Conversion of dimethyl ether into lower olefins on a La-Zr-HZSM-5/Al 2O3 zeolite catalyst

Article abstract of DOI:10.1134/S0965544111010026

The catalytic properties of La-Zr-HZSM-5/Al₂O₃ in the synthesis of olefins from dimethyl ether (DME) were studied. It was shown by the method of temperature-programmed ammonia desorption that acid sites of medium strength are responsible for the high catalyst selectivity for lower olefins. It was found that the preliminary high-temperature treatment of zeolite or the replacement of nitrogen with steam increased not only the selectivity of the catalyst for lower olefins, but also its activity and stability. The effect of the operating parameters of the DME conversion into the lower olefins and the dependence of the catalyst activity on the number of regenerations were studied.

Full text of DOI:10.1134/S0965544111010026

ISSN 0965ꢀ5441, Petroleum Chemistry, 2011, Vol. 51, No. 1, pp. 49–54. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.N. Biryukova, T.I. Goryainova, R.V. Kulumbegov, N.V. Kolesnichenko, S.N. Khadzhiev, 2011, published in Neftekhimiya, 2011, Vol. 51, No. 1, pp. 50–55.
Conversion of Dimethyl Ether into Lower Olefins
on a LaꢀZrꢀHZSMꢀ5/Al O Zeolite Catalyst
2
3
E. N. Biryukova, T. I. Goryainova, R. V. Kulumbegov, N. V. Kolesnichenko, and S. N. Khadzhiev
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991 Russia
eꢀmail: biryukova@ips.ac.ru
Received August 27, 2010
Abstract—The catalytic properties of LaꢀZrꢀHZSMꢀ5/Al O in the synthesis of olefins from dimethyl ether
2
3
(
DME) were studied. It was shown by the method of temperatureꢀprogrammed ammonia desorption that
acid sites of medium strength are responsible for the high catalyst selectivity for lower olefins . It was found
that the preliminary highꢀtemperature treatment of zeolite or the replacement of nitrogen with steam
increased not only the selectivity of the catalyst for lower olefins, but also its activity and stability. The effect
of the operating parameters of the DME conversion into the lower olefins and the dependence of the catalyst
activity on the number of regenerations were studied.
DOI: 10.1134/S0965544111010026
Olefins are important precursors for chemical zeolite forms are characterized by high thermal stabilꢀ
industry, with ethylene and propylene being among ity [4] and zirconiumꢀcontaining samples exhibit high
the most demanded. Lower olefins are a highꢀvolume acidity.
product with a continuous output growth. To date, the
total capacity of the plants producing lower olefins
EXPERIMENTAL
from petroleum in the Russian Federation does not
satisfy the growing industry demands for these valuꢀ
able chemicals [1, 2]. Therefore, investigation into
ethylene or propylene manufacturing from natural gas
is of great importance and applicability.
The feedstock chemical was DME (99.8%) proꢀ
duced at the OAO “Azot” Novomoskovsk joint stock
company.
Catalyst samples based on ZSMꢀ5 zeolite in the
The activation of methane by oxygen or chlorine
yielding synthesis gas or methyl chloride, respectively,
+
ammonium form (NH ) with a SiO /Al O mole ratio
4
2
2
3
usually precedes the conversion of natural gas into of 37 (the OAO “Angarsk Catalyst and Organic Feedꢀ
lower olefins. The first route of the methane activation stock Production Plant”) containing no more than
has found wide industrial use for methanol production 0.04 wt % of sodium oxide and modified with lanthaꢀ
from the synthesis gas, which was 41.9 million ton per num and zirconium were investigated. The hydrogen
+
year in 2008 [1]. The progress in zeolite catalysis has form of the zeolite (
opened the possibility for the synthesis of ethylene and 500
H
) is produced via calcination at
°С
for 4 h. The catalysts were prepared by mixing
propylene on microporous SAPOꢀ34 or ZSMꢀ5 zeoꢀ the HZSMꢀ5 zeolite with a binder, the aluminum
lites from methanol or from a methanol–DME mixꢀ oxide suspension (contains 23 wt % of dry Al O3, ZAO
2
ture with a yield of 75–90% [3]. The production of Industrial Catalysts, Ryazan) and the subsequent
С –С olefins from DME, which is the intermediate shaping of extrudates with an Al O3 concentration of
2
3
2
product of methanol conversion into olefins on the
zeolite catalysts, has some benefits in comparison with
the methanol methods. The more favorable thermoꢀ
dynamics allows for carrying out the DME synthesis at
a lower pressure than the methanol synthesis and
attaining a deeper СО/Н2 conversion per pass. Howꢀ
ever, the microporous SAPOꢀ34 zeolite, which is the
best catalyst for the olefin synthesis from methanol, is
not so efficient in the reaction with dimethyl ether in
terms of activity, selectivity, and stability.
3
3–34 wt % in the prepared catalyst. The introduction
of lanthanum and zirconium into zeolite was carried
out as described in our previous study [5], in which the
optimal procedures of their introduction and optimal
concentrations of these modifiers in the catalyst were
determined. The preliminary highꢀtemperature treatꢀ
ment of zeolite was carried out according to [6] at a
temperature of 750 С for 4 h.
°
The data on the temperatureꢀprogrammed desorpꢀ
tion (TPD) of ammonia were obtained according to
In this work, we studied the catalyst samples based the procedure described in [7] and processed by fitting
on the HZSMꢀ5 zeolite modified with La and Zr (Laꢀ the shapes of experimental and calculated curves
ZrꢀHZSMꢀ5/Al O3), because lanthanideꢀexchanged according to [8]. This allowed us to derive the total
2
49

50
BIRYUKOVA et al.
Table 1. DME conversion into lower olefins on zeoliteꢀcontaining catalysts
Product composition, wt %
DME
conversion, %
Sample
olefins
alkanes
C –C
methane
2
5
Σ
C –C
ethylene
propylene
2
5
HZSMꢀ5/Al O
67.4
77.0
44.7
65.4
9.2
14.9
27.4
1.3
1.1
54.0
33.5
2
3
LaꢀZrꢀHZSMꢀ5/Al O3
26.7
2
Notes: Conditions: T = 320°C, P = 0.1 MPa, vmix = 2000 h–1. Feed mixture: 20% DME + 80% N . The product analysis was carried out
2
after 3 h of catalyst operation.
Table 2. Dependence of the DME conversion and the selectivity for C –C olefins on the grain size of the LaꢀZrꢀHZSMꢀ5/Al O
2 3
2
5
catalyst
=
Catalyst grain size, mm
.3–1.6
DME conversion, %
Selectivity for ΣC –C , wt %
2
5
1
25.7
26.6
27.6
23.6
25.8
70.2
72.1
71.1
71.5
73.6
1–2
2–3
3–4
5–6
Notes: Conditions: T = 320°C, P = 0.1 MPa, vmix = 1600–2000 h–1. Feed mixture: 20% DME + 80% N . The product analysis was carried
2
out after 5 h of catalyst operation.
acidity and the distribution function for the acid sites
by activation energies of ammonia desorption in the
range of activation energy variation from the lowest
RESULTS AND DISCUSSION
The data in Table 1 show that the catalyst based on
HZSMꢀ5 is active in DME conversion into olefins,
value (Emin) to the highest value (Emax), as well as to but it is not sufficiently selective for ethylene and proꢀ
calculate the mean value (
〈
E
) characterizing the averꢀ pylene; the major products are alkanes. Zeolite modiꢀ
〉
fication with lanthanum and zirconium results in a sigꢀ
nificant increase in the selectivity for lower olefins,
with the proportion of ethylene and propylene
increasing and the amount of alkanes decreasing from
age acid strength of the sites. The range of the desorpꢀ
tion activation energies was divided on equal portions
by 5 kJ/mol, within which the sites were considered
homogeneous, and their strength was determined by
the mean value of the activation energy in the middle
of the portion.
54 to 33.5 wt %.
To determine the region in which the process
occurs, the effect of the grain size of the modified catꢀ
alyst was examined. The obtained data are listed in
Table 2. One can see that the DME conversion does
not depend on the catalyst grain size, the DME conꢀ
version into lower olefins occurs in the kinetic region,
and the internal diffusion does not affect the reaction
The catalyst testing procedure was similar to that
described in [5]. The catalyst loading into the reactor
3
was ~6 cm and the catalyst weight was 3 g. The feed
space velocity of the reactant gas mixture was varied
–1
from 2000 to 20000 h . The DME concentration in rate. The absence of retardation by external diffusion
the starting gas mixture obtained from the syngas conꢀ was established in a similar way by varying the linear
flow rate of the feedstock at its constant space velocity.
version unit was in the range of 10 to 30 vol %. The
reaction products were analyzed by GLC: a column
In addition, the results (Tables 1 and 2) show that
this catalyst sample has a low stability and the DME
conversion decreases to even 25% in 5 h of catalyst
operation.
(
25 m 0.26 mm) packed with Porapak Q with flame
×
ionization and thermal conductivity detectors, helium
as a carrier gas, 30 ml/min. The steam was supplied
with a liquid pump at a required rate. A dose of water
passed through a highꢀtemperature oven to the mixing
chamber into which DME was fed from a cylinder at a
It is known that highꢀtemperature pretreatment of
zeolite improves its catalytic characteristics. In order
to enhance the catalyst stability, the zeolite was subꢀ
jected to preliminary highꢀtemperature treatment
certain rate. The catalyst was regenerated in air at
00 over at least 3 h.
Т=
(
Т
= 750
°
С) followed by modification with lanthanum
5
°С
and zirconium (Table 3). From the data in Table 3 it is
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CONVERSION OF DIMETHYL ETHER INTO LOWER OLEFINS
51
Table 3. Effect of the highꢀtemperature pretreatment of zeolite on the catalytic characteristics of LaꢀZrꢀHZSMꢀ5/Al O
2
3
Product composition, wt %
DME
Sample
olefins
conversion, %
alkanes
C –C
methane
2
5
Σ
C –C
ethylene
propylene
2
5
LaꢀZrꢀHZSMꢀ5/Al O3
77.0
81.7
65.4
74.4
26.7
33.3
27.4
31.9
1.1
1.2
33.5
24.4
2
LaꢀZrꢀHZSMꢀ5(T)/Al O3
2
Notes: Conditions: T = 320°C, P = 0.1 MPa. Feed mixture: 20% DME + 80% N . The product analysis was carried out after 3 h of catalyst
2
operation.
Table 4. Acidic properties of the zeoliteꢀcontaining catalysts
Sample
HZSMꢀ5/Al O
Total acidity, μmol/g
Ed < 130 kJ/mol (I)
Ed > 130 kJ/mol (II)
I/II
757
586
461
275 (36%)
261 (45%)
265 (58%)
482 (64%)
325 (55%)
196 (42%)
0.6
0.8
1.4
2
3
LaꢀZrꢀHZSMꢀ5/Al O3
2
LaꢀZrꢀHZSMꢀ5(T)/Al O3
2
Note: The acidic properties were examined by L.E. Kitaev and V.V. Yushchenko.
seen that after the thermal treatment of the catalyst
Thus, it can be concluded on the basis of these
(
LaꢀZrꢀHZSMꢀ5(Т)/Al O3), the overall selectivity for results that in order to impart high selectivity for lower
2
olefins, it is necessary for the zeolite catalyst to have a
high fraction of acid sites of medium strength, which
presumably mediate the formation of ethylene and
propylene.
The effect of the process parameters on the catalyst
characteristics were studied for the LaꢀZrꢀHZSMꢀ
lower olefins increases by almost 10 wt % and the
selectivity for alkanes decreases. Moreover, the cataꢀ
lytic characteristics of LaꢀZrꢀHZSMꢀ5(Т)/Al O3
2
remain unchanged even after 30 h of catalyst operaꢀ
tion.
The ammonia TPD data on the acidic properties of 5(Т)/Al O3 catalyst taken as an example. First, the
2
the initial zeolite catalyst and the catalyst modified effect of temperature in the range of 320–360 С was
°
examined (Table 5). One can see that the DME conꢀ
version increases to reach almost 100% with an
increase in the temperature. However, the selectivity
with lanthanum and zirconium and subjected to therꢀ
mal treatment are listed in Table 4. One can see that
the introduction of lanthanum and zirconium into the
zeolite catalyst decreases the total acidity and
increases the relative amount of acid sites of medium
strength (I) as compared to the proportion of strong
acid sites (II). The highꢀtemperature pretreatment of
zeolite reduces the total acidity to an even greater
for С –С5 olefins decreases from 75.7 wt % at
2
Т
= 320°С
to 44.1 wt % at
Т
= 360 С, with the increasꢀ
°
ing content of gaseous alkanes and methane. Thus, the
rate of the secondary reactions increases with an
increase in the temperature, and byꢀproducts
(
alkanes) begin to prevail in the products. The optimal
extent and drastically increases the proportion of temperature for the synthesis of lower olefins under
mediumꢀstrength acid sites. the given conditions is = 320
Т
°С.
Table 5. Temperature dependence of the selectivity for lower olefins and of the DME conversion over the LaꢀZrꢀHZSMꢀ5(T)/Al O
2
3
catalyst
Product composition, wt %
DME
conversion, %
T
,
°
C
olefins
alkanes
C –C
methane
2
5
Σ
C –C5
2
ethylene
propylene
320
340
360
81.7
97.9
98.5
75.7
55.3
44.1
32.1
24.8
17.6
29.5
17.2
16.1
1.0
1.5
2.3
23.3
43.2
53.6
Notes: Conditions: P = 0.1 MPa, vmix = 2000 h–1. Feed mixture: 20% DME + 80% N . The product analysis was carried out after 3 h of
2
catalyst operation.
PETROLEUM CHEMISTRY Vol. 51
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52
BIRYUKOVA et al.
Table 6. The dependence of the DME conversion and of the selectivity in respect to C –C olefins on the DME concentration
2
5
in the feedstock (at constant WHSV) on the LaꢀZrꢀHZSMꢀ5(T)/Al O catalyst
2
3
Product composition, wt %
olefins
ethylene
DME concentraꢀ
tion in the starting
mixture, vol %
Space velocity
DME
of the mixture, h– conversion, %
1
alkanes
C –C
methane
2
5
Σ
C –C
propylene
2
5
10
20
30
3800
2000
1200
96.0
81.7
90.9
68.7
75.7
70.6
30.8
32.1
34.0
25.0
29.5
24.9
1.0
1.0
1.2
30.3
23.3
28.2
Notes: Conditions: T = 320°C, P = 0.1 MPa, vdme = const = 1.59 h–1. Nitrogen is diluent in all cases. The product analysis was carried out
in 3 h of the catalyst operation.
The study of the effect of the DME concentration into olefins [9]. An analysis of the published data and
in the feedstock on the catalytic characteristics of Laꢀ the results of preliminary investigations of the olefin
ZrꢀHZSMꢀ5(Т)/Al O showed (Table 6) that no subꢀ synthesis from DME on the similar zeolite catalysts
2
3
stantial changes in the product distribution are show that the catalyst activity and selectivity depend
observed at the same throughput, however, the selecꢀ not only on the degree of DME conversion and the
tivity for lower olefins attains the highest value at the reaction temperature, but also on the amount of water
feedstock composition of 20% DME + 80% N2
.
in the initial mixture.
The feedstock space velocity has a significant effect
on the DME conversion and selectivity for lower oleꢀ
fins (Fig. 1). The dependence of the DME conversion
Therefore, the effect of the water content in the
reactant mixture on the catalytic characteristics of Laꢀ
ZrꢀНZSMꢀ5/Al O3 was studied. One can see in Fig. 3
2
on the space time (1/
ity of the catalytic system to increase with an increase
in 1/ (or with a decrease in the space velocity of the
reactant mixture).
v
) given in Fig. 1 shows the activꢀ
that water significantly affects the DME conversion.
The highest activity of the LaꢀZrꢀНZSMꢀ5/Al O catꢀ
2
3
v
alyst in DME conversion is observed when the feedꢀ
stock has a water content of at least 60 wt %. The study
of the selectivity of the reaction at the constant conꢀ
version attained by varying the feed space velocity has
shown a substantial rise in the selectivity for С –С
+
However, the selectivity for ethylene and C2
alkanes slightly increases, the propylene content
2
4
decreases, and the selectivity for С –С olefins almost
2
5
olefins with an increase in the water content in the
mixture to 60–80 wt %. The highest selectivity for
does not change with an increase in the DME converꢀ
sion (Fig. 2).
С2
⎯С4 olefins is 80 wt % (Fig. 4). At the same time, it
There is no DME market to date. Dimethyl ether is
synthesized in many processes via methanol dehydraꢀ
tion on active alumina with the subsequent conversion
of the resulting DME, methanol, and water mixture
is known [4] that steam destroys the zeolite structure
90
0
8
70
=
1
00
С
2
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
=
60
50
40
30
С
3
+
Σ
C
2
C – C
2 5
=
Σ
20
10
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
, h
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
, h
1/
v
1/
v
Fig. 1. Dependence of the DME conversion on the space
time over the LaꢀZrꢀHZSMꢀ5(T)/Al O catalyst (
Fig. 2. Dependence of the selectivity for products on the
space time over the LaꢀZrꢀHZSMꢀ5(T)/Al O catalyst
T
=
2
3
2 3
–1
–1
3
20°C,
P
= 0.1 MPa,
v
= 2000—20000 h . Feed mixꢀ
(
T
= 320°C,
P
= 0.1 MPa,
v
= 2000—20000 h . Feed
mix
mix
ture: 20% DME + 80% N2).
mixture: 20% DME + 80% N2).
PETROLEUM CHEMISTRY Vol. 51
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CONVERSION OF DIMETHYL ETHER INTO LOWER OLEFINS
53
80
70
60
50
40
30
20
10
0
30
40
50
60
70
80
90
100
Water content in the feestock, wt %
Fig. 3. Dependence of the DME conversion on the water content in the feed DME : H O mixture on the LaꢀZrꢀHZSMꢀ
2
–1
5
(T)/Al O catalyst (
T
= 320°C,
P
= 0.1 MPa,
v
= 4200–33500 h ).
2
3
mix
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Σ
Σ
Σ
С2
+
=
=
С – C
2
4
=
=
3
С – C
2
3
0
40
50
60
70
80
90
100
Water content in the feedstock, wt %
Fig. 4. Dependence of the selectivity for products on the water content in the feed mixture DME : H O over the LaꢀZrꢀHZSMꢀ
2
5
(T)/Al O catalyst (at DME conversion ~68%).
2 3
Fresh
First regeneration
Second regeneration
Third regeneration
90
80
70
60
50
40
30
20
10
0
2
3
4
19
22
25
29
44
46
Catalyst onꢀstream time, h
Fig. 5. Dependence of the DME conversion on the number of catalyst regenerations.
PETROLEUM CHEMISTRY Vol. 51 No. 1 2011

54
BIRYUKOVA et al.
upon longꢀterm operation, resulting in its deactivation
and activity loss.
ACKNOWLEDGMENTS
This work was supported by the President of the
Russian Federation under the support program for
young scientists, grant no. MKꢀ1332.2009.3 (contract
no. 02.120.11.1332ꢀMK).
The LaꢀZrꢀНZSMꢀ5/Al O activity in the presence
2
3
of steam in the feed mixture is retained at the level of
0% for not less than 46 h (Fig. 5), with at least threeꢀ
7
fold oxidative catalyst regeneration having no effect on
the activity and selectivity of the zeolite catalyst based
on HZSMꢀ5.
REFERENCES
1. O. B. Braginskii, World Petroleum Refining and Petroꢀ
chemical Industry (Academia, Moscow, 2009) [in Rusꢀ
sian].
Thus, the replacement of nitrogen with steam can
not only enhance the selectivity of the LaꢀZrꢀНZSMꢀ
2
. V. A. Men’shchikov and M. Yu. Sinev, Katal. Promꢀsti,
No. 1, 25 (2005).
3. M. Stoker, Microporous Mesoporous Mater. 29, 3
1999).
5
/Al O catalyst, but also can extend the catalyst serꢀ
2 3
vice life.
(
The results of this study lead to the following conꢀ
4
. S. N. Khadzhiev, Cracking of Petroleum Fractions on
Zeolitic Catalysts (Khimiya, Moscow, 1982) [in Rusꢀ
sian].
clusions. The introduction of lanthanum and zircoꢀ
nium into the HZSMꢀ5 zeolite imparts a high activity
in DME conversion and a medium selectivity for
5. N. V. Kolesnichenko, O. V. Yashina, N. A. Markova,
et al., Neftekhimiya 49, 45 (2009) [Pet. Chem. 49, 42
С2⎯С5 olefins to the catalyst. The preliminary highꢀ
(2009)].
temperature treatment of the HZSMꢀ5 zeolite modiꢀ
fied by the lanthanum and zirconium compounds sigꢀ
nificantly increases the selectivity for lower olefins.
The introduction of steam into the reaction zone
6. P. T. Barger and A. Heights, US Patent No. 5095163
1992).
(
7
. N. V. Kolesnichenko, L. E. Kitaev, Z. M. Bukina, et al.,
Kinet. Katal. 48, 946 (2007).
increases the LaꢀZrꢀНZSMꢀ5/Al O catalyst activity
2
3
8. V. V. Yushchenko, Zh. Fiz. Khim. 71, 6 (1997).
. M. Hask, U. Koss, R. Konig, et al., US Patent
No. 7015369 (2006).
and selectivity and significantly prolongs its onꢀstream
time.
9
PETROLEUM CHEMISTRY Vol. 51
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2011