The effect of steam on the conversion of dimethyl ether to lower olefins and methanol over zeolite catalysts

Article abstract of DOI:10.1134/S0965544113060030

The effect of steam on the catalytic properties of La-Zr-HZSM-5/Al ₂O₃ and Mg-HZSM- 5/Al₂O₃ in the synthesis of olefins from dimethyl ether (DME) has been studied. It has been found that the presence of steam has a significant effect on the ethylene-to-propylene ratio regardless of the nature of the modifier; the formation of methanol was observed only on Mg-HZSM-5/Al₂O ₃. In situ high-temperature diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has revealed that the formation of methanol on Mg-HZSM-5/Al₂O₃ occurs owing to the formation of methoxy groups on the surface of the zeolite during the interaction between DME and basic sites. The resulting methoxy groups can be easily con- verted to methanol in the presence of steam. Pleiades Publishing, Ltd., 2013.

Full text of DOI:10.1134/S0965544113060030

ISSN 0965ꢀ5441, Petroleum Chemistry, 2013, Vol. 53, No. 6, pp. 383–387. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © T.I. Batova, E.Kh. Khivrich, G.N. Shirobokova, N.V. Kolesnichenko, Yu.V. Pavlyuk, G.N. Bondarenko, 2013, published in Neftekhimiya, 2013, Vol. 53, No. 6,
pp. 431–435.
The Effect of Steam on the Conversion of Dimethyl Ether
to Lower Olefins and Methanol over Zeolite Catalysts
T. I. Batova, E. Kh. Khivrich, G. N. Shirobokova, N. V. Kolesnichenko,
Yu. V. Pavlyuk, and G. N. Bondarenko
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
eꢀmail: batova.ti@ips.ac.ru
Received April 19, 2013
Abstract—The effect of steam on the catalytic properties of La–Zr–HZSMꢀ5/Al2O3 and Mg–HZSMꢀ
5/Al2O3 in the synthesis of olefins from dimethyl ether (DME) has been studied. It has been found that the
presence of steam has a significant effect on the ethyleneꢀtoꢀpropylene ratio regardless of the nature of the
modifier; the formation of methanol was observed only on Mg–HZSMꢀ5/Al2O3. In situ highꢀtemperature
diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has revealed that the formation of
methanol on Mg–HZSMꢀ5/Al2O3 occurs owing to the formation of methoxy groups on the surface of the
zeolite during the interaction between DME and basic sites. The resulting methoxy groups can be easily conꢀ
verted to methanol in the presence of steam.
Keywords: dimethyl ether, steam, methanol, zeolite catalysts, lower olefins, FTIR spectroscopy
DOI: 10.1134/S0965544113060030
Dimethyl ether (DME) can be regarded as one of
the possible key agents in the conversion of nonpetroꢀ
leum feedstock to motor fuels and valuable chemical
products, such as olefins [1]. A method for producing
lower olefins from DME has been developed at the
Topchiev Institute of Petrochemical Synthesis, Rusꢀ
sian Academy of Sciences. It is recommended that
zeolite catalysts based on ZSMꢀ5 modified with magꢀ
nesium, lanthanum, and zirconium should be used to
catalyze this process. Lower olefins are generally synꢀ
thesized in an inert gas environment at a DME conꢀ
centration of less than 30 vol %.
EXPERIMENTAL
DME with a purity of 99.8% (manufactured by
OAO NAK Azot, Novomoskovsk, Russia) was used as
a feedstock. The catalytically active systems for synꢀ
thesizing lower olefins from DME were prepared from
a ZSMꢀ5 zeolite in the ammonium form (
SiO2/Al2O3 molar ratio of 40 and a Na2O concentraꢀ
N
H+4 ) with
a
tion of at most 0.07 wt % (manufactured by OAO
AZKiOs, Russia) modified with lanthanum and zircoꢀ
nium and with magnesium. The catalysts were syntheꢀ
sized by mixing an HZSMꢀ5 zeolite with an alumina
slurry (contains 23 wt % of dry Al2O3, manufactured
by ZAO Promyshlennye katalizatory, Ryazan, Russia)
as a binder and the subsequent shaping of extrudates;
the concentration of the Al2O3 binder in the finished
catalyst was 33–34 wt %. Lanthanum and zirconium
were introduced by the incipient wetness impregnaꢀ
tion of the zeolite before mixing with the binder; magꢀ
nesium was introduced by impregnating the prepared
extrudates of the zeolite and the binder with an aqueꢀ
ous solution of the metal salt at room temperature with
If the process is conducted in a steam environment,
which is appropriate under industrial conditions, the
steamꢀtoꢀfeedstock ratio can have a significant effect
on the distribution of the DME conversion products
[2]. A change in this ratio can lead to both an increase
and decrease in the content of lowꢀmolecularꢀweight
С2–С4 olefins. In addition, in the synthesis of lower
olefins from CO and Н2 through DME, the producꢀ
tion of DME from CO and Н2 is accompanied by the
formation of water, which can be involved in the synꢀ
thesis of lower olefins.
the subsequent drying and calcination at 500°С for 4–
6 h.
Diffuse reflectance infrared Fourier transform
(DRIFT) spectra were recorded using a PIKE Techꢀ
nologies DiffusIR highꢀtemperature cell, which gives
the possibility to in situ record DRIFT spectra of the
surface of solid catalyst samples at room temperature
Therefore, this study is focused on the examination
of the effect of the steamꢀtoꢀfeedstock ratio on the
yield and selectivity for lower olefins over zeolite cataꢀ
lysts that contain magnesium and the ones containing
lanthanum and zirconium.
and above (up to 500°C). The cell is equipped with a
device for feeding gases and steams which interact
383

384
BATOVA et al.
= 350 C, W
DME = const = 4.1 h–1. The feed mixture: DME + H2O + N2, the data for 4 h)
Table 1. Effect of the steam content in the feed mixture on the selectivity for lower olefins in DME conversion over the La–Zr–
HZSMꢀ5/Al2O3 catalyst (
T
°
DME(20) +
H2O(25) + N2(55)
DME(20) +
H2O(50) + N2(30)
DME(20) +
H2O(75) + N2(5)
Feed mixture, vol %
DME(20) + N2(80)
53.3
DME conversion, %
56.8
55.0
54.3
Selectivity for hydrocarbons, wt %
29.7
C2=
C3=
27.0
34.9
16.4
69.3
19.2
0.8
32.6
27.9
10.0
67.4
27.0
1.2
35.7
30.1
8.7
29.7
12.6
67.9
26.0
1.0
Σ
C+4=
C2–C=4
C2+
71.5
23.5
1.2
Σ
Σ
C–2 C=3
/
with the surface of the powder placed in a special RRGꢀ10 gas flow regulators and a fluid pump, respecꢀ
ceramic crucible with the sample. The cell equipped tively.
with an electronic temperature controller was placed
in the cell compartment of a VERTEXꢀ70 Fourierꢀ
transform spectrometer. A weighted portion of the
RESULTS AND DISCUSSION
Initially, the effect of steam content in the feed
mixture on the catalytic properties La–Zr–NZSMꢀ5/
Al2O3 was studied. In this case, the starting point was
the feed mixture composed of 20 vol % DME and
80 vol % N2 80. In the subsequent experiments, the
DME concentration remained constant, while nitroꢀ
gen was partially replaced by steam. The results are
shown in Table 1.
zeolite (20 mg) in a ceramic crucible was heated at
350–400 until the complete dehydration of the surꢀ
face. After that, the zeolite was cooled in a flow of high
purity argon to 350 and exposed to DME (10 vol %)
mixed with nitrogen and steam fed at a flow rate of
0.3 L/h; the load on the catalyst in these experiments
was 2.75 h–1. Water vapor was added to the DME + N2
mixture by bubbling the mixture through water at
room temperature. DRIFT spectra were recorded
°C
°C
It is evident from the table that an increase in the
steam content in the feed mixture has little effect on
the total selectivity for С2–C4 olefins; however, the
selectivity for ethylene increases, while the selectivity
for propylene slightly decreases. A significant decrease
during the feeding of DME at 350°C in a continuous
mode every 5 min (200 scans) for 3 h (a recording
range of 4000–600 cm–1, a resolution of 2 cm–1). The
spectra of the catalysts were recorded and mathematiꢀ
cally processed (baseline and normalization) under
the same conditions; therefore, the relative intensity of
the bands under discussion can serve as a criterion for
the concentration of functional groups attributed to
these bands. The mathematical processing was carried
out using the OPUSꢀ7 software package.
The catalysts were tested in a flowꢀtype reactor
described in [3]. DME was used as a feedstock; nitroꢀ
gen and/or steam was used as a DME diluent. The
DME concentration in the feed gas mixture was 5 to
65 vol %. The space velocity of the feed gas mixture
was varied in a range of 2000–30000 h–1. The reaction
in the
C=4+. concentration is also observed. It should
Σ
be noted that methanol was not detected in the reacꢀ
tion products.
The effect of the DMEꢀtoꢀsteam ratio on the disꢀ
tribution of reaction products in the absence of nitroꢀ
gen was studied at a constant DME load. It is evident
from Table 2 that the selectivity for ethylene and proꢀ
pylene increases as this ratio decreases; in addition,
the formation of ethylene occurs faster than the forꢀ
mation of propylene with increasing water content.
The total selectivity for lower olefins also increases
with a decrease in the selectivity for paraffins. In this
case, the formation of methanol is not observed either.
Similar studies were conducted for Mg–HZSMꢀ
5/Al2O3. The results are shown in Fig. 1.
products were analyzed by GLC using a 27.5 m
0.32 mm 10 m capillary column equipped with
×
×
μ
flameꢀionization and thermalꢀconductivity detectors,
a nonpolar CPꢀPoraPLOT Q phase as an adsorbent,
and helium as a carrier gas. The resulting chromatoꢀ
It is evident from the figure that the reaction prodꢀ
grams were processed using the NetChromWin softꢀ ucts contain a large amount of methanol upon the
ware. To provide a desired feed space velocity, the gas addition of water to DME. Although the concentraꢀ
flow rate and the fluid flow rate were controlled with tion of methanol decreases with increasing steam conꢀ
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THE EFFECT OF STEAM ON THE CONVERSION OF DIMETHYL ETHER
385
Table 2. Effect of the DMEꢀtoꢀsteam ratio on the selectivity for lower olefins in DME conversion over the La–Zr–HZSMꢀ
5/Al2O3 catalyst (
for 4 h)
T
= 350
°
C,
W
DME = const = 4.1 h–1,
Ulin = const = 0.04 m/s). The feed mixture: DME + H2O, the data
Selectivity, wt %
DME
conversion, %
Conditions
DME : H2O = 50 : 50 vol %;
C2=
C3=
Σ
C2–
/
C=3 C=2
/
C3=
Σ
C–2 C=4
/
Σ
C2+
58.0
24.2
24.3
48.5
50.4
77.2
76.7
72.4
1.0
0.6
1.1
1.2
1.7
53.8
58.0
81.7
81.2
76.3
44.5
40.7
17.7
18.3
23.4
VDME : H O = 2428.6 h–1 (25.5 L/h);
2
WH O = 1.6 h–1
2
DME : H2O = 40 : 60 vol %;
55.0
78.7
66.0
70.6
19.2
40.9
41.4
46.0
31.2
36.3
35.3
26.4
VDME : H O = 3500 h–1 (24.5 L/h);
2
WH O = 3.1 h–1
2
DME : H2O = 20 : 80 vol %;
VDME : H O = 5785.7 h–1 (27 L/h);
2
WH O = 6.2 h–1
2
DME : H2O = 15 : 85 vol %;
VDME : H O = 7692.3 h–1 (25 L/h);
2
WH O = 8.7 h–1
2
DME : H2O = 5 : 95 vol %;
VDME : H O = 27931.0 h–1 (27 L/h);
2
WH O = 35.8 h–1
2
tent, the amount of it remains dominant. An increase of the bands from the isolated –OH groups at 3661 and
in the steam content and a decrease in the DME conꢀ 3720 cm–1; in this case, the broad band peaking at
centration in the feed mixture lead to a sharp increase 3562 cm–1 is the most intense; it can be attributed to
in the selectivity for ethylene, while propylene methanol adsorbed on the surface. The spectra of the
increases insignificantly. It should be noted that the zeolite surface purged with a mixture of DME and
presence of water on the Mg–HZSMꢀ5/Al2O3 catalyst water, along with the band at 3661 cm–1, exhibit a
new weak band from the isolated –OH groups at
+
has hardly any effect on the content of
Σ
C2 .paraffins.
3644 cm–1. The intensity of the bands from these
groups insignificantly decreases over time; however,
the intensity of the bands in the spectra of the surface
of Mg–HZSMꢀ5/Al2O3–DME–Н2О is slightly
higher than that of the bands in the spectra of Mg–
HZSMꢀ5/Al2O3–DME.
Thus, we can state that the presence of steam has a
significant effect on the ethyleneꢀtoꢀpropylene ratio;
in addition, depending on its concentration in the feed
mixture, a more considerable increase in this ratio is
observed on Mg–HZSMꢀ5/Al2O3. In this case, methꢀ
anol was formed only on Mg–HZSMꢀ5/Al2O3; this is
apparently attributed to the presence of more basic
sites on which DME interacts with Н2О to form methꢀ
anol.
The interaction between DME and the surface of
Mg–HZSMꢀ5/Al2O3 at a temperature of 350°C was
studied by in situ DRIFT spectroscopy in the absence
and presence of steam.
Thus, the flowing of DME through the zeolite
leads to a complete disappearance of the band at
3595 cm–1 corresponding to the BAS, a sharp decrease
in the intensity of the bands from the isolated –OH
groups on the zeolite surface, and the occurrence
of a band attributed to the surface of methanol at
3562 cm–1. The presence of steam in the gas mixture
leads to a higher intensity of the bands from the isoꢀ
lated –OH bonds and the appearance of a weak band
at 3644 cm–1, which is preserved throughout the
experiment.
The spectrum of Mg–HZSMꢀ5/Al2O3 heated at
350°C in an argon stream exhibits three bands from
the isolated –OH bonds (3661 and 3720 cm–1) and
one band from the weakly associated –OH
groups contained in the Brönsted acid site (BAS) at
The disappearance of the band from the BAS and
3595 cm–1 (Fig. 2). The feeding of DME leads to the decrease in the intensities of the bands at 3661 and
almost a complete disappearance of the band at 3720 cm–1 are accompanied by the appearance of a
3595 cm–1 (BAS) and a sharp decrease in the intensity number of bands in a region of 3020–2800 cm–1,
PETROLEUM CHEMISTRY Vol. 53
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386
BATOVA et al.
can be attributed to the methoxy groups (СН3–О–Al
)
50
45
40
35
30
25
20
15
10
5
formed on the surface [5, 6]. The bands from the C–O
bonds in the methoxy groups in a region of 1084 cm–1
[7] can be observed in the spectra of the surface of
Mg–HZSMꢀ5/Al2O3–DME, and its intensity
decreases with increasing time of interaction with
DME. This band in the spectrum of Mg–HZSMꢀ
5/Al2O3–DME (30ꢀmin contact) has a medium
intensity (Fig. 3); however, in the spectrum of Mg–
HZSMꢀ5/Al2O3–DME–H2O recorded under the
same conditions, this band is absent, while the intenꢀ
sity of the band at 1047 cm–1, which is the strongest
band in the spectrum of methanol, sharply increases.
The formation of methoxy groups on the zeolite surꢀ
face can occur during the interaction between DME
and the basic sites on the zeolite surface, which correꢀ
spond to the band at 3720 cm–1, according to
Scheme 1:
1
2
3
4
5
6
0
20
40
60
80
100
Water content in the feed mixture, vol %
Fig. 1. Effect of steam in the feed gas mixture on the cataꢀ
lytic properties of Mg–HZSMꢀ5/Al O in DME converꢀ
δ−
2
3
–1
sion (
const = 50%,
pump is 0.2 mL/min). The feed mixture (vol %): DME +
H O. ( ) MeOH, ( С –С , ( ) C =,
C+2 +, (
) C =, and ( ) C =.
T
= 350°C,
W = 3.4–10.3 h , DME conversion =
CH3 O CH3
OCH3
Al
OH
Al
P
= 0.1 MPa, the flow rate of H O from the
2
+ CH3OH.
1
2)
Σ
3)
Σ
4
2
5
2
4
3
(
6
2
4
Scheme 1
The methoxy groups formed on the surface in the
presence of steam can be easily converted to methanol
to form a new isolated –OH group (Scheme 2), a band
from which is detected in the spectrum at 3644 cm–1
(Fig. 2).
which are attributed to the stretching vibrations of the
C–H bonds (Fig. 2). The absence of bands at 2998,
2925, and 2817 cm–1, which are characteristic of the
methyl groups in DME [4], suggests that even a 5ꢀmin
contact between DME and the zeolite surface at a
temperature of 350°C leads to an instantaneous conꢀ
OH
CH3OH + Al
Scheme 2
OCH3
Al
version of DME. The two bands observed in the specꢀ
trum of the zeolite surface after a 5ꢀmin contact
between DME and the surface at 2848 and 2956 cm–1
+ HOH
.
Coord. K–M
12
4
7
9
3
6
3595
6
3661
2
3720
3562
3644
5
2956
3
2848
1
0
2600
2800
3000
3200
3400
3600
3800
cm–1
Fig. 2. Comparison of the spectra of the surface of Mg–HZSMꢀ5/Al O at 350°C in a stream of (
1
) Ar; (
2
) DME, 5 min;
2
3
(3) DME, 30 min; (4) DME, 120 min; (5) DME + H O, 5 min; (6) DME + H O, 30 min; and (7) DME + H O, 120 min.
2 2 2
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THE EFFECT OF STEAM ON THE CONVERSION OF DIMETHYL ETHER
387
Coord. K–M
30
1044
1047
1084
1012
20
2
1
10
980
1000
1020
1040
1060
1080
1100
cm–1
Fig. 3. Comparison of the spectra of the surface of (
1) Mg–HZSMꢀ5/Al O –DME–H O and (2) Mg–HZSMꢀ5/Al O –DME
2 3 2 2 3
after a 30ꢀmin contact in the region of absorption of MeOH.
Owing to this, the amount of methanol on the surꢀ state contract nos. 16.525.12.5009, 16.552.11.7072,
face of Mg–HZSMꢀ5/Al2O3–DME–H2O is signifiꢀ and 14.515.11.0035.
cantly higher than that detected on the surface of Mg–
HZSMꢀ5/Al2O3–DME under the same conditions
(Fig. 3). The intensity and position of the bands of the
REFERENCES
1. S. N. Khadzhiev, N. V. Kolesnichenko, and
stretching vibrations of CH in a region of 3200–
2800 cm–1 (Fig. 2) continuously change as the time of
flowing of DME through the zeolite increases; howꢀ
ever, the intensity of the bands on Mg–HZSMꢀ
5/Al2O3–DME is always higher than in the experiꢀ
ment on Mg–HZSMꢀ5/Al2O3–DME–H2O.
It should also be noted that no absorption bands
corresponding to the formation of methanol are
observed during the feeding of DME over La–Zr–
HZSMꢀ5/Al2O3.
N. N. Ezhova, Pet. Chem. 48, 325 (2008).
2. T. A. Lavrent’eva and O. N. Karatun, Vestn. AGTU,
No. 1 (48), 42 (2009).
3. N. V. Kolesnichenko, O. V. Yashina, N. A. Markova,
et al., Pet. Chem. 49, 42 (2009).
4. L. M. Sverdlov, M. A. Kovner, and E. P. Krainov, Vibraꢀ
tional Spectra of Polyatomic Molecules (Nauka, Mosꢀ
cow,1970) [in Russian].
5. S. Tamm, H. H. Ingelsten, M. Skoglundh, and
A. E. C. Palmqvist, J. Catal. 276, 402 (2010).
6. J. G. Chen, P. Basu, T. H. Ballinger, and J. T. Yates, Jr.,
ACKNOWLEDGMENTS
Langmuir 5, 352 (1989).
This work was supported by the federal target proꢀ
gram “Research and Development in Priority Fields
of Science and Engineering in Russia for 2007–2013,”
7. Davydov, A.A., IR Spectroscopy in Chemistry of Oxide
Surfaces (Nauka, Novosibirsk, 1984) [in Russian].
Translated by M. Timoshinina
PETROLEUM CHEMISTRY Vol. 53
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2013