Method for separating phenol monomer from mixed phenol

Abstract

The invention belongs to the technical field of organic separation, and particularly relates to a method for separating phenol monomers from mixed phenol. The method for separating the phenol monomer from the mixed phenol comprises the following steps: mixing and heating the mixed phenol, an acid catalyst, first phenol and zirconium phosphate for reaction to obtain a cracking product; adding sulfuric acid into the cracking product to form a reaction solution, and after the reaction is finished, filtering to obtain a cracking reforming product of the mixed phenol; and then rectifying and purifying the cracking reforming product in sequence. The method has the beneficial effects that ethyl in 2-ethyl-6-cresol in alkylphenol and isopropyl / propyl in o-isopropyl phenol are removed at a high temperature, 2, 4-xylenol and 2, 5-xylenol are subjected to transposition to obtain 3, 5-xylenol and mixed xylenol with high content of 2, 5-xylenol, and the content of 2, 5-xylenol is increased. And then controlling the temperature to be reduced to a certain temperature, carrying out step-by-step reaction on excessive phenol, ethylene and propylene in the presence of an acidic material catalyst, and rectifying to obtain products such as o-isopropylphenol and p-isopropylphenol.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic separation, and particularly relates to a method for separating phenolic monomers from mixed phenols. Background Art

[0002] The content of 2,4-xylenol / 2,5-xylenol in crude phenol extracted from medium and low temperature coal tar and coal liquefaction tar is relatively high, but the content of o-isopropylphenol / o-propylphenol and 2-ethyl-6-methylphenol is also relatively high. It is impossible to produce high-purity 2,4-xylenol / 2,5-xylenol products. In addition, the boiling points of 4-tert-butyl-2-methyl-6-ethylphenol and 4-tert-butyl-2,5-xylenol, and the boiling points of 6-tert-butyl-2-isopropylphenol and 6-tert-butyl-2,4-xylenol are close. It is difficult to separate 2,4-xylenol / 2,5-xylenol by alkylation, and it is difficult to produce 99.5% 2,4-xylenol and 2,5-xylenol.

[0003] The prior art discloses a process and system for isomerizing xylenol fractions to produce high-value xylenols. The process includes: rectifying and cutting the xylenol fraction to obtain a mixture fraction of 2,4-xylenol and 2,5-xylenol, and a mixed xylenol fraction depleted in 2,4-xylenol and 2,5-xylenol; subjecting the mixture fraction of 2,4-xylenol and 2,5-xylenol to melt crystallization to obtain 2,5-xylenol product and 2,4-xylenol product; subjecting the mixed xylenol fraction depleted in 2,4-xylenol and 2,5-xylenol to isomerization reaction to obtain a xylenol-rich material rich in 2,4-xylenol and 2,5-xylenol; mixing the xylenol fraction, the melt crystallization residue after melt crystallization of the mixture fraction of 2,4-xylenol and 2,5-xylenol, and the xylenol-rich material, and then carrying out rectifying and cutting them together. The invention realizes the separation and high-value utilization of mixed xylenols by isomerizing and enriching specific components in mixed xylenols through isomerization reaction. Since the ratio of 2,4-xylenol to 2,5-xylenol in xylenols extracted from coal tar is (1 - 2):1, and in medium and low-temperature coal tar it is even (1 - 1.3):1, that is, the content of 2,4-xylenol in 2,4-xylenol / 2,5-xylenol is 50 - 65%, and 2,5-xylenol is 35 - 50%. Such a mixture of contents is basically in a eutectic system, and it is difficult to obtain 99% 2,4-xylenol or 2,5-xylenol by solvent crystallization or melt crystallization; the conventional products of the isomerization reaction of the mixed xylenol fraction depleted in 2,4-xylenol and 2,5-xylenol (mainly composed of 2,4-xylenol / 2,5-xylenol, 2,3-xylenol, m,p-ethylphenol and a small amount of 3,5-xylenol) are mainly 3,5-xylenol, 2,5-xylenol, m-ethylphenol, etc., forming a mixture of 2,5-xylenol / 2,4-xylenol (ratio above 3:1), 3,5-xylenol, m,p-ethylphenol (m:p is about 2 - 3:1), 3,4-xylenol, and some 2,3-xylenol. After re-rectification, 2,5-xylenol / 2,4-xylenol (more than 75% of 2,5-xylenol), m,p-ethylphenol / 3,5-xylenol (mainly m-ethylphenol), crude 3,5-xylenol, and crude 3,4-xylenol can be obtained, rather than mainly 2,5-xylenol / 2,4-xylenol. The xylenol products obtained by transposition with different transposition catalysts vary greatly. Therefore, this prior art is not very suitable for medium and low-temperature xylenols, especially not suitable for the separation of xylenols extracted from medium and low-temperature coal tar. Summary of the Invention

[0004] The present application provides a method for separating phenolic monomers from mixed phenols, aiming to solve the problem of having a certain amount of impurities such as o-isopropylphenol / o-propylphenol and 2-ethyl-6-methylphenol in the 2,4-xylenol / 2,5-xylenol mixed phenol extracted from phenol-containing coal tar.

[0005] The present application provides a method for separating phenolic monomers from mixed phenols, including the following steps:

[0006] (1) Mix the mixed phenols, acidic catalyst, first phenol, and zirconium phosphate, heat for the first reaction to obtain the first cracking product; add sulfuric acid to the first cracking product to form a second reaction solution, carry out the second reaction, and after the reaction is completed, filter to obtain the cracking and reforming product of the mixed phenols. The mixed phenols include 2,4-xylenol, 2,5-xylenol, o-isopropylphenol, o-propylphenol, and 2-ethyl-6-methylphenol.

[0007] (2) Carry out rectification treatment on the cracking and reforming product of the mixed phenols to obtain second phenol, o-methyl fraction, m / p-cresol / o-ethylphenol, 2,5-xylenol / 2,4-xylenol / o-isopropylphenol, crude 2,3-xylenol, m / p-ethylphenol / 2,3-xylenol / 3,5-xylenol, crude 3,5-xylenol, crude 3,4-xylenol, and m / p-isopropylphenol / 3,4-xylenol.

[0008] (3) Mix the mixed phenols containing 2,5-xylenol, 2,4-xylenol, and o-isopropylphenol, 6-phenylethyl-2,4-xylenol, sulfuric acid, and styrene, carry out the third reaction, and after the reaction ends, adjust the pH of the reaction solution to 7-8. The reaction solution separates into layers. Filter to remove the water layer, wash the feed liquid with water, then distill off styrene from the obtained feed layer under reduced pressure, and then carry out rectification under reduced pressure to obtain 2,5-xylenol, 6-phenylethyl-2,4-xylenol, and a residue containing 4,6-diphenylethyl-2-isopropylphenol.

[0009] This application uses coal chemical 2,4-xylenol / 2,5-xylenol as the raw material (mainly 2,4-xylenol / 2,5-xylenol extracted from pyrolyzed phenol-containing coal tar, containing impurities such as more o-isopropylphenol and 2-ethyl-6-methylphenol). By using a dealkylation catalyst (which also has a transposition property) and zirconium phosphate, the propylene in o-isopropylphenol is removed to generate phenol at a higher temperature, and the ethyl group in 6-ethyl-2-methylphenol is removed to obtain cresol. Then, catalyst sulfuric acid is added, and the alkylation reaction of ethylene, propylene, and phenol occurs at an appropriate temperature to obtain ethylphenol and isopropylphenol. At the same time, 2,4-xylenol, etc. are transposed to generate 3,5-xylenol, 2,5-xylenol, etc. High-purity 2,5-xylenol / 2,4-xylenol, cresol, ethylphenol, isopropylphenol, and other phenolic products are obtained through rectification. The operation of the present invention is simple and easy, with less three wastes and low production costs.

[0010] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (1), the acidic catalyst includes one or more of silica, aluminum oxide, chromium oxide, strontium oxide, and molecular sieve.

[0011] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the acidic catalyst includes silica, aluminum oxide, and chromium oxide.

[0012] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the mass ratio of the silica, aluminum oxide, and chromium oxide is (10 - 5000):100:(1 - 10).

[0013] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the mass ratio of the mixed phenols, the acidic catalyst, the first phenol, and the zirconium phosphate is 100:(10 - 30):(20 - 200):(0.05 - 3).

[0014] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the first reaction is carried out in a sealed hydrogen atmosphere, the temperature of the first reaction is 280 - 400 °C, and the time of the first reaction is 4 - 12 h.

[0015] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the mixed phenols include the following raw materials in parts by weight: 50 - 97 parts of 2,4 - xylenol / 2,5 - xylenol, 1 - 30 parts of o - isopropylphenol / n - propylphenol, and 1 - 20 parts of 2 - ethyl - 6 - methylphenol.

[0016] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the first phenol is coking - grade phenol with a mass percentage of 90% - 99%, and the content of sulfur - and nitrogen - containing mixtures is ≥100 ppm.

[0017] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the second phenol is petrochemical - grade phenol, and the content of sulfur - and nitrogen - containing mixtures is ≤5 ppm.

[0018] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (1), the cracking and reforming product includes the second phenol, cresol, ethylphenol, o - isopropylphenol, m - isopropylphenol, p - isopropylphenol, and xylenol.

[0019] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the cresol in the cracking and reforming product is a mixed phenol mainly composed of m - cresol.

[0020] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the cresol in the cracking and reforming product includes o - cresol, p - cresol, and m - cresol.

[0021] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the ethylphenol in the cracking and reforming product is a mixed phenol mainly composed of m - ethylphenol.

[0022] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the ethylphenols in the cracking reforming product include o-ethylphenol, m-ethylphenol, and p-ethylphenol.

[0023] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the xylenols in the cracking reforming product are mixed phenols mainly composed of 2,5-xylenol and 3,5-xylenol.

[0024] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the xylenols in the cracking reforming product include 2,4-xylenol, 2,5-xylenol, 3,5-xylenol, 3,4-xylenol, and 2,3-xylenol.

[0025] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (1), the amount of sulfuric acid added to the first cracking product is 0.05%-2% of the mass of the mixed phenols.

[0026] According to some embodiments of the method for separating phenolic monomers from mixed phenols, after adding sulfuric acid to the first cracking product, under the condition that the cooling rate is 80-100 °C / h, the second reaction solution is cooled to 280-300 °C, and then under the condition that the cooling rate is 10-20 °C / h, the second reaction solution is cooled to 210-250 °C and kept at a constant temperature for reaction for 2-6 h until the pressure is stable (synthesizing ethylphenol); then under the condition that the cooling rate is 10-20 °C / h, the second reaction solution is cooled to 150-200 °C and kept at a constant temperature for reaction for 2-6 h to synthesize isopropylphenol until the pressure is stable and the second reaction ends.

[0027] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (2), the vacuum degree of the rectification is -0.085 to -0.095 MPa.

[0028] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (3), the mass ratio of the mixed phenols containing 2,5-xylenol, 2,4-xylenol, and o-isopropylphenol, 6-phenylethyl-2,4-xylenol, and sulfuric acid is 100:(0.1-1):(1-5).

[0029] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the molar ratio of the mixed phenols containing 2,5-xylenol, 2,4-xylenol, and o-isopropylphenol to styrene is 1:(1.1-3).

[0030] According to some embodiments of the method for separating phenolic monomers from mixed phenols, in step (3), the temperature of the third reaction is 60-120 °C, and the time of the third reaction is 5-15 h.

[0031] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the method further includes mixing the residue containing 4,6-diphenylethyl-2-isopropylphenol with sulfuric acid to carry out a fourth reaction. After the reaction is completed, the pH of the reaction solution is adjusted to 7-8. The reaction solution is layered, the aqueous layer is filtered off, and the feed liquid is washed with water. Then, the obtained feed layer is subjected to vacuum distillation to obtain o-isopropylphenol.

[0032] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the mass ratio of the residue containing 4,6-diphenylethyl-2-isopropylphenol to sulfuric acid is 100:(0.5-2).

[0033] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the temperature of the fourth reaction is 180-200 °C, and the time of the fourth reaction is 1-4 h.

[0034] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the method further includes mixing 6-phenylethyl-2,4-xylenol with sulfuric acid to carry out a reaction. After the reaction is completed, the pH of the reaction solution is adjusted to 7-8. The reaction solution is layered, the aqueous layer is filtered off, and the feed liquid is washed with water. Then, the obtained feed layer is subjected to vacuum distillation to obtain 2,4-xylenol.

[0035] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the mass ratio of 6-phenylethyl-2,4-xylenol to sulfuric acid is 100:(0.5-2).

[0036] According to some embodiments of the method for separating phenolic monomers from mixed phenols, the temperature of the reaction is 180-200 °C, and the time of the reaction is 0.5-3 h.

[0037] The beneficial effects of the present application include: The method for separating phenolic monomers from mixed phenols in the present application removes the ethyl group in 2-ethyl-6-methylphenol and the isopropyl / propyl group in o-isopropylphenol in alkylphenols by high temperature. 2,4-xylenol and 2,5-xylenol are transposed to obtain a mixed xylenol with a high content of 3,5-xylenol and 2,5-xylenol. At the same time, more xylenol products such as 3,5-xylenol, 2,3-xylenol, and 3,4-xylenol with a mass percentage of 99% are also obtained. Then, the temperature is controlled to drop to a certain temperature, and ethylene and propylene are reacted with excess phenol at different temperatures under the catalyst of an acidic substance, and o-ethylphenol, p-ethylphenol, o-isopropylphenol, p-isopropylphenol and other products are obtained by rectification.

[0038] The method for separating phenolic monomers from mixed phenols according to the present application reacts the mixed phenols with styrene to obtain a high-efficiency polymerization inhibitor and antioxidant 6-phenylethyl-2,4-xylenol, and a pharmaceutical intermediate 2,5-xylenol; reacting the crude 3,4-xylenol with isobutene can obtain 99% 3,4-xylenol and achieve the separation of 3,4-xylenol from 3,5-xylenol and m,p-cumylphenol. Detailed Embodiments

[0039] The embodiments of the present invention will be described in detail below. The examples of the embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0040] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0041] The embodiments of the present application provide a method for separating phenolic monomers from mixed phenols, including the following steps:

[0042] (1) Mix the mixed phenols, an acidic catalyst, a first phenol, and zirconium phosphate, heat for a first reaction to obtain a first cracking product; add sulfuric acid to the first cracking product to form a second reaction solution, carry out a second reaction, and after the reaction is completed, filter to obtain a cracking and reforming product of the mixed phenols; the mixed phenols include 2,4-xylenol, 2,5-xylenol, o-cumylphenol, o-propylphenol, and 2-ethyl-6-methylphenol;

[0043] (2) Carry out rectification treatment on the cracking and reforming product of the mixed phenols to obtain a second phenol, an o-methyl fraction, m,p-cresol / o-ethylphenol, 2,5-xylenol / 2,4-xylenol / o-cumylphenol, a crude 2,3-xylenol, m,p-ethylphenol / 2,3-xylenol / 3,5-xylenol, a crude 3,5-xylenol, a crude 3,4-xylenol, and m,p-cumylphenol / 3,4-xylenol;

[0044] (3) Mix the mixed phenols containing 2,5-xylenol, 2,4-xylenol and o-isopropylphenol, 6-phenethyl-2,4-xylenol, sulfuric acid and styrene, and carry out the third reaction. After the reaction is completed, adjust the pH of the reaction solution to 7-8. The reaction solution will be stratified. Filter off the aqueous layer and wash the feed liquid with water. Then distill off styrene from the obtained feed layer under reduced pressure, and then carry out vacuum rectification to obtain 2,5-xylenol, 6-phenethyl-2,4-xylenol and a residue containing 4,6-diphenethyl-2-isopropylphenol.

[0045] By controlling the reaction temperature and using appropriate catalysts, the method described in this application basically does not occur demethylation of xylenol and transfer reactions of methyl, ethyl, etc. between different xylenol molecules (mainly transposition reactions of methyl, ethyl, etc. on the same molecule) in the dealkylation reaction. Therefore, the cresol obtained by the demethylation transfer of xylenol and the reaction with phenol can be basically ignored; the mixture is rectified to obtain crude 2,5-xylenol, crude 3,5-xylenol, crude 2,3-xylenol, crude 3,4-xylenol, or high-purity 2,5-xylenol / 2,4-xylenol, 3,5-xylenol, etc. The crude product is further refined to obtain pure phenolic products. That is, the method described in this application removes o-isopropylphenol / o-propylphenol and 2-ethyl-6-cresol from the mixed phenols to obtain high-purity 2,5-xylenol / 2,4-xylenol, and at the same time basically realizes the purpose of converting o-isopropylphenol / o-propylphenol into isopropylphenol and 2-ethyl-6-cresol into cresol and ethylphenol.

[0046] By using a dealkylation catalyst and zirconium phosphate, the method described in this application removes propylene from o-isopropylphenol to generate phenol at a relatively high reaction temperature, removes the ethyl group from 6-ethyl-2-cresol to obtain cresol, and then controls the alkylation reaction of ethylene and propylene with phenol at an appropriate temperature to obtain ethylphenol and isopropylphenol; at the same time, 2,4-xylenol, etc. are transposed to generate 3,5-xylenol, 2,5-xylenol, etc. High-purity phenolic products such as 2,5-xylenol / 2,4-xylenol, cresol, ethylphenol, and isopropylphenol are obtained by rectification. The operation of the present invention is simple and easy, with less three wastes and low production cost.

[0047] In some embodiments of this application, in step (1), the acidic catalyst includes one or more of silica, aluminum oxide, chromium oxide, strontium oxide and molecular sieve.

[0048] The acidic catalyst described in this application can cause 2-ethyl-6-methylphenol to de-ethylate to form ethylene and cresol, and can cause o-isopropylphenol to de-isopropylate to form propylene and phenol. Adding zirconium phosphate can promote this reaction; at the same time, the addition of acidic catalysts such as chromium oxide and zirconium phosphate can cause the transposition reaction of cresol, 2,4-xylenol, etc., to form a cresol mixture mainly composed of m-cresol, and a mixed xylenol mainly composed of 3,5-xylenol and 2,5-xylenol. After subsequent alkylation, the transposition reaction of ethylphenol will also occur to form a mixed ethylphenol mainly composed of m-ethylphenol, etc.

[0049] In some embodiments of this application, the acidic catalyst includes silica, aluminum oxide, and chromium oxide. More preferably, the mass ratio of silica, aluminum oxide, and chromium oxide is (10 - 5000):100:(1 - 10).

[0050] In some embodiments of this application, the mass ratio of the mixed phenol, the acidic catalyst, the first phenol, and the zirconium phosphate is 100:(10 - 30):(20 - 200):(0.05 - 3).

[0051] In some embodiments of this application, the first reaction is carried out in a closed hydrogen atmosphere. The temperature of the first reaction is 280 - 400 °C, such as 280 °C, 300 °C, 320 °C, 350 °C, 400 °C, etc. The time of the first reaction is 4 - 12 h, such as 4 h, 5 h, 6 h, 8 h, 10 h, 12 h, etc. The hydrogen atmosphere is beneficial to removing impurities and can also prevent the oxidation of phenol.

[0052] In some embodiments of this application, the mixed phenol includes the following raw materials in parts by weight: 50 - 97 parts of 2,4-xylenol / 2,5-xylenol, 1 - 30 parts of o-isopropylphenol / propylphenol, and 1 - 20 parts of 2-ethyl-6-methylphenol.

[0053] In some embodiments of this application, the first phenol is coking-grade phenol with a mass percentage of 90% - 99%. The content of nitrogen and sulfur compounds is ≥100 ppm.

[0054] In some embodiments of this application, the second phenol is petrochemical-grade phenol, and the content of nitrogen and sulfur compounds is ≤5 ppm.

[0055] In some embodiments of this application, in step (1), the cracking and reforming product includes the second phenol, cresol, ethylphenol, o-isopropylphenol, m-isopropylphenol, p-isopropylphenol, and xylenol.

[0056] In some embodiments of this application, the cresol in the cracking and reforming product is a mixed phenol mainly composed of m-cresol.

[0057] In some embodiments of the present application, the cresols in the cracking and reforming product include o-cresol, p-cresol, and m-cresol.

[0058] In some embodiments of the present application, the ethylphenols in the cracking and reforming product are a mixed phenol with m-ethylphenol as the main raw material.

[0059] In some embodiments of the present application, the ethylphenols in the cracking and reforming product include o-ethylphenol, m-ethylphenol, and p-ethylphenol.

[0060] In some embodiments of the present application, the xylenols in the cracking and reforming product are a mixed phenol with 2,5-xylenol and 3,5-xylenol as the main raw materials.

[0061] In some embodiments of the present application, the xylenols in the cracking and reforming product include 2,4-xylenol, 2,5-xylenol, 3,5-xylenol, 3,4-xylenol, and 2,3-xylenol.

[0062] In some embodiments of the present application, in step (1), the amount of sulfuric acid added to the first cracking product is 0.05%-2% of the mass of the mixed phenol. Sulfuric acid is a catalyst for the ethylation and isopropylation reactions of phenolic substances. A certain amount of sulfuric acid needs to be added to carry out the ethylation reaction to generate ethylphenol at a certain temperature and the isopropylation reaction to generate isopropylphenol at a certain temperature. Controlling the amount of sulfuric acid within a certain range can reduce the occurrence of the reversible reactions of deethylation and deisopropylation.

[0063] In some embodiments of the present application, after adding sulfuric acid to the first cracking product, under the condition that the cooling rate is 80-100°C / h, the second reaction solution is cooled to 280-300°C, and then under the condition that the cooling rate is 10-20°C / h, the second reaction solution is cooled to 210-250°C and kept warm for reaction for 2-6 h until the pressure is stable; then under the condition that the cooling rate is 10-20°C / h, the second reaction solution is cooled to 150-200°C and kept warm for reaction for 2-6 h, and the second reaction ends.

[0064] Since the de-ethylation and de-propylation reactions of ethylphenol and propylphenol mainly occur above 280°C, to save time, the cooling rate should be faster. For the subsequent alkylation reactions of phenol with ethylene and propylene, which require a certain amount of time and to reduce side reactions, it is necessary to ensure the ethylatation reaction time above 200°C (the main reaction above 200 - 250°C is the production of ethylphenol through ethylatation, and above 200°C, isopropylphenol is unstable. Even if propylene reacts with phenol, most of the propylene will still be removed). By using slow cooling (cooling rate of 10 - 20°C / h), sufficient time is reserved for the reactions within this temperature range. Below 200°C, the main reaction is isopropylation (the main reaction between 150 - 200°C is the production of isopropylphenol from propylene and phenol), and slow cooling (cooling rate of 10 - 20°C / h) is also used to reserve sufficient time for the reactions within this temperature range.

[0065] In some embodiments of the present application, in step (2), the vacuum degree of the rectification is -0.085 to -0.095 MPa, such as -0.085 MPa, -0.09 MPa, -0.092 MPa, -0.095 MPa, etc.

[0066] In some embodiments of the present application, in step (3), the mass ratio of the mixed phenol containing 2,5-xylenol, 2,4-xylenol and o-isopropylphenol, 6-phenethyl-2,4-xylenol and sulfuric acid is 100:(0.1 - 1):(1 - 5); such as 100:1, 100:2, 100:3, 100:5, etc.

[0067] By controlling the mass ratio of the mixed phenol containing 2,5-xylenol, 2,4-xylenol and o-isopropylphenol and sulfuric acid, and adding high-efficiency polymerization inhibitors such as 6-phenethyl-2,4-xylenol, etc., can the phenethylation reaction rate be maximally ensured and the occurrence of styrene dealkylation and styrene polymerization reactions be prevented; similarly, the de-phenethylation reaction also needs to be controlled at an appropriate temperature and with an appropriate amount to ensure the de-phenethylation rate and prevent the reversible phenethylation reaction.

[0068] In some embodiments of the present application, the molar ratio of the mixed phenol containing 2,5-xylenol, 2,4-xylenol and o-isopropylphenol to styrene is 1:(1.1 - 3), such as 1:1.1, 1:1.8, 1:2, 1:2.6, 1:3, etc.

[0069] In some embodiments of the present application, in step (3), the temperature of the third reaction is 60 - 120°C, such as 60°C, 80°C, 93°C, 105°C, 113°C, 120°C, etc., and the time of the third reaction is 5 - 15 h, such as 5 h, 7 h, 9 h, 10 h, 12 h, 15 h, etc.

[0070] In some embodiments of the present application, the method further includes mixing the residue containing 4,6-diphenylethyl-2-isopropylphenol with sulfuric acid to carry out a fourth reaction. After the reaction is completed, the pH of the reaction solution is adjusted to 7-8. The reaction solution is layered, the aqueous layer is filtered off, the material solution is washed with water, and then the obtained material layer is subjected to vacuum distillation to obtain o-isopropylphenol.

[0071] In some embodiments of the present application, the mass ratio of the residue containing 4,6-diphenylethyl-2-isopropylphenol to sulfuric acid is 100:(0.5-2); for example, 100:0.5, 100:0.8, 100:1.2, 100:2, etc.

[0072] In some embodiments of the present application, the temperature of the fourth reaction is 180-200 °C, such as 180 °C, 185 °C, 190 °C, 193 °C, 200 °C, etc., and the time of the fourth reaction is 1-4 h, such as 1 h, 2 h, 3 h, 4 h, etc.

[0073] In some embodiments of the present application, the method further includes mixing 6-phenylethyl-2,4-xylenol with sulfuric acid to carry out a reaction. After the reaction is completed, the pH of the reaction solution is adjusted to 7-8. The reaction solution is layered, the aqueous layer is filtered off, the material solution is washed with water, and then the obtained material layer is subjected to vacuum distillation to obtain 2,4-xylenol.

[0074] In some embodiments of the present application, the mass ratio of 6-phenylethyl-2,4-xylenol to sulfuric acid is 100:(0.5-2).

[0075] In some embodiments of the present application, the temperature of the reaction is 180-200 °C, such as 180 °C, 190 °C, 195 °C, 200 °C, etc., and the time of the reaction is 0.5-3 h, such as 0.5 h, 0.8 h, 1.2 h, 2.3 h, 3 h, etc.

[0076] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0077] Example

[0078] A method for separating phenolic monomers from mixed phenols includes the following steps:

[0079] (1) Charge 1700 parts of acidic catalyst (mass percentage of silica, aluminum oxide, and chromium oxide is 200:100:10), 100 parts of zirconium phosphate into a stainless-steel high-pressure reactor with an external stainless-steel condenser and an internal coil. Add 8500.8 parts of mixed phenols (where the mixed phenols include 3778.6 parts of 2,4-xylenol, 2538.2 parts of 2,5-xylenol, 1536 parts of o-isopropylphenol and o-propylphenol, 648 parts of 2-ethyl-6-methylphenol), 3000 parts of the first phenol with a mass percentage of 95.3% (nitrogen-containing compounds 165 ppm, sulfur-containing compounds 133 ppm). Seal the reactor, introduce 5 parts of hydrogen, heat it up to 350 °C and react for 7 hours. When the pressure in the kettle rises to 5.1 MPa and no longer rises, end the reaction. Rapidly cool the heat transfer oil in the internal coil by programmed cooling (the temperature of the heat transfer oil gradually decreases slowly from a high temperature to 80 °C). Cool the above reaction solution to 280 °C at a cooling rate of 80 °C / h, constantly add 80 parts of 98% sulfuric acid under constant pressure to form a second reaction solution, and then cool the second reaction solution to 240 °C at a cooling rate of 20 °C / h and keep it warm for 3 h, observing that the reaction pressure has no obvious drop; continue to slowly cool it to 170 °C at 20 °C / h and keep it warm for 4 h. Finally, the pressure in the kettle stabilizes at 1.2 Mpa and remains unchanged. Continue to cool it to 150 °C, discharge a small amount of gas in the reactor to relieve the pressure to atmospheric pressure, let the gas out and cool it slightly, displace it with nitrogen for 0.5 h, and filter to obtain 11406.7 parts of the cracking and reforming product of mixed phenols, including 80 parts of sulfuric acid; 2331.2 parts of phenol, 80.1 parts of o-cresol, 89.6 parts of p-cresol, 371.8 parts of m-cresol, 56.1 parts of o-ethylphenol, 363.7 parts of m-ethylphenol, 140.3 parts of p-ethylphenol, 526.6 parts of o-isopropylphenol, 753 parts of m-isopropylphenol, 224.4 parts of p-isopropylphenol, 1004.8 parts of 2,4-xylenol, 3889.9 parts of 2,5-xylenol, 925.4 parts of 3,5-xylenol, 221.4 parts of 3,4-xylenol, 182.1 parts of 2,3-xylenol, and 166.3 parts of others).

[0080] (2) Add 11406.7 parts of the pyrolysis and reforming product of mixed phenols to the bottom of a distillation column (100 parts of dimethyl diphenyl ether high-boiling solvent have already been added to the bottom, with 250 theoretical plates), and conduct vacuum distillation (vacuum degree -0.088 MPa, reflux ratio 20:1) to obtain 2310.2 parts of second phenol with a mass percentage content of 99.6% (nitrides 1.8 ppm, sulfides 0.8 ppm), 91 parts of o-cresol fraction with a mass percentage content of 76.37% (phenol 6.8 parts, o-cresol 69.5 parts, p-cresol 2.6 parts, m-cresol 10.5 parts, o-ethylphenol 1.6 parts), 475.3 parts of m,p-cresol / o-ethylphenol with a mass percentage content of 99.87% (o-cresol 0.6 parts, p-cresol 81 parts, m-cresol 342.2 parts, o-ethylphenol 51.5 parts; nitrides 1.2 ppm, sulfides 0.6 ppm), 5355.6 parts of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol (p-cresol 5.1 parts, m-cresol 15.4 parts, o-ethylphenol 2.4 parts, 2,4-xylenol 985.6 parts, 2,5-xylenol 3819.7 parts, o-isopropylphenol 517.2 parts, 2,3-xylenol 10.2 parts, and 2,5-xylenol accounts for 71.32%), 213.2 parts of crude 2,3-xylenol with a mass percentage content of 72.14% (2,4-xylenol 8.3 parts, 2,5-xylenol 28.2 parts, o-isopropylphenol 3.7 parts, 2,3-xylenol 153.8 parts, 3,5-xylenol 0.8 parts, m-ethylphenol 13.3 parts, p-ethylphenol 5.1 parts), 468.1 parts of m,p-ethylphenol / 2,3-xylenol / 3,5-xylenol with a mass percentage content of 99.14% (2,4-xylenol 0.8 parts, 2,5-xylenol 3.1 parts, o-isopropylphenol 0.4 parts, 2,3-xylenol 12.5 parts, 3,5-xylenol 12.3 parts, m-ethylphenol 316.8 parts, p-ethylphenol 122.2 parts), 971.3 parts of crude 3,5-xylenol with a mass percentage content of 91.72% (2,3-xylenol 3.8 parts, 3,5-xylenol 890.9 parts, m-ethylphenol 29.5 parts, p-ethylphenol 11.5 parts, 3,4-xylenol 35.6 parts), 218.8 parts of crude 3,4-xylenol with a mass percentage content of 60.41% (3,5-xylenol 12.1 parts, m-ethylphenol 0.3 parts, p-ethylphenol 0.1 part, m-isopropylphenol 33.9 parts, p-isopropylphenol 10.1 parts, 3,4-xylenol 162.4 parts), and 950.3 parts of m,p-isopropylphenol / 3,4-xylenol with a mass percentage content of 99.41% (m-isopropylphenol 711.6 parts, p-isopropylphenol 212 parts, 3,4-xylenol 21.1 parts, others 5.6 parts, and the ratio of m-isopropylphenol to p-isopropylphenol is 3.35:1; nitrides 2.1 ppm, sulfides 0.9 ppm).

[0081] 99.6% phenol, 99.87% m / p-cresol / o-ethylphenol, 99.14% m / p-ethylphenol / 2,3-xylenol / 3,5-xylenol, 99.41% m / p-isopropylphenol / 3,4-xylenol are for external sale, mainly used in the production of enamel wire paint, photoresist, and flame-retardant plasticizer.

[0082] 76.37% o-cresol fraction is used to extract petrochemical-grade 99.5% o-cresol.

[0083] (3) Refining and separation

[0084] 3.1. Alkylation separation of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol

[0085] Add 1000 parts of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol (0.9 part of p-cresol, 2.9 parts of m-cresol, 0.4 part of o-ethylphenol, 184 parts of 2,4-xylenol, 713.2 parts of 2,5-xylenol, 96.6 parts of o-isopropylphenol, 1.9 parts of 2,3-xylenol, 2,5-xylenol accounting for 71.32%) obtained in the second step into the reactor and add it to the bottom of the distillation column (250 theoretical plates) for distillation (-0.085 MPa, reflux ratio 20:1) to obtain 979.6 parts of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol with a mass percentage content of 99.9% (181.2 parts of 2,4-xylenol, 702.5 parts of 2,5-xylenol, 95.1 parts of o-isopropylphenol, 0.8 part of others).

[0086] Add 979.6 parts of the mixed phenol of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol with a mass percentage content of 99.9% (181.2 parts of 2,4-xylenol, 702.5 parts of 2,5-xylenol, 95.1 parts of o-isopropylphenol, 0.8 part of others), 1300 parts of styrene (the amount of styrene is 1.45 times the molar mass of 2,5 / 2,4-xylenol), 2 parts of 6-phenethyl-2,4-xylenol, and 30 parts of 98% sulfuric acid into the reactor. Replace with nitrogen three times, start stirring, heat up to 80 °C and react for 8 hours. Take a sample for analysis. The content of 6-phenethyl-2-isopropylphenol being 0.28% is qualified; then add 77.6 parts of sodium hydroxide with a mass concentration of 31% to the reaction solution to neutralize the pH of the reaction solution to 7.5, layer separation. The material layer is washed once with another 100 parts of water, and all the water is separated. The material layer is distilled under reduced pressure to remove styrene and the previous fraction of 982 parts (the previous fraction refers to a small amount of un-phenethylated raw materials and a small amount of 2,5-xylenol), and then distilled under reduced pressure (250 theoretical plates of the column, -0.095 MPa, reflux ratio 15:1) to obtain 670.5 parts of 2,5-xylenol with a mass percentage content of 99.7%, 317.8 parts of 6-phenethyl-2,4-xylenol with a mass percentage content of 99.6%, and 240.5 parts of still residue (containing 239.3 parts of 4,6-diphenethyl-2-isopropylphenol);

[0087] Add 240.5 parts of the still residue into the decomposition kettle, then add 2.5 parts of concentrated sulfuric acid into the decomposition kettle. Heat up to 190 °C with stirring and maintain for 2 h. Stop the reaction when the content of 6-phenethyl-2-isopropylphenol detected by gas chromatography is 0.19%. Cool down slightly and neutralize the reaction solution with 6.8 parts of sodium hydroxide aqueous solution with a mass concentration of 31% to neutrality. Perform vacuum rectification (theoretical number of plates in the column is 250, -0.085 MPa, reflux ratio is 15:1) to obtain 90.7 parts of o-isopropylphenol with a mass percentage content of 99.7%, the yield is 95.6%, and 142.5 parts of recycled styrene are reserved for use.

[0088] 3.2. Synthesis of 2,4-xylenol

[0089] Add 100 parts of 99.6% 6-phenethyl-2,4-xylenol obtained in step 3.1 into the decomposition kettle, then add 1 part of 98% sulfuric acid into the decomposition kettle. Heat up to 195 °C with stirring and maintain for 1.5 h. Stop the reaction when the content of 6-phenethyl-2,4-xylenol detected by gas chromatography is 0.22%. Cool down slightly and neutralize the reaction solution with sodium hydroxide aqueous solution with a mass concentration of 31% to neutrality. Perform vacuum rectification (theoretical number of plates in the column is 250, -0.085 MPa, reflux ratio is 5:1) to obtain 51.7 parts of 2,4-xylenol with a mass percentage content of 99.9%, the yield is 95.7%, and 45.1 parts of recycled styrene are reserved for use.

[0090] 99.7% 2,5-xylenol, 99.6% 6-phenethyl-2,4-xylenol, and 99.7% o-isopropylphenol are sold as products.

[0091] 3.4. Separation of crude 2,3-xylenol

[0092] Add 213.2 parts of the crude 2,3-xylenol obtained in step (2) into the bottom of the rectification column (theoretical number of plates is 250) for rectification (-0.085 MPa, reflux ratio is 20:1) to obtain 38.3 parts of 2,5-xylenol / 2,4-xylenol / o-isopropylphenol with a mass percentage content of 99.21% (including 7.9 parts of 2,4-xylenol, 26.6 parts of 2,5-xylenol, 3.5 parts of o-isopropylphenol, and 0.3 parts of 2,3-xylenol), 157.2 parts of 2,3-xylenol with a mass percentage content of 96.56% (including 0.3 parts of 2,4-xylenol, 1.2 parts of 2,5-xylenol, 0.1 part of o-isopropylphenol, 151.8 parts of 2,3-xylenol, 2.7 parts of m-ethylphenol, and 1.1 parts of p-ethylphenol), and 15.5 parts of m,p-ethylphenol / 3,5-xylenol with a mass percentage content of 99.35% (including 0.1 part of 2,3-xylenol, 0.7 part of 3,5-xylenol, 10.4 parts of m-ethylphenol, and 4.3 parts of p-ethylphenol).

[0093] 99.21% 2,5-xylenol / 2,4-xylenol is separated by the alkylation separation method of 2,5-xylenol / 2,4-xylenol / o-cumenol in Step 3.1.

[0094] 99.35% m,p-ethylphenol / 3,5-xylenol is used for synthesizing non-toxic flame retardant plasticizer tris(ethylphenyl) phosphate for aerospace.

[0095] 3.5. Solvent crystallization of 2,3-xylenol

[0096] Add 157.2 parts of 2,3-xylenol with a mass percentage of 96.56% and 100 parts of methanol into the reactor, start stirring, heat up to 60 °C to completely dissolve the materials, then first cool down to 36 °C with circulating water for 2 h, and then cool down to -10 °C with freezing brine in 3 h, keep warm for 2 h, filter, drain, and dry to obtain 144.7 parts of 99.6% 2,3-xylenol, and the refined yield is 94.4%.

[0097] 3.6. Refining of 3,5-xylenol crude product

[0098] Add 971.3 parts of 3,5-xylenol crude product with a mass percentage of 91.72% in Step (2) and 900 parts of methanol into the reactor, start stirring, heat up to 60 °C to completely dissolve the materials, then first cool down to 33 °C with circulating water for 2 h, and then cool down to 0 °C with freezing brine in 3 h, keep warm for 2 h, filter, drain, and dry to obtain 765.5 parts of 99.85% 3,5-xylenol, and the refined yield is 85.8%.

[0099] 3.7. Alkylation separation of 3,4-xylenol

[0100] Add 218.8 parts of 3,4-xylenol crude product with a mass percentage of 60.41% in step (2) (containing 12.1 parts of 3,5-xylenol, 33.9 parts of m-cumenol, 10.1 parts of p-cumenol, 162.4 parts of 3,4-xylenol, and 0.4 parts of m,p-ethylphenol) and 5 parts of 98% sulfuric acid (the dosage is 2.29% of the mass of 3,4-xylenol crude product) into the reactor. Replace with nitrogen three times, start stirring, heat up to 90 °C and start to introduce isobutene for reaction. The introduction time is 6 h. After finishing the introduction, keep the temperature for reaction for 2 h and take samples for analysis. The content of 6-tert-butyl-3-isopropylphenol is 0.31%, which is qualified. A total of 175 parts of isobutene are introduced (the dosage of isobutene is 1.75 times the molar mass of 3,4-xylenol crude product); add 13 parts of 31% sodium hydroxide aqueous solution to neutralize to pH 7.5, separate the layers, wash the material layer with 15 parts of water once again, drain all the water, distill off diisobutene and the first fraction of 15.5 parts under reduced pressure from the material layer, and then carry out vacuum rectification (the number of theoretical plates in the column is 250, -0.095 MPa, reflux ratio 15:1) to obtain 10.1 parts of 99.5% 3,5-xylenol, 191.4 parts of 98.5% 6-tert-butyl-3,4-xylenol, 37.3 parts of 98.3% 6-tert-butyl-3-isopropylphenol, and 18.8 parts of still residue (containing 18.2 parts of 2,6-di-tert-butyl-4-isopropylphenol and 0.6 parts of others).

[0101] Add 191.4 parts of 6-tert-butyl-3,4-xylenol with a mass percentage of 98.5% into the decomposition kettle, and then add 2 parts of concentrated sulfuric acid (the dosage is 1.04% of the mass of 6-tert-butyl-3,4-xylenol crude product) into the decomposition kettle. Heat up to 195 °C under stirring and maintain for 2 h. Stop the reaction when the content of 6-tert-butyl-3,4-xylenol is 0.13% detected by gas chromatography. Cool down slightly and neutralize to neutral with 5.3 parts of 31% sodium hydroxide aqueous solution. Carry out vacuum rectification (the number of theoretical plates in the column is 250, -0.085 MPa, reflux ratio 15:1) to obtain 122.5 parts of 99.7% 3,4-xylenol, and the yield is 94.5%.

[0102] Add 37.3 parts of 6-tert-butyl-3-isopropylphenol with a mass percentage of 98.3% into the decomposition kettle, and then add 0.5 parts of concentrated sulfuric acid (the dosage is 1.34% of the mass of 6-tert-butyl-3-isopropylphenol). Heat up to 180 °C under stirring and maintain for 3 h. Stop the reaction when the content of 6-tert-butyl-3-isopropylphenol is 0.42% detected by gas chromatography. Cool down slightly and neutralize to neutral with 0.4 parts of 31% liquid alkali. Carry out vacuum rectification (the number of theoretical plates in the column is 250, -0.085 MPa, reflux ratio 15:1) to obtain 24.9 parts of 99.3% m-cumenol, and the yield is 93.8%.

[0103] The kettle residue is added into the decomposition kettle, 0.2 parts of concentrated sulfuric acid is added, the temperature is raised to 190 °C under stirring and maintained for 2.5 h. When the content of 2-tert-butyl-4-isopropylphenol in the gas chromatogram detection is 0.32%, the reaction is stopped. After slightly cooling, 0.52 parts of an aqueous sodium hydroxide solution with a mass concentration of 31% is used for neutralization to pH 7.5. Then, vacuum rectification (the number of theoretical plates in the column is 250, -0.085 MPa, reflux ratio 25:1) is carried out to obtain 9.1 parts of p-isopropylphenol with a purity of 99.6%, and the yield is 91.5%.

[0104] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limitations of the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A method for separating phenol monomers from mixed phenols, characterized in that: The following steps are involved: (1) Mixing a mixed phenol, an acidic catalyst, a first phenol and zirconium phosphate, heating to perform a first reaction, and obtaining a first cracking product; adding sulfuric acid to the first cracking product to form a second reaction solution, and performing a second reaction; after the reaction is completed, filtering to obtain a cracking and reforming product of the mixed phenol; the mixed phenol includes 2,4-xylenol, 2,5-xylenol, o-isopropylphenol, o-propylphenol and 2-ethyl-6-methylphenol; (2) subjecting the cracking and reforming products of the mixed phenol to distillation to obtain a second phenol, an o-cresol fraction, m-p-cresol / o-ethylphenol, 2,5-xylenol / 2,4-xylenol / o-isopropylphenol, crude 2,3-xylenol, m-p-ethylphenol / 2,3-xylenol / 3,5-xylenol, crude 3,5-xylenol, crude 3,4-xylenol, and m-p-isopropylphenol / 3,4-xylenol; (3) A mixed phenol containing 2,5-dimethylphenol, 2,4-dimethylphenol and o-isopropylphenol, 6-phenylethyl-2,4-dimethylphenol, sulfuric acid and styrene are mixed to carry out a third reaction. After the reaction is completed, the pH of the reaction solution is adjusted to 7-8, and the reaction solution is stratified. The water layer is filtered to remove the water layer and the feed liquid is washed with water. The obtained feed layer is then evaporated under reduced pressure to remove styrene, and then distilled under reduced pressure to obtain 2,5-dimethylphenol, 6-phenylethyl-2,4-dimethylphenol and a residue containing 4,6-diphenylethyl-2-isopropylphenol.

2. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: In step (1), the acidic catalyst comprises one or more of silicon dioxide and aluminum oxide, chromium oxide, strontium oxide and molecular sieve; preferably, the acidic catalyst comprises silicon dioxide, aluminum oxide and chromium oxide, and more preferably, the mass ratio of silicon dioxide, aluminum oxide and chromium oxide is (10-5000):100:(1-10); and / or, the mass ratio of the mixed phenol, the acidic catalyst, the first phenol and the zirconium phosphate is 100:(10-30):(20-200):(0.05-3); And / or, the first reaction is carried out in a closed hydrogen atmosphere, the temperature of the first reaction is 280-400° C., and the time of the first reaction is 4-12 hours; And / or, the mixed phenol comprises the following raw materials in parts by weight: 50-97 parts of 2,4-dimethylphenol / 2,5-dimethylphenol, 1-30 parts of o-isopropylphenol / propylphenol, and 1-20 parts of 2-ethyl-6-methylphenol; And / or, the first phenol is coking-grade phenol with a mass percentage of 90%-99%; And / or, the second phenol is petrochemical grade phenol.

3. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: In step (1), the cracking and reforming products include a second phenol, cresol, ethylphenol, o-isopropylphenol, m-isopropylphenol, p-isopropylphenol and xylenol; Preferably, the cresol in the cracking reforming product is a mixed phenol with m-cresol as the main raw material, and more preferably, the cresol in the cracking reforming product includes o-cresol, p-cresol and m-cresol; Preferably, the ethylphenol in the cracking and reforming product is a mixed phenol with m-ethylphenol as the main raw material, and more preferably, the ethylphenol in the cracking and reforming product includes o-ethylphenol, m-ethylphenol and p-ethylphenol; Preferably, the xylenol in the cracking reforming product is a mixed phenol with 2,5-xylenol and 3,5-xylenol as main raw materials; more preferably, the xylenol in the cracking reforming product includes 2,4-xylenol, 2,5-xylenol, 3,5-xylenol, 3,4-xylenol and 2,3-xylenol; and / or, adding sulfuric acid to the first cracking product in an amount of 0.05% to 2% of the mass of the mixed phenol; And / or, after adding sulfuric acid to the first cracking product, the second reaction liquid is cooled to 280-300°C at a cooling rate of 80-100°C / h, and then cooled to 210-250°C at a cooling rate of 10-20°C / h, and kept warm for 2-6 hours until the pressure stabilizes; then cooled to 150-200°C at a cooling rate of 10-20°C / h, and kept warm for 2-6 hours, and the second reaction is completed.

4. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: In step (2), the vacuum degree of the distillation is -0.085 to -0.095 MPa.

5. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: In step (3), the mass ratio of the mixed phenol containing 2,5-dimethylphenol, 2,4-dimethylphenol and o-isopropylphenol, 6-phenylethyl-2,4-dimethylphenol and sulfuric acid is 100:(0.1-1):(1-5); And / or, the molar ratio of the mixed phenol containing 2,5-dimethylphenol, 2,4-dimethylphenol and o-isopropylphenol to styrene is 1:(1.1-3).

6. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: In step (3), the temperature of the third reaction is 60-120° C., and the time of the third reaction is 5-15 hours.

7. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: The method further comprises mixing the residue containing 4,6-diphenylethyl-2-isopropylphenol with sulfuric acid to carry out a fourth reaction, and after the reaction is completed, adjusting the pH of the reaction solution to 7-8, causing the reaction solution to be stratified, filtering to remove the water layer, washing the feed liquid with water, and then subjecting the obtained feed layer to vacuum distillation to obtain o-isopropylphenol.

8. The method for separating phenol monomers from mixed phenols according to claim 7, characterized in that: The mass ratio of the residue containing 4,6-diphenylethyl-2-isopropylphenol to sulfuric acid is 100:(0.5-2); And / or, the temperature of the fourth reaction is 180-200° C., and the time of the fourth reaction is 1-4 hours.

9. The method for separating phenol monomers from mixed phenols according to claim 1, characterized in that: The method further comprises mixing 6-phenylethyl-2,4-dimethylphenol and sulfuric acid to react, and after the reaction is completed, adjusting the pH of the reaction solution to 7-8, the reaction solution is layered, filtering to remove the water layer, washing the material solution with water, and then distilling the obtained material layer under reduced pressure to obtain 2,4-dimethylphenol; And / or, the mass ratio of 6-phenylethyl-2,4-dimethylphenol to sulfuric acid is 100:(0.5-2); And / or, the reaction temperature is 180-200° C., and the reaction time is 0.5-3 h.