Effective transesterification of triglyceride with sulphonated modified SBA-15 (SBA-15-SO3H): Screening, process and mechanism

Article abstract of DOI:10.1016/j.ica.2018.07.032

Different morphologies of ZrO₂ were produced by different templates: ZrO₂(CaCO₃), ZrO₂(C₁₂H₂₅SO₃Na), ZrO₂(C₁₂H₂₅SO₄Na), ZrO₂(CTAB), and solid superacids, such as ZrO₂/SBA-15, SO₄^2-/ZrO₂, SO₄^2-/ZrO₂/SBA-15, and SBA-15-SO₃H. The catalytic transesterification activities of these catalysts were tested. The more highly acidic catalysts and higher surface areas led to higher catalytic activity. In particular, the conversion yield of triglyceride reached 90.1% and was maintained for 90 min at 200 °C with 5.0 wt% SBA-15-SO₃H, indicating this material to be one of most effective acid catalysts for the transesterification process. The mechanism indicated that the most important process was the abstraction of hydrogen from alcohols and α-substituted carboxylic glycerides. In the initial transesterification, the alcohol hydrogen atoms could be attracted onto the surface. Then, the nucleophilic attack of the alcohol led to the α-substituted carboxylic glyceride. Finally, monoglycerides, diglycerides or glycerine were released from the surface by proton (H⁺) replacement.

Full text of DOI:10.1016/j.ica.2018.07.032

Inorganica Chimica Acta 482 (2018) 846–853
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Effective transesterification of triglyceride with sulphonated modified SBA-
5 (SBA-15-SO H): Screening, process and mechanism
1
3
a
a
b
a
a
a
Ningmeng Hu , Zhaoni Kong , Liang He , Ping Ning , Junjie Gu , Rongrong Miao ,
c
a,⁎
d,⁎
Xiangqian Sun , Qingqing Guan , Peigao Duan
a
Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, China
Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming 650500, China
Faculty of Energy & Environment Science, Yunnan Normal University, Kunming 650500, China
Department of Applied Chemistry, Henan Polytechnic University, Jiaozuo 454003, China
b
c
d
A R T I C L E I N F O
A B S T R A C T
Keywords:
Biodiesel
Transesterification
Triglyceride
3
SBA-15-SO H
Different morphologies of ZrO
ZrO (C12H25SO Na), ZrO (CTAB), and solid superacids, such as ZrO /SBA-15, SO /ZrO , SO /ZrO /SBA-15,
2 4 2 2 4 2 4 2
2
were produced by different templates: ZrO
2
(CaCO
3
), ZrO
2
(C12
3
H25SO Na),
2
-
2-
and SBA-15-SO
acidic catalysts and higher surface areas led to higher catalytic activity. In particular, the conversion yield of
triglyceride reached 90.1% and was maintained for 90 min at 200 °C with 5.0 wt% SBA-15-SO H, indicating this
3
H. The catalytic transesterification activities of these catalysts were tested. The more highly
3
material to be one of most effective acid catalysts for the transesterification process. The mechanism indicated
that the most important process was the abstraction of hydrogen from alcohols and α-substituted carboxylic
glycerides. In the initial transesterification, the alcohol hydrogen atoms could be attracted onto the surface.
Then, the nucleophilic attack of the alcohol led to the α-substituted carboxylic glyceride. Finally, mono-
+
glycerides, diglycerides or glycerine were released from the surface by proton (H ) replacement.
1. Introduction
percentage of water or free fatty acids. Some researchers have tried to
use heterogeneous base catalysts; for instance, Lei et al. [11] showed
The declining availability of fossil energy and increased global
that an 87.0% conversion of methyl stearate was achieved at 120 °C for
4 h over MgAl layered double hydroxide. Kouzu et al. [5] reported a
yield of 89% for the transesterification of waste cooking oil with a CaO
heterogeneous base catalyst. Even heterogeneous base catalysts still
react with the free fatty acids to form soaps, though, so it is difficult to
the separate the products [12].
warming drive the exploration of alternative energy sources. Biomass
energy, which is renewable, sustainable and environmentally friendly,
has gained tremendous attention [1,2]. Biodiesel, which is normally
obtained from some animal fats and plant raw materials, has been
widely investigated and is already being used in commercial applica-
tions [3,4]. In 2016, the US had a biodiesel production capacity of
Acid catalysis is more suitable in this situation than is base catalysis
2.6 billion litres. Currently, transesterification is regarded as the best
2 4
[13]. Unfortunately, some mineral acids, such as H SO , are highly
method for producing higher quality biodiesel. However, transester-
ification reactions will proceed either slowly or not at all under normal
conditions. Thus, improvements to the production process of biodiesel
play an important role in this field [5].
Many researchers have tried to enhance the efficiency of biodiesel
production through the use of catalysts, such as enzymes [6], alkalis [7]
and acids [8]. Although using enzyme catalysts has some advantages, it
also suffers from high costs, large reaction volumes and slow reaction
rates [9,10]. Base catalysis is economical and requires low temperatures
and pressures, but the alkaline catalyst will react with the free fatty
acids to form soaps when the raw materials (oils or fats) have a high
corrosive [14]. To avoid the corrosion problems caused by mineral
acids, reusable, non-corrosive and easily removable heterogeneous
solid acid catalysts are a good choice, which can be easily recycled and
give rise to minimal corrosion. Therefore, solid catalysts are often
employed in transesterification reactions [15].
Previously, we reported transesterification by Lewis acid AlCl
3
catalysis in ethanol and carbon dioxide as cosolvents and by a high-
performing sulphonated multi-walled carbon nanotube (S-MWCNT)
[16,17]. In this work, we performed a further screening of different
catalysts. Additionally, some research has shown that mesoporous si-
lica, such as SBA-15 and mesoporous silica (OMS), has a tuneable pore
⁎
Corresponding authors.
E-mail addresses: 15545488@qq.com (Q. Guan), pgduan@hpu.edu.cn (P. Duan).
https://doi.org/10.1016/j.ica.2018.07.032
Received 26 April 2018; Received in revised form 21 July 2018; Accepted 21 July 2018
Available online 25 July 2018
0020-1693/ © 2018 Elsevier B.V. All rights reserved.

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
structure, high surface area and tailored composition, which may be
applied to adsorb compounds, separate gases and perform catalysis
Advance X-ray diffractometer, using Cu Kα radiation (k = 1.5404 Å) at
40 kV and 20 mA in the 2 θ range of 0.5–6.0°. Scanning electron mi-
croscopy (SEM) images of the samples were recorded on a QUANTA
F250 microscope. Transmission electron microscopy (TEM) was ob-
tained using a Tecnai G2 20 microscope operated at 100 kV. The sul-
phonation degree of SBA-15 was determined by X-ray photoelectron
spectroscopy (XPS). FTIR was recorded on a Nicolet iS50 FTIR spec-
trometer equipped with a smart collector using pressed KBr powder
discs.
[
18,19]. Specifically, the morphology of SBA-15 can be tailored ac-
cording to the given requirements [20–22], and the independent outer
particle surface and inner pore surfaces can also be functionalized
[
5,23]. SBA-15 might enhance the catalytic activity of the transester-
ification when acid-functionalized [24,25].
Herein, this work screened and compared different solid acid cata-
lysts under identical conditions. In particular, an efficient solid-acid
catalyst, SBA-15-SO
trilaurin in ethanol at temperatures of 160, 180, 200 and 230 °C. The
textural properties of SBA-15-SO H were characterized by BET, XRD,
3
H, was further studied for the transesterification of
2.4. Experimental process
3
SEM, TEM, XPS, FT-IR and Py-FTIR. The yields of each conversion
process were analysed by high-performance liquid chromatography
The experimental device has been described in detail in our pre-
vious work [16]. Transesterification reactions were performed with
triacylglycerol and liquid ethanol with a mass ratio of 1:10. The SBA-
3
5-SO H catalyst with 5.0 wt% loading was placed in the 4-mL reactor,
(
HPLC). Additionally, the mechanism was discussed to provide an in-
sight into the transesterification reactions of solid acid catalysts.
1
which was vertically positioned in a Techne fluidized sand bath (model
SBL-2). In addition, different kinds of catalysts were used, and then, the
best was selected as the core catalyst in this study. The transester-
ification reaction was carried out at a series of temperatures, i.e., 160,
2
. Experimental section
2.1. Materials
1
9
80, 200 and 230 °C, with a series of times of 15, 30, 45, 60, 75 or
0 min. The vessels were removed from the sand bath and cooled to
Triblock copolymer PEO20-PPO70-PEO20 (P123) and tetraethyl
orthosilicate (TEOS) were purchased from Sigma-Aldrich. (3-
Mercaptopropyl) trimethoxysilane (MPTMS, 98%) was purchased from
room temperature. At last, the products were washed with methanol at
least three times so that all products were recovered.
2 4
MACKLIN. Concentrated H SO (AR) and HCl (AR) were purchased
The products were analysed by HPLC equipped with an AcclaimTM
C18 column (4.6 mm i.d. × 250 mm length). HPLC was conducted
using a mobile phase of 65% methanol and 35% acetonitrile at a flow
rate of 0.8 mL/min for 25 min. The UV detector was set at 210 nm, and
the column temperature was 35.0 °C.
from Chengdu Kelong Chemical Reagent Factory (China) and Tianjin
Fengchuan Reagent Technologies Co. Ltd. (China), respectively.
Trilaurin (98%) and ethanol (99.9%) were supplied from Aladdin. All
other chemicals, including SDS, NaCl and NaOH, were analytic grade
and used without any further purification.
3. Results and discussion
2.2. Catalyst preparation
3.1. Screening of transesterifications by triglyceride catalysts
In this study, we choose different template methods for controlling
the morphologies of ZrO
screening the catalyst. We chose different templates and methods to
prepare ZrO , including, for example, ZrO (CaCO ), which used CaCO
cubes as templates to prepare novel ZrO hollow microboxes [26].
ZrO (SDS) was prepared by a lamellar liquid crystal template method,
using sodium dodecyl sulphate as the template to produce compounded
cubic phase spherical zirconia nanopowder [27].
The catalysts were synthesized using P123 as the template, TEOS as
the main silicon source, and MPTMS as an additional source of silicon.
2
, which has been rewritten in the section on
The experiments to screen and compare with different catalysts used
the transesterification of triglycerides with ethanol as a model reaction.
The different morphologies of ZrO produced by different templates,
including ZrO (CaCO ), ZrO (C12 25SO Na), ZrO (C12 25SO Na),
ZrO (CTAB) and solid superacids, such as ZrO /SBA-15, SO /ZrO
H, were tested. A blank reaction
2
2
3
3
2
2
2
3
2
H
3
2
H
4
2
2
-
2
2
4
2
,
2-
SO
4 2 3
/ZrO /SBA-15 and SBA-15-SO
was also conducted to make a comparison. The reaction time and
temperature were fixed at 60 min and 200 °C, respectively.
The efficiencies for the transesterification of triglyceride are shown
in Table 1. The triglyceride conversion rate of the blank experiment is
very low, but when the catalysts are introduced, the triglyceride con-
version rates increase significantly, indicating that the catalysts all
possess some catalytic activity for the transesterification of triglycer-
ides. However, the activity of different catalysts varies greatly.
The molar ratios of n(P123)/n(TEOS)/n (MPTMS)/n(HCl)/n(H
2
O)
−4
=
7 × 10 /x/0.004/0.24/6.67, where x represents the molar amount
of TEOS. First, 8 g P123 was dissolved in 195.16 ± 0.01 g deionized
water at room temperature, and the solution was stirred for 2 h. Then,
50.05 ± 0.01 g concentrated hydrochloric acid was added and stirred
for 30 min. Afterwards, 15.35 ± 0.01 g tetraethyl orthosilicate was
added and stirred for 45 min, and then, 1.607 ± 0.01 g MPTMS and
Table 1
1
4
6.73 ± 0.01 g hydrogen peroxide were added, followed by stirring at
0 °C for 20 h. The mixture was transferred into a Teflon-lined stainless-
Physicochemical properties and comparison of yield of different catalysts.
steel autoclave, which was then sealed and maintained at 100 °C for
4 h. Lastly, the mixtures were refluxed with 400 mL hydrochloric acid/
Sample
Surface area
Pore volume
(cm /g)
Yield (%)
2
3
(m /g)
2
ethanol solution (volume ratio 2/100) for 12 h to remove the template
P123. The resulting solid products were dried at 80 °C for 8 h to obtain
NO
0
0
1.5
ZrO
ZrO
ZrO
ZrO
2
2
2
2
2
2
2
(CaCO
3
)
67.02
102.01
88.13
69.57
59.87
57.1
63.79
65.42
794.45
567.14
260.53
768.48
0.286
0.39
21.7
38.1
27.5
14.1
19.1
46.7
37.8
49.7
4.7
the SBA-15-SO
.3. Characterization of SBA-15-SO
The N adsorption-desorption isotherms were measured at liquid
3
H.
(C12
(C12
H
H
25SO
25SO
3
Na)
Na)
4
0.393
0.134
0.316
0.137
0.245
0.293
1.036
0.468
0.418
0.891
(CTAB)
2
3
H catalysts
−
2−
SO
SO
4
/ZrO
/ZrO
2
[5%SO
[10%SO
4
(H
2
SO
(H SO
(NH ) SO ]
4
)]
−
2−
4
2
4
2
4
)]
−
2−
2
SO4 /ZrO [5%SO
2
4
4
2
4
2
−
2
nitrogen temperature, −196 °C, on a Micromeritics Tristar 3020 ana-
lyser, from which the specific surface area, pore volume and average
pore diameter were calculated by applying multiple-point Brunauer-
Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) models on ad-
sorption branches. XRD measurements were collected on a Bruker D8
SO
SBA-15
ZrO /SBA-15
4
/ZrO
2
[10%SO
4
(NH
4
)
2
SO
4
]
2
57.7
54.6
88.1
2−
SO
4
2
/ZrO /SBA-15
SBA-15-SO
3
H
847

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
2 3
Fig. 1. N adsorption-desorption isotherm of synthesized catalysts (a); pore size distributions of SBA-15-SO H (b).
3.2. Catalyst characterization
Fig. 1 shows the nitrogen adsorption-desorption isotherms and pore
size distributions. According to IUPAC, the isotherm is a typical type IV
28]. In Fig. 1a, the isotherms with a sharp capillary condensation step
[
in the adsorption and desorption curve, the presence of the H1 hys-
teresis loop indicates that the material has a uniform pore size and good
connectivity, with a 2D hexagonal structure of ordered mesoporous
materials [29]. The BET procedure using P/P at this area of the iso-
0
therms calculated the specific surface areas; using the BJH pore analysis
method yielded the pore size distribution. As seen, the average pore
diameters and pore size distributions of SBA-15-SO
Fig. 1b, showing a narrow pore size distribution.
3
H are displayed in
Fig. 2 shows the low-angle XRD patterns obtained for SBA-15 and
functionalized SBA-15-SO H. An intense diffraction peak at approxi-
mately 2θ = 0.9–1.0°, found in the XRD patterns, is indexed to the
1 0 0) plane, suggesting that the material was ordered in 2D P6 mm
hexagonal mesoporous structures with a uniform mesoporous size dis-
tribution [30]. Obviously, SBA-15-SO H has similar XRD patterns to
3
(
Fig. 2. Small-angle X-ray diffraction patterns for materials SBA-15 and SBA-15-
SO H.
3
3
those of the SBA-15 support, even after the sulphonic acid groups were
introduced into the SBA-15. Furthermore, the mesoporous structure
was virtually retained as evidenced by the SEM and TEM (Fig. 3a-b),
which show regular 2D P6 mm hexagonal mesoporous structures.
Moreover, compared with those of pure SBA-15, the (1 1 0) and (2 0 0)
According to Table 1, SO 2−
/ZrO
[5% SO
2−
4
2
4
4 2 4 2
(NH ) SO ], ZrO /SBA-
1
5 and SBA-15-SO H showed superior activity. These results are con-
sistent with our previous speculation that the more highly acidic cata-
lysts and higher surface areas lead to higher catalytic activity [16,17].
H, achieving an 88.1% yield
of triglyceride. As SBA-15 has no obvious activity in the transester-
3
diffraction peaks of the SBA-15-SO H materials gradually decreased,
3
The most active material was SBA-15-SO
3
and a slight shift in the peak position to higher angles suggested the
decrease in the pore size in the presence of the –SO H groups [31].
3
ification reaction, the increase in efficiency by the modification of
sulphonic acid to make solid superacids is obvious. Since SBA-15-SO
According to these results, it was revealed that the SBA-15-SO H pro-
3
3
H
duction process was successful, and the pore structure of the SBA-15
shows excellent catalytic performance compared with that of those
catalysts, further research will be described in the following section.
after introducing -SO H was not be damaged.
3
Fig. 4 shows the energy positions for the C 1s, O 1s, S 2p and Si 2s on
3
the SBA-15-SO H surface. Fig. 4b reveals the existence of S in the SBA-
3
Fig. 3. Scanning electron microscopy images (a) and transmission electron microscopy images (b) of SBA-15-SO H.
848

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
3
Fig. 4. XPS profiles of SBA-15-SO H.
3
Fig. 6. Py-FTIR spectrum of SBA-15-SO H.
3
Fig. 5. FT-IR spectra of samples: (a) SBA-15; (b) SBA-15-SO H.
the condensed silica network’s asymmetric stretching, symmetric
stretching and bending vibration, respectively [29]. Compared with
1
1
5-SO
68.36 and 169.33 eV are attributed to the binding energies of S 2p3/2
H. The results in-
3
H. As seen in Fig. 4c, the S 2p photoelectron peaks centred at
SBA-15, the SBA-15-SO
3
H has new IR absorption bands at 2918 and
and S 2p1/2, respectively, which are typical of -SO
dicate the complete oxidation of the mercapto groups to sulphonic
groups [32]. In the O 1 s spectrum, due to the chemical states of oxygen
in H SO and -SO H, there are peaks of the SeOH bonds and SeO bonds
2 4 3
located at 531.3 and 533.3 eV, respectively [33]. Therefore, we could
infer by the presence of oxygen and sulphur that sulphonic acid groups
3
−1
2849 cm , which could be reasonably assigned to the methylene C–H
−1
stretching vibration of propyl groups [29]. The IR band at 2575 cm
was presumably due to the S-H stretching vibration. However, in
Fig. 5b, the band has disappeared, due to the formation of -SO H groups
3
−1
after oxidation with
H
2
O
2
[34]. The bands at 3432 cm
can be assigned to SeOH stretching vibration. In addition,
O]S]O asymmetric and symmetric stretching vibrations of eSO
and
−1
1631 cm
3
were successfully attached to the surface of SBA-15-SO H [34].
3
H
FT-IR spectroscopy, plotted in Fig. 5, further evidences that the
organosulphonic acid groups are added into the mesoporous structure
of SBA-15. In the FT-IR spectrum, three peaks at 1100, 770 and
−1
−1
groups appeared at 1080 cm
existence of sulphonic acid groups in the SBA-15-SO
ganosulphonic groups have been successfully added into the SBA-15
and 1065 cm , which indicates the
3
H. In all, the or-
−1
450 cm belong to the vibrations of Si-O-Si bond, which correspond to
849

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
with SBA-15 was 4.7%, while that with SBA-15-SO
3
H reached 88.1%.
Therefore, the acid strength of the SO
catalysis.
3
H groups plays a vital role in
3
3.3. Transesterification of trilaurin by SBA-15-SO H
We further evaluated the effects of the sulphonated modified SBA-
5 catalyst on the efficiency of the transesterification of triglyceride.
1
The experiments were conducted using different temperatures and
times as parameters. The detailed reaction conditions were a trigly-
ceride mole ratio of 1:10 with ethanol, 5.0 wt% loading for the SBA-15-
SO H catalyst, reaction temperatures of 160, 180, 200 or 230 °C, and
3
reaction times of 15, 30, 60, 75 or 90 min.
In Fig. 7, we observed an approximately 90% yield of ethyl esters at
200 and 230 °C within 90 min. At the lower temperatures, however, the
ethyl ester yield was very low, with a maximum of approximately 6.5%.
At the same reaction time, with the increase in temperature, the yield of
ethyl ester steadily increased. Certainly, the longer time and higher
temperature benefit the transesterification of triglyceride.
Fig. 7. Ethyl ester yield as a function of reaction temperature and time on SBA-
3
15-SO H.
Guan et al. reported the kinetics of the trilaurin transesterification
to ethyl esters, in which the products include ethyl esters (EE), unethyl
esterified compounds (uEE) and glycerin (GL) [17]. Our experimental
results illustrate that a large amount of EE and uEE were produced; the
primary products were EE, with over 90% of the total yield, and the
others were uEE.
support to produce the SBA-15-SO
To elucidate the acid sites in the SBA-15-SO
spectrum of adsorbed pyridine. It can be seen from Fig. 6 that the in-
3
H catalyst.
3
H, we used the FTIR
−
1
frared absorption at 1450 cm is attributed to pyridine adsorption on
−1
the Lewis acid sites, while the infrared absorption at 1545 cm
longs to the Brønsted acid sites that were mainly due to the eSO
groups [35]. There are infrared absorption peaks at 1455 and
be-
3
H
Furuta et al. [7] compared the conversions of transesterification
2−
−1
with solid superacid catalysis of SO
4
2
/SnO (STO), tungstated zirco-
1
546 cm , which illustrate that the sample has Lewis and Brønsted
nia–alumina (WZA) and sulphated zirconia–alumina (SZA), finding
conversions of only 10%, 47% and 26% at 200 °C, respectively. To
reach 90% conversion, a high reaction temperature (250 °C) and long
reaction time (20 h) were required by the tungstated zirconia-alumina
(WZA) [37]. Jacobson et al. [38] reported low ester yields (65%) at
acid sites [36]. Moreover, the acidity of the sulphonic acid-functiona-
lized SBA-15 was determined by acid-base titration. A 0.05 g sample
was dispersed in 30 g NaCl (10 wt%) solution, stirred at room tem-
perature for 24 h, and then filtered. The filtrate was titrated with
−
1
0
1
.05 mol L
NaOH solution, and the acid amount was found to be
H, whereas blank SBA-15 had no acid
2−
10 h and 200 °C over WO
3
on ZrO
2 2
–Al O
3
. Additionally, SO
4
/ZrO
2
.95 mmol/g for SBA-15-SO
3
provided the highest yield of methyl esters, 90.3%, at 4 h and 200 °C
amount. When we performed the reaction for 60 min at a temperature
of 200 °C with 5.0 wt% catalyst, the conversion yield of triglyceride
2−
[
39]. Another study showed that SO
4
2
/ZrO only achieved a yield of
85% at 230 °C [37]. One of the solid zeolite catalysts was also applied to
3
Scheme 1. The mechanism of the catalytic transesterification by SBA-15-SO H.
850

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
Scheme 2. Homogeneous base-catalysed reaction mechanism for the transesterification.
the transesterification, but the highest biodiesel yield attained was only
6.6% at a rather high reaction temperature of 460 °C. Compared with
those catalysts, SBA-15-SO H in our study presented a high yield in a
short time and at a moderate temperature. Therefore, this catalyst is
one of most effective acid catalysts for the transesterification process.
hydrogens from alcohols and α-substituted carboxylic glyceride. The
following section will give a detailed discussion about the mechanism.
The abstraction of hydrogen from alcohols is the essential process
for the transesterification of triglyceride. Pham et al. [40] gave an in-
sight review about the ketonization of carboxylic acids over solid acids,
which is somewhat similar to the transesterification of triglyceride.
Ketonization (or ketonic decarboxylation) is a reaction that converts
two carboxylic acid molecules into a ketone, carbon dioxide, and water,
which has been well studied since 1858. The process proposes the re-
quirement for an α-hydrogen in at least one of the carboxylic acids
participating in the reaction, which has been well documented. The α-
2
3
3.4. Mechanism
The reactions of transesterification of triglyceride over solid acid
catalysts are different from the base catalysts, as shown in Scheme 1.
We postulated that the most important processes are the abstraction of
Scheme 3. Proposed β-ketoacid-based mechanism for the ketonization of carboxylic acid.
851

N. Hu et al.
Inorganica Chimica Acta 482 (2018) 846–853
hydrogen is defined as the hydrogen atom bonded to a carbon atom in
the α position relative to a carbonyl group. Similarly, we also proposed
the abstraction of hydrogen from alcohol onto the surface, which can
enhance the nucleophilicity of alcohols.
Environ. Prog. Sustain. Energy 33 (2014) 1432–1437.
[
5] A. Brito, M.E. Borges, N. Otero, Zeolite Y as a Heterogeneous Catalyst in Biodiesel
Fuel Production from Used Vegetable Oil, Energy Fuels 21 (2007) 3280–3283.
6] D. Royon, M. Daz, G. Ellenrieder, S. Locatelli, Enzymatic production of biodiesel
from cotton seed oil using t -butanol as a solvent, Bioresour. Technol. 98 (2007)
[
6
48–653.
There would be some disputes about which O atom of the trigly-
ceride would be attacked by the acidic surface. One potential pathway
is that the O atom of the carboxyl group would be protonated by the
acid catalyst surface, rather than the α position, i.e., the oxygen atom
on the CeOeC [41]. This pathway will be similar to a homogeneous
acid-catalysed reaction mechanism for the transesterification of trigly-
cerides proposed by Lotero, Liu, Lopez, Suwannakarn, Bruce and
Goodwin [42]. This mechanism involves protonation of the carbonyl
group by the acid catalyst and then nucleophilic attack of the alcohol,
forming a tetrahedral intermediate, followed by proton migration and
breakdown of the intermediate, as shown in Scheme 2. The mechanism
is similar to the β-ketoacid intermediate mechanism for the ketoniza-
tion of carboxylic acid. This mechanism is shown in Scheme 3, where M
represents a metal. Proton migration and breakdown of the inter-
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[
2
mediate tend to form H O as an intermediate [43]. However, we did not
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Thus, we prefer α-substituted carboxylic glyceride as the main
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[
[
3
trons for the eSO H. The attack to the oxygen atom will result in a
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[
[
3
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Scheme 1.
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3
5-Ph-SO H) as a novel hydrophobic nanoreactor solid acid catalyst for a one-pot
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3
catalysts and higher surface areas lead to higher catalytic activity. The
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glyceride. In the initial transesterification, the hydrogen atom of the
alcohol can be attracted to the surface. Then, the nucleophilic attack of
the alcohol leads to the α-substituted carboxylic glyceride. At last,
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[
[
[
[
[
3
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+
by proton (H ) replacement.
Acknowledgements
This work is supported by the National Natural Science Foundation
of China (21767015) and National Key R&D Program of China
2017YFC0210504), Collaborative Innovation Centre of Western
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3
H) as an efficient catalyst for the one-pot synthesis of
Typical Industry Environmental Pollution Control.
[
[
2
3
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at https://doi.org/10.1016/j.ica.2018.07.032.
[
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