Method for preparing oligomeric rosin by using slash pine rosin as raw material

Abstract

The invention provides a method for preparing oligomeric rosin by taking slash pine rosin as a raw material, which is characterized by comprising the following steps of: melting: putting crushed slash pine rosin into a melting tank, and heating and melting into liquid rosin under the protection of inert gas; dehydrating and removing low-boiling-point substances: transferring the liquid rosin into a reaction kettle, vacuumizing and heating; catalytic polymerization reaction: adding a composite catalyst into the reaction kettle after heating; high-temperature rectification and stabilization: continuously heating and adding a compound stabilizer at the same time; and cooling and discharging: stopping heating, cooling to break vacuum, and discharging to obtain an oligomeric rosin product. The slash pine rosin is adopted as a raw material, and a solvent-free high-vacuum high-temperature process and a synergistic effect of the composite catalyst and the stabilizer are combined, so that the acid value and color of the oligomeric rosin are effectively reduced, and meanwhile, the softening point of the oligomeric rosin is more moderate, so that the process is simplified, the pollution is reduced, and the production cost is reduced. And the processing stability and performance of the product in the application of hot melt adhesive and the like are improved.

Description

Technical Field

[0001] This invention belongs to the field of forest chemical industry and new materials technology, specifically relating to a method for preparing oligomeric rosin using wetland pine rosin as raw material. Background Technology

[0002] Rosin is a natural resin extracted from pine tree secretions. Its main component is resin acid, with small amounts of fatty acids and neutral substances. As an important renewable resource, rosin and its processed products are widely used in adhesives, coatings, inks, paints, papermaking, pharmaceuticals, and the electronics industry. However, natural rosin itself has drawbacks such as easy oxidation, easy crystallization, and a dark color. Therefore, it usually requires further processing through chemical modification methods such as polymerization and disproportionation to improve its application performance. Polymerized rosin is an important type of processed product that effectively improves the stability of rosin, reduces its crystallization tendency, and imparts a lighter color.

[0003] Currently, the mainstream raw material for industrial production of polymeric rosin is Masson pine rosin. Traditional production methods mainly include the sulfuric acid process, the zinc chloride process, and the boron trifluoride process. Among them, the sulfuric acid process is adopted by most manufacturers at home and abroad due to its mature technology, stable product quality, and high softening point. However, these traditional methods generally have some common problems: First, they require the use of organic solvents (such as gasoline or chloroform) in the production process, which not only brings flammable and explosive safety hazards, but also causes losses in the solvent recovery process, increasing production costs; second, the production process is complex, usually involving multiple unit operations such as polymerization, washing, and distillation, and will generate a large amount of acidic waste residue and acidic wastewater, which causes serious environmental pollution; third, the softening point of polymeric rosin produced by traditional methods is generally high, usually ranging from 110℃ to 145℃. Excessively high softening point limits its application in hot melt adhesives. When it is processed into rosin-modified resin, a high softening point can easily lead to problems such as incomplete melting, deposition, and equipment blockage during the hot melt adhesive production process. Even during the coating process, it may cause unsatisfactory phenomena such as uneven adhesive surface, particles, and poor flowability.

[0004] Existing technologies include methods for preparing oligomeric rosin using slash pine rosin as raw material, such as Chinese Patent CN101818026A, which involves heating under vacuum conditions and adding a catalyst and stabilizer for the reaction. However, this existing technology has a relatively broad range of catalyst selection options and fails to reveal the synergistic effect between specific composite catalysts; its process parameters are also relatively wide, lacking in-depth guidance and optimization on how to finely connect and coordinate the various steps to control product performance; furthermore, there is still room for improvement in the control of product performance indicators, such as how to simultaneously achieve lower acid values ​​and lighter colors.

[0005] Therefore, it is necessary to design a method for preparing oligomeric rosin using wetland pine rosin as raw material. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, a method for preparing oligomeric rosin using wetland pine rosin as raw material is provided.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing oligomeric rosin from wetland pine rosin includes the following steps: Melting: The crushed wet pine rosin is put into a melting tank and heated to 150°C to 180°C under the protection of inert gas, so that it is completely melted into liquid rosin; Dehydration and removal of low-boiling-point substances: Transfer liquid rosin to a reaction vessel, evacuate the vacuum, and heat to 200°C to 220°C. Maintain this condition for 30 to 60 minutes. Catalytic polymerization reaction: After the dehydration and degassing steps are completed, the composite catalyst is added to the reactor after heating, and the catalytic polymerization reaction is carried out under vacuum and stirring conditions; High-temperature distillation and stabilization: After the catalytic polymerization reaction is completed, the temperature is increased while a composite stabilizer is added. Distillation is carried out at this temperature and under high vacuum conditions, and the product is stabilized at the same time. Cooling and Discharging: After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 5°C to 8°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

[0008] In the melting step, the inert gas is nitrogen or argon, and the flow rate of the inert gas is controlled to be 0.5 liters to 2 liters per minute per kilogram of rosin.

[0009] In the dehydration and removal of low-boiling-point substances steps, the vacuum degree in the reactor is controlled to be between -0.090 MPa and -0.095 MPa, and the heating rate is controlled to be 2.5 °C per minute.

[0010] In the catalytic polymerization reaction step, the temperature is increased to 235°C to 255°C at a rate of 1°C to 1.5°C per minute, and the reaction time is controlled to be 2 hours to 2.5 hours.

[0011] In the catalytic polymerization reaction step, the composite catalyst is added at a rate of 0.08 to 0.4 parts by mass per 100 parts by mass of liquid rosin.

[0012] The composite catalyst is composed of a main catalyst and a co-catalyst; the mass ratio of the main catalyst to the co-catalyst is 1:0.3 to 1:0.8; wherein the main catalyst is at least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol) or 4,4'-thiobis(6-tert-butyl-m-cresol), and the co-catalyst is at least one of 2,6-di-tert-butyl-4-methylphenol or 2,2'-methylenebis(4-methyl-6-tert-butylphenol); The composite catalyst is added in batches, specifically: when the catalytic polymerization reaction temperature reaches the initial temperature of 235°C to 255°C, 60% to 70% of the total catalyst mass is added first, and the remaining part is added when the reaction has proceeded halfway.

[0013] In the high-temperature distillation and stabilization step, the temperature is increased to 315°C to 330°C at a rate of 2°C to 4°C per minute, and the holding time is controlled to be 50 to 70 minutes.

[0014] The amount of this composite stabilizer added is 0.1 to 0.4 parts by weight per 100 parts by weight of liquid rosin.

[0015] The composite stabilizer is composed of an antioxidant and a heat stabilizer, wherein the mass ratio of the antioxidant to the heat stabilizer is 1:0.5 to 1:1.5.

[0016] The antioxidant is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the heat stabilizer is at least one of tris(2,4-di-tert-butylphenyl) phosphite or tris(nonylphenyl) phosphite. The composite stabilizer is added in two equal parts, with half added at the start of heating and the other half when the temperature reaches the target temperature of 315°C to 330°C.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention uses wetland pine rosin as raw material and combines it with a solvent-free process under high vacuum and high temperature conditions, which effectively avoids the use of organic solvents in traditional methods, thereby reducing safety risks and environmental pollution in the production process.

[0018] 2. This invention utilizes a composite catalyst system, including the synergistic effect of a main catalyst and a co-catalyst, to optimize the polymerization process of rosin molecules by controlling their mass ratio and batch addition method. This arrangement enhances reaction selectivity, promotes the target polymerization reaction, and suppresses side reactions such as cracking and decarboxylation, thereby improving reaction efficiency and product stability, and contributing to obtaining a more uniform oligomeric rosin structure.

[0019] 3. The oligomeric rosin prepared by this invention exhibits improved properties in terms of softening point, acid value, and color, thanks to the rational formulation and staged addition of the composite stabilizer. The combined use of antioxidants and heat stabilizers enhances the thermal stability and antioxidant capacity of the product, thereby extending its shelf life and improving its processing performance in applications such as hot melt adhesives. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the specific embodiments of this application, the sources of various main raw materials are briefly described as follows: 4,4'-Thiobis(6-tert-butyl-3-methylphenol): Purchased from Huangshan Kebei New Material Technology Co., Ltd., CAS No. 96-69-5, product name: Antioxidant 300, melting point range: 160-164℃, purity ≥99%. 4,4'-Thiobis(6-tert-butyl-m-cresol): Purchased from Nanjing Shouqianshou Chemical Technology Co., Ltd., CAS No. 96-69-5, product name: Antioxidant 300, melting point range: 161-164℃, content ≥98%. 2,6-Di-tert-butyl-4-methylphenol: purchased from Hebei Fangqian New Material Technology Co., Ltd., CAS No. 128-37-0 2,2'-Methylenebis(4-methyl-6-tert-butylphenol): Purchased from Nanjing Bermuda Biotechnology Co., Ltd., CAS No. 119-47-1, product model: Antioxidant 2246 Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]: Purchased from Shandong Duoju Chemical Co., Ltd., CAS No. 6683-19-8, product name: Antioxidant 1010, melting point range: 110-125℃, purity ≥98%. β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester: purchased from Guangzhou Shanghe Chemical Technology Co., Ltd., CAS No. 2082-79-3, product name: Antioxidant 1076 Tris(2,4-di-tert-butylphenyl) phosphite: purchased from Beijing Jiyi Chemical Co., Ltd., CAS No. 95906-11-9. The product is a colorless to pale yellow liquid. Tris(nonylphenyl) phosphite: purchased from Shandong Xinheng Chemical Co., Ltd., CAS No. 26523-78-4 The technical solution of this application is as follows: A method for preparing oligomeric rosin from wetland pine rosin includes the following steps: Melting: The crushed wet pine rosin is put into a melting tank and heated to 150°C to 180°C under the protection of inert gas, so that it is completely melted into liquid rosin; Dehydration and removal of low-boiling-point substances: Transfer liquid rosin to a reaction vessel, evacuate the vacuum, and heat to 200°C to 220°C. Maintain this condition for 30 to 60 minutes. Catalytic polymerization reaction: After the dehydration and degassing steps are completed, the composite catalyst is added to the reactor after heating, and the catalytic polymerization reaction is carried out under vacuum and stirring conditions; High-temperature distillation and stabilization: After the catalytic polymerization reaction is completed, the temperature is increased while a composite stabilizer is added. Distillation is carried out at this temperature and under high vacuum conditions, and the product is stabilized at the same time. Cooling and Discharging: After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 5°C to 8°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

[0022] In the melting step, the inert gas is nitrogen or argon, and the flow rate of the inert gas is controlled to be 0.5 liters to 2 liters per minute per kilogram of rosin.

[0023] In the dehydration and removal of low-boiling-point substances steps, the vacuum degree in the reactor is controlled to be between -0.090 MPa and -0.095 MPa, and the heating rate is controlled to be 2.5 °C per minute.

[0024] In the catalytic polymerization reaction step, the temperature is increased to 235°C to 255°C at a rate of 1°C to 1.5°C per minute, and the reaction time is controlled to be 2 hours to 2.5 hours.

[0025] In the catalytic polymerization reaction step, the composite catalyst is added at a rate of 0.08 to 0.4 parts by mass per 100 parts by mass of liquid rosin.

[0026] The composite catalyst is composed of a main catalyst and a co-catalyst; the mass ratio of the main catalyst to the co-catalyst is 1:0.3 to 1:0.8; wherein the main catalyst is at least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol) or 4,4'-thiobis(6-tert-butyl-m-cresol), and the co-catalyst is at least one of 2,6-di-tert-butyl-4-methylphenol or 2,2'-methylenebis(4-methyl-6-tert-butylphenol); The composite catalyst is added in batches, specifically: when the catalytic polymerization reaction temperature reaches the initial temperature of 235°C to 255°C, 60% to 70% of the total catalyst mass is added first, and the remaining part is added when the reaction has proceeded halfway.

[0027] In the high-temperature distillation and stabilization step, the temperature is increased to 315°C to 330°C at a rate of 2°C to 4°C per minute, and the holding time is controlled to be 50 to 70 minutes.

[0028] The amount of this composite stabilizer added is 0.1 to 0.4 parts by weight per 100 parts by weight of liquid rosin.

[0029] The composite stabilizer is composed of an antioxidant and a heat stabilizer, wherein the mass ratio of the antioxidant to the heat stabilizer is 1:0.5 to 1:1.5.

[0030] The antioxidant is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the heat stabilizer is at least one of tris(2,4-di-tert-butylphenyl) phosphite or tris(nonylphenyl) phosphite. The composite stabilizer is added in two equal parts, with half added at the start of heating and the other half when the temperature reaches the target temperature of 315°C to 330°C.

[0031] The present invention will be described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited to these examples. Unless otherwise specified, the chemical reagents and raw materials used in the following examples and comparative examples are all conventional commercially available products.

[0032] Example 1 The crushed rosin from wet pine was added to a melting tank. Under nitrogen protection, the inert gas flow rate was controlled at 1.25 liters per kilogram of rosin per minute, and the mixture was heated to 180°C to completely melt it into liquid rosin. The liquid rosin was then transferred to a reaction vessel, and a vacuum was drawn to a degree of -0.0925 MPa. The temperature was increased to 200°C at a rate of 2.5°C per minute, and maintained under these conditions for 60 minutes to remove moisture and low-boiling-point substances.

[0033] After the dehydration and degassing steps are completed, the temperature is increased to 255°C at a rate of 1.0°C per minute. Then, a composite catalyst is added to the reactor at a rate of 0.08 parts by mass per 100 parts by mass of liquid rosin. The composite catalyst consists of the main catalyst 4,4'-thiobis(6-tert-butyl-3-methylphenol) and the co-catalyst 2,2'-methylenebis(4-methyl-6-tert-butylphenol), with a mass ratio of 1:0.8. The catalyst is added in batches. When the catalytic polymerization reaction temperature reaches 255°C, 65% of the total catalyst mass is added first, and the remaining part is added when the reaction is halfway through. The catalytic polymerization reaction is carried out under vacuum and stirring conditions for 2.25 hours.

[0034] After the catalytic polymerization reaction was completed, the temperature was increased to 330°C at a rate of 2°C per minute, while a composite stabilizer was added. The amount of composite stabilizer added was 0.1 parts by mass per 100 parts by mass of liquid rosin. The composite stabilizer consisted of the antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the heat stabilizer tris(2,4-di-tert-butylphenyl) phosphite, with a mass ratio of antioxidant to heat stabilizer of 1:1.5. The stabilizer was added in two equal parts, half at the beginning of the heating and half when the temperature reached 330°C. Distillation was carried out at this temperature and under high vacuum conditions to stabilize the product, and the holding time was 60 minutes.

[0035] After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 6.5°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

[0036] Example 2 In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: The crushed rosin from wet pine is put into a melting tank. Under the protection of argon, the flow rate of inert gas is controlled at 2 liters per kilogram of rosin per minute. The mixture is heated to 150°C to completely melt it into liquid rosin.

[0037] Liquid rosin was transferred to a reactor, and a vacuum of -0.090 MPa was created. The temperature was then increased to 210°C at a rate of 2.5°C per minute and maintained at this temperature for 30 minutes to remove moisture and low-boiling-point substances. After the dehydration and degassing steps were completed, the temperature was increased to 235°C at a rate of 1.25°C per minute. Subsequently, a composite catalyst was added to the reactor at a ratio of 0.24 parts by mass per 100 parts by mass of liquid rosin. The composite catalyst consisted of the main catalyst 4,4'-thiobis(6-tert-butyl-3-methylphenol) and the co-catalyst 2,2'-methylenebis(4-methyl-6-tert-butylphenol), with a mass ratio of 1:0.3. The catalyst was added in batches: 70% of the total catalyst mass was added when the catalytic polymerization temperature reached 235°C, and the remaining portion was added when the reaction was halfway through. The catalytic polymerization reaction was carried out under vacuum and stirring conditions for 2.5 hours.

[0038] After the catalytic polymerization reaction was completed, the temperature was increased to 315°C at a rate of 3°C per minute, while a composite stabilizer was added. The amount of composite stabilizer added was 0.25 parts by mass per 100 parts by mass of liquid rosin. The composite stabilizer consisted of the antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the heat stabilizer tris(2,4-di-tert-butylphenyl) phosphite, with a mass ratio of antioxidant to heat stabilizer of 1:0.5. The stabilizer was added in two equal parts, half at the beginning of the heating and half when the temperature reached 315°C. Distillation was carried out at this temperature and under high vacuum conditions to stabilize the product, and the holding time was 70 minutes.

[0039] After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 8°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

[0040] Example 3 In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: The crushed rosin from wet pine is put into a melting tank. Under nitrogen protection, the flow rate of inert gas is controlled at 0.5 liters per kilogram of rosin per minute. The mixture is heated to 165°C to completely melt it into liquid rosin.

[0041] Liquid rosin was transferred to a reaction vessel, and a vacuum was drawn to a vacuum degree of -0.095 MPa. The temperature was increased to 220°C at a rate of 2.5°C per minute and maintained under these conditions for 45 minutes to remove moisture and low-boiling-point substances.

[0042] After the dehydration and degassing steps are completed, the temperature is increased to 245°C at a rate of 1.5°C per minute. Then, a composite catalyst is added to the reactor at a rate of 0.4 parts by mass per 100 parts by mass of liquid rosin. The composite catalyst consists of the main catalyst 4,4'-thiobis(6-tert-butyl-3-methylphenol) and the co-catalyst 2,2'-methylenebis(4-methyl-6-tert-butylphenol), with a mass ratio of 1:0.55. The catalyst is added in batches. When the catalytic polymerization reaction temperature reaches 245°C, 60% of the total catalyst mass is added first, and the remaining part is added when the reaction is halfway through. The catalytic polymerization reaction is carried out under vacuum and stirring conditions for 2.0 hours.

[0043] After the catalytic polymerization reaction was completed, the temperature was increased to 322.5°C at a rate of 4°C per minute, while a composite stabilizer was added. The amount of composite stabilizer added was 0.4 parts by mass per 100 parts by mass of liquid rosin. The composite stabilizer consisted of the antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the heat stabilizer tris(2,4-di-tert-butylphenyl) phosphite, with a mass ratio of antioxidant to heat stabilizer of 1:1.0. The stabilizer was added in two equal parts, half at the beginning of the heating and half when the temperature reached 322.5°C. Distillation was carried out at this temperature and under high vacuum conditions to stabilize the product, and the holding time was 50 minutes.

[0044] After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 5°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

[0045] Comparative Example 1 The reaction was basically the same as in Example 1, but instead of a composite catalyst, a single catalyst, 4,4'-thiobis(6-tert-butyl-3-methylphenol), was used in the catalytic polymerization step, and the amount added was the same as the total amount of the composite catalyst in Example 1.

[0046] Comparative Example 2 It is basically the same as Example 2, but in the catalytic polymerization reaction step, the mass ratio of the main catalyst to the co-catalyst of the composite catalyst is adjusted to 1:0.2, which is beyond the scope of the technical solution.

[0047] Comparative Example 3 It is basically the same as Example 3, but in the high-temperature distillation and stabilization steps, the mass ratio of antioxidant to heat stabilizer in the composite stabilizer is adjusted to 1:2, which is beyond the scope of the technical solution.

[0048] Comparative Example 4 It is basically the same as Example 1, but the dehydration and low-boiling-point removal steps are not vacuumed, and heating is carried out only at atmospheric pressure.

[0049] Comparative Example 5 It is basically the same as Example 2, but in the cooling and unloading steps, the cooling rate is adjusted to 10°C per minute, which is beyond the scope of the technical solution.

[0050] Comparative Example 6 The conventional solvent method was used, with wet pine rosin as raw material and gasoline as solvent. The polymerization reaction was carried out according to the sulfuric acid process, including polymerization, washing and distillation steps, and other conditions were similar to those in Example 3.

[0051] Performance Test Results and Analysis Oligomeric rosin products were prepared according to the parameters of the examples and comparative examples, respectively. The oligomeric rosin products were tested, and the test results are shown in Table 1. Among them, the softening point was determined according to the ring and ball method, the acid value was determined according to the acid-base titration method and expressed as milligrams of KOH per gram, and the color was determined according to the iron-cobalt colorimetric method and expressed as the Ghana color scale.

[0052] As shown in Table 1, the oligomeric rosin prepared in the embodiments of this invention exhibits significant advantages in key performance indicators. Looking at the softening point data, the softening points of Examples 1 to 3 reach 98℃, 105℃, and 110℃ respectively, all within the ideal range of 90 to 120℃. This characteristic allows the product to completely melt during hot melt adhesive processing, avoiding deposition or clogging. Comparative Example 1, due to the absence of a composite catalyst system, achieved a softening point of 92℃, indicating that the catalytic system plays a crucial role in controlling the degree of polymerization. While Comparative Example 6, using a traditional solvent method, achieved a softening point of 115℃, considering other indicators, this high softening point comes at the cost of sacrificing the overall performance of the product.

[0053] Regarding the acid value, the test results for Examples 1 to 3 were 130, 135, and 128 mg KOH / g, respectively, significantly lower than those of the comparative examples. This result confirms that the synergistic effect of the composite catalyst system can effectively suppress side reactions such as cracking and decarboxylation. Comparative Example 1, using only a single catalyst, showed an acid value increase to 150 mg KOH / g, indicating that the lack of a co-catalyst leads to an increase in side reactions. Comparative Example 4, undergoing a dehydration and removal of low-boiling-point substances under normal pressure, further increased the acid value to 155 mg KOH / g, confirming the importance of vacuum conditions for removing acidic precursors. From the perspective of the reaction mechanism, a suitable vacuum level can promptly remove water and low-molecular-weight acids generated during the reaction, thereby promoting the resin acid polymerization reaction in the forward direction.

[0054] Table 1 Analysis of Test Results

[0055] Test results show that the color index test results also support the technical effects of the present invention. The color levels of Examples 1 to 3 reached Ghanaian color scale 6 to 7, while the comparative examples were generally between 8 and 10. In Comparative Example 3, the stabilizer ratio exceeded the preferred range, and the color deepened to level 8, indicating that an appropriate ratio of antioxidant to heat stabilizer is crucial for inhibiting product oxidative discoloration. Comparative Example 6 used a traditional solvent method, and the product color reached level 9, which may be due to solvent residue and impurities introduced during the washing process. From a chemical structure perspective, the phenolic antioxidant in the composite stabilizer can provide hydrogen atoms to terminate free radical chain reactions, while the phosphite heat stabilizer can decompose hydroperoxides. The synergistic effect of both effectively delays the oxidative discoloration process of the resin acid.

[0056] Through systematic analysis of the comparative examples, the synergistic effect of each element in the technical solution of this invention can be clearly seen. In Comparative Example 2, the imbalance of the catalyst ratio led to a comprehensive decline in product performance, indicating that a specific ratio of the main catalyst to the co-catalyst is crucial for achieving ideal polymerization results. In Comparative Example 5, the excessively rapid cooling rate resulted in uneven product performance, confirming the significant impact of controlling the cooling process on the crystallization behavior of the product. These results, from different perspectives, verify that this invention, through the synergistic effect of a composite catalyst system, precise process parameter control, and composite stabilizers, optimizes the overall performance of oligomeric rosin, effectively solving the technical problems of high softening point, high acid value, and dark color in products produced by traditional methods.

[0057] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing oligomeric rosin from wetland pine rosin, characterized in that, Includes the following steps: Melting: The crushed wet pine rosin is put into a melting tank and heated to 150°C to 180°C under the protection of inert gas, so that it is completely melted into liquid rosin; Dehydration and removal of low-boiling-point substances: Transfer liquid rosin to a reaction vessel, evacuate the vacuum, and heat to 200°C to 220°C. Maintain this condition for 30 to 60 minutes. Catalytic polymerization reaction: After the dehydration and degassing steps are completed, the composite catalyst is added to the reactor after heating, and the catalytic polymerization reaction is carried out under vacuum and stirring conditions; High-temperature distillation and stabilization: After the catalytic polymerization reaction is completed, the temperature is increased while a composite stabilizer is added. Distillation is carried out at this temperature and under high vacuum conditions, and the product is stabilized at the same time. Cooling and Discharging: After the distillation stabilization stage is completed, heating is stopped, and the material in the reactor is cooled to below 60°C at a cooling rate of 5°C to 8°C per minute. Then the vacuum is broken, and the oligomeric rosin product is discharged.

2. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, In the melting step, the inert gas is nitrogen or argon, and the flow rate of the inert gas is controlled to be 0.5 liters to 2 liters per minute per kilogram of rosin.

3. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, In the dehydration and removal of low-boiling-point substances steps, the vacuum degree in the reactor is controlled to be between -0.090 MPa and -0.095 MPa, and the heating rate is controlled to be 2.5 °C per minute.

4. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, In the catalytic polymerization reaction step, the temperature is increased to 235°C to 255°C at a rate of 1°C to 1.5°C per minute, and the reaction time is controlled to be 2 hours to 2.5 hours.

5. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, In the catalytic polymerization reaction step, the composite catalyst is added at a rate of 0.08 to 0.4 parts by mass per 100 parts by mass of liquid rosin.

6. The method for preparing oligomeric rosin from wetland pine rosin according to claim 5, characterized in that, The composite catalyst is composed of a main catalyst and a co-catalyst; the mass ratio of the main catalyst to the co-catalyst is 1:0.3 to 1:0.8; wherein the main catalyst is at least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol) or 4,4'-thiobis(6-tert-butyl-m-cresol), and the co-catalyst is at least one of 2,6-di-tert-butyl-4-methylphenol or 2,2'-methylenebis(4-methyl-6-tert-butylphenol); The composite catalyst is added in batches, specifically: when the catalytic polymerization reaction temperature reaches the initial temperature of 235°C to 255°C, 60% to 70% of the total catalyst mass is added first, and the remaining part is added when the reaction has proceeded halfway.

7. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, In the high-temperature distillation and stabilization step, the temperature is increased to 315°C to 330°C at a rate of 2°C to 4°C per minute, and the holding time is controlled to be 50 to 70 minutes.

8. The method for preparing oligomeric rosin from wetland pine rosin according to claim 1, characterized in that, The amount of this composite stabilizer added is 0.1 to 0.4 parts by weight per 100 parts by weight of liquid rosin.

9. A method for preparing oligomeric rosin from wetland pine rosin according to claim 8, characterized in that, The composite stabilizer is composed of an antioxidant and a heat stabilizer, wherein the mass ratio of the antioxidant to the heat stabilizer is 1:0.5 to 1:1.

5.

10. A method for preparing oligomeric rosin from wetland pine rosin according to claim 9, characterized in that, The antioxidant is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the heat stabilizer is at least one of tris(2,4-di-tert-butylphenyl) phosphite or tris(nonylphenyl) phosphite. The composite stabilizer is added in two equal parts, with half added at the start of heating and the other half when the temperature reaches the target temperature of 315°C to 330°C.

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