WO2012032349A1

WO2012032349A1 - Activated carbon material

Info

Publication number: WO2012032349A1
Application number: PCT/GB2011/051679
Authority: WO
Inventors: Peter Branton; An-hui LU; Wen-Cu Li
Original assignee: British American Tobacco (Investments) Limited
Priority date: 2010-09-10
Filing date: 2011-09-08
Publication date: 2012-03-15
Also published as: CN102398903A; AR082949A1

Abstract

The present invention provides a method of producing activated carbon from lignocellulosic material such as coconut shell. The method comprises the removal of accessible glucose units from the cellulose polysaccharides of the material prior to activation. The activated carbon material produced according to the method of the invention has a pore structure that is rich in micropores and mesopores. The material is suitable for use in tobacco smoke filtration, for example, in smoking article filters.

Description

Activated Carbon Material

Field of the Invention

The invention relates to a process for obtaining high surface area activated carbon material. More particularly, the invention provides a process for preparing activated carbon which has a pore structure that includes both mesopores and micropores.

Description

Activated carbon materials have become widely used as versatile adsorbents owing to their large surface area, microporous structure, and high degree of surface reactivity. In particular, these materials are especially effective in the adsorption of organic and inorganic compounds due to the high capacity of these molecules to bind to carbon. Activated carbons are commonly produced from materials including coconut shell, wood powder, peat, bone, coal tar, resins and related polymers. Coconut shell is particularly attractive as a raw material for the production of activated carbon because it is cheap and readily available, and is also environmentally sustainable. Furthermore, it is possible to produce from coconut shell activated carbon material which is highly pure and has a high surface area.

Coconut shell based activated carbon has been used in a wide variety of processes, and is extensively used in the process of refining and bleaching of vegetable oils and chemical solutions, water and air purification, recovery of solvents, recovery of gold etc. It is used in a wide range of gas filters, including cigarette filters, and gas masks.

The performance and suitability of activated carbon material as an adsorbent in different environments is determined by various physical properties of the material, including the shape and size of the particles, the pore size, the surface area of the material, and so on. These various parameters may be controlled by manipulating the process and conditions by which the activated carbon is produced. Generally, the larger the surface area of a porous material, the greater is the adsorption capacity of the material. However, as the surface area of the material is increased, the density and the structural integrity are reduced. Furthermore, while the surface area of a material may be increased by increasing the number of pores and making the pores smaller, as the size of the pores approaches the size of the target molecule, it is less likely that the target molecules will enter the pores and adsorb to the material. This is particularly true if the material being filtered has a high flow rate relative to the activated carbon material. In the present patent specification, and in accordance with nomenclature used by those skilled in the art, pores in an adsorbent material that are less than 2nm in diameter are called "micropores", and pores having diameters of between 2nm and 50nm are called "mesopores". Pores are referred to as "macropores" if the diameter exceeds 50nm. Pores having diameters greater than 500nm do not usually contribute significantly to the adsorbency of porous materials.

It is well known to incorporate porous carbon materials into smoking articles and smoke filters in order to reduce the level of certain components of the smoke. The distribution of pore sizes in a porous carbon material affects the adsorption characteristics, and it has been found that activated carbon material that is rich in micropores and mesopores is optimal for the filtration of unwanted substances from the vapour phase of tobacco smoke.

Coconut shell is widely used as a raw material in the production of activated carbon for use in smoking article filters. However, conventionally activated carbon produced from coconut shell can have the disadvantage of inconsistency or sub- optimal reproducibility and tends to have a pore structure which is exclusively microporous. For this reason, synthetic carbons are frequently used that are produced from carbonised polymers and synthetic resins. These materials have vastly superior reproducibility, but are far more expensive than coconut carbon. An aim of the present invention is to provide a method of producing an activated carbon material which is both microporous and mesoporous, and thus capable of the efficient filtration of tobacco smoke. A further aim of the present invention is to provide a method of producing an activated carbon material suitable for use in the filter of a smoking article such as a cigarette.

A yet further aim of the present invention is to provide a method of producing an activated carbon material which is based on inexpensive and readily available raw materials, a minimal number of processing steps, and that can be performed using existing or uncomplicated manufacturing processes and apparatus.

Statements of the Invention

According to a first aspect of the present invention, a method is provided for the production of activated carbon comprising cellulose digestion of the raw material.

Coconut shell is primarily composed of carbohydrates including cellulose, and it has surprisingly been found that when coconut shell material that has been treated to promote cellulose digestion is subsequently activated, an activated carbon material is generated which has a proportion of mesopores and micropores, resulting in a porous structure which offers improved filtration of tobacco smoke vapour phase toxicants compared to microporous carbon. This activated carbon is also of a more reproducible quality than has previously been possible with activated carbons produced from coconut shell.

Cellulose digestion may comprise the removal of glucose units from the raw material. For example, this may involve the removal or breakdown of glucose units which comprise the cellulose polysaccharides from which the raw material is composed.

The method may comprise fermentation of the raw material, which may be performed at a temperature of between 20 and 35°C, and may be for a period of between 3 and 7 days. Alternatively, the method may comprise the incubation of the raw material with a cellulase enzyme, which may be performed at a temperature of between 50 and 65°C. The method may comprise the use of coconut shell as the raw material.

Preferably the material is not carbonised prior to activation.

The method may comprise the production of activated carbon material having a pore structure that includes micropores and mesopores.

According to a second aspect of the present invention, an activated carbon material is provided that is obtained or obtainable by a method comprising cellulose digestion of the raw material.

According to a third aspect of the invention, a filter for a smoking article is provided comprising activated carbon material that is obtained or obtainable by a method comprising cellulose digestion of the raw material. According to a fourth aspect of the invention, a smoking article is provided comprising activated carbon material that is obtained or obtainable by a method comprising the cellulose digestion of the raw material.

As used herein, the term "smoking article" includes smokeable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes.

Description of the Drawing

For a fuller understanding of the invention, reference is made to the accompanying Figures in which:

Figure 1 is a diagram outlining the invention.

Figure 2 illustrates a filter cigarette which has been partially unwrapped comprising a filter according to an embodiment of the invention. The Figure is not to scale. Figure 3 shows the sorption isotherms and BJH plots of two porous carbon samples, Fl and F2, produced as described in Examples 1 and 2.

Figure 4 shows the sorption isotherms and BJH plots of porous carbon samples CI to C6 produced as described in Example 4.

Detailed Description

The present invention relates to a method of producing activated carbon, the method comprising cellulose digestion of the raw material. Introduction and definitions

Figure 1 illustrates the disclosed method of producing activated carbon material that is microporous and mesoporous from coconut shell and similar raw materials.

Cellulose is a major structural component of many plants. It is a polysaccharide polymer comprising linear chains of glucose monosaccharide units.

Cellulosic materials 1 including coconut shell are composed of lignin, hemicellulose, and cellulose and are commonly referred to as lignocellulosic materials. One of the primary functions of lignin is to provide structural support. Lignin encloses the other components of the material, such as cellulose and hemicellulose molecules, providing strength to the material (see Figure 1A).

Although cellulose consists of long chains of glucose molecules 2, the encapsulation by lignin makes the glucose inaccessible. Generally, in order to produce glucose from lignocellulosic material, the material is hydrolysed, for example by means of acid, enzymes, or thermochemical processes. However, processes according to embodiments of the present invention do not comprise a hydrolysis step of extracting glucose from the lignocellulosic material. Consequently, the vast majority of the glucose comprising the cellulose of the cellulosic material is not accessible. This glucose remains bound within the lignocellulose as a structural component of the material. However, after pulverisation of the cellulosic material (step I in Figure 1), in which the material is randomly broken down into smaller fragments, the resulting particles have cellulose, and in particular glucose units 3, present at or near the surface of the material (see Figure IB). These glucose units are therefore accessible to be removed from the material. Removal of glucose units in this way (step II) results in the formation of microscopic pits or cavities in the surface of the material 4 (see Figure 1C). The size of these pits may be equivalent to only one or a small number of glucose units. The diameter of a glucose molecule is approximately 0.5nm and the pits will therefore have a size of greater than around 0.5nm to 5nm.

The skilled person will recognise that this process is analogous to the use of pore formers to generate pits during the production of synthetic resins for conversion into activated carbon materials. During the subsequent activation of the material (step III), existing microscopic pits, pores, and cavities in the material are opened and enlarged to form micropores 5 and mesopores 6 in the material (see Figure ID).

In light of the above, 'cellulose digestion' as used herein, refers to any process which results in the removal of glucose units from cellulose. In particular, 'cellulose digestion' encompasses the removal of glucose by fermentation processes, by cellulase enzymes, or by other methods which result in the removal of glucose from cellulose. Raw Material

In one embodiment of the invention, the cellulosic material for use in the method is coconut shell. Other suitable materials include other nuts and nut shells, such as the shells of pistachio nuts and walnuts, and other fruit waste material, such as peach or apricot stones, palm kernels, or olive waste. Other organic matter, including untreated wheat straw, and wood material, is also suitable for use in the invention. In general, any organic matter comprising a large proportion of cellulosic material will be suitable for use in the invention. Coconut shell is preferred as a raw material because it can be used to produce a material having a robust structure with a very large surface area. It is also widely available and cheap, being essentially a waste product. Pulverisation

In one embodiment of the invention the cellulosic material is pulverised prior to fermentation and activation. By reducing the size of the fragments of cellulosic material in this way, a greater surface area is accessible for cellulose digestion. More specifically, the surface of the material will comprise cellulose molecules, from which glucose units may be removed.

The skilled person will be aware that different methods of pulverisation will be suitable for use in connection with different cellulosic materials. In general, pulverisation may be performed by any suitable method, which may include grinding, milling, pounding, compaction, or any other means of reducing solid matter into small fragments. With regards coconut shell raw material, the preferred method of pulverisation are pounding and cutting methods.

Following pulverisation, particles having an optimal size are selected. Size selection is by any suitable method, for example, by sieving of the pulverised material.

The preferred mean particle size of the pulverised material is in the range of between ΙΟμπι and 5000μπι, and preferably between 50μπι and 1500μπι. Most preferably the particle size is between 200μπι and 900μπι.

Cellulase Treatment

Cellulase refers to a class of enzymes that catalyze the cellulolysis (or hydrolysis) of cellulose and the removal of glucose units. Several different kinds of cellulases are known, which differ structurally and mechanistically. A number of different mechanisms of cellulolysis are known and may be catalysed by different cellulases. These include exo- and endo-cellulases, which catalyse the removal of glucose units from the ends of cellulose chains, or the internal cleavage of cellulose chains, respectively. A mixture of different cellulase enzymes may be used.

The preferred cellulase for use in the invention is JN-100 Acid Cellulase. When using this enzyme, the cellulase treatment is generally performed at a temperature of between 40°C and 70°C, more preferably between 50°C and 65°C, and most preferably the incubation is performed at a temperature of about 60°C. The pH may also be important, and the incubation is performed at a pH of between 4.0 and 6.0, and preferable at a pH of between 4.5 and 5.0.

Fermentation

Fermentation describes a chemical process in which organic compounds, and in particular sugars, are broken down in the absence of oxygen to yield alcohols and carbon dioxide. The fermentation of glucose into carbon dioxide and ethanol is a well-known process performed by both yeast and anaerobic bacteria.

Cellulosic materials such as coconut shell are composed of glucose molecules, and as such they can potentially be fermented into ethanol for use as an alternative fuel. The fermentation process of the present invention may be performed by any anaerobic organism. Yeast in particular is widely used to ferment glucose, for example, in the production of bread, beer, and ethanol biofuels. In particular, Saccharomyces yeasts are used extensively in industry, and are suitable for use in the claimed method. Generally, any yeast that is capable of fermenting glucose may be used in the claimed method. The preferred yeast is Saccharomyces cerevisiae.

The amount of yeast used is generally between about 2% and 40% by weight, and preferably, the amount of yeast used is between 5% and 20% by weight.

Recently, bacteria have drawn special attention from researchers because of their speed of fermentation. In general, bacteria can ferment in minutes, whereas the same process would take hours for yeast. Any bacteria which is capable of fermenting glucose is suitable for use in the claimed method. Since fermentation is an anaerobic process, the process obviously must be performed in the absence of oxygen. In a typical arrangement, the yeast is firstly cultured in a nutrient solution, and then mixed with the cellulosic material. This mixture is then incubated at the appropriate fermentation temperature, and is maintained at that temperature for the duration of the fermentation process.

Any suitable nutrient solution may be used to culture the yeast. In particular, preferred nutrient solutions include malt extract medium, potato medium, and / or glucose medium.

In the case of yeast, the fermentation process is generally performed at a

temperature of between 15°C and 40°C, more preferably between 20°C and 35°C. Most preferably the fermentation is performed at a temperature of about 25°C. The pH at which the fermentation process is performed may be important.

Preferably, at the start of the fermentation process, the acidity of the reaction medium may be between pH4 and pH4.5, and the preferred starting pH may be around pH4.3. During the fermentation process the acidity of the reaction medium may increase to between pH3.3 and pH4.0. Preferably the pH at the end of the fermentation process may be around pH3.6.

Duration of Treatment

Since the cellulose present in the cellulosic material is largely inaccessible to digestion, the digestion process can only proceed until all of the available glucose molecules have been removed. As a result, the digestion process will reach a natural conclusion regardless of the duration of incubation, amount of yeast or enzyme added, incubation temperature, etc. Therefore there is no value in incubating the material for longer than is sufficient to remove all of the available glucose. On the other hand, it is important that as much of the glucose as possible is removed as this will ultimately equate to the mesoporosity of the activated material. In general, when yeast is used, the cellulosic material may be fermented for between 2 and 12 days, and is preferably fermented for between 3 and 7 days. Most preferably the material is fermented for about 3 days.

When cellulase is used, the cellulosic material may be treated for between 1 and 14 days, and is preferably treated for between 2 and 10 days. Most preferably the material is treated for between about 3 and 6 days.

Washing

Following the cellulose digestion process, the material may be washed to remove any residual yeast or enzyme and any other unwanted material such as glucose, or the products of glucose fermentation. Furthermore, traces of yeast, enzyme, or other unwanted matter could interfere with the carbonisation or activation of the material. Preferably water is used to wash the material.

The material may be washed by any suitable method. A typical washing procedure involves mixing the material with distilled water, allowing the material to settle, and then removing the water by decanting. This washing process may be repeated, for example, for between 5 and 12 cycles, and preferably for about 8 cycles.

After washing, the material may be dried by any suitable method. Preferably the material is dried at 80°C overnight.

After washing, the mass of the material may be reduced by up to 10%. Typically, the mass may be reduced by between about 2% and 4%.

The colour of the digested coconut shell may be lighter than that of the starting material.

Carbonisation

Carbonisation describes the procedure in which the material is pyrolysed in the absence of air to remove most of the elements other than carbon as volatile compounds. An advantage of the claimed method is that the material does not require

carbonisation.

Under some circumstances, however, it may be preferable for the material to be carbonised. Carbonisation may be achieved using any suitable method, and such methods will be familiar to the skilled person. Suitable methods include the pit method, the drum method, and destructive distillation. Carbonisation methods which utilise H₃P0₄ or ZnCl₂ increase the proportion of micropores in the material, and also increase the proportion of carbon in the material. However, this process may also increase the proportion of undesirable mineral compounds in the carbon material. Such mineral compounds may be removed by an intensive washing procedure.

Activation

Activation of the carbon material is the name given to the process in which existing pores and pits in the material are opened and enlarged to yield a material with a large surface area. In the case of the claimed method, cavities, pits and pores resulting from the cellulose digestion and the removal of glucose molecules from cellulose are expanded during the activation process to provide a material that is rich in micropores and mesopores.

Without wishing to be restricted by any theory, it is thought that that the cavities and pits in the surface of the material formed by the cellulose digestion and removal of glucose, are expanded during the activation process to form mesopores.

Consequently, the mesoporosity of the material may be regulated by regulating the degree of cellulose digestion of the cellulosic material.

The material may be activated by any means, and the skilled person would be aware that either physical or chemical means may be suitable. Preferably the material is activated by physical means, and most preferably the material is activated using nitrogen and steam, or alternatively, C0₂. In one embodiment of the invention, the material is activated by reaction with steam under controlled nitrogen atmosphere in a kiln such as a rotary kiln.

The temperature is important during the activation process. If the temperature is too low, the reaction becomes slow and is uneconomical. On the other hand, if the temperature is too high, the reaction becomes diffusion controlled and results in loss of the material.

Activation of the material may be performed at a temperature of between 700°C and 1100°C, and preferably activation is performed at a temperature of between 800°C and 1000°C. Most preferably, the material is activated at about 850°C.

The activation process is preferably carried out for between 30 minutes and 4 hours. Most preferably, the material is activated for 1 hour. In an alternative embodiment, the material is activated by reaction with carbon dioxide. In this case, activation of the material may be performed at a temperature of between 700°C and 1100°C, and preferably activation is performed at a temperature of between 800°C and 1000°C. Most preferably, the material is activated at about 900°C.

The activation process is preferably carried out for between 1 and 4 hours. Most preferably, the material is activated for 2 hours.

Chemical activation methods may be used. For example, KOH or ZnCl₂ may be used to activate the material. However, chemical activation methods may result in the deposition of chemicals in the carbon material, which may be undesirable. Such chemicals may be removed using an intensive washing procedure.

Particle She

Following activation, the particle size of the material is reduced by between 10% and 40%, and preferably the particle size of the material is reduced by between 20% and 30%. Material produced according to the method of the invention will have particles that are small enough to provide a large surface area for smoke filtration. The particles of activated carbon material should, however, be large enough that the smoke drawn through the filter is not restricted. It is also important that the particles are large enough that they can't become entrained in the smoke and drawn through the filter to be inhaled by the smoker. The carbon is not harmful, but inhaling fragments would nevertheless be unpleasant for the user.

On the other hand, if the fragments are too large, then the surface area to volume ratio of the fragments will be such that the filtration efficiency would be reduced.

Taking these factors into account, activated carbon produced by the claimed method should preferably have a particle size in the range of between ΙΟμπι and 4000μπι. Preferably the mean particle size is between 50μπι and 2000μπι, and more preferably between ΙΟΟμπι and ΙΟΟΟμπι. Most preferably, the particles of activated carbon material have a mean size of between 150μπι and 550μπι.

Surface Area

The surface areas of activated carbon materials are estimated by measuring the variation of the volume of nitrogen adsorbed by the material in relation to the partial pressure of nitrogen at a constant temperature. Analysis of the results by mathematical models originated by Brunauer, Emmett and Teller results in a value known as the BET surface area. The BET surface area of the activated carbon materials produced by the method of the invention is at least 800m²/g, preferably at least 900m²/g, and desirably at least 1000, 1100, 1150, 1200, 1250, 1300, or 1350m²/g. Typical values for BET surface area of carbon materials produced by the method of the invention are up to about 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1400, 1500, 1600, 1700, 1800, or

1900m²/g. Porous carbon materials with BET surface areas of between 1000m²/g and 1500m²/g are preferred, and material with surface areas of between 1200m²/g and 1400m²/g are most preferred. Porosity

The relative volumes of micropores, mesopores and macropores in an activated carbon material can be estimated using well-known nitrogen adsorption and mercury porosimetry techniques. Mercury porosimetry can be used to estimate the volume of mesopores and macropores. Nitrogen adsorption can be used to estimate the volumes of micropores and mesopores, using the so-called BJH mathematical model. However, since the theoretical bases for the estimations are different, the values obtained by the two methods cannot be compared directly with each other. The method of the invention yields an activated carbon material having a pore structure that includes mesopores and micropores. In the preferred carbon materials of the present invention, at least 20% but desirably no more than 65% of the pore volume (as estimated by nitrogen adsorption) is in mesopores. Typical minimum values for the volume of mesopores as a percentage of the combined micropore and mesopore volumes of the carbon materials of the invention are 25%, 35%, or 45%. Typical maximum values for such volumes are 55%, 60%, or 65%. Preferably the mesopore volume of the carbon materials of the invention is in the range of between 25% and 55% of the combined mesopore and micropore volume. The porous carbon materials of the invention preferably have a pore volume (as estimated by nitrogen adsorption) of at least 0.4cm³/g, and desirably at least 0.5, 0.6, 0.7, 0.8, or 0.9cm³/g. Carbon materials with pore volumes of at least 0.5cm³/g are particularly useful as an adsorbent for tobacco smoke. Carbon materials with pore volumes significantly higher than the preferred values may be low in density, and are therefore less easy to handle in cigarette production equipment. Such carbon materials are less favourable for use in cigarettes or smoke filters for that reason.

Density

The pore structure and density of activated carbon material are closely related. Generally, the greater the pore volume of the material, the lower is the density. Activated carbon materials produced by the method of the invention preferably have bulk densities greater than 0.25g/cm³, and preferably greater than 0.3g/cm³. The activated carbon material may have a bulk density of up to 0.7g/cm³, 0.6g/cm³, or 0.5g/ cm³.

The true density of the materials may be greater than 0.4g/ cm³, and preferably greater than 0.45g/ cm³. The activated carbon material may have a true density of up to 0.55g/cm³, 0.60g/cm³, or 0.65g/cm³. Incorporation of Activated Carbon Material into a Filter

Figure 2 shows a smoking article 7 comprising a filter 8.

The filter 8 is substantially cylindrical and has a mouth end 9 and smoking material end 10. The filter comprises three segments wherein the segments at the mouth end 11 and smoking material end 12 comprise plugs of filter material. The central filter segment comprises a cavity 13 which contains the activated carbon material of the invention.

The filter 8 is wrapped in a plugwrap 14 around its circumferential surface. The smoking article further comprises a cylindrical rod of smokeable material, in this case tobacco 15, aligned with the filter 8 such that the end of the tobacco rod 15 abuts the end of the filter 8. The tobacco rod is joined to the filter 8 by tipping paper 16 in a conventional manner. Clearly the more activated carbon is present in the filter, the greater is the capacity to filter smoke. It is important, however, that the filter does not contain too much activated carbon. For example, if the density at which activated carbon is packed into the filter is too great, then this may inhibit the smoke flow path and the smoker will experience an unsatisfactorily high resistance to draw. In addition, if the size of the cavity is increased and the amount of filter plug material is reduced to compensate, then particulate material may not be sufficiently filtered from the smoke. Activated carbon may be incorporated into the filter by a number of methods, in addition to the cavity filter embodiment shown in Figure 2. In some embodiments, the filter may comprise a Dalmatian-type filter, wherein the activated carbon is distributed throughout the filter material. In other embodiments, the filter may comprise a patch-type filter wherein the activated carbon material is attached to the plugwrap or tipping paper. In further embodiments, activated carbon may be incorporated into the filter in a combination or two or more of the above methods.

The amount of activated carbon that can be incorporated into the filter depends upon the type of filter. For example, filters for use with Super Slim cigarettes typically comprise between 12 and 20mg, and preferably 16mg of activated carbon.

Filters for use in connection with King Size cigarettes on the other hand, typically comprise between 20 and 80mg, preferably between 30 and 60mg. In general, the filter may comprise between 5mg and 120mg of activated carbon, and preferably comprises between lOmg and lOOmg of activated carbon. In the embodiment shown in Figure 1, the filter comprises 60mg of activated carbon material produced according to the method of the invention.

Above is described what are believed to be the preferred embodiments of the invention. However, those skilled in the art will recognise that changes and modifications may be made without departing from the scope of the invention.

Examples

Example 1

A first sample of activated carbon material, termed Fl, was prepared from coconut shell by a method comprising yeast fermentation of the raw material in accordance with the method of the invention.

Briefly, the coconut shell raw material was pulverized by pounding and cutting and then washed thoroughly in water to remove any contaminants and dust generated by the pulverization. Washing was performed with distilled water at room temperature. A total of 8 washing cycles were performed. The coconut shell material was not carbonized, and instead, the particulate coconut shell material was fermented by Saccharomyces cerevisiae yeast (obtained from Angel Yeast Company, China). The yeast was preincubated in a glucose medium comprising (per 100ml) glucose (lg), Na₂S0₄ (0.2g), NaH₂P0₄ (O.lg), KCl (0.05g), MgS0₄ ^«7H₂0 (0.05g), Fe( 0₃)₃ (O.lg), and distilled water.

Fermentation of the particulate coconut shell material was performed in water at 25°C for 3 days. At the start of the fermentation process the pH of the medium was 4.3. After fermentation, the pH was 3.6.

After fermentation, the material was dried and then activated at 850°C for lh under steam in a nitrogen atmosphere.

Approximately l Og of activated carbon material was produced.

Example 2

A second sample of activated carbon material, termed F2, was prepared by a method identical to that described above, the only difference being that the sample was activated using C0₂ at 900°C for 2h.

Example 3

Various physical properties of the samples of activated carbon material, Fl and F2 were assessed.

For reference purposes, a control material was used, which was Ecosorb CX. This is a standard commercially available activated carbon, produced from coconut shell and activated by steam. Ecosorb CX activated carbon material has a structure which is entirely microporous.

The synthetic condition and texture parameters of the samples of activated carbon material are given in Table 1. The parameters examined are the BET surface area (S_BET), the total pore volume (V_totd), the total pore volume present in micropores (V_micropores), the total pore volume present in pores that are not micropores (V_other), and the mean pore diameter (D_peak). Table 1

The sorption isotherms and BJH plots of the two porous carbon samples are given in Figure 3. The skilled person will understand from the sorption isotherms that the activated carbon materials Fl and F2 comprise, in addition to micropores, pores having mean diameters of 3.9nm and 3.8nm respectively. Thus, these materials have a structure that is both microporous and mesoporous and is therefore suitable for use in tobacco smoke filtration.

Example 4

A number of samples of activated carbon material, samples CI to C6, were prepared from coconut shell by a method comprising cellulase treatment of the raw material. Briefly, in the preparation of sample CI, the coconut shell raw material was pulverized by pounding and cutting and then washed thoroughly in water to remove any contaminants and dust generated by the pulverization. Washing was performed with distilled water at room temperature. A total of 8 washing cycles were performed.

The comminuted coconut shell material was classified and particles of between 1 and 5mm in size were selected. Approximately 3.0g of the coconut shell material was incubated with 30g of cellulase solution having a concentration of 10g/dm³. The incubation was conducted at 55°C for 6 days.

After cellulase treatment, the material was washed 5 times with distilled water, and then dried at 50°C.

Finally, the material was activated. In a first phase, the temperature was increased to 400°C at a rate of 3°C/ min. The material was incubated at this temperature for

60mins. In a second phase, the temperature was further increased to 800°C at a rate of 5°C/ min. Once the temperature had reached 800 °C, the nitrogen atmosphere was exchanged for a nitrogen/ steam atmosphere, and the material was incubated under these conditions for 60mins. The water dosing rate was 0.12ml/min.

Sample C2 was produced by the same process as sample CI, with the exception that prior to treatment with cellulase, the coconut material was microwaved at 90°C for 120mins. Sample C3 was produced by the same process as sample CI, with the exception that the cellulase treatment was conducted at 60°C for 3 days. The second phase of the activation of C3 was conducted at 850°C for 60mins.

Sample C4 was produced by the same process as sample C3, with the exception that the concentration of the cellulase solution was 20g/ dm³.

Sample C5 was produced by the same process as sample C3, with the exception that the cellulase treatment was conducted for 6 days. Sample C6 was produced by the same process as sample C3, with the exception that the cellulase treatment was conducted for 12 days.

Example 5 Various physical properties of the samples of activated carbon material CI to C6 were assessed.

The synthetic condition and texture parameters of the samples of activated carbon material are given in Table 2. In addition to the parameters given in Table 1, the surface area of the material present in micropores (S_mic) is also provided.

Table 2

The sorption isotherms and BJH plots of the two porous carbon samples are given in Figure 4.

The skilled person will understand from the sorption isotherms that the activated carbon materials CI to C6 comprise, in addition to micropores, pores having mean diameters ranging in size between 4.01nm and 8.82nm. Thus, these materials have a structure that is both microporous and mesoporous and is therefore suitable for use in tobacco smoke filtration.

Example 6

The carbon samples, having a structure that is both microporous and mesoporous, were assessed for their capacity to adsorb selected smoke vapour phase toxicants. Approximately 60mg of sample Fl or F2 was used in a cavity filter, similar to that shown in Figure 2. The filters were attached to tobacco rods and the resulting smoking articles were conditioned at 22°C and 60% relative humidity for 3 weeks prior to smoking.

Smoke analysis was performed in accordance with the International Organization for Standardization (ISO) method for smoke collection, which comprises a 35ml puff lasting two seconds taken every 60 seconds. The composition of the smoke drawn through each filter was then assessed.

A control smoking article comprising 60mg of Ecosorb CX was used. In addition, a smoking article comprising an identical filter having no adsorbent was also studied under the same conditions.

The results of these analyses are given in Table

Table 3

Example 7 The percentage reductions in various components of tobacco smoke are given in Table 4. The efficacy of the sample activated carbons Fl and F2 in reducing the levels of various organic molecules in tobacco smoke is assessed in comparison to both the Ecosorb CX and the empty filters.

Table 4

In conclusion, it can be seen that the fermentation of coconut raw material generates activated carbon material having a pore structure that is rich in micropores and mesopores. This pore structure correlates with the capacity of the material to remove undesirable organic molecules from tobacco smoke since both of the activated carbons Fl and F2 remove these chemicals with greater efficiency than the exclusively microporous Ecosorb CX.

Furthermore, the sample Fl, which was activated using steam has a greater mesoporosity than F2, and has an accordingly greater capacity to remove the organic chemicals.

In summary, the Examples indicate that the samples of activated carbon material produced according to the method of the invention provide porous carbon materials that are suitable for incorporation into tobacco smoke filters.

Claims

1. A method for the production of activated carbon comprising cellulose digestion of a cellulosic material.

2. A method according to claim 1 , wherein the digestion is performed in the cellulosic material in its raw state.

3. A method according to either of claim 1 or claim 2, wherein the cellulosic material is coconut shell.

4. A method according to any of the claims 1 to 3, wherein the cellulose digestion comprises the removal of glucose from the cellulosic material.

5. A method according to any of the claims 1 to 4, wherein the method comprises the incubation of the cellulosic material with cellulase.

6. A method according to claim 5, wherein the incubation is performed at a temperature of between 50°C and 65°C.

7. A method according to any of claims 1 to 4, wherein the method comprises fermentation of the cellulosic material.

8. A method according to claim 7, wherein the cellulosic material is fermented for between 3 and 7 days.

9. A method according to either of claims 7 or 8, wherein the fermentation process is performed at a temperature of between 20°C and 35°C.

10. A method according to any of claims 1 to 9, wherein the material is not carbonised prior to activation.

11. A method according to any of claims 1 to 10, wherein the material produced has a pore structure that includes mesopores and micropores.

12. An activated carbon material obtained or obtainable by a method as claimed in any of claims 1 to 11.

13. A filter for a smoking article comprising activated carbon material obtained or obtainable by a method as claimed in any of claims 1 to 11.

14. A smoking article comprising activated carbon material obtained or obtainable by a method as claimed in any of claims 1 to 11.