Tobacco product carrying catalytically active material and its use in a smokers' article

Abstract

The tobacco product carries on its surface catalytically active material for improving the burning process. The catalytically active material is selected from the group of crystalline and non-crystalline oxides and hydroxides of aluminium, e.g. gibbsite, having a particle size of 1 to 100 μm and a specific surface of 75 to 250 m2/g. With the use of the catalyst in the tobacco, the amount of noxious compounds in the mainstream and sidestream smoke can be considerably reduced in the combustion process of the smokers' article during its consumption.

Description

[0001] This invention relates to a tobacco product carrying catalytically active material, to articles for smoking containing such a tobacco product and more particularly to cigarettes which contain non-zeolitic catalysts in the tobacco rod. The catalytically active material is useful for reducing toxic components in tobacco smoke of smokers' articles, particularly of cigarettes.

[0002] As is well known, two kinds of smoke arise during the smoking of a cigarette, the mainstream smoke and the sidestream smoke. The mainstream smoke is the smoke which enters the mouth of the smoker when he draws on the cigarette through the filter part, while the sidestream smoke is the smoke which is released by the smouldering combustion of the cigarette in the interim phases. From technical literature it can be learned that approximately twice as much tobacco is burned during the glowing of a cigarette between the puffs than during the puffs.

[0003] Although in the prior art many—albeit unsatisfactory—means of reducing the mainstream smoke of noxious substances have been proposed, there has been no solution so far which makes it possible to remove the noxious substances from the sidestream smoke in sufficient manner.

[0004] Large pore zeolites were the first catalysts to be found to reduce significant amounts of undesirable compounds in sidestream as well as mainstream smoke (U.S. Pat. No. 5,727,537, EP-A-0 740 907). However, zeolites have an inherent disadvantage in that larger PAH molecules like benzo(a)pyrine, one of the worst carcinogenic smoke constituents, are not reduced in the mainstream. The overall PAH reduction values are less than a 25% in the mainstream compared to over 50% in the sidestream. The disappointing performance in the mainstream has been assigned to the sieving effect of the pore openings in the zeolite framework structure (W. M. Meier and K. Siegmann, Microporous and Mesoporous Materials, 33 (1999) 307-310).

[0005] U.S. Pat. Nos. 3,572,348 and 3,703,901 suggest the use of zeolites for incorporating in tobacco material for reducing toxic compounds in the smoke. However, the proposed zeolite compounds contain substantial amounts of zinc besides palladium or platinum which are not suitable for several reasons for a product which cannot be recycled. These typical preparations known in petrochemistry of those days were heated in nitrogen (rather than burned in the presence of oxygen) and have little to do with a burning cigarette, and the process was pyrolysis rather than combustion. Mainstream and sidestream could not be distinguished in the set-up used. Moreover, the use of zinc is not permissible in open systems by environmental laws.

[0006] Described in EP-A-0 740 907 are smokers' articles wherein the tobacco comprises a catalyst of a zeolite compound. It is proposed that the catalyst in the tobacco be bound to the tobacco with or without a binding agent, such as silica gel or attapulgite, a meerschaum-like clay mineral. Attempts to fix catalyst particles on the tobacco by electrostatic deposition failed. The catalyst particles were observed to discharge on the tobacco fibers within seconds and sputtered. It was found that the use of binding agents has serious drawbacks because the catalytic activity of the material which is bound by the agent is affected. Without binding agent, the binding strength of the catalytically active material to the tobacco is not sufficient, and therefore a separation of the catalyst from the material can occur easily during the manufacturing process of smokers' articles or during transportation.

[0007] Zeolitic materials, both natural and synthetic, in appropriate form, can have catalytic capabilities for various kinds of organic reactions. Zeolites are microporous crystalline aluminosilicates which have definite crystal structures having a large number of cavities connected to each other by channels. These cavities and channels are absolutely uniform in size, and their dimensions can be determined by probe molecules as well as by crystal structure analysis. In most cases these data are known and do not have to be determined further. Since the dimensions of these pores are such that they sorb molecules of particular dimensions while rejecting those of larger dimensions, these materials have come to be known as “molecular sieves” and are utilized in a variety of ways to take advantage of these properties.

[0008] Such molecular sieves comprise a large variety of structural types (nearly 100; cf. D. H. Olson, W. M. Meier and Ch. Baerlocher, Atlas of Zeolite Framework Types, 5rd Edition, 2001, Elsevier, (formerly: Atlas of Zeolite Structure Types)) of crystalline aluminosilicates and isostructural materials with free pore diameters in the range of 0.3 to 1.3 nm or 3 to 13 Å. These aluminosilicates can be described as a rigid three-dimensional network of SiO4 and AlO4, wherein the tetrahedra are cross-linked by sharing of oxygen atoms, the ratio of all aluminium and silicon atoms to oxygen being 1:2. Such a network containing aluminium is negatively charged, and requires for charge balance one monovalent cation (e.g. Na or K) or half a divalent cation (e.g. Ca) for each Al in the network. These cations can be exchanged either completely or partially using standard ion exchange techniques. Cation exchange is a possible means of fine tuning the critical pore diameter in a particular application.

[0009] The pore volume of a typical zeolite is occupied by water molecules before dehydration. Dehydrated or activated zeolites are excellent sorbents for molecules which are small enough to pass through the apertures of the sieve. Syntheses using organic cations (such as tetrapropylammonium) have led to “high silica zeolites”, which contain only few Al in the network, if any at all, and the composition approaches that of SiO2. High silica zeolites are not unanimously considered to be zeolites; although they have the same kind of structure, their exchange capacities are comparatively low, their selectivities very different, and these materials are hydrophobic. Consequently they are referred to as zeolite-like molecular sieves in this specification, following widespread usage.

[0010] The sieving effect of the molecular sieve is based on the pore size. Sorption is also controlled by electrostatic interactions. Many of the chemical and physical properties are dependent upon the Al content of the zeolite. A rising Si/Al ratio means an increased temperature stability, up to 1000° C. in the case of silicalite, which is a molecular sieve with a pure SiO2 framework structure. The selectivity of the inner surfaces changes from strongly polar and hydrophilic in the case of the molecular sieves rich in aluminium to a polar and hydrophobic in the case of a zeolite with a modulus >400.

[0011] It has been discovered that the object of the present invention can be achieved by incorporating certain catalytically active materials, which fulfill the necessary catalytic criteria, into tobacco by distributing the catalytically active material regularly on conditioned tobacco and by pressing the catalytically active material on the tobacco. When incorporated into the tobacco rod of a cigarette, the catalytic properties of the material which is pressed on the tobacco can develop its catalytic activity completely. The advantage is that the pores of the material remain open. Moreover the method assures an even distribution of catalyst particles on the tobacco which is all-important.

[0012] Consequently there is a demand for smokers' articles, especially filter cigarettes, whose mainstream as well as sidestream smoke is significantly lower in noxious substances than with smokers' articles of prior art.

[0013] A first object of the present invention is therefore to provide a tobacco product having a considerably lower content of noxious compounds such as PAHs and nitrosamines in its smoke than known products and which is free of the above-mentioned drawbacks.

[0014] To overcome the shortcomings of large pore zeolites like NaY in the mainstream other catalyst materials have been investigated. Good results were obtained with oxides and hydroxides of aluminium. These materials should have a particle size of around 1 μm (not smaller and be dusty) and a surface of some 100 m2/g or more.

[0015] In a first aspect, one subject matter of the present invention is thus a tobacco product carrying on its surface catalytically active material for improving the burning process, wherein the catalytically active material is selected from the group of crystalline and non-crystalline oxides and hydroxides of aluminium

[0016] In a second aspect, a further subject matter of the present invention is a smokers' article comprising a filter, a tobacco rod and a wrapper in which the tobacco rod contains a catalyst selected from the group of oxides or hydroxides of aluminium. They are preferably acid or slightly acidic. The catalyst may contain Fe or Si in minor amounts (e.g. 0 to 3%) or more Si for amorphous material. The catalyst can comprise particles consisting of single crystals or particles consisting of agglomerates of smaller crystals which are bound with a binder as kaolinite (“granulate”). Normally the catalyst is not highly crystalline. Typically the catalyst is selected from the compounds of the group alumina (Al-oxide), diaspore, natural or synthetic boehmite, natural or synthetic gibbsite, natural or synthetic doylite, natural or synthetic nordstrandite, natural or synthetic bayerite and hydrargillite. Typically the particle size of the catalyst is in the range of 1 to 100 μm (e.g. 3, 5 or 10 μm) and its specific surface is in the range of 75 to 250 m2/g (e.g. 100 or 150 m2/g).

[0017] The following table lists a representative number of compounds which are suitable in the first aspect of the present invention.

TABLE A
Crystalline aluminium oxides and hydroxides and
characteristic lines according to Powder Diffraction File (PDF)
	d-values (in A) of the
Material	3 strongest lines	PDF #
Alumina (Al-oxide)	α-Al2O3	2.07	2.52	1.59	48-366
	β-Al2O3	1.40	11.97	2.68	10-414
	γ-Al2O3	1.98	1.40	2.39	10-425
		1.40	2.41	2.12	13-373
		1.40	1.98	2.39	29-63
	δ-Al2O3	1.39	2.60	2.46	46-1215
	Θ-Al2O3	1.39	2.84	2.73	23-1009
Diaspore	α-AlO(OH)	3.99	232	2.13	5-355
Boehmite, syn.	y-AlO(OH)	6.32	1.85	3.16	49-133
Gibbsite, syn.	Al(OH)3	4.85	4.37	2.39	33-18
Doylite	Al(OH)3	4.79	437	2.39	38-376
Nordstrandite, syn.	Al(OH)3	4.79	2.27	4.32	24-6
Bayerite, syn.	α-Al(OH)3	2.22	4.71	4.35	20-11
	δ-Al(OH)3	3.62	2.27	1.80	37-1377
Hydrargillite
(see gibbsite)

[0018] If not purely synthetic, these compounds frequently contain significant amounts of Si, Fe, Na and/or other elements. β-Alumina, widely listed as such, is not a true aluminium oxide, but at least in part a Na-aluminate. Many Al-compounds listed in Table A are alteration products, and are thus not highly crystalline. As indicated by the names, most of these compounds are also known minerals. They are environmentally safe, which is an important aspect in the present context.

[0019] Non-crystalline or X-ray-amorphous alumina can contain over 3% of Si and is then mesoporous.

[0020] In all these compounds Al is octahedrally coordinated by oxygen whereas in aluminosilicates (like felspars and zeolites) Al is in tetrahedral coordination.

Preparation and testing of cigarettes containing alumina-based catalysts

[0021] For initial testing, the cigarettes were hand-rolled and the tobacco was loaded with 5% of the catalyst. This was done by using a procedure wherein the tobacco is treated with catalytically active materials, consisting of the steps of

[0022] a) distributing catalytically active material on tobacco,

[0023] b) pressing the catalytically active material on the tobacco.

[0024] Advantageously the catalytically active material is distributed evenly on the smoking tobacco. The tobacco can consist of leaves or reconstituted tobacco sheets, cut or uncut.

[0025] Advantageously the tobacco is made reasonably soft by conditioning it, i.e. it has a defined degree of moisture. If the tobacco is too dry it is brittle and not suitable for receiving the catalytic material.

[0026] Preferably the catalyst is pressed on the tobacco by a single or double layer cylinder press. For a continuous working process such a press can work in combination with a conveyor belt. The process can be carried out with two or more distributing and pressing steps, e.g. on the upper and lower side of the tobacco. E.g. the catalyst content in relation to the tobacco is about 4-8% (wt/wt).

[0027] For PAH (polycyclic aromatic hydrocarbons) analyses, the method described by W. M. Meier and K.Siegmann [Microporous and Mesoporous Materials, 33 (1999) 307-310] was applied using a smoking machine. This method is based on a photoelectric PAH sensor in combination with a commercially available light scattering instrument which determines the total mass of particles smaller than 10 μm (PM-10). The signal of the photoelectric aerosol sensor is proportional to the amount of particle bound PAH. Light scattering reflects the number and size of particles, independently of chemical composition, and was found to agree with the results obtained with conventional methods in numerous tests. The method allows the simultaneous measurement of tar and PAH values.

Example 1

[0028] The tobacco blend (American blend type) was received from a tobacco lot and kept in a humidifier at 60% relative humidity. 5% by weight of synthetic gibbsite (obtained from Fluka, Switzerland) was evenly distributed over the tobacco, and then pressed on by a heavy cylinder on a rubber belt.

[0029] Hand-rolled cigarettes of 1 g tobacco each were then prepared without filter tips, i.e. using tobacco with catalyst and without catalyst (reference). The measurements gave reductions of

[0030] 48-53% PAH in the mainstream

[0031] 44-46% PAH in the sidestream

EXAMPLE 2

[0032] Following the same procedure as described in example 1, but using α-alumina (supplied by Dr. Markus Meier, Sierre, Switzerland) and tested by X-ray diffraction. These gave the following results

[0033] in mainstream 49% reduction in PAH

[0034] in sidestream 45% reduction in PAH

Example 3

[0035] Following the same procedure as described in example 1, but using X-ray amorphous Siral 1.5 (supplied by CONDEA GmbH, Hamburg, Germany) containing 1.5% silica and having a BET surface of 330 m2/g. The following results were obtained:

[0036] in mainstream 50-55% reduction in PAH

[0037] in sidestream 55-60% reduction in PAH

[0038] Note that the PAH reduction values in the mainstream are very much higher than those recorded for zeolite type catalysts (less than 20% overall measured by the same method).

[0039] A smoking panel noted a smoother taste without off-taste in the products of the above examples.

Claims

1. Tobacco product carrying on its surface catalytically active material for improving the burning process, wherein the catalytically active material is selected from the group of crystalline and non-crystalline oxides and hydroxides of aluminium.

2. Tobacco product according to claim 1 wherein the catalytically active material is bound to the surface, wherein the catalytically active material is preferably pressed into the tobacco surface so as to be bound without an adhesive in order to prevent the catalytically active material from being partially or completely inactivated by closed pores.

3. Tobacco product according to claim 1 or 2, wherein the oxides and hydroxides of aluminium are acid or slightly acidic.

4. Tobacco product according to claim 1, wherein the oxides and hydroxides of aluminium contain Fe in an amount of less than 3%.

5. Tobacco product according to claim 1, wherein the catalytically active material comprises crystalline hydroxides of aluminium which contain silicon in an amount of less than 3%.

6. Tobacco product according to claim 1, wherein the catalytically active material comprises amorphous hydroxides of aluminium which contain silicon in an amount of more than 3%.

7. Tobacco product according to claim 1, wherein the catalytically active material is not highly crystalline.

8. Tobacco product according to claim 1, wherein the catalytically active material comprises particles consisting of single crystals.

9. Tobacco product according to claim 1, wherein the catalytically active material comprises a granulate consisting of agglomerates of crystals which are bound to each other with a binder.

10. Tobacco product according to claim 9, wherein the binder is kaolinite.

11. Tobacco product according to claim 1, wherein the catalytically active material comprises X-ray amorphous hydroxides of aluminium having a particle size in the range of 1-100 μm and a specific surface of up to 550 m2/g.

12. Tobacco product according to claim 1, wherein the catalytically active material is selected from the compounds of the group alumina (Al-oxide), diaspore, natural or synthetic boehmite, natural or synthetic gibbsite, natural or synthetic doylite, natural or synthetic nordstrandite, natural or synthetic bayerite and hydrargillite.

13. Tobacco product according to claim 1, wherein the particle size of the catalyst is in the range of 1-100 μm, and its specific surface is in the range of 75 to 250 m2/g.

14. A smokers' article comprising a filter, a tobacco rod and a wrapper, wherein the tobacco rod consists of a tobacco product according to claim 1 or 2.

15. Use of a catalytically active material comprising an oxide or hydroxide of aluminium for adding to the tobacco of a tobacco rod of a smokers' article for reducing the amount of noxious compounds in the mainstream and sidestream smoke in the combustion process of the smokers' article during its consumption.

16. Use according to claim 15, wherein the catalytically active material is selected from the group consisting of alumina, diaspore, natural or synthetic boehmite, natural or synthetic gibbsite, natural or synthetic doylite, natural or synthetic nordstrandite, natural or synthetic bayerite and hydrargillite.

17. Use according to claim 16, wherein the catalytically active materials comprise finely ground natural counterparts of oxides and hydroxides of aluminium and granulated using a binder such as kaolinite.