Note: Descriptions are shown in the official language in which they were submitted.
CA 02565112 2011-01-24
SELECTIVE FILTRATION OF CIGARETTE SMOKE
USING CHITOSAN DERIVATIVES
15
FIELD OF INVENTION
This invention concerns improvements relating to tobacco smoke filers. More
particularly, the invention relates to a cigarette filter that can selectively
remove
undesirable constituents from tobacco smoke.
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BACKGROUND OF THE INVENTION
A wide variety of materials have been suggested in the prior art as filters
for tobacco
smoke. Examples of such filter materials include cotton, paper, cellulose
acetate, and certain
synthetics. Many of these filter materials, however, are only effective in the
removal of
particulates, tars and condensable components from tobacco smoke. The art is
replete with a
myriad of filtration techniques and materials for removing undesirable
components in smoke
and for causing other reactions as the smoke passes through filtration beds or
other reactive
media. Among the problems encountered with prior filters has been the plugging
or clogging
with use and the consumption or rendering ineffective of reactive filtering
surfaces and
materials.
Filters made from filamentary or fibrous material such as cellulose acetate
tow or
paper are somewhat effective in the removal of particulate phase constituents
of tobacco
smoke. However, they have little or no effect in removing certain gaseous
components in the
vapor phase of the tobacco smoke such as hydrogen cyanide, aldehydes,
carbonyls, metals
and sulphides. These volatile constituents can be removed by adsorption and
absorption on a
suitable surface or by chemical reaction.
Some known substances which act as absorbents and adsorbents include activated
carbon, porous minerals, and ion exchange resins. Ion-exchange resins of
porous structure
have been found to be somewhat effective, but their efficiency diminishes
during smoking, as
does that of carbon and porous minerals. This may be due to the material
becoming saturated
and, therefore, increasingly inactive or it may be due to the release of
adsorbed material by
thermal desorption of retained substances.
Resins which contain major proportions of tertiary amino or quaternary
ammonium
groups have been found not to be suitable for removing aldehydes from tobacco
smoke.
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Chitosan and chitosan with a maximum number of amino groups have been
found not to be effective. Among the problems encountered with these materials
is
that they do not provide a filtration media allowing for the continuous flow
of smoke
at a low pressure differential or gradient. Other problems with selective
filtration
medias have been found. For example, the use of certain amino acids, such as
glycine,
have been found effective in removing aldehydes in tobacco smoke. However, it
has
been discovered that while glycine can reduce the level of formaldehyde in
tobacco
smoke, it is not stable in the cigarette filter manufacturing process.
Moreover, the use
of amino acids causes the release of ammonia odor during storage.
SUMMARY OF THE INVENTION
It has been discovered that chitosan can be chemically modified to have the
physical attributes of a filter medium and have a chemical composition capable
of
effectively adsorbing and absorbing undesirable smoke ingredients, yielding
superior
performance as a cigarette filter.
Thus, the present invention provides cigarette filter arrangements and, more
particularly, cigarette filters that can selectively remove undesirable
constituents in
the vapor phase of tobacco smoke such as hydrogen cyanide, aldehydes, metals
and
sulphides without the drawbacks or disadvantages associated with the prior art
as
previously described.
There is also provided a novel cigarette and smoke filter embodying a porous
resin of cross-linked chitosan.
There is also provided cross-linked chitosan reactive materials having a high
ratio of surface-to-volume and having a reduced number of reactive amino
groups for
selective smoke filtration in a smoking article.
According to the present invention, a tobacco-smoke filter includes an
adsorbent/ absorbent for removal of undesirable volatile tobacco-smoke
constituents
such as hydrogen cyanide, aldehydes, carbonyls, metals and sulphides.
Chitosan is cross-linked with glyoxal to form porous resins having a high
surface area to mass ratio for the selective filtration of cigarette smoke,
particularly
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for the removal of undesirable smoke constituents such as aldehydes, hydrogen
cyanide, carbonyls, sulphides and metals.
Chitosan is a linear polyglucosamine polymer obtained from the deacetylation
of chitin, a polysaccharide found in the exoskeleton of crustaceans. Chitin
also occurs
in insects and in lesser quantities in many other animal and vegetable
organisms.
Chitin is a linear polymer of 2-deoxy, 2-acetyl-amino glucose analogous to
cellulose
in chemical structure. It is insoluble in almost all media except strong
mineral acids
and due to the acetylated amino group is relatively unreactive.
When chitin is deacetylated by treatment with strong alkalis, the product is
chitosan which contains one free amino group for each glucose building unit in
the
polymer. It is still a long chain linear polymer but is now a highly reactive
cationic
poly-electrolyte material. It will form salts with simple organic acids, such
as formic,
acetic, tartaric, citric, etc. and is soluble in dilute aqueous solutions of
such
substances. Chitosan is nontoxic and biodegradable, and it has found utility
in
numerous applications, including chromatography, drug delivery, and cosmetics.
A porous chitosan resin may be formed by a phase inversion technique. This is
accomplished by dissolving flaked or powdered chitosan in a suitable solvent,
such as
aqueous acid, and then coacervating in a solution of aqueous base to form
water
swollen chitosan gel beads. The beads may be cross-linked using glyoxal, to
improve
the mechanical strength and reduce the solubility of the beads. The wet beads
are then
freeze dried to yield a porous cross-linked resin. Drying may also be
accomplished by
vacuum or air drying.
A porous resin may also be prepared using a thermally induced phase
separation technique. This is accomplished by dissolving flaked or powdered
chitosan
in a suitable solvent, such as aqueous acetic acid, and then adding the
solution to a
non-solvent, such as methanol, and cooling the resulting solution below the
freezing
point of the chitosan solution which yields frozen beads. These beads may then
be
neutralized with a base and cross-linked with glutaraldehyde and separately
with
glyoxal to modify the final properties of the chitosan resin. The resulting
beads may
then be freeze dried to yield a porous cross-linked chitosan resin. Drying may
also be
accomplished by vacuum and by air drying.
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The cross-linked resins produced by both methods have a reduced number of
reactive amino groups. The reduced number of reactive amino groups is a result
of the
cross-linking reaction with glyoxal. It has been surprisingly discovered that
the
described invention, having a reduced number of reactive amino groups, is
selective
in removing hydrogen cyanide and formaldehyde from tobacco smoke. It has also
been surprisingly found that the cross-linked chitosan resin having a reduced
number
of reactive amino groups exhibits greater selective removal activity than that
associated with the prior art where a maximum number of reactive amino groups
have
been employed.
The porous resin of the present invention may be incorporated into a cigarette
in a variety of ways. The resin may be disposed between filter sections
wherein these
sections may be comprised of fibrous, filamentary and paper materials. The
resin may
also be dispersed throughout a filter tow. Alternatively, the resin may be
placed
within a filter bed in a filter section and the resin may be packed along the
filter bed.
The resin may also be incorporated into a part of the cigarette filter such as
the tipping
paper, a shaped paper insert, a plug, a space, or even a free-flow sleeve.
Additionally,
the resin may be incorporated into cigarette filter paper, attached to the
tobacco rod
with tipping paper or even incorporated within a cavity in the filter.
Accordingly, the present invention provides a tobacco-smoke filter comprising
a chitosan resin having chitosan cross-linked with glyoxal.
The present invention also provides a tobacco smoke filtration media obtained
by the steps of. dissolving chitosan in a first solution having acetic acid in
a range of
about 0.1% to about 10% forming a second solution having chitosan in a range
of
about 0.1% to about 20%; filtering said second solution; adding said second
solution
drop-wise to a precipitation bath, wherein said precipitation bath has sodium
hydroxide in a range of about I molar to about 5 molar, forming gel beads;
rinsing
said gel beads; suspending said gel beads in a cross-linking solution
containing a
solvent and a cross-linking compound glyoxyl for about 1 hour to about 24
hours
forming cross-linked beads; rinsing said cross-linked beads; and drying said
cross-
linked beads forming a porous chitosan crossed-linked resin bead.
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The present invention also provides a tobacco-smoke filter comprising in the
range of about 10 mg to about 200 mg of a chitosan cross-linked with glyoxal
resin,
said resin having a size within the range of about 16 mesh to about 70 mesh.
The present invention also provides a tobacco-smoke filter comprising
chitosan resin beads cross-linked with glyoxal, said cross-linked chitosan
resin beads
having a reduced number of reactive amino groups than said chitosan resin
beads
prior to cross-linking.
In a further aspect the present invention provides a method of smoke
filtration
comprising providing a smoking article filter having chitosan resin cross-
linked with
glyoxal, and passing smoke through said filter.
In a further aspect the present invention provides a method of fluid-flow
filtration that comprises providing a filtration bed having chitosan resin
cross-lined
with glyoxal in said bed and passing fluid containing constituents through
said
filtration bed, wherein said fluid is cigarette smoke and said constituents
comprise
pyrolysis products of cigarette materials.
In a further aspect the present invention provides a method of removing from
cigarette smoke pyrolysis products of cigarette materials comprising providing
a
filtration region having chitosan resin cross-linked with glyoxal disposed
throughout
the region and passing said pyrolysis products through said filtration region.
In a further aspect the present invention provides a method of manufacturing a
filter which is useful for removing a gaseous component of a gas mixture,
comprising
steps of. preparing a filter media having a cross-linking compound glyoxal,
wherein
said cross-linking compound is cross-linked to chitosan forming a bead; and
incorporating said filter media in a filter wherein said filter media removes
said
gaseous component of said gas mixture.
In a further aspect the present invention provides a method of removing a
gaseous component of a gas mixture comprising passing said gas mixture in
contact
with a filter, wherein said filter has a reagent comprising at least one
reactive
functional group cross-linked to chitosan such that said reagent adsorbs,
absorbs, or
chemically reacts with said gaseous component of said gas mixture and removes
said
gaseous component from said gas mixture, wherein said functional group is
glyoxal.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples of the present invention are given below by way of illustration and
not by way of limitation. These examples include two distinct methods of
preparing
chitosan beads as well as several distinct methods of cross-linking the
chitosan beads.
All of the following examples yield porous cross-linked chitosan resin beads
having a
reduced number of reactive amino groups.
EXAMPLES
EXAMPLE 1:
Porous chitosan resin was synthesized according to a phase inversion
technique. This was accomplished by preparing a 7% chitosan solution by
dissolving
approximately 20 grams of chitosan flakes (practical grade) in 3.5% acetic
acid. The
mixture increased in viscosity and gelled upon the completion of the chitosan
addition. Further dilution with acetic acid resulted in a solution having
approximately
3% chitosan flake. This provided for a chitosan solution having a more
manageable
viscosity. The total amount of acetic acid used to dissolve the chitosan flake
was
approximately 665 milliliters. The solution was then filtered to separate any
undissolved materials. This chitosan solution was then added dropwise to a
precipitation bath of 2 molar sodium hydroxide to yield water swollen gel
beads. The
gel beads were then filtered and washed with deionized water until neutral, pH
of the
wash water being approximately 7.
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Heterogeneous cross-linking of the chitosan beads was then accomplished by
suspending the beads for several hours in approximately 1 liter of 2.5%
aqueous solution of
glutaraldehyde. After cross-linking, the beads were then filtered and washed
with warm
deionized water to remove any excess glutaraldehyde. Subsequently, the beads
were freeze
dried which resulted in porous glutaraldehyde cross-linked chitosan resin
beads. The BET
surface area of the resin was measured to be approximately 120 m2/g. The beads
were then
milled and sieved to retain particles having approximately 16 to 70 mesh. A
surface area
analysis of the milled resin showed no appreciable change in surface area. The
BET surface
area of the sieved sample was measured to be approximately 117 m2/g.
EXAMPLE II:
Porous chitosan resin was synthesized according to the phase inversion
technique in
Example 1. In this example the heterogeneous cross-linking of the chitosan
beads was
accomplished by suspending the beads for several hours in a 2.5% aqueous
solution of
glyoxal. After cross-linking, the beads were filtered and washed with warm
deionized water
to remove any excess glyoxal. The beads were then freeze dried which resulted
in porous
glyoxal cross-linked chitosan resin beads.
EXAMPLE III:
Porous chitosan resin was prepared according to a thermally induced phase
separation
procedure. A 4% chitosan solution was prepared by dissolution of chitosan
powder (Vansen
Chemical; 92% deacetylation) in 3.5% acetic acid. A precipitation bath of
sodium hydroxide
(2 molar) in 20:80 methanol / water solution was prepared and cooled to 0 C.
The chitosan
solution was then added dropwise to the precipitation bath with moderate
stirring.
Precipitation of chitosan occurred shortly after addition of the solution to
the precipitation
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bath. The precipitation bath having the chitosan precipitate was then allowed
to return to
room temperature. The resulting beads were filtered and washed with deionized
water until
the wash water became neutral, having a pH of approximately 7.
Heterogeneous cross-linking of the chitosan beads was then accomplished by
suspending approximately 396 grams of wet beads in approximately 1980
milliliters of 2.5%
aqueous glutaraldehyde solution for several hours. After cross-linking, the
beads were
filtered and washed with both warm and cold deionized water to remove any
excess
glutaraldehyde. Subsequent freeze drying of the beads resulted in porous
glutaraldehyde
cross-linked chitosan resin beads. The beads were then milled and sieved to
approximately
16 to 70 mesh. The BET surface area of the resin was measured to be
approximately 210
m2/g.
EXAMPLE IV:
Porous chitosan resin was prepared according to the thermally induced phase
separation procedure in Example III. In this example, the heterogeneous cross-
linking of the
chitosan beads was accomplished by suspending approximately 261 grams of wet
beads in
approximately 1300 milliliters of 2.5% aqueous glyoxal solution for several
hours. After
cross-linking, the beads were filtered and washed with both warm and cold
deionized water
to remove any excess glyoxal. Subsequent freeze drying resulted in porous
glyoxal cross-
linked chitosan resin beads. The beads were then milled and sieved to
approximately 16 to
70 mesh. The BET surface area of the cross-linked resin was measured to be
approximately
145 m 2/g.
EXAMPLE V :
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Porous chitosan resin was prepared according to the thermally induced phase
separation procedure in Example III. In this example, the heterogeneous cross-
linking of the
chitosan beads was accomplished by suspending the beads in a solution of
glutaraldehyde and
ethanol for several hours. After cross-linking, the beads were filtered and
washed with
ethanol to remove any excess glutaraldehyde. Subsequent vacuum drying resulted
in porous
glutaraldehyde cross-linked chitosan resin beads.
EXAMPLE VI:
Porous chitosan resin was prepared according to the thermally induced phase
separation procedure in Example III. In this example, the heterogeneous cross-
linking of the
chitosan beads was accomplished by suspending the beads in a solution of
glutaraldehyde and
water for several hours. After cross-linking, the beads were filtered and
washed with ethanol
to remove any excess glutaraldehyde. Subsequent vacuum drying resulted in
porous
glutaraldehyde cross-linked chitosan resin beads.
Even though these examples specify amounts or concentrations of materials used
in
making several embodiments of the present invention, a wide range of
concentrations and
amounts of materials may be used to practice the present invention. For
example, the
crosslinker solution may be in a range of concentration of about 0.1 % to
about 50%, the
chitosan solution may be in a range of concentration of about 0.1% to about
20%, the acetic
acid solution may be in a range of about 0.1% to about 10%, and the base
solution may be in
a range of about 1 to about 5 molar sodium hydroxide. Additionally, the range
of hours for
cross-linking reaction may be from about 1 hour to up to about 24 hours.
EXAMPLES OF USE
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A cigarette typically contains two sections, a tobacco-containing portion
sometimes
referred to as the tobacco or cigarette rod, and a filter portion which may be
referred to as the
filter tipping. A cigarette sample with a cavity filter was prepared by
removing the existing
filter on a cigarette made by standard production techniques, and replacing
with a filter
tipping having a cellulose acetate section at the tobacco end of the filter
and a cellulose
acetate section at the mouth end of the filter leaving a middle cavity. Sample
sets of semolina
(an inert filler material), chitosan resin synthesized by phase inversion
technique and cross-
linked with glutaraldehyde (Ex. I), chitosan resin synthesized by the
thermally induced phase
separation procedure and cross-linked with glutaraldehyde (Ex. III), chitosan
resin
synthesized by the thermally induced phase separation procedure and cross-
linked with
glyoxal (Ex. IV), chitosan resin synthesized by the thermally induced phase
separation
procedure and cross-linked with glutaraldehyde in ethanol, washed with
ethanol, and vacuum
dried (Ex. V), and chitosan resin synthesized by the thermally induced phase
separation
procedure and cross-linked with glutaraldehyde in water, washed with ethanol,
and vacuum
dried (Ex. VI), were prepared using a 50 mg sample load in the middle cavity
of the filter
tipping. This loading was consistent for each sample to provide comparable
results. Resin
loading in a filter of the present invention may be in a range of about 10 mg
to about 200 mg.
Each sample was pressure drop selected to minimize smoke delivery variances.
Several tests were conducted to determine the ability of the cigarette filter
of the
present invention to remove undesirable constituents from tobacco smoke as
compared to
conventional devices. The tests measured the amount of undesirable
constituents removed
from the mainstream smoke after the cigarette was fully smoked. The following
data sets
illustrate the performance achieved in the filtration of volatile constituents
of tobacco smoke
for each of the preferred embodiments as compared to the control material,
semolina.
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Analytical results are reported on the vapor phase and whole smoke analyses as
indicated in
the following tables. Percent reduction refers to the difference, in %,
between the amount of
the analyte measured in the vapor phase or whole mainstream smoke of
cigarettes having
filter tipping containing semolina and chitosan resin.
Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Phase Inversion
Technique
Ex. I
Percent Reduction (%)
Analyte Chitosan cross-linked with glutaraldehyde
Ex. I
Hydrogen Cyanide 49
Acetaldehyde 10
Acetonitrile 11
Acrolein 15
Propionaldehyde 11
Acetone 7
Methyl Ethyl Ketone + Butyraldehyde 16
Crotonaldehyde 13
Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Phase
Inversion
Technique [Ex. I]
Percent Reduction (%)
Analyte Chitosan cross-linked with glutaraldehyde
Ex. I
Hydrogen Cyanide 41
Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Phase Inversion
Technique
Ex. I
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. I
Formaldehyde 36
Acetaldehyde 13
Acetone 5
Acrolein 11
Propionaldehyde 16
Crotonaldehyde 9
Butyraldehyde 17
Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Exs. III-IVi
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Percent Reduction (%)
Chitosan cross-linked with Chitosan cross-linked with
glutaraldehyde glyoxal
Ex. III Ex IV
Acetaldehyde 13 31
Acetone 21 30
Acetonitrile 18 26
Acrolein 29 36
Acrylonitrile 21 29
Crotonaldehyde 7 42
Hydrogen cyanide 60 45
Methyl ethyl
ketone 21 29
Propionaldehyde 23 36
i-Butyraldehyde 27 35
n-Butyraldehyde 27 40
Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally
Induced Phase Separation [Exs. III-IV]
Percent Reduction (%)
Chitosan cross-linked with Chitosan cross-linked with
glutaraldehyde glyoxal
Ex. III Ex IV
Hydrogen cyanide 54 29
Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Exs. III-IV]
Percent Reduction (%)
Chitosan cross-linked with Chitosan cross-linked with
glutaraldehyde glyoxal
Ex. III Ex IV
Acetaldehyde 1 2
Acetone 5 0
Acrolein 10 3
Butyraldehyde 14 8
Crotonaldehyde 20 9
Formaldehyde 50 46
Propionaldehyde 17 19
Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally
Induced
Phase Separation [Exs. III-IV]
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Percent Reduction (%)
Chitosan cross-linked with Chitosan cross-linked with
glutaraldehyde glyoxal
Ex. III Ex IV
Cadmium 32 38
Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Ex. VI
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. V
Acetaldehyde 9
Acetone 6
Acetonitrile 3
Acrolein 13
Crotonaldehyde 7
Hydrogen Cyanide 36
Methyl Ethyl Ketone 6
Propionaldehyde 11
i-Butyraldehyde 9
n-Butyraldehyde 10
Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally
Induced Phase Separation [Ex. V1
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. V
Hydrogen Cyanide 27
Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Ex. V1
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. V
Acetonitrile 3
Acetaldehyde 27
Acetone 24
Acrolein 32
Butyraldehyde 41
Crotonaldehyde 30
Formaldehyde 58
Propionaldehyde 33
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Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally
Induced
Phase Separation [Ex. VI
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. V
Cadmium 38
Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Ex. VIl
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. VI
Acetaldehyde 3
Acetone 4
Acrolein 9
Crotonaldehyde 11
Hydrogen Cyanide 30
Methyl Ethyl Ketone 11
Propionaldehyde 6
i-Butyraldehyde 7
n-Butyraldehyde 11
Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally
Induced Phase Separation [Ex. VI]
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. VI
Hydrogen Cyanide 30
Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced
Phase
Separation [Ex. VII
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. VI
Acetaldehyde 0
Acetone 0
Acrolein 0
Butanone 1
Butyraldehyde 14
Crotonaldehyde 36
Formaldehyde 37
Propionaldehyde 0
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Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally
Induced
Phase Separation [Ex. VII
Percent Reduction (%)
Chitosan cross-linked with glutaraldehyde
Ex. VI
Cadmium 26
The data surprisingly showed the cross-linked chitosan resin described in this
invention is selective in removing aldehydes and hydrogen cyanide in cigarette
smoke
compared to the inert semolina control. The glutaraldehyde cross-linked
chitosan resin
reduced the vapor phase delivery of hydrogen cyanide by 60% versus a control
sample (Ex.
III). In a separate test, non-crosslinked ground chitosan particles showed no
effect on the
vapor phase hydrogen cyanide delivery. The glutaraldehyde cross-linked
chitosan resin also
decreased whole smoke hydrogen cyanide delivery by 54%, and mainstream whole
smoke
formaldehyde delivery was decreased by 50% compared to the control sample (Ex.
III).
While the invention has been described with reference to preferred
embodiments, it is
to be understood that variations and modifications may be resorted to as will
be apparent to
those skilled in the art. Such variations and modifications are to be
considered within the
purview and scope of the invention as defined by the claims appended hereto.
