Cigarette filter using intermetallic compounds

[00002] This application claims priority under 35 U.S.C. §§ 119 and/or 365 to Provisional Application No. 60/180,681 filed in U.S. on Feb. 7, 2000 now abn.; the entire content of which is hereby incorporated by reference.

[00003] The invention relates to filtering of unsaturated hydrocarbons from mainstream cigarette smoke using intermetallic nano-clusters. The nano-clusters can be incorporated in cigarette filter elements in a manner which selectively removes gaseous components such as 1,3-butadiene, isoprene, toluene and the like from mainstream smoke.

[00004] Fresh activated carbon can be used to reduce the level of 1,3-butadiene in mainstream cigarette smoke. However, because activated carbon is a broad base physical adsorbent of gaseous compounds and removes a large number of volatile and gas-phase compounds from cigarette smoke, the result can produce undesired effects on the flavor of the tobacco smoke. Selective filtration, on the other hand, has the advantage of removing targeted gaseous compounds while minimizing the effect on flavor of the tobacco smoke.

[00005] The invention relates to a filter comprising an intermetallic reagent which binds with a gaseous component of a gas stream to remove the gaseous component from the gas stream. The invention also relates to a method of manufacturing a filter which is useful for removing a gaseous component of a gas stream, comprising incorporating an intermetallic reagent in a filter, the intermetallic reagent being effective to bind with a gaseous component of a gas stream sufficiently to selectively remove the gaseous component from the gas stream. The invention further relates to a method of removing a gaseous component from a gas stream, comprising passing the gas stream in contact with a filter comprising an intermetallic reagent which binds with a gaseous component of the gas stream and removes die gaseous component from the gas stream.

[00006] The filter can comprise a cigarette filter attached to a tobacco rod by tipping paper or die intermetallic reagent can be incorporated in one or more cigarette filter parts such as filter paper, shaped paper insert, a plug, a space, or a free-flow sleeve. The intermetallic reagent can comprise nanometer or micrometer size clusters of a transition metal or alloy containing a transition metal or a transitional metal salt. The transition metal can include iron and/or titanium and the intermetallic reagent can comprise nanometer or micrometer size clusters of an iron aluminide or a titanium aluminide. Preferably, the intermetallic reagent is a non-oxide intermetallic reagent or a crystalline intermetallic reagent.

[00007] The intermetallic reagent can be incorporated in or on a support material. The support material can comprise silica gel, porous carbon or a zeolite. According to a preferred embodiment, the intermetallic reagent selectively binds to unsaturated hydrocarbons in the gas stream and selectively removes the unsaturated hydrocarbons from the gas stream. A metal atom of the intermetallic reagent can bind to a C—H bond and/or a C—C bond of the gaseous component. The gaseous component to be removed from the gas stream can be an unsaturated hydrocarbon such as 1,3-butadiene, isoprene and/or toluene.

[00008] The intermetallic reagent can be incorporated in cigarette filter paper located within a free-flow filter, the filter paper optionally having a three-dimensional shape and/or the filter paper being a liner on the interior of a hollow tubular element. The intermetallic reagent can be incorporated with cellulose acetate fibers and/or polypropylene fibers forming a plug or a free-flow filter element.

[00009] According to a method of the invention, the filter can be attached to a tobacco rod with tipping paper or the intermetallic reagent can be incorporated in one or more cigarette filter parts selected from shaped paper insert, a plug, a space or a free-flow sleeve. According to a preferred method, a step of attaching the filter paper within a free-flow filter of a cigarette can comprise forming the filter paper into a three-dimensional shape, or attaching the filter paper as a liner on the interior of a hollow tubular element, or combining the intermetallic reagent with fibers and forming a filter element from the intermetallic reagent and fibers, or combining the intermetallic reagent with cellulose and/or polypropylene fibers and forming a plug or free-flow filter element, or incorporating the intermetallic reagent in a cavity of the filter. The intermetallic reagent can be loaded in or on a support material forming a filter element of the filter.

[00010] The gas stream can be formed by burning tobacco and directing tobacco smoke through the filter or one or more filter parts such that the component of the gas stream to be removed is brought into contact with the intermetallic reagent and prevented from reentering the gas stream.

[00011] According to a preferred method, where the porous support comprises silica gel, the silica gel can have an average particle diameter of at least 10 μm or the silica gel can be in the form of particles having a mesh size of at least 60, and the gas stream can be passed through a mass of particles of the silica gel. According to a further method, the silica gel can be incorporated with cellulose acetate fibers and/or polypropylene fibers and the gas stream can be a smoke stream from a burning cigarette.

[00015] According to the invention, small (nanometer or micrometer size) metal or metal alloy clusters can be incorporated in or on a support media (e.g., silica gel, porous carbon, zeolites, etc.) and the resulting filter material can be used to selectively bind to unsaturated hydrocarbons present in cigarette smoke. In a preferred embodiment, transition metals and metal alloys incorporated into the clusters can be used to remove gaseous components such as 1,3-butadiene from mainstream cigarette smoke as it passes through a filter containing the supported reactive metal clusters. The transition metals can include iron and titanium and alloys containing such elements such as iron alloys, titanium alloys, intermetallic compounds such as iron aluminide or titanium aluminide or transition metal salts (e.g., Cu, Fe, Zn, Al, Ce, V sulfates and/or phosphates) on high surface area support materials.

[00016] Using state-of-the-art theoretical techniques based on density functional theory and generalized gradient approximation for exchange and correlation potential, calculations of the binding energies of trans- and cis-form of butadiene to transition metal atom (Fe) as well as dimers (Fe₂, FeAl, and Al₂) were carried out. The objective of the study was to understand if (1) butadiene binds to these species and, if so, how the binding varies from one atom to another, (2) if one form of butadiene binds more strongly than the other, (3) where do the metal atoms insert and (4) if the structure of butadiene undergoes geometrical transformation as it binds to metal atoms. The study was carried out to see if suitable traps can be found for this organic molecule and to suggest experiments to prove the theoretical predictions.

[00017] In FIG. 1(a) the trans form of butadiene is given. It is a planar molecule. An Fe atom inserts into the C—H bond and gains an energy of 0.37 eV (see Table 1) over an isolated trans-butadiene and Fe atom. While interacting with the cis-form (FIG. 2), the Fe atom, on the other hand, attaches to the C—C double bond and the structure becomes three-dimensional. Energetically, the Fe-butadiene complex in the cis-form is more stable than the trans-form by 0.78 eV. This is particularly interesting as the trans- and cis-forms of butadiene are energetically nearly degenerate. Addition of Fe does seem to break this degeneracy.

[00018] Fe₂ does not bind to the trans- or cis-form of butadiene (FIG. 1(c)) as energetically this is higher than dissociated Fe₂ and butadiene. FeAl and Al₂ dimers, on the other hand, bind strongly to both the trans- and cis-forms of butadiene. While the bond between Fe and Al remains intact (see FIGS. 1(d) and 2(c)), that between Al and Al breaks (see FIGS. 1(e) and 2(d)). This is because the Fe—Al bond is stronger than the Al—Al bond. Nevertheless, a binding energy in excess of 1 eV between a metal dimer and butadiene is sufficient. The C—C and C—H bonds in butadiene do not change appreciably as metal atoms are bound to the molecule.

[00019] From the above discussion it is apparent that a metal atom either inserts into the C—H bond or attaches to a C—C bond in butadiene. As calculations presented in FIG. 1 and FIG. 2 and Table 1 are very complex and costly, the systematics of transition metal binding to CH and C₂ molecules was studied to see which atoms can possibly bond more strongly to butadiene than Fe. The corresponding energies are given in Table 2. The data indicates that Sc, Ti, V, Co, and Ni are better candidates than Fe whether they prefer to insert into the CH bond or attach to C—C bond. Calculations of Sc, Ti, V, Co, and Ni interacting with the complete butadiene molecule can be carried out to prove this hypothesis. Experimental studies of transition metal atoms and Al reacting with butadiene in the gas phase can also be carried out.

[00002]

TABLE 1
Binding Energy (eV)
	System	Trans (FIG. 1)	Cis (FIG. 2)
	C4H6	43.98	43.82
	C4H6Fe	0.37	1.15
	C4H6Fe2	—	—
	C4H6FeAl	1.35	1.76
	C4H6Al2	2.22	2.03
	Eb(C4H6) = E(C4H6) − 4E(C) − 6E(H)
	Eb(C4H6Fe) = E(C4H6Fe) − E(C4H6) − E(Fe)
	Eb(C4H6FeAl) = E(C4H6FeAl) − E(C4H6) − E(FeAl)
	Eb(C4H6Al2) = E(C4H6Al2) − E(C4H6) − E(Al2)
	Eb(Al2) = E(Al2) − 2E(Al) = 1.76 eV
	Eb(FeAl) = E(FeAl) − E(Fe) − E(Al) = 2.53 eV
	E = total energy, kEb = binding energy

[00002]

TABLE 2
Energetics of M—C2 and M—CH (M = Sc . . . Ni) in eV
M	Eb(MC2)	Eb(MCH)
Sc	6.76	9.02
Ti	6.95	6.21
V	7.28	4.95
Cr	4.37	4.08
Mn	5.03	3.61
Fe	4.86	4.68
Co	6.16	5.45
Ni	6.74	5.79
Eb(MC2) = E(MC2) − E(M) − E(C2)
Eb(MCH) = E(MCH) − E(M) − E(CH)

[00020] Clusters of nanosize intermetallic powders such as Fe₃Al, FeAl, TiAl, NiAl and Ni₃Al can be obtained by melting and atomization techniques. They can be processed by laser evaporation, and or chemical decomposition techniques. The powders can be produced in inert atmospheres such as argon or helium, or by bleeding a certain amount of oxygen, nitrogen, or ammonia to alter the surface property of the powders. The sizes of the particles may be altered by the residence time of the laser pulse, cooling time, temperature, etc. For instance, it is possible to synthesize nanoparticles of controlled size and composition using pulsed laser vaporization with controlled condensation (LVCC) in a diffusion cloud chamber under well-defined conditions of temperature and pressure.

[00021] While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.