KR19990037956A - Selective Non-catalytic Reduction of Toxic Gas Releases in Airbag Inflators - Google Patents

Abstract

The present invention relates to reducing the toxicity of effluent gases produced by combustion of non-azide gas generating compositions in which NH ₂ radical-generating compounds are used to inflate vehicle occupant safety systems regardless of the gas generator composition. N ₂ is formed by the selective reaction of NO and NH ₂ radicals in the combustion gas, which reduces the concentration of toxic nitrogen oxides. The placement of reducing compounds adjacent to the gas generator phase is associated with combustion gases and still provides a non-destructive method of reducing toxic gases.

Description

Selective Non-catalytic Reduction of Toxic Gas Releases in Airbag Inflators

FIELD OF THE INVENTION The present invention generally relates to reducing the toxicity of inflatable occupant safeguards in vehicles, and more particularly the release gases produced by nonazide gas generating compositions.

Inflatable occupant safety for vehicles has long been developed worldwide, including the development of gas generating compositions for inflating such occupant safety. Many gas generators currently in use are based on alkali or alkaline earth metal azides, especially sodium azide, because the expanded gas produced by the gas generator must meet limited toxicity requirements. When reacted with an oxidant, sodium azide forms a relatively nontoxic gas of primary nitrogen.

However, azide-based gas generators are inherently volatile and relatively high in risk for handling in manufacturing and processing. More specifically, the expanded gas produced by the azide-based gas generators is relatively non-toxic, whereas the metal azide itself is very toxic inversely, thereby providing extra costs for the production, storage and processing of the gas generators. Bringing danger. In addition to direct pollution, metal azides also readily react with acids and heavy metals to form highly sensitive compounds that can spontaneously ignite or explode.

In contrast, non-azide gas generators, such as those described in US Pat. No. 5,139,588 to Poole, include typical non-azide fuels selected from the group of tetrazole compounds and metal salts thereof and are at risk associated with toxicity during manufacturing and processing. This provides an important advantage for azide gas generators. Moreover, most non-azide gas generator compositions typically provide higher yields of gas (moles of gas per gram of gas generator) than conventional azide-based occupant safety gas generators.

However, many non-azide gas generators known and used so far produce high levels of toxic substances upon combustion. The most difficult toxic gases to control are various nitrogen oxides (NO _X ) and carbon monoxide (CO). Since the gas generator of the occupant's airbag is generally four times higher than the driver's side, NO _x and CO reduction requirements are considered to be the most sensitive when designing the occupant's airbag, even if interest is in the vehicle as well as other airbag systems.

Reduction of toxic NO _x and CO levels in the combustion of non-azide gas generators proves to be a difficult problem. For example, treatment of oxidants / fuels only reduces NO _x or CO. More specifically, increasing the ratio of oxidant to fuel minimizes CO content during combustion because excess oxygen oxidizes CO into carbon dioxide. Unfortunately, this approach results in an increased amount of NO _x . On the other hand, an increased amount of CO is produced if the oxidant / fuel ratio is lowered to remove excess oxygen and reduce the amount of NO _x produced.

One way to improve the toxicity of the combustion gas is to reduce the combustion temperature which reduces the initial concentrations of CO and NO _x . Although theoretically simple, it is virtually difficult to reduce combustion temperatures and maintain a sufficiently high gas generator combustion rate for practical applications in inflatable vehicle occupant safety devices. It is important to demonstrate that the rate of combustion of the gas generators is that the inflator is easy to operate properly. As a general rule, the combustion rate of the gas generator decreases as the combustion temperature decreases. By using less powerful fuels, especially those that generate less heat during combustion, the combustion temperature is reduced and the gas generator combustion rate is also reduced.

Thus, there is still a need to reduce the toxicity of the release gas produced by the non-azide gas generator without compromising the gas generator properties.

Summary of the Invention

The above-mentioned problem is solved by a non-azide gas generating composition which is inherently nontoxic and also produces an expanded gas with reduced NO _x and CO levels due to the use of compounds which produce NH ₂ radicals in the gas phase upon combustion. Is solved accordingly. Selective non-catalytic reduction (SNCR) uses NH ₂ radicals that selectively react with nitrogen oxides (NO) on the gas to form non-toxic nitrogen gas (N ₂ ). In the SNCR system, the basic requirements for NO reduction by the SNCR compound include a well mixed minimum 1: 1 ratio of NH ₂ radicals to NO, such that NH ₂ radicals are produced by SNCR chemicals and NO is a gas generator. From combustion. Moreover, the NH ₂ radicals must react for a sufficient residence time at temperatures in the range of 850-1150 ° C. Reduced amounts of toxic gases, such as NO _x and CO, have enabled the use of non-azide gas generators in vehicle occupant safety systems to date while protecting vehicle occupants from toxic gas exposure generated by non-azide gas generators.

More specifically, the present invention includes a non-azide gas generator composition, a separate NO _x reducing agent (SNCR) chemical that liberates NH ₂ radicals upon thermal decomposition and / or reaction with O ₂ . NO _x gas generated from the combustion of the gas generator, such as NO and NO ₂ , selectively reacts with NH ₂ radicals or NH ₃ and O ₂ to produce a harmless N ₂ gas. The corresponding reduction in CO has the side benefit of using some reducing agent such as (NH ₄ ) ₂ SO ₄ . In addition, the chemical properties of SNCR chemicals are nondestructive and do not interfere with the expected performance or stability of gas generator combustion.

Detailed description of the preferred embodiment

Vehicle occupant safety device using the SNCR system according to the invention comprises a gas generation body and the first de-NO _x. The de-NO _x agent is selected from the group comprising around the ends of the gas generators on the gas generator bed and comprising compounds that generate NH ₂ radicals on amides and imides, ammonium compounds, amine compounds or gas phases. . Examples of ammonium compounds include ammonium hydroxide (NH ₄ OH), ammonium carbonate ((NH 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 each of the amide and imide compounds are urea (H ₂ NCONH ₂ ) and cyanuric acid ((HNCO ₃ ). In the above-mentioned advantages, other gas generators such as azide-based compositions may be used in combination with SNCR. The gas generator is preferably biazide The SNCR chemical is preferably ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) based on the optimal and unexpected results given in Example 3. The (NH ₄ ) ₂ SO ₄ is It not only inhibits the production of toxic NO ₂ but also substantially reduces NO _{2 over} time In general, ammonium compounds produce the highest yields of NH ₂ radicals.

SNCR is well known and is commonly used in boilers industrially to reduce levels of toxic nitrogen oxides. To date, SNCR technology has not been successfully implemented in automatic airbag systems. NO is reduced to N ₂ by NH ₂ radicals and the following gas phase reaction:

NH₂+ NO → N₂+ H₂O (One)

Since NO ₂ is produced by NO, reduction in NO inevitably results in total NO _x reduction in the expander gas. Important parameters for the successful implementation of SNCR in some systems are reaction temperature, NH ₂ radical / NO ratio, mixing, residence time and initial NO level. In addition, the presence of oxygen (O ₂ ) is important when the SNCR chemical is an ammonia or ammonium compound.

In order to obtain NH ₂ radicals on the gas at the correct level, the SNCR chemicals must undergo thermal decomposition to produce NH ₂ radicals or NH ₃ (which must then react with O ₂ to form NH ₂ radicals). The degradation product determines how much NH ₂ radicals are generated on the gas phase versus what is liberated from the SNCR chemicals. The minimum NH ₂ radical / NO ratio in the gas phase reaction should be 1 mole NH ₂ radical for each NO mole. In general, some excess NH ₂ radicals simply result in the formation of small amounts of NH ₃ and provide minimal additional NO reduction. SNCR technology is most effective at high initial levels of NO. When an ammonium compound is used, oxygen is required to form NH ₂ radicals and must be present at levels of 0.1-11 volume percent.

When NH ₂ radicals are generated in the gas phase, the decomposition temperature is important because NH ₂ radicals are injected into the gas phase at the correct temperature to enable selective reduction of NO _x . For example, (NH _{4) 2} CO ₃ is for starting to break at room temperature (NH _{4) 2} SO ₄ is decomposed at 235 ℃. SNCR chemicals that decompose at lower temperatures during inflator deployment “inject” into the system more quickly as described in Example 4 and provide reduced reduction of nitrogen oxides:

NO + NH ₃ + 1/4 O ₂ → N ₂ + 3/2 H ₂ O (2)

NH ₃ + 5/4 O ₂ → NO + 3/2 H ₂ O (3)

The desired reaction (2) occurs at an important rate only at temperatures above 850-950 ° C. However, at temperatures above 1050-1150 ° C., reaction (3) becomes significant and undesirable NO is formed. In addition to temperature, the importance of good mixing and sufficient residence time is evident for the completion of any gas phase reaction. The gas temperature, degree of mixing, and residence time of a given inflator are primarily determined by the gas generator properties, inflator placement and operating conditions.

The gas temperature in the inflator is generally the highest at the generator combustion surface and the lowest at the inlet outlet. Although the temperature is very difficult to measure, variables such as the thermodynamic properties of the generator, the combustion speed of the generator, and the operating pressure of the cooling device and the expander in the expander contribute to the overall operating temperature of the SNCR system. The residence time of the gas in the inflator depends on the choked flow and the presence of operating pressure. One of ordinary skill in the art will readily recognize the recognition and control of these variables when gasoline selection allows for widespread use of the gaseous composition in combination with SNCR systems.

According to the present invention, the SNCR chemical is a nondestructive composition, whereby the normal combustion reaction of the gas generator is not disturbed or significantly altered. The invention is illustrated by the following examples.

Example 1

Ammonium carbonate ((NH ₄ ) ₂ CO ₃ )) was added directly to the generator of one of two NAPIs inflators with the same gas generator and hardware as a 1.4 wt% powder of the mass of the generator. . The inflator was deployed in a 100 ft ³ tank and gas emissions were measured for at least 30 minutes. Carbon monoxide (CO) and ammonia (NH ₃ ) were measured by FTIR while nitrogen (II) oxides (NO) nitrogen (IV), oxides (NO ₂ ) and total nitrogen oxides (NO _x ) were measured by chemiluminescence. . Weighted averages over time are reported below in ppm.

Inflator CO NO NO ₂ NO _x NH ₃ Control (Control) 665 85.7 29.6 117.6 14 1.4% (NH ₄ ) ₂ CO ₃ 705 52.8 0.9 53.6 96 Control percent 106% 62% 3% 46% 686%

This example illustrates that the addition of SNCR ammonium salts significantly reduces the levels of toxic nitrogen oxides while essentially CO remains unchanged.

Example 2

NAPIs with the same gas generator and hardware were made and tested as described in Example 1. However, the generator rod and cooling assembly were different from those used in Example 1. ((NH ₄ ) ₂ CO ₃ ) was added directly onto the generator of one of the expanders as a 2.6 wt% powder of the generator mass. The weighted average over time is reported below in ppm.

Inflator CO NO NO ₂ NO _x NH ₃ Control (Control) 822 106.1 50.5 162 16 2.6% (NH ₄ ) ₂ CO ₃ 798 82.0 30.7 116 147 Control percent 97% 77% 61% 72% 919%

This embodiment illustrates the importance of selecting the correct inflator configuration for successful implementation of SNCR technology in an airbag inflator. In addition, this example shows that excess SNCR chemistry results in high levels of NH ₃ production as well as NO _x reduction.

Example 3

Two NAPIs with the same gas generator and hardware were made and tested as described in Example 1. However, the generator rod and cooling assembly were different from those of Examples 1 and 2. (NH ₄ ) ₂ SO ₄ was added directly onto the generator of one of the expanders as a 1.2 wt% powder of the generator mass. The weighted average over time is reported below in ppm.

Inflator CO NO NO ₂ NO _x NH ₃ Control (Control) 437 59.6 12.5 73.3 8 1.2% (NH ₄ ) ₂ SO ₄ 406 62.2 5.2 67.7 57 Control percent 93% 104% 42% 92% 712

Two unexpected beneficial results were observed in these tests. First, a comparison of NO ₂ incidence in plaques shows a decrease over time of NO ₂ species in SNCR samples and an increase of NO ₂ species in control samples. For the control inflator, NO ₂ was 9.4 ppm at 3 minutes and 16.4 ppm at 30 minutes. This is normally seen because the initial NO produced slowly by the expander slowly converts to NO ₂ in the presence of O ₂ . For inflators with SNCR chemicals, NO ₂ was steadily decreased to 7.8 ppm in 3 minutes and 5.0 ppm in 30 minutes. This example illustrates the effect of this example in delaying the production of toxic NO ₂ despite the presence of increased amounts of relatively non-toxic NO and O ₂ .

Example 4

Four NAPIs with the same gas generator and hardware were made and tested as described in Example 1. However, the generator rod and cooling assembly were different from those used in Examples 1,2 or 3. (NH ₄ ) ₂ SO ₄ (decomposed at 235 ° C.) and H ₂ NCO ₂ NH ₄ (sublimed at 60 ° C.) were added directly onto the generator in one of the expanders, respectively, as a powder of 2.7 wt% of the mass of the generator. . The weighted average over time is reported below in ppm.

Inflator CO NO NO ₂ NO _x NH ₃ Control (Control) 552 82.2 30.2 115.2 10 2.7% (NH ₄ ) ₂ SO ₃ 453 81.5 6.2 66.2 105 2.7% H ₂ NCO ₂ NH ₄ 715 79 31 112.9 196

Again, addition of (NH ₄ ) ₂ SO ₄ resulted in reduction of NO _x and CO. In addition, the NO ₂ level ranged from 9.4 ppm at 3 minutes to 5.6 ppm at 30 minutes and the data presented in Example 3 demonstrate this. The decomposition and sublimation points of other compounds specify that the decomposition temperature should be considered as an important factor for the success of SNCR chemicals.

While preferred embodiments of the invention have been described, it is to be understood that the invention may be modified without departing from the scope of the following claims.

Claims (14)

Inflatable airbags; Gas generator; A gas generator compound located in the gas generator; And Vehicles interspersed near the gas generator compound and comprising an optional non-catalytic reducing compound selected from the group comprising ammonium salts, ammonium hydroxide (NH ₄ OH), amine compounds and amide and imide compounds Occupant safety system. The method of claim 1, The gas generator comprises a beaded composition; The ammonium salt is ammonium hydroxide (NH ₄ OH), ammonium carbonate ((NH 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); The amide compound is selected from the group consisting of urea (H ₂ NCONH ₂ ); And And said imide compound is selected from the group consisting of cyanuric acid ((HNCO) ₃ ). Interspersing a non-catalytic reducing compound selective to the gas generator composition in the gas generator; Reacting the toxicity of the release gas of the gas generator, which is used to inflate the airbag of the vehicle occupant safety system, comprising reacting with an optional non-catalyst gas product that reduces the compound to the gas combustion product of the gas generator composition. How to reduce. (none) The method of claim 1, The gas generator compound consists of a non-azide composition; The optional non-catalytic reducing compound is ammonium carbonate ((NH 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 a vehicle occupant safety system consisting of an ammonium salt selected from the group consisting of ammonium fluoride (NH ₄ F). The method of claim 1, The gas generator compound consists of a non-azide composition; The vehicle occupant safety system, wherein the optional non-catalytic reducing compound consists of urea (H ₂ NCONH ₂ ). The method of claim 1, The gas generator compound consists of a non-azide composition; A vehicle occupant safety system consisting of the optional non-catalytic reducing compound cyanuric acid ((HNCO) ₃ ). The method of claim 1, The gas generator compound consists of a non-azide composition; The vehicle occupant safety system, wherein the optional non-catalytic reducing compound consists of ammonium hydroxide (NH ₄ OH). The method of claim 1, The gas generator compound consists of a non-azide composition; A vehicle occupant stabilization system wherein said optional non-catalytic reducing compound consists of an amine compound. The method of claim 4, wherein the optional non-catalytic reducing compound is ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), ammonium chloride (NH ₄ Cl ₄ ), ammonium carba A vehicle occupant safety system consisting of an ammonium salt selected from the group consisting of mate (H ₂ NCO ₂ NH ₄ ) and ammonium fluoride (NH ₄ F). The method of claim 4, wherein said optional non-catalytic reducing compound consists of urea (H ₂ NCONH ₂ ). The method of claim 4, wherein said optional non-catalytic reducing compound consists of cyanuric acid ((HNCO) ₃ ). The method of claim 4, wherein said optional non-catalytic reducing compound consists of ammonium hydroxide (NH ₄ OH). 2. The vehicle occupant safety system of claim 1, wherein the optional non-catalytic reducing compound consists of an amine compound.