Synthesis of dimethyl ether from supercritical methanol in the presence of aluminum

Article abstract of DOI:10.1246/cl.2004.394

A novel method to synthesize dimethyl ether (DME) is presented. When methanol is treated with aluminum metal in supercritical conditions at a density of 0.39 kg/dm³, it is found that DME is generated above 275°C through a single-step procedure. The DME production increases with the temperature elevation, and it becomes the main product above 300°C with by-products of hydrogen and methane. DME is considered to be produced at the formation step of methyl derivative of boehmite and/or its surface catalytic effect.

Full text of DOI:10.1246/cl.2004.394

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94
Chemistry Letters Vol.33, No.4 (2004)
Synthesis of Dimethyl Ether from Supercritical Methanol in the Presence of Aluminum
Ã
Yuma Usui, Chihiro Wakai, Nobuyuki Matubayasi, and Masaru Nakahara
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011
(Received December 24, 2003; CL-031272)
A novel method to synthesize dimethyl ether (DME) is pre-
sented. When methanol is treated with aluminum metal in super-
magnesium powder (Nacalai Tesque) were used without further
purification. The powder size of aluminum was 850–425 mm
(about 18–35 mesh), and that of magnesium was 20–70 mesh
(about 740–210 mm). In a quartz tube reactor of 1.45 mm i.d.,
3:2 Æ 0:2 mg (0.12 mmol) of aluminium powder or 2:8 Æ
0:1 mg (0.12 mmol) of magnesium powder was placed, and
methanol (Wako) was added to 50% of the reactor volume
3
critical conditions at a density of 0.39 kg/dm , it is found that
ꢀ
DME is generated above 275 C through a single-step procedure.
The DME production increases with the temperature elevation,
ꢀ
and it becomes the main product above 300 C with by-products
of hydrogen and methane. DME is considered to be produced at
the formation step of methyl derivative of boehmite and/or its
surface catalytic effect.
À4
3
(1:3 Â 10 dm ). The air in the reactor was replaced by argon.
The reactor was then put into an electric furnace kept at 200–
ꢀ
ꢀ
3
25 C; the temperature was controlled within Æ1 C. Since
ꢀ
the critical temperature of methanol is 239 C, the solution sys-
tem at supercritical temperatures is homogeneous with interfaces
to metal powders and involves the methanol density of 0.39 kg/
ꢀ
Dimethyl ether (DME) liquefies at À25 C and 0.1 MPa or at
room temperature and 0.6 MPa. It costs low for transportation
and storage compared to the liquefied natural gas, which is con-
3
dm . After the reaction time, the sample was removed from the
ꢀ
veyed and stored at À160 C. In addition, SOx and soot are not
furnace and quenched in a water bath. After the reaction, alumi-
nium and magnesium powders were observed to be changed into
white or gray particles, and the liquid and gas phases coexisted in
the sample vessel. The liquid and gas phases were separately
produced at all with few NOx when DME is burned. Therefore,
the potential of DME as a clean energy source is promising and
1
its application is in preparation.
In the synthesis of DME, the catalyst improvement is sup-
1
13
measured by H and C NMR at room temperature (JEOL
ECA-400N). A D2O solution of 1,3,5-trioxane was used as an
external reference, which was filled in the NMR tube with the
sample vessel. In addition to metal aluminum, aluminum trieth-
2
–4
posed to be indispensable. For example, with solid-acid cata-
lysts, such as ꢀ-Al2O3, H-ZSM-5, amorphous alumina-silicas,
and titania-modified zirconia, the catalytic conversion of metha-
nol to DME is well characterized. Since DME needs to be pro-
duced on a large scale in the near future, its clean and convenient
method of synthesis is desirable to be established. In this study, a
novel synthetic method of DME is presented utilizing a modifi-
cation of aluminum. The starting materials in our method are on-
ly methanol and aluminum metal, which is abundant in our sur-
roundings and changes into unique forms in organic solvents.
Aluminum powder (Kojundo Chemical Laboratory) and
ꢀ
oxide (Aldrich) was examined at 300 C. In this case, the used
solvent was methanol and ethanol.
Figure 1 shows the proton spectra for the gas phase of the
sample with aluminum metal before and after the reaction. Be-
fore the reaction, only two peaks assigned to the external refer-
ence were detected; one peak at 2.6 ppm represents 1,3,5-triox-
ane, and another at 2.1 ppm stands for impurity HDO in D2O.
before the reaction
CH
3
OH
3
CH OH
before the reaction
HDO
(
(
CH
2
O)
3
HDO
(external reference)
external reference)
(
external reference)
(
(
CH O)
2
3
external reference)
after the reaction
2
H O
3 3
CH OCH
after the reaction
3 3
CH OCH
H
2
CH
4
CH
4
H
2
5
4
3
2
1
0
5
4
3
2
1
0
Chemical Shift / ppm
Chemical Shift / ppm
1
1
Figure 1. The gas-phase H NMR spectra of methanol with alu-
ꢀ
Figure 2. The liquid-phase H NMR spectra of methanol with
ꢀ
minum metal. The reaction was performed for 1 h at 300 C and
3
aluminum metal. The reaction was performed for 1 h at 300 C
3
the methanol density of 0.39 kg/dm . 1,3,5-trioxane employed
as an external reference is set at 2.6 ppm. A broad peak at
and the methanol density of 0.39 kg/dm . 1,3,5-trioxane em-
ployed as an external reference is set at 4.5 ppm. After the reac-
tion, the methanol OH peak was shifted to the lower magnetic
field.
1.4 ppm is methyl signal of liquid methanol which adheres to
the reactor wall.
Copyright ꢀ 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.4 (2004)
395
Figure 3. Temperature dependence of the product concentra-
tion from the methanol reaction with aluminum metal for 1 h.
The conversion ratios of H2, CH4, and DME refer to their mole
ratios to 0.5, 1, and 0.5 times of the initial methanol load, respec-
tively.
Figure 4. Time dependence of the product concentration and
the conversion ratio from the methanol reaction with aluminum
metal at 300 C.
ꢀ
generation of hydrogen, and the transformation into aluminum
oxides produces methane.
Inoue et al. found that aluminum was transformed at 250–
ꢀ
After the 1 h reaction at 300 C, three new peaks emerged; the
ꢀ
3
groups derived from solvent alcohol via aluminum alkoxide.
00 C into a layer structure of boehmite with alkyl pendant
peaks at 0.2, 3.3, and 4.6 ppm represent methane, DME, and hy-
drogen, respectively. Figure 2 shows the corresponding spectra
for the liquid phase. Before the reaction, two peaks at 3.4 ppm
and ꢁ5 ppm are assigned to methanol as a solvent. 1,3,5-trioxane
gives a peak at 4.5 ppm, and the impurity HDO in D2O at
7,8
If the aluminum transformation proceeds through the scheme
as Inoue et al. suggested, it is considered that DME is produced
at the formation step of the methyl derivative of boehmite from
aluminum methoxide and/or through the surface reaction on
boehmite. To further confirm the production of a symmetric al-
kyl ether from the corresponding alcohol in the presence of alu-
minum alkoxides, we also examined the reaction of methanol
4
4
.0 ppm. After the reaction, three peaks at 0.2, 3.3, and
.6 ppm appeared similarly and represent methane, DME, and
hydrogen, respectively. The H2O peak also emerged at
.4 ppm after the reaction. This shows that the dehydration is a
4
ꢀ
and ethanol at 300 C in the presence of aluminum ethoxide.
As a result, only DME was produced from methanol and only
diethyl ether was produced from ethanol.
step to form DME from methanol. Without metals, those prod-
ucts were not detected.
Figure 3 plots the concentrations and conversion ratios of
hydrogen, methane, and DME from the 1 h reaction against the
In this communication, we demonstrated that DME is
formed from methanol in the presence of aluminum metal. This
synthetic method opens a possibility of a simple and mass
production of DME.
ꢀ
temperature. At 200 C, no products are generated. Hydrogen
ꢀ
is the main product at 250 and 275 C, and is overwhelmed by
ꢀ
DME at higher temperatures. At 325 C, DME is produced as
ꢁ
3 times as hydrogen. In other words, the selectivity of DME
increases with the temperature rise. Figure 4 shows the product
This work is supported by the Grant-in-Aid for Scientific
Research (Nos. 14540531, 15205004, and 15076205) from the
Japan Society for the Promotion of Science, the Grant-in-Aid
for Creative Scientific Research (No. 13NP0201) from the Min-
istry of Education, Culture, Sports, Science, and Technology,
and by CREST (Core Research for Evolutional Science and
Technology) of Japan Science and Technology Corporation
ꢀ
concentrations and conversion ratios at 300 C against the reac-
tion time. The concentrations of hydrogen and methane increase
3
with the reaction time, and converge at 1.6 and 0.6 mol/dm , re-
spectively. At the initial stage of the reaction, DME is slowly
generated in comparison to hydrogen. At later stages, its concen-
tration rises to ꢁ3 times of that of hydrogen, and exhibits a con-
(
JST).
3
verging behavior at 4.5 mol/dm .
When the magnesium metal is used, DME was not detected
as a product. Only hydrogen was generated at a concentration of
References and Notes
1
2
3
4
5
http://www.enecho.meti.go.jp/info/committee/report/001004c/dme.
pdf
F. Mizukami, Y. Kiyozumi, T. Sano, S. Niwa, M. Toba, and S. Shin, J.
Sol-Gel Sci. Technol., 13, 1027 (1998).
P. K. Kiviranta-Paakkonen, L. K. Struckmann, J. A. Linnekoski, and
A. O. I. Krause, Ind. Eng. Chem. Res., 37, 18 (1998).
M. T. Xu, J. H. Lunsford, D. W. Goodman, and A. Bhattacharyya, Appl.
Catal., A, 149, 289 (1997).
3
ꢀ
1
.4 mol/dm above 150 C with a small amount of methane
ꢀ
5
above 200 C. Thus, the magnesium metal is not useful for
the DME production.
The known reactions which generate hydrogen from metha-
nol are the partial oxidization of methanol, steam reforming re-
6
action, and metal oxidation reaction. If our reaction is either the
3
The initial concentrations of Al and Mg are 1.8 mol/dm . Stoichiomet-
partial oxidation or steam reforming reaction, CO or CO2 will be
generated along with hydrogen. According to 13C NMR, howev-
er, only methane and DME were observed, and CO and CO2
were not. In addition, the total amount of hydrogen and methane
converged at ꢁ1:2 times of the mole amount of aluminum metal
rically, hydrogen and methane generated by the metal oxidation reac-
tion is equal to 1.5 times of Al and to Mg. In this experiment, their prod-
ucts amount to 80% of the theoretical concentrations, and about 20% of
metal had already been oxidized before the experiment started. Thus,
our results are consistent with the stoichiometric expectations.
J. Agrell, H. Birgersson, M. Boutonnet, I. Melian-Cabrera, R. M.
Navarro, and J. L. G. Fierro, J. Catal., 219, 389 (2003).
6
5
added. From these results, it is concluded that the metal oxida-
tion generates hydrogen and methane. In other words, the trans-
formation of aluminum into aluminum methoxide leads to the
7
8
M. Inoue, Y. Kondo, and T. Inui, Inorg. Chem., 27, 215 (1988).
M. Inoue, M. Kimura, and T. Inui, Chem. Mater., 12, 55 (2000).
Published on the web (Advance View) March 6, 2004; DOI 10.1246/cl.2004.394