WO2020252586A1

WO2020252586A1 - Method for producing plant extracts

Info

Publication number: WO2020252586A1
Application number: PCT/CA2020/050850
Authority: WO
Inventors: Lawerance Lincoln JOHNSON
Original assignee: Johnson Lawerance Lincoln
Priority date: 2019-06-20
Filing date: 2020-06-19
Publication date: 2020-12-24

Abstract

Plant extract is produced without immersing plant matter in an extraction solvent for an extended period. Plant matter is milled to into small pieces of uniform size and spread into a uniform and relatively thin layer over a porous support such as a screen or filter and very briefly subjected to contact with an appropriate solvent. Effective liquid alcohols include methanol, ethanol, propanol, isopropanol and butanol. Solubility is controlled by modifying solvent temperature. Uniform application of solvent is attained by spraying the solvent over the layer of plant material. The rate of solvent movement through the plant material is accelerated by applying a force across the layer; either a pressure differential is employed or centrifugal force is used to force the solvent through the plant material.

Description

METHOD FOR PRODUCING PLANT EXTRACTS

Cross-reference to Prior Applications

[0001 ] This application is based on and claims priority and benefit of U.S. Provisional Patent Application Serial No. 62/864,225, filed 20 June 2019.

U .S. Government Support

[0002] Not applicable.

Background of the Invention

Area of the Art

[0003] The present invention is in the area of secondary products and is more specifically directed to an improved device and method for producing plant extracts.

Description of the Background

[0004] Extracts can be made from a wide variety of plant matter and used for a variety of purposes, including but not limited to culinary, cosmetic, medicinal, or recreational purposes. Certain types of extracts, for example those made from spices and herbs, are often used to flavor and even preserve foods items. Medicinal extracts, for example those made from ginseng, are used in traditional medicine and have historically been used for alleviating medical symptoms. Many important drugs in Western medicine have been isolated from traditional medical extracts such as digitalis and related cardiac drugs from foxglove ( Digitalis purpurea L) and reserpine (one of the first effective treatments for hypertension from snakeroot ( Rauvolfia serpentina (L.) Benth. ex Kurz)). Other plant extracts, including those made from Cannabis sativa L, may be used in medicinal preparations, in food and beverages, and also be used recreationally in various formulations such as tinctures and currently as liquids in personal vaporizers (AKA "vape pens"). In the past few years, cannabis extracts have seen a rapid rise in popularity in the United States as a result of legalization of cannabis at the state level and the passage of the Agriculture Improvement Act of 2018 ("Farm Bill of 2018") which has legalized the cultivation of industrial hemp.

[0005] While methods for producing specific plant extracts vary depending on the species of plant and type of plant material that is subjected to extraction, typical methods involve immersing plant material in an extraction solvent for a significant length of time, during which chemical compounds in the plant material dissolve into the extraction solvent. Many plant extracts are then used directly as crude extracts. Perhaps the most well recognized of such "crude extracts" are coffee or tea where hot water is used to extract biologically active compounds (caffeine and theophylline, respectively) as well as various flavor components. Extracts such as coffee or tea are instructive of the important aspects of extraction. These extracts are made using hot water because the active components in coffee and tea are not appreciatively soluble in cold water. Generally, increasing the temperature of the extraction solvent increases the solubility of compounds from plant material. In making coffee or tea one does not use whole coffee beans or tea leaves. Generally, it is important to grind or mill the plant material to increase the surface area of the plant material exposed to the solvent. Different plant components have different solubilities in a specific solvent, so that solvent choice, particle size of the extracted plant material as well as time and temperature of the extraction all have important effects on the final extract. Excessive milling of coffee beans or excessive extraction ( e.g ., with a device such as a coffee percolator) results in a bitter product (excessive extraction of tannins) or even a somewhat unpalatable brew containing obvious films of coffee oil. Similarly, the temperature of the extraction can be critical, and coffee and tea aficionados often insist on specific water temperature for making their beverages. Time, temperature and plant material particle size are important to the quality of plant extracts particularly where there is a need to differentially extract compounds from the plant material. These factors apply no matter which solvent is used although the solubility of a given compound may vary widely depending on the solvent used.

[0006] In the case of extracts such as coffee or tea the crude extract is used directly. However, in many cases a botanical extract is then purified to isolate the desired components and separate out the undesirable plant compounds that are also present in the extract. In many cases, the solvent itself must be removed before the extracted components can be used. Simple immersion extraction, such as the use of a tea bag to make tea, can present significant technical drawbacks. One such drawback is that the transfer of specific chemical compounds from the plant matter into the extraction solvent can only be crudely controlled and undesirable components may be readily co-extracted into the solvent. For example, immersing cannabis plant material in an organic extraction solvent tends to result in an undesirable extraction of chlorophyll and fats, waxes, and other lipids from the cannabis. The chlorophyll and lipids must then be removed from the cannabis extract in subsequent processing steps. Any such subsequent steps increase both the time and cost needed to produce a commercially valuable cannabis extract. While the extraction of undesirable compounds can be reduced to some extent in immersion-based extraction methods by adjusting the conditions {e.g., solvent temperature and extraction time) under which an extraction is carried out, those adjustments are typically inadequate to both ensure complete extraction of the desired compounds and to eliminate the need to for subsequent processing to remove undesirable compounds from the extract. [0007] There is accordingly a need for a method to produce plant extracts that does not result in extraction of undesirable components as often results from extended immersion of plant matter in an extraction solvent.

Summary of the Invention

[0008] The present invention allows the production of a plant extract without immersing plant matter in an extraction solvent for an extended period. A quantity of plant matter is preferably milled to into small pieces of uniform size. The milled plant matter is spread into a uniform and relatively thin layer and very briefly subjected to contact with an appropriate solvent. A wide variety of hydrocarbon solvents can be used in the inventive process. This includes aliphatic as well as aromatic hydrocarbon liquids (or liquified gases) and alcohols and ketones. Effective liquid alcohols include methanol, ethanol, propanol, isopropanol and butanol as well as other alcohols, and mixtures of these. Effective liquid alkanes include pentane, heptane and hexane as well as other aliphatic and aromatic liquid hydrocarbons, and mixtures of these. Depending on miscibility, the characteristics of the solvent can be modified by addition of more polar compounds such as water. The solvent is chosen so that the desired compounds are the most soluble. Under these conditions, contact time with the solvent is so brief that only the most soluble compounds are extracted. Solubility can be controlled by modifying solvent temperature. Generally, the usable temperature range is between about - 80°C and the flash point of the solvent (e.g., 16.6°C for pure ethanol). Where undesired compounds are more soluble than the desired compounds, it is possible to pre-extract using a different solvent or solvent temperature to remove those undesirable compounds before the primary extraction.

[0009] Conceptually the inventive process consists of spreading the properly milled plant material (e.g., uniform particle size achieved, for example, a mill or similar device) into a uniform and relatively thin layer over a porous support such as a screen or filter which retains the plant material while allowing the solvent to pass through. Generally, the ideal particle size falls in the range of about 100mpi to about 5,000 mh\. The plant biomass can range from dry (desiccated) material to fresh frozen plant material. The amount of water in the plant material should be considered in selecting the solvent. An aliquot of chosen solvent at a predetermined temperature is rapidly and uniformly applied to the plant material and rapidly forced through the layer of plant material so that the solvent contacts the plant material for a brief and controlled period of time. Uniform application of solvent can be attained in several ways such as controlled drenching. The present inventor has found that spraying the solvent over the layer of plant material is an expeditious way of ensuring rapid and uniform exposure of the plant material to the solvent. Applying a pressure differential or other force across the plant material allows the time of solvent contact to be controlled to be sufficiently brief. For example, the porous support can be disposed to separate two chambers and the air pressure in the chamber containing the plant material can be adjusted to be higher than the pressure in the adjacent chamber. The rate of solvent movement through the plant material is then proportional to the pressure differential.

[0010] Fig. 1 shows a diagrammatic representation of an embodiment of the invention wherein pressure differential— such as an air pressure differential is used to control the rate of solvent movement through the material to be extracted. A vessel 10 is divided into an upper portion and a lower portion by a porous support 14 (e.g., a screen) upon which is deposited a thin layer 16 of plant material milled to relatively uniform particle size. A reagent input pipe 18 is used to pump solvent into the vessel 10. The reagent input pipe 18 has a terminal spray nozzle (not shown) which produces a fine spray 22 of solvent which strikes the layer 16 of plant material. The solvent penetrates the layer 16 and is removed through exit pipe 12. A gas input pipe 20 is used to maintain the pressure in the upper chamber above that in the lower chamber so the sprayed solvent rapidly penetrates the layer of plant material 16. It will be understood that by controlling the pressure differential, the rate of solvent spraying, the solvent temperature, and the thickness of the layer 16, the extraction process can be very carefully controlled. It is often advantageous to use an inert gas such as nitrogen to pressurize the vessel 10 to avoid oxidation of biomolecules in the layer of plant material 16. It is also possible to control the rate of solvent flow through the layer 16 by subjecting the lower chamber to a reduced pressure (vacuum). Generally, this reduced pressure approach is not preferred because of the solvent vapors that must be pumped from the chamber and must be kept from reaching the vacuum pump or other source of reduced pressure. As detailed below application of centrifugal force is presently the preferred method of moving the extraction solvent through the plant material.

Description of the Figures

[001 1 ] FIG. 1 shows a diagrammatic representation of a differential pressure embodiment of the invention; and

[0012] FIG. 2 shows a diagram of the preferred centrifuge embodiment of the invention.

Detailed Description of the Invention

[0013] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide a method to make improved cannabis extracts. [0014] The preferred method of applying force across the layer of plant material is to use centrifugal force. Essentially, the plant material is subjected to centrifugation, during which it is washed with an extraction solvent sprayed on the biomass layer. Because different compounds are preferentially extracted at different solvent temperatures and solvent dwell times, the residence time and temperature of the extraction solvent on the biomass can adjusted to maximize extraction of the desired compounds during short residence time of the solvent on the plant material while minimizing extraction of undesirable compounds. Fig. 2 shows a diagrammatic representation of the centrifugal extractor as seen from above. The rotor of the centrifuge consists of a porous (e.g. screen) barrier 24. In one embodiment this screen barrier is enclosed by a continuous torus shaped rotor. As in the typical centrifuge, the rotor is enclosed by a chamber within a cabinet and mechanically coupled to a motor which causes the rotor 26 to rotate as is suggested by the arrow in the drawing. A uniform layer 26 of plant material is deposited upon the porous barrier 24. The milled plant matter may be processed in batches of about one kg. A batch of milled plant matter is loaded into a centrifuge using a feeding device.

[0015] If loose plant material is introduced into the spinning centrifuge, it will rapidly become deposited as a uniform layer on the porous barrier 24. A plumbing system (not shown) conducts the solvent into the centrifuge where a nozzle 28 sprays the solvent onto the plant material layer 26 as it moves past, thereby ensuring uniform application of the solvent. The centrifugal force causes the solvent to move rapidly through the plant material and the porous barrier 24 where it falls to the bottom of the chamber and is collected. Multiple rounds of extraction may be carried out using the same batch of solvent to increase the extraction of desired chemical compounds from the milled plant material layer. The centrifuge includes a scraper assembly, which removes the milled plant material from the basket assembly after centrifugation; and a receiver hopper, in which the milled plant material removed by the scraper assembly can be collected. Following extraction, the solvent may be recovered for reuse. Residence time of solvent on the plant material is controlled by the thickness of the plant material layer, the rate at which solvent is sprayed and the strength of the centrifugal force. If the spraying rate and layer thickness remain constant, increasing the centrifugal force by increasing the rotation speed of the rotor decreases residence time of the solvent on the plant material layer.

[0016] In one embodiment the centrifugal extractor is accelerated to generate a relative centrifugal force of 1 ,000-6,000 g. Depending on the desired dwell time of the solvent and plant materials, useful centrifugal forces range between about 600 g and 8,000 g. It is important to distribute the loaded plant material into a uniform layer that covers the inner surface of the rotating basket. It is possible to preload the basket before the centrifugation begins; alternatively, the milled plant material can be added to the spinning device. While the basket spins, an extraction solvent is sprayed onto the milled plant matter layer by one or more pipes. The extraction solvent may be a non-polar solvent, such as a liquid hydrocarbon, or a polar solvent, such as an alcohol, ketone or water-ethanol mixture. As the plant material is spun at high speed in the centrifugal extractor, the residence time of the extraction solvent sprayed on the milled plant matter is controlled by the amount of centrifugal force, the thickness of the plant material layer and the rate of solvent addition. The extraction solvent passes through the plant material layer and the porous basket and leaves the centrifugal extractor through the liquid exit opening.

[0017] Spraying the extraction solvent onto the milled plant matter layer while centrifugal force is applied ensures that the residence time of the extraction solvent {i.e., the duration during which it is in contact with the milled plant matter) is controlled and is very short. Where the milled plant matter is subjected a relative centrifugal force of 1 ,000 g, the residence time of the extraction solvent may be in the order of 10 ms. A short residence time allows for heightened control over the extraction of compounds from the milled plant matter to the extraction solvent. Because some compounds within the milled plant matter are dissolved by the extraction solvent essentially immediately upon contact with the solvent while other compounds dissolve more slowly, the short residence time allows the extraction process to "select" for compounds in the former category. In cannabis, for example, cannabinoid compounds, such as Tetrahydrocannabinolic acid (THCA), Cannabidiolic acid (CBDA), Cannabigerolic acid (CBGA), Cannabichromenic acid (CBCA), and their decarboxylated forms A9-tetrahydrocannabinol (THC), Cannabidiol (CBD), Cannabigerol (CBG), and Cannabichromene (CBC) are quickly dissolved by an appropriate extraction solvent while undesirable substances, such as chlorophyll, waxes and plant lipids, are less soluble and extract more slowly. When an extraction solvent is applied to the cannabis with a short residence time, cannabinoids are selectively extracted from the cannabis by the extraction solvent.

[0018] The temperature of the extraction solvent may be adjusted to achieve further control over which compounds are transferred from the milled plant matter into the extraction solvent. For example, the solubility of chlorophyll in ethanol is limited at -60°C, such that milled plant matter can be in contact with ethanol for several minutes before chlorophyll is significantly extracted (i.e., dissolved) by the ethanol. At -67°C, the solubility of chlorophyll in ethanol is essentially zero— i.e., no extraction of chlorophyll by the ethanol will occur even after extended contact of the milled plant matter with the ethanol. [0019] When extraction is complete, the depleted milled plant matter, commonly known as "cake," can be cleared from the basket assembly by an integral scraper assembly. The cake is then collected in the receiver hopper and may then be discarded.

[0020] In some cases, it is preferable to "recycle" the extraction solvent through the washing pipe, such that a given volume of extraction solvent undergoes multiple "rounds" of spraying onto the milled plant matter. Each round of spraying results in the extraction of an additional quantity of compounds from the milled plant matter by the extraction solvent. Recycling the extraction solvent allows a larger quantity of compounds to be extracted by the extraction solvent from the milled plant matter. It will be understood that under specific temperature and solvent conditions a specific amount of solvent must be flowed through the plant material to ensure complete extraction of the desired compounds. Generally, the needed amount of solvent range from about 1 L/kg to about 30 L/kg of biomass.

[0021 ] One embodiment of the device employs two tanks of solvent. The first tank is the "recycle" tank in which the dissolved level of cannabinoids is fairly high. The second tank is a "rinse" solvent which is not recycled and is used only as a rinse after the majority of the cannabinoids have been removed by the "recycle" solvent. After the rinse, the centrifuge spins the last bit of solvent out of the biomass. This is illustrated in Table 1 , below.

[0022] Table 1 : Effect of the rinse on cannabinoid content.

[0023] To reduce the wastage of extraction solvent, additional steps can be carried out to separate extracted compounds from the extraction solvent, such that the extraction solvent can be used to extract a new batch of milled plant matter. For example, extraction solvent, containing the extracted plant components, is collected from the liquid exit opening of the centrifugal extractor; the extraction solvent is then filtered to remove any residual milled plant matter that may be present. Typically, up to three successive rounds of filtration are preferably carried out using plate-style filters with pore diameters of 25 pm, 5 pm, and 0.45 pm, respectively. The extraction solvent can then be recovered by distillation, membrane filtration or any other technique that separates the solvent from the extracted compounds.

[0024] The following claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the just- described preferred embodiment can be configured without departing from the scope of the invention and that the illustrated embodiment has been set forth only for the purposes of example and that should not be taken as limiting the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

What is claimed is:

1 . An improved method for producing a plant extract comprising the steps of:

distributing plant material in a layer on a porous support;

depositing a solvent on the layer while applying a force to accelerate movement of the solvent through the layer and the porous support; and

collecting the solvent that moves through the porous support to yield a plant extract.

2. The method of claim 1 , wherein the force is generated by making air pressure on a first surface of the porous support upon which the layer is disposed higher than air pressure on a second surface of the porous support opposite the first surface and wherein the force accelerates movement of the solvent through the layer and the porous support.

3. The method of claim 1 , wherein the force is a centrifugal force generated by spinning the porous support in a centrifugal extractor.

4. The method of claim 1 , wherein the solvent is deposited by spraying.

5. The method of claim 1 , wherein the solvent is chilled.

6. The method of claim 1 , wherein the extraction solvent is a hydrocarbon.

7. The method of claim 6, wherein the hydrocarbon is an alcohol or a ketone.

8. The method of claim 7, wherein the hydrocarbon is an alcohol or a ketone.

9. The method of claim 8, wherein the hydrocarbon is selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol and mixtures thereof.

10. The method of claim 7, wherein the hydrocarbon is selected from the group consisting of pentane, heptane, hexane and mixtures thereof.

1 1 . A centrifugal extractor for producing a plant extract comprising: a porous support for supporting a layer of plant material;

a motor in mechanical communication with the porous support for rotating the porous support;

a sprayer for spraying a solvent onto the layer while the porous support rotates, thereby applying centrifugal force to accelerate movement of the solvent through the layer and the porous support; and means for collecting the solvent that moves through the porous support wherein the collected solvent is the plant extract.

12. The method of claim 1 1 , wherein the centrifugal force is between about 1 ,000 and 6,000 g.