Modified silica gel adsorbent, its preparation method and application
By using a mesoporous silica matrix in cigarette filter rods and modifying it with silane coupling agents containing benzene rings or hydrophobic alkyl chains, a modified silica adsorbent was prepared. This solved the problems of insignificant tar reduction effect and high cost of existing materials, achieving efficient tar reduction while maintaining cigarette smoking quality, and is suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 山西昆明烟草有限责任公司
- Filing Date
- 2026-03-20
- Publication Date
- 2026-05-29
AI Technical Summary
The tar-reducing materials in existing cigarette filter rods have insignificant tar-reducing effects, are costly, and are difficult to produce industrially. Traditional materials generally have low tar removal rates and cannot effectively control harmful components in cigarette smoke.
Using mesoporous silica gel as the matrix, modified silica gel adsorbents were prepared by adding silane coupling agents containing benzene rings or hydrophobic alkyl chains. The efficient capture of tar was achieved by utilizing the electron cloud stacking effect between the benzene ring and the aromatic structure of tar, as well as the affinity adsorption of the alkyl chains.
Modified silica gel adsorbents can significantly improve tar removal rates, reaching over 40% and up to 75%, while reducing tar release and controlling the loss of nicotine and moisture, maintaining the satisfaction of smoking cigarettes, and at a lower cost than nanomaterials.
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Figure CN122098480A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of adsorption materials technology, specifically to a modified silica gel adsorbent, its preparation method, and its application. Background Technology
[0002] Tar is a major source of harmful substances in cigarette smoke. It is a product of the incomplete combustion of organic substances such as sugars and proteins in tobacco under anaerobic conditions. It consists of various hydrocarbons and complex compounds including hydrocarbon oxides, sulfides, and nitrogen oxides. Some of these harmful substances can lead to various diseases and seriously endanger human health when they enter the body. Therefore, countries around the world have clearly defined legal limits on the tar content of cigarettes and regard it as one of the main standards for measuring cigarette quality and safety.
[0003] In the field of cigarette tar reduction and harm reduction technology, common methods cover multiple directions, including breeding and cultivation optimization, cigarette formula adjustment, and improvement of auxiliary material structure design. Among them, adding functional materials to filter rods has become one of the key technical paths for reducing harmful components (especially tar) in cigarette smoke due to its convenient operation and strong targeting. Existing technologies have disclosed various functional materials suitable for filter rods and their preparation and application schemes. For example, patent literature (application number: CN202311427591.6) discloses a method for preparing diatomaceous earth particles that can reduce tar and CO in cigarette smoke. This method specifically includes: mixing diatomaceous earth, adhesive, and water to prepare a wet powder; placing the pellet core in a centrifugal shot blasting machine and granulating it by spraying a wetting agent, using centrifugal force to coat the wet powder onto the surface of the pellet core; and drying it to obtain diatomaceous earth particles with adsorption function. This technology, through the structural design of "diatomaceous earth powder wrapped around the particle core," endows the particles with adsorption properties for tar and CO. For example, patent (authorization announcement number: CN103126073B) discloses a filter rod fiber substrate additive and compound additive, as well as their application, which can reduce the tar content in mainstream cigarette smoke. This additive uses one or more citrate ester compounds as its effective active ingredient. After the fiber substrate containing this additive is made into a filter rod and applied to cigarette products, it can effectively reduce the tar content in mainstream cigarette smoke, with a maximum tar reduction of up to 10.3%. Some patents also use aerogel materials as tar adsorbents (authorization announcement number: CN112915979B). These materials have a high specific surface area, but involve freeze-drying and other preparation processes, which are energy-intensive, time-consuming, and costly, making them unsuitable for large-scale industrial production.
[0004] Currently, the functional materials used in cigarette filter rods have a certain effect on retaining harmful components in cigarette smoke, but these materials all have some common problems: (1) The tar removal rate is generally not high, with most having a tar removal rate of no more than 50%. (2) There is no potential for industrialization. The materials currently prepared often require complex pretreatment and a long preparation process, making it difficult to have industrialization potential. Therefore, it is necessary to study materials with good tar removal capabilities. Summary of the Invention
[0005] This invention addresses the shortcomings of existing tar-reducing adsorption materials in terms of adsorption efficiency, cost, and environmental impact by providing a method for preparing a modified silica gel adsorbent. The prepared modified silica gel adsorbent not only selectively and efficiently adsorbs harmful tar components but also effectively maintains the smoking satisfaction and smoke humidity of cigarettes.
[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a modified silica gel adsorbent, comprising the following steps: S1. Disperse silica gel particles in ethanol to obtain a dispersion; S2. Add ammonia and deionized water to the dispersion from step S1. S3. Add silane coupling agent to the mixture from step S2; S4. Place the mixture from step S3 on a heating plate, heat and stir, and wash after the reaction to obtain the modified silica gel adsorbent.
[0007] As a further limitation of the technical solution of the present invention, the particle size of the silica gel particles in step S1 is 20~80 mesh. If the raw material is within this mesh size, it does not need to be ground. If it is not within this mesh size, it can be ground to this particle size. The silica gel is at least one of pure silica gel, water-resistant silica gel, or silica-alumina gel. The mass-volume ratio of silica gel particles to ethanol in step S1 is 2~10g:15~120mL.
[0008] As a further limitation of the technical solution of the present invention, the volume ratio of ammonia, deionized water and ethanol in step S2 is 0.5~5:0.5~5:15~120; the mass concentration of the ammonia is 22-28%, and the preferred mass concentration of the ammonia is 25%.
[0009] Preferably, in step S2, the deionized water and ammonia water are each 3.5 mL.
[0010] As a further limitation of the technical solution of the present invention, the mass of the silane coupling agent added in step S3 is 0.5% to 12% of the mass of the silica gel particles in step S1.
[0011] As a further limitation of the technical solution of the present invention, the silane coupling agent mentioned in step S3 is at least one of phenyltrimethoxysilane (PTMS), octyltriethoxysilane (OTS), octyltrimethoxysilane and hexadecyltrimethoxysilane.
[0012] As a further limitation of the technical solution of the present invention, the reaction temperature in step S4 is 35~75℃, the stirring speed is 200~400rpm, and the heating and stirring time is 8h. Preferably, the reaction temperature is 45℃, the stirring speed is 400rpm, and the time is 8h.
[0013] The present invention also provides a modified silica adsorbent obtained by the above preparation method.
[0014] The present invention also provides the application of the modified silica adsorbent obtained by the above preparation method in reducing tar in cigarettes.
[0015] Compared with the prior art, the present invention has the following beneficial effects: Currently, most studies on cigarette products using adsorbents to reduce tar place the adsorbent particles in the hollow section of a two-section filter rod, allowing tar to be adsorbed as smoke passes through. This method allows for flexible adjustment of the amount and type of material used and can prevent some particulate dust from being inhaled. However, this placement method also presents challenges for the tar-reducing adsorbents. Because the smoke passes rapidly over the surface of the adsorbent in the hollow section, the adsorbent often does not have sufficient time to adsorb the tar, resulting in a less than significant tar-reducing effect. Furthermore, previous research on tar-reducing adsorbents has mainly focused on activated carbon, carbon nanotubes, zeolites, mesoporous molecular sieves, and polymers. Among these, carbon nanotubes and mesoporous molecular sieves have excellent tar-reducing effects, but their costs are too high. Zeolites and polymers typically cannot achieve adsorption of large molecules, resulting in poor tar-reducing effects. Activated carbon is relatively inexpensive, but its tar-reducing effect is only average. For example, HNO3-modified activated carbon only achieves a tar removal rate of 8.8% (Yuan Shuxia, Lü Chunxiang, Li Yonghong, et al. Effect of activated carbon modification on filter adsorption performance [J]. Journal of Taiyuan University of Technology, 2007, 38(6): 509-513.). Even when carbon nanotubes are used as adsorbents in the hollow section, their tar removal rate is only 25.7% (Zhou S, Ning M, Zhang Y, et al. Significant Removal of Harmful Compounds in Mainstream Cigarette Smoke Using Carbon Nanotubes Mixture Prepared by Catalytic Pyrolysis [J]. Adsorption Science and Technology, 2014, 32(6): 453-464.). It is evident that traditional activated carbon or novel carbon nanomaterials generally have low tar removal rates in hollow section filter rod applications. The tar-reducing adsorbent in this invention can achieve a tar removal rate of over 40%, reaching a maximum of 75%, which is the best tar reduction effect reported to date after adding the tar-reducing adsorbent in the hollow section. This tar reduction effect stems from the fact that the material design theory in the adsorbent design of this invention differs from current existing technologies: Current technologies mostly use activated carbon as the base material. However, activated carbon is predominantly microporous and lacks the ability to adsorb polycyclic aromatic hydrocarbons, which constitute the majority of tar. Previous literature has also largely employed methods of modifying with polar groups to improve tar reduction. However, the electron donor-acceptor interaction between polar groups and aromatic structures in tar is relatively weak, resulting in insufficient adsorption force. Furthermore, there is insufficient time for hydrogen bonding to form when the gas stream passes through rapidly. Therefore, it is essential to find adsorbents that interact strongly with the most abundant components in tar.
[0016] This invention is based on the principle that the main components of tar are aromatic hydrocarbons, i.e., most tar components are composed of benzene rings and alkyl chains. (1) Mesoporous silica gel is used as the matrix adsorbent, which is inexpensive and has large pores, capable of accommodating tar components of different sizes. (2) Silane coupling agents containing benzene rings or hydrophobic alkyl chains are modified on the support under mild conditions. On the one hand, the electron cloud stacking effect of benzene rings and tar aromatic structures (based on the principle of like dissolves like) is used to quickly capture tar. On the other hand, the hydrophobic alkyl chains are used to perform affinity adsorption with the alkyl chain structure in tar. This type of adsorption involves the entanglement of the alkyl chains modified on the surface of the adsorbent with the long alkyl chains in the tar molecules, which also achieves rapid capture of tar. (3) The captured molecules can further diffuse into the pores of the silica gel support with larger pores, thereby increasing the adsorption driving force and allowing subsequent tar adsorption to continue. (4) The particle size of the materials used in this invention is mostly around 0.5 mm to 2 mm. Compared with carbon nanotubes, which have a better tar reduction effect, the materials of this invention have a lower risk of inhalation. Moreover, the material particles of this micron to millimeter size have large gaps, which is conducive to the diffusion of flue gas into the interior of the adsorbent particle layer and increases the effective adsorption area. (5) The carrier and silane coupling agent used in this invention are both commercially available and mature on a large scale. The reaction conditions are mild and the production cost is much lower than that of nanomaterials such as carbon nanotubes.
[0017] The modified silica gel adsorbent prepared by the method of this invention has a highly efficient tar-reducing function and can significantly regulate the release of substances from cigarette smoke. It can effectively control the loss of nicotine and moisture while significantly reducing tar release, exhibiting excellent overall balance. This adsorbent not only selectively and efficiently adsorbs harmful tar components but also maintains the smoking satisfaction and smoke moisture of cigarettes, providing a clear direction for developing high-efficiency, low-impact tar-reducing technologies and effectively improving the safety of cigarette consumption. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the hollow section treatment of the filter tip in an embodiment of the present invention. Detailed Implementation
[0019] A method for preparing a modified silica gel adsorbent includes the following steps: S1. Disperse silica gel particles in ethanol to obtain a dispersion; S2. Add ammonia and deionized water to the dispersion from step S1. S3. Add silane coupling agent to the mixture from step S2; S4. Place the mixture from step S3 on a heating plate, heat and stir, and wash after the reaction to obtain the modified silica gel adsorbent.
[0020] In different embodiments, the mass-to-volume ratio of silica gel particles to ethanol in step S1 is 2~10g:15mL, 2~10g:20mL, 2~10g:25mL, 2~10g:30mL, 2~10g:35mL, 2~10g:40mL, 2~10g:45mL, 2~10g:50mL, 2~10g:55mL, 2~10g:60mL, 2~10g:65mL, 2~10g:70mL, 2~10g:75mL, 2~10g:80mL, 2~10g:85mL, 2~10g:90mL, 2~10g:95mL, 2~10g:100mL, 2~10g:105mL, 2~10g:100mL, 2~10g:115mL, and 2~10g:120mL.
[0021] In different embodiments, the volume ratio of ammonia, deionized water, and ethanol in step S2 is 0.5:0.5:15, 2:2:15, 3:3:15, 5:5:15, 0.5:0.5:30, 2:2:30, 3:3:30, 5:5:30, 0.5:0.5:45, 2:2:45, 3:3:45, 5:5:45, 0.5 :0.5:60, 2:2:60, 3:3:60, 5:5:60, 0.5:0.5:75, 2:2:75, 3:3:75, 5:5:75, 0.5:0.5:90, 2:2:90, 3:3:90, 5:5:90, 0.5:0.5:105, 2:2:105, 3:3:105, 5:5:120.
[0022] In different embodiments, the mass of silane coupling agent added in step S3 is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, or 12% of the mass of silica gel particles in step S1.
[0023] In different embodiments, the reaction temperature in step S4 is 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, and 75°C, and the stirring speed is 200 rpm, 250 rpm, 300 rpm, and 400 rpm.
[0024] The specific embodiments of the present invention will be described in detail below. Embodiment 1
[0025] Example 1 A modified water-resistant silica gel adsorbent, the preparation method of which is as follows: (1) 2.5g of ordinary water-resistant silica gel particles with different mesh sizes (as shown in Table 1) were dispersed in 120mL of ethanol to obtain a dispersion. (2) Add equal volumes of ammonia and deionized water to the dispersion from step (1); the mass concentration of ammonia is 25%. (3) Take PTMS and add it to the mixture in step (2) according to the PTMS / silica gel ratio in Table 1; (4) Place the mixture from step (3) on a heating plate, heat at 75°C and stir for 8 hours at 400 rpm. After the reaction is complete, wash with ethanol to obtain the nicotine adsorbent material, i.e., the modified water-resistant silica gel adsorbent.
[0026] Table 1 Material Preparation Formulation (Particle size and PTMS / silica gel ratio are variables; if the silica gel type is not specified, it is ordinary water-resistant silica gel).
[0027] The modified water-resistant silica gel adsorbent prepared in Example 1 was added to cigarette filters as a high-efficiency tar-reducing functional material. The addition amounts are shown in Figures 2-1, 2-2, and 2-3. Cigarettes without the added high-efficiency tar-reducing functional material served as a blank control group. The tar-reducing performance of the above materials was measured. The methods for replacing the adsorbent in the hollow section of the cigarette filter and testing its tar-reducing performance are as follows: 1. Sample selection Commercially available finished cigarettes were selected as the experimental base samples, and cigarettes with obvious defects were removed.
[0028] 2. Treatment of the hollow section of the filter tip Standard cigarette samples, selected based on appearance, circumference, hardness, and weight, are axially positioned and gently clamped in a customized V-shaped positioning fixture. The fixture must have an anti-rotation locking function to ensure no axial displacement or circumferential rotation of the cigarette during operation. Using ultra-fine pointed tweezers (made of non-magnetic stainless steel with specially polished tips), the tweezers are gently inserted along the interface between the filter forming paper and the cellulose acetate tow at a very small entry angle (typically <15°). A progressive axial peeling technique, rather than radial pulling, is used to separate the upper half of the cellulose acetate tow rod ( Figure 1 Part A) is completely separated from the inner wall of the forming paper. This process requires maintaining the fiber orientation and bundle structure of the filament bundles to form a complete cylindrical pre-fabricated hollow cavity. The extracted filament bundles should be temporarily placed in a clean, anti-static sample dish to prevent the fibers from scattering or adsorbing foreign matter. The exposed hollow cavity (…) Figure 1 Part B) was examined under a microscope to confirm the smoothness of its inner wall, the consistency of the cavity diameter, and whether the inner lining of the forming paper was intact, without damage or delamination.
[0029] 3. Adsorbent granule filling The sieved and dried adsorbent particles are quantitatively filled into the cleaned filter nozzle hollow cavity. The filling process uses slight vibration to ensure that the adsorbent particles are evenly and densely distributed, without any gaps, blockages, or leaks.
[0030] 4. Cigarette reassembly Holding the previously removed upper half of the fiber tow rod with tweezers, align it with the cavity opening along its original fiber orientation. Gently screw it in laterally or press it in vertically to return the fiber tow rod completely to its original cavity. This process must avoid causing shear stress or deformation to the fibers. After backfilling, the tip of the fiber tow rod should be flush with the original end face of the filter tip, with no abnormal protrusions or depressions. Check if the filter tip appearance has been restored, and whether the tipping paper and forming paper have wrinkles, damage, or glue residue cracks, and whether the end faces are clean. After assembly, place the cigarette in an environment with a temperature of 22±1℃ and a relative humidity of 60±3% for at least 48 hours to allow the overall structure to stabilize.
[0031] Mainstream smoke extraction test According to GB / T 19609-2024 "Determination of total particulate matter and tar using a conventional analysis smoking machine for cigarettes".
[0032] Because the blank samples are different, they are divided into three tables. The measurement results are shown in Tables 2-1, 2-2, 2-3, and 2-4.
[0033] Table 2-1
[0034] Table 2-2
[0035] Table 2-3
[0036] The coking performance of unmodified silica gel particles compared to samples 2, 9, and 10 is shown in Table 2-4. Table 2-4 The calculation method for the tar removal rate of each material is as follows: Tar removal rate = (sample value - blank value) / blank value × 100%, negative value indicates decrease, positive value indicates increase.
[0037] Table 3 summarizes the tar removal rates of the above materials.
[0038] As can be seen from the table above, the adsorbent obtained by this invention has excellent coke reduction performance. Moreover, the comparison between the three samples and the unmodified silica gel shows that the coke reduction performance of the adsorbent is significantly improved after modification, which further proves the necessity of surface modification.
[0039] Example 2 A modified ordinary water-resistant silica gel adsorbent (2-4 mm before grinding) is prepared as follows: (1) 2.5g of ordinary water-resistant silica gel particles with different mesh sizes (as shown in Table 4) were dispersed in 120mL of ethanol to obtain a dispersion. (2) Add equal volumes of ammonia and deionized water to the dispersion from step (1); the mass concentration of ammonia is 25%. (3) Take PTMS and add it to the mixture in step (2) according to the PTMS / silica gel ratio in the table; (4) Place the mixture from step (3) on a heating plate, heat at 75°C and stir for 8 hours at 400 rpm. After the reaction is complete, wash with ethanol to obtain the nicotine adsorbent material, i.e., the modified silica gel adsorbent.
[0040] Table 4 Material Preparation Formulation (Volumes of ammonia and deionized water and PTMS / silica gel ratio are variables)
[0041] The modified ordinary water-resistant silica gel adsorbent prepared in Example 2 was added to cigarette filters as a high-efficiency tar-reducing functional material. The amount added is shown in Tables 5-1 and 5-2. Cigarettes without the high-efficiency tar-reducing functional material were used as a blank control group. The tar-reducing performance of the above materials was measured. The method for replacing the adsorbent in the hollow section of the cigarette filter and testing the tar-reducing performance was the same as in Example 1. Since the blank samples were different, they are divided into three tables. The test results are shown in Tables 5-1 and 5-2.
[0042] Table 5-1
[0043] Table 5-2
[0044] The calculation method for the tar removal rate of each material is as follows: Tar removal rate = (sample value - blank value) / blank value × 100%, negative value indicates decrease, positive value indicates increase.
[0045] Table 6 summarizes the tar removal rates of the above materials.
[0046] Example 3 A modified water-resistant silica gel / aluminosilicate gel adsorbent, the preparation method of which is as follows: (1) 2.5g of silica gel particles of different mesh sizes (as shown in Table 7) were dispersed in 120mL of ethanol to obtain a dispersion; (2) Add equal volumes of ammonia and deionized water to the dispersion from step (1); the mass concentration of ammonia is 25%. (3) Take PTMS and add it to the mixture in step (2) according to the PTMS (or OTS or OTS+PTMS) / silica gel ratio in the table; (4) Place the mixture from step (3) on a heating plate, heat at 75°C and stir for 8 hours at 400 rpm. After the reaction is complete, wash with ethanol to obtain the nicotine adsorbent material, i.e., the modified silica gel adsorbent.
[0047] Table 7 Material Preparation Formulation (Silane Coupling Agent and Silica Gel Type are Variables)
[0048] The modified water-resistant silica gel / aluminosilicate adsorbent prepared in Example 3 was added to cigarette filters as a high-efficiency tar-reducing functional material. The addition amounts are shown in Tables 8-1 and 8-2. Cigarettes without the high-efficiency tar-reducing functional material were used as a blank control group. The tar-reducing performance of the above materials was measured. The methods for replacing the adsorbent in the hollow section of the cigarette filter and testing the tar-reducing performance were the same as in Example 1. Due to the different blank samples, the results are presented in three tables. The measurement results are shown in Tables 8-1 and 8-2.
[0049] Table 8-1
[0050] Table 8-2
[0051] The calculation method for the tar removal rate of each material is as follows: Tar removal rate = (sample value - blank value) / blank value × 100%, negative value indicates decrease, positive value indicates increase.
[0052] Table 9 Summary of Tar Removal Rates for the Above Materials
[0053] As shown in the table, PTMS modification still exhibits high tar reduction performance when using different cigarette types, and using aluminosilicate gel also yields similarly good results. Besides PTMS, OTS and a combination of PTMS and OTS can also significantly reduce tar. A mixture of PTMS and OTS can maintain a moderate tar reduction effect while mitigating the reduction in nicotine and water content, catering to different consumer preferences. OTS has a lower cost than PTMS, and depending on the application and cost of the cigarette, different types and proportions of silane coupling agents can be selected.
[0054] As shown in Tables 1-9, compared with the blank control sample, the high-efficiency tar-reducing functional material prepared by the method of this invention can significantly regulate the emissions from cigarette smoke. The tar removal rate is generally above 50%, reaching a maximum of 75%, significantly better than existing common tar-reducing materials. Furthermore, while significantly reducing tar release, it also has a certain removal effect on CO, and effectively controls the loss of nicotine and moisture, demonstrating excellent overall balance. This indicates that the material of this invention can not only selectively and efficiently adsorb harmful tar components, but also better maintain the smoking satisfaction and smoke moisture of cigarettes, providing a clear direction for the development of high-efficiency, low-impact tar-reducing technologies, and effectively improving the safety of cigarette smoking.
Claims
1. A method for preparing a modified silica gel adsorbent, characterized in that, Includes the following steps: S1. Disperse silica gel particles in ethanol to obtain a dispersion; S2. Add ammonia and deionized water to the dispersion from step S1. S3. Add silane coupling agent to the mixture from step S2; S4. Heat and stir the mixture from step S3. After the reaction is complete, wash to obtain the modified silica gel adsorbent.
2. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, The particle size of the silica gel particles in step S1 is 10~80 mesh; the mass-to-volume ratio of silica gel particles to ethanol in step S1 is 2~10g:15~120mL.
3. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, In step S1, the silicone is at least one of pure silicone, water-resistant silicone, and aluminum silicate.
4. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, In step S2, the volume ratio of ammonia, deionized water, and ethanol is 0.5~5:0.5~5:15~120; the mass concentration of the ammonia is 22-28%.
5. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, In step S3, the mass of the added silane coupling agent is 0.5% to 12% of the mass of the silica gel particles in step S1.
6. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, The silane coupling agent mentioned in step S3 is at least one of phenyltrimethoxysilane, octyltriethoxysilane, octyltrimethoxysilane, and hexadecyltrimethoxysilane.
7. The method for preparing a modified silica gel adsorbent according to claim 1, characterized in that, The reaction temperature in step S4 is 35~75℃, the stirring speed is 200~400rpm, and the heating and stirring time is 8h.
8. The modified silica gel adsorbent obtained by the preparation method according to any one of claims 1-7.
9. The application of the modified silica gel adsorbent obtained by the preparation method according to any one of claims 1-7 in reducing tar in cigarettes.