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Synthesis principle of general-purpose epoxy resin

with the high-speed development of the national economy, the quality requirements of epoxy resin are becoming more and more strict in industrial departments such as electrical insulation and electronic components. In order to ensure the reliability of insulation grade and electrical performance, these industrial departments require to improve the purity of epoxy resin and reduce the organic chlorine content. For this reason, a large number of patents and research results abroad introduce how to reduce the organic chlorine content of epoxy resin and improve the purity of epoxy resin every year

where does the organic chlorine in epoxy resin come from? As we all know, common epoxy resins are obtained by polycondensation of binary (or plural) phenols and epichlorohydrin with the participation of alkali. Due to the complexity of the reaction, there are main reactions and secondary reactions in both etherification stage and dehydrochlorination cyclization stage. At the same time, due to the high viscosity of the reaction system and the existence of mesophase, it is difficult to make the reaction tend to be complete

as a result of incomplete reaction, chlorohydrin ether remained in the finished resin. That is commonly known as "hydrolyzed chlorine" or "saponified chlorine" compounds. As a result of the side reaction, compounds called "non hydrolytic chlorine", "fatty chlorine" or "bound chlorine" are formed

the reasons for the formation of organochlorine are studied, which is conducive to adopting different methods to reduce the organochlorine content of epoxy resin. The methods and principles adopted in the comprehensive patent documents are mostly from trying to reduce or inhibit the side reaction and improve the degree of dehydrochlorination reaction. The specific summary is as follows:

in the polycondensation stage, change the main and speed up the construction of safety and health traceability system. In the materials related to food safety, the proportion of side reactions

it is considered that the concentration of alkali in the polycondensation reaction has a great impact on the process of the main and side reactions, and increasing the concentration of alkali in the reaction system is conducive to the progress of the main reaction. Therefore, there are certain requirements for water in the reaction system. In addition to controlling the concentration of alkali, it is also necessary to control the involved raw materials (especially recycled epichlorohydrin) and the water generated by the reaction within a certain content range. The method introduced in the data is to use 50% NaOH aqueous solution as dehydrochlorination agent, add alkali and azeotropic vacuum dehydration at the same time, so that the alkali concentration in the system is always maintained in a concentrated state. The molecular weight of the epoxy resin prepared by this method is, and the organic chlorine value is not more than 0.02%

on the basis of the above, some people further study the use of inert dipolar solvents to inhibit the occurrence of partial reactions. Dimethyl amide, dimethyl sulfoxide and dimethyl sulfone as solvents can improve the selectivity of the reaction and control the side reaction to a minimum. The hydrolyzed chlorine content of the prepared epoxy resin is about 0.02%. However, the high price of solvent used here and less resources limit the industrial application of this method

later, a method called "mesophase transfer method" was developed to produce epoxy resin with low chlorine content. In polycondensation reaction, mesophase catalyst is used to transfer the reaction from one phase (usually aqueous phase) to another phase (organic phase or upper phase), so that the reaction can be realized smoothly. It can improve the conversion of chlorohydrin

ether under relatively easy conditions. In the polycondensation process, the number of holes in polyethylene glycol 4 steel back or steel shoe dissolved in methyl butyl ketone; Alcohol (molecular weight =400) is used as the mesophase transfer catalyst, and concentrated NaOH aqueous solution is used as the dehydrochlorination agent at 110 ℃. The epoxy resin prepared in this way contains 0.0017% hydrolyzed chlorine and 0.041% bound chlorine

there are also methods to supplement dehydrochlorination with the help of mesophase catalyst. It is pointed out that in the polycondensation reaction, 48% NaOH aqueous solution is used as the dehydrochlorination agent, and the reaction is carried out at 80 ℃ with the participation of benzyl triethyl amine chloride and linear or cyclic etheride. The content of hydrolyzed chlorine in the phenolic polycyclic oxygen resin prepared in this way is 0.027% (0.035 without benzyl triethylamine chloride)

further improve the dehydrochlorination reaction in post-treatment

these methods mainly involve the selection of appropriate solvents and the amount of dehydrochlorination agent. Because what is involved here is how to further post-treatment the oligomer that has been polycondensated, so as to reduce the content of organic chlorine in it

as proposed in the method, a two-stage method is used to reduce the content of hydrolyzed chlorine. In the first stage, the epoxy resin is dissolved in organic solvent (toluene or acetone), and 0. 5% is added per mole of epoxy resin Molar alkali metal bromide or iodide, put the mesophase catalyst and% alcohol by weight of epoxy resin into the reactor, and process at ℃. In the second stage, the mixture is treated with an aqueous solution of alkali metal hydroxide of molar amount per mole of epoxy resin Hours at ℃. The content of hydrolyzed chlorine in the epoxy resin treated in this way can be reduced from 0.041% to 0.0003%

epoxy resin with high content can also be dissolved in methyl ethyl ketone, and then treated with concentrated NaOH aqueous solution. With this method, epoxy resin with chlorine content of 0.35% can be treated into resin with hydrolyzed chlorine content of 0.004% and bound chlorine content of 0.067%

in the above example, the finished epoxy resin is dissolved in a suitable solvent and necessary post-treatment is carried out to reduce the chlorine content. In fact, the organic chlorine content of the polycondensated semi-finished product can be analyzed through intermediate testing, and then the amount of alkali can be added according to its chlorine content, which is convenient for the production of epoxy resin with low chlorine content

in fact, the data is that the epoxy oligomer with a chlorine content of 0.88% in the middle test is reacted at 80 ℃ for 2 hours with an alkaline aqueous solution of% concentration in the presence of quaternary amine salt in a hydrophobic organic solvent. Thus, the obtained epoxy oligomer contains 0.03% hydrolyzed chlorine. It is also introduced in the data that the epoxy oligomer with chlorine content of 0.6% is used with 0.% The alkali solution is processed at 100 ℃ for 30 minutes to reduce the chlorine content to 0.02%

according to the research results of a large number of patent materials, it is considered that different types of solvents can be selected for different post-treatment methods. Hydrophobic organic solvents (such as aromatic hydrocarbons: benzene, toluene, xylene) are generally used to ensure that the residual water can be azeotropically evaporated after the completion of dehydrochlorination. These solvents are also suitable for mesophase catalysts. Compared with hydrocarbons, acetone is a solvent with slightly greater polarity, which is conducive to dechlorination when used as a solvent. 2. If there is no problem with the universal experimental machine, the hydrogen process can be carried out. It is introduced that epoxy resin with hydrolyzed chlorine content of 0.041% can be prepared by dehydrochlorination with alkaline aqueous solution in methyl ethyl ketone. Under the same conditions, when toluene is used as solvent, the hydrolyzed chlorine content of the epoxy resin is 0.156%. When ketones are used as solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone or a mixture of ketones and hydrocarbons are commonly used. Aliphatic alcohols with relatively polarity can also be used as solvents, such as n-butanol, isopropanol, etc. It is introduced that dehydrochlorination is carried out in n-butanol solvent with concentrated alkali solution at 60 ℃, and the obtained product has hydrolyzed chlorine of 0.01%. The patent believes that high-purity products can be prepared by using mixed solvents. For example, when methyl ethyl ketone: toluene: dimethyl sulfoxide =5:5:1, the epoxy resin with hydrolyzed chlorine content of 0.0008% and bound chlorine of 0.0206% can be prepared by reacting with 50% KOH solution at 90 ℃ for 3 hours

a large number of data show that the dehydrochlorination agent is generally NaOH, and KOH in some cases. Generally, oh:cl= (1..2): 1. Only in specific occasions can a large amount of alkali be used. For example, in the case of supplementing dehydrochlorination, the excess degree of alkali reaches times

some data show that sodium chloride formed in the reaction process has no slowing effect on the process of dehydrochlorination. On the contrary, a series of patents indicate that dehydrochlorination can be carried out with the participation of some inorganic salts. For example, the method introduced in the data is realized by adding alkali metal halides such as NaCl, KCl and LiCl to the reaction system. When dehydrochlorination is carried out at 65 ℃ with acetone as solvent and 50% NaOH as dehydrochlorination agent, the hydrolyzed chlorine can be reduced to 0.028% (without sodium chloride, the hydrolyzed chlorine content of epoxy resin is 0.046% under this test condition). In addition to adding the above salts, some people have also done experiments to add phosphorus, boron, carboxylic acid or their salts. The amount of these salts is generally (0..5) moles per mole of NaOH. Adding these compounds during the test can reduce the hydrolyzed chlorine content of the processed epoxy oligomer from 0.% Reduce to ≤ 0.02%

maintaining a certain amount of water in the reaction system is very important for the dehydrochlorination reaction. It is considered that this can reduce the hydrolysis reaction and maintain a high concentration of alkali. Data in the reaction process, methyl ethyl ketone is used as the solvent, 40% NaOH aqueous solution is used as the dehydrochlorination agent, and the reaction is carried out at 80 ℃. At the same time, the water is continuously evaporated so that the water content in the reaction system does not exceed 3%. In this way, the hydrolyzed chlorine content of the prepared epoxy resin is 0.002%, and the bound chlorine is 0.052%

there are many foreign patent documents about reducing the organic chlorine content of epoxy resin, which shows that foreign countries attach great importance to the research work in this area. It can also be seen from the practice of epoxy resin plants that have been introduced in China that the hydrolyzed chlorine content of epoxy resin produced by these plants can reach ≤ 0.03%, which can meet the requirements of electrical insulation and electronic components industry. Although the imported devices involve technical secrets, the methods introduced in a large number of patent documents are still very valuable. The key to people's consumption habits is to solve the engineering know-how

source: fine chemicals in the 21st century

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