Patent Application
20060260626
Various activated carbon materials have been employed as sorbents in smoking articles to remove or reduce smoke constituents. Activated carbons are useful sorbents and have a large capacity; however, they lack selectivity. While they are effective in removing targeted constituents from tobacco smoke, they also may remove volatile constituents which contribute to flavor, aroma and other desirable attributes. Further, activated carbon in a cigarette filter may be rapidly inactivated during storage by the adsorption of volatile compounds, or by contact with various constituents of mainstream smoke.
Zeolite-type molecular sieves have also been used in smoking articles to selectively remove constituents of tobacco smoke. Zeolite molecular sieve sorbents are capable of selectively removing one or more targeted constituents of mainstream smoke. However, zeolites have minimal capacities and are quickly exhausted before removing a significant amount of the targeted constituent.
There is interest in a filter system for use in smoking articles which can readily be manufactured in various shapes from commercially available activated carbons and zeolite materials and can be tailored to produce components which selectively remove or reduce the concentration of various smoke constituents while retaining desirable flavor constituents and having an extended shelf life.
A smoking article is provided which includes tobacco and a filter system comprising a composite composed of an activated carbon substrate and a zeolite-type membrane coated thereon. Also provided is a filter system, a method of making smoking articles containing said filter system and a method of selectively removing targeted constituents from tobacco smoke.
In one embodiment, a filter is prepared containing a composite made by the deposition of a molecular sieve membrane directly onto a carbon-containing substrate by hydrothermal synthesis of a given molecular sieve. Pre-treatment of the substrate may be desirable to achieve optimum adhesion and growth of the membrane on the substrate.
In another embodiment, cigarettes are prepared which contain tobacco and the filter mentioned above. A preferred smoking article is a traditional or non-traditional cigarette. The aforementioned composite preferably is incorporated into a filter of a cigarette.
Another embodiment relates to a method of making a filter cigarette, comprising: (i) providing a cut filler to a cigarette making machine and forming a tobacco column; (ii) placing a paper wrapper around the tobacco column and forming a tobacco rod; (iii) attaching a cigarette filter comprising the composite described above to the tobacco rod to form the cigarette.
In another embodiment, a method is provided of treating mainstream smoke of a smoking article to preferentially remove one or more targeted constituents from mainstream smoke by contacting the mainstream smoke with a composite as described above.
Cigarette filters and smoking articles are provided preferably containing a porous composite comprising an activated carbon substrate and a zeolite molecular sieve membrane coated thereon and capable of selectively removing selected constituents from mainstream smoke. Methods for making such cigarette filters and smoking articles, as well as a method of treating mainstream smoke, are also provided.
The term “sorption” denotes filtration by adsorption and/or absorption and is intended to encompass interactions on the outer surface of a sorbent, as well as interactions within the pores and channels thereof. A “sorbent” is a substance that has the ability to condense or hold molecules of other substances on its surface and/or the ability to take up other substances, i.e., through penetration of the other substances into its inner structure or into its pores. The term “sorbent” as used herein refers to either an adsorbent, an absorbent, or a substance that can function as both an adsorbent and an absorbent.
The term “remove” as used herein refers to adsorption and/or absorption of at least some portion of a selected constituent of mainstream tobacco smoke.
The term “mainstream smoke” includes the mixture of gases and aerosolized condensed matter which passes down a tobacco column and issues through the filter end, i.e., the amount of smoke issuing or drawn from the mouth end of a smoking article such as a cigarette during smoking. The mainstream smoke contains air that is drawn in through both the lit or heated region of the smoking article, as well as through the paper wrapper, and through any ventilation perforations that may be present.
Smoking articles, such as cigarettes, cigarillos and cigars, as well as non-traditional cigarettes, are provided. Non-traditional cigarettes include, for example, smoking articles which include combustible heat sources such as that shown in commonly assigned, U.S. Pat. No. 4,966,171, and cigarettes for electrical smoking systems as described in commonly-assigned U.S. Pat. Nos. 6,026,820; 5,988,176; 5,915,387; and 5,499,636.
The substrate portion of the aforementioned composite comprises an activated carbon. Activated forms of carbon generally have strong physical sorption forces, and high volumes of sorbing porosity. The activated carbon could be manufactured by any suitable method. Such methods include the carbonization of coconut husk, coal, wood, pitch, cellulose fibers, or polymer fibers, for example. Carbonization is usually carried out at high temperatures, i.e., 200-1000° C. in an inert atmosphere, followed by activation. The activated carbon used as the composite substrate could be in the form of carbon granules, beads, powder, fiber, fabric or shaped monoliths. The substrate could also be an admixture of carbon and an inorganic material. Suitable inorganic materials may comprise porous and/or catalytically active metal compounds such as oxides, hydroxides, silicates and phosphates.
Carbon-containing materials suitable as substrates may have a distribution of micropores, mesopores and macropores. The term “microporous” generally refers to such materials having pore sizes of about 20 Å or less while the term “mesoporous” generally refers to such materials with pore sizes of about 20 to 500 Å. “Macroporous” materials have pore sizes above about 500 Å. The relative amounts of micropores, mesopores and macropores in the carbon-containing substrate will depend upon the selected constituents from mainstream tobacco smoke that are to be targeted and removed. Thus, the pore sizes and pore distribution can be adjusted accordingly as needed for a certain application.
Another material in the filter system is a molecular sieve zeolite membrane. The term “molecular sieve” as used herein refers to a porous structure composed of an inorganic silicate material. Zeolites have channels or pores of uniform, molecular sized dimensions. There are many known unique zeolite structures having different sized and shaped channels or pores. The size and shape of the channels or pores can significantly affect the properties of these materials with regard to adsorption and separation characteristics. Zeolites can be used to separate molecules by size and shape possibly related to the orientation of the molecules in the channels or pores, and/or by differences in strength of sorption. By using one or more zeolites having channels or pores larger than selected constituents of mainstream smoke, only selected molecules that are small enough to pass through the pores of the molecular sieve material are able to enter the cavities and be sorbed by the zeolite.
Zeolite-type molecular sieves which are useful in the composites include crystalline aluminosilicates, silicoaluminophosphates (AlPO/SAPO) and mesoporous molecular sieves such as MCM-41, MCM-48 and SBA-15. This family of materials contains regular arrays of uniformly-sized channels and tunable internal active sites, and admits molecules below a certain size into their internal space which makes them useful as catalysts and sorbents where selectivity is critical. Microporous and mesoporous molecular sieves are preferred. They are selected for use in the filter composites based on the particular constituent or constituents to be removed from the mainstream smoke.
The term “microporous molecular sieves” generally refers to molecular sieve materials having pore sizes of about 20 Å or less. The term “mesoporous molecular sieves” generally refers to such materials with pore sizes of about 20 to 500 Å. Materials with pore sizes of about 500 Å or larger may be referred to as “macroporous molecular sieves.”
The composite preferably is prepared by a hydrothermal synthesis technique using zeolite precursor materials which form a coated membrane on the substrate. The hydrothermal synthesis of various zeolites can be accomplished by any techniques which would generate in situ a zeolite membrane on the carbon-containing substrate. Methods for the preparation of zeolite membranes on activated porous carbon monoliths and porous carbon membranes are disclosed in the following articles: “Preparation of hollow-fibre composite carbon-zeolite membranes,” Smith, S. P. J.; Linkov, V. M; Sanderson, R. D.; Petrik, L. F.; O'Connor, C. T.; Keiser, K., Microporous Materials, 1995, 4, pp. 385-390; “Preparation of an MFI zeolite coating on activated carbon,” van der Vaart, R.; Bosch, H.; Keizer, K.; Reith, T., Microporous Materials, 1997, 9, pp. 203-207, the entire disclosures of both articles incorporated herein in their entirety. In general, the substrates are contacted with the zeolite precursors and a hydrothermal synthesis conducted whereby the zeolite membrane is coated upon and/or into the pores of the substrate. If the carbon-containing substrate has not been activated before synthesis of the zeolite membrane, known activation techniques may be employed to remove volatiles and produce the final activated composite. The product is a composite filter system composed of a porous substrate of activated carbon having a zeolite membrane coated uniformly upon the surface and within the pores of the substrate.
In the hydrothermal synthesis of crystalline aluminosilicates, sodium hydroxide may be used as the alkaline source. Sodium aluminate (NaAlO2), aluminum nitrate (Al(NO3)39H2O), aluminum sulfate (Al2(SO4)318H2O), aluminum chloride (AlCl36H2O), aluminum hydroxide (Al(OH)3), aluminum alkoxide and alumina gel, etc. can be used as the source of alumina. Colloidal silica, fumed silica, water glass (sodium silicate aqueous solution), silica gel, etc. can be used as the silica source.
The factors affecting crystallization of aluminosilicate include the source of silica, the mole ratio of silica vs. alumina, pH, reaction temperature, reaction time, degree of aging in room temperature, presence of stirring, etc. The morphology and nature of zeolite produced are directly linked to these variations.
An example of a method of preparing a molecular sieve compound is described in U.S. Pat. No. 6,117,810, the entire disclosure of which is incorporated herein by reference. A sodium aluminate solution is made by adding a source of alumina to sodium hydroxide solution and stirring for about 20 to 60 minutes at about 70 to 120° C. to dissolve completely. The concentration of sodium hydroxide in solution is about 20 to 50 wt. %, especially about 30 to 40 wt. %. A sodium silicate composition is produced by stirring the sodium hydroxide solution and the silica source at a temperature of about 25° to 70° C. Thereafter, the sodium aluminate solution is admixed with a sodium silicate composition in SiO2/Al2O3 mole ratios of about 2.0 to 40.0, Na2O/SiO2 mole ratios of about 0.4 to 2.0 and H2O/Na2O mole ratios of about 15.0 to 70.0. Gelation is brought about by homogeneously stirring.
Following gelation, the gel composition is deposited onto and into the pores of the activated carbon substrate. In the above process, if the mole ratio of SiO2/Al2O3 is under 2.0, some of the alumina component remains in the final product. If the mole ratio is greater than 40, crystallization of the zeolite becomes difficult. If the mole ratio of Na2O/SiO2 is under 0.4, the activity of the silica component is low and it is slowly converted into zeolite. If the mole ratio is more than 2.0, a crystalline aluminosilicate is produced having a very low activity.
If the mole ratio of H2O/Na2O is under 15, alkalinity in solution is so high that side reactions can easily occur. If the ratio is more than 70.0, higher pressures and temperatures are required for the synthesis reaction.
The reaction mixture is allowed to age for about 2 to 96 hours at about 25 to 60° C. and crystallized at about 70 to 120° C., preferably at 80 to 100° C., and most preferably at 90 to 100° C. for 2 to 4 hours.
Upon completion of crystallization, the slurry phase is separated, the final product washed with water, and dried for about 4 to 12 hours at about 100 to 120° C. to provide the molecular sieve compound.
Preferred complex molecular sieve compounds produced are composed of microporous zeolites such as A, ZSM-5, X or Y type finely distributed onto the surfaces of the activated carbon. Therefore, the composites have both hydrophilic and hydrophobic adsorption properties derived from the activated carbon and zeolite.
To facilitate adhesion and growth of the zeolite membrane on the carbon-containing substrate, it may be desirable to pretreat the substrate to provide sufficient nucleation sites. Preferably, silanes are applied to the substrate followed by a heat treatment preferably in an oxidizing atmosphere. Suitable silanes include alkoxysilanes such as tetraethoxysilane. Alternatively, hydrophilic clays such as bentonite and montmorillonite may be admixed with the carbon-containing material before, during or after preparation of the substrate material. Preferably, the carbon-containing substrate includes activated carbon. As indicated above, if the substrate is not activated beforehand, it may be activated after deposition of the zeolite membrane such as by heating the composite which removes various volatiles used in the synthesis of the membrane while activating the substrate.
In a preferred embodiment, the composite is located in a filter portion of a cigarette. Typically, about 10 mg to about 300 mg of the composite can be used in a cigarette filter. For example, amounts such as at least about 20, 30, 50, 75, 100, 150, 200, or 250 mg of the composite can be used in the cigarette filter.
Various filter constructions may be used to locate the composite. Exemplary filter structures that can be used include, but are not limited to, a mono filter, a dual filter, a triple filter, a cavity filter, a recessed filter or a free-flow filter. Mono filters typically contain cellulose acetate tow or cellulose paper materials. Dual filters typically comprise a cellulose acetate mouthpiece filter plug and a second, different filter plug or segment. The composite is preferably located closer to the smoking material or tobacco side of a cigarette. The length and pressure drop of the two segments of the dual filter can be adjusted to provide optimal adsorption, while maintaining acceptable draw resistance.
Triple filters can include mouth and smoking material or tobacco side segments, and a middle segment comprising a material or paper. The aforementioned composite can be provided in the middle segment. Cavity filters typically include two segments, e.g., acetate-acetate, acetate-paper or paper-paper, separated by a cavity. The composite can preferably be provided in the cavity. Recessed filters include an open cavity on the mouth side, and the composite can be incorporated into the plug material. The filters may also optionally be ventilated, and/or comprise additional sorbents (such as activated carbon, charcoal or magnesium silicate), catalysts, flavorants or other additives.
The composite can be incorporated into the filter paper in a number of ways. For examples, particles or powders of the aforementioned composites can be mixed with water to form a slurry. The slurry can then be coated onto preformed filter paper and allowed to dry. The filter paper can then be incorporated into the filter portion of a cigarette in a manner shown in
Alternatively, the composite may be added to filter paper during the paper-making process. For example, the composite can be mixed with bulk cellulose to form a cellulose pulp mixture. The mixture can be then formed into filter paper.
In another embodiment, the aforementioned composite may be incorporated into the fibrous material of the cigarette filter portion itself. Such filter materials include, but are not limited to, fibrous filter materials including paper, cellulose acetate fibers, and polypropylene fibers. This embodiment is illustrated in
Various techniques can be used to apply the composite to filter fibers or other substrate supports. For example, the composite can be added to the filter fibers before they are formed into a filter cartridge, e.g., a tip for a cigarette. The composite can be added to the filter fibers, for example, in the form of a dry powder or a slurry. If the composite is applied in the form of a slurry, the fibers are allowed to dry before they are formed into a filter cartridge.
In another embodiment, the composite is employed in a hollow portion of a cigarette filter. For example, some cigarette filters have a plug/space/plug configuration in which the plugs comprise a fibrous filter material and the space is simply a void between the two filter plugs. That void can be filled with the aforementioned composite. An example of this embodiment is shown in
As explained above, composite can be incorporated in various support materials. When the composite is used in filter paper, the particles may have an average particle diameter of about 5 to 100 μm, preferably about 10 to 50 μm. When the composite is used in filter fibers or other mechanical supports, larger particles may be used. Such particles preferably have a mesh size from about 25 to 60, and more preferably from about 35 to 60 mesh.
The amount of composite employed in the cigarette filter by way of incorporation on a suitable support such as filter paper and/or filter fibers depends on the amount of constituents in the tobacco smoke and the amount of constituents desired to be removed. As an example, the filter paper and the filter fibers may contain from 10% to 50% by weight of the composite.
One embodiment relates to a method of making a filter. The method comprises incorporating the aforementioned composite into a cigarette filter. Most filters contain four main components: filter tow, plasticizer, plug wrap and adhesive. Often the filter tow comprises a bundle of cellulose acetate fibers or papers, that are bound together using the plasticizer, which acts as a hardening agent. The filter is contained in the plug wrap, usually a paper wrapper, which is secured using an adhesive. Any conventional or modified method of making cigarette filters may be used to incorporate the composite.
Another embodiment relates to methods for making cigarettes. For example, the method comprises: (i) providing a cut filler to a cigarette making machine to form a tobacco rod; (ii) placing a paper wrapper around the tobacco rod; and (iii) attaching a cigarette filter incorporating a composite to the tobacco rod to form the cigarette.
The composites may be used to prepare impregnated fibers. Particles or powders of the composite are first mechanically mixed with the fiber in a closed volume. The resulting impregnated fibers will thus have a Loading Factor (LF), which term is defined as the ratio of the weight of material in the fiber micro cavities divided by the weight of the fiber itself. The Loading Factor may be expressed as a percentage or as a decimal number.
The Loading Factor may vary between about 1% and about 150%. More preferably, the Loading Factor is between about 20% and about 80%, e.g., the Loading Factor can be about 40-60%. The fibers that are impregnated with the composite are formed into a cylindrical segment which is inserted in the space of a cigarette with a plug/space/plug filter configuration. Preferably, the segment is packed to a density to achieve a desired resistance to draw and contains an amount of the composite effective to filter out the selected smoke gas phase constituents. Tipping paper attaches the tobacco to the filter rod.
Activated carbons and zeolite-type molecular sieves when combined together can produce composite materials with tailored sorption capacity and selectivity for application in smoking articles to selectively reduce targeted smoke constituents. The composite can be provided with a surface area effective to preferentially sorb selected constituents from cigarette smoke. While surface area is inversely proportional to particle size, sorbents having small particle size may pack together too densely to permit mainstream smoke to flow through the filter during smoking. If particle size is too large, there will be less than desired surface area. Therefore, these factors should be considered in manufacturing a composite having a particular particle size.
The zeolite and activated carbon used in making the composite may be chosen to target selected constituents in mainstream smoke, while prolonging the shelf life of the activated carbon during storage of smoking articles containing the composite. The selection of starting materials permits the preferential removal of one or more selected constituents from mainstream smoke, while retaining other constituents, such as those relating to flavor. For example, smoke substituents relating to flavor of large size and/or molecular weight can pass through the filter to a greater extent than smaller smoke substituents, such as light gases, various aldehydes or other small molecules which may be targeted for removal. The selectivity of the composite can be fine tuned, particularly by the selection of zeolites and activated carbons as well as the choice of particle sizes and pore sizes. Mixtures of molecular sieves with varying compositions and geometries can be employed to tailor the removal of selected constituents of tobacco smoke while controlling access to the pores of the activated carbon substrate.
Selected constituents of mainstream smoke may be removed by the composite through one or more mechanisms such as molecular sieving, ion exchange, hydrophobic interactions, chelation, and/or chemical binding. The selected constituents of mainstream smoke that are removed preferably are composed of at least one of a hydrocarbon, a polar organic and/or non-polar organic compound. Preferably, the selected constituent of mainstream smoke that is removed is an aldehyde, ketone, diene or aromatic compound. Specific constituents which may be removed include carbon monoxide, 1,3-butadiene, isoprene, acrolein, acrylonitrile, hydrogen cyanide, o-toluidine, 2-naphthylamine, nitrogen oxide, benzene, phenol, and/or catechol. More preferably, the constituent is an aldehyde or diene.
Variations and modifications of the foregoing embodiments will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto.
| Number | Date | Country | |
|---|---|---|---|
| 60641134 | Jan 2005 | US |
