A Process For Increasing The Filling Capacity Of Tobacco

Abstract

A process of increasing the filling capacity of tobacco is provided in which tobacco and an impregnating organic liquid are contacted in one zone and contact of the tobacco with vapors of the liquid is continued in another zone until the tobacco is thoroughly impregnated. The impregnation is carried out at moderately elevated temperatures and pressures. After impregnation is substantially complete, the tobacco is withdrawn from the impregnating zone and immediately heated at a reduced pressure to an elevated temperature whereby expansion occurs. The heating is effected in a stream of circulating hot gas from which the tobacco is separated and the gas including vapors of the impregnating liquid are heated and recycled. The flow of impregnating fluid to the impregnating zone is controlled by the liquid level of the body of liquid impregnating fluid maintained in the impregnating zone.

Description

This invention relates to a process of treating tobacco and has for an object the process for increasing the filling capacity of a tobacco product.

Tobacco leaves when harvested contain a considerable quantity of water and during the normal tobacco curing process this water is removed by drying resulting in shrinkage of the leaf structure. In the usual process of preparing tobacco for storage and subsequent cigar or cigarette manufacture, the tobacco regains very little, if any, of the shrinkage resulting from the drying step so that a significant loss in the filling capacity of the tobacco is the result. Thus, the cured tobacco has a bulk density which is in excess of that required for making satisfactory cigarettes or cigars. Also, during cutting of leaf or strips for making cut filler for cigarettes, frequently the shreds are laminated together to form hard, dense particles which occupy far less volume than the original shreds occupied. This is wasteful since these hard compacted shreds are not necessary in a smoking product to produce a satisfactory article.

Several procedures have been suggested in the prior art for increasing the normal filling capacity of dry or cured tobacco. Certain of these procedures have involved puffing operations in which the tobacco is subjected to high pressure steam, followed by sudden release of pressure. Also, it has been suggested that the filling capacity of tobacco may be increased, (i.e., bulk density reduced) by exposing the tobacco particles or fibers to the vapors of an organic liquid or to an organic liquid followed by air drying at ordinary temperatures. However, these prior procedures have not been wholly satisfactory either because they are not effective for expanding the filling capacity to any great extent or they result in shattering of the tobacco structure and particles so that considerable waste incident to the formation of fines results.

In the copending application of James Donald Fredrickson, Ser. No. 720,406, filed Apr. 10, 1968, now Pat. No. 3,524,451, dated Aug. 18, 1970, there is disclosed a process of increasing the filling capacity of tobacco which involves contacting the tobacco with a volatile organic liquid to thoroughly impregnate the tobacco and thereafter passing a heated gas into contact with the tobacco whereby the tobacco is expanded and the liquid is separated therefrom in the vapor state. An improvement in the Fredrickson process is described in Moser and Stewart application Ser. No. 720,068, filed Apr. 10, 1968 now Pat. No. 3,524,452, dated Aug. 18, 1970. This latter application discloses a procedure in which a moist tobacco thoroughly impregnated with a volatile organic liquid is passed into a stream of a hot gas at a temperature between about 250.degree. F. and about 400.degree. F., whereby the tobacco is expanded and is recovered from the hot gases.

Accordingly, another object of this invention is the provision of a tobacco treating process which represents an improvement over the processes disclosed in the copending Fredrickson and Moser and Stewart applications above identified.

A further object of this invention is the provision of a process for increasing the filling capacity of tobacco under conditions such that the process can be readily controlled to produce the desired product.

A still further object of this invention is the provision of a process for increasing the filling capacity of tobacco in which the time required for the preliminary impregnation with the organic liquid is reduced.

An additional object of this invention is the provision of a process which is essentially continuous and may be readily controlled so that there is no net extraction of flavorants or aroma producing materials from the tobacco during the impregnation step.

A still further object of this invention is the provision of a process whereby the flow of impregnating fluid into the impregnating zone is controlled so that the impregnation will be maintained uniform at all times.

A still further object of this invention is the provision of a process which requires a minimum quantity of impregnating fluid to effect the necessary impregnation before subjecting the tobacco to the heating step.

Further and additional objects will appear from the following description and the appended claims.

In accordance with one embodiment of this invention, a process is provided in which an impregnating zone containing an organic fluid having a boiling point less than that of water is maintained under a superatmospheric pressure sufficient to provide within the zone a body of said fluid in the liquid state in a lower portion and an atmosphere of said fluid in a vapor state in the upper portion. Tobacco, preferably moistened with water, is introduced into the liquid-state body in order to wet it thoroughly with the organic liquid and the thus-wetted and moist tobacco is then passed into the atmosphere containing the vapors, the total residence time in the impregnating zone, both liquid and vapor phase, being sufficient so that the tobacco is substantially completely impregnated with the organic fluid. After the impregnation has been effected, the impregnated tobacco together with some of the organic fluid is withdrawn from an upper portion of the pressurized impregnating zone to a zone of lesser pressure and then immediately subjected to an elevated temperature to cause the desired expansion of the tobacco.

The tobacco to be treated in accordance with the process of this invention is preferably a cured tobacco and may be in the form of shreds, strips or leaves. However, the process is easier to control and the best results are obtained if tobacco shreds are used. This is for the reason that usually shreds are relatively easy to handle in continuous procedures and the final product of the process need not be subjected to shredding as may be necessary for cigarette manufacture. Shredding of the final product would result in compressing the product which would tend to destroy the ultimate objective of the process of this invention, namely, to expand the tobacco and eliminate compressed particles, as may have resulted from prior treatment including shredding. Any type of tobacco may be used in the practice of this invention and it is particularly useful for the processing of burley, flue-cured and Oriental (e.g., Turkish) tobaccos.

As suggested in the copending Moser and Stewart application, it is preferred that the tobacco subjected to treatment in accordance with this invention be one that is moistened with water. The presence of water moisture has been found to be desirable to soften the tobacco particles to permit proper expansion when the tobacco impregnated with the organic liquid is subjected to the elevated temperatures. At low moisture levels or in the absence of moisture, the tobacco when heated under expansion conditions tends to disintegrate and form fines which are not desired in a product which is to be used for the manufacture of cigarettes or cigars. If the moisture level is too high the tobacco may be difficult to handle and unnecessary expense may be incurred incident to the vaporization of the excess moisture during the expansion step. Preferably the tobacco to be processed in accordance with this invention has a moisture content equivalent to between about 10 and 30 parts by weight of water per 100 parts by weight of tobacco (dry basis). The moisture may be applied to the dried and cured tobacco in any desired manner and it may be incorporated during customary casing. It may be effected by spraying, wet steam treatment, or otherwise, as will be obvious to one skilled in the art.

The organic liquid employed for impregnating the tobacco is one which has a boiling point less than that of water at atmospheric pressure and is chemically inert to the tobacco treated. The organic liquid preferably has a boiling point at atmospheric pressure less than about 180.degree. F. but at the same time the boiling point is sufficiently high so that it may be readily liquefied under the pressures readily obtainable in the impregnation zone. Suitable organic liquids are the aromatic hydrocarbons such as benzene; the ketones such as acetone and methyl ethyl ketone; the ethers such as methyl ethyl ether, diethyl ether, diisopropyl ether, methyl butyl ether and tetrahydrofuran; the alcohols such as methanol, ethanol and isopropanol; the aliphatic hydrocarbons such as pentane, isopentane, 2,2-dimethyl butane, 2,3-dimethyl butane, and hexane; cyclo aliphatic hydrocarbons such as cyclobutane; and halogen substituted aliphatic hydrocarbons such as ethyl chloride, propyl chloride, isopropyl chloride, butyl chloride, sec-butyl chloride, tert-butyl bromide, methylene chloride, chloroform, carbon tetrachloride, ethylene dichloride, and ethylidene dichloride; and the compounds generally known as Freons such a trichloromonofluoromethane and trichlorotrifluoroethane. Mixtures of the several solvents may also be used and, if so, such mixtures are preferably azeotropic. The preferred impregnating organic liquid is one which is substantially immiscible with water and, for safety reasons, it is desirable that the organic liquid be noninflammable. Freon-11 (trichloromonofluoromethane) has been found to be particularly satisfactory.

As indicated, the tobacco impregnation preferably takes place in a pressure vessel which is maintained at a superatmospheric pressure and at a temperature such that a body or pool of the organic liquid at about its boiling point is present in the lower section of the zone and a saturated vapor atmosphere of the liquid is present in an upper portion of the zone. In one form of the invention, the impregnator takes the form of an elongated cylinder inclined to the horizontal and equipped with a screw conveyor for moving moistened tobacco from a lower portion of the impregnator into an upper portion thereof. Tobacco and the organic fluid are introduced into the lower section of the zone with the tobacco being introduced directly beneath the surface of the liquid whereby it becomes thoroughly wetted. The screw conveyor elevates the tobacco above the surface of the body of liquid and into the vapor atmosphere, during which process excess liquid drains back from the tobacco to the liquid body in the bottom of the zone. During this procedure and while the tobacco is moving upwardly to and through the upper saturated vapor section, the impregnation continues so that by the time it reaches the upper portion of the zone, the tobacco is substantially completely impregnated with the organic fluid. In one embodiment the elevated temperature of the impregnating zone is maintained by suitable heat exchange jackets and pressure locks are provided to permit the introduction and withdrawal of tobacco to and from the impregnating zone such that loss of pressure does not occur and a substantial continuous impregnating operation can be achieved. Under the conditions of impregnation as thus described, it has been found that substantially complete impregnation of the tobacco may be accomplished in from 10 to 30 minutes, depending upon the nature of the tobacco, the organic liquid employed, and the temperature and pressure maintained within the impregnator. It is preferred that the temperature of the tobacco in the impregnator should be less than about 180.degree. F. since at higher temperatures maintained for an extended period of time, the smoking quality of the tobacco may be impaired. Preferably the temperature ranges between about 100.degree. and 170.degree. F.

The substantially completely impregnated tobacco is then withdrawn or discharged from the upper section of the impregnating zone directly into a zone of reduced pressure (i.e., a pressure less than that obtained in the impregnator) and immediately heated to an elevated temperature above the atmospheric pressure boiling point of water, preferably between 250.degree. and 400.degree. F. Usually the temperature is in excess of 200.degree. F. higher than the boiling point temperature of the impregnating liquid at said reduced pressure. This immediate heating at reduced pressure causes the tobacco to expand quite rapidly in order to effect the desired increase in its filling capacity. It is important that the impregnated tobacco be subjected to the pressure decrease and temperature increase immediately upon discharge from the impregnating zone since otherwise the vapors of the impregnating fluid will slowly escape from the tobacco particles and laminations without effecting the desired expansion. The time for heating is generally less than 5, and suitably between 1 and 2, seconds following the pressure release.

In a preferred form of the invention, the expansion heating step for the impregnated tobacco is effected in a stream of hot gas into which the tobacco is fed. The gas is first heated to the appropriate temperature and the tobacco intermingled with it whereafter it expands rapidly. As noted in the Moser and Stewart application, this expansion is believed to occur within less than about 4 seconds at 250.degree. to 400.degree. F., although the process conditions and apparatus may be such that the tobacco remains in contact with the heated gas for a somewhat longer period. While temperatures of 250.degree. to 400.degree. F. are indicated as preferable, it is desirable that the tobacco not be maintained in contact with gases within this temperature range for any substantial length of time since the smoking qualities of the tobacco may become impaired.

After the expansion, the hot stream of tobacco and gases is passed to a separator for removing the tobacco from the gases. The separated gases, which may contain steam, air and a considerable percentage of vapors of the impregnating liquid, are reheated to the appropriate temperature and recycled for contact with additional impregnated tobacco withdrawn from the impregnator. A vapor side stream may be removed before reheating and passed to a recovery system for separating water and air and for recycle of impregnating fluid usually in the form of a liquid back to the impregnator. The tobacco discharged from the separator is steam stripped to remove all traces of the vapor of the impregnating fluid and is then reordered to the desired moisture content, usually 12 to 16 parts by weight of water per 100 parts by weight of tobacco (dry basis). During reordering the tobacco may be dressed and suitable flavorants may be added.

As above indicated, a feature of the invention is the provision of a procedure in which the impregnator contains the impregnating fluid in both the liquid phase and in the vapor phase. In the embodiment here described, the tobacco is introduced under the surface of the liquid phase of the fluid and the only withdrawal of impregnating fluid is through the upper portion of the impregnator. Inasmuch as the liquid drains back to the pool into which the tobacco is introduced and after an initial startup of the process, there is no net extraction of any flavorants or other aroma-producing substances from the tobacco so that the expanded product has essentially the same composition as the tobacco charged to the process .

For a more complete understanding of this invention, reference will now be made to the accompanying drawing which in diagrammatic form illustrates an apparatus for carrying out the process of this invention, In this embodiment shredded tobacco is passed by means of a conveyor 10 to a moistener 12 in which the moisture content of the tobacco, if necessary, is adjusted to between about 10 and 30 percent by weight dry basis. Suitably the moisture content is adjusted to 16 to 18 percent by weight. Under certain conditions of plant operation, the moisture content of the tobacco may already fall within the prescribed range and, accordingly, the tobacco charged to the process may bypass the moistener 12 by a conveyor 14 if desired. The moistened tobacco from the moistener 12 or the bypass conveyor 14 or a confluence of both passes to a rotary star valve 16 via conduit 18. The star valve serves to discharge the tobacco at a prescribed rate into the lower portion of an elongated impregnator 20.

The impregnator 20 is inclined at an angle (about 20.degree.) to the horizontal and is provided with a motor-driven screw conveyor 22 by which the tobacco is moved from the lower portion of the interior of the impregnator to the upper portion thereof. The rotary star valve 16 prevents pressure release during the introduction of tobacco into the impregnator thereby permitting a suitable pressure to be maintained within the impregnator. The selected organic liquid impregnating fluid is introduced into the lower portion of the impregnator via conduit 24. The impregnator is provided with an external jacket for receiving a heat-exchange medium whereby the temperature of the tobacco and impregnating fluid moving into and through the impregnator may be controlled and, if desired, similar heat-exchange means (not shown) may be provided in the shaft of the screw conveyor 22. The heat-exchange means supplies the required heat of vaporization for the organic fluid and in the upper section of the impregnator prevents condensation of liquid which is not necessary or desired in that portion of the equipment.

At the upper portion of the impregnator 20 there is provided a discharge conduit 26, a pressure release rotary star valve 28 and a conduit 30 which serves to discharge the impregnated tobacco directly into a stream of hot gas circulating through a conduit 32 and a vertical expander 34 of enlarged cross section to a tobacco separator 36 which may take the form of a conventional cyclone separator. The rotary star valve 28 is arranged to discharge the tobacco from the impregnator without materially affecting the superatmospheric pressure maintained therein.

Tobacco is discharged from the bottom of the separator 36 through a conveyor 38 to a steam stripper 40 in which any residual organic fluid is separated from the expanded tobacco and conveyed through line 42 to a conventional organic liquid recovery unit 44. Tobacco from the stripper 40 is moved by conveyor 46 to a reorderer 48 from which the final expanded tobacco product is discharged through a conveyor 50. In the reorderer, sufficient water and sometimes flavoring and dressing materials are added to provide the final desired product.

Water and air are withdrawn through lines 52 and 54 from the organic liquid recovery unit 44 and fresh organic liquid is fed to the unit through conduit 56. A level control valve 58 is provided in line 24 to regulate the flow of organic liquid to the impregnator 20 in response to the level 60 of the pool or body 62 of the organic liquid maintained in the lower portion of the impregnator. Organic fluid which may escape as vapor into the rotary valve 16 or into the tobacco conveying conduit 18 may be removed by fans or pumps 63 and 64 through conduits 66 and 68 to a line 70 which may discharge either into the stream of gases moving through conduit 72 from the upper portion of the separator 36 to a gas heater 78 or may be passed to the organic liquid recovery unit 44. Vapors to be recovered from the system are passed from the upper portion of the separator 36 through line 80 to the recovery system 44.

As previously indicated, the preferred organic liquid for use in accordance with this invention is trichloromonofluoromethane (i.e., Freon-11) having an atmospheric pressure boiling temperature of approximately 74.degree. F. When this solvent is utilized the tobacco having the appropriate moisture content is passed into the impregnator 20 through the rotary valve 16 and deposited under the surface 60 of the pool 62 of the Freon maintained in the bottom of the impregnator. This liquid level is maintained during operation by passing additional fluid to the impregnator through conduit 24 in response to the liquid level control valve 58. Heating fluid is passed to the jacket of the impregnator 20 to supply the necessary heat of vaporization for the organic liquid and to maintain the desired temperature within the impregnator. Under these conditions the Freon vapors generate a superatmospheric pressure which is necessary to maintain the body or pool 62 of liquid in the lower portion of the impregnator. The tobacco having been introduced underneath the surface of the organic liquid is thoroughly "wetted" and then elevated by the screw conveyor toward the upper portion of the impregnating zone. During this process the tobacco emerges from beneath the surface of the liquid and progresses upwardly through an atmosphere of saturated vapor and any excess liquid drains back to the pool 62. However, as the tobacco progresses upwardly through the impregnator under superatmospheric pressure through the saturated vapor atmosphere, impregnation of the tobacco continues to occur until it is essentially complete at the time that it reaches the upper portion of the impregnator. Thereafter the tobacco is discharged through conduit 26 and the rotary valve 28 to conduit 30 wherein the pressure is reduced to about atmospheric and it is then passed immediately into a rapidly moving stream of hot gases heated to above the boiling point of water, preferably between about 250.degree. and 400.degree. F. and suitably 310.degree. F. The tobacco suspended in the hot gases passes upwardly through the vertical expander 34 in which the tobacco is expanded to provide the desired filling capacity and it is thereafter separated from the vapors in the separator 36. The separated gas comprising a mixture of air and water and Freon vapors is then recycled through heater 78 and forced by fan 82 into contact with a fresh charge of impregnated tobacco from conduit 30.

In Table I there is shown a material balance for one specific operation carried out in the apparatus shown in the drawing. In this specific operation the impregnating fluid employed is trichloromonofluoromethane (Freon-11) and the temperature within the impregnator is approximately 112.degree. F. at 15 pounds per square inch gauge pressure. The volume of the impregnator 20 is approximately 300 cubic feet, the volume rate of flow of hot gas in the expander 34 is about 40,000 to 50,000 cubic feet per minute and the interval of time between the release of pressure with tobacco at the star valve 28 and its initial contact with the hot gas is less than 1 second. The tobacco charged to the process is a shredded flue-cured tobacco. ##SPC1##

The product obtained from the process after reordering to a moisture content between about 11 and 13 parts by weight of water per 100 parts by weight of tobacco (dry basis) in comparison with the tobacco charged to the impregnator is one in which its filling capacity has been expanded over 100 percent, as determined by the method described in the Moser and Stewart application. Essentially this method is as follows: A compressometer is used which is essentially composed of a cylinder 9.5 centimeters in diameter with a graduated scale on the side. A piston 9.4 centimeters in diameter slides in the cylinder. Pressure is applied to the piston, and volume in milliliters of a given weight of tobacco, 100 grams, is determined. Experiments have shown that this apparatus will accurately determine the volume (filling capacity) of a given amount of cut tobacco with good reproducibility. The pressure on the tobacco applied by the piston is 2.30 pounds per square inch applied for 5 seconds, at which time the volume reading was taken. This pressure corresponds closely to the pressure normally applied by the wrapping paper to tobacco in cigarettes.

The product of the process is essentially free of compressed laminated tobacco particles which are found incident to the initial shredding of the tobacco used as a charge stock. The product may be used to manufacture cigarettes in the conventional manner or it may be mixed with other tobaccos to provide a desired blend for use in the manufacture of cigarettes or other smoking articles.

While a particular embodiment of this invention has been described in the foregoing, it will, of course, be apparent that other modifications may be made without departing from the spirit and scope of the appended claims.

Claims

I claim:

1. A process of increasing the filling capacity of tobacco which comprises:

a. maintaining a tobacco impregnating zone containing an organic fluid having a boiling point less than that of water under a superatmospheric pressure sufficient to provide a body of said fluid in the liquid state in a lower portion of said zone and an atmosphere of said fluid in the vapor state in an upper portion thereof,

b. passing water-moistened tobacco into said liquid state body in said lower portion and then conveying said tobacco from said body into said atmosphere in said upper portion, the residence time of said tobacco in said zone being sufficient to impregnate said water-moistened tobacco with said organic fluid,

c. withdrawing portions of said water-moistened and impregnated tobacco from the upper portion of said zone to a zone of pressure less than that obtaining in the impregnating zone, and

d. thereafter immediately contacting the so withdrawn portions with a stream of a hot gas at an elevated temperature in an amount sufficient to expand the tobacco contained therein.

2. The process of claim 1 wherein organic fluid is added to said impregnating zone to replenish the organic fluid withdrawn with the tobacco.

3. The process of claim 1 in which the expanded tobacco is separated from said gas and vapors.

4. The process of claim 1 in which the organic fluid is essentially immiscible with water.

5. The process of claim 4 in which the fluid is a fluorocarbon.

6. The process of claim 5 in which the fluorocarbon is trichloromonofluoromethane.

7. The process of claim 1 in which the temperature of the hot gas is at least about 200.degree. F. higher than the boiling point of the fluid.

8. The process of claim 1 in which the tobacco passed into said liquid state body is shredded tobacco.

9. A process of increasing the filling capacity of tobacco which comprises:

a. maintaining a tobacco impregnating zone containing an organic fluid having a boiling point less than about 180.degree. F. at a temperature between the atmospheric pressure boiling point of the fluid and 180.degree. F. and under a superatmospheric pressure sufficient to provide a body of said fluid in the liquid state in a lower portion of said zone and a saturated vapor atmosphere of said fluid in an upper portion thereof,

b. passing tobacco beneath the surface of said body within said zone to wet the tobacco with said liquid,

c. thereafter passing the wetted tobacco to the upper portion of said zone whereby excess liquid drains away from the wetted tobacco, the residence time of said tobacco in said zone being sufficient to substantially completely impregnate same with said fluid,

d. withdrawing the drained and impregnated tobacco from the upper portion of said zone, and

e. thereafter immediately subjecting the so withdrawn tobacco to an elevated temperature and a reduced pressure sufficient to expand said tobacco.

10. The process of claim 9 wherein the tobacco treated is shredded tobacco.

11. The process of claim 9 wherein said last mentioned elevated temperature is above the boiling point of water at said reduced pressure.

12. The process of claim 9 wherein the tobacco passed into the impregnating zone has a moisture content of between about 10 and 30 parts by weight of water per 100 parts by weight of tobacco.

13. The process of claim 9 wherein the last-mentioned heating step is effected by passing the tobacco into a stream of hot gas and the expanded tobacco is thereafter separated from said stream.

14. The process of claim 13 is which the gas separated from the expanded tobacco includes a substantial percentage of vapors of the organic fluid and at least a portion of which provides the stream into which the tobacco is passed from the impregnating zone.

15. A process of treating tobacco which comprises

a. passing a stream of an organic fluid having a boiling point less than about 180.degree. F. into a tobacco impregnating zone,

b. heating said zone to a temperature above the atmospheric pressure boiling point of said fluid but below about 180.degree. F. under pressure sufficient to maintain a body of said fluid in the liquid state in a lower portion of said impregnating zone and a saturated vapor atmosphere of said fluid in an upper portion thereof,

c. passing a stream of tobacco having a moisture content of between about 10 and 30 parts by weight of water per 100 parts by weight of tobacco (dry basis) into said liquid body in the lower portion of a tobacco impregnating zone,

d. moving the organic liquid wetted tobacco to the upper portion of zone whereby excess liquid drains from the tobacco and returns to said lower portion,

e. withdrawing the drained and impregnated tobacco from the upper portion of said impregnating zone,

f. immediately contacting the so withdrawn tobacco with a stream of hot gas at a pressure less than that prevailing in said impregnating zone and at a temperature above the boiling point of water at said last-mentioned pressure,

g. separating the resulting expanded tobacco from said hot gas stream, and

h. recycling at least a portion of said hot gas stream as the stream for contacting the tobacco withdrawn from said contacting zone.

16. The process of claim 15 wherein the temperature at which the hot gas stream and tobacco are contacted is between about 250.degree. and 400.degree. F. and the time of contact is sufficient to expand the tobacco but insufficient significantly to impair the smoking qualities thereof.

17. The process of claim 15 wherein the temperature within said impregnating zone is between about 100.degree. and 170.degree. F. and the organic fluid is trichloromonofluoromethane.

18. The process of claim 15 in which the flow of said stream of organic fluid into said impregnating zone is controlled by the liquid level of said liquid body in the lower portion of said impregnating zone.