An extraction process for plant essential oils

Abstract

This invention belongs to the field of plant component extraction technology, specifically relating to an extraction process for plant essential oils. The hydrogen bond acceptor used in this invention contains two hydroxyethyl groups, forming a eutectic solvent with a high-density, three-dimensional hydrogen bond network with a polycarboxylic acid hydrogen bond donor. This solvent possesses both strong cell wall disruption ability and high affinity for essential oils. This invention offers advantages such as high yield, mild extraction conditions, short extraction time, and simple operation, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of plant component extraction technology, specifically relating to an extraction process for plant essential oils. Background Technology

[0002] Plant essential oils, botanically known as aromatic oils or essential oils, and chemically and pharmaceutically as volatile oils, are secondary metabolites of plants. They are composed of simple compounds with relatively small molecular weights and are mainly found in the glandular hairs, oil cavities, and secretory cells of plants. They are typically extracted from plant organs such as flowers, leaves, bark, roots, and fruits through physical methods such as distillation, extraction, adsorption, or pressing to obtain volatile, aromatic, oily substances. Because the substances obtained through these physical methods contain almost all the essence of the plant, they are called plant essential oils.

[0003] Plant essential oils are widely distributed in tropical and subtropical aromatic plants, with particularly rich content found in plants of the Asteraceae, Zingiberaceae, Pinaceae, Magnoliaceae, Lauraceae, Dipterocarpaceae, Rutaceae, Apiaceae, Lamiaceae, Apocynaceae, Amaryllidaceae, Rosaceae, Piperaceae, and Oleaceae families. Due to differences in the growing environment, cultivation techniques, and genetic conditions of aromatic plants, essential oils extracted from different plants vary greatly in aroma, composition, content, biological activity, and uses. Currently, over 3,000 types of essential oils have been discovered in nature, widely used in the pharmaceutical, food, fragrance, daily chemical, and cosmetic industries. Current extraction methods for plant essential oils mainly include pressing, steam distillation, organic solvent extraction, and supercritical fluid extraction.

[0004] Pressing is the oldest method for obtaining essential oils. It involves using mechanical pressure to squeeze the oil out of plant tissue, then allowing it to settle and separate into layers, or using a centrifuge to separate the oil into a crude product. This process does not require heating and can be carried out at room temperature, avoiding the decomposition of heat-sensitive components. However, essential oils obtained using this method usually contain impurities such as chlorophyll, cell tissue, and mucilage, resulting in lower purity. Furthermore, pressing is difficult to completely extract the volatile oils from the plant, so the residue after pressing needs to be steam distilled to extract as much of the essential oil as possible.

[0005] Steam distillation is the most commonly used traditional method in industry. Its principle involves azeotropic distillation of plant materials with water, using steam to carry away volatile essential oils. After condensation and separation, the essential oil is obtained. This method is simple to operate and has low equipment costs. However, steam distillation mainly relies on the azeotropic carrying effect of water molecules on the essential oil; the cell walls are not sufficiently broken down, making it difficult to completely release the essential oil from within the cells, resulting in a low extraction rate. For example, CN118006392A discloses a method for extracting rose essential oil using ultrasound-assisted steam distillation. Rose petals are mixed with water, and the resulting premix is ​​then ultrasonically mixed with sodium chloride before being distilled and separated into oil and water to obtain rose essential oil. However, the highest yield of rose essential oil obtained by this method is only about 0.8%, which needs further improvement.

[0006] Organic solvent extraction typically uses non-polar solvents such as petroleum ether and n-hexane, offering advantages such as high extraction efficiency and short processing time. However, organic solvents are volatile, flammable, and explosive, posing safety hazards. More importantly, the problem of organic solvent residue is difficult to completely resolve, and residual solvents may affect the quality and safety of essential oils, failing to meet the green and environmentally friendly requirements of natural fragrance products. This is especially true in the cosmetics and pharmaceutical fields, where high purity is required, where such methods are strictly limited.

[0007] Supercritical fluid extraction, especially supercritical fluid extraction Extraction has attracted widespread attention due to its advantages such as low operating temperature, no solvent residue, and good selectivity. This method can obtain high-quality essential oils, but supercritical extraction equipment requires large investments and has high operating costs, and the operating conditions are harsh (high pressure), making it difficult to promote and apply in small and medium-sized enterprises, thus limiting its industrial-scale popularization.

[0008] In recent years, deep eutectic solvents (DES) have shown great potential in the field of natural product extraction as a novel green solvent. DES is a eutectic mixture formed by hydrogen bond acceptors (such as quaternary ammonium salts and ionic liquids) and hydrogen bond donors (such as carboxylic acids, polyols, and urea) through hydrogen bond interactions. It possesses advantages such as low melting point, extremely low vapor pressure, high designability, and good biocompatibility. DES can effectively disrupt plant cell walls through hydrogen bonding, improving the extraction rate of target components. Its non-volatile nature avoids solvent residue problems, making it an ideal alternative to traditional organic solvents. However, existing DES systems for plant essential oils have insufficient affinity for some non-polar essential oils, resulting in low extraction efficiency. Furthermore, the strong hydrogen bonding between DES and essential oils makes it difficult to effectively separate the essential oil from the solvent after extraction, often requiring complex back-extraction or high-temperature distillation operations, which can easily lead to essential oil loss and damage to heat-sensitive components.

[0009] Therefore, it is of great significance to develop a green extraction process that can efficiently extract plant essential oils, achieve gentle separation of essential oils and solvents, and ensure the quality of essential oils. Summary of the Invention

[0010] To address the problems of low extraction rate and harsh extraction conditions in existing technologies, this invention aims to provide a new extraction process for plant essential oils. To achieve the above objective, this invention adopts the following technical solution: An extraction process for plant essential oils includes the following steps: Step 1): Mix the hydrogen bond acceptor and the organic acid hydrogen bond donor evenly and heat to form a clear and transparent viscous liquid. Then add deionized water to obtain an aqueous eutectic solvent and seal for later use. Step 2): Aromatic plants are added to deionized water and then pulverized to obtain a slurry; the slurry and the aqueous eutectic solvent obtained in step 1) are added to a reactor, ultrasonically extracted, filtered, and the filtrate is collected; Step 3): Add deionized water to the filtrate obtained in Step 2), and steam distill the diluted mixture to obtain an oil-water mixture. Separate the oil layer, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain plant essential oil. The structure of the hydrogen bond acceptor in step 1) is as follows: .

[0011] In some embodiments, the organic acid in step 1) is selected from one or more of citric acid, malic acid, lactic acid, oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, succinic acid, acetic acid, and propionic acid.

[0012] In some implementations, the molar ratio of hydrogen bond acceptor to hydrogen bond donor in step 1) is 1:(2~6); the heating temperature in step 1 is 60~90°C.

[0013] In some implementations, the water content of the aqueous eutectic solvent in step 1) is 20wt% to 40wt%.

[0014] In some implementations, the aromatic plant in step 2) is rose petals, camphor leaves, lavender, jasmine petals, mint, cloves, or cinnamon.

[0015] In some implementations, the mass-to-volume ratio of the aromatic plant to deionized water in step 2) is 1 g : (1~1.5) mL; and the volume ratio of the slurry to the aqueous eutectic solvent is 1 : (2~10).

[0016] In some implementations, the ultrasonic extraction in step 2) is performed at a temperature of 40-70°C, a power of 100-200W, and a time of 20-60 minutes.

[0017] In some implementations, the volume ratio of the filtrate to deionized water in step 3) is 1:(1~3).

[0018] In some embodiments, the method for preparing the hydrogen bond acceptor in step 1) includes the following steps: 1,4-bis(1-imidazolium)butane and 2-chloroethanol were dissolved in an organic solvent, heated to 50-80°C and stirred to react. After the reaction was completed, the mixture was cooled to room temperature. Then, diethyl ether was added to the reaction mixture to produce a precipitate. The precipitate was filtered and the filter cake was dried under vacuum to obtain a hydrogen bond acceptor. The reaction formula is: .

[0019] In some embodiments, the organic solvent is selected from one or more of DMF, DMSO, toluene, acetone, THF, and ethyl acetate; the molar ratio of 1,4-bis(1-imidazolium)butane to 2-chloroethanol is 1:(2~5). Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The hydrogen bond acceptor used in this invention contains two hydroxyethyl groups, forming a low-melting solvent with a high-density, three-dimensional hydrogen bond network with the polycarboxylic acid hydrogen bond donor. It has both strong cell wall breaking ability and high affinity for essential oils. In addition, this invention also utilizes the mechanism of water molecules competing for hydrogen bonds to achieve efficient release and recovery of plant essential oils, avoiding the losses of traditional separation methods.

[0020] 2) The yield of rose essential oil in this invention is as high as 0.18%, which is superior to existing extraction methods (such as CN118006392A). It also has the advantages of mild extraction conditions, short extraction time, and simple operation, making it suitable for industrial production. Detailed Implementation

[0021] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0022] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The invention is further described below by way of specific embodiments. All chemical reagents used in the embodiments of this invention, unless otherwise specified, are obtained through conventional commercial means.

[0023] The yield of plant essential oil is calculated as: (mass of extracted plant essential oil / wet weight of rose petals) x 100%. Preparation Example 1: Preparation of hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2

[0024] Dissolve 0.1 mol of 1,4-bis(1-imidazolium)butane and 0.4 mol of 2-chloroethanol in... N , N - Dimethylformamide (100 mL) was heated to 60 °C and stirred for 48 h. After the reaction was completed, the mixture was cooled to room temperature, and then diethyl ether (500 mL) was added to the reaction mixture, resulting in a precipitate. The precipitate was filtered, and the filter cake was dried under vacuum to obtain the hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2, with a yield of 78.5%.

[0025] 1 H-NMR (600 MHz, DMSO- d 6): δ(ppm): 9.32(s, 2H), 7.85(d, 2H), 7.79(d,2H), 5.22-5.16(m, 2H), 4.28(t, 4H), 4.23(s, 4H), 3.77-3.70(m, 4H), 1.82(s,4H).

[0026] Example 1 An extraction process for plant essential oils includes the following steps: Step 1): Add hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 and hydrogen bond donor citric acid to the reactor at a molar ratio of 1:3. Heat to 80°C and stir magnetically for 1 hour until the system becomes a clear and transparent viscous liquid. Keep the temperature at 80°C and slowly add the calculated amount of deionized water while stirring, so that the mass fraction of water in the final system is 20 wt%. Continue stirring for 15 minutes until the system is homogeneous, and obtain an aqueous eutectic solvent. Seal and store for later use. Step 2): Take 100 g of freshly picked Damask rose petals, add 100 mL of deionized water and crush them to obtain rose petal slurry; add the above rose petal slurry and 500 mL of the aqueous eutectic solvent obtained in step 1) into the reactor, and extract by ultrasonication for 30 min at 50℃ and 120W, filter and collect the filtrate. Step 3): Add 1000 mL of deionized water to the filtrate obtained in Step 2), transfer the diluted mixture to a steam distillation apparatus for steam distillation, and obtain an oil-water mixture distillate. Separate the oil layer using a separatory funnel, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain 0.18 g of plant essential oil, with a yield of 0.18%.

[0027] Example 2 An extraction process for plant essential oils includes the following steps: Step 1): Add the hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 and the hydrogen bond donor malic acid to the reactor at a molar ratio of 1:4. Heat the reactor to 70°C and stir magnetically for 1 hour until the system becomes a clear and transparent viscous liquid. Keep the temperature at 70°C and slowly add the calculated amount of deionized water while stirring, so that the final water mass fraction in the system is 30 wt%. Continue stirring for 15 minutes until the system is homogeneous, and obtain an aqueous eutectic solvent. Seal and store for later use. Step 2): Take 100 g of freshly picked Damask rose petals, add 100 mL of deionized water and crush them to obtain rose petal pulp; add the above rose petal pulp and 600 mL of the aqueous eutectic solvent obtained in step 1) into the reactor, and extract by ultrasonication at 60℃ and 150W for 20 min, filter and collect the filtrate. Step 3): Add 1000 mL of deionized water to the filtrate obtained in Step 2), transfer the diluted mixture to a steam distillation apparatus for steam distillation, and obtain an oil-water mixture distillate. Separate the oil layer using a separatory funnel, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain 0.16 g of plant essential oil, with a yield of 0.16%.

[0028] Example 3 An extraction process for plant essential oils includes the following steps: Step 1): Add hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 and hydrogen bond donor malonic acid to the reactor at a molar ratio of 1:3. Heat to 80°C and stir magnetically for 1 hour until the system becomes a clear and transparent viscous liquid. Keep the temperature at 80°C and slowly add the calculated amount of deionized water while stirring, so that the mass fraction of water in the final system is 20 wt%. Continue stirring for 15 minutes until the system is homogeneous, and obtain an aqueous eutectic solvent. Seal and store for later use. Step 2): Take 100 g of freshly picked Damask rose petals, add 100 mL of deionized water and crush them to obtain rose petal pulp; add the above rose petal pulp and 600 mL of the aqueous eutectic solvent obtained in step 1) into the reactor, and extract by ultrasonication at 60℃ and 150W for 30 min, filter and collect the filtrate. Step 3): Add 1000 mL of deionized water to the filtrate obtained in Step 2), transfer the diluted mixture to a steam distillation apparatus for steam distillation, and obtain an oil-water mixture distillate. Separate the oil layer using a separatory funnel, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain 0.13 g of plant essential oil, with a yield of 0.13%.

[0029] Example 4 An extraction process for plant essential oils includes the following steps: Step 1): Add hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 and hydrogen bond donor lauric acid to the reactor at a molar ratio of 1:3. Heat to 60°C and stir magnetically for 1 hour until the system becomes a clear and transparent viscous liquid. Keep the temperature at 60°C and slowly add the calculated amount of deionized water while stirring, so that the final water mass fraction in the system is 20 wt%. Continue stirring for 15 minutes until the system is homogeneous, and obtain an aqueous eutectic solvent. Seal and store for later use. Step 2): Take 100 g of freshly picked Damask rose petals, add 100 mL of deionized water and crush them to obtain rose petal pulp; add the above rose petal pulp and 600 mL of the aqueous eutectic solvent obtained in step 1) into the reactor, and extract by ultrasonication at 60℃ and 150W for 30 min, filter and collect the filtrate. Step 3): Add 1000 mL of deionized water to the filtrate obtained in Step 2), transfer the diluted mixture to a steam distillation apparatus for steam distillation, and obtain an oil-water mixture distillate. Separate the oil layer using a separatory funnel, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain 0.12 g of plant essential oil, with a yield of 0.12%.

[0030] Comparative Example 1 Based on Example 1, the hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 was replaced with choline chloride, which is commonly used in the art. Other operating steps and conditions were the same as in Example 1. The yield of the plant essential oil was 0.07%.

[0031] Comparative Example 2 Based on Example 1, the hydrogen bond acceptor [C4(C2H5Oim)2][Cl]2 was replaced with 1-butyl-3-methylimidazolium hydrochloride, and other operating steps and conditions were the same as in Example 1. The yield of plant essential oil was 0.09%.

[0032] Comparative Example 3 Based on Example 1, the organic acid hydrogen bond donor citric acid was replaced with the non-organic acid hydrogen bond donor ethanolamine, while other operating steps and conditions remained the same as in Example 1. The yield of the plant essential oil was 0.10%.

[0033] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A process for extracting plant essential oils, comprising the following steps: Step 1): Mix the hydrogen bond acceptor and the organic acid hydrogen bond donor evenly and heat to form a clear and transparent viscous liquid. Then add deionized water to obtain an aqueous eutectic solvent and seal for later use. Step 2): Aromatic plants are added to deionized water and then pulverized to obtain a slurry; the slurry and the aqueous eutectic solvent obtained in step 1) are added to a reactor, ultrasonically extracted, filtered, and the filtrate is collected; Step 3): Add deionized water to the filtrate obtained in Step 2), and steam distill the diluted mixture to obtain an oil-water mixture. Separate the oil layer, add anhydrous sodium sulfate to the oil layer for drying, and filter to obtain plant essential oil. The structure of the hydrogen bond acceptor in step 1) is as follows: 。 2. The extraction process according to claim 1, characterized in that, Step 1) The organic acid is selected from one or more of citric acid, malic acid, lactic acid, oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, succinic acid, acetic acid, and propionic acid.

3. The extraction process according to claim 1, characterized in that, In step 1), the molar ratio of hydrogen bond acceptor to hydrogen bond donor is 1:(2~6); the heating temperature in step 1 is 60~90℃.

4. The extraction process according to claim 1, characterized in that, The water content of the aqueous eutectic solvent in step 1) is 20wt%~40wt%.

5. The extraction process according to claim 1, characterized in that, Step 2) The aromatic plants mentioned are rose petals, camphor leaves, lavender, jasmine petals, mint, cloves or cinnamon.

6. The extraction process according to claim 1, characterized in that, Step 2) The mass-to-volume ratio of the aromatic plant to deionized water is 1 g : (1~1.5) mL; the volume ratio of the slurry to the aqueous eutectic solvent is 1 : (2~10).

7. The extraction process according to claim 1, characterized in that, Step 2) The ultrasonic extraction temperature is 40~70℃, the power is 100~200W, and the time is 20~60min.

8. The extraction process according to claim 1, characterized in that, Step 3) The volume ratio of the filtrate to deionized water is 1:(1~3).

9. The extraction process according to claim 1, characterized in that, Step 1) The method for preparing the hydrogen bond acceptor includes the following steps: 1,4-bis(1-imidazolium)butane and 2-chloroethanol were dissolved in an organic solvent, heated to 50-80°C and stirred to react. After the reaction was completed, the mixture was cooled to room temperature. Then, diethyl ether was added to the reaction mixture to produce a precipitate. The precipitate was filtered and the filter cake was dried under vacuum to obtain a hydrogen bond acceptor. The reaction formula is: 。 10. The extraction process according to claim 9, characterized in that, The organic solvent is selected from one or more of DMF, DMSO, toluene, acetone, THF and ethyl acetate; the molar ratio of 1,4-bis(1-imidazolium)butane to 2-chloroethanol is 1:(2~5).

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