Ionic liquid and solid HF equivalent amine-poly(hydrogen fluoride) complexes effecting efficient environmentally friendly isobutane-isobutylene alkylation

Article abstract of DOI:10.1021/ja0424878

Isoparaffin-olefin alkylation was investigated using liquid as well as solid onium poly(hydrogen fluoride) catalysts. These new immobilized anhydrous HF catalysts contain varied amines and nitrogen-containing polymers as complexing agents. The liquid poly(hydrogen fluoride) complexes of amines are typical ionic liquids, which are convenient media and serve as HF equivalent catalysts with decreased volatility for isoparaffin-olefin alkylation. Polymeric solid amine:poly(hydrogen fluoride) complexes are excellent solid HF equivalents for similar alkylation acid catalysis. Isobutane-isobutylene or 2-butene alkylation gave excellent yields of high octane alkylates (up to RON = 94). Apart from their excellent catalytic performance, the new catalyst systems significantly reduce environmental hazards due to the low volatility of complexed HF. They represent a new, green class of catalyst systems for alkylation reactions, maintaining activity of HF while minimizing its environmental hazards.

Full text of DOI:10.1021/ja0424878

Published on Web 04/05/2005
Ionic Liquid and Solid HF Equivalent Amine-Poly(Hydrogen
Fluoride) Complexes Effecting Efficient Environmentally
Friendly Isobutane-Isobutylene Alkylation
George A. Olah,* Thomas Mathew, Alain Goeppert, B e´ la T o¨ r o¨ k, Imre Bucsi,
Xing-Ya Li, Qi Wang, Eric R. Marinez, Patrice Batamack, Robert Aniszfeld, and
G. K. Surya Prakash*
Contribution from the Donald P. and Katherine B. Loker Hydrocarbon Research Institute
and Department of Chemistry, UniVersity of Southern California,
Los Angeles, California 90089-1661
Received December 14, 2004; E-mail: olah@usc.edu
Abstract: Isoparaffin-olefin alkylation was investigated using liquid as well as solid onium poly(hydrogen
fluoride) catalysts. These new immobilized anhydrous HF catalysts contain varied amines and nitrogen-
containing polymers as complexing agents. The liquid poly(hydrogen fluoride) complexes of amines are
typical ionic liquids, which are convenient media and serve as HF equivalent catalysts with decreased
volatility for isoparaffin-olefin alkylation. Polymeric solid amine:poly(hydrogen fluoride) complexes are
excellent solid HF equivalents for similar alkylation acid catalysis. Isobutane-isobutylene or 2-butene
alkylation gave excellent yields of high octane alkylates (up to RON ) 94). Apart from their excellent catalytic
performance, the new catalyst systems significantly reduce environmental hazards due to the low volatility
of complexed HF. They represent a new, “green” class of catalyst systems for alkylation reactions,
maintaining activity of HF while minimizing its environmental hazards.
5
Introduction
ethylamine and nitric acid. Many of the room-temperature ionic
Ionic liquids are gaining increasing significance in chemistry.1
liquids are salts of organic cations such as tetraalkylammonium,
tetraalkylphosphonium, N-alkylpyridinium, 1,3-dialkylimida-
Because of the toxic and hazardous nature of alkylation
processes, including widely practiced isoparaffin-olefin alky-
lations in petrochemical industry, great need exists for develop-
ing “greener” and safer reaction systems. This has prompted
the design of less toxic catalysts, which are not only safer but
at the same time efficient and recyclable. Some of the recent
2
a,6
zolium and trialkylsulfonium cations. Efforts by Osteryoung
and Wilkes in the 1970s and Hussey and Seddon
7
,8
9,10
in the
1
980s have given more insight into the properties and use of
ionic liquids and resulted in further development as reaction
media for organic synthesis as well as in biphasic catalysis.1
Since the reports by Wilkes and co-workers in the 1990s of
air and moisture stable imidazolium salts based on tetrafluo-
1,12
reviews discuss the potential of ionic liquids as solvents for
synthesis and catalysis.2,3 Generally, ionic liquids are ionic salts
-
- 13
roborate (BF4 ) and hexafluorophoshate (PF6 ), there has been
an exponential growth in the number and variety of ionic liquids
in recent years. Though less studied than the quarternary
nitrogen-based ionic liquids, their phosphorus-based analogues
such as tetraalkylphosphonium tosylates are used as media for
hydroformylation and tetraalkylphosphonium halides as solvents
for palladium catalyzed Heck reaction and Suzuki cross coupling
(
such as imidazolonium salts, vide infra), the melting points of
4
which are lower than room temperature. Walden in 1914
reported ethylammonium nitrate (mp 12-14 °C) as the first
room-temperature ionic liquid formed by the reaction of
(
1) (a) Welton, T. Chem. ReV. 1999, 99, 2071. (b) Sheldon, R. J. Chem. Soc.
Chem. Commun. 2001, 2399. (c) Bradaric, C. J.; Downard, A.; Kennedy,
C.; Robertson, A. J.; Zhou, Y. H. Strem. Chemiker 2003, 20, 1 and
references therein. (d) Yoshino, T.; Togo, H. Synlett 2004, 1604. (e) Koelle,
P.; Dronskowski, R. Eur. J. Inorg. Chem. 2004, 2989. (f) Benton, M. G.;
Brazel, C. S. Polymer Int. 2004, 53, 1113. (g) Zhou, M.-Y.; Li, Y.-Q. J.
Chem. Res. 2004, 328. (h) Xie, X.; Chen, B.; Lu, J.; Han, J.; She, X.; Pan,
X. Tetrahedron Lett. 2004, 45, 6235. (i) Panchgalle, S. P.; Kalkote, U. R.;
Niphadkar, P. S.; Joshi, P. N.; Chavan, S. P.; Chaphekar, G. M. Green
Chem. 2004, 6, 308. (j) Brausch, N.; Metlen, A.; Wasserscheid, P. J. Chem.
Soc. Chem. Commun. 2004, 1552. (k) Park, S. B.; Alper, H. Tetrahedron
Lett. 2004, 45, 5515.
(5) (a) Walden, P. Bull. Acad. Imper. Sci. (St. Petersburg) 1914, 1800. (b)
Sugden, S.; Wilkins, H. J. Chem. Soc. 1929, 1291.
(6) (a) Chum, H. L.; Koch, V. R.; Miller, L. L.; Osteryoung, R. A. J. Am.
Chem. Soc. 1975, 97, 3264. (b) Robinson, J.; Osteryoung, R. A. J. Am.
Chem. Soc. 1979, 101, 323.
(7) Wilkes, J. S. Green Chem. 2002, 73.
(8) Wilkes, J. S.; Levisky, J. A.; Wilson, R. A.; Hussey, C. L. Inorg. Chem.
1982, 21, 1263.
(
2) (a) Jones, H. L.; Osteryoung, R. A. AdV. Molten Salt Chem. 1975, 3, 121.
(9) Scheffler, T. B.; Hussey, C. L.; Seddon, K. R.; Kear, C. M.; Armitage, P.
D. Inorg. Chem. 1983, 22, 2099.
(b) Pagni, R. M. AdV. Molten Salt Chem. 1987, 6, 211.
(
3) (a) Carlin, R. T.; Wilkes, J. S. AdVances in Nonaqueous Chemistry;
Mamantov, G., Popov, A., Eds.; VCH Publishing: New York, 1994. (b)
Chauvin, Y.; Olivier-Bourbigou, H. CHEM-TECH 1995, 25, 26. (c) Seddon,
K. R. Kinet. Catal. 1996, 37, 693. (d) Olivier-Bourbigou, H. In Aqueous-
Phase Organometallic Catalyis: Concepts and Applications; Cornils, B.,
Hermann, W. A., Eds.; Wliey-VCH: Weinheim, 1998.
(10) Appleby, D.; Hussey, C. L.; Seddon, K. R.; Turp. J. E. Nature 1986, 323,
614.
(11) Boon, J. A.; Levisky, J. A.; Pflug, J. L.; Wilkes, J. S. J. Org. Chem. 1986,
51, 480.
(12) (a) Chauvin, Y.; Gilbert, B.; Gulbard, I. J. Chem. Soc. Chem. Comm. 1990,
1715. (b) Carlin, R. T.; Osteryoung, R. A. J. Mol. Catal. 1990, 63, 125.
(13) Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc. Chem. Comm. 1992, 965.
(
4) Hussey, C. L. AdV. Molten Salt Chem. 1983, 5, 185.
5964
9
J. AM. CHEM. SOC. 2005, 127, 5964-5969
10.1021/ja0424878 CCC: $30.25 © 2005 American Chemical Society

Ionic HF Equivalent Amine-Poly(Hydrogen Fluoride)
A R T I C L E S
Scheme 1
found that hydrogen fluoride, which itself is highly associated
2
1
in the liquid phase, gives poly-hydrogen fluorides not only
with pyridine or picoline, but with many alkyl and arylamines
and their derivatives. These ionic liquids of pyridine, picoline,
triethylamine, or triethanolamine containing up to 70 wt % of
HF give stable solutions which do not lose hydrogen fluoride
noticeably up to 50 °C. The 70% hydrogen fluoride/30%
pyridine solution studied in detail was found to be pyridinium
poly(hydrogen fluoride) containing a small amount of free
hydrogen fluoride in equilibrium acting as a reservoir of HF
and an equivalent of HF reagent. The 70/30 wt % composition
was found to be a convenient and an efficient fluorinating agent
in many organic fluorination reactions. Studies on physical
2
2
23
properties such as density, electrical conductivity, etc. of
amine-poly(hydrogen fluoride) ionic liquids have also revealed
their complexed ionic nature. Our investigations of these onium
poly(hydrogen fluoride) complexes, however, revealed that
higher HF content is needed for suitable catalytic activity for
alkylations and Friedel-Crafts type reactions. Therefore, these
compositions constitute a prominent class of ionic liquids which
can also act as very specific HF equivalent strong acid catalysts.
The 70-95% HF containing modified poly(hydrogen fluo-
ride) ionic liquids and related solid polymeric resins have helped
to alleviate the volatility and toxicity of neat anhydrous HF to
a great extent. A specific application that we report now is the
isobutane-isobutylene/2-butene alkylation using pyridinium
poly(hydrogen fluoride) (PPHF) as a catalyst and ionic reaction
medium. This and related systems are very efficient catalysts
for the alkylation process for producing high octane alkylate
reactions. Recently, Bradaric et al. have developed a diverse
range of new products by pairing tetraalkylphosphonium cations
with various counterions to produce ionic phosphonium liq-
uids.1 Wide range of ionic liquids containing various tetraalkyl-
ammonium and phosphonium cations with a diverse array of
anions are shown in Scheme 1. Many of the alkylammonium
halides are either commercially available or can be easily
prepared by reacting the corresponding haloalkane with amines.
4
+
Pyridinium and imidazolium halides, [emim]Cl (emim is
+
1
-ethyl-3-methylimidazolium cation), [bmim]Cl (bmim is
1
-butyl-3-methylimidazolium cation) etc., can be prepared
15-17
accordingly.
Merck KGaA has developed a number of
2
0
(The basis of UOP’s Alkad process).
halogen free ionic liquids with highly improved physical
properties, which can have wide application in catalysis,
extraction, metal deposition, and batteries.
Results and Discussion
Application of Amine-(HF)n Ionic Liquids (Onium Poly-
Hydrogen Fluorides) in Alkylation. Alkylation of isobutane
with various alkenes is a major process in petroleum industry.
The major alkylation plants utilize anhydrous hydrogen fluoride
Ionic liquids being environmentally benign reaction media,
open up exciting challenges and opportunities to clean catalytic
processes. They can be considered as “green” solvents due to
their low volatilities. Their chemical and physical properties
can be altered by the judicious selection of the components.
Over the years, some of us have explored the use of amine-
poly(hydrogen fluoride) as convenient fluorinating agents. These
24
or sulfuric acid based technology. These technologies however,
carry serious environmental and safety risks. In this context,
extensive efforts have been made to modify the existing
processes and to develop new catalysts, which are environmen-
18
materials are also ionic liquids in their own right.
25
tally more benign and stable. Isomerization of C5-8 paraffinic
Our work began with search for convenient fluorinating
agents using less volatile complexes of HF with varied n-donor
bases. In our extensive studies on amine-HF complexes, we
found that pyridine and its analogues forms remarkably stable
solutions with anhydrous hydrogen fluoride to give pyridinium
poly(hydrogen fluoride) (PPHF, Olah’s reagent)1 Since its
introduction in 1973, its properties as an ionic liquid have,
however, not been extensively explored. Olah and co-workers
hydrocarbons has been achieved with ionic liquids derived from
26
trialkylamine-HCl-AlCl3 combination. Similar catalysts have
been found to be useful for the alkylation of isobutane with
27
butenes. However, these systems due to the ionic combinations
9,20
(
21) (a) McLean, J. N.; Rossotti, F. J. C.; Rossotti, L. H. S. J. Inorg. Nucl.
Chem. 1962, 24, 1549. (b) Janzen, J.; Bartell, L. S. J. Chem. Phys. 1968,
5
0, 3611. (c) Kollman, P. A.; Allen, L. C. J. Chem. Phys. 1970, 52, 5085.
d) Diercksen, G. H. F.; Kraemer, W. P. Chem. Phys. Lett. 1970, 419.
22) Carre, J.; Barberi, P. J. Fluorine Chem. 1990, 50, 1.
(
(
(
14) (a) Bradaric, C. J.; Downard, A.; Kennedy, C.; Robertson, A. J.; Zhou, Y.
H. Green Chem. 2003, 5, 143. (b) Bradaric, C. J.; Downard, A.; Kennedy,
C.; Robertson, A. J.; Zhou, Y. H. ACS Symposium Series 2003, 856, 41.
15) Chan, B. K. M.; Chang, N. H.; Grimment, R. M. Aust. J. Chem. 1977, 30,
(23) (a) Meurs, J. H.; Sopher, D. W.; Eilenberg, W. Angew. Chem., Int. Ed.
Engl. 1989, 28, 927. (b) Huba, F.; Yeager, E. B.; Olah, G. A. Electrochim.
Acta 1979, 24, 489. (c) Laurent, E.; Marquet, B.; Tardivel, R.; Thiebault,
H. Tetrahedron Lett. 1987, 28, 2359. (d) Laurent, E.; Marquet, B.; Tardivel,
R. J. Fluorine Chem. 1990, 49, 115.
(
2
005.
(
16) Hurley, F. H.; Weir, T. P. J. Electrochem. Soc. 1951, 98, 203.
17) Dyson, P. J.; Grossel, M. C.; Sreenivasan, N.; Vine, T.; Welton, T.;
Williams, D. J.; White, A. J. P.; Zigras, T. J. Chem. Soc., Dalton Trans.
(24) (a) Albright, L. F., Ed. Industrial and Laboratory Alkylations, ACS
Symposium Series, Vol. 55, Am. Chem. Soc., Washington, DC. 1977. (b)
(
4
Schulze, J.; Homan, M., C -Hydrocarbons and DeriVatiVes; Springer-
1
997, 1263.
Verlag: Berlin, 1989, Chps. 3, 4. (c) Hoffmann, H. L. Hydrocarbon Proc.
1990, 53. (d) Olah, G. A.; Moln a´ r, AÄ . Hydrocarbon Chemistry; Wiley:
New York, 1995.
th
(
18) Olah, G. A.; Prakash, G. K. S. ORGN-319 In Abstracts of Papers, 228
ACS National Meeting, Philadelphia, PA, August 22-26, 2004.
(
19) (a) Olah, G. A.; Nojima, M.; Kerekes, I. Synthesis 1973, 779. (b) Olah, G.
A.; Nojima, M.; Kerekes, I. Synthesis 1973, 780. (c) Olah, G. A.; Nojima,
M.; Kerekes, I. J. Am. Chem. Soc. 1975, 97, 208. (d) Olah, G. A.; Welch,
J. T.; Vankar, Y. D.; Nojima, M.; Kerekes, I.; Olah, J. A. J. Org. Chem.
(25) (a) Corma, A.; Martinez, A. Catal. ReV. Sci. Eng. 1993, 35, 483. (b) Corma,
A. Chem. ReV. 1995, 95, 559.
(26) Vladimirovna, V. T.; Modestovich, K. L.; Vladislav, K.; Egorovich, Z.
Y.; Houzvicka, J.; John, C. European Patent, 2003, 1310472.
(27) Huang, C.; Liu, Z.; Xu, C.; Liu, Y. ShiyouLianzhi Yu Huagong 2002, 33,
11.
1
979, 44, 3872, and references cited there in.
(
20) Olah, G. A. US. Patent 1991, 5073674.
J. AM. CHEM. SOC.
9
VOL. 127, NO. 16, 2005 5965

A R T I C L E S
Olah et al.
Table 1. Alkylation of Isobutane with Isobutylene and 2-Butene
Catalyzed by Pyridine/HF (1:22) Complex
exp no.
I
II
III
IV
olefin/alkane
isobutylene/isobutane
2-butene/isobutane
ratio
time (min.)
T (°C)
C5
C6
1/12
3
36
6.9
6.4
6.6
1/12
20
36
7.5
7.0
7.5
1/12
1/12
3
36
9.3
2.6
40
32
6.0
5.8
6.2
C7
2.7
C8
51.7
29.8
71.6
28.5
87.3
61.1
34.5
83.1
17
65.8
38.9
83.8
16.2
91.1
41.3
13.4
55.9
44.1
85.9
2
,2,4-TMP
sum C5-C8
C9
RON
+
Figure 1. Pathway for the formation of light and heavy products in the
isobutane/butene alkylation.
90.3
HF:pyridine (or PEI) and were found to be effective for
isoparaffin-olefin alkylation giving high octane alkylate. The
studied systems are highly efficient and economic HF equivalent
catalysts as well as efficient ionic liquid media for alkylation.
Acid catalyzed alkylation is mechanistically considered as a
chain process as shown by eqs 1 and 2. In isobutane-isobutylene
alkylation, efficiency of alkylation is manifested through the
formation of high amounts of 2,2,4-trimethylpentane (2,2,4-
TMP, research octane number ) 100). It is formed through an
Table 2. Alkylation of Isobutane with Isobutylene and 2-butene
Catalyzed by Poly(ethylenimine)/HF (1:22) Complex
exp no.
I
II
III
IV
V
olefin/alkane
isobutylene/isobutane
2-butene/isobutane
ratio
time (min.)
1/12
3
1/24
3
1/12
3
1/24
3
1/12
10
T (°C)
C5
C6
36
4.6
5.1
36
3.7
4.5
36
5.7
5.7
36
3
4.1
36
5
5.5
C7
6
5.9
6.5
5.2
6.6
+
intermediate i-C8 cation that abstracts hydride from isobutane
forming the tert-butyl cation, which keeps the catalytic cycle
going.
C8
64.1
35.8
81.6
18.4
90.8
76.2
42.8
90.3
9.7
66.6
28.6
84.6
15.4
91.4
79.8
35.2
92.1
7.9
67.3
29.9
84.4
15.6
91.7
2
,2,4-TMP
sum C5-C8
C9
RON
+
93.3
93.7
in the involved ionic liquids can give complex products. As
mentioned earlier, we have been interested for some time in
ionic poly(hydrogen fluoride) complexes and developed, for
example a 30/70 pyridinium poly(hydrogen fluoride) based
liquid fluorinating agent. This system, however, is not suitable
as an HF equivalent catalysts for isobutane-isobutylene or
At the same time, a variety of side reactions can occur
depending on the reaction conditions. The i-C8 ion can undergo
2-butene alkylation process to give high octane alkylates. As
+
reported in the present paper only compositions containing
higher ratios of HF effect alkylations. Complexation of HF with
amines reduces the volatility significantly, making it a safer and
more convenient catalyst system for isoparaffin-olefin alkylation.
In the case of accidental release to the atmosphere, toxic HF
aerosol cloud formation is greatly reduced or diminished (up
to 95%) and the acid can be easily neutralized and washed off.
The PEIHF complex generated from ethyleneimine polymer
isomerization through skeletal and nonbranching rearrangements
caused by hydride and methyl shifts giving various isomeric
cations leading to the formation of different octane isomers.
The ion can add to isobutylene to form higher homologues ,
+
+
i-C12 , i-C16 , etc. These cations lead to the formation of heavier
alkanes (by hydride abstraction) or alkenes (by deprotonation).
The larger isomeric carbocations also tend to cleave into smaller
+
+
+
carbocations (C5 , C6 , and C7 ) and alkenes. These cleavage
(
PEI) is highly water soluble, and is still more advantageous
reactions, through a â-scission pattern, can be considered as
28a,b
in the synthesis of alkylates. Our recent studies
have shown
the reverse process of the addition of carbocations to alkenes
that modified HF equivalent systems contain sufficient amount
of immobilized HF, which provides sufficient acidity for the
isomerization of pivalaldehyde to methyl isopropyl ketone.
All presently studied HF complexes of selected poly-
29
(eqs 1-3 and Figure 1).
+
25
+
11
+
13
i-C H f i-C H + i-C H + i-C H + i-C H (3)
1
2
5
7
14
6
6
12
(
ethylenimine) (linear, low molecular weight and high molecular
It is well recognized that the alkylation of isobutane with olefins
depends on the acid strength. Catalyst acidity may affect
differently the major reaction pathway and the side reactions.
The acidity of the onium poly(hydrogen fluoride) complexes
depends on their composition affecting the equilibrium with free
HF, so does their catalytic activity for alkylation. In all of the
alkylation reactions, there was a 98-100% conversion of the
olefin. The alkylate composition and quality varied depending
weight) afforded high quality alkylate. The possible HF
contamination of the alkylate is minimal or can be eliminated
by aqueous washing. The reaction conditions were optimized
using PEIHF and PPHF as typical ionic liquid catalysts with
such variables as temperature, residence time, hydrocarbon ratio,
etc. (See Tables 1 and 2). The useful onium poly(hydrogen
fluoride) ionic liquid systems studied had up-to-a ratio 22:1 of
(
28) (a) Olah, G. A.; Mathew, T.; Goeppert, A.; Rasul, G.; Prakash, G. K. S.;
Esteves, P. M. J. Am. Soc. Mass Spectrosc. 2004, 15, 959. (b) Olah, G. A.;
Mathew, T.; Marinez, E. R.; Esteves, P. M.; Etzkorn, M.; Rasul, G.; Prakash,
G. K. S. J. Am. Chem. Soc. 2001, 123, 11556.
(29) (a) Weitkamp, J.; Jacobs, P. A.; Martens, J. A. Appl. Catal. 1983, 8, 123.
(b) Weitkamp, J.; Ernest, S. In Catalysis 1987; Ward, J. M., Ed.; Studies
in Surface Science and Catalysis, Vol. 38; Elsevier: Amsterdam, 1988; pp
367-382.
5966 J. AM. CHEM. SOC.
9
VOL. 127, NO. 16, 2005

Ionic HF Equivalent Amine-Poly(Hydrogen Fluoride)
A R T I C L E S
Table 3. Stability (Volatility) of HF and Onium Poly(Hydrogen
Scheme 2
Fluorides)
amine:
HF molar
ratio
threshold HF
volatility temp.
C)
HF or amine:
HF complex
amine:
HF wt %
(F, °
HF
pyridine:HF
0:100
15:85
0:100
1:22
1:16
1:12
1:9
18
32
36
42
50
30
36
40
50
23
34
39
32
34
32
32
33
37
24
2
2
3
0:80
5:75
0:70
triethylamine:HF
poly(ethylenimine):HF
18.7:81.3
1:22
1:17
1:15
1:13
1:22
1:12
1:10
1:22
1:18
1:20.3
1:22
1:21
1:18.1
1:22
2
2.7:77.3
5:75
2
2
7.4:72.6
8.9:91.1
15:85
1
7.7:82.3
aniline:HF
17.7:82.3
0:80
2
N,N-dimethylaniline:HF
22:78
17.6:82.4
14:86
26.3:73.7
19.5:80.5
4-picoline:HF
imidazole:HF
quinoline:HF
poly(vinylpyridine):HF
of BH+ ion and fluoride ion with the bulk hydrogen fluoride
1
9d,21,30
(network of hydrogen bonding).
This may not have a
simple correlation with the basicity of the original conjugate
base. Instead, such interactions can be best characterized by the
free energy changes (∆G(l)) for transferring the BH and fluoride
on the different conditions employed. At 36 °C, in 3 min
complete conversion of the olefin was observed.
+
Stability of the Onium Poly(Hydrogen Fluoride) Com-
plexes. The volatility of anhydrous hydrogen fluoride catalyst
can be substantially decreased or eliminated by forming
complexes with organic bases such as ammonia, alkylamines,
pyridine, and varied organic bases. HF complexes of a number
of bases were prepared and the stablility of these ionic liquids
have been studied (as defined by the threshold volatility
temperature). The temperature at which the complex loses more
than 1% weight is referred to as the threshold temperature of
HF-release. The data in Table 3 show that the threshold
temperature of volatility increases with increasing molar ratio
of bases to HF but changes little with the use of different bases
ion from gas phase into the hydrogen fluoride solution.
HF Immobilized on Solid Polymeric Amines as Alkylation
Catalysts. Attempts to replace liquid acid catalysts by solids
for efficient alkylation process have not yet been fully success-
3
1
ful. A wide variety of solid acids such as Nafion-H/silica
3
2
nanocomposite, sulfated zirconia and heteropoly acid deriva-
3
3
tives have been tested. Despite promising laboratory results,
fast deactivation of the catalyst impeded industrial application.
However, due to its enormous potential and practical importance,
solid acid catalysis is still in the forefront of alkylation
3
4
research. The immobilization of hydrogen fluoride with
35
polymers was first reported by Zupan and co-workers with
limited success. More recently, we reported the preparation of
a well immobilized form of hydrogen fluoride, i.e., poly(4-
vinylpyridinium) poly(hydrogen fluoride) (PVPHF, Scheme 4)
(mentioned in Table 3) in same molar ratio. Threshold volatility
temperature (F) of HF (18 °C) increases to 32 °C with the
addition of 15% (by weight) of pyridine.
3
6
We found that there are no simple relationships between the
basicity of the used additives and the stability of its correspond-
ing onium poly(hydrogen fluoride) ionic liquids formed with
the same molar ratio. For example, aniline, and N,N-dimethyl-
and its use as versatile fluorinating agent. Herein, we also
report the development and application of related environmen-
tally friendly solid HF complexes as alkylation catalysts to
produce high octane gasoline. Their use minimizes the envi-
ronmental hazards and provides easy and safe handling as these
catalysts can easily be separated from the alkylate and re-
+
aniline (pKa of BH 3-5) are much weaker bases compared to
+
+
pyridine (pKa of BH 9) and alkylamines (pKa of BH 10-
2). However, aniline:HF (molar ratio 1:22) and pyridine:HF
molar ratio 1:22) complexes have equal threshold decomposi-
3
7
1
(
cycled.
As a convenient solid catalyst base, commercially available
polymeric poly(4-vinylpyridine) (PVP) resin has been selected
giving the corresponding poly(hydrogen fluoride) complex
(PVPHF). The catalyst for alkylation reactions can be prepared
tion temperature of 32 °C. The process of the formation of
onium poly(hydrogen fluoride) can be divided into two steps,
+
-
i.e., the formation of BH and F in the gas phase by reacting
one mole base with one mole HF (reaction 4) and the process
3
6
easily by following our earlier method. The alkylation of
+
-
of transferring the BH and F ions from the gas phase into
the poly(hydrogen fluoride) liquid phase (eq 5).
(
(
(
30) McLean, C.; Mackor, E. L. J. Chem. Phys. 1961, 34, 2207.
31) Albright, L. F. Chemtech 1998, 46.
32) Corma, A.; Martinez, A.; Martinez, C. J. Catal. 1994, 149, 52.
B(g) + HF(g) f BH+ + F ∆G(g)
-
(33) Okuhara, T.; Yamashita, H.; Na, K.; Misono, M. Chem. Lett. 1994, 1451.
(34) (a) Olah, G. A.; Prakash, G. K. S.; T o¨ r o¨ k, B.; T o¨ r o¨ k, M. Catal. Lett. 1996,
(4)
(5)
(g)
(g)
4
0, 137. (b) Olah, G. A.; Marinez, E.; T o¨ r o¨ k, B.; Prakash, G. K. S. Catal.
+
-
+
-
n(l)
Lett. 1999, 61, 105. (c) Satoh, K.; Matsuhasi, H.; Arata, K. Chem. Lett.
1999, 231. (d) Zhao, Z.; Sun, W.; Yang, X.; Ye, X.; Wu, Y. Catal. Lett.
BH( + F + nHF f BH F(HF) ∆G(l)
g)
g
(l)
2000, 65, 115. (e) Clet, G.; Goupil, J. M.; Szabo, G.; Cornet, D. Appl.
Catal. A 2000, 202, 37.
Obviously basicity is a determining factor for the thermodynam-
(35) Zupan, M.; Sket, B.; Johar, Y. J. Macromol. Sci.-Chem. A 1982, 17, 759.
(36) (a) Olah, G. A.; Li, X.-Y. Synlett 1990, 267. (b) Olah, G. A.; Li, X.-Y.;
Wang, Q.; Prakash, G. K. S. Synthesis 1993, 693.
+
ics of BH formation. However, the stability of the onium poly-
(hydrogen fluoride) probably largely depends on the interaction
(37) Olah, G. A., US. Patent 2002, 6677269.
J. AM. CHEM. SOC.
9
VOL. 127, NO. 16, 2005 5967

A R T I C L E S
Scheme 3
Olah et al.
Scheme 4
Table 5. Comparison of N-Containing Polymer Immobilized HF
Catalysts with HF and Sulfuric Acid in the Isobutane-Isobutylene
Alkylation
catalyst
HF
H
2
SO
4
PPHF
PEIHF
PVPHF
olefin/alkane
isobutylene/isobutane
ratio
time (min.)
T (°C)
C5
C6
1/12
3
36
4.1
3.7
5.0
1/12
20
36
9.0
8.1
8.4
1/12
40
32
6.0
5.8
6.2
1/24
3
36
3.7
4.5
5.9
1/24
3
36
3.8
4.5
Table 4. Effect of Experimental Variables on the Alkylation of
Isobutane with Isobutylene/2-Butene Catalyzed by PVPHF
Complex
C7
5.7
C8
77.5
48.4
90.4
9.6
39.2
14.2
64.7
35.3
86.4
65.8
38.9
83.8
16.2
91.1
76.2
42.8
90.3
9.7
74.5
44.4
88.5
11.5
92.9
exp no.
I
II
III
IV
V
VI
VII
2,2,4-TMP
sum C5-C8
C9
RON
olefin/alkane isobutylene/isobutane
2-butene/isobutane
1/12 1/24 1/12 1/12 1/24
+
ratio
time (min.)
1/12
3
1/24
3
93.6
93.3
3
36
3
36
10
36
10
22
10
7
T (°C)
C5
C6
36
5.1
5.3
36
3.8
4.5
4.4
2.9
4.1
3.6
7.4
2.1
2.6
4.5
5.5
3.5
4.9
4.7
6
2.7
4.2
cracking. Since the HF alkylation reactions are carried out in
practice at 35-37 °C, we carried out majority of these reactions
at 36 °C except for temperature dependence studies.
The effect of residence time and temperature of the reaction
can be identified from change in the yield and quality of the
alkylate within given limits (Table 4). The alkylate quality
increases with longer reaction time and higher temperature (7-
C7
6.2
5.7
C8
67.9
39.9
84.5
15.5
91.3
74.5
44.4
88.5
11.5
92.9
73.7 81.8 70
33.1 38.8 31.7 32.3 27.4
73.7 68.8
2
,2,4-TMP
sum C5-C8
C9
RON
88
12
93.1 84.7 84.2 80.9
6.9 15.3 15.8 19.1
+
92.5 94
91.3 93
93.4
3
6 °C). However, this increase becomes limited after 20 min
isobutane with isobutylene/2-butene was carried out in a
pressurized well stirred closed batch reactor.38 The solid catalyst
was found to be stable at room temperature for prolonged times
and was repeatedly reused.
The structure of the polymeric resin expectedly has a
significant effect on the complex formation with HF. Linear
reaction time. Most likely the system reaches a close-to-
equilibrium state and the product distribution does not change
significantly further. One of the most important parameters is
the ratio of the alkane:alkene hydrocarbon mixture. Under
standard conditions isobutane: isobutylene ratio (molar) of 12:1
was used. Increase in this ratio to 24:1 significantly increased
the alkylate quality. As shown, the distribution of the most
valuable C8 fractions and isooctane increased considerably. This
enhancement is due to the dilution effect by the higher amount
of isobutane (hydride source), which increases the efficiency
of hydride-transfer to the cations formed, and suppresses the
(
(
non cross-linked) PVP did not give practically useful poly-
hydrogen fluoride) complex, it did not swell but formed only
a highly viscous and sticky material. Cross-linked samples can
immobilize limited amounts of HF, the swelling of the 25%
cross-linked sample is strongly limited due to the rigid backbone.
PVP with 2% cross-linking was found to be most suitable for
poly(hydrogen fluoride) complex preparation for catalytic
purpose, since it could immobilize high amount of HF (up to a
HF to PVP weight ratio ∼5) still remaining as a convenient
solid. As a result, alkylations were carried out using commercial
+
oligomerization reactions responsible for higher C9 hydrocar-
bons. Since the acidity of HF (containing some moisture) is
∼
H0 ) -11 (This is -15.1 if completely devoid of water), the
addition of polymeric organic bases in relatively small amounts
usually in HF/N ) 22 ratio) does not decrease the acidity below
(
(Sigma-Aldrich) 2% cross-linked PVP. For reported fluorination
3
9
the known optimum, that is ∼H0 ) -10.8 for alkylation
reactions PVPHF complex containing about 7 equivalents of
hydrogen fluoride to one equivalent of 4-vinylpyridine unit was
reactions.
Since the catalyst’s lifetime, regeneration and recycling are
also important factors in the evaluation of new catalyst system,
we tested the catalyst recycling in the alkylation reactions. The
PVPHF catalyst was reused in several concecutive reactions by
removing the alkylate from it and introducing the new reactant
mixture. The catalyst showed similar performance in the first
four reactions though noticeable change in selectivity/product
3
6
used. However, PVPHF complex containing 22 equivalents
of hydrogen fluoride to one equivalent of 4-vinylpyridine unit
has been used for alkylations due to the higher acidity
requirement of the reaction. As shown in Table 4, the product
distribution gradually changes with change in temperature.
Increase in temperature resulted in higher amount of light
products (C5-C7 fractions), with decrease in the amounts of
+
quality with higher ratio of C9 fraction was observed in further
reactions. This is most likely due to acidity decrease by slow
+
higher oligomers (C9 fraction). These changes are due to the
increasing acidity of the catalyst system, which initiates more
(
39) Olah, G. A.; Batamack, P.; Deffieux, D.; T o¨ r o¨ k, B.; Wang, Q.; Moln a´ r,
(38) Huston, T., Jr.; Logan, R. S. Hydrocarbon Proc. 1975, 54, 107.
AÄ .; Prakash, G. K. S. Appl. Catal. A 1996, 146, 107.
5
968 J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005
9

Ionic HF Equivalent Amine-Poly(Hydrogen Fluoride)
A R T I C L E S
HF leaching from the catalyst. The PVPHF systems have
catalytic efficiency comparable to that of HF with substantial
decrease of HF volatility. The alkylate quality obtained with
the amine based HF catalysts considerably exceeds that obtained
with H2SO4 and is very close to that obtained with neat HF
second autoclave (B, 600 mL, Monel) equipped with a dip tube reaching
to the bottom of the reactor 186 mL isobutane and 14 mL isobutylene
(12:1 molar ratio isobutane:isobutylene) were mixed at -78 °C. B was
than pressurized with argon to 500 psi and allowed to reach room
temperature. The dip tube of B was connected to the addition tube of
A and the isobutane/isobutylene mixture added to the acid phase under
stirring (720 rpm), maintaining the temperature of A at 36 °C using a
cooling loop. Addition valve was closed after a pressure of 200 psi
was reached in A. After 3 min, stirring was turned off and reaction
mixture was cooled to -78 °C (15 min). The pressure was slowly
released and the 2 phases were separated in a Nalgene separatory funnel.
The organic phase was placed in a 125 mL Nalgene flask over a known
amount of PVP to remove any amount of HF present in the alkylate,
allowed to reach 0 °C (ice bath) and stored in a freezer.
(Table 5). All the alkylates have suitable high octane charac-
teristics.
Conclusion
In conclusion, new environmentally safe, immobilized liquid
and solid modified HF catalysts were developed and used for
isobutane-olefin alkylations. Being ionic complexes of amines
and anhydrous HF, the ionic liquid compositions are efficient
media and HF equivalent catalysts for alkylations. They decrease
the volatility of anhydrous HF and as a result, HF release to
the atmosphere in case of accidents is decreased allowing easy
neutralization. The handling, use, recycling and regeneration
of the catalysts are convenient. Both the liquid and solid polymer
based poly(hydrogen fluoride) catalysts can be advantageously
applied in alkylation process representing environmentally
benign and safer conditions readily adaptable to the existing
refinery alkylation units.
GC analysis was performed on a Varian 3400 chromatograph
equipped with a FID and a petrocol DH 50.2 column (50 m × 0.2 mm
×
0.5 µm column head pressure 35 psi Helium) with temperature
program: 70 °C for 12 min, 15 °C/min to 220 °C, 10 min at 220 °C.
Prior to use the syringe was placed in a freezer to enable injection of
the cold alkylate.
The actual amount of alkylate obtained after reaction was determined
by subtracting the amount of isobutane present in the organic phase
+
(determined by GC). Once the alkylate amount (C
5
-C
9
) is known
the yield in C
, C , and C
5
and C
5
-C
8 5
can be determined. Identification of the C ,
C
6
7
8
hydrocarbons was based on comparison with authentic
Experimental Section
samples, while heavier hydrocarbons, except 2,2,5-trimethylhexane,
were not individually identified and treated as C9+ fraction. The
numerical results are given in wt % and the research octane numbers
Materials and Methods. Caution! HF and HF-amine complexes
are highly corrosiVe and can cause seVere damages to eyes, skin and
lungs. Precautions haVe to be taken (wearing proper safety masks,
gloVes and glasses) while handling them. Isobutane, isobutylene and
38
were calculated as described in the literature.
Determination of the Threshold Temperature of HF-Release of
Amine-HF Complexes. Into a 100 mL Nalgene bottle was charged
2
-butene were commercially available from Matheson (>99% purity)
and Sigma-Aldrich and used without further purification. Anhydrous
HF (Matheson, >99.5% purity) was condensed in an acetone-dry ice
bath and was used in liquid form. Pyridine, poly(ethylenimine) (Linear,
low molecular weight or high molecular weight) Poly(4-vinylpyridine)
7
0 g of the onium poly(hydrogen fluoride) and fitted at its top with a
polyethylene tube (diameter, 2 mm) which was kept under N at
2
atmospheric pressure. The bottle was then kept in a thermostatically
controlled bath at the chosen temperature for 1 h. The weight change
after the treatment was measured. The bath temperature was raised by
increments of 1 °C until more than 1% weight loss was found at a
given temperature. The temperature at which the complex loses more
than 1% weight is referred to as the threshold temperature of HF-release.
(2% cross linked) and all amines were purchased from Aldrich and
used as received.
The catalysts were prepared on the basis of methods described
earlier.1
9d,36
Pyridine (15 g) was taken into a 250 mL Nalgene bottle
and cooled in a dry ice-acetone bath (-78 °C). Liquid HF (85 g) was
added carefully in small portions (a few drops initially and increase
the amount slowly) at -78 °C. Complex is stored in a refrigerator.
Typical Alkylation Procedure. An autoclave (A, 600 mL, Monel)
equipped with a dropping tube reaching to half of the height of the
reactor was purged with argon and loaded with 100 g PPHF catalyst at
Acknowledgment. Support of our work by Loker Hydrocar-
bon Research Institute is gratefully acknowledged. A.G. grate-
fully acknowledges the Minist e` re des Affaires Etrang e` res
Fran c¸ ais for financial support (Lavoisier fellowship).
-
78 °C. It was then warmed to 36 °C under stirring (720 rpm). In a
JA0424878
J. AM. CHEM. SOC.
9
VOL. 127, NO. 16, 2005 5969