WO2011015861A2

WO2011015861A2 - Filter for a smoking article

Info

Publication number: WO2011015861A2
Application number: PCT/GB2010/051277
Authority: WO
Inventors: Mariana Ghosh; Peter Branton; Chuan Liu; Jian Hua Zhu; Ying Wang
Original assignee: British American Tobacco (Investments) Limited
Priority date: 2009-08-04
Filing date: 2010-08-03
Publication date: 2011-02-10
Also published as: GB0913509D0; AR080603A1; WO2011015861A3

Abstract

The invention relates to a filter for a smoking article, said filter comprising an adsorbent of phenol from smoke, said adsorbent comprising a porous solid material bearing an adsorption promoter in its pores and, optionally, on its outer surface; wherein said porous solid material, in the absence of said adsorption promoter, would contain micropores and/or mesopores; and wherein said adsorption promoter is a hydrophilic organic substance and both a hydrogen bond donor and acceptor, and is borne by said porous solid material in an amount sufficient to enhance the adsorption of phenol from smoke by the porous solid material. The invention also relates to a similar filter wherein the adsorbent comprises a particulate inorganic material bearing an adsorption promoter on its outer surface, wherein the adsorption promoter is a polyethylene glycol or end-capped polyethylene glycol.

Description

Filter for a smoking article

Description

The present invention relates to the use of certain treated materials for the removal of phenol from smoke, and smoke filters and smoking articles containing these treated materials.

Smoking articles such as cigarettes can comprise a filter at the mouth end, and a section containing the smokable material e.g. a tobacco rod. The filter is designed to reduce particulates and/ or vapour phase constituents of smoke inhaled during smoking. It is important that this is achieved without removing significant levels of desirable components such as organoleptic components, thereby degrading the quality or taste of the product. Cigarette filters are often composed of cellulose acetate fibres, which mechanically filter aerosol particles. It is also known to incorporate adsorbents into the filters, such as porous carbon materials, silicas or zeolites {e.g. dispersed amongst the cellulose acetate fibres, or in a cavity in the filter) to adsorb certain smoke constituents. Whereas porous carbon materials tend to be rather general adsorbents, zeolites are typically selective adsorbents capable of discriminating between molecules of different sizes with high precision.

For instance, CN 101053446 describes a cigarette filter containing a mesoporous material for adsorbing nitrosamines from smoke. The mesoporous material contains a film of a high viscosity, low volatility liquid such as glycerol on its inner and outer surfaces. The mesoporous material is, for instance, SBA-15 or MCM-41. However, the effect of the materials of CN 101053446 on smoke analytes other than nitrosamines was not examined in this document. The present inventors have found that specific impregnated materials disclosed in CN 101053446, when examined using a valid smoking method described in the Examples herein, show worse or at least no better adsorption of phenol than the corresponding non- impregnated materials. There is therefore room for improvement in the art in the provision of filters for removal of phenol from smoke.

Accordingly, the present inventors have devised the invention defined in the claims.

Figure Ia shows nitrogen adsorption-desorption isotherms for SBA-15 loaded with various amounts of glycerol, whereas Figure Ib shows the calculated pore size distributions from the isotherms of Figure Ia. Figure 2 shows nitrogen adsorption-desorption isotherms for activated carbon loaded with various amounts of glycerol.

Figure 3 shows the phenol adsorption of SBA-15 loaded with various amounts of glycerol, in a phenol adsorption model.

Figure 4 shows the phenol adsorption of activated carbon loaded with various amounts of glycerol, in a phenol adsorption model.

Figure 5a shows the phenol adsorption of SBA-15 loaded with various different impregnants, in a phenol adsorption model, whereas Figure 5b shows the corresponding results for activated carbon.

In the first aspect of the present invention, the filter comprises a porous solid material bearing an adsorption promoter in its pores and, optionally, on its outer surface. The porous solid material, in the absence of the adsorption promoter, contains micropores and/or mesopores, but in an embodiment it contains no macropores. Introduction of the adsorption promoter into the pores will inevitably change the pore structure of the material, but generally the adsorption promoter is used in a relatively low amount as discussed below, such that the pores are incompletely filled and micropores and/or mesopores still remain in the material. Preferably, the porous solid material containing the adsorption promoter has no macropores. The porous solid material may, for instance, be any micro- and/or mesoporous material capable of hydrogen bonding to the adsorption promoter in its pores. It may also bear cations in its pores. In an embodiment, the porous solid material is an inorganic material, preferably a silica, zeolite or zeolite-like material. In an embodiment, the porous solid material is not aluminia, and/or is not carbon, including activated carbon.

Suitable silicas include amorphous silica, SBA-15 and MCM-41. Suitable zeolites include MCM-22 and NaY. Suitable zeolite-like materials include the potassium calcium silicate CAS-I (Ca₄K₄(H₂O)₈Si₁₆O₃₈, C. R, Chimie, 8, 2005, 331-339). Silicas like SBA-15 and MCM-41, and zeolites like MCM-22 possess a long range ordered framework, whose pore size distribution {e.g. the proportion of micropores and mesopores) can be adjusted according to conventional, well-known methods. The porous solid material may be of any suitable form in the filter, such as particulate or a single integral filtration element. Preferably, however, it is particulate. In an embodiment, the particles of the porous solid material have an average particle size in the range 0.01-5 mm, preferably 0.05-4 mm, 0.1-3 mm, 0.15- 2 mm, 0.3-1 mm, or 0.4-0.8 mm.

The adsorption promoter is a hydrophilic organic substance and both a hydrogen bond donor and acceptor. This is advantageous since it allows simultaneous hydrogen bonding to the porous material and to phenol. Substances able to act as hydrogen bond donors and acceptors will be known to the skilled person and include those having one or more (preferably multiple) hydroxyl, thiol, carboxylic acid, amide, primary amine and/or secondary amine groups, preferably one or more hydroxyl groups. Preferably, the adsorption promoter is an alcohol, thiol, carboxylic acid, amide, primary amine and/ or secondary amine, preferably an alcohol, preferably a polyol, preferably a diol or triol. In an embodiment, the adsorption promoter is a compound with 2-5 carbon atoms. The small size of such compounds facilitates their easy access to small pores. - A -

Examples of suitable adsorption promoters include ethylene glycol, propylene glycol, propane-l,3-diol, glycerol, 1,2-butanediol, 1,3 -butane diol, 1,4-butanediol, 2,3-butanediol, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,2,3- pentanetriol, 1,2,4-pentanetriol, 1,2,5-pentanetriol, 1,3,4-pentanetriol, 1,3,5- pentanetriol, and 2,3,4-pentanetriol.

In an embodiment, the adsorption promoter has a boiling point higher than 50 ⁰C, preferably higher than 60, 70, 80, 90, 100, 120, or 150 ⁰C. Preferably, it is a liquid at 15, 20, 30 or 40 ⁰C.

The adsorption promoter advantageously has a low volatility, e.g. a volatility of 2 mmHg or less at 50 ⁰C, preferably 1, 0.5, 0.1, 0.05 or 0.01 mmHg or less at 50 ⁰C. Its hydrophilicity is preferably manifested in its solubility in water and/ or miscibility with water and/ or ethanol.

The adsorption promoter is used in an amount sufficient to enhance the adsorption of phenol from smoke by the porous solid material. The precise amount will vary depending upon the specific combination of adsorption promoter and porous solid material used, but can be determined without undue burden by the skilled person with reference to the information herein. In an embodiment, the porous solid material bears the adsorption promoter in an amount of up to 5 % by weight of the total weight of the porous solid material and adsorption promoter, preferably in the range of 0.01-4, 0.05-3, 0.1-3.5, 0.2-3, 0.3-2.5, 0.4-2, 0.5-1.5 or 0.8-1.2 % by weight.

Typically, the porous solid material is impregnated with the adsorption promoter, which can be achieved by conventional techniques. For instance, the adsorption promoter may be comprised in a fluid in which the porous material is washed or soaked. Alternatively, the porous material can be sprayed with the adsorption promoter. Simple admixture may also be suitable, for instance admixture of the adsorption promoter (at a temperature at which it is a liquid) with the porous material, allowing the liquid to seep into the pores. Such methods may additionally result in some adsorption promoter on the surface of the porous material; however, this should not be in a sufficient amount to block access of phenol to the pores.

In the second aspect of the invention, the filter comprises an adsorbent comprising a particulate inorganic material, which may not necessarily be porous but, in an embodiment, is porous. The adsorption promoter resides on the outer surface of the particulate material. When the particulate material is porous, in some embodiments the adsorption promoter may additionally be able to enter the pores, whereas in other embodiments the adsorption promoter may be too large to enter the pores to any great extent.

The adsorption promoter in this aspect of the invention is a polyethylene glycol or end-capped polyethylene glycol. Such substances are hydrophilic organic substances able to form at least three hydrogen bonds; they may not necessarily be hydrogen bond donors, but can still bond sufficiently strongly both to the particulate material and to phenol through multiple hydrogen bond acceptor groups.

By "end-capped" is meant that the adsorption promoter is of the formula HO-CH₂- (CH₂-O-CH₂)_n-CH₂-OH wherein one or both terminal -OH groups are converted to another group. In an embodiment, one or both terminal -OH groups are converted to alkoxy and/or ester groups. Preferably, the adsorption promoter is of the formula R^O-CH₂-(CH₂-O-CHa)_n-CH₂-O-R² wherein R¹ and R² are independently H, alkyl, or -C(O)alkyl, and the average n is 1-20, preferably 2-10, 3-8 or 4-5.

Preferably, the alkyl groups in R¹ and R² are C_1-5 alkyl groups, preferably C_1-3 alkyl groups, preferably methyl or ethyl.

Most preferred as the adsorption promoter is polyethylene glycol, e.g. PEG 200, PEG 300, or PEG 400. The particulate inorganic material may, for instance, be any material capable of hydrogen bonding to the adsorption promoter on its surface. It may be the porous solid material described in connection with the first aspect of the invention. In an embodiment, however, the particulate inorganic material may additionally be a porous carbon (especially activated carbon) or alumina material.

In an embodiment, the particles of the particulate inorganic material have an average particle size in the range 0.01-5 mm, preferably 0.05-4 mm, 0.1-3 mm, 0.15-2 mm, 0.3-1 mm, or 0.4-0.8 mm.

The particulate inorganic material bears the adsorption promoter in an amount sufficient to enhance the adsorption of phenol from smoke by the particulate material. As in the first aspect of the invention, the precise amount will vary depending upon the specific combination of adsorption promoter and porous particulate inorganic material used, but can be determined without undue burden by the skilled person with reference to the information herein. In an embodiment, the particulate inorganic material bears the adsorption promoter in an amount of up to 5 % by weight of the total weight of the particulate inorganic material and adsorption promoter, preferably in the range of 0.01-4, 0.05-3, 0.1-3.5, 0.2-3, 0.3- 2.5, 0.4-2, 0.5-1.5 or 0.8-1.2 % by weight.

The adsorption promoter may be loaded onto the particulate inorganic material by the same means as in the first aspect of the invention, i.e. by washing, soaking, spraying etc..

In the first and second aspects of the invention, the filter may be of any suitable construction, for instance a filter tip for incorporation into a smoking article, and the adsorbent can be incorporated into the filter by conventional means. For example, the filter may contain the adsorbent distributed evenly throughout fibrous filter material, such as cellulose acetate.

Another option is to make the filter in the form of a "cavity" filter comprising multiple sections, the adsorbent being confined to one cavity. For instance, the cavity containing the adsorbent may lie between two sections of fibrous filter material. Alternatively, the adsorbent may be located on a plug wrap of the filter, preferably on the radially inner surface thereof. This may be achieved in a conventional manner (c.f. GB 2,260,477, GB 2,261,152 and WO 2007/104908), for instance by applying a patch of adhesive to the plug wrap and sprinkling the adsorbent over this adhesive.

A further option is to provide the adsorbent in a form adhered to a thread (e.g. cotton thread) passing longitudinally through the filter, in a known manner. Other possibilities will be well known to the skilled person.

The third aspect of the invention relates to a smoking article comprising a filter of the invention. The filter can be incorporated into the smoking article by

conventional means. As used herein, the term "smoking article" includes smokable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, reconstituted tobacco or tobacco substitutes. The term also includes so-called "heat-not-burn" products, which produce smoke or a smoke-like aerosol. Preferably, the smoking article is a cigarette. The invention will now be illustrated by way of the following examples.

Example 1— Impregnation of SBA-15 with glycerol and effect on pore structure Powdered SBA-15 was obtained from Fudan University, Shanghai, China. 0.01 g glycerol was dissolved in 6 g ethanol, then 0.99 g of the SBA-15 was added. The mixture was stirred vigorously and then kept at a temperature of 313 K (40 ⁰C) to evaporate the ethanol, until the product was dried. The resulting sample contained 1 % w/w glycerol and was designated 1 gly/SBA-15.

Further samples of the SBA-15 with loading amounts of glycerol of 3 %, 5 %, 7 %, 10 % and 15 % w/w were prepared and designated in the same manner.

The samples were evacuated at 323 K (50 ⁰C) for 2 hours, and nitrogen adsorption- desorption isotherms were obtained at 77 K using a Micromeritics ASAP 2000 volumetric adsorption analyser. These are illustrated in Figure Ia, whereas the pore size distributions (calculated by BJH analysis of the adsorption isotherm) are illustrated in Figure Ib. Further details of the properties are given in the Table below.

⁺ Calculated using adsorption data at a relative pressure (P/P_o) range of 0.05-0.22 ^ Calculated by the /-plot method, according to statistical film thickness (/) in the range of 0.35-0.50 nm

* Calculated according to the amount of N₂ adsorbed at a P/P_o of about 0.99 # Average BJH value of the pore diameter

All of the nitrogen adsorption-desorption isotherms were of Type IV and exhibited an Hl hysteresis loop that was typical of mesoporous solids. The sharpness of these steps did not change with increasing glycerol content, indicating that the uniformity of the mesopore size distribution had been maintained after loading with glycerol. As will be understood from the Table above, the BET surface area and total pore volume decreased with increasing glycerol loading; the micropores were filled first due to the favourable surface curvature and tensility. By 3 % glycerol, no more micropores were left. Since the smaller pores are filled preferentially, the average pore size (D_B,_H) increased with increasing glycerol loading.

Comparative Example 1— Impregnation of carbon with glycerol and effect on pore structure A granular activated coconut carbon, EcoSorb® CX, was obtained from Jacobi Carbons. 1 %, 3 %, 5 % and 10 % w/w glycerol-containing samples of this material were produced in the same manner as in Example 1 and were designated 1 gly/AC, 3 gly/AC, 5 gly/AC and 10 gly/AC.

Nitrogen adsorption-desorption isotherms were obtained for the basic activated carbon material and the glycerol-impregnated samples, which are illustrated in Figure 2. Further details of the properties are given in the Table below.

* Calculated using adsorption data at a relative pressure (P/P_o) range of 0.05-0.22 ^ Calculated by the /-plot method, according to statistical film thickness (/) in the range of 0.35-0.50 nm

* Calculated according to the amount of N₂ adsorbed at a P/P_o of about 0.99

^* Average BJH value of the pore diameter

The surface area and total pore volume both declined rapidly with increasing addition of glycerol, suggesting that the glycerol preferentially occupies the micropores in the activated carbon as well as in SBA-15. However, whilst SBA-15 has a low percentage of its pore volume in micropores and the micropores are quickly eliminated upon addition of glycerol, the activated carbon has a high percentage of its pore volume in micropores initially and even 10 % w/w glycerol is not sufficient to fill all the micropores. Since micropores have a higher surface area to volume ratio than mesopores, the BET surface area saw a more dramatic drop with glycerol loading than for SBA-15, for the same drop in total pore volume.

Example 2 - Phenol adsorption model A stainless steel micro-reactor 3 mm in diameter and 150 mm in length was insetted deeply into the injector port of a Varian® 3380 gas chromatograph, and connected to a dimethylpolysiloxane separation column (SE-30, Agilent®). A particle size fraction of 1-2 mm (20-40 mesh) of the 1 gly/SBA-15 from Example 1 was sieved out, and 5 mg of this material was filled into the reactor and sealed with glass wool. The sample was directly heated to 353 K (80 ⁰C) by nitrogen with a flow rate of 20 ml/min. A 0.05 M solution of phenol in dichloromethane was pulse injected, 4 μl at a time, and the gaseous effluent was analysed by the Flame Ionization Detector of the GC to determine the decrease in ratio of phenol to dichloromethane, and thereby the amount of phenol adsorbed by the sample. This was repeated for the 10-gly/SBA-15, and for the non-impregnated SBA-15.

The amount of phenol adsorbed by each sample, versus the total amount of phenol supplied to the sample, is illustrated graphically in Figure 3.

As will be seen from this Figure, the sample containing 1 % glycerol showed higher adsorption capacity for phenol than the corresponding non-impregnated SBA-15. This sample became saturated with phenol by the time 0.8 mmol phenol /g sample had been added. As the glycerol loading was increased to 10 %, the adsorption capacity declined.

Comparative Example 2

Phenol adsorption was measured for the activated carbon samples obtained in Comparative Example 1, using the same technique described in Example 2 save for the use of 3 mg of the sample and pulse injection of 6 μl of the phenol solution at a time. Since the adsorptive ability of activated carbon is much higher than that of SBA-15, this experimental difference was necessary in order to reach the adsorptive equilibrium within a reasonable time. The results are shown in Figure 4. The activated carbon of Comparative Example 1 shows a higher absolute capacity to adsorb phenol than SBA-15. However, it will be seen from Figure 4 that glycerol impregnation did not improve the adsorptive capacity of any of the activated carbon samples. Performance deteriorated with increasing glycerol content. Example 3— Performance iα a cigarette filtet

Twenty cigarettes of standard construction were provided (56 mm tobacco rod, 24.6 mm circumference, modified Virginia blend, 27 mm filter), each filter having a cavity bounded on both sides by a cellulose acetate section. 60 mg of 1 gly/SBA-15 (20-40 mesh) was weighed into the filter cavity of each cigarette. The cigarettes were aged at 22 ⁰C and 60 % relative humidity for approximately 3 weeks prior to smoking. They were then smoked on an RM20 smoking machine under ISO conditions, i.e. a 35 ml puff of 2 s duration was taken every minute, onto a

Cambridge filter pad. The mainstream smoke was collected by a Tedlar® bag through a Teflon® tube (SKC Inc., USA). An Agilent® HP 6890 GC interfaced with a HP 5972 Mass Selective Detector Quadrupole Mass Spectrometer was used to analyze and determine the compounds in the vapour phase; peak assignments in the GC-MS chromatograms were made using the online Wiley Registry of Mass Spectral Data, 6^th Edition, F. W. McLafferty.

The same was done for 3 gly/SBA-15 and non-impregnated SBA-15.

Corresponding cigarettes with empty filter cavities were used as a control. The smoke yields are set out in the Table below.

As seen from the Table, the 1 gly/SBA-15 affords significantly greater removal of phenol from mainstream smoke than is achieved with no additive, untreated SBA- 15, or 3 gly/SBA-15. This correlates well with the results of the phenol adsorption model in Example 2.

Comparative Example 3

Performance of the AC, 1 gly/AC and 3 gly/AC of Comparative Example 1 was tested in a cigarette filter in the same manner as in Example 3. Results are shown below.

These results confirm that addition of glycerol to the activated carbon does not result in improvements in adsorption of phenol when used in a cigarette filter, as predicted by the phenol adsorption model.

Example 4 - Impregnation of different materials with glycerol

The following materials were obtained:

Amorphous silica gel ("silica" hereafter), particle size 20-40 mesh, CP purity - obtained from Qingdao Ocean Chemical Factory, Qingdao, China

γ-Al₂O₃— obtained from Nanjing Inorganic Chemical Factory

NaY— obtained from Nanjing Inorganic Chemical Factory

MCM-22— obtained from the Chinese Petroleum University

CAS-I— obtained from the Taiyuan University of Technology

MCM-41 - following the procedure of/. Pbys. Chem. B., 2000, 104, 7885-7894: 1.49 g cetyltrimethylammonium bromide (CTAB) was dissolved in 8.17 g of 36 % HCl and 51.8 g H₂O to form a clear solution, and 4.25 g tetraethylorthosilicate (TEOS) was added at 303 K. After stirring for 48 hours, the suspension was filtered and air-dried. The resulting solid was calcined at 823 K for 6 hours to remove the template.

These materials had the properties set out below. They were impregnated with 1 % w/w glycerol according to the process of Example 1 and the phenol adsorption was tested according to the process of Example 2 or Comparative Example 2. The results are shown below alongside the results obtained above for the corresponding SBA-15 and AC materials.

^a the average pore size

the pore size is too small to be measured using common methods

It will be seen that impregnation with 1 % w/w glycerol enhances phenol adsorption for all the materials tested except for AC and γ-Al₂O₃.

Example 5— Effect of different impregnants

Example 4 was repeated using tiϊacetin in place of glycerol, for all samples except amorphous silica and CAS-I, using the 3 mg sample/ 6 μl injection method.

Performance declined in all cases. Example 4 was also repeated for SBA-15 and AC using various different impregnants in place of glycerol and the 3 mg sample/6 μl injection method, affording the results shown below and in Figures 5a and 5b, presented alongside the results for glycerol and triacetin for these materials.

Example 6— Effect of polyethylene glycol

Example 4 was repeated using polyethylene glycol 200 in place of glycerol, using the

3 mg sample/6 μl injection method, affording the results shown below.

Without wishing to be limited by theory, it is thought that the PEG 200 may not enter the pores of the materials, and so may not fairly be described as an "impregnant". As will be seen from the results above, PEG 200 improves the adsorption of both the SBA-15 and activated carbon samples.

Claims

1. A filter for a smoking article, said filter comprising an adsorbent of phenol from smoke, said adsorbent comprising a porous solid material bearing an

adsorption promoter in its pores and, optionally, on its outer surface;

wherein said porous solid material, in the absence of said adsorption promoter, would contain micropores and/or mesopores; and wherein said

adsorption promoter is a hydrophilic organic substance and both a hydrogen bond donor and acceptor, and is borne by said porous solid material in an amount sufficient to enhance the adsorption of phenol from smoke by the porous solid material.

2. A filter as claimed in claim 1, wherein said porous solid material, in the absence of said adsorption promoter, would contain no macropores.

3. A filter as claimed in claim 1 or 2, wherein said porous solid material is an inorganic material, preferably a silica, zeolite or CAS-I.

4. A filter as claimed in any of the preceding claims, wherein said adsorption promoter bears one or more hydroxyl, thiol, carboxylic acid, amide, primary amine and/or secondary amine groups, preferably one or more hydroxyl groups.

5. A filter as claimed in claim 4, wherein said adsorption promoter is a compound with 2-5 carbon atoms and/or an alcohol, thiol, carboxylic acid, amide, primary amine and/or secondary amine, preferably an alcohol, preferably a polyol, preferably a diol or triol.

6. A filter as claimed in any of the preceding claims, wherein said adsorption promoter: a) has a boiling point higher than 50 ⁰C, preferably higher than 60, 70, 80, 90, 100, 120, or 150 ⁰C; and optionally b) is a liquid at 15 ⁰C.

7. A filter as claimed in any of the preceding claims, wherein said porous solid material bears said adsorption promoter in an amount of up to 5 % by weight of the total weight of the porous solid material and adsorption promoter, preferably 0.01- 4, 0.05-3, 0.1-3.5, 0.2-3, 0.3-2.5, 0.4-2, 0.5-1.5 or 0.8-1.2 % by weight.

8. A filter for a smoking article, said filter comprising an adsorbent of phenol from smoke, said adsorbent comprising a particulate inorganic material bearing an adsorption promoter on its outer surface;

wherein said adsorption promoter is a polyethylene glycol or end-capped polyethylene glycol, and is borne by said particulate inorganic material in an amount sufficient to enhance the adsorption of phenol from smoke by the particulate inorganic material.

9. A filter as claimed in claim 8, wherein said particulate inorganic material is a porous solid material, which preferably: a) is a carbon, alumina, silica, zeolite or CAS-I; and/or b) contains micropores and/or mesopores.

10. A filter as claimed in claim 9, wherein said adsorption promoter is of the formula R¹-O-CH₂-(CH₂-O-CH₂)_n-CH₂-O-R² wherein R¹ and R² are independently H, alkyl, or -C(O)alkyl, and the average n is 1-20, preferably 2-10, 3-8 or 4-5.

11. A filter as claimed in any of claims 8 to 10, wherein said particulate inorganic material bears said adsorption promoter in an amount of up to 5 % by weight of the total weight of the particulate inorganic material and adsorption promoter, preferably 0.01-4, 0.05-3, 0.1-3.5, 0.2-3, 0.3-2.5, 0.4-2, 0.5-1.5 or 0.8-1.2 % by weight.

12. A smoking article comprising a filter as claimed in any of the preceding claims.

13. Use of an adsorbent as defined in any of claims 1 to 11 for the filtration of smoke.