JP3426250B2 - Selective non-catalytic reduction (SNCR) of toxic effluents of airbag inflators - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates generally to inflatable occupant safety restraint systems in motor vehicles, and more particularly to reducing the toxicity of effluent gases produced by non-azide gas generating compositions.

Inflatable occupant safety restraints for motor vehicles have been developed around the world for many years, including the development of gas generating compositions for inflating such occupant restraints. Many of the gas generants currently in use are based on alkali metal azides or alkaline earth metal azides, especially sodium azide, as the inflation gas produced by the gas generant must meet stringent safety standards. . When reacted with oxidants, sodium azide produces a relatively non-toxic gas consisting primarily of nitrogen.

However, azide gas generants are inherently volatile to handle and are relatively dangerous to manufacture and dispose. More specifically, the inflation gas produced by the gas generant with an azide is relatively non-toxic, but the metal azide itself is, on the contrary, very toxic, which makes it redundant for the production, storage and disposal of the gas generant. Costs and risks.
In addition to direct pollution of the environment, metal azides also readily oppose acids or heavy metals to form highly reactive compounds that ignite or explode in an instant.

In contrast, non-azide gas generating agents such as those disclosed in Poole U.S. Pat.
It includes non-azide fuels selected from the group of tetrazole compounds and their metal salts and has a significant advantage over azide generators with regard to toxicity-related hazards during manufacturing and disposal. In addition, many non-azide gas generant compositions typically provide higher yields of gas (moles of gas per gram of gas generant) than conventional azide occupant restraint gas generants.

However, many non-azide gas generating agents known and used to date produce high levels of toxic substances upon combustion. The most difficult to control toxic gases are various nitrogen oxides (NO _x ) and carbon monoxide (C
O). The gas generant of passenger side airbags is typically four times higher than that of the driver side, so even if there is interest in other airbag systems in the vehicle, NO _x and C
The need for O reduction is felt most strongly when designing passenger side airbags.

Toxic NO _x and CO upon combustion of non-azide gas generant
Reducing the level of has been a difficult problem. For example, manipulating the ratio of oxidant to fuel is NO _x or C
It only reduces one of the O's. More specifically, increasing the ratio of oxidant to fuel reduces the CO content during combustion as excess oxygen oxidizes CO to carbon dioxide. But unfortunately this approach is no
will increase the amount of _x . Instead, reducing the ratio of oxidant to fuel removes excess oxygen, reduces the amount of NO _x produced, and produces increased amounts of CO.

One way to improve combustion gas toxicity is CO and NO.
_x A reduction in combustion temperature that reduces the initial concentration of both. Although theoretically simple, it is practically difficult to reduce the combustion temperature and to obtain a gas generant burn rate that is high enough for practical application in an inflatable occupant restraint system. It is important that the burning rate of the gas generant ensures that the inflator operates easily and properly. As a general rule, the burning rate of the gas generant decreases as the burning temperature decreases. Not only can the combustion temperature be reduced, but the gas generant burn rate is also reduced by using a less energy fuel, specifically a fuel that produces less heat upon combustion.

Therefore, there remains a need to reduce the toxicity of effluent gas produced by non-azide gas generants without compromising the properties of the gas generant.

SUMMARY OF THE INVENTION According to the invention, the aforesaid problems are associated with the combustion of an expansion gas which is inherently non-toxic and which has reduced levels of NO _x and CO due to the use of compounds which generate NH ₂ groups in the gas phase. It is solved by the resulting non-azide gas generating composition. Selective non-catalyt
ic reduction (SNCR)] is the nitrogen oxide (NO) in the gas phase.
NH that selectively reacts with nitrogen to form non-toxic nitrogen gas (N ₂ ).
_{Use 2} units. In the SNCR system, the basic requirement for NO reduction by SNCR chemicals is to include a minimum of 1: 1 well-mixed NH ₂ groups to NO, where the NH ₂ groups are
It is generated by R chemicals and NO is generated from gas generating combustion. Furthermore, the NH ₂ group must react at temperatures in the range of 850 to 1150 ° C. for a sufficient residence time. Reduced amount of toxic gases, such as of the NO _x and CO allow the use of non-azide gas generating agent in the occupant restraint system of the car, exposed to toxic gas which has been generated by the non-azide gas generating agent of the passenger car ever Protect from being exposed.

More particularly, the present invention comprises a non-azide gas generating composition and the thermal decomposition and / or another of the NO _x reducing agent which releases NH ₂ group by reaction with O ₂ (SNCR) Chemical. NO and N
NO _x gases resulting from the combustion of O ₂ or the like of the gas generating agent reacts selectively with the NH ₂ group or NH ₃ and O _2, to produce a non-toxic N ₂ gas. The corresponding decrease in CO is a coincidental benefit from the use of some reducing agents such as (NH ₄ ) ₂ SO ₄ . further,
The chemistry of SNCR Chemicals is non-intrusive and will not compromise the expected performance and stability of gas generant combustion.

According to DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention, restraint system device of an occupant of the car utilizing SNCR system includes a gas generator and de-NO _x agents.
De NO _x agents placed around the gas generating agent in the gas generating bed, amides and imides, ammonium compounds, selected from the group including any compound which produces a NH ₂ group with an amine compound or a gas phase. Examples of ammonium compounds are:
Ammonium hydroxide (NH ₄ OH), ammonium carbonate ((N
H _{4) 2} CO _3), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium chloride (NH ₄ Cl), ammonium carbamate (H
₂ NCO ₂ NH ₄ ) and ammonium fluoride (NH ₄ F).
Examples of amide compounds and imide compounds are urea (H ₂ NCONH ₂ ) and cyanuric acid ((HNCO) ₃ ), respectively.
Given the advantages described above, the gas generant is preferably non-azide, although other gas generants such as azide based compositions can be utilized in conjunction with the SNCR. The SNCR chemical is preferably ammonium sulphate ((NH ₄ ) ₂ SO ₄ ) based on the optimal and unexpected results given in Example 3 below. Not only does it inhibit the production of toxic NO ₂ (NH ₄ ) ₂ SO ₄ , it also reduces NO ₂ for a long time. In general, ammonium compounds will generate the highest yield of NH ₂ groups.

SNCRs are well known and commonly used in industrial boilers to reduce the levels of toxic nitrogen oxides.
To date, SNCR Engineering has not been successfully implemented in automotive airbag systems. NO is reduced to N ₂ by the following gas phase reaction with NH ₂ groups.

NH ₂ + NO → N ₂ + H ₂ O (1) Since NO ₂ is generated by NO, a decrease in NO always causes a decrease in NO _{x in} the inflator. Important parameters for the successful implementation of SNCR in any system are reaction temperature, NH ₂ group / NO ratio, mixing, residence time and initial NO level. Furthermore, when the SNCR chemical is ammonia or an ammonium compound, oxygen (O ₂ )
The existence of is important.

To obtain NH ₂ groups at a proper level in the gas phase, use SNCR
The chemical must be thermally decomposed to generate NH ₂ groups or NH ₃ which must then react with O ₂ to form NH ₂ groups. Degradation products determine how much NH ₂ groups are generated in the gas phase relative to those released directly from SNCR chemicals. The minimum NH ₂ group / NO ratio in the gas phase reaction should be 1 mole of NH ₂ groups for each mole of NO. Generally, NH ₂ groups slight excess becomes easily small amount of NH ₃ formed, it would give a very little additional NO reduction. SNCR engineering is most effective at high initial levels of NO. When using ammonium compounds,
Oxygen is required for the formation of NH ₂ groups and must be present at levels of 0.1-11% by volume.

The decomposition temperature, which is decisive when generating NH ₂ groups in the gas phase, requires the NH ₂ groups to be “injected” into the gas phase at the right temperature, which allows the selective reduction of NO _x. To For example, (NH ₄ ) ₂ SO ₄ decomposes at about 235 ° C,
(NH ₄ ) ₂ CO ₃ begins to decompose at room temperature. The SNCR chemicals that decompose at lower temperatures during inflator placement will "inject" into the system earlier, giving a reduced reduction of nitrogen oxides as described in Example 4. The importance of temperature is shown by the following reaction.

NO ＋ NH ₃ + 1 / 4O ₂ → N ₂ ＋ 3 / 2H ₂ O (2) NH ₃ ＋ 5 / 4O ₂ → NO ＋ 3 / 2H ₂ O (3) The desired reaction (2) is significant only at a temperature of about 850-950 ℃. Will happen at any rate. However, at temperatures above 1050-1150 ° C, reaction (3) becomes predominant and undesired NO
Is formed. In addition to temperature, the importance of good mixing and sufficient residence time is apparent for the completion of any gas phase reaction. The gas temperature, degree of mixing, and residence time for a given inflator are determined primarily by the nature of the gas generant, inflator placement and operating conditions.

The gas temperature of the inflator typically varies from the hottest point of the generant combustion surface to the coldest point of the inflator exit hole. Temperature is extremely difficult to measure, but the thermodynamic properties of the generant, the burning rate of the generant, the cooling device in the inflator and the operating pressure of the inflator are
Contributes to the overall operating temperature of the SNCR system. The residence time of the gas in the inflator depends on the presence of throttled flow and operating pressure. One of ordinary skill in the art, with the choice of one gas generant, will readily realize that recognition and adaptation of these variables allows the use of a wide variety of gas generant compositions with SNCR systems.

In accordance with the present invention, the SNCR chemical is a non-noxious composition that does not interfere with or significantly alter the normal combustion reaction of the gas generant. The invention is illustrated by the examples below.

Example 1 Two nonazide passenger inflators with the same gas generant and hardware.
(NAPIs)] was assembled. Ammonium carbonate ((NH ₄ )
₂ CO ₃ ) was added as powder at 1.4 wt% of the total amount of the generator directly to the generation bed of one inflator. Inflator 100
Placed in a cubic foot tank, the gaseous effluent was measured for 30 minutes. Carbon monoxide (CO) and ammonia (NH ₃ ) were measured by FTIR, nitrogen (II) oxide (NO),
Nitrogen (IV) oxide (NO ₂ ) and total nitrogen oxide (NO _x ) were measured by chemiluminescence. Ppm below the time-weighted average
To report.

This example shows that the addition of this SNCR ammonium salt significantly reduced the levels of toxic nitric oxide and did not essentially change CO.

Example 2 Two NAPIs with the same gas generant and hardware were assembled and tested as described in Example 1.
However, the generant filling and cooling assembly was different from that of Example 1. 2.6% by weight of (NH ₄ ) ₂ CO ₃
Powder was added directly to the bed where one of the inflators was generated.
The time weighted average is reported below in ppm.

This example demonstrates the importance of choosing the proper inflator placement for successful implementation of SNCR engineering on airbag inflators. In addition, this example
The SNCR chemical does not further reduce NO _x , but only produces higher levels of NH ₃ .

Example 3 Two NAPIs with the same gas generant and hardware were assembled and tested as described in Example 1.
However, the generant filling and cooling assembly was different from that of Examples 1 and 2. Ammonium sulfate ((NH ₄ ) ₂
SO ₄ ) was added as powder at 1.2% by weight of the total amount of the generator to the generating bed of one inflator directly. Time-weighted average down
Report in m.

Two quite unexpected but informative results were observed from these tests. First, the addition of _{((NH 4) 2 SO 4} ) produced a decrease in both NO _x and CO. Second, a comparison of NO ₂ generation in control and SNCR samples shows a decrease in NO ₂ species over time in SNCR samples and an increase in NO ₂ species in control samples. In the control inflator, NO ₂ is 9.4ppm in 3 minutes and 16.4p in 30 minutes.
It was pm. This is common as the NO initially produced by the inflator gradually converts to NO ₂ in the presence of O ₂ . In the control inflator, NO ₂ decreased to 7.8ppm in 3 minutes and steadily decreased to 5.0ppm in 30 minutes. This embodiment is relatively although there is an increase in non-toxic NO and the amount of O _2, showing the effectiveness of this aspect of preventing the occurrence of NO ₂ toxicity.

Example 4 Three NAPIs with the same gas generant and hardware were assembled and tested as described in Example 1.
However, the generant filling and cooling assembly is described in Example 1,
Different from that used in 2 or 3. (NH ₄ ) ₂ SO ₄
(Decomposed at 235 ° C.) and H ₂ NCO ₂ NH ₄ (sublimed at 60 ° C.) were respectively added as powders at 2.7% by weight based on the total amount of the generating agent to the generating bed of one inflator directly. The time weighted average is reported below in ppm.

Again, the addition of (NH _{4) 2} SO ₄ produced a decrease in both NO _x and CO. Also, the level of NO ₂ is 3 minutes and 9.4 ppm is 30 minutes.
It was 5.6 ppm, confirming the data shown in Example 3.
The decomposition and sublimation points of different compounds indicate that the decomposition point must be considered as an important factor for the success of SNCR chemicals.

While the preferred embodiments of the invention have been disclosed, the invention includes modifications that do not depart from the scope of the following claims.

─────────────────────────────────────────────────── —————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————— 37-72-49-72-27-27-27-27-29-49-49-49-26-26-26-26-27-26-28-28-28-28-28-28-28-09 Circle 6697 (56) Reference Japanese Unexamined Patent Publication No. 9-328387 (JP, A) Special Table 11-500098 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C06D 5/00 C06B 23/02 B60R 21/26 Patent file (PATOLIS)

Claims (3)

(57) [Claims] 1. A vehicle occupant restraint system comprising an inflatable air bag; a gas generator used to inflate the air bag; and a gas generator located within the gas generator and adapted for use. A nitrogen-oxide generating and / or nitrogen-dioxide generating gas generating compound; and a selective non-catalytic reducing compound proximate and interspersed with the gas generating compound, the selective non-catalytic A reducing compound is useful for non-intrusively reducing nitrogen oxides produced by combustion of the gas generant, and ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium sulfate ((NH ₄ ) ₂ S
O ₄ ), ammonium chloride (NH ₄ Cl), ammonium carbamate (H ₂ NCO ₂ NH ₄ ) and ammonium fluoride (NH ₄
Said selective non-catalytic reducing compound selected from the group consisting of F); 2. The vehicle occupant restraint system of claim 1, wherein the gas generant is a non-azide composition. 3. A method of reducing nitrogen oxides contained in the exhaled gas of a gas generator used to inflate an airbag of a vehicle occupant restraint system, the gas being in the generator. Around the generating composition, ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ),
Interspersing selective non-catalytic reducing compounds selected from the group consisting of ammonium chloride (NH ₄ Cl), ammonium carbamate (H ₂ NCO ₂ NH ₄ ) and ammonium fluoride (NH ₄ F); Burning the gas generating composition; and reacting a gaseous product from the selective non-catalytic reducing compound with nitrogen oxides resulting from the burning of the gas generating composition.