Method for extracting high linolenic acid based on flaxseed as raw material

Abstract

The invention relates to the technical field of flaxseed purification, and particularly discloses a method for extracting high linolenic acid based on flaxseeds as a raw material, raw material pretreatment: high-quality flaxseeds are selected, impurities such as stones and dust are removed through a specific gravity screening machine, and the impurity removal rate reaches 99% or above; according to raw material pretreatment, through efficient impurity removal, low-temperature shelling and smashing under inert gas protection, damage and oxidation of flaxseed kernels are reduced, high-quality raw materials are provided for subsequent extraction, subcritical solvent extraction is adopted and matched with pulse type stirring, and compared with a traditional squeezing method, the extraction efficiency is greatly improved; the linolenic acid extraction method has the advantages that the linolenic acid extraction method is simple, the risk of organic solvent residue in a conventional solvent extraction method is avoided, the product safety requirement is better met, meanwhile, oxidative deterioration of the linolenic acid is effectively prevented due to strict temperature control and inert gas protection, pollution to the environment is reduced due to efficient recovery and recycling of the solvent, and both environmental protection and economic benefits are considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flaxseed purification, and particularly relates to a method for extracting high linolenic acid based on flaxseed as raw material. BACKGROUND

[0002] As an important polyunsaturated fatty acid, linolenic acid has wide application value in the fields of food, medicine and health care products. Flaxseed is an important natural source of linolenic acid, has high oil content, and the proportion of linolenic acid in total fatty acid can reach more than 50%, so extracting high-purity linolenic acid from flaxseed has become one of the current research hotspots.

[0003] At present, the mainstream methods for extracting linolenic acid from flaxseed include pressing method, solvent extraction method, supercritical fluid extraction method and subsequent refining and purification process, but there are obvious limitations in practical application. The traditional pressing method has low extraction efficiency and high oil impurity content, which brings great difficulty to subsequent purification. The conventional solvent extraction method depends on organic solvents such as n-hexane, which not only has the risk of solvent residue, affecting product safety, but also pollutes the environment. If the temperature is not properly controlled during extraction, linolenic acid is easily oxidized and deteriorated. Although the supercritical fluid extraction method can improve the extraction efficiency and product purity, it is difficult to realize large-scale industrial production due to large equipment investment and high operating cost. In the purification process, the existing technology often uses single or combined processes such as urea inclusion, molecular distillation and column chromatography, but the purification effect is poor. Pure urea inclusion is difficult to completely remove saturated fatty acids and monounsaturated fatty acids, resulting in low purity of linolenic acid. If the parameters of molecular distillation are not properly controlled, linolenic acid is easily lost or the purity fluctuates. Column chromatography is complex to operate and sensitive to parameters such as eluent ratio and flow rate, so it is difficult to stably obtain high-purity products. SUMMARY

[0004] The present application aims to provide a method for extracting high linolenic acid based on flaxseed as raw material to solve the problems in the background art.

[0005] To achieve the above-mentioned purpose, the present application provides a method for extracting high linolenic acid based on flaxseed as raw material, comprising the following steps: S1: raw material pretreatment: selecting high-quality flaxseed, removing stones, dust and other impurities through a specific gravity screening machine, and the impurity removal rate reaches more than 99%; using low-temperature shelling technology to remove the shell, and the environmental temperature is controlled at 15-25 DEG C during the shelling process to avoid heating of the flaxseed kernel; then the shelled flaxseed is crushed into fine powder with a particle size of 60-100 mesh at a temperature not higher than 40 DEG C through multi-stage grinding equipment, and inert gas is introduced for protection during the crushing process to prevent oxidation of the flaxseed kernel.

[0006] S2: Preliminary Extraction: The flaxseed powder obtained in step S1 is mixed with subcritical butane or propane solvent at a material-to-liquid ratio of 1:3-5. Extraction is carried out in a closed extraction device at a temperature of 25-35℃ and a pressure of 0.3-0.6MPa for 40-60 minutes. Pulsed stirring is used during extraction at a frequency of 30-50 times / minute to obtain an extract containing flaxseed oil and other components. After extraction, the solvent is recovered through a three-stage vacuum flash evaporation system. The first-stage flash evaporation temperature is 40-50℃ and the pressure is 0.1-0.2MPa; the second-stage flash evaporation temperature is 30-40℃ and the pressure is 0.05-0.1MPa; and the third-stage flash evaporation temperature is 20-30℃ and the pressure is 0.01-0.05MPa. The solvent recovery rate reaches over 99.5%.

[0007] S3: Solid-liquid separation: The extract from step S2 is first coarsely filtered through a 200-mesh filter to remove large particulate impurities. Then, it is centrifuged in a disc centrifuge at 3000-4000 r / min for 10-15 minutes to separate the solid and liquid phases. The liquid phase is collected to obtain the preliminary extracted flaxseed oil solution. The solid residue is recycled after being washed with solvent twice.

[0008] S4: Refining and Impurity Removal: The flaxseed oil solution obtained in step S3 is refined by degumming. Phosphoric acid (0.1%-0.3% by mass) is added to the solution, and the mixture is stirred at 60-70℃ for 30-40 minutes at a stirring speed of 80-100 r / min to remove colloidal impurities such as phospholipids. Then, alkali refining and deacidification are performed by adding a 5%-8% sodium hydroxide solution and stirring at 50-60℃ for 20-30 minutes at a stirring speed of 60-80 r / min to neutralize free fatty acids. The oil is washed 2-3 times with hot water at 50-60℃ using a continuous washing device, with a water-to-oil volume ratio of 1:3-5 each time, until the pH of the washing water is 6-7, removing soap residue. Finally, a decolorization treatment is performed by adding 0.5%-1% activated clay by weight of the oil and stirring at 80-90℃ for 30-40 minutes at a stirring speed of 50-70 r / min to adsorb pigments and other impurities. Then, the oil is filtered through a plate and frame filter press at a pressure of 0.2-0.3 MPa to remove the activated clay, yielding pre-refined flaxseed oil.

[0009] S5: Dewaxing treatment: The flaxseed oil initially refined in step S4 is pumped into a jacketed cooling tank and cooled to 5-10°C at a rate of 0.5-1°C / hour by circulating chilled brine, and maintained for 12-18 hours to allow the wax to crystallize out; then the wax is separated by a vacuum drum filter under a vacuum of 0.06-0.08MPa and a filtration temperature of 5-10°C to obtain dewaxed flaxseed oil with a wax removal rate of over 98%.

[0010] S6: Ethyl esterification reaction: Dewaxed linseed oil and ethanol are mixed at a molar ratio of 1:2-3. Concentrated sulfuric acid (0.5%-1% by weight of oil) is added as a catalyst. The mixture is stirred under reflux for 3-5 hours at 65-75℃ in a stainless steel reactor equipped with a reflux condenser. The temperature of the condensate in the reflux condenser is controlled at 15-20℃, and the stirring speed is 80-100 r / min. The esterification reaction is carried out to produce a mixture of ethyl linoleate and other fatty acid ethyl esters. After the reaction is completed, sodium carbonate solution (5%-8% by mass) is added to neutralize the sulfuric acid and adjust the pH to 6-7. Then, the mixture is washed 2-3 times with hot water at 50-60℃, with a water-to-oil volume ratio of 1:3-5 each time, until the wash water is clear.

[0011] S7: Preliminary separation of urea inclusion complex: Prepare a urea-ethanol solution by mixing urea and ethanol at a mass ratio of 1:2-3, and heat to 50-60℃ to completely dissolve it. Then, slowly add the ethyl ester mixture obtained in step S6 to the urea-ethanol solution at a volume ratio of 1:(1-2). Reflux and stir at 50-60℃ for 30-60 minutes at a stirring speed of 60-80 r / min until the mixture is completely dissolved. Afterward, place the solution in a temperature-controlled crystallizer and cool it to room temperature at a rate of 1-2℃ / hour. Then, slowly cool the mixture to -5 to 0°C over 4-6 hours at a rate of 0.5-1°C / hour, causing saturated fatty acid ethyl esters and some monounsaturated fatty acid ethyl esters to form crystalline inclusion complexes with urea and precipitate out. Filter the mixture through a Buchner funnel and a vacuum pump at a pressure of 0.04-0.06 MPa to separate the filtrate. During filtration, wash the crystals 2-3 times with cold ethanol at 5-10°C, using 10%-20% of the crystal mass each time to reduce the loss of the target product in the filtrate. The filtrate mainly contains polyunsaturated fatty acid ethyl esters such as linoleic acid ethyl ester.

[0012] S8: Molecular distillation purification: The filtrate obtained in step S7 is subjected to molecular distillation using a two-stage scraped membrane molecular distillation apparatus. In the first stage of molecular distillation, the distillation temperature is controlled at 100-120℃, the pressure at 0.1-0.5Pa, and the scraping speed at 100-150r / min to remove light component impurities. Then, in the second stage of molecular distillation, the distillation temperature is controlled at 130-150℃, the pressure at 0.01-0.1Pa, and the scraping speed at 100-150r / min to collect ethyl linoleate with a purity of over 85%. During the molecular distillation process, the temperature fluctuation is controlled within ±1℃ by an intelligent temperature control system, and the pressure fluctuation of the vacuum system is controlled within ±0.01Pa.

[0013] S9: Column Chromatography for Deep Purification: The ethyl linoleate with a purity of over 85% obtained in step S8 is further purified by silica gel column chromatography. The silica gel column specifications are 2-3 cm in diameter and 20-30 cm in height, with a silica gel particle size of 100-200 mesh. Wet packing is used to ensure uniform silica gel packing. Hexane and ethyl acetate are used as the eluent at a volume ratio of 5-8:1, with the elution flow rate controlled at 1-2 mL / min. The eluent is collected in steps, every 5-10 mL. The purity of ethyl linoleate in the eluent is determined by thin-layer chromatography, and the combined purity is ≥95%. The eluent is then removed by vacuum distillation using a rotary evaporator at 40-50℃ and a vacuum degree of 0.08-0.09MPa to obtain a high-purity ethyl linoleate product with a purity of over 95%. If it is necessary to convert it into linolenic acid, the high-purity ethyl linoleate can be mixed with a 10%-15% sodium hydroxide solution at a mass ratio of 1:3-5, and hydrolyzed by stirring at 60-70℃ for 2-3 hours. Then, 10%-15% hydrochloric acid is added to acidify to a pH value of 2-3. After standing and separating the layers, the upper oil phase is collected and washed with water until neutral to obtain high-purity linolenic acid.

[0014] Furthermore, in S1.1: In the raw material pretreatment step S1, the gravity screening machine screens at a frequency of 50-60 times / minute. By adjusting the screen aperture and tilt angle, the impurity removal rate is ensured to reach over 99%. The low-temperature dehulling technology uses an airflow dehulling machine. By adjusting the airflow speed to 10-15m / s, the flaxseed shells are effectively separated from the kernels, and the kernel breakage rate is controlled within 5%.

[0015] S1.2: The pulverizing process uses an air-cooled pulverizer with a blade rotation speed of 3000-4000 r / min. The temperature of the pulverizing chamber is controlled at 30-40℃ through a cold air circulation system. At the same time, nitrogen is introduced as an inert protective gas with a flow rate of 0.5-1 L / min to prevent the loss of nutrients in flaxseed due to excessive temperature or contact with air.

[0016] Furthermore, S2.1: In the preliminary extraction step S2, the extraction equipment adopts an intermittent extraction vessel with a pulse stirring device. The pulse width of the pulse stirring is 1-2 seconds and the interval is 3-5 seconds, so that the flaxseed powder and the solvent are fully in contact, and the extraction efficiency is 15%-20% higher than that of conventional stirring.

[0017] S2.2: The condenser of the three-stage vacuum flash evaporation system uses a low-temperature ethylene glycol solution as the cooling medium, with the temperature controlled between -5 and 0℃ to ensure full condensation and recovery of the solvent. After precision filtration and dehydration, the recovered solvent has a purity of over 99.9% and can be directly recycled for subsequent extraction operations, reducing solvent costs and environmental pollution.

[0018] Furthermore, S4.1: In the refining and impurity removal step S4, after degumming, a disc centrifuge is used for solid-liquid separation. The centrifuge speed is 3000-4000 r / min, and the separation time is 10-15 minutes. The separated colloidal impurities can be recycled as feed additives after drying.

[0019] S4.2: After alkali refining and deacidification, the water temperature control accuracy of the continuous water washing device is ±1℃. During the water washing process, a stirring device is used with a stirring speed of 50-60r / min to ensure that soap residue and residual alkali are fully removed. The wastewater after water washing is treated by an oil-water separator and then recycled to reduce water waste.

[0020] S4.3: After decolorization treatment, the filter cloth pore size of the plate and frame filter press is 0.1-0.2μm, the filtration pressure is 0.2-0.3MPa, and the filtered activated clay can be reused after regeneration treatment with a regeneration rate of over 80%.

[0021] Furthermore, in step S5.1: In the dewaxing process S5, the stirring device of the jacketed cooling tank rotates at 30-40 r / min to ensure uniform cooling. The cooling rate is controlled by the flow rate of the circulating chilled brine, allowing the wax to slowly crystallize and precipitate, with the crystal particles reaching a diameter of 50-100 μm, thereby improving the wax separation effect.

[0022] S5.2: The filter cloth material of the vacuum drum filter is polytetrafluoroethylene. The filtration area is adjusted according to the throughput. The vacuum degree is controlled at 0.06-0.08MPa, and the filtration temperature is maintained at 5-10℃. The filtered wax can be used for industrial applications after solvent cleaning and drying, ensuring complete separation of wax and oil.

[0023] Furthermore, in step S6.1: In the esterification reaction step S6, the inner wall of the stainless steel reactor is polished to a roughness Ra≤0.8μm to prevent material from sticking to the wall; the condensation efficiency of the reflux condenser reaches more than 95% to ensure that ethanol is fully refluxed, improve the reaction conversion rate, and the esterification conversion rate reaches more than 90%.

[0024] S6.2: During the neutralization washing process, the sodium carbonate solution is added at a rate of 0.5-1 L / min. The pH value of the reaction system is monitored in real time by an online pH monitor to ensure accurate neutralization. Deionized water is used for hot water washing to avoid introducing new impurities.

[0025] Furthermore, in the preparation of the urea alcohol solution in S7.1, the stirring speed is 60-80 r / min, the temperature control accuracy of the program temperature control system is ±0.5℃, the diameter of the Buchner funnel used for filtration is selected according to the throughput, the filtration rate of the vacuum pump is adjustable, the filtration pressure is stable at 0.04-0.06 MPa, and the temperature of the cold ethanol is 5-10℃. S7.2: Spraying is used during the washing process to reduce the loss of the target product in the filtrate.

[0026] Furthermore, in step S8.1: In the molecular distillation purification step S8, both the primary and secondary molecular distillation equipment adopt a scraped film molecular distillation apparatus. The gap between the scraper and the distillation apparatus wall is 0.5-1 mm, and the scraping speed is controlled at 100-150 r / min, so that the material forms a uniform film on the distillation apparatus wall with a film thickness of 0.1-0.2 mm, thereby improving distillation efficiency.

[0027] S8.2: During molecular distillation, the vacuum system uses a two-stage vacuum pump group to ensure stable vacuum; the heating system uses electric heating and a PID control system to precisely control the distillation temperature, with temperature fluctuations controlled within ±1℃, ensuring consistent product quality and batch-to-batch purity differences ≤1%.

[0028] Furthermore, in step S9.1: In the column chromatography deep purification step S9, the silica gel column is packed at a rate of 5-10 mL / min. The solvent used for wet packing is the same as the eluent to ensure uniform silica gel packing and a column efficiency of ≥1000 theoretical plates / m. Thin-layer chromatography uses silica gel G plates and hexane-ethyl acetate 8:1 as the developing solvent. The purity of ethyl linoleate in the eluent is detected by UV detector at a wavelength of 254 nm.

[0029] S9.2: During the elution process, an automatic partial collector is used for stepwise collection, and the collection interval can be adjusted according to the elution rate; the evaporation rate of the rotary evaporator is 5-10 mL / min to ensure complete removal of the eluent and no loss of the target product; online stirring and temperature monitoring are used during hydrolysis and acidification to ensure that the reaction proceeds fully.

[0030] Compared with the prior art, the beneficial effects of the present invention are: Firstly, in this invention, the raw material pretreatment reduces damage and oxidation of flaxseed kernels through efficient impurity removal, low-temperature dehulling, and pulverization under inert gas protection, providing high-quality raw materials for subsequent extraction. The use of subcritical solvent extraction combined with pulse stirring significantly improves extraction efficiency compared to traditional pressing methods and avoids the risk of organic solvent residues in conventional solvent extraction methods, thus better meeting product safety requirements. At the same time, strict temperature control and inert gas protection effectively prevent linolenic acid oxidation and deterioration, and the efficient recovery and recycling of solvents also reduce environmental pollution, balancing environmental protection and economic benefits.

[0031] Secondly, this invention forms a highly efficient and synergistic purification system through the optimized combination of urea inclusion, molecular distillation, and column chromatography. This solves the problem of poor purification results in existing processes. Urea inclusion can more thoroughly remove impurity fatty acids, the precise parameter control of molecular distillation reduces the loss of target components and purity fluctuations, and the optimization of column chromatography simplifies the operation and can stably obtain high-purity products. In addition, the entire process uses conventional industrial equipment, requiring no high investment. The parameters of each step are clear and easy to control, facilitating large-scale production. At the same time, the effective recovery of by-products improves the utilization rate of raw materials and reduces production costs, making it suitable for large-scale industrial promotion. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see Figure 1 In this embodiment of the invention, a method for extracting high-linolenic acid from flaxseed includes the following steps: S1: Raw material pretreatment: Select high-quality flaxseeds and remove impurities such as stones and dust using a gravity screening machine, with an impurity removal rate of over 99%; use low-temperature dehulling technology to remove the outer shell, with the ambient temperature controlled at 15-25℃ during the dehulling process to avoid overheating of the flaxseed kernels; then pulverize the dehulled flaxseeds into fine powder with a particle size of 60-100 mesh using multi-stage grinding equipment at a temperature not exceeding 40℃, with inert gas introduced during the pulverizing process to prevent oxidation of the flaxseed kernels; S1.1: In the raw material pretreatment step S1, the gravity screening machine screens at a frequency of 50-60 times / minute. By adjusting the screen aperture and tilt angle, the impurity removal rate is ensured to reach over 99%. The low-temperature dehulling technology uses an airflow dehulling machine. By adjusting the airflow speed to 10-15m / s, the flaxseed shells are effectively separated from the kernels, and the kernel breakage rate is controlled within 5%. S1.2: The pulverizing process uses an air-cooled pulverizer with a blade rotation speed of 3000-4000 r / min. The temperature of the pulverizing chamber is controlled at 30-40℃ through a cold air circulation system. At the same time, nitrogen is introduced as an inert protective gas with a flow rate of 0.5-1 L / min to prevent the loss of nutrients in flaxseed due to excessive temperature or contact with air.

[0035] S2: Preliminary Extraction: The flaxseed powder obtained in step S1 is mixed with subcritical butane or propane solvent at a material-to-liquid ratio of 1:3-5. Extraction is carried out in a closed extraction device at a temperature of 25-35℃ and a pressure of 0.3-0.6MPa for 40-60 minutes. Pulsed stirring is used during extraction at a frequency of 30-50 times / minute to obtain an extract containing flaxseed oil and other components. After extraction, the solvent is recovered through a three-stage vacuum flash evaporation system. The first-stage flash evaporation temperature is 40-50℃ and the pressure is 0.1-0.2MPa; the second-stage flash evaporation temperature is 30-40℃ and the pressure is 0.05-0.1MPa; and the third-stage flash evaporation temperature is 20-30℃ and the pressure is 0.01-0.05MPa. The solvent recovery rate reaches over 99.5%. S2.1: In the preliminary extraction step S2, the extraction equipment adopts an intermittent extraction vessel with a pulse stirring device. The pulse width of the pulse stirring is 1-2 seconds and the interval is 3-5 seconds, so that the flaxseed powder and the solvent are fully in contact, and the extraction efficiency is 15%-20% higher than that of conventional stirring. S2.2: The condenser of the three-stage vacuum flash evaporation system uses a low-temperature ethylene glycol solution as the cooling medium, with the temperature controlled between -5 and 0℃ to ensure full condensation and recovery of the solvent. After precision filtration and dehydration, the recovered solvent has a purity of over 99.9% and can be directly recycled for subsequent extraction operations, reducing solvent costs and environmental pollution. S3: Solid-liquid separation: The extract from step S2 is first coarsely filtered through a 200-mesh filter to remove large particulate impurities. Then, it is centrifuged in a disc centrifuge at 3000-4000 r / min for 10-15 minutes to separate the solid and liquid phases. The liquid phase is collected to obtain the preliminary extracted flaxseed oil solution. The solid residue is recycled after being washed with solvent twice.

[0036] S4: Refining and Impurity Removal: The flaxseed oil solution obtained in step S3 is refined by degumming. Phosphoric acid (0.1%-0.3% by mass) is added to the solution, and the mixture is stirred at 60-70℃ for 30-40 minutes at a stirring speed of 80-100 r / min to remove colloidal impurities such as phospholipids. Then, alkali refining and deacidification are performed by adding a 5%-8% sodium hydroxide solution and stirring at 50-60℃ for 20-30 minutes at a stirring speed of 60-80 r / min to neutralize free fatty acids. The oil is washed 2-3 times with hot water at 50-60℃ using a continuous washing device, with a water-to-oil volume ratio of 1:3-5 each time, until the pH of the washing water is 6-7, removing soap residue. Finally, a decolorization treatment is performed by adding 0.5%-1% activated clay by weight of the oil and stirring at 80-90℃ for 30-40 minutes at a stirring speed of 50-70 r / min to adsorb pigments and other impurities. Then, the oil is filtered through a plate and frame filter press at a pressure of 0.2-0.3 MPa to remove the activated clay, yielding pre-refined flaxseed oil. S4.1: In the refining and impurity removal step S4, after degumming, a disc centrifuge is used for solid-liquid separation. The centrifuge speed is 3000-4000 r / min and the separation time is 10-15 minutes. The separated colloidal impurities can be recycled as feed additives after drying. S4.2: After alkali refining and deacidification, the water temperature control accuracy of the continuous water washing device is ±1℃. During the water washing process, a stirring device is used with a stirring speed of 50-60r / min to ensure that soap residue and residual alkali are fully removed. The wastewater after water washing is treated by an oil-water separator and then recycled to reduce water waste. S4.3: After decolorization treatment, the filter cloth pore size of the plate and frame filter press is 0.1-0.2μm, the filtration pressure is 0.2-0.3MPa, and the filtered activated clay can be reused after regeneration treatment with a regeneration rate of over 80%.

[0037] S5: Dewaxing treatment: The flaxseed oil initially refined in step S4 is pumped into a jacketed cooling tank and cooled to 5-10°C at a rate of 0.5-1°C / hour by circulating chilled brine, and maintained for 12-18 hours to allow the wax to crystallize out; then the wax is separated by a vacuum drum filter under a vacuum of 0.06-0.08MPa and a filtration temperature of 5-10°C to obtain dewaxed flaxseed oil with a wax removal rate of over 98%; S5.1: In the dewaxing step S5, the stirring device of the jacketed cooling tank rotates at 30-40 r / min to ensure uniform cooling. The cooling rate is controlled by the flow rate of the circulating chilled brine, allowing the wax to slowly crystallize and precipitate, with the crystal particle diameter reaching 50-100 μm, thereby improving the wax separation effect. S5.2: The filter cloth material of the vacuum drum filter is polytetrafluoroethylene (PTFE). The filtration area is adjusted according to the throughput. The vacuum degree is controlled at 0.06-0.08 MPa, and the filtration temperature is maintained at 5-10℃. The filtered wax can be used for industrial applications after solvent cleaning and drying, ensuring complete separation of wax and oil. S6: Ethyl esterification reaction: Dewaxed linseed oil and ethanol are mixed at a molar ratio of 1:2-3. Concentrated sulfuric acid (0.5%-1% by weight of oil) is added as a catalyst. The mixture is stirred under reflux for 3-5 hours at 65-75℃ in a stainless steel reactor equipped with a reflux condenser. The temperature of the condensate in the reflux condenser is controlled at 15-20℃, and the stirring speed is 80-100 r / min. The esterification reaction is carried out to produce a mixture of ethyl linoleate and other fatty acid ethyl esters. After the reaction is completed, sodium carbonate solution (5%-8% by mass) is added to neutralize the sulfuric acid and adjust the pH to 6-7. Then, the mixture is washed 2-3 times with hot water at 50-60℃, with a water-to-oil volume ratio of 1:3-5 each time, until the wash water is clear. S6.1: In the esterification reaction step S6, the inner wall of the stainless steel reactor is polished to a roughness Ra≤0.8μm to prevent material from sticking to the wall; the condensation efficiency of the reflux condenser reaches more than 95% to ensure that ethanol is fully refluxed, improve the reaction conversion rate, and the esterification conversion rate reaches more than 90%. S6.2: During the neutralization washing process, the sodium carbonate solution is added at a rate of 0.5-1 L / min. The pH value of the reaction system is monitored in real time by an online pH monitor to ensure accurate neutralization. Deionized water is used for hot water washing to avoid introducing new impurities.

[0038] S7: Preliminary separation of urea inclusion complex: Prepare a urea-ethanol solution by mixing urea and ethanol at a mass ratio of 1:2-3, and heat to 50-60℃ to completely dissolve it. Then, slowly add the ethyl ester mixture obtained in step S6 to the urea-ethanol solution at a volume ratio of 1:(1-2). Reflux and stir at 50-60℃ for 30-60 minutes at a stirring speed of 60-80 r / min until the mixture is completely dissolved. Afterward, place the solution in a temperature-controlled crystallizer and cool it to room temperature at a rate of 1-2℃ / hour. Then, slowly cool the mixture to -5 to 0°C over 4-6 hours at a rate of 0.5-1°C / hour, causing saturated fatty acid ethyl esters and some monounsaturated fatty acid ethyl esters to form crystalline inclusion complexes with urea and precipitate out. Filter the mixture through a Buchner funnel and a vacuum pump at a pressure of 0.04-0.06 MPa to separate the filtrate. During filtration, wash the crystals 2-3 times with cold ethanol at 5-10°C, using 10%-20% of the crystal mass each time to reduce the loss of the target product in the filtrate. The filtrate mainly contains polyunsaturated fatty acid ethyl esters such as linoleic acid ethyl ester.

[0039] S8: Molecular distillation purification: The filtrate obtained in step S7 is subjected to molecular distillation using a two-stage scraped-film molecular distillation apparatus. In the first stage, the distillation temperature is controlled at 100-120℃, the pressure at 0.1-0.5 Pa, and the scraping speed at 100-150 r / min to remove light component impurities. Then, in the second stage, the distillation temperature is controlled at 130-150℃, the pressure at 0.01-0.1 Pa, and the scraping speed at 100-150 r / min to collect ethyl linoleate with a purity of over 85%. During the molecular distillation process, the temperature fluctuation is controlled within ±1℃ using an intelligent temperature control system, and the pressure fluctuation of the vacuum system is controlled within ±0.01 Pa. S8.1: In the molecular distillation purification step S8, both the primary and secondary molecular distillation equipment adopt a scraped film molecular distillation apparatus. The gap between the scraper and the distillation apparatus wall is 0.5-1mm, and the scraper speed is controlled at 100-150r / min, so that the material forms a uniform film on the distillation apparatus wall with a film thickness of 0.1-0.2mm, thereby improving distillation efficiency. S8.2: During molecular distillation, the vacuum system uses a two-stage vacuum pump group to ensure stable vacuum; the heating system uses electric heating and a PID control system to precisely control the distillation temperature, with temperature fluctuations controlled within ±1℃, ensuring consistent product quality and batch-to-batch purity differences ≤1%.

[0040] S9: Column Chromatography for Deep Purification: The ethyl linoleate with a purity of over 85% obtained in step S8 is further purified by silica gel column chromatography. The silica gel column specifications are 2-3 cm in diameter and 20-30 cm in height, with a silica gel particle size of 100-200 mesh. Wet packing is used to ensure uniform silica gel packing. Hexane and ethyl acetate are used as the eluent at a volume ratio of 5-8:1, with the elution flow rate controlled at 1-2 mL / min. The eluent is collected in steps, every 5-10 mL. The purity of ethyl linoleate in the eluent is determined by thin-layer chromatography, and the combined purity is ≥95%. The eluent is then removed by vacuum distillation in a rotary evaporator at 40-50℃ and a vacuum degree of 0.08-0.09MPa to obtain a high-purity ethyl linoleate product with a purity of over 95%. If it is necessary to convert it into linolenic acid, the high-purity ethyl linoleate can be mixed with a 10%-15% sodium hydroxide solution at a mass ratio of 1:3-5, and stirred and hydrolyzed at 60-70℃ for 2-3 hours. Then, 10%-15% hydrochloric acid is added to acidify to a pH value of 2-3. After standing and separating the layers, the upper oil phase is collected and washed with water until neutral to obtain high-purity linolenic acid. S9.1: In the column chromatography deep purification step S9, the silica gel column packing speed is 5-10 mL / min, and the solvent used for wet packing is the same as the eluent to ensure uniform silica gel packing and column efficiency reaching a theoretical plate number ≥1000 / m; thin-layer chromatography uses silica gel G thin-layer plates, and the developing solvent is n-hexane-ethyl acetate 8:1. The purity of ethyl linoleate in the eluent is detected by UV detector at a wavelength of 254 nm. S9.2: During the elution process, an automatic partial collector is used for stepwise collection, and the collection interval can be adjusted according to the elution rate; the evaporation rate of the rotary evaporator is 5-10 mL / min to ensure complete removal of the eluent and no loss of the target product; online stirring and temperature monitoring are used during hydrolysis and acidification to ensure that the reaction proceeds fully.

[0041] The working principle of this invention is as follows: In the raw material pretreatment stage, impurities are first removed by gravity screening to ensure the purity of the raw materials and reduce interference in subsequent extraction; low-temperature dehulling technology uses airflow to separate the outer shell and kernel, while controlling the kernel breakage rate to avoid loss of effective components; low-temperature pulverization under inert gas protection increases the contact area between the raw materials and solvent by controlling temperature and particle size, while preventing the linolenic acid in flaxseed kernels from oxidizing and deteriorating due to high temperature or contact with air, laying the foundation for efficient extraction; during the initial extraction, subcritical butane or propane is used as the solvent, which can effectively dissolve flaxseed oil under specific temperature and pressure conditions, and pulse stirring can enhance the interaction between the solvent and the raw materials. The system improves contact efficiency and extraction rate. A three-stage vacuum flash evaporation system gradually reduces temperature and pressure, enabling efficient solvent recovery and recycling, thus reducing costs and environmental pollution. The solid-liquid separation stage combines coarse filtration and centrifugation to remove solid impurities from the extract, yielding a relatively pure flaxseed oil solution, providing high-quality raw materials for subsequent refining. During refining and impurity removal, degumming utilizes phosphoric acid to remove colloidal impurities such as phospholipids; alkali refining and deacidification neutralizes free fatty acids with sodium hydroxide and removes soap residue through washing; decolorization utilizes activated clay to adsorb pigments. These multi-stage processes significantly reduce the impurity content in the oil; and dewaxing causes wax crystallization through slow cooling. Vacuum filtration is then used to separate the flaxseed oil, avoiding the influence of wax on subsequent purification. Ethyl esterification converts flaxseed oil into a mixture of ethyl linoleate and other fatty acid ethyl esters, making the fatty acids easier to separate in subsequent processes. A reflux condenser ensures full ethanol participation in the reaction, improving the conversion rate. Neutralization washing removes the catalyst and residual impurities. Urea inclusion complexation is used for preliminary separation, utilizing the difference in binding ability of urea with fatty acid ethyl esters of different saturations. Under precise temperature control, saturated and some monounsaturated fatty acid ethyl esters form crystalline inclusion complexes, which are then filtered to obtain a filtrate rich in ethyl linoleate, achieving preliminary separation. Molecular distillation purification is based on the different molecular motion paths of various substances. The differences in linoleic acid are addressed through two-stage distillation to remove light component impurities and separate the target product. Precise control of temperature, pressure, and scraper rotation speed ensures purification efficiency and product stability. Column chromatography for deep purification utilizes the differences in adsorption and desorption capacity of silica gel for different fatty acid ethyl esters. Elution is performed with a specific ratio of eluent at a certain flow rate. High-purity linoleic acid ethyl ester fractions are collected by detection, and the eluent is removed by vacuum distillation to obtain the high-purity product. If conversion to linoleic acid is required, alkaline hydrolysis converts the ethyl ester to sodium salt, followed by acidification to obtain high-purity linoleic acid. The entire process achieves efficient and stable extraction of high-purity linoleic acid from flaxseed through precise control of parameters at each stage.

Claims

1. A method for extracting high-linolenic acid from flaxseed, characterized in that, Includes the following steps: S1: Raw material pretreatment: Select high-quality flaxseeds and remove impurities such as stones and dust using a gravity screening machine, with an impurity removal rate of over 99%; use low-temperature dehulling technology to remove the outer shell, with the ambient temperature controlled at 15-25℃ during the dehulling process to avoid overheating of the flaxseed kernels; then pulverize the dehulled flaxseeds into fine powder with a particle size of 60-100 mesh using multi-stage grinding equipment at a temperature not exceeding 40℃, with inert gas introduced during the pulverizing process to prevent oxidation of the flaxseed kernels; S2: Preliminary Extraction: The flaxseed powder obtained in step S1 is mixed with subcritical butane or propane solvent at a material-to-liquid ratio of 1:3-5. Extraction is carried out in a closed extraction device at a temperature of 25-35℃ and a pressure of 0.3-0.6MPa for 40-60 minutes. Pulsed stirring is used during extraction at a frequency of 30-50 times / minute to obtain an extract containing flaxseed oil and other components. After extraction, the solvent is recovered through a three-stage vacuum flash evaporation system. The first-stage flash evaporation temperature is 40-50℃ and the pressure is 0.1-0.2MPa; the second-stage flash evaporation temperature is 30-40℃ and the pressure is 0.05-0.1MPa; and the third-stage flash evaporation temperature is 20-30℃ and the pressure is 0.01-0.05MPa. The solvent recovery rate reaches over 99.5%. S3: Solid-liquid separation: The extract from step S2 is first coarsely filtered through a 200-mesh filter to remove large particulate impurities. Then, a disc centrifuge is used to centrifuge at 3000-4000 r / min for 10-15 minutes to separate the solid and liquid phases. The liquid phase is collected to obtain the preliminary extracted flaxseed oil solution. The solid residue is recycled after being washed with solvent twice. S4: Refining and Impurity Removal: The flaxseed oil solution obtained in step S3 is refined by degumming. Phosphoric acid (0.1%-0.3% by mass) is added to the solution, and the mixture is stirred at 60-70℃ for 30-40 minutes at a stirring speed of 80-100 r / min to remove colloidal impurities such as phospholipids. Then, alkali refining and deacidification are performed by adding a 5%-8% sodium hydroxide solution and stirring at 50-60℃ for 20-30 minutes at a stirring speed of 60-80 r / min to neutralize free fatty acids. The oil is washed 2-3 times with hot water at 50-60℃ using a continuous washing device, with a water-to-oil volume ratio of 1:3-5 each time, until the pH of the washing water is 6-7, removing soap residue. Finally, a decolorization treatment is performed by adding 0.5%-1% activated clay by weight of the oil and stirring at 80-90℃ for 30-40 minutes at a stirring speed of 50-70 r / min to adsorb pigments and other impurities. Then, the oil is filtered through a plate and frame filter press at a pressure of 0.2-0.3 MPa to remove the activated clay, yielding pre-refined flaxseed oil. S5: Dewaxing treatment: The flaxseed oil initially refined in step S4 is pumped into a jacketed cooling tank and cooled to 5-10°C at a rate of 0.5-1°C / hour by circulating chilled brine, and maintained for 12-18 hours to allow the wax to crystallize out; then the wax is separated by a vacuum drum filter under a vacuum of 0.06-0.08MPa and a filtration temperature of 5-10°C to obtain dewaxed flaxseed oil with a wax removal rate of over 98%; S6: Ethyl esterification reaction: Dewaxed linseed oil and ethanol are mixed at a molar ratio of 1:2-3. Concentrated sulfuric acid (0.5%-1% by weight of oil) is added as a catalyst. The mixture is stirred under reflux for 3-5 hours at 65-75℃ in a stainless steel reactor equipped with a reflux condenser. The temperature of the condensate in the reflux condenser is controlled at 15-20℃, and the stirring speed is 80-100 r / min. The esterification reaction is carried out to produce a mixture of ethyl linoleate and other fatty acid ethyl esters. After the reaction is completed, sodium carbonate solution (5%-8% by mass) is added to neutralize the sulfuric acid and adjust the pH to 6-7. Then, the mixture is washed 2-3 times with hot water at 50-60℃, with a water-to-oil volume ratio of 1:3-5 each time, until the wash water is clear. S7: Preliminary separation of urea inclusion complex: Prepare a urea-ethanol solution by mixing urea and ethanol at a mass ratio of 1:2-3, and heat to 50-60℃ to completely dissolve it. Then, slowly add the ethyl ester mixture obtained in step S6 to the urea-ethanol solution at a volume ratio of 1:(1-2). Reflux and stir at 50-60℃ for 30-60 minutes at a stirring speed of 60-80 r / min until the mixture is completely dissolved. Afterward, place the solution in a temperature-controlled crystallizer and cool it to room temperature at a rate of 1-2℃ / hour. Then, slowly cool the mixture to -5 to 0°C over 4-6 hours at a rate of 0.5-1°C / hour, causing saturated fatty acid ethyl esters and some monounsaturated fatty acid ethyl esters to form crystalline inclusion complexes with urea and precipitate out. Filter the mixture through a Buchner funnel and a vacuum pump at a pressure of 0.04-0.06 MPa to separate the filtrate. During filtration, wash the crystals 2-3 times with cold ethanol at 5-10°C, each time using 10%-20% of the crystal mass, to reduce the loss of the target product in the filtrate. The filtrate mainly contains polyunsaturated fatty acid ethyl esters such as linoleic acid ethyl ester. S8: Molecular distillation purification: The filtrate obtained in step S7 is subjected to molecular distillation using a two-stage scraped-film molecular distillation apparatus. In the first stage, the distillation temperature is controlled at 100-120℃, the pressure at 0.1-0.5 Pa, and the scraping speed at 100-150 r / min to remove light component impurities. Then, in the second stage, the distillation temperature is controlled at 130-150℃, the pressure at 0.01-0.1 Pa, and the scraping speed at 100-150 r / min to collect ethyl linoleate with a purity of over 85%. During the molecular distillation process, the temperature fluctuation is controlled within ±1℃ using an intelligent temperature control system, and the pressure fluctuation of the vacuum system is controlled within ±0.01 Pa. S9: Column Chromatography for Deep Purification: The ethyl linoleate with a purity of over 85% obtained in step S8 is further purified by silica gel column chromatography. The silica gel column specifications are 2-3 cm in diameter and 20-30 cm in height, with a silica gel particle size of 100-200 mesh. Wet packing is used to ensure uniform silica gel packing. Hexane and ethyl acetate are used as the eluent at a volume ratio of 5-8:1, with the elution flow rate controlled at 1-2 mL / min. The eluent is collected in steps, every 5-10 mL. The purity of ethyl linoleate in the eluent is determined by thin-layer chromatography, and the combined purity is ≥95%. The eluent is then removed by vacuum distillation using a rotary evaporator at 40-50℃ and a vacuum degree of 0.08-0.09MPa to obtain a high-purity ethyl linoleate product with a purity of over 95%. If it is necessary to convert it into linolenic acid, the high-purity ethyl linoleate can be mixed with a 10%-15% sodium hydroxide solution at a mass ratio of 1:3-5, and hydrolyzed by stirring at 60-70℃ for 2-3 hours. Then, 10%-15% hydrochloric acid is added to acidify to a pH value of 2-3. After standing and separating the layers, the upper oil phase is collected and washed with water until neutral to obtain high-purity linolenic acid.

2. The method for extracting high-linolenic acid from flaxseed as raw material according to claim 1, characterized in that: The screening frequency of the heavy screening machine in S1 is 50-60 times / minute, and the pulverizing blade speed of the pulverizer is 3000-4000 r / min. The temperature of the pulverizing chamber is controlled at 30-40℃ through a cold air circulation system. At the same time, nitrogen is introduced as an inert protective gas with a flow rate of 0.5-1L / min to prevent the nutrients in flaxseed from being oxidized and lost due to excessive temperature or contact with air.

3. The method for extracting high-linolenic acid from flaxseed as raw material according to claim 1, characterized in that: The S2 extraction equipment uses an intermittent extraction vessel with a pulse stirring device. The pulse width of the pulse stirring is 1-2 seconds, and the interval is 3-5 seconds, which ensures that the flaxseed powder and solvent are in full contact, and the extraction efficiency is 15%-20% higher than that of conventional stirring. The condenser of the three-stage vacuum flash evaporation system uses a low-temperature ethylene glycol solution as the cooling medium, and the temperature is controlled at -5-0℃.

4. The method for extracting high-linolenic acid from flaxseed as raw material according to claim 1, characterized in that: After degumming in step S4, a disc centrifuge is used for solid-liquid separation. The centrifuge speed is 3000-4000 r / min, and the separation time is 10-15 minutes. After alkali refining and deacidification, the water temperature control accuracy of the continuous water washing device is ±1℃. A stirring device is used during the water washing process, with a stirring speed of 50-60 r / min. The filter cloth pore size of the plate and frame filter press is 0.1-0.2 μm, and the filtration pressure is 0.2-0.3 MPa.

5. The method for extracting high-linolenic acid from flaxseed according to claim 1, characterized in that: The stirring device of the jacketed cooling tank in S5 has a rotation speed of 30-40 r / min, the filter cloth material of the vacuum drum filter is polytetrafluoroethylene, the vacuum degree is controlled at 0.06-0.08 MPa, and the filtration temperature is maintained at 5-10℃.

6. The method for extracting high-linolenic acid from flaxseed according to claim 1, characterized in that: The inner wall of the stainless steel reactor in S6 is polished to a roughness Ra≤0.8μm to prevent material from sticking to the wall. During the neutralization and washing process, the sodium carbonate solution is added at a rate of 0.5-1L / min. Deionized water is used for hot water washing to avoid introducing new impurities.

7. The method for extracting high-linolenic acid from flaxseed as raw material according to claim 1, characterized in that: During the preparation of the urea alcohol solution in S7, the stirring speed is 60-80 r / min, the temperature control accuracy of the program temperature control system is ±0.5℃, the diameter of the Buchner funnel used for filtration is selected according to the throughput, the filtration rate of the vacuum pump is adjustable, the filtration pressure is stable at 0.04-0.06 MPa, the temperature of the cold ethanol is 5-10℃, and a spray method is used during the washing process to reduce the loss of the target product in the filtrate.

8. The method for extracting high-linolenic acid from flaxseed according to claim 1, characterized in that: Both the primary and secondary molecular distillation equipment in S8 employ scraped-film molecular distillers. The gap between the scraper and the distillation vessel wall is 0.5-1 mm, and the scraping speed is controlled at 100-150 r / min. This ensures that the material forms a uniform thin film on the distillation vessel wall with a thickness of 0.1-0.2 mm, improving distillation efficiency. During molecular distillation, the vacuum system uses a two-stage vacuum pump group to ensure stable vacuum levels. The heating system uses electric heating, and the distillation temperature is precisely controlled by a PID control system, with temperature fluctuations controlled within ±1℃ to ensure consistent product quality and batch-to-batch purity differences ≤1%.

9. The method for extracting high-linolenic acid from flaxseed as raw material according to claim 1, characterized in that: The silica gel column in S9 is packed at a rate of 5-10 mL / min. The solvent and eluent used in wet packing are the same to ensure uniform silica gel packing and a column efficiency of ≥1000 theoretical plates / m. Thin-layer chromatography uses silica gel G plates with hexane-ethyl acetate 8:1 as the developing solvent. The purity of ethyl linoleate in the eluent is detected at 254 nm using a UV detector. During elution, an automatic fraction collector is used for stepwise collection. The rotary evaporator has an evaporation rate of 5-10 mL / min to ensure complete removal of the eluent and no loss of the target product. Online stirring and temperature monitoring are used during hydrolysis and acidification to ensure the reaction proceeds fully.

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