Note: Descriptions are shown in the official language in which they were submitted.
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AMMONIA OXIDATION CATALYST COMPRISING ALUMINIUM OXIDE, BISMUTH OXIDE AND
MANGANESE
OXIDE
The present invention describes catalysts to be used for nitrous oxide
production by
ammonia oxidation with molecular oxygen in chemical industry.
Along with a high activity, understood as conversion at a definite residence
time,
catalysts for ammonia oxidation to produce nitrous oxide should also meet the
following
demands:
~ they should provide a high selectivity towards nitrous oxide and a low
selectivity
towards nitrogen oxide in the whole temperature range of ammonia oxidation;
~o ~ they should perform well under conditions, when reaction mixture contains
oxygen
in stoichiometry amount or below the stpichiometry amount.
As a rule, the known catalysts do not comply with all above demands.
Thus a bulk manganese-bismuth catalyst [ 1 ] containing 5% Bi203 and 95% MnOz
has
a low activity. At a temperature of 200°C, when the selectivity towards
nitrous oxide is
is maximum, and equals 88.5% at an inlet ammonia concentration of 10.8 vol.%
in the oxygen
excess, a complete ammonia conversion occurs at a residence time of 5 s.
Meanwhile the
selectivity towards NO and N02 is 0.9%. As the process temperature increases
to 300°C, the
yields of nitrous oxide and NO+N02 are 79 and 3.1 % respectively. As ammonia
concentration decreases to 3.02 vol.%, the selectivity towards nitrous oxide
falls to 65%.
2o Therefore, beside a low activity in ammonia oxidation by the oxygen excess,
the catalyst
shows a high selectivity towards nitrogen oxides.
Another catalyst for ammonia oxidation consists of the oxides of iron, bismuth
and
manganese in the following ratio: 79.45% Fe203, 11.53% Bi203, 7.21 % Mn02 [2].
The
maximum yield of nitrous oxide in the said catalyst is 82%, and it is attained
under the
2s following conditions: temperature - 350°C; inlet concentrations:
ammonia - 10 vol.%, oxygen
- 90 vol%. However, at this temperature the selectivity towards nitrogen oxide
is 6%. At
300°C the selectivity towards nitrous oxide and nitrogen oxide is 79%
and 1.5% respectively.
Therefore, the catalyst does not meet all demands in concern, because it has a
low selectivity
towards nitrous oxide at a high selectivity towards nitrogen oxide.
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Catalyst with a composition of 5% Mn02, 5% Bi203, 90% Fe203 [3] is most close
in
performance and properties to the catalyst claimed in the present invention.
It shows the
following results. The maximum nitrous oxide yield is 87%, when reaction
mixture
containing 10% of ammonia in air (thus in oxygen excess, concentration 18.9
vol.%). If
s reaction mixture contains 1 ammonia part, 5 air parts, and 5 nitrogen parts,
and so it is close
to stoichiometry (9.1 vol.% ammonia and 9.55 voL% oxygen), then the yield of
nitrous oxide
is 81 %. At 275-300°C the residence time for complete conversion is 3.6
s. Therefore, the
catalyst has a low activity and not high enough selectivity towards nitrous
oxide under
conditions, when reaction mixture contains ammonia and oxygen in amounts close
to
io stoichiometry.
The present invention aims at providing catalysts that are highly active under
conditions, when reaction mixture contains oxygen in amount close or below the
stoichiometry one, showing a high selectivity towards nitrous oxide, and a low
selectivity
towards nitrogen oxide.
~s For the purpose the claimed catalysts for the nitrous oxide production by
ammonia
oxidation have the following composition (mass.%):
5.0-35.0 - manganese oxide (referred to Mn02}
4.5-30.0 - bismuth oxide (Bi203)
90.5-35.0 - aluminum oxide (A1203).
zo The catalysts of the said composition are prepared by impregnating alumina
with a
solution of Mn and Bi nitrates, or by mixing the powders of Mn and Bi oxides
with the
powder of aluminum hydroxide to be then molded, or depositing the said
components on an
inert support. At the final stage the catalysts are dried, and calcined at 375-
550°C. Thus
obtained catalysts show a high activity, when the oxygen content in the
reaction mixture is
2s close or lower the stoichiometry one, and exhibit a high selectivity
towards nitrous oxide, and
a low selectivity towards nitrogen oxide.
At a temperature of 350°C, and at a residence time of 0.7 sec,
ammonia/oxygen ratio
being 1.44, and ammonia concentration being 7.3 vol.%, ammonia conversion on
the said
catalysts is 82-99.2%. The selectivity towards nitrous and nitrogen oxides is
82-84.6 and 2.1-
T__.___.._.~..~..~_ __. . _ _ _ _ ___ _____~ __.~ ~.~.a....~...__.~_ ~...~.__
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2.7% respectively. After water and ammonia separation the final product
contains 79.6-81.7%
of nitrous oxide, 4.1-5.25% of nitrogen oxide, and 0.82-0.84% of oxygen.
At a temperature of 300°C, and at a residence time of 1.6 sec,
ammonia/oxygen ratio
being 1.44, and ammonia concentration being 7.3 vol.%, ammonia conversion on
the said
s catalysts is 82.5-99.0%. The selectivity towards nitrous and nitrogen oxides
is 83-86 and 0.3-
0.35% respectively. After water and ammonia separation the final product
contains 82.2-
84.9% of nitrous oxide, 0.6-0.69% of nitrogen oxide, and 0.75-0.77% of oxygen.
The high activity and selectivity of the claimed catalysts in ammonia
oxidation to
nitrous oxide is provided by its components at the said percent ratios.
io Catalyst specific surface area also has a positive effect. The tests show
that at a stable
high activity the catalyst shows the highest selectivity, when its specific
surface area ranges
within 5-80 m2/g.
Example 1. Catalyst with a composition of 13%MnOz/11 %Biz03/76%A1z03 is
prepared as follows. 100 g of alumina granules are impregnated by incipient
wetness with a
~s solution of Mn and Bi nitrates, are dried in air and then in a drying
chamber at 130°C for 2-4
h. Thus obtained product is once again impregnated with a solution of Mn and
Bi nitrates,
dried in air and in the drying chamber at 130°C for 4 hours. Then the
granules were calcined
in a furnace at 375-550°C for 2-4 h. Thus obtained catalyst is tested
under reaction conditions
similar to those described in [3], reaction mixture composition being 9%NH3
and 9%02. At
zo 350°C and at a residence time of 0.7 s ammonia conversion is 99.2%.
Selectivity towards
nitrous oxide and nitrogen oxide is 87 and 2.8% respectively. At 300°C
at the same gas
composition and at a contact time of 1.6 s ammonia conversion is 99.4%.
Selectivity towards
nitrous oxide and nitrogen oxide is 88.6 and 0.30% respectively. Ssp is 10
m2/g.
Example 2. Catalyst prepared as in example 1 is tested at ammonia to oxygen
ratio
zs equal to 1.44 and ammonia concentration equal to 7.3 vol.% in the reaction
mixture.
At 350°C and at a residence time of 0.7 s ammonia conversion is 82%.
Selectivity
towards nitrous oxide and nitrogen oxide is 84.6 and 2.7% respectively. In the
final product
nitrous oxide to oxygen ratio is 97.4, nitrous oxide to nitrogen oxide ratio
being 15.6. After
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ammonia and water separation the final product contains 82% of nitrous oxide,
5% of
nitrogen oxide, and 0.84% of oxygen.
At 300°C at the same gas composition and at a contact time of 1.6 s
ammonia
conversion is 82.5%. Selectivity towards nitrous oxide and nitrogen oxide is
86 and 0.35%
s respectively. In the final product nitrous oxide ratio to oxygen is 110,
while nitrous oxide to
nitrogen oxide ratio is 121. The final product (after ammonia and water
separation) contains
85.2% of nitrous oxide, 0.7% of nitrogen oxide, and 0.78% of oxygen.
Example 3. Catalyst with a composition of 5%Mn02/5%Bi203/Fez03 is prepared as
described in [3] and tested under the following conditions: reaction mixture
composition -
io 0.75%NH3, 1.5%02; residence time - 0.072 s, temperature - 350-300°C.
At 350°C ammonia
conversion is 73%. Selectivity towards nitrous oxide and nitrogen oxide is
76.9 and 3.9%
respectively. At 300°C ammonia conversion is 35%. Selectivity towards
nitrous oxide and
nitrogen oxide is 68 and 1.4% respectively. Ssp is 4 m2/g.
Example 4. Catalyst with a composition of 15%Mn02/15%Bi203/70%A1203 is
rs prepared as in example 1 and tested as in example 2. At 300°C
ammonia conversion is 38%.
Selectivity towards nitrous oxide and nitrogen oxide is 79 and 1.4%
respectively. Ssp is 1 I
m2/g.
Example 5. Catalyst with a composition of 13%Mn02/I 1 %Bi2O3/76%A12O3 1S
prepared as in example 1 and tested as in example 2. At 350°C ammonia
conversion is 76%.
2o Selectivity towards nitrous oxide and nitrogen oxide is 76% and 3.8%
respectively. At 300°C
ammonia conversion is 39%. Selectivity towards nitrous oxide and nitrogen
oxide is 83 and
1.3% respectively.
Example 6. Catalyst with a composition of 15%Mn02/7,5%Bi203/77.5%A1203 is
prepared as in example I and tested as in example 2. At 350°C ammonia
conversion is 93.2%.
is Selectivity towards nitrous oxide and nitrogen oxide is 78.7% and 3.9%
respectively. At
300°C ammonia conversion is 58.7%. Selectivity towards nitrous oxide
and nitrogen oxide is
80 and 1.2% respectively. Ssp is 11 m2/g.
Example 7. Catalyst with a composition of 10%Mn02/5%Bi203/85%A1203 is
prepared as in example 1 and tested as in example 2. At 350°C ammonia
conversion is 92.5%.
_ ._ . _ _ __ ___. .r._.~...-~......~._~___.__
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Selectivity towards nitrous oxide and nitrogen oxide is 80% and 3.7%
respectively. At 300°C
ammonia conversion is 62.4%. Selectivity towards nitrous oxide and nitrogen
oxide is 77 and
1.3% respectively. Ssp is 11 m2/g.
Example 8. Catalyst with a composition of 16%Mn02/16%Biz03/68%A1203 is
s prepared as in example 1 and tested as in example 2. At 350°C ammonia
conversion is 73%.
Selectivity towards nitrous oxide and nitrogen oxide is 78.8% and 3.9%
respectively. At
300°C ammonia conversion is 37%. Selectivity towards nitrous oxide and
nitrogen oxide is
37 and 1.4% respectively. Ssp is 39 m2lg.
Example 9. Catalyst with a composition of 5%Mn02/4.5%Bi203/90.5%A1203 is
~o prepared as follows. 100 g of alumina granules are impregnated by a
solution of Mn and Bi
nitrates, dried in air and in the drying chamber at 120-130°C for 4 h.
The obtained product
was calcined in the furnace in air at 375-550°C for 2-4 h. Thus
obtained catalyst was tested as
in example 2. At 350°C ammonia conversion is 79%. Selectivity towards
nitrous oxide and
nitrogen oxide is 76% and 3.6% respectively. At 300°C ammonia
conversion is 40%.
~s Selectivity towards nitrous oxide and nitrogen oxide is 80 and 1.3%
respectively. Ssp is 5
m2/g.
Example I0. Catalyst with a composition of 35%Mn02/30%Bi203/35%A1203
prepared mixing a mass containing 52 g of Mn oxide and Bi oxide powders and 35
g of
aluminum hydroxide powder with 25 cm3 of water to obtain a moldable paste.
Then the paste
zo was molded as cylinder granules 3 mm in diameter, dried at room temperature
for 10 h, dried
in the chamber at 120°C for 2 h, and calcined in the furnace at 375-
550°C for 2-4 h. Thus
obtained catalyst was tested as in example 2. At 350°C ammonia
conversion is 77%.
Selectivity towards nitrous oxide and nitrogen oxide is 78% and 3.1 %
respectively. At 300°C
ammonia conversion is 39%. Selectivity towards nitrous oxide and nitrogen
oxide is 74 and
2s I .l % respectively. Ssp is 80 m2/g.
References:
1. V.F. Postnikov, L.L. Kuz'min and N.K. Tsal'm,- J.Chem.Ind., 22, 1348 (1937)
2. Zawadzki, Discussions Faraday Soc., 1950, N8, p.140
3. Schlecht, L., and von Nagel, A., Ger. Patent 503200 ( 1930)
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Table 1
examplecontent,mass.% conversion, SN2o,% SNO,% TC
%
Mn02 Bi203
I 13 11 99.2 87 2.8 350
99.4 88.6 0.35 300
2 13 I1 82 84.6 2.7 350
82.5 86 0.35 300
3 5 5 73 76.9 3.9 350
35 68 1.4 300
4 15 15 38 79 1.4 300
13 11 76 76 3.8 350
39 83 1.3 300
6 15 7.5 93.2 78.7 3.9 350
58.7 80 1.2 300
7 10 5 92.5 80 3.7 350
62.4 77 1.3 300
8 16 16 73 78.8 3.9 350
37 74.7 1.4 300
9 5 4.5 79 76 3.6 350
40 80 1.3 300
35 30 77 78 3.1 350
39 74 1.1 300
_~_. ~~__ ._. __.__.___ . _ ____~~..___._._.. _ .. __.
