Hydrogenation of benzene in the presence of ruthenium on a modified montmorillonite support

Article abstract of DOI:10.1134/S0036024413090276

Liquid-state hydrogenation of benzene on a supported ruthenium catalyst is studied. The degree of utilization of the inner surface of the porous system is determined. In the presence of water, hydrogenation occurs with the formation of cyclohexene along with cyclohexane.

Full text of DOI:10.1134/S0036024413090276

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2013, Vol. 87, No. 9, pp. 1478–1481. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © A.B. Utelbaeva, M.N. Ermakhanov, N.Zh. Zhanabai, B.T. Utelbaev, A.A. Mel’deshov, 2013, published in Zhurnal Fizicheskoi Khimii, 2013, Vol. 87, No. 9,
pp. 1486–1489.
CHEMICAL KINETICS
AND CATALYSIS
Hydrogenation of Benzene in the Presence of Ruthenium
on a Modified Montmorillonite Support
a
a
a
b
b
A. B. Utelbaeva , M. N. Ermakhanov , N. Zh. Zhanabai , B. T. Utelbaev , and A. A. Mel’deshov
a
Auezov South Kazakhstan State University, Shymkent, 160012 Kazakhstan
b
Kazakhstan British Technical University, Almaty, 050010 Kazakhstan
eꢀmail: mako_01ꢀ777@mail.ru
Received October 25, 2012
Abstract—Liquidꢀstate hydrogenation of benzene on a supported ruthenium catalyst is studied. The degree
of utilization of the inner surface of the porous system is determined. In the presence of water, hydrogenation
occurs with the formation of cyclohexene along with cyclohexane.
Keywords: benzene, hydrogenation, catalysts, montmorillonite, modification, benzopyrene.
DOI: 10.1134/S0036024413090276
INTRODUCTION
columnar structure using aluminum polyhydroxo
complexes [5]. A sodium hydroxide solution was gradꢀ
ually poured into aqueous aluminum hydroxochloride
while constantly stirring the mixture to pH ~3 or 4.
The concentration of hydroxo complexes was calcuꢀ
lated on the basis of 5–30 mgꢀequiv of Аl per 1 g of
clay. A suspension of bentonite (~1.0 wt %) was preꢀ
pared by vigorously stirring bentonite in water for 4 h;
the pH of the suspension was ~8 or 9. The medium
acidity was monitored with an ORꢀ208/1 pHꢀmeter.
The suspension of clay was slowly added to the soluꢀ
tion of the aluminum polyhydroxo complex to avoid
its coagulation.
Reducing the content of aromatic hydrocarbons
and especially benzene in motor fuels continues to be
an important challenge. Accumulated in the environꢀ
ment, the toxic compound benzene and the carcinoꢀ
genic product of its partial oxidation benzopyrene
adversely affect human and animal biological activity
3+
[
1]. We must therefore improve oilꢀrefining technolꢀ
ogy and some of its stages in order to lower the content
of benzene and its derivatives. One such process is the
catalytic hydrodearomatization of aromatic hydrocarꢀ
bons into naphthenes. However, the presence of cataꢀ
lystꢀdeactivating heteroorganic compounds in oil disꢀ
tillates necessitates the further development of cataꢀ
lysts and detailed studies of the mechanism of the
catalytic transformation of hydrocarbons [2–5].
The hydrogenation and dehydrogenation of sixꢀ
membered cyclic hydrocarbons are of great interest to
hydrogen technology. Benzene and its derivatives are
unique compounds in the storage and transportation
of hydrogen. It is therefore necessary to develop cataꢀ
lysts for hydrogenation and dehydrogenation under
relatively mild conditions.
The coagulationꢀpreventing basicity reserve of
3+
–
Аl /ОН was 1/3. The suspension of clay treated with
aluminum hydroxochloride was stored for 24 h. The
precipitate was washed with water and condensed by
centrifuging. The sample was separated from the liquid
and dried at room temperature and then at 110
°С (2 h)
and 180 (4 h). The solid was cooled, ground, and
°
С
sieved. Fractions with definite grain sizes were impregꢀ
nated with aqueous ruthenium hydroxochloride
Ru(ОН)Cl3
The resulting thick mass was dried on a water bath.
It was then calcinated at 180 for 6 h.
⋅
4Н О of pure grade (0.5–1.0 wt % Ru).
2
The aim of this study was to investigate the
hydrodearomatization of benzene (a component of
motor fuels) in the presence of ruthenium catalysts on
a support of montmorillonite of bentonite clay with a
columnar structure.
°С
Determining Catalytic Activity
A catalyst sample (0.1 g) was reduced with hydroꢀ
gen at 250°С for 4 h before each experiment. After
reduction, the catalyst was cooled to room temperaꢀ
ture under hydrogen. It was then transferred under a
EXPERIMENTAL
Preparation of Catalysts
layer of cyclohexane to a steel autoclave (working
3
Ruthenium catalyst (0.5–1.0 wt % Ru) was preꢀ capacity, 100 cm ) equipped with a stirrer and samꢀ
3
pared on a support of modified montmorillonite of pling unit. A mixture (50 cm ) of benzene and cycloꢀ
bentonite clay. The natural clay was modified into a hexane of pure grade was used for hydrodearomatizaꢀ
1478

HYDROGENATION OF BENZENE IN THE PRESENCE OF RUTHENIUM
1479
Table 1. Dependence of the adsorption structural parameters of montmorillonite on the content of modifying aluminum
3+
Loss of thermal stability
[
Al ], mgꢀequiv/g
of clay
2
3
Ssp, m /g
d001, nm
V
, cm /g
2
t
,
°
C
Ssp, m /g
–
5
60
140
180
270
280
260
0.9
0.19
0.46
0.54
0.56
0.58
0.54
160
340
500
600
600
600
40
110
140
210
220
200
1.36
1.64
2.00
2.06
1.90
10
15
20
30
Note: [Al3+] is the content of aluminum ions and V is the total pore volume.
3
to 0.50–0.58 cm /g; the interlayer distance d001, from
tion
[
V(C H ) : V(C H ) = 1 : 1
. Dilution with cycloꢀ
]
6
6
6
12
0.9 to 2.06 nm.
hexane was needed to scatter the heat that evolved
during the hydrogenation of benzene in order to conꢀ
duct the process under ideal mixing conditions. The
initial rate of hydrogenation was determined differenꢀ
tially from the plot of the time dependence of benzene
concentration −dc/dτ = tan α. The hydrogen pressure
was measured with a manometer and varied from 0.5
to 6.0 MPa; the reaction temperature was varied from
The maximum distance of 2.00–2.06 nm correꢀ
sponds to an aluminum concentration of 15–20 mgꢀ
equiv/g of clay with oligomer aluminum ions on ionꢀ
exchange centers [6]. At aluminum concentrations of
over 20 mgꢀequiv/g of clay, the distance did not grow
because of the emergence of nonhydrolyzed alumiꢀ
num salts, which do not affect the formation of a layꢀ
ered columnar structure in solution. A similar effect
was reported for iron(III) polyhydroxo complexes [7].
1
20 to 200 С.
°
Xꢀray Diffraction and Chromatographic Analysis
Modifying montmorillonites of bentonite clays
makes them thermally stable. The specific surface
The XRD patterns of the samples were recorded on
2
2
70–280 m /g, determined after calcination at 180
°
С
,
a DRONꢀ3 diffractometer (Сu
K
radiation). The speꢀ
2
α
shrank to 210–220 m /g, respectively, at 600
°С. The
cific surface of the catalysts was determined by BET
and by gas chromatography from the retained volume
nonmodified bentonite clays collapsed at 160
specific surface being 40 m /g. The obtained modified
montmorillonites were used to prepare supported
°
С, their
2
of the familiar ꢀАl О adsorbent.
γ
2 3
The catalyst was analyzed on a Chromꢀ4 chroꢀ ruthenium catalysts (0.5–1.0 wt % Ru) on which the
matograph equipped with a flame ionization detector. hydrogenation of benzene was studied.
The column (length 3 m, diameter 3 mm) was filled
The catalytic systems in question have a quite
with solid KhromatonꢀN treated with liquid polyethꢀ
developed specific surface. In the first series of experiꢀ
yleneglycol adipate (15% of the mass of the substrate).
ments, the utilization of the inner surface of the cataꢀ
The column temperature was 100
°С; the evaporator
lysts was determined. The Tile–Zeldovich criterion
ϕ
temperature was 150 . Argon was used as the carrier
°
С
3
gas (flow rate, 50 cm /min).
Table 2. Dependence of efficiency on the particle size of
.5% Ru–substrate catalyst
0
RESULTS AND DISCUSSION
dav, mm
ϕ
tanh
ϕ
η
The use of adsorbents with a layered column strucꢀ
ture in catalytic and sorption processes has stimulated
the development of methods for synthesizing them
from natural aluminosilicates. Table 1 presents
selected physicochemical characteristics of ruthenium
catalysts on columnar montmorillonite substrates
obtained from bentonite clays from the southern
region of the Kazakh Republic.
0.2
0.14
0.31
0.47
0.62
0.75
1.56
0.15
0.30
0.44
0.55
0.64
0.97
0.99
0.98
0.94
0.90
0.84
0.63
0
.4
.6
0
0.8
1
.0
.0
2
Modification of bentonite clays with Al(III) polyꢀ
Note: mcat = 0.1 g, t = 120°C, pH2 = 40 atm, c
= 5.6 M; dav is
6 6
0C H
hydroxo complexes increased the specific surface from
2
the average diameter of the catalyst particles.
6
0 to 280 m /g; the total pore volume grew from 0.19
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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1480
UTELBAEVA et al.
Table 3. Hydrogenation of benzene in the presence of water on the 0.5% Ru–substrate catalyst
Yields of hydrogenation products (mol %) after different periods of time (min)
Initial mixture, mL
С Н
С Н
С Н
С Н
С Н
С Н
С Н
С Н
6
10
6
12
6
10
6
12
6
10
6
12
6
10
6
12
С Н
6
С Н
6
Н О
2
5
10
20
30
6
14
25
25
25
25
25
25
20
15
10
5
–
–
16.0
11.0
9.0
–
30
20
18
14
–
58
36
31
24
14
–
74
48
41
30
18
5
1.0
2.5
4.0
3.0
10
15
20
2.0
1.5
0.5
3.0
2.0
1.0
6.0
3.0
2.0
5.0
3.0
2.0
8.0
6.0
10.0
Note: mcat = 0.1 g, t = 120°C, and pH2 = 40 atm.
was included in our calculations. This criterion is in suggesting that the benzene was mainly in the liquid
direct proportion to the reduced radius of the catalyst: phase.
The rate constant of liquidꢀstate hydrogenation of
1
/2
ϕ = R0
(
k/D
)
,
benzene was determined using catalyst powder with a
–
2 –1
mean particle size of <0.1 mm (2.3
× 10 s for the
where R0 is the reduced radius of the catalyst particle
given case). The efficiency (the degree of utilization of
(
R0 = R/3 for spherical particles), is the reaction rate the inner surface of pores) was determined with the
constant, and is the effective diffusion coefficient of equation
reactant molecules on the inner surface of pores.
k
D
tanhϕ =
[
exp(ϕ) − exp(−ϕ)
]
/
[
exp(ϕ) + exp(−ϕ)
.
]
2
For gases, the diffusion coefficient is ~0.1 cm /s;
The calculated parameters of benzene hydrogenation
in the presence of porous catalysts are summarized in
Table 2.
It follows from the data of Table 2 that the effiꢀ
ciency is 0.84 for a particle with an average diameter
–
5
2
the molecular diffusion in liquid is ~10 cm /s [8].
The diffusion coefficient of the gas dissolved in the liqꢀ
uid is on the same order of magnitude as the liquid
–5
2
itself, ~10 cm /s. At 120
benzene vapors determined from the Kocks plot is
atm [9]. If we include the critical values of benzene
tcr = 288.6°C and pcr = 48.6 atm), the fugacity of benꢀ
°С, the pressure of saturated
>
1 mm and 0.63 for 2 mm. These data suggest that the
2
(
inner surface of pores during liquidꢀstate hydrogenaꢀ
tion is utilized effectively when the catalyst particle
size is less than 0.8 mm. For larger particles, the
observed rate diminished linearly (see figure).
In subsequent experiments, we used catalysts with
average particle sizes of <0.4 mm. Since the experiꢀ
ments were performed with vigorous stirring
(2000 rpm), the effect of external diffusion was
ignored.
v
zene vapors is
f = 0.80 atm. At 120°С, saturated vapor
pressure 2 atm, and constant pressure of the system
l
4
0 atm, the fugacity of liquid benzene is fl = 38 atm.
v
The phase equilibrium constant is
k
=
f
/
f
= 47.5,
2
W
×
10 , mol/(L s)
2
2
1
.4
The sole reduction product in the hydrogenation of
benzene under the given conditions was cyclohexane.
As is well known, varying the acidity of solid catalysts
often changes their selectivity. An important role is
played here by the preadsorbed water of the adsorbent,
which favors the formation of Brønsted and Lewis acid
centers on the aluminosilicate surface [3].
It was therefore of interest to study the behavior of
ruthenium catalysts on a columnar montmorillonite
substrate in the hydrogenation of benzene in the presꢀ
ence of water. Table 3 presents data on the reduction of
the aromatic ring by hydrogen.
According to Table 3, the presence of water in the
system during the hydrogenation of benzene after
.0
.6
0.4
0.8
1.2
1.6
2.0
, mm
−
d
2
0 min led to the formation of 6 mol % cyclohexene
Dependence of the rate of hydrogenation on the catalyst
particle size.
and 31 mol % cyclohexane at a water content of
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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HYDROGENATION OF BENZENE IN THE PRESENCE OF RUTHENIUM
1481
1
0 mL. A further increase in the volume of water fuels, especially the transformation of aromatic hydroꢀ
reduced the yield of hydrogenation products.
carbons into naphthenes.
After the addition of four hydrogen atoms, the benꢀ
zene ring is believed to have been hydrogenated to
cyclohexane without leaving the catalyst’s surface. In
addition, we think that the resulting cyclohexene was
ousted by water molecules; i.e., the rate of cyclohexꢀ
ene desorption was comparable to that of hydrogenaꢀ
tion [10–12]. This is indicative of the sequential addiꢀ
tion of hydrogen to the benzene ring.
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rate of cyclohexadiene hydrogenation is obviously
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CONCLUSIONS
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We studied the hydrogenation of benzene on a supꢀ
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water in the system led to stepwise reduction of benꢀ
zene on the catalyst’s surface, forming cyclohexane
and cyclohexene. The results from our experiments
can be used for the hydrodearomatization of motor
Translated by L. Smolina
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 9 2013