RU2156730C1 - Method of production of nitrogen oxides - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology. SUBSTANCE: invention relates to production of oxygen compounds of nitrogen, in part, nitrogen oxides by catalytic oxidation of molecular nitrogen with its oxygen compounds. Method involves preparing and mixing nitrogen-containing gas flow with gas flow containing oxidant as oxygen compounds of nitrogen, energetic flow using products of its combustion for carrying out the reaction of nitrogen oxidation where products of hydrogen-containing gas combustion are used and obtained by combustion or catalytic oxidation of hydrogen in air flow or other oxygen-containing gas. Catalyst is placed for some layers and gas flow with oxidant and gas flow carrying heat energy are added before each layer. Method provides partial or complete exception of ammonia as the parent raw for synthesis of nitrogen oxides at the 1-st catalyst step. EFFECT: enhanced effectiveness of oxidation process. 2 cl, 1 dwg, 2 ex

Description

 The invention relates to chemical technology, mainly for the production of oxygen compounds of nitrogen, and can be used in the chemical industry, for example, in the production of nitric acid, fertilizers, caprolactam, nitrite-nitrate salts and other nitrogen-containing compounds.

 Of the known methods for producing nitrogen oxides, the only one recognized and widely used in industry is the method of catalytic oxidation of ammonia by atmospheric oxygen to nitric oxide II (Karavaev M.M., Zasorin A.P., Kleschev N.F. "Catalytic oxidation of ammonia". M., Chemistry, 1983).

Oxidation is carried out on platinum or combined catalysts, at a temperature of 780-950 ^o C, at atmospheric or elevated pressures; the heat of ammonia oxidation is usually used to produce steam, and nitric oxide II is converted into nitric acid (Atrashenko VI, Kargin SI "Technology of nitric acid." M., Chemistry, 1970).

 The disadvantage of this method of producing nitrogen oxides is the use of ammonia in the process as a raw material, a synthetic product of multistage production using natural gas in the initial stage. Another disadvantage is the use of expensive and scarce platinum rhodium catalysts for the oxidation of ammonia.

 The closest in technological essence and the achieved effect is the stage of catalytic oxidation of molecular nitrogen by nitric acid vapors described in RF patent N2070865 dated 12/27/1996.

 In the above patent, it is provided that a gas stream containing oxygen compounds of nitrogen is introduced into the nitrous gases obtained during the oxidation of ammonia in the first stage of the catalyst and they oxidize molecular nitrogen of nitrous gases in the second stage of the catalyst.

As nitrogen compounds, nitric acid vapors or a mixture thereof with nitrogen oxides are used, and the process is carried out at temperatures of 900-450 ^o C.

 The disadvantage of the method for producing nitrogen oxides described in RF patent N2070865 is that expensive ammonia is used as a raw material for producing nitrous gases at the first stage, while only 65-85% of production acid is obtained due to the oxidation of molecular nitrogen.

 The aim of the invention is to increase the efficiency of the process of oxidation of molecular nitrogen due to the complete or partial elimination of ammonia from it, as a feedstock for the production of nitrogen oxides at the first stage of the catalyst.

This goal is achieved in that as the energy source required for the temperature regime of the oxidation reaction of N ₂ , use the products of combustion of a hydrogen-containing gas obtained by burning or catalytic oxidation of hydrogen in a stream of air or other oxygen-containing gas.

 The nitrogen oxidation catalyst in the reactor is arranged in several layers, in front of each of which a gas stream with an oxidizing agent is introduced and a stream of gas carrying energy can be introduced.

The novelty of the method is as follows. A distinctive ability of the processes of nitrogen oxidation by its oxygen compounds is the endothermicity of the chemical reactions occurring during this (Karavaev MM et al., Moscow, Chemical Industry, N11, p. 720, 1996). In the prototype, the energy necessary for the process is obtained due to the oxidation of ammonia by atmospheric oxygen and is supplied with a stream of nitrous gases. This limits the degree to which HNO _{3 is} obtained from molecular nitrogen in the overall process; on the other hand, it increases the likelihood of side processes due to the components of nitrous gases.

 In the proposed method, the flow of carrier energy and nitrogen is obtained due to the combustion of hydrogen in the air.

2H ₂ + O ₂ = 2H ₂ O + 483.2 kJ
During combustion, an energy of 10.786 kJ / l or 10786 kJ / m ³ H _{2 is released} and only water vapor is formed, that is, no components are introduced that could lead to parallel or sequential reactions in the process of oxidation of molecular nitrogen.

 At the same time, studies of the effect of water vapor on the catalytic reaction of nitrogen oxidation were not detected.

 Thus, the gas mixture obtained by combustion can be used to directly introduce it into a reactive medium requiring energy supply. This eliminates the need for external heating and mode restrictions associated with the occurrence of adverse reactions.

Hydrogen can be used both in pure form (H ₂ ) and in the form of a nitrogen-hydrogen mixture. Other variants of the gas mixture are possible, but their combustion products should not be poisons for the nitrogen oxidation catalyst. Hydrogen can be burned directly in air or other oxygen-containing gas. When technologically or technically necessary, hydrogen can also be oxidized on catalysts, for example a platinum group, having a low ignition temperature. With this option, a uniform distribution of gas temperature along the perimeter and volume of the reactor is ensured, which is important for the second stage of the process of nitrogen oxidation and mixing with a stream containing an oxidizing agent.

Chemically and technologically it is possible by the proposed method to obtain high concentrations of nitrogen oxides at the outlet, for which, of course, it is necessary to supply a greater amount of oxidizing agent vapor. This is technologically possible, but in turn requires the supply of more energy. However, raising the combustion temperature of hydrogen very high (for example, up to 2000 ^° C), in view of the possible chemical transformations of the oxidizing agent, is not practical. Therefore, an energy stream with a temperature below 1000 ^o C can be fed into the reactor, in the zone of nitrogen oxidation in several streams, for example in front of each layer.

 A gas stream with an oxidizing agent is obtained in a separate apparatus by passing a gas stream through several stages of a hot solution of nitric acid. The amount and concentration of acid vapor in the gas stream is determined by the given technological conditions, including the amount of energy supplied and can vary widely.

 Experimental, laboratory studies and engineering studies of the method were carried out.

The main apparatus of the laboratory setup (see drawing) made of quartz glass was a reactor (1). Air was supplied to the top of the latter. In the head of the reactor around the circumference there were devices (4) for supplying hydrogen, which could be simultaneously burners. Platinum grids were installed in the lower part of the burner, and in the middle part of the reactor was a layer of nitrogen oxidation catalyst. Before the layer through the switchgear, the PCVS (steam-acid-air mixture) flow was supplied into the gas mixture obtained by burning H ₂ . Having passed the catalyst bed, nitrous gases were discharged from the reactor, cooled, freed from nitrogen oxides and thrown out under draft.

 A gas mixture with an oxidizing agent (PCVS) was prepared by passing air through a layer of heated nitric acid, poured into a saturator vessel (3).

 The reactor (1) and the saturator (2) are equipped with electric heating, which allows you to set the set temperature of the gas mixture and liquid.

Based on the measurement of air and hydrogen flows (N ₂ - H ₂ ) with rheometers and the results of chemical analyzes of PCVS and nitrous gases, the material balance of the process and its indicators were calculated.

Example 1. Heats up the reactor and saturation. When reaching a temperature in the reactor of 300 ^o C included air supply D amount of 1940 l / h. After heating the Pt network and the oxide catalyst layer to the specified gas temperature, the hydrogen supply was turned on at the beginning in a small portion, then, after the Pt network was ignited, it was brought to 60 l / h. As a result of the interaction of hydrogen with oxygen by reaction
2H ₂ + O ₂ = 2H ₂ O + 483.2 kJ (1)
the temperature of the gases after the catalyst was brought to 850 ^o C.

400 l / h of air was supplied to the saturator, where it passed through a solution of 60% HNO ₃ at a temperature of about 95 ^° C and was saturated with acid and water vapors. The obtained PCVS was analyzed for the vapor content of HNO ₃ . It contained 20% HNO ₃ and 25.3% water vapor (calculated based on the saturation pressure of water vapor). Based on the measured air flow, this was 100 l / h of HNO ₃ vapor.

The side stream is introduced into the reactor after the grid into the hot gases generated during the combustion of hydrogen. Here he mixed and at a temperature of the mixture up to 750 ^o C entered the catalyst, where the oxidation of nitrogen
2HNO ₃ + N ₂ = 3NO + NO ₂ + H ₂ O - 355.0 kJ (2)
and decomposition of 2 unreacted acid vapors:
4HNO ₃ = 4NO ₂ + 2H ₂ O - O ₂ -191.0 kJ (3)
Since these reactions are endothermic, the temperature of the gas in the layer decreased to 485 ^o C.

After stabilization of the regime, analyzes were selected for the content of HNO ₃ vapors in PCVS and nitrogen oxides (NO ₂ ) in the outgoing nitrous gases.

 Based on the results of the analyzes, the material balance of experience and its indicators were calculated (on a computer according to a special program).

The gases before and after the catalyst had the composition:
Before the catalyst
HNO ₃ - 100 l / h 4.05%
H ₂ O - 206.3 L / h 8.35%
N ₂ - 1736.6 l / h 70.31%
O ₂ - 427.1 l / h 17.29%
Total: 2,470.0 L / hr 100%
After catalyst
H ₂ O - 256.3 L / h 10.0%
N ₂ - 1699.1 l / h 66.26%
O ₂ - 433.7 l / h 16.91%
NO - 112.5 L / h 4.39%
NO ₂ - 62.5 L / h 2.44%
Total: 2,564.1 l / h 100%
Process indicators were established by changing the volume (V) of the reacting components.

Степень разложения паров HNO₃ по реакции 3 находится по разности

Пример 2. Разогревали за счет электрообогрева, примерно до 300^oC реактор и до 90^oC насытитель с 60% HNO₃. В реактор подавался поток воздуха в количестве 560 л/час. Включалась подача водорода, он поджигался при выходе из горелок прямым пламенем. Расход водорода доводился до 140 л/час. Температура газа поднималась до 900^oC (регулировалась расходами компонентов и электрообогревом). В насытитель подавался воздух в количестве до 490 л/час, который при температуре 93^oC насыщался парами кислоты и воды (см. пример 1). Потоки смешивались и при температуре 760^oC поступали на катализатор, где протекали реакции окисления азота, разложение HNO₃ и окисление, в незначительной степени, NO кислородом.The degree of growth of nitrogen compounds (the degree of useful use of HNO ₃ vapor)

The degree of vapor decomposition of HNO ₃ according to reaction 3 is found by the difference

Example 2. Heated by electric heating, up to about 300 ^o C reactor and up to 90 ^o C saturator with 60% HNO ₃ . An air flow of 560 l / h was supplied to the reactor. The hydrogen supply was turned on; it was ignited when exiting the burners with a direct flame. The consumption of hydrogen was adjusted to 140 l / h. The temperature of the gas rose to 900 ^o C (regulated by the flow of components and electric heating). Air was supplied to the saturator in an amount of up to 490 l / h, which at a temperature of 93 ^° C was saturated with acid and water vapors (see Example 1). The streams were mixed and, at a temperature of 760 ^° C, entered the catalyst, where the reactions of nitrogen oxidation, decomposition of HNO ₃ and oxidation, to a small extent, of NO by oxygen took place.

На реакционной воде может быть выпущено 71% HNO₃. При выпуске 60% HNO₃ в абсорбционную колонну необходимо добавлять 235 кг H₂O/т HNO₃, то есть, трудностей с абсорбцией не должно быть. Концентрация оксидов азота составила 19,02 об.Gases had the composition:
To catalyst
HNO ₃ - 180.0 L / h 11.76%
N ₂ - 826.1 l / h 54.00%
O ₂ - 149.6 l / h 9.78%
H ₂ O - 374.3 L / h 24.48%
Total: 1,532.0 L / hr 100.00%
After catalyst
N ₂ - 754.1 l / h 44.33%
O ₂ - 158.6 l / h 9.32%
H ₂ O - 464.3 L / hr 27.40%
NO ₂ - 108.0 L / h 6.35%
NO - 218.0 L / hr 12.70%
Total: 1701.0 L / hr 100%

71% HNO ₃ can be released on reaction water. When 60% HNO ₃ is discharged, 235 kg of H ₂ O / t HNO ₃ must be added to the absorption column, that is, there should be no difficulties with absorption. The concentration of nitrogen oxides was 19.02 vol.

 Example 3. The experiment was conducted on the setup described in examples 1 and 2, however, instead of hydrogen, a nitrogen-hydrogen mixture was used. The methodology of experiment 2 was used.

173 liters of a nitrogen-hydrogen mixture (130 liters of hydrogen) and 620 liters of air were supplied to the burners. 400 l of air was supplied to the saturator at a temperature of nitric acid of 95 ^o C.

The composition of gases is determined on the basis of the results of analyzes, readings of rheometers and material balance
To the burner (calculated by measuring 2 streams)
H ₂ - 130.0 l / h 16.25% vol.

N ₂ - 533.4 l / h 66.67% vol.

O ₂ - 130.3 l / h 16.24% vol.

H ₂ O - 6.3 L / h 0.79% vol.

Газ может быть переработан в HNO₃, так как при концентрации прод. кислоты 60% HNO₃ орошение составляет ~ 250 кг H₂O/т HNO₃.Total: 800 l / h 100%
After burner
N ₂ - 533.4 l / hour 72.6%
O ₂ - 65.3 l / h 8.9%
H ₂ O - 136.3 L / h 18.5%
Total: 735.0 L / h 100%
Side stream
HNO ₃ -175.0 L / h 22.0%
H ₂ O -220.0 L / h 27.6%
O ₂ - 84.0 l / h 10.6%
N ₂ - 316.6 l / h 39.8%
Total: 795.0 L / hr 100%
To catalyst
HNO ₃ - 175.0 l / h 11.4%
N - 849.4 L / h 55.5%
O ₂ - 149.3 l / h 9.8%
H ₂ O - 356.3 L / h 23.3%
Total: 1,530 l / h 100%
After catalyst
N ₂ - 775.9 l / h 45.7%
O ₂ - 156.3 l / h 9.2%
H ₂ O - 443.8 l / h 26.1%
NO - 220.5 L / hr 13.0%
NO ₂ - 101.5 L / h 6.0%
Total: 1,698.0 l / h 100%

The gas can be processed into HNO ₃ , since at a concentration of prod. acid 60% HNO ₃ irrigation is ~ 250 kg H ₂ O / t HNO ₃ .

 The proposed method for conducting the process of producing nitrogen oxides can be adopted both under atmospheric and elevated pressure. It allows you to widely change the temperature, composition and amount of the head stream, and by changing the temperature, the concentration of acid and the amount of air - the volume of the supplied oxidizing agent.

 In turn, these capabilities provide the use of a new method for producing various products of bound nitrogen.

 The effectiveness of the method relative to the prototype is obvious - the production of hydrogen is only one of the stages of obtaining ammonia (raw materials in the prototype), and the least complicated.

Claims (2)

 1. A method of producing nitrogen oxides by the catalytic oxidation of molecular nitrogen by its oxygen compounds, comprising producing and mixing a stream of nitrogen-containing gas with a stream of gas containing an oxidizing agent in the form of oxygen compounds of nitrogen, for example, nitric acid vapor, an energy stream using its combustion products to carry out the oxidation reaction nitrogen in the catalyst bed at elevated temperature, characterized in that the products of combustion of a hydrogen-containing gas are used as an energy flow, obtained by burning or catalytic oxidation of hydrogen in a stream of air or other oxygen-containing gas.  2. The method according to claim 1, characterized in that the nitrogen oxidation catalyst in the reactor is arranged in several layers, in front of each of which a gas stream with an oxidizing agent is introduced and a gas stream carrying thermal energy can be introduced.

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