Activity of zeolites in dimethyl sulfide synthesis

Article abstract of DOI:10.1134/S002315841004018X

Dimethyl disulfide conversion into dimethyl sulfide over various zeolites in an inert medium at atmospheric pressure and T = 190-330°C is reported. A significant activity in dimethyl sulfide formation is shown by the decationized zeolites HNaY and HZSM-5, whose surface has strong protonic and nonprotonic acid sites. Cobalt-containing faujasite is more active than HNaY, and the activity of CoHZSM-5 is comparable with the activity of its decationized counterpart.

Full text of DOI:10.1134/S002315841004018X

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 4, pp. 579–583. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Mashkina, L.N. Khairulina, 2010, published in Kinetika i Kataliz, 2010, Vol. 51, No. 4, pp. 603–607.
Activity of Zeolites in Dimethyl Sulfide Synthesis
A. V. Mashkina and L. N. Khairulina
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
eꢀmail: amash@catalysis.ru
Received January 14, 2009
Abstract—Dimethyl disulfide conversion into dimethyl sulfide over various zeolites in an inert medium at
atmospheric pressure and
T = 190–330°C is reported. A significant activity in dimethyl sulfide formation is
shown by the decationized zeolites HNaY and HZSMꢀ5, whose surface has strong protonic and nonprotonic
acid sites. Cobaltꢀcontaining faujasite is more active than HNaY, and the activity of CoHZSMꢀ5 is compaꢀ
rable with the activity of its decationized counterpart.
DOI: 10.1134/S002315841004018X
Dimethyl sulfide (DMS) is the starting chemical in
the synthesis of dimethyl sulfoxide, which is used as a
medicine, a solvent in polysulfone production and
acrylonitrile polymerization, a complexing agent in
the extraction of noble and rare metals, and an extracꢀ
tant of aromatic hydrocarbons from petroleum prodꢀ
ucts. DMS to be converted into dimethyl sulfoxide is
synthesized by reacting methanol with hydrogen sulꢀ
fide or by methyl mercaptan (MM) condensation [1].
A readily available and cheap DMS precursor is dimeꢀ
thyl disulfide (DMDS), which is obtained in large
amounts in the removal of mercaptans from gases [2].
It was established earlier that DMDS decomposition
Catalytic tests were performed using an earlier
reported procedure [3]. Reaction products were idenꢀ
tified by the GC/MS method. Quantitative analyses
were made on an LKhMꢀ8MD chromatograph with a
thermalꢀconductivity detector (2 m
×
3 mm column
packed with Porapak Q + Porapak R (1 : 1), helium as
the carrier gas).
The residence time ( , s) was taken to be equal to
τ
the ratio of the catalyst volume (cm3) to the gas flow
rate (cm3/s) at room temperature and atmospheric
pressure. The results of the analyses were used to calꢀ
culate the DMDS conversion (
, mol %), DMS selectivity (
total DMDS conversion rate (
formation rate at = 70% per gram of catalyst (w1
Х
S
w
, %), product yields
, %) as , and the
, mmol/h) and DMS
in an inert medium at atmospheric pressure and
Т =
(
Y
Y/Х
190–350°С on zeolites HNaY and HZSMꢀ5 yields
DMS along with other products [3]. However, the
activity and selectivity of zeolite catalysts was not studꢀ
ied as a function of their composition.
X
,
mmol/h) or per gram of cobalt (w2, mmol/h).
Here, we report the activity of a variety of unsubstiꢀ
tuted and cobaltꢀcontaining zeolites in DMDS conꢀ
version into DMS in an inert medium.
RESULTS AND DISCUSSION
DMDS conversion was studied in helium at atmoꢀ
spheric pressure and = 190–350°С over NaX, NaY,
Т
HNaY, HZSMꢀ5, and cobaltꢀcontaining zeolites.
Each catalyst was tested at a fixed temperature and difꢀ
ferent residence times. From experimental data, we
derived the DMDS conversion and the yields of sulꢀ
furꢀcontaining products, namely, DMS, MM, hydroꢀ
gen sulfide, and carbon disulfide. Small amounts (1–
3 mol %) of methane were also observed. In the presꢀ
ence of the sodium form of zeolites—NaX and
NaY—the DMS yield was 1.1 mol % or below
EXPERIMENTAL
The catalysts were zeolites NaX (Si/Al = 1.5), NaY
(Si/Al = 2.25), HNaY, and HZSMꢀ5 (Si/Al = 17 and
35) without a binder and zeolite HZSMꢀ5 (Si/Al = 35)
with a binder (20% Al2O3), all calcined in flowing dry
air at 300–400°С. Cobalt (2–5 wt %) was introduced
into zeolites by impregnating them with an aqueous
solution of cobalt acetate. The impregnated samples
were dried in air at room temperature (12 h) and at
110°С (5 h) and were then calcined in flowing dry air
at = 400°С (5 h). The acid–base properties of the
Т =
(
Т
= 200°С, = 0.1 or 2.0 s, Х = 70–76%). The main
τ
product in this case was MM. Hydrogen sulfide and
carbon disulfide were also detected among the sulfurꢀ
containing products. At 350°С, the reaction needed a
much shorter residence time of 0.15 s, but the DMS
Т
zeolites were determined earlier by IR spectroscopy of
adsorbed probe molecules [1, 4, 5].
All chemicals were reagent grade or pure grade.
yield did not exceed 4.2 mol % at X = 62–70%.
579

580
MASHKINA, KHAIRULINA
Table 1. DMDS conversion and product yield data for decationized and cobaltꢀcontaining zeolites Y and ZSMꢀ5
Yield, %
Reaction
temperature, °C
Zeolite
τ
, s
Х, %
DMS
MM
H2S
CS2
HNaY
200
250
200
260
350
200
250
350
200
250
340
1.0
74
75
60
75
90
66
70
77
61
78
82
17
20
29
27
33
34
32
37
18
26
36
35
32
14
23
34
12
18
27
36
29
24
11
12
10
15
18
11
10
9
7
9
0.2
HZSMꢀ5
0.5
6
0.2
8
0.14
0.37
0.22
0.08
0.25
0.2
3
5% Co/HZSMꢀ5
5% Co/HNaY
5
9
3
1
5
11
8
12
10
0.09
A much higher DMS yield was attained with the on various oxide catalysts that, for DMS formation
decationized zeolites HNaY and HZSMꢀ5 and with from DMDS, it is necessary that the surface have both
cobaltꢀcontaining zeolites (Table 1).
mediumꢀstrength basic sites and strong protonic and
nonprotonic acid sites. When DMDS is in contact
with a catalyst, the sulfur atom of one CH3S group
binds to a PS; the sulfur atom of the other methanethio
group, to an Lꢀsite; and the carbon atom of a CH3
group, to a basic site. The decomposition of the resultꢀ
ing surface complex yields sulfur and DMS. A possible
cause of the low catalytic activity of zeolites NaX and
NaY in DMS formation is that they contain only weak
Lꢀsites.
The activity of the zeolites in DMDS conversion at
= 200–330°С decreases in the following order:
Т
HZSMꢀ5 > HNaY NaX > NaY.
ӷ
As for the DMS formation rate, the decationized zeoꢀ
lites are 1–2 orders of magnitude more efficient than
NaX or NaY.
The DMS selectivity of the sodium zeolites at
Х =
70% does not exceed 5.5%, while that of the decationꢀ
ized zeolites is 25–48% (Table 2). The rate of DMS
formation over HZSMꢀ5 (Si/Al = 35) with alumina
binder is 2.3 times higher than is observed for the same
zeolite without a binder. This is likely due to alumina
being involved in the process since this compound is
known to be very active in DMDS conversion [3].
Reducing the Si/Al ratio in zeolite HZSMꢀ5 from 35
to 17 raises the DMS formation rate at 250°С by a facꢀ
tor of 1.8.
The fact that NaY is less active than NaX is likely
due to NaY having a lower concentration of delocalꢀ
ized Na+ cations in NaY [6], which are involved in
DMDS activation. It is also very significant that the
sodium zeolites have no strong PS’s. It is possible,
however, that these sites appear under the action of the
reaction medium, including H2S resulting from
DMDS decomposition. The interaction between H2S
and a zeolite generates strong PS’s on the surface [1],
and this process is enhanced by increasing temperaꢀ
ture. It was established by IR spectroscopy of adsorbed
pyridine that treatment of zeolite NaX with hydrogen
sulfide at an elevated temperature produces strong
These findings can be explained in terms of the difꢀ
ference between the acid properties of the catalysts. All
of the zeolites contain mediumꢀstrength basic sites
(
РАb = 800–900 kJ/mol) and differ in the strength of
acid sites. Zeolites NaX and NaY have low acidity:
they do not contain strong protonic sites (PS’s) with
РАa < 1300 kJ/mol and have only weak Lewis sites
PS’s on its surface at a concentration of 12–24
[7, 8]. This may increase and . We indeed found
that passing a 15% Н2S + 85% Н2 mixture through
zeolite NaX at = 400°С for 1 h raises the w1 value at
= 200 and 250°С by a factor of 1.7–4. However,
µ
mol/g
w
S
(Lꢀsites) associated with Na+ cations with QCO
~
Т
Т
20 kJ/mol. The decationized zeolites are much more
acidic: they contain both strong PS’s with РАa
<
because the catalyst has no strong Lꢀsites, the w1 value
remains very low.
1200 kJ/mol and strong Lꢀsites associated with Al3+
1
The increased activity of the decationized versus
sodium zeolites in DMS formation is likely due to the
fact that the former have a higher concentration of
strong protonic and nonprotonic acid sites on their
cations (QCO = 32–54 kJ/mol) [1, 4, 5]. Earlier [3],
we deduced from the results of DMDS decomposition
1
2
b
a
Hereafter,
and are the powers of basic sites, PS’s, and Lꢀsites, respecꢀ
tively (kJ/mol).
C
is the site concentration (
µ
mol/m ) and РА , РА ,
surface. For example, HNaY contains PS’s with РАa
≤
Q
CO
1200 kJ/mol (
C
= 0.2 )
mol/m2) and Lꢀsites (Al3+
µ
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ACTIVITY OF ZEOLITES IN DIMETHYL SULFIDE SYNTHESIS
Table 2. Activity and selectivity of zeolites in DMDS conversion
581
Zeolite
Reaction temperature
,
°
С
w,
mmol/(h (g Cat))
w1
,
mmol/(h (g Cat))
S, %
NaY
NaX
200
240
300
330
200
200*
250
250*
300
330
350
200
240
300
330
200
250
300
330
190
250
250**
1.7
3.2
0.005
0.032
0.10
0.35
0.02
0.08
0.22
0.37
0.5
0.3
1.0
1.6
2.8
1.1
3
6.9
12.6
2.0
2.8
3.6
6
4.6
8
12.6
25.0
36.4
4.0
4
1.38
2.2
5.5
6.0
HNaY
1.0
25
29
36
38
46
40
41
39
48
45
44
11.2
25.1
31.6
6.3
3.2
9.0
12.0
2.9
HZSMꢀ5 (Si/Al = 17)
HZSMꢀ5 (Si/Al = 35)
14.1
31.6
56.2
4.8
6.4
12.9
21.9
2.3
8.0
3.6
19.1
8.4
* Catalyst was treated with an H S + H mixture at T = 400°C before the test.
2
2
** Zeolite with a binder.
with QCO = 32–35 kJ/mol (
C
= 0.16
mol/m2). Zeoꢀ at least during 3ꢀhꢀlong continuous operation. At
µ
lite HZSMꢀ5 with Si/Al = 17 contains PS’s with higher temperatures, the initial catalytic activity
РАa = 1700–1800 kJ/mol (
sites (Al3+) with QCO = 33–54 kJ/mol (
0.19
mol/m2). Owing to its higher surface acidity,
C
= 0.33
mol/m2) and Lꢀ
µ
decreases in the course of the reaction, and deactivaꢀ
tion increases progressively as the temperature is
C
=
raised. For example, at
conversion on HNaY and HZSMꢀ5 (Si/Al = 17)
decreases by a factor of 5–30 and by a factor of 20–
T = 340°C the initial DMDS
µ
HZSMꢀ5 is somewhat superior to HNaY in DMS forꢀ
mation activity. Raising the Si/Al ratio in HZSMꢀ5
from 17 to 35 reduces the concentration of strong acid
sites. The concentrations of PS’s and nonprotonic
S
30 in 3 h. The low performance e stability of these catꢀ
alysts is likely explained by the high concentration of
strong PS’s, which are favorable for the formation of
polymers like (CH2S)n at elevated temperatures [9].
These polymers accumulate in the pores of the zeoꢀ
lites, thus reducing their activity.
sites decrease to 0.16
µ
mol/m2 and 0.04 mol/m2,
µ
becoming lower than those in the Si/Al = 17 zeolite by
a factor of 2.1 and 4.8, respectively. It is likely this fact
that is responsible for the lower DMS formation activꢀ
ity of the Si/Al = 35 zeolite.
The introduction of cobalt into the decationized
zeolites changes the DMS formation rate relative to
that observed with the initial zeolite (compare the data
listed in Tables 2 and 3). The CoHNaY catalyst is 2.3–
3.6 times more active than HNaY, and 2%CoHZSMꢀ
5 (Si/Al = 17) is ~2 times more active than HZSMꢀ5.
The catalysts richer in cobalt are similar in activity to
pentasil or are inferior to it.
The initial activity of the sodium zeolites decreases
during the reaction. At
conversion and decrease by a factor of ~3 in 3 h; at
= 340°С, these parameters decrease in 3 h by a facꢀ
Т = 200°С, the initial DMDS
S
Т
tor of 35 and 12, respectively. The low performance
stability of these catalysts is likely due the long resiꢀ
dence times, which are favorable for the formation of
substances blocking the active sites of the catalyst.
The difference between the activities of the cobaltꢀ
With the decationized zeolites at
T = 200–250°С, the containing and cobaltꢀfree zeolites with Si/Al = 17
initial conversion and DMS selectivity do not decrease can be explained as follows. The Co2+ cations introꢀ
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582
MASHKINA, KHAIRULINA
Table 3. Activity and selectivity of cobaltꢀcontaining zeolites in DMDS conversion
Reaction
temperature, °C
Catalyst pretreatment*
w1,
mmol/(h (g Cat))
Catalyst
5% CoHNaY
w,
mmol/(h (g Cat))
S, %
temperature, °C
200
250
250
250
340
190
190
250
250
300
190
250
250
300
250
250
250
250
200
–
12.0
22.7
25.3
42.0
58.1
6.1
3.6
7.3
30
32
34
32
33
46
48
46
45
38
38
38
42
40
30
32
31
42
200
400
400
–
8.6
13.4
19.1
2.8
2% CoHZSMꢀ5
Si/Al = 17
190
200
400
400
–
12.3
14.0
24.2
35.5
0.5
5.9
2.5% CoHZSMꢀ5
Si/Al = 17
6.4
10.9
13.5
0.2
5% CoHZSMꢀ5
Si/Al = 17
200
400
400
–
6.3
2.4
12.7
27.8
3.6
5.3
11.1
1.1
5% CoHZSMꢀ5
Si/Al = 35
200
400
400
6.4
2.0
7.2
2.2
5% CoHZSMꢀ5
Si/Al = 35 with a binder
13.3
5.6
* 15% H S + 85% H .
2
2
duced into the channels of zeolite HZSMꢀ5 bind to Si/Al = 17 HZSMꢀ5 catalysts is likely due to the fact
that the concentration of Al3+ Lꢀsites decreases as the
Si/Al ratio is increased. Accordingly, the introduction
of cobalt into the Si/Al = 35 zeolite generates a smaller
number of strong Co2+ Lꢀsites.
extraframework Al3+; as a result, the zeolites containꢀ
ing 2 or 5% Co have a lower acidity: the concentration
of strong PS’s decreases by a factor of 1.6–1.7 and the
Lꢀsites due to Al3+ disappear completely, but strong
Lꢀsites with QCO = 37.7–59.5 kJ/mol due to Co2+
appear at the same time [5, 10, 11]. This raises the
DMDS decomposition rate and DMS selectivity. The
difference between the activities of the Si/Al = 35 and
An important parameter of the cobaltꢀcontaining
zeolites is the temperature of their activation with
hydrogen sulfide: the rate of DMS formation on the
catalysts treated with an H2S + Н2 mixture at T = 200–
400°С is ~2 times higher than that observed for the
nonsulfided catalysts. As compared to the decationꢀ
ized zeolites, the cobaltꢀcontaining zeolites show 2–3
times more stable catalytic activity during the reacꢀ
tion. This is likely due to the lower PS concentration
in the latter.
w1
10
w2
Variation of the cobalt concentration in HZSMꢀ5
demonstrated that the catalysts in which HZSMꢀ5
contains up to 2.5 wt % Co are 1.5–2 times more
400
200
6
2
active at
Т = 250°С than the decationized zeolite;
however, at higher Co contents of 3–10 wt %, w1 and
w2 decrease (Fig. 1). In the highꢀsilica zeolite containꢀ
ing up to 3 wt % Co, the metal is almost entirely
located in zeolite channels as isolated Co2+ ions or
oneꢀdimensional CoO or СоAl2O3 nanoparticles.
Twoꢀ and threeꢀdimensional particles appear at higher
Co contents. In addition, Co0 nanoparticles form in a
reductive medium [10]. Treating CoHZSMꢀ5 with an
H2S + H2 mixture at an elevated temperature generꢀ
2
6
10
Co content, wt %
Fig. 1.
w
and
w
as a function of the cobalt content of zeoꢀ
1
2
lite HZSMꢀ5 (Si/Al = 17).
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ACTIVITY OF ZEOLITES IN DIMETHYL SULFIDE SYNTHESIS
583
Table 4. Effects of the residence time and initial DMDS conꢀ
centration on the DMDS conversion and product selectivities
for the 2.5%CoHZSMꢀ5 (Si/Al = 17) catalyst at 250°C
route: DMDS decomposes to MM, which then conꢀ
denses into DMS, releasing hydrogen sulfide. Similar
trends were observed earlier for DMDS conversion
into DMS under the action of other catalysts [3]. As
the reaction temperature is raised, the DMS formaꢀ
tion rate increases and the DMS selectivity falls
(Fig. 2).
S
, %
[DMDS]0,
vol %
τ
, s
Х, %
DMS MM Н2S
CS2
0.18
0.15
0.16
0.17
0.10
0.13
0.16
0.21
0.36
1.2
1.6
1.9
3.1
1.6
1.7
1.6
1.8
1.5
65
68
72
68
48
61
70
84
98
42
44
47
45
37
40
44
46
50
25
27
26
24
41
35
29
20
16
16
14
16
14
11
12
14
17
19
14
14
11
16
10
11
12
15
14
Thus, the decationized and cobaltꢀcontaining zeoꢀ
lites are active catalysts for DMDS conversion into
DMS. The most efficient catalyst is 2.5%CoHZSMꢀ5
(Si/Al = 17).
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(
1
X
) DMS formation rate (
= (2) 70 and (3) 98% as a function of temperaꢀ
P
) and (
2
,
3
) DMS selecꢀ
S
tivity at
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[DMDS] = 3.2 vol %.
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2010