COMBINED FILTER FOR REMOVING TARS AND TOXIC COMPOUNDS FROM TOBACCO SMOKE

Abstract

 The invention relates to a combined filter for removing tars and toxic compounds from tobacco smoke, which is applied to any type of tobacco rod, comprising a primary membrane (M1) located at the end of the tobacco rod, made up of at least one disc of impervious material and perforated with at least one hole that extends through same in a direction perpendicular to the cross-section of the membrane, so that the perforated surface has a free flow area of 0.2 % to 30 % of the total cross-section of the membrane; an outer membrane (M3) located at the end in contact with the smoker and made up of a cellulose-acetate fibre; which can include a cylindrical intermediate membrane (M2) formed by an adsorbent material between the primary membrane (M1) and the outer membrane (M3).

Description

Field of the invention

[0001] The object of the present patent is the description of a combined filter for reducing tars, nicotine and other toxic compounds in the tobacco smoke gas stream.

[0002] The field of application of the present invention is the tobacco industry sector related to cigarettes and specifically to sets of filters for use with cigarettes.

State of the art

[0003] The consumption of tobacco represents a major global health problem. The toxicity of tobacco smoke is widely known. On a scientific level, it can be said that more than 5,600 compounds in tobacco smoke have been identified (The complexity of tobacco and tobacco smoke, TA Perfetti and A. Rodgman, Beitráge zur Tabakforschung International/Contributions to Tobacco Research, vol 24, No. 5 May 2011). Although according to some authors this list could increase up to 100,000, the compounds already identified account for around 99 % of the smoke. Among these compounds, around 100 are recognised as toxic or carcinogenic by the FDA (Federal Register /Vol. 77, No. 64 /Tuesday, April 3, 2012). For this reason, intensive research has been carried out for many years to reduce the amount of smoke (or toxic compounds) inhaled by smokers.

[0004] Cigarettes consist basically of a paper cylinder containing the tobacco mixture and a filter. With regard to paper, it can be said, for example, that the permeability thereof has been studied and the combustion thereof has been modified, for example, as disclosed in the document "Effect of potassium inorganic and organic salts on the pyrolysis kinetics of cigarette paper" by Deqing Zao et al., (Journal of Analytical and Applied Pyrolysis, 102 (2013) 114-123). Papers that favour the self-extinction of cigarettes have also been developed and applied, such as, for example, that disclosed in document PCT/KR2009/003425, inter alia.

[0005] With regard to tobacco, genetic modifications have been studied with the aim of modifying the emission of nicotine and tars (WHO study group on tobacco product regulation, Report on the scientific basis of tobacco product regulations: Fifth report of a WHO group study, ISBN 978 922 4 120989 2, 2015) or the use of catalysts to reduce the emission of toxic products (Reduction of tobacco smoke components yield in commercial cigarette brands by addition of HUSY, NaY and AI-MCM-41 to the cigarette rod, A. Marcilla et al., Toxicology Reports (Open access), 2 (2015b) 152-164), inter alia.

[0006] Lastly, with regard to filters, different patents that describe different configurations are known, wherein the trajectory of the smoke through the filter is modified, wherein adsorbent active substances such as activated carbons, zeolites and mesoporous solids are used, which are capable of reducing the inhalation of tars and modifying the composition of the smoke, namely, for example, document WO2008142420; filters wherein said substances also include polar chemical components in various elements; or document WO2008018617, wherein the adsorbent substances are supported by granular materials.

[0007] Solutions involving multiple filters that combine different, more or less active elements with different designs are also known, wherein an activated carbon filter is disposed between two cellulose acetate filters, as disclosed in document US20060196513.

[0008] Filters have been developed which include particles of adsorbent materials evenly distributed throughout the entire filter; filters whose cross-section includes liquid fatty acids, as in the case of document TW I243026; or cigarette filters wherein the adsorbent layers comprise thermostable synthetic resin matrices, such as phenol-formaldehyde resin, as disclosed in document US2003070686. Others include concentric cylinders made of adsorbent material distributed in the main cellulose acetate filter; ventilated structures which house different membranes, as defined in document DE1 9924205658; or filters with helical grooves which include adsorbent materials, as disclosed in document EA200401360.

[0009] Systems capable of acting on the hydrodynamics of the tobacco smoke aerosol stream have also been developed. In particular, the system known as "tar gard", disclosed in a large number of patents, for example, in patent US3434480.

[0010] A very interesting article, "The intractable cigarette 'filter problem" (by B Harris, Tobacco Control, 2011 20 suppl 1, H0-H6), analyses the history and problems of filters, and reveals the existence of a conflict of interests. Apart from the technical difficulties in the design thereof, it also addresses the strategies of the different players, tobacco companies, authorities, etc., in addition to the problem of costs in many of the most sophisticated designs. All the solutions adopted have potential advantages and drawbacks, and conclude on the effectiveness of cellulose acetate filters, which have been commercially imposed, in addition to the effectiveness of the ventilation thereof. However, said article reveals that the problem remains unsolved, due to which new solutions must be developed.

[0011] In view of the solutions and backgrounds existing in the state of the art, the present invention develops a new type of filter which comprises up to three types of membranes, each with specific features, wherein the location of said membranes is essential to achieve the aim of improving the results of removing tars and toxic compounds from tobacco smoke, which can be applied to any type of cigarette.

Description of the invention

[0012] The present invention consists of a filter which comprises up to three types of membranes for removing tars and toxic compounds from tobacco smoke. Specifically, the present document studies the relative position of the membranes that make up said filter and the type of materials used, obtaining a valuable and selective result. This study reveals that the membranes disposed in that position improve the results of removing tars and toxic compounds from tobacco smoke.

[0013] As mentioned earlier, this filter is applicable to any cigarette: both commercially manufactured cigarette varieties and fillable tubes, filters for rolling tobacco or even complementary systems of conventional filters, as described herein.

[0014] Another differentiating aspect is the simplicity and low cost of the membranes used, which offers a very attractive solution that is easily applicable to the commercial market.

[0015] The use of these membranes and their position in the filter makes it possible to create more effective systems at a lower price.

[0016] Based on the foregoing, a combined filter for removing tars and toxic compounds from tobacco smoke has been developed which comprises the following elements:

- A primary membrane.

[0017] The first of the elements is an impermeable membrane that causes the condensation of tars and removes part of the nicotine contained in the tobacco smoke aerosol and which preferably must be disposed immediately after the tobacco rod, in contact therewith. This membrane comprises at least one impermeable disc, which can be made of different materials, and includes a series of small holes.

[0018] The inclusion of this membrane makes it possible to controllably reduce the inhalation of tars and, therefore, of nicotine and other substances when smoking a cigarette whose filter includes this system. It suffices to regulate the number of holes and their diameter. The larger the number of holes and their diameter, the greater the amount of tars that penetrate the membrane, but the load loss in the smoking process will be smaller. A balance must be struck between both aspects, so as to make the smoking process as pleasant as that of a conventional cigarette.

[0019] In order to achieve this effect, a plurality of holes are disposed wherethrough the smoke undergoes an acceleration and post-hole expansion, causing it to condense. The essential features of this system are the number of holes and their diameter, the length of the holes (membrane thickness), and the material from which it is made, provided that it is impermeable, do not affect their effectiveness, provided that it is located immediately following the tobacco rod. This differential fact makes it possible to use different materials and different thicknesses in its manufacture, with the sole condition of being manageable according to the application in which they will be used. By way of example, they may be made of paper, cardboard, poster board, wood, plastic, metal, closed-pore foam of any material or any other, with the sole condition of being impermeable and non-toxic. In order to manufacture filters for commercial cigarettes, or tubes, or filters which include them, they will preferably have a thickness of around 2 to 4 mm, although for applications such as rolling tobacco it would suffice to manually include a membrane made of paper, poster board or cardboard of micron thickness, conveniently perforated. Therefore, the possibilities of application of this type of membranes are endless and may have different variants according to the final use.

[0020] In summary, the primary membrane is made up of any non-toxic and impermeable or semi-permeable material, preferably impermeable, manufactured using any industrial, semi-industrial or manual method, wherein the material may be paper, cardboard, wood, ceramic, cellulose acetate, aluminium or other metal, closed-pore plastic material foams, wherein the membrane is circular or cylindrical, with a diameter equal to that of the tobacco rod or conventional filter, with holes or ducts with a small diameter, which penetrate it in a direction perpendicular to the circular cross-section and evenly distributed in said cross-section, located in contact with the tobacco rod, between said rod and the adjacent membranes, such that it only allows the cigarette smoke (or most of it, if semi-permeable) to pass through the holes or ducts that penetrate it. The length of the membrane (cylinder side) ranges from microns (paper) to 10 mm, preferably being from 1 to 3 mm, to facilitate handling. The membrane includes a number of holes with a diameter such that they have a free flow area of 0.2 % to 30 %, preferably 2 % to 15 %. In this sense, they may include from one to ten holes, with diameters comprised between 0.5 and 1 mm, preferably being two to five holes with a diameter between 0.7 and 1.2 mm. These holes have a non-circular hole cross-section. Lastly, these membranes may include an adhesive, or self-adhesive, layer to facilitate their inclusion, particularly if directly applied by the consumer to the rolling tobacco rod (T).

[0021] These membranes are also capable of including aromas or flavours such as menthol, cocoa, vanilla or any other additive, including nicotine, so that the smoke carries these substances as it passes through the holes, transmitting the corresponding sensations to the smoker while ensuring less inhalation of tars and toxic substances and opening the possibility to many combinations of flavours and reductions.

- An intermediate membrane.

[0022] The second membrane is made up of an adsorbent material composed of solids such as mesoporous silica SBA-15, MCM-41, zeolites or mesoporous activated carbons, included or not in a permeable matrix of plastic material or in cellulose-acetate fibres and which acts on the gases generated, adsorbing certain compounds. The material of this second membrane may include aluminium or other active metals in the structure thereof, with the aim of promoting the adsorption of certain compounds and reducing the inhalation of the same by the smoker.

[0023] This membrane can be directly prepared with these materials using the adequate granulometry in a layer of a certain thickness, or manufactured from cellulose-acetate fibres or other fibres capable of being used in the filters, such as cotton fibres, whereto these materials are added, either by physically mixing with the finished fibre or in the manufacturing process thereof.

[0024] The effect of this type of filters is complementary to that of the primary membrane, since it can act on certain compounds such as carbon monoxide or others mainly present in the gas phase of the tobacco smoke and more specifically the lightest compounds, whereon the condensation promoted by said membrane leaves them practically unaltered in the gas stream.

[0025] This type of membrane also enables the inclusion of flavours, aromas or nicotine, being more effective for this purpose than the primary membrane. For this reason, the joint use of the two membranes is especially attractive, although both may be used separately.

- An outer membrane

[0026] The filter includes an outer membrane, tertiary or third component of the filter, which is the membrane in contact with the smoker's mouth, which is a cylinder of the adequate length of a conventional filter and made up of cellulose-acetate fibre, and which may include ducts of different cross-sections or other varieties. This membrane is capable of including capsules of aromas, flavours or nicotine or containing said compounds adsorbed or as a physical mixture so that they are released into the main stream when the tobacco smoke penetrates the filters that contain them.

[0027] One of the differences between the use of the primary membrane and the known holders that use this principle and are positioned at the end of the filter in contact with the smoker's mouth is that if this membrane is placed in that same position, the condensation would take place inside the mouth, giving the smoker an unpleasant sensation, in addition to increasing the adverse consequences for their oral health. Additionally, it would cause an adverse aesthetic effect by producing tar stains on the filter visible to the smoker.

[0028] For this reason, the aforementioned holders existing in the market are manufactured from plastic materials and have a system for collecting said tars and avoiding contact with the smoker. The fact that they can be transparent is an intentional commercial strategy, since it makes it possible to observe what they are able to keep away from the smoker, since what is condensed thereon would have passed into their body had they not been used. However, since the holders are fitted to the cigarette, their design must enable said fit, resulting in the corresponding complexity and cost.

[0029] In the present invention, this membrane is located immediately after the tobacco rod and in contact therewith. This makes it possible to achieve an effect similar to those described for the aforementioned holders, i.e., the condensation of tars, which do not come in contact with the smoker's mouth, but rather are retained in the adjacent membranes and also, the visual effect for the smoker is just as evident, since they can easily observe that the end of the filter in contact with their mouth is clearly cleaner than a conventional filter that uses this system. The rest of the membranes adjacently disposed serve to improve and amplify the good final results. All at a considerably lower cost and making it easy to dispense flavours or aromas to the smoker.

[0030] Additionally, these membranes can be grouped into smoking paper booklets, wherein said container contains a series of membranes of the type described previously, evenly disposed in the container itself, and said membranes can be easily separated from the container and must be placed on the exterior of the filter in contact with the tobacco.

[0031] In this regard, it should be noted that the foregoing membranes can be manufactured separately. If the primary and secondary membranes were manufactured separately, they could be used directly by the consumer when filling their conventional tubes or when preparing their cigarettes with rolling tobacco, assembling said membranes in their cigarette. Alternatively, they may already be assembled in commercial filters that include them, either including aromas or flavours or in their neutral form.

[0032] Lastly, these membranes can be utilised or used in filters for any type of tobacco rod, such as, for example, conventional cigarettes, cigars, cheroots, unfiltered cigarettes or those commonly known as hand-rolled cigarettes.

[0033] As a complement to the description being made, and for the purpose of helping to make the features of the invention more readily understandable, said description is accompanied by figures which, by way of illustration and not limitation, represent the following:

Figure 1 is a drawing which shows a sectional view of any one rod followed by a filter with a primary and outer membrane.

Figure 2 is a drawing, according to the preceding figure, which shows the any one rod and filter assembly.

Figure 3 is a drawing which shows a sectional view of the primary membrane wherein the holes or perforations made therein can be observed.

Figure 4 is a drawing which shows a sectional view of any one rod followed by a filter with the primary, intermediate and outer membrane.

Figure 5 is a drawing, according to the preceding figure, which shows the any one rod and filter assembly.

Detailed description of the embodiments

[0034] Smoking experiments were conducted using 3R4F tobacco from the University of Kentucky. The preparation and smoking conditions described in the ISO 3308 standard were used. To prepare the cigarettes, the tobacco was removed from the 3R4F cigarettes. The same 3R4F tubes were always used, wherein the described filters were incorporated, either the filters themselves (extracted and re-incorporated) or the filters including the corresponding membranes (M1, M2, M3). A smoking machine known in this industry sector was used. The composition of the gases obtained was analysed, in addition to the composition of the matter condensed on Cambridge filters disposed adjacent to the studied filters, representing the tars that the smoker would inhale.

[0035] 15 cigarettes are smoked following the specifications of the ISO 3308 standard (2-second puffs, aspired volume of 35 ml, puff frequency of 60 seconds, loss of puff pressure of less than 300 Pa and smoking up to 4 mm of the filter).

[0036] The cigarettes are conditioned at room temperature and with a relative humidity of 60 %, placing them in a desiccator with a saturated sodium nitrite solution for at least 48 hours before being smoked.

[0037] During the smoking process, the smoke, including CO, CO2 and other non-condensable products, penetrates the cigarette filter and a trap (fibreglass Cambridge filter), wherein the condensable products that would be inhaled by the smoker are collected. The non-condensable products are collected in a Tedlar gas sampling bag, located behind the Cambridge filter, which is reserved for subsequent analysis by gas chromatography (GC).

[0038] The condensable products retained in the trap behind the filter are extracted with 2-propanol, making sure that all the compounds retained in the trap are recovered. Next, the extract is dried with sodium sulfate and reserved for subsequent analysis by GC.

[0039] The determination of the CO and CO2 content in the non-condensable fraction is carried out by GC, using a thermal conductivity detector (GC-TCD) and a concentric rod (CTRI), in a SHIMADZU GC-14A unit, calibrated using external patterns. The quantification was performed by calculating the response factor (grams of compound/peak area) of these compounds by injecting different volumes (between 0.5 and 2.5 ml) of the corresponding pattern (carbon monoxide, carbon dioxide, hydrogen, methane and oxygen). The analysis conditions are:

Carrier gas: He

Injector temperature: 28 °C

Detector temperature: 110 °C

Injected volume: 2.5 ml

Constant rod flow: 40 ml/min

Oven temperature program: isothermal at 110 °C

Analysis time: 20 min

The other non-condensable components are analysed by GC using a flame ionisation detector (GC-FID), using a GasPro rod and under the following conditions:

Injector temperature: 150 °C

Detector temperature: 210 °C

Carrier gas: Helium

Injected sample volume: 150 µl

Constant rod flow: 2 ml/min Oven temperature program:

Initial rod temperature 35 °C for 10 min

Heating up to 100 °C with a ramp of 5 °C/min

Heating up to 200 °C with a ramp of 15 °C/min

Final time: 10 min

The condensable compounds (extracted using 2-propanol from the cigarette filters and smoke traps) are analysed by GC using a mass spectrometry detector (GC-MS), using a HP-5MS rod and under the following conditions:

Injector temperature: 250 °C

Carrier gas: Helium

Injected sample volume: 1 pL

Constant rod flow: 2 ml/min

Oven temperature program:

Initial rod temperature 40 °C for 5 min

Heating up to 320 °C with a ramp of 12 °C/min

Final time: 25 min

[0040] In order to quantify the compounds present in the condensed phase of the tobacco smoke, nicotine patterns with different concentrations (between 5 and 300 ppm) were prepared. They were injected in the unit and the value of the corresponding response factor was obtained from the slope of the straight line obtained from the graphic representation of the amount of compound injected against the peak area. The response factor obtained for the nicotine was used for the other compounds analysed, since the nicotine is the majority compound. The quantification was carried out in the same manner as for the gases, wherein there were patterns for many of the compounds and an average response factor was used in those cases where there was no corresponding response factor. The compounds were identified using the Wiley MS library.

[0041] What follows is a description of some exemplary embodiments resulting from the use of this type of system in smoking experiments.

Embodiment 1

[0042] The first example, as represented in Figures 1, 2 and 3, shows the result of using a primary membrane (M1), consisting of a circle of filter paper with an 8 mm diameter having two perforations or holes (1) with a 0.7 mm diameter. This primary membrane (M1) in contact with the tobacco rod (T) is followed by the outer membrane (M3). Therefore, in this example only membranes 1 and 3 were used, given the small thickness of the primary membrane (M1) used, and the outer membrane (M3) was not modified with respect to the original filter of the 3R4F cigarette.

[0043] Considerable condensation of tars takes place immediately after the holes. The end of the filter, the outer membrane (M3), in contact with the smoker, is considerably less dirty than in the case of not using the primary membrane (M1). Table 1 shows the amount of nicotine, tars and carbon monoxide collected in the gas stream and in the tars condensed on the Cambridge filter, in addition to that of a series of majority compounds in the chromatogram corresponding to the condensed gases and products. It can be observed that a reduction of 60 % in nicotine and tars has taken place. In the case of the CO and other compounds present in the gases, the reduction obtained is much lower.

[0044] Table 1. Reductions (100x(mg of compound i, obtained after smoking a cigarette of 3R4F tobacco, with the 3R4F cigarette filter-mg of compound i, obtained after smoking a cigarette of 3R4F tobacco, with the described filter)/ mg of compound i, obtained after smoking a cigarette of 3R4F tobacco, with the 3R4F cigarette filter) obtained after using the M1 paper membrane, with two holes with a 0.7 mm diameter.

Compound	Reduction %
Tars	65
Nicotine	61
CO	14

In condensed phase
Pyridine, 4-methyl-	59
Pyrazine, methyl-	59
Furfural	60
2-Pentanone, 4-hydroxy-4-methyl-	63
Ethanol, 2-(1-methylethoxy)-	62
2-Furanmethanol	60
Pyridine, 3-methyl-	59
2-Propanone, 1-(acetyloxy)-	58
4-Cyclopentene-1,3-dione	59
Styrene	63
2-Cyclopenten-1-one, 2-methyl-	60
2-Acetylfuran	61
2(5H)-furanone	61
Pyrazine, 2,3-dimethyl-	63
2-Hydroxycyclopent-2-en-1-one	58
Pyridine, 3,5-dimethyl-	63
2,5-Dimethyl-2-cyclopentenone	66
Butanoic acid, 3-methyl-	61
Ethanol, 2-butoxy-	66
Benzaldehyde	66
Furfural, 5-methyl-	60
Pyridine, 3-ethenyl-	60
2(5H)-Furanone, 3-methyl-	61
Phenol	61
2-isopropylfuran	65
2-Cyclopenten-1-one, 2-hydroxy-3-methyl-	61
Limonene	61
2,3-Dimethyl-2-cyclopenten-1 -one	65

Compound	Reduction %
Indeno	62
o-Cresol	64
2-Acetylpyrrole	63
Phenol, 4-methoxy-	61
3-Ethylcyclopent-2-en-1-one	66
p-Cresol	66
2 ethyl thiophene	66
Phenol, 2-methoxy-	63
2-Propanamine	64
Nicotinamide	66
3-Ethyl-2-hydroxy-2-cyclopenten-1-one	61
Benzeneacetonitrile	65
2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one	65
Phenol, 2,4-dimethyl-	67
Phenol, 2,3-dimethyl-	68
Phenol, 4-ethyl-	65
Naphthalene	66
2,3-Dihydro-benzofuran	66
2-furancarboxaldehyde, 5-(hydroxymethyl)-	68
1 H-Inden-1-one, 2,3-dihydro-	63
Hydroquinone	62
1 H-Indole	64
4-vinyl-2-methoxy-phenol	66
1 H-Indole, 3-methyl-	65
Myosmine	65
Phenol, 2-methoxy-4-(2-propenyl)-	68
Nicotyrine	65
Norsolanadione	68
2,3'-Bipyridine	65
1,4-dihydrophenanthrene	65
Diethyl phthalate	68
Mepastigmatrienone	67
2,4 dimethyl-6-(2-furyl)pyridine	68
N-propyl-nornicotine	66
Cotinine	68
5-Tetradecene	65
N(b)-formylnornicotine	68
Neophytadiene	69
Farnesol	65
Hexadecanoic acid, ethyl ester	66
Citric acid, tributyl ester,	67
2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-hexamethyl-	68
Heptacosane	66
Triacontane	68
Octadecane	67
Tocopherol	65
Gases
methane	5
ethane	2
ethylene	5
isoprene	12
benzene	14
toluene	8
crotonaldehyde	9

[0045] The number of puffs is similar in both cases, evidencing that the loss in pressure is of the same order. Furthermore, these cigarettes were tested by voluntary smokers who observed that the smoking characteristics are identical.

Embodiment 2

[0046] Cigarettes using filters of the same type as those described in the first embodiment (M1-2) were smoked, but with one (M1-1) and three (M1-3) holes in the first membrane (M1). The results show that the reductions are progressively greater as the number of holes decreases, but the number of puffs increases considerably, such that with one hole a significant difference with the cigarette without the primary membrane (M1) can be observed. In this case, the voluntary smokers observed greater smoking resistance. Experiments were also carried out wherein the diameter of the holes was varied. It can be observed that the results depend on the free flow area of the holes. Such that similar results can be achieved with two holes with a 1 mm diameter (S=1.57 mm2), as with four with a 0.7 mm diameter (S=1.54 mm2). Based on the foregoing, it can be concluded that these devices are very effective for reducing tars and nicotine in tobacco smoke. An effect easily perceptible to the smoker was achieved, since the end of the filter in contact with their mouth was much cleaner. Additionally, this effect can be easily controlled by the number and diameter of the holes, adjusting the pressure loss so that it does not differ greatly from that of conventional filters.

Table 2. Reductions (%) obtained using M1-1, M1-2 and M1-3 filters

Filter	M1-1	M1-2	M1-3
Tars	75	65	41
Nicotine	74	61	43
CO	13	14	5
number of puffs	12.5	8.7	8.5

Embodiment 3

[0047] Cigarettes were smoked using the primary membrane (M1) with two holes with a 0.7 mm diameter and an outer membrane (M3) 5 mm shorter in length than the conventional one. The results obtained indicate that the primary membrane (M1) is much more effective than the outer membrane (M3), such that the decrease in length of said membrane is barely noticeable, which would imply savings in filter manufacturing costs upon requiring a smaller amount of material for the same filtering effectiveness.

Embodiment 4

[0048] The examples shown up until now correspond to experiments wherein the primary membrane (M1) was prepared using filter paper. In this case, a 2 mm thick EVA foam plate was used, holes with an 8 mm diameter were punched and two holes with a 0.7 mm diameter were made. In this case, the length of the outer membrane (M3) was reduced to 2 mm, to compensate the thickness of M1, such that the length of the filtering system was the same as in conventional cigarettes. The results obtained are practically identical to those obtained using the primary membrane (M1) of the filter paper with the same two 0.7 mm diameter holes. It can be concluded that the material and thickness of the membrane have a smaller effect on their behaviour.

Embodiment 5

[0049] In the embodiments shown up until now, only the primary membrane (M1) and outer membrane (M3) were used. The effect achieved on the CO and gases was very small. For this reason, different experiments have been conducted wherein the intermediate membrane (M2) was used. Said membrane contains an adsorbent material. In our case, SBA-15 (M2S) and activated carbons (M2C) were tested.

[0050] In order to prepare the intermediate membrane (M2), cellulose-acetate fibre from 3R4F cigarette filters, conveniently disaggregated and cut, was physically mixed with the adsorbent material to be assayed. The degree of compaction of this membrane is a parameter which has a significant effect on the behaviour observed. In our case, the three adsorbent materials were firstly analysed and the membranes prepared so that their apparent density was the same as that of the original filter, such that 5 mm of the cellulose acetate filter were eliminated and replaced with the amount of mixture of cellulose-acetate fibre mixed with the adsorbent in a ratio of 1:1 (this ratio is also an important parameter in the design of this type of filter), introducing the same mass as that of the replaced filter. The obtained results are shown in Table 3.

[0051] It can be observed, as represented in Figures 3, 4 and 5, that all of these materials are capable of increasing the observed reduction of tars and nicotine with respect to the use of the primary membrane (M1) and outer membrane (M3), naturally much more than the outer membrane (M3) alone. But even more important is the reduction in CO and other components of the gas stream, over which the primary membrane (M1) had very little effect.

Table 3. Reductions (%) obtained using M2S and M2C filters

Filter	M2S	M2C
Tars	73	75
Nicotine	70	74
CO	36	47

Gases
methane	31	41
ethane	28	32
ethylene	33	25
isoprene	31	40
benzene	22	37
toluene	34	39
crotonaldehyde	44	55

[0052] The compaction of these membranes (or their apparent density) increases their effectiveness, but has the corresponding effect on smoking resistance observed by the smokers who performed the tests. For this reason, this parameter, together with the ratio of adsorbent and fibre, the thickness of this membrane and the preparation method may considerably affect the results.

Embodiment 6

[0053] Lastly, flavours and aromas or nicotine can be very effectively added to any of the two primary (M1) or intermediate (M2) membranes. Specifically, examples were prepared including menthol in both the primary membrane (M1) and intermediate membrane (M2). The results obtained show the same reduction as in the case of not using menthol, but a very intense peak corresponding to menthol was detected in the chromatogram of the condensates. The smokers who tested these cigarettes found them to be completely similar to commercial menthol cigarettes.

[0054] In conclusion, after preparing all the previously indicated embodiments, it should be noted that although these types of studies have been previously carried out in this industry sector for other types of filters, to date such favourable results had never been obtained after analysing the joint use of the primary (M1), intermediate (M2) and outer (M3) type membranes therebetween; neither had the results of these combinations disposing a membrane of the primary (M1) type in said position been analysed; nor had the possibility of using or not using a membrane of the intermediate (M2) type in an intermediate position of the filter, as can be observed in the figures, been studied, wherein Figures 1 and 2 represent the filter with the primary membrane (M1) and outer membrane (M3), and wherein Figures 4 and 5 represent the filter with the primary membrane (M1), intermediate membrane (M2) and outer membrane (M3).

Claims

1. A combined filter for removing tars and toxic compounds from tobacco smoke, which is applied to any type of tobacco rod (T), characterised in that it comprises:

- a primary membrane (M1) located at the end of tobacco rod and which comprises at least one disc of impervious material, is cylindrical and has the same cross-section as the tobacco rod (T) and is perforated by at least one hole (1) which penetrates it in a direction perpendicular to the cross-section of the membrane, such that the perforated surface has a free flow area of 0.2 % to 30 % of the total cross-section of the membrane; and

- an outer membrane (M3) located at the end in contact with the smoker, which is cylindrical and is made up of cellulose-acetate fibre.

2. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 1, characterised in that a cylindrical intermediate membrane (M2) formed by an adsorbent material which comprises solids of silica SBA-15, MCM-41, zeolites or mesoporous activated carbons in the composition thereof is disposed between the primary membrane (M1) and the outer membrane (M3).

3. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 2, characterised in that the intermediate membrane (M2) comprises an impregnation of flavour or aroma.

4. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 1, characterised in that the primary membrane (M1) disposes one to ten holes evenly distributed in a cross-section of the membrane and with a diameter comprised between 0.5 and 1.5 mm.

5. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 1, characterised in that the primary membrane (M1) comprises an impregnation of flavour or aroma.

6. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 1, characterised in that the primary membrane (M1) comprises an adhesive layer to be fixed to the tobacco rod (T).

7. The combined filter for removing tars and toxic compounds from tobacco smoke, according to claim 6, characterised in that the adhesive layer of the primary membrane (M1) is fixed to a conventional filter for preparing a rolled cigarette.

Drawing