and selectivity [13].
Zeolites are microporous, crystalline aluminosilicates having very
regular pore structures of molecular dimensions. By generating the
mesoporosity in their matrix, their catalytic performance can be im-
proved on account of increased diffusion rate [14,15]. Post-synthesis
treatment with alkaline solution is one of the simple, feasible and highly
effective methods to prepare hierarchically structured zeolites with
combined advantages of microporous and mesoporous molecular sieves
[16–20]. The concentration of the base is one of the process parameters
to tailor the characteristics of such bimodal micro–mesoporous zeolite
derivatives. Protonic form of the bimodal micro–mesoporous zeolite
beta derivative has exhibited catalytic activity in α-pinene isomerization
[21], n-hexane isomerization [22] and selective hydrocracking of heavier
where substantial research efforts are being invested with a view
to achieve sustainable energy supply and production of value-added
chemicals. Ethyl levulinate (EL) is a short-chain fatty ester and possesses
unique properties which make it as: a) a very attractive candidate as
novel diesel and gasoline miscible biofuel [1,2], b) a chemical feedstock
in flavoring and fragrance industries [3] and c) a substrate for various
kinds of organic condensation and addition reactions [4]. After realizing
the drawbacks of homogeneous catalysts such as mineral acids [4–7],
considerable efforts were made to develop environmentally benign
heterogeneous catalysts [8–12] which are recyclable and efficient for
esterification of levulinic acid (LA). In esterification of LA with ethanol,
the performance of non-zeolitic catalysts, in particular, Amberlyst-15
and sulfated oxides was found to depend on the total acidity, whereas,
in case of the zeolite catalysts, it depends on the pore structure (large
cavities) rather than the total acidity [10]. Heterogeneous catalysts
resulted from the effective confinement of H
within the mesoporous channels of SiO mesoporous (H
SiO ) were also reported as the efficient and recyclable catalysts for the
synthesis of methyl and ethyl levulinates [12]. Thus, for improved
performance, it is necessary to use the zeolite catalyst with larger cavities
to favor the formation of the transition state in esterification of LA
with ethanol. Although great progress has been made for the catalytic
preparation of EL, still the development of catalysts including efficient
reaction systems and establishing the structure–property relationships
5
hydrocarbons to C –C11 hydrocarbons [23] because of mesopore
formation resulting from the alkaline treatment.
The benefits of protonic form of zeolite beta (H/BEA) and the
challenges associated with the further improvement in productivity
and selectivity for EL have triggered our interest to prepare and
examine the performance of bimodal micro–mesoporous H/BEA
zeolite derivatives in the synthesis of EL. In this communication, a
series of bimodal micro–mesoporous H/BEA zeolite derivatives
were prepared by the post-synthesis modification of H/BEA zeolite
by NaOH treatment. The effect of NaOH concentration on the XRD
crystallinity, textural and acidic properties, chemical composition
and catalytic performance in EL synthesis is investigated. An attempt
was made to establish the structure–property–activity relationships. In
view of maximizing the EL yield, the reaction parameters such as catalyst
loading, LA:ethanol molar ratio and time on stream were optimized using
optimum catalyst.
4
SiW12
O40 (up to 30 wt.%)
2
4
SiW12
40
O –
2
⁎
Corresponding author. Tel.: +91 20 25902457; fax: +91 20 25902633.
E-mail address: pn.joshi@ncl.res.in (P.N. Joshi).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.10.006

C.R. Patil et al. / Catalysis Communications 43 (2014) 188–191
189
4
00
H/BEA
H/BEA0.05
(
0)
H/BEA
H/BEA
1
.20
.30
H/BEA0.10
H/BEA0.15
(
55)
74)
300
0
H/BEA0.30
(
H/BEA
H/BEA1.20
0
.15
2
00
H/BEA
(95)
0.10
(
97)
H/BEA
100
0
0.05
(100)
H/BEA
0
.0
0.2
0.4
0.6
P/Po
0.8
1.0
1
0
20
30
40
50
2
Theta (degree)
Fig. 2. Low temperature nitrogen adsorption–desorption isotherms of H/BEA and its
bimodal micro–mesoporous derivatives.
Fig. 1. Powder XRD patterns for H/BEA and its bimodal micro–mesoporous derivatives
bracketed numbers indicate the % crystallinity).
(
2
. Experimental
on corresponding XRD patterns. Although, % crystallinity was
dropped with an increase in the NaOH concentration, the zeolitic
structure was practically preserved with a negligible drop in crystallinity
from 100% to 95% up to 0.10 M NaOH concentration. Further increase
in the concentration resulted in the decrease in crystallinity and a com-
pletely XRD amorphous sample was obtained with 1.20 M NaOH. It is
also evident from Table 1 that, the molar Si/Al ratio decreases with the
2
.1. Synthesis and characterization
The overall procedure employed to prepare the parent sample
(
H/BEA) and characterization techniques used are similar to that
of described earlier [24]. Details regarding the procedure followed
for the post-synthesis modification of H/BEA zeolite by NaOH
increase in alkali concentration. The N
2
adsorption–desorption isotherms
(
0.05 M–1.20 M) treatment and characterization of the bimodal
and the textural parameters of H/BEA and its bimodal micro–
mesoporous derivatives are presented in Fig. 2 and in Table 1 respectively.
Microporous character of H/BEA has been well reflected in its isotherm
type-I with plateau at higher relative pressures. It also showed a small
hysteresis loop which might be associated with the presence of the
interparticle voids [21]. The type of the isotherm and hysteresis loop
showed by the NaOH-treated samples indicated their bimodal micro–
mesoporous nature. With increase in the NaOH concentration, the
contribution of micropore surface area in total surface area was found to
micro–mesoporous H/BEA zeolite derivatives are described in the
supplementary information. The protonic form obtained after NaOH
treatment was designated as H/BEAx.yz, where x.yz is the concentration
of NaOH with which H/BEA was treated.
2
.2. Synthesis of EL
Catalytic liquid phase esterification of levulinic acid with ethanol
2
and analysis of the reactants and products were carried out as per the
details provided in the supplementary information.
drop and it reached to a minimum value of 89 m /g in XRD amorphous
sample. As a result of an introduction of hierarchical mesopores,
samples have shown the decreasing trend in the mesopore volume
as: H/BEA1.20 N H/BEA0.30 N H/BEA0.15 N H/BEA0.10 N H/BEA0.05 N H/BEA.
The acidic properties of H/BEA and its bimodal micro–mesoporous
3
. Results and discussion
3
.1. Characterization
3
derivatives were investigated by NH -TPD and the results based on high
temperature peak are summarized in Table 1. An acid amount was
found to increase with an increase in the NaOH concentration up to
0.10 M and then decreases with the further increase in the NaOH
concentration. The use of NaOH with concentration N0.10M has resulted
in the decrease in % crystallinity which might be contributing to the
decrease in an acid amount. In the samples possessing % crystallinity in
the range of 100–95, the increase in the acid amount may be attributed
to the increased number of strong acid due to the lowering of Si/Al ratio
Fig. 1 shows powder X-ray diffraction (XRD) patterns of H/BEA and
its bimodal micro–mesoporous derivatives obtained by NaOH treat-
ments with different concentrations. H/BEA has shown the characteristic
peaks of zeolite BEA [24] with no contribution due to other crystalline
or amorphous phase/s. H/BEA sample was treated as a reference
sample with 100% crystallinity and the relative crystallinities of
different derivatives were estimated and shown as bracketed figures
Table 1
Chemical composition, acidic and textural properties of H/BEA and its bimodal micro–mesoporous derivatives.
a
a
Pore volume (cm3 g−1
)
Sample
Acid amount
NH
mmol desorbed g−1)
Si/Al ratio
S
BET
2
S
micro
2
S
meso
(m g−1)
(m g−1
)
(m g−1)
2
(
3
a
b
V
micro
V
meso
H/BEA
0.53
0.59
0.69
0.45
0.27
0.19
14
12
10
8
5
3
580
597
620
678
507
303
529
473
350
329
203
89
51
124
270
349
304
214
0.22
0.16
0.16
0.14
0.09
0.01
0.18
0.28
0.32
0.39
0.57
0.79
H/BEA0.05
H/BEA0.10
H/BEA0.15
H/BEA0.30
H/BEA1.20
a
By t-plot.
By BJH method.
b

190
C.R. Patil et al. / Catalysis Communications 43 (2014) 188–191
5
4
0
0
and the preserved long-range crystal ordering [17,18]. Interestingly, an
XRD amorphous H/BEA1.20 has shown an acid amount which is almost
A
36% of that of H/BEA. This indicated that, H/BEA1.20 contains small crystals
of zeolite BEA that are short range ordering, below the XRD detection
limit and responsible for imparting acidic character [24].
3
.2. Esterification of LA over H/BEA and its bimodal micro–mesoporous
30
20
10
0
derivatives
Under an identical set of reaction conditions, the performance of
H/BEA sample and its bimodal micro–mesoporous derivatives in
esterification of LA to EL was evaluated. The results are depicted in
Fig. 3. With no catalyst, 3.5% LA conversion was obtained after the
5
th h under the same reaction conditions. H/BEA showed the lowest
activity in spite of having acidity, 100% crystallinity and maximum
microporosity. The activity of the bimodal micro–mesoporous derivative
initially increases with an increase in the NaOH concentration, reaches
to maximum and then decreases with the further increase in concen-
tration. H/BEA0.10 gave the highest conversion (40%) among all the
bimodal micro–mesoporous H/BEA derivatives which can be attributed
to enhanced acidity and accessibility of these acidic sites due to the
formation of mesopores in microporous matrix with almost no damage
to its crystallinity. Interestingly, XRD amorphous H/BEA1.20 has shown
better activity than 100% crystalline parent sample H/BEA. This improved
catalytic behavior of H/BEA1.20 may be associated with the preservation
of enough active catalytic sites that are necessary for the LA esterification
and the large amount of mesoporosity. The trend observed in LA
10
15
20
25
30
35
40
Catalyst loading, wt%
5
4
3
2
1
0
0
0
0
0
0
B
conversion over all the catalysts screened was shown as: H/BEA0.10
H/BEA0.05 N H/BEA0.15 N H/BEA0.30 N H/BEA1.20 N H/BEA.
In view of maximizing the LA conversion, the reaction parameters
viz. catalyst loading and LA:ethanol molar ratio were optimized using
an optimum H/BEA0.10 catalyst. The catalyst loading was varied from
N
1
0 to 40% (w/w) of LA keeping all other parameters constant. The
results obtained after 5th h are depicted in Fig. 4A. The conversion of
LA to EL using 10 wt.% catalyst loading showed the minimum
conversion. With further increase in catalyst loading to 20 wt.%, the LA
conversion was found to increase from 7% to 40%. Further increase in
catalyst loading made no significant improvement in the conversion of
LA as the excess concentration of catalyst limits the further increase in
L-L-S mass transfer rate, which restricts the further enhancement in
catalytic activity. Thus, 20 wt.% catalyst loading was found to be
optimum and hence this catalyst amount was used further to optimize
LA:ethanol molar ratio. The LA:ethanol molar ratio was varied in the
range of 1:4–1:10 keeping all other parameters identical. The results
4
6
8
10
Molar ratio (Ethanol/LA)
5
4
0
0
C
5
4
3
2
1
0
0
0
0
0
0
30
H/BEA
H/BEA0.05
H/BEA0.10
2
1
0
0
0
H/BEA0.15
H/BEA0.30
H/BEA1.20
fresh catalyst 1 recycle 2nd recycle 3rd recycle 4th recycle
st
Fig. 4. Influence of (A) catalyst loading, (B) LA:ethanol molar ratio and (C) recyclability of
H/BEA0.10 in the LA conversion (reaction conditions for A: LA:ethanol molar ratio = 1:6;
temp = 78 °C; time = 5 h, reaction conditions for B: Catalyst loading = 20 wt.% of LA;
temp = 78 °C; time = 5 h, reaction conditions for C: Catalyst loading = 20 wt.% of LA;
temp = 78 °C; time = 5 h, LA:ethanol molar ratio = 1:6).
1
2
3
4
5
Time, h
obtained after the 5th h are depicted in Fig. 4B. The conversion was
found to increase from 30% to 40% with the increase in the mole ratio
from 1:4 to 1:6. Marginal increase in conversion was observed when
Fig. 3. Esterification of levulinic acid to ethyl levulinate over H/BEA zeolite and its bimodal
micro–mesoporous derivatives (reaction conditions: LA:ethanol molar ratio = 1:6;
temp = 78 °C; time = 5 h; catalyst loading = 20 wt.% of LA).

C.R. Patil et al. / Catalysis Communications 43 (2014) 188–191
191
the mole ratio was further increased to 1:8 and 1:10. This may be partly
attributed to the fact that, the more ethanol may dilute the reactant;
thereby restricting further increase in conversion due to mass transfer
limitations. The selectivity for EL was found to be 98% during all the
experiments. Thus, in present studies, the LA:ethanol molar ratio =
Projects—Catalysts for Specialty Chemicals and BLB. The financial support
under CSIR-NCL Project Code CSC0125 is gratefully acknowledged.
Appendix A. Supplementary data
1
:6 was observed to be an optimum. With these optimized reaction
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2013.10.006.
parameters, an optimum H/BEA0.10 catalyst was subjected to recycling
experiments to examine the catalyst recyclability. The re-employing
the catalyst was done for four times by keeping the reaction parameters
same. Between each run, the catalyst was filtered, washed with ethanol
and dried at 70°C. Fig. 4C reveals that, the catalyst remained active with
an almost unchanged conversion of LA compared with the fresh
catalyst, indicating its recyclable nature at least up to 4 recycles.
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Acknowledgments
The Authors thank Miss Sharda Kondawar for scanning and providing
the data on NH TPD. This work was carried out under the CSIR-XII FYP
3