Patent Publication Number: US-2005133049-A1

Title: Smoking articles and filters including zeolite molecular sieve sorbent

Description:
BACKGROUND  
      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.  
     SUMMARY  
      Cigarette filters, smoking articles, and methods for selectively removing selected constituents from mainstream smoke, are provided. In a preferred embodiment, one or more selected constituents are selectively removed from mainstream smoke, to a greater extent than other constituents of the mainstream smoke.  
      The cigarette filters comprise zeolite molecular sieve sorbent capable of selectively removing at least one selected constituent of mainstream smoke. The filters can be incorporated in various smoking articles, including traditional and non-traditional cigarettes. The zeolite molecular sieve sorbent is preferably located in the cigarette filter.  
      The zeolite molecular sieve sorbent may be incorporated in various types of cigarette filters, as well as in one or more cigarette filter parts.  
      In a preferred embodiment, a cigarette filter comprises a molecular sieve sorbent including zeolite BETA. The zeolite BETA is capable of selectively removing at least one of acrolein and 1,3-butadiene from mainstream tobacco smoke.  
      In another embodiment, the zeolite molecular sieve sorbent may optionally be located in a tobacco rod of the smoking article.  
      In another embodiment, methods of smoking a cigarette are provided, which comprise heating or lighting the cigarette to form smoke and drawing the smoke through the cigarette. During smoking of the cigarette, the zeolite molecular sieve sorbent selectively removes one or more selected constituents from mainstream smoke. The methods can be practiced with traditional and non-traditional cigarettes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates a cigarette, which can include folded paper containing zeolite molecular sieve sorbent inserted into a hollow portion of a tubular filter element of the cigarette.  
       FIG. 2  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in folded paper and inserted into a hollow portion of a first free-flow sleeve of a tubular filter element next to a second free-flow sleeve.  
       FIG. 3  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in a plug-space-plug filter element.  
       FIG. 4  illustrates another embodiment, which can include zeolite molecular sieve sorbent incorporated in a three-piece filter element having three plugs.  
       FIG. 5  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in a four-piece filter element having a plug-space-plug arrangement, and a hollow sleeve.  
       FIG. 6  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in a three-part filter element having two plugs and a hollow sleeve.  
       FIG. 7  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in a two-part filter element having two plugs.  
       FIG. 8  illustrates another embodiment of a cigarette, which can include zeolite molecular sieve sorbent incorporated in a filter element, which may be used in a smoking article. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Cigarette filters and smoking articles are provided, which comprise a zeolite molecular sieve sorbent that is capable of selectively removing selected constituents from mainstream smoke. Methods for making such cigarette filters and smoking articles, and methods of smoking cigarettes including the zeolite molecular sieve sorbent, are also provided.  
      The term “sorption” denotes filtration through adsorption and/or absorption. Sorption is intended to encompass interactions on the outer surface of the zeolite sorbent, as well as interactions within the pores and channels of the sorbent. In other words, a “sorbent” material 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 so that the amount of that constituent is reduced in the mainstream tobacco smoke.  
      The term “mainstream smoke” includes the mixture of gases that passes down the tobacco rod and through the filter end, i.e., the amount of smoke issuing or drawn from the mouth end of a smoking article during smoking of the cigarette. 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.  
      The term “molecular sieve” as used herein refers to a porous material having a porous structure including pores, such as channels or cavities, of molecular-sized dimensions. These materials are capable of sorbing molecules of particular dimensions, while rejecting molecules of larger dimensions.  
      Smoking articles, such as cigarettes, pipes, and cigars, as well as non-traditional cigarettes, are provided. Non-traditional cigarettes include, for example, cigarettes for electrical smoking systems described in commonly-assigned U.S. Pat. Nos. 6,026,820; 5,988,176; 5,915,387; 5,692,526; 5,692,525; 5,666,976; and 5,499,636.  
      Activated carbon has been used in smoking articles as an adsorbent to reduce levels of constituents in the smoke stream. However, activated carbon is a “broadband adsorbent,” i.e., it has a pore structure that removes smoke stream constituents non-selectively. Consequently, activated carbon removes constituents from the smoke stream that are not targeted for removal, e.g., flavor constituents. Further, activated carbon contained in a cigarette filter may become inactivated during storage by the adsorption of volatile compounds, or during smoking by contact with various constituents of mainstream smoke.  
      Accordingly, cigarette filters and smoking articles including a sorbent capable of selectively removing one or more selected constituents from mainstream smoke, and also capable of not removing (i.e., retaining) other constituents in the mainstream smoke, such as flavor constituents, are desired. As described below, certain zeolites can provide both selective removal and retention of mainstream smoke constituents.  
      In preferred embodiments, cigarette filters and smoking articles comprise one or more zeolites. Zeolites include crystalline aluminosilicates having pores, e.g., channels, or cavities of uniform, molecular sized dimensions. Zeolites include natural and synthetic materials. There are many known unique zeolite structures having pores of different sizes and shapes. The size and shape of the pores can significantly affect the properties of these materials with regard to their sorption and separation performance characteristics. Molecules can be separated by zeolites by size and shape effects related to the possible orientation of the molecules or pores, and/or by differences in strength of sorption. By using one or more zeolites having pores, e.g. channels, larger than one or more selected constituents of mainstream smoke, only molecules that are small enough to enter the pores of the zeolite are able to be sorbed.  
      In preferred embodiments, zeolite BETA, and optionally zeolite ZSM-5, can be used as a zeolite molecular sieve sorbent in smoking articles, such as in cigarette filters and tobacco mixtures, for example, tobacco rods of smoking articles. Zeolite ZSM-5 is in the MFI structural classification family and represented by the crystal chemical formula [Na n (Al n Si 96-n O 192 )˜16H 2 O, with n&lt;27, orthorhombic, Pnma]. Zeolite BETA is in the BEA structural classification family and represented by the crystal chemical formula [Na 7 (Al 7 Si 57 O 128 ) tetragonal, P4 1 22]. Zeolites ZSM-5 and BETA are thermally stable at temperatures up to about 800° C., allowing them to be incorporated in the cigarette filter, and/or tobacco rod of smoking articles. It has been discovered that zeolite ZSM-5 and zeolite BETA can selectively remove selected constituents from mainstream smoke, including acrolein and 1,3-butadiene.  
      The term “microporous molecular sieve” generally refers to a molecular sieve material having a pore size of about 20 Å or less; “mesoporous molecular sieve” generally refers to such material with a pore size of about 20-500 Å; and “macroporous molecular sieve” generally refers to a material with a pore size of about 500 Å or larger. In embodiments, one or more different types of molecular sieves may be used in combination, e.g., one or more microporous molecular sieve and one or more mesoporous molecular sieve.  
      Exemplary microporous zeolites are described in U.S. Pat. Nos. 3,702,886 (zeolite ZSM-5); 2,882,243 (zeolite A); 2,882,244 (zeolite X); 3,130,007 (zeolite Y); 3,055,654 (zeolite K-G); 3,247,195 (zeolite ZK-5); 3,308,069 (zeolite BETA); and 3,314,752 (zeolite ZK-4), each of which is hereby incorporated by reference in its entirety. Natural zeolite is commercially available, for example, from the St. Cloud Mining Company, Truth or Consequences, New Mexico. In addition to zeolite ZSM-5 and zeolite BETA, other zeolite materials described above can be incorporated into cigarette filters and smoking articles.  
      In addition to zeolite BETA and zeolite ZSM-5, other microporous, mesoporous, and/or macroporous molecular sieve sorbents may be used in cigarette filters and smoking articles. Such other materials include, for example, microporous zeolites other than zeolite BETA and zeolite ZSM-5 (e.g., one or more of zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeolite ZK-4, or the like), mesoporous silicates, alumino-phosphates, mesoporous aluminosilicates, and other related porous materials, such as mixed oxide gels, which may optionally further comprise inorganic or organic ions and/or metals. The additional sorbent material can be selected based on the particular constituent(s) of mainstream smoke that are targeted for removal.  
      The pore size of the molecular sieve sorbent can be selected based on the size of one or more selected constituents that are preferably removed from mainstream smoke. In preferred embodiments, zeolite molecular sieve sorbent has an average pore diameter larger than such selected constituents, and smaller than the diameter of at least one tobacco smoke constituent that is desired to be retained in the mainstream smoke. Preferably, the zeolite molecular sieve sorbent has an average pore diameter larger than at least one of acrolein and 1,3-butadiene, but smaller than the diameter of at least one tobacco smoke constituent that is desired to be retained in the mainstream smoke, such as flavor constituents. In preferred embodiments, zeolite molecular sieve sorbent is selected that is capable of removing at least one of 1,3-butadiene and acrolein from mainstream smoke. Other constituents that can be selectively removed include, for example, other aldehydes, such as acetaldehyde and isobutraldehyde, and isoprene.  
      In a preferred embodiment, zeolite molecular sieve sorbent material is incorporated into, onto, or with, a support. The support composition and/or structure is not limited and can include, for example, paper or fibers. In embodiments, the paper can be 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 be used.  
      In a preferred embodiment, the zeolite molecular sieve sorbent is located in at least a filter portion of a smoking article. Typically, about 10 mg to about 300 mg of the zeolite molecular sieve sorbent can be used in a cigarette filter. For example, within the usual range, amounts such as about 20, 30, 50, 75, 100, 150, 200, or 250 mg of the zeolite molecular sieve sorbent can be used in the cigarette filter.  
      In some embodiments, the zeolite molecular sieve sorbent is located in both the filter and tobacco rod of a cigarette. For example, zeolite BETA and optionally zeolite ZSM-5 can be located in the filter, and at least one of these zeolites can be located in the tobacco rod.  
      Zeolite molecular sieve sorbent capable of selectively removing at least one selected constituent of mainstream smoke can be incorporated in various filter constructions. 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 inside materials. Pure mono cellulose filters or paper filters offer good tar and nicotine retention, and are highly degradable. Dual filters typically comprise a cellulose acetate mouth side and a pure cellulose, or cellulose acetate segment. In such dual filters, zeolite molecular sieve sorbent is preferably provided 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 can include mouth and smoking material or tobacco side segments, and a middle segment comprising a material or paper. Zeolite molecular sieve sorbent can preferably 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. Zeolite molecular sieve sorbent can preferably be provided in the cavity. Recessed filters include an open cavity on the mouth side, and can incorporate the zeolite 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, flavorants or other additives used in the cigarette filter art.  
       FIG. 1  illustrates a cigarette  2  including a tobacco rod  4 , a filter portion  6 , and a mouthpiece filter plug  8 . Zeolite molecular sieve sorbent can be loaded on, or incorporated into, folded paper  10  inserted into a hollow cavity, such as the interior of a free-flow sleeve  12  forming part of the filter portion  6 .  
       FIG. 2  shows a cigarette  2  including a tobacco rod  4  and a filter portion  6 . Folded paper  10  is located in the hollow cavity of a first free-flow sleeve  13  located between the mouthpiece filter  8  and a second free-flow sleeve  15 . The paper  10  can be used in forms other than a folded sheet. For instance, the paper  10  can comprise one or more individual strips, a wound roll, or the like. A desired amount of zeolite molecular sieve sorbent can be provided in the cigarette filter portion loaded on, or incorporated into, the paper. For example, the zeolite molecular sieve sorbent can be provided by a combination of the coated amount of reagent/area of the paper and/or the total area of coated paper employed in the filter (e.g., greater amounts of zeolite molecular sieve sorbent can be provided simply by using larger pieces of coated paper.) In the cigarettes shown in  FIGS. 1 and 2 , the tobacco rod  4  and the filter portion  6  are joined together with tipping paper  14 . In both cigarettes, the filter portion  6  may be held together by filter overwrap  11 .  
      Zeolite molecular sieve sorbent can be incorporated into the filter paper in a number of ways. For example, zeolite molecular sieve sorbent can be mixed with water to form a slurry. The slurry can 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  FIGS. 1 and 2 . Alternatively, dried paper can be formed into a plug or other shape, and inserted into a filter portion of the cigarette. For example, the paper can be wrapped into a plug shape and inserted as a plug into the interior of a free-flow filter element, such as a polypropylene or cellulose acetate sleeve. In another arrangement, the paper can comprise an inner liner of such a free-flow filter element.  
      In another preferred embodiment, zeolite molecular sieve sorbent is added to the filter paper during the paper-making process. For example, zeolite molecular sieve sorbent can be mixed with bulk cellulose to form a cellulose pulp mixture. The mixture can be then formed into filter paper by known methods.  
      In a further preferred embodiment, zeolite molecular sieve sorbent is incorporated on, or with, 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. An exemplary embodiment is illustrated in  FIG. 3 , which shows a cigarette  2  including a tobacco rod  4  and a filter portion  6  in the form of a plug-space-plug filter having a mouthpiece filter  8 , a plug  16  and a space  18 . The plug  16  can comprise a tube or solid piece of material, such as polypropylene or cellulose acetate fibers. The tobacco rod  4  and the filter portion  6  are joined together with tipping paper  14 . The filter portion  6  may include a filter overwrap  11  containing traditional fibrous filter material. Zeolite molecular sieve sorbent can be incorporated on the filter overwrap  11 , such as by coating. Alternatively or additionally, zeolite molecular sieve sorbent can be incorporated in the plug  16 , and/or in the space  18 .  
       FIG. 4  shows a cigarette  2  including a tobacco rod  4  and filter portion  6 . This arrangement is similar to the cigarette shown in  FIG. 3  except the space  18  is filled with granules of zeolite molecular sieve sorbent, or contains a plug  15  made of material, such as fibrous polypropylene or cellulose acetate, containing zeolite molecular sieve sorbent. The plug  16  can be hollow or solid, and the tobacco rod  4  and filter portion  6  are joined together with tipping paper  14 . The cigarette also includes a filter overwrap  11 .  
       FIG. 5  shows a cigarette  2  including a tobacco rod  4  and a filter portion  6 . The filter portion  6  includes a mouthpiece filter  8 , a filter overwrap  11 , tipping paper  14  joining the tobacco rod  4  and filter portion  6 , a space  18 , a plug  16 , and a hollow sleeve  20 . Zeolite molecular sieve sorbent can be incorporated into one or more elements of the filter portion  6 . For example, zeolite molecular sieve sorbent can be incorporated into the sleeve  20 , or granules of zeolite molecular sieve sorbent can be filled into the space within the sleeve  20 . If desired, the plug  16  and sleeve  20  can be made of material, such as fibrous polypropylene or cellulose acetate containing zeolite molecular sieve sorbent. The plug  16  can be hollow or solid.  
       FIGS. 6 and 7  show further versions of the filter portion  6 . In  FIG. 6 , cigarette  2  includes a tobacco rod  4  and filter portion  6 . The filter portion  6  includes a mouthpiece filter  8 , a filter overwrap  11 , a plug  22 , and a sleeve  20 . Zeolite molecular sieve sorbent can be incorporated in one or more of these filter elements.  
      In the embodiment shown in  FIG. 7 , the filter portion  6  includes a mouthpiece filter  8  and a plug  24 . The plug  24  can be solid or hollow. Zeolite molecular sieve sorbent can be incorporated in at least the plug  24 . In the cigarettes shown in  FIGS. 6 and 7 , the tobacco rod  4  and filter portion  6  are joined together by tipping paper  14 .  
      Various techniques can be used to apply zeolite molecular sieve sorbent to filter fibers or other supports. For example, zeolite molecular sieve sorbent can be added to filter fibers before forming them into a cigarette filter rod. Zeolite molecular sieve sorbent can be added to filter fibers in the form of a dry powder or slurry by any suitable method. If zeolite molecular sieve sorbent is applied in the form of a slurry, the fibers are preferably allowed to dry before being formed into a cigarette filter.  
      In another preferred embodiment, zeolite molecular sieve sorbent is employed in a hollow portion of a cigarette filter. For example, as described above, 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 plugs. The void can be filled with zeolite molecular sieve sorbent, such as in powder or particle form. An example of this embodiment is shown in  FIG. 3 . Zeolite molecular sieve sorbent can be in granular form, or can alternatively be loaded onto or incorporated with a suitable support, such as fibers or threads.  
      In another embodiment, zeolite molecular sieve sorbent is placed in a filter portion of a cigarette for use with a smoking device as described in U.S. Pat. No. 5,692,525, which is hereby incorporated by reference in its entirety.  FIG. 8  illustrates one type of construction of a cigarette  100 , which can be used with an electrical smoking device. As shown, the cigarette  100  includes a tobacco rod  60  and a filter portion  62  joined by tipping paper  64 . The filter portion  62  preferably contains a tubular free-flow filter element  102  and a mouthpiece filter plug  104 . The free-flow filter element  102  and mouthpiece filter plug  104  may be joined together as a combined plug  110  with plug wrap  112 . The tobacco rod  60  can have various forms incorporating one or more of the following items: an overwrap  71 , another tubular free-flow filter element  74 , a cylindrical tobacco plug  80  preferably wrapped in a plug wrap  84 , a tobacco web  66  comprising a base web  68  and tobacco flavor material  70 , and a void space  91 . The free-flow filter element  74  provides structural definition and support at the tipped end  72  of the tobacco rod  60 . At the free end  78  of the tobacco rod  60 , the tobacco web  66  together with overwrap  71  are wrapped about cylindrical tobacco plug  80 . Various modifications can be made to a filter arrangement for such a cigarette incorporating the zeolite molecular sieve sorbent.  
      In an embodiment, the zeolite molecular sieve sorbent is incorporated into a filter portion of a non-traditional cigarette. For example, zeolite molecular sieve sorbent can be incorporated in various ways, such as by being loaded on, into, or with, paper or other substrate material, disposed in the passageway of the tubular free-flow filter element  102  therein. Zeolite molecular sieve sorbent may also be used as a liner or a plug in the interior of the tubular free-flow filter element  102 . Alternatively, zeolite molecular sieve sorbent can be incorporated into the fibrous wall portions of the tubular free-flow filter element  102 . For example, the tubular free-flow filter element or sleeve  102  can be made of a suitable material, such as polypropylene or cellulose acetate fibers. Zeolite molecular sieve sorbent can be mixed with such fibers prior to, or as part of, the sleeve forming process.  
      As in above-described embodiments, zeolite molecular sieve sorbent may be incorporated into more than one component of a filter portion, such as into the tubular free-flow filter element  102  and another component. The filter portion  62  of  FIG. 8  can also be modified to create a void space into which zeolite molecular sieve sorbent can be inserted.  
      As explained above, zeolite molecular sieve sorbent can be incorporated in various support materials. When zeolite molecular sieve sorbent is used in filter paper, the particles may have an average particle diameter of up to 100 μm, preferably 2 to 50 μm.  
      When zeolite molecular sieve sorbent is used in granular form, e.g., in a space or void in a filter, larger particles may be used. Such particles preferably have a mesh size of from about 18 to 60 mesh (1000 to 250 microns, U.S. Standard, ASTM E11), and more preferably from about 30 to 60 mesh (600 to 250 microns). To form such particles, larger particles of zeolite material can be broken up into smaller particles having a desired size by any suitable technique, such as milling. The smaller particles can be separated to produce a desired particle size range by any suitable technique, such as sieving.  
      The zeolite molecular sieve sorbent can also be used in monolithic form in cigarette filters. For example, zeolite particles can be formed into a monolithic structure using any suitable binder, e.g., a resin, to bond the zeolite particles together. The monolithic structure can have any suitable shape and size that can be incorporated into a cigarette filter. For example, the monolithic structure can be cylindrical-shaped, disc shaped, or the like. The size of the monolithic structure can be determined based on an effective amount of the zeolite material that is effective to selectively remove one or more selected constituents of mainstream smoke when incorporated in a cigarette.  
      The zeolite molecular sieve material can also be provided in bead form. For example, the material can be loaded on a spherical, substantially spherical, or like-shaped support by any suitable coating process to form beads. The beads preferably have a mesh size of from 18 to 60 mesh, and more preferably from 30 to 60 mesh.  
      The amount of zeolite molecular sieve sorbent provided in the cigarette filter by being incorporated on, into, or with, a suitable support, such as filter paper and/or filter fibers, or placed in a space or void, is dependent on the amount of constituents in the tobacco smoke, as well as the amount of the constituents that is desired to be removed from the smoke. Filter paper and the filter fibers may contain from 10% to 50% by weight of zeolite molecular sieve sorbent to remove the constituents from tobacco smoke, for example.  
      An exemplary embodiment of a method of making a filter comprises incorporating zeolite BETA into a cigarette filter. The zeolite BETA is capable of selectively removing one or more selected constituents from mainstream smoke. Any conventional or modified method of making cigarette filters can be used to incorporate the zeolite BETA.  
      An exemplary embodiment of a method of making cigarettes comprises providing a cut filler to a cigarette making machine to form a tobacco column; placing a paper wrapper around the tobacco column to form a tobacco rod; and attaching a cigarette filter comprising zeolite molecular sieve sorbent to the tobacco rod to form the cigarette.  
      Exemplary suitable types of tobacco materials that can be used include flue-cured, Burley, Maryland or Oriental tobaccos, the rare or specialty tobaccos, and blends thereof. The tobacco material can have any suitable form including, but not limited to, 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. Tobacco substitutes can also be used.  
      In cigarette manufacture, tobacco is normally 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 known flavors or other additives (e.g., burn additives, combustion modifying agents, coloring agents, binders, and the like).  
      Techniques for cigarette manufacture are known, and may be used to incorporate the zeolite molecular sieve sorbent. The resulting cigarettes can be manufactured to any desired specification using standard or modified cigarette making techniques and equipment. The cigarettes may have a length ranging from about 50 mm to about 120 mm. 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/cm 3  to about 300 mg/cm 3 , and preferably 150 mg/cm 3  to about 275 mg/cm 3 .  
      Another embodiment relates to methods of smoking the cigarette described above, which involve heating or lighting the cigarette to form smoke, and drawing the smoke through the cigarette. During smoking of the cigarette, the zeolite molecular sieve sorbent selectively removes one or more selected constituents from mainstream smoke. Preferably at least 10%, 20%, 30%, 40%, 50% or more of the selected constituent is removed from the tobacco smoke by the sorbent.  
      “Smoking” of a cigarette means the heating or combustion of the cigarette to form tobacco smoke. 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 may also be smoked by other means. For example, the cigarette may be smoked by heating the cigarette using an electrical heater described, for example, in commonly-assigned U.S. Pat. Nos. 6,053,176; 5,934,289; 5,591,368 or 5,322,075, each of which is incorporated herein by reference in its entirety.  
     EXAMPLE  
      Samples 1-4 are prepared by modifying four industry reference 1R4F cigarettes. Particularly, approximately 100 mg of zeolite NH4-Ferrierite, zeolite NH4-ZSM-5 (zeolite ZSM-5), zeolite H-BETA (zeolite BETA) and zeolite H-Y, respectively, is sieved to a mesh size of about 18 to 40 mesh (1000 to 425 microns), and loaded into a space of a plug-space-plug filter configuration of a 1R4F cigarette. An unmodified 1R4F cigarette and the four modified cigarettes are smoked under FTC conditions (2 second, 35 cm 3  puff every 60 seconds). The fourth puff is analyzed using gas chromatography/mass spectrometry. For each of Samples 1-4, the percent delivered of the gas phase smoke constituents 1,3-butadiene, isoprene, acetaldehyde, acrolein, and isobutraldehyde, is calculated in comparison to that of the unmodified 1R4F cigarette. The results are shown in the following Table.  
               TABLE                          Percent of Constituent Delivered by       Modified Cigarette Versus 1R4F Cigarette                                         1,3-Buta-   Acro-   Acetal-   Iso-   Isobutral-           diene   lein   dehyde   prene   dehyde                                                 Sample 1   67   21   27   77   56       (zeolite NH4-       Ferrierite)       Sample 2   24    9   21   32   20       (zeolite ZSM-5)       Sample 3   65    6   21   35    9       (zeolite BETA)       Sample 4   89   12   29   38    5       (zeolite H-Y)                  
 
      As shown in the Table, Sample 2 containing zeolite ZSM-5 is significantly more efficient in removing 1,3-butadiene (i.e., of delivering a smaller percentage of 1,3-butadiene) than are Samples 1, 3 and 4 containing other zeolites (i.e., 24% versus 67%, 65 % and 89%, respectively). Sample 2 also more selectively removes acrolein than molecular-smaller acetaldehyde and molecular-larger isobutraldehyde (i.e., 9% versus 21% and 20%, respectively). Sample 3 containing zeolite BETA more selectively removes acrolein than acetaldehyde (i.e., 6% versus 21%, respectively).  
      These test results demonstrate that cigarette filters containing zeolite BETA and zeolite ZSM-5 can selectively remove a substantial amount of acrolein from mainstream smoke, and that the inclusion of zeolite ZSM-5 is highly efficient in removing a substantial amount of 1,3-butadiene from mainstream smoke. Accordingly, in an embodiment, zeolite BETA and zeolite ZSM-5 can be used in combination in smoking articles to selectively remove acrolein and 1,3-butadiene. Preferably, other constituents, such as flavor constituents, remain in the mainstream tobacco smoke. The zeolites can be incorporated in the tobacco rod, as well as in the filter.  
      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.