Direct synthesis of ethyl acetate from ethanol carried out under pressure

Article abstract of DOI:10.1006/jcat.2002.3769

Direct synthesis of ethyl acetate from ethanol over a Cu-Zn-Zr-AI-O catalyst was studied under pressured conditions between 473 and 533 K. The selectivity to ethyl acetate and the space-time yield of ethyl acetate increased with increasing reaction pressure, whereas ethanol conversion decreased. The highest spacetime yield of ethyl acetate was achieved at a reaction pressure of about 0.8 MPa with maximum selectivity of 93 wt %. The products observed in the effluent include ethyl acetate, acetaldehyde, butanone, 1-butanol, and propanone. In the reaction of acetaldehyde in a flow of N₂ hardly any converted to ethyl acetate and a small amount of acetaldol derivatives, e.g., 2-butenal and butanal, were observed. In contrast, the reaction of acetaldehyde in an H₂ flow was accompanied by the formation of ethyl acetate as a major product and hydrogenated products, e.g., ethanol and 1-butanol. In the reaction of an equimolar mixture of acetaldehyde and ethanol in an N₂ flow, the product distribution was also similar to that observed in the reaction of ethanol. Butanone was the major product of the 1,3-butanediol reaction.

Full text of DOI:10.1006/jcat.2002.3769

Journal of Catalysis 212, 207–215 (2002)
doi:10.1006/jcat.2002.3769
Direct Synthesis of Ethyl Acetate from Ethanol Carried Out
under Pressure
∗
, ,1,2
Kanichiro Inui, †
Toru Kurabayashi,† and Satoshi Sato‡
∗
Graduate School of Science and Technology, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan; †Chisso Petrochemical Corporation,
5
-1 Goi-kaigan, Ichihara 290-8551, Japan; and ‡Department of Materials Technology, Faculty of Engineering,
Chiba University, Yayoi, Inage, Chiba 263-8522, Japan
Received May 14, 2002; revised July 19, 2002; accepted July 19, 2002
The dehydrogenative dimerization of ethanol to ethyl
Direct synthesis of ethyl acetate from ethanol over a Cu–Zn– acetate is a simple, noncorrosive, and less-toxic process,
Zr–Al–O catalyst was investigated under pressured conditions be- requiring only an ethanol feedstock. There are several
tween 473 and 533 K. Both the selectivity to ethyl acetate and the
space-time yield of ethyl acetate increase with increasing reaction
pressure, whereas ethanol conversion decreases. The highest space-
time yield of ethyl acetate is attained at a reaction pressure of about
pioneering studies of the dehydrogenative dimerization of
ethanol using Cu-based catalysts (11–19). However, these
studies have not answered questions of economy, especially
in terms of selectivity to ethyl acetate and space-time yield
0
.8 MPa with maximum selectivity of 93 wt%. During the process,
(
STY) of ethyl acetate under atmospheric pressure. In 1999,
ethanol is first dehydrogenated to acetaldehyde and is then coupled
with another ethanol molecule to form hemiacetal, which is further
dehydrogenated to ethyl acetate. The concentration of by-products
such as 1-butanol and butanone, which form after the aldol addition
Kvaerner Process Technology announced the development
of a process of dehydrogenative dimerization of ethanol to
ethyl acetate (20), which operates under pressure (21). The
of acetaldehyde, decreases with increasing reaction pressure. Since process requires a copper catalyst and results in about 30 to
the equilibrium of the dehydrogenation of ethanol to acetaldehyde 40% ethanol conversion and about 95% ethyl acetate selec-
−
1
shifts to an ethanol-rich composition at high pressure, the decrease tivity with liquid hourly space velocity (LHSV) = 1.0 h at
in the partial pressure of acetaldehyde explains the suppression of
the by-products formed through acetaldol. ꢀc 2002 Elsevier Science (USA)
Key Words: ethyl acetate; ethanol; pressured condition.
4
96 K and 2.86 MPa (21). Although it has high selectivity to
ethyl acetate, the STY of ethyl acetate is not yet satisfactory.
To improve the STY of ethyl acetate, we must consider
the reaction mechanism of ethyl acetate formation and
other by-products. Elementary reactions in the process are
divided into three types: (a) reactions preferred by high
pressure, (b) reactions preferred by low pressure, and (c)
reactions that do not depend on pressure. The dehydro-
genative dimerization of ethanol to ethyl acetate is a combi-
nation of dehydrogenation, which is preferred by low pres-
sure, and dimerization, which is preferred by high pressure.
Furthermore, most of the by-products are formed through
elementary reactions which are preferred both by high and
low pressure. The reaction rate is also important in manu-
facturing processes. It is advantageous that the rate of for-
mation of ethyl acetate is accelerated at high pressure by
the increase in intermolecular collision frequency together
with the formation of by-products.
We recently reported an effective catalyst system, Cu–
Zn–Zr–Al–O, for the dehydrogenative dimerization of
ethanol at ambient pressure (22). The present study clari-
fies the efficiency of the high-pressure process using the Cu–
Zn–Zr–Al–O catalyst, that is, the effect of reaction pressure
on the total reaction rate of ethyl acetate as well as on the
product selectivity. We also discuss the reaction mechanism
of ethyl acetate formation from ethanol.
INTRODUCTION
Ethyl acetate is an environmentally friendly organic sol-
vent used in paint and adhesive, thus eliminating the use of
aromatic compounds, in the working environment. Ethyl
acetate can be produced industrially in three ways (1): the
Fischer esterification process (2–4), the Tishchenko reac-
tion of acetaldehyde (5, 6), and the addition of acetic acid to
ethylene(7–10). Theconventionalprocesses, however, have
some disadvantages. Both conventional esterification and
the addition of acetic acid to ethylene require stock tanks
and apparatuses for plural feedstocks; the use of acetic acid
causes corrosion of the apparatuses. Acetaldehyde is only
available in a petrochemical industrial area and is difficult
to handle because of its toxicity. Therefore, a novel process
for the production of ethyl acetate is desirable.
1
To whom correspondence should be addressed. E-mail: inui@chisso.
co.jp.
2
Current address: Chisso Petrochemical Corp. 5-1 Goi-kaigan, Ichihara
2
90-8551, Japan.
207
0
021-9517/02 $35.00
c 2002 Elsevier Science (USA)
All rights reserved.
ꢀ

2
08
INUI, KURABAYASHI, AND SATO
EXPERIMENTAL
Since the reaction rate is low at the low temperature of
73 K, the actual conversion of ethanol is lower than the
4
Catalyst Sample
equilibrium conversion. Nevertheless, the actual ethanol
conversion above 493 K is greater than the equilibrium
conversion. Since theproducedacetaldehydeis further con-
verted to other by-products, such as butanone and butanol,
at high temperatures, the actual conversion is greater than
the equilibrium conversion of ethanol to ethyl acetate.
Table 1 lists typical product distributions in the reaction
of the dehydrogenative dimerization of ethanol over the
Cu–Zn–Zr–Al–O catalyst at different reaction pressures.
In the reaction, total mass in the effluent liquid and gas
is balanced to the mass of inlet ethanol. A wide variety
of products, such as ethyl acetate, acetaldehyde, butanone,
propanone, 2-pentanone, 1-butanol, ethyl butyrate, butyl
acetate, water, and a small number of unidentified prod-
ucts, were found in the effluent. Both at 473 and 513 K, the
selectivity to ethyl acetate increases with increasing reac-
tion pressure. The selectivity of by-products decreases with
increasing reaction pressure. In particular, we observed a
considerable suppression of the formation of acetaldehyde
and butanone at higher pressure. This significant suppres-
sion leads to a high ethyl acetate selectivity of 92.6 wt%. In
addition, a trace amount of butanal was formed during this
reaction, whereas no 2-butenal is detected. It is reported
that butanal is formed from acetaldehyde over acetaldol
The Cu–Zn–Zr–Al–O catalyst was prepared by conven-
tional coprecipitation using the corresponding nitrates and
a sodium hydroxide solution (about 3 mol dm ) as the
precipitant. The atomic ratio of Cu/Zn/Zr/Al was fixed at
−
3
1
2 : 1 : 2 : 4. After precipitation, the precipitate was stored at
room temperature for 18 h and was then washed with deion-
ized water. The resulting precipitate was dried at 353 K for
1
0 h followed by calcination in a N2 flow at 773 K for 3 h.
The specific surface area calculated using the BET method
2
−1
for N2 adsorption at 77 K was 99.7 m g , and the Cu sur-
face area measured by TPR titration of Cu oxidized by N2O
2
−1
(
23) was 38.7 m g
.
Catalytic Reaction
Dehydrogenativedimerizationofethanolwascarriedout
at a reaction pressure between 0.1 and 1.0 MPa using a con-
ventional fixed-bed down-flow stainless steel reactor. Prior
to the catalytic reaction, the catalyst was reduced in a flow of
3
−1
H2–N2 (H2/N2 = 10 : 90) at 100 cm min at temperatures
of up to 443 K. The carrier gas was then switched to N2 and
thesamplewasheatedataprescribedreactiontemperature.
The ethanol reactant was introduced into the reactor at a
temperature between 473 and 533 K at W/F = 0.018–7.9 h,
where W and F are catalyst weight [kg] and flow rate of
(
16, 17). It is reasonable that 2-butenal and butanal are hy-
drogenated to 1-butanol as soon as they are formed over
the catalyst.
In the analysis of gaseous products, hydrogen and carbon
dioxide were observed: more than 99 mol% of the gaseous
products was hydrogen with a small amount of CO2. CO2
is probably produced from the decomposition of acetaldol
−1
3
−1
ethanol [kg h ], respectively. N2 carrier gas (30 cm min
was used at 0.1 MPa, whereas no carrier gas was used at
0.1 MPa. The partial pressures of inlet ethanol in the re-
)
>
action operated at 0.1 MPa are 0.072 and 0.091 MPa at W/F
of 3.16 and 1.58 h, respectively. The reactant was heated
and vaporized in the preheating zone in front of the cata-
lyst bed. The products were recovered by cooling at 195 K.
The effluent was collected periodically and analyzed by gas
chromatography (Shimadzu GC-14A) using a capillary col-
umn (G-100, Kagakuhin Kensa Kyokai) with toluene as the
internal standard. The water content in the effluent was de-
termined using a Karl-Fischer moisture meter. The gaseous
products, such as H2 and CO2, that did not condense at
1
95 K were collected in a plastic bag and analyzed by gas
chromatography (Shimadzu GC-9A) in a packed column
active carbon).
(
RESULTS
Figure 1 shows the conversion of ethanol over the Cu–
Zn–Zr–Al–O catalyst at temperatures between 473 and
13 K and the equilibrium conversion calculated for the
5
dehydrogenation of ethanol to ethyl acetate as a function
of reaction pressure. We did not observe a decrease in the
catalytic activity during the process time. At each temper-
ature, the observed conversion of ethanol and the equilib-
FIG. 1. Changes in conversion with ethanol partial pressure
(
W/F = 3.16 h). Reaction temperature: ꢀ, 473; ꢁ, 493; ꢂ, 513 K; lines
represent equilibrium conversion of ethanol calculated at (a) 473, (b) 493,
rium conversion decrease with increasing reaction pressure. and (c) 513 K.

SYNTHESIS OF ETHYL ACETATE UNDER PRESSURE
209
TABLE 1
Catalytic Results over Cu–Zn–Zr–Al–O Catalyst for the Reaction of Ethanol
Selectivity (wt%)
a
Temp. (K) Press. (MPa) X (%) AcOEt AcH MEK AcMe 2PN 1BO EB BE H2O H2 Others
473
0.1
60.3
57.1
56.4
51.6
51.4
46.3
84.8
89.2
92.1
91.3
92.9
91.6
3.6
2.1
1.0
1.0
0.8
0.7
3.7
2.0
0.9
0.7
0.5
0.3
0.5
0.3
0.1
0.1
0.1
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.2
0.2
0.2
0.2
0.2
0.1
0.6
0.5
0.5
0.5
0.3
0.2
0.3
0.2
0.2
0.2
0.1
0.1
1.1
0.5
0.2
0.1
0.1
0.9
4.2
4.2
4.2
4.2
4.2
4.2
0.9
0.9
0.8
1.8
1.0
1.9
0
0
0
0
1
.2
.4
.6
.8
.0
513
0.1
82.1
77.2
69.3
66.4
62.9
62.4
75.9
78.0
81.5
82.6
84.2
83.5
3.8
2.9
1.6
1.6
1.3
1.1
5.8
4.3
3.3
2.7
2.2
1.6
2.2
1.5
1.1
0.9
0.7
0.3
0.4
0.3
0.3
0.2
0.2
0.1
0.6
1.1
0.8
1.1
0.9
0.5
1.1
2.0
0.9
1.4
1.0
0.6
0.9
1.7
0.6
0.8
0.5
0.3
1.9
1.6
1.8
1.5
1.5
2.1
4.2
4.2
4.2
4.2
4.2
4.2
3.2
2.4
4.1
3.1
3.4
5.8
0
0
0
0
1
.2
.4
.6
.8
.0
Note. AcOEt, ethyl acetate; AcH, acetaldehyde; MEK, butanone; AcMe, propanone; 2PN, 2-pentanone; 1BO, 1-butanol;
EB, ethyl butyrate; BE, butyl acetate. Others indicates a small number of unidentified products.
a
Conversion of ethanol; W/F = 3.16 h.
to propanone. The amount of hydrogen produced corre- acetate greatly increased with increasing reaction pressure,
sponded to the sum of the derivatives from the dehydro- and reached a plateau at around 0.4 MPa at 473 K. At higher
genation. Since hydrogen and water were observed as in- temperatures, a much higher pressure is needed to improve
organic products, dehydrogenation and dehydration surely the ethyl acetate selectivity. At all temperatures, the sum
proceed over the catalysts.
of the selectivities to acetaldol derivatives decreased with
Figure 2 shows the changes in the selectivity to ethyl increasing reaction pressure.
acetate with reaction pressure together with the sum of
Figure 3 shows the changes in the STY of ethyl acetate
the selectivities to acetaldol derivatives. Here, the acetal- and the selectivity to ethyl acetate with W/F at 1.0 MPa.
dol derivatives include butanal, 1-butanol, ethyl butyrate, The STY decreased with increasing W/F and increased
butyl acetate, butanone, propanone, and 2-pentanone. At with increasing reaction temperature. The maximum STY
−
1
−1
an ambient pressure of 0.1 MPa, the maximum selectiv- exceeded 20 mol h kg at 533 K. At all temperatures,
cat
ity to ethyl acetate was 85.0 wt% at the low temperature of the selectivity to ethyl acetate increased with increasing
4
73 K. At each reaction temperature, the selectivity to ethyl W/F and reached a maximum at W/F = ca. 0.5–1.0 h. This
FIG. 3. Changes in STY of ethyl acetate (ꢄ) and selectivity to ethyl
FIG. 2. Changes in the selectivity to ethyl acetate (ꢃ) and aldol
derivatives (ꢄ) with ethanol partial pressure. Reaction temperature:
a) 473, (b) 493, (c) 513 K; W/F = 3.16 h.
acetate (ꢂ) with W/F. Reaction temperature: (a) 473, (b) 493, (c) 513,
(d) 533 K; pressure, 1.0 MPa. Reference data:(ꢃ) STY, (ꢅ) selectivity,
(498 K 2.7 M Pa; Ref. 21).
(

2
10
INUI, KURABAYASHI, AND SATO
FIG. 4. Changes in STY of ethyl acetate with W/F at 513 K. Reaction
pressure: (a) 0.1, (b) 0.4, (c) 0.8, (d) 1.0 MPa.
FIG. 5. Changes in conversion and selectivity with W/F at 533 K
and 0.1 MPa: (ꢅ) ethanol conversion, (ꢁ) ethyl acetate selectivity,
ꢃ) acetaldehyde selectivity.
(
demonstrates that a high STY of ethyl acetate with high
selectivity to ethyl acetate can be achieved over the present acetaldehyde was preferentially formed and ethyl acetate
Cu–Zn–Zr–Al–O catalyst; 92.6 wt% selectivity was ob- increasedwithincreasingethanolconversionwith W/F. The
tained at 493 K, 1.0 MPa, and W/F = 0.53 h with STY ethyl acetate selectivity reached a maximum at W/F = 1–
−
1
−1
of 8 mol h kg , compared with a reference STY of 2 h. Since by-products are produced at W/F > 2 h, the ethyl
−
1
−1
2
.8 mol h kg , which was calculated assuming a catalyst acetate selectivity decreased.
bulk density of 1.68 g cm , as reported for a CuO-based
catalyst at 498 K and 2.7 MPa (21).
cat
−3
Table 2 lists the reaction results of acetaldehyde, ethanol,
and 1,3-butandiol as the feedstock over the Cu–Zn–Zr–
Figure 4 shows the changes in the STY of ethyl acetate Al–O catalyst under different conditions. In a reaction of
at 513 K with W/F. The STY increased with increasing re- acetaldehyde in a flow of N2 hardly any converted to ethyl
action pressure. The STY reached maxima at the low pres- acetate and a small amount of acetaldol derivatives such
sures of 0.1 and 0.4 MPa and a linear decrease with increas- as 2-butenal and butanal were observed. In contrast, the
ing W/F at high pressures. This indicates that the maximum reaction of acetaldehyde in an H2 flow was accompanied
in STY shifts to lower W/F with increasing reaction pres- by the formation of ethyl acetate as a major product. Hy-
sure.
drogenated products such as ethanol and 1-butanol were
Figure 5 shows the changes in ethanol conversion, ethyl also observed in an H2 flow. However, hardly any 2-butenal
acetate selectivity, and acetaldehyde selectivity with W/F. was detected in the presence of H2 (Table 2). The prod-
Over the Cu–Zn–Zr–Al–O catalyst at 533 K and 0.1 MPa, uct distribution in an H2 flow is similar to that observed
the ethanol conversion increased with increasing W/F, in the reaction of ethanol in an N2 flow. In the reac-
while the acetaldehyde selectivity decreased. At low W/F, tion of an equimolar mixture of acetaldehyde and ethanol
TABLE 2
Reaction of Other Feedstocks over Cu–Zn–Zr–Al–O Catalyst
Composition of products (wt%)
Feedstock
AcH
AcH
EtOH
Carrier gas
EtOH
AcH
13BD
AcOEt
MEK
AcMe
CA
BA
1BO
2PN
EB
BE
Others
N2
H2
N2
N2
N2
H2
2.1
16.9
38.5
30.7
5.4
83.0
10.6
5.6
14.8
4.9
0
0
0
0
0
3.3
46.8
39.0
31.1
1.2
0.3
2.9
4.7
6.3
47.4
44.4
1.6
5.0
0.7
1.4
4.1
4.1
3.3
0
0
0
0
3.9
0.6
0
0
0
0.1
1.6
0.5
1.8
4.4
4.6
0.3
1.9
0.2
0.5
0.3
0.2
0.7
4.1
0.8
1.8
1.3
1.0
0.3
4.1
0.5
1.9
1.0
1.0
1.1
5.5
9.5
9.7
30.0
33.0
AcH + EtOH
1
1
3BD
3BD
7.4
3.1
trace
1.2
0
0
3
−1
Note. Reaction temperature, 493 K; pressure, 0.1 MPa; W/F = 1.58 h; carrier gas flow rate = 30 cm min . 13BD, 1,3-butanediol; MEK, butanone;
AcMe, propanone; AcH, acetaldehyde; EtOH, ethanol; AcOEt, ethyl acetate; CA, 2-butenal; BA, butanal; 1BO, 1-butanol; 2PN, 2-pentanone; EB,
ethyl butyrate; BE, butyl acetate. Others indicates water, hydrogen, and unidentified liquid products.

SYNTHESIS OF ETHYL ACETATE UNDER PRESSURE
211
in an N2 flow, the product distribution is also similar to reactions are divided into three types: reactions preferred
that observed in the reaction of ethanol. Butanone is the by high pressure, reactions preferred by low pressure, and
major product of the 1,3-butanediol reaction and small reactions that do not depend on pressure (Table 3). A large
amounts of acetaldehyde, 1-butanol, ethanol, propanone, number of elementary reactions are pressure-sensitive
and ethyl acetate were detected. Furthermore, in the 1,3- (Tables 3A and 3B).
butanediol reactions with N2 and H2 as carrier gases, the
It is obvious that pressure affects the catalytic reaction;
water detected in the effluent was 15.0 and 17.0 wt%, re- i.e., the ethanol conversion (Fig. 1) and product distribu-
spectively.
tion (Table 1). High-pressure operation suppresses both
the ethanol conversion and the formation of by-products
such as butanone and 1-butanol, derived from acetaldol,
whichcanberationalizedbythedecreaseinthepartialpres-
sure of acetaldehyde caused by a shift in equilibrium among
ethanol, acetaldehyde, and hydrogen at high pressure. Con-
DISCUSSION
. Reaction Mechanism
1
First, we propose a total products map of ethanol con- sequently, a high selectivity to ethyl acetate is achieved by
version over the Cu–Zn–Zr–Al–O catalyst (Scheme 1). We suppressing the acetaldehyde partial pressure in the ini-
must consider each elementary reaction and the depen- tial elementary reaction rather than by suppressing each
dence of its equilibrium on pressure for each of the routes elementary reaction for the by-products. The following dis-
and discuss the total reaction mechanism. The elementary cussion deals with the elementary reactions.
SCHEME 1. Possible reaction routes over Cu–Zn–Zr–Al–O catalyst: (A) routes to major products, (B) routes to acetaldehyde derivatives. Materials
shown in squares with no shadow represent the products detected in this work, whereas substrates shown in squares with shadows are undetected
products.

2
12
INUI, KURABAYASHI, AND SATO
TABLE 3A
High-Pressure Preferable Elementary Reactions
a-1. CH3CHO + H2 → CH3CH2OH
acetaldehyde ethanol
a-2. CH3CHO + CH3CH2OH → CH3CH(OH)OC2H5
acetaldehyde ethanol hemiacetal
a-3. 2CH3CHO → CH3CH(OH)CH2CHO
acetaldehyde acetaldol
a-4. CH3CH == CHCHO + H2 → CH3(CH2)2CHO
-butenal butanal
a-5. CH3(CH2)2CHO + H2 → CH3(CH2)3OH
butanal 1-butanol
a-6. CH3CH(OH)CH2CHO + H2 → CH3CH(OH)CH2CH2(OH)
acetaldol 1,3-butanediol
a-7. CH3CH(OH)CH == CH2 + H2 → CH3CH(OH)CH2CH3
-hydroxy-1-butene 2-butanol
a-8. CH3COCH2CH3 + H2 → CH3CH(OH)CH2CH3
butanone 2-butanol
a-9. CH3CH(OH)CH2CHO + O(S) → CH3CH(OH)CH2COO(S)
acetaldol carboxylate adsorbed
a-10. CH3COCH3 + H2 → CH3CH(OH)CH3
propanone 2-propanol
a-11. CH3COCH3 + CH3CHO → CH3COCH2CH(OH)CH3
propanone acetaldehyde 4-hydroxy-2-pentanone
a-12. CH3COCH == CHCH3 + H2 → CH3CO(CH2)2CH3
-pentene-2-one 2-pentanone
a-13. CH3(CH2)2CHO + CH3CH2OH → C3H7CH(OH)OC2H5
butanal ethanol hemiacetal
a-14. CH3CHO + CH3(CH2)2CH2OH → CH3CH(OH)OC4H9
acetaldehyde butanol hemiacetal
Hydrogenation (b-1)
Hemiacetal formation
Aldol addition (b-3)
Hydrogenation
2
Hydrogenation (b-5)
Hydrogenation (b-6)
Hydrogenation
3
Hydrogenation (b-8)
Oxidation
Hydrogenation (b-10)
Aldol addition (b-11)
Hydrogenation
3
Hemiacetal formation
Hemiacetal formation
Note. Reaction numbers in parentheses indicate the number of the reverse reaction shown in Table 3B.
1
.1. Formation of ethyl acetate. Figure 5 strongly sug- differs from that of route 1 via the Tishchenko reaction. Fur-
gests that the formation of ethyl acetate proceeds stepwise thermore, Takeshita et al. did not use the Tishchenko route
via acetaldehyde, which is an intermediate. It is obvious that over a reduced copper catalyst, because propanal did not
the dehydrogenation step is not a rate-determining step in condense to give the corresponding ester (15). Takezawa
the formation of ethyl acetate from ethanol, because the and Iwasa proposed route 2, the nucleophilic addition of
product distribution in the reaction of acetaldehyde in H2 either ethanol or surface ethoxide to acetaldehyde to form
flow is similar to that observed in the reaction of ethanol a hemiacetal, followed by dehydrogenation to ethyl acetate
(
Table 2).
over a supported copper catalyst (Cu/SiO2; 16). Takeshita
Two possible routes of ethyl acetate formation from also proposed the same route over a reduced copper cata-
ethanol are proposed. Route 1, the Tishchenko reaction, lyst (19). The results in Table 2 indicate that a hydrogenated
consists of dehydrogenation followed by coupling of ac- acetaldehyde, e.g., ethanol, is needed for the formation of
etaldehyde:
an intermediate in ethyl acetate production. Thus, we con-
clude that route 2 is the probable route for the formation of
ethyl acetate over the present system of Cu–Zn–Zr–Al–O
rather than the Tishchenko reaction. The stepwise reactions
via hemiacetal (route 2) consist of a reaction a-2 (listed in
Table 3), which is preferred by high pressure, and reactions
b-1 and b-2, which are preferred by low pressure.
2
C2H5OH → 2CH3CHO → CH3COOC2H5.
[1]
Route 2 consists of dehydrogenation followed by addition
of ethanol to acetaldehyde:
2
C2H5OH→CH3CHO+C2H5OH
CH3CH(OH)OC2H5→CH3COOC2H5. [2]
→
1.2. Butanone and propanone. The by-products of
The result of the reaction of acetaldehyde in an inert car- the ethanol reaction are divided into two groups: some
rier gas of N2 over the Cu–Zn–Zr–Al–O catalyst (Table 2) arise from acetaldol, formed by the aldol addition of

SYNTHESIS OF ETHYL ACETATE UNDER PRESSURE
213
TABLE 3B
Low-Pressure Preferable Elementary Reactions
b-1. CH3CH2OH → CH3CHO + H2
ethanol acetaldehyde
b-2. CH3CH(OH)OC2H5 → CH3COOC2H5 + H2
hemiacetal ethyl acetate
b-3. CH3CH(OH)CH2CHO → 2CH3CHO
acetaldol acetaldehyde
b-4. CH3CH(OH)CH2CHO → CH3CH == CHCHO + H2O
acetaldol 2-butenal
b-5. CH3(CH2)3OH → CH3(CH2)2CHO + H2
-butanol butanal
b-6. CH3CH(OH)CH2CH2(OH) → CH3CH(OH)CH2CHO + H2
,3-butanediol acetaldol
b-7. CH3CH(OH)CH2CH2(OH) → CH3CH(OH)CH == CH2 + H2O
,3-butanediol 3-hydroxy-1-butene
b-8. CH3CH(OH)CH2CH3 → CH3COCH2CH3 + H2
-butanol butanone
b-9. CH3CH(OH)CH2COO(S) → CH3COCH3 + H2 + CO2
carboxylate adsorbed propanone
b-10. CH3CH(OH)CH3 → CH3COCH3 + H2
-propanol propanone
b-11. CH3COCH2CH(OH)CH3 → CH3COCH3 + CH3CHO
-hydroxy-2-pentanone propanone acetaldehyde
b-12. CH3COCH2CH(OH)CH3 → CH3COCH == CHCH3 + H2O
-hydroxy-2-pentanone 2-penten-4-one
b-13. CH3(CH2)2CH(OH)OC2H5 → C3H7COOC2H5 + H2
hemiacetal ethyl butyrate
b-14. CH3CH(OH)OC4H9 → CH3COOC4H9 + H2
hemiacetal butyl acetate
Dehydrogenation (a-1)
Dehydrogenation
Reverse aldol addition (a-3)
Dehydration
Dehydrogenation (a-5)
Dehydrogenation (a-6)
Dehydration
1
1
1
Dehydrogenation (a-8)
Ketonization
2
Dehydrogenation (a-10)
Reverse aldol addition (a-11)
Dehydration
2
4
4
Dehydrogenation
Dehydrogenation
Note. Reaction numbers in parentheses indicate the number of the reverse reaction shown in Table 3A.
acetaldehyde, and others do not form this way. Elliot and ketone, as proposed by Wrzyszcz et al. (24), is not possible
Pennella proposed a reaction mechanism for butanone and because propanone decreased with increasing concentra-
propanone formation over Cu/ZnO/Al2O3 (17). According tion of ethyl acetate at high pressure (Table 1).
totheirmechanism(Eqs. [3]–[5]), butanoneformsfromace-
taldol(Eq. [3])accompaniedbytheformationoflatticeoxy-
gen, represented as O(S) in Eq. [4] where the subscript (S)
represents a surface-adsorbed species. They also described
how lattice oxygen was consumed by propanone formation
2CH3CHO → CH3CH(OH)CH2CHO
[3]
CH3CH(OH)CH2CHO + H2 → CH3CH(OH)CH2CH3 + O(S)
CH3COCH2CH3 + H2
→
[4]
CH3CH(OH)CH2CHO + O(S) → CH3CH(OH)CH2COO(S)
(
Eq. [5]). Althoughthelatticeoxygenwasneededtoexplain
the formation of propanone (Eq. [5]), the generation of the
lattice oxygen described in Eq. [4] is invalid. The first part
of Eq. [4] must contain several elemental reactions such as
→ CH COCH + CO + H . [5]
3
3
2
2
On the other hand, Chung et al. investigated the reac-
hydrogenation, dehydration, and the decomposition of wa- tion of 1,3-butanediol over Cu/ZnO catalyst (25). They
ter. The generation of the lattice oxygen may be consistent reported that butanone and butanal formed from 1,3-
with the decomposition of water: H2O → H2 + O(S). If the butanediol. Butanoneisthemajorproductinthereactionof
O
(
derives from water, then we accept the mechanism. 1,3-butanediol over the present Cu–Zn–Zr–Al–O catalyst
S)
Furthermore, ketonization of esters to form a symmetric (Table 2). Since the hydrogenation is fast, as shown in the
TABLE 3C
Pressure-Independent Elementary Reactions
c-1. 2CH3CH2OH → C2H5OC2H5 + H2O
ethanol diethyl ether
c-2. CH3COOC2H5 + H2O → CH3COOH + C2H5OH
ethyl acetate acetic acid ethanol
Dehydration
Hydrolysis (reversible)

2
14
INUI, KURABAYASHI, AND SATO
acetaldehyde-in-H2 reaction (Table 2), 1,3-butanediol must formation. These routes consist of the elementary reactions
be formed during the hydrogenation of acetaldol. Because a-13, a-14, b-13, and b-14 (Table 3).
acetaldehyde, ethanol, and propanone were observed in
1
.6. Diethyl ether and acetic acid. By-products that do
the reaction of 1,3-butanediol, even propanone must form
through acetaldol. Both hydrogenation and dehydrogena-
tion, in addition to the reverse aldol addition, can proceed
smoothly over the present catalyst. These results indicate
that 1,3-butanediol, the hydrogenated acetaldol, is a pos-
sible intermediate of the major by-product butanone. The
following reaction sequence described in Eq. [6] consists
of the elementary reactions a-6, b-7, a-7, and b-8 listed in
Table 3:
not form through acetaldol are diethyl ether and acetic
acid. Diethyl ether forms in the intermolecular dehydration
of ethanol. This reaction is pressure-independent (c-1 in
Table 3C).
Cu/Al2O3 catalyzes the formation of dimethyl ether as
well as methyl formate in the reaction of methanol (26).
The formation of dimethyl ether is probably due to the sur-
face acidity of alumina. The formation of less diethyl ether
over Cu–Zn–Zr–Al–O indicates that the surface acidity of
the Cu–Zn–Zr–Al–O catalyst is relatively low. The combi-
nation of aluminum oxide with Zn and Zr oxides probably
reduces the acidity of alumina.
Acetic acid forms by hydrolysis of ethyl acetate (c-2 in
Table 3C). This pathway requires water, i.e., the water con-
centration in the ethanol feedstock affects the selectivity to
acetic acid (data not shown). The selectivity to acetic acid
increases with increasing water content in the ethanol feed-
stock. Thus, a higher concentration of water in the reactor
causes a high selectivity to acetic acid, whereas acetic acid is
hardly detected in the reactions carried out under pressure
in our study.
CH3CH(OH)CH2CHO + H2
→
→
→
→
CH3CH(OH)CH2CH2OH
CH3CH(OH)CH == CH2 + H2O
CH3CH(OH)CH2CH3(–H2)
CH3COCH2CH3 + H2.
[6]
1
.3.1-Butanol. A series of the reactions b-4, a-4, and a-5
(
Table3)originatesfromthealdoladditionofacetaldehyde.
Acetaldol, 2-butenal, and butanal should have formed as
intermediates of 1-butanol. 2-Butenal and butanal are ob-
served in the reaction of acetaldehyde (Table 2), whereas
they were barely detected in the ethanol reaction. They
would be rapidly hydrogenated on the catalyst forming bu-
tanal and 1-butanol, respectively. Takezawa and Iwasa (16)
2
. Optimum Conditions in Pressured Reaction
We explained that the reaction pressure greatly affected
and Elliot and Pennella (17) support the mechanism. On product selectivity. The initial reaction of ethanol dehydro-
the other hand, Iwasa and Takezawa also described that genation is preferred by low pressure (b-1 in Table 3B).
butanal did not form on KOH-treated Cu/Al2O3 (18). It is Nevertheless, the effective production of ethyl acetate oc-
also reported that hardly any butanal and 1-butanol formed curs under high pressure. The high-pressure operation has
over pure Cu (18, 19). Therefore, the aldol addition proba- two effects on the reaction: (1) the effect on the equilib-
bly occurs either on an acid site or on acid–base concerted rium of the dehydrogenation of ethanol, where the product,
sites formed on the metal–oxide support.
acetaldehyde, forms in the reaction preferred by low pres-
Since both the dehydrogenation of alcohols and the re- sure, and (2) the effect of prolonging contact time at high
verse hydrogenation of carbonyl compounds are rapid in pressure. In the formation of ethyl acetate from ethanol,
the total reactions, the irreversible dehydration of alco- the stepwise reaction requires a prolonged contact time,
hols determines the by-products’ distribution. In Table 2, whereas much longer contact times cause by-products to
the product distributions, with the exception of ethyl ac- form (Fig. 5). When acetaldehyde has a high partial pres-
etate, are roughly the same as in the reactions of 1,3- sure in the reactor, an acetaldehyde molecule reacts with
butanediol, ethanol, ethanol and acetaldehyde, and ac- another acetaldehyde molecule to form acetaldol through
etaldehyde and H2. 1,3-Butanediol is an intermediate of aldol addition. Therefore, by-products other than ethyl ac-
1
-butanol, as shown in Scheme 1.
etate hardly form at high pressure.
An optimum W/F is about 0.5 h in a practical operation
at 1.0 MPa because of the relatively high STY of ethyl ac-
etate together with the highest selectivity to ethyl acetate
and tolerably low selectivity to butanone. Thus, Figs. 3 and
1
.4.2-Pentanone. It is very probable that 2-pentanone
forms through aldol condensation of acetaldehyde and
propanone followed by dehydration and hydrogenation.
These are speculations, because no intermediate was de-
tected in the present work. The formation route of
4
indicate the most suitable operating conditions for the
effective production of ethyl acetate.
2
-pantanone consists of the elementary reactions a-11, a-12,
and b-12 (Table 3).
.5. Ethyl butyrate and butyl acetate. Butanal and
-butanol can be other sources of esters. Ethyl butyrate and
CONCLUSIONS
1
1
The dehydrogenative dimerization of ethanol over a Cu–
butyl acetate form through a mechanism similar to route 2 Zn–Zr–Al–O catalyst was investigated under pressure.
for the formation of ethyl acetate by means of hemiacetal The product distribution is greatly affected by the reaction

SYNTHESIS OF ETHYL ACETATE UNDER PRESSURE
215
pressure. The high-pressure operation suppresses both
ethanol conversion and the formation of by-products
derived from acetaldol. A selectivity to ethyl acetate
of 92.6 wt%, which corresponds to 96 mol% based on
ethanol, is achieved over the catalyst at 493 K, 1.0 MPa,
7. Sato, T., and Hagiwara, T., Tokuyama Sekiyu Kagaku, K. K.,
JP 11140017 (1999).
8
. Gregory, R., Smith, D. J. H., and Westlake, D. J., Clay Miner. 18, 431
1983).
(
9. Sano, K., Nishiyama, M., Suzuki, T., Wakabayashi, S., and
Miyahara, K., Showa Denko, K. K., EP 0562139 (1993).
and W/F = 0.53 h, while the STY of ethyl acetate exceeds 10. Atkins, M. P., and Sharma, B., BP Chemicals, EP 0757027 (1997).
−
1
−1
8
mol h kg
.
11. Deschamps, J., Compt. Rend. 1285 (1953).
cat
1
2. Kunugi, T., Matsuura, T., and Kono, T., Kagaku Kougyozasshi
Japanese) 71, 1517 (1968).
3. Nakamura, S., and Kawamoto, K., Bull. Chem. Soc. Jpn. 44, 1072
1971).
Ethyl acetate probably formed stepwise from ethanol.
Initially ethanol was dehydrogenated to acetaldehyde, fol-
lowed by nucleophilic addition of ethanol to acetaldehyde
(
1
(
to form a hemiacetal, and finally the hemiacetal was dehy- 14. Kawamoto, K., and Nishimura, Y., Bull. Chem. Soc. Jpn. 44, 819
drogenated to ethyl acetate. Most of the by-products form
via the acetaldol, which is formed from two molecules of ac-
etaldehyde through aldol addition. A long residence time
and high concentration of acetaldehyde in the reactor lead
to the formation of acetaldol, resulting in a decrease in ethyl
acetate selectivity.
(1971).
1
5. Takeshita, K., Nakamura, S., and Kawamoto, K., Bull. Chem. Soc. Jpn.
51, 2622 (1978).
1
1
1
6. Takezawa, N., and Iwasa, N., Shokubai (Japanese) 30, 148 (1988).
7. Elliot, D. J., and Pennella, F., J. Catal. 119, 359 (1989).
8. Iwasa, N., and Takezawa, N., Bull. Chem. Soc. Jpn. 64, 2619
(1991).
1
9. Takeshita, K., J. Sci. Hiroshima Univ. A 54, 99 (1990).
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