Note: Descriptions are shown in the official language in which they were submitted.
CA 02452462 2003-12-09
06152 USA
TITLE OF INVENTION
DOUBLE WALLED VESSELS FOR ODORANT CONTAINMENTS
BACKGROUND OF THE INVENTION
The present invention relates to fluid leak detection, and in particular to
the leak
detection of gases by odor generated by adding odiferous materials to the
gases.
With the advent of the fuel cell technology and a drive for clean fuel,
hydrogen
gas is emerging as a leading candidate for the fuel of choice. In addition to
the benefit of
being oxidizable in an emission free manner, hydrogen may be obtained from an
abundant, renewable, resource, water.
For hydrogen to became a consumer fuel for automobile and domestic power
generation, safety is paramount. Although safe handling and use of hydrogen is
well
understood, warnings are needed to alert against any leaks. Hydrogen sensors
are
commercially available but are not considered to be an absolute safeguard
against leaks
due to their potential for malfunctioning, change of air currents, etc. Human
senses, in
particular, the sense of smell, are considered to be the ultimate safeguard
against leaks.
Since hydrogen is an odorless gas, odorants are preferably incorporated in
hydrogen for
easy leak detection. A review of the codes, standards, regulations,
recommendations,
and certifications on the safety of gaseous fuels is addressed in a report,
Proc. U.S. DOE
Hydrogen Program Rev. (1996), Vol. 2, pages 569-604.
Odorization of gases for leak detection is well known in the natural gas and
petroleum gas industries. For example, a paper by IVLJ. Usher (Proc. Int.
Scho.
Hydrocarbon Meas. 73~d, pages 743-48 (1998)) reviE~ws the history,
application,
compounds, and safety practices in selecting and applying odorants in the
natural gas
industry. Mixing small quantities of odorants with gases is a substantially
universal
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CA 02452462 2003-12-09
practice in natural and petroleum gases. For example, a paper by I. Katuran
(Proc. Int.
Sch. Hydrocarbon Meas., 64t", pages 325-30 (1989)) reports on natural gas
odorants,
their safety and handling precautions, handling techniques, and methods of
adding
odorants to gases.
Nearly all of the methods for odorization of natural and petroleum gases
consist
of metering a certain amount of the odorant into a gas stream to a level where
detection
can be made by the human sense of smell. Natural gas for public gas supplies
typically
contains 5-10 mg of sulfur per cubic meter of gas. However, odorants for
hydrogen used
as an energy source for fuel cells have unique requirements which must be met.
This is
because most of the commercial odorants used in gas leak detection act as
poisons for
the catalysts used in hydrogen based fuel cells, most specifically for the PEM
(polymer
electrolyte membrane or proton exchange membrane) fuel cells. Chemical
compounds
based on mixtures of acrylic acid and nitrogen compounds have been adopted to
achieve a sulfur-free odorization of a gas. See, for example, W(J 00/11120
(PCT/EP99/05639) by Haarmann & Reimer GmbH. However, these formulations are
either ineffective or do not have general acceptance by users. Also, in the
use of natural
gas and other petroleum gases for hydrogen generation for fuel cell
applications, sulfur
free natural or petroleum gases are needed, or else a desulfurization step
must be
incorporated in the reforming process, which adds further cost to hydrogen
generation.
The PEM fuel cells are sulfur intolerant because sulfur compounds poison the
noble metal catalysts used in these fuel cells. If sulfur-containing odorants
are used, it
would be necessary to remove sulfur containing materials, like mercaptan
odorants, from
the feed gas using materials like zinc oxide. The sulfur containing materials,
like
thiophenes, cannot be removed by zinc oxide and may require a
hydrodesulfurization
process, using hydrogen gas, to remove sulfur. This all wilt add to the cost
of the
process.
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CA 02452462 2003-12-09
A further complexity far hydrogen fuel comes fre~m the nature of the hydrogen
flame propagation. When gases burn in air, their flames propagate upwards with
greater
ease than they propagate downwards. This is primarily clue to the natural
convection of
hot burnt gases in an upward direction. For petroleum gases, propane and
methane,
the upward and downward propagating lean limits of combustion are
approximately the
same. However, for hydrogen, since they differ by a factor of 2.5 , the amount
of odorant
needed for leak detection in hydrogen could be > 2.5 times that needed for
methane or
propane. The higher quantity of the odorant needed for hydrogen odor detection
further
complicates the sulfur poisoning problems for hydrogen gas used in the PEM
fuel cells.
In several other gas applications, particularly when gases are odorless,
toxic, or
are otherwise harmful, methods of leak detection using odiferous materials are
also
desirable. The gases included in this category are, for example, nitrogen,
carbon
monoxide, nitrogen trifluoride, ethylene oxide, carbon tetrafluoride and other
perfluoro
gases.
Several other issues also have been encountered in the odorization of the
natural
and petroleum gases. The key ones are (1) hydrocarbon masking the odor of the
odiferous materials, (2) adsorption of the odorant on the storage vessel and
pipe walls,
(3) reaction of the odorants with low molecular weight mer~captans (naturally
occurring in
the gas), (4) condensation of the odorants in the gas storage vessel and
pipes, and (5)
physical scrubbing of the mercaptans from the gas with liquids (associated
with the
natural gas).
Today, approximately twenty-five different blends are used as natural gas
odorants. Of these twenty-five blends, seven blends are more prevalent. Almost
all of
the odorant agents are sulfur compounds, e.g., mercaptans (tetrabutyl
mercaptan,
isopropyl mercaptan, normal propyl mercaptan, secondary butyl mercaptans,
ethyl
mercaptans, normal butyl mercaptan, etc.), thiophenes (tetrahydrothiophene),
sulfides
(dimethyl sulfide, methyl ethyl sulfide), etc.
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CA 02452462 2003-12-09
In addition to the pungent odors of these chemicals, the chemicals used are
also
expected to have certain other attributes, such as low vapor pressure (high
boiling point),
low freezing point, low specific gravity so that they are fully dispersed in
the gas, and
appropriate thermal properties (e.g., they will not freeze a,t appropriate
temperatures and
will not cause over odorization in the hot weather). The c~enerai quality
requirements, as
specified for sulfur containing odorants in ISOlDIS 1373., are: (1) a cloud
point of less
than -30 degrees Celsius, (2) a boiling point of less than 130 degrees
Celsius, and (3)
evaporation residue of less than 0.2 %.
Requirements for odorants further will likely include an odorant concentration
high enough to allow detection with a fuel gas concentration of 1I5 the lean
limit of
combustion. These requirements exist for natural gas (SAE J 1616, NFPA 52-
1992) and
petroleum gas (NFPA 58-1989).
It is desired to have a method and system for the use of odorants in gas
storage
and delivery systems in which the odorants are nat dispersed in the bulk gas
but are
accessible only to the leaking gas streams, thus leaving the gas
uncontaminated and
making leak detection by smell viable without adding odorants in the entire
gas stream.
It is further desired to have a system and method for the use of odorants in
gas
storage and delivery systems which can be used for gas leak detection with the
use of
an odorant(s), where the odorant(s) do not contaminate the bulk gas stream.
It is also desired to have such a system and method which overcomes the
difficulties and disadvantages of the prior art to provide better and more
advantageous
results.
BRIEF SUMMARY OF THE INVENTION
The present invention is an apparatus and a method for detecting a leak of a
fluid
from a vessel. There are several embodiments of the apparatus and the method,
as
discussed below. In a number of the embodiments, the fluid is a pressurized
gas.
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CA 02452462 2003-12-09
With regard to the apparatus of the present invention, a first embodiment is
an
apparatus for detecting a leak of a fluid from a first vessel having an outer
surface. The
apparatus includes a second vessel and an odorant material. The second vessel
has an
outer surface and an inner surface spaced apart from and surrounding the outer
surface
of the first vessel, thereby forming an annulus between the outer surface of
the first
vessel and the inner surface of the second vessel. The odorant material is
disposed in
at feast a portion of the annulus, at least a portion of the odorant material
having at feast
one detectable odor.
There are several variations of this first embodiment of the apparatus. In one
variation, a flow of the fluid flows from the first vessel to the annulus,
whereby the flow of
the fluid picks up and transmits a portion of the odorant material into an
atmosphere
surrounding the outer surface of the second vessel.
In another variation, the detectable odor is detectable by a sense of smell of
a
living being. In yet another variation, the fluid is hydrogen. In another
variation, at feast
a portion of the fluid is a gas stored and/or transported in the first vessel.
In a variant of
that variation, at least a portion of the gas is at or above an ambient
pressure.
In another variation of the first embodiment of the .apparatus, at least a
portion of
the odorant material is selected from a group consisting of mercaptans
(tetrabutyl
mercaptan, isopropyl mercaptan, normal propyl mercaptan, secondary butyl
mercaptans,
ethyl mercaptans, normal butyl mercaptan), thiophenes (tetrahydrothiophene),
sulfides
(dimethyl sulfide, methyl ethyl sulfide), and combinations thereof, and
odorants selected
from a group consisting of derivatives of acrylic acid, alf;yl ethers of C4-
C~, carboxylic
acids, and combinations thereof.
A second embodiment of the apparatus is similar to the first embodiment but
includes a pressure relief device in fluid communication with the annulus. In
a variation
of the second embodiment, a flow of the fluid flows from the first vessel to
the annulus
where the fluid has an annulus pressure, whereby the flow of the fluid picks
up and
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CA 02452462 2003-12-09
transmits a portion of the odorant material into an atmosphere surrounding the
outer
surface of the second vessel via the pressure relief device when the annulus
pressure
reaches or exceeds a predetermined pressure.
A third embodiment of the apparatus of the present invention is an apparatus
for
detecting a leak of a fluid from a vessel having a first suirface. The
apparatus includes
an annular space and an odorant material. The annular space is between the
first
surface and a second surface spaced apart from the first surface. The odorant
material
is disposed in at least a portion of the annular space, at least a portion of
the odorant
material having at least one detectable odor.
There are several variations of the third embodiment of the apparatus. In one
variation, the second surface surrounds at least a substantial portion of the
first surface.
In another variation, the first surfiace surrounds at least a substantial
portion of the first
surface. In another variation, the first surface surrounds at least a
substantial portion of
the second surface. In yet another variation, a flow of a fluid flows through
the first
surface and the second surface, whereby the fluid picks up and transmits a
portion of the
odorant material from the annular space into an atmasphere surrounding the
vessel.
A fourth embodiment of the apparatus is similar to the third embodiment but
includes a pressure release device in fluid communication with the annular
space. In a
variation of the fourth embodiment, a flow of the fluid flows from the annular
space where
the fluid has an annulus pressure, whereby the flow of the fluid picks up and
transmits a
portion of the odorant material into an atmosphere surrounding the vessel via
the
pressure relief device when the annulus pressure reaches a predetermined
pressure.
A fifth embodiment of the apparatus of the present invention is an apparatus
for
detecting a leak of a pressurized gas from a first vessel having an outer
surface. The
apparatus includes a second vessel, an odorant material, and a pressure relief
device.
The second vessel has an outer surface and an inner surface spaced apart from
and
surrounding the outer surface of the first vessel, thereby forming an annulus
between the
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CA 02452462 2003-12-09
outer surface of the first vessel and the inner surface of the second vessel.
The odorant
material is disposed in at least a portion of the annulus, at least a portion
of the odorant
material having at least one detectable odor. The pressure relief device is in
fluid
communication with the annulus, wherein a flow of the pressurized gas flows
from the
first vessel to the annulus where the pressurized gas has an annulus pressure,
whereby
the flow of the pressurized gas picks up and transmits a portion of the
odorant material
into an atmosphere surrounding the outer surface of the second vessel via the
pressure
relief device when the annulus pressure reaches or exceeds a predetermined
pressure.
With regard to the method of the present invention, there also are several
embodiments. The first embodiment is a method for detecting a flow of a fluid
from a
first vessel having an outer surface. The method includes multiple steps. The
first step
is to provide a second vessel having an outer surface and an inner surface
spaced apart
from and surrounding the outer surface of the first vessel, thereby forming an
annulus
between the outer surface of the first vessel and the inner surface of the
second vessel.
The second step is to provide an odorant material disposed in at least a
portion of the
annulus, at least a portion of the odorant material having at least one
detectable odor.
The third step is to provide a pressure relief device in fluid communication
with the
annulus. The fourth step is to transmit the flow of the fluid from the first
vessel to the
annulus where the fluid has an annulus pressure, whereby the flow of the fluid
picks up
and transmits a portion of the odorant materiai having the detectable odor
into an
atmosphere surrounding the outer surface of the second vessel via the pressure
relief
device when the annulus pressure reaches or exceeds a predetermined pressure.
The
fifth step is to detect the detectable odor in the surroundincl atmosphere.
There are several variations of the first embodiment of the method. In one
variation, the detectable odor is detectable by a sense of smell of a living
being. In
another variation the fluid is hydrogen. In yet another variation, at least a
portion of the
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CA 02452462 2003-12-09
fluid is a gas stored and/or transported in the first vessel. In a variant of
that variation, at
least a portion of the gas is at or above an ambient pressure.
In another variation of the method, at least a portion of the odorant material
is
selected from a group consisting of mercaptans (tetrabutyl mercaptan,
isopropyl
mercaptan, normal propyl mercaptan, secondary butyl mercaptans, ethyl
mercaptans,
normal butyl mercaptan), thiophenes {tetrahydrothiophene, sulfides (dimethyl
sulfide,
methyl ethyl sulfide), and combinations thereof, and odorants selected from a
group
consisting of derivatives of acrylic acid, alkyl ethers of C4-C~, carboxylic
acids, and
combinations thereof.
Another embodiment is a method for detecting a flow of a pressurized gas
leaking from a first vessel having an outer surface. The method includes
multiple steps.
The first step is to provide a second vessel having an outer surface and an
inner surface
spaced apart from and surrounding the outer surface of the vessel, thereby
forming an
annulus between the outer surface of the first vessel and the inner surface of
the second
vessel. The second step is to provide an odorant material disposed in at least
a portion
of the annulus, at feast a portion of the odorant material having at least one
detectable
odor. The third step is to provide a pressure relief device in fluid
communication with the
annulus. The fourth step is to transmit the flow of the pressurized gas from
the first
vessel to the annulus where the pressurized gas has an annulus pressure,
whereby the
flow of the pressurized gas picks up and transmits a portion of the odorant
material
having the detectable odor into an atmosphere surrounding the outer surface of
the
second vessel via the pressure relief device when the annulus pressure reaches
or
exceeds a predetermined pressure. The fifth step is to detect the detectable
odor in the
surrounding atmosphere.
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BRIEF DESCRIPTION OF THE DRA1NINGS
FIG. 1 is a simplified, partial, cross-sectional view of a vessel in
accordance one
embodiment of the present invention; and
FIG. 2 is a simplified, partial, cross-sectional view of the vessel of FIG. 1
showing
a leak point of gas through the vessel wall.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a system and method which can be used for
gas leak detection with the use of odorants, where the c~dorants are not mixed
with the
bulk gas stream.
Specifically, a system and method of leak detection for non-odorous, flammable
and toxic gases is provided in which odorants are not mixed in the bulk gas
but are
placed in the path of the gas leak. in the system and method of the present
invention,
odorants are filled in the gap between the outer walls and an additional
barrier of the gas
storage vessels or piping. The odorants are filled in the gap by pumping of
the adorant
materials as such or in diluted form. Alternately, the odorants are sorbed in
an
appropriate solid carrier, which is then filled in the annulus space.
For purposes of the present invention, the term "vessel" is intended to
include
any vessel or other piping or piping system capable of containing a
pressurized gas.
The term "appurtenance" is intended to include any fittings, valves, meters,
and any
other device or object attached to the vessel which forms a part of the total
gas storage
space.
fn the event of a gas teak from the gas vessel or piping, gas will travel from
the
bulk storage within the vessel to the gas leak spot due to the gas pressure
gradient. For
the leaking gas to travel from the bulk storage to the leak :spot, it must
permeate through
the annulus which contains the odorant material. As the gas passes through the
odorant
material, it carries with it a portion of the odorant material and a mixture
of the gas and
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the odorant material is released from the leak spot. A:> a result, the gas
leak may be
detected by the smelt of the odorant. Thus, a gas leak may be detected without
contaminating the bulk gas supply. The odorant material volatility is such
that it has a
certain vapor pressure at the storage temperature and it diffuses into the
leaking gas to
impart to it a detectable amount of the odorant. Alternatively, the odorant
can be
physically carried (entrained) by the high pressure leaking gas to impart in
the gas a
detectable amount of odorant. Both of these mechanisms may prevail at any
given time
when gas is Peaking from the vessel.
Double walled vessels or containers are used in industry to contain leaks from
primary vessels or containers. The strength of the secondary containers in
those cases
is generally comparable to the primary containers. A double wall container can
be made
much less expensive if the secondary container is much more inferior in
strength
compared to the primary container. The hazard of doing this is that the gas
leak may not
be contained. However, if the annulus is filled with an odorant, in the event
of a gas leak
and failure of the secondary cantainer, the leak can be detected by smell.
In one embodiment of the present invention, primary and secondary containers
are used and the annulus between the primary container and the secondary
container is
filled with a pre-determined quantity of an odorant material. Odorants tend to
condense
in high pressure and low temperature storage and phase separate from the gas.
Therefore, the odorant material also can be encapsulated or sorbed on an
appropriate
media. The secondary container is equipped with an appropriate pressure
release
device, such as a rupture disc, pressure release valve, etc. When a leak
occurs in the
primary vessel, gas travels to the secondary vessel, where the leaking gas
mixes with
the odorant material. The leaking gas builds up pressure in the annulus and
upon
reaching a certain pre-set pressure, the relief device releases the gas laced
with the
odorant material. A leak is thus detectable by smell.
CA 02452462 2003-12-09
Referring now to the drawings, FIG.1 shows a simplified portion of a cross
section of a primary vessel 10 (or piping) storing gas 15 in accordance with
one
embodiment of the present invention. The vessel 10 has an inner wall 18 and an
outer
wall 20 surrounded by an odorant layer 30. The odorant layer 30 fully covers
the outer
wall 20, i.e., the entire exterior of the vessel 10. A secondary vessel 40
surrounds the
odorant layer 30.
As shown in FIG. 2, when a leak develops in the primary vessel 10, the stored
gas 15 rushes through the leak site orifice 25 from the inner wall 18, i.e.,
the
high-pressure side of the primary vessel 10, to the outer wall 20, i.e., the
low-pressure
side of the primary vessel 10. Since the leaking gas 15 has to permeate
through the
odorant layer 30 and then pass by bursting through the sE:condary vessel 40,
the leaking
gas carries with it an appropriate amount of the odorant layer 30, thus
imparting an odor
in the leaking gas.
The invention will be illustrated in more detail with reference to the
following
Examples, but it should be understood that the present invention is not
limited thereto.
EXAMPLES
Example 1: An inner gas pressure vessel made of metal, reinforced plastic or
other structural material is lined externally with an outer vessel made of
metal, glass,
fiberglass, plastic, or other structural material capable of holding a lower
gas pressure,
e.g., in the range of about 5 to 100 psig, than the inner pressure vessel
itself. The gap
between the outer and the inner vessels is filled with one or more odorant
materials or
their blends. The barrier layer of the inner vessel material therefore
separates the gas in
the vessel and the odorant material. Generally, the odoriferous materials such
as:
mercaptans (tetrabuty6 mercaptan, isopropyl mercaptan, normal propyl
mercaptan,
secondary butyl mercaptans, ethyl mercaptans, normal butyl mercaptan, etc.),
thiophenes (tetrahydrothiophene), sulfides (dimethyl sulfide, methyl ethyl
sulfide), and
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CA 02452462 2003-12-09
the like, and their combinations, and odorants selected from a group
consisting of
derivatives of acrylic acid, alkyl ethers of C4-C~, carboxylic acids, and
combinations
thereof, are used. In the event of a gas leak, gas must pass through the gap
between the
inner and the outer vessel in which the odorant material resides. The leaking
gas will
mix with the odorant material imparting to it an odorant. The outer pressure
vessel is
equipped with a rupture disk or a pressure relief valve at a predetermined
setting
between about 5 to 100-psig. The leaking gas builds up pressure in the
annulus, and
when this pressure exceeds a pre-set relief pressure, the rupture disk or the
pressure
relief valve releases gases laced with the odoriferous materials have odors
detectable by
the human sense of smell.
Example 2. A nonodorant gas, such as nitrogen, helium, argon, carbon dioxide,
etc., dilutes the odorant placed in the annulus of Example 1.
Example 3. A nonodorant liquid, such as water, dilutes the odorant in Example
1.
Example 4. A solid sorbent or adsorbent is used to store the odorant in
Example
1. The odorant material is sorbed on an appropriate substrate in which it
exists in a
condensate form held by the capillary forces. The sorbed material is placed in
the
annulus of the gas vessel in a predetermined quantity. At the gas storage
temperature
and pressure, the odorant material releases a certain amount of the odorant to
the
leaking gas providing it with the needed concentration of the odorant material
to
generate an odor in the leaking gas. The adsorbent materials can be from
natural
sources, such as celiulosic materials, carbons and clays, or they can be
synthetic
sorbents, such as polymers and zeolites, etc. The type and amount of the
odorant on
these adsorbents can be determined on the basis of the desired odorant
concentration in
the leaking gas. For the sulfur containing odorants, such a concentration is
generally
about 1-10 mg S/iiter or more of gas.
Example 5. The odorant material is microencapsulated in an appropriate media
and is filled in the gap of Example 1. The encapsulation of the odorant
material can be
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CA 02452462 2003-12-09
done by the known techniques in the literature. The organic and inorganic
membrane
encapsulation methods are taught by the various coating methods. The art of
forming
polymeric semi-permeable membranes and microporous membranes is well
documented
in text books, for example, in R.E. Kesting and A.K. Fritzsche, Polymeric Gas
Separation
Membranes, Wiley (1983) and in R.E. Kesting, Synthenic Polymer Membranes,
Wiley
(1985). The art of making microporous inorganic membranes is well documented,
for
example, in C.J. Brinker and G.W. Scherer, Sol-Gel Science, Academic Press
(1990).
The thin encapsulating layer is formed on the odorant, for example, using a
rubbery
polymer such as polydimethyl siloxane amongst other rubbery materials and
glassy
polymers such as polyimides, polysulfones, polyamides, polyarylates,
polyolefins, and
the like. The art of making coatings of the rubbery materials and their cross-
linking is
taught by J.H.Henis and M.K. Tripodi in U.S. Patent No. 4,230,463 and
described in a
paper published in the Journal of Membrane Science, 8, 233 (1981 ).
Example 6. A gas-containing pipe made of metal, reinforced plastic, or other
structural material is lined with an outer coating or lining made of metal,
glass, fiberglass,
plastic, or other structural materials. The gap between the outer coating and
the inner
vessel is filled with one or more odorant materials or their blends. The
barrier layer of the
inner coating or fining material therefore separates the gas in the vessel and
the odorant
material. fn the event of a gas leak, gas must pass from the vessel walls
through the gap
in which the odorant material resides to the outer lining. The gas mixes with
the odorant
material and hence any leaks from the outer Pining is detectable by the human
sense of
smell.
Example 7. A nonodorant gas such as nitrogen dilutes the odorant in Example 6.
Example 8. A nonodorant liquid such as water dilutes the odorant in Example 6.
Example 9. A solid sorbent or adsorbent is used as diiuents for the odorant in
Example 6. The odorant material is sorbed on an appropriate substrate in which
it exists
in a condensate form held by the capillary forces. The sorbed material is
placed in the
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CA 02452462 2003-12-09
gap between the inner vessel and outer lining in a predetermined quantity. The
leaking
gas passing through the annulus picks up sufficient odorant to impart an odor
to it.
Example 10. The odorant material is microencapsulated in an appropriate media
and is filled in the gap of Example 6. The encapsulation of the odorant
material can be
done by the known techniques in the literature cited in Example 5.
While various embodiments of the invention have been described in detail with
reference to the drawings and the specific examples above, it will be apparent
to one
skilled in the art that various changes and modifications can be made to those
embodiments, drawings, and examples without departing 'from the spirit and
scope of the
invention as defined in the claims which follow.
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