Synthesis of efficient SBA-15 immobilized ionic liquid catalyst and its performance for Friedel–Crafts reaction

Article abstract of DOI:10.1016/j.cattod.2016.01.045

Friedel–Crafts alkylation of benzene with 1-dodecene, which is an important reaction of synthetic detergent, was studied via ionic liquid [bmim][TFSI]/AlCl₃ (1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide/AlCl₃) immobilized on SBA-15 catalysts. XRD, BET, TEM, TG, ammonia TPD investigations were used to search insight into catalyst characteristic. The immobilized catalysts preserved ordered structure and presented high specific surface areas. The utilization of active sites was significantly improved by immobilization. Based on ammonia TPD, immobilized catalysts exhibited higher Lewis acidity than aluminum chloride grafted SBA-15. TG indicated that thermal stability of ionic liquid has been improved by immobilization. The influences of various reaction conditions including reaction time, benzene/1-dodecene ratio were studied. Immobilized ionic liquids have better performance of no matter 1-dodecene conversion or 2-linear alkyl benzene (2-LAB) selectivity, than bulk ionic liquid catalysts or aluminum chloride grafted mesoporous materials. 2-LAB selectivity can be increased from about 35% with bulk ionic liquid to more than 60% with immobilized catalysts. Under optimal condition, 2-LAB selectivity reached as high as 80%. The immobilized catalysts could be reused. And at 3th cycle of catalysts, 1-dodecene conversion could still reach more than 50%. The role of deactivation was proposed based on TEM, BET and TG investigations. By-products as oligomer, produced by oligomerization of olefin, blocked or covered the pores, led to deactivation of catalysts.

Full text of DOI:10.1016/j.cattod.2016.01.045

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Synthesis of efficient SBA-15 immobilized ionic liquid catalyst and its
performance for Friedel–Crafts reaction
∗
Yibo He, Qinghua Zhang , Xiaoli Zhan, Dang-guo Cheng, Fengqiu Chen
College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Friedel–Crafts alkylation of benzene with 1-dodecene, which is an important reaction of syn-
thetic detergent, was studied via ionic liquid [bmim][TFSI]/AlCl3 (1-butyl-3-methylimidazolium
bis((trifluoromethyl)sulfonyl)imide/AlCl3) immobilized on SBA-15 catalysts. XRD, BET, TEM, TG, ammo-
nia TPD investigations were used to search insight into catalyst characteristic. The immobilized catalysts
preserved ordered structure and presented high specific surface areas. The utilization of active sites
was significantly improved by immobilization. Based on ammonia TPD, immobilized catalysts exhibited
higher Lewis acidity than aluminum chloride grafted SBA-15. TG indicated that thermal stability of ionic
liquid has been improved by immobilization. The influences of various reaction conditions including reac-
tion time, benzene/1-dodecene ratio were studied. Immobilized ionic liquids have better performance
of no matter 1-dodecene conversion or 2-linear alkyl benzene (2-LAB) selectivity, than bulk ionic liquid
catalysts or aluminum chloride grafted mesoporous materials. 2-LAB selectivity can be increased from
about 35% with bulk ionic liquid to more than 60% with immobilized catalysts. Under optimal condition,
Received 20 October 2015
Received in revised form 19 January 2016
Accepted 22 January 2016
Available online xxx
Keyword:
Ionic liquid
Friedel–Crafts alkylation
SBA-15
1
-dodecene
2
-LAB selectivity reached as high as 80%. The immobilized catalysts could be reused. And at 3th cycle of
catalysts, 1-dodecene conversion could still reach more than 50%. The role of deactivation was proposed
based on TEM, BET and TG investigations. By-products as oligomer, produced by oligomerization of olefin,
blocked or covered the pores, led to deactivation of catalysts.
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
ronment contamination and difficult separation. The most effectual
method to solve these problems is introducing heterogeneous cat-
alyst [7]. While the recently announced “Detal ” process, which
TM
Friedel–Crafts alkylation of benzene with 1-dodecene is an
important reaction of synthetic detergent, which is essential to
human [1,2]. It is an electrophilic substitution of hydrogen in aro-
matic compounds, catalyzed by Lewis acid. Generally, it is known
that synthetic detergent made from linear alkyl benzene (LAB) has
better biodegradability than that made from branched alkyl ben-
zene (BAB). The phenyl group position of LAB has an effect on its
surface-active properties and biodegradability of linear alkyl ben-
zene sulfonate (LAS). Among the isomers of LAB, 2-LAB exhibits
the highest biodegradability, making it a dominant detergent
intermediate [3,4]. LAB is produced industrially over HF or AlCl3
homogenous catalysts, which has serious disadvantages including
environmental contamination, difficult separation and low 2-LAB
selectivity. The 2-LAB selectivity catalyzed by homogeneous cata-
was developed by UOP as the first fixed-bed catalyst alkylation
technology requires benzene/1-dodecene ratio as high as 30:1 [1].
Aluminum chloride grafted catalysts is the other one of heteroge-
neous catalysts for this reaction. Aluminum chloride can be grafted
on the surface of such solid to produce Lewis acidic sites, which
Friedel–Crafts alkylation needed [8–11]. Bordoloi et al. has syn-
thesized AlMCM-41/beta zeolite and discussed the shape selective
synthesis of LAB [12]. Some other modification of zeolites such as
desilicated zeolites, 10-ring zeolites (TUN, IMF, etc.) and alkaline-
modified mordenite were also widely reported [13–15].
In recent years, ionic liquids have attracted much interest for
their unique properties such as non-volatility, non-flammability,
high chemical and thermal stability [16,17]. Some of ionic liquids
can provide Lewis or Brønsted acidic sites. It is reported that hygro-
scopic ionic liquid catalysts like [cation][HSO ], [bmim][Al Cl Br],
lysts AlCl or HF is in the ranges from 26–33% [1] and 14–20% [5,6].
3
Moreover, homogeneous system is one of main reasons to envi-
4
2
6
[
bmim][FeCl ], [Et NHCl][FeCl ] and [Et NHCl][AlCl ] would result
4 3 3 3 3
in high acitivity [18–22]. A novel ionic liquid [bmim][TFSI]/AlCl3
catalyst has been developed in our previous work, which has better
properties of stability and durability due to the existing of per-
∗ Corresponding author.
E-mail address: qhzhang@zju.edu.cn (Q. Zhang).
http://dx.doi.org/10.1016/j.cattod.2016.01.045
0
920-5861/© 2016 Elsevier B.V. All rights reserved.
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2
2. Experiment
2.1. Materials
Ionic liquid 1-butyl-3-methylimidazolium bromide ([bmim]Br),
bistrifluoromethanesulfonimidate (LiTFSI) and triblock copoly-
mers Pluronic® P123 (EO20PO70EO20) were obtained from Aladdin
Reagents Co., Ltd. Anhydrous aluminum chloride, chloroform and
other reactants or feedstock were purchased from Sinopharm
Chemical Reagent Co., Ltd. Before use, liquid reagent should be
refluxed using calcium hydride to remove water, then purified by
distillation under nitrogen. Solid material and ionic liquid were
dried for 24 h.
2.2. Catalysts preparation
Fig. 1. X-ray diffraction of different catalyst samples.
SBA-15 mesoporous materials used in this work was synthe-
®
sized in a typical method [34,35]. 4 g of Pluoronic P123, water and
◦
HCl (0.28 M) were stirred at 35 C for 16 h. The appropriate amount
fluoroalkyl groups [23]. But ionic liquid catalyst amount used in
reaction still as high as 5% to 10%, even 20% [24,25].
of tetraethylorthosilicate (TEOS, 8.5 g) was then added dropwise to
the surfactant solution, followed by stirring for 24 h. The resulting
gel was introduced into a Teflon lined stainless steel autoclave and
Indeed, many reports have become available, describing the use
of the ionic liquids immobilized on various supports for synthesis
of diphenylmethane, synthesis of dimethyl carbonate and epoxida-
tion [26–28]. German researchers reported an immobilized ionic
liquid catalyst for alkylation [29]. And no leaching ionic liquid in
reaction mixture was found in that research. The immobilization
process transferring the desired catalytic properties of the liquids
to solid catalysts could combine the advantages of ionic liquids
with those of heterogeneous support materials. It overcomes some
shortcomings and extends the application of ionic liquid, signifi-
cantly [30–33].
◦
heated at 100 C for two days. The products were filtered, washed
◦
with warm distilled water and finally dried at 100 C, followed by
calcination in air at 500 C, then kept under dry argon.
◦
◦
Ionic liquid [bmim]Br was heated gently at 80 C. The lithium
salt LiTFSI was added to the melt under N2 and stirred for 24 h.
Adding CH Cl , LiBr was precipitated and separated by filtration.
2
2
The filtrate was evaporated to dryness then the [bmim][TFSI]
◦
obtained [36]. The ionic liquid [bmim][TFSI] was heated to 80 C,
and AlCl was slowly dissolved in [bmim][TFSI] with stirring for 6 h
3
to ensure complete mixing [23]. The ionic liquid [bmim][TFSI]/AlCl3
was denoted as Al(1.5)-IL. The number in brackets demonstrated
In this work, highly ordering mesoporous material SBA-15 has
been synthesized. Aiming at declining in the ionic liquid catalyst
amount, ionic liquid [bmim][TFSI]/AlCl3 was immobilized on SBA-
the molar ratio of AlCl : [bmim][TFSI].
3
As previously reported, the air present in the cavities of porous
materials can be completely removed through evacuation under
vacuum conditions, so that filling the cavities with ionic liquid
becomes relatively easy [37]. 1 g of SBA-15 was placed in a two-
neck flask, one of the necks was equipped a liquid addition injector,
the other was connected to a vacuum equipment. The flask with
1
5. XRD, BET, TEM, TG analysis were carried out to investigate the
structure of catalysts. Ionic liquids thermal stability and ionic liq-
uids loading amount of immobilization catalysts were measured
by TG analysis. TEM gave insight into nano-scale structure of cata-
lysts. Ammonia TPD was used to measure Lewis acidity of catalysts.
And the effects of various reaction condition, which were on the
synthesis of LAB, were discussed. Moreover, the role of catalysts
deactivation was proposed based on TEM, BET and TG investigation.
◦
mesoporous materials was heated at 185 C for 4 h under vacuum
conditions to draw out the gas inside the SiO . Then 0.5 g of ionic
2
liquid [bmim][TFSI]/AlCl3 dissolved in CH Cl2 was transferred into
2
Fig. 2. Illustrations to the ionic liquid catalyst & immobilized catalyst system.
Please cite this article in press as: Y. He, et al., Synthesis of efficient SBA-15 immobilized ionic liquid catalyst and its performance for
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Table 1
N2 adsorption–desorption isotherms analysis of different samples.
2
3
Samples
BET surface area (m /g)
Volume of pores (cm /g)
Average pore diameter (nm)
SBA-15
751.1
322.8
224.0
33.2
1.24
0.61
0.33
0.06
0.03
6.65
5.51
5.56
3.96
2.34
Al(1.5)-IL@SBA-15
Al(2.0)-IL@SBA-15
Al(1.5)-IL@SBA-15 AR
Al(2.0)-IL@SBA-15 AR
7.7
was performed in AutoChem II 2920, equipped with a thermal con-
ductivity detector (TCD). The thermal stabilities were measured
using a TA-Q500 thermogravimetric analyzer (TGA). Transmission
electron microscope (TEM) images were obtained with Tecnai G2
F20 S-TWIN. Materials and products of reaction were investigated
by gas chromatography (GC). GC was equipped with HP-5 column
(30 m).
2.4. Friedel–Crafts alkylation reaction
The alkylation reaction was conducted in a 150 ml flask with a
magnetic stirrer. Catalyst was added into the flask quantitatively,
followed by benzene and 1-dodecene. After the completion of the
reaction, the organic layer containing the products and reactants
unreacted was separated by centrifugation. The organic layer was
washed with water, dried over Na SO4 and analyzed by GC. The
2
catalyst separated by centrifugation was washed by benzene, then
was used for recycling experiments.
Conversion of 1-dodecene and LAB selectivity were calculated
as follows:
Fig. 3. Average diameter of pore size of different catalyst samples.
dodeceneunreacted
dodecenefeed
dodecene conversion = 1 −
× 100%
LABi
LAB selectivity =
× 100%
i
ꢀ
6
2
LAB isomers
i
3
. Results and discussion
3.1. Characterization
X-ray diffraction (XRD) patterns of SBA-15, and catalysts with
different Al-IL were shown in Fig. 1. In the case of SBA-15, the three
◦
typical peaks were observed in the region of 2Â < 5 , which can
be indexed as the (1 0 0), (1 1 0) and (2 0 0) reflections of ordered
mesoporous structure. XRD peak intensity of Al(1.5)-IL@SBA-15
and Al(2.0)-IL@SBA-15 was decreased and became broader, as com-
pared with that of SBA-15 [40]. It was even decreased as compared
with that of Al-SBA-15, it resulted from the disturbs on the struc-
ture order, which was a consequence of the surface modification.
Though the peak intensity was decreased after immobilization, the
diffraction peaks could still be detected even after immobilization,
which indicated that ordering mesoporous structure was partial
preserved [32,41,42].
Fig. 4. Ammonia TPD analysis of different catalysis samples.
the flask through a syringe, and the mixture was refluxed for 6 h at
0 C to fill the pores with ionic liquids. The solvent was distilled
◦
6
out and the resulting mixture was cooled for 3 h at room tempera-
ture. The immobilized samples were separated and further purified
through three cycles of washing with CH Cl , to completely remove
2
2
the [bmim][TFSI]/AlCl adsorbed on the surface. Then, immobilized
3
◦
catalysts were dried for 12 h at 50 C (denoted as Al(1.5)-IL@SBA-
In previous reports, ionic liquids [bmim][TFSI]/AlCl catalyst has
3
1
5 or Al(2.0)-IL@SBA-15) [38]. Aluminum chloride grafted SBA-15
been proved to have properties of stability and durability. Fig. 2
demonstrates the illustrations to the ionic liquid catalysts and
immobilized catalysts system. As shown in Fig. 2, fluoro ionic liq-
uid mixed with the active sites, and filled in their surroundings.
The ionic liquid catalyst was immobilized on SBA-15, and covered
the internal surface of mesoporous pores, as shown in Fig. 2. Reac-
tants like benzene and olefin could diffuse through the layer of ionic
liquid and contact with active sites [23].
was synthesized in a reported method (denoted as Al-SBA-15) [39].
2.3. Characterization
N2 adsorption–desorption isotherms analysis of the catalysts
were measured using N2 as a sorbate at 77 K in a static volumet-
ric apparatus (Micromeritics ASAP2020). The phase identification
of catalysts was carried out by powder X-ray diffraction (XRD) on
XRD 6000 (Shimadzu) equipped with Cu K␣ radiation at 40 kV and
The results of catalysts surface properties investigation are given
in Table 1. The specific surface areas of SBA-15 mesoporous mate-
rial, which was synthesized in a typical method, was estimated
3
0 mA. Temperature-programmed desorption (TPD) of ammonia
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Fig. 5. Illustrations to (a) Al-SBA-15 (b) Al-IL@SBA-15 samples.
2
as 751 m /g. After immobilization of ionic liquid catalyst, the spe-
cific surface areas, volume of pores and average pore diameter all
decreased. The pore diameter of immobilized catalysts became nar-
rower because the internal surface of the pore was covered by ionic
liquid. It also led to decreasing of the volume of pores and average
pore diameter. This led to decreasing of the specific surface areas
and volume of pores. While adding the Al species content in ionic
liquid, the specific surface areas was declined slightly. In this case,
ionic liquid may not only cover the internal surface of the pores,
but also fill the pores. When deactivation of catalysts occurred after
reaction was conducted several times (denoted as Al(1.5)-IL@SBA-
1
5 AR & Al(2.0)-IL@SBA-15 AR, mark “AR” mean “After Reaction”),
the specific surface areas, volume of pores and average pore diam-
eter declined significantly. It may be caused by blockage of pores,
which resulted from oligomerization of olefin. Despite the specific
surface areas, and volume of pores were greatly reduced compared
with parent SBA-15, the data might not as accurate as other sam-
ples, it still indicated qualitatively the decline tendency of BET
surface.
Fig. 3 gives the average diameter of pore size distribution of
different catalyst samples before and after immobilization. The
average pore size of parent SBA-15 was slightly larger than that
of other samples after surface modification. The pore diameter of
immobilized catalysts became narrower because ionic liquid cov-
ered the surface of the pore. Immobilization of ionic liquid may also
cause some damages and partially collapsed of pore structure. The
coverage or the filling enlarged the thickness of pores wall, reduced
the specific surface and volume of pores. While partially damage or
collapse increased volume of pores. As a result, pore size distribu-
tion became wider after surface modification. But in this case, the
effect of pore coverage greatly exceeded the effect of pore collapse.
That was the reason why decreasing of pore volumes and becom-
ing lower of the distribution peaks of SBA-15 were observed for
immobilized ionic liquid catalysts.
The density of acid sites was determined by ammonia thermos-
desorption (ammonia TPD). Fig. 4 shows the parent SBA-15, the
ammonia TPD of aluminum chloride grafted mesoporous material
and other two Al-IL supported mesoporous materials. Desorp-
tion curves of supported Al-IL mesoporous material presented
◦
◦
two important peaks at 170 C, and 250 C, while aluminum chlo-
ride grafted mesoporous material presented only one, the parent
SBA-15 almost showed no peaks between test temperature. Peaks
◦
◦
around 200 C and 250 C are attributed to Lewis acid type [8,43]. In
this case, higher content of Al species in Al-IL led to higher density
of acid sites, because Lewis acid sites were produced by tetrahedral
4
-coordinate Al species. Comparing with two ionic liquid supported
◦
SBA-15, peak presented by Al-SBA-15 was very weak at 250 C,
and peak around 170 C also was weaker than SBA-15 supported
◦
Fig. 6. TG analysis of (a) Al(1.5)-IL@SBA-15 (b) Al(2.0)-IL@SBA-15 (c) Al-SBA-15
samples.
Al-IL neither. It can be explained by higher Al atom utilization of
SBA-15 immobilized Al-IL. Moreover, as our previous report, ionic
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Table 2
Calculation results of TG analysis.
∼200 ◦C weight loss
200–500 C weight loss
◦
Total weight loss
Sample
Al-IL
Al(1.5)-IL@SBA-15
Al(2.0)-IL@SBA-15
22.08%
2.75%
2.69%
62.95%
8.77%
8.74%
85.02%
11.52%
11.43%
Fig. 7. TEM images of (a) SBA-15 (b) SBA-15 immobilized ionic liquid (c) immobilized catalysts after deactivation.
liquid catalysts had higher stability than AlCl . Dubé reported that
of the salt and finally a stable residue was obtained. Between
3
◦
◦
AlCl3 supported catalysts may loss Lewis sites when exposed to
ambient air moisture, resulted in declining of the signal in ammo-
nia desorbed [8]. Due to the stability of ionic liquid, the density of
Lewis acid sites can be kept for SBA-15 immobilized Al-IL. However,
decomposition might be happened for ionic liquid when tempera-
ture was excessively high, thus the temperature in ammonia TPD
250 C to 500 C, weight loss in composite material was due to
the decomposition of different species in ionic liquid. In Fig. 6,
TGA curve of immobilized catalysts were similar to that of Al-IL,
but the temperature of each main mass-loss stage became higher
after immobilization. Similar curves were evidence of successful
immobilization of ionic liquid. It has been reported that the con-
finement in the nano-pores led to a compression of molecular size
and an increase in the melting point [47]. Therefore, immobilization
on SBA-15 contributed to enhancing the thermal stability of ionic
liquid catalysts. Comparing with IL@SBA-15, TG profile of Al-SBA-
15 sample presented a similar peak, which indicated atmospheric
◦
was limited to 280 C.
As shown in Fig. 5, when AlCl was grafted onto SBA-15 material,
3
partial Al atoms could connect more than 3 O atoms. It resulted in
octahedral 6-coordinated Al species, which have no reaction activ-
ity [8,44]. On the contrary, all ionic liquid surrounding Al species
kept reactivity [23,45,46]. In this opinion, SBA-15 immobilized ionic
liquid catalysts had higher atom utilization ratio than that of AlCl3
grafted, and more satisfied the green chemical feature.
◦
water, below 200 C. However, peaks could hardly be found after
◦
300 C for Al-SBA-15. It is because that almost no organic content
existed in Al-SBA-15 sample.
Besides XRD profile, thermal gravimetric analysis of the cat-
alysts gave qualitative information about the success of the
immobilization. As shown in Fig. 6, atmospheric water, which was
absorbed during the handling of hygroscopic species, was elim-
The calculation results of TG analysis were demonstrated in
◦
Table 2. Ionic liquid lost about 22% weight before 200 C due to its
◦
◦
hygroscopicity. Between 200 C to 500 C, samples lost their resid-
ual organic component. Therefore, calculating weight loss between
◦
◦ ◦
200 C to 500 C would result in the quantitative loading of ionic liq-
inated about 150 C. The following step was the decomposition
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Fig. 8. GC spectrum examples of Friedel–Crafts alkylation products of benzene with 1-dodecene.
Table 3
The results of the benzene alkylation with 1-dodecene over various catalysts.
Catalyst
Catalyst amount
Conversion
Selectivity
2
–
-LAB
3-LAB
4-LAB
5-LAB
6-LAB
Al(1.5)-IL
Al(2.0)-IL
0.5%
10%
5%
2%
5%
0.0%
–
–
–
–
98.9%
97.2%
36.1%
98.2%
99.4%
99.2%
32.7%
49.0%
67.6%
60.0%
57.5%
59.5%
19.0%
21.3%
18.3%
20.3%
20.7%
18.9%
15.1%
14.1%
6.8%
8.7%
9.1%
8.1%
17.2%
8.7%
4.4%
6.3%
7.5%
6.4%
16.1%
6.9%
3.0%
4.6%
5.2%
7.1%
AlCl3@SBA-15
Al(1.5)-IL@SBA-15
Al(1.5)-IL@SBA-15
Al(2.0)-IL@SBA-15
Al(1.5)-IL@SBA-15
5%
10%
uids. And according to the calculating, two ionic liquid immobilized
catalyst samples lost about 8.7% weight, it demonstrated that they
have similar ionic liquid capacity, though Al species of these two
samples were different.
The ordered mesostructure of parent mesoporous material,
immobilized catalysts and catalysts after deactivation can be
further confirmed by TEM analysis. In Fig. 7, x1 (a1, b1, c1) demon-
strated the panorama of mesoporous material, x2 (a2, b2, c2)
presented the direction along and x3 (a3, b3, c3) presented per-
pendicular to the pore axis. The TEM images of SBA-15 synthesized
before are given in Fig. 7(a1–3). All of them showed clear pore and
pore wall, demonstrated highly ordered hexagonal array of SBA-
1
5. After ionic liquid immobilization, pore and pore wall, which
are shown in Fig. 7(b1–3), cannot be identified as clear as before.
However, combining the XRD results with TEM observations, it was
clear that the immobilized sample retained its structural integrity
and the parallel alignment of channels were essentially unchanged
after successive ionic liquid loading process. These observations
also suggested that the successful modification of inner pore of
ionic liquids on their surface. TEM images of immobilized catalysts
after deactivation are shown in Fig. 7(c1–3), some shadow can be
seen clearly in these images, which came from oligomer, produced
by oligomerization of olefin. After reaction cycled several times,
oligomer accumulated and its molecular weight increased, then the
active sites were encapsulated and pores were blocked. As results,
the specific surface areas of catalysts decreased, reactivity was lost
gradually.
3.2. Alkylation results
The GC spectrum examples of alkylation products of benzene
with 1-dodecene are shown in Fig. 8. Different peaks appeared in
Fig. 8 indicated different isomers of LAB. These spectrum peaks are
assigned as 6-LAB, 5-LAB, 4-LAB, 3-LAB and 2-LAB with increasing
retention time, respectively. LAB selectivity were calculated based
on the integral area of different isomers of LAB with the formula
mentioned before. In Fig. 8(a)–(c), 2-LAB selectivity in the cases
were about 35%, 60% and 80% respectively. It can be obviously seen
Fig. 9. The influences of reaction time for the alkylation reaction (a) 1-dodecene
conversion (b) the distribution of product.
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Al species content in Al-IL of Al-IL@SBA-15 also caused increasing
of the concentration of active sites, and decline the 2-LAB selectiv-
ity. Moreover, excessively high Al species in Al-IL led to the waste
of active species.
The influences of reaction time for the alkylation reaction were
studied under well-optimized conditions, results are shown in
Fig. 9. 1-dodecene could reach its highest conversion within 3 h
in the alkylation reaction. When reaction was carried out for 0.5 h,
1
-dodecene conversion was only about 23%, while 2-LAB selectivity
was as high as 80%. During 0.5 h, only small amount of 1-dodecene
changed into carbenium ion, so the concentration of carbenium
ion was really low. It resulted in insufficiency of isomerization, and
higher 2-LAB selectivity. Longer reaction time gave more feedstock
for isomerization, which resulted in the decline of 2-LAB selectivity.
The influences of benzene/1-dodecene (molar ratio) for the
alkylation reaction were studied under well-optimized conditions,
results are shown in Fig. 10. As the ratio of benzene/1-dodecene
increased from 3 to 10, 2-LAB selectivity increased from 55% to
nearly 70%, 5-LAB or 6-LAB selectivity decreased from 10% to about
Fig. 10. The influences of benzene/1-dodecene (molar ratio) for the alkylation reac-
tion on the distribution of product.
5
%. With the same Lewis acidity, increasing the ratio of benzene/1-
dodecene indicated the carbenium ion concentration diluted. The
reduced carbenium ion concentration could inhibit the hydrogen
shift reactions and isomerization, resulting in increase of 2-LAB
selectivity. That is why benzene/1-dodecene ratio is as high as
TM
3
0 in industrial “Detal ” process. However, a higher benzene/1-
dodecene ratio causes a higher cost, which is resulted from surplus
benzene separation and recycle.
The reusability is one of the most important properties for
catalysts, which was studied in the alkylation reaction under well-
optimized conditions. The results are showed in Fig. 11.
The reaction could reach nearly 100% conversion of 1-dodecene
when the first cycle of the immobilized ionic liquid catalysts. With
recycle time increasing, the reaction rate reduced quickly, but
2
-LAB selectivity increase slightly. 2-LAB selectivity with Al(2.0)-
IL@SBA-15 was lower than that with Al(1.5)-IL@SBA-15 at first, but
it became higher at last. 2-LAB selectivity was negatively associated
with 1-dodecene conversion. Lower 1-dodecene conversion gave
smaller feedstock concentration for isomerization, which resulted
in the decline of 2-LAB selectivity. At the 3th cycle of catalysts,
1-dodecene conversion could still reach more than 50%. Higher
Al species content in ionic liquid may enhance the Lewis acidity
and reactivity of catalyst, while it declined the reusability. The role
of deactivation was proposed based on investigation of TEM and
BET, as shown in Fig. 12. The TG analysis of deactivated catalyst
is showed in Fig. 13, sample continuous lost weight with temper-
ature rising. The continuous weight loss might be resulted from
decomposing of oligomer with different molecular weight.
For active catalyst, the ionic liquid covered the carrier surface.
Reactants like benzene and olefin could diffuse through the layer
of ionic liquid and contact with active sites. During reaction, by-
products as oligomer produced by oligomerization of olefin. With
the molecular weight increasing, pores were blocked and active
sites were covered, as the shadow in TEM images. The oligomer-
ization prevented the reactants from contacting with active sites,
then the deactivation of catalyst occurred.
Fig. 11. The reusability of the immobilized ionic liquid catalysts.
that 2-LAB selectivity with immobilized ionic liquid catalyst (more
than 60%, Fig. 8(b)) was higher than that with Al-IL catalyst (about
5%, Fig. 8(a)). Under certain conditions, 2-LAB selectivity reached
about 80% (Fig. 8(c)).
The results of the benzene alkylation with 1-dodecene over
various catalysts at benzene/1-dodecene (molar ratio = 5), 35 C
are present in Table 3. Al(1.5)-IL and Al(2.0)-IL were liquid cata-
lysts. The reaction highly conducted when add 10 wt% catalysts.
It indicated that the reaction can conduct quickly, and the cat-
alyst amount can be lower than 10 wt%. In this case, mole of Al
species in Al(2.0)-IL was much higher than that of Al(1.5)-IL@SBA-
3
◦
1
5, due to the existing of silica in Al(1.5)-IL@SBA-15. When mole
of Al species were equal, reaction with Al(1.5)-IL@SBA-15 (5 wt%)
conducted while reaction with Al(1.5)-IL did not. With the same
amount of Al species, immobilized catalysts dispersed active sites
better than ionic liquid, due to the highly specific surface areas
of supporter. While reaction could only conduct on the surface
of ionic liquid droplet with ionic liquid heterogeneous catalysts.
Thus higher efficiency could be reached for immobilized catalysts.
With solid catalysts, 2-LAB selectivity was lower for reaction with
no ionic liquid, Al(2.0)-IL, than others. The distribution of product
was tend toward high substituent formation. Ionic liquid may have
the ability to maintain 2- isomer stable, and inhibit the isomeriza-
tion. Higher catalyst amount resulted in more active sites, led to
stronger interaction between the reactants and active sites, higher
concentration of carbenium ion, and lower 2-LAB selectivity. But
proper amount of catalyst led to economic reaction rate. 5 wt% was
chosen as a proper ratio of catalysts for the reaction. Aluminum
species were the active sites in the alkylation reaction. Adding the
4. Conclusion
Highly ordering mesoporous material SBA-15, which has the
property of high specific surface areas, has been successful syn-
thesized. Based on XRD, BET, TEM, TG analysis, ionic liquid
[bmim][TFSI]/AlCl3 was proved to be immobilized on SBA-15, cov-
ered the internal surface of the pores. XRD and TEM analysis
indicated that the mesoporous structure (the hexagonal arranged
pore array) and the high specific surface areas were preserved
Please cite this article in press as: Y. He, et al., Synthesis of efficient SBA-15 immobilized ionic liquid catalyst and its performance for
Friedel–Crafts reaction, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.045

G Model
CATTOD-10016; No. of Pages9
ARTICLE IN PRESS
8
Y. He et al. / Catalysis Today xxx (2016) xxx–xxx
Fig. 12. Illustration to the role of deactivation.
Fig. 13. TG analysis of catalysts sample after deactivation.
after immobilization. Compared to aluminum chloride grafted
mesoporous material, SBA-15 immobilized ionic liquids presented
higher Lewis acidity according to ammonia TPD analysis. In ammo-
nia TPD analysis, immobilized ionic liquid catalysts presented peaks
By-products as oligomer, produced by oligomerization of olefin in
the reactant, blocked or covered the pores, prevented the reactants
from contacting with active sites, and reduced the specific surface
areas of catalysts.
◦
around 250 C while Al-SBA-15 showed none. Compared to bulk
ionic liquid [bmim][TFSI]/AlCl , immobilized ionic liquids present
3
Acknowledgement
higher decomposition temperature and thermal stability. Bulk ionic
◦
liquids started to lose organic content from 250 C. And immobi-
This work was supported by the National Natural Science Foun-
dation of China (U1362102).
◦
lized catalysts improved this temperature to about 300 C.
The SBA-15 immobilized ionic liquid catalysts were proved to
be active for Friedel–Crafts alkylation of benzene with 1-dodecene.
Different catalysts and various parameters were investigated,
including reaction time, benzene/1-dodecene, etc. Immobilization
of ionic liquid reduced the usage of ionic liquid catalysts due to
the dispersion and high contact areas given by SBA-15. Thus, the
utilization of active sites was significantly improved by immo-
bilization. Immobilized ionic liquid catalysts gave higher 2-LAB
selectivity, due to the ability of maintaining the stability of 2-
isomer. Under certain conditions, 2-LAB selectivity was as high as
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Please cite this article in press as: Y. He, et al., Synthesis of efficient SBA-15 immobilized ionic liquid catalyst and its performance for
Friedel–Crafts reaction, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.045