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Published on the web May 14, 2011
Fast and Quantitative Dehydration of Lower Alcohols to Corresponding Olefins
on Mesoporous Silica Catalyst
Teruki Haishi, Kouji Kasai, and Masakazu Iwamoto*
Chemical Resources Laboratory, Tokyo Institute of Technology,
259-R1-5 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503
4
(
Received March 25, 2011; CL-110254; E-mail: iwamoto@res.titech.ac.jp)
Ethanol, 1-propanol, 2-propanol, and 1-butanol were
respectively. The hexagonal structure of resulting M41 was
confirmed by appearance of 2ª = 2.580, 4.476, and 5.124
degree peaks in X-ray diffraction patterns (Cu K¡, Ni filter),
which corresponded to (100), (110), and (200), respectively. The
Si/Al atomic ratio was 237, in which the origin of Al was an
impurity of the raw material, colloidal silica. The catalytic
reaction was carried out by using a fixed bed flow reactor at
atmospheric pressure. 0.050.5 g of catalyst was loaded in the
reactor and heated under N2 at 673 K, and then EtOH (PEtOH =
quantitatively dehydrated to the corresponding olefins on
mesoporous silica MCM-41 catalyst. The reaction rates were
high and no deactivation was observed for 50 h. Two reaction
routes were suggested: the intermolecular dehydration of alcohol
and subsequent decomposition of ether and the direct de-
hydration of alcohol.
¹
1
Utilization of bioethanol (bEtOH) as alternative to or as an
additive of automobile fuel has rapidly expanded all over the
world. This is of course a way to use renewable resources and
suppress carbon dioxide emission, while another challenge is
the conversion of bEtOH to various olefins and their use for
2.812.6%, N balance, total flow rate 10300 mL min ) was
2
allowed to flow into the reactor at the desired temperature. The
product distribution was determined by an on-line gas chromato-
graph.
The dependence of conversion of EtOH on the reaction
temperature was first measured. The degree of EtOH conversion
reached approximately 100% at 623 K as shown in Figure 1.
1
production of chemicals and polymers. The latter would be very
significant to fix carbon dioxide for the long-term period. Many
efforts have, therefore, been devoted to development of selective
=
C2 was almost quantitatively produced at this temperature
=
conversion systems of bEtOH to ethene (C2 ). It is widely
though diethyl ether (DEE) was produced as a by-product at
=
known that the dehydration of alcohols is well catalyzed on
473573 K. It is worth noting that no C4 was observed at 473
2
various types of acids including modified aluminas, supported
773 K, being completely different from the results on zeolites on
3
48
9
=
=
heteropolyacids, zeolites,
mesoporous materials, and oth-
which the productions of C4 and C6 olefins (C6 ) and some
1
0
48
ers, but the activity and selectivity reported so far have been
insufficient. For example, the reaction rates and the selectivity of
C2 on proton- or metal-modified zeolites should be improved,
aromatics were reported. It is widely recognized that strong
=
=
=
acid sites induce oligomerization of C2 to C4 and C6 ;
therefore, the quantitative progress in dehydration shown in
Figure 1 could be clearly attributed to mild and uniform acidity
of the M41 catalyst.
=
the selectivity is often restricted to ca. 96% due to strong acidic
sites which cause oligomerization, polymerization, and fission of
the produced lower olefins.5 The various reactions in the zeolite
,6
To reveal the effect of the mesoporous structure of M41
on the catalytic activity, SiO2 was separately prepared under
vigorous stirring by using the same raw materials as those
5
7
pores finally result in coke formation and short lifetime.
8
Niobium silicate or silicotungstic acid supported on meso-
porous silica have been reported to show good selectivity for
C2 formation, but the reaction rates are not high due to the low
3
=
surface areas. In addition, the low stability of loaded active
components under high partial pressure of water would be a
disadvantage for practical use.
The novel acidic properties of mesoporous silica material,
1
1,12
MCM-41 (M41), have been reported from the present
and
1
3
other groups. The acidity is not strong but unique to promote
various selective catalyses. Our efforts have, therefore, been
devoted to revealing the catalytic activity of M41 for the
dehydration of EtOH, 1- and 2-propanol (PrOH), and 1-butanol
=
=
=
(
BuOH) to C2 , propene (C3 ), and butenes (C4 ). We found
the fast, quantitative, and stable catalyst can solve the above
problems. The catalytic dehydration of alcohols is well known
to be an easy heterogeneous catalytic reaction, but quantitative
progress without deactivation is still necessary.
M41 was prepared in the reported manner by using
C12H25N(CH3)3Br as the template and colloidal silica as the
Figure 1. Reaction temperature dependence of conversion of
¹1
EtOH on M41. Catalyst wt. 0.5 g, total flow rate 10 mL min
1
4
¹1
silica source. After calcination of M41 at 873 K for 6 h in air,
the BET surface area and the BJH pore diameter determined by
(GHSV 400 h ), PEtOH 5.5% (N balance). Symbols: closed
2
=
circle, conversion of EtOH; open circle, yield of C2 ; open
2
¹1
a N2 adsorption measurement were 1010 m g and 2.12 nm,
triangle, DEE; open square, acetaldehyde (AA).
Chem. Lett. 2011, 40, 614616
© 2011 The Chemical Society of Japan