Tobacco Expansion Process

Abstract

A process of expanding the filling capacity of tobacco which comprises introducing tobacco and a stream of vapors of a compound having an atmospheric pressure boiling point between about -50.degree. and +80.degree. C. into one end of an impregnating zone wherein the temperature of the tobacco and of the vapors introduced into said zone are, respectively, below and above the boiling point of the compound at the prevailing pressure. The tobacco is impregnated with the compound and the impregnated tobacco is withdrawn from the impregnation zone and subjected to vapor-expanding conditions such as immediate treatment with a hot gas to expand the tobacco. The relative amounts of the compound and the tobacco introduced into the impregnating zone and in the impregnated tobacco at the time of expansion is within the range of about 5 to 200 parts by weight of compound per 100 parts by weight of tobacco (dry basis). The flow of vapors to the impregnating zone is controlled with respect to the rate at which the tobacco is introduced into said zone.

Description

BACKGROUND OF THE INVENTION

This invention relates to a process of treating tobacco and is related to the process disclosed in U.S. Pat. No. 3,524,452 of Glenn P. Moser and Grant M. Stewart issued Aug. 18, 1970. That patent describes a method of increasing the filling capacity of tobacco which involves impregnating tobacco with an organic liquid and then subjecting the impregnated tobacco to a stream of hot gas whereby the liquid is quickly vaporized with the simultaneous puffing or expansion of the tobacco particles. This invention relates to a process which is a modification of, and in certain respects an improvement over, the process described in said patent.

An object of this invention is the provision of a tobacco expansion process in which the amount of impregnating fluid introduced into the tobacco and present in the tobacco at the time it is subjected to the expanding conditions may be readily and accurately controlled.

A further object of this invention is the provision of a process in which the impregnating fluid is applied to the tobacco in the vapor state and liquid leaching of soluble constituents normally present in the tobacco being treated is minimized.

A still further object of this invention is the provision of a process which permits the use of reduced amounts of impregnating fluid thereby avoiding the expense incident to the vaporization, recovering and recycle of excess quantities of impregnant.

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

GENERAL DESCRIPTION OF THE INVENTION

In accordance with one embodiment of this invention, a process is provided in which tobacco is introduced into one end of an impregnating zone at a predetermined rate. Simultaneously a stream of vapors of an impregnating compound having an atmospheric boiling point between about -50.degree. and +80.degree. C. is introduced into the same end of the impregnating zone and into contact with the tobacco whereby the tobacco is impregnated with said compound. The temperature of the tobacco introduced into the impregnating zone is below the boiling point of the impregnating compound at the prevailing pressure and the temperature of the vapor stream is above said boiling point. The flow of the vapor stream into the impregnating zone is controlled so that for each 100 parts by weight of tobacco (dry basis) introduced there are also introduced at least 5 parts by weight of impregnating compound in the vapor state. Preferably, rate of vapor flow into the impregnating zone is in the range of about 5 to about 200 parts by weight of compound for each 100 parts by weight of tobacco (dry basis) introduced into the zone. The mixture of compound and tobacco is then moved in concurrent flow relationship to another end of the impregnating zone during which time the tobacco becomes thoroughly impregnated with the compound. After the impregnation has occurred, the merged stream comprising tobacco and the impregnating fluid, including vapors and any condensed impregnant, is withdrawn from the other end of the impregnating zone and suddently subjected to vapor expanding conditions whereby the impregnant in the tobacco is vaporized causing the tobacco to expand. Such expanding conditions are preferably achieved by rapidly increasing the temperature of the impregnated tobacco by introducing it into a stream of hot gas in the manner described in said U.S. Pat. No. 3,524,452. A feature of this invention is the provision of a process in which the rate of flow of vapors to the impregnating zone is controlled with respect to the rate of introduction of tobacco into the impregnating zone.

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, leaves, stems or sheets of reconstituted tobacco. 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 results in compressing the product which tends 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.

Burley and flue-cured tobaccos used in the manufacture of cigarettes ordinarily have a moisture content of about 10 to 15 percent by weight. In the practice of this invention, the moisture content of the tobacco when contacted with the organic vapor is usually in excess of about 10 percent by weight and preferably within the range of 10 to 30 percent by weight of the tobacco. The desired moisture content may be achieved by any suitable procedure such as sprinkling, spraying, wet steam treatment, or the like, as is known to those skilled in the art. The presence of the indicated percentage of moisture is desired since the internal structure of the tobacco is thereby rendered sufficiently pliable or flexible to permit the expansion or puffing when the impregnating compound expands within the tobacco upon heating. If the moisture content is less than about 10 percent, the process results in the production of an excess of tobacco fines during the expansion step. A tobacco having greater than about 30 percent moisture has a tendency to be mushy or soggy and is difficult to handle in commercial operations.

In accordance with this invention, the temperatures of the vapor and tobacco and the rates of flow of each into the impregnating zone are such that a substantial portion of the impregnating vapor condenses directly in and on the tobacco thereby providing an impregnating liquid which vaporizes and expands when the impregnated tobacco is subjected to the tobacco expanding step. It is important that the impregnating compound be contacted with the tobacco in the impregnating zone while the compound is in the vapor state. The amount of vapors employed and the pressure and temperature conditions within the impregnator are such that, while vapor condensation within the tobacco does occur, the accumulation of separate pools of liquid is avoided. The atmosphere within the impregnator consists essentially of vapors of the impregnating compound and under these conditions a condition of substantial pressure-temperature equilibrium prevails. The pressure within the impregnating zone may be atmospheric, superatmospheric or subatmospheric and the pressure-temperature conditions are such that the only liquid which impregnates the tobacco is that which is formed by the condensation of the impregnating vapor directly within the mass of tobacco. The quantity of liquid impregnant that condenses in and on the tobacco is subject to control and depends on the relative rates at which the tobacco and vapor are introduced into the impregnating zone as well as on the temperatures of each. While some vapor may escape at the points where the tobacco is entering and leaving the impregnating chamber, it is preferred that this escape be minimized by conveying the tobacco into and out of the chamber through suitable vapor locks.

The volatile compound or mixture employed for impregnating the tobacco is preferably one which is organic in nature, is chemically inert to the tobacco being treated and has a boiling point at atmospheric pressure between about -50.degree. C. and +80.degree. C. Compounds having atmospheric pressure boiling points about +80.degree. C. do not provide good tobacco expansion and are difficult to remove completely from the tobacco without adversely affecting its flavor and aroma. Compounds having very low atmospheric pressure boiling points (i.e., below -50.degree. C.) are so volatile under readily obtainable pressures in commercial operations that the vapors do not readily condense during the impregnation step and are so fugitive that they are not present as condensate in the tobacco in the desired concentration at the time the vapor expanding conditions are applied. Preferably, the atmospheric pressure boiling point of the compound is between -40.degree. C. and +40.degree. C. Illustrative inert organic compounds are: ketones such as acetone and methyl ethyl ketone; aliphatic or cyclic ethers such as methyl ethyl ether, diethyl ether, diisopropyl ether, methyl butyl ether, dimethoxymethane, furan and tetrahydrofuran; aliphatic alcohols such as methanol, ethanol and 2-propanol; esters such as methyl formate, ethyl formate and methyl acetate; aliphatic hydrocarbons such as butane, pentane, isopentane, hexane and the corresponding unsaturated hydrocarbons; the cyclo aliphatic hydrocarbons such as cyclobutane, cyclohexane and cyclopentane; the halo-hydrocarbons ethyl chloride, propyl chloride, isopropyl chloride, sec-butyl chloride, t-butyl chloride, methyl bromide, ethyl bromide, t-butyl bromide, methylene chloride, chloroform, carbon tetrachloride, ethylene dichloride, ethylidene chloride; and the fluorinated hydrocarbons represented by trichloromonofluoromethane, dichlorodifluoromethane, monochlorodifluoromethane, 1,1-difluoroethane, chloropentafluoroethane, octafluorocyclobutane, 1,1,1-trichlorodifluoroethane and 1,2-dichlorotetrafluoroethane. The organic materials that are preferred are the non-oxygenated compounds which are relatively non-polar in nature and are relatively or substantially immiscible in water. These preferred compounds as a group have a relatively low latent heat of vaporization and thus require only a low energy input to cause the impregnant to vaporize and expand within the tobacco. Preferred materials are the hydrocarbons and the halogenated hydrocarbons of the types indicated above. Mixtures of vapors of several compounds may also be used if the boiling points of the liquid mixtures are within the indicated temperature range. Such mixtures include the azeotropes such as the trichloromonofluoromethane-isopentane azeotrope.

The tobacco remains in the impregnating zone for a sufficient time for condensed impregnating compound to penetrate into the cellular structure of the tobacco. The time required may vary from a few minutes to a few hours (e.g., 10 minutes to 2 hours) depending upon the compound used, the nature of the tobacco and the conditions of temperature and pressure.

The tobacco withdrawn from the impregnating zone contains about 5 to about 200 parts, preferably about 10 to about 100 parts, by weight of impregnating fluid for each 100 parts by weight of tobacco (dry basis). The withdrawn tobacco is next subjected to tobacco expanding conditions. This may be effected by suddenly reducing the ambient pressure. However, it is preferred that it be effected by suddenly subjecting the impregnated tobacco to heat such as may be imparted by a stream of hot gas as disclosed in said patent No. 3,524,452. The heat is rapidly applied such that the temperature of the impregnated tobacco is suddenly elevated to at least about 18.degree. C. above and preferably about 80.degree. C. above the boiling point of the impregnating compound at the prevailing pressures within a period of less than about 10 seconds, preferably within a period of less than about 4 seconds.

It is preferred that the temperature-pressure conditions within the impregnating zone be maintained at essentially equilibrium. This may be readily accomplished when an impregnating compound having a boiling point within the range of -40.degree. C. to +40.degree. C. is used and the temperature of the vapor stream introduced into the impregnator is not more than about 15.degree. C. above and the temperature of the tobacco introduced is not more than about 20.degree. C. below the boiling point of the compound at the pressure prevailing in the impregnator. A particular advantage in operating under these conditions is that the ratio of tobacco to impregnant in the tobacco to be expanded with the hot gas may be readily and automatically controlled even though the feed rate of the tobacco may be intentionally or inadvertently varied. Under a given set of conditions, the weight ratio of impregnant to tobacco in the impregnated tobacco withdrawn from the impregnator is determined largely by the respective temperatures of the tobacco and impregnating vapors entering the impregnator. Other factors which may have a considerable influence include the operating pressures, the boiling point of the impregnating fluid and the amount of external heat (if any) supplied to the impregnator. When substantially equilibrated conditions prevail within the impregnation zone, the ratio of impregnant to tobacco in the impregnated product is conveniently adjusted by varying the temperature within the impregnator either by changing the temperature of the vapor introduced or by changing the amount of external heat (if any) supplied to the impregnator. Alternatively, selection of a lower operating pressure results in a lower vapor temperature with a corresponding decrease in the ratio of impregnant to tobacco. Accordingly, if the rate of flow of the cooler tobacco to the impregnator is increased, causing more condensate to form, the pressure will have a tendency to drop. This will require more impregnant to maintain the desired equilibrium. In accordance with one embodiment of this invention, a pressure responsive sensor is positioned in the impregnation zone and is arranged to regulate the supply of liquid impregnant to the vaporizer so that the vapor supply to the impregnator will increase in proportion to the increase in supply of tobacco. When trichloromonofluoromethane is used as the impregnant, the pressure in the impregnator is preferably between about 0 to 30 p.s.i.g.

DESCRIPTION OF THE DRAWING

For a more complete understanding of this invention, reference will now be made to the accompanying drawing which shows in schematic form an apparatus in which the process may be carried out. In this illustrated embodiment, the processing equipment comprises a tobacco moistener 2, a vapor impregnator 4, an expander 6, a separator 8, a steam stripper 10, a product reorderer 12, a liquid recovery unit 14, a liquid storage tank 16, a pressure control valve 18 and a vaporizer 20. Shredded flue-cured or burley tobacco is charged via a conveyor 22 to the moistener 2 in which, if necessary, the water content of the tobacco is adjusted to 10 to 30 percent, suitably to about 18 percent, by weight. If moistening of the tobacco is not required, the tobacco may by-pass the moistener via conveyor 24. After moistening, the tobacco is conveyed by conveyor 25, a star feed valve 26 and duct 28 to one end of the impregnator 4. The tobacco is discharged into a screw conveyor 30 within the impregnator and is advanced therethrough from left to right as shown in the drawing. Motor 31 drives the conveyor 30.

Simultaneously the vapors of the impregnating compound are introduced through vapor line 32 into the impregnator 4 adjacent the point of introduction of the tobacco. The vapors come into contact with the tobacco moving in the screw conveyor 30 and at least a portion of the vapor is condensed in and on the tobacco particles. The feed rate of vapor passing through line 32 (as hereinafter described) and into the impregnator 4 is determined by the pressure within the impregnator which, in turn, is influenced by the rate at which relatively cool tobacco enters through valve 26. At a given pressure, which is selected on the basis of the particular impregnating fluid being used, the vapor feed rates are easily controlled by valve 18 to give an impregnated tobacco containing between 5 and 200 parts by weight of impregnant per 100 parts by weight of tobacco (dry basis). During the concurrent flow of tobacco and impregnant in the conveyor 30, the tobacco is thoroughly impregnated with the compound and a substantial proportion of the latter condenses on the tobacco due to the fact that the temperature of the tobacco and vapors introduced into the impregnator 4 are, respectively, below and above the boiling point of the impregnating compound.

The tobacco impregnated with the compound in the above-indicated weight ratio is discharged from the impregnator 4 through duct 34 and a star feed valve 36 into a rapidly moving stream of hot gas (e.g., steam) in duct 38 and then conveyed to the expander 6. The hot gas stream in duct 38 has a temperature substantially greater than the boiling point of the tobacco impregnating compound at the prevailing pressure so that when the tobacco contacts the hot gas, the impregnating compound will vaporize or the vapors within the tobacco will expand to cause the concomitant expansion of the tobacco. This expansion occurs within the short period (e.g., less than 10 seconds) during which the gas and tobacco flow through duct 38 and the expander 6. This expansion step is essentially the same as that described in said U.S. Pat. No. 3,524,452. After expansion, the tobacco, heating gas and vapors of impregnating compound are conveyed through conduit 40 to the cyclone separator 8 from which the expanded tobacco is passed through an air lock 41 to the stripper 10. Residual impregnating fluid is removed by vaporization from the tobacco in stripper 10 and the tobacco effluent is passed to a reorderer 12 in which the product is adjusted to the desired moisture content, suitably 12 to 14 percent, so that it may be used in the manufacture of cigarettes. The gases including steam and vapors of the impregnating fluid are withdrawn from the separator 8 through conduit 42, are heated to the desired extent in a heater 44 and cycled through duct 46 and a fan 48 to duct 38. A side stream of gases from conduit 42 is taken through line 50, control valve 52 and line 54 to the liquid compound recovery unit 14 for recovering impregnating fluid, which latter is then passed through line 56 to storage 16. Vapors from the stripper 10 are passed through line 58 to the recovery unit for salvaging additional amounts of impregnating compound. Water and air or other non-condensible gases are removed from unit 14 through line 60 and 62, respectively. In order to supply impregnating compound vapors for the tobacco, liquid compound is withdrawn from the storage unit 16 through line 64, pump 65, the pressure control valve 18, line 66, vaporizer 20 and line 32 to the impregnator. A pressure responsive element 68 is positioned within the impregnator for controlling the amount of liquid flow through the control valve 18 and hence the flow of vapors into the impregnator 4. The vaporizer 20 and the impregnator 4 are equipped with outer jackets 70 and 72 through which heat exchange media may be circulated for appropriate temperature control.

As previously suggested, the temperature and pressure conditions for effecting the impregnation and for effecting the expansion may be varied over wide ranges, depending upon the selection of the particular impregnating compound, the moisture content of the tobacco being treated, the ratio of impregnating vapor to tobacco introduced into the impregnator and in the merged stream withdrawn therefrom, and the degree of tobacco expansion desired. In any event, the temperature should be well below those which will adversely affect the flavor and aroma of the end product but should be sufficiently high to enable efficient impregnation and expansion after impregnation.

SPECIFIC EXAMPLE

Reference will now be made to a specific example to illustrate the process herein-described and claimed. In this example, impregnator 4 is a horizontal steel cylinder 35 feet in length and 42 inches in diameter mounted at an angle of 20.degree. from the horizontal. Expander 6 is a round vertical pipe 55 feet high and 58 inches in diameter. Duct 38 from fan 48 to expander 6 is a horizontal pipe 34 inches wide and 38 inches high.

The impregnating fluid, trichloromonofluoromethane, is drawn from liquid storage tank 16, through line 64 and into pump 65. This liquid is pumped into vaporizer 20 jacketed with a hot water-heated heat exchanger 70. In vaporizer 20 the liquid boils and trichloromonofluoromethane vapor passes through line 32 to impregnator 4 at a temperature of about 52.degree. to 55.degree. C. Vapor flow is regulated, as necessary, by valve 18 to maintain a pressure inside impregnator 4 of about 14 pounds per square inch gauge. Impregnator 4 is initially warmed by circulating hot water through the jacket 72 around the outside wall. Warming of impregnator 4 is also initially hastened by some condensation of trichloromonofluoromethane on the inside wall of the impregnator. After the impregnator has reached an equilibrium temperature, condensation stops. This equilibrium temperature is about 43.degree. C. (which is the approximate boiling point of trichloromonofluoromethane at 14 p.s.i.g.), but it could be slightly lower if there is much air in the impregnator. At this time all condensate is then withdrawn from impregnator 4 through a valve (not shown) at the bottom. The equipment is then in a substantially equilibrated condition and ready to receive tobacco.

The tobacco used is shredded flue-cured tobacco of moisture content 20.7 percent (equivalent to 26.1 percent moisture based on dry tobacco). At this moisture level, moistener 2 may be by-passed, and the shredded tobacco at room temperature, i.e., about 28.degree. C., is fed directly to conveyor 25 at 50 pounds per minute. The tobacco drops through star vapor lock 26 into impregnator 4 and is moved through the impregnator by the screw impeller 30. As the tobacco is conveyed through the impregnator, trichloromonofluoromethane is introduced through line 32 at the rate of about 45 pounds per minute and condenses on the tobacco, penetrating into the cellular structure of the individual shreds of tobacco. The total residence time of the tobacco in the impregnator is about 35 minutes.

The impregnated tobacco then drops into duct 34, through star vapor lock 36, and down into a rapidly moving stream of heated gas in duct 38 at approximately ambient pressure. This recycled gas, after reaching equilibrium operating conditions, contains some air that is introduced with tobacco, steam from moisture in tobacco, and vapor of the impregnating compound, trichloromonofluoromethane. The temperature of this heated vapor at the point tobacco enters duct 38 is about 110.degree. C. and is cycled through the system at the rate of about 40,000 standard cubic feet per minute. The tobacco travels with the hot vapor around a gentle bend in duct 38 and is moved upward through expander 6.

From expander 6 the vapor stream and tobacco pass through duct 40 into cyclone separator 8. Vapor leaves the top of the separator, through duct 42, and is passed through heater 44, where it is again heated to about 110.degree. C. by contact with superheated steam coils. The vapor stream, restored to full heat, is passed through duct 46 and blown by fan 48 back into duct 38 to contact a fresh charge of impregnated tobacco. Expanded tobacco drops from the bottom of separator 8 and through air lock 41 directly to reorderer 12, which is an inclined rotating drum in which a fine spray of water restores moisture content of the expanded tobacco product to about 12 to 13 percent moisture. Optional equipment for removing most of the residual impregnant from expanded tobacco is the steam stripper 10 between lock 41 and reorderer 12. In the steam stripper, tobacco remains for a few minutes in a hot, moist atmosphere that consists of wet steam diluted slightly with ambient air. In the absence of a steam stripper, expanded tobacco is stored for several hours at a moisture content of at least 12 percent to allow residual impregnating fluid to evaporate and escape.

The tobacco heating step in the conduit 38 and expander 6 in the foregoing operating causes an increase in total quantity of vapor in the hot, recycled vapor stream. Excess vapor is withdrawn continuously through line 50 at a rate regulated by valve 52. The excess vapor is routed to the recovery system 14 which consists essentially of a condenser. Recovered liquid trichloromonofluoromethane is passed to a liquid storage tank from which it is drawn by pump 65 through the valve 18 to the vaporizer 20.

In one operation, a flue-cured tobacco at room temperature (i.e., about 28.degree. C.) was charged to the impregnator at the rate of about 2,500 pounds per hour and the total residence time in the impregnator was about 35 minutes. At the same time, vapors of trichloromonofluoromethane were charged through the conduit 32 at a temperature of 52.degree. to 55.degree. C. and at the rate of about 1900 pounds per hour. The effluent from the impregnator was dropped into a stream of the hot gas heated to 110.degree. C. in duct 38. The filling capacity, when measured by the procedure set forth in said U.S. Pat. No. 3,524,452, increased from about 420 to about 790 milliliters per 100 grams, the tobacco moisture level being 12 percent for both measurements.

It will be apparent that by utilizing vapor in the impregnation step of this invention, it is possible to accurately control the amount of impregnating fluid introduced into the tobacco and thus the degree of expansion. Also, less impregnating fluid is required than is required in those processes in which the tobacco is first soaked in liquid before it is withdrawn from the impregnator and introduced to the expansion zone. Moreover, by eliminating contact of the tobacco with a liquid pool, extraction and redistribution of soluble constituents within the tobacco are minimized.

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

Claims

What is claimed is:

1. A process of treating tobacco which comprises introducing tobacco into a impregnating zone, simultaneously introducing into said zone and into contact with said tobacco a stream of vapors of an organic compound having an atmospheric pressure boiling point between about -50.degree. and +80.degree. C., the temperatures of said tobacco and said vapor introduced into said zone being, respectively, below and above the boiling point of said compound at the pressure prevailing therein, withdrawing the tobacco impregnated with said compound from said zone, controlling the rate of vapor introduction into said zone with respect to the rate of tobacco introduction thereinto such that the weight ratio of compound in the withdrawn impregnated tobacco is in the range of about 5 to about 200 parts by weight of compound per 100 parts by weight of tobacco (dry basis), and suddenly subjecting the withdrawn impregnated tobacco to vapor expanding conditions whereby the tobacco is also expanded.

2. The process of claim 1 in which the weight ratio of vapor to tobacco introduced into said zone is between about 10 and about 100 parts of vapor per 100 parts of tobacco (dry basis).

3. The process of claim 2 in which the vapor expanding conditions are effected by contacting the withdrawn impregnated tobacco with a stream of a hot gas.

4. A process of treating tobacco which comprises introducing tobacco into one end of an impregnating zone, simultaneously introducing into said one end a stream of vapors of an organic compound having an atmospheric pressure boiling point between about -40.degree. and +40.degree. C., the temperatures of said tobacco and said vapor when introduced into said one end being, respectively, below and above the boiling point of said compound at the pressure prevailing in said zone, merging said tobacco and said vapor stream in said one end and passing the resulting mixture in contacting, concurrent flow relationship through said zone to another end thereof whereby said tobacco is impregnated with said compound, withdrawing the resulting merged stream of tobacco and compound from said other end, controlling the rate of vapor introduction into said one end with respect to the rate of tobacco introduction into said one end such that the weight ratio of compound to tobacco in the withdrawn stream is between about 10 and about 100 parts of compound per 100 parts of tobacco (dry basis), and then suddendly contacting the withdrawn impregnated tobacco with a stream of a hot gas at a temperature at least 18.degree. C. higher than the boiling point of the compound at the pressure prevailing during contact whereby the tobacco is expanded.

5. The process of claim 4 in which said tobacco temperature is not more than about 20.degree. C. below and said vapor temperature is not more than about 15.degree. C. above said boiling point at said prevailing pressure.

6. The process of claim 4 including the steps of separating vapors of said compound from the expanded tobacco, condensing the separated vapors to a liquid, continuously flowing a stream of the condensed liquid to a vaporization zone whereby continuously to produce the stream of vapors introduced into said one end of said impregnation zone, and regulating the rate of flow of said condensed liquid stream to said vaporization zone in response to the pressure prevailing within said impregnation zone.

7. A process of treating tobacco which comprises flowing a stream of an organic compound having an atmospheric pressure boiling point between about -40.degree. and +40.degree. C. in the liquid state to a vaporizing zone for vaporization therein, flowing a stream of the resulting vapors from the vaporizing zone into one end of an impregnating zone, simultaneously introducing tobacco into said one end of said impregnating zone, the temperatures of said tobacco and said vapor stream when introduced into said one end being, respectively, below and above the boiling point of said compound at the pressure prevailing in said impregnating zone, merging said vapor stream and said tobacco in said impregnating zone and passing the resulting mixture in contacting relationship to another end thereof whereby the tobacco is impregnated with said compound, withdrawing the impregnated tobacco from said other end, controlling the rate of flow of liquid to said vaporizing zone in response to the pressure prevailing within said impregnation zone, the rate of introduction of said tobacco into said one end being such that the weight ratio of compound to tobacco in the withdrawn impregnated tobacco is in the range of about 5 to about 200 parts by weight of compound per 100 parts by weight of tobacco (dry basis), and suddenly subjecting the withdrawn impregnated tobacco to vapor expanding conditions whereby the tobacco is also expanded.

8. The process of claim 7 in which said tobacco temperature is not more than about 20.degree. C. below and said vapor temperature is not more than about 15.degree. C. above said boiling point at said prevailing pressure.

9. A continuous process of treating tobacco which comprises continuously introducing tobacco into an impregnating zone at a predetermined rate, simultaneously introducing into said zone and into contact with said tobacco a stream of vapors of an organic compound selected from the group consisting of hydrocarbons and halogenated hydrocarbons and having an atmospheric pressure boiling point between about -40.degree. and +40.degree. C. whereby the tobacco is impregnated with said compound, the temperatures of said tobacco and said vapor when introduced into said zone being, respectively, below and above the boiling point of said compound at the pressure prevailing therein, withdrawing impregnated tobacco from said zone, controlling the rate of vapor introduction into said zone with respect to the rate of tobacco introduction thereinto such that the weight ratio of said compound in the vapor state and the tobacco introduced into said zone is in the range of about 5 to about 200 parts by weight of vapors per 100 parts by weight of tobacco (dry basis), and thereafter suddenly contacting said impregnated tobacco with a hot gas whereby the tobacco is expanded.

10. The process of claim 9 in which the organic compound in trichloromonofluoromethane and the impregnating zone is maintained under substantially equilibrium temperature and pressure conditions at a pressure of between about 0 and 30 p.s.i.g.

11. The process of claim 9 in which said tobacco temperature is not more than about 20.degree. C. below and said vapor temperature is not more than about 15.degree. C. above said boiling point at said prevailing pressure.