Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02567295 2006-11-17
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Application of Mesoporous Molecular Sieves as
Selective Smoke Filtration Additives
by
Rodney D. Schluter and
Lamar Perry
CROSS-REFERENCE TO RELATED APPLICATIONS
This international patent application claims Paris Convention priority to and
benefit
from, currently pending, U.S. Patent Application serial number 10/860,775,
filed on 03 June
2004.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
Not applicable.
REFERENCE TO A "SEQUENTIAL LISTING," A TABLE, OR A COMPUTER
PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC
Not applicable.
BACKGROUND OF THE INVENTION
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.
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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 20A or less, while the
term "mesoporous"
generally refers to such materials with pore sizes of about 20-500A. 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 (2-50nm), 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.
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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.
SUMMARY OF THE INVENTION
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 M41 S, are useful in
smoking article
filter elements. M41 S 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 M41 S family, and contains a highly organized hexagonal array
of uniform
pores with controllable diameters from about 15 A to about 100 A. 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 (CTAC1), H20,
Na20, and
SiOZ. 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. Patent 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.)
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MCM-41 is effective for reducing levels of alcohols, aldehydes, ketones,
nitriles, 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-4 1.
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-4 1. MCM-41 can be impregnated with copper oxide for
greater HCN
and H2S reduction.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
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FIG. 1 is a graph showing total particulate matter normalized percentage
reductions of
various vapor phase analytes when utilizing MCM-41 in a cigarette filter.
FIG. 2 is a graph showing total particulate matter normalized percentage
reductions of
mainstream smoke carbonyls.
FIG. 3 is a graph showing selected vapor phase analytes percentage reductions
of
MCM-41 and Sorbite.
FIG. 4 is a graph showing mainstream smoke carbonyl percentage reductions of
MCM-41 and Sorbite.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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-4 1, 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
=0.3g/cm3 and a BET surface area of =1000m2/g. Although pore wall thickness
may vary,
MCM-41 typically has a uniform pore diameter of ;zz:3.7nm, 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.
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Example 1
MCM-41 ADSORPTIVE PROPERTIES
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
sainple 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 250mL 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 .5 hours, and then placed under static autogenous conditions (121 C, 1
8psi) 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
= 1300m2/g.
Sample sets of cigarettes containing 50mg 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.
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Cigarettes with cavities containing 50mg 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-4 1:
TABLE A. Vapor Phase Smoke Analysis Data (Ng/cig)
T Semolina (50 MCM-41 (50
Analyte
mg/tip) mg/tip)
H dro en sulfide 21.0 22.3
H dro en cyanide 76.4 68.1
Methanol 79.5 30.4
Acetaldehyde 647.0 536.1
Vinyl chloride 0.0 0.0
1,3-Butadiene 55.6 54.2
Acetonitrile 69.6 33.6
Propylene oxide 2.9 1.8
Acrolein 82.0 45.8
Furan 27.9 22.4
Pro ionaideh de 62.7 33.3
Acetone 228.5 91.1
Acrylonitrile 10.3 6.0
Carbon disulfide 3.8 4.0
Iso rene 396.4 371.5
Propionitrile 11.6 4.5
i-But raideh de 18.1 10.0
Methacrylonitrile 2.2 1.2
n-But raideh de 6.5 3.5
Methyl ethyl ketone 48.3 15.0
Crotonaldeh de 12.6 6.8
Benzene 35.1 33.3
Toluene 35.1 28.1
Styrene 3.0 1.3
Total TMVP 1936.1 1424.3
TPM m /ci 13.1 12.7
TMVP/TPM 147.8 112.1
(pg/mg)
MCM-41 showed a greater reduction of analytes in the TMVP/TPM of 112.1 g/mg.
TMVP/TPM was higher with semolina (147.8 g/mg). FIG. 1 shows computed total
particulate matter (TPM) normalized percentage reductions for various vapor
phase
constituents. These data suggest that the MCM-41 sample exhibited high
filtration
efficiencies for nitriles, ketones, and aldehydes when compared to the
semolina control.
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Large percentage reductions were shown for the analytes Propionitrile (58%),
Methanol
(59%), Methyl Ethyl Ketone (66%), and Propionaldehyde (43%). Overall, TMVP
deliveries
were reduced by 24% when utilizing MCM-41.
Mainstream smoke (MSS) carbonyl deliveries for semolina and MCM-41 are
compared in TABLE B:
TABLE B. MSS Carbonyl Deliveries ( g/cig)
Analyte Semolina MCM-41
(50 mg/tip) (50 mg/tip)
Acetaldeh de 701.7 444.8
Acetone 276.4 72.4
Acrolein 115.1 46.2
Butanone 84.6 17.9
But raideh de 45.8 14.1
Crotonaldeh de 28.0 10.9
Formaldehyde 55.7 34.4
Pro ionaideh de 58.2 24.5
Total 1366.0 664.0
TPM m /ci 13.1 12.7
Total/TPM 104.3 52.3
(pg/mg)
MCM-41 yielded less carbonyl in the mainstream smoke delivery than did
semolina:
52.3 g/mg compared with 104.3 g/mg, respectively. TPM normalized percentage
reduction
for mainstream smoke carbonyls is shown in FIG. 2. The data indicates that the
MCM-41
sample displayed an increased affinity for MSS carbonyls versus the semolina
control. The
MCM-41 sample reduced mainstream smoke carbonyl deliveries by a total of 49%
compared
to the semolina sample. MCM-41 reductions above 50% were calculated, versus
the control,
for the analytes acrolein, acetone, butanone, and butyraldehyde. Measured
formaldehyde
deliveries, when using MCM-41, showed a 34% reduction versus semolina.
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TABLE C shows a summary of mean polycyclic aromatic hydrocarbon (PAH)
deliveries in particulate phase smoke:
TABLE C. The Mean Levels of PAHs for the Cigarette Sam ples
Semolina MCM-41
Naphthalene 365.6 284.5
Fluorene 127.2 134.9
Phenanthrene 103.4 113.7
Anthracene 40.3 43.6
Fluoranthene 58.7 61.5
Pyrene 38.4 39.1
Benzofluorene 30.3 32.0
Benzanthracene 16.8 17.2
Chrysene 17.2 18.2
Benzofluoranthene 7.0 7.3
Benzo e rene 3.7 3.8
Benzo[a]pyrene
(BAP) 5.8 6.1
Pe lene 0.6 0.7
Dibenzanthracene 0.2 0.2
Benzo e lene 1.1 1.2
Total PAH (ng/cig) 816.4 763.9
TPM m /ci 11.3 11.8
Puff Number 6.9 6.8
PAH per TPM
n /m 72.0 64.6
BAP per TPM
n /m 0.52 0.51
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,
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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
nitriles,
aldehydes, and ketones when compared to the semolina control. In addition, MCM-
41
displayed selectivity for naphthalene.
Example 2
MCM-41 IN COMPARISON TO SORBITE AS A CIGARETTE FILTER ADDITIVE
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:
TABLE D. Loadin Amounts for Filter Components
Filter Components Loading (mg)
MCM-41/Semolina 50/50
Sorbite/Semolina 50/50
Semolina Control 100
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:
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TABLE E. Vapor Phase Smoke Analysis Data ( g/cig)
Semolina Sorbite/Semolina MCM-41/Semolina
1,3-Butadiene 69.8 69.8 69.7
Acetaldehyde 627.1 636.2 541.9
Acetone 294.7 216.5 120.9
Acetonitrile 84.2 69.6 45.2
Acrolein 75.9 50.6 43.4
Acrylonitrile 13.3 10.0 8.7
Benzene 58.9 31.6 41.2
Carbon Disulfide 4.1 3.9 3.9
Crotonaldehyde 21.6 6.3 8.3
Furan 41.4 39.1 38.9
H dro en Cyanide 78.0 73.3 70.7
H dro en Sulfide 20.0 15.1 19.9
Iso rene 551.4 426.2 473.7
Methacrylonitrile 2.5 1.5 1.3
Methanol 80.9 72.3 34.9
Methyl Ethyl Ketone 68.4 32.0 17.1
Pro ionaldeh de 58.2 45.7 39.4
Propionitrile 13.6 8.1 5.2
Propylene Oxide 3.8 3.8 3.0
Styrene 5.8 2.5 3.6
Toluene 62.7 23.8 35.7
Vinyl Chloride BQL BQL BQL
I-Bu raldeh de 28.7 21.0 18.2
N-Butyraldehyde 8.7 5.3 4.4
TMVP 2273.1 1863.7 1648.7
TPM 12.6 12.8 12.5
TMVP/TPM 180.4 145.6 131.9
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 FIG. 3 displays the
selectivity of
MCM-41.
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All three samples were also analyzed for mainstream smoke carbonyls with the
deliveries listed in TABLE F:
TABLE F. MSS Carbonyl Deliveries (Ng/cig)
Semolina Sorbite/Sem* MCM41/Sem*
Acetaldeh de 641.5 561.2 539.8
Acetone 256.7 164.2 104.9
Acrolein 106.7 64.4 67.4
Butanone 74.7 33.0 24.8
But raldeh de 40.8 19.8 18.5
Crotonaldeh de 27.2 16.7 11.6
Formaldehyde 51.8 43.6 40.1
Pro ionaideh de 53.9 33.6 35.0
Total Carbon Is 1253.3 936.6 842.0
Total Carbon Is/TPM 99.5 73.2 67.4
*Sem= Semolina
TABLE F shows mainstream smoke carbonyl deliveries comparing semolina,
Sorbite/semolina, and MCM-4 1 /semolina. MCM-41 delivered 842.0 g/cigarette
total
carbonyls, while Sorbite delivered more carbonyls: 936.6 g/cigarette. FIG. 4
shows
normalized percentage reductions for mainstream smoke carbonyls of MCM-41 and
Sorbite.
These results were consistent with the results of the vapor phase analyses.
Reductions
observed for the surfactant templated silica were (at a minimum) comparable to
reductions for
the Sorbite samples. A few analytes, such as acetone and crotonaldehyde, had
greater
reductions.
Deliveries of polycyclic aromatic hydrocarbons (PAHs) were measured because of
known reductions in naphthalene for samples containing MCM-4 1. TABLE G shows
a
complete list of PAH test results:
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TABLE G. Polycyclic Aromatic Hydrocarbons (PAH) Analysis Data (pg/cig)
PAHS - FTC Semolina Sorbite/Sem MCM41/Sem
Anthrecene 40.8 41.4 42.1
Benzanthracene 16.4 16.9 17.2
Benzo a rene 6.2 6.2 6.2
Benzo e rene 4.4 4.6 4.5
Benzofluoranthene 7.4 7.5 7.4
Benzofluorene 28.5 28.7 30.6
Benzo e lene 1.2 1.2 1.2
Chrysene 18.8 19.0 19.4
Dibenzanthracene 0.2 0.2 0.2
Fluoranthene 47.0 45.8 49.4
Fluorene 130.0 126.0 131.5
Naphthalene 453.0 198.0 271.0
Pe iene 0.6 0.6 0.6
Phenanthrene 111.0 110.5 111.0
Pyrene 39.5 39.0 39.9
PAHS TPM 13.3 12.7 13.2
Total PAH 904.9 645.3 732.0
Total PAH / TPM 68.3 50.7 55.4
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.
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EXAMPLE 3
COPPER OXIDE IMPREGNATED MCM-41
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.
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