WO2012172292A1

WO2012172292A1 - Tobacco smoke filter with activated carbon

Info

Publication number: WO2012172292A1
Application number: PCT/GB2012/000521
Authority: WO
Inventors: Anthony Denis Mccormack; Stephen Robert Tennison; Oleksandr Prokopovych Kozynchenko
Original assignee: Filtrona Filter Products Development Co. Pte. Ltd
Priority date: 2011-06-17
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: GB201110369D0

Abstract

A Group II metal modified activated carbon derived from a phenolic resin.

Description

Tobacco smoke filter with activated carbon

This invention relates to activated carbon. In particular it relates to activated carbon for use in smoking articles such as cigarettes.

The use of activated carbon and volatile flavourants in smoking articles such as cigarettes is well known. However, the use of activated carbon and a volatile flavourant (such as menthol) together may be problematic because the carbon will adsorb the flavourant, thereby (i) preventing release of flavourant into the smoke stream and (ii) limiting the ability of the carbon to adsorb toxic volatile organic compounds from smoke, because of prior adsorption of volatile flavourant.

Various attempts have made to overcome these difficulties. For example, the flavourant may be encapsulated in a frangible capsule within a carbon-bearing filter (e.g. see WO 2005/032287) which is broken by the smoker immediately before smoking to release flavourant. In another example, activated carbon particles are coated in a glucan film to which flavourant has been applied (e.g. see WO 2008/072627); the film dissolves in water produced during the smoking of the cigarette to release flavourant. However, both these concepts suffer from various limitations, e.g. inflexibility and limited functionality.

The present applicants previously filed a patent application (published as WO 2004/04757) for a tobacco smoke filter containing activated carbon of defined pore size distribution properties; a relatively low micropore volume combined with relatively high mesopore volume. The main benefit of this filter is the ability to release menthol that had been applied to the filter, whilst simultaneously removing vapour phase compounds. Performance is good, although the levels of flavour (e.g. menthol) released and the efficiency of vapour phase removal tend to be fairly low in comparison to cigarette filters containing menthol only or carbon only respectively.

Thus, it is desirable to produce a flavoured carbon filter (i.e. which includes active carbon and flavourant) which releases relatively high and easily controllable levels of flavour, whilst simultaneously removing high levels of vapour phase compounds without the need for interaction from the smoker such as physical breaking of capsules.

It is known to produce activated carbons derived from solid beads of polymer material, e.g. from phenolic resin beads. These activated carbons are described, for example, in WO 2002/12380 and WO 2008/043982, and beaded carbons of these types are available as Novacarb S from MAST Carbon. This type of ethylene glycol pore forming technology is suitable for manufacturing carbons with controlled pore size distributions over the micro-, meso- and macro-pore size regions. However, these technologies tend to be unsuitable for producing carbons with low micropore volumes, e.g. those defined in Filtrona WO 2004/04757. According to the present invention there is provided a Group II metal modified (e.g. catalysed) activated carbon derived from a phenolic resin. This may be a Group II catalytic metal modified and activated carbon derived from a phenolic resin. Preferably the Group II metal is calcium. The Group II metal may be calcium in the form of calcium acetate.

Preferably the Group II metal modified activated carbon has a BET surface area of 800 m²/g or less, more preferably 799 m²/g or less. Preferably the Group II metal modified activated carbon includes micropores of under 2 nm pore diameter which provide a micropore volume of up to 0.38 cm³/g (N₂), for example up to 0.26 cm³/g (N₂). Preferably the Group II metal modified activated carbon includes carbon mesopores of 2 to 50 nm pore diameter which provide a mesopore volume of at least 0.19 cm³/g (N₂), for example at least 0.25 cm³/g (N₂). The designation of pores of less than 2 nm, 2 to 50 nm, and over 50 nm size (diameter) as micro-, meso- and macro-pores is in accord with accepted lUPAC terminology and definition. Herein a pore volume expressed in cm³/g (N₂) means said volume as measured by nitrogen porosimetry, that is, by measurement of the nitrogen adsorption/desorption isotherms and characterising the pore size distribution on the adsorption branch of the isotherm. This technique is well known to those skilled in the art. Such pore volumes may be measured using e.g. a icromeritics Tristar 3000. In some preferred examples the micropore volume may be 0.15 cm³/g (N₂) or less. The mesopore volume provided by 2 to 50 nm mesopores may for example be about 0.3 cm³/g (N₂) and is preferably over 0.4 or over 0.5 cm³/g (N₂); the preferred range is thus from 0.19 to 0.5 or higher cm³/g (N₂). The mesopore volume provided by 7 to 50 nm larger mesopores may be preferably 0.13 cm³/g (Hg) or higher, and can be over 0.3 or over 0.5 cm³/g (Hg); the preferred range is thus from 0.13 to 0.5 or higher cm³/g (Hg). The Group II metal modified activated carbon may have 65.5% or more of the total pore volume as meso- and macropores.

A manufacturing process based on Group II metal (e.g. calcium) catalyzed activation has been developed and used to produce the activated carbon according to aspects of the invention. The effect of the calcium is to direct activation to the meso/macropore domain with little or no development of the micropores, thereby producing phenolic resin-based carbons with relatively low micropore volumes. The applicants have surprisingly found that calcium catalyzed activated carbons derived from phenolic resins are highly effective when used together with flavourant - e.g. menthol - when used in filters for flavoured - e.g. mentholated - cigarettes. The applicants have also surprisingly found these benefits may be significantly enhanced depending on when the Group II metal (e.g. calcium) is introduced to the manufacturing process. Activated carbons are normally prepared via the following multi-stage process: (i) bead (resin) formation (typically using a solvent based mix of phenolic resin and hexamine, for example with a further step of forming resin beads via hot oil disperse procedure), see for example WO 2002/12380 and WO 2008/043982, or formation of pellets or agglomerates (e.g. by casting and milling the solvent based mix of phenolic resin and hexamine); (ii) centrifugation; (iii) vacuum drying; (iv) pyrolysis; (v) sieving and (vi) activation. There are several different ways and stages in which calcium (in the form of a calcium salt, typically calcium acetate, or other soluble calcium salt such as calcium nitrate) can be added to such a process, according to the invention; for example, it is possible to introduce calcium into the mix at stages (i), (iv) or (vi). The applicants have surprisingly found that the stage at which the calcium is introduced has a significant effect upon the performance of the resulting activated carbons in cigarette filters in which flavours, notably menthol, are also present. The introduction of calcium immediately prior to stage (vi) - that is, immediately prior to activation, rather than at the resin formation stage or immediately prior to pyrolysis - may provide significant improvement in flavourant (e.g. menthol) delivery from a flavoured (e.g. mentholated) cigarette including a filter incorporating such an activated carbon, whilst simultaneously providing much higher levels of vapour phase retention than the prior art filters.

According to the present invention in a further aspect there is provided an activated carbon produced by a process comprising a step of (e.g. catalysed) activation of carbon in which a Group II metal catalyst is added to the carbon immediately prior to, or during, activation (prior to, or during, the activation step). The Group (I metal catalyst may be added to carbon which has been produced - e.g. by pyrolysis (by a further step of pyrolysis). The carbon (e.g. pyrolysed carbon) may, for example, be derived from a phenolic resin (e.g. is a phenolic resin based carbon) or may be derived from a sulphonated styrene divinyl benzene polymer or another suitably porous carbonisable polymer. The phenolic resin may be formed using a solvent based mix of uncured phenolic resin and hexamine. Preferably the Group II metal is calcium. The Group II metal may be calcium in the form of calcium acetate.

The term "activation" is generally understood in the art and means herein exposure of a raw material or carbonised (e.g. pyrolysed) material to oxidizing atmospheres (e.g. carbon dioxide, oxygen, or steam) at temperatures above 350 °C, usually in the temperature range of 600-1200 °C. As discussed above, the applicants have found that addition of a Group II metal catalyst (e.g. calcium e.g. calcium in the form of calcium acetate) to carbon (e.g. in the form of a phenolic resin based carbon, e.g. a phenolic resin based carbon which has been produced by pyrolysis) immediately prior to, or during, activation, may provide activated carbon which has superior performance in tobacco smoke filtering applications (especially for applications when a flavouring agent is also present). Preferably the oxidising atmosphere (during activation) is or includes carbon dioxide. Preferably the oxidising atmosphere (during activation) is or includes carbon dioxide and the temperature during activation is 800 °C or above.

The activation step may lead to a (burn-off) weight loss corresponding to up to 50 % of the weight of the carbon prior to activation. Preferably the activation step provides a (burn-off) weight loss corresponding to 10-20% of the weight of the carbon prior to activation weight.

Preferably the activated carbon has a BET surface area of 800 m²/g or less, more preferably 799 m²/g or less. Preferably the activated carbon includes micropores of under 2 nm pore diameter which provide a micropore volume of up to 0.38 cm³/g (N₂), for example up to 0.26 cm³/g (N₂). Preferably the activated carbon includes carbon mesopores of 2 to 50 nm pore diameter which provide a mesopore volume of at least 0.19 cm³/g (N₂), for example at least 0.25 cm³/g (N₂). The activated carbon may have 65.5% or more of the total pore volume as meso- and macropores.

According to the present invention in a further aspect there is provided a tobacco smoke filter or filter element including an activated carbon according to any preceding claim, optionally further comprising a flavouring agent. The tobacco smoke filter or filter element may comprise a longitudinally extending core of tobacco smoke filtering material; an activated carbon according to any preceding claim; and optionally a flavouring agent.

The tobacco smoke filtering material may be for example any of those materials (usually filamentary, fibrous, web or extruded) conventionally employed for tobacco smoke filter manufacture. The filtering material may be natural or synthetic filamentary tow, e.g. of cotton or plastics such as polyethylene or polypropylene, or cellulose acetate filamentary tow. It may be, for example, natural or synthetic staple fibres, cotton wool, web material such as paper (usually creped) and synthetic non-wovens, and extruded material (e.g. starch, synthetic foams). The tobacco smoke filtering material (e.g. cellulose acetate filamentary tow) may further comprise a plasticiser (e.g. triacetin). The tobacco smoke filtering material may be over wrapped with a wrapper, for example a wrapper of paper, for example a wrapper of an air-permeable paper.

The activated carbon may be included in the filter or filter element by any means known in the art. The filter or filter element according to the invention may be of any design previously proposed for particulate sorbent- containing tobacco smoke filters. For example the activated carbon may be dispersed throughout a filter plug, carried on the tow or fibres or sheet of filtering material which is gathered to form the plug; it may instead be adhered to one or more threads which extend through the matrix of the filter plug or be adhered to the inner face of a wrapper around the filter plug; or it may form a bed sandwiched between a pair ofplugs^~(e.g? of cellulose acetate tow) in a common wrapper.

The flavouring agent, if present, may be any flavouring agent (flavourant) known or suitable for use in a smoking article such as a cigarette. The flavouring agent may be for example menthol, spearmint, nutmeg etc. A preferred flavouring agent is menthol.

The activated carbon may be treated with the flavouring agent prior to filter production so that it acts as a carrier for the flavouring agent and minimises migration of the flavouring agent during storage. In another example, the activated carbon may be used in a suitable filter in the unflavoured state, with the flavouring agent being added to another part of the filter and/or to the cigarette with which the filter is used and/or to the filter cigarette packaging. The flavouring agent may be carried on a wrapper around a filter plug or on one or more threads through a filter plug, and such plug may be the plug which also carries the activated carbon or a separate plug.

The tobacco smoke filter or filter element according to the invention may be of circumference 14 to 28 mm, for example 16 to 26 mm, for example 16 to 17 mm or 24 to 25 mm. A tobacco smoke filter of the invention may be of length 10 to 40 mm, e.g. 15 to 35 mm, e.g. 20 to 30 mm. A tobacco smoke filter element of the invention may be of length 5 to 30mm, e.g. 6 to 20mm, e.g. 8 to 15 mm, e.g. 10 to 12 mm.

A filter element according to the invention may be used as a segment of a dual, triple, or other multi component (multiple segment), filter. Dual and other multiple component filters are known in the art. In an example, a dual, triple, or other multi component, filter includes an activated carbon of the invention or a filter element according to the invention. It is preferred that the filter element of the invention (which includes the activated carbon) does not form the mouth end segment of a dual or multiple segment filter.

It is preferred that the filter element of the invention (which includes the activated carbon) is used towards the tobacco end of a dual or other multiple filter. In such instances, the mouth end filter element may be of any construction that does not include a granular additive, so as to present a pleasing end appearance.

Filters according to the invention may be used in machine made cigarettes (e.g. those mass produced and packaged). Filters according to the invention may also be used as a filter tip for use with a individually rolled cigarette (e.g. a hand rolled cigarette) or a Roll

Your Own or ake-Your-Own product.

According to the present invention in a further aspect, there is provided a filter cigarette which includes a tobacco smoke filter or filter element according to the invention.

In a filter cigarette according to the invention, a filter of the invention (or a filter which includes a filter element of the invention) is joined to a wrapped tobacco rod with one end toward the tobacco. The filter may, for example, be joined to the wrapped tobacco rod by ring tipping (which engages around just the adjacent ends of a [wrapped] filter and rod to leave much of the filter wrapper exposed) or by a full tipping overwrap (which engages around the full filter length and adjacent end of the tobacco rod). Any filter or filter cigarette according to the invention may be unventilated, or may be ventilated by methods well known in the art, e.g. by use of a pre-perforated or air-permeable plugwrap, and/or laser perforation of plugwrap and tipping overwrap.

The filters or filter elements according to the invention may be made (by methods known in the art) as continuous rods. The continuous rod as it issues continuously from the production machine outlet is cut into finite lengths for subsequent use. This cutting may be into individual filters or filter elements as defined and described above, each of which is then attached to an individual wrapped tobacco rod to form a filter cigarette. More usually, however the continuously issuing rod of filters is first cut into double or higher multiple (usually quadruple or sextuple) lengths for subsequent use; when the initial cut is into quadruple or higher lengths, then the latter are subsequently cut into double lengths for the filter cigarette assembly - in which the double length filter rod is assembled and joined (by ring tipping or full tipping overwrap) between a pair of wrapped tobacco rods with the combination then being severed centrally to give two individual filter cigarettes. Similar techniques are used with e.g. double length filter elements which are combined to make dual or multiple filters, as is known in the art. The invention includes double and higher multiple length filter rods (and/ or filter element rods).

Herein the term "Group II metal catalysed activated carbon" or "Group II metal modified activated carbon" means activated carbon which has been activated in the presence of a Group II metal (ion) by exposure to oxidizing atmospheres (carbon dioxide, oxygen, or steam) at temperatures above 250 °C, usually in the temperature range of 600- 1200 °C. Preferably, the Group II metal is added (to the carbon) immediately prior to, or during, activation. The Group II metal may be added to carbon which has been carbonised - e.g. by pyrolysis. However, the term Group II metal modified activated carbon includes activated carbon which has been activated in the presence of Group II metal which was added to the carbon earlier in the process, for example during bead, pellet or agglomeration formation, or during a pyrolysis/carbonisation step. Preferably the oxidising atmosphere (during activation) is or includes carbon dioxide. Preferably the oxidising atmosphere (during activation) is or includes carbon dioxide and the temperature during activation is 800 °C or above.

Detailed description of the invention

The present invention will now be illustrated with reference to following examples. Example 1

Four samples of activated carbon were prepared by MAST Carbon of the UK. Samples 1A and 1B were prepared by their conventional 'Novacarb' technology (i.e. without the use of calcium catalyzed activation) - see e.g. WO 2002/12380 and WO 2008/043982. Samples 1C and 1D were prepared using a modified route in which calcium acetate was added at the bead formation stage to inhibit subsequent micropore formation during activation. By varying the ratios of the ingredients used to prepare the resin beads and the level of burn off during activation, it was possible to tailor the pore size characteristics of these carbons, using methods known to those skilled in the art.

Sample 1A

Stage i) A hot (~90 C) freshly prepared solution containing Novolak phenolic resin (average Mw = 800-1000 D), salicylic acid, calcium acetate monohydrate, hexamethylenetetramine and ethylene glycol in weight ratio 5 : 0.3 : 0.33 : 1 : 7.5 was mixed with hot (150 - 160 C) transformer oil (e.g. - EnergOil of the Shell Corp.) at the solution to oil volume ratios 1 : 3 to 1 : 10. The oil also contained 0.5 - 1% (by volume) of the drying oil as a dispersing agent. Further heating was applied to gradually regain the temperature of 150-155 C after which the resin beads slurry was cooled down. Stage ii). The resin beads were separated from at least 90% of the oil by filtration or centrifugation (or other appropriate technique).

Stage iii) The majority of the ethylene glycol pore former and some residual oil was removed from the formed beads by vacuum drying (1 - 5 mm Hg and the temperature 120- 130 C). The dried resin bead yield was 50-55%. Stages iv) and vi). The vacuum dried resin was carbonised and activated in one procedure. A sample of 150 g of resin was placed into a stainless steel mesh tray lined with silica cloth. The tray containing the resin beads was heated in the tube furnace from room temperature to 800 C at ramp 3 C/min in a carbon dioxide flow of 300 ml/min and was then held at 800 C for 100 min. After cooling down the activated material (60.0 g) was classified to different particle size fractions by sieving or another appropriate technique. The level of activation was estimated by comparing with the yield of carbonisation run at the same conditions but in nitrogen gas flow. The carbon was given the code 23C (23% loss in carbon dioxide) though it is clear that total weight loss is a sum of hydrated calcium acetate transformation into calcium carbonate and activation burn-off itself. The selected fraction (250/500 urn) was washed from calcium carbonate with excess dilute hydrochloric acid and demineralised water until negative result was achieved with chloride probe (with silver nitrate solution). It was then dried at 105 C to constant weight.

Sample 1B.

Stage i) A hot (-90 C) freshly prepared solution containing Novolak phenolic resin (average Mw = 800-1000 D), salicylic acid, calcium acetate monohydrate, hexamethylenetetramine and ethylene glycol in weight ratio 6.67 : 0.4 : 0.44 : 1 : 13.4 was mixed with hot (150 - 160 C) transformer oil (e.g. - EnergOil of the Shell Corp.) at the solution to oil volume ratios 1 : 3 to 1 : 10. The oil also contained 0.5 - 1% (by volume) of the drying oil as a dispersing agent. Further heating was applied to gradually regain the temperature of 150- 155 C after which the resin beads slurry was cooled down.

Stage ii). Separation was as for sample 1 A.

Stage iii) The resin beads were dried from most of the ethylene glycol and residual oil in vacuum 1 - 5 mm Hg and the temperature 120-130 C, the yield of dried beads was 40- 45%.

Stages iv) and vi). Vacuum dried resin was carbonised and activated in a single step. A sample of 150 g of resin was placed into a stainless steel mesh tray lined with silica cloth. The tray with resin was heated in the tube furnace from room temperature to 800 C at 3 C/min in the carbon dioxide flow 300 ml/min and was held at 800 C for 100 min. After cooling down the activated material (50.0 g) was classified to different particle size fractions by sieving or another appropriate technique. The level of activation was estimated by comparing with the yield of carbonisation run at the same conditions but in nitrogen gas flow. The carbon was given the code 37C though it is clear that total weight loss is a sum of hydrated calcium acetate transformation into calcium carbonate and activation burn-off itself.

The selected fraction (250/500 um) was washed from calcium carbonate with excess dilute hydrochloric acid and demineralised water until negative chloride probe (with silver nitrate solution) was achieved and dried at 105 C to constant weight.

Sample 1C.

Stage i). A hot (~ 90 C) freshly prepared solution containing Novolak phenolic resin (Mav = 800-1000 D), hexamethylenetetramine (hexamine) and ethylene glycol in weight ratio 5 : 1 : 9 was mixed with hot (150 - 160 C) transformer oil (e.g. - EnergOil of the Shell Corp.) at the solution to oil volume ratios 1 : 3 to 1 : 10. The oil also contained 0.5 - 1% (by volume) of the drying oil as a dispersing agent. Further heating was applied to gradually regain the temperature of 150-155 C after which the resin beads slurry was cooled down. Stage ii). Separation was as for sample 1A.

Stage iii) The resin beads were dried from most of ethylene glycol and residual oil in vacuum 1 - 5 mm Hg and the temperature 120-130 C. The dried resin bead yield was 42- 47%. Alternatively the resin could be washed repeatedly with hot water (cascade washing).

Stage iv). Vacuum dried or hot water washed resin was carbonised by heating from room temperature to 800 C at ramp 3 C/min in the carbon dioxide flow and held at 800 C for 30 min. After cooling down the carbonised material was classified to different particle size fractions by sieving or another appropriate technique.

Stage vi) Activation. Sample of 100 g of dried to constant weight carbonised beads (fraction 250/500 urn) was placed into a stainless steel mesh tray lined with silica cloth. The tray with carbon was heated in the tube furnace from room temperature to 900 C at ramp 6 C/min in carbon dioxide flow and kept at 900 C for 7 hrs in carbon dioxide flow and cooled back to room temperature in carbon dioxide flow to yield 60 g of activated carbon (40% weight loss).

Sample 1D

Stage i). A hot (~ 90 C) freshly prepared solution containing Novolak phenolic resin (Mav = 800-1000 D), hexamethylenetetramine (hexamine) and ethylene glycol in weight ratio 5 : 1 : 15 was mixed with hot (150 - 160 C) transformer oil (e.g. - EnergOil of the Shell Corp.) at the solution to oil volume ratios 1 : 3 to 1 : 10. The oil also contained 0.5 - 1% (by volume) of the drying oil as a dispersing agent. Further heating was applied to gradually regain the temperature of 150-155 C after which the resin beads slurry was cooled down.

Stage ii). Separation was as for sample 1A.

Stage iii) The resin beads were dried from most of ethylene glycol and residual oil in vacuum 1 - 5 mm Hg and the temperature 120-130 C. The dried resin bead yield was 30- 40%. Alternatively the resin could be washed repeatedly with hot water (cascade washing). Stage iv). Vacuum dried or hot water washed resin was carbonised by heating from room temperature to 800 C at ramp 3 C/min in the carbon dioxide flow and held at 800 C for 30 min. After cooling down the carbonised material was classified to different particle size fractions by sieving or another appropriate technique. Stage vi) Activation. Sample of 100 g of dried to constant weight carbonised beads (fraction 250/500 um) was placed into a stainless steel mesh tray lined with silica cloth. The tray with carbon was heated in the tube furnace from room temperature to 900 C at ramp 6 C/min in carbon dioxide flow and kept at 900 C for 7 hrs in carbon dioxide flow and cooled back to room temperature in carbon dioxide flow to yield 60 g of activated carbon (40% weight loss).

The BET surface area, micropore, mesopore and macropore volumes of these four carbons were estimated from nitrogen adsorption/desorption isotherms as measured on a Micromeritics Gemini instrument. 5 Each of carbons 1A to 1D (in the form of beads of 0.25 - 0.50mm diameter) was mixed with a set proportion of natural menthol crystals by continually agitating in a sealed vessel maintained at 60°C for a period of six hours to prepare a 'mentholated carbon'. Thus, for example, a 20% mentholated carbon refers to 2.0 g menthol having been added to 10.0 g carbon. Cigarette filters were then prepared incorporating a known weight of these 0 mentholated carbons and the assembled filter cigarettes smoked under ISO conditions, as is well known. The menthol yields (of filter cigarettes incorporating 100 mg of mentholated carbon) and mean vapour phase retention (of filter cigarettes incorporating 60 mg of mentholated carbon) were measured. Mean vapour phase retention is expressed as the arithmetic mean reduction of 12 major volatile compounds found in cigarette smoke by the 5 carbon filtered cigarette as compared to an equivalent cigarette with no carbon in the filter.

The mean vapour phase retention of filter cigarettes containing 60mg of the un- mentholated carbon ("as received") was also measured for comparative purposes. The results obtained are given in table 1 below.

Table 1

It can be seen that the use of calcium catalyzed activation in samples 1A and 1B did indeed inhibit micropore formation. It can also been seen that, consistent with WO 2004/04757, a low micropore volume (< 0.30 cc/g) and a high mesopore volume (≥0.25 cc/g) were both required to give simultaneous release of menthol and reasonable levels of vapour phase retention.

Example 2

A further three samples of calcium modified activated carbon were prepared, labeled 2A, 2B and 2C. Samples 2A and 2B were manufactured using similar procedures to those used to prepare samples 1A and 1B, whilst for sample 2C the calcium was added to the pyrolyzed beads prior to the activation stage rather than at the bead formation stage.

Sample 2A

Stage vii) High temperature treatment. Sample 1B (before demineralization) was heated in helium atmosphere at ramp 10 C/min to 1500 C and kept at this temperature for 30 min. After cooling down the carbon' was demineralised (diluted HCI followed by demineralised water) and dried as 1 B.

Sample 2B.

Staged i) - iii) were similar to 1 B. Stage iv) Carbonisation. Sample of the resin dried in vacuum (200 g) was placed into a stainless steel mesh tray lined with silica cloth. The tray with resin was heated in the tube furnace from room temperature to 720 C at ramp 3 C/min in the carbon dioxide flow 300 ml/min and the residence at 720 C for 10 min. After cooling down the carbonised bead material (104.0 g, 52%) was classified to different particle size fractions by sieving or another appropriate technique.

Stage vi) Activation. Sample of carbonised beads (100.0 g) was placed into a stainless steel mesh tray lined with silica cloth. The tray with beds was heated in the tube furnace from room temperature to 800 C at ramp 6 C/min in the carbon dioxide flow 300 ml/min and the residence at 800 C for 80 min. After cooling down the activated carbon bead material (57.0 g - 43% burn-off) was demineralised as B and dried.

Stage vii). High temperature treatment. Demineralised and dried activated carbon was heated in helium atmosphere at ramp 10 C/min to 1500 C, kept at this temperature for 30 min. and cooled down. W

Sample 2e.—

Stages i) - iv) were carried out as for the Sample 1D.

Stage v) Impregnation. 1 kg of carbonised material from iv) (particle size fraction 0.25 - 0.5 mm) was thoroughly mixed at room temperature with 3 kg of water solution containing 1 mole of calcium acetate and left overnight for equilibration. The resulting slurry was maintained at 50 C under reduced pressure or in the stream of dry air to evaporate water until constant weight.

Stage vi) Activation. 150 g of dried to constant weight impregnated carbon was placed into a stainless steel mesh tray lined with silica cloth. The tray with carbon was heated in the tube furnace from room temperature to 800 C at ramp 3 C/min in carbon dioxide flow and kept at 800 C for 30 min in carbon dioxide flow and cooled back to room temperature in carbon dioxide flow to yield 126 g of activated carbon - calcium carbonate mix (16% weight loss). The carbon was given the code 6C though it is clear that total weight loss is a sum of hydrated calcium acetate transformation into calcium carbonate, strongly adsorbed water desorption and activation burn-off itself.

Activated carbon 2C was washed from calcium carbonate (demineralised) with dilute hydrochloric acid followed by demineralised water until negative chloride probe (with silver nitrate solution) was achieved and dried at 105 C to constant weight.

The results obtained are given in Table 2 below (n.b. in this instance, the pore volumes were measured using a icromeritics Tristar instrument):

Table 2

It can be seen that sample 2C, in which calcium was added immediately prior to the activation stage, gave a remarkable increase in menthol release combined with reduced loss in vapour phase retention as compared to similar carbons where calcium was added at an earlier stage. The micropore and mesopore volumes of sample 2C are similar to those of the other samples, implying that factors in addition to pore size distribution characteristics may account for this remarkable performance improvement when used in a mentholated cigarette application. Example 3

A further three samples of calcium modified activated carbon were prepared, labeled 3A, 3B and 3C, for all of which calcium was added to the pyrolyzed beads immediately prior to the activation stage. Samples 3A and 3B differed in the ratios of ingredients used at the resin formation stage that are known to affect meso- and macropore characteristic, such that 3A would be of lower total meso- and macropore volume than 3B. Samples 3B and 3C differed in the nature of the oxidizing gas used during the activation phase (3B used carbon dioxide, which is the standard medium employed for all other samples, whilst 3C used steam).

Sample 3A.

Stages i) - iv) were carried out as for the Sample 1 C.

Stage v). Impregnation. 1 kg of carbonised material from iv) (particle size fraction 0.25 - 0.5 mm) was thoroughly mixed at room temperature with 1.3 kg of water solution containing 1 mole of calcium acetate and left overnight for equilibration. The resulting slurry was maintained at 50 C under reduced pressure or in the stream of dry air or in any other way to evaporate water until constant weight.

Stage vi). Activation. was carried out in the same way as for the sample 2C with subsequent similar demineralisation.

Sample 3B. Replica of the Sample 2B. Sample 3C.

Stages i) - v) were carried out as for the Samples 2C and 3B.

Stage vi) Sample of impregnated and dried carbonised beads (150 g) was placed into a stainless steel mesh tray lined with silica cloth. The tray with carbon was heated in the tube furnace from room temperature to 400 C at ramp 3 C/min in carbon dioxide flow and from 400 C to 720 C - in a water steam flow of 5g/min, kept at 720 C for 36 min in water steam flow, cooled down to 400 C when the gas flow was switched back from steam to carbon dioxide and cooled back to room temperature in carbon dioxide flow to yield 124.5 g of activated carbon - calcium carbonate mix (17% weight loss). The carbon was given the code 17C though it is clear that total weight loss is a sum of hydrated calcium acetate transformation into calcium carbonate, strongly adsorbed water desorption and activation burn-off itself. Activated carbon 3C was washed from calcium carbonate (demineralised) with dilute hydrochloric acid followed by demineralised water until negative chloride probe (with silver nitrate solution) was achieved and dried at 105 C to constant weight.

The results obtained are given in Table 3 below (n.b. the quoted pore volumes refer to 5 those measured using a Micromeritics Gemini instrument and the level of menthol applied to the carbon prior to smoking was lower at 15% than the 20% levels used in comparative examples 1 and 2). When all other factors are kept constant, it will be appreciated that a lower level of menthol application leads to lower levels of menthol release on smoking, but to higher levels of mean VP reduction.

Table 3

It can be seen that remarkable levels of menthol release and simultaneous high levels of 15 VP reduction continue to be observed from these carbons where calcium was added to the pyrolyzed carbon prior to activation. Furthermore, the performance benefits in cigarette applications continue to be observed over a range of mesopore levels and also using different oxidizing gases at the activation stage (although higher mesopore levels and carbon dioxide activation are preferred as these give rise to higher levels of menthol 20 release on smoking). Lower levels of 'burn-off' are preferred during the activation stage, typically corresponding to 10-20% weight loss, although burn-off could be as high as 50%.

Example 4

A further three samples of calcium modified activated carbon were prepared, labeled 4A, 25 4B and 4C, for all of which calcium was added to the pyrolyzed beads immediately prior to the activation stage. The samples differed in the molar ratio of calcium acetate applied to the carbonized beads, namely 0.75, 1 .0 and 1 .25 mol Ca / kg for samples 4A, 4B and 4C respectively.

30 Sample 4A-4C.

Sample 4B is in all preparation details a replica of Samples 2C and 3B. Samples 4A and 4C are very similar to 4B save one parameter on stage v) (impregnation). For 4A 3 kg of water solution of 0.75 moles of calcium acetate per 1 kg of carbonised beads was usedT For 4C 1.25 moles of calcium acetate in 3 kg of water solution was used per 1 kg of carbonised beads.

The results obtained are given in Table 4 below (n.b. pore volumes measured using Micromeritics Gemini instrument).

Table 4

10 It can be seen that calcium acetate loadings greater than 1.0 mol Ca / kg pyrolyzed carbon are preferred, although lower levels still give reasonable performance in cigarette applications. It is unclear why measured micropore volumes from these samples appear to be higher than those of previous similar samples.

15 Discussion

It is evident from Examples 1 to 4 that calcium catalyzed activated carbons derived from phenolic resins are highly effective when used in filters for menthol cigarettes. These benefits are significantly enhanced when calcium is added to the pyrolyzed resin prior to activation rather than at the resin formation stage or immediately prior to pyrolysis.

20

Example 5

A 'triple granular' cigarette filters was formed by methods well known in the art. Each filter comprises a non-wrapped cellulose acetate downstream filtering plug and a non-wrapped cellulose acetate upstream filter plug spaced longitudinally upstream therefrom, with a filter 25 wrapper engaging around and joining the spaced plugs to define a cavity therebetween.

100 mg of mentholated carbon of Example 2C is packed between two cellulose acetate filter segments within the cavity. These filters may be formed by methods well known in the art and attached to tobacco rods to form filter cigarettes, also by methods known in the art.

30

Claims

1. A Group II metal modified activated carbon derived from a phenolic resin.

2. An activated carbon produced by a process comprising a step of activation of carbon in which a Group II metal catalyst is added to the carbon immediately prior to, or during, activation.

3. An activated carbon according to claim 2 wherein the carbon is derived from a phenolic resin (e.g. is a phenolic resin based carbon) or is derived from a styrene divinyl benzene polymer.

4. An activated carbon according to any preceding claim wherein the Group II metal is calcium.

5. An activated carbon according to any preceding claim wherein the Group II metal is calcium in the form of calcium acetate.

6. An activated carbon according to any preceding claim wherein the Group II metal is added to carbon which has been carbonised (for example by pyrolysis) prior to activation.

7. An activated carbon according to any preceding claim wherein the activation uses an oxidising atmosphere which includes carbon dioxide.

8. An activated carbon according to any preceding claim wherein the activation is at a temperature of 800°C or above.

9. An activated carbon according to any preceding claim having a BET surface area of 800 m²/g or less, more preferably 799 m²/g or less.

10. An activated carbon according to any preceding claim including micropores of under 2 nm pore diameter which provide a micropore volume of up to 0.38 cm³/g (N₂), for example up to 0.26 cm³/g (N₂).

11. An activated carbon according to any preceding claim including carbon mesopores of 2 to 50 nm pore diameter which provide a mesopore volume of at least 0.19 cm³/g (N₂).

12. An activated carbon produced by a process comprising a step of activation of carbon in which a Group II metal catalyst is added to the carbon immediately prior to, or during, activation, wherein the carbon is derived from a phenolic resin (e.g. is a pnenolic resin based carbon) or is derived from a styrene divinyl benzene polymer.

13. A Group II metal modified activated carbon derived from a phenolic resin, wherein the Group II metal is calcium in the form of calcium acetate.

14. A tobacco smoke filter or filter element including an activated carbon according to any preceding claim.

15. A tobacco smoke filter or filter according to claim 14 further comprising a flavouring agent.

16. A filter cigarette including activated carbon according to any of claims 1 to 13.

17. A filter cigarette including a tobacco smoke filter or filter element according to claim 14 or claim 15.