Preparation process of high yellowing-resistant antioxidant 1010

Abstract

The application relates to a preparation process of a high-yellowing-resistance antioxidant 1010, and belongs to the technical field of polymer material processing aids. The four aspects of composite catalysis for inhibiting the generation of colored impurities, reaction process oxygen blocking by pure nitrogen micro-negative pressure control, physical adsorption and chemical catalysis cooperation for pre-decolorization, and ternary solvent regulation and control of solubility and gradient cooling recrystallization deep purification are combined to realize the control of quinone colored impurities in the whole chain of the production of the antioxidant 1010, so that the yellowing resistance is improved, and the application is suitable for the fields of high-transparency polyolefins, optical films and food contact materials.

Description

Technical Field

[0001] This invention relates to the field of polymer processing aids, and more particularly to antioxidant 1010, specifically a preparation method for reducing product color number and improving yellowing resistance through a composite catalyst system, strict control of oxygen content, and gradient decolorization and recrystallization process. Background Technology

[0002] Antioxidant 1010 ([β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester) is currently the most widely used high molecular weight hindered phenolic antioxidant. Its molecule contains four hindered phenolic functional groups, which can efficiently capture peroxide free radicals generated during the thermal oxidation of polymers. It is widely used in polymer materials such as polypropylene (PP), polyethylene (PE), ABS, and polyoxymethylene, and has both long-term thermal stability and processing stability.

[0003] Industrially, antioxidant 1010 is typically prepared by transesterification of methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (β-ester) with pentaerythritol. Traditional processes use organotin compounds such as dibutyltin dilaurate as catalysts, which exhibit high catalytic activity and good reaction depth, and have long held the dominant position in this process.

[0004] In recent years, Annex XVII of the EU REACH Regulation has included organotin compounds in the list of restricted substances, strictly limiting their residue levels in industrial products, food contact materials, and daily plastic products. Products produced by traditional tin catalytic processes face serious export trade barriers, and the development of efficient tin-free catalytic systems has become an industry necessity.

[0005] Existing alternative routes for Wuxi mainly include three categories: organozinc, titanates, and alkali metal alkoxides. Organozinc has low catalytic activity, high reaction temperature, large residual triesters, and insufficient product purity. Ordinary titanates easily form colored titanium phenol complexes with hindered phenolic hydroxyl groups, resulting in a sharp increase in product color and failing to meet the requirements of high-end applications. Alkali metal alkoxides, especially lithium-based alkoxides, have gradually entered the industry's field of vision due to their catalytic activity being close to that of organozinc and their low raw material cost, becoming one of the most promising alternative routes for organozinc.

[0006] However, the existing lithium catalytic process still has many difficult-to-overcome defects: (1) The catalyst is easy to volatilize and lose: the commonly used low molecular weight lithium alcohols such as lithium methoxide and lithium ethanol have low boiling points. During the high vacuum removal of methanol in the later stage of the reaction, they are easy to be azeotropically distilled out with the by-product methanol, resulting in a cliff drop in the catalytic activity of the system. The rate-controlling step of the conversion of triester to tetraester is not fully reacted, the residual triester is too high, and the product purity is insufficient; (2) The product color deteriorates significantly: lithium alkoxides are strongly alkaline. If the local alkalinity of the reaction system is too high, it will catalyze the oxidation of phenolic hydroxyl groups and generate quinone colored by-products, resulting in a dark initial color of crude product. It is difficult to remove the by-products in subsequent recrystallization. The final product has low light transmittance and poor resistance to yellowing, and can only reach the level of ordinary industrial grade; (3) The side reaction is difficult to control: under strong alkaline conditions, it is easy to trigger by-product reactions such as ester bond alcoholysis and product decomposition. It is difficult to balance product yield and purity.

[0007] To improve the color issue, the industry has also tried using alkaline ionic liquids as transesterification catalysts. Imidazole alkaline ionic liquids have excellent thermal stability, mild alkalinity, and are non-volatile. They have fewer side reactions in the catalytic process and produce good initial color. However, when used alone, their catalytic activity is much lower than that of organotin and lithium catalysts. The reaction rate is slow, the reaction depth is insufficient, and the residual amount of triesters is generally higher than 3%, which cannot meet the efficiency and quality requirements of industrial production.

[0008] To date, existing technologies have not yet combined chelated organic lithium with alkaline ionic liquids to construct a synergistic catalytic system, nor have they formed a solution that simultaneously meets the three core requirements of Wuxi compliance, high reaction depth, and low color number and yellowing resistance. As a result, the products are difficult to match the high-end imported products and cannot be applied to high-end scenarios such as high-transparency polyolefins, optical films, and food contact materials. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention proposes a preparation process for a high-yellowing-resistant antioxidant 1010 to improve the yellowing resistance of antioxidant 1010.

[0010] The technical problem to be solved by the present invention is achieved through the following technical solution: A preparation process for a highly resistant yellowing antioxidant 1010 includes the following steps: S1 transesterification reaction Methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (β-ester) and pentaerythritolamine were added to a reactor equipped with a distillation column in a molar ratio of (4-4.5):1, and a ternary composite catalytic system was added. First, high-purity nitrogen was introduced to purge the air inside the reactor at least three times to control the oxygen content ≤50 ppm. Then, a micro-negative pressure system was activated to maintain the absolute pressure of the system at 80-95 kPa while continuously introducing trace amounts of nitrogen. The transesterification reaction was carried out with a gradient temperature increase: the first stage was at 130-145℃ for 2-3 h, the second stage at 160-170℃ for 3-4 h, and the third stage was at 180-188℃ with the vacuum level and absolute pressure gradually increased by 1-5 kPa. The reaction continued for 1.5-2.5 h until no methanol distilled off. The reaction endpoint was determined by detecting the content of the triester and tetraester; the tetraester was ≥96%, and the triester was ≤2.5%.

[0011] The ternary composite catalytic system consists of a main catalyst, a co-catalyst, and an antioxidant stabilizer, with a mass ratio of 100:(20-35):(1.5-4).

[0012] The main catalyst is a chelated organic lithium catalyst, which is composed of lithium isooctanoate and lithium acetylacetonate in a mass ratio of (1.5-3):1. Lithium isooctanoate provides the core Lewis acid catalytic activity and activates the ester carbonyl group. Lithium acetylacetonate stabilizes the lithium center through a bidentate chelate structure, inhibits the volatilization and loss of lithium salt under high temperature and high vacuum, and at the same time weakens the strong basicity of lithium and reduces the side reaction of phenol oxidation.

[0013] The cocatalyst is an imidazole alkoxy ionic liquid, selected from one or more of 1-butyl-3-methylimidazolium methanol, 1-ethyl-3-methylimidazolium tert-butanol, and 1-butyl-3-methylimidazolium isooctanoate, preferably 1-butyl-3-methylimidazolium methanol. It acts as a Brønsted base center to activate the hydroxyl group of pentaerythritol, forming a dual activation synergistic effect with the lithium main catalyst: Lewis acid activation of carbonyl group and Brønsted base active hydroxyl group. At the same time, it acts as a solvation stabilizer for lithium salt, avoiding excessively high local base concentration and further reducing oxidation side reactions.

[0014] The antioxidant stabilizer is a phosphite compound, selected from one or more of tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168) and pentaerythritol diphosphite (antioxidant 626), preferably tris(2,4-di-tert-butylphenyl) phosphite. The hydroperoxide generated in the in-situ decomposition system during the high-temperature reaction stage quenches phenolic free radicals and blocks the chain reaction of quinone colored substances.

[0015] The total amount of the catalytic system is 0.35-0.8% of the mass of methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Before feeding, chelated organic lithium and alkaline ionic liquid are premixed and stirred at 50-70℃ for 20-40 min to form a homogeneous catalytic liquid before feeding, in order to avoid local alkalinity causing discoloration.

[0016] S2 crude product neutralization and decolorization After the reaction is complete, the temperature is lowered to 100-110℃, and an organic acid is added to neutralize the catalyst until the pH of the system is 5.5-7.0. Then, the temperature is gradually increased and the vacuum is increased to remove excess β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate raw material and low-boiling substances by thin-film evaporation. The crude molten product after raw material removal is pumped into a dissolving vessel, and 3-5 times the mass of alcohol solvent is added. The mixture is stirred and heated to 70-90℃ to completely dissolve the crude product. A composite decolorizing agent is added, and the mixture is kept warm and stirred for 30-60 min to decolorize. While still hot, the decolorizing agent and insoluble matter are removed by precision filtration.

[0017] The composite decolorizing agent is composed of powdered activated carbon and activated clay in a mass ratio of 1:(1-3), with a total dosage of 0.5-3.0% of the crude product weight. Activated carbon primarily removes macromolecular organic matter through physical adsorption, while activated clay catalytically decomposes trace amounts of quinone structures through its surface acidic sites. The two work synergistically to achieve deep decolorization. The organic acid is selected from glacial acetic acid, citric acid, and oxalic acid.

[0018] S3 gradient cooling recrystallization The decolorized filtrate was transferred to a jacketed, temperature-controlled crystallizer. Acetates and deionized water were added to prepare an alcohol-ester-water ternary complex solvent system. Stirring was started, and the temperature was controlled at 70-75℃ to form a homogeneous, transparent solution. Then, crystallization was carried out using a three-stage gradient cooling process. First stage: Slowly cool to 55-58℃ at a rate of 2-3℃ / h, add α-type crystal seeds accounting for 0.3-0.8% of the solute mass, and maintain constant temperature for 1-2 hours to induce the formation of uniform crystal nuclei; The second stage involves cooling the temperature to 35-40℃ at a rate of 3-5℃ / h and holding it at that temperature for 1-1.5 hours to promote crystal growth. Third stage: Cool down to 10-15℃ at a rate of 5-8℃ / h, and hold at the temperature for 2-3 hours to allow crystallization to complete.

[0019] After crystallization, the filter cake is centrifuged and filtered, washed with cold solvent, and then vacuum dried to obtain the α-crystalline antioxidant 1010 product. The mother liquor is distilled to recover the solvent for recycling.

[0020] In the ternary compound solvent system, the mass ratio of alcohol, ester and water is (65-80):(15-25):(3-10), the alcohol is selected from one or more of methanol, ethanol and isopropanol, and the acetate is selected from one or two of methyl acetate and ethyl acetate.

[0021] In this invention, the organic acid mentioned in step S2 is glacial acetic acid.

[0022] In this invention, the entire chain of control over quinone colored impurities is achieved through four dimensions: inhibiting their formation at the source, blocking oxidation during the process, pre-decolorizing to destroy their structure, and deep separation through recrystallization. (1) Ternary composite catalytic system to reduce colored impurities at the source of reaction. Traditional single-component organotin compounds require temperatures above 200°C to ensure transesterification conversion, and high temperatures are precisely the core inducing factor for the oxidation of phenolic groups and the formation of quinone colored compounds. In this scheme, lithium isooctanoate provides the core catalytic activity, and Li... + As a soft Lewis acid, it can coordinate with the carbonyl oxygen of β-esters, polarizing the ester carbonyl group, reducing the electron cloud density of carbon atoms, and enhancing electrophilic reactivity. The long-chain isooctanoate ion ensures excellent solubility of the catalyst in the molten reaction system. The ionic liquid, as a base-co-catalyst center, can remove the proton from the pentaerythritol hydroxyl group, generating a highly nucleophilic alkoxy anion. The two work synergistically to lower the transesterification activation energy and increase the reaction rate. Lithium acetylacetonate stabilizes the lithium center through a bidentate chelate structure, inhibiting the volatilization and decomposition of lithium salts at high temperatures. The high-boiling-point ionic liquid forms a solvation-stabilized structure with the lithium salt. The high-vacuum de-alcoholization stage does not distill off with methanol, allowing the catalyst to maintain high catalytic activity in the rate-controlling step of the triester to tetraester conversion. The chelate structure weakens the strong basicity of lithium and reduces the side reaction of phenol hydroxyl oxidation. The ionic liquid acts as a dispersion medium and stabilizer, and the imidazolium cation stabilizes the negative electrons of the reaction transition state through electrostatic interaction, further reducing the reaction energy barrier. At the same time, it avoids the aggregation of lithium salt in the molten system. The phosphite quenches free radicals in situ. All three factors together offset the defect that the basic catalyst easily causes phenol oxidation and discoloration, reducing the initial color of the crude product from the source and achieving a balance between high activity and low color.

[0023] (2) High-purity nitrogen and micro-negative pressure control of oxygen achieve dual thermodynamic and kinetic blocking of phenol oxidation. The root cause of the product's yellowing is the formation of a byproduct containing a conjugated quinone structure: 3,5-di-tert-butyl-4-hydroxyphenyl. Under high-temperature and aerobic conditions, the phenolic hydroxyl group loses electrons to form a phenoloxy radical, which is further oxidized to generate 3,5-di-tert-butyl-p-benzoquinone and other conjugated structures. This structure contains a large π-bond conjugated system, which can undergo π-π reactions. * Electron transitions occur, absorbing visible light in the 400-500 nm wavelength range, resulting in a macroscopic appearance of yellow to yellowish-brown. Oxygen is a necessary reactant for this oxidation reaction, and the higher the oxygen concentration and the higher the temperature, the more exponentially the oxidation reaction rate increases.

[0024] This scheme maintains an oxygen content ≤50 ppm, applies a slight negative pressure of 80-95 kPa, and continuously supplies nitrogen during the reaction. From a kinetic perspective, this controls the oxygen partial pressure at an extremely low level. According to oxidation reaction kinetics, a lower oxygen concentration leads to a lower oxidation rate, thus reducing the oxidation rate of phenol. From a thermodynamic perspective, the slight negative pressure lowers the boiling point of the byproduct methanol, allowing it to be rapidly precipitated at lower temperatures. This shifts the transesterification equilibrium to the positive side, further shortening the high-temperature reaction time and creating a positive cycle with the low-temperature catalysis. Furthermore, under the slight negative pressure, the system maintains a stable inward pressure gradient. Combined with the continuous introduction of trace amounts of nitrogen, this creates a unidirectional nitrogen flow that continuously carries away any trace amounts of oxygen that might seep in through gaps.

[0025] (3) Activated carbon and activated clay can directionally destroy chromogenic groups from two dimensions: physical adsorption and chemical catalysis. Powdered activated carbon possesses a well-developed mesoporous / microporous structure and an extremely high specific surface area. It can efficiently adsorb large molecular weight impurities such as colored polymers and quinone coupling products by relying on van der Waals forces. However, it exhibits poor selectivity for small-molecule monoquinone impurities, as these impurities have polarities similar to the products and are small in size, easily competing with the products for adsorption. Activated clay's main component is montmorillonite silicate, and its surface is rich in Al. 3+ Acidic sites and polar silanol groups on the surface can catalyze affinity addition, ring-opening, or reduction reactions in quinone structures, directly disrupting the large π-conjugated system of the quinone structure. This transforms colored quinones into colorless phenols or open-chain aliphatic structures, fundamentally eliminating chromogenic groups. Simultaneously, the polarity of the bleaching clay surface, coupled with the significantly stronger polarity of quinone impurities compared to the weakly polar antioxidant 1010 molecule, allows the bleaching clay to selectively adsorb polar colored impurities, reducing the amount of product adsorbed and exhibiting superior selectivity compared to activated carbon. The complementary properties of activated carbon and activated bleaching clay, when combined, effectively enhance decolorization, reducing purification pressure for subsequent recrystallization.

[0026] (4) Ternary solvent and three-stage gradient crystallization, precisely controlled according to solubility, to achieve deep purification. The efficiency of recrystallization depends on the difference in solubility between the target product and impurities in the solvent. Traditional single alcohols have a single polarity, and the solubility of the product and quinone impurities tends to be similar with temperature. At low temperatures, the impurities tend to precipitate along with the product. This scheme introduces acetates to construct an alcohol-ester-water ternary system. The product antioxidant 1010 is a high molecular weight, weakly polar, and its solubility in weakly to moderately polar solvents is sensitive to temperature changes. The colored quinone impurities contain polar carbonyl groups, which are significantly more polar than the product and are more easily soluble in solvents with higher polarity. In the ternary system, the alcohol provides basic solubility, the ester adjusts the solvent polarity to moderate, and water further enhances the polarity gradient. The combination of the three results in a high degree of matching between the overall solvent solubility parameters and the product, and a low degree of matching with the impurities. That is, the product completely dissolves at high temperatures, and at low temperatures, the product solubility drops sharply and a large amount precipitates out, while the polar quinone impurities remain in the mother liquor at low temperatures due to the solubilizing effect of the ester and water and do not precipitate with the product crystallization.

[0027] The crystallization process includes two stages: nucleation and growth. This scheme achieves precise control of supersaturation through a three-stage gradient cooling process: The first stage is slow cooling, which cools the crystal at an extremely slow rate to a low supersaturation range. Seed crystals are added to induce heterogeneous nucleation, avoiding spontaneous nucleation that produces a large number of fine crystals. The isothermal crystal growth allows the crystal to grow orderly along the seed crystal, resulting in a smooth crystal surface. The second stage is medium-speed cooling, which maintains a moderate supersaturation level, allowing the crystal to grow steadily. While ensuring the growth rate, it avoids the increase of crystal defects and impurities embedded in the crystal lattice due to excessively high supersaturation. The third stage is rapid cooling, which minimizes the solubility of the product and increases the final yield. At this point, the crystal has grown completely, and the small amount of precipitated product is deposited only on the existing crystal surface without introducing new impurities.

[0028] Compared with the prior art, the present invention has the following advantages: (1) This application adopts a dual-activation catalytic architecture of chelated organic lithium and alkaline ionic liquid, which solves the problems of easy volatility and poor color of single lithium, while improving the reaction rate and reaction depth. The peak reaction temperature is controlled within 188℃, achieving excellent performance while adding tin. (2) This application introduces trace amounts of phosphite as an in-situ antioxidant stabilizer into the catalytic system, which instantly quenches oxidative free radicals during the high-temperature reaction stage, breaks the correlation between alkaline catalysis-phenol oxidation-quinone formation, and blocks the chain reaction of quinone formation; (3) The reaction process of this application is carried out under the protection of high-purity nitrogen and under slight negative pressure. The oxygen content is extremely low, which inhibits the formation of quinones during the reaction process and significantly improves the initial color of the crude product. (4) In view of the structural characteristics of quinone colored by-products, this application adopts a composite decolorization scheme that combines physical adsorption of activated carbon with catalytic decomposition of activated clay. The synergistic effect of the two effectively improves the decolorization efficiency and removes colored impurities in a targeted manner. (5) The ternary solvent system of this application adjusts the solvent polarity and thus adjusts the solubility parameter, which can effectively retain quinone impurities in the mother liquor during crystallization. The three-stage gradient cooling degree precisely controls the nucleation and growth process. With the help of seed induction, a single crystal form and uniform particle size α crystal product can be directly obtained, which improves the product transmittance and reduces the thermal aging yellowing index. (6) This application constructs a color control system for the final product from several aspects, including catalytic cooling and anti-oxidation, oxygen isolation throughout the process, pre-decolorization and gradient recrystallization. The various technical means cooperate with each other to greatly improve the yellowing resistance of the product. Attached Figure Description

[0029] Figure 1 This is a flowchart of the preparation process in this application; Figure 2 This is a schematic diagram illustrating the ternary solvent and gradient cooling principle in the recrystallization process of this application. Figure 3 This is a comparison chart of the XRD patterns of the product in this application and the standard XRD pattern of antioxidant 1010; Figure 4 This is a chromatogram comparing the product of this application with that of the prior art; Figure 5 This is a comparison chart of the light transmittance of the products in this application; Figure 6 This is a comparison chart of the yellowing index of the products in this application. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment provides a preferred scheme for the preparation process of a high-yellowing-resistant antioxidant 1010, as follows: Figure 1 As shown, the specific steps are as follows: (1) Transesterification reaction: 200 kg (0.684 kmol) of methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and 22.2 kg (0.163 kmol) of pentaerythritol were added to a 500 L stainless steel reactor equipped with a distillation column, stirrer and vacuum system, with a molar ratio of about 4.2:1.

[0033] 320 g of lithium isooctanoate, 160 g of lithium acetylacetonate and 120 g of 1-butyl-3-methylimidazolium methanol salt were premixed and stirred at 60°C for 30 min, and then 10 g of antioxidant 168 was added to form a homogeneous catalytic system. The total amount used was about 0.305% of the mass of β-ester.

[0034] The air inside the reactor was replaced three times with high-purity nitrogen, and the oxygen content was measured to be 30 ppm. The micro-negative pressure system was then activated to maintain the absolute pressure of the system at approximately 90 kPa while a trace amount of nitrogen was continuously introduced.

[0035] Gradient heating reaction: The temperature was increased to 140℃ and held for 2.5 h, then increased to 165℃ and held for 3.5 h, and finally increased to 185℃. The vacuum was gradually increased to an absolute pressure of approximately 3 kPa, and the reaction was held for 2 h until no methanol distillation occurred. Sampling and analysis showed that the tetraester content was 97.8% and the triester content was 2.1%.

[0036] (2) Neutralization and decolorization of crude product: Cool down to 105℃, slowly add glacial acetic acid to neutralize to pH about 6.2, heat up to 220℃ and under an absolute pressure of 100 Pa, remove excess β-ester and low-boiling substances by thin-film evaporation.

[0037] Approximately 198 kg of the molten crude product was added to a dissolving vessel, along with 800 L of anhydrous ethanol. The mixture was heated to 80°C and stirred to dissolve. A composite decolorizing agent was then added: 1.5 kg of powdered activated carbon and 2.5 kg of activated clay, with the total amount being 2.02% of the crude product weight. The mixture was kept at 80°C and stirred for 45 min to decolorize. The decolorizing agent was then removed by a precision plate and frame filter.

[0038] (3) Gradient cooling recrystallization: The green leaves were transferred to the crystallization vessel, and 180 kg of ethyl acetate and 40 kg of deionized water were added to form an ethanol-ethyl acetate-water ternary solvent system. The temperature was raised to 72°C to form a homogeneous solution, and the programmed cooling was started: First stage: Cool down to 56℃ at a rate of 2.5℃ / h, add 600 g of α-crystal seed crystals (approximately 0.31% of the solute), and maintain the temperature for 1.5 h to grow crystals; Second stage: Cool down to 38℃ at a rate of 4℃ / h, and hold at that temperature for 1 hour; Third stage: Cool down to 12℃ at a rate of 6℃ / h, and hold at that temperature for 2.5 h.

[0039] Centrifuge and filter, wash the filter cake with cold ethanol, and dry under vacuum at 60°C for 12 h to obtain 176.0 kg of white crystalline powder, with a yield of approximately 91.6%.

[0040] Product testing: XRD, etc. Figure 3 As shown, the HPLC main peak content of tetraester was 97.8%, the total effective components (triester + tetraester) were 99.5%, the Gardner color number was <1, the APHA color number was 17, the transmittance of toluene solution was 98.2% at 425 nm and 99.4% at 500 nm, the yellowing index ΔYI of the PP test piece after 2 h of air heat aging at 180℃ was 0.76, and tin residue was not detected (<1 ppm).

[0041] Example 2

[0042] This embodiment is based on Embodiment 1, and a new implementation scheme is formed by adjusting some materials and their quantities and process parameters. The difference between this embodiment and Embodiment 1 is as follows: Composite catalyst: 280 g lithium isooctanoate, 140 g lithium acetylacetonate, 130 g 1-ethyl-3-methylimidazolium tert-butoxide, 12 g antioxidant 626; Reaction temperature gradient: 135℃ / 3 h, 162℃ / 4 h, 182℃ / 2.5 h; Ternary solvent: Methanol-methyl acetate-water system, mass ratio 75:18:7; The final product yielded 174.8 kg, with a yield of 91.0%. Product testing showed: HPLC tetraester main peak content of 97.5%, total effective components of 99.4%, Gardner color number <1, ​​APHA color number 19, toluene solution transmittance of 98.0% at 425 nm and 99.3% at 500 nm, and yellowing index ΔYI of PP test pieces after 2 hours of air heat aging at 180℃ was 0.80.

[0043] Example 3

[0044] This embodiment is based on Embodiment 1, and a new implementation scheme is formed by adjusting some materials and their quantities and process parameters. The difference between this embodiment and Embodiment 1 is as follows: The molar ratio of β-ester to pentaerythritol was 4.3:1, and the amount of pentaerythritol fed was 21.7 kg. The total amount of composite catalyst is 0.45% of the mass of β-ester, the mass ratio of lithium isooctanoate to lithium acetylacetonate is 2.5:1, and the ionic liquid accounts for 30% of the mass of the main catalyst. Oxygen content should be controlled below 25 ppm; Composite decolorizing agent: 1 kg activated carbon, 3 kg activated clay.

[0045] The final product yield was 177.3 kg, with a yield of 92.0%. Product testing: HPLC showed a tetraester main peak content of 97.91%, total effective components of 99.6%, Gardner color number <1, ​​APHA color number 15, toluene solution transmittance of 98.5% at 425 nm and 99.5% at 500 nm, and a yellowing index ΔYI of 0.68 for PP test pieces after 2 hours of air heat aging at 180℃.

[0046] Example 4

[0047] This embodiment sets up a control experiment, using Example 1 as the complete optimized process as the benchmark, and sets up a comparative example. Each group only adjusts one core process variable, which is completely consistent with the field and raw material ratios in Example 1.

[0048] (1) Scheme design Comparative Example 1 uses a traditional industrial benchmark process, employing a single-component dibutyltin dilaurate catalyst at a dosage of 0.5% of the β-ester mass, without antioxidant stabilizers; the reaction is protected under nitrogen atmosphere at atmospheric pressure, with an oxygen content of approximately 300 ppm in the reactor; the peak reaction temperature is 200℃; no dedicated composite decolorization process is included, and the crude product is naturally cooled and recrystallized using a single methanol solvent; Comparative Example 2 is a single lithium methoxide catalytic process. The catalyst used is only a single, equal mass of lithium methoxide, without ionic liquid and antioxidant components. The other process parameters are exactly the same as those in Example 1. Comparative Example 3 is a single alkaline ionic liquid catalytic process. The catalyst used is only a single 1-butyl-3-methylimidazolium methanol salt of equal mass, without organic lithium components. The other process parameters are exactly the same as those in Example 1. Comparative Example 4 removed the antioxidant stabilizer, and the catalytic system retained only chelated organic lithium and alkaline ionic liquid, without adding phosphite antioxidant stabilizers. The remaining process parameters were exactly the same as in Example 1. Comparative Example 5 removed the micro-negative pressure oxygen control measures and used 0.02 MPa nitrogen positive pressure protection throughout the reaction process. The oxygen content in the reactor was about 200 ppm. The remaining process parameters were exactly the same as those in Example 1. Comparative Example 6 uses single activated carbon for decolorization. The decolorization process uses only equal mass of powdered activated carbon, without adding activated clay. The total amount of decolorizing agent remains unchanged, and the other process parameters are exactly the same as those in Example 1. Comparative Example 7 uses a single solvent for recrystallization. The recrystallization process uses only anhydrous ethanol as the solvent, without adding ethyl acetate or deionized water. The total amount of solvent used is the same as in Example 1, and the other process parameters are exactly the same as in Example 1. Comparative Example 8 uses direct rapid cooling crystallization. The three-stage gradient cooling process and seed crystal addition are eliminated in the crystallization process. The homogeneous solution at 72°C is directly cooled to 12°C at a rate of 10°C / h and then filtered at a constant temperature. The remaining process parameters are exactly the same as those in Example 1.

[0049] (2) Performance testing The samples obtained in Example 1 and Comparative Examples 1-6 were tested in parallel under the same environmental conditions. The test items and execution standards are as follows.

[0050] Liquid chromatography purity: GB / T 25277-2010 "Plastic Antioxidant 1010", high performance liquid chromatography (C18 reversed-phase column, methanol-water gradient elution, 276 nm detection wavelength) was used for quantification. The content of the tetraester main peak (the proportion of the target product as a single component) and the total effective components (the combined proportion of the triester and tetraester, both of which are hindered phenolic components with antioxidant activity) were calculated separately. Gardner color code: GB / T 22295-2008 "Determination of color of transparent liquids (Gardner colorimetric method)", prepare a 100 g / L sample toluene solution and visually compare it with the standard color scale for determination; APHA (Platinum-Cobalt) color code: GB / T 3141-1982 "Determination of color of liquid chemical products (Hazen units-platinum-cobalt color code)", prepare a 100 g / L sample toluene solution and compare it with the platinum-cobalt standard colorimetric solution for determination; Toluene solution transmittance: GB / T 25277-2010, prepare a 10 g / L sample toluene solution, and use pure toluene as a reference, and measure the transmittance at wavelengths of 425 nm and 500 nm respectively; The difference in yellowing index due to heat aging (ΔYI): GB / T 7141-2008 "Test Method for Heat Aging of Plastics" and GB / T2409-2008 "Test Method for Yellowing Index of Plastics" were used. Antioxidant was added at 0.2% and mixed with blank homopolymer PP base resin. After twin-screw extrusion, standard test pieces with a thickness of 1 mm were prepared by injection molding. The test pieces were placed in a 180℃ forced-air aging chamber for 2 h of heat aging. The yellowing index of the test pieces before and after aging was measured and the difference ΔYI was calculated. Product yield: Based on the amount of pentaerythritol fed, the mass yield of the product after separation and drying is calculated according to the theoretical yield.

[0051] (3) Test results The performance test results of each group of samples are shown in Table 1 and Figure 4-6 As shown.

[0052] Table 1 shows a comparison of the performance test results between Example 1 and the comparative example.

[0053] (4) Results Analysis 1. Excellent overall performance The complete process of this invention (Example 1) achieves a tetraester main peak of 97.8%, a total effective component of 99.5%, an APHA color number of 17, a transmittance of 98.2% at 425 nm, and a thermal aging ΔYI of 0.76 for the PP sample. All indicators are significantly superior to domestic superior products, reaching the level of imported high-end products overall, with some indicators approaching the level of imported high-purity products. Furthermore, it has been detected in Wuxi and can meet the application requirements of high-transparency polyolefins, optical films, food contact materials, and other high-end scenarios, possessing import substitution potential.

[0054] 2. Each innovation contributes independently and quantifiable to the yellowing resistance. Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that: The single-component lithium methanol catalytic reaction has a high reaction depth, but the excessive alkalinity leads to numerous side reactions in phenol oxidation, resulting in significant deterioration of the product's color and resistance to yellowing; the single-component alkaline ionic liquid produces a good color but lacks sufficient catalytic activity, with a tetraester content of only 95.8%, failing to meet the requirements of high-end products. The system of this invention achieves both a tetraester content of 97.8% and an APHA color of 17, both significantly superior to the two single-component catalysts, demonstrating a clear effect.

[0055] After removing the antioxidant stabilizer, the transmittance at 425 nm decreased by 0.9%, and ΔYI increased by 0.36, verifying the key role of in-situ free radical quenching in color control during the high-temperature reaction stage; the color deterioration was greater after removing the micro-negative pressure oxygen control, proving that oxygen partial pressure is the core influencing factor of phenolic hydroxyl oxidation; single solvent recrystallization directly determines the level of impurity residue in the final product.

[0056] Comparing Example 1 and Comparative Example 6, it can be seen that when only activated carbon is used for decolorization, the transmittance at 425 nm decreases by 0.8%, and ΔYI increases by 0.39. Activated carbon can only remove large colored polymers through physical adsorption, and its removal of small polar quinone impurities is limited. Activated clay, on the other hand, can catalyze the destruction of quinone conjugated structures through acidic sites on its surface, converting colored quinones into colorless phenols, while simultaneously adsorbing polar impurities.

[0057] Comparing Example 1 and Comparative Example 8, it can be seen that after removing the extraction cooling and seeding, the content of the tetraester main peak decreased by 0.8%, and ΔYI increased by 0.52. Rapid cooling will cause the supersaturation of the system to rise sharply. The explosive nucleation and rapid growth cause a large amount of mother liquor and impurities to be wrapped inside the crystal lattice. The three-stage gradient temperature control can precisely control the supersaturation. Combined with the α seed to induce the generation of regular and dense seed crystals, the crystal lattice wrapping of impurities is greatly reduced, which is an important guarantee for the high purity and low color number of the final product.

[0058] 3. The entire supply chain management demonstrates significant synergistic and efficiency-enhancing effects. As can be seen from the data comparison, a single technological improvement can only bring about a local performance improvement. When the two technologies are combined in this invention, the performance improvement is much greater than the simple sum of the individual improvements. Compared with the traditional benchmark process (Comparative Example 1), the 425nm transmittance of the complete process is increased from 94.7% to 98.2%, the ΔYI of the PP sample is reduced from 1.90 to 0.76, and the APHA color number is reduced from 52 to 17. Such a magnitude of improvement cannot be achieved through a single process optimization, which fully demonstrates the synergistic effect of the whole-chain control of this invention.

Claims

1. A preparation process for a high-resistance yellowing antioxidant 1010, characterized in that, Includes the following steps: S1 transesterification reaction: methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (abbreviated as β-ester) and pentaerythritolamine in a molar ratio of (4-4.5):1 are added to a reaction vessel equipped with a distillation column. A composite catalytic system is added, and high-purity nitrogen is introduced to replace the air in the vessel. A slight negative pressure is turned on and a small amount of nitrogen is continuously introduced. The transesterification reaction is carried out by gradient heating until no methanol is distilled off. S2 Crude Product Neutralization and Decolorization: After the reaction is complete, the temperature is lowered, and an organic acid is added to neutralize the catalyst until the system pH is 5.5-7.

0. The temperature is gradually increased and the vacuum degree is increased. Excess β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate raw material and low-boiling substances are removed by thin-film evaporation. The molten crude product after raw material removal is pumped into a dissolving vessel, and 3-5 times the mass of alcohol solvent is added. The mixture is stirred and heated to 70-90℃ to completely dissolve the crude product. A composite decolorizing agent is added, and the mixture is kept warm and stirred for 30-60 min to decolorize. While still hot, the decolorizing agent and insoluble matter are removed by fine filtration. S3 Gradient Cooling Recrystallization: The decolorized filtrate is transferred to a jacketed temperature-controlled crystallization vessel, and acetate esters and deionized water are added to prepare an alcohol-ester-water ternary complex solvent system. Stirring is started, and the temperature is controlled at 70-75℃ to form a homogeneous transparent solution. Then, the solution is crystallized by gradient cooling in a three-stage program. After crystallization, the solution is centrifuged and filtered. The filter cake is washed with cold solvent and then vacuum dried to obtain the α-crystalline antioxidant 1010 product.

2. The preparation process according to claim 1, characterized in that, The composite catalytic system consists of a main catalyst, a co-catalyst, and a trace amount of antioxidant stabilizer. The main catalyst is a chelated organic lithium catalyst, which is composed of lithium isooctanoate and lithium acetylacetonate in a mass ratio of (1.5-3):

1. The co-catalyst is an imidazole alkoxy ionic liquid, selected from one or more of 1-butyl-3-methylimidazolium methanol, 1-ethyl-3-methylimidazolium tert-butanol, and 1-butyl-3-methylimidazolium isooctanoate. The antioxidant stabilizer is a phosphite compound, selected from one or more of triphenyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, and pentaerythritol diphosphite (2,4-di-tert-butylphenyl) phosphite.

3. The preparation process according to claim 2, characterized in that, In the composite catalytic system, the mass ratio of the main catalyst, the co-catalyst, and the trace antioxidant stabilizer is 100:(20-35):(1.5-4), and the amount used is 0.35-0.8% of the mass of methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Before feeding, chelated organic lithium and alkaline ionic liquid are premixed and stirred at 50-70℃ for 20-40 min to form a homogeneous catalytic liquid before feeding.

4. The preparation process according to claim 1, characterized in that, During the reaction in S1, the oxygen content in the reactor is ≤50ppm, and the absolute pressure of the system is controlled at 80-95 kPa.

5. The preparation process according to claim 1, characterized in that, The reaction gradient temperature control in S1 is as follows: The first stage involves a reaction at 130-145℃ for 2-3 hours. The second stage involves a reaction at 160-170℃ for 3-4 hours. In the third stage, the temperature is raised to 180-188℃ and the vacuum level and absolute pressure are gradually increased by 1-5 kPa. The reaction continues for 1.5-2.5 hours until no methanol distillation occurs.

6. The preparation process according to claim 1, characterized in that, The composite decolorizing agent is composed of powdered activated carbon and activated clay in a mass ratio of 1:(1-3), and the total amount used is 0.5-3.0% of the crude mass.

7. The preparation process according to claim 1, characterized in that, In the alcohol-ester-water ternary compound solvent system, the mass ratio of alcohol, ester and water is (65-80):(15-25):(3-10), the alcohol is selected from one or more of methanol, ethanol and isopropanol, and the acetate is selected from one or two of methyl acetate and ethyl acetate.

8. The preparation process according to claim 1, characterized in that, The three-stage gradient cooling crystallization process in S3 is as follows: First stage: Slowly cool down to 55-58℃ at a rate of 2-3℃ / h, add α-crystal seed crystals, and maintain constant temperature for 1-2 hours to induce the formation of uniform crystal nuclei; The second stage involves cooling the temperature to 35-40℃ at a rate of 3-5℃ / h and holding it at that temperature for 1-1.5 hours to promote crystal growth. Third stage: Cool down to 10-15℃ at a rate of 5-8℃ / h, and hold at the temperature for 2-3 hours to allow crystallization to complete.

9. The preparation process according to claim 8, characterized in that, The amount of α-type seed crystals added in S3 accounts for 0.3-0.8% of the solute mass.

10. The preparation process according to claim 1, characterized in that, The organic acid in S2 is selected from glacial acetic acid, citric acid, and oxalic acid.

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