Direct Synthesis of Dimethyl Ether (DME) from Syngas

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Direct Synthesis of Dimethyl Ether (DME) from Syngas
Kaoru TAKEISHI, and Yoshimi AKAIKE
Department of Materials Science and Chemical Engineering
Shizuoka University
3-5-1, Jouhoku, Naka-ku, Hamamatsu-shi, Shzuoka-ken, 432-8561
JAPAN
[email protected]
Abstract: We have developed appropriate and excellent catalysts for direct DME synthesis. The catalysts,
Cu-Zn/Al2O3 catalysts prepared by the sol-gel method, produce DME with high DME activity and high DME
selectivity under milder reaction temperature and pressure compared with the usual direct DME synthesis catalysts
(mixed catalysts of methanol synthesis catalysts and methanol dehydration catalysts). It will be the reason why the
methanol synthesis active sites (copper) and the methanol dehydration active sites (alumina) on the sol-gel
Cu/Al2O3 catalysts exist closer than those of the mixed catalysts.
Key-Words: Dimethyl ether, DME, hydrogen, clean fuel, catalyst, sol-gel method, alumina, copper, direct
synthesis, syngas.
used. This mixed catalyst is similar catalysts for patent
catalysts for direct DME synthesis [4]. The all
catalysts were calcined at 500 oC for 5 h and were
reduced by flowing H2 at 450 oC for 10 h. This severe
pretreatment was particularly performed for reactive
comparison to avoid the catalytic deterioration with
sintering of the catalysts by the reaction heat on
continuous experiments with the same catalysts. A
flow reactor was used for CO hydrogenation. The used
weight of catalysts was 0.5 g, and the supply of the
reaction gas flow was mainly H2/CO/Ar = 7.5/7.5/1.5
ml min-1. Argon gas was an internal standard for gas
chromatography. The reaction gas and products were
analyzed by gas chromatographs (TCD and FID).
Scanning electron microscopy - energy dispersion
X-ray spectrometry (SEM-EDS) analysis was
performed for the surface characterization.
1 Introduction
Dimethyl ether (DME) is slightly expensive chemical
now, because DME is manufactured by dehydration
process of methanol. However, DME is expected as a
clean fuel for the 21st century, from the reasons that
DME does not contain poisonous substances, and
DME burns without particulate matters (PM) [1].
DME will be used as substitutes of liquefied
petroleum gas (LPG) and diesel oil, and will be used
for hydrogen carrier. Therefore, demand of DME will
increase rapidly, and it is necessary to mass-produce
DME economically. There is a method, direct
synthesis of DME, that DME is synthesized directly
from syngas (hydrogen and carbon monoxide), not
synthesized by dehydration of methanol. Excellent
catalysts for the direct synthesis are necessary. In this
study, copper alumina catalysts prepared by the
sol-gel method that is appropriate for DME steam
reforming [2, 3] are applied for direct DME synthesis
(3H2 + 3CO → CH3OCH3 + 2CO2) that is similar
reaction of DME steam reforming (CH3OCH3 + 3H2O
→ 3H2 + 2CO2).
3 Results and discussion
3.1 CO hydrogenation
The single type catalyst and the mixed catalyst were
carried out for CO hydrogenation. The part of the
results is shown in Fig. 1. Much amount of DME was
produced over Cu-Zn(36-4wt.%)/Al2O3 catalyst
prepared by the sol-gel method at 250 oC of the lower
reaction temperature. The less amount of DME was
produced over the mixed catalyst of the methanol
synthesis catalyst (N211) and the methanol
dehydration catalyst (BK-105) at 310 oC of the higher
reaction temperature. In other experiments, even if the
reaction gases contain some oxygen, the sol-gel
2 Experimenals
For hydrogenation of carbon monoxide, Cu-Zn
(36-4wt.%)/Al2O3 catalyst prepared by the sol-gel
method was used in single, not mixed with other
catalysts such as alumina. As the comparison, a mixed
catalyst with a commercial catalyst CuO-ZnO
(50-50wt.%) (N211, Nikki Chemical Co., Ltd.) and
alumina (BK-105, Sumitomo Chemical Co., Ltd.) was
ISSN: 1790-5095
408
ISBN: 978-960-474-159-5
RECENT ADVANCES in ENERGY & ENVIRONMENT
Durability test for direct DME synthesis, catalyst
life-time test was carried out. Fig.5 and Fig. 6 show the
part of the results. In case of DME production rate,
there was a decrease of about 100 μmol g-cat-1 h-1 from
the first biggest rate. However, the DME rate
production is almost constant after this decrease. Rate
production of methane and methanol also slightly
decreased. However, there is no obvious big
deactivation such as less production. The further
development is still need, but the catalysts are stable
and they have enough capability for practical use.
Cu-Zn/Al2O3 catalysts produce DME effectively with
long durability. The single type catalysts that have
copper sites for methanol synthesis and alumina sites
for methanol dehydration on the surface are more
appropriate and more excellent for direct DME
synthesis than the mixed catalysts that are one of the
patent catalysts for direct DME synthesis.
3.2 Hydrogen ratio for direct DME synthesis
Dependency of H2/(H2+CO) ratio was investigated on
Cu-Zn(36-4wt.%)/Al2O3 catalyst prepared by the
sol-gel method. Fig. 2 shows the part of the results.
DME is produced with the fastest production rate at
the ratio of H2/(H2+CO) = 0.5. It is suggested that
DME is produced over Cu-Zn/Al2O3 catalyst prepared
by the sol-gel method, with the reaction of the
chemical equation, 3H2 + 3CO → CH3OCH3 + CO2.
4 Conclusion
We have developed the appropriate and excellent
catalyst for direct DME synthesis. The catalysts,
Cu-Zn/Al2O3 catalysts prepared by the sol-gel method,
produce DME with high activity and high selectivity
under the mild reaction temperature and pressure.
3.3 Surface analysis of the catalysts
SEM-EDS analysis confirmed that copper sites for
methanol synthesis (and water gas shift reaction) and
alumina sites for methanol dehydration are co-existing
and the both sites are dispersed well on the surface of
Cu-Zn/Al2O3 catalyst prepared by the sol-gel method.
The distances of the sites for each reaction (methanol
synthesis, methanol dehydration, and water gas shift
reaction) are shorter than those of the mixed catalyst,
so the reactions are more sequentially and
systematically occurred, and the DME production rate
will be faster.
References:
[1] T. H. Fleisch, A. Basu, M. J. Gradassi, J. G. Masin,
Dimethyl ether: A fuel for the 21st century, Studies
in Surface Science and Catalysis, Vol. 107, 1997,
pp. 117-125.
[2] K. Takeishi, H. Suzuki, Steam reforming of
dimethyl ether, Applied Catalysis A: General, Vol.
260, 2004, pp. 111-117.
[3] K. Takeishi, K. Yamamoto, Catalysts for hydrogen
production from dimethyl ether, Japan Patent No.
3951127; US Patent No. 7,241,718; etc.
[4] WO93/10069; JP1991-8446; JP1991-181435;
JP1992-264046; etc.
[5] K. Takeishi, Dimethyl ether and catalyst
development for production from syngas, Biofuels,
Vol. 1, No. 1, 2010, pp. 217-226.
3.4 Pressure effect for direct DME synthesis
Dependency of pressure for CO hydrogenation was
investigated on Cu-Zn(36-4wt.%)/Al2O3 catalyst
prepared by the sol-gel method. Fig. 3 and Fig. 4 show
the part of the results. Rate of DME production is
linearly increased with increasing of the reaction
absolute pressure. Production rate of methanol also
increases with increasing the pressure. Methane
production rate is almost stable. (Cf. Fig. 3) From
these phenomena, selectivity for DME is increased to
100% depending on the increase of the reaction
pressure. The DME selectivity is 98% under the
pressure of 1.6 MPa. (Cf. Fig. 4) This value is very
high compared with some companies’ data and the
reaction condition is milder than those of the
companies’ (Cf. Table 1 [5]).
3.5 Durability test of the catalyst for direct
DME synthesis
ISSN: 1790-5095
409
ISBN: 978-960-474-159-5
Me2O(N211)
MeOH(N211)
20
15
10
5
0
140
180
220
260
300
340
380
Temperature / ℃
8
300
6
200
4
100
2
0
0
0.0
0.3
0.6
0.9
1.2
1.5
1.8
Fig. 3. Effect of pressure on activity of CO
hydrogenation over Cu-Zn(36-4wt.%)Al2O3 catalyst
at 220 oC. Catalyst: 0.5g, H2/CO/Ar = 7.5/7.5/1.5 ml
min-1.
45
100
20
40
90
80
18
16
Selectivity for DME / C . %
-1
-1
400
Absolute pressure / MPa
Fig. 1.
Activity of CO hydrogenation over
Cu-Zn(36-4wt.%)/Al2O3 (Sol), and a catalyst (N211)
physically mixed CuO-ZnO(50-50wt.%) and Al2O3.
Catalyst: 0.5 g, H2/CO/Ar = 7.5/7.5/1.5 ml min-1.
Production rate / C . µmol g-cat h
10
Me2O
CH4
C1
MeOH
35
30
Me2O
25
CH4
20
15
10
5
70
Me2O
14
60
50
CH4
C1
12
10
MeOH
40
30
8
6
20
10
4
2
0
0
0
0.0
0.2
0.3
0.4
0.5
0.6
H2/(H2+CO)
0.7
0.8
0.3
0.6
0.9
1.2
1.5
Absolute pressure / MPa
1.8
Fig. 4. Effect of pressure on selectivity of CO
hydrogenation over Cu-Zn(36-4wt.%)Al2O3
catalyst at 220 oC. Catalyst: 0.5g, H2/CO/Ar =
7.5/7.5/1.5 ml min-1.
Fig. 2. H2/(H2+CO) and activity of CO hydrogenation
over Cu-Zn(36-4wt%)/Al2O3 at 220 oC. Catalyst:
0.5 g, (H2+CO)/Ar = (Total 15 ml min-1)/1.5 ml
min-1.
ISSN: 1790-5095
Selectivity for methane or
methanol / C . %
25
500
-1
Me2O(Sol)
-1
-1
Production rate / C .µmol g-cat h
Rate of DME production / C . µmol g -cat h
30
Rate of methane or methanol
-1 -1
production / C . µmol g -cat h
-1
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410
ISBN: 978-960-474-159-5
100
45
40
35
400
30
300
25
20
200
15
100
10
5
0
Selectivity for DME / C . %
500
CH4
Rate of methane or methanol
-1 -1
produtcion / C . µmol g -cat h
50
Me2O
MeOH
80
40
80
120
160
Reaction time / h
Me2O
CH4
MeOH
8
60
6
40
4
20
2
0
0
0
0
0
10
Selectivity for methane or
methanol / C . %
600
-1
Rate of DME production/ C . µmol g -cat- h
-1
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40
200
80
120
160
Reaction time / h
200
Fig. 6.
Time course of selectivity on CO
hydrogenation over Cu-Zn(36-4wt.%)Al2O3 catalyst
at 220 oC under 1.1 MPa. Catalyst: 0.5g, H2/CO/Ar =
7.5/7.5/1.5 ml min-1.
Fig. 5. Time course of activity on CO hydrogenation
over Cu-Zn(36-4wt.%)Al2O3 catalyst at 220 oC under
1.1 MPa. Catalyst: 0.5g, H2/CO/Ar = 7.5/7.5/1.5 ml
min-1.
Table 1 Comparison of reaction results on direct DME synthesis between our single-type catalyst and
some mixed catalysts developed by some companies [5]
Catalystr
Developer
H2/CO Ratio
Reactor type
Reaction temperature (oC)
Reaction pressure (MPa)
One-pass conversion (%)
DME/(DME+Methanol)(%)
ISSN: 1790-5095
Single type
(Cu-Zn/Al2O3
prepared using
sol-gel method)
Mixed type
(Methanol-synthesis, dehydration condensation, and
water-gas shift reaction catalysts)
Shizuoka Univ.
JFE (NKK)
Air Products
1.0
Fixed bed
reactor
220
1.6
5-15
98
1.0
Slurry
reactor
250-280
5-6
55-60
90
0.7
Slurry
reactor
250-280
5-10
33
30-80
411
Haldor
Topsoe
2
Fixed bed
reactor
210-290
7-8
18
60-70
KOGAS
1.0
Fixed bed
reactor
240-260
5-6
?
85-95
ISBN: 978-960-474-159-5

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