The study of industrializable ionic liquid catalysts for long-chain alkenes Friedel–Crafts alkylation

Article abstract of DOI:10.1002/aoc.5878

Catalysts based on different halo-alkanes structures with durable catalytic performance were synthesized and applied to the Friedel–Crafts alkylation of long-chain alkenes (mixed C_16–24 olefins) with toluene. Surprisingly, compared with the usual industrial catalysts (~10 runs), the cyclic times of the ionic liquid (IL) catalysts reached up to 24 runs, which greatly promotes the industrialization process. Then, Lewis acids of catalysts with different precursor/AlCl₃ molar ratios were investigated and a close relation was discovered between the Lewis acid and catalytic activity. In addition, a comparison of the different halo-alkanes structures about those catalysts was made. The results showed that the [C₆Et₃N]Cl–AlCl₃ had the strongest Lewis acid, corresponding to the highest catalytic performance. Also, the structures of precursors and the specific gravity and active site species of catalysts were investigated by Fourier transform infrared and Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). Meanwhile, the various parameters (catalyst dosage, toluene/olefin molar ratio, reaction temperature and reaction time) of long-chain alkenes alkylation with toluene were studied. Finally, under the optimized reaction conditions, the conversion and selectivity of long-chain alkenes alkylation reached 99.92 and 32.99percent, respectively.

Full text of DOI:10.1002/aoc.5878

Received: 13 January 2020
DOI: 10.1002/aoc.5878
Revised: 19 May 2020
Accepted: 26 May 2020
F U L L P A P E R
The study of industrializable ionic liquid catalysts for long-
chain alkenes Friedel–Crafts alkylation
Gaoyang Ge
| Yuming Zhou | Xiaoli Sheng
| Yonghui Liu |
Beibei Wang | Haiyong Yang | Xiao Sha
School of Chemistry and Chemical
Catalysts based on different halo-alkanes structures with durable catalytic
performance were synthesized and applied to the Friedel–Crafts alkylation of
long-chain alkenes (mixed C16–24 olefins) with toluene. Surprisingly, compared
with the usual industrial catalysts (ꢀ10 runs), the cyclic times of the ionic
liquid (IL) catalysts reached up to 24 runs, which greatly promotes the
industrialization process. Then, Lewis acids of catalysts with different
Engineering, Jiangsu Optoelectronic
Functional Materials and Engineering
Laboratory, Southeast University,
Nanjing, 211189, P. R. China
Correspondence
Yuming Zhou, School of Chemistry and
Chemical Engineering, Jiangsu
Optoelectronic Functional Materials and
Engineering Laboratory, Southeast
University, Nanjing 211189, P. R. China,
Email: ymzhou@seu.edu.cn
precursor/AlCl molar ratios were investigated and a close relation was discov-
3
ered between the Lewis acid and catalytic activity. In addition, a comparison
of the different halo-alkanes structures about those catalysts was made. The
results showed that the [C Et N]Cl–AlCl had the strongest Lewis acid,
6
3
3
Funding information
corresponding to the highest catalytic performance. Also, the structures of
precursors and the specific gravity and active site species of catalysts were
investigated by Fourier transform infrared and Magic Angle Spinning Nuclear
Magnetic Resonance (MAS NMR). Meanwhile, the various parameters
(catalyst dosage, toluene/olefin molar ratio, reaction temperature and reaction
time) of long-chain alkenes alkylation with toluene were studied. Finally,
under the optimized reaction conditions, the conversion and selectivity of
long-chain alkenes alkylation reached 99.92 and 32.99%, respectively.
Transformation of Scientific and
Technological Achievements of Jiangsu,
Grant/Award Number: BA2018045;
Priority Academic Program Development
of Jiangsu Higher Education Institutions,
Grant/Award Number: 1107047002
K E Y W O R D S
Friedel–Crafts alkylation, high cyclicity, industrializable IL catalysts, long-chain alkenes
1
| INTRODUCTION
harmfull to health. Hence, HF should be replaced
[
6,7]
urgently as an alkylation catalyst.
Solid acid has not
Long-chain alkyl benzene is mainly used to produce sur-
factants in tertiary oil recovery technology, and has
been industrialized on a large scale owing to its difficult
[
8,9]
regeneration and high cost.
For these reasons, ionic
[1,2]
attracted more and more attention.
The current com-
liquids (ILs) are being investigated for their unique
chemical and physical properties such as low vapor pres-
sure, non-flammability, mild reaction conditions, thermal
mercial catalysts for heavy alkyl benzene are concentrated
[3]
hydrofluoric acid (HF) or solid acid. Although these two
catalysts show high catalytic activity and selectivity in the
reaction, the processes have plenty of drawbacks,
including equipment corrosion and high post-processing
[
10–13]
stability and recyclability.
The key characteristic of
an IL is its designability, which can be improved and opti-
mized by properly adjusting the types of anions and
cations and their substituents. These properties lead to a
[4,5]
cost.
HF is highly toxic and can form aerosol clouds
[14,15]
containing deadly hydrogen fluoride, which is very
wide range of applications, including materials,
Appl Organomet Chem. 2020;e5878.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.5878

2
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GE ET AL.
[
16]
[17]
organic synthesis,
electrochemistry
membrane separating processes,
In fact, simultaneously increasing the conductivity
and the selectivity of alkylation is impossible for indus-
trial production. However, as is well known, few studies
have been reported on long-chain alkene alkylation and
high cyclic performance concurrently. Therefore, it is
highly desirable to develop IL catalysts with high cyclic
performance and focus more on the long-chain alkenes.
Herein, a series of IL catalysts were prepared successfully
from halogenated alkane, triethylamine and metal
[
18]
[19,20]
and catalysis.
Apart from this,
ILs show great potential in industrialized applications. To
our best knowledge, ILs have not only been applied
extensively to chemical reactions as green solvents, but
are also used as reusable catalysts for Friedel–Crafts alkyl-
[21,22]
ation.
For example, Zhao et al. investigated Friedel–
Crafts alkylation of 2-methylnaphthalene with long-chain
alkenes in ethyl-containing amine chloroaluminate ILs
modified with HCl as environmentally friendly cata-
Su et al. synthesized an IL catalyst ([Dabco-C8]
FeCl ]) and applied it to various electron-deficient ole-
fins, including chalcones,enones and nitro-olefins, and it
had good performance for the corresponding 3-alkylindole
derivatives in good yields under mild conditions within
salt (AlCl ). The mechanism and reaction process of
3
[23]
lysts.
long-chain alkenes alkylation with toluene is illustrated
in Figure 1. Then the Lewis acidity of the catalysts
is studied by acetonitrile probe Fourier transform
infrared (FT-IR) spectroscopy. The catalytic activities
of catalyst employed to alkylation were investigated
respectively according to the conditions (catalyst dosage,
toluene/olefin molar ratio, reaction temperature and
reaction time) of the alkylation reaction. In addition, as
shown in Figure 2, the present work took a step closer to
continuous industrial production of long-chain alkenes.
[
4
[24]
short times.
In terms of alkylation with toluene, IL-catalysts like
[
25]
[26]
3,
[27]
[
C mim]Cl–AlCl
[Et NHCl]–AlCl
[bmim]Cl–
and [C mim]
n
3,
3
[22]
AlCl /CuCl,
[HO S-C Et N]Cl-MCl
have resulted in high activity. Meanwhile,
3
3
3
3
n
[28]
[
NTf2],
research on the durability of ILs catalysts has been
reported. For instance, He et al. have successfully synthe-
sized durable IL [bmim][TFSI]/AlCl , which demon-
2 | EXPERIMENTAL
3
−
strated the enhanced durability with anion [TFSI]
[29]
around active sites.
Furthermore, Liu et al. synthe-
2.1 | Chemicals and reagents
sized Brønsted–Lewis acidic ILs (possessing Brønsted and
Lewis dual acids) which had good catalytic performance
in the conversion and selectivity with strong cycle perfor-
mance owing to the synergetic effect of Brønsted and
All reagents were used as received without further purifi-
cation. 1-Chlorobutane (≥99.0%, AR), 1-chlorohexane
(98%, AR), 1-chlorooctane (99%, AR), triethylamine (99%,
AR), toluene, aluminum chloride (99%, AR), zinc
[5]
Lewis acidic sites.
FIGURE 1 Flowchart of whole reaction

GE ET AL.
3 of 11
FIGURE 2 Flowchart of
industrial production
chloride (99%, AR) and ferric chloride (99%, AR) were all
purchased from Macklin Chemical Reagent Co. Ltd.
AlCl had completely dissolved. Finally, dark brown ILs
3
were obtained. Different precursor/AlCl molar ratio of
3
1
-Octadecene was obtained from the chemical market.
ILs catalysts were prepared by adjusting the number of
AlCl moles added.
3
2
.2 | Preparation of precursor and IL
catalysts
2.3 | Characterization of catalysts
2
.2.1 | Synthesis of precursor ([C Et N]Cl,
4 3 8 3
A series of chloroaluminate ILs was synthesized follow-
ing the above procedure. All synthesized acidic ILs cata-
lysts were characterized by FT-IR, specific gravity and Al
Magic Angle Spinning Nuclear Magnetic Resonance
(MAS NMR). FT-IR spectra of various catalysts were
obtained using a KBr wafer on a Bruker IFS-28 spectrom-
6
3
[C Et N]Cl and [C Et N]Cl)
Triethylamine and 1-chlorohexane (molar ratio of 1:1.1)
were added to a three-neck round-bottom flask at room
temperature, then warmed to 388.15 K and reacted
with stirring for 24 h under refluxing. A yellow liquid
precursor was obtained finally. Moreover, [C Et N]Cl
−1
eter in the range of 4,000–500 cm . Determination of
specific gravity was obtained using a density bottle
method. Al MAS NMR spectra were recorded on a
Bruker Ultrashield spectrometer (Avance AV-500). The
4
3
and [C Et N]Cl were approximately in step with the
synthesis of [C Et N]Cl.
8
3
6
3
[19]
Al NMR spectra of the IL were recorded in CD Cl
2
2.
2.2.2 | Synthesis of IL catalysts
2.4 | Determination of alkylation catalyst
Precursors were added to a dry three-neck round-bottom
flask, and a suitable amount of toluene added as solvent.
activity
Then, anhydrous AlCl was added in batches at room
temperature with constant stirring. It was heated to
Toluene and dehydrated long-chain alkenes are added to
a three-mouth flask at a certain molar ratios, then kept at
a constant temperature in a water bath with magnetic
3
3
53.15 K for 6 h under N protection until the anhydrous
2

4
of 11
GE ET AL.
stirring. After the reactants had reached a certain temper-
ature, a pipette was used to quickly add a certain volume
of IL into the three vials, and the reaction time was
recorded. When the reaction was complete, the mixture
was divided, with the top layer being a mixture of toluene
and the product and the bottom layer being a mixture of
IL and toluene. At the end of the reaction, the upper liq-
uid was extracted and analyzed by high performance liq-
uid chromatography (HPLC) and bromine value. The
lower layer catalyst was restarted for recycling and new
toluene and dehydrated long-chain alkenes were added
to the three-mouth flask at the same time.
The bromine value of the alkylation products was
measured in accordance with standard test method
GB/T1815. The bromine value is an evaluation of unsatu-
rated olefins, which showed that 100 ml of product was
equivalent to the amount of bromine. The bromine value
of product was calculated as follows:
stretching vibration of C–H. Apparently, two absorption
peaks are located at 1460 and 748 cm− belonging to
1
−
1
bending vibrations of C–H, while the peak at 1400 cm
is attributed to the stretching vibration of C–N.
[30]
In
summary, all three precursors possess the same structural
characteristics.
3.1.2 | Specific gravity of IL catalysts
The specific gravity of liquids indicates whether they sink
or float in another fluid. Therefore, the determination of
specific gravity as the ratio of the density of the material
(completely densified) to the density under pure H O
2
3
(999.972 kg/m ) at standard atmospheric pressure and
277.13 K is essential. Table S1 indicates the specific
gravity of the product and catalysts. As can be seen, the
specific gravity of [C Et N]Cl–AlCl , [C Et N]Cl–AlCl
4
3
3
6
3
3
and [C Et N]Cl–AlCl and products were 1.1428, 1.1833,
8
3
3
ðV1 −V2Þ × 0:008 × 100
1.2244 and 0.7721, respectively. Hence, this indicates that
catalysts sink in the product fluid, which means the rapid
separation of catalysts and products owing to their having
a specific gravity of >1.20.
Bromine value ðg=100mlÞ =
5
where V1 and V2 represent the consumed Na S O3
2 2
volume of the blank experiment and products, respec-
tively, and 0.008 represents the 1 ml sodium thiosulfate
standard solution equivalent to the amount of bromine.
The formulas used were as follows:
27
3.1.3 | Al MAS NMR
The [C Et N]Cl–AlCl ILs analogs were characterized by
6
3
3
27
ðinitial moles of olefin−residual moles of olefinÞ × 100
Conversion of olefin ð%Þ =
the Al MAS NMR spectra to study the structure and the
Al species. As shown in Figure S2, only one anionic Al
species peak (103.93 ppm) appeared in the spectrum for
[C Et N]Cl–AlCl . The peak (103.93 ppm) was attributed
initial moles of olefin
moles of 2−alkylate × 100
Yield of 2−alkylate ð%Þ =
6
3
3
initial moles of olefin
to the resonance signal of the anionic Al species of
[
31]
[
C Et N]Cl–AlCl
Therefore, the peak at 103.93 ppm
6
3
3.
yield of 2−alkylate × 100
Selectivity of 2−alkylate ð%Þ =
represents the active component in the catalyst, which
conversion of olefin
−
most likely corresponds to Al Cl without another Al
species.
2
7
[
32]
This also verified the mechanism of the
Friedel–Crafts alkylation catalyzed by IL as follows:
−
under the influence of Al Cl , the structure of C=C
2
7
3
3
3
| RESULTS AND DISCUSSION
.1 | Characterization of catalysts
.1.1 | FT-IR spectra of precursor
changes to carbocation with strong electrophilic proper-
ties. Because of the carbocation rearrangement, different
products of 1-alkylate and 2-alkylate (the structure
is shown in Figure 1; the alkyl benzene sulfonate
prepared by 2-alkylate is more likely to form a
molecular film in solution and its biodegradability is the
best, so it is more suitable as a surfactant in tertiary oil
recovery technology), 3-alkylate, 4-alkylate, 5-alkylate
and 6-alkylate are also produced. The carbocation first
interacts with the electron cloud of toluene to form the π
complex and then forms a stable σ complex at a carbon
atom in the toluene ring. The protons of the toluene ring
leave to form alkyl benzene. The entire catalytic process
is also illustrated Figure 1.
Precursors play a significant role in the catalytic perfor-
mance of IL catalysts, especially depending on their
chemical structure (such as the length of cationic compo-
nents, the kinds of cationic and anionic components and
the molar ratios). The chemical structure of the
precursors ([C Et N]Cl, [C Et N]Cl and [C Et N]Cl) was
4
3
6
3
8
3
detected using FT-IR spectra as indicated in Figure S1.
The intense peak at 2930 cm was ascribed to the
−1

GE ET AL.
5 of 11
3
3
.2 | Effect of alkylation conditions
.2.1 | Toluene/olefin molar ratio
increase, which is very economically unfavorable. There-
fore, the catalyst performance and industrial production
demand should be considered comprehensively, and a
10:1 rario of T/O should be selected as the appropriate
Using [C Et N]Cl–AlCl as a catalyst with the molar ratio
reaction ratio.
6
3
3
0
.45 at 333.15 K with a reaction time of 30 min, the effect
of toluene–olefin (T/O) molar ratio on the alkylation
reaction is shown in Figure 3a. As can be seen, with the
increase in the ratio of T/O, the yield of alkyl benzene
and the selectivity of 2-alkylate increased. In the
alkylation experiment, the higher T/O ratio greatly
reduced the probability of effective collision between
olefin molecules and self-polymerization of olefin to form
by-products, which ensured that the products had very
high alkyl benzene conversion. The increase in T/O ratio
made the relative concentration of olefin decrease, so the
concentration of carbocation decreased and effective
collision with toluene was more likely. This also means
that the probability of the rearrangement of carbocation
decreased, which also explains the increase in selectivity
of 2-alkylate. From the perspective of product quality, it
is undoubtedly beneficial to increase the molar ratio of
toluene. However, in industrial production, under a high
molar ratio of toluene to obtain the same yield of alkyl
benzene, the consumption of resources will undoubtedly
3.2.2 | Reaction temperature
Temperature is an important factor in chemical reactions.
ꢁ
In general, for every 10 C increase in temperature, the
[33]
chemical reaction rate usually increases 2–10 times.
Using the IL [C Et N]Cl–AlCl with the molar ratio of
6
3
3
precursor/AlCl at 0.45 as the catalyst, the reaction was
3
conducted under the following conditions: T/O molar
ratio, 10:1 and reaction time, 30 min.
In this work, different experimental temperatures
were investigated, and the variation trend of the conver-
sion rate with the increase in temperature is discussed.
From Figure 3b, it can be seen that the rate of conversion
of the reactants increased with the increase in tempera-
ture before 333.15 K. The selectivity of 2-alkylate
decreased with the increase in temperature, especially
when the temperature was high. The adjustment of
the electron cloud structure caused the carbocation
FIGURE 3 Effect of (a) toluene/olefin molar ratio, (b) reaction temperature, (c) catalyst dosage and (d) reaction time on the reaction

6
of 11
GE ET AL.
rearrangement, and then the carbocation collided with
3.2.5 | Length of olefin
[34]
toluene to form alkyl benzene.
The effect of tempera-
ture increase on the carbocation rearrangement reaction
was prominent, so the isomerization rate increased. As a
result, the temperature of the reaction was optimal at
According to the above discussion, the optimal condi-
tions for the ILs catalytic alkylation of long-chain olefin
with toluene are as follows: catalyst/olefins molar ratio of
0.3:1, toluene/olefins molar ratio of 10:1, reaction time of
3
33.15 K.
3
1
0 min and reaction temperature of 333.15 K. Using
-hexadecene, 1-octadecene and the mixed olefins of C –
2
0
3
.2.3 | Catalyst/olefin molar ratio
C , the influence of different lengths of olefin on the cat-
24
alytic alkylation of IL is shown in Table S2. It can be seen
from Table S2 that under the same catalyst dosage, the
conversion rate of C –C olefin was lower than those of
In a certain range, the amount of the catalyst used will
affect the reaction rate, which is directly related to the
production cost. Figure 3c shows the catalytic reaction
results of the alkylation experiments under different
dosages of catalyst. For the catalyst [C Et N]Cl–AlCl
20
24
1-hexadecene and 1-octadecene. Meanwhile, compared
with 1-hexadecene and 1-octadecene, the selected prod-
ucts of the mixed olefins of C –C alkylation with tolu-
6
3
3
20
24
with the molar ratio of precursor/AlCl3 at 0.45, the
reaction was conducted under the following conditions:
T/O molar ratio, 10:1; reaction time, 30 min; and
reaction temperature, 333.15 K. It can be seen that, with
the increase of catalyst consumption, the olefin conversion
rate increased while the selectivity of 2-alkylate decreased.
When the amount of catalyst was large enough, a large
amount of heat released in a short time made the tempera-
ture rise, which intensified the carbocation rearrangement
reaction. The resulted in a decrease in the selectivity of
ene were relatively complex and the selectivity of
2-alkylbenzene was relatively low. In the experiment, it
was found that the alkylation of C –C olefin with tolu-
20
24
ene was more difficult than that of 1-decylene and
1-dodecene, because with the increase in olefin chain
length and the constant catalyst concentration, the prob-
ability of olefin double bond contacting the catalyst was
reduced, so it is more difficult to form carbocation. Con-
sequently, with the increase of the olefin chain length,
[
35]
the catalytic performance decreased slightly.
2-alkylate. At the same time, the catalytic efficiency was
improved, and the yield of alkyl benzene was also
improved. Therefore, it has been demonstrated that the
appropriate catalyst/olefin molar ratio is 0.3:1.
3.3 | Effect of halo-alkane structure
The effects of halo-alkane structure on long-chain
alkenes alkylation with toluene was investigated by syn-
thesizing the different IL catalysts ([C Et N]Cl–AlCl ,
3.2.4 | Reaction time
4
3
3
[
C Et N]Cl–AlCl and [C Et N]Cl–AlCl ) with diverse
6
3
3
8
3
3
The reaction time of the alkylation was investigated
Figure 3d). Using [C Et N]Cl–AlCl with a molar ratio
halo-alkanes structures. A study of the catalytic effects on
account of the different halo-alkanes structures was con-
ducted at 333.15 K for 30 min, with a catalyst/olefins
molar ratio of 0.3:1 and a toluene/olefins molar ratio of
10:1. The results are summarized in Table 1.
(
6
3
3
of precursor/AlCl at 0.45 as the catalyst, the reaction
3
was conducted under the following conditions: T/O
molar ratio, 10:1 and reaction temperature, 333.15 K. It
can be seen from Figure 3d that the reactant conversion
rate increases from 10 to 40 min. After 30 min, it showed
no variation tendency and this demonstrated that
long-chain alkene alkylation with toluene is a fast reac-
[34]
TABLE 1 Catalytic performance of the ionic liquid catalysts
with different halo-alkane structures
tion.
Over time, the selectivity of 2-alkylate decreased
slightly. This is because the catalyst has a very high
catalytic efficiency, so more heat is released at the initial
stage of the reaction, leading to a rise in the temperature
of the reaction. At this point, with the formation of
carbocation, the unreacted alkenes are more likely to
be rearranged, resulting in an increase in the yield of
alkyl benzene and a decrease in the selectivity. Therefore,
in terms of the efficiency of the plant and making
sure that the response is adequate, the optimal reaction
time is 30 min.
Bromine value (g/100 ml)
Catalyst
1
2
3
Average
0.072
[C
4
6
8
Et
3
Et
3
Et
3
N]Cl–AlCl
N]Cl–AlCl
N]Cl–AlCl
3
3
3
0.077
0.013
0.025
0.068
0.018
0.031
0.071
0.016
0.019
[C
0.016
[C
0.025
a
Conditions: precursor/AlCl
-hexadecene, 0.01 mol; reaction temperature, 333.15 K; reaction
time, 30 min; and toluene–olefin (T/O) molar ratio, 10:1.
3
molar ratio, 0.45; catalyst, 0.003 mol;
1

GE ET AL.
7 of 11
3.3.1 | Catalytic performance
reaction efficiency. Combined with the above two factors,
C is the best carbon chain length for the catalyst.
6
[35]
As shown in Table 1, The catalytic activity of [C Et N]
6
3
Cl–AlCl shown by the bromine value was better than
3
those of [C Et N]Cl–AlCl and [C Et N]Cl–AlCl , which
3.3.2 | Lewis acidity
4
3
3
8
3
3
was the lowest (0.016 g/100 ml). In addition, the con-
version and selectivity of products are plotted against the
different halo-alkanes structure catalysts to better
demonstrate the influence of the different halo-alkanes
on their catalytic performance in Figure 4. It can be seen
that four or five kinds of alkylation products are
synthesized and the selectivity of 2-alkylate is the highest
of the alkylate products in Figure 4. Moreover, the pro-
ducts catalyzed by [C Et N]Cl–AlCl have the highest
In Figure 5, the wavenumbers at 2254 and 2291 cm− are
characteristic signals of acetonitrile. When acetonitrile
mixes with Lewis acidic sites, a new infrared absorption
1
−1
peak appears near 2333 cm , and the infrared absorption
peak at 2291 cm− is shifted to higher wavenumbers. As
can be seen from Figure 5, when the ILs interact with
acetonitrile, the characteristic peak of the interaction
between Lewis acid and acetonitrile appears at nearly
1
6
3
3
−
1
productivity in 2-alkylate. Meanwhile, it is clear that
2333 cm , and the characteristic peak of acetonitrile
appears blue shifted at 2291 cm . In addition, the char-
−
1
[
C Et N]Cl–AlCl has 5-alkylate products but [C Et N]
6
3
3
4
3
Cl–AlCl3 and [C Et N]Cl–AlCl do not. To sum up,
various halo-alkane structures of ILs catalysts lead to
different catalytic trends and the catalytic performance of
acteristic peak of [C Et N]Cl–AlCl increases at nearly
8
3
3
6
3
3
−
1
2333 cm , and the blue shift of the characteristic peak at
2291 cm− become stronger, which means that [C Et N]
1
6
3
[
C Et N]Cl–AlCl meets the needs of industry better. It is
Cl–AlCl had better Lewis acidity than [C Et N]Cl–AlCl
6
3
3
3
4
3
3
well known that the length of the chain of the catalyst
directly affects two factors, namely hydrophobicity and
viscosity. On the one hand, the longer the carbon chain
of the catalyst is, the stronger its hydrophobicity is, which
is conducive to protecting the active sites of the catalyst
and thus improving the stability of the catalyst. On the
other hand, when the carbon chain of the catalyst
becomes longer, its viscosity becomes larger and its mass
transfer becomes weaker, which is not conducive to the
collision of molecules in the reaction, thus reducing the
and [C Et N]Cl–AlCl . Meanwhile, the Lewis acidity is
consistent with the above conclusion.
8
3
3
[
36]
3.4 | Effect of precursor/AlCl molar ratio
3
The effect of precursor/AlCl molar ratio in the catalysts
3
of [C Et N]Cl–AlCl have been researched in our work.
6
3
3
It can be seen from the Figure 6 that when the catalysts
with the molar ratio of precursor/AlCl more than or
3
FIGURE 4 Selectivity of products
catalyzed by different catalysts

8
of 11
GE ET AL.
FIGURE 5 Lewis acidity of [C
4
Et
3
N]Cl–
AlCl , [C Et N]Cl–AlCl and [C Et N]Cl–AlCl
3
6
3
3
8
3 3
FIGURE 6 Lewis acidity of [C
6
Et N]Cl–
3
AlCl with different precursor/AlCl
3
3
molar ratio
1
equal to 0.60 interacts with acetonitrile, the wavenumber
acetonitrile at 2291 cm− increases with the increase in
−1
has no characteristic peak near 2,333 cm , and the infra-
red absorption peak of acetonitrile at 2291 cm−1 has no
blue shift phenomenon, that is, the IL with the molar
the mole fraction of precursor/AlCl in the IL catalysts.
This means that Lewis acid exists in the IL with the
molar fraction of precursor/AlCl <0.55. The dosage of
3
3
fraction of precursor/AlCl more than 0.60 has no Lewis
AlCl is fixed with the decrease in the amount of precur-
3
3
acid. For ILs with the molar fraction of precursor/AlCl3
less than or equal to 0.55, the characteristic peak of
sor, and the molar fraction of precursor/AlCl in the IL
increases as the acidity increases.
3
[
36]
−
1
acetonitrile at characteristic 2,291 cm of Lewis acid and
acetonitrile interaction appears near wavenumber
Meanwhile, the effect of precursor/AlCl molar ratio
3
to the catalytic performance of IL catalysts was investi-
gated as shown in Table 2 under the following
−
1
2
,333 cm , and the characteristic peak area of

GE ET AL.
9 of 11
conditions: T/O molar ratio, 10:1; catalyst/olefins molar
ratio, 0.3:1; reaction time, 30 min; and reaction tempera-
ture, 333.15 K. From Table 2, it can be seen that the IL
catalysts with the molar ratio of AlCl more than or equal
3
to 0.60 have no catalytic performance. When the
precursor/AlCl molar ratio is 0.55, the bromine values
3
do not meet the factory requirements (<0.08) and the
higher bromine value means the lower the olefin conver-
sion in alkylation. Then, the bromine values are on a
declining curve with the precursor/AlCl3 molar ratio
from 0.55 to 0.45 and when the precursor/AlCl molar
3
ratio is from 0.45 to 0.30, the declining tendency stops
and it becomes stable at bromine value 0.015.
In view of the above, the Lewis acidity of the catalyst
is an important factor in the reaction system. In other
words, the Lewis acidity of the catalyst determines the
catalytic performance. [C Et N]Cl–AlCl with the
6
3
3
FIGURE 7 The cycle property of catalysts
precursor/AlCl molar ratio at 0.45 with stronger Lewis
3
acidity has a better catalytic performance, compared with
the molar ratio at 0.50 and 0.55. Meanwhile, in terms of
industrialization, the catalyst with the precursor/AlCl3
molar ratio at 0.45 is more economic and environmen-
tally friendly than the ratio at 0.40, 0.35 and 0.30. In
our analysis, there is an explanation that with the
precursor/AlCl3 molar ratio >0.50, the anions mainly
the factory requirements is <0.08. So, at the ninth cycle of
[Et NH]Cl–AlCl , the bromine value of the product is
3
3
>0.08 and this means that the catalyst is deactivated at the
ninth cycle, while the cycle times of [C Et N]Cl–AlCl ,
4
3
3
[C Et N]Cl–AlCl and [C Et N]Cl–AlCl are 18, 24 and
6
3
3
8
3
3
22 runs, respectively. In other words, the IL catalyst in our
work greatly enhances the recycling times and meets the
requirements of industrialization better. [C Et N]Cl–AlCl
−
−
exist as AlCl , while the anions mainly exist as Al Cl
4
2
7
6
3
3
−
at values <0.45, and Al Cl7 is the main ion form of
is the optimal one of the three catalysts and it is further
confirmed that the halo-alkane structure is the crucial fac-
tor in catalytic and cyclic performance.
2
catalytic active site, which plays an important role in
[32]
long-chain alkenes alkylation.
Therefore, [C Et N]Cl–
6
3
AlCl with the precursor/AlCl molar ratio at 0.45 is the
optimum selection in terms of industrialization.
Meanwhile, In order to better explore the reasons for
catalyst inactivation, acetonitrile probe FT-IR showed
how the Lewis acidity changed (Figure 8). With the
increase in cycle times, the peak intensity of absorbance
3
3
3.5 | Cyclic performance of catalyst
−
1
around 2333 cm decreased, while the -CN stretching
vibration band at 2254 cm− showed a red shift, indicat-
ing that Lewis acid density decreased. In addition, the
1
The most important factor to determine whether a
catalyst can be industrialized is the recyclability of the cat-
alyst, which was studied in the alkylation reaction with a
−1
band shifts around 2303 and 2291 cm also demonstrate
[
36]
molar ratio of precursor/AlCl at 0.45 under the following
reduced Lewis acid strength.
Overall, with the increase
3
conditions: T/O molar ratio, 10:1; reaction time, 30 min;
and reaction temperature, 333.15 K. From Figure 7, the
reaction was conducted with four different IL catalysts
in cycle times, the activity of the catalyst decreased.
The specific gravity of catalyst [C Et N]Cl–AlCl before
6
3
3
and after inactivation is listed in Table 3. It indicates that
(
[Et NH]Cl–AlCl , [C Et N]Cl–AlCl , [C Et N]Cl–AlCl
the specific gravity of catalyst [C Et N]Cl–AlCl before
3
3
4
3
3
6
3
3
6
3
3
and [C Et N]Cl–AlCl ) and [Et NH]Cl–AlCl is the
and after deactivation decreased from 1.1944 to 1.0422,
from 1.2034 to 1.1047, and from 1.2132 to 1.1242, which
may be related to the loss of aluminum trichloride.
8
3
3
3
3
most commonly used catalyst of long-chain alkene in
[37]
Friedel–Crafts alkylation in industry.
ing recycling time, the bromine value rises slowly
the conversion rates reduced) and the bromine value of
With the increas-
27
Figure 9 shows the Al MAS NMR of catalyst
(
[C Et N]Cl–AlCl before and after inactivation. It can be
6
3
3
TABLE 2 Catalytic performance of [C
6
Et
3
N]Cl–AlCl
3
with different precursor/AlCl
3
molar ratios
Precursor/AlCl
3
Molar ratio
0.65
/
0.60
/
0.55
0.50
0.45
0.40
0.35
0.30
Bromine values
0.096
0.054
0.013
0.016
0.014
0.012
*
Condition: catalyst, 0.003 mol; 1-hexadecene, 0.01 mol; reaction temperature, 333.15 K; reaction time, 30 min; and T/O molar ratio, 10:1.

10 of 11
GE ET AL.
FIGURE 8 Lewis acidity of [C
AlCl after recycling
6
Et
3
N]Cl–
3
TABLE 3 Specific gravity of [C
6
Et
3
3
N]Cl–AlCl before and after inactivation
1
2
3
Before
After
1.0422
Before
After
Before
After
Specific gravity
1.1944
1.2034
1.1047
1.2132
1.1242
2
7
FIGURE 9
Al MAS NMR of
catalyst before and after inactivation
seen that a peak at 103.90 ppm occurred after catalyst
failure, and the peak shifted from 70.65 to 69.33 ppm.
This may be related to the loss of most aluminum
trichloride or the hydrolysis of aluminum trichloride into
other existing forms of compounds, which is consistent
with the above results. The possible reason for catalyst
deactivation is the moisture in tiny quantities contacting
with active sites and leading to hydrolysis of active sites.
cyclic performance have been prepared, and the catalysts
meet the requirements of continuous industrial produc-
tion owing to their advantage of easy sedimentation
2
7
and separation according to the specific gravity. Al
MAS NMR investigation indicated that tetrahedral
−
4-coordinate Al Cl7 is the main catalytic site of the
2
ILs catalyst. In addition, by discussing various parame-
ters, the optimized reaction conditions were as follows:
catalyst/olefin molar ratio, 0.3:1; precursor/AlCl molar
3
ratio, 0.45; reaction temperature, 333.15 K; reaction time,
30 min; and toluene/olefin molar ratio, 10:1. The catalyst
4
| CONCLUSION
[
C Et N]Cl–AlCl had the highest conversion rate and
6
3
3
In summary, three new chloroaluminate IL catalysts
based on different halo-alkanes structures with high
selectivity in terms of the different halo-alkane struc-
tures. Afterwards, the Lewis acid of [C Et N]Cl–AlCl
6
3
3

GE ET AL.
11 of 11
with different precursor/AlCl molar ratio differed from
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[
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each other according to the acetonitrile probe FT-IR and
the results show that catalytic activity is closely related to
the Lewis acid. Finally, the conversion and selectivity of
long-chain alkenes alkylation reached 99.92 and 32.99%,
which met the standard for industrial production. Com-
pared with industrial IL catalysts (10 runs), the IL cata-
lysts ([C Et N]Cl–AlCl , [C Et N]Cl–AlCl and [C Et N]
2
18] K. S. Kim, S. Choi, D. Demberelnyamba, Chem. Commun.
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Cl–AlCl ) have high cyclic performance, corresponding
3
3641.
to 18, 24 and 22 runs, respectively. To sum up, benefiting
from the improved cyclicity and enhanced catalytic
activity of the catalyst, this work took a step toward the
industrialization of IL catalysts.
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ACKNOWLEDGEMENTS
This Project Funded by the Priority Academic Program
Development of Jiangsu Higher Education Institutions
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ORCID
Gaoyang Ge https://orcid.org/0000-0003-0688-5447
Xiaoli Sheng https://orcid.org/0000-0003-3837-2232
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