A method and apparatus for purifying diglycerides by molecular distillation

Abstract

This invention discloses a method for purifying diglycerides by molecular distillation. (1) Near-infrared spectroscopy is used to detect the crude diglyceride product online to obtain the proportions of diglycerides, triglycerides, and free fatty acids; (2) The crude product is fed into a multi-stage molecular distillation system; (3) A purification stage is set after the distillation stage, and diglycerides with different carbon chain lengths are separated by multiple sets of traps. The separated diglycerides are condensed and gradually cooled from 100°C to 20°C to achieve targeted removal of trace impurities. This invention improves the purity and stability of diglycerides, reduces energy consumption, and extends the continuous operation time of the equipment.

Description

Technical Field

[0001] This invention relates to the field of diglyceride purification technology, and specifically to a method and apparatus for purifying diglycerides by molecular distillation. Background Technology

[0002] Diacylglycerol (DAG) is a naturally occurring trace component in oils and fats, characterized by its safety, nutritional value, and good processing adaptability, making it a promising candidate for applications in food, pharmaceuticals, and cosmetics. The preparation of high-purity diacylglycerol is crucial for its industrial application, and molecular distillation technology, due to its advantages of low temperature, high efficiency, and zero pollution, has become the primary method for diacylglycerol purification.

[0003] However, existing molecular distillation purification techniques for diglycerides have the following problems: traditional fixed-parameter molecular distillation is difficult to adapt to the differences in the characteristics of raw materials from different sources, resulting in unstable product purity; diglycerides are prone to carbonization and coking at high temperatures, affecting the heat transfer efficiency and continuous operation time of the equipment; trace impurities with boiling points close to those of diglycerides are difficult to remove effectively, affecting the preparation of high-purity products; energy consumption is high, and the product is prone to oxidation, producing off-odors and affecting product quality.

[0004] Therefore, it is of great significance to develop a method and apparatus for the molecular distillation purification of diglycerides that is efficient, stable and low in energy consumption. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for molecular distillation purification of diglycerides, so as to improve the purity and stability of diglycerides, reduce energy consumption, and extend the continuous operation time of the equipment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for purifying diglycerides by molecular distillation includes the following steps: a) Near-infrared spectroscopy was used to detect crude diglycerides online to obtain the real-time proportions of diglycerides, triglycerides, and free fatty acids. b) Based on the test results, the crude product is fed into a multi-stage molecular distillation system. The first stage removes the light component, free fatty acids, with the vacuum degree controlled at 0.1-1 Pa, the distillation temperature at 120-150℃, and the scraper rotation speed at 200-400 r / min. The second stage removes the heavy components, monoglycerides and triglycerides, with the vacuum degree controlled at 0.01-0.1 Pa and the distillation temperature at 180-220℃. c) A fine purification section is added after the main distillation section. By gradually reducing the vacuum degree from 0.05 Pa to 0.01 Pa and the collector temperature gradually decreasing from 100℃ to 20℃, the targeted removal of trace impurities is achieved.

[0007] Preferably, a pretreatment step is included before step a): the crude product with high free fatty acid content is pretreated by low carbon alcohol extraction-low temperature crystallization method to reduce the free fatty acid content to below 5%.

[0008] Preferably, in the pretreatment step, the mass ratio of ethanol to crude product is 1:2-3, free fatty acids are extracted at 40-50℃, and then the extract phase is cooled to 0-5℃ to crystallize and remove some saturated free fatty acids.

[0009] Preferably, the system also includes an inert gas atmosphere for protection and end-of-pipe degassing, with high-purity nitrogen continuously introduced into the distillation column at a flow rate of 0.1-0.3 L / min; and a vacuum degassing tower is added after the product collection tank, with a vacuum degree of 1-5 Pa and a temperature of 60-80 °C.

[0010] Preferably, by controlling the temperature gradient of multiple sets of traps, the traps are collected in 3-4 stages within the 202-210℃ range to achieve the separation of diglycerides with different carbon chain lengths.

[0011] The present invention also provides a molecular distillation purification apparatus for implementing the above method, comprising: The raw material pretreatment unit is used to pretreat crude diglycerides; Near-infrared spectroscopy online detection unit is used for real-time detection of the content of each component in the crude product; The multi-stage molecular distillation unit includes a first stage for removing light components and a second stage for removing heavy components; The purification stage employs a stepped condenser trap for targeted removal of trace impurities; Degassing system.

[0012] Preferably, the scraping assembly in the multi-segment molecular distillation unit is an integrated rotor of "scraping-ultrasonic decoking-inert gas purging". The scraping blade is made of polytetrafluoroethylene-ceramic composite material, and the edge of the blade integrates a high-frequency ultrasonic transducer with a frequency of 20-40kHz. The rotor's central shaft has a built-in inert gas guide channel.

[0013] Preferably, it also includes a short-path distillation unit, which is integrated in series with the molecular distillation unit for pretreatment of high-viscosity crude products.

[0014] Preferably, the stepped condenser includes a first-stage condenser, a second-stage condenser, and a third-stage condenser, which are controlled between 80-100℃, 40-60℃, and 0-20℃, respectively.

[0015] Preferably, the purification section further includes multiple sets of traps to achieve temperature gradient control for separating diglycerides with different carbon chain lengths.

[0016] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: This invention achieves precise matching of different raw materials to a multi-stage molecular distillation system through online near-infrared spectroscopy detection and adaptive parameter adjustment. It solves the contradiction of "incomplete removal of light components" or "thermal decomposition of target components" under traditional fixed parameters, and enables the purity of diglycerides from different raw materials to stably reach over 90%.

[0017] The integrated rotor of this invention, which combines "film scraping - ultrasonic decoking - inert gas purging," effectively solves the problem of easy carbonization and coking of diglycerides at high temperatures, extending the continuous operating time of the equipment from the traditional 8-12 hours to over 48 hours. The film scraping speed is 220-300 r / min; the ultrasonic frequency is 20-40 kHz; the power density is 1.2 W / cm²; and the N₂ flow rate is ≥0.2 L / min.

[0018] This invention achieves targeted removal of trace impurities close to the boiling point of diglycerides through gradient vacuum and temperature control in the purification stage, reducing the impurity content from 0.5%-1% to below 0.05%, providing an effective method for the preparation of high-purity diglycerides (≥95%).

[0019] The condensation coupling system and solvent pretreatment synergistic process of this invention reduce distillation energy consumption by 30%-40% and cooling water consumption by 40%, which is in line with the development trend of green processes.

[0020] This invention employs an inert gas atmosphere for protection and end-of-pipe degassing, effectively solving the problem of oxidative odor during the purification process of diglycerides. The treated product, when stored at 40°C for 6 months, shows only a 0.5-1 meq / kg increase in peroxide value and no obvious odor.

[0021] This invention achieves the separation of diglycerides with different carbon chain lengths through temperature gradient control of multiple traps, and can prepare diglyceride products with specific fatty acid compositions according to the needs of different application scenarios, thus expanding its application range. Attached Figure Description

[0022] Figure 1 This is a flowchart of the molecular distillation purification process of the present invention; The diagram shows: 1 Near-infrared spectroscopy online detection unit, 2 Short-path distillation unit, 3 Single-stage molecular distillation unit, 4 Two-stage molecular distillation unit, 5 Refining and purification section, 6 Collection tank, 7 Degassing system, 8 Raw material pretreatment unit, and 9 Multiple sets of traps. Figure 2 This is a film scraping assembly in a molecular distillation unit of the present invention; 301 Central spindle, 302 scraper, 303 ultrasonic transducer, 304 balance block, 305 guide hole position, 306 air nozzle hole, 307 wiring groove, 308 temperature sensor, 309 one-way valve, 3010 air inlet. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments.

[0024] The present invention provides a molecular distillation purification device, which includes a raw material pretreatment unit 8, a near-infrared spectroscopy online detection unit 1, a short-range distillation unit 2, a first-stage molecular distillation unit 3, a second-stage molecular distillation unit 4, a purification section (stepped condenser trap) 5, a collection tank 6, and a degassing system 7 connected in sequence.

[0025] One of the molecular distillation units is a scraping assembly that integrates scraping, ultrasonic decoking, and inert gas purging. The scraping blade is made of polytetrafluoroethylene-ceramic composite material, and the edge of the blade integrates a high-frequency ultrasonic transducer with a frequency of 30kHz. The rotor's central shaft has a built-in inert gas guide channel.

[0026] The rotor has a central axis-radial scraper symmetrical structure. Its diameter is designed according to the inner diameter of the molecular distillation vessel, and its length is matched with the heating section of the distillation vessel. It consists of four parts: a central main shaft, a polytetrafluoroethylene-ceramic composite scraper, a high-frequency ultrasonic transducer, and an inert gas guiding system, which ensures high temperature resistance and solvent corrosion resistance.

[0027] The central main shaft is hollow, with radial air passage interfaces evenly distributed along its shaft, corresponding one-to-one with the scrapers. A bearing connection section for coupling with the drive motor is located at the upper part of the shaft, and an inert gas inlet on the shaft connects to an external high-purity nitrogen source. A main inert gas guide hole is located at the center of the main shaft, branching out to each scraper and connecting to the internal air passages of the scrapers. A one-way valve is installed at the end of each branch hole to prevent material backflow into the air passages.

[0028] The PTFE-ceramic composite scraper consists of 3-4 thin blades evenly distributed around the circumference of the main shaft, with an included angle of 90° / 120°. The rigid scraper is 5-8mm thick, and the blade edges are rounded to avoid scratching the inner wall of the distillation vessel. The outer layer on the side in contact with the material is a ceramic coating, 0.5-1mm thick, to enhance wear resistance and prevent material adhesion. The inner layer on the side connected to the main shaft is made of PTFE vinyl material, which is resistant to high temperatures and has low friction, ensuring a uniform liquid film. An inert gas distribution chamber is located on the scraper side near the main shaft. This cuboid cavity is connected to the branch guide holes of the main shaft. Gas nozzles are evenly distributed on the inner side of the scraper blade near the vessel wall, and these nozzles are connected to the distribution chamber, allowing inert gas to be ejected directly from the nozzles to purge the gap between the vessel wall and the scraper.

[0029] High-frequency ultrasonic transducers: 1-2 cylindrical ultrasonic transducers, each with a power of 50-100W, are embedded at the base of each scraper. The transducers are sealed and fixed to the scraper with high-temperature resistant epoxy resin. The power cord of the transducer passes through the inside of the scraper, along the wiring groove of the main shaft, and through a U-shaped groove on the surface of the main shaft, extending to the shaft end to connect with the external ultrasonic generator. The outside of the wiring groove is sealed with a polytetrafluoroethylene cover to prevent material from entering and damaging the wiring.

[0030] Stainless steel balance blocks are installed at the connection between the main shaft and the scraper, with one block for each scraper, to ensure that there is no eccentric vibration when the rotor rotates at high speed.

[0031] A temperature sensor is embedded near the scraper on the main shaft to detect the real-time temperature of the scraper and the material, preventing overheating and coking. The sensor circuitry and the ultrasonic power supply line share the same wiring channel.

[0032] The stepped condenser trap includes primary condensation, secondary condensation and tertiary condensation, which are controlled between 80-100℃, 40-60℃ and 0-20℃ respectively.

[0033] The apparatus also includes a short-path distillation unit 8, which is integrated in series with the molecular distillation unit for pretreatment of high-viscosity crude products.

[0034] The purification section also includes multiple traps 9, which can achieve temperature gradient control and are used to separate diglycerides with different carbon chain lengths.

[0035] Example 1 A method for purifying diglycerides by molecular distillation includes the following steps: a) Near-infrared spectroscopy was used to detect the crude corn oil-based diglyceride. The results showed that the content of triglycerides was 15.0%, the content of free fatty acids was 8.0%, the content of diglycerides was 76.9%, and the content of other impurities was 0.1%.

[0036] b) Based on the test results, the crude product was fed into a multi-stage molecular distillation system. The first stage removed the light component, free fatty acids, while maintaining a vacuum of 0.5 Pa, a distillation temperature of 135℃, a scraper rotation speed of 300 r / min, an ultrasonic frequency of 30 kHz, and a power density of 1.2 W / cm³. 2 High-purity nitrogen gas is continuously introduced into the distillation column of molecular distillation through a scraping membrane assembly at a flow rate of 0.2 L / min; the second stage removes heavy components monoglycerides and triglycerides, with the vacuum degree controlled at 0.05 Pa and the distillation temperature at 200 °C. c) A purification section is set up after the main distillation section, through which the vacuum degree is gradually reduced from 0.05Pa to 0.01Pa, the first-stage condensation temperature is 90℃, the second-stage condensation temperature is 50℃, and the third-stage condensation temperature is 10℃, so as to achieve targeted removal of trace impurities.

[0037] d) Install a vacuum degassing tower after the product collection tank, and control the vacuum degree to 3 Pa and the temperature to 70 °C.

[0038] After processing using the above method, the purity of diglycerides reached 96.5%, the impurity content was 0.04%, and after storage at 40℃ for 6 months, the peroxide value increased by 0.8 meq / kg, with no obvious off-odor.

[0039] Example 2 A method for purifying diglycerides by molecular distillation includes the following steps: a) Pretreatment of crude corn oil diglycerides with high free fatty acid content (20%): Free fatty acids were extracted at 45°C with ethanol at a mass ratio of 1:2.5 to crude product. The extracted phase was then cooled to 3°C to crystallize and remove some saturated free fatty acids. After pretreatment, the free fatty acid content of the crude product was reduced to 4.2%.

[0040] b) The pretreated crude product was subjected to online near-infrared spectroscopy and the content of triglycerides was found to be 12%, and the content of other impurities was 0.3%.

[0041] c) The crude product is pretreated in a short-path distillation unit under controlled vacuum of 3 Pa and temperature of 175 °C to remove more than 80% of the triglycerides; then it is fed into a multi-stage molecular distillation system, in which the first stage removes the light component, free fatty acids, under controlled vacuum of 0.8 Pa, distillation temperature of 140 °C, scraper rotation speed of 350 r / min, ultrasonic frequency of 30 kHz, and power density of 1.2 W / cm³. 2 High-purity nitrogen gas is continuously introduced into the distillation column of molecular distillation through a scraping membrane assembly at a flow rate of 0.2 L / min; the second stage removes heavy components monoglycerides and triglycerides, with the vacuum degree controlled at 0.08 Pa and the distillation temperature at 210 °C.

[0042] d) A purification section is set up after the molecular distillation section, and the vacuum degree is gradually reduced from 0.05 Pa to 0.01 Pa. The first-stage condensation temperature is 90℃, the second-stage condensation temperature is 50℃, and the third-stage condensation temperature is 10℃, so as to achieve targeted removal of trace impurities.

[0043] e) By controlling the temperature gradient of multiple traps, three-stage trapping is performed in the 202-210℃ range to achieve the separation of diglycerides with different carbon chain lengths.

[0044] f) Install a vacuum degassing tower after the product collection tank, and control the vacuum degree to 3 Pa and the temperature to 70 °C.

[0045] After processing using the above method, the purity of diglycerides reached 97.2%, the proportion of target fatty acid type diglycerides was 86%, diglycerides of different carbon chain lengths could be significantly separated, the impurity content was 0.03%, and the energy consumption was reduced by 35% compared with traditional single molecular distillation.

[0046] Comparative Example 1 A method for purifying diglycerides by molecular distillation includes the following steps: a) Near-infrared spectroscopy was used to detect the crude corn oil-based diglyceride. The results showed that the content of triglycerides was 15.0%, the content of free fatty acids was 8.0%, the content of diglycerides was 76.9%, and the content of other impurities was 0.1%.

[0047] b) Based on the test results, the crude product was fed into a multi-stage molecular distillation system. The first stage removed the light component, free fatty acids, while maintaining a vacuum of 0.5 Pa, a distillation temperature of 135℃, a scraper rotation speed of 300 r / min, an ultrasonic frequency of 30 kHz, and a power density of 1.2 W / cm³. 2 High-purity nitrogen gas is continuously introduced into the distillation column of molecular distillation through a scraping membrane assembly at a flow rate of 0.2 L / min; the second stage removes heavy components monoglycerides and triglycerides, with the vacuum degree controlled at 0.05 Pa and the distillation temperature at 200 °C. c) Install a vacuum degassing tower after the product collection tank, and control the vacuum degree to 3 Pa and the temperature to 70 °C.

[0048] After processing using the above method, the diglyceride purity was 93.8%, the impurity content was 0.08%, and there was no obvious off-odor.

[0049] Comparative Example 2 A method for purifying diglycerides by molecular distillation includes the following steps: a) Near-infrared spectroscopy was used to detect the crude corn oil-based diglyceride. The results showed that the content of triglycerides was 15.0%, the content of free fatty acids was 8.0%, the content of diglycerides was 76.9%, and the content of other impurities was 0.1%.

[0050] b) Based on the test results, the crude product is sent to a multi-stage molecular distillation system (a commonly used molecular distillation system). The first stage removes the light component, free fatty acids, with the vacuum degree controlled at 0.5 Pa and the distillation temperature at 135 °C. The second stage removes the heavy components, monoglycerides and triglycerides, with the vacuum degree controlled at 0.05 Pa and the distillation temperature at 200 °C. c) A purification section is set up after the main distillation section, through which the vacuum degree is gradually reduced from 0.05Pa to 0.01Pa, the first-stage condensation temperature is 90℃, the second-stage condensation temperature is 50℃, and the third-stage condensation temperature is 10℃, so as to achieve targeted removal of trace impurities.

[0051] d) Install a vacuum degassing tower after the product collection tank, and control the vacuum degree to 3 Pa and the temperature to 70 °C.

[0052] After processing using the above method, the purity of diglycerides reached 90.3%, the impurity content was 0.09%, and after storage at 40℃ for 6 months, the peroxide value increased by 0.8 meq / kg, with no obvious off-odor.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for purifying diglycerides by molecular distillation, characterized in that, Includes the following steps: (1) Near-infrared spectroscopy was used to detect the crude diglyceride and obtain the proportions of diglyceride, triglyceride and free fatty acids. (2) Based on the test results, the crude product was fed into a multi-stage molecular distillation system. The first stage removed the light component, free fatty acids. The vacuum degree was controlled at 0.1-1 Pa, the distillation temperature was 120-150℃, the scraper rotation speed was 200-400 r / min, the ultrasonic frequency was 20-40 kHz, and the power density was 1.2 W / cm³. 2 In the molecular distillation system, high-purity nitrogen gas is continuously introduced into the distillation column at a flow rate of 0.1-0.3 L / min; the second stage removes heavy components monoglycerides and triglycerides, with the vacuum degree controlled between 0.01-0.1 Pa and the distillation temperature between 180-220℃. (3) A purification section is set up after the distillation section, and the vacuum degree is gradually reduced from 0.05 Pa to 0.01 Pa. The separated diglycerides are condensed. The first-stage condensation temperature is 80-100℃, the second-stage condensation temperature is 40-60℃, and the third-stage condensation temperature is 0-20℃, so as to achieve targeted removal of trace impurities. The separation of diglycerides with different carbon chain lengths is achieved by controlling the temperature gradient of multiple sets of traps.

2. The method according to claim 1, characterized in that, Before step (1), a pretreatment step is also included: the crude product with high free fatty acid content is pretreated by low carbon alcohol extraction-low temperature crystallization method to reduce the free fatty acid content to below 5%.

3. The method according to claim 2, characterized in that, In the pretreatment step, the low-carbon alcohol is ethanol, and the mass ratio of ethanol to crude product is 1:2-3. Free fatty acids are extracted at 40-50℃, and then the extract phase is cooled to 0-5℃ to crystallize and remove some saturated free fatty acids.

4. The method according to claim 1, characterized in that, It also includes introducing end-of-pipe degassing in the distillation system: a vacuum degassing tower is installed after the product collection tank, with a vacuum degree of 1-5 Pa and a temperature of 60-80℃.

5. The method according to claim 1, characterized in that, By controlling the temperature gradient of multiple traps, the separation of diglycerides with different carbon chain lengths is achieved through 3-4 stages of trapping in the 202-210℃ range.

6. A molecular distillation purification apparatus for implementing the method according to any one of claims 1-5, characterized in that, include: The raw material pretreatment unit is used to pretreat crude diglycerides; Near-infrared spectroscopy online detection unit is used for real-time detection of the content of each component in the crude product; The multi-stage molecular distillation unit includes a first stage for removing light components and a second stage for removing heavy components. The scraping assembly in the multi-stage molecular distillation unit is an integrated rotor that combines "scraping, ultrasonic decoking, and inert gas purging". The scraping blade is made of polytetrafluoroethylene-ceramic composite material, and the edge of the blade integrates a high-frequency ultrasonic transducer with a frequency of 20-40kHz. The rotor's central shaft has a built-in inert gas guide channel. The purification section employs a stepped condenser trap to target and remove trace impurities; the purification section also includes multiple traps to separate diglycerides of different carbon chain lengths by controlling the temperature gradient. Inert gas protection and degassing system.

7. The apparatus according to claim 6, characterized in that, It also includes a short-path distillation unit, which is integrated in series with the molecular distillation unit for pretreatment of high-viscosity crude products.

8. The apparatus according to claim 6, characterized in that, The stepped condenser includes primary condensation, secondary condensation and tertiary condensation, which are controlled at 80-100℃, 40-60℃ and 0-20℃ respectively.

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