Antioxidant and polymerization inhibitor for oil refining apparatus and method for preparing the same

Abstract

The application discloses an antioxidant and polymerization inhibitor for oil refining devices and a preparation method thereof. The antioxidant and polymerization inhibitor comprises an isocyanurate-based star-shaped antioxidant and polymerization inhibitor. The isocyanurate-based star-shaped antioxidant takes an isocyanurate ring as a core skeleton and radiates three functionalized branches outward, one of which comprises a substituted phenol group and a thioether bond, and the other two of which comprise thioether bonds and long-chain alkyl groups. The preparation method of the application can realize the construction of the target molecule under mild conditions, the raw materials are easy to obtain, the operation is simple, the reaction selectivity is high, the post-treatment is convenient, and the method is suitable for industrialized batch production.

Description

Technical Field

[0001] This invention belongs to the field of petroleum refining technology, specifically relating to an antioxidant and polymerization inhibitor for oil refining equipment and its preparation method. Background Technology

[0002] In the petroleum refining industry, catalytic cracking units are the core processing units for converting heavy oil into lighter oil. The overhead condenser cooling system of the catalytic cracking fractionator faces harsh operating conditions of high temperature, oxygen content, and metal catalysis. Under these conditions, unsaturated hydrocarbons and sulfides in the overhead circulating oil readily undergo free radical chain oxidation reactions, generating large molecular polymers such as gums and asphaltenes. These polymers gradually deposit on the inner wall of the condenser tube bundle, forming a dense coking layer. This leads to decreased heat transfer efficiency, increased system pressure drop, and in severe cases, unplanned shutdowns for coking removal, significantly impacting the long-term stable operation and economic benefits of the unit.

[0003] Currently, most commonly used antioxidant polymerization inhibitors in industry are single-function additives, relying either solely on hindered phenolic structures to provide the main antioxidant effect or solely on sulfur-containing compounds to decompose hydrogen peroxide. These additives face the following technical bottlenecks: First, their single function makes it difficult to simultaneously address multiple antioxidant needs such as free radical termination and hydrogen peroxide decomposition; second, their insufficient molecular thermal stability makes them prone to decomposition or volatilization in high-temperature oil and gas environments, resulting in a short effective period; third, their poor oil solubility and dispersibility make it difficult to form a stable homogeneous system in petroleum fractions, limiting the full realization of their antioxidant efficacy; fourth, traditional linear additives exhibit weak intermolecular synergistic effects and low effective functional group density per unit mass, making it difficult to achieve efficient polymerization inhibition. Therefore, developing a novel antioxidant polymerization inhibitor with multi-functional group synergistic effects, excellent thermal stability, and oil solubility is of significant practical importance for extending the operating cycle of catalytic cracking units, reducing coking frequency, and improving refinery economic efficiency. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides an antioxidant and polymerization inhibitor for oil refining equipment and its preparation method.

[0005] The technical solution to achieve the objective of this invention is as follows: An antioxidant polymerization inhibitor for oil refining equipment, comprising an isocyanurate-based star-shaped antioxidant polymerization inhibitor; the isocyanurate-based star-shaped antioxidant polymerization inhibitor has an isocyanurate ring as its core skeleton, with three functionalized branches radiating outward, one of which includes a substituted phenolic group and a thioether bond, and the other two branches include a thioether bond and a long-chain alkyl group, wherein the substituted phenolic group, the thioether bond, and the long-chain alkyl group are connected to the nitrogen atom on the isocyanurate ring through a 2-hydroxy-1,3-propylidene spacer chain.

[0006] The method for preparing the antioxidant polymerization inhibitor for the oil refining unit includes the following steps: S1. Preparation of imine-type thiol intermediate: Under inert gas protection, 2-aminoethanethiol and substituted hydroxybenzaldehyde were dissolved in a dry solvent, a dehydrating agent was added, and the reaction was stirred at room temperature to obtain an imine-type thiol intermediate; S2. Preparation of monosubstituted isocyanurate intermediate: Under inert gas protection, the imine thiol intermediate obtained in step S1 was dissolved in a dry solvent, and triglycidyl isocyanurate and a tertiary amine catalyst were added. The mixture was heated and stirred to react. After the reaction was completed, the monosubstituted isocyanurate intermediate was obtained. S3. Preparation of imine reduction intermediate: The monosubstituted isocyanurate intermediate obtained in step S2 was dissolved in a solvent, cooled in an ice-water bath, and a reducing agent was added in batches. The reaction was stirred at low temperature, and the reaction was quenched by slowly adding a saturated inorganic salt solution under temperature control in an ice-water bath. The pH was adjusted to near neutral to obtain the reduced amination intermediate. S4. Preparation of isocyanurate-based star-shaped antioxidant polymerization inhibitor: Under inert gas protection, the reduced amination intermediate obtained in step S3 is dissolved in a dry solvent, a long-chain alkyl thiol and a tertiary amine catalyst are added, the mixture is heated and stirred to react, and after the reaction is completed, the antioxidant polymerization inhibitor for oil refining units is obtained by purification.

[0007] Preferably, the molar ratio of 2-aminoethanethiol to substituted hydroxybenzaldehyde in step S1 is 1:(1.0~1.5).

[0008] Preferably, the substituted hydroxybenzaldehyde in step S1 is selected from one or more of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 4-hydroxy-3,5-bis(isopropyl)benzaldehyde, and 3,5-dimethyl-4-hydroxybenzaldehyde; the dehydrating agent is anhydrous magnesium sulfate or anhydrous sodium sulfate, and the amount used is 10-30% of the mass of the substituted hydroxybenzaldehyde.

[0009] Preferably, the molar ratio of the imine thiol intermediate to triglycidyl isocyanurate in step S2 is 1:(1.0~1.2); the tertiary amine catalyst is selected from one or more of triethylamine, N,N-diisopropylethylamine, tripropylamine, tributylamine, N-methylmorpholine, 4-methylmorpholine, and N,N-dimethylbenzylamine, and is used in an amount of 15~25% of the molar amount of the imine thiol intermediate.

[0010] In step S2, when the imine-type thiol intermediate reacts with triglycidyl isocyanurate, its nucleophilicity decreases due to the lone pair electrons of the imine nitrogen participating in the C=N double bond conjugation, and it does not undergo a ring-opening reaction with the epoxy group under weakly basic conditions. However, the thiol group, after deprotonation by triethylamine, forms a highly nucleophilic thiolate anion, which selectively performs nucleophilic ring-opening on one of the epoxy groups of triglycidyl isocyanurate, generating a monosubstituted thioether product. This selectivity stems from the difference in nucleophilicity between the thiolate anion and the imine nitrogen, and the monosubstituted selectivity was confirmed by thin-layer chromatography.

[0011] Preferably, the reducing agent in step S3 is sodium borohydride, and the amount used is 1.0 to 1.5 times the molar amount of the monosubstituted isocyanurate intermediate.

[0012] In step S3, instead of in-situ reduction and alkylation of amines and aldehydes, selective reduction of the pre-formed Schiff base, i.e., the C=N double bond, with sodium borohydride is performed to obtain a benzylamine thioether intermediate. This operation is carried out in a weakly acidic methanol system at 0°C to avoid contact between the reducing agent and the epoxy group.

[0013] Preferably, the molar ratio of the reductive amination intermediate to the long-chain alkyl thiol in step S4 is 1:(2.0~3.0).

[0014] Preferably, the long-chain alkyl thiol in step S4 is selected from one or more of 1-hexanethiol, 1-octanethiol, 1-decanethiol, 1-dodecylthiol, 1-tetradecylthiol, 1-hexadecylthiol, and 1-octadecylthiol.

[0015] Preferably, the tertiary amine catalyst in step S4 is selected from one or more of triethylamine, N,N-diisopropylethylamine, tripropylamine, tributylamine, N-methylmorpholine, 4-methylmorpholine, and N,N-dimethylbenzylamine, and is used in an amount of 15-25% of the molar amount of the reducing amination intermediate.

[0016] In step S4, although the intermediate contains a secondary amine group, under the catalysis of a tertiary amine, the thiol is more readily deprotonated to form a highly nucleophilic thiolate anion. The ring-opening reaction rate of this anion with the epoxide is much higher than the direct nucleophilic attack of the neutral secondary amine. By controlling the reaction temperature and the dropping rate of the thiol, the side reactions involving the secondary amine can be effectively suppressed, and the target product can be obtained with high selectivity.

[0017] Another object of the present invention is to protect the application of the antioxidant polymerization inhibitor for oil refining equipment or the antioxidant polymerization inhibitor for oil refining equipment prepared by the method of preparing the antioxidant polymerization inhibitor for oil refining equipment as an antioxidant polymerization inhibitor in the field of petroleum refining.

[0018] Specifically, the effective addition amount of the antioxidant polymerization inhibitor in the feedstock oil is 10~500 ppm, preferably 50~300 ppm. The isocyanurate-based star-shaped antioxidant polymerization inhibitor provided by this invention integrates multiple antioxidant mechanisms. The mechanism of action of this structure can be explained from the following three aspects: First, the main antioxidant mechanism. The hindered phenolic groups at the ends of the molecular arms act as hydrogen donors, rapidly capturing alkyl and alkoxy radicals generated during oil oxidation and converting them into stable phenoxy radicals, thereby interrupting the propagation of free radical chain reactions. Due to the spatial support of the isocyanate ring, the hindered phenolic groups are radially distributed at the molecular ends, forming functional zones with thioether-assisted antioxidant groups and long-chain alkyl oil-soluble groups, increasing the probability of collision with free radicals and improving antioxidant efficiency. The phenoxy radicals themselves can be stabilized through resonance without initiating new chain reactions, ensuring the sustainability of the antioxidant process.

[0019] Secondly, it assists in the antioxidant mechanism. The thioether groups in the molecular branches have the function of decomposing hydroperoxides, which can reduce the hydroperoxides generated during oil oxidation into stable alcohol compounds, preventing them from further decomposing and generating new free radical initiators, thereby slowing down the spread of the oxidation reaction from the source. The introduction of the thioether groups and the hindered phenols form a synergistic antioxidant system, with the phenolic structure responsible for terminating the free radicals that have already been generated, and the thioether structure responsible for eliminating potential free radical precursors. The two functions complement each other, significantly improving the overall antioxidant efficacy.

[0020] Third, the oil-soluble dispersion and thermal stability mechanism. The isocyanurate ring, as the molecular core, possesses excellent thermal stability and chemical inertness, maintaining the integrity of the molecular skeleton under high-temperature conditions and preventing functional failure due to core structural decomposition. The introduction of long-chain alkyl branches endows the molecule with suitable hydrophobic and oleophilic properties, enabling it to disperse uniformly in petroleum fractions, preventing precipitation or sedimentation, and ensuring the continuous and stable function of the antioxidant and polymerization inhibitor in oil products. Compared to traditional linear structures, the star-shaped molecular configuration has a greater steric hindrance effect, effectively preventing the entanglement and aggregation of polymer molecules, thereby achieving polymerization inhibition at the molecular level.

[0021] Beneficial effects

[0022] Compared with existing technologies, the isocyanurate-based star-shaped antioxidant polymerization inhibitor and its preparation method provided by this invention have the following technical advantages: I. Synergistic Effect of Multiple Functional Groups. This invention, through molecular design, integrates the hindered phenolic main antioxidant group, the thioether auxiliary antioxidant group, and the long-chain alkyl oil-soluble group into the same star-shaped molecular structure, achieving an organic unity of free radical capture, hydroperoxide decomposition, and oil-soluble dispersion functions. There is no mutual interference between the functional groups; instead, their rational spatial arrangement produces a synergistic effect, resulting in significantly superior antioxidant and polymerization-inhibiting performance compared to single-functional additives and simple physical compound systems.

[0023] II. Excellent thermal stability. The isocyanurate ring, as the core molecular framework, has outstanding heat resistance and chemical stability, enabling the antioxidant polymerization inhibitor of this invention to maintain structural integrity and effective function for a long time under the high-temperature conditions of catalytic cracking units, overcoming the technical defects of traditional additives that result in short-term action due to thermal decomposition or volatilization loss.

[0024] III. Excellent oil solubility and dispersion stability. The introduction of long-chain alkyl thiols imparts a suitable lipophilic-hydrophobic balance to the molecule, giving it excellent solubility in petroleum fractions such as n-heptane and catalytic cracked diesel, with a low cloud point. No stratification or precipitation occurs under long-term static conditions at high temperatures, ensuring uniform dispersion and sustained effectiveness of the antioxidant polymerization inhibitor in practical industrial applications.

[0025] IV. Excellent Industrial Application Results. Adding the antioxidant and polymerization inhibitor of this invention to the top circulation system of a catalytic cracking fractionation tower effectively inhibits the coking rate of the top condenser, slows down the increase in system pressure drop, and extends the safe operating cycle of the unit. Simultaneously, the gum content and acid value in the circulating oil are significantly improved, helping to maintain the processing quality of the oil and reducing the burden on subsequent processing steps.

[0026] V. Simple and easy preparation process. The preparation method of this invention adopts a stepwise coupling strategy, and the target molecule can be constructed under mild conditions through classical organic reactions such as imine condensation, epoxide ring opening, reductive amination, and thiol addition. The raw materials are readily available, the operation is simple, the reaction selectivity is high, and the post-processing is convenient, making it suitable for industrial mass production. Attached Figure Description

[0027] Figure 1 The synthetic route for isocyanurate-based star-shaped antioxidant polymerization inhibitor 1 is described.

[0028] Figure 2 The 1H NMR spectrum of isocyanurate-based star-shaped antioxidant polymerization inhibitor 1. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0031] The raw materials and equipment used in the examples and comparative examples are described below, where eq represents molar equivalent: Example Example 1

[0032] Isocyanurate-based star-shaped antioxidant polymerization inhibitor 1: Self-made, preparation method as follows: Under nitrogen protection, 1.0 eq of 2-aminoethanethiol and 1.0 eq of 3,5-di-tert-butyl-4-hydroxybenzaldehyde were dissolved in anhydrous methanol. Anhydrous magnesium sulfate (15% by weight of 3,5-di-tert-butyl-4-hydroxybenzaldehyde) was added as a dehydrating agent, and the mixture was stirred at room temperature for 5 h. The desiccant was removed by filtration, and the solvent was removed by rotary evaporation under reduced pressure at 25 °C and a vacuum of ≥-0.09 MPa to obtain an imine-type thiol intermediate, which was directly used in the next step. Under nitrogen protection, 1.0 eq of the above imine-type thiol intermediate was dissolved in dry toluene, and 1.05 eq of triglycidyl isocyanurate and 0.2 eq of triethylamine were added. The mixture was heated to 70 °C and stirred for 10 h. Thin-layer chromatography was used to monitor the disappearance of the imine-type thiol intermediate spots. After the reaction, the mixture was diluted with n-hexane, washed with saturated brine until neutral, dried with anhydrous sodium sulfate, and then dried under reduced pressure at 25 °C and a vacuum of ≥-0.09 MPa. The solvent was removed by rotary evaporation under reduced pressure at MPa. The residue was purified by neutral alumina column chromatography using a gradient mixture of petroleum ether and ethyl acetate (volume ratio 10-5:1) as eluent. The main fraction was collected and the solvent was removed by rotary evaporation under reduced pressure at 25°C and a vacuum of ≥-0.09 MPa to obtain a monosubstituted isocyanurate intermediate, which was directly used in the next step. 1.0 eq of the above monosubstituted isocyanurate intermediate was dissolved in anhydrous methanol and cooled to 0°C in an ice-water bath. 1.2 eq of sodium borohydride was added in portions. After the addition was complete, the mixture was stirred at 0-5°C for 3 h. Saturated ammonium chloride solution was slowly added dropwise under temperature control in an ice-water bath to quench the reaction until no bubbles were generated. The pH was adjusted to 7.5 with 0.5 M hydrochloric acid solution. The mixture was extracted with ethyl acetate, and the organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation under reduced pressure at 25-30°C and a vacuum of ≥-0.09 MPa to obtain a reduced amination intermediate, which was directly used in the next step. Under nitrogen protection, 1.0 eq of the above monosubstituted isocyanurate intermediate was dissolved in anhydrous methanol and cooled to 0°C in an ice-water bath. The above-mentioned reducing amination intermediate was dissolved in dry toluene, and 2.1 eq of 1-dodecyl mercaptan and 0.2 eq of triethylamine were slowly added dropwise. The mixture was heated to 80 °C and stirred for 10 h. The reaction endpoint was monitored by thin-layer chromatography. After the reaction was completed, the mixture was diluted with n-hexane, filtered to remove trace amounts of insoluble matter, and the filtrate was purified by silica gel column chromatography. The filtrate was eluted with a gradient mixed solvent of petroleum ether and ethyl acetate in a volume ratio of (10~4):1 and containing 0.5% triethylamine. The main fraction was collected, and the solvent was removed by rotary evaporation under reduced pressure at 45 °C and a vacuum degree ≥ -0.09 MPa. The residual mercaptan was then removed under high vacuum at 60 °C and an absolute pressure ≤ 100 Pa for 2 h to obtain isocyanurate-based star-shaped antioxidant polymerization inhibitor 1, with the structure shown in the following formula: .

[0033] Example 2

[0034] Isocyanurate-based star-shaped antioxidant polymerization inhibitor 2: Prepared in-house, the method differs from that of isocyanurate-based star-shaped antioxidant polymerization inhibitor 1 in that 3,5-di-tert-butyl-4-hydroxybenzaldehyde is replaced with 4-hydroxy-3,5-bis(isopropyl)benzaldehyde, while all other conditions remain unchanged. The resulting isocyanurate-based star-shaped antioxidant polymerization inhibitor 2 has the structure shown below: .

[0035] Example 3

[0036] Isocyanurate-based star-shaped antioxidant polymerization inhibitor 3: Prepared in-house, the method differs from that of isocyanurate-based star-shaped antioxidant polymerization inhibitor 1 in that 3,5-di-tert-butyl-4-hydroxybenzaldehyde is replaced with 3,5-dimethyl-4-hydroxybenzaldehyde, while all other conditions remain unchanged. The resulting isocyanurate-based star-shaped antioxidant polymerization inhibitor 3 has the following structure: .

[0037] Example 4

[0038] Isocyanurate-based star-shaped antioxidant polymerization inhibitor 4: Prepared in-house, the method differs from that of isocyanurate-based star-shaped antioxidant polymerization inhibitor 1 in that 1-dodecyl mercaptan is replaced with 1-hexanethiol, while all other conditions remain unchanged. The resulting isocyanurate-based star-shaped antioxidant polymerization inhibitor 4 has the structure shown below: .

[0039] Comparative Example 1 Glycidyl ether-based star-shaped antioxidant polymerization inhibitor 5: self-made. The preparation method is the same as that of isocyanurate-based star-shaped antioxidant polymerization inhibitor 1, except that triglycidyl isocyanurate is replaced with trimethylolpropane triglycidyl ether, while other conditions remain unchanged, thus obtaining glycidyl ether-based star-shaped antioxidant polymerization inhibitor 5.

[0040] Comparative Example 2 Antioxidant 3114: 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, commercially available.

[0041] blank sample No antioxidants or polymerization inhibitors are added.

[0042] The following are the test methods for performance parameters involved in this invention: 1. Nuclear magnetic resonance hydrogen spectrum test: Characterization was performed using a nuclear magnetic resonance spectrometer (Bruker AM-600, Avance 600).

[0043] 2. Industrial Testing of Antioxidant and Polymerization Inhibition Performance of FCC Fractionation Tower Top Condensation System: The top circulation system of a catalytic cracking unit in an oil refinery was selected as the test object. The unit has a designed capacity of 1.2 million tons per year. The test period was 30 days. The first 15 days were a blank period under normal production conditions without the addition of antioxidant and polymerization inhibitor. Starting from the 16th day, the isocyanurate-based star-shaped antioxidant and polymerization inhibitor prepared in the example was continuously injected into the circulating oil of the fractionation tower using a metering pump. The addition amount was 100 to 200 ppm. The following 15 days were the addition period. The pressure difference between the inlet and outlet of the fractionation tower top condenser was recorded on the start and end dates of the blank period, and the pressure difference at the same location on the start and end dates of the addition period. The average daily increase in pressure drop was calculated using the formula: the average daily increase in pressure drop equals the pressure drop on the end date minus the pressure drop on the start date, divided by the number of days. When the pressure differential of the condensation system at the top of the fractionation tower reaches the design limit of 0.35 MPa, the tower must be shut down for decoking. The operating time is then calculated based on this, using the formula: operating time = 0.35 MPa divided by the average daily increase in pressure drop. Simultaneously, circulating oil samples are collected from the top of the tower on the 15th day of the blank period and the 15th day of the additive period. The actual gum content and acid value are determined according to standard methods SY / T 7550-2024 and GB / T 264-1983 as auxiliary evaluation indicators. Note: The operating time calculated during the blank period reflects the theoretical lifespan under no-additive conditions; the operating time calculated during the additive period is calculated using the formula 0.35 MPa / average daily increase during the additive period, reflecting the theoretical lifespan assuming operation under the additive conditions from the beginning. This is only used to compare the inhibition trends of different samples and does not constitute an accurate prediction of the actual shutdown cycle. In actual operation, the pressure drop increase may be non-linear and accelerated, requiring comprehensive evaluation in conjunction with historical data of the unit.

[0044] 3. High-Temperature Oxidative Coking Simulation Test: A 316L stainless steel high-pressure reactor was used, with a built-in rack suspending pre-weighed 316L stainless steel plates. 300g of catalytic cracked diesel oil was added to the reactor as model oil, along with 200ppm of the antioxidants from the examples and comparative examples. After sealing, a nitrogen mixture containing 1.0% oxygen by volume was introduced at 0.1 L / min, the temperature was raised to 300℃, the stirring speed was 200 rpm, and the reaction was maintained at this temperature for 6 h. After the reaction, the plates were removed, ultrasonically cleaned with acetone for 30 min, and dried at 105℃ to constant weight. The coking weight gain was measured, and the coking inhibition rate was calculated using the formula: coking inhibition rate equals the coking amount of the blank sample minus the coking amount of the additive sample, divided by the coking amount of the blank sample, multiplied by 100%. Simultaneously, the actual gum content and the oxidation induction period of the rotating oxygen bomb were measured in the model oil after the reaction to quantify the antioxidant and polymerization inhibition performance.

[0045] 4. Rotating oxygen bomb oxidation stability test: According to the standard method ASTM D2112-15, the antioxidants of the examples and comparative examples were added to the catalytic cracking diesel oil at 100 ppm, 200 ppm and 500 ppm respectively, and the oxidation induction period was determined at 150°C and oxygen pressure of 0.62 MPa.

[0046] 5. Oil solubility and dispersion stability test: The product of this invention was gradually added to n-heptane or catalytic cracked diesel oil at 1.0%, 3.0%, and 5.0% by mass. The dissolution was observed by stirring at 25°C, and the maximum solubility and cloud point were recorded. At the same time, a diesel oil solution containing 500 ppm of the product of this invention was prepared and allowed to stand at 60°C for 72 h. The presence of stratification or precipitation was observed to verify its dispersion stability in oil products.

[0047] Table 1. Results of high-temperature oxidative coking simulation test

[0048] Table 2. Industrial Test Results of Antioxidant and Antipolymerization Performance of FCC Fractionating Tower Top Condensation System

[0049] Table 3 Results of Oxidation Stability Tests for Rotating Oxygen Bombs

[0050] Table 4 Results of oil solubility and dispersion stability tests

[0051] The isocyanurate-based star-shaped antioxidant polymerization inhibitor prepared in Example 1 exhibited the best coking inhibition ability in high-temperature oxidative coking simulation tests, with the lowest coking amount among all tested samples and a significantly higher coking inhibition rate than other groups. This product also showed the longest oxidation induction period in the rotating oxygen bomb oxidation stability test, indicating its outstanding primary antioxidant efficacy. In industrial application tests, the addition of this antioxidant polymerization inhibitor significantly slowed the pressure drop growth rate of the fractionation tower top condenser system, resulting in a substantial extension of the operating cycle compared to the blank period, and effectively controlling the gum content and acid value in the circulating oil. This product exhibits good solubility in both n-heptane and catalytic cracking diesel, with a low cloud point, and shows no stratification or precipitation under high-temperature static conditions, demonstrating excellent oil solubility and dispersion stability. The superior performance can be attributed to the following structural features: First, 3,5-di-tert-butyl-4-hydroxyphenyl, as a classic hindered phenol structure, can provide highly efficient main antioxidant activity; second, the isocyanurate ring, as the molecular core, endows the molecule with excellent thermal stability and multi-arm synergistic effect; third, the introduction of dodecyl long-chain alkyl thiol not only provides hydroperoxide decomposition function, but also significantly improves the molecule's oil solubility and interfacial activity; fourth, the star-shaped molecular structure allows the functional groups to be rationally distributed in space, maximizing the synergistic effect of antioxidant and polymerization inhibition.

[0052] Example 2 replaced the tert-butyl group in the phenolic structure with isopropyl. The resulting product maintained high antioxidant activity, but its performance indicators were slightly lower than those of Example 1. In the high-temperature coking test, its coking inhibition rate remained high, but the amount of coking was slightly higher than in Example 1. The oxidation induction period in the rotating oxygen bomb test was also shortened. The pressure drop control effect and the degree of improvement in circulating oil quality in industrial tests were between those of Example 1 and Example 3. Regarding oil solubility, because the hydrophobicity of isopropyl is weaker than that of tert-butyl, the solubility of this product in n-heptane and diesel oil was slightly lower than that of Example 1, and the cloud point was correspondingly higher, but it still met the requirements of practical applications. The above differences are mainly due to the fact that the steric hindrance effect and electron-donating ability of isopropyl are both weaker than those of tert-butyl, resulting in a decrease in the antioxidant activity of the phenolic hydroxyl group and the oil solubility of the entire molecule.

[0053] Example 3 used 3,5-dimethyl-4-hydroxybenzaldehyde as the phenol source, further reducing steric hindrance, resulting in a significant decrease in the antioxidant properties of the obtained product. The coking amount in the high-temperature coking test was significantly higher than in Examples 1 and 2, with a corresponding decrease in coking inhibition rate. The oxidation induction period in the rotating oxygen bomb test was shortened even more significantly. In industrial applications, the product's inhibitory effect on pressure drop growth is limited, and the reduction in recycle oil gum content and acid value is less than in Examples 1 and 2. Regarding oil solubility, due to the weakest hydrophobicity of the methyl group, the solubility of this product in n-heptane further decreased, and the cloud point increased, but it still maintained an acceptable solubility level in diesel fuel. These results indicate that the sterically hindered group ortho-position to the phenolic hydroxyl group has a significant impact on antioxidant properties and oil solubility, and the protective effect of large sterically hindered groups such as the tert-butyl group is key to ensuring the efficient antioxidant activity of the hindered phenol.

[0054] In Example 4, the long-chain alkyl mercaptan was replaced with hexyl instead of dodecyl, resulting in a significant decrease in the product's oil solubility due to the shortened carbon chain length. In the high-temperature coking test, its coking inhibition rate was significantly lower than in Example 1, mainly because the short-chain alkyl group had insufficient solubility in the oil, preventing the antioxidant from being fully dispersed in the oil phase to exert its effect. The oxidation induction period in the rotating bomb oxidation test was also correspondingly shortened. In industrial tests, the product showed a weak inhibitory effect on system pressure drop. Oil solubility tests showed a significant decrease in the maximum solubility of the product in n-heptane, a positive cloud point, and a significant decrease in solubility in diesel fuel. Although only slight turbidity and incomplete stratification occurred in the high-temperature static test, this indicates that the short-chain alkyl mercaptan is detrimental to the stable dispersion of the product in oil. These results fully demonstrate that the introduction of long-chain alkyl groups is crucial for ensuring good oil solubility and dispersion stability of the star-shaped antioxidant in petroleum fractions.

[0055] Comparative Example 1 used a glycidyl ether group to replace the isocyanurate ring as the molecular core, and the properties of the resulting product were significantly inferior to those of Example 1. In the high-temperature coking test, the amount of coking was much higher than that of Example 1, and the coking inhibition rate was at a low level. The oxidation induction period in the rotating oxygen bomb test was significantly shortened. In industrial testing, the product had limited effect on suppressing pressure drop, and the estimated start-up cycle extension was the smallest. In the oil solubility test, the product had extremely low solubility in n-heptane, the highest cloud point, and showed trace bottom deposition under high-temperature static conditions, indicating poor dispersion stability. The above results show that the isocyanurate ring plays an irreplaceable role in maintaining the thermal stability, spatial configuration, and oil solubility of the star-shaped molecule, and the introduction of the glycidyl ether group disrupts the overall synergistic effect of the molecule.

[0056] Comparative Example 2 used commercially available antioxidant 3114 as a reference. While this product contains an isocyanurate core and a three-arm hindered phenol structure, it lacks a thioether group. In the high-temperature coking test, its coking amount was lower than Comparative Example 1 but higher than Example 1, and its coking inhibition rate was at a moderately low level, significantly lower than Example 1. In the rotating bomb oxidation test, its oxidation induction period was also lower than Example 1 but higher than Comparative Example 1. Its overall performance in industrial testing was better than Comparative Example 1 but worse than each example. Regarding oil solubility, because antioxidant 3114 lacks long-chain alkyl thioether groups, its solubility in n-heptane is lower than in Example 1, and its cloud point is higher. This comparative example fully demonstrates that the introduction of thioether groups plays an important role in decomposing hydrogen peroxide, inhibiting free radical chain reactions, and improving oil solubility. At the same time, the lack of long-chain alkyl groups also leads to insufficient oil solubility, affecting its antioxidant efficacy. Both demonstrate that thioether bonds and long-chain alkyl groups are key structural elements for achieving a synergistic effect of primary and secondary antioxidants and good oil solubility.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An antioxidant polymerization inhibitor for oil refining equipment, characterized in that, The antioxidant polymerization inhibitor includes an isocyanurate-based star-shaped antioxidant polymerization inhibitor; the isocyanurate-based star-shaped antioxidant polymerization inhibitor has an isocyanurate ring as the core skeleton, with three functionalized branches radiating outward, one of which includes a substituted phenolic group and a thioether bond, and the other two branches include a thioether bond and a long-chain alkyl group. The substituted phenolic group, the thioether bond, and the long-chain alkyl group are connected to the nitrogen atom on the isocyanurate ring through a 2-hydroxy-1,3-propylidene spacer chain.

2. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 1, characterized in that, Includes the following steps: S1. Preparation of imine-type thiol intermediate: Under inert gas protection, 2-aminoethanethiol and substituted hydroxybenzaldehyde were dissolved in a dry solvent, a dehydrating agent was added, and the reaction was stirred at room temperature to obtain an imine-type thiol intermediate; S2. Preparation of monosubstituted isocyanurate intermediate: Under inert gas protection, the imine thiol intermediate obtained in step S1 was dissolved in a dry solvent, and triglycidyl isocyanurate and a tertiary amine catalyst were added. The mixture was heated and stirred to react. After the reaction was completed, the monosubstituted isocyanurate intermediate was obtained. S3. Preparation of imine reduction intermediate: The monosubstituted isocyanurate intermediate obtained in step S2 was dissolved in a solvent, cooled in an ice-water bath, and a reducing agent was added in batches. The reaction was stirred at low temperature, and the reaction was quenched by slowly adding a saturated inorganic salt solution under temperature control in an ice-water bath. The pH was adjusted to near neutral to obtain the reduced amination intermediate. S4. Preparation of isocyanurate-based star-shaped antioxidant polymerization inhibitor: Under inert gas protection, the reduced amination intermediate obtained in step S3 is dissolved in a dry solvent, a long-chain alkyl thiol and a tertiary amine catalyst are added, the mixture is heated and stirred to react, and after the reaction is completed, the antioxidant polymerization inhibitor for oil refining units is obtained by purification.

3. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The molar ratio of 2-aminoethanethiol to substituted hydroxybenzaldehyde in step S1 is 1:(1.0~1.5).

4. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The substituted hydroxybenzaldehyde in step S1 is selected from one or more of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 4-hydroxy-3,5-bis(isopropyl)benzaldehyde, and 3,5-dimethyl-4-hydroxybenzaldehyde; the dehydrating agent is anhydrous magnesium sulfate or anhydrous sodium sulfate, and the amount used is 10-30% of the mass of the substituted hydroxybenzaldehyde.

5. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, In step S2, the molar ratio of the imine-type thiol intermediate to triglycidyl isocyanurate is 1:(1.0~1.2); the tertiary amine catalyst is selected from one or more of triethylamine, N,N-diisopropylethylamine, tripropylamine, tributylamine, N-methylmorpholine, 4-methylmorpholine, and N,N-dimethylbenzylamine, and the amount used is 15~25% of the molar amount of the imine-type thiol intermediate.

6. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The reducing agent in step S3 is sodium borohydride, and the amount used is 1.0 to 1.5 times the molar amount of the monosubstituted isocyanurate intermediate.

7. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The molar ratio of the reductive amination intermediate to the long-chain alkyl thiol in step S4 is 1:(2.0~3.0).

8. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The long-chain alkyl thiols mentioned in step S4 are selected from one or more of 1-hexanethiol, 1-octanethiol, 1-decanethiol, 1-dodecylthiol, 1-tetradecylthiol, 1-hexadecylthiol, and 1-octadecylthiol.

9. The method for preparing the antioxidant polymerization inhibitor for oil refining units as described in claim 2, characterized in that, The tertiary amine catalyst in step S4 is selected from one or more of triethylamine, N,N-diisopropylethylamine, tripropylamine, tributylamine, N-methylmorpholine, 4-methylmorpholine, and N,N-dimethylbenzylamine, and is used in an amount of 15-25% of the molar amount of the reducing amination intermediate.

10. The application of the antioxidant polymerization inhibitor for oil refining units as described in claim 1 or the antioxidant polymerization inhibitor for oil refining units prepared by the preparation method of any one of claims 2 to 9 as an antioxidant polymerization inhibitor in the field of petroleum refining.

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