WO1998050324A1

WO1998050324A1 - Reducing pollutant gases in gas mixtures from pyrotechnic reactions

Info

Publication number: WO1998050324A1
Application number: PCT/EP1998/002562
Authority: WO
Inventors: Ulrich Bley; Klaus Redecker; Martin Reichelt; Waldemar Weuter
Original assignee: Dynamit Nobel Gmbh Explosivstoff- Und Systemtechnik
Priority date: 1997-05-02
Filing date: 1998-04-30
Publication date: 1998-11-12
Also published as: DE19819623A1; BR9808712A; JP2001525782A; EP0979219A1; CN1253538A

Abstract

The invention relates to a method, agents and a device for reducing pollutant gases in gas mixtures resulting from pyrotechnic reactions. To this end, at least one additive from the group of metallocenes, metallocene derivatives, urea, urea devivatives, sulphur and/or sulphur compounds is vaporized during the pyrotechnic reaction, as a result of the temperature released during said reaction. The pollutant gases are converted into non-toxic compounds in a homogenous gas phase reaction.

Description

Reduction of harmful gases in gas mixtures from pyrotechnic reactions

The present invention relates to the reduction of harmful gases in gas mixtures from pyrotechnic reactions

An airbag system consists of the basic components of the impact bag, gas generator and trigger device, which, if necessary, initiates an electrical ignition in the gas generator if a predetermined trigger threshold is exceeded.This produces a gas within a very short time (approx. 40 ms, depending on the airbag module) an airbag flows in, which spreads between the vehicle occupant and the point of impact A gas mixture (propellant, propellant) is a solid mixture of fuel, oxidizing agent and additives in the form of tablets, which reacts within 10 to 40 ms within the combustion chamber after ignition

So far, mainly sodium azide (NaJS) has been used as fuel for gas generation as a gas-producing substance (blowing agent, propellant). The great advantage of azide generators is that the released gas consists of almost 100 percent nitrogen and is therefore not hazardous to health because of the high toxicity of sodium azide (LD ₅₀ value of 27 mg / kg), which is comparable to potassium cyanide (cyanide), however, the problems with the disposal and recycling of airbag gas generators of the end-of-life vehicles as well as the dangers and risks of criminal misuse increased with further use become

Suitable alternative substances are organic, nitrogen-rich compounds that achieve similarly good performance values (gas yield, pressure curve, etc.) as sodium azide. Extensive studies and analyzes by the applicant have shown that 5-aminotetrazole is suitable as an environmentally compatible alternative fuel. The result was a blowing agent made of 5- Aminotetrazole, oxidizing agents and additives called SINCO When alternative solid fuels such as 5-aminotetrazole are burned up, not only the non-toxic working gases nitrogen, carbon dioxide and water vapor, but also parts of the toxic gases carbon monoxide, nitrogen monoxide and nitrogen dioxide are produced

The object of the present invention was therefore to achieve a minimization of the harmful gas concentrations when using the alternative solid fuels

The NO formation (all types) is generally favored at higher temperatures and longer dwell times of the gases or exhaust gases in the high-temperature range.The processes for nitrogen oxide reduction known to date in the prior art are mainly based on a lowering of the combustion temperature Cooling of the exhaust gases prevented However, the low combustion temperatures have the disadvantage that they increase the CO formation. Uneven combustion processes can lead to the strong formation of both harmful gases. Local or short-term overheating causes NO formation and local or short-term supercooling causes CO formation

An alternative to NO negative pressure is combustion in catalyst-coated pores or capillary spaces. Catalytic combustion processes are very low in pollutants, but also sensitive to the operating conditions and require expensive catalyst materials

The object on which the invention is based was achieved by introducing substances into the flow path of the working gas, for example by coating components of the gas generator. The introduced substance is evaporated by the heat of combustion, which causes the harmful gases to be converted into nontoxic compounds in a homogeneous gas phase reaction

The substances to be used according to the invention for reducing nitrogen oxides for use in airbag gas generators must meet the following requirements Non-toxic

- »Problems with disposal and recycling are avoided.

Melting point> 105 ° C

- In strong sunlight, the airbag module can be heated up to 105 ° C. It must be ensured that the additive does not liquefy in such a case and escapes from the airbag module. Therefore, only substances with a melting point> 105 ° C can be used.

Evaporation below 400 ° C

- At the points in the gas generator where the additive is to evaporate, the rapid cooling of the gas does not result in temperatures higher than 400 ° C.

Long-term stability (15 years)

- »A gas generator should be fully operational over the entire lifespan of a car (up to 15 years).

• No health hazard due to gases

-> The gases released during evaporation must not be harmful to health and must not undergo any reactions that lead to toxic compounds.

• Effect of nitrogen oxide reduction

- »The introduced substance should reduce nitrogen oxides in a homogeneous gas phase reaction.

Inexpensive The following substances, which can be divided into three groups of substances, meet these criteria (Table 1).

Metallocenes and urea and sulfur and their derivatives urea derivatives sulfur compounds

Ferrocene urea sulfur

1, 1 '-diacetylferrocene N-formylurea (Titanocenpentasulfid)

Titanocene pentasulfide N, N '-dimethylurea N.N-dimethylurea

Table 1: Overview of the substances used

The tests were carried out in an apparatus which enables the measurement of the concentration curves of nitrogen monoxide and nitrogen dioxide over time in a reaction vessel with a volume of 60 l.

The process flow diagram of the experimental apparatus is shown in FIG. 1. It can be divided into the following system parts:

• the gas supply

• the batch reactor

• the nitrogen oxide analyzer with its auxiliary units.

The experimental apparatus essentially consists of the plastic set reactor and the nitrogen oxide analyzer. At the beginning of each experiment, nitrogen monoxide is metered into the reactor, which partially converts with the atmospheric oxygen into nitrogen dioxide after an equilibrium reaction. The temperature in the reactor is 45 ° C. in all experiments. After about 10 minutes, when the nitrogen dioxide concentration hardly changes, the respective substance is evaporated in the container. By regularly recording the values for nitrogen dioxide or Nitrogen monoxide concentration, the concentration curves can be determined, which allow statements about the effectiveness of the respective substance

With this experimental apparatus, results can be achieved that enable a comparison of substances with regard to their effectiveness for reducing nitrogen oxides

The experiments have surprisingly shown

- A reduction of the nitrogen dioxide concentration was achieved with all tested substances

- Ferrocene shows the best effect. With comparatively small amounts, a quick breakdown of nitrogen dioxide is achieved

The following experiments are intended to explain the invention without restricting it

Experiment setup:

Plastic was chosen as the material for the reactor in order to avoid reactions that can occur on a metallic wall. The plastic container used is not very temperature-resistant.Therefore, the temperature in the container should not exceed 45 ° C, so that no deformation of the container wall occurs the reactor has an evaporator and a fan heater The evaporator essentially consists of a heating plate that can be continuously heated to 350 ° C, on which the test substances can be heated to sublimation or boiling temperature in a glass dish. The fan heater is used to set a desired temperature and to intensive mixing of the reaction mixture The mixing is necessary in order to ensure the same reactant concentrations and temperatures throughout the reactor. With one connected to the heater of the fan heater, the temperature in the reactor can be set and readjusted manually The temperature in the container must be adjusted due to the heat loss via the wall, the heat supply via the heating plate and the endothermic or exothermic reactions taking place in the reactor. The temperature is measured using a thermocouple connected to a voltmeter For the concentration measurement of the nitrogen oxides (NO, NO ₂ ), a chemiluminescence device is used, to which the bypass pump, the silica gel drying cartridge and the ozone destroyer / pump unit are connected. To protect the chemiluminescence device from contamination, the reactor and the chemiluminescence device built a microfiber filter

The nitrogen monoxide is supplied with the help of a gas bag, which, once filled, is connected to the three-way valve. The calibration gas (nitrogen with 80 ppm nitrogen monoxide) is fed directly from the pressure bottle to the chemiluminescence device via a pressure reducer. The gas should therefore flow into the analyzer without pressure Flowing out approx. 50% or 0.6 1 / min of the required amount of gas via a T-piece with an excess line. The excess is led into a fume cupboard. The excess line has a length of more than 2 m in order to avoid mixing the calibration gas with the atmospheric air In addition, a flow meter is attached to the line in order to be able to control the specified value for the volume flow. Only pipes with a smooth surface and made of inert material such as PTFE, glass or steel were used as gas lines

Carrying out the experiment:

A certain amount of the substance to be tested is weighed into a glass bowl and evenly distributed on the glass bottom. Then the glass is placed in the middle of the heating plate and the temperature setting of the evaporator is checked. Then you put the lid on the plastic container and press the lever on the clamping ring Now the screw connections on the container connections are tightened to ensure that the container is watertight. The thermocouple is connected to the voltmeter and the cables from the fume cupboard and filter must be set with the three-way cocks on the container cover, which must be set so that the container is closed. When the container air is heated to 45 ° C with the fan heater, the calibration can be carried out As soon as the temperature in the reactor has reached 45 ° C, 1 nitrogen monoxide is metered into the container via a gas bag on the three-way valve Same Weight reaction partly in nitrogen dioxide implemented As soon as the nitrogen monoxide is in the reactor, the measurement of the time is started

The first measured value is recorded after about 30 seconds and the second after about 5 minutes. The preheating time that was determined before the measurement determines a point in time at which the evaporator is switched on, so that the substance evaporates after about 10 minutes begins At this time, the plastic container is in a state in which the nitrogen dioxide concentration changes only slowly

Shortly before the substance evaporates, a measured value is read from the chemiluminescence device and entered in the measurement protocol. The time intervals between the measurement points after the boiling point has been reached depend on the course of the reaction that results with a specific substance. The measurement values are recorded over a period of 25 - 30 minutes carried out During the entire measurement, the temperature in the reactor must be constantly checked and, if necessary, readjusted by hand using a dimmer

After completing the measurement, the plastic container must be opened outdoors and ventilated for at least 15 minutes. Then the hoses, filter, container and three-way cock are thoroughly cleaned and dried

Trial program:

First, three experiments were carried out without the evaporation of an additive. As a result, the course of the concentration of nitrogen monoxide and nitrogen dioxide could be shown without the influence of a substance converted into the gas phase. It was also possible to compare the experimentally determined values with the theoretically calculated values.

Table 2 shows an overview of the tests carried out with the additives.

Table 2. Overview of the tests carried out From Table 2 it can be seen that for some substances - a substance was selected from each group of substances - the influence of carbon monoxide gas on the reactions taking place in the container was also investigated.

Influence of ferrocene on nitrogen oxide concentrations:

The effects of the evaporation of 0.015 g ferrocene on the nitrogen monoxide and nitrogen dioxide concentrations were determined in the test apparatus. In the initial phase of the measurement, the concentration over time is as expected. The nitrogen monoxide concentration falls due to the oxidation of the nitrogen monoxide with the atmospheric oxygen, which increases the nitrogen dioxide concentration. As soon as the ferrocene is in the gas phase (after 540 s) a steep, almost linear decrease in the nitrogen dioxide concentration begins. It decreases by 40 ppm within 35 seconds. The nitrogen monoxide concentration remains constant at a value of 178 ppm during this period. Then it continues to drop and the nitrogen dioxide concentration increases again.

To check the first measurement, two further tests were carried out with 0.015 g ferrocene and similar nitrogen oxide concentrations. In the two repeat measurements, the same concentration profiles are shown as in the first measurement. As soon as the ferrocene is in the gas phase, the nitrogen dioxide concentrations decrease rapidly. In experiment no.2 it is 39 ppm in 43 s and in experiment no.3 it is 45 ppm in 45 s. The nitrogen monoxide concentrations remain constant during this time.

When the amount of ferrocene is increased to 0.0225 g ferrocene, the drop in the concentration of nitrogen dioxide increases. The concentration drops by 90 ppm in 88 s. This corresponds to a reduction twice as large as in the tests with an amount of 0.015 g of ferrocene. On the other hand, a further increase in the amount of substance to 0.03 g does not result in an increase in the reduction in concentration. The nitrogen dioxide concentration is reduced by 88 ppm within 75 s. The results were confirmed in two further measurements.

Table 3 clearly shows the nitrogen dioxide reduction values for all measurements.

Table 3: Overview of nitrogen dioxide reduction by ferrocene in the gas phase

The combustion gases of a gas generator contain not only nitrogen oxides, but also carbon monoxide. For this reason, 3 measurements with a substance amount of 0.03 g ferrocene and the same test conditions as in the previous tests were additionally carried out with carbon monoxide gas in order to identify possible effects of carbon monoxide on the results. The ratio CO to NO ₂ in the combustion gases of a gas generator is about 10 to 1. This concentration ratio was set in the reactor. The CO gas content was measured using Dräger tubes (relative standard deviation: ± 10 to 15%). The results show that the nitrogen monoxide and nitrogen dioxide concentration curve does not change with carbon monoxide gas. Table 4 compares the values for nitrogen dioxide reduction with and without carbon monoxide.

Table 4: Overview of nitrogen dioxide reduction with and without carbon monoxide Interpretation of the results:

In order to explain the results of the experiments with ferrocene, an FT-IR analysis of the residue that forms in the reactor was carried out. For this purpose, the reactor was rinsed out with water after an experiment. The resulting mixture was then evaporated in a rotary evaporator Residue dried in the drying cabinet, the KBr compact was made for FT-IR analysis and then analyzed in an FT-IR device

In addition to the FT-ER analysis, a GC analysis was also carried out to identify the gaseous products. 100 mg of ferrocene were stored in a headspace glass for two hours at 80 ° C. in order to convert part of the ferrocene into the gas phase Glasses 3 ml of a NO / NO ₂ mixture added 2 ml of gas from the headspace glass were analyzed in a gas chromatograph. It was found that cyclopentadiene is also in the gas phase in addition to the ferrocene and air components.

The previous investigations suggest that ferrocene reacts with nitrogen dioxide in a redox reaction to give ferric oxide, cyclopentadiene and nitrogen

3 N02 2 2 FFeΘ∑2OÜa3 ++ 88 (6 (J)

, , -5 N

This equation explains the rapid decrease in nitrogen dioxide concentrations in the experiments. The constant nitrogen monoxide values could be due to the fact that the nitrogen dioxide is only partially reduced to nitrogen monoxide and therefore formation and degradation are in equilibrium Influence of U'-diacetylferrocene on nitrogen oxide concentrations:

The course of the nitrogen oxide concentrations was investigated in an experiment with 0.1 g of 1,1'-diacetylferrocene. The concentrations change as expected until the substance evaporates. The nitrogen monoxide values decrease due to the oxidation and the nitrogen dioxide values increase shortly after the start of the The evaporation process increases the nitrogen monoxide concentration by 23 ppm in 233 s - initially stronger, then becoming weaker - The nitrogen dioxide concentration also drops by 26 ppm. Then the normal NO / NO ₂ equilibrium is restored

The results of the 1 experiment were confirmed in two further measurements with 0.1 g of 1,1'-diacetylferrocene. In the 2 experiment, the NO ₂ concentration decreased by 23 ppm in 262 s and the NO concentration increased by 25 ppm In a 3 experiment it was determined that the NO values drop by 24 ppm in 250 s and the NO values increase by 23 ppm

When only 0.05 g of 1,1'-diacetylferrocene was introduced into the gas phase, it was found that the values for the decrease in nitrogen dioxide and for the increase in nitrogen monoxide were about half lower than the tests with 0.1 g (Table 5) Qualitatively, the course of the concentrations as a function of time are identical

Table 5 clearly shows all the results of the experiments with 1,1'-diacetylferrocene

Table 5: Overview of the increase and decrease in the concentrations of NO and N0 ₂ Interpretation of the results:

From Table 5 it can be seen that a decrease in nitrogen dioxide results in a corresponding increase in nitrogen monoxide. This effect probably results from a redox reaction of l, l'-diacetylferrocene with nitrogen dioxide, which is accordingly reduced to nitrogen monoxide. Compared to ferrocene, the ferrocene derivative 1,1'-diacetylferrocene is a much poorer reducing agent with the additional disadvantage of nitrogen monoxide formation.

Influence of titanocene pentasulfide on nitrogen oxide concentrations:

The effects on nitrogen monoxide and nitrogen dioxide, which result from the evaporation of 0.05 g of titanocene pentasulfide, were investigated. The nitrogen dioxide concentration drops almost linearly in 25 s from 253 ppm to 225 ppm due to titanocene pentasulfide in the gas phase. The nitrogen monoxide concentration, however, increases in the same way from 269 ppm to 298 ppm. Before the evaporation and after the reaction of the titanocene pentasulfide with the nitrogen oxides, the normal concentration courses result, i.e. Decrease in nitrogen monoxide due to oxidation and consequently an increase in nitrogen dioxide.

Two further experiments with 0.05 g of titanocene pentasulfide led to similar results as in the first experiment. The exact values for the changes in the concentrations can be found in Table 6, in which all the results of the three measurements are summarized.

Table 6: Overview of the increase and decrease in the concentrations of NO and NO ₂

By increasing the amount of substance from 0.05 g to 0.1 g, the values for the increase in nitrogen monoxide and the reduction in nitrogen dioxide have roughly doubled. In 103 s, the nitrogen dioxide concentration dropped from 351 ppm by 50 ppm to 301 ppm. During the same period, the nitrogen monoxide concentration increased from 306 ppm by 48 ppm to 354 ppm. Two further tests with 0.1 g of titanocene pentasulfide give consistent results, which are summarized in Table 7.

Table 7: Overview of the increase and decrease in the concentrations of NO and NO

An increase in the amount of substance to 0.15 g caused a further decrease in nitrogen dioxide and a corresponding increase in nitrogen monoxide. The nitrogen monoxide concentration increases by 75 ppm in 130 s, at the same time the nitrogen dioxide concentration drops by 77 ppm. Comparable results are achieved in the two replicate tests (see Table 8), which are shown in Figures A.19 and A.20 in the Appendix.

Table 8: Overview of the increase and decrease in the concentrations of NO and NO ₂

Interpretation of the results:

An FT-IR analysis of the residue that has formed in the reactor should provide information about the reaction mechanism. In the FT-ER spectrum obtained, everything indicates that the residue consists of titanocene pentasulfide and titanium (IV) oxide (TiO ₂ ) There is therefore a high probability that the titanocene pentasulfide will undergo a redox reaction with nitrogen dioxide, in which the reaction products cyclopentadiene, nitrogen monoxide, titanium (IV) oxide and sulfur are formed. This explains the simultaneous formation of nitrogen monoxide during the decomposition of nitrogen dioxide

Influence of urea on nitrogen oxide concentrations:

With nitrogen monoxide there are no noticeable changes in the concentration curve when urea is evaporated in the reactor.On the other hand, there is a decrease in the concentration of nitrogen dioxide from 82 ppm to 54 ppm.This reduction of 28 ppm takes place in 410 s to The two replicate tests confirm these results. Table 9 shows all the results of the tests with 0.1 g of urea

Table 9: Overview of the decrease in the NO ₂ concentration

When using 0.4 g of urea, the nitrogen dioxide is broken down significantly more than when 0.1 g of urea is added. In the first 300 s after the start of the evaporation process, the nitrogen dioxide concentration decreases relatively quickly. The values then decrease further with decreasing speed. At the end of the measurement, a drop in the nitrogen dioxide concentration can still be determined. Overall, the nitrogen dioxide is reduced by 111 ppm in 20 minutes. Table 10 shows all the results obtained with 0.4 g of urea.

Table 10: Overview of the decrease in the NO ₂ concentration

An increase in the amount of urea to 0.7 g leads to even higher values for the decrease in nitrogen dioxide. The nitrogen dioxide concentration is reduced by 179 ppm in 1200 s. Otherwise, the qualitative course of the measured values is identical to the course that resulted when using 0.4 g of urea. The results of the repeat tests can be found in Table 11.

Table 11: Overview of the decrease in the NO ₂ concentration

Interpretation of the results:

When the urea is heated above the melting point, ammonia (NH ₃ ) is produced, which is known as a reducing agent for nitrogen oxide reduction. It can be assumed that the nitrogen dioxide decomposition takes place through a homogeneous gas phase reaction of ammonia with nitrogen dioxide. The reduction of NO ₂ with NH ₃ can be described by the following gross reaction equations:

Main reactions 6 NO ₂ + 8 NH ₃ 7 N ₂ + 12 H ₂ O

2 NO ₂ + 4 NH ₃ + O ₂ 3 N ₂ 6 H ₂ O

Side reaction

12 NO ₂ + 16 NH ₃ + 7 O ₂ 14 N ₂ O + 24 H ₂ O

• The reaction products of this selective reduction are nitrogen (N ₂ ) and water vapor in the main reactions. The undesirable dinitrogen monoxide (N ₂ O) from the side reaction does not seem to form to a substantial extent.

Nitrogen monoxide is inert compared to nitrogen dioxide. This could be the reason why the nitrogen monoxide is not reduced with ammonia at a temperature of 45 ° C. Influence of N-formylurea on nitrogen oxide concentrations:

When 0.1 g of N-formylurea is evaporated, the nitrogen dioxide concentration begins to drop relatively slowly from the time 750 s to the time 1230 s. The concentration is reduced from 162 ppm by 12 ppm to 150 ppm. After that, the values remain almost constant. There are no noticeable changes in the nitrogen monoxide concentration curve.

Table 12 summarizes all the results which were achieved in the 3 experiments with 0.1 g of N-formylurea.

Table 12: Overview of the decrease in the NO ₂ concentration

In order to investigate the effects on nitrogen oxides when increasing the amount of substance, 3 tests were carried out with 0.4 g and 0.7 g N-formylurea.

By evaporating 0.4 g of N-formylurea, the nitrogen dioxide concentration is reduced by 63 ppm in 460 s. Similar results are obtained in the 2nd and 3rd experiments with an NO reduction of 54 ppm and 66 ppm, respectively. Table 13 gives an overview of all results. There were no changes in the qualitative course of the concentrations compared to the tests with 0.1 g.

Table 13: Overview of the decrease in the NO ₂ concentration

In contrast to the tests with 0.1 g or 0.4 g quantity of substance, the nitrogen dioxide concentration drops even more slowly after using a relatively quick decrease when using 0.7 g N-formylurea. This results in a selected period of 1000 s a nitrogen dioxide reduction of 85 ppm The two replicate tests confirm this result (see Tab. 14)

Table 14: Overview of the decrease in the NO ₂ concentration

Interpretation of the results:

When N-formylurea is heated above the melting point, ammonia is presumably formed. The homogeneous gas phase reactions that result from this are the same as stated for urea. N-formylurea has a higher molar mass than urea because of the formyl group N-formylurea less ammonia than with urea This explains the poorer values for nitrogen dioxide reduction compared to the tests with urea

Influence of N, N'-dimethylurea on nitrogen oxide concentrations:

The influence of 0.1 g of N, N'-dimethylurea was investigated. With nitrogen monoxide there were no changes compared to the normal course of the concentration the nitrogen dioxide content is reduced by 48 ppm in 465 s. After this reduction, the values for the nitrogen dioxide concentration remain almost constant until the end of the measurement. Table 15 shows all the results of the 3 experiments with 0.1 g of N, N'-dimethylurea. The results of the repeat attempts show no significant differences from the first attempt.

Table 15: Overview of the decrease in the NO ₂ concentration

Evaporation of 0.4 g of N, N'-dimethylurea in the reactor leads to the following changes in the NO ₂ concentration curve. The nitrogen dioxide concentration drops from 210 ppm by 106 ppm to 102 ppm in 286 s. Then the measured values rise again comparatively slowly. In the 2nd and 3rd experiment with 0.4 g of N, N'-dimethylurea, values of 101 ppm and 102 ppm for the nitrogen dioxide decrease are obtained. All results are clearly shown in Table 16

Table 16: Overview of the decrease in the NO ₂ concentration

An increase in the amount of substance to 0.7 g did not lead to a significant increase in the values for the nitrogen dioxide decrease compared to the tests with 0.4 g. It was found that the nitrogen dioxide concentration decreased by 105 ppm in a period of 675 s. In addition to this result, Table 17 also shows the results of the two replicate tests.

Table 17: Overview of the decrease in the NO ₂ concentration

In order to also be able to investigate possible influences of carbon monoxide, 3 tests were carried out with 0.1 g of N, N'-dimethylurea and a carbon monoxide / nitrogen oxide mixture. Compared to the measurement without carbon monoxide, there are no noticeable changes in Table 18 as in the two repeat tests an overview of the results with and without carbon monoxide

Table 18: Overview of nitrogen dioxide reduction with and without carbon monoxide

Interpretation of the results:

When N, N'-dimethylurea is heated above the melting point, ammonia is likely to form, which reduces part of the nitrogen dioxide by means of homogeneous gas-phase reactions. If one compares the results with those obtained in the tests with urea, it is clear that the effect of Use of N, N'-dimethylurea is worse, except for the experiments with 0.1 g of substance. The worse values for nitrogen dioxide degradation depend, as with N-formylurea, with the higher molar mass and thus the smaller amount of ammonia that is produced when heated. together The better values when comparing the tests with 0.1 g substance amount may result from a positive influence of the two methyl groups. This can also be the reason that the values for nitrogen dioxide degradation compared to the tests with N-formylurea are higher Influence of N y'-dimethylurea on the nitrogen oxide concentrations:

The influence on the nitrogen oxide concentrations due to the evaporation of 0.1 g of N, N'-dimethylurea was investigated. With nitrogen monoxide there are no changes compared to the normal course of the concentration. In contrast, the nitrogen dioxide content is reduced by 48 ppm in 465 s the values for the nitrogen dioxide concentration almost constant until the end of the measurement. Table 19 lists all the results of the 3 tests with 0.1 g of N, N'-dimethylurea. The results of the repeat tests show no significant differences from the 1 test

Table 19: Overview of the decrease in the NO ₂ concentration

The evaporation of 0.4 g of N, N'-dimethylurea in the reactor leads to changes in the NO ₂ concentration curve. The nitrogen dioxide concentration drops from 210 ppm in 286 s to 106 ppm after 102 ppm. The measured values then rise again comparatively slowly 2 and 3 tests with 0.4 g of N, N'-dimethylurea give values of 101 ppm and 102 ppm for the decrease in nitrogen dioxide. All results are clearly shown in Table 20

Table 20: Overview of the decrease in the NO ₂ concentration An increase in the amount of substance to 0.7 g did not lead to a significant increase in the values for the nitrogen dioxide decrease compared to the tests with 0.4 g. The nitrogen dioxide concentration decreases by 105 ppm in a period of 675 s This result also shows the results of the two repeat attempts

Table 21: Overview of the decrease in the NO ₂ concentration

In order to also be able to investigate possible influences of carbon monoxide, 3 tests were carried out with 0.1 g of N, N'-dimethylurea and a carbon monoxide / nitrogen oxide mixture. As with the two repeat attempts, there are no noticeable changes in Table 22 compared to the measurement without carbon monoxide an overview of the results with and without carbon monoxide

Table 22: Overview of nitrogen dioxide reduction with and without carbon monoxide

Interpretation of the results:

When N, N'-dimethylurea is heated above the melting point, ammonia is likely to form, which reduces part of the nitrogen dioxide by means of homogeneous gas-phase reactions. If one compares the results with those obtained in the tests with urea, it is clear that the effect of Use of N, N'-dimethylurea is worse, except for the experiments with 0.1 g of substance As with N-formylurea, the poorer values for nitrogen dioxide degradation are related to the higher molar mass and thus the smaller amount of ammonia that is produced when heated. The better values when comparing the tests with 0.1 g of substance may result from a positive influence of the two methyl groups This can also be the reason why the values for the nitrogen dioxide degradation are higher than those of the experiments with N-formylurea

Influence of N, N-dimethylurea on nitrogen oxide concentrations

Evaporation of 0.1 g of N, N-dimethylurea resulted in a reduction of the nitrogen dioxide concentration by 46 ppm. It decreases from 102 ppm to 66 ppm in 690 s and then increases again slightly. Dimethyl urea obviously no influence. Experiments Nos. 2 and 3 give identical results. Table 23 summarizes all the results of the 3 experiments

Table 23: Overview of the decrease in the NO ₂ concentration

0.4 g of N, N-dimethylurea, compared to the tests with 0.1 g, caused the values for the nitrogen dioxide reduction to double in a shorter period of time. The results of the 3 tests carried out are summarized in Table 24

Table 24: Overview of the decrease in the NO ₂ concentration

A further decrease in the NO ₂ concentration was achieved with 0.7 g of N, N-dimethylurea. The NO ₂ content drops by 101 ppm in 330 s. The corresponding values of the two replicate tests are shown in Table 25.

Table 25: Overview of nitrogen dioxide reduction

Interpretation of the results:

The results of the experiments with N, N'-dimethylurea and N, N-dimethylurea are very similar. Consequently, the different arrangement of the methyl groups on the urea is not so important. The explanation of the results is analogous to that for the experiments with N, N'-dimethylurea.

Influence of sulfur on nitrogen oxide concentrations:

The use of 0.05 g of sulfur causes the nitrogen dioxide concentration to decrease by 20 ppm and the nitrogen monoxide concentration to increase by 9 ppm within 355 s. The nitrogen dioxide then slowly rises again due to the oxidation of the nitrogen monoxide, which is thereby reduced. The two repeat attempts lead to the same results, as shown in Table 26.

Table 26: Overview of the increase and decrease in the concentrations of NO and NO ₂

In a test with 0.1 g of sulfur, compared to the test with 0.05 g of sulfur, there are slightly different values for the NO increase or the NO ₂ decrease. In a period of 375 s, the nitrogen dioxide concentration decreases by 30 ppm and the nitrogen monoxide concentration increases by 10 ppm. These values are confirmed by tests No. 2 and 3. The results of all measurements with 0.1 g sulfur are given in Table 27.

Table 27: Overview of the increase and decrease in the concentrations of NO and NO ₂

With a sulfur amount of 0.15 g, the nitrogen dioxide concentration could be reduced even further, but the nitrogen monoxide concentration also increased somewhat. The nitrogen dioxide content decreases by 39 ppm within 370 s, while the nitrogen monoxide content increases by 21 ppm. The two replicate tests produce corresponding results, which are also shown in Table 28.

Table 28: Overview of the increase and decrease in the concentrations of NO and NO ₂

In addition, three tests with 0.1 g sulfur and a carbon monoxide / nitrogen oxide mixture were carried out. As can be seen from Table 29, no effect of carbon monoxide on the results can be determined. The nitrogen dioxide concentration decreases by 31 ppm in 390 s and the nitrogen monoxide concentration increases by 10 ppm.

Table 29: Increase or decrease in the concentrations of NO and NO with and without CO

Interpretation of the results: Sulfur ignites at approx. 260 ° C and burns with a weak blue flame to sulfur dioxide and up to 40% sulfur trioxide. Below 300 ° C, NO ₂ reacts immediately with SO ₂ :

NO ₂ + SO ₂ NO + SO ₃

In addition to sulfur trioxide, this also produces nitrogen monoxide, which presumably can also react with sulfur dioxide:

2 NO + SO ₂ N ₂ O + SO ₃

This equation would also explain why NO does not increase as NO _{2 is} broken down.

Claims

Claims:

1. A process for reducing harmful gases in gas mixtures from pyrotechnic reactions, characterized in that in the pyrotechnic reaction at least one additive from the group of metallocenes, metallocene derivatives, urea, urea derivatives, sulfur and / or sulfur compounds is released by the pyrotechnic reaction increasing temperature is evaporated and the harmful gases are converted into non-toxic compounds in a homogeneous gas phase reaction.

2. A method for reducing harmful gases in gas mixtures from pyrotechnic reactions according to claim 1, characterized in that the selected additive has a melting point> 105 ° C and evaporates below 400 ° C.

3. A method for reducing harmful gases in gas mixtures from pyrotechnic reactions according to claim 1 or 2, characterized in that as an additive ferrocene, 1,1 '-diacetylferrocene, titanocene pentasulfide, urea, N-formylurea, N, N'-dimethylurea, N, N-dimethylurea and / or sulfur, preferably ferrocene, is used.

4. Means for pyrotechnic gas production, characterized in that it contains an additive from the group of metallocenes, metallocene derivatives, urea, urea derivatives, sulfur and / or sulfur compounds in addition to the gas-generating substance, which evaporates by the temperature released during the pyrotechnic reaction.

5. agent for pyrotechnic gas generation according to claim 4, characterized in that the selected additive has a melting point> 105 ° C and evaporates below 400 ° C.

Agent for pyrotechnic gas generation according to claim 4 or 5, characterized in that as additive ferrocene, 1,1 '-diacetylferrocene, titanocene penta- sulfide, urea, N-formyl urea, N, N'-dimethyl urea, N, N-dimethyl urea and / or sulfur, preferably ferrocene, is used.

7. Agent for pyrotechnic gas generation according to one of claims 4 to 6, characterized in that at least one component of the gas-generating substance is coated with the additive.

8. A device for pyrotechnic gas generation, characterized in that at least one additive from the group of metallocenes, metallocene derivatives, urea, urea derivatives, sulfur and / or in the flow path of the working gas

Sulfur compounds is introduced.

9. A device for pyrotechnic gas generation, characterized in that the selected additive has a melting point> 105 ° C and evaporates below 400 ° C.

10. A device for pyrotechnic gas production, characterized in that as an additive ferrocene, 1,1 '-diacetylferrocene, titanocene pentasulfide, urea, N-formylurea, N, N'-dimethylurea, N, N-dimethylurea and / or Schwei, preferably Ferrocene is used.