Ionic liquid enhanced alkylation of iso-butane and 1-butene

Article abstract of DOI:10.1016/j.cattod.2012.06.008

The alkylation of iso-butane with 1-butene was catalyzed by triflic acid (TFOH) coupled with a series of protic ammonium-based ionic liquids (AMILs), and the addition of the AMILs dramatically enhanced the efficiency of TFOH for the alkylation reaction. Up to 85.1% trimethylpentanes (TMP) selectivity and 98 research octane number (RON) were achieved with the optimized TFOH/AMIL catalyst (75 vol.% triflic acid and 25 vol.% triethylammonium hydrogen sulfate), which were much better than that with the commercial H₂SO₄ catalyst (65% TMP selectivity, 97 RON) and pure triflic acid. The addition of AMILs increased the I/O ratio dissolved in the catalyst system and adjusted the acidity of the TFOH/AMILs catalyst system, which were highly beneficial to the alkylation reaction and resulted in high TMP selectivity and high RON.

Full text of DOI:10.1016/j.cattod.2012.06.008

Catalysis Today 200 (2013) 30–35
Contents lists available at SciVerse ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Ionic liquid enhanced alkylation of iso-butane and 1-butene
Peng Cuia,b, Guoying Zhaob, Hailing Rena,b, Jun Huanga,∗, Suojiang Zhangb,∗
a State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, 210009 Nanjing, PR China
b Beijing Key Laboratory of Ionic Liquids Clean Process, Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex System, Institute of Process
Engineering, Chinese Academy of Sciences, Beijing 100190, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 March 2012
Received in revised form 1 June 2012
Accepted 13 June 2012
Available online 4 August 2012
The alkylation of iso-butane with 1-butene was catalyzed by triflic acid (TFOH) coupled with a series of
protic ammonium-based ionic liquids (AMILs), and the addition of the AMILs dramatically enhanced the
efficiency of TFOH for the alkylation reaction. Up to 85.1% trimethylpentanes (TMP) selectivity and 98
research octane number (RON) were achieved with the optimized TFOH/AMIL catalyst (75 vol.% triflic
acid and 25 vol.% triethylammonium hydrogen sulfate), which were much better than that with the
commercial H2SO4 catalyst (65% TMP selectivity, 97 RON) and pure triflic acid. The addition of AMILs
increased the I/O ratio dissolved in the catalyst system and adjusted the acidity of the TFOH/AMILs catalyst
system, which were highly beneficial to the alkylation reaction and resulted in high TMP selectivity and
high RON.
Keywords:
Ionic liquids
Alkylation
iso-Butane
Butene
© 2012 Elsevier B.V. All rights reserved.
Triflic acid
1. Introduction
petroengineering [25–27]. However, it is difficult to control the
acidity of the chloroaluminated ILs. Moreover, chloroaluminated
The alkylation of iso-butane with butene is an important tech-
nology to produce branched alkanes for the gasoline pool [1–3].
However, the current alkylation technologies cause both environ-
mental and human health concerns because sulfuric acid and HF are
used as catalysts. Thereafter, it is highly desirable to develop safe,
green and efficient catalysts for the iso-butane alkylation process.
In order to improve the safety and environmental friendliness,
solid catalysts were developed for the alkylation process [4–13].
Polymeric acids [5–7], zeolites [8,9], and heteropolyacids [10–13]
had been investigated intensively in the last 50 years, and some
of them were applied successfully for the iso-butane alkylation
on a small scale [1]. However, the deactivation of the solid cata-
lysts is still a “bottleneck” for the alkylation process, which limits
the industrial application of solid acids. In order to improve the
efficiency and depress the waste emission, liquid acidic catalysts,
especially acidic ILs have been developed for the alkylation process
[2,14,15].
ILs are extremely sensitive to moisture, and deactivated rapidly
though the irreversible hydrolysis [26,27]. Therefore, much effort
was put into developing highly acidic, non-chloroaluminate sys-
tems for the alkylation.
Coupled of six imidazolium-based ILs, TFOH was applied suc-
cessfully as catalysts for the iso-butane alkylation by Tang recently
[15]. The coupled catalyst systems were much better (higher
selectivity and better reusability) than TFOH, and good conver-
sion (>95%), high C8-alkylates selectivity (>70%) and high ratio of
trimethylpentane/dimethylhexane (TMP/DMH > 7) were achieved
with the IL/TFOH mixtures. The fundamental physical–chemical
properties of the IL/TFOH system, such as acidity, solubility and
interfacial properties were modified to be favorable for the alky-
lation reaction, as it is well known that the iso-butane–olefin
(2-butene) ratio (I/O) has significant effect on the TMP selectiv-
ity. With higher I/O iso-butane–olefin ratios feed, the alkylation
of olefin with iso-butane is faster than the olefin polymerization,
resulting in high selectivity of TMP. Moreover Scovazzo [28,29]
group reported the solubility property and Henry’s law constant for
hydrocarbons in imidazolium-, phosphonium-, and ammonium-
based ionic liquids. The ratio of alkane to alkene is higher dissolved
in ammonium based ILs than in imidazolium based ILs. Thereafter,
ammonium based ILs may be beneficial as co-catalysts of TFOH for
the alkylation.
ILs have been applied as solvents and/or catalysts in many
research fields [16–19]. Acidic ILs were used widely as effi-
cient catalysts for many reactions such as etherification [20],
Friedel–Crafts [21,22], alkylation [2,15,23] and isomerization [24].
In the last decades, chloroaluminated ILs had been investi-
gated extensively for iso-butane alkylation in petrochemistry and
To further improve the quality of alkylate (TMP selectivity an−d
RON), a series of protic ammonium-based ionic liquids with HSO4
and TFO− anion were synthesized and applied with TFOH as cata-
lysts for the iso-butane alkylation. The effects of reaction variables,
∗
Corresponding authors.
E-mail addresses: junhuang@njut.edu.cn, gyzhao@home.ipe.ac.cn (J. Huang),
sjzhang@home.ipe.ac.cn (S. Zhang).
0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2012.06.008

P. Cui et al. / Catalysis Today 200 (2013) 30–35
31
such as the ionic structures and catalyst hydrocarbon ratio for the
alkylate compositions, have been investigated and optimized for
the alkylation. The addition of the AMILs dramatically enhanced the
efficiency of the TFOH for the alkylation reaction, and high selec-
tivity (up to 85.1% of TMP) and high RON (up to 98) were achieved
with the optimized TFOH/IL catalyst system.
O, 50.32%; S, 20.12. Found: C, 14.97%; H, 6.00%; N, 8.87%; O, 50.68%;
S, 19.95%.
N,N-diethyl ethanolammonium hydrogen sulfate [DEEA] [HSO4]:
[DEEA] [HSO4] was synthesized from N,N-diethyl ethanolamine
and sulfuric acid according to the typical procedure. 1H NMR
(600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.19–7.16 (s, 1H), 3.68–3.62 (m,
4H), 3.15–3.12 (t, 2H), 2.99–2.96 (t, 2H), 2.74 (s, 1H), 2.65 (m, 6H),
2.12–2.07 (s, 1H). ESI/MS: m/z (+) 118.1230, m/z (−) 96.9620. Cal-
culate for C6H17NO5S: C, 33.49%; H, 7.91%; N, 6.51%; O, 37.21%; S,
14.88%. Found: C, 33.30%; H, 8.06%; N, 7.55%; O, 37.80%; S, 14.50%.
N-methyl diethanolammonium hydrogen sulfate [MDEA] [HSO4]:
[MDEA] [HSO4] was synthesized from N-methyl diethanolamine
and sulfuric acid according to the typical procedure. 1H NMR
(600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.15–7.10 (s, 1H), 3.73 (t,
J = 5.34 Hz, 4H), 3.16–3.06 (t, J = 7.11 Hz, 4H), 2.63 (s, 2H), 1.17–1.10
(s, 3H), 2.10–2.06 (s, 1H). ESI/MS: m/z (+) 120.1018, m/z (−) 96.9618.
Calculate for C5H15NO6S: C, 27.65%; H, 6.91%; N, 6.45%; O, 44.24%;
S, 14.75%. Found: C, 27.46%; H, 7.16%; N, 7.02%; O, 44.99%; S, 14.81%.
Triethylammonium hydrogen sulfate [TEA] [HSO4]: [TEA] [HSO4]
was synthesized from triethylamine and sulfuric acid according to
the typical procedure. 1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm)
7.11–7.07 (s, 1H), 3.07–3.03 (m, 6H), 1.13 (m, 9H), 2.13–2.08 (s,
1H). ESI/MS: m/z (+) 96.9618, m/z (−) 102.1271. Calculate for
C6H17NO4S: C, 36.18%; H, 8.54%; N, 7.04%; O, 32.16%; S, 16.08%.
Found: C, 36.28%; H, 8.54%; N, 7.16%; O, 32.81%; S, 15.60%.
N,N-dimethyl isopropanolammonium triflate [DMIPA] [CF3SO3]:
[DMIPA] [CF3SO3] was synthesized from N,N-dimethyl iso-
propanolamine and TFOH according to the typical procedure. 1H
NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.21–7.16 (s, 1H), 4.27–4.24
(m, 1H), 3.24–3.15 (d, J = 6.54 Hz, 2H), 2.98 (s, 6H), 2.83 (s, 1H), 1.31
(d, J = 6.36 Hz, 3H). ESI/MS: m/z (+) 104.1064, m/z (−) 148.9580. Cal-
culate for C6H14NO4SF3: C, 28.46%; H, 5.53%; N, 5.53%; O, 25.27%; S,
12.65%. Found: C, 27.96%; H, 5.75%; N, 5.62%; O, 25.84%; S, 12.52%.
N-methyl diethanolammonium triflate [MDEA] [CF3SO3]: [MDEA]
[CF3SO3] was synthesized from N-methyl diethanolamine and
TFOH according to the typical procedure. 1H NMR (600 MHz, CDCl3,
25 ◦C): ı (ppm) 7.18–7.13 (s, 1H), 4.09–4.07 (t, J = 8.71 Hz, 4H),
3.61–3.57 (t, J = 8.54 Hz, 4H), 3.11 (s, 3H), 2.61 (s, 2H). ESI/MS:
m/z (+) 120.1020, m/z (−) 148.9581. Calculate for C6H14NO5SF3: C,
26.77%; H, 5.20%; N, 5.20%; O, 29.74%; S, 11.90%. Found: C, 25.99%;
H, 5.14%; N, 5.52%; O, 30.27%; S, 11.88%.
2. Experimental
2.1. Material
TFOH (>99.9% in purity) was purchased from 718th Research
Institute of China Shipbuilding Industry Corporation. The mix-
ture of iso-butane and 1-butene with a mole ratio of 10:1
was obtained from Airgas, Ltd., USA. Other chemicals including
sulfuric acid (98 wt.%), N,N-dimethyl isopropanolamine, N,N-
dimethyl ethanolamine, N-methyl diethanolamine, N,N-diethyl
ethanolamine and triethylamine were purchased from Alfa Aesar.
All reagents were used as received without further purification. The
research octane number (RON) of alkylate was calculated according
to the method applied in Ref. [30].
2.2. Ionic liquid synthesis
2.2.1. General procedure for the synthesis of protic ionic liquids
N,N-diethyl ethanolammonium triflate [DEEA] [CF3SO3]: The
ammonium-based ionic liquids were synthesized by neutraliza-
tion of the amines and the TFOH. In a typical procedure, 100 mL
N,N-diethyl ethanolamine was added into a three-neck flask. Then
63.7 mL TFOH was dropped into the flask with vigorous stirring
under nitrogen atmosphere in a cold water bath. After the reac-
tion was complete, the ionic liquid was dried by vacuum overnight
before use. The products were analyzed by 1H NMR (JOEL JNM –
ECA600), ESI/MS (Bruker microTOF Q.), Element analysis (vario EL.
cube). 1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.17–7.13 (s, 1H),
4.02 (t, J = 5.34 Hz, 2H), 3.44–3.35 (t, J = 6.5 Hz, 2H), 3.04–3.01 (m,
4H), 2.73 (s, 1H), 1.43–1.34 (m, 6H). ESI/MS: m/z (+) 118.1226, m/z
(−) 148.9579. Calculate for C7H16NO4SF3: C, 31.46%; H, 5.99%; N,
5.24%; O, 23.97%; S, 11.99%. Found: C, 30.52%; H, 5.95%; N, 5.38%;
O, 25.01%; S, 11.92%.
N,N-dimethyl isopropanolammonium hydrogen sulfate[DMIPA]
[HSO4]: [DMIPA] [HSO4] was synthesized from N,N-dimethyl iso-
propanolamine and sulfuric acid according to the typical procedure.
1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.12–7.06 (s, 1H),
4.13–4.07 (m, 1H), 3.10–2.98 (m, 2H), 2.87 (s, 1H), 2.84–2.81 (s, 6H),
2.10–2.07 (s, 1H), 1.14 (d, J = 6.42 Hz, 3H). ESI/MS: m/z (+) 104.1072,
m/z (−) 96.9618. Calculate for C5H15NO5S: C, 29.85%; H, 7.46%; N,
6.96%; O, 39.80%; S, 15.92%. Found: C, 28.22%; H, 7.81%; N, 6.92%;
O, 40.06%; S, 15.41%.
Triethylammonium triflate [TEA] [CF3SO3]: [TEA] [CF3SO3] was
synthesized from triethylamine and TFOH according to the typi-
cal procedure. 1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.10–7.06
(s, 1H), 3.15–3.12 (m, 6H), 1.12 (m, 9H). ESI/MS: m/z (+) 102.1269,
m/z (−) 148.9583. Calculate for C7H16NO3SF3: C, 33.47%; H, 6.38%;
N, 5.58%; O, 19.12%; S, 12.75%. Found: C, 33.32%; H, 6.62%; N, 5.75%;
O, 20.01%; S, 13.01%.
2.3. The alkylation procedure
N,N-dimethyl ethanolammonium hydrogen sulfate [DMEA]
[HSO4]: [DMEA] [HSO4] was synthesized from N,N-dimethyl
ethanolamine and sulfuric acid according to the typical procedure.
1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm) 7.12–7.06 (s, 1H), 3.58
(t, J = 5.22 Hz, 2H), 1.98 (t, J = 5.22 Hz, 2H), 2.64 (s, 1H), 2.61 (s,
6H), 2.12–2.06 (s, 1H). ESI/MS: m/z (+) 90.0915, m/z (−) 96.9623.
Calculate for C4H13NO5S: C, 25.67%; H, 6.95%; N, 7.49%; O, 42.78%;
S, 17.11%. Found: C, 25.22%; H, 7.20%; N, 7.80%; O, 43.62%; S,
16.82%.
Ethanolammonium hydrogen sulfate [MEA] [HSO4]: [MEA] [HSO4]
was synthesized from ethanolamine and sulfuric acid according to
the typical procedure. 1H NMR (600 MHz, CDCl3, 25 ◦C): ı (ppm)
7.17–7.11 (s, 3H), 4.11 (t, J = 5.28 Hz, 2H), 3.74 (t, J = 4.92 Hz, 2H),
2.33–2.29 (s, 1H), 2.13–2.08 (s, 1H). ESI/MS: m/z (+) 62.0613, m/z
(−) 96.9624. Calculate for C2H9NO5S: C, 15.09%; H, 5.66%; N, 8.81%;
The alkylation was carried out in a 200 mL autoclave with a
PTEF lining. A low temperature thermostat bath was used to control
the reaction temperature with ethanol as a working fluid. The ILs
and TFOH were premixed at the desired temperature with stirring
under argon (0.5 Mpa). And then the liquefied C4 gas was injected
into the liquid phase using a pump at a flow rate of 500 mL/h
with stirring. The reaction mixture was stirred for 10 min at the
desired temperature under argon. After the reaction completed,
the tail gas was collected and analyzed by a SP-6890 gas chro-
matography (GC), equipped with a flame ionization detector and a
HP-PLOT Al2O3 S column (50 m × 0.53 mm × 15 ␮m). The analysis
conditions were: split ratio = 100:1, constant column temperature
100 ◦C hold for 20 min, injector temperature = 250 ◦C, detector tem-
perature = 250 ◦C. The changes of the 1-butene contents in the feed

32
P. Cui et al. / Catalysis Today 200 (2013) 30–35
using the TFOH/[DMIPA] [HSO4] catalyst system ([DMIPA] [HSO4],
25 vol.%). With 50 mL of the hydrocarbon feed, the catalyst system
varied from 20 mL to 60 mL, and the results are shown in Fig. 1.
Good selectivity of C8 (79%) and high RON (95) were obtained with
50 mL of the catalyst system at 100% conversion of 1-butene, and
the optimized ratio of the TFOH/IL catalyst to hydrocarbon was 1:1.
Side products were increased with more or less the TFOH/IL cata-
lyst system. It is generally believed that the alkylate is produced
at the interfaces of the acid/hydrocarbon. Hence, a high interfacial
surface area between the acid catalyst and the hydrocarbon is ben-
eficial to the production of alkylate. However, the interfacial area is
decided by acid/hydrocarbon ratio, acid composition, agitation rate
and temperature generally. Additionally, a continuous dispersion
of the acid in the hydrocarbon is highly desirable to reduce the
consumption of acid and improve the TMP selectivity. For the
H2SO4 catalyst system, the optimized acid/hydrocarbon ratio is
in the range of 45–60%. Below this acid/hydrocarbon ratio, an
emulsion of H2SO4 in the hydrocarbon was formed continuously,
which resulted in poor product selectivity and potential runaway
of the acid. In the TFOH/[DMIPA] [HSO4] catalyst system, similar
optimized acid/hydrocarbon ratio was obtained for the alkylation.
At this acid/hydrocarbon ratio, full conversion, good selectivity
and high RON were obtained due to a combination effect of the
acidity, the interfacial area and the solubility. Thus, the 1:1 ratio of
the TFOH/IL to hydrocarbon was used for further investigation.
3.2. The effect of the content and cation types of ILs with
hydrogen sulfate anion
Coupled with TFOH, six ILs with hydrogen sulfate anion were
examined for the alkylation of iso-butane with butene. The ILs con-
tents in the catalyst system were optimized, and the typical results
(ILs [DMIPA] [HSO4] and [TEA] [HSO4] as additives for the alkyla-
tion) are shown in Fig. 2. The results (using other ILs) were added
in supporting information (SI Figs. 1s–4s). As shown from Fig. 2, the
optimized content of [DMIPA] [HSO4] and [TEA] [HSO4] in the cat-
alyst systems were around 15 vol.% and 25 vol.% respectively for
the alkylation. According to Tang [15], the best results (conver-
sions and selectivity) were obtained with around 25 wt.% IL (around
30 vol.%) [Omim] [HSO4]/TFOH catalytic system. For the AMILs with
hydroxyl group, including [DMIPA] [HSO4], [DMEA] [HSO4], [MEA]
[HSO4], [DEEA] [HSO4] and [MDEA] [HSO4], the optimized ILs’ con-
tents were less and typically around 15 vol.%. And this may be due
to the hydroxyl group reacted with triflic acid and more TFOH was
required in the alkylation process. The optimized contents of all
ILs are listed and compared in Table 1. We were delighted that
all the six catalyst systems (TFOH/ILs) exhibited high selectivity
of C8 (88–92%) with high RON (up to 98) at full conversion of
1-butene (see Table 1). The I/O solubility ratio maybe played an
important role for the alkylation, since the ammonium-based ionic
liquids have a higher I/O solubility ratio than imdazolium based
ionic liquids [28,29]. The I/O ratio has significant effect on the TMP
selectivity [31] for the alkylation. With higher I/O ratios feed, the
alkylation of olefin with iso-butane was much faster than the poly-
merization of the butene, which results in higher selectivity of the
C8 product. Thus high selectivity of C8 (88–92%) and high RON (up
to 98) were obtained in our catalyst system, as ammonium-based
ionic liquids were used as co-catalysts in the TFOH catalyst system
for the alkylation.
Fig. 1. The optimization of catalyst volume in the reaction system. (A), the product
distribution on the IL content in the catalyst system; (B), the ratio of TMP to DMH
and the RON on the IL content in the catalyst system.
Reaction conditions: the reaction temperature, 10 ◦C; argon pressure, 0.5 MPa; reac-
tion time, 10 min; stirring speed, 1000 rpm; the TFOH/[DMIPA] [HSO4] (75/25 by
vol.) catalyst, 50 mL; the premixed hydrocarbon feed (iso-butane: 1-butene = 10:1),
50 mL; I/O, 10. (ꢀ) C5–C7; (ꢀ) C8; (ꢁ) C9+; (ꢁ) TMP/DMH; (♦) RON. Data were
obtained at full conversion of 1-butene for optimized IL contents.
gas and tails gas was used to calculate the 1-butene conversion as
the iso-butane in feed gas is far excessive.
The alkylate oil was immediately separated from the cata-
lyst phase (TFOH/IL). The oil was washed with water and then
analyzed by GC (gas chromatography, SHIMADZU GC 2014),
equipped with a flame ionization detector and a DB-petro cap-
illary column (100 m × 0.25 mm). The analysis conditions were:
split ratio = 100:1, injector temperature = 250 ◦C, detector temper-
ature = 280 ◦C, carrier gas flow rate = 1 mL/min. The temperature
program for GC analysis was as follows: initial column temperature
40 ◦C, 2 ◦C/min to 100 ◦C, then 25 ◦C/min to 250 ◦C hold for 20 min.
Products were identified on an HP 6890/5975 gas chromatogra-
phy/mass spectrometry (GC/MS) system. For all the GC analysis,
nitrogen is used as carrier gas and with flame ionization detec-
tor. S content (light triflic ester) in the products of every cycle was
determined by elemental analysis.
3. Results and discussions
3.3. The effect of the content and anion types of ILs
3.1. The effect of catalyst system to hydrocarbon ratio
Then ILs with triflate anion (TFO−) were also synthesized and
applied for the iso-butane/1-butene alkylation. The contents of ILs
in the catalyst systems were optimized, and the results with ILs
[DEEA] [CF3SO3] and [TEA] [CF3SO3] are shown in Fig. 3. Other
For the alkylation of iso-butane and 1-butene, the
acid/hydrocarbon ratio is an important process variable. Herein, the
ratio of the catalyst system/hydrocarbon was firstly investigated

P. Cui et al. / Catalysis Today 200 (2013) 30–35
33
Fig. 2. The optimization of [DMIPA] [HSO4] and [TEA] [HSO4] content in the catalyst system. (A) and (C), the product distribution on the IL content in the catalyst system; (B)
and (D), the ratio of TMP to DMH and the RON on the IL content in the catalyst system.
Reaction conditions: the reaction temperature, 10 ◦C; argon pressure, 0.5 MPa; reaction time, 10 min; stirring speed, 1000 rpm; the catalyst, 50 mL (A and B, TFOH/[DMIPA]
[HSO4]; C and D, TFOH/[TEA] [HSO4]); the premixed hydrocarbon feed (iso-butane: 1-butene = 10:1), 50 mL; I/O, 10. (ꢀ) C5–C7; (ꢀ) C8; (ꢁ) C9+; (ꢁ) TMP/DMH; (♦) RON. Data
were obtained at full conversion of 1-butene for optimized IL contents.
Table 1
−
The alkylate compositions produced by the optimized TFOH/IL with HSO4
.
Entry
Ionic liquid
C5–C7 (%)
C8 (%)
C9+ (%)
TMP/DMH
RON
1
2
3
4
5
6
[DMIPA] [HSO4] (15 vol.%)
[MDEA] [HSO4] (15 vol.%)
[DEEA] [HSO4] (15 vol.%)
[DMEA] [HSO4] (15 vol.%)
[MEA] [HSO4] (15 vol.%)
[TEA] [HSO4] (25 vol.%)
3.8
2.5
3.5
3.8
2.9
1.9
88.9
92.1
87.3
89.6
87.9
91.5
7.3
5.4
9.1
6.6
9.1
6.6
12.1
12.0
13.5
12.9
10.4
13.5
97.4
97.8
97.4
97.7
97.0
98.0
Reaction conditions: temperature, 10 ◦C; pressure, 0.5 Mpa; reaction time, 10 min; stirring speed, 1000 rpm; the TFOH/IL coupled catalyst, 50 mL; the premixed hydrocarbon
feed, 50 mL; I/O, 10. Data were obtained at full conversion of 1-butene for optimized IL contents.
results are shown in SI (Figs. 5s and 6s). The optimized contents
of [DEEA] [CF3SO3] and [TEA] [CF3SO3] were around 25 vol.% and
40 vol.% respectively for the alkylatio−n. The catalysts of TFOH/ILs
with TFO− and TFOH/ILs with HSO4 were compared in terms
of RON, total C8, 2,2,4-TMP, DMH and other products (Table 2).
The ILs with TFO− showed lower activity and selectivity. This was
presumably because the TFOH/ILs systems with TFO anion can dis-
solve more hydrocarbons, including reaction intermediates, the
products, iso-butane and 1-butene, but with lower I/O ratio. Anions
usually play an important role for the solubility of the hydrocar-
bons in the ILs [32]. The general characteristics of the TFOH/ILs
catalysts are very similar to those of the conventional liquid acidic
Table 2
Comparison of the alkylate composition produced by the optimized TFOH/IL catalysts with [TFO]− and [HSO4]−
.
Components
[DEEA] [HSO4]
(15 vol.%)
[DEEA] [CF3SO3]
(25 vol.%)
[DMIPA] [HSO4]
(15 vol.%)
[DMIPA] [CF3SO3]
(25 vol.%)
[TEA] [HSO4]
(25 vol.%)
[TEA] [CF3SO3]
(40 vol.%)
C5–C7
3.5
51.2
30.1
6.0
3.7
48.0
32.4
5.8
3.8
47.2
34.9
6.8
3.1
44.2
35.5
6.6
1.9
49.9
35.2
6.4
2.0
37.4
42.5
7.3
2,2,4-TMP
Other TMPs
DMH
Total C8
C9+ (%)
RON
87.3
9.1
97.4
86.2
6.3
97.0
88.9
7.3
97.4
86.3
10.6
96.4
91.5
6.6
98.0
87.2
10.7
96.9
Reaction conditions: temperature, 10 ◦C; pressure, 0.5 Mpa; reaction time, 10 min; stirring speed, 1000 rpm; the TFOH/IL coupled catalyst, 50 mL; the premixed hydrocarbon
feed, 50 mL; I/O, 10. Data were obtained at full conversion of 1-butene for optimized IL contents.

34
P. Cui et al. / Catalysis Today 200 (2013) 30–35
Fig. 3. The optimization of [DEEA] [CF3SO3] and [TEA] [CF3SO3] content in the catalyst system. (A) and (C), the product distribution on the IL content in the catalyst system;
(B) and (D), the ratio of TMP to DMH and the RON on the IL content in the catalyst system.
Reaction conditions: the reaction temperature, 10 ◦C; argon pressure, 0.5 MPa; reaction time, 10 min; stirring speed, 1000 rpm; the catalyst, 50 mL (A and B, TFOH/[DEEA]
[CF3SO3]; C and D, TFOH/[TEA] [CF3SO3]); the premixed hydrocarbon feed (iso-butane: 1-butene = 10:1), 50 mL; I/O, 10. (ꢀ) C5–C7; (ꢀ) C8; (ꢁ) C9+; (ꢁ) TMP/DMH; (♦) RON.
Data were obtained at full conversion of 1-butene for optimized IL contents.
catalysts (H2SO4 and HF) for the alkylation reaction. Higher I/O
solubility ratio in the catalyst system is highly favorable for the
hydride transfer (hydride from i-C4 to C8+) rather than for the side
third cycle and did not change much in the next 7 cycles. After 10
using cycles, the catalyst system became a viscous dark-brown gel.
The sulfur content (S) in the products for the 10 reaction cycles
was investigated by element analysis (shown in Fig. 6). The S con-
tent in the products was relatively low in the first five cycles and
increased significantly from 110 ppm at the 6th cycle to 290 ppm at
the 7th cycle. The sulfur in the product should be esters of sulfate
or triflate formed from the intermediates in the catalyst system.
The raising of S content in the products indicated that the acidity of
+
+
chain propagation (the formation of C12 and C16 from C8+). In
addition, TFO− is a weak coordinating anion and this may be harm-
ful to the stability of carbocations, resulting in low selectivity of
C8 and low RON [33]. During Tang’s study [15], the imidazolium-
based ionic liquids with TFO− were also found to produce less
C8 products and more byproducts. In addition, the 2,2,4-sec-TMP+
(−314.80211) is the most stable intermediate, formed by degra-
dation and isomerization of other TMP isomers [34]. High
iso-butane/1-butene solubility ratio is highly favorable for the pro-
duction of iso-octane and 2,2,4-TMP.
3.4. The reusability of the catalyst system
The reusability of TFOH/[TEA] [HSO4] catalyst system was stud-
ied in a batch mode and the results are shown in Figs. 4 and 5. After
every cycle of the reaction, the catalyst was separated from the
hydrocarbon phase through a separation funnel. The TFOH/IL was
the lower layer. The recovered catalyst without further treatment
was used again for the alkylation of iso-butane/1-butene under the
same reaction conditions. As shown from Figs. 4 and 5, the cata-
lyst could be reused at least five cycles with full conversion and
high selectivity of C8 (close to 90%), but deactivated rapidly from
6th cycles. The selectivity of C8, and the RON dropped slowly from
91.5 and 98.0 at the first cycle down to 87.9 and 97.1 at the fifth
cycle and then rapidly down to 82.7 and 95.9 at the sixth cycle.
The selectivity of 2, 2, 4-trimethylpentane decreased slowly in the
10 cycles. But the selectivity of 2,3,4-trimethylpentane increased
gradually from 12.1 wt.% at the first cycle up to 23.2 wt.% at the
Fig. 4. The reusability of the TFOH/[TEA] [HSO4] catalyst.
Reaction conditions: the reaction temperature, 10 ◦C; argon pressure, 0.5 MPa; reac-
tion time, 10 min; stirring speed, 1000 rpm; the TFOH/[TEA] [HSO4] (75/25 by
vol.) catalyst, 50 mL; the premixed hydrocarbon feed (iso-butane: 1-butene = 10:1),
50 mL; I/O, 10. (ꢀ) C5–C7; (ꢀ) C8; (ꢁ) C9+; (♦) RON. Data were obtained at full
conversion of 1-butene for first cycles.

P. Cui et al. / Catalysis Today 200 (2013) 30–35
35
liquids to TFOH and the anion structure have significant effects on
−
the alkylate composition, and HSO4 was much better anion than
TFO− in the ILs for the alkylation process. Furthermore, the cata-
lyst system can be reused at least 5 runs without significant loss of
activity. It was believed the addition of AMILs increased the I/O ratio
in the TFOH/AMILs catalyst system and adjusted the acidity of the
TFOH/AMILs catalyst system, which were beneficial for the alkyla-
tion reaction. Moreover, the addition of ILs changed the interfacial
area and the solubility of the catalyst system with hydrocarbon,
which affected the product compositions.
Acknowledgments
The work was finally supported by the Beijing Natural Sci-
ence Foundation (2122052), and the foundation from State Key
Laboratory of Materials-Oriented Chemical Engineering (grant No.
ZK201003).
Appendix A. Supplementary data
Fig. 5. iso-Octane distributions of the products with the reused TFOH/[TEA] [HSO4]
catalyst.
Reaction conditions: the reaction temperature, 10 ◦C; argon pressure, 0.5 MPa; reac-
tion time, 10 min; stirring speed, 1000 rpm; the TFOH/[TEA] [HSO4] (75/25 by
vol.) catalyst, 50 mL; the premixed hydrocarbon feed (iso-butane: 1-butene = 10:1),
50 mL; I/O, 10. (ꢀ) C5–C7; (ꢀ) C8; (ꢁ) C9+; (♦) RON. Data were obtained at full
conversion of 1-butene for first 7 cycles.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.cattod.
2012.06.008.
References
[1] S.I. Hommeltoft, Applied Catalysis A 221 (2001) 421–428.
[2] T.L.T. Bui, W. Korth, S. Aschauerb, A. Jess, Green Chemistry 11 (2009)
1961–1967.
[3] J. Weitkamp, Y. Traa, Catalysis Today 49 (1999) 193–199.
[4] V.R. Sarsani, B. Subramaniam, Green Chemistry 11 (2009) 102–108.
[5] W. Shen, Y. Gu, H.L. Xu, D. Dube, S. Kaliaguine, Applied Catalysis A 377 (2010)
1–8.
[6] F. Martinez, G. Morales, A. Martin, R. van Grieken, Applied Catalysis A 347 (2008)
169–178.
[7] G. Morales, R. van Grieken, A. Martín, F. Martínez, Chemical Engineering Journal
166 (2010) 388–396.
[8] B.O.D. Costa, C.A. Querini, Applied Catalysis A 385 (2010) 144–152.
[9] A.S. Chellappa, R.C. Miller, W.J. Thomson, Applied Catalysis A 209 (2001)
359–374.
[10] T. Blasco, A. Corma, A. Martinez, P. Martinez-Escolano, Journal of Catalysis 177
(1998) 306–313.
[11] V. Sarsani, Y. Wang, B. Subramaniam, Industrial and Engineering Chemistry
Research 44 (2005) 6491–6495.
[12] M.J. Janik, R.J. Davis, M. Neurock, Journal of Catalysis 244 (2006) 65–77.
[13] G. Baronetti, H. Thomas, C.A. Querini, Applied Catalysis
131–141.
A 217 (2001)
[14] M.A. Harmer, C.P. Junk, V.V. Rostovtsev, W.J. Marshall, Green Chemistry 11
(2009) 517–525.
[15] S. Tang, A.M. Scurto, B. Subramaniam, Journal of Catalysis 268 (2009) 243–250.
[16] J. Esser, P. Wasserscheid, A. Jess, Green Chemistry 6 (2004) 316–322.
[17] R.D. Rogers, Nature 447 (2007) 917–918.
Fig. 6. S content of the products with the reused TFOH/[TEA] [HSO4] catalyst.
the catalyst system became lower than the optimized acidity range
for the iso-butane/1-butene alkylation from the 7th cycle, which
resulted in decreased selectivity of C8 and decreased RON since
appreciable amount of light acid soluble oil (ASO) was formed. The
loss of TFOH in the catalyst system by vaporization, dissolution and
entrainment during the transfer operations may be the main reason
for the acidity reduction in the first five cycles. And the formation
of byproducts, such as light ASO and heavy ASO accelerated the
acidity reduction and the deactivation of the catalyst since the 6th
cycle.
[18] A. Ahosseini, W. Ren, A.M. Scurto, Industrial and Engineering Chemistry
Research 48 (2009) 4254–4265.
[19] M. Antonietti, D. Kuang, B. Smarsly, Y. Zhou, Angewandte Chemie International
Edition 43 (2004) 4988–5499.
[20] J. Bender, D. Jepkens, H.H. Sken, Organic Process Research and Development 14
(2010) 716–721.
[21] S.V. Malhotra, Y. Xiao, Journal of Organic Chemistry 690 (2005) 3609–3613.
[22] M.J. Earle, K.R. Seddon, C.J. Adams, G. Roberts, Chemical Communications
(1988) 2097–2098.
[23] P. Kumar, W. Vermeiren, J.P. Dath, Applied Catalysis A 304 (2006) 131–141.
[24] L. Wang, J.J. Zou, X.W. Zhang, L. Wang, Fuel 91 (2012) 164–169.
[25] J. Zhang, C.P. Huang, B.H. Chen, Journal of Catalysis 249 (2007) 261–266.
[26] J. Zhang, C.P. Huang, B.H. Chen, J.W. Li, Y.X. Li, Korean Journal of Chemical
Engineering 245 (2008) 982–986.
[27] A.S. Berenblyum, E.A. Katsman, Y.Z. Karasev, Applied Catalysis 315 (2006)
128–134.
4. Conclusions
[28] R. Condemarin, P. Scovazzo, Chemical Engineering Journal 147 (2009) 51–57.
[29] L. Ferguson, P. Scovazzo, Industrial & Engineering Chemistry Research 46 (2007)
1369–1374.
[30] Y. Chauvin, A. Hirschauer, H. Olivier, Journal of Molecular Catalysis 92 (1994)
155–165.
[31] W. Chen, Applied Catalysis A 255 (2003) 231–237.
[32] U. Doman´ ska, Pure and Applied Chemistry 77 (2005) 543–557.
[33] G.A. Olah, P. Batamack, D. Deffieux, B. Török, et al., Applied Catalysis A 146
(1996) 107–117.
The alkylation of iso-butane with 1-butene was catalyzed by
TFOH with a series of protic ammonium-based ILs, and the addition
of the ILs dramatically enhanced the alkylation reaction. Up to 85.1%
trimethylpentane selectivity and a high research octane number of
98 were obtained with the optimized TFOH/AMILs catalyst system
(TFOH/[TEA] [HSO4], 75/25 vol.%), which were far better than those
with the commercial H2SO4 and pure triflic acid. The ratio of ionic
[34] P. Wang, D.X. Wang, C.M. Xu, J.S. Gao, Applied Catalysis 332 (2007) 22–26.