Effect of reaction medium on the composition of vanadium-titanium catalyst in oxidative ammonolysis of alkylpyridines

Article abstract of DOI:10.1023/A:1020712212790

The influence exerted by the concentration of alkylpyridines on the chemical composition of a vanadium-titanium catalyst under oxidative ammonolysis conditions was subjected to a comparative study.

Full text of DOI:10.1023/A:1020712212790

Russian Journal of Applied Chemistry, Vol. 75, No. 7, 2002, pp. 1104 1107. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 7,
2002, pp. 1121 1124.
Original Russian Text Copyright
2002 by Saurambaeva, Sembaev.
CATALYSIS
Effect of Reaction Medium on the Composition
of Vanadium Titanium Catalyst in Oxidative Ammonolysis
of Alkylpyridines
L. I. Saurambaeva and D. Kh. Sembaev
Bekturov Institute of Chemical Sciences, Almaty, Kazakhstan
Received July 25, 2001; in final form, January 2002
Abstract The influence exerted by the concentration of alkylpyridines on the chemical composition of
a vanadium titanium catalyst under oxidative ammonolysis conditions was subjected to a comparative study.
In the course of catalysis, a catalyst undergoes
transformations as a result of its interaction with reac-
tants. The steady-state composition of the catalyst,
which determines its activity and selectivity, is
formed under the influence of the reaction medium.
Under the conditions of oxidative ammonolysis, as
also in other reactions, the extent to which the medi-
um affects the catalyst depends on numerous factors,
among which the relative amounts of air (oxidizing
agent) and an organic compound are important. The
change in the composition of a catalyst and, in par-
ticular, of a vanadium oxide catalyst modified with
oxides of titanium(IV), tin(IV), and other metals is
due to reduction of vanadium(V) oxide. For example,
it has been shown [1 5] that vanadium(V) oxide in
a vanadium titanium catalyst is reduced under the
action of the reaction medium, with the result that
the ratio of V O to the VO TiO solid solution,
EXPERIMENTAL
The starting 2-methyl-5-ethylpyridine (MEP) and
-picoline of pure grade contained no less than 98%
main substance.
Experiments on oxidative ammonolysis of alkyl-
pyridines were performed on a flow-through installa-
tion with the reaction tube (length 130 mm, diameter
20 mm) made of quartz glass. The reaction products
were absorbed with water and analyzed chromato-
graphically with a flame-ionization detector on a col-
umn packed with 15% Carbowax 20M on Chromaton
N-AW (0.16 0.20 mm). The analytical procedure
with programmed heating from 100 to 180 C at a rate
1
of 10 deg min enabled determination of pyridine,
3-methylpyridine, 2-methyl-5-ethyl-, 2-methyl-5-
vinyl-, 3-cyano-, 2-cyano-5-ethyl-, and 2-cyano-5-
vinylpyridines. 2,5-Dicyanopyridine was determined
polarographically after its conversion to isocin-
chomeronic acid by base hydrolysis.
2
5
2
2
which determines the activity and selectivity of the
catalyst, also changes.
Carbon oxides were analyzed chromatographically
with a heat conductivity detector.
The extent to which the reaction medium affects
a catalyst depends on the degree of conversion of
an organic substance, which is determined by the
nature of this substance [6]. Therefore, in selecting
a catalyst and determining the optimal conditions
of the oxidative process, account should be taken
of the catalyst composition, which is formed in the
course of catalysis under the influence of the reaction
medium and ensures the stability of the catalyst opera-
tion [7].
The vanadium titanium catalysts were prepared
by mixing vanadium(V) and titanium(IV) oxides of
analytically pure grade with subsequent compaction of
the stock into pellets and calcination at 800 C in air
flow for 2 h.
X-ray phase analysis of the catalysts was carried
out on a DRON-0.5 diffractometer with CuK radia-
tion. The content of vanadium(V) oxide in the cata-
lysts was determined by IR spectroscopy [8]. Samples
for analysis were prepared as KBr pellets.
This study was aimed to reveal how the structure
of alkylpyridines affects the composition and, con-
sequently, catalytic properties of the vanadium titani-
um oxide catalyst.
The oxidative ammonolysis of MEP on a vana-
dium titanium oxide catalyst with the molar ratio
1070-4272/02/7507-1104$27.00 2002 MAIK Nauka/Interperiodica

EFFECT OF REACTION MEDIUM ON THE COMPOSITION
V O : TiO = 1 : 16 at MEP : O : NH : H O =
1105
2
5
2
2
3
2
A, %
c, rel. %
1 : 42 : 25 : 124, temperature of 380 C, contact time
of 0.83 s, and load of 15 g of MEP per 1 l of catalyst
1
1
per hour (henceforth, g l cat. h ) proceeded to give
virtually a single product of partial conversion, 3-cya-
nopyridine, in 70 mol % yield (Fig. 1, points a).
Under these conditions, the catalyst operated efficient-
ly and stably for a long time (1200 h). The content of
V O in the catalyst decreased, compared to that in
b
c
d
e
2
5
the initial catalyst, by 51.6 wt %. According to the
results of X-ray phase and IR analyses, the catalyst
had the form of an oxide system composed of V O
2
5
and a VO TiO solid solution.
2
2
1
1
Raising the load (MEP) to 27 g l cat. h caused
a minor decrease in the content of vanadium(V) oxide
in the catalyst (Fig. 1, point b, curve 6). This led to a
decrease in the selectivity of nicotinonitrile formation
to 58.6% (curve 4) and to the appearance in the cata-
lyst of nitriles of 5-ethyl- and 5-vinylpicolinic and
pyridine-2,5-dicarboxylic acids (Fig. 1, points b,
curves 1 3).
MEP, %
Fig. 1. Effect of conversion
on the selectivity A and
MEP
V O content c of the catalyst with V O : TiO = 1 : 16.
2
5
2
5
2
Raising the concentration of dialkylpyridine in the
reaction zone further caused an even more significant
decrease in the V O content and enrichment of
Temperature 380 C, contact time 0.83 s. MEP feed rate
1
1
(g l cat. h ): (a) 15, (b) 27, (c) 40, (d) 68, and (e) 92.
Product: (1) 2-cyano-5-ethylpyridine, (2) 2-cyano-5-vinyl-
pyridine, (3) 2,5-dicyanopyridine, (5) CO , and (6) V O .
2
5
the solid solution with the forming vanadium(IV)
oxide. As a result, the conversion of the starting com-
pound decreased and the selectivity of formation
of 5-ethyl- and 5-vinylpicolinonitriles and 2,5-di-
cyanopyridine increased to a total of 55% for MEP
2
2 5
of oxidative transformations changed fundamentally:
CN
1
1
+
CO2
C2H5
feed of 68 g l cat. h (Fig. 1, points d).
N
H3C
1
1
With a feed of 92 g l cat. h of MEP, the entire
amount of V O contained in the catalyst was re-
N
CH=CH2
,
2
5
duced. On a catalyst in the form of a V O TiO
2
5
2
H3C
C2H5
N
solid solution, the conversion of the pyridine base did
not exceed 68%, and the major reaction products were
nitriles of 5-ethyl- and 5-vinylpicolinic and pyridine-
2.5-dicarboxylic acids (Fig. 1, points e, curves 1 3).
The intensity of deep oxidation processes decreased
dramatically: the selectivity with respect to carbon
dioxide did not exceed 3%.
,
CH=CH2
,
NC
NC
N
N
.
NC
NC
N
On a catalyst rich in vanadium(V) oxide, oxidative
ammonolysis proceeded with oxidative elimination of
the methyl group of MEP, and 3-cyanopyridine was
the major reaction product. On a catalyst containing
a small amount of V O (with solid solution the rest),
The experimental data presented in Fig. 1 indicate
strong changes in the composition of the vanadium-
containing catalyst under the influence of the com-
position of the reaction medium. In the course of
vanadium(V) reduction, both the V O /(VO TiO )
ratio and the composition of the solid solution
changed. At high MEP concentration in the reaction
medium, the catalyst was a solid solution. To each
composition of the reaction mixture corresponded
a certain chemical composition of the catalyst, which
determined its activity and selectivity. As a result,
the conversion of MEP decreased and the direction
2
5
2
5
2
2
the yield of products with two carbon atoms retained
at the pyridine ring increased. These compounds were
the major products of the reaction occurring on a
catalyst containing minor amounts of V O and solid
2
5
solution.
The results obtained in studying the effect of opera-
tion time of a freshly prepared vanadium titanium
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002

1106
SAURAMBAEVA, SEMBAEV
tioned products changed only slightly. The main reac-
, %
A, %
tion products were 2-cyano-5-ethyl- and 2,5-dicyano-
pyridines. The yield of 3-cyanopyridine was not
higher than 7 mol %. The main direction of the oxida-
tive ammonolysis of MEP on a catalyst in the form of
a VO TiO solid solution is associated with conver-
2
2
sion of one or both alkyl groups into nitrile groups.
The share of oxidative elimination of alkyl substit-
uents is low on a catalyst of this kind, which is in-
dicated by the low selectivity of 3-cyanopyridine for-
mation and virtually total absence of CO in the
2
catalyzate.
A comparative study of the influence exerted by
the reaction medium with varied 3-methylpyridine
concentration on the composition of the vanadium
titanium oxide catalyst and on the yield of products
formed in oxidative ammonolysis was carried out.
The feed rate of the pyridine base was varied between
27.5 and 100 g l cat. h at constant molar ratio of
-picoline, oxygen, ammonia, and water, equal to
1 : 37 : 8 : 47. The reaction temperature was 380 C,
and the contact time, 0.47 s.
, h
Fig. 2. Effect of the operation time
of catalyst with
V O : TiO = 1 : 16 on the conversion of V O in the
1
1
2
5
2
2 5
catalyst and on the conversion of MEP and yield of prod-
ucts formed in oxidative ammonolysis of 2-methyl-5-ethyl-
pyridine, A. Feed rate: MEP 92, air 1980 l, ammonia 100 g,
and water 590 g l cat. h ; temperature 380 C; contact
time 0.27 s. (1) MEP conversion; yield of products:
(2) 2-methyl-5-vinylpyridine, (3) 2-cyano-5-ethylpyridine,
(4) 2-cyano-5-vinylpyridine, (5) 2,5-dicyanopyridine, and
(6) 3-cyanopyridine; (7) V O conversion.
1
1
The experimental results presented in the table
indicate that the reaction medium with widely varied
-picoline feed rate exerts no significant influence
on the chemical composition of the catalyst and
catalyzate. At a feed of the picoline base at a rate of
2
5
catalyst at high load (MEP) are presented in Fig. 2.
An analysis of the catalyzate after 10 h of operation
demonstrated that a minor decrease in the V O con-
tent of the catalyst changed the reaction direction.
In this case, 2-methyl-5-vinyl- and 2-cyano-5-ethyl-
pyridines, and also 2-cyano-5-vinyl- and 2,5-ethyl-
pyridines, whose total yield is as high as 70%, became
the major reaction products of oxidative ammonolysis
of MEP. 3-Cyanopyridine was obtained in a yield as
low as 18 mol %.
1
1
100 g l cat. h for 60 h, the amount of V O in
2
5
the catalyst decreased by 1 2% relative to the initial
content, with the conversion of -picoline decreasing
by only 0.2 0.3%, and the yield of 3-cyanopyridine
2
5
and CO , by 1.4 and 0.4%, respectively. Prolonged
2
operation of the catalyst (>200 h) under these condi-
tions did not lead to any new changes in the steady
state of the catalyst or in the catalyzate composition.
The data obtained are in agreement with the results
of previous experiments on o-xylene oxidation into
phthalic anhydride on the same catalyst at hydrocar-
In prolonged operation of the catalyst (>50 h)
under these conditions, the yield of the above-men-
1
1
bon load exceeding 100 g l cat. h [1].
Effect of 3-methylpyridine load on the yield of products
formed in oxidative ammonolysis on catalyst with
V2O5 : TiO2 = 1 : 16
The stronger influence of MEP on the chemical
composition of the vanadium titanium oxide catalyst,
compared with that of 3-methylpyridine and o-xylene
[1, 9], is due to the presence in the molecule of an
ethyl group subjected to dehydrogenation, which can
be judged from the composition of products formed
in oxidative ammonolysis (Figs. 1, 2). The appearance
of hydrogen in the catalytic system causes intensive
reduction of V O to VO , which becomes a com-
Yield, mol %
-Picoline load,
-Picoline
conversion
1
g l 1 cat. h
3-cyanopyridine CO2
27.5
49.9
60.0
82.0
100.0
98.0
97.8
97.7
97.8
97.7
95.0
94.2
94.8
93.8
93.6
3.0
3.0
2.8
2.7
2.6
2
5
2
ponent of the continuous series of substitutional VO
2
TiO solid solutions [1].
2
Thus, we found that the extent to which the reac-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002

EFFECT OF REACTION MEDIUM ON THE COMPOSITION
tion medium affects the composition of the vanadi-
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1107
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