Cross-reference to Prior Applications

[0001 ] This application is based on and claims the priority and benefit of U.S. Provisional Patent Application No. 62/821 ,333 filed on 20 March 2019.

U.S. Government Support

[0002] Not Applicable

Background of the Invention

Area of the Art

[0003] The present invention is in the art of producing extracts of plant material and is more specifically addressed to an improved process for making cannabis extracts.

Description of the Background Art

[0004] The widespread legalization of medical cannabis followed by the legalization of recreational cannabis by an increasing number of U.S. states as well as foreign countries is rapidly changing how cannabis products are produced and consumed. In the 1960s when illegal cannabis first became widely popular in the U.S., the majority of cannabis consumed in the U.S. was dried herbal material brought in illegally from foreign countries. It will be appreciated that patterns of cannabis consumption vary country by country and that there are countries where cannabis had been legally consumed for centuries, if not millennia. In the 1960s, there was little, if any, quality control and the product usually contained“stems and seeds that you don’t need” (Cheech and Chong [album] 1971 ). Mexican cannabis fields, a common source of imported cannabis, were frequently sprayed with toxic paraquat and similar weed killers in an attempt to eradicate the fields to discourage cultivation of cannabis. Faced with the possibility that imported cannabis was contaminated with weed killer, domestic production (often in Northern California, Oregon and Washington) of higher quality cannabis was quickly established. It was widely believed that domestic cannabis was safer although there was no adequate quality control to ensure that the domestic product did not contain toxic pesticides just like the imported material.

[0005] Even before the trend towards legalization started in the U.S., a range of cannabis products besides smokable herbal material was being developed. Historically, cannabis resin known as‘hashish’ was a well-known product in many countries, particularly in Asia. Hashish is a yellow to brown solid that consists largely of the glandular trichomes that cover cannabis inflorescences. Virtually all of the cannabinoids produced by a cannabis plant are present in the glandular trichomes so that hashish represented a concentrated form of the active cannabis components. Traditional hashish was produced by a labor-intensive process not suitable for use in the U.S. Soon, alternative cannabis concentrates were developed to replace hashish. These concentrates were primarily extracts of cannabinoids produced by using solvents to dissolve cannabinoids and other natural products from cannabis plant material. Typically, organic solvents such as ethanol or other alcohols were used. Initially, these extracts were rather crude and contained a wide variety of natural products as well as contaminants present on or in the cannabis material as well as considerable quantities of residual organic solvents. Organic compounds such as butane, which are gases at room temperature, were adopted allowing easier removal of the solvent from the extract. It will be appreciated that butane gas can be explosive so that complex equipment is required for butane extraction processes. Liquid carbon dioxide was adopted as a non-toxic solvent although the equipment to use carbon dioxide as an extracting solvent is expensive and complex. It will be understood that each different solvent extracts a somewhat different range of compounds although all of the solvents mentioned are capable of dissolving at least some of the cannabinoids.

[0006] Cannabis extracts have been developed on a hit or miss basis. Although cannabis plants contain many different cannabinoids as well as a variety of other bioactive compounds, most early extracts were tested only to see if the extract made one “high” following consumption of the extract. Cannabis extracts may be consumed by eating or by smoking. However, the extracts are usually sticky or gummy and do not readily burn. This necessitates mixing with combustible material such as herbal cannabis for smoking purposes. However, an alternative means of consumption is to vaporize the extract using, for example, an electrically heated element. This form of consumption is known as“vaporizing” or“vaping” and is rapidly becoming the preferred way of consuming cannabis. Because no organic material is combusted, vaping is considered safer than traditional smoking: not only because there is no actual flame with the attendant danger of causing a fire, but also because the lack of combustion eliminates carbon monoxide and other harmful agents found in smoke. In theory, the vapor will contain only those constituents of the extract that are vaporized by the heating element. However, the extraction process can concentrate pesticides and other contaminants that are vaporized and inhaled during“vaping” cannabis extracts. Furthermore, the extracts may also contain a variety of organic compounds present in the plant material that may also be inhaled. Even when these other compounds do not vaporize, they often “gum up” the vaporizing mechanism and render it unusable. There is need for a simple, reproducible extraction process that yields extracts of known concentration and composition. The ideal process should produce a contaminant-free product that does not clog vaporizer mechanisms. The process should be quick, minimize the use and release of potentially toxic chemicals.

Summary of the Invention

[0007] Cold ethanol is used for producing cannabis extracts milled cannabis material. In a preferred embodiment, the milled cannabis material is packed into permeable containers (bags) which are immersed in a tank of cold ethanol. The containers are removed from the tank and solvent removed from the material and recycled to the tank as needed. Fresh containers of milled cannabis are placed in the same tank and extracted. This is repeated several times with the concentration of extracted cannabis compounds in the solvent increasing with each cycle. Next, the ethanolic extract is filtered to remove insoluble material. The filtered extract is then distilled to recover ethanol for reuse in subsequent extractions. This yields a crude cannabis oil that is distilled at reduced pressures to remove terpenoids yielding a terpenoid-free cannabis oil. Purified cannabinoids are then prepared by fractionally distilling the terpenoid-free cannabis oil. Water-soluble toxic materials can be removed from the purified cannabinoids through a salt wash. Organic-soluble toxic materials can be removed chromatographically. Some or all of the color (usually light to dark amber) can removed using additional chromatographic separation steps.

Description of the Figures

[0008] FIG. 1 is a flow diagram of the inventive process.

Detailed Description of the Invention

[0009] 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 inventors of carrying out their 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 for producing high quality cannabis extracts.

[0010] The inflorescence of the pistillate or“female” cannabis plant consists of a raceme (often with secondary and even tertiary branches) in which the actual flowers are surrounded by a complex of floral bracts and more-or-less leaf-like bracts. These bracts bear the glandular trichomes containing essentially all the cannabinoids and other active compounds. The inflorescence is colloquially known as“flower” or“buds.” While it is possible to extract the entire inflorescence, tightly packed portions of the inflorescence are sold as high-quality herbal cannabis and are generally economically more valuable. However, the consumer has come to expect high quality herbal cannabis to consist of tightly packed“nuggets” or“buds” of inflorescence rather than leaf or bract fragments. Such tightly packed portions are prepared by cutting and trimming the inflorescence. The trimming process also produces large quantities of bract fragments known as“trim.” Although trim can be smoked, it is not as desirable as“buds” so that generally trim becomes the raw material for producing cannabis extracts. Because many cannabis farmers do not have the facilities for extracting cannabinoids and other active compounds from the trim they produce, there is a need for an adaptable extraction process that can efficiently use trim, including trim collected from a large number of different growers to produce high quality, consistent extracts.

[001 1 ] A problem with prior art organic solvent extractions is that many undesirable organic compounds are dissolved (extracted) from the biomass and must be subsequently removed from the extract. In a traditional ethanol extraction of cannabis material, large amounts of chlorophyll as well as fats, waxes and other lipids can be present in the crude extract and must be removed before further processing. Such removal is frequently achieved by “winterizing” the extract, which consists of storage of the crude extract at a low temperature to allow many of the waxes and other lipids to separate out because these compounds have reduced solubility at low temperatures. Unfortunately, such low temperature separation takes a number of days and depending on how separation from the extract is achieved (e.g., by filtration) considerable quantities of desirable cannabinoids and other high-value substances may be removed from the extract by the winterization process. The current inventors have discovered that extracting the prepared trim at low temperatures with chilled ethanol (about minus 40 °C) is the target temperature with the extraction temperature never exceeding minus 25 °C) surprisingly extracts the desirable cannabinoids while dissolving few of the unwanted waxes and other lipids. So, rather than having to remove extracted waxes by means of a further winterization process, the waxes and similar contaminants are never even extracted from the biomass in the first place.

[0012] As shown in Fig. 1 , the inventive process starts by collecting trim which can come from any number of different growers. The inventive process uses approximately 1 ,000 lbs. (about 454 kg.) of trim per batch. The trim material consists of leaf and bract fragments of various sizes. An initial analysis of cannabinoid content is made so that sub-batches of about 25 bags contain approximately the same average level of THC (A ⁹ -tetrahydrocannabinol). It will be understood that modern cannabis cultivars (colloquially known as“strains”) contain high levels of THC with some cultivars producing inflorescences that contain 25% or more THC by dry weight (actually the raw plant material contains tetrahydrocannabinolic acid [THCA] which can be readily converted to THC). Although CBD (cannabidiol) and other cannabinoids can be important, THC is dominant in most cultivars so that standardizing the THC concentration of the starting material aids in standardizing the overall extraction process. The raw trim is prepare in the first step 10 by chopping (for example with a knife mill with a No. 3 screen) to produce a more uniform biomass wherein the largest particles are about 2-4 mm ² in area.

[0013] The chopped cannabis material is aliquoted at the second step 12 into cylindrical mesh filter bags having a diameter of about 30 cm and a length of about 60 cm and a mesh size of about 75-100 pm with each bag holding about 3-5 lbs. (1 .36-2.27 kg) of chopped trim. An extraction tank is filled with about 450 L of chilled ethanol (95-100% food grade ethanol) at minus 40 °C or lower. At the third step 14 eight to ten filter bags of prepared trim are immersed in the tank and allowed to soak with gentle agitation for about 5 to 25 min. with 15 min being preferred. The bags are removed from the tank and centrifuged at 100-130 RPM for about 7 min. with a rotor having a radius of about 20 in (50.8 cm) at the fourth step 16 About 50 L of ethanolic extract are recovered from the centrifugation for each batch of eight bags. The centrifuged bags are then opened, and the extracted trim is discarded as waste material. The extraction process removes virtually all of the cannabinoids; analysis shows that the waste material contains less than 1 .5% by weight cannabinoids whereas the starting trim material contains at least 25% cannabinoids by weight.

[0014] While the extracted bags are being centrifuged, a fresh set of eight to ten trim-filled bags are immersed 14 in the tank and the soaking process is repeated. When those bags are removed for centrifugation, ethanol from the centrifugation of the first set of bags is added to the tank to maintain the ethanol level in the extraction tank. Small amounts of additional chilled ethanol may be periodically added to the tank, as necessary, to make up for ethanol that evaporates or cannot be easily centrifuged from the extracted trim. This sequence is continued until up to about 1 ,000 lb. (about 454 kg) of material have been processed yielding about 900 to 1 ,100 L of ethanolic extract. The crude extract is then filtered at the fifth step 18 through a lenticular filter or a filter sack having a pore size of about 1 pm. Optionally, colored impurities can be reduced by passing the filtered crude extract though a short column containing about 20 L of activated carbon to yield filtered decolorized crude extract.

[0015] The majority of the ethanol solvent is then recovered for reuse in the sixth step 20 Recovery can be achieved by using 20 L rotary evaporator, a 75 L falling film evaporator or similar devices. The number, type and size of the evaporator can be selected according to desired rate of throughput. The ethanol solvent may also contain terpenes or similar volatiles extracted from the cannabis material. Multiple distillation steps can be used to remove such volatiles. Removal of the majority of the ethanol from the extract yields crude cannabis oil. Depending on the mix of cultivars in the trim between about 16 and 30 g of crude oil can be recovered from each liter of ethanolic extract. The process yields between about 60 and 80 g of crude oil per kilogram of trim processed. [0016] In the seventh step 22 removes the terpenes and terpenoids. These compounds are more volatile than the cannabinoids and are removed first so there is no inadvertent contamination of the cannabinoids in subsequent steps. The terpenes and terpenoids are removed by short path distillation at a reduced pressure. The use of a reduced pressure for distillation causes the terpenes and terpenoids to boil at lower temperatures which allows one to shorten the time and temperature to which the crude oil is exposed thereby limiting thermal decomposition of the cannabinoids. Typically, the crude cannabis oil contains about 6-15% (depending on the mixture of cultivars that provide the trim) by weight terpenes/terpenoids as determined by weighing the recovered terpenes/terpenoids. Distillation is carried out on about 12 L of crude oil at a time at reduced pressure (about 0.1— 0.5 Torr = 13.3— 66.7 Pa) using temperatures up to about 200 °C with a condenser temperature of OTT The crude oil is first heated to about 50 °C and after any vigorous boiling subsides, the temperature is raised by 5°C. The temperature is increased by 5°C increments (waiting for vigorous boiling to subside at each step) until a maximum temperature of about 200 °C is reached. The entire process takes less than about one hour. It will be appreciated that during this heating and distillation process decarboxylation of THCA to THC also takes place. This step yields terpene-free crude oil.

[0017] The terpene-free crude oil is then fractionally distilled in the eighth step 24 to separate the various cannabinoids using a fractionating distillation column or distilled using a wiped film evaporator at a reduced pressure below about 0.005— 0.03 Torr (about 0.667— 3.99 Pa). Feed temperature for the wiped film evaporator is about 100Ό to ensure that the oil flows. The use of a wiped film evaporator is preferred because it limits the amount of time that the crude oil is exposed to elevated temperatures. It will be appreciated that THC distills at a lower temperature than other major cannabinoids so that the distillation temperature, the condenser temperature and the level of reduced pressure can be manipulated to separate THC from the other cannabinoids. Under the above-conditions THC distills at a temperature of about 175 °C with a condenser temperature of 90 Ό The THC fractions are light yellow to gold in color while the higher boiling fractions are darker red-amber in color and may represent as much as 10- 15% (by weight) of the cannabinoids. As compared to the starting material, the process recovers between about 96-99% of the cannabinoids. Recovery of THC is 88-94% with 99% purity. Many modern cannabis cultivars produce primarily THC or THC and CBD so that these compounds are generally the desired end products of the purification process. However, the distillation process can readily be adjusted to separate other cannabinoids.

[0018] Depending on the source trim, there may be some pesticides and other potentially toxic materials in the extract. The water-soluble toxic material are eliminated in step 26 by subjecting the purified cannabinoid fractions to repeated water washes-salt water (brine) washes being preferred. For brine washes 7.5-15L of an approximately 0.026% (by weight) sodium chloride solution is used to wash each 5-10L of purified fractions diluted 50:50 with solvent (hexane and/or heptane). Organic solvent dilution, while not essential, makes it easier to mix the cannabinoids with water. It will be understood that other ionic salt solutions can be readily substituted for the sodium chloride solution. The water-organic mixture is stirred or shaken thoroughly and then allowed to phase separate. In most cases, the initial water washes will be somewhat to strongly colored. The wash water is drawn off and the wash is repeated until the aqueous phase is essentially colorless. This can take up to about 26 wash cycles. Chromatographic separation can be substituted for the water wash

[0019] Organic soluble pesticides or other toxic materials are removed in step 28. The washed organic solution (from step 26) is subjected to column chromatography on activated magnesium silicate (e.g., MagSil-PR or Florisil®, trademark of US Silica) or similar chromatographic media to remove organic soluble contaminates. Such chromatographic purification ensures that the final product meets all regulations concerning pesticide presence.

[0020] Additional chromatographic steps 30 can be inserted to remove colored components to produce an essentially colorless product 32 although such steps results in some loss (as much as 10-12% of THC). Following the purification steps the organic solution is subjected to distillation to remove the added solvent using the same methods as those used to remove ethanol from the crude extract.

[0021 ] 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 could be configured without departing from the scope of 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.