EP0117355B1

EP0117355B1 - Process for making a carbon heat source and smoking article including the heat source and a flavor generator

Info

Publication number: EP0117355B1
Application number: EP83307492A
Authority: EP
Inventors: John R. Hearn; Harry Vincent Lanzillotti; George Henry Burnett
Original assignee: Philip Morris Products Inc
Current assignee: Philip Morris Products Inc
Priority date: 1982-12-16
Filing date: 1983-12-08
Publication date: 1991-03-20
Also published as: EP0117355A3; DE3382221D1; EP0117355A2

Description

The present invention relates to a process for making a carbon source and to a smoking article comprising the carbon source and a flavor generator. More particularly, the present invention relates to a process for producing a carbon source from a preformed ligno-cellulosic material and to a smoking article, such as a cigarette, which includes the carbon source and a flavor generator.
One previously disclosed smoking article comprises a tube formed of combustible material which has a mouthpiece attached at one end. An axial inner tube of material, which is breakable when heated, is contained within the tube of combustible material and is coated on its inner surface with an additive material such as nicotine. Thus, on smoking, hot gases are drawn through the inner tube and release the nicotine in the form of an aerosol for inhalation by the smoker. With this device, however, there is an appreciable loss of nicotine and other desirable compounds, such as flavorants, during smolder. There is also a tendency for the inner tube to protrude unattractively from the burning end during smoking.
Another such cigarette-simulating smokeable device for releasing an aerosol into the mouth of a smoker comprises a rod of fuel having a longitudinally extending passage therethrough and a chamber in gaseous communication with an end of the passage whereby during smoking hot gases from the burning fuel rod enter the chamber. Inhalant material is located in the chamber which, when contacted by the hot gases during smoking, forms an aerosol for inhalation by the smoker. The chamber has, at an end remote from the fuel rod, a mouth-end closure member which is permeable to the aerosol. The chamber and the mouth-end closure member of this smoking article are of unitary construction and are formed by molding or extruding a conventional smoke filter plug to provide a chamber to contain the inhalant material. Preferably, the fuel rod is a molding or extrusion of reconstituted tobacco and/or tobacco substitute. The wall of the fuel rod is preferably impermeable to air.
A smoking article comprising a tubular heat source comprising heat-treated cellulose and a flavour generator disposed adjacent to the mouth-end of the article and comprising a substrate material containing at least one thermally releasable flavourant is described in FR-A-2469133. The heat source is a fuel rod extruded or molded from tobacco or a tobacco substitute or is formed of a mixture of tobacco substitute material and carbon or alternatively formed of other suitable combustible material, eg wood pulp, straw end heat-treated cellulose or an SCMC and carbon mixture.
A process for producing a combustible carbonised material by pyrolyzing preformed ligno-cellulosic material in a non-oxidizing atmosphere for a time of about 60 minutes is described in GB-A-1481056. This process comprises the thermal reaction of a cellulosic material in a non-oxidizing atmosphere and at a temperature within the range of 275 to 750°C until the weight loss of the cellulosic material is at least 60% and in which the cellulosic material subjected to the thermal reaction contains 3 to 15% by weight of an alkaline earth metal salt. The product is to be used as a filler in cigars, cigarettes and pipes and/or as a wrapper for cigars and cigarettes.
The present invention provides a process for producing a carbon heat source which is substantially tasteless when fabricated as a smoking article and smoked. This process is characterized by pyrolizing a preformed article in a continuously exchanged inert atmosphere at a temperature in the range of 800° to 1100°C for 0.5 to 3 hours, cooling the pyrolized article in the inert atmosphere at a rate of 500° to 10°C per hour to a temperature within the range of 275° to 25°C, and then subjecting the pyrolized article to at least one additional treatment selected from oxygen absorption, water desorption, and salt impregnation with subsequent heat treatment to obtain a tasteless carbon heat source.
The present invention also relates to a smoking article of the type described above, characterized in that the heat source is a carbon heat source produced by the process of the present invention having a porosity sufficient to support combustion and a density such that puff-induced air flow passes through the tube.
As exemplified by its preferred embodiments herein, the process of the present invention comprises three basic steps: a pyrolysis step, a controlled cooling step, and at least one additional process step selected from an oxygen absorption step, a water desorption step, and a salt impregnation and subsequent heat treatment step.
The pyrolysis step is carried out in an inert atmosphere in order to avoid combustion of the preformed article. Typically, the preformed ligno-celluslosic article is pyrolyzed in an oven which has controlled temperature zones and a quartz reaction chamber in which the articles to be pyrolyzed are placed. The quartz chamber is connected to a source of an inert gas, such as dry nitrogen or argon, and purged in order to remove the air. Throughout the process, a continuous flow of inert gas is passed through the quartz reaction chamber, hereinafter referred to as the pyrolyzing chamber, so that the inert atmosphere is continuously exchanged, whereby the volatiles driven off during pyrolysis are removed from the pyrolyzing chamber. This continuous exchange is believed to be important to the production of an essentially tasteless carbon heat source.
The article to be pyrolyzed is heated to a temperature within the range of from about 800° to about 1100°C, and more preferably from about 950° to about 1000°C, and is maintained at this temperature for from about 0.5 to about 3 hours, preferably from about 0.5 to about 1.5 hours, and more preferably from about 0.75 to about 1.25 hours. Typically, the inert gas employed is dry nitrogen and the flow rate through the pyrolyzing chamber is adjusted to within the range of from about 0.5 to about 5 liters per minute, preferably from about 1 to about 1.5 liters per minute, during pyrolysis. During pyrolysis, the ligno-cellulosic material generally experiences a weight loss of about 70% to about 80% and a dimensional shrinkage generally within the range of about 30% to about 35%.
Upon completion of pyrolysis, the pyrolyzed material is gradually cooled to a temperature within the range of from about 275°C to about 25°C, preferably about 100°C to about 25°C. Typical rate of cooling will be from about 500° to about 10°C per hour, preferably from about 100° to about 60°C per hour. It is important that the rate of cooling be gradual and controlled. It has been observed that a rapid quench, such as immersion in liquid nitrogen, will adversely affect the burn properties of the pyrolyzed material.
According to the oxygen absorption step, which functions to add oxygen to the pyrolyzed article, air or oxygen is gradually introduced into the inert gas stream as the temperature falls to within the range of from about 275°C to about 25°C, preferably from about 100°C to about 35°C. While oxygen absorption may be initiated at temperatures as high as 530°C or as low as 25°C, it is preferred to operate within the above ranges. The oxygen is gradually introduced and the flow rate increased until the oxygen substantially replaces the inert gas. It is important to gradually introduce the oxygen as the cooling continues in order to avoid excessive oxidation of the pyrolyzed material. Preferably, the oxygen is introduced such that the ratio of the volume of nitrogen to the volume of oxygen is within the range of about 1:4 to about 8:1, most preferably about 4:1. During the oxygen absorption step, the pyrolyzed material is either at or is cooled to room temperature.
According to the impregnation and heat treatment step, the pyrolyzed article, which has been cooled to room temperature either with or without the oxygen absorption step, is first impregnated with an aqueous solution of salts of a cation selected from the group consisting of K⁺, Fe^+², Fe⁺³, Mg⁺², Mn⁺², Ca⁺² and mixtures thereof. The pyrolyzed material is impregnated such that it contains from about 0.5 to about 11% of the cation on a dry weight basis, preferably from about 1% to about 3%. Any means known to those skilled in the art may be used to impregnate the pyrolyzed material with the salt solution. One particularly preferred means is vacuum impregnation. After impregnation, the material is then dried at a temperature within the range of from about 40° to about 100°C, preferably from about 50° to about 70°C, in vacuum.
The dried, impregnated, pyrolyzed material is then gradually heated to a temperature within the range of from about 550° to about 750°C, preferably to about 650°C, in an inert atmosphere and is maintained at this temperature for from about 5 to about 60 minutes, preferably from about 15 to about 30 minutes. The material is then cooled in the inert atmosphere.
According to the water desorption step, which, when employed, is preferably the final process step, the pyrolyzed article is subjected to a desiccant environment for at least about 8 hours preferably from about 12 hours to about 48 hours. The purpose of this step is to maintain an existing, or establish and maintain, a relatively moisture-free state in the carbon heat source. This step is preferably practiced by placing the pyrolyzed article in a desiccator containing CaSO₄. It has been observed that this process step improves the burn properties of the carbon heat source.
Any one or combination of the additional process steps may be employed. When salt impregnation and oxygen absorption are both employed, it is preferred that the oxygen absorption step follow the impregnation step.
As the ligno-cellulosic material, tobacco, peanut shells, coffee bean shells, paper, cardboard, bamboo, oak leaves, or a similar such material is suitably employed. The material may preferably be admixed with a binder, such as hydroxypropyl cellulose prior to formation into the desired shape.
The ligno-cellulosic material is preformed, prior to pyrolysis, into the shape desired upon completion of the pyrolysis and subsequent treatment steps, taking into account the dimensional shrinkage experienced during pyrolysis. Extrusion, rolling, injection-molding or the like may be employed to shape the article. preferably, extruded, substantially tube-shaped articles with porous material located in the core of the tubes are employed. The article, once pyrolyzed, must be sufficiently rigid to maintain the shape of the smoking article during smoking and must have a porosity sufficient to absorb the salt solution and oxygen, when employed, yet less porous than the material in the core, when present, so that the gaseous combustion products will flow through the central passage to the flavor source and not through the pyrolyzed material.
The present invention also relates to smoking articles comprising a flavor generator and a carbon heat source. The carbon heat source is the pyrolyzed material prepared according to the process of the present invention. While the carbon source may be prepared in any of the various commercially available shapes of smoking articles, the smoking article will be described with respect to a cigarette.
According to this embodiment, the smoking article is prepared by pyrolyzing a tube-shaped article of lignocellulosic material and then attaching the flavor generator adjacent the mouth end thereof. The tube-shaped carbon heat source may be formed with a porous, preferably open-cell foam, combustible material in the core, as by a co-extrusion process, or, preferably, with at least one porous, combustible plug disposed within the passage. When only one plug is employed, it is preferably disposed at the coal end of the cigarette to prevent flash jetting while the cigarette is being lit. When a porous core is employed, the core material is less dense than the surrounding tube-shaped material so that the combustion gases will flow through the central core to the flavor generator rather than through the carbon source. By selecting the type and amount of material placed in the passage, the temperature of the gases reaching the flavor generator can be established within a range such that thermally releasable flavorants are released without undergoing thermally induced decomposition to products which are not desirable as flavorants.
The flavor generator comprises a substrate material, such as alumina, magnesium hydroxide, zeolites, glass wool, charcoal, tobacco filler, fuller's earth, natural clays, and activated clays, which is impregnated with at least one thermally releasable flavorant, or which inherently contains at least one thermally releasable flavorant. The flavoring agent may consist of any suitable blend of natural or synthetic flavorants such as nicotine, glycerol, menthol, vanilla, eucalyptol, octyl acetate, orange, mint, or isoamyl isovalerate. The flavor generator is preferably cylindrical and of a diameter substantially equal to the diameter of the carbon source, and may be placed in abutting end-to-end relation to the carbon source or may be spaced therefrom. The carbon source and flavor generator may be wrapped in cigarette paper and, if desired, a conventional filter, such as cellulose acetate filter, may be placed after the flavor generator and joined thereto by tipping paper or the like. The flavor generator may comprise a flavored, foamed core containing readily volatilized flavors that are not subject to thermal degradation.
As the hot gases flow through the channel or bore in the carbon source and over the flavor generator, most of the flavors are distilled from the substrate material and the distillate is carried toward the smoker's mouth due to the drawing action. As the flavor-laden gases pass away from the flavor generator toward the cooler portion of the cigarette, the oils contained in the distillate recondense into relatively small droplets, forming a mist or aerosol, and pass into the mouth and nose of the smoker where they create a sensation by taste and smell. A sufficient amount of flavorant should be provided such that the flavorant is continuously released until the smoking article is extinguished.
When extruded tobacco articles are employed as the ligno-cellulosic material in the present process, they are preferably prepared according to the process disclosed in US-A 4 347 855 (see also GB-A 2 078 087 or DE-A 31 18 472.

Examples

The following examples present illustrative but non-limiting embodiments of the present invention. A comparative example is also presented.
In each of the following examples 1 through 9, extruded tobacco tubes prepared according to the method disclosed in U.S. Patent 4,347,855 were employed as the preformed ligno-cellulosic material and were pyrolyzed in a Lindberg, 3-zone furnace having a chamber 152 mm in diameter and 914 mm long surrounding a quartz tube pyrolizing chamber 134 mm in diameter and 1.32m long. The furnace was equipped with seven thermocouples spaced along the length of the quartz tube and could achieve a maximum temperature of about 1200°C.

Example 1

Extruded tobacco tubes were prepared using -20+30 mesh (0.60-0.84 mm) tobacco. Two sets of tobacco tubes were employed; one set had an outside diameter of 8 mm and an inside diameter of 5 mm, and the other had an outside diameter of 12 mm and an inside diameter of 5 mm. The tobacco tubes were pyrolyzed according to the procedure summarized below in Table 1.
The pyrolyzed samples were measured and weighed and it was determined that the samples experienced an average weight loss of 84.7%, an average decrease in length of 33.66%, an average decrease in outside diameter of 33.25%, and an average decrease in inside diameter of 33.05%. The pyrolyzed samples burned statically when lit. Static burning occurs when a cigarette rod continues to smoulder, once it has been lit, in the absence of air drafts and puff induced air flow.

Example 2

Two sets of extruded tobacco tubes were pyrolyzed; one set had an outside diameter of 12 mm and an inside diameter of 5 mm, the other set had an outside diameter of 8 mm and an inside diameter of 2.5 mm. The tobacco tubes were pyrolyzed according to the procedure summarized below in Table 2.
The pyrolyzed tobacco tubes evidenced a 72% weight loss and a 4 to 4.5% dimensional decrease for the larger diameter tubes and a 69% weight loss and 37.5% dimensional decrease for the smaller diameter tubes.

Example 3

Extruded tobacco tubes were pyrolyzed according to the procedure summarized below in Table 3.
The pyrolyzed tobacco tubes maintained a static burn when lit both before and after being placed in a desiccator containing CaSO₄ for about 48 hours. It was determined that the pyrolyzed tubes experienced a decrease in length of 27.24%, a decrease in outside diamter of 7.5%, and a decrease in inside diameter of 19.29%.

Example 4

Two sets of extruded tobacco tubes were prepared; one set from tobacco material 60% of which was below 60 mesh (0.25mm)and 40% of - 20+30 mesh, (0.42-0.60mm) and the other set from tobacco material 60% of which was below 60 mesh and 40% of -30+40 mesh. The tobacco tubes were 65 mm in length, and had an outside diameter of 8 mm and an inside diameter of 5 mm. The tobacco tubes were pyrolyzed according to the procedure summarized below in Table 4.
Both sets of pyrolyzed tobacco tubes maintained a static burn.

Example 5

Two sets of extruded tobacco tubes were prepared; one set from tobacco material 60% of which was -60 mesh and 40% was -30+40 mesh, and the other set from tobacco material 60% of which was -60 mesh and 40% was -20+30 mesh. The tobacco tubes had an outside diameter of 12 mm and an inside diameter of 7 mm. The tobacco tubes were pyrolyzed according to the procedure summarized below in Table 5.

Example 6

Extruded tobacco tubes were pyrolyzed according to the procedure summarized below in Table 6.
The samples were removed from the furnace and placed in a desiccator containing CaSO₄. The pyrolyzed tobacco tubes maintained a static burn.

Example 7

Four sets of extruded tobacco tubes were prepared; one set from -30+40 mesh tobacco particles, a second set from -20 mesh tobacco particles, a third set from -20+30 mesh tobacco particles, and a fourth set from -20+30 mesh, recycled tobacco particles. The extruded tobacco tubes were pyrolyzed according to the procedure summarized below in Table 7.
It was determined that the pyrolyzed tobacco tubes experienced a weight loss in the range of 78% to 79%, and a dimensional decrease within the range of from about 27% to about 33%. All of the pyrolyzed tobacco tubes maintained a static burn.

Example 8

Previously pyrolyzed tobacco tubes were vacuum impregnated with a saturated solution of either KNO₃, Mg(CH₃COO)₂, FeCl₃, K₃C₆H₅O₇, FeCl₂ or MgCl₂. The impregnated pyrolyzed tubes were dried in an oven in vacuum at 50°C, and then heat treated in the Lindberg furnace described above according to the procedure summarized below in Table 8.
The salt treated, pyrolyzed tubes containing absorbed oxygen, maintained a static burn when ignited.

Example 9

Extruded tobacco tubes were prepared from tobacco material of mesh size +60. The extruded tobacco tubes had an outside diameter of 12mm, and an inside diameter of 5mm and were pyrolyzed according to the procedure summarized below in Table 9.
The pyrolyzed samples were measured and weighed and it was determined that the samples experienced an average weight loss of 73.47%, and an average shrinkage loss of 31.41%. The samples would not sustain static burning.
The following example is comparative.

Comparative Example 1

Extruded tobacco tubes were prepared from tobacco material of mesh size -20. The extruded tobacco tubes, which were 90mm in length, with an outside diameter of 12mm and an inside diameter of 10mm, were pyrolyzed inside a quartz tube in the chamber of a Lindberg 55035-A oven. The oven was equipped with one thermocouple positioned over the center of the longitudinal axis of the tube. The procedure used is summarized below in Table 10.
The pyrolyzed samples were removed from the chamber and quenched in liquid nitrogen. The samples were then weighed and measured, and it was determined that the samples experienced an average decrease in length of 31.6%, an average decrease in outside diameter of 28.29%, and an average decrease in inside diameter of 34%. The pyrolyzed samples would not sustain static burning.

Claims

A process for producing a combustible carbonized material by pyrolizing preformed ligno-cellulosic material in a non-oxidizing atmosphere,the process comprising pyrolizing a preformed article in a continuously exchanged inert atmosphere at a temperature in the rang of 800° to 1100°C for 0.5 to 3 hours, cooling the pyrolized article in the inert atmosphere at a rate of 500° to 10°C per hour to a temperature within the range of 275°C to 25°C, and then subjecting the pyrolized article to at least one additional treatment selected from oxygen absorption, water desorption, and salt impregnation with subsequent heat treatment to obtain a tasteless carbon heat source.
A process according to claim 1, characterized by adding oxygen to the pyrolized article and then, as a final step, subjecting the pyrolized article to a desiccant environment.
A process according to claim 1, characterized by contacting the pyrolized article with a salt solution comprising a salt of at least one of the cations K⁺, Fe⁺³, Fe⁺², Mg⁺², Ca⁺², drying the article at a temperature within the range of 50° to 70°C in vacuum, gradually heating the article to a temperature of about 650° C in an inert atmosphere and maintaining the article at said temperature for 5 to 60 minutes, and then cooling the article in the inert atmosphere at a rate of 500° to 10°C per hour to a temperature within the range of 275°C to 25°C.
A process according to claim 3, characterized by adding oxygen to the pyrolized article after the second cooling step.
A process according to claim 3 or 4, characterized by subjecting the pyrolized article to a desiccant environment, as a final step.
A process according to any of claims 3 to 5, characterized in that the pyrolized material is contacted with the salt solution by vacuum impregnation.
A process according to any of claims 1 to 6, characterized in that cellulosic material is selected from cardboard, paper, bamboo, oak leaves and extruded tobacco.
A smoking article comprising a substantially tubular heat source comprising heat-treated cellulose and a flavour generator disposed adjacent the mouth end of the article and comprising a substrate material containing at least one thermally releasable flavorant, characterized in that the heat source is a carbon heat source produced by a process according to any of claims 1 to 7, having a porosity sufficient to support combustion and a density such that puff-induced air flow passes through the tube.
A smoking article according to claim 8, characterized in that the substrate is selected from alumina, tobacco filler, magnesium hydroxide, zeolites, glass wool, charcoal, fuller's earth, natural clays, and activated clays.
A smoking article according to claim 8 or 9 characterized by a porous, combustible material disposed within the tube passage and having a porosity greater than the porosity of the carbon heat source.