Purification method for supercritical CO2 extracted pericarpium citri reticulatae essential oil

Abstract

The invention belongs to the technical field of natural product extraction, and relates to a method for purifying pericarpium citri reticulatae essential oil through supercritical CO2 extraction, in particular to a method for extracting high-purity pericarpium citri reticulatae essential oil by adopting supercritical CO2 extraction combined with a molecular distillation technology. According to the method disclosed by the invention, two-stage molecular distillation is organically combined, and particularly, the second-stage molecular distillation is operated under the specific conditions of 90-120 DEG C and 0.1-1 Pa, so that high-boiling-point impurities such as pigments and waxiness in the supercritical extract of the pericarpium citri reticulatae can be efficiently removed. The dried orange peel essential oil treated by the method disclosed by the invention is light yellow to light yellow transparent liquid, and the sensory quality of the product is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of natural product extraction technology, and relates to a method for purifying tangerine peel essential oil by supercritical CO2 extraction, specifically a method for extracting high-purity tangerine peel essential oil using supercritical CO2 extraction combined with molecular distillation technology. Background Technology

[0002] Dried tangerine peel (Chenpi) is the dried, mature peel of the citrus reticulata Blanco plant (Citrus reticulata Blanco) and its cultivated varieties. It is a traditional Chinese medicine used for both food and medicine, with aged peel considered superior, hence the name "Chenpi" (aged peel). Chenpi contains abundant volatile oils (essential oils), flavonoids (such as hesperidin), alkaloids, and other active ingredients. Among these, tangerine peel essential oil has a rich citrus aroma, and its main components are limonene, γ-terpinene, and linalool. It has broad application prospects in food flavoring, the fragrance industry, daily chemical products, and aromatherapy, and has been proven to possess certain antioxidant, antibacterial, and anti-inflammatory biological activities.

[0003] Currently, the commonly used methods for extracting plant essential oils mainly include the following:

[0004] 1. Steam distillation: This is the most traditional and commonly used method for extracting essential oils. The principle is to use steam to carry away the more volatile essential oil components, which are then separated into oil and water after condensation. The advantages of this method are its simplicity, low equipment cost, and high safety. However, its disadvantages are also quite obvious: the extraction temperature is relatively high (usually close to 100℃), and the heating time is long, which can easily cause hydrolysis, polymerization, or oxidation of heat-sensitive terpenoid aroma components, destroying the natural aroma of the essential oil; at the same time, the extraction rate is relatively low, and some high-boiling-point components are difficult to distill out.

[0005] 2. Organic solvent extraction: This method involves soaking the raw material in organic solvents such as petroleum ether or n-hexane to dissolve the essential oil, followed by evaporation to remove the solvent. While this method yields a high amount of oil, it carries the risk of solvent residue, affecting the purity and safety of the product. Furthermore, the resulting extract often contains significant amounts of fat-soluble impurities such as waxes and pigments, requiring further refining.

[0006] 3. Pressing method: Primarily used for citrus peels, this method uses mechanical pressure to break the oil sacs and extract the essential oil. This method preserves the natural aroma of the essential oil, but the resulting product often contains impurities such as moisture and cell fragments, is prone to spoilage, and has a low extraction rate.

[0007] In recent years, supercritical CO2 extraction technology has been widely used due to its green, pollution-free, high extraction efficiency, and low operating temperature. This technology utilizes the dual gaseous and liquid properties of CO2 in its supercritical state to selectively extract target components. However, in practical applications, it has been found that during the extraction of tangerine peel essential oil, due to the nonpolarity and strong dissolving power of CO2, while extracting the target aroma components, a large amount of pigments (such as chlorophyll and carotenoids), waxes, fatty acids, and other fat-soluble impurities from the tangerine peel are often extracted along with it. This results in an extract that is not a pure volatile essential oil, but rather a dark brown or dark green paste (commonly known as "crude essential oil" or "extract"). This crude product has poor flowability and a high impurity content, and cannot directly meet the requirements of the high-end market for essential oil products in terms of color, clarity, and purity, necessitating subsequent refining and purification.

[0008] Molecular distillation is a liquid-liquid separation technique performed under high vacuum conditions. It utilizes the differences in the free path of molecular motion of different substances to achieve separation at temperatures far below the boiling points of the substances. This technique has advantages such as low distillation temperature, short heating time, and high degree of separation, making it particularly suitable for the separation and purification of heat-sensitive and high-boiling-point substances. It has been used in the purification of natural products.

[0009] Although there are reports of combining supercritical fluid extraction with molecular distillation for essential oil extraction from other plants (such as garlic and ginger), the essential oil composition of tangerine peel is complex and contains a large number of pigments and waxes. How to optimize the combination of process parameters, especially considering the characteristics of tangerine peel, and design reasonable molecular distillation stages and process conditions to efficiently remove impurities (especially pigments and waxes) while maximally retaining the characteristic aroma components (such as limonene and linalool) in tangerine peel to obtain high-quality tangerine peel essential oil remains a technical problem that needs further research and solutions. Summary of the Invention

[0010] To address the shortcomings of the existing technology, the present invention aims to provide a molecular distillation method for extracting tangerine peel essential oil, which overcomes the deficiencies of existing tangerine peel extracts, such as high impurity content, dark color, and significant aroma loss. By combining supercritical CO2 extraction with multi-stage molecular distillation technology using specific process parameters, a high-quality tangerine peel essential oil with light color, high purity, and a realistic aroma can be obtained.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] The first aspect of this invention discloses a method for refining tangerine peel essential oil, comprising the following steps:

[0013] (1) Using coarse powder of dried tangerine peel as raw material and anhydrous ethanol as entrainer, the tangerine peel extract was obtained under the conditions of extraction pressure of 25-35 MPa, extraction temperature of 40-55℃, CO2 flow rate of 20-30 L / h, and extraction time of 1.5-3 h.

[0014] (2) The tangerine peel extract obtained in step (1) is subjected to at least two stages of molecular distillation to remove impurities and separate the target essential oil components;

[0015] The first-stage molecular distillation is used to remove residual entrainers and low-boiling-point impurities from the tangerine peel extract; the conditions for the first-stage molecular distillation are: evaporation temperature 60-75℃, operating pressure 1-10Pa.

[0016] Second-stage molecular distillation is used to separate the target essential oil components from high-boiling-point impurities; the conditions for second-stage molecular distillation are: evaporation temperature 90-120℃, operating pressure 0.1-1Pa;

[0017] (3) Collect the target fraction after molecular distillation to obtain refined tangerine peel essential oil.

[0018] Preferably, the tangerine peel component in step (1) is obtained by drying, pulverizing, and sieving the tangerine peel raw material.

[0019] Preferably, the dried tangerine peel is Xinhui dried tangerine peel aged for more than 3 years.

[0020] Preferably, the dried tangerine peel raw material is dried to a moisture content of less than 10% before pulverization.

[0021] Preferably, the entrainer in step (1) is anhydrous ethanol, and its dosage is 3%-8% of the raw material mass. In order to improve the extraction rate of the target aroma components (especially relatively polar alcohols and esters), the addition of entrainers (such as ethanol) is commonly used in the art. While the addition of ethanol can significantly improve extraction efficiency and aroma integrity, it also enhances the co-extraction ability of polar impurities in the raw material (such as some pigments and resins), resulting in a more complex impurity composition in the crude extract, further increasing the difficulty of subsequent purification.

[0022] Preferably, the molecular distillation in step (2) is a scraped-film molecular distillation.

[0023] Preferably, the light phase fraction collected on the condensation surface by the second-stage molecular distillation is used as refined tangerine peel essential oil.

[0024] The second aspect of this invention discloses a high-purity tangerine peel essential oil prepared according to the above-described refining method.

[0025] The third aspect of this invention discloses the application of the aforementioned tangerine peel essential oil in essential oil products, characterized in that the application includes aromatherapy. Specifically, it involves using tangerine peel essential oil to prepare aromatherapy preparations for improving environmental odors.

[0026] Compared with the prior art, the beneficial effects of this invention are as follows:

[0027] 1. This invention utilizes a two-stage molecular distillation process, particularly the second-stage distillation operating under specific conditions of 90-120℃ and 0.1-1 Pa, to efficiently remove high-boiling-point impurities such as pigments and waxes from the supercritical fluid extract of dried tangerine peel. The dried tangerine peel essential oil processed by this method is a pale yellow to light yellow transparent liquid, significantly improving the sensory quality of the product.

[0028] 2. Compared with the traditional steam distillation refining method, the method of the present invention avoids the loss of aroma components by hydrolysis and pyrolysis, and the yield (based on crude extract) can reach 67.6%-77.2%. At the same time, the obtained product has no solvent residue, high purity, and GC-MS analysis shows that the content of characteristic aroma components is high and there are no obvious impurity peaks.

[0029] 3. The pretreatment process in this invention, involving a first-stage solvent removal step (60-75℃, 1-10 Pa), is a prerequisite for ensuring efficient separation in the second stage. If the first stage is skipped and high-temperature molecular distillation is performed directly, residual ethanol will cause instability in the vacuum system, leading to mist entrainment. Even with the optimal temperature (110℃) in the second stage, a clear and transparent product cannot be obtained. This invention achieves unexpected technical effects through two-stage molecular distillation. Detailed Implementation

[0030] The technical solution of the present invention will be described in detail below with reference to embodiments, but this does not limit the present invention to the scope of the embodiments described. Process parameters not specified in the embodiments of this application can be performed according to conventional methods, and all raw materials used can be obtained through commercial channels.

[0031] Experimental materials:

[0032] Chenpi (dried tangerine peel): Purchased from Xinhui, Guangdong, it is the peel of a tangerine peel aged for 5 years.

[0033] CO2 gas: purity ≥ 99.9%, food grade.

[0034] Anhydrous ethanol: analytical grade or food grade.

[0035] Example 1: Preparation of high-purity, lightly aromatic tangerine peel essential oil

[0036] 1. Raw material pretreatment: Take 5 kg of Xinhui tangerine peel that has been aged for 5 years, dry it in a 60℃ oven until the moisture content is about 8%, crush it with a pulverizer, pass it through a 40-mesh sieve to obtain coarse tangerine peel powder, and set it aside.

[0037] 2. Supercritical CO2 extraction:

[0038] Equipment: 5L supercritical CO2 extraction unit

[0039] Procedure: Add 5 kg of coarse dried tangerine peel powder to the extraction vessel and seal. Turn on the CO2 high-pressure pump, set the extraction pressure to 30 MPa, the extraction temperature to 50℃, and the CO2 flow rate to 25 L / h. Simultaneously, add anhydrous ethanol via an entrainer pump, at a dosage of 5% of the material mass (i.e., 250 g). Extraction time: 2 hours.

[0040] Results: After extraction, the extract was released from the primary separation vessel to obtain a crude extract of tangerine peel essential oil, which was a dark brown paste weighing approximately 145g.

[0041] 3. First-stage molecular distillation (degassing / desolvent removal):

[0042] Equipment: Scraped membrane molecular distillation apparatus

[0043] Procedure: Place the crude extract in the feed tank and preheat to 50°C. Turn on the vacuum system and, after the operating pressure stabilizes at 5Pa, turn on the feed pump and scraper. Set the evaporation temperature to 70°C, the condensation temperature to 0°C, the scraper speed to 200 rpm, and the feed rate to approximately 2 mL / min.

[0044] Results: The light phase component (mainly residual ethanol and a small amount of water) was condensed and collected; the heavy phase component (the material after solvent removal) flowed into the intermediate tank for the next stage of processing.

[0045] 4. Second-stage molecular distillation (main separation):

[0046] Operation: Use the first-stage heavy phase material as feed and preheat it to 60℃. Set the evaporation temperature to 110℃, the condensation temperature to 10℃, the operating pressure to 0.3Pa, the scraper rotation speed to 300rpm, and the feed rate to approximately 1.5mL / min.

[0047] Results: Under these conditions, the target tangerine peel essential oil components evaporate and condense into a liquid (light phase) on the condensing surface, which is collected from the light phase outlet; high-boiling-point pigments, waxes and other impurities remain on the inner surface of the heated evaporation cylinder and are discharged from the heavy phase outlet as heavy phase residue.

[0048] 5. Product collection and testing:

[0049] The light phase component on the condenser surface of the second-stage molecular distillation was collected to obtain a pale yellow, transparent essential oil product with a fresh tangerine peel aroma, weighing approximately 98g, with an extraction rate of approximately 1.96% (based on dry raw material).

[0050] GC-MS analysis showed that the essential oil contained limonene up to 86%, γ-terpinene about 8%, and linalool about 3%, with no obvious large molecular impurity peaks in the chromatogram and a clear and bright appearance.

[0051] Example 2: Preparation of a richly aromatic tangerine peel essential oil

[0052] The difference between this embodiment and Embodiment 1 is that the conditions of the second-stage molecular distillation were adjusted in order to obtain an essential oil product with a richer aroma and a longer-lasting fragrance.

[0053] Steps 1-3 are the same as in Example 1.

[0054] 4. Second-stage molecular distillation (main separation):

[0055] Preheat the first-stage heavy phase material to 60℃. Set the evaporation temperature to 100℃, the condensation temperature to 10℃, the operating pressure to 0.5Pa, the scraper rotation speed to 250rpm, and the feed rate to approximately 1.5mL / min.

[0056] 5. Product collection and testing:

[0057] The light phase components on the condenser surface of the second-stage molecular distillation were collected to obtain a light yellow essential oil product with a richer and fuller aroma and more complex layers, weighing approximately 112g, with an extraction rate of approximately 2.24%.

[0058] GC-MS analysis revealed that the essential oil contained approximately 78% limonene, 10% γ-terpinene, and 5% linalool. Some sesquiterpenoids with higher boiling points were also detected, resulting in a more complete aroma composition and a longer-lasting fragrance.

[0059] Comparative Example 1: Supercritical extraction only (without molecular distillation purification)

[0060] After supercritical CO2 extraction according to steps 1 and 2 of Example 1, the extract was collected directly without molecular distillation.

[0061] The obtained extract was a dark brown paste, semi-solid at room temperature, with poor flowability. Observation revealed that the product contained a large amount of wax and pigment, and had a cloudy appearance, failing to meet market quality requirements for commercial essential oils. Direct use in blending would affect the appearance and stability of the final product.

[0062] Comparative Example 2: Supercritical extraction followed by steam distillation purification

[0063] Supercritical CO2 extraction was performed according to steps 1 and 2 of Example 1 to obtain crude extract.

[0064] The crude extract was added to a steam distillation apparatus, water was added, and the mixture was heated and distilled for 2 hours. The distillate was collected and separated by an oil-water separator to obtain the essential oil.

[0065] The obtained essential oil was a pale yellow liquid, but its aroma differed significantly from that of the raw tangerine peel, exhibiting a noticeable cooked taste and losing some of its freshness. GC-MS analysis showed that while the limonene content remained high, the content of low-boiling-point and heat-sensitive components such as linalool was significantly reduced, and peaks of some oxidation products were observed. The yield was only about 50% of the crude extract, indicating a substantial loss.

[0066] project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Appearance pale yellow transparent liquid light yellow transparent liquid Dark brown paste pale yellow liquid aroma Fresh tangerine peel aroma Rich and full-bodied tangerine peel aroma The aroma of dried tangerine peel with a hint of off-flavor It tastes bland after being cooked, lacking freshness. Yield (based on crude extract) 67.6% 77.2% 100% Approximately 50% Solvent residue Not detected Not detected Small amount of ethanol none Overall evaluation Excellent, suitable for daily chemical products and aromatherapy. Excellent, suitable for food and perfume. Poor quality, cannot be used directly. In the middle, the aroma quality declines.

[0067] Comparative Example 3: Direct purification by single-stage molecular distillation

[0068] This study aims to verify whether high-quality tangerine peel essential oil can be obtained by directly using high-temperature molecular distillation without a first-stage desolventizing process, thus demonstrating the synergistic effect of the two-stage process.

[0069] Operating steps:

[0070] Raw material preparation: Take 150g of the crude extract of dried tangerine peel (dark brown paste containing about 5% residual ethanol) obtained by supercritical CO2 extraction as in Example 1 for later use.

[0071] Procedure: Place the crude extract in the feed tank and preheat to 50°C. Turn on the vacuum system, set the evaporation temperature to 110°C (the same as the second stage temperature in Example 1), the condensation temperature to 10°C, the target operating pressure to 0.3 Pa, the scraper rotation speed to 300 rpm, and the feed rate to 1.5 mL / min.

[0072] After the equipment is started, the vacuum level is difficult to maintain stably at 0.3 Pa, and the fluctuation range is 0.3-5 Pa.

[0073] The observation window shows the material bubbling and splashing violently on the heating surface, with some droplets splashing directly onto the condensing surface (a mist entrainment phenomenon).

[0074] The light phase component was collected to obtain a light brown turbid liquid. After standing for 24 hours, a precipitate appeared at the bottom.

[0075] It weighs approximately 112g, with a yield of approximately 74.7%.

[0076] Even with the theoretically optimal separation temperature (110℃), the failure to remove residual ethanol from the crude extract first resulted in: ① instability of the vacuum system; ② entrainment of droplets, with impurities entering the lighter phase along with the droplets.

[0077] Comparative Example 4: Two-stage molecular distillation - second-stage temperature too low

[0078] Objective: To verify whether waxy impurities can be effectively removed when the second-stage evaporation temperature is lower than the lower limit of this invention (90°C).

[0079] Operating steps:

[0080] First-stage molecular distillation: Same as step 3 in Example 1 (evaporation temperature 70°C, operating pressure 5Pa) to remove residual ethanol.

[0081] Second-stage molecular distillation:

[0082] The evaporation temperature was set to 80°C (lower than the 90°C lower limit of this invention), the operating pressure to 0.3Pa, the condensation temperature to 10°C, the scraper rotation speed to 300rpm, and the feed rate to 1.5mL / min.

[0083] Product collection:

[0084] The light phase component was collected to obtain a pale yellow, turbid liquid with poor fluidity, which was semi-fluid at room temperature. The weight was approximately 89 g, with a yield of approximately 59.3% (based on the crude extract).

[0085] Comparative Example 5: Two-stage molecular distillation - second-stage temperature too high (verifying the criticality of the temperature window - upper limit)

[0086] Objective: To verify whether the heat-sensitive aroma components are destroyed when the second-stage evaporation temperature is higher than the upper limit of the present invention (120°C).

[0087] Operating steps:

[0088] First-stage molecular distillation: Same as step 3 in Example 1 (evaporation temperature 70°C, operating pressure 5Pa) to remove residual ethanol.

[0089] Second-stage molecular distillation:

[0090] The evaporation temperature was set to 130℃ (higher than the 120℃ upper limit of this invention), the operating pressure to 0.3Pa, the condensation temperature to 10℃, the scraper rotation speed to 300rpm, and the feed rate to 1.5mL / min.

[0091] Process observation:

[0092] The equipment operates stably, and the amount of light phase extracted is relatively large.

[0093] Product collection:

[0094] The light phase component was collected to obtain a light yellow transparent liquid with acceptable appearance.

[0095] The weight was approximately 121g, and the yield was approximately 80.7% (based on crude extract).

[0096] in conclusion:

[0097] When the second-stage evaporation temperature drops to 80℃, the wax molecules fail to gain sufficient kinetic energy to escape from the liquid surface, resulting in a large amount of wax remaining mixed in the lighter phase. This indicates that 90℃ is the lower limit of the critical temperature for effective wax separation; below this temperature, clear and transparent essential oil products cannot be obtained.

[0098] Although the wax is completely removed at 130℃ (resulting in a clear appearance), excessively high temperatures cause oxidation and thermal polymerization of heat-sensitive aroma components (such as limonene), severely degrading the aroma quality. This indicates that 120℃ is the upper limit of the critical temperature for ensuring aroma integrity; temperatures above this level can remove impurities but will sacrifice the aroma quality of the product.

[0099] project Example 1 Comparative Example 3 (without Level 1) Comparative Example 4 (80℃) Comparative Example 5 (130℃) First stage (solvent removal) 70℃ none 70℃ 70℃ Second-level temperature 110℃ 110℃ 80℃ 130℃ Second level of pressure 0.3Pa Unstable 0.3Pa 0.3Pa Appearance pale yellow and transparent Light brown and cloudy pale yellow and cloudy pale yellow and transparent aroma Fresh and pure It has an off-taste It has a waxy smell Cooked yield 67.6% 74.7% 59.3% 80.7%

[0100] In summary, the first-stage solvent removal is irreplaceable (Comparative Example 3): even if the second stage uses the optimal separation temperature, without the first-stage pretreatment, the residual solvent will disrupt the vacuum stability and cause mist entrainment, leading to separation failure.

[0101] The above experimental data fully demonstrate that the two-stage molecular distillation process parameters (especially the second-stage evaporation temperature of 90-120℃ and the operating pressure of 0.1-1Pa) defined in this invention were not obtained through conventional optimization. The selection of their range and the choice of the second-stage molecular distillation have unexpected technical effects.

[0102] If the solvent is not removed first, vaporization at 110°C will cause mist entrainment. The contribution of the first-stage solvent removal is not only to "remove ethanol", but also to eliminate interfering factors, so that the second-stage molecular distillation can stably remove the remaining impurities.

[0103] This invention is not limited to the above-described embodiments. Any changes in shape or structure are within the scope of protection of this invention. The scope of protection of this invention is defined by the appended claims. Those skilled in the art can make various changes, modifications, substitutions, combinations, and simplifications to these embodiments without departing from the principles and essence of this invention. All such changes and simplifications should be considered equivalent substitutions and fall within the scope of protection of this invention.

Claims

1. A method for refining tangerine peel essential oil, characterized in that, Includes the following steps: (1) Using coarse powder of dried tangerine peel as raw material and anhydrous ethanol as entrainer, the tangerine peel extract was obtained under the conditions of extraction pressure of 25-35 MPa, extraction temperature of 40-55℃, CO2 flow rate of 20-30 L / h, and extraction time of 1.5-3 h. (2) The tangerine peel extract obtained in step (1) is subjected to at least two stages of molecular distillation to remove impurities and separate the target essential oil components; The first-stage molecular distillation is used to remove residual entrainers and low-boiling-point impurities from the tangerine peel extract; the conditions for the first-stage molecular distillation are: evaporation temperature 60-75℃, operating pressure 1-10Pa. Second-stage molecular distillation is used to separate the target essential oil components from high-boiling-point impurities; the conditions for second-stage molecular distillation are: evaporation temperature 90-120℃, operating pressure 0.1-1Pa; (3) Collect the target fraction after molecular distillation to obtain refined tangerine peel essential oil.

2. The refining method for tangerine peel essential oil according to claim 1, characterized in that, In step (1), the tangerine peel component is obtained by drying, pulverizing, and sieving the tangerine peel raw material.

3. The refining method for tangerine peel essential oil according to claim 1, characterized in that, The tangerine peel mentioned is Xinhui tangerine peel that has been aged for more than 3 years.

4. The refining method for tangerine peel essential oil according to claim 2 or 3, characterized in that, The dried tangerine peel raw material is dried to a moisture content of less than 10% before being pulverized.

5. The refining method for tangerine peel essential oil according to claim 1, characterized in that, The entrainer mentioned in step (1) is anhydrous ethanol, and its dosage is 3%-8% of the raw material mass.

6. The refining method for tangerine peel essential oil according to claim 1, characterized in that, The molecular distillation described in step (2) is a scraped-film molecular distillation.

7. The refining method for tangerine peel essential oil according to claim 6, characterized in that, The second-stage molecular distillation collects the light phase fraction from the condensation surface as refined tangerine peel essential oil.

8. High-purity tangerine peel essential oil prepared by the refining method according to any one of claims 1-7.

9. The application of tangerine peel essential oil in essential oil products as described in claim 8, characterized in that, The applications include aromatherapy.

10. The application according to claim 9, characterized in that, The applications include using tangerine peel essential oil to prepare aromatherapy preparations to improve environmental odor.