The catalytic properties of tungstated zirconia in n-heptane isomerization

Article abstract of DOI:10.1134/S0965544112020119

The catalytic properties of zirconia modified with different amounts of tungstate anions in the hydroisomerization of n-heptane and its mixtures with benzene or toluene have been studied. It has been found that at a low temperature of 170°C, the yield of isoheptanes reaches 62.8% with a fairly high selectivity of 87.6% on the Pt/WO²_4-/ZrO₂ catalyst prepared by impregnation to contain 17.6 mol % tungstate anions. Under the same conditions, the yield of isoheptanes on a sulfated Pt/SO ²_4-/ZrO₂ catalyst is as low as 14.0% with a selectivity of 20.3%. The hydroisomerization process effectively occurs on the tungstated catalyst in the presence of benzene or toluene. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0965544112020119

ISSN 0965ꢀ5441, Petroleum Chemistry, 2012, Vol. 52, No. 2, pp. 86–90. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © L.I. Kuznetsova, A.V. Kazbanova, P.N. Kuznetsov, 2012, published in Neftekhimiya, 2012, Vol. 52, No. 2, pp. 104–108.
The Catalytic Properties of Tungstated Zirconia
in nꢀHeptane Isomerization
L. I. Kuznetsova, A. V. Kazbanova, and P. N. Kuznetsov
Institute of Chemistry and Chemical Technology, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, Russia
eꢀmail: kpn@icct.ru
Received September 12, 2011
Abstract—The catalytic properties of zirconia modified with different amounts of tungstate anions in the
hydroisomerization of nꢀheptane and its mixtures with benzene or toluene have been studied. It has been
found that at a low temperature of 170°C, the yield of isoheptanes reaches 62.8% with a fairly high selectivity
2
–
of 87.6% on the Pt/WO /ZrO catalyst prepared by impregnation to contain 17.6 mol % tungstate anions.
4
2
2–
Under the same conditions, the yield of isoheptanes on a sulfated Pt/SO /ZrO catalyst is as low as 14.0%
4
2
with a selectivity of 20.3%. The hydroisomerization process effectively occurs on the tungstated catalyst in the
presence of benzene or toluene.
DOI: 10.1134/S0965544112020119
The efficient use of hydrocarbon resources, such as including those based on chlorinated alumina, various
light hydrocarbon feedstock derived from crude oils types of zeolites, mesoporous aluminosilicates and silꢀ
and gas condensates, is an urgent problem of the icates (such as MCM), silicoaluminophosphates
petroleum refining industry. Straightꢀrun gasoline (SAPO), salts of heteropoly acids, anionꢀmodified
fractions contain significant amounts of
with a low octane number. One of the effective ways of carbides of molybdenum and tungsten [11–19]. The
nꢀalkanes metal oxides, and catalysts based on porous oxides and
using them for manufacturing highꢀperformance gasꢀ
olines is isomerization yielding highꢀoctane skeletal
isomers that satisfy all requirements for quality and
miscibility. At the same time, the requirements for the
environmental characteristics of motor fuels have also
sharply increased. Both international and domestic
standards for gasolines introduce everꢀtightening
restrictions on the content of toxic aromatic hydrocarꢀ
bons, first of all, benzene (up to 1%) [1, 2].
most active and selective platinized catalysts based on
aluminum chloride, which give a possibility to run the
process at a low temperature (below 180
based on highꢀsilica zeolites, which are efficient at
higher temperatures (above 250 ), have found wide
°С), and those
°
С
use in industrial processes [4–7, 20, 21]. New catalysts
based on sulfated zirconia have gained acceptance in
recent years; they are superior to zeolites in catalytic
activity and are highly competitive with chlorinated
alumina. In particular, sulfated zirconia catalysts
The above factors are responsible for the recent
keen demand for process technologies of isomerizaꢀ manufactured by Neftekhim are used at some domesꢀ
tion of n
ꢀalkanes to skeletal isomers. These processes tic plants [2, 7].
are used in the developed countries of Western Europe
and in the United States, where the proportion of
isomerizates in the gasolines produced is at least 5%;
in Russia, it does not exceed 1.5% [3]. Moreover, most
of the catalysts used in the existing isomerization units
in Russia are imported [2–9]. The development of
efficient domestic catalysts for the isomerization of
alkanes is one of the important lines in the developꢀ conia modified with
ment of Russian oil refining. The isomerization of
alkanes to skeletal isomers is a reversible exothermic
process; low temperatures favor the formation of highꢀ
octane isoalkanes with a high yield [10]. Therefore,
the process performance characteristics are largely
determined by catalyst activity.
It is noteworthy that currently existing industrial
catalysts are used for the isomerization of nꢀbutane
and lowꢀboilingꢀpoint pentane–hexane petroleum
fractions. They are not very effective in the isomerizaꢀ
tion of alkanes with longer hydrocarbon chains
because of low selectivity. The catalysts based on zirꢀ
2
–
2–
W
O4 and MoO4 anions are of
everꢀgrowing interest for this purpose [5, 13, 22].
However, the physicochemical principles of their forꢀ
mation and catalytic activity are still poorly underꢀ
stood and the data of different authors are often conꢀ
tradictory. In many respects, this can be attributed to
the metastability of the active modification of zircoꢀ
There are a large number of studies reported in the nia, which is responsible for the fact that its structural
literature on the synthesis and analysis of the isomerꢀ characteristics and catalytic activity substantially
ization properties of various types of acid catalysts, depend on the preparation procedure.
86

THE CATALYTIC PROPERTIES OF TUNGSTATED ZIRCONIA
87
The aim of this study is to analyze the influence of
Surface
2
5
80
60
40
20
the concentration of tungstate anions on the properꢀ
2
4
–
ties of Pt/W
O
/ZrO2 catalysts in the
nꢀheptane
hydroisomerization reaction and to compare them
with the properties of sulfated zirconia.
20
15
EXPERIMENTAL
The catalysts were prepared by impregnating amorꢀ
phous zirconium hydroxide with an aqueous solution
10
5
Pores
of ammonium metatungstate [(NH ) (H W O )
·
4
6
2
12 40
1
8H O]. The thermal treatment of the modified
2
hydroxide was carried out at a temperature of 700
°С.
Platinum was deposited from a solution of chloroplaꢀ
0
4
8
12 16 20 24
Concentration of WO2–
mol %
tinic acid by impregnating calcined oxide samples of
,
2
4
–
W
O
/ZrO2. The specific surface area was deterꢀ
mined using the BET nitrogen adsorption technique.
The average pore size was calculated from the desorpꢀ
tion branch of the isotherm. The surface area value was
used to estimate the average size of particles on the
assumption of their spherical shape.
Fig. 1. Specific surface area and average pore size of
Pt/W O4 /ZrO2 as a function of the WO42– concentration.
2
–
The experiments on the isomerization of nꢀhepꢀ
quasiꢀsteady state, in which the reaction characterisꢀ
tics vary only slightly over time, was established on the
platinized catalysts within 30 min. The process paramꢀ
eters given below refer to this reaction time.
tane were carried out using a BIꢀCATflow 4.2(A) catꢀ
alytic setup (model of the Boreskov Institute of Catalꢀ
ysis, Siberian Branch, Russian Academy of Sciences)
with a flow reactor at atmospheric pressure. The cataꢀ
lyst was charged into the reactor in the form of a fracꢀ
tion with a grain size of 0.2–1 mm. It was activated via
heat treatment: first, in an argon stream at a temperaꢀ
The effect of the concentration of tungstate anions
was studied using the example of a set of samples conꢀ
–1
taining 0.5 wt % Pt at a space velocity of 1 h and a
temperature of 170 (Table 1). At a low tungstate
ꢀheptane was varied from 0.3 to content (5.9 mol %), the yield of heptane isomers was
h at a molar ratio of Н2 С7 = 3 : 1. The reaction as low as 3.1 wt % with a selectivity of 86.3 wt %. An
was run at 170 and 200
ture of 350
°
С
and then in hydrogen at 250
°
С
.
°С
The space velocity of
n
–1
2
: nꢀ
°С. The isomerization products
increase in the concentration of tungstate anions led
to an increase in the catalyst activity, whereas the
selectivity varied only slightly. The maximum yield of
heptane isomers of 62.8 wt % was achieved on the catꢀ
were analyzed in the onꢀline mode using a gas chroꢀ
matograph as part of the catalytic setup equipped with
a capillary column and a flame ionization detector.
The chromatograms were recorded and processed
2–
using the GEPARD software. The values of research alyst that contained 17.6 mol %
octane numbers of the isomerizate were calculated
according to the additivity scheme.
WO4 . The research
octane number of the isomerizate produced on this
catalyst was 45. A further increase in the concentration
2–
of
W
O4 resulted in a decrease in activity.
A comparison of the data in Fig. 1 and Table 1
shows that the most active catalyst has the highest speꢀ
RESULTS AND DISCUSSION
According to Xꢀray diffraction data [22, 23], the
synthesized catalysts samples are tetragonal zirconia
promoted by tungstate groups in different amounts cific surface area. However, a quantitative comparison
(
1
5.9 to 21.9 mol %). The ZrO2 crystallite size is 13– of the texture characteristics with the isomerization
6 nm. Figure 1 shows the specific surface area and the activity shows that, as the concentration of tungstate
average pore diameter as a function of the concentraꢀ
tion of tungstate groups. It is seen that the minimum
average pore size of 7–8 nm and the maximum speꢀ
anions increases from 5.9 to 17.6%, the specific surꢀ
face area of the catalysts increases only by a factor of
1
.4 (Fig. 1) and the yield of isoheptanes increases by
2
cific surface area of the dioxide of 76–77 m /g (this
more than a factor of 20 (Table 1). In addition, there is
no correlation between the isomerization characterisꢀ
tics and the catalyst pore size, a fact that indicates the
absence of internalꢀdiffusion limitation on the reacꢀ
tion. This is also confirmed by the finding in prelimiꢀ
nary tests that the reaction characteristics did not vary
corresponds to the average particle size of 12–13 nm)
are formed by introducing the tungstate groups in the
amount of 12.9–17.6 mol %.
During the isomerization of
n
ꢀheptane on
2–
W
O
/ZrO2 (without Pt), we observed a sharp
4
decrease in the conversion during the initial period. A upon a change in the grain size of the catalysts in the
PETROLEUM CHEMISTRY Vol. 52
No. 2
2012

88
KUZNETSOVA et al.
2
–
2–
Table 1. Characteristics of
n
ꢀheptane isomerization on the Pt/WO4 /ZrO and Pt/SO4 /ZrO catalysts at a temperature
2
2
of 170°C and
v
= 1 h–1
2
–
2–
Sample
Pt/WO4 /ZrO2
Pt/SO4 /ZrO2
Concentration of anions, mol %
Conversion of ꢀheptane, wt %
5.9
3.6
86.3
3.1
0.5
0.91
12.9
17.6
71.7
87.6
62.8
8.9
21.9
44.3
87.7
38.8
5.5
6.5
68.8
20.3
14.0
54.8
0.97
52
n
60.9
82.2
50.0
10.8
0.98
36
Selectivity for isoheptanes, wt %
Yield of heptane isomers, wt %
Yield of C –C alkanes, wt %
1
6
C /C (mole) ratio
1.0
45
0.98
25
3
4
Octane number (ON)
2
range of 0.06 to 1.5 mm. This implies that the isomerꢀ
fered little from that on the tungstated sample
68.8 wt % versus 71.7 wt %); however, the yield of the
desired isoheptane products was only 14.0 wt %, and
the selectivity was 20.3 wt % (Table 1). The dominant
reaction was acid cracking, which yielded propane and
isobutane in a ratio close to unity.
2–
(
izing activity of different Pt/W O4 /ZrO2 samples is
not determined by textural properties and seems to
depend in a certain way on the concentration and state
of surface tungstate anions.
The reaction products are mostly composed of
methylhexanes and dimethylpentanes as heptane isoꢀ
The data on the effect of space velocity on the charꢀ
acteristics of isomerization on the tungstated catalyst
with the optimum composition are given in Table 2. It
is seen that as the space velocity increases from 0.3 to
2
–
mers. An increase in the concentrations of
WO4
groups leads to an increase in the yield of mainly
methylhexanes (Fig. 2). In addition to isoheptanes, a
–1
2
h , the conversion of
nꢀheptane decreases from 92.0
to 49.7 wt %, the yield of isoheptanes reduces from
small amount of С –С6 alkanes is formed; among
1
6
5
8.2 to 46.8 wt %, the octane number decreases from
9 to 27, and the isoheptane selectivity, in contrast,
them, С3 and С4 alkanes with a ratio close to unity are
dominant, which is indicative of the occurrence of the
side cracking reaction of the С7 molecule by breaking
the central bond via the carbennium ion mechanism.
For comparison, under the same conditions, we
increases from 74.2 to 94.4 wt %. At different space
velocities, the С /С4 molar ratio in the cracking prodꢀ
3
uct is close to unity.
Thus, the catalyst based on tungstated zirconia
2
4
–
tested a Pt/S
O
/ZrO2 catalyst based on sulfated zirꢀ with the optimum content of tungstate groups (17.6%)
conia with an optimum concentration of sulfate exhibited a relatively high activity and selectivity in
groups of 6.5 mol % [22]. It was found that the degree
n
ꢀheptane isomerization. Note that in the case of
of conversion of
n
ꢀheptane on the sulfated catalyst difꢀ industrial catalysts, including sulfated zirconia, the
allowed concentration of heptanes in the feedstock
(
С –С6 fraction) is at most 10–15% and that of benꢀ
5
zene is no more than 1%.
Methylhexanes
50
40
30
20
10
0
Industrial gasoline fractions of crude oil always
contain a significant amount of aromatic hydrocarꢀ
bons. In order to examine their effect on the isomerꢀ
ization characteristics, the catalyst with the optimum
concentration of tungstate groups was tested in the
isomerization of nꢀheptane in the presence of 10 wt %
benzene and toluene.
The hydroisomerization of the mixtures proceeded
almost in the steadyꢀstate regime. However, the cataꢀ
lyst activity significantly decreased in comparison with
the activity in the reaction with individual heptane. At
Dimethylpentanes
4
8
12
16
20
%
170°C, the conversion of heptane in the presence of
benzene (10%) was 41.8 wt % against 71.7 wt % in the
case of heptane alone (Table 3). As the temperature
Concentration of WO 42 –, mol
increased to 200
°C, the conversion increased to
Fig. 2. Variation in the yield of the heptane isomers methꢀ
7
5.8 wt % with an isoheptane selectivity of 68.7 wt %.
For the mixture with toluene, the conversion characꢀ
teristics and the yield of heptane isomers decreased by
ylhexanes and dimethylpentanes as a function of the
2
–
W
O
concentration.
4
PETROLEUM CHEMISTRY Vol. 52
No. 2
2012

THE CATALYTIC PROPERTIES OF TUNGSTATED ZIRCONIA
89
2–
Table 2. Effect of the space velocity of heptane on the characteristics of isomerization on the Pt/WO4 /ZrO catalyst. The
2
2
–
concentration of WO4 is 17.6 mol %; the Pt content is 0.5 wt %; the reaction temperature is 170
°
C
Space velocity of heptane, h–1
Characteristics
ꢀheptane, wt %
0
.3
0.5
1
2
Conversion of
n
92.0
74.2
68.2
75.1
85.2
64.0
71.7
87.6
62.8
49.7
94.4
46.8
Selectivity for isoheptanes, wt %
Yield of isoheptanes, wt %
Σ
DMP/
Σ
MH
0.35
0.98
59
0.23
0.97
45
0.22
1.00
45
0.18
0.96
27
C /C (molar) ratio
3
4
Octane number (ON)
2–
Table 3. Characteristics of nꢀheptane isomerization in a mixture with benzene or toluene on Pt/WO4 /ZrO at 170 and
2
2
00
°
C and
Reaction temperature,
Feedstock
Conversion of nꢀheptane, wt %
v
= 1 h–1
°
C
170
200
170
200
200
heptane heptane heptane + benzene heptane + benzene heptane + benzene
71.7
–
87.5
–
41.8
99.8
83.8
35.2
2.2
–
75.8
99.9
68.7
52.1
4.9
–
68.2
99.5
71.7
48.9
–
Conversion of benzene (toluene), wt %
Selectivity for isoheptanes, wt %
Yield of isoheptanes, wt %
Methylcyclopentane
87.6
62.8
–
61.8
54.2
–
Methylcyclohexane
–
–
3.5
–
Cyclohexane
–
–
7.6
–
5.0
–
Dimethylcyclopentanes
C /C (mole) ratio
–
–
6.0
1.0
45
0.99
47
0.86
26
0.97
42
0.92
3
4
Octane number (ON)
42
3
–8% compared to the mixture with benzene. In this to note that the isomerization of
n
ꢀheptane on the
process, benzene or toluene was almost complete conꢀ tungstated catalyst is fairly effective in the presence of
sumed for hydrogenation and hydroisomerization a benzene or toluene admixture, which are converted
to cyclohexane (53 wt %) and methylcyclopentane into the respective naphthenic derivatives (methylcyꢀ
(
47 wt %) or methylcyclohexane (38 wt %) and dimeꢀ clopentane, cyclohexane, methylcyclohexane, and
thylcyclopentanes (62 wt %), respectively.
dimethylcyclopentane) by 99.7–99.9%.
The octane numbers of the products obtained via
the hydroisomerization of the mixtures at 200°С
These results show that catalyst systems based on
zirconia modified with tungstate anions are promising
for designing a new isomerization process, which can
involve components of the heptane fraction. By comꢀ
pounding the isomerizate with reforming products, it
is possible to produce environmentally clean highꢀ
grade gasolines with a low concentration of toxic benꢀ
zene.
decreased by 5 points compared to the heptane
isomerizate because of lower yields of the isomers and
lower octane numbers of the benzene and toluene
hydroisomerization products.
2–
Thus, it has been found that the Pt/WO4 /ZrO2
2
–
catalyst containing 17.6%
WO4 is the most efficient.
Its isomerization efficiency is manifested in a good
general activity (yield of isoheptanes is 62.8 wt %)
combined with a quite high selectivity (87.6 wt %) in
REFERENCES
1. Special Technical Regulations “The Quality Specificaꢀ
the lowꢀtemperature region of 170
°
С. It is important
tions for Gasolines, Diesel Fuel, and Certain Combustiꢀ
PETROLEUM CHEMISTRY Vol. 52
No. 2
2012

9
0
KUZNETSOVA et al.
bles&Lubricants, Russian Federal Law, 2008 [in Rusꢀ 13. H. Hattori, Top. Catal. 53, 432 (2010).
sian].
14. B. Bardin and R. J. Davis, Top. Catal. 6, 77 (1998).
2
. Ya. M. Polunkin, M. N. Anikeev, V. A. Romashkin,
et al., Katal. Promꢀsti, No. 5, 19 (2007).
1
5. P. Meriaudeau, V. A. Tuan, G. Sapaly, et al., Catal.
Today 49, 285 (1999).
3. E. F. Kaminskii, V. A. Khavkin, B. B. Zharkov, and
A. N. Shakun, Tekhnol. Nefti Gaza, No. 1, 3 (2005).
1
1
1
1
2
2
2
6. R. Roldan, et al., Microporous Mesoporous Mater. 99
,
288 (2007).
4. V. K. Duplyakin, Ross. Khim. Zh. 51 (4), 11 (2007).
7. A.ꢀF. Lamic, C.ꢀH. Shin, G. DjegaꢀMariadassou, and
5. A. V. Lavrenov, I. A. Basova, M. O. Kazakov, et al.,
C. Potvin, Appl. Catal. A: Gen. 302, 5 (2006).
Ross. Khim. Zh. 51 (4), 75 (2007).
. P. N. Kuznetsov, L. I. Kuznetsova, and V. P. Tverꢀ
dokhlebov, Tekhnol. Nefti Gaza 38 (3), 20 (2005).
8. S. P. Elangovan, C. Bischof, and M. Hartmann,
6
7
8
9
J. Catal. Lett. 80, 35 (2009).
9. C. Bouchy, C. PhamꢀHuu, B. Heinrich, et al., Appl.
. E. A. Yasakova, A. V. Sitdikova, and A. F. Akhmetov,
Neftegaz. Delo, No. 1, 24 (2010).
. V. E. Agabekov and G. M. Sen’kov, Katal. Khim.
Neftekhim. Promꢀsti, No. 5, 3 (2006).
Catal. A: Gen. 215, 175 (2001).
0. Bui Chong Khan, Nguen Van Ty, and A. F. Akhmetov,
Neftepererab. Neftekhim., No. 2, 22 (2008).
1. V. V. Ezhov, V. V. Melekhin, K. G. Kamalov, et al.,
Neftepererabotka, No. 9, 76 (2006).
2. P. N. Kuznetsov, L. I. Kuznetsova, and A. V. Kazbanꢀ
ova, Khim. Interes. Ustoich. Razvit., No. 18, 299
. A. I. Bashinskii, A. G. Vikhman, A. A. Mirimanyan,
et al., http://www.ectꢀservice.ru/public/public3.php.
10. Yu. M. Zhorov, Izomerization of Hydrocarbons
(Khimiya, Moscow, 1983) [in Russian].
(2010).
1
1. T. Okuhara, J. Jpn. Pet. Inst. 47, 1 (2004).
2
3. P. N. Kuznetsov, V. P. Tverdokhlebov, L. I. Kuznetsova,
et al., Zh. Sib. Fed. Univ., Tekh. Tekhnol., No. 4, 437
(2011).
12. A. Chica, U. Diaz, V. Forne, and A. Corma, Catal.
Today 147, 179 (2009).
PETROLEUM CHEMISTRY Vol. 52
No. 2
2012