Direct conversion of terminal alkenes to aldehydes via ozonolysis reaction in rotating zigzag bed

Article abstract of DOI:10.1007/s13738-020-01933-y

In this study, continuous ozonolysis of terminal alkenes in a rotating zigzag bed was developed. Rotating zigzag bed is a new type high gravity unit relative to the previous rotating packed bed and can intensify mass transfer remarkably. The rotating zigzag bed takes advantage of centrifugal force to mix liquid and gas phase effectively. The H₂O in acetone acts as an in situ reducing agent for the carbonyl oxide intermediate, providing aldehydes directly from the reaction mixture. Critical factors were investigated and achieved optimum reaction conditions. Under these conditions, the yields of series aldehydes ranged from 72.3 to 95.8percent. The discrepancy in product yields among different olefin substrates likely originates from the electronic stability of the carbonyl oxide intermediate, which is longer lived for aryl olefines with electron donor group and longer carbon chain alkene (C_nH_2n, n ≥ 10).

Full text of DOI:10.1007/s13738-020-01933-y

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-01933-y
ORIGINAL PAPER
Direct conversion of terminal alkenes to aldehydes via ozonolysis
reaction in rotating zigzag bed
Zhengyong Liang1 · Tong Wei1 · Jun Xie1 · Hua Li1 · Hui Liu2
Received: 9 December 2019 / Accepted: 6 April 2020
© Iranian Chemical Society 2020
Abstract
In this study, continuous ozonolysis of terminal alkenes in a rotating zigzag bed was developed. Rotating zigzag bed is a new
type high gravity unit relative to the previous rotating packed bed and can intensify mass transfer remarkably. The rotating
zigzag bed takes advantage of centrifugal force to mix liquid and gas phase efectively. The H2O in acetone acts as an in situ
reducing agent for the carbonyl oxide intermediate, providing aldehydes directly from the reaction mixture. Critical factors
were investigated and achieved optimum reaction conditions. Under these conditions, the yields of series aldehydes ranged
from 72.3 to 95.8%. The discrepancy in product yields among diferent olefn substrates likely originates from the electronic
stability of the carbonyl oxide intermediate, which is longer lived for aryl olefnes with electron donor group and longer
carbon chain alkene (CnH2n, n≥10).
Keywords Ozonolysis · Terminal alkene · Rotating zigzag bed · Flow chemistry
List of symbols
conditions, the ozonolysis of alkenes generates ozonides and
other peroxidic ozonolysis products, which must be reduced
in a separate step to form the desired aldehydes [3, 4]. The
common reductants, such as Me2S, PPh3, Pt/H2, Zn/HOAc
and NaHSO3, often have troublesome problem of low elec-
trical selectivity or complex product separation, which limits
the large-scale process of ozonolysis of alkenes.
G
Gas volumetric fow rate, m3/h
L
Liquid volumetric fow rate, L/h
Substrate concentration of the liquid phase,
mol/L
C
N2r
ꢀ =
N
Super gravity factor
900
ꢀ
Rotational speed, rpm
r2+ro2
i
r =
Geometric radius, m
To solve these drawbacks, trapping of carbonyl oxides by
reagents, such as water and N-oxides, had been introduced in
ozonolysis reaction and achieved great progress [5–7]. But
batch reactions and water-miscible polar organic solvents in
this method had difculties in industrial scale, which was the
most signifcant defciencies [8].
2
ri
ro
Inner radius of RZB rotor, m
Outer radius of RZB rotor, m
Introduction
It is generally known that high gravity technology, which
was invented by New Science Group in Imperial Chemical
Industries, has developed into one of the most promising
branches of process intensifcation [9]. Rotating zigzag bed
(RZB) is a new high gravity unit with the advantages of mul-
tilayer rotors in one unit, high mass transfer efciency and
service durability than traditional rotating packed bed (RPB)
[10]. According to the reports in the current literature, RZB
has been widely used in absorption and distillation, but it
was seldom utilized for ozonolysis of mass transfer limited
gas–liquid reacting systems. To expand the approach of
in situ carbonyl oxide reduction with water, while taking
advantages of the safety and scalability of fow ozonolysis,
Ozone is a highly reactive oxidant and applied widely in
modern organic chemistry with the advantages of high atom
economy, absence of metals or hypervalent iodine and the
straightforward synthesis of ozone from O2. So, ozonolysis is
a popular method for the oxidative cleavage of alkene to pro-
duce aldehyde and ketone [1, 2]. However, on the traditional
* Zhengyong Liang
lzy781103@126.com
1
School of Chemical Engineering, Zhengzhou University,
Zhengzhou 450001, People’s Republic of China
2
Luoyang Petrochemical Engineering Corporation
Ltd/SINOPEC, Luoyang 410300, People’s Republic of China
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
we developed a high-throughput fow method using a RZB
Specifcation of ozone generator and main reagents
in this paper.
HD-500 ozone generator (ozone output is 500 g/h, average
concentration of ozone is about 100 mg/L, power is 4.5 kw)
was provided by Yinhe Ozone Equipment Co., Ltd (Zhu-
hai, China). Commercially available reagents, such as sty-
rene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene,
1-decene, 1-dodecene and 1-hexene, were purchased from
Aladdin Chemical Reagent Co., Ltd (Shanghai, China) and
used directly without further purifcation. Standard prod-
uct samples such as benzaldehyde, 4-methylbenzaldehyde,
4-methoxybenzaldehyde, 4-nitrobenzadehyde, 1-nonanal,
1-undecanal and valeraldehyde were purchased from Merck
Chemical Technology (Shanghai) Co., Ltd. Product yield
was determined by Agilent 4890 gas chromatograph.
Experimental
Mechanism of ozonolysis reaction with water
as zwitterion
The mechanism is shown in Fig. 1, and during the course
of ozonolysis reaction, carbonyl oxides 4 and 5 are active
intermediates, which can be trapped by water which is a
common nucleophile. The oxygen atom of water can be used
as a nucleophilic center, which attacks the carbonyl oxide
and generates a gem-hydroperoxy alcohol. Under the reac-
tion conditions, the intermediate decomposes with liberation
of the aldehyde or ketone and H2O2 [11, 12].
Experimental procedure
Continuous operation of ozonolysis reaction in RZB
Figure 2 shows the diagram of experimental setup for the
ozonolysis reaction. The major components include a RZB,
a ozone generator, a heat exchanger, a gas–liquid separator,
a liquid pump, a O2 cylinder, two liquid tanks and other
auxiliary equipment.
Structure of the RZB
The RZB has two rotors with an inner diameter of 11.8 cm
and outer diameter of 28.5 cm and a height of 5.0 cm, with a
casing of diameter 38.0 cm and height 21.0 cm and a liquid
distributor located at the center of rotor. The nine stationary
bafes with the height of 3.8 cm have diameters of 13.0,
15.8, 18.0, 20.0, 1.8, 23.6, 25.3, 26.8, 28.5 cm. In addition,
there is a layer of stainless steel packing with a thickness
of 4 mm sticking to the inside surface of every stationary
bafe. The nine rotational bafes with the height 4.3 cm
have diameters 11.8, 14.5, 16.9, 18.9, 20.8, 22.8, 24.3, 26.0,
27.5 cm. Every rotating bafe is 4.3 cm and comprises two
regions: The upper region is 2.8 cm high and perforated
with small holes of 0.15 cm diameter and 0.25 cm distance
between holes, and the lower region was blank with a height
of 1.5 cm.
Preparation of olefn solutions: Taking styrene solution
(1.5 mmol/L) for an example, 9.37 kg styrene and 4.86 kg
deionized water were used as trapping agent and reduct-
ant was added into storage tank. Then, acetone solvent was
added into storage tank slowly and constant volume to 60 L.
The other terminal alkenes are listed in Table 1, and diferent
concentration solutions were obtained by referencing this
method.
Typical ozonolysis operation: The O2 valve was opened
and adjusted flow to 5.0 m3/h when the ozone genera-
tor was kept switch off. Then, conveying pump and heat
exchanger were started successively, and the substrate
flow was adjusted to 6.0 L/h and 5 °C. After a period of
stabilization, the switch of ozone generator was shifted.
O
O
HCH
O
R CHO
O
O
O
3
O3
4
R CH CH2
R C CH2
H
O
R
C
H
CH2
O
O
O
CH2O
R CH
5
1
2
7
6
Substrate
primary ozonide
secondary ozonide
H2O
OOH
R
C
H
O
R CH
carbonyl oxides
OH
H2O2
3
Product
Fig. 1 Ozonolysis reaction mechanism of terminal alkenes with water as zwitterion derived from references [11, 12]
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Journal of the Iranian Chemical Society
Off-gas
Gas-liquid separator
TI
O3 /O2
O2
LI
Sampler
TI
Heat exchanger
O2
O3 generator
Rotating zigzag bed
cylinder
Product
tank
Reactants
tank
Fig. 2 Schematic diagram of the experimental apparatus
Table 1 Ozone reaction efects of diferent substrates
Results and discussion
It is well known that ozonization of terminal alkene is
gas–liquid phase reaction. So, improving the capacity of heat
and mass transfer between phases is a efective measure.
Taking ozonization of styrene as an example, some impor-
tant factors such as rotation speed, reaction temperature,
liquid volumetric fow and the concentration of substrate
were discussed in detail.
Entry
1
Alkene
Aldehyde (%)
94.7
Acid (%)
2.1
2
3
4
95.8
92.6
74.8
2.7
H3C
4.3
CH O
3
Rotation speed
Trace
O2N
The rotational speeds ranged from 800 to 1600 rpm, with
an interval of 200 rpm. The yields of benzaldehyde (main
product) and benzoic acid (by-product) are shown in Fig. 3.
Figure 3 shows the rotational speed has great infuence
on ozonization. When the rotation speed was low, the super
gravity factor was small, the liquid material was not dis-
persed enough, and the mass transfer rate between phases
was small. With the increase in rotation speed, thinner liquid
flm and better dispersion of liquid cause the mass transfer
rate to increase, so the yield of benzaldehyde also increases
[13]. When the rotation speed reached 1200 rpm, the yield
of benzaldehyde reached the peak value of 94.7% (the super
gravity factor β reached 340.2 at this moment). But further
increase in the rotation speed can cause the oxidation of
benzaldehyde, which leads to the amount of benzoic acid.
5
6
7
CH2 =CH(CH2)7CH3
CH2 =CH(CH2)9CH3
CH2 =CH(CH2)3CH3
89.7
91.8
72.3
6.8
3.7
16.9
Conditions: G=5.0 m3/h, L=6.0 L/h, T=5 °C, N=1200 rpm,
C=1.5 mol/L
The ozonization of substrate occurred at the same time.
The samples were collected from product flow by a sam-
pler at 10-min intervals (10 min, 20 min, 30 min) and
detected by GC. The measurements of the samples were
averaged to obtain the corresponding yields of aldehyde
and acid.
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Journal of the Iranian Chemical Society
100
80
60
40
20
0
out at a higher temperature than traditional batch reaction
mode to obtain a higher reaction rate and shorten the reac-
tion time. From Fig. 4, it can be found that the side reaction
had not been occurred remarkably when reaction was car-
ried out at about 5 °C. But, when temperature is higher than
10 °C, side reaction would occur signifcantly, and the yield
of benzaldehyde was dropped remarkably.
Benzaldehyde
Benzoic acid
Change of liquid fow rate
The ozone output of the ozone generator we used is about
500 g/h regardless of input change of O2, so we mainly
discussed the relationship between yield of products and
the change of liquid fow rate, and the results are shown in
Fig. 5.
800
1000
1200
1400
1600
n/rpm
From Fig. 5, it can be found that when the liquid phase
fow was <4.5 L/h, the ozone in the gas phase was in large
excess, which would lead to excessive oxidation of benza-
ldehyde, so the product yield was lower. With the increase
in liquid phase fow rate, more liquid jets and tinier liquid
droplets leaving the rotational bafes were produced, thus
increasing mass transfer rate. At the same time, the trend
of peroxidation gradually decreases. When the liquid phase
fow rate increases to 6.0 L/h, the mole ratio of O3 and sub-
strate obtains a optimal value, and the yield of benzaldehyde
can reach the peak of 94.7%. If the liquid fow continues to
increase, the styrene was in an excessive state conversely,
which could basically eliminate the excessive oxidation
side reaction and improve the selectivity of benzaldehyde.
However, the larger liquid volumetric fow rate reduces the
Conditions: G=5.0 m3/h, L=6.0 L/h, T=5ć
and C=1.5 mol/L
Fig. 3 Efect of rotational speed on yield of benzaldehyde and
benzoic acid. Conditions: G=5.0 m3/h, L=6.0 L/h, T=5 °C and
C=1.5 mol/L
Infuence of temperature
Figure 4 illustrates the infuence of reaction temperature. It
is well known that ozonization is a strong exothermic reac-
tion [14], so temperature has great infuence on it. Because
of the good heat transfer efect in this reaction system, it
seldom forms local hot spots. So, ozonization can be carried
100
80
100
80
60
40
20
0
Benzaldehyde
Benzoic acid
60
Benzaldehyde
Benzoic acid
40
20
0
-20
-15
-10
-5
0
5
10
15
20
25
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
Reaction temp. /oC
L/(L/h)
Conditions: N=1200rpm, G=5.0 m3/h, L=6.0
L/h, and C=1.5 mol/L
Conditions: N=1200rpm, G=5.0 m3/h, T=5ć,
and C=1.5 mol/L
Fig. 4 Infuence of temperature on yield of benzaldehyde and ben-
zoic acid. Conditions: N=1200 rpm, G=5.0 m3/h, L=6.0 L/h and
C=1.5 mol/L
Fig. 5 Infuence of liquid fow rate on yield of benzaldehyde and
benzoic acid. Conditions: N=1200 rpm, G=5.0 m3/h, T=5 °C and
C=1.5 mol/L
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Journal of the Iranian Chemical Society
100
the oxidation reaction. However, the yield of aldehyde is
abnormally reduced due to the easy oxidation of p-methoxy
benzaldehyde into p-methoxybenzoic acid. An alkene with
an electron-absorbing group, such as p-nitrostyrene, has
low activity but very high selectivity, and the selectivity
of aldehyde is about 100%. For aliphatic terminal alkenes,
the primary ozonates of the long-chain alkenes whose car-
bon chain length is over 10 are dominant in the cleavage
mode to produce the corresponding aldehydes, so the yields
of aldehydes are higher. In contrast, while for short-chain
aldehydes whose carbon chain length is < 6, their ozonide
activity is too high, and it is easy to produce more stable
acids and polymers.
80
60
40
20
0
Benzaldehyde
Benzoic acid
1.0
1.2
1.4
1.6
1.8
2.0
C/(mol/L)
Conditions: N=1200rpm, G=5.0 m3/h, T=5ć,
and L=6.0 L/h
Conclusions
In this study, a novel kind of Higee device of rotating zig-
zag bed was applied to the continuous ozonolysis reaction
of some terminal alkenes to produce aldehydes. Under the
optimum conditions, the yields of corresponding aldehydes
(main product) were between 72.3% and 95.8%, and only a
small amount of acids (by-product) were produced simul-
taneously. The mixture of acetone and water is a suitable
solvent with its excellent solubility and fast capture abil-
ity for carbonyl oxide intermediates. Rotational speed, ratio
of liquid–gas and temperature all have great efect on the
reaction and must be well matched each other. Generally
speaking, the continuous ozonolysis reaction in RZB is a
good example that high gravity can be used to intensify a
chemistry reaction process.
Fig. 6 Infuence of substrate concentration on the yield of benzal-
dehyde and benzoic acid. Conditions: N=1200 rpm, G=5.0 m3/h,
T=5 °C and L=6.0 L/h
dispersion efect, leading to a decrease in the reaction ef-
ciency and a signifcant decrease in the yield of benzalde-
hyde [15].
Change of substrate concentration in liquid fow
The liquid and gas volumetric fow rates were held constants
of 6.0 L/h and 5.0 m3/h, respectively. That is to say, the ratio
of gas to liquid was maintained under the condition of opti-
mization, and the mass transfer coefcient between liquid
gas phases remained basically unchanged. Under this major
premise, the relationship between substrate concentration
variation and product yields was investigated. Concentration
variation ranged from 1.0 mol/L to 2.0 mol/L. The results
are shown in Fig. 6.
Acknowledgements This work was supported by Key Technology
Research Project of Henan Province (No. 152102210043) and Foun-
dation of Henan Educational Committee (No. 16A430045).
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only oxidate alkene substrate sufciently but also guarantee
over-oxidation of benzaldehyde at a low level, so the yield
of benzaldehyde can reach about 94.7%.
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