Efficient synthesis of diphenyl carbonate from dibutyl carbonate and phenol using square-shaped Zn-Ti-O nanoplates as solid acid catalysts

Article abstract of DOI:10.1039/c5ra17655g

Square-shaped Zn/Ti oxides were prepared by a co-precipitation method and used for the synthesis of diphenyl carbonate (DPC) via transesterification of dibutyl carbonate (DBC) with phenol. The results showed that a 51% yield of butyl phenyl carbonate (BPC) and 13% yield of DPC could be achieved at 205 °C in the presence of 3ZnTi-400 (Zn : Ti molar ratio 3 : 1). Moreover, it is found that 3ZnTi-400 was also an active catalyst for the disproportionation of BPC to DPC, and 80% conversion of BPC was obtained at 190 °C. The prepared catalysts could be reused for three runs of the transesterification without noticeable deactivation. The catalysts were characterized by XRD, SEM, XPS, and TPD with the aim of establishing the relationship between catalytic performance and structure.

Full text of DOI:10.1039/c5ra17655g

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PAPER
Efficient synthesis of diphenyl carbonate from
dibutyl carbonate and phenol using square-shaped
Zn–Ti–O nanoplates as solid acid catalysts†
Cite this: RSC Adv., 2015, 5, 84621
ab
a
ab
ab
c
Peixue Wang, Shimin Liu, Feng Zhou, Benqun Yang, Ahmad S. Alshammari
and Youquan Deng*a
Square-shaped Zn/Ti oxides were prepared by a co-precipitation method and used for the synthesis of
diphenyl carbonate (DPC) via transesterification of dibutyl carbonate (DBC) with phenol. The results
showed that a 51% yield of butyl phenyl carbonate (BPC) and 13% yield of DPC could be achieved at
ꢀ
2
05 C in the presence of 3ZnTi-400 (Zn : Ti molar ratio 3 : 1). Moreover, it is found that 3ZnTi-400 was
Received 31st August 2015
Accepted 1st October 2015
also an active catalyst for the disproportionation of BPC to DPC, and 80% conversion of BPC was
ꢀ
obtained at 190 C. The prepared catalysts could be reused for three runs of the transesterification
DOI: 10.1039/c5ra17655g
without noticeable deactivation. The catalysts were characterized by XRD, SEM, XPS, and TPD with the
aim of establishing the relationship between catalytic performance and structure.
www.rsc.org/advances
1
0–19
production of DPC.
DMC and PhOH to yield DPC is thermodynamically unfavor-
Diphenyl carbonate (DPC) is extensively used for the able, and low yield and selectivity to DPC were obtained even
Nonetheless, the transesterication of
1
. Introduction
2
0
production of many organic compounds and polymer mate- at elevated temperatures. On the other hand, the separation
rials, particularly as an important intermediate for the between DMC and methanol has been become very difficult
1
,2
synthesis of polycarbonate avoiding phosgene. According to due to the formation of azeotrope. Moreover, the reaction
the different carbonyl sources, such as COCl , CO, CO
, urea, efficiency is inferior under atmospheric pressure, since DMC
2
2
dimethyl oxalate (DMO) and dimethyl carbonate (DMC), the as the raw material easily slips out during the reaction. So, the
processes for the synthesis of DPC involve phosgenation, reaction must be conducted under pressure for breaking
oxidative carbonylation of phenol (PhOH), esterication of reaction equilibrium, which would cause much higher cost
CO with PhOH, phenolysis of urea, and transesterication of for production equipment.
2
carbonates with PhOH. The obvious disadvantages of phos-
In order to avoid such azeotrope, dibutyl carbonate (DBC)
genation technique are using corrosive and highly toxic instead of DMC was used in this work. Because the DBC (boiling
ꢀ
phosgene as a raw material and the forming chlorine salts as point is 207 C) and butanol could not form azeotrope, the co-
3
a by-product. Though the process of oxidative carbonylation product of butanol can be easily removed from the reaction
is simple, the employ of noble catalyst (e.g. palladium system under atmospheric pressure and used again as a raw
complex) and the low yield of DPC limit its industrializa- material of DBC. In this process, high purity DBC can be
4
,5
21,22
tion. Similarly, DPC via direct reaction of PhOH with urea or produced from low-priced urea (Scheme 1 reaction 1),
6
,7
CO also suffer the low yield. Another method to DPC is the and then reacted with PhOH to butyl phenyl carbonate (BPC)
2
8
,9
transesterication of DMO and PhOH, however, the subse- and DPC (Scheme 1 reaction 2). Next, BPC can also be dis-
quent decarbonylation hampers its practicability. In this proportionated to DPC and DBC (Scheme 1 reaction 3).
context, the transesterication of DMC and PhOH is consid-
ered to be the most suitable method for commercial
a
Centre for Green Chemistry and Catalysis, State Key Laboratory of Solid Lubrication,
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou,
7
30000, China. E-mail: ydeng@licp.cas.cn; Fax: +86-931-4968116; Tel: +86-931-
968116
4
b
Graduate School of the Chinese Academy of Sciences, Beijing, 100049, China
National Nanotechnology Research Center, King Abdulaziz City for Science and
c
Technology, P.O. Box 6086, Riyadh 11442, Saudi Arabia
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c5ra17655g
1
Scheme 1 The processes for the synthesis of DPC.
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In the previous reports, the organic compound of Sn and Ti at room temperature for 1 h and ushed again with argon gas
2
3
as catalysts were used in this process, but the separation for 1 h to remove any physico-adsorbed NH . The desorption
3
ꢀ
ꢂ1
problems between homogeneous catalysts and DPC as well as prole was recorded at a heating rate of 10 C min from room
the recovery of catalysts still remained. Therefore, developing temperature to 400 C and maintained until the TCD signal of
ꢀ
3 3
an effective and stable heterogeneous catalyst is still highly NH returned to the baseline. The quantitative analysis for NH
desirable for this important process due to the signicance in desorption is calculated based on the integration of the corre-
industrial manufacture. Since we note that Ti may be the active sponding TPD traces, preliminarily calibrated by the injection
component based on previously extensive catalysts screening, of pure NH
here, we report that 3ZnTi-400 is an effective catalyst for both
the transesterication of DBC with PhOH and the dispropor-
3
pulses.
2
.2 DPC synthesis from DBC and PhOH
tionation of BPC to DPC. XRD, SEM, XPS, and NH -TPD studies
3
The reaction was carried out in a 250 mL three-neck round-
bottom ask equipped with a thermometer, a nitrogen inlet
and a fractional column connected to a liquid dividing head.
PhOH (0.2 mol), DBC (0.1 mol) and 1 g catalyst were added
were conducted to explore the relationship between structure
and performance. Moreover, the inuences of the catalysts with
different components, optimal catalyst activation, and reaction
variables (such as temperature, molar ratio of PhOH/DBC) were
also investigated in a batch reactor system.
ꢀ
under nitrogen, the reaction proceeded at 205 C for 6 h with
stirring. Meantime, the pressure was atmospheric pressure
while distilling off butanol. Aer reaching a steady state at the
designated temperature, the samples were taken at intervals of
2 h. The compositions of the liquid samples were qualitatively
identied by HP-6890 GC-MS equipped with a SE-54 capillary
column. The quantitative analysis of the products was deter-
mined by Agilent 7890 GC equipped with a HP-5 capillary
column and a FID detector (octane was used as internal
standard).
Aer 6 h reaction, the pressure was reduced to 3 kPa to
conduct disproportionation reaction of BPC for 3 h while
distilling off both PhOH and DBC. Aer the total reaction, the
mixture was cooled to room temperature and the catalyst was
2
. Experimental
2.1 Catalysts preparation and characterization
Chemicals used in this study including PhOH, aqueous
ammonia and octane obtained from Tianjin Chemical Reagent
Factory (analytical reagent, >99%). Zinc acetate and tetra-n-butyl
titanate were analytical grades, and were purchased from
Sinopharm Chemical Reagent Co., Ltd DBC was synthesized
from urea and butanol in our Lab, and the purity of the DBC was
specied as >99%.
A titanium precursor solution was prepared by adding tetra-
butyl titanate to diluted nitric acid solution slowly under
vigorous stirring. Subsequently, upper butanol formed during
the hydrolysis of tetrabutyl titanate was carefully separated by
a separatory funnel. A solution containing titanium acid was

ltered, while the ltrate was further analyzed by gas
chromatography.
3 2 2
obtained and added to the solution of Zn(CH COO) $2H O.
3
. Results and discussion
Aqueous ammonia (50%) was added dropwise until the pH of
mixed solution reached 5 ꢁ 6. The resulting precipitate was
aged, ltrated, washed, dried and calcined in static air for 4 h.
The prepared catalysts are denoted as xZnTi-T, x is molar ratio
of Zn and Ti, T is the calcination temperature.
3.1 Results of the catalysts characterization
XRD patterns of the Zn/Ti binary oxides with different propor-
tions are shown in Fig. 1. The 1ZnTi-400 (Fig. 1a) displayed poor
The morphological structures were examined by eld emis-
sion scanning electron microscopy (FE-SEM, JSM-6701F).
X-ray diffraction (XRD) was measured on a Siemens D/max-
RB powder X-ray diffract meter. Diffraction patterns were
recorded with Cu Ka radiation (40 mA, 40 kV) over a 2q range of
ꢀ
ꢀ
2
0
0 to 80 and a position-sensitive detector using a step size of
ꢀ
.01 and a step time of 0.15 s.
Surface analysis of the catalysts was performed by X-ray
photoelectron spectroscopy (XPS) on VG ESCALAB210 using
a Mg Ka radiation at a pass energy of 20 eV. The energy scale was
calibrated and corrected for charging using the C1s (285.0 eV)
line as the binding energy reference.
The surface acid properties of the catalysts were measured by
3
temperature programmed desorption (TPD) of NH and carried
out on TPD ow system equipped with a TCD detector. In
a typical experiment, the solid sample (100 mg with particle size
ꢀ
1

60–200 mm) was pretreated at 300 C for 1 h under argon gas
ꢂ1
ow (50 mL min ) and then cooled to room temperature. The
sample was subsequently exposed to NH
Fig. 1 XRD patterns of (a) 1ZnTi-400; (b) 2ZnTi-400; (c) 3ZnTi-400; (d)
3ZnTi-400-reused; (e) 5ZnTi-400.
ꢂ1
3
stream (50 mL min
)
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3
crystalline structure of rhombohedral zinc titanate (ZnTiO )
phases. Compared to the 1ZnTi-400, the characteristic peaks
ꢀ
(
29.8, 35.2, 56.5 and 62.0 ) of cubic Zn TiO were observed in
2
4
2
ZnTi-400 (Fig. 1b), and the peaks of Zn TiO are sharp and
2 4
2 4
narrow, indicating that the Zn TiO phase was well crystallized.
It can be seen that the crystalline phases including ZnO and
Zn TiO were formed aer increasing the molar ratio of Zn : Ti
2
4
to 3 : 1. With further increasing Zn content, only ZnO crystal
phase was present in 5ZnTi-400. Consequently, it can be
deduced that the phase composition of the powders depends on
the Zn : Ti molar ratio. In addition, the characteristic peaks of
ZnO became sharper aer reuse for three times, suggesting that
calcination procedure for regenerating the catalytic activity aer
each recycling run lead to the further crystallization of ZnO.
The X-ray photoelectron spectroscopy (XPS) analyses of
binary Zn/Ti oxide samples (Zn/Ti ¼ 3 : 1, calcined at 300–500
ꢀ
C) was performed (Table 1). The binding energy (BE) with range
Fig. 2 O1s XPS spectra of (a) 3ZnTi-300; (b) 3ZnTi-400; (c) 3ZnTi-500.
from 1022.0–1022.3 eV and 458.7–458.8 eV could be attributed
to Zn2p3/2, Ti2p3/2, respectively, suggesting that the chemical
states of Zn and Ti species on the catalyst surface were mainly
ꢀ
sites. The intensity of the peak at 120 C became weaker with
2
+
4+
Zn and Ti . The O1s peaks with their binding energy at 530.1
and 531.8 eV should be assigned to O1at1s (lattice oxygen) and
increase of calcination temperature or aer reuse for three
times (Fig. 4c). Besides, a shoulder peak at 175 C also appeared
in 3ZnTi-300, which was ascribed to strong strength acidic sites.
In comparison with the 3ZnTi-400, the NH
ZnTi-400, 2ZnTi-400 and 5ZnTi-400 (Fig. 4e–g) show a small
peak at 120 C, meaning that there were less medium strength
acidic sites on these catalysts.
ꢀ
24,25
O
ad1s (adsorbed oxygen), respectively (Fig. 2).
It was found
that percentage of the surface lattice oxygen (O1at) reached
3
-TPD prole of the
ꢀ
maximum for the sample calcined at 400 C. Moreover, XPS
1
2
+
analyses manifested that the surface atom ratios of Zn and
ꢀ
4
+
Ti over 3ZnTi-300, 3ZnTi-400 and 3ZnTi-500 are 1.4, 0.7 and
.8, respectively, which are lower than the theoretical value 3,
meaning that Ti species enriched on the surface of catalysts.
0
In Fig. 3, SEM was carried out for exploring the morphology 3.2 Synthesis of BPC and DPC
of 3ZnTi-400. The distinct square-shaped nanoplates with about
The transesterication of DBC and PhOH for DPC synthesis
was investigated over various catalysts (Table 2). For the Zn/Ti
composite oxides with different proportions (entries 1–4), the
catalyst 3ZnTi-400 displayed the highest catalytic activity and
the conversion of DBC can reach 65% with 98% total selectivity
of BPC and DPC. With increasing Zn content in catalyst, the
conversion of DBC increased. For 5ZnTi-400 with extremely
low concentration of acid sites gives the highest amount of
byproducts; this may due to the missing of Ti crystal phase in
1
00 nm side lengths can be observed in 3ZnTi-400. The four
ꢀ
angles of the square are around 90 , which means these nano-
structures are precise rectangles. Besides, some nanoparticles
distribute in the gap of square-shaped nanoplates, implying the
materials are the mixture of Zn TiO and ZnO. The obtained
2
4
results were consistent with the XRD analyses, i.e. crystalline
phases are composed of ZnO and Zn TiO in 3ZnTi-400.
The acid properties of these composite oxide catalysts were
2
4
studied by TPD of adsorbed NH
NH
3
(Fig. 4). Generally, a peak of
desorption appeared at about 60 C and was observed over
5
ZnTi-400. Over the above catalysts, butoxybenzene (BPE) was
ꢀ
3
detected in the products, which probably due to the side
reaction between DBC and PhOH. The impact of the different
calcined temperatures of Zn/Ti composite oxides as catalyst on
the BPC synthesis was also tested (entries 5–6). These results
showed that the best catalytic performance could be obtained
all the tested samples, which was derived from the weak
strength acidic sites. For the 3ZnTi-300, 3ZnTi-400 and 3ZnTi-
ꢀ
5
00 (Fig. 4a, b and d), another broad peak centered at 120 C
was detected, which was attributed to medium strength acidic
Table 1 Binding energies and atomic ratios of binary Zn/Ti oxides according to XPS results
Binding energy (eV)
Atomic ratio
Zn/Ti
a
ꢂ1
Catalyst
Ti2p3/2
O
lat
O
ad
Zn2p3/2
Total acidic amount (reused) (mmol g
)
3
3
3
ZnTi-300
ZnTi-400
ZnTi-500
458.7
458.8
458.7
530.1
530.1
530.2
531.9
531.8
532.0
1022.3
1022.2
1022.0
1.4
0.7
0.8
174
72 (50)
24
a
Determined by TPD.
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Table 2 Effect of proportions and activation temperature on the
a
catalytic activity of the binary Zn/Ti oxide
Yield (%)
DBC
BPC +
Entry Catalyst
conv. (%) BPC DPC BPE DPC sel.(%)
1
2
3
4
5
6
7
8
9
1ZnTi-400
2ZnTi-400
3ZnTi-400
5ZnTi-400
3ZnTi-300
3ZnTi-5001
3ZnTi-4002
3ZnTi-4003
3ZnTi-400
58
63
65
71
60
41
63
61
59
41
44
51
37
33
30
50
49
46
8
9
13
8
4
1
12
10
9
14
5
1
26
23
10
1
78
92
98
63
62
76
98
97
92
st
nd
rd
2
4
a
ꢀ
Reaction conditions: 18.8 g PhOH, 17.4 g DBC, 1 g catalyst, 205 C, 6 h.
Fig. 3 SEM image of the sample 3ZnTi-400.
reuse the 3ZnTi-400 catalyst 3 times by ltration, washing with
ethanol, and calcining aer each run. The results obtained
(
entries 7–9) indicated that the catalyst can be reused with
slightly decrease in activity in the subsequent runs. XRD
results showed that the characteristic peaks of ZnO became
sharper in the used catalyst, indicating that the structural
changes occurred during the reaction. This may be a reason
for the slightly decrease of DBC conversion over spent cata-
lysts. Besides, the total acidic amount of reused catalyst
ꢂ1
ꢂ1
decreased from 72 mmol g to 50 mmol g (Table 1) was also
caused decrease of catalytic activity.
3.3 Effect of reaction conditions
In order to optimize reaction conditions, the inuence of
various reaction parameters was studied. The impact of
temperatures on DPC synthesis was rst optimized (Fig. 5A).
The BPC yield is sharply increased in the temperature range of
ꢀ
1
80–205 C and decreases slightly as the reaction temperature
Fig. 4 The NH
3
5
3
-TPD profiles of (a) 3ZnTi-300; (b) 3ZnTi-400; (c)
ZnTi-400-reused; (d) 3ZnTi-500; (e) 1ZnTi-400; (f) 2ZnTi-400; (g)
ZnTi-400.
ꢀ
exceeds 205 C, which may be due to the side reaction between
DBC and PhOH at high temperature. Above 205 C, although the
ꢀ
yield of DPC was up to 14%, slow growth rate was observed.
Therefore, to avoid the formation of butoxybenzene as a by-
ꢀ
product, the favorable temperature was 205 C.
ꢀ
as the calcined temperature was 400 C. Generally, it was
widely accepted that transesterication reaction was efficiently
improved by acid–base catalysts via a nucleophilic substitu-
Then, the impact of the PhOH/DBC molar ratio on DPC
synthesis was investigated, as shown in Fig. 5B. A signicant
increase in BPC and DPC yield was obtained when the PhOH/
DBC molar ratio increased from 1 to 2, but thereaer both
BPC yield and DPC yield declined. Theoretically, higher PhOH/
DBC molar ratio favors an increase of the DPC yield; neverthe-
less, further increasing the PhOH/DBC molar ratio to 4, the
yield of DPC was greatly reduced again. At this stage, although
the detailed reason is still not clear, it can be conjectured that
insufficient availability of catalyst species may be one of the
reasons due to the remarkable increase of reaction volume
when excessive PhOH was added.
2
6
tion mechanism. Based on this reaction mechanism, the
lower catalytic activity and selectivity of the 3ZnTi-500 might
be due to its weak acidity, which was unfavorable for the
nucleophilic attack on the carbonyl of the DBC. The catalyst
3
ZnTi-300 with large amounts of acidic sites shown relatively
lower catalytic selectivity was considered to be related to the
presence of strong acidic sites, which would promote the by-
product formation. Therefore, incorporation of a Zn compo-
nent into Ti may not only affect both the acidity strength and
the number of acidic sites, but also affect the structural of
catalyst, which may result in higher catalytic activity of 3ZnTi-
Finally, the impact of the amount of catalyst on DPC
synthesis was investigated, as shown in Fig. 5C. It can be seen
that the DPC yield increases with the increase of the amount of
catalyst charged initially. When the amount of catalyst charged
4
00. Apart from the catalytic activity, the reusability of catalyst
is another important issue. Therefore, attempts were made to
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3.4 Disproportionation with distillation
Since the disproportionation of BPC is an equilibrium process,
the DPC yield can be increased by removing DBC from the
system during the reaction. The reaction was carried out under
reduced pressure (3 kPa) in the distillation apparatus, where
DBC could be distilled off. An 80% BPC conversion was ob-
ꢀ
tained at 190 C in 3 h over 3ZnTi-400. Aer the completion of
the reaction for 9 h as total, DPC was isolated by distillation.
The yield of DPC was 6.8 g (32%).
4. Conclusions
In summary, binary Zn/Ti composite oxides with different
proportions were prepared by co-precipitation method and used
in the synthesis of DPC via a two-step process from DBC as
a starting material. 3ZnTi-400 showed high activity and selec-
tivity for the transesterication of DBC with PhOH as well as the
disproportionation of BPC into DPC. Moreover, the catalytic
activity can be regenerated aer a simple calcination handling.
Therefore, DBC based two-step DPC synthesis will be one of the
preferable alternatives in the quest for an environmentally
benign route.
Acknowledgements
This work was supported by National Natural Science Founda-
tion of China (No. 21173240).
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