Method and device for purifying diglyceride through molecular distillation

Abstract

The invention discloses a method for purifying diglyceride by molecular distillation, which comprises the following steps: (1) carrying out near infrared spectrum on-line detection on a diglyceride crude product to obtain the proportions of diglyceride, triglyceride and free fatty acid; (2) feeding the crude product into a multi-section molecular distillation system; and (3) arranging a fine purification section behind the distillation section, separating diacylglycerol with different carbon chain lengths through a plurality of groups of traps, condensing the separated diacylglycerol, and carrying out gradient cooling from 100 DEG C to 20 DEG C so as to realize targeted removal of trace impurities. The purity and stability of diglyceride are improved, energy consumption is reduced, and the continuous operation time of equipment is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of purification of diglyceride, and particularly relates to a method and device for purifying diglyceride by molecular distillation. BACKGROUND

[0002] Diglyceride (DAG) is a trace component naturally existing in oil and fat, and has the characteristics of safety, nutrition and good processing adaptability, and has wide application prospects in the fields of food, medicine and cosmetics. The preparation of high-purity diglyceride is the key to its industrial application, and the molecular distillation technology has become the main method for purifying diglyceride due to its low temperature, high efficiency, no pollution and other advantages.

[0003] However, the existing molecular distillation technology for purifying diglyceride has the following problems: the traditional fixed-parameter molecular distillation is difficult to adapt to the characteristic differences of raw materials from different sources, resulting in unstable product purity; diglyceride is easy to carbonize and coking at high temperature, affecting the heat transfer efficiency of the equipment and the continuous operation time; trace impurities with a boiling point close to that of diglyceride are difficult to effectively remove, affecting the preparation of high-purity products; the energy consumption is high, and the product is easy to oxidize and produce odor, affecting the product quality.

[0004] Therefore, it is of great significance to develop a method and device for molecular distillation of diglyceride with high efficiency, stability and low energy consumption. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art, and provides a method and device for molecular distillation of diglyceride, so as to improve the purity and stability of diglyceride, reduce energy consumption and prolong the continuous operation time of the equipment.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A method for molecular distillation of diglyceride, comprising the following steps: a) performing online near-infrared spectrum detection on the crude diglyceride to obtain the real-time proportion of diglyceride, triglyceride and free fatty acid therein; b) according to the detection results, feeding the crude product into a multi-stage molecular distillation system, wherein the first stage removes light components of free fatty acid, the vacuum degree is controlled at 0.1-1Pa, the distillation temperature is 120-150℃, and the scraping membrane rotation speed is 200-400r / min; the second stage removes heavy components of monoglyceride and triglyceride, the vacuum degree is controlled at 0.01-0.1Pa, and the distillation temperature is 180-220℃; c) a fine purification stage is added after the main distillation stage, the vacuum degree is gradiently reduced from 0.05Pa to 0.01Pa, and the temperature of the trap is gradiently reduced from 100℃ to 20℃, so as to realize the targeted removal of trace impurities.

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

[0008] Preferably, in the pretreatment step, the mass ratio of ethanol to the crude product is 1:2-3, the free fatty acid is extracted at 40-50 DEG C, and then the extraction phase is cooled to 0-5 DEG C to crystallize and remove part of the saturated free fatty acid.

[0009] Preferably, an inert atmosphere protection is further introduced in the system, end degassing is performed, high-purity nitrogen is continuously introduced into the distillation column, the flow rate is 0.1-0.3 L / min, and a vacuum degassing tower is additionally arranged after the product collection tank, the vacuum degree is 1-5 Pa, and the temperature is 60-80 DEG C.

[0010] Preferably, through temperature gradient control of multiple groups of traps, 3-4 stages of trapping are performed in the range of 202-210 DEG C, so that glycerol diesters with different carbon chain lengths are separated.

[0011] The application further provides a molecular distillation purification device for realizing the above method, comprising: A raw material pretreatment unit is used for pretreating the crude glycerol diester; A near-infrared spectrum online detection unit is used for real-time detection of the content of each component in the crude product; A multi-stage molecular distillation unit comprises a first stage for removing light components and a second stage for removing heavy components; A fine purification stage adopts a stepped condensation trap for targeted removal of trace impurities; A degassing system.

[0012] Preferably, the wiper film assembly in the multi-stage molecular distillation unit is a "wiper film-ultrasonic decoking-inert gas blowing" integrated rotor, the wiper film knife adopts a polytetrafluoroethylene-ceramic composite material, the knife edge is integrated with a high-frequency ultrasonic vibrator, the frequency is 20-40 kHz, and the center shaft of the rotor is internally provided with an inert gas guide channel.

[0013] Preferably, a short-path rectification unit is further included and is integrated in series with the molecular distillation unit, and is used for pretreating a high-viscosity crude product.

[0014] Preferably, the stepped condensation trap comprises a first-stage condensation, a second-stage condensation and a third-stage condensation, and is controlled at 80-100 DEG C, 40-60 DEG C and 0-20 DEG C respectively.

[0015] Preferably, the fine purification stage further comprises multiple groups of traps, temperature gradient control can be realized, and glycerol diesters with different carbon chain lengths are separated.

[0016] Beneficial effects Compared with the prior art, the application has the following beneficial effects: The present application realizes precise matching of different raw materials by near-infrared spectrum online detection and parameter self-adaptive adjustment, solves the contradiction of "incomplete removal of light components" or "thermal decomposition of target components" under traditional fixed parameters, and makes the purity of different raw materials of glyceride all reach more than 90%.

[0017] The "scraped film-ultrasonic decoking-inert gas blowing" integrated rotor of the present application effectively solves the problem of glyceride carbonization and coking at high temperature, prolongs the continuous operation time of the equipment from 8-12 hours of the traditional method to more than 48 hours. The scraped film rotation speed is 220-300 r / min; the ultrasonic frequency is 20-40 kHz, and the power density is 1.2 W / cm²; and the N2 flow rate is ≥0.2 L / min.

[0018] The present application realizes targeted removal of trace impurities close to the boiling point of glyceride by gradient vacuum and temperature control of the fine purification section, reduces the impurity content from 0.5%-1% to below 0.05%, and provides an effective way for the preparation of high-purity glyceride (≥95%).

[0019] The condensation coupling system and solvent pretreatment synergistic process of the present application reduces the distillation energy consumption by 30%-40% and reduces the cooling water consumption by 40%, which meets the development trend of green process.

[0020] The present application effectively solves the problem of oxidative off-flavor in the glyceride purification process by adopting inert atmosphere protection and end degassing, and the peroxide value of the treated product only increases by 0.5-1 meq / kg after storage at 40℃ for 6 months, and there is no obvious off-flavor.

[0021] The present application realizes the separation of glycerides with different carbon chain lengths by temperature gradient control of multiple traps, can prepare glyceride products with specific fatty acid composition according to the needs of different application scenarios, and expands the application range. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flow chart of the molecular distillation purification of the present application; In the figure, 1 is a near-infrared spectrum online detection unit, 2 is a short-path rectification unit, 3 is a one-stage molecular distillation unit, 4 is a two-stage molecular distillation unit, 5 is a fine purification section, 6 is a collection tank, 7 is a degassing system, 8 is a raw material pretreatment unit, and 9 is a plurality of traps. Figure 2 The scraped film assembly in the one-stage molecular distillation unit of the present application; 301 center main shaft, 302 scraper, 303 ultrasonic transducer, 304 balance block, 305 flow guide hole position, 306 air nozzle hole, 307 wiring groove, 308 temperature sensor, 309 one-way valve, 3010 air inlet hole. DETAILED DESCRIPTION

[0023] The application will be further described in detail below in combination with specific examples.

[0024] The application provides a molecular distillation purification device, which comprises, in sequence, a raw material pretreatment unit 8, an online near-infrared spectrum detection unit 1, a short-path rectification unit 2, a first-stage molecular distillation unit 3, a second-stage molecular distillation unit 4, a fine purification stage (ladder-type condensation trap) 5, a collection tank 6, and a degassing system 7.

[0025] The scraping membrane assembly in the first-stage molecular distillation unit is a "scraping membrane-ultrasonic defouling-inert gas blowing" integrated rotor, the scraping membrane knife is made of polytetrafluoroethylene-ceramic composite material, the edge of the blade is integrated with a high-frequency ultrasonic vibrator, the frequency is 30 kHz, and the central shaft of the rotor is internally provided with an inert gas guide channel.

[0026] The rotor has a central shaft-radial scraper symmetric structure, the diameter is designed according to the inner diameter of the molecular distillation kettle, and the length is matched with the heating section of the distillation kettle, the rotor is composed of a central shaft, a polytetrafluoroethylene-ceramic composite scraper, a high-frequency ultrasonic vibrator and an inert gas guide system, and is ensured to be resistant to high temperature and solvent corrosion.

[0027] The central shaft is a hollow shaft, the shaft body is uniformly distributed with radial gas path interfaces corresponding to the scrapers, a bearing connecting section is arranged on the upper part of the shaft and coupled with a driving motor, and an inert gas inlet on the shaft is connected with an external high-purity nitrogen source. A main inert gas guide hole is arranged in the center of the shaft, branch guide holes are arranged from the main guide hole to the direction of each scraper and are communicated with the internal gas path of the scraper, a one-way valve is arranged at the end of each branch hole to prevent material from flowing back into the gas path.

[0028] The polytetrafluoroethylene-ceramic composite scraper has a sheet shape, is uniformly distributed along the circumference of the main shaft, has 3-4 sheets, and has an included angle of 90° / 120°. The rigid scraper has a thickness of 5-8 mm, the edge of the blade is treated with a circular arc transition to avoid scratching the inner wall of the distillation kettle. The outer layer on the side in contact with the material is a ceramic coating with a thickness of 0.5-1 mm, which enhances wear resistance and prevents material adhesion. The inner layer on the side connected with the main shaft is a polytetrafluoroethylene base material, which is resistant to high temperature and low friction and ensures uniform liquid film. The scraper near the main shaft is provided with an inert gas shunt cavity, which is a rectangular cavity and is communicated with the branch guide holes of the main shaft. Gas nozzle holes are uniformly arranged on the inner side of the blade of the scraper near the kettle wall, the gas nozzle holes are communicated with the shunt cavity, inert gas can be sprayed out of the gas nozzle holes to directly blow the gap between the kettle wall and the scraper.

[0029] High-frequency ultrasonic vibrator: 1-2 cylindrical ultrasonic vibrators are embeddedly installed at the root of each scraper, with a power of 50-100 W per vibrator. The vibrator is sealed and fixed with the scraper through high-temperature-resistant epoxy resin. The power line of the vibrator penetrates from the inside of the scraper, along the wiring groove of the main shaft, the U-shaped groove opened on the surface of the main shaft, and extends to the shaft end, which is connected with the external ultrasonic generator. The outside of the wiring groove is sealed with a polytetrafluoroethylene cover plate to prevent materials from entering and damaging the circuit.

[0030] A stainless steel balance block is installed at the connection part of the main shaft and the scraper, with one block corresponding to each scraper, to ensure that there is no eccentric vibration when the rotor rotates at high speed.

[0031] A temperature sensor is embeddedly installed at the position of the main shaft close to the scraper to detect the real-time temperature of the scraper and the material, avoid overheating and coking, and the sensor line shares the wiring groove with the ultrasonic power line.

[0032] The stepped condensation trap includes a first-stage condensation, a second-stage condensation, and a third-stage condensation, which are controlled at 80-100℃, 40-60℃, and 0-20℃, respectively.

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

[0034] The purification section also includes multiple sets of traps 9, which can realize temperature gradient control, for separating glycerol diesters with different carbon chain lengths.

[0035] Example 1 A method for purifying glycerol diesters by molecular distillation, comprising the following steps: a) Online near-infrared spectroscopy detection is performed on the corn oil-based glycerol diester crude product, and it is measured that the content of glycerol triesters is 15.0%, the content of free fatty acids is 8.0%, the content of glycerol diesters is 76.9%, and the content of other impurities is 0.1%.

[0036] b) According to the detection results, the crude product is sent to a multi-stage molecular distillation system, in which the first stage removes light components free fatty acids, the vacuum degree is controlled at 0.5 Pa, the distillation temperature is controlled at 135℃, the scraper membrane rotation speed is controlled at 300 r / min, the ultrasonic frequency is controlled at 30 kHz, and the power density is controlled at 1.2 W / cm 2 High-purity nitrogen gas is continuously introduced into the distillation column through the scraper membrane assembly during molecular distillation, with a flow rate of 0.2 L / min; the second stage removes heavy components glycerol monoesters and glycerol triesters, with a vacuum degree of 0.05 Pa and a distillation temperature of 200℃; c) A purification section is provided after the main 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℃, to realize 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 of purifying diglycerides by molecular distillation, characterized in that, The method comprises the following steps: (1) online detection of crude diglyceride by near-infrared spectroscopy to obtain the proportion of diglyceride, triglyceride and free fatty acid; (2) according to the detection result, the crude product is sent to a multi-stage molecular distillation system, wherein the first stage removes light components of free fatty acid, the vacuum degree is controlled at 0.1-1 Pa, the distillation temperature is 120-150 DEG C, and the scraping membrane rotating speed is 200-400 r / min; the second stage removes heavy components of monoglyceride and triglyceride, the vacuum degree is controlled at 0.01-0.1 Pa, and the distillation temperature is 180-220 DEG C; (3) a fine purification section is arranged after the distillation section, the vacuum degree is gradually reduced from 0.05 Pa to 0.01 Pa, different carbon chain length diglycerides are separated by multiple traps, and the separated diglycerides are condensed from 100 DEG C to 20 DEG C to realize targeted removal of trace impurities.

2. The method of claim 1, wherein, Before step (1), a pretreatment step is further included: a low-carbon alcohol extraction-low-temperature crystallization method is used to pretreat the crude product with high free fatty acid content, so that the free fatty acid content is reduced to below 5%.

3. The method of claim 2, wherein, In the pretreatment step, the mass ratio of ethanol to crude product is 1:2-3, the free fatty acid is extracted at 40-50 DEG C, and then the extraction phase is cooled to 0-5 DEG C to crystallize and remove part of the saturated free fatty acid.

4. The method of claim 1, wherein, An inert atmosphere protection and end degassing system is further introduced into the distillation system: high-purity nitrogen is continuously introduced into the distillation column at a flow rate of 0.1-0.3 L / min; a vacuum degassing tower is arranged after the product collection tank, the vacuum degree is 1-5 Pa, and the temperature is 60-80 DEG C.

5. The method of claim 1, wherein, Through temperature gradient control of multiple traps, 3-4 stages of trapping are performed in the range of 202-210 DEG C to separate different carbon chain length diglycerides.

6. A molecular distillation purification apparatus implementing the method of any one of claims 1 to 5, characterized in that, It comprises: a raw material pretreatment unit for pretreating crude diglyceride; a near-infrared spectroscopy online detection unit for real-time detection of the content of each component in the crude product; a multi-stage molecular distillation unit including a first stage for removing light components and a second stage for removing heavy components; a fine purification section using a stepwise condensation trap for targeted removal of trace impurities; an inert gas protection and degassing system.

7. The apparatus of claim 6, wherein, The scraping membrane assembly in the multi-stage molecular distillation unit is an integrated rotor of "scraping membrane-ultrasonic decoking-inert gas blowing", the scraping membrane knife is made of polytetrafluoroethylene-ceramic composite material, the knife edge is integrated with a high-frequency ultrasonic vibrator with a frequency of 20-40 kHz, and the rotor center shaft is provided with an inert gas guide channel.

8. The apparatus of claim 6, wherein, It further comprises a short-path rectification unit integrated in series with the molecular distillation unit for pretreating high-viscosity crude product.

9. The apparatus of claim 6, wherein, The stepwise condensation trap comprises primary condensation, secondary condensation and tertiary condensation controlled at 80-100 DEG C, 40-60 DEG C and 0-20 DEG C, respectively.

10. The apparatus of claim 6, wherein, The fine purification section further comprises multiple separators, and temperature gradient control is used to separate diglycerides of different carbon chain lengths.

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