Conversion of ethanol to propylene by H-ZSM-5 with Si/Al2 ratio of 280

Article abstract of DOI:10.1007/s10562-010-0315-2

A catalytic conversion of ethanol to propylene was carried out by use of H-ZSM-5 with Si/Al₂ ratio of 280. In H-ZSM-5 modified at a molar ratio of La to Al₂ of 2.2, the propylene selectivity was 31% at 0.1 MPa, 550 °C and was higher than those of non-modified and other metal modified catalysts. In the La-modified H-ZSM-5, a rapid increase in ethylene formation was also depressed and the propylene selectivity was still high (24%) even after 28 h-reaction. Graphical Abstract: A catalytic conversion of ethanol to propylene was carried out by use of H-ZSM-5 with Si/Al₂ ratio of 280. In H-ZSM-5 modified at a molar ratio of La to Al₂ of 2.2, the propylene selectivity was 31% at 0.1 MPa, 550 °C and was higher than those of non-modified and other metal modified catalysts. In the La-modified H-ZSM-5, a rapid increase in ethylene formation was also depressed and the propylene selectivity was still high (24%) even after 28 h-reaction.

Full text of DOI:10.1007/s10562-010-0315-2

Catal Lett (2010) 136:14–19
DOI 10.1007/s10562-010-0315-2
Conversion of Ethanol to Propylene by H-ZSM-5 with Si/Al2 Ratio
of 280
•
•
•
Kenichiro Inoue Megumu Inaba Isao Takahara
Kazuhisa Murata
Received: 27 December 2009 / Accepted: 18 February 2010 / Published online: 9 March 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A catalytic conversion of ethanol to propylene
was carried out by use of H-ZSM-5 with Si/Al2 ratio of
280. In H-ZSM-5 modified at a molar ratio of La to Al2 of
2.2, the propylene selectivity was 31% at 0.1 MPa, 550 °C
and was higher than those of non-modified and other metal
modified catalysts. In the La-modified H-ZSM-5, a rapid
increase in ethylene formation was also depressed and the
propylene selectivity was still high (24%) even after 28 h-
reaction.
aromatic hydrocarbons from ethanol [4–9]. Especially,
ethylene is easily produced by a dehydration of ethanol
and, therefore, this process has already been established.
Earlier study has revealed that propylene is formed by the
cracking of larger olefins over H-ZSM-5 [10]. However,
there are few reports on a direct conversion of bio-ethanol
into propylene.
The authors [11] have studied on ethanol conversion
into lower olefins by H-ZSM-5 with Si/Al2 ratio of 29.
Modification of H-ZSM-5 by W and La reduced aromati-
zation and olefin hydrogenation, as a result, the propylene
selectivity was improved in which the highest selectivity
was 32.1% at 450 °C. Song et al. [12] reported that the use
of H-ZSM-5 with Si/Al2 ratio of 80 afforded high propyl-
ene yield. Zr-modified catalyst gave the highest propylene
yield of 32% at 500 °C. The surface acidity and the pres-
ence of metal ions played important roles in the production
of propylene.
Keywords Ethanol Á Propylene Á H-ZSM-5 Á
Si/Al2 ratio of 280
1 Introduction
Attention has been paid to biomass energy instead of fossil
fuel. Because biomass-derived materials are carbon neu-
tral, in general, the biomass utilization would lead to the
prevention of global warming. One of the essential raw
materials in the petrochemical industry is propylene and it
is widely produced as co-product of ethylene by steam
thermal cracking of naphtha, although the propylene
selectivity is not high. Thus, the development of propylene
production processes from biomass resources such as bio-
ethanol is highly desirable.
These results demonstrate that H-ZSM-5 with low
Si/Al2 ratio is highly effective for the conversion to pro-
pylene from ethanol. However, to our knowledge, there
have been no reports that high propylene selectivity is
obtained in H-ZSM-5 with higher Si/Al2 ratio. In this
study, the activities of H-ZSM-5 with higher Si/Al2 ratio of
280 were examined. The effects of temperature, metal
modification, and stability of catalyst on the ethanol con-
version are reported in this paper.
Processes for the conversion of methanol to olefins
(MTO) are well established [1–3]. In addition, there are
many reports on production of ethylene, gasoline, or
2 Experimental
K. Inoue (&) Á M. Inaba Á I. Takahara Á K. Murata
National Institute of Advanced Industrial Science and
Technology (AIST), AIST Tsukuba Central 5, 1-1-1, Higashi,
Tsukuba, Ibaraki 305-8565, Japan
2.1 Catalyst Preparation
H-ZSM-5 catalysts with Si/Al2 ratio of 30, 280, and 400 were
prepared by calcinating NH4-ZSM-5 catalysts commercially
e-mail: inoue-ki@aist.go.jp
123

Conversion of Ethanol to Propylene by H-ZSM-5 with Si/Al2 Ratio of 280
15
available from Zeolyst Corp. The calcination was carried out
for 6 h at 500 °C. The metal modified H-ZSM-5 catalysts
with Si/Al2 ratio of 280 were prepared. The H-ZSM-5 cat-
alyst was impregnated with an aqueous solution of
Cr(NO3)3Á9H2O, FeCl3Á6H2O, ZrO(NO3)2Á2H2O, La(NO3)3Á
6H2O, Ce(NO3)3Á6H2O (Wako pure chemical industries), or
(NH4)6H2W12O40 (Strem chemicals) and dried at 100 °C,
followed by calcination for 5 h at 600 °C. The molar ratios of
metal to Al2 were 2.2. In La modification, La/Al2 molar ratios
of 1.0, 2.2, 4.0, and 6.0 were used. These values correspond
to 1.6, 3.6, 6.6, and 9.9 wt%, respectively. In W modifica-
tion, the molar ratios of 2.2, 4.2, and 6.0 were used, these
values correspond to 4.8, 9.1, and 13 wt%, respectively.
3 Results and Discussion
3.1 Effects of Si/Al2 Ratio
Figure 1 shows the selectivity and carbon conversion
efficiency at 550 °C of three kinds of H-ZSM-5 catalyst
whose Si/Al2 ratios are 30, 280, and 400. The reaction
products containing carbon consist of each aliphatic
hydrocarbon of C1–C10, BTX (sum of benzene, toluene,
and xylenes), trimethylbenzenes, and COx (x = 1 or 2, sum
of carbon monoxide and carbon dioxide). The selectivity
was defined as a carbon-based amount of the product to
sum of the carbon-based amount of each product. The
carbon conversion efficiency was defined as sum of the
carbon-based amount of each product to the carbon-based
amount of ethanol introduced.
2.2 Reaction Procedure
Catalytic reaction tests were performed in a fixed-bed reac-
tor, where 1.5 g of catalyst and 2.0 g of quartz sand were
used. A quartz reaction tube of inner diameter of 12 mm was
used. A thermocouple near the catalyst bed was installed to
measure the temperature. Ethanol (purity [99.5%, Wako
pure chemical industries) was fed into a vaporizer (250 °C)
by using pump (LC-10AD VP, Shimadzu) and mixed with
N2 (purity[99.9995%, Japan Fine Products). The mixed gas
flowed continuously through the reaction tube placed in a
furnace at atmospheric pressure. A total flow rate was
19 mL min-1 and the percentages of ethanol and N2 were 44
and 56 vol.%, respectively. A weight hourly space velocity
(WHSV), defined as the weight ratio of the flow rate of
ethanol gas to the catalyst packed, was 0.63 h-1. Since it
took for about 30 min to reach steady state, the reaction data
shown in 3.1–3.3 were measured after 40 min.
The conversion mechanism of MTO was well discussed
[13–15]. Based on this, the conversion mechanism of eth-
anol to propylene is assumed as follows. In first step, a
dehydration of ethanol forms ethylene path through diethyl
ether. In the ethanol conversion, the ethylene can be easily
formed by dehydration, whereas in methanol conversion, a
carbon–carbon bond between C1 reactants must be formed
before production of ethylene [16]. Furthermore, the eth-
ylene is converted to hydrocarbons of higher carbon
numbers by oligomerization-cracking. In the case of pro-
pylene production, the ethylene is converted to C4 hydro-
carbons by dimerization and then C6 hydrocarbons by
trimerization, which is converted to propylene by b-fission
[17]. In general, these conversions proceed over Brønsted
acid sites of the catalyst.
Increasing the Si/Al2 ratio reduces the surface acidity on
H-ZSM-5. As shown in Fig. 1, the production of ethylene
by the dehydration of ethanol was larger in the weak sur-
face acidity, and the strong surface acidity led to the
The reaction gaseous products were analyzed by on-line
gas chromatographs. In the gas chromatographs with a
thermal conductivity detector (GC-14B and GC-2014, Shi-
madzu), a Molecular Sieves and a PoraPak Q columns were
used to determine the concentrations of inorganic gases such
as CO, CO2 and C1, C2 hydrocarbons. In the gas chromato-
graphs with a hydrogen-flame ionization detector (GC-2014,
Shimadzu), a Plot column for C1–C5 hydrocarbons, a CBP-1
column for C5–C10 hydrocarbons, a UA-CW column for
ethanol were used. In the CBP-1 column, the concentrations
of aromatic hydrocarbons (benzene, toluene, xylenes, and
trimethylbenzenes) were also determined.
30
280
400
X-ray diffraction (XRD) patterns were obtained for a
phase identification (Mac Science, M18XHF22-SRA, Cu
Ka radiation, 40 kV, 150 mA). The patterns were recorded
over the 2h angle ranging from 5° to 55° at a scan rate of
8° min-1. In order to estimate carbon deposition amount
on catalysts after reaction, measurements by thermogravi-
metry (TG DTA 2000, MAC Science) of the catalysts were
performed in the flow of air with the temperature varying
0
20
40
60
80
60
80
100
Selectivity (%)
Conversion (%)
Propylene
Propane
Methane
C4
Ethane
BTX
Ethylene
COx
Fig. 1 Effect of Si/Al2 ratio on products distribution over H-ZSM-5
at 550 °C
from room temperature to 800 °C at 10 °C min-1
.
123

16
K. Inoue et al.
conversion of more paraffins and aromatics by the oligo-
merization-cracking. The authors [11] reported the highest
propylene selectivity was obtained at H-ZSM-5 with Si/Al2
ratio of 29, and the selectivity decreased at H-ZSM-5 with
higher Si/Al2 ratio (weak surface acidity). Since WHSV
was higher (1.3 h-1) in the previous report, a contact time
to catalyst of gas was shorter than that in this study. With
the decrease in the contact time, the selectivity of ethylene
increased and those of higher hydrocarbons decreased.
When WHSV increased to 0.97 and 1.2, the propylene
selectivity at 550 °C decreased to 24 and 17%, respec-
tively, in the high silica zeolite with Si/Al2 ratio of 280.
Thus, lower WHSV (0.63 h-1) was required for the
increase in the propylene selectivity.
temperature and the selectivities to higher hydrocarbons
such as C4 decreased. The propylene selectivity was the
highest at 550–600 °C. In un-modified H-ZSM-5 catalyst,
the propylene selectivity was the highest at 550 °C and the
value was 29%, the selectivity ratio of propylene to eth-
ylene was 0.98.
3.3 Effects of Metal Modification
As shown in Fig. 2, in Ce and W-modified zeolites, the
propylene selectivities were the highest at 600 °C and these
values were 29 and 28%, respectively, while the selectivity
ratios of propylene to ethylene were 0.66 and 0.72. In La-
modified catalyst, the propylene selectivity was the highest
value of 31% at 550 °C and this value was higher than
those of other catalysts. The selectivity ratio of propylene
to ethylene was 0.93.
3.2 Effects of Temperature
Figure 3 shows the XRD patterns of non-modified and
La-modified H-ZSM-5 with Si/Al2 ratio of 280. The XRD
profiles exhibit crystalline MFI phase. Diffraction charac-
teristic peaks of La oxide and the crystal phase of new
species cannot be observed in La-modified catalyst.
Figure 2 shows the dependences of products distribution
upon temperature of non-modified and metal (La, Ce, or
W)-modified H-ZSM-5 catalysts with Si/Al2 ratio of 280.
Ethylene selectivity increased with the increase in
Fig. 2 Effect of temperature on
products distribution over non-
and metal-modified H-ZSM-5
(Si/Al2 ratio: 280). Metal/Al2
ratio: 2.2
100
100
La
Non
80
60
40
20
0
80
60
40
20
0
300
400
500
600
700
300
400
500
600
700
Temperature (ºC)
Temperature (ºC)
100
100
80
60
40
20
0
W
Ce
80
60
40
20
0
300
400
500
600
700
300
400
500
600
700
Temperature (ºC)
Temperature (ºC)
Methane
Ethane
Ethylene
C4
Propane
BTX
Propylene
Conversion
123

Conversion of Ethanol to Propylene by H-ZSM-5 with Si/Al2 Ratio of 280
17
carbon dioxide were higher in comparison with the other
catalysts.
Figure 5 shows the dependences of selectivity and car-
bon conversion efficiency upon metal modification ratio
over H-ZSM-5 with Si/Al2 ratio of 280 at 550 and 600 °C.
The La and W metals were examined because of high
propylene selectivity, and the molar ratios of metal to Al2
were varied in the range of 0.0–6.0. The selectivity of
ethylene at 600 °C was higher than that at 550 °C in all
ratios. In previous report [11], the propylene selectivities of
non- and W (10 wt%)-modified H-ZSM-5 with Si/Al2 ratio
of 29 were 8.69 and 24.4%, respectively. The propylene
selectivity was greatly improved in W-modified catalyst.
However, there was not large difference in the propylene
selectivity very much in H-ZSM-5 with the ratio of 280.
When the ratio of La to Al2 was 2.2, 31% of the highest
selectivity was obtained at 550 °C, although the values
were 28–29% in the ratio of 0.0, 1.0, 4.0 and 6.0. The total
surface acidity and acid strength distribution on H-ZSM-5
decrease after La introduction [4]. The decrease in acidity
results in the decrease of coke formation during the reac-
tions and the increase the catalyst stability [18]. The eth-
ylene production was promoted in lower surface acidity
(La/Al2 ratio: 4.0, 6.0), whereas higher surface acidity
(La/Al2 ratio: 0.0, 1.0) led to the production of more pro-
pane, C4, and aromatics. Therefore, the highest propylene
selectivity was obtained in the moderate surface acidity
(La/Al2 ratio: 2.2). Previous work [11] reported that the
selectivity for propylene formation may be associated with
the percentage of Brønsted acid sites on the catalyst
surface.
Non-modified
La-modified
La-modified,
after 28 h-reaction
0
10
20
30
40
50
60
2
(degree)
Fig. 3 XRD patterns of non- and La-modified H-ZSM-5 (Si/Al2
ratio: 280). La/Al2 ratio: 2.2
The propylene selectivity was the highest at about 550–
600 °C in this study. As already reported [11], the pro-
pylene selectivity was the highest at about 450 °C and the
value was 24.4% over W-modified H-ZSM-5 with Si/Al2
ratio of 29. The ethylene selectivity was 71.4% at 500 °C
and was higher than propylene selectivity. In the literature
report, the contact time to catalyst of gas was shorter than
that in this study, as mentioned above. With the decrease in
the contact time, the ethylene selectivity increased and
higher hydrocarbons selectivities decreased. Therefore,
possibly, the temperature of the highest propylene selec-
tivity differs.
The effects of various metals modified H-ZSM-5 with
Si/Al2 ratio of 280 were compared. The metals were Cr, Fe,
Zr, La, Ce, and W. The molar ratios of metal to Al2 were
2.2. Figure 4 shows the selectivity and carbon conversion
efficiency at 550 and 600 °C. The ethylene selectivity at
600 °C was higher than that at 550 °C. In Cr and Fe-
modified catalysts, the selectivity of propylene was lower
and those of methane, ethane, carbon monoxide, and
3.4 Stability of Catalyst
The propylene and ethylene selectivities of H-ZSM-5 cat-
alysts are shown in Fig. 6 as a function of gas supplied time
at 550 °C. The catalysts tested were H-ZSM-5 modified by
Fig. 4 Effect of metal
modification on products
Non
550 ˚C
600 ˚C
Non
distribution over H-ZSM-5
(Si/Al2 ratio: 280). Metal/Al2
ratio: 2.2
Cr
Fe
Zr
Cr
Fe
Zr
La
Ce
W
La
Ce
W
0
20
40
60
80
60
80
100
0
20
40
60
80
60
80
100
Selectivity (%)
Conversion (%)
Selectivity (%)
Conversion (%)
Propylene
Propane
Methane
C4
Ethane
BTX
Ethylene
COx
123

18
K. Inoue et al.
Fig. 5 Effect of La or W
modification ratio on products
distribution over H-ZSM-5
(Si/Al2 ratio: 280)
La, 550 ˚C
La, 600 ˚C
0.0
1.0
2.2
4.0
6.0
0.0
1.0
2.2
4.0
6.0
0
20 40 60 80
60
80
100
0
20 40 60 80
60
80
100
Selectivity (%) Conversion (%)
W, 550 ˚C
Selectivity (%)
W, 600 ˚C
Conversion (%)
0.0
2.2
4.2
6.0
0.0
2.2
4.2
6.0
0
20 40 60 80
0
20 40 60 80
60
80
100
60
80
100
Selectivity (%) Conversion (%)
Selectivity (%) Conversion (%)
Propylene
Propane
Methane
C4
Ethane
BTX
Ethylene
La (La/Al2 ratio: 2.2), Ce (Ce/Al2 ratio: 2.2), and W (W/Al2
ratio: 4.2) which showed the high propylene selectivity as
well as non-modified H-ZSM-5 catalyst. There was the
tendency that ethylene selectivity increased as the reaction
preceded in all catalysts. In non-modified H-ZSM-5 cata-
lyst, the selectivity ratio of propylene to ethylene after
8.2 h was 0.69. The selectivity ratios of La, Ce, and
W-modified catalysts were 0.88, 0.60, and 0.61, respec-
tively. In the La-modified catalyst, the selectivity ratio was
found to remain constant under the conditions. La and W
co-modified H-ZSM-5 with Si/Al2 ratio of 29 showed high
propylene selectivity in the previous report [11]. However,
the selectivity ratio of the catalyst co-modified La (La/Al2
ratio: 2.2) and W (W/Al2 ratio: 4.2) rapidly decreased in
this work. Since the generation of ethylene was prevented
and propylene selectivity was high in La-modified catalyst,
the stability test was carried out during 28.2 h. The results
were shown in Fig. 7.
selectivity decreases. Figure 3 also shows the XRD pat-
terns of La-modified H-ZSM-5 after the reaction of 28 h.
The product of intensity multiplied by half width of the
peak at angle 2h of 23° was calculated. The ratio of the
value after the reaction to the initial value was found to be
approximately 0.85. It suggested that the dealumination
occurred as the reaction proceeded, although the overall
crystal structure remained. As shown in Fig. 7, ethylene
selectivity reached 56% after 28.2 h and other components
decreased as the reaction proceeded. The propylene
selectivities of initial and after 28.2 h were 31 and 24%,
respectively, and La-modified H-ZSM-5 with Si/Al2 ratio
of 280 kept highly effective.
4 Conclusions
The catalytic conversion of ethanol was carried out by use
of H-ZSM-5 with Si/Al2 ratio of 280 at 0.1 MPa and 400–
650 °C. The ethylene selectivity increased with the
increase in temperature, while the selectivities to higher
hydrocarbons such as C4 decreased. In H-ZSM-5 modified
at the molar ratio of La to Al2 of 2.2, the propylene
selectivity was 31% at 550 °C and was higher than those of
non-modified and other metal modified catalysts. The rapid
increase in ethylene formation was also depressed, the
propylene selectivity was still high even after 28 h-reac-
tion. Thus, the La-modified H-ZSM-5 with Si/Al2 ratio of
280 was found to be highly effective.
A carbon deposition on the surface and a dealumination
would cause H-ZSM-5 activity decline. The weight ratio of
deposited carbon amount to used catalyst amount was
determined by thermogravimetry. The carbon deposition
ratios of La-modified catalyst reacted for 8.2 and 28.2 h
were 0.35 and 0.52%, respectively. Even if the reaction
time increased to 3.4 times, the ratio increased to only 1.5
times. Therefore, the deposition of carbon was not pro-
moted during this reaction time (8.2–28.2 h) very much. In
the meantime, the dealumination is promoted by water
generated during the reaction [16], consequently propylene
123

Conversion of Ethanol to Propylene by H-ZSM-5 with Si/Al2 Ratio of 280
19
60
40
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Fig. 7 Catalytic stability of ethanol conversion over La-modified
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123