Durability enhanced ionic liquid catalyst for Friedel-Crafts reaction between benzene and 1-dodecene: Insight into catalyst deactivation

Article abstract of DOI:10.1039/c5ra10117d

Friedel-Crafts alkylation of benzene with 1-dodecene, which is an important reaction of synthetic detergent, was studied using the catalyst [bmim][TFSI]/AlCl₃ (1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide/AlCl₃). These ionic liquid catalysts show biphasic behaviors at a specific condition. Active site species and Lewis acidity were determined by NMR and acetonitrile probe FT-IR. NMR spectroscopy investigations indicated that coordinated and uncoordinated [TFSI]^- existed in the ionic liquid catalyst system simultaneously, while tetrahedral 4-coordinate Al₂Cl₇^- was the main active species for Friedel-Crafts alkylation. The complex [AlCl_x(TFSI)_y]^- tends to decompose and release 4-coordinated Al₂Cl₇^- and [TFSI]^-. The phase behavior study of the ionic liquid [bmim][TFSI]/AlCl₃ demonstrated that the upper phase could be used as an efficient heterogeneous catalyst when AlCl₃/IL ≥ 1.5. Due to the presence of the anion [TFSI]^- around the active sites, especially [TFSI]^- at the uncoordinated state, the ionic liquid formed a stable and hydrophobic chemical environment, which enhanced catalyst durability. The influence of various reaction conditions including catalyst reusability on the alkylation reaction was studied, and the potential reasons for catalyst deactivation were discussed. The highest 2-LAB selectivity was more than 50% when 1-dodecene conversion was nearly 100%. Compared with liquid or solid acid catalyst, ionic liquid catalysts have many advantages concerning energy and the environment.

Full text of DOI:10.1039/c5ra10117d

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DOI: 10.1039/C5RA10117D
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Durability Enhanced Ionic Liquid Catalyst for Friedel-Craft
Reaction between Benzene and 1-Dodecene: Insight of Catalyst
Deactivation
Received 00th January 20xx,
Accepted 00th January 20xx
Yibo He,a Chao Wan,a Qinghua Zhang,a* Xiaoli Zhan,a Dang-guo Cheng,a Fengqiu Chena
DOI: 10.1039/x0xx00000x
Friedel-Craft alkylation of benzene with 1-dodecene, which is an important reaction of synthetic detergent, was studied
using the catalyst of [bmim][TFSI]/AlCl3 (1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide/AlCl3). These
ionic liquid catalysts show biphasic behaviors at specific condition. Active site species and Lewis acidity were determined
by NMR and acetonitrile probe FT-IR. NMR spectroscopy investigations indicated that "Coordinated" and "uncoordinated"
www.rsc.org/
[TFSI]- existed in the ionic liquid catalyst system sumultaneity, while tetrahedral 4-coordinate Al2Cl7 was the main active
-
-
specie for Friedel-Craft alkylation. The complexation [AlClx(TFSI)y]- tend to decompose and release 4-coordinated Al2Cl7
and [TFSI]-. The phase behaviors study of the ionic liquid [bmim][TFSI]/AlCl3 demonstrated that the upper phase could be
used as an efficient heterogeneous catalyst when AlCl3/IL≥1.5. Due to the presence of anion [TFSI]- around active sites,
especially [TFSI]- at "uncoordinated" state, ionic liquid formed a stable and hydrophobic chemical environment, which
enhanced catalysts durability. The influence of various reaction conditions including catalyst reusability on the alkylation
reaction was studied, and the potential reasons to catalyst deactivation were discussed. The highest 2-LAB selectivity was
more than 50% when 1-dodecene conversion was nearly 100%. Comparing with liquid or solid acid catalyst, ionic liquid
catalysts have many advantages in perspectives concerning energy and environmental.
ionic liquids have attracted much interest for their unique
properties such as non-volatility, non-flammability, high
1
Introduction
Synthetic detergents made from branched alkyl benzene (BAB)
have been widely applied in all sorts of areas in our daily life.1-4
However, the increasing usage of detergent leads to branched
alkyl benzene sulfonate (BAS) accumulation and environment
contamination. Generally, it is generally known that synthetic
detergent made from linear alkyl benzene (LAB) has better
biodegradability than that made from BAB or natural soap.5
The phenyl group position of LAB has an effect on its surface-
active property and biodegradability of linear alkyl benzene
sulfonate (LAS). Among the isomers of LAB, 2-LAB exhibits the
highest biodegradability, making it dominant detergent
intermediate.6-8
chemical and thermal stability.11-15 The use of ionic liquid
catalysts like [cation][HSO4], [bmim][Al2Cl6Br], [bmim][FeCl4],
[Et3NHCl][FeCl3] and [Et3NHCl][AlCl3] would result in high
activity. These kinds of ionic liquid catalysts could not be
reused for many times because of their moisture sensitivity.16-
20
Improving the durability of ionic liquid could promote its
efficiency and reduce the cost. Researchers became more
interested in developing stable and durable ionic liquid
catalysts.21-24 Perfluoroalkyl groups have properties of stability
and hydrophobicity. Fluoro-ionic liquids are considered to be
catalysts with high catalytic activity, good chemical stability
and durability.
HF or AlCl3 was commonly used as a homogenous catalyst in
the industrial production of LAB. This kind of catalysts showed
serious problems including environment contamination,
equipment corrosion, difficult separation, and low 2-LAB
selectivity. The 2-LAB selectivity catalysed by AlCl3 or HF is in
the ranges from 26~33%1, 2 and 14~20%.9, 10 While the recently
announced Detal™ process, which developed by UOP as the
first fixed-bed catalyst alkylation technology requires
benzene/1-dodecene ratio as high as 30:1. In recent years,
In this work, ionic liquid was prepared from 1-butyl-3-
methylimidazolium
bromide
([bmim]Br),
lithium
bis((trifluoromethyl)sulfonyl)imide (LiTFSI) and AlCl3. The Lewis
acidity of the catalysts was investigated by acetonitrile probe
FT-IR spectroscopic. Species of ionic liquid catalysts were
demonstrated by NMR spectroscopy. The effects of various
reaction conditions on the synthesis of LAB were investigated.
Moreover, the potential reasons to catalyst deactivation were
discussed.
2 Experiment
2.1
Materials and pre-treatment:
a.College of Chemical and Biological Engineering, Zhejiang University, Zheda Road
38, Hangzhou 310027, P. R. China. E-mail: qhzhang@zju.edu.cn; Phone: 86-0571-
87953382
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Ionic liquid [bmim]Br, lithium salt LiTFSI were obtained from
Aladdin Reagents Co., LTD. Anhydrous aluminum chloride,
acetonitrile and chloroform were purchased from Sinopharm
Chemical Reagent Co., LTD. Before use, liquid reagent should
be refluxed using calcium hydride to remove water, then
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purified by distillation under nitrogen, solid material and ionic started to become monophasic again. All these bi-phase
liquid was dried for 24 h.
systems became monophasic when heateDdOaI:t1o0r.1a0Vb3i9eow/vCAe5rRt8icA0le10Oº1Cn1l7.inDe
2.2
Catalyst preparation and alkylation reaction:
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.
The result product was dissolved in CH2Cl2. LiCl was
precipitated and separated by filtration. The filtrate was
evaporated to dryness then the [bmim][TFSI] obtained.25 The
ionic liquid [bmim][TFSI] was heated to 80 °C, and AlCl3 was
slowly dissolved in [bmim][TFSI] with stirring for 6 h to ensure
complete mixing. Separation of different layers was promoted
by centrifugation, then different layers of the ionic liquids
obtained by decantation.
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
decantation. The organic layer was washed with water, dried
over Na2SO4 and analyzed by gas chromatography. For the
recycling experiments, the ionic liquid was extracted three
times with cyclohexane, then the experiment was repeated as
described above.
Figure 1. Phase behavior phenomena of [bmim][TFSI]/AlCl3.
(a)AlCl3/IL=1.0, (b)AlCl3/IL=1.5, (c)AlCl3/IL=2.0, (d)AlCl3/IL=3.0
Ionic liquids like AlCl3/IL have been used as catalyst for Friedel-
Crafts alkylation reaction.29-31 The upper phase and lower
phase were used as catalyst directly for alkylation reaction of
benzene and 1-dodecene respectively. Only the upper phase
demonstrated catalysis activity when ratio of AlCl3/IL≥1.5. The
result shows that adding AlCl3 to [bmim][TFSI] induced
different structure of coordination compounds, which
indicated that, different AlCl3 content produces different
structure of coordination compounds, which was related to
the reaction activity. Among these coordination compounds,
catalytic activity was shared within some coordination
compounds, while some still remained inactive. Not
considering the case of biphasic behaviors, while direct
application of this ionic liquid as catalyst will result in
inaccurate measurement of the catalyst and a waste of the
ionic liquid.32 It is necessary to obtain deeper understanding of
compound structures and Lewis acidity changing in biphasic
behavior.
2.3
Analysis:
FT-IR spectra was obtained by Nicolet 5700 Fourier Transform
Infrared Spectrometer, and analyzed by Nicolet OMINC 8.2
software. IR test samples were prepared by mixing ionic liquid
catalyst and acetonitrile at the molar ratio of 1:1. The samples
were diluted with chloroform appropriately, injected to a
liquid pool with KBr windows, tested directly by Nicolet 5700
Fourier Transform Infrared spectrometer. 12C-NMR, 19F-NMR,
27Al-NMR analysis were carried out by Agilent DD2-600 nuclear
magnetic resonance spectrometer. Materials and products of
reaction were investigated by gas chromatography (GC). GC
was equipped with HP-5 column (30 m). The initial column
temperature maintained at 110 °C for 3 min, raised at the rate
of 15 °C/min and maintained at 300 °C for 9 min. The injection
temperature was at 300 °C.
3.1.2 NMR analysis
The upper and the lower layer of the catalyst system were
studied by 12C-NMR, 19F-NMR and 27Al-NMR spectroscopy to
gain insights into the catalysis active species at AlCl3/IL=1.5.
Figure 2 (a) shows 12C-NMR spectra for the upper and the
lower phase of an example. Resonances at δ=56 ppm, δ=80
ppm are the peaks of solvent. The resonances, which were
observed at 15.9 ppm, 22.0 ppm, 34.5 ppm, 39.6 ppm, 53.0
ppm, 125.0 ppm, 126.6 ppm, 137.6 ppm were attributed to
[bmim]+. Interestingly, no [bmim]+ signal can be found in the
lower phase. Resonances around 120~122 ppm were
indications of [TFSI]-. Two CF3 quartets were observed in 12C-
NMR spectra. The two quartets were attributed to
"coordinated" and "uncoordinated" [TFSI]-.27 [TFSI]- at
"uncoordinated" state formed a chemical environment, which
was stable and hydrophobic. Compared with [bmim]+
resonances in the upper phase, [TFSI]- resonances were too
small to distinguish.
3 Result and discussion
3.1
Catalyst
3.1.1 Phase behaviors of catalyst
[bmim][TFSI]/AlCl3 mixtures show biphasic behavior under
some specific composition ranges. Many kinds of ionic liquids
show these biphasic behaviors.26-28 Wasserscheid et al.
indicated that most of [cation][TFSI]/AlCl3 ionic liquids showed
biphasic behavior. Typically, a certain amount of AlCl3 can be
homogeneously dissolved in this kind of ionic liquids up to the
lower limit of biphasic regime. With further addition of AlCl3,
phase separation began. Rocher et al. also investigated
biphasic behavior of some ionic liquids at low AlCl3 mole
fraction (<0.5). However, few researchers have discussed the
relationship between the reaction activity and the compounds
structure of two-phase above. The catalysts used in this work
were of relatively high AlCl3 mole fraction than that of
Figure 2 (b) shows 19F-NMR spectra for the upper and lower
phase. [TFSI]- resonances were observed clearly in both the
upper and lower phase. It was showed that all [bmim]+
concentrate in the upper phase, there was no [bmim]+ in the
lower phase. However, [TFSI]- existed in both the upper phase
and lower phase. 27Al-NMR spectroscopy has been widely used
to discuss the chemical speciation of aluminum. 4-coordinate
(tetrahedral) and 6-coordinate (octahedral) were detected in
references before. Figure
1
shows the experimental
phenomena of biphasic behavior. At AlCl3/IL=1.0, the mixture
formed a bi-phase, containing a light brown upper layer, and a
turbid lower layer. At AlCl3/IL=1.5, the upper layer turned
opaque, and the color became darker, the lower layer turned
transparent and clear. The volume of the lower phase
decreased with the further addition of AlCl3. Exceeding the
upper limit of the bi-phase regime (AlCl3/IL=3), the system
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both liquid phase respectively.28 A sharp resonance signal, NMR spectroscopy investigations indicated that tVeietrwaAhrteicdlerOanlli4ne-
discovered at 104 ppm in Figure 2 (c), was attributed to the coordinate species was active site for Friedel-Crafts alkylation,
DOI: 10.1039/C5RA10117D
-
-
presence of tetrahedral AlCl4 and Al2Cl7 . Resonances around - [TFSI]- which existed in the upper layer that formed stable and
15~20 ppm were indications of octahedral aluminum species hydrophobic chemical environment. As shown in Figure 3,
[Al(TFSI)3] among which several isomers were found in Figure 2 fluoro hydrophobic groups mixed with the active sites, and
(c). A small resonance was also apparent at δ=98 ppm, which filled in their surroundings of them. It makes the active sites
was identified to be a product of the reaction with residual not easy to be contacted by the moisture of reactants.
water. Little resonances at δ=-3 ppm and δ=94 ppm, assigned However, the hydrophobic groups produced no limitation to
to [AlCl2(NTf2)2]- and [AlCl3(NTf2)]- species, appeared to exist the transportation and diffusion of the reactants. Reactants
stably only at the high temperature. The addition of AlCl3 to like benzene and olefin could diffuse through the layer of
[bmim][TFSI] led to complexation with [TFSI] first, then fluoro-ionic liquid and contact with active sites. Thus, fluoro
disproportionation of the [AlClx(TFSI)y]- complexes generated groups formed stable and hydrophobic chemical environment
- 33
Al(TFSI)3 and AlCl4 .
And [AlClx(TFSI)y]- may tend to and the ionic liquid catalyst had good water-resisting property
decompose and release AlCl4 and [TFSI]- in the system to and high reactivity.
-
maintain the balance of ionic content.
Figure 3. Illustration to the ionic liquid catalyst system
3.1.3 Lewis Acidity of Ionic Liquids
Acetonitrile probe FT-IR was performed to measure the Lewis
acidity of ionic liquids, and the results are displayed in Figure
4.34 The region from around 2252 cm-1 and 2293 cm-1 are
signals of –CN stretching vibrations of acetonitrile, while ionic
liquid catalyst showed no signal in regions ranging from 2500
to 2000 cm-1. Once the acetonitrile mixed with Lewis acidic
sites, which came from ionic liquid catalyst, the –CN stretching
vibration bands shifted to higher wavenumber. The magnitude
of shift could be contributed to the strength of the Lewis acidic
sites.16
Figure 4. FT-IR of the mixture of acetonitrile and the ionic
liquid catalyst
Figure 2. the upper and lower phase at AlCl3/IL=1.5, (a) 12C-
NMR, (b) 19F-NMR, (c) 27Al-NMR
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A new absorbance peak around 2330 cm-1 indicated the Alkylation reaction was conducted quickly so that 1-dodecene
existence of Lewis acidic sites when the acetonitrile is mixed could reach its highest conversion within a shortVtieiwmAert.icAlesOntlhinee
DOI: 10.1039/C5RA10117D
with ionic liquid catalyst. At AlCl3/IL=1.2, though ionic liquid ratio of benzene/1-dodecene increased, 2-LAB selectivity
system showed no catalytic activity, but still showed Lewis increased from 35% to about 40%. With the same Lewis acidity,
acidity. At this ratio of AlCl3/IL, signal at 2252 cm-1 and 2293 increasing the ratio of benzene/1-dodecene indicated the
cm-1 became weaker, and signal at 2293 cm-1 shifted to higher carbenium ion concentration diluted. The reduced carbenium
slightly. With more AlCl3 addition into ionic liquid system, the ion concentration could inhibit the hydrogen shift reactions
magnitude of bands at 2293 cm-1 shifting became larger, the and isomerization, resulting increased of 2-LAB selectivity. This
intensity of bands at 2330 cm-1 became stronger while that of is why benzene/1-dodecene ratio is as high as 30 in industrial
2252 cm-1 became weaker. At AlCl3/IL=2.0, bands at 2252 cm-1 “Detal™” process.35, 36 However, a higher benzene/1-dodecene
shift magnitude, and the intensity of bands at 2310 cm-1 ratio causes a higher cost, which is resulted from surplus
became stronger compared with that at AlCl3/IL=1.5. With the benzene separation and recycle.
increasing addition of AlCl3, the intensity of shifted -CN The influence of catalyst amount and catalyst type in the
stretching vibrations of acetonitrile became weaker, thus reaction system is showed in Figure 6 at AlCl3/IL=1.5, 35 ºC,
indicating the Lewis acidic strength of the ionic liquid catalyst benzene/1-dodecene=1.5. As showed in Figure 6, the amount
system increased with AlCl3 addition. At low AlCl3 of ionic liquid catalyst affected not only the conversion of 1-
concentration (AlCl3/IL≤2.0), the Lewis acidic strength dodecene but also the selectivity of 2-LAB. Reaction was faster
increased significantly, while the Lewis acidic strength does over AlCl3 than that of AlCl3/IL for reasons of that more contact
not go on increase obviously at high AlCl3 concentration between reactant and catalyst was realized by a homogeneous
reactions system. Although the reaction was faster catalyzed
(AlCl3/IL
＞
2.0).
Alkylation of benzene with 1-dodecene
3.2.1 The effect of various reaction conditions
of AlCl3, homogeneous reaction system led to a recycle
difficulty. Therefore, as heterogeneous reaction catalyst,
AlCl3/IL was much more favourable.
3.2
The influences of benzene/1-dodecene (molar ratio) for the
alkylation reaction were studied at cata. =0.9 wt%, AlCl3/IL=2.0,
35 °C, results is showed in Figure 5 (a) and (b).
Figure 6. The effect of catalyst amount
The selectivity of 2-LAB remained at about 30% when the
reaction catalyzed by AlCl3. At low concentration (
＜4.0 wt%＝
of ionic liquid catalyst, selectivity of 2-LAB reached over 40%
with the increased concentration of the ionic liquid catalyst, 2-
LAB selectivity was levelled down to that of AlCl3. Obviously,
increased concentration of the ionic liquid catalyst caused an
enhanced interaction between the reactants and the Lewis
acidic species and an increasing concentration of carbenium
ion. As a result, with the addition of the ionic liquid catalyst,
the reaction process was much faster, yet resulted in a lower
2-LAB selectivity. Therefore, to obtain an ideal product quality,
amount of the ionic liquid catalyst should be lower than 4.0
wt%.
The ionic liquid catalyst systems contained different
proportion of AlCl3 were applied in alkylation reaction at
benzene/1-dodecene=1.5, 35 ºC, as shown in Figure 7.
Figure 5. The effect of benzene/1-dodecene ratio on (a)
conversion of 1-dodecene, (b) 2-LAB selectivity
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was not optimal. A small amount of moisture in the system
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had a positive effect on the activity of the ionic liquid catalyst.
DOI: 10.1039/C5RA10117D
Slight moisture may cause the generation of H+ in the system,
which would accelerate the reaction. However, with the
further increased moisture in the system, the activity of the
ionic liquid catalyst decreased due to the decomposition of the
Lewis acidic species, while 2-LAB selectivity increased slightly.
This also might be ascribed to the concentration reduce of the
activity species, and the carbenium, and then the
isomerization was inhibited. It was worth noting that the ionic
liquid catalyst could maintain a high reactivity, when the mole
of moisture was larger than catalyst itself. It meant that the
ionic liquid catalyst [bmim][TFSI]/AlCl3 had a good water-
resisting property.
Figure 7. The effect of AlCl3/IL
Aluminum species were the catalysis active centres in the
alkylation reaction. The content of AlCl3 influenced reaction
significantly. As demonstrated in Figure 7, at the same the
ionic liquid catalyst amount, a higher content of AlCl3 in the
ionic liquid catalyst resulted in a faster reaction rate but a
lower 2-LAB selectivity. Obviously, when AlCl3/IL was infinite,
namely large enough, the reaction results were the same with
that catalyzed by merely AlCl3. Meanwhile, doubling the ionic
liquid catalyst caused the increase of the reaction rate and
decrease of 2-LAB selectivity.
For Friedel-Craft alkylation reaction, Lewis acid strength and
Lewis acidic density significantly affected reaction. More AlCl3
content in the ionic liquid catalyst induced higher Lewis acidity,
namely Lewis acid strength. More amount of the ionic liquid
catalyst in reaction system induced more catalysis active sites,
namely Lewis acidic density. Higher Lewis acidity and larger
Lewis acidic density increased the reaction rate, but decreased
the 2-LAB selectivity. When Lewis acidity and acid sites were
infinite, the reaction results were the same with that catalyzed
by merely AlCl3. Therefore, to obtain an ideal product quality,
catalyst amount and catalyst composition should be controlled
in a reasonable range.
3.2.2 Water-resisting property and reusability
Figure 9. (a) The reusability of the ionic liquid catalyst before 5
cycles, (b) The reusability of the ionic liquid catalyst for 12 h
per cycle
The reusability is one of the most important properties for the
ionic liquid catalyst, which was studied in the alkylation
reaction at benzene/1-dodecene=5, AlCl3/IL=2.0, cata.=9.0
wt%, 35 ºC. As shown in Figure 9 (a), the reaction carried out
quickly with the fresh ionic liquid catalyst. With recycle time
increasing, the reaction rate reduced slowly. At the 5th cycle of
catalyst, 1-dodecene conversion could still reach 50% within
20 min. In order to obtain a deeper understanding of the
reusability of the ionic liquid catalyst, the reaction time was
extended to 12 h, the reaction results are shown in Figure 9 (b)
and Table 1. Conversion of 1-dodecene could reach nearly 100%
in 12 h when catalyst recycling less than seven times.
Increasing the recycle times, catalyst activity decreased
significant. Conversion of 1-dodecene could only reach 20%
after reaction for 12 h, while 2-LAB selectivity increased
Figure 8. The effect of moisture in reaction
The influence of the moisture to the reaction system is showed
in Figure 8. Due to the high moisture sensitivity of AlCl3, it is
important to investigate the effect of the moisture on the ionic
liquid catalyst. As showed in Figure 8, strict dried condition
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slightly with the increasing of the recycle times. It might be weight of oligomer, the diffusion of the reactantVwiewillArbtieclemOnolirnee
caused by Lewis acidity changes.
difficult. Thus the by-product might accumulate around the
active sites, and encapsulate them in the end. As a result,
DOI: 10.1039/C5RA10117D
Table 1. The reusability data of the ionic liquid catalyst for 12 h reactants could not pass through and contact with the existing
from 4th to 9th cycle.
Cycles
active sites. The acetonitrile probe FT-IR investigation also
proved the catalyst acidity after deactivation. Another possible
reason to catalyst deactivation was the moisture in tiny
quantities passing through the hydrophobic group, and
contacting with active sites, leading to hydrolysis of active
sites.37, 38
4
5
6
7
8
9
Conversion (%)
98.1 97.2 98.1 98.0 85.5 19.9
2-LAB Selectivity (%) 43.2 43.5 44.0 43.9 45.5 46.0
Acetonitrile probe FT-IR showed how the Lewis acidity
changed, as shown in Figure 10. As the recycle times increased,
intensity of absorbance peak around 2330 cm-1 became
weaker while that of –CN stretching vibrations band at 2253
cm-1 became stronger which meant the decrease of the Lewis
acidic density. Besides, shifting of band around 2330 cm-1 and
band around 2310 cm-1 proved the decrease of the Lewis
acidic strength.
4 Conclusions
The phase behaviors of [bmim][TFSI]/AlCl3 was investigated,
the upper phase of [bmim][TFSI]/AlCl3 could be used as the
heterogeneous ionic liquid catalyst when AlCl3/IL≥1.5. Based
on 19F-NMR and 12C-NMR investigations, no [bmim]+ signals
can be found in the lower phase, [TFSI]- existed in both phase
at “coordinated” and “uncoordinated” state. “Uncoordinated”
state [TFSI]- formed a stable and hydrophobic chemical
environment, enhanced catalyst durability and water-resisting
property of catalyst. 27Al-NMR investigation showed that 4-
coordinate (tetrahedral) aluminum species concentrated in the
upper phase and 6-coordinate (octahedral) aluminum species
concentrated in the lower phase. Catalysis activity of the ionic
liquid catalyst was attributed to the presence of tetrahedral 4-
-
coordinate Al2Cl7 .
Acetonitrile probe FT-IR investigation showed the relationship
between Lewis acidity, density, and reaction. Various
parameters were investigated, including benzene/1-dodecene
ratio, amount of the ionic liquid catalyst, AlCl3/IL, moisture,
recycle times. It is concluded that larger catalyst amount and
higher AlCl3 content, would result in the increase of Lewis acid
density and Lewis acidity, causing a faster alkylation reaction
and a lower 2-LAB selectivity, which can be explained by
carbenium ion concentration. Benzene/1-dodecene ratio also
significantly affected the reaction. Two potential reasons to
deactivation were discussed. By-products as oligomer
accumulated around and encapsulated the active sites would
prevent reactants from contacting with active sites. Another
possible reason to catalyst deactivation was the moisture in
tiny quantities passing through the hydrophobic group, and
contacting with active sites, leading to hydrolysis of active sites.
Figure 10. FT-IR of the mixture of acetonitrile and different
cycle of the ionic liquid catalyst
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (U1362102).
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Figure 11. Illustration to the ionic liquid catalyst system after
several times cycles
When the catalyst gradually lost reactivity, the situation of the
catalyst was predicted and the case was showed in Figure 11.
As
a side-reaction, oligomer would be produced by
polymerization of 1-dodecene. With the increased molecular
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