CA2261969A1 - Selective non-catalytic reduction (sncr) of toxic gaseous effluents in airbag inflators - Google Patents
Selective non-catalytic reduction (sncr) of toxic gaseous effluents in airbag inflators Download PDFInfo
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- CA2261969A1 CA2261969A1 CA002261969A CA2261969A CA2261969A1 CA 2261969 A1 CA2261969 A1 CA 2261969A1 CA 002261969 A CA002261969 A CA 002261969A CA 2261969 A CA2261969 A CA 2261969A CA 2261969 A1 CA2261969 A1 CA 2261969A1
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- ammonium
- selective non
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
- C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
- C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
- C06B23/02—Compositions characterised by non-explosive or non-thermic constituents for neutralising poisonous gases from explosives produced during blasting
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
- C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
- C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids
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- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
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- Toxicology (AREA)
- Air Bags (AREA)
Abstract
NH2 radical-generating compounds, independent of the gas generant composition, reduce the toxicity of effluent gases produced by combustion of nonazide gas generating compositions used to inflate vehicle occupant restraint systems. By selective reactive of the NH2 radical with NO in the combustion gas, N2 is formed thereby decreasing the concentration of toxic nitrogen oxides therein. Placement of the reducing compounds proximate to the gas generant bed ensures intimate contact with the combustion gases, and yet still provides a noninvasive method of toxic gas reduction.
Description
W O 98/06682 PCTrUS97/13501 8ELECTIVE NON-CATALYTIC REDUCT~ION (SNCR) OF TOXIC
GA8EOUS EFFLUENTS IN ~T~ INFLATOR8 BACKGROUND OF THE I~NTION
The present invention relates generally to inflatable occupant safety restraints in motor vehicles, and more particularly to reducing the toxi-ity of effluent gases produced by nonazide gas generating (ompositions.
Inflatable occupant restraint devices for motor vehicles have been under development ~orldwide for many years, including the development of gas generating compositions for inflating such occupant restraints. Because the inflating gases produced by the gas generants must meet strict toxicity ret~uirements, many gas generants now in use are based on alkali or alkaline earth metal azides, pa]ticularly sodium azide.
When reacted with an oxidizing agent, sodium azide forms a relatively nontoxic gas consisting plimarily of nitrogen.
However, azide-based gas generants are inherently volatile to handle and entail relatively high risk in manufacture and disposal. More s~ecifically, whereas the inflating gases produced by azide-based gas generants are relatively nontoxic, the metal azides themcelves are conversely highly toxic, thereby resulting in e~tra expense and risk in gas generant manufacture, storage, and disposal. In addition to direct contamination of the environment, metal azides also readily react with acids and heavy metals to form extremely sensitive compounds that may spontane~usly ignite or detonate.
In contradistinction, nonaz de gas generants, such as those disclosed in U.S. Patent No. 5,139,588 to Poole, typically comprise a nonazide fuel selected from the group of tetrazole compounds and metal salts thereof, and provide _ significant advantages over azide-b~sed gas generants with respect to toxicity related hazard~ during manufacture and disposal. Moreover, most nonazide gas generant compositions typically supply a higher yield of gas (moles of gas per gram W098/06682 PCT~S97/13501 of gas generant) than conventional azide-based occupant restraint gas generants.
However, many nonazide gas generants heretofore known and used produce high levels of toxic substances upon combustion. The most difficult toxic gases to control are the various oxides of nitrogen (N0X) and carbon monoxide (C0).
Because the gas generant of the passenger-side airbags is generally four times greater than that of the driver-side, the need for N0~ and C0 reduction is most keenly felt when designing passenger-side airbags, although the concern exists for other airbag systems within the vehicle as well.
~ eduction of the level of toxic N0x and C0 upon combustion of nonazide gas generants has proven to be a difficult problem. For instance, manipulation of the oxidizer/fuel ratio only reduces either the N0X or C0. More specifically, increasing the ratio of oxidizer to fuel minimizes the C0 content upon combustion because the extra oxygen oxidizes the C0 to carbon dioxide. Unfortunately, however, this approach results in increased amounts of N0x.
Alternatively, if the oxidizer/fuel ratio is lowered to eliminate excess oxygen and reduce the amount of N0x produced, increased amounts of C0 are produced.
one way to improve the toxicity of the combustion gases is to reduce the combustion temperature which would reduce the initial concentrations of both C0 and N0X. Although simple in theory, it is difficult in practice to reduce the combustion temperature and to also retain a sufficiently high gas generant burn rate for practical application in an inflatable vehicle occupant restraint system. The burn rate of the gas generant is important to insure that the inflator will operate readily and properly. As a general rule, the burn rate of the gas generant decreases as the combustion temperature decreases. By using less energetic fuels, specifically fuels which produce less heat upon combustion, the combustion temperature may be reduced but the gas generant burn rate is also reduced.
W O9~/0~ PCT~US97/13501 Therefore, a need still ~xists for reducing the toxicity of effluent gases produced by nonazide gas generants without compromising the gas generanl: properties.
SUMMARY OF THE INVENTION
5The aforesaid problems are solved, in accordance with the present invention, by a nonazide cas generating composition which in and of itself is nontoxic, ald which upon combustion, also produces inflating gases that hlve reduced levels Of NOI
and CO due to the use of a compound that generates NH2 radicals in the gas phase. Selective non-catalytic reduction (SNCR) employs an NH2 radical that selectiv~ly reacts with nitrogen oxide (NO) in the gas phase to forrl non-toxic nitrogen gas (N2). In an SNCR system, basic requi-ements for the reduction of NO by an SNCR chemical include a well-mixed minimal 1:1 ratio of NH2 radical to NO, whereby th~ NH2 radical is generated by the SNCR chemical and the NO is generated from the gas generant combustion. Furthermore, tlhe NH2 radical must react for a sufficient residence time at ~ temperature within the range of 850-1150~C. The reduced content of toxic gases, such as NO~ and CO, allows the use of nonazide gas generants in vehicle occupant restraint systems while protecting the occupants of the vehicle from exposure to toxic gases which heretofore have been produced by nonazide gas generants.
More specifically, the present invention comprises a nonazide gas generant composition, ard a separate NO~ reducing agent (SNCR) chemical that liberates NH2 radical upon thermal decomposition and/or reaction with ~2 The NO" gases generated from the combustion of the gas genelant, such as NO and NO2, selectively react with the NH2 radicaLs, or NH3 and ~2 ~ thereby producing a harmless gas of N2. A corresponding reduction in CO is an incidental benefit with the use of some of the reducing agents, such as (NH4)2S04. Il addition, the chemistry of the SNCR chemical is noninvasive and will not interfere with the expected performance or stabi.ity of a gas generant combustion.
W098106682 PCT~S97/13501 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT~S) In accordance with the present invention, a vehicle occupant restraint device utilizing an SNCR system comprises a gas generant and a de-NO~ agent. The de-NO~ agent is disposed around the periphery of the gas generant within the gas generant bed and is selected from a group including amides and imides, ammonium compounds, amine compounds, or any compound which produces an NH2 radical in the gas phase. Examples of ammonium compounds include ammonium hydroxide (NH40H), ammonium carbonate ((NH4)2C03), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NC02NH4), and ammonium fluoride (NH4F). Examples of amide and imide compounds, respectively, compounds are urea (H2NCONH2) and cyanuric acid ((HNCO)3). Given the aforementioned benefits, the gas lS generant is preferably nonazide, although other gas generants such as an azide-based composition may be utilized in conjunction with SNCR. The SNCR chemical is preferably ammonium sulfate ((NH4)2S04) based on the optimum and unexpected results given in Example 3 below. Not only does (NH4)2SO4 inhibit production of toxic NO2, it actually reduces NO2 over time. In general, ammonium compounds will generate the highest yield of NH2 radicals.
SNCR is well known and commonly used in industrial boilers to decrease the levels of toxic nitrogen oxides. Until now, SNCR technology has not been successfully implemented in automotive airbag systems. NO is reduced to N2 by the following gas phase reaction with an NH2 radical:
NH2 + NO ~ N2 + H20 (l) Because NO2 is generated by NO, a reduction in NO necessarily causes an overall NOX reduction within the inflator gas. The critical parameters for the successful implementation of SNCR
in any system are the reaction temperature, NH2 radical/NO
ratio, mixing, residence time, and initial NO level. In ........ ... . . .. ...
GA8EOUS EFFLUENTS IN ~T~ INFLATOR8 BACKGROUND OF THE I~NTION
The present invention relates generally to inflatable occupant safety restraints in motor vehicles, and more particularly to reducing the toxi-ity of effluent gases produced by nonazide gas generating (ompositions.
Inflatable occupant restraint devices for motor vehicles have been under development ~orldwide for many years, including the development of gas generating compositions for inflating such occupant restraints. Because the inflating gases produced by the gas generants must meet strict toxicity ret~uirements, many gas generants now in use are based on alkali or alkaline earth metal azides, pa]ticularly sodium azide.
When reacted with an oxidizing agent, sodium azide forms a relatively nontoxic gas consisting plimarily of nitrogen.
However, azide-based gas generants are inherently volatile to handle and entail relatively high risk in manufacture and disposal. More s~ecifically, whereas the inflating gases produced by azide-based gas generants are relatively nontoxic, the metal azides themcelves are conversely highly toxic, thereby resulting in e~tra expense and risk in gas generant manufacture, storage, and disposal. In addition to direct contamination of the environment, metal azides also readily react with acids and heavy metals to form extremely sensitive compounds that may spontane~usly ignite or detonate.
In contradistinction, nonaz de gas generants, such as those disclosed in U.S. Patent No. 5,139,588 to Poole, typically comprise a nonazide fuel selected from the group of tetrazole compounds and metal salts thereof, and provide _ significant advantages over azide-b~sed gas generants with respect to toxicity related hazard~ during manufacture and disposal. Moreover, most nonazide gas generant compositions typically supply a higher yield of gas (moles of gas per gram W098/06682 PCT~S97/13501 of gas generant) than conventional azide-based occupant restraint gas generants.
However, many nonazide gas generants heretofore known and used produce high levels of toxic substances upon combustion. The most difficult toxic gases to control are the various oxides of nitrogen (N0X) and carbon monoxide (C0).
Because the gas generant of the passenger-side airbags is generally four times greater than that of the driver-side, the need for N0~ and C0 reduction is most keenly felt when designing passenger-side airbags, although the concern exists for other airbag systems within the vehicle as well.
~ eduction of the level of toxic N0x and C0 upon combustion of nonazide gas generants has proven to be a difficult problem. For instance, manipulation of the oxidizer/fuel ratio only reduces either the N0X or C0. More specifically, increasing the ratio of oxidizer to fuel minimizes the C0 content upon combustion because the extra oxygen oxidizes the C0 to carbon dioxide. Unfortunately, however, this approach results in increased amounts of N0x.
Alternatively, if the oxidizer/fuel ratio is lowered to eliminate excess oxygen and reduce the amount of N0x produced, increased amounts of C0 are produced.
one way to improve the toxicity of the combustion gases is to reduce the combustion temperature which would reduce the initial concentrations of both C0 and N0X. Although simple in theory, it is difficult in practice to reduce the combustion temperature and to also retain a sufficiently high gas generant burn rate for practical application in an inflatable vehicle occupant restraint system. The burn rate of the gas generant is important to insure that the inflator will operate readily and properly. As a general rule, the burn rate of the gas generant decreases as the combustion temperature decreases. By using less energetic fuels, specifically fuels which produce less heat upon combustion, the combustion temperature may be reduced but the gas generant burn rate is also reduced.
W O9~/0~ PCT~US97/13501 Therefore, a need still ~xists for reducing the toxicity of effluent gases produced by nonazide gas generants without compromising the gas generanl: properties.
SUMMARY OF THE INVENTION
5The aforesaid problems are solved, in accordance with the present invention, by a nonazide cas generating composition which in and of itself is nontoxic, ald which upon combustion, also produces inflating gases that hlve reduced levels Of NOI
and CO due to the use of a compound that generates NH2 radicals in the gas phase. Selective non-catalytic reduction (SNCR) employs an NH2 radical that selectiv~ly reacts with nitrogen oxide (NO) in the gas phase to forrl non-toxic nitrogen gas (N2). In an SNCR system, basic requi-ements for the reduction of NO by an SNCR chemical include a well-mixed minimal 1:1 ratio of NH2 radical to NO, whereby th~ NH2 radical is generated by the SNCR chemical and the NO is generated from the gas generant combustion. Furthermore, tlhe NH2 radical must react for a sufficient residence time at ~ temperature within the range of 850-1150~C. The reduced content of toxic gases, such as NO~ and CO, allows the use of nonazide gas generants in vehicle occupant restraint systems while protecting the occupants of the vehicle from exposure to toxic gases which heretofore have been produced by nonazide gas generants.
More specifically, the present invention comprises a nonazide gas generant composition, ard a separate NO~ reducing agent (SNCR) chemical that liberates NH2 radical upon thermal decomposition and/or reaction with ~2 The NO" gases generated from the combustion of the gas genelant, such as NO and NO2, selectively react with the NH2 radicaLs, or NH3 and ~2 ~ thereby producing a harmless gas of N2. A corresponding reduction in CO is an incidental benefit with the use of some of the reducing agents, such as (NH4)2S04. Il addition, the chemistry of the SNCR chemical is noninvasive and will not interfere with the expected performance or stabi.ity of a gas generant combustion.
W098106682 PCT~S97/13501 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT~S) In accordance with the present invention, a vehicle occupant restraint device utilizing an SNCR system comprises a gas generant and a de-NO~ agent. The de-NO~ agent is disposed around the periphery of the gas generant within the gas generant bed and is selected from a group including amides and imides, ammonium compounds, amine compounds, or any compound which produces an NH2 radical in the gas phase. Examples of ammonium compounds include ammonium hydroxide (NH40H), ammonium carbonate ((NH4)2C03), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NC02NH4), and ammonium fluoride (NH4F). Examples of amide and imide compounds, respectively, compounds are urea (H2NCONH2) and cyanuric acid ((HNCO)3). Given the aforementioned benefits, the gas lS generant is preferably nonazide, although other gas generants such as an azide-based composition may be utilized in conjunction with SNCR. The SNCR chemical is preferably ammonium sulfate ((NH4)2S04) based on the optimum and unexpected results given in Example 3 below. Not only does (NH4)2SO4 inhibit production of toxic NO2, it actually reduces NO2 over time. In general, ammonium compounds will generate the highest yield of NH2 radicals.
SNCR is well known and commonly used in industrial boilers to decrease the levels of toxic nitrogen oxides. Until now, SNCR technology has not been successfully implemented in automotive airbag systems. NO is reduced to N2 by the following gas phase reaction with an NH2 radical:
NH2 + NO ~ N2 + H20 (l) Because NO2 is generated by NO, a reduction in NO necessarily causes an overall NOX reduction within the inflator gas. The critical parameters for the successful implementation of SNCR
in any system are the reaction temperature, NH2 radical/NO
ratio, mixing, residence time, and initial NO level. In ........ ... . . .. ...
2 PCT~US97113501 addition, the presence of oxygen (~2) is critical when the SNCR
chemical is ammonia or an ammonium c~mpounds.
To obtain NH2 radical in th~ ! gas phase at the correct level, the SNCR chemical must thermaLly decompose to generate the NH2 radical or NH3 (which must sub;equently react with ~2 to form the NH2 radical). The decompocition products determine how much of the NH2 radical is generated in the gas phase versus what is liberated directly frcm the SNCR chemical. The minimum NH2 radical/N0 ratio in the ~las phase reaction should be 1 mole of NH2 radical for each mcle of N0. In general, a small excess of the NH2 radical will simply result in the formation of small amounts of N~3 and provide minimal additional N0 reduction. SNCR technclogy is most effective at high initial levels of N0. When amm~nium compounds are used, oxygen is necessary for the formation of NH2 radicals, and should be present at levels of 0.1 t~ 11 volume percent.
The decomposition temperature, determinative of when NH2 radicals are generated in the gas phase, is critical because the NH2 radical must be "injl-cted" into the gas phase at the correct temperature thereby enabling the selective reduction reaction of NO~. For exampLe, (NH4)2SO4 decomposes at about 235~C while (NH4)2C03 begins to decompose at room temperature. During an inflator deployment, an SNCR chemical that decomposes at a lower temperatu~e will be "injected" into the system sooner and, as illustrate~ in Example 4, provide a decreased reduction of nitrogen oxides. The importance of temperature is demonstrated by the f~llowing reactions:
NO + NH3 + 1/4~2 - N2 + 3/2H20 (2) NH3 + 5/402 - NO + 3/2H20 (3) The desired reaction, (2 , will only occur at a significant rate at temperatures abo~e 850-950~C. However, at temperatures above 1050-1150~C, reaction (3) becomes dominant and undesirable N0 is formed. In adcition to temperature, the _ .
W O 98/06682 PCTrUS97/13501 importance of good mixing and a sufficient residence time are obvious for the completion of any gas phase reaction. The gas temperatures, degree of mixing, and residence time for a given inflator are determined primarily by the gas generant properties and the inflator configuration and operating conditions.
The temperature of the gases in an inflator will generally vary from the hottest at the generant burning surface to the coolest at the inflator exit ports. Although temperature is extremely difficult to measure, variables such as the thermodynamic properties of the generant, the burning rate of the generant, the cooling devices within the inflator, - and the operating pressure of the inflator each contribute to the overall operating temperature of the SNCR system. The residence time of the gases in an inflator is dependent on the presence of choked flow and the operating pressure. One skilled in the art will readily realize that cognizance and tailoring of these variables when choosing a gas generant will enable the use of a wide variety of gas generant compositions in conjunction with the SNCR system.
In accordance with the present invention, the SNCR
chemical is a noninvasive composition whereby the normal combustion reaction of the gas generant is not interrupted or significantly altered. The present invention is illustrated by the following examples.
Two nonazide passenger inflators (NAPIs) with the same gas generant and hardware were built. Ammonium carbonate ((NH4)2CO3) was added directly to the generant bed of one of the inflators as a powder at 1.4 wt% of the generant mass. The inflators were deployed in a 100 ft3 tank and the gaseous effluents were measured over a 30 minute time period. Carbon monoxide (CO) and ammonia (NH3) were measured by FTI~ while nitrogen (II) oxide (NO), nitrogen lIV) oxide (NO2), and total nitrogen oxides (NOX) were measured by Chemiluminescence. The time weighted averages are reported below in ppm.
WO~8/0~6Q~ PCT~S97/13~1 Inflator C0 NO N~2 NOx NH3 Control 66585.7 29.6 117.6 14 1.4% (NH4) 2C~3 70552.8 0.9 53.6 96 Percent of Control 106%62% 3% 46% 686%
This example illustrates that the addition of this SNCR
ammonium salt significantly reduces the levels of toxic nitrogen oxides while leaving the C0 essentially unchanged.
s Two NAPIs with the same gls generant and hardware were built and tested as described in Example 1. However, the generant load and the cooling assembly differed from that used in Example 1. ((NH4)2C03) was added directly to the generant bed of one of the inflators as a powder at 2.6 wt% of the generant mass. The time weighted averages are reported below in ppm.
Inflator C0 NO N~2 NO~ NH3 Control 822106.1 50.5 162 16 2.6~(NH4)2C03 79882.0 30.7 116 147 Percent of Control 97% 77% 61% 72% 919%
This example demonstrates the imp~)rtance of choosing the correct inflator configuration for su~:cessful implementation of SNCR technology in an airbag inflator. In addition, this example shows that an excess of an SNCR chemical does not result in further N0X reduction, but only in higher levels of NH3 production.
Two NAPIs with the same gas generant and hardware were built and tested as described ir Example 1. However, the generant load and the cooling assembly differed from that of Examples 1 and 2. (NH4) 2S04 was added directly to the generant bed of one of the inflators as a pl~wder at 1.2 wt % of the generant mass. The time weighted avl~rages are reported below in ppm.
W O98/06682 PCTrUS97/13501 Inflator CO N0 No2 N0x NH3 Control 43759.6 12.5 73.3 8 1.2% ~NH4)2S04 406 62.2 5.2 67.7 57 Percent of Control93% 104% 42% 92% 712 Two quite unexpected, yet beneficial results were observed from these tests. First, the addition of ((NH4)2S04) resulted in a reduction of both N0x and C0. Secondly, a comparison of the N02 evolution in the control and in the SNCR
samples indicates a decline over time of the N02 species in the SNCR sample and an increase in the N02 species in the control sample. For the control inflator, the N02 was 9.4 ppm at 3 minutes and 16.4 ppm at 30 minutes. This is what is normally seen since the N0 initially produced by the inflator slowly converts to N02 in the presence ~f ~2- For the inflator with the SNCR chemical, the N02 was 7.8 ppm at 3 minutes and steadily decreased to 5.0 ppm at 30 minutes. This example illustrates the effectiveness of this embodiment in retarding the generation of toxic N02, despite the presence of increased amounts of relatively nontoxic N0 and ~2 Four NAPIs with the same gas generant and hardware were built and tested as described in Example 1. However, the generant load and the cooling assembly differed from that used in Examples 1,2, or 3. (NH4)2S04 (decomposes at 235DC) and H2NC02NH4 (sublimes at 60~C) were each added directly to the generant bed of one of the inflators as a powder at 2.7 wt % of the generant mass. The time weighted averages are reported below in ppm.
Inflator C0 N0 No2 N0x NH3 Control 552 82.2 30.2 115.2 ~0 2.7% (NH4)2S04 453 81.5 6.2 66.2 105 2.7% H2NC02NH4 715 79 31 112.9 196 CA 0226l969 l999-0l-22 W O 98~0~'Q~ PCT~US97/13~01 Again, the addition of (NH4)2S04 resulted in a reduction of NOx and CO. Also, the NO2 level went fron 9.4 ppm at 3 minutes to 5.6 ppm at 30 minutes, verifying the data shown in Example 3.
The decomposition and sublimation ?oints of the different compounds are provided to demonstrate that the decomposition temperature must be considered as ~ critical factor to the success of the SNCR chemical.
While the preferred embodirlent of the invention has been disclosed, it should be appreciated that the invention is susceptible of modification without d~parting from the scope of the following claims.
chemical is ammonia or an ammonium c~mpounds.
To obtain NH2 radical in th~ ! gas phase at the correct level, the SNCR chemical must thermaLly decompose to generate the NH2 radical or NH3 (which must sub;equently react with ~2 to form the NH2 radical). The decompocition products determine how much of the NH2 radical is generated in the gas phase versus what is liberated directly frcm the SNCR chemical. The minimum NH2 radical/N0 ratio in the ~las phase reaction should be 1 mole of NH2 radical for each mcle of N0. In general, a small excess of the NH2 radical will simply result in the formation of small amounts of N~3 and provide minimal additional N0 reduction. SNCR technclogy is most effective at high initial levels of N0. When amm~nium compounds are used, oxygen is necessary for the formation of NH2 radicals, and should be present at levels of 0.1 t~ 11 volume percent.
The decomposition temperature, determinative of when NH2 radicals are generated in the gas phase, is critical because the NH2 radical must be "injl-cted" into the gas phase at the correct temperature thereby enabling the selective reduction reaction of NO~. For exampLe, (NH4)2SO4 decomposes at about 235~C while (NH4)2C03 begins to decompose at room temperature. During an inflator deployment, an SNCR chemical that decomposes at a lower temperatu~e will be "injected" into the system sooner and, as illustrate~ in Example 4, provide a decreased reduction of nitrogen oxides. The importance of temperature is demonstrated by the f~llowing reactions:
NO + NH3 + 1/4~2 - N2 + 3/2H20 (2) NH3 + 5/402 - NO + 3/2H20 (3) The desired reaction, (2 , will only occur at a significant rate at temperatures abo~e 850-950~C. However, at temperatures above 1050-1150~C, reaction (3) becomes dominant and undesirable N0 is formed. In adcition to temperature, the _ .
W O 98/06682 PCTrUS97/13501 importance of good mixing and a sufficient residence time are obvious for the completion of any gas phase reaction. The gas temperatures, degree of mixing, and residence time for a given inflator are determined primarily by the gas generant properties and the inflator configuration and operating conditions.
The temperature of the gases in an inflator will generally vary from the hottest at the generant burning surface to the coolest at the inflator exit ports. Although temperature is extremely difficult to measure, variables such as the thermodynamic properties of the generant, the burning rate of the generant, the cooling devices within the inflator, - and the operating pressure of the inflator each contribute to the overall operating temperature of the SNCR system. The residence time of the gases in an inflator is dependent on the presence of choked flow and the operating pressure. One skilled in the art will readily realize that cognizance and tailoring of these variables when choosing a gas generant will enable the use of a wide variety of gas generant compositions in conjunction with the SNCR system.
In accordance with the present invention, the SNCR
chemical is a noninvasive composition whereby the normal combustion reaction of the gas generant is not interrupted or significantly altered. The present invention is illustrated by the following examples.
Two nonazide passenger inflators (NAPIs) with the same gas generant and hardware were built. Ammonium carbonate ((NH4)2CO3) was added directly to the generant bed of one of the inflators as a powder at 1.4 wt% of the generant mass. The inflators were deployed in a 100 ft3 tank and the gaseous effluents were measured over a 30 minute time period. Carbon monoxide (CO) and ammonia (NH3) were measured by FTI~ while nitrogen (II) oxide (NO), nitrogen lIV) oxide (NO2), and total nitrogen oxides (NOX) were measured by Chemiluminescence. The time weighted averages are reported below in ppm.
WO~8/0~6Q~ PCT~S97/13~1 Inflator C0 NO N~2 NOx NH3 Control 66585.7 29.6 117.6 14 1.4% (NH4) 2C~3 70552.8 0.9 53.6 96 Percent of Control 106%62% 3% 46% 686%
This example illustrates that the addition of this SNCR
ammonium salt significantly reduces the levels of toxic nitrogen oxides while leaving the C0 essentially unchanged.
s Two NAPIs with the same gls generant and hardware were built and tested as described in Example 1. However, the generant load and the cooling assembly differed from that used in Example 1. ((NH4)2C03) was added directly to the generant bed of one of the inflators as a powder at 2.6 wt% of the generant mass. The time weighted averages are reported below in ppm.
Inflator C0 NO N~2 NO~ NH3 Control 822106.1 50.5 162 16 2.6~(NH4)2C03 79882.0 30.7 116 147 Percent of Control 97% 77% 61% 72% 919%
This example demonstrates the imp~)rtance of choosing the correct inflator configuration for su~:cessful implementation of SNCR technology in an airbag inflator. In addition, this example shows that an excess of an SNCR chemical does not result in further N0X reduction, but only in higher levels of NH3 production.
Two NAPIs with the same gas generant and hardware were built and tested as described ir Example 1. However, the generant load and the cooling assembly differed from that of Examples 1 and 2. (NH4) 2S04 was added directly to the generant bed of one of the inflators as a pl~wder at 1.2 wt % of the generant mass. The time weighted avl~rages are reported below in ppm.
W O98/06682 PCTrUS97/13501 Inflator CO N0 No2 N0x NH3 Control 43759.6 12.5 73.3 8 1.2% ~NH4)2S04 406 62.2 5.2 67.7 57 Percent of Control93% 104% 42% 92% 712 Two quite unexpected, yet beneficial results were observed from these tests. First, the addition of ((NH4)2S04) resulted in a reduction of both N0x and C0. Secondly, a comparison of the N02 evolution in the control and in the SNCR
samples indicates a decline over time of the N02 species in the SNCR sample and an increase in the N02 species in the control sample. For the control inflator, the N02 was 9.4 ppm at 3 minutes and 16.4 ppm at 30 minutes. This is what is normally seen since the N0 initially produced by the inflator slowly converts to N02 in the presence ~f ~2- For the inflator with the SNCR chemical, the N02 was 7.8 ppm at 3 minutes and steadily decreased to 5.0 ppm at 30 minutes. This example illustrates the effectiveness of this embodiment in retarding the generation of toxic N02, despite the presence of increased amounts of relatively nontoxic N0 and ~2 Four NAPIs with the same gas generant and hardware were built and tested as described in Example 1. However, the generant load and the cooling assembly differed from that used in Examples 1,2, or 3. (NH4)2S04 (decomposes at 235DC) and H2NC02NH4 (sublimes at 60~C) were each added directly to the generant bed of one of the inflators as a powder at 2.7 wt % of the generant mass. The time weighted averages are reported below in ppm.
Inflator C0 N0 No2 N0x NH3 Control 552 82.2 30.2 115.2 ~0 2.7% (NH4)2S04 453 81.5 6.2 66.2 105 2.7% H2NC02NH4 715 79 31 112.9 196 CA 0226l969 l999-0l-22 W O 98~0~'Q~ PCT~US97/13~01 Again, the addition of (NH4)2S04 resulted in a reduction of NOx and CO. Also, the NO2 level went fron 9.4 ppm at 3 minutes to 5.6 ppm at 30 minutes, verifying the data shown in Example 3.
The decomposition and sublimation ?oints of the different compounds are provided to demonstrate that the decomposition temperature must be considered as ~ critical factor to the success of the SNCR chemical.
While the preferred embodirlent of the invention has been disclosed, it should be appreciated that the invention is susceptible of modification without d~parting from the scope of the following claims.
Claims (13)
1. A vehicle occupant restraint system comprising:
an inflatable air bag;
a gas generator;
a gas generant compound located within said gas generator; and a selective non-catalytic reducing compound proximate to and interspersed about said gas generant compound, placed wherein said selective non-catalytic reducing compound is selected from the group comprising ammonium salts, ammonium hydroxide (NH4OH), amine compounds, and amide and imide compounds.
an inflatable air bag;
a gas generator;
a gas generant compound located within said gas generator; and a selective non-catalytic reducing compound proximate to and interspersed about said gas generant compound, placed wherein said selective non-catalytic reducing compound is selected from the group comprising ammonium salts, ammonium hydroxide (NH4OH), amine compounds, and amide and imide compounds.
2. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant comprises a nonazide composition;
said ammonium salt is selected from a group consisting of ammonium hydroxide (NH4OH), ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F); and said amide compound is selected from a group consisting of urea (H2NCONH2); and said imide compound is selected from a group consisting of cyanuric acid ((HNCO)3).
said gas generant comprises a nonazide composition;
said ammonium salt is selected from a group consisting of ammonium hydroxide (NH4OH), ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F); and said amide compound is selected from a group consisting of urea (H2NCONH2); and said imide compound is selected from a group consisting of cyanuric acid ((HNCO)3).
3. A method of reducing the toxicity of effluent gases of a gas generator, used to inflate an airbag of a vehicle occupant restraint system, comprising the step of:
interspersing a selective non-catalytic reducing compound about a gas generant composition within the gas generator; and reacting with gaseous products of the selective non-catalytic reducing compound with the gaseous combustion products of the gas generant composition.
interspersing a selective non-catalytic reducing compound about a gas generant composition within the gas generator; and reacting with gaseous products of the selective non-catalytic reducing compound with the gaseous combustion products of the gas generant composition.
4. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of an ammonium salt selected from a group consisting of ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F).
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of an ammonium salt selected from a group consisting of ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F).
5. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of urea (H2NCONH2).
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of urea (H2NCONH2).
6. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of cyanuric acid ((HNCO) 3).
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of cyanuric acid ((HNCO) 3).
7. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of ammonium hydroxide (NH4OH).
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of ammonium hydroxide (NH4OH).
8. A vehicle occupant restraint system of Claim 1 wherein:
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of an amine compound.
said gas generant compound consists of a nonazide composition; and said selective non-catalytic reducing compound consists of an amine compound.
9. The method of claim 3 wherein:
said selective non-catalytic reducing compound consists of an ammonium salt selected from a group consisting of ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F).
said selective non-catalytic reducing compound consists of an ammonium salt selected from a group consisting of ammonium carbonate ((NH4)2CO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonium carbamate (H2NCO2NH4), and ammonium fluoride (NH4F).
10. The method of claim 3 wherein:
said selective non-catalytic reducing compound consists of urea (H2NCONH2).
said selective non-catalytic reducing compound consists of urea (H2NCONH2).
11. The method of claim 3 wherein:
said selective non-catalytic reducing compound consists of cyanuric acid ((HNCO)3).
said selective non-catalytic reducing compound consists of cyanuric acid ((HNCO)3).
12. The method of claim 3 wherein:
said selective non-catalytic reducing compound consists of ammonium hydroxide (NH4OH).
said selective non-catalytic reducing compound consists of ammonium hydroxide (NH4OH).
13. A vehicle occupant restraint system of Claim 1 wherein:
said selective non-catalytic reducing compound consists of an amine compound.
said selective non-catalytic reducing compound consists of an amine compound.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US69595496A | 1996-08-12 | 1996-08-12 | |
| US695,954 | 1996-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2261969A1 true CA2261969A1 (en) | 1998-02-19 |
Family
ID=24795123
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002261969A Abandoned CA2261969A1 (en) | 1996-08-12 | 1997-07-31 | Selective non-catalytic reduction (sncr) of toxic gaseous effluents in airbag inflators |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0950040A4 (en) |
| JP (1) | JP3426250B2 (en) |
| KR (1) | KR19990037956A (en) |
| AU (1) | AU3967997A (en) |
| CA (1) | CA2261969A1 (en) |
| WO (1) | WO1998006682A2 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6332404B1 (en) | 1996-04-15 | 2001-12-25 | Autoliv Asp, Inc. | Airbag inflation gas generation via a dissociating material and the moderation thereof |
| US7575648B1 (en) * | 1996-08-12 | 2009-08-18 | Automotive Systems Laboratory, Inc. | Selective non-catalytic reduction (SNCR) of toxic gaseous effluents |
| EP0979219A1 (en) * | 1997-05-02 | 2000-02-16 | Dynamit Nobel GmbH Explosivstoff- und Systemtechnik | Reducing pollutant gases in gas mixtures from pyrotechnic reactions |
| EP0997450B1 (en) * | 1998-04-20 | 2018-04-11 | Daicel Chemical Industries, Ltd. | METHOD OF REDUCING NO x |
| US6634302B1 (en) | 2000-02-02 | 2003-10-21 | Autoliv Asp, Inc. | Airbag inflation gas generation |
| US6673173B1 (en) | 2000-02-02 | 2004-01-06 | Autoliv Asp. Inc. | Gas generation with reduced NOx formation |
| JP2002302010A (en) * | 2001-04-04 | 2002-10-15 | Daicel Chem Ind Ltd | Reduction method of nitrogen oxides for hybrid inflator |
| DE102004001625B4 (en) * | 2004-01-12 | 2014-02-13 | Trw Airbag Systems Gmbh | A method of inflating an airbag and airbag module for use in the method |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3721102A (en) * | 1969-12-04 | 1973-03-20 | Rocket Research Corp | Cool working gas generator |
| US3715131A (en) * | 1971-06-04 | 1973-02-06 | Hercules Inc | Chemical gas generating device for an automobile safety system |
| US3785674A (en) * | 1971-06-14 | 1974-01-15 | Rocket Research Corp | Crash restraint nitrogen generating inflation system |
| US3797854A (en) * | 1971-06-14 | 1974-03-19 | Rocket Research Corp | Crash restraint air generating inflation system |
| DE4220019A1 (en) * | 1991-06-21 | 1992-12-24 | Dynamit Nobel Ag | DRIVING AGENT FOR GAS GENERATORS |
| US5682014A (en) * | 1993-08-02 | 1997-10-28 | Thiokol Corporation | Bitetrazoleamine gas generant compositions |
| US5538567A (en) * | 1994-03-18 | 1996-07-23 | Olin Corporation | Gas generating propellant |
| US5460668A (en) * | 1994-07-11 | 1995-10-24 | Automotive Systems Laboratory, Inc. | Nonazide gas generating compositions with reduced toxicity upon combustion |
| DE19505568A1 (en) * | 1995-02-18 | 1996-08-22 | Dynamit Nobel Ag | Gas generating mixtures |
-
1997
- 1997-07-31 CA CA002261969A patent/CA2261969A1/en not_active Abandoned
- 1997-07-31 WO PCT/US1997/013501 patent/WO1998006682A2/en not_active Application Discontinuation
- 1997-07-31 EP EP97937077A patent/EP0950040A4/en not_active Withdrawn
- 1997-07-31 JP JP50978998A patent/JP3426250B2/en not_active Expired - Fee Related
- 1997-07-31 AU AU39679/97A patent/AU3967997A/en not_active Abandoned
-
1999
- 1999-02-12 KR KR1019997001228A patent/KR19990037956A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0950040A4 (en) | 1999-12-22 |
| KR19990037956A (en) | 1999-05-25 |
| JP2000514395A (en) | 2000-10-31 |
| EP0950040A2 (en) | 1999-10-20 |
| WO1998006682A3 (en) | 1998-07-09 |
| JP3426250B2 (en) | 2003-07-14 |
| WO1998006682A2 (en) | 1998-02-19 |
| AU3967997A (en) | 1998-03-06 |
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| FZDE | Discontinued | ||
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