Synthesis of glycerol carbonate from glycerol and dimethyl carbonate over DABCO embedded porous organic polymer as a bifunctional and robust catalyst

Article abstract of DOI:10.1016/j.apcata.2018.06.022

A large surplus of glycerol from the rapidly growing biodiesel industry has led to the conversion of glycerol into higher value-added products being of great industrial importance. In this paper, a promising route for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate is described using DABCO (1,4-diazabicyclo[2.2.2]octane) embedded porous organic polymer as an efficient and robust catalyst. The porous catalyst with base sites and hydrophilic units (monoquaternized DABCO) was facilely synthesized through a one-pot radical copolymerization of divinylbenzene and vinyl functionalized DABCO monomer. By simply varying the mass ratio between divinylbenzene/DABCO monomer, the surface area, pore volume and surface wettability of the catalyst can be easily adjusted. Results of activity evaluations indicated that the catalyst with high surface area and excellent amphiphilicity exhibits much higher activity than other samples due to the enhanced accessibility of catalytic sites and mass transfer efficiency. Under the optimum reaction conditions, a 0.75 mol% catalyst loading is sufficient for excellent yield of glycerol carbonate in 60 min. Moreover, the optimized catalyst also shows excellent reusability and could be reused up to 13 consecutive recycles without obvious deactivation in activity.

Full text of DOI:10.1016/j.apcata.2018.06.022

Accepted Manuscript
Title: Synthesis of glycerol carbonate from glycerol and
dimethyl carbonate over DABCO embedded porous organic
polymer as a bifunctional and robust catalyst
Authors: Yali Wan, Yizhu Lei, Guosong Lan, Dingfu Liu,
Guangxing Li, Rongxian Bai
PII:
S0926-860X(18)30276-X
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2018.06.022
APCATA 16710
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
27-2-2018
10-5-2018
5-6-2018
Please cite this article as: Wan Y, Lei Y, Lan G, Liu D, Li G, Bai R, Synthesis of
glycerol carbonate from glycerol and dimethyl carbonate over DABCO embedded
porous organic polymer as a bifunctional and robust catalyst, Applied Catalysis A,
General (2018), https://doi.org/10.1016/j.apcata.2018.06.022
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Synthesis of glycerol carbonate from glycerol and dimethyl carbonate over
DABCO embedded porous organic polymer as a bifunctional and robust catalyst
Yali Wan a,c, Yizhu Lei a,* , Guosong Lan a, Dingfu Liu c, Guangxing Li b,* , Rongxian
Bai b
a
School of Chemistry and Materials Engineering, Liupanshui Normal University,
Liupanshui, Guizhou 553004, PR China
b
School of Chemistry and Chemical Engineering, Huazhong University of Science
and Technology, Wuhan, Hubei 430074, PR China
c
School of Chemistry and Chemical Engineering, Guizhou University, Guiyang,
Guizhou 550025, PR China
*Corresponding authors.
E-mail addresses: yzleiabc@126.com (Y. Lei), ligxabc@163.com (G. Li).
Graphical Abstract
Highlights
•
A bifunctional catalyst that contains base sites and hydrophilic units was
prepared.
•
•
•
The surface area, pore volumes and wettability can be adjusted.
The catalyst exhibits high catalytic activity and excellent reusability.
The amphiphilic and porous structure led to the superior performance.
Abstract
A large surplus of glycerol from the rapidly growing biodiesel industry has led to
the conversion of glycerol into higher value-added products being of great industrial
1

importance. In this paper, a promising route for the synthesis of glycerol carbonate
from glycerol and dimethyl carbonate is described using DABCO
(1,4-diazabicyclo[2.2.2]octane) embedded porous organic polymer as an efficient and
robust catalyst. The porous catalyst with base sites and hydrophilic units
(monoquaternized DABCO) was facilely synthesized through a one-pot radical
copolymerization of divinylbenzene and vinyl functionalized DABCO monomer. By
simply varying the mass ratio between divinylbenzene/DABCO monomer, the surface
area, pore volume and surface wettability of the catalyst can be easily adjusted.
Results of activity evaluations indicated that the catalyst with high surface area and
excellent amphiphilicity exhibits much higher activity than other samples due to the
enhanced accessibility of catalytic sites and mass transfer efficiency. Under the
optimum reaction conditions, a 0.75 mol% catalyst loading is sufficient for excellent
yield of glycerol carbonate in 60 min. Moreover, the optimized catalyst also shows
excellent reusability and could be reused up to 13 consecutive recycles without
obvious deactivation in activity.
Keywords: Glycerol carbonate; Glycerol; Transesterification; Porous organic
polymers; Bifunctional catalyst.
1. Introduction
Biodiesel, as a renewable clean energy, plays an important role in the sustainable
energy supply [1]. However, with the rapid growth of biodiesel industry, a large
2

amount of glycerol (GL) is generated as a main by-product during the production of
biodiesel [2]. The overplus of GL weakens the competitiveness of biodiesel industry
[3]. Therefore, the efficient utilization method of GL is becoming vital importance for
promoting biodiesel commercialization. To date, various GL derivatives have been
successfully prepared from GL [4-6]. Among them, glycerol carbonate (GC) is one of
the most promising chemical, which can be used as polar solvent, surfactant
component, gas separation membranes, carries in batteries and polymer intermediates
[7,8].
Several approaches have been reported in literatures for the synthesis of GC from
GL. These approaches include phosgenation [9], oxidative carbonylation with carbon
monoxide and oxygen [10-12], carbonation with CO2 [13,14], glycerolysis of urea
[15,16], transesterification with dimethyl carbonate (DMC) [17] and so on. Among
them, transesterification of GL with DMC represents one of the most promising
method for the preparation of GC, because this method helps avoid unfavorable
thermodynamic equilibrium, low reaction rate, toxic materials and harsh reaction
conditions [18].
The key in the transesterification reaction of GL with DMC is to develop highly
efficient catalysts. Therefore, a number of catalytic systems have been developed in
recent years. Homogeneous catalysts, such as NaOH, KOH, K2CO3, 1,8-diazabicyclo
[5.4.0]
undec-7-ene
(DBU),
1,4-diazabicyclo[2.2.2]octane
(DABCO),
p-toluenesulfonic acid and H2SO4, were demonstrated to be highly active for this
transesterification [19-24]. Although the homogeneous systems usually exhibit high
3

catalytic activity, they suffer from the practical problems in terms of catalyst
separation and reuse. And besides, after the reaction, the distillation separation of GC
and GL in the presence of homogeneous catalysts often results in severe
decomposition of GC.
For facile catalyst recovery and product separation, calcium based catalysts such
as CaO and CaCO3, were used as efficient catalysts for the transesterification of GL
with DMC. However, it was found that highly active homogeneous calcium species
was formed during the transesterification reaction [25]. Moreover, other solid
catalysts, such as mixed metal oxides [26-31], silicates [18], NaOH/γ-Al2O3 [32],
KF/Al2O3 [33] and Ti-SBA-15 [34], were also tested towards this transesterification.
But these solid catalysts suffered from either high catalyst loadings or poor
reusability.
Recently, Kim and Lee et al. made an important contribution to the catalytic
transesterification of GL and DMC by anchoring DABCO on Merrifield peptide resin
as an active and heterogeneous catalyst [35]. This “post-immobilization” method
provides a solution to the problems of organocatalyst recovery and reuse. However,
“anchored” molecular catalysts often suffer from poor stability, less and
inhomogeneously distributed active sites, as well as low efficiency in mass transport
[36,37]. To solve these problems, we suspected that the construction of DABCO
functionalized porous organic polymers directly from the radical copolymerization of
divinylbenzene (DVB) and vinyl functionalized DABCO monomer through a
“bottom-up” strategy, may possibly overcome these drawbacks. Porous organic
4

polymers, which were prepared by radical polymerization of vinyl monomer under
solvothermal conditions, often possess large surface areas and hierarchical porosities
[38-40]. Generally, the catalysts with these properties could greatly increase the
accessibility of catalytic sites and facilitate the mass transfer process. Indeed, this
bottom-up approach for constructing porous catalysts with hierarchical porosities has
recently found success [41-44].
Another point to be noted in this transesterification reaction is that hydrophilic
GL and hydrophobic DMC are not miscible and the reaction is reversible [45]. The
reaction inevitably suffers from high mass transfer resistance, and thus led to the low
reaction efficiency. To overcome this problem, co-solvent or excessive amount of
DMC are usually added to reduce mass transfer resistance [7]. However, extra
procedures and energy are usually needed to remove these solvent or excessive
amount of DMC from the final products. In view of this, design and synthesis of
functional catalyst that has excellent solubilization capacity for the immiscible
substrates is worthy of careful study.
Herein, a bifunctional catalyst that has excellent solubilization capacity and high
catalytic activity was facilely synthesized in a nearly quantitative yield through a
one-pot radical copolymerization of divinylbenzene (DVB) and vinyl functionalized
DABCO monomer. By varying the mass ratio between DVB/DABCO monomer, five
porous polymers with different DABCO contents were obtained. The obtained
catalysts are characterized by FT-IR, BET, SEM, TEM, XPS, TGA, Solid state 13C
NMR, elemental analysis and wettability measurement. The catalytic performances of
5

the prepared catalysts were evaluated on the transesterification of GL with DMC.
Meanwhile, the catalytic activities of the synthesized catalysts were also compared
with that of a DABCO post-modified poly(divinylbenzene-co-vinylbenzyl chloride).
2. Experimental
2.1. Chemicals
1,4-Diazabicyclo[2.2.2]octane (DABCO) and 4-vinylbenzyl chloride (VBC, 90%)
were purchased from Energy Chemical and used as received. Divinylbenzene (DVB,
85%) was purchased from Alfa Aesar and washed with NaOH aqueous solution (0.5
M) and deionized water for three times before use. 2,2’-Azobis(2-methylpropionitrile)
(AIBN) was got from Aladdin Chemistry Co., Ltd. (Shanghai, China). Glycerol,
dimethyl carbonate and glycerol carbonate were analytical reagent grade and used
without further purification.
2.2 Synthesis of DABCO monomer
Vinyl functionalized DABCO monomer (DABCO monomer) was prepared via a
simple quaternization reaction between 4-vinylbenzyl chloride and DABCO at room
temperature. As a typical run, 1.68 g (15 mmol) of DABCO was dissolved in 10 mL
of ethyl acetate. Then, a solution of 4-vinylbenzyl chloride (1.53 g, 10 mmol) in 6 mL
ethyl acetate was dropwise added. Under N2 atmosphere, the mixture was stirred at
room temperature for 1 h. The resulting yellow precipitate was filtered, washed with
ethyl acetate, and then vacuum dried at 25 °C (2.23 g, 84% yield).
2.3 Preparation of P(DVB-DABCO)-x
In a typical procedure, DVB (1.2 g), DABCO monomer (0.8 g), DMF (20 mL) and
6

AIBN (50 mg) were added into in a 100 mL Teflon autoclave. After replacement of air
with nitrogen and stirring at room temperature for 1 h, the autoclave was heating in
oven at 100 °C for 24 h. The resulting solid monolith was extracted with ethanol and
dried under vacuum (30 °C). The obtained pale-yellow solid was denoted as
P(DVB-DABCO)-0.4, where x (x = 0.4) refers to the mass ratio of DABCO monomer
in the total monomers. Other P(DVB-DABCO)-x samples that have different DABCO
monomer ratios, were prepared as the same synthetic procedures of
P(DVB-DABCO)-0.4.
2.4 Preparation of P(DVB-VBC)-DABCO
P(DVB-VBC)-DABCO, which has DABCO grafted on pre-made porous
copolymer of DVB and VBC, was prepared as follows. DVB (1.2 g), VBC (0.51 g),
THF (15 mL) and AIBN (50 mg) were added into a 100 mL Teflon autoclave. After
replacement of air with nitrogen and stirring at room temperature for 1 h, the
autoclave was heating in oven at 100 °C for 24 h. The resulting solid was extracted
with ethanol and dried under vacuum (30 °C). The obtained white solid was denoted
as P(DVB-VCB). Then, P(DVB-VCB) (1.0 g) and DABCO (0.6 g) were well mixed
in 30 ml DMF, and stirred at 40 °C for 8 h. The resulting solid monolith was washed
with ethanol and vacuum dried at 30 °C for 24 h. The obtained pale-yellow solid was
denoted as P(DVB-VBC)-DABCO.
2.5 Transesterification of DMC with GL
The transesterification reaction was conducted in a 50 mL three-necked flask and
fitted with condenser and nitrogen balloon. Generally, GL (60 mmol) and DMC (180
7

mmol) were loaded into the flask where they formed two phases. After replacement of
air with nitrogen, the mixture was heated with stirring to 85 °C (the reactants are still
in two phases at this temperature) and the catalyst was subsequently added to start the
reaction. After reacting at 85 °C for 60 min, the flask was cooled to room temperature,
and the solid catalyst was separated by centrifugation and washed with methanol for
three times. For the recycling experiments, the obtained solid catalyst was dried under
vacuum (30 °C), and then engaged in a new catalytic run.
2.6 The number of basic sites
The number of basic sites (tertiary amine) was calculated from the amount of
hydrochloric acid that reacted with the prepared samples [46]. Generally, 0.5 g sample
was added into 30 mL HCl solution (0.05 mol/l). After magnetically stirred for 24 h,
15 mL of the filtrate was pipetted, and the excessive acid was titrated with 0.05 mol/l
NaOH (phenolphthalein as an indicator). All titrations were carried out at room
temperature. All experiments were run thrice and mean values were reported, with
relative deviation lower than 3%.
2.7 Catalyst characterization
Nitrogen sorption isotherms were performed by a Micrometrics ASAP 2020 system
at 77 K, and the catalysts were pre-treated under vacuum at 90 °C for 12 h before the
measurements. The surface area was calculated by using the Brunauer-Emmett-Teller
(BET) method. The pore size distribution was calculated by the nonlocal density
functional theory (NLDFT) method. Fourier Transform Infrared Spectroscopy (FT-IR)
was recorded on a Bruker Equinox 55 FT-IR spectrophotometer using KBr pellet
8

technique, over a range of 4000-400 cm-1 at 2 cm-1 resolution. The thermogravimetric
analysis (TGA) was measured on a NETZSCH STA 449 F5 instrument under a
dynamic argon atmosphere, and the sample was analyzed from room temperature to
500 °C with a heating rate of 10 Kmin-1. The size and morphology of the catalyst
were observed with a TESCAN MIRA3 field emission scanning electron microscope
(FE-SEM) operated at an accelerating voltage of 15 kV. Transmission electron
microscopy (TEM) was measured on a FEI Tecnai G2 F30 instrument. X-ray
photoelectron spectroscopy (XPS) was carried out on a VG multilab 2000
spectrometer using a Mg-AlKa X-ray source, and the C1s transition was adjusted to
284.8 eV. The elemental analysis was performed on an Elementar Vario MICRO
Elemental analyzer, and the samples were pre-treated under vacuum at 90 °C for 12 h
1
before the measurements. H and 13C NMR spectra were recorded on a Bruker
AVANCE III NMR spectrometer (400 and 100 MHz) at ambient temperature with
CDCl3 as solvent. Solid-state 13C NMR spectra were carried out on a Bruker
AVANCE III 600 Bruker spectrometer equipped with a 4 mm double resonance MAS
probe.
2.8 Product analysis
All the components were analyzed on a gas chromatograph (Scientific™ TRACE™
1310 apparatus) equipped with a TRACE TR-WAX capillary column and a flame
ionization detector (FID). The internal standard method was used with N,N-dimethyl
formamide as an internal standard substance. Nitrogen (99.99%) was used as the
carrier gas with a flow rate of 25 mL/min. The injector and detector temperatures
9

were set as 280 °C. The column temperature was programmed to have a 1 min initial
hold at 60 °C, a 20 °C/min ramp from 60 °C to 250 °C and an 8 min hold at 250 °C.
The conversion of GL, the yield and selectivity of GC were determined using Eqs. (1),
(2) and (3), respectively:
GLi ni t i al - GLresi dual
Conversion (mol%), C =
 100%
 100%
(1)
GL
i ni t i al
GC
GL
Yield (mol%), Y =
 100%
(2)
i ni t i al
GC
Selectivity (mol%), S =
(3)
GLi ni t i al - GLresi dual
3. Results
3.1. Synthesis of P(DVB-DABCO)-x
DABCO embedded porous organic polymers P(DVB-DABCO)-x, where x refers
to the mass fraction of DABCO monomer in the total monomers, were synthesized in
almost quantitative yields under N2 atmosphere through the radical copolymerization
reaction of DVB and DABCO monomer at 100 °C for 24 h (Scheme 1). By varying
the mass fraction of DABCO monomer, five porous polymers with different DABCO
contents were obtained (P(DVB-DABCO)-x, x = 0.2, 0.3, 0.4, 0.5, 0.6).
<Scheme 1>
3.2. The porous structure and morphology of the catalysts
BET surface areas, pore volumes and average pore radius of the prepared catalysts
are shown in Table 1. The results suggest that both the specific surface areas and pore
volumes are falling rapidly with the increase of DABCO contents (Table 1, entries
1-5). The samples with low DABCO contents, P(DVB-DABCO)-0.2,
10

P(DVB-DABCO)-0.3 and P(DVB-DABCO)-0.4, show high surface areas of 781
m2g-1, 644 m2g-1 and 412 m2g-1, respectively. While the samples with higher
DABCO contents, P(DVB-DABCO)-0.5 and P(DVB-DABCO)-0.6, show lower
surface areas of 191 m2g-1 and 20 m2g-1, respectively. The rapid decrease in surface
areas and pore volumes should be attributed to the decreased cross-linking degrees of
the samples and the increased pore blockage by the DABCO unit. For comparison,
P(DVB-VBC)-DABCO, which has a similar chemical composition to that of
P(DVB-DABCO)-0.4, was prepared by a post-modification method. However, only a
11 m2g-1 surface area was observed. Nitrogen adsorption-desorption isotherms of
P(DVB-DABCO)-x (x = 0.2, 0.3, 0.4, 0.5) and pore size distribution curve of
P(DVB-DABCO)-0.4 are shown in Fig. 1. The samples with x varied from 0.2 to 0.4
exhibit combined sorption behavior of type I and type IV. The adsorption at low
pressure (P/P0 < 0.01) is due to the filling of micropores, the hysteresis loops at higher
relative pressure (P/P0 = 0.7-1.0) implies the presence of mesoporosity and a sharp
rise at medium and high-pressure regions (P/P0 = 0.8-1.0) indicates the presence of
macropores in these materials. Pore size distribution curve of P(DVB-DABCO)-0.4
based upon the NLDFT calculation method reveals that the sample has a very broad
pore size distribution, suggesting its hierarchical porous structure comprised of
micropores, mesopores and macropores.
< Table 1>
< Fig. 1>
SEM images of the samples are shown in Fig. 2 and Fig. S1 (Supplementary
material). The images show that the primary particles of the copolymers are irregular
11

small particles in nanometer level. When the x values of the samples are lower than
0.5 (x = 0.2, 0.3, 0.4), the small particles are loosely packed into large aggregates,
resulting in coralline-like morphology. However, the particles of the samples with
higher x values (x = 0.5, 0.6) are tightly interacted and packed into microspheres.
Representative TEM images (Fig. S2, Supplementary material) of
P(DVB-DABCO)-0.4 further confirm its rough surface, loosely packed and
coralline-like morphology.
< Fig. 2>
3.3. The chemical composition of catalysts
The FT-IR
spectra
of P(DVB-VCB),
P(DVB-VBC)-DABCO and
P(DVB-DABCO)-x (x=0.3, 0.4, 0.5) are shown in Fig. 3. The results show that the
catalysts that were prepared by both post-immobilization and one-pot strategy have
very similar infrared absorption (Fig. 3, b-e). The bands at 2921 and 2841 cm−1 are
attributed to the stretching vibration of -CH2 and -CH groups. Bands at 1607 and 1453
cm-1 correspond to C-C stretching vibrations in aromatic ring. To confirm the
quaternization of P(DVB-VCB), the FT-IR spectrum of P(DVB-VCB) was also
analyzed. As depicted in Fig. 3 (a), P(DVB-VCB) shows a C-Cl stretching band at
1265 cm−1 [47]. While the band at 1265 cm−1 is disappeared in
P(DVB-VBC)-DABCO. These results indicate that the quaternization reaction
between P(DVB-VCB) and DABCO was finished.
< Fig. 3>
To obtain information on the elemental compositions, XPS analyses have been
performed on P(DVB-DABCO)-0.3, P(DVB-DABCO)-0.4 and P(DVB-DABCO)-0.5.
12

In Fig. 4(a), XPS full spectra of the samples conform that N, C and Cl elements are
present in the copolymers. In Fig. 4(b), XPS results for N1s show that two types of N
namely -N (399.8 eV) and -N+ (402.4 eV) [48] are present in the samples. These
results confirm the successful incorporation of DABCO unit into the prepared
polymer.
< Fig. 4>
The amount of total N (quaternary and tertiary N) and tertiary N were determined
by elemental analysis and HCl titration, respectively (Tables S1 and S2 in the
Supplementary material). The results show that both the total N and tertiary N are
very close to the nominal amount, with relative deviation lower than 5%. Hence,
nominal DABCO amount was used for the following catalytic experiments.
Solid-state
13C
NMR
spectra
of
the
P(DVB-DABCO)-0.2
and
P(DVB-DABCO)-0.4 polymers are shown in Fig. 5. The signals ranged from 127.2 to
145.0 ppm are assignable to the aromatic carbons [44] of the polymers. Compare to
13
the C NMR spectrum of DABCO monomer (Supplementary material), the signal at
67.8 ppm could be attributed to the “−CH2−’’ linker between aromatic ring and
quaternary nitrogen atom. And the signals at 52.3 ppm and 45.2 ppm should be
assigned to the carbon atoms in the DABCO units that bonded to tertiary and
quaternary nitrogen, respectively. These results are consistent with the signal
intensities of the two samples at 67.8, 52.3 and 45.2 ppm. These signal intensities of
P(DVB-DABCO)-0.2 are lower than that of P(DVB-DABCO)-0.4 due to the lower
content of the DABCO units. Moreover, the signals at 40.6 ppm could be attributed to
the polymerized vinyl groups [49]. These observations provide further evidence for
13

the successful synthesis of a base catalyst.
< Fig. 5>
The thermostability of the samples was examined by thermogravimetric analysis
(TGA). As depicted in Fig. 6, the samples with different x values show similar TGA
curves. There are no obvious weight losses below 250 C, and rapid weight losses
take place at 350-500 C. These results suggested that the samples can be at least
stable up to 250 C.
< Fig. 6>
3.4. The wettability measurement of catalysts
Previous work by Xiao et al. demonstrated that polydivinylbenzene (PDVB) is
superhydrophobic [50]. Given that DABCO moiety could impart the wettability of the
samples, the wettability of P(DVB-DABCO)-x polymers were thus tested. The
wettability was firstly examined by the contact angle measurements (Fig. 7). Fig. 7(a)
and Fig. 7(b) illustrate the contact angles of P(DVB-DABCO)-0.2 and
P(DVB-DABCO)-0.3 for water, respectively. The contact angle between water and
P(DVB-DABCO)-0.2 was only 30, indicating its good hydrophilicity. While for
P(DVB-DABCO)-0.3, the water was quickly absorbed without any residue, the
contact angle was recorded as 0°. Indeed, other samples which have bigger x values,
show the same phenomenon as that of P(DVB-DABCO)-0.3. These results indicate
that highly hydrophilic P(DVB-DABCO)-x polymers could be obtained by varying
the mass fraction of the hydrophilic DABCO unit, and higher mass fractions of
DABCO unit led to more hydrophilic polymers. The wetting properties of the samples
for GL were also tested. Considering the high viscosity and hygroscopicity of GL, the
14

pictures of the GL droplets on the surface of the samples were taken at 30 seconds
after their contact. The representative photographs were depicted in Fig. 7(c-f). The
contact angles were about 35° and 14° for P(DVB-DABCO)-0.2 and
P(DVB-DABCO)-0.3, respectively. For the samples with higher x values (x = 0.4, 0.5
and 0.6), the GL droplets were absorbed without any residue within 30 seconds, the
contact angles were recorded as 0°. To test the lipophilicity of P(DVB-DABCO)-x
polymers, contact angle measurements between DMC and the polymers were also
conducted. The DMC drops were quickly absorbed without any residue for all of the
prepared P(DVB-DABCO)-x polymers, suggesting their very high lipophilicity.
Experiment results of contact angle measurements show that the prepared copolymers
exhibit excellent wettability for GL and DMC, especially the samples with higher x
values. This implies excellent miscibility of GL with DMC in the P(DVB-DABCO)-x
samples.
The samples were also dispersed in H2O and hexane to further investigate their
amphiphilicity and solubilization capacity for hydrophilic and hydrophobic substances.
Fig. S3 in the Supplementary material shows the dispersion behaviors of the prepared
samples in pure water. The results suggest that all of the prepared P(DVB-DABCO)-x
polymers could be well dispersed in water. For comparison, the superhydrophobic
PDVB that was prepared according to the procedures in the literature [43], was
suspended at the water surface. Fig. S4 shows the dispersion behaviors of the
polymers after adding a certain amount of hexane. The results show that the
superhydrophobic PDVB was well dispersed in hexane, and P(DVB-DABCO)-0.2
15

was also extracted to the upper phase. But it is not difficult to notice that the water
volume in the aqueous phase was reduced in Fig. S4 (b) when compared to that of Fig.
S3 (b). This could be attributed to the porous and amphiphilic structure of
P(DVB-DABCO)-0.2. These properties enable the excellent solubilization capacity of
water and hexane in the pores of the sample. Indeed, much better solubilization
capacities were observed for P(DVB-DABCO)-0.3 and P(DVB-DABCO)-0.4, and
almost no phase separation was observed in Fig. S4 (c). However, the more
hydrophilic P(DVB-DABCO)-0.5 and P(DVB-DABCO)-0.6 showed lower
solubilization capacities than that of P(DVB-DABCO)-0.3 and P(DVB-DABCO)-0.4,
this could be ascribed to their low surface areas and pore volumes. Given that the
hydrophilic GL and hydrophobic DMC are not miscible, the excellent solubilization
capacity for hydrophilic and hydrophobic substances might be a helpful feature for the
transesterification reaction between hydrophilic GL and hydrophobic DMC.
< Fig. 7>
3.5. Catalytic performance on transesterification
3.5.1. Effect of catalysts
Table 2 presents the catalytic data for the transesterification of GL and DMC over
various catalysts. P(DVB-DABCO)-0.2, which has the highest surface area and pore
volume, however, gave GC in the lowest yield (Table 2, entry 1). The low catalytic
activity of P(DVB-DABCO)-0.2 could be attributed to its relatively low
hydrophilicity, which results in inferior miscibility between GL and DMC. From this
point of view, improving the hydrophilicity of the catalysts may enhance the catalytic
activity. As expected, the yields were significantly increased by increasing the mass
16

fraction of hydrophilic DABCO unit from 0.2 to 0.4 (Table 2, entries 1-3). And
P(DVB-DABCO)-0.4 shows the highest catalytic activity, giving GC in an 80.4%
yield. However, further increasing the mass fraction of hydrophilic DABCO unit led
to lower conversions of GL (Table 2, entries 4 and 5). Considering the well
hydrophilic property of P(DVB-DABCO)-0.5 and P(DVB-DABCO)-0.6, the inferior
catalytic performances should be attributed to their low surface areas and pore
volumes. The low surface areas and pore volumes of the samples decreased the
accessibility of the active sites and their solubilization capacities towards the reactants.
To further validate the importance of surface areas and pore volumes, the catalytic
activity of P(DVB-VBC)-DABCO was also tested. However, only a 18.3 % yield of
GC was gained. Considering that P(DVB-VBC)-DABCO has a similar chemical
composition to that of P(DVB-DABCO)-0.4, its low catalytic activity should be a
result of the low surface area and pore volume (Table 2, entry 6). Based on the above
results of physical properties and catalytic activities, we could conclude that both the
amphiphilic and textural properties of the catalysts have great impact on their catalytic
activities. The excellent amphiphilicity could provide a miscible reaction
microenvironment for the immiscible GL and DMC. While the high surface area and
hierarchical porosity of the catalyst make its catalytic sites easy accessible to the
substrates. And these factors work synergistically to enhance the catalytic activity.
< Table 2>
3.5.2. Effect of reaction temperature on GC synthesis
Previous studies have demonstrated that the reaction temperature has a dramatical
17

impact on the reactivity of GL transesterification. Thus, the transesterification reaction
was carried out in the temperature range of 60-90 °C using P(DVB-DABCO)-0.4 as a
catalyst, the results are present in Fig. 8. The GL conversions and GC yields gradually
increased with the reaction temperature varied from 60 °C to 85 °C. And a maximum
yield of 95.5% with a 98.2% selectivity of GC was achieved at 85 °C. Further
increasing the temperature to above 85 °C, a slight decrease in GC selectivity was
observed.
< Fig. 8>
3.5.3. Effect of reaction time on GC synthesis
The influence of reaction time on the catalytic reaction was investigated in the
range of 15-90 min at 85 °C using P(DVB-DABCO)-0.4 as a catalyst. As shown in
Fig. 9, the conversions of GL gradually increase as prolonging the reaction time,
achieving a maximum conversion of 97.2% at 60 min. Further increase of reaction
time over 90 min, GL conversion and GC yield almost remain in a constant amount.
< Fig. 9>
3.5.4. Effect of DMC/GL molar ratio on GC synthesis
The effect of DMC/GL molar ratio on the transesterification reaction was also
investigated at 85 °C for 60 min (Fig. 10). It can be observed that the yield of GC
continuously increased with the molar ratio of DMC/GL varied from 1 to 3. However,
further increase of the molar ratio to 4, the GC selectivity decreased slightly, and side
products such as diglycerol tri-carbonate were produced from the secondary reactions
of GC with DMC or GL [35,51].
< Fig. 10>
3.5.5. Effect of catalyst loading on GC synthesis
18

The effect of catalyst loading ranging from 0.25 mol% to 3.0 mol% was
investigated at 85 °C for 60 min. It is observed in Fig. 11 that the GC yields rapidly
increased from 43.2% to 95.1% with the increase of catalyst loadings from 0.25 mol%
to 0.75 mol%. However, further increasing the catalyst loading to 1.5 mol%, the GC
yields remained at about 95%. However, when the catalyst loading was over 1.5
mol%, the GC yields decreased. This could be explained by the fact that the prepared
P(DVB-DABCO)-0.4 has high adsorption capacity towards the reactants due to its
porous, flexible and amphiphilic framework. The special porous structure could
enhance the reaction rate by providing a reaction microenvironment with good
miscibility of GL and DMC. However, too much catalyst in the reaction system
resulted in a highly viscous reaction mixture (Fig. S6 and S7 in the Supplementary
material), which affected the mass transfer process of the catalytic reaction, thus
decreasing the reaction rate.
< Fig. 11>
3.6 Recycling experiments
In addition to catalytic activity, the recovery and reuse ability of the catalyst are
also crucial in the evaluation of economic feasibility of a catalytic process. Recycling
experiments were conducted under the optimal conditions: P(DVB-DABCO)-0.4
(0.75 mol%, based on the nominal DABCO amount and respect to the GL mole
amount), 60 min reaction time, 3:1 DMC/GL molar ratio, and 85 °C reaction
temperature. After each transesterification reaction, the catalyst was separated by
simple centrifugation, washed with methanol, dried under vacuum at 30 °C, and used
for the next run. The obtained liquid was analyzed by gas chromatography. As shown
19

in Fig. 12, P(DVB-DABCO)-0.4 could be reused at least for 13 times with only a
slight decrease in activity (This can be attributed partially to a physical loss of the
catalyst during the operation). The total TON (Turnover numbers = mole ratio of total
GC/catalyst) for all the 13 recycles was up to 1768. To strictly test the stability of the
catalyst, the recycling experiments were also conducted at lower conversions [52].
The recycling results at lower conversions (Fig. S9) show that the catalytic activity
could be almost preserved even after 16 recycles. The elemental analysis and HCl
titration experiments showed that the C, H, N contents and the number of basic sites
in the recovered P(DVB-DABCO)-0.4 did not change appreciably even after 16
recycles.
< Fig. 12>
To prove the heterogeneous nature of the catalyst, a hot filtration test was carried
out. Under the optimal conditions, the heterogeneous catalyst was filtered off after
reacting for 30 min (57.7% yield), the resulting liquid was then injected to another
reaction tube and allowed to react for a prolonged reaction time. The yields of GC
were remained at about 57% even after 75 min. These results further conform the
heterogeneous nature and excellent stability of the catalyst. The excellent stability and
recyclability are very encouraging and promising from a practical application point of
view.
< Fig. 13>
4. Conclusions
In summary, an efficient, robust and bifunctional catalyst with adjustable surface
20

area and amphiphilicity was successfully prepared for the transesterification of
glycerol and dimethyl carbonate. The critical innovation in this process was the
introduction of a hydrophilic DABCO monomer for synthesizing the porous catalyst.
In addition to acting as catalytic sites, these hydrophilic DABCO units could facilitate
the miscibility of immiscible glycerol and dimethyl carbonate in the pores of the
catalyst through regulating its hydrophilicity. Catalytic results suggest that both the
amphiphilic and porous properties of the catalyst have great impact on its catalytic
activities. The excellent amphiphilicity could provide a miscible reaction
microenvironment for the immiscible substrates. While the high surface area and
hierarchical porosity of the catalyst make its catalytic sites easy accessible to the
substrates. Hence, this method not only provides an efficient heterogeneous catalyst
for eco-friendly production of glycerol carbonate, but also some clues to prepare
highly efficient heterogeneous catalysts for many other heterogeneous systems where
the reactants are immiscible.
Acknowledgement
We acknowledge the financial support by the National Natural Science Foundation
of China [grant number 21763017]; the Science and Technology Fund Project of
Guizhou Province [grant number qian ke he ji chu [2018]1414 and [2016]1133]; the
Youth Talent Growth Project of Educational Department of Guizhou Province [grant
number qian jiao he KY [2016]264]; the Science and Technology Creative Team
21

Project of Liupanshui Normal University [grant number LPSSYKJTD201501]; the
School-Level Key Discipline of Chemistry [grant number LPSSYZDXK201602]; and
the Liupanshui Key Laboratory of High Performance Fibers and Advanced Porous
Materials [grant number 52020-2017-02-02].
22

References
[1] X. Song, Y. Wu, F. Cai, D. Pan, G. Xiao, Appl. Catal. A: Gen. 532 (2017) 77-85.
[2] J. Granados-Reyes, P. Salagre, Y. Cesteros, Appl. Catal. A: Gen. 536 (2017) 9-17.
[3] T. Rajkhowa, G. B. Marin, J. W. Thybaut, Appl. Catal. B: Environ. 205 (2017)
469-480.
[4] T. Ennaert, J. Van Aelst, J. Dijkmans, R. De Clercq, W. Schutyser, M. Dusselier, D.
Verboekend, B.F. Sels, Chem. Soc. Rev. 45 (2016) 584-611.
[5] M. Besson, P. Gallezot, C. Pinel, Chem. Rev. 114 (2013) 1827-1870.
[6] C.H.C. Zhou, J.N. Beltramini, Y.X. Fan, G.M. Lu, Chem. Soc. Rev. 37 (2008)
527-549.
[7] Z.I. Ishak, N.A. Sairi, Y. Alias, M.K.T. Aroua, R. Yusoff, Chem. Eng. J. 297 (2016)
128-138.
[8] M.O. Sonnati, S. Amigoni, E.P.T. de Givenchy, T. Darmanin, O. Choulet, F.
Guittard, Green Chem. 15 (2013) 283-306.
[9] S. Huang, B. Yan, S. Wang, X. Ma, Chem. Soc. Rev. 44 (2015) 3079-3116.
[10] J. Hu, J. Li, Y. Gu, Z. Guan, W. Mo, Y. Ni, T. Li, G. Li, Appl. Catal. A: Gen. 386
(2010) 188-193.
[11] J. Hu, Y. Gu, Z. Guan, J. Li, W. Mo, T. Li, G. Li, ChemSusChem 4 (2011)
1767-1772.
[12] M. Casiello, A. Monopoli, P. Cotugno, A. Milella, M.M. Dell’Anna, F. Ciminale,
A. Nacci, J. Mol. Catal. A: Chem. 381 (2014) 99-106.
[13] M. Aresta, A. Dibenedetto, F. Nocito, C. Pastore, J. Mol. Catal. A: Chem. 257
(2006) 149-153.
[14] J. George, Y. Patel, S.M. Pillai, P. Munshi, J. Mol. Catal. A: Chem. 304 (2009)
1-7.
[15] G.P. Fernandes, G.D. Yadav, Catal. Today 309 (2018) 153-160.
[16] M. Aresta, A. Dibenedetto, F. Nocito, C. Ferragina, J. Catal. 268 (2009) 106-114.
[17] P. Lu, H. Wang, K. Hu, Chem. Eng. J. 228 (2013) 147-154.
[18] S. Wang, P. Hao, S. Li, A. Zhang, Y. Guan, L. Zhang, Appl. Catal. A: Gen. 542
(2017) 174-181.
[19] J.R. Ochoa-Gómez, O. Gómez-Jiménez-Aberasturi, B. Maestro-Madurga, A.
Pesquera-Rodríguez, C. Ramírez-López, L. Lorenzo-Ibarreta, J. Torrecilla-Soria,
M.C. Villarán-Velasco, Appl. Catal. A: Gen. 366 (2009) 315-324.
[20] A.C. Simao, B. Lynikaite-Pukleviciene, C. Rousseau, A. Tatibouët, S. Cassel, A.
Sackus, A.P. Rauter, P. Rollin, Lett. Org. Chem. 3 (2006) 744-748.
[21] A.A.G. Shaikh, S. Sivaram, Chem. Rev. 96 (1996) 951-976.
[22] S.C. Kim, Y.H. Kim, H. Lee, B.K. Song, J. Mol. Catal. B: Enzym. 49 (2007)
75-78.
[23] M.K. Munshi, S.M. Gade, M.V. Mane, D. Mishra, S. Pal, K. Vanka, V.H. Rane,
A.A. Kelkar, J. Mol. Catal. A: Chem. 391 (2014) 144-149.
[24] M. K. Munshi, S.M. Gade, V.H. Rane, A.A. Kelkar, RSC Adv. 4 (2014)
23

32127-32133.
[25] F.S.H. Simanjuntak, T.K. Kim, S.D. Lee, B.S. Ahn, H.S. Kim, H. Lee, Appl.
Catal. A: Gen. 401 (2011) 220-225.
[26] A. Takagaki, K. Iwatani, S. Nishimura, K. Ebitani, Green Chem. 12 (2010)
578-581.
[27] F.S.H. Simanjuntak, V.T. Widyaya, C.S. Kim, B.S. Ahn, Y.J. Kim, H. Lee, Chem.
Eng. Sci. 94 (2013) 265-270.
[28] M. Malyaadri, K. Jagadeeswaraiah, P.S. Prasad, N. Lingaiah, Appl. Catal. A: Gen.
401 (2011) 153-157.
[29] P. Liu, M. Derchi, E. J. Hensen, Appl. Catal. B: Environ. 144 (2014) 135-143.
[30] G. Parameswaram, M. Srinivas, B.H. Babu, P.S.S. Prasad, N. Lingaiah, Catal.
Sci.Technol. 3 (2013) 3242-3249.
[31] M S. Khayoon, B.H. Hameed, Appl. Catal. A: Gen. 466 (2013) 272-281.
[32] R. Bai, Y. Wang, S. Wang, F. Mei, T. Li, G. Li, Fuel Process. Technol. 106 (2013)
209-214.
[33] R. Bai, S. Wang, F. Mei, T. Li, G.J. Li, J. Ind. Eng. Chem. 17 (2011) 777-781.
[34] P. Devi, U. Das, A.K. Dalai, Chem. Eng. J. 346 (2018) 477-488.
[35] F.S.H. Simanjuntak, J.S. Choi, G. Lee, H.J. Lee, S.D. Lee, M. Cheong, H.S. Kim,
H. Lee, Appl. Catal. B: Environ. 165 (2015) 642-650.
[36] F. Zhang, X. Yang, L. Jiang, C. Liang, R. Zhu, H. Li, Green Chem. 15 (2013)
1665-1672.
[37] C.A. Wang, Z.K. Zhang, T. Yue, Y.L. Sun, L. Wang, W.D. Wang, Y. Zhang, C.
Liu, W. Wang, Chem. Eur. J. 18 (2012) 6718-6723.
[38] Q. Sun, Z. Dai, X. Meng, F.S. Xiao, Chem. Soc. Rev. 44 (2015) 6018-6034.
[39] Q. Sun, Z. Dai, X. Meng, L. Wang, F. S. Xiao, ACS Catal. 5 (2015) 4556-4567.
[40] K. Dong, Q. Sun, X. Meng, F. S. Xiao, Catal. Sci. Technol. 7 (2017) 1028-1039.
[41] W. Wang, C. Li, L. Yan, Y. Wang, M. Jiang, Y. Ding, ACS Catal. 6 (2016)
6091-6100.
[42] Q. Sun, Y. Jin, B. Aguila, X. Meng, S. Ma, F. S. Xiao, ChemSusChem, 10 (2017)
1160-1165.
[43] Z. Jia, K. Wang, B. Tan, Y. Gu, ACS Catal. 7 (2017) 3693-3702.
[44] Q. Sun, Z. Dai, X. Liu, N. Sheng, F. Deng, X. Meng, F. S. Xiao, J. Am. Chem.
Soc. 137 (2015) 5204-5209.
[45] C. Chiappe, S. Rajamani, Pure Appl. Chem. 84 (2012) 755-762.
[46] L. Jia, X. Yao, J. Ma, C. Long, Microp. Mesop. Mater. 241 (2017) 178-184.
[47] B. Movassagh, N. Rezaei, Tetrahedron 70 (2014) 8885-8892.
[48] M. L. Kantam, M. Roy, S. Roy, B. Sreedhar, R.L. De, Catal. Commun. 9 (2008)
2226-2230.
[49] Q. Sun, M. Jiang, Z. Shen, Y. Jin, S. Pan, L. Wang, X. Meng, W. Chen, Y. Ding, J.
Li, F.-S. Xiao, Chem. Commun. 50 (2014) 11844-11847.
[50] Y. Zhang, S. Wei, F. Liu, Y. Du, S. Liu, Y. Ji, T. Yokoi, T. Tatsumi, F.S. Xiao,
Nano Today 4 (2009) 135-142.
[51] G. Rokicki, P. Rakoczy, P. Parzuchowski, M. Sobiecki, Green Chem. 7 (2005)
529-539.
24

[52] C.W. Jones, Top Catal. 53 (2010) 942-952.
25

Figures captions
Fig. 1. N2 adsorption–desorption isotherms of P(DVB-DABCO)-x (x = 0.2, 0.3, 0.4, 0.5) and pore
size distribution curve of P(DVB-DABCO)-0.4.
Fig. 2. SEM images of (a) P(DVB-DABCO)-0.2, (b) P(DVB-DABCO)-0.3, (c)
P(DVB-DABCO)-0.4, and (d) P(DVB-DABCO)-0.5.
26

Fig. 3. FTIR spectra of (a) P(DVB-VBC), (b) P(DVB-VBC)-DABCO, (c)
P(DVB-DABCO)-0.3, (d) P(DVB-DABCO)-0.4, and (e) P(DVB-DABCO)-0.5.
Fig. 4. XPS spectra of P(DVB-DABCO)-0.3, P(DVB-DABCO)-0.4 and P(DVB-DABCO)-0.5, (a)
the XPS full spectra, (b) XPS results for N1s.
27

Fig. 5. Solid-state 13C NMR spectra of (a) P(DVB-DABCO)-0.2 and (b) P(DVB-DABCO)-0.4.
Fig. 6. TGA curves of P(DVB-DABCO)-x samples (x = 0.2, 0.3, 0.4 and 0.5).
28

Fig. 7. Images of contact angle measurements. Photographs of a water droplet: (a)
P(DVB-DABCO)-0.2, (b) P(DVB-DABCO)-0.3; photographs of a glycerol droplet: (c)
P(DVB-DABCO)-0.2, (d) P(DVB-DABCO)-0.3, (e) P(DVB-DABCO)-0.4 and (f)
P(DVB-DABCO)-0.5.
Fig. 8. Effect of reaction temperature on GC synthesis in the presence of P(DVB-DABCO)-0.4 as
a catalyst. Reaction conditions: P(DVB-DABCO)-0.4 (397 mg), Cat/GL molar ratio: 0.01 (based
on DABCO unit); glycerol: 5.52g; DMC/glycerol molar ratio: 3; reaction time: 60 min.
29