G Model
CATTOD-9412; No. of Pages7
ARTICLE IN PRESS
R. Mbeleck et al. / Catalysis Today xxx (2015) xxx–xxx
3
O
CH3
CH3
C
PBI.Mo
H C
C
OH
OH
+
+
H C
OOH
OOH
+
3
3
CH3
CH3
CH3
1
,2-epoxycyclododecane
Cyclododecene
CH
C
3
PBI.Mo
H C
C
+ H C
3
3
O
CH3
CH
3
Dodecene
1,2-epoxydodecane
t-butanol
TBHP
Fig. 2. Reaction scheme for epoxidation of cyclododecene and dodecene catalysed by PBI.Mo complex.
4
. Results and discussion
TBHP to the corresponding epoxide. As shown in Fig. 3, it is evi-
dent that variation of temperature clearly influences the outcome
of cyclododecene and dodecene epoxidation catalysed by PBI.Mo.
Epoxidation of cyclododecene at 353 K gave ∼98% yield of
1,2-epoxycyclododecane after 350 min, while the reactions con-
ducted at 343 K and 333 K achieved 86% and 59% yield of
1,2-epoxycyclododecene, respectively during the same period
(Fig. 3a). In case of dodecene epoxidation, the conversion of TBHP to
epoxide is much lower than the values obtained for epoxidation of
cyclododecene. For instance, ∼77% yield of 1,2-epoxydodecane was
achieved after 350 min for reaction conducted at 353 K, whilst the
conversion of TBHP decreased significantly to 51% and 28%, when
the reactions were carried out at 343 K and 333 K, respectively
(Fig. 3b).
In this work, we have studied the catalytic activity of PBI.Mo for
cyclododecene and dodecene epoxidation by studying the effect of
reaction temperature, catalyst loading and alkene to TBHP molar
ratio on the conversion of TBHP to epoxide. In addition, the cata-
lyst reusability and supernatant studies have been carried out to
evaluate the long term stability of the polymer supported cata-
lyst for epoxidation reaction. This information will be very useful
when performing continuous epoxidation experiments. It should
be noted that aerobic oxidation of alkenes involving PBI supported
metal complexes tends to yield allylic oxidation products via a free
radical mechanism, and that a mono-oxygen source such as TBHP is
required to achieve alkene epoxidation via a non-free radical selec-
tive mechanisms [26]. However, no allylic oxidation was detected
in the present system, thus, any participation by molecular oxy-
gen as an oxidant seems unlikely. Thermal decomposition of TBHP
was also negligible under the reaction conditions employed in the
present study. The analytical error for this study was found to be
within ± 3% for all the experiments.
The effect of temperature for batch epoxidation experiments
gives us important information about the optimum reaction tem-
perature required for obtaining high yield of epoxide for the
continuous epoxidation of cyclododecene and dodecene in a reac-
tive distillation column (RDC).
4.3. Effect of catalyst loading on the epoxidation of cyclododecene
4.1. Investigation of mass transfer resistances
and dodecene catalysed by PBI.Mo
Two types of mass transfer resistances exist in heteroge-
In this work, catalyst loading was defined based on the active
Mo component instead of the total mass of PBI.Mo catalyst in
order to take into account any differences in Mo content between
different batches of the prepared PBI.Mo catalyst. However, all
experiments in this work were carried out using one batch of the
prepared catalyst. The effect of catalyst loading (i.e. mole ratio of
Mo to TBHP × 100%) was investigated at 0.15 mol% Mo, 0.3 mol%
Mo and 0.6 mol% Mo. Fig. 4a shows that the kinetic profiles of TBHP
conversion to 1,2-epoxycyclododecane were similar for epoxida-
tion of cyclododecene carried out at 0.15 mol% and 0.3 mol% Mo,
i.e. the yield of epoxide at 350 min was ∼97% in both cases. On
the other hand, the rate of epoxide formation increases slightly
when 0.6 mol% Mo was used and the conversion of TBHP to 1,2-
epoxycyclododecane reached ∼100% at 290 min.
neous catalysed alkene epoxidation with TBHP. One across the
solid–liquid interface, i.e. the influence of external mass transfer
resistance caused as a result of stirring the reaction mixture. The
other mass transfer resistance occurs in the intraparticle space, i.e.
internal mass transfer resistance that is connected with the dif-
ferent catalyst particle size and catalyst internal structure such as
the chemical structure, pore size distribution and porosity. A jack-
eted stirred batch reactor was used to study the existence of mass
transfer resistance for alkene epoxidation with TBHP catalysed by
PBI.Mo complex. It was observed that there was negligible external
mass transfer resistance when epoxidation experiments were car-
ried out using the stirrer speed of 300–400 rpm under otherwise
identical conditions. On the other hand, PBI.Mo catalyst particles
are within the size rage of 243–335 m, which are fairly uniform.
A negligible change in catalytic performance was observed within
this size range. Therefore, it can be concluded that both external
and internal mass transfer resistances were absent in this work.
On the basis of these investigations, all batch epoxidation experi-
ments were carried out with stirrer speed of 400 rpm using PBI.Mo
catalyst as prepared.
In case of dodecene epoxidation, the rate of TBHP conversion to
1
,2-epoxydodecane are almost identical throughout the reaction
for all the catalyst loadings investigated (Fig. 4b). The experiments
conducted using 0.15 mol% Mo and 0.3 mol% Mo achieved ∼70%
conversion of TBHP to 1,2-epoxydodecane at 350 min, while a
slight increase in the conversion of TBHP (76%) was recorded when
0
.6 mol% Mo was used. Thus, it can be concluded that epoxida-
tion of dodecene with TBHP was slightly influenced by increasing
the PBI.Mo loading above 0.15 mol% Mo. Indeed dodecene being
conversion of TBHP to epoxide.
4
.2. Effect of reaction temperature on the epoxidation of
cyclododecene and dodecene catalysed by PBI.Mo
Reactions were carried out at 333 K, 343 K and 353 K in order
to study the effect of reaction temperature on the conversion of
Please cite this article in press as: R. Mbeleck, et al., Efficient epoxidation of cyclododecene and dodecene catalysed by polybenzimidazole