CA2330782A1

CA2330782A1 - An effective filtering device for removing hazardous chemicals in tobacco smoke

Info

Publication number: CA2330782A1
Application number: CA 2330782
Authority: CA
Inventors: Rupesh N. Pandey; Raj N. Pandey; Jai N. Pandey; Shamsuddin Ahmed
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-01-05
Filing date: 2001-01-05
Publication date: 2002-07-05

Abstract

The present invention provides an effective filtering device for removing hazardous chemicals in tobacco smoke that comprises of a small cylindrical shaped pellet (or disc), made from a mixture of microporous coconut shell carbon and naturally occurring clay material through a binding and compaction technique. The device is capable of substantially removing harmful constituents of mainstream tobacco smoke including carbon monoxide, tar, nicotine and a vast range of volatile and semi-volatile hydrocarbons, phenols and polycyclic aromatic hydrocarbons (PAHs) rendering the cigarette smoke safer

Description

FIELD OF THE INVENTIOr~
This invention relates generally to an innovative adsorbent filter for removing harmful components from tobacco smoke. Specifically, it relates to a novel, efficient cigarette s filter consisting of a small cylindrical shaped pellet (or disc), made from a mixture of microporous coconut shell carbon and naturally occurring clay material through a binding and compaction technique, that is capable of substantially removing harmful constituents of mainstream tobacco smoke including carbon monoxide, tar, nicotine and a vast range of volatile and semi-volatile hydrocarbons, phenols and polycyclic hydrocarbons 1o rendering the cigarette smoke safer.
BACKGROUND OF THE INVENTION
Tobacco smoke is a complex mixture of over 4,000 chemicals, more than fifty of which 15 are known to cause cancer, while many others are suspected to contribute to lung and cardiovascular diseases.
Tobacco - smoke related disease is recognized as one of the major causes of premature deaths in the world. About 1.2 billion people in the world smoke cigarettes on a regular 2o basis causing premature death of nearly four million of these users every year.
According to World Health Organization (WHO) if cigarette smoking is not controlled, the global annual death toll will reach 10 million by the year 2030.
The removal of harmful or potentially harmful components of the tobacco smoke has 2s been the subject of intensive research. It is true that there may not be such a thing as a totally safe cigarette. However, the risk can be significantly reduced by removing the most hazardous components in smoke. Several methods are being tried to reduce health hazards associated with tobacco smoking. These methods include trapping harmful constituents via passing the tobacco smoke through a filter or introducing in the tobacco 3o certain materials that are capable of reducing the harmful constituents.
Efforts are made to reduce such harmful components in tobacco smoke as carbon monoxide, hydrogen cyanide, formaldehyde, acroleiin, nicotine, phenols, tars, polycylic hydrocarbons and other toxic materials.
At present, commercial cigarette filters are mainly formed from cellulose acetate fibers.
The filter element is attached to the end of the cigarette rod to trap some of the particulate matters in the smoke and thus reduce the quantity of tar and nicotine in the mainstream smoke. Cigarettes are used by a smoker by lighting one end of the tobacco rod.
The smoker then receives the mainstream smoke into his/her mouth by drawing on the opposite end (that is, the filter end) of the cigarette.
In efforts to reduce harmful components of tobacco smoke, a number of substances have been applied to the cigarette filter. For example, U.S. Pat. No. 4,753,250 (1988) discloses a cigarette filter containing L-ascorbic acid (Vitamin C), that is capable of chemically trapping formaldehyde present in the cigarette smoke. U.S. Patent No.
4,414,988 (1983) describes a tobacco filter treated with an aqueous solution of ferric ion binding protoporphyrin structure for the purpose of removing carcinogenic substances in tobacco smoke. U.S. Patent No. 3,943,940 (1976) describes a filter containing potassium permanganate to remove nicotine from tobacco smoke.
2o U.S. Patent No. 5,671, 758 (1997) discloses a process of reducing carbon monoxide in cigarette smoke by applying materials such as vanadium pentoxide, molybdenum trioxide or rhodium oxides during the manufacturing process to the tobacco itself. To reduce harmful components, U.S. Patent No. 4,125,118 (1978) discusses incorporation of a catalytic amount of transition metal compound into the tobacco, and U.S.
Patent No.
3,782,393 (1974) discloses adding calcium sulfamate to the cigarette paper.
The application of these hazardous and reactive chemicals such as oxides of vanadium, molybdenum and rhodium is a subject of major concern when human health is considered.

There are other patents disclosing incorporation of materials such as carbon in the filter elements (U.S. Pat. Nos. 2, 881, 770 : 3, 353, 543 ; 3, 101, 723; 4,481, 958 (1984) ; and European Patent Application No. 532, 329). There are certain commercially available filters having particles, granules or threads of carbon dispersed within cellulose acetate 5 tow. Examples of such commercially available filters include SCS IV Dual Solid Charcoal Filter from America Filtrona Corp.; Triple Solid Charcoal Filter from FIL
International. Ltd. ; Triple Cavity Filter from Baumgartner ; and ACT from FIL
International Ltd.
to Cigarette filter elements which iincorporate carbon have the capability to trap a number of gaseous constituents present in the mainstream smoke, resulting in a lowering of harmful health effects of the smoke.
However, carbon containing filter elements, referred to above, have carbon dispersed in the cellulose acetate matrix. lfn such a design of filter, carbon is not so effective in trapping hydrocarbons and other harmful constituents of smoke, because bulk of the gas escapes through cellulose acetate tow without having contacted carbon particles.
There is another difficulty associated with a filter element that is designed using granular or particulate carbon, which arises from the presence of a large amount of loosely held fine dusts in carbon of above-mentioned forms. During the smoking process, a smoker is likely to inhale some of the dust. These dusts eventually would deposit in lungs and other vital organs of a smoker causing potential health risks.
There is yet another difficulty with the use of activated carbon in granular form, which arises from its relatively low packing density. The adsorption capacity of a microporous adsorbent, such as activated .carbon, generally increases with its increasing internal surface area and pore volume. However, it has been observed that the higher the surface area of microporous carbon, the lower is its packing density (that is, lesser weight of 3o carbon material can be packed into a fixed volume). This decrease of packing density is due partly to interparticle void spaces left while packing and partly to intraparticle voidage created as a result of development of micropores within the carbon network.
Thus, although there is usually an increase in adsorption capacity on a weight basis of microporous carbon with increase in the surface area, very little gain is made in the adsorption capacity on a volume basis. However, in the case of a cigarette, due to its length and volume constraints, it is desirable to consolidate the microporous carbon particles constituting the filter element by some means, so that it's (filter's) adsorption capacity on a volume basis is enhanced.
The presently known art of consolidating the microporous carbon particles into shaped to body is based mainly on the use of organic materials such as polyvinyl alcohol, phenolic resins, polyvinylidene chloride;, coal tar pitch and petroleum pitch. However, these organic binders pose the potential risk of releasing toxic and carcinogenic substances during the smoking process. For example, polyvinylidene chloride based binders pose the risk of releasing HCl and vinyl chloride, phenolic resins present the risk of releasing is phenols and formaldehyde, and pitches present the risk of releasing polycyclic aromatic hydrocarbons (PAH's), especially benzo-a-pyrene. Consequently, the organic materials based binders are not suitable for inclusion in cigarette filters due to potential health risks associated with these materials.
2o Indeed, one of the main obstacles in the development of technology using adsorbents for effectively decontaminating the cigarette smoke has been the choice of suitable materials for binding and compacting the adsorbent particles. While the materials of choice should provide adequate binding of the adsorbent particles, they must not add harmful contaminants to the smoke.
2s It is, therefore, desirable to provide a filter element incorporating carbon in such a form or configuration that it is highly effective in adsorbing and/or absorbing harmful components of smoke, prevents inhaling of carbon dusts by the smoker and is compact with relatively high packing density.

SUMMARY OF THE INVENTION
Accordingly, it is an object of tlhe present invention to overcome deficiencies in the prior art of tobacco smoke filter, such as indicated above.
s It is another object of the present invention to provide a cigarette filter element containing microporous carbon which will effectively reduce harmful components present in the mainstream tobacco smoke upon passing through such filter elements.
1o It is a further object of the present invention to provide a means of producing a cylindrical shaped carbon filter via mixing the microporous carbon particles with a suitable harmless binding material and molding the carbon-binder mix into a cylindrical shaped pellet.
is It is yet another object of the present invention to provide an improved means of substantially reducing or eliminating the most harmful components from the tobacco smoke.
It is yet a further object of the present invention to remove, in substantial quantities, 2o carbon monoxide, harmful gasf;ous hydrocarbon constituents, tars and nicotine from the cigarette smoke.
Other objects and advantages of the present invention will become apparent from the accompanying description and examples.
2s BRIEF DESCRIPTIONS OF DRAWINGS
FIGURES 1A , 1B and 1C are comparative gas chromatograms using flame ionization detector. Figure 1 A shows a ga.s chromatogram of mainstream smoke from a typical 3o cigarette (Player's Plain , manufactured by John Player & Sons).

FIGURE 1B shows a gas chromatogram of mainstream smoke from the same brand of cigarette but incorporating filter from a Player's Light brand cigarette.
FIGURE 1 C shows a gas chromatogram of mainstream smoke from the same brand of cigarette but incorporating carbon-pellet filter in accordance with the present invention.
FIGURE 2 shows mass selective detection gas chromatogram of some of the smoke components held by carbon pellet filter in accordance with the present invention as was determined by thermal desorption of the device used in this invention.
to DESCRITPION OF THE IN~~ENTION
This invention relates to an ei~cient cigarette filter consisting of a small cylindrical-shaped pellet (or disc) that is made from a mixture of microporous coconut shell carbon and naturally occurring clay material through a binding and compaction technique. The said filter element is capable of accomplishing a substantial reduction of harmful constituents of mainstream tobacco smoke including carbon monoxide, tar, nicotine and a vast range of volatile and semi-volatile hydrocarbons, phenols and polycylic hydrocarbons.
According to a preferred embodiment of this invention, there is provided a method of making a cylindrical pellet or diisc of microporous carbon that is suitable for use as a filter element in a cigarette, which comprises of the following steps:
a) crushing and milling; the granular carbon into fine particles;
b) preparing an aqueous dispersion of the naturally-occurring clay material suitable for binding the carbon particles according to this invention, by adding the clay material to water (25 mL to 50 mL water per gram of clay) and 3o thoroughly stirring the mix to form a uniform dispersion;

c) mixing dry or prewetted carbon particles of step (a) with the water dispersion of the binder of step (b) in appropriate proportions to make a slurry of carbon and binding agent.
d) drying of the carbon-binding agent slurry of step (c) to desired moisture content ranging from about 80% to about 125% based on the weight of carbon, by partially evaporating water while stirring;
e) consolidating carbon-binder mix of step (d) by gentle compression at ambient 1o temperature in a suitable pelleting device to provide a cylindrical pellet of microporous carbon; and f) drying the pellets in steps at a temperature of about 60°C to about 70°C and at temperature of about 120°C to about 140°('. in air atmosphere.
According to one preferred aspect of the above-described method of making cigarette filter comprising cylindrical carbon pellets, the said microporous carbon of step (a) is prepared from coconut shells by a two-stage process of carbonization and activation. The raw coconut shells were crushed to particle size of about 5-10 mm, washed with water 2o and dried at a temperature of about 110°C and then subjected to carbonization by heating to a temperature of about 600"(: to about 700°C in an inert atmosphere.
The char so produced was crushed, screened to 8-30 mesh size and then submitted to partial gasification with such an oxidising agent as carbon dioxide at a temperature of about 750°C to about 850°C. The resultant product was a granular microporous carbon having a surface area in the range 1000 - 1500 m2/g.
The source of microporous carlbon suited for the use in making tobacco filter element in accordance with this invention is an inexpensive and abundant coconut shell.
However, the present invention is not restricted to coconut shell as the only source of microporous 3o carbon. Microporous carbons derived from other inexpensive sources such as coal, coal coke, petroleum coke, wood and rice husks can also be used for making cylindrical carbon discs for using as tobacco filters.
According to another preferred aspect of the above described method of making tobacco 5 filter comprising carbon rod (pe;llet), the said binding agent is an inorganic clay material selected from a group consisting; of bentonite, attapulgite and sepiolite, or a combination thereof. The said clay materials used for the purpose of this invention are naturally occurring substances that are available in abundance and also are inexpensive.
to The binding and compaction of carbon particles according to the method of this invention binds together all carbon particles, including fine dusts, into one single cylindrical body.
This body is virtually free of dusts, thus overcoming the drawback of possible inhalation of carbon dusts by a smoker associated with the prior art of using granular carbons in making tobacco filters.
is The binding and compaction according to the method of this invention increases the packing density of carbon particles by 1.5 to 2 times compared to its granular counterpart, thus overcoming the low packing density problem associated with the prior art of using granular carbons in making cigarette smoke filter.
The inorganic clay materials used as binders according to the method of this invention are non-toxic and non-hazardous rr~aterials having no sources) for releasing toxic or cancer causing organic compounds. T hese binding materials therefore are, unlike those of the organic binders, fully acceptable for adding into cigarette filters from health considerations.
According to one variation of this invention, the carbon pellet filter can be designed with narrow monolithic channels to overcome pressure drop, if any, experienced during the smoking process.

The present inventors have unexpectedly found that the cigarette filter made using the method and materials in accordance with this invention is capable of substantially reducing carbon monoxide, nicotine and a vast range of organic compounds from the mainstream tobacco smoke.
The following examples illustrate the materials and the process of the invention.

Fabrication of the Cylindrical Shaped Carbon Pellet for Use as a Cigarette Smoke Filter Preparation of Microporous Carbon from coconut shell Microporous carbon, for the fabrication of cylindrical carbon pellet for use as a tobacco filter, was prepared from coconut shell by a two-stage process:
to 1. Carbonization of driE;d coconut shell at 600°C under Nz atmosphere.

2. Activation of coconut char by partial gasification with C02 at 800°C.
The coconut shell was cleaned of loose fibres and traces of kernel, crushed to a particle size of about 10 mm, washed with water and dried at 110°C overnight.
The crushed and dried coconut shell was placed i,n a stainless steel reactor and purged with N2. The vessel was mounted vertically in a tuba furnace and heated to 600°C at a rate of about 5°C min-1, held at that temperature for about 3 hours and then allowed to cool to room temperature.
A NZ purge was maintained at all times to drive off the volatile tarry materials produced 2o during carbonization. The char was crushed, screened and 8/30 mesh fraction selected for activation.
Coconut Char (about 10 g), as produced above, was placed into a quartz reactor that was mounted in a vertical tube furnace. The reactor was heated to about 800°C at a rate of about 10°C/min under a Nz flow (50 mL/min), held at the final temperature for 1 hour and then gas flow was switched to COz (activating gas) flowing at about 100 mL/min.
Activation process was carried out for about 8 hours at about 800°C
after which the sample was cooled to room temperature under NZ flow. The BET surface area and micropore volume of the product were determined and found to about 1100 m2/g and 0.50 mL/g.

Fabrication of Carbon pellet for use as Tobacco Filter Microporous carbon granules, prepared as described above, was ground in a ball mill apparatus (particle size 100 -- 250 mesh). A known quantity of carbon particles was taken for making carbon pellets. A water dispersion of a known quantity of bentonite clay was prepared. The amount of benonite clay taken for preparing the dispersion was so chosen that the binder to carbon ratio in the carbon-binder mix corresponds to 1 :10 to 1:15. Carbon particles were added to the binder dispersion and two were thoroughly blended to make a uniform slurry. The slurry was then partially evaporated with constant 1o stirring until the moisture contf;nt of the resultant paste corresponded to the range from about 80% to about 125% by weight (based on the weight of dry carbon particles used in the preparation).
A portion of the paste (weighing 1 to 2 g) was placed inside a 10 mm O.D (8mm >D) glass tube holder and was compacted by pressing from two ends with two rods.
The compacted pellet was dried in-situ in the glass tube holder in steps, first at 60°C for 2 hr and then at 120°C for 4 hr. 'The density of a pellet was determined from its dry weight and its geometric volume. The density of a typical pellet was about 0.65 g/mL
to about 0.70 g/mL.
The efficiency of the pellets in reducing harmful constituents of tobacco smoke was examined and results are discussed in Examples 2- 4 given below.

Ef~'icien~r Test of Carbon Pellet Filters in Reduci~ Harmful Organic Constituents of Cigarette Smoke The carbon pellet prepared in accordance with this invention was examined for its 3o capability in reducing harmful organic constituents of cigarette smoke as follows:

To one end of the glass tube housing the pellet filter, a "Player's Plain"
brand cigarette (manufactured by John Player & Sons) was attached. The other end of the glass tube was connected to an assembly having provisions for continuously drawing (pumping) the cigarette smoke (in fact, a mixture of smoke and air) through the filter element at a defined flow rate (using a diaphragm pump). The assembly also was provided with the provision for the withdrawal of l:he smoke sample for analysis by gas chromatography.
The carbon filter elements used in the tests were about 1.5 - 2.0 cm in length and 0.8 cm in diameter.
to The cigarette smoke was drawn through the carbon pellet filter element at a rate of about 1 L/min. This flowrate is similar to the puffing rate of 35 mL in 2 secs.
duration as applied in experiments conducted with commercial smoking machine. The smoke was sampled and analyzed by gas chromatography using flame ionization detection. A
DB-624 (supplied by J.W. Scientific) capillary column (30 m x 0.53 mm i.d. x 3.0 pm film thickness) was used for the ;>eparation of smoke products. The chromatogram of mainstream smoke sample that has passed through carbon-pellet filter of this invention is shown in Fig. 1C. A number of experiments were conducted with different pellet samples and different cigarette samples.
Figure 1A shows the chromatogram of the Reference Smoke sample for comparative purpose. Reference smoke sample is the smoke from same Player's Plain brand cigarette produced under same conditions as described for Figure 1 C, but without carbon-pellet filter being placed in the glass tube connecting glass tube and the smoke drawing unit.
Also was analyzed the smoke from the same Player's Plain brand cigarette but using a commercial filter that was taken from Player's Light brand cigarette, instead of a carbon-pellet filter of this invention. The chromatogram is shown in Figure 1 B.
3o Quantitative comparison of three chromatograms showed that carbon-pellet filter of this invention is capable of removing (that is, trapping) harmful constituents from the mainstream smoke by as much. as 70 - 80 percent as compared to that present in a filterless or a commercial filter based mainstream cigarette smoke.
It was also found that the carbon-pellet filter of this invention is capable of reducing 5 nicotine (peak at retention tinne of about 43.5 min in Figs 1A-C) content of the mainstream smoke by about tS5 to 85 percent when compared to a filterless or a commercial filter based cigarettf;.
The results are summarized in Table A.
to TABLE A
Hvdrocarbons and Nicotine Removal Efficient' of Carbon Pellet Cigarette Filter Percent Reduction Total Hydrocarbons 70 - 80 Nicotine 65 - 85 Efficiency Test of Carbon Pelllets in Reducing Carbon Monoxide Present in Cigarette 2o Smoke The carbon pellet prepared in accordance with this invention was examined for reducing carbon monoxide present in cigarette smoke. The tests were conducted in the same manner and under same conditions as in the case of Example 2.
However, the gas chromatography with a thermal conductivity detection and a Molecular Sieve SA chromatographic column (9ft x 1/8") was used for analysis of carbon monoxide.

It was found that the carbon pellet filter of this invention is capable of reducing carbon monoxide content of the smoke by more than 85 percent, as presented in Table B
below.
TABLE B
Carbon Monoxide Removal Efficienc~of Carbon Pellet Cigarette Filter Percent Reduction Carbon Monoxide >85 to In order to further confirm that: the carbon-pellet filter element indeed trapped harmful constituents from the mainstream smoke, a carbon-pellet filter that was used in an experiment similar to those presented in Example 2 and Example 3 was analyzed for the presence of hydrocarbons held adsorbed in the filter.
The analysis was conducted by desorbing the carbon-pellet filter using the technique of Purge and Trap/Gas chromatography - Mass Spectrometry (P & T/GC-MS). The carbon-2o pellet sample was contained in a gas-tight glass vessel and heated to 150°C while being purged with a stream of helium gas. This caused hydrocarbon components present in the pellet to be desorbed (at least, in part). The desorbed gases were analyzed by standard technique of Purge & Trap (iC-MS. The GC-MS column used for separation and detection by Mass Selective Detector was a DB-624 (0.30 mm x 0.25 mm ID, 1.5 pm film thickness).
Figure 2 shows a typical de:>orption chromatogram of some of the components of mainstream smoke that were :held by the carbon pellet filter of this invention. These hydrocarbon components are listed in Table C. It may be noted that the smoke contaminants included in Table C is in fact a partial list of mainstream tobacco smoke components that were held by tlhe carbon pellet filter of this invention. In other words, these are the components which could be desorbed from the pellet by heating it to 150°C.
Other components of cigarette smoke which could not be desorbed at this temperature and required much higher temperature are not observed. Blank experiment was conducted with a carbon pellet not exposed t:o tobacco smoke. No hydrocarbon peaks were detected in the chromatogram of the blank carbon pellet filter implying that the filter itself is free from contaminants.

Table C
GC-MS Analysis of Desorbed Hydrocabons Components from Carbon Pellet Used as Mainstream Smoke Filter according to this Invention Retention time Component min 3.33 Isoprene or Pentadiene 5.43 Furan, 2-meth 1-7,75 Benzene _ Cyclo entanamine, 1-meth 1-g.3g 9.20 Acetic acid 11.44 Toluene 12.03 P ridine 13.04 1 H-P mole 13.70 P rimidine, 5-meth 1-13.99 2-Furancarboxaldeh de _ Benzene:, eth 1-14.32 14. 5 5 p-Xyl ene 14.74 2-Furancarboxaldeh de . 3 3 1, 3, 5, 7-Cyclooctatetraene/Styrene 15.52 2,3-Hexadiene, 2-meth 1-15.80 2-Furanmethanol 16.46 2-Methyl-2-c clo enten-1-one 16. C clohexene, 1,3-dimeth I-_ Benzene, 1-eth I-2-meth 1-17.00 _ 4-Methyl-1,4-he tadiene 17.14 17.25 2,6-Octa_diene, 2,7-dimethyl-17.43 6-Octen-l-ol, 3,7-dimeth 1-17.58 P ridine, 3,5-dimeth 1-17.91 P ridine, 3-eth 1-18.14 5-Methyl Furfural 18.39 Limonene 18.67 4-Oct ne _ 2,4-Hexadiene, 2,5-dimethyl-18.95 19.11 Ethanone, I-(1-cyclohexen-1-yl)-19.26 1 7 , 3,8-o-Menthatriene _ 1 H-Indene 19.40 19.76 Phenol 19.94 2,3-Dimeth lcyclopent-2-en-1-one 20.09 Benzene, 1-methyl-2-(2-propenyl -20.28 ~ Ethanone, 1-(1-cyclohexen-1-yl)-20.42 Benzene, 1,2,3-trimeth 1-Table C continued Retention time Component min _ 20.82 3-Oct n-1-oL or 1H-P rzaole, 3 meth 1-20.97 Phenol, 2-methoxy-21. 50 2,4-Dime_thylcyclopent-4-ene-1,3-dione 21.58 Cresol 21.70 1H-Indene, 1-meth 1-22.18 2,3,4-Trimeth lfuran _ o-Methox Benz 1 alcohol 22.41 22. 50 Benzeneacetonitrile 22.75 Na hthalene white tar) 22.98 Ethanone, 1-(2-methylphenyl)-23.09 1,3-Benzenediol, 4-eth 1-23.57 1-Tridecene 23.65 Tridecane 23.78 1 H-Indene, 1,1-dimethyl-23.87 Naphthalene, 1,2-dihydro-6-meth 24. 09 1,4-dimeth lindene 24.28 Na thalene, 1,2-dih dro-3meth 24.99 3-Nonene (c,t) 25.28 Na hthalene, 2-meth 1 25.77 Na hthalene, 1-meth 1 25.99 5-Tetradecene 26.08 n-Tetradecane 26.88 Solanone 28.20 ~ 2,6,10 -- Trimeth 1-2,6,10-dodecatriene _ ~ 1,5-Heptadiene, 3,3,5-trimethyl-28.55 Note: Identifications of compounds listed in Table C are according to Hewlett Packard supplied WILEY275 database.

Claims

1. A cigarette mainstream smoke filter consisting of a small cylindrical pellet (or disc) made from a mixture of microporous carbon and naturally occurring clay material by a binding and compaction method.

2. A cigarette smoke filter according to claim 1, wherein said binding and compaction method comprises the steps of:
a) crushing and milling the granular carbon into fine particles;
b) preparing an aqueous dispersion of the naturally-occurring clay material suitable for binding the carbon particles according to this invention, by adding the clay material to water (25 mL to 50 mL water per gram of clay) and thoroughly stirring the mix to form a uniform dispersion;
c) mixing dry or prewetted carbon particles of step (a) with the water dispersion of the binder of step (b) in appropriate proportions to make a slurry of carbon and binding agent;
d) drying of the carbon-binding agent slurry of step (c) to desired moisture content ranging from about 80% to about 125% based on the weight of carbon, by partially evaporating water while stirring;
e) consolidating carbon-binder mix of step (d) by gentle compression at ambient temperature in a suitable pellleting device to provide a cylindrical pellet of microporous carbon; and f) drying the pellets in steps at a temperature of 60°C to about 70°C and at temperature of about 120°C to about 140°C in air atmosphere.

3. A cigarette filter according to claim 1, wherein said microporous carbon is derived from carbonaceous materials such as coconut shell, wood, coal, various kinds of pitch, and petroleum tar either by chemical activation in an inert atmosphere with KOH, phosphoric acid or ZnCl2 at a temperature of about 300°C to about 600°C or by carbonization at a temperature of about 600°C to about 800°C, followed by partial gasification with CO2 or water vapour - N2 mixture at a temperature of about 700°C
to about 850°C.

4. A cigarette smoke filter according to claim 1 and 3, wherein said microporous carbon is derived from coconut shell by carbonization in inert atmosphere at a temperature of about 600°C to about 700°C and then subjecting the char so produced to partial gasification with CO2 at a temperature of about 750°C to about 850°C.

5. A cigarette filter according to claim 1,3, and 4, wherein said microporous carbon has a surface area in the range 1000 - 1500 m2/g and micropore volume in the range 0.45 - 0.65 mL/g.

6. A cigarette smoke filter according to claim 1 and 2, wherein said naturally occurring clay material used for binding and compacting carbon particles into cylindrical pellets is chosen from a group consisting of bentonite clay, attapulgite clay, sepiolite clay or a combination thereof.

7. A cigarette smoke filter according to claim 1,2 and 6, wherein said clay material used for binding and compacting carbon particles to produce cylindrical pellets is bentonite clay.

8. A cigarette smoke filter according to claim 1,2,6 and 7, wherein, in fabricating carbon pellet, said bentonite clay is mixed with carbon particles at a ratio of 0.10 -0.20 gram of bentonite clay per gram of microporous carbon particles.

9. A cigarette smoke filter according to claim 1 to 8, wherein said filter element when attached to the end of a cigarette rod, substantially reduces the harmful components of the mainstream tobacco smoke.

10. A cigarette smoke filter according to claim 1 to 9, wherein said filter element when attached to the end of a cigarette rod substantially reduces undesirable hydrocarbons and nicotine components of the mainstream cigarette smoke.

11. A cigarette smoke filter according to claim to 1 to 9, wherein said filter element when attached to the end of the cigarette substantially reduces toxic carbon monoxide component of the mainstream cigarette smoke.

12. A cigarette smoke filter according to claim 1,2,6,7 and 8, wherein said binding materials are naturally occurring inorganic materials.

13. A cigarette smoke filter according to claim 1,2,6,7 and 8, wherein said method of binding and materials used for this purpose results into binding of carbon particles.

14. A cigarette smoke filter according to claim 1,2,6,7 and 8, wherein said method of binding and the materials used for this purpose results in a substantial increase in the packing density of filter material (carbon particle), thereby substantially enhancing the adsorption capacity of smoke components by the filter element on its volume basis.

15. A cigarette smoke filter according to claim 1 to 8, wherein said compacted filter is not only suitable for purifying cigarette smoke, but also can be used for purifying tobacco pipe smoke.

16. A cigarette smoke filter according to claim 1 to 8 wherein said compacted filter is not only limited to decontaminating mainstream smoke, but also can be used for decontaminating the side stream smoke by suitable modification of the device by those who are well versed in the art of mechanical ventilation.

17. A cigarette smoke filter according to claim 1 to 8, wherein the density of said compacted filter can be increased or decreased as desired by the required efficiency of removal of the contaminants.

18. A cigarette smoke filter according to claim 1 to 8, wherein the pressure drop across said filter during the smoking process can be adjusted, if required, by introducing monolithic channels within its matrix.

19. A cigarette smoke filter according to claim 1 to 8, where the desired degree of compaction, adherence and consolidation of microporous carbon particles constituting the said filter can be more readily achieved by the application of compaction pressure in varying magnitude, either manually or by automation.