Patent Application
20050133053
Certain filter materials have been suggested for incorporation into cigarette filters, including cotton, paper, cellulose, and certain synthetic fibers. However, such filter materials generally only remove particulate and condensable components from tobacco smoke. Thus, they are usually not optimal for the removal of certain gaseous components from tobacco smoke, e.g., volatile organic compounds.
Copper-exchanged molecular sieve catalysts for the removal of NO2 and/or NO from mainstream smoke are provided.
In one embodiment, smoking articles, filters and/or cut filler are provided, which comprise copper-exchanged molecular sieve catalyst, wherein the copper-exchanged molecular sieve catalyst is capable of removing at least one of NO and NO2 from mainstream smoke, wherein the copper-exchanged molecular sieve catalyst comprises a microporous molecular sieve substrate having pores with an average pore size of from about 3 Å to about 15 Å, and further wherein at least some of the pores of the microporous molecular sieve substrate contain Cu+2 ions.
In another embodiment, the microporous molecular sieve substrate comprises pores sufficiently small enough to substantially exclude constituents in mainstream smoke having more than 12 carbon atoms. In another preferred embodiment, the copper-exchanged molecular sieve catalyst is capable of selectively removing more benzene and/or 1,3-butadiene from mainstream smoke, than molecules larger than benzene. Preferably, the microporous molecular sieve substrate has pores with an average pore size of about 8 Å or smaller and more preferably about 6 Å or smaller. In a further embodiment, the copper-exchanged molecular sieve catalyst is in particle form having an average mesh size of from about 20 mesh to about 60 mesh.
In an embodiment, the microporous molecular sieve substrate may be a zeolite selected from the group consisting of zeolite ZSM-5, zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixtures thereof. In a preferred embodiment, the cooper-exchanged molecular sieve catalyst is Cu(II)-ZSM-5.
In an embodiment, smoking articles, cigarette filters and/or cut filler may further comprise a second molecular sieve material, wherein the second molecular sieve material is capable of selectively removing at least some of at least one constituent of mainstream smoke that is not substantially removed by the copper-exchanged molecular sieve catalyst. Preferably, the second molecular sieve material comprises a catalytic metal other than copper(II). Preferably, the catalytic metal is selected from the group consisting of iron, manganese, copper oxide, and mixtures thereof.
Examples of smoking articles that may comprise the copper-exchanged molecular sieve catalyst include, but are not limited to, the group consisting of cigarettes, pipes, cigars and non-traditional cigarettes. Preferably, the smoking article is a cigarette. In a preferred embodiment, the copper-exchanged molecular sieve catalyst is incorporated into the smoking mixture and/or a filter portion of the smoking article.
In an embodiment, the smoking articles and filters may comprise from about 10 mg to about 300 mg of the copper-exchanged molecular sieve catalyst, or preferably from about 50 mg to about 150 mg of the copper-exchanged molecular sieve catalyst.
In another embodiment, methods for making a cigarette filter are provided, which comprise incorporating a copper-exchanged molecular sieve catalyst into a cigarette filter, wherein the copper-exchanged molecular sieve catalyst is capable of removing at least one of NO and NO2 from mainstream smoke, wherein the copper-exchanged molecular sieve catalyst comprises a microporous molecular sieve substrate having pores with an average pore size of from about 3 Å to about 15 Å, and further wherein at least some of the pores of the microporous molecular sieve substrate contain Cu+2 ions.
In another embodiment, methods for smoking a cigarette comprising a copper-exchanged molecular sieve catalyst are provided, which involve lighting the cigarette to form smoke and drawing the smoke through the cigarette, wherein during the smoking of the cigarette, the copper-exchanged molecular sieve catalyst removes NO and/or NO2 from the mainstream smoke.
Copper-exchanged molecular sieve catalysts for selective and effective removal of certain selected constituents of mainstream tobacco smoke are provided. Preferably, other constituents in mainstream smoke, such as those relating to flavor, will preferably not be removed to any great extent. By “removed” is meant that the concentration of at least some of the NOx constituents in mainstream smoke is lowered. This can be accomplished by a variety of mechanisms. For example, the NOx constituents may chemically react with the copper-exchanged molecular sieve catalysts, i.e., be reduced directly by the copper ion. Alternatively, the copper-exchanged molecular sieve catalyst may catalyze the conversion of the NOx constituents into other compounds. Further, the NOx constituents may be sequestered within the pores of the microporous molecular sieve substrate, thus removed from mainstream tobacco smoke before reaching the smoker. By combining catalytic and sorbent materials, tailored or optimized for a particular selectivity, a desired removal of multiple selected constituents from mainstream smoke can be achieved.
The term “sorption” denotes filtration through absorption and/or adsorption. Sorption is intended to cover interactions on the outer surface of the sorbent, as well as interactions within the pores, such as channels or cavities of the sorbent. In other words, 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 another substance, i.e., through penetration of the other substance into its inner structure or into its pores. The term adsorption also denotes filtration through physical sieving, i.e., capture of certain constituents in the pores of the carbon-modified sorbent. The term “sorbent” as used herein refers to either an adsorbent, an absorbent, or a substance that functions as both an adsorbent and an absorbent.
As an example, the combination of specialized sorbents in different portions of a smoking article, such as in the tobacco rod and in the filter portion of a cigarette, a multi-stage multifunctional system is provided wherein a plurality of selected constituents may be more effectively accomplished by a combination of selective materials than by any single broadly catalytic or sorbent material or a combination of more broadly sorbent materials.
Preferably, the smoking articles, tobacco compositions and filters will incorporate copper-exchanged molecular sieves having pore sizes and other characteristics that will remove selected constituents from mainstream smoke. By incorporating a second molecular sieve material that is tailored for removal of at least some of a different selected constituent of mainstream smoke in a smoking article, the composition of the mainstream smoke may be adjusted. A combination of different materials can be used to achieve improved multifunctional removal of selectively targeted constituents of mainstream smoke, while allowing other smoke constituents (such as flavor constituents) to remain in the mainstream smoke.
The abbreviation “NOx” as used herein includes either or both of NO and NO2. Molecular sieve materials containing copper ions, such as copper-exchanged zeolite, have been found to be a highly efficient and selective catalyst of the conversion of ammonia and NOx to molecular nitrogen and water at moderately high temperatures, i.e., 400° C., through reactions such as the following:
4NH3+4NO+O2→4N2+6H2O;
and
4NH3+2NO+2NO2→4N2+6H2O.
However, copper-exchanged zeolite catalysts can be affected by common constituents of smoke. In particular, these catalysts can be inactivated by the presence of SO2, and may be inactivated by organic compounds that are adsorbed in the pores of some molecular sieve materials. For example, where the pores of the molecular sieve are large enough to admit larger organic compounds, such as components larger than benzene which can form tar, these compounds can block the pores of the molecular sieve so that the catalytic reduction of NOx is impaired. In a preferred embodiment, molecular sieve materials that exclude high molecular weight organic compounds can achieve highly effective and selective reduction of NO and NO2 in mainstream tobacco smoke.
The term “molecular sieve” as used herein refers to an ordered porous material, such as crystalline aluminosilicates, commonly called zeolites, or crystalline aluminophosphates, mesoporous silicates, and mesoporous aluminosilicates. A molecular sieve as used herein further refers to a material having pores with dimensions less than about 500 Å, preferably less than 300 Å, including microporous and mesoporous molecular sieves. The term “microporous molecular sieves” generally refers to such materials having pore sizes below about 20 Å while the term “mesoporous molecular sieves” generally refers to such materials with pore sizes of about 20-500 Å, preferably 20 to 300 Å.
In a copper-exchanged molecular sieve, ions of copper are incorporated into the molecular sieve substrate by displacing ions of the substrate and thereby become part of the molecular matrix of the substrate.
Pores of the preferred zeolite molecular sieve substrate may be more or less uniform and may have pore dimensions over a range of sizes. Synthetic zeolite materials may have more uniform pore dimensions and a more ordered structure. Various zeolite types are described, for example, in U.S. Pat. No. 3,702,886 (zeolite ZSM-5), U.S. Pat. No. 2,882,243 (zeolite A), U.S. Pat. No. 2,882,244 (zeolite X), U.S. Pat. No. 3,130,007 (zeolite Y), U.S. Pat. No. 3,055,654 (zeolite K-G), U.S. Pat. No. 3,247,195 (zeolite ZK-5), U.S. Pat. No. 3,308,069 (zeolite Beta), U.S. Pat. No. 3,314,752 (zeolite ZK-4). A source of natural zeolite in North America is the St. Cloud Mining Company, Truth or Consequences, N. Mex.
Molecular sieve materials derive their name from the ability to selectively exclude or adsorb molecules from or within pores including interior channels depending on the dimensions of the molecules. A copper-exchanged molecular sieve having a pore size that is small enough to substantially exclude higher molecular weight components of tobacco smoke provides improved selectivity and effectiveness for selective catalytic reduction of NOx from mainstream tobacco smoke. The molecular sieve material may be chosen according to its pore diameter as determined by x-ray or neutron diffraction methods. For example a microporous molecular sieve may be chosen with a mean pore size of less than about 15 Å, e.g., less than about 8 Å, preferably less than about 6 Å. Such molecular sieves effectively exclude compounds with a larger molecular dimension. Alternatively, a molecular sieve material may be chosen by measurements under conditions that simulate the environment in which it will function. For example, a molecular sieve may be chosen which significantly or substantially excludes organic molecules having 4, 6, 8, 10, 12 or more carbon atoms. Alternatively, a molecular sieve material may be chosen by its ability to significantly or substantially exclude hydrocarbon molecules which comprise the tar component of tobacco smoke. Or, a molecular sieve material may be chosen by its ability to significantly or substantially exclude a selected category of organic molecules such as cyclic hydrocarbons of more than four carbons, aromatic hydrocarbons (i.e., benzene), larger alkanes or the like. The ability of a molecular sieve material to exclude molecules can be determined by measuring adsorption of a given compound in a conventional test apparatus.
The adsorption or exclusion of a given molecule can be expressed relative to adsorption of a standard molecular compound such as N2. When comparing the adsorption of molecular sieve materials of a given compound as a function of pore size, one generally observes a sharp drop in adsorption of a compound as the pore size of the molecular sieve materials approaches a cut-off size. The cut-off pore size for a given compound may be identified by comparing similarly structured materials with a range of pore sizes. The cut-off pore size corresponds to the maximum pore size at which less than about 95% of the maximum adsorption of that compound is adsorbed in a range of similar porous materials having pore sizes both larger and smaller than the molecular dimension of the compound. Similar materials means materials of similar atomic composition, i.e., zeolites.
For purposes of categorizing the molecular sieves, to significantly exclude a certain molecular compound means that a molecular sieve material adsorbs an amount of that compound at or below the midpoint of a size exclusion curve, i.e., it adsorbs less than about 50% of the maximal adsorption of that compound by a similar molecular sieve material with a pore size substantially larger than the cutoff size pore size. To substantially exclude a certain molecular compound means that a molecular sieve material adsorbs less than about 10% of the maximal adsorption of that compound by similar molecular sieve material with a pore size substantially larger than the cut off pore size for that compound.
By choosing, or modifying, a molecular sieve material to have a pore size that exclude organic compounds of about the size of octane or larger compounds, or to exclude molecules the size of benzene and larger, the interior pores of the molecular sieve can be maintained sufficiently free of organic compounds to achieve improved effectiveness for the reduction of NOx.
In an alternative embodiment, the selective reduction of NOx may be combined with selective adsorption of selected small organic compounds by use of a molecular sieve substrate having pores that admit molecules of selected constituents, e.g., benzene or 1,3-butadiene, while excluding larger constituents of mainstream smoke. By selectively adsorbing smaller molecules that do not substantially impair NOx reduction, a desirable multifunctional capability is achieved with effective selective reduction of NOx.
In a preferred embodiment, the copper-exchanged molecular sieve material is provided in particle form which may be mixed into the smoking mixture of the tobacco rod of a cigarette where the increased temperature of the zone adjacent to the burning zone of the tobacco rod promotes catalytic activity.
In another embodiment, a plurality of selective molecular sieve materials may be incorporated in a smoking article to achieve multifunctional reduction of selected components of mainstream smoke. For example, molecular sieve materials exchanged with different catalytic metals, including oxide forms of copper, which can provide improved selective catalysis of CO to CO2, may be combined in the tobacco rod with copper ion exchanged molecular sieve. In alternative embodiments, copper ion exchanged molecular sieve materials may be combined with molecular sieve materials comprising zinc, vanadium, chromium, manganese, iron, cobalt, rhodium, palladium, platinum, and/or molybdenum; with manganese and iron being preferred. Molecular sieve materials having pore sizes that admit higher molecular weight compounds may be incorporated into smoking articles in combination with copper ion exchanged materials having smaller pore sizes. For example, molecular sieve materials having pore sizes of about 15 Å or larger can be further incorporated into smoking articles.
The preferred molecular sieve substrates for making a material designed for the removal of NOx include at least one of ZSM-5 and Y-type zeolite ion exchanged with Cu+2 ions. ZSM-5 type zeolite is most preferred because it has well ordered pores of less than about 6 Å. The copper ion exchanged form of ZSM-5 is designated Cu(II)-ZSM-5 and is the most preferred copper ion exchanged molecular sieve material.
The copper-exchanged molecular sieve may be made by any suitable method. In a preferred method, the metal may be dispersed as a salt solution and impregnated into the molecular sieve where it is incorporated by cation exchange. For example, to make a Cu(II)-ZSM-5 molecular sieve material, the zeolite molecular sieve may be soaked for several hours (e.g., 8-24 hours) in a solution (i.e., 1 M) of CuCl2 after which the molecular sieve is briefly washed and thoroughly dried at elevated temperature (e.g., 100-400° C. for 2-24 hours).
In one embodiment, copper-exchanged molecular sieve material is incorporated into cut tobacco filler or other smoking material, which may then be included in the tobacco rod of a cigarette. The copper-exchanged molecular sieve can be incorporated into the smoking mixture in a number of ways. For example, the copper-exchanged molecular sieve can be added as a powder to the cut filler material supplied to a cigarette making machine.
The amount of copper-exchanged molecular sieve incorporated into the smoking mixture can be selected as a function of the amount of constituents in the tobacco smoke to be removed. As an example, the smoking mixture may contain from 1% to 50% by weight of the copper-exchanged molecular sieve, preferably from about 5% to about 15% by weight. In a method for making cigarettes, the method comprises: (i) providing a cut filler comprising the copper-exchanged molecular sieve preferably in the form of powder to a cigarette making machine to form a tobacco column; (ii) placing a paper wrapper around the tobacco column to form a tobacco rod; and (iii) attaching the cigarette filter to the tobacco rod to form the cigarette.
Examples of suitable types of tobacco materials that may be used include flue-cured, Burley, Maryland or Oriental tobaccos, rare or specialty tobaccos, and blends thereof. The tobacco material can be provided in the form of tobacco lamina; processed tobacco materials such as volume expanded or puffed tobacco, processed tobacco stems such as cut-rolled or cut-puffed stems, reconstituted tobacco materials; or blends thereof. The tobacco materials may include tobacco substitutes.
In cigarette manufacture, the tobacco is normally employed in the form of cut filler, i.e., in the form of shreds or strands cut into widths ranging from about {fraction (1/10)} inch to about {fraction (1/20)} inch or even {fraction (1/40)} inch. The lengths of the strands range from between about 0.25 inches to about 3.0 inches. The cigarettes may further comprise one or more flavorants or other additives (e.g., burn additives, combustion modifying agents, coloring agents, binders, etc.).
Cigarettes can be manufactured to any desired specification using standard or modified cigarette making techniques and equipment. The cigarettes may range from about 50 mm to about 120 mm in length. Generally, a regular cigarette is about 70 mm long, a “King Size” is about 85 mm long, a “Super King Size” is about 100 mm long, and a “Long” is usually about 120 mm in length. The circumference is from about 15 mm to about 30 mm in circumference, and preferably around 25 mm. The packing density is typically between the range of about 100 mg/cm3 to about 300 mg/cm3, and preferably 150 mg/cm3 to about 275 mg/cm3.
Yet another embodiment relates to methods of smoking the cigarettes described above, which involve lighting a cigarette to form smoke and drawing the smoke through the cigarette, wherein during the smoking of the cigarette, the metal exchanged molecular sieve is capable of catalytically reducing and optionally adsorbing one or more selected components from mainstream smoke.
“Smoking” of a cigarette means the heating or combustion of the cigarette to form smoke, which can be drawn through the cigarette, e.g., via a smoking machine or person. Generally, smoking of a cigarette involves lighting one end of the cigarette and drawing the cigarette smoke through the mouth end of the cigarette, while the tobacco contained therein undergoes a combustion reaction. However, the cigarette need not be combusted. For example, the cigarette may be smoked by heating the cigarette using an electrical heater, as described in commonly-assigned U.S. Pat. Nos. 6,026,820; 5,988,176; 5,915,387; 5,692,525; 5,666,976; and 5,499,636, for example.
In a preferred embodiment, a copper-exchanged molecular sieve sorbent as described above is incorporated into or onto a support such as lightly or tightly folded paper inserted into a hollow portion of the cigarette filter. The support is preferably in the form of a sheet material such as crepe paper, filter paper, or tipping paper. However, other suitable support materials such as organic or inorganic cigarette compatible materials can also be used.
The copper-exchanged molecular sieve catalyst material may be located in a filter portion of a smoking article in which it can act as a sorbent.
Any conventional or modified filter design may be used, which comprises the copper-exchanged molecular sieve catalyst. Examples of filter designs 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 a variety of cellulose acetate tow or cellulose paper materials. Pure mono cellulose filters or paper filters offer good tar and nicotine retention, and are highly degradable. The copper-exchanged molecular sieve catalyst may be incorporated into the cellulose filters or paper filters. Dual filters usually comprise a cellulose acetate mouth side and a pure cellulose segment or cellulose acetate segment, with copper-exchanged molecular sieve catalyst on the smoking material or tobacco side. 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 may have mouth and smoking material or tobacco side segments, while the middle segment comprises a material or paper containing the copper-exchanged molecular sieve catalyst. Cavity filters have two segments, e.g., acetate-acetate, acetate-paper or paper-paper, separated by a cavity containing the copper-exchanged molecular sieve catalyst. Recessed filters have an open cavity on the mouth side, and typically incorporate the copper-exchanged molecular sieve sorbent into the plug material. The filters may also optionally be ventilated, and/or comprise additional sorbents (such as charcoal or magnesium silicate), catalysts, flavors, or other like additives.
Copper-exchanged molecular sieve catalyst can be incorporated into the filter paper in a number of ways. For example, copper-exchanged molecular sieve catalyst can be mixed with water to form a slurry. The slurry can then be coated onto pre-formed filter paper and allowed to dry. The filter paper can then be incorporated into the filter portion of a cigarette in the manner shown in
Alternatively and preferably, copper-exchanged molecular sieve catalyst is added to the filter paper during the paper-making process. For example, copper-exchanged molecular sieve catalyst can be mixed with bulk cellulose to form a cellulose pulp mixture. The mixture can be formed into filter paper by any suitable method.
In another preferred embodiment, copper-exchanged molecular sieve catalyst is 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 copper-exchanged molecular sieve catalyst to filter fibers or other substrate supports. For example, copper-exchanged molecular sieve catalyst can be added to the filter fibers before they are formed into a filter cartridge, e.g., a tip for a cigarette. Copper-exchanged molecular sieve catalyst can be added to the filter fibers, for example, in the form of a dry powder or a slurry. If copper-exchanged molecular sieve catalyst is applied in the form of a slurry, the fibers are allowed to dry before they are formed into a filter cartridge.
In another preferred embodiment, copper-exchanged molecular sieve sorbent 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 a void between the two filter plugs. That void can contain the copper-exchanged molecular sieve catalyst. An example of this embodiment is shown in
In another embodiment, the copper-exchanged molecular sieve catalyst is employed in a filter portion of a cigarette for use with a smoking device as described in U.S. Pat. No. 5,692,525, the entire content of which is hereby incorporated by reference.
In such a cigarette, copper-exchanged molecular sieve catalyst can be incorporated in various ways, such as by being loaded onto paper or other substrate material which is fitted into the passageway of the tubular free-flow filter element 102 therein. It may also be deployed as a liner or a plug in the interior of the tubular free-flow filter element 102. Alternatively, copper-exchanged molecular sieve catalyst can be incorporated into the fibrous wall portions of the tubular free-flow filter element 102 itself. For instance, the tubular free-flow filter element or sleeve 102 can be made of suitable materials such as polypropylene or cellulose acetate fibers, and copper-exchanged molecular sieve catalyst can be mixed with such fibers prior to or as part of the sleeve forming process.
In another embodiment, copper-exchanged molecular sieve catalyst can be incorporated into the mouthpiece filter plug 104 instead of in the element 102. However, as in the previously described embodiments, copper-exchanged molecular sieve catalyst may be incorporated into more than one constituent of a filter portion, such as by being incorporated into the mouthpiece filter plug 104 and into the tubular free-flow filter element 102. The filter portion 62 of
While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.
All of the above-mentioned references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.
