Beckmann rearrangement reaction of cyclohexanone oxime in sub/supercritical water: Byproduct and selectivity

Article abstract of DOI:10.1039/c5ra01929j

As an important green synthesis technology of caprolactam, the Beckmann rearrangement reaction of cyclohexanone oxime using high temperature and pressure water as the reaction media was carefully studied with a microreactor. An important byproduct-acetamide was confirmed with a selectivity higher than 40% in the subcritical water, which was more serious than the reported cyclohexanone. The effects of phase state and operating conditions, such as reaction temperature, pressure, flow rate ratio and reactant residence time, on the cyclohexanone oxime conversion and caprolactam selectivity were carefully analyzed, and the results showed that keeping the reaction close to the supercritical state was critical for the preparation of caprolactam. This journal is

Full text of DOI:10.1039/c5ra01929j

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Beckmann rearrangement reaction of
cyclohexanone oxime in sub/supercritical water:
byproduct and selectivity
Cite this: RSC Adv., 2015, 5, 25365
Yang Li, Kai Wang,* Kang Qin and Tao Wang*
As an important green synthesis technology of caprolactam, the Beckmann rearrangement reaction of
cyclohexanone oxime using high temperature and pressure water as the reaction media was carefully
studied with a microreactor. An important byproduct – acetamide was confirmed with a selectivity
higher than 40% in the subcritical water, which was more serious than the reported cyclohexanone. The
effects of phase state and operating conditions, such as reaction temperature, pressure, flow rate ratio
and reactant residence time, on the cyclohexanone oxime conversion and caprolactam selectivity were
carefully analyzed, and the results showed that keeping the reaction close to the supercritical state was
critical for the preparation of caprolactam.
Received 31st January 2015
Accepted 3rd March 2015
DOI: 10.1039/c5ra01929j
www.rsc.org/advances
such as methyl allyl aryl ether Claisen rearrangement reaction at
1
Introduction
ꢀ
14
5
MPa and 265
C
and Friedel–Cras alkylation reaction of
ꢀ
15
The Beckmann rearrangement reaction of cyclohexanone oxime phenol at 275 C in the absence of any acid catalyst. Using
is an important chemical process for the preparation of capro- supercritical water instead of organic solvent, organic catalyst and
1
lactam, the monomer of Nylon-6, as shown in Scheme 1. In the fuming sulfuric acid catalyst offers a great opportunity to prevent
industrial process, more than 90% caprolactam is synthesized environment problems and the generation of useless ammonium
from the conventional cyclohexanone route catalyzed by fuming sulfate. In the area of cyclohexanone oxime Beckmann rear-
2
16–19
sulfuric acid. As a strong corrosion process, it still has some rangement in supercritical water, Ikushima et al.
have repor-
drawbacks, such as the large amount of byproduct ammonium ted some prospective works. In a preliminary batch reaction study,
sulfate, it is unfriendly for environment and has serious safety they found when the cyclohexanone oxime aqueous solution was
3,4
ꢀ
problems.
Since caprolactam is an important chemical heated up to the critical point (374.2 C, 22.13 MPa), caprolactam
product with growing demand, there have been lots of studies can be measured, but the yield was only 1.9%. Lots of cyclohex-
on developing new Beckmann rearrangement processes. In the anone was obtained as the main byproduct generated from the
last 10 years, a large number of solid-acid catalysts, such as hydrolysis of cyclohexanone oxime. The authors believed the
5
6
7
2 3 2 5
B O , Nb O
, and zeolite have been investigated to proceed temperature raising took so much time resulted the yield of
the Beckmann rearrangement reaction at the vapor state, which cyclohexanone during the subcritical water state, where the ion
ꢀ
are usually operated at a temperature higher than 300 C and product (K
w
) was much bigger than the ambient water and the
nearly 0.1 MPa pressure. Besides, the liquid Beckmann rear- cyclohexanone oxime became unstable. A supercritical water
rangement reaction using organic acid catalyst is another hot- microreactor system with instant heating function according to
8
9,10
point area. For example, Ronchin et al. reported 92% selec- fast mixing of hot water and cool cyclohexanone oxime solution
tivity of caprolactam was achieved, catalyzed by triuoroacetic was therefore invented, achieving nearly 80% yield of caprolactam
ꢀ
acid in aprotic solvents such as toluene.
at 40 MPa and 375 C. Then, the system achieved nearly 100%
The Beckmann rearrangement reaction in high temperature yield of caprolactam by using some dilute acid as the catalyst.
and pressure water is another hot point for the synthesis of Cyclohexanone was the unique reported byproduct in their papers
caprolactam, which attracts rising interest in recent years. Since
the thermodynamic properties of water can be easily changed
11–13
with the variation of pressure and temperature,
nonpolar
organic compounds become miscible in supercritical water. The
sub/supercritical water also works as a catalyst in some reactions,
State Key Laboratory of Chemical Engineering, Department of Chemical Engineering,
Tsinghua University, Beijing 100084, China. E-mail: taowang@tsinghua.edu.cn;
kaiwang@tsinghua.edu.cn; Tel: +86 10 62784877; +86 10 62788568
Scheme
oxime in industrial process.
1 Beckmann rearrangement reaction of cyclohexanone
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 25365–25371 | 25365

View Article Online
RSC Advances
Paper
ꢀ
and the use of dilute acid did not realize a genuine green ranged from 320 to 420 C. The mixture was then introduced
synthesis. Further work on the byproduct generation rules in sub/ into a 1/16 inch reaction tube, whose inner diameter was 0.6
supercritical water is still an important issue in this area.
mm. The temperature at the reaction tube inlet was moni-
In this paper, we developed a similar work using a capillary tored by a sensor and its value was used to adjust the
microreaction system with fast heating and fast quenching temperature of heat preservation room with a deviation less
ꢀ
functions. Considering the subcritical phase was unavoidable than 10 C. According to the temperature values aer the rst
in the caprolactam synthesis, which was important for the micromixer, the mixing of hot water and cold cyclohexanone
reaction yield, we paid more attention in this part and another oxime aqueous solution was almost complete, which xed
byproduct acetamide was discovered, which was ignored in heat balance, and this phenomenon accorded to our previous
2
0,21
previous reports. The variation rules of cyclohexanone oxime studies
on micromixing process, which mixing time was in
conversion and caprolactam selectivity were carefully analysis several milliseconds. In order to give a strict control of the
and the importance of mixing and phase state were also reaction time, the reacting mixture was quenched by mixing
discussed.
with another stream of cold water at the second T-type
micromixer, which was not adapted in Ikushima's work.
1
7,18
The temperature of this new mixture was also monitored by a
temperature senor, whose values varied from 90 to 160 C. The
2
Experimental
ꢀ
2
.1 Experimental setup and procedures
mixture was further cooled to room temperature in a cooler,
who had a cooling tube with inner diameter 2 mm in it. The
solution was nally ltered and released to the gas–liquid
separator in order to collect the liquid samples. The reaction
pressure was controlled by a back-pressure regulator from 16
to 32 MPa. In every experiment, pressure test using a ow of
pure water was rst made to exclude leaking, and then the
heaters and cooler were turned on. As the system temperature
reached the set value, the cyclohexanone oxime aqueous
solution was pumped in, instead of the pre-fed water. 20 min
was needed for the system reaching a steady state, and
samples were collected in 3 min.
The Beckmann rearrangement reaction was conducted in a
capillary microreaction setup, as shown in Fig. 1. It was
organized by three feeding pumps, a heating oven, a heat
preservation room, two micromixers, a reaction tube, three
temperature sensors, a cooler, a lter, a back-pressure valve
and a gas–liquid separator. Among those devices, the most
important parts were the two T-type micromixers, which inner
diameter was 0.75 mm. In the experiment, a stream of water at
ambient temperature was rst heated into the oven using a 2
m long, 1/8 inch diameter Hastelloy C-276 tube as the pre-
heater. The max temperature of this hot water was about
5
and the pre-heating tube was embedded in the copper plate to
ꢀ
00 C. A heating plate made by copper was placed in the oven
2.2 Materials and analysis
deliver heat. A stream of cyclohexanone oxime aqueous In the experiment, the reactant cyclohexanone oxime (CHO)
solution at ambient temperature was then mixed with the and the byproduct cyclohexanone (OH) were purchased from
high temperature supercritical water out of the pre-heating Alfa Aesar Co., Ltd. The caprolactam (CPL) was purchased
tube in the rst T-type micromixer and the cyclohexanone from Aladdin Co., Ltd. Chromatographically pure solvents
oxime solution was quickly heated to a reaction temperature, used in analysis (acetonitrile, chloroform) at were provided by
Fig. 1 Scheme diagram of the experimental setup.
25366 | RSC Adv., 2015, 5, 25365–25371
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Beijing Chemical Works. Ultrapure water (18.2 MU cm) was
used as the reaction medium. The soluble O2 in water was
ðQCHO þ Qhw þ QcwÞW
i
M
CHO
S
i
¼ Q
(3)
CHO
W
in-
CHO ꢁ ðQCHO þ Qhw þ QcwÞWCHO
M
i
removed by 30 min N bubbling. Since the concentration of
2
ꢁ1
cyclohexanone oxime used in the reaction was 1 g L , the where Win-CHO is the initial mass concentration of cyclohexa-
physical properties of reacting solution was evaluated by pure none oxime in aqueous solution, WCHO is the mass concentra-
water, which data are published on the web site of US National tion of cyclohexanone oxime in the mixer aer reaction, Qcw is
Institute of Science and Technology (NIST, http:// the mass ow rate of cold water coming into the second
webbook.nist.gov). The residence time in the reaction tube micromixer; i refers to cyclohexanone, acetamide or capro-
between two micromixers was calculated from the volume of lactam, W
is the mass concentration of i aer the reaction, M is
i
i
the reactor and the mass velocity of the mixture as the the molecular weight of species i and MCHO is the molecular
following equation:
weight of cyclohexanone oxime.
Samples of product from the outlet of microreaction system
(1) were mainly analyzed by a high performance liquid chromato-
V
reactor ꢂ r
s ¼ Q
CHO þ Qhw
graph (HPLC, Agilent 1260, wavelength of UV detector: 201 nm,
where Vreactor is the reaction tube volume; Qhw is the mass ow mobile phase: 35% acetonitrile and 65% DI water, ow rate: 0.5
ꢁ
1
rate of hot water from the pre-heater; QCHO is the mass ow rate mL min ). What's more, some samples were extracted by
of cyclohexanone oxime aqueous solution; r is water density at chloroform 3 times, and then the organic phase was analyzed by
reaction temperature and pressure. The cyclohexanone oxime a gas chromatography (GC, Agilent 7890A, FID detector, gas: N ;
2
ꢀ
ꢀ
conversion X, and the selectivity (S
i
) of cyclohexanone, acet- injection temperature: 250 C; column temperature: 170 C;
ꢀ
amide and caprolactam were calculated by the following detector temperature: 240 C) in order to analyze the selectivity
equations:
of cyclohexanone. A gas chromatography-mass spectrometry
GC-MS, Thermo Fisher) was used to conrm the main
(
Q
CHO þ Qhw þ Qcw
CHO
W
CHO
X ¼ 1 ꢁ
(2)
byproduct using a 30 m ꢂ 0.25 m ꢂ 0.25 mm nonpolar capillary
Q
W
in-CHO
column and a ame ionization detector. The temperature
ꢁ
1
Fig. 2 HPLC spectrometry of samples: (a) sample from the Beckmann rearrangement reaction. The flow rate of hot water was Qhw ¼ 4 g min
.
ꢁ1
The flow rate of cyclohexanone oxime solution was QCHO ¼ 1 g min . The flow rate of cooling water at the second micromixer was Qcw ¼ 9.99 g
ꢁ1
ꢁ1
ꢀ
min . The concentration of cyclohexanone oxime was WCHO ¼ 1 g L . The reaction temperature was 400 C. The pressure of the system was p
30 MPa. (b) Aqueous phase sample after the extraction by chloroform. (c) Purchased acetamide aqueous solution.
¼
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 25365–25371 | 25367

View Article Online
RSC Advances
Paper
ꢀ
ꢁ1
ꢀ
ꢀ
gradient in operation was 10 C min from 60 to 300 C and the a rotary evaporator at 50 C. The collected samples were dis-
retention time was 20 min. The ion source temperature was 250 solved in methanol, and the methanol solution was then
ꢀ
C and the electron beam energy was 70 eV.
analyzed by a GC-MS in order to gure out the residual
composition.
Fig. 3(a) shows the mass spectrogram of the byproduct in the
methanol solution and Fig. 3(b) shows the standard sample of
acetamide in methanol solution. The mass spectrogram of the
unknown byproduct is in fair agreement with the purchased
3
Results and discussion
3.1 Stability of caprolactam
In order to discuss the Beckmann rearrangement reaction of
cyclohexanone oxime, the stability of caprolactam in subcritical
and supercritical water was an important issue, since it might
be open loop hydrolyzed and the product 6-aminocaproic acid
was hard to analysis by the UV detector in HPLC. An aqueous
solution of caprolactam was carried out rst, instead of the
cyclohexanone oxime aqueous solution. Relative errors of
caprolactam concentration in Table 1 showed that almost none
hydrolyzation took place in a short residence time less than 2.5
s. So the caprolactam produced by the Beckmann rearrange-
ment reaction was sufficiently stable in both subcritical and
supercritical water.
3.2 Byproduct analysis
The sample of Beckmann rearrangement reaction of cyclohex-
anone oxime collected aer the experiment was analyzed by
HPLC rstly. There were three high peaks in our results as
shown in Fig. 2(a). The second peak was caprolactam and the
third one was cyclohexanone oxime, which were easily certied.
The retention time of reported byproduct cyclohexanone was at
13 min, which is not obvious in our HPLC spectra, as shown in
Fig. 2(a), but its retention time was conrmed by a purchased
cyclohexanone sample in our HPLC. In order to gure out the
undened byproduct of the rst peak, several 25 mL samples
ꢀ
were extracted by chloroform (25 mL) 3 times at 40 C. Then, the
products were separated into two phases in a separating funnel Fig. 3 Mass spectrometry of the byproduct acetamide: (a) obtained in
ꢁ
1
ꢁ1
the experiment: Qhw ¼ 4 g min , QCHO ¼ 1 g min , Qcw ¼ 9.99 g
and the aqueous phase was analyzed by HPLC again and a
typical result is given by Fig. 2(b). This result shows only the
undened byproduct exits in the residual water phase. The
organic chloroform phase was then analyzed by a GC in order to
ꢁ1
ꢁ1
min , WCHO ¼ 1 g L , the temperature and pressure of the system
ꢀ
were 400 C and 30 MPa; (b) purchased acetamide in methanol
solution.

gure out the selectivity of cyclohexanone. The residual
aqueous phase was then completely evaporated and collected in
a
Table 1 Stability of caprolactam in sub/supercritical water
ꢀ
ꢁ3
T ( C)
p (MPa)
r (kg m
)
kWmix ꢁ Wk/Wmix
s (s)
1
2
3
3
3
3
64
38
43
66
72
90
30
30
30
30
30
30
920
841
662
594
571
371
1.29%
2.25%
0.12%
1.10%
1.97%
2.23%
2.5
2.3
1.8
1.6
1.5
1.0
a
ꢁ1
A stream of hot supercritical water (4 g min ) and a stream of
ꢁ1
ꢁ1
caprolactam aqueous solution (1 g min , WCPL ¼ 0.9 g L ) at
ambient temperature were mixed in the experiment. Then the mixed
ꢁ1
solution was mixed with another ambient water (9.99 g min ) and
the caprolactam concentration in the nal mixture was Wmix. The
caprolactam concentration in the outlet solution, W, is analyzed by a
HPLC with instrumental error less than 5%.
Scheme 2 Mechanism of the Beckmann rearrangement reaction in
sub/supercritical water.
25368 | RSC Adv., 2015, 5, 25365–25371
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
acetamide. HPLC spectrogram of the sample attained from Ltd was 97%. One possible for the existing methyl 2,2-dime-
Beckmann rearrangement reaction in Fig. 2(a) is also in accor- thoxyacetate was from the source material rather than reaction.
dance with the purchased acetamide solution as shown in So in this paper we will not discuss other byproduct any more.
Fig. 2(c). Thus, the main byproduct in our Beckmann rear-
rangement reaction is conrmed to acetamide. The results
obtained by GC of the organic phase tell us there was a little 3.3 Effects of operating conditions
cyclohexanone produced in our experiment with a selectivity
less than 10% and the selectivity changed a little at different
the temperature, it is necessary to discuss the effect of
reaction conditions. Limited by the lack of the mechanism
As the thermodynamics properties of water varies seriously with
temperature on the reaction performance. The experiment was
theory, an explanation was proposed according to the reported
carried out in subcritical and supercritical water at 30 MPa by
22
mechanism in literature. As shown in Scheme 2, during the
reaction, the rst step is the initial protonation of the oxygen
atom in cyclohexanone oxime in the supercritical water, then
the rearrangement occurs. But when this process is operated in
subcritical water, the carbon ring becomes unstable for the high
ionic strength, and one result is the broken of ring, producing a
nitrilium ion and leading to the yield of the acetamide. When
doing the GC-MS, we also found some other compounds in our
sample, such as the methyl 2,2-dimethoxyacetate (CAS:89-91-8).
However, the area ratio of peaks acetamide to methyl 2,2-
dimethoxyacetate was nearly 100 : 1, thus there was very little
methyl 2,2-dimethoxyacetate in our sample. What's more, the
purity of cyclohexanone oxime purchased from Alfa Aesar Co.,
setting different temperatures of the pre-heater. Fig. 4 shows
that the reaction temperature measured by the sensor in the
reaction tube plays a great role. The conversion of cyclohexa-
none oxime rises from 78% to 95% with the increase of
temperature. The selectivity of caprolactam rises from 8% to
38% with the increase of temperature, and the selectivity of
acetamide decreases from 77% to 38%. While, the selectivity of
cyclohexanone is less than 10% with little changes at different
temperatures. These results mean that the supercritical condi-
tion is more favorable for the product of caprolactam. It is
proved that Beckmann rearrangement reaction of cyclohexa-
none oxime followed a proton-catalyzed reaction mecha-
19,22
nism.
At higher temperature, the non-polar solvent
Fig. 4 Effect of reaction temperature on the Beckmann rearrange-
ꢁ
ꢁ1
1
ꢀ
ꢁ1
ment reaction. Qhw ¼ 4 g min (360–500 C), QCHO ¼ 1 g min , Qcw Fig. 5 Effect of the flow ratio of the hot water and cyclohexanone
ꢁ1
ꢁ1
ꢀ
¼
9.99 g min . WCHO ¼ 1 g L . The pressure of the system was p ¼ 30 oxime aqueous solution. Qhw ¼ 2–7 g min (530–420 C). QCHO ¼ 1 g
ꢁ1 ꢁ1 ꢁ1
MPa.
min . Qcw ¼ 9.99 g min . WCHO ¼ 1 g L . The pressure was 30 MPa.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 25365–25371 | 25369

View Article Online
RSC Advances
Paper
environment would contribute to the breakdown of H–O bond, study the inuence of pressure at a given reaction temperature
ꢀ
enhancing the generation of caprolactam.
of 400 C. The selectivity of caprolactam in Fig. 6 increases with
The reaction performance was also affected by the propor- the pressure rising, which reaches 48% at 32 MPa. It may be
tion of the hot water and cyclohexanone oxime solution, which more enhanced at a higher pressure, but we could not verify the
changed the reaction temperature too. In the experiment, the prediction because of the limitation of our pumps. In this

ow rate of cyclohexanone oxime solution was constant at 1 mL reaction, pressure proved to sustain the formation of capro-
ꢁ
1
w 2
min and the cooling water in the second micromixer was the lactam. The ionic product (K ) of H O increases with the
maximum value of our pump 9.99 mL min . We change the increasing of pressure at 400 C. When coming to the super-
reaction temperature by varying the ow rate ratio of hot water critical condition, the increasing H concentration in solvent
ꢁ1
ꢀ
+
and cyclohexanone oxime solution in this experiment, which may explain the increase of the yield of caprolactam, since it has
17
was different from changing the temperature of the pre-heater been demonstrated by Ikushima et al. that the addition of
in the last experiment. The results in Fig. 5 show that the ow dilute acid aqueous solution could contribute to the yield.
rate ratio have an optimum for the yield of caprolactam. When
Another research point on the Beckmann rearrangement
the ow rate is small, the reaction temperature was low. Side reaction is to explore the inuence of residence time on the
reaction were easily proceeded in subcritical state as the result cyclohexanone oxime conversion and caprolactam selectivity. A
in Fig. 4. When the ow rate is high, a potential reason for the simple way of adjusting the residence time is changing the
low selectivity is that the mixing between supercritical water length of the reaction tube. So we carried out the experiments at
23
and ambient solution is not good at extreme ow rate ratio. So different temperatures and 30 MPa. The results are shown in
the ow ratio of the ambient water and cyclohexanone oxime Fig. 7. The residence time exerts a great inuence on the
aqueous solution should have an optimum in the reaction.
conversation of cyclohexanone oxime, which increased with the
Considering the high dilatation coefficient of water with the increasing residence time at a constant temperature. 93% of the
ꢀ
increase of pressure, a series of experiments were carried out to conversation could be achieved at 400 C in less than 3.5 s. The
selectivity of caprolactam decreases with the rising of residence
Fig. 6 Effect of pressure on the generation of caprolactam. The
ꢁ1
ꢀ
experimental details were Qhw ¼ 4 g min (400–450 C), QCHO ¼ 1 g Fig. 7 Effect of the residence time on the Beckmann rearrangement
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢀ
ꢁ1
min , Qcw ¼ 9.99 g min . WCHO ¼ 1 g L . The reaction temperature reaction. Qhw ¼ 4 g min (360–550 C), QCHO ¼ 1 g min , Qcw ¼ 9.99 g
ꢀ
ꢁ1
ꢁ1
was 370 C.
min , WCHO ¼ 1 g L . The pressure of the system was p ¼ 30 MPa.
25370 | RSC Adv., 2015, 5, 25365–25371
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
time and this result show the advantage of caprolactam gener-
ation at the early state of this reaction.
7 G. P. Heitmann, G. Dahlhoff and W. F. Holderich, J. Catal.,
1999, 186, 12–19.
8
S. R. Narahari, B. R. Reguri and K. Mukkanti, Tetrahedron
Lett., 2011, 52, 4888–4891.
4
Conclusions
9
L. Ronchin and A. Vavasori, J. Mol. Catal. A: Chem., 2009, 313,
22–30.
In this work, a new byproduct acetamide is found when investigate
the Beckmann rearrangement reaction in subcritical and super- 10 L. Ronchin, A. Vavasori and M. Bortoluzzi, Catal. Commun.,
critical water. We also nd that the phase state of water is impor-
2008, 10, 251–256.
tant for the yield of caprolactam. A selectivity of 50% caprolactam 11 D. Broll, C. Kaul, A. Kramer, P. Krammer, T. Richter, M. Jung,
and 90% conversation of cyclohexanone oxime could be achieved
within less than 0.75 s at 32 MPa and 400 C. It is demonstrated
H. Vogel and P. Zehner, Angew. Chem., Int. Ed., 1999, 38,
2999–3014.
ꢀ
that high temperature and pressure improve the selectivity of 12 E. Kiranand and J. F. Brennecke, ACS Symp. Ser., 1993, 514,
caprolactam, but the optimized value still allows further studies.
1–8.
1
1
3 S. Marre, Y. Roig and C. Aymonier, J. Supercrit. Fluids, 2012,
66, 251–264.
Acknowledgements
4 H. Kawanami, M. Sato, M. Chatterjee, N. Otabe, T. Tuji,
Y. Ikushima, T. Ishizaka, T. Yokoyama and T. M. Suzuki,
Chem. Eng. J., 2011, 167, 572–577.
We would like to acknowledge the supports from the National
Natural Science Foundation of China (91334201, U1463208) and
the State Key Lab of Chemical Engineering of China (SKL-ChE-
15 P. E. Savage, Chem. Rev., 1999, 99, 603–621.
12T01) on this work.
16 Y. Ikushima, K. Hatakeda, O. Sato, T. Yokoyama and M. Arai,
J. Am. Chem. Soc., 2000, 122, 1908–1918.
References
17 Y. Ikushima, K. Hatakeda, M. Sato, O. Sato and M. Arai,
Chem. Commun., 2002, 2208–2209.
1
G. Dahlhoff, J. Niederer and W. F. Hoelderich, Catal. Rev.:
Sci. Eng., 2001, 43, 381–441.
1
1
2
2
2
2
8 Y. Ikushima, O. Sato, M. Sato, K. Hatakeda and M. Arai,
Chem. Eng. Sci., 2003, 58, 935–941.
9 Y. Masuda, A. Suzuki and Y. Ikushima, Int. J. Heat Mass
Transfer, 2006, 33, 419–425.
0 J. S. Zhang, K. Wang, Y. C. Lu and G. S. Luo, Chem. Eng.
Process., 2010, 49, 740–747.
2
C. Yan, J. Fraga-Dubreuil, E. Garcia-Verdugo, P. A. Hamley,
M. Poliakoff, I. Pearson and A. S. Coote, Green Chem., 2008,
1
0, 98.
K. T. Zuidhof, M. de Croon and J. C. Schouten, AIChE J., 2010,
6, 1297–1304.
J. S. Zhang, K. Wang, Y. C. Lu and G. S. Luo, AIChE J., 2012,
8, 3156–3160.
D. S. Mao, Q. L. Chen and G. Z. Lu, Appl. Catal., A, 2003, 244,
73–282.
M. Anilkumar and W. F. Hoelderich, J. Catal., 2012, 293, 76–
4.
3
4
5
6
5
1 Z. D. Liu, Y. C. Lv, J. W. Wang and G. S. Luo, Chem. Eng. J.,
2
012, 181–182, 597–606.
2 Y. Yamaguchi, N. Yasutake and M. Nagaoka, J. Mol. Struct.,
003, 639, 137–150.
3 X. Y. Lin, K. Wang, J. S. Zhang and G. S. Luo, Chem. Eng. Sci.,
015, 127, 60–71.
5
2
2
2
8
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 25365–25371 | 25371