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L. Wang et al. / Applied Catalysis A: General 471 (2014) 19–27
Scheme 1. One-pot process for DEC synthesis from ethylene oxide, CO2 and ethanol.
The synthesis of diethyl carbonate (DEC) using CO2 as building
La(NO3)3·6H2O, Ce(NO3)3·6H2O, were purchased from Sinopharm
Chemical Reagent Co., Ltd. NaI was purchased from Tianjin Guangfu
Fine Chemical Research Institute. KI, KCl, ethanol, Mg(NO3)3·6H2O,
Al(NO3)3·9H2O, Zn(NO3)3·6H2O, MgO were purchased from Xilong
Chemical Industry Incorporated Co., Ltd. KBr was purchased
from PIKE Technologies Spectroscopic Creativity. Magnesium
carbonate (MgCO3) was purchased from Adamas Reagent Co.,
Ltd. CO2 (>99.9% purity) and N2 (99.999% purity) were purchased
purity) was purchased from Sigma-Aldrich. Glycidyl isopropyl
ether, glycidyl phenyl ether, butyl glycidyl ether, styrene oxide,
1,2-epoxycyclohexane and allyl glycidyl ether were purchased
from TCI. All the chemicals were of analytical grade and used
without further purification unless noted otherwise.
block is a promising route. Ideally, the process starts from CO2 and
harsh conditions due to the thermodynamic limitations [24,25].
To address this issue, chemical dehydration reagent was usually
involvedto shiftthereactionforwardsto thecarbonateside, leading
to equivalent waste [26]. Although great efforts have been devoted
to the synthesis of DEC from CO2 over various catalysts [24–26],
the effective utilization of CO2 to synthesize DEC still remains a
It is proposed that the addition of chemicals with high energy
is favorable for the activation of the inert CO2. Recently, in order to
overcome the drawbacks of thermodynamic constrains, the usage
of butylene oxide as a chemical water trap was reported [27,28].
According to the results [27], 15.6% ethanol conversion and 10%
DEC yield were obtained over cerium (IV) oxide at 180 ◦C and
9 MPa pressure. Although the yield was 9-fold enhancement com-
pared with the method without water removal, unfortunately, the
DEC yield was not high enough in this system and needed to be
improved. It is worth mentioning that the synthesis of cyclic car-
bonate from epoxide and CO2 was well established in industrial
manufacture. Furthermore, the transesterification of cyclic carbon-
ate with ethanol to produce DEC was also proved to be feasible
[29]. In principal, the DEC could be synthesized via the consequent
two-step reaction. However, in view of the energy consumption,
productivity and investment, the one-pot reaction directly from
CO2 was undoubtedly superior to the two-step separate reaction.
Thus, the development of a more effective one-pot reaction to
improve the productivity of DEC directly from CO2 is highly desired.
With the aim of developing effective methods for activation
and utilization of CO2 to synthesize high-valued chemical of DEC,
herein, we describe a new methodology for the synthesis of DEC
through one-pot reaction from commodity chemicals of EO, carbon
dioxide and ethanol, as shown in Scheme 1. In this process, glycol
was simultaneously co-produced, which is also an important raw
material in the manufacture of polyester fibers and fabric indus-
try. The varied catalyst species and reaction variables, e.g. catalyst
composition, reaction temperature, molar ratio of the reactants,
reaction pressure, reaction time, were systematically evaluated.
Subsequently, catalyst recyclability was also investigated. To the
best of our knowledge, this is the first work to study one-pot reac-
tion for efficient synthesis of DEC from ethylene oxide, CO2 and
ethanol. Additionally, thermodynamic calculation was used to pre-
dict the reaction spontaneity as a function of temperature. On the
basis of the experimental results, a possible reaction mechanism
was also proposed. Moreover, the scope of substrates was extended
to terminal epoxides. In comparison with the reported processes,
this route has provided an effective way to realize the synthesis of
DEC directly from abundant CO2 via one-pot reaction.
2.2. Catalyst preparation
The typical solid basic catalysts, e.g. La2O3, CeO2, MgO,
MgAl-LDO, ZnMgOx, were prepared according to the procedure
mentioned in the literatures with slight modifications [30–34].
Specifically, La2O3 was prepared by precipitation method with
mixed base solution. 25.98 g La(NO3)3·6H2O was dissolved in
400 mL de-ionized water. The solution was slowly titrated by mix-
ture of KOH and K2CO3 until pH = 10 at 85 ◦C. The precipitate was
refluxed for 24 h, filtered and washed with de-ionized water until
the pH of the filtrated water became neutral. The resultant cata-
lyst was dried at 100 ◦C for 12 h and calcined at 550 ◦C in air for 6 h
before use. CeO2, MgO, MgAl-LDO, ZnMgOx were prepared accord-
ing to the methods used in the literatures with slight modifications,
i.e. CeO2 was obtained by calcining Ce(NO3)3·6H2O at 800 ◦C for 3 h
[31], MgO was obtained commercially and calcined at 650 ◦C for 3 h
[32], MgAl-LDO was obtained by calcining the Mg–Al hydrotalcite
precursor at 450 ◦C for 3 h in air [33], ZnMgOx was obtained with
molar ratio of Zn/Mg equal to7/3 in initial solution and calcined at
800 ◦C for 4 h [34].
2.3. Catalytic activity test
In a typical catalytic evaluation, 45 mmol EO, 31.4 g ethanol and
0.2 g total amount of catalyst were added into a stainless autoclave
reactor with an inner volume of 150 mL. CO2 was introduced with
an initial pressure of 3.0 MPa at room temperature, and the auto-
clave was completely sealed. The reactor was heated and stirred
constantly at desired temperature (e.g. 423 K) during the reaction.
The reaction was conducted in a batch operation mode. After the
reaction, the reactor was cooled to room temperature and the resid-
ual gas was depressurized slowly passing through the trap with
ethanol as an absorbent. The compositions of the resulting mix-
ture were measured by GC–MS (Agilent 6890N/5975B). In order to
quantitatively analyze the composition of the resulting mixture, the
liquid products were analyzed by a gas chromatograph (Shimadzu)
with a capillary column (Rtx-WAX 30 m × 0.25 mm × 0.25 m)
equipped with a flame ionization detector (FID) and an automatic
sampler using an external standard technique. The yield of product
was defined and calculated as follows:
2. Experimental
2.1. Materials
Ethylene oxide (EO), propylene oxide (PO), tributy-
lamine (Bu3N), triethylamine (Et3N), tetrabutyl ammonium
iodide (Bu4NI), tetramethyl ammonium iodide (Me4NI), 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU), sodium ethoxide (EtONa),
mole of product i
mole of epoxide charged
yield of product Yi(%) =
× 100%