DE305124C - - Google Patents

Description

It probably needs the fact that the pressure combustion process for nitrogen oxide production is all other, especially the electrical High-voltage flame arc process is far superior, no further explanation, if you just keep in mind that every conversion of heat into energy is associated with a * loss of at least 90 percent.

The emergence of ^ ^ nitrogen oxides at I the usual gas combustion processes and the gas explosion operations, has now attracted no technical significance, since on the one hand not exceeding in the usual custom built in refractory ovens about 2000 ° temperatures at these | Reactions compared to electric arcs have been too low for a technically usable yield, on the other hand, no suitable catalysts were known for the furnace designs available.

More recent experiments have shown that an increase in the pressure under which the reactants _come together has a

has significantly greater influence on the nitrogen oxide yield, J | than || a ^ increase in temperature alone, where specifically $, in the case of the so-called flameless j £ surface combustion as yet unexplained influences (apparently more catalytic Nature) come into question, which significantly accelerate the formation of nitrogen oxide. The best yields were obtained when the pressure and temperature were increased. Working at high pressure and at high temperature, however, there are technical difficulties associated with those of the simultaneous The application of both sets certain limits. There has also been no cheap filing so far and enough resistant contact substance under these working conditions.

Through the patent specification 281084 ^em process has become known to obtain by combustion of air with the help of carbon compounds, especially methane (natural gas), initially nitrogen oxides and then in a known manner nitric acid. It was also intended to allow the combustion to proceed within a refractory mass consisting of zirconium-containing substances in the manner of the known surface combustion.

Experiments have now shown that this is catalytically stimulated Combustion the aluminum nitride as a contact substance is particularly suitable or the by exposure to nitrogen in the presence of reducing agents on clay, e.g. B.

Bauxite, nascent and aluminum nitride-containing materials, namely, is, each the higher the aluminum content, the greater the catalytic effect. This contact body show properties analogous to those of platinum with regard to the absorption, compression and chemical bonding of gases or platinum sponge. But what is particularly noteworthy is that they allow, in proportion low pressures and temperatures to achieve economically satisfactory yields as the basis of technically applicable working conditions in large companies.

Advantageously, these contact substances can also have activating additives added, such as oxides or nitrides of iron, copper, cobalt, nickel, manganese, chromium, calcium, barium, cerium, thor, Titanium, vanadium.

This extremely beneficial effect of the new catalyst is. in nitrogen oxide production of particular importance, since nitrogen is known to react very slowly with oxygen and the economy of nitrogen oxide formation depends to a large extent on the rate of reaction depends. It has been found in the experiments that the equilibrium between nitrogen oxide and its elements in those in question Temperatures and pressures in narrow reaction cylinder furnaces with subsequent widths Expansion chambers in the event of a strange cooling or quenching of the nitrogen oxides formed immediately after formation in a short time Time to be produced as completely as possible and to be maintained continuously with a high yield was.

The great durability of the, especially the one described elsewhere Process produced, high aluminum content aluminum nitrides against high temperatures has the consequence that these contact substances also burn in the nitrogen do not melt together at the highest, technically permissible temperatures or sinter, but remain porous and loose and therefore retain their effectiveness for a long time and at the same time chemically withstand a large excess of oxygen, which cannot be foreseen to this extent was.

If surface combustion is arranged for this purpose, one can say very hot, but short heating surfaces and let the combustion take place very suddenly.

The present process gives yields of nitrogen oxides which not insignificantly exceed those obtained so far by the process of patent 281084, and one can use ordinary, preheated compressed air or, depending on the prevailing conditions, with a very small addition of pure oxygen (about 5 percent ) get along with the same. So were z. B. with surface combustion, where aluminum nitride was used as a ^{highly refractory catalyst, per methane burned in 3} (about 8800 CaI. 15 °, 760 mm) under pressure of 10 atm. when using highly heated compressed air without the addition of oxygen, 380 to 490 g HNO ₃ (100 percent) are obtained.

With regard to the economy of the process, the omission of a larger one The addition of pure oxygen is of crucial importance. In industrial terms, the difficulties that have existed so far are those in the lack of technically viable equipment for high temperatures and pressures were established, overcome.

The following comparison _{table for HNO 3} -AuS-hives when using the flameless 100th surface combustion and various contact materials provide information about this:

Patent 281084 (with 30 percent addition of oxygen).

Overpressure
Atm. Preheating the
Compressed air and des
Methane
temperature HNO ₃ content in the ^3rd
Exhaust gas with zircon
(Patent 281084) HNO ₃ content on the ^3rd
Methane with zircon
(Patent 281084) 3
5
IO 250 ⁰ C
250 ⁰ C
250 ⁰ C 14 to 16 g
. 22 to 28 g
34 to 39 g 108 to 114 g
162 to 206 g
240 to 310 g

After expiry (o'.ne addition of oxygen).

Overpressure
Atm. . Preheating the
Compressed air and
of methane
temperature ENT ₃ content in im ^!
Exhaust gas with Al nitride
(58.2 percent Al ₂ O ₃ ) HNO ₃ content on the ^3rd
Methane with Al nitride
(58.2 percent Al ₂ O ₃ ) 3
5
. IO 300 ° C
300 ° C
300 ⁰ C 20 to 22 g
32 to 36 g
45 to 48 g 160 to 200 g
250 to 270 g
380 to 490 g

With the addition of activating bodies such. B. oxides or nitrides of iron, nickel, copper, cerium, thor, etc., to the contact _{substance Al nitride, the latter test numbers of the HN O 3} yield increased by 15 to 20 percent, depending on the substances used.

Example.

The main feature of the furnace construction is that the combustion of the gases under high pressure in a narrow area exposed to the flameless surface combustion highly refractory pressure cylinder with built-in catalyst takes place in which through Supply of methane and air in numerous streams directed from top to bottom in a wide variety of directions a highly intensive turbulence of the gases brought about and ' so that very high temperatures can be reached quickly in the smallest of ■ reaction spaces is. In the same way as the installation of the combustion cylinder with The catalyst that takes into account the nature of the formation of nitrogen oxide is the constructive one Formation of the pressure furnace in its lower part of the requirement for rapid cooling of the nitrogen oxide generated and adapted to the combustion gases and rapid removal of the condensation water.

From the numerous experiments under the most varied of conditions, z. B. the following average values of the maximum yields of nitrogen oxides at 10 atm. Overpressure, a preheating of the compressed air (without the addition of pure oxygen) and the methane to 300 ⁰ C:

HNO ₃ content 1 cbm burned methane:

ä) for aluminum nitride with 55.1 percent Al ₂ O ₃ content: 340 g,

b) for aluminum nitride with 58.2 percent Al ₂ O ₃ content: 380 g,

c) for aluminum nitride with 67.5 percent Al ₂ O ₃ content: 490 g.

It also turned out that for

Production of aluminum nitride from bauxite one with a maximum of 2 to 3 percent SiO ₂ catalytically works most appropriately.

Claims (2)

P ATENT claims: I. Process for the production of nitrogen oxides from air, the oxidation the air with the help of carbon compounds through flameless surface combustion takes place within a highly refractory contact mass, characterized in that, that the contact mass consists essentially of aluminum nitride. 2. The method according to claim 1, characterized characterized in that containing aluminum nitride as the main component Contact body activating additives, such as the oxides and nitrides of Iron, copper, cobalt, nickel, manganese, chromium, calcium, barium, cerium, thor, Titanium.