Note: Descriptions are shown in the official language in which they were submitted.
Various processes have been proposed for expanding tobacco.
For example, to~acco has been contacted with a gas under scme-
what greater than atmospherlc pressure, followed by a release
of the pressure, whereby the tobacco cells are expanded to in-
crease the volume of the treated tobacco. Other methods
which have been employed or suggested have included the treat-
ment of tobacco with various liquids, such as water or re-
latively volatile organic liquids, to impregnate the tobacco
with the same, after which the liquids are driven off to ex-
pand the tobacco. Additional methods which have been suggestedhave included the treatment of tobacco with solid materials
which, when heated, decompose to produce gases which serve to
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 expand-
ing 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 expan-
sion 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 expand-
ing the volume of tobacco in order to make up the loss of
--1--
weight caused in curing tobacco lea~. 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 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 ex-
panded 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. Sowa, 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 moisture vapor causes expansion of the tobacco.
- A series of patents to Roger 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 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
t
carbohydra.es co 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 car-
bohydrate solution may also contain organic acids and/or
certain salts which are used to improve the flavor and
smoking qualities of the stems.
A publication in the "Tobacco Reporter" of November 1969
by P. S. Meyer describes and summarizes tobacco puffing or ex-
pansion procedures or investigations for expanding and manipu-
lating tobacco for purposes of reducing costs and also as the
means for reducing the "tar" content by reduction in the de-
livery 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 expansion
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 Reporter" article
was published, a number of tobacco expansion techniques, in-
cluding 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 3ames D. Frederickson, both issued in
1970, relate to the expansion 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
1273 and British Specification 1,293,735 to American Brands,
Inc., published in 1972, both relate to freeze-drying methods
f~or expanding tobacco.
South African applications 70/8291 and 70/8282 to R. J.
Reynolds Tobacco Company, both filed in 1970, relate to
tobacco expansion employing chemical compounds which decompose
to form a gas or with inert solutions of a gas under pressure
to maintain the gas in solution until it impregnates the
tobacco.
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 de-
composed by heat to release the gases w thin the tobacco
cells and to cause expansion of the tobacco.
Despite all of the above-described advances in the art,
no completely satisfactory process has been found. The dif-
ficulty with the various earlier suggestions for expanding
tohacco is that, in many cases, the volume is only slightly
or at best only moderately increased. For example, freeze-
4 --
~6 ;~
drying operations have the disad~antages of requiring elabor-
ate and expensive equipment and ~ery 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 re-
spond effectively to this type of process.
The use of special expanding agents, for example, halo-
genated hydrocarbons, such as are mentioned in the Meyer pub-
lication for expanding tobacco, is also not completely satis-
factory, because some of the materials employed are not al-
ways desired as additives. 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 ex-
traneous substances used or developed from the combustion of
the treated tobacco.
The use of carbonated water has also not been found to
~ 20 be effecti~ve.
While the method employing ammonia and carbon dioxide
.: gases is an improvement over the earlier described m~thods,
it is 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 Offen-
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 con-
nection with these uses, of the use of gaseous 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 Canadian Patent No. 1,013,640 to de la
Burde and Aument (two of the present co-inventors) and
assigned to the same assignee as the present application and
~n Belgian 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
20 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 ex-
- pansion of the tobacco.
In our earlier work with gaseous CO2, at pressures of
about 100 psia, we had found that only minute amounts of
carbon dioxide gas could be incorporated in the tobacco and
held there sufficiently long for the tobacco to be heated
and expanded. Thus, we ~ound no substantial improvement over
the prior art and gaseous CO2 was believed to be much less
; effective as an expanding agent than the liquid carbon
dioxide employed in the expansion process of the above-mentioned
Canadian Patent No. 1,013,640. We have now
found that gaseous carbon dioxide can be introduced into
tobacco in a manner whereby the gaseous carbon dioxide remains
in the tobacco in an amount of one per cent or more to form a
product which can then be expanded. Unexpectedly superior
results and advantages can be achieved by employing gaseous
C2 in the manner set forth in the present specification. The
present process may be described as follows: A process for
expanding tobacco to achieve at least about 50 per cent
increase in cylinder volume, comprising the steps of
(l) impregnating tobacco with gaseous carbon dioxide under a
pressure of at least about 250 psig and at sufficient tempera-
ture that substantially all of the carbon dioxide is maintain-
ed in gaseous form, (2) decreasing the pressure on the carbon
dioxide-impregnated tobacco and (3) heating the impregnated
tobacco under conditions effective to liberate the carbon
dioxide therein so as to cause expansion of the tobacco. The
present invention also relates to an improvement in that
process and have found that gaseous carbon dioxide can be in-
troduced into tobacco in a manner whereby the gaseous carbon
dioxide remains in the tobacco in an amount as high as three
per cent or more to form a product which can then be expanded.
Unexpectedly superior results and advantages can be achieved
' ~
by employing gaseous CO2 in the manner set forth in the
present specification.
This divisional application provides a process
for expanding tobacco to achieve at least about 50 per cent
increase in cylinder volume, comprising the steps (l)
impregnating tobacco with gaseous carbon dioxide under a
pressure of 400 to 800 psig for a period of l/4 to 30 minutes
and at sufficient temperature that substantially all of the
carbon dioxide is maintained in gaseous form, (2) decreasing
the pressure on the carbon dioxide-impregnated tobacco and
(3) heating the impregnated tobacco under conditions effective
to liberate the carbon dioxide therein so as to cause
expansion of the tobacco.
A novel tobacco product comprises tobacco containing
gaseous carbon dioxide in an amount of at least 1 part of
gaseous carbon dioxide per 100 parts of tobacco. The
product, when rapidly heated is converted to expanded tobacco.
An improved process for the expansion of tobacco is also
- provided which employs carbon dioxide as the expansion agent.
Tobacco, generally having a moisture content of from about
5 to about 35% by weight, is placed in a pressure vessel or
similar confinable space. Carbon dioxide gas may be passed
through to flush the vessel. Carbon dioxide pressure
is then increased and brought to a value of from about
250 pounds per square inch gauge (psig) to about 1057 psig
or even higher, and preferably to about 400 to 800 psig.
The tobacco is maintained under such a pressure under conditions
A
whereby the carbon dioxide is substantially gaseous for form
about 1/4 to about 30 minutes, to impregnate the tobacco
with carbon dioxide. The pressure is then reduced in a
period of from 1 to 800 seconds, preferably 10 to 120
seconds, preferably to atmospheric pressure, to produce a
: product comprising tobacco containing at least 1% by weight
of gaseous carbon dioxide, based on the weight of tobacco.
The resulting gaseous carbon dioxide-containing tobacco may
then be heated in the same vessel but is preferably rapidly
transferred, preferably within a few minutes, to a separate
zone where it is subjected to conditions of temperature and
i pressure, as by rapid heating in a gas at 100 to 370C and
`: at or near atmospheric pressure for a period of from about
1 second to about 10 minutes, to expand the tobacco.
An improvement on the above-described invention wherein
. the tobacco/CO2 system is cooled during or after pressurization,
',
"
;''
`:
- 8(a) -
. .
. ~ .
as by circulation of a cooling agent through the jacket of the
cha~her, to a te~perature close to the saturation temperature
of carbon dioxide but not lower than -23C. As an alternative
to using a cooling jacket in the improved process CO2 gas can
be caused to flow through the system by venting a portion of
the CO2 gas either during or following pressurization, pre-
~erably while maintaining an infeed of CO2 gas such that there
is not a loss in the system pressure due to the venting. With
cooling, the resulting conditions are such that the carbon
dioxide at the prevailing temperature and pressure remains sub-
stantially in the gaseous state, but further such that the
carbon dioxide, upon rapid reduction of pressure upon the sys-
tem, is converted partially to a condensed state within the
tobacco. Such conditions may be defined as such that the
enthalpy of the carbon dioxide is kept at a value which is less
than about 140 BTU per lbm. By this means a significantly
greater residue of carbon dioxide remains in the tobacco at
the beginning of the expansion step, than is the case without
the cooling before pressure release, wherein the carbon
dioxide, at higher enthalpy, remains primarily in the gas phase
throughout. A further method of reducing the enthalpy of the
system thereby causing an increased retention of carbon dioxide
involves admission of additional quantities of CO2 gas during
venting thereby causing additional sweeping of CO2 gas to flow
through the system.
In connection with the present invention, if desired,
the retention of carbon dioxide in the tobacco can be increased
by pre-cooling or pre-freezing the tobacco prior to the impreg-
nation cycle to cause a reduction in the system enthalpy. A
still further method of increasing the retention of carbon
dioxide in the tobacco involves "pre-snowing" the tobacco with
finely divided solid carbon dioxide (dry ice) prior to the im-
_ ~ _
pregnation cycle wh~ch accomplishes both a pre-cooling of the
tobacco and serves an an additional source for providing
carbon dioxide to the tobacco; applied in proper amounts of
~rom about 5-50~ by weight of the tobacco, at least a portion
of the dry ice will be incorporated into the tobacco during
the pressurization cycle and by varying the amount of dry ice
applied, a method of increasing and controlling the amount of
carbon dioxide retained by the tobacco becomes possible. When
such methods are involved, the tobacco/CO2 system may be main-
tained for 1/4 to 30 minutes during the impregnation step,where the pressure is at least 250 psig, to impregnate the
tobacco with carbon dioxide. The pressure is then reduced, in
a period of 1 to 800 seconds, preferably 10 to 120 seconds and
preferably but notnecessarily to atmospheric pressure. The
tobacco is then rapidly transferred to a zone where it is
subjected to conditions of temperature and pressure, as by
rapid heating in a gas at 100 to 370C and at or near atmos-
pheric pressure ~or one second to 10 minutes to expand the tobacco.
This invention relates broadly to an improved process
for expanding tobacco employing a readily-available, relative-
ly inexpensive, non-combustible, inoffensive, and non-toxic
expansion agent and more particularly, to the production of
an expanded tobacco product of substantially reduced density
and increased filling power. The improved process employs
carbon dioxide as the expansion agent. In general, the pro-
cess comprises placing tobacco, preferably having a moisture
content of from about 5 to about 35~, by weight, in a vessel
or similar confinable space; the vessel or space may then be
flushed with gaseous CO2 to remove most of the associated air,
3Q although this is not essential to the invention. The vessel
is closed except ~or an inlet port, and carbon dioxide gas
is introduced ar;d the pressure increased, by continued gas in-
- 10 --
P _ ~
troduction or heating or both, under conditions whereby the CO2
in the ~essel remains primarily in the gas state to a final
pressure of at least 250 psig, preferably 400 to 800 psig.
The required temperature to maintain the CO2 in a substantially
gaseous state at a given pressure may be determined readily by
one familiar with the use of phase diagrams or critical tables.
Wh~le pressures as high as 900 psig might be economically em-
ployed, and a pressure of about 1057 would be acceptable,
there is no known upper limit to the useful impregnation pres-
lQ sure range other than that imposed by the capabilities of the
equipment available. However, operation below the critical
temperature is preferred for ease of control. The tobacco
may fie maintained under these impregnating conditions from
about 1/4 to 30 minutes, the longer times being in general
applicable to lower pressure operation. Reference to the
pressure~enthalpy diagram for CO2 as set forth in Figure 1 of
the drawing will be of help in selecting desired conditions.
After the impregnation step, the gas pressure is reduced by
venting. The final pressure may be atmospheric or some pres-
sure near that to be employed in the expansion step, but pre-
ferably the former. The time of pressure reduction is from
1 to about 800 seconds. The gaseous carbon dioxide-containing
tobacco is then transferred to a zone where it is subjected to
.
conditions whereby the carbon dioxide is removed to expand
the tobacco. The transfer of the carbon dioxide-containing
tofiacco to the heating or expansion zone should preferably be
effected within as short a time as possible, preferably within
about five minutes, and most preferably within about two
minutes. As an alternative to rapid transfer, if desired,
3Q the carbon dioxide-containing tobacco may be stored in an
insulated bulker or chilled or otherwise maintained in a re-
latively cool condition. The heating or expansion step prefer-
~~
ably involves exposing the carbon dioxide-containing tobacco
to rapid heat;ng at a temperature of about 100 to 370C for a
period o~ time of ~rom about 1 second to 10 minutes and sub-
stantially atmospheric pressure.
In accordance with improvement in the present invention,
the impregnation step is modified, as will be set forth in de-
tail later in this specification. After the impregnation step,
the gas pressure is reduced by venting. The final pressure may
be atmospheric or some pressure near that to be employed
lQ in the expansion step, but preferably the former. The time
of pressure reduction is from 1 to about 800 seconds. The
gaseous carbon dioxide-containing tobacco is then transferred
to a zone where it is subjected to conditions whereby the
carbon dioxide is removed to expand the tobacco. The transfer
of the carbon dioxide-containing tobacco to the heating or
expansion zone should preferably be effected within as short
a time as possi~le, preferably within about five minutes, and
most pre~erably within about two minutes. As an alternative
to rapid transfer, if desired, the carbon dioxide-containing
tobacco may fie stored in an insulated bulker or chilled or
otherwise maintained in a relatively cool condition. The heat-
ing or expansion step preferably involves exposing the carbon
dioxide-containing tobacco to rapid heating at a temperature
o~ ahout 100 to 370C for a period of time of from about
1 second to 10 minutes and substantia]ly atmospheric pressure.
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 treated may have a particle size of from about
10 to about 100 mesh, but is preferably not smaller than
about 30 mesh.
:,.
~ 12 -
The tobacco may contain the natural moisture content of
tobacco and may contain from about 5 to about 35% by weight
; moisture. It is preferred, however, for best results that the
tobacco have at least about 8~ moisture (by weight) and no
~ore than about 22% (by weight) moisture. As used herein,
% moisture may be considered equivalent to oven volatiles
(OV~ since not more than about 0.9~ of the tobacco weight is
volatiles other than water. The procedure for determining
oven volatiles is set forth later in this specification.
10The tobacco will generally be placed in a pressure vessel
which will be more fully described hereinafter. For example,
it may be placed in a wire cage or on a platform positioned
within the vessel.
The tobacco-containing pressure vessel may be then purged
with carbon dioxide gas. The benefits of purging are the
removal of gases that might interfere with a carbon dioxide
recovery process and/or that might interfere with full
penetration of the gaseous carbon dioxide. As an alternative
to purging with carbon dioxide gas, the vessel may be evacuated
prior to introduction of the carbon dioxide gas.
Either with or without a preliminary purging or evacuation
of the vessel, carbon dioxide gas is fed to the vessel under
conditions whereby the carbon dioxide gas pressure in the
vessel is increased under conditions whereby the tobacco in the
vessel is preferably at a temperature of from about -10 to
about 60C, and the pressure in the vessel is above about
25Q psig, preferably about 400 to 800 psig. The tobacco is
- 13 -
.' ' " ~
- - -
~aintained unde~ cond~tions whe~ehy the carbon dioxide is
at ~ p~essure afiove afiout 25Q psig and is under conditions
afiove and to the right o$ the saturated vapor line of Figure 1
of the drawing ~rom a period of from about 15 seconds to
a~out 30 ~inutes. The pressure is then reduced over a period
of ~rom 1 to about 800 seconds, preferably 10 to 120 seconds,
such that the temperature at no point drops below the satura-
tion temperature for carbon dioxide at the simultaneous pres-
sure, and the tobacco is brought to a temperature below about
lQ lQC, and atmospheric pressure or the pressure at which the
expansion step is to be carried out.
In the ~mprovement on this invention, the tobacco/C02
system during the impregnation step is cooled, as for example,
by circulation of a refrigerant through the jacket of the
Yessel containing the system, to reduce the enthalpy of the
carbon dioxide fielow about 140 BTU/lbm, preferably while the
pres-sure is maintained relatively constant by admission of
additional carbon dioxide gas. The cooling is limited so that
the carbon dioxide is not condensed to any significant degree
2Q and is not cooled to a temperature lower than -23C. The
system is maintained under these impregnating conditions from
about 1~4 to 30 minutes, the longer times being in general
applicable to lower pressure operation. Reference to the afore-
mentioned phase diagram or critical tables for carbon dioxide
will be of help in selecting desired conditions. The pressure-
temperature relationship is preferably maintained to keep the
carbon dioxide gas at or near the saturation point. It is be-
lieved that when the conditions are close to or at saturation,
the absorption/adsorption characteristics of gaseous CO2 are
greatly enhanced. This results in improved retention of gaseous
CO2. The final pressure, when the pressure is reduced, may be
atmospherlc or some pressure near that to be employed in the
expansion step, but is preferably atmospheric. The time of
- 14 -
pressure re~tion may be from about 1 to about 800 seconds.
It has been found that after the impregnation step, under
conditions where the cooling of the improved process is not
employed, a product will be formed having at least one part of
carbon dioxide gas per one hundred parts of tobacco. By this is
~eant that at least one part of carbon dioxide gas, per one
hundred parts of tobacco, will be associated with the tobacco
in some manner, chemically and/or physically, for example by
being absorbed by the tobacco. The product may have as high
as three parts or more of gaseous carbon dioxide when the process
~s so conducted. This has been found to occur in the absence
of added adsorbents or the like. Adsorbents, absorbents or the
like may be present; however, it is preferred that they not be
present since the process is effective without them and they might
introduce undesired elements into the smoke or might not release
the carbon dioxide in a totally effective manner. It has been
found that after tne impregnation step, the tobacco may contain
eyen greater amounts of carbon dioxide, as high as 3 parts (per
hundred of tobacco~ or more. The pressure-temperature relation-
shIp is preferably maintained to keep the gas at or near thesaturation point. It is believed that when the conditions are
close to or at saturation, the absorption/adsorptlon character-
istics of gaseous CO2 are greatly enhanced. This results in
improved retention of gaseous CO2. The final pressure, when
pressure is reduced, may be atmospheric or some pressure near
that to be employed in the expansion step, but is preferably
atmospheric. The time of pressure reduction may be from about 1
to about 800 seconds.
We have found that after the impregnation step, under
3Q conditions where the cooling of the improvement in the present
invention is employed, a product will be formed which may have
as high as three parts or more of gaseous carbon dioxide, per
.
one hundred parts of tobacco. By this is meant that at least
three parts of carbon dio~ide gas, per one hundred parts of
tobacco, will be associated with the tobacco in some manner,
chemically and/or physically, for example, by being absorbed
by the tobacco. I have found this to occur in the absence of
added adsorbents or the like. Adsorbents, absorbents or the
like may be present; however, it is preferred that they not be
present since the process is effective without them and they
might introduce undesired elements into the smoke or might
not release the carbon dioxide in a totally effective manner.
The tofiacco, after the impregnation step, may then be
transported to a zone where it is subjected to conditions such
that the carbon dioxide is removed and the tobacco is expanded,
preferably by exposure to rapid heating at 100 to 370C for 1
second to 10 minutes and substantially atmospheric pressure.
~ description of the improvement on the presently claimed
- process will be described below, said improvement relating
specifically to the impregnation step.
To carry out the improvement on the present process, one
may treat either whole cured tobacco leaf, tobacco in cut or
chopped form, or selected parts of tobacco, such as tobacco stems
: or ~ay be reconstituted tobacco. In comminuted form, the
tohacco to fie treated may have a particle size of from
ahout 10 to about 100 mesh but is preferably not smaller than
about 30 mesh.
The tobacco may contain the natural moisture content of
tobacco and may contain from about 5 to about 35~ by weight
moisture. It is preferred, however, for best results that the
tobacco have at least about 8% moisture (by weight) and no more
` 30 than about 22% (by weight) moisture. As used herein, % moisture
may be considered equivalent to oven volatiles (OV) since not
more than about 0.2% of tobacco weight is volatile other than
water. Oven volatiles determination is a simple measurement
~ 16 -
of weight loss on exposure in a circulating air oven for 3 hours
at 100C.
The tobacco will generally be placed in a pressure vessel
which will be more fully described hereinafter. For example, it
may be placed in a wire cage or on a platform positioned within
the ~essel.
The tobacco-containing pressure vessel may be then purged
with carbon dioxide gas. The benefits of purging are the re-
moval of gases that might interfere with a carbon dioxide re-
lQ covery process and/or tha~ might interfere with full penetration
of the gaseous carbon dioxide. As an alternative to purging
with carbon dioxide gas, the vessel may be evacuated prior to
introduction of the carbon dioxide gas.
The carbon dioxide which is employed in the process of this
inyention will generally be obtained from a storage vessel where
it is maintained at a pressure of from about 215 to 305 psig and
temperatures o~ from -29 to-16C. The carbon dioxide may be
introduced into the pressure vessel at 215 to 320 psig and -29 to
-14C, but is preferably brought, by suitable means, to a tempera-
20 ture above -23C, and a pressure above 250 psig before being
introduced into the pressure vessel.
Either with or without a preliminary purging or evacuation
of the vessel, carbon dioxide gas is fed to the vessel under
conditions whereby the carbon dioxide gas pressure in the vessel
is increased under conditions whereby the tobacco in the vessel
is at a temperature of from about -10 to about 60C and the
pressure in the vessel is above about 250 psig, preferably about
400 to 800 psig. The tobacco/CO2 system is cooled in such a way
that the CO2 enthalpy is brought below about 140 BTU/lbm but the
gas is preferably not condensed to any significant degree, while
the pressure is, preferably, held substantially constant by admis-
sion of additional gas, and the system is maintained at these
:
- 17 -
. .
P~
;`
conditions from about 15 seconds to about 30 minutes. The
pressure is then reduced over a period of from about 1 to about
800 seconds, ~hereby the tobacco is brought to a temperature below
10C, and atmospheric pressure or the pressure at which the
expansion step is to be carried out.
The resulting carbon dioxide-treated tobacco may then be
rapidly transported, as described earlier in this specification
to a zone where it ls exposed to expansion conditions by sub-
~ecting it to heat or the equivalent in order to remove the
carhon dioxide from the tobacco. This may comprise the use of
hot surfaces, or a stream of hot air, a mixture of gases and
steam, or exposure to other energy sources, such as microwave
energy or infrared radiation. It has been found that the use
of a gas composition comprising at least 50%(by weight) f
steam, and preferably above 80% (by weight) of steam, provides
particularly satisfactory results. A convenient means of ex-
; panding the 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 turbulent air stream maintained, for
example, at a temperature of from about 150 to about 260C (as
low as 100C and as high as 370C~ for a period of about 1
second to lQ minutes. The impregnated tobacco may also be
heated by being placed on a moving belt and exposed to infrared
heating fiy exposure in a cyclone dryer, by contact in a tower
with superheated steam or a mixture of steam and air or the
like. Any such contacting steps should not raise the tempera-
ture o~ the atmosphere with which the tobacco is in contact
to above about 370C and should preferably be from at about
100 to about 30ac r most preferably 150 to 260C when conducted
3Q at atmospheric pressure.
As is ~ell known in the processing of any organic matter,
overheating can cause damage, first to colour, such as undue
:.
- 18 -
darkening and, finally, .o the extent of charring. The necessary
and sufficient temperature and exposure time for expansion without
such da~age is a function of these two variables as well as the
state of subdivlsion of the tobacco. Thus, to avoid undesirable
da~age in the heating step, the impregnated tobacco should not be
~; exposed to the higher temperature levels, e.g. 370C, longer than
1 to 2 seconds.
One method for causing the expansion of the tobacco cells
is to use the radiation methods described in either U.S.
Patents 3,40g,022 or 3,409,027. 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, usually preferred, 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, usually called hereafter
a tower. The temperature in the dryer may range from about 120 to
370C with contact time in the dryer of about 1 to 10 seconds. In
2Q general, a 1 to 6 second contact time is utilized when the hot gas
temperature is 260 to 315C or somewhat higher. As stated before,
other known types of heating means may be used as long as they are
capable of causing the impregnated tobacco to expand without
excessive darkening. Th~ presence of a steam atmosphere of 20%
or more of the total hot gas composition aids in obtaining the best
expansion; a high proportion (e.g., over 80% volume) of steam is
preferred.
The present invention may be further understood by referring
to the drawings. In the drawings:
Fig. 1 is a standard phase diagram plotting pressure of
C2 (in p.s.i.a.) vs temperature (in F) of the tobacco bed for
the carbon dioxide-tobacco system, with line I-II-III drawn
thereon as an illustration of the system involved here.
-- 19 --
Fig. 2 is a standard pressure enthalpy diagram, with line
i I~I~ drawn thereon to further illustrate the present invention.
Fig. 3 is a standard pressure enthalpy diagram, with line
- I-IV drawn thereon to illustrate the process of the present
invention.
As a general illustration of the practice of this invention,
reference may be made to Fig. 1. The conditions may, for example,
- be such as are represented by line I-II-III on Fig. 1. For example,
the tobacco, at about 12% OV in the form of cut bright filler, is
placed in a pressure vessel capable of handling the desired
pressure, for example, capable of handling a pressure of 1057 psig.
The vessel may be similar to the impregnation vessel described in
Canadian Patent No. 1,013,640, but, in distinction to that appara-
tus, need have no means for the handling of liquid CO2. The vessel
may be f~ushed with gaseous CO2 or may be evacuated and is
pressured with gaseous CO2 to bring the contents to a condition
(at II~ where the pressure is greater than 250 psig and the
temperature is not less than -23C. The pressure is then released
(to III). The conditions of the entire sequence (as shown by line
I-II-III) are such that the carbon dioxide is maintained below
and to the right of the saturated vapor line on Fig. 1.
In one form of the invention, as may be seen from Fig. 2,
the enthalpy of the CO2 is greater than about 140 BTU/lbm and
the CO2 is present in gaseous form. The vessel may be maintained
at these conditions for 1/4 to 30 minutes, as illustrated by line
I-III. The pressure may then be reduced rapidly, preferably
within 10 to 120 seconds, preferably to atmospheric pressure, as
illustrated by line III-IV in Fig. 2.
The impregnated tobacco then is transferred (preferably but
not necessarily directly) to a rapid heating zone or vessel such
as the heating vessel described in Canadian Patent No. 1,013,640
mentioned above or as described earlier in this specification,
- 20 -
for example, an expansion tower, microwave chamber, or the like.
The temperature at which the impregnated tobacco is main-
tained prior to the expansion or rapid heating step will largely
govern how long the CO2 remains in the tobacco in sufficient
quantity to cause the desired expansion. If there is little
insulation or means to keep the temperature down, the transfer
should be rapid, preferably less than a few minutes. An insulated
"bulking" container is preferred to accomplish the transfer.
Supplementary cooling may also be provided as, for example, by
lQ applying crushed or powdered dry ice or by spraying liquid nitro-
gen on the impregnated tobacco.
The rapid heating causes expansion of the tobacco at a
temperature where the tobacco is pliable and elastic and the
tobacco can be expanded without fracture to an approximation of
its green leaf state. A significant and useful degree of
expansion is realized.
Referring to the Fig. 3, an illustration of the present
invention is shown. Tobacco at about 12% OV in the form of cut
bright filler is placed in a pressure vessel. The vessel may be
similar to the impregnation vessel described in Canadian Patent
No. 1,013,640 but, in distinction to that apparatus, need have
no means for the handling of liquid CO2. The vessel may be flushed
with gaseous CO2 or may be evacuated and is pressured with CO2
to bring the contents to a condition wherein the pressure is
greater than 250 psia and the temperature is not less than -23C,
and the enthalpy is at or above 140 BTU/lbm as shown by line I-II
in the drawing. The enthalpy of the CO2 is then reduced by cooling
below about 140 BTU/lbm (but at conditions of temperature and
pressure such that the CO2 is present primarily as gas) as shown
by line II-III. The vessel is maintained at these conditions for
1/4 to 30 minutes. The pressure is then reduced rapidly, preferably
within 10 to 120 seconds, for example, to atmospheric pressure, as
- 21 -
y
illustrated by line III~
The impregnated tobacco then is transferred (preferably but
not necessarily directly) to a rapid heating zone or vessel such
as the heating vessel described in Canadian Patent No. 1,013,640,
mentioned above, or as described earlier in this specification,
for example, an expansion tower, microwave chamber, or the like.
The rapid heating causes expansion of the tobacco at a temperature
where the tobacco is pliable and elastic and the tobacco can be
expanded without fracture to an approximation of its green leaf
state. A significant and useful degree of expansion is realized.
The temperature at which the impregnated tobacco is maintained
prior to the expansion or rapid heating step will largely govern
how long the CO2 remains in the tobacco in sufficient quantity to
cause the desired expansion. If there is little insulation or
means to keep the temperature down, the transfer should be rapid,
preferably less than a few minutes. An insulated "bulking" con-
tainer is preferred to accomplish the transfer. Supplementary
`~ cooling may also be provided as, for example, by applying crushed
or powdered dry ice or by spraying liquid nitrogen on the
impregnated tobacco.
The following examples are illustrative:
EXAMPLE 1
A l-pound sample of commercial cased bright tobacco filler
at 12.5% OV was placed in an autoclave-type pressure vessel and
was pressurized to 800 psig with CO2 gas obtained from a CO2
supply tank which was maintained at a CO2 pressure at least
` slightly above the desired impregnation pressure. The impregnator
system temperature was maintained above 30C during the pressure
cycle by supplying extra heat to the system, when necessary, to
prevent any formation of liquid or solid CO2 during the entire
processing cycle. After a 15-minute contact time, the pressure
and temperature conditions of the CO2 gas in the impregnator
- 22 -
~L ~, - r ' ~ r~
were found to correspond to an enthalpy ~alue of about 142 BTU/lb
f C2 gas. The pressure was released by venting in about 30
seconds after which the tobacco temperature was found to be 2.2C.
The impregnated sample had a weight gain of 2.0~ which is
attributable to the gaseous CO2 contained therein. The impreg-
nated material was then, within about 5 minutes time, exposed to
heating in a 3-inch diameter tobacco expansion tower by contact
with superheated steam at 288C and a velocity of 140 ft/sec for
about 4 seconds. The product exiting the expansion tower had an
OV of 2.1%. The product was equilibrated at standard conditions
of 23.9C and 60% RH for about 18 hours. The filling power of
the equilibrated product was measured by the standardized
cylinder volume (CV~ test described later in this specification
as 74 cc/10 g at 11.2~ OV. This gave a corrected CV (CCV) value
at 11% OV of 76 cc/10 g. An unexpanded control was found to have
a cylinder volume of 36 cc/10 g. The sample after processing,
therefore, had a 111% increase in filling power as measured by
the CV method.
EXAMPLE 2
A series of bright tobacco samples were treated as in
Example 1 under conditions where gaseous CO2 and substantially
no liquid or solid CO2 would be formed. The tobacco feed OV
was varied from 9% to 14.6%. The conditions of each test and
the test results are shown in Table I. Where no value is shown
in the Table for a variable, the value is as in Example 1.
Table I
~ ller Expansion with Gaseous CO2
:
.: .
Test # 1 2 3
Tobacco Feed OV 9.0% 10.3% 14.6%
Impregnation Pressure, psig 800 800 800
C2 Temperature Prior to Vent, C 31.7 31.7 32.2
C2 Enthalpy Prior to Vent, BTU/lb. 143 143 143
Tobacco Temp. after Venting, C -20.0 -22.8 ~2.8
% C2 Retention on Tobacco 2.9 2.4 1.5
Product OV after Expansion 1.7% 1.8% 3.2%
Reordered Product CV 62 94 74
Reordered Product OV 11.6 10.3 11.3
Correct CV at 11% OV 66 88 76
% Increase in Filling Power 83 144 111
EXAMPLE 3
; A series of bright tobacco samples were treated as in
Example 1 under conditions where gaseous CO2 and substantially
no liquid or solid CO2 would be formed. The hold time was varied.
The conditions and test results are shown in Table II. Where no
value is shown in the Table for a variable, the value is as in
Example 1.
Table II
Filler Expansion with Gaseous CO2
Test # 3 4 5
Tobacco Feed O~ 14.2%14.4%15.3%
: Impregnation Pressure, psig 800 800 800
Hold Time, Minutes 1 2 20
C2 Temperature prior to Vent, C 58.9 30.0 35.6
C2 Enthalpy prior to Vent, BTU/lb. 160 142 144
Tobacco Temp. after Venting, C 8.3 -5.6 4.4
% C2 Retention on Tobacco 2.0 2.6 1.5
Product OV after Expansion 2.2%2.0 3.8
Reordered Product CV 71.274.0 76.2
Reordered Product OV 11.111.6 11.6
Corrected CV at 11% OV 72 78 80
% Increase in Filling Power 100 117 122
Example 4
30A series of bright tobacco samples were treated as in
Example 1 at conditions where no liquid or solid CO2 would be
expected to be formed. The impregnation pressure was varied.
The test results are shown in Table III. Where no value is
- 24 -
shown in the Table for a variable, the value ls as in Example 1.
Table III
Filler Expansion with Gaseous CO2
Test # 6 7 8 9 10 11
Tobacco Feed OV 14.5 13.6 lQ.3 16.1 13.2 13.3
Impregnation Pres-
sure, psig 300 4Q0 500 600 700 800
Hold Time, Minutes 15 15 15 25 15 15
C2 Temperature prior
to Vent, C -11.7 NA 20.6 20.6 19.4 53.9
10 C2 Enthalpy prior
to Vent, BTU/lb. 143 NA 15Q 145 142 155
Tobacco Temp. after
Venting, C -13.9 NA 3.3 -5.6 -16.7 20.6
Product OV after
Expansion 2.2 1.9 2.1 2.1 3.4 2.7
Reordered Product CV 62 66 59 75 74 60
Reordered Product OV 10.7 11.5 11.7 11.4 11.5 11.6
Corrected CV at 11%
OV 66 69 64 79 7/ 65
Increase in Filling
Power 83 92 78 119 114 81
~` .
EXAMPLE 5
A l-pound sample of commercial cased bright tobacco
filler at 11.1% OV was placed in an FS-3 pressure vessel and
'! pressurized to 800 psig with ~2 gas as in the procedure of
Example 1. The impregnation system t~mperature was cooled by
circulating a cooling solution through a jacket surrounding
the impregnation vessel until the CO2 gas in the impregnator
was cooled to near its saturation temperature. After a 15-
minute contact time, the pressure and temperature conditions
of ~he CO2 gas in the impregnator were found to correspond to
an enthalpy ~alue of about 130 BTU/lb. of CO2 gas. Although
some CO2 condensation probably occurred within the vessel, the
C2 was present primarily as a gas. The pressure was released
- 25 -
by venting in about 30 seconds after which the tobacco temperature
was found to he -37.8C. The impregnated sample had a weight
gain of about 3.5% attributable to CO2. This impregnated material
was then heated as in Example 1. The product exiting the exp2n-
sion tower had an OV of 1.9%. The equilibrated product had a CV
of 90.6 at an OV of 10.8%. This corresponds to a CCV of 89 or an
increase in filling power of 147% over the unexpanded control
; (36 cc/10 g).
EXAMPLE 6
A series of bright tobacco samples were treated as in
Example 5 at conditions where the CO2 gas would be coGled to
near saturation prior to pressure release at three different
pressures. The conditions and test results are shown in Table
IV. Where no value is shown in the Table for a variable, the
value is as in Example 1.
Table IV
:
Filler Expansion with Gaseous CO2
-
Test # 12 13 14
~- Tobacco Feed OV 9.5% 10.8 12.1
Impregnation Pressure, psig 800 600 500
Hold Time, Minutes 15 15 20
C2 Temperature prior to Vent, C 19.4 7.2 2.2
C2 Enthalpy prior to Vent, BTU/lb. 129 139 139
` Tobacco Temp. after Venting, C -38.9 -27.8 -18.3
% C2 Retention on Tobacco 3.7 2.6 2.4
Product OV after Expansion 1.3% 1.4 1.9
Reordered Product CV 89 88 71
Reordered Product OV 10.5 10.9 11.9
Corrected CV at 11% OV 85 87 78
% Increase in Filling Power 136 142 117
EXAMPLE 7
The procedure of Example 5 was repeated using cased
burley tobacco. The equilibrated expanded product was found
to have a CV of 92.4 at 10.1% OV or an increase of about 100%
over the unexpanded control.
EXAMPLE 8
The procedure of Example 5 was repeated using a tobacco
blend as normally used in cigarette manufacture. The product
- 26 -
was found to have a CV of 78.1 at 11.1~ OV or an increase of
about lQ5~ o~er the unexpanded control.
EXAMPLE 9
A l~pound sample of cased bright tobacco was processed
as in Example 1 and found to have a CCV of 81. This product
was blended at 25% with conventional tobacco blend. Cigarettes
were smoked and found to have a desirable taste and aroma;
firmness of the tobacco rod was acceptable.
EXAMPLE 10
A 13-pound sample of cased bright tobacco was processed
as in Example 5. The product was found to have a CCV of 78.
EXAMPLE 11
A 5-pound sample of cased bright tobacco was
impregnated as in Example 5 but was then subjected to heating
in a static bed using 149C steam for a 5-minute exposure. The
equilibrated product was found to have a CV of 85.
EXAMPLE 12
A series of runs was conducted following the process
of Example 5 and the runs were found to give cylinder volume
results of 80, 80, 80, 79, 84, 78, 79, 78 and 79, respectively.
This gives an average CV of 80 for the 9 trials or an increase
in filling power of 121% over the untreated control.
EXAMPLE 13
A series of 3 runs was conducted according to the pro-
cess of Example 5, except that the feed tobacco was pre-chilled
to a temperature just below -20C before the tobacco was con-
tacted with the pressurized CO2 gas. The reordered product
CV results under these circumstances were found to be 92, 92
and 87, respectively. This gave an average increase in filling
power of 151% over the untreated control.
EXAMPLE 14
Two series of runs were conducted in a manner similar
to Example 1. However, conditions were as indicated in Table
- 27 -
V with a ten~minute hold period and the tower conditions were:
3-inch tower at 60,QF, with lQ0% steam. Series #2 was run
under similar conditions to Series #1.
The results of both series of these runs are given in
' Table V together with the results for an unexpanded control
sample and for a control sample which was expanded, without any
C2 treatment:
Table V
S-eries #l Series #2
%Reordered % Reordered
Press. (psig), OV CV/OV CCV OV CV/OV CCV
Control 11.836.8/12.6 - - - -
Exp.control - - - 1.9 64.6/10.9
, 250 2.572.8/10.8 71.2 1.5 73.8/10.8 72.3
300 2.876.3/10.8 74.9 1.2 81.4/10.7 78.9
, 325 2.677.2/10.8 75.9 1.2 79.6/10.7 77.5
~, 350 2.378.4/11.0 78.4 1.2 77.3/11.2 78.5
375 2.480.6/11.1 81.0 1.4 78.7/11.1 79.6
4Qo 2.678.5/11.2 79.9 1.4 82.0/11.1 85.6
800 2.892.0/11.2 93.3 1.5 97.6/11.1 98.0
It will be seen that pressures of 250 psig through 800
psig provided excellent expansion, compared with the controls.
The following experiments were also conducted:
Experiment 1
The impregnation procedure of Example 11 was repeated
but the impregnated material was simply allowed to warm to room
temperature and was not subjected to tower expansion. The re-
sulting product showed no gain, and perhaps a slight loss, in
CV compared to the untreated control.
Experiment 2
A comparison run of gaseous vs. liquid CO2 impregnation
- 28 -
was conducted in the following manner.
1~ Liquid CO2~Three pounds of cased commercial
bright tobacco filler (OV of 12.7%) was impregnated with liquid
C2 at 800 psig, cooled to 19.6C, and held for 15 minutes.
Thereafter the excess liquid was drained and the pressure was re-
leased. A 23% gain in weight was attributed to CO2 pickup.
The material was somewhat clumped together because of the large
amount of retained CO2.
2. Gaseous CO2--Three pounds of cased commercial
; 10 bright tobacco filler (OV of 13.3%~ was pressurized with
gaseous CO2 at 800 psig and 19.6C for l5 minutes. Thereafter
the pressure was released. A 3% gain in weight was attributed
to CO2 pickup. The material was free-flowing and easy to
handle.
Roth samples were processed in a 4-inch diameter
tobacco expansion tower and the samples were equilibrated and
measured for cylinder volume. The samples which utilized
the liquid impregnation was found to have a CCV of 79 and the
comparable sample impregnated with CO2 gas was found to have a
CCV of 82.
Experiment 3
A series of trials was conducted over an impregnation
pressure range of 20, 40, 60, 80, 100, 200, 300, 400, 600 and
800 psig, employing 10-minute contact time, following the
pattern of Example 1, with expansion in the tower with a steam
temperature of 316 C. These samples were run, together with
an unexpanded control and with a control which was not contacted
with CO2 with the conditions and the results set forth in Table
VI:
- 29 -
Table VI
Reordered
Pressure (psig) OV% CV OV CCV
Control 13.630.8 13.3 33.2
Exp. control 2.249.3 12.2 50.1
2.955.7 11.8 57.2
2.454.3 11.9 56.3
2.057.7 11.6 58.2
2.557.7 11.7 58.7
100 2.655.7 11.7 56.7
200 2.356.4 11.7 57.4
300 2.755.0 11.8 56.5
400 1,965.9 11.5 68.9
600 1.875.9 11.6 80.7
800 1.884.4 11.5 88.4
, 10
Table VI illustrates that some expansion may be obtain-
ed at lower pressures, but pressures of about 400 psig may be
necessary to achieve product objectives. It will be seen, how-
ever, from Example 14, that a pressure of 250 psig can be
effective to produce a satisfactory degree of expansion.
The terms "cylinder volume" and "corrected cylinder
volume" are units for measuring the degree of expansion of
- tobacco. The term "oven-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:
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
reported as cylinder volume. This test is carried out at
standard environmental conditions of 23.9C and 60% RH; con-
ventionally unless otherwise stated, the sample is pre-condition-
ed in this environment for 18 hours.
- 30 -
Corrected Cylinder Volume (CCV~
The CV value may be ad~usted to some specified oven-
volatile cc,ntent in order to facilitate comparisons.
CV ~ CV + F (OV - OVs) where OVs is the specified OV
and F is a correction factor (Yolume per %) predetermined for
the particular type of tobacco filler being dealt with.
Oven-Volatiles Content (OV)
The sample of tobacco filler is weighed before and
after exposure for 3 hours in a circulating air oven controlled
at 100C. The weight loss as percentage of ir.itial weight is
oven-volatiles content.
For bright tobacco employed in the present application,
the value of F in the calculation of CCV is 7.6 on average for
- gaseous CO2 expanded tobacco.
Unless otherwise indicated, all percentages used herein
are by weight.
- 31 -
