Isomerization of α-Pinene over Immobilized AlCl3 Catalysts

Article abstract of DOI:10.1016/S1872-2067(10)60244-6

Immobilized AlCl₃ catalysts supported on γ-Al₂O₃ and SiO₂ were prepared by a two-step vapor method and their catalytic activities were evaluated by the liquid phase isomerization of α-pinene for the first time. The results showed that the immobilized AlCl₃ catalyst gave excellent catalytic performance for the isomerization of α-pinene. The AlCl₃/SiO₂ catalyst gave 98.4% conversion of α-pinene and 93.7% selectivity for the main products such as camphene, limonene, and terpinolene at a reaction temperature of 40 °C. The AlCl₃/γ-Al₂O₃ catalyst gave much higher activity, 95.5% conversion of α-pinene and 94.4% selectivity for the main products even at temperatures as low as 30 °C. The excellent catalytic performance of the immobilized AlCl₃ catalysts is due to their strong acidity.

Full text of DOI:10.1016/S1872-2067(10)60244-6

CHINESE JOURNAL OF CATALYSIS
Volume 32, Issue 7, 2011
Online English edition of the Chinese language journal
Cite this article as: Chin. J. Catal., 2011, 32: 1138–1142.
SHORT COMMUNICATION
Isomerization of Ơ-Pinene over Immobilized AlCl3 Catalysts
WU Yihui, TIAN Fuping*, HE Min, CAI Tianxi
State Key Laboratory of Fine Chemicals, Institute of Chemistry, Dalian University of Technology, Dalian 116024, Liaoning, China
Abstract: Immobilized AlCl3 catalysts supported on Ȗ-Al2O3 and SiO2 were prepared by a two-step vapor method and their catalytic ac-
tivities were evaluated by the liquid phase isomerization of Į-pinene for the first time. The results showed that the immobilized AlCl3
catalyst gave excellent catalytic performance for the isomerization of Į-pinene. The AlCl3/SiO2 catalyst gave 98.4% conversion of Į-pinene
and 93.7% selectivity for the main products such as camphene, limonene, and terpinolene at a reaction temperature of 40 °C. The
AlCl3/Ȗ-Al2O3 catalyst gave much higher activity, 95.5% conversion of Į-pinene and 94.4% selectivity for the main products even at tem-
peratures as low as 30 °C. The excellent catalytic performance of the immobilized AlCl3 catalysts is due to their strong acidity.
Key words: immobilization; aluminum chloride; Į-pinene; isomerization; silica; alumina;
Į-Pinene is the main component of turpentine, which is the
most abundantly produced natural essential oil in the world.
Although turpentine has been used directly and extensively as a
solvent, a diluent, and a skin irritant etc., more attention should
be paid to the exploitation and utilization of its potential value
[1]. Į-pinene, as one of the most important bicyclic monoter-
penes, is a very reactive substrate because of its unique struc-
ture. A large number of fine chemicals and raw materials have
been obtained by these acid catalyzed reactions such as the
isomerization, esterification, and polymerization of Į-pinene
[2]. The products obtained by the acid catalyzed isomerization
of Į-pinene are important intermediates for perfumes, phar-
maceuticals, flavors, and fine chemicals. For example, cam-
phene is obtained by ring expansion and is the main raw ma-
terial for the synthesis of compounds such as camphor, santal,
and toxaphene. Limonene is obtained by ring opening and it
possesses an antitumor effect but it can also be used to syn-
thesize many perfumes such as carvone, lavender alcohol, and
menthol (Scheme 1). Therefore, it is of great economic interest
to transform turpentine into high value products.
Į-pinene and the selectivity toward the target products with
high values cannot usually be achieved simultaneously because
of the complexity of this reaction, further study is necessary to
find effective catalysts that will function under mild reaction
conditions. Therefore, developing an environmentally friendly
catalyst with high performance, low cost, and high selectivity
toward the main products is the main objective of much re-
search. Immobilized AlCl3 catalysts, which give unique cata-
lytic performance for aromatic alkylation and olefin polym-
erization [11–14] are a type of environmentally friendly and
high activity solid acid catalyst. This paper, for the first time,
reports on the isomerization of Į-pinene upon catalysis by
immobilized AlCl3 catalysts, which showed high catalytic
performance and selectivity toward the main products such as
camphene, limonene, and terpinolene under mild conditions.
The immobilized AlCl3 catalysts were prepared by a
two-step method. Silica gel and Ȗ-Al2O3, which are produced
by the Qingdao Haiyang Chemical Plant Co. and the Changling
Petrochemical Refining Co., China, respectively, were used as
supports. First, the Ȗ-Al2O3 support was dehydrated at 400 °C
in a lower reactor under a N2 stream for 2 h before use. The
AlCl3 that was produced in situ by the reaction between CCl4
and pure Ȗ-Al2O3 in an upper reactor at 500 °C was carried into
the lower reactor by a N2 stream and it was immobilized on the
pretreated support at 300 °C for 3 h. After that, excess and
physically adsorbed AlCl3 was removed by flowing N2 at 400
Various types of catalysts such as metal oxides [3], heter-
opolyacids [4], ion exchanged resins [5], clays [6], solid su-
peracids [7], and micro- or mesoporous molecular sieves
[8–10] have been investigated for the isomerization of
Į-pinene. Considering that industrial Į-pinene isomerization is
an energy consuming process and that the conversion of
Received 15 April 2011. Accepted 16 May 2011.
*Corresponding author. Tel: +86-411-84708901; Fax: +86-411-84706313; E-mail: fptian@dlut.edu.cn
Copyright © 2011, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(10)60244-6

WU Yihui et al. / Chinese Journal of Catalysis, 2011, 32: 1138–1142
H+
H+
H+
Á-pinene
pinanyl cation
isobornyl cation
H+
p-methenyl cation
H+
terpinolene
camphene
limonene
Á-terpinene Ã-terpinene
Scheme 1. Reaction pathway for Į-pinene isomerization[2].
°C. Finally, the immobilized catalysts were cooled to room
temperature under N2 protection and the resultant catalyst was
denoted AlCl3/Ȗ-Al2O3. A catalyst supported on SiO2 was also
prepared as per the above description except that the pre-
treatment and the purging process were carried out at 300 °C.
The resultant catalyst was denoted AlCl3/SiO2. The chloride
content of the catalyst was determined by potentiometric titra-
tion. The isomerization reaction was carried out at atmospheric
pressure in a glass reactor with a reflux condenser under con-
tinuous magnetic stirring. For a typical run, 0.10 g of the
catalyst and 2 ml of Į-pinene (Aldrich, 98%) were charged into
the reactor. The reaction time and temperature were investi-
gated systematically. The samples were analyzed using a gas
chromatograph equipped with a flame ionization detector
(FID) and a HP 6890N-5975B (GC-MS). The conversion of
Į-pinene and selectivity toward the products were obtained by
the area normalization method.
Table 1 shows the catalytic performance of the AlCl3/SiO2
catalyst for Į-pinene isomerization at different temperatures.
AlCl3/SiO2 gave high catalytic activity and the conversion of
Į-pinene increased significantly with an increase in the tem-
perature. Almost 100% conversion of Į-pinene was achieved at
60 °C for 30 min but the selectivity toward camphene and
limonene decreased while the amount of high retention prod-
ucts increased. The reduction of limonene indicated that
limonene transformed into Į- and Ȗ-terpinene by consecutive
reactions at relatively high temperatures (Scheme 1). Increas-
ing the reaction time at a relatively low temperature (Fig. 1)
100
(1)
80
60
40
20
0
(3)
The chemical analysis results indicate that the mass fractions
of [–O–AlCl2] on SiO2 and Ȗ-Al2O3 were 10.6% and 8.5%,
respectively. Previous studies have shown that the immobili-
zation of AlCl3 onto the surface of supports can be achieved by
the reaction between AlCl3 and the surface hydroxyl groups on
the support and this is accompanied by HCl release [15,16].
Over 90% of the chloroaluminum species on the surface of the
immobilized catalyst have a composition of [–O–AlCl2].
Therefore, the different [–O–AlCl2] loadings on the SiO2 and
Ȗ-Al2O3 supports can be attributed to different amounts of
surface hydroxyl groups.
(2)
(4)
20
40
60
80
100
120
Reaction time (min)
Fig. 1. Effect of reaction time on Į-pinene isomerization over the
o
AlCl3/SiO2 catalyst at 40 C. (1) Conversion of Į-pinene; (2) Selectivity
for camphene; (3) Selectivity for limonene; (4) Selectivity for terpino-
lene.
Table 1 Catalytic performance of the immobilized AlCl3/SiO2 catalyst during Į-pinene isomerization
Reaction time
Reaction temperature
Conversion
(%)
Selectivity (%)
Limonene
Entry
(min)
30
(oC)
Camphene
31.7
Terpinolene
Others
3.4
1
2
3
4
30
40.0
56.8
56.0
55.3
46.7
8.1
9.1
30
40
75.0
31.3
3.6
30
50
88.0
30.2
9.8
4.7
30
60
99.8
28.5
13.4
11.4

WU Yihui et al. / Chinese Journal of Catalysis, 2011, 32: 1138–1142
Table 2 Catalytic performance of the immobilized AlCl3/Ȗ-Al2O3 catalyst during Į-pinene isomerization
Reaction time
Reaction temperature
Conversion
(%)
Selectivity (%)
Limonene Terpinolene
Entry
(min)
30
(oC)
Camphene
41.2
Others
3.5
1
2
3
4
30
80.6
53.9
52.7
52.5
51.3
1.4
1.7
1.8
1.5
30
40
96.4
40.6
5.0
30
45
100.0
95.5
40.6
5.1
60
30
41.6
5.6
resulted in an evident improvement in the conversion of
Į-pinene whereas selectivity toward camphene and limonene
remained nearly constant. For example, 98.4% Į-pinene con-
version and 93.7% selectivity toward the main products were
obtained when the reaction was carried out at 40 °C for 120
min.
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