WO1999031315A1

WO1999031315A1 - Separation and determination of cellulosic components from plant material

Info

Publication number: WO1999031315A1
Application number: PCT/GB1998/003697
Authority: WO
Inventors: Ian Geoffrey Marchmont Anderson; Mark Edwards; Philip Gordon Riby
Original assignee: British American Tobacco (Investments) Limited
Priority date: 1997-12-12
Filing date: 1998-12-10
Publication date: 1999-06-24
Also published as: AU1496799A; GB9726218D0

Abstract

A method for separating cellulosic components from, and determining cellulosic component content of, plant material. Plant material and an electromagnetic active solvent, e.g. ethanol, are heated by means of electromagnetic radiation (e.g. microwave radiation), whilst the material and solvent are in contact each with the other and are located in a closed chamber. The temperature of the solvent and the vapour pressure in the chamber are increased thus to effect solution in the solvent of non-cellulosic components of the plant material. The cellulosic components of the plant material are isolated from the solvent and the solute therein. A gravimetric determination may then be made of the cellulosic component content of the plant material.

Description

Separation and Determination of Cellulosic Components from Plant Material

The present invention relates to the separation and determination of cellulosic components from plant material, for example.

Various methods are known for the separation and determination of cellulosic components from tobacco and other plant material. These methods normally involve the use of harsh chemicals, such as strong acids, for example nitric acid. Such harsh chemicals are hazardous to both the environment and users.

Such harsh conditions have also been used for the separation and determination of other components from plant material .

There have been various attempts to develop extraction methods which operate under much milder conditions. For example, in U.S. 4,554,132 a method is disclosed for quantitatively determining volatiles, solids and solvent extractables in a sample of, for example, food products, waste products, blood and other organic materials. The method is based upon the use of solvent extraction, which eliminates the need for utilising harsh chemicals. Microwave drying of test samples to rapidly drive off moisture prior to solvent extraction and then, if necessary, again after solvent extraction is disclosed. The method is particularly directed to analysis of materials which have a high water content, which thus require the evaporation of such water to determine the solids and other materials present without removing or destroying the other materials in the process of removing the water or moisture.

Further, U.S. 5,338,557 discloses a method for extracting volatile oils from plant and animal biological matter. Microwave energy is employed to generate a temperature increase in the sample biological matter while the matter is in contact with a suitable non-aqueous organic solvent or extractant . The extractant must be a solvent which is incapable of being heated by microwave energy, that is to say, one which does not significantly absorb microwave energy, for example an alkane, e.g. hexane . Hence, differential heating between the biological matter and the extractant occurs. Heating of the biological matter causes internal glandular or vascular systems to rupture and the volatile oils contained therein to be expressed from the matter into the extractant. Preferably, the extraction is conducted under reduced pressure conditions, for example under vacuum conditions.

Both U.S. 4,554,132 and U.S. 5,338,557 disclose mild extraction processes, neither of which would efficiently effect separation of cellulosic components from plant material, for subsequent determination of the cellulosic components for example. As shown in U.S. 5,338,557, extraction of volatile oils is an extremely delicate procedure requiring minimal breakdown of the biological matter. However, during the separation of cellulosic components from plant material the plant material is substantially broken down. U.S. 4,554,132 discloses a method for use with high water content materials which requires rapid removal of water prior to solvent extraction, which water removal is achieved using microwave heating. If such solvent extraction, as disclosed in U.S. 4,554,132, were utilised for the separation of cellulosic components from plant material the process would be uneconomical and unfeasible due to the length of time required to complete such a process.

It is an object of the present invention to provide a rapid method for the separation and determination of cellulosic components from plant material, tobacco for example, without resort being had to harsh chemicals.

According to a first aspect thereof, the present invention provides a method of determination of the cellulosic component content of plant material, wherein plant material and an electromagnetic active solvent are heated by means of electromagnetic radiation, whilst said material and said solvent are in contact each with the other and are located in a closed chamber, such that the temperature of said solvent and the vapour pressure in said chamber are increased thus to effect solution in said solvent of non- cellulosic components of said plant material, the cellulosic components of said plant material are isolated from said solvent and the solute therein, and a gravimetric determination is made of the cellulosic component content of said plant material. Preferably, the heating stage occurs for a period of time sufficient to ensure that all, or substantially all, of the non-cellulosic components of the plant material go into solution in said solvent.

According to a second aspect thereof, the present invention further provides a method for separating cellulosic components from non-cellulosic components of plant material, wherein plant material and an electromagnetic active solvent are heated by means of electromagnetic radiation, whilst said material and said solvent are in contact each with the other and are located in a closed chamber, such that the temperature of said solvent and the pressure in said chamber are increased, thus to effect solution in said solvent of non-cellulosic components of said plant material, and the cellulosic components of said plant material are isolated from said solvent and the solute therein.

Preferably, the heating stage occurs for a period of time sufficient to ensure that a great majority, at least, of the non-cellulosic components of the plant material go into solution in said solvent.

As used herein the term "plant material" encompasses material from both trees and plants. Trees may be, for example, those used in the paper making and pulping industry, for example Eucalyptus. Alternatively, the plant material may be tobacco material, particularly tobacco leaf material.

The plant material may be comminuted, ground or homogenised prior to separating the cellulosic components therefrom. The term "electromagnetic active solvent" is used herein to mean a solvent which is capable of being heated upon exposure to electromagnetic radiation (that is to say capable of absorbing electromagnetic energy) . The electromagnetic active solvent may be a polar solvent, for example methanol or ethanol, which polar solvent may be an aqueous solution, for example comprising 20% water, or the polar solvent may be water per se . Alternatively, the electromagnetic active solvent may be a non-polar solvent, such as for example hexane, spiked with a small amount of either water or polar solvent. Non-polar solvents per se are not capable of being heated upon exposure to electromagnetic radiation (that is to say they are incapable of significantly absorbing electromagnetic energy) , but when spiked with a small amount of either water or polar solvent, to provide a dipole, they become capable of being heated by exposure to electromagnetic radiation. As those skilled in the art will readily appreciate, the electromagnetic active solvent may contain a mixture of more than one electromagnetic active solvent.

As will be readily apparent to those skilled in the art, the term "to effect solution", as used herein, is not limited to the physical phenomenon of solution per se but includes also the physical mechanism of the dispersal of particulate non-cellulosic components of the plant material in the solvent .

The electromagnetic radiation may be one or both of microwave radiation or radio frequency radiation. The method according to the first and second aspects of the present invention may, if necessary or if deemed appropriate, comprise a multi-stage process wherein, following the solution of the non-cellulosic components of the plant material in the electromagnetic active solvent, spent electromagnetic active solvent is replaced by fresh electromagnetic active solvent and the process is repeated. When such a multi-stage process is used, the number of replenishments of the solvent will be such as to ensure the requisite degree of separation of the cellulosic components from the non-cellulosic components.

A weak acid may be added to the electromagnetic active solvent .

The method according to the second aspect of the present invention is applicable for industrial use and may be used in continuous flow operations or continuous batch flow operations .

Heating of the plant material and electromagnetic active solvent by means of electromagnetic radiation may be combined with one or more, different mode(s) of heating, for example, conventional convection heating.

When the plant material and the electromagnetic active solvent are subjected to electromagnetic radiation the vapour pressure in the closed chamber increases and the temperature of both the plant material and electromagnetic active solvent increases. Increased vapour pressure within the closed chamber enables the electromagnetic active solvent to be heated to a high temperature whilst remaining in the liquid phase .

The chamber is preferably formed of a non-metallic material (s). A suitable material, for example, would be polyfluoranated composite materials such as those comprising Teflon™ or tetrafluoromethacrylate (TFM) which materials are capable of withstanding high pressures, such as 1600psi (1.103 KPa) . The chamber may be equipped with inlet and outlet fluid pressure locks. The term "fluid pressure locks" is used herein to mean one-way valve means which allows for the flow of plant material and solvent into and out of the chamber with maintenance of the elevated pressure within the chamber.

Rapid and efficient separation of the cellulosic components of the plant material from the non-cellulosic components of the plant material is effected with minimised energy input and under mild chemical conditions as compared with conventional, prior art cellulose separation processes.

The cellulosic components can be readily isolated from the non-cellulosic components and solvent by standard isolation techniques, such as, for example, filtration, decanting and centrifugation. The cellulosic components may undergo one or more washing steps following isolation from the non-cellulosic components such as, for example, washing to remove residual solvent. Drying of the washed cellulosic components may then be effected by conventional heating means or by electromagnetic radiation heating or by a combination thereof. Determination of cellulosic component content is effected gravimetrically . Thus, for example, one of the components, either the cellulosic component or the non- cellulosic component is weighed directly and determination of the cellulosic content of the plant material is calculated by reference to the original weight of the plant material sample. If the determination is to be conducted on a dry weight basis, drying of the original plant material sample in order to remove the moisture therefrom, may be effected by conventional heating means or by electromagnetic radiation heating or by a combination thereof.

In, for example, a continuous, industrial operation comminuted plant material may be carried in a carrier component, which carrier component may comprise the electromagnetic active solvent, through a closed chamber where the plant material and electromagnetic active solvent are exposed to electromagnetic radiation. The flow of plant material and electromagnetic active solvent/carrier through the closed chamber, is preferably regulated such that the flow of plant material and electromagnetic active solvent/carrier through the chamber is at a constant, or substantially constant, flow rate, thereby to ensure that the plant material and solvent carrier remain in the chamber for a predetermined length of time. The closed chamber in a continuous operation may be provided by a tube of a coiled configuration, wherein the material (s) constituting the tube can withstand high pressures and temperatures. A suitable material for such tube would be, for example, Teflon™. The coiled tubing providing the closed chamber may be situated within the cabinet of an electromagnetic radiation generator. A continuous operation, for example in apparatus comprising a coiled tube, makes it possible for there to be present in the electromagnetic heating zone of the system at any one time, only low amounts of electromagnetic active solvent and plant material, and therefore the risk of economic loss due to unwanted stoppages of the system is reduced.

In order that the present invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, wherein:

Figure 1 shows a flow chart of a method according to the first aspect of the present invention; and

Figure 2 shows apparatus for carrying out a method according to the second aspect of the present invention.

In Figure 1 the reference numerals indicate the following:

(1)- Grind, dry and weigh tobacco material

(2)- Place tobacco material + aqueous ethanol/acetic acid in a container (3)- Close the container and place in microwave oven (4) - Apply microwave radiation

(5) - Increase temperature of tobacco material + ethanol/acetic acid; increase vapour pressure in closed container (6) - Non-cellulosic components of tobacco material go into solution m the ethanol/acetic acid (7) - Isolate the cellulosic components from the non- cellulosic components of plant material + solvent by filtration

(8) - Wash cellulosic components with aqueous ethanol

(9) - Dry cellulosic components

(10) - Weigh cellulosic components

(11) - Incinerate (or ash) cellulosic components in an oven at 900°C, thus to remove all organic components therefrom, and then weigh the cooled residual inorganic ash. The weight of the cellulosic components (less inorganics) of the tobacco material is then calculated on a dry weight basis.

As illustrated in Figure 1, a sample of tobacco material was ground in a grinder, dried in a conventional oven and weighed (1). 0.5g of the dried, ground tobacco was placed in a container with 25ml of aqueous ethanol/aqueous acetic acid solvent (2) (60% ethanol; 20% water : 20% acetic acid), such that the tobacco was impregnated by the solvent . The container was an advanced composite container designed to withstand high temperatures and pressures, and suitable for use with microwave radiation. The container was comprised of

Teflon PFA (Teflon PFA is a trademark of the E.I. DuPont

Company) . The container was closed and placed in a microwave oven (3) . Microwave energy at 1200W (80% of oven power) and at 2450 MHz was supplied for 30 minutes (4), thus to increase the temperature of the solvent and of the tobacco material to

195°C, and thereby to increase the vapour pressure within the closed container (5) to 600 psi over a period of 15 minutes. This pressure was maintained for a further 15 minute period. All, or substantially all, of the non-cellulosic components of the plant material were dissolved in the solvent (6) . Upon completion of the microwave heating step, the container was removed from the microwave oven and the contents of the container were subject to filtration in order to isolate the cellulosic components from the solvent and the non-cellulosic components dissolved/dispersed therein (7) . The cellulosic components were then washed in aqueous ethanol (8) . The cellulosic components isolated were replaced in the container with 25ml of fresh aqueous ethanol/acetic acid solvent and the process steps 3-8 were repeated. Once more the spent solvent was replaced with fresh solvent and steps 3-8 were repeated. Thereafter the washed cellulosic components were dried in an oven (9) at a temperature of 100°C for about 2 hours until constant mass was achieved. The washed, dried cellulosic components were then weighed. Finally, the cellulosic components were incinerated (or ashed) (11) in an oven at 900°C to remove all organic components therefrom, leaving only a small amount of inorganic ash. The cooled inorganic ash was then weighed and the cellulosic component content (less inorganics) of the tobacco material was determined (10) , this being expressed as a percentage by weight .

As shown diagrammatically in Figure 2, in a continuous, industrial operation comminuted tobacco material is carried in aqueous ethanol/acetic acid solvent into and through a closed chamber 1, which chamber 1 is provided by a tube 2 of a coiled configuration. The tube 2 is made from Teflon™, in order that the tube is able to withstand high pressures and temperatures. It is arranged that the tobacco and solvent flow through the chamber 1 at a uniform flow rate, thus resulting in a constant residence time in the chamber 1. In that the tobacco particles and the ethanol solvent are in intimate contact, the solvent impregnates the particles. In the chamber 1 the tobacco and aqueous ethanol/acetic acid are exposed to microwave radiation. By means of inlet and outlet fluid pressure locks it is possible to maintain the uniform flow of tobacco and aqueous ethanol/acetic acid through the chamber 1 in conjunction with the maintenance of an elevated pressure within the chamber 1. The inlet fluid pressure lock may be a centrifugal pump 3 and the outlet fluid pressure lock may be a turbine 4. The pump 3 is driven by a motor 5 and pumps tobacco and aqueous ethanol/acetic acid from a reservoir 6 into the chamber 1. The conditions of operation are selected such as to ensure that a great majority, at least, of the non-cellulosic components of the tobacco material go into solution in the ethanol/acetic acid. The chamber 1 is situated within a microwave radiation generator cabinet 7, the configuration and dimensions of the tube 2 providing the chamber 1 being such that the tobacco and aqueous ethanol/acetic acid within chamber 1 are heated by the microwave energy. Following the microwave heating step the tobacco and aqueous ethanol/acetic acid are removed from the chamber 1 via the turbine 4. The turbine 4 may be connected to an electricity generator 8, which electricity generator 8 produces electricity which may be supplied to a microwave radiation generator and/or the motor 5 in order to supplement the electricity supply thereto from other sources. The path of the tobacco and aqueous ethanol/acetic acid may further pass through a heat exchanger 9 , such that the temperature of the tobacco and ethanol/acetic acid is reduced to about room temperature. Further processing (as denoted by reference numeral 10) of the tobacco and aqueous ethanol is conducted inter alia in order to separate the cellulosic components of the tobacco from the non-cellulosic components and the aqueous ethanol/acetic acid. The cellulosic components of the tobacco are isolated from the aqueous ethanol/acetic acid and non-cellulosic components therein via centrifugation and/or filtration. The cellulosic components are then washed with aqueous ethanol/acetic acid.

If the method is continued under the same or differing conditions for a longer period of time than is necessary to separate the cellulosic components from the plant material, there may be effected a breakdown of the cellulosic components into soluble sub-units thereof, which sub-units may comprise further carbohydrates such as sugars. Such sub- units may be isolated and determined.

Claims

1. A method of determination of the cellulosic component content of plant material, wherein plant material and an electromagnetic active solvent are heated by means of electromagnetic radiation, whilst said material and said solvent are in contact each with the other and are located in a closed chamber, such that the temperature of said solvent and the vapour pressure in said chamber are increased thus to effect solution in said solvent of non-cellulosic components of said plant material, the cellulosic components of said plant material are isolated from said solvent and the solute therein, and a gravimetric determination is made of the cellulosic component content of said plant material .

2. A method according to Claim 1, wherein said temperature of said solvent and said vapour pressure in said chamber are maintained at elevated values for a period of time sufficient to ensure that all, or substantially all, of said non-cellulosic components of said plant material go into solution in said solvent.

3. A method for separating cellulosic components from non- cellulosic components of plant material, wherein plant material and an electromagnetic active solvent are heated by means of electromagnetic radiation, whilst said material and said solvent are in contact each with the other and are located in a closed chamber, such that the temperature of said solvent and the pressure in said chamber are increased, thus to effect solution in said solvent of non-cellulosic components of said plant material, and the cellulosic components of said plant material are isolated from said solvent and the solute therein.

4. A method according to Claim 3 , wherein said temperature of said solvent and said pressure in said chamber are maintained at elevated values for a period of time sufficient to ensure that a great majority, at least, of the non-cellulosic components of the plant material go into solution in said solvent.

5. A method according to any one of the preceding claims, wherein said electromagnetic active solvent is a polar solvent .

6. A method according to Claim 5, wherein said polar solvent is any one or more of the group consisting of methanol, ethanol and water.

7. A method according to any one of Claims 1 to 4 , wherein the electromagnetic active solvent is a non-polar solvent spiked with a small amount of a polar solvent.

8. A method according to Claim 7, wherein said non-polar solvent is hexane.

9. A method according to any one of the preceding claims, wherein said electromagnetic radiation is one or both of microwave radiation or radio frequency radiation.

10. A method according to Claim 1 or 2 , or any one of Claims 5 to 9 as appended to Claim 1 or 2 , wherein prior to the making of said gravimetric determination, the prior steps of said method are repeated, in the or each repeat fresh said solvent, as a replacement for spent said solvent, being brought into contact with said isolated cellulosic components.

11. A method according to Claim 3 or 4 , or any one of Claims 5 to 9 as appended to Claim 3 or 4 , wherein the steps of said method are repeated, in the or each repeat fresh said solvent, as a replacement for spent said solvent, being brought into contact with said isolated cellulosic components .

12. A method according to any one of Claims 3 or 4 , or any one of Claims 5 to 9 and 11 as appended to Claim 3 or 4 , wherein said method is operated in continuous flow mode.

13. A method according to any one of the preceding claims, wherein a weak acid is added to said electromagnetic active solvent.

14. A method according to Claim 13, wherein said weak acid is acetic acid.