Note: Descriptions are shown in the official language in which they were submitted.
~879S
Various processes have been proposed for expanding
tobacco. For example, tobacco has been contacted with a gas under
somewhat greater than atmospheric pressure, followed by a release
of the pressure, whereby the tobacco cells are expanded to in-
crease the volume of the treated tobacco. Cther methods which
have been employed or suggested have included the treatment of
tobacco with various liquids, such as water or relatively volatile
organic liquids, to impregnate the tobacco with the same, after
which the liquids are driven off to expand the tobacco, Addition_
al methods which have been suggested have included the treatment
of tobacco with solid materials which, when heated, decompose to
produce gases which serve to expand the tobacco. Cther methods
include the treatment of tobacco with gas-containing liquids,
such as carbon dioxide-containing water, under pressure to incor-
porate the gas in the tobacco and when the tobacco impregnated
therewith is heated or the pressure thereon is reduced to thereby
expand the tobacco. Additional techniques have been developed for
expanding t~bacco which involve the treatment of tobacco with
gases which react to form solid chemical reaction products within
the tobacco, which solid reaction products may then decompose by heat
to produce gases within the tobacco which cause expansion of the
tobacco upon their release. More specifically:
A patent to ~ilford J. Hawkins, U.S. Patent 1,789,435,
granted in 1931, describes a method and apparatus for expanding the
volume of tobacco in order to make up the loss of volume caused
in curing tobacco leaf. To acco~plish this object, the cured and
conditioned tobacco is contacted with a gas, which may be air,
carbon dioxide or steam under about 20 pounds of pressure and the
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~ ~ 9 ~n7~ S
pressure is then relieved, whereby the tobacco tends to expand.
The patent states that the volume of the tobacco may, by that
process, be increased to the extent of about 5 - 15%.
An alien property custodian document No. 304,214 to
Joachim Bohme, dated 1943, indicate8 that tobacco can be expanded
using a high_frequency generator but that there are limitations
to the degree of expansion which can be achieved without affecting
the quality of the tobacco.
A patent to Frank J. Scwa, U.S. Patent 2,596,183, granted
in 1952, sets forth a method for increasing the volume of shredded
tobacco by adding additional water to the tobacco to cause the
tobacco to swell and thereafter heating the moisture containing
tobacco, whereby the moisture evaporates and the resulting mois-
ture vapor causes expansion of the tobacco.
A series of patents to Roger Z. de la Burde, U.S. Patents
3,409,022, 3,409,023, 3,409,027 and 3,409,028, granted in 1968,
relate to various processes for enhancing the utility of tobacco
stems for use in smoking products by subjecting the stems to ex-
pansion operations utilizing various types of heat treatment or
microwave energy.
A patent to John D. Hind, U.S. Patent 3,425,425, granted
in 1969, which is assigned to the same assignee as the assignee
of the present invention, relates to the use of carbohydrates to
improve the puffing of tobacco stems. In that process, tobacco
stems are soaked in an aqueous solution of carbohydrates and then
heated to puff the stems. The carbohydrate solution may also con-
tain organic ucids and/or certain salts which are used to improve
the flavor and smoking qualities of the stems.
B~3S
A publication in the "Tobacco Reporter" of November 1969
by P. S. Meyer describes and summarizes tobacco puffing or expan-
sion procedures or investigations for expanding and manipulating
tobacco for purposes of reducing costs and also as the means for
reducing the "tar" content by reduction in the delivery of smoke.
Mention is made in this publication of puffing tobacco by dif-
ferent procedures including the use of halogenated hydrocarbons,
low pressure or vacuum operation, or high pressure steam treat_
ment that causes leaf expansion from inside the cell when outside
pressure is suddenly released. Mention is also made in this pub-
lication of freeze_drying tobacco which can also be employed to
obtain an increase in volume.
Since the above-mentioned "Tobacco Reporter" article was
published, a number of tobacco expansion techniques, including some
of the techniques described in the article, have been described in
patents and/or published patent applications. For example, U.S.
Patent 3,524,452 to Glenn P. Moser et al. and U.S. Patent 3,524,451
to James D. Frederickson, both issued in 1970, relate to the ex-
pansion of tobacco using a volatile organic liquid, such as a
halogenated hydrocarbon.
U.S. Patent 3,734,104 to William M. Buchanan et al, which
is assigned to the same assignee as the assignee of the present
invention, issued in 1973, relates to a particular process for
the expansion of tobacco stems.
U.S. Patent 3,710,802 to William H. Johnson, issued in 1973
and British Specification 1,293,735 to American Brands, Inc., pub-
lished in 1972, both relate to freeze-drying methods for expanding
tobacco.
1~39~ 5
A patent to Robert G. Armstrong, U.S. Patent 3,771,533,
issued in 1973, which is assigned to the same assignee as the
assignee of the present invention, involves a treatment of
tobacco with carbon dioxide and ammonia gases whereby the
tobacco is saturated with these gases and ammonium carbonate
is formed in situ. The ammonium carbonate is thereafter
decomposed by heat to release the gases within the tobacco cells
to cause expansion of the tobacco.
Despite all of the above-described advances in the
art, no completely satisfactory process has been found. The
difficulty with the various earlier suggestions for expanding
tobacco is that, in many cases, the volume is only slightly or
at best only moderately increased. For example, freeze-drying
operations have the disadvantages of requiring elaborate and
expensive equipment and very substantial operating costs. With
respect to the teaching of using heat energy, infrared or
radiant microwave energy to expand tobacco stems, the difficulty
is that while stems respond to these heating procedures,
tobacco leaf has not generally been found to respond
effectively to this type of process.
The use of special expanding agents,for example,
halogenated hydrocarbons, such as are mentioned in the Meyer
publication for expanding tobacco, is also not completely
satisfactory because
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,i,. ,~,
~L~9i~7~S
these substances are generally required to volatilize or other-
wise be removed after the tobacco has been expanded. Furthermore,
the introduction, in considerable concentration, of materials
which are foreign to tobacco presents the problem of removing
the expansion agent after the treatment has been completed in
order to avoid affecting aroma and other properties of the smoke
due to extraneous substances used or developed from the combustion
of the treated tobacco.
The ùse of carbonated water has also not been found to
be effective.
While the method employing a~monia and carbon dioxide
gases is an improvement ~ver the earlier described methods, it
i8 not completely satisfactory under some circumstances, in that
undesired deposition of salts can result during the process.
Carbon dioxide has been used in the food industry as a
coolant and, more recently, has been suggested as an extractant
for food flavors. It has also been described in German Cffen_
legungsschrift 2,142,205 (Anmeldetag: 23 August 1971) for use,
in either gaseous or liquid form, to extract aromatic materials
from tobacco However, there has been no suggestion, in connec-
tion with these uses, of the use of liquid carbon dioxide for
the expansion of these materials.
A process employing liquid carbon dioxide has been found
to overcome many of the disadvantages of the above-mentioned prior
art processes The expansion of tobacco, using liquid carbon
dioxide is described in Belgian Patent 821,568, which corresponds
to U.S. Application Serial No. 441,767 to de la Burde et al and
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~9~7~5
assigned to the same assignee as the present application and in
Belgian Patent 825,133 to Airco, Illc. This process may be des-
cribed as a process for expanding tobacco comprising the steps
of (1) contacting the tobacco with liquid carbon dioxide to im_
pregnate the tobacco with the liquid carbon dioxide, (2) subject_
ing the liquid carbon dioxide-impregnated tobacco to conditions
such that the liquid carbon dioxide i8 converted to solid carbon
dioxide and (3) thereafter subjecting the solid carbon dioxide-
containing tobacco to conditions whereby the solid carbon dioxide
is vaporized to cause expansion of the tobacco. The present in-
vention involves modifications of the basic process which provide
significant improvements thereto.
This invention relates broadly to an improved process for
expanding tobacco and involves certain modifications of the basic
process for expanding tobacco comprising the steps of (1) contact-
ing the tobacco with liquid carbon dioxide to impregnate the
tobacco with the liquid carbon dioxide, (2) subjecting the liquid
carbon dioxide-impregnated tobacco to conditions such that the
liquid carbon dioxide is converted to solid carbon dioxide and
(3) thereafter subjecting the solid carbon dioxide-containing
t obacco to conditions whereby the solid carbon dioxide is vaporized
to cause expansion of the tobacco. The present invention pertains,
in one embodiment, to an improvement in the basic process which
involves controlling the moisture content of the tobacco which is
employed in the first step of the basic process. A second embodi-
ment of the present invention involves draining off excess liquid
carbon dioxide, under controlled conditions, after the first step
--6--
~9~37~5
of the basic process and prior to the second step of the basic
process. The present invention pertains, in a third embodiment,
to an improvement which involves controlling the output
moisture of the product which is recovered from the third step
of the basic process. The present invention further relates
to various combinations of the three embodiments set forth
above and to an overall process which employs all three
embodiments in a manner which permits exceptionally advantageous
results.
This invention relates broadly to improvements in
the process for expanding tobacco which employs liquid carbon
dioxide as the expansion agent. It comprises the steps of
(1) impregnating the tobacco with the liquid carbon dioxide
under conditions such that carbon dioxide is maintained in
liquid form to impregnate the tobacco with the liquid carbon
dioxide, (2) subjecting the liquid carbon dioxide-impregnated
tobacco to conditions such that the liquid carbon dioxide is
converted to solid carbon dioxide and (3) thereafter subjecting
the solid carbon dioxide-containing tobacco to conditions
whereby the solid carbon dioxide is vaporized to cause expansion
of the tobacco, the improvement which comprises (i) utilizing
as the tobacco which is employed in step (1) a tobacco which
has an initial OV content of from about 17 to about 30%, and
(ii) conducting the first step under pressure in the range of
from about 250 psia to about 525 psia.
In another aspect the present invention provides, in
the method of expanding tobacco which comprises the steps of
(1) impregnating the tobacco with liquid carbon dioxide under
conditions such that substantially all of the liquid carbon
dioxide is maintained in liquid form to impregnate the tobacco
7 _
B
~87Y!5
with the liquid carbon dioxide, (2) subjecting the liquid carbon
dioxide-impregnated tobacco to conditions such that the liquid
carbon dioxide is converted to solid carbon dioxide and (3)
thereafter subjecting the solid carbon dioxide-containing
tobacco to conditions whereby the solid carbon dioxide is
vaporized to cause expansion of the tobacco, the improvement
which comprises: (i) utilizing as the tobacco which is employed
in step (1) a tobacco which has an OV content of from about
17 to about 30~, (ii) conducting the first step under pressure
in the range of from about 250 psia to about 525 psia, and
(iii) conducting the third step in such a manner that the
moisture content of the expanded tobacco obtained from the
third step is no higher than about 6~.
In still a further aspect the present invention
provides, in the method of expanding tobacco which comprises
the steps of (1) impregnating the tobacco with liquid carbon
dioxide in a vessel under conditions such that substantially
all of the liquid carbon dioxide is maintained in liquid form
to impregnate the tobacco with the liquid carbon dioxide,
(2) subjecting the liquid carbon dioxide-impregnated tobacco
to conditions such that the liquid carbon dioxide is converted
to solid carbon dioxide and (3) thereafter subjecting the
solid carbon dioxide-containing tobacco to conditions whereby
the solid carbon dioxide is vaporized to cause expansion of
the tobacco, the improvement which comprises: (i) utilizing
as the tobacco which is employed in step (l) a tobacco which
has an OV content of from about 17 to about 30~, (ii) conduct-
ing the first step under pressure in the range of from about
250 psia to about 525 psia, and (iii) draining excess liquid
carbon dioxide from the vessel of step (1), while maintaining
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379S
the carbon dioxide in liquid form, continuing to drain the
liquid carbon dioxide from said vessel to a point where
continuous liquid flow ceases, maintaining a post-drain holding
period of at least 2 minutes to permit a further removal of
liquid carbon dioxide from the impregnated tobacco and
thereafter again draining liquid carbon dioxide from said
vessel until further liquid flow ceases before commencing
step (2).
The invention, in certain aspects, may relate to a
process for expanding tobacco employing a single agent which is
a readily available, relatively inexpensive, non-combustible
and exceptionally effective and more particularly to the
production of an expanded tobacco product of substantially
reduced density produced by impregnating tobacco under pressure
with liquid carbon dioxide, converting the liquid carbon
dioxide to solid carbon dioxide ln situ, which may be accom-
plished by rapidly releasing the pressure, and thereafter
causing the solid carbon dioxide to vaporize and expand the
tobacco, which may be accomplished by subjecting the impregnated
tobacco to heat, radiant energy or similar energy generating
conditions which will cause the solid carbon dioxide which is
in the tobacco to rapidly vaporize.
To carry out the process of the invention, one may
treat either whole cured tobacco leaf, tobacco in cut or
chopped form, or selected parts of tobacco such as tobacco
stems or may be reconstituted tobacco. In comminuted form,
the tobacco to be
- 7(b) -
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impregnated may have a particle size of from about 20 to 100 mesh,
but is preferably not less than about 30 mesh. The material to
be treated may be in relatively dry form, or may contain the
natural moisture content of tobacco or even more.
Generally, the tobacco to be treated will have at lea~t
about 8% moisture ~y weight) and less than about 50% moisture.
A specific improvement in the process, which is an embodiment of
the present invention, involves the disc wery that the moisture
content of the tobacco which is employed in the first step of the
process should have a value of from about 17% to about 25% de_
pending on the particular pressure used. AB used herein, the
tobacco moisture content may be termed "input moisture" or
"input W " and is approximately equivalent to oven volatiles (OV),
since generally, no more than about 0.9% by weight of tobacco
weight is volatiles other than water. We have found that, unex-
pectedly, by utilizing an input ov in this range, the first step
of the process may be more advantageously operated at pressures
lower than were heretofore considered optimal. A detailed dis-
cussion of pressures employed in the first stage of the process
is set forth later in this specification; however, with regard to
this particular embodiment, we have found that the following input
OV's are preferred for the following pressures:
at 300 psig an input CV of from about 18 to about 25%
at 400 psig an input OV of from about 17 to about 25%
at 450 psig an input OV of from about 17 to about 25%
at 500 psig an input ov of from about 16 to about 23%
at 625 psig an input OV of from about 14 to about 19%
at 750 psig an input OV of from about 13 to about 18%
at 850 psig an input ov of from about 12 to about 18%
To raise the moisture content of a tobacco to the desired
input moisture level, the tobacco may be sprayed with water, con_
tacted with steam or the like until the desired level is reached,
preferably by water spray. To lower the moisture content of
tobacco to the desired level, the tobacco may be heated, prefer-
ably by indirect steam heat, until the desired level is reached.
We have found that this improvement in the basic process
permits obtaining desired levels of expansion at lower pressures
than were heretofore found to be needed to obtain such expansion.
For example, prior to the present discovery, while a broad range
of pressures was found workable, it was believed necessary to
operate the process at a pressure of about 515 psia or above to
obtain a product having a cylinder volume (CV) approaching a
value of about 70 (which generally represents a level of expansion
that is clearly commercially desirable) It has now been found,
surprisingly, that a cylinder volume of 68 can be obtained at a
pressure of 315 psia, by operating with an input ov of about 20%
and an output ov of less than about 6%.
The terms "cylinder volume" and "corrected cylinder volume"
are units for measuring the degree of expansion of tobacco. The
term "ove~volatiles content" or "oven volatiles" is a unit for
measuring moisture content (or percentage of moisture) in tobacco.
As used throughout this application, the values employed, in
connection with these terms, are determined as follows:
_ g_
~ ~9 ~ 7 ~ S
Cylinder Volume (CV)
Tobacco filler weighing 10.000 g is placed in a 3.358-cm
diameter cylinder and compressed by a 1875-g piston 3.335 cm in
diameter for 5 minutes. The resulting volume of filler is re_
ported as cylinder volume. This test is carried out at standard
environmental conditions of 23.9C and 60% RH; conventionally
unless otherwise stated, the sample is preconditioned in this
environment for 18 hours,
Corrected Cylinder Volume (CCV)
The CV value may be adjusted to some specified oven-
volatile content in order to facilitate comparisons.
CCV - CV + F (OV _ OVs) where Ws is the specified ov and
F is a correction factor (volume per %) predetermined for the
particular type of tobacco filler being dealt with.
Oven_Volatiles Content (W)
The s~mple of tobacco filler is weighed before and after
exposure for 3 hours in a circulating air oven controlled at 100C.
The weight log6 as percentage of initial weight is oven-volatiles
content
For expanded bright tobacco employed in the present appli-
cation, the value of F in the calculation of CCV is 7.4.
The tobacco, at the desired input moisture level, will
generally be placed in a pressure vessel in a manner whereby it
can be suitably immersed or contacted by liquid carbon dioxide.
For example, a wire cage or platform may be used.
The tobacco-containing pressure vessel may be purged with
carbon dioxide gas, by vacuum or with another inert gas, the
- 10-
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purging operation generally taking from about 1 to 4 minutes.
The purging step may be eliminated without detriment to the final
product. The benefits of purging are the removal of gases that
could interfere with a carbon dioxide recovery process and to
flush out of the tobacco any foreign gases which might interfere
with full penetration of the liquid carbon dioxide.
The liquid carbon dioxide which is employed in the pro-
cess of this invention may be obtained from a storage vessel
where it will, generally, be maintained at a pressure of from
about 250 to 305 psig. The liquid carbon dioxide may be intro-
duced into the pressure vessel at 250 to 400 psig or over the
range of 250 to 525 psig. At the time the liquid carbon dioxide
is introduced into the pressure vessel, the interior of the
vessel, including the tobacco to be treated, should preferably be
at a pressure at least sufficient to maintain the carbon dioxide
in a liqui~ state.
The liquid carbon dioxide is introduced into the vessel
in a manner which permits it to completely contact the tobacco
and sufficient liquid carbon dioxide should preferably be employed
to completely saturate the tobacco. Generally, this will comprise
using about 1 to 10 parts by weight of liquid carbon dioxide per
part of tobacco. Excess liquid carbon dioxide will be wasteful
but will work. The temperature of the liquid carbon dioxide
should, preferably, not be permitted to exceed about 31C, during
this impregnation step.
The pressure during the contacting step involving the
first embodiment of this invention is preferably maintained at a
~ ~ 9 ~7~ 5
pressure of fr~ about 250 to 525 psig, employing heating of the
vessel, using heating coils or the like, where needed.
The tobacco and liquid carbon dioxide may be maintained
in contact under these conditions for a period of from about 0.1
to 30 minutes.
After the liquid carbon dioxide has been permitted to
saturate the tobacco, generally for a total period of from about
0.1 to 30 minutes and preferably from about 0.2 to about 1 minute,
any excess liquid carbon dioxide which may be present is drained
out of the vessel, perferably while maintaining the conditians of
temperature and pressure at the same levels as during the contact-
ing step.
A specific improvement in the process which is a second
embodiment of this invention involves the utilization of a post-
drain period. This embodiment may be utilized in combination with
the first embodiment described above in the preferred pressure
range during the contacting step of from about 250 to about 525
psig; however, this embodiment may be utilized over a broader
pressure range of from about 215 to about 950 psig, its benefits
20 being greater at the lower portion of this pressure range. In
accordance with the process after a soaking time of at least 0.1
minute and up to 30 minutes to achieve impregnation of the liquid
carbon dioxide into the tobacco, the liquid is generally removed
from the tobacco mass, for example, through an exit port at the
bottom of the chamber, while maintaining the pressure in the
vessel. We have found that unexpected advantages are obtained
by utilizing a post-drain period of at least 2 minutes beyond the
~2~ ~ 7 ~ 5
point where the continuous flow of liquid carbon dioxide draining
from the vessel has stopped. Prior to the present invention, a
method for controlling the process at this point involved observing
the liquid carbon dioKide level through a sight glass attached to
the impregnation vessel, as the liquid C02 was withdrawn and
stopping the draining at a point when liquid was no longer observed,
that is, when there was no longer a continuous flow of liquid C02.
A brief check for additional liquid, immediately after stopping
the draining was sometimes e~ployed. In accordance with the pre-
sent invention, a post_drain period, involving waiting for atleast about two minutes, and preferably at least about three
minutes, and thereafter draining the liquid for a second time,
until continuous flow of liquid stops a second time, is employed.
The second flow of liquid may, generally, last less than a minute.
Such a post_drain period serves to ensure that excess liquid is
removed from the tobacco surfaces. The post draining step may be
aided by a downward sweep of C2 or other gas through the mass.
We have found that the post-drain period results in substantially
complete drain_off and provides: (1) more complete recovery of
C02 as liquid rather than as gas (which requires condensation in
recovery steps), (2) the removal of liquid from the surface of
the tobacco, which otherwise upon pressure reduction, has been
found to be partially converted to solid on the tobacco surfaces,
which solid binds the tobacco in clumps, making it hard to handle
and required to be broken up attendant with formation of tobacco
"fines", and (3) a reduction of the heat load on the expansion
equipment by removing the necessity for vaporizing ineffective
solid C ~ from the surface.
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The post-drain period should be at least about 2 minutes,
but is preferably from about 2_1/2 to about 6 minutes, longer
times providing little additional advantage but being satisfactory,
and depends on the configuration and size of the vessels, to a
considerable extent.
After the impregnation, draining and post-draining, the
gas pressure is reduced at a sufficiently rapid rate that at
least a portion of the carbon dioxide within the tobacco is con-
verted to solid
The pressure in the vessel is released, by venting the
gases in order to bring the contents of the vessel to atmospheric
pressure. This venting generally takes from about 0.75 to 15
minutes, depending on the size of the vessel, but should prefer-
ably take no longer than 3 minutes, after which the temperature
in the vessel will generally be from about -85 to -95C and the
liquid carban dioxide in the tobacco will be partially converted
to solid carbon dioxide. The pressure need not be reduced to
atmospheric, but need only be reduced below about 60 psig Cb-
viously, this is not as preferable from a commercial viewpoint as
reducing the pressure to atmospheric.
The drain and post-drain should preferably be such that
the tobacco contains from about 6 to about 25% by weight of solid
C2 and most preferably from about 10 to about 20% by weight of
solid C02
After the carbon dioxide in the tobacco is converted to
its solid form, the solid carbon dioxide-containing tobacco is
then exposed to expansion conditions by subjecting the treated
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product to heat or the equivalent in order to vaporize and remove
the solid carbon dioxide from the tobacco. This may comprise the
use of hot surfaces~ or a stream of hot air, a mixture of gas and
steam, or exposure to other energy sources such as radiant micro-
wave energy or infrared radiation. A convenient means of expand-
ing the solid carbon dioxide-co~taining tobacco is to place it or
to entrain it in a stream of heated gas, such as superheated steam
or to place it in a turbulent air stream maintained, for example,
at a temperature as low as about 100C and as high as about 370C
and preferably at a tem~erature of from about 150 to about 260C
for a period of about 0.2 to 10 seconds. The impregnated tobacco
may also be heated by being placed on a moving belt and exposed
to infrared heating, by exposure in a cyclone dryer, by contact
in a dispersion dryer with superheated steam or a mixture of steam
and air or the like. Any such contacting steps should not raise
the temperature of the atmosphere with which the tobacco is in
contact to above about 370C and should preferably be from at
about 100C to about 300-C, most preferably 150 to 260C when
conducted at atmospheric pressure.
As is well kn~wn in processing of any organic matter,
overheating can cause damage, first to color, such as undue darken_
ing, and finally, to the extent of charring. The necessary and
sufficient temperature and exposure time for expansion without
such damage is a function of these two variables as well as the
state of subdivision of the tobacco. Thus, to avoid undesirable
damage in the heating step, the impregnated tobacco should not be
exposed to the higher temperature levels, e.g. 370C, for longer
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~ 7 ~ 5
than several tenths of a second.
One method for causing the expansion of the tobacco cells
is to use the radiation methods described in either U.S. Patent
3,409,022 or U.S. Patent 3,409,027. Another method involves the
use of a heat gun such as the Dayton heat gun or the equivalent,
operating at an exit air temperature of 190-344C for a period of
about 0.2 second to 4 minutes~ the shorter times, of course,
being given for the higher temperatures. In this operation, the
tobacco never attains a temperature above about 140C, being
cooled by the rapid evolution of gases. The presence of steam
during heating assists in obtaining optimum results.
Another system is to use a dispersion dryer, for example,
one that is supplied either with steam alone or in combination
with air. An example of such a dryer is a Proctor ~ Schwartz PB
dispersion dryer. The temperature in the dryer may range from
about 121 to 371C with contact time in the dryer of about 4
minutes at the lowest temperature to about 0.1 to 0,2 second at
the highest temperature. In general, a 0.1 to 0.2 second contact
time is utilized when the hot gas temperature is 260_315C or
somewhat higher. As stated before, other known types of heating
means may be used so long as they are capable of causing the im-
pregnated tobacco to expand without excessive darkening. It
should be noted, that where a high percentage of oxygen is pre-
sent in the hot gases, it will contribute to dsrkening, so that
if a hot_steam mixture is employed, a high proportion (e.g., over
80% volume) of steam is preferred. The presence of a steam
atmosphere of 20% or more of the total hot gas composition aids
in obtaining the best expansion.
-16_
~`987~i
A third embodiment of the present invention involves
controlling the output or exit moisture of the product of the
heating step, for the expansion of the tobacco, so that the
output moisture is preferably no higher than 6% and most
preferably no higher than 3.0%, determined as OV.
As set forth above, it is important that the product
from the heating/expansion step have an exit OV content of not
more than 6%. The result of this relatively dry condition is
an optimum permanent expansion, after reordering to standard
moisture conditions. Such exit OV can be achieved by the
proper balance between feed rate of impregnated tobacco to the
dryer and temperature of dryer gas, assuming a fixed gas flow;
the flow rate is another variable to be considered. The exit
OV can also be brought down to a desired level by further
treatment of the product, as in a dryer.
After the tobacco has been recovered from the heating/
expansion step at the desired exit OV, it is then, generally,
equilibrated (reordered) at conditions which are well ~nown
in the trade. Reordering is preferably done at standard
conditions, which generally involve maintaining the tobacco at
a temperature of 23.9C and 60% RH (relative humidity) for at
least 18 hours.
The present process may be conducted in various forms
of apparatus, for example, such as are described in Belgian pat-
ents 821,568 and 825,133.
It is important that the apparatus in which the liquid
carbon dioxide-containing tobacco is converted to solid carbon
dioxide-containing tobacco is able to contain gases at the ele-
vated pressures which may be employed, in some instances, as
-17-
~ 7 ~ 5
high as 1000 psig or more. This vessel is preferably employed for
the initial contact of the liquid carbon dioxide with the tobacco.
There may be numerous arrangements of the pressure vessel, How_
ever, there should preferably be a valved inlet from a source of
liquid carbon dioxide and a valved outlet at the bottom of the
vessel whereby liquid may be drained off; a second valved outlet
near the top, for venting, may be added, and could be inserted as
part of the inlet line, if desired, placed between the vessel and
the inlet valve. A means of heating the vessel and/or the supply
vessel, such as external heating coils, may be employed. Support_
ing the vessel on a load cell greatly simplifies measuring the
carbon dioxide charge. A supplementary vessel similarly equipped
with weighing means and heating coils is advantageous, though not
essential, because it permits preheating a charge of liquid carbon
dioxide from its usual low storage temperature of -20C (which may
be about 215 psig. In operation, the filler may be placed in the
main pressure vessel in a suitable holder such as a wire basket
suspended above the bottom of the vessel. The closed vessel may
then be purged with carbon dioxide gas and the outlets closed, then
liquid carbon dioxide is introduced from storage, for example, at
250 psig, in an amount sufficient to cover all of the tobacco
present in the vessel. The temperature is raised by the heating
means, e.g., heating coils to bring the tobacco to the desired
temperature, whichshould be less than 31C (the critical tempera-
ture of carbon dioxide) and this condition is preferably maintained
for 1 to 20 minutes while impregnation takes place. Excess liquid
carbon dioxide is then drained off by opening the lower outlet of
~ 7 ~ S
the vessel to a suitable reservoir or the like disposal system,
and when all excess liquid has been removed from the vessel,
the vessel is vented to atmospheric pressure. The tobacco is
then subjected to an operation to volatilize the solid carbon
dioxide, preferably by removing the solid carbon dioxide_contain_
ing tobacco from the vessel andpassing it through any of several
rapid heating systems to achieve expansion. As indicated
earlier in this specification, systems for this expansion pro-
cess are most satisfactory which provide rapid, turbulent con-
tact with the hot gas or vapor. With proper control of tempera-
ture and exposure time, the product may be recovered in the ex-
panded state at the desired moisture content.
The overall process, apart from the specific improvements
set forth in the present specification, may be generally in
accordance with the teachings in copending United States applica-
tion 441,767 or Belgian patent 821,568.
The following examples are illustrative.
EXAMPLE 1
ohe hundred pounds of bright tobacco particles of
cigarette filler size having 20% W content was placed in a wire
basket in a pressure vessel. The vessel was closed except for a
port for admission of CQ2 gas. The gas was introduced to a
pressure of 400 psig and the port closed. The vessel was then
filled with liquid C02 at 400 psig and _7C sufficient to cover
the tobacco mass. The system was held at these conditions for
30 seconds, then a bottom port was opened to allow the liquid to
be pumped out. The port was closed and after three minutes it
- 1 9-
9~3S
was reopened to release the accumulated liquid. This port was
closed and the vessel opened to the atmosphere through a valve
at the top so that the pressure was released in a period of 180
seconds. When the top was removed from the vessel and the
basket weighed, it was found that 18.0 lb. of C02 was retained
by the tobacco. The product was not difficult to separate and
could be fed at a controlled rate to the next stage. A similar
batch without the drain period retained 31.5 lb. of C02 and was
b adly clumped
An eight-inch diameter vertical dryer supplied with
125 ft./sec. of 85% superheated steam in air at 249C was used
for expansion The product from C2 treatment was ed at 3.7
lb./min. to the dryer where contact with the steam was estimated
to be three seconds. The product collected in a cyclone
separator had OV content, when cool, of 1.8%. Its reordered
cylinder volume, corrected to 11% OV, was 74.0 cc/10 g as com-
pared with the original CV of 34.0 cc/10 g for the untreated
bright filler at its standard moisture content of 12.5% OV.
EXAMPT.F. 2
~e hundred pound batches of bright tobacco similar
to that used in the preceding example and having slmilar input
moisture content were processed as before, with blowdawn in
177 - 190 seconds, except for elimination of the 3-minute drain-
ing period and for variations in the expansion procedure and
conditions. The result was varying exit OV content and product
filling power, as measured by CCV. The results and conditions
for these runs, in duplicate, are compared in Table 1. Expan_
sion was by tawer exposure, about 3 seconds, to 81 to 88% steam.
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~3B7~
It will be seen that optimum filling power is realized at low
OV for product exiting from the expansion stage, and that OV
of less than 6.0% is desirable and less than 2.5% is most de-
sirable.
Table 1
Feed to Tower
lb /min Tower Temp. C Exit av % ccv, cc /lOg
5.5 149 12 0, 12.2 59.4, 65.5
5.0 177 8.5, 7.8 65.0, 67.8
4.25 204 4.5, 4.8 67.8, 69.2
3.13 249 1.8, 2.5 69.5, 75.4
EXAMPLE 3
Bright tobacco weighing 100 lb. and having 20% OV wasprepared for immersion as in Example 1. Liquid carbon dioxide
was admitted to the chamber, previously pressurized to 300 psig,
at the same pressure until the tobacco was covered, and held
thus for 30 seconds; the temperature was about -16.7C. The
liquid was pumped off through a bottom valve and a five-mint~te
sweep of C2 gas from top to bottom of the vessel helped remove
undrained C02 liquid. The vessel was then vented to the atmos-
phere in 152 seconds and the chilled product was removed.
This product was not clum~ed; it was introduced into an
expansion tower having 85% steam flow of 125 ft./sec. at 249C,
at a rate of about 4.3 lb./min. total weight. Exposure was
estimated at 3 seconds. The product contained 2.1% OV and upon
reordering to 12.0% OV it showed a cylinder volume, corrected
to 11.0% OV, of 68.0 cc/10 g. The starting filler had CCV of
37.3 cc/10 g at 12.5% OV.
~987~i
EXAMPLE 4
Cne hundred-pound lots of bright tobacc o of varying
OV content were treated by the process of Example 1 (impreg-
nation, liquid removal, drain, pressure release, and expansion
by tawer exposure) with only the tower gas temperature varied
from 232 to 254C to compensate for increasing OV levels of
input. The exit av of all samples was between 1.3% and 2.8%
OV. After being reconditioned, all samples were checked for
CV, corrected to 11.0% OV. The results shown in Table 2 indi-
cate that a moisture (OV) needed to achieve the best expansion,
in this series at least 68 cc/10 g CCV, is 17% minimum.
Tab le 2
Cylinder Volume vs. Input Moisture
with 400 psig Impregnation
Output Fillin~ Power
Input Reordered CCV, 11% OV
OV % CV~ cc/10 ~ _ cc/10 g
10.1 44.5 50.6
10.6 52.5 55.0
10.9, 10.9 47.9, 48.5 53.1, 52.6
11.7 59.6 62.3
15.5 60.7 66.5
16.0, 16.0 59.6, 60,4 64.6, 67.0
17.1, 17.0 61.0, 62.2 69.1, 69.0
17.4, 17.5 62.2, 58.6 68.7, 67.9
17.7, 17.9 68.7, 64.6 72.9, 68.2
18.0, 18.4 62.0, 67.1 70.9, 72.5
19.0, 19.1 60.9, 63.2 68.3, 70.1
18.0, 18.3 69.2, 60.8 74.4, 68.1
19.4, 19.5 60.9, 56.9 72.6, 69.4
19.7, 20.6 63.0, 68.9 73.8, 73.4
21.9, 21.9 68.2, 71.4 73.0, 76.5
23.0 59.1 6~.6
23.5, 23.5 63.9, 66.3 70.7, 71.0
23.9, 24.2 58.6, 58.9 68.4, 68.6
25.7 58.6 68.4
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7 ~ S
EXAMPLE 5
Batches of bright tobacco filler were impregnated and
subsequently expanded exactly as described in Example 1 except
that the drain time (from closing to reopening of the port) was
varied as shown in the tables. The first batches (Table 3) were
100-pound and had a depth in the impregnator of 36 inches; the
second group (Table 4) weighed 185 pounds and had a depth of 60
inches. m e ov at exit from the expansion tower was in the
neighborhood of two percent in every run. The products were
measured for cylinder volume and were also sieved for comparison
of size reductions. me 3-minute purge was similar to a 3-minute
drain time, except that C02 gas was blown down through the im-
pregnated tobacco as a purge gas.
Tables 3 and 4 tabulate the results. Since a distri_
bution approximating that of the control is desirable, and in
particular a total of "smalls" and "fines" (S ~ F) no greater
than about 2% is sought, it will be seen that the drain times of
two minutes or longer gave the best results. There appeared to
be little or no effect on corrected CV.
Table 3
Effect of ~rain Time on Sieve Fractions with
100-Pound Batches
Sieve Fractions %
CCV
~rain Time, cc/10 g
Mins.~& Med. Short Small Fine L~M S~F at 11%
Unexpanded 55.5 35.9 7.0 0.9 0.6 91.4 1.5 --
Control
0 38.2 50,0 9.2 1.2 1.2 88.2 2.4 74.6
1 41.9 47.7 8.1 1.2 1.2 89.6 2.4 73.7
2 43,7 47.0 7.3 1.0 0.9 90.7 1.9 76.3
3 42.2 49.2 6.8 0.7 1.0 91.4 1.7 74.2
3_Minute 42.7 48.5 6.9 1.0 1.0 91.2 2.0 75.0
Purge
_23_
~8~5
Table 4
Effect of Drain Time of Sieve Fractions with
185_ Pound Batches
.
Sieve Fractions, %
Drain Time CCV
Mins. ~ Med.Short Small Fine L+M S+F cc/10 g.
Control 52.0 38.97.5 1.1 0.5 90.9 1.6 _-
0 38.3 48.510.0 2.0 1.3 86.8 3.3 74.4
3 44.5 45.77.7 1.2 0.9 90.2 2.1 76.6
6 44.1 46.17.7 1.2 0.9 90.2 2.1 76.8
As employed in the above example, the various sieve
fractions are defined as follaws: Long = +10 (i.e. the particles
are retained on a 10 mesh sieve); Medium - -10 to +20; Short
-20 to +30; Small ~ _30 to +50; and Fine = -50.
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