Production of n-butyl levulinate over modified KIT-6 catalysts: comparison of the activity of KIT-SO3H and Al-KIT-6 catalysts

Article abstract of DOI:10.1007/s13738-019-01677-4

The catalytic activity of propylsulfonic acid-functionalized mesoporous silica (KIT-SO₃H) was compared to the performance of alumina-incorporated KIT-6 (Al-KIT-6) in the esterification reaction of the biomass-derived levulinic acid with n-butanol. The catalysts were prepared by functionalization of the silica support with propylsulfonic acid (Pr-SO₃H) by post-synthesis grafting using 3-mercaptopropyltrimethoxysilane as a propyl-thiol precursor followed by oxidation. In addition, Al-KIT-6 was synthesized according to in situ synthesis. Catalysts were characterized using various techniques such as XRD, nitrogen adsorption/desorption, SEM, TGA, ICP-OES, FT-IR and elemental analysis. It is evident that increases in catalyst loading, butyl alcohol-to-levulinic acid ratio and reaction temperature significantly enhance the butyl levulinate yield. The reusability and stability of catalysts were evaluated, and it was found that while esterification reaction by KIT-SO₃H compound catalyzed under milder conditions, the stability of Al-KIT-6 catalyst was better.

Full text of DOI:10.1007/s13738-019-01677-4

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01677-4
ORIGINAL PAPER
Production of n‑butyl levulinate over modiꢀed KIT‑6 catalysts:
comparison of the activity of KIT‑SO H and Al‑KIT‑6 catalysts
3
Alireza Najaf Chermahini1 · Matin Assar1
Received: 20 October 2018 / Accepted: 15 April 2019
©
Iranian Chemical Society 2019
Abstract
The catalytic activity of propylsulfonic acid-functionalized mesoporous silica (KIT-SO H) was compared to the performance
3
of alumina-incorporated KIT-6 (Al-KIT-6) in the esteriꢀcation reaction of the biomass-derived levulinic acid with n-butanol.
The catalysts were prepared by functionalization of the silica support with propylsulfonic acid (Pr-SO H) by post-synthesis
3
grafting using 3-mercaptopropyltrimethoxysilane as a propyl-thiol precursor followed by oxidation. In addition, Al-KIT-6
was synthesized according to in situ synthesis. Catalysts were characterized using various techniques such as XRD, nitrogen
adsorption/desorption, SEM, TGA, ICP-OES, FT-IR and elemental analysis. It is evident that increases in catalyst loading,
butyl alcohol-to-levulinic acid ratio and reaction temperature signiꢀcantly enhance the butyl levulinate yield. The reusability
and stability of catalysts were evaluated, and it was found that while esteriꢀcation reaction by KIT-SO H compound catalyzed
3
under milder conditions, the stability of Al-KIT-6 catalyst was better.
Keywords Esteriꢀcation reaction · Butyl levulinate · Levulinic acid · Solid acid catalyst · KIT-6
Introduction
stability, high lubricity and moderate ꢁow properties under
the low temperature that make their properties similar to
traditional fuel additives [9–11]. In addition, like other esters
with a short-chain alkyl group, the alkyl levulinates ꢀnd
extensive application either in the ꢁavoring and fragrance
industries [12, 13]. For example, n-butyl levulinate has been
used in organic process industries for diꢂerent purposes
such as plasticizing agent, solvents and odorous substances
[14–16]. Generally, alkyl esters of levulinic acid can be pre-
pared by the esteriꢀcation of LA with alcohols or alcoholysis
of furfuryl alcohol [17–20]. Various homogeneous [21–23]
or heterogeneous catalysts [24–26] have been utilized in
the esteriꢀcation of LA with alcohols. With more attention
to the progress of green processes, many eꢂorts have been
made to advance environmentally friendly technologies for
esteriꢀcation reactions. So, various heterogeneous catalysts
have been reported for conversion of LA to alkyl levulinates.
For example, Tejero et al. [27] have reported esteriꢀcation
of LA with 1-butanol over ion exchange resins. They have
found that butyl levulinate (BL) yields were in the range
of 90.5–93.5% with 99.5% selectivity. Recently, Zhou et al.
Conꢀdent technology for its progress needs initial sources
of energy and material. Therefore, replacement of fossil
fuel-based technologies with renewable and sustainable
technologies which consume biomass-derived materials is
necessary. One of the top 10 important compounds derived
from biomass is levulinic acid (LA) [1–3] that has been uti-
lized as a precursor for the production of chemicals, such
as gamma-valerolactone (a green solvent and potentially
useful polyester monomer) [4, 5], methyltetrahydrofuran
[
6] (a valuable solvent or gasoline blending component),
methyl vinyl ketone [7] and α-angelica lactone [8]. Among
the LA derivatives, alkyl levulinates such as methyl, ethyl,
propyl and butyl levulinates are of particular interest due to
their speciꢀc physicochemical properties such as ꢁash point
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01677-4) contains
supplementary material, which is available to authorized users.
[
28] have used a modiꢀed phosphotungstic acid as a novel
*
Alireza Najaꢀ Chermahini
anajaꢀ@cc.iut.ac.ir; najafy@gmail.com
eꢃcient catalyst for the synthesis of n-butyl levulinate. They
found 99% yield but did not report any catalyst recycling.
Cirujano et al. [29] used zirconium-containing MOF to
1
Department of Chemistry, Isfahan University of Technology,
8
4154-83111 Isfahan, Iran
Vol.:(0
1
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3

Journal of the Iranian Chemical Society
synthesize n-butyl levulinate and observed that the product
formed quantitatively after 5 h.
Synthesis of Al‑KIT‑6 and KIT‑SO H catalysts
3
In the present paper, a mesoporous silica material KIT-6
was synthesized and characterized. The KIT-6 material was
then functionalized with aluminum through in situ synthesis
or grafted by propylsulfonic acid groups and used as the
solid acid catalyst to the conversion of biomass-derived
levulinic acid to n-butyl, levulinate. For this purpose, reac-
tion conditions such as temperature, amount of the catalyst
loading, and the eꢂect of reaction time were optimized. In
addition, the recycling and reusability of the catalysts under
optimized reaction conditions are achieved.
Functionalization of KIT-6 with sulfonic acid groups was
achieved by a previously reported method [30]. Brieꢁy, to
a mixture of 30 mL of dry toluene and 2 mL of 3-mercap-
topropyltrimethoxysilane (MPTMS), 1.00 g of mesoporous
KIT-6 was added and the mixture was reꢁuxed for 24 h.
The thiol-functionalized precipitate was ꢀltered and then
soxhleted with methanol as the extractor solvent, and then,
the catalyst was dried at 80 °C overnight. In the next step,
the mercapto groups were oxidized into –SO H groups
3
using hydrogen peroxide as the oxidant under stirring for
2
4 h at room temperature. The ꢀnal product was ꢀltered
and washed with methanol and oven-dried at 80 °C over-
night. The preparation of aluminum-modiꢀed KIT-6 was
done according to the previous report with some modiꢀ-
cations [31]. Shortly, 2.4 g Pluronic P123 was dissolved
in 86.4 g water followed by the addition of 4.7 g HCl
(35%) at 35 °C. To this mixture was added 2.4 g n-butanol
and was stirred for 1 h, followed by the addition of 2.6 g
TEOS and 0.4 g aluminum iso-propoxide as the aluminum
source. The mixture was aged at 100 °C under static con-
dition for 24 h. Finally, the white precipitate was ꢀltered,
dried at 100 °C and calcined at 550 °C to remove organic
template.
Experimental
Materials and instruments
Tri-block copolymer (Pluronic P123), levulinic acid,
n-butanol, tetraethyl orthosilicate (TEOS, 98%), alu-
minum iso-propoxide (98%), 3-mercaptopropyltrimethox-
ysilane, and all of the used solvents were purchased from
Sigma–Aldrich. All of the other chemicals were analytical
grade and were applied without further puriꢀcation. The
nitrogen adsorption/desorption isotherms were collected at
7
7 K by using a PHS-1020 (PHSCHINA) device. The mor-
phology of the catalysts was evaluated by SEM analysis on
a VEGA\\TESCAN-LMU microscope, and high-resolution
transmission electron microscopy (HRTEM) was used with
a Philips CN120 device. Powder X-ray diꢂraction (XRD)
patterns of samples were taken using a Asenware XDM-300
diꢂractometer using Ni-ꢀltered Cu Kα (K = 0.15406 nm)
radiation. Elemental analysis was carried out by a CHNS
analyzer (Elementar, Vario EL III).
Esterifcation oꢀ levulinic acid
Esteriꢀcation of LA with n-butanol was performed under
atmospheric pressure. In a typical catalytic reaction, 5 mL
n-butanol and 0.615 g LA were added to a round-bottomed
two-necked ꢁask and was heated in the presence of 50 mg of
mesoporous KIT-6-Al or KIT-SO H under continuous stir-
3
ring. Then, the reaction mixture was cooled and centrifuged,
Catalyst preparation
and the solid catalyst was recovered for recycling and reus-
ing in the next run. For this purpose, the KIT-SO H catalyst
3
Synthesis of KIT‑6
was thoroughly washed with acetone and dried at 120 °C and
reused. For the recycling of KIT-6-Al catalyst, the solid was
washed with acetone, and dried and calcined at 120 °C and
500 °C for 3 h, respectively. It is notable that to examine the
reproducibility of the results, the esteriꢀcation of LA with
alcohols were performed in duplicate.
The synthesis of mesoporous KIT-6 material was achieved
by dissolving P123 as a structure directing agent and
n-butanol as a co-solvent under acidic conditions. The prepa-
ration of the mesoporous silica was carried out as follows:
7
.0 g of Pluronic P123 was dissolved in 253 g of distilled
water and 13.7 g of HCl solution (35 wt%). Then n-butanol
4.0 g) was added at once to the above mixture, under vigor-
(
Reaction monitoring and product identifcation
ous stirring at 35 °C. Then, TEOS (15.05 g) was added and
the solution was stirred for 24 h. After that, the suspension
was kept under static conditions at the same temperature.
Then, the solid product obtained was ꢀltered without any
washing and dried at 100 °C for 12 h. Finally, the template
was removed by calcination of prepared silica at 550 °C for
The progress of the reaction was monitored on an Agi-
lent (6890 N) gas chromatograph equipped with a ꢁame
ionization detector and using a DB5 capillary column
(30 m × 0.25 mm, DF = 0.25 µm), using helium as the
carrier gas and air for the detector function (total ꢁow of
1.3 mL/min). For the determination of butyl levulinate in the
6
h.
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Journal of the Iranian Chemical Society
samples, calibration curve by analyzing standard solutions
with known amounts of products was used.
Butyl levulinate yield was calculated according to the fol-
lowing equation:
is the characteristic of large and uniform mesopores with
narrow pore size distribution. In addition, the corresponding
pore size distribution curves estimated from the BJH method
are plotted in Fig. 2. The formation of large and uniform
channel-like ordered mesopores is evident by the narrow
pore size distribution within a range of 2–7 nm.
moles of produced alkyl levulinate
Yield (mol%) =
× 100
moles of starting LA
The textural properties of the samples are presented in
Table 1. For the pristine KIT-6, BET surface areas, pore size
(1)
For identiꢀcation of products, GC–MS analysis was per-
formed and the results are presented in the supplementary
information.
2
−1
3
and pore volume were 840 m g , 3.15 nm and 0.797 cm
−1
g , respectively. After surface modiꢀcation with propyl-
sulfonic acid groups, the S
and pore volume changed
BET
2
−1
3
−1
to 394 m g and 0.592 cm g , respectively. In addition,
after alumina loading, the BET surface area and pore volume
Results and discussion
2
−1
3
−1
drastically reduced to 175 m g and 0.287 cm g , respec-
tively. This indicates that some pores were blocked during
surface modiꢀcation. Pore size distribution was intact after
surface modiꢀcation of KIT-6.
Catalyst characterization
Low-angle XRD measurements were used to study of order-
ing degree of samples. For the KIT-6 sample, Bragg reꢁec-
tions appeared at 2θ=0.98, 1.2 and 1.69, degree correspond-
ing to (2 1 1), (2 2 0) and (4 2 0) reꢁections, respectively
The surface morphology of pristine KIT-6, KIT-Pr-SO H
3
and KIT-6-Al catalysts were analyzed by SEM technique
(
Fig. 3). The SEM image of KIT-6 (Fig. 3a) displays large
three-dimensional rock structure, a unique characteristic of
the KIT-6. SEM image of KIT-6-Al is compared with the
morphology of KIT-6 which indicates that the surface mor-
phology smoothness was not aꢂected (Fig. 3b). Addition-
(
Fig. 1).
The results confirm the formation of well-ordered
mesoporous material with Ia3d bicontinuous cubic space
32]. For the KIT-SO H and Al-KIT-6 catalysts, the inten-
[
3
ally, for the KIT-SO H catalyst, the SEM image shows the
3
sity of sharp peak at the 2θ=0.98 was decreased probably
because of the introduction of Al O or propylsulfonic acid
irregular shape and the morphology was rough (Fig. 3c). The
TEM image of KIT-6 mesoporous material is displayed in
Fig. 3d, showing a three-dimensional cubic arrangement of
pores with Ia3d space group.
2
3
groups. However, the position of the diꢂraction peak is not
obviously changed, indicating the order of structure is intact.
It is known that the surface area and pore size of hetero-
geneous catalysts are of the highest importance because of
their role in the diꢂusion of the reagents to the active sites.
Figure 2 shows the adsorption–desorption isotherms of KIT-
For the evaluation of the total organic content of KIT-
SO H sample, the thermogravimetric analysis results of
3
pristine KIT-6 and KIT-SO H catalyst with heating from
3
room temperature to 800 °C under N atmosphere are pro-
2
6
, KIT-6-Al and KIT-Pr-SO H samples, exhibiting type IV
3
vided in Fig. 4. For the KIT-6, total reduction of 3% in the
weight occurred below 150 °C related to losing moisture.
With keeping in mind about 3% adsorbed water, the total
isotherms with H1 hysteresis loop according to the IUPAC
classiꢀcation. The samples show sharp nitrogen capillary
condensation step in the P/P0 between 0.5 and 0.9 which
organic content of 11% assigned to the KIT-SO H catalyst.
3
−
1
This value corresponds to 7 mmol g sulfonic acid groups
anchored to mesoporous material. Furthermore, based on
elemental analysis of KIT-SO H catalyst, 1.64% sulfur
3
−
1
which corresponds to 5.1 mmol g sulfonic acid groups
was anchored to the surface of KIT-6 mesoporous mate-
rial. In addition, according to ICP analysis total aluminum
loading on the surface of KIT-6-Al solid acid catalyst was
determined 1.1%.
The FT-IR spectra of KIT-6, KIT-6-SO H and Al-KCC-6
3
catalysts are presented in Fig. 5. For the samples the broad
−
1
peak appeared at 3650 cm is assigned to stretching vibra-
tion of hydroxyl groups. Moreover, the low-intensity peak
−
1
at 1630 cm is attributed to the water molecules adsorbed
on the surface of KIT-6. The broad absorption bands around
−
1
1
100 cm are assigned to Si–O–Si unsymmetrical stretch-
Fig. 1 Small-angle XRD patterns of KIT-6, KIT-SO H and Al-KIT-6
3
samples
ing vibration.
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Journal of the Iranian Chemical Society
Fig. 2 Nitrogen adsorption–desorption isotherms at 77 K of mesoporous KIT-6, KIT-SO H and Al-KIT-6. The right column is the pore size dis-
3
tribution of samples
Table 1 Textural properties of KIT-6, KIT-SO3H and Al-KIT-6
Catalytic perꢀormance oꢀ the catalysts
SBET (m g−1)
2
rp (nm)
V (cm g−1)
3
Sample
T
In the present study, catalytic activity of a Bronsted solid
KIT-6
KIT-SO H
Al-KIT-6
840
394
175
3.15
3.15
3.15
0.797
0.592
0.287
acid catalyst (KIT-SO H) is compared to a Lewis acid cata-
3
3
lyst (Al-KIT-6) for the synthesis of butyl levulinate (BL).
At ꢀrst, KIT-SO H was applied in the synthesis of BL from
3
esteriꢀcation of levulinic acid with n-butanol under the
SBET is the BET surface area deduced from the isotherm analysis
rp is the pore diameter calculated using the BJH method
VT is the pore volume at a relative pressure of 0.95
conditions of levulinic acid-to-butanol molar ratio of 1:6,
1
0 mg catalyst, in the temperature range of 70–120 °C and
reaction time of 6 h. The experiments were carried out in a
ꢁ
ask; therefore, the temperature range was selected closed
to the boiling point of n-butanol. The results are presented
in Fig. 6.
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Journal of the Iranian Chemical Society
Fig. 3 SEM images of mesoporous KIT-6 (a), KIT-SO H catalyst (b), Al-KIT-6 catalyst (c) and TEM images of KIT-6 (d)
3
Fig. 4 TGA curves of a KIT-6
and Al-KIT-6 samples under N
2
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Journal of the Iranian Chemical Society
One of the most important parameters in the Fischer
esteriꢀcation reactions is the molar ratio of the alcohol to
carboxylic acid. Since the esteriꢀcation of LA with alcohols
is a reversible reaction, by minimizing the backward reaction
high conversion could be achieved. In this reaction, water
is produced and due to its boiling point which is near the
n-butanol and could not be removed during the reaction, the
higher molar ratio of the alcohol should be used. However,
in higher molar ratios, the molecules occupy the active sites
and reduce catalytic activity. Figure 6 shows the eꢂect of
molar ratio of LA to n-butanol varied from 1:2 to 1:20 at
9
0 °C and using 10 mg KIT-SO H catalyst and reaction time
3
of 6 h. It is evident that with the increase in the molar ratio
of LA to alcohol from 1:2 to 1:14, the ester yield increased
from 11 to 59% suggesting the optimum LA-to-alcohol
molar ratio is 1:14. Further increase in molar ratio to 1:20
decreased the ester yield. In all cases, the n-butyl levulinate
selectivity was near 100%.
Fig. 5 FT-IR spectra of KIT-6, KIT-SO H and Al-KIT-6 samples
3
The highest BL yield was reached at 90 °C. As can be
seen, by increasing the temperature the ester yield increased;
however, in higher temperatures the yield decreased. This
may be attributed to this fact that at higher temperatures the
equilibrium in the esteriꢀcation reaction reversed. Therefore,
The study was further extended to investigation of the
eꢂect of reaction time on the esteriꢀcation reaction. Fig-
ure 7 illustrates the eꢂect of reaction time from 2 to 10 h
for esteriꢀcation at 90 °C and LA-to-alcohol ratio 1:14
and application of 10 mg catalyst dosage. The conversion
was observed to be signiꢀcantly increased up to a reaction
time of 8 h from 18 to 69%. The conversion was found to
9
0 °C was selected as the optimum temperature in further
experiments.
Fig. 6 Conversion of LA to BL under diꢂerent conditions. Reaction condition for each case is given in the main text
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Journal of the Iranian Chemical Society
Fig. 7 Conversion of LA to BL under diꢂerent conditions using Al-KIT-6 catalyst. Reaction condition for each case is given in the main text
be slightly decreased beyond 8 h probably due to revers-
ing the equilibrium backward in prolong time. Thus, the
optimum reaction time was found to be 8 h.
In the next step, the eꢂect of n-butanol-to-LA molar ratio
was examined by using 10 mg Al-KIT-6 catalyst at 130 °C
for 4 h reaction times was examined. The n-butanol-to-LA
molar ratio varied from 2 to 10, and the results are depicted
in Fig. 7. A closer look at the results indicates with the
increase in the alcohol-to-LA ratio from 2 to 6, the yield
increased from 47 to 56%. However, further increase in
molar ratio to 1:10 decreases BL yield probably because of
mass transfer limitation caused by dilution. So in this part,
molar ratio of LA to ethanol 1:6 was chosen as the optimum
ratio.
The eꢂect of catalyst loading amount on the conver-
sion of LA to BL with reaction time of 8 h, molar ratio of
acid to alcohol at 1:14 and reaction temperature of 90 °C
is presented in Fig. 7. A closer look at the results reveals
with the increase in the catalyst amount from 10 to 50 mg,
the BL yield increased from 59 to 95%. Further increase
in catalyst amount decreased the product yield to 61%.
Therefore, the optimum catalyst amount in this reaction
was selected as 50 mg KIT-SO H. For the demonstra-
To evaluate the catalytic activity of Al-KIT-6 catalyst, its
performance was examined at diꢂerent reaction times under
constant other reaction conditions including temperature
130 °C, catalyst loading 10 mg and n-butanol-to-LA ratio
of 6. As shown in Fig. 7c, the maximum yield of BL (66%)
reached at a reaction time of 8 h. When the reaction time was
prolonged to 10 h, the yield decreased to 62%.
3
tion of catalytic activity of KIT-SO H, a reaction under
3
optimum condition (90 °C temperature, 8 h, alcohol to
LA 1:14) without catalyst was performed, and according
to GC analysis, 9% BL was observed. The levulinic acid
esteriꢀcation with alcohols occurs even in the absence of
catalyst due to auto-catalyzed reaction by itself.
In the next stage and in comparison with the catalytic
Subsequently, the eꢂect of the catalyst dosage on the
esteriꢀcation reaction was assessed by changing the amount
of Al-KIT-6 from 10 to 70 mg under optimum reaction con-
ditions: reaction temperature 130 °C, molar ratio of 8:1 of
n-butyl alcohol to LA and reaction time of 8 h. Generally, by
providing more active sites the catalytic activity along with
the increasing catalyst amount could improve. The results
shown in Fig. 7d show that with the increase in catalyst
amount from 10 to 50 mg, the BL yield changed from 66
to 95%. Nevertheless, when catalyst dosage is increased to
70 mg the BL yield decreased to 73%. The results are in
agreement with the reported similar studies in the literature
activity of Al-KIT-6 with KIT-SO H catalyst, the esteriꢀ-
3
cation reaction LA with n-butanol was carried out and the
results are presented in Fig. 7.
The eꢂect of temperature in the range 90–130 °C on
the esterification reaction of LA with n-butanol was
examined on Al-KIT-6 catalyst, and the results are pre-
sented in Fig. 7. The results indicated that the BL yield
was improved with the increase in the temperature. When
the temperature rose to 130 °C, the BL yield increased to
5
5%. Thus, the selected temperature for further studies
was 130 °C.
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Journal of the Iranian Chemical Society
[
33]. This observation may be attributed to this fact that
This may be attributed to deposition of products or interme-
diates on the surface of the catalyst.
more availability of active sites may facilitate the revers
esteriꢀcation reaction. Therefore, under the optimum condi-
tions including reaction time 8 h, temperature 130 °C, molar
ratio of 8:1 of n-butyl alcohol to LA and catalyst amount of
Table 2 shows the results of comparison between activ-
ity of KIT-SO H and Al-KIT-6 compounds and other cata-
3
lysts reported in the literatures for the esteriꢀcation of LA
with n-butanol. A literature survey illustrated that the pre-
sent study is more eꢃcient than the earlier reported val-
ues. Maheria et al. [34] reported maximum BL yield was
obtained as 82.2% using H-BEA zeolite as the solid acid
catalyst. Dharne and Bokade used dodecatungstophosphoric
acid supported on montmorillonite K10 as the heterogene-
ous catalyst in the esteriꢀcation of LA with n-butanol and
obtained 97% BL yield. However, the catalyst was reused
only for two cycles [35].
5
0 mg, a relatively high n-butyl levulinate yield of 95% over
Al-KIT-6 catalyst was obtained.
One of the most important beneꢀts of heterogeneous
catalysts is their ability for regeneration and recycling for
successive runs. In fact, due to economic and environmental
purposes the stability of a heterogeneous catalyst is critical.
After each catalytic run, the catalysts (Al-KIT-6 as well
as KIT-SO H) was recovered by centrifugation, washed by
3
acetone and water (two times), and dried in oven for the use
in the next run. Herein, the reusability of two catalysts was
Recently, Jiang et al. have studied esteriꢀcation LA with
n-butanol by using lipase-based biocatalyst. They reported
74.59% of ester yield after 12 h of reaction time [36]. Song
and co-workers were synthesized series of heteropoly acid
evaluated for six cycles (Fig. 8). For the KIT-SO H catalyst,
3
the catalytic activity was retained in three successive runs.
However, the catalytic performance gradually decreased so
that at 6th run the BL yield was 40%. Since the reactions
were performed at the relatively high temperature and pro-
long time, deactivation of the catalyst may be attributed to
breaking down of propylsulfonic acid groups. The CHNS
analysis evidenced the sulfur content decreased to 0.59%.
For the Al-KIT-6 catalyst, the performance of the catalyst
was observed to be stable for four runs with slight. However,
the catalytic activity slightly decreased from the ꢀfth run.
and ZrO bifunctional organosilica nanotubes (PW12/
2
ZrO –Si(Et)Si–NTs) and studied their catalytic activity in
2
the esteriꢀcation reaction. They reported 69.4% BL yield
after 1 under reꢁux temperature [37]. Zhou et al. prepared
ammonium co-doped phosphotungstic acid and used as the
catalyst in the synthesis of BL. They reported the yield of
esteriꢀcation reaction as 99% after 2 h reaction time without
catalyst recycling [38].
Fig. 8 Recycling of the catalysts in the esteriꢀcation of LA with n-butanol under optimum reaction conditions
Table 2 Comparison of the
Entry
Catalyst
Time (h)
Temperature
°C)
Yield %
References
yields of n-butyl levulinate
obtained in the present study
with those reported in the
literature
(
1
2
3
4
5
6
7
H-BEA zeolite
HPA/K10
4
4
12
1
2
8
120
120
40
120
120
90
82.2
97
74.5
69.6
99
95
95
[34]
[35]
[36]
[37]
[38]
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Immobilized lipase
PW /ZrO –Si(Et)Si–NTs
1
2
2
(NH )0.5Ag0.5H2PW
4
KIT-SO3H
Al-KIT-6
8
130
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Journal of the Iranian Chemical Society
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3
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ꢀ
cation of LA with n-butanol. The successful formation of
KIT-SO H as well as Al-KIT-6 catalysts was conꢀrmed by
3
XRD, nitrogen adsorption/desorption and elemental analysis
techniques. While optimum reaction conditions for the ester-
iꢀcation of LA using KIT-SO3H catalyst were temperature
17. Z. Mohammadbagheri, A.N. Chermahini, J. Ind. Eng. Chem. 62,
4
01–408 (2018)
1
1
2
2
8. A.N. Chermahini, M. Nazeri, Fuel Process. Technol. 167, 442–
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50 (2017)
9
0 °C, alcohol-to-LA molar ratio 14, reaction time 8 h and
9. Z. Mohammadbagheri, A.N. Chermahini, Chem. Eng. J. 361,
450–460 (2019)
catalyst dosage 50 mg, for the Al-KIT-6 the optimum condi-
tions found to be temperature 130 °C, alcohol-to-LA molar
ratio 6, reaction time 8 h and catalyst dosage 50 mg. The
stability and reusability of catalysts were evaluated, and it
was found that Al-KIT-6 showed better stability under reac-
0. Z. Babaei, A.N. Chermahini, M. Dinari, Chem. Eng. J. 352, 45–52
(
2019)
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tion conditions. Therefore, the hybrid catalyst (KIT-SO H)
3
2
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exhibits more eꢃcient catalyst and reaction was carried out
under milder conditions, while Al-KIT-6 catalyst was more
stable.
2
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Acknowledgements The authors are pleased to acknowledge the ꢀnan-
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