Properties of mixed polyfunctional fluoride catalysts for synthesis of pyridine bases from acetylene and ammonia (methanol)

Article abstract of DOI:10.1023/A:1026332211453

New catalysts based on cadmium, zinc, chromium, iron, and aluminum compounds were synthesized and their properties were studied. A pilot catalyst batch was obtained and tested on a pilot installation.

Full text of DOI:10.1023/A:1026332211453

Russian Journal of Applied Chemistry, Vol. 76, No. 6, 2003, pp. 939 942. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 6, 2003,
pp. 969 972.
Original Russian Text Copyright
2003 by Khamidullaev, Yusupov.
CATALYSIS
Properties of Mixed Polyfunctional Fluoride Catalysts
for Synthesis of Pyridine Bases from Acetylene
and Ammonia (Methanol)
R. A. Khamidullaev and D. Yusupov
Tashkent Chemical Engineering Institute of Uzbekistan Republic, Tashkent, Uzbekistan
Received March 5, 2003
Abstract New catalysts based on cadmium, zinc, chromium, iron, and aluminum compounds were synthe-
sized and their properties were studied. A pilot catalyst batch was obtained and tested on a pilot installation.
Pyridine and its homologs are widely used in pro-
duction of chemicals and pharmaceuticals and in
agriculture [1, 2]. The interest in these compounds
increased after the appearance of pesticides of selec-
tive and total action such as Reglon, Fusilad, Parskvat,
Lontrel, etc. [3].
mium, iron, and aluminum form hydroxofluorides
Cd(OH)F, Zn(OH)F, Al(OH)2F, Al(OH)F2, etc.,
which are, probably, responsible for the high catalytic
activity of the catalysts [12, 13].
The zinc and cadmium ions favor activation of
acetylene and ammonia molecules, and the basic cen-
ters on the catalyst surface (O , F , OH ) favor forma-
tion of amide groups from ammonia and amines:
Among the known methods for preparing pyridine
bases, their synthesis from acetylene and ammonia
(methanol) is the most promising [4 7]. Wide in-
dustrial use of this method is impeded by the lack of
highly active and stable catalysts. The available cata-
lysts for synthesis of pyridine bases from acetylene
and ammonia work with constant activity for 72 h at
best [8, 9].
MF(NH2) + H2O
M(OH)F(NH3)
M(OH)(NH2) + HF
where M is Zn2+, Cd2+, Fe2+, etc.
An X-ray diffraction study showed that the cat-
alysts are fairly active in the semiamorphous-crystal-
line state, in which they contain chemically bound
water. With the calcination temperature from 450 to
650 C, the fraction of the crystalline phase grows,
the content of chemically bound water decreases, and
hydroxofluorides start to decompose. As a result, the
specific surface area and activity of the catalyst de-
crease.
Formation of pyridine bases from acetylene and
ammonia or acetylene, ammonia, and methanol is
a result of complex combination of parallel-successive
reactions accompanied by vinylation, dehydrocycliza-
tion, isomerization, trimerization, etc.
In the gas phase, this is only possible with poly-
functional catalysts.
An analysis of published data on the mechanism
of acetylene and amine activation showed that d-metal
(zinc, cadmium, chromium, iron, cobalt, etc.) com-
pounds, which are also active in reactions of addition
of various molecules to acetylene can catalyze am-
monia and amine vinylation in the gas phase. Such
compounds are typical catalysts for dehydrogenation
and dehydration [10, 11].
We found that, when catalysts contain, along with
zinc, cadmium, and aluminum hydroxofluorides, also
3.0 5.0 wt % zinc and chromium(III) [or iron(III)]
oxides, they are fairly active, selective, and stable in
synthesis of pyridines from acetylene, and ammonia
(methanol). Taking this circumstance into account, we
synthesized more than 30 catalysts; their compositions
and properties are listed in Table 1.
Studies of promotion of cadmium and zinc com-
pounds with metal fluorides and X-ray diffraction
analysis of other polyfunctional catalytic systems
showed that, during catalyst preparation, zinc, cad-
As seen, the KTsZhKhA-5 catalyst is the most
active and stable in synthesis of 2- and 4-methylpyr-
idines, while the KTsKhZhA-6 catalyst is the best
in synthesis of pyridine and a mixture of isomeric
1070-4272/03/7606-0939 $25.00 2003 MAIK Nauka/Interperiodica

940
KHAMIDULLAEV, YUSUPOV
Table 1. Comparative characteristics of catalysts
Catalyzate (organic layer) composition, %
Composition,
Catalyst
wt %
2-methyl-
pyridine
3- and 4-meth-
ylpyridines
pyridine
KTsA-1
CdF2 3.0,
ZnO 5.0,
AlF3 3.0,
Al2O3 89.0
CdF2 3.0,
ZnO 3.0,
Cr2O3 3.0,
AlF3 3.0,
Al2O3 88.0
CdF2 3.0,
ZnO 5.0,
Cr2O3 3.0,
AlF3 5.0,
Al2O3 86.0
CdF2 5.0,
ZnO 7.0,
96.0 172.0
120.0 165.0
4.2
4.8
96.0
85.0
88.0
42.0
24.0
(4-methylpyridine)
KTsKhA-2
112.0
30.0
31.0
18.0
24.0
22.0
KTsKhA-3
KTsZhA-4
96.0 165.0
120.0 203.0
4.6
5.6
96.0
85.0
90.1
44.0
28.0
132.0
32.1
ZnF2 3.0,
AlF3 3.0,
Fe2O3 3.0,
Al2O3 80.0
CdF2 2.0,
Cr2O3 3.0,
ZnF2 3.0,
ZnO 3.0,
Fe2O3 3.0,
Al2O3 86.0
CdF2 1.5,
Cr2O3 2.0,
ZnF2 1.5,
AlF3 3.0,
ZnO 3.0,
KTsZhKhA-5
KTsKhZhA-6
144.0 232.0
180.0 196.0
6.1
6.4
152.0
163.0
92.0
92.0
52.0
22.0
34.0
24.0
34.0
Fe2O3 3.0,
Al2O3 86.0
methylpyridines. Promotion of zinc-chromium-alumi-
num and zinc-chromium-iron-aluminum catalysts with
1.5 3.0 wt % cadmium, zinc, and aluminum fluorides
raises the acetylene conversion and catalyst productiv-
ity by a factor of 1.5 2.0. In the process, the loss
of cadmium metal from the catalyst is probably pre-
vented by introduction of cadmium fluoride into the
defective spinel structure characteristic of -Al2O3
and by its fixation in this structure.
ume, phase composition, and mechanical strength of
the catalysts. The acidity of the KtsKhZhA-6 catalyst
strongly differs from that of the other catalysts. It
acidifies water within the first 20 s by 1.2 pH units;
after 40 min, the pH value stabilizes. The other cat-
alysts acidify water by 0.4 to 0.8 pH units within the
first 20 30 s (see figure).
Probably, it is hydroxofluorides that produce acidic
centers on the catalyst surface. The presence of hy-
droxofluorides on the catalyst enhances sorption of
acetylene, ammonia, and methanol molecules, with
the result that their molecules are polarized.
To determine the dependence of the activity of cat-
alysts on their texture properties, we measured the
specific surface area, acidity, pore radius and vol-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 6 2003

PROPERTIES OF MIXED POLYFUNCTIONAL FLUORIDE CATALYSTS
941
1
Table 2. Characterization of synthesis of pyridine bases on KTsKhZhA-6 catalyst [T 280 360 C, Wtot 150 180 h ,
C2H2 : NH3 = 1 : 2 (vol : vol)]
Acetylene
T, C conver-
sion, %
Catalyzate composition, wt %
Synthesis
time, h
2-methylpyridine
4-methylpyridine
acetonitrile
sum of by-products
0 30
30 60
60 90
90 120
120 150
150 160
180 200
280
290
300
310
320
330
340
98.0
95.0
92.0
90.0
86.0
82.0
70.0
35.5
39.6
42.0
44.0
47.0
51.0
53.0
16.4
23.2
21.0
24.0
22.0
25.0
27.0
32.0
26.0
21.0
16.0
12.0
8.0
15.0
13.0
10.0
25.0
19.0
26.0
17.0
3.0
It was found that, in the first 60 h, the selectivity of
a fresh catalyst with respect to pyridine yield is un-
stable; the major products are acetonitrile, benzene,
propionitrile, etc. After 70 h, the process selectivity
becomes stable, and the acetonitrile content in the cat-
alyzate gradually decreases (Table 2).
X-ray diffraction patterns of the catalysts were re-
corded on a DRON-2 diffractometer (CuK radiation).
The specific surface area was measured by the BET
method. The catalyst acidity was determined pH-met-
rically with a pH-673 pH-meter equipped with an
ESL-43-07 glass electrode. The pore structure of the
catalyst was studied by mercury porosimetry.
After 180 h of work and subsequent regeneration,
the catalyst becomes completely ripened. In this case,
the content of acetonitrile, by-products, and tars in
the catalyzate does not exceed 20 25%.
The catalytic condensation of acethylene with am-
monia and methanol was performed in a 25 1000 mm
cylindrical stainless steel flow-through reactor. The
temperature, space velocity, and ratio of the initial
components were varied.
We found that the specific surface area of the cat-
alyst decreases with time by 30 m2 g 1 on the average.
Simultaneously, its mechanical strength increases by
approximately 0.8 1.0 MPa. It should be noted that,
in the course of catalyst operation, a new crystalline
phase is formed, which makes the catalyst more stable.
The reaction products were analyzed by GLC
[Chrom-5 chromatograph, Apiezon-M (12 15 wt %)
on Celite 545 as stationary phase, column tempera-
ture 120 C, toluene as internal reference, carrier gas
1
helium, flow rate 2.4 l h ].
The KTsKhZhA-6 catalyst was tested in the con-
tinuous mode for 1500 h in synthesis of pyridine and
isomeric methylpyridines from acetylene, ammonia,
and methanol. The following optimal process param-
eters were found: temperature 360 440 C; acetylene :
ammonia : methanol molar ratio 1.0 : 2.0 : 0.8; total
The products were separated by catalyzate frac-
tionation on a 30-TP column and identified by their
physical constants and also by obtaining their picrates
and chloroplatinates.
1
space of the velocity 100 200 h . The catalyzate
(organic layer) obtained under these conditions has
the following composition (wt%): pyridine 28.0 33.0,
2-methylpyridine 12.0 25.0, 3-methylpyridine 18.0
21.0, 4-methylpyridine 12.0 15.0, with the remainder
being higher pyridines, acetonitrile, and tars.
Thus, new catalysts based on cadmium, zinc, chro-
mium, iron, and aluminum oxides and fluorides were
developed and tested in synthesis of pyridine bases
from acethylene, ammonia, and methanol.
The catalysts were prepared by suspending, fol-
lowed by molding, drying, and calcination. Alumi-
num hydroxide (calcination loss 33.0%) was used as
support.
Variation with time t of pH of water contacting with the
catalyst surface. Catalyst: (1) KTsKhZhA-6, (2) KTsZhKhA-
5, and (3) KTsMA-4.
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KHAMIDULLAEV, YUSUPOV
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