A catalytic process for preparation of thiophene from furan and hydrogen sulfide

Article abstract of DOI:10.1134/S1070427211070172

Thiophene formation under various conditions from furan and H₂S in the presence of γ-Al₂O₃, both unpromoted and promoted with transition metal oxides, was examined. The conditions enabling preparation of thiophene in a 95-98 mol% yield were determined.

Full text of DOI:10.1134/S1070427211070172

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 7, pp. 1223−1228. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.V. Mashkina, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 7, pp. 1152−1157.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
A Catalytic Process for Preparation of Thiophene
from Furan and Hydrogen Sulfide
A. V. Mashkina
Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
Received July 9, 2010
Abstract—Thiophene formation under various conditions from furan and Н2S in the presence of γ-Al2O3, both
unpromoted and promoted with transition metal oxides, was examined. The conditions enabling preparation of
thiophene in a 95–98 mol% yield were determined.
DOI: 10.1134/S1070427211070172
Thiophene is an important sulfur compound suitable
for preparation of physiologically active substances, poly-
mers, dyes, and oil additives [1]. It can be synthesized by
various routes among which an important place belongs
to that utilizing furan. The latter is produced in signifi-
cant quantities from processing of pentosan-containing
waste from agriculture, forestry, and woodworking [2].
It was found [3] that, in the presence of solid catalysts
at atmospheric pressure and 300–600°C, furan reacts
catalytically with Н2S to give thiophene:
the acid and basic sites on their surface and an important
role played by Lewis acid sites (L-sites) was established.
A mechanism was postulated according to which the re-
action proceeds via formation of a surface intermediate
through coordination of the α carbon atoms of the furan
ring with the L-site and with the sulfur atom from the
Н2S molecule nondissociatively adsorbed on the basic
site (BS). The significance of the L-sites for the catalyst
activity in the furan conversion to thiophene received
further confirmation [8]. It was found that an increase in
theAl2O3 precalcination temperature from 500 to 1300°C
causes the concentration of the surface L-sites to decrease,
thereby reducing the thiophene yield from 90 to 10%.
The best performance in thiophene synthesis is exhibited
by alumina-based catalysts [7]. However, the reaction
catalyzed by them was not studied in detail; in particular,
the activity of the catalysts was not examined in relation
to the concentration of the transition metal oxide additions
introduced into Al2O3.
+ H2S
+ H2O.
S
O
In the presence of alumina, both unpromoted and
promoted with Cr, Cu, and Th oxides, thiophene was
obtained in a 20–37 mol% yield; the reaction is ac-
companied by the formation of abundant by-products
responsible for the catalyst deactivation [3]. More recent
studies [4–7] showed that, when catalyzed by promoted
alumina, this reaction gives thiophene in a higher yield.
The characteristics displayed in the reaction of thiophene
synthesis from furan and hydrogen sulfide at atmospheric
pressure and 400°C in the kinetic region were compared
for catalysts of different nature, zeolites and SiO2- and
Al2O3-supported acids, alkalis, and metal oxides [7]. It
was shown that the activity and selectivity of the catalysts
is governed by the type, strength, and concentration of
Here, we measured in the kinetic region the activity
and selectivity ofAl2O3, both unpromoted and promoted
with tungsten, molybdenum, chromium, and cobalt ox-
ides. Our experiments demonstrated that unpromoted
alumina performs better. In order to choose a catalyst
best suited for practical application, we compared the
Al2O3 samples differing in the specific surface area, pore
structure, phase composition, catalyst grain size, and
structural sodium content. For the most efficient catalyst
1223

1224
MASHKINA
furan; γ-Al2O3 with Ssp=200 m2 g–1 served as catalyst
and support. The supported catalysts were prepared by
impregnation of γ-Al2O3 having the grain size dgrain
=
0.25–0.5 mm with aqueous solutions of cobalt chloride,
ammonium tungstate, ammonium molybdate, or chro-
mium nitrate. The impregnated samples were dried, first
in air at room temperature for 12 h and subsequently at
110°C for 5 h, after which they were calcined in a dry
air stream at 500°C for 5 h. Also, we used commercial
and prototype granular alumina samples as catalysts.
The experiments were carried out in a flow reactor with
a fixed bed of catalyst at atmospheric pressure. Helium
from a cylinder was fed into a cooled saturator filled with
furan. Helium-saturated furan was supplied to a mixer
into which undiluted Н2S, or an Н2S–helium mixture, was
supplied from another cylinder. The resulting gas mixture
was fed into the heated reactor charged with the cata-
lyst. The initial mixture and the reaction products were
analyzed on an LKhM-8 MD chromatograph equipped
with a katharometer [a 2 m × 3 mm column packed with
Porapak phase Q + R (1 : 1)]. The time of the experiment
was 1 and 3.5 h in the case when the catalyst activity and
the catalyst stability were determined, respectively.
Fig. 1. (I) Degree of furan conversion X, %, and (II) thiophene
yield y, %, at 400°C in the presence of catalysts with dgrain
0.25–0.5 mm vs. contact time τ, s: (1) γ-Al2O3 and (2) Cr2O3/γ-
=
Al2O3.
revealed, the kinetic relationships were examined, and the
thiophene synthesis conditions were optimized.1
EXPERIMENTAL
Hydrogen sulfide (99.5% pure) was prepared by
the reaction of hydrogen with sulfur over an alumi-
num–nickel–molybdenum catalyst. We used pure-grade
The conditional contact time τ, s, was determined
as the ratio of the catalyst volume to the gas flow rate,
expressed in units of cubic centimeters and cubic cen-
timeters per second, respectively, at atmospheric pres-
sure and room temperature. Based on the results of the
analysis we calculated the degree of reactant conversion
X, %, thiophene yield y, mol%, selectivity with respect
to thiophene S, %, S = y/X, and average rate of thiophene
formation at X = 50% per catalyst gram w, mmol h–1g–1,
which was taken as the measure of the catalyst activity.
Table 1. Thiophene formation from furan and hydrogen sulfide
at 400°C in the presence of catalysts of different composition
Thiophene
yield, mol%
Catalyst
γ-Al2O3
τ, s
S, %
1.0
1.5
1.4
1.3
1.4
1.8
8.0
1.3
1.3
5.4
1.5
1.5
45
72
46
44
44
10
42
36
12
38
35
21
100
100
100
96
3% WO3/γ-Al2O3
15% WO3/γ-Al2O3
1.5% MoO3/γ-Al2O3
20% MoO3/γ-Al2O3
In the presence ofA2O3, both unpromoted and promot-
ed with different amounts of transition metal oxides, in the
kinetic region (dgrain=0.25–0.5 mm) we studied the reac-
tion of Н2S with furan at atmospheric pressure, 400°C,
initial furan concentration 1.5 ± 0.2 vol%, Н2S/furan
molar ratio M = 6.5–7.0, and different contact times. The
main reaction product was thiophene, and minor amounts
of carbon monoxide and ethylene by-products were
obtained. Table 1 presents some of the results obtained.
We found that, with all the catalysts examined, the degree
of furan conversion and thiophene yield increased with
increasing contact time (Fig. 1). For most of the catalysts
examined these characteristics are virtually identical over
a broad range of contact times, which suggests a close to
100% selectivity of thiophene formation. Table 1 shows
that, at brief contact times (τ = 1.2–1.5 s), unpromoted
100
97
90
0.5% Cr2O3/γ-Аl2O3
2.3% Cr2O3/γ-Al2O3
98
96
92
4% CoO/γ-Al2O3
10% CoО/γ-Al2O3
97
96
________________________
1
The experimental part of work was carried out with partici-
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A CATALYTIC PROCESS FOR PREPARATION OF THIOPHENE
1225
γ-Al2O3 affords higher thiophene yield than does pro-
moted γ-Al2O3. The activities of the γ-Al2O3 catalysts
containing relatively small amounts of reactive substances
vary as follows:
Addition
Without addition
2.9
WO3
1.5
MoO3
1.3
Cr2O3
1.2
CoO
1.2
H2SO4
0.8
(NH4)2WO4
0.6
Na2O
0.4
w, mmol h–1 g–1
The catalysts containing W, Mo, Co, and Cr oxides
are less active than unpromoted γ-Al2O3 by factors of 2
and over. For these catalysts an increase in the amount
of addition caused the reaction to decelerate (Table 1).
Н2S, but their strength remains unchanged [11]. These
sites on the γ-Al2O3 surface contribute to a high rate of
furan conversion to thiophene. Adding small amounts
of Mo, Cr, W, and Co oxides to γ-Al2O3 causes the
strength of the L-sites from Al3+ to somewhat increase
(QCO = 36–37 kJ mol–1), and the strength of the BS
sites varies only slightly. However, at a high content of
these additions in the catalyst the L-sites are represented
mostly by transition metal cations whose Lewis acidity
is lower than that of Al3 + [9], which leads to decreased
activity of the catalyst in thiophene formation. Our
data suggest that, in the reaction of thiophene synthesis
from furan and hydrogen sulfide, unpromoted γ-Al2O3
comprising strong L-sites and moderately strong
BSs performs better than does promoted alumina.
The catalytic properties of alumina can be affected
by various factors: phase composition, pore structure,
The acid-base properties of alumina-based catalysts
were examined previously using IR spectroscopy of
adsorbed probe molecules [2, 9, 10]. On the γ-Al2O3
surface there are L-sites due to the presence ofAl3+; their
strength was estimated from the heat of adsorption of
carbon monoxide QCO. Most of the sites have a moderate
strength QCO=34 kJ mol–1 in the concentration c =
2.3 μmol m–2; also, there are strong L-sites with QCO
=
41 kJ mol–1, c = 0.2 μmol m–2. Basic sites contained
in γ-Al2O3 in the concentration c = 4 μmol m–2 have
a moderate strength of 800–900 kJ mol–1, as estimated
from the affinity of deuterium in CDCl3 to the BS [9].
At high temperatures some of these sites are blocked by
Table 2. Influence of the nature of alumina on its activity in thiophene synthesis
Phase composition
Vpore
at R = 70–100 nm mmol h–1 g–1
w,a
Shape
Grain size, mm
Ssp, m2 g–1
Na, wt%
of Al2O3
γ –Al2O3
Spherical
4–5
4–5
350
350
350
350
220
210
210
200
200
345
0.03
0.10
0.03
0.03
0.03
0.03
0.02
0.02
0.02
0.06
0.08
0.08
0.08
0.08
0.07
0.04
0.07
0.34
0.34
0.12
1.3
1.0
1.4
1.8
0.7
0.6
1.0
1.1
1.2
0.9
"
"
2–3
"
0.25–0.5
3–4
Rod-like
"
3–4
"
2–3
"
4–5
Spherical
"
0.25–0.5
4–5
50% γ-Al2O3 +
50% χ-Al2O3
50% γ-Al2O3 +
40% χ-Al2O3 +
10% η-Al2O3
"
4–5
350
0.07
0.05
0.4
a The activity of whole catalyst grains was measured at 400°C, furan concentration ~2%, M = 5.2–5.5, and X = 60–70%.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 7 2011

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MASHKINA
specific surface area, grain size, and structural sodium (Na
incorporated into the γ-Al2O3 lattice) impurity content.
Therefore, we examined a series of alumina catalysts
with different parameters. Table 2 summarizes the results
obtained.
estimated from the ratio of the observed reaction rate to
the rate achieved under presumption of the accessibility
of the entire inner surface of the catalyst for the reactants
and products [12].
We carried out experiments with γ-Al2O3 samples
characterized by various crushing degrees and found
that the reaction rate is unaffected by a decrease in the
grain size beyond 0.25–0.5 mm. Therefore, the degree
of the surface utilization was estimated from the ratio
of the reaction rates on the whole grains and grains
with a size of 0.25–0.5 mm. We found that surface
is utilized nearly exhaustively at the transport pore
volume of 0.34 cm3 g–1, below which level the degree
of the surface utilization does not exceed 0.7–0.8.
The process parameters were examined in relation to the
reaction conditions in the presence of γ-Al2O3 with Ssp =
330 m2 g–1, Na content 0.03 wt%, and dgrain = 0.25–0.5 mm
in the kinetic region. The experiments were carried out
at atmospheric pressure, temperature 250–480°C, initial
furan concentration 1–20 vol%, Н2S concentration
9–60 vol%, M = 2.8–20, and different contact times.
Table 3 and Fig. 2 present the results obtained.
It is seen that, with decreasing grain size, the activ-
ity of alumina tends to increase. With the transport pore
volume and structural sodium impurity content being
identical, the reaction rate tends to increase proportion-
ally to increase in the specific surface area of the catalyst.
The catalyst comprised of γ-Al2O3 and χ-Al2O3 exhibits
a lower activity; the catalyst based on (γ + χ + η)-Al2O3,
which moreover has a small volume of transport pores,
is even less active.
Heterogeneous catalytic processes are typically
complicated by diffusion phenomena [12]. It was shown
experimentally that the observed rate of thiophene forma-
tion from furan and hydrogen sulfide is independent of the
gas velocities no lower than 0.8 l h–1. Also, the reaction
is substantially accelerated with increasing temperature.
Apparently, there is no significant external diffusion
inhibition. The specific surface area and pore structure
of the catalyst affect the reaction rate, which fact may be
indicative of internal diffusion complications. The degree
of utilization of the surface of whole catalyst grains is
It is seen that, when the temperature and initial
concentrations of the reactants are constant, the degree
of furan conversion and thiophene yield tend to increase
with increasing contact time; the selectivity of thiophene
formation is 97–100%. When the contact time and Н2S/
furan molar ratio remain constant, the degree of furan
conversion and thiophene yield are virtually unaffected
by an increase in the initial furan concentration. At
a constant Н2S concentration the reaction rate tends to
increase in direct proportion to the running concentration
of furan, and at a constant furan concentration it also
increases in direct proportion to increase in the running
concentration of Н2S. The reaction is described by a first-
order equation with respect to both furan and hydrogen
sulfide. When the temperature and initial concentration
of furan are kept constant, an increase in M from 1 to
16 causes the thiophene formation rate to increase by
nearly an order of magnitude. For example, at 400°C and
furan concentration of 2 vol% we obtained the following
results:
log c2
log w2
log w1
H2S/ furan
1.0 3.1 4.5 6.2 8.5 11.2 16.0
log c1 + 1
w, mmol h–1 g–1 0.4 1.0 1.4 1.6 2.0 2.7 3.6
Fig. 2. (1) Furan conversion rate w1 vs. running furan concen-
tration c1 at the initial Н2S concentration of 10–11 vol% and
(2) hydrogen sulfide conversion rate w2 vs. running H2S con-
centration c2 at the initial furan concentration of 12–13 vol%.
An increase in temperature leads not only to accel-
eration of the thiophene formation but also to a certain
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A CATALYTIC PROCESS FOR PREPARATION OF THIOPHENE
1227
decrease in selectivity. Given below are the data obtained
at the initial furan concentration of 1.5 vol% and M = 7:
Тexp, °С
w, mmol h–1 g–1 0.2 0.6 0.8 1.6 1.8 2.2 2.7
S, % 100 99 97 96 96 95 94
250 300 350 400 420 450 480
The experiments aimed to determine the stability of
the catalyst showed that the relative rate of thiophene
formation w/w0, where w0 and w are the thiophene forma-
tion rates in the initial period and during the experiment,
respectively, increases in the case when Н2S is taken in
a large excess over furan (Fig. 3).
Fig. 3. Initial rate of thiophene formation vs. experiment time
t, h. Catalyst γ-Al2O3, τ = 1.8–2.0 s. (w/w0) Rate ratio, %. M:
(1) 4–5 and (2) 2.
Our data suggest that synthesis of thiophene from
furan and Н2S is to be catalyzed by γ-Al2O3 unpromoted
with metal oxides, having the following characteristics:
grain size ~3 mm, specific surface area ≥ 330 m2 g–1,
structural sodium content <0.05 wt%, and the specific
volume of transport pores ≥ 0.08 cm3 g–1.
Table 3. Furan conversion in an Н2S medium at 400°C in the
presence of granular γ-Al2O3
Initial concen-
tration, vol%
Selectivity
with respect
to thiophene,
%
Thiophene
yield,
mol%
τ, s
Н2S/furan
As follows from our calculations, thiophene can be
synthesized from furan and hydrogen sulfide in an adia-
batic fixed-bed reactor with alumina having grain size
~3 mm at atmospheric pressure, temperature 400–450°C,
furan supply rate 0.3–0.7 kg h–1 kg–1, furan initial con-
centration 12–14 vol%, and Н2S/furan molar ratio 4–5.
Under the recommended conditions the thiophene yield
is 95–98 mol%. This process is more efficient than the
known processes employed for thiophene preparation
by the reaction of furan with hydrogen sulfide [4–6],
catalyzed by promoted alumina.
furan Н2S
0.6
1.2
1.6
2.4
2.6
3.0
3.9
1.5
2.5
2.5
2.4
2.6
2.8
2.5
1.4
9.7
7.1
6.3
7.0
6.8
7.1
7.0
6.7
18
23
46
57
71
75
82
95
83
94
78
77
76
38
82
28
96
100
98
97
99
98
99
98
97
96
97
98
96
97
98
1.7 10.7
1.6 11.3
1.5 10.2
1.6 11.4
1.4
9.8
1.7 11.4
4.4 79
4.0 80
CONCLUSIONS
(1) The highest activity in thiophene synthesis from
furan and hydrogen sulfide at atmospheric pressure is
exhibited by unpromoted γ-Al2O3 containing strong L-
sites and basic sites of moderate strength.
20
1.2
9.2
7.6
7.1
6.9
3.0
10
1.7 12
5.0 34
8.6 26
8.2 82
(2) The activity of γ-Al2O3 tends to increase with
increasing catalyst surface area and transport pore
volume, as well as with decreasing grain size; it decreases
in the presence of χ- and η-phases, along with γ-phase,
in alumina and at a high content of structural sodium.
2.4 13
36
2.8
(3) The reaction of furan with hydrogen sulfide over
γ-Al2O3, is described by a first-order order equation with
respect to furan and hydrogen sulfide; the thiophene
formation is accelerated with increasing Н2S/furan
2.6 12
2.4 20
52
60
4.3
3.0
46
30
97
96
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1228
MASHKINA
4. BE Patent 1008868.
5. BE Patent 623801.
6. RF Patent 2263537.
molar ratio and temperature rising from 250 to 480°C.
ACKNOWLEDGMENTS
7. Mashkina, A.V. and Khairulina, L.N., Kinet. Katal., 2008,
The author is grateful to V.N. Kashkin from Bores-
kov Institute of Catalysis, Siberian Branch, Russian
Academy of Sciences, for the calculations performed.
vol. 49, no. 2, pp. 258–265.
8. Li, Q., Xu, Y., Liu, C., and Kim, J., Catal. Lett., 2008,
vol. 122, no. 2, pp. 354–358.
9. Paukshtis, E.A., Infrakrasnaya spektroskopiya v geterogen-
nom kislotno-osnovnom katalize (Infrared Spectroscopy in
HeterogeneousAcid-Base Catalysis), Novosibirsk: Nauka,
1992.
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