Note: Descriptions are shown in the official language in which they were submitted.
~i33~ :
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 increase the volume of the treated tobacco. Other 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 of to expand
the tobacco. Addi-tional methods which have been sug~ested have
included the treatment of tobacco with solid materials which,
when heated, decompose to produce gases which serve t`o expand
the tobacco. Other methods include the treatment of tobacco
with gas-containing liquids, such as carbon dioxide-containing ;~
water, under pressure to incorporate 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 tobacco
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 Wilford J. Hawkins, U.S. Patent 1,789,435,
granted in 1931, describes a method and apparatus for expanding
the volume of ~obacco in order to make up the loss of volume
caused in curin~ tobacco leaf. To accomplish 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 pressure is then relieved, whereby the tobacco
33~ :
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, indicates that tobacco can be
expanded using a high-frequency generato.r 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. Sowa, U.S. Patent 2,596,183,
granted in 1952, sets forth a method for increasing the volume
of shredded tobacco by addln~ adaitional water to the tobacco
to cause the tobacco to swell and thereafter heating the
moisture containin~ tobacco, whereby the moisture evaporates
and the resulting moisture 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 enhan~ing the utility
of tobacco stems for~use in smoking products by sub~ectiny the ~-
~stems to~expansion 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. T~e carb~
hydrate solution may also contain organic acids and/or certain
salts which are.used to improve the flavor and smoking qualities
of the stems.
, J~:;
- 2 -
:_
'
3~5
A publication in the "Tobacco Reporter" of
November 1969 by P. S. Meyer describes and summarizes tobacco
puffing or expansion procedures or investigations for expanding
and manipulating tobacco for purposes of redu~ing 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 different procedures including the use of
halogenated hydrocarbons, low pressure or vacuum operation,
or high pressure steam treatment that causes leaf e~pansion
from inside the cell when outside pressure is suddenly released.
Mention is also made in this publication of freeze-drying
tobacco which can also be employed to obtain an increase in
volume.
Since the above-mentioned "Tobacco~Reporterl' 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 ~ames D. Frederickson, both issued
in 1970, relate to the expansivn 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 Brans,
Inc., published in 1972, both relate to freeze-drying methods
for expanding tobacco.
.
A patent to Robert ~. Armstrong, ~.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 lea~ has not generally been found to respond
effectively to this type of process.
The use cf special expanding agents,for example,
halogenated hydrocarbons, such as are mentioned in the Meyer ;
publication for expanding tobacco, is also not completely
satisfactory because
-- 4 --
~ 33~
these substances axe genarally required to volatilize or
otherwise 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 affec~ing aroma and other properties
of the smoke due to extraneous substances used or developed
from the combustion of the treated tobacco.
The use of carbonated water has also not been found
to be effective. ~ ;
While the method employing ammonia and carbon dioxide
gases is an improvement over the earlier described methods,
it is not completely satisfactory under some circumstancesr
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 ~een described in
German Offenlegungsschrift 2,142,205 ~Anmeldetag: 23 August
1971) for use, in either gaseous or liquid form, to extract
aromatic materials from tobacco. ~owever, there has been no
suggestion, in connection 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 assigned to the same assignee
- . ; . : ; .~. -. - . ~
3~ ;
as the present application and in Bel~ian Patent 825,133 to
Airco, Inc. This process may be described as a process for
expanding tobacco comprising the steps of (1) contacting 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 tobacco to conditions whereby the solid carbon
dioxide is vaporized to cause expansion of the tobacco. The
present invention 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~ contacting 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 tobacco to conditions whereby
the solid carbon dioxide is vaporized to cause expansion of
the tobacco. The present invention pertàins, 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
embodiment of the present invention involves draining off
excess liquid carbon dioxide, under controlled conditions,
after the first step
~L~h33~
of the basic process and prior to the sec~nd step o~ 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 rPlates
to various combinations o 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
cQnverted to solid carbon dioxide and (3) thereafter subjecting
the solid carbon dioxide-containing tobacco to conditions
whereby the solid carbon dioxide is vaporized ~o 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 substantiall~ all of the liquid carbon
dioxide is maintained in liquid form to impregnate the tobacco
~33~5 -:
:::
with the liquid carbon dioxide, (2) subjec~ing the liquid carbon
dioxide-impregnated tobacco to conditions such that the liquid
carbon dioxide is converted to solid carbon dioxid~ and (3) .
thereafter subjecting the solid carbon dioxide-containing :
tobacco to conditions whereby the solid carbon dioxide is ~;~
vaporized ~o 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 which forms the su~ject ~ ~.
matter of this divisional specification the present invention
provides, in the method of expanding tobacco which comprises
the steps of (1~ impregnating the tobacco with liquid carbon di-
oxide in a vessel under conditions such that substantially all
of the ll~uid carbon dioxide is maintained in liquid form to ;
impregnate the tobacco with the liquid carbon dioxide, (2) sub- ~:
jecting the liquid carbon dioxide-impregnated tobacco to con-
ditions 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) conducting the
first step under pressure in the range of from about 215 to
about 950 psig, and (iil draining excess liquid carbon dioxide ;
from the vessel of step (1), while maintaining
~:
_ 7(a) - ~
3~
the carbon dioxide in liqui.d 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, relatlvely 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 s~ch as tobacco ~:
stems or may be reconstituted tobacco. In comminuted form,
the tobacco to be
;:
- 7(b) -
, ::
- , . . . . . .
3~ :
~;
impregnated may have a particle size of from about 20 to
100 mesh, but is preferably not less than about 30 mesh. The
material ~o be treated may be in rela~ively dry form, or may
contain the natural moisture content of tobacco or even more.
Generally, the tobacco to be treated will have ~t
least about 8~ moisture (by weight) and less than about 50
moisture. A specific improvement in the process, wh~ch is an
embodiment of the present invention, involves the discovery
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~ depending on the particular pressure
used. As used herein, the tobacco moisture content may be ~ -
termed "input moisture" or "input OV" and is approximately ;
equivalent to oven volatiles ~O~), since genera].ly, no more
than about 0.9% by weight of tobacco weight is volatiles
other than water. We have found that, unexpectedly, 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. ~ detailed discussion
of pressures employed in the ~irst stage of the process is
set forth later in~this specification; however, with r~gard
to this particular em~odiment, we have found that the following
input OV's are preferred for the following pre~sures:
at 300 psig an input OV 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 O~ of from about 17 to about 25%
at 500 psig an input OV of from about 16 to about 2~3%
at 62-5 psig an input OV of from~about 14 to about l9
at 750 psig an input OV of from a~out 13 to about 18%
at 850 pslg an lnput OV of rrom about l2 to about 18
.
. ~
.
To raise the moisture content of a tobacco to the
desired inpu~ moisture leveI, the tobacco may be sprayed with
water, contacted with steam or the like until the desired
level is reached, preferably by water spray. To lower the
moisture con~ent of tobacco to the desired level, the tobacco
may be heated, preferably 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 ~o 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 o less than about 6%. -
The terms "cylinder volume" and "corrected cylinder
volume" are units or measuring the deyree of expansion of
tobacco. The term "oven-volatiles content" or "oven
volatiles" is a unit for measuring moisture content (or
percentage of moistuxe) in tobacco. ~s used throughout this
application, the values employedr in connection with these
terms, are determined as follows: -
C~linder Volume (CV)
Tobacco filler weighing lO.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 reported as cylinder volume. This test is carried
out at standard environmental conditions of 23.9C and 60% R~; ;
conventionally unless otherwise stated, the sample is
preconditioned in this environment for 18 hours.
Corrected Cyli_der 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 Vs 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 Conten-t (OV) ~ ;
The sample of tobacco filler is weighed before and
after exposure ~or 3 hours in a circulating air oven controlled ~~
at 100C. The weight loss as percentage~of initial weight ;~ ;
is oven-volatiles content. ~-
For expanded bright tobacco employed in the present
application, 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 purging operation generally taken from about l 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 flus~ out of the tobacco any foreign gases
-- 10 --
3~
which might interfere with full penetration of the liquid
carbon dioxide.
The liquid carbon dioxide which is employed in the
process 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 introduced into the pressure vessel at 250 to 400 psig or
over the range of 250 to 525 psig. At the time the li~uid
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 lîquid state.
The li~uid carbon dioxide is introduced into the ;~
vessel in a manner which permits it to completely con-tact the ~ `
tobacco and sufficient liquid carhon 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. ~xcess 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 pressure of from 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. ;
Aft~r the li~uid carbon dioxide has been permitted
to saturate the tobacco, generally for a total period of from
~33~
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, preferably while
maintaining the conditions of temperature and pressure at the
same levels as du~ing the contacting 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
prefexred 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 being greater at the lower
portion of this pressure rangeO 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
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 dioxide level through a
sight glass attached to the impregnation vessel, as the liquid
C2 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 CO2. A brief check for -~
additional liquid, immediately after s~opping the draining was
- 12 -
3335
sometimes employed. In accordance with the present invention, ~:
a post-drain period, involving waiting for at least about two
minutes, and preEerably 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 li~uid may, generally, last less than a
minute. Such a post-drain period serves to ensure that excess
liquid is removed from the tobacco surfacesO The post draining
step may be aided by a downward sweep of CO2 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 CO2 as liquid rather than as ~ .
gas (which re~uires:;condensation in recovery steps), ~2) the ~ ;~
removal of liquid from the surface of the tobacco, which
otherwise upon pressure reduction, has been folmd to be
partially converted to solid on -the tobacco surfaces, which
solid binds the tobacco in clumps, makiny 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 CO2 from the surface. i .
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 tobac~o
is converted to solid. :~
- 13 -
3~
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 ~enerally takes from
about 0.75 to 15 minutes, depending on the size of the vessel,
but should preferably take no longer than 3 minutes, after
which the temperature in the vessel will generally be from
about -85 to -95C and the liquid carbon dioxide in the
tobacco will b~ partially converted to solid carbon dioxide.
The pressure need not be reduced to atmospheric, but need only
be reduced below about 60 psig. Obviously, this is not as
preferable from a`commercial viewpoint- as reducing the
pressure to atmospheric.
The drain and post-drain should preerably bè such
that the tobacco contains from about 6 to about 25% by weight
of solid CO2 and most preferably from about 10 to about 20%
by weight of solid CO2.
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 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 microwave energy or infrared radiation. A
convenient m~ans of expanding the solid carbon dioxide-
containing 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 turbulant air stream maintained, for example, at a `~ -~
temperature as low as about 100C and as high as about 370C ~
and preferably at a temperature of from about 150 to about ~ -
- 14 - ~
3~9
260C for a period of about 0.2 to 10 seconcls. The impregnated
tobacco may also be heated by being placed on a moving belt
and exposed to infrared heating, by exposure in a cycline
dryer, by contact in a dispersion dryer with superheated
steam or a mixture of steam and air or the like. ~ny 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 fxom at about 100C to about
300C, most preferably 150 to 260C when conducted at
atmospheric pressure.
As is well known in processing of any organic
matter, overheating can cause damage, first to color, such
as undue darkening, 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, Eor longer 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 minut~s, the
shorter time, o~ course, being given for the higher
temperatures. In this operation, the tobacco ne~en attains
- 15 -
.. . . . . .. . . . .. ... .. . .. . . ..
~33~
a temperature above about 140C, be.ing cooled by the r~pid
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 i5
a Proctor & Schwartz PB ~ispersion 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.~ second at the highest tempera-
ture. 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
causiny the impregnated tobacco to expand without excessive
darkening. It should be noted, that where a high percentage
of oxygen is present in the hot gases, lt will contribute
to darkening, 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 -
A third embodiment of the present invention involves
controlling the output or exit moistur2 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 variahle 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 whlch 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% ~H (relative humidity) for at ~;
least 18 hours.
The present process may be conducted in various fo~ms
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-
~.
,, . , , . .. ,, , .. .. : ~
3~;~
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. However, there should preferably be a valved
inlet ~rom 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 lnlet line,
if desired, placed between the vessel and the inlet valve.
A means of heating-the vessel a~d/or the supply vessel, such
as external heating coils/ may be employed. Supporting the
vessel on a load cell greatly simp1ifies 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
chàrge of li~uid 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 li~uid 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 b~ the heating means, e.g., heating coils to bring "
the tobacco to the desired temperature, which should be less
than 31C (the critical temperature of carbon dioxide) and
this condition is preferably maintained for 1 to 20 minutes
while impregnation takes place. Excess li~uid carbon dioxide
is then drained off by opening the lower outlet of the vessel
- 18 - ;
~33;~
the vessel to a suitable reservoir or the like dispos~l sy~tem,
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 vola-tilize the solid carbon
dioxide, preferably by removing the solid carbon dioxide contain- ;
ing tobacco from the vessel and passing it through any of
several rapid heating systems to achieve expansion. As indicated
earlier in this specifica~ion, systems for this expansion
process are most satisfactory which provide rapid, turbulent
contact with the hot gas or vapor. With proper control of
temperature and exposure time, the product may be recovered
in the expanded state at the desired moisture content.
The overall process, apart from the specif~ improve-
ments set forth in the present specification, may be generally
~in accordance with the teachings in copending United States
application 441,767 or Belgian patent ~21,568.
:`
The following examples are illustrative. -
EXAMPLE 1
One hundred pounds of bright tobacco particles of --
cigarette filler size having 20% OV content was placed in a
wire basket in a pressure vessel. The vessel was closed
except for a port for admission of C02 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 li~uid to be pumped out. ~he port
was closed and after three minutes it was reopened to release
- the accumulated liquid. This port was closed and the vessel
-19-
::
~L333~ !
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 diffi~ult 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 ;~
C2 and was badly clumped.
An eight-inch diameter vertical dryer supplied with
125 ft./sec. of 85% superheated steam in air at 249C was
used for expansion. ~he product from C0~ treatment was fed
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% ~V, was 74.0 cc/10 g
as compared with the ori~inal CV of 34.0 cc/10 g for the
untreated br~ght filler at its standard moisture content of
12.5% OV.
EXAMPLE_2
One hundred pound batches of bright tobacco similar
to that used in the preceding example and having similar
input moisture content were processed as before, with blowdown
in 177 - 190 seconds, except for elimination of the 3-minute
draining 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.
Expansion was by tower exposure, about 3 seconds, to 81 to 88~
steam. r
-20-
- , , .~ ~ .
~33;3~
It t~ill 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
desirable.
Table 1
Feed to Tower
_ lb./min. Towex T~. C ~xit CV, % CCV,cc/lOg_
5.5 1491200, 12.2 59.4, 65.5
5.0 1778~5, 7.8 65.0, 67.8
4.25 2044.5, 4.8 67.8, 69.2
3.13 2491~8, 2.5 69.5, 75.4
EXAMPLE 3
Bright tobacco weighing 100 lb. and having 20% OV was
prepared 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- ;
minute sweep of C02 gas from top to bottom of the vessel helped
remove undrained C02 li~Uid. The vessel was then vented to
the atmosphere in 152 seconds and the chilled product was
removed.
This product was not clumpedt 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, o~ 68.0 cc/10 g. The starting filler had CCV of
37.3 cc/10 g at 12.5% OV.
~' ''
-21~
:' ,
L3~3~;
EX~MP~E 4
One hundred-pound lots of bright tobacco of varying
oV content were treated by the process of ~.xample 1 (impreg-
nation, liquid removal, drain, pressure release, and expansion
by tower exposure) with only the tower gas temperature varied
from 232 to 254C to compensate for increasing oV levels of :
input. The exit OV of all samples was between 1.3~ and 2.B~
OV. After being reconditioned, all samples.were checked for OV,
corrected to ll.Q% OV. The results shown in Table 2 indicate
that a moisture (OV) needed to achieve the best expansion,
in this series at least 68 cc/10 g CCV, is 17% minimum.
Table 2
Cylinder Volume vs. Input Moisture ~ :: with 400 psig Impregnation
. Out~ut Fillin~ Power
Input Reordered CCV, 11% OV :~
OV % '~V, '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, ~7.1 70.9, 72.5
19.0, l9ul 60.9, 63.2 68.3, 70.1
18.0, 18.3 69.2, 60.~ 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, ?l.9 68.2, 71.4 73.0, 76.5 r
23.0 59.1 6g.6
23.5, 23.5 63.9, 66.3 70.7, 71.0 .
23.9, 24.2 58.6, 58.9 68.~, 68.6
25.7 58.6 68.4 :~
:
-22- ~;
; 33~
EXAMPI,E 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. The 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. The 3-minute purge was similar to a 3-minute
drain time, except that C02 gas was blown down through the
impregnated 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 t 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 Drain Time on Sieve Fractions with
100-Pound Batches
Sieve Fractions, %
Drain Time, CCV
Mins. ~ edO Short Small Fine L+ M S~F cc/10 g
~ at 11%
OV
Unexpanded 55.5 35.9 7.0 0.9 0.691.4 1.5 --
Control
0 38.2 50.0 9.2 1.2 1.2 8~.2 2.474.6
1 41.9 47.7 8.1 1.2 1.2 89.6 2.473.7
2 43.7 47.0 7.3 1.0 0.9 90.7 1.976.3
3 42.2 49.2 6.8 0.7 1.0 91.4 1.774.2
3-Minute 42.7 48~5 6.9 1.0 1.0 91.2 2.075.0
Purge
- 23 -
Table 4
Effect of Drain Time of Sieve Fractions with
185-Pound Batches
Sieve Fractions, ~O
Drain Time CCV
Mins. Long 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.~10.0 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 ~.2 0.9 90.2 2.1 76.8 ,
As employed in the above example, the various sieve
fractions are defined as follows~ Long= ~ 10 (i.e, the
particles are retained on a lO mesh sieve)' Medium= - lO to -~20; ,~
Short= -20 to ~30; Small= ~30 to ~50;and Fine-~50.
`, ' :
,: :, ,
.
;: ~ '.`' . '
~ .
- -, '
~;
.
:':
"~
;~:
~';;
