Synthesis process of epoxy resin and anhydrous epoxy resin system

Abstract

This invention belongs to the field of epoxy resin synthesis technology, specifically relating to epoxy resin and an anhydrous epoxy resin synthesis process. The anhydrous epoxy resin synthesis process of this invention includes the following steps: dissolving bisphenol A in an organic solvent, adding sodium dithionite and mixing thoroughly, then adding solid sodium hydroxide, reacting under negative pressure and heating conditions, filtering after the reaction, adding the sodium bisphenol A solution to epichlorohydrin containing solid sodium hydroxide, and heating to carry out the resin synthesis reaction; after the reaction, performing solid-liquid separation, collecting the liquid phase and performing vacuum distillation to remove the solvent and unreacted epichlorohydrin, obtaining the epoxy resin. The anhydrous epoxy resin synthesis process provided by this invention avoids epichlorohydrin hydrolysis and is a novel epoxy resin synthesis process that is low-cost, highly efficient, and ensures excellent product color. The epoxy resin prepared by this invention guarantees product quality, with low color and low epoxy equivalent.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin synthesis technology, specifically relating to epoxy resin and the synthesis process of anhydrous epoxy resin systems. Background Technology

[0002] Epoxy resins are an important class of thermosetting resins, widely used in coatings, electronics, composite materials, and civil engineering due to their excellent adhesive properties, mechanical strength, electrical insulation, and chemical resistance. Their synthesis process, particularly based on the condensation reaction of bisphenol A and epichlorohydrin, is a core technology in the industry.

[0003] In traditional epoxy resin synthesis processes, epichlorohydrin (ECH) is both a reactant and often used as a solvent. One of the core steps in this process is heating the reaction under alkaline conditions to generate epoxy groups. However, epichlorohydrin is highly susceptible to hydrolysis under alkaline conditions, producing the non-target product chloropropanediol. This not only directly consumes expensive epichlorohydrin raw materials, increasing production costs, but also reduces the epoxy value and reaction yield of the final product.

[0004] To suppress the hydrolysis consumption of epichlorohydrin, existing technologies have mainly proposed two improved methods: the solid alkali method and the sodium salt method.

[0005] The solid alkali process uses solid sodium hydroxide as the alkali source for the reaction. To control the rapid exothermic reaction rate, a batch-by-batch, slow dropwise addition of solid alkali is typically employed. However, this method has significant drawbacks: First, solid alkali is highly susceptible to moisture absorption and clumping during feeding and mixing, leading to blockages in the feed pipes and reaction equipment, severely impacting the continuity and stability of production. Second, solid alkali is difficult to disperse quickly and uniformly in viscous resin systems, easily resulting in excessively high local alkali concentrations, which in turn exacerbates the hydrolysis of epichlorohydrin and may cause side reactions, affecting the uniformity of product quality. More importantly, when solid sodium hydroxide reacts with reaction intermediates, a small amount of water is inevitably produced. This water continues to trigger the hydrolysis and consumption of epichlorohydrin. Therefore, this method fails to address the hydrolysis problem at its root, and raw material consumption remains high.

[0006] The sodium salt method uses a pre-prepared sodium salt (such as sodium phenolate) solution for the reaction. To overcome the shortcomings of the solid alkali method, existing technologies (such as CN117720706A) propose a scheme to pre-prepare bisphenol A potassium / sodium salts before reacting them with epichlorohydrin. Although this method improves the dispersibility of the alkali to some extent, it still suffers from insufficient color control, reaction efficiency, and cost issues. During the preparation and storage of phenolates, if strict anti-oxidation measures are not taken, phenolates are easily oxidized by air to generate colored impurities such as quinones, resulting in a high color of the final resin product, affecting its application in fields with high appearance requirements (such as electronic encapsulation and light-colored coatings). Existing phenolate methods typically involve redissolving dried solid phenolates in a solvent (such as ethanol) for the reaction. This process involves multiple steps, including phenolate synthesis, crystallization, filtration, drying, and redissolution, resulting in a long process flow, high energy consumption, and the preparation of solid phenolates itself faces cumbersome operations and potential oxidation risks.

[0007] Even when using alcohol solvents, the presence of trace amounts of water and alcohol hydroxyl groups in the system still provides opportunities for the hydrolysis side reactions of epichlorohydrin, limiting further reductions in epichlorohydrin consumption. Simultaneously, the reaction time is often long (e.g., several hours), requiring improvements in production efficiency. While solution-based feeding avoids the clumping and uneven dispersion problems of the solid-alkali method, this method introduces new technical challenges. On one hand, sodium salt (especially sodium phenolate) solutions are highly susceptible to oxidation by air during preparation and storage, generating colored impurities such as anthraquinones. These impurities can enter the final epoxy resin product, resulting in high product color (e.g., platinum-cobalt color), severely limiting its application in high-end, light-colored products. On the other hand, compared to strong solid alkalis, sodium salt solutions are relatively weakly alkaline, resulting in lower reactivity with epichlorohydrin. To achieve higher reaction yields, it is often necessary to significantly extend the reaction time or increase the reaction temperature (which exacerbates side reactions), leading to low production efficiency and increased energy consumption. Summary of the Invention

[0008] The technical problem this invention aims to solve is to overcome the aforementioned deficiencies in existing technologies and provide a novel epoxy resin synthesis process that avoids epichlorohydrin hydrolysis, while also offering low cost, high efficiency, and ensuring excellent product color. The epoxy resin prepared by this invention guarantees product quality, exhibiting low color and high epoxy equivalent.

[0009] The epoxy resin anhydrous system synthesis process of the present invention includes the following steps:

[0010] (1) Preparation of phenol salt: Under anaerobic conditions, bisphenol A was dissolved in the organic solvent n-butanol, sodium dithionite was added and mixed evenly, and then sodium hydroxide solid was added. The reaction was carried out under negative pressure and heating conditions. After the reaction was completed, the solution of sodium bisphenol A was obtained by filtration.

[0011] (2) Resin synthesis reaction: Under anaerobic conditions, bisphenol A sodium salt solution is added to epichlorohydrin containing sodium hydroxide solid, and the resin synthesis reaction is carried out by heating;

[0012] (3) Post-processing: After the reaction is completed, solid-liquid separation is performed, the liquid phase is collected and vacuum distilled to remove the solvent and unreacted epichlorohydrin to obtain epoxy resin.

[0013] In step (1), the negative pressure condition is an absolute pressure of 10~30 kPa, the heating condition is 60~80℃, and the reaction time is 1~2 h.

[0014] In step (1), the molar ratio of bisphenol A, sodium dithionite, and sodium hydroxide is 1:0.001~0.005:2.1~2.3.

[0015] The mass ratio of bisphenol A to organic solvent is 1:2.5~4.

[0016] The heating temperature for the reaction in step (2) is 100~130℃, and the reaction time is 10~30 min.

[0017] The molar ratio of each material in step (2) is based on bisphenol A in step (1): Bisphenol A: Sodium hydroxide: Epichlorohydrin = 1:0.01~0.1:4~5. The sodium hydroxide here is the solid sodium hydroxide in step (2).

[0018] In step (3), the solid-liquid separation is carried out by centrifugation; the temperature of the vacuum distillation is 120~140℃.

[0019] The anaerobic conditions in steps (1) and (2) are achieved and maintained by introducing nitrogen or inert gas into the reaction system.

[0020] An epoxy resin is synthesized using the anhydrous epoxy resin synthesis process described above.

[0021] Specifically, the anhydrous epoxy resin system synthesis process includes the following steps:

[0022] (1) Under anaerobic conditions, bisphenol A (BPA) was dissolved in n-butanol, sodium dithionite was added and stirred evenly, and then sodium hydroxide solid was added and mixed evenly (molar ratio BPA: sodium dithionite: sodium hydroxide = 1: 0.001~0.005: 2.1~2.3, mass ratio BPA: n-butanol = 1: 2.5-4). The vacuum was drawn to an absolute pressure of 10~30 kPa, the temperature was raised to 60~80℃, and the reaction was carried out for 1~2 h. After the vacuum was broken to normal pressure with nitrogen, the solution of sodium bisphenol A was obtained by filtration.

[0023] (2) Under anaerobic conditions, add the sodium bisphenol A solution to epichlorohydrin (ECH) containing sodium hydroxide solid and stir until homogeneous (molar ratio BPA:sodium hydroxide:ECH=1:0.01~0.1:4~5), heat rapidly to 100~130℃, and keep warm for 10~30 min.

[0024] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and evaporate it at 120~140℃ to remove n-butanol and unreacted epichlorohydrin to obtain resin product and conduct product index testing.

[0025] This invention first dissolves bisphenol A in an organic solvent and adds sodium dithionite (sodium hydrosulfite) and stirs until homogeneous. Solid sodium hydroxide is then added, and the reaction is carried out under negative pressure heating to obtain a sodium bisphenol A solution. This sodium bisphenol A solution is then filtered. The sodium bisphenol A solution is added to epichlorohydrin containing a small amount of solid sodium hydroxide. Under the catalysis of sodium hydroxide, a rapid reaction is achieved to obtain bisphenol A-type epoxy resin and byproduct industrial salt. The byproduct industrial salt and catalyst sodium hydroxide are removed by centrifugation, yielding an epoxy resin solution. This solution is then removed by rotary evaporation under reduced pressure to remove the solvent and unreacted ECH, resulting in the final product resin. The epoxy resin synthesis method of this invention is carried out entirely under anhydrous conditions, resulting in low consumption; the epichlorohydrin consumption is only 0.541 g / g. The reaction time is significantly shortened; compared to the 4-6 hours of the traditional process, the reaction time of this invention is less than 0.5 hours, which is beneficial for continuous production. Furthermore, while maintaining the same BPA to ECH feed ratio, the epoxy resin produced using this invention exhibits superior color, epoxy equivalent, and viscosity compared to products from traditional processes.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) The epoxy resin anhydrous system synthesis process of the present invention is carried out under anhydrous conditions throughout the process. ECH does not undergo hydrolysis and consumption, does not generate high-salt wastewater, and the reaction time is greatly shortened. Compared with the traditional process, it is safer, more environmentally friendly and more efficient.

[0028] (2) The epoxy resin obtained by the synthesis process of the present invention has better color, epoxy equivalent and viscosity than the products of the existing process. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments.

[0030] All raw materials and additives used in the following examples and comparative examples are commercially available.

[0031] Example 1

[0032] The aforementioned epoxy resin anhydrous system synthesis process includes the following steps:

[0033] (1) Under anaerobic conditions, 114g of bisphenol A was dissolved in 285g of n-butanol, 0.09g of sodium dithionite was added and stirred evenly, then 42g of sodium hydroxide solid was added and mixed evenly. The vacuum was drawn to an absolute pressure of 30kPa, the temperature was raised to 60℃, and after reacting for 2h, the vacuum was broken with nitrogen to atmospheric pressure, and the solution of sodium bisphenol A was obtained by filtration.

[0034] (2) Under anaerobic conditions, add the sodium bisphenol A solution to epichlorohydrin containing sodium hydroxide solid (0.2 g sodium hydroxide solid, 185 g epichlorohydrin), stir and mix evenly, then heat rapidly to 100°C and keep warm for 30 min.

[0035] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and rotary evaporate at 120°C to remove n-butanol and unreacted epichlorohydrin. Collect the rotary evaporated liquid containing epichlorohydrin to obtain the resin product and conduct product index testing.

[0036] Example 2

[0037] The aforementioned epoxy resin anhydrous system synthesis process includes the following steps:

[0038] (1) Under anaerobic conditions, 114g of bisphenol A was dissolved in 342g of n-butanol, 0.18g of sodium dithionite was added and stirred evenly, then 43g of sodium hydroxide solid was added and mixed evenly. The vacuum was drawn to an absolute pressure of 25kPa, the temperature was raised to 65℃, and the reaction was carried out for 1.8h. The vacuum was broken with nitrogen gas to atmospheric pressure, and the solution of sodium bisphenol A was obtained by filtration.

[0039] (2) Under anaerobic conditions, add bisphenol A sodium salt solution to epichlorohydrin containing sodium hydroxide solid (0.6 g sodium hydroxide solid, 200 g epichlorohydrin), stir and mix evenly, then heat rapidly to 110 °C and keep warm for 25 min.

[0040] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and rotary evaporate at 125°C to remove n-butanol and unreacted epichlorohydrin. Collect the rotary evaporated liquid containing epichlorohydrin to obtain the resin product and conduct product index testing.

[0041] Example 3

[0042] The aforementioned epoxy resin anhydrous system synthesis process includes the following steps:

[0043] (1) Under anaerobic conditions, 114g of bisphenol A was dissolved in 365g of n-butanol, 0.26g of sodium dithionite was added and stirred evenly, then 44g of sodium hydroxide solid was added and mixed evenly. The vacuum was drawn to an absolute pressure of 20kPa, the temperature was raised to 70℃, and the reaction was carried out for 1.5h. The vacuum was broken with nitrogen gas to atmospheric pressure, and the solution of sodium bisphenol A was obtained by filtration.

[0044] (2) Under anaerobic conditions, add the sodium bisphenol A solution to epichlorohydrin containing sodium hydroxide solid (1g sodium hydroxide solid, 210g epichlorohydrin), stir and mix evenly, then heat rapidly to 120°C and keep warm for 20 min.

[0045] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and rotary evaporate at 130°C to remove n-butanol and unreacted epichlorohydrin. Collect the rotary evaporated liquid containing epichlorohydrin to obtain the resin product and conduct product index testing.

[0046] Example 4

[0047] The aforementioned epoxy resin anhydrous system synthesis process includes the following steps:

[0048] (1) Under anaerobic conditions, 114g of bisphenol A was dissolved in 400g of n-butanol, 0.35g of sodium dithionite was added and stirred evenly, then 45g of sodium hydroxide solid was added and mixed evenly. The vacuum was drawn to an absolute pressure of 15kPa, the temperature was raised to 75℃, and the reaction was carried out for 1.3h. The vacuum was broken with nitrogen gas to atmospheric pressure, and the solution of sodium bisphenol A was obtained by filtration.

[0049] (2) Under anaerobic conditions, add the sodium bisphenol A solution to epichlorohydrin containing sodium hydroxide solid (1.6 g sodium hydroxide solid, 222 g epichlorohydrin), stir and mix evenly, then heat rapidly to 125 °C and keep warm for 15 min.

[0050] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and rotary evaporate at 135°C to remove n-butanol and unreacted epichlorohydrin. Collect the rotary evaporated liquid containing epichlorohydrin to obtain the resin product and conduct product index testing.

[0051] Example 5

[0052] The aforementioned epoxy resin anhydrous system synthesis process includes the following steps:

[0053] (1) Under anaerobic conditions, 114g of bisphenol A was dissolved in 456g of n-butanol, 0.43g of sodium dithionite was added and stirred evenly, then 46g of sodium hydroxide solid was added and mixed evenly. The vacuum was drawn to an absolute pressure of 10kPa, the temperature was raised to 80℃, and after reacting for 1h, the vacuum was broken with nitrogen to atmospheric pressure, and the solution of sodium bisphenol A was obtained by filtration.

[0054] (2) Under anaerobic conditions, add the sodium bisphenol A solution to epichlorohydrin containing sodium hydroxide solid (2g sodium hydroxide solid, 232g epichlorohydrin), stir and mix evenly, then heat rapidly to 130℃ and keep warm for 10min.

[0055] (3) After the reaction is completed, centrifuge and separate solid and liquid. Take the supernatant and rotary evaporate at 140°C to remove n-butanol and unreacted epichlorohydrin. Collect the rotary evaporated liquid containing epichlorohydrin to obtain the resin product and conduct product index testing.

[0056] Comparative Example 1

[0057] This comparative example is the same as Example 1, except that n-butanol in step (1) is replaced with ethanol, and other preparation conditions are the same.

[0058] Comparative Example 2

[0059] This comparative example is the same as Example 1, except that sodium dithionite is not used in step (1), and the other preparation conditions are the same.

[0060] Comparative Example 3

[0061] A process for synthesizing epoxy resin includes the following steps:

[0062] Under anaerobic conditions, 114g of bisphenol A and 232g of epichlorohydrin were mixed evenly, and the mixture was heated to 56℃ until the bisphenol A was completely dissolved. Then, 6g of 50wt% sodium hydroxide aqueous solution was added at once, and the reaction was maintained at this temperature for 3 hours. Then, under the conditions of 20kPa absolute pressure and 64℃ temperature, 64g of 50wt% sodium hydroxide aqueous solution was added dropwise over 4 hours. After the reaction was completed, epichlorohydrin was recovered at 130℃. 200g of toluene and 200g of water were added to the recovered mixture, and the mixture was stirred and dissolved at 70℃ for 30 minutes. After standing for 30 minutes, the aqueous layer was separated to obtain toluene resin. The toluene resin was then removed by rotary evaporation at 150℃ to obtain crude resin. After filtration, the finished resin was obtained and its product indicators were tested.

[0063] Comparative Example 4

[0064] A process for synthesizing epoxy resin includes the following steps:

[0065] (1) Under anaerobic conditions, 114g of bisphenol A, 250mL of n-butanol, and then 80g of sodium hydroxide solid were added and mixed evenly. The mixture was reacted at room temperature for 1h, allowed to stand and crystallize for 12h, filtered and collected the solid and placed in a vacuum oven at 200℃ for 24h to obtain sodium bisphenol A salt solid.

[0066] (2) Mix 136g of the obtained sodium bisphenol A salt solid, 500mL of n-butanol, and 232g of epichlorohydrin evenly, stir and react at room temperature for 7h, and filter to collect the filtrate. Remove n-butanol and epichlorohydrin from the filtrate by rotary evaporation at 120℃, collect the rotary evaporator containing epichlorohydrin to obtain the crude product, add 400g of xylene solvent to the crude product, wash with 1000mL of deionized water three times, and separate the aqueous phase. Remove the remaining organic phase by rotary evaporation at 150℃ to remove xylene, and obtain the finished resin for product index testing.

[0067] The finished resins prepared in the above examples and comparative examples were tested for epoxy equivalent, platinum-cobalt color and viscosity according to the test requirements of GB / T13657-2011. The collected rotary evaporation liquid containing epichlorohydrin was analyzed by refractive index testing to calculate the epichlorohydrin content (at 20℃, the refractive index of n-butanol was 1.3993, ethanol was 1.3611, and epichlorohydrin was 1.4382). Linear fitting revealed the following relationship between the refractive index y1 and epichlorohydrin content x in the n-butanol / epicochlorohydrin mixture: y1 = 0.0389x + 1.3993; and the relationship between the refractive index y2 and epichlorohydrin content x in the ethanol / epicochlorohydrin mixture: y2 = 0.0771x + 1.3611. (In traditional processes, since the rotary evaporation liquid is a mixture of water and epichlorohydrin, which are immiscible, the unreacted epichlorohydrin mass can be directly separated to obtain the epichlorohydrin consumption.) The product's test results are shown in Table 1.

[0068] Table 1 Test Results

[0069]

[0070] In Comparative Example 3, the mixture of water and epichlorohydrin obtained by rotary evaporation was separated to obtain 140.16g of epichlorohydrin, thus consuming 91.84g of epichlorohydrin. The final epichlorohydrin consumption of this method in Comparative Example 3 was 0.555g / g.

[0071] Compared to Comparative Example 1, the products from Example 1 showed significant differences in epoxy equivalent and viscosity. This is because the boiling point of ethanol is lower than that of n-butanol. During the resin synthesis reaction, a large amount of ethanol evaporates at high temperatures, increasing the resin concentration and the probability of polymerization between resin molecules, ultimately leading to an increase in epoxy equivalent and viscosity. The epoxy equivalent, color, and viscosity of the product from Example 1 were superior to those of Comparative Example 2. This is mainly because Comparative Example 2 did not use sodium hydrosulfite during the synthesis of bisphenol A sodium salt, resulting in the oxidation of bisphenol A sodium salt to anthracene. Quinone-based color-developing substances further dissolve into the resin, causing a comprehensive increase in epoxy equivalent, color, and viscosity. Compared with Comparative Example 3, Example 5 shows a significant improvement in product indicators and epichlorohydrin consumption. In Example 5, no water was present throughout the reaction process, and epichlorohydrin hardly underwent hydrolysis, resulting in minimal additional consumption. In contrast, in Comparative Example 3, one of the raw materials, a 50wt% sodium hydroxide aqueous solution, contained a large amount of water during the resin synthesis reaction. Although the water was removed promptly under negative pressure, a large amount of epichlorohydrin still underwent hydrolysis, resulting in additional consumption. Furthermore, the negative pressure state during the resin synthesis reaction in Comparative Example 3 caused the absorption of a small amount of air, leading to an increase in resin color. The single addition of liquid alkali during the etherification reaction resulted in excessively high local concentrations, inevitably causing premature polymerization of the resin and resulting in persistently high epoxy equivalent and viscosity in the final product. In contrast, Example 5 was conducted under normal pressure and nitrogen protection during resin synthesis, preventing air from entering and resulting in lower color. Furthermore, the reactants dissolved in the solvent to form a homogeneous system, avoiding premature resin polymerization. Consequently, the epoxy equivalent and viscosity were lower. The product of Example 5, due to the use of sodium hydrosulfite, exhibited superior color, epoxy equivalent, and viscosity compared to the product of Comparative Example 4. Additionally, Example 5 employed heating catalysis to accelerate the reaction process during resin synthesis, significantly shortening the reaction time.

[0072] Through the analysis of the above examples and comparative examples, under the same reaction ratio conditions, the product produced by the present invention has the advantages of low color, low epoxy equivalent, low viscosity, and low consumption of epichlorohydrin. The method is simple, the reaction is rapid, and the resin synthesis time is greatly shortened.

Claims

1. An epoxy resin anhydrous system synthesis process characterized by, The process comprises the following steps: (1) phenate preparation: under anaerobic conditions, bisphenol A is dissolved in an organic solvent n-butanol, sodium dithionite is added and mixed uniformly, then sodium hydroxide solid is added, and the reaction is carried out under negative pressure and heating conditions; after the reaction is completed, filtration is carried out to obtain a bisphenol A sodium salt solution; the negative pressure condition is an absolute pressure of 10-30 kPa, the heating condition is 60-80℃, and the reaction time is 1-2 h; (2) resin synthesis reaction: under anaerobic conditions, the bisphenol A sodium salt solution is added to the epoxy chloropropane containing sodium hydroxide solid, and the reaction is heated; (3) post-treatment: after the reaction is completed, solid-liquid separation is carried out, the liquid phase is collected and subjected to vacuum distillation to remove the solvent and unreacted epoxy chloropropane, and an epoxy resin is obtained.

2. The process for synthesis of anhydrous epoxy resin system according to claim 1, wherein: In step (1), the molar ratio of bisphenol A, sodium dithionite and sodium hydroxide is 1:0.001-0.005:2.1-2.

3.

3. The process for synthesis of anhydrous epoxy resin system as claimed in claim 1, wherein: The mass ratio of bisphenol A to the organic solvent is 1:2.5-4.

4. The process for synthesis of anhydrous epoxy resin system according to claim 1, characterized in that: In step (2), the temperature of the heating reaction is 100-130℃, and the reaction time is 10-30 min.

5. The process for synthesis of anhydrous epoxy resin system according to claim 4, wherein: In step (2), the molar feeding ratio of each material is based on bisphenol A in step (1): bisphenol A:sodium hydroxide:epoxy chloropropane = 1:0.01-0.1:4-5.

6. The process for synthesis of anhydrous epoxy resin system according to claim 1, wherein: In step (3), the solid-liquid separation adopts centrifugal separation; the temperature of the vacuum distillation is 120-140℃.

7. The process for synthesis of anhydrous epoxy resin system according to claim 1, wherein: The anaerobic conditions in steps (1) and (2) are achieved and maintained by filling nitrogen into the reaction system.

8. The process for synthesis of anhydrous epoxy resin system as claimed in claim 1, wherein: The anaerobic conditions in steps (1) and (2) are achieved and maintained by filling an inert gas into the reaction system.

9. An epoxy resin characterized by: is synthesized by the epoxy resin anhydrous system synthesis process of any one of claims 1-8.

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