Method of reducing NOx

Details Method of reducing NOx Method of reducing NOx

1999-12-20

2003-11-25

Miller, Edward A. (Department: 3641)

Ammunition and explosives

Jacketed or cartridge gas generator

For gas-powered tools or means

C149S108400, C149S019100, C149S036000, C149S046000, C149S061000, C280S741000

Reexamination Certificate

active

06651565

ABSTRACT:

This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP99/00680 which has an International filing date of Feb. 17, 1999, which designated the United States of America.
TECHNICAL FIELD WHICH THE PRESENT INVENTION BELONGS
This invention relates to an NOx reducing method for decreasing the amount of NOx generated by the combustion of a gas generating agent for air bag in an inflator of an air bag system installed in automobiles, airplanes, etc, for protecting human bodies.
This invention relates further to an inflator adopting the above NOx reducing method and an inflator system using the above NOx reducing method and the inflator.
PRIOR ART
Sodium azide is well known at present as a combustion component of a gas generating agent used in air bag systems. The gas generating agent using sodium azide has a high decomposition temperature of 400° C. or above and is excellent in thermal stability. This agent has no problem of its combustion characteristics, in particular, and has therefore gained a wide practical application. However, it is known that sodium azide might result in environmental pollution when it is discarded in large quantities because, for example, sodium azide forms explosive compounds upon reacting with heavy metals, and its peroral toxicity LD
50
of a mouse and a rat is 27 mg/kg.
To solve these problems, novel compounds that may substitute for sodium azide have been examined. For example, JP-B 6-57629 discloses a gas generating agent containing a transition metal complex of tetrazole or triazole. JP-A 5-254977 discloses a gas generating agent containing triaminoguanidine nitrate. JP-A 6-239683 discloses a gas generating agent containing carbohydrazide. JP-A 7-61885 discloses a gas generating agent that contains cellulose acetate, potassium perchlorate and an nitrogen-containing nonmetallic compound. U.S. Pat. No. 5,125,684 discloses a gas generating agent containing 15 to 30% of a cellulose base binder such as nitrocellulose, and an energetic material. JP-A 4-265292 discloses a gas generating composition comprising the combination of tetrazole and triazole derivatives, an oxidizing agent and a slag-forming agent.
A gas generating composition composed of a nitrogen-containing organic compound has, in general, defects such that the heat content is large, a combustion temperature is high, a linear burning rate is small and a trace amount of poisonous gas generates, in comparison with a gas generating composition of an inorganic azide compound when it burns with an oxidizing agent to generate oxygen gas in the stoichiometric amount, that is, in so much an amount as to burn non-oxidized elements such as carbon, hydrogen and others contained in the molecule of the nitrogen-containing organic compound.
Among the gases generated by the combustion of the gas generating agent, it is CO and NOx that render the particular problem. These gases are generated substantially always when organic compounds are burn. When the amount of the organic compound is greater than the theoretical amount of complete oxidation, the trace CO concentration in the generated gas increases, and when the amount of the organic compound is equal to, or smaller than, the theoretical amount of complete oxidation, the trace NOx concentration in the generated gas increases, although the absolute numerical values vary with the kinds of the organic compound and the oxidizing agent used for the gas generating agent. Both of them never reach zero in the combustion of the gas generating agent, and the range within which the optimal balance between them can be maintained must be searched. From the aspect of protection of users, it is demanded that the concentrations of the generated CO and NOx gases should be further reduced, however, no effective method of reducing these has yet to be in practical use. Particularly because the NOx concentration does not much decrease even when the mixing ratio between the organic compound and the oxidizing agent is changed, it is extremely difficult to reduce the NOx concentration.
One of the known NOx reducing methods is a denitration technology in a large-scale process using a boiler and a burner for burning heavy oil, kerosene, coal, propane gas, and so forth. A typical example of this denitration technology is the selective reducing method using NH
3
for removing NOx by the following reaction:
NO+NH
3
+¼O
2
→N
2
+3/2H
2
O
One may attempt to utilize this selective reducing method for the inflator. However, it is not possible to use NH
3
which is a gas (boiling point: −33.4° C.) for a reducing agent. The method using urea in place of the NH
3
gas is known, but this method cannot be applied to practical application because decomposition and sublimation take place in the high temperature test required for the inflator.
WO98/06682 discloses an NOx reducing method using the reducing material selected from the group consisting of ammonium salts, typified by (NH
4
)
2
CO
3
, (NH
4
)
2
SO
4
, NH
4
Cl, H
2
NCO
2
NH
4
and NH
4
F, ammonium hydroxide, amine compounds, amide compounds, typified by H
2
NCONH
2
, and imide compounds typified by cyanuric acid (HNCO)
3
. However, these reducing materials involve various problems caused from the factors such that they have low thermal stability and that they are likely to undergo decomposition with the passage of time.
In the thermal stability test at 105° C., for example, the weight loss ratio of both of (NH
4
)
2
CO
3
and H
2
NCO
2
NH
4
after 18 hours was 100%, whereas the weight loss ratio of H
2
NCONH
2
after 408 hours in the same test was 2.11%. When the reducing materials are decomposed and their weight decreases in this way, a sufficient reduction effect cannot be exhibited, and the rise of the internal pressure due to the generation of the decomposition gas may break the seal of the vessel. Furthermore, ammonia and amino radicals, etc. as the decomposition gas of the reducing materials have high reactivity, so that the decomposition of the gas generating agent itself is induced and therefore, service life of the inflator is shortened. Incidentally, though cyanuric acid is hardly decomposed by heat, its reducing power is low as is obvious from its structure. Therefore, its NOx reducing effect is small.
The reducing materials disclosed in WO98/06682 generate harmful gases to the human body upon decomposition. For example, H
2
S and SOx are generated from (NH
4
)
2
SO
4
; HCl and Cl
2
are generated from NH
4
Cl; and H
2
F and F
2
are generated from NH
4
F. Leak of these harmful gases outside the inflator system cannot be neglected when the influences on the human body are taken into consideration, and also lowers safety of the system as a whole.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a NOx reducing method, in an inflator of an air bag system, such that the amount of the NOx generated by the combustion of a gas generating agent for the air bag can be reduced, and therefore, safety can be further improved in view of the protection of users.
In the inflator for the air bag, the method of the present invention reduces NOx, generated by the combustion of the gas generating agent, using a reducing material or its decomposition products, and reduces the amount of these NOx.
The inflator generally includes a ignition means, the gas generating agent and a coolant/filter.
Preferably, the reducing material is placed in an ignition means accommodation chamber, or in a combustion chamber storing the gas generating agent, or at a position in the proximity of a gas outlet from the ignition means accommodation chamber inside the combustion chamber that stores the gas generating agent, or at a coolant/filter portion.
Preferred examples of the reducing materials include amide compounds, imide compounds, amine compounds, guanidine derivatives, tetrazole derivatives, hydrazine derivatives, triazine derivatives, hydroxylamine salts, sodium salts, NH
4
OH, ammonium salts, cyanates, dicyanamide salt, ammine complexes and CDH complexes.

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