Patent Application
20050268925
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1. Field of the Invention
The present invention relates to a smoking article having a filter element and/or smokable material containing a highly structured mesoporous molecular sieve, and more specifically, a smoking article having a filter element and/or smokable material containing a highly porous amorphous silica (hereinafter referred to as “MCM-41”), as the highly structured mesoporous molecular sieve for filtering vapor phase constituents in mainstream smoke.
2. Description of the Related Art
Typical smoking articles, such as cigarettes, have a cylindrical filter element axially aligned with a cylindrical tobacco-filled rod. The filter element, and even the tobacco-filled rod, incorporate various materials that work to remove particular components from the mainstream smoke. Often, these materials are non-selective, thereby removing desirable components from the mainstream smoke and resulting in an undesirable taste.
Certain cigarettes have filter elements which incorporate materials such as carbon.
Exemplary cigarettes and filters are described in U.S. Patent Pub. No. 2003/0159703, to Yang, et al., and U.S. Patent Pub. No. 2003/0154993, to Paine, III et al. Generally, surface area is inversely proportional to carbon particle size. If the particle size is too large, there may be insufficient surface area to accomplish the desired filtration. This factor must be taken into careful consideration when selecting a particular carbon particle size. Also, filter elements which incorporate carbon often yield a metallic flavor during smoking. Carbon is often impregnated with a flavorant in an attempt to camouflage the metallic flavor and may actually block the pores, an impediment to filtration, and finding a preferred flavorant loading percentage is difficult and inefficient. Furthermore, filter elements which incorporate carbon vary in proportion of micropores to mesopores, where the term “microporous” generally refers to such materials having pore sizes of about 20 Å or less, while the term “mesoporous” generally refers to such materials with pore sizes of about 20-500 Å. Uniform pore size distribution is more favorable. By having a more uniform pore size distribution, more of the porosity can be assured to be in the mesoporous range (2-50 nm), which is more effective at filtering smoke than microporous materials. A variety of pore sizes is more likely to filter a variety of compounds, and filters for specific analytes are more desirable.
A smoking article with a filter element capable of filtering vapor phase components that is efficient to produce and does not yield a metallic flavor is desired. Also, a filter element with a mesoporous molecular sieve that has uniform pore size is desired.
In view of known deficiencies associated with earlier smoking article filter elements, a smoking article with a mesoporous molecular sieve to filter vapor phase constituents from mainstream tobacco smoke is provided.
It has been found that a family of highly ordered mesoporous molecular sieves, manufactured by the Mobil Corporation and identified as M41S, are useful in smoking article filter elements. M41S materials are non-crystalline surfactant templated silica having a narrow pore size distribution. MCM-41 is a highly porous surfactant templated silica gel belonging to the M41S family, and contains a highly organized hexagonal array of uniform pores with controllable diameters from about 15 Å to about 100 Å. The term “hexagonal” encompasses materials that exhibit mathematically perfect hexagonal symmetry and materials with significant observable deviations from perfection. MCM refers to Mobil Composition of Matter or Mobil Crystalline Material, and was developed as a catalyst substrate by Mobil
The surface chemistry of siliceous MCM-41 is comprised of silanol groups (SiOH), and may be synthesized using cetyltrimethylammonium chloride (CTACl), H2O, Na2O, and SiO2. The formed MCM-41 may be utilized as a mesoporous molecular sieve in smoking articles. MCM-41 has a highly condensed surface with less SiOH groups than silica, and its uniqueness is in the shape it adopts by forming around a template which is subsequently removed. The use of mesopores as an absorbent is taught by U.S. Pat. No. 5,580,370, to Kuma, et al. Furthermore, MCM-41 has a large surface area, where the BET surface area is approximately 1000 m2/g, and thus has a high sorption capacity. (“BET” refers to Brunaur, Emmett, and Teller, three scientists who optimized the theory for measuring surface areas.) MCM-41 is effective for reducing levels of alcohols, aldehydes, ketones, nitrites, and naphthalene.
It is an object of the present invention to provide a smoking article with a filter element having a mesoporous molecular sieve, MCM-41. A preferred smoking article is a cigarette with MCM-41 disposed within the filter element.
It is another object to provide a smokable material in a smokable rod of the smoking article having the mesoporous molecular sieve, MCM-41. A preferred smoking article is a cigarette and a preferred smokable material is tobacco. In this embodiment, MCM-41 is disposed within the smokable material in the rod.
It is yet another object to provide the filter element and the smokable material in the smokable rod of the smoking article both having the mesoporous molecular sieve, MCM-41. In this embodiment, MCM-41 is disposed within the filter element and throughout the smokable material in the rod.
It is still yet a further object to provide either or both the filter element or the smokable material in the smokable rod of the smoking article having the mesoporous molecular sieve, MCM-41, in combination with charcoal, an ion-exchange resin, or both.
It is still yet another object to provide either or both the filter element or the smokable material in the smokable rod of the smoking article having an impregnated mesoporous molecular sieve, MCM-41. MCM-41 can be impregnated with copper oxide for greater HCN and H2S reduction.
The aspects and advantages of the present invention will be better understood when the detailed description of the preferred embodiment is taken in conjunction with the accompanying drawings, in which:
While this invention is susceptible of embodiments in many different forms, there are shown in the figures and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, and is not intended to limit the broad aspects of the invention to the embodiments illustrated.
The present invention provides for an article for smoking with a mesoporous molecular sieve, MCM-41, to filter vapor phase constituents from mainstream tobacco smoke. Vapor phase constituents to be filtered contact MCM-41 and are retained within the pores, thereby providing a separation of the undesirable constituents from the remainder of the vapor. MCM-41 is typically a black or white granular material with a density of ˜0.3 g/cm3 and a BET surface area of ˜1000 m2/g. Although pore wall thickness may vary, MCM-41 typically has a uniform pore diameter of 3.7 nm, when cetyltrimethyl ammonium bromide is used.
The following examples are given for illustrative purposes only and are not to be deemed as limitative of the scope of the invention.
To evaluate the adsorptive properties of MCM-41, MCM-41 was tested in hand-made cavity filters and compared to semolina (inert flour granules used to simulate a granule-filled cavity). Hand-made cavity filters can be made by first removing the cellulose acetate (CA) filter of a cigarette. Shortened segments of CA on the tobacco and mouth end of the filter create a cavity to hold the granular material.
The MCM-41 sample sets were prepared according to usual synthesis procedure, except for minor modifications. MCM-41 was developed by Exxon/Mobil, but sample sets for experiment purposes were developed in the laboratory. Water, the surfactant cetyltrimethyl ammonium bromide (CTAB), and tetraethyl orthosilicate (TEOS) were mixed, in order, in a 250 mL glass bottle until a cloudy white suspension was achieved. CTAB and TEOS were combined with a surfactant:silica mole ratio of 1:2. The solution's surfactant concentration, by total weight, equaled 25%. Concentrated sulfuric acid was added drop wise until the mixture changed to a clear liquid. The solution was stirred at approximately 400 rpm for 0.5 hours, and then placed under static autogenous conditions. (121° C., 18 psi) for 1 hour. The resulting gel was removed from the autoclave and allowed to cool before being washed thoroughly with deionized water. The washed material was heated at 570° C. for six to eight hours in air, resulting in a porous material with a BET surface area of ˜1300 m2/g.
Sample sets of cigarettes containing 50 mg of a granular additive in a hand-made cavity filter were prepared using either MCM-41 synthesized as described above or semolina. Each sample set was pressure drop selected to decrease smoke delivery variances. Samples were conditioned (65% relative humidity and 75° C. for 48 hours) and analyzed for total measured vapor phase (TMVP), mainstream smoke (MSS)HCN, and MSS carbonyl deliveries.
Cigarettes with cavities containing 50 mg of either semolina or MCM-41 were analyzed for TMVP smoke deliveries. TABLE A shows the results for selected vapor phase smoke compounds, comparing semolina with MCM-41:
MCM-41 showed a greater reduction of analytes in the TMVP/TPM of 112.1 μg/mg. TMVP/TPM was higher with semolina (147.8 μg/mg).
Mainstream smoke (MSS) carbonyl deliveries for semolina and MCM-41 are compared in TABLE B:
MCM-41 yielded less carbonyl in the mainstream smoke delivery than did semolina: 52.3 g/mg compared with 104.3 μg/mg, respectively. TPM normalized percentage reduction for mainstream smoke carbonyls is shown in
TABLE C shows a summary of mean polycyclic aromatic hydrocarbon (PAH) deliveries in particulate phase smoke:
When comparing the semolina with MCM-41, total particulate matter (TPM) normalized results suggest naphthalene deliveries were reduced by ˜29%. This effect may be due to the fact that naphthalene is the smallest and most volatile of the PAHs measured, demonstrating MCM-41's high affinity for small and volatile compounds. All other PAH compounds analyzed failed to show an appreciable affinity for the MCM-41 sample versus the control.
To summarize, the MCM-41 samples were found to be an effective adsorbent for select constituents found in mainstream smoke. Significant reductions were observed for nitrile, aldehyde, and ketone deliveries. In addition, PAH deliveries indicate reduction for naphthalene. MCM-41 has an affinity for molecules that form strong intermolecular bonds, and therefore, no reductions were observed for the analytes 1,3-butadiene, isoprene, furan, and benzene. The MCM-41 samples exhibited high filtration efficiencies for nitrites, aldehydes, and ketones when compared to the semolina control. In addition, MCM-41 displayed selectivity for naphthalene.
To evaluate the filtration efficiency of MCM-41, MCM-41 and Sorbite, a coal-based activated carbon derived from semi-anthracite coal, available from Calgon Carbons, were placed in hand-made cavity filtered cigarettes, the properties of which are explained above, and the filtration efficiencies of both were compared. Semolina was utilized as a control. The highly porous nature of MCM-41 invited the comparison to activated carbons, such as Sorbite. The MCM-41 samples were prepared according to the above-stated method. Sorbite was used without modification.
Three sample sets were prepared with hand-made cavity filtered cigarettes. TABLE D lists the filter additives and loadings for each sample:
The samples were pressure drop selected to diminish variances in aerosol deliveries. After conditioning, the samples were analyzed for total measured vapor phase (TMVP), polycyclic aromatic hydrocarbon (PAH), and mainstream smoke carbonyl (MSS carbonyl) deliveries.
All three samples were analyzed for TMVP. TABLE E lists vapor phase deliveries for each sample:
A direct comparison of the vapor phase data for MCM-41 and Sorbite reveals that, while activated carbons are a good general adsorbent for a broad range of analytes, MCM-41 is selective for the more polar analytes such as nitriles, aldehydes, ketones, and alcohols. This affinity for polar molecules can be explained by their strong intermolecular bonding with pendant hydroxide groups on the surface of the silica, and
All three samples were also analyzed for mainstream smoke carbonyls with the deliveries listed in TABLE F:
*Sem = Semolina
TABLE F shows mainstream smoke carbonyl deliveries comparing semolina, Sorbite/semolina, and MCM-41/semolina. MCM-41 delivered 842.0 μg/cigarette total carbonyls, while Sorbite delivered more carbonyls: 936.6 μg/cigarette.
Deliveries of polycyclic aromatic hydrocarbons (PAHs) were measured because of known reductions in naphthalene for samples containing MCM-41. TABLE G shows a complete list of PAH test results:
Total particulate matter (TPM) normalized reductions of naphthalene versus a semolina control for MCM-41 was ˜40%, and for Sorbite was ˜54%. No other reductions in PAHs were observed. Although naphthalene is the smallest and most volatile of the PAH analytes measured, reductions in naphthalene are presumably due to its volatility and not its size. The pore diameter of MCM-41 is large relative to anthracene, the next smallest analyte measured, in which no reductions were observed. These numbers reflect the capacity of Sorbite to adsorb non-polar molecules.
To summarize, the MCM-41 sample was found to be more selective for polar smoke constituents and outperformed the Sorbite for the removal of nitriles, ketones, alcohols, and aldehydes. The Sorbite sample was more selective for non-polar smoke constituents such as benzene, toluene, styrene, isoprene, and naphthalene. MCM-41 can compliment Sorbite and other additives, such as an ion-exchange resin, as a co-additive.
A sample of MCM-41 was prepared using the process as described in EXAMPLE 1. Additionally, copper nitrate was introduced into the MCM-41 reaction solution with a concentration of 3% by weight. The resulting gel was calcined at 400° C., forming a copper oxide impregnated MCM-41 having the same high surface area and vapor phase capacity as pure MCM-41, but with the added ability to reduce hydrogen cyanide and hydrogen sulfide. Compared to the semolina control as previously described, copper oxide impregnated MCM-41 showed a 56% reduction in HCN ad a 35% reduction in H2S.
The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modifications will become obvious to those skilled in the art upon reading this disclosure, and may be made without departing from the spirit of the invention and scope of the appended claims.
