Effect of phosphorus-oxygen compounds on structural, acidic, and catalytic properties of γ-alumina in the acetic acid ammonolysis reaction

Article abstract of DOI:10.1134/S0965544114050041

The effect of a promoter on the acidic and catalytic properties of aluminum oxide in the reaction of acetic acid ammonolysis has been studied. It has been shown that the promotion of γ-Al₂O₃ with phosphorus-oxygen compounds results in a change in the porous structure, an increase in the concentration of acid sites, and site strength redistribution, thereby enhancing the activity and selectivity of the catalyst. The change in the acid properties of γ-Al₂O₃ surface has a significant effect on the second stage of the process, the dehydration of acetamide.

Full text of DOI:10.1134/S0965544114050041

ISSN 0965ꢀ5441, Petroleum Chemistry, 2014, Vol. 54, No. 5, pp. 387–391. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © S.I. Galanov, O.I. Sidorova, 2014, published in Neftekhimiya, 2014, Vol. 54, No. 5, pp. 394–398.
Effect of Phosphorus–Oxygen Compounds on Structural, Acidic,
and Catalytic Properties of ꢀAlumina in the Acetic Acid
γ
Ammonolysis Reaction
S. I. Galanov and O. I. Sidorova
Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia
eꢀmail: galanov@xf.tsu.ru
Received April 9, 2014
Abstract—The effect of a promoter on the acidic and catalytic properties of aluminum oxide in the reaction
of acetic acid ammonolysis has been studied. It has been shown that the promotion of ꢀAl2O3 with phosphoꢀ
γ
rus–oxygen compounds results in a change in the porous structure, an increase in the concentration of acid
sites, and site strength redistribution, thereby enhancing the activity and selectivity of the catalyst. The
change in the acid properties of ꢀAl2O3 surface has a significant effect on the second stage of the process, the
dehydration of acetamide.
γ
Keywords: acetic acid ammonolysis, acetonitrile, phosphorus–oxygen compounds, acetamide
DOI: 10.1134/S0965544114050041
Acetonitrile is an important intermediate in
organic, pharmaceutical, and petrochemical syntheꢀ
ses [1]. It is also widely used as a solvent and a compoꢀ
nent in extractive and azeotropic distillation of hydroꢀ
carbons in petrochemical processes [2] and as a
mobile phase in highꢀperformance liquid chromatogꢀ
raphy [3]. Today, acetonitrile is mainly produced as a
byproduct in the ammonolysis of propylene to acryꢀ
lonitrile [4], but acetonitrile obtained in this process
contains hydrocyanic acid as an impurity, which
demands additional and rather significant costs for its
purification and use in subsequent target transformaꢀ
tions. The processes under development for manufacꢀ
turing of acetonitrile by ammonolysis of paraffins [5]
and olefins [6] are also characterized by the formation
of hydrocyanic acid as a byproduct in addition to a low
yield of the desired product. However, in the case of
acetonitrile production by ammonolysis of acetic acid
[7, 8] or alcohols [9, 10], it is possible to avoid the forꢀ
mation of hydrogen cyanide and, hence, make these
processes promising in terms of reduced operating
The aim of this work was to reveal the effect of the
amount of the added promoter (oxygen compounds of
phosphorus) on the structural, acidic, and catalytic
properties of ꢀAl2O3 in the reactions of acetic acid
γ
ammonolysis and dehydration of the intermediate
product acetamide.
EXPERIMENTAL
The experiments were performed in a flow steel
(12Ch18N10T grade) riser reactor with preheating the
reaction mixture to the reaction temperature [11], the
acetic acid and acetamide feed space velocity of
1.05 h–1 at molar ratios of NH3 : CH3COOH = 2 : 1
and NH3 : CH3CONH2 = 1 : 1.
The starting
with phosphoric acid to have 2 or 4 wt% on a Р2О5
basis and then calcined for 4 h in an air stream at
400 and for 5 h in a nitrogen stream at = 500
γꢀAl2O3 (Aꢀ64 grade) was promoted
Т
°С.
=
°С
Т
The products were analyzed on a ChromatecꢀKriꢀ
stall 5000.1 chromatograph with two thermal conducꢀ
costs for the separation and purification of the final tivity detectors. Conditions of the analysis: helium
carrier gas; flow rate, 0.0012 m3/h; column temperaꢀ
product acetonitrile. In the studies on the ammonolyꢀ
ture, 180°С; a column 2 m in length with Separon
sis of oxygenꢀcontaining compounds [7–10], alumina
SDA sorbent for detecting ammonia, hydrocyanic
acid, water, acetonitrile, acetone, ammonium acetate,
and acetamide; a 3 m long column packed with Carꢀ
bosieve SꢀII for detecting ammonia, carbon monoxꢀ
ide, and carbon dioxide. Thermal studies of the
cocked catalysts were conducted using a Netzsch
STAꢀ449 synchronous TG–DTA/DSC thermal anaꢀ
lyzer (Germany); temperature rise rate, 10°C/min in
promoted with phosphoric acid [7] or modified with
Co, Ni [9], or Cu [10] metals, or
S
O24– /ZrO2 [8] is
used as the base catalyst. The alumina modification
reported in [7–10] was performed in order to reduce
the reaction temperature, enhance the yield of the
desired product, and increase the catalyst onꢀstream
time.
387

388
GALANOV, SIDOROVA
Table 1. Effect of
γ
space velocity of 1.05 h–1. Freshly prepared catalysts, nos. 1–3; catalysts after 120 h of operation, nos. 4–6
ꢀAl2O3 promotion on the porosity parameters and catalytic properties at
T
= 360°C and an acetic acid
Ssp
,
Pore size,
Å
Micropore volume
3.3–5.4 Å, cm3/g
Pore volume
Yield
of acetonitrile, %
No.
Sample
CP, wt %
17–3000 Å, cm3/g
m2/g
1
2
3
4
5
6
γ
ꢀAl2O3
2% P2O5
4% P2O5/
ꢀAl2O3
171
150
129
156
137
120
0.660
0.629
0.573
0.614
0.587
0.569
130–113
145–119
160–124
120–109
148–121
173–128
0.0051
0.0090
0.0122
–
–
–
73.3
95.6
98.5
56.5
92.1
96.3
/
γ
ꢀAl2O3
ꢀAl2O3
γ
–
γ
5.04
2.52
2.14
2% P2O5/
4% P2O5/
γ
ꢀAl2O3
ꢀAl2O3
0.0092
0.0125
γ
an air stream. The parameters of the porous structure modifying the starting γꢀAl2O3; at the same time, the
and the specific surface area of the samples were deterꢀ micropore volume increases with an increase in the
mined carried out on a Micromeritics TriStar II 3020 amount of Р2О5 in comparison with the initial alumina
porosity analyzer (USA). An ammonia temperatureꢀ sample. After 120 h onꢀstream at
Т = 360°С for all
programmed desorption (TPD) study was performed samples of the catalysts the formation of condensation
on a Micromeritics ChemiSorb 2750 instrument products (CP) was observed: the maximum amount
(USA) at an ammonia adsorption temperature of for unpromoted
γꢀAl2O3 and an amount smaller by a
100 and a heating rate of 10°C/min. The acidic factor of 2 or 2.4 for the sample promoted with 2 or 4%
°
С
properties of the surface of catalyst samples were Р2О5, respectively. For all of the cocked samples, a
determined using titration in a nonaqueous medium decrease in the specific surface area and pore volume
with an indicator [12]. The amount of acid sites was is observed as compared with the freshly prepared
found by titration with a benzylamine solution (C = samples (Table 1): micropores are completely plugged
0.01 N) of a suspension in dry dimethylformamide of with condensation products in the case of unpromoted
the powdered catalyst with a preꢀadsorbed indicator. 4%Р2О5/
The quantity of benzylamine spent for titration correꢀ promoted samples. According to the data in Table 1,
sponds to the number of acid sites ( mol/g) with an the yield of acetonitrile in the case of the freshly preꢀ
acid strength greater than or equal to the Ка of the pared samples is higher for the promoted catalysts and
indicator used. For adsorption, the following indicaꢀ the yield of the desired product varies slightly after
tors were used: methyl red (р а = 4.8), ꢀdimethylamiꢀ 120 h onꢀstream for the 2% and 4% Р2О5/ ꢀAl2O3 sysꢀ
noazobenzene (р а=3.3), ꢀaminoꢀ5ꢀazotoluene tems, unlike the case of unpromoted alumina.
Ка = 2.0), brilliant green (
violet ( Ка = 0.8).
γꢀAl2O3 and remain intact in the case of the
µ
р
К
p
γ
К
2
(
р
рКа = 1.3), and crystal
According to Fig. 1, ammonia desorption from the
surface of all the catalysts is characterized by one peak
р
with
Тmax = 220°С and close activation energies of
desorption, 49.1–50.2 kJ/mol. The areas of the
ammonia TPD peaks increase after the promotion of
ꢀAl2O3 with phosphoric acid, thereby indicating an
increase in the concentration of acid sites on the surꢀ
face of the promoted alumina (Fig. 1, Table 2). It is
impossible to differentiate surface acid sites by their
strength from the ammonia TPD spectra.
RESULTS AND DISCUSSION
The reaction of acetonitrile synthesis from acetic
acid and ammonia is an equilibrium twoꢀstage proꢀ
cesses involving the formation of acetamide as an
intermediate product [7, 13]:
γ
1. NH3 + CH3COOH
⇔
CH3CONH2 + H2O,
,
ΔH = –2.18 kJ/mol
According to the indicator titration data (Table 2),
the promotion of ꢀAl2O3 with phosphoric acid in
γ
2. CH3CONH2
⇔
CH3CN + H2O,
addition to increasing the total concentration of acid
sites alters the acid strength distribution of the sites;
i.e., the concentration of strong acid sites with the
Hammett acidity function of Нo < 2.0 decreases and
ΔH = 84.37 kJ/mol.
The intermediate formation reaction is slightly
exothermic; the equilibrium constant Kp is greater
than 1 in the temperature range of 250–450°С. Acetaꢀ
mide dehydration reaction (2) is endothermic, the
equilibrium constant becomes higher than 1 at a temꢀ
that of acid sites of a medium strength with 3.3
≥
Но >
2.0 significantly increases. Phosphoric acid in alumina
modified with phosphorus compounds is adsorbed on
lowꢀcoordinationꢀnumber aluminum ions (Lewis acid
perature above 320
°С.
The promotion of
γ
ꢀAl2O3 with 2 or 4 wt % phosꢀ sites) to form Brönsted acid sites. In this case, polyꢀ
phoric acid (in terms of Р2О5) results in a decrease in phosphate structures are likely to be formed on the
the specific surface area and pore volume of the cataꢀ surface of the contact catalysts during the calcination
lyst (Table 1). The average pore size is also increased by of the promoted samples [14]. The concentration of
PETROLEUM CHEMISTRY Vol. 54
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EFFECT OF PHOSPHORUS–OXYGEN COMPOUNDS
389
3
2
1
100
200
300
400
500
600 T, °C
Fig. 1. Spectra of ammonia thermalꢀprogrammed desorption from the surface of the catalysts (
1)
γ
ꢀAl O , (
2
) 2% P O / ꢀAl O .
γ
2
3
2
5 2 3
and ( ) 4% P O / ꢀAl O .
3
γ
2
5
2 3
acid sites measured by the indicator method is underꢀ were not detected by indicator titration, probably,
estimated in comparison with the ammonia temperaꢀ
tureꢀprogrammed desorption data (Table 2). This difꢀ
ference is due to the fact that the large size of indicator
molecules as compared with ammonia hinders their
adsorption in alumina pores, whose size is equal to or
smaller than that the indicator molecule. A decrease in
the concentration of strong acid sites on the catalyst
surface with the addition of Р2О5, which sites presumꢀ
ably mediate the decomposition and decarboxylation
of adsorbed acetic acid, leads to a decrease in the
amount of CP during acetic acid ammonolysis
(Table 1). Thus, along with changes in the structural
characteristics of the surface, catalyst operation for
120 h leads to a decrease in the concentration of acid
sites; a significant decrease in the concentration of
acid sites, especially strong sites, is observed for
because of their blocking with CP (Table 2). At the
same time, an increase in the concentration of
mediumꢀstrength acid sites for the freshly prepared
catalysts significantly increases the acetic acid converꢀ
sion accompanied by enhancement of the selectivity
for acetonitrile, especially, at low temperatures of
350–360
with unpromoted
Р2О5/ ꢀAl2O3 catalyst, the concentration of medium
°С
for 2%Р2О5/γꢀAl2O3 as compared
γꢀAl2O3 (Fig. 2). For the 4%
γ
strength acid sites increases (Table 2), thereby slightly
improving the conversion of СН3СООН compared
with the 2% Р2О5/
for acetonitrile is higher than 90% at low temperaꢀ
tures, 350–360 , in this case (Fig. 2).
γꢀAl2O3 system, but the selectivity
°С
These findings suggest that the Brönsted acid sites
of medium strength are responsible for the occurrence
of reaction (2), the dehydration of acetamide to acetoꢀ
nitrile (scheme). Thus, when acetamide and ammonia
are used as a feedstock under conditions identical to
ammonolysis of acetic acid, along with the desired
acetamide dehydration reaction, reverse reaction (1)
unpromoted ꢀAl2O3 (Table 2; no. 1, 4). In the case of
γ
the promoted catalysts (Table 2), a decrease in the
concentration of acid sites with the Hammett acidity
function of 4.8
concentration of sites with the acidity of 2.0
decreases noticeably. For all the catalysts after operaꢀ
tion in the reaction mixture, acid sites with 1.3
≥
Но > 2.0 is insignificant, whereas the
≥
Но > 1.3
≥
Но (see Scheme) of the hydrolysis of acetamide produced
Table 2. Concentration of acid sites per gram of the catalyst according to NH3 TPD and indicator adsorption data. Acid
strength distribution of the sites, according to adsorption of indicators. H0 is the Hammett acidity function. Freshly preꢀ
pared catalysts: nos. 1–3; catalysts after 120 h of operation: nos. 4–6
Acid sites concentration
benzylamine,
μmol
No.
Catalyst
μ
mol
total
quantity
NH3
2
4.8
≥
H0 > 3.3 3.3
≥
H0 > .0 2.0
≥
H0 > 1.3 1.3
≥
H0 > 0.8 0.8 ≥ H0
1
2
3
4
5
6
γ
ꢀAl2O3
220.6
ꢀAl2O3 305.9
ꢀAl2O3 355.7
122.9
81.0
88.5
60.1
51.0
86.2
59.2
12.7
53.1
99.7
6.5
57.2
22.2
16.0
27.5
12.4
6.1
0.7
0.5
0.2
–
4.5
3.0
–
155.9
167.3
176.0
85.0
2% P2O5/
γ
γ
4% P2O5/
γꢀAl2O3
–
2% P2O5/
γ
ꢀAl2O3 272.5
ꢀAl2O3 327.6
49.6
93.8
–
–
148.2
159.1
4% P2O5/
γ
–
–
PETROLEUM CHEMISTRY Vol. 54
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390
GALANOV, SIDOROVA
S, %
K, %
100
90
80
70
60
50
3
5
100
90
6
4
2
1
80
70
65
350
360
370
380
T, °C
Fig. 2. Dependence of the selectivity for acetonitrile (solid lines) and the acetic acid conversion (dashed lines) from the reactor
temperature over the ( ꢀAl O , ( ) 2% P O / ꢀAl O and ( ) 4% P O / ꢀAl O catalysts.
1)
γ
2
γ
3
γ
2
3
2
5
2
3
2
5
2 3
in reaction (2) proceeds on unpromoted
γꢀAl2O3 at specific surface area and the volume of mesoꢀ and
Т
= 360 to give ammonium acetate (Table 3).
°С
macropores of the catalyst; at the same time, the proꢀ
motion contributes to an increase in the micropore
volume. The addition of phosphorus–oxygen comꢀ
An increase in the reactor temperature to 380°С, in
accordance with the thermodynamic equilibrium
[13], facilitates the conversion of acetamide and
reduces the selectivity for ammonium acetate.
Increasing the concentration of Brönsted acid sites in
pounds to ꢀAl2O3 can decrease the concentration of
γ
strong acid surface sites, at which the irreversible
adsorption of acetic acid take place followed by its
decomposition and formation of byproducts, mainly
СО2 and acetone (decarboxylation reaction), as well as
condensation products, which lower the catalyst activꢀ
ity and shorten the onꢀstream time. At the same time,
the case of the 2%Р2О5/ ꢀAl2O3 catalyst leads to a sigꢀ
γ
nificant increase in the conversion of СН3СОNH2
and significantly reduces the rate of the reverse reacꢀ
tion of acetamide hydrolysis to ammonium acetate.
For the 4%Р2О5/ ꢀAl2O3 sample, an increase in the
γ
the promotion of ꢀAl2O3 with phosphoric acid lead to
γ
concentration of Brönsted acid sites on the catalyst
surface makes it possible to achieve 100% conversion
of acetamide with the complete inhibition of the
hydrolysis reaction to have the 100% selectivity for
acetonitrile (Table 3).
an increase in the concentration of mediumꢀstrength
Brönsted acid sites, which mediate the dehydration
reaction of the intermediate acetamide to acetonitrile,
thereby significantly enhancing the conversion of aceꢀ
tic acid and the yield of the desired product acetoniꢀ
The foregoing suggests that the promotion of
γꢀAl2O3 with phosphoric acid leads to a decrease in the trile in the ammonolysis reaction.
Table 3. Effect of temperature and amount of the promoter on the acetamide dehydration reaction (reaction mixture, acꢀ
etamide : ammonia = 1 : 1 molar ratio; acetamide space velocity, 1.05 h–1
)
Selectivity
for ammonium
acetate, %
Selectivity
for acetonitrile, %
Yield
of acetonitrile, %
Catalyst
ꢀAl2O3
T
, °C
K, %
γ
360
380
360
380
360
380
92.0
98.0
98.3
99.4
99.9
100
97.4
99.5
99.5
99.4
100
2.5
0.5
0.5
0.2
–
89.6
97.6
97.7
98.8
99.9
100
2% P2O5/
γ
ꢀAl2O3
ꢀAl2O3
4% P2O5/
γ
100
–
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EFFECT OF PHOSPHORUS–OXYGEN COMPOUNDS
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8. Hou XueꢀMei, Yan Li, Zhang Xin, et al., Jilin Norm.
Univ. J. (Nat. Sci. Ed.) 30, 108 (2009).
9. Cheng Feng, Yuecheng Zhang, Yining Zhang, et al.,
Catal. Lett. 141, 168 (2011).
10. Y. Hu, J. Cao, J. Deng, et al., React. Kinet. Mechaꢀ
REFERENCES
1. S. Lida and H. Togo, Tetrahedron 63 (34), 8274 (2007).
2. O. S. Pavlov, S. A. Karsakov, and S. Yu. Pavlov, Theor.
Found. Chem. Eng. 45, 858 (2011).
nisms Catal. 106, 127 (2012).
11. S. I. Galanov, O. I. Sidorova, A. K. Golovko, et al.,
Eurasian ChemTech J., No. 3, 173 (2001).
3. H. Henke, FlussigꢀChromatographie: analytische und
praparative Trennungen (Vogel, Wurzburg, 1999).
4. A. Andersson, S. L. T. Andersson, G. Centi, et al., Stud.
12. K. Tanabe, Catalysts and Catalytic Processes (Mir, Mosꢀ
Surf. Sci. Catal. 75, 691 (1993).
cow, 1993) [in Russian].
13. S. I. Galanov, O. I. Sidorova, L. N. Kurina, and
A. K. Golovko, Catal. Ind., No. 1, 27 (2004).
5. S. S. Shepelev and K. G. Ione, USSR Inventor’s Cerꢀ
tificate No. 1321722, Byull. Izobret., No. 25 (1987).
6. J. E. Mahan, US Patent No. 2 535082, 1950.
14. S. N. Vereshchagin, N. N. Shishkina, and
A. G. Anshits, Catal. Today 13, 651 (1992).
7. S. I. Galanov, L. N. Kurina, O. I. Sidorova, and
A. K. Golovko, Pet. Chem. 43, 283 (2003).
Translated by V. Makhaev
PETROLEUM CHEMISTRY Vol. 54
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