Efficient synthesis of amylbenzenes over zeolite catalysts

Article abstract of DOI:10.1246/cl.2007.138

The liquid-phase heterogeneous alkylation of benzene with 2-methyl-2-butene takes place actively and selectively over large-pore zeolite catalysts, which implies an environmentally friendly route for the synthesis of fert-amylbenzene. Copyright

Full text of DOI:10.1246/cl.2007.138

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Chemistry Letters Vol.36, No.1 (2007)
Efficient Synthesis of Amylbenzenes over Zeolite Catalysts
ꢀ
Huanyan Zhang, Yueming Liu, Haihong Wu, Yongwen Jiang, Mingyuan He, and Peng Wu
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry,
East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P. R. China
(Received October 23, 2006; CL-061244; E-mail: pwu@chem.ecnu.edu.cn)
The liquid-phase heterogeneous alkylation of benzene with
-methyl-2-butene takes place actively and selectively over
large-pore zeolite catalysts, which implies an environmentally
phase at 3.5 MPa using a down-flow fixed-bed microreactor.
The reaction was started by injecting the mixture of benzene
and MeB (95%, Acros) into the reactor, and conducted continu-
ously.
2
friendly route for the synthesis of tert-amylbenzene.
The benzene isopentylation showed a relatively complicated
product distribution. The careful analyses with GC-MS have
identified various products. According to the alkylation mecha-
nism shown latter, they could be classified into five categories,
that is, the main product of t-AB; its isomers of sec-amylbenzene
(s-AB); t-butylbenzene (t-BB), and hexylbenzene (HB) isomers;
oligomers (mostly C10-olefins); and heavy products like dialkyl-
benzenes.
tert-Amylbenzene (t-AB) is an important intermediate
chemical in the production of 2-amylanthraquinone (AMQ)
which serves as an efficient working solution in the manufacture
of H2O2.1 Having a better solubility, AMQ gives the higher
catalytic activity, stability, and H2O2 yield than conventional
,2
2-ethylanthraquinone. With an increasing development of
H2O2-based clean chemical processes, the needs of AMQ are
anticipated to increase annually. The conventional manufactur-
ing methods for t-AB, the raw material for AMQ synthesis,
are thus becoming a bottleneck restraining its wide application.
Moreover, t-AB with good solvent properties and a low vapor
pressure proves to be a suitable solvent in pharmaceutical, fine
Table 1 compares the catalytic activity and product selectiv-
ity among ZSM-5, USY, MCM-22, and Beta zeolites. The
activity of ZSM-5 was very poor even when the alkylation
ꢁ
was carried out at a higher temperature of 350 C in gas-phase
(No. 1). The constrained 10-MR pores of MFI structure restrict-
ed the formation of bulky alkylbenzene like t-AB. MCM-22,
Beta and USY zeolites, on the other hand, turned to be signifi-
cantly active. Particularly, Beta and USY were capable of
converting MeB completely (Nos. 3–6). It is reasonable that
the t-AB formation requires a relative open reaction space.
These results are very similar to the benzene alkylation with
3
chemical and electronical manufactures.
The conventional processes for t-AB production are based
on two kinds of catalytic reactions. One is the Friedel–Crafts
alkylation of benzene with 2-methyl-2-butene (MeB) catalyzed
by homogeneous catalysts such as H2SO4, BF3, AlCl3, FeCl2,
1
6
etc. The other is the side-chain alkylation of cumene or ethylene
performed on the solid base catalysts such as alkali metals,
propene to cumene.
MCM-22, a talent catalyst used successfully in the selective
4
7
alkaline earth metal compounds, and alkali metal hydrides.
production of ethylene and cumene, was less active (No. 2).
Both methods suffer the problems such as hard handling, danger,
corrosion, and waste disposal. It is urgent to develop alternative
heterogeneous catalyst systems which are environmentally
benign, benefit, and sustainable.
Owing to the space hindrance effects on bulky molecules, the
benzene isopentylation were presumably restricted to the 12-
MR side pockets on the external surface of crystals rather than
8
two interlayer and interlayer 10-MR channels. The interlayer
Zeolites have been applied successfully to the commercial
processes for the clean production of alkylbenzenes such as cu-
mene and ethylbenzene. These have substituted the convention-
supercages accessible through only 10-MR windows are
seemingly not useful to the present alkylation. Furthermore,
MCM-22 produced more undesirable butylbenzene, hexylben-
zene, and heavy products.
Compared with Beta, USY gave an enhanced selectivity for
BB and HB, and a lower selectivity to s-AB (Nos. 3 and 4). A
declined s-AB selectivity would be favorable of increasing the
t-AB selectivity in ultimate amylbenzene products. Thus, the
5
al alkylation processes operated with phosphoric acid and AlCl3
catalysts. Analogously, it is desirable to develop zeolite-based
innovative, green and heterogeneous chemical process for
t-AB synthesis via benzene alkylation. Nevertheless, unlike
ethylene and propylene, MeB as an alkylation agent is character-
istic of bulkier molecular dimension and higher polymerization
reactivity. This may lead to complicated product distribution
and alkylation behaviors. We communicate here for the first time
the catalytic properties and product distribution of benzene
alkylation with MeB over various zeolites. Large-pore zeolites
of 12-membered ring (MR) have been found to be promising
catalysts for the selective formation of t-AB. The reaction
pathways have been clarified on the basis of the results achieved
with various reaction conditions.
Table 1. The results of benzene isopentylation on zeolitesa
Product distribution/%
Cokec
Conv.
No.
Cat
Si/Al
¼
/%
C10 t-AB s-AB BB+HB Heavy /%
1b ZSM-5 25
<10
91
— —
2.3 64.6
—
8.3
6.2
—
18.5
18.5
7.1
—
6.1
2.5
1.9
3.2
6.0
4.6
6.8
8.0
6.6
5.4
5.6
2
3
4
5
6
MCM-22 15
USY
Beta1
Beta2
Beta3
3.4
100
100
100
98
0
0
0
0
72.8
12
23
34
76.4 14.6
73.9 14.0
71.6 12.1
8.8
10.2
¼
Proton-type zeolites (ZSM-5, Beta, MCM-22, and USY)
were physically mixed with ꢀ-Al2O3 binder at a weight ratio
of 70 to 30 and shaped into particles of 0.83–1-mm diameter.
The alkylation of benzene with MeB was conducted in liquid-
a
ꢂ1
Reaction condition: cat., 0.5 g; pressure, 3.5 MPa; B/C5 , 60; WHSV, 36 h
;
ꢁ
b
ꢁ
Temp, 175 C. This reaction was carried out at 350 C in gas phase. No reliable
c
selectivity was obtained because of too low yield of products. Accumulated
amount of coke at 7 h of TOS (analyzed with TG-DTA).
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.1 (2007)
139
1
00
=
C
10
8
6
0
0
+
Oligomerization
+
=
Isomerization +
4 6
C + C
2
0
0
0
Cracking
1
Benzene
alkylation
C
6
0
.0
0.5
1.0
)
1.5
t-BB
HB
ln ( 1 +
τ
t-AB S1-AB S2-AB
C
m
¼
C
n
Figure 1. Dependence of C5 olefin conversion ( ), selectivity
of t-AB ( ), s-AB ( ), oligomers ( ), and the sum of BB and
HB ( ) on ln (1 + ꢁ). Condition: Beta1, 0.5–1 g; pressure,
Dialkylation
Figure 2. Reaction pathways.
¼
ꢁ
3
.5 MPa; B/C5 , 60; Temp, 150 C. ꢁ, contact time, the recipro-
cal of WHSV in min.
benzene to produce BB and HB. All above monoalkylbenzenes
undergo further alkylation reactions to yield dialkylbenzenes.
The AB selectivity reached ca. 90% when increasing the
t-AB selectivity was very comparable between USY and Beta.
However, USY with high acid concentration suffered a fatal
drawback of shorter catalytic life. It deactivated severely after
¼
benzene/C5 molar ratio to 60. Like the longer contact time,
2
h of time on stream (TOS) owing to rapid coke deposition
the lower olefin concentration favored the formation of amylben-
zenes but disfavored the production of oligomers, BB and HB,
which further supported the reaction pathway proposed.
inside the pores, whereas the life time of Beta prolonged to a
TOS of 24 h.
Beta zeolites with various Si/Al ratios have been synthe-
sized and then applied to the alkylation. With increasing Si/Al
ratio, the catalytic activity decreased slightly, while the produc-
tion of oligomers, BB and HB tended to be enhanced (Nos. 4–6).
These trends suggest that a lower framework Al content, that is
smaller amount of acid sites, favors the oligomerization versus
In conclusion, Beta zeolite appears to be one of the most
efficient catalysts for liquid-phase alkylation of benzene with
MeB. By controlling the framework Al content and reaction con-
ditions such as contact time, reaction temperature and benzene/
C5 ratio, the selective and green production of amylbenzenes
proves to be possible with Beta zeolite catalysts.
¼
9
the alkylation reaction.
Figure 1 shows the dependence of MeB conversion and
product selectivities on the reaction contact time. The selectivity
of oligomers ascended sharply when the contact time approach-
ed to zero. Oligomerization, taking place parallel to the benzene
isopentylation, was undoubtedly one of primary reactions.
With increasing contact time, the oligomer selectivity decreased
gradually, whereas that of BB and HB increased correlatively
and reached a maximum flexion. These results implied that
BB and HB were the secondary products of oligomers. Addition-
ally, the selectivities of t-AB and s-AB increased monotonously
with prolonging contact time.
The reaction mixture cumulatively collected was injected
into the reactor containing Beta zeolite. The composition essen-
tially remained the same, which confirmed us that neither mono-
molecule isomerization of t-AB nor bimolecular trans-alkylation
between t-AB and benzene was feasible because of the thermo-
dynamic respect and the great space hindrance in the channel of
zeolites. s-AB, BB, and HB were thus not the secondary products
from t-AB.
A tentative reaction pathway for the benzene alkylation
with MeB over zeolite catalysts was obtained on the basis of
the reaction results (Figure 2). MeB is initially protonated on
the acid sites to form the active intermediate, t-amyl cations.
The carbenium ions induce uphill isomerization forming the
secondary cations10 as well as oligomerization producing the
oligomers of C10 olefins. The successive alkylations of t- and
s-amyl cations yield the alkylbenzenes of t-AB and s-AB,
respectively. The C10 oligomers formed, in succession, crack
into t-butyl cation and hexene isomers which further alkylate
We are grateful to the financial supports by NCET-04-0423,
Pujiang Program (No. 05PJ14041), 973 Program (No.
2003CB6158019), NSFC (Nos. 20473027 and 20233030), and
STCSM (Nos. 05DZ22306 and 05JC14069).
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Published on the web (Advance View) December 9, 2006; doi:10.1246/cl.2007.138