KR100851091B1 - Selective filtration of cigarette smoke using chitosan derivatives - Google Patents

Abstract

A smoking article filter comprising a chitosan derivative and having a porous resin having a high surface area to mass ratio. Preferred embodiments contain chitosan crosslinked with glutaraldehyde and chitosan crosslinked with glyoxal. Chitosan derivatives are responsible for the selective filtration of tobacco smoke, specifically the removal of aldehydes, hydrogen cyanide, heavy metals and carbonyls.

Chitosan derivatives, tobacco filters, porous resins, selective filtration, glutaraldehyde, glyoxal, aldehydes, hydrogen cyanide, heavy metals, carbonyl

Description

Selective Filtration of Cigarette Smoke Using Chitosan Derivatives {SELECTIVE FILTRATION OF CIGARETTE SMOKE USING CHITOSAN DERIVATIVES}

Reference Description for Related Applications

This application is a Paris Treaty and claims priority to co-pending US patent application Ser. No. 10 / 842,165, filed May 10, 2004.

The present invention relates to improvements related to tobacco smoke filters. More specifically, the present invention relates to tobacco filters capable of selectively removing undesirable components from tobacco smoke.

There are various types of filter material for tobacco smoke proposed in the prior art. Examples include cotton, paper, cellulose acetate and certain synthetics. However, most of these filter materials are effective only in the removal of particulates, tars and condensation components from tobacco smoke. The art is equipped with numerous filtration techniques and materials that remove undesirable components of the smoke and cause other reactions as the smoke passes through the filtration layer or other reactive medium. Among the problems encountered in conventional filters are the problem of invalidating reactive filtration surfaces and materials or clogging during use and consumption.

Filters made of filamentous or fibrous materials, such as cellulose acetate tow or paper, are rather effective at removing particulate components of tobacco smoke. However, this filter has little or no effect on the removal of certain gaseous components in the gas phase of tobacco smoke, such as hydrogen cyanide, aldehydes, carbonyls, metals and sulfides. Such volatile components can be removed through adsorption and absorption or chemical reactions on appropriate surfaces.

Some known materials that act as absorbers and adsorbents include activated carbon, porous inorganic materials and ion exchange resins. Ion exchange resins of porous structure have been found to be slightly effective, but the effects are reduced during smoking, as are carbon and porous inorganic materials. This may be because the material begins to saturate and become increasingly inert, or the adsorbed material is released due to thermal desorption of the retained material.

Resin mainly containing tertiary amino or quaternary ammonium groups are known to be unsuitable for removing aldehydes from tobacco smoke. It is also known that chitosan with the maximum number of chitosan and amino groups is not effective. Among the problems with these materials is the failure to provide a filtration medium that allows the flow of smoke to continue at low pressure differentials or low pressure gradients. Other problems with selective filtration media are also known. For example, the use of certain amino acids such as glycine is known to be effective in removing aldehydes in tobacco smoke. However, glycine has been found to be unstable during the tobacco filter manufacturing process, while reducing the concentration of formaldehyde in tobacco smoke. Moreover, the use of amino acids generates ammonia odor during storage.

Summary of the Invention

It has been found that chitosan can be chemically modified to possess the physical properties of the filter media and to have a chemical composition that can effectively adsorb and absorb undesirable smoke constituents, thus providing excellent performance as a tobacco filter.

That is, it is an object of the present invention to present a tobacco filter device, more particularly, present on the gas of tobacco smoke, such as hydrogen cyanide, aldehydes, metals and sulfides, without the disadvantages or drawbacks associated with the prior art as described above. To provide a tobacco filter that can selectively remove the components that are not.

Another object is to provide a novel tobacco and smoke filter comprising a porous resin of crosslinked chitosan.

Another object is to provide a crosslinked chitosan reactive material for selective smoke filtration of smoking articles with a high surface-to-volume ratio and a reduced number of reactive amino groups.

According to the invention, the tobacco smoke filter comprises an adsorbent / absorbent for removing undesirable volatile tobacco smoke components such as hydrogen cyanide, aldehydes, carbonyls, metals and sulfides. In particular, the present invention relates to a particularly effective tobacco smoke filtration composite of chitosan crosslinked with glutaraldehyde and chitosan crosslinked with glyoxal.

Chitosan is crosslinked by glutaraldehyde and glyoxal, which can selectively filter tobacco smoke, specifically removing undesirable smoke components such as aldehydes, hydrogen cyanide, carbonyls, sulfides and metals It forms a porous resin with a high surface area to mass ratio.

Chitosan is a linear polyglucosamine polymer obtained from deacetylation of chitin, a polysaccharide found in the exoskeleton of shellfish. Chitin is also found in insects and in small amounts in many other animal and vegetable organisms. Chitin is a linear polymer of 2-deoxy, 2-acetyl-amino glucose whose chemical structure is similar to cellulose. Chitin is insoluble in almost all media except strong inorganic acids and relatively unreactive due to acetylated amino groups.

Chitin is deacetylated by strong alkali treatment, resulting in chitosan containing one free amino group for each glucose structural unit of the polymer. Chitosan is still a long chain linear polymer but a highly reactive cationic polyelectrolyte material. It forms salts with simple organic acids such as formic acid, acetic acid, tartaric acid, citric acid and the like and is soluble in dilute aqueous solutions of these materials. Chitosan is nontoxic and biodegradable and finds utility in numerous applications including chromatography, drug delivery and cosmetics.

Porous chitosan resins can be formed by phase inversion techniques. This technique is accomplished by dissolving chitosan flakes or powder in a suitable solvent such as aqueous acid and then coacervating in an aqueous base solution to form water swelling chitosan gel beads. These beads can be crosslinked, respectively, by glutaraldehyde and glyoxal to increase mechanical strength and decrease bead solubility. The wet beads then freeze-dried to form a porous crosslinked resin. Drying may also be carried out via vacuum drying or air drying.

Porous resins may also be prepared by heat induced phase separation techniques. This technique dissolves chitosan flakes or powders in a suitable solvent such as aqueous acetic acid, then adds the solution to a nonsolvent such as methanol, and cools the resulting solution below the freezing point of the chitosan solution to produce frozen beads. To achieve. These beads can then be neutralized with a base and then crosslinked with glutaraldehyde and glyoxal respectively to modify the final properties of the chitosan resin. The resulting beads are lyophilized to produce a porous crosslinked chitosan resin. Drying may be accomplished via vacuum drying and air drying.

The crosslinked resin produced through these two methods is a reduced number of reactive amino groups. The reduced number of reactive amino groups is the result of the crosslinking reaction with glutaraldehyde or glyoxal. Surprisingly, it has been found that the present invention with reduced number of reactive amino groups is selective for removing hydrogen cyanide and formaldehyde from tobacco smoke. In addition, it has been surprisingly found that crosslinked chitosan resins with reduced number of reactive amino groups are superior in selective removal activity than by the prior art in which the maximum number of reactive amino groups has been used.

The porous resin of the present invention can be incorporated into tobacco in a variety of ways. The resin may be disposed between filter sections, which may be composed of fibrous, filamentary and paper materials. The resin may also be dispersed throughout the filter tow. Alternatively, the resin may be disposed in the filter bed of the filter section and filled with the filter bed. The resin may also be incorporated into portions of tobacco filters, such as tip paper, shaped paper inserts, plugs, spaces or even free flow sleeves. The resin may also be incorporated into tobacco filter paper and attached to the tobacco rod with the tip paper, or incorporated into the hollow of the filter.

Detailed Description of the Preferred Embodiments

In the following, examples of the present invention are illustrated for purposes of illustration and not limitation. This example illustrates two different methods of making chitosan beads and several other methods of crosslinking chitosan beads. The following examples all produce porous crosslinked chitosan resin beads with reduced number of reactive amino groups.

Example I:

Porous chitosan resins were synthesized by a phase inversion technique. This technique was performed by dissolving about 20 g of chitosan flakes (utility grade) in 3.5% acetic acid to prepare a 7% chitosan solution. The mixture increased in viscosity and gelled upon completion of chitosan addition. Further dilution with acetic acid gave a solution with about 3% chitosan flakes. This solution produced a chitosan solution of more easily handled viscosity. The total amount of acetic acid used to dissolve the chitosan flakes was about 665 ml. This solution was then filtered to separate off any insoluble material. This chitosan solution was then added dropwise to a 2 molar sodium hydroxide precipitation bath to obtain water swollen gel beads. The gel beads were then filtered and washed with deionized water until the wash water had a neutral pH of about 7.

The beads were then suspended in about 1 liter of an aqueous 2.5% glutaraldehyde solution for several hours to complete heterogeneous crosslinking of the chitosan beads. After crosslinking, the beads were filtered and washed with warm deionized water to remove any excess glutaraldehyde. Thereafter, the beads were lyophilized to obtain porous glutaraldehyde crosslinked chitosan resin beads. The BET surface area of this resin was determined to be about 120 m 2 / g. These beads were then ground and sieved to yield particles having a particle size of about 16 to 70 mesh. Analysis of the surface area of the pulverized resin confirmed that there was no appreciable change on the surface. The BET surface area of the sieved sample was about 117 m 2 / g.

Example II:

Porous chitosan resins were synthesized according to the phase inversion technique of Example I. In this example, chitosan beads were suspended in 2.5% aqueous glyoxal solution for several hours to complete heterogeneous crosslinking of the beads. After crosslinking, the beads were filtered and washed with warm deionized water to remove any excess glyoxal. These beads were lyophilized to obtain porous glyoxal crosslinked chitosan resin beads.

Example III:

Porous chitosan resins were prepared according to heat induced phase separation techniques. First, chitosan powder (Vansen Chemical: 92% deacetylation) was dissolved in 3.5% acetic acid to prepare a 4% chitosan solution. A precipitation bath containing sodium hydroxide (2 mol) in a 20:80 methanol / water solution was prepared and cooled to 0 ° C. Chitosan solution was then added dropwise to the precipitation tank under stirring at a suitable rate. Immediately after addition of the solution to the settling bath, precipitation of chitosan occurred. The settling bath containing the chitosan precipitate was then warmed up to room temperature. The resulting beads were filtered and washed with deionized water until the wash water had a neutral pH of about 7.

The heterogeneous crosslinking of the chitosan beads was then completed by suspending about 396 g of the wet beads in about 1980 ml of an aqueous 2.5% glutaraldehyde solution for several hours. After crosslinking, the beads were filtered and washed with warm deionized and cold deionized water to remove any excess glutaraldehyde. The beads were then lyophilized to obtain porous glutaraldehyde crosslinked chitosan resin beads. The beads were then ground and sieved to yield about 16 to 70 mesh particles. The BET surface area of this resin was about 210 m 2 / g as a result of the measurement.

Example IV:

Porous chitosan resins were prepared according to the heat induced phase separation technique of Example III. In this example, heterogeneous crosslinking of chitosan beads was accomplished by suspending about 261 g of wet beads in about 1300 ml of an aqueous 2.5% glyoxal solution for several hours. After crosslinking, the beads were filtered and washed with warm deionized and cold deionized water to remove any excess glyoxal. The beads were then lyophilized to obtain porous glyoxal crosslinked chitosan resin beads. The beads were then ground and sieved to yield about 16 to 70 mesh particles. The BET surface area of this crosslinked resin was about 145 m <2> / g as a result of a measurement.

Example V:

Porous chitosan resins were prepared according to the heat induced phase separation technique of Example III. In this example, heterogeneous crosslinking of chitosan beads was accomplished by suspending the beads in a glutaraldehyde and ethanol solution for several hours. After crosslinking, the beads were filtered and washed with ethanol to remove any excess glutaraldehyde. Subsequently, it was dried in vacuo to obtain porous glutaraldehyde crosslinked chitosan resin beads.

Example VI:

Porous chitosan resins were prepared according to the heat induced phase separation technique of Example III. In this example, chitosan beads were suspended in an aqueous glutaraldehyde solution for several hours to complete heterogeneous crosslinking of the chitosan beads. After crosslinking, the beads were filtered and washed with ethanol to remove any excess glutaraldehyde. Subsequently, it was dried in vacuo to obtain porous glutaraldehyde crosslinked chitosan resin beads.

While the above examples specify the amount or concentration of the materials used to prepare the various aspects of the invention, various ranges of concentrations and amounts of materials can be used in the practice of the invention. For example, the crosslinker solution may be used in a concentration range of about 0.1% to about 50%, the chitosan solution may be used in a concentration range of about 0.1% to about 20%, the acetic acid solution may range from about 0.1% to about 10%, The base solution may be used in the range of about 1 mole to about 5 moles of sodium hydroxide. In addition, the time range of the crosslinking reaction may also range from about 1 hour up to about 24 hours.

Example

Tobacco generally contains two sections, a tobacco containing portion, sometimes called a tobacco rod, and a filter portion, also called a filter tip. Tobacco samples with a hollow filter were removed from a cigarette made with standard manufacturing techniques, and then replaced with a filter tip with a cellulose acetate section at the end of the cigarette filter, with a cellulose acetate section at the mouth end of the filter, with an intermediate hollow. Manufactured. As a group of samples, a chitosan resin synthesized by a semolina (inert filler), a phase inversion technique and crosslinked with glutaraldehyde (Example I), a chitosan resin synthesized by a heat-induced phase separation technique and crosslinked with a glutaraldehyde (execution) Example III), chitosan resin synthesized by a heat induced phase separation technique and crosslinked with glyoxal (Example IV), synthesized by a heat induced phase separation technique, crosslinked with glutaraldehyde in ethanol, washed with ethanol and vacuum 50 mg of a sample of dry chitosan resin (Example V) and a heat-induced phase separation technique, crosslinked with an aqueous solution of glutaraldehyde, washed with ethanol and vacuum dried chitosan resin (Example VI) in the middle hollow of the filter tip It prepared using the sample loading amount. This load was constant for each sample to provide comparable results. The amount of resin loaded into the filter of the present invention may range from about 10 mg to about 200 mg. Each sample was decompressed to minimize smoke delivery parameters.

Various tests were performed in comparison with conventional instruments to determine the ability of the tobacco filter according to the invention to remove undesirable components from tobacco smoke. Each test measured the amount of undesirable components removed from the smoke mainstream after the cigarette had been fully smoked. The following data set illustrates the performance achieved when filtering the volatile constituents of tobacco smoke in each preferred embodiment compared to the control material semolina.

The analysis results for gas phase and total smoke analysis are summarized in the following table. % Reduction refers to the difference in% between the total smoke liquor or the amount of analyte measured in the gas phase of the cigarette containing the semolina and chitosan resin in the filter tip.

Gas Phase Smoke Analysis of Chitosan Resin (Example I) Prepared by Phase Inversion Technology

 Analytes % Reduction Chitosan Crosslinked by Glutaraldehyde (Example I) Hydrogen cyanide 49 Acetaldehyde 10 Acetonitrile 11 Acrolein 15 Propionaldehyde 11 Acetone 7 Methyl Ethyl Ketone + Butyraldehyde 16 Crotonaldehyde 13

Hydrogen Cyanide Analysis in Total Smoke on Chitosan Resin (Example I) Prepared by Phase Inversion Technique

 Analytes % Reduction Chitosan Crosslinked by Glutaraldehyde (Example I) Hydrogen cyanide 41

Chitosan resin produced by the phase inversion technique ( Example  Carbonyl Analysis in Total Smoke for I)

 Analytes % Reduction Chitosan Crosslinked by Glutaraldehyde (Example I) Formaldehyde 36 Acetaldehyde 13 Acetone 5 Acrolein 11 Propionaldehyde 16 Crotonaldehyde 9 Butyraldehyde 17

heating Induction  Chitosan resin prepared by the phase separation technique ( Example  Gas phase smoke analysis for III and IV)

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example III) Chitosan Crosslinked by Glyoxal (Example IV) Acetaldehyde 13 31 Acetone 21 30 Acetonitrile 18 26 Acrolein 29 36 Acrylonitrile 21 29 Crotonaldehyde 7 42 Hydrogen cyanide 60 45 Methyl ethyl ketone 21 29 Propionaldehyde 23 36 i-butyraldehyde 27 35 n-butyraldehyde 27 40

Hydrogen Cyanide Analysis in Total Smoke for Chitosan Resin (Examples III and IV) Prepared by Heat-Induced Phase Separation Techniques

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example III) Chitosan Crosslinked by Glyoxal (Example IV) Hydrogen cyanide 54 29

heating Induction  Chitosan resin prepared by the phase separation technique ( Example  Carbonyl Analysis in Total Smoke for III and IV)

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example III) Chitosan Crosslinked by Glyoxal (Example IV) Acetaldehyde One 2 Acetone 5 0 Acrolein 10 3 Butyraldehyde 14 8 Crotonaldehyde 20 9 Formaldehyde 50 46 Propionaldehyde 17 19

Trace Metal Analysis in Total Smoke on Chitosan Resin (Examples III and IV) Prepared by Heat-Induced Phase Separation Techniques

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example III) Chitosan Crosslinked by Glyoxal (Example IV) cadmium 32 38

heating Induction  Chitosan resin prepared by the phase separation technique ( Example  Gas phase smoke analysis for V)

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example V) Acetaldehyde 9 Acetone 6 Acetonitrile 3 Acrolein 13 Crotonaldehyde 7 Hydrogen cyanide 36 Methyl ethyl ketone 6 Propionaldehyde 11 i-butyraldehyde 9 n-butyraldehyde 10

Hydrogen Cyanide Analysis in Total Smoke for Chitosan Resin (Example V) Prepared by Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example V) Hydrogen cyanide 27

Carbonyl Analysis in Total Smoke on Chitosan Resin (Example V) Prepared by Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example V) Acetonitrile 3 Acetaldehyde 27 Acetone 24 Acrolein 32 Butyraldehyde 41 Crotonaldehyde 30 Formaldehyde 58 Propionaldehyde 33

Trace Metal Analysis in Total Smoke on Chitosan Resin (Example V) Prepared by Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example V) cadmium 38

heating Induction  Chitosan resin prepared by the phase separation technique ( Example  VI) Body  Smoke analysis

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example VI) Acetaldehyde 3 Acetone 4 Acrolein 9 Crotonaldehyde 11 Hydrogen cyanide 30 Methyl ethyl ketone 11 Propionaldehyde 6 i-butyraldehyde 7 n-butyraldehyde 11

Hydrogen Cyanide Analysis in Total Smoke for Chitosan Resin (Example VI) Prepared by Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example VI) Hydrogen cyanide 30

Carbonyl Analysis in Total Smoke on Chitosan Resin (Example VI) Prepared by Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example VI) Acetaldehyde 0 Acetone 0 Acrolein 0 Butanone One Butyraldehyde 14 Crotonaldehyde 36 Formaldehyde 37 Propionaldehyde 0

Trace Metal Analysis in Total Smoke on Chitosan Resin (Example VI) Prepared by a Heat-Induced Phase Separation Technique

% Reduction Chitosan Crosslinked by Glutaraldehyde (Example VI) cadmium 26

The above data showed that the crosslinked chitosan resins described herein were surprisingly selective in removing aldehydes and hydrogen cyanide in tobacco smoke as compared to inert semolina controls. Glutaraldehyde crosslinked chitosan resins reduced gas phase delivery of hydrogen cyanide by 60% compared to control samples (Example III). In a separate test, the uncrosslinked ground chitosan particles had no effect on gaseous hydrogen cyanide delivery. In addition, glutaraldehyde crosslinked chitosan resins reduced hydrogen cyanide delivery in total smoke by 54% and formaldehyde delivery in total smoke liquor by 50% compared to control samples (Example III).

While the present invention has been described with reference to preferred embodiments, it will be appreciated that variations thereof will be apparent to those skilled in the art. Such modifications should also be considered within the scope and scope of the invention as defined in the following claims.

Claims (34)

A tobacco smoke filter comprising chitosan resin having chitosan crosslinked with glyoxal. The filter as claimed in claim 1, wherein said resin is in the form of particulates in the range of 17 mesh to 70 mesh size. A filter as claimed in claim 1, wherein said resin contains pulverized particles. 2. The filter of claim 1, wherein the tobacco smoke filter retains the resin in the range of 10 mg to 200 mg. The filter of claim 1, wherein the resin is in particulate form and disposed between the filter sections, the filter sections having a material selected from the group consisting of fibrous, filamentous, paper, and combinations thereof. The filter as claimed in claim 1, wherein said resin is in particulate form and dispersed in filter tow. Preparing a smoking article filter having a chitosan resin crosslinked with glyoxal, and passing smoke through the filter. Preparing a filtration bed containing a glyoxal crosslinked chitosan resin in the bed, and passing a fluid containing components reactive with the resin through the filtration bed. 10. The method of claim 8, wherein preparing the filter bed comprises filling the chitosan resin in the bed. 10. The method of claim 8, wherein said resin is in the form of fine particles of 16 mesh size. 9. The method of claim 8, wherein preparing the filtration bed further comprises filling a crosslinked chitosan resin in the bed. 9. The method of claim 8, wherein said fluid is tobacco smoke and said component contains a pyrolysis product of tobacco material. Removing a pyrolysis product of tobacco material from tobacco smoke, the method comprising preparing a filtration zone generally disposed of glyoxal crosslinked chitosan resin, and passing the pyrolysis product of tobacco material through the filtration zone. Way. Dissolving chitosan in a first solution comprising 0.1% to 10% acetic acid to prepare a second solution having chitosan in a range of 0.1% to 20%; Filtering the second solution; Dropping the second solution into a precipitation bath having sodium hydroxide in the range of 1 to 5 moles to form gel beads; Washing the gel beads; Suspending the gel beads in a crosslinking solution containing 0.1% to 50% of the crosslinking compound glyoxal for 1 to 24 hours to form crosslinked beads; Washing the crosslinked beads; And Drying the crosslinked beads to form porous chitosan crosslinked resin beads. Dissolving chitosan in an acetic acid solution containing 0.1% to 10% of acetic acid to produce a chitosan solution having a chitosan in a range of 0.1% to 20%; Cooling the precipitation bath containing sodium hydroxide, water and methanol to below ambient room temperature; Adding the chitosan solution dropwise to the precipitation tank to form gel beads; Heating the settling bath containing such gel beads to ambient room temperature; Washing the gel beads; Suspending the gel beads for 1 hour to 24 hours in a crosslinking solution containing 0.1% to 50% of glyoxal crosslinking compound to form crosslinked beads; Washing the crosslinked beads; And Drying the crosslinked beads to form porous chitosan crosslinked resin beads. A tobacco smoke filter comprising glyoxal crosslinked chitosan resin in the range of 10 mg to 200 mg, ranging in size from 16 mesh to 70 mesh. 17. A tobacco smoke filter according to claim 16, wherein the filter is attached to the tobacco rod by a tip paper. The resin of claim 16 wherein the resin is selected from the group consisting of tip paper, shaped paper inserts, plugs, spaces and free-flow sleeves. A tobacco smoke filter characterized by being incorporated into at least one tobacco filter portion. The tobacco smoke filter according to claim 16, wherein the resin is incorporated in tobacco filter paper. Preparing a filter medium consisting of glyoxal and having a crosslinking compound crosslinked to chitosan; And A method of making a filter useful for removing a gaseous component of a gaseous mixture, the method comprising incorporating the filter medium that removes the gaseous component of a gaseous mixture into a filter. 21. The method of claim 20, further comprising attaching the filter to a tobacco rod using a tip paper. 21. The method of claim 20, wherein said filter media is incorporated in at least one tobacco filter portion selected from the group consisting of tip paper, molded paper insert, plug, space and free flow sleeve. The method of claim 20, wherein the crosslinking compound is incorporated into the hollow of the filter. A method of removing gaseous components of a gaseous mixture comprising passing a gaseous mixture in contact with a filter, the filter having a reagent comprising at least one reactive functional group crosslinked to chitosan, such that And chemically reacting with the gas component to remove the gas component from the gas mixture, wherein the functional group is glyoxal. 25. The method of claim 24, further comprising generating a gas mixture and causing a gas stream containing the gas mixture to pass through the filter such that the components of the gas mixture to be removed are chemically reacted with the reagents to produce the gas mixture. Preventing reintroduction into the residence. delete delete delete delete delete delete delete delete delete