Influence of inlet gas composition on dimethyl ether carbonylation and the subsequent hydrogenation of methyl acetate in two-stage ethanol synthesis

Article abstract of DOI:10.1039/c6nj01109h

Ethanol was synthesized indirectly from dimethyl ether (DME), CO, and H₂ using a system of two fixed bed reactors in series. In the first stage of DME carbonylation over an HMOR catalyst, the presence of H₂ decreased DME conversion and methyl acetate (MA) selectivity by suppressing the reaction of CO with the intermediate methyl. In the improved scheme, H₂ was introduced directly into the following MA hydrogenation stage. As a result, the high DME conversion was maintained. The in situ Fourier transform infrared spectra of the Cu/SBA-15 catalyst show that CO was adsorbed mainly on Cu⁺, which disrupted the balance between Cu⁺ and Cu⁰ in the hydrogenation. Moreover, methane and some methanol were generated by the hydrogenation of methyl and methoxyl groups derived from DME decomposition.

Full text of DOI:10.1039/c6nj01109h

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Influence of Inlet Gas Composition on Dimethyl Ether
Carbonylation and Subsequent Hydrogenation of Methyl Acetate
in Two-Stage Ethanol Synthesis
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
*
Shurong Wang , Shi Yin, Wenwen Guo, Yincong Liu, Lingjun Zhu, and Xiaoliu Wang
www.rsc.org/
Ethanol was synthesized indirectly from dimethyl ether (DME), CO, and H
series. In the first stage of DME carbonylation over HMOR catalyst, the presence of H
methyl acetate (MA) selectivity by suppressing the reaction of CO with the intermediate methyl. In the improved scheme,
2
using a system of two fixed bed reactors in
2
decreased DME conversion and
H
2
was introduced directly into the following MA hydrogenation stage. As a result, the high DME conversion was
+
maintained. In-situ Fourier transform infrared spectra of Cu/SBA-15 catalyst show that CO was adsorbed mainly on Cu ,
+
0
which disrupted the balance between Cu and Cu in the hydrogenation. Moreover, the methane and some methanol were
generated from the hydrogenation of methyl and methoxyl groups derived from DME decomposition.
Brønsted acid sites inside eight-membered-ring (8MR) and
twelve-membered-ring (12MR) pore channels. Cu-based
catalysts, in particular, are efficient in MA hydrogenation,
Introduction
Ethanol, a gasoline additive, can be used to improve the
performance and quality of gasoline and thereby ease the
petroleum supply crisis. Ethanol is also an important raw
feedstock for the production of various synthetic chemicals.
Ethanol is mainly produced through microbiological
fermentation or synthesis. However, the use of starch as raw
material for fermentation may aggravate the food crisis, and
those bio-chemical processes that utilize cellulose have to face
which is a key stage in the indirect synthesis of ethanol. Our
previous work revealed that the Cu/SBA-15 catalyst prepared
by homogeneous deposition–precipitation method exhibited
high catalytic performances in the hydrogenation of MA. The
conversion of MA in this reaction was 99.5% and its selectivity
2
toward ethanol was 99.5% at n (H )/n (MA) =60, T=493K,
1
1
12
13
P=2MPa. Recently, Yang et al. and Zhang et al. studied the
indirect synthesis of ethanol from DME and syngas in a single
stage using the composite catalyst, HMOR/Cu-ZnO. In a
1
the problem of its high cost. Furthermore, synthesis of
ethanol using the ethylene hydration method still relies on oil
2
resources. Recently, a new route of indirect ethanol synthesis
1
4
subsequent study, Peng et al. improved the carbonylation
catalyst and used Pt/HMOR and Cu/ZnO catalysts to synthesize
ethanol indirectly. They obtained a DME conversion of 35.2%
and ethanol selectivity of 32.6% at 493 K, 1.5 MPa, n (Ar)/n
was proposed. Here, methyl acetate (MA) is synthesized
through dimethyl ether (DME) carbonylation (R1), and then
3
, 4
ethanol is produced through MA hydrogenation (R2).
overall reaction is shown in R3.
The
(DME)/n (CO)/n (H
2
)=1.55/2.35/46.1/50.
In the indirect synthesis of ethanol from DME and syngas,
CH OCH +CO→CH COOCH
(R1)
(R2)
3
3
3
3
the composition of the inlet gas has influences on DME
CH COOCH +2H →CH CH OH+CH OH
carbonylation and MA hydrogenation. The presence of H flow
2
3
3
2
3
2
3
might influence DME carbonylation, and the outlet gaseous
CH OCH +CO+2H →CH CH OH+CH OH
(R3)
3
3
2
3
2
3
products of the carbonylation could also affect the following
MA hydrogenation. However, there are few reports related to
the effect of the inlet gas composition on the indirect synthesis
of ethanol. Therefore, a system having two fixed bed reactors
Acidic zeolites are most commonly used as catalysts in
DME carbonylation for their high activity and thermal
5
stability. Among the known zeolites, HMOR presents high
-8
9
activity in DME carbonylation. Bhan et al. and Cheung et al.
10
in series with flexible H
2
inlet positions was designed in this
flowing into the
found that the activity of HMOR in DME carbonylation was
closely related to the acid sites in the catalyst, especially
study. Results of ethanol synthesis with H
2
first carbonylation stage and directly to the second
hydrogenation stages were compared. Furthermore, the
influence of CO and DME on MA hydrogenation, were also
analyzed by Fourier transform infrared (FTIR) spectroscopy.
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ARTICLE
Journal Name
Experimental
[a]
Table 1 Effect of temperature on DME carbonylation over HMOR catalyst.
Reaction system
Temperature [K]
X
DME [%] SMA [%]
S
methanol [%]
S
CH4 [%]
Fig. 1 shows the flow chart of the indirect synthesis of
ethanol from dimethyl ether and syngas. DME carbonylation
over HMOR and MA hydrogenation over Cu/SBA-15 were
conducted in two reactors, respectively. The two reactors can
function independently, but they can also function in series in
4
63
473
78
483
26.4
37.8
58.6
67.0
93.0
95.5
97.2
98.2
6.8
4.7
2.6
1.6
0.1
0.1
0.1
0.3
4
the indirect synthesis of ethanol. The DME/CO/N
introduced into the carbonylation stage, while H
introduced into the carbonylation or hydrogenation stage by
using controlled valve. The mixture of CO and DME, H were
introduced into the reactors at various ratios. The mole ratio
of CO to DME was set at 19. N
introduced into the carbonylation stage at a flow rate of 3 mL 19) : 15 mL min . P = 1.8 MPa
2
mixture was
2
could be
4
5
93
03
69.1
68.2
96.2
94.3
3.1
4.3
0.7
1.4
2
, the internal standard gas, was [a] Reaction conditions: The mixture flow of DME and CO (n(CO)/n(DME) =
−1
2
-1
-1
min together with 15 mL min of CO/DME mixture under
typical conditions. And the purities of DME, CO, N and H
2
2
were above 99.999%, 99.9%, 99.999% and 99.999%,
respectively. After 2 h on stream, the catalytic performance of
HMOR became stable and then the activity maintained till the
time on stream of 6 h. After that, the HMOR catalyst
underwent an obvious deactivation. In the catalytic activity
tests, the corresponding data were recorded during the time
ni
Si(%)=
×100%
(R5)
(R6)
n
∑ i
Yethanol (%)=XDME×Sethanol
on stream of 2.5 h to 5.5 h. And the catalytic results during the Where nDMEin and nDMEout represent the mole number of
same time of stream for every catalytic run were compared
and exhibited in error bar or average value. Reaction
parameters, including the amounts of HMOR and Cu/SBA-15
DME in the feed and outlet, respectively.
i
n is the mole
number of product i. All of the selectivity values of products in
14, 16
this paper were calculated in molecular selectivity.
(0.5 and 2 g, respectively), are identical to those used in our
previous work.
1
1, 15
Before reactions, Cu/SBA-15 was activated
Catalyst preparation
with pure H
temperature. The mixture of CO and DME, H
2
at 623 K for 3 h and then cooled to the reaction
were introduced
2
2
2 3
HMOR (SiO /Al O = 18) was purchased from Tosoh Catalyst
into the reactors at various ratios. The mole ratio of CO to
DME was set at 19. The composition of the total products was
analysed by using an online GC system (Huaai GC 9560). In
order to prevent condensation, the reactor effluent was
introduced into the GC system through transfer lines held at
Plant. Before the reaction, HMOR was calcined at 773 K for 5 h
in a muffle furnace to remove water. The hydrogenation
catalyst (here denoted as Cu/SBA-15) was prepared through
11
homogeneous precipitation method. Cu (NO ) ∙3H O (3.8 g)
3 2 2
and urea (13.4 g) were dissolved in deionized water (223 mL)
at ambient temperature to obtain an aqueous solution, and
then SBA-15 (5.0 g) was added to the solution to form a
suspension. The suspension was then kept at 363 K for 7 h. The
precipitate was separated by filtration, washed with deionized
453 K. CO, H , and N were separated and detected by a
2 2
thermal conductivity detector. Hydrocarbons and oxygenated
hydrocarbons were detected by a flame ionization detector.
The amounts of products were determined by the internal
calibration method.
i
The DME conversion (XDME), products selectivities (S ), and water, and then dried at 383 K overnight. It was finally calcined
ethanol yield (Yethanol) were calculated through the following at 723 K for 4 h.
equations:
Catalyst characterization
nDME −nDME
in
out
XDME (%) =
×100%
(R4)
FTIR spectra were recorded on
spectrometer with resolution of
a
Bruker Tensor 27
-1
cm . The in-situ
nDMEin
a
4
adsorption and desorption experiments were carried out in a
cell with KBr windows. Before adsorption, CuO/SBA-15
samples were pretreated at 623 K for 3 h in H
2
atmosphere
and then for 1 h in N atmosphere, and finally cooled to 503 K.
2
After that, CO (>99.9% purity) was introduced into the in-situ
cell until adsorption saturation. The IR spectra of adsorption
information were recorded. Then the sample was purged with
N
2
for 40 min. Subsequently, the temperature was raised to
5
73 K, and the sample was swept with N flow for 20 min. The
2
corresponding IR spectra of desorption information were
recorded. Adsorption of the mixture of CO and DME was
carried out in the same manner as that for CO adsorption.
Fig. 1 Flow chart of two-stage ethanol synthesis from DME and syngas.
2
| J. Name., 2012, 00, 1-3
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[
a]
2
Table 2. Effect of H flow into the carbonylation reactor on the indirect ethanol synthesis.
−
1
H
2
[mL min ]
X
DME [%]
S
ethanol [%]
S
methanol [%]
S
MA [%]
28.7
S
EA [%]
8.5
S
CH4 [%]
Y
ethanol [%]
5
52.8
35.4
21.1
41.5
0.3
11.1
1
0
31.0
45.6
16.1
4.8
2.3
11.0
1
3
5
0
30.4
27.5
34.7
32.3
43.5
56.0
11.1
0
4.6
0
6.2
10.5
8.8
11.8
−1
[
a] Reaction conditions: The mixture flow of DME and CO (n(CO)/n(DME) = 19) : 15 mL min . P=1.8MPa.
Results and Discussion
Influence of Reaction Temperature on DME Carbonylation
100
Temperature has a serious effect on the carbonylation. The
effect of temperature on carbonylation reaction was studied in
the single reactor. Table 1 shows the DME conversion and
products selectivities over HMOR at various reaction
temperatures. The conversion of DME increased from 26.4 to
90
N2
H2
8
7
6
5
4
3
2
0
0
0
0
0
0
0
67.0% with reaction temperature increasing from 463 to 483 K.
The further increase of temperature had little effect on the
DME conversion. The MA selectivity increased initially and
then decreased while the methanol selectivity showed the
opposite trend. Furthermore, a small amount of methane was
generated in the reaction. It may be caused by the
performance of acid sites in HMOR. At the appropriate
temperature, the carbonylation of methyl formed from the
reaction of DME with Brønsted protons was promoted, which
led to the high DME conversion and MA selectivity. A slightly
change of DME conversion and a sharply decrease of MA
selectivity in DME carbonylation was reported ranging from
10
0
0
0.35
0
.7
1.05
n(H or N )/n(CO)
2
2
(a)
1
4
the temperature of 493 K to 533 K.
2
Effect of H Presence on DME Carbonylation in the Two-stage
Ethanol Synthesis
In previous reports, H was directly passed into the
2
1
2, 14
carbonylation.
2
It is necessary to study the effect of H on
carbonylation reaction. In this part, H2 was fed into the
reaction system with DME and CO, and here the temperature
for carbonylation was set at 483 K, and the reaction
temperature of MA hydrogenation was set at 503 K, according
1
1
to the previous experimental results. Table 2 shows the DME
conversion and products selectivities. When H flow increased
2
−1
(b)
from 5 to 30 mL min , the DME conversion decreased sharply
from 52.8% to 27.5%, ethanol and methanol and methane
selectivities increased while MA and ethyl acetate (EA)
Fig. 2 (a) Effect of n (H
2 2
or N )/n (CO) on DME conversion. (b) Effect of
n (H or N )/n (CO) on products selectivities.
2
2
−
1
2
selectivities decreased. When H flow reached to 30 mL min ,
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1
7
Table 3 Effect of n (H
2
or N
2
)/n (CO) on the space-time yield of MA and than those in R7 and R8. Cheung et al. pointed out that the
[a]
3
CH OH
formation of acetyl species was the rate-limiting reaction step
in the carbonylation of DME over HMOR. Furthermore,
19
Rasmussen et al. proposed that the acetyl carbocation
MA
CH
3
−1
OH
−1
-1
-1
n (H
2
or N
2
)/n (CO)
[mg gcat min ]
[mg gcat min ]
formed from the reaction of CO with methyl group was short-
lived and likely to be transformed into ketene, acting as a
potential reaction intermediate, which was verified in their
experimental study. By the high-level DFT calculations,
0
4.76
0.04
0.35
3.74
2.46
1.20
0.08
0.12
0.12
1
9
H
2
0.7
Rasmussen et al. also found that the formation rate of acetyl
was significantly faster in the 8 MR than that in the 12 MR of
1.05
-1
HMOR with the barrier difference of 6 kJ mol . Besides, the H
2
0
.35
3.80
3.46
3.34
0.08
0.12
0.14
molecule interacts with active sites and two typical adsorption
complexes are formed, one is the adsorption on a Brønsted
N2
0.7
.05
2
0
1
acid site and the other is on an extraframework cation, which
may inhibit the adsorption of DME on Brønsted acid sites and
acetyl groups.
[
1
a] Reaction conditions: The mixture flow of DME and CO (n(CO)/n(DME) =
−1
9) : 15 mL min . P=1.8MPa. T=483K.
+
+
CH OCH + H → CH OH + CH
(R7)
(R8)
3
3
3
3
+
+
CH OH + H →CH + H O
3
3
2
the ethanol and methanol selectivities were 32.3% and 56.0%,
respectively. Specially, large amounts of methane were
generated under this condition, and its selectivity was 11.8%
and the conversion of MA and EA were 100%.
+
+
CH
+CO →CH
CO
(R9)
3
3
+
+
CH OCH + CH CO → CH COOCH + CH
(R10)
3
3
3
3
3
3
To further explore the influence of H2 presence, DME
Table 3 lists the space-time yields (STYs) of MA and
carbonylation was carried out in a single-tube reactor using methanol with the variation of H2 or N2 addition. At the
the HMOR catalyst. The feed gas was composed of identical mole ratios of H /CO and N /CO, almost the same STY
2
2
DME/CO/N
Fig. 2a shows the DME conversion under different H
rates. The existence of H or N led to a decrease in DME
conversion. This is because that DME conversion is proportional
2
(internal standard gas)/H
2
or DME/CO/N
2
mixture.
of methanol could be obtained. It indicates that the presence
of H did not influence methanol production apparently. For
the MA, however, more obviously decrease of STY was
observed with the addition of H . For example, the STYs of MA
2
and N
2
flow
2
2
2
1
7
2
to the partial pressure of CO, as reported by Cheung et al.
Notably, the influence of H on the reaction was apparently larger
than that of N . When the flow rates of H and N were 15 mL
min , the corresponding molar ratio of H or N to CO was 1.05.
The DME conversions were 24.0% and 44.2%, respectively.
Similarly, the change in selectivity was more obvious under H
atmosphere (Fig. 2b). When N /CO mole ratio increased from 0.35
to 1.05, the MA selectivity decreased from 95.6% to 93.5%, and
the methanol selectivity increased from 4.2% to 5.9%. Under H
atmosphere, however, the MA selectivity decreased from 95.2% to the further depression of DME conversion was caused by the
−1
-1
were 1.20 and 3.34 mg gcat min when n (H
)/n (CO) were 1.05, respectively. Furthermore, a slightly
increase of methane selectivities was detected with the
addition of H or N , especially for the H addition. In the
process of DME carbonylation, when the rate-limiting reaction
of R9 was depressed by the presence of H or N , DME was
facilitated to form methanol by the reaction of DME with
Brønsted protons or water in HMOR. With the presence of H
2
)/n (CO) and n
2
(N
2
2
2
2
−1
2
2
2
2
2
2
2
2
2
2
,
2
8
0.4%, and the methanol selectivity increased from 4.5% to 19.1%. dissociated adsorption of H . Meanwhile, the reaction of
2
In the detailed studies on the pathways of DME methyl group with hydrogen to form methane was promoted.
1
7
carbonylation, Cheung et al. proposed that DME first reacted Besides, the hydration of active ketene would form acetic acid
with Brønsted protons, producing methanol and methyl (R7). and then the reaction of acetic acid with DME could also
1
9
Then methanol reacted with other Brønsted acid sites, produce methanol. However, the methanol formed by this
producing water and methyl group (R8). CO reacted with pathway decreased with the addition of H or N , since fewer
2
2
methyl, forming acetyl (R9), which then reacted with DME, acetyl species formed. Therefore, H had more obviously effect
2
1
8
producing MA and methyl group (R10). Boront et al. found on the DME carbonylation and the formation of methanol
that the reactions in R9 and R10 were less likely to proceed
[
a]
2
Table 4 Effect of H flow into the hydrogenation stage on the indirect ethanol synthesis.
−
1
H
2
[mL min ]
X
DME [%]
S
ethanol [%]
S
methanol [%]
S
MA [%]
56.9
S
EA [%]
3.2
S
CH4 [%]
4.0
Y
ethanol [%]
5
72.0
73.7
14.3
21.6
10.3
1
0
23.9
34.0
28.5
4.3
9.2
17.6
1
3
5
0
70.6
72.1
25.7
37.8
39.1
47.0
20.4
3.5
3.8
1.3
11.1
10.4
18.1
27.3
−1
[
a] Reaction conditions: The mixture flow of DME and CO (n(CO)/n(DME) = 19) : 15 mL min . P=1.8 MPa.
4
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Table 5 Comparison with various previous results in the indirect ethanol synthesis
Selectivity
DME
Ethanol
Reference
[12]
Catalysts
Inlet composition
Reactor type
Temperature(K)
calculation
method
Conversion
Selectivity
HMOR-Cu/ZnO
Cu/HMOR-Cu/ZnO
HMOR-Cu/ZnO
Ar/DME/CO/H =
Dual-catalyst
bed reactor
Molecular
base
56.3
93.8
39.3
44.1
2
4
93
1.55/1/47.45/50
21.0
23.7
23.6
32.7
31.6
24.4
24.8
28.7
Ru/HMOR-Cu/ZnO
Pd/HMOR-Cu/ZnO
Pt/HMOR-Cu/ZnO
Ar/DME/CO/H
2
=
Dual-catalyst
bed reactor
Molecular
base
[14]
1
6
.55/2.35/46.10/50.00
493
N /DME/CO/H =
2
Two-stage
reactor
Carbonylation:483
Hydrogenation:503
Molecular
base
2
HMOR-Cu/SBA-15
72.1
37.8
Our work
.25/1.56/29.69/62.50
Though DME conversion increased obviously in the case that
2
was fed directly into the MA hydrogenation stage, the MA
though little difference was observed for the apparent STYs of
methanol.
H
conversion and ethanol selectivity were still lower than that of
a single-tube MA hydrogenation reaction with only MA and H
as inlet gases. For example, Table 3 shows that without the
introduction of H or N , the space-time yield of MA in the
2
Effect of DME and CO Presence on MA Hydrogenation in the Two-
stage Ethanol Synthesis
2
2
−1
-1
carbonylation stage was 4.76 mg gcat min . In the two-stage
ethanol synthesis process, this produced MA would be
Because of the adverse effect of H on DME carbonylation, H
2
2
flow was adjusted to be introduced into the MA hydrogenation introduced to the hydrogenation stage. Thus, the value of n
-1
reactor directly rather than with DME and CO. As listed in (H )/n (MA) was 41 when H flow was 30 mL min . According
2
2
Table 4, with the increase of H
2
flow, the DME conversion kept to the previous results for single-tube hydrogenation, MA was
almost unchanged within the range of 70.6-73.7%; Ethanol and converted completely when n (H )/n (MA) was higher than
2
1
1
methanol selectivities increased, while MA and EA selectivities 20. However, 3.5% of MA still remained in the two-stage
decreased. The selectivities of ethanol and methanol and MA synthesis of ethanol, indicating that CO and DME affected MA
-
1
at H
respectively. It worth noting that the methane selectivity was CO and DME on hydrogenation reaction, a single-tube MA
up to 11.4%. In order to explain the result, CO and H were hydrogenation experiment was carried out using Cu/SBA-15 as
2
flow rate of 30 ml min were 37.8%, 46.0% and 3.5%, hydrogenation over Cu/SBA-15. In order to study the effect of
2
passed into the carbonylation reactorat 483K. Methane was catalyst and H /DME/CO as feed gas with different ratios.
2
not detected in the products, which indicates methane may be Without the introduction of CO or DME, the MA conversion
generated through another way.
2
and ethanol selectivity at n (H )/n (MA) of 15 were 87.2% and
Table 5 listed the comparison of the DME conversion and 46.2%, respectively (Table 6). However, when CO flow was at
−
1
ethanol selectivity with the previous reports. The reason for 21 mL min , the MA conversion and ethanol selectivity
the good performance of HMOR and Cu/SBA-15 can be decreased to 54.6% and 38.8%, respectively, indicating that
attributed to that the hydrogen was directly passed into the the presence of CO had an adverse effect on MA conversion.
−
1
hydrogenation stage, and the DME conversion was not When CO/DME mixture with 21 mL min was introduced into
affected by the hydrogen. In addition, the supporting of Cu the stage, the MA conversion and ethanol selectivity
could promote the carbonylation thus increasing the DME decreased to 37.2% and 36.5%, respectively. This change
1
2
conversion.
suggests that DME had a stronger influence than that of CO on
hydrogenation. To determine how CO and DME affect
hydrogenation, in-situ FTIR spectroscopy was used to
investigate DME and CO adsorption on the catalyst.
In order to make sure the effect of CO on the hydrogenation
reaction, the pure CO was firstly used as FTIR reaction
atmosphere. Fig. 3a shows the FTIR spectra of the Cu/SBA-15
sample after CO adsorption at 503 K. The peaks at 2057 and
[
a]
Table 6 Effect of CO and DME on MA hydrogenation for ethanol synthesis.
CO
H
2
H /MA
XMA [%]
Sethanol[%]
2
-
1
-1
[
mL min ]
[mL min ]
−
1
0
0
84
84
84
15
15
15
87.2
54.6
37.2
46.2
38.8
36.5
2
117 cm are assigned to CO bounding to Cu and the peak at
2130 cm to the typical Cu –CO carbonyl complex.
−
1
+
21, 22
2
1
b
2+
Considering that no Cu existed in the reduced sample, the
2
1(DME+CO)
−1
+
23, 24
2
peak at 2172 cm was ascribed to Cu (CO) dicarbonyls.
[
a] Reaction conditions: P=1.8 MPa, T=503 K. [b] The mixture flow of DME
Fig. 3b shows the FTIR spectra of Cu/SBA-15 adsorbing CO
upon N sweeping at various temperatures. The peaks at 2057,
and CO (n(CO)/n(DME) = 19).
2
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1
32
catalyst surface. Chen et al. also reported that DME was
molecularly adsorbed on alumina surface at low temperature
while it formed surface methoxy species when heated to high
+
temperatures. Thus, part of DME was adsorbed on Cu , while
the other part underwent further decomposition. It was
reported that DME was easily decomposed to adsorbed CH
3
3
2
3
and CH O species on the surface of catalysts. As shown in
Table 2 and Table 4, the methane selectivity increased
(a)
(a)
2
130
503K de 5min
503K de 15min
503K de 40min
573K de 5min
573K de 20min
0
.2
(
b)
Fig. 3 (a) In-situ FTIR spectra of Cu/SBA-15 after CO adsorption. (b) In-situ
FTIR spectra of Cu/SBA-15 upon N sweeping.
2
2172
−
117, and 2172 cm disappeared gradually with extended
1
2
sweeping time. When the temperature increased to 573 K,
−
only a small peak existed at 2130 cm . Therefore, it indicates
1
2100
2120
2140
2160
2180
2200
+
that CO easily interacts with Cu species, thereby reducing the
-1
Wavenumber /cm
+
amount of Cu that participates in MA hydrogenation. It has
(
b)
0
been reported that Cu promotes H
+
dissociation and Cu can
2
2
stabilize methyl and acetyl. CO adsorbed on Cu could thus
5
+
2933
503K ad 1min
503K ad 5min
503K ad 15min
0
.05
0
break the balance between Cu and Cu resulting in a decrease
+
2892
503K ad 20min
2
6
2
833
in catalytic activity.
In order to make sure the effect of DME on the
hydrogenation reaction, the CO/DME mixture was used as the
FTIR reaction atmosphere. Fig. 4a, Fig 4c and Fig 4d show
adsorption spectra of CO or DME from a CO/DME mixture. Fig.
3000
4
b, Fig. 4e and Fig 4f show the adsorption spectra of CO or
−1
2
DME after N swept. The peaks at 2130 and 2175 cm are in
accord with those peaks in Fig. 3a, which are ascribed to the
Cu -CO and Cu (CO) , respectively. It has been reported that
2
750 2800 2850 2900 2950 3000 3050
+
+
2
-1
+
Cu could not only activate CO under reaction conditions, but
Wavenumber /cm
(c)
2
also adsorb DME. Relevant bands of DME are found at 2990-
7
-1 28
2820, 1456, 1173, 1098 and 926 cm . Fig. 4c and Fig. 4e
display the peaks between 2800 and 3050 cm . The peaks at
503K ad 1min
503K ad 5min
503K ad 15min
−1
1195
0.05
1173
-1
2833, 2892, and 3000 cm are ascribed to the symmetric
stretching, deformation and antisymmetric stretching of
methyl, respectively. The peak at 2933 cm is ascribed to the
5
03K ad 20min
-1
2
9, 30
saturated C-H stretching.
wavenumbers, the bands of Fig. 4d and Fig. 4f in the σ(C-H)
In the region of low
1
120
-1
region are also detectable at 1400 cm as σ(CH ) bending
3
1100
-1
1
275
vibration mode. The bands observed at 1270 and 1173 cm
are due to the γ(CH ) vibration mode and ρ(CH ) rocking mode,
respectively. In addition, a strong absorption band from C-O
1397
1400
3
3
3
1
1000
1100
1200
1300-1
Wavenumber /cm
-1
stretching in methoxyl is observed at 1100 cm , reflecting the
existence of terminal methoxy adsorption species on the
(d)
6
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Acknowledgement
5
5
5
5
5
03K de 5min
03K de 15min
03K de 40min
73K de 5min
73K de 20min
0.002
2933
This work was supported by the National Science and
Technology Supporting Plan Through Contract
2015BAD15B06), the National Natural Science Foundation of
3000
2892
2833
(
China (51276166).
Notes and references
2
750 2800 2850 2900 2950 3000 3050
-1
1
2
3
4
5
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FTIR adsorption peaks after N sweeping. (c, d) DME FTIR adsorption peaks
after CO/DME mixture adsorption. (e, f) DME FTIR adsorption peaks after N
sweeping.
2
0
1
2
2
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2
1
64, 425-428.
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1
1
1
1
3
4
5
6
Y. Zhang, X. G. San, N. Tsubaki, Y. S. Tan and J. F. Chen,
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Conclusions
Two-stage synthesis of ethanol was carried out in this study.
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2
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2
2
interacting with active sites inhibited the reaction between CO
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and dimethyl ether had influence on methyl acetate
hydrogenation. The methane and methanol selectivities
1
9
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40.
2
2
increased obviously with the increase of H flow. Combined
2
with the Fourier transform infrared spectroscopy results, it can
be deduced that methane and methanol were generated
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from dimethyl ether decomposition. Therefore, the presence
of dimethyl ether had stronger effect on methyl acetate
conversion.
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ARTICLE
Journal Name
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Two-stage reactor loaded with HMOR and Cu/SBA-15 separately was used to improve the
indirect ethanol synthesis.
CH OCH + CO + 2H2
CH OH + CH CH OH
3
3
3
3
2
+
0
Cu
Cu