U.S. patent application number 11/025818 was filed with the patent office on 2006-07-06 for surface-modified activated carbon in smoking articles.
This patent application is currently assigned to PHILIP MORRIS USA INC.. Invention is credited to JayA Fournier, Mohammad R. Hajaligol, Peter Lipowicz, Zhaohua Luan, John B. III Paine, Shuzhong Zhuang.
Application Number | 20060144410 11/025818 |
Document ID | / |
Family ID | 36143682 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060144410 |
Kind Code |
A1 |
Luan; Zhaohua ; et
al. |
July 6, 2006 |
Surface-modified activated carbon in smoking articles
Abstract
A surface-modified activated carbon is provided to reduce the
amount of free fine carbon particles among the activated carbon. By
surface-modifying the activated carbon with a layer, the activated
carbon can have increased mechanical strength and the fine carbon
particles among the activated carbon can be fastened to the layer.
Therefore, the layer allows for the level of free fine carbon
particles among the activated carbon to be reduced.
Surface-modified activated carbon can be used in smoking articles
so as to allow for adsorption by the activated carbon with reduced
free fine carbon particles in the smoking article and the smoke
produced.
Inventors: |
Luan; Zhaohua; (Midlothian,
VA) ; Fournier; JayA; (Richmond, VA) ;
Lipowicz; Peter; (Midlothian, VA) ; Hajaligol;
Mohammad R.; (Midlothian, VA) ; Zhuang; Shuzhong;
(Richmond, VA) ; Paine; John B. III; (Midlothian,
VA) |
Correspondence
Address: |
BUCHANAN INGERSOLL PC;(INCLUDING BURNS, DOANE, SWECKER & MATHIS)
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
PHILIP MORRIS USA INC.
|
Family ID: |
36143682 |
Appl. No.: |
11/025818 |
Filed: |
December 30, 2004 |
Current U.S.
Class: |
131/207 ;
131/202 |
Current CPC
Class: |
C01B 32/372 20170801;
A24D 3/163 20130101 |
Class at
Publication: |
131/207 ;
131/202 |
International
Class: |
A24F 1/20 20060101
A24F001/20 |
Claims
1. A cigarette, comprising: a tobacco rod including tobacco and a
filter, wherein said filter includes a surface-modified activated
carbon comprising: activated carbon; fine carbon particles on a
surface of the activated carbon; and a layer on a surface of the
activated carbon, wherein the layer comprises a hydrocarbon
compound, an additional layer of carbon or a polymer on the
activated carbon, wherein if the layer is a polymer, the polymer is
about 9-20 wt % of the surface-modified activated carbon total
weight.
2. The cigarette of claim 1, wherein the hydrocarbon compound
comprises a non-polar, weakly polar hydrocarbon compound, wax,
chained or branched paraffin or a polymeric hydrocarbon, wherein
the additional layer of carbon comprises a non-activated carbon
which at least partially fills pores in the surface-modified
activated carbon, or wherein the polymer is present in an amount of
10-18 wt % or 11-17 wt % of the surface-modified activated carbon
total weight.
3. The cigarette of claim 1, wherein the layer comprises an
additional layer of carbon, wherein the layer of carbon has a
different density than the activated carbon and modifies the pore
size distribution of the activated carbon.
4. The cigarette of claim 1, wherein the layer comprises an
additional layer of carbon, wherein the additional layer of carbon
has a higher density than the activated carbon.
5. The cigarette of claim 1, wherein the layer comprises a polymer,
wherein the polymer comprises a non-toxic, biodegradable and/or
permeable polymer.
6. The cigarette of claim 1, wherein the layer comprises a polymer,
wherein the polymer comprises polypropylene, polyethylene, silicone
polymer, poly(ethylene oxide), poly(ethylene glycol), poly(acrylic
acid), poly(vinyl acetate), poly(vinyl alcohol), pectin, alginate,
starch or block poly(ethylene oxide)-poly(propylene
oxide)copolymers or their derivatives.
7. The cigarette of claim 1, wherein the activated carbon comprises
granules, spheres, monoliths, beads, powders or fibers of activated
carbon.
8. The cigarette of claim 1, wherein the layer entraps the fine
carbon particles within the bulk of the layer, fastens the fine
carbon particles to surfaces of the layer or the activated carbon,
or increases the mechanical strength of the surface-modified
activated carbon to a mechanical strength greater than the
activated carbon without the layer.
9. The cigarette of claim 1, wherein the layer has a thickness
sufficient to at least partially cover the activated carbon and the
fine carbon particles.
10. The cigarette of claim 1, wherein the layer is effective for
adsorbing a targeted gas phase constituent when the cigarette is
smoked.
11. The cigarette of claim 1, wherein the layer is electrically
charged to attach the fine carbon particles on a surface of the
layer with a force greater than a force of a smoke stream formed
when the cigarette is smoked.
12. The cigarette of claim 1, wherein the surface-modified
activated carbon is located in a cavity of the filter.
13. The cigarette of claim 1, wherein the fine carbon particles are
less than 10 microns in diameter.
14. A cigarette filter, comprising: a filter with a cavity, wherein
said cavity includes a surface-modified activated carbon therein
comprising: activated carbon; fine carbon particles on a surface of
the activated carbon; and a layer on a surface of the activated
carbon, wherein the layer comprises a hydrocarbon compound, an
additional layer of carbon or a polymer, wherein if the layer is a
polymer, the polymer is about 9-20 wt % of the surface-modified
activated carbon total weight.
15. The cigarette filter of claim 14, wherein the hydrocarbon
compound comprises a non-polar or weak polar hydrocarbon compound,
wax, chained or branched paraffin, or a polymeric hydrocarbon,
wherein the additional layer of carbon comprises a non-activated
carbon which at least partially fills pores in the surface-modified
activated carbon, or wherein the polymer is present in an amount of
10-18 wt % or 11-17 wt % of the surface-modified activated carbon
total weight.
16. The cigarette filter of claim 14, wherein the layer comprises
an additional layer of carbon, wherein the additional layer of
carbon has a higher density than the activated carbon and modifies
the pore size distribution of the activated carbon.
17. The cigarette filter of claim 14, wherein the layer comprises a
polymer, wherein the polymer comprises a non-toxic, biodegradable
and/or permeable polymer.
18. The cigarette filter of claim 14, wherein the layer comprises a
polymer, wherein the polymer comprises polypropylene, polyethylene,
silicone polymer, poly(ethylene oxide), poly(ethylene glycol),
poly(acrylic acid), poly(vinyl acetate), poly(vinyl alcohol),
pectin, alginate, starch or block poly(ethylene
oxide)-poly(propylene oxide)copolymers or their derivatives.
19. The cigarette filter of claim 14, wherein the activated carbon
comprises granules, spheres, monoliths, beads, powders or fibers of
activated carbon.
20. The cigarette filter of claim 14, wherein the layer entraps the
fine carbon particles within the bulk of the layer, fastens the
fine carbon particles to surfaces of the layer or the activated
carbon, or increases the mechanical strength of the
surface-modified activated carbon to a mechanical strength greater
than the activated carbon without the layer.
21. The cigarette filter of claim 14, wherein the layer has a
thickness sufficient to at least partially cover the activated
carbon and the fine carbon particles.
22. A method of manufacturing a cigarette, comprising: forming
surface-modified activated carbon by: providing activated carbon
having fine carbon particles on surfaces thereof; and forming a
layer on surfaces of the activated carbon, wherein the layer
comprises hydrocarbon compound, carbon or polymer on the activated
carbon, wherein if the layer is polymer, the polymer is about 9-20
wt % of the surface-modified activated carbon total weight;
incorporating the surface-modified activated carbon into a
cigarette filter; and attaching the cigarette filter to a tobacco
rod to form a cigarette.
23. The method of claim 22, wherein the forming a layer on surfaces
of the activated carbon comprises: melting or dissolving a layer
compound in a solvent or solvent mixture to form a liquid solution;
suspending activated carbon in the liquid solution to impregnate
the layer compound into the activated carbon; and removing the
solvent or solvent mixture.
24. The method of claim 23, wherein the melting or dissolving the
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving petroleum pitch, coal tar pitch, pine tar pitch or a
synthetic aromatic polymer in a solvent or solvent mixture.
25. The method of claim 23, wherein the melting or dissolving the
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving an aromatic compound in 1-methyl-2-pyrrolidinone (NMP),
quinoline, trichlorobenzene, toluene, xylene or a mixture
thereof.
26. The method of claim 23, wherein the melting or dissolving a
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving a low-volatility, non-polar or weak-polar organic
compound or organic compound mixture with a boiling point above
about 150.degree. C. at about one atmosphere with low vapor
pressure at ambient conditions in a solvent or solvent mixture.
27. The method of claim 23, wherein the melting or dissolving the
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving wax, chained or branched paraffin, a polymeric
hydrocarbon, or a mixture thereof in a solvent or solvent
mixture.
28. The method of claim 23, wherein the melting or dissolving a
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving a non-toxic and biodegradable and/or permeable polymer
in a solvent or solvent mixture.
29. The method of claim 23, wherein the melting or dissolving a
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving polypropylene, polyethylene, silicone polymer,
poly(ethylene oxide), poly(ethylene glycol), poly(acrylic acid),
poly(vinyl acetate), poly(vinyl alcohol), pectin, alginate, starch,
poly(ethylene oxide)-poly(propylene oxide)copolymer or their
derivatives in a solvent or a solvent mixture.
30. The method of claim 23, wherein the melting or dissolving a
layer compound in a solvent or solvent mixture comprises: mixing or
dissolving a polymer compound in water, alcohol, hexane or a
mixture thereof.
31. The method of claim 23, wherein the suspending activated carbon
in the liquid solution to impregnate the layer compound into the
activated carbon comprises: suspending activated carbon granules,
spheres, monoliths, beads, powders or fibers in the liquid solution
to impregnate the layer compound into the activated carbon
granules, spheres, monoliths, beads, powders or fibers.
32. The method of claim 23, wherein the suspending activated carbon
in the liquid solution to impregnate the layer compound into the
activated carbon comprises: suspending activated carbon and fine
carbon particles in the liquid solution to impregnate the layer
compound into the activated carbon, wherein the layer compound
entraps the fine carbon particles within the layer compound.
33. The method of claim 23, wherein the suspending activated carbon
in the liquid solution to impregnate the layer compound into the
activated carbon, comprises suspending activated carbon and fine
carbon particles with a diameter of less than 10 microns in the
liquid solution to impregnate the layer compound into the activated
carbon and fasten the fine carbon particles on surfaces of the
activated carbon.
34. The method of claim 23, wherein the forming of the layer step
further comprises: carbonizing the layer compound by heating the
layer compound after removing the solvent or solvent mixture,
wherein the carbonizing of the layer compound forms a carbon layer
with a density different from the activated carbon.
35. The method of claim 34, wherein the carbonizing of the layer
compound by heating the layer compound comprises heating the layer
compound in an environment with a temperature between about
300.degree. C. and 1000.degree. C.
36. The method of claim 23, wherein the suspending activated carbon
in the liquid solution to impregnate the layer compound into the
activated carbon comprises wetness-incipient impregnation of the
layer compound into the activated carbon, rinsing the layer
compound through an activated carbon bed, or soaking activated
carbon in the layer compound.
37. A method of treating mainstream tobacco smoke, comprising:
drawing smoke from the smoking article, wherein the smoke passes
through a filter containing surface-modified activated carbon
comprising: activated carbon; and a layer on an internal surface
and an external surface of the activated carbon, wherein the layer
comprises a hydrocarbon compound, an additional layer of carbon or
a polymer on the activated carbon, wherein if the layer is a
polymer, the polymer is about 9-20 wt % of the surface-modified
activated carbon total weight.
38. The method of claim 37, wherein the layer is adapted to reduce
free fine carbon particles in the smoking article that are drawn
when smoke passes though the filter containing surface-modified
activated carbon.
Description
BACKGROUND
[0001] The present invention relates to activated carbon which is
treated to reduce the presence of fine particles in smoking
articles.
SUMMARY
[0002] In a first embodiment, activated carbon is treated to reduce
the formation and presence of fine particles in smoking articles.
The surface of the activated carbon is modified to improve the
mechanical integrity of the activated carbon and thus decrease the
propensity of the activated carbon to form fine particles. The
surface of the activated carbon is also modified to attach or
fasten existing fine particles to the activated carbon to reduce
the presence of fine particles. The surface of the activated carbon
can be modified by forming a hydrocarbon compound layer, a polymer
layer or a carbon layer on external and internal surfaces of the
activated carbon.
[0003] In another embodiment, a cigarette, comprises a tobacco rod
including tobacco and a filter, wherein said filter includes a
surface-modified activated carbon comprising activated carbon; fine
carbon particles on surfaces of the activated carbon; and a layer
on an internal surface and an external surface of the activated
carbon, wherein the layer comprises a hydrocarbon compound, an
additional layer of carbon or a polymer on the activated carbon,
wherein if the layer is a polymer, the polymer is about 9-20 wt %
of the surface-modified activated carbon total weight.
[0004] In another embodiment, a cigarette filter, comprises a
filter with a cavity, wherein said cavity includes a
surface-modified activated carbon therein comprising: activated
carbon; fine carbon particles on surfaces of the activated carbon;
and a layer on an internal surface and an external surface of the
activated carbon, wherein the layer comprises a hydrocarbon
compound, an additional layer of carbon or a polymer on the
activated carbon, wherein if the layer is a polymer, the polymer is
about 9-20 wt % of the surface-modified activated carbon total
weight.
[0005] In another embodiment, a method of manufacturing a
cigarette, comprises forming surface-modified activated carbon by
providing activated carbon having fine carbon particles on surfaces
thereof; and forming a layer on internal and external surfaces of
the activated carbon, wherein the layer comprises hydrocarbon
compound, carbon or polymer on the activated carbon, wherein if the
layer is polymer, the polymer is about 9-20 wt % of the
surface-modified activated carbon total weight; incorporating the
surface-modified activated carbon into a cigarette filter; and
attaching the cigarette filter to a tobacco rod to form a
cigarette.
[0006] In another embodiment, a method of treating mainstream
tobacco smoke by drawing the mainstream tobacco smoke through a
filter containing surface-modified activated carbon comprising:
activated carbon; fine carbon particles on surfaces of the
activated carbon; and a layer on an internal surface and an
external surface of the activated carbon, wherein the layer
comprises a hydrocarbon compound, an additional layer of carbon or
a polymer on the activated carbon, wherein if the layer is a
polymer, the polymer is about 9-20 wt % of the surface-modified
activated carbon total weight.
DETAILED DESCRIPTION
[0007] Activated carbon is a generic term used to describe a family
of carbonaceous adsorbents with an extensively developed internal
pore structure. Activated carbon can be produced by activating an
amorphous (non-graphitic) carbon, wherein amorphous (non-graphitic)
carbon can be produced by carbonizing a precursor, such as wood,
lignite, coal, coconut husk, peat, pitch, polymers, cellulose
fibers, or polymer fibers, etc., to form char. Preferably,
carbonization is carried out at high temperatures, i.e.,
300-1000.degree. C., preferably above 600.degree. C. in an inert
atmosphere. After carbonization, activation can be carried out by
heat treating the amorphous carbon or char with an oxidizing agent,
e.g., carbon dioxide or steam. During activation, some of the
carbon of the amorphous carbon or char is reacted with the
oxidizing agent and pores of various sizes, e.g., on the order of
angstroms to microns, are formed in the activated carbon.
[0008] The activated carbon could be in the form of granules,
spheres, monoliths, beads, powders or fibers. In exemplary
embodiments, the activated carbon can have an average particle size
of about 6 mesh to 300 mesh.
[0009] Activated carbon may include a distribution of micropores,
mesopores and macropores. The term "microporous" generally refers
to such materials having pore sizes of about 20 .ANG. or less,
while the term "mesoporous" generally refers to such materials with
pore sizes of about 20 to 500 .ANG.. The term "macroporous" refers
to pore sizes above 500 .ANG.. The relative amounts of micropores,
mesopores and macropores can be pre-selected relative to the
selected components from mainstream tobacco smoke that are to be
targeted and removed. Thus, the pore sizes and pore distribution
can be adjusted accordingly as needed for a certain
application.
[0010] Activated carbon can be incorporated in one or more
locations of the smoking article. Activated carbon is preferably
placed in filters to reduce their interaction with tobacco, such as
tobacco in the tobacco rod. For example, activated carbon can be
placed in the passageway of a tubular free-flow filter, in the
free-flow filter, intermingled with fibrous material, and/or in a
void space.
[0011] Highly activated carbon is dusty in nature due to intrinsic
porous structure resulting from the harsh carbonization and
activation treatment. Fine particles or "dust" of carbon with
particle sizes less than 10 microns are often created during either
or both of the carbonization and activation processes due to the
harshness of the processes on the mechanical integrity of the
activated carbon. Moreover, during cigarette manufacture wherein
carbon particles are added to a cavity of a cigarette filter,
mechanical handling of the carbon particles can lead to additional
fine particle generation.
[0012] During smoking, it would be desirable to avoid such fine
particles from becoming entrained in the smoke stream drawn through
the cigarette.
[0013] Conventionally, these fine particles have been removed by
washing the activated carbon with water under agitation. However,
additional fine particles can be formed after the washing due to
the somewhat fragile nature of the activated carbon.
[0014] The quantity of fine particles and the mechanical strength
of the activated carbon vary depending on the origin of the
precursor and the activation treatment. For example, activated
carbon formed from lower density precursors, such as coconut husks,
tend to have a lower density and a lower mechanical strength than
activated carbon formed from higher density precursors, such as
pitch. However, processing pitch tends to be more expensive and may
not be available in some forms, such as particles for example.
Thus, less expensive activated carbon may have lower mechanical
strength and thus may also lead to increased amounts of fine
particles.
[0015] Additionally, after the activation process, fine particles
may also be generated due to the somewhat fragile nature of
activated carbon as mentioned above. For example, when activated
carbon is provided in smoking articles, fine particles may be
formed in the smoking articles by attrition, abrasion between
activated carbon particles and compaction of the activated carbons
during the packaging, transporting, and/or other processing of the
activated carbons. Therefore, embodiments provided herein increase
the mechanical strength of activated carbon and in turn decrease
the amount of fine particles present.
[0016] As used herein "surface-modified activated carbon" includes
mechanically strengthened activated carbon with a layer thereon or
activated carbon that has undergone surface modification by forming
a layer thereon, then treating the layer to convert the layer into
a higher strength surface modification.
[0017] A preferred embodiment includes a method of reducing fine
particles by forming a surface-modified activated carbon to reduce
the presence and production of fine particles in smoking articles.
By forming a surface-modified activated carbon, the activated
carbon can have increased mechanical strength against breakage and
reduced formation of fine particles. Additionally, by using the
surface-modified activated carbon, any fine particles present can
be fastened on a surface of the surface-modified activated carbon,
thus reducing contamination by the fine particles in smoking
articles.
[0018] As used herein, the term "hydrocarbon compound" is intended
to include lower molecular weight hydrocarbons, while the term
"polymer" is intended to include higher molecular weight
hydrocarbons, as well as other polymer compositions. For example,
exemplary hydrocarbon compounds include waxes, paraffins, etc.,
while exemplary polymers include polypropylene, pectin, etc.
[0019] As provided, the activated carbon can be surface-modified by
forming a layer of hydrocarbon compound, such as a wax, onto the
activated carbon, wherein the hydrocarbon compound can adhere to
external and internal surfaces of activated carbon. By this
adherence, the hydrocarbon compound can strengthen the activated
carbon by increasing the mechanical integrity of the activated
carbon, as well as fasten fine particles by coating the fine
particles into the layer.
[0020] Alternatively, the activated carbon can be surface-modified
by forming a layer of polymer, such as a polypropylene or pectin,
onto the activated carbon wherein the polymer, similar to the wax,
can adhere to external and internal surfaces of activated carbon.
Again, by this adherence, the polymer can strengthen the activated
carbon by increasing the mechanical integrity of the activated
carbon, as well as, fasten fine particles by coating the fine
particles into the layer.
[0021] Or, as yet another alternative, a surface-modified activated
carbon can be formed by providing an aromatic compound, such as
pitch, on external and internal surfaces of activated carbon before
heat treating the aromatic compound and the activated carbon to
form a carbon layer on the activated carbon. By forming this carbon
layer on the porous framework of the activated carbon, some of the
pores can be filled thus changing the pore distribution of the
activated carbon. Also, the addition of the carbon layer allows for
the density of the activated carbon to be increased which in turn
can cause the strength of the activated carbon to be increased.
Also, the addition of the carbon layer allows for fine particles to
be fastened by the carbon layer. Finally, the carbon layer can be
formed using a precursor material with a higher density than the
precursor material used to form the activated carbon. By providing,
for example, a pitch precursor for forming the carbon layer while
providing coconut husk precursor for the activated carbon, a carbon
coated activated carbon can be formed with the increased mechanical
strength from the pitch precursor carbon layer with decreased cost
by providing a base of less expensive coconut husk precursor
activated carbon.
[0022] As mentioned above, the surface-modified activated carbon
improves the mechanical strength and reduces the amount of fine
particles of the activated carbon. Desirably, the surface
modification can be used to reduce breakage of the activated carbon
and to reduce the amount of broken portions of the activated carbon
that may become loose in a smoking article during storage of the
smoking article.
[0023] If a hydrocarbon compound is used to surface-modify the
activated carbon, the hydrocarbon compound can be formed on
internal and external surfaces of the activated carbon. This is
done by first, forming a liquid solution, preferably a homogeneous
liquid solution, by melting or dissolving the hydrocarbon compound
in a solvent or solvent mixture. Next, the activated carbon can be
suspended in the liquid solution to impregnate the hydrocarbon
compound into the activated carbon, thus covering the internal and
external surfaces of the activated carbon with the hydrocarbon
compound. Next, the solvent can be removed by evaporating or
extracting the solvent from the activated carbon to form a
hydrocarbon compound layer, preferably a thin, uniform thickness
layer, on internal and external surfaces of the activated
carbon.
[0024] By forming the hydrocarbon compound layer on the activated
carbon, fine particles existing on internal or external surfaces of
the activated carbon can be entrapped within the hydrocarbon
compound layer or can be covered or fastened onto the internal or
external surfaces of the activated carbon by the layer, thus
reducing the number of free fine particles. Additionally, the
hydrocarbon compound layer on the activated carbon can increase the
mechanical integrity of the activated carbon such that if the
layered activated carbon is subjected to vibration or other
mechanical disturbance, fewer fine particles are formed and/or
discharged, which in turn can reduce the levels of the fine
particles. In other words, for example, a viscous wax layer can be
formed on activated carbon, wherein the viscous wax layer sticks to
both the activated carbon and the fine particles, and the viscous
wax layer also increases the mechanical strength of the activated
carbon because of its viscosity.
[0025] Preferably, the hydrocarbon compound is either non-polar or
weakly polar to minimize surface tension between the hydrocarbon
compound layer and the activated carbon, which is often weakly
polar. By using non-polar or weakly polar hydrocarbon compounds, an
improved uniformity of the layer can be realized based on the
polarity. Additionally, the non-polarity or weak polarity of the
hydrocarbon compounds can change the selectivity of the activated
carbon to target non-polar or weakly polar smoke constituents.
[0026] The hydrocarbon compound is preferably a low volatility
material with a boiling point over about 150.degree. C. at about
one atmosphere with a low vapor pressure at ambient conditions to
ensure stability of the hydrocarbon compound on the activated
carbon. Thus, the hydrocarbon compound can be provided to not
vaporize during smoking of a cigarette with hydrocarbon compound
coated activated carbon therein.
[0027] Examples of hydrocarbon compounds that may be used to coat
activated carbon include, but are not limited to: waxes, chained or
branched paraffin, or polymeric hydrocarbons, wherein the
hydrocarbon compounds can be provided in solid or liquid form.
Preferably, such hydrocarbon compounds, however, have a high
viscosity on the activated carbon to prevent migration. Exemplary
solvents include, but are not limited to: organic solvents, such as
ethers, acetone, MEK (methyl ethyl ketone), hexane, toluene, and
xylene.
[0028] As an alternative to hydrocarbon compounds, as mentioned
above, polymers can also be used to coat activated carbon. If a
polymer is used to surface modify the activated carbon, the polymer
can be formed on internal and external surfaces of the activated
carbon. This is preferably done by first, forming a liquid
solution, preferably a homogeneous liquid solution, by melting or
dissolving the polymer in a solvent or a solvent mixture. Next, the
polymer can be loaded into the activated carbon by allowing the
liquid solution to soak into the activated carbon, thus
impregnating the polymer into the activated carbon. The impregnated
polymer can then form a polymer layer, preferably a thin, uniform
thickness layer, on internal and external surfaces of the activated
carbon. For example, the activated carbon can be layered by
wetness-incipient impregnation by the liquid solution, by flowing
the liquid solution through a bed of activated carbon, or by
soaking the carbon in the liquid solution and then removing the
excess solution. Next, a stepwise thermal treatment can be
performed to release solvent and open the porous structure of the
activated carbon without adversely impacting the internal porous
structure of the activated carbon. For example, a stepwise thermal
treatment in a temperature range of 100 to 300.degree. C. can be
used to release a solvent, such as hexane.
[0029] Preferably, the amount of polymer coated on the activated
carbon is about 9 to 20 wt % of the total polymer coated activated
carbon weight in order to provide mechanical strength, while still
providing accessibility to the pores and thus the activated carbon
smoke adsorption properties. Alternatively, the polymer is
preferably provided in about 10-18%, 11-17 wt %, 12-16 wt %, 10-12
wt %, 12-14 wt %, 14-16 wt %, 16-18 wt % or 18-20 wt % to balance
the mechanical strength of the activated carbon with the adsorption
properties of the activated carbon.
[0030] In addition to the benefits mentioned above, another benefit
to using a polymer layer is that the polymer layer can possess
electrical charges capable of trapping fine particles with
electrical forces, such as by static electricity force.
[0031] Additionally, the permeability of a polymer layer can be
tunable, thus allowing for adsorption selectivity of targeted
constituents by the layered activated carbon. For example, a
polymer layered activated carbon in a cigarette filter can include
a polymer specifically selected to allow the activated carbon to
selectively adsorb carbon monoxide or other specific gaseous
constituents of the cigarette smoke when the cigarette is
smoked.
[0032] Exemplary polymers are non-toxic and are preferably
biodegradable and/or smoke permeable, such that cigarette smoke can
permeate the polymer to access the activated carbon. Additionally,
exemplary polymers preferably have been approved by the Food and
Drug Administration (FDA) and have a prolonged shelf life. Examples
of such polymers include, but are not limited to: synthetic
polymers, such as polypropylene, polyethylene, silicone polymer,
poly(ethylene oxide), poly(ethylene glycol), poly(acrylic acid),
poly(vinyl acetate), poly(vinyl alcohol), various block
poly(ethylene oxide)-poly(propylene oxide)copolymers, other
copolymers or other block copolymers or their derivatives and/or
natural polymers, such as pectin, alginate or starch.
[0033] Exemplary solvents or co-solvents preferably have relatively
low boiling points, and can solvate the exemplary polymers listed
above, for example, exemplary solvents include, but are not limited
to: water, alcohol, such as methanol or ethanol, or hexane.
[0034] If a carbon layer from an aromatic compound is used to
surface modify the activated carbon rather than hydrocarbon
compounds or polymers, the aromatic compound can be formed on
internal and external surfaces of the activated carbon. This is
done by first, forming a liquid solution, preferably a homogeneous
liquid solution, by melting or dissolving the aromatic compound in
a solvent or solvent mixture. Next, the activated carbon can be
suspended in the liquid solution to allow the aromatic compounds to
impregnate the activated carbon, thus covering the surfaces of the
activated carbon. Next, the solvent can be removed by filtering,
then evaporating or extracting the remaining solvent.
[0035] After the solvent is removed, the layered activated carbon
can be stabilized by heating according to a predetermined heating
schedule, such that the aromatic compounds can be converted into a
stabilized, infusible form prior to carbonization. Next, the
stabilized, infusible form aromatic compounds can be carbonized by
heat treating the stabilized, infusible form aromatic compounds on
the activated carbon in an inert environment. By carbonizing the
stabilized, infusible form aromatic compounds, a new carbon layer
can thereby be formed on the surfaces of the activated carbon.
[0036] Preferably, the carbon layer on the activated carbon is not
itself activated, as activation of the carbon layer may cause loss
of at least part of the carbon layer, and a decrease of its
mechanical strength. Thus, while activation of the carbon layer may
be done, such activation is not preferred due to possible loss
issues.
[0037] Examples of aromatic compounds that may be used include, but
are not limited to: petroleum pitches, coal tar pitches and pine
tar pitches, other natural or synthetic aromatic compounds, and
mixtures thereof. These aromatic compounds are preferred because of
their high density, which in turn after carbonization, leads to
higher mechanical strength carbon than can be achieved by
carbonizing lower density carbonaceous precursors. Thus, by coating
and carbonizing a pitch precursor on a lower density precursor
activated carbon, the higher mechanical strength of a carbonized
pitch can be provided on a lower cost, lower density precursor
activated carbon.
[0038] Examples of solvents that may be used to melt or dissolve
the aromatic compounds may include, but are not limited to:
N-methyl-2-pyrrolidinone (NMP), quinoline, trichlorobenzene,
toluene, xylene, other solvents used for dissolving aromatic
compounds and mixtures thereof.
C. Smoking Articles
[0039] The surface-modified activated carbons are preferably used
in smoking articles, specifically filter portions of smoking
articles. The smoking articles envisioned herein include
cigarettes, such as traditional and non-traditional cigarettes,
cigars and other smoking devices. Non-traditional cigarettes
include, for example, cigarettes for electrical smoking systems as
described in commonly-assigned U.S. Pat. Nos. 6,026,820; 5,988,176;
5,915,387; 5,692,526; 5,692,525; 5,666,976; and 5,499,636, the
disclosures of which are incorporated by reference herein in their
entireties.
[0040] A cigarette typically contains two sections, a
tobacco-containing portion often referred to as the tobacco or
cigarette rod, and a filter portion, which may be referred to as a
filter tipping. The tipping paper overlaps an end portion of the
tobacco rod to hold the filter and tobacco rod together.
[0041] The tobacco rod, or tobacco containing element of the
cigarette, typically includes a cigarette wrapping paper in which
shreds of tobacco is wrapped with an adhesive holding the seams of
the paper together.
[0042] When the tobacco rod is lit or heated for smoking,
mainstream tobacco smoke is drawn from the lit or heated end
downstream to the filter end of the tobacco rod and further
downstream through the filter.
[0043] The term "mainstream smoke" includes the mixture of gases
and/or aerosols passing down a smoking article, such as a tobacco
rod, and issuing from an end, such as through the filter end, i.e.,
the amount of smoke issuing or drawn from the mouth end of a
cigarette during smoking of the cigarette. The mainstream smoke
contains air that is drawn in through the heated region of the
cigarette and through the paper wrapper.
[0044] "Smoking" of a cigarette (or smoking article) generally
involves lighting one end of the cigarette and drawing the smoke
downstream through the mouth end of the cigarette, while the
tobacco contained therein undergoes a combustion reaction or
heating. However, the cigarette may also be smoked by other means.
For example, the cigarette may be smoked by heating the cigarette
using an electrical heater, as described, for example, in
commonly-assigned U.S. Pat. Nos. 6,053,176; 5,934,289; 5,591,368 or
5,322,075, each of which is incorporated herein by reference in its
entirety.
[0045] Examples of suitable types of tobacco materials that may be
used include, but are not limited to, flue-cured tobacco, Burley
tobacco, Maryland tobacco, Oriental tobacco, rare tobacco,
specialty tobacco, reconstituted tobacco, blends thereof and the
like. The tobacco material may be provided in any suitable form,
including, but not limited to, tobacco lamina, processed tobacco
materials, such as volume expanded or puffed tobacco, processed
tobacco stems, such as cut-rolled or cut-puffed stems,
reconstituted tobacco materials, blends thereof, and the like.
Tobacco substitutes may also be used.
[0046] In cigarette manufacture, the tobacco is normally used in
the form of cut filler, i.e., in the form of shreds or strands cut
into widths ranging from about 1/10 inch to about 1/20 inch or even
about 1/40 inch. The lengths of the strands range from between
about 0.25 inch to about 3.0 inches. The cigarettes may further
comprise one or more flavors, as described above, or other
additives (e.g., burn additives, combustion modifying agents,
coloring agents, binders, etc.).
[0047] The filter material of the filter may be any of the variety
of fibrous materials for use in tobacco smoke filter elements.
Typical materials include cellulose acetate, polypropylene or
paper. Preferably, the filter material will be cellulose
acetate.
[0048] Various cigarette filter constructions may be used, where
exemplary filter structures that may be used include, but are not
limited to, a mono filter, a dual filter, a triple filter, a single
or multi-cavity filter, a recessed filter, a free-flow filter,
combinations thereof and the like.
[0049] Mono filters typically contain cellulose acetate tow or
cellulose paper materials. Pure mono cellulose filters or paper
filters offer good tar and nicotine retention, and are highly
degradable. Dual filters typically comprise a cellulose acetate
mouth end and a pure cellulose or cellulose acetate segment. The
length and pressure drop of the segments in a dual filter may be
adjusted to provide optimal sorption, while maintaining acceptable
draw resistance. Triple filters may include mouth and smoking
material or tobacco side segments, and a middle segment comprising
paper. Cavity filters include two segments, e.g., acetate-acetate,
acetate-paper or paper-paper, separated by at least one cavity.
Recessed filters include an open cavity on the mouth side.
[0050] Preferably, the surface-modified activated carbon is
provided in filters of the smoking articles, as mentioned above.
The filters may also be ventilated and/or may include in addition
to the surface-modified activated carbon, other sorbents, catalysts
or other additives suitable for use in filters of smoking
articles.
[0051] Variations and modifications of the foregoing will be
apparent to those skilled in the art. Such variations and
modifications are to be considered within the purview and scope of
the claims appended hereto.
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