High-iodine oleic acid and preparation method thereof

Abstract

The invention relates to the technical field of grease chemical industry, and discloses high-iodine oleic acid and a preparation method thereof.The preparation method comprises the steps that waste grease is pretreated; adding a polar modifier into supercritical CO2 to selectively extract oleic acid; adding a polar accelerant compound system into the supercritical system to carry out iodination reaction; refining and separating the product through pressure gradient; and establishing a circulating reiodination system, and returning medium and low iodination products to the iodination step for continuous reaction through a supercritical phase back-mixing technology and precise iodine source addition. According to the method, the oleic acid extraction selectivity coefficient is increased by 40-60% by introducing the polar modifier, the iodination reaction rate is increased by 50-80% through a polar accelerant compounding system, the total yield is increased to 75-85% from 60-70% through a circulating reiodination system, the product purity reaches 95-98%, high-value utilization of the waste grease is achieved, the production cost is greatly reduced by 40-60%, and the method is suitable for industrial production. No organic solvent is left, and the method is environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of oleochemical technology, and more specifically, to a periodic oleic acid and its preparation method. Background Technology

[0002] Periodic oleic acid is an iodinated derivative obtained by introducing iodine atoms into the unsaturated double bonds of oleic acid molecules. Due to its organic iodine form and lipid solubility, it has application value in fields such as medical imaging and nutritional supplementation. Traditional methods for preparing periodic oleic acid mainly use refined vegetable oils as raw materials, carrying out liquid-phase iodination reactions in organic solvents. This method suffers from problems such as high raw material costs, large consumption of organic solvents, serious environmental pollution, low iodination selectivity, and low product purity. my country generates a large amount of waste oils (waste cooking oil, expired cooking oil, etc.) every year, which contain 20-30% oleic acid components, possessing potential for resource utilization. However, due to their complex composition and high impurity content, existing technologies struggle to achieve efficient conversion.

[0003] Supercritical CO2 fluid technology has promising applications in oil processing due to its advantages such as being environmentally friendly and easy to separate. However, there are three key technical obstacles in its application to the preparation of high-iodine oleic acid from waste oils: First, when extracting waste oils with supercritical CO2, the selectivity for oleic acid is small (<15%) compared to other unsaturated fatty acids with similar structures (linoleic acid, linolenic acid, etc.), and polar impurities in waste oils (free fatty acids, phospholipids, glycerides, etc.) may form associated complexes with oleic acid, reducing the extraction selectivity. Second, supercritical CO2 is a non-polar medium, and the polar environment required for traditional iodination reactions is lacking, leading to inhibited iodine source dissociation and activation, and the iodination reaction activity may decrease by 40-60%. Third, the low- and medium-iodination products generated during the pressure gradient separation process (accounting for 20-35% of the total iodination products) face reuse obstacles such as phase and pressure mismatch, difficulty in maintaining the continuity of the logistics, and inaccurate iodine source addition. Summary of the Invention

[0004] This invention proposes to introduce a polar modifier in the supercritical CO2 extraction stage to improve the extraction selectivity for oleic acid, and to combine a polar promoter system in the supercritical iodination stage to overcome the limitations of the non-polar environment. A recycling reiodination system with supercritical phase backmixing and precise iodine source addition is established to achieve efficient utilization of low- and medium-iodination products, thereby realizing a green and efficient process for preparing high-purity high-iodine oleic acid from waste oils. A method for preparing periodic oleic acid includes the following steps: Step 1: Pre-treat the waste oil to obtain pre-treated waste oil, in which the oleic acid content is 20-30%; Step 2: Use supercritical CO2 extraction to pretreat waste oil at a temperature of 40-60℃ and a pressure of 15-30 MPa. Add a polar modifier to the supercritical CO2. The polar modifier is selected from one or more of short-chain alcohols, short-chain organic acids, and short-chain ketones. The amount added is 1-8% of the mass of supercritical CO2 to obtain a supercritical CO2 solution containing oleic acid. Step 3: The supercritical CO2 solution containing oleic acid obtained in Step 2 is directly subjected to iodination reaction. A polar accelerator compound system is added to the reaction system. The polar accelerator compound system includes a polar reaction medium additive, a surface activity accelerator, and an iodine source activation aid. The iodine source is a combination of potassium iodide and elemental iodine. The catalyst is a weak base catalyst or a phase transfer catalyst. The reaction temperature is 50-80℃ and the pressure is 20-35 MPa to obtain a mixture of high-iodine oleic acid with different degrees of iodination. Step 4: Separate the mixture obtained in Step 3 by pressure gradient. In the first stage, the pressure is reduced to 8-12 MPa to precipitate low iodide products. In the second stage, the pressure is reduced to 5-8 MPa to precipitate medium iodide products. In the third stage, the pressure is reduced to normal pressure to obtain high iodide products. Step 5: After pressurizing the low- and medium-iodide products precipitated in the first and second stages of Step 4, mix them with supercritical CO2 to form a supercritical or subcritical mixed phase. After adding an iodine source, mix the mixture back into the iodization reactor of Step 3 to continue the reaction.

[0005] Preferably, the polar modifier in step two is selected from one or more of methanol, ethanol, isopropanol, acetic acid, propionic acid, acetone, and butanone.

[0006] Preferably, the polar reaction medium additive in step three is selected from one or more of low molecular weight polyethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone, and the amount added is 5-12% of the reaction system; the surface activity promoter is selected from one or more of perfluoropolyether compounds, organosiloxane surfactants, and fatty acid esters, and the amount added is 1-3% of the reaction system; the iodine source activation aid is selected from one or more of triethylamine, pyridine compounds, and Lewis bases, and the amount added is 5-15% of the iodine source mass.

[0007] Preferably, in step three, the molar ratio of potassium iodide to elemental iodine is 1:1 to 3:1, and the total molar amount of iodine is 1.2 to 1.5 times the molar amount of oleic acid.

[0008] Preferably, the weakly basic catalyst in step three is selected from one or more of potassium carbonate, sodium carbonate, and sodium bicarbonate, the phase transfer catalyst is a quaternary ammonium salt compound, and the amount of catalyst used is 1-5% of the mass of oleic acid.

[0009] Preferably, in step four, each pressure gradient is divided into 3-5 buffer segments, each segment has a pressure reduction of 2-3 MPa, and the pressure is stabilized and held for 5-10 minutes after the pressure reduction.

[0010] Preferably, in step five, the temporary storage buffer tank maintains a pressure of 5-12 MPa, the low-iodide product is pressurized to 18-30 MPa, the injected supercritical CO2 oxygen content is less than 10 ppm, and the mass ratio of CO2 to product is 2:1 to 5:1.

[0011] Preferably, the iodine source added in step five is a supercritical CO2 solution of potassium iodide and elemental iodine, with a molar ratio of potassium iodide to elemental iodine of 1:1 to 3:1. The amount of iodine added is calculated based on the flow rate and average degree of iodization of the low-to-medium iodide products, with the error controlled within 5%.

[0012] Preferably, in step five, the iodization reactor is divided into a fresh oleic acid iodization zone and a recycled product reiodization zone. The temperature of the recycled product reiodization zone is 5-10°C higher than that of the fresh oleic acid iodization zone, and the catalyst concentration is increased by 20-30%.

[0013] Preferably, the low- and medium-quality iodized products before remixing in step five are subjected to quality testing and grading. High-quality recycled products with iodization degree of 40-80% and impurities of less than 3% are directly remixed. Medium-quality products with iodization degree of 30-50% and impurities of 3-8% are purified and then remixed. Low-quality products with iodization degree of less than 30% and impurities of more than 8% are not remixed. The maximum number of cycles is 2-3.

[0014] The beneficial effects of this invention are: through supercritical... The addition of 1-8% polar modifiers has overcome the technical bottleneck of traditional supercritical extraction, which suffers from small selectivity differences (<15%) for unsaturated fatty acids with similar structures. Through a triple synergistic effect of selective solubility regulation, association inhibition, and improved extraction efficiency, the polar modifiers expand the solubility difference between oleic acid and other unsaturated fatty acids to 30-50%, increase the extraction selectivity coefficient by 40-60%, improve the purity of extracted oleic acid from 70-75% to 85-92%, and reduce polar impurity migration by 60-75%, providing a high-quality substrate for subsequent efficient iodization.

[0015] For supercritical To address the issue of non-polar environments limiting the efficiency of iodination reactions, an innovative ternary polar accelerator system was developed, consisting of a polar reaction medium additive, a surfactant promoter, and an iodine source activator. This system works synergistically at the macroscopic, microscopic, and molecular levels, providing the necessary polar microenvironment for the iodination reaction while maintaining the green advantages of supercritical systems. This increases the supercritical iodination reaction rate by 50-80%, shortens the reaction time from 6-8 hours to 2-4 hours, and reduces the by-product formation rate by 40-50%, achieving a highly efficient extraction-reaction integrated process.

[0016] By establishing a cyclic reiodination system that integrates supercritical phase backmixing, precise iodine source addition, segmented iodination, quality monitoring, and purification intervention, the system successfully addressed the reuse obstacles faced by low- and medium-iodinated products (accounting for 20-35% of total iodinated products), such as phase and pressure mismatch, difficulties in logistics continuity, and inaccurate iodine source addition. The cyclic reiodination system converts over 70% of low- and medium-iodinated products into the main product, periodic oleic acid, increasing the overall yield from 60-70% to 75-85% and iodine utilization from 70-80% to 90-95%, thus achieving full resource utilization and maximizing economic benefits. Attached Figure Description

[0017] Figure 1 This is a comparison diagram showing the effect of the polar modifier of the present invention on the selectivity of supercritical extraction; Figure 2 This is the curve showing the change in iodide degree as a function of reaction time according to the present invention; Figure 3 This is the curve showing the change in the proportion of high iodide products over time according to the present invention; Figure 4 This is a curve showing the change in the proportion of by-products of this invention over time; Figure 5 This is a comparison of the final product distribution and reaction rate of the present invention. Detailed Implementation

[0018] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0019] Example 1: This example presents a method for preparing periodic oleic acid, comprising the following steps: Step 1: Pre-treat the waste oil to obtain pre-treated waste oil with an oleic acid content of 25%; Step 2: Use supercritical CO2 extraction to pretreat waste oil at 50°C and 22 MPa. Add a polar modifier to the supercritical CO2. The polar modifier is selected from short-chain alcohols and the amount added is 5% of the mass of supercritical CO2 to obtain a supercritical CO2 solution containing oleic acid. Step 3: The supercritical CO2 solution containing oleic acid obtained in Step 2 is directly subjected to iodination reaction. A polar accelerator compound system is added to the reaction system. The polar accelerator compound system includes a polar reaction medium additive, a surface activity accelerator, and an iodine source activation aid. The iodine source is a combination of potassium iodide and elemental iodine. The catalyst is a weakly basic catalyst. The reaction temperature is 65℃ and the pressure is 28 MPa to obtain a mixture of high-iodine oleic acid with different degrees of iodination. Step 4: Separate the mixture obtained in Step 3 by pressure gradient. In the first stage, the pressure is reduced to 10 MPa to precipitate low-iodide products. In the second stage, the pressure is reduced to 6 MPa to precipitate medium-iodide products. In the third stage, the pressure is reduced to normal pressure to obtain high-iodide products. Step 5: After pressurizing the low- and medium-iodide products precipitated in the first and second stages of Step 4, mix them with supercritical CO2 to form a supercritical or subcritical mixed phase. After adding an iodine source, mix the mixture back into the iodization reactor of Step 3 to continue the reaction.

[0020] In step two, the polar modifier is selected from methanol.

[0021] The polar reaction medium additive in step three is selected from low molecular weight polyethylene glycol, and the amount added is 8% of the reaction system; The surfactant accelerator is selected from perfluoropolyether compounds and is added at 2% of the reaction system. The iodine source activation aid is selected from triethylamine, and the amount added is 10% of the mass of the iodine source.

[0022] In step three, the molar ratio of potassium iodide to elemental iodine is 2:1, and the total molar amount of iodine is 1.4 times the molar amount of oleic acid.

[0023] In step three, the weakly basic catalyst is selected from potassium carbonate, the phase transfer catalyst is a quaternary ammonium salt compound, and the amount of catalyst used is 3% of the mass of oleic acid.

[0024] In step four, each pressure gradient is divided into four buffer segments, with each segment having a pressure reduction of 2.5 MPa. After the pressure reduction, the pressure is stabilized and held for 8 minutes.

[0025] In step five, the temporary storage buffer tank maintains a pressure of 9 MPa, while the pressure of the low-iodide product is increased to 24 MPa. The injected supercritical CO2 has an oxygen content of less than 10 ppm, and the mass ratio of CO2 to product is 3:1.

[0026] The iodine source added in step five is a supercritical CO2 solution of potassium iodide and elemental iodine, with a molar ratio of potassium iodide to elemental iodine of 2:1. The amount of iodine to be added is calculated based on the flow rate and average degree of iodization of the low-to-medium iodide products, with the error controlled within 5%.

[0027] In step five, the iodization reactor is divided into a fresh oleic acid iodization zone and a recycled product reiodization zone. The temperature of the recycled product reiodization zone is increased by 8°C compared to the fresh oleic acid iodization zone, and the catalyst concentration is increased by 25%.

[0028] Before remixing in step five, the low- and medium-quality iodized products undergo quality testing and grading. High-quality recycled products with iodization of 60% and impurities of less than 3% are directly remixed. Medium-quality products with iodization of 40% and impurities of 5% are purified before remixing. Low-quality products with iodization of less than 30% and impurities of more than 8% are not remixed. The maximum number of cycles is 2.

[0029] Example 2 differs from Example 1 in that: Step 1, the waste oil is pretreated to obtain pretreated waste oil, wherein the oleic acid content is 20%; Step 2: Use supercritical CO2 extraction to pretreat waste oil at a temperature of 40℃ and a pressure of 15 MPa. Add a polar modifier to the supercritical CO2. The polar modifier is selected from short-chain organic acids and the amount added is 1% of the mass of supercritical CO2 to obtain a supercritical CO2 solution containing oleic acid. Step 3: A phase transfer catalyst was used as the catalyst, and the reaction temperature was 50℃ and the pressure was 20 MPa to obtain a mixture of high iodide oleic acid with different degrees of iodization. Step 4: Through pressure gradient separation, the mixture obtained in Step 3 is depressurized in stages. In the first stage, the pressure is reduced to 8 MPa to precipitate low-iodide products. In the second stage, the pressure is reduced to 5 MPa to precipitate medium-iodide products. In the third stage, the pressure is reduced to atmospheric pressure to obtain high-iodide products.

[0030] The polar modifier in step two is selected from ethanol.

[0031] The polar reaction medium additive in step three is selected from dimethyl sulfoxide, and the amount added is 5% of the reaction system; The surfactant accelerator is selected from organosiloxane surfactants and is added at 1% of the reaction system. The iodine source activation aid is selected from pyridine compounds and is added at 5% of the iodine source mass.

[0032] In step three, the molar ratio of potassium iodide to elemental iodine is 1:1, and the total molar amount of iodine is 1.2 times the molar amount of oleic acid.

[0033] In step three, the weakly basic catalyst is selected from sodium carbonate, the phase transfer catalyst is a quaternary ammonium salt compound, and the amount of catalyst used is 1% of the mass of oleic acid.

[0034] In step four, each pressure gradient is divided into three buffer segments, with each segment having a pressure reduction of 2 MPa. After the pressure is reduced, the pressure is stabilized and held for 5 minutes.

[0035] In step five, the temporary storage buffer tank maintains a pressure of 5 MPa, while the pressure of the low-iodide product is increased to 18 MPa. The injected supercritical CO2 has an oxygen content of less than 10 ppm, and the mass ratio of CO2 to product is 2:1.

[0036] The iodine source added in step five is a supercritical CO2 solution of potassium iodide and elemental iodine, with a molar ratio of potassium iodide to elemental iodine of 1:1. The amount of iodine to be added is calculated based on the flow rate and average degree of iodization of the low-to-medium iodide products, with the error controlled within 5%.

[0037] In step five, the iodization reactor is divided into a fresh oleic acid iodization zone and a recycled product reiodization zone. The temperature of the recycled product reiodization zone is increased by 5°C compared to the fresh oleic acid iodization zone, and the catalyst concentration is increased by 20%.

[0038] In step five, the low- and medium-quality iodized products before remixing undergo quality testing and grading. High-quality recycled products with an iodization degree of 40% and impurities of less than 3% are directly remixed. Medium-quality products with an iodization degree of 30% and impurities of 3% are purified before remixing. Low-quality products with an iodization degree of less than 30% and impurities of more than 8% are not remixed. The maximum number of cycles is 2.

[0039] Example 3 differs from Example 1 in that: Step 1, the waste oil is pretreated to obtain pretreated waste oil, wherein the oleic acid content is 30%; Step 2: Use supercritical CO2 extraction to pretreat waste oil at a temperature of 60℃ and a pressure of 30 MPa. Add a polar modifier to the supercritical CO2. The polar modifier is selected from short-chain alcohols, short-chain organic acids, and short-chain ketones. The amount added is 8% of the mass of supercritical CO2 to obtain a supercritical CO2 solution containing oleic acid. Step 3: A weakly basic catalyst or a phase transfer catalyst is used as the catalyst. The reaction temperature is 80℃ and the pressure is 35 MPa to obtain a mixture of high-iodine oleic acid with different degrees of iodization. Step 4: Through pressure gradient separation, the mixture obtained in Step 3 is depressurized in stages. In the first stage, the pressure is reduced to 12 MPa to precipitate low-iodide products. In the second stage, the pressure is reduced to 8 MPa to precipitate medium-iodide products. In the third stage, the pressure is reduced to atmospheric pressure to obtain high-iodide products.

[0040] The polar modifier in step two is selected from methanol, ethanol, isopropanol, acetic acid, propionic acid, acetone, and butanone.

[0041] The polar reaction medium additive in step three is selected from low molecular weight polyethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone, and the amount added is 12% of the reaction system; The surfactant accelerator is selected from perfluoropolyether compounds, organosiloxane surfactants, and fatty acid esters, and the addition amount is 3% of the reaction system; The iodine source activation aid is selected from triethylamine, pyridine compounds, and Lewis bases, and the amount added is 15% of the mass of the iodine source.

[0042] In step three, the molar ratio of potassium iodide to elemental iodine is 3:1, and the total molar amount of iodine is 1.5 times the molar amount of oleic acid.

[0043] In step three, the weakly basic catalyst is selected from potassium carbonate, sodium carbonate, and sodium bicarbonate, the phase transfer catalyst is a quaternary ammonium salt compound, and the amount of catalyst used is 5% of the mass of oleic acid.

[0044] In step four, each pressure gradient is divided into 5 buffer segments, with each segment having a pressure reduction of 3 MPa. After the pressure is reduced, the pressure is stabilized and held for 10 minutes.

[0045] In step five, the temporary storage buffer tank maintains a pressure of 12 MPa, and the pressure of the low-iodide product is increased to 30 MPa. The injected supercritical CO2 has an oxygen content of less than 10 ppm, and the mass ratio of CO2 to product is 5:1.

[0046] The iodine source added in step five is a supercritical CO2 solution of potassium iodide and elemental iodine, with a molar ratio of potassium iodide to elemental iodine of 3:1. The amount of iodine to be added is calculated based on the flow rate and average degree of iodization of the low-to-medium iodide products, with the error controlled within 5%.

[0047] In step five, the iodization reactor is divided into a fresh oleic acid iodization zone and a recycled product reiodization zone. The temperature of the recycled product reiodization zone is increased by 10°C compared to the fresh oleic acid iodization zone, and the catalyst concentration is increased by 30%.

[0048] In step five, the low- and medium-quality iodized products before remixing undergo quality testing and grading. High-quality recycled products with iodization of 80% and impurities of less than 3% are directly remixed. Medium-quality products with iodization of 50% and impurities of 8% are purified before remixing. Low-quality products with iodization of less than 30% and impurities of more than 8% are not remixed. The maximum number of cycles is 3.

[0049] Example 4 presents a method for preparing periodic oleic acid, including the following steps. Step 1: Pretreatment of waste oil Waste oil (including waste cooking oil, expired cooking oil, and byproducts of oil processing) undergoes pretreatment through processes such as decolorization, deodorization, and deacidification to remove impurities such as pigments, odors, and some free fatty acids, resulting in pretreated waste oil. The oleic acid content in the pretreated waste oil is 20-30%.

[0050] Specific pretreatment methods include: (1) Degumming: using hydration degumming or acid degumming to remove phospholipids and other gums, with a degumming temperature of 60-90℃; (2) Deacidification: using alkali refining or physical refining to remove free fatty acids, reducing the free fatty acid content to below 3%; (3) Decolorization: adding activated clay or activated carbon (the amount added is 2-5% of the oil mass), stirring and contacting for 30-60 minutes at 80-110℃ and a vacuum of 2-5 kPa, and filtering to remove the adsorbent; (4) Deodorization: passing steam through at 200-260℃ and a vacuum of 0.3-0.8 kPa for 1-3 hours to remove odor substances.

[0051] Preferred pretreatment scheme: hydration degumming (temperature 70℃, water added at 3% of oil mass, stirring for 30 minutes), alkali refining deacidification (using 10% sodium hydroxide solution, the amount calculated based on the free fatty acid content, excess coefficient 1.2, temperature 60℃), activated clay decolorization (addition amount 3% of oil mass, temperature 90℃, vacuum degree 3 kPa, time 40 minutes), and steam deodorization (temperature 240℃, vacuum degree 0.5 kPa, time 2 hours).

[0052] Step 2: Supercritical CO2 extraction to separate oleic acid (adding a polar modifier to improve selectivity) This step overcomes the technical bottleneck of insufficient selectivity in traditional supercritical extraction by introducing a polar modifier into supercritical CO2 extraction.

[0053] (1) Determination of extraction conditions Supercritical CO2 fluid was used to extract pretreated waste oil. The supercritical extraction operating conditions were: temperature 40-60℃ and pressure 15-30 MPa. Under these conditions, CO2 is in a supercritical state, exhibiting liquid-like dissolving ability and gas-like diffusion properties.

[0054] (2) Selection and addition of polar modifiers (core innovation) The core innovation of this embodiment lies in adding a polar modifier (also known as an entrainer or co-solvent) to supercritical CO2. The polar modifier is selected from one or more of short-chain alcohols (methanol, ethanol, isopropanol), short-chain organic acids (acetic acid, propionic acid), and short-chain ketones (acetone, butanone), and the amount added is 1-8% of the mass of supercritical CO2.

[0055] The selection principles for polar modifiers are: (1) good miscibility in supercritical CO2; (2) differentiated interaction with oleic acid and impurities; (3) low boiling point, easy to separate and recover later; (4) chemically stable and does not react with oleic acid or CO2.

[0056] Preferred method: Ethanol is used as a polar modifier, added at 5% of the mass of supercritical CO2, with an extraction temperature of 50℃, an extraction pressure of 20 MPa, and an extraction time of 2 hours. Ethanol has moderate polarity, is inexpensive, easy to recover, and meets food safety requirements. Under these preferred conditions, the purity of the extracted oleic acid can reach 88-92%.

[0057] (3) The working principle of polar modifiers to enhance extraction selectivity Compared to the existing pure supercritical CO2 extraction technology, this embodiment produces a triple synergistic effect by adding a polar modifier: Function 1: Selective dissolution regulation The addition of polar modifiers alters the polarity and solubility properties of supercritical fluids. Although oleic acid (monounsaturated fatty acid, C18:1), linoleic acid (diunsaturated fatty acid, C18:2), and linolenic acid (triunsaturated fatty acid, C18:3) have the same carbon chain length, their degrees of unsaturation differ, leading to different interactions with polar modifiers. The addition of polar modifiers preferentially increases the solubility of oleic acid in the supercritical fluid, while the increase in solubility of polyunsaturated fatty acids is smaller. This widens the solubility difference between oleic acid and other unsaturated fatty acids, increasing the original difference from <15% to 30-50%, significantly improving the selectivity coefficient of extraction.

[0058] Function 2: Association inhibition Polar impurities in waste oils (free fatty acids, phospholipids, monoglycerides, diglycerides, etc.) may form associated complexes with oleic acid through hydrogen bonds or van der Waals forces during supercritical fluid extraction. This association alters the apparent solubility and extraction behavior of oleic acid, causing the polar impurities to enter the extraction phase along with the associated complexes. Polar modifiers can preferentially bind to these polar impurities through hydrogen bonding or solvation, disrupting or weakening the association between the impurities and oleic acid. The polar modifier essentially "competitively" binds to the impurities, releasing oleic acid from the associated complexes and restoring its normal extraction behavior. Simultaneously, the polar modifier-impurity complex has low solubility in supercritical CO2 and tends to remain in the raffinate phase, thus reducing the migration of impurities into the extraction phase.

[0059] Function 3: Improved extraction efficiency Appropriate amounts of polar modifiers can improve the overall solubility and mass transfer efficiency of supercritical CO2. Polar modifiers improve the interaction between supercritical fluid and oil phase, enhance the penetration and dissolution of oil by supercritical fluid, accelerate the mass transfer process of oleic acid from the oil phase to the supercritical phase, shorten the extraction time by 20-35%, and increase the extraction yield of oleic acid by 8-15%.

[0060] (4) Implementation of the extraction process Pretreated waste oil is added to an extraction vessel, and supercritical CO2, pre-mixed with a polar modifier, is introduced. The extraction process can be continuous or semi-continuous, with the extraction time determined based on the amount of raw material and the equipment scale, generally 1-3 hours. The resulting supercritical CO2 solution containing oleic acid (extract phase) directly enters the next step of the iodination reaction without vacuum separation.

[0061] (5) Extraction results This step increases the purity of oleic acid obtained from extraction from 70-75% using traditional supercritical fluid extraction to 85-92%. The migration of polar impurities into the extract phase is reduced by 60-75%, specifically manifested as a reduction of over 50% in free fatty acid content and over 70% in phospholipid and glycerol ester impurities. The extraction selectivity coefficient (oleic acid relative to other unsaturated fatty acids) increases by 40-60%.

[0062] Step 3: Iodination reaction in a supercritical system (adding a polar promoter to enhance reaction activity) This step is the second key innovation step. By compounding a polar promoter in the supercritical CO2 iodination system, the limitation of the non-polar environment on the iodination reaction is overcome, and the extraction-reaction integration is realized.

[0063] (1) Implementation of integrated extraction-reaction The supercritical CO2 solution containing oleic acid obtained in step two is directly transferred to the iodization reactor or subjected to in-situ iodization in the extraction vessel without depressurization. In addition to oleic acid and supercritical CO2, this solution also contains the polar modifiers added in step two (such as ethanol, accounting for 1-8% of the system mass). These polar modifiers improve the polarity of supercritical CO2 during the iodization stage, but they alone are insufficient to provide a sufficiently polar environment for the iodization reaction; therefore, a further polar promoter compound system is required. This integrated operation avoids intermediate separation and transfer of oleic acid, reduces material loss and oxidation risks, and simplifies the process flow.

[0064] (2) Composition and addition of polar accelerator compound system A complex system of polar accelerators was added to the supercritical iodization system. This system consists of three synergistic components: Component 1: Polar reaction medium additive One or more polar compounds selected from low molecular weight polyethylene glycol (PEG-200 to PEG-400), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP) and other compounds with certain solubility in supercritical CO2 are added, and the amount added is 5-12% of the reaction system.

[0065] Preferred option: Use a compound of PEG-300 and DMSO in a mass ratio of 2:1, with the total addition amount being 8% of the reaction system.

[0066] Mechanism of action: These polar compounds do not form macroscopic phase separation in supercritical CO2, but rather form micropolar regions or polar microenvironments. Within these micropolar regions, the dissociation and activation of the iodine source proceed more readily, and reactive species (such as iodide ions) are more readily generated. The formation and stability of (or equivalent active species) are improved, providing a local environment similar to conventional polar solvents for the iodination reaction.

[0067] Component 2: Surfactant Surfactants with good solubility in supercritical CO2, such as one or more of perfluoropolyether compounds, organosiloxane surfactants, or fatty acid esters, are used, and the amount added is 1-3% of the reaction system.

[0068] Preferred option: Use a perfluoropolyether surfactant (molecular weight 1200) at a concentration of 2% of the reaction system.

[0069] Mechanism of action: These surfactants form reverse micelles or microemulsion structures in supercritical systems, encapsulating oleic acid, iodine source, and catalyst within tiny reaction microenvironments. The core of the reverse micelles provides a relatively polar reaction space, while the outer shell is compatible with supercritical CO2. This structure optimizes local polarity and concentration, promoting effective contact and reaction between reactants, while simultaneously improving the dispersion uniformity of the iodine source and catalyst in the supercritical system.

[0070] Component 3: Iodine source activator Add an auxiliary agent that can form a complex or adduct with the iodine source, such as one or more of triethylamine, pyridine compounds, or Lewis bases, in an amount of 5-15% of the mass of the iodine source.

[0071] Preferred option: Use triethylamine, with an addition amount of 10% of the iodine source mass.

[0072] Mechanism of action: Lewis bases such as triethylamine can react with I₂I. - Iodine species in the system form complexes (such as I2-triethylamine complexes and polyiodide ion-triethylamine complexes). Complexation increases the reactivity of iodine species, lowers the activation energy of the iodination reaction, and enhances the reactivity of the iodine source in nonpolar environments. The complexed iodine source is more likely to undergo addition reactions with the double bonds of oleic acid.

[0073] (3) Synergistic effect of polar accelerator compound system Compared with the existing pure supercritical CO2 iodization system, the three-component polar accelerator compound system of this embodiment produces a significant synergistic effect: Polar reaction medium additives provide the macroscopic polar environment required for the reaction, improving the polarity of the entire supercritical system; surfactant promoters construct nano- to micro-scale reaction microspaces, further optimizing the reaction environment and promoting mass transfer at the microscale; iodine source activating agents act directly on iodine source molecules, enhancing their activity at the molecular level. These three agents work synergistically at the macroscopic, microscopic, and molecular levels, increasing the rate of iodination reactions in the supercritical system by 50-80%, significantly improving reaction selectivity, and reducing side reactions (such as the oxidation and polymerization of oleic acid).

[0074] (4) Iodination reaction conditions and catalysts The iodination reaction conditions are: temperature 50-80℃, pressure 20-35 MPa, and reaction time 2-4 hours. The iodine source is a combination of potassium iodide and elemental iodine. The system forms polyiodide ions as active iodide species, with a molar ratio of potassium iodide to elemental iodine of 1:1 to 3:1.

[0075] The catalyst used is a weakly basic catalyst (such as potassium carbonate, sodium carbonate, sodium bicarbonate) or a phase transfer catalyst (such as quaternary ammonium salt compounds), and the amount of catalyst used is 1-5% of the mass of oleic acid.

[0076] The working principle of catalysts: Weakly basic catalysts provide a moderately alkaline environment (pH approximately 8-10) in the reaction system, promoting the electrophilic addition reaction of polyiodide ions to the double bonds of oleic acid. The alkaline environment facilitates the formation of iodide cations, which act as electrophiles, attacking the carbon-carbon double bonds in the oleic acid molecule, resulting in an electrophilic addition reaction to form iodoalkanes. Phase transfer catalysts (quaternary ammonium salts) promote the dissolution and dispersion of the iodine source and catalyst in the supercritical CO2 nonpolar system by forming ion pairs, thereby improving the contact efficiency between reactants.

[0077] The catalyst's form in the supercritical system: Due to the extremely low solubility of inorganic salt catalysts such as potassium carbonate in pure supercritical CO2, this embodiment provides a dissolution environment for the catalyst through a complex system of added polar promoters (especially polar reaction medium additives such as PEG and DMSO). Part of the catalyst dissolves in the polar microenvironment, while a portion is suspended and dispersed in the supercritical fluid as fine solid particles. The reverse micelle structure formed by the surface-active promoters further stabilizes the catalyst dispersion, enabling effective contact between the catalyst and the oleic acid and iodine source.

[0078] Iodination reaction equation: Oleic acid undergoes an electrophilic addition reaction with polyiodide ions: ; The complete reaction process includes: 1. Activation of the iodine source: (Further formation under alkaline conditions) 1. Polyiodide ion formation: Polyiodide ions attack the oleic acid double bond to form an iodonium ion intermediate. 2. Electrophilic addition: Polyiodide ions attack the oleic acid double bond to form an iodonium ion intermediate. 3. Product formation: The iodonium ion intermediate undergoes ring opening to form diiodostearic acid (periodooleic acid). Preferred scheme: Potassium iodide and elemental iodine are used as the iodine source, with a molar ratio of 2:1. The total molar amount of iodine is 1.3 times the molar amount of oleic acid (with a slight excess to ensure complete reaction). Potassium carbonate is used as the catalyst, at 2% of the mass of oleic acid. The reaction temperature is 65℃, the pressure is 25 MPa, and the reaction time is 3 hours. Under these preferred conditions, high iodination products (degree of iodide > 85%) account for 65-75% of the total iodination products.

[0079] (5) Monitoring of the iodination reaction process During the iodination reaction, the reaction progress is monitored through sampling analysis or online monitoring methods (such as ultraviolet-visible spectroscopy, iodine value determination, etc.). When the degree of iodination reaches the predetermined target or the iodine value no longer changes significantly, it indicates that the reaction is basically complete.

[0080] (6) Results of iodination reaction The iodination reaction yields a mixture of periodic oleic acids with varying degrees of iodization, including: - High-iodinated products (iodization degree > 85%): the target product, accounting for 60-75% of the total iodinated products. - Medium-iodinated products (iodization degree 50-80%): accounting for 20-30% of the total iodinated products. - Low-iodinated products (iodization degree < 50%): accounting for 5-10% of the total iodinated products. - A small amount of unreacted oleic acid: <5%. Through the polar accelerator compound system in this step, the supercritical iodination reaction rate is higher than that of pure supercritical iodination. The system efficiency is improved by 50-80%, and the reaction time is shortened from the original 6-8 hours to 2-4 hours. The selectivity of hyperiodide products is improved, and the formation rate of by-products (oxidation products, polymers, etc.) is reduced by 40-50%.

[0081] Step 4: Pressure gradient purification and separation in the supercritical system After the iodination reaction is complete, the products are purified by gradient separation through pressure control of the supercritical system. This step utilizes products with different degrees of iodination in the supercritical fluid. Due to differences in solubility, the products are separated by staged pressure reduction, precipitating out sequentially according to their iodide degree from low to high.

[0082] Because a polar accelerator complex system (including polar reaction medium additives, surfactant accelerators, and iodine source activators) was added in step three, these polar components altered the supercritical fluid dynamics. Solubility characteristics of the system. Although hyperiodide products are highly polar, their solubility is improved in supercritical systems containing polar components due to their interaction with those components. Hypoiodide products, on the other hand, are less polar and interact less with polar components, resulting in relatively lower solubility in such systems. Therefore, during depressurization, hypoiodide products preferentially precipitate from the supercritical phase, followed by mesoiodide products, with hyperiodide products precipitating last, achieving separation according to the iodide degree gradient.

[0083] Meanwhile, due to the catalyst (inorganic salts such as potassium carbonate) in supercritical conditions With extremely low solubility, the catalyst mainly exists in the form of solid particles or suspension. During the depressurization process, it preferentially precipitates along with the low-iodide products and medium-iodide products, thereby achieving the initial separation of the catalyst from the high-iodide products.

[0084] The first stage of depressurization separation involves reducing the system pressure from the reaction pressure (20-35 MPa) to 8-12 MPa, causing unreacted iodine sources and low-iodination products (iodination degree <50%) to precipitate and separate from the supercritical phase. These products are then collected and enter the recycling system.

[0085] The second stage of depressurization separation: the pressure is further reduced to 5-8 MPa to allow the moderate iodized products (iodization degree 50-80%) to precipitate and separate, and then collected and sent to the recycling system.

[0086] The third stage is complete depressurization: the pressure is reduced to normal pressure to obtain a highly iodinated product (iodization degree > 85%), which is the final product, periodic oleic acid.

[0087] To protect product stability, a segmented buffer pressure reduction method is adopted: each pressure gradient is divided into 3-5 buffer segments, each segment with a pressure reduction of 2-3 MPa, and the pressure is stabilized for 5-10 minutes after pressure reduction to allow the system temperature and phase state to gradually reach equilibrium, thereby reducing temperature fluctuations and thermal shock.

[0088] The preferred depressurization separation scheme is as follows: In the first stage, the reaction pressure is reduced from 25 MPa to 10 MPa, divided into 4 buffer segments (25→21→17→13→10 MPa), with each segment depressurized by 4 MPa and held for 8 minutes; in the second stage, the pressure is reduced from 10 MPa to 6 MPa, divided into 2 buffer segments (10→8→6 MPa), with each segment depressurized by 2 MPa and held for 6 minutes; in the third stage, the pressure is reduced from 6 MPa to atmospheric pressure, using a slow and continuous depressurization method, with the depressurization rate controlled at 0.5 MPa / minute.

[0089] Step 5: Recycling and Reiodination System By establishing a cyclic reiodination system, the low- and medium-iodination products obtained by pressure gradient separation are returned to the supercritical iodination step for further reaction, thereby making full use of the intermediate products and significantly improving the overall yield and iodine utilization rate.

[0090] (1) Supercritical phase remixing technology Temporary storage and repressurization of low and medium iodide products In step four, the low-to-medium iodination products precipitated in the first and second stages (including products with iodination degree <50% and iodination degree 50-80%) are collected in a temporary storage buffer tank. This tank is maintained at a moderate pressure (5-12 MPa) to avoid energy loss from repressurization after the product has completely cooled to atmospheric pressure. The product in the temporary storage tank is then pressurized to near the operating pressure of the main iodination reactor (18-30 MPa) using a pressurization device (high-pressure pump or booster).

[0091] During the pressurization process, deoxygenated high-purity [product] is injected into the product. (Oxygen content <10 ppm), so that the product and The mixture forms a supercritical or subcritical mixed phase. The mixing ratio is adjusted according to the viscosity and flowability of the product, generally... The mass ratio of the mixed phase to the product is 2:1 to 5:1. The density and fluidity of this mixed phase are close to those of the supercritical state, which facilitates its reinjection into the iodination reactor.

[0092] Continuous remix feed The pressurized "product" The mixed phase is continuously or intermittently injected into the main iodization reactor through a dedicated remixing inlet. The remixing inlet employs a distributed injection or multi-point feeding method (e.g., setting 3-5 inlet points evenly distributed at different heights or positions in the reactor), allowing the remixed material to disperse rapidly and mix thoroughly with the fresh oleic acid feedstock, iodine source, and catalyst in the reactor. Utilizing the high diffusivity and low viscosity of supercritical fluids, the mixing time can be controlled within 2 minutes.

[0093] The remix flow rate is dynamically adjusted based on the main reactor's throughput and the amount of low- and medium-iodide products generated to maintain the system's material balance and pressure stability. Generally, the remix flow rate is 20-40% of the fresh oleic acid feed flow rate.

[0094] (2) Precise iodine source supplementation and segmented iodization strategy Precise calculation of iodine requirements The low-to-medium iodination products have already consumed some iodine. To continue iodization to achieve a high degree of iodization (>85%), an additional iodine source is required. The amount of additional iodine needed to reach the target degree of iodization is calculated based on the flow rate and average degree of iodization of the low-to-medium iodination products (determined through online or offline analysis, such as iodine value determination, gas chromatography, etc.).

[0095] The calculation formula considers factors such as the current degree of iodide, molecular weight, target degree of iodide, and excess reaction coefficient of the product. Through an optimized calculation model, the accuracy of the iodine source addition is ensured, with the error controlled within 5%.

[0096] Online supplementation of iodine source Before or after the remixed material enters the main iodization reactor, the required iodine source is added to the remixed material via an iodine source addition device (such as a high-pressure metering pump, iodine source solution injection system, etc.). The iodine source is a combination of potassium iodide and elemental iodine. Supercritical systems In the solution, the molar ratio of potassium iodide to elemental iodine is kept consistent with that of the main reaction system (1:1 to 3:1, preferably 2:1).

[0097] The additional iodine source is thoroughly mixed with the remixed material in the feed pipe or a dedicated mixing zone, and the iodine source is evenly distributed by a static mixer or a pipeline mixer (a conventional mixing device in the art).

[0098] Implementation of segmented iodization reaction zones The main iodination reactor is divided into two reaction zones, either spatially or temporally: Fresh oleic acid iodization zone: This zone processes oleic acid directly from the supercritical extraction step in step two, performing the initial iodization reaction. The reaction conditions in this zone are standard iodization conditions (temperature 50-80℃, pressure 20-35 MPa, catalyst concentration 1-5% of the oleic acid mass).

[0099] Reiodination zone for recycled products: This zone processes the recycled low-to-medium iodinated products (already supplemented with iodine source) and performs additional iodination to a high degree of iodination. The reaction conditions in this zone are optimized based on the characteristics of the recycled products. Since the recycled products are partially iodized, their reactivity and reaction characteristics may differ from fresh oleic acid. The optimized conditions are: an appropriate increase in temperature of 5-10°C (e.g., reaching 70-85°C), an increase in catalyst concentration of 20-30%, and an appropriate extension of residence time of 10-20%.

[0100] Spatial segmentation: In a tubular reactor, the front section is the fresh oleic acid iodization zone, and the rear section is the recycled product reiodization zone; in a stirred tank reactor, relative segmentation is achieved through feed location and material flow control.

[0101] Time segmentation method: In intermittent or semi-continuous operation, fresh oleic acid is first iodized. After a certain conversion rate is achieved, recycled products and additional iodine source are introduced to continue the reaction.

[0102] The segmented iodination strategy allows for different optimization conditions to be applied to different substrates, maximizing overall iodination efficiency and selectivity.

[0103] Preferred cyclic re-iodination scheme: The temporary storage tank maintains a pressure of 8 MPa, and the low-to-medium iodinated products are pressurized to 24 MPa before being combined with... mix( (Product mass ratio 3:1), injected Oxygen content <5 ppm; Four feed points are set at the remix feed inlet, and the remix flow rate is 30% of the fresh oleic acid feed flow rate; The reaction conditions in the reiodination zone of the recycled product are: temperature 72℃ (7℃ higher than the 65℃ in the fresh oleic acid iodination zone), catalyst concentration 2.5% of the oleic acid mass (25% higher), and residence time 3.5 hours (extended by about 15%).

[0104] (3) Quality monitoring and purification intervention of recycled products Online or rapid offline quality monitoring Rapid quality testing is performed on low- and medium-iodized products in each batch or continuous flow. Testing indicators include iodide distribution, impurity content (byproducts, oxidation products, etc.), color, and viscosity. Rapid analytical methods, such as near-infrared spectroscopy (NIR), ultraviolet-visible spectroscopy (UV-Vis), viscometers, and rapid iodine value determination, are employed to achieve quality assessment within 5-10 minutes.

[0105] Quality grading Based on the quality monitoring results, low- and medium-iodized products are classified into different grades, and a differentiated treatment strategy is adopted: High-quality recycled products (iodide degree 40-80%, impurities <3%, light color, normal viscosity): of good quality, can be directly remixed into the re-iodination step without additional treatment.

[0106] Medium-quality products (iodide degree 30-50%, impurities 3-8%, darker color or higher viscosity): The quality is acceptable but needs improvement. After simple purification, the product should be remixed.

[0107] Low-quality products (iodide degree <30%, impurities >8%, dark color, abnormal viscosity): The quality does not meet the recycling requirements, and they are not remixed. They are collected separately for downgrading and utilization (such as as medium-iodide oleic acid products for applications with low purity requirements, such as surfactant raw materials, lubricant additives, etc.).

[0108] Quality grading avoids contamination of the main process by low-quality products, ensuring the stability of the recycling system and the quality of the final product.

[0109] Simple purification intervention method For recycled products of medium quality, a simple purification process is performed before remixing, including: Adsorption treatment: Add a trace amount of adsorbent (such as activated carbon, silica gel, kaolin, etc., 0.5-2%), stir and contact for 20-30 minutes at room temperature or under appropriate heating to remove pigments, oxidation products, polar impurities, etc. After adsorption treatment, remove the adsorbent by filtration.

[0110] Water washing or alkaline washing: For recycled products containing a large amount of free fatty acids and residual catalysts, wash with a small amount of water or dilute alkaline solution (such as 0.5-2% sodium hydroxide aqueous solution) to remove water-soluble impurities. After washing, perform oil-water separation and drying.

[0111] Antioxidant supplementation: Add antioxidants (such as vitamin E, butylated hydroxyanisole (BHA), etc., at a rate of 0.1-0.3%) to the recycled products to prevent further oxidation during reiodination.

[0112] The purification process is quick and simple, with a total processing time of less than 30 minutes. It does not significantly increase costs, but can effectively improve the quality of recycled products, increase reiodination efficiency, and improve the purity of the final product.

[0113] Loop count control Establish a cycle tracking method to record or mark the number of times a material is recycled. Methods could include: creating a file for each batch of material to record its recycling history; or inferring the number of cycles based on certain characteristic parameters of the material (such as viscosity changes, color changes, etc.).

[0114] The maximum number of cycles is set to 2-3. Once the maximum number of cycles is reached, the material is no longer re-circulated but collected separately as a medium-iodide oleic acid product. Controlling the number of cycles prevents cumulative quality deterioration and efficiency reduction caused by infinite circulation, ensuring the stability of the final product's quality.

[0115] Optimal purification and recycling control scheme: For medium-quality recycled products, a simple purification process is performed: add 1% activated carbon, stir and contact at 40°C for 25 minutes, then filter; if the free fatty acid content is >2%, wash once with 1% sodium hydroxide aqueous solution; supplement with 0.2% vitamin E as an antioxidant. The maximum number of cycles is set at 2, and the recycling history is recorded using a batch number tracking method.

[0116] (4) Overall effect of the cyclic reiodination system Through the comprehensive implementation of the aforementioned supercritical phase backmixing technology, precise iodine source addition, segmented iodization strategy, quality monitoring, and purification intervention, most (>70%) of the low-to-medium iodization products (accounting for 20-35% of the total iodization products) were successfully converted into the main product, periodic oleic acid. After one re-iodization, the proportion reaching a high degree of iodization (>85%) was >85%, and a small portion of the products that did not meet the standard could be recycled a second time.

[0117] The recycling and reiodination system increases the total yield of waste oil to periodic oleic acid from 60-70% to 75-85% without recycling, and increases iodine utilization from 70-80% to 90-95%, significantly improving resource utilization efficiency and economic benefits.

[0118] Step Six: Product Collection and Post-processing The high-iodine oleic acid (iodide degree > 85%, purity > 95%) obtained from the third stage of step four after complete depressurization undergoes post-processing, including: (1) Catalyst removal: Because the catalyst (inorganic salts such as potassium carbonate) is in supercritical... The catalyst has extremely low solubility. During the pressure gradient separation process in step four, the catalyst mainly precipitates along with the low-iodide and medium-iodide products, leaving very little catalyst residue (<0.1%) in the high-iodide products. The method for removing residual catalyst is as follows: wash the product with a small amount of water (water to product mass ratio of 1:10 to 1:20). The catalyst dissolves in the aqueous phase. After washing 1-2 times, perform oil-water separation and vacuum drying (temperature 50-60℃, vacuum degree <0.1 kPa, drying time 2-4 hours) to reduce the catalyst residue in the product to <0.01%. Preferred method: use deionized water, with a water to product mass ratio of 1:15, wash twice (each time thoroughly stirred and mixed for 10 minutes, then allowed to stand for separation), and vacuum dry under the following conditions: temperature 55℃, vacuum degree 0.05 kPa, drying time 3 hours.

[0119] (2) Adding antioxidants: Add antioxidants (such as vitamin E, rosemary extract, etc., at a rate of 0.1-0.3%) to the dried periodic oleic acid as product stabilizers to prevent oxidation during storage and use. Preferred option: Use vitamin E (α-tocopherol), at a rate of 0.2% of the product mass, and mix thoroughly at 50°C.

[0120] (3) Filtration and packaging: If necessary, filtration is performed to remove trace amounts of insoluble matter. The final product is packaged under nitrogen protection to prevent oxidation and obtain a high-purity, high-stability high-iodine oleic acid product.

[0121] Step Seven and recycling of iodine sources supercritical It is recycled throughout the entire process. Step four, pressure gradient separation releases... After being recovered, deoxygenated (by adsorption or chemical deoxygenation to reduce the oxygen content to <10 ppm), and compressed, it is reused for extraction in step two and iodination in step three. Recycling rate > 95%. Preferred deoxygenation method: Molecular sieve adsorption deoxygenation, using 3A or 4A molecular sieves (filling amount of...). (5-10% of the flux), under conditions of 20-30℃ and operating pressure of 2-3 MPa, contact adsorption for 15-20 minutes, so that... When the oxygen content is reduced to <5 ppm, the molecular sieve can be reused by heating and regenerating (120-150℃, 2-3 hours).

[0122] The unreacted iodine source separated and recovered in the first stage of step four can be reused after simple processing (such as conventional methods such as filtration and purification) and returned to the iodination step in step three. The iodine source recycling rate is >80%.

[0123] Experimental verification Experiment 1: Verification of the effect of polar modifiers on improving the selectivity of supercritical extraction 1. Experimental Objective Verification in supercritical The addition of polar modifiers during the extraction of waste oils has been shown to improve the extraction selectivity and purity of oleic acid. The results demonstrate that polar modifiers can increase the extraction selectivity by 40 to 60% and improve the purity of the extracted oleic acid from 70 to 75% to 85 to 92%.

[0124] 2. Preparation of experimental samples Experimental materials: Pretreated waste cooking oil, which has been degummed, deacidified, decolorized and deodorized, with an oleic acid content of 25%, a linoleic acid content of 35%, an alpha-linolenic acid content of 15%, and other fatty acid contents of 25%.

[0125] Polar modifier: analytical grade ethanol (purity greater than or equal to 99.7%).

[0126] Supercritical fluid: Industrial grade (Purity greater than or equal to 99.9%).

[0127] 3. Experimental conditions Supercritical extraction equipment: 500 mL supercritical extraction vessel, equipped with a high-pressure pump, temperature control system, and pressure control system.

[0128] Control group: Pure supercritical Extraction, without the addition of polar modifiers.

[0129] Experimental group: Supercritical Add 5% (mass fraction) ethanol as a polar modifier.

[0130] Extraction conditions: temperature 50℃, pressure 20 MPa, extraction time 2 hours. Flow rate 20 g / min.

[0131] Each experiment was repeated 3 times, and the average value was taken.

[0132] 4. Experimental Procedure Step 1: Add 100 g of pretreated waste oil to the extraction vessel, seal it, and then heat and pressurize it to the set conditions (50℃, 20 MPa).

[0133] Step 2: The control group is introduced with pure supercritical fluid. The experimental group was introduced with supercritical fluid pre-mixed with 5% ethanol. The flow rate was 20 g / min.

[0134] Step 3: After extraction for 2 hours, the extract phase is separated under reduced pressure in a separation vessel, and the oleic acid concentrate obtained from the extraction is collected.

[0135] Step 4: Analyze the fatty acid composition of the extract using gas chromatography (GC) and determine the content of each component, such as oleic acid, linoleic acid, and linolenic acid.

[0136] Step 5: Calculate the purity of oleic acid (the percentage of oleic acid content in total fatty acids) and the oleic acid extraction yield (the percentage of the mass of extracted oleic acid in the total mass of oleic acid in the raw material).

[0137] Step 6: Calculate the extraction selectivity coefficient (the ratio of the enrichment coefficient of oleic acid in the extract phase to the enrichment coefficients of other unsaturated fatty acids).

[0138] 5. Experimental Results Table 1. Effect of polar modifiers on the selectivity of supercritical extraction

[0139] Note: The extraction selectivity coefficient is defined as (mass fraction of oleic acid in the extract phase / mass fraction of oleic acid in the feed). (Mass fraction of other unsaturated fatty acids in the extract phase / Mass fraction of other unsaturated fatty acids in the feed). The selectivity coefficient of the control group was normalized to 1.00.

[0140] Figure 1 This is a comparison chart showing the effect of polar modifiers on the selectivity of supercritical extraction.

[0141] 6. Analysis and Summary Experimental results show that in supercritical... After adding 5% ethanol as a polar modifier to the extraction system, the purity of oleic acid increased significantly from 72.4% in the control group to 89.3%, an increase of 16.9 percentage points; the extraction yield of oleic acid increased from 68.5% to 76.7%, an increase of 8.2 percentage points; and the extraction selectivity coefficient increased from 1.00 to 1.48, an increase of 48.0%.

[0142] Meanwhile, after adding the polar modifier, the linoleic acid content in the extract decreased from 18.6% to 7.3%, and the linolenic acid content decreased from 5.2% to 1.8%, proving that the polar modifier effectively improved the supercritical fluid extraction process. The selective extraction capability for oleic acid significantly reduces the co-extraction of other unsaturated fatty acids.

[0143] Experiment 2: Verification of the effect of a polar accelerator compound system on increasing the rate of iodination reaction. 1. Experimental Objective Verification in supercritical The effect of adding a polar accelerator compound system on the iodination reaction rate has been demonstrated. The polar accelerator compound system can increase the supercritical iodination reaction rate by 50 to 80%, shorten the reaction time from 6 to 8 hours to 2 to 4 hours, improve the selectivity of high iodination products, and reduce the by-product formation rate by 40 to 50%.

[0144] 2. Preparation of experimental samples Experimental materials: Oleic acid enrichment obtained by supercritical extraction in step two (oleic acid purity 89%), and oleic acid-containing supercritical extraction obtained in simulating embodiment 1. Solution.

[0145] Iodine source: a combination of potassium iodide (analytical grade) and elemental iodine (analytical grade) in a molar ratio of 2:1. The total molar amount of iodine is 1.3 times the molar amount of oleic acid.

[0146] Catalyst: Potassium carbonate (analytical grade), used at 2% of the mass of oleic acid.

[0147] Polar accelerator compound system: Polar reaction medium additive: PEG-300 and DMSO composite (mass ratio 2:1), with a total addition amount of 8% of the reaction system. Surfactant accelerator: Perfluoropolyether surfactant (molecular weight 1200), with an addition amount of 2% of the reaction system. Iodine source activation aid: Triethylamine (analytical grade), with an addition amount of 10% of the iodine source mass.

[0148] 3. Experimental conditions Supercritical iodination reaction equipment: 1 L supercritical reactor, equipped with high-pressure pump, temperature control system, pressure control system, stirring device, and online sampling system.

[0149] Control group: Pure supercritical Iodization system, a compound system without the addition of polar accelerators.

[0150] Experimental group: Supercritical A compound system with polar accelerators added to the iodination system.

[0151] Iodination reaction conditions: temperature 65℃, pressure 25 MPa, reaction time 0 to 8 hours (sampling at different time points).

[0152] Each experiment was repeated 3 times, and the average value was taken.

[0153] 4. Experimental Procedure Step 1: Add 200 g of oleic acid concentrate, iodine source, and catalyst to the reactor. The control group is directly introduced into the supercritical fluid. The experimental group first added a polar promoter compound system before introducing supercritical fluid. .

[0154] Step 2: Increase the temperature and pressure to the set conditions (65℃, 25 MPa), turn on the stirrer, and start the timer.

[0155] Step 3: Take samples at 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours and 8 hours after the reaction has proceeded.

[0156] Step 4: The iodide content of the samples at each time point was determined by the iodine value determination method, and the product composition was analyzed by gas chromatography (GC). The contents of high iodide products (iodide content greater than 85%), medium iodide products (iodide content 50 to 80%), low iodide products (iodide content less than 50%), and by-products (oxidation products, polymers, etc.) were determined.

[0157] Step 5: Plot the curve of iodide degree as a function of reaction time, and calculate the reaction rate (measured by the time required to reach 85% iodide degree).

[0158] Step 6: Analyze the by-product content and calculate the by-product formation rate (the percentage of by-product mass to the total product mass).

[0159] 5. Experimental Results Table 2. Effect of polar accelerator compound system on iodination reaction rate

[0160] Note: Iodization degree refers to the average iodization degree of the product mixture, which represents the average degree of bonding between iodine atoms and oleic acid molecules; high iodization products refer to products with an iodization degree greater than 85%; by-products include oxidation products and polymers, etc.

[0161] Table 3 Comparison of iodination reaction rate and byproduct formation rate

[0162] Note: Reaction rate increase rate = (time required in control group / time required in experimental group - 1) × 100%; Byproduct reduction rate = (byproduct percentage in control group - byproduct percentage in experimental group) / byproduct percentage in control group × 100%.

[0163] Figure 2 This is a curve showing the change in degree of iodide over reaction time; Figure 3 The curve showing the change in the proportion of hyperiodide products over time; Figure 4The curve shows the change in the proportion of by-products over time. Figure 5 For comparison of final product distribution and reaction rate.

[0164] 6. Analysis and Summary Experimental results show that in supercritical... The addition of a polar accelerator to the iodination system significantly increased the iodination reaction rate. The control group required 7.8 hours to reach 85% iodination, while the experimental group only required 2.9 hours, representing a 169.0% increase in reaction rate (equivalent to an increase of approximately 70%), consistent with the 50-80% increase in reaction rate described in this invention.

[0165] The curves showing the change in iodide degree over time indicate that the iodination rate in the experimental group was significantly faster than that in the control group during the initial stage of the reaction (0.5 to 2 hours). By 3 hours of reaction, the iodide degree had reached 88.6%, while that in the control group was only 52.7%. This demonstrates that the polar promoter compound system effectively promoted the dissociation and activation of the iodine source, accelerating the iodination reaction process.

[0166] In terms of product distribution, the proportion of hyperiodide products in the experimental group (75.6%) was significantly higher than that in the control group (62.3%), an increase of 13.3 percentage points; the proportion of by-products in the experimental group (1.9%) was much lower than that in the control group (13.6%), a decrease of 86.0%, proving that the polar promoter compound system not only improved the reaction rate, but also significantly improved the reaction selectivity and reduced the occurrence of side reactions such as oxidation and polymerization.

[0167] The curve showing the change of by-product percentage with reaction time indicates that the by-product percentage in the control group increased continuously with the extension of reaction time, reaching 13.6% at 8 hours; while the by-product percentage in the experimental group remained at a low level (1.5% to 1.9%), indicating that the polar promoter compound system effectively inhibited the occurrence of side reactions.

[0168] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing periodic oleic acid, characterized in that, Includes the following steps: Step 1: Pre-treat the waste oil to obtain pre-treated waste oil, in which the oleic acid content is 20-30%; Step 2: Use supercritical CO2 extraction to pretreat waste oil at a temperature of 40-60℃ and a pressure of 15-30 MPa. Add a polar modifier to the supercritical CO2. The polar modifier is selected from one or more of short-chain alcohols, short-chain organic acids, and short-chain ketones. The amount added is 1-8% of the mass of supercritical CO2 to obtain a supercritical CO2 solution containing oleic acid. Step 3: The supercritical CO2 solution containing oleic acid obtained in Step 2 is directly subjected to iodination reaction. A polar accelerator compound system is added to the reaction system. The polar accelerator compound system includes a polar reaction medium additive, a surface activity accelerator, and an iodine source activation aid. The iodine source is a combination of potassium iodide and elemental iodine. The catalyst is a weak base catalyst or a phase transfer catalyst. The reaction temperature is 50-80℃ and the pressure is 20-35 MPa to obtain a mixture of high-iodine oleic acid with different degrees of iodination. Step 4: Separate the mixture obtained in Step 3 by pressure gradient. In the first stage, the pressure is reduced to 8-12 MPa to precipitate low-iodide products. In the second stage, the pressure is reduced to 5-8 MPa to precipitate medium-iodide products. In the third stage, the pressure is reduced to normal pressure to obtain high-iodide products. Step 5: After pressurizing the low- and medium-iodide products precipitated in the first and second stages of Step 4, mix them with supercritical CO2 to form a supercritical or subcritical mixed phase. After adding an iodine source, mix the mixture back into the iodization reactor of Step 3 to continue the reaction.

2. The method for preparing periodic oleic acid according to claim 1, characterized in that, The polar modifier in step two is selected from one or more of methanol, ethanol, isopropanol, acetic acid, propionic acid, acetone, and butanone.

3. The method for preparing periodic oleic acid according to claim 1, characterized in that, The polar reaction medium additive in step three is selected from one or more of low molecular weight polyethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone, and the amount added is 5-12% of the reaction system; the surface activity promoter is selected from one or more of perfluoropolyether compounds, organosiloxane surfactants, and fatty acid esters, and the amount added is 1-3% of the reaction system; the iodine source activation aid is selected from one or more of triethylamine, pyridine compounds, and Lewis bases, and the amount added is 5-15% of the iodine source mass.

4. The method for preparing periodic oleic acid according to claim 1, characterized in that, In step three, the molar ratio of potassium iodide to elemental iodine is 1:1 to 3:1, and the total molar amount of iodine is 1.2 to 1.5 times the molar amount of oleic acid.

5. The method for preparing periodic oleic acid according to claim 1, characterized in that, In step three, the weakly basic catalyst is selected from one or more of potassium carbonate, sodium carbonate, and sodium bicarbonate, the phase transfer catalyst is a quaternary ammonium salt compound, and the amount of catalyst used is 1-5% of the mass of oleic acid.

6. The method for preparing periodic oleic acid according to claim 1, characterized in that, In step four, each pressure gradient is divided into 3-5 buffer segments, with each segment having a pressure reduction of 2-3 MPa. After the pressure is reduced, the pressure is maintained for 5-10 minutes.

7. The method for preparing periodic oleic acid according to claim 1, characterized in that, In step five, the temporary storage buffer tank maintains a pressure of 5-12 MPa, and the low-iodide products are pressurized to 18-30 MPa. The injected supercritical CO2 has an oxygen content of less than 10 ppm, and the mass ratio of CO2 to the product is 2:1 to 5:

1.

8. The method for preparing periodic oleic acid according to claim 1, characterized in that, The iodine source added in step five is a supercritical CO2 solution of potassium iodide and elemental iodine, with a molar ratio of potassium iodide to elemental iodine of 1:1 to 3:

1. The amount of iodine to be added is calculated based on the flow rate and average degree of iodization of the low-to-medium iodide products, with the error controlled within 5%.

9. The method for preparing periodic oleic acid according to claim 1, characterized in that, In step five, the iodization reactor is divided into a fresh oleic acid iodization zone and a recycled product reiodization zone. The temperature of the recycled product reiodization zone is 5-10°C higher than that of the fresh oleic acid iodization zone, and the catalyst concentration is increased by 20-30%.

10. The method for preparing periodic oleic acid according to claim 1, characterized in that, Before remixing in step five, the low- and medium-quality iodized products are subjected to quality testing and classification. High-quality recycled products with iodization degree of 40-80% and impurities of less than 3% are directly remixed. Medium-quality products with iodization degree of 30-50% and impurities of 3-8% are purified and then remixed. Low-quality products with iodization degree of less than 30% and impurities of more than 8% are not remixed. The maximum number of cycles is 2-3.

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