Conversion of ethanol into polyolefin building blocks: Reaction pathways on nickel ion-loaded mesoporous silica

Article abstract of DOI:10.1002/cssc.201100168

Ethanol to olefins: Very fast, selective, and stable formation of ethene, propene, and butenes from ethanol is achieved on Ni-MCM-41 at 573-723K, without deactivation. Two reaction pathways via diethyl ether and acetaldehyde are suggested. The results are relevant for the possible use of bioethanol as a renewable material for the production of plastics.

Full text of DOI:10.1002/cssc.201100168

DOI: 10.1002/cssc.201100168
Conversion of Ethanol into Polyolefin Building Blocks: Reaction Pathways
on Nickel Ion-loaded Mesoporous Silica
[
a]
Masakazu Iwamoto,* Kouji Kasai, and Teruki Haishi
The use of bioethanol (bEtOH) as an alternative (or additive)
for automobile fuels has increased rapidly all over the world.
This is one way of using renewable resources to suppress
carbon dioxide emissions, while another challenge is the con-
version of bEtOH to various olefins and their use for produc-
The influence of temperature on EtOH conversion over Ni-
M41 is summarized in Figure 1. Many kinds of products were
=
formed in addition to C2 . Diethylether (DEE) was mainly ob-
[
1–7]
tion of chemicals and polymers.
The latter would be very
significant for the long-term fixation of carbon dioxide. Many
efforts have therefore been devoted to the development of
=
systems for converting bEtOH to ethene (C2 ) and other lower
=
olefins. In particular conversion to propene (C3 ) is desirable
=
due to the greater demand for C3 derivatives, such as pro-
[
2]
pene oxide, acrylonitrile, and polypropene.
Catalytic conversions of EtOH on zeolites
[
3–5]
and metal
have been widely studied. On zeolites, the activity
[
6,7]
oxides
and selectivity in the many studies reported so far are insuffi-
cient. The major weakness is catalyst deactivation. For exam-
=
ple, the selectivity towards C3 on proton- or metal-modified
zeolites is usually ca. 20–30% and decreases with reaction
=
time, although sometimes higher C3 selectivity values are ob-
[
3–5]
served upon catalyst degradation.
Oligomerization, poly-
Figure 1. Dependence of EtOH conversion over a Ni-M41 (Si/Ni=23) catalyst
merization, and fission reactions on strong acid sites in zeolite
ꢀ1
on reaction temperature. Catalyst wt. 0.2 g, flow rate 10 mLmin , PEtOH
=
=
=
=
pores result in the formation of C3 and butenes (C4 ) due to
5.6 kPa (N balance). Conversion of EtOH (*), yield of C2 (*), C3 (~),
2
=
[
3–5]
C4 (&), DEE ( ), and AA (&).
~
shape selectivity.
However, the random reactions in the
pores finally result in coke formation and short catalyst life
times. EtOH can also react on metal oxide surfaces to give vari-
ous chemicals. Acid sites are widely recognized to lead to de-
tained at around 523 K. DEE has been reported earlier as an in-
termediate compound in the dehydration, decomposing to
=
hydration of EtOH, giving C2 , while basic sites lead to dehy-
[
6,7]
=
[8b]
=
drogenation to yield acetaldehyde (AA).
As a result, many
yield EtOH and C2 at higher temperatures. The C2 yield
sharply increased at 573 K, and reached ca. 70% at 623 K or
=
kinds of products, for example aldehydes, ketones, C2 , and
=
=
C4 , have been observed on oxide catalysts. In this catalysis,
above. The C4 yield reached a maximum at 623 K, while
=
=
C4 and other higher olefins are produced by oligomerization
maxima in C3 yield occurred at 673 and 723 K. Notably, AA
=
=
of C2 , but as far as we are aware significant C3 production
on oxide catalysts has not been reported.
was formed at 573–723 K, although not in large amounts,
which will be discussed later.
Nickel ion-loaded mesoporous silica MCM-41 (Ni-M41) has
The stability of Ni-M41 was examined at 673 K. As shown in
Figure 2, the catalytic activity did not change during 20 h of
continuous time on stream. In addition, the carbon-based
mass balances were always ca. 100%, within the experimental
errors. The results demonstrate the stable catalytic activity of
Ni-M41. However, there is the possibility that losses of catalytic
activity could not be determined under these conditions be-
cause the catalytic activity of Ni-M41 was very high, as will be
revealed in a following paragraph, and the conversion levels of
=
been reported to be active towards the synthesis of C3 from
=
=
C2 , by dimerization of C2 and subsequent metathesis of the
=
= [8]
resulting C4 with unreacted C2 . Therefore, Ni-M41 is a pos-
=
sible catalyst for the conversion of EtOH to C3 since M41 is
=
[8b]
active for the dehydration of EtOH to yield C2 . Indeed, this
[9]
was confirmed by preliminary results from our group and
[
10]
subsequently by Sugiyama et al. The pore diameters of M41
are usually 1.5–5.0 nm, and, therefore the product distribution
on the catalysts is not controlled by shape selectivity. The reac-
tion mechanism/pathways are of interest, and the target of our
present study.
=
=
=
EtOH were always ca. 100%. The yields of C2 , C3 , C4 , and
AA were 67, 16, 5, and 7%, respectively. The values should be
=
compared with those of the reaction of C2 reported previous-
=
ly on the same catalyst. At 673 K and P
C2
=
=10 vol%, the C2
=
=
[
a] Prof. M. Iwamoto, Dr. K. Kasai, Dr. T. Haishi
Chemical Resources Laboratory, Tokyo Institute of Technology
conversion and selectivities to C3 and C4 were reported to
[8a]
be 42, 47, and 40%, respectively. Clearly, the product distri-
4
259-R1-5 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
=
bution for the EtOH reaction is different from that of the C2
Fax: (+81)45-924-5228
E-mail: iwamoto@res.titech.ac.jp
reaction. This difference might result from a change in active
ChemSusChem 2011, 4, 1055 – 1058
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1055

Figure 2. Time course of the catalytic activity of Ni-M41 (Si/Ni=23) at 673 K.
Figure 3. Conversion of EtOH on Ni-M41 (Si/Ni=23–28) as a function of
ꢀ1
ꢀ1
Catalyst wt. 0.2 g, flow rate 10 mLmin , PEtOH 5.6 kPa (N
sion of EtOH (*), carbon balance (ꢁ), yield of C2 (*), C3 (~), C4
DEE (~), and AA (
).
2
=
balance). Conver-
space velocity. Catalyst wt. 0.05–0.4 g, flow rate 10–300 mLmin , PEtOH
=
=
=
=
(
&
),
5.6 kPa (N balance). Conversion of EtOH (*), selectivity of C2 (*), C3 (~),
2
=
&
&
), DEE (~), and AA (
).
&
C4
(
2
CH CH OH ðEtOHÞ ! CH CH OCH CH ðDEEÞ þ H O
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
3
2
3
2
2
3
2
sites through adsorption of EtOH, AA, or intermediates, or
from a difference in reaction mechanism. The dependence on
¼
CH CH OCH CH ! CH ¼CH ðC2 Þ þ CH CH OH
3
2
2
3
2
2
3
2
ðC4¼Þ
the partial pressure of EtOH was also studied at P =3.0–
2 CH
2
¼CH
2
! CH
2
¼CHCH
2
CH
3
EtOH
ꢀ
1
1
3.2 kPa and a space velocity (SV) of 1000 h . Little depend-
CH ¼CHCH CH ! CH CH¼CHCH
=
2
2
3
3
3
ence of C3 formation on PEtOH was observed in the present
conditions, probably indicating strong adsorption of EtOH on
the active sites.
CH
CH¼CHCH
þ CH
¼CH
! 2 CH
¼CHCH
ðC3¼Þ
3
3
2
2
2
3
A similar reaction of EtOH on proton-exchanged ZSM-5 zeo-
lites was reported to be retarded in the presence of water
Although the formation of DEE from EtOH and the subse-
=
quent decomposition to yield C2 and EtOH was already re-
[
3–5]
[8b]
vapor.
The effect of water addition on the catalytic activity
ported on a M41 catalyst,
the progress is here confirmed
of Ni-M41 was studied here. When EtOH/water ratios were
varied in the range 100:0–75:25 (w/w), the EtOH conversion
levels and product distribution changed only a little. This result
is very significant for the application of the present system to
bEtOH conversion, because coarsely distilled bEtOH usually
contains 5–10 vol% water.
separately. In Figure 4, DEE was employed as a substrate and
the product distribution was examined as a function of reac-
=
tion temperature. The conversion of DEE to EtOH and C2 was
again confirmed at 523 K. At 573 K the major products were
=
=
,
=
C2 and C4 and only a small amount of C3 was produced.
The product distribution as a function of space velocity was
studied on Ni-M41 at 673 K. The dependence is summarized in
ꢀ
1
Figure 3. At SV=70000 h the conversion level of EtOH was
ca. 50%, but at 20000 or below it increased to 95% or more. It
follows that Ni-M41 is very active for the catalytic conversion
of EtOH. The product distribution depends strongly on the
ꢀ
1
space velocity. At higher SVs (in the region 10000–100000 h )
AA is produced in large amounts, and the amount decreases
monotonically with decreasing SV. DEE was also produced and
its formation showed a behavior similar to that of AA, al-
=
though the amount formed was very small. C2 was always a
major product in the reaction, and its yield reached a maxi-
ꢀ
1
=
mum at 2000–3000 h . On the other hand the yields of C3
=
and C4 gradually increased with decreasing SV, indicating that
these compounds are products from the terminal phases of
consecutive reactions.
On the basis of above results, we suggest the following re-
=
=
Figure 4. Change in conversion of DEE on Ni-M41 (Si/Ni=23) with reaction
action pathways to form C3 via DEE and C2 as intermediates.
ꢀ1
temperature and time. Catalyst wt. 0.2 g, flow rate 10 mLmin , PDEE 5.1 kPa
=
=
=
(
N
2
balance). Conversion of DEE (~), yield of C2 (*), C3 (~), C4
EtOH (*), and AA (
).
&
( ),
&
1
056
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ChemSusChem 2011, 4, 1055 – 1058

=
=
=
At 673 K the produced C2 and C4 were converted to C3
occurs, however, is almost the same as that of the former be-
[
8a]
=
through metathesis, as reported previously.
cause the yields of C2 and AA were roughly equal to each
=
There is one more important question in the results of
Figure 3: the meaning of the increment in AA at higher SV
values. The results showed that AA was an intermediate to
other at high SV values, as shown in Figure 3. The C2 pro-
=
duced was converted to C3 through dimerization, isomeriza-
tion, and metathesis (Equations 3–5). The present results indi-
=
=
form C2 , although the reaction was never suggested. The fol-
cate that the formation of C3 can be achieved not by the
lowing reaction is widely accepted to proceed on various
catalysts.
shape selectivity, but by control of the reaction mechanism.
Experimental Section
CH CH OH ! CH CHO þ H
ð6Þ
3
2
3
2
[11]
M41 was prepared according to a reported procedure by using
Br as the template and colloidal silica as the silica
source. Nickel ion was loaded onto M41 by the template ion ex-
The possibility that mixtures of AA and hydrogen really give
C H25N(CH )
12 3 3
=
C2 is examined here. An equimolar mixture of AA and H2
[8,11]
change (TIE) method using a nickel nitrate aqueous solution.
(
6 kPa, respectively, N balance) was introduced onto the Ni-
2
ꢀ
1
As-prepared Ni-MCM-41 was calcined at 773 K for 6 h in air, in
which the sample was thinly (less than 2 mm thick) spread onto a
M41 catalyst at 573–773 K and a SV of 4600 h , but no reac-
tion was observed except for condensation of AA and low
ꢀ1
ceramic board and heated at 0.2–0.5 Kmin . The slow heating
=
levels of methane and C2 formation (2–3%, respectively). The
with the shallow bed method was important to obtain good and
reproducible catalytic activity. The Brunauer–Emmett–Teller (BET)
surface area and the Barrett–Joyner–Halenda (BJH) pore diameter
possibility that the reverse reaction of Equation (6) and subse-
quent dehydration of resultant EtOH might lead to the forma-
=
tion of C2 is therefore ruled out. Next, an equimolar mixture
determined by
1
a
N
2
adsorption measurement were 873–
010 m g and 2.2 nm, respectively. The hexagonal structure of
the resulting M41 was confirmed by the appearance of 2q=
.5808, 4.4768, and 5.1248 peaks in X-ray diffraction patterns (Cu Ka,
2
ꢀ1
of EtOH and AA (5 kPa respectively, N balance) was introduced
2
ꢀ
1
onto the Ni-M41 catalyst at 673 K and a SV of 990 h . The con-
version levels of EtOH and AA were 100 and 65%, and the se-
2
Ni filter), corresponding to (100), (110), and (200), respectively. The
Si/Ni atomic ratios were 23–28. The Si/Al atomic ratio was 237–243,
in which the origin of Al was an impurity of the raw material: col-
loidal silica. The catalytic reaction was carried out by using a fixed-
bed flow reactor at an atmospheric pressure. The catalyst of 0.05–
=
=
=
lectivities to C2 , C3 , and C4 were 61, 15, and 12%, respec-
tively. The selectivity was very similar to that observed in Fig-
=
ures 1–3. AA can be converted into C2 in the presence of
EtOH and Equations (3–5) subsequently proceed in this reac-
tion system.
0.5 g was loaded in the reactor, heated in N
EtOH (PEtOH =2.8–12.8 kPa, N2 balance, total flow rate 10–
at 673 K, and then
2
In the experiments of Figure 3, a trace amount of ethylace-
tate (EA) was observed, although the amount was not quanti-
ꢀ
1
3
00 mLmin ) was let into the reactor at a desired temperature by
=
using a syringe-type microfeeder (Furue Science, Japan, model JP-
S). The product distribution was determined by on-line gas chro-
matography.
fied. The following reactions explain the formation of C2 from
AA and EtOH.
2
CH CHO ! CH COOCH CH ðEAÞ
ð7aÞ
ð7bÞ
ð8Þ
3
3
2
3
Acknowledgements
CH CHO þ CH CH OH ! CH COOCH CH ðEAÞ þ H
3
3
2
3
2
3
2
CH COOCH CH ! CH COOH þ CH ¼CH
3
2
3
3
2
2
This work was supported by Grants-in-Aids from the Ministry of
Education, Culture, Sports, Science, and Technology, NEDO, and
ALCA of Japan.
CH COOH þ CH CH OH ! CH COOCH CH þ H O
ð9Þ
3
3
2
3
2
3
2
CH COOH þ H ! CH CHO þ H O
ð10Þ
3
2
3
2
Keywords: ethanol · mesoporous silica · metathesis · nickel ·
propene
Equation (7a) is well-known as the Tishchenko reaction, and
Equation (9) as the Fisher esterification. Hydrolysis of EA gives
acetic acid and EtOH, while Equation (8) is not popular. The re-
verse reaction of Equation (8), however, was already confirmed
to catalytically proceed and was put to practical use by Showa
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Published online on June 20, 2011
1
058
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