Smoke filters comprising porous carbon materials and smoking articles incorporating such filters

ES 2 379 639 T3

DESCRIPTION

Smoke filters comprising porous carbon materials and smoker's articles incorporating such filters

This invention relates to porous carbon materials and smoking articles and smoke filters therefor incorporating such materials.

It is well known to incorporate porous carbon materials into smoking articles and smoke filters therefor in order to reduce the level of certain harmful materials in the smoke. Porous carbon materials can be produced in many different ways. The physical properties of porous carbon materials, including particle size and shape, particle size distribution in a sample, particle wear rate, pore size, pore size distribution and the surface area, all of them vary widely according to the way in which they have been produced. These variations greatly affect the performance or suitability of the material as an adsorbent in different environments.

Generally, the larger the surface area of ​​a porous material, the more efficient it is at adsorption. The surface areas of porous materials are estimated by measuring the variation in the volume of nitrogen adsorbed by the material with a partial pressure of nitrogen at a constant temperature. The analysis of the results by mathematical models originated by Brunauer, Emmett and Teller results in a value known as the BET surface area.

Carbon materials can be treated in order to increase their surface areas by a procedure known as activation. Activation can be effected, for example, by heating carbon that has been treated with phosphoric acid or zinc chloride, or by heating carbon with steam or carbon dioxide. Activation by carbon dioxide is sometimes followed by an air modification step, which involves heating the carbon in air. The activation procedure removes material from the inner surface of the carbon particles, resulting in a reduction in weight, the weight loss being proportional to the treatment period.

The distribution of pore sizes in a porous carbon material also affects its adsorption characteristics. In the present patent specification, and in accordance with the nomenclature used by those skilled in the art, the pores in an adsorbent material are called "micropores" if their pore size is less than 2 nm (<2 x 10^-9 m) in diameter, and "mesopores" if their pore size is in the range 2-50 nm. Pores are called "macropores" if their pore size exceeds 50 nm. Pores having diameters greater than 500 nm usually do not contribute significantly to the adsorbance of porous materials. For practical purposes, therefore, pores having diameters in the range of 50 nm to 500 nm, more typically 50-300 nm or 50-200 nm, can be classified as macropores.

The relative volumes of micropores, mesopores and macropores in a porous material can be estimated using well known nitrogen adsorption and mercury porosimetry techniques. Mercury porosimetry can be used to estimate the volume of macro- and mesopores; Nitrogen adsorption can be used to estimate the volumes of micro- and mesopores, using the so-called BJH mathematical model. However, since the theoretical bases for the estimates are different, the values ​​obtained by the two methods cannot be directly compared with each other.

Porous carbon can be produced from natural sources. For example, coconut charcoal is obtained by charring coconut bark; Furnace black is obtained by pyrolysis or combustion of petroleum residues, and thermal black is produced from natural gas. United States and Great Britain Patent Specifications Nos. US-3909449, US-4045368 and GB-1383085 all describe processes for producing activated charcoal spheres from pitch.

Porous carbon materials can also be obtained by carbonizing organic resins. For example, international patent publication WO 02/12380 describes a process for producing porous carbon by carbonizing an organic resin that has been produced by condensing a nucleophilic component such as a novolak resin with an electrophilic crosslinking agent such as hexamethylenetetramine in the presence of a former. pore such as ethylene glycol.

International patent publication WO 01/19904 describes a process for producing monolithic porous carbon by carbonizing an organic resin produced by polymerization of a system such as resorcinol / formaldehyde, divinylbenzene / styrene and vinylidene chloride or vinylidene chloride / divinylbenzene, in the presence of a surfactant.

Porous carbon materials can also be produced by agglomerating fine carbon particles with binders. For example, US Patent Specification No. 3351071 describes a process for producing spherical carbon particles by mixing an aggregate of cellulose crystallite and activated carbon with water in a mill, spherical processing and drying. The carbon particles can then be activated and used in cigarette filters.

US Patent Specification No. 4029600 describes a process for producing a material of

ES 2 379 639 T3 particulate carbon by mixing spheres of carbon black with a resinous binder, and then charring and pulverizing the mixture.

British Patent Specification GB-2395650 compares the effect of various carbon materials having various volumes of micropores and mesopores on the taste of tobacco smoke containing flavorings such as menthol. It is stated that carbon materials with a volume of micropores no greater than 0.3 cm²/ g and a mesopore volume of at least 0.25 cm³ per gram they adsorb less menthol than materials with different pore size distributions, and are therefore considered to be more suitable for use in a cigarette filter in flavored cigarettes.

International patent publication No. WO / 03/059096 A1 describes cigarettes comprising a tobacco rod and a filter component having a carbon-filled cavity in the form of small spherical balls with diameters from 0.2 to 0, 7 mm, BET surface areas in the range 1000-1600 m²/ g, and a pore size distribution predominantly in the range of micropores and small mesopores.

US Patent Specification No. 6,814,786 describes a filter comprising at least two monolithic activated carbon adsorbent segments.

In accordance with this invention, the inventors have identified a class of porous carbon materials that are particularly effective in reducing one or more harmful components of tobacco smoke.

The materials of the present invention are characterized by a combination of physical properties.

According to one aspect of the present invention, there is provided a smoke filter for a smoking article comprising a porous carbon material having a BET surface area of ​​at least 800 µm.²/ g, a density of not more than 0.5 g / cm³, a pore structure that includes mesopores and micropores, and a pore volume (measured by nitrogen adsorption) of at least 0.9 cm³/ g.

The porous carbon materials of the invention preferably have a bulk density of less than 0.5 g / cm³. Typical upper values ​​for the density range of the carbon materials of the present invention are 0.45 g / cm³, 0.40 g / cm³ and 0.35 g / cm³. Preferably, the bulk density of the carbon materials of the invention is in the range 0.5 to 0.2 g / cm³.

The carbon materials of the invention can also be characterized by their pore structure rather than their density.

According to this aspect of the invention, there is provided a smoke filter for a smoking article comprising a porous carbon material having a BET surface area of ​​at least 800 µm.²/ g, a pore structure including mesopores and micropores, and a pore volume (measured by nitrogen adsorption) of at least 0.9 cm³/ g, of which between 15 and 65% is in micropores.

The preferred porous carbon materials of the invention can also be characterized by a pore structure in which the pore volume (measured by nitrogen adsorption) is at least 1.0 cm³/ g, but less than 20% of the pore volume is in pores between 2-10 nm. Usually less than 15%, and often less than 10% of the combined pore volume is in pores between 2-10 nm.

The density and pore structure of the porous carbon material are closely related. In general, the inventors have found that in the carbon material samples of the invention, the higher the combined volume of micro-, meso- and macropores, the lower the density, because the pores increase the volume of a given mass of material without increasing its weight. furthermore, as the density decreases, so the ratio of macro- and mesopores to micropores increases. That is, in general, the lower the density of the carbon material of the invention, the higher the ratio of the pore volume in mesopores and macropores compared to the pore volume in micropores. However, the correlation between density and pore volume, determined by nitrogen adsorption, is not accurate. Therefore, some carbon materials of the invention that have the pore structure defined in either of the two preceding paragraphs may have densities greater than 0.5 g / cm³, for example densities up to 0.52, 0.55, 0.60 or 0.65 g / cm³. Conversely, some carbon materials of the invention may have densities less than 0.5 g / cm³ and a pore structure in which less than 15% (eg, 12%, 10%, or 5%) of the combined volume of mesopores and micropores is in mesopores.

The lack of a complete correlation between density and structure of micro- and mesopores arises because the nitrogen adsorption technique used to estimate the pore size distribution is not capable of detecting pore sizes greater than about 50 nm. The total pore volume of a material estimated by nitrogen adsorption techniques therefore corresponds to the combined pore volumes of micropores and mesopores. The macropore volume of a material is not revealed by this technique. Thus, where the carbon materials of the invention have a low density and a relatively low proportion of mesopores, detected by nitrogen adsorption, the low density is attributable to a relatively high pore volume in the macropore range immediately adjacent to the range. of mesopores, that is, in the range of 50 nm to 500 nm. Even if

ES 2 379 639 T3 pore volumes in the macropore range can be estimated by mercury porosimetry, the results obtained using this technique do not agree with those obtained using nitrogen adsorption. Therefore, it is difficult to accurately estimate the pore volume of a material over the entire pore size range between 2-500 nm.

The invention also includes a smoking article comprising a smoking material and a porous carbon material according to the invention.

The BET surface area of ​​the preferred porous carbon materials of the invention is at least 800 µm²/ g, preferably at least 900 μm²/ g and desirably at least 1000 m²/ g. Typical values ​​for the BET surface area of ​​the carbon materials of the invention are approximately 1000, 1100, 1150, 1200, 1250 and 1300 µm.²/ g. Porous carbon materials with BET surface areas up to 1250 m²/ g, eg 1000-1250 m²/ g, are the most preferred.

The porous carbon materials of the invention preferably have a pore volume (estimated by nitrogen adsorption) of at least 0.95 g / cm³, and desirably at least 1 g / cm³. Carbon materials with pore volumes of at least 1.1 cm³/ g are particularly useful as adsorbents for tobacco smoke. Typical values ​​for the pore volumes of the carbon materials of the invention are 1.15 cm³/ g, 1.2 cm³/ g, 1.25 cm³/ g and 1.3 cm³/ g. Usually the combined pore volume will be in the range 1.1 to 2.0 cm³/ g. Carbon materials according to the invention with pore volumes significantly higher than 2.1 cm³/ g, for example 2.2 or 2.3 cm³/ g, are low in density and are therefore less easy to handle in cigarette production equipment. Such carbon materials are less favorable for use in cigarettes or smoke filters for that reason.

In the preferred carbon materials of the present invention, at least 30%, but desirably not more than 65% of the pore volume (estimated by nitrogen adsorption) is in mesopores. Typical minimum values ​​for mesopore volume as a percentage of the combined mesopore and micropore volumes of the carbon materials of the invention are 35%, 40%, or 45%. Typical maximum values ​​for such volumes are 65%, 60%, and 55%. Preferably, the mesopore volume of the carbon materials of the invention is in the range 35-55% of the combined mesopore and micropore volume.

The porous carbon materials of the invention can be obtained from any source. However, the porous carbon materials of the invention that are formed from charred organic resin are preferred over porous carbon materials obtained from other sources, eg coconut charcoal. Examples of suitable resins include hydroxyl substituted aromatic resins, such as those derived from phenol, bis-phenol A, aminophenols, or resorcinol, and non-phenolic resins such as those derived from styrene and vinylpyrrolidone or from styrene and divinylbenzene. Hydroxyl substituted aromatic resins are preferred, especially those derived from phenols.

The preferred carbon materials of the invention are obtained by condensing a nucleophilic component with an electrophilic crosslinking agent in the presence of a pore former, as described in international patent application WO-A-02/12380.

A process for producing a porous carbon material comprises the steps of condensing a nucleophilic component with an electrophilic crosslinking agent in the presence of a pore former to form a resin, charring the resin, and activating the resulting carbon material.

The reaction to form the resin can be carried out in the presence of a catalyst. A solvent can also be used, but preferably the pore former also acts as a solvent. The nucleophilic component can be, for example, a phenolic resin, such as a novolac resin, or another resin based on copolymers of phenolic compounds, such as m-amino-phenol, diphenols such as resorcinol, hydroquinone, or amines such as aniline, melamine or urea with aldehydes such as formaldehyde, furfural or salicylic aldehyde. The crosslinking agent can be, for example, formaldehyde, furfural or hexamethylenetetramine. The pore former can be, for example, a diol, a diol ether, a cyclic ester, a substituted linear or cyclic amide or an amino alcohol. Ethylene glycol and diethylene glycol are preferred. Details of suitable materials are described in International Patent Publication No. WO 02/12380 A2. Preferred resins for use in the production of the porous carbon materials of the invention are novolak resins crosslinked with hexamethylenetetramine in the presence of ethylene glycol.

The pore former is preferably used in amounts sufficient to dissolve the components of the resin system. The weight ratio of the pore former to the resin system components is preferably at least 1: 1. The crosslinking agent is normally used in an amount of 5 to 40 parts by weight per 100 parts by weight of the nucleophilic components, typically 10 to 30 (eg, 10, 15 or 20) parts by weight of the crosslinking agent. crosslinking per 100 parts by weight of nucleophilic component.

Preferred resins have weight average molecular weights (Mw) in the range of 300 to 3000 prior to crosslinking. Where novolac resins are used, resins with Mw values ​​at the lower end of this scale are viscous liquids, and at the upper end of the scale they are solids with melting points in the region of 100 ° C. Mw novolac resins less than 2000 and preferably less than 1500 form resins which, with the

ES 2 379 639 T3 carbonization, tend to produce carbons with desired pore size distributions using lower amounts of pore former.

As described in the international patent application WO 02/12380 A2, the reaction conditions for the resin can be controlled such that the resulting material is in the form of small balls with a desired range of particle size. Small balls can be formed by pouring a prepolymeric solution of the electrophilic component, nucleophilic crosslinking agent, and pore former into a hot, liquid suspension medium in which the mixture is immiscible, such as mineral oil, with stirring, e.g. eg, by stirring, to form a suspension of resin globules, and allowing the resin to solidify into small balls. The average particle size of the small balls will depend on the stirring procedure and its intensity, the temperature and viscosity of the suspending medium, the temperature and viscosity of the prepolymer solution, and the volume ratio of the prepolymer solution and the suspending medium. The precise conditions necessary to achieve a desired particle size can easily be established by routine experiments. The small balls are then separated from the suspending medium, washed thoroughly or dried under vacuum, and then heated to cause charring.

The pore size distribution of the activated carbon material is affected by several factors, including the nature of the electrophilic component and the crosslinking agents used, the presence of a catalyst, the presence of a solvent, and the rate of reaction. Higher temperatures and the presence of a catalyst tend to promote higher porosities in the carbon material. Heat transfer in the reaction system also influences porosity. Sudden or rapid changes in temperature tend to reduce the formation of micropores and promote the formation of mesopores. Removal of the carbon material from the pore former at low temperatures prior to carbonization, eg, by washing or vacuum drying, also affects the pore size distribution. Carbon materials that have been treated to remove the pore former prior to carbonization have higher mesopore volumes than similar materials in which the pore former is removed during carbonization.

Carbonization of the resin is preferably effected by heating it in an inert atmosphere to a temperature of 600-850 ° C or more. The resulting carbon material can then be activated, for example, by treatment in air at 400-450 ° C, in steam at 750 ° C or more, or carbon dioxide at 800 ° C or more.

The inventors have found that a particular class of porous carbon materials is particularly effective in adsorbing hydrogen cyanide from the vapor phase of tobacco smoke. These materials are formed by carbonizing a nitrogen-containing organic resin, for example an organic resin formed by condensing a nucleophilic component with a nitrogen-containing crosslinking agent, such as hexamethylene tetramine or melamine, or produced from nucleophilic precursors such as aminophenols.

Without wishing to be bound by theory, it is considered that when the nitrogen-containing organic resin is carbonized, the resulting porous carbon material will contain residual nitrogen or nitrogen sites, with which HCN is believed to interact particularly strongly. .

The porous carbon material can be a monolithic structure, adapted for use in a filter for a smoking article. For example, the material can be formed into a cylindrical filter element with an axial passage that allows the mass of smoke to flow through it while bringing the smoke into contact with the carbon material. Preferably, however, the porous carbon material is particulate.

When particulate porous carbon material is incorporated into smoking articles such as cigarettes, or smoke filters therefor, the amount of material for each cigarette or filter must be measured and delivered with high precision. The shape and size of the particles, and the distribution of particle sizes affect the flow and handling of the material. Thus, coconut charcoal has a wide particle size distribution, and a high rate of wear, and therefore tends to produce dust, which can interfere with the operation of high-speed machinery. Also, since the coconut charcoal particles are irregular in shape, they have relatively poor flow characteristics, which creates difficulties in the measurement of material delivery to the cigarette or filter.

Preferably, the porous carbon material is in the form of microbeads, that is, generally spherical particles 50-1000 µm in size. The flow characteristics of the microbeads are particularly favorable for ease of handling in the manufacture of smoking articles and smoke filters therefor.

Smoke filters typically comprise a short stick of an absorbent material such as cellulose acetate. One method of incorporating particulate porous carbon material into the filter is to form a tow from the absorbent material, passing the tow continuously through a first station where the tow is impregnated with a plasticizer such as triacetin, a second station in which particles of porous carbon material are fed from a hopper over the tow and from there to further processing to a filter element. As long as the flow of carbon material from the hopper to the tow and the speed of movement of the tow are uniform, the loading of the tow with the carbon material will also be uniform. Certain carbon materials, however, particularly coconut carbon, have poor flow characteristics. The particles tend to stick together due to their irregular and non-uniform shape. Therefore, the load

ES 2 379 639 T3 of the material on the filter tow is difficult to control. By using the particulate porous carbon materials in the form of microbeads, the risk of sticking and non-uniform loading of the tow is greatly reduced.

Another advantage of using a particulate porous carbon material formed from organic resins in smoking articles or smoke filters arises from the fact that such materials have relatively low wear rates compared to natural charcoal. The higher the wear rate of a particulate material, the more dust it generates during handling. Dust interferes with manufacturing processes, especially high-speed processes used to make cigarettes or cigarette filters. In the production of porous carbon materials from charred organic resin, the reaction conditions for the resin can be controlled such that the resulting carbon particles have a reduced wear rate compared to, for example, charcoal. coconut.

Another physical property of the particulate porous carbon material that affects its suitability for use in smoking articles or smoke filters is its particle size, and more particularly its particle size distribution. The porous carbon materials of the invention preferably have a mean particle size in the range 50-1000 pm, desirably 100-700 pm. For tobacco smoke filtration, porous carbon materials with smaller mean particle sizes, e.g. 150-250 pm, usually perform better than materials with larger mean particle sizes, e.g. ., 250-500 pm, which in turn usually perform better than materials with a mean particle size in the range 500-1000 pm.

Any particulate matter sample will have a statistical particle size distribution around a mean value. The ratio of the 90th percentile (D90) to the 10th percentile (D10) gives a measure (D90 / D10) of the extent of the particle size distribution in the sample. For coconut charcoal, the mean particle size will typically be in the range 100-1000 µm, with a D90 / D10 ratio of 20 or more, with a significant proportion of the particles being less than 20 µm in size. This relatively wide size distribution can result in uneven charcoal distribution in the filter, and a high risk of contamination from manufacturing by dust.

In the production of porous carbon materials from charred organic resin, the reaction conditions for the resin can be controlled such that the resulting material has a narrower particle size distribution compared to, for example, carbon. coconut vegetable. The carbon materials of the invention preferably have a D90 / D10 particle size distribution that is at least 10, desirably at least 5, and most advantageously about 2.

Materials that are substantially dust-free create less handling and contamination problems in the manufacture of smoking articles and smoke filters. The porous carbon material of the invention is therefore substantially free also, preferably, of particles smaller than 10 microns. Desirably, it is also substantially free of particles smaller than 20 microns, and most advantageously it is free of particles smaller than 30 microns.

The smoking articles of the invention can take any form. For example, the smoking article may be one in which the tobacco is smoked by igniting the smoking material and inhaling the combustion products, such as in a cigarette or cigar. Alternatively, the smoking article may be one in which the smoking material is heated to a temperature at which decomposition to non-combustion pyrolysis products occurs. Such articles are well known, and incorporate electrical or other heating means such as a charcoal element.

In particular, the smoking article may comprise a stick of smoking material, optionally within a wrapper, with or without a filter. The wrapper can be made of paper, tobacco leaf, or reconstituted tobacco. Alternatively, when, for example, the smoking article is intended to produce low emissions from the sidestream smoke, or lower levels of pyrolysis products in the mainstream smoke, the wrapper may be composed of a non-organic inorganic material. fuel such as a ceramic material. The filter can be of any suitable material, for example fibrous cellulose acetate, polypropylene or polyethylene, or paper.

The smoking material is preferably tobacco, but may be a smoking material other than tobacco. Examples of non-tobacco smoking materials are dried and cured plant materials, including fruit derived materials, and a synthetic smoking material such as that which can be produced from alginates and an aerosol generating substance such as ethylene glycol. . The smoking material may comprise a mixture of tobacco and non-tobacco smoking materials. Where the smoking material comprises tobacco, the tobacco may be of any suitable type, or a mixture thereof, including air-cured, fire-cured, hot-air-cured, or sun-cured foil or vein, and may have been processed using any appropriate procedure. For example, tobacco can be cut, curled, expanded, or reconstituted. The smoking material can also include conventional additives, such as softeners, colorants, humectants (such as glycerol and propylene glycol), and flavorings (such as sugar, licorice, and cocoa).

ES 2 379 639 T3

The porous carbon material can be incorporated into the smoking material. Accordingly, the invention includes a smoking material incorporating a porous carbon material having any of the characteristics described above in connection with the invention.

Preferably, the smoking article comprises a filter, and the porous carbon material is incorporated into the filter.

The present invention also includes a smoke filter for a smoking article comprising a porous carbon material of the invention. The smoke filter can be in the form of a container for a smoking article, such as a cigarette or cigar container, or it can be produced as a filter tip for incorporation into a smoking article.

The smoke filter can be of any conventional construction. For example, it may be in the form of a "Dalmatian" filter comprising a section of fibrous filter material, such as cellulose acetate, with the porous carbon material being in particulate form and distributed throughout the section. Alternatively, the filter may be in the form of a "cavity" filter, comprising multiple sections, the porous carbon material being confined in one such section. For example, the porous carbon material can be between two adjacent sections of the fibrous filter material.

The smoke filter can also comprise other adsorbent materials, such as an ion exchange resin, a zeolite, silica, alumina, or amberlite.

The preferred smoking articles of the invention are cigarettes, comprising a tobacco rod, a wrapper and a filter, the porous carbon material being incorporated into a filter.

One method of treating the decomposition products of a smoking material comprises contacting the decomposition products with a porous carbon material of the invention.

In order that the invention may be better understood, the preferred embodiments thereof will now be described, by way of example only, in which reference will be made to the following Figures:

Figure 1 - which is a graph.

Figure 2 - which is a graph.

Figure 3 - which is a graph.

Figure 4a - which is a graph.

Figure 4b - which is a graph.

Figure 4c - which is a graph.

Figure 4d - which is a graph.

Figure 4e - which is a graph.

Figure 4f - which is a graph.

Figure 4g - which is a graph.

Figure 4h - which is a graph.

Figure 4i - which is a graph.

Figure 4j - which is a graph.

Figure 4k - which is a graph.

Figure 5 - which is a graph.

Figure 6 - which is a graph.

Figure 7 - which is a diagrammatic representation of a smoking article.

Figure 8 - which is a diagrammatic representation of a smoking article.

Referring to Table 1, organic resin samples were prepared by mixing 100 parts by weight of the commercially available phenol-formaldehyde novolak resins specified in Table 1 with the ethylene glycol pore former in the proportions indicated in Table 1, at elevated temperature and with stirring, to enhance the formation of a clear solution, the temperature of which was later stabilized at 65-70 ° C.

ES 2 379 639 T3

The crosslinking agent hexamethylenetetramine ("hexamine") was then added in the proportions indicated in Table 1. The resulting stirred mixture was then heated to the specified temperature and reaction time.

The commercial grades of the novolac resins used were J1058F, available from Hexion Specialty Chemicals Inc (formerly Borden Chemical inc), with a Mw of about 2400 and containing 5% by weight of hexamethylenetetramine; TPR210, with a Mw of about 1030, which contained salicylic acid to catalyze crosslinking, and J1089F, with a Mw of about 1110.

In each case, the resulting viscous solution was poured as a stream with stirring into 2 to 4 times its volume of a preheated mineral oil (115-120 ° C) containing 0.5% by volume of a drying oil (commercially known as Danish oil) to delay coalescence. The temperature of the resulting emulsion initially dropped to 105-110 ° C, but with further heating crosslinking occurred at approximately 115 120 ° C. Additional heating was applied at a rate of about 0.5 ° C per minute up to 150 ° C to complete the reaction. After cooling, the resulting small resin balls were filtered off from the oil and washed several times with hot water to remove most of the ethylene glycol and a small amount (less than 5% of the total) of low molecular weight polymer. The resulting porous spherical resin, containing water, residual oil, residual pore former, and low molecular weight fraction was carbonized by heating at 800 ° C to produce a spherical porous carbon material. The carbon material was then activated with superheated steam, or carbon dioxide, to achieve the weight reduction or "burnout" indicated in Table 1.

Table 1

<td>Ex. No.</td><td></td><td colspan="3">Resin precursor</td>

<td></td><td>Ethylene glycol (parts by weight)</td><td>Hexamine (parts by weight)</td><td>Novolac (100 parts by weight)</td><td>Activation conditions</td>

<td> 1</td><td> 200</td><td> 15</td><td>J1058F</td><td>Steam at 850 ° C</td>

<td> 2</td><td> 200</td><td> 11</td><td>_“</td><td>34% (CO2 + modification with air)</td>

<td> 3</td><td> 200</td><td> 11</td><td></td><td>34% (CO2)</td>

<td> 4</td><td> 200</td><td> 11</td><td></td><td> 38</td>

<td> 5</td><td> 200</td><td> 11</td><td></td><td>34% (CO2)</td>

<td> 6</td><td> 300</td><td> 11</td><td></td><td>33% (CO2)</td>

<td> 7</td><td> 200</td><td> 15</td><td></td><td>37% (CO2)</td>

<td> 8</td><td> 400</td><td> 11</td><td>_“</td><td>36% (CO2 + modification with air)</td>

<td> 9</td><td> 400</td><td> 11</td><td></td><td>36% (CO2)</td>

<td> 10</td><td> 600</td><td> 11</td><td></td><td>36% (CO2)</td>

<td> 11</td><td> 200</td><td> 11</td><td></td><td>53% (CO2)</td>

<td> 12</td><td> 400</td><td> 11</td><td></td><td>37% (CO2)</td>

<td> 13</td><td> 400</td><td> 11</td><td>_“</td><td>37% (CO2 + modification with air)</td>

The resulting small balls exhibited high durability and a very low wear rate compared to carbon derived from coconut bark. In particular, when physically handled, the small balls had little to no fouling effect on the hands when rubbed, and when physically shaken they formed very little dust. The small balls also had excellent flow characteristics, causing the spherical shape of the small balls to allow the material to flow easily and to form much flatter heaps, that is, conical piles with an angle of fall, or angle of repose, much more. lower than natural carbon.

For comparison purposes, two additional samples of carbon material were prepared (Comparative Examples

ES 2 379 639 T3

B and C) by a technique similar to that described above, using the ingredients and activation conditions referred to in Table 2. A sample of commercially available coconut charcoal, of 208C quality, was also used for comparison purposes ( Comparative example A).

Table 2

<td>Ex. No.</td><td></td><td colspan="3">Resin precursor</td>

<td></td><td>Pore ​​former</td><td>Crosslinking agent</td><td>Resin</td><td>Activation conditions</td>

<td>B</td><td>100 parts by weight of ethylene glycol</td><td>11 parts by weight of hexamine</td><td>100 parts by weight of Novolaca j1058F</td><td>36% (CO2)</td>

<td>C</td><td>Water</td><td></td><td>m-amino-phenolformaldehyde</td><td>27% (CO2)</td>

<td>TO</td><td colspan="3">208C Quality Activated Coconut Charcoal</td><td> -</td>

Figures 1 to 3 show the pore size distribution determined by mercury porosimetry for the porous carbon materials of Examples 3 and 9, and Comparative Example A (coconut charcoal). In each graph, the ordinate on the left indicates the logarithm (log) of the differential intrusion of mercury in the sample in ml / g, the ordinate on the right indicates the cumulative intrusion of mercury in ml / g, and the abscissa indicates, in a logarithmic scale, the pore size diameter in nanometers over the range 5 nm-1 x 10⁶ nm. The large peak on the left side of each graph is caused by mercury intrusion into the gaps between individual particles within the sample. The peaks towards the right side of the graph are caused by mercury intrusion into the micro-, meso- and macropores.

Figures 4a-k show the pore size distribution for the material samples determined by nitrogen adsorption. In these drawings, the average pore size in Angstrom units is plotted on a logarithmic scale on the abscissa against a value indicative of the number of pores of a particular size obtained from nitrogen adsorption studies, which is the differential of pore volume versus logarithm of pore size (dV / dlogR).

The BET surface area and porosity of the activated porous carbon materials described in Tables 1 and 2 are shown in Table 3, and the corresponding properties of comparative samples A, B, and C are shown in Table 4. The areas BET surface areas were calculated using the BET method over a partial pressure range for nitrogen (P / P₀ N₂) of 0.07-0.3. Figures shown for nitrogen adsorption are the amount of nitrogen in milliliters adsorbed under ambient conditions per gram of carbon sample at a relative nitrogen pressure (P / P0) of 0.98, but normalized by the specific gravity of liquid nitrogen. at the corresponding temperature.

Table 3

<td>Ex. No.</td><td>Small balls size (pm)</td><td>Superficial area BET, m²/ g</td><td>Nitrogen adsorption cm³/ g</td><td>Apparent density g / cm³</td><td>Total pore volume₃l cm³/ g (by N2)</td><td>Volume of mesopores cm³/ g (by N2)</td><td>Volume of micropores cm³/ g (by N2)</td><td>% micropores (per N2)</td><td>% of mesopores (by N2)</td>

<td> 1</td><td> 250-500</td><td> 908</td><td> 1,05</td><td></td><td> 1,26</td><td> 0,66</td><td> 0,60</td><td> 47,62</td><td> 53,38</td>

<td> 2</td><td> 250-500</td><td> 1077</td><td> 1,04</td><td> 0,41</td><td> 1,30</td><td> 0,58</td><td> 0,72</td><td> 55,38</td><td> 44,62</td>

<td> 3</td><td> 250-500</td><td> 1094</td><td> 1,09</td><td> 0,41</td><td> 1,35</td><td> 0,62</td><td> 0,73</td><td> 54,07</td><td> 45,93</td>

<td> 4</td><td> 250-500</td><td> 1155</td><td> 1,16</td><td> 0,59</td><td> 1,41</td><td> 0,66</td><td> 0,75</td><td> 53,19</td><td> 46,81</td>

<td> 5</td><td> 150-250</td><td> 1057</td><td> 1,14</td><td> 0,39</td><td> 1,42</td><td> 0,68</td><td> 0,74</td><td> 52,11</td><td> 47,89</td>

<td> 6</td><td> 250-500</td><td> 1165</td><td> 1,25</td><td> 0,27</td><td> 1,51</td><td> 0,73</td><td> 0,78</td><td> 51,66</td><td> 48,34</td>

<td> 7</td><td> 250-500</td><td> 1057</td><td> 1,23</td><td> 0,36</td><td> 1,51</td><td> 0,79</td><td> 0,72</td><td> 47,68</td><td> 52,32</td>

ES 2 379 639 T3

<td>Ex. No.</td><td>Small balls size (pm)</td><td>Superficial area BET, m²/ g</td><td>Nitrogen adsorption cm³/ g</td><td>Apparent density g / cm³</td><td>Total pore volume cm³/ g (by N2)</td><td>Volume of mesopores cm³/ g (by N2)</td><td>Volume of micropores cm³/ g (by N2)</td><td>% micropores (per N2)</td><td>% of mesopores (by N2)</td>

<td> 8</td><td> 250-500</td><td> 1203</td><td> 1,27</td><td> 0,23</td><td> 1,53</td><td> 0,72</td><td> 0,81</td><td> 52,94</td><td> 47,06</td>

<td> 9</td><td> 250-500</td><td> 1230</td><td> 1,36</td><td> 0,23</td><td> 1,62</td><td> 0,79</td><td> 0,83</td><td> 51,23</td><td> 48,77</td>

<td> 10</td><td> 250-500</td><td> 1139</td><td> 1,37</td><td> 0,25</td><td> 1,62</td><td> 0,87</td><td> 0,75</td><td> 46,30</td><td> 53,70</td>

<td> 11</td><td> 250-500</td><td> 1466</td><td> 1,48</td><td> 0,33</td><td> 1,68</td><td> 0,84</td><td> 0,84</td><td> 50,00</td><td> 50,00</td>

<td> 12</td><td> 500-1000</td><td> 1085</td><td> 1,44</td><td> 0,22</td><td> 1,73</td><td> 0,96</td><td> 0,77</td><td> 44,51</td><td> 55,49</td>

<td> 13</td><td> 500-1000</td><td> 1186</td><td> 1,60</td><td> 0,20</td><td> 1,86</td><td> 1,08</td><td> 0,78</td><td> 41,94</td><td> 58,06</td>

Table 4

<td>Ex. No.</td><td>Small balls size (pm)</td><td>BET surface area m²/ g</td><td>Nitrogen adsorption cm³/ g</td><td>Apparent density g / cm³</td><td>Pore ​​volume ^total₃^lcm³/ g</td><td>Volume of mesopores cm³/ g</td><td>Volume of micropores cm³/ g</td><td>% of micropores</td><td>% of mesopores</td>

<td>TO</td><td></td><td> 996</td><td> 0,55</td><td> 0,5</td><td> 0,78</td><td> 0,04</td><td> 0,74</td><td> 94,87</td><td> 5,13</td>

<td>B</td><td> 250-500</td><td> 1040</td><td> 0,6</td><td> 0,61</td><td> 0,87</td><td> 0,09</td><td> 0,78</td><td> 89,66</td><td> 10,34</td>

<td>C</td><td> 250-500</td><td> 726</td><td> 0,65</td><td> 0,59</td><td> 0,9</td><td> 0,31</td><td> 0,59</td><td> 65,56</td><td> 34,44</td>

Table 5 gives additional details of the pore size distribution of Examples 2, 3, 4, 7, 8, 9, 12 and 13, and 5 of Comparative Examples A and C.

Table 5

<td rowspan="2">Example No.</td><td colspan="4">Pore ​​size distribution (N2 adsorption) (% of total pore volume by pore size)</td>

<td>&gt; 10 nm</td><td>5-10 nm</td><td>2-5 nm</td><td>&lt;2 nm</td>

<td> 2</td><td> 34,62</td><td> 5,38</td><td> 7,69</td><td> 52,31</td>

<td> 3</td><td> 36,30</td><td> 6,67</td><td> 6,67</td><td> 50,37</td>

<td> 4</td><td> 34,04</td><td> 8,51</td><td> 7,80</td><td> 49,65</td>

<td> 7</td><td> 46,00</td><td> 4,00</td><td> 5,33</td><td> 44,67</td>

<td> 8</td><td> 39,87</td><td> 3,92</td><td> 7,84</td><td> 48,37</td>

<td> 9</td><td> 42,56</td><td> 3,09</td><td> 5,56</td><td> 48,77</td>

<td> 12</td><td> 51,45</td><td> 2,31</td><td> 4,05</td><td> 42,20</td>

<td> 13</td><td> 53,76</td><td> 2,15</td><td> 4,84</td><td> 39,25</td>

<td>TO</td><td> 1,28</td><td> 1,58</td><td> 7,69</td><td> 89,74</td>

<td>C</td><td> 31,11</td><td> 1,11</td><td> 5,56</td><td> 62,22</td>

It can be seen from the above Tables and Figures 1-4a-k that the carbon materials of the invention

ES 2 379 639 T3 have a particle size distribution that spans the ranges of micro-, meso- and sometimes macropores. Although nitrogen adsorption cannot be used to estimate macropore volumes, the presence of significant macropore volumes is indicated by the positive slope of the pore size distribution curve towards the upper end of the range of nitrogen adsorption measurements, as seen for Examples 8 (Fig. 4f), 9 (Fig. 4g), 10 (Fig. 4e), 12 (Fig. 4g) and 13 (Fig. 4i). The presence of macropores can be confirmed by mercury porosimetry studies, as shown in Figures 2 and 3.

It can also be seen from the nitrogen adsorption measurements that there is a minimal gap in the pore size distribution of the carbon materials of the Examples of the invention, in each case in the range 2-10 nm. Within this range the mesopores represent less than 20% of the combined meso- and micropore volumes, usually less than 15% and more often less than 10% of the combined volume.

The effect of the carbon materials of the examples on tobacco smoke was tested by preparing standard cigarettes comprising a stick wrapped in American style blended tobacco paper and a 27 mm long smoke filter connected to the stick by a paper. nozzle. Each filter consisted of two pieces of cellulose acetate separated by a 3-5 mm well containing a 60 mg sample of the material, the length of the well being adjusted to accommodate the sample well. The cigarettes were smoked up to 3mm from the end of the mouthpiece paper in a conventional cigarette smoking engine according to an ISO standard smoking regimen. The levels of volatile carbonyl compounds were estimated by trapping the entire mainstream smoke for each cigarette in stabilized 2,4-dinitrophenylhydrazine with a pH buffer, and the aldehyl components were analyzed by liquid chromatography (HPLC) with an ultraviolet detection system. . The levels of vapor phase components of the smoke were estimated by passing the main stream of the smoke through a Cambridge filter pad of 44 mm to remove the particulate material, collecting the vapor phase of the smoke in a bag of Tedlar 31 , and analyzing the vapor by CGMS (gas chromatography coupled to mass spectrometry). The levels of hydrogen cyanide (HCN) in the smoke were estimated by trapping the entire mainstream of the smoke in an aqueous solution of sodium hydroxide and subjecting the solution to continuous flow analysis. Each test was repeated on four samples, and the means were calculated in each case. For each sample, comparative tests were performed using a control sample, which comprised a cigarette with an identical filter having a 4 mm long empty cavity, and a sample with a cavity containing 60 mg of coconut charcoal.

Table 6 summarizes the analytical results for 1,3-butadiene and hydrogen cyanide (HCN). In order to conveniently compare the yields to coconut charcoal, the results for each sample were normalized to the results for coconut charcoal. The normalized data is graphed in Figures 5 and 6, which are scatter diagrams that graphically represent the percent reduction in 1,3-butadiene and HCN, normalized relative to the coconut charcoal of Comparative Example A, versus volume combined total of meso- and micropores, and the% volume of micropores, respectively.

Table 6

<td>Example No.</td><td>% reduction of 1,3-butadiene vs. control</td><td>% reduction of 1,3-butadiene normalized compared to Example A</td><td>% reduction in HCN vs. control</td><td>% reduction of HCN normalized compared to Example A</td>

<td> 2</td><td> 46,09</td><td> 1,70</td><td> 54,09</td><td> 1,05</td>

<td> 3</td><td> 57,34</td><td> 2,12</td><td> 58,55</td><td> 1,14</td>

<td> 4</td><td> 70,68</td><td> 2,61</td><td> 60,77</td><td> 1,18</td>

<td> 5</td><td> 64,25</td><td> 2,38</td><td> 78,56</td><td> 1,53</td>

<td> 6</td><td> 53,74</td><td> 1,99</td><td> 85,22</td><td> 1,66</td>

<td> 7</td><td> 73,94</td><td> 2,73</td><td> 79,38</td><td> 1,54</td>

<td> 8</td><td> 60,03</td><td> 2,22</td><td> 78,83</td><td> 1,53</td>

<td> 9</td><td> 71,48</td><td> 2,64</td><td> 84,62</td><td> 1,65</td>

<td> 10</td><td> 73,94</td><td> 2,73</td><td> 79,38</td><td> 1,54</td>

<td> 11</td><td> 57,50</td><td> 2,13</td><td> 73,18</td><td> 1,42</td>

<td> 12</td><td> 56,58</td><td> 2,09</td><td> 75,01</td><td> 1,46</td>

ES 2 379 639 T3

<td> 13</td><td> 50,72</td><td> 1,88</td><td> 64,82</td><td> 1,26</td>

<td>TO</td><td> 27,05</td><td> 1,00</td><td> 51,41</td><td> 1,00</td>

<td>B</td><td> 20,33</td><td> 0,75</td><td> 36,22</td><td> 0,70</td>

<td>C</td><td> 12,88</td><td> 0,48</td><td> 22,24</td><td> 0,43</td>

As can be seen from the data and Figures 5 and 6, the carbon materials of the invention, with higher total pore volumes and higher ratios of mesopore volumes than coconut charcoal, performed significantly better in relation to the adsorption of HCN and, especially, 1,3-butadiene, from tobacco smoke.

The materials tested showed similar adsorption characteristics relative to Examples A, B and C for acreolin, propionaldehyde, crotonaldehyde, methyl ethyl ketone and butyraldehyde.

Table 7 summarizes the properties of five additional examples of carbon materials according to the invention in the form of microbeads (Examples 14-18), together with two comparative examples, also in the form of microbeads in the same particle size range. (Examples D and E). All of the small balls had a particle size in the range 250-500 microns.

The carbon material of Example 14 is similar to that of Comparative Example C, and was prepared from a resin (MAP) produced by polymerizing m-aminophenol and formaldehyde in the presence of water as a pore former, but the small balls were subjected to to a more extensive activation in carbon dioxide to achieve a higher surface area. Although mesopores form a relatively low proportion of the combined meso- and micropore volume of this sample, their bulk density is also low, indicating that a significant pore volume is in small macropores, not detected by nitrogen adsorption.

The carbon material of Example 15 was prepared by carbonizing a commercially available styrene divinylpyrrolidone (SDP) polymer and activating in carbon dioxide.

The carbon material of Example 16 was prepared from a phenol-formaldehyde (PF) resin obtained by polymerizing 100 parts by weight of phenol and formaldehyde in the presence of 200 parts by weight of ethylene glycol as pore former, without any crosslinking agent. additional. The resulting polymer was washed, charred, and then activated in carbon dioxide to achieve 40% burn.

The carbon material of Example 17 was prepared from a phenol-formaldehyde (PF) resin obtained in a similar manner to that of Example 16, but using 175 parts by weight of ethylene glycol, with an additional wash and in carbon dioxide. to get a burn of 36%.

The carbon material of Example 18 was prepared from a phenol-formaldehyde (PF) resin obtained in a similar manner to Example 17, but using 150 parts by weight of ethylene glycol. Like the material of Example 14, the mesopores form a relatively low proportion of the combined meso- and micropore volume of this sample, however their bulk density is also low, indicating that a significant pore volume is in small macropores, not detected by nitrogen adsorption.

The carbon material of Comparative Example D was prepared using a styrene vinylpyrrolidone polymer similar to that used in Example 15. The resulting material had a lower combined volume of micro- and mesopores and a relatively high density.

The carbon material of Comparative Example E was prepared using a phenol-formaldehyde resin obtained in a similar manner to that of Example 17. The resulting material had a lower mesopore volume ratio, and a higher density.

The yields of the carbon materials in reducing the formaldehyde, acetaldehyde, 1,3-butadiene and HCN components of tobacco smoke were tested using the same test procedures described above. Results are also set forth in Table 7. Yields are evaluated in terms of% reductions of analytes in tobacco smoke, normalized to corresponding reductions measured using coconut bark carbon.

It can be seen that the carbon materials according to the invention have a better performance relative to coconut shell carbon in the removal of at least three of the four smoke analytes tested, and that the comparative examples performed worse than the coconut bark carbon in relation to the four analytes.

ES 2 379 639 T3

Table 7

<td rowspan="2">Ex N °</td><td rowspan="2">Resin</td><td rowspan="2">TO. S. BET m²/ g</td><td rowspan="2">Apparent density g / cm³</td><td rowspan="2">Vol. Of mesopores cm³/ g</td><td rowspan="2">Volume of micropores cm³/ g</td><td rowspan="2">Combined pore volume cm³/ g</td><td rowspan="2">% vol. of mesopores</td><td colspan="4">% of normalized reductions</td>

<td>Formaldehyde</td><td>Acetaldehyde</td><td>1,3butadiene</td><td>HCN</td>

<td> 14</td><td>MAP</td><td> 1059</td><td> 0,35</td><td> 0,16</td><td> 0,75</td><td> 0,91</td><td> 17,6</td><td> 1,26</td><td> 1,09</td><td> 0,79</td><td> 1,66</td>

<td> 15</td><td>SVP</td><td> 1638</td><td> 0,36</td><td> 0,50</td><td> 0,91</td><td> 1,41</td><td> 35,5</td><td> 0,54</td><td> 1,04</td><td> 2,06</td><td> 1,01</td>

<td> 16</td><td>Pf</td><td> 1055</td><td> 0,25</td><td> 0,90</td><td> 0,57</td><td> 1,47</td><td> 61,2</td><td> 2,00</td><td> 1,62</td><td> 2,71</td><td> 1,54</td>

<td> 17</td><td>Pf</td><td> 1119</td><td> 0,33</td><td> 0,83</td><td> 0,77</td><td> 1,60</td><td> 51,9</td><td> 1,09</td><td> 1,07</td><td> 1,80</td><td> 0,96</td>

<td> 18</td><td>Pf</td><td> 1075</td><td> 0,30</td><td> 0,05</td><td> 0,97</td><td> 1,02</td><td> 4,90</td><td> 1,42</td><td> 1,42</td><td> 2,26</td><td> 1,08</td>

<td>D</td><td>SVP</td><td> 1048</td><td> 0,51</td><td> 0,22</td><td> 0,64</td><td> 0,86</td><td> 25,6</td><td> 0,52</td><td> 0,48</td><td> 0,40</td><td> 0,69</td>

<td>AND</td><td>Pf</td><td> 1085</td><td> 0,60</td><td> 0,13</td><td> 0,81</td><td> 0,94</td><td> 13,8</td><td> 0,67</td><td> 0,67</td><td> 0,60</td><td> 0,32</td>

Specific embodiments of smoking articles and smoke filters according to the invention will now be described by way of example only, with reference to Figures 6 and 7, in which Figure 6 is a side elevation view, partly in cross-section. longitudinal and partially split, of a smoking article with a smoke filter according to the invention.

Figure 7 is a view similar to Figure 6 of a smoking article with an alternative smoke filter according to the invention.

In the drawings, which are not to scale, like features are given like reference numerals.

Referring to the drawings, Figures 7 and 8 illustrate smoking articles in the form of cigarettes having a tobacco rod 1 covered by a wrapper 2 attached to a smoke filter 3 by means of a tipping paper 4. For clarity, the tipping paper 4 is shown separated from the wrapper 2, but in fact they will be in close contact.

In Figure 7, the smoke filter 3 comprises two cylindrical filter elements 3a and 3b. The first filter element 3a at the end of the filter that is brought to the mouth is 15 mm long, it is composed of cellulose acetate tow impregnated with 7% by weight of the plasticizer triacetin, which has a gauge pressure drop of 25 mm water over its length. The second filter element 3b, positioned adjacent to bar 1, is 12 mm long, has a 90 mm gauge water pressure drop over its length, and comprises 80 mg of cellulose acetate tow impregnated with 4% by weight of triacetin, and has 30 mg of a porous activated carbon material according to the invention distributed evenly throughout its volume in a "Dalmatian" style.

The cigarette shown in Figure 8 is similar to that of Figure 7, except that the smoke filter 3 has three coaxial, cylindrical filter elements 3a, 3b and 3c. The first filter element 3a at the mouth end of the cigarette is 10mm in length, and is composed of cellulose acetate tow impregnated with 7% by weight of the plasticizer triacetin. The second filter element 3b, positioned adjacent to the first filter element 3a, is a 7 mm long cavity containing 100 mg of a porous activated carbon material according to the invention. The third filter element 3c adjacent to the second filter element 3b is 10 mm in length and comprises cellulose acetate tow impregnated with 7% by weight of triacetin. A ring of ventilation holes 5 is formed in the nozzle paper 4 in a radial plane AA, which delivers air to the second filter element 3b approximately 3 mm downstream of the junction with the third filter element 3c when the smoke is inhaled through cigarette.

In summary, the Examples provide a porous carbon material suitable for incorporation into cigarette smoke filters, having a BET surface area of ​​at least 800 µm.²/ g and a pore structure that includes mesopores and micropores. The pore volume (measured by nitrogen adsorption) is at least 0.9 cm³/ g and 15 to 65% of the pore volume is in mesopores. The pore structure of the material provides a bulk density, generally less than 0.5 g / cm³. The material can be produced by charring and activating organic resins, and can be in the form of small balls for ease of handling.