Background of the Invention
[0001] The invention relates to a process for tobacco expansion. More specifically, the
invention relates to a process for expanding tobacco to reduce its bulk density and
thereby increase its volume and filling capacity. The process is especially suitable
for treating cigarette cut filler.
[0002] In the past two decades, tobacco expansion processes have become an important part
of the cigarette manufacturing process. Tobacco expansion processes are used to restore
tobacco bulk density and/or volume which are lost during curing and storage of tobacco
leaf. In addition, expanded tobacco is an important component of many low tar and
ultra low tar cigarettes.
[0003] Commercially significant tobacco expansion processes are described in U.S. Patent
3,524,451 to Fredrickson and U.S. Patent No. 3,524,452 to Moser et al. These patents
describe processes wherein tobacco is contacted with a volatile organic impregnant
and then heated by rapidly passing a stream of hot gas in contact with the impregnated
tobacco to volatilize the impregnant and expand the tobacco. A variation of these
processes is described in U.S. Patent No. 3,683,937 to Fredrickson et al. which discloses
a tobacco expansion process wherein tobacco is impregnated with a volatile organic
compound in the vapor state and in the absence of any liquid or solid phase. The impregnated
tobacco is expanded either by heating or rapidly reducing pressure. Heat can be applied
through a stream of hot gas or through microwave treatment.
[0004] Following development and commercialization of the tobacco expansion processes described
above, extensive and continuing efforts have been directed to the identification of
specific expansion agents and processes for expansion of tobacco. For example, U.S.
Patent No. 4,235,250 to Utsch; U.S. Patent No. 4,258,729 to Burde et al. and U.S.
Patent No. 4,336,814 to Sykes et al., among others, disclose the use of carbon dioxide
for expanding tobacco. In these and related processes, carbon dioxide, either in gas
or in liquid form, is contacted with tobacco to impregnate tobacco and thereafter
the carbon dioxide-impregnated tobacco is subjected to rapid heating conditions to
volatilize the carbon dioxide and thereby expand the tobacco. Carbon dioxide is a
substantial component of the atmosphere and is readily available. Nevertheless, in
the carbon dioxide tobacco expansion processes, it is typically necessary to heat
the tobacco excessively in order to achieve substantial stable expansion which can
result in harm to the tobacco flavor and the generation of excessive amounts of tobacco
fines. In addition, those commercially available processes which use liquid carbon
dioxide to impregnate tobacco result in impregnated tobacco in the form of solid blocks
of tobacco containing dry ice which must be broken up prior to heat treatment, thereby
harming the tobacco and increasing the complexity of the process.
[0005] U.S. Patent No. 4,461,310 to Zeihn and U.S. Patent No. 4,289,148 to Zeihn describe
the expansion of tobacco employing supercritical nitrogen or argon impregnation of
tobacco. These gases are removed from the tobacco during a rapid pressure reduction
and the tobacco is expanded by exposure to heated gas or microwave. These processes
require treatment of tobacco at pressures in excess of 2,000 or 4,000 psi up to above
10,000 psi in order to achieve substantial tobacco expansion.
[0006] U.S. Patent No. 4,531,529 to White et al. describes a process for increasing the
filling capacity of tobacco wherein the tobacco is impregnated with a low-boiling
and highly volatile expansion agent such as a normally gaseous halocarbon or hydrocarbon
at process conditions above or near the critical pressure and temperature of the expansion
agent. The pressure is quickly released to atmospheric so that the tobacco expands
without the necessity of a heating step to either expand the tobacco or to fix the
tobacco in the expanded condition.
[0007] Various processes have been disclosed for the microwave treatment of tobacco to provide
tobacco expansion in U.S. Patent No. 3,765,425 to Stungis et al., U.S. Patent No.
3,842,846 to Laszio et al. and U.S. Patent No. 3,881,498 to Wochnowski, among others.
In the Stungis et al. disclosure, tobacco is treated to increase its moisture level
or to impregnate the tobacco with an organic expansion agent which absorbs microwaves.
Alternatively, the tobacco is treated with an organic expansion agent which does not
absorb microwaves, in combination with water and thereafter in any case, the tobacco
is exposed to microwave energy to volatilize the moisture and/or organic expansion
agent, resulting in tobacco expansion.
[0008] Numerous other compounds have been proposed or suggested for expanding tobacco including
alkanes, alkenes, alcohols, aldehydes, ketones and ethers. In most instances, various
practical problems are encountered however, such as the extraction of desirable flavors
from the tobacco during the impregnation step and/or the expansion step; insufficient
amount of tobacco expansion; non-uniformity of expansion; reactions between the expansion
agent and various components in tobacco; adverse impact on tobacco processing equipment;
high levels of retained residual in the final expanded tobacco; and/or hazards such
as flammability associated with expansion agents.
[0009] There has thus continued to be a search for improvements in known tobacco expansion
processes and for new and improved tobacco expansion processes and agents, in general.
Yet despite the continuing efforts, commercial success in the field of tobacco expansion
has been limited.
Summary of the Invention
[0010] The invention provides a tobacco expansion process which employs sulfur hexafluoride
as the expansion agent. It has been found that sulfur hexafluoride can be used to
expand tobacco without substantial physical harm to the tobacco and without significant
change of tobacco taste and flavors. The process of the invention is conducted by
impregnating tobacco with sulfur hexafluoride which is advantageously in liquid form
and maintained at a pressure of greater than about 300 psi. Preferably, the impregnation
step is conducted at a pressure of between about 350 psi and 2500 psi. The impregnated
tobacco is discharged from the impregnation zone at a temperature between about -40°C
and about 35°C, preferably between about -25°C and about 20°C. At these temperature
conditions, the tobacco is in a substantially pliable state and will retain between
about 0.50% and about 20%, preferably between about 1.0% and about 10.0% by weight,
sulfur hexafluoride. The impregnated tobacco is thereafter heated rapidly in an expansion
zone to liberate the retained sulfur hexafluoride and thereby expand the tobacco.
Relatively mild heating conditions of between for example, 70°C and 300°C, advantageously
between about 90°C and 250°C can be successfully employed to achieve substantial tobacco
expansion of greater than 50% increase in filling power.
[0011] The expansion agent used in the process of this invention, sulfur hexafluoride, is
an odorless, tasteless, colorless and nontoxic gas at room temperature. At atmospheric
pressure it sublimes from a solid to gas at -64°C. Despite the low sublimation point
of this material, it has been found that sulfur hexafluoride is retained by tobacco
at temperatures between -30°C and 30°C, advantageously between -20 and 20°C, for short
periods of time, thus allowing time for transport of impregnated tobacco to a heated
expansion zone or for the temporary storage of the impregnated tobacco in an insulated
or refrigerated holding zone. Typically, sulfur hexafluoride is retained in the tobacco
in amount ranging from about 0.5% by weight to about 20% by weight. Despite the fact
that the triple point of sulfur hexafluoride is above atmospheric pressure, (at atmospheric
pressure sulfur hexafluoride sublimes from a solid to a gas without passing through
a liquid phase) it has been found that tobacco impregnated with sulfur hexafluoride
and having a temperature above about -30°C or preferably above about -20°C, remains
substantially pliable, that is, does not contain large blocks of solid tobacco which
must later be broken up.
[0012] At suitable impregnation temperatures of between about -10°C and about 45°C, preferably
above 10°C, impregnation of sulfur hexafluoride into tobacco has been found to be
both rapid and thorough; thus, impregnation times of less than 15 minutes, for example,
between 1 and 10 minutes are conveniently employed. Impregnation pressures used in
the process of the invention, although superatmospheric, are not excessive. Because
relatively mild temperatures can be employed to expand the impregnated tobacco of
the invention, tobacco fines generation can be minimized and the impact on tobacco
flavor and taste due to heating can be eliminated or minimized. Moreover, there is
little if any sulfur hexafluoride retention by the expanded tobacco.
[0013] Still another benefit of the expansion process of the invention is that under the
impregnation temperatures and pressures employed herein, there is advantageously little
if any extraction of valuable flavor components from the tobacco during the impregnation
step. Thus, the tobacco removed from the impregnation zone can advantageously be in
a substantially unextracted condition. This preserves the taste of the expanded tobacco
and also allows for simplification of impregnant recovery steps.
[0014] In one advantageous embodiment of the invention, sulfur hexafluoride impregnated
tobacco can be expanded employing a microwave treatment. In this embodiment, the tobacco
is preferably treated prior to impregnation to provide a moisture content of greater
than 15%, preferably between about 25% and about 40%. Following impregnation, the
tobacco is rapidly passed through a microwave heating zone. Although sulfur hexafluoride
absorbs only minor amounts of microwave energy, the moisture present in the tobacco
will absorb microwave energy and generate heat to rapidly volatilize the sulfur hexafluoride
expansion agent. Because the volatilization of moisture and sulfur hexafluoride during
the microwave heat treatment exerts a cooling effect, the tobacco is maintained at
temperatures of about 100°C or less throughout the heating step. The expanded tobacco
can be recovered at a moisture content of, for example, between 7% and 13% by weight,
thus eliminating or minimizing the need for a separate, reordering treatment following
tobacco expansion.
Brief Description of the Drawing
[0015] In the drawings which form a portion of the original disclosure of the invention:
Figure 1 schematically illustrates one preferred embodiment of the invention wherein
tobacco is impregnated with sulfur hexafluoride; discharged from the impregnation
zone; and passed to a hot air column for expansion of the tobacco; and
Figure 2 schematically illustrates another preferred embodiment of the invention in
which sulfur hexafluoride impregnated tobacco is expanded in a microwave heating zone.
Description of the Preferred Embodiments
[0016] Various preferred embodiments of the invention are described below. It will be understood
however that the invention is not limited to the described embodiments; to the contrary,
the invention includes various alternatives, modifications and equivalents within
its spirit and scope as will be apparent to the skilled artisan.
[0017] Tobacco to be treated in the expansion process of the invention can be provided in
any of various forms, for example in the form of leaf, strip or cigarette cut filler.
Shredded tobacco of 20 to 40 cuts per inch, i.e., cut filler, is preferred because
the process is more effective with this smaller particle size and also some of the
increase in filling capacity may be lost if expanded tobacco in the form of leaf or
strip were subsequently run through a cutter or shredder. If desired, the tobacco
may be cased with various flavorants, humectants and the like prior to expansion treatment.
[0018] The tobacco to be treated should be in a pliable condition to minimize breakage or
shattering during handling and processing. The traditional way of making tobacco pliable
is to adjust the water content to within the range of between about 10 and 30%, preferably
between about 20 and about 30% moisture. Higher moisture contents also can be, and
advantageously are, employed in the process of the invention, particularly when microwave
treatment is used to expand the tobacco.
[0019] With reference to Fig. 1, tobacco,
10 which is preferably in the form of cigarette cut filler is passed to a batch impregnation
zone
12 via a conventional loading means such as a conveyor
13. As illustrated in Figure 1, the impregnator
12 constitutes a batch-type high pressure vessel, such as will be known to the skilled
artisan. Any of various and numerous arrangements and accessories can be employed
for the pressure vessel. The vessel should advantageously include a valved inlet,
near the top or bottom of the vessel for admitting sulfur hexafluoride and a valved
outlet at the top or near the bottom of the vessel for removing sulfur hexafluoride.
Plural valved outlets at both the top and bottom of the vessel as illustrated in the
drawings can also be employed. In addition, a heating or cooling means, such as an
external heated jacket, heating coils, or a cooling jacket can be optionally employed
in order to maintain the sulfur hexafluoride and tobacco at an impregnating temperature
of above about -10°C, preferably between about 0°C and about 45°C.
[0020] Returning to Figure 1, a supply of sulfur hexafluoride
14, such as a pressurized storage tank containing liquid sulfur hexafluoride, provides
sulfur hexafluoride through line
16 via valve
18 to a filter
20 and then to heat exchanger
22. The liquid sulfur hexafluoride is cooled in the heat exchanger by 5°C to 20°C to
prevent cavitation during pumping. The thus cooled liquid sulfur hexafluoride is pumped
by means of high pressure liquid pump
24 through a heat exchanger
26 which heats or cools the sulfur hexafluoride to obtain the desired temperature of
between for example about -10°C and about 90°C, preferably greater than about 10°C.
The temperature of the sulfur hexafluoride exiting heat exchanger
26 will likely be different than the desired impregnation temperature since the temperature
of the tobacco will affect the temperature of the sulfur hexafluoride upon mixing.
Thus the sulfur hexafluoride can advantageously be heated to a temperature of, for
example, 10°C-75°C. Upon addition of the sulfur hexafluoride to the tobacco to via
valve
28, the system will reach an equilibrium temperature of between, for example, 10°C to
45°C.
[0021] The sulfur hexafluoride in the impregnator is preferably maintained in liquid form
once the vessel has been filled and equilibrium reached and is advantageously supplied
in sufficient amount to fully immerse the tobacco in the sulfur hexafluoride. Pressure
within the impregnator is at a level sufficient to maintain the sulfur hexafluoride
as a liquid and can range from about 220 psi to about 3000 psi or greater with pressures
of between 350 psi and 2500 psi being preferred. Advantageously, the temperature during
impregnation is maintained at greater than about 10°C, preferably greater than about
20°C, under which conditions a short impregnation time ranging from about 1 to about
30 minutes, preferably between about 2 and about 15 minutes is employed.
[0022] Following impregnation for a suitable amount of time, valve
30 is opened allowing sulphur hexafluoride liquid to exit impregnator
12 via line
31. As the liquid exits via line
31, evaporation within the impregnation zone causes the temperature within the impregnator
12 to decrease. If heating has been employed during the impregnation step, it is advantageously
discontinued to allow the impregnated tobacco to cool as the liquid sulfur hexafluoride
is removed from the impregnator. An outlet line
32 is also provided at the top of the impregnator vessel. Sulfur hexafluoride can be
removed in gaseous form via line
32 by opening valve
33 to provide the desired amount of cooling of the impregnated tobacco. Depending on
impregnation temperatures and pressures, both upper and lower gas and liquid removal
lines
32 and
31, respectively, can be employed for removal of sulfur hexafluoride, or only a single
line can be used. Sulfur hexafluoride gas exiting through upper line
32 is passed to a conventional recovery zone (not shown) for recovery and liquification
of the sulfur hexafluoride which is then returned to supply tank
14.
[0023] Excessive cooling is to be avoided during removal of the sulfur hexafluoride in order
to prevent the formation of large, solid blocks of tobacco. Thus, the temperature
of the tobacco following discharge of the impregnant is best kept between about -30°C
and 30°C., preferably between about -25°C and about 20°C., most preferably between
-20°C and 0°C at which temperatures the impregnated tobacco will be in a substantially
pliable form. By "substantially pliable", it is meant that no large frozen solid blocks
of tobacco will be formed which need to be broken up prior to heat treatment. Small
solid clumps of tobacco may be found and a conventional detangling treatment may be
desirable.
[0024] The liquid sulfur hexafluoride removed from the impregnator is passed via line
31 through a pump
34 and following any necessary treatment for removal of solids, moisture, or other contaminants,
is returned to supply vessel
14.
[0025] Tobacco is thereafter removed from the impregnator and advantageously the entire
batch of impregnated tobacco is passed to an insulated or refrigerated holding tank
38 although if desired, the tobacco can be passed directly to a heating zone. Upon removal
from the impregnator, the tobacco will typically contain from about 1% to about 20%
by weight, preferably less than 15% by weight, sulfur hexafluoride. At temperatures
of between about -40°C and about 30°C, preferably less than 20°C, sulfur hexafluoride
will be retained in the tobacco in a sufficient amount for subsequent expansion of
the tobacco for a time period of up to several minutes e.g. 2 to 10 minutes or longer,
without the necessity of cooling or insulating the tobacco. While not wishing to be
bound by theory, it is believed that the sulfur hexafluoride is retained by the tobacco
because the molecular size of sulfur hexafluoride is relatively large and diffusion
of sulfur hexafluoride out of the impregnated tobacco is relatively slow. It is not
known whether the sulfur hexafluoride exists within the cellular structure of tobacco
primarily as a solid, gas or as a solute. At atmospheric pressure, it is known that
sulfur hexafluoride sublimes directly from the solid phase to the gas phase without
passing through a liquid phase. Thus, sulfur hexafluoride may exist within the tobacco
cellular structure as small solid particles. Nevertheless, it has been found that
the process of this invention can be conducted without generation of large solid blocks
of tobacco which require a special breaking prior to heat treatment.
[0026] Returning to Fig. 1, the entire batch of impregnated tobacco is advantageously passed
to holding tank
38 which is preferably insulated and/or refrigerated. Holding tank
38 is preferably sealed during storage of tobacco. Various recovery means (not shown)
can be provided in combination with holding tank
38 for recovery of sulfur hexafluoride gas which escapes the impregnated tobacco during
the holding period. Such recovery means can take the form of gas lines provided at
the top or the bottom of the holding tank for continuously removing sulfur hexafluoride
gas during the holding period.
[0027] Impregnated tobacco is passed directly from the holding tank via a rotary star valve
40 into the lower portion
42 of an expansion zone. In the lower portion
42 of the expansion zone, the impregnated tobacco is mixed with a rapidly moving stream
of hot gases which is provided via a heater (not shown) and fan
44. A source of steam
46 can be provided at a location upstream for mixing with gases which are being recirculated
within the expander.
[0028] The tobacco is carried by the force of the hot gas stream upwardly through expansion
zone
48 and into separator
50. During movement of the tobacco through expansion zones
42 and
48, the sulfur hexafluoride rapidly volatilizes from the tobacco resulting in the stable
expansion of the tobacco.
[0029] The degree of heating of the tobacco within expansion zone
48 is advantageously kept to a minimum to avoid harming the tobacco flavor and/or to
avoid excessive fines generation. Temperatures above 300°C are preferably avoided
in the expansion zone in order to prevent evaporation of excessive moisture from the
tobacco and to prevent overheating of the tobacco, although the skilled artisan will
recognize that such temperatures can be used, if desired. Advantageously, the expansion
zone will contain heated gases at a temperature of between about 90°C and about 250°C,
preferably between about 100°C and 225°C, most preferably between about 100°C and
200°C.
[0030] Expanded tobacco within cyclone-type separator
50 falls to the bottom portion thereof and is continuously removed by rotary star valve
52. The expanded tobacco
54 is collected on any of various conventional tobacco recovery apparatus such as conveyor
58.
[0031] If desired, the expanded tobacco can be passed to a reordering zone and/or a sulfur
hexafluoride recovery zone. The reordering process, as is well known to the skilled
artisan, comprises a moisture treatment in which expanded tobacco is treated with
steam, water vapor or the like in order to increase the moisture content of the tobacco
to the desired range of 10%-13%. Typically, the expanded tobacco exiting separator
50 will contain only a minute amount of residual sulfur hexafluoride, for example, 0.15%
by weight or less. Due to the high volatility of the sulfur hexafluoride under expansion
conditions, the expanded tobacco will, in many cases, depending upon the expansion
temperature and composition of the expansion gas, exit the expansion zone with a sulfur
hexafluoride content of less than 0.10% by weight.
[0032] A portion of the hot gases in the expansion zone are removed via line
60 and are passed to a sulfur hexafluoride stripping zone
62. Sulfur hexafluoride recovered in the stripping zone is passed via line
64 to the sulfur hexafluoride supply tank
14. A portion of the expansion gases, which may include sulfur hexafluoride volatilized
from the tobacco, are recirculated via pipe
66 for use in expanding freshly impregnated tobacco.
[0033] Figure 2 illustrates another preferred embodiment of the invention. Tobacco
10 is carried by conveyor
13, for admission into a conditioning drum
102. The tobacco
10 will typically have a moisture content of 12%-15% by weight, and as previously indicated,
can have been previously treated by the application of casing or the like. Conditioning
drum
102 includes a pipe
104 which admits steam or moisture into the interior thereof. A plurality of nozzles
106, shown in phantom, treat the tobacco inside the conditioning drum with steam or finely
divided water. The drum rotates so that all of the tobacco particles are uniformly
exposed to the steam or moisture. A plurality of interior flights or vanes (not shown)
are preferably provided on the inside of rotating drum
102 so that tobacco is gently agitated while being treated in the conditioning drum.
The tobacco is maintained within the conditioning drum for a period of time and under
conditions sufficient to raise the equilibrium moisture of the tobacco to greater
than 20% by weight, preferably greater than 25% by weight, most advantageously to
between about 30% and about 40% by weight.
[0034] The treatment to increase moisture content provided in conditioning drum
102, is conducted in order to provide sufficient moisture in the tobacco for later absorption
of microwave energy. It has been found that a moisture content in excess of 15% and
up to 50% by weight, increases tobacco expansion in the process of the invention when
microwave energy is employed for heating the tobacco. Particularly when the moisture
content of the tobacco is to be increased to greater than about 25% by weight, the
moisturizing conditioning process is conducted at a time close to the impregnation
step, for example, from several minutes to several days prior to the impregnation
step, preferably less than 24 hours prior to the impregnation step. This can prevent
molding of the moist tobacco during storage.
[0035] The moistened tobacco
108 is removed from the conditioning drum and carried via a second conveyor
110 to impregnator
12 for the impregnation step in the manner described previously. Tobacco removed from
impregnator
12 is then passed to holding tank
38 as previously described.
[0036] Tobacco is admitted via star valve
40 into a microwave treatment zone
120 for heating and expansion of the tobacco. The microwave treatment zone is preferably
provided within a sealed chamber
122 so that sulfur hexafluoride volatized during the heat treatment can be recovered
via line
124.
[0037] The microwave treatment zone includes a magnetron
126 which generates microwaves which are transported through waveguide
128. A conveyor belt
130 carries impregnated tobacco
132 through the waveguide
128 wherein the tobacco is exposed to microwaves for a period ranging from several seconds
up to about a minute, for example, 5-20 seconds, to thereby heat the moisture in the
tobacco which, in turn, volatizes the sulfur hexafluoride in the impregnated tobacco,
causing the tobacco to expand. Any microwave energy which passes through the waveguide
128 and is not absorbed by the tobacco is received and absorbed by a conventional water
load
133.
[0038] Expanded tobacco
54 is removed from the microwave treatment zone by conveyor
130 and passed via rotary star valve
134, to a conventional conveying means such as a conveyor belt
58. The expanded tobacco exiting the microwave treatment zone
120 advantageously has a moisture content in the range of between about 7% and about
13% by weight. The expanded tobacco can be passed to a conventional reordering treatment
(not shown) and/or to a sulfur hexafluoride stripping zone; however, typically the
tobacco will have a sulfur hexafluoride content of less than about 0.15% by weight
so that recovery of the residual sulfur hexafluoride may be unnecessary.
[0039] Any of various commercially available microwave heating units may be employed for
the microwave treatment of sulfur hexafluoride impregnated tobacco. An exposure time
of 9-12 seconds has been employed in a 4.5-5.5 kilowatt treatment zone having a frequency
of 2375 MHz and an efficiency of about 50% to treat 1/4 to 1/2 pound per minute. When
the bed depth of the impregnated tobacco is expected to exceed several inches, the
microwave treatment zone can advantageously include an agitating means for agitating
the tobacco during the microwave treatment to ensure that all of the tobacco is uniformly
exposed to microwave energy and also to ensure that the impregnated tobacco is not
excessively compressed during heating which could interfere with expansion of the
tobacco. Such agitation means can include, for example, the use of a microwave-transparent
rotary drum within the waveguide; gas lines for fluidizing the tobacco within the
waveguide or the like. As will be apparent, the power of the microwave unit will be
selected depending upon the amount of tobacco being treated. Exposure times can be
increased or decreased also depending upon the amount of tobacco being treated. However,
a short, relatively high energy treatment is preferred to ensure maximum tobacco expansion.
[0040] In the process of the invention wherein tobacco moisture is adjusted to above about
20% prior to the impregnation step, and particularly when microwave heating is employed,
it is preferred that the moisture be fully equilibrated within the tobacco. For example,
if the moisture content is increased simply by spraying ambient temperature moisture
onto ambient temperature tobacco, the moisture will not rapidly penetrate into the
cells of the tobacco. If subsequent microwave heating of the tobacco is conducted
within only a few hours, the surface moisture can simply evaporate off of the tobacco
without supplying sufficient heat to the sulfur hexafluoride within the interior of
the tobacco to promote maximum expansion which would be achievable if the moisture
were fully equilibrated into the tobacco. On the other hand, if the tobacco is treated
by spraying with water and the moistened tobacco stored for a period of for example,
24 hours, the moisture will fully equilibrate through the cellular structure of the
tobacco. Alternatively, treating the tobacco with moisture in the form of steam, as
illustrated in Figure 2, enhances the rate of moisture penetration into the tobacco.
[0041] As discussed previously, the impregnation step of the invention can be conducted
over a wide range of temperatures and pressures. The time period for complete impregnation
will depend, at least in part, upon the temperature and pressure employed during the
impregnation step. Thus, higher temperatures and pressures tend to promote more rapid
impregnation whereas lower temperatures and pressures can increase the amount of time
required for impregnation. Generally, at temperatures above about 20°C and impregnation
pressures of between 750 psi and 2,500 psi, an impregnation time of less than about
15 minutes will be sufficient. Preferred impregnation temperatures range from about
20°C up to as high as 44°C-45°C. At these preferred temperatures, impregnation is
rapid. Preferred impregnation pressures range from about 1,000 to about 2,500 psi,
preferably between about 1,200 psi and about 2,000 psi.
[0042] Advantageously, temperature and pressure conditions within the impregnation zone
are maintained so that substantially all of the sulfur hexafluoride will be in the
liquid phase. Operation within the liquid phase provides substantial contact between
the sulfur hexafluoride and the tobacco thereby enhancing rapid and full impregnation.
In addition, operation within the liquid phase is believed to increase the amount
of sulfur hexafluoride absorbed by the tobacco. However, tobacco can also be impregnated
with sulfur hexafluoride in accordance with this invention by operating at temperatures
and pressures wherein a portion or all of the sulfur hexafluoride is maintained in
the gas phase. In such instances, impregnation times may need be increased and/or
the amount of cooling following impregnation may need to be increased in order to
provide sufficient impregnation of sulfur hexafluoride into the tobacco and/or sufficient
retention of sulfur hexafluoride by the tobacco.
[0043] Heating of the impregnated tobacco in order to effect expansion can be accomplished
by means other than those discussed previously. Thus the impregnated tobacco can also
be heated by radiant means to effect expansion. In another preferred embodiment, the
tobacco can be heated in a fluidized bed at a temperature of from 90°C up to 300°C.
Fluidized beds are known in the art and described for example in U.S. Patent No. 4,270,553
to Conrad et al. which is hereby incorporated herein by reference. The fluidized bed
can be used with or without the added hot particles described in this patent.
[0044] If desired, various additives may be employed in the process of the invention. Thus,
for example, the tobacco may be pretreated with various alcohols such as ethanol,
or with other additives, for example hydrocarbons such as pentane or hexane, in order
to promote better expansion.
[0045] The invention has been described in connection with various batch embodiments. However,
a continual flow process may be used when employing an apparatus having slidably engaged
ceramic seals at the entrance and exit ends thereof as described in our European Application
90306604.1 filed on 18 June 1990, which claims priority of U.S. Patent Application
Serial No. 07/367,589 filed June 19, 1989 by Anatoly I. Kramer entitled "Process and
Apparatus for the Expansion of Tobacco" and is assigned to the assignee of the present
invention, which is hereby incorporated herein by reference.
[0046] The following examples are provided for a more complete understanding of the invention
and not by way of limitation. Tobacco moisture content as reported in the examples
is expressed as the percent reduction in the tobacco weight upon heating in a convection
oven for five minutes at 92°C. Filling capacity measurements of expanded and untreated
tobacco samples were performed using a specially designed and electronically automated
filling capacity meter in which a solid piston of 3.625 inches in diameter is slidably
positioned in a cylinder and exerts a pressure of 26 psi on a tobacco sample located
in the cylinder. These parameters are believed to simulate the packing conditions
to which tobacco is subjected in cigarette making apparatus during the formation of
a cigarette rod. The moisture content of tobacco affects the filling values determined
by this method. Therefore, all expanded and unexpanded tobacco samples were submitted
for moisture determination. These results were taken into account for calculating
corrected filling capacities of tobacco samples through previously obtained correlation
tables. Measured tobacco samples were as follows: 100g. for unexpanded tobacco and
50g. for expanded tobacco.
[0047] The percent increase in filling capacity or percent expansion as reported in the
following examples was computed by subtracting the corrected filling capacity of the
unexpanded control sample from the corrected filling capacity of the expanded sample,
dividing this difference by the corrected filling capacity of the unexpanded control
sample and multiplying this quotient times 100.
EXAMPLE 1
[0048] Samples of tobacco cut filler were impregnated in a pressure vessel having a volume
of 2 liters. The pressure vessel included a thermocouple installed inside the vessel,
close to the top thereof, to measure the temperature of the vessel contents and a
pressure gauge for indicating the pressure in the vessel. Sulfur hexafluoride was
introduced into the vessel through a valve at the bottom of the vessel and removed
from the vessel by two valves at the top of the vessel, by opening the valves and
allowing the gas contents to escape. A thermostatically controlled heating jacket
was provided around the vessel for heating during the impregnation.
[0049] A number of samples of tobacco, each weighing 130-170 grams were prepared. The tobacco
samples consisted of a blend of cased flue cured and burley tobacco lamina in the
form of cut filler. Moisture of the samples was recorded and measured as set forth
below. The samples were then impregnated with sulfur hexafluoride for the times set
forth below and at the temperature and pressures set forth below. Following impregnation,
the tobacco was removed from the treating vessel and heated with a hot air gun. The
percent expansion achieved is as set forth below.
TABLE I
Run # |
Impreg. Pressure (psi) |
Impreg. Temp. (°C) |
Impreg. Time (min.) |
% Moisture Initial |
Percent Expansion |
1 |
480 |
44 |
60 |
17 |
32 |
2 |
2030 |
27 |
60 |
19 |
65 |
3 |
3000 |
25 |
60 |
18 |
60 |
4 |
3000 |
45 |
45 |
21.5 |
57 |
5 |
3000 |
45 |
45 |
21.5 |
72 |
[0050] Heating with a hot air gun involves various difficulties including non-uniform heating
of the tobacco due to the fact that hot air can be directed only upon a limited tobacco
area and the temperature of the air reaching the tobacco is only 50°C-75°C. Nevertheless,
as seen above, substantial tobacco expansion was achieved.
EXAMPLE 2
[0051] Tobacco samples having a weight of about 150 grams were impregnated using the apparatus
of Example 1. The tobacco consisted of the same cased blend of flue cured and burley
tobaccos as used in Example 1. The impregnated samples were removed from the impregnating
vessel and hand carried, without refrigeration or insulation, to a microwave heating
apparatus substantially as illustrated in Figure 2 except that no gas recovery system
was used. The average transport time to microwave processing was about 1.5 to about
2.5 minutes. The waveguide or microwave treating zone had a length of about four feet.
The tobacco was carried on a moving belt through the waveguide to provide an exposure
time of 9-12 seconds. The power of the microwave was variable up to 6.0 kW maximum.
The power setting for the microwave apparatus was as set forth below. In addition
to the parameters reported in Example 1, the temperature in the vessel following removal
of the sulfur hexafluoride impregnant by venting the sulfur hexafluoride through the
top valves was recorded. These temperatures are reported below as "Discharge Temperature".
TABLE II
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
300 |
21 |
15 |
-15 |
20 |
4.5 |
30 |
2 |
360 |
23 |
15 |
-26 |
27 |
4.5 |
49 |
3 |
360 |
24 |
15 |
-19 |
21 |
4.5 |
47 |
EXAMPLE 3
[0052] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE III
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
400 |
16 |
15 |
-30 |
25 |
5 |
42 |
2 |
400 |
24 |
15 |
-23 |
27 |
5 |
58 |
3 |
400 |
20 |
15 |
-27 |
35 |
5.5 |
62 |
[0053] In Run #1 above, some small frozen tobacco lumps were observed. It is believed that
the amount of microwave energy used was insufficient to heat the tobacco fully in
view of this icing.
EXAMPLE 4
[0054] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE IV
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
500 |
24 |
15 |
-23 |
19 |
4.5 |
39 |
2 |
500 |
27 |
15 |
-10 |
19 |
4.5 |
50 |
3 |
500 |
31 |
15 |
+3 |
25 |
5.0 |
71 |
[0055] In Run #1 some small frozen tobacco lumps were observed and it is believed that the
microwave power was insufficient to fully heat the tobacco. Additionally, it is believed
that the increased moisture content of Run #3 was at least partially responsible for
the increased amount of tobacco expansion observed.
EXAMPLE 5
[0056] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE V
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
600 |
25 |
15 |
-10 |
19 |
4.5 |
38 |
2 |
600 |
31 |
15 |
+6 |
25 |
4.5 |
47 |
[0057] It can be seen that the increased moisture content of the tobacco and increased impregnation
temperature provided for improved expansion.
EXAMPLE 6
[0058] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone but with different impregnation temperatures
and pressures.
TABLE VI
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
700 |
33 |
15 |
+3 |
19 |
5.5 |
46 |
2 |
700 |
25 |
15 |
-22 |
23.5 |
5.5 |
46 |
3 |
700 |
28 |
15 |
-13 |
36 |
5.5 |
67 |
[0059] As with the previous examples, increasing the moisture content and impregnation temperature
increased the percent tobacco expansion.
EXAMPLE 7
[0060] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE VII
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
900 |
28 |
15 |
-18 |
19 |
5.5 |
53 |
2 |
900 |
31 |
15 |
-15 |
25 |
4.7 |
61 |
3 |
900 |
30 |
15 |
-14 |
32 |
5.0 |
65 |
EXAMPLE 8
[0061] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE VIII
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
1100 |
38 |
7 |
-3 |
25 |
5.0 |
71 |
2 |
1100 |
37 |
15 |
-5 |
35 |
5.5 |
77 |
3 |
1100 |
36 |
15 |
-5 |
31 |
5.5 |
83 |
EXAMPLE 9
[0062] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE IX
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
1500 |
39 |
7 |
-6 |
19 |
5.0 |
58 |
2 |
1500 |
36 |
7 |
-10 |
25 |
5.0 |
74 |
3 |
1500 |
39 |
7 |
-7 |
35 |
5.5 |
80 |
4 |
1500 |
35 |
7 |
-5 |
39 |
5.5 |
89 |
EXAMPLE 10
[0063] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE X
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
1700 |
43 |
15 |
-1 |
19 |
4.5 |
57 |
2 |
1700 |
44 |
7 |
-2 |
19 |
4.5 |
51 |
3 |
1700 |
38 |
7 |
-10 |
23 |
5.0 |
76 |
4 |
1700 |
41 |
7 |
-5 |
35 |
5.0 |
84 |
[0064] As is apparent, substantially less tobacco expansion was obtained when the moisture
content of the tobacco was lower.
EXAMPLE 11
[0065] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures. In this example, moisture contents were kept low to observe the moisture
content effect in microwave expansion.
TABLE XI
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
1700 |
44 |
7 |
-1 |
12.5 |
4.0 |
36 |
2 |
1700 |
41 |
15 |
-6 |
16 |
5.0 |
39 |
[0066] It can be seen that moisture content can have a significant impact on tobacco expansion.
EXAMPLE 12
[0067] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE XII
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
2000 |
44 |
7 |
0 |
25 |
5.0 |
79 |
2 |
2000 |
36 |
7 |
-4 |
35 |
5.0 |
82 |
3 |
2000 |
41 |
7 |
-4 |
21.5 |
5.0 |
60 |
EXAMPLE 13
[0068] The procedures of Example 2 were repeated using the same types of tobacco samples,
treating vessel, and microwave heating zone, but with different impregnation temperatures
and pressures.
TABLE XIII
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
2500 |
43 |
7 |
-6 |
21 |
5.0 |
68 |
2 |
2500 |
41 |
7 |
+3 |
30 |
5.0 |
79 |
3 |
2500 |
43 |
15 |
-2 |
35 |
5.0 |
89 |
4 |
2500 |
44 |
7 |
+2 |
35 |
5.0 |
84 |
5 |
2500 |
45 |
7 |
-1 |
35 |
5.5 |
94 |
EXAMPLE 14
[0069] The procedures of Example 2 were repeated except that following impregnation, the
sulfur hexafluoride was removed from the bottom of the vessel as a liquid and thus
the temperature of the impregnated tobacco was substantially higher due to less cooling
from evaporation of sulfur hexafluoride during the decompression step. The following
results were obtained.
TABLE XIV
Run # |
Impreg. Pressure (psig) |
Impreg. Temp. (°C) |
Impreg. Time (Minutes) |
Discharge Temp. (°C) |
%Moisture Initial |
Micro. Power kW |
Percent Expansion |
1 |
1700 |
43 |
7 |
23 |
35 |
5.5 |
60 |
2 |
1700 |
43 |
7 |
21 |
35 |
5.5 |
62 |
[0070] It can be seen that even when the tobacco was removed from the impregnation zone
at a high temperature, sufficient sulfur hexafluoride was retained by the tobacco
during the approximate one minute transport time between the impregnation zone and
the microwave heating zone, so that substantial tobacco expansion was achieved.
EXAMPLE 15
[0071] Tobacco samples were impregnated as in Example 2. The tobacco samples were weighed
immediately before and immediately after impregnation. The difference in weight was
assumed to be due to absorbed sulfur hexafluoride. Impregnation pressures were generally
about 1700 psi. Impregnation temperatures and time were generally about 40°C and 7
minutes, respectively. The discharge temperature upon decompression of the impregnation
vessel was generally between -5°C and 0°C. It was found that immediately after impregnation,
the samples contained between 1.2% and 2.8% by weight, sulfur hexafluoride. The samples
were allowed to stand, open to the atmosphere at 25°C for a period of 1 minute, and
were then weighed again. It was found that approximately 35%-40% of the retained sulfur
hexafluoride had been lost to the atmosphere by evaporation. Nevertheless, substantial
expansion could be obtained by heating the impregnated samples of tobacco.
EXAMPLE 16
[0072] The impregnation procedures of Example 2 were repeated and the entire batch of impregnated
tobacco was heated in a fluidized bed. The impregnation pressure was 1,700 psi. The
impregnation temperature and time were 39°C and 9 minutes, respectively. The initial
moisture of the sample was 35% by weight. Hot air having a temperature of 90°C was
employed as the fluidizing medium and the tobacco was heated for about 50 seconds.
Following heat treatment, the tobacco had obtained a 52% increase in filling capacity.
The expanded tobacco was recovered with a moisture content of about 12% by weight.
[0073] The invention has been described in considerable detail with specific reference to
preferred embodiments. However, it will be apparent that variations and modifications
can be made within the spirit and scope of the invention as described in the foregoing
detailed specification and defined in the appended claims.