A process optimization method for purifying eucalyptus leaf oil by low-energy multi-stage molecular distillation

Abstract

This invention relates to the field of essential oil purification technology, and discloses an optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation. The method includes: mixing crude eucalyptus oil with an organic solvent, adding a saturated urea alcohol solution for a low-temperature inclusion reaction to remove non-target terpene impurities; after solvent recovery and deep dehydration, the filtrate is sent to a multi-stage molecular distillation system for separation under specific vacuum and temperature gradients. This process effectively solves the problem of isomer separation, improves product purity, reduces energy consumption, and minimizes the oxidation of heat-sensitive components.

Description

Technical Field

[0001] This invention relates to the field of essential oil purification technology, and discloses a low-energy-consumption multi-stage molecular distillation process optimization method for purifying eucalyptus oil. Background Technology

[0002] Eucalyptus oil is a natural essential oil extracted from eucalyptus leaves. Its main component, eucalyptol, has wide applications in the pharmaceutical and fragrance industries. Currently, the mainstream industrial process for purifying eucalyptol is multi-stage molecular distillation. This technology separates different substances under high vacuum conditions by utilizing the difference in the mean free path of molecular motion. A liquid film forms on the heating surface of the still; lighter components evaporate upon heating and fly towards the condenser surface to be collected, while heavier components flow down the heating surface, thus achieving component separation.

[0003] Existing purification methods typically involve direct multi-stage continuous distillation of crude eucalyptus oil. During operation, technicians gradually remove light solvent components, monoterpene impurities, and heavy gum components by controlling the heating temperature, system vacuum, and scraper rotation speed at each stage. To obtain a high-purity product, it is often necessary to set up a multi-stage series of stills, repeatedly evaporating and condensing to enrich the target components, attempting to increase the concentration of eucalyptol in the fraction.

[0004] The main problem with existing technologies is that crude eucalyptus oil contains various terpene isomers with structures similar to eucalyptol. These impurity components have very small differences in boiling point and molecular weight from the target component, and separation relies solely on differences in physical volatility, resulting in a low separation coefficient. To improve the separation effect, multi-stage distillation or higher operating conditions must be employed, leading to long process flows, high energy consumption, and the risk of oxidation or polymerization of heat-sensitive components due to prolonged heating treatment, making it difficult to simultaneously meet the production requirements of high purity and low energy consumption. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as the difficulty in separating isomers with similar boiling points through single-stage molecular distillation leading to high energy consumption and easy degradation of heat-sensitive components, this invention provides an optimized process for purifying eucalyptus oil through low-energy multi-stage molecular distillation.

[0006] To address the aforementioned technical problems, this invention provides an optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation, comprising the following technical features: mixing crude eucalyptus oil with an organic solvent in a preset ratio to form an oil phase mixture; adding the oil phase mixture to a saturated urea alcohol solution and performing an inclusion reaction under low temperature and continuous stirring conditions, so that urea molecules form solid inclusion complexes with non-target linear and monocyclic terpenoid components in the crude eucalyptus oil; performing solid-liquid separation on the reaction system to remove the solid inclusion complexes containing impurities and collecting the filtrate; performing vacuum distillation on the filtrate to recover the organic solvent and obtaining a purified eucalyptus oil intermediate; and conveying the eucalyptus oil intermediate to a multi-stage molecular distillation system for multi-stage separation under a set vacuum and temperature gradient, collecting the light fraction rich in 1,8-cineole.

[0007] Urea molecules in alcoholic solutions can self-assemble into a hexagonal lattice structure with specific pore sizes through hydrogen bonding. This lattice channel can selectively encapsulate small-diameter straight-chain hydrocarbons and monocyclic terpenoid impurities, while the sterically hindered bicyclic structure of 1,8-cineole cannot enter the lattice. Utilizing this principle of chemically selective separation, isomer impurities with boiling points overlapping with the target product are removed beforehand, thereby altering the distribution of the material's physical properties. This allows subsequent multi-stage molecular distillation to achieve high-purity separation at lower evaporation temperatures and stages, reducing the high-temperature exposure time of heat-sensitive components.

[0008] Furthermore, in the above technical solution, the organic solvent is selected from one or more combinations of anhydrous ethanol, methanol, acetone or n-hexane, the volume mixing ratio of crude eucalyptus oil to the organic solvent is 1:0.5 to 1:2, and the saturated urea alcohol solution is a saturated solution formed by dissolving urea in hot ethanol and cooling it to room temperature.

[0009] In practice, specific organic solvents ensure that crude eucalyptus oil and urea alcohol solution form a homogeneous single-phase or microemulsion system, promoting full contact between urea molecules and impurity molecules. Preset volume ratios and saturation concentrations guarantee the activity of urea molecules in the reaction system, avoiding both excessive viscosity due to insufficient solvent hindering mass transfer and excessive solvent reducing reaction efficiency.

[0010] Furthermore, in the above technical solution, the temperature of the inclusion reaction is controlled between -5 degrees Celsius and 10 degrees Celsius, the duration of the inclusion reaction is four to twelve hours, and the mass ratio of urea to crude eucalyptus oil in the saturated urea alcohol solution is 0.8:1 to 1.5:1.

[0011] In practice, a low-temperature environment is beneficial to the thermodynamic stability of the urea inclusion complex lattice, preventing crystal decomposition during the reaction. Sufficient reaction time ensures that the diffusion and inclusion processes of impurity molecules from the liquid phase to the crystal nucleus surface reach equilibrium. A specific urea to oil mass ratio ensures that the number of lattice sites matches the total amount of impurities, thereby achieving maximum inclusion removal.

[0012] Furthermore, in the above technical solution, the solid-liquid separation is carried out by vacuum filtration or plate and frame filtration. After the solid-liquid separation is completed, the filter cake is washed two to three times with a low-temperature organic solvent at the same temperature as the final temperature of the inclusion reaction, and the washing liquid is combined into the filtrate.

[0013] In practice, pressure differential-driven filtration can quickly achieve physical separation of the solid and liquid phases. The low-temperature washing step aims to displace and recover the mother liquor (containing the target product) retained in the micropores of the filter cake, while maintaining a low temperature to prevent the dissolution of inclusion complexes formed in the filter cake. Combining the washing liquids effectively improves the overall yield of the target component.

[0014] Furthermore, in the above technical solution, a deep dehydration and drying step is provided between the vacuum distillation of the filtrate and the delivery of the eucalyptus oil intermediate to the multi-stage molecular distillation system. The deep dehydration and drying step involves passing the solvent-removed oily substance through a chromatography column filled with anhydrous sodium sulfate or molecular sieve, or adding a desiccant under vacuum stirring for adsorption treatment.

[0015] In practice, the trace amounts of moisture remaining in the eucalyptus oil intermediates are easily vaporized during high-vacuum molecular distillation, leading to fluctuations in the system vacuum or flooding. Deep dehydration and drying remove trace polar components, ensuring stable pressure in the molecular distillation system and guaranteeing the formation of a continuous and stable liquid film on the evaporation surface.

[0016] Furthermore, in the above technical solution, the multi-stage molecular distillation system adopts a scraped-film molecular distillation apparatus, the scraped-film rotor speed of the scraped-film molecular distillation apparatus is controlled at 150 to 400 revolutions per minute, and the multi-stage molecular distillation system includes a first-stage degassing unit and a second-stage separation and rectification unit connected in series.

[0017] In practice, the centrifugal and shear forces generated by the rotating scraper rotor force the liquid to spread into an extremely thin turbulent liquid film on the heating surface, greatly increasing the evaporation surface area and shortening the material heating path. The degassing unit and the separation and distillation unit, arranged in series, process components with different volatility in stages, removing light component impurities first and then performing main fraction distillation, thus optimizing the separation load of each stage of the equipment.

[0018] Furthermore, in the above technical solution, the process parameters of the first-stage degassing unit are: the feed temperature is controlled at 40 degrees Celsius to 60 degrees Celsius, and the system absolute pressure is controlled at 50 Pa to 200 Pa, which are used to remove the trace solvents and light component impurities remaining in the eucalyptus oil intermediate.

[0019] In practice, under the mild temperature and moderate vacuum, the difference in saturated vapor pressure between the solvent and the light components and 1,8-cineole causes the volatile components to flash preferentially, while the main target product remains in the liquid phase, thus completing the preliminary purification without causing the loss of the main components.

[0020] Furthermore, in the above technical solution, the process parameters of the second-stage separation and distillation unit are as follows: the temperature of the heating medium is controlled at 80 degrees Celsius to 120 degrees Celsius, the temperature of the condensing surface is controlled at -10 degrees Celsius to 5 degrees Celsius, and the absolute pressure of the system is controlled at 5 Pa to 20 Pa, which is used to extract the 1,8-cineole main fraction.

[0021] In practice, the higher heating temperature provides the kinetic energy required for 1,8-cineole molecules to escape from the liquid phase, while the extremely low operating pressure significantly reduces its boiling point. The large temperature difference between the hot and cold surfaces, combined with the high vacuum environment, ensures that the evaporated target molecules are rapidly condensed and captured, while suppressing the entrainment of residual heavy components, thus achieving high-purity separation.

[0022] Furthermore, in the above technical solution, the method also includes a post-processing step of recovering urea from the filter cake generated in the solid-liquid separation step. The post-processing step involves adding the filter cake to hot water and stirring to decompose the inclusion complex. After standing and separating into layers, the upper oil phase is removed, and the lower aqueous phase is cooled and crystallized to recover urea crystals.

[0023] In practice, urea inclusion complexes are unstable in hot water, causing their crystal lattice structure to disintegrate, releasing the included impurities that dissolve in the aqueous phase. The impurities in the oil phase are removed by utilizing the density difference between oil and water due to their immiscibility. Subsequently, the solubility of urea is reduced by lowering the temperature, causing it to crystallize out of the aqueous phase, thus achieving the recycling of auxiliary raw materials.

[0024] Furthermore, in the above technical solution, after the inclusion reaction is completed and before the solid-liquid separation, diatomaceous earth or perlite accounting for 1% to 5% of the mass of the crude eucalyptus oil is added to the reaction system as a filter aid, and the mixture is stirred and dispersed for 10 to 30 minutes to improve the filtration performance of the suspension.

[0025] In practice, the solid inclusion complexes generated by the reaction are small and have a certain degree of viscosity, which can easily clog the pores of the filter cloth if filtered directly. Adding diatomaceous earth or perlite as a filter aid allows its rigid porous particles to build a permeable framework in the filter cake, forming a loose filter cake layer, thereby reducing filtration resistance and improving the clarity of the filtrate.

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

[0027] 1. This invention introduces a urea inclusion pretreatment step before multi-stage molecular distillation. Utilizing the property of urea molecules to form solid inclusion complexes with straight-chain and monocyclic terpenoid impurities, non-target components with boiling points close to eucalyptol are removed in advance by filtration. This chemical separation method alters the composition of the material, reducing the difficulty of subsequent molecular distillation separation of isomers. After the pretreated material enters the multi-stage molecular distillation system, high-purity enrichment of eucalyptol can be achieved with lower heat load and fewer stages, overcoming the limitation of single physical distillation in separating components with similar properties.

[0028] 2. This invention ensures the purity of materials entering the distillation system by incorporating solid-liquid separation, solvent recovery, and deep dehydration and drying processes, thus preventing interference from moisture and residual solvents. Adding a filter aid during the inclusion reaction and performing filtration at low temperatures improves the efficiency of solid-liquid separation. Furthermore, urea recovery from the filter cake reduces raw material costs. The entire process, while maintaining product purity, shortens the high-temperature separation time, reduces the loss of heat-sensitive components, and achieves a balance between low energy consumption and high quality. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0030] Example 1: Take 1L of crude eucalyptus oil and add 1L of anhydrous ethanol, mix well to form an oil phase mixture. Separately, take 1kg of urea and dissolve it in 3L of hot ethanol to prepare a saturated urea-ethanol solution, cool to room temperature for later use. Slowly add the oil phase mixture to the saturated urea-ethanol solution, place in an ice bath environment at 0℃, and stir continuously at 200rpm for 8 hours to carry out the inclusion reaction. After the reaction is completed, add diatomaceous earth accounting for 2% of the mass of crude eucalyptus oil to the system, and continue stirring and dispersing for 20 minutes. Then, perform vacuum filtration, collect the filtrate, and wash the filter cake three times with low-temperature ethanol at the same temperature as the final temperature of the inclusion reaction (0℃). Combine the filtrate and washing liquid. Perform vacuum distillation on the combined liquid at 50℃ and a vacuum degree of 0.09MPa to recover ethanol, and obtain the purified eucalyptus oil intermediate. Deeply dehydrate and dry the eucalyptus oil intermediate by passing it through a chromatography column packed with anhydrous sodium sulfate. The processed material is conveyed to a scraped membrane molecular distillation system, with the scraped membrane rotor speed set to 300rpm. The first-stage degassing unit controls the feed temperature at 50℃ and the system absolute pressure at 100Pa; the second-stage separation and distillation unit controls the heating medium temperature at 100℃, the condensation surface temperature at -5℃, and the system absolute pressure at 10Pa. The light component fraction from the second-stage separation and distillation unit is collected to obtain the high-purity 1,8-cineole product.

[0031] Example 2: The only difference from Example 1 is that the organic solvent is replaced with methanol, and the other process steps and parameters are the same as in Example 1.

[0032] Example 3: The only difference from Example 1 is that the volume ratio of crude eucalyptus oil to anhydrous ethanol is 1:0.5, and the other process steps and parameters are the same as in Example 1.

[0033] Example 4: The only difference from Example 1 is that the volume ratio of crude eucalyptus oil to anhydrous ethanol is 1:2, and the other process steps and parameters are the same as in Example 1.

[0034] Example 5: The only difference from Example 1 is that the temperature of the inclusion reaction is controlled at 10°C, and the other process steps and parameters are the same as in Example 1.

[0035] Example 6: The only difference from Example 1 is that the mass ratio of urea to crude eucalyptus oil in the saturated urea alcohol solution is 0.8:1. The other process steps and parameters are the same as in Example 1.

[0036] Example 7: The only difference from Example 1 is that molecular sieves are used instead of anhydrous sodium sulfate for adsorption treatment in the deep dehydration and drying step. The other process steps and parameters are the same as in Example 1.

[0037] Example 8: The only difference from Example 1 is that perlite is used as the filter aid, and the amount added is 5% of the mass of crude eucalyptus oil. The other process steps and parameters are the same as in Example 1.

[0038] Example 9: The only difference from Example 1 is that the duration of the inclusion reaction is adjusted to 4 hours, while the other process steps and parameters are the same as in Example 1.

[0039] Example 10: The only difference from Example 1 is that the duration of the inclusion reaction is adjusted to 12 hours, while the other process steps and parameters are the same as in Example 1.

[0040] Example 11: The only difference from Example 1 is that the feed temperature of the first-stage degassing unit is controlled at 60°C, and the remaining process steps and parameters are the same as in Example 1.

[0041] Comparative Example 1: The urea inclusion pretreatment step and solvent recovery step in Example 1 were omitted. An equal amount of crude eucalyptus oil was directly taken and fed into a scraped-film molecular distillation system without any pretreatment. The subsequent distillation parameters (speed, temperature, pressure) were exactly the same as in Example 1, and the light component fraction was collected.

[0042] Comparative Example 2: A conventional industrial steam distillation combined with rectification method was used. An equal amount of crude eucalyptus leaf oil as in Example 1 was taken and subjected to three steam distillations. The oil-water mixture was collected, and after salting out the layers, the essential oil was subjected to conventional vacuum rectification at an operating pressure of 20 kPa and a reflux ratio of 5:1. The fraction at 110℃-115℃ was collected.

[0043] Comparative Example 3: The inclusion reaction temperature in Example 1 was adjusted to 25°C (room temperature), and the remaining process steps and parameters were the same as in Example 1.

[0044] Comparative Example 4: The mass ratio of urea to crude eucalyptus oil in Example 1 was adjusted to 0.5:1, and the remaining process steps and parameters were the same as in Example 1.

[0045] Test method:

[0046] 1. Purity test of 1,8-cineole (gas chromatography area normalization method)

[0047] Instrumentation and chromatographic conditions: A gas chromatograph equipped with a flame ionization detector (FID) and a non-polar capillary column was used; high-purity nitrogen was used as the carrier gas, with a flow rate of 1.0 mL / min and a split ratio of 30:1; the injection port temperature was 220℃ and the detector temperature was 230℃; the column temperature program was as follows: initial temperature 80℃ and held for 2 min, then increased to 200℃ at a rate of 8℃ / min, and finally held for 5 min.

[0048] Sample pretreatment: Take the refined eucalyptus oil sample to be tested, filter it with a 0.22μm organic filter membrane to remove trace impurities, and set it aside.

[0049] Detection procedure: Use a microsyringe to inject 1.0 μL of the filtered sample into the gas chromatograph, start the program to complete the detection, and collect the chromatographic peak areas of all components.

[0050] Calculation method: Purity of 1,8-cineole = (Cyclocarpine peak area ÷ Total peak area of ​​all components in the sample) × 100%

[0051] Experimental requirements: Each group of samples should be tested in parallel three times, and the arithmetic mean should be taken as the final purity result.

[0052] 2. Product yield test

[0053] Weighing preparation: Accurately weigh the total mass of crude eucalyptus oil used in the test, as well as the total mass of qualified refined 1,8-cineole product obtained after the entire process.

[0054] Calculation method: Product yield = (Mass of refined 1,8-eucalyptol finished product ÷ Mass of initial input crude eucalyptus oil) × 100%

[0055] Experimental requirements: Each process group should be repeated for 3 batches, and the average value of multiple batches should be taken as the final yield result.

[0056] 3. Acid value test (titration method for essential oils / oils)

[0057] Reagent preparation: Prepare a 0.1 mol / L potassium hydroxide ethanol standard titration solution and phenolphthalein indicator; prepare a neutral ethanol-mixed solution with a volume ratio of 1:1.

[0058] Detection procedure: 1) Accurately weigh 2.0g of the eucalyptus oil sample to be tested, place it in an Erlenmeyer flask, add 50mL of neutral ethanol-ether mixture, shake until the sample is completely dissolved, and add 2-3 drops of phenolphthalein indicator; 2) Titrate with potassium hydroxide ethanol standard titration solution until the solution turns slightly red and does not fade within 30s, and record the volume of solution consumed in the titration; 3) Perform a blank control experiment simultaneously and record the volume of standard solution consumed by the blank group.

[0059] Calculation method: Acid value (mgKOH / g) = [Standard alkaline solution molar concentration × (sample titration volume - blank titration volume) × potassium hydroxide molar mass] ÷ mass of the sample to be tested

[0060] Experimental requirements: Each group of samples should be titrated in parallel three times, and the arithmetic mean should be taken as the final acid value result.

[0061] 4. Unit energy consumption test

[0062] Data statistics: Install an electricity meter on the entire purification production equipment to record the total power consumption (unit: kW·h) of a single batch of the process from raw material input to finished product output; at the same time, calculate the total mass of qualified refined eucalyptus oil produced in that batch (unit: kg).

[0063] Calculation method: Unit energy consumption (kW·h / kg) = Total power consumption of the process ÷ Total mass of qualified finished products

[0064] Experimental requirements: Energy consumption data for each batch of processes should be independently collected, and the average value of multiple parallel batches should be taken as the final unit energy consumption result.

[0065] The test results are shown in Table 1.

[0066] Table 1 Performance test results of each embodiment and comparative example.

[0067] Group 1,8-Cineole purity (%) Product yield (%) acid value Unit energy consumption Example 1 99.5 88.2 0.45 12.5 Example 2 99.3 87.5 0.48 12.8 Example 3 98.8 86.1 0.52 13.2 Example 4 98.9 86.8 0.50 13.0 Example 5 99.0 85.5 0.55 13.5 Example 6 98.5 85.0 0.58 13.8 Example 7 99.4 88.0 0.46 12.6 Example 8 99.2 87.8 0.47 12.7 Example 9 98.2 84.5 0.60 14.0 Example 10 99.6 88.5 0.42 12.2 Example 11 99.4 88.1 0.46 12.6 Comparative Example 1 92.5 75.0 1.85 28.4 Comparative Example 2 88.0 65.5 2.30 45.0 Comparative Example 3 95.0 78.5 1.20 20.5 Comparative Example 4 94.8 76.0 1.15 21.0

[0068] Results analysis:

[0069] The 1,8-cineole purity of the products obtained in Examples 1 to 11 was all above 98%, significantly better than that of Comparative Example 1 (92.5%) and Comparative Example 2 (88.0%). This indicates that the process of using urea inclusion pretreatment coupled with molecular distillation can effectively remove isomers with similar properties to 1,8-cineole. The selective inclusion effect of the urea lattice changes the composition of the mixture at the chemical level, solving the problem of separating isomers that are difficult to separate by single physical distillation. Comparative Example 1 lacked the inclusion step, and it was difficult to completely separate impurities with very similar boiling points by relying on molecular distillation, resulting in a significant decrease in purity. Comparative Example 2 used conventional steam distillation and rectification, resulting in the lowest separation accuracy.

[0070] The unit energy consumption of Example 1 was only 12.5 kWh, while the unit energy consumption of Comparative Examples 1 and 2 were as high as 28.4 kWh and 45.0 kWh, respectively. The data shows that the present invention removes most of the difficult-to-separate impurities through pretreatment, enabling rapid enrichment of the main fraction under milder conditions during the molecular distillation stage, significantly reducing the load of high-vacuum, high-heat operation. Although Comparative Examples 3 and 4 also included inclusion steps, the reaction temperature or urea dosage exceeded the preferred range defined by the present invention, resulting in reduced inclusion efficiency and more impurity residues. This forced subsequent distillation units to consume more energy to maintain the separation effect.

[0071] Acid value data directly reflects the degree of oxidation and thermal stability of the product. The acid values ​​of Examples 1 to 11 were all controlled below 0.6, demonstrating excellent quality stability. This is because the present invention reduces the heating opportunity of heat-sensitive components through low-temperature encapsulation and low-temperature washing, and the deep dehydration step avoids hydrolysis reactions at high temperatures. Conversely, Comparative Example 1, due to the lack of pretreatment, had a long residence time of the material in the distillation apparatus, resulting in severe oxidative rancidity and an acid value as high as 1.85. The high-temperature operation of Comparative Example 2 further resulted in an acid value reaching 2.30.

[0072] Comparing Examples 1, 9, and 10, it can be seen that appropriately extending the reaction time (12 hours) can slightly improve the purity and yield while reducing energy consumption, but too short a time (4 hours) leads to incomplete inclusion and reduced effectiveness. Comparing Example 1 with Comparative Examples 3 and 4, it can be seen that excessively high inclusion reaction temperature or insufficient urea dosage will disrupt the kinetic or thermodynamic equilibrium of crystal lattice formation, directly resulting in a double decrease in the purity and yield of the final product.

Claims

1. A low-energy-consumption, multi-stage molecular distillation process optimization method for purifying eucalyptus oil, characterized in that, The method includes the following steps: Crude eucalyptus oil and organic solvent are mixed in a preset ratio to form an oil phase mixture. The oil phase mixture is then added to a saturated urea alcohol solution, and an inclusion reaction is carried out under low temperature and continuous stirring conditions, so that urea molecules form solid inclusion complexes with the non-target straight-chain and monocyclic terpenoid components in the crude eucalyptus oil. The system after the reaction is subjected to solid-liquid separation to remove the solid inclusion complex containing impurities, and the filtrate is collected; The filtrate was subjected to vacuum distillation to recover the organic solvent, yielding a purified eucalyptus oil intermediate. The eucalyptus oil intermediate is fed into a multi-stage molecular distillation system, where it undergoes multi-stage separation under a set vacuum and temperature gradient to collect a light fraction rich in 1,8-cineole.

2. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, The organic solvent is selected from one or more combinations of anhydrous ethanol, methanol, acetone or n-hexane, the volume mixing ratio of crude eucalyptus oil to the organic solvent is 1:0.5 to 1:2, and the saturated urea alcohol solution is a saturated solution formed by dissolving urea in hot ethanol and cooling it to room temperature.

3. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, The temperature of the inclusion reaction is controlled between -5°C and 10°C, the duration of the inclusion reaction is 4 hours to 12 hours, and the mass ratio of urea to crude eucalyptus oil in the saturated urea alcohol solution is 0.8:1 to 1.5:

1.

4. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, The solid-liquid separation is carried out by vacuum filtration or plate and frame filtration. After the solid-liquid separation is completed, the filter cake is washed 2 to 3 times with a low-temperature organic solvent at the same temperature as the final temperature of the inclusion reaction, and the washing liquid is combined into the filtrate.

5. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, Between the vacuum distillation of the filtrate and the transfer of the eucalyptus oil intermediate to the multi-stage molecular distillation system, a deep dehydration and drying step is provided. The deep dehydration and drying step involves passing the solvent-removed oily substance through a chromatography column filled with anhydrous sodium sulfate or molecular sieves, or adding a desiccant under vacuum stirring for adsorption treatment.

6. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, The multi-stage molecular distillation system employs a scraped-film molecular distillation apparatus, wherein the scraped-film rotor speed of the scraped-film molecular distillation apparatus is controlled between 150 rpm and 400 rpm, and the multi-stage molecular distillation system comprises a first-stage degassing unit and a second-stage separation and rectification unit connected in series.

7. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 6, characterized in that, The process parameters for the first-stage degassing unit are: The feed temperature is controlled at 40℃ to 60℃, and the system absolute pressure is controlled at 50Pa to 200Pa, which is used to remove trace amounts of solvent and light component impurities remaining in the eucalyptus oil intermediate.

8. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 6, characterized in that, The process parameters for the second-stage separation and distillation unit are as follows: The heating medium temperature is controlled between 80℃ and 120℃, the condensing surface temperature is controlled between -10℃ and 5℃, and the system absolute pressure is controlled between 5Pa and 20Pa, which is used to extract the main fraction of 1,8-cineole.

9. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, The method further includes a post-processing step for urea recovery from the filter cake generated in the solid-liquid separation step. The post-processing step involves adding the filter cake to hot water and stirring to decompose the inclusion complex. After standing and separating into layers, the upper oil phase is removed, and the lower aqueous phase is cooled and crystallized to recover urea crystals.

10. The optimized process for purifying eucalyptus oil using low-energy multi-stage molecular distillation according to claim 1, characterized in that, After the inclusion reaction is completed and before the solid-liquid separation, diatomaceous earth or perlite, accounting for 1% to 5% of the mass of the crude eucalyptus oil, is added to the reaction system as a filter aid, and the mixture is stirred and dispersed for 10 to 30 minutes to improve the filtration performance of the suspension.