Synthesis of dimethyl carbonate over waste eggshell catalyst

Article abstract of DOI:10.1016/j.cattod.2011.12.004

Dimethyl carbonate is an important methylating and carbonylating agent. Eggshell catalysts, prepared from eggshell waste, were tested in the synthesis of dimethyl carbonate from propylene carbonate and methanol. The eggshell-derived catalyst was characterized by using techniques of nitrogen physisorption, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and energy dispersive X-ray spectroscopy (EDS). The effects of calcination temperature on structure and activity of eggshell catalysts were investigated. The reusability of eggshell catalysts was also examined. It was found that highly active, reusable solid catalyst was obtained by just calcining eggshell. Dimethyl carbonate yield of 75% can be achieved at 25 °C and 1 atm pressure. Utilization of eggshell as a catalyst for dimethyl carbonate production not only provides a cost-effective and environmental friendly way of recycling this solid eggshell waste, but also makes the process of dimethyl carbonate production economic and fully ecologically friendly.

Full text of DOI:10.1016/j.cattod.2011.12.004

Catalysis Today 190 (2012) 107–111
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Catalysis Today
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Synthesis of dimethyl carbonate over waste eggshell catalyst
Yuan Gaoa,b, Chunli Xua,b,∗
a Key Laboratory of Applied Surface and Colloid Chemistry (Shaanxi Normal University), Ministry of Education, Xi’an 710062, PR China
b School of Chemistry and Chemical Engineering, Shaanxi Normal University, Chang’an South Road 199, Xi’an 710062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Dimethyl carbonate is an important methylating and carbonylating agent. Eggshell catalysts, prepared
from eggshell waste, were tested in the synthesis of dimethyl carbonate from propylene carbonate and
methanol. The eggshell-derived catalyst was characterized by using techniques of nitrogen physisorp-
tion, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and energy dispersive X-ray spectroscopy
(EDS). The effects of calcination temperature on structure and activity of eggshell catalysts were investi-
gated. The reusability of eggshell catalysts was also examined. It was found that highly active, reusable
solid catalyst was obtained by just calcining eggshell. Dimethyl carbonate yield of 75% can be achieved
at 25 ◦C and 1 atm pressure. Utilization of eggshell as a catalyst for dimethyl carbonate production not
only provides a cost-effective and environmental friendly way of recycling this solid eggshell waste, but
also makes the process of dimethyl carbonate production economic and fully ecologically friendly.
© 2011 Elsevier B.V. All rights reserved.
Received 8 August 2011
Received in revised form
30 November 2011
Accepted 1 December 2011
Available online 20 January 2012
Keywords:
Transesterification
Dimethyl carbonate
Environmental chemistry
Heterogeneous catalysis
Eggshell waste
1. Introduction
In our recent work, we found that waste eggshell could be used
as an active heterogeneous catalyst for biodiesel synthesis [9]. It
Eggs are consumed worldwide because they contain all essential
amino acids, vitamins, and minerals. Eggshell weighs approxi-
mately 10% of the total mass (ca. 60 g) of hen egg, and eggshell
is the significant solid waste produced from food processing and
manufacturing plants [1]. In China, for example, it is estimated that
annually about 4,000,000 tonnes is generated and this will con-
tinue to grow in future [2]. Most of the eggshell waste is commonly
disposed in landfills without any pretreatment because it was tradi-
tionally useless. However, the waste management is not a desirable
practice in view of the environmental odor from biodegradation
[3,4]. Eggshell has a little porosity and pure CaCO3 as an important
constituent. The chemical composition (by weight) of eggshell has
been reported as follows: calcium carbonate (94%), magnesium car-
bonate (1%), calcium phosphate (1%) and organic matter (4%) [1].
In recent years, a great deal of effort has been conducted for the
application of eggshell as value-added products. These major appli-
cations included a possible bone substitute [5], the starting material
for preparing calcium phosphate bioceramics (e.g. hydroxyapatite)
[6], coating pigments for inkjet printing paper [7], and a low-cost
adsorbent for removal of ionic pollutant and dyes from the aqueous
solution [3,8].
was proved that eggshell was an interesting unconventional het-
erogeneous basic catalyst for biodiesel synthesis [10,11]. Except for
the reaction of biodiesel synthesis, only one other reaction, lactose
isomerization, was reported utilizing eggshell as a basic catalyst
[12]. However, base catalysis is important in chemical industry
where it is widely applied [13]. Investigation of eggshell as a catalyst
for base-catalyzed reaction is not only helpful recycling this solid
eggshell waste, but also could make the reaction process environ-
mentally benign. Though it was already demonstrated that CaO is
the active phase of the eggshell waste-derived catalysts [9], there
is no report to date comparing of pure CaO and eggshell waste-
derived materials.
Dimethyl carbonate (DMC) is considered as an environmentally
benign chemical due to negligible ecotoxicity, low bioaccumulation
and low persistence [14]. Therefore, the production and chemi-
cal application of DMC have attracted much attention in the view
of so-called ‘sustainable society’ and ‘green chemistry’, mainly
for replacing dimethylsulfate and methylhalides in methylation
reactions and for replacing harmful phosgene in polycarbonate
and isocyanate syntheses [15]. Generally, DMC has been mainly
produced through two environmentally compatible routes: oxida-
tive carbonylation of methanol and transesterification between
methanol and propylene carbonate (PC) or ethylene carbonate (EC).
Transesterification of cyclic carbonate and methanol is a green pro-
cess, which uses naturally abundant CO2 as a starting material as
shown in Scheme 1. In the first step, cyclic carbonate can be synthe-
sized with conversion and selectivity close to 100% under moderate
∗
Corresponding author at: School of Chemistry and Chemical Engineering,
Shaanxi Normal University, Chang’an South Street 199, Xi’an 710062, PR China. Tel.:
+86 29 85300970; fax: +86 29 85307774.
E-mail address: xuchunli@snnu.edu.cn (C. Xu).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.12.004

108
Y. Gao, C. Xu / Catalysis Today 190 (2012) 107–111
O
O
C
Catalyst
O
O
CO2
+
CH
R
CH2
CH2
R
C
H
O
O
HO
OH
CH
C
C
Eggshell Catalyst
+ 2CH3OH
H2C
R
O
O
+
O
O
CH2
R
C
CH3
CH3
H
Scheme 1. Synthesis of DMC by transesterification.
conditions. Therefore, much attention has been paid to the trans-
esterification of cyclic carbonate and methanol. Both acid and base
catalysts catalyzed the reaction, and base catalysis was reported
to be more effective. However, homogeneous basic catalysts, such
as alkali alcoholates or hydroxides and trialkyl amine, give rise to
the problems of product separation and catalyst reuse, and conse-
quently, solid base catalysts are of much interest [16–19].
In this paper, we studied the catalytic properties of eggshell-
derived catalyst for DMC synthesis from the transesterification of
PC and methanol. One aim of this investigation was to examine
the feasibility of using eggshell as a solid base catalyst for DMC
synthesis. The other aim was to compare the catalytic activity of
pure CaO and eggshell catalysts.
0.995. Pore volume and pore-size distribution were obtained from
analysis of the desorption branches of the nitrogen isotherms using
the BJH (Barrett–Joyner–Halenda) method.
TGA experiments were carried out using a Q600 SDT thermal
analysis machine (TA Instruments, USA) under a flow of nitrogen.
The sample weight used was about 20 milligrams, and the temper-
ature ranged from 38 to 1000 ◦C with a ramping rate of 20 ◦C/min.
2.3. Reaction procedure
The reactions were carried out in a standard round bottom flask
at 25 ◦C temperature and 1 atmosphere pressure under vigorous
stirring. During the experiments, the flask was equipped with a
ground-glass stopper. Except the stopper, no special management
was conducted to control the effect of CO2 from the atmosphere.
Typical reactions were performed with 1.63 g of PC and 5.64 g of
methanol using 0.8 wt% (catalyst to PC weight ratio) of eggshells
catalyst for the specified time (2 h). The products were analyzed on
a Shimadzu GC-2014 gas chromatograph with a flame ionization
detector. A Rtx-Wax capillary column (30 m × 0.32 mm × 0.5 ␮m)
was used for separation. N-butanol was used as internal standard
for analysis.
Using the standard calibration curves that were prepared for all
the components, the integrated areas were converted to moles per-
centages for each component present in the sample. For each data
point, selectivity of DMC, conversion of PC, and yield of DMC were
calculated. Selectivity is defined as the ratio of the number of moles
of the product formation to that of the PC consumed in the reaction,
taking into account the stoichiometric coefficient. Conversion of PC
is defined as the ratio of number of moles of PC in the reaction to
total moles of PC initially present. Yield of DMC is defined as the
ratio of the number of DMC produced to the theoretical number of
moles of DMC.
2. Experimental
2.1. Materials
Eggshell was collected from local bakeries. The preparation
method of eggshell catalyst was described elsewhere [9]. To remove
impurity and interference material, the eggshell was rinsed several
times with deionized water. Then, the eggshell was dried at 100 ◦C
for 24 h in the dry oven. Calcination was performed in the muffle
furnace at 1000 ◦C for 2 h under static air after crushing the dried
eggshell.
Pure CaO (analytical reagent, 98.0%) used was a commercial
sample (Sinopham Chemical Reagent Co., Ltd., China). It was acti-
vated at 1000 ◦C for 2 h in static air before the reaction test.
2.2. Catalyst characterizations
XRD patterns were recorded using a D/Max-3C X-ray powder
diffractometer (Rigaku Co., Japan), using a Cu-K␣ source fitted with
an Inel CPS 120 hemispherical detector.
Elemental analysis was determined by an FEI Quanta 200 scan-
ning electron microscopy equipped with energy dispersive X-ray
spectroscopy (EDS).
3. Results and discussion
The surface area and pore characteristics of the catalysts were
determined using a Micromeritics ASAP 2020 instrument. The sam-
ple was degassed at 250 ◦C for 4 h in N2 prior to surface area
measurement. Nitrogen adsorption and desorption isotherms were
measured at −96 ◦C, and the specific surface areas of the catalysts
were determined by applying the BET (Brunauer–Emmett–Teller)
method to nitrogen adsorption data obtained in the relative pres-
sure range from 0.06 to 0.30. Total pore volumes were estimated
from the amount of nitrogen adsorbed at a relative pressure of
3.1. Characterization of eggshell waste-derived catalysts
3.1.1. BET surface area and pore size
Table 1 presents the nitrogen physisorption data of natu-
ral eggshell, calcined eggshell and pure CaO (A.R.). The surface
area and pore volume of natural eggshell were 0.84 m2 g−1 and
0.0049 cm3 g−1, respectively (Table 1, entry 1), which indicated that
natural eggshell processed low porosity [20]. Both the surface area
and pore volume of other samples (i.e. calcined eggshell and pure

Y. Gao, C. Xu / Catalysis Today 190 (2012) 107–111
109
Table 1
Nitrogen physisorption data of natural eggshell, calcined eggshell and pure CaO
(A.R.).
Entry
Sample
Surface area
Pore volume
Average pore
width (Å)
(m2 g−1
)
(cm3 g−1
)
1
2
Natural eggshell
Eggshell calcined at
600 ◦C
0.84
3.26
0.0049
0.0559
32.15
53.30
3
4
Eggshell calcined at
0.21
5.35
0.0053
0.0064
7.82
6.53
1000 ◦C
CaO (A.R.)
CaO) were similar to that of natural eggshell (Table 1, entries 2–4).
They also processed low porosity.
3.1.2. Chemical composition of eggshell waste-derived catalysts
Element analysis by EDS reveals that natural eggshell contains
calcium, carbon and oxygen, as well as two minor constituents (i.e.
Mg, and P) (Fig. 1a). The composition of eggshell was consistent to
the results reported by Stadelman [1]. The composition of calcined
eggshell was similar to that of natural eggshell, but with a difference
in the content of carbon (Fig. 1b). The calcined eggshell contained
less carbon, which may result from the decomposition of organics
and calcium carbonate. Pure CaO (A.R.) contained only calcium and
oxygen (Fig. 1c).
3.1.3. TGA analysis
In order to explain the effect of calcination temperature, we
investigated the calcination process of eggshell with thermal gravi-
metric analysis (Fig. 2). TGA result showed the temperatures, at
which the eggshell precursors decomposed when heated in a con-
trolled environment at a given ramp rate. Between 38 ◦C and 600 ◦C,
the weight loss was less than 3%. There is one distinguished weight
loss peak between 600 ◦C and 812 ◦C. Water and organics were
removedfrom the precursorsbelow 600 ◦C, whereascarbondioxide
was lost between 700 and 800 ◦C.
3.1.4. XRD analysis
Fig. 3 shows the XRD patterns of natural eggshell, calcined
eggshell, and pure CaO (A.R.). The natural eggshell displayed diffrac-
tion reflections characteristic of CaCO3 [9]. Thermal pre-treatment
resulted in a change in the X-ray diffraction pattern, caused by the
removal of CO2 from the starting material. The diffraction patterns
of the samples heated at temperatures <700 ◦C were character-
istic of CaCO3, while samples activated at temperatures >700 ◦C
displayed diffraction reflections characteristic of CaO. Samples cal-
cined at 700 ◦C for 2 h contain CaCO3 as the major phase and CaO
as a minor phase. Pure CaO (A.R.) exhibited diffraction reflections
characteristic of CaO.
3.2. Transesterification over eggshell waste-derived catalysts
3.2.1. Effect of calcination temperature
Fig. 1. EDS spectrum of (a) natural eggshell, (b) eggshell calcined at 1000 ◦C, and (c)
To determine the influence of the calcination temperature on
the activity of the eggshell-derived catalyst, eggshell was calcined
at different temperatures between 300 ◦C and 1000 ◦C and then
tested for the transesterification of PC and methanol to produce
DMC (Table 2). The results show that eggshell sample calcined
above 800 ◦C was the most active catalyst. A DMC yield of 80% was
obtained in the presence of the eggshell sample calcined above
800 ◦C (Table 2, entries 5 and 6). When the calcination tempera-
ture was 700 ◦C, a DMC yield of 16% was achieved (Table 2, entry
4), whereas, a low level of activity was observed when the calcina-
tion temperature was <600 ◦C. The PC conversion was <7% and no
apparent DMC yield was gained in the presence of eggshell sample
calcined <600 ◦C (Table 2, entries 1–3). As shown in Table 2 and
pure CaO (A.R.).
Figs. 4–6, the selectivity to DMC was less than 100%. The side reac-
tion of this reaction might be the slow polymerization of PC after
equilibrium [21].
The changes observed in the XRD patterns (Fig. 3) coincided with
a change in the catalytic activity (Table 2). Calcination below 700 ◦C
did not lead to the formation of CaO, and, consequently, the catalytic
activity was very low. The best catalytic performance was obtained
for calcination temperatures above 800 ◦C, when the XRD patterns
corresponded to a crystalline CaO. Samples calcined at 700 ◦C con-
tain CaCO3 as the major phase and CaO as a minor phase, hence

110
Y. Gao, C. Xu / Catalysis Today 190 (2012) 107–111
Table 2
The catalytic activity of natural eggshell, calcined eggshell and pure CaO (A.R.).
Entry
Catalyst
Conversion of PC (%)
Yield of DMC (%)
Selectivity to DMC (%)
Yield of 1,2-propanediol (%)
1
2
3
4
5
6
7
Natural eggshell
4
7
7
40
83
81
83
–
–
–
16
80
79
77
–
–
–
39
96
97
93
–
–
–
12
60
66
64
Eggshell calcined at 300 ◦
Eggshell calcined at 600 ◦
Eggshell calcined at 700 ◦
Eggshell calcined at 800 ◦
C
C
C
C
Eggshell calcined at 1000 ◦
CaO (A.R.)
C
100
-2
100
80
-4
90
80
70
60
50
-6
-8
60
-10
-12
-14
-16
40
DMC yield
DMC selectivity
1,2-propanediol yield
PC conversion
20
0
200
400
600
800
1000
Temperature ( oC)
0
0
2
4
6
8
10
12
Molar ratio of methanol to PC
Fig. 2. TGA curves of eggshell.
Fig. 4. Effect of methanol to PC molar ratio on transesterification of PC with
methanol. Reaction conditions: catalyst amount, 0.8 wt%; reaction temperature,
25 ◦C; pressure, 1 atm; reaction time, 2 h.
middle yield were obtained. Therefore it can be concluded that CaO
is the active phase of the eggshell derived catalysts.
3.2.2. Effect of reaction variables
the DMC yield and PC conversion, suggesting that the reaction has
reached equilibrium.
The stoichiometric ratio for transesterification is 2:1
(methanol/PC). Because this is an equilibrium reaction, an
excess of methanol will increase the PC conversion by shifting this
equilibrium to producing DMC. The effect of methanol to PC molar
ratio on transesterification of PC with methanol was investigated.
The DMC yield and PC conversion increased with increasing the
molar ratio of methanol to PC, reaching the maximum when the
ratio was above 9 (Fig. 4). The molar ratio above 9 did not increase
When a small amount of catalyst was used the maximum prod-
uct yield could not be reached. However, increasing the amount
of catalyst lead to the slurry (mixture of catalyst and reactants)
becoming too viscous, giving rise to a problem of mixing and
higher power consumption for adequate stirring. To avoid this kind
of problem, an optimum amount of catalyst loading was deter-
mined. As shown in Fig. 5, the yield increased with increasing the
100
80
60
40
DMC yield
DMC selectivity
20
1,2-propanediol yield
PC conversion
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Amount of catalyst (wt%)
Fig. 5. Effect of catalyst amount on transesterification of PC with methanol. Reaction
conditions: methanol to PC molar ratio, 10:1; reaction temperature, 25 ◦C, pressure,
1 atm; reaction time, 2 h.
Fig. 3. XRD patterns of natural eggshell, the materials obtained by calcining natural
eggshell in the range of 300–1000 ◦C, and the pure CaO (A.R.).

Y. Gao, C. Xu / Catalysis Today 190 (2012) 107–111
111
100
80
60
40
20
0
for DMC manufacture. We attempted to reuse the catalyst by
the following method. The used eggshell catalyst was separated
from the reaction solution by centrifugation. It was then applied
as the catalyst for the repeated reactions. Repeat reactions were
run under the same reaction conditions. As shown in Table 3,
the eggshell catalyst can be reused at least four times with little
deactivation.
4. Conclusion
This is the first report of the synthesis of DMC by trans-
esterification through the use of eggshell-derived catalyst. The
eggshell-derived catalyst was active and reusable for DMC synthe-
sis. CaO was proved to be the active phase of eggshell catalysts. The
experimental results showed that under the optimum conditions, a
10:1 molar ratio of methanol to PC, addition of 0.8 wt% eggshell cat-
alysts, room temperatures and 1 atm pressure gave the best results,
and conversion of PC and yield of DMC reached maximum value
(PC conversion = 80%, DMC yield = 75%) after 1 h. In addition, this
work further demonstrates that the eggshell-derived material is an
effective solid base catalyst.
DMC yield
DMC selectivity
1,2-propanediol yield
PC conversion
0
20
40
60
80
100
120
140
160
180
Rection time (min)
Fig. 6. Effect of reaction time on transesterification of PC with methanol. Reaction
conditions: catalyst amount, 0.8 wt%; methanol to PC molar ratio, 10:1; reaction
temperature, 25 ◦C; pressure, 1 atm.
Table 3
Acknowledgments
Recycling experiments for eggshell catalyst.a
Reused times
Conversion
of PC (%)
Yield of
DMC (%)
Selectivity
to DMC (%)
Yield of
1,2-propanediol (%)
This work was supported by the project funded by Natural Sci-
ence Basic Research Plan in Shaanxi Province of China (Program
No. 2010JM2003) and by the Fundamental Research Funds for the
Central Universities (Program No. GK200902006).
First use
81
79
85
84
79
77
75
75
97
97
89
89
66
67
60
69
Second use
Third use
Fourth use
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Reaction conditions: methanol to PC molar ratio, 10:1; catalyst amount, 0.8 wt%;
reaction temperature, 25 ◦C; pressure, 1 atm; reaction time, 2 h.
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3.2.4. Reusability of eggshell waste-derived catalysts
Recovery and reuse of the catalyst is an important factor in
the economics of the use of the heterogeneous catalytic process