Synthesis of Isobutylene from Ethanol in the Presence of Catalysts Containing Zinc Oxide and Zirconia

Article abstract of DOI:10.1134/S0965544118120113

Abstract: Synthesis of isobutylene from ethanol in the presence of ZnO/ZrO₂ catalysts has been studied. The samples have been synthesized by incipient wetness impregnation of zirconium hydroxide derived from zirconyl chloride with zinc nitrate and subsequent calcination at 550°C. The synthesized samples have been studied by low-temperature nitrogen adsorption, SEM, XRD, IR spectroscopy of adsorbed CO, and TGA–DTA. Studies of the effect of the catalyst composition and the test conditions have revealed that, during the synthesis of isobutylene from ethanol, an optimum Zr : Zn molar ratio providing the production of isobutylene with a selectivity of 45–50% is 8–20 and optimum conditions for ethanol conversion to isobutylene are 500°C, a feed space velocity of 3 g/(g h), and a feedstock in the form of a 50% ethanol solution in water. According to thermogravimetric analysis, an increase in the zinc content in the samples leads to a decrease in the amount of coke deposits.

Full text of DOI:10.1134/S0965544118120113

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 12, pp. 1023–1031. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © O.A. Ponomareva, P.A. Shaposhnik, P.A. Kots, S.V. Konnov, B.A. Kolozhvari, I.I. Ivanova, 2018, published in Neftekhimiya, 2018, Vol. 58, No. 6,
pp. 677–685.
Synthesis of Isobutylene from Ethanol in the Presence of Catalysts
Containing Zinc Oxide and Zirconia
a, b,
b
b
a
O. A. Ponomareva *, P. A. Shaposhnik , P. A. Kots , S. V. Konnov ,
a, b
a, b
B. A. Kolozhvari , and I. I. Ivanova
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
a
b
Faculty of Chemistry, Moscow State University, Moscow, Russia
*
e-mail: oaponomareva@phys.chem.msu.ru
Received June 15, 2018
Abstract⎯ Synthesis of isobutylene from ethanol in the presence of ZnO/ZrO catalysts has been studied. The
2
samples have been synthesized by incipient wetness impregnation of zirconium hydroxide derived from zir-
conyl chloride with zinc nitrate and subsequent calcination at 550°C. The synthesized samples have been
studied by low-temperature nitrogen adsorption, SEM, XRD, IR spectroscopy of adsorbed CO, and TGA–
DTA. Studies of the effect of the catalyst composition and the test conditions have revealed that, during the
synthesis of isobutylene from ethanol, an optimum Zr : Zn molar ratio providing the production of isobuty-
lene with a selectivity of 45–50% is 8–20 and optimum conditions for ethanol conversion to isobutylene are
5
00°C, a feed space velocity of 3 g/(g h), and a feedstock in the form of a 50% ethanol solution in water.
According to thermogravimetric analysis, an increase in the zinc content in the samples leads to a decrease
in the amount of coke deposits.
Keywords: ethanol, isobutylene, zinc oxide, zirconia, incipient wetness impregnation
DOI: 10.1134/S0965544118120113
Bioethanol, which is one of the most readily avail- oligomerization, and coke formation [10]. Synthesis of
able renewable resources derived by plant matter fer- Zn Zr O by incipient wetness impregnation of zirco-
x
y
z
mentation, is a feedstock for synthesizing a wide range nium hydroxide with zinc salt solutions provides the
of products, such as ethylene [1–4], aromatic hydro- formation of catalysts characterized by the presence
carbons [2], propylene [1, 5–8], isobutylene [9–13], only of Lewis acid–base sites; this feature contributes
butadiene [14], butanol [3, 15], ethyl acetate [16, 17], to an increase in the stable on-stream time of the cat-
hydrogen [18], acetone [3, 17, 19, 20], acetaldehyde alysts [10]. Studies of the effect of the composition of
[
15, 17], and acetic acid [21]. One of the most promis- the zinc salts used to synthesize the catalyst showed
ing ethanol-based processes is the single-stage synthe- that an important role is played by the size of the zinc
sis of isobutylene [8–13]. Isobutylene, which is a feed- salt anion. The most active catalyst was obtained using
stock for large-scale processes aimed at the production zinc acetate [12]. The authors of that study attribute
of methyl methacrylate, polymers, and methyl tert- this finding to the fact that Zn Zr O synthesized by
x
y
z
butyl ether [22], is currently produced by oil refining.
Since the demand for isobutylene is constantly
increasing, while the oil reserves are being depleted,
an urgent problem is to develop alternative isobutylene
synthesis methods to decrease the dependence of the
production on fossil natural resources and hydrocar-
bon market fluctuations.
impregnation with zinc acetate is characterized by an
optimum balance of acid and base sites, a high degree
of dispersion of zinc, and a stronger interaction of the
metal oxide with the substrate. Recently, An et al. have
published data on the synergistic effect of chromium
additives to a Zn Zr O catalyst prepared by a tem-
x
y
z
plate-assisted technique in the synthesis of isobuty-
lene from ethanol [13].
Isobutylene has been first synthesized from ethanol
by Wang et al. in the presence of a Zn Zr O mixed
Despite the fact that the synthesis of Zn Zr O cat-
x y z
x
y
z
bifunctional oxide catalyst prepared by the hard tem- alysts by incipient wetness impregnation of zirconium
plate-assisted synthesis [9]. It was found that a key role hydroxide with zinc salts is simpler, more adaptable to
in the production of isobutylene is played by Lewis streamlined production, and cheaper, most of the
acid–base pairs, whereas the presence of Brønsted reports are focused on Zn Zr O prepared by hard
x y z
acid sites (BASs) contributes to the occurrence of side template-assisted synthesis [9–11, 13]. There are no
reactions, namely, isobutylene isomerization, butene published data on the effect of the composition of
1023

1024
PONOMAREVA et al.
–
1
Zn Zr O catalysts synthesized by incipient wetness with a resolution of 4 cm . A 20-mg catalyst sample
x
y
z
impregnation on the catalytic properties of these sam- was compressed into a disc with a diameter of 2 cm at
ples and no data on thermogravimetric and differential a pressure of 100 atm. Water was removed from the
thermal analysis (TGA–DTA) of the samples coked samples on a vacuum unit equipped with absolute
–4
during the synthesis of isobutylene from ethanol.
pressure sensors with a working vacuum of 5 × 10 Pa.
A pellet of the sample was placed in an IR cell, heated
to 450°C for 2 h, and held at 450°C for 1 h. Carbon
monoxide adsorption was conducted at the liquid
nitrogen temperature (77 K) by dosing the gas until
complete saturation. The recorded IR spectra
were processed using the OMNIC ESP software, ver-
sion 7.3.
The deactivated samples were studied by TGA–
DTA on a NETZSCHSTA 409 PC/PG instrument
combined with a mass spectrometer. Analysis was
conducted using 20–30 mg of the sample. The sample
was heated in a dry air stream (100 mL/min) from
room temperature to 800°C at a rate of 10°C/min.
This study is focused on ethanol conversion to
isobutylene in the presence of Zn Zr O catalysts that
x
y
z
are synthesized by incipient wetness impregnation of
zirconium hydroxide with a zinc nitrate solution and
contain different amounts of zinc oxide and zirconia;
the effect of reaction conditions on the process param-
eters is determined; the deactivated catalysts of differ-
ent compositions are studied by TGA–DTA.
EXPERIMENTAL
Catalysts based on zirconia modified with zinc
compounds were studied in the synthesis of isobuty-
lene from ethanol; the catalysts were prepared by
incipient wetness impregnation of zirconium hydrox-
ide derived from ZrOCl ⋅ 8H O by precipitation with
Catalytic tests were conducted in a flow reactor at
atmospheric pressure in a temperature range of 440–
5
00°C at space velocities of the feedstock (50% etha-
2
2
nol solution in water) of 1.3–14.5 g/(g h) in the pres-
ence of nitrogen (10 mL/min). The feedstock compo-
sition was varied by varying the ethanol content in
water from 20 to 80 wt %. Nitrogen and dioxane were
used as the internal standard for gases and liquid sam-
ples, respectively.
a 5 M NaOH solution to provide the Zn : Zr ratio in
the resulting catalyst of 1 : 2, 1 : 6, 1 : 8, 1 : 14, 1 : 20,
and 1 : 40 and subsequent calcination at 550°C. In
addition, for comparison, original ZrO was synthe-
2
sized by the calcination of zirconium hydroxide
derived from ZrOCl ⋅ 8H O by precipitation with a
2
2
Liquid and gaseous reaction products were ana-
lyzed on a Kristall 2000M gas–liquid chromatograph
equipped with a flame ionization detector using nitro-
gen as the carrier gas and a 30 m quartz capillary col-
umn coated with the SE-30 nonpolar liquid phase.
The amount of CO was determined on a Kristall
000M gas–liquid chromatograph equipped with a
5
M NaOH at 550°C for 6 h.
The chemical composition of the samples was
determined by X-ray fluorescence analysis on a
Thermo Scientific ARL Perform`X instrument
equipped with a 3.5-kW rhodium tube.
2
The surface morphology of the synthesized sam-
2
ples was studied by scanning electron microscopy
thermal conductivity detector using hydrogen as the
carrier gas and a 3 m packed column with the Porapak-
Q phase. Isobutylene and butadiene were separated on
a Kristall 5000.2 chromatograph equipped with a
flame ionization detector using hydrogen as the carrier
(
SEM) on
a
Hitachi Tabletop Microscope
TM3030Plus electron microscope. The voltage across
the accelerating electrode was 15 kV; the used magni-
fications were ×500 to 20000.
Characteristics of the pore structure of the catalysts gas and a 25 m quartz capillary column with the
were studied on a Micrometrics ASAP 2000 automatic KCl/Al O phase. Reaction products were identified
2
3
sorption meter.
on a Thermo Trace GC Ultra chromatograph com-
bined with a Thermo DSQ II mass spectrometer using
a 50 m quartz capillary column with the Ultra 1 non-
polar liquid phase.
X-ray diffraction patterns (XRD analysis) were
recorded at room temperature on a Bruker D2
PHASER powder diffractometer in the θ–θ geometry.
The generator mode was 30 kV and 10 mA; an X-ray
Catalyst activity was characterized according to
tube with a copper anode was used (CuK radiation, ethanol conversion and reaction product selectivity.
α1
λ = 1.5418 Å). Diffraction patterns were recorded Ethanol conversion, selectivities, and target product
while rotating samples in a horizontal plane in a yields were calculated using results of chromato-
2
θ angular range of 5°–50° in increments of 0.05°; the graphic analysis.
slit width at the outlet of the tube and in front of the
detector was 0.6 and 1.15 mm, respectively; the acqui-
sition time was 3 s per point. The diffraction patterns
Ethanol conversion (К) and ith product selectivity
were calculated by the following formulas:
were processed using the Bruker DIFFRAC.EVA soft- К = (mfed ethanol – munreacted ethanol) ×100 mfed ethanol , %
ware package. Phases were identified in accordance
with the ICDD PDF2 database.
S = 100 × (kQ M ) m , %
reacted ethanol
i
i
i
ri
Infrared spectra were recorded on a Nicolet Pro-
tege 460 Fourier transform IR spectrometer equipped
with an MCT detector in a range of 4000–400 cm–
Y = KS 100, %
i
i
1
Ywith respect to theor. = Y 100 ×Ytheor., %,
i
PETROLEUM CHEMISTRY
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SYNTHESIS OF ISOBUTYLENE FROM ETHANOL
Table 1. Physicochemical properties of the samples
1025
2
3
Sample
Zn : Zr ratio, mol/mol ZnO content, wt %
SBET, m /g
Vpore, cm /g
Dpore, Å
ZnO/2ZrO2
ZnO/6ZrO2
ZnO/8ZrO2
ZnO/14ZrO2
ZnO/20ZrO2
ZnO/40ZrO2
ZrO2
1 : 2
1 : 6
1 : 8
1 : 14
1 : 20
1 : 40
0
24.5
10.0
7.6
4.5
3.2
1.6
0
34
36
35
32
42
33
44
0.039
0.042
0.048
0.046
0.065
0.055
0.099
46
53
55
57
62
66
91
where S is the weight fraction of the ith product, M is
After calcination at 550°C, all the ZnО/ZrO sam-
i
ri
2
2
the molecular weight of the ith product, m
is
is
fed ethanol
ples have a low specific surface area of 30–40 m /g and
the weight of ethanol fed within 1 h, m
unreacted ethanol
a small pore volume; the pore diameter of ZnO/ZrO
2
the weight of unreacted ethanol, and k is a coefficient
i
is approximately the same at a level of about 50–60 Å,
whereas zirconia is characterized by an average pore
volume of 91 Å.
taking into account the number of ethanol molecules
required for the formation of the product. The yield of
the ith product was calculated as follows:
Scanning electron microscopy studies of the sam-
ples showed that their morphology does not depend
on the composition. A micrograph of the synthesized
Y = KS 100, %.
i
i
Isobutylene yield with respect to the theoretical ZnO/8ZrO sample is shown in Fig. 1. The samples
2
value was calculated as follows:
are agglomerates of irregularly shaped particles with a
broad size distribution.
Ywith respect to theor. = Y 100 ×Ytheor., %,
i
X-ray diffraction data for the ZnО/ZrO samples
2
of different compositions and ZrO are shown in
2
in accordance with their reaction equation
Fig. 2. Zirconia derived by the calcination of
3
С Н ОН + Н О = i-C H + 2CO + 6H .
ZrO(OH) at 550°C is a mixture of two—tetragonal
2
2
5
2
4
8
2
2
and monoclinic—phases (ICDD 50-1089, 37-1484).
After the modification of ZrO(OH) with zinc nitrate
2
RESULTS AND DISCUSSION
Physicochemical Properties of the Catalysts
and calcination at 550°C, the ZnO/40ZrO sample
2
still exhibits reflections corresponding to the mono-
clinic phase, although their intensity is significantly
The physicochemical properties of the samples and lower than that in ZrO ; with an increase in the zinc
2
their designations are shown in Table 1.
content, reflections corresponding only to the tetrag-
300 μm
30 μm
Fig. 1. Scanning electron microscopy micrographs of ZnO/8ZrO at the different magnifications.
2
PETROLEUM CHEMISTRY Vol. 58 No. 12 2018

1026
PONOMAREVA et al.
Monoclinic phase
Tetragonal phase
1
2
3
4
5
0
10
20
30
40
θ, deg
50
60
70
80
2
Fig. 2. Diffraction patterns of (1) the ZrO , (2) ZnO/40ZrO , (3) ZnO/8ZrO , (4) ZnO/6ZrO , and (5) ZnO/2ZrO samples.
2
2
2
2
2
onal phase of zirconia were observed. This fact sug- shown in Fig. 3. The spectra exhibit absorption bands
–
1
gests that zinc oxide is in a highly dispersed state and
hinders the tetragonal to monoclinic phase transition
at 2204 cm , which correspond to CO adsorption on
2+
–1
Zn ; at 2154 cm , which correspond to CO adsorp-
tion on weak BASs; and at 2168 and 2180 cm , which
correspond to CO adsorption on weak and strong
Lewis acid sites (LASs), respectively. In addition,
Fig. 3 shows the amount of CO adsorbed on acid sites
of ZrO . These results are in agreement with the data
–1
2
of Zavodinskii [23], who showed that doping zirconia
with oxides of various metals facilitates the stabiliza-
tion of zirconia in the metastable phase state.
The nature and number of acid sites were studied of different strengths for ZrO
by IR spectroscopy of adsorbed CO. The data are of zinc oxide. It is evident that an increase in the zinc
with different amounts
2
1
.4
.2
.0
ZrO2
ZnO/20ZrO2
ZnO/14ZrO2
ZnO/8ZrO2
ZnO/6ZrO2
B···CO
L···CO
2168
2
154
1
2138
L···CO
Zn2+···CO 2180
1
2204
ZnO/8ZrO2
0.8
0.6
0.4
0.2
0
2250
2200
2150
см
2100
2050
–
1
2
204
2180
2168
2154
–1
Oscillation frequency of adsorbed CO, cm
Fig. 3. Data of IR spectroscopy of adsorbed CO and the amount of CO adsorbed on acid sites of different strengths.
PETROLEUM CHEMISTRY Vol. 58 No. 12
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SYNTHESIS OF ISOBUTYLENE FROM ETHANOL
1027
content has hardly any effect on the amount of CO Effect of Catalyst Composition on Catalytic Properties
adsorbed on zinc cations; this finding suggests that an
The synthesized samples were studied in ethanol
increase in the zinc oxide content leads to the particle conversion to isobutylene. The reaction equation is as
coarsening. An increase in the zinc content does not follows:
lead to an increase in the number of strong LASs
either, whereas the amount of adsorbed CO on weak
LASs and BASs decreases.
3
С Н ОН + Н О = i-C H + 2CO + 6H .
2 5 2 4 8 2 2
Ethanol conversion leads, in addition to the syn-
thesis of the main reaction product (isobutylene), to
the formation of byproducts, such as С –С hydrocar-
1
4
If we assume that strong LASs are located on the
crystal faces, while weak LASs and BASs are located
on the crystal planes, then the derived data indicate
that, upon modification, zinc oxide is located on the
crystal planes and thereby leads to a decrease in the
number of weak LASs and BASs in ZrO2.
bon gases, carbon dioxide, С –С aliphatic hydrocar-
5
6
bons, isopropanol, acetone, acetaldehyde, ethyl ace-
tate, butanal, butenal, butanone, acetic acid, penta-
none, pentenone, and mesityl oxide. The assumed
reaction scheme and possible routes of formation of
the observed products are shown in Scheme 1.
−H2O
2
−H O
OH
O
Ethanol
H2
Diethyl ether
Ethylene
−
+
O
O
Acetaldehyde
OH
+
O
−H2O
O
O
O
Crotonaldehyde
Aldol
O
+H2
+H2
Ethyl acetate
+
H2O
O
3-butene-1-olOH
O
Butanal
OH +Acetic acidOH
−H2
Ethanol
O
+
OH
OH
Butadiene
+
OH
OH
O
−
Isopropanol
Acetone
O
−H2O
+
O
−H2O
+
+
H2
Propylene
O
OH
O
Pentanone
Diacetone alcohol
O
CH + CO
4
2
OH
Acetic acid
Isobutylene
Scheme 1. Possible conversions of ethanol to isobutylene.
The catalytic conversion of ethanol to isobutylene acetic acid undergoes ketonization to form acetone,
occurs through the dehydrogenation of ethanol to which undergoes aldol condensation to diacetone
acetaldehyde with subsequent disproportionation by alcohol, which further forms the desired product
the Tishchenko reaction to ethyl acetate, which is fur- isobutylene and acetic acid. The side reactions, i.e.,
ther hydrolyzed to acetic acid and ethanol. After that, dehydration, hydrogenation, condensation, isomeri-
PETROLEUM CHEMISTRY Vol. 58 No. 12 2018

1028
PONOMAREVA et al.
zation, oligomerization, dehydrocyclization, etc., lead Therefore, the ZnO : 8ZrO sample was selected for
2
to the formation of a wide range of the observed prod- further studies of the effect of reaction conditions on
ucts.
the process parameters.
Table 2 shows results of catalytic tests on the syn-
Effect of reaction temperature. In the temperature
thesis of isobutylene from ethanol in the presence of range of 440–500°C, the ethanol conversion is 100%.
ZnO/ZrO samples of different compositions. In the An increase in temperature from 440 to 500°C at a feed
2
presence of ZrO , the main reaction products are eth- space velocity of 3.1 g/(g h) leads to an increase in the
2
selectivity from 0.8 to 4.0% for methane, from 5.8 to
ylene and propylene; the selectivity for these products
is 79 mol %. In this case, the selectivity for the target
product does not exceed 1.2%. This finding suggests
that these catalysts provide the occurrence of dehydra-
tion to form ethylene. Propylene can be formed via
various routes: either via the oligomerization of three
ethylene molecules and subsequent metathesis or via
the formation of acetone, which subsequently under-
goes hydrogenation to isopropanol, which is further
dehydrated to propylene. Another possible route of the
formation of propylene is the condensation of two
acetaldehyde molecules formed via the dehydrogena-
tion of ethanol to 3-ol-butanal, which is further con-
verted to butenal, which undergoes decomposition to
propylene and CO. All the Zn-containing catalysts are
active in the formation of isobutylene; with an increase
in the zinc oxide content in the samples from 1.6 to
1
2.0% for propylene, and from 7.4 to 43.9% for isobu-
tylene and to a decrease in the acetone selectivity from
6
1.6 to 12.2%. In this case, the selectivity for ethylene
and CO remained almost unchanged (Fig. 5).
2
Thus, at a temperature of 440°C, the main reaction
is the formation of acetone, whereas the contribution
of the isobutylene formation reaction is small. An
increase in temperature leads to an increase in the
contribution of the aldol condensation of acetone to
form diacetone alcohol, which further undergoes
decomposition to isobutylene, methane, and CO.
Thus, an increase in the reaction temperature contrib-
utes to an increase in the yield of the desired product,
i.e., isobutylene.
Effect of feed space velocity. Figure 5 shows data on
the dependence of the product selectivity on the feed
space velocity. An increase in the feed space velocity
2
4.5 wt %, the isobutylene selectivity passes through a
maximum. The introduction of small amounts of zinc
oxide leads to an abrupt decrease in the number of
weak LASs and BASs responsible for the occurrence
of reactions leading to the formation of ethylene and
propylene, the selectivity for which in the presence of
–1
from 1.3 to 3.1 h at 500°C does not lead to significant
changes in the distribution of products, whereas an
–1
increase in the space velocity to 14.5 h leads to a
marked increase in the acetone selectivity and a
decrease in the selectivity for isobutylene, propylene,
and methane; this fact suggests that isobutylene, pro-
pylene, and methane are formed owing to secondary
conversions of acetone, which is consistent with the
ZnO/20ZrO is 5 times lower than that in the case of
2
ZrO . Zinc oxide mediates the dehydrogenation of
2
ethanol to acetaldehyde, while the acid–base sites
provide the occurrence of the aldolization, ketoniza-
tion, and condensation reactions leading to the forma-
tion of the target product, i.e., isobutylene
conversion scheme. At all contact times, ZnO/8ZrO
2
exhibited a stable on-stream behavior throughout the
entire test.
(
Scheme 1). An increase in the zinc oxide content led
The highest isobutylene selectivity (43.9 mol %)
was observed at a feed space velocity of 3.1 g/(g h); in
this case, the isobutylene yield with respect to the the-
oretical value was 65.8%.
to the formation of a large amount of acetone, which
is apparently attributed to a decrease in the number
and strength of acid sites mediating the formation of
isobutylene from acetone. The optimum composition
providing an isobutylene selectivity of 44–48% is the
Effect of feedstock composition. Table 3 shows
ZnO : ZrO ratio in a range of 1 : 20 to 1 : 8; at these results of studying the effect of the feedstock composi-
2
tion on the parameters of ethanol conversion to isobu-
tylene in the presence of ZnO/8ZrO at 500°C,
ratios, the isobutylene yield with respect to the theo-
retical value is 73–66%. Comparison of acidic (Fig. 3)
2
and catalytic properties (Table 2) suggests that the for- 3.1 g/(g h), and VN2 = 10 mL/min.
mation of isobutylene occurs on strong LASs.
With an increase in the ethanol content in the feed-
All the ZnO/ZrO catalysts exhibited a stable on- stock, the acetone selectivity significantly decreases,
2
stream behavior throughout the entire test, except for because the formation of acetone involves water. In
ZnO/40ZrO , the activity of which decreased by 20% this case, the selectivity for ethylene, propylene, and
2
within 2.5 h of reaction.
pentenes increases; these products are apparently
formed owing to the isobutylene oligomerization reac-
tions followed by cracking to form propylene and
pentenes. Figure 6 shows dependences of the isobuty-
lene yield with respect to the theoretical value on the
reaction time for different feedstock compositions in
Effect of Reaction Conditions on the Process Parameters
Studies of the activity of the Zn–Zr-containing
oxide catalysts showed that samples with a ratio of
the presence of ZnO/8ZrO at 500°C, 3.1 g/(g h), and
ZnO : ZrO (Zn : Zr) = (1 : 8)–(1 : 20) are the most
2
2
selective in the synthesis of isobutylene from ethanol. V 2
= 10 mL/min. The catalyst exhibited a stable on-
N
PETROLEUM CHEMISTRY
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SYNTHESIS OF ISOBUTYLENE FROM ETHANOL
1029
Table 2. Ethanol conversion in the presence of ZnO/ZrO at 500°С, 3.1 g/(g h), a 50% ethanol solution, and V = 10 mL/min
2
N2
ZnO/
ZnO/
20ZrO2
ZnO/
14ZrO2
ZnO/
8ZrO2
ZnO/
6ZrO2
ZnO/
2ZrO2
Catalyst/Product
ZrO2
100.0
40ZrO2
Ethanol conversion, %
Selectivity for C, mol %
Methane
98.6
99.3
99.8
99.9
100.0
92.5
3.8
53.6
8.7
25.1
0.0
1.2
6.9
12.5
19.8
8.0
0.8
30.6
0.0
3.9
4.7
20.2
12.4
0.1
4.3
4.0
20.8
12.3
0.5
4.0
4.8
21.7
12.0
0.3
4.0
2.2
19.3
8.2
0.0
29.1
0.0
2.1
3.5
19.3
7.7
8.2
25.8
0.0
Ethylene
CO2
Propylene
Acetaldehyde
Isobutylene
С Н
48.7
0.0
45.2
0.0
43.9
0.0
0.1
4
8
Acetone
6.1
1.1
20.4
0.5
7.4
1.3
11.2
0.8
12.2
0.6
35.5
0.6
32.9
0.0
С Н + С Н
8
5
10
5
Other
0.0
0.1
0.0
0.1
0.1
0.1
0.4
Isobutylene yield with respect
to theoretical value, %
1.8
45.3
72.6
67.7
65.8
47.3
35.8
stream behavior if the feedstock was a 20 or 50% etha- isobutylene readily undergoes oligomerization, which
nol solution in water. At a high ethanol content in the leads to a rapid deactivation of the catalyst.
feedstock, the catalyst rapidly undergoes deactivation.
Thus, the best parameters in the synthesis of isobu-
This finding is apparently attributed to the fact that, in tylene from ethanol were achieved using a 50% etha-
the absence of dilution with water vapors, the resulting nol solution in water.
Methane
Ethylene
Acetone
CO2
Propylene
Other
Isobutylene
70
60
50
40
30
20
10
0
4
40
460
480
500
°C
Fig. 4. Temperature dependence of the ethanol conversion product selectivity in the presence of ZnO/8ZrO at 3.1 g/(g h), a 50%
2
ethanol solution, and VN2 = 10 mL/min. Ethanol conversion is 100%.
PETROLEUM CHEMISTRY Vol. 58 No. 12 2018

1030
PONOMAREVA et al.
Ethylene CO2
Acetone
Methane
Propylene
Other
60
50
40
30
20
Isobutylene
10
0
1.3
3.1
g/(g h)
14.5
Fig. 5. Dependence of the ethanol conversion product selectivity on the feed space velocity in the presence of ZnO/8ZrO at
2
500°C, a 50% ethanol solution, and VN2 = 10 mL/min. Ethanol conversion is 100%.
Analysis of Deactivated Samples
Table 4 shows data on the weight loss and the peak
The data suggest that, for all the deactivated sam-
ples, the peak temperature in the heat flow curves lies
in a temperature range of 300–412°C; the weight loss
by the samples in a temperature range of 200–650°C is
1.3–3.0 wt %. The highest weight loss of 3.0 wt % was
temperature in the heat flow curves according to
TGA–DTA for ZnO/ZrO samples of different com-
2
positions after a 3.5-h ethanol conversion reaction at
00°C, 3.1 g/(g h), and VN2 =10 mL/min.
observed for the ZnO/40ZrO sample. These results
2
5
are consistent with the catalytic test data indicating
Table 3. Ethanol conversion in the presence of ZnO/8ZrO at 500°C, 3.1 g/(g h), and V = 10 mL/min
2
N2
Product/feedstock composition
Ethanol conversion, %
20% ethanol solution
50% ethanol solution
99.9
80% ethanol solution
99.7
99.7
Selectivity for C, mol %
Methane
Ethylene
3.4
1.4
4.0
4.8
1.9
5.0
CO2
15.8
6.3
0.1
36.8
36.1
0.0
21.7
12.0
0.3
43.9
12.2
0.6
19.2
21.9
0.0
29.1
16.2
4.5
Propylene
Acetaldehyde
Isobutylene
Acetone
С Н + С Н
8
5
10
5
Other
0.0
0.1
2.2
Isobutylene yield with respect
to theoretical value, %
55.1
65.8
43.6
PETROLEUM CHEMISTRY
Vol. 58
No. 12
2018

SYNTHESIS OF ISOBUTYLENE FROM ETHANOL
ACKNOWLEDGMENTS
1031
8
6
4
2
0
0
0
0
0
5
0% ethanol solution
This work was performed under the state task to
Topchiev Institute of Petrochemical Synthesis, Rus-
sian Academy of Sciences.
2
0% ethanol solution
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Translated by M. Timoshinina
PETROLEUM CHEMISTRY Vol. 58 No. 12 2018